Comparative study on two-step concentrated acid hydrolysis for the extraction of sugars from lignocellulosic biomass

•Two-step concentrated acid hydrolysis has been conducted with oak, pine, and EFB.•Oak, pine, and EFB have been characterized in the compositional and XRD analysis.•Crystalline structure change in raw biomass has been clearly shown in XRD analysis.•Optimum condition was selected on the highest sugar recovery in the shortest time.•Pine has the highest recalcitrance based on the CrI and sugar recovery correlation. Among all the feasible thermochemical conversion processes, concentrated acid hydrolysis has been applied to break the crystalline structure of cellulose efficiently and scale up for mass production as lignocellulosic biomass fractionation process. Process conditions are optimized by investigating the effect of decrystallization sulfuric acid concentration (65–80wt%), hydrolysis temperature (80°C and 100°C), hydrolysis reaction time (during two hours), and biomass species (oak wood, pine wood, and empty fruit bunch (EFB) of palm oil) toward sugar recovery. At the optimum process condition, 78–96% sugars out of theoretically extractable sugars have been fractionated by concentrated sulfuric acid hydrolysis of the three different biomass species with 87–90g/L sugar concentration in the hydrolyzate and highest recalcitrance of pine (softwood) was determined by the correlation of crystallinity index and sugar yield considering reaction severity.