Hydrochloric acid

Applications

Hydrochloric acid is a strong inorganic acid that is used in many industrial processes. The application often determines the required product quality.

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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.

Related Topics:
Ion exchange resin - Cation exchange - Ion - Aqueous - Demineralized

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:: Na+ is replaced by H3O+

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:: Ca2+ is replaced by 2H3O+

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Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries.

Related Topics:
Drinking water - Food

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pH control and neutralization

A very common application of hydrochloric acid is to regulate the basicity (pH) of solutions.

Related Topics:
Basicity - PH

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:: OH- + HCl → H2O + Cl-

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In industry demanding purity (food, pharmaceutical, drinking water), high-quality hydrochloric 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.

Related Topics:
Neutralizing - Swimming pool

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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.

Related Topics:
Pickling - Metal - Rust - Iron oxide - Iron - Steel - Extrusion - Rolling - Galvanizing

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:: Fe2O3 + Fe + 6HCl → 3FeCl2 + 3H2O

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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.

Related Topics:
Spent acid - Ferrous chloride - Heavy metal

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In recent years the steel pickling industry has however developed hydrochloric acid regeneration processes, such as the spray roaster or the fluidised bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. One of the most common regeneration processes is the Dependeq - Process, applying the following formula:

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:: 4FeCl2 + 4H2O + O2 → 8HCl+ 2Fe2O3

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By this means 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.

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n.b.: HCl is not a common pickling agent for stainless steel grades.

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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 poly aluminium chloride (PAC).

Related Topics:
Acid-base reactions - Inorganic - Iron(III) chloride - Poly aluminium chloride (PAC)

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:: Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O

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Both iron(III) chloride and PAC are used as flocculation and coagulation agents in wastewater treatment, drinking water production, and paper production.

Related Topics:
Iron(III) chloride - PAC - Flocculation - Wastewater treatment - Drinking water - Paper

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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.

Related Topics:
Calcium chloride - Nickel(II) chloride - Electroplating - Zinc chloride - Galvanizing - Battery

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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 hydrochloric acid that never actually reaches the open market. Other organic compounds produced with hydrochloric acid include bisphenol A for polycarbonate, activated carbon, and ascorbic acid, as well as numerous pharmaceutical products.

Related Topics:
Organic compounds - Vinyl chloride - PVC - MDI - TDI - Polyurethane - Organic - Bisphenol A - Polycarbonate - Activated carbon - Ascorbic acid - Pharmaceutical

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Other applications

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.

Related Topics:
Leather - Cleaning - Building - Construction - Oil production - Oil well - North Sea

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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 protein, and gelatin. Food grade (extra pure) hydrochloric acid can be applied when needed for the final product.

Related Topics:
Food - Ingredients - Food additive - Aspartame - Fructose - Citric acid - Lysine - Protein - Gelatin

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