Highly Efficient Conversion of Cellulose to Bio-Oil in Hot-Compressed Water with Ultrasonic Pretreatment

Ultrasonic pretreatment was developed to increase conversion of cellulose to bio-oil in hot-compressed water. The physical structures of cellulose were greatly changed by ultrasonic pretreatment, resulting in excellent swelling and dispersion of cellulose in the water. With the increased surface area and decreased crystallinity and degree of polymerization of cellulose, the bio-oil yield was increased remarkably. The highest bio-oil yield (61.5%) was obtained at 260 degrees C with a residence time of 0 min for the 1 h pretreated cellulose. Under the optimum reaction conditions, ultrasonic pretreatment increased the bio-oil yield by 22.1% and reduced residence time by 5 min. GC-MS analysis results showed that ultrasonic pretreatment affected the chemical compositions of bio-oils and significantly improved the content of 5-hydroxymethylfurfural in heavy oils.