Pyrolysis of Canarium schweinfurthii hard-shell: Thermochemical characterisation and pyrolytic kinetics studies

Abstract

Canarium schweinfurthii fruit used in food and cosmetics produces waste nuts with a hard shell (hard-shell) and kernel. The hard-shell contained lignin and holocellulose, besides 51.99 wt% carbon, 6.0 wt% hydrogen, 41.68 wt% oxygen, and 70.97 wt% volatile matter. Therefore, this study commenced thermochemical investigations on the hard-shell through extensive intermediate pyrolysis and kinetic studies. During the active stage of thermogravimetric pyrolysis, the hard-shell lost a maximum of 56.45 wt%, and the activation energies obtained by the Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink methods were 223, 221 and 217 kJ/mol, respectively. The Flynn-Wall-Ozawa method depicted the degradation process accurately, where the Coat-Redfern method's contraction and diffusion mechanisms governed the pyrolysis reactions at activation energies of 16.62 kJ/mol and 38.83 kJ/mol, respectively. The pyrolysis process produced 25 wt% biochar and 25 wt% bio-oil under optimum conditions. The calorific values of the bio-oils with 6.81–7.11 wt% hydrogen and 68.01–71.12 wt% carbon was 26.32–27.83 MJ/kg, with phenolics and n-hexadecanoic and oleic acids as major compounds. Biochar, by contrast, has a high carbon content of 75.11–79.32 wt% and calorific values of 25.45–28.61 MJ/kg. These properties assert the biochar and bio-oils among viable bioenergy sources.