SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOUR PERMEATION

 This study deals with polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) composite membranes for propane separation from propane/nitrogen mixtures, which is relevant to the recovery of propane in petroleum and chemical industry. The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope (SEM). The surface morphology of PDMS/PVDF composite membranes is very dense. There are three layers, the thin dense top layer, finger-like porous middle layer and sponge-like under layer in the cross-section SEM image of PDMS/PVDF composite membranes. The effects of the types of cross-linking agents and pressure on the membrane permselectivity were investigated. The permeability of nitrogen was independent of feed pressure. However, the permeability of propane increased with the pressure increasing for all membranes. The membrane cured by a tri-functional crosslinker with attached vinyl groups had better performance than the tetra-functional one, in both selectivity and permeation flux. The total permeation flux is 1.769× 10^-2 cm³(STP)/(cm²·s) and the separation factor is 19.17 when the mole percent of propane in the gas mixture is 10 at the 0.2 MPa pressure difference and 25°C.     

SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOR PERMEATION

This study deals with polydimethylsiloxane(PDMS)/polyvinylidene fluoride(PVDF) composite membranes for propane separation from propane/nitrogen mixtures,which is relevant to the recovery of propane in petroleum and chemical industry.The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope(SEM).The surface morphology of PDMS/PVDF composite membranes is very dense.There are three layers,the thin dense top layer,finger-like porous middle layer an...     

Synthesis and characterization of silicalite-1/carbon-graphite membranes

Silicalite-1/carbon-graphite composite membranes have been prepared using a standard hydrothermal synthesis method and characterized by XRD, SEM, TGA, BET and permeation experiments. Single gas permeation fluxes and binary mixtures separation and selectivity data are reported for methane, ethane and propane using the composite membranes. Carbon-graphite oxidized for 4 h prior to membrane preparation had the most promising separation properties. The permeation fluxes for the binary mixtures reflect that of the single component flux ratios. At 20 degrees C the membranes show high separation selectivity toward lighter component in binary mixtures. Single gas permeances for methane and ethane were found to decrease with increasing temperatures while that of propane fluctuates.     

Enhanced Propene/Propane Separation by Directional Decoration of the 12-Membered Rings of Mordenite with ZIF Fragments

Propene/propane separation is challenging due to the very small difference in molecular sizes, boiling points and condensabilities between these molecules. Herein, we report a strategy of introducing ZIF fragments into traditional mordenite (MOR) zeolite to decorate the 12-membered ring of MOR. After decoration, the originally ineffective zeolite MOR exhibited high kinetic propene/propane selectivities (139 at 25 °C) and achieved efficient propene/propane separation. The propene/propane separation potentials of the resulting adsorbents were further confirmed by breakthrough experiments with equimolar propene/propane (50/50) mixtures.     

Enhanced Propene/Propane Separation by Directional Decoration of the 12‐Membered Rings of Mordenite with ZIF Fragments

Propene/propane separation is challenging due to the very small difference in molecular sizes, boiling points and condensabilities between these molecules. Herein, we report a strategy of introducing ZIF fragments into traditional mordenite (MOR) zeolite to decorate the 12‐membered ring of MOR. After decoration, the originally ineffective zeolite MOR exhibited high kinetic propene/propane selectivities (139 at 25 °C) and achieved efficient propene/propane separation. The propene/propane separation potentials of the resulting adsorbents were further confirmed by breakthrough experiments with equimolar propene/propane (50/50) mixtures.     

Surface modification of mesoporous membranes by fluoro-silane coupling reagent for CO2 separation

The potential of hybrid organic–inorganic membranes for separating organic molecules from air, based on solubility selective mechanism, was evaluated. Alumina and titana membranes with average pore size near 4 nm were surface modified using trimethoxysilane fluorinated coupling reagent. The permeabilities to helium, nitrogen, methane, ethane, propane, butane and carbon dioxide were evaluated at feed pressures lying between (1.5 × 10⁵ and 3.5 × 10⁵ Pa) 1.5 and 3.5 bar and permeate outlet near 1 × 10⁵ Pa (1 bar). The permeabilities of the grafted membranes generally decreased by about two to three orders of magnitude compared with the untreated membranes. The CO₂/N₂ permselectivity increased significantly in the case of the TiO₂ grafted membrane. The membranes performances were compared and the TiO₂ grafted membrane exhibits higher permselectivity and permeability, so that, it is a good candidate for CO₂ to N₂ separation and CO₂ to hydrocarbon separation.     

Solubility-based gas separation with oligomer-modified inorganic membranes: Part III. Effects of synthesis conditions

As in previous papers in this series, we created membranes for solubility-based gas separations by reacting the surfaces of microporous alumina substrates with alkylchlorosilanes. In this paper, we explored our ability to rationally modify the permselectivity properties of these membranes through the control of several synthesis variables. In particular, we studied three different hydration states of the alumina surface (dehydrated, normal, and superhydrated), two different degrees of chlorosilane functionality (mono and tri), and two different sizes of alkyl group (methyl and octadecyl). We measured the permeability of the hybrid membranes to propane and nitrogen gases to characterize their separation properties; we also carried out X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) experiments to characterize the amount and nature of organic surface coverage. Our results showed significant correlations of permeation properties with all of the synthesis variables. Dehydration of the alumina surface before trichlorosilane treatment resulted in a lower organic surface coverage and a lower propane/nitrogen selectivity; superhydration resulted in the formation of a dense organic surface layer with a large number of macroscopic defects that virtually eliminated selectivity. Under normal hydration conditions, the octadecyltrichlorosilane yielded a far more selective membrane than the methyltrichlorosilane. Finally, the monochlorosilane reagents produced no significant organic surface coverage, based on both XPS and gas permeation analyses. We discuss our results in the context of previous work on (1) self-assembled monolayers on nonporous substrates and (2) the design of solubility-selective membranes.     

Cross‐linked Copolyimide Membranes for the Separation of Gaseous and Liquid Mixtures

Cross‐linked polymer structures gain increasing attention as membrane materials because they can fullfill the demands for industrial applications. Thereby, not only good separation characteristics but also high temperature stability and chemical resistancy are required. Furthermore, it is important that the membrane materials be plasticization resistant, because it is found that this causes strong increasing permeability with a drastic loss in selectivity. Plasticization effects occur with polyimide membranes in the presence of high CO₂concentrations, hydrocarbons as propylene, propane, or aromatics. Unfortunately, these components are present in mixtures with high relevance being separated economically by membrane units or hybrid processes. In this article, the advantages of cross‐linked 6FDA (4,4′hexafluoro isopropylidene diphthalic acid anhydride)‐copolyimides are discussed based on experimental results for the separation of propylene/propane, benzene/cyclohexane, and high‐pressure CO₂/CH₄mixtures. Additionally, opportunities for implementing the membrane units in conventional separation processes are discussed.     

All‐Nanoporous Hybrid Membranes: Redefining Upper Limits on Molecular Separation Properties

New membrane‐based molecular separation processes are an essential part of the strategy for sustainable chemical production. A large literature on “hybrid” or “mixed‐matrix” membranes exists, in which nanoparticles of a higher‐performance porous material are dispersed in a polymeric matrix to boost performance. We demonstrate that the hybrid membrane concept can be redefined to achieve much higher performance if the membrane matrix and the dispersed phase are both nanoporous crystalline materials, with no polymeric phase. As the first example of such a system, we find that surface‐treated nanoparticles of the zeolite MFI can be incorporated in situ during growth of a polycrystalline membrane of the MOF ZIF‐8. The resulting all‐nanoporous hybrid membrane shows propylene/propane separation characteristics that exceed known upper‐bound performance limits defined for polymers, nanoporous materials, and polymer‐based hybrid membranes. This serves as a starting point for a new generation of chemical separation membranes containing interconnected nanoporous crystalline phases.     

三烷基氧化膦辐照分解气态烃类的气相色谱测定

报告了萃取剂三烷基氧化膦在γ射线辐下分解产生的气态烃类的气相色谱分析法。测定了甲烷、乙烷、乙烯、丙烷和丙烯。采用预空取样,ＧＤＸ１０２充柱,氢火焰离子化检测器。方法简便、快速,用此法测定了辐照剂量１０＾４～１０＾６Ｇｙ的三烷基氧化膦样品,获得满意结果。     

Ionic liquid silver salt complexes for propene/propane separation

Properties of the room-temperature liquid complex salt [Ag(propene)(x)][Tf(2)N] have been studied to probe its suitability for acting as active separation layer in immobilised liquid membrane (ILM) concepts for propane/propene separation. The pressure/temperature range of complex formation has been determined and the thermal properties of Ag[Tf(2)N] and [Ag(propene)(x)][Tf(2)N] have been studied by DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis) measurements. Pressure dependent measurements of solubility and diffusivity showed that the observed membrane selectivity is dominated by the solubility selectivity. The self-diffusion coefficient of propene is always smaller compared to propane as propene is temporarily bound to the silver ion in the [Ag(propene)(x)][Tf(2)N] ionic liquid.     

Relationships between the chemical structures and the solubility,diffusivity, and permselectivity of propylene and propane in 6FDA‐based polyimides

The solubility, diffusivity, and permselectivity of propylene and propane in 40 different polyimides synthesized from 2,2‐bis(3,4‐decarboxyphenyl)hexafluoropropane dianhydride (6FDA) were determined at 298 K. The influence of the chemical structures on the physical and gas permeation properties of the 6FDA‐based polyimides was studied. The solubility of propylene in an unrelaxed volume of a polymer matrix mainly contributes to the total solubility of propylene for various 6FDA‐based polyimides. The diffusivity, the permeability of propylene, and the permselectivity in the propylene/propane mixed‐gas system depend on the solubility of propylene. This is thought to be associated with the penetrant‐induced plasticization effect. 6FDA‐based polyimides, which have a high glass‐transition temperature and a large fractional free volume, exhibit a high permeability with a relatively low permselectivity. Changing the number of  CH3 substituents in the phenylene linkage and changing the connectivity in the main chain are good ways of controlling the solubility of propylene and the corresponding permselectivity in the propylene/propane mixed‐gas system. Some 6FDA‐based polyimides restrict the solubility of propylene through the introduction of a  CONH linkage between the phenylene linkage; the  Cl substituent in the phenylene linkage at the diamine moiety exhibits a high separation performance in the mixed‐gas system. The polyimides are potentially useful membrane materials for the separation of propylene and propane in the petrochemical industry. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2525–2536, 2000     

面向丙烯/丙烷吸附分离的金属有机骨架材料的高通量计算筛选

丙烯、丙烷作为分子尺寸相近的共沸物,其分离一直是化工领域研究热点。金属有机骨架(MOFs)材料因其高度可调的孔道结构,在丙烯/丙烷分离应用上已展现出诱人潜能。本文基于Core MOF 2019数据库,采用巨正则蒙特卡洛基高通量计算筛选技术,获得了分离性优异的MOFs结构,发现其拥有适中的丙烯吸附量和较弱的丙烷吸附能力,且骨架孔径为3.70～4.10?、孔隙率中等(0.35～0.44),并揭示了孔道中心吸附位的选择性与丙烯/丙烷分离系数间关系。本研究阐明了高丙烯/丙烷分离性的骨架材料的结构和性能特征,为设计MOFs实现丙烯/丙烷的高效分离提供理论指导和数据支撑。     

Olefin Recovery by *BEA-Type Zeolite Membrane: Affinity-Based Separation with Olefin−Ag+ Interaction

Ag⁺ was introduced into *BEA-type zeolite membrane by an ion-exchange method to enhance olefin selectivity. Ag−*BEA membrane exhibited superior olefin separation performance for both ethylene/ethane and propylene/propane mixtures. Particularly, the separation factor for ethylene at 373 K reached 57 with the ethylene permeance of 1.6×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹. Adsorption properties of olefin and paraffin were evaluated to discuss contribution of Ag⁺ to separation performance enhancement. A strong interaction between olefin and Ag⁺ in the membrane caused preferential adsorption of olefin against paraffin, leading to selective permeation of olefin. Ag−*BEA membrane also exhibited high olefin selectivities from olefin/N₂ mixtures. The affinity-based separation through Ag−*BEA membrane showed a high potential for olefin recovery and purification from various gas mixtures.     

C2 and C3 hydrocarbon separations in poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes

The transport of olefin and paraffin namely ethane, ethylene, propane and propylene in aromatic poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes was investigated. The gas permeability coefficients were measured at pressures from 2.5 to 16 atm for the C₂ hydrocarbon gases and pressures up to 8.4 atm for C₃ systems at 35 °C. This membrane exhibits permeabilities of 0.15, 0.87, 0.023 and 0.24 Barrer with respect to pure ethane, ethylene, propane and propylene, and shows an ideal selectivity of 5.8 for the separation of ethylene/ethane, 10 for propylene/propane, 7.6 for nitrogen/ethane and 50 for nitrogen/propane. The olefins showed a preferred permeability to paraffins and discussion were drawn to the permeability, diffusivity and solubility coefficients. The activation energies of permeation, diffusion and solution were also reported and the effect of temperature on the permeation properties was discussed for the pure gas permeability data obtained from 30 to 50 °C. The plasticisation effect was also found for propane and propylene, respectively, although it was neither detected in the saturated nor unsaturated C₂ hydrocarbons at pressures up to 16 atm.     

Facilitated transport of olefin through solid PAAm and PAAm-graft composite membranes with silver ions

Solid poly(acrylamide) (PAAm) composite membranes containing silver ions have been investigated for olefin/paraffin separation. The propylene permeance increased significantly for a solid PAAm/AgBF₄ composite membrane with increasing loading amount of silver ions. Silver ions in solid PAAm form reversible complexes with propylene, resulting in the facilitated transport of propylene. The propylene selectivity of 100 over propane was obtained when the mole ratio of silver ions to acrylamide unit was 1. This high separation performance would be obtained predominantly because of the high loading of the propylene carrier, silver ions. PAAm-graft/AgBF₄ composite membranes were prepared in order to improve the gas permeance. Introduction of PAAm grafts on a polysulfone microporous membrane surface was confirmed by FT-IR spectroscopy. The propylene permeance was increased through the PAAm-graft/AgBF₄ membranes compared to that through of the PAAm/AgBF₄ composite membranes, indicating the formation of ultra-thin top layer.     

Polyurethane–poly(vinylidene fluoride) (PU–PVDF) thin film composite membranes for gas separation

Aqueous polyurethane dispersions (PUDs) with poly(dimethylsiloxane) (PDMS), or mixed poly(dimethylsiloxane)/poly(ethylene glycol) (PDMS/PEG) as the soft segment were synthesized, and made into thin films for characterization with differential scanning calorimetry (DSC), thermogarvimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC) and transmission electron microscopy (TEM). Seven thin film composite (TFC) membranes prepared on PUDs and PVDF substrates were evaluated by the separation of air as well as hydrocarbon–nitrogen mixtures. A promising membrane was then selected for further investigation of the morphological structure and permselectivities, using pure gases and binary mixtures of ethylene, ethane, propylene and propane with nitrogen at ambient temperature. It was found that PDMS/PEG-based PU membrane was typically solubility-selective for condensable hydrocarbons, and nitrogen permeance was marginally enhanced in hydrocarbon–nitrogen mixtures. It appears that the copolymer membrane with both urethane and PEG segments can effectively tolerate the swelling caused by the condensable gases. As a result, the selectivities of propylene and propane to nitrogen were substantially improved, e.g., in a mixture containing 28% propylene and 72% nitrogen, the selectivity of propylene to nitrogen reached 29.2 with a propylene permeance of 34.4 gas permeation unit (GPU).     

Hydrophilic modification of polyvinylidene fluoride membrane by blending amphiphilic copolymer via thermally induced phase separation

A new amphiphilic copolymer TD‐A is melt‐blended with polyvinylidene fluoride to fabricate hollow fiber membranes in order to improve the hydrophilicity and anti‐fouling property. Membrane samples with different blending ratios are prepared via thermally induced phase separation method. An optimum blending ratio of TD‐A (10 wt%) is determined by a series of characterizations to evaluate the effects of TD‐A contents on membrane properties. The hydrophilicity of the blended membrane samples increases with the increasing blending ratio, but excessive content of TD‐A in blended membranes can lead to structural defects and reduction of mechanical properties. TD‐A blended hollow fiber membrane with optimum blending ratio shows excellent bi‐continuous structure and high water flux. Membrane fouling is remarkably reduced due to the incorporation of TD‐A by static absorption and cyclic filtration tests of bovine serum albumin. Moreover, constant surface chemical compositions and stable flux during long‐term chemical cleaning demonstrate the hydrophilic stability of the blended membrane.     

Pervaporation separation of water/ethanol mixture by TGN/PSF blending membrane

The separation performance of plasticizer/polysulfone (TGN/PSF) pervaporation membrane was studied. The optimum amount of plasticizer (TGN) in PSF membranes improved the diffusion selectivity of water to ethanol, which was due to the increase in the permeate diffusion rate difference between water to ethanol molecules. On the other hand, the solubility selectivity of water to ethanol in PSF membrane showed a minor change with increasing the plasticizer content in TGN/PSF membrane. The feed ethanol concentration showed a significant influence on the degree of swelling as well as the separation performance of TGN/PSF membrane. It was found that the dominant factor of permeate transport through membranes was the diffusion rate difference, especially at high ethanol concentrations in feed. This study indicated that a good separation performance could be achieved at high ethanol concentrations in feed. This investigation also proves that the flexible polymer chain mobility, which was due to both the addition of TGN in the membrane and the swelling effect of the membrane at the high ethanol concentration in feed solution, strongly influences the separation properties of TGN/PSF membrane.