Enhanced permeation performance of polyether-polyamide block copolymer membranes through incorporating ZIF-8 nanocrystals

Membrane-based CO2 separation is a promising alternative in terms of energy and environmental issues to other conventional techniques.Polyether-polyamide block copolymer (Pebax) membranes are promising for CO2 separation because of their excellent selectivity,but limited by their moderate gas permeability.In this study,fresh-prepared zeolitic imidazolate framework-8 (ZIF-8) nanocrystals were integrated into the Pebax(R)1657 matrices to form mixed matrix membranes.The resulting membrane exhibits significantly improved CO2 permeability (as high as 300％ increase),without the sacrifice of the selectivity,to the pristine polymer membrane.Several physical characterization techniques were employed to confirm the good interfacial interaction between ZIF-8 fillers and Pebax matrices.The effect of added ZIF-8 fillers on the transport mechanism through MMMs is also explored.Mixed-gas permeation for both CO2/N2 and CO2/CH4 was also evaluated.The separation performance for CO2/CH4 mixtures on the ZIF-8/Pebax MMMs is very close to the Roberson upper bound,and thus is technologically attractive for purification of natural gas.     

High speed spin coating in fabrication of Pebax 1657 based mixed matrix membrane filled with ultra-porous ZIF-8 particles for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

Modified ultra-porous ZIF-8 particles were used to prepare novel ZIF-8/Pebax 1657 mixed matrix membranes (MMMs) on PES support for separation of CO₂ from CH₄ using spin coating method. TEM and SEM were used to characterize modified ZIF-8 particles. SEM was also used to investigate the morphology of synthesized MMMs. The MMMs with thinner selective layer showed higher CO₂ permeability and lower CO₂/CH₄ selectivity in permeation tests compared to MMMs with thicker selective layer. The plasticization was recognized as the main reason for rise in CO₂ permeability and drop in CO₂/CH₄ selectivity of thinner MMMs. The gas sorption results showed that the high permeability of CO₂ in MMMs is mainly due to the high solubility of this gas in MMMs, leading to high CO₂/CH₄ solubility selectivity for MMMs. The fractional free volume and void volume fraction of MMMs increased as the thickness of membrane decreased. Applying higher mixed feed pressures and permeation tests temperatures resulted in increase in CO₂ permeability and decrease in CO₂/CH₄ selectivity. At highest testing temperature (60 °C), the CO₂ permeability of synthesized MMMs with thinner selective layer remarkably increased.     

The effect of ZIF-90 particle in Pebax/Psf composite membrane on the transport properties of CO2, CH4 and N2 gases by Molecular Dynamics Simulation method

Nowadays, mixed matrix membranes (MMMs) have considered by many researchers to overcome the problems of polymeric membranes. In addition, molecular dynamics (MD) and Monte Carlo (MC) simulation Methods are suitable tools for studying transport properties and morphology in MMMs. For this purpose, in this study using material studio 2017 (MS) software, the transport properties of CO₂, CH₄ and N₂ in Pebax, Psf neat Pebax/Psf composite and Pebax/Psf composite filled with ZIF-90 particles have been investigated. By adding Psf to Pebax matrix, the selectivity of CO₂/CH₄ and CO₂/N₂ gases has significantly increased. In addition, adding ZIF-90 particles to the Pebax/Psf composite increased the permeability of CO₂, CH₄ and N₂ compared to neat and composite membranes. The morphological properties of the membranes, such as the fractional free volume (FFV), radial distribution function (RDF), glass transition temperature (T_G), X-ray diffraction (XRD) and equilibrium density have calculated and acceptable results have obtained.     

Enhanced CO2 selectivity of polyimide membranes through dispersion of polyethyleneimine decorated UiO-66 particles

Branched polyethyleneimine (PEI) functionalized UiO-66 were synthesized and used as fillers to fabricated mixed-matrix membranes (MMMs) for CO₂/CH₄ separation. The purpose of introducing amino-functional groups in the filler is to improve the interfacial compatibility of the filler with the polymer through the formation of hydrogen bonds with the carbonyl group of 6FDA-ODA. Additionally, the amino group can facilitate CO₂ transport through a reversible reaction, enhancing the CO₂/CH₄ separation properties of MMM. The chemical structure and morphology of fillers and membranes were characterized by employing X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), Derivative thermogravimetry (DTG) and scanning electron microscope (SEM). Furthermore, the effects of filler loading and feed pressure on CO₂ permeability and CO₂/CH₄ selectivity have been investigated. MMMs present higher gas separation performance than pure 6FDA-ODA due to the presence of amino groups and the improvement of interface morphology. In particular, the MMM with 15 wt% loading of UiO-66-PEI shows optimum CO₂ permeability of 28.23 Barrer and CO₂/CH₄ selectivity of 56.49. Therefore, post-synthetic modification of UiO-66 particle with PEI is a promising alternative to improved membrane performance.     

Preparation and characterization of CO2-selective Pebax/NaY mixed matrix membranes

CO₂-selective Pebax/NaY mixed matrix membranes (MMMs) were prepared by incorporating NaY zeolite into Pebax matrix. The morphology, chemical groups, thermal stability, and microstructure of the MMMs were investigated by scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction, respectively. The effects of zeolite loading amount, permeation temperature and pressure on the CO₂/N₂ separation performance of the resultant membranes were studied. The as-prepared MMMs are much superior to the pristine Pebax membranes in terms of permeability and selectivity. The CO₂ permeability and CO₂/N₂ selectivity can respectively reach to 131.8 Barrer and 130.8 for MMMs made by the starting materials containing 40 wt % NaY. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48398.     

Pebax-based mixed matrix membranes loaded with graphene oxide/core shell ZIF-8@ZIF-67 nanocomposites improved CO2 permeability and selectivity

In order to facilitate CO₂ transport in Pebax-based membranes, graphene oxide (GO)/core shell ZIF-8@ZIF-67 nanocomposites were loaded in Pebax copolymer to improve CO₂ permeability and selectivity. The 0.5 wt% GO doped core shell ZIF-8@ZIF-67, which gave highest CO₂ adsorption capacity of 1.12 mmol/g, was used as nanocomposite. The incorporated GO/core shell ZIF enhanced CO₂ adsorption via unsaturated metal sites (Zn-O or Co-O), because O atoms in GO substituted for N atoms coordinated with Zn and Co single atoms in core shell ZIF-8@ZIF-67. Positron annihilation lifetime spectroscopy indicated that GO-templated core shell ZIF nanocomposites generated extra free volume and provided low-resistance channels to facilitate CO₂ transport. Fourier transform infrared spectroscopy analysis revealed that hydrogen bonds were generated between Pebax polymer chains and GO-templated core shell ZIF which improved swelling resistance and reduced interface defects. Therefore, Pebax-based MMMs loaded with 5 wt% GO/core shell ZIF-8@ZIF-67 exhibited optimum CO₂ permeability (173.2 barrers) and ideal selectivity of CO₂/N₂ (61.9) and CO₂/H₂ (11.6), which were 99.7%, 66.4%, and 20.8% higher than Pebax membranes and surpass Robeson 2008 upper bound. The tensile strength increased by 17.6% to 28.8 MPa and elongation at break increased by 7.61%–554.6% when pure Pebax membranes were incorporated with 2.5 wt% GO/core shell ZIF-8@ZIF-67.     

Fabrication and testing of mixed matrix membranes of UiO-66-NH2 in cellulose acetate for CO2 separation from model biogas

Mixed Matrix Membranes (MMMs) of UiO-66-NH₂ nanoparticles dispersed in Cellulose Acetate (CA) were prepared with filler loading of 2–20 wt%. MMMs were tested for the upgradation of model biogas (60%–40%) mixture of CH₄/CO₂ at a feed pressure of 2 bar and 1.5 bar. Detailed characterization of MMMs was performed with Fourier transform infrared spectroscopy (FTIR), Thermo-gravimetric analysis (TGA), Differential scanning calorimetry (DSC), and Field emission scanning electron microscopy (FESEM) to investigate the physical and thermal properties. MMMs formed are defects-free, voids-free, and without polymer rigidification, indicating a better filler polymer interface. MMMs showed improved CO₂ permeability while retaining the CO₂/CH₄ selectivity. The 10 wt.% UiO-66-NH₂/CA MMM showed optimum gas separation performance with CO₂ permeability of 11 Barrer and CO₂/CH₄ selectivity of 10. The UiO-66-NH₂/CA MMMs performed better when compared to the pure CA membrane. The experimental permeability and selectivity data were compared with the predicted data using Maxwell, Lewis–Nielsen, Higuchi, and Bruggeman's model.     

Prestructured MXene fillers with uniform channels to enhance CO2 selective permeation in mixed matrix membranes

The packing pattern of two-dimensional (2D) sheet-like fillers in membranes is relatively random, leading to the unfavorable permeability from tortuous diffusion pathway. A new strategy that using prestructured materials with uniform channels as fillers was proposed. In this work, Ti₃AlC₂ is etched to prepare multilayered MXene (m-MXene), the channels aggregate as a whole unit, ensure the impossibility of ineffective packing compared with traditional individual sheets, largely facilitating the selective permeation. Then, the m-MXene/Poly (amide-6-b-ethylene oxide) (Pebax) MMMs are synthesized. SEM images demonstrate the accordion shaped structure of filler, which is the multi-channels laminates. Furthermore, the results of gas permeation test exhibit enhanced performance of m-MXene/Pebax MMMs. MMM with 0.5 wt.% m-MXene behaved best, CO₂ permeability of 86.22 Barrer as well as CO₂/N₂ selectivity of 104.85, transcending the Robeson upper bound (2008). Having distinct enhancement for CO₂ separation, the m-MXene/Pebax MMMs in this work offer prospective practical applications.     

Membranes for CO2 /CH4 and CO2/N2 Gas Separation

Membrane technology has emerged as a leading tool worldwide for effective CO₂ separation because of its well-known advantages, including high surface area, compact design, ease of maintenance, environmentally friendly nature, and cost-effectiveness. Polymeric and inorganic membranes are generally utilized for the separation of gas mixtures. The mixed-matrix membrane (MMM) utilizes the advantages of both polymeric and inorganic membranes to surpass the trade-off limits. The high permeability and selectivity of MMMs by incorporating different types of fillers exhibit the best performance for CO₂ separation from natural gas and other flue gases. The recent progress made in the field of MMMs having different types of fillers is emphasized. Specifically, CO₂/CH₄ and CO₂/N₂ separation from various types of MMMs are comprehensively reviewed that are closely relevant to natural gas purification and compositional flue gas treatment     

Mixed matrix membranes containing polymer-embedded metal-organic framework microspheres

The controlling filler aggregation and strengthening interfacial interaction are of great scientific significance for mixed matrix membranes (MMMs). In this study, the polymer-embedded metal-organic framework (pMOF) microspheres (MSs) are designed by one-pot synthesis and employed as microfillers for improving separation performance of MMMs. Through adding polymer during solvothermal crystallization, the polymer chains are embedded into the MOF materials, and the morphologies of the MOFs are transformed from nanopaticles to polycrystalline MSs. Since the embedding of the identical polymer promotes the compatibility of polymeric matrixes and fillers, as well as the micrometer-sized porous MSs offer additionally superior and permanent transport pathways, the resulted MMMs display simultaneously enhanced selectivity and permeability for carbon capture. The CO₂/CH₄ selectivity and CO₂ permeability of the pMOF MMMs are achieved at 1.3 and 2.2 times as those of the pure polymeric membranes, and 1.5 and 1.2 times as those of the MOF MMMs, respectively.     

Efficient CO2 Separation Using a PIM-PI-Functionalized UiO-66 MOF Incorporated Mixed Matrix Membrane in a PIM-PI-1 Polymer

Metal–organic framework (MOF) incorporated mixed–matrix membranes (MMMs) attract great interest for gas separation applications because they overcome limitations faced by typical polymer membranes, including permeability–selectivity trade-off, aging effect, and plasticization phenomenon. However, optimal MOF–polymer interface compatibility is the key challenge in fabricating defect-free high-performance gas-separation MMMs. Here, a surface modification strategy of the UiO-66-NH₂ MOF using a covalently bound PIM-PI-oligomer is developed to engineer interface compatibility with the polymer that has an identical chemical structure (PIM-PI-1) in the MMMs. A series of MMMs are prepared with different loadings of homogeneously distributed PIM-PI-functionalized MOFs (PPM). Significant improvements in CO₂/N₂ and CO₂/CH₄ selectivity and permeability are achieved with these MMMs, ranging from 5 to 10 wt% of the PPM loadings. The MMM with 10 wt% loading (PPM-10@MMM) shows a CO₂ permeability of 3827.3 Barrer and a CO₂/N₂ and CO₂/CH₄ selectivity of 24 and 13.4, respectively. This surpasses the 2008 Robeson upper bound for CO₂/N₂ and is very close to the 2008 upper bound for CO₂/CH₄. The experimental results are further compared using Maxwell's equation for MMMs. The resulting MMMs show a plasticization resistance against CO₂ up to 25 atm pressure and anti-aging performance for 180 h.     

Pebax–polydopamine microsphere mixed‐matrix membranes for efficient CO2 separation

Novel facilitated‐transport mixed‐matrix membrane (MMM) were prepared through the incorporation of polydopamine (PDA) microspheres into a poly(amide‐b‐ethylene oxide) (Pebax MH 1657) matrix to separate CO₂–CH₄ gas mixtures. The Pebax–PDA microsphere MMMs were characterized by Fourier transform infrared spectroscopy, scanning electron microcopy, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The PDA microspheres acted as an adhesive filler and generated strong interfacial interactions with the polymer matrix; this generated a polymer chain rigidification region near the polymer–filler interface. Polymer chain rigidification usually results in a larger resistance to the transport of gas with a larger molecular diameter and a higher CO₂–CH₄ selectivity. In addition, the surface of PDA microspheres contained larger numbers of amine, imine, and catechol groups; these were beneficial to the improvement of the CO₂ separation performance. Compared with the pristine Pebax membrane, the MMM with a 5 wt % PDA microsphere loading displayed a higher gas permeability and selectivity; their CO₂ permeability and CO₂–CH₄ selectivity were increased by 61 and 60%, respectively, and surpassed the 2008 Robeson upper bound line. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44564.     

功能化Zr-MOF强化混合基质膜CO2分离

混合基质膜（MMMs）在气体分离领域具有良好的应用前景,金属有机框架（MOFs）由于具有高孔隙率和有机连接基团,常被用作填料制备MMMs。但由于MOFs与聚合物的界面相容性问题,MMMs的气体分离性能提升受到限制。本文合成了功能化的Zr-MOF（UiO-66-AC）,并利用其与聚醚共聚酰胺（Pebax）共同制备了混合基质膜。填料中引入的羰基和羧基等基团提供了MOFs与聚合物基质之间较强的界面相互作用。与纯Pebax膜相比,UiO-66-AC/Pebax MMMs的气体渗透性能得到了显著提高。当填料质量分数为6%时,膜的CO₂渗透系数为102.4 Barrer,CO₂/N₂和CO₂/CH₄选择性分别为90.6和26.0,CO₂/N₂分离性能突破了Robeson上限(2008),表明该混合基质膜在CO₂的分离应用上具有潜力。     

Fabrication of mixed‐matrix membranes with MOF‐derived porous carbon for CO2 separation

Mixed‐matrix membranes (MMMs) have shown great advantages but still face some challenges, such as the trade‐off between permeability and selectivity, stability, and the lack of efficient ways to enhance them simultaneously. Here, the fabrication of MMMs with metal‐organic frameworks derived porous carbons (MOF‐PCs) as fillers which exhibit selective‐facilitating CO₂ transport passage originating from interactions between fillers and CO₂ is showed. With the aid of the developed multicalcination method, MOF‐PCs with variable N‐contents were prepared and incorporated into PPO‐PEG matrix for the first time to prepare MMMs, which show excellent separation performance for CO₂/CH₄ mixture with a tunable separation performance by combining different N‐contents and surface areas of MOF‐PCs. Moreover, the developed MMMs have hydrothermal and chemical stability. This work not only presents a series of MMMs with both good separation properties and stability, it also provides useful information for guiding the fabrication of high performance MMMs for practical application. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3400–3409, 2018     

Effect of graphene oxide on the behavior of poly(amide‐6‐b‐ethylene oxide)/graphene oxide mixed‐matrix membranes in the permeation process

Polyether‐block‐amide (Pebax)/graphene oxide (GO) mixed‐matrix membranes (MMMs) were prepared with a solution casting method, and their gas‐separation performance and mechanical properties were investigated. Compared with the pristine Pebax membrane, the crystallinity of the Pebax/GO MMMs showed a little increase. The incorporation of GO induced an increase in the elastic modulus, whereas the strain at break and tensile strength decreased. The apparent activation energies (E_p) of CO₂, N₂, H₂, and CH₄ permeation through the Pebax/GO MMMs increased because of the greater difficulty of polymer chain rotation. The E_p value of CO₂ changed from 16.5 kJ/mol of the pristine Pebax to 23.7 kJ/mol of the Pebax/GO MMMs with 3.85 vol % GO. Because of the impermeable nature of GO, the gas permeabilities of the Pebax/GO MMMs decreased remarkably with increasing GO content, in particular for the larger gases. The CO₂ permeability of the Pebax/GO MMMs with 3.85 vol % GO decreased by about 70% of that of the pristine Pebax membrane. Rather than the Maxwell model, the permeation properties of the Pebax/GO MMMs could be described successfully with the Lape model, which considered the influence of the geometrical shape and arrangement pattern of GO on the gas transport. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42624.     

Water-stable ZIF-300/Ultrason(R) mixed-matrix membranes for selective CO2 capture from humid post combustion flue gas

Water stable mixed-matrix membranes (MMMs) were developed to help control the global warming by capturing and sequestrating carbon dioxide (CO2) from post-combustion flue gas originated from burning of fossil fuels.MMMs of different compositions were prepared by doping glassy polymer Ultrason(R) S 6010 (US) with nanocrystals of zeolitic imidazolate frameworks (ZIF-300) in varying degrees.Solution-casting technique was used to fabricate various MMMs to optimize their CO2 capturing performance from both dry and wet gases.The prepared composite membranes indicated enhanced filler-polymer interfacial adhesion,consistent distribution of nanofiller,and thermally established matrix configuration.CO2 permeability of the membranes was enhanced as demonstrated by gas sorption and permeation experiments performed under both dry and wet conditions.As compared to neat Ultrason(R) membrane,CO2 permeability of the composite membrane doped with 40 wt％ ZIF-300 nanocrystals was increased by four times without disturbing CO2/N2 ideal selectivity.In contrast to majority of previously reported membranes,key features of the fabricated MMMs include their structural stability under humid conditions coupled with better and unaffected gas separation performance.     

Effects of halloysite nanotubes on the morphology and CO2/CH4 separation performance of Pebax/polyetherimide thin-film composite membranes

Enhancing the performance of gas separation membranes is one of the major concerns of membrane researchers. Thus, in this study, poly(ether-block-amide) (Pebax)/polyetherimide (PEI) thin-film composite membranes were prepared and their CO₂/CH₄ gas separation performance was investigated by means of pure and mixed gases permeation tests. To improve the properties of these membranes, halloysite nanotubes (HNT) were added to Pebax layer at different loadings of 0.5, 1, 2, and 5 wt % to form Pebax-HNT/PEI membranes. Scanning electron microscopy, gas sorption, X-ray diffraction, Fourier-transform infrared, and differential scanning calorimetry tests were also performed to investigate the impact of HNT on structure and properties of prepared membranes. Results showed that both CO₂/CH₄ selectivity and CO₂ permeance increased by adding HNT to Pebax layer up to 2 wt %. By increasing HNT loading to 5 wt %, the CO₂/CH₄ selectivity decreased from 32 to 18, while CO₂ permeance increased from 3.25 to 4.2 GPU. Pebax/PEI and Pebax-HNT/PEI membranes containing 2 wt % of HNT were tested using CO₂/CH₄ gas mixtures at different feed CO₂ concentrations and feed pressure of 4 bar. The results showed that with increasing CO₂ concentration from 20 to 80 vol %, CO₂/CH₄ selectivity of Pebax/PEI composite membranes increased by 19%, while, in Pebax-HNT/PEI membrane, CO₂/CH₄ selectivity decreased by 40%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48860.     

Synthesis,characterization, and gas separation performances of polysulfone and cellulose acetate-based mixed matrix membranes

ABSTRACT

The combination of polymeric and inorganic fillers inside mixed matrix membranes (MMMs) becomes a hot research topic due to the gas permeability-selectivity trade-off in polymeric membranes. Until recently, the problem of voids hampers the real application of MMMs, hence deep understanding on polymer-particle compatibility is required. This study focuses on the synthesis and characterization of polysulfone and cellulose acetate-based MMMs that combined with ZIF-8 and TiO₂ particles. ZIF-8 dispersed more uniform than TiO₂. The crystallinity of MMMs was higher than pure polymeric membrane. In addition, micro voids in MMMs resulted a slight decrease in CO₂/N₂ selectivity (from 15 to 12).     

Synthesis of dual-functionalized mixed matrix membrane with amino-GO-Bent/PVDF for efficient separation of CO2/CH4 and CO2/N2

Mixed matrix membranes (MMMs), which combine the characteristics of inorganic nanofillers and organic matrices, have received wide attention because of their good permeability and selective performance for separating CO₂ from industrial waste gases. In this work, the amino-GO-loaded bentonite (amino GO-Bent) was prepared by loading  NH₂ on the GO surface with a large number of functional sites. Firstly, by introducing  NH₂ on the surface of GO and then interacting with bentonite (Bent) organically modified by silane coupling agents through amide bonding. Mixed matrix membranes (MMMs) with an area of 623.7 cm² and homogeneous texture were prepared using amino-GO-Bent as inorganic filler to improve the membrane selectivity for CO₂/N₂ and CO₂/CH₄ separation. The results show that the introduction of amino GO-Bent in MMMs can greatly improve the CO₂ permeability and obtain high CO₂ permeation performance: 2.67945 × 10⁻⁷ cm³ (STP)·cm/s/cm²/cmHg, and the selectivity of CO₂/N₂ and CO₂/CH₄ can reach 307.28 and 325.97, respectively. The two selective values were 14 and 18 times higher than those of pure PVDF membranes, and the performance of MMMs far exceeded the Robeson upper limit in 2008, respectively.     

Preparation and characterization of polyvinylchloride based mixed matrix membrane filled with multi walled carbon nano tubes for carbon dioxide separation

Poly vinyl chloride/multi wall carbon nano tubes (PVC/MWCNTs) mixed matrix membranes (MMMs) were prepared for gas separation. Raw and functionalized MWCNTs (R-MWCNTs and C-MWCNTs) were utilized in membranes preparation. The C-MWCNT shows better performance compared to raw ones. Membrane (CO₂/CH₄) selectivity was increased from 39.21 to 52.18 at 2 bar pressure by MWCNT loading ratio. The modified membranes with styrene butadiene rubber (SBR-MMMs) showed 63.52 and 34.70 selectivity for (CO₂/CH₄) and (CO₂/N₂) at 2 bar pressure. Mechanical properties analysis exhibited tensile module improvement utilizing blending modification. Increase of feed pressure led to membrane gas permeability decreasing. But gas pair selectivity follows a nearly constant behavior for MMMs and increasing behavior for blend MMMs.