HYDROCHLORIC ACID PRODUCTION

Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride gas. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrochloric acid is a strong inorganic acid widely used chemical. The largest end uses for hydrochloric acid are steel pickling, oil well acidizing, food manufacturing, producing calcium chloride, and ore processing.

Formula: HCl

Molar mass: 36.46 g/mol

Appearance: Colourless, transparent liquid

It is a simple diatomic molecule consisting of a hydrogen atom and a chlorine atom connected with a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom, the covalent bond between the atoms is polar.

When dissolved in water, toxic hydrogen chloride gas will completely dissociate into its constituent ions to form hydrochloric acid. Aqueous HCl has water-like fluidity, color and appearance unless impurities such as iron (III) chloride are present that cause the solution to turn slightly yellow. Hydrochloric acid has a sharp, pungent, quickly-irritating odor that increases in potency and hazard with rising solution concentrations.

Traditional HCl concentrations are manufactured within the 31.5% to 38% weight/weight (wt%) range. Lower strength solutions are produced through dilution. Concentrated grades are considered 35-38 wt% HCl and are considered fuming hydrochloric acid due to the release of HCl gas from the solution. Higher concentrations are chemically possible but the properties of HCl make handling and long-term storage of these concentrations difficult due to necessary physical requirements, the generated fumes, and likelihood of evaporative loss. The pH of an HCl solution will be low, even for dilute mixtures, with a pH around zero or below to be expected for pure, concentrated solutions.

Molecularly, hydrochloric acid is an inorganic acid solution of the anhydrous gas dissolved in water. Upon dissolution, HCl reacts with water molecules to produce a mixture of hydronium ions, H3O+, and chloride ions, Cl-. The following equation demonstrates the reaction:

H2O(l) + HCl(g) ⇄ H3O+ (aq) + Cl-(aq)

The above reaction establishes an equilibrium but chemical properties and reactivity significantly favor production of the hydronium and chloride ions. The equilibrium shifts more to the production of HCl gas with increasing hydrochloric acid concentrations, (and also heat), eventually leading to fuming hydrochloric acid concentration strengths due to evolving gas vapors. Fumes from HCl solutions are HCl gas and are considered noxious and potentially corrosive.

Aqueous hydrochloric acid is used in recovery of semiprecious metals from used catalysts, as a catalyst in synthesis, use in catalyst regeneration, pH control, regeneration of ion exchange resins used in wastewater treatment and electric utilities, neutralization of alkaline products or waste materials, and in brine acidification for use in the production of chlorine and caustic soda. The pharmaceutical industry consumes hydrochloric acid as a catalyst in synthesis, for pH control, for deionization of water and as a reduction agent (e.g., in the production of ascorbic acid and Para- aminobenzoic acid).

Numerous other uses of hydrochloric acid include the manufacture of dyes and pigments; the removal of sludge and scale from industrial equipment; the de-liming, tanning and dying of hides by the leather industry; manufacture of permanent wave lotion; the carbonizing of wool; use as a bleaching and dyeing assistant in the textile industry; and the purification of sand and clay.

Hydrochloric acid is a solution of hydrogen chloride gas in water. Hydrogen chloride gas is found in the volcame gases. The order designation, muriatic acid, proposed by Lavoisier in 1789, was based on the term muriate, inclicating the presence of chloride is an inagam’c compound. Thus, it is also know as muriat’c acid. The archaic designation is still used in US industry to refer to the commercial farm. Similarly, the arbitrary specific gravity scall devised in the eighteenth century by the Franch chemist Baune is still used to characterize the commercial grades of the acid. The Twaddell density scale which approximates the concentration, is also less commonly used. The relationship of the varius density units of the concentration of the three standard commercial grades of hydrochloric acid is shown in Table 1.