GB834278A - Process for working up crude formamide - Google Patents

Abstract

Crude formamide, as is obtained by reacting carbon monoxide with ammonia under pressure in the presence of methanol and an alkali alcoholate, is purified by continuously passing the crude product at atmospheric pressure and 130 DEG to 160 DEG C. through a distillation column in which it remains for short periods just sufficient to ensure that all constituents lower-boiling than the formamide are substantially separated, and subjecting the residue discharged from the column to a simple continuous vacuum distillation, the formamide being recovered as distillate. Crude formamide is pumped through preheater 3, wherein it is heated to 100 DEG C., to the upper part of packed distillation column 4 having top and bottoms temperatures of 100 DEG and 145 DEG C. Vapours of ammonia, methyl formate and methanol are removed as overheads and condensed in condenser 5 to be used for further synthesis. The bottoms fraction withdrawn <PICT:0834278/III/1> through cooler 8 to vessel 9 comprises formamide, not more than 1% methanol, only traces of water, and all the alkali metal compounds. This product is transferred to vacuum distillation retort 10 which is externally heated to 120 DEG to 130 DEG C., and is operated under a vacuum of 10 mm. Hg. at such a rate that evaporation is immediate and no liquid collects therein. The formamide condensed in condenser 11 and passed to receiver 13 has a purity of 99.8% and a specific gravity of 1.131. A second vacuum retort can be arranged in parallel for use while the alkali metal salts are washed from the first retort with water.