Screening of acidic and alkaline pretreatments for walnut shell and corn stover biorefining using two way heterogeneity evaluation

This study was aimed at screening acidic (HCl, HNO3, and H2SO4) and alkaline (NaOH, KOH and Ca(OH)2) pretreatments for the biorefining settings (enzymatic hydrolysis and furan production routes) of walnut shell (WS) and corn stover (CS) using two way heterogeneity (biomass vs pretreatment reagents). Both the substrates were pretreated at constant severity level (3% v/v, solid loading 10%, 121 °C, and 60 min). The applied pretreatments were evaluated using three criteria i.e. total reducing sugars, total sugars to inhibitors ratio, and cellulose to lignin ratio (C/L). Out of the six pretreatments, HNO3, NaOH and KOH removed 45–77% lignin from WS and 73–88% from CS. The variable glucose yield was obtained for these reagents: 80, 60 and 54% for pretreated WS, and 82.4, 100 and 100% for pretreated CS. Both HCl and H2SO4 were not found suitable for enzymatic hydrolysis (bioethanol route) rather they preferably converted released sugars into furans (biochemical route). This study implies that two way higher order heterogeneity evaluation is necessary to search for promising biorefining routes and to realize the scale up potential for biorefinery settings.