Polymer Hollow Fiber Membranes Research Articles

Preparation of amino-functionalized polyethylene-silica composite membrane and FDH immobilization

Enzymatic CO2 conversion represents a highly efficient, energy-conserving, and environmentally sustainable approach to mitigating the increasing pressure caused by huge carbon emissions and generating valuable products. However, several challenges associate with the process including the instability and recovery difficulty of free enzyme, as well as low solubility of CO2 in mild conditions. Immobilizing enzyme on the amino-functionalized supports presents a viable solution to these issues. Considering the wide application of polymer hollow fiber membranes in the field of CO2 gas–liquid membrane contactor and the characteristics of hydrophilic, biocompatible, and high specific surface area of silica nanoparticles, the amino-functionalized polyethylene (PE)-silica (APS) composite membranes were fabricated via different routes. The morphologies, the loading rates of modified SiO2 and reusability of APS membranes were characterized for a crude screening. Following that, seven kinds of APS membranes were used as the carriers of formate dehydrogenase (FDH) that could catalyze the reduction of CO2 to formate, and their immobilization efficiency and catalytic performance were compared. The results show that 1# and 2# membranes based on carboxyl-modified PE with a loading rate of 5.5 %∼5.6 % and the reusability of above 99 % were more ideal carriers than others. The enzyme activity recovery rate of APS-immobilized FDH (FDH-APS) was separately 367 % and 256 %, proving the intensification action of carriers on the enzymatic reaction. After 10 cycles of use, the relative activity of two kinds of FDH-APS was around 70 % and 78 %, much higher than corresponding particles or membrane attached FDH (25.3 % and 20.4 %). After storage at 4 °C for 20 days, the relative activity of FDH-APS was 82.7 % and 81.0 %, while it was only 61.4 % for free enzyme.

Regulation of dual-scale structure of polypropylene/poly(ethylene-co-vinyl alcohol) hollow fiber membranes with bimodal pore base on lamellae optimization during annealing

Solvent-free manufacturing process of high performance polymer hollow fiber membranes has always been a desirable direction. Therefore, maleic anhydride grafted polypropylene (PP-g-MAH) as compatibilize, the polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes (PMEHFMs) with bimodal pore were manufactured via melt-spinning and stretching. Bimodal pore structure was constructed for improving the porosity and retaining the rejection performance. Based on the effect of EVOH on nucleation behavior and crystal growth of PP phase, the effect of annealing temperature on microscopic lamellar structure of hollow fibers with adding EVOH was investigated in detail, and the results were expected to guide the regulation of dual-scale structure of bimodal pore. With rising annealing temperature, long period of crystal (L) gradually increased, but thickness of lamellae (Lc) and rigid amorphous (Ltr) firstly increased and then decreased when annealing temperature increased to 160 °C, and optimum values were obtained when annealing temperature was 150 °C. The optimum crystallinity and lamellar orientation of annealed hollow fiber annealed at 150 °C were 48.48% and 0.863, respectively. As the annealing temperature increased, the most probable pore size of small scale pores in PMEHFMs increased firstly and then stabilized at 183 nm, which was correspond to the change of lamellar thickness in annealed hollow fibers. Whereas, the most probable pore size of large scale pores did not show a significant change trend. The porosity increased firstly and then decreased with the increase of annealing temperature, which was also correspond to the change of pure water fluxes of PMEHFMs. The porosity and pure water flux of PMEHFM reached the maximum when the annealing temperature was 150 °C.

Covalent Furan‐Benzimidazole‐Linked Polymer Hollow Fiber Membrane for Clean and Efficient Photosynthesis of Hydrogen Peroxide

AbstractPhotocatalytic H2O2 production by conversion of O2 in aqueous solution is often challenged by the use of sacrificial agents, the separation of powdery photocatalysts, solution, and contaminants, and low activity of photocatalyst. Herein, a membrane of covalent furan‐benzimidazole‐linked polymer (Furan‐BILP) with both O‐ and N‐containing heterocycles bonded via OCCN is reported for the first time as a photocatalyst to harvest clean H2O2 in pure water with high‐performance. A coordination‐polymer hard template strategy is developed to produce Furan‐BILP hollow microfibers that can be further assembled into membranes with desired sizes. The resultant Furan‐BILP membrane directly delivers clean H2O2 solution as the product with a high H2O2 production rate of 2200 µmol g−1 h−1 in pure water. Density functional theory calculations and experiment results indicate that the C atom from Furan ring on the linkage binds to the adsorbed OOH*, the H atom of OOH* forms a hydrogen bond with the N atom in the benzimidazole ring, thus the intermediate six‐membered ring structure stabilizes the OOH* and favors 2e‐ORR. The strategy using both molecular engineering to tune the electronic structure and macrostructural engineering to shape the morphology may be applied to design other coordination organic polymer photocatalysts with further improved performance.

A Membrane Contactor Enabling Energy-Efficient CO2 Capture from Point Sources with Deep Eutectic Solvents

We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO2 capture. This process uses a deep eutectic solvent (DES) in an HFMC to provide close interfacial interactions and contact between the DES and CO2. This approach overcomes disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO2 capture methods. Commercial low-cost polymer hollow fiber membranes (e.g., microporous polypropylene) were evaluated for CO2 capture with reline, a prototypical DES. Single-gas measurements showed that the DES-based polypropylene HFMC can capture and separate CO2 while rejecting N2. From a mixed gas containing 50 mol % N2 and 50 mol % CO2, the DES-based HFMC separated CO2 with a purity of 96.9 mol %. The effect of several process parameters including solvent flow rate, pressure, and temperature on the CO2 separation performance was studied. The flux of the recovered CO2 was 67.43 mmole/m2/h at a feed pressure of 4 bar. In situ Fourier transform infrared (FTIR) measurements combined with density functional theory (DFT)-based molecular dynamics simulations revealed that reline absorbs CO2 by physical absorption without forming a new chemical compound, and CO2 separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about physical solvent-based separation processes and a pathway toward practical deployment.

On the quest of reliable 3D dynamic in vitro blood-brain barrier models using polymer hollow fiber membranes: Pitfalls, progress, and future perspectives.

With the increasing concern of neurodegenerative diseases, the development of new therapies and effective pharmaceuticals targeted to central nervous system (CNS) illnesses is crucial for ensuring social and economic sustainability in an ageing world. Unfortunately, many promising treatments at the initial stages of the pharmaceutical development process, that is at the in vitro screening stages, do not finally show the expected results at the clinical level due to their inability to cross the human blood-brain barrier (BBB), highlighting the inefficiency of in vitro BBB models to recapitulate the real functionality of the human BBB. In the last decades research has focused on the development of in vitro BBB models from basic 2D monolayer cultures to 3D cell co-cultures employing different system configurations. Particularly, the use of polymeric hollow fiber membranes (HFs) as scaffolds plays a key role in perfusing 3D dynamic in vitro BBB (DIV-BBB) models. Their incorporation into a perfusion bioreactor system may potentially enhance the vascularization and oxygenation of 3D cell cultures improving cell communication and the exchange of nutrients and metabolites through the microporous membranes. The quest for developing a benchmark 3D dynamic in vitro blood brain barrier model requires the critical assessment of the different aspects that limits the technology. This article will focus on identifying the advantages and main limitations of the HFs in terms of polymer materials, microscopic porous morphology, and other practical issues that play an important role to adequately mimic the physiological environment and recapitulate BBB architecture. Based on this study, we consider that future strategic advances of this technology to become fully implemented as a gold standard DIV-BBB model will require the exploration of novel polymers and/or composite materials, and the optimization of the morphology of the membranes towards thinner HFs (<50μm) with higher porosities and surface pore sizes of 1-2µm to facilitate the intercommunication via regulatory factors between the cell co-culture models of the BBB.

Zeolite Imidazolate Framework Membranes on Polymeric Substrates Modified with Poly(vinyl alcohol) and Alginate Composite Hydrogels.

Poly(vinyl alcohol)-sodium alginate composite hydrogels were first introduced to synthesize robust and well-intergrown zeolite imidazolate framework (ZIF)/polymer hollow fiber membranes. Through enough adsorption interaction with metal ions by chelation, sufficient nucleation sites for in situ metal-organic framework (MOF) preparation are provided. Using this method, we can not only easily prepare defect-free MOF membranes ignoring the complex modification process and seed deposition but also structurally fix crystalline MOF layers and greatly improve the stiffness and durability of MOF composite membranes. The strategy also gives the appropriate level of generality for synthesis of versatile dense MOF membranes on a variety of polymeric supports. The fabricated ZIF-8/polyethersulfone membrane presented remarkable gas separation performance with H2 permeance of as high as 9.66 × 10-7 mol m-2 s-1 Pa-1 and a high H2/CO2 separation factor of up to 29.0.

Inorganic particle enhanced polymer hollow fiber membranes with high mechanical properties

Inorganic particle/polymer hollow fiber membranes with different inorganic particle sizes and particle loadings were synthesized and characterized in terms of morphology and mechanical properties. The incorporation of inorganic particles induces the formation of large surface pores in the skin layer yet decreases the pore size of large voids in the support layer. The particle size and particle loading are determining factors in such morphology changes. Moreover, due to the different out-diffusion ability of inorganic particles with different sizes, smaller particles migrated and diffused out from polymer much more easily; therefore nano-sized inorganic particles were usually observed on the top surface of polymer whereas micron-sized inorganic particles were usually partially embedded inside the polymer. As a result of such morphology changes and the intrinsic mechanical properties of inorganic particles, both tensile and compressive properties were improved in such inorganic-polymer composite membranes compared to the pristine membranes. Specifically, the tensile strength can be increased by 47.2% with 1.96 wt% nano-sized alumina whereas the yield compressive strength was enhanced by 55.4% with 76.9 wt% micron-sized alumina in comparison with the pristine polymeric membranes. Besides the improvement of strength, the tensile and compressive Young's modulus was increased and the micron-sized particles are more effective to enhance the Young's modulus than the nano-sized particles. Besides the improvement in mechanical properties, the permeability of polymeric membranes was also enhanced via the inorganic particle incorporation. Therefore, such inorganic-polymer hollow fiber membranes are more promising to be used for practical industrial filtration applications regarding their higher mechanical properties to resist breakage and deformation and their higher permeability in comparison with the polymeric hollow fiber membranes.

Fabrication of Collagen Gel Hollow Fibers by Covalent Cross-Linking for Construction of Bioengineering Renal Tubules.

Collagen, the most used natural biomacromolecule, has been extensively utilized to make scaffolds for cell cultures in tissue engineering, but has never been fabricated into the configuration of a hollow fiber (HF) for cell culture due to its poor mechanical properties. In this study, renal tubular cell-laden collagen hollow fiber (Col HF) was fabricated by dissolving sacrificial Ca-alginate cores from collagen shells strengthened by carbodiimide cross-linking. The inner/outer diameters of the Col HF were precisely controlled by the flow rates of core alginate/shell collagen solution in the microfluidic device. As found, the renal tubular cells self-assembled into renal tubules with diameters of 50-200 μm post to the culture in Col HF for 10 days. According to the 3D reconstructed confocal images or HE staining, the renal cells appeared as a tight tubular monolayer on the Col HF inner surface, sustaining more 3D cell morphology than the cell layer on the 2D flat collagen gel surface. Moreover, compared with the cultures in either a Transwell or polymer HF membrane, the renal tubules in Col HF exhibited at least 1-fold higher activity on brush border enzymes of alkaline phosphatase and γ-glutamyltransferase, consistent with their gene expressions. The enhancement occurred similarly on multidrug resistance protein 2 and glucose uptake. Such bioengineered renal tubules in Col HF will present great potential as alternatives to synthetic HF in both clinical use and pharmaceutical investigation.

Pressure-Assisted Synthesis of HKUST-1 Thin Film on Polymer Hollow Fiber at Room Temperature toward Gas Separation

The scalable fabrication of continuous and defect-free metal-organic framework (MOF) films on the surface of polymeric hollow fibers, departing from ceramic supported or dense composite membranes, is a huge challenge. The critical way is to reduce the growth temperature of MOFs in aqueous or ethanol solvents. In the present work, a pressure-assisted room temperature growth strategy was carried out to fabricate continuous and well-intergrown HKUST-1 films on a polymer hollow fiber by using solid copper hydroxide nanostrands as the copper source within 40 min. These HKUST-1 films/polyvinylidenefluoride (PVDF) hollow fiber composite membranes exhibit good separation performance for binary gases with selectivity 116% higher than Knudsen values via both inside-out and outside-in modes. This provides a new way to enable for scale-up preparation of HKUST-1/polymer hollow fiber membranes, due to its superior economic and ecological advantages.

Separation of Sulfur Hexafluoride from a Nitrogen/Sulfur Hexafluoride Mixture Using a Polymer Hollow Fiber Membrane

Sulfur hexafluoride (SF6) has been evaluated by the Intergovernmental Panel on Climate Change (IPCC) as the substance with the highest global warming index. Because of its superior insulating and arc clearing capacities, it is commonly used as an insulator in electrical machines. SF6 waste products form in the process of storing, maintaining, and repairing the machines. SF6 emitted into the atmosphere remains for 3,200 years, causing global warming. Release into the mesosphere leads to photolysis and creation of highly toxic and corrosive by-products. A review of the literature related to the retrieval and separation of SF6 using a separating membrane indicates that research on the permeability of the separating membrane material is lacking. Additionally, research on the concentrations of the SF6 waste products and the separation/retrieval with operating conditions with optimal energy efficiency is only in the initial stages. Therefore, this research assessed the permeability of commercialized separation membranes polysulfone (PSf), polycarbonate (PC), and polyimide (PI) using the gases SF6 and N2. Using an SF6/N2 mixture with the same concentration as the SF6 waste products, we studied the separation and retrieval capacities of PSf, PC, and PI separation membranes under varying operating conditions. The permeability tests showed that the selective permeability of N2/SF6 is highest for the PI membrane and lowest for the PC membrane. When the concentrations of SF6 retrieved from the mixture separation process were compared, the PC membrane was found to be the highest, with 95.6 % at 0.5 MPa. The retrieval percentage of SF6 was highest for PSf, with 97.8 % at an operating pressure of 0.3 MPa and a waste production of 150 cm3/min. The retrieval rates and retrieval failure rates have an inverse relationship. In total, 99 % of the supply of SF6 was identified via the retrieval rates and retrieval failure rates, so it could be confirmed that the separation of the SF6/N2 mixture using a macromolecular hollow fiber separation membrane works properly.

Used lubricating oil recycling using a membrane filtration: Analysis of efficiency, structural and composing

Three kinds of polymer hollow fiber membranes—polyethersulphone (PES), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN)—were used for recycling of used lubricating oil. The efficiency of membrane separation was characterized by means of the membrane rejection and the physical and chemical properties of the oils. The separation and analytical methods, for example, Fourier Transform Infrared (FTIR), UV-visible absorption spectra, column chromatography, etc. were employed to illustrate the separation mechanism and the potential structures of used lubricant oil so as to assess the differences between the used lubricating oil and the permeate. Results show that the membrane process can not only remove metal particles and dusts from waste lubricant oil, but also improve its liquidity and flash point. Further, the ultrafiltration membrane (PAN) has higher rejection than microfiltration membranes (PES and PVDF). The results of FT-IR and UV absorption spectra show that waste lubricant oil has almost 90% long chain saturated hydrocarbons, which are originally from the base oil. The middle polarity compositions may be lactones, esters, aldehydes, ketones, carboxylic acids, which may come from the oxidation of base oil and additives during the use of lubricating oil. Moreover, the molecules of the retentate contain aromatic rings as the basic unit in structure. The conjugated aromatic rings in the unit are mainly composed of two rings and three rings, whose connections are “linear order”, namely cata-condensed. Overall, it will provide much more reference data for optimizing the regeneration processes of used lubricant oil.

Macrovoids in Hybrid Organic/Inorganic Hollow Fiber Membranes

Large, characteristically tear- or finger-shaped voids found in polymer hollow fiber membranes, termed macrovoids, have been known since the early development of asymmetric membranes. These voids are undesirable as they decrease the mechanical integrity of the hollow fiber membrane, limiting the use of high pressure feeds for separations. Moreover, if such macrovoids penetrate the selective layer they become and even more serious problem for membrane performance. With current membrane technology moving toward a mixed-matrix hybrid format with inorganic and carbon molecular sieves embedded in a polymer matrix, additional complications caused by the presence of particulates within the spinning dope toward the formation of macrovoids must be considered. While numerous hypotheses have been suggested regarding the formation of macrovoids formed in polymer-only membranes, no mention so far has been made of such macrovoids initiated in hollow fiber membranes by particles present in the spinning dope. This paper ...

Permeation time lag in polymeric hollow fiber membranes

Permeation time lag in polymer hollow fiber membrane is investigated with the dual mode sorption isotherm and the partially immobilized diffusion model. Analytical solutions are derived for the time lag at the two limit cases while numerical solutions are provided for the general case. It is shown that curvature ratio plays an important role for the permeation time lag in polymer hollow fiber membranes at intermediate pressure range.

Protein adsorption-resistant hollow fibers for blood purification.

Nonfouling polysulfone (PSf) hollow fiber membranes resistant to protein adsorption and deposition were newly developed by the addition of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. To improve hydrophilicity, permeability, and nonfouling characteristics of the PSf hollow fiber in a hemodialyzer, we synthesized a MPC polymer which can be blended with PSf for preparing the polymer alloy (PSf/MPC polymer). The composition of the MPC polymer blended in the PSf was in the range between 7.0 and 15 wt%. From the PSf/MPC polymer solution, flat membranes and hollow fibers could be prepared. These membranes took an asymmetric structure, and its mechanical strength was good. The surface characterization of the PSf/MPC polymer hollow fiber membrane by X-ray photoelectron spectroscopy revealed that the MPC units were concentrated at the surface. The permeability for solutes through the PSf/MPC polymer membrane was higher, and the amount of protein adsorbed on the PSf/MPC polymer membrane was lower than those of the PSf membrane. Moreover, platelet adhesion was also effectively inhibited on the PSf/MPC polymer membrane.