•Water was used as the solvent to fabricate hyperbranched polymer emulsion.•HBP micelles were controlled in water by varied concentrations.•The HBP composite membranes was used in separating aromatic/aliphatic mixtures.•PSI of the membrane formed using water as solvent was increased 3.3-fold than DMF.•The strategy is facile in pervaporation separation of aromatic/aliphatic mixture.The separation of aromatic/aliphatic mixtures is significant in chemical industry. Pervaporation has attracted increasing attention due to its low energy consumption and environmentally friendly process. However, the formation of membranes mostly use toxic organic solvents, whereas in this study water was used instead to prepare membrane in separating aromatic/aliphatic mixtures. W3000 were dispersed in water to form micelles, which were then deposited onto the surface of the tubular porous ceramic substrate through the negative pressure-driven assembly method. The emulsion and composite membranes were characterized by TEM, SEM and FTIR. The crosslinking density of W3000 was also tested using NMR XLD analyzing system. The membranes were used for separating aromatic/aliphatic mixtures through pervaporation. The results showed that compared with the membrane prepared by DMF, the pervaporation separation index (PSI) of the composite membrane formed using water as solvent was 3.3-fold increased for separating toluene/n-heptane mixtures. The as-prepared composite membranes showed a better comprehensive pervaporation performance. This facile strategy may have a potential in the application of pervaporation for separating aromatic/aliphatic mixtures in industry.In this study, a facile strategy was reported to prepare composite membranes for separating aromatic/aliphatic mixtures.Download high-res image (146KB)Download full-size image

•Thin selective layer was prepared to in situ repair the defects in industrial ceramic supports.•The assembly of nanohybrid multilayers simplified the layer-by-layer procedures.•The integrality of the membrane was evaluated in the nanofiltration of dye solutions.Large defects have important impact on performance of separation membranes. In this paper, in order to reduce the large defects of the industrial ceramic supports, we prepared a nanohybrid separation membrane with a selective layer and a sub layer on the macroporous substrate with polyelectrolyte-coated nanoparticles. SEM, EDS and pore size analyses suggest that the although ZrO2 nanoparticles can migrate into the large defects to modify the membrane pores, the matching of pore-mouth size and diameter of NPs plays important role in the in situ modification of the substrates. The integrality of the as-prepared nanohybrid multilayer membrane was evaluated in the nanofiltration of dye solutions. The organic-inorganic composite membranes perform high flux and retention for separation. Membranes were prepared to study the separation performance on different substrates and with different building blocks (polyelectrolyte molecule weights and polyelectrolyte molecule structure). We found that the pore-mouth size of substrates and the structure of building blocks mainly affected the structure and the nanofiltration performance of the composite membranes. Such assembly allow us to in situ modify the large defects of inorganic substrates while preparing the selective layer.

•NH2-UiO-66/PEI MMMs were prepared for acetic acid dehydration.•The MMMs were deposited on surface of NaA zeolite tubular substrate.•The composite membrane showed good pervaporation performance.Acetic acid dehydration is significant in chemical industry. Pervaporation has attracted increasing attention due to its low energy consumption and environmentally friendly process. However, there is still lack of efficient membrane materials for the pervaporation separation of acetic acid/water mixtures. Therefore, developing new material to prepare pervaporation membrane is currently the main task. In this study, an acid stable Zr-MOF NH2-UiO-66 was synthesized and incorporated into poly(ethyleneimine) (PEI) to form mixed matrix membranes (MMMs) for separating acetic acid/water mixtures. The NH2-UiO-66/PEI MMMs were deposited on the surface of NaA zeolite tubular substrate to form composite membranes using dip-coating method. The morphologies and structures of the particles and composite membranes were characterized by SEM, EDX, FTIR and contact angle. The effects of membrane preparation conditions on the separation performance were investigated. The results indicated that the NH2-UiO-66/PEI composite membranes showed good acetic acid dehydration behavior, because of the high porosity and hydrophilicity of the particles. Moreover, the particles had good compatibility with polymer and strong combination with substrate. Therefore, this study may provide a new material and facile strategy for preparing composite membrane in the separation of acetic acid/water mixtures.

•A self-crosslinkable hyperbranched polymer was introduced as formation material.•Tubular composite membrane was fabricated by simple self-crosslinking strategy.•“Pore-filling” composite membrane showed a desirable stable performance.•Potential application of “pore-filling” membrane in aromatic/aliphatic separation.The stability of membrane is a key issue for pervaporation separation of aromatic/aliphatic hydrocarbon mixtures. In this study, in order to enhance the stability, composite membrane with “pore-filling” structure was formed on porous ceramic tubular substrate. A simple self-crosslinking strategy based on the unique hyperbranched macromolecule, Boltorn W3000, was utilized in the preparation procedure. The hydroxyl and carboxyl groups on Boltorn W3000 molecules reacted at intramolecular and intermolecular during thermal cross-linking process, and then hyperbranched polymers were assembled onto the top layer and sublayer of the ceramic substrate. The morphologies and structures of “pore-filling” composite membrane were characterized by FTIR, SEM, and Nano Indenter. Moreover, “non-pore-filling” membrane was also prepared by the same method with an additional “plugging-holes” step. Both of these two composite membranes were used for separating toluene/n-heptane mixtures. The results indicated that the “pore-filling” membrane showed more stable separation performance, due to its excellent anti-swelling properties. This work thus not only illustrated a new approach for the preparation of “pore-filling” membrane, but also produced a potentially useful organic/inorganic composite membrane for aromatic/aliphatic hydrocarbon mixtures separation.

•Adsorption and diffusion properties of PEBA were determined by IGC technique.•PEBA/ceramic tubular composite membrane was fabricated by thermal crosslinking.•Aromatic/aliphatic separation by PEBA/ceramic tubular pervaporation membrane.Pervaporation could be a cost-competitive process for separating aromatic/aliphatic hydrocarbon mixtures in the chemical industry. In this study, commercial poly(ether-block-amide) (PEBA) and ceramic tubular substrates were used to prepare pervaporation membrane for separating aromatic/aliphatic mixtures through a facile thermal crosslinking method. The adsorption and diffusion properties of toluene and n-heptane in PEBA were determined by swelling experiment and inverse gas chromatography technique. FTIR and XRD were used to investigate the hydrogen bonding and crystallinity of PEBA molecule through thermal crosslinking. The morphology and structure of PEBA/ceramic composite membrane were characterized by SEM and EDX. The separation performance of the composite membrane can be adjusted by controlling PEBA concentration, thermal crosslinking temperature and time. Ceramic tubular substrate could suppress the excessive swelling and thereby enhance the stability of the membrane. Furthermore, different types of fillers were incorporated into PEBA matrix to improve the separation performance. The results demonstrate that PEBA/graphite hybrid membrane has the highest separation factor for separating 50 wt% toluene/n-heptane mixtures. This study is expected to extend the membrane material and simplify the membrane preparation procedures in aromatic/aliphatic pervaporation fields.

•Modified silicalite-1 compatibility with PDMS by tuning its sizes and morphologies.•Improved silicalite-1 compatibility with PDMS through its functional modifications.•Optimized ethanol/water separation performance of PDMS hybrid membranes.The silicalite-1/PDMS hybrid membranes have been widely studied in alcohol perm-selective pervaporation separations. However, the poor compatibility between silicalite-1 particles and PDMS has already rebated the separation performance of these hybrid membranes. In this paper, two approaches were investigated to improve/tune the compatibility of the silicalite-1 particles and PDMS matrix. Firstly, silicalite-1 crystal particles with different sizes were synthesized. The effects of the particle size on the compatibility between silicalite-1 and PDMS were investigated. It was found that smaller silicalite-1 crystals (about 100 nm) have a better compatibility with PDMS matrix, thereby an enhanced separation performance of their hybrid membranes. Subsequently, the surface of silicalite-1 particles were modified through three kinds of silane coupling agents with different functional groups, which was confirmed to be feasible in increasing the compatibility with PDMS. In ethanol/water pervaporation separation, a higher selectivity was achieved in the PDMS hybrid membrane with TMDS-modified small silicalite-1 crystals. Moreover, silicalite-1 crystals provide many separate channels, so that the separation performance of the hybrid membrane has dramatically increased.

Inspired by the complementary roles of surface energy and roughness on natural nonwetting surfaces, a superhydrophobic surface has been successfully designed and prepared by self-assembled monolayer modification on a hierarchical ZIF-8/polymer hybrid membrane. The as-prepared membrane exhibited the best overall performance for n-butanol pervaporation.

The use of self-assembled monolayers (SAMs) has recently been recognized as an effective way to tailor the surface properties of films used in various applications. However, application of SAMs in the preparation of separation membranes remains unexplored. In the present study, surface-modified poly(dimethylsiloxane) (PDMS) membranes were prepared using SAMs to fabricate a membrane for use in pervaporation separation of ethanol/water mixtures. A cross-linked PDMS/polysulfone (PSf) composite membrane was transformed by introducing hydroxyl functionalities on the PDMS surface through a UV/ozone conversion process. (Tridecafluoroctyl)triethoxysilane was allowed to be adsorbed on the resulting Si–OH substrate to increase the hydrophobicity of the membrane. Results from Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy, and contact angle analyses suggest that the fluoroalkylsilane monolayer was successfully formed on the modified PDMS/PSf membrane treated by 60 min UV/ozone exposure. The newly SAM-modified membrane exhibited a separation factor of 13.1 and a permeate flux of 412.9 g/(m2 h), which are higher than those obtained from PDMS membranes.

The layer-by-layer (LbL) assembled polyelectrolyte multilayer has recently been recognized as a new class of promising membrane material for various separation uses. However, there is a lack of understanding about the influences of separation mixtures on the adsorbed polyelectrolytes. Therefore, clear understanding on it would be very important for the design and application of a type of new functional composite membrane. In this paper, the multilayer of weak polyelectrolytes polyethyleneimine and polyacrylic acid was constructed onto a hydrolyzed hollow fiber polyacrylonitrile support membrane under a negative pressure condition. The salt-, pH- and oxidant-responsive pervaporation behaviors of polyelectrolyte multilayer membranes were evaluated by post-treating with sodium chloride, hydrochloric acid, sodium hydroxide and sodium hypochlorite aqueous solutions, respectively. The pervaporation performances for separation of ethanol/water were compared before and after post-treatments. Scanning electron microscopy and atomic force microscopy confirmed the microtopographical changes of membrane surfaces. Optical microscopy was also used to real-time observe surface morphologies of polyelectrolyte multilayers deposited on the quartz substrates. Finally, the comparison of zeta potential values of inner surface before and after post-treatment also demonstrated the changes of surface electrical property.

In this article, a layer-by-layer (LbL)-assembled coordination multilayer on planar and 3D substrates was explored by the alternate deposition of a transition-metal-containing polyelectrolyte and a ligand-containing polymer via the formation of complexes. The metal−ligand coordination between the building blocks of Co2+-exchanged poly(styrene sulfonate) (PSS) and poly(4-vinyl pyridine) (P4 VP) has been demonstrated using UV−vis, FTIR, and XPS. The film thickness, structure, and morphology as well as the wettability as a function of bilayer number have been systematically investigated by profilometry, SEM, AFM, and contact angle analyzers. For the purpose of separation applications, the metal−ligand-coordinated multilayer was assembled on both flat sheet and hollow fiber polymeric porous substrates using a dynamic pressure-driven LbL technique. It was demonstrated that the LbL-assembled PSS(Co)1/2/P4 VP multilayer membrane had high dehydration performance with respect to different solvent−water mixtures; it also had aromatic compound permselectivity from aromatic−aliphatic hydrocarbons and water-softening capacity. Meanwhile, the successful assembly of multilayers on hollow fibers indicates that the dynamic pressure-driven LbL technique is a unique approach to the construction of multilayers on porous 3-D substrates. Therefore, the metal−ligand-coordinated self-assembly could emerge as a powerful technique for the preparation of a range of separation membranes in different types of modules.

The purpose of this study is to provide some fundamental understanding for the design of industrial hollow fiber pervaporation membrane module. Inner skin hollow fiber pervaporation membrane modules were fabricated by a dynamic negative pressure layer-by-layer (LbL) technique. The influences of dynamic negative pressure and recycling velocity of polyelectrolyte solutions on the formation of non-porous selective layer were firstly investigated using mini-modules during the dynamic assembly process. Since none of reported works dealt with the effects of packing density of hollow fiber module, pilot-scale modules (diameter × length = 1 in. × 20 cm) were therefore prepared by filling different amounts of hollow fibers into a membrane shell. The experimental results show that the higher packing density of 500 m2/m3 rendered both total flux and selectivity to decrease significantly. As for a 1 m long module that has been commonly used in industry, further investigations were conducted using a 1-m long hollow fiber module. The vacuum drop along the axial direction of hollow fibers was noted, especially near to the vacuum suction opening. Despite of this, the relatively high and stable selectivity could be obtained even the fiber length increased to 1 m.

In the past studies, electrostatic layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes has proven to be a promising method for the preparation of polyelectrolyte multilayer membranes (PEMMs). Till now, this method was mainly used to assemble flat sheet and tubular membranes. Since hollow fiber membrane has some advantages such as high-packing density, self-contained mechanical support and hence the consequent economical superiority, this study therefore seeked to assemble inner skin hollow fiber PEMMs by using a dynamic LbL adsorption technique. The assembly process was successfully accomplished by alternatively dynamically filtrating polyacrylic acid (PAA) and polyethyleneimine (PEI) on a hydrolyzed hollow fiber polyacrylonitrile (PAN) membrane under a negative pressure condition. In the case of pervaporation separation of 95 wt.% ethanol–water mixture (50 °C), the membrane obtained with only 4.5 and 6.5 bilayers had separation factor of 245 and 1338 while the permeate fluxes were 290 and 120 g/(m2 h), respectively. The pervaporation separation behavior of various alcohol/water mixtures with the alcohols being t-butanol, 2-propanol and ethanol were also investigated. Finally, scanning electron microscopy and atomic force microscopy clearly confirms a uniform and defect-free layer formed on the inner surface of hollow fiber support. Since different polyelectrolyte pairs could be used to assemble PEMMs for different uses, it was expected that the dynamic negative pressure LbL adsorption technique could also potentially be used to prepare many types of PEMMs in other fields.

•Membrane distillation (MD) is a promising desalination technology.•Enhancing the thermal efficiency of MD is a major research focus.•Transfer mechanism of the MD process was introduced.•Various factors affecting the thermal efficiency were analyzed.•Several heat recovery techniques in the MD field were reviewed.Membrane distillation (MD) is a promising desalination technology for water recovery from high-salinity solutions such as RO brine. Despite its great potential, MD has not been industrially realized because this technique generates a lower flux than reverse osmosis processes and exhibits a lower thermal efficiency than multi-stage flash. Enhancing the flux and thermal efficiency of MD is a major research focus for membrane researchers. In this study, the principles, transfer mechanism and thermal efficiency characterization of the MD process were introduced. Various factors affecting the thermal efficiency were analyzed. Several heat recovery techniques in the MD field that have been developed and widely employed were reviewed.