GB812134A - Process for removal of carbon dioxide and (where necessary) hydrogen sulphide from gases containing these constituents - Google Patents

Abstract

A process for separating carbon dioxide or hydrogen sulphide from a synthesis gas comprising hydrogen and carbon monoxide and utilizing the separated gases, comprises purifying the synthesis gas by contacting with an aqueous solution of an inorganic salt rendered alkaline with ammonia, which solution reacts with the carbon dioxide or hydrogen sulphide to form an aqueous solution of a crystallizable salt and a precipitate of a salt less soluble than the crystallizable salt, removing the precipitated less soluble salt, subsequently crystallizing and removing the more soluble crystallizable salt, converting all or a portion of the purified synthesis gas to ammonia, dissolving fresh inorganic salt, and all or a portion of the synthesized ammonia, in the residual solution after the removal of the less soluble salt and before or after the more soluble crystallizable salt, and recycling the solution remaining remainkng after the removal of the more soluble salt, and after dissolution of the fresh inorganic salt and synthesized ammonia, to the synthesis gas-purifying step. Hydrogen sulphide and carbon dioxide may be separately removed in succession by the above method. The remaining purified gas, if any, may be used in a fuel or alcohol synthesis process. Crystallization of the more soluble salt may be effected by cooling with water and/or liquid synthesized ammonia, gaseous ammonia evolved from said liquid ammonia being dissolved in said residual solution. The synthesis gas may be washed before purification in one or more towers with a circulating solution containing carbon dioxide and ammonia in a ratio of not less than 1.29 and may be washed after purification in one or more towers with a circulating solution containing carbon dioxide and ammonia in a ratio of not more than 1.29. Inorganic salts specified for the separation of carbon dioxide are sodium nitrate, chloride, sulphate, and phosphate, calcium chloride, sulphate and phosphate, and barium nitrate, and chloride. Inorganic salts specified for the separation of hydrogen sulphide are the sulphate of iron, zinc, nickel and copper. The synthesis gas may pass up a tower in countercurrent to the ammoniacal solution (Fig. 1, not shown), or may be bubbled into a vessel which contains the ammoniacal solution (Figs. 2, 3 and 4, not shown). According to Fig. 3, the gas is further purified by countercurrent tower washing first with aqueous ammonia or an ammoniacal salt solution, then with acid, and finally with water. According to Fig. 4, the gas may in addition be prepurified by countercurrent tower washing with aqueous ammonia or ammoniacal salt solution.