Patent ID: 6657082
Filing Date: 2003-12-02
Classification: C07C

Abstract:
An improved process for preparing thiourea, said process comprising:(a) providing a reaction vessel containing a slurry comprising water and a major part of a calcium cyanamide charge; (b) sparging carbon dioxide and hydrogen sulphide into said slurry; (c) maintaining a pH of said slurry alkaline; (d) providing said slurry at an initial temperature of at least about room temperature and permitting said slurry to achieve a process temperature of at least 56Â° C. and not more than 80Â° C; (e) stopping said hydrogen sulphide sparging while maintaining said carbon dioxide sparging; (f) adding a remaining part of said calcium cyanamide charge to said slurry to form a reaction mass in said reaction vessel; (g) retaining said reaction mass in said reaction vessel for 2 to 5 hours to complete secondary reactions to form thiourea; (h) increasing a carbon dioxide sparging rate for a period of 1.6 to 6 hours to effect decomposition of Ca(SH)2; (i) terminating said carbon dioxide sparging; (j) separating thiourea solution from said slurry; and (k) isolating said thiourea from said thiourea solution, wherein calcium cyanamide, carbon dioxide and hydrogen sulphide are the only reagents employed in said process.