| Lignin is the only renewable organic aromatic carbon source in nature and is an ideal raw material to replace conventional petrochemicals for the production of aromatic compounds.Catalytic pyrolysis of lignin is a proven way to prepare aromatic compounds,but due to the relatively low effective hydrogen to carbon ratio of lignin,the catalyst is easily deactivated by carbon accumulation during catalytic pyrolysis.To solve this problem it is necessary to increase the effective hydrogen to carbon ratio during pyrolysis,while spent bleaching clay,as an oily solid waste,contains residual oil that can provide a hydrogen source for lignin pyrolysis,and the oxygen-containing compounds in the spent bleaching clay matrix have certain catalytic effects.Therefore,the integrated treatment of the two solid wastes is an effective way,but the co-pyrolysis characteristics and the methods to improve the selectivity and stability of the catalyst in the subsequent catalytic upgrading process are not clear.This study aims to convert lignin and spent bleaching clay into high-value aromatic hydrocarbon compounds by catalytic co-pyrolysis technology.After clarifying the synergistic properties of co-pyrolysis of the two solid wastes,the problems in the catalytic pyrolysis process were solved by constructing an efficient catalytic system and a new catalyst,clarifying the co-pyrolysis properties of lignin and spent bleaching clay and the reaction path and coke deposition pattern of catalytic co-pyrolysis to prepare aromatic hydrocarbon compounds,and elucidating the directional regulation mechanism of catalytic co-pyrolysis of lignin and spent bleaching clay to prepare aromatic hydrocarbon compounds.The main study components and findings are as follows:(1)Using the spent bleaching clay with "hydrogen supply" and "catalytic" effects and lignin for co-pyrolysis,the synergistic characteristics of the co-pyrolysis were investigated.The study showed that the introduction of spent bleaching clay reduced the activation energy required during lignin pyrolysis and enhanced the deoxygenation reaction during pyrolysis.It promoted the formation of aromatic hydrocarbons and P-type phenols(without methoxy),while the production of G-type phenols(containing one methoxy),S-type phenols(containing two methoxy)and other oxygenated compounds was inhibited.At the reaction temperature of550°C and lignin doping ratio of 75%,the yield and quality of bio-oil reached a good balance.(2)A dual catalytic system was constructed for the catalytic conversion of co-pyrolysis vapor of lignin and spent bleaching clay using calcined spent bleaching clay(CSBC)as a precatalyst for HZSM-5,and the catalytic pyrolysis mechanism was investigated in this system.The study showed that the pre-catalysis of CSBC increased the content of monocyclic aromatic hydrocarbons(MAHs)and decreased the content of polycyclic aromatic hydrocarbons(PAHs)in bio-oil,which achieved the component modulation of aromatic compounds in bio-oil.Among them,at the reaction temperature of 550 ℃,the ratio of CSBC to HZSM-5 was 1:1and the ratio of feedstock to catalyst was 1:2,the relative content of MAHs in bio-oil was higher at 73.34% and the relative content of PAHs was lower at 23.01%.(3)CSBC and HZSM-5 were synthesized into CSHZ catalyst by agglomeration method for catalytic conversion of co-pyrolysis vapor of lignin and spent bleaching clay,and the catalytic pyrolysis mechanism and coke evolution process under this system were investigated.It was shown that the acidity and pore size of the CSHZ catalyst could be regulated by adjusting the ratio of CSBC to HZSM-5.With the addition of CSBC as binder,HZSM-5showed better selectivity to MAHs.The selectivity of MAHs in bio-oil reached 78.02% using CSHZ11 catalyst at a reaction temperature of 550 °C and a feedstock-to-catalyst ratio of 1:2,which was 19.12% higher than that of HZSM-5 alone.Meanwhile,the addition of CSBC improved the performance of HZSM-5 against graphite-like coke.After three reaction-regeneration cycles,the catalytic activity of regenerated CSHZ11 for MAHs was maintained at 71.11% of the original catalyst,showing good catalyst stability.In this study,the co-pyrolysis characteristics of lignin and spent bleaching clay were investigated,followed by the construction of a dual catalytic system of CSBC and HZSM-5and the synthesis of a CSHZ composite catalyst to achieve the efficient conversion of lignin and spent bleaching clay to high-value aromatic compounds.The reaction pathways and coke evolution pathways of the catalytic pyrolysis process of lignin and spent bleaching clay were obtained,and the mechanism of directional regulation of aromatic hydrocarbons in the catalytic pyrolysis process was clarified.This study provides theoretical reference and data support for the targeted preparation of high quality fuels and chemicals from lignin and spent bleaching clay. |
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