Study on the concentration of acids by membrane distillation

Abstract The membrane distillation (MD) process was applied for the concentration of different mineral acids, such as, sulfuric phosphoric, hydrochloric and nitric acids. The MD of a citric acid solution as an example of an organic acid was also investigated. The experiments were carried out keeping the warm feed and cold solution temperatures at 333 and 293 K, respectively. The data obtained indicate that the volume flux of a permeate decreased with an increase of acid concentration in the feed. The reduction of acid content in the permeate, close to 100%, for non-volatile acids was independent of the acid concentration in the feed. The amounts of hydrochloric or nitric acids in the permeate increased with a rise of the acid concentration in the feed, reaching the azeotropic composition. The effect of the polarisation phenomena on the concentration process of sulfuric acid is discussed.