(195f) Enhancement of Aromatic Production From Bioethanol Dehydration Using Dual-Bed Catalytic Systems

Aromatics are not only produced from conventional petroleum-based feedstocks, but they can be also converted from bioethanol via the catalytic dehydration, which is an alternative process that has gained high attention from petrochemical industries. Modified HZSM-5 catalysts were proven to be effective catalysts for the direct conversion of ethanol to aromatics. Since ethylene is an intermediate for aromatic formation via ethanol dehydration, the aromatic production was expected to be improved by using a dual-bed catalytic system, which ethylene is produced in the first bed and aromatics are formed from ethylene aromatization in the second consecutive bed. The objective of this work was to compare the activity of single-bed catalytic systems (using Ga₂O₃/HZSM-5 or ZnO/HZSM-5) with that of dual-bed systems (using MgHPO₄/Al₂O₃ as the ethylene-producing catalyst coupled with one of the modified HZSM-5 as aromatization catalysts). The HZSM-5 and Ga₂O₃- and ZnO-doped HZSM-5 were individually tested in the single-bed system for their activity on aromatic production under the temperature of 500 °C. For the dual-bed systems, the first catalytic bed contained 0.5 wt% MgHPO₄/Al₂O₃, which was fixed for all experiments, whereas the second bed contained either Ga₂O₃/HZSM-5 or ZnO/HZSM-5. The temperatures of the 1^st and 2^nd beds were separately controlled at 370 °C and 500 °C, respectively. The results revealed that the ethanol conversion range of 83 – 85 % was observed from all cases for both systems. The aromatic yields gained from the single-bed systems were found increasing in the order: HZSM-5 (9.1 %) < ZnO/HZSM-5 (12.7 %) < Ga2O3/HZSM-5 (16.8 %). Using the dual-bed systems, the aromatic yield was increased by 70.3 % and 31.5% with using the HZSM-5 and Ga₂O₃/HZSM-5 as the second-bed catalysts, respectively. In contrast, the aromatic yield obtained from using ZnO/HZSM-5 in the second bed was slightly decreased by 3.1 %. In conclusion, the aromatic yield can be significantly enhanced by using the dual-bed system of MgHPO₄/Al₂O₃ coupled with a catalyst that has high ethylene aromatization activity.