Study of Ultrasonic-assisted Alkali Pretreatment on Cotton Stalk

Suitable pretreatment is essential for increasing the utilization rate of cotton stalk in ethanol production. Ultrasonic wave was used together during the pretreatment of cotton stalk using alkali solution and the conditions were optimized. The single-factor design and the Box-Behnken design were used to arrange the experiments and analyze the obtained data. Regression models were established to express the influences of treating time, sodium hydroxide concentration, and liquid to solid ratio on the contents of cellulose and lignin in the treated cotton stalk. The obtained models were significant in the tests, indicating its capability in predicting results. The tested factors showed influence on the contents of cellulose and lignin in the treated stalks following the order of treating timesodium hydroxide concentrationliquid to solid ratio. The optimum conditions for the highest cellulose content and the lowest lignin content were obtained at ultrasonic power 420 W, sodium hydroxide 3.5%, processing time 90 min, and liquid to solid ratio 21:1. The resulted cellulose content in the treated cotton stalk under the optimum conditions was 58.02% , being 45.60% higher than the original value. Images of Scanning Electronic Microscopy showed that most hemicellulose and part of lignin were dissolved out of the stalk during the pretreatment and thus the crystalline structure was efficiently broken. Overall, application of ultrasonic wave showed remarkable effect on the alkali pretreatment of cotton stalk.