High-efficiency Membrane Research Articles

Multifactorial evaluation of an ultra-fast process for electrospinning of recycled expanded polystyrene to manufacture high-efficiency membranes for nanoparticle air filtration

The increased production of polystyrene waste has led to the need to find efficient ways to dispose of it. One possibility is the use of solid waste to produce filter media by the electrospinning technique. The aim of this work was to develop an ultra-fast electrospinning process applied to recycled polystyrene, with statistical evaluation of the influence of polymeric solution parameters (polymer concentration and percentage of DL-limonene) and process variables (flow rate, voltage, and type of support) on nanoparticle collection efficiency, air permeability, and fiber diameter. An extensive characterization of the materials and evaluation of the morphology of the fibers was also carried out. It was found that recycled expanded polystyrene could be used in electrospinning to produce polymeric membranes. The optimized condition that resulted in the highest nanoparticle collection efficiency was a polymer concentration of 13.5%, percentage of DL-limonene of 50%, voltage of 25 kV, and flow rate of 1.2 mL/h, resulting in values of 99.97 ± 0.01%, 2.6 ± 0.5 × 10−13 m2, 0.19 Pa-1, and 708 ± 176 nm for the collection efficiency of nanoparticles in the range from 6.38 to 232.9 nm, permeability, quality factor, and mean fiber diameter, respectively. All the parameters were found to influence collection efficiency and fiber diameter. The use of DL-limonene, a natural solvent, provided benefits including increased collection efficiency and decreased fiber size. In addition, the electrostatic filtration mechanism was evaluated using the presence of a copper grid as a support for the nanofibers. The findings demonstrated that an electrospinning time of only 5 min was sufficient to obtain filters with high collection efficiencies and low pressure drops, opening perspectives for the application of polystyrene waste in the development of materials with excellent characteristics for application in the area of atmospheric pollution mitigation.

Tailored surface wettability and pore structure of hydrophobic SiO2/SiC membranes for preparing monodisperse emulsion with high-efficiency

The combustion efficiency of diesel can be significantly improved in the form of emulsion, contributing to the reduced emission of nitrogen oxides. It is thus worthwhile to develop an energy-efficient way to prepare stable diesel emulsions with uniform droplet size. Ceramic membranes with hydrophobic surface are highly desirable for high-efficient membrane emulsification process. We proposed a novel and straightforward approach of immersing silicon carbide (SiC) membrane into hydrophobic silica solutions obtained by co-hydrolysis to tailoring hydrophobic SiO2/SiC membranes. The effects of methyltriethoxysilane addition and aging days on the hydrophobicity of these silica particles were systematically investigated. Then, the deposition of silica particles on the SiC substrates was further controlled by regulating the dipping duration and dipping times. The membranes (M2-SiO2/SiC) prepared with 240 s and dipping 4 times showed an increased contact angle (136°), mean pore size of 0.4 μm, open porosity of 30 %, and pure water permeance of ∼ 1500 L·m−2·h−1·bar−1. Moreover, the modified membranes were demonstrated to be mechanically stable. Furthermore, monodisperse diesel emulsions with an average droplet size of 2.1 μm and droplet size distribution of 0.61 can be generated by using the optimized M2-SiO2/SiC membranes at high emulsifying flux (1910 L·m−2·h−1). This work proposed an efficient strategy to simultaneously optimize the surface wettability and pore structure of ceramic membranes, satisfactorily for membrane emulsification applications with high efficiency.

A cost-effective and high efficient Janus membrane for the treatment of oily brine using membrane distillation

Membrane distillation technology could utilize low-grade heat to desalinate brine, but the membrane material often suffers from disadvantages of low permeation flux and weak robustness to contaminants. To address these issues, the commercial polytetrafluoroethylene (PTFE) membrane was modified by cost-effective chemicals of tannic acid and (3-Aminopropyl)-triethoxysilane (APTES) to construct hydrophilic/underwater superoleophobic nano-rough structures on the surface to enhance its flux and oil-fouling resistance in direct contact membrane distillation. The results show that a high underwater oil contact angle of 180° is observed to the membrane surface due to the rough nanostructures functionalized by abundant hydroxyl groups. Despite the additional mass transfer resistance provided by the rough nanostructures, the flux was increased noticeably. This is mainly attributed to the strong interactions between the abundant hydroxyl groups of hydrophilic layer surface and water molecules, leading to a part of free water staying at intermediate transition state (IW). The mass transfer resistance of the hydrophilic layer itself is reduced as a consequence of decreased evaporation enthalpy of water, thereby increasing the flux. Moreover, while the flux of the pristine membrane is reduced by 84.18%, the flux of Janus membrane remains the same when treating mineral oil brine emulsions with oil concentration up to 1500 ppm in comparison with the result for 35 g l−1 brine solution, indicating that the Janus membrane is safe from the oil contamination. Our work provides a fine guidance for membrane distillation to treat high oily brine.

Dialdehyde cellulose (DAC) and polyethyleneimine (PEI) coated polyvinylidene fluoride (PVDF) membrane for simultaneously removing emulsified oils and anionic dyes

Developing high-efficiency membrane for oil and dye removal is very urgent, because wastewater containing them can cause great damage to human and environment. In this study, a coated membrane was fabricated by applying DAC and PEI onto the commercial PVDF microfiltration membrane for supplying the demand. The coated membrane presents superhydrophlic and superoleophobic properties with a water contact angle of 0o and underwater oil contact angle exceed 150°, as well as excellent low underwater oil adhesion performance. The coated membrane shows high separation efficiency exceeded 99.0% and flux 350.0 L·m−2·h−1 when used for separating for six kinds of oil including pump oil, sunflower oil, n-hexadecane, soybean oil, diesel and kerosene in water emulsions. Additionally, the coated membrane can effectively remove anionic dyes, achieving rejection rates of 94.7%, 93.4%, 92.3%, 90.7% for the CR, MB, RB5, AR66, respectively. More importantly, the membrane was able to simultaneously remove emulsified oil and soluble anionic dyes in wastewater containing both of them. Therefore, this novel coated membrane can be a promising candidate for treating complex wastewater.

Rapid, Massive, and Green Synthesis of Polyoxometalate-Based Metal-Organic Frameworks to Fabricate POMOF/PAN Nanofiber Membranes for Selective Filtration of Cationic Dyes.

Developing high-efficiency membrane materials for the rapid removal of organic dyes is crucial but remains a challenge. Polyoxometalates (POMs) clusters with anionic structures are promising candidates for the removal of cationic dyes via electrostatic interactions. However, their shortcomings, such as their solubility and inability to be mass-produced, hinder their application in water pollution treatment. Here, we propose a simple and green strategy utilizing the room temperature stirring method to mass produce nanoscale polyoxometalate-based metal-organic frameworks (POMOFs) with porous rhomboid-shaped dodecahedral and hexagonal prism structures. The products were labeled as POMOF1 (POMOF-PW12) and POMOF2 (POMOF-PMo12). Subsequently, a series of x wt% POMOF1/PAN (x = 0, 3, 5, and 10) nanofiber membranes (NFMs) were prepared using electrospinning technology, where polyacrylonitrile (PAN) acts as a "glue" molecule facilitating the bonding of POMOF1 nanoparticles. The as-prepared samples were comprehensively characterized and exhibited obvious water stability, as well as rapid selective adsorption filtration performance towards cationic dyes. The 5 wt% POMOF1/PAN NFM possessed the highest removal efficiency of 96.7% for RhB, 95.8% for MB, and 86.4% for CV dyes, which realized the selective separation over 95% of positively charged dyes from the mixed solution. The adsorption mechanism was explained using FT-IR, SEM, Zeta potential, and adsorption kinetics model, which proved that separation was determined via electrostatic interaction, hydrogen bonding, and π-π interactions. Moreover, the POMOF1/PAN membrane presented an outstanding recoverable and stable removal rate after four cycles. This study provides a new direction for the systematic design and manufacture of membrane separation materials with outstanding properties for contaminant removal.

Field-Scale Testing of a High-Efficiency Membrane Reactor (MR)-Adsorptive Reactor (AR) Process for H2 Generation and Pre-Combustion CO2 Capture.

The study objective was to field-validate the technical feasibility of a membrane- and adsorption-enhanced water gas shift reaction process employing a carbon molecular sieve membrane (CMSM)-based membrane reactor (MR) followed by an adsorptive reactor (AR) for pre-combustion CO2 capture. The project was carried out in two different phases. In Phase I, the field-scale experimental MR-AR system was designed and constructed, the membranes, and adsorbents were prepared, and the unit was tested with simulated syngas to validate functionality. In Phase II, the unit was installed at the test site, field-tested using real syngas, and a technoeconomic analysis (TEA) of the technology was completed. All project milestones were met. Specifically, (i) high-performance CMSMs were prepared meeting the target H2 permeance (>1 m3/(m2.hbar) and H2/CO selectivity of >80 at temperatures of up to 300 °C and pressures of up to 25 bar with a <10% performance decline over the testing period; (ii) pelletized adsorbents were prepared for use in relevant conditions (250 °C < T < 450 °C, pressures up to 25 bar) with a working capacity of >2.5 wt.% and an attrition rate of <0.2; (iii) TEA showed that the MR-AR technology met the CO2 capture goals of 95% CO2 purity at a cost of electricity (COE) 30% less than baseline approaches.

An exploration of novel natural gas leak detection based on the efficient CH4/N2 separation of polymer blend membrane

The CH4/N2 high-efficiency membrane separation technology is capable of effectively enriching CH4 from natural gas, and holds great potential for application in the fields of biogas purification and natural gas pipeline leak detection. However, preparing high-performance separation membranes is challenging due to the similarity between CH4 and N2 molecules. To enhance the CH4/N2 separation performance, block polyetheramide copolymer (Pebax)/EVA blended membranes were fabricated in this study. Additionally, a novel gas leakage detection tube was prepared. The EVA14 (14 wt% VA) membrane exhibits an optimal transport-facilitated channel among a series of pure EVA membranes, resulting in a CH4 permeability of 21.41 Barrer and CH4/N2 selectivity reaches 1.80 under mixed-gas feed conditions at 35 °C. The CH4 permeability of Pebax/EVA (30 wt%) reaches 120.5 Barrer by physical blending, and the CH4 permeability is increased by 191 % in comparison with pure EVA14 membrane. The Pebax/EVA (10 wt%) membrane exhibits the optimum CH4/N2 selectivity, and compared with pure EVA membrane increased by 35.5 %. EVA and Pebax polymers are blended for the first time for CH4/N2 separation, and the blending of block polyetheramide copolymer intensifies the membrane's separation performance comprehensively. The natural gas leak detection tube was fabricated with a membrane, offering a new and efficient CH4/N2 separation strategy.

Commercialization of High–efficiency Membrane Concentration Technology (Osmotically Assisted Reverse Osmosis (OARO) Process) for Achieving a Decarbonized Society

Commercialization of High–efficiency Membrane Concentration Technology (Osmotically Assisted Reverse Osmosis (OARO) Process) for Achieving a Decarbonized Society

Penetrating honeycomb structured MOF flexible membrane with ultra-high flux and excellent catalytic activity

MOF-polymer mixed matrix catalytic membrane has excellent potential for applications in continuous flow separation and catalysis. However, scalable fabrication methods to produce ultra-high flux mixed matrix catalytic membranes are urgently needed yet to be largely met. Inspired by the honeycomb structure, composite MOF with polymer materials possessing rapidly prepare large area MOF-polymer mixed matrix catalytic membrane with penetrated honeycomb structure. The bulk loading of MOFs linked the walls of the honeycomb, endowing the MOF-polymer mixed matrix membrane with large surface areas and abundant pore channels. The porous MOF material links the pore walls of the honeycomb structure, which not only enables the rapid passage of reactants, but also greatly enhances the mutual contact between the membrane and the reactants, achieving rapid passage and efficient catalysis. The 0.6-ZIF-8/Pd-TPU porosity reaches 69% and the specific surface area can reach 828.35 m2/g. The water flux reached 3290 L m−2 h−1 and the treatment efficiency of different dyes and 4-NP under vacuum pump filtration reached 99%. This preparation method was extended to other porous materials, and membranes were successfully prepared with good catalytic effects. This strategy paves the way for the development of high flux and efficient catalytic membranes.

Efficient oily wastewater treatment by a novel electroflotation-membrane separation system consisting a Ni-Cu-P membrane prepared by electroless nickel plating

Electroflotation-membrane separation system with a conductive membrane has recently emerged as a promising technology for oily wastewater treatment. However, the conductive membrane prepared by electroless plating often suffers the problems of low stability and high activation cost. To solve these problems, this work proposed a new strategy regarding surface metallization of polymeric membrane by surface nickel-catalyzed electroless nickel plating of nickel‑copper‑phosphorus alloys for the first time. It was found that, addition of copper source remarkably enhanced the membranes' hydrophilicity, corrosion resistance and fouling resistance. The Ni-Cu-P membrane had an underwater oil contact angle of up to 140°, and simultaneously possessed rejection rate > 98 % with rather high flux of 65,663.0 L·m−2·h−1 and excellent cycling stability when separating n-hexane/water mixtures under gravity drive. The permeability is higher than the state-of-the-art membranes for oil/water separation. The Ni-Cu-P membrane as the cathode can be assembled into an electroflotation-membrane separation system, allowing to separate oil-in-water emulsion with 99 % rejection. Meanwhile, the applied electric field significantly improved membrane flux and fouling resistance (flux recovery up to 91 %) when separate kaolin suspensions. Polarization curve and Nyquist curve analysis further confirmed that addition of Cu element obviously enhanced corrosion resistance of the Ni modified membrane. This work provided a novel strategy to make up high-efficiency membranes for oily wastewater treatment.

Construction of bipolar membrane electrodialysis reactor for removal and recovery of nitrogen and phosphorus from wastewater

Bipolar membrane electrodialysis is a high efficiency membrane reaction method which is developed by taking advantage of the unique hydrolysis separation property of bipolar membranes. In this work, a bipolar membrane electrodialysis method was used to treat simulated nitrogen and phosphorus wastewater. The separation and enrichment efficiency and migration rate of NH4+ and PO43- were determined. The energy consumption and current efficiency of NH4+ and PO43- separation and enrichment were analyzed. The results showed that the removal rates of PO43- and NH4+ increased with the extension of time. Meanwhile, with the increase of current density, the removal rate of NH4+ and PO43- in wastewater chamber is accelerated. With the increase of current density, the energy consumption increases gradually.

Fabrication of antifouling two-dimensional MoS2 layered PVDF membrane: Experimental and density functional theory calculation

Two-dimensional MoS2 nanosheets were synthesized with the exfoliation method, and deposited on PVDF support to develop high-efficiency membranes for water treatment. A variety of analyses were performed on the nanosheets, including FESEM, FTIR, UV–Visible, XRD, and EDS. In addition, the bulk and nanosheet of MoS2 were theoretically investigated using density functional theory (DFT). The theoretical and experimental results demonstrate the successful formation of MoS2 nanosheets. Analyses related to flux and membrane fouling were carried out on MoS2/PVDF membranes with various contents of the coating layer; these analyses were supported by FESEM, EDS, water contact angle, AFM, and zeta potential measurements. The antifouling properties as well as the water flux in the modified samples have improved compared to the bare sample. This is primarily related to the increase in hydrophilic properties due to the addition of nanosheets. The modified membranes also show better performance when purifying dyes, BSA, and Na2SO4. Based on these results, we conclude that PVDF/MoS2 membranes provide excellent water purification performance.

Fabrication of fibrous MXene nanoribbons (MNRs) membrane with efficient performance for oil-water separation

Oily wastewater discharge due to industrial activities and oil spills has taken great tolls on human health and global environment. Fabrication of high-efficiency membrane is of critical importance since membrane separation has emerged as one of the best solutions to oily wastewater problem. In this work, fibrous MXene nanoribbons (MNRs) were firstly prepared and then combined with mixed cellulose (MCE) membrane to obtain a novel two-dimensional MCE-MNRs membrane. The MCE-MNRs membrane displayed superhydrophilicity and underwater superoleophobicity, corresponding to outstanding resistance to oil droplets. The filtration experiments illustrated that the MCE-MNRs membrane possessed an extremely high pure water permeance (PWP) of 15860 L m−2 h−1·bar−1, and simultaneously over 99% rejection rates for filtration of four typical oil-water mixtures (diesel, gasoline, edible oil and n-hexane). The performance outperforms those of the state-of-the-art membranes for oil-water separation to our knowledge. The excellent performance can be put down to a water layer formed on the membrane surface during filtration, which allow water to pass through freely but block oil droplets. In addition, the MCE-MNRs membrane possessed the photocatalytic self-cleaning ability which can efficiently raise the flux recovery rate (FRR) by ultraviolet light irradiation. The facile preparation method and excellent separation performance of the MCE-MNRs membrane cater to the current industrial production needs and show a promising application prospect in oil-water separation.

Simultaneous solar water desalination and energy generation by high efficient graphene oxide-melanin photothermal membrane

Clean water and energy remain crucial for human well-being, poverty alleviation and economic development. It has been challenging to achieve sustainable decarbonized systems, specifically for clean water and energy. Herein, we experimentally demonstrate graphene oxide–melanin (GOM) composite film with above 90 % approximate absorptivity; almost covering the entire solar spectrum. The light absorbed in presence of melanin consequently achieves 65 °C at GOM surface and yields 35.5 °C for water. GOM acts as an absolute vapor generator facilitated by vertically assembled GO channels and the solar to vapor conversion efficiency exceeds 93 % with high endurance up to 1.6 kg m−2 h−1 for water. The water evaporation rate in presence of mixed salts ranges in between 1.05 and 1.35 kg m-2 h-1 with 66–86 % efficiency depending on solution chemistry. Furthermore, we exploit simultaneous clean water and energy system by combining thermoelectric technology. The TEG device can produce a maximum power density of 0.9 W m−2 at relative humidity of 60 %. All of these results demonstrate synergistic effects of GOM, effective heat dissipation and utilization with continuous water transport. This work provides new understandings on the interplay between water and energy context.

Tannic acid (TA)-based coating modified membrane enhanced by successive inkjet printing of Fe3+ and sodium periodate (SP) for efficient oil-water separation

Wettability of membrane is of vital importance for treatment of oily wastewater. In recent years, hydrophilic modifications based on plant polyphenol have been widely investigated to enhance the anti-fouling property of membranes due to their mild conditions, versatility and low cost. However, there are still some problems in improving raw material utilization and hydrophilicity. Herein, a facile method was proposed to optimize tannic acid (TA)-based membrane modification process by synergistically inducing TA deposition by Fe3+ and SP with the assistance of inkjet printing. The hydrophobicity of polyvinylidene fluoride (PVDF) membrane was converted to hydrophilicity (WCA = 34.6°) and underwater oleophobicity (UOCA = 144.4°) in very short time (10 min). The optimum PVDF/Fe-TA-SP422 membrane possessed high flux (4968.4–7340.4 L m−2 h−1·bar−1) for a number of oil/water emulsions with high separation efficiency (>98%), outperforming most state-of-the-art membranes for oil-water separation. Furthermore, the optimized membrane displayed not only high antifouling property and reusability with flux recovery ratio of 89.1%–98.0% after eight-cycle filtration, but also desired stability under near neutral pH conditions during long-term running. The combination of inkjet printing method with these materials proposed in this study is convenient, efficient and low cost, and the prepared membranes are versatility, providing novel insights into preparation of high efficiency membranes for oily wastewater treatment.

High Efficiency Membranes Based on PTMSP and Hyper-Crosslinked Polystyrene for Toxic Volatile Compounds Removal from Wastewater.

For the first time, membranes based on poly(1-trimethylsilyl-1-propyne) (PTMSP) with 5–50 wt% loading of hyper-crosslinked polystyrene sorbent particles (HCPS) were obtained; the membranes were investigated for the problem of effective removal of volatile organic compounds from aqueous solutions using vacuum pervaporation. The industrial HCPS sorbent Purolite Macronet™ MN200 was chosen due to its high sorption capacity for organic solvents. It has been found that the membranes are asymmetric when HCPS content is higher than 30 wt%; scanning electron microscopy of the cross-sections the membranes demonstrate that they have a clearly defined thin layer, consisting mainly of PTMSP, and a thick porous layer, consisting mainly of HCPS. The transport and separation characteristics of PTMSP membranes with different HCPS loading were studied during the pervaporation separation of binary and multicomponent mixtures of water with benzene, toluene and xylene. It was shown that the addition of HCPS up to 30 wt% not only increases the permeate fluxes by 4–7 times, but at the same time leads to 1.5–2 fold increase in the separation factor. It was possible to obtain separation factors exceeding 1000 for all studied mixtures at high permeate fluxes (0.5–1 kg/m2∙h) in pervaporation separation of binary solutions.

Novel solar membrane distillation system based on Ti3C2TX MXene nanofluids with high photothermal conversion efficiency

As a new desalination process, membrane distillation (MD) technology effectively combines thermal treatment with membrane separation and has great commercial application potential owing to its lower operating temperature and pressure requirements. Meanwhile, solar energy can be used to save conventional fossil energy consumption. However, the high efficient solar membrane distillation (SMD) with a simple system design is still challenging due to the low photo-thermal conversion efficiency. In this work, a new type of photo-thermal conversion material based on Ti3C2Tx MXene was developed and further integrated into a novel SMD system. In this system, the distillation process is driven by sunlight irradiating photo-thermal conversion particles to heat the feedwater, completely eliminating the extra energy input. Specifically, single-layer Ti3C2Tx MXene is selected as the high efficient photo-thermal conversion particle. Experiments results show that the membrane flux of the system can reach 2.375 kg·m−2·h−1, much higher than that of most reported SMD systems. Our research provides both experimental and theoretical basis for achieving efficient utilization of solar energy and membrane distillation seawater desalination.

Porous organic cage supramolecular membrane showing superior monovalent/divalent salts separation

Nanofiltration process has been perceived as one of the promising approaches in desalination and separation of monovalent/divalent salts. Despite significant progresses has been made in permeability and salt rejection, the industrial separation for monovalent/divalent salts is limited by the insufficient selectivity for ions with different charges and sizes. This work firstly proposed a porous organic cage supramolecular membrane with topologically structured “window-to-window” channels for the fast transport of monovalent ions and water molecules. Specifically, porous organic cage (RCC3) molecule and nonpolar alkyl of dodecyltrimethylammonium bromide (DTAB) were assembled into supramolecular RCC3@DTAB through hydrophobic interaction by molecular recognition of polar cavity. Furthermore, terephthaloyl chloride (TPC) was employed as a crosslinker by interfacial polymerization to construct RCC3@DTAB-TPC supramolecular film onto the surface of polydopamine modified polysulfone (PSf) substrate. The results suggested that RCC3@DTAB-TPC membrane displayed a high permeability of 13.9 L m−2 h−1 bar−1, and attractive performance for monovalent/divalent salts separation and small molecule solutions desalination. The salt rejections to Na2SO4, MgSO4, NaCl and MgCl2 are 98.5%, 90.1%, 19.8% and 12.8%, and the selectivities of NaCl/Na2SO4 and NaCl/MgSO4 reached 42.6 and 7.8, respectively. Besides, the separation factors for NaCl/medicine and NaCl/dye mixtures are 95.5 of δNaCl/DG and 76.6 of δNaCl/CR, respectively. The excellent separation performance of RCC3@DTAB-TPC supramolecular membrane provides a new idea for developing high-efficiency membranes for monovalent/divalent salts separation.

Smart Janus membrane for on-demand separation of oil, bacteria, dye, and metal ions from complex wastewater

• Multifunctional Janus membranes fabricated for complex wastewater separation. • Oil-in-water and water-in-oil emulsions were separated with high efficiency. • ZnO photocatalyst provided antibacterial and dye degradation functionality. • This work provides practical design strategy for producing high-efficiency membrane. Oil spills and oily wastewater discharged from industries and households have resulted in environmental and economic concerns. Therefore, emerging Janus membranes with anisotropic wettability have attracted significant attention as next-generation oil/water separation membranes owing to their specific, on-demand separation ability. However, the one-step separation of complex wastewater has not yet been achieved. Herein, a pH-responsive siloxane modified polystyrene microsphere/zinc oxide/carbon nanotube/polyvinylidene fluoride (S/PS/ZnO/CNTs/PVDF) membrane was rationally designed with Janus surfaces for providing hydrophilicity/underwater lipophobicity and lipophilicity/underoil hydrophobicity functionality. This study demonstrates that the underlying mechanism of on-demand separation of water-in-oil and oil-in-water emulsion is related to wettability, adhesive forces, and intrusion pressure. The proposed Janus membrane can achieve one-step separation of complex wastewater comprising oil, bacteria, organic dye, and metal ions. The effective removal of dyes is due to synergistic effects of electrostatic adsorption and photodegradation. This facile strategy for fabricating smart Janus separation membranes has application potential in on-demand oil/water separation and practical complex wastewater separation.

Novel Sandwich-Structured Hollow Fiber Membrane for High-Efficiency Membrane Distillation and Scale-Up for Pilot Validation.

Hollow fiber membranes were produced from a commercial polyvinylidene fluoride (PVDF) polymer, Kynar HSV 900, with a unique sandwich structure consisting of two sponge-like layers connected to the outer and inner skin layers while the middle layer comprises macrovoids. The sponge-like layer allows the membrane to have good mechanical strength even at low skin thickness and favors water vapor transportation during vacuum membrane distillation (VMD). The middle layer with macrovoids helps to significantly reduce the trans-membrane resistance during water vapor transportation from the feed side to the permeate side. Together, these novel structural characteristics are expected to render the PVDF hollow fiber membranes more efficient in terms of vapor flux as well as mechanical integrity. Using the chemistry and process conditions adopted from previous work, we were able to scale up the membrane fabrication from a laboratory scale of 1.5 kg to a manufacturing scale of 50 kg with consistent membrane performance. The produced PVDF membrane, with a liquid entry pressure (LEPw) of >3 bar and a pure water flux of >30 L/m2·hr (LMH) under VMD conditions at 70–80 °C, is perfectly suitable for next-generation high-efficiency membranes for desalination and industrial wastewater applications. The technology translation efforts, including membrane and module scale-up as well as the preliminary pilot-scale validation study, are discussed in detail in this paper.