The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon^® AF and Hyflon^® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles.

In this work, perspective polymeric materials were developed for membrane contactor applications, e.g., for the dissolved oxygen removal from amine CO₂ capture solvents. Several polymeric blends based on poly[1-trimethylsilyl-1-propyne] (PTMSP) and poly[vinyltrimethylsilane] (PVTMS) were studied. The gas and water vapor sorption and permeability coefficients for the PTMSP/PVTMS blend membranes at different PVTMS contents (0–100%) were obtained under temperatures of 30 and 60 °C for the first time. As the PVTMS content increases, the O₂ and CO₂ permeabilities decrease by 160 and 195 times at 30 °C, respectively. The fractional accessible volume of the polymer blends decreases accordingly. The transport of the CO₂ capture solvent vapors through the PTMSP/PVTMS blend membranes were determined in thermo-pervaporation (TPV) mode using aqueous monoethanolamine (30%), N-methyldiethanolamine (40%), and 2-amino-2-methyl-1-propanol (30%) solutions as model amine solvents at 60 °C. The membranes demonstrated high pervaporation separation factors with respect to water, resulting in low amine losses. A joint analysis of the gas permeabilities and aqueous alkanolamine TPV data allowed us to conclude that the polymer blend composition of PTMSP/PVTMS 70/30 provides an optimal combination of a sufficiently high oxygen permeability and the pervaporation separation factor at a temperature of 60 °C.

In this work, PPSUs with different molecular weights were synthesized for the development of highly permeable ultrafiltration hollow fiber membranes for the first time. The M_W of the synthesized polymers was controlled by varying the monomers molar ratio within 1:1–1.15 under the same synthesis conditions. Based on the study of the rheological properties of polymer solutions, a high molecular weight PPSU (M_W = 102,000 g/mol) was chosen for the formation of hollow fiber membranes. The addition of PEG400 to the spinning solution led to an increase in viscosity, which makes it possible to work in the region of lower PPSU concentrations (18–20 wt. %) and to form membranes with a less dense porous structure. With the addition of PEG400 to the spinning solution, the membrane permeance increased sharply by more than two orders of magnitude (from 0.2 to 96 L/m²·h bar). At the same time, the membranes had high rejection coefficients (99.9%) of Blue Dextran model filtered substance (M_W = 69,000 g/mol).

The development of membrane materials with high transport and separation properties for the removal of higher hydrocarbons from gas mixtures is an important and complex task. This work examines the effect of a cross-linking agent on the structure and transport properties of polydecylmethylsiloxane (C10), a material characterized by high selectivity towards C₃₊ hydrocarbons. C10 was cross-linked with various diene hydrocarbons, such as 1,7-octadiene (C10-OD), 1,9-decadiene (C10-DD), 1,11-dodecadiene (C10-DdD), and vinyl-terminated polysiloxanes, of different molecular weights: 500 g/mol (C10-Sil500) and 25,000 g/mol (C10-Sil25-OD). Using a number of characterization methods (IR-spectroscopy, WAXS, DSC, toluene sorption, and gas permeability), it was revealed that a change in the type and length of the cross-linking agent (at the same mole concentration of cross-linking agent) led to a significant change in the structure of the polymer material. The nature of cross-linking agent affected the arrangement of the decyl side-groups of the polymer, resulting in noticeable differences in the solubility, diffusivity, permeability, and selectivity of tested gases (N₂, CH₄, C₂H₆, and C₄H₁₀). For instance, an increase in the length of the hydrocarbon cross-linker was associated with a drop of n-butane permeability from 5510 (C10-OD) to 3000 Barrer (C10-DdD); however, the transition to a polysiloxane cross-linker led to an increase in corresponded permeability up to 8200 Barrer (C10-Sil25-OD). The n-butane/nitrogen selectivity was significantly higher for diene-type cross-linkers, and the maximum value was achieved for 1,7-octadiene (α(C₄H₁₀/N₂) = 104).

The permeability of n-butane and methane as well as their mixture through a PDecMS/MFFK composite membrane at reduced temperatures up to 0°C is for the first time studied in this work. According to the data of SEM, the thickness of the selective layer of PDecMS is 5 μm. It is shown that both the permeability coefficient of butane and ideal butane/methane selectivity \({{\alpha }_{{{{{{{\text{C}}}_{{\text{4}}}}{{{\text{H}}}_{{{\text{10}}}}}} \mathord{\left/ {\vphantom {{{{{\text{C}}}_{{\text{4}}}}{{{\text{H}}}_{{{\text{10}}}}}} {{\text{C}}{{{\text{H}}}_{{\text{4}}}}}}} \right. \kern-0em} {{\text{C}}{{{\text{H}}}_{{\text{4}}}}}}}}}\) increase as the temperature decreases from 60 down to 0°C. Thus, the permeability coefficient of butane is 11 400 Barrer at 0°C. It is important to emphasize that the ideal butane/methane selectivity of PDecMS/MFFK of 60 at 0°C is twofold higher than similar values for MDK and PDMS membranes (27 and 32, respectively). This is first of all associated with the difference in the values of the sorption selectivity α^S of these polymers. Thus, the values of \(\alpha _{{{{{{{\text{C}}}_{{\text{4}}}}{{{\text{H}}}_{{{\text{10}}}}}} \mathord{\left/ {\vphantom {{{{{\text{C}}}_{{\text{4}}}}{{{\text{H}}}_{{{\text{10}}}}}} {{\text{C}}{{{\text{H}}}_{{\text{4}}}}}}} \right. \kern-0em} {{\text{C}}{{{\text{H}}}_{{\text{4}}}}}}}}^{{\text{S}}}\) for PDecMS and PDMS at 0°C estimated based on the enthalpy of sorption are 170 and 95, respectively. In addition, the difference in the activation energies of diffusion of methane in PDecMS, PDMS, and MDK provides a sharper increase in the butane/methane permselectivity for PDecMS when compared to PDMS and MDK in the case of decreasing the measurement temperature. In the case of a C₄H₁₀ (35 vol %)/CH₄ mixture, the butane/methane permselectivity of a PDecMS/MFFK membrane decreases down to 34, which is typical for all the membranes based on polysiloxanes.