Dilute alkali pretreatment and subsequent enzymatic hydrolysis of amur silvergrass for ethanol production

Abstract

A dilute alkali pretreatment (NaOH) was used to remove lignin and some hemicelluloses, as well as to efficiently increase the accessibility of enzymes to the cellulose in Amur silvergrass. A single factor experiment was designed with 4 factors (1 to 5% w/w NaOH, 1/6 to 1/14 solid to liquid ratio, 15 to 90 min residence time, and 80 to 125 °C digestion temperature) with 3 duplicates of 5 levels for each factor. On the basis of the single factor test, an L8 (24)-orthogonal experiment was conducted to identify the main influencing factor and the optimal factor combinations verified by an enzymatic hydrolysis and fermentation experiment. The main factors influencing ethanol production were NaOH concentration and digestion temperature, while residence time and solid to liquid ratio had a lesser effect. The enzymatic hydrolysis rate of cellulose reached 82.6%, and the highest conversion rate of ethanol was 78.3% with 4.0% (w/w) NaOH and a 1:6 solid to liquid ratio at 100 °C for 15 min. Scanning electron microscope (SEM) images of the lignocellulosic surface structure of non-pretreated and optimum pretreated Amur silvergrass displayed obvious differences. The lignin was the key recalcitrance-causing factor for ethanol production, which can be effectively removed by the NaOH.