Modeling of a SrCe_(0.95)Yb_(0.05)O_3-αHollow Fibre Membrane Reactor for Methane Coupling

Proton-hole mixed conductor, SrCeo.95Yb0.05O3-α(SCYb), has the potential to be used as a membrane for dehydrogenation reactions such as methane coupling due to its high C2-selectivity and its simplicity for fabricating reactor systems. In addition, the mixed conducting membrane in the hollow fibre geometry is capable of providing high surface area per unit volume. In this study, mechanism of methane coupling reaction on the SCYb membrane was proposed and the kinetic parameters were obtained by regression of experimental data. A mathematical model describing the methane coupling in the SCYb hollow fibre membrane reactor was also developed. With this mathematical model, various operating conditions such as the operation mode, operation pressure and feed concentrations affecting performance of the reactor were investigated. The simulation results show that the cocurrent flow in the reactor exhibits higher conversion of methane and higher yield of ethylene compared to the countercurrent flow. In order to a     

Filtering surface water with a polyurethane-based hollow fiber membrane: effects of operating pressure on membrane fouling

Membrane fouling seriously restricts applications of membrane technology. A novel strategy was ap-plied in this study to retard membrane fouling by changing operating pressure with the pressure responsibility membrane. A polyurethane-based hollow fiber membrane was used to treat surface water for evaluating the effect of operating pressure on membrane fouling. Some bench-scale tests in dead-end mode were carried out. In the experi-ments without backwashing, as operating pressure increased, severe membrane fouling occurred on membrane sur-face, while the permeate quality was improved obviously, which is considered to be due to shrinkage deformation. The total resistance, irreversible resistance and reversible resistance under different backwash pressures were de-termined in filtration/backwashing test. With the increase of backwash pressure, the total resistance decreased, and more importantly, the irreversible resistance also decreased, which implies that small particles deposited inside membrane pores and cake layers on membrane surface are effectively removed. Similar results could be obtained in mass balance tests. The results of the present study indicate that the application of pressure responsibility membrane in surface water treatment may be an effective strategy for reducing membrane fouling.     

甲烷空气部分氧化制合成气喷动床反应器的研究

On the basis of hydrodynamic and scaling-up studies, a pilot-plant-scale thermal spouted bed reactor (50 mm in ID and 1500 mm in height) was designed and fabricated by scaling-down cold simulators. It was tested for making syngas via catalytic partial oxidation (CPO) of methane by air. The effects of various operating conditions such as operating pressure and temperature, feed composition, and gas flowrate etc. on the CPO process were investigated. CH4 conversion of 92.20％ and selectivity of 92.3% and 83.30/0 to CO and H2, respectively, were achieved at the pressure of 2.1 MPa. It was found that when the spouted bed reactor was operated within the stable spouting flow regime, the temperature profiles along the bed axis were much more uniform than those operated within the fixed-bed regime. The CH4 conversion and syngas selectivity were found to be close to thermodynamic equilibrium limits. The results of the present investigation showed that spouted bed could be considered as a potential type of chemical reactor for the CPO process of methane.     

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogena-tion method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and significant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.     

用于VOC回收的PVDMS-Al2O3中空纤维复合膜

Sorption isotherm of chloroform in polyvinyl dimethylsiloxane （PVDMS） polymer film was measured via the gravimetric method, and this film was confirmed experimentally to be good membrane material to recover chloroform from gas stream with high sorption capacity. A new PVDMS-Al2O3 composite hollow fibre membrane was further prepared by coating a PVDMS film on the outer surface of Al2O3 hollow fibre porpous substrate prepared by a dry/wet phase inversion method. Microstructure of the composite membranes was examined by scanning electron microscopy （SEM）, indicating the PVDMS coating layer was uniform, free of defects, and around 15μm thick. Performance of the PVDMS-Al2O3 composite hollow fibre membranes for chloroform recovery was investigated. By comparing the experimental data that derived from a mathematical model, the permeabilities of chloroform and nitrogen in the PVDMS polymer membrane were obtained. The effects of temperature and feed flow rate on the chloroform recovery and permeate concentration were investigated both experimentally and theoretically.     

PVDMS-Al_2O_3 Composite Hollow Fibre Membranes for Chloroform Recovery from Gas Streams

Sorption isotherm of chloroform in polyvinyl dimethylsiloxane(PVDMS)polymer film was measured via the gravimetric method,and this film was confirmed experimentally to be good membrane material to recover chloroform from gas stream with high sorption capacity.A new PVDMS-Al_2O_3 composite hollow fibre membrane was further prepared by coating a PVDMS film on the outer surface of Al_2O_3 hollow fibre porpous substrate prepared by a dry/wet phase inversion method.Microstructure of the composite membranes was examined by scanning electron microscopy(SEM),indicating the PVDMS coating layer was uniform,free of defects,and around 15μm thick.Performance of the PVDMS-Al_2O_3 composite hollow fibre membranes for chloroform recovery was investigated.By comparing the experimental data that derived from a mathematical model,the permeabilities of chloroform and nitrogen in the PVDMS polymer membrane were obtained.The effects of temperature and feed flow rate on the chloroform recovery and permeate concentration were investigated both experimentally and theoretically.     

中空纤维支撑液膜萃取Cu(II)的传递性能

The transport of Cu(II) from aqueous solutions containing buffer media through hollow fiber supported liquid membrane (HFSLM) using di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in kerosene as membrane phase and hydrochloric acid as striping phase was investigated. A set of factors were studied, including tube side velocity, shell side velocity, pH of the feed phase, Cu(II) concentration in the feed phase, buffer media concentration and D2EHPA concentration in the membrane phase. Experimental results indicate that the mass transfer coefficient increases with increasing both carrier concentration in the organic phase and flow rates on the tube side and shell side, and decreases with increasing initial Cu(II) concentration in the feed phase. With increasing pH value and acetate concentration in the feed phase, the mass transfer coefficient reaches a maximum value then decreases. The optimal operating conditions are obtained at pH value of 4.44 and 0.1 mol&;#8226;L－1 acetic ion concentration in feed phase, and carrier volume fraction of around 10% in kerosene as organic phase. A mathematical model of the transport mechanism through HFSLM is devel-oped. The modeled results agree well with the experimental ones.     

Modeling investigation of geometric size effect on pervaporation dehydration through scaled-up hollow fiber NaA zeolite membranes

A mass transfer model in consideration of multi-layer resistances through NaA zeolite membrane and lumen pressure drop in the permeate sidewas developed to describe pervaporation dehydration through scaled-up hollowfiber supported NaA zeolitemembrane. Itwas found that the transfer resistance in the lumen of the permeate side is strongly related with geometric size of hollow fiber zeolite membrane,which could not be neglected. The effect of geometric size on pervaporation dehydration could bemore significant under higher vacuumpressure in the permeate side. The transfer resistance in the lumen increaseswith the hollowfiber length but decreaseswith lumen diameter. The geometric structure could be optimized in terms of the ratio of lumen diameter to membrane length. A critical value of dI/L (Rc) to achieve high permeation flux was empirically correlated with extraction pressure in the permeate side. Typically, for a hollow fiber supported NaA zeolite membrane with length of 0.40 m, the lumen diameter should be larger than 2.0 mm under the extraction pressure of 1500 Pa.     

新型惰性膜反应器中丁烷氧化脱氢制丁二烯和丁烯

The oxidative dehydrogenation of butane to butadiene and butene was studied using a conventional fixed-bed ractor (FBR), inert membrane reactor (IMR) and mixed inert membrane reactor (MIMR). When IMR and MIMR were employed, a ceramic membrane modified by partially coating with glaze was used to distribute oxygen to a fixed-bed of 24-V-Mg-O catalyst. The oxygen partial pressure in the catalyst bed could be decreased. The effect of feeding modes and operation conditions were investigated. The selectivity of C4 dehydrogenation products (bntene and bntadiene) was found to be higher in IMR than in FBR. The feeding mode with 20% of air mixing with butane in MIMR was found to be more efficient than the feeding mode with all air permeating through ceramic membrane. The MIMR gave the most smooth temperature profile along the bed.     

Distinguished discriminatory separation of CO2 from its methane-containing gas mixture via PEBAX mixed matrix membrane

Highly selective separation of CO2 from its methane-containing binary gas mixture can be achieved by using Poly(ether-block-amide) (PEBAX) mixed matrix membranes (MMMs).According to FESEM and AFM analyses,silica-based nanoparticles were homogenously integrated within the polymer matrix,facilitating penetration of CO2 through the membrane while acting as barrier for methane gas.The membrane containing 4.6 wt％ fumed silica (FS) (PEBAX/4.6 wt％ FS) exhibits astonishing selectivity results where binary gas mixture of CO2/CH4 was used as feed gas.As detected by gas chromatography,in the permeate side,data showed a significant increase of CO2 permeance,while CH4 transport through the mixed matrix membrane was not detectable.Moreover,PEBAX/4.6 wt％ FS greatly exceeds the Robeson limit.According to data reported on CO2/CH4 gas pair separation in the literature,the results achieved in this work are beyond those data reported in the literature,particularly when PEBAX/4.6 wt％ FS membrane was utilized.     

热致相分离法iPP中空纤维微空膜结构与性能--稀释剂的作用

Isotactic polypropylene （iPP） hollow fiber microporous membranes were prepared using thermally induced phase separation （TIPS） method. Di-n-butyl phthalate （DBP）, dioctyl phthalate （DOP）, and the mixed solvent were used as diluents. The effect of α （DOP mass fraction in diluent） on the morphology and performance of the hollow fiber was investigated. With increasing α, the morphology of the resulting hollow fiber changes from typical cellular structure to mixed structure, and then to typical particulate structure. As a result, the permeability of the hollow fiber increases sharply, and the mechanical properties of the hollow fiber decrease obviously. It is suggested that the morphology and performances of iPP hollow fiber microporous membrane can be controlled via adjusting the compatibility between iPP and diluent.     

Diffusion Characteristics in Microcapsules

An equation of diffusion for microcapsules(hollow sphere)was developed,employing the mathematicalmodel for the diffusion characteristics of solid sphere.In the proposed equation,a combination diffusion coeffi-cient was introduced as a substitute for the diffusion coefficient in the solid sphere mathematical model and ex-pressed as a function of the diffusion coefficient inside solution of hollow sphere,as well as in the polymer mem-brane.With this modified model,the diffusion coefficients of glucose in NaCS(sodium cellulose sulfate)-PDADMAC(Poly-diallyl-dimethyl-ammonium chloride)membrane and in Ca-alginate gel membrane were deter-mined.The diffusion coefficient in NaCS-PDADMAC membrane was found to be 2.12×10~(-11)m~2·s~(-1)and thatin Ca-alginate membrane 2.62×10~(-10)m~2·s~(-1).     

PREPARATION OF ETHYLENE GLYCOL ACETATE THROUGH CATALYTIC OXIDATION OF ETHYLENE——ONE-STEP PROCESS WITH SIMULTANEOUS INTRODUCTION OF OXYGEN AND ETHYLENE INTO A Pd-Cu CATALYTIC SOLUTION

Ethylene glycol acetate can be prepared from ethylene by employing PdCl_2-CuCl_2-Cu(OAc)_2 in anacetic acid solution,usually involves two steps-acetoxylation and the regeneration of catalyst.In thispaper,a one-step process has been studied with oxygen and ethylene introduced simultaneously in a singlereactor.It was observed that there must be enough partial pressure of oxygen to oxidize Cu~+ to Cu~(2+)by keeping oxygen content at 8-10% in the raw binary gas mixture of oxygen and ethylene,whereby theactivity of the catalytic system could be maintained without formaton of CuCl residue.By using nitrogen as a diluent,the ratio of O_2/C_2H_2 could be kept in the non-explosive range.Itis claimed that 95% of the converted ethylene from the feed gas exists as ethylene glycol monoacetateand diacetate.     

超临界流体萃取制备脱沥青油与沥青微粒

A continuous three-stage supercritical fluid extraction (SFE) process with a capacity of 1.0kg.h^-1 was setup to extract petroleum residue by pentane to obtain more oil for further upgrading. A discharging system integrated to the bottom of the extractor was used to recover solvent as gas while asphalt was obtained as fine particles. The influence of operating conditions on the yield and quality of extracts, i.e., deasphalted oil (DAO) and resin, was studied in the range of temperature 150-220℃, pressure of 4.0-6.0 MPa and the mass ratio of solvent to oil feed (S/O) 2.5-5.0. The particle size distribution, apparent forms and the packing density, which vary with operating pressure, were measured. The particle structures were observed by SEM as well. With the modification to conventional processes, furnace can be eliminated for solvent recovery from asphalt phase, so as to reduce energy consumption.     

A METHOD FOR CALCULATING THE EXTENT OF REACTION OF SOLID PARTICLES WITH FLUID IN COMPLETELY MIXED REACTORS CONNECTED IN SERIES

When solid particles react with a fluid,the overall rate is influened by the fraction of the solidunconverted as well as by the operating conditions such as temperature and pressure.Calculation of solidsconversion in the individual reactor of a multi-stage reactor system has therefore to be based upon thesolids residence time distribution (RTD) in the respective stages.By using either the Dirac function δ(0) or the probability density function of the sum of independentrandom variables,the solids RTD in any stage of completely mixed reactors connected in series with nointerstage backflow has been obtained.The latter method has also been used in deriving general formu-las for the calculation of solids conversion when the order of chemical reaction is simple.For complexchemical reaction rate equations a stagewise procedure for numerical computation is proposed,and twocases are discussed according to whether the rate equation is expressed in its integral or differential formrespectively.     

用于污水处理的柔性纤维膜反应器氧传递及动力学研究

A flexible fibre biofilm reactor was developed for treatment of organic wastewaters. The hydrodynamic characteristics and mass transfer coefficients of oxygen were studied and compared with those of the conventional activated sludge processes. Tracer experiments were performed to obtain the residence time distributions of the reactors. The results indicated that both reactors could be treated as mixed flow reactors. The effects of flow rates of water and air on the overall mass transfer coefficient of oxygen were investigated, and the correlations between the mass transfer coefficient and the ratio of flow rates were obtained. Compared to the conventional activated sludge reactor, the mass transfer coefficients in the flexible fibre reactor were similar to but slightly lower, and less sensitive to the variation in the ratio of flow rates. It indicated that the fibre packing in the reactor hindered the oxygen transfer to some extent.     

反渗透过程的浓度极化及其传质系数测定

The relationship between osmotic pressure difference across the membrane and mass transfer coefficient is developed in this paper. On the basis of this relationship, a method for measuring mass transfer coefficient by using experimental data on reverse osmosis is established. Pitzer's equations are used to calculate osmotic pressure differences in order to assure accuracy of results. Under the conditions of constant operating pressure and bulk flow, mass transfer coefficient is scarcely affected by membrane structure, but decreases slightly with increasing feed concentration. The solute concentration in the polarization layer is calculated by using the measured values of mass transfer coefficient. Polarization layer concentration increases with augmentation in bulk concentration. However, their difference increases with increasing bulk concentration until a maximum difference is reached, and then decreases. Mass transfer coefficient increases with higher velocity of bulk flow. If mass transfer coefficient is so large that the ratio(PwΔπσ/k)becomes very small, polarization could be neglected.     

CFD modeling of turbulent reacting flow in a semi-batch stirred-tank reactor

For the mixing-sensitive reactions,both chemical kinetics and mixing conditions of the reactants determine the distributions of products.The direct quadrature method of moments combining with the interaction by exchange with the mean micro-mixing model (DQMOM-IEM) has been validated for the chemical reacting flows in microreactors.Quite encouraging simulation results offer great promise,but the applicability of this method is needed to be explored furthermore,such as in stirred reactors.In this work,the two-environment DQMOM-IEM model was created with C language and used to customize Fluent through the user-defined functions.The mixing effects on the course of parallel competing chemical reactions carried out in a semi-batch single-phase stirred reactor were predicted.The simulation results show that the rising feed velocity enlarges the volume of reaction zone and maximize the yield of the by-product,which also indicates that the feed stream is more difficultly dispersed into the main stream and the zone surrounding feedpipe exit with high turbulent kinetic dissipation rate cannot be efficiently used.     

合成气制二甲醚三相淤浆床反应器的数学模型研究

A mathematical model for a bubble column slurry reactor is presented for dimethyl ether synthesis from syngas. Methanol synthesis from carbon monoxide and carbon dioxide by hydrogenation and the methanol dehydration are considered as independent reactions, in which methanol, dimethyl ether and carbon dioxide are the key components. In this model, the gas phase is considered to be in plug flow and the liquid phase to be in partly back mixing with axial distribution of solid catalyst. The simulation results show that the axial dispersion of solid catalysts, the operational height of the slurry phase in the bubble column slurry reactor, and the reaction results are influenced by the reaction temperature and pressure, which are the basic data for the scale-up of reactor.     

Suppressing secondary reactions of coal pyrolysis by reducing pressure and mounting internals in fixed-bed reactor

Pyrolysis of Shenmu coal was performed in fixed-bed reactors indirectly heated by reducing operating pressure and mounting internals in the reactor to explore their synergetic effects on coal pyrolysis. Mounting internals particularly designed greatly improved the heat transfer inside coal bed and raised the yield of tar production.Reducing pressure further facilitated the production of tar through its suppression of secondary reactions occurring in the reactor. The absolute increase in tar yield reached 3.33 wt% in comparison with the pyrolysis in the reactor without internals under atmospheric pressure. The obtained tar yield in the reactor with internals under reduced pressure was even higher than the yield of Gray–King assay. Through experiments in a laboratory fixed bed reactor, it was also clarified that the effect of reducing pressure is related to volatile release rate in pyrolysis. It did not obviously vary tar yield at pyrolysis temperatures below 600 °C, while the effect was evident at 650 and 700 °C but became limited again above 800 °C. Under reduced pressure the produced tar contained more aliphatics and phenols but less aromatics.