Non-phosgene synthesis of hexamethylene-1,6-diisocyanate from thermal decomposition of hexamethylene-1,6-dicarbamate over Zn–Co bimetallic supported ZSM-5 catalyst

A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate (HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate (HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst. The catalyst was characterized by FTIR and XRD analyses. Three solvents dioctyl sebacate (DOS), dibutyl sebacate (DBS) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF 4 ) were investigated and compared; DOS gave better performance. The catalytic performances for thermal decomposition of HDC to HDI using DOS as solvent were then investigated, and the results showed that, under the optimized reaction conditions, i.e. ,10 wt% concentration of HDC in DOS, 250 °C temperature, 60 min reaction time, 83.8% yield of HDI had been achieved over Zn–Co/ZSM-5. Decomposition of the intermediate hexamethylene-1-carbamate-6-isocyanate (HMI) over Zn–Co/ZSM-5 in DOS solvent was further studied and the results indicated that yield of HDI from HMI reached to 69.6% (98.6% HDI selectively) at 270 °C, which further increased the yield of the total HDI (HDI tol ) to as high as 95.0%. Recycling of catalyst showed that HDI and HMI yield slightly decreased, and by-product yield increased after the catalyst was reused for 4 times. At last possible reaction mechanism was proposed.