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Abstract: In addition to gas permeation simulation in polymeric membranes, much progress has been attained on the theories whereby the mechanisms of transport are described. In this way, numerous studies are assigned to achieve methods for determination of diffusion coefficient. Consequently, some correlated equations are obtained which consider diffusivity dependency on concentration, position or time, or any conjunction of them. Compared to the traditional time lag, a comprehensive approach developed by Frisch gives a general mathematical procedure for achieving the concentration dependent diffusion coefficient, disregarding the effect of membrane physical properties. In this study, a comprehensive algorithm is presented for direct determination of diffusion coefficient. It determines diffusion coefficient by two approaches: first, through the traditional time lag method, and second, considering the concentration dependent system. A comprehensive mathematical model was developed and solved for CO2 gas permeation through a nonporous polymeric membrane. The results showed that considering the concentration dependent system (CDS) for diffusion coefficient led to the small deviation of about 13%, while the deviation of 360% by the concentration independent system (CIS) was acquired. Finally, a reasonable conformity between the predicted values based on concentration dependant method and experimental data was perceived. [Copyright &y& Elsevier]

Abstract: CO2 removal from different gas streams via the polymeric membranes has been propounded as an important issue in greenhouse gas emissions control, natural gas upgrading, and enhanced oil recovery. Here, polymeric blend membranes were prepared from acrylonitrile–butadiene–styrene (ABS) and poly vinyl acetate (PVAc), and their CO2/N2 and CO2/CH4 separation characteristics were investigated. The influence of different PVAc contents on gas separation performance and the effect of pressure, ranging from 1 to 8bar, on CO2 permeability were studied. Furthermore, the morphology of the membranes was analyzed by FTIR, XRD, DSC and SEM. It was shown that the highest CO2 permeability of 5.72 Barrer for the membrane containing 10wt.% PVAc, the highest CO2/CH4 selectivity was 29 in 20wt.% PVAc and CO2/N2 was 40.41 in 30wt.% PVAc contents. These results comprised from different effective factors such as PVAc acetate polar groups, compactness in polymer matrix at the presence of high molecular weight PVAc, and the acrylonitrile and flexible butadiene contents of ABS. Furthermore, in the transmembrane pressure of 2–8bar the CO2 permeability approximately descended with the pressure increase for PVAc content of 0–40wt.%, and it ascended for 50–60wt.%. Generally, the prepared membranes can be taken into account as better membranes for CO2/N2 separation than CO2/CH4. [Copyright &y& Elsevier]

[Display omitted] • Application of biodegradable polymers as membrane materials was studied. • The bio-based and petroleum-based biodegradable polymers were investigated. • Advanced methods for improving the membrane separation performance were introduced. • Modification strategies, limitations and future remarks were discussed. Fossil sources are the main raw materials for polymer synthesis, while only a small amount of these resources are renewable. Nevertheless, the production of polymers from both bio-based and petroleum-based materials with renewable properties is increasing. Biodegradability is the key feature of developing these materials to open a new horizon into a promising future for modern membrane separation technology. The present review focuses on the synthesis, preparation methods, and modifications of different bio-based and petroleum-based biodegradable polymers, which are classified based on their origin, i.e., vegetable, animal, and synthetic. In this case, state-of-the-art membranes are prepared through tailoring the biodegradable polymers with varying strategies, including blending, copolymerization, cross-linking, and their composites with nanoparticles, which are highlighted. Moreover, symmetric/asymmetric dense film-forming, electrospinning, developing the thin-film composite, and multi-layer assemblies are introduced as four different preparation methods. Finally, various applications in membrane-based processes such as oil/water emulsion separation, wastewater treatment, pervaporation, gas separation, and fuel cell will be discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • PIMs and TR polymers are referred to polymers with a highly microporous structure. • The major challenge of PIMs and TR polymers is achieving a high permselectivity. • We studied the monomer molecular design of energy-efficient PIM/TR based membranes. • Different methods for synthesizing PIMs and TR polymers are described. • The presence of functional/pendant groups such as are investigated. • Different strategies for preparation and tailoring of their properties are discussed. In the last decades, many novel polymeric materials have been considered to prepare highly energy-efficient gas separation membranes. There is a continuous search to overcome the trade-off relationship between the gas permeability and selectivity to improve the membrane separation performance during long-term operation. One of the most important research fields of molecular design and polymer chemistry is the synthesis of new polymers with a highly microporous structure, referred to as polymers of intrinsic microporosity (PIMs) and thermally rearranged (TR) polymers. The major challenge of PIMs and TR polymers, required for their application in membrane gas separation, is achieving a high permeability and selectivity, which remain stable over prolonged periods and under all possible operating conditions. Limits of their use can be low mechanical stability, sophisticated and challanging synthesis methods, physical aging of PIMs, etc. For TR polymers, identifying the optimum temperature in the thermal treatment process is challenging, and the preparation of thin-film TR membranes from PBO precursor via conventional methods is difficult. Moreover, the productivity of the membrane modules and the adhesion between the support/polymer and nanomaterials/polymer need to be improved in mixed matrix membranes (MMMs). Also, the formation of defects in the membrane structure is the main challenge to overcome for the fabrication of thin-film composites (TFCs). In this manuscript, we carefully review the molecular design and the properties and performance of PIMs and TR materials as energy-efficient membranes for various gas separations, emphasizing CO 2 /CH 4 and CO 2 /N 2. Different methods for synthesizing PIMs and TR polymers are described, and the resulting polymers are evaluated for gas separation. Structure designing for the synthesis of PIMs and TR membranes and the influence of different chemical structures of monomers for creating chain rigidity by non-planar groups, and tuning the angle of contorted centres, are investigated. Moreover, the presence of functional groups and other substituents, such as fluorinated, sulfonated, carboxylic, tetrazole, and other groups, are investigated. Different strategies for membrane preparation and tailoring of their properties, such as cross-linking, co-polymerization, blending with other polymeric or organic and inorganic materials, are discussed as well. [ABSTRACT FROM AUTHOR]

• We present a new analytical model for calculation of gas concentration in the MMMs. • The outer surface of a dense nanoparticle is called adsorption zone. • In the vicinity of a nanoparticle, gas molecules attract to the adsorption zone. • Gas molecules pass the adsorption zone much faster than the polymer matrix. • Gas concentration gradient in the polymer matrix deviates from its linear behavior. • This phenomena occurs on the upper hemispherical of nanoparticle surface. Mixed Matrix Membranes (MMMs) are composed of dispersed (nano) particles into a continuous polymer matrix with a complex structure. Here, we present a new analytical model for calculation of gas concentration in the MMMs. In this regard, it is determined the gas concentration in the two zones of an MMM including the polymer matrix and the outer surface of a dense nanoparticle which is called adsorption zone. Therefore, mass transfer equations developed for polymer matrix/nanoparticles interface. A 3D model for MMM considered in which the spherical shape dense nanoparticles are randomly dispersed in the polymer matrix. In the vicinity of a nanoparticle, gas molecules attract to the adsorption zone. Achieved results indicated that when a gas molecule passing from up- to downstream side of an MMM, its concentration changes linearly through the polymer matrix, however changes nonlinearly near to the adsorption zone. Indeed, gas molecules pass the adsorption zone much faster than the polymer matrix and abandon the membrane non-uniformly. It was also concluded that penetrant concentration at the adsorption zone is directly related to the gas diffusion coefficient at the nanoparticle surface (D adsorp) which is two orders of magnitude higher than gas diffusion coefficient in the polymer matrix (D p). Moreover, the results showed that at the nanoparticle surface where the theta (azimuthal angle) is equal to zero, the gas concentration has its minimum value. The more molecules adsorb on the nanoparticle surface, the higher concentration gradient between the polymer matrix and the nanoparticle surface is achieved. Gas concentration gradient in the polymer matrix deviates from its linear behavior on the upper hemispherical of nanoparticle surface (which is first facing point of the gas-adsorption zone). In addition, it is observed that the gas concentration at the bottom of the adsorption zone (the lower hemispherical of nanoparticle surface) is higher than that of the polymer matrix in a same width of the membrane because at this zone the gas molecules are desorbed in the polymer matrix again. An important result obtained here is that the concentration gradient in the adsorption zone is much higher than that for the polymer matrix along the membrane width. This makes mass transfer in the absorption zone to be greater than the polymer matrix. [ABSTRACT FROM AUTHOR]