Microwave-assisted pyrolysis of pine sawdust (Pinus patula) with subsequent bio-oil transesterification for biodiesel production

Abstract

This study aims to thermochemically convert pine sawdust to crude bio-oil via the microwave-assisted pyrolysis technique with subsequent bio-oil transesterification. American Society for Testing and Materials (ASTM) standards were followed in the characterization of the feedstock and pyrolysis products. The thermal degradation behaviour of pine sawdust was studied using thermogravimetric analysis. The components in the bio-oil organic phase were upgraded to fatty acid methyl esters via the transesterification process. The composition of the organic phase and the fatty acid methyl esters was analysed using gas chromatography–mass spectrometry (GC-MS) and Fourier transform infrared (FT-IR). The thermal degradation behaviour of pine sawdust showed three distinct phases of weight loss. These were the drying stage (30–200 °C), the devolatilization stage (200–450 °C), and the char formation stage (>450 °C). The process yielded 42.28 wt.% of bio-oil, constituting 24 and 76 wt.% of the organic and aqueous phases, respectively. GC-MS and FT-IR compositional analysis identified various organic compounds and functional groups, with phenolics contributing a greater percentage. Transesterification improved the bio-oil properties by converting the organic acids and oxygenated compounds to methyl esters with a concentration of 510.05 mg/L. The bio-oil has proven to be a promising sustainable raw material for the production of biofuels and value-added biochemicals.

Keywords:

• Biomass pyrolysis
• biomass characterization
• bio-oil
• transesterification
• biodiesel

Acknowledgements

The authors express their sincere gratitude to the Department of Fuels and Energy and Chinhoyi University of Technology, Vice Chancellors Scholarship of Excellence, for rendering all the indispensable support and funds needed in this work.

CRediT authorship contribution statement

Denzel Christopher Makepa: conceptualization, methodology, investigation, writing – original draft. Chido Hermes Chihobo: conceptualization, validation, resources, supervision, funding acquisition, writing – review and editing. Downmore Musademba: validation, supervision, writing – review and editing.

Disclosure statement

No potential conflict of interest was reported by the authors.