Conversion of Cornstalk to Bio-oil in Hot-Compressed
Water: Effects of Ultrasonic Pretreatment on the Yield and Chemical
Composition of Bio-oil, Carbon Balance, and Energy Recovery
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Abstract
An
ultrasonic pretreatment method was developed to enhance the
yield of bio-oil obtained from the liquefaction of cornstalks in hot-compressed
water at different reaction temperatures (260–340 °C)
and residence times (0–40 min). Influences of ultrasonic pretreatment
on the physicochemical properties of cornstalks and bio-oil yields
were investigated. The results show that ultrasonic pretreatment obviously
increases surface areas of cornstalks, decreases crystallinities,
and erodes the structures of lignin, leading to more exposure of cellulose
and hemicellulose. The yield of bio-oil was increased remarkably by
10.1% for 40 min sonicated cornstalks under the optimum liquefied
conditions (300 °C for 0 min of residence time). Carbon balance
indicates that ultrasonic pretreatment increases the carbon conversion
of cornstalks to heavy oil and water-soluble oil. Energy balance indicates
that the sonicated cornstalks have positive energy efficiencies. GC-MS
analyses demonstrate ultrasonic pretreatment increases the contents
of the phenols in heavy oil and water-soluble oil