Sergey S. Kryuchkov

This work presents an integrated experimental and modeling study of post-combustion CO₂ capture using polysulfone hollow-fiber membranes in a three-module «Continuous Membrane Column» cascade. Polysulfone hollow fibers were fabricated by dry–wet spinning, defect-healed with silicone, and characterized using both single gases and a humid four-component flue-gas mixture containing N₂/O₂/H₂O/CO₂ = 73.0/4.4/11.0/11.6 mol.%. The selected membrane exhibited a mixed-gas CO₂ permeance of 117 GPU with CO₂/N₂ and O₂/N₂ selectivities of 21.3 and 4.1, respectively. These experimentally determined transport parameters were implemented directly in an Aspen Plus model of the cascade. Two complementary simulation cases were considered: a process-scale calculation used for membrane-area sensitivity analysis and a laboratory-scale calculation using the actual membrane areas and feed-flow range employed in the experiments. In contrast to our previous studies, which were limited to process simulation, the present work extends the «Continuous Membrane Column» concept to full experimental validation using independently fabricated hollow-fiber membranes and a humid multicomponent feed. Both simulation scales predicted essentially the same characteristic behavior, with increasing overall stage cut leading to higher CO₂ recovery, lower residual CO₂ concentration, and reduced product purity. At the upper part of the investigated stage-cut range, the experimental CO₂ recovery reached approximately 80–81%, compared with approximately 82–83% predicted by the laboratory-scale model; the residual CO₂ concentration decreased below 1 mol.% experimentally, compared with approximately 1.8–1.9 mol.% predicted, while the product CO₂ concentration was approximately 67–70 mol.% experimentally and approximately 68–70 mol.% in the simulation. The results demonstrate that the model correctly reproduces the principal purity–recovery trade-off and the relevant operating window, while the remaining quantitative deviations indicate the influence of non-ideal hydrodynamic and engineering effects not captured by the idealized membrane-module description.

Biogas upgrading to biomethane is an important route for increasing the energy value of renewable gas streams and enabling their wider use in fuel, heat, and power applications. In the present study, a two-stage membrane process for biogas upgrading was developed and validated using polysulfone (PSF) and polyetherimide (PEI) hollow-fiber membranes. The main original aspects of this work include the formulation of a PEI/DMF/IPA spinning dope composition (27/60/13 wt.%), the mixed-gas testing of PSF and PEI hollow-fiber membranes in a six-component model biogas mixture, and the combined simulation, experimental validation, and techno-economic evaluation of a two-stage membrane process. Mixed-gas permeation experiments with a six-component model biogas mixture were used as the basis for process simulation of four membrane-stage configurations. Only the PSF + PEI cascade simultaneously provided methane recovery above 90%, methane concentration in the product above 95 mol.%, and residual carbon dioxide content below 2 mol.%. Experimental verification confirmed the modeled process concept and demonstrated that the target biomethane quality was achieved at feed flow rates of 0.9–1.1 L min⁻¹, where methane recovery reached 93.5–95.2% and methane purity was 95.5–96.2 mol.%. A preliminary techno-economic analysis for a 100 m³ h⁻¹ unit indicated an upgrading penalty of USD 96.4 per ton of 95.5 mol.% CH₄. PSF membranes provided higher carbon dioxide permeance, whereas PEI membranes exhibited higher CO₂/CH₄ selectivity, which explains the efficiency of their combination in the two-stage scheme. The results show that the proposed PSF + PEI cascade is a promising membrane-based approach for energy-efficient biogas upgrading.

In this study, the task of integrating capture and conversion of CO₂ into a single material platform is realized by developing bifunctional membranes based on polymer ionic liquids (PILs). The novelty of this work lies in the fabrication and comprehensive evaluation of PIL-based membrane materials that combine catalytic activity toward CO₂ conversion with gas separation performance within one material system. In contrast to most previously reported imidazolium-based PILs, which have mainly been considered either as catalysts or as membrane materials, the present approach focuses on their dual functionality under both catalytic and gas transport conditions. A series of imidazolium-based PILs, including homopolymers and block copolymers with polystyrene, were synthesized. The materials were characterized to determine their catalytic activity during the cycloaddition of CO₂ to epichlorohydrin and to determine their gas transport properties using pure gases (N₂, O₂, CO₂) and a simulated dry flue gas mixture; membrane morphology was studied by scanning electron microscopy. Block copolymers exhibited higher catalytic conversions (up to 82.7%) than homopolymers, with selectivities above 93%. Chloride-containing block copolymers gave the best combination of CO₂ permeability (up to 7.5 Barrer) and CO₂/N₂ selectivity (18–22) under mixed-gas conditions. Iodide-containing analogs demonstrated higher selectivity (up to 30) but lower CO₂ permeability. Morphological analysis confirmed the presence of dense, defect-free structures in materials with the chloride anion, while materials with the iodide anion showed increased free volume and microheterogeneity. These results indicate that by altering the polymer and anion architecture, PIL-based membranes can effectively combine catalytic activity with selective CO₂ transport, providing a promising avenue for enhancing carbon capture and utilization processes.

Hybrid gas separation technologies combining different physicochemical mechanisms represent a promising approach for the efficient treatment of complex natural gas mixtures. In this work, a hybrid process integrating gas hydrate crystallization and membrane gas separation was investigated for the upgrading of multicomponent natural gas-containing hydrocarbons (C₁–C₄), acid gases (CO₂ and H₂S), and inert components. Polysulfone hollow-fiber membranes were fabricated, and their gas transport properties were experimentally determined using an eight-component quasi-real natural gas mixture under elevated pressure conditions. The obtained mixed-gas permeance values were used as input parameters for the development of a detailed mathematical model of a hollow-fiber membrane module implemented in the Aspen Custom Modeler. The model was applied to simulate membrane separation of both gas- and hydrate-derived streams produced by the gas hydrate crystallizer. Simulation results were analyzed in terms of hydrocarbon composition, acid gas removal efficiency, and hydrocarbon recovery as a function of the stage-cut. The modeling predictions were validated experimentally using a laboratory membrane module integrated with the gas hydrate crystallization unit. Good agreement between the experimental data and simulation results was observed for all major components. The deviation between modeled and experimental concentrations remained small, while the discrepancy in hydrocarbon recovery was higher and reached approximately 10–20%, which is attributed to the cumulative uncertainty of flow rate and composition measurements. These results confirm the adequacy of the developed model. The hybrid process demonstrates strong complementarity between the thermodynamic selectivity of hydrate formation and the transport selectivity of membrane separation, enabling efficient removal of acid gases while maintaining acceptable hydrocarbon recovery. The results indicate that the proposed gas hydrate–membrane hybrid process is a promising strategy for advanced natural gas purification and upgrading.

Polyetherimide (Ultem-1000) hollow-fiber membranes were developed for biogas purification with emphasis on the relationship between spinning conditions, membrane morphology, gas transport properties, and module performance. Hollow fibers were prepared from dope solutions based on dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) at different conditions, followed by post-treatment with 1 and 3 wt.% silicone solution in n-heptane to reduce nonselective defects and improve selectivity toward the intrinsic behavior of dense PEI films. SEM analysis revealed that DMF-based fibers formed a more open, macrovoid-rich structure, whereas NMP-based fibers exhibited a more homogeneous sponge-like morphology with a better-defined selective layer. DMF-based fibers experienced faster demixing, which promoted macrovoid formation, increased pore connectivity of the substructure, lowered mass transfer resistance, and at the same time increased the probability of nonselective pathways and defect-related loss of selectivity. This structural evolution was reflected in gas transport properties: untreated DMF fibers showed high mixed-gas permeance but limited selectivity, while NMP fibers demonstrated lower permeance and selectivity values closer to those of the dense film. Silicone post-treatment significantly improved separation performance, with 3 wt.% coating being markedly more effective than 1 wt.% coating. The best compromise between permeance and selectivity was achieved for the DMF-based fibers treated with 3 wt.% silicone, which exhibited CO₂ and H₂S permeances of 39.4 and 47.12 GPU, respectively, together with selectivity values of 22.4, 26.8 and 20.2 for CO₂/CH₄, H₂S/CH₄ and CO₂/N₂. A membrane module containing 500 fibers was studied during the quasi-real biogas upgrading. With increasing stage-cut, the CH₄ concentration in the retentate increased from ~74 to 96 mol.%, while CO₂ decreased from ~21 to 2 mol.%. The results demonstrate that structure control combined with silicone post-treatment is an effective strategy for producing PEI hollow fibers suitable for simultaneous methane enrichment and removal of acid impurities from biogas.

This study reports the synthesis and catalytic evaluation of a series of imidazolium-based polymeric ionic liquids (PILs) for the cycloaddition of CO₂ to epichlorohydrin (ECH). The synthesized catalysts include homopolymers, poly(3-hydroxyethyl-1-vinylimidazole chloride) (p[HVIm][Cl]) and poly(3-carboxymethyl-1-vinylimidazole chloride) (p[CMVIm][Cl]), and their block copolymers with polystyrene, synthesized for the first time, pS-b-p[HVIm][Cl] and pS-b-p[CMVIm][Cl]. Structural characterization by NMR, IR spectroscopy, and gel permeation chromatography confirmed the successful synthesis. The block copolymers exhibited a low polydispersity index (PDI 1.1–1.2), which is indicative of homogeneous chain lengths and the propensity to form ordered nanostructures, whereas the homopolymers showed higher PDI (2.4–2.9). Catalytic testing at 90 °C and 1 MPa CO₂ for 4 h revealed a clear activity trend: p[CMVIm][Cl] < p[HVIm][Cl] < pS-b-p[CMVIm][Cl] < pS-b-p[HVIm][Cl], with conversions exceeding 75% for all catalysts and a maximum of 82.69% for pS-b-p[HVIm][Cl]. These results demonstrate that the catalytic performance of PILs is governed by a synergistic interplay between the local chemical functionality of the ionic moiety and the overall polymer architecture. Based on these results, the synthesized polymeric ionic liquids, particularly pS-b-p[HVIm][Cl], demonstrate strong potential for creating multifunctional materials. Their ability to self-assemble into ordered nanostructures with distinct hydrophobic and hydrophilic domains provides a foundational architecture for combined gas separation and catalysis. The observed “micellar catalytic effect”, which enhances local reagent concentration near active sites, could be leveraged in a membrane reactor to simultaneously capture and convert CO₂ directly within the membrane. This integrated “separation–reaction” approach represents a promising strategy for advancing circular carbon economy technologies.

This study presents a comprehensive evaluation of a modified membrane cascade operating in “Continuous Membrane Column” mode for selective CO₂ capture in combined heat power plants. For the first time, a novel membrane cascade configuration for separating four-component wet flue gases is analyzed and compared with existing technologies in terms of the capital and operating costs required to capture one ton of CO₂. The proposed membrane cascade generates two countercurrent recirculating streams: one continuously depleted of the permeate component and the other enriched in it. Because the internal recirculation streams significantly exceed the bypass product streams, the system demonstrates a multiplicative increase in separation efficiency. As a result, the required membrane area and compression energy can be significantly reduced. The analysis demonstrates that the proposed cascade configuration meets all current performance requirements for CO₂ recovery and the target composition of the product and residual streams. Furthermore, due to its balanced material and energy cost ratio, the system can serve as a competitive alternative to previously developed membrane CO₂ capture technologies, offering lower overall capture losses.

This work presents a comprehensive study on hydrogen recovery from a CO₂-containing mixture (75/25 mol %) using commercial polymer membranes. The gas transport properties of polyimide (PI), polysulfone (PSF), polyphenylene oxide (PPO), polyetherimide (PEI), and a PEI + PI composite were evaluated. A significant discrepancy was found between single-gas and mixture permeation data, highlighting the necessity of using mixture-based permeance for accurate process design. The PEI membrane demonstrated the optimal combination of H₂/CO₂ selectivity (5.07) and permeance. An optimized two-stage membrane process with recirculation was developed using Aspen Plus simulation, achieving a hydrogen purity of 95 mol % with 90% recovery. The techno-economic assessment confirmed the process feasibility, demonstrating a lower cost of hydrogen production compared to traditional methods.

This present study covers a complex approach to study a hybrid separation technique: membrane-assisted gas absorption for CO₂ capture from flue gases. It includes not only the engineering aspects of the process, particularly the cell design, flow organization, and process conditions, but also a complex study of the materials. It covers the spinning of hollow fibers with specific properties that provide sufficient mass transfer for their implementation in the hybrid membrane-assisted gas absorption technique and the design of an absorbent with a new ionic liquid—bis(2-hydroxyethyl) dimethylammonium glycinate, which allows the selective capture of carbon dioxide. In addition, the obtained hollow fibers are characterized not only by single gas permeation but with regard to mixed gases, including the transfer of water vapors. A quasi-real flue gas, which consists of nitrogen, oxygen, carbon dioxide, and water vapors, is used to evaluate the separation efficiency of the proposed membrane-assisted gas absorption technique and to determine its ultimate performance in terms of the CO₂ content in the product flow and recovery rate. As a result of this study, it is found that highly permeable fibers in combination with the obtained absorbent provide sufficient separation and their implementation is preferable compared to a selective but much less permeable membrane.

The presented work is aimed at studying the gas transport characteristics of polymeric hollow-fibre gas separation membranes. Such materials as: polysulfone (PSF), polyphenylene oxide (PFO), polyetherimide (PEI), polyetherimide with polyimide (PEI+PI) were studied on the example of air mixture separation. The values of the permeances of pure gases O2 and N2 and the mixed permeances of oxygen and nitrogen during air separation were obtained. Mathematical models of the gas separation process built on the basis of these values show significant discrepancies. To obtain a gas mixture with 95 mol.% nitrogen from air, taking into account the mixture permeance, 15.8% more PSF membrane area is required than taking into account the permeance of pure gases. For a PPO membrane this value is 13.9%, for PEI 19.8% less area is required, and for PEI+PI 15.9% less. In the design of industrial or semi-industrial membrane installations, such discrepancies can lead to significant errors, including technical and economic ones.