The dewatering of ethyl acetate (EA) holds a significant role in the production and application of this important chemical material. In this study, pervaporation dehydration of EA is investigated using polybenzimidazole/poly(ether imide) (PBI/PEI) dual-layer hollow fiber membranes. The spinning parameters during the membrane fabrication, including the take-up speed and air gap distance, are varied and found to have a marked influence on the resultant separation performance. Besides, cross-linking modification and post-thermal treatment are applied on the PBI/PEI hollow fiber membranes and their effects on the membrane performance are also investigated. A benchmarking shows that the pervaporation performance of the dual-layer PBI/PEI hollow fiber membranes is superior to most other polymeric membranes for EA dehydration.

•P(SSA-co-MA)-Na is employed as a novel draw solute in FO process.•P(SSA-co-MA)-Na shows high water flux and negligible solute leakage.•Chemical structure, osmotic pressure, viscosity of the draw solution are studied.•P(SSA-co-MA)-Na draw solution for dye-containing wastewater treatment is efficient.The selection of proper draw solution is crucial to guarantee a high-performance FO process with minimal reverse solute flux and easy draw solution recovery. In this study, a polyelectrolyte salt-poly (4-styrenesulfonic acid-co-maleic acid) sodium (P(SSA-co-MA)-Na), was applied as draw solutes in FO process. The effects of the chemical structure, osmotic pressure, viscosity of the draw solution and the resulted FO performance are investigated systematically. Because of the high osmotic pressure of the solution and the large molecular size, P(SSA-co-MA)-Na exhibits a higher water flux and a lower salt leakage as compared with polyacrylic acid sodium salts (PAA-Na) and poly (sodium-4-styrenesulfonate) (PSS-Na). Especially, a high water flux of about 15 LMH and a significantly lower solute leakage of about 0.04 gMH can be generated with 0.25 g/ml P(SSA-co-MA)-Na draw solution and deionized water as the feed solution under PRO mode. The potential of P(SSA-co-MA)-Na draw solution is further evaluated for water recovery from the dye-containing wastewater via FO process. In addition, the diluted P(SSA-co-MA)-Na can also be regenerated by nanofiltration (NF) system. The overall performance proves that P(SSA-co-MA)-Na as draw solute in FO process is applicable.Download high-res image (193KB)Download full-size image

•Novel tricarbohydrazide BTCH is synthesized and characterized.•Network cross-linking of PI membranes by BTCH for pervaporation dehydration.•Higher BTCH content results in higher cross-linking degree and hydrophilicity.•Membrane-forming temperature affects membrane properties and performance.Amine cross-linking is one of the popular modifications of polyimide membranes in order to improve their operation stability and separation performance. In this work, a novel kind of cross-linker tricarbohydrazide — 1,3,5-benzenetricarboxylic acid trihydrazide (BTCH), is synthesized and incorporated into polyimide membranes for isopropanol dehydration via pervaporation. The chemical structure of BTCH is examined by NMR and FTIR to confirm the successful synthesis. The effects of BTCH content and membrane-forming temperature on the membrane physicochemical properties and separation performance are studied and characterized by various techniques. And the possible reaction mechanism during the chemical cross-linking is proposed and analyzed. This work is believed to shed useful insights on the chemical modification of polyimide membranes for pervaporation and other membrane-based separation applications.Download high-res image (160KB)Download full-size image

•Novel tripodal amine TAEA is employed to in-situ modify TFC membranes.•TAEA exhibits dual role of catalyst and reactive amine monomer.•Significant changes in overall properties are introduced after modification.•Modified membranes possess better separation performance and antifouling property.Forward osmosis (FO) has drawn growing attention in recent years, while the lack of desirable FO membranes has been restricting its further development in industrial applications. In this work, a novel tripodal amine — tris(2-aminoethyl)amine (TAEA), with a dual role of catalyst and reactive amine monomer, is incorporated in the PA selective layer for the first time, to in-situ modify the thin-film composite (TFC) membrane. A series of characterization techniques are employed to investigate the modification mechanism involved, as well as changes in chemical properties and the microstructure of the PA layer in terms of the TAEA content and the amine solution pH. The separation performance and anti-fouling behavior of the TAEA-modified TFC membranes are studied correspondingly. In comparison with the control TFC membrane, modified TFC membranes possess higher water permeability, higher salt rejection, and much lower fouling propensity, and may hold a great potential for FO applications.Download high-res image (270KB)Download full-size image

•SIP modification of TFC membranes by PEI with various molecular weights.•Post-treatment of PEI-modified membranes in basic or acidic solution is conducted.•Modified membranes exhibit higher hydrophilicity and fractional free volume.•Modified membranes possess better separation performance and antifouling property.In this work, simple and effective second interfacial polymerization (SIP) of thin-film composite (TFC) membranes is performed with polyethyleneimine (PEI) of various molecular weights, in order to improve the separation performance for forward osmosis (FO) applications. Various characterization techniques are employed to examine the modification mechanism. Compared to the control TFC membrane, PEI-modified membranes exhibit higher water permeabilities, acceptable salt rejection and lower fouling propensity. The effects of PEI molecular weight on the membrane morphology and separation performance are investigated systematically with various characterizations. Post-treatment of PEI-modified membranes in alkaline and acidic aqueous solutions is further investigated, and its effects on the FO performance, intrinsic separation properties and antifouling properties of these post-treated membranes are studied. In comparison with pristine PEI-modified TFC membranes, the post-treated TFC membranes show further enhanced water flux and improved anti-fouling properties.Download high-res image (149KB)Download full-size image

•PFSA incorporated PVDF substrate is employed in preparing TFC FO membrane.•PFSA incorporation favors to lower transport resistance and membrane tortuosity.•PFSA incorporation benefits a better formation of polyamide layer.•Modified membranes possess better water permeation and selectivity.In this work, a small amount of hydrophilic perfluorosulfonic acid (PFSA) is incorporated into the polyvinylidene fluoride (PVDF) substrate to develop the high-performance thin-film composite (TFC) membrane for forward osmosis applications. Because of the hydrophilicity and excellent compatibility with PVDF, PFSA not only significantly improves the wettability of the modified membrane substrate, but also well optimizes the pore size by changing the membrane morphology of PVDF/PFSA substrate. These two factors effectively mitigate the water transport resistance and favor the better formation of the polyamide (PA) layer during the interfacial polymerization, thus improving both the water flux and membrane selectivity of the resultant TFC membranes simultaneously. Effects of the PFSA concentration on the overall properties of the modified substrates and corresponding PVDF/PFSA TFC membranes are systematically investigated via various characterizations. Consequently, the PVDF/PFSA TFC membrane achieves a best water flux (JV) of 54.4 LMH and a reverse salt flux (JS) of 10.9 gMH in AL-DS mode, and a JV of 27.0 LMH with JS of 8.4 gMH in AL-FS mode using deionized (DI) water and 1 M NaCl aqueous solution as the feed and draw solutions respectively. This work may provide a new orientation in developing TFC membranes on the hydrophobic substrate with its intrinsic advantages maximized.Download high-res image (256KB)Download full-size image

The development of suitable draw solution in forward osmosis (FO) process has attracted the growing attention for water treatment purpose. In this study, a series of organic phosphonate salts (OPSs) are synthesized by one-step Mannich-like reaction, confirmed by FTIR and NMR characterizations, and applied as novel draw solutes in FO applications. Their solution properties including osmotic pressures and viscosities, as well as their FO performance as a function of the solution concentration are investigated systematically. In FO process, a higher water flux of 47–54 LMH and a negligible reverse solute flux can be achieved in the PRO (AL-DS) mode (active layer faces the draw solution) using a homemade thin-film composite membrane (PSF-TFC) and deionized water as the feed solution. Among all OPS draw solutes, the tetraethylenepentamine heptakis(methylphosphonic) sodium salt (TPHMP-Na) exhibits the best FO flux at 0.5 mol/kg concentration, which is further applied for the separation of emulsified oil–water mixture. The recovery of diluted OPS solutions is carried out via a nanofiltration (NF) system with a rejection above 92%. The aforementioned features show the great potential of OPS compounds as a novel class of draw solutes for FO applications.

Draw solution is one important factor to determine the separation performance in forward osmosis (FO) process. However, most draw solutions face severe reverse solute leakage and energy-intensive recovery problems, which lead to a significant performance decline. Exploration of renewable natural compounds as draw solutes may effectively break out the predicament of most current draw solution. In this work, a series of renewable, no-toxic gluconate salts are systematically investigated as draw solutes for FO applications. Their physicochemical properties are investigated systematically and related to the FO performance. The result shows that 2 M Glu-K draw solution may generate a comparable water flux (∼23.17 LMH) to that of NaCl solution, but with a significantly lower solute leakage (∼1.09 gMH), with DI water as the feed solution under PRO mode. Glu-K draw solution is further applied for juice reconcentration with a reasonable good performance achieved. Draw solution recovery by nanofiltration (NF) is also performed. This study provides useful information on using natural draw solutes in the FO process and facilitates its practical applications in the food processing field.Keywords: Draw solution; Forward osmosis; Gluconate salt; Juice reconcentration; Membrane separation;

Phenol is an important commodity in chemical industries and dewatering is a critical process in its application. In this work, polybenzimidazole (PBI) membranes with various morphologies are employed for phenol dehydration via pervaporation, including flat-sheet dense membranes, single-layer and dual-layer hollow fiber membranes. Effects of cross-linking modification and post-thermal treatment on the performance of PBI flat-sheet dense membranes were investigated; effects of the operation temperature and feed composition are also studied, not only in terms of flux and separation factor, but also of the intrinsic permeance and selectivity of the membrane. In order to achieve a higher permeation flux, PBI single-layer hollow fiber membranes of thinner selective layers were developed and studied with the effect of different spinning parameters. The preliminary study of dual-layer PBI/PBI and PBI/poly(vinylidene fluoride) (PVDF) dual-layer hollow fiber membranes are also carried out to explore the potential of high-performance composite membranes for phenol dehydration. The promising separation performance of PBI membranes exhibited via benchmarking shows its great potential for phenol dehydration, and it may open new perspectives for the development of high-performance membranes for the pervaporation dehydration of phenol or other corrosive organics.