Catalytic Degradation Liquefaction Of Lignin In Ionic Liquids

Lignin, only after cellulose, is the second most abundant natural polymer in nature, and is the most important renewable resource to produce aromatic chemicals. It has become an important high-value-added utilization way for lignin resource to be degradation liquefied into bio-oil. The bio-oil can be put to separate fine chemicals firstly, and the left part can be continuously converted into bio-diesel through complete hydrogenation. Ionic liquids, well-known green solvents, are good solvents for lignin as well as medium for its degradation liquefaction. In this work, catalytic degradation liquefaction of lignin in ionic liquids has been studied and the main works are as follows:Firstly, hydrochloric acid was applied as catalyst for degradation of lignin in ionic liquids, and the effect of reaction conditions on the liquefaction efficiency and the structures of liquefied products were studied. The optimized condition was 150℃,6 h with lignin to BnMIMC1 mass ratio of 1:10, and the liquefaction efficiency of lignin was as high as 66.54%. Although introduction of microwave could reduce reaction temperature and shorten reaction time, the liquefaction efficiency of lignin reduced by about 8%. The percentage of phenolic compounds in liquefied products was above 60%, while the percentage increased to above 80% when lignin was degraded in IL assisted by microwave.Furthermore, the degradation of lignin in ionic liquid catalyzed by mesoporous solid acids was studied. Sulphuric acid and silicotungstic acid were adopted separately to acidize MCM-41 molecular sieves by soaking, refluxing and evaporation methods. It was found that the H2SO4/MCM-41 prepared by soaking method had the best catalytic performance, and the liquefaction efficiency of lignin was increased to 74.02%. The percentage of phenolic compounds in liquefied products was above 80%, and vanillin, 1-(4-hydroxy-3-methoxyphenyl)-ethanone, vanillic acid and 4-hydroxy-3-methoxy-benzenepropanol were the main low molecular chemcals in the liquefied products.In order to restrain the formation of ketones and esters as well as the re-polymerization of the segments generated in the process of lignin degradation, transition metals (Raney-Ni, Pd/C) were conducted to catalyze lignin hydrogenation degradation. Compared with the results of lignin degradation catalyzed by hydrochloric acid and solid acids, the percentage of phenolic compounds in liquefied products increased by about 10% and the re-polymerization reaction was restrained effectively, but the liquefaction efficiency decreased slightly when using Pd/C as catalyst. The main compositions in the liquefied products included vanillin, acetovanillone, vanillic acid, homovanillic acid, and 4-hydroxy-3-methoxy-benzenepropanol.Finally, the recycled solids were used for the preparation of activated carbon. It was manifested that appropriately increasing impregnation ratio, activation temperature and time contributed to the formation of more micro-pores and improved the adsorption property of activated carbon. While over a certain extent, parts of the micro-pores occurred reaming effect, and the adsorption property would reduce. The optimized condition for the preparation of activated carbon was proved to be 800℃,2 h with impregnation ratio of 1:1. Under the optimized condition, the yield of activate carbon was 32.8% and the specific surface area was 1747.10 m2/g. The methylene blue adsorption value and the iodine adsorption value reached 487.9 and 1375.8 mg/g respectively.