Thermochemical Transformation of Residual Avocado Seeds: Torrefaction and Carbonization

This paper describes the energy valorization of residual avocado seeds through their thermochemical transformation in a rotary reactor. This experimental investigation reports the chemical, physical and fuel properties of the solids and liquids obtained in the temperature range between 150 and 900 degrees C. Optimum torrefaction conditions were obtained at 304 degrees C and yielded a solid product (50 wt%) with 36.7 wt% fixed carbon, 0.47 O/C ratio, and 23.2 MJ/kg of LHV, for an energy yield of 76.7 %. The carbonization at temperatures between 500 and 900 degrees C yielded between 20.0 and 25.1 wt% biochar that exhibited LHV up to 57-66 % higher than the original biomass. The liquid fraction represents 53-56 wt% of the original biomass and contains 70-75 wt% of water. These liquids exhibit limited elemental carbon contents (up to 16 wt%) and higher heating values (up to 3 MJ/kg). The utility of a predictive model has been tested and series of equations have been produced predicting the chemical and energy properties of the solid fraction derived from the torrefaction and carbonization process. Linear correlations were observed between the solid fraction yield and elemental/proximate compositions, and exponential correlations between solid and energy yields.