Abstract

Hydrogen chloride, a gas at ambient temperature and pressure, is very soluble in water. Hydrogen chloride can be produced by direct reaction of the elements, by reaction of metal chlorides and acids, and as a by-product from many chemical manufacturing processes such as those for chlorinated hydrocarbons. Over 90% of the hydrogen chloride produced in the United States is as a by-product from various chemical processes. HCl is produced as a by-product in the manufacture of chlorofluorohydrocarbons, aliphatic and aromatic hydrocarbons, production of high surface area silica, and the manufacture of phosphoric acid and esters of phosphoric acid. Crude by-product HCl is generally contaminated with impurities of the process. A wide variety of techniques are employed to treat the HCl streams to obtain either anhydrous HCl or hydrochloric acid. Technologies have been developed for burning or pyrolyzing waste organics and recovering the chlorine values as hydrogen chloride.

Hydrogen chloride and its aqueous solution, muriatic acid, find application in many industries. In general, anhydrous HCl is consumed for its chlorine value, whereas aqueous hydrochloric acid is often utilized as a nonoxidizing acid, in metal-cleaning operations, chemical manufacturing, petroleum well activation, and the production of food and synthetic rubber. Most of the HCl produced is consumed captively either in integrated operations, eg, chlorinated methane plants, or in separate HCl-consuming operations at the same location.