| Lignin is an important biomass resource for the renewable production of chemicals and energy. It is a three dimensional amorphous polymer consisting of phenylpropane units, and it constitutes one of the major components of plant skeleton. Lignin is a by-product of wood hydrolysis and paper making industry, most of which is underutilized. The existing markets for lignin utilization focus on low added value products and present lignin conversion methods have the deficiencies such as long reaction time, harsh condition, low selectivity of product and so on.Microwave, as a new heating method, has the advantages like fast heating, high heating efficiency, no temperature gradient and no hysteresis effect. Reactions assisted by microwave show the priority of fast reaction velocity, high selectivity and low power consumption. Hydrogen-donor solvent is able to afford active hydrogen atoms so as to control coking, and its solvent effect can improve the product selectivity. Therefore, with the assistance of microwave and hydrogen-donor solvents, it is possible to overcome the deficiencies mentioned above.Several lignin model compounds were selected to represent the ether bonds in lignin molecule, and studies were carried out on their catalytic degradation with the assistance of microwave and hydrogen-donor solvents. Based on the degradation data, the effect of catalysts and hydrogen-donor solvents on degradation was studied; besides, the cleavage regularity of ether bonds and the effect of microwave in degradation were discussed, and the degradation mechanism was speculated preliminarily. The research work is summarized as follows.Benzyl phenyl ether (or BPE) was selected as a lignin model compound to study the effect of catalysts and hydrogen-donor solvents on degradation. Studies were carried out on its degradation under the condition of tetralin as the hydrogen-donor solvent,433.15K and different catalysts and under the condition of p-toluenesulfonic acid (or PTSA) as the catalyst,433.15K and different hydrogen-donor solvents. The results showed that under the same condition, sulfonic acids had good catalytic effect in BPE degradation, and especially PTSA could improve phenol yield which was chose as the catalyst in the following experiments; and that under the same condition, hydrogenated aromatics especially anthracene and tetralin could well donate hydrogen. Because of tetralin’s low price, it was chose as the hydrogen-donor solvent in the following experiments.Anisole (or BME), diphenyl ether, BPE and phenethyl phenyl ether (or PPE) were selected as lignin model compounds and studies were carried out on their catalytic degradation with the assistance of microwave and tetralin. The results showed that the cleavage of ether bonds in lignin molecule was selective. The ether bonds represented by BPE and PPE could cleave fast and ether bond represented by BME cleaved relatively slowly, while ether bond represented by diphenyl ether could not cleave under the experiment conditions. Through kinetic equation fitting of degradation data and Arrhenius correlation of rate constants, the degradation apparent activation energies were evaluated for BME62.91kJ·mol-1in microwave reactor and97.77kJ-mol-1in batch reactor and for PPE81.97kJ·mol-1in microwave reactor and113.37kJ-mol-1in batch reactor. The comparison of apparent activation energies in microwave reactor and batch reactor could show that microwave could reduce the degradation apparent activation energy of lignin model compounds in tetralin. Besides, through qualitative and quantitative analysis of the substances in degradation of lignin model compounds, the mechanism was proposed based on the formation of transition states and ring closure. |
