Catalytic Pyrolysis Of Coal-based Model Compounds Catalyzed By Two Iron-based Catalysts

Coal pyrolysis is an important process in coal transformation process.Catalysts can regulate the products of coal pyrolysis.Iron-based catalysts are important for pyrolysis and liquefaction,thus it is significant to study the catalytic pyrolysis mechanism of iron-based catalysts in coal pyrolysis process.The pyrolysis behavior of coal-like model compounds with the iron-based catalysts was studied on the fixed bed.By comparing the distribution of pyrolysis products and the theoretical calculation of weak bonds of model compounds under different conditions,the possible catalytic pyrolysis pathways of these model compounds with iron-based catalysts were proposed,which provided a reference for the catalytic pyrolysis of coal.The main contents of this thesis include:（1）The pyrolysis behaviors of phenyl ether model compounds（anisole,phenetole（PEE）,benzyl phenyl ether（BOB））and diaryl alkanes model compound bibenzyl（BB）were investigated on a fixed-bed reactor catalyzed by pyrite（main component is FeS₂）.By comparing the pyrolysis products,the possible mechanism of model compounds with pyrite in pyrolysis process was proposed.The experimental results showed that pyrite could improve the pyrolysis conversion,gas and liquid yields of the model compounds and reduce the residual coke.Because of the different structure of each model compound,the effect of pyrite was different.The dissociation energy of the weak bond structure with pyrite was lower than itself.The effect of pyrite on pyrolysis was also different in different pyrolysis temperature.In order to further explore the effect of pyrite in pyrolysis process,the dissociation energies of weak bonds of phenyl benzyl ether and bibenzyl with pyrite were calculated by VASP.The results showed that pyrite could reduce the dissociation energy of weak bonds of phenyl benzyl ether and bibenzyl,thus promoting the breaking of weak bonds.To have an adequate demonstration on the role of pyrite in catalytic pyrolysis,hydrogen solvent tetrahydronaphthalene（Te）was added through the pulse inlet in bibenzyl pyrolysis process.There was a significant synergistic effect between tetrahydronaphthalene and the pyrite in the pyrolysis process of BB.The pyrite was conducive to produce pyrolysis free radicals,which could be stablized timely by tetrahydronaphthalene.The conversion of BB increased further in the presence of tetrahydronaphthalene and pyrite simultaneously.（2）Iron-based catalysts Fe/ZSM-5 with different loads were prepared.The pyrolysis behaviors of coal-related model compounds（phenetole and bibenzyl）were investigated on a fixed-bed reactor catalyzed by Fe/ZSM-5.The results indicated that Fe/ZSM-5 could also increase the conversion of the model compounds and the yield of liquid and gas,while decrease the char yield.When the loading amount of iron was 7.5 wt.%,the catalytic performance of Fe/ZSM-5 was the best.The conversion of phenetole and bibenzyl reached45.6%and 35.3%,respectively.The catalytic performance of Fe/ZSM-5 was superior to that of pyrite,which could promote the cleavage of C_aliphatic–O bond of phenetole and C_aryl–C_aliphaticliphatic bond of bibenzyl.For Fe/ZSM-5,the acidity of support ZSM-5 played the main role in the pyrolysis process of phenetole,while the supported metals played a main role in the pyrolysis process of bibenzyl.