Decomposition Mechanism In Formic Acid Of Wheat Straw Lignin-Carbohydrate Complex

In order to remove lignin completely, we need to understand the changes in the strcture of Lignin-Carbohydrate Complex during the process of pulp. In this paper, LCC of wheat straw was decomposed with formic acid and the new forms LCC were produced between wheat lignin and carbohydrate for the first time. The fomic acid treated LCC were analyzed by elementary analysis, 1H-NMR, 13C-NMR, FTIR, GC and GC-MS and were compared with Lignin-Carbohydrate Complex.The results were as follows:1. In wheat straw LCC, lignin was mainly combinated with xylose and glucose. After formic acid, glucose was comparatively stable.2. The characteristics of lignin, cellulose and hemicellulose are existed in LCC of wheat straw. Through acid treatment, the carbohydrates in LCC were degradated and the lignin content was increased.3. After formic acid processing, the aromatic series was obviously increased, and fatty group was reduced, which showed the content of lignin was increased. The lignin in LCC, which was combined with carbohydrate by ester linkage, as well as a part ofβ-O-4 structures, were quite stable in formic acid.4. The ratio between G and S unit was 38.30% to 20.82% in the acid dissolved product. In the degradated product, vanilla aldehyde and vanilla acid were existed. The lignin on the side chain position were oxidated to cause linkage broken and new hydroxyl and carbonyl increased.5. The new phenol ether bonds were produced between the xylose and lignin, and benzonitrile ether bonds were probably formed, when MWL and xylose were treated with formic acid.In this paper, it is discovered the wheat straw LCC was unstable in formic acid, and confirmed the new linkage was produced between the lignin and the carbohydrate. It is significant to optimize the pulping process, remove lignin and improve product quality.