Patent ID: 7244862

Claim:
A process comprising the steps of: a) contacting an aqueous solution of hydrochloric acid with sodium oxalate in a reaction zone at a temperature between about 35° C. and about 140° C. to form a mixture, wherein the molar ratio of the water to the sodium oxalate is between 20 to 1 and 350 to 1, and the molar ratio of the hydrochloric acid to the sodium oxalate is greater than 3 to 1 and less than 45 to 1; b) cooling the mixture to a temperature between about −10° C. and about 25° C. to form precipitated oxalic acid dihydrate in a slurry; c) separating the precipitated oxalic acid dihydrate from the slurry, thereby leaving a first residual solution; d) neutralizing the first residual solution with a sodium-containing base to form precipitated sodium oxalate in a slurry; e) separating the precipitated sodium oxalate from the slurry, thereby leaving a second residual solution; and f) recycling the separated sodium oxalate to the reaction zone.