Boudouard reaction accompanied by graphitization of wrinkled carbon layers in coke gasification: A theoretical insight into the classical understanding

The carbon dioxide gasification mechanism of coke was investigated by combining a particulate coke reaction experiment and theoretical calculations. Characterization results obtained via X-ray diffraction and X-ray photoelectron spectroscopy showed that the increase of graphitic carbon proportion, that is, a graphitization process, led to a decrease in the strength of the coke residue. Molecular dynamics simulations based on a reactive force field corresponded closely to the experimental characterization results. From this, the main formation path of carbon monoxide was identified to be accompanied by the reconstruction of carbon matrix. It is confirmed that defects on the carbon layer acted as key intermediates in the layer reconstruction and flattening. The energy and potential barrier of the obtained elementary reactions were determined by means of density functional theory. The highest potential barrier of the carbon layer oxidation by carbon dioxide molecules indicated that it was the rate-controlling step of the coke gasification process. Moreover, compared with the other carbon atoms, those with large wrinkle degree were likely to react with carbon dioxide to form a flat carbon layer. This work explains why different coke samples have significantly different activation energies for the carbon dioxide gasification reaction. Furthermore, the essential relationship between the coke strength and the gasification reaction is established, thereby providing theoretical support for improved utilization of coke in a blast furnace.

Automated summary

The carbon dioxide gasification mechanism of coke was investigated by combining experimental and theoretical methods, revealing that the increase of graphitic carbon proportion led to a decrease in coke strength and defects on the carbon layer played a key role in layer reconstruction and flattening. The oxidation of the carbon layer by carbon dioxide molecules was identified as the rate-controlling step of the coke gasification process.