High-grade bio-oil produced from coconut shell: A comparative study of microwave reactor and core-shell catalyst

The quality of bio-oil can be improved by conducting biomass pyrolysis either over a core-shell hierarchical zeolite catalyst or in a microwave reactor. However, there is a lack of comparative studies on the individual effects of each factor (e.g., catalysts, reactors) on bio-oil production. In this regard, the catalytic pyrolysis of coconut shell in a fixed-bed reactor and in a microwave reactor using the conventional ZSM-5 and core-shell hierarchical ZSM-5@SBA-15 catalysts was evaluated. With an emphasize on the production of hydrocarbons and phenols, the comparative effect of the core-shell catalyst and microwave reactor was demonstrated. The core-shell catalyst had the dual effect of regulating the bio-oil yield and composition. Compared to conventional ZSM-5 (25) with a SiO₂/Al₂O₃ ratio of 25, the core-shell ZSM-5 (25)@SBA-15 not only increased the bio-oil yield by at least 40%, but also approximately doubled the production of hydrocarbons, irrespective of the reactor type. In contrast, the microwave reactor played a greater role in regulating the bio-oil composition. Irrespective of the catalyst used, the fixed-bed reactor tended to generate phenolic-rich bio-oil, while the microwave reactor sharply reduced the phenol selectivity by at least doubling that for aromatics.