Pebax Membrane Research Articles

Upgrading CO2/CH4 separation performances of Pebax-based mixed-matrix membranes incorporated with core/shell-structured ZIF-L(Co)@ZIF-8 composite nanosheets

The development of high-performance mixed matrix membranes (MMMs) with satisfactory structure stability has attracted much attention for the past few years. The rational design and synthesis of fillers to well coordinate themselves in the polymeric matrix is still challenging. The core-shell structured fillers were synthesized via the heteroepitaxial growth of ZIF-8 on ZIF-L(Co) surface (ZIF-L(Co)@ZIF-8), which were then embedded into Pebax to fabricate MMMs for enhanced CO2/CH4 separation. The synthesized fillers and MMMs were characterized via SEM with EDS mapping, TEM, XRD, FIIR and nanoindentation measurements. The effects of ZIF-L(Co)@ZIF-8 loading and filler components on gas separation performance were studied with the evaluation of membrane stability. The experimental results indicated that the filled ZIF-L(Co)@ZIF-8 could be evenly distributed within the bulky Pebax. The synergistic effect of the core-shell structured fillers in adsorption and molecular sieving endowed the synthesized MMMs with superior gas separation performances. The optimal separation performance is achieved for the MMM containing 3 wt% of ZIF-L(Co)@ZIF-8 with a CO2 permeability of 145.7 Barrer and a CO2/CH4 selectivity of 40.9, corresponding to 79.1% and 110.1% increases over pure Pebax membrane.

Boosting the CO2/N2 selectivity of MMMs by vesicle shaped ZIF-8 with high amino content

The amino functionalization of MOFs has been verified to be effective in improving the selective permeation of CO2. However, the introduction of amino groups into ZIF-8 by mixed ligands strategy is hard to achieve due to the high steric hindrance of benzene ring in 2-aminobenzimidazole ligand, resulting in insufficient content of amino groups. Therefore, in this work, polystyrene-acrylate (PSA) template is proposed to provide abundant adsorption and reaction sites for the rapid synthesis of NH2-ZIF-8 with high content of 2-aminobenzimidazole. Furthermore, the incomplete etching strategy is used to construct PSA modified hollow NH2-ZIF-8 nanospheres (PHNZ). Importantly, the thickness of PSA layer and the hollow size are adjusted by the etching time, as revealed by the SEM and TEM images. In this PHNZ, the modified PSA can provide good interface compatibility between PHNZ and Pebax matrix to enhance the CO2 selectivity, while the hollow structure can reduce the mass transfer resistance and improve the gas permeability. Moreover, the introduced amino groups can enhance the CO2 affinity of PHNZ and further improve the CO2/N2 selectivity of the PHNZ-based mixed matrix membranes (MMMs). Benefiting from the synergy of good interface compatibility and enhanced CO2 affinity from the amino groups, the PHNZ/Pebax MMMs present greatly improved CO2/N2 selectivity in contrast with pure Pebax and NH2-ZIF-8 based membranes. Besides, as the etching time increases, the PHNZ-2 and PHNZ-3 based MMMs present a higher CO2 permeability than that of NH2-ZIF-8 based MMM, revealing the significance of the hollow structure. The PHNZ-2/Pebax MMM with filler loading of 10 wt% expresses the best gas separation performance with the CO2 permeability of 121.9 Barrer and CO2/N2 selectivity of 96.6, respectively, showing an increase of 54.7 % and 98.0 % in contrast with pure Pebax membrane. Meanwhile, this CO2 separation performance is far beyond the Robeson upper bound in 2008 and close to the McKeown upper bound in 2019, demonstrating that the proposed PHNZ displays a promising and competitive potential in MMM based CO2 capture.

Mixed matrix membranes containing Cu-based metal organic framework and functionalized ionic liquid for efficient NH3 separation

Membranes that both have high gas permeability and selectivity is still challenging. Aiming to efficiently separate and purify ammonia-containing gases, this work constructed a novel ternary mixed matrix membranes (MMMs) by introducing functionalized ionic liquid ([Bim][NTf2]) and Cu-based metal organic framework (CuBTC). It was proved that the interaction networks consisted of hydrogen bonding and electrostatic interactions are formed in the IL-based MMMs, leading to the improved compatibility, decreased crystallinity and amorphous morphology. The ammonia separation performance was evaluated through pure gases and mixed gases. The PCu3-IL100 MMM exhibits great ideal selectivities (αNH3/N2 = 530.1 and αNH3/H2 = 94.2) and optimal NH3 permeability up to 3680.0 barrer, which is 260% and 129% higher than the pristine Pebax membrane and the PCu3 MMM, respectively. The improving NH3 separation performance is attributed to the synergistic interaction of hydrogen bonding and Lewis acid-base between IL-based MMMs and NH3 molecules, significantly increasing NH3 solubility coefficient and solubility selectivity. The IL-based MMMs also show exceptional NH3 mixed separation performance and long-term operation stability.

Enhancing CO2 separation performance of mixed matrix membranes by incorporation of L-cysteine-functionalized MoS2

The incorporation of lamellar materials into polymer matrix can improve the gas separation performance of mixed matrix membranes (MMMs), which have great potential in chemical separation process. However, few intrinsic selectivity sites on MoS2 sheets suppress further employment in the membrane separation. In this work, the vacancies and defects-containing MoS2 sheets were prepared by high temperature oxidation and hydrothermal reaction in NaOH solution, and then L-cysteine-functionalized MoS2 (Cys-MoS2) was synthesized by a thiol-click chemistry reaction between S vacancies and thiol groups as confirmed by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 absorption. After blending with polyether-block-amide (Pebax), the as-prepared MMMs showed outstanding mechanical properties as a result of the homogeneous dispersion of Cys-MoS2 and hydrogen bonding between two phases as evidenced by attenuated total reflectance-FTIR, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The highest permeability of 297 Barrer accompanied with a CO2/N2 selectivity of 120 was obtained for MMMs loaded with 1.5 wt% Cys-MoS2, which were enhanced by 206.2 % and 124.7 % over the pristine Pebax membrane, respectively. Meanwhile, this value was superior to that of the previously reported Pebax-based MMMs, transcending 2019 upper bound. The enhanced gas separation performance is due to the improved CO2 adsorption selectivity by the vacancies and defects of Cys-MoS2, while the amine groups carrier enhanced CO2 reactivity selectivity.

A novel IL/MOF/polymer mixed matrix membrane having superior CO2/N2 selectivity

In this work, we synthesized an ionic liquid (IL)/metal organic framework (MOF) composite, 1-ethyl-3-methylimidazolium acetate/copper-1,3,5-benzenetricarboxylate ([EMIM][OAc]/CuBTC) and used it as a filler in a polymer, Pebax, to fabricate novel IL/MOF/polymer mixed matrix membranes (MMMs). CuBTC/Pebax and [EMIM][OAc]/CuBTC/Pebax MMMs having different filler loadings of 10, 15, and 20 wt.% were prepared by solution casting method and characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Uniform dispersion of MOF and IL/MOF fillers in the MMMs was observed. Incorporation of IL/MOF composite into Pebax significantly improved CO2 permeability and CO2/N2 selectivity of the polymer by 2.5- and 5.5-times, respectively. Gas permeability measurements showed that the MMM having 15 wt.% IL/MOF loading exhibits significantly higher CO2 permeability of 335 Barrer and CO2/N2 selectivity of 176 than the Pebax membrane having CO2 permeability of 135 Barrer and CO2/N2 selectivity of 32. CO2/N2 selectivity of the [EMIM][OAc]/CuBTC/Pebax MMM with 15 wt.% [EMIM][OAc]/CuBTC filler loading was the highest among the selectivity values reported for other types of IL/MOF/polymer MMMs in the literature. All the CuBTC/Pebax MMMs and [EMIM][OAc]/CuBTC/Pebax MMMs that we fabricated in this work exceeded the Robeson's updated upper bound, showing the excellent potential of these novel membranes for CO2/N2 separation.

The Effect of Solution Casting Temperature and Ultrasound Treatment on PEBAX MH-1657/ZIF-8 Mixed Matrix Membranes Morphology and Performance.

Approximately two-thirds of anthropogenic emissions causing global warming are from carbon dioxide. Carbon capture is essential, with membranes proving to be a low cost and energy-efficient solution to alternative technologies. In particular, mixed matrix membranes (MMMs) can have higher permeability and selectivity than pure polymer membranes. The fabrication conditions affect the formation of defects within the membranes. In this work, MMMs were created using a PEBAX MH-1657 polymer and a ZIF-8 filler. The effect of casting plate temperature, varying from −5 °C to 50 °C, and the effect of ultrasound treatment time (80–400 min) and method (filler solution only, filler and polymer combined solution only and filler solution followed by combined solution) were investigated, aiming to reduce defect formations hence improving the performance of the MMMs. SEM images and permeation tests using pure CO2 and N2 gas, replicating flue gas for carbon capture, were used to investigate and compare the membranes morphology and performance. The results indicated that the MMMs maintained their permeabilities and selectivities at all tested casting temperatures. However, the neat PEBAX membranes demonstrated increased phase separation of the polyamide and polyether oxide phases at higher temperatures, causing a reduction in permeability due to the higher crystallinity degree, confirmed by DSC experiment. The MMMs fabricated at low ultrasound times displayed a large amount of aggregation with large particle size causing channeling. At high ultrasound times, a well-dispersed filler with small filler diameters was observed, providing a high membrane performance. Overall, defect-free membranes were successfully fabricated, leading to improved performance, with the best membrane resulting from the longest ultrasound time reaching the Robeson bound upper limits.

Constructing rapid water vapor transport channels within mixed matrix membranes based on two-dimensional mesoporous nanosheets

Membrane technology is an effective strategy for gas dehumidification and fuel cell humidification. In this study, cerium fluoride oxide (F-Ce) two-dimensional (2D) mesoporous nanosheets and their composite with 1-ethyl-3-methylimidazolium dicyanamide ([Emim][DCA]) ionic liquids (ILs) (IL@F-Ce) are introduced as fillers into polyether block amide (PEBAX® 1074) to fabricate mixed matrix membranes (MMMs). The slit-shaped mesoporous structure of the nanosheets facilitates the construction of water vapor rapid transport channels in MMMs. The permeability and selectivity of water vapor for MMMs loaded with F-Ce nanosheets are greatly improved, and the performance of MMMs loaded with IL@F-Ce nanosheets are much better than the former. Particularly, the MMM with IL@F-Ce content of 4 wt.% achieves the highest H2O permeability of 4.53 × 105 Barrer, which is more than twice that of the pure PEBAX membrane, and the selectivity is increased by 83%. Thus, the MMMs based on 2D mesoporous nanosheets have considerable potential application in industrial-scale dehydration and humidification processes.

3D hollow CoNi-LDH nanocages based MMMs with low resistance and CO2-philic transport channel to boost CO2 capture

Layered double hydroxide (LDH) bearing numerous hydroxyl groups shows high affinity with CO2 and is promising in mixed matrix membranes (MMMs) based CO2 capture. However, its non-porous structure limits the further improvement of CO2 permeability. In this work, 3D hollow CoNi-LDH nanocages were developed to construct low-resistance and CO2-philic transport channel in MMM by in-situ etching of ZIF-67 template. The resultant material exhibits hollow structure with cavity size of about 500 nm, mesopores and micropores from LDH stacking and ZIF-67 template. The outer layered CoNi-LDH nanosheets can attract more CO2 molecules by their abundant hydroxyl groups, resulting in an improvement in dissolution selectivity of CO2 over N2. Meanwhile, the tortuous gas diffusion paths originated from 2D nanosheet stacking can further enhance the CO2 selectivity over N2. Moreover, the hollow nanocages provide CO2 molecules with fast transport path, resulting in high CO2 permeability. As a result, compared with pure Pebax membrane and 2D LDH/Pebax MMM, all the 3D hollow CoNi-LDH/Pebax MMMs present enhanced CO2 permeability. The 3D hollow CoNi-LDH-2h/Pebax MMM performs the highest CO2 permeability of 135.49 Barrer, which are increased by 141.95% and 71.50% than those of the above two membranes, respectively. The selectivity of 3D hollow CoNi-LDH-2h/Pebax MMM is about 26.30% higher than that of the pure Pebax membrane. The present membrane presents comparable CO2 capture capacity in contrast with most reported Pebax based MMMs and surpasses the Robeson upper bond. Together with the good long-term stability, the 3D hollow CoNi-LDH nanocages are believed to be a promising candidate for MMMs to improve CO2 capture.

A general strategy for fabricating polymer/nanofiller composite membranes with enhanced CO2/N2 separation performance

Aggregation of nanofillers, one of the critical challenges for developing high-performance composite membranes, induces non-selective gas transport paths, and thus reduces the gas separation selectivity. Here, we propose a facile and general filtration-spray strategy for fabricating polymer/nanofiller composite membranes to inhibit nanofiller aggregation. In this way, the nanofiller scaffold is first deposited on the surface of the porous substrate through filtration. Then, the polymer covers the scaffold via a spray method. Finally, a defect-free membrane is formed after penetration of polymer and thus filling of the inter-filler gaps during the solvent evaporation process. This strategy avoids redispersion and aggregation of nanofillers in polymer matrix, thus diminishing the non-selective defects of interparticles caused by nanofiller aggregation and forming dense polymer/nanofiller composite membranes with well-dispersed nanofillers. The as-prepared Pebax/PEI-ZIF-62 (polyethyleneimine functionalized ZIF-62) membrane exhibits an enhanced gas separation performance with a CO2 permeance of 58 GPU and a CO2/N2 selectivity of 83, which are 45% and 51% higher than those of the pure Pebax membrane, respectively, surpassing Robeson 2008 upper bound. However, the CO2 separation selectivity of PEI-ZIF-62@Pebax membrane prepared via spraying the mixed solution of Pebax and PEI-ZIF-62 decreases to 38, probably due to the formation of non-selective voids. To demonstrate the versatility of this facile strategy, various nanofillers, such as SiO2, ZIF-8, zeolite, and porous polymer sphere, have been used to prepare the composite membranes by this strategy, showing improved CO2 separation performance. Overall, these results demonstrate that the filtration-spray fabrication strategy is effective in preventing nanofiller aggregation in composite membranes.

Evaluation of CO2 separation performance with enhanced features of materials – Pebax® 2533 mixed matrix membranes containing ZIF-8-PEI@[P(3)HIm][Tf2N

Zeolitic imidazolate framework (ZIF-8) was functionalized by polyethyleneimine (PEI) and subsequently decorated with ionic liquid (IL) – [P(3)HIm][Tf2N]. ZIF-8-PEI@IL/Pebax® 2533 mixed matrix membranes (MMMs) were fabricated to enhance the CO2 capture performance of Pebax membranes. The amino groups and IL in ZIF-8-PEI improved the gas separation performance of the MMMs due to the additional CO2 transporting pathways by using the reversible reaction with amino groups and the high affinity between IL and CO2. The modified ZIF-8 particles demonstrated enhanced interfacial interactions and compatibility between fillers and polymer matrix due to the presence of amino groups and IL, confirmed by the enhanced gas separation performance, improved elongation at break, and tensile strength of MMMs. Comparing with the pristine membranes, CO2 permeability of MMMs containing 15 wt% ZIF-8-PEI@IL increased by 123% to 285 Barrer, and the CO2/N2 and CO2/CH4 ideal selectivity increased from 17 and 12 to 76 and 25, respectively.

Incorporating amino acids functionalized graphene oxide nanosheets into Pebax membranes for CO2 separation

Graphene oxide (GO) nanosheets, as versatile nanofillers, can create two-dimensional passageways in mixed matrixed membranes (MMMs), yet the flexible manipulation of GO nanosheets is hampered by the lack of appropriate chemical functional groups. In this study, we chose amino acids（arginine, histidine and cysteine）to modify GO nanosheets by direct crosslinking and the loading content of amino acids on GO nanosheets was more than 20%. The modified GO nanosheets were then filled into the Pebax matrix to prepare MMMs. The CO2 separation performance of MMMs with different nanofillers was compared and different amino acids modified GO nanosheets could fortify the solution mechanism for CO2 in the order of arginine@GO ＞ histidine@GO ＞ cysteine@GO. Density functional theory (DFT) calculations were conducted to further elucidate the interaction mechanism between gases molecules and amino acids. Under dry state, the complexation energy (Ec) between CO2 and amine groups was similar to the Ec between CO2 and carboxylic groups in amino acids. In particular, 0.4 wt% arg@GO nanosheets rendered the membranes with promising CO2 permeance of 169 Barrer and CO2/N2 selectivity of 70, and surpassed the 2008 upper bound. The amino acids modified GO nanosheets may enlighten an alternative way to explore CO2 transfer mechanism within MMMs and fabricate high separation performance membranes.

Bottom-up synthesis of two-dimensional composite via CuBDC-ns growth on multilayered MoS2 to boost CO2 permeability and selectivity in Pebax-based mixed matrix membranes

In order to conquer the obstacle that increased CO2 selectivity in two-dimensional nanosheet incorporated-mixed matrix membranes (MMMs) is accompanied with sacrifice of CO2 permeability, CuBDC-ns was grown on multilayered MoS2 nanosheets via bottom-up synthesis strategy to obtain two-dimensional nanosheet composite, which was incorporated into Pebax-based MMM for efficient CO2 separation. The synthesized [email protected]2 composite with abundant unsaturated metal sites (Cu-S and Cu-O) achieve superior CO2 adsorption capacity compared to pristine CuBDC-ns. This is attributed to formation of coordination complex between Cu ions on CuBDC-ns and S atoms in multilayered MoS2 nanosheets, as revealed on FTIR and XPS analysis. Therefore, the incorporated [email protected]2 composites not only increase CO2 separation selectivity via lamellar morphology and narrow pore aperture, but also enhance CO2 solubility and diffusivity via coordination complex and unsaturated metal sites, boosting CO2 permeability and separation selectivity simultaneously. Gas permeation experiments demonstrate that Pebax-based MMMs incorporated with 2.5 wt% of [email protected]2 composite achieve CO2 permeability of 123 Barrers, as well as superior CO2/CH4 and CO2/N2 selectivities of 18 and 69. They are higher by 42.5 %, 19.2 %, and 80.2 %, respectively, than those of pristine Pebax membrane.

Mixed-matrix membranes consisting of Pebax and novel nitrogen-doped porous carbons for CO2 separation

Fabricating high-performance mixed matrix membranes (MMMs) for CO 2 separation is of great importance for industrial application, but the poor compatibility between polymer and filler hinders their further development. Herein, novel nitrogen-doped porous carbons (NPC) were gained by a facile hydrothermal reaction between glucose and melamine, subsequently KOH activation. Highly micropore NPC with the BET surface area of 1229.36 m 2 g −1 and Langmuir surface area of 1868.46 m 2 g −1 accompanied with the BJH pore volume of 0.68 cm 3 g −1 was achieved by scanning electron microscopy (SEM) and N 2 adsorption. After blending with polyether-block-amide (Pebax), the as-obtained MMMs showed excellent mechanical properties probably due to the homogeneous dispersion of NPC in the Pebax as shown in SEM results. The nitrogen in MMMs was expected to be significantly increased upon incorporation with NPC, as verified by attenuated total reflectance Fourier-transform infrared spectroscopy, thus increased the CO 2 transport. MMM with 5 wt% NPC exhibited a CO 2 permeability of 553 Barrer. This value is much higher than that of the pristine Pebax membrane. Surprisingly, a significantly improved CO 2 /N 2 selectivity of as high as 56.4 was observed for MMMs. Thus, MMM having a 5 wt% NPC had an excellent gas separation, approaching Robeson's upper bound revised in 2019, which was superior to the one incorporated with other activated carbons prepared from similar reactants. The enhanced separation performance is mainly ascribed to the presence of nitrogen-containing groups for high CO 2 affinity and also the micropore structure to promote CO 2 diffusion in NPC. These results indicated that the improvement in gas permeability and ideal selectivity simultaneously could be achieved by MMMs using the microporous and functional nanofillers. • Novel nitrogen-doped porous carbons were introduced to Pebax to prepare MMMs for high performance CO 2 separation. • The nitrogen in porous carbons can provide more affinity sites for CO 2 transport. • Thus, a CO 2 permeability of as high as 553 Barrer with a CO 2 /N 2 selectivity of 56.4 was observed.

Mixed‐matrix membranes based on Li1.6Mn1.6O4 (LMO) ultrathin nanosheet for high‐performance CO2 separation

AbstractTwo‐dimensional flake Li1.6Mn1.6O4 (LMO) was added to the Pebax®MH 1657 (Pebax) matrix to prepare mixed‐matrix membranes (MMMs) for CO2/CH4 mixed gas separation. The average pore diameter of the LMO nanosheet was about 10.79 nm: a fast CO2 transport channel could be established in the membrane. In addition, the Li and oxygen defect site (Oδ−) in the LMO had an affinity for CO2, which improved the permeability of the membrane and the selectivity for CO2 separation. Furthermore, the ultrathin structure of LMO with large aspect ratio was also conducive to gas separation. When the LMO filling amount was 2.0 wt%, the permeation rate of pure CO2 gas of Pebax/LMO‐2.0 membrane was 117.9 Barrer, and the CO2/CH4 ideal selectivity was 18.74, which were 119.7 and 35.8% higher than Pebax membrane, respectively. The CO2/CH4 mixed gas separation results of Pebax/LMO‐2.0 membrane showed that the CO2 permeability and CO2/CH4 selectivity were 158.54 Barrer and 33.41, respectively, and were increased by 83.24 and 23.15%, compared with Pebax membrane.

Dual-function biomimetic carrier based facilitated transport mixed matrix membranes with high stability for efficient CO2/N2 separation

Realizing efficient carbon capture by high-performance CO2 separation membrane is significant to mitigate the increasing emissions of greenhouse gas CO2. Inspired by the extraordinary CO2 hydration ability of carbonic anhydrase (CA), a biomimetic MOF (CFA-1) which can mimic the CO2 hydration sites of CA but possesses better stability and the lower price was incorporated into Pebax to fabricated high-performance facilitated transport mixed matrix membranes. The optimal membrane has a CO2 permeability of 869 Barrer with a CO2/N2 ideal selectivity of 88.6 at 1 bar and 30 °C, which is 9.2 times and 2.8 times than the pristine Pebax membrane. Such superior CO2/N2 separation performance (far surpasses 2008 upper bound) is original from the dual-function of CFA-1: (1) provide extra pathways for gas diffusion and affinity sites for preferential CO2 adsorption; (2) facilitate CO2 transport in the membrane by efficiently catalyze CO2 hydration reaction. Furthermore, the Pebax/CFA-1 membranes fabricated can also exhibit excellent stability after being treated under high temperature and harsh pH, which is not available in the Pebax/CA membranes. Overall, such biomimetic dual-function MOFs may pave a new avenue to advance the high-performance CO2 facilitated transport membranes with excellent stability.

A novel high-performance facilitated transport membrane by simultaneously using semi-mobile and fixed carriers for CO2/N2 separation

In this study, poly (ether-block-amide) (Pebax) facilitated transport membranes (FTMs) containing aniline, and ionic liquid (IL) modified alumina (M-Al) particles were prepared. Aniline molecules acted as semi-mobile carriers and IL-modified particles as fixed carriers for CO2 molecules in these membranes. Different amounts of M-Al particles were added to the Pebax/aniline (50 wt%) membrane, and a facilitated transport membrane containing 5 wt% M-Al particles was obtained as the optimal membrane. For Pebax/aniline (50 wt%)/M-Al (5 wt%) membrane, CO2 permeability was 167 barrer, and CO2/N2 selectivity was 123 increased by 94% and 168% compared to pure Pebax membrane, respectively. The CO2 separation performance of the prepared FTMs was also evaluated in the humidified state. The results showed that in the presence of water, the amino groups in the structure of aniline and IL performed better and improved the facilitated transport mechanism. Therefore, for all FTMs, CO2 permeability significantly increased in the humidified state so that CO2 permeability and CO2/N2 selectivity reached 406 barrer and 123, respectively, for optimal membrane. The molecular simulation was used to study details of the motion of aniline molecules in the polymeric matrix. The simulation and experimental results confirmed each other and showed that the presence of aniline prevents the hopping mechanism from stopping even at low concentrations of particles as fixed carriers and creates a combined hopping-vehicle mechanism in the membrane structure that results in excellent performance membranes.

Poly(ether-block-amide) Copolymer Membranes in CO2 Separation Applications

Poly(ether-block-amide) (PEBA, commercialized as Pebax) copolymer membranes show a highly promising platform for preparing high-performance membranes for CO2 capture from process streams containing CH4 and N2. Pebax combines high CO2 affinity with the desired mechanical strength for polymeric membranes thanks to its flexible polyether segment and hard polyamide block, respectively. Furthermore, researchers have been improving the performance of these membranes by preparing a thin Pebax selective layer on top of porous supports and by incorporating inorganic and organic nanofillers into the Pebax matrix to overcome the permeance-selectivity limit. The chemical and structural characteristics of Pebax membranes according to the different fabrication techniques and parameters are discussed first. Then, the recent developments in terms of both Pebax-based thin film composite and mixed matrix membranes are summarized. Finally, thermal and water stabilities of these membranes are addressed.

Comparison of acidic and basic ionic liquids effects on dispersion of alumina particles in Pebax composite membranes for CO2/N2 separation: Experimental study and molecular simulation

In this study, two types of acidic and basic ionic liquids (ILs) were used to modify the γ-Al2O3 particles. Different amounts of modified particles were added to the poly (ether-block-amide) (Pebax) polymeric matrix, and various composite membranes were prepared. FTIR (Fourier transform infrared), SEM (scanning electron microscopy), XRD (X-ray diffraction), DSC (differential scanning calorimetry), tensile and gas permeation analyses, as well as molecular simulations, were used to study the effect of ILs on the structure of membranes and their performances. The results indicated that ILs prevented well the sedimentation and agglomeration of particles through the electrostatic and steric forces. The electrostatic forces were more effective than steric forces. In addition to improving membrane separation performance and overcoming the trade-off limit, the modification of γ-Al2O3 particles has improved membranes mechanical strength. The comparison of ILs performances showed that the acidic IL had a better effect on the particle dispersion than the basic one. The CO2 permeability and CO2/N2 selectivity in the membrane containing 10 wt% acidic IL-modified particles increased about 47% and 124%, respectively, compared to the pure Pebax membrane. The molecular simulation confirmed the experimental results and showed that the employed ILs had different effects on the diffusivity and solubility coefficients of CO2 molecules in the membranes. Based on simulation results, the acidic IL improved the solubility coefficient by 95%, and the basic IL enhanced the diffusivity coefficient by 71%.

Pebax/two-dimensional MFI nanosheets mixed-matrix membranes for enhanced CO2 separation

Zeolite crystals as inorganic fillers were widely applied in fabricating mixed matrix membranes (MMMs) for CO2 separation. The poor filler-matrix interaction and the aggregation of high-loaded fillers in MMMs restrict their advantage of overcoming the trade-off limitation between permeability and selectivity. The novel MMMs with two-dimensional (2D) MFI nanosheets as inorganic fillers and Pebax MH 1657 as the matrix were synthesized and applied to achieve an efficient separation of CO2/CH4 gas mixture for the first time. The large interfacial contact areas between MFI nanosheets and Pebax matrix improve their compatibility to form defect-free MMMs with better mechanical properties. The high-aspect-ratio MFI nanosheets function as solid and selective barriers to make MMMs possess a significant promotion in both CO2 permeability and CO2/CH4 selectivity without the trade-off limitation. The MMM containing 5 wt% of MFI nanosheets exhibited the optimum performance with CO2 permeability of 159.1 Barrer and CO2/CH4 selectivity of 27.4. The as-prepared MMMs showed an improvement of 63.5% in CO2 permeability and 76.4% in CO2/CH4 selectivity, compared to pristine Pebax membranes.

Cross-linking of poly (ether-block-amide) by poly (ethylene glycol) diacrylate to prepare plasticizing-resistant CO2-selective membranes

In this study, poly (ethylene glycol) diacrylate (PEGDA) comprising CO2-philic ether oxygen groups was used as a cross-linking agent to develop plasticizing-resistant poly (ether-block-amide) (Pebax-1657) composite membranes with high performance for CO2 separation. The effect of PEGDA concentration on the structure and properties of the membranes as well as gas separation efficiency was investigated. The FT-IR analysis and swelling measurements confirmed the influential role of PEGDA as the cross-linking agent in the prepared membranes. Based on the performed characterization analyzes, it was found that the concentration of the cross-linking agent strongly affects the structural and CO2 separation properties of the cross-linked Pebax membranes. By introducing a cross-linking reaction, the tightness and crystallinity of modified Pebax membranes enhanced compared to the uncross-linked Pebax membrane. The DSC analysis indicated the Tg of the prepared Pebax membranes increased from −54.7 °C to −52.45 °C by increasing the PEGDA content. When the PEGDA concentration increased from 0 wt% to 6 wt%, the selectivity of CO2/N2, CO2/CH4, and CH4/N2 enhanced by 294%, 105%, and 92%, respectively, while the gas permeabilities slightly decreased. The cross-linked Pebax-1657 membrane containing 6 wt% of PEGDA surpassed the Robeson’s upper bound and denoted a prosperous separation performance in the case of CO2 separation from CH4 and N2, compared to the uncross-linked Pebax.