Mechanism Studies On The Wheat Straw Lignin Acidolyzed With Formic Acid

In this paper, the MWL of wheat straw was acidolyzed with formic acid and hydrogen peroxide. The acidolysis products were analyzed by elementary analysis, 1H-NMR, IR, GPC and GC-MS and were compared with MWL. The results were as follows:1. The C₉ unit empirical formula of MWL was: C₉H_8.35O_3.61(OCH₃)_1.342, with 0.35 Ph-OH and 1.342 methoxyl group in each C₉ unit. The C₉ unit empirical formula of the product of F was: C₉H_6.72O_3.07(OCH₃)1.52, with 0.43 Ph-OH and 1.52 methoxyl group in each C₉ unit. The C₉ unit empirical formula of the product of FP was: C₉H_7.96O_3.86(OCH₃)_1.43, with 0.51 Ph-OH and 1.43 methoxyl group in each C₉ unit.2. The Mn of MWL was 4611, Mw was 6627, and Mw/ Mn was 1.44. There was little small molecule and more big molecule in MWL, and its molecular-weight distribution is narrow. The Mw, Mn and polydispersity were all found to have increased after the acidolysis, indicating condensation occurred simultaneously with degradation.3. The MWL of wheat straw was GSH type. After F acidolysis, there was hardly H unit discovered, but S unit took a large proportion in the lignin. After FP acidolysis, the lignin was once again found to be GSH type just like MWL. However, the proportions of G and H unit were lower, and the proportion of S unit was higher. More free Ph-OH was discovered after the acidolysis, which indicated that hydroxyl group on the lateral chain was abscised and more Ph-OH was produced. This proved that formic acid was good for the process of delignification..4. The ratio between G and S unit was 33.24% to 36.22% in the acid solvent of F, which was 58.4%to 9.52% of FP. G and S unit together counted for 69.46% of the total products in the acid solvent of F, and 67.92% of FP. With the accession of hydrogen peroxide, more small molecules were produced.