2-TEMPERATURE DILUTE-ACID PREHYDROLYSIS OF HARDWOOD XYLAN USING A PERCOLATION PROCESS

A novel two-temperature dilute-acid prehydrolysis of hybrid poplar xyl an that exploits the xylan biphasic kinetics at moderate temperatures is described. A lower temperature (140 degrees C) is applied to hydrol yze the easily hydrolyzable xylan, and a higher temperature (170 degre es C) is subsequently applied to hydrolyze the remaining xylan. Using a bench-scale percolation reactor, yields of soluble xylose expressed in monomeric xylose equivalents as high as 92% of theoretical have bee n achieved with only 2% of the xylan being degraded to furfural. The l ignocellulosic substrate produced from the pretreatment is readily con verted to ethanol at a yield of 94% of theoretical via a simultaneous saccharification and fermentation process in 48 h. In terms of both yi eld of xylose equivalents and ethanol production level and rate, these improvements are far superior to those previously reported using a si ngle-temperature dilute-acid pretreatment.