Kinetic and Regenerator Modeling of Coke Combustion in The Moving Bed MTP Process

Significance Statement

There is intensive research on studying methanol-to-hydrocarbons process from both academia and industry. This undivided attention can solely be attributed to the fact that the process has for a long time been seen to possess potential for developing alternative energy to fuels and petrochemicals. In this methanol-to-hydrocarbons reaction, product distribution defers with catalyst type and reaction conditions. The medium pore zeolite ZSM-5 possesses high resistance to coke and high propylene selectivity, which facilitates a specific technology targeting propylene: methanol to propylene. This methanol-to-propylene process guarantees continuous operation through switching the reaction-regeneration status of three fixed bed reactors which in return complicates the operating mode. Moreover, the catalyst performance experiences an induction period and a decreasing period in each reaction-regeneration cycle. The presence of such demerits motivate the need for such a study. Furthermore, in reference to previous studies on methanol-to- propylene reaction mechanism and kinetics, minimal research on the regeneration of ZSM-5 catalyst has been undertaken.
Zuwei Liao and colleagues, from the State Key Laboratory of Chemical Engineering, at Zhejiang University in China introduced the moving bed regenerator concept to the regeneration of ZSM-5 catalyst in the methanol-to-propylene process. They hoped to advance a coke combustion kinetic model that considers the effect of coke content and oxygen partial pressures. Their research work is now published in the peer-reviewed journal, Chemical Engineering Research and Design.
To begin with, the regeneration kinetics of the coked catalyst obtained under the reaction conditions of moving bed methanol-to-propylene process were carried out under varying temperature and oxygen content. The researchers then applied the resulting kinetic model in the modeling and optimizing of an industrial scale moving bed regenerator. More so, the team advanced two novel regeneration modes so as to intensify the advantages of the methanol-to- propylene process.
The authors of the paper made a crucial observation in that the ‘multi-zone’ operation was seen to increase the coke conversion as well as decrease the regeneration gas requirements. They also noted that the ‘flow direction changing’ operation mode enhanced the coke content uniformity of reactivated catalyst which in return favored the performance of the reactor.
Using the proposed kinetic model and the moving bed regenerator model, the regeneration process has been simulated. A coke combustion kinetic model has been obtained by considering the effect of coke content and oxygen pressure. Then a moving bed regenerator model is proposed, implying a radial cross flow between catalyst and regeneration gas. Results from the two simulations have also been compared with conventional data and proven better regeneration of the catalyst. A ‘reversal phenomena’ has been observed both in the temperature and coke distribution in the regenerator. A multi zone and a flow direction changing operation mode have been advanced thus making the whole regeneration process more effective.

Reference

Binbo Jiang, Bingjie Zhou, Yuntao Jiang, Xiang Feng, Zuwei Liao, Zhengliang Huang, Jingdai Wang, Yongrong Yang. Kinetic and regenerator modeling of the coke combustion in the moving bed MTP process. chemical engineering research and design volume 122(2017) pages 52–62.

 

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