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BACKGROUND Copper‐benzene‐1, 3, 5‐tricarboxylic acid (CuBTC) is a pre‐eminent member of the metal–organic framework material family with excellent CO2 adsorption capacity and size‐sieving characteristics for CO2/methane (CH4) separation. Although a few reports have addressed the use of micro‐sized CuBTC particles in mixed matrix membranes (MMMs), the application of nano‐sized particles has not yet been explored. RESULTS: Micro‐sized and nano‐sized CuBTC particles were synthesized by Cu(NO3)2·3H2O and Cu(OH)2 precursors, respectively. Mixed matrix membranes composed of 5–35 wt% CuBTC in poly (amide‐6‐b‐ethylene oxide) (PEBA) were fabricated to investigate the CO2/CH4 separation performance of the samples. Synthesized particles and membranes were characterized by X‐ray diffraction, Fourier transform infrared and field emission scanning electron microscopy techniques. Membrane separation performance was determined at different pressures of pure CO2, CH4 and N2. At 35 wt% loading of nano‐sized CuBTC, CO2 permeability and CO2/CH4 selectivity were enhanced to 178.9 Barrer and 34.6; 80.3% and 13.8% higher than those of pristine polymer, respectively. The corresponding results for micro‐sized CuBTC were 138.9 Barrer and 33.9. A mixed gas permeation test carried out on a mixture of CO2‐CH4 (10:90 mol%) at 12 bar showed the best separation performance at 25 wt% loading of nano‐sized CuBTC with CO2 permeability of 92.6 Barrer and CO2/CH4 selectivity of 23.1. CONCLUSION: Filler size had a great impact on the MMM separation performance. As a result of the nano‐sizing of CuBTC particles, higher CO2 permeability and CO2/CH4 selectivity could be obtained because of the uniform dispersion of the filler in the matrix and higher interface area/volume. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

• Different loadings of NH 2 -MIL-125 (Ti) nanofillers incorporated into 6FDA-based polyimide for fabrication of mixed matrix membranes. • Resultant membranes were characterized by using different characterization tools including XRD, BET, FESEM, EDX, TGA and FFV. • Incorporation of the amine-functionalized MIL-125 (Ti) nanofillers enhanced the membranes performances significantly. This work reported on the fabrication of mixed matrix membranes by incorporating NH 2 -MIL-125 (Ti) nanofiller into 6FDA–durene polymer matrix for CO 2 /CH 4 separation. The structural properties and morphology of the nanofillers and resultant membranes were investigated by X-ray diffraction, Brunauer Emmett and Teller, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy mapping, thermogravimetric analysis and free fractional volume. The results showed that the CO 2 and CH 4 single gas permeability, as well as CO 2 /CH 4 ideal selectivity were improved by incorporating NH 2 -MIL-125 (Ti) into the polymer matrix. Membrane loaded with 7.0 wt% of NH 2 -MIL-125 (Ti) filler showed the highest CO 2 permeability of 1115.70 Barrer and CO 2 /CH 4 selectivity of 37.10, surpassing the 2008 Robeson upper bound. Furthermore, improvement of CO 2 permeability of 119% and increment of 331% for gas pair selectivity in comparison with pure membrane were achieved. The results obtained in this work is due to the high porosity of nanofillers besides the attraction of amine functional group towards CO 2. Overall, incorporation of amine-functionalized MIL-125 (Ti) nanofillers into 6FDA–durene polymer matrix has enhanced the separation performance of the membrane in CO 2 /CH 4 separation. [ABSTRACT FROM AUTHOR]

The production of biomethane from the biogas purification process depends on the capacity of the separation technique employed to separate methane from carbon dioxide. Mixed matrix membranes (MMMs) combine the benefits of polymeric and inorganic materials, and it is believed that the trade-off between gas permeability and selectivity in polymeric membranes can be hampered by MMMs. Until recently, the development of MMMs for the biogas purification process has been constrained in lab scales. To be applied in large scales, the increase in gas permeability as well as the membrane performance under the influence of CO2 plasticization needs to be investigated. This paper reports the evaluation of gas permeability and CO2/CH4 gas separation performances of nano zeolitic imidazolate framework (ZIF)-8/Pebax-1657 to be used for biogas purification processes. In addition, the study on the CO2 plasticization behavior of MMMs fabricated with co-polymer Pebax was investigated. The incorporation of nanoZIF-8 particles inhibited the increase of CO2 permeability due to the reduced polymer flexibility. In addition, the diffusional selectivity of ZIF-8 improves the permeation behavior of both gases through MMMs. With nanoZIF-8/Pebax-1657 MMMs, the incorporation of particles improves the gas permeability with a slight decrease in gas selectivity, indicating a potentiality of the membranes used for biogas purification processes. [ABSTRACT FROM AUTHOR]

SAPO-34 molecular sieves have a high adsorption capacity in separation of CO2 from CO2/CH4 mixture. In this study, SAPO-34 was modified by different solutions at various operating conditions to enhance the removal of carbon dioxide from the methane gas. Modifications can change pore size and also Si/Al ratio in SAPO-34 and make changes in the acidity of the adsorbent via the ion exchange process. The effects of temperature and pressure on the separation were studied using the design of experiments. Finally, based on the results of the experimental optimization process applying central composite design (CCD) method, the highest yield of CO2 separation from the methane gas (95%) was obtained when using P-SAPO-34 sample at 17.4°C and 4.6 bar. [ABSTRACT FROM AUTHOR]

The exquisite combination of heterometallic [TbIIIMnII(CO2)3(H2O)2] clusters with the hexacarboxylate ligand of H6TDP generates one water-stable 3D heterometallic TbIII/MnII-organic framework material {TbMn-(HTDP)-(H2O)2]·5DMF·4H2O}n (NUC-3; H6TDP = 2,4,6-tri-(2′,4′-dicarboxyphenyl)-pyridine), which consists of functionalized noninterspersed opening nanochannels shaped by six rows of [TbIIIMnII(CO2)3(H2O)2] clusters. Based on the single-component sorption measurements, activated NUC-3 framework exhibits effective CO2/CH4 separation associated with high uptake and moderate adsorption enthalpy of CO2. Dynamic breakthrough experiments reveal that NUC-3 could be competent for the separation of CO2/CH4 (50:50, v:v) mixture. Moreover, the kinetic and equilibrium experiments of iodine adsorption indicate that NUC-3 possess excellent adsorption capacity for iodine molecules in cyclohexane solution. The excellent structural stability and functional internal surface makes NUC-3 a prospective adsorbent for practical CO2/CH4 separation and adsorption elimination of iodine molecules, opening up the insight of heterometallic MOFs for pratical application. [ABSTRACT FROM AUTHOR]

Silica (SiO2) nanoparticles were first functionalized using (3-aminopropyl) triethoxysilane (APTES) and then utilized as filler for the preparation of poly (ether-block-amide) (Pebax®-1074) based mixed-matrix membranes (MMMs). To characterize the modified nanoparticles and the prepared membranes, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were conducted. The influences of the pure and amine-modified nanoparticles content, and feed temperature and pressure on CO2 and CH4 permeability and ideal CO2/CH4 selectivity values of the membranes were studied. The permeation experiments exhibited that the incorporation of 12.5 wt% of amine-functionalized SiO2 nanoparticles into the Pebax matrix raises the CO2 permeability and ideal CO2/CH4 selectivity about 100 and 32%, respectively. [ABSTRACT FROM AUTHOR]

• Gas permeation through a polymeric hollow fibres membrane for CO 2 -containing mixtures. • Effect of the humidity of the feed stream on permeation of CO 2 , and CH 4. • CH 4 recovery. Membrane gas separation is more and more gaining room of application in biogas upgrading to biomethane to be directly fed to pipelines. The water vapour contained in the biogas stream affects the separation performance of membranes; therefore, it is important to consider this aspect for the design of the separation stage. In this work, we developed performance maps taking into account the water vapour effect on the performance of a membrane gas separation by considering different CO 2 /CH 4 selectivities (from 25 to 100), pressure ratio and flow rate/membrane area ratio. The presence of water vapour induced significant changes in membrane performance, with consequent repercussions in CH 4 recovery, which in some cases, reduced from 85.3% to 80.9% from dry to wet conditions. [ABSTRACT FROM AUTHOR]

• α,ω-Dihydroxypolydimethylsiloxane (PDMS) was successfully coated on the surface of SAPO-34 membrane. • Coating solution concentration and viscosity were critical for forming protective layer. • The SAPO-34 membrane was affected by water vapor in CO 2 /CH 4 mixture. • The PDMS/SAPO-34 membrane showed an improved CO 2 /CH 4 separation and stability under wet condition. The excellent performance of SAPO-34 membranes for CO 2 /CH 4 separation is detracted by the water interaction, resulting in membrane instability and low durability. Herein, a new facile coating strategy using α, ω-dihydroxypolydimethylsiloxane (PDMS) has been developed for surface protection of SAPO-34 membranes by dip-coating. The fabrication of coating layer was optimized by finely tailoring the coating solution parameters, such as the viscosity and PDMS concentration. The developed membranes were evaluated under dry and wet CO 2 /CH 4 mixture systems with effect of temperature and pressure. PDMS/SAPO-34 membrane could provide high separation performance in both systems. The separation selectivity of 68 and CO 2 permeance of 1.41 × 10−7 mol m−2 s−1 Pa−1 was achieved for wet mixture of CO 2 /CH 4 at 80 °C during 120 h continuous operation. Furthermore, the PDMS/SAPO-34 membrane showed a wonderful performance after half a year storage, with 5–8% changes of CO 2 permeance and selectivity for the dry CO 2 /CH 4 mixtures, while for un-modified SAPO-34 membrane, a decline of 71% in CO 2 permeance and 85% in CO 2 /CH 4 separation selectivity was observed. The results demonstrated that the PDMS-coated SAPO-34 membrane could be a promising candidate for natural gas purification. [ABSTRACT FROM AUTHOR]

[Display omitted] • In situ ion activation method for the preparation of porous carbon spheres IE-HC. • The formation of 'knot-like' structures of polymer chains within the membrane increases the mechanical properties. • Interconnected ultra-micropores for excellent CO 2 /CH 4 separation performance. • Pore structure control provides a strategy for gas membrane separation. Herein, ion-exchanged porous carbon (IE-HC) with uniform and interconnected ultra-microporous was prepared using the in situ ion activation method. Then, the IE-HC was doped into Pebax to prepare mixed matrix membranes (MMMs). Notably, the IE-HC is uniformly dispersed in the membrane matrix and the polymer chains form a 'knot-like' structure, resulting in considerably enhanced mechanical properties of the MMMs. The interconnected, uniform ultra-microporous structure creates multi-dimensional diffusion channels for gas diffusion. Meanwhile, the filler IE-HC builds tortuous paths within the membrane, and the functional groups on its surface improve the selectivity for CO 2 gas. When the loading amount of the IE-HC is 7 wt%, the separation performance of the membrane reaches its optimal level. The CO 2 permeability and selectivity of MMMs are 211.2% and 158.0%, respectively, higher than those of pure Pebax. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOFs UiO-66 and MOF-808 synthesized sustainably via microwave-assisted method. • DMF replaced by water and acetone for reducing environmental impact. • MOFs incorporated up to 10 wt% in PIM-1 matrix for mixed matrix membranes (MMMs). • PIM-1/MOF MMMs exhibit enhanced CO 2 /CH 4 separation. • Physical aging showed a significant impact on CO 2 /CH 4 separation performance. This study presents a sustainable microwave-assisted synthesis, based on the use of acetone and a water/acetic acid mixture instead of typical harmful DMF, to fabricate Zr-metal–organic frameworks (MOFs) UiO-66 and MOF-808 as fillers in a PIM-1 matrix for gas separation application. The mixed matrix membranes (MMMs) were prepared with varying loadings (2.5–10 wt%) of MOFs. The physicochemical properties (1H NMR, FTIR, XRD, N 2 adsorption, TGA and SEM) of the resulting PIM-1, MOFs and MMMs were analyzed. The CO 2 /CH 4 separation performance and membrane aging characteristics of the MMMs were evaluated. The incorporation of MOF fillers significantly improved CO 2 permeability and CO 2 /CH 4 selectivity, attributed to their CO 2 -philicity and narrow pore size (UiO-66 ≈ 0.6 nm and MOF-808 ≈ 1.8 nm). The MMMs with higher filler loadings (7.5 and 10 wt%) exhibited the most favorable separation performance. Due to the better crystallinity and textural properties, MOF-808 produced the best separation results at 10 wt% filler loading (a CO 2 /CH 4 separation selectivity of 16.2 at 9090 Barrer of CO 2 permeability). Aging led to a decrease in CO 2 permeability but a slight increase in CO 2 /CH 4 selectivity for all MMMs. Overall, the study highlights the potential of PIM-1/UiO-66 and PIM-1/MOF-808 MMMs as efficient materials for (CO 2 /CH 4) separation comparing with the pristine PIM-1. [ABSTRACT FROM AUTHOR]

Gas separation properties are reported for self-standing polymer of intrinsic microporosity (PIM) films after addition of palladium (II) acetate or iron (II) acetate by solid state or liquid state mixing. Membranes, with thicknesses in the range 35–55 μm, were prepared from three high molar mass PIMs, two different branched versions of the much-reported PIM-1 (PIM-1a and PIM-1b) and of PIM-Py. Addition of either Fe(OAc) 2 or Pd(OAc) 2 to all three PIMs led to a reduction in permeability and increase in selectivity, but the permeability reduction was much greater for Pd(OAc) 2 , which is able to interact with branch points in the PIM and crosslink the polymer. CO 2 /CH 4 selectivity of membranes containing Pd(OAc) 2 was poor upon aging, especially after solid state addition to the PIM-1 polymers, for which CO 2 permeabilities dropped to below 200 Barrer after 85 days. Hydrogen permeability and H 2 /N 2 selectivity of membranes containing Pd(OAc) 2 did more closely follow conventional permeability/selectivity trade off upon aging. This illustrates the profound differences that can arise in gas permeation properties and aging behaviour from variations in chemical structure and macromolecular characteristics, and from the addition of metal acetates that interact with the polymer in different ways. [Display omitted] • Branched PIM-1 crosslinked with Pd(OAc) 2 produced membranes with reduced permeability. • Loss in CO 2 permeability on aging not matched with increase in CO 2 /CH 4 selectivity. • Loss in H 2 permeability on aging matched with increase in H 2 /N 2 selectivity. • Crosslinks block smaller free volume elements that dominate CO 2 /CH 4 selectivity. • Fe(OAc) 2 mixed PIM-1 membranes maintain permeability/selectivity balance. [ABSTRACT FROM AUTHOR]

• Dispersing LDH in PEBAX® 1657 films have enhanced CO 2 separation performance. • Dispersing LDH in PEBAX® has enhanced its mechanical properties and thermal stability. • CO 2 facilitated transport mechanism is dominated by the anion content in LDH gallery. The effect of incorporating layered double hydroxide (LDH) nanoparticles containing different molar ratios of metals on the thermal, mechanical, and gas permeation properties of membranes based on PEBAX® was evaluated. The three nanoparticles were synthesized using molar x -ratios (x = Al/(Mg + Al)) equal to 0.20, 0.25 and 0.33. The dispersed nanoparticles changed thermal resistance, improved mechanical properties and CO 2 /CH 4 separation performance of MMM when compared to the membranes of neat PEBAX®. The addition of 2 % of LDH in PEBAX® 1657 promoted an increase of about 17 % in the elastic modulus and 10 % in the stress at break. The best result of permeation tests (1657–0.33–5 % MMM at 0.5 bar), shows increase CO 2 permeability by 44 % and CO 2 /CH 4 selectivity by 115 % as compared to the neat material. Gas permeation results showed that LDH with more anions favors the facilitated transport of CO 2. [ABSTRACT FROM AUTHOR]

Processes, such as biogas upgrading and natural gas sweetening, make CO2/CH4 separation an environmentally relevant and current topic. One way to overcome this separation issue is the application of membranes. An increase in separation efficiency can be achieved by applying mixed-matrix membranes, in which filler materials are introduced into polymer matrices. In this work, we report the covalent triazine framework CTF-biphenyl as filler material in a matrix of the glassy polyimide Matrimid®. MMMs with 8, 16, and 24 wt% of the filler material are applied for CO2/CH4 mixed-gas separation measurements. With a CTF-biphenyl loading of only 16 wt%, the CO2 permeability is more than doubled compared to the pure polymer membrane, while maintaining the high CO2/CH4 selectivity of Matrimid®.

Membrane technologies as conservative approaches have absorbed much attention in chemical and petroleum engineering, recently. The current research presents the preparation of effectively mixed matrix membranes (MMMs) using polyether-block-amide (Pebax-1657) as a polymeric matrix and zinc oxide (ZnO) nanoparticles with various contents (0.0, 2.5, 5.0, 7.5, and 10.0 wt%) as a filler. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and field emission scanning microscopy (FESEM) were conducted to characterize the prepared membranes. The membrane performance was evaluated by caring out permeation experiments of the CO2 and CH4 at a pressure of 3 bar and temperature of 30 °C. Based on the obtained results, the CO2 permeability and ideal CO2/CH4 selectivity increased about 13 and 21%, respectively at 10.0 wt% loading of ZnO in the polymer matrix. [ABSTRACT FROM AUTHOR]

• TiNT-TEPA was synthesized as filler particles for blended Pebax/PEG600 nanocomposite membrane based on DOE and RSM methods. • Adsorption capacity of as-synthesized and functionalized nanotubes investigated. • Nanocomposite membranes' CO 2 permeability and CO 2 /CH 4 selectivity considerably increased compared with neat membrane. • Effect of operating temperature and transmembrane pressure were studied for single and mixed gases. Raw and tetraethylene pentamine (TEPA) functionalized titanium oxide nanotubes (TiNTs) were used as filler particles to prepare nanocomposite membranes. Polyethylene glycol (PEG) was blended with the Pebax-1657 as matrix and incorporated by TiNT-TEPA to prepare Pebax-1657/PEG/TiNT-TEPA nanocomposite membranes based on Response Surface and Central Composite Design methods of experimental design. The TiNT-TEPA and the Pebax/PEG/TiNT-TEPA were characterized using TEM, FESEM, SEM, FTIR or ATR-FTIR, XRD (EDS) and mechanical strength analysis. CO 2 adsorption capacity of TiNTs and TiNT-TEPA-70% were found as 0.71 and 4.2 mmol/g, respectively. CO 2 permeability and ideal selectivity of optimum (in term of separation performance) membrane, as Pebax (7 wt.%) /PEG (7.5 wt.%)/TiNT-TEPA (3 wt.%), were increased by 67.7 and 11.7%, respectively, compared with the neat Pebax membrane. The optimum membrane's CO 2 permeability and CO 2 /CH 4 ideal selectivity were investigated at operating temperatures of 20–45 °C and reveled 18.5 and −9% changes, respectively. Its transmembrane pressures increment form 4 to 10 bar for single and CO 2 (50)/CH 4 (50) mixed gas resulted in CO 2 permeability and CO 2 /CH 4 ideal selectivity enhancements by 19 and 20%, respectively. The optimum membranes' mixed gas separation performance were found lower than that of single pure gases at the same operating condition. [ABSTRACT FROM AUTHOR]

• Cryogenic distillation process of CO 2 /CH 4 separation is adopted to upgrade biogas. • New technique is developed to mitigate CO 2 freeze-out in the distillation column. • With avoiding freezing, CH 4 purity is enhanced from 60 to 97.2% by only one column. • High-purity liquid CO 2 (>99%) is also generated on merit as a valuable by-product. • The system showed promising energy and cost efficiency against traditional methods. In this paper, ideas for improving the cryogenic separation of CO 2 /CH 4 mixture are drawn in order to upgrade biogas to biomethane, matching natural gas standards. On this basis, a novel technique is developed to mitigate CO 2 freeze-out, which was a crucial obstacle upon implementing cryogenic approaches. In the proposed process, four-stage compression, one distillation column combined with flash separator, and sufficient heat recovery are adopted. The process is simulated in ASPEN HYSYS. The thermodynamic framework is validated against experimental data. Additionally, to reveal the efficacy of the added modifications, different configurations are modeled, starting from the simple system to the proposed one. The operating conditions – distillation pressure, reflux ratio, feed tray location, and inlet composition – are optimized towards minimizing energy demand and diminishing frosting danger. With avoiding frosting presence, the suggested process can boost CH 4 purity from 60% up to 97.2% (mol), which has not been reached before in any previous studies using only one column, suitable for commercial uses. Also, a valuable by-product of high-purity liquid CO 2 (above 99%) can be generated rather than being emitted into air. Compared to former cryogenic systems, the present process achieves not only the highest CH 4 purity (97.2%) – even higher than previous study utilized two columns – but also the least energy penalty (0.38 kWh/Nm3cleaned_gas). Another comparison held against conventional approaches, the proposed process stands among the highest in CH 4 and CO 2 purities generated, witnesses the lowest in methane loss, is among the least in energy consumption, and shows high competitiveness in investment cost. [ABSTRACT FROM AUTHOR]

Membranes have attracted much attention as economical methods for industrial chemical processes. The effects of the titanium dioxide nanoparticle load on the morphology and CO2/CH4 separation performance of poly (ether-block-amide) (PEBAX-1657) mixed matrix membranes (MMMs) were investigated from pressures of 3–12 bar and temperatures of 30°C–60°C. The PEBAX membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, atomic force microscopy and tensile strength analysis. The incorporation of TiO2 nanoparticles into the polymeric MMMs improved the CO2/CH4 gas separation performance (both the permeability and selectivity) of the membranes. The CO2 permeability and ideal CO2/CH4 selectivity values of the nanocomposite membrane loaded with 8 wt-% TiO2 were 172.32 Barrer and 24.79, respectively whereas those of the neat membrane were 129.87 Barrer and 21.39, respectively. [ABSTRACT FROM AUTHOR]

BACKGROUND Biogas is an alternative renewable energy produced by anaerobic digestion of various organic wastes mainly from agriculture, households and biomass and food industries. Typically, raw biogas consists of 50–70% methane (CH4), 30–50% carbon dioxide (CO2), and small amounts of hydrogen sulfide (H2S) and water vapour. Purifying biogas by removing CO2 and other trace impurities is required in order to achieve higher calorific value, safe operation and to meet fuel standards. As CO2 is the second largest component of biogas, this study focused on its removal from CH4. RESULTS: Composite membranes of blended PEG 400/Pebax 1657 polymer and graphene oxide (GO) were developed for CO2/CH4 gas separation. The effects of GO loading and PEG 400 addition on CO2/CH4 separation performance were investigated. Optimal loadings of 0.25 wt% GO and 50 wt% PEG 400 obtained the best membrane performance with 12.4 GPU of CO2 permeance and 14 of CO2/CH4 separation factor. CONCLUSION: Incorporating GO to the polymer membrane enhanced CO2/CH4 separation, whereas PEG 400 addition increased CO2 permeance. The advantages from each component led to an enhancement of CO2 permeance and CO2/CH4 separation. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Ultra-thin MFI zeolite membranes with different Si/Al ratios (152, 47 and 26) were prepared on graded α-alumina supports in the presence of organic template molecules and evaluated for separation of equimolar CO 2 /CH 4 mixtures at temperatures from 315 to 249 K. The thicknesses of all membranes were less than 500 nm and permporometry showed that the number and size of defects were low for the two membranes with the highest Si/Al ratio (152 and 47). The membrane with the lowest Si/Al ratio (26) also had low amounts of defects in the mesopore range, but did have a few macropore defects. All membranes showed very high CO 2 permeances in the entire temperature range studied and the permeances increased with increasing temperature. The CO 2 permances were also correlated to the Si/Al ratio of the membranes. The higher permeances was observed for membranes with higher Si/Al ratio. The highest observed CO 2 permeance was 142 × 10−7 mol s−1 m−2 Pa−1 at room temperature for the membrane with Si/Al = 152. The separation factor, on the other hand, increased with decreasing temperature for the two membranes with the highest Si/Al ratio (152 and 47), but for the membrane with a Si/Al ratio of 26, the separation factor went through a maximum at ca. 270 K. The highest separation factor observed was 7.1 at 249 K for the membrane with Si/Al = 47. These observations are consistent with an adsorption controlled separation mechanism. Image 1 • MFI membranes with different Si/Al ratios were prepared by using organic template. • The defects distributions for different membranes were evaluated and analysed. • Very high CO 2 premance was obtained for separation of equimolar CO 2 /CH 4 mixture. • The separation factors and CO 2 permances are correlated to the Si/Al ratios. [ABSTRACT FROM AUTHOR]

In this research, mixed matrix membranes (MMMs) composed of poly(ether-block-amide) (PebaxⓇ-1074) and silica (SiO2) were prepared. Silica nanoparticles were distributed uniformly in the PebaxⓇ matrix without significant agglomerations and defects at the loadings of 0.0, 2.5, 5.0, 7.5 and 10 wt.%, confirming by field emission scanning electron microscopy (FESEM). Attenuated total reflection-Fourier transfer infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA) were also carried out to identify functional groups, crystalline structure and thermal stability of the prepared membranes, respectively. The incorporation of silica nanoparticles resulted in significant improvements in CO2 permeability and consequently ideal CO2/CH4 selectivity. At 10 wt.% loading of silica nanoparticles, the MMM exhibited the best separation performance with the CO2 permeability of 105.94 Barrer and CO2/CH4 selectivity of 26.09 which are significantly higher than the neat membrane properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Pyrolyzed chitosan-based sorbents are prepared with different structural properties. • Materials are tested in the CO 2 /CH 4 adsorption-separation showing CO 2 selectivity. • Supercritical CO 2 dried samples show the best CO 2 adsorption and selectivity profiles. • The best material is suitable to adsorb pure carbon dioxide. Abstract Chitosan is a biopolymer obtained by deacetylation of chitin extracted from sub-products of the food industry and it is rich in nitrogen content. Pyrolyzed chitosan– and chitosan-periodic mesoporous organosilica (PMO)– based porous materials with different pore structures and chemical features are prepared using different dry methods and ensuing pyrolysis at 800 °C, for application in the CO 2 /CH 4 adsorption/separation. The highest CO 2 adsorption capacity (1.37 mol·kg−1 at 100 kPa; 1.9 mol·kg−1 at 500 kPa) and the best selectivity for CO 2 /CH 4 separation (95 at 500 kPa) is obtained using 1.5% (m/v) of chitosan solution dried under supercritical CO 2. This material combines a good CO 2 adsorption capacity with one of the highest selectivities for CO 2 /CH 4 separation of the literature, arising as a promising alternative adsorbent for natural gas or biogas upgrading at reduced cost. The presence of high nitrogen content together with pores of diameter around 2 nm leads to an increase of the CO 2 adsorption capacity. In the case of chitosan-PMO-based materials, the activation step using both acid and crushing methods is crucial to increase the CO 2 adsorbed amount. Here, the highest CO 2 adsorption capacity and the highest selectivity are obtained by the chitosan-PMO crushed adsorbent and the chitosan-PMO material activated with sulfuric acid, respectively. These observations indicate the importance of the controlled attack of the material surface to enhance the diffusion of the target gases within the adsorbent, avoiding the adsorption of other species. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) comprised of organic selective polymers and inorganic nano‐particles under the name of fillers have attracted much attention in the field of gas separation. In this study, poly (amide‐6‐b‐ethylene oxide) [PEBA]/Fe2O3 mixed matrix membranes were prepared using the dry phase separation technique with ethanol / water (70/30 wt%) as solvent. Various amount of Fe2O3 nanoparticles were chosen to disperse within the polymer matrix (0, 0.5, 1, 1.5 and 2 wt% of polymer). To prepare this type of novel membrane, a magnetic field of 0.3 T was used to align the position of NPs. The structural properties and surface morphology of prepared membranes were characterized by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Field emission scanning electron microscopy analysis was also used to study the physical bonding. Phase identification and crystallinity, effective area, and distribution of pore size were investigated by X‐ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analysis. Carbon dioxide permeability through these membranes increased with pressure in the range of 2 to 14 bar. Magnetic membrane loaded with 1.5 wt% of Fe2O3 gave the best performance: CO2 permeability, CO2/CH4, and CO2/N2 selectivity were enhanced by 30, 42 and 81%, compared to a pure membrane, respectively. The results indicated that the magnetic MMMs gave better separation performance than pure membranes. Molecular simulation has also been used to investigate the structural and transport properties of fabricated membranes. Structural characterizations like radial distribution function (RDF), fractional free volume (FFV), and X‐ray diffraction were applied to the simulated membrane cells. Grand canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations, were used to calculate the selectivity and diffusivity of membranes. Results from experimental tests and simulation runs revealed that the selectivity and permeability of fabricated and simulated membranes are consistent. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highly permeable, selective, and stable asymmetric membranes are required to replace the traditional separation approaches for natural gas purification with higher energy efficiency and smaller footprints. Herein, we report on the design and engineering of defect‐free asymmetric hollow fiber membranes with a thin dense skin and highly porous substrate to effectively deal with aggressive natural gas. A crosslinkable polymer with rigid molecular structure and high molecular weight was synthesized for developing spinning dope with desirable solution properties. Phase separation behavior of the polymer was carefully controlled by systematic formulation of the dope composition and optimizing spinning conditions, thereby realizing simultaneously tuning dense skins and porous substrates of the spun asymmetric hollow fiber membranes. The crosslinked hollow fiber membrane, with well‐preserved delicate asymmetric nanostructures, exhibited unprecedentedly high and stable separation performance for long‐term processing extremely aggressive CO2/CH4 mixtures (with pressure up to 820 psi containing C6+ hydrocarbons), thereby showing great potential for practical application of natural gas purification. This work offers a new platform to create hollow fiber membranes with both high permeance and plasticization resistance in natural gas service. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1269–1280, 2019 [ABSTRACT FROM AUTHOR]

Abstract The physicochemical properties of filler materials are critical considerations influencing the separation performances of mixed-matrix membranes (MMMs). Herein, a three-dimensional covalent organic framework (3D-COF) with a secondary amine-containing backbone was designed to offer large surface area, high porosity and good affinity toward CO 2 molecules. Membranes prepared from this 3D-COF filler and a 6FDA-DAM polyimide matrix demonstrated a more significant enhancement in the CO 2 /CH 4 separation performance, which was unattainable by its 2D-COF analogue. Specifically, with 10 and 15 wt% loadings of 3D-COF fillers, the MMMs membranes were able to enhance the CO 2 permeability by ~57% and 140%, respectively, at a comparable, if not better, CO 2 /CH 4 selectivity than the unfilled membrane. Furthermore, glassy polymers of high fractional free volume such as 6FDA-DAM tend to suffer from a ubiquitous loss in performance over time due to a physical aging effect. In this regard, the 3D-COF was effective in slowing down the aging process by capitalizing on its high surface area and amine functional groups to immobilize and rigidify the 6FDA-DAM polymer chains, preventing the collapse of the free volume. This allows 97% of the initial membrane performances to be effectively retained after 240 days of aging. Our findings suggest the potential of morphologically-tuned COFs to develop high-performance MMMs with strong practical relevance. Graphical abstract fx1 Highlights • A 3D covalent organic framework filler was synthesized using a Schiff-base reaction. • High morphologically induced surface area, porosity and affinity toward CO 2 molecules. • The 3D-COF was paired with 6FDA-DAM polymer to give mixed-matrix membranes. • Mixed-matrix membranes showed performances beyond the 2008 Robeson upper bound. • The 3D-COF retarded aging by retaining 97% of the initial performance after 240 days. [ABSTRACT FROM AUTHOR]

Abstract Membrane technology has aroused great attention for gas separations due to its high energy efficiency, small capital investment, easy and continuous operation. Mixed matrix membranes (MMMs) constructed from a continuous polymer phase and a dispersed filler phase offer new opportunities to achieve a breakthrough in fabricating high-performance membranes. Metal–organic frameworks (MOFs) have been regarded as potential fillers to boost the MMM separation performance. However, MOFs occasionally exhibit limited compatibility with the polymer matrixes owing to their partially inorganic structure and tendency of agglomeration in the membranes. Here, an interfacial design strategy is demonstrated by coating size-selective MOF cores with covalent organic framework (COF) layers to construct MOF@COF hybrids as fillers in MMMs for enhanced polymer-filler compatibility. The pure organic COF layers exhibit high affinity to the polymer matrix, thereby preventing the formation of nonselective interfacial voids and alleviating filler agglomeration. With the incorporation of only 5 wt% of MOF@COF fillers, the resultant MMM exhibits 48% and 79% enhancements in CO 2 permeability and CO 2 /CH 4 selectivity, respectively, with better operational stability compared to that of the pure polymeric membrane. These results reveal a novel filler design strategy for the tailored synthesis of high-performance MMMs for natural gas and biogas purification. Graphical abstract fx1 Highlights • A novel MOF@COF hybrid was successfully prepared and explored as a promising membrane filler in polysulfone matrix. • The COF coating layer can largely improve the polymer-filler interfacial compatibility in MOF@COF-based MMMs. • A simultaneous increase in CO 2 permeability and CO 2 /CH 4 selectivity has been achieved in MOF@COF-based MMMs. [ABSTRACT FROM AUTHOR]

Abstract CHA zeolite (chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of chabazite crystals and membranes were investigated. Highly crystalline chabazite and uniform chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO 2 , N 2 and CH 4 permeances and mixed gas separations in CO 2 /N 2 and CO 2 /CH 4 binary mixtures through chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO 2 /N 2 and CO 2 /CH 4 separation selectivities as high as 16 and 46 together with CO 2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO 2 /N 2 and CO 2 /CH 4 binary mixtures, respectively. The CO 2 /N 2 and CO 2 /CH 4 selectivities lost only 11% and 15%, and CO 2 permeances lost only 18% and 20% in equimolar wet CO 2 /N 2 and CO 2 /CH 4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K. Graphical abstract fx1 Highlights • Tubular CHA zeolite (chabazite) membranes were prepared from the OSDA-free gel. • The Cs and F ions played important roles on chabazite crystal and membrane growth. • OSDA-free chabazite membranes had highly CO 2 -selective in CO 2 /CH 4 and CO 2 /N 2 mixtures. • This membrane showed good stabilities in long-term operations and under humid conditions. [ABSTRACT FROM AUTHOR]

Abstract One of the major limitations in mixed matrix membrane (MMM) development is difficulty in achieving homogenous filler dispersion in polymer continuous phase. In the past, fillers are often functionalized to improve their dispersion properties in polymer matrix. However, this method is laborious and could deteriorate the intrinsic properties of the native filler particles. Instead of functionalizing the filler, a technique of integrating hybrid fillers for dispersion enhancement is attempted in this work. Accordingly, two different carbonaceous nanofillers, namely carbon nanofiber (CNF) and graphene oxide (GO) were synergistically incorporated into glassy polymer to synthesize a novel MMM for CO 2 /CH 4 separation. The collegial effect of combining two nanofillers was found to render homogenous filler dispersion quality especially at 2 wt% CNF/3 wt% GO (2C/3G) and 3 wt% CNF/2 wt% GO (3C/2G) filler loadings. The CNF particles dispersed between GO nanosheets and inhibited the restacking of GO, whilst the strong steric effect imposed by GO nanosheets improved the dispersion of CNF particles in the polymer matrix. Upon the addition of hybrid fillers, thermal and mechanical properties of MMMs were enhanced. The optimum gas separation performance was found at 2C/3G filler loading with CO 2 /CH 4 selectivity of 59.70 and CO 2 permeability of 62.32 Barrer. This revealed a notable enhancement of 712% and 23% in CO 2 /CH 4 selectivity and CO 2 permeability, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Improved SSZ-13 membrane was prepared using asymmetric support. • Separations in CO 2 /CH 4 and N 2 /CH 4 mixtures were studied. • The effect of water vapor was investigated. • Single gas permeances were modeled. Abstract High-quality SSZ-13 membranes were synthesized on 200 nm asymmetric α-alumina supports via a single hydrothermal secondary growth. Single CO 2 , N 2 and CH 4 permeances and mixed gas separations in CO 2 /CH 4 and N 2 /CH 4 binary mixtures through SSZ-13 membranes were measured. Synthesis conditions such as membrane substrate, gel composition and membrane calcination were modified. The best SSZ-13 membrane displayed N 2 and CO 2 permeance as high as 8.9 × 10−8 mol/(m2 s Pa) and 5.6 × 10−7 mol/(m2 s Pa) and N 2 /CH 4 and CO 2 /CH 4 selectivities of 10 and 56.5 for equimolar N 2 /CH 4 and CO 2 /CH 4 gas mixtures at 298 K and 0.2 MPa feed pressure, respectively. Nitrogen permeance of current SSZ-13 membrane in the mixture was 3.7 times higher than that of our previous SSZ-13 membrane. The membrane synthesis was reproducible. Temperature and pressure dependences of separation performance in the two binary mixtures were also discussed. Single CO 2 , N 2 and CH 4 permeances dependent of pressure were predicted by the Maxwell–Stefan diffusion model and the predicted values were fitted well with the measured ones. The stability of SSZ-13 membrane in the wet mixture was investigated. The current SSZ-13 membrane has excellent potentials for CO 2 and N 2 removals from natural gas. [ABSTRACT FROM AUTHOR]

Abstract Carbon molecular sieve (CMS) membranes are a promising candidate for natural gas processing due to their peculiar pore structure-induced excellent separation performance. Formulating ultrathin, defect-free CMS hollow fiber membranes is, however, still challenging due to damage on porous sub-structures induced by thermal relaxation of polymer chains during pyrolysis. Herein, we report a new methodology enabling high separation performance and good plasticization resistance in CMS fiber membranes by uniform integration of double-stranded polysilsesquioxanes into the polyimide matrix. Our polyimide/ladder-structured polysilsesquioxane CMS fibers substantially enhanced CO 2 permeance by as much as 546% compared to the precursor fiber analogues due to the thin molecular sieve selective layer. Also, poly(dimethylsiloxane) coating delayed physical aging, still showing a high CO 2 permeance of 354 GPU with CO 2 /CH 4 selectivity of 56 after 72 days of aging. Furthermore, they exhibited excellent plasticization resistance up to a CO 2 partial pressure of 13.2 bar with CO 2 /CH 4 separation factor of 74 for an equimolar CO 2 /CH 4 feed mixture. Graphical abstract fx1 Highlights • Homogeneous precursors of polyimide/ladder-structured polysilsesquioxane were made. • Defect-free PI/LPSQ precursor fibers were fabricated by dry-jet/wet-quench process. • LPSQ suppressed substructure collapse in carbon molecular sieve (CMS) fibers. • CMS fibers showed 546% enhancement in initial CO 2 permeance relative to precursors. • PDMS-coated CMS fibers delayed physical aging with good plasticization resistance. [ABSTRACT FROM AUTHOR]

Abstract A new UiO-66-NH 2 based MOF named UiO-66-NH 2 @ICA has been prepared by grafting imidazole-2-carbaldehyde (ICA) to UiO-66-NH 2 through a post-synthesis reaction via amine condensation. FESEM, XRD, 1H NMR, FT-IR and N 2 adsorption were used to characterize the morphology and structure of UiO-66-NH 2 @ICA. The grafted ICA mainly reduces the pore volume of UiO-66-NH 2 but increases the number of nitrogen atom as binding site of CO 2. The UiO-66-NH 2 @ICA showed less BET surface area but a higher CO 2 /CH 4 adsorption selectivity in comparison with UiO-66-NH 2. UiO-66-NH 2 @ICA and UiO-66-NH 2 crystals were dispersed in Matrimid®5218 to form mixed-matrix membranes (MMMs). Single gas permeation and mixed gas separation was carried out to investigate the effects of filler loading and feed gas pressure on the separation performances of the MMMs. The UiO-66-NH 2 @ICA/Matrimid® MMM with 10 wt % filler showed a high CO 2 /CH 4 selectivity with a separation factor of 64.7, which is an increase by 40% in comparison with UiO-66-NH 2 /Matrimid® MMM. Graphical abstract Image 1 Highlights • UiO-66-NH 2 @ICA was prepared by grafting imidazole-2-carbaldehyde (ICA) to UiO-66-NH 2. • Nitrogen atoms as CO 2 binding site increased after post-synthetic modification of UiO-66-NH 2. • UiO-66-NH 2 @ICA showed a higher CO 2 /CH 4 adsorption selectivity than UiO-66-NH 2. • UiO-66-NH 2 @ICA/Matrimid® MMMs displayed a high CO 2 /CH 4 separation selectivity. [ABSTRACT FROM AUTHOR]

Zeolitic membranes synthesized using organic structure‐directing agents (SDAs) require an activation step to remove the SDA and open their porosity. Activation is typically achieved by high‐temperature (>673 K) calcination. This process has multiple disadvantages, including coke formation due to incomplete removal of the SDA as well as the formation of cracks and other defects due to differential thermal expansion of the membrane layer and the underlying support material. Here we report that high‐performance hollow fiber membranes of the small‐pore (0.38 nm) zeolite SSZ‐13 can be produced via UV irradiation to decompose and remove the SDA. Remarkably, UV irradiation allowed complete removal of the bulky SDA (trimethyladamantylammonium hydroxide) from the pores at near‐ambient conditions, whereas membranes activated by calcination exhibited severe cracking. The UV‐activated SSZ‐13 membranes showed excellent H2/C3H8 and CO2/CH4 mixture selectivities (up to 810 and 110 whereas the conventionally activated membranes showed poor selectivity (<5). The combined demonstration of hollow fiber membrane synthesis and low‐temperature membrane activation of small‐pore zeolite membranes is a significant step in the effort to create reliable, scalable, and low‐cost fabrication processes for zeolite membranes for gas separations. Small‐pore SSZ‐13 zeolite hollow fiber membranes activated by UV irradiation show excellent separation properties, allow elimination of membrane defects caused by high‐temperature calcination, and increase the scalability of zeolite membrane fabrication for gas separation. [ABSTRACT FROM AUTHOR]

CO2 enhanced oil recovery (CO2-EOR) technology is a competitive strategy to improve oil field economic returns and reduce greenhouse gas emissions. However, the arbitrary emissions or combustion of the associated gas, which mainly consists of CO2 and CH4, will cause the aggravation of the greenhouse effect and a huge waste of resources. In this paper, the high-performance facilitated transport multilayer composite membrane for CO2/CH4 separation was prepared by individually adjusting the membrane structure of each layer. The effect of test conditions on the CO2/CH4 separation performance was systematically investigated. The membrane exhibits high CO2 permeance of 3.451 × 10−7 mol·m−2·s−1·Pa−1 and CO2/CH4 selectivity of 62 at 298 K and 0.15 MPa feed gas pressure. The cost analysis was investigated by simulating the two-stage system. When the recovery rate and purity of CH4 are 98%, the minimum specific cost of separating CO2/CH4 (45/55 vol%) can be reduced to 0.046 $·Nm−3 CH4. The excellent short-to-mid-term stability indicates the great potential of large industrial application in the CH4 recovery and CO2 reinjection from oilfield associated gas.

Polyimides (PIs) have gained recognition as highly desirable membrane materials for efficient CO 2 /CH 4 separation. However, the practical utilization of these materials has been impeded by the issue of the substantial susceptibility to plasticization when exposed to high-feed-pressure conditions. Although thermal cross-linking has been widely employed to enhance plasticization resistance in PI membranes, cross-linking will normally sacrifice CO 2 permeability. Thus, the advancement of PI membranes that exhibit both remarkable CO 2 permeability and exceptional plasticization resistance is highly desired. The current work designed a series of cross-linkable PIs with different polymer chain orientation degrees. Different from conventional PIs, by properly controlling the polymer chain orientation, the CO 2 permeability can be enhanced by 2.3 times without compromising the membrane plasticization resistance. Various techniques, including FTIR, WAXD, TGA, and DMA, were employed to thoroughly characterize the obtained membranes. These characterizations verified that optimizing the polymer chain orientation constitutes an efficacious strategy to enhance the resistance of PI membranes against plasticization, while simultaneously preserving their CO 2 permeability. Additionally, the thermally cross-linked membranes exhibited good long-term stability during an 1100-h test. [Display omitted] • The thermal cross-linking process is significantly influenced by the degree of polymer orientation. • After thermal cross-linking, the CO 2 permeability of the 6FDA-TFDB-DABA membrane increased by a factor of 2.3. • The cross-linked PI membrane demonstrated good long-term stability over 1100 h. • Polymer chain orientation degree strongly correlates to the CO 2 permeability change before and after cross-linking. [ABSTRACT FROM AUTHOR]

From the practical perspective, innovative porous carbon material is needed for gas adsorption and separation. Here, flexible porous carbon cloths are successfully prepared from viscose rayon cloth via controllable adjusted KOH activation. In order to optimize such flexible porous carbon cloths, the relationship between KOH activation condition and the porous carbon cloths property have been systematically studied. The effect factors on CO 2 capture, CO 2 /CH 4 separation and methanol adsorption have been analyzed in depth. Due to the largest narrow micropore volume (PV 1 nm), ACC-240–800 exhibits the best CO 2 uptake capacity of 4.11 mmol g−1 under ambient condition. Based on the ideal adsorbed solution theory model, the ACC-240–700 exhibits the highest selectivity of 3.73, 3.13 and 2.65 for CO 2 /CH 4 mixing proportion of 30/70, 46/60 and 50/50, respectively, at 25 °C and 1 bar, owing to the synergetic result of O&N content and PV 1 nm. The CO 2 /CH 4 separation performance on ACC-240–700 is analyzed and confirmed by Q st calculation for CO 2 and CH 4 , and dynamic breakthrough experiments with equimolar binary CO 2 /CH 4 (50/50) mixture. The determining factors on methanol adsorption is mainly the porosity structure. The best methanol adsorption uptake of 12.87 mmol g−1 is observed on ACC-240–800 at 25 °C and 95 mbar, because of the largest values of S BET , V micro and PV 1mn. The flexible porous carbon cloths provided in this work can act as effective adsorbent for carbon capture, low-quality nature gas upgrading and methanol adsorption in the industrial processes. [Display omitted] • Flexible porous carbon cloths are successfully prepared. • The condition of KOH activation is controllable adjusted. • The carbon cloths are used for carbon capture, CO 2 /CH 4 separation and methanol adsorption. • The optimization performance is systematically analyzed and cautiously discussed. [ABSTRACT FROM AUTHOR]

Membrane technology is a simple and energy-conservative separation option that is considered to be a green alternative for CO2 capture processes. However, commercially available membranes still face challenges regarding water and chemical resistance. In this study, the effect of water and organic contaminants in the feed stream on the CO2/CH4 separation performance is evaluated as a function of the hydrophilic and permselective features of the top layer of the membrane. The membranes were a commercial hydrophobic membrane with a polydimethylsiloxane (PDMS) top layer (Sulzer Chemtech) and a hydrophilic flat composite membrane with a hydrophilic [emim][ac] ionic liquid–chitosan (IL–CS) thin layer on a commercial polyethersulfone (PES) support developed in our laboratory. Both membranes were immersed in NaOH 1M solutions and washed thoroughly before characterization. The CO2 permeance was similar for both NaOH-treated membranes in the whole range of feed concentration (up to 250 GPU). The presence of water vapor and organic impurities of the feed gas largely affects the gas permeance through the hydrophobic PDMS membrane, while the behavior of the hydrophilic IL–CS/PES membranes is scarcely affected. The effects of the interaction of the contaminants in the membrane selective layer are being further evaluated.

Abstract Three 3D Cd(II) complexes, namely, {[Cd 4 (L) 2 (dioxane) 3 (H 2 O) 3 ]·DMA·5H 2 O} n (1), {[Cd 2 (L)(phen)(H 2 O) 3.5 ]·4H 2 O} n (2) and {[Cd 2 (L)(phen)(H 2 O) 4 ]·3H 2 O·DMA} n (3) have been synthesized from the ligand of 3,5-di(2′,5-dicarboxylphenyl)pyridine (H 4 L) with or without the assistance of phen auxiliary linker (phen = 1,10-phenanthroline). Complex 1 displays a 3D (4,4,9)-connected net with the point symbol of {3.45}{32.414.55.611.72.82}{45.6}. Complex 2 shows a 3D (4,8)-connected net with the point symbol of {43. 63} 2 {46.619.83}. Complex 3 presents a 3D 4-connected net with the point symbol of {43.62.8}. The fluorescence measurements showed 1 – 3 exhibit sensitive detection of Fe(III) and Cr(VI) ions with a low detection limit. In addition, the gas sorption isotherms of complex 3 for N 2 , H 2 , CO 2 and CH 4 were investigated, and the corresponding uptakes are 239.8 cm3 g−1 for N 2 and 93.9 cm3 g−1 for H 2 at 77 K, 50.5 cm3 g−1 for CO 2 and 17.0 cm3 g−1 for CH 4 at 298 K, 54.8 cm3 g−1 for CO 2 and 24.2 cm3 g−1 for CH 4 at 273 K, respectively. Based on the N 2 isotherm, the Brunauer−Emmett−Teller (BET) and Langmuir surface area of 3 were calculated to be 610.1 and 710.5 m2 g−1, respectively. Moreover, the two binary gas mixtures adsorption was also studied, indicating that the adsorption of 3 for CO 2 is better than that of CH 4 , which was verified by ideal adsorbed solution theory (IAST) with the adsorption selectivity being 8.5 (landfill gas, CO 2 /CH 4 = 0.5/0.5) and 7.2 (natural gas, CO 2 /CH 4 = 0.05/0.95). Graphical abstract Three 3D Cd(II) complexes have been synthesized from the ligand of 3,5-di(2′,5-dicarboxylphenyl)pyridine (H 4 L) with or without the assistance of phen auxiliary linker (phen = 1,10-phenanthroline). For complexes 1 – 3 , the fluorescence measurements were studied, exhibiting sensitive detection of Fe(III) and Cr(VI) ions. In addition, the gas sorption isotherms of complex 3 for N 2 , H 2 , CO 2 and CH 4 were investigated. fx1 Highlights • Three Cd(II) complexes have been constructed from 3,5-di(2′,5-dicarboxylphenyl)pyridine (H 4 L) with or without the help of phen. • In addition, luminescent properties of complexes, the adsorption behaviors and the selectivity of 3 for CO 2 /CH 4 separation were investigated. [ABSTRACT FROM AUTHOR]

This study demonstrates how incorporation of polyethylene glycol (PEG-200) into poly (ether-block-amide) (Pebax-2533) can improve the prepared membrane performance in separating CO2from CH4. Additionally, the effect of various PEG-200 loadings on CH4and CO2permeability and CO2/CH4selectivity values was investigated. The prepared membranes were examined using Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. Permeation experiments of the gasses through the neat Pebax and the blended (Pebax-2533/PEG-200) membranes were carried out at a temperature of 25 ∘C and pressure range of 2 to 10 bar. The gas permeation experiments indicated that the performance of blended membranes is better than that of the neat membrane. As an example, CO2permeability and ideal CO2/CH4selectivity values for the blended membrane with 40 wt.% of PEG-200 loading are 351.65 and 9.17 Barrer, while those values for the neat membrane are 187.54 and 7.28 Barrer, respectively. [ABSTRACT FROM AUTHOR]

Membrane processes are economical techniques which have attracted many attentions in petroleum engineering particularly in the gas separation, recently. In this study, effective mixed matrix membranes were prepared using polyether-block-amide (Pebax-1074) as base polymer and ZIF-7 nanoparticles with different loadings as fillers. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and field emission scanning microscopy (FESEM) analyses were used to characterize the synthesized nanoparticles and membranes. To investigate performance of the membranes, permeation experiments of the CO2 and CH4 through the membranes were carried out at pressure of 3 bar and temperature of 30°C. The obtained results indicated that the mixed matrix membranes have higher CO2/CH4 selectivities compared to the neat membrane. [ABSTRACT FROM AUTHOR]

Membrane processes are economical techniques which have attracted many attentions in petroleum engineering particularly in the gas separation, recently. In this study, effective mixed matrix membranes were prepared using polyether-block-amide (Pebax-1074) as base polymer and ZIF-7 nanoparticles with different loadings as fillers. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and field emission scanning microscopy (FESEM) analyses were used to characterize the synthesized nanoparticles and membranes. To investigate performance of the membranes, permeation experiments of the CO2 and CH4 through the membranes were carried out at pressure of 3 bar and temperature of 30°C. The obtained results indicated that the mixed matrix membranes have higher CO2/CH4 selectivities compared to the neat membrane. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MWCNTs were amine functionalized using Tetraethylene Pentamine (TEPA). • MWCNT-TEPA/PU nanocomposite membranes were prepared for CO 2 /CH 4 separation. • Membranes’ permeability and ideal selectivity increased by 99.8 and 9.6%, respectively. • The KJN model was used for prediction of CO 2 and CH 4 gas permeation. • The model was modified considering void formation to reduce AARE of 31.6–5.7%. Abstract In the current study, multiwall carbon nanotubes (MWCNTs) were functionalized with Tetraethylene Pentamine (TEPA) and added into polyurethane (PU) polymer matrix to prepare PU-MWCNT-TEPA nanocomposite membranes. The prepared membranes were characterized using FT-IR, XRD and SEM analysis. The analysis results showed that MWCNTs were properly functionalized with TEPA and also uniformly dispersed in polymer matrix. The CO 2 permeability increased by 99.8% at 10 wt.% loading of MWCNTs-TEPA. The nanocomposite membrane’s CO 2 /CH 4 selectivity was also increased by 9.6%. Impacts of operating pressure and temperature on the membranes’ CO 2 permeability and CO 2 /CH 4 ideal selectivity were also investigated. Finally, the gaseous penetrants permeabilities through the nanocomposite membranes were predicted using the Maxwell, the KJN, and the modified KJN models by AAREs of 31.4–35.2, 27.8–31.6, and 4.4–5.7%, respectively. [ABSTRACT FROM AUTHOR]

Membranes that are resistant to water vapor permeation have potential in natural gas sweetening by reducing the need for pretreatment. The perfluorinated polymer Teflon AF1600 has proven resistance to water vapor, which is adapted here in the form of composite membranes consisting of a Teflon AF1600 protective layer on membranes of the polyimide 4,4′-(hexafluoroisopropylidene) diphthalic anhydride 2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TMPDA) as well as Polymer of Intrinsic Micro-porosity (PIM-1). The permeability of CO2 and CH4 through the composite membranes was shown to be a function of the respective permeabilities of the individual polymer layers, with the Teflon AF1600 layer providing the majority of the resistance to mass transfer. Upon exposure to water, the composite membranes had reduced water permeation of 7–13% compared to pure membranes of 6FDA-TMPDA and PIM-1, because of the water resistance of the Teflon AF1600 layer. It was observed that water permeated as clusters through the composite structure. Under CO2-CH4 mixed gas conditions, 6FDA-TMPDA layer permselectivity performance was reduced and became comparable to Teflon AF1600, while the PIM-1 layer retained much of its high permselectivity performance. Importantly, at water activities below 0.2 the PIM-1 composite membrane achieved higher permeability for CO2 compared to water. [ABSTRACT FROM AUTHOR]

Abstract: Achieving homogeneous dispersion of nanoporous fillers within membrane architectures remains a great challenge for mixed‐matrix membrane (MMMs) technology. Imparting solution processability of nanoporous materials would help advance the development of MMMs for membrane‐based gas separations. A mechanochemically assisted oxidative coupling polymerization strategy was used to create a new family of soluble nanoporous polymer networks. The solid‐state ball‐milling method affords inherent molecular weight control over polymer growth and therefore provides unexpected solubility for the resulting nanoporous frameworks. MMM‐based CO2/CH4 separation performance was significantly accelerated by these new soluble fillers. We anticipate this facile method will facilitate new possibilities for the rational design and synthesis of soluble nanoporous polymer networks and promote their applications in membrane‐based gas separations. [ABSTRACT FROM AUTHOR]

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 CH2) 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 %). The 1-alkyl-3-methylimidazolium acetate impregnated membrane leads to a slightly lower CO2/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 stable than 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • One-step construction of integrated ionic ultra-microporous skeletons by ionic liquids. • In-situ designed functional MOFs with uniformly CO 2 affinity sites. • The CO 2 adsorption capacity of microporous materials is up to 149 cm3 g−1 at room temperature. • Efficient separation of CH 4 / CO 2 is achieved with IAST up to 22 at 298 K, 1 bar. • The synergistic effect of unsaturated Cu2+ site and functional site is analyzed theoretically. The high-efficiency capture of CO 2 from biogas by adsorption is highly desirable, which, yet faces the challenges regards of the unsatisfactory adsorption efficiency, selectivity, and regeneration performance. Herein, ionic ultramicroporous metal organic frameworks (IUM-MOFs) with high CO 2 affinity are constructed by one-step in-situ coordination strategy and used for CO 2 /CH 4 separation. The phenoxylate anion-functionalized ionic liquid (FIL) serves as competitive ligands in the formation of IUM-MOFs. The oxyl group exhibits high affinity with CO 2 as the Lewis basic center, while the rigid counterion occupies the adsorption space of CH 4 in the cavities of IUM-MOFs, thus bringing about superior CO 2 adsorption capacity of 149 cm3 g−1 (150% higher than that of Cu-BTC) and high IAST predicted selectivity with CH 4 of 22 under atmospheric condition. Mechanism analysis demonstrated that the formation of hydrogen bonds between CO 2 with coordinated IL and H 2 O and IL-enhanced polarity of MOFs benefit to the CO 2 adsorption. In addition, the IUM-MOFs could be facilely regenerated at 120 °C with favorable recycling stability. This work provides facile strategy for the rational design of IUM-MOFs and lays useful insights for structural tuning to promote their applications. [ABSTRACT FROM AUTHOR]

• Techno-economic feasibility of a chitosan-based membrane system was assessed. • CO 2 /CH 4 separation was studied from a multistage membrane process simulation. • Three separation stages were required for targets of high-quality CO 2 and CH 4. • Total costs and contribution of terms were estimated at different process scales. • The unitary total costs went down to 0.3 € (Nm3)-1 for a large plant (1000 Nm3 h−1). The use of biopolymers as membrane materials is a recent approach for reducing the environmental impact of CO 2 separation processes. By considering previous process engineering tasks, it was concluded that no membrane currently provides sufficient purity and recovery to meet the requirements for the simultaneous direct separation of CO 2 and CH 4 in a single stage. The aim of this study is to simulate and optimise the separation of CO 2 and CH 4 from different sources using a simple multistage process, considering up to three stages. A chitosan biopolymer-based composite membrane with organic (ionic liquid) and different inorganic fillers in the selective layer was used to tune the selectivity and robustness of commercially available membranes. The process configuration utilized membrane units operating in series to enrich CO 2 in the product stream from the permeate line, whereas the retentate line produced a CH 4 -enriched stream by mixing the retentate units of each stage. The target objectives were up to 95% purity and recovery of CO 2 in the permeate outlet, corresponding to a recovery of CH 4 higher than 97% in the retentate outlet stream of the multistage process. The decision variables included the permeance of each component, and thus the pair selectivity (CO 2 /CH 4) and process-related parameters, such as the stage cut of each stage. Economic evaluation of the proposed three-stage separation process was performed for different process scales, from small installations to large plants. The total costs, the contribution of each term to the total costs, and the unitary costs were estimated for each operational scale, with reference to the feed flow rate based on the plant capacity. The lowest total cost was 0.3 € (Nm3)-1 for a large plant with a flow rate of 1000 Nm3 h−1. [ABSTRACT FROM AUTHOR]