GB999800A - Purification of gases - Google Patents

Abstract

Hydrogen sulphide is removed from a gas, e.g. town gas, by washing the gas with an aqueous solution of ferric and ferrous iron chelates, which comprise iron chelated with a polyamino carboxylic acid chelating agent, the solution being regenerated by oxidation with a free oxygen-containing gas, e.g. air or oxygen, the regeneration being so controlled that a substantial proportion of ferrous iron chelate remains in the regenerated solution. The proportion of ferrous iron chelate remaining should be 15 to 75%, preferably 20 to 50%, of the total iron present, and the volume of air or oxygen used for regeneration may be varied manually or automatically to maintain the correct proportion of ferrous iron chelate, which may be determined by chemical analysis or by measuring the redox potential of the solution. The air or oxygen may be mixed with the gas to be purified before contacting the gas with the solution, purification and regeneration occurring simultaneously, or may be mixed with an inert gas, e.g. the purified gas, for contacting the used solution, or the methods may be combined, e.g. when the free oxygen content of the purified gas must be kept below a level which does not allow sufficient regeneration of the solution to take place during purification. In the latter case, the further regeneration may be carried out under pressure. The chelating agent may be an amino acid as described in Specification 999,799. The reoxidation step may be additionally controlled in relation to the oxygen content of the gas entering and leaving the washing plant, but no details are given. Specification 855,421 also is referred to.