The Research Of Aromatics Production From Catalytic Cracking Of Lignin

Lignin constitutes one of major components of lignocellulosic biomass. It was revealed that lignin is a three dimensional amorphous polymer and lignin is the only nature renewable resource which can provide large quantities of aromatic compounds. In the recent years, there is considerable interest in the production of chemicals and bio-fuels from lignin through pyrolysis, catalytic pyrolysis, hydrogenationm reduction, gasification, biochemical conversion and so on. Benzene, Toluene, and xylenes (BTX) together with ethylbenzene and cumene are are important aromatic platform compounds. By now the production of these aromatic platforms are based on non-renewable resources such as oil or coal. Our research is foucs on how to use lignin to produce high value-added aromatic compounds.1. Production of BTX through catalytic depolymerization of ligninIn present work, we investigated catalysts with different pore size and acidity. The transformation of lignin into benzene, toluene, and xylenes was studied over the HZSM-5, HY and MCM-22catalysts, and the HZSM-5catalyst showed the highest carbon yield of BTX. The reaction conditions strongly impacts the distribution of the products:The aromatic selectivities of BTX increased by rising the reaction temperature, but the BYX yield decreased when the reaction temperature reaches over600℃due to the second cracking of organics liquid. It was found that the BTX selectivity showed a positive dependence on the catalyst/lignin ratio, however, the BTX yield showed a slight decrease, which accounts for an increase in yield of gas products and a decrease in liquid yield.. The carbon yield of BTX reached about25.3C-mol%and the aromatic selectivities of BTX reached about79.8C-mol%over HZSM-5catalyst under T=550℃,f(N2)=300cm3min-1, and catalyst/lignin ratio of2. Catalyst plays an important role in the process of depolymerization and the ultimate organic liquid has a very low yield of BTX without the addition of catalyst The main components of lignin pyrolysis products are small molecular oxygen containing compounds. Formation of BTX through catalytic cracking of lignin proceeded through lignin depolymerizaton followed by the dehydration, decarboxylation and decarbonylation process. 2. Directional synthesis of ethylbenzene through catalytic transformation of ligninThis work explored the production of ethylbenzene from lignin through the directional catalytic depolymerization of lignin into the aromatic monomers followed by the selective alkylation of the aromatic monomers. For the first step, the aromatics selectivity of benzene derived from the catalytic depolymerizationof lignin over the composite catalyst of Re-Y/HZSM-5(25) at600℃. The lignin-derived oil contains83.2C-mol%benzene.For the alkylation of the aromatic monomers in the second step, the selectivity of ethylbenzene was about62.5C-mol%at T=35O℃, feed: EtOH=1:1(in mol ratio), WHSV=1.0.oover the HZSM-5(25) catalyst. The main by-products include di-ethylbenzene and toluene. Increase of benzene content in the reactants is useful to restrain the generation of diethylbenzene, and decrease the reaction temperature can effectively restrain the formation of toluene3. Exploration the production of cumene from ligninUse benzene, ethanol, isopropanol as model compounds to produce ethylbenzene and cumene. As the selective production of ethylene and propylene from bio-oil can be achieved, this study laid a foundation to future research——All raw materials derived from biomass. The aromatics selectivity of ethylbenzene and cumene reached about75.4C-mol%over HZSM-5(50) catalyst and the conversion of alcohols (ethanol and isopropano) in our test range near100%Rise the reaction temperature can largely enhance the conversion of benzene but can also increase the formation of by-products (toluene, diethylbenzene, propylbenzene). When alkylation temperature is280℃, the total aromatics selectivity of ethylbenzene and cumene can reach91.7C-mol%。This dissertation studies preliminarily the mechanism and reaction pathway of alkylation of benzene to cumene.