GB999799A - Purification of gases - Google Patents

Abstract

Hydrogen sulphide is removed from a gas, e.g. town gas made by the catalytic cracking with steam of heavy oil, by washing the gas with an aqueous solution containing a ferric iron chelate, in which the chelating agent is an amino acid of the general formula <FORM:0999799/C4-C5/1> in which R is an alkylene group in which at least 2, but not more than 3 carbon atoms separate the N atoms, or is a 1.2 cyclohexylene group; X and X2 is an acetic or propionic acid residue; X1 and X3 is a hydrogen atom, or an ethylol group, or an acetic or propionic acid residue, or, when R is an alkylene group, X3 is a group of the general formula-RNXX2. The pH of the solution is below the value at which precipitation of iron salts occurs from the solution, but above the value at which hydroxylation of the iron chelate begins. The pH may be from 2.5 to 9 depending on the acid used. The R group is preferably an ethylene or trimethylene group, but propylene or isobutylene is permissible. Preferred acids are ethylene diamine N,N,N1,N1 - tetra - acetic acid, C-methyl ethylene diamine N,N,N1,N1-tetra-acetic acid, 1,2-diaminocyclohexane N,N,N1,N1-tetra-acetic acid, N-hydroxyethylethylene diamine-N,N1,N1 - triacetic acid, diethylenetriamine N,N,N1,N11,N11 - penta - acetic acid, and ethylenediamine N,N1-diacetic acid. The solution may be reoxidized by passing an oxygen-containing gas, e.g. air, therethrough, or may be effected by free oxygen present in the gas to be purified. Specification 855,421 is referred to.