A novel ceramic membrane reactor system for the continuous enzymatic synthesis of oligosaccharides

The continuous enzymatic production of galactosyl-oligosaccharides (GOS) from lactose as a substrate using a new type of ceramic membrane reactor system was investigated. GOS are non-digestible oligosaccharides and have recently attracted interest as prebiotics. However, the composition of oligosaccharides fraction and the variability in β-glycosidic linkages depend on the enzyme source. In the study presented below, native, physically immobilized, β-galactosidase from Kluyveromyceslactis (EC 3.2.1.23) was used as enzyme to catalyse transgalactosylation reaction to produce GOS, competed against the hydrolysis of lactose into its two component monosaccharides, glucose and galactose. To optimize GOS yielded, process conditions were varied: the average residence time of the enzyme was varied in the range of 13 to 24 min, the trans-membrane pressure (TMP) was in the range of 1 to 2 bar and the initial concentration of substrate was varied from 10 to 30% (w/w). Regarding the conditions investigated here, the maximum oligosaccharide concentration exceeded 38% (w/w) when the average residence time was 24 min, the TMP was 2 bar and an initial lactose concentration of 30% (w/w) was adjusted.     

Isobutane dehydrogenation reaction in a packed bed catalytic membrane reactor

A packed-bed catalytic ceramic membrane reactor (PBCMR) was used for the isobutane dehydrogenation reaction. The experimental results have shown that through the use of the membrane reactor one can attain better conversions and yields than in a conventional reactor operating under the same outlet pressure and temperature, and feed composition conditions.     

Methyl tert-butyl ether decomposition over heteropoly acid catalyst in a cellulose acetate membrane reactor

In this study the methyl tert-butyl ether (MTBE) decomposition over H₃PW₁₂O₄₀ was carried out in a cellulose acetate membrane reactor. The permeability of methanol through the cellulose acetate membrane was about 30 and 300 times higher than that of either isobutene or MTBE, respectively. The isobutene selectivity in the fixed bed reactor was only slightly higher than the methanol selectivity due to the side reaction. In the cellulose acetate membrane reactor, however, the isobutene selectivity in the rejected stream was 68% and the methanol selectivity in the permeated stream was up to 97%. The MTBE conversion in the membrane reactor was about 7% higher than that in the membrane-free fixed bed reactor under the same reaction conditions. The enhanced performance of the membrane reactor in this reversible reaction was mainly due to the selective permeation of methanol which resulted in a methanol-deficient condition suppressing MTBE synthesis reaction.     

Application of heteropoly acid catalyst in an inert polymer membrane catalytic reactor in ethanol dehydration

The ethanol dehydration reaction was carried out in an inert membrane catalytic reactor. 12-Tungstophosporic acid as a catalyst and polysulfone as an inert membrane were used in this study. Ethanol conversion and ethylene selectivity were remarkably enhanced in comparison with those in a fixed-bed reactor under the same reaction condition.     

Contribution to emission reduction of CO2 by a fluidized-bed membrane dual-type reactor in methanol synthesis process

In this work, a fluidized-bed membrane dual-type reactor was evaluated for CO₂ removal in methanol synthesis process. The feed synthesis gas is preheated in the tubes of the gas-cooled reactor and flowing in a counter-current mode with reacting gas mixture in the shell side. Due to the hydrogen partial pressure driving force, hydrogen can penetrate from feed synthesis gas into the reaction side through the membrane. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed-bed reactor and the chemical reaction is initiated by the catalyst. The methanol-containing gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. A two-phase dynamic model in bubbling regime of fluidization was developed in the presence of long-term catalyst deactivation. This model is used to compare the removal of CO₂ in a FBMDMR with a conventional dual-type methanol synthesis reactor (CDMR) and a membrane dual-type methanol synthesis reactor (MDMR). The simulation results show a considerable enhancement in the CO₂ conversion due to have a favourable profile of temperature and activity along the fluidized-bed membrane dual-type reactor relative to membrane and conventional dual-type reactor systems.     

Selective hydrogenation of sunflower seed oil in a three-phase catalytic membrane reactor

Continuous hydrogenation of sunflower seed oil has been carried out in a novel three-phase catalytic membrane hydrogenation reactor. The membrane reactor consisted of a membrane impregnated with Pd as the active catalyst, which provided a catalytic interface between the gas phase (H₂) and the oil. Hydrogenations were carried out at different pressures, temperatures, and selectivities, and the formation of trans isomers was monitored during the hydrogenation runs. For the three-phase catalytic membrane reactor, interfacial transport resistances and intraparticle diffusion limitations did not influence the hydrogenation reaction. Hydrogenation runs under kinetically controlled conditions showed that oleic and elaidic acid were not hydrogenated in the presence of linoleic acid. Initial formation of stearic acid was caused by direct conversion of linoleic acid into stearic acid by a shunt reaction. Furthermore, high selectivities led to high trans levels, which is in accordance with the many published data on hydrogenation of vegetable oils in slurry reactors. Finally, the catalytic membrane showed severe catalyst deactivation. Only partial recovery of the catalyst activity was possible.     

Distribution of soap in a membrane reactor in the production of fame from waste cooking oil

A continuous‐flow membrane reactor was constructed for the production of fatty acid methyl ester (FAME) from waste vegetable oil with high free fatty acid (FFA) content. FAME was produced via base‐catalysed transesterification with methanol at two FFA levels: 4.8 and 10 mass%. The effect of the ceramic membrane pore size on the separation of soap and triglycerides from the FAME in the reactor was investigated. In all cases, the triglyceride was completely retained in the reactor, yielding free and total glycerine contents in the produced FAME significantly below the maximum limits of the ASTM D6751 standard. The soaps produced in the reaction mixture were not completely retained in the reactor and did not affect the FAME production process. © 2012 Canadian Society for Chemical Engineering     

Comparison of a contactor catalytic membrane reactor with a conventional reactor: example of wet air oxidation

A wet air oxidation reaction was carried out in a gas/liquid catalytic membrane reactor of the contactor type. The oxidation of formic acid was used as a model reaction. The mesoporous top-layer of a ceramic tubular membrane was used as catalyst (Pt) support, and was placed at the interface of the gas (air) and liquid (HCOOH solution) phases.

A similar reaction was carried out in a conventional batch reactor, using a steering rate high enough to avoid gas-diffusion limitations, and exactly identical conditions than for the CMR (amount of catalyst, pressure, etc.). At room temperature, the CMR showed an initial activity three to six times higher than the conventional reactor. This activity increase was attributed to an easier oxygen access to the catalytic sites. Nevertheless, the catalytic membrane gradually deactivated after a few hours of operation. Different deactivation mechanisms are presented.     

Simulation study of production of fine ceramic powders in a cyclone reactor

A numerical simulation study of production of fine ceramic powders in an innovative vapor-phase aerosol reactor is described. Arrangement is typical of reverse-flow cyclone equipment; no similar device is present in current scientific literature and industrial technology. The cyclone reactor has a potential technological application as it realizes process intensification by two simultaneous operating advantages: (i) curly flow reduces recirculation of as-synthesized particles towards flame region, and (ii) cyclone arrangement segregates large particles. As a result, ceramic powders with narrower particle size distribution can be produced with regard to traditional equipment. The study is based on the re-modeling of an existing industrial reactor for production of fine TiO₂ according to a cyclone configuration; particle size distributions from simulation and plant are compared.     

陶瓷膜反应器中环己酮氨肟化的催化剂失活机制与再生

基于陶瓷膜反应器开发出无有机溶剂的环己酮氨肟化新工艺,探讨TS-1催化剂失活机制。采用XRD及Rietveld全谱拟合、FT-IR、N₂吸附-脱附、TGA/DSC、GC-MS等手段对TS-1分子筛的骨架结构、晶胞参数、比表面积和有机物种类进行了表征分析。结果表明,无有机溶剂的环己酮氨肟化反应过程中,存在硅流失的现象,但TS-1骨架完整,晶胞参数未明显变化;环己酮、环己酮肟及反应副产物等吸附在TS-1催化剂的表面及孔道内,使比表面积下降52.6%、孔体积减少了41.6%,是造成TS-1失活的主要原因,空气氛围中于600℃煅烧3 h,可以恢复催化剂的活性。     

Comparative analysis for fouling characteristics of river water,secondary effluent,and humic acid solution in ceramic membrane ultrafiltration

Ceramic membrane ultrafiltration experiments were performed with 7-channel tubular membrane (molecular weight cutoff = 300 kD) at a constant transmembrane pressure and crossflow rate under recirculation mode. In the experiments, the fouling characteristics of river water (RW, dissolved organic carbon (DOC) = 3.4 mg/L) were compared with humic acid solution (HA1, DOC = 3.7 mg/L). Also, the fouling behaviors of secondary effluent (SE, DOC = 7.9 mg/L) were compared with HA2 (DOC = 8.5 mg/L). Fluorescence excitation-emission matrix, modified Hermia’s model, and resistance-in-series model were used to analyze the fouling characteristics. Results demonstrated that RW and SE could cause ceramic membrane fouling more rapidly due to their hydrophilic organic compositions in comparison with hydrophobic HA.     

Selectivity of partial hydrogenation reactions performed in a pore-through-flow catalytic membrane reactor

The selectivity of partial hydrogenation reactions of unsaturated substrates was studied in a membrane reactor operating at 323 K and 40 bar hydrogen pressure. The reactor system was constructed as a loop of a saturation vessel and a membrane module in which the reaction mixture was resaturated with hydrogen up to 100 times. In a porous membrane made from cross-linked polyacrylic acid palladium nanoparticles were incorporated as catalysts. A well-defined residence time within the membrane was achieved due to a defined pore structure of the membrane and a convective mass flow of the reaction mixture through the membrane. The selectivity for the partially hydrogenated products was investigated as a function of the pore size of the PAA membrane and was compared to commercially available catalysts. Compared to experiments with supported catalysts (Pd/C and Pd/Al₂O₃) in a slurry and a fixed bed reactor the selectivity for the desired products could be increased by 3% (1-octyne) up to 40% (geraniol).     

Theoretical and experimental analysis of methane steam reforming in a membrane reactor

Thermal effects on methane steam reforming process were analyzed, in a Pd-Ag (23wt%) membrane reactor as a function of several parameters, such as temperature, reactant and sweep-gas flow rate, and reactant molar ratio. Heat transfer from the oven was very important for the outlet methane conversion, which also depends on the temperature profile along the reactor. In particular, when the reactant flow rate was high the conversion degree decreased because the energy supplied was not sufficient to maintain the temperature in the reactor. A non-isothermal mathematical model was presented which reproduced the experimental data.     

Upgrading of a syngas mixture for pure hydrogen production in a Pd-Ag membrane reactor

Water gas shift (WGS) is a thermodynamics limited reaction and CO equilibrium conversion of a traditional reactor is furthermore reduced owing to the presence of H₂ (ca. 50%) in the feed stream coming from a reformer.The upgrading of a simulated reformate stream was experimentally investigated as a function of temperature (280-320 °C), feed pressure (up to 600 kPa), gas hourly space velocity (GHSV), etc. using a Pd-alloy membrane reactor (MR) packed with a commercial catalyst CuO/CeO₂/Al₂O₃; no sweep gas was used. The MR performance was also evaluated using new parameters such as conversion index, H₂ recovery and extraction index, etc., which evidence the advantages with respect to a traditional reactor.A Pd-based MR operated successfully overcoming the thermodynamic constraints of a traditional reactor and, specifically, the drawback introduced by the hydrogen presence. In fact, a CO conversion of 90% significantly exceeded (three times) the thermodynamics upper limit (<36%) of a traditional reactor owing to ca. 80% of hydrogen permeated through the membrane.The overall process performance was significantly improved by the presence of the Pd-based membrane and, thus, by the high reaction pressure which allowed and drove the hydrogen permeation.     

Hydrogen production from oxidative steam reforming of ethanol in a palladium-silver alloy composite membrane reactor

In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd-Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. An ethanol-water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2, 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn-Cu commercial catalyst (MDC-3). The reaction temperatures were set at 593-723 K and the pressures at 3-10 atm. The hydrogen flux in the permeation side increased proportionately with increasing pressure; however, it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd-Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO₂ increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same.     

Catalytic partial oxidation of methane to synthesis gas in a ceramic membrane reactor

Methane has been selectively converted to synthesis gas using a two-zone fixed bed of a Ni/Al₂O₃ catalyst inside a modified ceramic membrane. The first zone of the reactor was surrounded by an impervious wall, and therefore behaved as a conventional fixed bed reactor. In the second zone, some of the reaction products could preferentially diffuse out of the reactor, which yielded higher than equilibrium methane conversions. The influence of the different operating conditions has been studied, and the performance of the membrane reactor has been compared to that of a fixed bed reactor. The membrane reactor has also been used at pressures above atmospheric (2 bar), with good conversions and selectivities.     

CFD simulation of flow field and resistance in a 19-core tandem ceramic membrane module

CFD simulation of the permeation process of a 19-core tandem ceramic membrane module was established to investigate flow field and resistance and its change in permeate flux to the membrane element position and the channel of each membrane element. The results show that when the volume flow rate changes from26 m~3·h~(-1) to 89 m~3·h~(-1), the resistance of each part of the membrane module increases gradually. The increase in resistance loss in the membrane element is faster than the plates and the bell mouths. In a single ceramic membrane module, the maximum difference in flow rate of each membrane tube is 7.23%. In a single membrane tube,the outer ring channels 3–5, 3–6, 3–7, 3–8 are relatively slow. The maximum mass flow deviation from the mean is 2.7%. This work helps to clarify the flow mechanism within the modules, optimize the structure of the equipment and provide a reliable basis for the improvement of industrial ceramic membrane modules.     

Investigation on the partial oxidation of methane to syngas in a tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane reactor

A perovskite material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al₂O₃ catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO₂ reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm² min oxygen permeation flux.     

Electrolytic synthesis of succinic acid in a flow reactor with solid polymer electrolyte membrane

This paper describes the galvanostatic synthesis of succinic acid from maleic acid in an ion exchange membrane flow cell. The electrolysis was carried out at stainless steel, lead and copper cathodes under variable conditions of current density and substrate concentration. Depending upon the experimental conditions, the yield of succinic acid varied from 95 and 99% with a coulombic efficiency of 80–99%. The product was characterized by various physicochemical techniques, viz. ¹H-NMR, IR and UV–Visible spectroscopy and elemental analysis. The operational conditions giving maximum yield of product were identified. The mechanism of electrochemical reduction of maleic acid and advantages of using a catholyte without supporting electrolyte are discussed.