Effect of Low Temperatures and Residence Times of Pretreatment on Glucan Reactivity of Sodium Hydroxide-Pretreated Rice Straw

Abstract

Alkaline pretreatment of lignocellulosic biomass is an approach to enhance the susceptibility of the biomass that is subsequently converted into fermentable sugars. The efficacy of the sodium hydroxide pretreatment of rice straw RD41 was evaluated in terms of total solid removal, lignin removal, glucan recovery, and glucan conversion yields. The pretreatment conditions were 50, 60, 70, 80, and 100 °C, and each temperature kept for 1 to 5 h. The effect of pretreatment temperatures was more pronounced than that of the pretreatment times. The elevated temperatures caused higher total solid removal and lignin removal. The highest total solid removal (52.5 to 55.8 %) was found in the pretreatment at 100 °C. At this temperature, the highest lignin removal (~87 %) could be obtained regardless of the residence times of the pretreatment. Most of the glucan (~80 to 100 %) was preserved in the pretreated rice straw. Lower temperatures (50 and 60 °C) favored higher glucan preservation (> 90 %) in the pretreated solids. Glucan conversion of the 3 h pretreatment time samples of each pretreatment temperature revealed that more than 80 % of glucan conversion could be accounted for in samples pretreated at 70 to 100 °C within 24 h of saccharification. The lower temperatures required a prolonged pretreatment time to reach a higher glucan conversion (~90 %), as found in the 50 °C, 5 h pretreated rice straw. The optimal conditions of this simple method are economically feasible, and can be applied to testing the reactivity of herbaceous lignocellulose in future research.