1. Northwest A&F University, Yangling 712100, China
2. Paulownia Research and Development Center, National Forestry and Grassland Administration, Zhengzhou 450003, China
Abstract：Pretreatment is one of the key steps in the efficient conversion of lignocellulose into fuel ethanol. During the pretreatment process, a large amount of barrier components such as lignin and hemicellulose can be removed, which can effectively increase the productive adsorption of the cellulase to cellulose, thereby effectively improving the subsequent enzymatic hydrolysis yield. Paulownia has a large annual output, short growth cycle and high processing waste. It is a potential material for the preparation of bio-energy and other chemicals. In order to achieve high-efficiency conversion of paulownia woody biomass material to bioethanol, and promote efficient enzymatic hydrolysis of paulownia material, the raw material was pretreated to break its original biological resistance, degrade and remove enzymatic hydrolysis barrier components, expose and retain more cellulose components. In this work, Paulownia was used as the experimental material, and the raw material was chemically pretreated with acetic acid and sodium sulfite, analyzing the effect of different treatment methods on the chemical compositions and structural characteristics of samples. The composition analysis showed that the relative content of glucan in the samples increased to different degrees after pretreatment, and the alkaline sodium sulfite synergistic treatment of paulownia increased most obviously. The data showed that the alkaline sodium sulfite synergistic treatment had a good delignification effect and could degrade some xylan component, so the relative content of glucan was significantly increased to 67.48% (the relative content of glucan in the raw material was 46.81%). In addition, the physicochemical structures of all paulownia samples were analyzed by FTIR, XRD and XPS to explore the effects of different pretreatments on the structure of samples. FTIR analysis showed that the characteristic absorption of lignin was significantly weakened by the alkaline sodium sulfite synergistic treatment, and the characteristic absorption of cellulose was enhanced, indicating that the lignin had a certain removal, and the relative content of cellulose had increased; XRD analysis showed that the fiber surface of pretreated Paulownia was destroyed, the amorphous substances such as lignin and hemicellulose were partially removed, and the crystallinity of cellulose increased to varying degrees. Among them, after alkaline sodium sulfite synergistic treatment, the cellulose crystallinity increased significantly to 58.98% (the cellulose crystallinity of the raw material was about 40.23%), the peak position of 002 shifted to the right, the diffraction intensity of diffraction peak increased obviously, the peak shape became higher and the sharpness increased; XPS analysis showed that the surface carbohydrate content increased and the surface lignin content decreased after the alkaline sodium sulfite synergistic treatment. All the structural characterization analysis showed that the alkaline sodium sulfite synergistic treatment had the greatest destructive effect on the structure of Paulownia, the most lignin degradation and the best cellulose retention, which could increase the accessibility of cellulase to cellulose and effectively improve the subsequent cellulase hydrolysis efficiency, and thereby promote the efficient conversion of paulownia raw material to fuel ethanol. The results of structural characterization analysis were consistent with the chemical composition rules.
