Industrial method for producing IPDI (isophorone dicarbamate) through thermal cracking of n-butyl isophorone dicarbamate

The invention relates to the technical field of industrial urea method synthesis of IPDI (isophorone diisocyanate), in particular to an industrial method for producing IPDI through IPDU-B (isophorone diisocyanate-B) continuous thermal cracking. The industrial method comprises the following continuous processes: 1) carrying out two-stage thermal decomposition reaction by using two thermal decomposition reactors (a first thermal decomposition reactor and a second thermal decomposition reactor) in combination with rectification operation to prepare a reaction product with relatively high IPDI content; 2) discharging a circulating heavy component material of the two-stage thermal decomposition reactor, and recovering a solvent; and 3) a rectification operation step: separating the thermal decomposition product, separating almost all n-butyl alcohol (accounting for 99.6% or above of the total amount) at the top of the first tower by using a two-tower process of a first rectification tower (light component removal