ABSORBENT REGENERATION USING CARBON REGENERANT

1,238,065. Recovering sulphur values. NORTH AMERICAN ROCKWELL CORP. 14 May, 1968 [15 May, 1967], No. 38265/70. Divided out of 1,238,063. Heading C1A. Sulphur values are recovered from a molten salt mixture containing alkali metal sulphites and sulphates by reaction at at least 350‹ C., preferably 350-650‹ C., with either (a) a carbon containing material to form alkali metal sulphides which are further reacted with carbon dioxide and steam or (b) a carbon and hydrogen containing material; whereby alkali metal carbonates are formed in the salt mixture and hydrogen sulphide is evolved. The recovery stage forms part of the cycle of the parent case 22914/68 for removing sulphur oxides from flue gas by adsorption in a molten salt mixture containing alkali metal carbonates to form alkali metal sulphites and sulphates from which the carbonates are regenerated by the above recovery process. The feedstock for the recovery stage preferably contains 10-30 mole per cent of alkali metal sulphite and may contain lithium, potassium and sodium cations and carbonate and chloride anions. In the method (a) above the carbonaceous material may be activated carbon, charcoal, coke, asphalt, tar, pitch or a hydrocarbon and carbon dioxide generated in the first reduction step may be used as a reactant in the final stage of converting the sulphides to the carbonates. The final stage may also be carried out at temperatures as low as 100‹ C. when the salt mixture containin the sulphides is solid. In the method (b) above the hydrogen and carbon containing material may be a solid carbonaceous material, e.g. activated carbon, a hydrocarbon or sludges, cokes, asphalts, tars and pitches produced from petroleum and coal refining, supplemented with hydrogen where necessary. Alternatively steam and a carbonaceous material may be used, when hydrogen is generated in situ.