Design of hydrothermal and subsequent lime pretreatment for fermentable sugar and bioethanol production from acacia wood

Abstract

In this study, lime (calcium hydroxide) treatment (LT) was applied as an alkaline pretreatment subsequent to hydrothermal treatment (HT) in terms of fermentable sugar and bioethanol production from acacia wood. To maximize the hydrolysis of cellulose and hemicellulose, the condition of 200 °C for 10 min of HT was selected for subsequent lime treatment. The optimum conditions of LT were established to be a ratio of calcium hydroxide to hydrothermally treated acacia biomass of 12.2%, temperature of 70.9 °C, and reaction time of 23.5 h using a response surface methodology, and the maximum glucose yield by prediction and experiment were determined to be 74.4% and 73.5%, respectively. Further mechanical refining accelerated the access of the enzyme to glucan, resulting in an increase in glucose conversion (80.5%). Although the glucose yield by LT was 21.5% higher than that of HT, the ethanol yield was 33.5% lower due to the negative effect of residual calcium ions on yeast fermentation.