Catalytic combustion behaviors of petroleum coke with hematite catalyst in a micro fluidized bed thermogravimetric analysis

Abstract

Both conventional TGA and fluidized bed have some inherent limitations in the accurate measurement of gas–solid reaction. To characterize the gas–solid process under the fluidization state, a micro fluidized bed thermogravimetric analysis (MFB-TGA) was developed based on the real-time measurement with precision of 0.1 mg mass, 0.1°C temperature, and 0.01 kPa pressure. In this study, we preliminarily applied the MFB-TGA in evaluating catalytic combustion of petroleum coke with respect to deducing Fe2O3 catalytic mechanism, lattice oxygen migration pathway, and apparent combustion kinetics. The measurement stability of MFB-TGA was impacted by various factors, such as inhomogeneous temperature distribution and slight gas disturbance. Even char combustion heat could destabilize the weight signal by inducing vigorous particle collisions. The lightweight design and several structural optimizations were implemented to improve the MFB-TGA performance with the result of realizing smooth weight loss curves with 0.1 mg errors during the entire experiment. The experimental analysis revealed that the catalytic mechanism of hematite was identified as CO homogeneous catalysis. Hematite accelerated the char combustion rate by intensifying the driving force of bulk oxygen diffusion to the carbon surface. It served as an oxygen carrier, transferring lattice oxygen to oxidize carbon monoxide surrounding char particles. The apparent intrinsic kinetics of 33.73 kJ/mol was determined by the isothermal differential approach, which was lower than the published results measured in regular TGA. The zero-order model exhibited an excellent linear correlation in describing combustion behaviors based on a function fitting process. The MFB-TGA had the potential for extensive application by providing a reliable and straightforward method in characterizing gas–solid reactions under a fluidization state.