Internal cross-linked anion exchange membranes with improved dimensional stability for electrodialysis

A Viable and sustainable flat- membrane plate-and-frame module for spent acid regeneration and metal ion recovery

This study provides techno-economical insights for acid regeneration and metal recovery from spent acidic wastewater by a diffusion dialysis plate-and-frame module using Quaternized Polyepichlorohydrin - Polyacrylonitrile (QPECH-PAN) membranes. Quaternized Polyepichlorohydrin (QPECH) membranes were synthesized using 1,4-diazobicyclo[2.2.2]octane (DABCO) and blended with polyacrylonitrile (PAN). Said membranes were analyzed in terms of their mechanical, physicochemical, and electrochemical characteristics, providing significant results comparable to the commercial membranes (IEC: 1.76 mmol/g, SD: 60.91%, Permselectivity: 79.5 ± 0.31%, and transport no. t_(-): 0.5). Mechanical characterization reveals that the QPECH-PAN membranes possess comparable mechanical strengths (tensile strength: 329.56 MPa). Further, sheet resistivity (6.11 Ω cm²) and conductivity (0.16 S/cm²) reveal the relative conductive nature of these membranes. Percent acid recovery and metal ion recovery ratios were found to be 72% and 48% respectively, and separation factors were 126.8 and 84.57 respectively. The QPECH-PAN membrane's techno-economic feasibility was also analyzed within the context of a textile industry processing up to 5500 kg/d of acidic wastewater. It indicates a potential cost saving of US $0.53 million on H₂SO₄ and NaOH, as well as an OPEX saving of 40.91% against a semi-continuous acid neutralizer.

Anion Exchange Membrane Based on BPPO/PECH with Net Structure for Acid Recovery via Diffusion Dialysis

In order to improve the performance of the anion exchange membrane (AEM) used in acid recovery from industrial wastewater, this study adopted a new strategy in which brominated poly (2,6-dimethyl-1,4-phenyleneoxide) (BPPO) and polyepichlorohydrin (PECH) were used as the polymer backbone of the prepared membrane. The new anion exchange membrane with a net structure was formed by quaternizing BPPO/PECH with N,N,N,N-tetramethyl-1,6-hexanediamine (TMHD). The application performance and physicochemical property of the membrane were adjusted by changing the content of PECH. The experimental study found that the prepared anion exchange membrane had good mechanical performance, thermostability, acid resistance and an appropriate water absorption and expansion ratio. The acid dialysis coefficient (U_H⁺) of anion exchange membranes with different contents of PECH and BPPO was 0.0173-0.0262 m/h at 25 °C. The separation factors (S) of the anion exchange membranes were 24.6 to 27.0 at 25 °C. Compared with the commercial BPPO membrane (DF-120B), the prepared membrane had higher values of U_H⁺ and S in this paper. In conclusion, this work indicated that the prepared BPPO/PECH anion exchange membrane had the potential for acid recovery using the DD method.

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.