Gas permeability of homogeneous and composite membranes based on poly(trimethylsilylpropyne)/poly(vinyltrimethylsilane) blends

Gas transport properties of membranes based on a blend of two silicon-hydrocarbon polymers, poly(trimethylsilylpropyne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS), have been investigated. The N₂ and CO₂ permeability of the membranes decreases by two orders of magnitude, and CO₂/N₂ selectivity increases about threefold with increasing PVTMS content in the blend from 0 to 100%. The effect of the volume contraction of the membranes has been found. The results of the experiments and calculations showed that the membrane properties throughout all the range of concentrations are in good agreement with the single-phase blend permeability model. The results of the research open the possibility of preparing PTMSP/PVTMS membranes with stable gas separation properties combining a high permeability of PTMSP and a rather high selectivity of PVTMS.     

Vapor-phase membrane concentration of bioethanol and biobutanol using hydrophobic membranes based on glassy polymers

Pervaporation and vapor-phase membrane separation methods for the recovery of bioalcohols from dilute aqueous solutions have been critically compared. The importance of taking into account the liquid–vapor equilibrium diagram in studies on the separation of binary aqueous–alcoholic liquid media by these methods has been shown. Previously published experimental data on the transport of water, ethanol, and n-butanol vapors in hydrophobic membranes based on the glassy polymers poly(vinyltrimethylsilane) (PVTMS), poly(1-trimethylsilyl-1-propyne) (PTMSP), and poly(4-methyl-1-pentyne) (PMP) have been analyzed. Schemes of butanol and ethanol recovery by the vapor-phase membrane separation process from fermentation broths for the cases of application of water-selective and alcohol-selective membranes have been presented, as well as the results of mathematical simulation of the process and assessment of energy consumption.     

Hybrid Gas Separation Membranes Containing Star-Shaped Polystyrene with the Fullerene (C<Subscript>60</Subscript>) Core

A physicochemical study of novel hybrid polymer membranes based on polyphenylene oxide with a star-shaped modifier incorporated into the matrix has been conducted, and the transport properties of the membranes in the gas separation process have been studied. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been selected as the polymer matrix because of the low cost and high mechanical strength of this material. Star-shaped macromolecules (up to 5 wt %) containing six polystyrene arms grafted onto a fullerene(C₆₀) central core have been used as the filler. The structure and physical properties of the resulting membranes have been characterized by scanning electron microscopy, membrane density measurements, differential scanning calorimetry, and thermogravimetric analysis. Film surface has been studied by contact angle measurements. The gas separation properties of the membranes have been studied by the barometric method for the following individual gases: H₂, O₂, N₂, and CH₄. Data on the separation properties have been plotted as a Robeson diagram to compare with published data. It has been shown that the incorporation of star-shaped polystyrene into the PPO matrix leads to an improvement of the separation efficiency for selected gas pairs and an increase in selectivity compared with that of the unmodified membrane.     

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions

The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m³ (STP) (m² h bar)^?1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.     

Simulation of the temperature-driven pervaporation of dilute 1-butanol aqueous mixtures through a PTMSP membrane in a cross-flow module

The selective thermal pervaporation (TPV) of dilute aqueous mixtures of 1-butanol through a hydrophobic poly(1-trimethylsilyl-1-propyne) (PTMSP) membrane in plate-and-frame modules with an air gap has been investigated experimentally and theoretically for the first time. The dependences of the composition and the permeate flow on the temperature and initial concentration of the mixture, the liquid coolant temperature, and the membrane thickness have been measured. It has been shown that a permeate flow across the PTMSP membrane can be achieved in the TPV mode that is not inferior to that of vacuum pervaporation at condensation temperatures of 0.5–15.0°C. The permeation and diffusion activation energies have been estimated from the measured temperature dependences of the partial fluxes. Equations for the TPV process have been derived in terms of the one-dimensional resistance model. The temperature dependences of the diffusion coefficients of 1-butanol and water in the membrane have been determined, and the linear temperature and concentration fields of the components in the module for membranes of different thickness have been calculated from the experimental data using these equations.     

Gas separation characteristics of new membrane materials based on poly(ethylene glycol)-crosslinked polymers and ionic liquids

Gas transport characteristics (permeability and diffusion and solubility coefficients for CO₂, O₂, N₂, H₂) of new crosslinked membrane materials synthesized by copolymerization of poly(ethylene glycol) dimethacrylate and poly(ethylene glycol) methyl ether methacrylate in the presence of various ionic liquids have been studied. Comparison of the characteristics of specimens with and without ionic liquids has revealed that the presence of ionic liquids enhances the permeability of the membranes, especially to CO₂. It has been shown that the enhancement of the CO₂ permeability of films incorporating ionic liquid is due to an increase in CO₂ solubility and the increase in selectivity for pairs of gases containing CO₂ is determined by thermodynamic selectivity of separation.     

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes

Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N₂, O₂, CH₄ and C₃H₈) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.     

Ion transport in hybrid membranes based on MF-4SC and silica surface-modified with proton acceptor groups

Methods for synthesizing hybrid MF-4SC membranes containing silica whose surface has been modified with proton acceptor amine-containing groups (3-aminopropyl- and 3-(2-imidazoline-1-yl)-propyl-) are proposed. The incorporation of surface-modified silica particles into the membrane matrix leads to a decrease in the water uptake and exchange capacity compared to a membrane containing pure SiO₂. The proton conductivity and diffusion permeability of NaCl and HCl solutions and the H⁺/Na⁺ ion interdiffusion are studied. The proton conductivity of the membranes containing surface-modified silica is higher than that of the parent membrane and the membrane containing pure SiO₂. It is shown that the surface modification of silica with 5 mol % of nitrogen-containing groups results in a decrease in the diffusion permeability and an improvement in the ion transport selectivity. This extraordinary change in the properties is caused by an increase in the size of the pores and the channels that connect them, along with a significant decrease in the free volume within the pores. At the same time, an increase in the amount of modifying groups to 10 mol % leads to a sharp acceleration of the diffusion permeability and interdiffusion processes because of the formation of through pores in the membrane matrix.     

Polydimethylsilalkylene-dimethylsiloxanes as advanced membrane materials for thermopervaporative recovery of oxygenates from aqueous reaction media

Polydimethylsildimethylene-dimethylsiloxane (PSDMS) and polydimethylsiltrimethylenedimethylsiloxane (PSTMS) have been first studied as pervaporation membrane materials for the recovery of butanol from aqueous media. New synthesis procedures that make it possible to obtain the monomers 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane (1) and 2,2,6,6-tetramethyl-1-oxa-2,6-disilacyclohexane (2) in high yields and with high purity required for subsequent polymerization have been developed. The optimum concentration of the crosslinking agent (tetraethoxysilane (TEOS)) of 5% has been found, which provides the maximum degree of crosslinking without sacrificing high values of separation factor and permeate flux. It has been shown that the permselectivity of PSDMS or PSTMS for butanol–water is higher by a factor of 1.5 or- almost 2, respectively, than the selectivity of the industrial membrane polymer, PDMS, at comparable values of the butanol permeability coefficient.     

金属有机框架膜材料用于CO2分离过程的研究进展

金属有机框架材料(MOFs)具有孔隙率高、比表面积大、孔道可调节、结构多样等特点,将其添加到高分子膜中,可显著提升膜材料对CO₂的透过性和选择性。综述了近年来MOF膜材料用于CO₂分离过程的研究进展:①介绍了MOF膜材料的CO₂分离机理和合成工艺;②总结了几种主要的MOF膜材料在CO₂分离过程中的应用研究进展;③提出了MOF膜材料在CO₂分离领域的发展方向。      

Carbon Dioxide Desorption from Amine Solution in a Nonporous Membrane Contactor

Long-term testing of a membrane contactor based on a blend of the nonporous polymers polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) has been carried out. The flat-sheet membrane contactor has been tested for CO₂ desorption from an aqueous methyldiethanolamine solution at 100°C. It has been found that the mass transfer parameters (CO₂ flux and stripping efficiency) of the 95%PTMSP/5%PVTMS membrane stabilize after the 7th day of testing. The CO₂ mass transfer coefficient in the membrane contactor has been evaluated, and optimal desorption parameters have been determined.     

Nanofiltration and sorption of organic solvents in poly(1-trimethylsilyl-1-propyne) samples of different microstructures

For two PTMSP samples synthesized on various catalytic systems (TaCl₅/TIBA and NbCl₅) and having different chain configurations (the ratio of cis/trans units is equal to 50/50 or 63/37 for PTMSP/Ta and PTMSP/Nb, respectively), sorption and organic solvent nanofiltration (OSN) behavior is studied. Equilibrium sorption (a homological series of linear alcohols C₁-C₁₀, diols and ketones for PTMSP/Ta and a homological series of linear alcohols C₁-C₁₀ for PTMSP/Nb) and equilibrium swelling of polymers in the above solvents are estimated. Nanofiltration of dilute ethanol solutions of three dyes (Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R) is studied for the PTMSP/Ta sample, and the resultant nanofiltration characteristics of this sample are compared with the earlier data on PTMSP/Nb. Analysis of the experimental results on sorption and swelling of the PTMSP/Ta samples makes it possible to conclude that PTMSP contains sorption sites which are able to coordinate two hydroxyl groups. Structure of the PTMSP/Ta and PTMSP/Nb samples is studied by the methods of vibrational IR spectroscopy and quantum chemistry. The nature of sorption sites in PTMSP is likely to be related to an exceptionally high polarity of the C=C and Si-C bonds in the repeat polymer units. Computational simulation for the model composed of five PTMSP units in the presence of ethanol monomer shows that, in this system, a complex with ΔE = 18 kJ/mol is formed. Nanofiltration studies indicate that, for the PTMSP/Ta sample, the permeability coefficient of ethanol and overall flux of dye-containing ethanol solutions are nearly two times lower than those for PTMSP/Nb. For both PTMSP samples, dye retention increases in the following order: Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R, and this tendency agrees with the increase in the partition coefficients of the above dyes. For the PTMSP/Ta sample, dye retention of Solvent Blue 35 and Safranine O dyes with molecular masses of 350 g/mol appears to be lower than that of the PTMSP/Nb samples. Sorption and nanofiltration behavior of PTMSP/Ta and PTMSP/Nb can be reasonably explained in line with the existing approaches which treat glassy amorphous polymers as microheterogeneous systems containing structural regions with different ordering of polymer chains, and the observed difference in their sorption behaviour and membrane characteristics can be explained by the fact that packing of polymer chains in the PTMSP/Ta is more loosened as compared with that of the PTMSP/Nb sample.     

Effect of Pd–Ru alloy membrane thickness on H<Subscript>2</Subscript> flux from steam reforming products

The influence of the thickness of a Pd–Ru alloy membrane on the H₂ flux from binary mixtures containing about 5 and 20% CO, CO₂, CH₄, and steam has been studied. It has been shown that with a decrease in the membrane thickness from 30 to 10 μm, the negative influence of these impurities on the H₂ flux increases. In experiments with pure H₂, it has been established that a decrease in the membrane thickness does not affect the nature of the rate-limiting step in the H₂ flow mechanism. The values for the effective activation energy of the H₂ permeability of the 30- and 10-μm membranes are 13.6 and 23.4 kJ/mol, respectively. A mathematical model describing the flow of hydrogen from binary mixtures through membranes of various thicknesses with varying temperature and pressure is proposed.     

氨基碳点/聚酰亚胺混合基质膜的制备及CO2分离性能研究

将水热合成法制备的氨基碳点与聚酰亚胺复合得到混合基质膜。通过SEM、FT-IR、XRD和DSC考查了氨基碳点掺杂质量分数对混合基质膜形貌和结构的影响。氨基碳点表面的氨基可以提供碱性环境,同时增加了膜内的自由体积,促进CO₂传递。当氨基碳点掺杂质量分数为0.3%时,混合基质膜的CO₂分离性能最佳,其CO₂、CH₄、N₂渗透通量分别为85.87 barrer、1.69 barrer、2.62 barrer,CO₂/CH₄、CO₂/N₂选择性分别为50.81和32.77。      

Effect of temperature on gas transport properties of supported ionic liquid membranes

The separations of the CO₂/N₂ and CO₂/CH₄ gas pairs using supported ionic liquid membranes (SILMs) with the immobilized ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF₄]) and 1-butyl-3-methylimidazolium bis(2-ethylhexyl)sulfosuccinate (bmim[doc]) have been compared. The temperature dependences of the gas permeability, diffusion, and solubility coefficients have been obtained experimentally, and the temperature dependence of selectivity has been calculated. It has been found that the selectivity of membranes based on bmim[BF4] slightly decreases with temperature and the separation selectivity of CO₂/N₂ and CO₂/CH₄ systems on the membranes impregnated with bmim[doc] is almost independent of temperature.     

Structure and properties of poly(4-methylpentene-1) track-etched membranes

The influence of irradiation and the subsequent etching of latent tracks in poly(4-methylpentene-1) (PMP) films on the transport parameters of the resulting membranes has been studied. The films have been irradiated with accelerated Kr and Xe ions of 4.5 and 1.2 MeV/nucleon in energy at a fluence of 10⁶–10⁹ cm^?2. It has been found that the irradiation followed by etching makes it possible to obtain an anisotropic membrane with a nonporous selective layer between two porous layers with tapered pores. The CH₄, CO₂, and He transport characteristics of the membranes have been examined. It has been shown that these modification methods can significantly increase the gas flux through the membrane. It is believed that the ion track etching procedure as applied to PMP can form the basis for fabricating membranes with a highly permeable, nonporous, gas-selective layer.     

Gas–liquid membrane contactors for carbon dioxide capture from gaseous streams

Membrane technology is characterized by high efficiency, compatibility and flexibility of various membrane processes in integrated systems, low power consumption, high stability and environmental safety of processes, comparative ease and simplicity of controlling and scaling-up, as well as a unique functional flexibility of the membrane processes. This is why the membrane technology is considered as a promising way to reduce anthropogenic emissions of carbon dioxide into the atmosphere. Gas–liquid membrane contactors are a prime example of high-performance hybrid processes using membrane technologies. Integrating several separation methods in one device (membrane contactor) makes it possible to retain benefits of membrane technology, such as small size and flexibility, complementing them with high separation selectivity typical of CO₂ absorption. This review presents the basic principles of operation and design of membrane contactors, and a wide range of materials, membranes, and liquid absorbents for membrane CO₂ absorption/stripping are considered. Particular attention has been paid to current studies on CO₂ removal from thermal power plant flue gas, natural gas, biogas, and syngas. The examples of pilot-scale and semi-commercial implementation of CO₂ absorption/stripping in membrane contactors have been given.     

Asymmetry of ion transport in hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia

Results of studies of the properties of hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia nanoparticles through the thickness prepared by layer-by-layer casting from a polymer solution are described. The effect of the dopant concentration on the properties of the membranes is studied. At a low oxide concentration, the water uptake and ionic conductivity of the resulting samples increase compared to the original MF-4SC membrane. It is found that the diffusion permeability of HCl and NaCl solutions across these membranes exhibits an asymmetric behavior. It is shown that the diffusion permeability is higher in the case of diffusion of the solutions from the unmodified side of the membrane. The maximum asymmetry coefficient is obtained for a membrane containing 10% ZrO₂ in the modified layer for the diffusion of 0.1 M HCl solution (38%). The causes of the diffusion permeability asymmetry are discussed.     

Increase in gas separation selectivity during physical aging of OH-containing polyimide

Gas transport characteristics of new polyimide (PI) containing hydroxyl groups in the diamine moiety for seven permanent gases have been investigated: H₂, He, O₂, N₂, CO, CO₂, and CH₄. Changes in the gas separation properties of polyimide during its physical aging over a year have been experimentally revealed. It has been shown that a slow decrease in the permeability coefficients of H₂, He, and O₂ in the polyimide physical aging process and a sharp decrease in those of N₂, CO, CO₂, and CH₄ lead to an exponential increase in the selectivity of gas separation and a displacement of values in the permeability-selectivity plot beyond the upper limit in the case of the O₂/N₂ gas pair.     

Structure and gas permeability of nanoporous metal oxide coatings produced by the alkoxide method

Peculiarities of the preparation of selective nanoporous metal oxide coatings on the surface of macroporous rutile support (pore size 0.1 μm and mixed aluminum and titanium oxides (pore size 0.05 μm) are presented. Gas selective coatings of empirical formula of P _x Ti_{1 ? 0.5x} O_{2 ± δ} with uniform distribution of nanosized pores have been obtained with the alkoxide method using titanium alkoxide and ettriol phosphite (precursor of the phosphorous-containing component) at their various total concentrations. Surface morphology of the obtained membranes has been investigated and major parameters of gas selective coatings have been determined. It has been shown that the dependences of the He, N₂, CO₂, and C₃H₈ gas permeability on temperature and pressure drop are consistent with the molecular regime of gas flow. The reproducible effect of permeability anisotropy of ～502?60% is observed when the integral vacuum method is used.