Investigation On Process Of Rapid Pyrolysisof Low-Rank Coal In Volatile Matter Catalytic Upgrading

The clean and efficient conversion and utilization of low-rank coals is one of the most important solutions to alleviate the shortage of oil resources in China,optimize the energy consumption structure,and promote the construction of ecological civilization,which is also in line with the energy structure characteristics of China's energy poor oil,low gas and relatively rich coal as well as economic and environmental co-development strategy.Pyrolysis is one of the main approaches for the conversion of low-rank coals with productions of pyrolysis gas,coal tar and char.Moreover,catalysis involved into the in-situ pyrolysis process or product upgrading will significantly enhance the pyrolysis efficiency and improve the condensable product quality.Zeolites,which have ordered microporous pores,large specific surface areas and superior thermal/hydrothermal stabilities,can be used as catalysts in the pyrolysis of low-rank coals with the purpose of catalytic upgrading of the pyrolysis volatiles.However,the catalytic upgrading mechanism of pyrolysis volatiles from low-rank coals by zeolites is still unclear,which seriously constrain its development process.Hence,we proposed a systematic study of the structure effects(such as framework type,Si/Al ratio,and hierarchical porosity)of zeolites on their catalytic performances in pyrolysis and product upgrading of low-rank coals.(1)Design of pyrolysis reactor: a two-stage catalytic pyrolysis reactor was developed to realize the coupling of rapid pyrolysis of low-rank coals and catalytic upgrading of pyrolysis volatiles,and the optimum operating conditions(pyrolysis temperature: 600 ?,standing time: 30min)of the reactor was determined with the highest yield of coal tar.(2)Design of pyrolysis catalyst: the structure effects of zeolite pyrolysis catalysts,such as framework type,Si/Al ratio,and hierarchical porosity,on their catalytic performances in pyrolysis volatile upgrading were systematically studied as follow,1)The effects of framework types and micropore pore structure on the catalytic upgrading pyrolysis volatiles were investigated using four type zeolite catalysts(SAPO-34,ZSM-5,Beta and HY).The results showed that with the increase of the micropore diameter,the coke capacity was gradually improved in the catalytic upgrading process of Shendong coal pyrolysis volatiles,while the coal tar yield gradually decreased.ZSM-5 catalyst showed the best performance in both coal tar yield and quality.Comparing with the coal tar from simple Shendong coal pyrolysis,the light fraction(methanol solubles)of the catalytic pyrolysis tar by ZSM-5 increased 72.98%,the GC-MS detectable component increased 109.55 %,and the BTX and aromatic content increased 253.32 % and 210.51 %,respectively.2)ZSM-5 zeolite catalysts with Si/Al ratios of 50,100,150,and 200 were prepared,and further used to investigate the effect of Si/Al ratio on the catalytic upgrading performance.The results showed that ZSM-5 zeolite with the Si/Al ratio of 80 was the most suitable catalyst for the catalytic upgrading of the pyrolysis volatiles from Shendong coal with the highest yield of aromatic compounds.Comparing with the coal tar from simple Shendong coal pyrolysis,the light fraction(methanol solubles)of the catalytic pyrolysis tar by ZSM-5 with the Si/Al ratio 80 increased 62.68 %,the GC-MS detectable component increased 165.92 %,and the BTX and aromatic content increased 471.36 % and 359.24 %,respectively.3)Hierarchical ZSM-5 zeolites with meso-/microporosity were synthesized using organosilane surfactant TPOAC as a mesoporous structure directing agent,further used to investigate the effect of hierarchical porous structure on the catalytic upgrading performance.Comparing with the sole micropore ZSM-5,the content of light fraction(methanol solubles)of catalytic pyrolysis tar by hierarchical ZSM-5 increased 35.71 %,the content of detectable components of GC-MS increased 32.93 %,and the total content of aromatic hydrocarbons increased by 55.10 %,in which benzene-toluene-xylene(BTX),single-ring aromatic compounds,and bicyclic aromatic compounds were increased 49.01 %,71.34%,and 77.73 %,respectively.