Mixed Matrix Hollow Fiber Membranes Research Articles

Development of Amine-Functionalized Metal-Organic Frameworks Hollow Fiber Mixed Matrix Membranes for CO2 and CH4 Separation: A Review.

CO2 separation from raw natural gas can be achieved through the use of the promising membrane-based technology. Polymeric membranes are a known method for separating CO2 but suffer from trade-offs between its permeability and selectivity. Therefore, through the use of mixed matrix membranes (MMMs) which utilizes inorganic or hybrid fillers such as metal-organic frameworks (MOFs) in polymeric matrix, the permeability and selectivity trade-off can be overcome and possibly surpass the Robeson Upper Bounds. In this study, various types of MOFs are explored in terms of its structure and properties such as thermal and chemical stability. Next, the use of amine and non-amine functionalized MOFs in MMMs development are compared in order to investigate the effects of amine functionalization on the membrane gas separation performance for flat sheet and hollow fiber configurations as reported in the literature. Moreover, the gas transport properties and various challenges faced by hollow fiber mixed matrix membranes (HFMMMs) are discussed. In addition, the utilization of amine functionalization MOF for mitigating the challenges faced is included. Finally, the future directions of amine-functionalized MOF HFMMMs are discussed for the fields of CO2 separation.

Graphene nanoplatelets based polyimide/Pebax dual-layer mixed matrix hollow fiber membranes for CO2/CH4 and He/N2 separations

Mixed matrix membranes are key in the preparation of stable, stretchy, durable and efficient membranes for gas separation applications. To this aim, the perfect filler nanomaterials’ dispersion is needed. At the same time the replacement of toxic solvents with green ones is also a priority in science, including the membrane technology. Herein, we present the development steps, their structural characteristics and the gas selectivity properties of graphene nanoplatelets (GNPs) based mixed matrix hollow fiber (HF) membranes. In specific, dual-layer composite polymeric hollow fiber membranes, for CO2/CH4 and He/N2 gas separations, were prepared by directly dip-coating a single selective layer on prepared porous HF supports without the use of any gutter layer. Asymmetric BTDA-TDI/MDI (P84) co-polyimide-based HFs that acted as porous supports, were fabricated via the dry-wet phase inversion process and the commercial poly(ether-block-amide) Pebax-1657 was chosen as a high CO2-selective separation layer material, dip-coated on the HF supports. The positive influence of the incorporation of GNPs as promising nanofiller in both, the polymeric matrix (support) and the selective layer, in parallel with the partial replacement of toxic NMP by GBL -a "green" solvent- in the support's spinning process, were all evaluated and confirmed. CO2/CH4 and He/N2 selectivities up to 82 and 20, respectively with CO2 and He permeances of 3 and 2.7 GPU, respectively were measured under real binary gas mixture conditions at 1.3 bar(a) transmembrane pressure at 298 K for dual-layer composite, with GNPs filler, HF (DL-HF) membranes.

Hollow Fiber Mixed Matrix Membranes Engineered Via the Combination of “Anionic Crosslinking and In-Situ Biomineralization” for Deep Dye Separation

Hollow Fiber Mixed Matrix Membranes Engineered Via the Combination of “Anionic Crosslinking and In-Situ Biomineralization” for Deep Dye Separation

Application of Il/Zif-8 Mixed Matrix Hollow Fiber Membrane for Co2 Capture from the Post-Combustion System

Application of Il/Zif-8 Mixed Matrix Hollow Fiber Membrane for Co2 Capture from the Post-Combustion System

Highly Permeable Mixed Matrix Hollow Fiber Membrane as a Latent Route for Hydrogen Purification from Hydrocarbons/Carbon Dioxide.

This work reported on the fabrication and investigation of a mixed matrix hollow fiber membrane (MMHFM) by incorporating commercially available alumina particles into a polyetherimide (PEI) polymer matrix. These MMHFMs were prepared by the dry-wet spinning technique. Accordingly, optimizing the spinning parameters, including the air gap distance and flow rate ratio, is key to determining the gas separation performance. However, there are few studies regarding the effect of the filler dimensions. Consequently, three sizes of alumina particles, 20 nm, 30 nm, and 1000 nm, were respectively added into the PEI phase to examine the influence of filler size on gas permeation property. Moreover, the permeation properties of lower hydrocarbons (i.e., ethane and propane) were also measured to evaluate potential for emerging applications. The results indicated the as-synthesized membrane exhibited a remarkable hydrogen permeance of 1065.24 GPU, and relatively high separation factors of 4.53, 5.77, and 5.39 for H2/CO2, H2/C2H6, and H2/C3H8, respectively. This resulted from good compatibility between the larger fillers and the PEI polymer, as well as a reduction in the finger-like voids. Overall, the MMHFM in this work was deemed to be a promising candidate to separate hydrogen from gas streams, based on the comparison of the separation performance against other reported studies.

Preparation of Hollow Fiber Membrane Containing ZnO Nanoparticles to Remove Natural Organic Matter

Polyethersulfone/zinc oxide mixed matrix hollow fiber membrane was fabricated using dry/wet phase inversion method. Zinc oxide nanoparticles (2 wt.%) were dispersed in N,N-dimethylacetamide (DMAc) solvent in the present of polyvinylepyrrolidene. The dope solution speed and take up speed was similar with performing the spinning process at room temperature. The produced membranes were characterized using scanning electron microscope (SEM), atomic force microscope (AFM), and Fourier transform infrared (FTIR) analysis. Membrane performance was evaluated using pure water flux (PWF), relative flux ration (RFR), and total organic carbon (TOC) removal efficiency. From SEM analysis, it was found that the nanoparticles were well dispersed in the polymeric matrix. From AFM results, it was observed that the modified membrane has higher surface roughness. The PWF of the modified membrane was enhanced, while the RFR showed to increase due to rougher membrane surface. The NOM remaoval of PES/ZnO membrane was higher than that of PES membrane and reached to 27% compared to only 16.9 % for pristine PES.

Thin Film Mixed Matrix Hollow Fiber Membrane Fabricated by Incorporation of Amine Functionalized Metal-Organic Framework for CO2/N2 Separation.

Membrane separation technology can used to capture carbon dioxide from flue gas. However, plenty of research has been focused on the flat sheet mixed matrix membrane rather than the mixed matrix thin film hollow fiber membranes. In this work, mixed matrix thin film hollow fiber membranes were fabricated by incorporating amine functionalized UiO-66 nanoparticles into the Pebax® 2533 thin selective layer on the polypropylene (PP) hollow fiber supports via dip-coating process. The attenuated total reflection-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping analysis, and thermal analysis (TGA-DTA) were used to characterize the synthesized UiO-66-NH2 nanoparticles. The morphology, surface chemistry, and the gas separation performance of the fabricated Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes were characterized by using SEM, ATR-FTIR, and gas permeance measurements, respectively. It was found that the surface morphology of the prepared membranes was influenced by the incorporation of UiO-66 nanoparticles. The CO2 permeance increased along with an increase of UiO-66 nanoparticles content in the prepared membranes, while the CO2/N2 ideal gas selectively firstly increased then decreased due to the aggregation of UiO-66 nanoparticles. The Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes containing 10 wt% UiO-66 nanoparticles exhibited the CO2 permeance of 26 GPU and CO2/N2 selectivity of 37.

PVDF/ MWCNT hollow fiber mixed matrix membranes for gas absorption by Al2O3 nanofluid

The study aims to investigate mixed matrix membranes for absorption of CO2in gas-liquid contacting process by AL2O3 nanofluid as liquid absorbent. PVDF/MWCNT hollow fiber mixed matrix membranes were fabricated absorbent and characterized via relevant characterizations. This study showed that the addition of MWCNT to the matrix led macro cavities to be expanded at the cross section of the membrane. According to the results of gas permeation, surface porosity experienced an increasing trend and in contrast surface pore size reduced. By placing the CNTs in porous PVDF, an increase in the surface contact angle and hydrophobicity of the composite membranes was revealed which could be related to the hydrophobic nature of the added nanopaticles as well as increasing the absorbent average surface roughness.

Performance of polysulfone hollow fiber membranes encompassing ZIF-8, SiO2/ZIF-8, and amine-modified SiO2/ZIF-8 nanofillers for CO2/CH4 and CO2/N2 gas separation

High tunable properties of metal–organic frameworks (MOFs) allows different modifications to be used for distinct applications. Zeolitic imidazolate frameworks-8 or ZIF-8 are hybrid organic–inorganic porous materials that have shown great potential in membrane-based gas separations. In our study, SiO2/ZIF-8 (S/ZIF-8) nanofiller was synthesized via a facile one-step strategy. Furthermore, the S/ZIF-8 nanofiller was subjected to amine modification using an ammonium hydroxide solution. X-ray photoelectron spectroscopy (XPS) analysis confirms the strong binding of amine and SiO2 on ZIF-8 nanofillers. The synthesized ZIF-8, S/ZIF-8, and amine-modified S/ZIF-8 (A@S/ZIF-8) of 0.5 wt% were incorporated into the polysulfone (PSf) matrix, and the hollow fiber mixed matrix membranes (MMMs) were fabricated using dry–wet phase inversion technique. The inclusion of an amine group in the S/ZIF-8 nanofillers enhances the interaction between the nanofillers and PSf matrices, thus improving the CO2/CH4 and CO2/N2 separation performances. The fabricated membranes were morphologically characterized by Scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) surface area, and the pore size distribution. It is noteworthy that the BET surface area was enhanced with nanofillers addition and significantly increased gas separation performance. The fabricated asymmetric hollow fiber MMMs were further studied for gas permeation experiments for CO2, N2, and CH4. PSf with A@S/ZIF-8 MMMs showed the best performance as observed from the Robeson upper bound limit, CO2 permeability of 4.25 barrer with the improvements in CO2/N2 and CO2/CH4 selectivities of 89.75 and 61.46% respectively, compared with neat PSf membrane. The enhanced permselectivity of PSf–A@S/ZIF-8 membranes is explained by CO2-facilitated transport, where the high CO2 affinity of the amine group allows the selective transport of CO2 rather than CH4 and N2.

In vitro study of dual layer mixed matrix hollow fiber membranes for outside-in filtration of human blood plasma

Hemodialysis mainly removes small water-soluble uremic toxins but cannot effectively remove middle molecules and protein-bound uremic toxins. Besides, the therapy is intermittent leading to fluctuating blood values and fluid status which adversely impacts patients’ health. Prolonged hemodialysis (with adequate anticoagulation) could improve the removal of toxins and the development of portable and wearable artificial kidneys could offer more flexibility in the dialysis scheme. This would enhance patients’ overall health, autonomy, mobility and flexibility, allowing patients to participate in social and economic life. However, the time that patients’ blood is exposed to the dialyzer material is longer during prolonged hemodialysis, and blood clots could obstruct the fiber lumen, resulting in a decrease of the effective membrane surface area available for toxin removal. The outside-in filtration (OIF) mode, wherein blood flows through the inter-fiber space instead of through the fiber lumina, has been applied widely in blood oxygenators to prevent fiber clotting, but not in hemodialysis.In this study, we present for the first time the development of a mixed matrix membrane (MMM) for OIF of human blood plasma. This MMM combines diffusion and adsorption and consists of a polymeric membrane matrix with activated carbon (AC) particles on the inside layer, and a polymeric particle-free layer on the outer fiber layer. Our results show that in vitro MMM fibers for OIF demonstrate superior removal of the protein-bound uremic toxins, indoxyl sulfate and hippuric acid, compared to both earlier MMM fibers designed for inside-out filtration mode and commercial high-flux fibers. Statement of significanceCurrent hemodialysis therapy cannot effectively remove protein-bound toxins. Prolonged hemodialysis could improve toxin removal. However, during prolonged hemodialysis, blood clots could obstruct the fiber lumen, resulting in decreased effective membrane surface area available for toxin removal.We have prepared, for the first time, dual layer mixed matrix hollow fiber membranes (MMM) for outside-in filtration (OIF). The OIF mode wherein blood would flow through the inter-fiber space instead of through the fiber lumina could prevent fiber clotting. Moreover, the MMMs combine diffusion and adsorption to improve (protein-bound) toxin removal.We believe that the new design of our MMM fibers is an important contribution concerning the development of artificial kidney systems and the improvement of the health and well-being of patients with renal failure.

CO2/CH4 mixed gas separation using graphene oxide nanosheets embedded hollow fiber membranes: Evaluating effect of filler concentration on performance

Graphene oxide (GO) nanosheets-based composite polymeric membranes are being explored for the effective separation of gases owing to hydrophilic nature and abundant oxygen moieties on their surface that attracts the polar gases. In this study, the effect of GO nanosheets concentration on the CO2/CH4 mixed gas separation performance of polysulfone (Psf) hollow fiber mixed matrix membranes (HFMMMs) was examined. The different concentration of GO, i.e., 0.25, 0.5, and 0.75 wt% of the polymer dope solution, was used. Hollow fiber membranes (HFMs) were prepared using dry/wet quench method with water as non-solvent, and physicochemical properties were evaluated. Morphological changes were observed in the Psf/GO HFMMMs. The gas separation performance study of the HFM samples was carried out using pure CO2 and CH4 gases at 1–5 bar transmembrane pressure and 25 ± 2 °C. It was found that HFMMMs with 0.25 wt% GO nanosheets (PG25) showed 137% higher ideal CO2/CH4 selectivity than the pristine HFMs. In case of the mixed gas permeation studies using feed consisting of 50:50 vol% of CO2 and CH4, the PG25 HFMMMs showed 201% higher CO2/CH4 selectivity than that of the pristine HFMs. Moreover, the PG25 HFMMMs showed separation performance stability when they were applied for the long-term stability study. These results indicate that 0.25 wt% GO nanosheets in Psf is the optimum concentration which gives improved CO2/CH4 mixed gas separation performance.

Interfacial manipulation of MOFs/polymer mixed matrix membranes for gas separations: A review

Membrane-based separation technology holds great promise to effectively address separation needs in chemical industries due to advantages in energy efficiency, scalability, and small footprint. Mixed matrix membranes based on polymer/metal organic frameworks (MOFs), which combine the ease of processability of polymer materials with the excellent adsorption characteristics of MOFs, have been widely investigated for gas separations. The preparation of gas separation membrane materials with both high flux and gas selectivity is the key to achieving efficient gas separation. Recent research results show that the permeability coefficient and gas pair selectivity of mixed matrix membrane materials are hardly improved simultaneously by adding second phase materials such as MOFs. When the loading of MOFs increases, most membranes have common problems such as particle agglomeration and non-selective interfacial defective structures, which lead to a significant decrease in separation performance. To resolve these issues, research scientists are devoted to tailoring the interfacial microstructure of mixed matrix membranes with an aim to exceed the Robeson upper limit. Many novel characterization techniques coupled with simulation studies were carried out to probe the filler dispersion behavior and interfacial structure within membranes in order to provide rules for rationally designing mixed matrix membranes. A variety of approaches have been proposed to finely tune the interfacial interaction by constructing hydrogen bonding and covalent bonding in the membranes. For example, synthesizing functionalized MOFs via mixed-linker or ligand exchange methods provides a good option to enhance interfacial adhesion within membranes. The amino groups, hydroxyl groups and other organic functional groups in MOFs have the capability to create hydrogen bonding. Moreover, these groups can preferentially adsorb specific gas molecules (such as CO2 molecules) to improve gas selectivity. Some researchers post-functionalized MOFs to graft reactive groups on their surface, incorporating them with cross-linkable polymers. Then the light/heat induced crosslinking reaction occurred within the membrane to seal its defective structure, thereby achieving a substantial improvement in membrane separation performance. The past publications on mixed matrix membranes in the decade demonstrated that the researchers have much more in-depth understanding and insights on the fabrication process, membrane morphology, and structure-property relationship of mixed matrix membrane materials. With respect to fundamental research, research scientists are committed to investigating the MOFs properties including crystal morphology, coordinated metal ion, functional groups on membrane performance. To yield high performance mixed matrix membranes, highly permeable polymers were rationally designed as the polymer matrix. However, to complement their widespread industrial application, scale-up of hollow fiber mixed matrix membranes needs to be further investigated. The membrane stability in humid gas feeds is required to be improved. It is also of importance to develop stable, cost-effective and scalable MOFs fillers. With a specific focus on interfacial manipulation of MOFs/polymer mixed matrix membranes for gas separations, this paper mainly reviewed the research progress in the fields of MOFs/polymer-based hybrid matrix membranes for gas separations. It focuses on three aspects: (1) Research progress on optimizing and characterizing the interfacial structure; (2) fundamental understanding of the influences of MOFs and polymers properties on membrane performance; (3) research progress on scale-up of mixed matrix membranes. Finally, the future development direction of mixed matrix membrane materials is proposed in order to provide research ideas for the rational design of high-performance mixed matrix membranes.

Transforming polymer hollow fiber membrane modules to mixed-matrix hollow fiber membrane modules for propylene/propane separation

Mixed-matrix membranes (MMMs) have shown promising performances for gas separation, in particular, propylene/propane separation. Their commercial applications require to fabricate MMMs in scalable forms, i.e., asymmetric mixed-matrix hollow fiber membranes (MMHFMs). Up until now, however, there have been few reports on MMHFMs due to the fundamental engineering challenges associated with current fiber spinning processes using filler-suspended dope solutions. Recently, we proposed a scalable MMM fabrication strategy, namely polymer-modification-enabled in-situ metal-organic framework formation (PMMOF). The PMMOF has potential to overcome some of the engineering challenges since it decouples hollow fiber spinning step and MMM formation step. Herein, we report asymmetric 6FDA-DAM (4,4′-(hexafluoroisopropylidene) diphthalic anhydride-2,4,6-trimethyl-1,3-diaminobenzene)/ZIF-8 MMHFM modules by transforming 6FDA-DAM coated hollow fiber membrane (HFM) modules using the PMMOF. The resulting asymmetric MMHFM modules showed a promising propylene/propane separation performance (i.e., propylene permeance of ~2.15 GPU and separation factor of ~23.4) without additional defect healing steps. The membranes showed stable separation performance over a period of up to 25 days and at the total feed pressures of up to 6 bar. Finally, we demonstrated MMHFM modules consisting of up to seven individual fiber strands. To the best of our knowledge, this is the first multi-strand MMHFM modules showing promising propylene/propane separation performances, thereby opening up the possibility of the commercial applications of MMMs.

Oxone®-Mediated TEMPO-Oxidized Cellulose Nanomaterial Ultrafiltration and Dialysis Mixed-Matrix Hollow Fiber Membranes.

Recent exploration of cellulose nanomaterials has resulted in the creation of Oxone®-Mediated TEMPO-Oxidized Cellulose Nanomaterials (OTO-CNMs). These materials, when incorporated into a polymer matrix, have properties showing increased flux, decreased membrane resistance, and improved clearance, making them an ideal material for dialysis. This study is the first to focus on the implementation of OTO-CNMs into hollow fiber membranes and a comparison of these membranes for ultrafiltration and dialysis. Ultrafiltration and dialysis were performed using bovine serum albumin (BSA), lysozyme, and urea to analyze various properties of each hollow fiber membrane type. The results presented in this study provide the first quantitative evaluation of the clearance and sieving characteristics of Oxone®-Mediated TEMPO-Oxidized Cellulose-Nanomaterial-doped cellulose triacetate mixed-matrix hemodialyzers. While the cellulose nanomaterials increased flux (10–30%) in ultrafiltration mode, this was offset by increased removal of albumin. However, in dialysis mode, these materials drastically increased the mass transfer of components (50–100%), which could lead to significantly lower dialysis times for patients. This change in the performance between the two different modes is most likely due to the increased porosity of the cellulose nanomaterials.

Multicomponent transport model-based scaling up of long-term adsorptive filtration of MOF incorporated mixed matrix hollow fiber membrane: Treatment of textile effluent

The present work describes the preparation and detailed characterization of porous chromium terephthalate metal–organic framework (MOF) impregnated polyacrylonitrile based hollow fiber membrane. The hollow fibers were characterized by their surface morphology, zeta potential, permeability, average pore diameter, molecular weight cut off (MWCO) and contact angle. Variation of MOF concentration upto 10 wt% resulted in 43% reduction in membrane permeability. The corresponding change in MWCO was from 140 kDa to 70 kDa. The addition of MOF made the membrane more hydrophilic and at 10 wt% MOF, the contact angle was reduced to 52° from 86°. The Fourier Transform Infrared Spectra (FTIR) of mixed matrix membrane (MMM) showed that there existed strong chemical interaction between MOF particles and polymer backbone, precluding the leaching of MOF from the membrane matrix over long term use. The MOF incorporated MMM exhibited tremendous adsorption capacity (197–260 mg/g for 10 wt% MOF doped fiber) towards reactive dyes commonly used in the textile industry. As the dye removal by MMM hollow fiber was based on the adsorption mechanism, the breakthrough behavior of the membrane was important to estimate the membrane life and onset of membrane regeneration. In the present work, a detailed two-dimensional transient transport model was developed for a multi-component real-life textile effluent from the first principles using the equation of continuity, momentum balance, species balance based on convective-diffusive-adsorptive solute transport in the hollow fiber. The model results were validated with the experimental data of a textile effluent having four reactive dyes. The multicomponent model was used for scaling up the actual hollow fiber based filtration system and the performance curve was generated relating the breakthrough volume, number and length of fibers.

ZIF-8 based polysulfone hollow fiber membranes for natural gas purification

Mixed matrix membranes (MMMs) have received worldwide attention for natural gas purification due to their superior performance in terms of permeability and selectivity. The zeolitic imidazole framework-8 (ZIF-8) blended polysulfone (PSf) membranes have been fabricated for natural gas purification. ZIF-8 was selected due to its low cost, remarkable thermal and chemical stabilities, and tunable microporous structure. The neat PSf hollow fiber membrane and mixed matrix hollow fiber membranes incorporated with the various ZIF-8 loadings up to 1.25% were fabricated. The prepared membranes were evaluated using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and gas separation performance. The low loading of ZIF-8 nanoparticles to the MMM improved thermal stability and glass transition temperature and yielded low surface roughness. MMMs were tested using pure gases with a significant improvement of 36% in CO2 permeability and 28% in CO2/CH4 selectivity compared to the neat membrane. However, the high ZIF-8 loading reduced the separation performances. Moreover, CO2/CH4 selectivity decreased at elevated pressure (8 and 10 bar) due to CO2-induced plasticization. Previously, the incorporation of ZIF-8 particles has primarily been subjected to the fabrication of flat sheet membranes, whereas this work focused on hollow fiber membranes which are rarely investigated. Hence, the promising results obtained at low feed pressure in this study demonstrated the potential of ZIF-8 based hollow fiber membrane for natural gas purification.

Preparation and characterization of PVDF-filled MWCNT hollow fiber mixed matrix membranes for gas absorption by Al2O3 nanofluid absorbent via gas–liquid membrane contactor

Porous polyvinylidene fluoride (PVDF)-filled MWCNT hollow fiber mixed matrix membranes were fabricated and applied for carbon dioxide absorption in a gas–liquid membrane contactor with Al2O3 water-based nanofluid absorbent. The formation of MWCNTs’ nanotubes was verified through Transmission electron microscopy (TEM) and Field emission scanning electron microscopy (FESEM) images while the resultant membranes were characterized for their morphology, gas permeation rate, pore size, porosity, surface hydrophilicity and wettability resistance. Upon the incorporation of MWCNT into the matrix, the formation of finger-like pores was facilitated and surface roughness increased. Gas permeation test results showed increasing the surface porosity and reducing the pore size. The surface contact angle also was improved from 83°±1.5 for the unfilled membrane to 103°±1.5 for the membrane containing 5wt% CNT. CO2 absorption flux also was enhanced considerably. For instance, the flux of the membrane containing 5wt% CNT as the best performing membrane at a liquid velocity of 2.5m/s and Al2O3 water-based nanofluid as absorbent was 3.85×10−3mol/m2s which was approximately 200% higher than that of the plain membrane at the same operating conditions. A long-term absorption test also revealed non-wetting tendencies of the membranes as well as the unclogged membrane pores by the nanomaterials existed in the nanofluid absorbent. Therefore, it could be hypothesized that the improved membrane structure and synthesized nanofluid absorbent considering their superior performance to several commercial and in-house made membranes can be suitable alternatives to the current polymeric membranes and commercial used absorbents, respectively.

Study on the effect of process parameters on CO2/CH4 binary gas separation performance over NH2-MIL-53(Al)/cellulose acetate hollow fiber mixed matrix membrane

The aim of current work is to study the interaction of process parameters including, temperature, CO2 feed composition and feed pressure were towards CO2 separation from CO2/CH4 binary gas mixture over hollow fiber mixed matrix membrane using design of experiment (DoE) approach. The hollow fiber mixed matrix membrane (HFMMM) containing NH2-MIL-53(Al) filler and cellulose acetate polymer was successfully spun and fibers with outer diameter of approximately 250–290 nm were obtained. The separation results revealed that the increment of temperature from 30 °C to 50 °C reduced the CO2/CH4 separation factor while, increasing feed pressure from 3 bar to 15 and increment of CO2 feed composition from 15 to 42.5 vol% increased the separation factor of HFMMM. The DoE results showed that the feed pressure was the most significant process parameter that intensely affected the CH4 permeance, CO2 permeance and CO2/CH4 separation factor. Based on the experimental results obtained, maximum CO2 permeance of 3.82 GPU was achieved at feed pressure of 3 bar, temperature of 50 °C and CO2 feed composition of 70 vol%. Meanwhile, minimum CH4 permeance of 0.01 GPU was obtained at feed pressure of 15 bar and temperature of 30 °C and CO2 feed composition of 70 vol%. Besides, maximum CO2/CH4 separation factor of 14.4 was achieved at feed pressure of 15 bar and temperature of 30 °C and CO2 feed composition of 15 vol%. Overall, the study on the interaction between separation processes parameters using central composite design (CCD) coupled with response surface methodology (RSM) possesses significant importance prior to the application of NH2-MIL-53(Al)/Cellulose Acetate HFMMM at industrial scale of natural gas purification.

In-situ linker doping as an effective means to tune zeolitic-imidazolate framework-8 (ZIF-8) fillers in mixed-matrix membranes for propylene/propane separation

Zeolitic-imidazole framework-8 (ZIF-8) has been extensively studied as a molecular sieving filler in mixed-matrix membranes (MMMs) for propylene/propane (C3) separation. The C3 separation performance of ZIF-8-containing MMMs has yet to meet the commercial viability criteria. Recently, doping or mixing linkers in ZIF-8 framework has been found effective in tuning the molecular sieving properties of ZIF-8. Herein, we attempted to tune the molecular sieving properties of ZIF-8 fillers in MMMs by doping with 2-ethylimidazole (eIm) linkers in order to improve their C3 separation performance. MMMs were prepared by in-situ forming eIm-doped ZIF-8 fillers in polyimide using our recently reported polymer-modification-enabled in-situ MOF formation (PMMOF) process. As eIm linkers were doped into ZIF-8 filler crystals, the propylene/propane separation factor of the resulting MMMs was dramatically enhanced. Lastly, doped-linker ZIF-8 based mixed-matrix hollow fiber membranes were successfully prepared, demonstrating potential of their scalable practical applications.

PBI mixed matrix hollow fiber membrane: Influence of ZIF-8 filler over H2/CO2 separation performance at high temperature and pressure

High performance and commercially attractive mixed-matrix membranes were developed for H2/CO2 separation via a scalable hollow fiber spinning process. Thin (~300 nm) and defect-free selective layers were successfully created with a uniform distribution of the nanosized (~60 nm) zeolitic-imidazole framework (ZIF-8) filler within the polymer (polybenzimidazole, PBI) matrix. These membranes were able to operate at high temperature (150 °C) and pressure (up to 30 bar) process conditions required in treatment of pre-combustion and syngas process gas streams. Compared with neat PBI hollow fibers, filler incorporation into the polymer matrix leads to a strong increase in H2 permeance from 65 GPU to 107 GPU at 150 °C and 7 bar, while the ideal H2/CO2 selectivity remained constant at 18. For mixed gas permeation, there is competition between H2 and CO2 transport inside ZIF-8 structure. Adsorption of CO2 in the nanocavities of the filler suppresses the transport of the faster permeating H2 and consequently decreases the H2 permeance with total feed pressure down to values equal to the pure PBI hollow fibers for the end pressure of 30 bar. Therefore, the improvement of fiber performance for gas separation with filler addition is compromised at high operating feed pressures, which emphasizes the importance of membrane evaluation under relevant process conditions.