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Preview: Chemical Engineering & Technology

Chemical Engineering & Technology

Wiley Online Library : Chemical Engineering & Technology

Published: 2017-11-01T00:00:00-05:00


Treatments of lignocellulosic hydrolysates and continuous-flow hydrogenation of xylose to xylitol


Xylitol is produced by heterogeneous catalytic hydrogenation of xylose over Raney®-nickel. Hydrogenation is followed by several purification steps, which makes the chemical production relatively complex and expensive. Our goal was to investigate the treatments (activated carbon, bio-purification) of corn stover hydrolysates and to hydrogenate xylose to xylitol. An activated carbon treatment was used for eliminating inhibitor compounds and increasing the efficiency of the bio-purification step. It was found that glucose can completely be eliminated from the hydrolysate. Hydrogenations of corn stover hydrolysate showed that high reaction temperature resulted in high sugar alcohol yields and selectivity. The flow rate, at a given temperature, had no significant effect on xylitol yield.

Emulsion prevention with supported liquid membrane permeation


The urge to achieve climate protection goals and a more prevalent interest in finding alternatives to fossil fuel based products focus attention increasingly on cascade raw material utilization respectively to intensify commercial production processes. The present project provides a study on the combination of liquid/liquid extraction and esterification using the system acetic acid/octanol and 4-dodecylbenzenesulfonic acid as catalyst. The surfactant 4-dodecylbenzenesulfonic acid causes emulsification during extraction, but emulsification was successfully avoided by using supported liquid membrane permeation equipment.

Experimental characterization of novel carbon foam corrugated structured packing with varied corrugation angle


Carbon foam has been utilized to develop corrugated structured packing in distillation for the first time. The hydrodynamics and mass transfer performance of CFP-400X and CFP-500W with 60° and 75° corrugation angle were determined by total reflux experiments. The results indicate that increasing the corrugation angle will improve the capacity but decrease the mass transfer efficiency. Comparisons among CFP-400X, SCFP-500X, BX-500 and B1-500X are made with respect to the performance of hydrodynamics and mass transfer. CFP-400X shows advantages on capacity and efficiency compared with other two metal packings. SCFP-500X has better mass transfer efficiency than CFP-400X because of its better wettability of test liquid which is supported by the liquid flow behavior experiment.

Hydroisomerization of Long-Chain n-Alkanes over Bifunctional Zeolites with 10-Membered- and 12-Membered-Ring Pores


The hydroisomerization of a C10–C13 n-alkane mixture was investigated over six bifunctional platinum-containing zeolite catalysts with 10- and 12-membered-ring pore systems. The catalysts with 12-membered-ring zeolties are more active than those with 10-membered-ring zeolites. In contrast, higher yields of the desired mono-branched isomers are obtained over the 10-membered-ring zeolites due to shape-selectivity effects. For the 10-membered-ring zeolites, higher reaction temperatures are required for achieving the maximum isomer yields, which leads to more cracking products compared to the 12-membered-ring zeolites.

Axial backmixing and residence time distribution in a miniaturized, stirred-pulsed extraction column


Axial backmixing is an important issue in extraction columns, since it heavily affects mass transfer performance. A miniaturized, stirred-pulsed column was investigated regarding its backmixing characteristics in the continuous phase using the system water/n-butyl acetate. Residence time distributions were determined through pulse experiments with potassium chloride, which was detected via electrical conductivity. To perform the conductivity measurement without distortion of the two-phase flow, electrodes with an annular design were manufactured, which precisely line up with the inner column wall. This design is a promising alternative for using in small-scale tubular devices, where commercial electrodes do not fit, and in applications, where interference with the flow must be avoided.

Fabrication of solvent-resistant copolyimide membranes for pervaporation recovery of amide solvents


In the present study, ceramic supported copolyimide membranes were synthesized via the two-step thermal imidization method and applied to pervaporation recovery of amide solvents including dimethylformamide (DMF) and dimethylacetamide (DMAc). The prepared membrane demonstrated high resistant to the two amides under a wide range of concentration. Moreover, effects of operating parameters such as feed temperature, feed concentration on pervaporation performances of the membrane were investigated. The copolyimide membrane displayed optimum permeation flux of 210 and 402 g m−2 h−1 with corresponding separation factors of 66 and 175, respectively, for H2O/DMF and H2O/DMAc mixtures with a water concentration of 20 wt % at 333 K.

A method for designing and fabricating concentration gradient generator with two and three inlets in microfluidic chips


This paper introduces a simple and low cost method for designing and fabricating the concentration gradient generators with two and three inlets which can generate different concentration gradients at varying flow velocities. In the study, the structure of microchannel is designed to s-shape and left-right symmetry. The concentration gradient generator is simulated basing on the finite element method. In the experiment, the microchannels are processed using a CNC engraving and milling machine on PMMA substrate and then two concentration gradient generators are fabricated by hot bonding technology. The experimental result is observed by the stereoscopic microscope. By comparing the results of experiment and simulation, the feasibility of designing and fabricating method is proved. The work demonstrates flow velocity is an important factor for generating different concentration gradients. The concentration gradient profiles of concentration gradient generators with two and three inlets respectively presents approximate linear and quadratic curve. It is very helpful to the paper for demonstrating the trends study of cell and molecule in the biochemical engineering.

Development of mathematical model for numerical simulation of organic compound recovery using membrane separation process


The current work presents a novel methodology in design and simulation of membrane-based purification of organic solvents. A solution of water/alcohol (ethanol) was considered as model feed for assessment of the developed methodology in this work. Mass transfer as well as momentum transfer equations were derived and solved numerically in order to obtain the process output as function of process parameters. Water was considered as penetrant throughout the simulations and the considered process was pervaporation in which a non-porous polymeric membrane is used for purification of ethanol. Feed inlet concentration and velocity were considered as process input, whereas water outlet concentration and removal efficiency was considered output. Maxwell-Stefan mass transfer approach was used for estimation of diffusion. Finite element approach was used for numerical simulation of the process. The results indicated that decreasing feed velocity increases the water removal efficiency. Moreover, the results revealed that the developed methodology is robust for design and simulation of membrane-based purification processes.

Affinitive PVDF membranes for Enhancing Au (III) separation with extremely high selectivity


Th-PVDF resin was synthesized and then cast into affinitive microporous membranes for Au (III) adsorption. The addition degree of thiourea to the resin was promoted from 22.6% to 36.3% when using NaOH as the catalyst. Higher addition degree resulted in increased resin adsorption capacity. It also led to increased membrane hydrophilicity, enhanced membrane loading capacity and membrane utilization efficiency. The membrane had extremely high selectivity toward Au (III) over other metal ions, and was regenerated with ease for re-use without performance deterioration within four ‘adsorption-regeneration’ cycles. XPS analysis and SEM observation revealed that Au (III) was partially bonded to the membrane as gold chloride, and partially reduced to Au (0) as gold particles.

Influence of an added fraction of hygroscopic salt particles on the operating behavior of surface filters for dust separation


This paper describes a new approach to manipulating the operating behavior of surface filters for dust separation by doing raw gas conditioning using hygroscopic salt particles.The basis for a targeted manipulation of the operating behavior of surface filters is, as a rule, always attributable to the fact that a favorable performance adjusts itself at long cycle times. These are obtained by a slow increase in pressure drop during the filtration phase and by a low residual pressure drop after the regeneration. Technically, such states can be realized by so-called raw gas conditioning, which means that the characteristics of dust particles during the flight phase or in the dust cake are selectively modified by dosing additives or introducing energies. The deliquescence and efflorescence properties of hygroscopic salt particles, which can be induced by a transient increase in gas humidity, can be considered as possibilities for the formation of solid bridges between dust particles in the dust cake. With this raw gas conditioning concept, a flexible and targeted strengthening of the cohesion in the dust cake without an accompanying modification of the adhesion between the cake layer and the filter medium is theoretically possible. Experimental setup and methods for the study are described in this paper. Results of basic experiments are presented.

Synthesis and Characterization of Thin Film Nanocomposite Nanofiltration Membranes Incorporated with Graphene Oxide for Phosphorus Removal


For the first time, thin film nanocomposite (TFN) nanofiltration membranes incorporated with graphene oxide (GO) were synthesized and used to separate phosphorus from water source of different properties. Prior to phosphorus removal tests, the properties of the two TFN membranes (TFN-1 and TFN-2 with GO loadings of 0.15 and 0.3 wt%, respectively) and one control thin film composite (TFC) membrane were subject to standard characterizations to determine pure water flux, salt rejection, surface hydrophilicity, pore size and porosity. Results showed that upon incorporation of GO, the water flux of composite membrane could be significantly improved with minimum decrease in salt rejection. This is mainly due to improved surface hydrophilicity coupled with enlarged pore size and overall structural porosity. The TFN-1 membrane in particular is found to perform better owing to its good combination of water flux and solute rejection. When tested with feed solution containing 10 mg L-1 phosphorus, the TFN-1 membrane showed water flux of 13.2 L m-2 h-1, i.e., 17.9% higher than the water flux achieved by the TFC membrane. Its total phosphorus rejection meanwhile recorded at 80% compared to 84% achieved by the TFC membrane. The TFN-1 membrane also exhibited higher water flux and comparable phosphorus rejection in comparison to the TFC membrane when both membranes were used to treat phosphorus solution containing humic acids. Although the incorporation of GO tended to produce the TFN membrane with larger surface pore size, the significant improvement in membrane water flux and surface hydrophilicity had outweighed the small decrease in phosphorus removal rate.

Evaluation of Consolidation Behaviors by Combined Membrane Filtration and Stepped Cake Compression


A method was proposed for determining the compression-permeability data expressed as the dependences of the local specific cake resistance and local cake porosity on the solid compressive pressure from a combined membrane filtration and stepped cake compression test. Filtration employing a membrane with a high flow resistance which provided the pressure dependence of the average specific cake resistance was followed by step-up compression which gave cake porosities at several compressive pressures. On the basis of these data collected as the time variation of the dewatering volume, the compression-permeability data of bentonite slurry were evaluated. Consolidation behaviors of the filter cake and semi-solid material were accurately described based on the compression-permeability data.

Production of higher hydrocarbons from carbon dioxides over nanosized iron catalysts


In the present article, the effects of Fe/Cu/K catalyst particle size have been considered on the CO and CO2 hydrogenation reactions. The variation of crucial factors such as surface area and basicity, reduction, carburization and catalytic behavior of precipitated Fe/Cu/K catalysts were scrutinized. Various surface tensions hematite nanoparticles catalysts were produced by homogeneous precipitation in alcohol/water mixed solvents. The CO2-TPD results revealed that the basicity of the potassium promoted iron catalyst is increased in iron catalysts with lower particle size. Increasing in K-basic sites at surface of lower particle size catalysts is attributed to their higher surface areas. Moreover, the CO-TPR results proved that the elevation of catalyst basicity leads to increasing in dissociative adsorption of CO considerably. Shifting the oxygen removal pattern to lower temperature is the consequence of faster nucleation of FeCx crystallites on promoted surface oxides. The results also indicate that the CO2 hydrogenation reaction can occurred in two distinct direct and indirect routs via Fischer-Tropsch mechanism.

Hydrocracking of Fischer-Tropsch Wax with Tungstovanadophosphoric Salts as Catalysts


The synthesis of liquid hydrocarbons from CO2 and H2 (based on renewable energy and H2O electrolysis, respectively) in a power-to-liquid process is a promising concept for substitution of fossil fuels. Such a process is based on Fischer-Tropsch synthesis (FTS) followed by hydrocracking to convert waxy products into transportation fuels such as gasoline and diesel oil. Heteropoly acid (HPA) cesium salts as catalysts show appropriate activity for hydrocracking, and the selectivity of cracking model hydrocarbons as well as FT wax can be tuned by the catalyst's vanadium content. Thermal stability and surface properties were investigated, and the catalysts are compared with a classical H-Y type zeolite used for hydrocracking.

Thermodynamic analysis of α-pinene and limonene allylic oxidation over FePcCl16-NH2-SiO2 catalyst


From oxidation over FePcCl16-NH2-SiO2 catalyst and tert-butyl hydroperoxide (TBHP) as oxidant, verbenone, α-pinene epoxide and verbenol are obtained from α-pinene and carvone, limonene 1,2-epoxide and carveol are produced from limonene; where TBHP decomposes into O2, tert-butanol and di-tert-butyl peroxide (DTBP). With the aim of carry out the batch reactor conceptual design, the thermodynamic analysis of α-pinene and limonene oxidation was studied. Standard enthalpy and entropy of formation, liquid heat capacity, enthalpy of reaction and vaporization, and Gibbs free energy were determined by group contribution methods using Aspen Plus® simulation and those values were compared with available data reported. Although the results depend on the method, it was found that α-pinene (ΔHR,313 = -537.8 kJ/mol) and limonene (ΔHR,313 = -481.0 kJ/mol) oxidations were exothermic and spontaneous at the reaction temperature (313 K); however, TBHP decomposition into O2 and tert-butanol (ΔHR,313 = 85.7 kJ/mol) and DTBP (ΔHR, 313 = 6.7 kJ/mol) were endothermic reactions.

Chemical-free pest control by dielectric heating with radio waves – Selective heating


Dielectric heating with radio waves (RW) and microwaves (MW) are alternatives to treatments with hazardous chemicals or hot air for pest control. In particular, RW can be used to heat up bulky materials with larger size (in the meter range) homogeneously and smoothly in order to eliminate embedded pest organisms. Dielectric heating, in principle, enables selective overheating of certain materials in a heterogeneous mixture. This unique feature of electromagnetic heating methods, in contrast to techniques being based on thermal conduction, is caused by significant differences in the dielectric properties of pest organisms and matrix materials. The present study proves unambiguously that selective heating of cylindrical pest organisms in wood matrices occurs under defined conditions. The selective heating effect strongly depends on the orientation of the pest organisms in the electric field. For a parallel alignment, maximum overheating factors (ratio of adiabatic local heating rates) of 2 to 3 were determined experimentally. In case of a perpendicular alignment, no overheating was detected. A simulation of electric field and power loss density distributions in pest organisms and in their vicinity in the wood matrix, using a finite element method, can qualitatively explain the experimental results. According to the simulation, the overheating occurs not directly within the pest organism but in the wood matrix in the vicinity on both ends of the cylinder-shaped pest organism.

Performance Evaluation of Nanofiltration-like Forward Osmosis Membranes for Aerobically-treated Palm Oil Mill Effluent Treatment


For the first time, engineered osmosis was performed using commercial nanofiltration (NF) membranes (NF90 and NF270) for the treatment process of aerobically-treated palm oil mill effluent (AT-POME). Compared to the conventional forward osmosis (FO) membranes with dense rejection layer, the NF-like FO membranes offer higher magnitude of water flux with minimum reverse solute flux provided appropriate solutes (divalent salts or polyelectrolytes) were used in draw solution. The experimental results showed that both NF membranes were able to treat the AT-POME by completely preventing the colour component from passing through the permeate side under FO and pressure retarded osmosis (PRO) orientation. The water fluxes of the membranes however were higher under PRO orientation owing to the reduced internal concentration polarization (ICP) effect. The adoption of relatively loose membranes for the engineered osmosis application could address severe surface fouling of membranes tested under pressure driven filtration process at 10 bar. Nevertheless, in order to achieve higher water permeability without compromising the selectivity of organic matters and draw solutes during FO/PRO process, more research is needed to tailor a thin film composite membrane with ideal surface pore structure and substrate properties to reduce the ICP effect.

Chemical-free pest control by dielectric heating with radio waves and microwaves - Thermal effects


Thermal pest control with hot air is widely accepted as an alternative to chemical methods. However, it requires relatively long treatment times due to the low thermal conductivity of wood. Direct dielectric heating applying radio waves or microwaves has the advantage of a more homogeneous heating. However, sound experimental data on this technique are rare at present. Therefore, thermal treatment of wood-destroying insects with radio waves and microwaves was studied with two model pests, Anobium punctatum and Hylotrupes bajulus, and with Tenebrio molitor as reference. It was shown that a secure elimination of pests can be achieved by temperatures above 55°C; the corresponding treatment time was in the range of a few minutes. Temperature profiles were more homogeneous when applying radio waves.

Supported Electrospun Ultrafine Fibrous PTFE/ZnO Porous Membranes and Their Photocatalytic Applications


Supported photocatalytic poly(tetrafluoroethylene) (PTFE)/ZnO porous membranes were prepared by sintering electrospun PTFE/poly(vinylalcohol) (PVA) /zinc acetate dehydrate composite membranes. Electrospun PTFE membranes were utilized as the supports which exhibit excellent chemical stability and high specific surface area, while the photocatalyst-ZnO particles derived from the thermal decomposition of zinc acetate dehydrate were homogeneously immobilized on the surface of ultrafine PTFE fibers. In photocatalytic experiments, the degradation rate of Rhodamine B reached 97% in 5 h under UV light and remained above 70% while the mechanical strength loss of membranes was 3.8% after 5 cycles. The PTFE/ZnO membranes could be easily recovered and reused after the water treatment. We expected that PTFE/ZnO membranes have a wide range of potential application in photocatalysis and photocatalysis-membrane reactor, which plays the role of a catalyst as well as a selective barrier against contaminants of interest.

Selective separation of dye and brine recovery of nanofiltration membranes from textile wastewater


The present study investigates the selective separation mechanisms of three textile dyes with 2000 ppm of NaCl solution by nanofiltration membranes during brine recovery at three different pH medium pH-3, pH-7 and pH 10 respectively. Tests were performed with the purpose of relating flux decline, brine recovery and dye rejection behavior to membrane characteristics (Molecular weight cutoff, contact angle, zeta potential), charge of the dye molecules, and solution chemistry. Salt-organic separation factor was estimated in order to rank and choose the most suitable NF membranes for brine recovery with high degree of flux. Out of these membranes tested in this study, only NF-270 was capable of operating up to 56-70% brine recovery with high flux ranging from 78.07 to 114.80 Lh-1m-2.

Combined Depth and Cake Filtration Model Coupled with Flow Simulation for Flat and Pleated Filters


Filtration processes characterized by initial depth filtration, followed by a stage during which the cake acts as both a depth and surface filtering medium are studied. Such phenomena can occur especially for polydisperse dust. Based on one-dimensional depth filtration modeling, a combined depth and cake filtration model is formulated and coupled with the fluid flow. The evolution of flow resistivity and filtration efficiencies is studied in the case of relatively dilute suspensions and constant flow rates. Numerical simulations of single-pass experiments are performed for both flat and pleated filter media. The model presented here is able to predict a nonlinear pressure drop for incompressible filter cakes due to the reduction of pore volume by particle deposition in the cake region.

Synthesis and Characterization of Nanocomposite PVA-SnO2 Mixed Matrix Membranes and Application in Textile Effluent Treatment


Thin film nanocomposite membranes were prepared by dip-coating poly(vinyl alcohol) (PVA) and tin oxide (SnO2) nanoparticles over polyethersulfone (PES) membrane support. PVA was cross-linked using malic acid for stability. The membranes were characterized by FTIR, FEG-SEM, EDX, TGA, AFM and contact angle; and nanoparticles by DLS and TEM. The membranes were subjected to filtration of synthetic dyes wastewater which gave maximum rejection of 97%. The prepared membranes performance was compared with membranes without SnO2 nanoparticles. The fouling study was conducted using humic acid and had flux recovery rate (FRR) of 96.5%. The structural property of membranes was calculated using extended Nernst-Plank equation.

Issues and Current Trend of Hollow Fiber Mixed Matrix Membranes for CO2 Separation from N2 and CH4


In the recent year, the presence of CO2 in atmosphere has been increased tremendously after industrial revolution and it has been projected that the temperature of atmosphere will be raised about 1.4 ºC to 5.8 ºC by 2100. Therefore, it is important to control the emission of CO2 from industries. On the other hands, it is well documented in the literature that membrane technology is preferred over the conventional technologies (i.e. adsorption, absorption and cryogenic) due to its advantages including reliability, operational simplicity, low capital cost and easy maintenance. Among the various types of membranes, hollow fiber mixed matrix membranes (HFMMMs) exhibits great potential for CO2 separation because they offer large surface area, low pressure drop, high pressure stability, high separation performance and easy scale up compared to flat sheet mixed matrix membranes (FSMMMs) and spiral wound mixed matrix membranes (SWMMMs). Thus, there have been numerous works where researchers incorporated various inorganic fillers (i.e. zeolites, carbon, metal organic frameworks (MOFs) etc.) into different types of polymeric materials for the fabrication of HFMMMs. Despite of significant progress made in the recent year; highlights on current trends, issues and transport models of HFMMMs in CO2/N2 and CO2/CH4 separation are very limited. Therefore, in the present review article, we focused on the performance and issues of various materials based HFMMMs for CO2/CH4 and CO2/N2 separation. Major features of this review are reflected in the following three aspects: (i) comprehensive study on the performance of HFMMMs for CO2/N2 and CO2/CH4 separation (ii) issues with the fabrication of HFMMMs in CO2/N2 and CO2/CH4 separation (iii) prediction of transport models for HFMMMs in gases separation. In the present review article, it has been observed that the MOF based HFMMMs showed higher CO2/N2 and CO2/CH4 separation performance compared to the zeolite, carbon and other fillers based HFMMMs. On the other hand, ZIF-8, ZIF-93 and amine functionalized MIL-based HFMMMs showed higher CO2/N2 and CO2/CH4 separation performance compared to other fillers based HFMMMs. Among MOF based HFMMMs, amine functionalized MIL based HFMMM showed great potential for CO2 separation from N2 and CH4. Furthermore, the present paper reviewed the different issues with fabrication of HFMMMs including dope fluid composition; bore fluid composition and spinning parameters. It has been found that the spinning parameters including, dope fluid flow rate, bore fluid flow rate, dry gap height, force convection gas flow rate, take up speed, jet–stretch ratio and draw ratio effects the morphology of membrane and thus, performance of HFMMMs in CO2 separation. Therefore, the achievement of optimum and proper value of spinning parameters during the fabrication of HFMMMs is also need to be explored to enhance the performance of the membranes. Besides, from the review work on the transport models used for HFMMMs in gases permeations, it has been concluded that modified Maxwell model and modified Pal model will be more appropriate model to study the transport behavior of gases through HFMMMs contains low and higher loading of fillers, respectively.

Investigations on ethanol purification using polymeric membranes by pervaporation process


A comprehensive computational fluid dynamics simulation was developed to rational design of bioethanol purification system via pervaporation process by tailoring hydrodynamics of the process. The process involves removal of water from a water/ethanol liquid mixture using a dense polymeric membrane. The model domain was divided into two compartments including feed and membrane. For description of water transport in the feed solution, Maxwell-Stefan approach was used, while for mass transfer inside the membrane the molecular diffusion mechanism was assumed. The governing equations were solved numerically using finite element method. The model was capable of predicting mass transfer along with momentum transfer in the feed and membrane compartments. The results also confirmed that formation of concentration layer can be easily predicted using Maxwell-Stefan approach in dewatering of organic compounds using pervaporation process.

Chitosan-functionalized graphene oxide enhancing the permeability and antifouling performance of polyvinylidene fluoride ultrafiltration membranes


Chitosan-functionalized graphene oxide (CS–GO) was synthesized and incorporated into PVDF ultrafiltration membrane. The effect of CS–GO addition on the morphology and membrane performance was studied with water contact angle (CA), scanning electron microscopy (SEM), atomic force microscopy (AFM), porosity and pore size, permeation measurements, rejection tests and antifouling experiments. We found that the water flux of CS–GO/PVDF composite membrane increased by 44% after incorporating 0.6 wt% of CS-GO into the PVDF matrix versus pristine PVDF membrane. In addition, the CS-GO/PVDF membrane exhibited higher water flux, BSA rejection rate, water flux recovery ratio and lower BSA solution flux attenuation rate than unfilled PVDF membranes, CS/PVDF, and GO/PVDF membranes. The excellent water permeability and antifouling performance can be attributed to the high hydrophilicity and good dispersion of CS–GO in the matrix.

Predicting Transmembrane Pressure Rise from Biofouling Layer Compressibility and Permeability


The operation of filtration membranes for wastewater treatment is severely affected by biofouling formation, which causes a rapid increase in transmembrane pressure (TMP) in constant rate filtration. The TMP rise is often attributed to particulate fouling within the membrane, but the external fouling layer or filter cake contributes significantly. The fouling is highly compressible, so any model must incorporate cake compression. A one-dimensional controlled rate model based on compressible cakes and accurate sludge properties is proposed to predict the TMP rise needed to maintain constant flux. Increased compressibility results in more rapid TMP rise. Model predictions were compared to pilot-plant data and showed good correlation, without assuming fouling within the membrane. Optimization of cycle times and flux rates are performed.

A Model to evaluate the Dustiness of Powders and binary Powder Mixtures


Dust emissions of powder handling processes lead to several problems in regards to health, environment and product quality. Currently there is no universal method to predict the character and extent of dust release. Therefore in this article a model to evaluate the dustiness of powders and binary powder mixtures is introduced and discussed. The disperse characteristics, different particulate material compositions and the effective adhesive forces are considered as the leading factors affecting the dustiness. The outcome of the model enables one to compare theoretical dust emissions from different designed powders and to predict the composition of the released dust. Based on corundum-blended limestone powder the model is demonstrated. The study also yields a comparison to experimental data.

Location and Network Planning for Modular Container Plants in the Process Industry


The application of mobile production units enables the production close to the customers or the raw materials source. The choice of location depends on the demand and requirements of the customers and their geographical distribution. Therefore, economic and qualitative evaluation criteria have to be considered. A method to develop a modular production network, validated in a case study, is presented in this paper.

A Comparative Study of Fuzzy Techniques to Handle Uncertainty: An Industrial Grinding Process


The deterministic optimization models for chemical processes assume perfect information, i.e., the system parameters involved in the models should have fixed values. However, the knowledge about these parameters is often either not easy to obtain or, if available, subjected to uncertainty involved in determining them (e.g. experiments, regression etc.). The optimization results obtained using these deterministic models are, therefore, not robust to uncertainties in the parameters of the system. In this work, fuzzy based approaches, e.g. fuzzy chance constrained programming (FCCP) and fuzzy expected value model (FEVM), have been applied to a multi-objective optimization problem of the industrial grinding process to carry out the uncertainty analysis and the results are compared with respect to the power of risk averseness adopted in the approaches used. These methods assume the uncertain parameters as fuzzy numbers and membership function is used to represent the degree of uncertainty in them. The extent of constraint satisfaction due to the presence of uncertain parameters can be accommodated assuming credibility of constraint satisfaction under FCCP framework whereas the robust set of parameters in the FEVM approach is determined by considering the expectation terms for objectives and constraints. Moreover, the issue of nonlinear relation of uncertain parameters has been handled by adopting simulation based approaches while computing the credibility. The results obtained by FCCP technique show how the presence of uncertainty leads to an operating zone of varied risk appetite of a decision maker by using different uncertain measures such as credibility, possibility and necessity. These approaches are very generic and can be adopted for the study of parametric sensitivity for any process model in a novel manner.

Facile Preparation of Positively Charged and Solvent-Resistant Cellulose Acetate/LSCF Nanofiltration Membranes


Positively charged nanofiltration membranes often exhibit excellent antibacterial and antifouling properties. Nanofiltration membranes with high solvent resistance also find special applications in industrial waste water separation. Cellulose acetate is used to prepare various separation membranes due to its comprehensive performance. LSCF (La0.6Sr0.4Co0.2Fe0.8O3), a kind of cathode and electrolyte material, shows good conductivity in water solution. The nanosized hydrophilic inorganic additive LSCF is added to the casting solution to improve the performance of cellulose acetate nanofiltration membranes. After reaction with glutaraldehyde and trichloro dihydroxypropyl trimethylammonium chloride (TTAC), the prepared membrane demonstrates positively charged characteristics and excellent solvent resistance. For a broader application of nanofiltration (NF) membranes, the development of positively charged and solvent-resistant membranes by a simple method seems highly important. The nanosized hydrophilic inorganic additive LSCF was added to the casting solution to improve the performance of cellulose acetate NF membranes which exhibit positively charged characteristics and excellent solvent resistance.

Separation of Small Particles by Diffusio- and Thermophoresis in a Gas-Liquid Cross-Flow Array


A wet scrubber technique was studied for the separation of particles < 2.5 μm from exhaust gas by a gas-liquid cross-flow array. The cleaning water of the separator flows vertically down along many regularly configured wires and the generated water film acts as an independent sink for particle collection. Due to the surface-orientated horizontal particle movement caused by diffusio- (DP) and thermophoresis (TP), the particles can be captured by the water films. Since wastewater from the same production process can be used, the necessary cleaning water recycling costs can be saved due to the already available water treatment device. Experiments on a laboratory-scale test rig show the particle grade removal efficiency (PGRE) for different inlet gas-water temperature gradients and for a constant vapor injection. A new fine dust wet scrubber technique with a gas-liquid cross-flow array is reported. Apart from diffusion, interception, and inertia, the particles are also captured by diffusio- and thermophoresis. Experimental results and model calculations for different gas-liquid temperatures and vapor injection show that the grade efficiency can be improved by diffusio- and thermophoresis.

Chemical Absorption of Carbon Dioxide Using Aqueous Piperidine Derivatives


The heat of CO2 absorption is one of the important factors determining the operating cost of the CO2 absorption process when using aqueous amine solutions. Aqueous monoethanolamine (MEA) solution is a commercial absorbent, but has several drawbacks. Although piperidine (PIPD) has a high heat of absorption, it shows good CO2 absorption performance, including a high rate of CO2 absorption and a high CO2 loading capacity in comparison to MEA. PIPD derivatives were selected to identify the effect of functional groups of PIPD on the CO2 loading and heat of absorption. Introduction of a methyl group to the PIPD molecule increased the heat of absorption, whereas a hydroxyl group reduced it. The results indicate that the introduction of functional groups in particular positions could provide advantages in CO2 absorption and stripping performance. The heat of CO2 absorption is a key factor governing the operating cost of the CO2 absorption process when using aqueous amine solutions. Piperidine derivatives were tested in order to identify the effect of the functional groups on CO2 loading and heat of absorption. The introduction of functional groups could be advantageous in CO2 absorption and stripping performance.

Hydrogen Production from Co-Gasification of Coal and Biomass in the Presence of CaO as a Sorbent


Among the options for clean energy production, the gasification process is receiving increasing attention as it offers the best combination of investment and value of produced electricity compared to other methods. An Aspen Plus model of co-gasification of biomass and coal with in situ CO2 capture was developed to evaluate its potential for hydrogen production and cracking of organic impurities, i.e., tars. The effects of some critical operational variables on gas composition and yields of hydrogen gas and tar were investigated. The obtained results indicate that the fuel particle size plays a minor role in the process; smaller particles favor the conversion of tar and production of more hydrogen gas. For clean energy production, gasification offers the best combination of investment and value of produced electricity compared to other methods. A parametric study of co-gasification of biomass and coal in a circulation fluidized-bed gasification system was performed using an Aspen Plus simulator. Particular focus was lying on the hydrogen and tar yields obtained by this technology.

Gas Sparger Orifice Sizes and Solid Particle Characteristics in a Bubble Column – Relative Effect on Hydrodynamics and Mass Transfer


The relative effects of the size of gas sparger orifices and properties of solid particles on gas-liquid mass transfer are not yet fully understood. Here, the impact of sparger orifice sizes, solid particle shapes, and their loading amounts in a bubble column reactor on the absorption of oxygen in tap water was investigated. Their influence on the mass transfer coefficient and bubble hydrodynamic parameters was evaluated. The results show that the addition of solid particles can have both positive and negative effects on hydrodynamics and mass transfer, depending on the orifice size of the gas sparger. The introduction of ring-shaped solid particles can improve the mass transfer rate by up to 28 % without requiring any significant additional power. Effects of sparger orifice sizes, solid particle shapes, and their loading amounts in a bubble column reactor were investigated with respect to oxygen absorption in tap water. Both positive and negative effects were observed depending on the gas sparger orifice size and characteristics of the solid particles. Ring-shaped solid particles were the most appropriate for enhancing the mass transfer rate.

Continuous Waste Cooking Oil Transesterification with Microwave Heating and Strontium Oxide Catalyst


Biodiesel produced from waste cooking oils (WCOs) mixed with methanol was efficiently transesterified using a continuous fluid flow system with a focused microwave heating device. Strontium oxide (SrO) was added as the catalyst. The factors that most influence the biodiesel conversion rate were first estimated by considering the effects of oil-to-methanol ratio, added quantity of SrO, and microwave heating power on reaction time in a built-in batch unit. The optimal parameter values were then applied to a continuous fluid flow system, which simulates the conversion of a scaled-up quantity of WCOs into biodiesel. Under the optimum fluid flow velocity and an appropriate output temperature, a biodiesel conversion rate of ca. 93 % was reached, associated with the decomposition of ester bonds and the formation of a tetrahedral intermediate substance during the reaction. Recycling of waste products into biodiesel is favorable, both economically and environmentally. A scale-up process for biodiesel production from waste cooking oils was developed and the factors influencing the transesterification reaction or biodiesel conversion rate were minimized. The proposed pilot-scale process has the potential for converting such waste oils into biodiesel.

Concentration-Dependent Diffusion Coefficients for Fructose in Highly Permeable Chitosan Polymers


The concentration-dependent diffusion coefficient of fructose in precipitated chitosan membranes was determined using diffusion cells. Experiments showed that boundary layers on both sides of the membrane could not be neglected when the diffusion coefficient in chitosan is close to the free diffusion coefficient. Hence, the influence of the boundary layers was covered by measuring membranes with different thickness. The diffusion coefficient in chitosan at infinite dilution was found to be around the free diffusion coefficient. With increasing concentration, the diffusion coefficient in chitosan decreases faster than the free diffusion coefficient. Thus, the product of diffusion coefficient and concentration difference shows a maximum implying an optimum concentration for mass transfer. A method for the determination of true diffusion coefficients in highly permeable chitosan membranes is presented. Measurements with varying membrane thickness allowed the assessment of effects of boundary layers. The concentration-dependent diffusion coefficient of fructose was determined and an optimum fructose concentration was deduced at which the maximum diffusive flux is obtained.

Angular Dependence of Si3N4 Etching in C4F6/CH2F2/O2/Ar Plasmas


The dependence of Si3N4 etching on ion-incident angles is investigated at various CH2F2 flow rates in C4F6/CH2F2/O2/Ar plasmas. The normalized etch yield (NEY) curves for Si3N4 imply that physical sputtering is a major contributor to Si3N4 etching. An increase in the amount of CH2F2 in the plasma produces thicker and more etch-resistant fluorocarbon films. Systematic analyses on deposition and etching of the passively deposited fluorocarbon films on Si3N4 in a C4F6/CH2F2/O2/Ar plasma show that the normalized deposition rate of the fluorocarbon film is nearly the same and unaffected by the CH2F2 flow rate while etching of fluorocarbon films is similar to etching of Si3N4, thus, etching of the fluorocarbon film, rather than its deposition, limits Si3N4 etching in C4F6/CH2F2/O2/Ar plasmas. In order to predict and control etch selectivities and profiles, it is essential to understand the angular dependence of the Si3N4 etch rate. The normalized etch yield (NEY) is obtained for a Si3N4 etching in C4F6/CH2F2/O2/Ar plasmas. The NEY curves revealed that physical sputtering is a major contributor to Si3N4 etching in C4F6/CH2F2/O2/Ar plasmas.

Online Flooding Supervision in Packed Towers: An Integrated Data-Driven Statistical Monitoring Method


The development of simple and efficient monitoring methods for flooding supervision is an important but difficult task for the safe operation of packed towers. A data-driven online flooding monitoring method named Bayesian integrated dynamic principal component analysis (IDPCA) is assessed. In the first step of IDPCA, using the fuzzy c-means clustering method, the multivariate samples collected during plant operation are first classified into several groups. Then, in each subset a dynamic principal component analysis (DPCA) model is constructed to extract the process characteristics. To improve the monitoring performance, Bayesian inference is utilized to combine these DPCA models in a suitable manner. Consequently, the control limits are formulated using the probabilistic analysis. The superiority of IDPCA is illustrated using a lab-scale packed tower by comparison with the conventional principal component analysis (PCA) and DPCA methods. For the safe operation of packed towers, efficient methods for flooding supervision are necessary. A novel data-driven Bayesian monitoring method is proposed for online flooding supervision. It integrates the information extracted from multiple local models and thus provides more reliable performance. Its superiority is illustrated using a lab-scale packed tower, compared with other methods.

Graphite Sheets as High-Performance Low-Cost Anodes for Microbial Fuel Cells Using Real Food Wastewater


Graphite paper is introduced as efficient and low-cost anode in an air-cathode microbial fuel cell (MFC) for simultaneous wastewater treatment and power generation using real food wastewater. Graphite paper as the cheapest investigated material provided the best electrochemical results in an MFC with an excellent open cell voltage. The significantly increased power generation could be attributed to the large surface area of the anode, leading to enhanced bacterial attachment on the graphite anode surface. Regarding wastewater treatment, the graphite anode exhibited the highest removal of organic pollutants and the highest coulombic efficiency. It shows an excellent efficiency as a bio-anode in the air-MFC for producing electricity and treating industrial wastewaters without requiring external mediators. Microbial fuel cell (MFC) technology is a promising tool for generating renewable clean energy from wastewaters using active microorganisms as biocatalysts. For simultaneous wastewater treatment and power generation, graphite paper is introduced as a simple, efficient, and low-cost anode in an air-cathode MFC employing real food wastewater without external mediators.

An Efficient Numerical Approach for Transient Simulation of Multiphase Flow Behavior in Centrifuges


Solid bowl centrifuges are applied for the separation of small particles in a variety of industries. However, the particles accumulate at the rotor wall, which leads to a time-dependent separation efficiency. A numerical approach for spatial and time-resolved simulations of the separation process in a tube centrifuge is developed and some numerical results are presented. The back coupling of the dispersed and sedimented particles is realized by locally defined viscosity functions. The open source computation software OpenFOAM was used to simulate the turbulent multiphase flow within the centrifuge. The numerical investigations demonstrate the significant influence of the growing sediment on the flow conditions and of the rheological behavior of the sediment on the sediment shape. Growing computational power and developed methods establish numerical simulations as an alternative to costly experiments, leading to highly resolved results and advanced process knowledge. A time-efficient numerical approach was developed for simulating the separation process considering buildup and material behavior of the sediment within solid bowl centrifuges.

Performance Analysis on an Entrained-Flow Gasifier by Coal Moisture


The performance of a 300-MW-class Shell entrained-flow gasifier along with moisture contents in low-rank coal was studied by a rigorous dynamic model. The developed model predicted the steady-state reference data well. The gas and slag temperature profiles decreased with higher coal moisture content, which led to an increase of the slag thickness on the gasifier wall. The high-moisture coal resulted in reduced power generation together with reduced low heating value (LHV) of syngas, higher amount of oxygen supply, and less energy recovery in the membrane. The amount of coal required to produce the same total LHV of syngas was smallest when the coal was dried to 5 % moisture. Therefore, the coal-drying level for appropriate power production was between 5 and 10 %. The performance of a coal gasifier determines the composition and amount of syngas. A rigorous dynamic model for the full-scale Shell entrained-flow gasifier incorporated with a quenching system of syngas circulation and a syngas cooling system was developed for the performance evaluation by coal moisture contents. Low-moisture coal had a positive effect on power generation.

Development of a Dynamic Process Model for the Mechanical Fluid Separation in Decanter Centrifuges


A dynamic process model for the simulation of the separation process in countercurrent decanter centrifuges is presented. The numerical approach uses an interconnection of compartments to characterize the residence time distribution of the particles within the centrifuge. First, the theoretical basis of the numerical approach is described. Compared to the state-of-the-art modeling of decanter centrifuges, the proposed approach allows the simulation of the temporal filling process. The short computing time results in further advantages of the dynamic process model. The so-called real-time simulation is an opportunity for a model-based control of the separation process. An exemplary simulation with the product limestone demonstrates the main features of the numerical approach. Dynamic flow sheet simulation is a common tool for design and optimization of particulate processes. State-of-the-art models for numerical simulation do not reflect transient effects of the flow domain and sediment buildup. Considering the temporal filling process and residence time distribution makes the models also applicable to predict critical states which can occur during centrifuge operation.

Effect of 1-Methylimidazole on CO2 Absorption by Diethylenetriamine Aqueous Solutions


Phase-splitting absorbents represent a promising technology in relation to the low energy levels required during the CO2 capture process. 1-Methylimidazole was added to a diethylenetriamine (DETA) aqueous solution for high CO2 loading via phase splitting of absorbents during CO2 absorption. Phase splitting was observed during the absorption process when the CO2 loading reached a value suitable for the mixture of DETA, 1-methylimidazole, and water. The distribution of individual components in each phase was determined according to the total organic carbon and gas chromatography. DETA and CO2 were concentrated in the bottom phase, 1-methylimidazole mostly in the top phase. Phase splitting during CO2 absorption was mainly due to the solubility limitation of DETA carbamate into 1-methylimidazole. Aqueous amine solvents are known to be effective in chemical CO2 absorption but high amounts of energy are required during the solvent regeneration step. In order to solve this problem, phase-splitting absorbents are a promising technology. 1-Methylimidazole was added to a diethylenetriamine aqueous solution for high CO2 loading via phase splitting of absorbents during CO2 absorption.

Cake Filtration of Multicomponent Suspensions


To investigate the separation behavior of multicomponent suspensions (emulsion slurries) consisting of oil droplets and solid particles suspended in water, cake filtration experiments were conducted. Results indicated that up to a certain volumetric content of oil droplets all oil was held back by the filter cake. Due to the deposition of the oil droplets inside the filter cakes, low porosities were obtained, which led to high specific cake resistances. The relationship between resistance and porosity could be well described using an established power law approach. Consequently, the results show an extended range of validity to lower filter cake porosities. The separation behavior of multicomponent suspensions is investigated using batch filtration experiments. Such suspensions contain both solid particles and droplets dispersed in a continuous liquid phase and, therefore, exhibit complex interaction and filtration properties. The correlation between resistance and porosity is successfully described using an established power law approach.

Performance of New and Artificially Aged Electret Filters in Indoor Air Cleaners


Mobile air cleaners, in particular such with fibrous electret filters, are widely used to improve the indoor air quality. The particle size dependence of the air cleaning efficiency was investigated and concluded that recent testing standards overestimate the cleaning performance with respect to relevant indoor aerosols if considering only particles larger than 0.3 µm. Furthermore, the filters were artificially aged with cigarette smoke to evaluate their long-term stability. Finally, the results were compared to an aging method proposed by a recent testing standard and a very distinct aging behavior was found. The particle size dependence of the cleaning efficiency of a mobile air purifier was evaluated and as a result it was stated that ultrafine particles should be taken into account for a praxis-oriented testing standard. The progress of aging with cigarette smoke strongly depends on particle size and aging method, which is related to the electret properties of the filters used.

Phase Behavior of Ethylene-co-Vinyl Acetate and Alkyl Acrylate Copolymer in High-Pressure Dimethyl Ether


The phase-behavior data are presented for three kinds of commercial polymer-bonded explosive (PBX) elastomers in dimethyl ether (DME). Ethylene-co-vinyl acetate (with vinyl acetate contents of 40 % (EVA40) and 60 % by mass (EVA60)) and alkyl acrylate (ACM) copolymers were used as the PBX elastomers. For each elastomer/DME system, the cloud- and/or bubble-point (phase-boundary) pressures were measured as a function of temperature and elastomer composition using a high-pressure phase-equilibrium apparatus equipped with a variable-volume view cell. For the EVA60/DME system, the cloud-point pressure increased as the EVA60 composition increased. The ACM elastomer was readily soluble in saturated liquid-state DME at most temperature and elastomer composition ranges. The phase behavior of several polymeric elastomers in compressed liquid dimethyl ether (DME) was measured through cloud- or bubble-point experiments, and characterized as a function of pressure, temperature, and polymer concentration. This information is useful for establishing operating conditions for the organic-solvent-free coating of microparticles of energetic materials.

Anti-Coke Properties of Acid-Treated Bentonite-Supported Nickel-Boron Catalyst


Boron was introduced into nickel/acid-treated bentonite (Ni/A-Bn) catalysts to improve the anti-coking ability of the nickel-based catalyst in the hydrogenation of nitrobenzene. The results showed the B-doped Ni/A-Bn catalyst was more active than that without B. During an extended reaction period, Ni-B/acid-treated bentonite (Ni-B/A-Bn) resulted in a high nitrobenzene conversion and a high aniline selectivity. The lifetime of Ni-B/A-Bn was extended significantly compared with that of Ni/A-Bn. The addition of B into Ni/A-Bn decreased the NiO particle size, improved the dispersion of active components, and decreased carbon deposition. The combination of B and Ni prevented coke deposition on metallic Ni during nitrobenzene hydrogenation, which reduced carbon deposition on the surface of Ni-B/A-Bn. Catalytic function is improved through boron doping. The addition of boron to nickel-based bentonite catalysts helps to reduce carbon deposition on the active catalyst surface. Boron also decreases the NiO particle size, improves NiO dispersion, and enhances the catalytic activity. Optimal reaction conditions for catalyzed hydrogenation of nitrobenzene are reported.

Biosorption and Binding Mechanisms of Ni2+ and Cd2+ with Aerobic Granules Cultivated in Different Synthetic Media


Aerobic granules synthesized by feeding real wastewater (R-granules) in a sequencing batch reactor were applied to remove Ni2+ and Cd2+ from aqueous solutions and compared with granules cultivated with laboratory-synthesized wastewater (S-granules). Metal biosorption was related to solution pH, initial metal concentration, and reaction time. The chemically modified R-granules showed increased removal efficiency for the examined metals, and the results were almost identical to those of S-granules. Ion-exchange and complexation with extracellular polymeric substances were the predominant mechanisms involved in Ni2+ and Cd2+ loading onto the granules, whereby different groups were associated with the binding. The oxygen atom in peptide bonds interacted more with heavy metals than the nitrogen atom. from aqueous solutions using aerobic granules cultivated with real wastewater was successfully achieved. The biosorption and binding mechanisms as well as biosorption capacities of such granules were evaluated.

Natural Calcium-Based Residues for Carbon Dioxide Capture in a Bubbling Fluidized-Bed Reactor


Used clamshells (Paphia undulata), as a precursor of calcium oxide (CaO) sorbents, were employed for carbon dioxide (CO2) adsorption in a bubbling fluidized-bed reactor. To find the optimal calcination conditions, a 2k experimental design was used to vary the ground clamshell particle size, heating rate, and calcination time at 950 °C under a nitrogen atmosphere. The heating rate was the most significant factor affecting the CO2 adsorption capacity of the obtained CaO sorbent. The maximum CO2 adsorption capacity of the CaO obtained under these study conditions was higher than that of commercial CaO. Reducing the amount of industrially emitted CO2 is increasingly important because of global warming. This study investigates calcium oxide as a CO2 adsorbent in fluidized-bed systems. CaO can be generated from the decomposition of calcium carbonate, which is abundant throughout nature. Using such natural calcium-based materials can help reduce agricultural waste and support ecofriendly materials.

Simultaneous Sodium Hydroxide Production by Membrane Electrolysis and Carbon Dioxide Capture


The simultaneous process of NaOH production via electrolysis of NaCl and CO2 capture was investigated due to the expectation of reduction in capital cost. It was found that seawater concentration of NaCl solution was adaptable to be used as both anolyte and catholyte and that 90 °C was the most proper temperature for NaOH production among the test conditions in this work. Under these electrolyte and temperature conditions, the simultaneous NaOH production and CO2 capture processes were conducted and more than 98.83 % of OH− was reacted with CO2 to yield aqueous carbonate solutions. Additional electrochemical CO2 capture tests were carried out depending on the different CO2 concentration of mixed gases. A one-step process for generation of NaOH via electrolysis of NaCl and CO2 absorption simultaneously in an electrochemical device allows reducing the capital cost in the entire process for carbonate mineral production. The simultaneous process was performed in an electrolyzer and produced aqueous carbonate/bicarbonate solutions prior to the mineralization process.

Dynamic Change in Color Filter Layers during the Baking Process by Multi-Speckle Diffusing Wave Spectroscopy


Undercut defects of color filter (CF) layers, which inevitably occur in UV curing and development processes for liquid crystal displays and white organic light-emitting diodes, should be elucidated to ensure product quality and processability. The dynamic changes of the green CF layer are investigated during the baking process by examining the motion of pigment particles within the thin CF layer via multi-speckle diffusing wave spectroscopy (MSDWS). Autocorrelation functions and characteristic times for the α-relaxation, which are determined using light intensities scattered from the CF layer, directly indicate thermal melting and curing stages in the process. It is confirmed that MSDWS is a reliable non-contact measurement tool for quantitatively analyzing the initial change of the CF layer during the baking process. The so-called undercut defect is generated in the photolithography process for color filter layers and should be clarified to ensure product quality and processability. An innovative light scattering method, namely, multi-speckle diffusing wave spectroscopy, for characterizing the real-time dynamical changes of the color filter layer in the thermal baking process was developed.

Reaction Engineering for Continuous Production of Silver Nanoparticles


A scalable process for the production of silver nanoparticles that allows for complete conversion of the limiting reactant is analyzed in detail. The kinetics of silver nanoparticle synthesis using citrate reduction are investigated and used for development of a reaction engineering model to facilitate the reactor design. The effect of temperature, pH, concentration and mixing (axial dispersion) on the rates of nucleation and growth are analyzed quantitatively. An approach that considers reaction kinetics coupled with quality of dispersion is developed for reactor design as well as selection of reactor configurations for the synthesis of specific particle sizes. The developed approach has been applied for continuous production of 10-L suspension silver nanoparticles with very narrow particle size distribution. The reaction kinetics of synthesis of well-controlled silver nanoparticles with silver nitrate and trisodium citrate as reducing agents are investigated and applied for facilitated reactor design and evaluation of different reactor configurations. A scalable process for the production of silver nanoparticles enabling complete conversion of the limiting reactant is considered in detail.

Surface Modification of Polysulfone Membranes Using Poly(Acrylic Acid)-Decorated Alumina Nanoparticles


Alumina nanoparticles were decorated with poly(acrylic acid) (PAA) as a hydrophilic polymer by thermal polymerization of acrylic acid in the presence of alumina nanoparticles. The obtained PAA-decorated alumina (PAA-d-Al) nanoparticles were embedded in the polysulfone membrane matrix via nanofiller dispersion in the casting solution. The prepared membranes were characterized by porosity and water contact angle measurements, scanning electron and atomic force microscopy, and fouling tests using whey proteins. The presence of nanoparticles had significant effects on the membrane hydrophilicity and surface softness, resulting in fouling mitigation and flux recovery enhancement compared with the virgin polysulfone membrane. Moreover, the prepared membrane embedded with 0.25 wt % of PAA-d-Al nanofillers showed a remarkable durability and reusability during the filtration tests. Fouling problems associated with polymeric membranes affect the efficiency of many membrane filtration processes. Poly(acrylic acid)-decorated alumina nanoparticles were embedded in a polysulfone membrane matrix via nanofiller dispersion in the casting solution. The thus improved membrane hydrophilicity and surface softness resulted in less fouling and enhanced flux recovery.

Optimization of a Micromixer with Two-Layer Serpentine Crossing Channels at Multiple Reynolds Numbers


Multiobjective optimizations of a micromixer with two-layer serpentine crossing channels were performed at two different Reynolds numbers by using a multiobjective genetic algorithm and surrogate modeling based on a Navier-Stokes analysis. The optimizations included three dimensionless design variables, namely, ratios of the diagonal channel width to the pitch length, the main channel width to the pitch length, and the channel depth to the pitch length. The design space was confirmed by a parametric study, and the Latin hypercube sampling technique was used to select design points within the design space. The Kriging meta-model was applied for surrogate modeling of the objective functions. Concave Pareto-optimal fronts representing the trade-offs between the objective functions were obtained through the optimizations. In order to enhance further the mixing performance of a formerly proposed micromixer, multiobjective optimizations at low and high Reynolds numbers were accomplished by multiobjective genetic algorithm and surrogate modeling based on 3D Navier-Stokes analysis. The data provided various options for the design of a micromixer by considering mixing performance, pressure drop, and Reynolds number.

Comparing the Dynamic Flow Properties and Compaction Properties of Pharmaceutical Powder Mixtures


The dynamic flow properties and compaction characteristics of mannitol and mannitol-sodium carbonate mixtures were measured using a Freeman FT4 powder rheometer. The results showed that the mixtures containing up to 30 % sodium carbonate had better flow properties and improved compaction characteristics when compared with mannitol alone. The mixtures were also analyzed using a shear cell, which gave flow functions that varied little between the samples. The feasibility of combining a more expensive pharmaceutical excipient with a cheaper ingredient is demonstrated, without compromising desired powder characteristics. The study may also provide a useful method for assessing the suitability of new formulations for application as direct compression bases, as part of a wider range of powder flow tests. The compaction and flow properties of a range of mannitol/sodium carbonate mixtures using the Freeman FT4 tester are examined. It demonstrated the feasibility of using the tester to optimize the formulation that would give the best compressibility and cohesion suitable for tablet production. It also proved that the method detected differences missed by a conventional shear cell method.

Low-Cost Noninvasive Real-Time Imaging for Tubular Continuous-Flow Crystallization


A key design limitation to the effective monitoring and control of continuous crystallization processes is the ability to characterize crystals in real time. A low-cost system composed of a basic stereomicroscope and video camera for the in situ imaging of sub-millimeter crystals through curved walls of millifluidic tubular crystallizers is described. Real-time videos taken for millimeter-size slurry slugs are used to guide the experimental design for a recently developed multiphase-flow crystallization process, including the improvement of the slug aspect ratio, visualization of crystal shapes, and observation of the extent of aggregation. Design considerations are also discussed for the use of multiple stereomicroscopes in other continuous-flow tubular experiments. An in situ imaging system based on a stereomicroscope is presented to visualize crystals in slurry slugs through a curved wall of tubular multiphase millifluidic-flow crystallizers. Slugs, crystal shapes, and extent of aggregation are evaluated and improved via real-time videos. Design considerations are provided for imaging other continuous-flow experiments.

Efficient Control of Microbubble Properties by Alcohol Shear Flows in Ceramic Membrane Channels


Efficient control of microbubbles is achieved by alcohol shear flows in ceramic membrane channels. The dependence of hydrodynamic and mass transfer properties of microbubbles on liquid viscosity was investigated in a bubble column. The multichannel ceramic membrane worked as the gas sparger, and the shear flow on the membrane surface controlled the microbubble generation. Oxygen gas and glycerin solutions with different viscosities served as gas phase and liquid phase, respectively. The microbubbles were massively generated at different liquid viscosities. With increasing viscosity, the bubble size first decreased and then increased. The dual effect of viscosity on bubble size was related to bubble coalescence. However, an impact of viscosity on gas holdup was not observed for microbubbles. The potential of alcohol shear flows to effectively control microbubble properties is experimentally investigated. Large-scale preparation of microbubbles is achieved using a multichannel ceramic membrane. The dependency of hydrodynamic and mass transfer properties of microbubbles on liquid viscosity is evaluated. The liquid viscosity exhibits a dual effect on bubble size distribution.

Capturing CO2 by Using a Microalgae Culture Recycle Solution


The capture of CO2 by means of a microalgae culture solution was explored in a continuous bubble-column scrubber under a constant pH environment. Optimum conditions for a pilot-scale study were evaluated. With the Taguchi method, a total of sixteen runs were required. Absorption rate, absorption efficiency, overall mass transfer coefficient, and gas-liquid flow rate ratio were determined by a material balance model and a two-film model under steady-state conditions. From the signal-to-noise ratio, the sequence of parameters could be stated. Uncontrolled experiments were also performed and empirical equations were discussed. The growth of algae requires CO2 as one of the main nutrients, so there is an opportunity to sequester CO2 by using flue gas emissions from industrial sources as the feed for algae cultivation. A microalgae culture recycle solution was successfully reused to capture CO2 in a continuous bubble-column scrubber under a constant pH environment. Optimum conditions were elaborated.

Advanced Operating Strategies to Extend the Applications of Simulated Moving Bed Chromatography


Chromatographic separation with solid stationary and fluid mobile phases is widely used to isolate and purify compounds. One of the most productive improvements in preparative chromatography is the simulated moving bed (SMB) process, which enables continuous feed supply and product removal by periodic operation of a multicolumn to simulate a countercurrent flow between the phases. The SMB process produces high-purity compounds, even with low selectivity, and offers higher productivity and lower eluent consumption than batch chromatography. Recently, intensive efforts have been made to expand the range of applications through the design, modeling, and optimization of the SMB process to produce advanced operating strategies, which are described and evaluated in this review. The simulated moving bed process is considered as one of the most productive improvements in preparative chromatography, by periodic operation of a multicolumn to simulate a countercurrent flow between the phases. Advances in this process are described with a focus on introducing novel concepts and providing examples and advantages of recently proposed operating strategies in specific areas.

Start-and-Stop Operation of Fixed-Bed Methanation Reactors – Results from Modeling and Simulation


The production of synthetic natural gas (SNG) from renewable sources in cases requires a dynamic and intermitted operation of the methanation reactors. This may lead to catalyst damage. Therefore, the present work is aiming at identifying restrictions and optimization approaches of the start-and-stop operation of fixed-bed methanation reactors. 2D modeling and simulation work is conducted and the warm-start behavior of a fixed-bed reactor after one to four hours operation intermittence is analyzed. The result reveals the possibility for an operation interruption of up to four hours without high adaptation effort to restart the reactor. After approximately four hours, the catalyst bed at the inlet part of the reactor reaches a temperature that provokes problems for a subsequent warm start. A two-dimensional simulation of a fixed-bed methanation reactor is conducted and the warm-start behavior after one to four hours operation intermittence is analyzed. The possibility for an operation interruption of up to four hours without high adaptation effort to restart the reactor is revealed. Longer operation intermittence provokes problems for a subsequent warm start.

Rapid Degradation of Rhodamine B via Poly(dopamine)-Modified Membranes with Silver Nanoparticles


Rapid and convenient removal of organic dyes from water still remains a great challenge. The fast degradation of Rhodamine B (RhB) with NaBH4 as a reducing agent catalyzed by a catalytic membrane fabricated by poly(dopamine)-modified poly(vinylidene difluoride) (PVDF) powders and silver nanoparticles (NPs) is described. Results indicate that the catalytic membrane shows an excellent performance for RhB degradation under a static state and cross-flow catalysis. Compared to static catalysis, cross-flow catalysis can efficiently enhance the degradation of RhB due to the silver NPs and the high flowing rate of reactants on the membrane surface. The penetrated fluid can be directly excluded due to the RhB with a high conversion coming out from the membrane pores with silver NPs. The convenient operation avoids additional steps to separate catalysts from the system and, therefore, has a promising potential in degradation of organic dyes. Rapid and effective removal of organic dyes from water still means a challenging issue. A catalytic membrane containing silver nanoparticles was applied for degradation of Rhodamine B in cross-flow catalysis. This dye can be quickly degraded by recycling reactants on the surface of the catalytic membrane while the products with high conversion can be obtained by the penetrative fluid.

Investigation of the Blockage Conditions in a Laminated-Sheet Microchannel Reactor


The microchannel reactor is a generally adopted laminated-sheet structure in which several microchannel sheets with the same or different structures are laminated together and tightened by welding or other connection methods into a single reaction unit. Uniform velocity distribution among the microchannels can improve the heat and mass transfer efficiency. When one or more microchannels are blocked, the uniformity of the velocity distribution is inevitably affected. In this work, the velocity distributions among the microchannels in a single-sheet and a double-sheet laminated structure are investigated under different blockage conditions. It is demonstrated in detail that the different blockage conditions in the microchannels and laminated structure display different effects on the velocity value, the shape of the velocity distribution, and the evaluation parameter for uniformity. The performance of a laminated-sheet microchannel reactor is greatly influenced by the velocity distribution among its microchannels. Different blockage conditions in the microchannels, such as single and double blockages at different positions in one or two sheets, have different effects on the velocity value, the shape of the velocity distribution, and the evaluation parameter for uniformity.

Absorption of CO2 with Amino Acid-Based Ionic Liquids and Corresponding Amino Acid Precursors


A comparative study for CO2 absorption among amino acids (AAs) and ionic liquids (ILs) containing tetramethylammonium [TMA] and tetrabutylphosphonium [TBP] as cations and the corresponding deprotonated amino acid as anions, namely, [TMA][AA] and [TBP][AA], is reported. Amino acids show an excellent performance for CO2 capture, better than the corresponding [TMA][AA], but AAs are less efficient than [TBP][AA]. In addition, [TBP][AA] present faster kinetics of absorption than the corresponding AA. [TBP][lysinate] exhibits the highest CO2 absorption capacity. A novel and fast method with low energy demand for microwave-assisted regeneration of the absorbents from the CO2-saturated solution is also described for the first time. Chemical absorption is an attractive technology for CO2 capture. Among different chemical absorbents suggested for this application, ionic liquids containing amino acids as anions are promising candidates for industrial implementation. A fast and effective method with low energy requirement in terms of microwave-assisted regeneration of the absorbents from the CO2-saturated solution is proposed.

Formation of Spherical Agglomerates in Cooling Crystallization of Hexahydro-1,3,5-trinitro-1,3,5-triazine


The production of spherical agglomerates of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from acetone by cooling crystallization with poly(vinylpyrrolidone) (PVP) is described. It was found that PVP suppresses the nucleation of RDX at the initial stage, but tremendous nucleation of RDX occurred abruptly after the induction period. The rapid nucleation may be associated with the primary nucleation due to the presence of PVP. It can be concluded that the addition of PVP results in the formation of RDX particles with sufficient number density for spherical agglomeration. It was found that such spherical agglomeration propagates very rapidly after nucleation within one minute and the size of spherical agglomerates is affected by the cooling rate. RDX by cooling crystallization from acetone was demonstrated. A proposed mechanism for this process is an extremely rapid nucleation induced due to primary nucleation by a polymeric additive. This rapid nucleation provides a high enough number density of particles for the formation of spherical agglomerates.

Enhanced CO2 Capture Performance of Limestone by Industrial Waste Sludge


Although inert supports have been proved effective to enhance CO2 capture performance of CaO sorbents, more commonly used supports are derived from expensive raw materials such as nitrates and organometallic precursors. Cheap waste sludge from the steel plant was utilized, which has a high daily output and has not received effective reuse, to promote the CO2 capture performance. The results showed that the sludge effectively promoted the performance of limestone. Homogeneously dispersed inert material of MgO, acting as the metal framework to resist sintering, was responsible for the enhanced performance. The introduction of waste sludge into the calcium looping could not only improve the sorbent performance, but also provide a potentially effective way to reuse the waste sludge. Commonly applied inert solid supports are considered effective to improve the CO2 capture performance of CaO sorbents, but stem from expensive raw materials. Cheap waste sludge from steel plants is premixed with natural limestone and fed into a calcium looping system. Thereby, both the enhanced CO2 capture performance of limestone and the reuse of the waste industrial sludge could be implemented.

Dynamic Membrane Filtration: Formation, Filtration, Cleaning, and Applications


Applications of dynamic membrane (DM) filtration and factors affecting formation, filtration, and cleaning are introduced. DMs have been studied extensively for wastewater treatment in recent years. DM formation methods and mechanisms are explained. Effects of supporting material, deposited material, formation pressure, and pH on the DM formation are discussed in detail. The impacts of operation pressure, aeration intensity, cross-flow velocity, temperature, and other parameters on the DM filtration process are evaluated and different DM cleaning strategies are reviewed. The applications of DMs to treatments of municipal wastewater, surface water, oily water, industrial wastewater, sludge, and microalgae harvesting are discussed. Finally, possible future research directions and some guidelines for DM technology are given. High flux, low cost, and low operation pressure are the main advantages of dynamic membranes over traditional membrane technology in wastewater treatment. Different formation and filtration conditions as well as cleaning strategies for dynamic membranes are investigated. An overview of dynamic membrane applications in wastewater and sludge treatment is presented.

Multi-Step Consecutive Photo-Chlorination of 1,2-Dichloroethane: Kinetics and Reactive Distillation Experiment


The development and validation of a novel kinetic model for the chlorination of 1,2-dichloroethane to ultimately hexachloroethane catalyzed by blue light are presented. A factor (Xm) related to the chlorination depth was introduced into the kinetics model, and the results showed that the dynamic features of the photo-chlorination are better predicted by the modified model than by the conventional one. Furthermore, to enhance the selectivity towards tetrachloroethane and pentachloroethane, a novel reactive distillation with side-reactor configuration (SRC) for the photo-chlorination process was proposed. In order to demonstrate the technical feasibility of the process, semi-batch SRC experiments on the laboratory scale were carried out. Up to 96.5 wt % of tetrachloroethane and pentachloroethane with molar ratios varying from 7 to 0.7 over time were obtained in the bottom product. A factor related to the chlorination depth was introduced into the kinetic model for the multi-step consecutive photo-chlorination of 1,2-dichloroethane. Reactive distillation with side-reactors was proposed for the process and proven feasible to enhance the selectivity toward the intermediates.

A Novel Approach for Measuring Gas Solubility in Liquids Using a Tube-in-Tube Membrane Contactor


A novel approach using a semipermeable Teflon AF-2400 tube-in-tube membrane contactor was developed for the measurement of gas solubility in organic solvents. This membrane ensures gas saturation of liquids in continuous flow at a specific pressure and temperature. After liquid decompression, the amount of gas outgassed was measured with a bubble meter and used for solubility calculation. The proposed method was applied to the measurement of oxygen solubility in toluene and benzyl alcohol. Validation experiments were initially performed by comparing the obtained oxygen solubility in toluene with literature data. With higher temperature, the solubility of oxygen in benzyl alcohol was found to increase, indicating that the oxygen-dissolving process is endothermic. Finally, an empirical correlation of Henry's law constant as a function of temperature was determined. Data on oxygen solubility in organic solvents are essential for catalyst evaluation, reactor design, and process safety of catalytic aerobic oxidations. An innovative method with a Teflon AF-2400 tube-in-tube membrane contactor is proposed for measuring oxygen solubility in toluene and benzyl alcohol. An empirical correlation of Henry's law constant as a function of temperature is determined.

Improvement of Bio-crude Oil Yield and Phosphorus Content by Hydrothermal Liquefaction Using Microalgae


Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet biomass such as microalgae into bio-crude oil. Four main products, gas, bio-crude oil, an aqueous phase, and solid residue, are generated through HTL. In this study, various HTL conditions were investigated to enhance the phosphorus content in the aqueous phase as well as the yield of bio-crude oil. Tetraselmis sp. was used as the microalgae feedstock, and the product yields according to catalyst type were explored. The phosphate ion (PO43−) content in the aqueous phase was significantly enhanced when acetic acid was added because of the effect of pH. In addition, it was found that both the bio-crude oil yield and the ammonium ion content could be increased by recycling the post-HTL aqueous phase, while the phosphate content was not. Biofuels produced by microalgae may help to solve the environmental problems associated with the use of fossil fuels. Various hydrothermal liquefaction conditions were investigated for the conversion of wet microalgal biomass into bio-crude oil, with the goal of increasing the phosphorus content in the aqueous phase and the bio-crude oil yield.

Experimental Investigation on Gas-Solid Behavior in Fluidized Beds with Superfine Particles


Fluidized beds are commercially utilized in gas-solid contacting processes such as the fluid catalytic cracking (FCC) process. Attempts have been made for bubbling fluidized beds to enhance the gas exchange between the bubble phase and the emulsion phase as well as to increase bubble holdup. Low-density superfine particles 5070S were selected with average diameters of about 10 μm. Unlike agglomerate particulate fluidization of superfine particles on which other researchers have reported, the smaller bubbles, whose diameter is less than 10 mm, uniformly dispersed in the whole bed. Additionally, the gas exchange rate with 5070S became larger than with the FCC particles. Such a unique gas-solid behavior is probably due to the proper density difference between particle aggregate and fluidizing gas. Fluidized beds are widely used in gas-solid contacting processes, but the gas exchange between bubble phase and emulsion phase still is not optimized. The possibility of applying low-density microparticles for a gas-solid fluidized-bed reactor with higher contact efficiency is demonstrated. Hollow borosilicate glass microparticles were successfully employed as superfine particles for fluidization.

Analysis of In Situ Microscopy Images of Flocculated Sediment Volumes


An in situ microscopy method was employed to study the sediment volumes that result from batch settling of polymer-flocculated kaolin suspensions. Statistical methods were applied including chord length distributions, perimeter-based fractal dimension of the void areas, white area image ratio, and gray level co-occurrence (GLCM) features. Several GLCM features have a good linear relationship with aggregation state, and the parameters of aggregate and void chord distributions can be interpreted to help explain the flocculation results. The methods applied here are suggested for the measurement of the aggregation state or relative aggregate volume on bench or industrial scale when the settled suspension interface is not available, such as in a continuous process or reaction. In situ nondestructive methods to determine properties of aggregates in networked suspensions are rare. The correlation between statistical image features and aggregation state in polyacrylamide-flocculated kaolin suspensions is evaluated by comparing microscopic images of the settled bed of aggregates with the accurately measured bed height to determine the sediment volume.

Asymmetrical Microchannel Emulsification Plates for Production of Small-Sized Monodispersed Emulsion Droplets


Monodispersed emulsion droplets have promising advantages in food, pharmaceutical, and chemical industries. Previous microchannel emulsification (MCE) plates having the capacity of generating small-sized droplets exhibited very low droplet productivity since these plates operate at a low dispersed-phase flow rate and with a relatively small number of microchannels. An innovative MCE plate with 176 176 circular asymmetric through-holes was manufactured, which is comprised of a series of discrete outlets on each microchannel line with an effective cross-sectional area of 1 cm2. The newly fabricated MCE plate is capable to produce monodispersed emulsion droplets with small Sauter mean diameters. Microchannel emulsification is a progressive technique for production of monodispersed emulsion droplets with great potential in food, pharmaceutical, and chemical industries. An asymmetrical straight-through microchannel emulsification plate for generation of small uniform droplets with higher productivity was designed, intended for mass production of monodispersed small-sized droplets.

Biodiesel Purification Using Polymeric Nanofiltration Composite Membranes Highly Resistant to Harsh Conditions


Biodiesel as alternative for conventional diesel fuel is mainly produced by the catalytic reaction of triglycerides with an alcohol. In this work, the purification of biodiesel was carried out with two lab-made solvent-resistant composite nanofiltration membranes of poly(vinylidene difluoride) (PVDF) as support and poly(dimethylsiloxane) as coating layer. Biodiesel was obtained from the esterification of partially refined soy oil with bioethanol (EtOH) and NaOH as catalyst. The best biodiesel purification performance was achieved with the PVDF-12SI membrane reaching high retention of glycerol, total glycerides, and soap. PVDF-SI membranes were found to have an excellent stability for biodiesel permeation, achieving a flux recovery ratio of EtOH as high as 0.94 after twenty cycles of use. Nanofiltration polymeric membranes are considered as a feasible and efficient way for the purification of biodiesel. Two lab-made solvent-resistant composite nanofiltration membranes were evaluated for optimum purification performance, achieving high retention of glycerol, total glycerides, and soap. The membranes exhibit a high stability even under harsh conditions.

Cover Picture: Chem. Eng. Technol. 11/2017



Editorial Board: Chem. Eng. Technol. 11/2017


Overview Contents: Chem. Eng. Technol. 11/2017


Highlights: Chem. Eng. Technol. 11/2017




No abstract.

Shell of Planet Earth – Global Batch Bioreactor


Our planet Earth, precisely speaking its surface shell, might be considered as a huge multiphase batch biochemical reactor heated by the Sun, whose energy is a unique resource. The Sun ensures our earthly life unconditionally; moreover, it compensates the heat losses of land, water, and ice by radiation emitted from the Earth surface to its surrounding space at night. It is evident that in this macroreactor the complex transport phenomena occur in many phases, involving mass, heat, and momentum. Obviously, such a responsive batch system is strongly limited by raw resources of all elements including carbon materials necessary for a good living standard and utilized both in the energy production and for the main industrial chemical processes. The planet Earth can be considered as a huge multiphase batch biochemical reactor heated by the Sun. Our living space on its surface shell, regarded as a responsive batch system, is strongly limited by raw resources of carbon and all other elements. The exponential trends in population, exploitation of resources, and energy demand will be unsustainable for the future.

Dropwise Condensation on Advanced Functional Surfaces – Theory and Experimental Setup


Compared to filmwise condensation on conventional condenser surfaces, heat transfer can be significantly enhanced by tuning the wettability of the surface to promote dropwise condensation. Following rapid advances in surface engineering, the last years have seen an unprecedented interest in dropwise condensation research. This brief review highlights recent advances in theory and experimental investigation regarding dropwise condensation on smooth hydrophobic surfaces, micro- and nanostructured superhydrophobic surfaces, biphilic surfaces with patterned wettability, and lubricant-infused surfaces. Research on dropwise condensation has gained a lot of traction in recent years. This review provides an overview on emerging approaches for surface functionalization and the corresponding wetting properties that promote dropwise condensation. The implications for enhanced heat transfer and advances in heat transfer modeling are also discussed.

Offshore Floating Packed-Bed Reactors: Key Challenges and Potential Solutions


The influence of floating vessel motions on the hydrodynamic behavior of multiphase flows in porous media was studied using a hexapod ship motion emulator with an embarked packed column. The response of gas-liquid distribution, pressure drop, liquid saturation, and flow regime transition to column inclinations and roll motions was compared to those of the corresponding static vertical and inclined configurations. Two-phase flow patterns in terms of local liquid saturation distribution were visualized online by means of a capacitance wire-mesh sensor positioned firmly on the floating packed bed. The hydrodynamic performance of packed beds under roll motion deviates strongly from that of the static beds, indicating that the known characteristics of the conventional land-based trickle-bed reactors cannot be transposed on a one-to-one basis for design and scale-up of the floating reactor configurations. Packed beds are embarked on mobile offshore platforms for onboard treatment and refining of hydrocarbons extracted from undersea reservoirs. The effects of offshore floating platform motions on the hydrodynamic behavior of multiphase flows in porous media were investigated. Ship rolling motions cause periodic gas-liquid segregation and induce transverse displacements in two-phase flow packed beds.

Hydrodynamics and Mass Transfer of Gas-Liquid and Liquid-Liquid Taylor Flow in Microchannels


Hydrodynamics and mass transfer of both gas-liquid and liquid-liquid Taylor flow simulation in microchannels are reviewed. Theoretical approaches for description of hydrodynamic parameters and mass transfer characteristics are corroborated by comparison with available experimental results. Similarities and peculiarities of liquid-liquid flows versus gas-liquid Taylor flows in capillaries are discussed. Tools of mass transfer intensification of gas-liquid and liquid-liquid Taylor flow in microchannels are analyzed and optimal process conditions for gas-liquid Taylor flows are evaluated. A review is given on mathematical modeling of hydrodynamics and mass transfer of gas-liquid and liquid-liquid Taylor flows in microchannels by means of a theoretical approach using classical equations and modern formulae necessary to close the model. The state of the art of process intensification in mini- and microchannels and optimal process conditions for gas-liquid Taylor flows are evaluated.

CO2 Capture from Air Using Amine-Functionalized Kaolin-Based Zeolites


Several inexpensive zeolites such as ZSM-5 (MFI), zeolite Y (FAU), and SAPO-34 (CHA) were developed from kaolin clay and applied for CO2 capture from air. These molecular sieves were functionalized with tetraethylenepentamine (TEPA) in order to further improve their CO2 capacity. The obtained kaolin-based zeolites exhibited similar properties than those of zeolites prepared with other sources. They also revealed a bimodal pore network consisting of both micropores and mesopores. The effect of amine loading on CO2 capture was investigated and the results demonstrated that TEPA-modified zeolite Y with 10 wt % TEPA had a higher capacity than other zeolites due to its larger mesopore volume. The presence of mesopores in the zeolite Y framework facilitated a better accessibility of CO2 molecules to the amine sites. The development of bimodal pore-network zeolites from a cheap and abundant source such as kaolin clay is of practical importance in various processes related to separation and catalysis. Different zeolites were synthesized from kaolin clay and evaluated for CO2 adsorption from air. The subsequent functionalization of these materials is largely dependent on their porosity and pore network.

Process Intensification of n-Butane Oxidation to Maleic Anhydride in a Millistructured Reactor


The oxidation of n-butane to maleic anhydride over an industrial vanadyl pyrophosphate oxide catalyst was investigated experimentally in millistructured reactors with varying slit widths to investigate the process intensification potential of this reaction. Although the smaller reactor behaved isothermally, even in the presence of high n-butane concentrations, moderate hot spots never exceeding more than 15 K above the salt bath temperature occurred in the larger catalyst channel. After exposure to high n-butane concentrations, a certain amount of catalyst deactivation was observed, which could be partly restored through reoxidation with pure oxygen. The reactor-specific maleic anhydride productivities obtained are much larger than those in conventional multitubular reactors. Micro- and millistructured reactors are a promising technology for the purpose of process intensification. Results are presented for the highly exothermic, heterogeneously catalyzed, gas-phase oxidation of n-butane over a commercial vanadyl pyrophosphate oxide catalyst conducted in the explosive regime. Reactor productivities can be significantly increased compared with those of multitubular reactors.

Effect of Acetonitrile-Based Crystallization Conditions on the Crystal Quality of Vitamin D3


To design an integrated continuous crystallization setup that is directly coupled to a photochemical synthesis in flow, the crystallization of vitamin D3 was studied in detail. Because of the high solubility of the vitamin in the reaction solvent tert-butylmethyl ether, a solvent swap to acetonitrile was necessary. While other methods use a multistep procedure, with the proposed approach, crystalline vitamin D3 can be obtained within one crystallization step. The influence of crystallization parameters, such as the initial concentration of vitamin D3, stirring as well as cooling temperature, rate, and time, on the obtained results in terms of yield, crystal shape, polymorphism, and particle size distribution are discussed in detail. The crystallization process of vitamin D3 and the way how to directly obtain different qualities and types of crystal polymorphs are still not well understood. All relevant crystallization process conditions were evaluated and an integrated continuous crystallization setup directly coupled to a photochemical synthesis in flow was applied to study the crystallization of vitamin D3 in detail.

Performance Testing of Hydrodesulfurization Catalysts Using a Single-Pellet-String Reactor


Small-scale parallel trickle-bed reactors were used to evaluate the performance of a commercial hydrodesulfurization catalyst under industrially relevant conditions. Catalyst extrudates were loaded as a single string in reactor tubes. It is demonstrated that product sulfur levels and densities obtained with the single-pellet-string reactor are close to the results obtained in a bench-scale fixed-bed reactor operated under the same conditions. Moreover, parallel single-pellet-string reactors show high reproducibility. To study the hydrodynamic effects of the catalyst-bed packing, the catalyst-bed length was varied by loading different amounts of catalysts, and crushed catalyst was also loaded. The hydrodesul-furization of gasoil is a key process in refineries. Small-scale parallel trickle-bed reactors have been used to evaluate the performance of a commercial hydrodesulfurization catalyst under industrially relevant conditions. Catalyst extrudates were loaded as a single string in reactor tubes. The hydrodynamic effects of the catalyst-bed packing were also studied.

Urea Decomposition in Selective Catalytic Reduction on V2O5/WO3/TiO2 Catalyst in Diesel Exhaust


Selective catalytic reduction (SCR) of NOx by AdBlue and NH3 on monolithic V2O5/WO3/TiO2 catalyst was studied under flow conditions realistic for diesel exhaust. The tests provided same standard and fast SCR for AdBlue and NH3 from 150 to 350 °C. For standard urea-SCR, axial concentration profiles were checked by monoliths with different lengths evidencing incomplete conversion of urea and isocyanic acid at low temperatures. But SCR was not clearly affected by under-stoichiometric NH3 as substantiated by kinetic analysis. However, above 250 °C, SCR was limited by internal mass transport indicated by Weisz-Prater criterion and lower activation barrier. Formation of deposits was investigated at 175 °C and below showing some urea around the nozzle, whereas cyanuric acid and biuret additionally formed around the catalyst. Selective catalytic reduction (SCR) and NOx storage reduction catalysts are well-known means for the reduction of nitrogen oxides in diesel exhaust. SCR on a traditional monolithic V2O5/WO3/TiO2 catalyst with urea as reducing agent is investigated with major focus on the interaction of SCR reaction and urea conversion over the length of the catalyst at realistic Reynolds numbers.

An Eulerian-Eulerian Computational Approach for Simulating Descending Gas-Liquid Flows in Reactors with Solid Foam Internals


Chemical reactors with new types of packings, such as metallic and ceramic open-pore foams, have become subjects of scientific and engineering interest in the past decades. For trickle bed reactors, the new packing types provide favorable conditions, such as high specific surface area and low pressure drop, which are believed to contribute to an intensification of mass and heat transfer. Here, an attempt was made to model and predict the flow pattern and liquid distribution in a trickle bed reactor with solid foams, using computational fluid dynamics. A three-dimensional model based on the relative permeability approach was adopted, where gas and liquid phases flow co-currently downwards through a reactor with SiSiC ceramic foams as internals. The influence of both mechanical and capillary dispersion was included and studied in detail for foams of two different pore densities and for different initial distribution patterns. A three-dimensional computational fluid dynamics model based on a relative permeability approach was developed in order to simulate the flow through a reactor with ceramic foams as internals. The influence of capillary and mechanical dispersion forces on the liquid distribution was also discussed in detail. The results were validated against experimental data.

Homogeneous Gas-Liquid Distribution for Monolithic Structures via a Needle Distributor


Structured catalysts are a widely discussed approach for process intensification of chemical multiphase reactors. But equal to common catalyst structures, homogeneous educt distribution along the catalytic surface is mandatory for high reactor performance. Especially monolithic structures require a homogeneous initial fluid distribution. A novel distribution concept for gas-liquid flow through arbitrary channel matrices is presented. It is based on the injection principle where gas and liquid are inserted directly into the channels. A prototype for different cell densities was built and tested by various measurement techniques: gravimetry, X-ray tomography, and an optical fiber sensor. Additionally, the flow regime per channel was detected as equal to single-channel conditions. The industrial use of monolithic structures as catalyst carriers for three-phase reactions is still limited to the availability of a gas-liquid distributor to create the mandatory homogeneous initial distribution. A novel distribution concept for gas-liquid flow through arbitrary channel matrices is proposed, providing a satisfactory initial condition for intensified multiphase reactions.

Meniscus Asymmetry and Chemo-Marangoni Convection in Capillaries


A liquid-liquid system inside a capillary in which an interfacial reaction leads to in situ production of a surfactant was studied experimentally. The resulting chemo-Marangoni convection induces periodic spreading-dewetting cycles in laboratory experiments. By selected experiments in microgravity, the individual phenomena of the system dynamics could be isolated. The spreading-dewetting cycles result from a complex interplay between the decrease in interfacial tension due to the production of surfactant, the chemo-Marangoni convection, and the gravity-driven deformation of the meniscus shape. Marangoni convection is relevant to mass transfer in capillary microreactors. In an experimental capillary setup, surfactant was produced by an interfacial reaction. The resulting chemo-Marangoni convection induced spreading-dewetting cycles. The meniscus deformation is reduced in microgravity, but still exists.

Development of a Robust Fixed-Bed Reactor Model for Supercritical Citral Hydrogenation


The hydrogenation of citral in a fixed-bed reactor by using supercritical carbon dioxide was studied. A numerical model was set up by using the commercial software Aspen Custom Modeler®. By applying literature experimental data, a parameter estimation for the kinetic parameters was carried out. A good fit was reached with the presented model. Furthermore, a sensitivity analysis was performed. The influence of process pressure, inlet CO2 and H2 concentration, and catalyst particle size on conversion, reactor length, space time yield, yield of the intermediate product 3,7-dimethyl-2-octenal, and pressure drop was investigated. Numerical models allow optimization of process parameters for improved performance. Experimental data from the literature are applied in a numerical model for supercritical citral hydrogenation in a fixed-bed reactor to estimate the kinetic parameters. The influence of process parameters on conversion, reactor length, space time yield, yield of the intermediate product 3,7-dimethyl-2-octenal, and pressure drop is discussed.

Activity Hysteresis during Cyclic Temperature-Programmed Reactions in the Partial Oxidation of Acrolein to Acrylic Acid


Oxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by transient (cyclic temperature-programmed (TP)) as well as steady-state methods. TP reactions (TPReactions) exhibit an activity hysteresis of the catalyst with respect to temperature. As a result of the steady-state measurements, the activity hysteresis is not related to multiple steady states and is exclusively a transient phenomenon. Generally, the dynamics of bulk oxygen plays a key role leading to a reversible oxidation/reduction of the catalyst surface which influences the activity. This means the bulk acts as oxygen buffer. In this context, a reaction model, which involves the participation of bulk oxygen, was deduced and verified by modeling. Oxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by cyclic temperature-programmed (TP) as well as steady-state measurements. TPReactions exhibit an activity hysteresis of the catalyst with respect to temperature. As main cause of this activity hysteresis, which is exclusively a transient phenomenon, the dynamics of bulk oxygen were verified.

Transfer Functions for Periodic Reactor Operation: Fundamental Methodology for Simple Reaction Networks


A method for frequency response analysis of chemical reactors with periodically modulated inlet concentration is presented and demonstrated for simple first-order irreversible consecutive and parallel as well as reversible reactions applying an isothermal continuous stirred-tank reactor (CSTR). The frequency response of these reaction types is studied by simulations in time and frequency domain, the latter being based on Laplace transformation of the material balance. The results allow for clearly distinguish between the quasi and relaxed steady state as well as the full transient region with impact on designing reactors for dynamic operation. Furthermore, the relation between the dynamic response and the time constants of the system is discussed. The utilization of renewable electrical energy in chemical processes is highly demanding due to its inherently fluctuating availability, which induces the need for dynamic operation of chemical reactors. A methodology is presented and validated to describe chemical reactors under unsteady-state conditions with transfer functions in order to provide a link between electrical and chemical systems.

Thermochemical Biomass Conversion for Decentralized Power Generation with the Inverse Brayton Cycle


Biomass is an important energy source for decentralized power generation. The combination of a two-stage thermochemical conversion unit with an inverse Brayton cycle (IBC) is the subject of current research activities. Several advantages are expected compared to commercially available concepts. A commercially proven turbocharger from the automotive industry is used for the IBC unit. No cost-intensive gas cleaning is required due to an almost dust- and tar-free biomass conversion. The influence of the feedstock characteristics on the thermochemical conversion, the emissions, and the overall plant performance is subject to process optimization studies. Furthermore, validation of the concept is the target of a demonstration phase planned for a later stage of the research activities. A new concept combining a two-stage thermochemical conversion unit with an inverse Brayton cycle for decentralized power generation from biomass is introduced. The aim of the concept is to provide a simple and cost-efficient alternative to commercially available technologies. Preliminary laboratory results and process calculations are presented.

Continuous Hydrogenation of L-Arabinose and D-Galactose in a Mini Packed-Bed Reactor


The continuous hydrogenation of a mixture of L-arabinose and D-galactose over a Ru/C catalyst was investigated in a miniaturized packed-bed reactor. The reaction is one important step of the transformation of the naturally occurring hemicellulose arabinogalactan into valuable sugar alcohols. Process intensification was accomplished by reducing the reactor dimensions to a few millimeters; thus leading to better mass and heat transfer performance. The effects of temperature, pressure, and liquid flow rate on the yield and by-product formation are discussed. Based on a kinetic model derived from batch experiments, a model of the continuous reactor was developed and used for scale-up purposes. Sugar alcohols are versatile molecules that can be produced from renewable feedstocks. A kinetic model for the hydrogenation of L-arabinose and D-galactose over a ruthenium catalyst is reported. Experimental studies in a continuous miniaturized packed-bed reactor show that process safety and volumetric space-time-yield can be enhanced compared with a conventional slurry batch reactor.

Rotor-Stator Spinning Disc Reactor: Characterization of the Single-Phase Stator-Side Heat Transfer


The single-phase fluid-stator heat transfer in a rotor-stator spinning disc reactor in dependence on rotational Reynolds number, dimensionless throughput, Prandtl number, and aspect ratio is examined. For the selected ranges of these parameters, an increase in the stator-side Nusselt number with increasing Reynolds number, Prandtl number, and a higher throughput is found. Laminar and turbulent flow regions are observed, which coincide with a throughput- and a rotation-governed heat transfer regime, respectively. A Nusselt correlation to predict the experimental data in the turbulent flow regime within 20 % accuracy was established. A distinct increase in the overall volumetric heat transfer coefficient for a rise in Reynolds number was observed, being considerably higher compared to conventional tube reactors and twice as large in contrast with a similar rotor-stator setup. Stator-fluid heat transfer coefficients in a rotor-stator spinning disc reactor are investigated in dependence of the rotational Reynolds number, the dimensionless volumetric throughput, the Prandtl number, and the aspect ratio. A Nusselt number correlation is deduced from the experimental data giving design criteria for a better heat transport in rotor-stator reactors.

Local Mass Transfer Phenomena and Chemical Selectivity of Gas-Liquid Reactions in Capillaries


Gas-liquid reactions in microreactors play an important role in scientific research and industry. Enhancing heat and mass transfer allows overcoming mass transfer limitations in gas-liquid reactions. Mass transfer can be further increased by employing helically coiled capillaries, which induce Dean vortices and improve radial mixing. A colorimetric technique is proposed for gas-liquid reactions in straight and helically coiled capillaries in order to visualize local mass transfer phenomena and concentration distributions. This method is based on the consecutive oxidation of leuco-indigo carmine and enables noninvasive investigation of mass transfer and chemical selectivity in microchannels with high temporal and spatial resolution. A colorimetric technique is proposed to study local mass transfer phenomena and consecutive gas-liquid reactions in straight and coiled capillaries. This method enables noninvasive investigation of mass transfer and chemical selectivity in microchannels with high spatial resolution. An image processing algorithm is employed to derive concentrations from color intensity values.

Reaction Calorimetry for Exothermic Reactions in Plate-Type Microreactors Using Seebeck Elements


A flexible reactor and measurement setup to safely obtain thermokinetic data for exothermic chemical reactions in plate-type microreactors is presented. Precise heat flux measurement is realized by means of Seebeck elements and allows for direct as well as space- and time-resolved heat flux determination across the reactor. The microreactor used in this work is manufactured from poly(vinylidene fluoride) foils and consists of 11 SZ-shaped mixing channel elements. The Seebeck elements are calibrated by the Joule effect, while its performance is demonstrated in heat transfer and neutralization reaction experiments. Furthermore, the local resolution enables an estimation of mixing time scale for rapid reactions. A comparison of obtained results indicates good accordance with literature data and is the base of further investigations using the calorimeter. A Seebeck element-based reaction calorimeter for measuring temporally and spatially resolved heat flux profiles across a continuously operated microreactor is proposed. With it, hot spots can be localized, thermokinetic data can be obtained, and mixing time scales can be derived from the heat flux profiles. At the same time, transparent material allows for optical observation of the chemical reaction.

Overview Contents: Chemie Ingenieur Technik 11/2017