Patent GB-661370-A (GB)
Title: Improvements in or relating to the limitation of the corrosive action of aqueous amine solutions, and the stabilisation of such solutions against oxidation
IPC: C23F11/06
Filed: 1948-01-20
Abstract: A method of reducing the tendency of an aqueous amine solution to enter into undesired reactions, in a cyclic process of the type employing such amine solution for separating mixed gases under oxydizing conditions, consists in adding as a stabilizer to the amine solution material capable of ensuring by ionization the presence in the reaction cycle of iodine-containing ions and a method of reducing the amount of cupriferous material required and also reducing the oxidation of amine in a process for inhibiting corrosion of apparatus in contact with aqueous amine solutions, used in the cyclic processes for the separation of mixed fluids, subjected to oxydizing conditions, by adding cupriferous components thereto, which consists in adding to the aqueous amine solution, a material which will ensure by ionization the presence of iodine-containing ions, said material being added in minor amounts equivalent to about 0.1 per cent of potassium iodide.  The iodine-containing ion alone reduces plant corrosion.  Any aqueous amine solution which is commercially useful in cyclic processes for the separation of mixed fluids may be treated and primary, secondary and tertiary ethanolamines, monoisopropanolamine, diaminopropanolamine and other amino or aminohydroxy compounds containing less than ten carbon atoms are mentioned.  Sources of iodine-containing ions mentioned include iodine, alkali metal, ammonium and alkaline earth metal salts of iodine including iodides and iodates, hydroiodic acid or the anhydrides of the iodic acids and organic iodine compounds of iodine, it being merely necessary that the material be soluble at least to some extent in the amine solution, and others are mentioned in the examples.  Copper itself or compounds thereof soluble at least to some extent in the fluids of the primary separating process may be used, e.g. cupric sulphate.  Cuprous iodide provides both copper and iodide ions at once.  In examples oxidation of heated aqueous amino alcohol solutions contacted with gaseous mixtures of oxygen and carbon dioxide is inhibited by varying proportions of iodine - containing compounds.  Results are shown in tables I and II of adding potassium iodide to mono-and diethanol-amine, monoisopropanolamine and diaminoisopropanolamine solutions; III of the addition of barium, calcium, cuprous, magnesium, potassium, hexyl, n-amyl, cetyl and tertiary butyl iodides, potassium iodate, triiodobenzoic acid and iodoform to monoethanolamine solutions; and IV and V of the reduction of corrosion of a steel plate immersed in heated aqueous solutions of diethanolamine and monoisopropanolamine treated with a gaseous mixture of oxygen and carbon dioxide on the addition of copper sulphate and potassium iodide separately and together.  The Specification as open to inspection under Sect. 91 comprises also a method of inhibiting oxidation of an aqueous amine solution comprising providing in the solution iodine or its ionizable compounds.  This subject-matter does not appear in the Specification as accepted.