Environmentally sustainable production of bio-based mineral acids

Abstract

The production of bio-based mineral acids, using hydrochloric acid as a model, was revisited here. Simple, affordable, renewable and non-hazardous reactants –namely sodium chloride and oxalic acid– enabled the preparation of concentrated solutions of hydrochloric acid (6 N) in good yields and in mild conditions, including at pilot scale. The process was easily implemented by mixing the two reactants in refluxing water, followed by azeotropic distillation of the reaction mixture. This approach was extended to other mineral acids such as HBr, HI and HNO₃, using the corresponding sodium salt. The described process was compared with current industrial methods for HCl production, highlighting its efficiency, improved safety through the elimination of hazardous substances such as chlorine or concentrated sulfuric acid and its precursors, and enhanced sustainability through reduced of energy consumption and the exclusive use of bio-based reactants. This process exemplifies how green chemistry can contribute to cleaner production by addressing both environmental and sustainability challenges.