Catalyst evaluation for renewable fuels production from cocoa bean shell pyrolysis

Growing concerns about Climate Change are driving the exploration of renewable technologies to replace fossil fuels, of which the pyrolysis process emerges as a promising solution. However, the efficiency of this thermochemical process requires enhancement, primarily concerning the quality of its products. To explore into improving this alternative, this study investigates the application of four different catalysts (zeolite HZSM-5, hydrotalcite (HTC), Ni-Re/Nb₂O₅ and Ni/Nb₂O₅) employing analytical pyrolysis of cocoa bean shells under helium atmosphere. The pyrolysis experiments involved three stages assessing the effects of: catalyst type, temperature and catalyst proportion. All four catalysts, evaluated at 550 °C with a catalyst-to-biomass (C:B) proportion of 3:1, displayed the ability to reduce oxygenated compounds when compared to the tests conducted on pure biomass that generated heterogeneous products with a prevalence of oxygenated compounds. However, niobium-based catalysts converted oxygenated into nitrogenated compounds, mainly long-chain nitriles, constituting 24 % with Ni/Nb₂O₅. Further tests with HTC and HZSM-5 at 450, 650, and 750 °C revealed that HTC's results improved at higher temperatures, producing 43 % of hydrocarbons at 750 °C. As the HZSM 5 catalyst proved to be more efficient, achieving values around 70 % of hydrocarbons in the product composition, it was selected for the final stage of experiments, conducted at 550 and 750 °C, with C:B ratios of 1:1 and 5:1. In conclusion, HZSM-5 exhibited satisfactory results for enhancing the pyrolytic products quality while also demonstrating low-temperature efficiency. Best results were achieved at 550 °C, where 90 % of the compounds were hydrocarbons, of which 82 % were aromatic.