Study of different ultrasound pretreatment conditions on sugarcane straw and its influence on the enzymatic hydrolysis step for the production of bioethanol

This work aimed to evaluate the best conditions for the ultrasound pretreatment on sugarcane straw, in order to obtain a saccharide material with high performance and low formation of inhibitors, and also to evaluate the effect of pretreatment in the saccharification stage. At the ultrasound pretreatment three different conditions were studied: alkaline (NaOH solution 1 % (w/v)) and acid medium (H₂SO₄ solution 1 % (w/v)), times of 30, 25, 20, 15, 10, 5, 1 minutes, under solid/liquid ratio of 1/10 (w/v) at room temperature. And, as a control samples, reactions also were conducted in a water medium. Regardless of the medium in which the reactions were carried out, the yield was around 87%. It was performed a chemical characterization of samples for quantification of cellulose, hemicellulose and lignin amounts. It was observed that the in an alkaline medium, there was a significant solubilization of lignin (22 %) and hemicellulose (24 %). In acid medium, there was preferential solubilization of hemicellulose, reaching 31% of removal (in 25 minutes of reaction). The samples pretreated in NaOH medium presented the best values of enzymatic conversion of cellulose (about 56 %). It was also performed delignification of pre-treated straw with NaOH solution (1% w/v) by 1 hour at 100°C. The pulp obtained from pretreated straw in alkaline medium presented the higher values of enzymatic conversion (around 88%) and was observed in the samples with the highest values of residual lignin the best results of enzymatic conversion.

[Acknowledgments: FAPESP, CAPES and CNPq, Brazilian agencies]