hmdi had a purity of 92 and a hmdi chromatography yield of 95 then the mixing liquid was subjected to rectification the isolated hmdi yield was 91 the residual product after rectification was subjected to the next thermal cracking for circulation in turn the ionic liquid could be reused for several times in to a thermal cracking device 500 g of 1 2 dimethyl 3 ethylimidazole hexafluorophosphoric acid ionic liquid emmim pf 6 and 0 8 g of supported metal oxide solid catalyst e were added at 190 u00b0 c under an absolute pressure of 6500 pa and a stirring rotation speed of 500 rounds min 240 g of dicyclohexylmethane 4 4 dibutylurethane was further added after reacting for 0 5 h dicyclohexylmethane 4 4 diisocyanate hmdi and butanol were collected in the pre about 0 u00b0 c post about u2212 20 u00b0 c collecting devices respectively the reaction was continued for 1 hours at 200 u00b0 c under a degree of vacuum of 6500 pa then the temperature was turned to 240 u00b0 c under the same degree of vacuum for 10 min all of the products raw materials and intermediates in the thermal cracking device were collected into the pre collecting device to obtain a mixture containing bicyclohexylmethane 4 isocyanate 4 butylurethane monoisocyanate dicyclohexylmethane 4 4 dibutylurethane and hmdi the mixing liquid was subjected to chromatography analysis the measured hmdi had a purity of 94 and a hmdi chromatography yield of 92 then the mixing liquid was subjected to rectification the isolated hmdi yield was 88 the residual product after rectification was subjected.