Research On The Production Of Aromatic Hydrocarbons From Fast Catalytic Pyrolysis Of Lignin

Lignin, as one of three major components of biomass, is a natural aromatic polymer with a complex three dimensional structure. It is known as an abundant source of renewable energy and can be converted to higher-value chemicals such as benzene, toluene by fast pyrolysis, which have great application prospect in the future. However, due to the difficulty of removing phenolic hydroxyl groups from the intermediates produced from lignin fast pyrolysis, the yield and selectivity of aromatic hydrocarbons are not high. Therefore, in this work black-liquor lignin and its main pyrolysis products were selected as raw materials to study the production of aromatic hydrocarbons with the unmodified and modified catalyst and to explore the deoxidization reaction mechanism.First of all, the directly fast pyrolysis of lignin under different pyrolysis temperature was studied through Py-GC/MS. It was found that the total amount of aromatic monomers achieved the maximum value at 700?. Aromatic hydrocarbons, the target products, were only detected after 700? and the amount was remarkably increased with the elevated temperature. Among the products generated from the directly fast pyrolysis of black-liquor lignin, guaiacol,4-methylguaiacol,4-ethylguaiacol and 4-vinylguaiacol were the main products of guaiacol-type compounds; syringol was the main product of syringol-type compounds; and phenol, methylphenol and ethylphenol were the main products of phenol-type compounds.Secondly, the catalytic reforming of guaiacol was investigated with HZSM-5(25) under different reaction temperature to choose an opptimal temperature for the catalytic reforming experiments of the lignin main pyrolysis protucts. Considering both the yield of aromatic hydrocarbons and the coke yield on the used catalyst,600? was selected as the best reaction temperature for the catalytic reforming of the lignin main pyrolysis protucts. The influence of six kinds of zeolite catalysts (H-??H-USY?HZSM-5(25)?HZSM-5(38)?HZSM-5(50)? HZSM-5(200)) and metal-modified (Ni, Co, Fe, Pd) HZSM-5 catalyst on the catalytic conversion of the lignin main pyrolysis products to aromatic hydrocarbons was studied at 600?. It was found that HZSM-5(25) was the best catalyst for the production of aromatic hydrocarbons from guaiacol-type compounds and syringol, and H-USY zeolite showed the best performance for enhancing the formation of benzene from phenol. As the acid strength and acid amount of HZSM-5 catalyst were increased, the demethoxylation and dehydroxylation of phenolic compounds were accordingly promoted to generate more aromatic hydrocarbons. Comparing the three zeolite catalysts with different channel structure, H-? zeolite had the highest coke yield. With the enhancement of the amount of Bronsted acid, the amount of coke deposited on the catalyst was also increased. The addition of metal component to zeolite catalyst made the amount of Bronsted acid decrease and the amount of Lewis acid increase, which inhibited the polycondensation reaction for producing polycyclic aromatic hydrocarbons and the dehydroxylation of methylphenol for producing toluene.Finally, the fast catalytic pyrolysis of black-liquor lignin was studied with four metal-modified catalysts (1%Ni/HZSM-5(25)?3%Co/HZSM-5(25)?3%Fe/HZSM-5(25)? 5%Pd/HZSM-5(25)) which had better performance in the catalytic reforming experiments of guaiacol to examine the effect of pyrolysis temperature on the product distribution. It was shown that the optimal temperature for the production of aromatic hydrocarbons from the fast catalytic pyrolysis of lignin was different due to the addition of different catalyst. Comparing the four kinds of catalysts, the best temperature for producing aromatic hydrocarbons from lignin with 1%Ni/HZSM-5(25) catalyst was the highest (900?), while the maximum yield of aromatic hydrocarbons was achieved at 700? with 3%Co/HZSM-5(25) as the catalyst. The production of aromatic monomers from the fast catalytic pyrolysis of black-liquor lignin was more violent as the metal-modified catalyst has the bigger surface area and pore volume. The higher the acid strength of catalyst was, the higher the activity of catalyst at high temperature was, which lead to the optimum temperature for the formation of aromatic hydrocarbons was higher. These related research results could lay a theoretical foundation for the high-value utilization of lignin and the cascade utilization of all components in biomass.