Isolation And Structual Characterization Of Lignocellulose Lignin Based On LiCl/DMSO Solution

In this research, straw lignocellulose was used as main raw material to be dissolved in a new dissolution system of LiCl/DMSO developed recently. The changes of structural characteristics of the main chemical compositions from different parts of straw during dissolution and regeneration of Li Cl/DMSO system, the structural differences between lignin from different parts of straw, as well as dissolution behaviors in Li Cl/DMSO dissolution system were investigated in detail. A novel isolation method of cellulolytic enzyme lignin from regenerated straw materials based on Li Cl/DMSO solution system has also been set up. The research results were significantly instructive to develop efficient conversion and utilization technology of the lignocellulose biomass, as well to elucidate their chemical conversions and reaction mechanisms. The main results were described as follows:1. Dissolution behavior of chemical compositions of the lignocellulosic biomass during dissolution and regeneration of LiCl/DMSO systemBoth of rice straw with 1 h of ball milling and bamboo with 2 h of ball milling could be completely dissolved into Li Cl/DMSO solution system. It showed strong ability of regeneration for lignin and carbohydrate after dissolution. Cellulose crystalline region was destructed severely to some extent and crystallity was decreased remarkably even after 1h of milling. In contrast, both ball milling and regeneration were never structurally significantly for bamboo lignin. As for rice straw, more units of guaiacyl, syringyl and p-hydroxyphenyl of lignin were released from lignin structure druing ball milling, especially guaiacyl and p-hydroxyphenyl units for internode meal, that could give rise to the yield of nitrobenzene oxidation product.The presence of LiCl showed a marked impact on the dissolution of cellulose and no sighnificant influence on that of lignin when Li Cl/DMSO system dissolving ball milled straw. For lignin, its further dissolution in LiCl/DMSO system was not caused by Li Cl, but was along with cellulose dissolution. Lignin in enzymatic hydrolysis residue of regenerated straw materials after ball milling may represent original lignin due to its quantity and quality preserved during dissolution and regeneration of Li Cl/DMSO system compared with lignin in raw material.For poplar and masson pine, both regenerated ability were high with the yield over 80% after dissolution and regeneration of LiCl/DMSO system. Lignins obtained from different ball milling time still remained structural difference caused by mechanical operation after regeneration, and the lignin itself was not suffering any destruction during regeneration. 90% of lignin(based on original total lignin) was retained in enzymatic hydrolysis residue with lignin structure well preserved, which could represent original lignin in initial raw wood meal.2. Effect of pretreatment on the main chemical composition of straw lignocellulose biomass during dissolution and regeneration of Li Cl/DMSO systemSingle treatment with Li Cl/DMSO system offered a higher regenerated yield of chemical composition and resulted adverse effect on enzymatic hydrolysis efficiency, using extractive free rice straw and bamboo meal as material respectively.Combined with LiCl/DMSO dissolution and regeneration, regenerated abilities of chemical compositions of rice straw with ball milling or EDA treatment were different, and so were bamboo. EDA pretreatment became more prone to remove lignin in comparison with cellulose dissolution. Almost all of the carbohydrates in the regenerated straw were dissolved when treated with cellulase, but about a half lignin, even more than 80% for bamboo with 2h of ball milling, remained as solid residue after enzymatic hydrolysis. Both ball milling and EDA treatment had a significant effect on the lignin content of regenerated DMSO/Li Cl straw mass.3. Isolation and characterization of lignin from straw lignocellulose biomass based on Li Cl/DMSO systemThe combined procedure of ball milling, dissolution in LiCl/DMSO system, and regeneration in water, followed by enzymatic hydrolysis, made it possible to isolate a larger proportion of lignin from the rice straw, especially higher from bamboo, than the procedure that does not include dissolution and regeneration. This novel isolated method had better protective action for lignin structure and selective degradation to carbohydrate. A detailed comparison of the lignin structure revealed no significant differences between these two lignin products. As this procedure recovered a large proportion of plant protolignin, it appeared likely that the chemical structure of recovered lignin was more representative of the in situ lignin. The results also illustrated that its pyrolysis characteristic difference was determined by chemical structure of lignin itself.