Hydrochloric Acid

HCl

IUPAC name: hydrogen chloride
Others name : muriatic acid; marine acid; spirit of salt.
CAS number
: 7647-01-10

An inorganic chemical product, HCl is a colourless, very irritating gas; it generates fumes in the air (because it condenses atmospheric moisture); it is more appropriately called hydrogen chloride (the hydrochloric acid denomination should be reserved to its aqueous solutions.) Hydrochloric acid is soluble in water (with marked release of heat), where it dissociates completely into H+ ions (or protons that bind with the water molecules to form hydronium ions, H30+) and chloride ions CI-; it behaves therefore as a very strong acid. The saturated solution at room temperature contains about 37% by weight of HCl. The commercial concentrated hydrochloric acid is called muriatic acid (its characteristic yellow colour is given by FeCl3 iron trichloride impurities.) Hydrochloric acid attacks almost all metals (except the noble ones like gold, platinum, and tantalum), generating hydrogen. Its salts are called chlorides. It is transported in glass or synthetic resins containers.

Manufacture

Several processes are available, depending on the availability of the reagents, the demand for by-products, or the Hydrochloric acid purity requirements. The most important are:

  1. 1. Recovery from the organic chemical industry. This is not the preferred method if a product of high level of purity is desired; the hydrochloric acid can be contaminated by non-reacted chlorine, chlorinated organic compounds and catalysts’ residues.
  2. 2. Substitution reaction of NaCl with sulphuric acid.. This process is not industrially feasible because sulphuric acid is more expensive than hydrochloric acid.
  3. 3. Hargreaves process, a variation of the previous process. In the same way as for the substitution reaction, the suitability of the process is linked to the availability of NaCl and the demand for sodium sulphate.
  4. Direct synthesis from the elements. The preparation by direct reaction between gaseous chlorine (Cl2) and hydrogen (H2) is the process utilised to obtain a product of high purity. The reaction is highly exothermic and can also be explosive; it requires therefore special installations with very efficient heat absorbers and the cost of the reagents is very high.

The Hydrochloric Acid that we market is obtained mostly by the direct synthesis of not-dried gaseous Chlorine and Hydrogen. The gaseous hydrochloric acid obtained from the synthesis is absorbed in high quality demineralised water. Our product is available in solutions of concentrations ranging from 32% to 37%.
In Italy, only a minor portion of Hydrochloric Acid is obtained by direct synthesis of Chlorine and Hydrogen, while most of it is obtained as “waste” product of other manufacturing processes (see above.)

Principal uses

The main uses, linked to the product quality, are found in the pharmaceutical and food industry and as intermediate in the preparation of flocculants for water purification (Aluminium Polychloride.) The other uses are in the preparation of chloride salts, in the dyes industry, in tanning, in galvanisation processes, and in the treatment of minerals and raw phosphates. It is present in industrial organic processes as a reagent or as a by-product and it is used in the pickling and surface treatment of metals.
It is a base product in the manufacture of chlorinated organic derivatives of great industrial importance such as vinyl chloride, used to produce polyvinyl chloride or PVC, and chloroprene utilised to manufacture synthetic rubber. It is also found in scale and incrustation control products for sanitary services and piping and it is used as a cleaning agent at worksites for acid-resistant floors in order to eliminate traces of cement and plaster.