Sugar yields from sunflower stalks treated by hydrothermolysis and subsequent enzymatic hydrolysis

To produce fermentable sugar with fewer microbial inhibitors via few processes, batch-type hydrothermal treatments of sunflower stalks were performed, followed by enzymatic hydrolysis of pretreatment slurries with Cellic CTec2 and Cellic HTec2 (9:1, v/v, 0.1 ml/g dry biomass, 8.1 FPU). The yields of hemicellulosic sugars were maximized at the pretreatment condition of 180 °C for 30 min, while the furfural and 5-hydroxymethyl-2-furaldehyde (HMF) concentrations remained low. The glucose yield, however, was only 67.0% of the theoretical glucose yield (TGY). Either the treatment of raw biomass prior to pretreatment or the post-treatment of pretreated residue prior to enzymatic hydrolysis increased the glucose yield as follows: washing the pretreated solid with solvents (90% TGY) > partial removal of liquid fraction from the pretreatment slurry (PS, 83%) > removal of hot-water extractives from the biomass prior to pretreatment (77%) > prewetting of the biomass (70%).