Enhancing sugar recovery from sugarcane bagasse by kinetic analysis of a two-step dilute acid pretreatment process

Maximising sugar recovery from pretreatment and enzymatic hydrolysis is a determining factor in the economic viability of bio-refineries using lignocellulose as feedstock. Single-step dilute acid treatment of sugarcane bagasse was investigated at times and temperatures ranging between 12 and 22 min and 422-442 K, respectively. Maximum sugar recovery equalled 78% of the mass fraction polysaccharides (recovered as hydrolysis products xylose and glucose) present in sugarcane bagasse. Preferred operating conditions, as determined by response surface methodology (RSM), included an acid (H2SO4) concentration range of 45-55 mmol.L−1, a time of 14.0 min and temperature of 442 K. Complete recovery of both xylose and glucose could not be achieved through the combination of single-step dilute acid treatment and enzymatic hydrolysis. Whereas a short pretreatment time and low pretreatment temperature process was required for maximum xylose recovery, opposing operating conditions had to be applied to maximise glucose recovery. In order to circumvent some of the limitations associated with the single-step process, the use of a two-step process was tested through RSM simulations. A 4.8% increase in the total sugar recovery yield and a 36.1% reduction in furfural production were calculated for the two - in lieu of the one-stage method. The improvement was attributed to the avoidance of xylose degradation reactions but also the production of low enzymatically-digestible solids.