Effect of cellulose buffer layer on synthesis and gas permeation properties of NaA zeolite membrane

NaA zeolite membrane coating was successfully synthesized on a porous alumina substrate by hydrothermal treatment. The effects of synthesis parameters like, seeding type (ex situ, in situ), time, temperature, sol concentration, coating stages, application of intermediate layer, etc. on membrane characteristics were investigated. A continuous membrane was formed on a seeded substrate. Surface seeding (ex situ crystallization) not only accelerates the zeolite crystallization process on the support surface, but can also enhance the formation of homogeneous NaA zeolite layer. The NaA zeolite membrane with a synthesis time of 4 h shows the best microstructure and the quality of membrane was improved by employing the multi-stage coating. But the main problem associated with membrane synthesis was crack formation, and it can be reduced by applying intermediate layer, between support surface and seed layer. A thin cellulose layer was applied to the support surface before applying seed crystals. The performance of the membranes was evaluated by gas permeation measurement. The permeance of O₂, N₂ decreased as kinetic diameter of gases increased. The permselectivity of O₂/N₂ was 1.9–2.34. This value showed the molecular sieving effect of NaA zeolite membrane.     

MFI型分子筛膜的制备及表征

采用无模板剂的二次生长合成方法,在-αA l2O3基膜上合成了MFI型分子筛膜,用XRD,SEM和气体渗透实验等方法进行表征,表明合成在-αA l2O3基膜的物质为MFI型分子筛。二次生长分子筛膜的正/异丁烷理想分离系数在298 K和473 K时分别为77和70,气体分离数据表明,2种分子筛膜对气体分离是由分子筛分占主导,同时分子筛膜完整无裂缺。不同温度,通过MFI分子筛膜渗透汽化分离质量分数分别为5%、50%和95%的乙醇/水的渗透通量和分离因子,结果表明渗透通量随温度的升高而升高,而分离因子随温度的升高却降低;渗透通量随乙醇质量分数的升高而降低,分离因子却随质量分数的升高而升高。     

Synthesis and preliminary gas permeation studies of a tubular NaA zeolite membrane (NZM)

Different from traditional seeded method, NaA zeolite membranes (NZMs) were prepared by in situ synthesis onto the inner side of porous α-alumina tubular supports in a hydrothermal synthesis reactor. The influences of pretreatment of porous tubular support, temperature, time, and synthetic cycle for the synthesis of the zeolite membranes were investigated. The operating conditions were optimized. Characterization of the membranes by scanning electron microscopy and X-ray diffraction showed that the crystalline materials on the inner surface of the porous α-alumina tubes were NaA-type zeolite. Single- and binary-gas permeation tests were conducted. Single-component permeabilities of hydrogen and nitrogen through the NZM changed slightly when the transmembrane pressure difference varied from 80 to 420?kPa. Its selectivity for H₂ relative to N₂ was about 5.3, which was greater than that of the Knudsen diffusion. The separation factors of binary gases H₂/N₂ and H₂/CO₂ at 473?K were 3.9 and 5.7, respectively, again exceeding the Knudsen diffusion level. The separation of binary gases suggests that the NaA-type zeolite membranes on α-alumina substrate were defect free and able to provide molecular sieving. The results demonstrate that the unseeded synthetic method presented in this work is successful and reliable.     

Influence of PVP buffer layer on the formation of NaA zeolite membrane

The support substrates were modified with the aqueous solutions of 1 and 3 wt% of polyvinyl pyrrolidine (PVP) as intermediate buffer layer followed by NaA zeolite seed (prepared hydrothermally at 85 °C for 2 h) coating with 2.5 wt% aqueous dispersion in each case. A better surface coverage with the oriented layer of NaA seed crystals was found with 1 wt% PVP buffer layer. The secondary crystallization of NaA membranes in the PVP-seed-coated supports was carried out hydrothermally at 65 °C for 2, 4, 6 h (single-stage each) and (2 + 2), (4 + 2)h (double-stage each) crystal growth processes. The crystallization behaviours of NaA membranes were studied by X-ray diffraction (XRD) while the microstructures of the same films were observed by scanning electron microscope (SEM). The single-stage secondary crystallization at 65 °C for 4 h showed highly interlocked and oriented NaA grains in the membranes and it rendered the permeance value of 2.2 × 10⁻⁸ mol m⁻²s⁻¹Pa⁻¹ for single gas, nitrogen (N₂) at ambient temperature (30 °C).     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Enhancement of NaA zeolite membrane properties through organic cation addition

Thin NaA zeolite membranes, with uniform and small crystals, were prepared on the tubular -Al₂O₃ support by adding a small amount of tetramethylammonium hydroxide (TMAOH) in the clear synthesis solution. The as-synthesized NaA zeolite membranes were characterized by XRD and SEM. The permeation properties of the membranes were evaluated by pervaporation and gas permeation. The effects of TMAOH amount on membrane formation and permeation properties were investigated. By addition of suitable amount of TMAOH in the clear synthesis solution, the crystals size of NaA zeolite could be remarkably reduced from about 10 μm to 3–4 μm, and the membrane thickness correspondingly reduced from about 16 μm to 5 μm. The thinner membrane prepared by adding TMAOH in the clear synthesis solution, with uniform and small crystal, displayed higher perm-selective properties than that without adding TMAOH. For the as-synthesized NaA zeolite membrane prepared with adding suitable amount of TMAOH (x = 1), the separation factor (water/isopropanol) was 4700 and the flux was 1.67 kg/(m² h), which were higher than that without adding TMAOH of 339 and 1.08 kg/(m² h), respectively. The ideal separation factor of H₂/N₂ was 6.60, higher than that without adding TMAOH of 3.41.     

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。     

含甲基纤维素的NaA沸石膜的制备和表征

NaA沸石膜具有规则的孔道结构,利于分子传输,在有机物脱水领域有一定的应用。为使沸石膜生长更连续均匀,提高渗透汽化性能,本文以甲基纤维素作为空间限制剂加入合成液,探究碱度、晶化温度以及晶化时间对膜的影响,按最优条件制备合成液,并依据质量比m(MC)∶m(H₂O)=1∶100添加甲基纤维素,制备NaA沸石膜。表征方法采用XRD、SEM和渗透汽化3种方式,结果表明添加甲基纤维素的沸石膜表面结构完整,生长致密且性能优良,在75℃下对0.6mol/L的NaCl水溶液做渗透汽化测试时,通量达8.33kg/(m²·h),盐离子截留率为99.95%。在0.6mol/L的NaCl的水溶液中测试72h,结果表明添加甲基纤维素的NaA沸石膜时间依存性更好,通量保持在8.30kg/(m²·h)左右,离子截留率稳定在99.90%。渗透汽化分离ω(C₂H₆O)=90%乙醇的水溶液,随着温度从60℃升高到75℃,沸石膜的通量由1.55kg/(m²·h)升高到2.56kg/(m²·h),渗透侧水含量保持在99.90%左右。     

The growth of SAPO 34 membrane layer on support surface for gas permeation application

The formation stage of SAPO 34 zeolite membrane on a tubular mullite support has been investigated. XRD, FESEM, IR and EDAX analysis techniques were used to explain the changes in crystallization stages as well as formation of membrane on tubular clay-alumina support with time. From the studies, the evidence tends to support that crystallization of SAPO 34 started from initial gel, proceed through cluster formation and accumulation followed by segregation and crystallization process. The study also showed the gradual incorporation of Si into AlPO₄ phase and form cubical CHA phase after 120 h of synthesis time.Single gas permeation of CO₂ and H₂ showed that upto 300 KPa of feed pressure permeability of CO₂ is more than that of H₂. But at higher pressure the results show the reverse trend, flux is more for H₂. This may be due to more adsorption of CO₂ on SAPO 34 surface and less desorption from the surface than hydrogen with increasing pressure. The selectivity of H₂/CO₂ increases from 0.85 to 2.67.     

Effect of support layer on gas permeation properties of composite polymeric membranes

PES/Pebax and PEI/Pebax composite membranes were prepared by coating the porous PES and PEI substrate membranes with Pebax-1657. The morphology and performance of the prepared membranes were investigated by SEM and CO₂ and CH₄ permeation tests. The CO₂ permeances of 28 and 52 GPU were achieved for PES/Pebax and PEI/Pebax composite membranes, respectively, with CO₂/CH₄ selectivities almost equal to that of Pebax (26). The experimental data were further subjected to a theoretical analysis using the resistance model. It was found that the porosity and the thickness of the dense section of PES substrate were an order of magnitude higher than those of PEI substitute. The porosity/thickness ratio of PEI substrate was, however, higher than PES, explaining the higher permeance of PEI/Pebax composite membrane. Substrates with porosities much higher than the Henis-Tripodi gas separation membrane were used in this work, aiming to achieve the selectivity of Pebax, rather than those of the substrate membrane materials.     

在壳聚糖改性的硅锆复合中间层上原位水热合成b-轴取向silicalite-1分子筛膜

引言 分子筛是一类具有特殊孔道或笼状结构的多孔介质,可以根据分子的动力学尺寸大小、形状以及极性等进行选择性吸附.     

Thermal and dielectric properties of low-density polyethylene/NaA zeolite composites

The effect of the weight fraction of NaA zeolite on thermal properties (specific heat capacity, thermal diffusivity, thermal conductivity) and dielectric properties (electrical conductivity, real and imaginary electric permittivity) of composites based on low-density polyethylene (LDPE) and NaA zeolite is examined. Composite samples containing from 5 to 30 wt% zeolite are prepared using the compression molding technique. The degree of dispersion and the weight fraction of filler in the LDPE/NaA zeolite composites are determined using X-ray diffraction. A linear decrease in the values of the specific heat capacity with an increase in the weight fraction of zeolite is observed using differential scanning calorimetry. The laser flash method is used to determine the thermal diffusivity of the composites. An increase in effective thermal diffusivity and abrupt increase in the range from 15 to 20 wt% of zeolite are established. It is demonstrated that effective thermal conductivity increases with an increase in the weight fraction of zeolite, and an abrupt increase in the range from 15 to 20 wt% is observed. Dielectric spectroscopy measurements are performed to determine the real and imaginary parts of permittivity. An increase of real and imaginary parts of permittivity of LDPE/NaA zeolite composites, with increasing weight fraction of zeolite, is established. Two relaxation peaks of the imaginary parts of permittivity of LDPE/NaA zeolite composites are detected. An increase of electrical conductivity with increasing weight fraction of zeolite and abrupt increase in the range 15 to 20 wt% are noticed. © 2021 Society of Industrial Chemistry.     

Effect of intermediate layer on gas separation performance of disk supported carbon membrane

Porous alumina disk ceramic was decorated with various types of intermediate layers via one-step spray coating-carbonization technique. P-84 (BTDA-TDI/MDI) polymeric solution was sprayed on the alumina disk with an incorporation of intermediate layer. The membrane was carbonized at 700°C under nitrogen (N₂) atmosphere with a heating rate of 3°C/min. The resultant carbon membrane was characterized in terms of its thermal stability, structural morphology, and gas permeation properties. A high-performance carbon membrane was obtained with the intermediate layer of the alumina powder, which exhibited the best selectivity of O₂/N₂, CO₂/N₂ and CO₂/CH₄ of 4.39, 19.89 and 58.43, respectively.     

The seeds effect on zeolite NU-87: synthesis parameters and structural properties

EU-1 and NU-87 zeolites, which possess certain similarity in structure, were used as seeds for synthesizing zeolite NU-87. The usage of seeds greatly enhanced the crystallization rate and widened the composition range of initial gel. As compared with the hetero-structural seeds, the homo-structural seeds were more favorable for the synthesis of zeolite NU-87, also resulted in extremely decreased template agent and greatly shortened crystallization time. However, hetero-structural seeds EU-1 resulted in the much smaller particle size of the as-synthesized zeolite NU-87, due to the distinct properties of seeds.     

Ion beam irradiation effect on gas permeation properties of polyimide films

This study deals with the ion beam irradiation effect on gas permeation properties of polyimide films. 2 MeV α, 500 keV, and 170 keV N⁺ ions were used for modifying the membranes. It was found that there are two different effects according to the implantation dose. In the case of small-dose irradiation, ion implantation causes a raise of permeability both for CH₄ and H₂. When the implantation dose reaches a more important level, the implanted membranes have at the same time high permselectivity for H₂/CH₄ and high permeability for H₂. The relationships between the permeation properties and microstructure of the films are also discussed. © 1995 John Wiley & Sons, Inc.     

Effects of water vapor on gas permeation and separation properties of MFI zeolite membranes at high temperatures

Understanding the effects of water vapor on gas permeation and separation properties of MFI zeolite membranes, especially at high temperatures, is important to the applications of these zeolite membranes for chemical reactions and separation involving water vapor. The effects of water vapor on H₂ and CO₂ permeation and separation properties of ZSM‐5 (Si/Al ～ 80) zeolite and aluminum‐free silicalite membranes were studied by comparing permeation properties of H₂ and CO₂ with the feed of equimolar H₂/CO₂ binary and H₂/CO₂/H₂O ternary mixtures in 300–550°C. For both membranes, the presence of water vapor lowers H₂ and CO₂ permeance to the same extent, resulting in negligible effect on the H₂/CO₂ separation factor. The suppression effect of water vapor on H₂ and CO₂ permeation is larger for the less hydrophobic ZSM‐5 zeolite membrane than for the hydrophobic silicalite membrane, and, for both membranes, is stronger at lower temperatures and higher water vapor partial pressures. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of stabilization temperature on gas permeation properties of carbon hollow fiber membrane

Carbon hollow fiber membranes (CHFMs) derived from polymer blend of polyetherimide (PEI) and polyvinylpyrrolidone (PVP) were extensively prepared through stabilization under air atmosphere followed by carbonization under N₂ atmosphere. The effects of the stabilization temperature on the morphological structure, chemical structure, and gas permeation properties were investigated thoroughly by means of scanning electron microscopy, Fourier transform infrared spectroscopy, and single gas permeation system. The experiment results indicate that the transport mechanism of small gas molecules of N₂, CO₂, and CH₄ is dominated by the molecular sieving effect. Based on morphological structure and gas permeation properties, an optimum stabilization condition for the preparation of CHFM derived from PEI/PVP was found at 300°C under air atmosphere. The selectivity of ?55 and 41 for CO₂/CH₄ and CO₂/N₂, respectively, were obtained for CHFMs prepared at stabilization temperature of 300°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

水-乙醇体系对双极膜中间界面层的影响

选取Neosepta BP-1,Fumasep FBM,CJ-BPM三种商业标准双极膜作为研究对象,以水-乙醇为研究体系,通过改变不同乙醇含量,测定双极膜的交流阻抗谱,并且对双极膜的耐溶剂性能进行评价,结果表明BP-1具有良好的耐溶剂性,FBM,CJ-BPM耐溶剂性相对较弱;水解离现象发生在LiCl水-乙醇混合溶液中,随着乙醇含量的增加,双极膜的阻值增加,而水解离程度降低。这种现象可以解释为醇解离能力要远远小于水解离能力,因此乙醇的存在使得中间界面层区域的水浓度降低,进而降低了水解离程度;通过简化算法计算出了不同乙醇含量下,BP-1,FBM的中间界面层厚度,更直观地看出乙醇对双极膜水解离性能的影响。     

Measurement and interpretation of zeolite NaA builder performance

Ion exchange isotherms are commonly used to describe the distribution of ions between a solid and liquid phase under equilibrium conditions. In the detergent industry, the Ca-Na-zeolite A isotherm can be utilized to determine the builder performance of zeolite NaA under a specific set of experimental conditions. In this paper, we demonstrate how the Ca-Na-zeolite A isotherm is developed and utilized in measuring and interpreting the calcium exchange capacity score of zeolite NaA. Owing to the large number of testing parameters that affect the equilibrium distribution of calcium between the zeolite and solution phases, and hence the calcium exchange capacity score of the zeolite, a recommendation is made as to a standard set of test conditions that provide for both analytical precision and convenience. With this approach, builder performance differences between any two zeolites can then easily be measured and assessed. As an extension to the isotherm principles developed in this paper, the prediction of zeolite performance in real detergent systems is illustrated. Particular attention is given to the more efficient utilization of the ion exchange capacity of zeolite NaA by the recently developed concentrated detergent systems. A portion of this paper was presented at the 1992 Annual AOCS Meeting in Toronto, Canada.     

Influence of oxidation temperature on the gas permeation and separation properties in a microporous carbon membrane

Of thermosetting polymers, polyphenylene oxide (PPO) is considered as one of the promising alternative polymeric precursors for carbon membrane preparation. In this study, the PPO derived carbon membranes were prepared by carbonization and followed by air-oxidation as post-treatment method to modify the membrane pore structures. The characterization of the pore properties showed that air-oxidation enlarged the pore structure for the postoxidized carbon materials. The permeation results for the post-oxidized carbon membranes showed that the extent of the permeation modification was strongly dependent on the oxidation temperature. In the binary mixture gas systems, the permeation performance of the adsorbing gas species increased due to the surface diffusion mechanism. It is considered in the oxidation effect on the permeation modification that the post-oxidation of the carbon membranes increased gas permeation and separation properties.