Clean Production of Sugars from Brewer’s Spent Grains Using Subcritical Water Hydrolysis and Steam Explosion

Abstract

Brewer’s spent grains (BSG) are a by-product of the beer industry and can be used to produce biofuels. In this case, the objective of this study was to obtain reducing sugars from this biomass by subcritical water hydrolysis in a semi-continuous mode after steam explosion. Temperatures of 120–180 °C, reaction times of 1–5 min, and pressures of 15–25 MPa were used for the steam explosion without CO2. Moistures of 10–50% (w/v), temperatures of 120–180 °C, reaction times of 1–5 min, and pressures of 15–25 MPa were used for the steam explosion with CO2. Subcritical water hydrolysis of solid-exploded material was developed at 210 °C, 15 MPa, a solid/feed ratio of 16 g/g, and a flow rate of 20 mL/min. The characterization of BSG, reducing sugar yields, kinetic profiles, the composition of monosaccharides and furanic moieties, and the characterization of remaining solid by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were performed. For steam explosion with CO2, the significant variables were the temperature and moisture, and the optimized conditions were moisture of 50% (w/v), 120 °C, pretreatment for 1 min, and 15 MPa, with a reducing sugars yield of 18.41 ± 1.02 g/100 g BSG. For steam explosion without CO2, the significant variables were the time and temperature, and the optimized conditions were 120 °C, pretreatment for 1 min, and 15 MPa, with a reducing sugars yield of 17.05 ± 0.48 g/100 g BSG. The process was successful because the steam explosion ruptured the lignocellulosic matrix, and the subsequent process of subcritical water hydrolysis could dissociate the polymers into low-chain saccharides.