Manufacture of Hydrochloric acid, Chemistry tutorial


The chemical compound hydrochloric acid is the aqueous (that is, water-based) solution of hydrogen chloride gas. The Hydrochloric acid or muriatic acid is a strong acid, the main component of gastric acid and of broad industrial use. This is a highly corrosive liquid. Muriatic acid was first introduced by the alchemist Jabir ibnHayyan around 800AD by mixing common salt by sulphuric acid. Throughout the industrial revolution in Europe, there was an increased demand for soda and as such the new industrial soda method (that is, Leblanc method) which enabled cheap large-scale production was used. In this method, salt is transformed to soda ash, by employing sulphuric acid, limestone and coal discharging hydrogen chloride as a by-product. This by-product was absorbed in the water, thereby producing hydrochloric acid on an industrial scale. Though, by the substitution of Leblanc's process with Solvay procedure which doesn't produce hydrochloric acid as by-product, it is now generated by other production methods.

Hydrochloric Acid:

The Hydrochloric acid is a versatile chemical employed in a verity of chemical methods, comprising hydrometallurgical processing (example: production of alumina and titanium dioxide), chlorine dioxide synthesis, hydrogen production, activation of petroleum wells and so on HCl is employed by masons to clean finished brick work. It is as well a favored acid for catalyzing the organic method. Muriatic acid is as well utilized in some household cleaning products.

Hydrochloric acid is an extremely acidic, corrosive and non-flammable liquid; the typical concentration is in the range of around 30% HCl by weight (generally termed as concentrated hydrochloric acid), however solutions of up to 38% (generally thermed as fuming hydrochloric acid) and there are as well lower concentrations of this acid.

Manufacture of Hydrochloric Acid:

Muriatic acid can be prepared by several different processes, however over 90% of the HCL generated in the U.S. is a by-product of the chlorination reaction. This in organic acid is generated by any of the given methods:

1) Synthesis from elements:

H2 + Cl2HCl →

2) Reaction of metallic chlorides, specifically sodium chloride (NaCl) by sulphuric acid or a hydrogen sulphate:

NaCl + H2SO4 → NaHSO4 + HCl

NaCl + NaHSO4 → Na2SO4 + HCl

2NaCl + H2SO4 → Na2SO4 + 2HCl

3) As a by-product of chlorination, example: in the production of dichloromethane, trichloroethylene, perchloroethylene or vinyl chloride:

C2H4 + Cl2 → C2H4Cl2  

C2H4Cl2 → C2H3Cl + HCl

4) Via thermal decomposition of the hydrated heavy-metal chlorides from spent pickle liquor in the metal treatment.

2FeCl3 + 6H2O → Fe2O3 + 3H2O + 6HCl

5) From incineration of chlorinated organic waste:

C4H6Cl2 + 5O2 → 4CO2 + 2H2O + 2HCl

=> Production of HCl from the chlorination method:

In the chlorination method, an HCl-containing gas stream is produced. This gas stream proceeds to an absorption column, where concentrated liquid HCl is produced by the absorption of HCl vapors to a weak solution of hydrochloric acid. The HCl-free chlorination gases are eliminated for further processing. The liquid acid is then either sold or employed elsewhere in the plant. The final gas stream is sent to the scrubber to take away the remaining HCl prior to venting. 

A simplified diagram of the steps employed for the production of by product HCl from the chlorination process is illustrated in the figure below:

704_HCl production from chlorination process.jpg

Fig: HCl production from chlorination process

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