An Overview of Studies on Pilot Scale: Lignocellulosic Biomass Pretreatment Processes Used in the Production of Second Generation Bioethanol

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source for the fossil fuel. There are three main unit operations involved in the entire bioethanol production: pretreatment for conversion of xylan to soluble xylose, enzymatic hydrolysis of pretreated biomass to produce glucose, and fermentation of the mixed sugars to ethanol. Recent investigations show that cellulosic ethanol process can be competitive with the conventional and well established corn to ethanol process. The present review provides an overview of different physico-chemical pretreatments, with special emphasis on the more industrially scalable dilute acid and steam pretreatment methods. Different pilot scale pretreatments at high solids content are also being reported with various feedstocks and their impact on the formation of reducing sugars. Dilute mixed acid strategy has shown the synergistic effects of single acids mixed together, which improves the formation of reducing sugars (glucose and xylose) with low inhibitor concentrations at an optimum cost. A graphical presentation of the generalized process is produced below: [GRAPHICS] .