Comparison of liquid hot water and saturated steam pretreatments to evaluate the enzymatic hydrolysis yield of elephant grass

Elephant grass is a promising lignocellulosic biomass for use in biorefineries due to its composition and productivity. To enhance the use of elephant grass (Pennisetum purpureum Schum.) as a raw material for the production of fermentable sugars, two different hydrothermal pretreatment methodologies were studied, using liquid hot water and saturated steam. Hydrothermal pretreatments were carried out according to a central composite design, varying the time (1-12 min) and temperature (170-220 degrees C) of the processes. Solid fractions were subjected to hydrolysis using the enzymatic complex produced by Pennicilium echinulatum. Both methodologies tested showed a strong positive linear correlation between the severity factor [logRo] of the pretreatments and the removal of hemicellulose, allowing a high recovery of cellulose in the solid fraction. In pretreatments with an intermediate severity factor, between 2.87 and 3.88, the liquid hot water pretreatment improved the enzymatic hydrolysis yield, in addition to presenting the best fractionation of hemicellulose and total glucose yield. However, at pretreatment severity factors equal to or greater than 4.30, saturated steam pretreatment allowed a greater increase in hydrolysis yield. The maximum enzymatic hydrolysis yield was 65.6 mol%, obtained in saturated steam pretreatment at 220 degrees C for 6.5 min, being 147 mol% higher than the yield of untreated elephant grass. Mathematical models describing the enzymatic hydrolysis yield as a function of time and temperature used in each pretreatment methodology are proposed.