Valorization of peanut wastes into a catalyst in production of biodiesel

To offer an innovative way to valorize industrial crop waste into the diverse types of biofuels, the thermochemical process of peanut waste (PW) was investigated. In particular, this study laid a great stress on the use of PW-derived biochar as a cheap catalytic material in the production of biodiesel. Specifically, biochar derived from the pyrolysis of PW was used as a catalytic and porous medium for biodiesel production to enhance reaction kinetics and lower reaction temperature, compared to conventional methods. Two PW-derived biochars produced at 600°C (PWB-600) and 700°C (PWB-700) were effective on the transesterification of soybean oil, showing higher than 95 wt% of biodiesel yield after 1 minute of transesterification reaction at ≥210°C. As a comparison, a commercially used reaction, alkali-catalyzed transesterification, was conducted at 60°C with a KOH catalyst. Biodiesel yield from the alkali-catalyzed reaction was less than 90 wt% even after 6 hours of reaction. Given that the biochar formation process results in the generation of pyrolytic gases and oils, both pyrolysates at different temperatures were also monitored. Pyrolytic gases included syngas and C_1-2 hydrocarbons, whereas pyrolytic oils consisted of phenolic compounds that can be used as intermediates for the synthesis of value-added chemicals. Thus, the results confirmed that the thermochemical upgrading of PW produces value-added industrial chemicals (pyrolytic gases and oils) and biochars that are highly active for the biodiesel production process.