Cold alkaline extraction of Elephant grass for optimal subsequent extraction of hemicelluloses and energy production

Abstract

There is growing scientific and industrial interest in obtaining useful substances by fractionating lignocellulosic biomass from non-food plant crops for use by the bioenergy industry. The primary goals are to ensure process sustainability and to comply with the principles of circular economy. In this work, we optimized energy production from Elephant grass by previously using cold alkaline extraction to remove its hemicellulose fraction. Elephant grass contains a high proportion of lignin (20%) and hemicelluloses (27.4%), and therefore is an excellent alternative to wood materials for energy production by direct burning. Energy production was optimized to identify the best operating conditions among those tested, namely: alkali concentrations of 80–120 g NaOH L–1, temperatures of 20–40 °C, and treatment times of 30–90 min. Using the optimum conditions thus established (viz., 100 g NaOH L–1, 30 °C, and 30 min) raised the high heating value (HHV) to 19.151 MJ kg–1 (i.e., by 4% relative to the starting material). Also, it allowed the content in elemental C to be preserved, that in H increased by 4.86% and, more environmentally significant, most sulphur (46.9%) to be removed from the solid phase upon treatment. Cold alkaline extraction of the raw material additionally enabled relatively selective separation of the hemicellulose fraction from the cellulose and lignin fractions. Thus, 30.1% of all hemicellulose was dissolved in the treatment liquor and made valorizable while 93.0% of cellulose and 82.1% of lignin present in the raw material remained in the solid phase.