Gas Separation Properties of Polyimide-Zeolite Mixed Matrix Membranes

Mixed matrix membranes (MMMs) of polyimide (PI) and zeolite 13X, ZSM-5 and 4A were prepared by a solution-casting procedure. The effect of zeolite loading, pore size, and hydrophilicity/hydrophobicity of zeolite on the gas separation properties of these mixed matrix membranes were studied. Experimental results indicate that permeability of He, H₂, CO₂, and N₂ increased with zeolite loadings. Selectivity of H₂/N₂ shows a slight improvement for low loadings of zeolites 13X and ZSM-5 but has a decreasing trend for zeolite 4A and high loadings of zeolites 13X and ZSM-5. In addition, selectivity of H₂/CO₂ remains low (1–3) while selectivity of CO₂/N₂ is significantly improved with the incorporation of the three zeolites in the polyimide membrane. Experimental permeabilities are higher than those predicted by the Maxwell model except for H₂ and N₂ permeabilities of the PI-4A system which are consistent with the predicted permeabilities. The proposed modified Maxwell model is capable of predicting the permeabilities of polyimide-zeolite 4A MMMs, but fails to simulate the permeability increase induced by interface voids in the polyimide-zeolite 13X and ZSM-5 systems.     

Effect of Dispersed Multi-Walled Carbon Nanotubes on Mixed Matrix Membrane for O2/N2 Separation

Mixed matrix membranes (MMMs) consisting of multiwalled carbon nanotubes (MWCNTs) embedded within polyetherimide were prepared. Surfactants of different charges were utilized to disperse the nanotubes through a simple non-covalent approach. The characterization results suggest that proper selection of the dispersing agent contributed to better dispersion of nanotubes. The MMMs exhibited improved thermal stability and mechanical strength, which indicate the improvement of dispersion and compatibility within the polymer matrix. The resulting membrane exhibited permeance improvement of O₂ and N₂ as much as 87.7% and 120% respectively compared to that of neat polyetherimide. The results implied that Triton-X100 treated MWCNTs is a promising filler to enhance gas permeability.     

Novel Composite Membranes for Gas Separation: Preparation and Performance

High performance composite membranes based on molecular sieving silica (MSS) were synthesized using sols containing silicon co-polymers (methyltriethoxysilane and tetraethylorthosilicate). Alpha alumina supports were treated with hydrochloric acid prior to sol deposition. Permselectivity of CO2 over CH4 as high as 16.68 was achieved whilst permeability of CO2 up to 36.7 GPU (10–6 cm3 (STP) cm–2 · s–1 · cm Hg–1) was measured. The best membrane's permeability was finger printed during various stages of the synthesis process showing an increase in CO2/CH4 permselectivity by over 25 times from initial support condition (no membrane film) to the completion of pore structure tailoring. Transport measurement results indicate that the membrane pretreated with HCl has highest permselectivity and permeation rate. In particular, there is a definite cut-off pore size between 3.3 and 3.4 angstroms which is just below the kinetic diameters of Ar and CH4. This demonstrates that the mechanism for the separation in the prepared composite membrane is molecular sieving (activated diffusion), rather than Knudsen diffusion.     

Magnetic Mixed Matrix Membranes Consisting of PPO Matrix and Magnetic Filler in Gas Separation

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and magnetic neodymium powder particles MQP-14-12 have been used for the preparation of magnetic mixed matrix membranes. Permeability diffusion and sorption coefficients of O₂, N₂, and synthetic air components were estimated for homogeneous and heterogeneous membranes using the Time Lag method based on dynamic experiments in a constant pressure system. The influence of magnetic field and magnetic powder particles on the gas transport properties of MMMs was studied. The results showed that the membrane permeation properties were improved with the magnetic neodymium particle filling. It was observed that the magnetic ethylcellulose and poly(2,6-dimethyl-1,4-phenylene oxide) membranes showed higher gas permeability, while their permselectivity and solubility were rather maintained or slightly increased. The results also showed that the magnetic powder addition enhanced gas diffusivity significantly in EC and PPO membranes.     

Effect of Raw Multi-Wall Carbon Nanotubes on Morphology and Separation Properties of Polyimide Membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO₂ and CH₄ showed that the addition of r-MWCNTs into the dope solution increased the CO₂/CH₄ separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO₂ in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO₂/CH₄ separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO₂/CH₄ separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r–MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs.     

Ion Rejection in Single and Binary Mixed Electrolyte Systems by Nanofiltration: Effect of Feed Concentration

Abstract

The objectives of this work were to investigate and compare the separation behavior of ions in single and binary mixed electrolyte systems by NF70, with emphasis on the effect of feed concentration. Experimental results showed that the anion rejection is lower in the binary mixed system compared to the single salt system. Anion rejection decreases with the enhancement of feed concentration of co‐existing electrolyte. As for cation rejection, Na⁺ rejection in the mixed electrolyte system is generally greater than that in the single NaCl system; whereas the separation performance of Ca²⁺ at high feed concentrations shows the opposite trend, and cannot be explained by the Donnan theory. Several possible mechanisms have been evaluated. Finally, the Spiegler‐Kedem equation was used and parameters were calculated.     

膜技术在含烃类气体分离中的研究及前景

气体膜分离技术在膜分离中占有相当的比重。简要介绍了气体膜分离技术的基本原理,并对天然气、沼气、炼厂气等含烃类气体的膜法处理技术与传统加工技术进行对比,突出了膜法的技术及经济优势。着重介绍了用于含烃气体处理的各种材质膜的研究以及应用现状,并对气体分离膜、膜组件的发展及应用前景进行的简单的阐述。     

MOF‐Based Mixed‐Matrix Membranes in Gas Separation – Mystery and Reality

Microporous additives like nanosized metal‐organic framework (MOF) particles can improve the gas separation performance of polymer membranes. These membranes which consist of added filler particles in a continuous polymer phase are called mixed‐matrix membranes (MMM). While inorganic zeolites and organic polymers do not match well, the preparation of defect‐free MOF‐based MMMs is much easier. However, some problems can also occur during the preparation. Solutions how to avoid them and prepare perfect MMMs are given. In practical gas separation, the selectivity of the MMMs was found to be even higher than predicted by the Maxwell model.     

Y型沸石/炭杂化膜的制备及其气体分离性能

以聚酰胺酸为前驱体,Y型沸石为掺杂物,经高温炭化制备了Y型沸石/炭杂化膜.通过纯组分气体(H2,CO2,O2,N2)的渗透实验对杂化膜的气体渗透性能进行测定,并使用透射电镜,X射线衍射对杂化膜的微结构进行表征.研究了沸石的含量以及炭化温度对杂化炭膜的气体渗透性能和微结构的影响.结果表明,随着膜内沸石含量的提高,Y型沸石/炭杂化膜的气体渗透性能明显提高,而随着炭化温度的升高,Y型沸石/炭杂化膜的渗透系数降低,选择性提高.与纯炭膜相比,Y型沸石/炭杂化膜在保持高O2N2选择性的前提下,其渗透性能显著提高.炭化温度为700℃,沸石含量为15%,Y型沸石/炭杂化膜O2的气体渗透系数为501 bareer,O2/N2选择性为15.6.当炭化温度超过800℃以后,杂化膜中的沸石晶体结构被破坏,其气体渗透系数接近纯炭膜的气体渗透系数.因此,保持沸石孔道结构的完整是制备高性能沸石/炭杂化膜的关键因素之一.     

单外皮层PES中空纤维气体分离膜制备的研究

以聚醚砜(PES)作膜材料,N-甲基吡咯烷酮(NMP)为溶剂,乙醇(Ethanol)作非溶剂,NMP-Water为芯液,获得PES/NMP/Ethanol铸膜液[m(PES)∶m(NMP)∶m(Ethanol)=35∶57∶8],采用相转化法制备了PES中空纤维气体分离不对称膜,研究了保存时间、硅橡胶种类、芯液浓度、芯液流量和凝胶温度等对PES中空纤维膜O2/N2渗透性能的影响。同时,分析了单外皮层PES中空纤维气体分离膜的结构,讨论了PES中空纤维气体分离膜的机械性能。当芯液组成的m(NMP)∶m(H2O)=86∶14和凝胶温度17℃时,涂3%硅橡胶A后的PES中空纤维气体分离膜气体分离性能如下:αO2/N2=6.68,JO2=2.26GPU,JN2=0.33GPU。     

高气速选择性分离氨碳混和气模拟实验

采用二级串联鼓泡吸收器对NH3／CO2摩尔比为2：1的混和气体进行高气速选择性吸收,获得氨的总吸收率为96．7％,二氧化碳的总吸收率为33．1％,二级吸收器出口气相CO2摩尔含量达90．9％,液相氨碳摩尔比为5．85。将此吸收液在加压下精馏分离氨,基本可以把吸收液中游离氨回收。分离游离氨后的溶液在常压下进行解吸,蒸馏塔出口液体含NH3和CO2量仅为0．014％和0．006％,解吸气回串联吸收器进行循环吸收分离。对预计工业分离过程进行物料和能量衡算,分离1kg液氨需1MPa的蒸汽约3.2kg。     

Synthesis and Characterization of Polyimide Mixed Matrix Membranes

Polyimides of Matrimid 5218 and P84 as backbone and different fillers including silica aerosil, zeolite 4A, carbon nanotubes, and carbon molecular sieves were used to synthesize flat mixed matrix membranes (MMMs). Effects of different polymer types and concentrations, different filler types and contents, and fabrication procedure were investigated. Scanning Electron Microscopy (SEM) analysis showed acceptable connections between the two phases and the MMMs performed higher performance compared to the polymeric membranes. Thermal treatment of the MMMs, as a defect repairing technique, was found very effective. Performed pervaporation and gas permeation experiments showed better separation performances of the MMMs with respect to those of the neat polymeric membranes. The results showed up to seven and two times increment in separation factors of MMMs regarding to neat polymeric membranes for pervaporation and gas separation experiments, respectively, while permeation rates nearly remained constant indicating effectiveness of the proper filler incorporation within polymer matrices approach.     

气体膜分离技术及应用

简要介绍了有关气体膜分离的基本原理、材料及其在氢气分离回收、空气分离和酸性气处理中的应用,并对气体膜分离的发展前景提出了自己的见解。     

气体膜分离技术的进展及其应用

介绍了气体分离膜材料的种类;叙述了介绍了气体膜分离技术在分离空气制备富氧、富氮,水蒸气、有机蒸汽的分离和氢气回收等工业领域的应用.介绍了气体膜分离技术的研究进展,并提出了我国气体膜分离技术发展方向.     

采用增大凝结液滴方法的锥芯超音速旋流分离装置性能研究

To improve the separation performance of a supersonic gas separation device for the treatment of gas mixture with a single heavy component, a novel structure with shorter settlement distance was constructed and a method of droplet enlargement was applied. A series of experiments were carried out in the improved separation device under various conditions, using air-ethanol vapor as the medium and micro water droplets as nucleation centers. The effects of the inlet pressure, temperature and relative humidity, the swirling intensity, and mass flow rate of water on the separation performance were investigated. The separation was improved by increasing the inlet pressure and relative humidity. With the decrease of swirling intensity and mass flow rate of water, the separation efficiency increased first and then decreased. The inlet temperature had a slight effect on the separation. The results showed that the separation performance was effectively improved using the proposed structure and method, and the best separation in this study was obtained with the ethanol removal rate about 55% and dew point depression 27 K. The addition of water had little pollution to the air-ethanol vapor system since the water carry-over rate was within the range of %-0 in most cases.     

PCDL含量对混和软段的PUE相分离和阻尼性能的影响

以甲苯二异氰酸酯（TDI）、1,4-丁二醇（BDO）为硬段,聚碳酸酯二醇（PCDL）和聚醚二醇（PPG）混合物为软段,采用预聚体法制备了不同软段组成的聚氨酯弹性体（PUE）。采用DSC、FT—IR和DMA等分析手段研究了PCDL含量对PUE的微相分离程度和阻尼性能的影响。结果表明,随着软段中PCDL含量的增加,PUE中氨酯羰基的氢键化程度减小,相分离程度减小,而且PUE的储能模量随着PCDL含量的增加而减小;与单一组分软段的PUE相比较,混合软段的PUE具有相对较好的阻尼性能。     

气体膜分离的进展及在石油化工中的应用

综述了气体膜分离技术在膜组件和膜材料方面的进展及在石油化工领域中的应用。     

多元混合气体在硅橡胶膜中的渗透传质研究

以O2、N2和Co2单组分及其多元混合气为目标气体,系统研究了他们在硅橡胶膜中的渗透传质行为,考察了压差和进气组成等因素对渗透通量和透过气组成的影响。实验结果表明,气体渗透通量随着压差的升高而增加,渗透快的气体在透过气中的含量也随着压差的升高而增加;透过气中慢气N2的体积分率总是低于其在进气中的体积分率,快气CO2的变化与之相反,而透过气中O2的体积分率可能高于也可能低于其在进气中的体积分率,取决于混合气中其他组分的性质及相互比例关系。     

气体分离膜材料研究进展

介绍了高分子材料、无机材料、有机－无机杂化材料三类气体分离膜材料,主要包括聚酰亚胺、聚砜、聚二甲基硅氧烷、聚[1-(三甲基硅氧烷）－1－丙炔]等高分子材料,以及致密无机膜和多孔无机膜材料,并且对有机－无机杂化材料作了简要概述。在评价了各种膜材料性能的基础上,展望了气体分离膜材料的发展前景。     

Separation of CO2/N2 Gas Mixture through Carbon Membranes: Monte Carlo Simulation

Abstract

Monte Carlo simulation method is employed to investigate separation behavior of gas mixture composed of carbon dioxide and nitrogen through a model carbon membrane under the different conditions. The simulation gives insight into the separation mechanism to a certain extent, which is based on the loading and diffusion of carbon dioxide and nitrogen in the carbon membrane with different pore size. The simulation results indicate that the carbon dioxide can be adsorbed on the surface of membrane wall more strongly, whereas the diffusion rate of nitrogen is more prominent. When the separation condition alters, the influence of the two main factors mentioned above on transport of gas molecules in membranes becomes different. Therefore, the equilibrium selectivity of nitrogen and carbon dioxide changes correspondingly.