Evaluation of gas switch effect on isothermal gas-solid reactions in a thermogravimetric analyzer

• Published in: Fuel (Guildford) 2019-03, Vol.239, p.1173-1178
• Main Authors: Zhang, Qian, Yuan, Quan, Wang, Hongliang, Wang, Zhiqing, Yu, Zhongliang, Liang, Litong, Fang, Yitian, Huang, Wei
• Format: Article
• Language: English
• Subjects: Atmosphere; Carbon dioxide; Diffusion effects; Evaluation; Gas evolution; Gas switch effect; Gas-solid reactions; Gaseous diffusion; Gases; Gasification; Isothermal reaction; Kinetics; Parameter estimation; Rare gases; Switching; Temperature; Thermogravimetric analyzer
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2018.11.101

•Gas switch effect were evaluated on isothermal gas-solid reactions in TGA.•Gas switch from Ar to CO2 affected the isothermal gasification curve of graphite.•The variation of the CO2 concentrations during gas switch caused the difference.•Gas switch effect become more significant with temperature increase.•Gas switch step affected the existence of the maximum rate of gasification. The effect of gas switching during isothermal gas-solid reactions were evaluated by taking CO2 gasification of graphite in a thermogravimetric analyzer as an example. The evolution behavior of the gases during gasification with or without the gas switch step were recorded and analyzed by an on-line mass spectrometer. The gasification curve from the procedure with gas switch step showed an obvious difference with that obtained from all CO2 atmosphere. For the procedure with gas switch step, the reaction indeed occurs in a mixture atmosphere of CO2 and the inert gas initially, which greatly restrict the gasification reaction and completely changes the reaction rate curve trends. Moreover, the effect of gas switching is in proportion to the gasification temperature. With the increase of the gasification temperature, the effect of gas switching becomes more significant. The activation energy calculated using the data from the gas switch method become lower for the gas diffusion effect. This research indicate that the previous study which does not consider the gas switch effect would contain some errors on the evaluation of the samples reactivity and kinetic parameters. Estimate the gas evolution behavior is needed before doing the isothermal gas-solid reaction experiments using the gas switch method.