Bioethanol and succinic acid co-production from imidazole-pretreated soybean hulls

Abstract

The soybean is an important crop in the world, where soybean hull (SH) comprehends 8–10 % of grain dry matter. SH is rich in carbohydrates, mainly in holocellulose fibers, showing to be a promising bio-based material to generate new bio-products. Imidazole is a promissing solvent for pretreatment of lignocellulosic biomass due its delignificant and depolymerizing power. Besides, this reagent presents low to moderate toxicity against many classes of living organisms. Thus, the thermochemical conversion of SH into fermentable sugars using imidazole was carried out at 120 °C for 1 h. The objective of this work was to use a more sustainable pretreatment reagent for the co-production of second-generation bioethanol and succinic acid from soybean hull. After pretreatment, the solid yield was 57.1 wt.%, consisting principally of cellulose. The cellulose-rich fraction was further hydrolyzed using commercial enzymes and achieving 89.9 wt.% and 95.6 wt.% of glucose and xylose yields, respectively. The hydrolysate was fermented using two yeasts: Saccharomyces cerevisiae and Pichia stipitis. Approximately, from 1 ton of SH, it was estimated that 124.0 kg of bioethanol and 36.5 kg of succinic acid could be obtained using S. cerevisiae, while P. stipitis could achieve productions of 116.2 kg of bioethanol and 20.4 kg of the organic acid. This study demonstrated the co-production of biomolecules of industrial interests, carrying out a more environmentally friendly pretreatment process.