Search

Polybenzimidazole (PBI) with a strong size-sieving ability exhibits attractive H2/CO2 separation properties for blue H2 production and CO2 capture. Herein, we report that PBI can be facilely cross-linked with polycarboxylic acids, oxalic acid (OA), and trans-aconitic acid (TaA) to improve its separation performance. The acids react with the amines on the PBI chains, decreasing free volume and increasing size-sieving ability. The acid doping increases H2/CO2 selectivity from 12 to as high as 45 at 35 °C. The acid-doped samples demonstrate stable H2/CO2 separation performance when challenged with simulated syngas containing water vapor at 150 °C, which surpasses state-of-the-art polymers and Robeson's upper bound for H2/CO2 separation.

Palladium (Pd) and palladium alloy nanowires (PdM; M = Ag, Ni, Cu, Y) of varying compositions were synthesized by facile and scalable one-pot polyol reduction of metallic salts using poly(vinylpyrrolidone) (PVP) as a capping agent. Alloy nanowires with a high surface area-to-volume ratio and an interconnected network (fractal-like) morphology may provide pathways for rapid hydrogen (H2) transport through a mixed-matrix membrane (MMM) containing them. The use of PdM nanowires provides two benefits. First, incorporation of a metal like Ag, Cu, Y, or Ni into Pd at an appropriate level can increase the H2 diffusivity while reducing the use of Pd. Second, alloying can reduce Pd embrittlement and susceptibility to poisoning. Polybenzimidazole (PBI) membranes loaded with PdM nanowires were prepared and tested at 150 °C and 100 psig for mixed gas H2/CO2 separation. MMMs containing 50 mass% pure Pd nanowires and 50 mass% Pd0.75Ag0.25 alloy nanowires showed H2 permeabilities of 53 and 38 barrer, respectively, which were dramatically increased from the permeability of 25 barrer for pure PBI.

Controlling the microstructure of heterogeneous, polymer membranes used in gas barrier and gas separation technologies is challenging. Being able to control composite structures is beneficial to achieve an optimum combination of gas permeation and mechanical performance. In addition, unique properties such as anisotropy and confined transport can be controlled by tailoring the size and position of constituent materials. Two-stage reactive polymer (TSRP) networks are an emerging dual-cure polymer material for spatially varying cross-linking density via photopatterning. In this work a thiol–acrylate-based TSRP was used to investigate the effects of pattern geometry on CO₂ permeability and mechanical properties. Line and square patterns of alternating high and low cross-linking density, with characteristic dimension between 1 mm and 10 μm, were generated in TSRP membranes. Notably, synergistic enhanced barrier properties were observed for 10 μm square patterns of lower cross-linking density (or higher permeability) material exhibiting two confined dimensions compared to line gratings with only one confined dimension.

To study the relationship between crystal structures of amine-carbamates and regeneration energy consumptions, two new solid–liquid phase-changing solutions of ethylenediamine/N,N-dimethylacetamide (EDA/DMA) and ethylenediamine/N,N-dimethylformamide (EDA/DMF) were prepared to capture CO2 efficiently and regulate the crystal structures of CO2 absorption products (EDA-carbamates). The CO2 absorption capacity and peak absorption rate of EDA/DMA and EDA/DMF solutions were both 30% and 67%, respectively, higher than those of EDA/water solution. EDA-carbamates in EDA/DMA and EDA/DMF solutions had the same molecular structures but different molecular arrangements (they belonged to orthorhombic and monoclinic crystals, respectively). The regeneration heat of EDA-carbamates in EDA/DMF solution (181.28 kJ/mol) was higher than orthorhombic EDA-carbamates in EDA/DMA solution (133.76 kJ/mol), which was attributed to the endothermic process (recrystallization process) during the transition from monoclinic EDA-carbamates to orthorhombic EDA-carbamates.

To break through the permeability-selectivity trade-off in solution-diffusion membranes, novel three-dimensional hollow zeolitic imidazolate framework (ZIF) nanoparticles like open cocoons were built and then in-situ embedded in cross-linked poly(ethylene oxide) backbone by a simple one-step untraviolet polymerization. Those nanoparticles, which were evenly distributed in the polymer, acted as a “CO2 transport promoter” and developed low-resistance inner channels for CO2 Knudsen diffusion in the solution-diffusion membrane. Simultaneously, embedded nanoparticles broke the crosslinking of poly(ethylene oxide), thereby reducing the crystallinity of the polymer and then increasing the flexibility of polymer chains. Therefore, adding open-cocoon ZIF nanoparticles exponentially increased CO2 permeability with small changes in CO2/H2, CO2/CH4 and CO2/N2 selectivity. Specifically, adding 10 wt% open-cocoon ZIF nanoparticles in the polymer increased CO2 permeability by ∼190%, from ∼ 130 Barrers to ∼373 Barrers, with a 15% increase in CO2/H2 selectivity and a 10% decrease in CO2/N2 selectivity.

In order to solve the problems of deficient CO2 adsorption sites on Zn/Co zeolitic imidazolate frameworks (ZIFs), Zn/Co ZIFs were thermally treated to promote physical adsorption sites on Zn-N and Co-N bonds and then impregnated with polyethyleneimine (PEI) to promote NH and NH2 chemical adsorption sites. The CO2 adsorption capacity detected on Micromeritics ASAP 2020C increased by 53% to 1.07 mmol/g at 298 K and 1 bar, when Zn/Co ZIF was treated at optimal temperature of 450 °C to obtain the maximum Me-N2 unsaturated adsorption sites. This was because of a partial cleavage of coordination bonds between Zn N, Co N, C N and C N along with dissociation of rationally free methyl groups in the framework ligands, which was supported on density functional theory (DFT) calculation. The Zn/Co ZIF treated at 450 °C and then impregnated with 40 wt% PEI exhibited the highest CO2 adsorption capacity of 1.82 mmol/g under the condition of at 298 K and 1 bar, which was 2.6 times higher than that of raw Zn/Co ZIF. In addition, this adsorbent is proved to be regenerable and stable during 9 cycle CO2 adsorption-desorption tests, therefore, PEI- thermally treated Zn/Co ZIF exhibits a very promising application in CO2 capture from flue gas and natural gas.

Model systems are developed and investigated to better understand the effect of polyether-metal ion interactions on gas separation characteristics. These systems help answer current questions raised by the substantial body of research on metal-organic frameworks (MOFs) dispersed in polyethers to improve gas separation performance, where favorable interactions between the metal centers and polyethers are preferred to improve interfacial compatibility. Specifically, we investigate CO2/gas transport properties of supramolecular networks comprising cross-linked poly(ethylene oxide) (XLPEO) and dissociable salts, including LiClO4, Ni(BF4)2, and Cu(BF4)2. Increasing the salt content increases the glass transition temperature (Tg) and generally decreases gas diffusivity and permeability, which can be successfully described using a Tg-integrated free volume model with an expression similar to the Vogel-Tammann-Fulcher (VTF) equation. Surprisingly, low loadings of LiClO4 and Cu(BF4)2 (2 mass% or less) can increase gas permeability by 30%–70% without affecting the CO2/gas selectivity. This increase correlates with polyether-metal ion dynamics as measured by dielectric spectroscopy. Understanding how interaction-mediated dynamics affect gas transport will be instrumental to designing MOF-based mixed matrix materials for gas separations.

Amorphous polymers containing poly(ethylene oxide) are leading membrane materials for CO2 capture from fossil fuel-derived flue gas and syngas, such as those prepared from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) methyl ether acrylate (PEGMEA). This work shows that introduction of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles in these polymers increases CO2 permeability with minimal effect on CO2/H2 and CO2/N2 selectivity. Specifically, ZIF-8 nanoparticles with a size of 150–250 nm were synthesized and fabricated into mixed matrix materials (MMMs). The effect of ZIF-8 loading on gas transport properties at 35 °C in MMMs was systematically investigated. Adding 10 wt% ZIF-8 in the crosslinked PEGDA increases CO2 permeability from 130 Barrers to 320 Barrers unexpectedly by 170% without any reduction of CO2/light gas selectivity. While the CO2/light gas selectivity in the MMMs can be satisfactorily described using the Lewis-Nielsen model, the model underestimates the gas permeability. Despite a body of studies of MMMs comprising ZIFs, this work represents one of the few on the MMMs based on amorphous rubbery polymers elucidating the effect of ZIF-8 loading on the polymer properties and demonstrating their impact in achieving superior CO2/H2 and CO2/N2 separation properties.

An ionic liquid (IL) [P66614][Triz] with a low regeneration temperature was loaded on a graphene nanoplatelet (GNP) and reduced graphene oxide (RGO) to accelerate the CO2 absorption rate. High-resolution transmission electron microscopy (HRTEM) patterns showed that GNP was composed of a regular “honeycomb” lattice, but a regular lattice structure was not observed for RGO as a result of the functional group on it. The CO2 absorption capacity (63.6 mg of CO2/g of IL) and absorption peak rate (22.4 mg of CO2 g–1 of IL min–1) of IL loaded on GNP were increased by 8.2 and 72.3%, respectively, compared to those of neat IL. The supported IL performed better because [P66614][Triz] was oriented in a favorable dispersion as a result of the negative ζ potential of the GNP surface. In contrast, the CO2 absorption rate of RGO–20% IL (mass ratio of RGO/IL = 4:1) was lower than that of IL, which could be attributed to the hydrogen bond between surface oxygen functional groups and IL. 13C nuclear magnetic resonance and M...

Mesoporous molecular sieves SBA-15 with four pore structures were loaded with an ionic liquid [P66614][Triz] to adsorb CO2 from raw biohythane. The hybrid sorbents of SBA-15 loaded with [P66614][Triz] were characterized by using N2 adsorption analyzer, thermogravimetric analyzer, scanning electron microscopy, and high-resolution transmission electron microscopy. The molecular sieve SBA-15 (with the most probable pore size of 4.3 nm) loaded with 50% ionic liquid (IL), which was called SBA-15 (4.3) − 50% IL, exhibited the fastest CO2 absorption rate and the shortest equilibrium time, which was approximately one-third of the equilibrium times of the other three hybrid sorbents. An intraparticle diffusion model was used to clarify that SBA-15 (4.3) − 50% IL (with the shortest pore length of 120 nm) executed a two-stage CO2 absorption process, which reduced the CO2 absorption time. The rate constant kI in the first stage of the CO2 absorption of SBA-15 (4.3) − 50% IL was approximately four times as much as those of the other three hybrid sorbents because the cross-section area of its total pores was approximately three times higher than those of the other three hybrid sorbents. Results showed that pore length had significant effect on CO2 absorption performance.

In order to reduce energy consumption of absorbent regeneration, an amine absorbent piperazine (PZ) was dissolved in an organic solvent N, N-dimethylformamide (DMF) to prepare a phase-changing PZ/DMF solution for CO2 absorption with solid precipitate of PZ-carbamate. The CO2 absorption capacity and peak rate of PZ/DMF solution were 22.9% and 29% higher than those of PZ/water solution, respectively. Based on differential scanning calorimetry/thermogravimetry experiments, biscarbamate PZ(CO2)22− and protonation PZ(H)22+ compositions (34.5 wt%) in the PZ-carbamate precipitate mainly decomposed at peak temperature of 91.9 °C due to their instability, and then PZ(CO2) composition (65.5 wt%) in the PZ-carbamate precipitate decomposed at peak temperature of 125.7 °C. The electrochemical corrosion tests and scanning electron microscopy revealed that PZ/DMF solution had much lower corrosivity than PZ/water solution.

In order to overcome “trade-off” Robeson upper bound 2008 and simultaneously increase the CO2 permeability and selectivity of traditional poly (ethylene oxide) polymer membrane, three anion pillared hybrid ultramicroporous materials (SIFSIX-2-Cu-i, TIFSIX-2-Cu-i and GEFSIX-2-Cu-i) were incorporated into Pebax/PEGDME polymer to fabricate mixed matrix membranes (MMMs). DFT-D2 calculation revealed that the C···F distance (2.62 A) between CO2 molecule and pillared anion (GeF62-) in GEFSIX-2-Cu-i was lower than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. The synergistic effects of C···F van der Waals (vdW) interactions and O···H hydrogen bonding interactions in GEFSIX-2-Cu-i gave a higher CO2 binding energy (34.5 kJ/mol) than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. It was verified that GEFSIX-2-Cu-i with higher CO2 binding energy and specific surface area exhibited higher CO2 adsorption capacity of 5.02 mmol/g than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. These anion-pillared hybrid ultramicroporous materials with suitable porosity and surface chemistry, enabling multiple host–guest interactions, created unique Rubik’s tube-like “expressway” channels for CO2 molecule passage through the membrane. Results showed that the MMMs with 1 wt% GEFSIX-2-Cu-i nanoparticles exhibited optimal CO2 separation performance in terms of CO2 permeability (460 Barrers) and CO2/H2 (17, an increase of 12.2%), CO2/CH4 (18, an increase of 24.1%), and CO2/N2 (57, an increase of 9.6%) selectivities, as compared with the pure Pebax/PEGDME membrane. As GEFSIX-2-Cu-i loading increase from 1 to 10 wt%, the overall CO2 separation performance decrease due to the aggregation of these nanoparticles. Positron annihilation lifetime spectroscopy (PALS) experiments revealed that the fractional free volume of MMMs with 1 wt% GEFSIX-2-Cu-i nanofillers (FFV = 3.63%) was higher than those of MMMs incorporated with a higher loading (2.5–10 wt%) of GEFSIX-2-Cu-i.

Surface grafting modification was proposed to improve the surface polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane (PDMS) membrane. The initiator 3-aminopropyltriethoxysilane containing one amine group was integrated into PDMS, and polyvinyl pyrrolidone (PVP) with strong polarity was connected to the surface by reacting with amine groups. Surface grafting modification was proven on X-ray photoelectron spectroscopy. The sharp decrease (from ∼98° to ∼28°) in water contact angle of the PDMS membrane indicated the significant improvement in surface polarity after the modification. The surface roughness of the PDMS membrane increased with the modification, and the PDMS surface immersed for 40s was almost covered with PVP. The membrane immersed in PVP solution for 10s improved CO2/H2, CO2/CH4, and CO2/N2 selectivities. While CO2 permeance slightly decreased from ∼2500 GPU to ∼2440 GPU. For the separation of CO2/CH4 and CO2/N2 mixed gases, all CO2/CH4 and CO2/N2 selectivities were improved after the modification. For the separation of CO2/H2 mixed gas, CO2/H2 selectivity was improved when the immersion time was below 30 s.

Despite decades of research, metallic corrosion remains a long-standing challenge in many engineering applications. Specifically, designing a material that can resist corrosion both in abiotic as well as biotic environments remains elusive. Here a lightweight sulfur-selenium (S-Se) alloy is designed with high stiffness and ductility that can serve as an excellent corrosion-resistant coating with protection efficiency of ≈99.9% for steel in a wide range of diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7 orders of magnitude lower than bare metal in abiotic (simulated seawater and sodium sulfate solution) and biotic (sulfate-reducing bacterial medium) environments. The coating is strongly adhesive, mechanically robust, and demonstrates excellent damage/deformation recovery properties, which provide the added advantage of significantly reducing the probability of a defect being generated and sustained in the coating, thus improving its longevity. The high corrosion resistance of the alloy is attributed in diverse environments to its semicrystalline, nonporous, antimicrobial, and viscoelastic nature with superior mechanical performance, enabling it to successfully block a variety of diffusing species.

A phase-change solvent for CO2 absorption was prepared by mixing N-methyl-1,3-diaminopropane (MAPA) and N,N-dimethylformamide (DMF). In this MAPA/DMF solvent, MAPA-carbamate precipitate was formed after CO2 absorption to facilitate reducing energy consumption of amine regeneration. The CO2 uptake of MAPA/DMF solvent (14.8 mg/g solvent) was increased by 22% compared with that of MAPA/water solvent (12.1 mg/g solvent). For MAPA/DMF solvent, time was reduced by 22% to reach the CO2 absorption equilibrium. The maximum CO2 uptake rate of MAPA/DMF solvent was 30% higher than that of MAPA/water solvent because DMF displayed higher CO2 solubility and lower MAPA-carbamate solubility than water. Differential scanning calorimetry and thermogravimetry experiments revealed that MAPA(H+)2 and MAPA(CO2–)2 compositions in MAPA-carbamate precipitate first decomposed (peak temperature = 59.9 °C). Subsequently, the MAPACO2 compositions in precipitate also decomposed (peak temperature = 124.2 °C).

This study aimed to improve surface polarity of polydimethylsiloxane (PDMS) membranes and provide surface active sites which were easy to react with other chemicals. 3-Aminopropyltriethoxysilane (APTES) containing an amino group was introduced into a PDMS membrane by crosslinking to prepare polyacrylonitrile hollow fiber-supported PDMS membranes with an amino-functionalized surface. Fourier transform infrared and X-ray photoelectron spectroscopic analyses proved the existence of APTES and its amino group in the PDMS membrane. The concentration of N atoms on the PDMS membrane surface reached ∼6% when the mass ratio of APTES/PDMS oligomer in the PDMS coating solution was increased to 4/3. The water contact angle decreased from ∼114° to ∼87.5°, indicating the improved surface polarization of the PDMS membrane. The density and swelling degree of the PDMS membrane decreased and increased, respectively, with increasing APTES content in PDMS. This phenomenon increased CO 2 permeability and decreased CO 2 /H 2 selectivity, CO 2 /CH 4 selectivity, and CO 2 /N 2 selectivity. When the mass ratio of APTES/PDMS oligomer was increased from 0 to 4/3, the CO 2 permeation rate of the hollow fiber-supported PDMS membranes initially decreased from ∼2370 GPU to ∼860 GPU and then increased to ∼2000 GPU due to the change in coating solution viscosity.

To research effects of CO 2 absorption capacity and type of CO 2 absorbent on the CO 2 separation and free-volume properties of facilitated transport membranes, two types of CO 2 absorbents, namely monoethanolamine (MEA) and ionic liquids (ILs:[P 66614 ][Triz] and [P 66614 ][2-Op]), were adopted. The CO 2 absorption capacities of MEA, [P 66614 ][Triz] and [P 66614 ][2-Op] were about 0.561 mol CO 2 per mol, 0.95 mol CO 2 per mol and 1.60 mol CO 2 per mol, respectively. All mean free-volume hole radiuses of membranes decreased after blending CO 2 absorbents. After polymer membrane blended with two ILs, number of free-volume hole increased, resulting in modest increase of the fractional free volume. Both CO 2 permeability and selectivity increased after blending MEA and ILs. The increasing range of CO 2 permeability corresponded with CO 2 absorption capacity of CO 2 absorbents, and membrane blending with [P 66614 ][2-Op] showed the highest CO 2 permeability of 672.1 Barrers at 25 °C. Pebax/PEGDME membrane blending with MEA obtained the highest CO 2 /H 2 and CO 2 /CH 4 selectivity at 17.8 and 20.5, respectively.

Mixed matrix membranes with ionic liquids and molecular sieve particles had high CO 2 permeabilities, but CO 2 separation from small gas molecules such as H 2 was dissatisfied because of bad interfacial interaction between ionic liquid and molecular sieve particles. To solve that, amine groups were introduced to modify surface of molecular sieve particles before loading with ionic liquid. SAPO 34 was adopted as the original filler, and four mixed matrix membranes with different fillers were prepared on the outer surface of ceramic hollow fibers. Both surface voids and hard agglomerations disappeared, and the surface became smooth after SAPO 34 was modified by amine groups and ionic liquid [P 66614 ][2-Op]. Mixed matrix membranes with composites of amine-modified SAPO 34 and ionic liquid exhibited excellent CO 2 permeability (408.9 Barrers) and CO 2 /H 2 selectivity (22.1).

With the upgrading of fermentative biogas to produce gaseous transport fuel, ionic liquid (IL) [P66614][2-Op], which adsorbed CO2 through multiple-site cooperative interactions, was loaded onto molecular sieve MCM-41 to adsorb CO2 in a biohythane atmosphere (CH4 + H2 + CO2). [P66614][2-Op] loaded onto MCM-41 exhibited a higher CO2 adsorption rate than pure IL during the initial stage because of its larger reaction surface area. However, the CO2 adsorption rate of [P66614][2-Op] loaded onto MCM-41 became lower than that of pure IL as the reaction continued because CO2 was inaccessible to the IL blocked within the inner pores of MCM-41. The CO2 adsorption rate of IL loaded onto the molecular sieve (MCM-41–50% IL) was (51.5 mg of CO2 g–1 of IL min–1) 2.1 times higher than that of pure IL during the initial 1 min in a pure CO2 atmosphere and was (24.6 mg of CO2 g–1 of IL min–1) 2.2 times higher than that of pure IL during the initial 2 min in a biohythane atmosphere.

Mixed matrix materials (MMMs) comprising porous fillers in polymers can exhibit superior gas separation properties, yet their practical use has been limited by poor interfacial compatibility between the two components. Herein we report a bottom-up approach to synthesize the MMMs by dispersing a metal-organic polyhedron (MOP-3) in monomer solutions before rapid photopolymerization to form interpenetrating networks (IPNs), where the porous MOP-3 nanoparticles serve as molecular dopants. Specifically, MOP-3 with particle sizes of ≈5 nm was dispersed in and infiltrated by either a macromonomer of poly(ethylene glycol) diacrylate (PEGDA) or poly(1,3 dioxolane) acrylate (PDXLA). The introduction of the MOP-3 in the polyethers decreases their glass transition temperatures and even induces the crystallization of polyPDXLA at high loadings. Increasing the MOP loading increases CO2 permeability with a slight decrease in CO2/gas selectivity. For example, as the MOP content increases from 0 to 30 mass% in polyPDXLA, CO2 permeability increases from 190 Barrer to 580 Barrer, and CO2/N2 selectivity decreases from 70 to 62 at 35 °C. These IPNs-based MMMs exhibit separation properties above the Robeson's upper bounds for CO2/N2 and CO2/H2 separation. As the MOPs are soluble in solvents, this approach can be easily integrated into industrial membrane fabrication processes to produce MMMs-based composite membranes in large-scale.

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.

To improve the permeation performance of a ceramic hollow fiber-supported poly (amide-b-ethylene oxide) (Pebax)/polyethylene glycol dimethylether (PEGDME) composite membrane during CO2 separation from biohydrogen, a room temperature ionic liquid (RTIL), namely, [P66614][2-Op], with a high CO2 capacity, was adopted to blend in the selective layer. An RTIL-blended selective layer without defects was prepared on the surface of the ceramic hollow fibre. The physicochemical properties and CO2/H2 separation performance of the Pebax/PEGDME/RTIL composite membrane were then compared with those of the Pebax/PEGDME composite membrane. Intermolecular hydrogen bonds were produced after blending RTIL with the Pebax/PEGDME selective layer, and the surface roughness of the composite membrane increased. The CO2 permeation rate increased by ∼35% and reached up to ∼75 GPU at 50 °C, and the CO2/H2 selectivity was maintained at a high value of ∼15 at 30 °C. Blending RTIL with the selective layer inhibited the positive effect of CO2-induced plasticisation on H2 permeability. However, this process improved CO2/H2 selectivity in mixed gases relative to the ideal selectivity by enhancing competitive sorption among gas molecules.

To upgrade the mixed gas of fermentative hydrogen and methane for the preparation of biohythane as a gaseous fuel for vehicles, a composite membrane of poly(amide-b-ethylene oxide) (Pebax® MH 1657) and polyethylene glycol dimethylether (PEGDME) coated on a porous ceramic hollow fiber was originally proposed for CO2 separation. The Pebax/PEGDME selective layer with high CO2 selectivity was closely adhered and evenly distributed to the porous ceramic hollow fiber as a highly permeable support. The ideal CO2/H2 selectivity of the composite membrane increased from 12 ± 0.7 to 26 ± 1.7 when the temperature decreased from 50 °C to 10 °C. Competitive sorption between different gas molecules was found in the composite membrane. The fast diffusion of small molecular gas (H2) through the nanopores in the selective layer improved the diffusion of relatively large molecular gases (CO2 and CH4) in the gas mixture. On the contrary, the slow diffusion of large molecular gas (CH4) worsened the diffusion of relatively small molecular gases (CO2 and H2).

To optimize the CO2 permeation and CO2/H2 separation performance of hollow fiber-supported polydimethylsiloxane (PDMS) membranes, the effect of the viscosity of the PDMS coating solution on surface morphologies, thickness of PDMS layer, and solution intrusion into surface pores of hollow fiber supports was investigated. Increases in both stirring time and standing time could increase the viscosity of the PDMS solution. The PDMS layer thickness increased when the coating solution viscosity increased, whereas the surface roughness of the PDMS layer markedly decreased and then slightly changed. Moreover, when the stirring time of the PDMS coating solution was 9 min and the standing time was increased from 2 min to 25 min, the CO2 permeance first decreased, then increased to ∼2250 GPU probably due to the decreased intrusion depth, and finally decreased because of the substantially increased thickness of the PDMS layer. However, the CO2/H2 selectivity increased to 3.4 with an increase in coating solution viscosity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45765.