A comparison of aqueous and dilute-acid single-temperature pretreatment ofyellow poplar sawdust

Pretreatment of fresh yellow poplar sawdust (< 6 mm, 25-30 wt % moisture) w ith hot: liquid water (190-220 degreesC, 2.0-7.5 min, 2-7 wt % solids loadi ng) or steam (220 degreesC, 2.0 min) was compared with dilute acid pretreat ment (0.8% w/v sulfuric acid, 175 degreesC, 10 min, 20-25 wt % solids loadi ng). The most favorable conditions for hot liquid water pretreatment (220 d egreesC, 2.0 min, 5 wt % solids loading) performed as well as the dilute ac id pretreatment (175 degreesC, 10.0 min, 0.8% sulfuric acid, 20 wt % solids loading) for fermentation of the cellulosic fraction of the pretreated fib ers by simultaneous saccharification and fermentation (SSF), using Saccharo myces cerevisiae and 25 IFPU cellulase/g of cellulose. Ethanol yields of 97 and 92 wt % of the theoretical yield and xylan recoveries of 85 and 70 wt % (92 and 96 wt % solubilization) were achieved with the hot liquid water a nd dilute acid pretreatments, respectively. Steam pretreatment (220 degrees C, 2 min) was not as effective as the dilute acid pretreatment, resulting i n an ethanol yield of 70 wt % of the theoretical yield, with 88 wt % xylan recovery (54 wt % solubilization). A positive correlation was found between xylan removal and the ethanol yield obtained by SSF. Xylan recovery, howev er, was inversely proportional to xylan solubilization. Removal of up to 57 wt % of the acid-insoluble lignin in yellow poplar was also possible with hot liquid water pretreatment, with 75 wt % of this acid-insoluble lignin r ecoverable by simple filtration of the liquid pretreatment products.