GB1110859A - A process for the separation of dimethylformamide from the reaction product of a dimethylformam ide synthesis - Google Patents

Abstract

The reaction product, consisting mainly of dimethylformamide, methanol, methyl formate, catalyst salts, monomethylformamide and dissolved carbon monoxide, which is obtained from a single-stage synthesis plant for the production of dimethylformamide from methanolic dimethylamine solution and carbon monoxide in the presence of methyl formate and sodium methylate as catalyst at temperatures of about 100 DEG C. and pressure of about 200 atmospheres, is treated by a process which consists in expanding the products to atmospheric pressure, removing and cooling the liberated carbon monoxide, subjecting the remaining product mixture to total evaporation, removing the residual salts, distilling in a gaseous state the salt-free product mixture obtained at atmospheric pressure into a fraction having a boiling point lower than that of dimethylformamide and a sump fraction consisting of crude dimethylformamide, and further in separating the crude dimethylformamide obtained as the sump fraction, by distillation under reduced pressure in a second distillation stage into a crude monomethylformamide as a sump fraction and a distillate, separating from the vaporous distillate by fractional condensation, in a first condensation stage, substantially pure dimethylformamide and in a second condensation stage dimethylformamide contaminated with lower boiling products, and in using the previously separated fraction with a boiling point lower than that of dimethylformamide obtained from the first distillation stage as a circulating product in the single stage synthesis plant and, if desired, adding part of this fraction to the reaction product mixture, and in recirculating the impure dimethylformamide obtained in the second condensation stage to the reaction product mixture.