Methyl isocyanate process

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a process for preparation of methyl isocyanate (MIC) by thermal dehydrochlorination of a solution of methyl carbamyl chloride (MCC) in an aprotic nonpolar solvent at a temperature above the boiling point of MCC: ##STR3## initially condensing the resultant reaction gases at a temperature above the boiling point of MIC so as to provide a liquid condensate containing MIC, MCC and said solvent wherein the ratio of MIC to MCC is greater than it is in said reaction solution; separating said liquid condensate from the gases remaining after said initial condensation; separating MIC from said condensate; and separating HCl from said remaining gases by condensing said remaining gases at a temperature below that at which said initial condensation step was performed.
Because the liquid condensate resulting from the initial condensation step is richer in MIC than is the reaction solution, the gases remaining after the initial condensate step are richer in HCl than are the reaction gases.
The enrichment of MIC in the initial condensate and the enrichment of HCl in the uncondensed gases promote more efficient conversion to and recovery of MIC as well as more effective removal of HCl.
The process of this invention comprising the use of an aprotic non-polar organic solvent and said initial condensation technique gives an unexpectedly efficient enrichment of MIC relative to MCC and solvent in the initial condensate.
Separation of MIC from the initial condensate gives yields of MIC as high as 96% with surprisingly low loss of MCC as the result of bi- and tri-molecular condensation to trimethyl triazinetrione and related undesirable by-products such as allophanoyl chloride.
This process is characterized by: a high temperature shift of the MCC .
revreaction.
MIC + HCl equilibrium; an enriched MIC initial condensate stream; short vapor-condensate contact time in the initial condensation step; an organic solvent which reduces condensation side reactions of MCC; and efficient recovery of MIC from the enriched MIC condensate