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A fluorescein‐based diamine, 2‐(3,6‐bis(4‐amino‐3‐hydroxyphenoxy)‐9H‐xanthen‐9‐yl) benzoic acid (CADA), was synthesized and copolymerized with Durene and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to form a 6FDA‐Durene/CADA (3:2) copolyimide. The copolyimide was thermally cross‐linked at 300–425°C to form a series of decarboxylated cross‐linked polyimides. Compared with the 6FDA‐CADA polyimide, the incorporation of Durene diamine increased gas permeability of the pristine and the thermally cross‐linked polyimides greatly. The copolyimide cross‐linked at 375°C showed separation performance to the O2/N2 gas pair beyond the 1991 Robeson upper limit, while the CO2/CH4 separation property of the copolyimide cross‐linked at 425°C (PI‐425) was close to the 2008 Robeson upper limit. Moreover, the anti‐CO2‐induced plasticization property of the 6FDA‐Durene/CADA(3:2) copolyimides was improved by cross‐linking. The copolyimides cross‐linked at 350°C and above were not plasticized at a CO2 pressure up to 30 atm. This study showed that gas transport property of the decarboxylated cross‐linked polyimides could be improved significantly by the incorporation of bulky diamino moiety. The fluorescein‐based copolyimide had great potentials for gas separation applications. [ABSTRACT FROM AUTHOR]

This paper mainly reviewed the study progress of CO2 separation membranes based on zeolite materials, including the CO2/CH4 separation performance of zeolite inorganic membranes with different topological structures and zeolite-filled mixed matrix membranes. The current research bottlenecks and corresponding improvement methods of the two membranes were discussed. According to the above points, the following two points were proposed as future research focus to promote the industrialization of zeolite- based CO2 separation membranes: preparation and defects-healing of ultra-thin inorganic membranes, structural regulation and structure-activity relationship research of mixed matrix membranes. [ABSTRACT FROM AUTHOR]

The selective separation of CO2 from CH4‐containing gases is crucial to produce clean energy gases. In this study, triazole anion‐functionalized ionic liquids (TAFILs) were designed by combining low molecular weight cations with triazole anions containing N electronegative site and further mixed with physical solvents to form physicochemical absorbents. The results indicated that [Cho][Triz]/TMS (80 wt%/20 wt%) not only absorbs 0.125 g CO2/g absorbent equal to that of 30 wt% MEA solution at 40°C and 1 bar, but also has low enthalpy of −35.76 kJ/mol less than half of 30 wt% MEA solution. Simultaneously, a super high CO2/CH4 selectivity of 191.0, higher than most of the reported absorbents, is obtained for [Cho][Triz]/TMS solvents. Such great performance of CO2 separation was attributed to relatively weak chemical and physical interaction between CO2 and TAFIL binary absorbents. This study may provide novel promising ionic liquid absorbents for CO2 capture applications from clean energy gases. [ABSTRACT FROM AUTHOR]

In this study, the aim was to purify CH4, an efficient and renewable clean energy source, which often contains CO2 that needs to be removed to improve its combustion efficiency. To achieve this, hybrid hollow fiber membranes were developed using BTDA‐TDI/MDI (P84) and polyethersulfone (PES) through a dry jet‐wet spinning process. The effects of different parameters, including core liquid composition, solidification bath composition and temperature, spinneret temperature, and air gap distance, were studied to optimize membrane structure, morphology, and CO2/CH4 separation performance. The P84/PES hollow fiber membrane obtained through this process demonstrated good CO2/CH4 separation performance, with CO2 permeation of 2.12 GPU and a selectivity of 51.23. To further improve the membrane's performance, a coating of poly(ether block‐amide) (PEBA) was applied to the P84/PES hollow fiber membrane. This modification resulted in a P84/PES‐PEBA hollow fiber membrane with increased CO2 affinity due to the polar poly(ethylene oxide) groups of PEBA. The P84/PES‐PEBA hollow fiber membrane exhibited high selectivity of 56.5 and CO2 permeance of 1.42 GPU at 25°C. [ABSTRACT FROM AUTHOR]

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This study aimed to utilize three conventional food wastes for the production of activated carbon to be used as fillers in mixed matrix membranes for CO2 separation. Carbonated soft drinks, rice husk, and wheat husk wastes have been used as precursors for the synthesis of activated carbon (AC) with two-step activation by KOH and ZnCl2. The fabricated AC powders were separately introduced into the matrix of PVA and PES to prepare mixed matrix membranes (MMMs) for CO2/CH4 separation. The analysis of SEM, XRD, FTIR, and N2 adsorption-desorption along with DFT pore size distribution (PSD) and BET analysis were used for the characterization of MMMs. It was determined that the pore structure of all synthesized AC samples is composed of both micropore and mesopore resulting from two-stage activation of raw carbon materials. The highest pore volume (0.843 ml/g) and BET surface area (984 m2/g) belonged to samples synthesized from carbonated soft drink wastes. Pure gas permeation tests were applied to determine the CO2/CH4 separation performance of synthesized AC/PVA and AC/PES MMMs. The highest CO2/CH4 separation performance resulted from AC/PES MMM synthesized from carbonated soft drink wastes with CO2 permeance of 88 GPU and CO2/CH4 ideal selectivity of 24.4. The main cost of AC production (81%) was determined to be related to the total price of activating agents. The total cost of AC production in this study is estimated to become 3.99 $ per kilogram of produced AC which is an economically attractive cost for the scale-up of the process based on the literature report. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) provide the opportunity to test new porous materials in challenging applications. A series of low-cost porous organic polymer (POPs) networks, possessing tunable porosity and high CO2 uptake, has been obtained by aromatic electrophilic substitution reactions of biphenyl, 9,10-dihydro-9,10-dimethyl-9,10-ethanoanthracene (DMDHA), triptycene and 1,3,5-triphenylbenzene (135TPB) with dimethoxymethane (DMM). These materials have been characterized by FTIR, 13C NMR, WAXD, TGA, SEM, and CO2 uptake. Finally, different loadings of these POPs have been introduced into Matrimid, Pebax, and chitosan:polyvinyl alcohol blends as polymeric matrices to prepare MMMs. The CO2/CH4 separation performance of these MMMs has been evaluated by single and mixed gas permeation experiments at 4 bar and room temperature. The effect of the porosity of the porous fillers on the membrane separation behavior and the compatibility between them and the different polymer matrices on membrane design and fabrication has been studied by Maxwell model equations as a function of the gas permeability of the pure polymers, porosity, and loading of the fillers in the MMMs. Although the gas transport properties showed an increasing deviation from ideal Maxwell equation prediction with increasing porosity of the POP fillers and increasing hydrophilicity of the polymer matrices, the behavior of biopolymer-based CS:PVA MMMs approached that of Pebax-based MMMs, giving scope to not only new filler materials but also sustainable polymer choices to find a place in membrane technology. [ABSTRACT FROM AUTHOR]

With the use of the polyether–polyamide block copolymer (Pebax) as a polymer membrane matrix, two-dimensional silicon dioxide (SiO2) nanosheets were obtained through the acid treatment of vermiculite and applied as fillers to prepare mixed matrix membranes (MMMs) with different filler amounts. Building transport channels for CO2 transfer in the membranes and enhancing the separation performance of CO2/CH4 are feasible owing to the structure of the SiO2 nanosheets and their propensity for horizontal alignment in the MMMs. The investigation of the characteristics and gas separation capabilities of Pebax–SiO2 MMMs revealed that the combination of SiO2 nanosheets considerably improved the separation effect of the MMMS in the CO2/CH4 system. The Pebax–SiO2 MMMs demonstrated an excellent CO2 separation efficiency with a CO2 permeation coefficient of 313.24 barrer and a CO2/CH4 selectivity of 31.26 at the filling quantity of 1.0 wt %. [ABSTRACT FROM AUTHOR]

In this work, a steam-assisted method is used to prepare bimetallic organic framework materials （bimetallic MOFs). Co, Fe, Mn, Zn, and Ni as the secondary metals are exchanged in the structure of PCN-6 which has large specific surface area and high porosity, and a series of PCN-6（M）（M=Co/Fe/Mn/Zn/Ni） bimetallic materials are obtained. Their structure, morphology, composition, and adsorption properties are characterized by powder X-ray diffraction（PXRD), scanning electron microscopy（SEM), energy dispersive spectroscopy（EDS), inductively coupled plasma-atomic emission spectroscopy（ICP-OES), and gas adsorption methods. The results show that the diffraction peaks and morphology of the PCN-6（M） series bimetallic materials are consistent with the parent material PCN-6, and the exchanged metals content reaches 12. 1% for Co, 22. 0% for Fe, 16. 1% for Mn, 17. 5% for Zn, and 16. 8% for Ni, respectively, which is much higher than the metal exchange capacity of solvothermal method （about 5. 0%） under the same conditions. In terms of gas adsorption performance, PCN-6（Zn), PCN-6（Ni） and PCN-6（Co） have better adsorption capacity for CH4 and CO2 than the parent material, especially at low pressure. In addition, the adsorption selectivity of V（CO2 ）∶V（CH4 ）=50∶50, PCN-6 （Fe） is superior to the parent material by theoretical ideal adsorption solution theory （IAST） calculation. The preparation of bimetallic MOFs by steam-assisted method can improve the exchange capacity of metals and change the affinity of MOFs to different gas molecules, thereby improving the gas adsorption performance and selectivity of materials. The steam-assisted method provides a new idea for the preparation of bimetallic MOFs, which is expected to be used in the preparation of other materials. [ABSTRACT FROM AUTHOR]

Two ionic liquids (ILs) having the same cation with different anions offering opposite hydrophilic/hydrophobic characters, 1-n-butyl-1-methylpyrrolidinium dicyanamide ([BMPyr]-[DCA]) and 1-n-butyl-1-methylpyrrolidinium hexafluorophosphate ([BMPyr]-[PF6]), were impregnated onto two different reduced graphene aerogels (rGAs) prepared by the thermal treatment of GAs at 300 and 500 °C to investigate the consequences of the changes in the hydrophilic character of ILs and the reduction temperature of the GAs on the corresponding gas sorption and separation performance of the IL/rGAs. The structural analyses of nanoporous rGAs and IL/rGAs pointed to a change in the quantity of oxygenated functional groups upon thermal treatment and a change in the direct interactions between IL molecules and the host rGA surface upon IL deposition. Single-component CO2 and CH4 sorption measurements were performed for each rGA and IL/rGA composite, and both ideal and mixture CO2/CH4 selectivities were calculated. The samples prepared by reducing the GA at 300 and 500 °C yielded ideal CO2/CH4 selectivities of 3.6 and 18 at 1 mbar and 25 °C, respectively. Among IL/rGA composites, the one prepared at 300 °C displayed a remarkable CO2/CH4 separation performance when combined with the hydrophobic [BMPyr]-[PF6], offering an ideal selectivity of 450.9 at 1 mbar and 25 °C, whereas the composite prepared with rGA500 yielded a substantially high CO2/CH4 selectivity of 173.5 after the incorporation of the hydrophilic [BMPyr]-[DCA] at 1 mbar and 25 °C. The ideal CO2/CH4 selectivities of [BMPyr]-[PF6]/rGA300 and [BMPyr]-[DCA]/rGA500 surpassed most of the previously reported selectivities of carbon-based materials in the literature. These results demonstrate the broad potential of IL/rGAs in sorption-based gas separations owing to the highly tunable nature of both the structure of IL and the surface characteristics of rGA. [ABSTRACT FROM AUTHOR]

This study reviews the major biogas upgrading technologies, with specific regard to recent progress in the field of membrane technology. More specifically, the objective of the present work is to provide the state-of-the-art of membrane-based processes for biogas upgrading, focusing primarily on the latest advances in membrane configurations/materials (e.g. for producing novel composite or mixed matrix membranes) and on hybrid technologies which integrate biogas upgrading with established membrane-based processes, such as the membrane bioreactor, membrane electrolysis or gas-liquid absorption. In order to demonstrate the potential of membrane technology for biogas upgrading in real field applications, the review also presents some cutting-edge biogas upgrading plants, located and operated in Europe and USA, and a brief summary of recent research studies (conducted during the last 5 years), which examine the economic feasibility of membrane-based technologies for biogas upgrading. Finally, challenges and future perspectives of applying membrane-based processes for biogas upgrading are discussed. [Display omitted] • Membrane technologies are increasingly applied in biogas upgrading in recent years. • Membrane biogas upgrading is eco-friendly & presents simple operation/equipment. • Composite membranes & integration of established processes are being researched. • MMM with MOF, zeolites & silica/alumina show improved permeability & selectivity. • Integration of AnMBR in biogas upgrading is successfully tested at research level. [ABSTRACT FROM AUTHOR]

The increase in the global population has caused an increment in energy demand, and therefore, energy production has to be maximized through various means including the burning of natural gas. However, the purification of natural gas has caused CO2 levels to increase. Hollow fiber membranes offer advantages over other carbon capture technologies mainly due to their large surface-to-volume ratio, smaller footprint, and higher energy efficiency. In this work, hollow fiber mixed matrix membranes (HFMMMs) were fabricated by utilizing cellulose triacetate (CTA) as the polymer and amine-functionalized metal-organic framework (NH2-MIL-125(Ti)) as the filler for CO2 and CH4 gas permeation. CTA and NH2-MIL-125(Ti) are known for exhibiting a high affinity towards CO2. In addition, the utilization of these components as membrane materials for CO2 and CH4 gas permeation is hardly found in the literature. In this work, NH2-MIL-125(Ti)/CTA HFMMMs were spun by varying the air gap ranging from 1 cm to 7 cm. The filler dispersion, crystallinity, and functional groups of the fabricated HFMMMs were examined using EDX mapping, SEM, XRD, and FTIR. From the gas permeation testing, it was found that the NH2-MIL-125(Ti)/CTA HFMMM spun at an air gap of 1 cm demonstrated a CO2/CH4 ideal gas selectivity of 6.87 and a CO2 permeability of 26.46 GPU. [ABSTRACT FROM AUTHOR]

Due to their interfacial defects between inorganic fillers and polymer matrices, research into mixed matrix membranes (MMMs) is challenging. In the application of CO2 separation, these defects can potentially jeopardize the performance of membranes. In this study, aminosilane functionalization is employed to improve the nano-sized zeolite Y (ZeY) particle dispersion and adhesion in polyether block amide (Pebax). The performance of CO2/CH4 separation of Pebax mixed matrix composite hollow fiber membranes, incorporated with ZeY and aminosilane-modified zeolite Y (Mo-ZeY), is investigated. The addition of the zeolite filler at a small loading at 5 wt.% has a positive impact on both gas permeability and separation factor. Due to the CO2-facilitated transport effect, the performance of MMMs is further improved by the amino-functional groups modified on the ZeY. When 5 wt.% of Mo-ZeY is incorporated, the gas permeability and CO2/CH4 separation factor of the Pebax membrane are enhanced by over 100% and 35%, respectively. [ABSTRACT FROM AUTHOR]

In natural gas refining, separation of CO 2 from methane is an important research issue, because CO 2 wastes natural gas energy and causes pipeline corrosion. Compared to common technologies, adsorption-based processes are noteworthy for gas separation because they are inexpensive and have high efficiency. A type of composite consists of a polymer matrix and organic or inorganic fillers. By integrating metal-organic frameworks (MOFs) into the polymer matrix, composites with a defect-free surface are formed because organic linkers in MOFs can provide a suitable combination with organic polymers to form a proper membrane for separation of the CO 2 /CH 4 gases. Here, an attempt has been made to investigate various types of composites based on their nature, the impact of functional groups in the structure of MOFs, as well as two-dimensional MOFs on the separation efficiency of CO 2 and CH 4 gases. [Display omitted] • ● The selective separation of CO 2 from CH 4 utilizing MOF composites. • ● The synergistic effect of MOF and support material in the gas separation process. • ● The effect of some features of the MOFs on the performance of the composites. [ABSTRACT FROM AUTHOR]

A customized alkaline Zinc-aminotriazole MOF with a unique pore environment and optimal pore aperture of 3.6 Å and capable of preferentially capturing CO 2 from four-component CO 2 /O 2 /N 2 /CH 4 mixtures show strong affinity and electrostatic interactions for CO 2 due to carboxylic acid oxygen atoms located on the middle of the pore channel. Single-component adsorption isotherms exhibit high the low-pressure CO 2 uptake of 51 cm3 g−1, and ultra-high CO 2 /CH 4 (>104), CO 2 /N 2 (>106), and CO 2 /O 2 (>103) selectivity with negligible co-adsorption in dynamic CO 2 /N 2 and CO 2 /N 2 /O 2 (15/80/5) breakthrough experiments. [Display omitted] • Non-toxic water as the solvent is not only environmentally friendly but also reduces synthesized costs. • Unique alkaline pore environment and electrostatic effects enable this material to preferentially capture CO 2. • Ultra-high CO 2 uptake capacity of 51 cm3 g−1 in the low-pressure and benchmark CO 2 /N 2 , CO 2 /CH 4 and CO 2 /O 2 selectivity are exhibited in ZnATZox H 2 O. • ZnATZox H 2 O exhibits remarkably dynamic CO 2 /N 2 and CO 2 /N 2 /O 2 breakthrough experiments with negligible co-adsorption. CO 2 capture from natural gas and N 2 -rich flue gas is essential for improving the utilization of natural resource gases reducing CO 2 emission, thereby alleviating the greenhouse effect. However, achieving effective Adsorptive separation of CO 2 from CH 4 , N 2 , and O 2 based on molecular sieving is still challenging and rarely reported, but selectively capturing CO 2 places high desires on maximizing separation efficiency. Here, we report a zinc-aminotriazole ultramicroporous metal–organic framework (ZnATZoxH 2 O), constructed from zinc carbonate, 3-amino-1,2,4-triazole (ATZ), and oxalic acid with water as the only solvent. ZnATZoxH 2 O features NH 2 -functionalized and pore channels around 3.6 Å, which preferentially adsorb CO 2. This material exhibits high CO 2 uptake of 61.9 cm3 g−1 at 298 K and 1 bar and significantly high IAST selectivity for CO 2 /N 2 (>103) and CO 2 /CH 4 (>105) and CO 2 /O 2 (>104). Theoretical GCMC simulations reveal that negatively charged amino groups decorated on the pore channel surface and carboxylic acid in the pore environment enhance the binding affinity over CO 2 through electrostatic interactions for preferential capture of CO 2. Single-component adsorption experiments and dynamic breakthrough experiments mutually validated the superior separation performance of this material and dynamic column breakthrough tests to produce high dynamic CO 2 separation productivity of 2.017 mmol g−1 and 3.4 mmol g−1 for CO 2 /N 2 (15/85), CO 2 /CH 4 (50/50), and 2.26mmol g−1 CO 2 /N 2 /O 2 (15/80/5). Non-hazardous water as a synthetic solvent to assemble highly stable and efficient CO 2 -selective materials makes it promising for practical industrial applications. [ABSTRACT FROM AUTHOR]

Efficient capture of carbon dioxide (CO 2) from flue gas and biogas through physical adsorption are urgently required. Here we report an ultramicroporous adenine-based MOF, Cu-AD-SA (AD=adenine, SA=succinic acid), bearing abundant Lewis basic sites (adenine nitrogen atom), exhibits a CO 2 capacity of 3.47 mmol g−1, and high selectivities of CO 2 over CH 4 and N 2 under 1 bar and 298 K. Furthermore, the exceptional moisture stability of Cu-AD-SA promises its potential applications under real conditions. More importantly, Cu-AD-SA showed the lower Q st of CO 2 (22.4 kJ mol−1), which is beneficial to sorbent regeneration in an industrial process. Molecular simulation and in-situ spectroscopy reveal that both N···C and hydrogen bond interactions between Cu-AD-SA and CO 2 play important roles in its adsorption of CO 2. Breakthrough experiments have confirmed that Cu-AD-SA has excellent performances in separating CO 2 /N 2 and CO 2 /CH 4 at 298 K humid conditions (>57 % RH). [Display omitted] • Cu-AD-SA shows high CO 2 selectivity from flue gas and biogas. • The adsorbed CO 2 can be easily stripped out under mild conditions. • Moisture stability allows efficient CO 2 capture from wet mixed gases. • The mechanism for superior CO 2 affinity was explored systematically. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of SION-8, a novel metal-organic framework (MOF) based on Ca(II) and a tetracarboxylate ligand TBAPy4- endowed with two chemically distinct types of pores characterized by their hydrophobic and hydrophilic properties. By altering the activation conditions, we gained access to two bulk materials: the fully activated SION-8F and the partially activated SION-8P with exclusively the hydrophobic pores activated. SION-8P shows high affinity for both CO2 ( Qst = 28.4 kJ/mol) and CH4 ( Qst = 21.4 kJ/mol), while upon full activation, the difference in affinity for CO2 ( Qst = 23.4 kJ/mol) and CH4 ( Qst = 16.0 kJ/mol) is more pronounced. The intrinsic flexibility of both materials results in complex adsorption behavior and greater adsorption of gas molecules than if the materials were rigid. Their CO2/CH4 separation performance was tested in fixed-bed breakthrough experiments using binary gas mixtures of different compositions and rationalized in terms of molecular interactions. SION-8F showed a 40-160% increase (depending on the temperature and the gas mixture composition probed) of the CO2/CH4 dynamic breakthrough selectivity compared to SION-8P, demonstrating the possibility to rationally tune the separation performance of a single MOF by manipulating the stepwise activation made possible by the MOF's biporous nature.

Copper nanospikes (Cu) were introduced as fillers to Pebax MH 1657 (Pebax) matrix to enhance the CO2 separation performance in mixed matrix membranes (MMMs). The polymer chains were wound on copper nanospikes with high aspect ratios, further increasing the mechanical strength of the MMMs. Pebax-Cu MMMs exhibit higher tensile strength and Young's modulus compared to pure Pebax membranes. The Young's modulus of Pebax-Cu MMMs filled with 5 wt % (Pebax-Cu-5 MMMs) was 145 MPa in the tensile test, an increase of 170.5% over the pure Pebax membrane. The addition of copper nanospike to MMMs improves the membrane's affinity for CO2. Furthermore, the copper nanospikes with a high aspect ratio in the membrane matrix tend to align horizontally, enhancing the diffusion route of gas molecules and improving membrane selectivity. As a result, the Pebax-Cu-5 MMMs had the best gas separation performance, with a CO2 permeability of 487 Barrer and CO2/CH4 separation factor of 41. [ABSTRACT FROM AUTHOR]

As one of the gas separation membranes, the thin-film nanocomposite (TFN) membrane can effectively reduce gas transport resistance and improve gas permeance. However, due to the high mobility of the chain in the thin film, it is still a great challenge to realize the TFN membrane with stable separation performance. In this work, we report a less destructive and efficient cross-linking strategy based on metal-ion coordination to improve the stability of the TFN membrane for CO2/CH4 separation. The selective layer is made of carboxylated polyimide as a matrix and UiO-66 nanoparticles (diameters of ∼50 nm) as fillers. By simply immersing TFN membranes in Cu-(NO3)2 solution, coordination bonds are successfully constructed between Cu2+ and carboxyl groups (−COOH). The cross-linked TFN membranes exhibit high CO2/CH4 selectivity of up to 29–35 with CO2 permeance of 110–350 GPU, outperforming most previously reported membranes. Moreover, the plasticization pressure of the cross-linked membranes improves from 0.3–0.9 to 0.9–1.5 MPa, higher than most reported asymmetric and hollow fiber membranes. In the CO2/CH4 (50:50 v/v) mixed-gas permeation tests, the cross-linked membranes retain constant CO2/CH4 selectivity at 23.9–25.2 with increasing mixed-gas feed pressure. The cross-linked membranes also demonstrate stable CO2/CH4 selectivity in the range of 27.2–31.2 within 100 h of testing time under a 1.0 MPa CO2 partial pressure. [ABSTRACT FROM AUTHOR]

• A stable and cost-effective MOF was prepared for benchmark CO 2 capture. • High CO 2 capacity with record CO 2 /N 2 and CO 2 /CH 4 selectivity was achieved. • Impressive CO 2 capacity of 2.60 mmol/g in CO 2 /N 2 breakthrough experiments. • MOF beads were granulated with high MOF loading and retained separation performance. The design of porous materials for CO 2 capture from flue gas and natural gas is highly demanded. However, it is challenging to target materials that combine high CO 2 capacity and CO 2 selectivity. In this work, we report a robust metal–organic framework (MOF) Zn-ox-mtz with one dimensional channels and narrow windows for excellent CO 2 capture from CO 2 /N 2 (simulated flue gas) and CO 2 /CH 4 (simulated natural gas) with high selectivity. Zn-ox-mtz exhibits a high CO 2 capacity (58.0 STP cm3 g−1 at 15 kPa), excellent CO 2 /N 2 (15/85, S > 106) and CO 2 /CH 4 (50/50, S > 105) selectivity and good chemical stability. In addition, the practical separation performance is demonstrated by breakthrough experiments under various process conditions. A efficient separation is achieved with the impressive CO 2 capacity of 2.60 ± 0.12 mmol g−1 at 298 K. Importantly, the outstanding performance is sustained under high humidity. The molecular sieving mechanism investigated by theoretical calculations indicated that CO 2 with small molecular size is tightly trapped by multiple C = O···H-C hydrogen bonding and O = C···O forces in the cavity while CH 4 and N 2 with larger molecular size display overlarge energy barrier to cross the contract pore windows. Moreover, the granulation of Zn-ox-mtz by hydroxypropyl cellulose is realized with high MOF loading (93.8 %) and the granulated Zn-ox-mtz beads retained the excellent CO 2 /N 2 and CO 2 /CH 4 separation performance. [ABSTRACT FROM AUTHOR]

• Hexagonal Co-fa nanoplates were simply synthesized without the addition of any modifier. • Defect-free MMMs were fabricated by embedding HG-Co-fa nanoplates in 6FDA-DAM at a maximum loading of 10 wt%. • MMMs simultaneously enhanced CO 2 permeability (56% up) and CO 2 /CH 4 selectivity (27% up) breaking the 2008 trade-off line. Plate-like or sheet-like porous materials with nanometer thickness have been considered as the preferred fillers to improve mixed-matrix membranes (MMMs)-based separation. Herein, hexagonal Co-fa (HG-Co-fa) nanoplates were simply synthesized without the addition of any modifier and used as fillers to construct 6FDA-DAM-based MMMs for efficient CO 2 /CH 4 separation. HG-Co-fa nanoplates exhibit high dispersion and interface compatibility in 6FDA-DAM matrix. The results demonstrated that the CO 2 /CH 4 separation performance of 6FDA-DAM was obviously improved after the incorporation of HG-Co-fa nanoplates. The resultant MMMs with nanoplate loading of 10 wt% showed CO 2 /CH 4 selectivity of 27 and CO 2 permeability of 1419 Barrer at 25 ℃ and 0.2 MPa, surpassing 2008 Robeson upper bound. Meanwhile, the high lattice integrity and structural stability of HG-Co-fa nanoplates contribute to the excellent thermal and mechanical stability of MMMs, contributing to their anti-plasticization property up to 14 bar and long-term stability up to 240 h, indicating their potential for natural gas separation. [ABSTRACT FROM AUTHOR]

Mixed-matrix membranes, which are fabricated by incorporating dispersed fillers into continuous polymers, have been considered as a promising and feasible platform for highly efficient gas separation. However, few have impurity-adapted nanochannels. Herein we present a group of mixed-matrix membranes (MMMs) incorporating a soft metal-organic framework (NTU-88c , activated NTU-88) into 6FDA-DAM. The rotation of the pyridyl rings of the ligands in NTU-88c creates a nanochannel with an aperture size of 3.4 Å, which falls between the kinetic parameters of CO 2 (3.3 Å) and CH 4 (3.8 Å). The membrane shows enhanced CO 2 permeability (1140 Barrer) at 60 °C, accompanied by a good separation factor of 45. In addition, an increase in feed gas pressure 1.0 MPa (25 °C) resulted in a notable enhancement in CO 2 permeability (645 Barrer), accompanied by a high CO 2 /CH 4 separation factor (41). More importantly, the MMM has demonstrated durable and stable CO 2 /CH 4 separation performance in long-term test, exceeding the Robeson upper-bound, suggesting a promising potential for natural gas purification. Moving forward, the findings of this work not only demonstrate the importance of porous fillers that have impurity-adapted nanochannels for membrane separation, but also offer a route to design and construct high-performance MMMs for feasible applications. [Display omitted] • Mixed-matrix membranes were prepared with a soft MOF having a CO 2 -adapted nanochannel. • The CO 2 -adapted nanochannel was confirmed by gas-loaded X-ray diffraction analysis and modelling calculations. • The separation performance of the MMM with NTU-88 was sharply enhanced at a relatively high pressure and temperature. • The CO 2 /CH 4 separation performance of this MMM exceeds the Robeson upper-bound. [ABSTRACT FROM AUTHOR]

Towards natural gas purification, polymeric membranes generally face challenges of trade-off between permeability and selectivity, as well as CO 2 -induced plasticization effect. Previous works demonstrated that incorporating high-performing nanofillers and crosslinking the polymers are effective methods to overcome these two issues, respectively. In this work, we aimed to simultaneously improve permeability, selectivity and plasticization resistance of polymeric membranes by incorporating surface-engineered nanoporous fillers for CO 2 /CH 4 separation. DD3R zeolite nanoparticles with high purity were synthesized and then surface-functionalized by 3-aminopropyl trimethoxysilane (APTMS) to serve as the filler. Mixed-gas permeation measurements showed that DD3R zeolites offered CO 2 -selective channels in 6FDA-DAM polyimide based on molecular sieving effect of zeolitic aperture. 30 wt% DD3R-APTMS zeolite imparted the membrane with CO 2 permeability of 1661 Barrer (increased by 71.7%) and CO 2 /CH 4 selectivity of 28.0 (increased by 44.5%), which was beyond the upper-bound of polymeric membranes. Meanwhile, the hydrogen bond interaction between amino groups on APTMS and carboxyl groups on 6FDA-DAM rendered the resulting DD3R-APTMS MMMs highly enhanced plasticization resistance over 40 bar when equimolar CO 2 /CH 4 mixture as the feed. This work demonstrates a facile approach to simultaneously enhance separation performance and mitigate the plasticization effect. [Display omitted] • High-purity DD3R zeolite are prepared by tuning ADA amount in synthesis solution. • Well-defined zeolitic pores improve CO 2 permeability and CO 2 /CH 4 selectivity. • Hydrogen interaction enhances separation performance and plasticization resistance. [ABSTRACT FROM AUTHOR]

The separation of carbon dioxide and methane is vital for biogas upgradation and natural gas sweetening applications. Membrane separation is one of the techniques used for CO2 and CH4 separation for biogas upgradation and natural gas sweetening owing to its energy efficiency, low capital cost, portable, and ease of operation. Polymer membranes and inorganic membranes have a trade-off relationship between permeability and selectivity. A new class of membranes known as Mixed Matrix Membranes (MMMs) is being explored to overcome this trade-off by dispersing inorganic fillers in the polymer matrix. However, the addition of filler poses new interfacial morphological difficulties, such as poor dispersion, very strong interaction between filler and polymer, and formation of voids. These challenges can be tackled by suitable choice of filler and polymer, functionalization of filler and polymer, polymer blending. The hybrid membranes separation process or use of two or more strategies can lead to the formation of defect-free membranes with improved separation performance. In this review article, we provide a concise literature review and analysis of the strategies for improving the transport properties of MMMs based on MOF as filter materials for CO2/CH4 separation. [ABSTRACT FROM AUTHOR]

The present study aims at evaluating the suitability of producing activated carbons (ACs) derived from wheat straw by a one-step synthesis approach, as an alternative to more conventional two steps production processes (i.e., pyrolysis and subsequent activation). The performance of the produced ACs, in one or two steps, as sustainable and selective CO 2 adsorbents for CH 4 /CO 2 separation is compared. In addition, the influence of pyrolysis conditions on the properties of the resulting two-step ACs is carefully analyzed. We show that the biochar-based precursors of ACs presenting the best textural properties were obtained under mild conditions of maximum temperature and absolute pressure during pyrolysis. The one-step ACs were fully comparable —in terms of textural properties as well as CO 2 uptake and selectivity— to those produced by the more conventional two-step synthesis process. In addition, results obtained from breakthrough curve simulations highlight that the best AC in terms of CH 4 recovery under dynamic conditions was produced by a one-step activation. Therefore, the one-step process appears to be as an attractive route for the production of engineered carbon materials, which can lead to significant cost savings in large-scale production systems. [Display omitted] [ABSTRACT FROM AUTHOR]

A catalyst-free Schiff base reaction was applied to synthesize two imine-linked covalent organic frameworks (COFs). The condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) with 4,4′-biphenyldicarboxaldehyde led to the structure of HHU-COF-1 (HHU = Heinrich-Heine University). The fluorinated analog HHU-COF-2 was obtained with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarboxaldehyde. Solid-state NMR, infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis confirmed the successful formation of the two network structures. The crystalline materials are characterized by high Brunauer–Emmett–Teller surface areas of 2352 m2/g for HHU-COF-1 and 1356 m2/g for HHU-COF-2. The products of a larger-scale synthesis were applied to prepare mixed-matrix membranes (MMMs) with the polymer Matrimid. CO2/CH4 permeation tests revealed a moderate increase in CO2 permeability at constant selectivity for HHU-COF-1 as a dispersed phase, whereas application of the fluorinated COF led to a CO2/CH4 selectivity increase from 42 for the pure Matrimid membrane to 51 for 8 wt% of HHU-COF-2 and a permeability increase from 6.8 to 13.0 Barrer for the 24 wt% MMM. [ABSTRACT FROM AUTHOR]

CO2 separation from raw natural gas can be achieved through the use of the promising membrane-based technology. Polymeric membranes are a known method for separating CO2 but suffer from trade-offs between its permeability and selectivity. Therefore, through the use of mixed matrix membranes (MMMs) which utilizes inorganic or hybrid fillers such as metal-organic frameworks (MOFs) in polymeric matrix, the permeability and selectivity trade-off can be overcome and possibly surpass the Robeson Upper Bounds. In this study, various types of MOFs are explored in terms of its structure and properties such as thermal and chemical stability. Next, the use of amine and non-amine functionalized MOFs in MMMs development are compared in order to investigate the effects of amine functionalization on the membrane gas separation performance for flat sheet and hollow fiber configurations as reported in the literature. Moreover, the gas transport properties and various challenges faced by hollow fiber mixed matrix membranes (HFMMMs) are discussed. In addition, the utilization of amine functionalization MOF for mitigating the challenges faced is included. Finally, the future directions of amine-functionalized MOF HFMMMs are discussed for the fields of CO2 separation. [ABSTRACT FROM AUTHOR]

Membrane separation is a promising alternative for gas purification. Facilitated transport (FT) membranes, with reversible reactions to promote CO2 transport, can simultaneously obtain high CO2 permeability and selectivity of CO2 over other gases, such as CH4, making FT membranes particularly interesting for CO2/CH4 separation. An overview of the state-of-the-art FT membranes used for CO2/CH4 separation is desired for the R&D of industrial membrane applications. This paper has reviewed the development progress and advances in various FT membranes for CO2/CH4 separation, including mobile carrier FT membranes, fixed site carrier FT membranes, and mixed matrix FT membranes. Over 100 different kinds of membrane materials with over 500 gas separation data have been summarized with performance data collected and analyzed. Perspectives of FT membranes for CO2/CH4 separation are also proposed. [ABSTRACT FROM AUTHOR]

Membrane separation is a promising alternative for gas purification. Facilitated transport (FT) membranes, with reversible reactions to promote CO2 transport, can simultaneously obtain high CO2 permeability and selectivity of CO2 over other gases, such as CH4, making FT membranes particularly interesting for CO2/CH4 separation. An overview of the state-of-the-art FT membranes used for CO2/CH4 separation is desired for the R&D of industrial membrane applications. This paper has reviewed the development progress and advances in various FT membranes for CO2/CH4 separation, including mobile carrier FT membranes, fixed site carrier FT membranes, and mixed matrix FT membranes. Over 100 different kinds of membrane materials with over 500 gas separation data have been summarized with performance data collected and analyzed. Perspectives of FT membranes for CO2/CH4 separation are also proposed.

The increase in the global population has caused an increment in energy demand, and therefore, energy production has to be maximized through various means including the burning of natural gas. However, the purification of natural gas has caused CO2 levels to increase. Hollow fiber membranes offer advantages over other carbon capture technologies mainly due to their large surface-to-volume ratio, smaller footprint, and higher energy efficiency. In this work, hollow fiber mixed matrix membranes (HFMMMs) were fabricated by utilizing cellulose triacetate (CTA) as the polymer and amine-functionalized metal-organic framework (NH2-MIL-125(Ti)) as the filler for CO2 and CH4 gas permeation. CTA and NH2-MIL-125(Ti) are known for exhibiting a high affinity towards CO2. In addition, the utilization of these components as membrane materials for CO2 and CH4 gas permeation is hardly found in the literature. In this work, NH2-MIL-125(Ti)/CTA HFMMMs were spun by varying the air gap ranging from 1 cm to 7 cm. The filler dispersion, crystallinity, and functional groups of the fabricated HFMMMs were examined using EDX mapping, SEM, XRD, and FTIR. From the gas permeation testing, it was found that the NH2-MIL-125(Ti)/CTA HFMMM spun at an air gap of 1 cm demonstrated a CO2/CH4 ideal gas selectivity of 6.87 and a CO2 permeability of 26.46 GPU.

[Display omitted] • Enhanced surface area and pore size of halloysite nanotubes (HNTs). • Successful nanocomposite membranes preparation using the modified HNTs (mHNTs). • 10 wt.% mHNTs loaded Pebax membrane enhanced CO 2 permeability by 46.7%. • Pebax membrane CO 2 /CH 4 selectivity increased by 2 folds at mHNTs 10 wt.% loading. In this study, halloysite nanotubes (HNTs) filler particles were treated in a basic solution with a pH of 11 for their better dispersion during incorporation in Pebax-1657 matrix by 1, 2, 5, 10, 15 wt.% loadings to prepare some HNTs-Pebax nanocomposite membranes. The treated HNTs were evaluated by XRD analysis and the prepared nanocomposite membranes were characterized by DSC, TGA, and FESEM analysis. Treatment of the HNTs in basic solution increased their porosity, pore volume, and specific surface area. CO 2 adsorption capacity of the raw and the modified HNTs were measured as 45.7 and 48 mol/kg adsorbent and those of CH 4 were evaluated as 34.6 and 32.4 mol/kg adsorbent, respectively. Gas permeation performance of the neat Pebax-1657 and the modified HNTs-Pebax nanocomposite membranes were investigated for CO 2 /CH 4 separation. The 10 wt.% loaded raw HNTs membrane's CO 2 permeability and ideal CO 2 /CH 4 selectivity increased to 132.1 Barrer and 18.6 from those for the neat Pebax as 98.4 Barrer and 13.6 while those of 10 wt.% loaded modified HNTs were measured as 144.4 Barrer and 27.2, respectively. The modified HNTs-Pebax nanocomposite membranes' separation performance considerably approached the Robeson upper bound limit of 2008. [ABSTRACT FROM AUTHOR]

Nanocomposite membranes were prepared using Pebax 1657, glycerol triacetate (GTA), and alumina nanotubes (ANTs) by solution casting method. Hydrothermally synthesized ANTs were characterized using SEM, FTIR, and XRD, and additional analysis of FESEM and DSC was also performed on the prepared membranes. ANTs loadings and employed solvent type, dimethylformamide (DMF) or ethanol/water mixture, impacts were investigated on CO2 permeability and ideal CO2/CH4 selectivity of the nanocomposite membranes. CO2 permeability of the ANTs — Pebax nanocomposite membranes was improved compared with the neat Pebax membrane. In the 4 wt% ANTs loaded nanocomposite membrane, chain packing and fractional free volume of its polymeric matrix were tuned by GTA addition (10–40 wt%) to improve the penetrants' permeability through. The Pebax membrane loaded by 4 and 40 wt% of ANTs and GTA revealed 73.75 and −4.97% changes in its CO2 permeability and ideal CO2/CH4 selectivity, respectively. Successful ANTs functionalization by 3-aminopropyltriethoxysilane agent (FC-ANTs), for their higher compatibility with the polymeric chains, was confirmed using FTIR analysis. 2 wt% FC-ANTs loaded nanocomposite membranes' ideal selectivity prepared by using DMF and ethanol/water mixture solvents improved by 5.71 and 14.7%, respectively, while their CO2 permeability decreased by 11.95 and 11.8%. [ABSTRACT FROM AUTHOR]

Cellulose acetate, some polyimides and polysulfones are mainly used in commercial membranes for gas separation processes. Although these polymers meet the desired combination of properties, the design of novel polymers possessing improved permeability and/or separation selectivity of gases could lead to enhanced gas separation efficiency and minimized energy costs. Here, we report gas permeability data of two isomeric vinyl-addition polymers derived from available ester-functionalized norbornenes that exhibit remarkable ideal and mixed gas selectivity as well as permeability for industrially important pairs of gases (CO 2 with N 2 and CH 4). In particular, polynorbornene bearing acetoxy side groups (AcPNB) demonstrated carbon dioxide permeability of 270 Barrer and selectivity of CO 2 /N 2 separation above 20, superposing to that of cellulose acetate (CA) in CO 2 separation performance. The polymer containing methoxycarbonyl groups (McPNB), which is an isomer of AcPNB , showed even higher separation performance for CO 2 -containing gas mixtures. Carbon dioxide permeability and selectivity of CO 2 /N 2 for McPNB exceeded 350 Barrer and 50, respectively. The data on CO 2 /N 2 separation for McPNB are on the upper bound of Robeson plot of 2008 year. Mixed gas experiments performed for binary mixtures of CO 2 with N 2 and CH 4 confirmed promising gas-separation parameters of the studied polymer, displaying attractive CO 2 /gas selectivity and CO 2 permeability. Therefore, considering the simple and cheap syntheses of these polymers and the CO 2 separation performance, they can be considered as promising candidates as selective layers for membrane gas separation processes. [Display omitted] • Polynorbornenes with acetoxy and methoxycarbonyl groups displayed high efficiency of CO 2 /gas separation with stable properties over time. • Polymer with acetoxy groups showed CO 2 permeability of 270 Barrer and selectivity of CO 2 /N 2 separation above 20. • CO 2 permeability and CO 2 /N 2 selectivity of the polymer with methoxycarbonyl groups (McPNB) exceeded 350 Barrer and 50. • The way ester groups are linked to backbones of polynorbornene has a significant impact on efficiency of CO 2 /gas separation. • Mixed-gas study of McPNB for CO 2 /N 2 and CO 2 /CH 4 gas pairs confirmed its promising CO 2 /gas separation performance. [ABSTRACT FROM AUTHOR]

The use of renewable resources to generate energy is growing, but regrettably, the large amount of CO2 emissions it releases harms the environment. The main greenhouse gas, CO2, is a major factor in global climate change, which eventually disrupts the delicate balance of ecosystems within the globe. Therefore, the development of effective and sustainable technology for CO2 capture and storage is both urgent and compelling. Among many different approaches for CO2 capture, membrane separation has shown to be one of the most promising, yielding excellent results in terms of effectiveness as well as affordability. Nonetheless, to enhance membrane performance more significantly in CO2 separation, researchers have focused on ionic liquids, a family of organic salts recognized for their high thermal stability, low volatility, and tuneable characteristics. Because of this, ionic liquids have attracted a lot of attention from the academic and industrial sectors as possible additions to enhance membranes’ capacity for CO2 separation. This study explores the potential of Tetrahexyl tetradecyl phosphonium chloride incorporated into Pebax-1657 to enhance CO2/CH4 separation performance. Ion gel membranes were synthesized with varying ionic liquid concentrations (5, 10, 20 wt%) and characterized for structural and morphological evaluations. Gas separation performance was assessed through permeation experiments, showing increased CO2/CH4 selectivity from 19.23 to 21.81 with higher IL concentrations, especially under high pressure. CO2 permeability increased from 70.01 to 273.61 barrer with the addition of 20% [THTDP][Cl]. Density functional theory calculations provided theoretical insights into the interaction energies between ionic liquid and gas molecules, corroborating experimental findings. The study demonstrates the novelty of integrating phosphonium-based ionic liquid with Pebax-1657, significantly enhancing CO2/CH4 selectivity due to strong CO2 interactions. This research offers a promising approach to developing advanced membranes for efficient and selective CO2 capture, contributing to sustainable gas separation technologies.Graphical Abstract: The use of renewable resources to generate energy is growing, but regrettably, the large amount of CO2 emissions it releases harms the environment. The main greenhouse gas, CO2, is a major factor in global climate change, which eventually disrupts the delicate balance of ecosystems within the globe. Therefore, the development of effective and sustainable technology for CO2 capture and storage is both urgent and compelling. Among many different approaches for CO2 capture, membrane separation has shown to be one of the most promising, yielding excellent results in terms of effectiveness as well as affordability. Nonetheless, to enhance membrane performance more significantly in CO2 separation, researchers have focused on ionic liquids, a family of organic salts recognized for their high thermal stability, low volatility, and tuneable characteristics. Because of this, ionic liquids have attracted a lot of attention from the academic and industrial sectors as possible additions to enhance membranes’ capacity for CO2 separation. This study explores the potential of Tetrahexyl tetradecyl phosphonium chloride incorporated into Pebax-1657 to enhance CO2/CH4 separation performance. Ion gel membranes were synthesized with varying ionic liquid concentrations (5, 10, 20 wt%) and characterized for structural and morphological evaluations. Gas separation performance was assessed through permeation experiments, showing increased CO2/CH4 selectivity from 19.23 to 21.81 with higher IL concentrations, especially under high pressure. CO2 permeability increased from 70.01 to 273.61 barrer with the addition of 20% [THTDP][Cl]. Density functional theory calculations provided theoretical insights into the interaction energies between ionic liquid and gas molecules, corroborating experimental findings. The study demonstrates the novelty of integrating phosphonium-based ionic liquid with Pebax-1657, significantly enhancing CO2/CH4 selectivity due to strong CO2 interactions. This research offers a promising approach to developing advanced membranes for efficient and selective CO2 capture, contributing to sustainable gas separation technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • A gradiently nanofiber performs interconnected sieve ultramicropores and mesopores. • The in-situ escape of the coordinated zinc on nanofiber creates funnel-type channel. • The PCF-800 realizes superior selectivity of CO 2 /CH 4 and fast kinetic of CO 2 capturing. • Impressive practical dynamic separation performance keeps after multiple cycles. Adsorption-based capture of carbon dioxide (CO 2) to upgrade natural gas offer a promising solution for energy crisis and the reduction of CO 2 emission. However, trade-off between high adsorption selectivity and rapid kinetic is an inherent shortcoming of size-sieving based adsorptive separation of gas molecules at similar sizes, hindering the launch of sieving adsorbent for practical challenging selective gas capture. Herein, a gradiently porous carbon nanofiber PCF-800 with interconnected sieving ultramicropores and low-proportion surficial mesopores is tailor-made to simultaneously realize the exclusive and rapid capture of CO 2 from CH 4. Arising from the unique interconnected micro-mesoporous structure, the as-prepared PCF-800 not only achieves remarkable uptake ratio of 45 (298 K, 1 bar) for CO 2 /CH 4 separation via size-sieving effect but also shows fast kinetic with diffusion rate of 1.35 × 10-3 s−1, outperforming the conventional ultramicroporous counterpart. Moreover, the impressive dynamic CO 2 /CH 4 separation factor up to 21.7 and satisfying cycling durability revealed by the breakthrough experiments further imply the industrial potential of PCF-800 in practical CH 4 purification. This work may shed light on the design of gradient sieving carbonaceous adsorbent with high selectivity and fast kinetic for extensive high-performance small gas separation. [ABSTRACT FROM AUTHOR]

In the present study, the permeabilities of CO2 and CH4 in terms of ideal and actual CO2/CH4 selectivity were investigated through the synthesized membranes of poly (ether-block-amide) (Pebax 1657) accompanied with poly (ethylene glycol) (PEG 400) and NH2-MIL125 nanoparticles. NH2-MIL125 nanofillers were added to the blend of PEG 400 and Pebax 1657 at various weight fractions to fabricate polymeric nanocomposite membranes. Several analyses such as the crystalline structure of the synthesized membranes, field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD) were utilized to investigate the cross-sectional and surface morphology of the membranes; the formation of the chemical bonds was identified by Fourier transform infrared (FTIR). This study presents the permeation of both pure and mixed gases ofmethane and carbon dioxide through Pebax 1657, Pebax/PEG blend, and the Pebax/PEG/NH2-MIL125 nanocomposite membranes in a pressure range of 2-8 bar and at ambient temperature. The findings demonstrated that the synthesized nanocomposite membranes had a positive effect on the separation performance in comparison with the membranes made of neat polymer and polymer blends.

Alternative materials are needed to tackle the sustainability of membrane fabrication in light of the circular economy, so that membrane technology keeps playing a role as sustainable technology in CO2 separation processes. In this work, chitosan (CS)-based mixed matrix thin layers have been coated onto commercial polyethersulfone (PES) supports. The CS matrix was loaded by non-toxic 1-Ethyl-3-methylimidazolium acetate ionic liquid (IL) and/or laminar nanoporous AM-4 and UZAR-S3 silicates prepared without costly organic surfactants to improve CO2 permselectivity and mechanical robustness. The CO2/CH4 separation behavior of these membranes was evaluated experimentally at different feed gas composition (CO2/CH4 feed mixture from 20:80 to 70:30%), covering different separation applications associated with this separation. A cross-flow membrane cell model built using Aspen Custom Modeler was used to validate the process performance and relate the membrane properties with the target objectives of CO2 and CH4 recovery and purity in the permeate and retentate streams, respectively. The purely organic IL-CS and mixed matrix AM-4:IL-CS composite membranes showed the most promising results in terms of CO2 and CH4 purity and recovery. This is correlated with their higher hydrophilicity and CO2 adsorption and lower swelling degree, i.e., mechanical robustness, than UZAR-S3 loaded composite membranes. The purity and recovery of the 10 wt.% AM-4:IL-CS/PES composite membrane were close or even surpassed those of the hydrophobic commercial membrane used as reference. This work provides scope for membranes fabricated from renewable or biodegradable polymers and non-toxic fillers that show at least comparable CO2/CH4 separation as existing membranes, as well as the simultaneous feedback on membrane development by the simultaneous correlation of the process requirements with the membrane properties to achieve those process targets.

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO2/CH4 separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO2 permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

Poly(amide‐6‐b‐ethylene oxide)(PEBA) mixed matrix membranes (MMMs) containing different metal‐organic frameworks (MOFs) of CuBTC, ZIF‐8, and ZIF‐67 have been dip‐coated on asymmetric PAN supports. To optimize the ideal skin‐layer parameters, MOF loadings of 5, 15, 25, and 35 wt% were applied. The synthesized MOFs and MMMs were structurally characterized using X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), and field emission scanning electron microscopy (FESEM). The average sizes of the synthesized ZIF‐8, ZIF‐67, and CuBTC have been determined about 100, 400, and 60–500 nm, respectively. Permeability tests of the MMMs performed using 12‐bar feed streams of pure CO2, CH4, and N2, showed 200–338% enhancements of CO2 permeability and up to a 43% increase in CO2/CH4 selectivity relative to the neat PEBA membrane. The membrane performances were also examined by the mixed gas feeds of CO2:CH4 (10:90). © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Mixed-matrix gas separation membranes were prepared by embedding various content of halloysite nanotubes (HNTs) (0, 0.5, 1, 1.5, and 2 wt%) within poly (ether-block-amide) matrix. XRD, FT-IR, TGA, and SEM analyses were conducted to study crystal structure, chemical bonds changes, thermal resistance, and cross-sectional morphology of the resultant membranes, respectively. Permeability values of pure CH4 and CO2 gases through the synthesized neat and mixed-matrix membranes (MMMs) were experimentally determined at constant temperature (25 °C) and several pressures (4, 6, 8, and 10 bar). The obtained results exhibited improved CO2 permeability of the MMMs comparing with the pristine Pebax membrane. As an example, at a pressure of 4 bar, raising the incorporated HNTs loading from 0 to 2 wt% enhanced the permeability of CO2 from 76.50 to 101.23 Barrer. [ABSTRACT FROM AUTHOR]

In this work, we introduced COFInformatics, a computational approach merging molecular simulations and machine learning (ML) algorithms, to evaluate all synthesized and hypothetical covalent organic frameworks (COFs) for the CO 2 /CH 4 mixture separation under four different adsorption-based processes: pressure swing adsorption (PSA), vacuum swing adsorption (VSA), temperature swing adsorption (TSA), and pressure-temperature swing adsorption (PTSA). We first extracted structural, chemical, energy-based, and graph-based molecular fingerprint features of every single COF structure in the very large COF space, consisting of nearly 70,000 materials, and then performed grand canonical Monte Carlo simulations to calculate the CO 2 /CH 4 mixture adsorption properties of 7540 COFs. These features and simulation results were used to develop ML models that accurately and rapidly predict CO 2 /CH 4 mixture adsorption and separation properties of all 68,614 COFs. The most efficient separation process and the best adsorbent candidates among the entire COF spectrum were identified and analyzed in detail to reveal the most important molecular features that lead to high-performance adsorbents. Our results showed that (i) many hypoCOFs outperform synthesized COFs by achieving higher CO 2 /CH 4 selectivities; (ii) the top COF adsorbents consist of narrow pores and linkers comprising aromatic, triazine, and halogen groups; and (iii) PTSA is the most efficient process to use COF adsorbents for natural gas purification. We believe that COFInformatics promises to expedite the evaluation of COF adsorbents for CO 2 /CH 4 separation, thereby circumventing the extensive, time- and resource-intensive molecular simulations.

Zeolite 5A with particle sizes of 100 nm and 1 μm were synthesized and leveraged as filler materials in carbon molecular sieve membranes (CMSMs) using Matrimid® 5218 as the polymeric precursor. Our results show that nanosized zeolite 5A fillers are capable of creating substantially improved CO2 and O2 permeability as compared to the large-sized zeolite 5A at 1 μm, owing to an increase in interfacial surface areas between the filler and carbon matrix. Accordingly, the mixed-matrix CMSMs with 20 wt% loading of nanosized zeolite 5A at 100 nm demonstrated up to 2 orders of magnitude higher permeability than the unfilled CMSM, which not only compensated for the marginal drop in membrane selectivity (between 34 to 41%), but also resulted in performances that transcend the 2008 Robeson upper bound for CO2/CH4 separation. From a different perspective, the effectiveness of the fillers at different loadings was also confirmed using a filler enhancement index, Findex, which is a new composite rating that accounts for both permeability and selectivity enhancements. Our evaluations showed that nanosized zeolite 5A fillers at 100 nm are indeed more competent than the large-sized zeolite 5A crystals in improving the separation performances of the mixed-matrix CMSMs. Essentially, nanosizing filler materials for mixed-matrix CMSMs is a straightforward and effective strategy to elevate separation performances of CMSMs, making this approach highly relevant for biogas (CO2/CH4) and air (O2/N2) separations.

In this work, we have modified a synthesized Y-type zeolite (Si/Al = 2.5), with three different amines to investigate of the influence of adsorbent’s surface modification on CO2 selectivity over CH4. The pristine and amine-functionalized NaY zeolites were characterized by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared (FT-IR), and N2 adsorption. The results showed that the structure of zeolite was preserved after amine modification. The adsorption capacity of CO2 and CH4 on these adsorbents was measured by the volumetric method at 298 K and 348 K. In comparison to CH4, CO2 was preferentially adsorbed on these adsorbents. the results demonstrated that incorporation of amines into zeolites structure improved significantly the selectivity towards carbon dioxide so that the optimal selectivity of CO2 over CH4 reached to 4.04 on zeolite modified with 2-methylaminoethanol at 348 K. Chemical interaction between adsorbate and sorbents as well as the steric effects were assessed to be the main reasons of high selective adsorption of carbon dioxide on amine-functionalized zeolites. Two of the most common adsorption models, the Langmuir and Sips isotherms, were used to correlate the experimental data of CO2 adsorption on the adsorbents The results revealed that the amine-functionalized NaY zeolites could be a good sorbent for use in flue and natural gas separation processes.

Some 1-alkyl-3-methylimidazolium-based ionic liquids were synthesized, characterized, and immobilized on membranes to form supported ionic liquid membranes. The supported ionic liquid membranes were characterized by SEM. The initial transmembrane pressures were investigated for each type of impregnated membrane. The CO2/CH4 single gas and mixed gas permeability (CO2 and CH4) have been investigated. The results showed that the CO2/CH4 ideal selectivities and mixed gas selectivities reached 15.45 – 23.9 and 13.91 – 22.82, respectively (equivalent to separation yields of 93.3 – 95.98 %).mThe 1-alkyl-3-methylimidazolium acetate impregnated membrane leads to a slightly lowermCO2/CH4 selectivity, however, this ionic liquid is stable, free of halogen and has a low price. The impregnated membranes prepared from polyvinylidene fluoride are more stablemthan those from polyethersulfone support, and have a higher affinity for CO2 compared to other gas. The obtained high CO2/CH4 selectivities indicate that immobilized membranes can be used for CO2 separation processes.

Incorporation of inorganic fillers into Polysulfone (PSF) to constitute mixed matrix membranes (MMMs) has become a viable solution to prevail over limitations of the pristine materials in natural gas sweetening process. Nevertheless, preparation of MMMs without defects and empirical investigation of membrane that exhibits characteristic of improved CO2/CH4 separation performance at experimental scale are difficult that require prior knowledge on compatibility between the filler and polymer. A computational framework has been conducted to construct validated PSF based MMMs using silica (SiO2) as inorganic fillers. It is known that nanosized SiO2 can coexist in varying polymorph configurations (ie, α‐Quartz, α‐Cristobalite, α‐Tridymite) but molecular simulation study of SiO2 polymorphs to form MMMs is limited. Therefore, this work is a pioneering study to elucidate feasibility in facile utilization of polymorphs to improve gas separation performance of MMMs. Physical properties and gas transport behavior of the simulated PSF based MMMs with different SiO2 polymorphs and loadings have been elucidated. The optimal MMM has been found to be PSF/25 wt% α‐Cristobalite at 55°C. The success in molecular simulation has shed light on how computational tools can provide understandings at molecular level to elucidate compatibility between varying pristine materials to MMMs for natural gas processing. [ABSTRACT FROM AUTHOR]