Synthesis of polyaniline-coated composite anion exchange membranes based on polyacrylonitrile for the separation of tartaric acid via electrodialysis

Abstract

The increasing need to tackle major societal challenges such as environmental sustainability and resource scarcity has heightened global interest in green and efficient separation technologies. The separation of organic acids, particularly tartaric acid, holds significant industrial importance in the food and pharmaceutical sectors. Purifying tartaric acid is crucial due to its roles as a chiral catalyst, antioxidant, and stabilizer, which are vital for ensuring product quality and efficiency. In this study, we synthesized heterogeneous anion exchange membranes by casting a solution of polyacrylonitrile (PAN) homogeneously dispersed with micronized anion exchange resin [polystyrene-divinylbenzene-trimethyl ammonium chloride (PS-DVB-TAC)]. These membranes were further coated with polyaniline (PANI) through in situ polymerization at different time intervals such as 2, 12, and 24 h. Cation exchange membranes were also prepared by solution casting of PAN dispersed with micronized cation exchange resin, sulfonated poly-styrene-co-divinylbenzene, and SPS-DVB. These synthesized anion exchange membranes with and without a PANI coating were examined for their separation performance of tartaric acid, along with the cation exchange membranes in a four-compartment electrodialyser at a constant voltage. The newly fabricated membranes were characterized by different techniques, including attenuated total reflectance-Fourier transform infrared spectroscopy for functional group analysis, scanning electron microscopy for their surface morphology, and the four-probe method for electrical conductivity. In addition, ion exchange capacity and water uptake have been measured. The electrodialysis experiments showed that 14.82 wt% of tartrate ions moved into the product compartment through the uncoated anion exchange membrane within 30 min at a voltage of 30 V. Under the same conditions, membranes coated with PANI at 2, 12, and 24 h raised the separation efficiency to 21.19%, 34.13%, and 37.21%, respectively. Findings indicate that membranes coated with PANI for extended periods demonstrate superior separation efficiency for tartaric acid. Consequently, this energy-efficient method shows significant potential for application in the food and pharmaceutical industries for separating tartaric acid and other organic and amino acids. This research can advance practical and sustainable separation technologies, addressing critical societal issues like resource efficiency and environmental sustainability.