Poplar woodchip as a biorefinery feedstock-prehydrolysis with formic/acetic acid/water system, xylitol production from hydrolysate and kraft pulping of residual woodchips

Formic acid/acetic acid/water mixture used as solvent for acid hydrolysis or pre-hydrolysis of poplar woodchips yields the highest yield of xylose (69.89%) at 105 °C, with a liquor-to-solid ratio of 12:1 (mL/g) for 90 min. The hydrolysate was obtained after recovering formic and acetic acids. Concentrated and neutralized hydrolysate was fermented with Candida tropicalis to produce xylitol. Immobilization of Candida tropicalis was found to enhance the fermentation efficiency. Optimized conditions for preparation and fermentation with Ca-alginate-chitosan beads immobilized Candida tropicalis were determined. The highest yield of xylitol was 40.2%, obtained under the following fermentation conditions: a rotation speed of 120 rpm, 6 ml of nitrogen source, an initial pH of 6.0, and a volume ratio of 1:4. Hydrolytic residual woodchips were used to produce kraft pulp. Although lower lignin content was found in the residual woodchips, higher chemical charges were needed compared to the untreated woodchips. Lower pulp yield was obtained and the quality of pulps generated at similar pulping conditions was found to be significantly different from the pulps produced from untreated woodchips. The organic solvent treated poplar woodchips could be pulped, however; optimizing the Kraft pulping process is expected. Alternative use of the fibers is to be expected.