GB806970A - Improvements in or relating to a process for the preparation of salts and of acids - Google Patents

Abstract

An acid and a salt of a metal (including ammonium) are prepared by reacting in the solid state another salt of said metal with a homogeneous solution containing water, the acid whose anion is to be bound to said metal to form the first-said salt and a solvent having limited miscibility with water, in which both reactant and product salts are not appreciably soluble and in which the reactant and product acids are soluble, and separating the solvent phase containing the product acid from the solid salt reaction product. Solvents referred to are alcohols having 3 or more carbon atoms, e.g. a propanol, a butanol or a pentanol or mixtures thereof, and ketones and ethers having more than 4 carbon atoms. Reactant acids specified are nitric, phosphoric and sulphuric acids, which may be reacted with alkali metal or ammonium chlorides to form the corresponding nitrates, phosphates or sulphates and hydrochloric acid; salts such as gallium and mercuric sulphates which are very soluble or decompose in an aqueous solution may be prepared; chromic acid may be obtained together with sodium sulphate by reaction of sulphuric acid and sodium chromate; by two such processes it may be possible to obtain a salt, e.g. barium chromate, which is otherwise difficult to obtain; thus sodium chlorate by reaction with hydrochloric acid gives chloric acid (and sodium chloride) and the chloric acid by further reaction with barium chloride gives the desired barium chlorate. In examples: (1) potassium nitrate is obtained with hydrochloric acid by reaction of potassium chloride with nitric acid using isoamyl alcohol as organic solvent; (2) ammonium sulphate and hydrochloric acid are obtained from ammonium chloride and sulphuric acid using a mixture of iso-amyl alcohol and butanol as organic solvent; (3) sodium nitrate and hydrochloric acid are obtained from sodium chloride and nitric acid using n-butanol as organic solvent; and (4) potassium dihydrogen phosphate and hydrochloric acid are obtained from potassium chloride and phosphoric acid using n-butyl alcohol as solvent. The process may be carried out batchwise or by continuously reacting the solid in counter-current to the homogeneous liquid phase. Where as a result of a batchwise process a salt mixture is formed, the operation may be repeated with a fresh quantity of the acid-solvent mixture or the mixture may be resolved by fractional crystallization or froth flotation. The reactants may be employed in equivalent quantities or a stoichiometric excess of one component may be used; ambient temperatures are suitable; suitable acid concentrations are from 1-4 N. The solvent phase separated from the solid may, if desired, be first washed once or a number of times or counter-currently scrubbed to remove one of the acids preferentially, e.g. with water to remove sulphuric acid, or hydrochloric acid from nitric or phosphoric acid, or with a saturated chloride brine to wash out nitric acid from hydrochloric. In the latter case the chloride brine is preferably that corresponding to the metal (or ammonium) in the salt. A solvent may be thereafter added to the separated solvent phase which mixes therewith but is not miscible with aqueous acids (e.g. petroleum hydrocarbons, benzene toluene and xylene) whereby two phases are formed; the solvent phase may be fractionally distilled and the components separately returned to the appropriate stage in the process and the aqueous phase also treated by distillation (in the case of sulphuric or phosphoric acid under atmospheric pressure, in the case of nitric acid in vacuo) or (to separate sulphuric and hydrochloric acids) by stripping with a stream of warm air.