Effect of Alkaline Black Liquor Recycling on Alkali Combined with Ozone Pretreatment of Corn Stalk

In the early stage, the best conditions for alkali-bound ozone pretreatment were studied. But after treatment, the alkaline black liquor was directly discarded due to the large amount of organic matter, resulting in environmental pollution and waste of resources. In this paper, the alkaline black liquor was recycled under the optimal pretreatment conditions. The results showed that the number of alkaline black liquor cycles had little effect on hemicellulose content, and had a great influence on cellulose content and lignin content. Through structural characterization of corn stover, it was found that the pretreatment caused structural changes of lignin in straw. However, when the alkaline black liquor was recycled for the fourth time, the ether bond in the side chain of lignin and the covalent bond between the components were not sufficiently destroyed, and the damage to the phenolic hydroxyl group was also weakened. It was indicated that when the alkaline black liquor was recycled for the fourth time, the destruction effect of the alkaline black liquor on the straw was significantly inhibited. Therefore, the optimal circulation time of alkaline black liquor was three times, and the cellulolytic conversion rate was 81.53%.