Purification and recovery of NaCl from epoxy resin waste salt through an integrated process based on aqueous two-phase systems (ATPS)

Abstract

A substantial amount of waste salt is generated during epoxy resin production, which is accompanied by a high concentration of organic contaminants. This hampers the potential for waste salt reuse, resulting in resource waste. While the direct pyrolysis treatment of epoxy resin waste sodium chloride (NaCl) can remove 99.6 % of the organic contaminants at 550 °C, the treatment cost is relatively high (500 RMB/t). This study proposed a cost-effective, near-zero discharge integrated process for purifying epoxy resin waste salts. Initially, ethanol was introduced into a waste salt solution (300 g/L) to form aqueous two-phase systems (ATPS) with salt, and 95.4 % of the total organic carbon (TOC) was efficiently removed. The recrystallized salt obtained from the ATPS treatment was further purified by washing with water (water/salt ratio, 5:8), reducing the TOC to 62.88 mg/kg. Electrolysis evaluation revealed that the voltage of the purified salt treated using the integrated process closely resembled that of the pure salt. This indicated that the purified salt could be utilized as a resource akin to pure salt. Furthermore, compared to direct pyrolysis, the proposed integrated process could reduce the treatment cost to 235 RMB/t and energy consumption by 47.10 %, contributing to a reduction in carbon emissions. Thus, this study proposed a viable method for efficiently separating salt and organic contaminants, enabling the recovery of waste NaCl from epoxy resin production.