3.3 Pilot-scale cyclohexene esterification–hydrogenation
Taking into account of the reaction characteristics of cyclohexene esterification, we transferred this reaction onto a reactive distillation reactor, which is capable of breaking through the thermodynamic limitation imposed on the conversion while retaining the high reaction rate for the exothermic reaction.36 On conventional slurry-phase reactor or fixed-bed reactor, the intrinsic conflict between the conversion and reaction rate in cyclohexene esterification cannot be disentangled. On the basis of the above experimental thermodynamic and kinetic data and Aspen Plus simulations, a reactive distillation reactor was built for cyclohexene esterification, on which the operation parameters were further experimentally optimized, which are out of the scope of the present work. The optimized operation parameters for the reactive distillation reactor are presented in Table S5. And the corresponding temperature and composition profiles in the reactive distillation reactor are illustrated in Figure S3. Then, we established a pilot-scale demonstration unit with a capacity of 8000 t/a using the reactive distillation reactor for cyclohexene esterification in conjugation with a fixed-bed reactor for ester hydrogenation at Baling Petrochemical Company, SINOPEC (Figure S4). On the reactive distillation reactor, the cyclohexene conversion is further improved to >99.2% with high selectivity to cyclohexyl acetate of ~99.0% (Figure 6A). Moreover, the reaction proceeds smoothly for more than 1000 h on stream with no indication of deactivation.
The cyclohexyl acetate produced from the reactive distillation reactor was directly fed into the successive fixed-bed reactor for hydrogenation. Figure 6B shows that the conversion of cyclohexyl acetate is always close to 100%, and the cyclohexanol selectivity is always >99% during more than 1000 h on stream, giving rise to the conversion of 99.8% and the selectivity of 99.4% on average. In addition, the ethanol selectivity is 99.5% on average during the whole reaction span.