Optimization of soybean hull acid hydrolysis and its characterization as a potential substrate for bioprocessing

Present global soybean production generates about 20 Mt of lignocellulosic by-products that can be converted into bioethanol and other bioprocess molecules. In this work, the chemical composition and the kinetics of diluted acid hydrolysis of soybean hull were investigated. The chemical composition (mass fraction % on a dry basis) of soybean hull showed a content of approximately 40% of cellulose, 26% of xylose, 9% of lignin, and 13% of proteins. Hydrolyses were carried out under different conditions of temperature and acid concentrations following a 22 central composite design (CCD) to evaluate the release of fermentable sugars (glucose, xylose, and arabinose), and toxic compounds (furfural, hydroxymethilfurfural, acetic acid, and soluble lignin). An objective function was defined to estimate the best treatment for high sugar release and low toxic compounds generation. The kinetics of hydrolyses showed that the best condition for recovering sugars were 153 °C and mass fraction of 1.7% H2SO4 for 60 min with a hydrolysis efficiency of 87%. The objective function, considering a non-inhibiting concentration of toxic compounds (<4 g dm−3), was 118 °C and 2.7% H2SO4 (mass fraction) for 40 min with 59% of hydrolysis efficiency concerning the total sugar content of soybean hulls.