Co-Pyrolysis Characteristics Of Fischer-Tropsch Synthesis Waste Catalyst And Coal

The main process for the preparation of oil products by indirect coal liquefaction is the high-temperature slurry bed Fischer-Tropsch synthesis technology,companying with the production of a large amount of iron-based waste catalysts.The treatment of iron-based wasted catalysts is generally in the form of stacking,which will not only cause serious pollution to the environment but also cause waste of resources.Therefore,the treatment of waste catalyst for Fischer-Tropsch synthesis has become an urgent problem to be solved.The composition of wasted catalyst is mainly wax oil and active metals majorly composed of iron,cobalt,etc.Compared with coal,the wax oil has a higher H/C atomic ratio and active metals can promote coal pyrolysis.The co-pyrolysis of waste catalyst and coal not only can realize the lightweight of coal tar but also limits the environmental pollution caused by waste catalyst.In this thesis,two kinds of Fischer-Tropsch wasted catalysts,Yangchangwan coal,Meihuajing coal and their mixture were used as raw materials.Thermogravimetric-mass spectrometry(TG-MS)and pyrolysis-gas chromatography-mass spectrometry(Py-GC-MS)were used to carry out pyrolysis experiments.Combined with X-ray diffraction and Fourier transform infrared spectroscopy,the co-pyrolysis characteristics of Fischer-Tropsch waste catalysts and coal in different proportions were studied.The emission characteristic of volatile and interaction mechanism of Fischer-Tropsch waste catalysts and coal during co-pyrolysis were discussed.The purpose is to provide a new idea for the treatment of Fischer-Tropsch waste catalyst.The main contents and conclusions are as follows:The pyrolysis characteristics of the waste catalysts were studied by TG-MS and Py-GC-MS.It was found that the pyrolysis of the waste catalyst was mainly the decomposition of long-chain alkanes with carbon number greater than 21 at 200-500? to produce hydrocarbons C11-C20.When the temperature was above 500?,the iron species in the waste catalyst were reduced or decomposed into metallic iron and played a catalytic role in wax cracking.At 400-600 ?,small molecules such as H2,CH4,H2O,CO and CO2 are mainly released,while the existence of iron species leads to the formation of CO2 and CO above 650?.With the increase of temperature,the hydrocarbons of C21+were first decomposed to C11-C20,and then decomposed to C5-C10 olefins.The total olefin content of C5-C10 and C11-C20 increased to 70.3%at 900?,and the total olefin content of C5-C10 was about 40%.Paraffin polymerization and aromatization occurred above 700? leading to the formation of aromatic compounds.The co-pyrolysis characteristics of waste catalysts and different coals were investigated,and it was found that their co-pyrolysis behavior characteristics were basically similiar.The added waste catalysts in the low temperature region showed a positive effect on the release of volatiles in the co-pyrolysis process.The positive effect was stronger with the proportion increase of the waste catalysts,but inhibitory effect of the waste catalysts happened in the high temperature region.At the same time,the addition of waste catalyst inhibited the formation of aromatic compounds.With the increase of waste catalyst content,aromatics in co-pyrolysis tar decreased,and olefins increased.In other words,the presence of waste catalyst inhibited the polycondensation during the co-pyrolysis.Four kinetic models were used to study the kinetics of individual pyrolysis and co-pyrolysis of coal and waste catalyst.It was found that the activation energies of individual pyrolysis of waste catalyst was 129.40-330.90 kJ/mol,the activation energy of Meihuajing coal and Yangchangwan coal was 253.48 kJ/mol and 216.51 kJ/mol,respectively.The activation energy of co-pyrolysis of waste catalyst with Yangchangwan coal and Meihuajing coal was 196.39 kJ/mol and 218.38 kJ/mol,respectively.This proved that the addition of wasted catalyst reduced the activation energy of coal pyrolysis.