Enhanced thermochemical valorization of coconut husk through carbon dioxide integration: A sustainable approach to agricultural residue utilization

In this study, we aimed to develop a sustainable valorization platform for agricultural residues, mainly focusing on harnessing these residues as a renewable energy source. We conducted a case study involving the pyrolysis of coconut husk to create a sustainable pathway for its valorization. To enhance environmental compatibility, carbon dioxide (CO2) was employed as the reaction medium. CO2 acted as a partial oxidant, leading to the oxidation of carbons in the bio-oil and the formation of carbon monoxide (CO). In detail, this study experimentally proved the mechanistic contribution of CO2 to shifting carbon in pyrogenic oil into gases, particularly CO. To enhance the reactivity of CO2, the catalytic pyrolysis of coconut husk was conducted using a nickel-based egg-shell-type (Ni-ES) catalyst. Catalyst introduction resulted in the increased concentration of syngas compared with conditions without a catalyst in the presence of CO2. In particular, syngas production from catalytic pyrolysis under CO2 conditions was enhanced by >6.5-fold compared with that from single-stage pyrolysis under N2 conditions. Simultaneously, the evolution of pyrogenic oil was significantly reduced under CO2 condition in the presence of the Ni-ES catalyst. This confirms the catalytic potential in further optimizing the valorization of agricultural residues for sustainable energy production.