Synthesis of MTBE in zeolite membrane reactors

A zeolite membrane was employed to selectively remove water from the reaction atmosphere during the gas-phase synthesis of methyl-tert-butyl ether (MTBE) from tert-butanol and methanol. This reaction was carried out over a bed of Amberlyst™ 15 catalyst packed on the inside of a zeolite tubular membrane. The results obtained with different hydrophilic membranes (mordenite or NaA zeolite) are presented. Prior to reaction, the zeolite membranes were characterized by measuring their performance in the separation of the equilibrium mixture containing water, methanol, tert-butanol, MTBE and isobutene. The results obtained with zeolite membrane reactors (ZMR) were compared with those of a fixed bed reactor (FBR) under the same operating conditions. MTBE yields obtained with the ZMR at 334 K reached 67.6%, under conditions where the equilibrium value without product removal (FBR) would be 60.9%.     

Membrane reactors in chemical production processes and the application to the pervaporation-assisted esterification

When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process. In this paper a review on membrane reactors with special emphasis on membrane-assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation-assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction. The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation-assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.     

含氟体系中MFI型分子筛膜的制备及其乙醇/水分离性能

以氟化铵为矿化剂、四丙基溴化铵为模板剂,在负载晶种的钇稳定氧化锆(YSZ)中空纤维支撑体表面合成了MFI型分子筛膜,并用于乙醇/水的分离;系统考察了氟硅比(n_NH4F/n_SiO2)、合成时间等条件对膜分离性能的影响,在n_NH4F/n_SiO2为0.8、合成时间为8 h下合成出高性能膜,其通量达8.2 kg·m^-2·h^-1、乙醇/水分离因子为47;同时研究了MFI型分子筛膜在乙醇/水体系中的分离稳定性,揭示出该方法所合成膜表面无Si-OH,从而避免了Si-OH与乙醇反应而带来膜分离性能的下降.     

沸石膜反应器苯脱氢反应性能

采用管式沸石膜反应器,研究了乙苯脱氢反应生成苯乙烯的性能。考察了不同渗透分离性能的沸石膜对乙苯脱氢反应的影响和不同沸石膜反应器上乙苯脱氢反应的规律。结果表明,与固定床操作条件下相比,沸石膜反应器乙苯转化率可提高近10％－16％,苯乙烯选择性可提高3％－5％。渗透分离性能是决定沸石膜提高脱氢反应性能的最重要因素,H2渗透量越大、H2／C3H8分离系数越高,对反应越有利。渗透分离性能相近但类型不同的沸石膜对乙苯脱氢反应性能有差异,其中Fe-ZSM-5沸石膜反应性能较好,这是杂原子Fe进入沸石骨架后引起的。反应后膜的渗透分离性能略有变化。     

TMCS修饰MFI分子筛膜的制备及乙醇/水分离稳定性的研究

采用三甲基氯硅烷（TMCS）作为修饰源对MFI分子筛膜进行表面改性,系统考察了TMCS浓度以及修饰时间对于MFI分子筛膜在分离乙醇/水混合物时的性能影响。SEM、XRD、²⁹Si NMR、FT-IR、接触角实验及分离实验结果表明,TMCS可以与硅羟基反应,嫁接分子筛膜表面,在消除膜表面硅缺陷的同时提高膜的疏水性及膜分离性能的稳定性。随着TMCS浓度以及反应时间的增加,修饰后MFI分子筛膜的通量及分离因子略有下降,但稳定性增强。在TMCS的浓度为0.4%（质量）,修饰时间为2 h时,所得到的膜具有最佳渗透汽化分离性能,并可在60℃下分离5%（质量）乙醇/水混合物时保持良好的稳定性。在连续90 h渗透汽化分离过程中,其渗透通量稳定在1.61 kg·m^-2·h^-1 左右,分离因子保持在20以上。     

Incorporation of vapor permeation process to esterification reaction of propionic acid and isopropanol for performance improvement

A commercial tubular zeolite membrane (NaA) was employed in a vapor permeation system to dehydrate the reaction mixture during the esterification of propionic acid with isopropanol. The reaction was performed in a batch reactor, using Amberlyst 15 as a catalyst with different weight fractions relative to propionic acid. Experiments were conducted to investigate the effect of the alcohol-to-acid molar ratio on the performance of the hybrid process. The integration of the chemical reaction with the vapor permeation process significantly enhanced the conversion of the reversible esterification reaction. It was observed that contrary to the effect of increasing alcohol-to-acid molar ratio from 1: 1 to 1.5: 1, the acid conversion and the permeated water flux decreased when the reactants molar ratio increased from 1.5: 1 to 3: 1. This effect was due to the reducing effect of reaction mixture composition on the boiling point and reaction and evaporation rates during the hybrid process. Also, increasing catalyst loading had noticeable influence on the acid conversion and the permeated water flux.     

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concen-tration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle. Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.     

HY分子筛催化合成油酸乙酯

采用NaY分子筛催化剂,经离子交换和高温焙烧制得HY分子筛,以油酸和乙醇为原料,在间歇反应釜进行酯化反应研究。考察反应温度、原料配比、催化剂用量和反应时间等条件对酯化反应的影响。结果表明,在反应温度180 ℃、n(油酸)∶n(乙醇)＝1∶2.5、催化剂用量为原料总质量的1.0%和反应时间4 h条件下,油酸转化率可达81.18%。实验中的HY分子筛表现出较高的活性和良好的稳定性。     

Mixed matrix membranes prepared from natural rubber/poly(vinyl alcohol) semi-interpenetrating polymer network (NR/PVA semi-IPN) incorporating with zeolite 4A for the pervaporation dehydration of water-ethanol mixtures

The pervaporation dehydration of water-ethanol mixtures was investigated using the mixed matrix (MM) membranes prepared from natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) semi-IPN embedded with the zeolite 4A. With the presence of NR as well as zeolite, the swelling of MM membranes in water was effectively suppressed. Examined by DSC, the non-freezing bound water in the MM membranes was found decreasing with more zeolite loading because the water-polymer interaction is diminishing. The sorption study of MM membranes revealed a preferential sorption to water with improved water sorption selectivity as increasing the zeolite loading. For pervaporation at 5 vol% water in feed, the reversed trade-off with respect to the zeolite loading was encountered such that the total permeation flux increased along with an enhancement of the water separation factor. For higher feed water concentration, despite the greater total permeation flux, the separation factor was reduced owing to the extensive swelling of the polymer matrix. The temperature dependency of the partial water and ethanol fluxes followed the Arrhenius relationship and the estimated activation energies for water flux were lower than those of the ethanol flux, suggesting that the developed MM membranes are highly water selective.     

Application of zeolite T membrane to vapor-permeation-aided esterification of lactic acid with ethanol

Zeolite T membranes were applied to vapor-permeation-aided esterification of lactic acid with ethanol. The hybrid process provided almost complete conversion within a short reaction time by removing water from the reaction mixture. Zeolite T membrane worked steadily for a long time. The reaction time-courses were described by a model based on the assumptions that the esterification obeyed second-order kinetics and the permeation flux of each component was proportional to its concentration in the reaction mixture. The final reaction liquid mixtures consisted mostly of ethyl lactate and ethanol with little ester of polylactic acids, although concentrated lactic acid solution was used as a source.     

Enhanced Conversion in the Direct Synthesis of Diethyl Carbonate from Ethanol and CO2 by Process Intensification

To overcome the low equilibrium conversion in the direct synthesis of diethyl carbonate from ethanol and CO₂ under moderate reaction conditions, the reaction was conducted in a membrane reactor packed with pelletized Cu‐Ni:3‐1 supported on activated carbon. A SiO₂/γ‐Al₂O₃ commercial membrane and zeolite A membranes synthesized on commercial Al₂O₃ supports were evaluated in the membrane reactor. Although characterization of the membranes by X‐ray diffraction confirmed the presence of a zeolite A layer on the supports, gas permeation and permselectivity tests of ethanol and water evidenced some defects of the synthesized membranes. An increase in conversion with respect to a conventional packed‐bed reactor was observed in the membrane reactors prepared on Al₂O₃, but equilibrium conversion was not attained. However, with the commercial membrane, the ethanol conversion was higher than the equilibrium conversion.     

Scale-up of NaA zeolite membranes onα-Al2O3 hollow fibers by a secondary growth method with vacuum seeding

NaA zeolite membranes were prepared by secondary growth method on the outer surface ofα-Al2O3 hollow fiber supports. Vacuum seeding method was used for planting zeolite seeds on the support surfaces. Hydrother-mal crystallization was then carried out in a synthesis solution with molar ratio of Al2O3:SiO2:Na2O:H2O=1:2:2:120 at 100 °C for 4 h. Effects of seeding conditions on preparation of hollow fiber NaA zeolite membranes were extensively investigated. Moreover, hollow fiber membrane modules with packing membrane areas of ca. 0.1 and 0.2 m2 were fabricated to separate ethanol/water mixture. It is found that the thickness of seed layer is obviously affected by seed suspension concentration, coating time and vacuum degree. Close-packing seed layer is required to obtain high-quality membranes. The optimized seeding conditions (seed suspension mass concentration of 0.5%–0.7%, coating time of 5 s and vacuum degree of 10 kPa) lead to dense NaA zeolite layer with a thickness of 6–8μm. Typically, an as-synthesized hollow fiber NaA zeolite membrane exhibits good pervaporation performance with a permeation flux of 7.02 kg·m?2·h?1 and separation factor N 10000 for sepa-ration of 90%(by mass) ethanol/water mixture at 75 °C. High reproducibility has been achieved for batch-scale production of hollow fiber NaA zeolite membranes by the hydrothermal synthesis approach.     

Tuning the framework polarity in MFI membranes by deboronation: Effect on mass transport

The polarity of a zeolite is an important parameter determining the transport and separation properties in zeolite packed beds and membranes. This study focuses on the systematic variation of the zeolite polarity for membrane applications by varying the amount of silanol groups within the framework of the MFI zeolite by deboronation and consecutive heat treatment from 9 to 4 silanol groups per unit cell. The decrease in the number of silanol groups after heat treatment is confirmed by diffuse reflection infrared Fourier transform (DRIFT) and ²⁹Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The permeation of pure water through the modified silicalite membranes is insensitive to the number of silanol groups, attributed to a decreased adsorption compensated by an increased diffusivity. The ethanol selectivity in water/ethanol mixtures shows an increase with decreasing amount of silanol groups. Residual boron in the zeolite may react with ethanol and decrease its adsorption capacity. A reduction in flux through the debronated MFI membranes was not observed after ethanol/water permeation.     

T型分子筛膜的制备及其对含酸乙腈-水的分离性能

石化医药行业会产生大量乙腈废液,通过无机分子筛膜分离技术进行回收可以创造可观的经济价值。然而,乙腈废液水含量较高,并且具有一定的酸性,目前应用比较广泛的NaA型分子筛膜不能在该体系下长期使用。使用自制的平均粒径为600 nm的T型分子筛作为晶种,采用真空涂敷法将晶种负载在α-Al₂O₃载体管表面,在150 ℃下水热晶化16 h制备出T型分子筛膜,并对其做膜性能评价实验。结果表明,自制的T型分子筛膜在进料流量为3.5 L/h、温度为100 ℃条件下对含有1%（质量分数）乙酸和10%水（质量分数）的乙腈混合溶液进行膜分离脱水实验,渗透通量为2.51 kg/（m ²·h）;在120 h长时间运行过程中,分离系数保持在2 250以上,T型分子筛膜性能基本保持不变。     

On a rapid method to characterize intercrystalline defects in zeolite membranes using pervaporation data

This work presents a mass-balance-based model devoted to the characterization of intercrystalline defects active to permeation in film-like zeolite membranes using pervaporation data. Relevant structural information concerning such domains can be obtained from the slope and intercept of the line that describes the increase of the flux pervaporated through a membrane with the absolute pressure in the liquid feed. Capillary forces appear to govern mass transfer within intercrystalline pores. The suitability of the model is assessed by using a collection of zeolite NaA membranes prepared on our premises for the separation of ethanol/water mixtures. The results show that, although a membrane displays high selectivity, a reduced number of defects in the zeolite layers cannot be ruled out. The model offers the advantage of enabling the characterization of large defects in pervaporation membranes at experimental conditions similar to those in which they are likely to be used.     

两步变温水热合成制备纯硅分子筛膜及其渗透性能

采用两步变温水热法在多孔不锈钢载体管上合成了Silicalite-1沸石膜,对合成的Silicalite-1膜进行了X射线衍射和扫描电镜及单成分气体渗透表征,并将其应用于渗透脱除水中乙醇,考察了晶化温度、合成液组成及合成次数对渗透性能的影响. 结果表明,用两步变温合成法可得到高性能的纯硅沸石膜,水/硅(摩尔比)为80且第二步晶化温度为165℃的条件下,只需经一次合成,可获得对乙醇水溶液具有高分离性能的膜,在60℃、乙醇浓度为4.8%(w)时,膜的通量为1.25 kg/(m2×h),分离系数为36.2,但经再次合成后,通量和分离系数均劣化. 水/硅(摩尔比)为225且第二步晶化温度为150℃条件下,经过再次合成,通量和分离系数均得到大大提高,在60℃和乙醇浓度为4.52%(w)时,通量和分离系数分别高达2.8 kg/(m2×h)和34.3,在如此高的分离系数下该通量达到了国内外报道的最高值.     

微波合成的NaA型分子筛膜在乙醇脱水中试及3万吨/年工业示范装置的蒸汽渗透性能研究

设计并搭建了分子筛膜脱水中试装置,对本课题组微波加热技术合成的工业级NaA型分子筛膜进行乙醇/水体系蒸汽渗透的性能研究,得到了NaA型分子筛膜的水渗透通量方程,水透量与原料液含水量、雷诺数之间的关系及变化规律。对精馏与膜分离耦合工艺进行流程模拟,提出了精馏与膜分离的最佳耦合点,并且给出了分子筛膜的价格和寿命对总费用的影响,为NaA型分子筛膜工业应用提供重要参考依据。根据中试结果,在江苏索普集团醋酸加氢制乙醇项目中建设完成了3万吨/年的分子筛膜乙醇脱水装置,是目前国内单套最大的分子筛膜脱水装置。目前,装置已连续运行超过1000h,运行结果良好。     

管式支撑体内表面NaA分子筛膜的合成与表征

采用转动合成方式通过二次生长法在管式α-Al₂O₃支撑体内表面合成了NaA分子筛膜,采用X射线衍射仪（XRD）、场发射扫描式电子显微镜（FE-SEM）和渗透汽化分离技术对所合成的膜进行了系统表征。考察了合成釜转速对分子筛膜合成的影响,结果表明合成釜转速的提高有利于分子筛膜合成。在转速为4 r·min^-1时所合成NaA分子筛膜分离因子高达2370,渗透通量1.86 kg·h^-1·m^-2左右（乙醇/相似文献   

Preparation and characterization of Silicalite‐1/PDMS surface sieving pervaporation membrane for separation of ethanol/water mixture

To improve the pervaporation performance of Silicalite‐1/PDMS composite membrane by adding a small amount of Silicalite‐1 zeolite, novel Silicalite‐1/PDMS surface sieving membranes (SSMs) were prepared by attaching Silicalite‐1 particles on the PDMS membrane surface. The obtained membranes and traditional mixed‐matrix membranes (MMMs) were characterized by SEM, XRD, TGA, FT‐IR, and pervaporation separation of ethanol–water mixture. Effects of Silicalite‐1 particles content, feed temperatures, and feed compositions on the separation performance were discussed. From the cross‐section view SEM images of SSMs, a two‐layer structure was observed. The thickness of the Silicalite‐1 layer was about 300 nm to 2 μm. The TGA analysis indicates that the zeolite concentration in 3 wt % SSM is lower than 10 wt % MMMs. In the ethanol/water pervaporation experiment, the separation factor of Silicalite‐1/PDMS SSMs increased considerably compared with pure PDMS membrane. When the suspensions concentrations of Silicalite‐1 particles reached 3 wt %, the separation factor was about 217% increase over pure PDMS membrane and 52.9% increase over 10 wt % Silicalite‐1/PDMS MMMs. As the ethanol concentration in the feed increases, the separation factor of SSMs increases, whereas permeation flux decreases. At the same time, with increasing operating temperature, the permeation flux of SSMs increased. The stability of SSMs at high temperature is better than the traditional MMMs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42460.     

Properties of modified poly(vinyl alcohol) membranes prepared by the grafting of new polyelectrolyte copolymers for water–ethanol mixture separation

For the preparation of a water‐selective membrane for the pervaporation separation of an azeotropic solution, a series of grafted copolymers were synthesized by the reaction of poly(vinyl alcohol) (PVA) with poly(sodium salt styrene sulfonic acid‐co‐maleic acid) (PSStSA‐co‐MA). The esterification was performed between the hydroxyl groups of PVA and the carboxylic groups of the copolymer with a heat treatment. PSStSA‐co‐MA was prepared with sodium salt styrene sulfonic acid and maleic anhydride copolymerization in dimethyl sulfoxide with azobisisobutyronitrile as an initiator. The reaction mechanism and resultant structure were confirmed with IR spectra. The effect of the heat‐treatment time on the gel content was investigated. The permeation flux decreased and the separation factor increased as the crosslinking agent content rose. A membrane containing 15 wt % PSStSA‐co‐MA was used for water–ethanol azeotropic solution pervaporation at 30°C, and a flux of 0.43 kg/m² h and a separation factor of 190 were obtained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2854–2859, 2002