| Lignin is the main component of black liquor generated by the pulp and paper industry. As the only renewable source of aromatic fine chemicals and a readily available non-petrochemical resource in nature, it is regarded as replacement of petrochemical products in future by transforming lignin into a variety of high-added-value phenolic derivatives. Research focused on direct and efficient conversion of lignin to lower-molecular weight aromatic compounds is of great significance to solve the energy and environment issues. Thus, this study is gaining momentum in light of the dwindling of our fossil-based resources and getting widely attention from both academic and industrial circles. This thesis is focused on exploring easy access to degrade lignin to phenolic derivatives directly and effectively under mild reaction conditions, and the major research works are summarized as follows:(1) The vanadium substituted phosphotungstic acid and phosphomolybdic acid were synthesized by the method of step-by-step acidification and extraction using diethyl ether. The structure of phosphotungstic acid, phosphomolybdic acid, phosphatic tungstic vanadic acid and molybdovanadophosphoric acid was characterized by infrared and ultraviolet-visible spectrum. The above four heteropoly aids were found to be active for the oxidative degradation of lignin under visible light, providing syringic acid, syringaldehyde, vanillin and acetosyringone as main phenolic products. Among the four catalysts examined, phosphotungstic acid showed the best result. With phosphotungstic acid as a photocatalyst, we investigated its catalytic performance in water or acetone-water solvent for the present degradation, and checked the effect of reaction conditions such as illumination time, dosage of catalyst and substrate on this degradation. Under the optimized conditions, the phosphotungstic acid could achieve36.05%degradation rate of lignin, providing ca.3.63%yield for the main phenolic products.(2) The nano CuO-1catalyst was synthesized by precipitation and calcination method with copper nitrate as a raw material, and another nano CuO-2catalyst was prepared by solvent thermal method. Then the obtained catalysts were characterized by X-ray diffraction, UV-Vis, SEM and nitrogen adsorption-desorption. Both the catalysts CuO-1and CuO-2and the commercially available CuO-3were used to catalyze the oxidative degradation reaction of lignin in alkaline medium under mild reaction conditions (<100℃,1atm O2). Results showed that CuO-1had a better catalytic performance than CuO-2and CuO-3under the same reaction conditions; The reaction conditions such as reaction temperature, time, catalyst dosage, NaOH concentration and reaction solvent quantity were optimized using CuO-1as a catalyst; Under the optimized conditions, the catalyst CuO-1could give ca.66.64%degradation rate of lignin and ca.14.7%yield for the main phenolic products.(3) Respectively using copper nitrate and hydrazine hydrate as a copper source and a chemical reduction reagent, a series of CuO, CuO-Cu2O and Cu2O catalysts were prepared by precipitation method and then partial or complete reduction. These resulting catalysts were characterized by X-ray diffraction, UV-Vis, SEM, XPS and nitrogen adsorption-desorption. And their catalytic performance for the conversion of lignin to phenolic derivatives was checked under low temperature and atmospheric pressure. Results showed that Cu2O possessed a higher catalytic activity than CuO. Moreover, the catalyst CuO-Cu2O, which was prepared by partial reduction with a stoichiometric amount of H4N2as the reduction reagent(according to the molar ratio1:8of H4N2:Cu2+), was more efficient than Cu2O, and could achieve68.89%degradation rate of lignin and16.65%yield for the main phenolic products under the optimum reaction conditions. |
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