Py-GC/MS based analysis of the influence of citric acid leaching of sugarcane residues as a pretreatment to fast pyrolysis

Abstract

Sugarcane trash (SCT) and sugarcane bagasse (SCB) are prospective feedstock materials for fast pyrolysis. However, their relatively high inorganic content, especially alkali and alkaline earth metals (AAEMs), affects the quality of the produced bio-oil. This study evaluates the effect of SCT and SCB leaching by citric acid (CA) on the chemical composition of pyrolysis vapors, viz. by applying micro-pyrolysis (Py-GC/MS). Comparison was made between CA and well-known leaching agents including H2SO4, HCl and water. Accordingly, biomass samples were previously leached at different temperatures and leaching times. The results indicate that leaching with either citric acid or well-known inorganic acids causes the yields of levoglucosan in the pyrolysis vapors to increase by 5–8 fold. The mild structural changes in the lignocellulosic matrix, caused by hydrolysis during leaching, demonstrated to be as important for subsequent thermal degradation behavior (and thus increased anhydrosugars production) as the suppression of the intrinsic catalytic effect of the inorganic constituents by their removal during leaching. CA treatment generally favored the reduction in the total production of ketones and furans independently of leaching conditions (temperature, time). Differences in the range of leaching conditions tested (T = 25–50 °C; t = 1–12 h) had only minor influence on the composition of the pyrolysis vapors derived from CA pretreated sugarcane residues.