Study of light, middle and severe torrefaction and effects of extractives and chemical compositions on torrefaction process by thermogravimetric analysis in five fast-growing plantations of Costa Rica

Light (Tlight), middle (Tmiddle) and severe (Tsevere) torrefaction processes by TGA in woody biomass were evaluated in relation to devolatilization rate (Drate), maximum devolatilization rate (DRmax), temperature at the level of 50% weight loss (T50), rate of weight loss at T50 (R50) and weight loss during torrefaction (Wloss-DT). The relationship between these parameters with cellulose, lignin and extractives content was established. The TGA and devolatilization curves showed that DRmax was of 4.16, 1.80 and 0.70%/min for Tlight, Tmiddle and Tsevere respectively. Wloss-DT in Tlight ranges between 3 and 6%, between 9 and 14% in Tmiddle and from 11 to 16% in Tsevere. G. arborea showed the highest Wloss-DT, with 29.10% for Tsevere and C. Lusitania and T. grandis the lowest Wloss-DT, with 15% for Tsevere. The duration of Dmax was of 5 min in Tlight and Tmiddle and 6 min in Tsevere. Cellulose, lignin and carbon presented statistically significant correlations with R50, T50, Wloss-DT and DRmax. Ash content was correlated with Wloss-DT and DRmax in all torrefaction condition. Extractives in dichloromethane was significantly in many parameters. We conclude that the torrefaction of different woody species can be optimized as biomass feedstocks with a specific temperature and time of torrefaction.