Selection of the best chemical pretreatment for lignocellulosic substrate Prosopis juliflora

Pretreatment is a pre-requisite step in bioethanol production from lignocellulosic biomass required to remove lignin and increase the porosity of the substrate for saccharification. In the present study, chemical pretreatment of Prosopis juliflora was performed using alkali (NaOH, KOH, and NH3), reducing agents (Na2S2O4, Na2SO3) and NaClO2 in different concentration ranges at room temperature (30 ± 2 °C) to remove maximum lignin with minimum sugar loss. Further, biphasic acid hydrolysis of the various pretreated substrates was performed at mild temperatures. Considering the amount of holocellulose hydrolyzed and inhibitors released during hydrolysis, best chemical pretreatment was selected. Among all the chemicals investigated, pretreatment with sodium dithionite at concentration of 2% (w/v) removed maximum lignin (80.46 ± 1.35%) with a minimum sugar loss (2.56 ± 0.021%). Subsequent biphasic acid hydrolysis of the sodium dithionite pretreated substrate hydrolyzed 40.09 ± 1.22% of holocellulose and released minimum amount of phenolics (1.04 ± 0.022 g/L) and furans (0.41 ± 0.012 g/L) in the hydrolysate.