Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.     

Transient behavior of a zeolite membrane under non-linear conditions

A simplified mathematical model is proposed to provide an analytic solution for the transient behavior of a Langmuirian zeolite membrane subjected to a step increase in sorbate pressure at the upstream surface at time zero. The concentration profiles derived from the simplified model agree with those calculated by numerical solution of the governing partial differential equation. The model is used to investigate the validity of the classical time-delay method of measuring diffusion in the adsorbed phase. Under non-linear conditions the time delay depends on the degree of non-linearity as well as on the diffusional time constant. Under highly non-linear conditions application of the classical linear model yields apparent diffusivity values that are about four times larger than the limiting value (D₀).The new model is used to reanalyze experimental permeation diffusivity data for p-xylene in a single crystal zeolite membrane. The resulting D₀ values are shown to be consistent with the values determined by other experimental techniques.     

Synthesis of zeolite L membranes with sub-micron to micron thicknesses

The growth of zeolite membranes with controlled thicknesses in the sub-micron to micron region is examined, using zeolite L as the example. It was demonstrated that by controlling the concentration of the zeolite solid load and suspension viscosity, dip-coating provided a method to prepare zeolite seed layers of controlled thicknesses. Disk-shaped zeolite L crystals, with size distribution of 0.5–2 μm in diameter, were used as seed crystals for the growth of 2–7 μm thick membranes. By choosing the composition of the secondary growth medium, as well as time and temperature, crystal growth primarily occurred along the xy-plane in these micron plus-thickness membranes, with eventual thickness similar to the originally deposited seed layer. For the synthesis of sub-micron-sized membranes, seed crystals from 20 to 60 nm were used and growth was observed along the z-axis. The optimum secondary growth conditions was found to occur at 60 h of growth time (40 h for sub-micron membranes) using a temperature of 110 °C with a solution composition of 10K₂O:1Al₂O₃:20SiO₂:2000H₂O. Membranes were characterized by electron microscopy and single gas permeation studies, providing confirmation of membrane densification.     

Permeation behavior during the catalytic oxidation of CO in a Pt-loaded Y-type zeolite membrane

A Pt-loaded Y-type zeolite (Pt/NaY) membrane was prepared on the surface of a porous α-Al₂O₃ support tube by hydrothermal synthesis and then ion-exchanged with platinum. The thickness of the zeolite layer and the amount of Pt loaded were ca. and , respectively. The membrane was employed in the form of a cylindrical thin catalyst for the selective oxidation of CO in an H₂-rich mixture. A mixture of CO, O₂ and H₂ was fed to the outer surface of the membrane, and CO was selectively oxidized during its permeation through the thin layer. The permeation fluxes for H₂ and CO were determined at 423-. Permeation fluxes also calculated by means of a mathematical model using effective diffusion coefficients and reaction kinetics. The effective diffusion coefficients through the zeolite membrane were estimated from gas permeation test data, obtained at 423-, and the oxidation rates of CO were determined over a particulate catalyst that had the same composition as the Pt/NaY membrane. As a result, the diffusion coefficients of O₂, N₂ and CO were determined to be (0.7-1.0) at 423-, and the activation energies for the rate constants for CO oxidation were 61-. The predicted permeation fluxes of H₂ and CO using the mathematical model were in good agreement with the experimental data, when the oxidation selectivity of CO to H₂ was assumed to be 80% in the model calculation.     

On the isopropylation of naphthalene over zeolite catalysts in the high-pressure fixed-bed flow reactor

Catalytic performances of various dealuminated mordenite catalysts for the isopropylation of naphthalene by isopropyl alcohol with decalin or cyclohexane as a solvent were investigated in a high-pressure fixed-bed flow reactor. It was found that dealumination of H-mordenite could substantially improve the catalytic conversion, selectivity and stability. The catalyst with steam treatment at 700 °C followed by acid leaching was revealed to exhibit high and comparatively stable conversion of ca. 37% with the high 2,6-/2,7-DIPN ratio of ca. 3. Reaction conditions, such as reaction temperature, pressure, space velocity and solvent, could significantly influence the catalytic performance, except for the 2,6-/2,7-DIPN ratio. The catalytic behavior is discussed in relation with catalyst porosity and acidity.     

凹凸棒黏土直接碱溶合成4A分子筛的研究

以凹凸棒黏土为原料,采用直接碱溶法合成4A分子筛.探讨了晶化温度、水钠比、硅铝比、晶化时间等对钙离子交换能力的影响.     

用工业品甲基叔丁基醚合成TBHQ的研究

研究了以工业品甲基叔丁基醚（MTBE）和对苯二酚（HQ）为原料,在硫酸催化下,合成食品抗氧剂TBHQ的工艺参数。对催化剂的活性、原料的配比和反应时间等进行了优化考察。当对苯二酚∶甲基叔丁基醚∶硫酸=1∶1∶0.5（mol）,反应温度为115℃,反应时间3 h,TBHQ的收率达77.65%。与传统方法相比,该方法具有价廉、操作简单的特点,具有较高的开发、应用价值。     

超声波条件下膨润土合成4A沸石

在低温条件下,膨润土在超声波下快速合成了4A沸石,分别用粒度、XRD、SEM等进行了表征.结果表明,膨润土在超声波下合成4A沸石的速度是膨润土酸化法的4倍,合成产物的白度为95%,钙离子交换量为328 mg/g4A沸石,平均粒径为460 nm.     

Synthesis of mordenite using kaolin as Si and Al source

The main purpose of this work was to study mordenite synthesis using kaolin as a Si and Al source. The influence of crystallization time and seed addition were studied. The obtained zeolites were characterized by: XRD, SEM, nitrogen adsorption and chemical analysis. Kaolin showed to be a promising source of Si and Al for mordenite synthesis. Seed addition led to more highly crystalline phases. Kaolin yielded mordenite whereas ZSM-5 was obtained from calcined kaolin. Longer synthesis times and seed addition favored mordenite formation.     

A composite catalytic polymer membrane reactor using heteropolyacid-blended polymer membrane

The vapor-phase MTBE decomposition was examined in a shell and tube-type catalytic membrane reactor (CMR). 12-Tungstophosphoric acid (PW) was used as a catalyst and poly-2,6-dimethyl-1,4-phenylene oxide (PPO) was used as a polymer material. A single-phase CMR (PW-PPO/Al₂O₃, type-1) and a composite CMR (PW-PPO/ PPO/ Al₂O₃, type-2) were successfully designed and characterized. It was revealed that the single-phase PW-PPO/ Al₂O₃ showed perm-selectivities for reaction products. The selective removal of methanol through the catalytic membrane shifted the chemical equilibrium toward the favorable direction in the MTBE decomposition. The PWPPO/ PPO/ Al₂O₃ showed the better performance than PW-PPO/ Al₂O₃. The enhanced performance of PW-PPO/ PPO/ Al₂O₃ CMR was due to the intrinsic perm-selectivity of PW-PPO and the additional separation capability of sub-layered PPO membrane.     

Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA zeolite composite membrane

High-quality zeolite NaA membranes were synthesized on modified α-alumina supports. The surface of macroporous α-alumina supports was modified by deposition of an ultrafiltration layer of γ-alumina. The zeolitic top layers were synthesized via the secondary growth method. The required seeds for the membrane synthesis were prepared via the hydrothermal synthesis using organic template of tetra methyl ammonium hydroxide (TMAOH) to obtain nano-sized seeds. The synthesized seeds and membranes were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The separation performance of membranes was evaluated in pervaporation (PV) dehydration of ethylene glycol (EG). Effect of operational parameters including feed composition, feed flow rate, and feed temperature on separation performance of the synthesized NaA zeolite membranes were investigated. The membranes showed separation factor of 10,996 and high total flux of 7.16 kg m⁻² h⁻¹ for feed temperature of 80 °C, feed flow rate of 1.5 L/min, and feed concentration of 90 wt.% EG.     

分子筛膜合成的研究进展

作者主要就分子筛膜最新合成方法展开论述,主要介绍了最近十年来分子筛膜合成方法取得的新进展,如二次合成法、微波合成法、堵孔法、脉冲激光沉积法、电泳沉积法、汽相法、两步变温法、两步变浓度法等方法的应用,能够给该领域或即将踏入该领域的研究者提供一定的参考价值.     

Solid electrolyte membrane reactors: Status and trends

A survey of recently published research work on solid electrolyte (SE) membrane reactors is given, with focus on high-temperature oxygen ion conductors, high-temperature proton conductors and low-temperature proton conductors. In these three material classes, the current status and the future trends of membrane reactor development are briefly elucidated. SE membrane reactor principles are realized in gas sensors, fuel cells, electrolyzers and reactors for partial oxidation. In all these fields SE membranes are in contact with porous electrolyte layers at which anodic or cathodic electrochemical reactions take place. In the area of membrane reactors using high-temperature oxygen ion conductors, there is a trend towards lower operating temperatures on order to ensure stable long-term operation of the membrane materials, and to match the optimal temperature window of the applied catalysts. As a younger generation of ion conducting ceramics, high-temperature proton conductors offer new possibilities for the implementation of electrochemical membrane reactors. Finally, current trends in the application of low-temperature proton conductors being based on polymeric materials are discussed. These materials can not only be used for fuel cells but also as membranes in hydrogenation or oxidation reactors.     

改性β沸石催化剂用于甲醇和异丁烯合成MTBE

采用改性β沸石催化剂,以甲醇和异丁烯为原料气相合成甲基叔丁基醚(MTBE),发现在一定范围内适当增加沸石酸性有利于MTBE的合成,并用FTIR对改性沸石的结构和性能进行了表征。     

Techno-economic evaluation of the direct conversion of CO2 to dimethyl carbonate using catalytic membrane reactors

The production of dimethyl carbonate (DMC) caught more interest in the past decades due to its versatile use (e.g. as fuel additive), low toxicity and fast biodegradability. Different ‘green’ production routes are being developed to replace the conventional and rather toxic production of DMC via phosgene. The direct conversion of CO₂ and methanol toward DMC is an environmental and economically interesting production route for the chemical industry.This work describes the process design of the direct conversion of CO₂ to dimethyl carbonate, providing a valuable insight and a better understanding of the process limitations. In this design, membrane reactors are used for continuous removal of water by-product, in order to overcome the equilibrium limitations. The rigorous Aspen Plus simulations show that even when using an excess of methanol, the attainable conversion is low and the DMC concentration in the reactor effluent is less than 1.5 mol%. Purifying this diluted stream to the desired concentrations demands large size equipment and a substantial amount of energy (13.61 kWh/kg DMC) resulting in high investment and utility costs, thus making the process not profitable. The focus for new membrane reactors could be on the selective removal of DMC (instead of water) from the reaction area to allow for a more concentrated DMC stream.     

Performance of ceramic composite membrane for the separation of VOCs

Zeolite composite membranes were prepared for the separation of VOCs by the pressurized coating method. On the top of the composite membrane, TiO₂, polyimide or polyethersulfone were coated by the same tech-100 nm-sized nique.ZSM-5 coated membranes show higher selectivity for n-hexane in n-hexane/benzene mixture than 500 nm sized ZSM-5 coated membrane. Composite membrane coated with 100 nm zeolite and polymer showed the highest selectivity (44) for n-hexane/benzene.     

Preparation of ITQ-29 (Al-free zeolite A) membranes

Membranes consisting of Al-free ITQ-29 (a zeolite with the LTA-type structure) have been prepared on alumina tubular supports by seeded liquid phase hydrothermal synthesis. A supramolecular organic structure-directing agent (SDA) was used for the synthesis of ITQ-29 that must be removed from the zeolite pores to activate the membrane for permeation. The high temperature needed to decompose SDA from small-pore zeolites could create thermal stresses that affect the final membrane quality. Because of this, the effect of the atmosphere (N₂, O₂, air and O₃/air) and temperature of the membrane calcination process has been studied. An ITQ-29 membrane activated by means of the combination of pyrolytic (at 723 K) and ozonization (at 473–573 K) treatments gave the best results, with N₂/CH₄ and N₂/propane selectivities well above the corresponding Knudsen values.     

Progress in membrane gas–liquid reactors

Gas–liquid reactions are crucially important in chemical synthesis and industries. In recent years, membrane gas–liquid reactors have attracted great attentions due to their high selectivity, productivity and efficiency, and easy process control and scale‐up. Membrane gas–liquid reactors can be divided into three categories: dispersive membrane reactor, non‐dispersive membrane reactor and pore flowthrough reactor. The progress in membrane gas–liquid reactors, including features, applications, advantages and limits, is briefly reviewed. © 2012 Society of Chemical Industry     

合成MTBE催化剂的研究动态

综述了合成ＭＴＢＥ的催化剂的发展及现状,并对各种催化剂的性能进行了评价,提出了我国发展ＭＴＢＥ生产的迫切性,并对今后催化剂的开发提出了建议。     

Synthesis of nano crystalline zeolite Y from bentonite

Zeolite Y was synthesized from bentonite via the hydrothermal method. The effects of various parameters on the synthesis were investigated. The samples were characterized by XRD, XRF, IR, DTG and wet chemical analysis. The results show that crystallization temperature, aging time and concentration of sodium hydroxide play important roles in the formation of the zeolite. P zeolite was the competitive phase and present in most of the products. However, under optimized conditions, such as crystallization temperature (97 °C), aging time (20 h), concentration of NaOH (3N), pure zeolite Y with high crystallinity was synthesized. The results showed that optimization of the process results in a commercial route to synthesis zeolite Y from bentonite.