Removal of hydrogen sulfide from methane using PEO-segmented copolymer-based multilayer composite membrane

The thermoplastic poly(urethane-urea) (PUU) was synthesized using polyethylene-glycol, 4,4?-methylenediphenyl diisocyanate (MDI), and 1,2-ethandiamine (EDA) as a chain extender. A novel multilayer composite membrane consisting of the synthesized PUU, as a selective layer, a silicon rubber, as an interlayer, and the polyacrylonitrile (PAN) microporous support was prepared for the removal of acid gas. Moreover, the physical properties of the synthesized PEG-based polyurethane were investigated. Based on Differential Scanning Calorimeter (DSC) and ANDFourier Transform Infra-red Spectroscopy (FTIR) analyses, a higher microphase separation of hard and soft segments was observed for PUU. The permeabilities of pure CO₂, pure CH₄, and a ternary mixture of CH₄, CO₂, and H₂S through the multilayer composite membrane were measured at different temperatures and pressures. The maximum values of selectivity, i.e., 52 and 15 for H₂S/CH₄ and CO₂/CH₄, respectively, were found at 25°C and 5 bar. The permeances of H₂S and CO₂ in the ternary mixture decreased on increasing the feed pressure because of membrane compression. The higher the temperature, the higher was the permeability of the gases due to the more molecular movement of the polymer chains. Therefore, the gas selectivity in the synthesized composite membrane decreased by increasing the temperature. The experiments showed that replacing the pure-gas measurements with the gas mixture measurements can substantially produce more relevant results.     

大规模膜法空气分离技术应用进展

富氧空气、氧气、氮气以及其他一些空气分离产品应用领域的增加 ,极大地推动了空气分离新技术的大规模发展。膜法空气分离以其节能、便利、安全等优异特性在空气分离产品的工业生产中展现出了极大的发展潜力。综述了现有膜材料的氧氮分离性能、制氧装置和制氮装置的研究开发及其在柴油发动机富氧燃烧等方面的应用研究 ,分析了膜法空气分离大规模商业化必须克服的技术障碍 ,从新型高性能膜材料的合成与制备方面提出了实现大规模膜法空气分离应用应采取的措施。     

High-performance SSZ-13 membranes prepared using ball-milled nanosized seeds for carbon dioxide and nitrogen separations from methane

SSZ-13 membranes with high separation performances were prepared using ball-milled nanosized seeds by once hydrothermal synthesis. Separation performances of SSZ-13 membranes in CO_2/CH_4 and N_2/CH_4 mixtures were enhanced after synthesis modification. Single-gas permeances of CO_2, N_2 and CH_4 and ideal selectivities were recorded through SSZ-13 membranes. The effects of temperature, pressure, feed flow rate and humidity on separation performance of the membranes were discussed. Three membranes prepared after synthesis modifications had an average CO_2 permeance of 1.16 × 10~(-6) mol·(m~2· s·Pa)~(-1)(equal to 3554 GPU) with an average CO_2/CH_4 selectivity of 213 in a 50 vol%/50 vol% CO_2/CH_4 mixture. It suggests that membrane synthesis has a good reproducible. The membrane also displayed a N_2 permeance of 1.07 × 10~(-7) mol·(m~2·s·Pa)~(-1)(equal to 320 GPU) with a N_2/CH_4 selectivity of 13 for a 50 vol%/50 vol% N_2/CH_4 mixture. SSZ-13 membrane displayed stable and good separation performance in the wet CO_2/CH_4 mixture for a long test period over 100 h at 348 K. The current SSZ-13 membranes show great potentials for the simultaneous removals of CO_2 and N_2 in natural gas purification as a facile process suitable for industrial application.     

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.     

气体超声速凝结与旋流分离研究进展

超声速旋流分离技术是天然气加工处理领域的一大技术创新,它将膨胀降温、旋流式气/液分离、再压缩等处理过程集中在密闭紧凑装置中完成。本文总结了超声速旋流分离装置种类、原理及优缺点,并从理论分析、数值模拟、实验和现场应用等方面回顾了易凝气体低温凝结理论和超声速旋流分离技术研究现状和最新进展。大量实验及现场应用均表明超声速旋流分离装置具有结构紧凑轻巧、节能环保、安全可靠等优点,同时该技术的应用不断趋于多元化,从传统的脱水、脱重烃逐渐向脱酸气和天然气液化领域拓展,应用前景广阔,但在应用过程中也存在液滴二次蒸发与能量损失较大等问题。下一步研究工作可以从多组分混合物凝结过程的交互作用机制、凝结液滴的运动特性和碰撞聚并机理等方面入手,在此基础上探索提高凝结效率和降低能量损耗的方法,以促进超声速旋流分离技术多元化的工业应用。     

On-stream modification of MFI zeolite membranes for enhancing hydrogen separation at high temperature

-Alumina-supported MFI zeolite membranes were modified by on-stream catalytic thermal cracking of methyldiethoxysilane (MDES) molecules inside the zeolitic channels during the separation of H₂/CO₂ gas mixture at 450 °C and atmospheric pressure. The MDES vapor was carried by the H₂/CO₂ feed gas and the effect of modification was monitored continuously through online analysis of the permeate stream. The modified membrane exhibited a significant increase in H₂ selectivity over CO₂ with a moderate decrease in H₂ permeance. At 450 °C, the modified MFI membrane obtained a H₂/CO₂ permselectivity of 17.5 with H₂ single gas permeance of 1.86 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ as compared to a permselectivity of 2.78 and permeance of 2.75 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ for the membrane before modification. The modified membrane also showed good performance and stability in separation of H₂/CO₂ gas mixture containing up to 28.4% water vapor at 450 °C and atmospheric pressure.     

Permeation through CO2selective glassy polymeric membranes in the presence of hydrogen sulfide

Minor components present in feed gas streams can have a significant influence on the separation performance of polymeric membranes. Hydrogen sulfide is present in many of the processes where CO₂ capture is possible and can therefore undergo competitive sorption with CO₂ for transport through the membrane, as well as influence the membrane morphology inducing plasticization. This study investigates the change in CO₂ permeability and CO₂/N₂ selectivity of two glassy polymeric membranes; polysulfone and 6FDA‐TMPDA, when 500 ppm H₂S is present in the gas mixture. The outcomes of this study reveal that H₂S in trace amounts has a strong influence on the separation performance of both membranes. For both membranes, a plasticization partial pressure ～0.5–0.6 kPa H₂S is observed. H₂S competitive sorption is also observed and is modeled by competitive dual‐sorption theory. Results suggest that mixed gas permeation influences the amount of each gas immobilized within the Langmuir voids in addition to the expected competitive sorption effects. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Evaluation of hydrogen separation performance of Ni-BaCe0.85Fe0.15O3-δ cermet membranes

Adding metal phase as the electronic transport channels in mixed protonic and electronic conductors is an effective method to enhance the conductivity and hydrogen permeability. Ceramic-metal (cermet) Ni-BaCe_0.85Fe_0.15O_3-δ (Ni-BCF8515) dual-phase membranes were successfully fabricated in this article, where BaCe_0.85Fe_0.15O_3-δ (BCF8515) served as the protonic conductor and Ni acted as the electronic conductor. The hydrogen permeability of Ni-BCF8515 dual-phase membrane was improved apparently, reaching 0.325?mL?min^?1?cm^?2 at 1000?°C, which is four times higher than that of the single phase BCF8515 membrane. Hydrogen permeability of Ni-BCF8515 dual-phase membrane under different hydration conditions was studied here. Moreover, Ni-BCF8515 dual-phase membrane showed stable hydrogen permeability under the reducing atmosphere for 50?h.     

界面聚合技术制备分离膜的研究进展

界面聚合技术具有许多优良性能，如反应条件温和、可控性强、可以实现自封闭和自终止等，被广泛应用于分离膜制备中。本文阐述了界面聚合技术的原理，详细介绍了界面聚合在膜分离中的应用情况，包括纳滤膜、反渗透膜和气体分离膜，并综述了界面聚合技术在微胶囊、导电聚合物、纤维材料等方面的应用现状。最后，对界面聚合技术制备分离膜的研究前景进行了展望。     

Preparation of composite membranes with polyimides and poly (amide-imide)s skin via interfacial condensation for air separation

Composite membranes were prepared by the interfacial condensation of water-soluble diamines with an organic solvent (dichloromethane)-soluble dicarbo-methoxy terephthaloyl chloride or carbomethoxy terephthaloyl chloride on top of a porous aluminum oxide support. The morphology of skin on the composite membranes is different in the two different procedures. The polyimide composite membranes with 40-times coatings provide a high gas permeation rate of oxygen and good permselectivity [α(O₂/N₂)]. The composite membrane with the polyimides skin at 40-times coatings had a gas permeation rate of oxygen range from 83 × 10⁻⁵ to 130 × 10⁻⁵ cm³(STP) s⁻¹ cm⁻² cmHg⁻¹, and a permselectivity [α(O₂/N₂)] range of 3.57 to 5.60. The composite membrane with poly (amide-imide)s skin at 40-times coatings had a gas permeation rate of oxygen range from 102 × 10⁻⁵ to 146 × 10⁻⁵ cm³(STP) s⁻¹ cm⁻² cmHg⁻¹, and the permselectivity (α(O₂/N₂)) range from 3.20 to 4.96.     

合成氨弛放气、排放气的氢气回收技术

介绍了从合成氨排放气、弛放气中回收氢气的膜分离技术、变压吸附技术和深冷分离技术 ,并对该三种方法进行了比较     

Modelling diffusion and reaction accompanied by capillary condensation using three-dimensional pore networks. Part 2. Dusty gas model and general reaction kinetics

A pore network model incorporating a rigorous model of diffusion/reaction and an analysis of pore filling by capillary condensation has been developed. This paper presents an extension of the algorithm described in part 1 to cover multicomponent diffusion and reaction represented by any type of kinetic expression. The novel aspects of the model reported here are that reactions of interest to industry can be simulated since realistic rate equations, such as Langmuir-Hinshelwood expressions, are represented and the possibility of capillary condensation in the pores is also accounted for. Bulk diffusion, Knudsen diffusion and convection of multicomponent vapours are analysed using the dusty gas model, representing a more comprehensive approach to modelling transport in a pore than the Fickian model applied in part 1. The model is used to simulate thiophene hydrogenation over a Co-Mo/Al₂O₃ catalyst. At temperatures and pressures close to the dew point, capillary condensation occurs in the network. For example at 553 K and 21.5 bar, 55% of the pores are liquid filled. Capillary condensation in the network leads to a decrease in thiophene conversion at the network centre. This effect is particularly pronounced when the percolation threshold of the network is approached. The reduction of thiophene conversion in networks containing condensate is thought to result from loss of surface area available for vapour phase reaction and an increased fraction of dead-end pores, which contribute less to the flux of reactants than open pores. The effect of the size of the network used in the simulations upon the range of pressures over which capillary condensation and percolation phenomena occur is considered.     

乳液液膜法对水中对氨基苯甲酸分离富集的研究

用以磷酸三丁脂(TBP)为流动载体的乳液液膜体系对水中的对氨基苯甲酸(PABA)的分离富集进行了研究,考察了影响液膜分离富集PABA的各种因素,同时对PABA在不同pH值水溶液中的存在形态、PABA在液膜分离富集中的传质机理等进行了分析讨论。结果表明在适宜的乳液液膜操作条件下,对含有500mg/L对氨基苯甲酸的料液,经过一级液膜提取分离,对氨基苯甲酸的提取率可达99%,提取分离效果良好。     

气体膜分离混合气中二氧化碳的研究进展

气体膜分离技术作为碳捕获方案被国际社会认为是最有发展潜力的脱碳方法之一.综述介绍了中空纤维膜接触器、膜结构、系统工艺和吸收剂的研究现状.相对于水和碳酸盐类,醇胺具有的二氧化碳吸收率高、反应热低、反应速度快以及容易再生等优点,在研究与工业过程中是应用最广泛的吸收剂之一.     

Preparations of metal impregnated porous inorganic membranes for hydrogen separation by multi-step pore modifications

In this research, porous inorganic membranes for hydrogen separation were prepared with α-alumina support by multi-step pore modification method. Porous inorganic membranes were made by three consecutive steps: sol-gel method,in-situ hydrolysis of tetraethylorthosilicate (TEOS) and soaking and vapor deposition (SVD) method. In order to enhance the hydrogen selectivity, we used nickel (Ni) and palladium (Pd) particles in the first and final pore modification steps. Although both nickel and palladium induced surface diffusion, palladium was shown more effective for hydrogen selective adsorption than nickel. This multi-step method produced porous membranes with a moderate hydrogen selectivity and excellent hydrogen permeability at high temperature up to 773 K and at transmembrane pressure (ΔP) as high as 310 kPa. The separation factor of hydrogen relative to nitrogen was maintained at about 7 even when the transmembrane pressure was 70 kPa, and the hydrogen permeability was still much higher than that of non-porous polymeric membranes. Furthermore, the distributions of nickel and palladium within the intermediate layer formed at the membrane cross-section were examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis.     

Theoretical limiting prediction of H2S removal efficiency from coal gasification streams using an intermediate temperature electrochemical separation process

A mathematical model has been developed to predict the theoretical limiting H2S removal efficiency of an electrochemical membrane separator (EMS) in the presence of overwhelming levels of H2O and CO2 (as would be found in syn-gas). Thermodynamic principles gave the minimum potential requirements for cell operation. Factors including electrokinetics, mass transfer, chemical equilibria and internal resistance, occuring with application of current, were incorporated into the prediction. Theoretical predictions, which represent a limiting value, show achievable current efficiencies close to 100% for high H2S levels (1000ppm) at 90% removal. At this same removal level with 100 or 10ppm inlet gas, the predicted maximum current efficiencies dropped, due to concentration effects, to 93% and 40%, respectively. This solidifies the economic importance of obtaining close to 100% current efficiencies at sour gas levels compared to polishing applications where the removal, not the current efficiency, is more important. Predicted cell potentials were consistently in the same range, –0.450 to –0.550V, for all concentration levels at 90% removal. Comparison with experimental data gave good agreement; actual current efficiencies were consistently within 15% of the maximum predicted values at coinciding removal levels. However, actual potentials were lower (less negative) because of hydrogen leakage through the cell membrane. While lower potentials require less power, sulfur production at the anode was reduced.     

Optimization of structure and properties of polyphenylene sulfide porous membrane by controlling the process of thermally induced phase separation

Polyphenylene sulfide (PPS) porous membranes were successfully prepared from miscible blends of PPS and polyethersulfone (PES) via thermally induced phase separation followed by subsequent extraction of the PES diluent. The morphologies, crystalline structures, mechanical properties, pore structures and permeate fluxes of the PPS porous membranes obtained from different phase separation processes were characterized and are discussed. During the phase separation in the heating process, PPS and PES mainly underwent liquid–liquid phase separation, and then a nonhomogeneous porous structure with a mean pore size of 100 μm and a honeycomb‐like internal structure formed on the membrane surface. The phase separation of PPS/PES occurring in the cooling process was easier to control and the related pore diameter distribution was more regular. In the process of direct annealing, as the phase separation temperature decreased, the pore size distribution became more homogeneous and the mean diameter of the pores also decreased gradually. When the phase separation temperature decreased to 200 °C, PPS membranes with a network structure and a uniform as well as well‐interconnected porous structure could be obtained. In addition, the maximum permeation flux reached 1718.03 L m^–2 h^–1 when the phase separation temperature was 230 °C. The most probable pore diameter was 6.665 nm, and the permeate flux of this membrane was 2.00 L m^–2 h^–1; its tensile strength was 17.07 MPa. Finally, these PPS porous membranes with controllable pore structure as well as size can be widely used in the chemical industry and energy field for liquid purification. © 2020 Society of Chemical Industry     

Plasma polymer membranes from hexafluoroethane/hydrogen mixtures for separation of oxygen and nitrogen

Thin plasma polymer layers were produced employing feed mixtures of hexafluoroethane and hydrogen in an rf parallel-plate reactor. The layers are intended for use in membrane-based separation of oxygen and nitrogen. The hexafluoroethane-to-hydrogen mixture ratio was varied over a wide range, whereas all other process parameters (power, pressure, substrate temperature, and total gas flow) were held constant. The plasma polymers were examined by scanning electron microscopy, X-ray analysis, quantitative elemental analysis, and X-ray photoelectron spectroscopy. Permeability coefficients of oxygen and nitrogen and selectivities of the pure gases were determined. Pinhole-free plasma polymer films containing different amounts of fluorine, carbon, and hydrogen were formed. The distributions of fluorine and hydrogen in the products reflect their distributions in the feed gas. Traces of oxygen in some of the polymers are explained by the reaction of trapped radicals with atmospheric oxygen on the samples' exposure to air. Fluorine-containing carbon moieties such as CF₃, CF₂, and CF, and carbon moieties with fluorine atoms exclusively in secondary positions are present. A method of calculating crosslink density using the analytical data is described. The oxygen permeability coefficient and the selectivity of the plasma polymers increase as the hexafluoroethane content of the feed gas is raised. This behavior is attributed to growing solubility selectivity as a result of the rising fluorine content of the polymers. Maximum selectivity amounts to 3.4 at an oxygen permeability coefficient of 21 Barrer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1517–1526, 1997     

Efficient separation of N2 and he at low temperature using MFI membranes

Ultra‐thin MFI membranes were evaluated for N₂/He separation over the temperature range of 85–260 K for the first time. The membranes were rather nitrogen selective at all the conditions investigated. A highest N₂/He selectivity of 75.7 with a high N₂ flux of 83 kg/m²/h was observed at 124 K. The separation was attributed to adsorption selectivity to N₂, effectively hindering the transport of He in the zeolite pores. The exceedingly high permeance even at low temperatures was ascribed to the ultrathin (<1μm) membrane used. As the pressure ratios increased, a better separation performance was obtained. A mathematical model showed the largest difference of adsorbed loading over the film at ca. 120 K was the main reason for the observed maximum selectivity. Further, the modelling indicated the selectivity would increase 2–3 times by reducing the influence of defects, concentration polarization, and pressure drop over the support. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2833–2842, 2016     

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。