Gas Permeation Performance Research Articles

Mixed and single gas permeation performance analysis of amino-modified ZIF based mixed matrix membrane

Dense and translucent CA/PEG 1000/ZIF membranes were synthesized in acetone, utilizing solution casting. Membrane characterization was carried out using FT-IR, SEM and tensile testing. SEM proved presence of dense membranes and increase in the filler amount may have formed voids, raising the permeability of both gases. Single and mixed gas (CO2/CH4) permeation testing showed an increased permeability, on addition of more filler, which is probably due to formation of nano-gaps. A maximum selectivity of 39.49 and 34.86 for single and mixed gases respectively, and maximum permeabilities of 49.7685 and 1.41 barrers were observed. Tensile testing showed that strength peaked then decreased on increased loading, due to agglomeration on adding more ZIF, which introduced defects in structure. To conclude, selectivity of higher loaded membranes is favourable whereas tensile strength of lower loaded membrane is superior, but we have a trade-off between selectivity and tensile strength, so a higher-loaded membrane is most suitable. [Formula: see text]

Improving gas permeation performance of PDMS by incorporating hollow polyimide nanoparticles with microporous shells and preparing defect-free composite membranes for gas separation

Recently, various types of hollow materials have been added into polymer matrices to improve the gas permeation and separation performance of polymer materials. In this study, hollow polyimide (PI) nanoparticles with microporous shells were synthesized by interfacial polymerization between 4,4-(9-fluorenylidene)-dianiline and 1,2,4,5-benzenetetracarbonyl tetrachloride in the microemulsion. Free-standing polydimethylsiloxane (PDMS)/hollow PI nanoparticles mixed matrix membranes were prepared and the gas permeation-separation performance was investigated. The hollow and porous structure of the nanoparticles was well-preserved in membranes, which reduced the mass transport resistance. The permeability firstly increased and then decreased as the nanoparticle loading increased without sacrificing the permselectivity. Compared to the neat PMDS membranes with O2 and CO2 permeability of 786 and 3484 Barrer, respectively, the mixed matrix membranes with 3 wt% hollow PI nanoparticles achieved a O2 permeability up to 1664 Barrer accompanied with an O2/N2 permselectivity of 2.3 and a CO2 permeability up to 6639 Barrer accompanied with a CO2/N2 permselectivity of 9.1 at 35 °C and 0.2 MPa. Mixed-matrix composite membranes were fabricated by dip-coating the porous polyetherimide substrate into a PDMS solution with 3 wt% nanoparticles. The resultant defect-free mixed-matrix composite membrane showed excellent O2 and CO2 permeances of up to 1677 and 6502 GPU, respectively. The air separation measurement showed that the composite membranes could produce oxygen-enriched permeate stream enriched to ca. 30 vol%.

Ethylene vinyl acetate copolymer/Mg–Al‐layered double hydroxide nanocomposite membranes applied in CO2/N2 gas separation

AbstractSeries of ethylene vinyl acetate (EVA) copolymer/layered double hydroxide (LDH) nanocomposite membranes with 40 wt% vinyl acetate content (EVA/12AA–LDH) were prepared by solution blending and casting, and applied in membrane gas separation. The organically modification of LDH nanolayers (12AA–LDH) was manufactured by using 12‐aminododecanoic acid (12AA) as an intercalation agent via co‐precipitation method. The distance between the 12AA–LDH nanolayers was approximately 2.10 nm from calculation of the XRD diffraction pattern, which resulted from the successful intercalation of 12AA within the LDH. The result of CO2 adsorption isotherms shows that 12AA–LDH is much more attractive than the neat LDH, which enhances the performance in membrane separation. Furthermore, the exfoliated/intercalated morphology of 12AA–LDH/LDH structures within EVA matrix was prepared successfully and can be observed clearly by transmission electron microscopy micrographs. The gas permeation performance of the EVA/12AA–LDH nanocomposite membranes was measured, and the results show that the best selectivity of CO2/N2 increased to 20 with a CO2 permeability of 119.21 barrer for the composite membrane containing 1.0 wt% 12AA–LDH. This result not only attributed to the exfoliation of the 12AA–LDH nanolayers within the EVA matrix, but also the amino group of 12AA interacted more with CO2 compared with N2 and O2. This result illustrated that 12AA–LDH shows highly potential for use as an additive in CO2 capture membranes.

Cellulose acetate-based membranes by interfacial engineering and integration of ZIF-62 glass nanoparticles for CO2 separation

Composite membranes typically used for gas separation are susceptible to interfacial voids and CO2 plasticization which adversely affects the gas permeation performance. This paper evaluates routes towards the enhancement of CO2 permeation performance and CO2 plasticization resistance of composite membranes using non-stoichiometric ZIF-62 MOF glass and cellulose acetate (CA). Single and mixed gas permeation results, obtained with CO2 and CH4, demonstrate that the presence of ZIF-62 glass in CA polymer enhanced the CO2 permeability and CO2/CH4 ideal selectivity from 15.8 to 84.8 Barrer and 12.2–35.3, respectively. The composite membrane loaded with 8 wt% of ZIF-62 glass showed the highest CO2 permeability and CO2/CH4 ideal selectivity of 84.8 Barrer and 35.3, which were 436.7% and 189.3% higher compared to the pristine CA membrane, respectively. A CO2 plasticization pressure of 26 bar was achieved for the composite membranes, which is 160% higher compared to the pristine CA membranes, at about 10 bar. The mechanisms for the materials stabilization and greater separation performance were attributed to higher pore size (7.3 Å) and significant CO2 adsorption on the unsaturated metal nodes followed by metal cites electrostatic interaction with CO2. These findings confirm the potential of ZIF-62 glass materials as promising materials solutions towards the design of composite membranes for CO2 separation at industrial scale.

Effect of silica nanoparticles on carbon dioxide separation performances of PVA/PEG cross-linked membranes

Novel PVA/PEG cross-linked membranes were prepared with (0–20 wt. %) of silica nanoparticles. The presence of both the polymers and additive was confirmed by FTIR analysis. The thermal properties of the membranes were analyzed by TGA and DSC analysis. The morphological and mechanical properties of the membranes were studied by SEM analysis and tensile testing, respectively. The gas permeation performances of the membranes were examined using state-of-the-art gas permeability cell. It was found that permeability of all the gases increased with the increase of silica loading, whereas ideal selectivity of carbon dioxide with respect to nitrogen and methane increased up to 10 wt. % loading and then became nearly constant on further loading. 20 wt. % silica loaded membrane was found to be the best performance membrane. The gas permeability of CO2 was also compared with different gas permeation models and was found to be in close agreement with Maxwell Model. The effect of temperature and pressure of feed gas pressure was also studied on permeation performances and optimum performances were achieved around 65 °C. The gas permeation performances were observed to decrease slightly with the increase in feed gas pressure up to 20 bar which confirms the absence of plasticization phenomenon up to 20 bar. Finally, gas permeation performances were compared with 2008 Robeson trade-off lines and it was found that at 20 wt. % loading, gas permeation performances surpassed the trade-off line for CO2/N2, and for CO2/CH4, the gas permeation performances approached the trade-off line.

Enhanced gas permeation performance of mixed matrix membranes containing polysulfone and modified mesoporous MCM-41

The aim of this study was the development of mixed matrix membranes (MMMs) based on silica MCM-41 dispersed in polysulfone (PSf) for the separation of carbon dioxide from methane. For this purpose, MCM-41 was synthesized by a hydrothermal method and was modified with 3-aminopropyltrietoxysilane (APTES). SEM, FTIR, BET and XRD analyses were used for characterization of the modified and unmodified particles. Then, various MMMs containing PSf at different weight percents (5, 10, 15 and 20) of modified and unmodified particles were prepared and the morphology and structure of the prepared membranes were studied using SEM and XRD analyses. Regardless of the particle type, the addition of MCM-41 to PSf caused an increase in gas permeability compared to a neat PSf membrane. Adding unmodified particles to PSf matrix resulted in undesirable effects, including particle agglomeration and/or the formation of interfacial voids. The MMMs with modified MCM-41 showed relatively better separation performance compared to MMMs with unmodified MCM-41. As a result, the MMM of PSf with 20 wt. % modified MCM-41 showed a significant increase in selectivity of carbon dioxide/methane and the value of selectivity reached 25.24.

Spatially Controlled Permeability and Stiffness in Photopatterned Two-Stage Reactive Polymer Films for Enhanced CO2 Barrier and Mechanical Toughness

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.

Gas separation through polyurethane–ZnO mixed matrix membranes and mathematical modeling of the interfacial morphology

AbstractA series of polyurethane/ZnO membranes was fabricated via thermal phase inversion of the solution of polymer/nanoparticle in N,N‐dimethylformamide solvent. The polyurethane synthesis was done via two‐step polymerization method using polytetramethylene glycol, isophorone diisocyanate, and 1,4‐butanediol in the ratio of 1:3:2. Different concentrations of zinc oxide nanoparticles (5, 10, 15, and 20) were incorporated into the polyurethane matrix. FTIR, SEM, and X‐Ray analysis were performed to characterize the membranes. FTIR and SEM results suggests an increment in the phase mixing of polyurethane with ZnO loading. Gas permeation performance through polyurethane‐ZnO mixed matrix membranes with ZnO loading by as much as 20 wt% were elucidated for pure N2, O2, CH4, and CO2 and gases. Based on the results, all permeability values decreased as the loading of ZnO nanoparticles increased, whereas CO2/N2 and CO2/CH4 selectivities increased. Moreover, interfacial structure of the polyurethane/ZnO nanocomposites were characterized by molecular probing approach. The results revealed the presence of a rigidified polymer chain layer with 65 ± 6 Å thickness around the ZnO nanoparticles.

Incorporation of thermally labile additives in polyimide carbon membrane for hydrogen separation

In this study, three thermally labile additives microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC), and polyvinylpyrrolidone (PVP) were introduced to the P84-copolyimide (PI) solution. PI-based carbon tubular membranes were fabricated using dip-coating method, followed by sample characterizations in order to determine their structural morphologies, thermal stability and gas permeation performance. NCC was added as the membrane pore former for the hydrogen gas (H2) separation. While tests involving pure H2 and N2 permeation were carried out at room temperature, carbon membranes were carbonized at a final temperature of 800 °C, with the heating rate of 3 °C/min under the Ar flow. Excellent result of H2/N2 selectivity was obtained with value of 430.06 ± 4.16. Addition of NCC has significantly increased the number of pore channels in the membrane, hence, contributing to high gas permeance and selectivity. NCC has shown potential as a good additive for an enhanced hydrogen separation performance.

Reducing the crystallinity of high molecular weight poly (ethylene oxide) using ultraviolet cross‐linking for preparation of gas separation membranes

AbstractCO2‐selective cross‐linked poly (ethylene oxide) (PEO) membranes were prepared by the UV irradiation of high molecular weight PEO in the presence of benzophenone as photo‐initiator, which act as a hydrogen‐abstracting agent. The main goal was to study the effects of the cross‐linking process on the structural properties of hydrogel films intended for the gas separation applications. It was found that the gel fraction, and cross‐link density enhanced, and the crystallinity, and the size of spherulites decreased by the cross‐linking process. Moreover, the permeation performances for N2, O2, CH4, and CO2 and the relationship between the gas permeation performances and physical properties were investigated. The results indicated that the degree of cross‐linking and crystallinity could be controlled by changing the initiator concentration, as by increasing the initiator content, the crystallinity percent and gas permeability of the membranes decreased, and the gas pair ideal selectivity of CO2/N2, CO2/CH4, CH4/N2, and O2/N2 increased.

Functionalized KIT-6/Polysulfone Mixed Matrix Membranes for Enhanced CO2/CH4 Gas Separation.

The development of mixed matrix membranes (MMMs) for effective gas separation has been gaining popularity in recent years. The current study aimed at the fabrication of MMMs incorporated with various loadings (0–4 wt%) of functionalized KIT-6 (NH2KIT-6) [KIT: Korea Advanced Institute of Science and Technology] for enhanced gas permeation and separation performance. NH2KIT-6 was characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and N2 adsorption–desorption analysis. The fabricated membranes were subjected to FESEM and FTIR analyses. The effect of NH2KIT-6 loading on the CO2 permeability and ideal CO2/CH4 selectivity of the fabricated membranes were investigated in gas permeation and separation studies. The successfulness of (3-Aminopropyl) triethoxysilane (APTES) functionalization on KIT-6 was confirmed by FTIR analysis. As observed from FESEM images, MMMs with no voids in the matrix were successfully fabricated at a low NH2KIT-6 loading of 0 to 2 wt%. The CO2 permeability and ideal CO2/CH4 selectivity increased when NH2KIT-6 loading was increased from 0 to 2 wt%. However, a further increase in NH2KIT-6 loading beyond 2 wt% led to a drop in ideal CO2/CH4 selectivity. In the current study, a significant increase of about 47% in ideal CO2/CH4 selectivity was achieved by incorporating optimum 2 wt% NH2KIT-6 into the MMMs.

Effect of triglyceride on the microstructure and gas permeation performance of Pebax-based blend membranes

A series of Pebax 2533/triglyceride (20 wt%) blend membranes were prepared to study the influence of triglyceride structure on Pebax-based membrane for the first time. The microstructure and morphology of blend membranes were characterized by XRD and SEM. The interaction and compatibility between Pebax and triglyceride were characterized by ATR-FTIR and DSC. The mechanical property of Pebax/triglyceride blend membrane was tested by universal testing machine. The thermal stability and the triglyceride content in blend membranes were characterized by TGA. Pebax showed relatively high compatibility with tripropionin (TPP), tributyrin (TBT) and tricapronin (TCP) and Pebax/triglyceride blend membranes showed reasonable mechanical property. The thermal stability of the Pebax/triglyceride blend membranes increased with the increase of triglyceride alkyl chain and Pebax/TCP blend membrane showed the highest thermal stability. For gas permeation of Pebax/triglyceride blend membranes, it relied on the combined action of ester group concentration, plasticization of triglyceride and volume resistance of alkyl chain. CO2 permeability of Pebax/triglyceride blend membranes all increased in comparison with Pebax membrane. However, due to the decline of ester group concentration and the increase of volume resistance with the increase of triglyceride alkyl chain length, the degree of CO2 permeability enhancement of blend membranes decreased, that was Pebax/TPP > Pebax/TBT > Pebax/TCP. More specifically, for Pebax/triglyceride blend membranes, diffusion coefficients were the major factors contributing to the improvement of CO2 permeability. While solubility coefficients were the major factors to determine the trend of CO2 permeability. Thus, Pebax/TPP blend membrane showed the highest CO2 permeability of 566 Barrer with moderate CO2/N2 selectivity of 25 at 35 °C. While Pebax/TCP blend membrane showed constant CO2 permeability around 508 Barrer within 120 h gas permeation testing.

Effect of introduction of fluoromonomer copolymerization on properties of polyimide hollow fibers

The novel copolymerization polyimide (PI) hollow fibers (HFs) of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) containing –CF3 groups were prepared and investigated through both simulation and experiment. To demonstrate the alteration attributable to the introduction of fluoromonomers, the condensed states of pyromellitic dianhydride (PMDA)/4,4′-oxybisbenzenamine (ODA), PMDA/6FDA/ODA, and 6FDA/ODA PI were constructed by Material Studio, and we simulated the mobility of molecular chain, free volume fraction, and O2/N2 dissolution–diffusion process. The molecular dynamics simulation results demonstrated that the properties of the copolymerized PI system with 6FDA were significantly improved, while the selectivity remained almost unchanged. Then, the films of copolymerized PI and HFs were prepared by the two-step method, and O2/N2 permeability of the PI copolymer films was characterized, indicating that although the gas permeation performance was greatly improved, the selectivity was not so satisfactory. However, the selection factor increased heavily after polydimethylsiloxane coating.

Microstructure and gas permeation performance of porous silicon nitride ceramics with unidirectionally aligned channels

AbstractPorous Si3N4 ceramics with unidirectionally aligned channels were prepared via freezing ceramics suspension with distinct solid contents under different freezing temperatures. The samples obtained using lower solid content in ceramic suspension at higher freezing temperature exhibit larger Darcian and non‐Darcian constants due to their higher open porosity, larger pore size and lower tortuosity. Moreover the investigation on individual contributions of viscous energy losses and inertial energy losses on the total pressure drop during permeation process indicates that with decreasing the solid content or the freezing temperature the viscous energy losses increase but the inertial energy losses decrease for samples owing to the differences in their pore structures. It is worth mentioning that porous Si3N4 ceramics with unidirectionally aligned channels exhibit larger Darcian and non‐Darcian constants than those with similar pore size distributions and open porosity owing to their lower tortuosity, thus rendering them appropriate for filters and membrane supports.

WITHDRAWN: Preparation and characterization of polyimide carbon membrane concerning thermally labile additives for hydrogen separation performance

Abstract In this study, thermally labile additives, microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC), and polyvinylpyrrolidone (PVP) were introduced to the P84-copolyimide (PI) solution. The dip-coating method was used to fabricate PI-based carbon tubular membranes, followed by several characterizations in order to determine their structural morphology, thermal stability and gas permeation performance. NCC was added as the membrane pore former for the hydrogen gas (H2) separation. The addition of NCC had significantly increased the pore channels in the membrane, hence, contributing to high gas permeance and selectivity. Tests involving pure H2 and N2 permeation were carried out at room temperature. Carbon membranes that were carbonized at a final temperature of 800 C, with the heating rate of 3 °C/min under the Ar flow had achieved excellent H2/N2 selectivity of 434.68 ± 1.39, hence, proving the potential of NCC as a good additive.

Dipeptide membranes for CO2 separation: A molecular simulation study

Molecular crystals of dipeptides with a high density of uniform pores have received growing interest for gas separation. Particularly, hydrophobic dipeptides can form one-dimensional straight pores with sizes ranging from 0.37 to 0.50 nm. A molecular simulation study is reported here to investigate the membrane separation of CO2/N2 and CO2/CH4 mixtures in eight dipeptides namely Ala-Val (AV), Val-Ala (VA), Ala-Ile (AI), Ile-Ala (IA), Val-Ile (VI), Ile-Val (IV), Val-Val (VV) and Leu-Ser (LS). The gas permeation and separation performance are evaluated using a molecular dynamics simulation method with a constant-pressure difference. The pore size and helicity are revealed to be the key factors governing permeation. A higher permeability can be achieved in a dipeptide membrane with a larger pore size or a lower helicity. Among the eight, six (AV, LS, AI, VA, VV and VI) surpass the Robeson upper bound for both gas mixtures. It is identified that AI and AV outperform other dipeptides for CO2/N2 separation, while AI, VA and VV are better for CO2/CH4 separation. The permselective separation of both gas mixtures is dominated by the preferential sorption of CO2 over N2 and CH4, respectively. This simulation study provides microscopic insights into CO2 separation in dipeptide membranes and suggests their potential use for gas separation.

Pebax-based mixed matrix membranes containing hollow polypyrrole nanospheres with mesoporous shells for enhanced gas permeation performance

Mixed matrix membranes (MMMs) have shown great advantages in overcoming the Robeson trade-off effect, and various fillers have been utilized to improve the gas permeation and separation performance. In this study, hollow polypyrrole (PPy) nanospheres with mesoporous shells were synthesized by chemical polymerization using hard template method. The hollow PPy nanospheres with mesoporous shells were investigated by transmission electron microscopy, scanning electron microscopy, Brunauer Emmett Teller and small-angle X-ray scattering. We introduced hollow PPy nanospheres into poly(ether-block-amide) (Pebax1657) as fillers to prepare MMMs for CO2 separation. The effects of the hollow PPy nanospheres on the physical properties and the gas permeation and separation performance were studied. The results showed that the addition of hollow PPy nanospheres contributed to the improvement of the gas permeability. At 1 wt% loading of hollow PPy nanospheres, the MMMs exhibited a highest CO2 permeability of 274 Barrer, which was more than double compared with that of the pure Pebax membrane, accompanied by the slightly increased CO2/N2 selectivity of 40.1 and the slightly increased CO2/CH4 selectivity of 12.8. MMMs with hollow polymer nanospheres display a positive potential application for industrial-scale CO2 separation.

Fabrication of 6FDA-based composite membranes loaded with MIL-125 (Ti) for CO2/CH4 separation

Carbon dioxide (CO2 ) separation is necessary for natural gas purification to enhance the calorific value of methane gas (CH4 ), besides reducing the corrosion risk in pipelines with the presence of water or moisture. This work focuses on the development of new combination of composite membrane materials containing titanium-based metal organic frameworks (MOFs) and 6FDA-based polymer for CO2 and CH4 gases permeation. The composite membranes were successfully fabricated by incorporating 0.5, 1.0, 3.0 and 5.0 wt% of MIL-125 (Ti) fillers into 6FDA-durene polymer by using solvent evaporation method. The resultant fillers and composite membranes were characterized by using different analytical tools including XRD, FESEM and EDX. Then, the permeability test was conducted by using single gas of CO2 and CH4. The results showed that composite membrane loaded with 5wt% of MIL-125(Ti) showed the highest CO2 permeability of 814.9 Barrer, and CO2/CH4 ideal selectivity of 18.1 compared to pure 6FDA-durene membrane with CO2 permeability of 510.3 Barrer and CO2/CH4 ideal selectivity of 8.6. It was found that the incorporation of fillers, MIL-125 (Ti) into 6FDA-durene polymer matrix led to the enhancement of gas permeation performance due to good compatibility between fillers and polymer matrix. Besides, the presence of organic ligand in MIL-125 (Ti) filler has potentially reduced the interfacial voids between the filler and polymer.

Gas permeation performance of porous silicon nitride ceramics with controllable pore structures

Porous Si3N4 ceramics with controllable pore structures were prepared by polymethyl methacrylate (PMMA) as the pore agent combined with cold isostatic pressing (CIP) method. The pore structures of specimens were tailored via the changes in the content and particle size of PMMA. The higher the addition and particle size of PMMA, the larger the open porosity and pore size respectively. The increased Darcian and non-Darcian permeability coefficients are obtained as the open porosity and pore size of pore structures increase. The ratio of Darcian and non-Darcian permeability coefficient representing the individual contribution of viscous and inertial resistance during permeation process, that is strongly dependent on the pore size and open porosity, but there is distinct relationship for small and larger pores. Moreover, the comparison of the theoretical permeability coefficients with the experimental permeability constants of porous materials is presented in this work.

H2/CO2 Gas Transport Performance in Poly (Ethylene Oxide) Reverse-selective Membrane with Star-like Structures

A series of poly (ethylene oxide) (PEO) membranes with star-like structures for CO2/ H2 separation were prepared by the photo-polymerization method. The structure of PEO membrane was characterized by Fourier transform infrared spectroscopy (FTIR). The thermal property and inter-segmental distance of polymer chain were investigated by differential scanning calorimetry and wide-angle X-ray diffraction, respectively. The density was determined by hydrostatic weighing method. The gas permeability, solubility and diffusivity of CO2 and H2 were investigated in the star-like PEO membranes. The relationship between gas permeation performances and physical properties was also discussed. The membrane exhibits outstanding CO2 permeability (about 9.7×10-11 cm3 (STP) cm/cm2/s/Pa) and CO2/H2 selectivity (about 11) compared with other membranes.