Biochar as a catalyst in the production of syngas and biodiesel from peanut waste

Energy harvesting from agricultural waste provides an opportunity for simultaneous production of renewable energy and mitigation of fossil fuel consumption. When the agricultural waste is also used as a catalyst to promote energy production, the process can be more beneficial environmentally and economically. In this study, an integrated upgrading process of peanut waste was introduced for the production of syngas/biochar and biodiesel through pyrolysis and transesterification, respectively. In addition, solid residue from pyrolysis (ie, biochar) was then used as a catalyst to improve syngas and biodiesel formations. Lipid fraction in peanut waste was extracted, and the residual solid was converted into pyrolysis products. When peanut waste biochar (produced at 700°C) was used as a catalyst, syngas production was doubled due to the catalytic capability of alkaline materials in biochar (K, Mg, and Ca). Alkaline contents and porosity of biochars also promoted the thermally-induced transesterification reaction. Thermally-induced transesterification using SiO₂ showed 94.3% biodiesel yield at 365°C for 1 minute of reaction. However, the reaction with peanut waste biochars (produced at 600 and 700°C) achieved 95.2% and 96.6% biodiesel yield at 300°C. Thermally-induced transesterification had much faster reaction kinetics than homogeneous reaction with KOH catalyst (67.8% biodiesel yield at 60°C for 6 hours). All experimental results confirmed that peanut waste is a useful waste material to produce biofuels (biodiesel/syngas) and catalyst (biochar).