4. CONCLUSIONS
We successfully demonstrated the feasibility of the novel cyclohexene
esterification–hydrogenolysis process for the production of
cyclohexanol, the intermediate for the production ofε -caprolactam. The bench-scale studies verified that cyclohexene
esterification is thermodynamically and kinetically more favorable than
cyclohexene hydration. And the
Cu1Zn1Si2La0.1catalyst afforded high conversion and selectivity in the hydrogenation
of cyclohexyl acetate to cyclohexanol. The cyclohexene
esterification–hydrogenation process was operated smoothly in a long
term on a pilot-scale demonstration unit. Moreover, this process not
only shows high overall atom economy comparable to the cyclohexene
hydration process, but also exhibits much higher catalytic efficiency
than the phenol hydrogenation process. This work elegantly bridges the
gap between the Asahi’s process of benzene partial hydrogenation to
cyclohexene and Thomas and Raja’s process of one-step transformation of
cyclohexanone to ε -caprolactam, thus completing the last
technological puzzle for the development of a next-generation process
for the manufacture of nylon-6 from benzene in a safe, efficient, and
green manner.