Two-stage dilute-acid pretreatment of softwoods

Whole tree chips obtained from softwood forest thinnings were pretreated vi a single- and two-stage dilute-sulfuric acid pretreatment. Whole-free chips were impregnated with dilute sulfuric acid and steam treated in a 4-L stea m explosion react-or. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at: low severity to maximize hemicellulose recovery. Solub ilized sugars were recovered from the first-stage prehydrolysate by washing with water. Tn the second stage, water-insoluble solids from first-stage p rehydrolysate were impregnated with dilute sulfuric acid, then steam treate d at more severe conditions to hydrolyze a portion of the remaining cellulo se to glucose and to improve the enzyme digestibility. The total sugar yiel ds obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultane ous saccharification and fermentation using an adapted Saccharomyces cerevi siae yeast strain further improved cellulose conversion yield and lowered t he enzyme requirement.