Hydrochloric Acid at 30–35 wt% concentration can be produced from any diluted raw Hydrochloric Acid. Using extractive rectification, weak Hydrochloric Acid is mixed with an extraction agent and fed into the rectification column. Water is absorbed by the extraction agent and the volatility of the Hydrochloric Acid stream is increased. At the head of the column, medium concentration Hydrochloric Acid is refined. Diluted extraction agent is obtained in the sump, reconcentrated in an external evaporator and fed back into the column. CaCl2, MgCl2 or H2SO4 may be used as extractive agents to remove water. The dual-pressure process is also available for the production of medium concentration Hydrochloric Acid. In the first step, preconcentrated acid at 22–24 wt% HCl is split into the head product with about 30–35wt% HCl and the sump product azeotropic acid using rectification under pressure. In the second step, the azeotropic acid is restrengthened by evaporating water at vacuum conditions up to 22–24wt% HCl and then recycled to the first step. As an alternative, the azeotropic acid can be restrengthened using concentrated HCl gas. | |