Influence of lignin on wood carbonization and charcoal properties of Miombo woodland native species

Abstract

The majority of the Mozambican population use charcoal from natural forests to satisfy their domestic energy needs. Nevertheless, few studies have been done aiming at assessing the quality of wood used for charcoal production and its relationship with the sustainable use of natural forests. Most of the studies on charcoal production and marketing in Mozambique are aimed at understanding its contribution to the well-being of local communities, poverty alleviation and deforestation. Therefore, the objective of this study was to evaluate the qualitative and quantitative effects of lignin on the thermal degradation of wood, gravimetric yield and the quality of charcoal produced from five species of Miombo woodlands in northern Mozambique, namely B. boehmi, B. spciformis, J. globiflora, P. curatellifolia and U. kirkiana. Total lignin, its units syringyl (S), guaiacyl (G) and their ratio (S/G) were determined after thermogravimetric analysis. Gravimetric yields of charcoal, proximate analysis, heating value and apparent relative density were determined after the carbonization of wood samples at a final temperature of 450 °C. The values of G and S units ranged from 0.78 to 0.60 mmol. L−1 and 0.60 to 0.78 mmol. L−1, respectively, while the S/G ratio varied between 0.35 and 1.24. High lignin content and low S/G ratio influenced the thermal stability of wood and increased the charcoal yield, while S units positively influenced the quality of charcoal. J. globiflora and Uapaca kirkiana are the most recommended species for energy production in Mozambique.