A theoretical analysis of non-chemical separation of hydrogen sulfide from methane by nano-porous membranes using capillary condensation

The potential of a nano-porous membrane to perform non-chemical separation of a gas mixture has been explored theoretically. Separation of hydrogen sulfide from its mixture with methane by capillary condensation has been selected as the model case. Because of its much lower condensation pressure compared to methane, hydrogen sulfide preferentially condenses in the fine pores and get transported by Poiseuille flow. Permeation rate up to 600 gmol/m² s bar has been achieved at a temperature lower than the critical temperature of the permeating species and higher than the critical temperature of the non-permeating species. Since methane has a much lower critical temperature than hydrogen sulfide, it gets physically dissolved in the condensed phase of hydrogen sulfide. An equation of state (EOS) approach ha s been adopted to calculate the fugacity of methane in the gas as well as in the condensed phase-in order to estimate its solubility. Computation of permeation flux of the condensed phase as well as of the separation factor of hydrogen sulfide has been performed over a wide range of temperature, pressure and gas composition. The separation factor which is expectedly a function of these variables, ranged from 700 to 100. The separation technique is expected to have an enhanced attraction since it is clean and does not require a solvent as in the conventional separation of acid gases.     

Actual air separation across multilayer composite membranes

Multilayer composite membranes are fabricated from six types of thin films as selective layers, an ethyl cellulose (EC) thin film as a flexible spacer, and poly(ether sulfone) (PES) with 15–45 nm pore size or 100–120 μm thickness as a porous support layer. The effects of the thin‐film type and its layer number, operating temperature, and transmembrane pressure difference, as well as the operational time on the actual air‐separation properties through the composite membranes, are investigated by a constant pressure‐variable volume method. The results show that a pure polystyrene thin‐film composite membrane exhibits poor actual air‐separation performance due to its brittleness, although it has a higher ideal oxygen over nitrogen separation factor. The oxygen‐enrichment air (OEA) flux through all of the composite membranes tested increases significantly with increasing operating temperature and pressure difference. The oxygen concentration in the OEA increases slightly with an increase in operating temperature, and the oxygen concentration through the polystyrene/cholesteryl oleyl carbonate blend, top layer composite membrane exhibits the maximal value. As the transmembrane pressure difference increases, the oxygen concentration in the OEA also exhibits the maximal value. The maximum oxygen concentration can reach 39.1%, which is achieved by the multilayer composite membrane consisting of a polystyrene/cholesteryl oleyl carbonate (95/5) monolayer, an EC single flexible spacer, and a PES support at 35°C and a transmembrane pressure difference of 550 kPa. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2396–2403, 2000     

钯－银合金膜分离氢气的研究

采用厚为５０μｍ的Ｐｄ／Ａｇ（２３）合金膜进行了氢气渗透系数的测定和Ｈ＿２／Ｎ＿２混和气分离的研究，得出温度、压力、膜厚、进料气流量、膜的预处理和再活化及膜表面中毒等因素对氢气渗透的影响。分离Ｈ＿２／Ｎ＿２混和气可获得高纯氢气。     

钯－银合金膜分离氢气的研究

采用厚为５０μｍ的Ｐｄ／Ａｇ（２３）合金膜进行了氢气渗透系数的测定和Ｈ＿２／Ｎ＿２混和气分离的研究，得出温度、压力、膜厚、进料气流量、膜的预处理和再活化及膜表面中毒等因素对氢气渗透的影响。分离Ｈ＿２／Ｎ＿２混和气可获得高纯氢气。     

疏水SiO2/PTFPMS杂化复合膜的制备及其气体分离性能

为了提高气体分离膜的耐溶胀特性,以多孔聚醚酰亚胺（PEI）为支撑层,采用溶液共混法制备了疏水SiO₂/PTFPMS杂化复合膜,研究了疏水SiO₂质量共混比对膜形态、耐溶胀性以及不同操作压差下的纯气渗透分离性能的影响。光学显微照片显示,当共混比不超过0.018时,杂化膜的透明度较高,表明疏水SiO₂与PTFPMS具有较好的相容性;当SiO₂与PTFPMS的共混比超过0.018时,SiO₂团聚明显。SEM表征结果显示,杂化膜表面光洁,断面杂化涂层紧密贴合支撑层。疏水SiO₂/PTFPMS杂化膜在异辛烷中的溶胀度为0,在乙酸乙酯中的溶胀度比PTFPMS均质膜的下降了11.9%,显示了其优异的耐溶胀性能。在操作压力为1.0 MPa,操作温度为25℃下,SiO₂共混比为0.012时,疏水SiO₂/PTFPMS杂化复合膜的CO₂渗透通量达到最高156.1GPU,CO₂/N₂选择性为15.86。     

Removal of hydrogen sulfide from biogas on sludge-derived adsorbents

Desulfurization adsorbents were prepared from the mixtures of sewage sludge and metal sludge of various compositions and individual sludges by pyrolyses at 650, 800 and 950 °C. The resulting materials were used as adsorbents of hydrogen sulfide from simulated digester gas mixture. The adsorbents before and after H₂S removal were characterized using adsorption of nitrogen, elemental analysis, pH measurements, and thermal analysis. The behavior of materials as desulfurization media does not depend strongly on the humidification pretreatment. The pyrolysis temperature and composition of the mixture play a role in the development of final properties of adsorbents. When the content of sewage sludge is high the strong synergetic effect is noticed after high temperature of pyrolysis. Such factors as development of mesoporosity and new catalytic phases formed as a result of solid-state reactions contribute to this behavior. The removal of hydrogen sulfide on the materials obtained is complex due to the competition between H₂S and CO₂ for adsorption centers and deactivation of those centers by CO₂/H₂CO₃.     

Experimental demonstration of enhanced hydrogen permeation in palladium via a composite catalytic‐permselective membrane

A composite catalytic‐permselective (CCP) membrane comprised of a 500‐μm Cu(II)O/Al₂O₃ catalyst film washcoated overtop a 27‐μm electroless‐plated dense palladium thin film was constructed on a porous less‐steel substrate. Hydrogen purification experiments performed under ideal (H₂–Ar) nonreactive mixtures and simulated reformate (5% CO, 7.5% H₂O, 15% H₂, 1.5% CO₂, and balance Ar) over a range of residence times at 623–773 K confirm up to 30% enhancement in observed hydrogen permeance of the palladium film, achieved using the CCP membrane design in which the catalyst layer modifies the gas‐phase composition in direct contact with the permselective Pd film. Scanning electron microscopy analysis of the palladium film after ～10‐h exposure to reaction conditions and Cu(II)O catalyst confirm no corrosion of the film, while observed hydrogen permselectivities remained in excess of 10,000:1. These experimental results confirm that the CCP membrane design is capable of significantly improving palladium membrane performance. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1627–1634, 2013     

Removal of hydrogen sulfide from methane using commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes

The performance of commercially available poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) and Cardotype polyimide (PI) hollow fiber membranes was investigated in removing hydrogen sulfide from methane in a series of bench-scale experiments. It was observed that in the concentration range of hydrogen sulfide in methane from 101 to 401 ppm, the methane permeability decreased in the presence of hydrogen sulfide for Cardo-type polyimide hollow fiber membranes, whereas the PPO membrane performance was not affected. The separation coefficients of hydrogen sulfide/methane were 6 and 4 for PI and PPO membranes, respectively. Effects of temperature on the performance of PI and PPO membranes were investigated. It was observed that the permeabilities of both components of the mixture increased by increasing temperature, whereas the selectivities remained constant.     

Oxygen enrichment from air through multilayer thin low‐density polyethylene films

Several multilayer thin low‐density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 μm and an area of 130 cm². They were characterized for their oxygen‐enrichment performance from air by a constant pressure–variable volume method in a round permeate cell with an effective area of 73.9 cm². The relationship between oxygen‐enrichment properties, including oxygen‐enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen‐enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen‐enriching membrane directly from air, based on the easily obtained thin LDPE films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3013–3021, 2002; DOI 10.1002/app.2331     

离子液体吸收分离硫化氢进展

针对近年来离子液体在吸收分离硫化氢(H₂S)气体方面的研究进展, 重点论述了H₂S在离子液体中的溶解度及对其他气体的选择性、H₂S-离子液体体系的热力学性质及模型。对离子液体吸收H₂S的机理进行了分析, 阐述了离子液体阴阳离子种类、结构以及取代基等对H₂S分离性能的影响规律, 简要提出了该领域存在的研究难点和未来的发展方向。     

Removal of FeCl3 from aqueous solution by ultrafiltration using ordered mesoporous MCM-48 ceramic composite membrane

Mesoporous MCM-48 membrane was prepared on a low-cost circular-shaped ceramic support by a hydrothermal crystallization technique. The characteristics of MCM-48 powder and composite membrane were evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), porosity and water permeation test. The porosity and pore size of the composite membrane were found to be 22% and 0.142 µm, respectively. The MCM-48 composite membrane was investigated for the separation potential of FeCl₃ from aqueous solution and a maximum rejection of 86% was obtained for a feed concentration of 250 ppm at lower pH 2.     

Promotion of hydrogen permeation on metal-dispersed alumina membranes and its application to a membrane reactor for methane steam reforming

A mesoporous membrane for selective separation of hydrogen was prepared usingthe sol-gel method. Some metal salts such as RuCl₃, Pd(NH₃)₄Cl₂, RhCl₃,, and H ₂PtCl₆, were added to the boehmite sol and coated on a porous alumina substrate before firing at 500°C. It was foundthat the permeability of hydrogen and the separation factor for a hydrogen-nitrogen gaseous mixture of these metaldispersed membranes exceeded the limitations of the Knudsen diffusion mechanism. Although the gas permeation through a neat alumina membrane is governed by the Knudsen diffusion, the metals dispersed in alumina membranes were effective in promoting hydrogen permeation. These metaldispersed alumina membranes were also used in a membrane reactor for methane steam reforming at low temperature. In the temperature range of 300 to 500°C, the membrane reactor attained a methane conversion twice as high as the equilibrium value of the packed bed catalytic reactor system as a result of the selective removal of hydrogen from the reaction system.     

Pure hydrogen production by methane steam reforming with hydrogen-permeable membrane reactor

Low temperature steam reforming of methane mainly to hydrogen and carbon dioxide (CH₄ + 2H₂O → 4H₂ + CO₂) has been performed at 773 and 823 K over a commercial nickel catalyst in an equilibrium-shift reactor with an 11-μm thick palladium membrane (Mem-L) on a stainless steel porous metal filter. The methane conversion with the reactor is significantly higher than its equilibrium value without membrane due to the equilibrium-shift combined with separation of pure hydrogen through the membrane. The methane conversion in a reactor with an 8-μm membrane (Mem-H) is similar to that with Mem-L, although the hydrogen permeance through Mem-H is almost double of that through Mem-L. The amount of hydrogen separated in the reaction with Mem-H is significantly large, showing that the hydrogen separation overwhelms the hydrogen production because of the insufficient catalytic activity.     

聚醚砜酮基炭膜的制备及其气体分离性能

采用浸渍涂膜法,以商用聚醚砜酮(PPESK)为前驱体制备了管式复合炭膜,考察了涂膜次数、改性剂及其加入量对所制备炭膜的气体分离性能的影响.结果表明,随着涂膜次数增多,气体分子的渗透速率逐渐减小而选择性呈增大趋势;加入改性剂后的复合炭膜渗透速率和分离系数均有不同程度的提高,表明改性剂不仅改善了涂膜液与支撑体之间的复合效果、减少涂膜次数,同时也促进了气体渗透速率的提高.利用扫描电镜对复合炭膜的微观形貌进行观测,可以看出,复合炭膜由支撑体和分离膜层2部分组成.膜表面很致密均匀,无明显缺陷,分离层薄而均一,厚度在5μm左右,且与支撑体结合紧密.     

膜分离-变压吸附集成工艺脱除天然气中酸性气体

天然气中含有酸性气体,在使用或输送前必须去除。介绍了两种天然气脱除酸性气体的技术:气体膜分离技术和变压吸附技术,单独使用其中任何一种技术都不能达到经济地脱除酸性气体的目的。集成两种技术的优点,开发出膜分离-变压吸附集成工艺,可以在满足天然气酸性气体含量指标的同时,提高了回收率,为天然气工业提供一定的借鉴和参考。     

An effective strategy to boost hydrogen separation performance through stable mixed proton-electron conducting membrane

Hydrogen separation and purification are key to widespread application of hydrogen energy. Hydrogen permeable membranes based on lanthanum tungstate (LWO) attract attention due to favorable mechanical strength and chemical stability. However, industrial application of LWO-based membranes has remained challenging because of modest hydrogen permeances. Here we report a novel graded porous supported symmetric (GPSS) LWO-based membrane with improved transport properties, gas exchange dynamics, and operational stability, boosting stable hydrogen flux by several times over previously reported state-of-the-art membranes.     

CO2 separation performance by chitosan/tetraethylenepentamine/poly(ether sulfone) composite membrane

CO₂ separation from CO₂/N₂ (20:80) gas mixture has been demonstrated by tetraethylenepentamine blended with chitosan (CS‐TEPA) membrane. Optimization of CS and TEPA weight ratio were carried out based on characterization details involving thermogravimetric analysis, Fourier transform infrared spectroscopy, X‐ray diffraction, atomic force microscope, and field emission scanning electron microscope. Effects of water flow rate, pressure, and temperature were concurrently studied on CS‐TEPA membranes through gas permeation. Almost twofold increase in CO₂ permeance (24.7 GPU) was detected in CS blend with 30% (w/w) of TEPA (CS70) as compared to pure CS membrane (12.5 GPU). CS70 yielded CO₂/N₂ selectivity of 80 whereas CS demonstrated a maximum of 54 at 90 °C. The membrane also exhibited improved stability at temperatures less than 120 °C which was evident from TGA isotherm trace. The proposed composite membrane can be a promising candidate for flue gas separation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45206.     

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

Composite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N₂ adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO₂ permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO₂/N₂ and CO₂/CH₄ also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO₂ preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO₂ solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44999.     

硅橡胶复合膜用于含酚水溶液渗透萃取传质过程

以苯酚为模型污染物,以氢氧化钠溶液为萃取液,利用平板复合膜［聚二甲基硅氧烷（PDMS）/聚偏氟乙烯（PVDF）］构造渗透萃取体系,系统地研究了该体系渗透萃取含酚水溶液的传质过程与特性。探讨了料液与萃取液的浓度及流量、运行温度等操作条件及活性层厚度对渗透萃取传质性能的影响。结果表明,pH>13时,总传质系数K_ov不随萃取液流量及浓度变化而变化;苯酚的液膜传质系数kf与膜面流动Reynolds数Re^0.46呈正比,传质通量与温度符合Arrhenius方程。在苯酚初始浓度5.0～15.0 g•L^-1范围内,K_ov为定值。活性皮层厚度为4、6、8 μm的膜扩散传质系数分别为15.0×10^-7、9.9×10^-7及7.5×10^-7m•s^-1（323.2 K）,较均质膜提高了2～4倍。苯酚在复合膜中的传质仍属膜阻控制的传质。     

聚醚酰亚胺/硅橡胶复合膜分离有机蒸汽的研究

膜分离技术是21世纪高新技术之一,它具有能耗低、操作简单、无二次污染等优点。本文将聚醚酰亚胺/硅橡胶复合膜用于回收氮气中的醋酸甲酯蒸汽,研究了操作温度、渗透侧压力、原料气浓度,流量对分离过程的影响,得到了较佳的工艺条件。