The utility of selected kraft hardwood and softwood pulps for fuel ethanol production

Abstract Seven kraft hardwood (two poplar species, aspen, beech, and birch) and softwood (pine, bleached and unbleached) pulps were converted to ethanol to evaluate the effect of botanical origin and residual lignin content in a cellulosic pulp on ethanol yield and raw spirit composition. Successive steps of this process, such as (I) kraft pulping (by the sulfate method), (II) enzymatic saccharification, (III) alcohol fermentation and (IV) alcohol distillation were performed using a modified 15 l reactor. The highest ethanol yield was obtained from the bleached pine pulp (nearly 0.46 g/g d.w. pulp, 0.20 g/g d.w. wood) while only 0.04 g ethanol/g d.w. pulp was obtained from the unbleached pine pulp (only around 0.02 g/g d.w. wood). Ethanol yields from the hardwood pulps were around 0.24–0.26 g/g d.w. pulp that corresponded to 0.11–0.14 g/ g d.w. wood. The modified bioreactor equipped with an attachment enabling distillation of ethanol from the fermentation broth, may be used for production of fuel ethanol from superfluous and/or low quality woodchips and cellulosic pulps that cannot be used for paper production.