Surface modification of anion exchange membrane using layer-by-layer polyelectrolytes deposition facilitating monovalent organic acid transport

Surface modification of commercial anion exchange membrane (AEM) to improve permselectivity for mono carboxylate anions was achieved through layer-by-layer deposition of polyelectrolytes of different polarities (poly (sodium 4-styrene sulfonate), PSS and poly (ethyleneimine), PEI). Improvement in adherence of polyelectrolytes layers was achieved by cross linking with glutaraldehyde, GA. Impact of the number of bi-layers on selective transport was investigated with 2, 5 and 10 bi-layers coatings over commercial AEM. Surface morphology (FESEM), functional groups (FTIR), hydrophilicity/hydrophobicity (contact angle), physico-chemical (ion exchange capacity and water uptake) and electrochemical (permselectivity and membrane resistance) properties were characterized with modified (2, 5 and 10 bi-layers) and unmodified AEMs. Contact angle lowering with increase in number of coated bi-layers confirmed rise in hydrophilicity of the modified AEM surface. 10 bi-layer coated AEM showed 4 times improvement (relative to unmodified AEM) in permselectivity with acetate (AA⁻) ions during batch electrodialysis (ED) of ternary acid mixture (acetic, malic and citric). Energy consumptions per kg of acetic acid recovery with modified (M10) and unmodified AEMs were 0.66 kW h and 0.56 kW h respectively indicating rise in resistance with coating. Permselectivity values of modified membrane (bi-ionic potential) confirmed the observed trend in ED recovery (acetate, AA⁻ > malate, MA²⁻ > citrate, CA³⁻).