Heat-pump-assisted reactive distillation for direct hydration of cyclohexene to cyclohexanol: a sustainable alternative

As an important raw material to produce many useful chemicals, cyclohexanol production attracts much attention to obtain high purity product, leading to high energy consumption. Traditional technologies include three routes: oxidation of cyclohexane, hydrogenation of phenol and direct hydration of cyclohexene. Without the risk of explosion and having a low price of raw material, the direct hydration of the cyclohexene route is selected in this paper. Four processes with different phase-refluxed or with/without a stripper configuration for the direct hydration of cyclohexene are investigated, including aqueous-phase-refluxed conventional reactive distillation (ACRD), an organic-phase-refluxed conventional reactive distillation (OCRD), an aqueous-phase-refluxed reactive distillation with a stripper (ARDS), and an Organic-phase-refluxed reactive distillation with a stripper (ORDS). The results show that the conventional reactive distillation (ACRD and OCRD) has a relatively low capital cost but has high operating costs due to high energy consumption, while the ARDS and ORDS show better performance than the OCRD and ACRD, but still have considerably high energy consumption. The ORDS shows better performance due to a slightly higher conversion of cyclohexene to cyclohexanol and the potential to achieve the better performance in terms of energy and economic considerations. Integration of a novel confirmation with heat pump assisted reactive distillation (HPRD) is investigated to further improve the energy efficiency and thereby reduce CO2 emission. The results show that the HPRD process realizes a significant energy saving of 58% and achieves 62% and 24% reductions in specific CO2 emission and total annualized cost, respectively, compared to ORDS, demonstrating high feasibility and environmental sustainability.