A fundamental mass transport model based on molecular insights for pervaporation desalination

Development of high performance pervaporation desalination membranes: A brief review

Desalination is the process of removing salts and minerals from saline water to produce potable water. It is a critical global challenge due to the increasing demand for freshwater. Pervaporation (PV) is a membrane-based separation process that combines sorption and permeation, and it has emerged as a promising alternative to traditional desalination methods. This review provides a comprehensive overview of recent advancements in the development and application of polymer membranes for PV desalination. We begin by discussing the fundamental principles of PV and exploring its mechanism, underscoring its preparation methods, such as solution coating, solution casting, and interfacial polymerization. The review then delves into various types of polymer membranes used in PV desalination, such as cellulose and its derivatives, polyvinyl alcohol, polyacrylonitrile, polyamides and sulfonated block copolymers, describing their chemical structures, synthetic techniques, and performance characteristics. Special attention is given to the role of membrane properties—such as hydrophilicity, compositions and functionality—in determining the efficiency of salt rejection and water flux. Then, the cleaning of contaminated PV polymer-based membranes is reviewed. Furthermore, we discuss the challenges and limitations associated with polymer membranes in PV desalination, which include fouling, swelling, and chemical degradation, and present strategies to mitigate these issues. The review aims to serve as a resource for researchers, engineers, and policymakers interested in advancing the state of the art in PV desalination technologies and addressing the global water scarcity crisis through innovative membrane science.

Studies on the fouling behavior and cleaning method of pervaporation desalination membranes for reclamation of reverse osmosis concentrated water

Polyvinyl alcohol (PVA) is a promising membrane material for pervaporation (PV) desalination. However, the adjustment and control of the cross‐linking structure is still a challenge for PVA membrane. In this study, a novel pH‐resistant PVA‐based composite membrane for efficient pervaporation desalination was developed by precisely adjusting the cross‐linking behavior. Vinyl alcohol‐vinylamine copolymer (VA‐co‐VAm) containing both hydroxyl and amino groups was synthesized. Cross‐linking reaction was carried out based on the Schiff base reaction between amino groups (in VAm moiety) and glutaraldehyde (GA) under alkaline conditions. Cross‐linking degree of PVA selective layer was carefully controlled by adjusting the amino group content in copolymer. Results showed that membrane prepared with VA‐co‐VAm that containing 5 wt% N‐vinylformamide (NVF) displayed superior hydrophilicity and the largest free volume fraction. Pervaporation test indicated that the modified cross‐linking membrane showed good stability under extreme pH conditions. Specifically, under strong acid conditions (pH ~ 1) and alkaline conditions (pH ~ 14), the membrane showed excellent desalination performance with water flux over 12 kg/(m2 h), and the salt rejection higher than 99.95%. Based on the above results, the prepared membrane offers a promising platform for desalination under extreme pH conditions, which shows great potential in industrial wastewater treatment.

Treatment of hypersaline waters is a critical environmental challenge. Pervaporation (PV) desalination is a promising technique to address this challenge, but current PV membranes still suffer from challenging issues such as low flux and insufficient stability. Herein, we propose in situ nanoseeding followed by a secondary growth strategy to fabricate a high-quality stable metal-organic framework (MOF) thin membrane (UiO-66) for high-performance pervaporation desalination of hypersaline waters. To address the issue of membrane quality, a TiO2 nano-interlayer was introduced on coarse mullite substrates to favor the growth of a UiO-66 nanoseed layer, on which a well-intergrown UiO-66 selective membrane layer with thickness as low as 1 μm was finally produced via subsequent secondary growth. The PV separation performance for hypersaline waters was systematically investigated at different salt concentrations, feed temperatures, and long-term operation in different extreme chemical environments. Besides having nearly complete rejection (99.9%), the UiO-66 membrane exhibited high flux (37.4 L·m-2·h-1) for hypersaline waters, outperforming current existing zeolite and MOF membranes. The membrane also demonstrated superior long-term operational stability under various harsh environments (hypersaline, hot, and acidic/alkaline feed water) and mild fouling behavior. The rational design proposed in this study is not only applicable for the development of a high-quality UiO-66 membrane enabling harsh hypersaline water treatment but can also be potentially extended to other next-generation nanoporous MOF membranes for more environmental applications.

Water flux of pervaporation (PV) desalination composite membranes can be increased by either decreasing the selective layer thickness or reducing the support layer resistance. The former method has...

Although pervaporation (PV) desalination is a promising solution to global freshwater scarcity, membranes suffer from unstable separation performance. This study utilized resource recycling to prepare a porous ceramic membrane using solid waste fly ash as raw material, which was then combined with polyimide (PI) to produce a high-performance composite membrane (abbreviated to as PI/ceramic membrane). In this composite membrane, the ceramic membrane provides mechanical support and promotes rapid water passage, while the PI layer intercepts hydrated salt ions through size screening and electronic repulsion. Through their synergistic action, the composite membrane can preferentially adsorb and diffuse water molecules while retaining. Results indicate in addition to a retention efficiency of nearly 99.9%, the PI/ceramic membranes achieved a permeability of 10.88 L (m−2 h−1), which is superior to other existing polymer-modified membranes. Simultaneously, the membrane demonstrates selective ion rejection (e.g., SO42− and Mg2+) while maintaining stable rejection performance at 90 °C. A 45-hour continuous operation test confirmed the composite membrane's stability, demonstrating consistent performance. This study provides a novel approach for the preparation of polymer-modified membranes for industrial wastewater desalination.

High performance of graphene oxide (GO)-thiosemicarbazide (TSC) modified membrane for pervaporation desalination with TSC performed as a novel cross-linker

Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. Here in this work we deployed molecular dynamics simulations to optimise the selection of crosslinking compounds that overcome this trade-off relationship. We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m−2 h−1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. Key to achieving this state-of-the-art desalination performance is the spray coating of 0.73 μm thick crosslinked dense, hydrophilic polymers on to electrospun nanofiber mats. The desalination performances of our polymer nanocomposites are harnessed here in this work to produce freshwater from brackish water, seawater and brine solutions, addressing the key environmental issue of freshwater scarcity.

Spray-coated tough thin film composite membrane for pervaporation desalination

Tuning interlayer structure to construct steady dual-crosslinked graphene oxide membranes for desalination of hypersaline brine via pervaporation

General permeation equations based on the solution-diffusion model were proposed for pervaporation (PV), vapor permeation (VP) and reverse osmosis (RO) on two different assumptions about the pressure gradient inside a membrane: a flat gradient (case 1) and a linear gradient (case 2). With these equations the permeation properties in PV, RO and VP can be estimated once the transport parameter of a membrane is known.The effect of upstream pressure on selectivity and flux in RO and PV was estimated by sample calculations for water- and ethanol-selective membranes in ethanol–water system. Flux and selectivity in RO is smaller and, reaching that in PV at infinite pressure. This ultimate value is different in cases 1 and 2, and in the latter the molar volume ratio of the permeants becomes important. The effect of downstream pressure in PV was also estimated and compared with the case of vacuum-enhanced membrane distillation (MD) with a porous membrane. With increasing pressure the separation factor approaches that of vapor–liquid equilibrium in both PV and MD. With decreasing pressure that in MD is governed by the ratio of diffusion coefficients inside the membrane. Since the Knudsen diffusion coefficient of water is larger than that of ethanol, the separation factor decreases in ethanol–water separation with decreasing downstream pressure. This was verified by experiment, using PTFE membranes.

Molecular design of chlorine-resistant polymer for pervaporation desalination

The permeation behavior of ethanol and water in pervaporation (PV) experiments using organic composite membrane; that is a polyvinyl alcohol (PVA) based active layer and a polyacrylo nitrile (PAN) supported layer was studied by measuring permeation flux and separation factor. The effects of permeate pressure (20-50 mbar), feed water concentration (5-1 wt%), and feed temperature (65-75 °C) were examined in this study. It was found that permeate pressure raised with reducing permeate flux and separation factor. Permeation flux enhanced and separation factor reduced with increasing feed water concentration and feed temperature. The solution-diffusion model that was derived by combination of Henry’s law of sorption and Fick’s law of diffusion was proposed to predict the solution-diffusion-desorption steps with a general driving force term and a permeation term. The activity coefficient of component in the ethanol water mixtures was calculated with UNIQUAC model. The solution-diffusion model was applied to predict the pervaporation flux through the PVA/PAN composite membrane. This model was successfully applied to the correlation of experimental results obtained with an organic composite membrane

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013