METHOD FOR PURIFYING TOLUENE DIISOCYANATE INTRODUCED INTO DIVIDING-WALL DISTILLATION COLUMN FOR FINAL DISTILLATION WITH IMPROVED PURITY AT LOW COST

摘要

PURPOSE: Provided is a method for purifying toluene diisocyanate(TDI) introduced into a dividing-wall distillation column for final distillation of TDI product, by which the amount of low boiling point impurities is decreased and the TDI purity is increased, while reducing the energy and cost needed therefor. CONSTITUTION: The method for purifying toluene diisocyanate comprises the steps of: (a) fractionating crude distillation charge comprising less than 2 wt% of phosgene to remove the solvent optionally with reaction residues and to form a crude toluylene diisocyanate comprising less than 20 wt% of solvent; and (b) separating the crude toluylene diisocyanate in a dividing-wall distillation column into four types of fractionation products P1-P4. In the method, P1 is a vapor stream enriched with vaporous low-boiling substances and solvent, P2 is a product enriched with low-boiling substances and solvent, P3 is a bottom product enriched with high-boiling substances including TDI, and P4 is a TDI product stream deficient in low-boiling substances, high-boiling substances and reaction residues.