Separation Technology Research Articles

Development of cost-effective cellulose-based bilayer hybrid composite membranes for CO2 separation in biogas purification.

CO2 is the main pollutant in biogas, reducing its calorific value. Among various technological methods to eliminate carbon dioxide from biogas, membrane separation technology stands out for large-scale industrial biogas purification due to its advantages. The selection of membrane material and preparation process are key factors in membrane separation technology. In this study, a premixing process was initially used to blend different masses of packed molecular sieves TS-1 (or ZSM-5) and cellulose derivatives (ethyl cellulose, cellulose acetate) separately. These mixtures were then coated onto porous PVDF substrates using a coating process to create various bilayer hybrid composite membranes. Among these, PVDF/EC-ZSM-5 (containing 15% ZSM-5) bilayer hybrid composite membrane is the most fitting. For CO2/CH4 gas mixtures, the gas selectivity of this membrane surpassed Robeson's 1991 standard line (the CO2 permeability was 597.48 Barrer, and the CO2/CH4 selectivity was 9.14). Overall, this composite membrane, made for the first time from PVDF, ZSM-5, and EC, is expected to be a promising CO2 selective separation membrane material for biogas purification in large-scale industrial processes due to its simple production process.

Characterisation of blackwater from human transportation systems equipped with vacuum toilets and controlled emissions tanks and its impact on solid/liquid separation technologies

The first ever detailed characterisation of blackwater from human transportation systems equipped with vacuum toilets and Controlled Emissions Tanks (CET) revealed a stream that is very concentrated in salts and nutrients when compared to other blackwater sources. Escherichia Coli (E. coli) levels in the blackwater characterised were comparatively lower than the range reported for septic tanks, for example. Suspended solids were significantly lower than the levels found in pit latrines, but closely comparable to those reported for gravity toilets. The average COD of 3566 ± 2049 mg/L was typically lower than in pit latrines and gravity flush toilets. These findings then show that the characteristics of the blackwater from human transportation systems are directly impacted by a combination of the low flush vacuum toilets, storage in the CET, and different behaviour for passengers with increased usage for urination over defecation when compared to common uses of toilets. Such factors collectively dictate the nature of the blackwater and require that a solid/liquid separation technology for further processing is fundamentally robust in operation. The greater solids pulverisation, largely resulting from vacuum flushing combined with the storage environment, reduces the suitability of centrifugal and settling technologies whilst making filtration the most suitable option.

Classification of coal gangue and identification of coal type based on first-derivative of mid-infrared spectrum

Efficiently sorting coal gangue and identifying coal types are vital operations in coal preparation, yet they are traditionally resource-consuming, labor-intensive, and potentially hazardous. This work puts forward an straightforward method employing mid-infrared spectroscopy with first derivative spectrum to address these issues. The proposed technique focuses on the delineation and enhancement of characteristic spectra to detect subtle differences among samples. The method utilizes just a few characteristic spectra of 3740–3700 cm−1, 1790–1750 cm−1, 1615–1583 cm−1, 1580–1540 cm−1, 1550–1440 cm−1, 1270–1210 cm−1 and 867–854 cm−1 to achieve 100 % high-accuracy classification of coal gangue and identification of coal types with total 250 spectra, such as bituminite, anthracite, lignite, roof sandstone and gangue, without the need for secondary sample processing or the assistance of machine learning algorithms, simplifying the process considerably. Such a strategy not only significantly improves the efficiency of coal sorting but also endorses real-time on-site detection. It offers a theoretical foundation for advanced coal separation technology and its implementation in real-world mining operations.

Plant-wide modeling and techno-economic optimization of a low-pressure microwave-assisted ammonia synthesis process with adsorption separation

Ammonia production has traditionally been done by using the Haber-Bosch process, that operates at extremely high pressure (200–300 bar), has a large carbon footprint, and requires significant energy. For ammonia to be used as a hydrogen carrier, it is desired that it is produced by using modular technologies under benign conditions, yet the economics remain commercially viable. This paper investigates a novel technology for ammonia synthesis by using a microwave-assisted low-pressure reactor. Microwave reactors are compact and can be readily modularized and started/shutdown thus making them ideal to be integrated with the electric grid or with regional/local renewable-based electric generation facilities. For separation of unreacted reactants from the product ammonia, if the traditional condensation separation technology used in the high-pressure Haber-Bosch process is used, then the separation process needs to be operated under cryogenic condition thus adversely affecting the economics. A solid sorbent based separation technology is investigated in this paper. A kinetic model for the microwave-catalytic synthesis process is used. An isotherm model is developed for MgCl2–Si adsorbent and used for modeling the dynamic adsorption-desorption cycle. A plant-wide model with heat and mass integration is developed. An economic model is developed and used for economic optimization by using an equation-oriented approach. Since the adsorption-desorption process is dynamic, for techno-economic optimization, a reduced order model for the key performance measures of the adsorption-desorption process as a function of its input and decision variable is developed under cyclic steady-state conditions. For the optimized MW-assisted process, the levelized cost of ammonia is $772/mt as opposed to $808/mt for the conventional Haber-Bosch process for a hydrogen price of $2.07/kg. The MW-assisted process is found to be economically viable in the US market if the hydrogen price is below $4/kg.

Biogenic formation of amorphous carbon in anaerobic digestion: Discovery and regulation with exogenous CO2 and zero valent iron

Anaerobic digestion (AD), a pivotal technology for organic waste reduction and biogas production, has recently gained notable attention for its role in CO2 bioconversion. As membrane separation technologies mature, methane separated from biogas is integrated into natural gas grid, while CO2 can be recycled back into AD reactors, promoting methane production. However, the biogenic formation of amorphous carbon from CO2 in AD is scarcely reported. This study confirmed the presence of amorphous carbon in AD and successfully regulated its growth via exogenous CO2 and zero valent scrap iron (ZVSI), proposing a potential method for CO2 fixation in AD. The results indicated that ZVSI promoted amorphous carbon formation, further boosted by CO2 introduction. Reactors with 80 g/L ZVSI exhibited a 31.4 % increase in amorphous carbon content compared to the control. Concurrently, methane production was also enhanced, with reactors containing 40 g/L ZVSI marking an increase between 9.6 % and 29.8 % over the control. This was attributed to the introduced inorganic carbon, which was further enhanced by the electron donors. Isotopic tracing revealed that the majority of the introduced inorganic carbon was channeled into methane, while a portion formed amorphous carbon. An in-depth microbial community analysis associated potential methanogens (Methanobacteriales, Methanosarcinales, and Methanomicrobiales) with the biogenic formation of amorphous carbon. A potential formation pathway of amorphous carbon was proposed according to metagenomic sequencing analysis. Based on the concept of low carbon, this study breathes new life into traditional anaerobic digestion and also identifies novel pathways for biological CO2 fixation.

Recent Advances in Fluorescent Polyimides.

Polyimide (PI) refers to a type of high-performance polymer containing imide rings in the main chain, which has been widely used in fields of aerospace, microelectronic and photonic devices, gas separation technology, and so on. However, traditional aromatic PIs are, in general, the inefficient fluorescence or even no fluorescence, due to the strong inter- and intramolecular charge transfer (CT) interactions causing unavoidable fluorescence quenching, which greatly restricts their applications as light-emitting functional layers in the fabrication of organic light-emitting diode (OLED) devices. As such, the development of fluorescent PIs with high fluorescence quantum efficiency for their application fields in the OLED is an important research direction in the near future. In this review, we provide a comprehensive overview of fluorescent PIs as well as the methods to improve the fluorescence quantum efficiency of PIs. It is anticipated that this review will serve as a valuable reference and offer guidance for the design and development of fluorescent PIs with high fluorescence quantum efficiency, ultimately fostering further progress in OLED research.

Synthesis of metal-doped covalent triazine frameworks: Incorporation into 6FDA-Durene polyimide for CO2 separation through mixed matrix membranes

The development of advanced mixed matrix membranes (MMMs) is expanding through the design of functionalized materials and efficient hybrid mass transfer mechanisms to meet the growing needs for practical and cost-effective gas separation technologies. Here, a novel series of transition metal-doped covalent triazine frameworks (M2+CTFs) was synthesized and incorporated into a 6FDA-Durene polyimide (PI) matrix in the range of 0–0.5 wt% to prepare cost-effective facilitated transport MMMs with high CO2 separation performance. Qualitative and quantitative analyses including FTIR, XPS, CHN, XRF, BET, XRD, TGA, DLS, FESEM, EDX, and TEM were carried out. The presence of nucleophilic N sites and electron-rich heterocycles in highly porous CTFs (through the π–π-stacking interactions with CO2 molecules), together with transition metal ions (Fe2+, Cu2+, and Zn2+) as the fixed site active carriers (with strong CO2 facilitated transport through the π complexation/decomplexation reaction), improves the affinity for CO2 molecules, facilitates their transport, and subsequently increases the CO2/non-polar gas selectivity of MMMs. The resultant M2+CTF/PI MMMs successfully surpass the 2008 upper bound at filler loading of 0.4 wt% for CO2/CH4 and CO2/N2 separations. Embedding M2+CTFs into the PI matrix improves the mechanical properties of the membranes. The Zn2+CTF/PI MMM represents the best separation performance with a CO2 permeability of 1408 Barrer, a CO2/N2 selectivity of 37, and a CO2/CH4 selectivity of 39, which represents a 120 %, 111 %, and 110 % increase compared to the neat PI membrane at a feed pressure of 2 bar. The excellent results of the present study indicate the high potential of cost-efficient synthesized M2+CTF particles and related facilitated transport MMMs for possible application in industrial processes.

Oxyfuel combustion based carbon capture onboard ships

Reducing greenhouse gas emissions in the shipping sector is a challenging task. While renewable fuels stand out as the most promising long-term solution, their near- and mid-term viability is hampered by limited availability and high costs. An alternative approach is onboard carbon capture, which can reduce emissions from new ships as well as retrofitted vessels. This paper examines the techno-economic potential of oxyfuel combustion based carbon capture on ships. The oxyfuel concept uses an oxygen-rich atmosphere in the combustion process, resulting in a mixture of carbon dioxide and water. After the condensation of water, the carbon dioxide rich gas can be directly stored on board. Various onboard oxygen supply concepts are investigated, including different technologies for onboard air separation and liquid oxygen bunkering. Influences on the ship energy system are studied by system simulation of a deep-sea container vessel. Benchmarked against a technologically mature post-combustion carbon capture system, the results show that the oxyfuel concepts have limited competitiveness because of reduced engine efficiencies and high energy demands for onboard oxygen supply. Avoiding onboard oxygen supply by using liquefied oxygen as a byproduct from onshore electrolysis increases energy efficiency and the competitiveness of oxyfuel combustion but requires additional storage space. Sensitivity analyses highlight that the engine combustion concept and engine efficiency are the most critical influences on the techno-economic performance.

Preparation of isoreticular MIL-101(Cr) based on pre- and post-synthetic strategy and study for carbon dioxide capture

The functionalization of MIL-101(Cr) presents a formidable challenge when employing covalent bonds, due to the inherent difficulty of incorporating reactive organic groups into its structure. In this work, we have successfully synthesized MIL-101-CHO tagged with formyl by adopting a pre-synthetic strategy, utilizing 3‑hydroxy-1-oxo-1,3-dihydroisobenzofuran-5-carboxylic acid as the key ligand. Then the integrity of the formyl group and the phase purity of the resulting MIL-101-CHO were rigorously confirmed through FT-IR and 1H NMR characterization. Employing post-synthetic strategy, four amine-MOFs were prepared through cascade reaction of Schiff-base condensation and NaBH4 reduction. The CO2 adsorption properties of all isoreticular MIL-101(Cr) materials were thoroughly investigated. Notably, MIL-101-TAEA demonstrated exceptional performance, with the highest Qst 70.1 kJ/mol at low coverage, the best adsorption capability 2.34 mmol/g at 298 K under 1 bar CO2, and the selectivity 172 for CO2/N2. Furthermore, the good regenerability of MIL-101-TAEA was proved by the CO2 temperature swing adsorption tests. Ultimately, MIL-101-TAEA maintain 60 % performance for trace CO2 capture after 16 cycles under the mimic atmosphere conditions, showing its potential for practical applications in gas separation and capture technologies.

Numerical study on the mechanism of microplastic separation from water by cyclonic air flotation

Microplastics have attracted considerable attention as emerging contaminants that threaten water bodies. The removal of microplastics from a mini-hydrocyclone, enhanced by air flotation, was studied numerically. The three-phase flow was modeled using the Eulerian-Eulerian model coupled with interphase interactions. The characteristics of the flow field and distribution of microplastics and microbubbles were discussed, and the mechanism of cyclonic air flotation separation was analyzed. It was found that injecting microbubbles accelerated the axial migration of microplastics and moved the enriched area upward toward the overflow. The coalescence rate of the bubbles near the axis was higher than their breakage rate, which led to the formation of an air core. The length and diameter of the air core increased with the inlet gas holdup. When the air core size closely matched the overflow, the constrained flow channel prevented the discharge of microplastics. The optimal air holdup must be determined to ensure the efficiency of the cyclonic air flotation process. The sizes of the microbubbles used for cyclonic air flotation should be comparable to those of the separated microplastics. The upper cone angle significantly promoted the migration of microplastics to the axis. This study was conducted to purify microplastic-containing wastewater using an environmentally friendly and energy-efficient technique and to provide a theoretical basis and practical reference for applying microplastic separation technology in water.

Covalent organic framework membranes achieving Mg/Li separation by permeating Mg2+ while retaining Li+

Due to the growing demand for lithium in the new energy industry, significant attention has been focused on developing lithium extraction technologies from salt-lake brine. However, the high Mg/Li ratio in salt-lake brine presents challenges for membrane separation technology. If a membrane can allow Mg2+ and water molecules to pass through while retaining Li+, the retained brine will have concentrated Li+ with a reduced Mg/Li ratio, creating the facilitation of further lithium extraction. In this study, we discovered through non-equilibrium molecular dynamics simulations that strongly hydrophilic covalent organic frameworks membranes capture Li+ in their pores, preventing additional Li+ from entering the nanopores. Meanwhile, Mg2+ can freely penetrate these nanopores along with water molecules. This adsorption of Li+ and the free permeation of Mg2+ with water molecules result in the effective separation of Li+ and Mg2+. Consequently, the retained brine becomes lithium-rich with reduced Mg/Li ratio. The findings of this work provide valuable guidance for designing nanofiltration membranes for extracting lithium from salt lakes with high Mg/Li ratio.

The Chemistry of Metal-Organic Frameworks for Multicomponent Gas Separation.

Adsorbents-based gas separation technologies are regarded as the potential energy-efficient alternatives towards current thermal-driven methods, and the study on multi-component gas separation is essential to deepen our understanding of the adsorbents for practical use. Relative to the ideal two-component mixtures, both the adsorption behavior and separation mechanisms are obviously more complex in multiple gas mixtures due to their close or even overlapped sizes and properties. The emergence of metal-organic frameworks with controllable pore size and pore chemistry provides the platform for the tailor-made pore structure to satisfy the harsh requirements of multi-component gas separation. This minireview highlights the recent advance of multi-component gas separation using metal-organic frameworks, including multiple impurities removal and selective molecular capture. Combining with the typical cases of hydrocarbon separations (C2, C4, and C8), the detailed discussion about the developed strategies (e.g. self-adaptive binding sites, multiple binding spaces, synergistic binding sites, synergistic sorbent separation technology, gate-opening effect, size and thermodynamic combine effect) that are adaptive to different scenarios would be provided. The review will conclude with our perspective on the existing barriers and the future direction of this topic.

A “like-zwitterionic” forward osmosis membranes with electrostatic deposition of aluminosilicate nanotubes for resisting positively and negatively charged protein and oil contaminant

Membrane fouling has always been a huge obstacle to the development of membrane separation technology, including forward osmosis (FO) technology. In this work, polyamide (PA) thin-film composite (TFC) membranes were simply immersed in aluminosilicate nanotubes (ANTs) dispersions to obtain thin-film nanocomposite (TFN) FO membranes. With the help of the opposite surface charge of ANTs and PA layer, and the representative “peak-valley” structure of PA TFC membrane, ANTs are stably bound to the surface of TFC membrane by electrostatic adsorption and physical confinement. The TFN membrane has greatly enhanced hydration ability due to the rich hydrophilic hydroxyl groups of ANTs, “like-zwitterionic” surface composition and rough nanostructure morphology, resulting in good underwater superoleophobicity. Combined with the water transport channel formed by its nanoporous structure, the surface anti-protein adhesion and anti-oil–water emulsion adhesion can be achieved without affecting the water flux. It is worth noting that the surface potential of TFN membrane is close to neutral due to charge neutralization. This avoids the electrostatic interaction between the membrane surface and the contaminant, and further achieves a universal anti-fouling ability that is not affected by protein or emulsion charge, and the irreversible adsorption is close to zero. In addition, the rigid ANTs coating exhibits excellent stability and reusability under long-term use, and the water flux after cleaning can be restored to nearly 99.9%. In general, this method of using ANTs deposition to improve the antifouling performance of PA based TFC membrane is simple, efficient, stable, and easy scalable. This method is not only limited to FO membrane, but also can be extended to PA based reverse osmosis and nanofiltration membranes, which has great practical application potential.

Adaptive generic model control scheme for an optimized external heat integrated air separation column using unscented kalman filter

An External Heat-Integrated Air Separation Column (E-HIASC) process is a promising air separation technology. This study focuses on the operational stability of the optimized E-HIASC process for separating nitrogen, oxygen, and argon mixtures. The operation stability of process is achieved through an Adaptive Generic Model Control (AGMC) scheme which is designed by incorporating the identified E-HIASC state-space dynamic model into the controller algorithm. The controller synthesizes the Generic Model Control (GMC) algorithm, decoupled ARX model, and Unscented Kalman Filter (UKF) algorithm to enable the auto-regression and exogenous (ARX) for model identification and the UKF algorithm to estimate time-varying parameters and compute unmeasured E-HIASC state parameters required in the GMC algorithm. A Generic Model Control (GMC) and Multivariable PID (M-PID) control schemes were also designed for benchmarking study. Simulation results show that an AGMC scheme performs better than the GMC and M-PID schemes in tracking the product concentration set point and disturbances rejection.

Ozone/percarbonate-Fe3+ conditioning enhanced pressurized electro-osmotic dewatering (PEOD) of waste activated sludge: Feasibility and mechanisms

Pressurized electro-osmotic dewatering (PEOD) process is an emerging technology for high-efficiency solid-liquid separation of sludge and has garnered extensive interest. This study proposed a novel sequential conditioning process based on ozone (O3)/percarbonate (SPC) treatment followed by Fe3+ coagulation, namely O3/SPC-Fe3+ conditioning, to improve the performance of PEOD. The optimal operating conditions and the related dewatering performance of O3/SPC-Fe3+ conditioning-PEOD process were investigated to verify the feasibility. The mechanisms of the O3/SPC-Fe3+ conditioning on improving PEOD process were also discussed from the enhancement of the water/filtrate flow in pores. The results showed that 53.44 % water content and 0.95 g/g dry solid (DS) of bound water in dewatered sludge cake were attained in the O3/SPC-Fe3+ conditioning-PEOD process with optimal O3 aeration time of 12 min, SPC dosage of 0.0610 g/g DS and Fe3+ dosage of 0.0310 g/g DS for sludge conditioning then 346 kPa mechanical pressure and 40 V voltage for dewatering. During the O3/SPC-Fe3+ conditioning-PEOD process, the extracellular polymeric substance (EPS) matrix was disintegrated, and the inner EPS migrated to the outside along with water. The values of α-helix/(β-sheet + random coil) adjusted by O3/SPC-Fe3+ conditioning process decreased to 7.38 and 5.12 in slime and LB-EPS, respectively, and these changes transformed to expose more hydrophobic sites. After conditioning, the proportion of protein-N decreased drastically from 81.67 % to 62.34 %, while the proportion of inorganic-N increased significantly from 18.33 % to 37.66 %, indicating that partial protein-N in EPS altered to inorganic-N. The enhancement of PEOD by the O3/SPC-Fe3+ process can be attributed to the EPS hydrophobicity transformation and the degradation/mineralization of EPS by oxidation of generated ·OH. The former triggered the reduction of water/filtrate viscosity within the interfacial region of pores. The latter provoked the decrease of bulk viscosity of water/filtrate within the pores. These two effects relieved the viscous resistance to water/filtrate flow within pores and promoted dewatering.

Porous Polymeric Electrodes for Electrochemical Carbon Dioxide Capture.

Carbon capture is a promising technology to mitigate greenhouse gas emissions to achieve net carbon neutrality. Electro-swing reactive adsorption has emerged as an attractive approach for sustainable decarbonization. However, current electrodes with limited gas transport present a major barrier that hinders their practical implementation. Herein, porous polymeric electrodes are developed to effectively enhance CO2 transport without the need for additional gas diffusion conduits. Such all-in-one porous electrodes also enable more accessible redox active sites (e.g., quinones) for CO2 sorption, leading to an increased materials utilization efficiency of ≈90%. A continuous flow-through carbon capture and release operation with high Faradaic efficiency and excellent stability under practical working conditions is further demonstrated. Together with low cost and robust mechanical properties, the as-developed porous polymeric electrodes highlight the potential to advance the future implementation of electrochemical separation technologies.

Controlling the nano-channel configuration of hierarchical MoS2 framework membranes via covalent functionalization with amino acids for enhanced sieving ability

As the utilization of nanolaminates composed of two-dimensional (2D) materials has become promising candidates for precise molecule/ion separations, precisely controlling the size, chemistry and configuration of the intra-nanochannel is crucial for further development of membranes. Herein, we developed covalently functionalized MoS2 membranes with amino acids (AAs) pillars via polarized N-Mo bonding for substantially improving the selectivity and permeability towards high-concentration salts and micropollutants. The optimized Glycine-Proline configuration in tailorable nanochannels, combined with the steric hindrance imposed by the protruding AAs and the ion-confined partitioning of Pyrrole-N and Carboxyl-O functionalities, contribute to achieving selectivity of MgCl2/Na2SO4 up to 11.2 and 8.1 in single and binary solutions. Meanwhile, the synergy between the hierarchical network of water pathways and the decorated hydrophobic pyrrolidine rings effectively facilitates low-friction water transport across the confined nanochannels. Impressively, the improved HM-GP demonstrates rejection rates of 95.7% for 0.6 M NaCl with a water flux of 15.2 l m−2 h−1 bar−1 under osmosis-driven condition, and it maintains a high salt rejection of 93.2% with a water flux of 17.5 l m−2 h−1 in pressure-driven process. This work not only offers an efficient strategy for designing robust HM-GPs with great potential in sustainable water purification and ion sieving, but also provide valuable guidance for developing separation technologies based on 2D material membranes.

Zero-dimensional quantum dot-modified membrane materials for the effective treatment of industrial wastewater: A comprehensive review

The efficient treatment and recycling of industrial wastewater is an important way to improve water resource utilization. Membrane separation technology has been widely used in the field of industrial wastewater treatment due to its high separation efficiency, low energy consumption, good scalability, and other advantages. A recent breakthrough in membrane technologies is the emergence of various nanocomposite membranes, which not only breaks the trade-off between membrane selectivity and permeability, but also enhances the anti-fouling ability and multi-scale separation effects of membranes. Among the nanomaterials used for membrane fabrication, zero-dimensional quantum dots (QDs) with size-dependent optical properties and excellent photocatalytic potential have become promising candidates for novel nanocomposite membrane construction. Significant improvements in membrane surface hydrophilicity, anti-fouling property, and permeability can be achieved by incorporating QDs during the membrane formation process or through membrane post-modification. This review focuses on recent advances in QD-modified membranes for industrial wastewater treatment. The synthesis methods of QDs were summarized firstly, especially for carbon-based and semiconductor QDs. Based on the blending modification and surface modification, the research progress in the modification strategies of QD-modified membranes is presented. Subsequently, the state-of-the-art studies of QD-modified membranes in the application of industrial wastewater treatment are reviewed. Finally, the current challenges and opportunities in QD-modified membranes are discussed.

Facile infiltration of polyethyleneimine as a strong CO2 retardant in scalable dual-polymer membranes for H2/CO2 separation

Successful pre-combustion CO2 capture from synthetic gas for H2 production requires effective membrane separation technology. While polymer-based membrane materials offer promising industrial scalability, they generally lack a sufficiently high H2/CO2 selectivity to make this process energy-efficient. In this work, we have designed a scalable dual-polymer blend membrane consisting of sulfonated polyphenylsulfone (sPPSU) and polybenzimidazole (PBI), and then being infiltrated with amine-rich poly(ethyleneimine) (PEI) molecules as effective CO2 retardants to substantially elevate the H2/CO2 selectivity. PEI molecules were infiltrated into the dual-polymer matrix via solution-treatment to crosslink the polymer network and retard CO2 transport using its amine-rich nature. The PEI infiltration dramatically increased the H2/CO2 selectivity of the dual-polymer matrix from 4.6 to up to 59.3 while maintaining a minimum H2 permeability of 2.49 Barrer at a low temperature of 35 °C, which not only surpasses the Robeson upper bound but also places the newly developed membrane among the best-performing polymer-based membranes. More importantly, the solution infiltration of PEI incurs no phase segregation, maintaining the polymer mechanical robustness, which is crucial for industrial scaling. This study offers promising opportunities to develop three-polymer membrane systems for H2/CO2 separation using synergistic polymer blends and CO2-retarding molecules.

Polymer-modified nanofillers for enhancing CO2 separation performance of MMMs: A comparative study on the role of bridging ligands

Advanced CO2 separation technology is one of the key technologies for reducing carbon emissions and can make significant contributions to reducing the negative impact of the greenhouse effect on human survival. Membrane separation technology is regarded as a new generation of carbon capture technology because of its great potential to reduce carbon capture energy consumption and improve net carbon capture efficiency. Mixed matrix membranes (MMMs) can break through the performance limit of traditional polymer membranes, but the influence of bridging agents for post-modifying nanofillers on membrane structure and properties needs further systematic investigation. In this work, four types of ligands were selected for synthesizing polymer-modified nanofillers and then incorporated into poly (vinylamine) (PVAm) to prepare MMMs. The comparative analysis results indicate that bridging ligands with superior flexibility are conducive to enhancing the gas permeability within the pores by diminishing the compactness of the polymer shell. The constructed phase interface transition area with uniformly enhanced mechanical strength demonstrates the improved interface compatibility between the matrix and nanofillers bridged via the flexible ligand. Techno-economic evaluation verifies the industrial application potential of the optimal MMMs targeting CO2 capture from post-combustion gas.