Kinetic modeling of deoiled asphaltene particle pyrolysis in thermogravimetric analysis
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The pyrolysis behavior of deoiled asphaltene particles was experimentally studied by thermogravimetric analysis. Considering that the activation energy would change with the evolution of pyrolysis reactions, a modified competition model was proposed to appropriately describe the pyrolysis kinetics. The model parameters were fitted with experimental results. Compared with the original two-stage model, the modified competition model showed the capability of predicting the asphaltene pyrolysis at various heating conditions using fixed kinetic parameters. The results exhibited that the modified competition model can well simulate the asphaltene pyrolysis in the main mass loss temperature range from 500 to 900 K as well as the slow decomposition at the temperatures greater than 900 K during the devolatilization process of asphaltene particles at hundred micrometer size. The modified competition model was further coupled with a heat transfer model at particle scale, including the heat exchange between the particle and the surrounding atmosphere as well as the heat transfer inside the particle. It is found that during the thermogravimetric analysis, the particle surface temperature was close to that of atmosphere, and the heat transfer effect inside the particle could be ignored for hundred-micron-sized particles. However, the temperature gradient inside particles should be considered for millimeter-sized particles. Thus, the particle samples should be sieved to hundred micron sized or smaller when studying the basic pyrolysis behaviors in order to acquire kinetic parameters for asphaltene pyrolysis by thermogravimetric analysis.
KeywordsAsphaltene Pyrolysis kinetics Thermogravimetric analysis Single-particle modeling
Financial supports from the National Basic Research Program of China (973 Program No. 2012CB720301) and the National Science and Technology Key Supporting Project (2013BAF08B04), PetroChina Innovation Foundation (2013D-5006-0508) are acknowledged.
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