| Coal is one of the most important fossil fuels which is rich in various chemical compositions and molecular structures.Thermal conversion is the main way of coal utilization.Coal pyrolysis is one of the most vital technologies of coal conversions.However,there are still some problems such as low quality of pyrolysis tar,separation of high temperature gas and solid and separation of oil and dust.Catalytic pyrolysis is an important way to solve such problems.The catalytic pyrolysis can not only improve the conversion rate of coal pyrolysis,minish the reaction temperature;but control the composition and distribution of coal pyrolysis products.It is very meaningful to research the high efficiency pyrolysis catalyst according to the target products.In this paper,we developed a series of catalysts which can control the composition and distribution of pyrolysis products effectively and improve the content of BTX in tar and high value-added chemicals in the low temperature pyrolysis system of low rank coal.TG-FTIR and self-powder particle fluidized bed were used to analyze the pyrolysis and catalytic pyrolysis of Shendong coal.TG-FTIR experiments showed that the pyrolysis process of Shendong coal loss is mainly concentrated in the active pyrolysis stage,which accounted for about 70%of the total weight loss.The total loss of Shendong coal was 30.36%at 800℃.Compared with Shendong coal pyrolysis,the weight loss of all catalytic pyrolysis increased.Dynamic analysis showed that the activation energy of coal pyrolysis in 400-500℃ and 500-700℃was 38.69 kJ/mol and 15.86 kJ/mol,respectively.The activation energy of catalytic pyrolysis is lower than coal pyrolysis at 400-500℃,the order of activation energy as follow:Ni/y-Al2O3<γ-Al2O3<Ce-Ni/γ-Al2O3<Ce-Co/γ-Al2O3<Co/γ-Al2O3<Raw coal;and the activation energy of catalytic pyrolysis is lower than coal pyrolysis at 500-700℃,the order of activation energy as follow:Ce-Ni/γ-Al2O3<Ce-Co/γ-Al2O3<Co/γ-Al2O3<Ni/γ-Al2O3<Raw coal.The results showed that the catalysts had a great influence on coal pyrolysis.The power-particle fluidized bed was used to analyze the fast pyrolysis of Shendong under different conditions.The research showed that with increasing pyrolysis temperature,the tar yield increased and then decreased and the maximum tar yield was 13.76%at 650℃;pyrolysis gas yield showed a monotonically increasing trend and the maximum gas yield was 10.80×10-2 L/g at 700℃;the char yield monotonically decreased from 63.69%at 500℃ to 80.43%at 700℃.At different pyrolysis temperature,the content of BTX increased monotonically with the increase of final pyrolysis temperature.Among them,the proportion of benzene,toluene and xylene in the product are different as the pyrolysis temperature increased.The content of benzene increased slowly,while the content of toluene and xylene increased rapidly.Compared with silica sand as the fluidizing medium,Ni/γ-Al2O3 and Ce-Ni/γ-Al2O3 catalyst as the fluidizing medium,the tar and char yield changed slightly,while the gas yield increased;the content of BTX in tar increased 76.96%and 96.71%,and the monocyclic aromatics increased 15.55%and 13.88%,respectively.Compared with silica sand as the fluidizing medium,Co/γ-Al2O3 and Ce-Co/γ-Al2O3 catalyst as the fluidizing medium,the tar and char yield changed slightly,while the gas yield increased;the content of BTX in tar increased 71.71%and 97.37%,and the monocyclic aromatics increased 14.47%and 17.39%,respectively. |
