Aqueous amine solutions and a method of reducing corrosion of corrodible metal surfaces in contact with aqueous amine solutions

摘要

Aqueous amine solutions, for use in dissolving a normally gaseous inorganic acidic compound, contain a minor proportion of an alkali metal orthophosphate; the amine is normally liquid or solid, has a boiling point not substantially below 100 DEG C., and does not contain oxygen in the form of a carbonyl or carboxyl group. During the regeneration by heating of such a solution, corrosion of metal surfaces in contact with the solution is reduced. Suitable orthophosphates, which may be present in an amount of 0.1-3 per cent by weight of the amine solution, are trisodium phosphate, tripotassium phosphate, trilithium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium dihydrogen phosphate, sodium potassium hydrogen phosphate, and sodium dipotassium phosphate. Amines specified are hexylamine, diproplyamine, trimethylenediamine, mono-ethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, benzylamine, phenylethylamine, methylphenylamine, cyclohexylamine, ethylcyclohexylamine, and tetrahydroortho-toluidine. The solution may contain more than 50 per cent by weight of an aliphatic liquid polyhydric alcohol, e.g. ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol. A solubilizing agent for the phosphate may also be present; examples are watersoluble carboxylic acids, e.g. acetic acid, and water-soluble phenols, e.g. phenol and/or cresol. Processes in which the amine solutions may have been used are the recovery of carbon dioxide from flue gases, the recovery of sulphur dioxide from roasting furnace gases, and the removal of carbon dioxide, sulphur dioxide, and hydrogen sulphide from natural gas, refinery gas, water gas, or hydrogen. Corrosion of iron, steel, aluminium, "Monel" metal (Registered Trade Mark) or nickel is prevented at temperatures above 100 DEG C. Tests are described showing the effect on corrosion of various proportion of phosphates and water in the amine solutions.