Comparison of alkaline and acid-catalyzed steam pretreatments for ethanol production from tobacco stalk

In this study, tobacco stalk (TS), the solid residue from tobacco industry, was utilized as the raw material for the production of bioethanol through combining processes of alkaline pretreatment or acid-catalyzed (AC) steam pretreatment followed by enzymatic hydrolysis and fermentation. The results indicate that both the two pretreatment strategies could efficiently improve the enzymatic digestibility of TS. Compared to alkaline pretreatment, AC steam pretreatment solubilized more xylan into the liquid phase while preserving more lignin in the pretreated solid substrate. Following enzymatic saccharification of whole pretreated materials from two pretreatment methods at a modest enzyme loading of 15 mg protein/g glucan, the slurry from alkaline pretreatment achieved a slightly higher total monomeric sugar yields than that of AC steam pretreatment. The sugars in the obtained enzymatic hydrolysates from both the two pretreatment technologies showed good sugar-to-ethanol conversion during fermentation with Saccharomyces cerevisiae Lg8-1 strain. The overall mass balances showed that yields of ethanol were 2.75 and 2.69 kg per 10 kg of untreated TS for alkaline and AC steam pretreatments, respectively.