Thermochemical valorization of pesticide-contaminated cocoa bean shells: Enhancing sustainable energy recovery and minimizing toxic byproducts

The intensive use of pesticides in large-scale farming (plantations) has led to the accumulation of pesticidecontaminated byproducts (waste), hindering their valorization. In particular, the enormous generation of cocoa bean shells (CBSs) contaminated with pesticides has resulted in significant environmental issues, such as the leaching of agrochemicals into land and water. This study proposed a thermochemical process for energy recovery while decomposing toxic chemicals from plantation waste (CBS). To this end, carbon dioxide (CO2) was employed as a partial oxidative reagent. CO2 reacted with volatile matter thermally evolved from CBSs, resulting in an enhanced formation of carbon monoxide (CO) with a decrease in pyrogenic oil production. Considering that the pyrogenic oil contained toxic chemicals such as polyaromatic hydrocarbons (PAHs), CO2-assisted pyrolysis promoted the rearrangement of carbon in the CBSs toward CO instead of oil, thereby mitigating environmental risks. To facilitate the reaction kinetics, CO2 and Ni-based catalysts were used for catalytic pyrolysis. This test configuration notably increased syngas production, with the syngas yield in CO2 reaching 15.93 mmol g-1, a 50 % increase compared to that under N2 conditions. Pesticides in the CBSs were completely decomposed during catalytic pyrolysis, confirming the feasibility of biochar applications with minimal environmental risk. CBSs biochar produced under CO2 conditions had enhanced physicochemical properties (surface area, porosity, and cation exchange capacity (CEC)) compared to biochar produced under N2 conditions. In addition, water retention and nutrition availability were also improved in CBSs biochar produced under CO2 conditions, reinforcing its practical use in diverse environmental applications. Our approach contributes to the development of sustainable plantation systems.