Highly selective separation of acetic acid and hydrochloric acid by alkylamide based on double hydrogen bond coupling mechanism

Recovering acetic acid (HAc) and hydrochloric acid (HCl) from wastewater is environmentally and economically significant. In this research, six different amides were used to extract HAc and the general rule of the influence of alkyl chain is studied. Among them, n-C₁₈H₃₇NO performs better in terms of extraction efficiency, stripping efficiency and separation factor. After optimizing extraction temperature, extractant composition and phase ratio, the separation factor of HAc to HCl is high up to 36.7 and HCl product was obtained. The interaction mechanism of HAc extracted by amide is revealed by applying stoichiometry, FT-IR and quantum chemical calculations and double hydrogen bond coupling extraction mechanism is proposed to explain the preferential extraction of HAc to HCl. The results demonstrate that double hydrogen bonds formed within amide-HAc complexes result in the high separation factor of HAc to HCl. Finally, high-purity HAc product (97%) is stripped from amide by increasing temperature according to thermodynamics analysis and the recycling process was studied. It's believed that double hydrogen bond coupling extraction is a promising and recyclable way to separate acetic acid and hydrochloric acid effectively.