Recent developments of organic solvent resistant materials for membrane separations.

Solute purification, solvent recovery, solvent separation in organic solvents are more and more widely used in the chemical industries, pharmaceuticals and food processing. Fast and efficient separations can be realized using membrane separation technology. Materials with strong organic solvent resistance for membrane preparation have attracted growing research interest and have been regarded as a necessary approach for various environmental and energy-related separations. Kinds of novel polymers, metal/covalent-organic framework, carbon materials, polymers of intrinsic microporosity and conjugated microporous polymers provide possibilities and solutions to prepare organic solvent resistant membranes. In view of the tremendous progress made over the past few years, it is valuable to summarize the recent developments timely and systematically in this multidisciplinary field, from which researchers can forecast trends in the future. In this review, we firstly introduced advanced membrane separation technologies, including pervaporation, organic solvent ultrafiltration, organic solvent nanofiltration, organic solvent reverse osmosis and organic solvent forward osmosis. Then we highlighted novel membrane materials and preparations in recent years and introduced the applications in the dyes separation, petroleum industry, food processing, pharmaceuticals, separation of organic solvents and wastewater treatment. Lastly, some unsolved problems and challenges at the scientific and technical level related to perspectives are discussed, prompting the further development of next-generation organic solvent resistant membranes.

A Novel Green Diluent for the Preparation of Poly(4-methyl-1-pentene) Membranes via a Thermally-Induced Phase Separation Method.

The use of green solvents satisfies safer chemical engineering practices and environmental security. Herein, myristic acid (MA)-a green diluent-was selected to prepare poly- (4-methyl-1-pentene) (PMP) membranes with bicontinuous porous structure via a thermally induced phase separation (TIPS) process to maintain a high gas permeability. Firstly, based on the Hansen solubility parameter 'distance', Ra, the effect of four natural fatty acids on the PMP membrane structure was compared and studied to determine the optimal green diluent, MA. The thermodynamic phase diagram of the PMP-MA system was calculated and presented to show that a liquid-liquid phase separation region could be found during the TIPS process and the monotectic point was around 34.89 wt%. Then, the effect of the PMP concentration on the morphologies and crystallization behavior was systematically investigated to determine a proper PMP concentration for the membrane preparation. Finally, PMP hollow fiber (HF) membranes were fabricated with a PMP concentration of 30 wt% for the membrane performance characterization. The resultant PMP HF membranes possessed good performances that the porosity was 70%, the tensile strength was 96 cN, and the nitrogen flux was 8.20 ± 0.10 mL·(bar·cm2·min)-1. We believe that this work can be a beneficial reference for people interested in the preparation of PMP membranes for medical applications.

Stitch and copolymerization of thin-film composite membranes to enhance hydrophilicity and organics resistance for the separation of glycerol-based wastewater.

Many industries produce large amounts of glycerol-based wastewater, which always contains hazardous organic chlorides. Compared with complicated biological treatments or physical adsorption, membrane separation decreases the cost and saves energy. Strong swelling of traditional thin-film composite (TFC) membranes influence the performance in the separation of organic molecules. Here we prepared TFC membranes with an acrylamide-grafted PAN support layer to copolymerize with m-phenylenediamine (MPD) and trimesoyl chloride (TMC). The link of separative layer and support layer was created like a zipper stitching to enhance the stability and resistance for the removal of organic molecules. An aquatic grass-like layer of acrylamide enlarges the surface area and hydrophilicity with superior separation performances (15.8 LMH bar-1 flux, 72.0% rejection of dichloropropanol (DCP) and 64.6% rejection of glycerol (Gl)). The trade-off upper bound was improved to a high level. We also established the simulations of evaporation using Aspen Plus and mathematical models of reverse osmosis to calculate the energy consumption corresponding to the recycle of glycerol-based wastewater. The experimental and theoretical results illustrate the advantages of acrylamide-grafted TFC membranes in the ap-plications to concentrate organic solutes and treat wastewater.

Technical and Economic Evaluation of WWTP Renovation Based on Applying Ultrafiltration Membrane.

Nowadays, the standards of discharging are gradually becoming stricter, since much attention has been paid to the protection of natural water resources around the world. Therefore, it is urgent to upgrade the existing wastewater treatment plant (WWTP), to improve the effluent quality, and reduce the discharged pollutants to the natural environment. In this paper, taking the "Liaocheng UESH (UE Envirotech) WWTP in Shandong province of China" as an example, the existing problems and the detailed measures for a renovation were systemically discussed by technical and economic evaluation, before and after the renovation. During the renovation, the ultrafiltration membrane was added as the final stage of the designed process route, while upgrading the operation conditions of biochemical process at the same time. After the renovation, the removal rates of chemical oxygen demand (CODcr), biochemical oxygen demand (BOD5), total phosphorus (TP) and other major pollutants were improved greatly, and the results fully achieved the standards of surface water class IV. The ultrafiltration system performs a stable permeability around 1.5 LMH/kPa. Besides, the economic performance of the renovation was evaluated via the net present value (NPV) method. The result reveals that the NPV of the renovation of the WWTP within the 20 year life cycle is CNY 72.51 million and the overall investment cost can be recovered within the fourth year after the reoperation of the plant. This research does not only indicate that it is feasible to take an ultrafiltration membrane as the main technology, both from technical and economic perspectives, while upgrading the biochemical process section in the meantime, but also provides a new strategy for the renovation of existing WWTPs to achieve more stringent emission standards.

Organic-Inorganic Artificial Ion Channel Polyvinylidene Fluoride Membranes for Controllable Selectivity Transport of Alkali Metal Cations.

In this article, organic-inorganic hybrid materials with different functional groups were used to form organic-inorganic hybrid dense membranes for selective separation of mono/divalent ions by blending these materials and polyvinylidene fluoride (PVDF) in dimethylacetamide with HCl as the catalyst. The membranes prepared by 3-(ureido benzene) propyltriethoxysilane (H1), 3-(ureido-4-methoxyphenyl) propyltriethoxysilane (H2), 3-(ureido-3-chloro-4-methoxyphenyl) propyltriethoxysilane (H3), 3-(ureidoindazolyl) propyltrieth-oxysilane (H4), or 3-(ureidopentanol) propyltriethoxysilane (H5) were labeled as HM1-HM5, respectively. The transport properties of different chlorides were tested. The effects of different anions on sodium cation transport were also tested. The results showed that HM1-HM4 could transport monovalent Li+, Na+, and K+ except Ca2+ and Mg2+, and the permeability of Li+, Na+, and K+ through the hybrid membranes followed the order of PNa+ > PK+ > PLi+. Moreover, membranes with different H2 content were also prepared due to HM2 having the best ion transport performance. The ion transport performance increased accordingly with the mass ratio of H2 to PVDF, and the permeability of Na+ was twice that of Li+ and K+ when the mass ratio was 15/10. Under this condition, it was also proved that NH4+ could not transport through the hybrid membrane with various selectivity for different anions as Cl- > NO3- > HCO3- > SO42-.

Effects of Room Temperature Stretching and Annealing on the Crystallization Behavior and Performance of Polyvinylidene Fluoride Hollow Fiber Membranes.

A treatment consisting of room temperature stretching and subsequent annealing was utilized to regulate the morphology and performance of polyvinylidene fluoride (PVDF) hollow fiber membranes. The effects of stretching ratios and stretching rates on the crystallization behavior, morphology, and performance of the PVDF membranes were investigated. The results showed that the treatment resulted in generation of the ß crystalline phase PVDF and increased the crystallinity of the membrane materials. The treatment also brought about the orientation of the membrane pores along the stretching direction and led to an increase in the mean pore size of the membranes. In addition, as the stretching ratio increased, the tensile strength and permeation flux were improved while the elongation at break was depressed. However, compared to the stretching ratio, the stretching rate had less influence on the membrane structure and performance. In general, as the stretching ratio was 50% and the stretching rate was 20 mm/min, the tensile strength was increased by 36% to 7.47 MPa, and the pure water flux was as high as 776.28 L/(m2·h·0.1bar), while the mean pore size was not changed significantly. This research proved that the room temperature stretching and subsequent annealing was a simple but effective method for regulating the structure and the performance of the PVDF porous membranes.

Amphipathic Janus Membrane with Hierarchical Multiscale Hyperporous Structure for Interfacial Catalysis.

The rational design and realization of multiscale porous structures has been a long-standing challenge in membrane science. Block copolymers (BCPs) with their self-assembly-enabled nanodomains have the potential to make structural breakthroughs. An amphipathic Janus membrane, with a hierarchical multiscale hyperporous structure constituted by polystyrene-b-poly(4-vinylpyridine) (PS4VP) and polyvinylidene fluoride (PVDF) blocks, was designed and synthesized in this work. Hydrophobic PVDF dominated one side of the membrane, and hydrophilic PS4VP, with nanopores that formed inside the macroporous channels of PVDF via a self-assembly approach, dominated the other side. Candida Rugosa Lipase (CRL), as a model biocatalyst, was immobilized in the PS4VP nanopores via injection. The immobilized lipase was exactly suspended at the interface of the organic and aqueous phases, owing to the amphipathic property of the Janus membrane. The designed structures and catalysis performances were further characterized. The immobilized lipase exhibited a three times higher specific activity than free lipase, and the relative activity still remained above 90% after 10 cycles of reusing, indicating the observable promotion and the guaranteed stability of the Janus membrane in interfacial catalysis. This work provided a general, facile and unique example for the design and synthesis of a hierarchical multiscale hyperporous membrane for interfacial catalysis.