Study of process configuration and catalyst concentration in integrated alkaline extrusion of barley straw for bioethanol production

Barley straw was pretreated with alkali (NaOH) at increasing NaOH/DM ratios (6–10%) and neutralized in a twin-screw extruder, obtaining a substrate ready for the incubation with enzymes. Two process configurations were evaluated: with and without filtration inside the extruder. The enzymatic digestibility of the pretreated substrates was evaluated and filtration was proved to be beneficial for the enzymatic hydrolysis. A maximum enzymatic hydrolysis yield of 71% was attained for the barley straw pretreated with 8 g NaOH/100 g dry barley straw and filtration inside the extruder. The ethanol production was evaluated on this substrate for increasing solid loadings, 2.5, 15 and 20% (w/v). A global process yield based on ethanol production, including hydrolysis and fermentation, was calculated over the pretreated material in experiments at 20% (w/v) solids, reaching 53% of the maximum theoretical. The concentration of ethanol reached up to 29 g/l in these conditions.