The Research Of Selective Depolymerization Of Lignin By Electrochemical Method

Lignin is one of the abundant biomass resources in the nature, and it contains a lot of structure units of aromatic compounds, because of its big molecular weight, low reactivity, the utilization rate of lignin is very low. If we can cleavage the linkages among structural units in lignin in a selective way, we can get low-molecular-weight (LMW) aromatic compounds and realize the recycling utilization of lignin. One of the major difficulties of lignin depolymerization is caused by the improvement of depolymerization rate and the complexity of depolymerization products for subsequent product separation. In our study, we use the RuO2/Ti as anode and ORR as cathode. Firstly, the factors of electrolysis conditions in anodic or cathodic area on the yield of low-molecular-weight (LMW) aromatic compounds and their distribution of lignin by electrochemical method were studied based on an ionic exchange membrane cell. And then in a non-diaphragm electrolytic cell we utilize the synergistic action between anodic and cathodic reaction for in-depth depolymerization of lignin. GC-MS and LC-MS can provide LMW aromatic compounds with objective analysis and UV spectrophotometry, weight difference method can provide LMW aromatic compounds with quantitative analysis. The C9 structural unit of lignin and gel permeation chromatography (GPC) method can provide the change of lignin structure and molecular weight after electrolysis.With the help of a diaphragm cell we study the effect of two types of electrochemical depolymerization respectively in our research, the results show that cathode is mainly to cleavage ?-O-4 ether bond and anode is mainly to cause the cleavage of C-C bond. The yield of kinds of LMW compounds are influenced by electrolytic conditions significantly. The improvement of the electrolysis temperature, electrolysis time or H2O2 concentration can improve the yield of LMW compounds, However, the amount of the products would increase for longer electrolysis time and higher temperature due to further oxidation of the LMW compounds.The synergistic action between anodic and cathodic reaction could increase the deploymerization yield with better product selectivity. The result shows that after electrolysis for 2 hours in the cylindrical non-diaphragm cell, we can get 4 kinds of LMW compounds and the yield of LMW compounds can reach 35.62%.At the same time the molecular weight of lignin extract have changed from 3021 to 937.By GC-MS and UV spectrophotometry we can find that a certain amount of methanol is produced in the process of electrolysis. The presence of methanol can cause polymerization reaction. If we separate gas from electrolysis system in time, the efficiency of electrolysis will be improved.Finally the study of lignin aqueous electrolyte circulation experiment was carried out, the results show that the experimental method and results can be well meet the requirements of the industry, and it has laid a good foundation for the following experiments.