Preparation method for methyl isocyanate

The invention discloses a preparation method for methyl isocyanate (iso-ester for short), comprising the following steps of: mixing methylaminoformyl chloride with a non-ozone-depleting substance (ODS) trichloromethane solvent to form a 15-25% methylaminoformyl/trichloromethane organic solution; continuously decomposing via a decomposer; performing product and solvent separation on the decomposition solution via a cyclone-type steam-liquid separator; and rectifying via a coarse esterification tower and a fine esterification tower to obtain methyl isocyanate having a purity of greater than 99%. The reaction equation is shown in the specification; and in the preparation method disclosed by the invention, with the adoption of a process taking the non-ODS substance, namely, trichloromethane, as the solvent of the decomposition reaction, and with the adoption of the cyclone-type steam-liquid separator, ODS substances with damages on environment, such as benzene, methylbenzene and chlorobenzene, are replaced, and t