Hydrochloric acid is a strong inorganic acid that is used in many industrial processes. The application often determines the required product quality.
Regeneration of ion exchangers
An important application of high-quality hydrochloric acid is the regeneration of ion exchange resins. Cation exchange is widely used to remove ions such as Na+ and Ca2+ from aqueous solutions, producing demineralized water.
Na+ is replaced by H3O+
Ca2+ is replaced by 2 H3O+
Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries.
pH Control and neutralization
A very common application of Hydrochloric acid is to regulate the basicity (pH) of solutions.
OH- + HCl H2O + Cl-
In industry demanding purity (food, pharmaceutical, drinking water), high-quality Muriatic acid is used to control the pH of process water streams. In less-demanding industry, technical-quality hydrochloric acid suffices for neutralizing waste streams and swimming pool treatment.
Pickling of steel
Pickling is an essential step in metal surface treatment, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling, galvanizing, and other techniques. Technical-quality HCl at typically 18% concentration is the most commonly-used pickling agent for the pickling of carbon steel grades.
Fe2O3 + Fe + 6 HCl 3 FeCl2 + 3 H2O
The spent acid has long been re-used as ferrous chloride solutions, but high heavy-metal levels in the pickling liquor has decreased this practice.
In recent years, the steel pickling industry has, however, developed hydrochloric acid regeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula:
4 FeCl2 + 4 H2O + O2 8 HCl+ 2 Fe2O3
By recuperation of the spent acid, a closed acid loop is established. The ferric oxide by product of the regeneration process is a valuable by-product, used in a variety of secondary industries.
Hydrochloric Acid is not a common pickling agent for stainless steel grades.
Production of inorganic compounds
Numerous products can be produced with hydrochloric acid in normal acid-base reactions, resulting in inorganic compounds. These include water treatment chemicals such as iron(III) chloride and polyaluminium chloride (PAC).
Fe2O3 + 6 HCl 2 FeCl3 + 3 H2O
Both iron(III) chloride and PAC are used as flocculation and coagulation agents in wastewater treatment, drinking water production, and paper production.
Other inorganic compounds produced with hydrochloric acid include road application salt calcium chloride, nickel(II) chloride for electroplating, and zinc chloride for the galvanizing industry and battery production.
Production of organic compounds
The largest Hydrochloric acid consumption is in the production of organic compounds such as vinyl chloride for PVC, and MDI and TDI for polyurethane. This is often captive use, consuming locally-produced Muriatic acid that never actually reaches the open market. Other organic compounds produced with Muriatic acid include bisphenol A for polycarbonate, activated carbon, and ascorbic acid, as well as numerous pharmaceutical products.
Domestic and Industrial as cleaning Compound :
Hydrochloric acid is a fundamental chemical, and as such it is used for a large number of small-scale applications, such as leather processing, household cleaning, and building construction. In addition, a way of stimulating oil production is by injecting Hydrochloric acid into the rock formation of an oil well, dissolving a portion of the rock, and creating a large-pore structure. Oil-well acidizing is a common process in the North Sea oil production industry.
Many chemical reactions involving Hydrochloric acid are applied in the production of food, food ingredients, and food additives. Typical products include aspartame, fructose, citric acid, lysine, hydrolyzed (vegetable) protein as food enhancer, and in gelatin production. Food-grade (extra-pure) Muriatic acid can be applied when needed for the final product.
