Reactive extraction of carboxylic acids from apolar hydrocarbons using aqueous solutions of sodium hydrogen carbonate with back-recovery using carbon dioxide under pressure

A combination of using an aqueous solution of sodium hydrogen carbonate for forward-extraction of carboxylic acids from a dilute apolar organic solvent, and carbon dioxide under pressure for its back-recovery, is studied. Used in combination, these two steps might provide a technique for the recovery of a carboxylic acid from an organic solution in which no formation of by-products (inorganic salts) occurs and only environmentally benign chemicals are used. Results show that the aqueous solution of sodium hydrogen carbonate provides distribution ratios for several aromatic and aliphatic acids as high as 200, whereas the solubility of the organic solvent in the aqueous solution remains unchanged relative to pure water. Two options for the back-recovery of the extracted acids based on the use of CO2 under pressure are evaluated: by new phase (liquid or solid) formation or by back-extraction. Equilibrium stage recoveries of around 50% are obtained in both cases. That recovery can be further improved by addition of a salting-out agent in the aqueous phase. In that case the recoveries of up to 90% are achieved, where the recovery of 50% is already reached at a CO2 pressure of 5 bar. Therefore, both forward-extraction using an aqueous solution of sodium hydrogen carbonate and back-recovery by carbon dioxide under pressure are feasible options for the recovery of carboxylic acids from organic solvents.