Primary Constitution and Proximal Analysis of Three Fabaceae by the Thermogravimetric and Chemical Methods for Their Potential Use as Bioenergy

The standard methods for determining the basic chemical composition of wood are well-established, but include processes that demand a great deal of time and diverse chemical reagents. TGA and DTG analyses, in contrast, offer precise results in less time. This study was designed to identify the primary components and results of the proximal analysis of wood from three species –Acacia farnesiana, A. pennatula and Albizia plurijuga—using TGA with deconvolution of the DTG curve and a chemical method. Higher heating value (HHV) was determined using a bomb calorimeter and mathematical models. Elemental organic and inorganic analyses were conducted. No statistically significant differences appeared in the results of the TGA-DTG and chemical methods for the wood in terms of cellulose, lignin, and volatile material content. Results were especially accurate in the samples of A. pennatula and A. plurijuga for hemicelluloses, extractives, and moisture. Regarding HHV, the wood of A. plurijuga showed no statistically significant differences between the bomb calorimeter test, calculations as a function of chemical composition, or the proximal analysis. Elemental organic results were C = 43.76–46.65%; H = 6.70–6.95%; O = 46.06–48.95%; N = 0.21–0.42%; and S = 0.06–0.11%. For the inorganic fraction we identified 18 elements in the ash. We conclude that the TGA-DTG method made it possible to obtain results in a short time with no need for the numerous reagents that chemical processes require. Findings suggest that in the absence of a bomb calorimeter, the best model for calculating HHV is proximal analysis.