Omer Ozyurek and Adriaan van Heiningen
University of Maine, Chemical & Biological Engineering 5737, Jenness Hall, USA
Wheat straw is the second largest agricultural residue in the world. Presently much of the wheat straw with low-no economic value is burnt or left in the field after harvest. Similar to other lignocellulosic biomass, wheat straw consists of cellulose (33-40% w/w), hemicelluloses (20-25% w/w) and lignin (15-20%% w/w) and a small amount of extractives and mostly silica-containing ash (3-7% w/w). With a significant carbohydrate content of about 65% w/w, wheat straw is a potential cheap and abundant feedstock for production of fermentable sugars for bioethanol production. However a cost efficient pretreatment technology and low enzymatic charge is required for competitive sugar production at industrial scale. Autohydrolysis would be a good pretreatment process because only water/steam is needed. Unfortunately the presence of "sticky lignin" precipitates in the hydrolysate leads to severe plugging in the hydrolysis reactor and downstream equipment in a continuous process. Earlier we found that the presence of formic acid (FA) at a low concentration (5-20 g/L) during hot water (160 °C) treatment of hardwood chips significantly reduced the amount of lignin precipitates in the pre-hydrolysate. In addition, the FA reinforced hydrolysate contained much more monomeric hemicellulose sugars than that without FA supplementation. In this study we will quantify the effect of low FA concentrations during pretreatment of wheat straw on hemicellulose dissolution and lignin precipitate formation, followed by the effect of FA-reinforced pretreatment and refining of the pretreated straw on enzymatic hydrolysis to produce fermentable sugars.
Keywords: Autohydrolysis, bioethanol, enzymatic hydrolysis, formic acid, lignin precipitates, pretreatment, refining, wheat straw.