多孔石墨烯气体分离膜分子渗透机理

通过分子动力学方法模拟了4种不同气体分子（He,H₂,N₂和CH₄）在多孔石墨烯气体分离膜中的穿透过程,揭示了气体分子穿透石墨烯纳米孔的渗透机理,指出分子的渗透不仅与其动力学参数有关,如分子直径和质量,还与分子在石墨烯表面的吸附有关。石墨烯表面的吸附层给气体分子的渗透提供了一个额外的路径,因此分子在石墨烯表面的吸附越强,分子的渗透通量越大。同时,不同大小的纳米孔下H₂分子的渗透通量都随着压力的增加而线性增加。     

Characteristics of permeation and separation of aqueous alcoholic solutions with chitosan derivative membranes

Permeation and separation characteristics for the feed vapours from aqueous alcoholic solutions through chitosan derivative membranes such as chitosan acetate (GA-ChitoA), chitosan (GA-Chito), and carboxymethyl chitosan acetate (GA-CM-ChitoA) membrane crosslinked with glutaraldehyde were investigated by evapomeation. The GA-Chito and GA-CM-ChitoA membranes prepared from casting solutions containing an optimum amount of glutaraldehyde showed a high permeation rate and high water permselectivity for an azeotropic composition in an aqueous ethanol solution. The permselectivity for water through the GA-CM-ChitoA membrane in evapomeation was in the order of aqueous solutions of methanol < ethanol < 1-propanol. The effect of the chemical and physical structure of these hydrophilic membranes on the permeation and separation characteristics is discussed.     

Influence of novel surface modifying macromolecules and coagulation media on the gas permeation properties of different polymeric gas separation membranes

Integrally skinned asymmetric membranes for the separation of O₂ and N₂ were fabricated by the phase inversion technique from polysulfone, polyetherimide, and polyimide. Two types of surface modifying macromolecules (SMMs) including hydrophilic SMM (LSMM) and charged SMM (cSMM) were synthesized and blended with the casting solution to modify the membrane surface. The cast film was then immersed in the first coagulant alcohol (methanol, ethanol, or isopropanol) for a predetermined period, before being immersed in the second coagulant (water). The SMMs used in these experiments were laboratory synthesized by the two‐step process of polyurethane prepolymer synthesis and end capping, before being characterized by differential scanning calorimetry. Their molecular structure was determined from the molecular weight obtained by gel permeation chromatography. The membranes were characterized by contact angle measurement and O₂ and N₂ gas permeation performance. Attempts were made to interpret the gas permeation data by delayed demixing affected by solubility parameters of polymer, solvent, and nonsolvent. Furthermore, the permeation performance of cSMM membranes was interpreted by the solvation of the charged sulfonate groups present in cSMM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Studies on syntheses and permeabilities of special polymer membranes. V. Effect of casting solution composition on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The permeation characteristics of cellulose acetate membranes in separation of polymers from their aqueous solutions were investigated by changing the preparation conditions of the membranes, that are the solvent evaporation period and the casting solution composition consisting of a mixture of cellulose acetate (CA), acetone (A), and formamide (FA). The rates of pure water permeability were influenced remarkably by the solvent evaporation period and the casting solution composition. When the solvent evaporation period was short, the rates of pure water permeability increased with a decrease in A/CA, increase in FA/A, and increase in FA/CA in the casting solution. From the experimental results using poly(vinyl alcohol) as poly(ethylene glycol) as feed solute, it was seen that the changes of solvent evaporation period and casting solution composition related to the change of microporous structure of the resulting membranes. The effect of feed concentration and operating pressure on the permeation characteristics were also studied. There was found a concentration polarization of poly(vinyl alcohol) molecules on the surface of the membrane, and a compaction of the membrane occurred under pressure.     

High flux freeze-dried cellulose acetate reverse osmosis membranes as microporous barriers in gas permeation and separation

The permeations of helium, hydrogen, methane, ethylene, nitrogen, and argon, and helium–methane, nitrogen–ethylene, oxygen–nitrogen, and sulfur dioxide–nitrogen mixtures have been studied using freeze-dried porous cellulose acetate reverse osmosis membranes. The results illustrate the existence of mobile and immobile sorbed layers and the governing influence of surface flow in gas-phase reverse osmosis separations. Preshrunk freeze-dried porous cellulose acetate membranes seem to offer a practical means of utilizing the reverse osmosis process for recovering helium from natural gas and separating sulfur dioxide from flue gases.     

Studies on syntheses and permeabilities of special polymer membranes. X. Effects of conditions of membrane preparation on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The effects of casting solvents, dissolution temperature of casting solution, and pH and temperature of gelation solution, etc. on the permeation characteristics of cellulose acetate membranes in the separation of polymers from their aqueous solutions were investigated, using aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) as feed. The permeation characteristics were influenced significantly by the conditions of membrane preparation and of the permeation. It was found that a concentration polarization at the membrane surface occurred with poly(vinyl alcohol) molecules, but it was very small with poly(ethylene glycol). The above results were discussed in detail from points of view of structure of the resulting membranes and the interactions between the solvent, the solute in the feed and the cellulose acetate molecules.     

Plasticization of gas separation membranes

For the investigation of the plasticizing effect of carbon dioxide on polymers used for gas separation membranes new experimental methods have been developed that measure the sorption kinetics as well as the dilation kinetics. Comparing dilation and sorption kinetics at low and elevated pressures gives information about different types of swelling behaviour depending on the pressure level. Volume relaxation in the form of a slow volume increase in time can be observed above a certain pressure, called plasticization pressure. An interpretation of these experimental facts as a process of slow loosening of densely packed entanglements is suggested. By using sorption kinetics experiments at various temperatures the plasticizing effect of C0₂ is apparent by a decreasing activation energy for diffusion with increasing penetrant concentration.     

Gas permeation and separation properties of sulfonated polyimide membranes

Permeability and selectivity of pure gas H₂, CO₂, O₂, N₂ and CH₄ as well as a mixture of CO₂/N₂ for sulfonated homopolyimides prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoro propane disulfonic acid (BAPHFDS) were measured and compared to those of the non-sulfonated homopolyimide having the same polymer backbone. The polyimide in a proton form (NTDA-BAPHFDS(H)) displayed higher selectivity of H₂ over CH₄ without loss of H₂ permeability. Strong intermolecular interaction induced by sulfonic acid groups decreased diffusivity of the larger molecules. The CO₂/N₂ (19/81) mixed gas permeation was investigated as a function of humidity. With increasing relative humidity from 0% RH to 90% RH, the CO₂ permeability for NTDA-BAPHFDS(H) polyimide increased by more than one order of magnitude, and the selectivity of CO₂/N₂ also increased twice or more. On the other hand, the gas permeability for the non-sulfonated polyimide slightly decreased with increasing humidity. NTDA-BAPHFDS(H) polyimide displayed a CO₂ permeability of 290×10⁻¹⁰ cm³ (STP) cm/(cm² s cmHg) and a separation factor of CO₂/N₂ of 51 at 96% RH, 50 °C and total pressure of 1 atm.     

Preparation and gas permeation of immobilized fullerene membranes

Fullerene‐dispersed membranes were homogeneously prepared under the conditions in which a 10 wt % polystyrene solution containing 1 wt % fullerene was dried under a reduced pressure of 50 cmHg at room temperature. The fullerene membranes prepared with 1,2‐dichlorobenzene were found to have the darkest color, and showed no evidence of fullerene crystals in their photomicrographs. UV‐visible and infrared absorption spectra of the fullerene membranes showed fullerene bands, which indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of pure nitrogen, oxygen, carbon dioxide, ethane, and ethylene were found to increase significantly in the fullerene membranes compared to those in the polystyrene membranes, although the ideal separation factors for oxygen/nitrogen and ethylene/ethane in the fullerene membranes (i.e., 4.3 and 1.7, respectively) were slightly less than the separation factors in the polystyrene membranes. The permeability increase originated from the increase in diffusion coefficients in the fullerene membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 529–537, 2000     

The separation of multicomponent mixtures by gas permeation

Two types of modules are most common in gas permeation: the hollow fibre module and the spiral wound module. With some simplifying assumptions regarding the flow pattern, the separation characteristics of such modules can be calculated for binary and ternary mixtures.More important in practice, however, is the separation of multicomponent mixtures. This paper discusses the design of multicomponent systems including cases where non-permeating components or carrier gases at the permeate side are present.The results of some calculations are discussed and compared with the usual short-cut method based on the assumption of a pseudo-binary mixture. The results demonstrate that the reduction of a multicomponent mixture to a pseudo-binary mixture is only reasonable when components of similar permeability are lumped together. Serious deviations with respect to membrane area or product composition must be expected for larger differences in permeabilities.     

热致相分离法制备聚(偏氟乙烯-六氟丙烯)/离子液体凝胶膜及 气体渗透性能

采用热致相分离（TIPS）法制备p(VDF-HFP)/[BMIM]PF6凝胶膜,对该膜的内部结构及机械性能进行表征,探讨了[BMIM]PF6添加量对凝胶膜的CO2/N2渗透性能影响。结果表明：随着[BMIM]PF6添加量的增加,p(VDF-HFP)/[BMIM]PF6体系的凝胶温度逐渐降低,凝胶膜的聚合物骨架结构由致密变成疏松的球晶结构;同时[BMIM]PF6的添加降低了凝胶膜的结晶度,改善了p(VDF-HFP)链段的柔韧性,因而膜的CO2和N2渗透系数显著增加,CO2/N2渗透选择性则先升高后降低;凝胶膜受扩散过程控制,当[BMIM]PF6添加量（质量分数）由0增加到60%时,凝胶膜的CO2渗透性系数从0.2 Barrer增加到94.3 Barrer。     

Fabrication of hollow fibre gas separation membranes

Over a century ago, researchers discovered that membranes could separate gases. However, this technology has been commercialized only recently, mainly because the early membranes had low permeance and permselectivity, making them uneconomical. With the discovery of thin barrier membranes, either in dense, asymmetric, or thin-film composite form, gas separation by membranes has become commercially viable. Furthermore, the discovery of hollow fibre technology has permitted low-cost membrane fabrication and high-efficiency module design. Homogeneous dense hollow fibre membranes are fabricated from polymer melts using a special die. Asymmetric membranes with integral dense skins, however, are made by controlled coagulation of polymer solutions. Finally, thin-film composite membranes, where a thin dense barrier layer is made separately on a microporous substrate, are made either by simple dip coating or by complex interfacial processes. The latter concept is versatile because it permits formation of thin barrier layers by a variety of methods. The apparatus used to fabricate various membrane types and the critical factors influencing the membrane properties are discussed.     

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.     

Effects of polydispersity on critical concentration of polymer solutions

A semiempirical equation is developed to compute the unperturbed parameter from the critical concentration of polymer solutions derived from the viscometric and kinetic data. This equation gives satisfactory results for various vinyl polymers including poly(vinyl chloride), polystyrene and poly(methyl methacrylate) among others that follow the Schulz molecular weight distribution function. It is found that the segments of a Gaussian polymer chain are associated with an equal number of foreign segments near its center of mass, when the polymer solution has attained a uniform segment density at the critical concentration. The effect of molecular weight distribution on the present studies is significantly large that it merits an empirical treatment. Defects of the model is also discussed.     

Waterborne poly(urethane‐urea) gas permeation membranes for CO2/CH4 separation

In this work, dense membranes from aqueous dispersions of poly(urethane‐urea) (PUU) based on poly(propylene glycol) (PPG) and a block copolymer composed of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG), EG‐b‐PG, with 7 wt % of the former were obtained. Nonpolluting formulations were synthesized with proportions of PPG and EG‐b‐PG as 1:0, 1:1, 1:3, and 3:1 in terms of equivalent number ratios. The effect of small and gradual increases in PEG segments was evaluated for the permeability of pure CO₂, CH₄, and N₂, at room temperature. Slight increases in PEG‐based segments in PUU promoted some remarkable properties, which led to a simultaneous increase in CO₂ permeability and ideal selectivity for CH₄ (300%) and N₂ (380%). Infrared spectroscopy showed that the PEG portions induced hydrogen bonds between ? NH of urethane and ether groups in the PEG portions, which promoted ordering of the flexible segments, confirmed by X‐ray diffractometry and small‐angle X‐ray scattering. Diffractometry techniques also confirmed the absence of crystalline domains, as did dynamic mechanical analysis. The produced membranes showed performance above Robeson's 2008 upper bound and seemed to be a superior polymeric material for CO₂/CH₄ and CO₂/N₂ separation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46003.     

Carbon molecular sieves used in gas separation membranes

The preparation of unsupported and supported carbon molecular sieve membrances has been studied. It proved impossible to prepare a continuous membrane, but measurements of the mass transfer of gases showed that diffusion across the membranes occurred both in the gas phase within large interstices and on the surface of the carbons. As a result it was possible to obtain some separation of gases.     

有机框架膜在气体分离中的研究进展

高渗透性、高选择性和高稳定性的膜材料是决定膜分离过程效率的关键。有机框架膜（organic framework membranes,OFMs）具有孔隙率高、孔道长程有序、易于官能化修饰、稳定性强等特点,在气体膜分离领域具有重要发展前景。综述了有机框架膜的化学组成、结构特征、制备方法及其在二氧化碳捕集与分离、烯烃/烷烃分离及稀有气体分离等气体分离过程中的应用。最后,对有机框架膜在气体分离领域的机遇和挑战进行了总结,并对其发展方向进行了展望。