H2 Purification Research Articles

Greenhouse Gas Emissions and Net Energy Production of Dark Fermentation from Food Waste Followed by Anaerobic Digestion

There are diverse estimations regarding the carbon reduction effects of alternative hydrogen production technologies. This study assessed the greenhouse gas (GHG) emissions and energy balance of a two-stage process combining dark fermentative hydrogen production and anaerobic digestion from food waste using the cradle-to-gate life cycle assessment (LCA). The system boundary included collection and transportation, pretreatment and feedstock storage, dark fermentation, H2 purification, anaerobic digestion and heat and power generation and the estimated GHG emission was compared with a single anaerobic digestion of food waste. GHG emission of the biohydrogen production was estimated as 2.48 kg CO₂-eq per kg H₂ without considering avoided emissions from heat and power generation. The environmental impacts were majorly influenced by electricity use. The net energy ratio of the two-stage process was calculated to be 8.18, confirming a net energy gain and the potential GHG emission avoidance for electricity and heat use. Given that the single-stage anaerobic digestion of 16 tons of food waste is replaced by the two-stage dark fermentation process, 76.6 kg CO₂-eq would be avoided. Sensitivity analysis revealed that energy-saving strategies are the most sensitive factors for achieving positive net energy production and low global warming potential.

Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Hydrate-based H2 purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H2–CO2–CO) from natural gas reforming products. The results identified H2–CO2–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H2, CO2, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO2 content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO2 in the hydrate was the highest, followed by H2, and CO was the least abundant. The molecule dynamics simulation results show CO2 molecule numbers reflected trends in 51262 cages, H2 numbers correlated with changes in 512 cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO2, H2, and CO.

Innovative Charge-Tuning for Highly Dispersed Pt Catalysts: Achieving Deep CO Removal in Industrial H2 Purification for Fuel Cells.

Proton exchange membrane fuel cells have strict requirements for the CO concentration in H2-rich fuel gas. Here, from the perspective of industrial practicability, a highly dispersed Pt catalyst (2-4 nm) supported on activated carbon (AC), which was modified by electronic promoters (K+) and structural promoters (isopropanol), is studied in detail. Compared with traditional metal oxide supports, the K-Pt/AC catalysts, which benefit from the tuned charge distribution, achieve a significant reduction of CO (from 1% to <0.1 ppb) under H2-rich conditions and show potential for used in large-scale industrial hydrogen purification. Experimental results and theoretical calculations reveal that the K atom, with its lower electronegativity, contributes to the shift of surface Pt2+ to a lower binding energy due to the presence of oxygen species on the AC surface. This facilitates oxygen activation and accelerates desorption of the CO2 product, thereby accelerating the reaction process and enabling the deep removal of CO in a hydrogen-rich atmosphere.

CO-Free Fuel Processing of Water Gas Shift Feedstocks: Effect of Support on CuMn Spinel Performance

AbstractCleaning up carbon monoxide (CO) in water gas shift feedstocks is crucial for fuel cell applications. The catalytic transformation of CO in hydrogen-rich feeds poses a significant challenge in environmental catalysis. To address this issue, a range of Cu–Mn-based monometallic and bimetallic catalysts with diverse supports (such as alumina, silica, zirconia, and titania) were employed. Temperature programming techniques were utilised to observe the reduction and oxidation behaviours of these catalysts. The investigation involved testing CO oxidation at various temperatures over copper and manganese-based supported catalysts in the presence of H2O and CO2 (simulating realistic conditions). A positive impact of H2O on catalytic performance was noted, whereas CO2 had a suppressive effect. Furthermore, the specific support materials (Al2O3, SiO2, TiO2, and ZrO2) were studied to understand their roles in CO oxidation under realistic conditions. In the presence of water, alumina catalysts containing bimetallic metals (Cu–Mn) exhibited 100% CO conversion even at a lower temperature of 160 °C. Conversely, under the predominant influence of CO2, alumina catalyst (Cu–Mn) showed 55% CO conversion. The exceptional performance was attributed to CO preferential adsorption on highly active Cu–Mn sites and a small H2-oxidative atmosphere of the catalysts. The activity results highlighted the strong dependence of CO conversion on reaction temperatures, the presence of metals, and the types of supports. Overall, these findings suggest the potential use of these catalysts for H2 purification under realistic conditions. Graphical Abstract

Low pressure-drop CuO/CeO2/UiO-66 catalysts for H2 purification

Pressure drop is responsible of a great part of the energy cost in industry due the energy consumed by pumps driving a fluid through the installation, and heterogeneous catalysis industrial processes suffer from this pressure drop penalty. This study demonstrates that UiO-66 significantly improves the catalytic performance of the CuO/CeO2 active phase for preferential CO oxidation in H2 streams with regard to a conventional γ-Al2O3 carrier due to the particular porous and crystalline properties of MOF materials. A packed bed of UiO-66 produces very low-pressure drop in comparison to conventional catalytic carriers, such as γ-Al2O3 or beta zeolite, being 4 times lower for UiO-66 than for γ-Al2O3 under 2 L/min flow of N2, and this ratio increases and approaches ∞ for lower gas flow rates. This feature of UiO-66 not only decreases the energy required to pump gases through the catalytic bed, but also improves catalytic performance of UiO-66-supported catalysts due to the enhanced gas diffusion into the catalytic bed. The reaction gases flow through the interparticle space left by the catalyst in a packed bed of CuO/CeO2/γ-Al2O3, and this produces high pressure drop, preferential gas pathways and mass transport limitations, negatively affecting the reaction rate. On the contrary, the reaction gases are able to flow through the UiO-66 material without channel constrictions, and the CuO/CeO2/UiO-66 catalysts avoid the gas diffusion restrictions of conventional catalysts.

Ultraselective carbon hollow fiber membrane for H2 extraction from blended natural gas

Blending hydrogen into natural gas (H2NG) pipelines is a feasible solution for low-cost hydrogen delivery while purifying H2 at end-use remains challenging due to its high pressure and low H2 concentration. Herein, biomass-derived carbon hollow fiber membranes (CHFMs) with ultrahigh H2/CH4 separation factor of 4149.0 under a simulated H2NG (10 mol% H2/90 mol% CH4) at 30 bar were reported, and the separation performance maintained within 150 h in a dynamic durability test. Furthermore, the CHFMs showed good stability under fluctuating temperature feeds (up to 100 °C). To evaluate the feasibility of the CHFMs for H2 extraction from H2NG, a three-stage membrane system was designed based on the mixed gas separation performances. It suggested that 99.99 mol% H2 can be achieved with a 90 % recovery, and the specific H2 purification cost was 0.245 $/Nm3 for a 1.8 × 105 Nm3/h production scale, which provides the possibility of hydrogen extraction from H2NG pipelines.

H2 and CO purification by CO2 removal from syngas coupling membrane module and water-absorption unit: An economic analysis

Hydrogen represents today a necessary alternative to fossil fuels to limit the greenhouse gas effect due to the CO2 emissions. In this work, a plant configuration able to get pure H2 and concentrated CO (about 94%) from a syngas mixture is proposed and simulated by coupling a selective membrane unit and a water absorption column. In addition, an economic assessment on the simulated plant is carried out to estimate the feasibility of this process in terms of economic potential, studying its dependence on several parameters, such as raw material price, membrane cost, membrane feed pressure, column temperature and feed flow rate.Separation performance is improved by the higher feed membrane pressure (greater H2 recovery and CO purity), whereas the increment of the column temperature especially affects the CO recovery. Hence, the economic potential presents a maximum with pressure and temperature (e.g., about 246ꞏ103 $/y at 40 bar of feed membrane pressure and about 282ꞏ103 $/y at 50 °C of column temperature), due to the balance between the higher compression/solvent cost and the increment of H2 or CO recovery. In addition, the simulated plant shows a positive economic potential in a wide range of syngas price (e.g., from 0.126 to 0.25 $/Nm3), being also not affected significantly by the cost of the palladium-based membrane module. A bigger plant size (i.e., feed flow rate from 10 to 100 kmol/h) can lead to a twelve times greater economic potential (from about 242ꞏ103 to about 2954ꞏ103 $/y at 30 bar), reducing the H2 purification cost and making the net present value positive.

Bioorganic activated carbon from cashew nut shells for H2 adsorption and H2/CO2, H2/CH4, CO2/CH4, H2/CO2/CH4 selectivity in industrial applications

This research explores the production of activated carbon (AC) from cashew nut shells using a potassium hydroxide (KOH) activation method, with a focus on its application in high-pressure gas adsorption. Among the synthesized samples, AC850 demonstrated the highest efficiency, displaying a specific surface area of 1972 m2/g and total and micropore volumes of 0.847 cm3/g and 0.724 cm3/g, respectively. The bioorganic activated carbon exhibited significant sorption capabilities for H2, with uptake values of 13.34 mmol/g (2.69 wt%) at 10 bar and 25 °C, and a H2/CH4 selectivity range between 43.4 and 2.6. Calculations were also conducted for selectivity in a mixture of three gases (H2, CO2, and CH4) in industrial settings. Advanced characterization methods such as N2/CO2 adsorption isotherms, FT-IR, Raman spectroscopy, SEM, and TGA were employed to analyze the structural and chemical properties of the produced AC, including its functional groups and molecular structure. The research underscores the potential of utilizing agricultural waste, particularly cashew nut shells, to develop efficient materials for H2 storage and purification. The high-pressure adsorption capability and eco-friendly nature of the manufactured activated carbon make it suitable for both environmental and industrial applications.

Molecular-scale hybrid membranes containing benzimidazole linkages on large-area α-alumina tubes for H2 purification

H2/CO2 separation is important in industry. Polymer, inorganic and hybrid membranes have been reported, however, high performance membranes with good scalability and large area are still lacked. Here, we fabricated a series of molecular-scale hybrid membranes (MHMs) containing benzimidazole linkages on rough α-alumina tubes. The membranes, with an area of 37.7 cm2 for each, exhibited a H2/CO2 selectivity of 14.2 (with a corresponding H2 permeance of 29.5 GPU) at 423 K and high H2 permeance of 310 GPU (with a corresponding H2/CO2 selectivity of 9.37) at 523 K. The membranes had good pressure and temperature tolerance. Besides, a two-stage membrane system was designed to study the effect of pressure and membrane area on hydrogen production.

Simultaneously enhancing H2 recovery and CO2 captured pressure during the hydrogen purification process of medium-temperature shifting gas by coupled wet CO2 separation-PSA technology: From laboratory to industrial scale test

The petrochemical industry has a significant demand for high-purity hydrogen. It primarily obtained from the H2 purification unit by using pressure swing adsorption (PSA) technology to recover H2 from medium-temperature shifting gas (MTSG). The the coupled wet CO2 separation-PSA process was introduced in this work, aiming to capture CO2 from MTSG while simultaneously increasing the H2 recovery rate. To enhance the desorption pressure of CO2 separation unit in the coupled process to facilitate the storage or utilization of the captured CO2, firstly, a rigorous thermodynamic study was carried out to provide a theoretical basis for the development of an improved CO2 solvent. Subsequently, a pilot-scale test was executed to validate the theoretical findings. Finally, the patented coupled process was implemented at an industrial scale for the first time. The results showed that the capacity of PSA unit for H2 purification increased from 6800 to 12,000 tons per year and the H2 recovery rate increased from 84.6 % to 93.6 %; the CO2 desorption pressure increased from about 0.03 MPa (traditional Benfield process) to 0.15 MPa, which reduced the energy consumption of CO2 compression, and the total average annual economic benefits increased by US $ 15.55 million.

Regulation of MOF-74 nanosheet channels for precise H2 purification

Mixed matrix membranes (MMMs), composed of functional fillers and a polymer matrix, are considered effective demonstrations for overcoming the trade-off limitation of polymeric membrane-based gas separations. MOF-74, with its high density of open metal sites and one-dimensional straight honeycomb channels, is an extremely attractive filler material. However, the intrinsically large pore aperture and micron-sized, spindle-shaped grain morphology hinder the use of high-performance, interfacial defect-free MMMs for small gas separations. Herein, we report novel mixed matrix membranes integrated with dual-metallic MOF-74 nanosheets and poly(vinylamine) for precise molecular sieving for H2 purification applications. The nanosheets of parallel orientation within the membrane maximize the exposure of channels for polymeric chain penetration. The amino side groups anchored on the polymeric chains coordinate with the open metal sites on the channel walls of MOF-74 nanosheets, exposing the hydrophobic alkyl backbones to shrink the originally large channel apertures and simultaneously enhancing the interfacial compatibility between MOF-74 and the polymer matrix. Benefiting from the merits of these elegant channel regulations, MMMs exhibit superior H2/CH4 and H2/CO2 separation performances toward binary, ternary and even quaternary feedstocks, along with remarkable long-term separation stability. This MMM is expected to constitute a new membrane paradigm that holds great promise for practical H2 purification and separation.

Insights into Cis-Amide-Modified Carbon Nanotubes for Selective Purification of CH4 and H2 from Gas Mixtures: A Comparative DFT Study.

Among a plethora of mixtures, the methane (CH4) and hydrogen (H2) mixture has garnered considerable attention for multiple reasons, especially in the framework of energy production and industrial processes as well as ecological considerations. Despite the fact that the CH4/H2 mixture performs many critical tasks, the presence of other gases, such as carbon dioxide, sulfur compounds like H2S, and water vapor, leads to many undesirable consequences. Thus purification of this mixture from these gases assumes considerable relevance. In the current research, first-principle calculations in the frame of density functional theory are carried out to propose a new functional group for vertically aligned carbon nanotubes (VA-CNTs) interacting preferentially with polar molecules rather than CH4 and H2 in order to obtain a more efficient methane and hydrogen separations The binding energies associated with the interactions between several chemical groups and target gases were calculated first, and then a functional group formed by a modified ethylene glycol and acetyl amide was selected. This functional group was attached to the CNT edge with an appropriate diameter, and hence the binding energies with the target gases and steric hindrance were evaluated. The binding energy of the most polar molecule (H2O) was found to be more than six times higher than that of H2, indicating a significant enhancement of the nanotube tip's affinity toward polar gases. Thus, this functionalization is beneficial for enhancing the capability of highly packed functionalized VA-CNT membranes to purify CH4/H2 gas mixtures.

Highly-efficient hydrogen purification with the T-C3N2 membrane via strain and charge engineering as well as their synergistic effect

The efficient separation and purification of high-purity hydrogen is imperative and desirable. We systematically explored the H2 purification performance of the T-C3N2 membrane with and without biaxial compressive (BC) strain and charge engineering by using MD simulations and DFT calculations. We found that the pure T-C3N2 membrane has relatively poor H2 selectivity as CO2 can also permeate through the membrane, and two modulation methods of BC-strain and charge were thus introduced separately to enhance the H2 separation performance for the first time. The T-C3N2 membrane with BC-strains modulation (1 %–3%) has excellent H2 permeance of 1.60 × 107–1.85 × 107 GPU at 300 K with 15.6 % enhancement with respect to the pure T-C3N2 membrane. The selectivity of H2 over gases (CO, N2, CO2, H2O, CH4) was drastically improved, for example, H2/CH4 is enhanced from 5.8 × 1020 to 2.1 × 1036 under 3 % strain engineering. The introduction of charge (1e–3e, 1e−–2e−) also enhances the H2 permeance of 1.47 × 107–1.68 × 107 GPU and the selectivity at 300 K. In particular, the charge (1e) and (1e−) modulations exhibit a desired permeance-selectivity trade-off for H2 purification with the enhancement of 5 % permeability and at least 1.3 times selectivity of H2 to other gases, respectively. Finally, the synergistic effect of BC-strain and charge on the H2 separation was studied, and it is much superior to separated BC-strain and charge engineering for H2 purification, where the H2 permeance enhances up to 1.86 × 107–1.89 × 107 GPU, and the H2 selectivity at 300 K is also enlarged at least ten times compared with that of the most effective modification of the isolated 2 % BC-strain and 1e charge, indicating synergistic effect further enhances the H2 separation performance. Therefore, the excellent modulations of appropriate BC-strain and charge engineering, particularly for their synergistic effect make the T-C3N2 membrane a promising candidate for highly permeant and selective H2 separation and purification that would be easily realized experimentally.

Enhanced ammonia adsorption-desorption properties of synthesized zeolite-carbon composite with the effect of Si/Al ratio

Effective ammonia (NH3) adsorbent is crucial for removing undecomposed NH3 residue after splitting into N2 and H2 fuel. In this study, a zeolite-activated carbon (AC) hybrid was successfully synthesized with a trace AC amount and different Si/Al ratios via hydrothermal method. The NH3 adsorption–desorption properties and mechanisms were investigated through two major activity tests, employing high pressure adsorption isotherm analyzer and breakthrough set up. Incorporating AC at 1 wt%, effectively shortened the regeneration period of the pure zeolite by ∼50 % due to the AC’s pore-widening effect on zeolite network, reducing the trapping of adsorbed NH3 in the zeolite pores. Interestingly, an optimum Si/Al ratio of 1.6 led to the highest specific surface area of 977.57 m2/g by the formation of zeolite mixture with coexisting NaX (faujasite zeolite with high Al atoms per cell) and NaY (higher crystalline faujasite zeolite with low Al atoms per cell). These improved structural characteristics consequently exhibited the highest NH3 (99.9995 %) storage capacity of 15.6 mmol/g at a partial pressure of 300 kPa in isotherm analysis at 25 °C. Besides, the initial breakthrough adsorption capacity for dilute NH3 (5%/N2 balance) under atmospheric conditions reached 8.9 mmol/g, accurately equivalent to isotherm analysis result at 5 kPa. This reproducibility of consistent adsorption uptake within low pressure region in both tests was credited to the compositional presence of both acidic and alkaline surface functionalities in the optimum zeolite-AC hybrid as stable NH3 adsorption sites. These active sites also provided a uniform dynamic adsorption capacity of ∼4 mmol/g throughout 15 cycles. Conclusively, this work highlighted the importance of zeolite composition and AC-incorporated proportion for the H2 purification aspect.

Hydrogen purification in nitrogen-doped two-dimensional conjugated microporous polymers

Conjugated microporous polymers (CMPs) have emerged as advanced membranes with unique pore structures for the separation of small kinetic diameter gases, including H2. In this work, we present a comprehensive investigation into the potential of N-doped pyridinyl functionalized conjugated microporous polymers, denoted as CHNX (X = 1, 2, 6), in H2 purification by using molecular dynamic simulations. Our findings demonstrate that CHNX membranes exhibit exceptional H2 purification performance with both high H2 selectivity and permeance. Notably, the CHN6 membrane shows the highest H2 permeance of 2.61 × 10−5 mol m−2 s−1 Pa−1, owing to its larger pore area relative to the other membranes. Moreover, both CHN and CHN2 membranes achieve 100 % gas selectivity based on the molar sieving mechanism. To gain deeper insights into the gas separation process, we analyze the gas-membrane interaction, 2D density distribution, center of mass, mean square displacement, etc. The elucidation of these dynamics enhances our understanding of the underlying gas separation mechanisms. Ultimately, this work provides crucial theoretical guidance for the future development of gas separation membranes in hydrogen purification applications, thereby advancing the field of sustainable energy production.

Unveiling the mechanism of CO oxidation catalyzed by sulfur-doped fullerenes with the DFT calculations

As an important intermediate for dual carbon targets, catalytic CO oxidation under mild conditions has received sufficient attention, as the reaction mechanism is directly related to the type of employed catalyst. High performance computing is performed with density functional theory to elucidate the mechanism of CO oxidation catalyzed by sulfur doped fullerene (C60-xSx (x = 1 ∼ 3)). The total activation energy for the first CO oxidation on C59S, C58S2, and C57S3 increases gradually, as implies that the CO oxidation on C59S should be easier than those on the other two dopants. Distinct electrons (0.852 e and 1.479 e) are transferred to oxygen atoms (O2) from C59S with the adsorption of O2 and CO. There is no synergistic effect for the doping S atoms. All elementary reactions on C59S are exothermic processes. This means that C59S is a potential material for addressing environmental protection issues and H2 purification for fuel cell applications.

Engineering robust porous/dense composite hollow fiber membranes for highly efficient hydrogen separation

BaZr0.7Ce0.2Y0.1O3-δ (BZCY), a perovskite-type mixed protonic and electronic conducting oxide, holds significant potential for H2 separation and purification as a membrane. The introduction of a porous modification layer as an exchange-active component offers a potential solution to enhance H2 permeability. However, achieving the desired porous/dense structure presents a notable challenge for practical implementation. In this study, various methods were developed to address sintering kinetics, encompassing both chemical aspects (e.g., interlayer reactions) and physical factors (e.g., thermal expansion), for fabricating a porous BZCY modification layer on a 4-channel BZCY hollow fiber membrane. The optimal composite hollow fiber membrane, resulting from a combination of readily sintered hollow fiber and powders for constructing the porous layers, exhibits an exceptional H2 permeation flux of 0.48 mL min−1 cm−2 at 900 °C using 50 % H2/N2 as the feed gas, which represents a threefold increase compared to the performance of the bare BZCY membrane. The H2 permeation flux stabilized at 0.52 mL min−1 cm−2 for 500 h under water vapor conditions. These findings enabled us to identify the most effective approach, unlocking the full potential of surface-modified hollow fiber membranes and advancing their capabilities in H2 permeation applications.

Enhanced gas separation performance for H2 purification using MIL-68(ln)-nh2/PES mixed-matrix membranes

The growing demand for sustainable and efficient gas separation technologies has prompted the exploration of advanced materials to enhance the gas permeability and selectivity. Polyethersulfone (PES) membranes are widely used in gas separation, gas upgrading, and clean energy production owing to their environmental friendliness and low cost. However, their gas permeability and selectivity can be further improved for commercial application. This study explored the incorporation of 10 wt % of MIL-68(ln)-NH2 into PES membranes using a phase-inversion approach to enhance gas permeability and selectivity. The morphological, structural, and thermal properties of the resulting MOF/PES membrane were characterized using SEM, AFM, BET, XRD, FTIR, and TGA-DTG. Gas permeation experiments were conducted using different gases (CO2, N2, CH4, and H2) under different heating conditions (20–60 °C) to evaluate the gas permeability and selectivity of the MOF/PES membrane. The results showed that the incorporation of MOF into the mixed matrix membrane (MMMs) led to a 9% increase in porosity, 87% reduction in roughness, and 32% decrease in pore size compared to neat PES membranes. Significant changes in the morphology, crystallinity, and thermal stability were observed, with notable improvements of up to 22%. Moreover, the MOF/PES membrane exhibited high gas permeability (CO2 = 124656, N2 = 83650, CH4 = 159298, and H2 = 427075 Barrer) and selectivity (H2/N2 = 5.7, H2/CO2 = 4, CH4/N2 = 2, and CH4/CO2 = 1.7) for flammable gases. The optimal gas separation performance was observed at 20 °C and 60 °C for H2/N2 and H2/CO2 separation, respectively. These findings demonstrate the potential of MOF-based PES membranes for gas separation applications, particularly in H2 purification.

Insights into micro-structure and separation mechanism of benzimidazole-linked polymer membrane for H2/CO2 separation

Separation of hydrogen from carbon dioxide for sustainable H2 production and CO2 capture still faces great challenges due to the smaller size of H2 and higher condensability of CO2. Herein, a high-performance benzimidazole-linked polymer (BILP) membrane for hydrogen separation was directly prepared on α-Al2O3 substrate through a facile interfacial polymerization approach at room temperature. The separation performance of the BILP membrane were regulated by controlling the reaction time and the microstructure was systematically characterized. Molecular simulations were performed to deep understand the separation mechanism in the BILP membrane. The best performance membrane displays an extraordinary mixed gas selectivity of 40 for H2/CO2 together with outstanding H2 permeance of 250 gas permeation units (GPU) at 473 K, far exceeding the Robeson’s upper bound. Besides, the membrane can withstand high temperature and pressure, and also shows good H2/N2 and H2/CH4 selectivity. The excellent separation performance, coupled with high temperature and pressure resistance and easy preparation, render BILP membranes great potential for economic H2 purification, H2 recovery, and natural gas treatment.

Membranes with Molecular Gatekeepers for Efficient CO2 Capture and H2 Purification.

The urgent need for CO2 capture and hydrogen energy has attracted great attention owing to greenhouse gas emissions and global warming problems. Efficient CO2 capture and H2 purification with membrane technology will reduce greenhouse gas emissions and help reach a carbon-neutral society. Here, 4-sulfocalix[4]arene (SC), which has an intrinsic cavity, was embedded into the Matrimid membrane as a molecular gatekeeper for CO2 capture and H2 purification. The interactions between SC and the Matrimid polymer chains immobilize SC molecules into the interchain gaps of the Matrimid membrane, and the strong hydrogen and ionic bondings were able to form homogeneous mixed-matrix membranes. The incorporation of the SC molecular gatekeeper with exceptional molecular-sieving properties improved the gas separation performance of the mixed-matrix membranes. Compared with that of the Matrimid membrane, the CO2 permeability of the Matrimid-SC-3% membrane increased from 16.75 to 119.78 Barrer, the CO2/N2 selectivity increased from 29.39 to 106.95, and the CO2/CH4 selectivity increased from 29.91 to 140.92. Furthermore, when the permeability of H2 was increased to 172.20 Barrer, the H2/N2 and H2/CH4 selectivities reached approximately 153.75 and 202.59, respectively, which are far superior to those of most existing Matrimid-based materials. The mixed-matrix membranes also exhibited excellent long-term operation stability, with separation performance for several important gas pairs still overtaking the Robeson upper limit after aging for 400 days.