FRACTIONATION OF WHEAT-STRAW BY STEAM-EXPLOSION PRETREATMENT AND ALKALI DELIGNIFICATION - CELLULOSE PULP AND BY-PRODUCTS FROM HEMICELLULOSEAND LIGNIN

The fractionation of wheat straw was studied using a two-stage process based on an hydrolytic pretreatment followed by alkali delignificatio n. The hydrolytic pretreatment was performed by steam explosion. Straw was steamed at temperatures comprised between 205 and 230 degrees C f or 2 min. The steamed straw was washed with hot water to yield a solut ion rich in hemicellulose-derived mono- and oligosaccharides. The wash ed fiber was delignified by alkali at 160 degrees C for 60 min using a NaOH load of 20%. The alkali-soluble lignin was recovered by filtrati on after acidification of the black liquor. The delignified pulp was s creened and bleached to produce viscose-grade cellulose. The optimizat ion of the pretreatment conditions led to the following results at a p retreatment severity of log(R-0) = 3.80: yield of viscose-grade cellul ose = 70% of the potential; lignin recovery = 70% of the Klason lignin present in the untreated straw; hemicellulose sugars = 55% of the pot ential, recovered as molasses.