Hydrochloric Acid

Preconcentration

A raw Hydrochloric Acid with a low HCI content is separated by rectification into the head product water and the sump product azeotropic Hydrochloric Acid.

According to the operating pressure, the azeotropic concentration is between 18 and 24 % HCI. At atmospheric conditions it is approx. 20 % HCl. Hydrochloric Acid is purified using additional process steps during pre-concentration.

Volatile compounds are evaporated together with the water. The volatility of some compounds can be increased by chemical treatment. For example dissolved bromide can be oxidised to volatile bromide. To reach highest purity the pre-concentrated Hydrochloric Acid is evaporated in a second step. Salts and non-volatile compounds remain in the sump product. The evaporation of volatile impurities in this step can be avoided by chemical treatment. Hydrofluoric acid for example is bonded by dosing aluminium chloride.

 

 


Fields of application for the pre-concentration of Hydrochloric Acid are the processing of waste water containing HCl or of diluted Hydrochloric Acid, which occur during chemical processes and during the purification of waste air. Purified pre-concentrated Hydrochloric Acid may be recycled into the initial process or used for other purposes, such as regenerating ion exchangers or neutralising alkaline waste water.

An example for recycling of the HCl is the production of vinyl chloride from ethylene. In the first step dichloroethane is produced by the reaction of ethylene with chlorine. In the second step vinyl chloride is produced from the dichloroethane and HCl gas is obtained as by-product. The HCl is recovered as Hydrochloric Acid and recycled to the electrolysis of chlorine, which is then reused in the first step. The direct recycling of HCl gas is possible, when producing the dichloroethane by oxchlorination of ethane using HCl and O2.