A kinetic and statistical model for carbon deposition on Ni/Al₂O₃ catalyst in the steam methane reforming

Abstract

An experimental and statistical study was performed for the carbon deposition on Ni/Al₂O₃ catalyst in the methane steam reforming process. Carbon deposition plays a significant role in the catalyst deactivation. Thus, applying a statistical model and a kinetic rate for carbon deposition is so valuable. The central composite design (CCD) was used for the modeling of the carbon deposition process. The statistical analysis of model, as obtained from the CCD method, revealed that a polynomial equation with the F-value = 456.94, the p value < 0.0001, and the R ² = 0.9919, could appropriately predict the experimental data. Based on the established models, an increase in steam to methane ratio (S/C) caused carbon deposition sharply decreased. As pressure increased from 1.81 to 4.19 bar, carbon deposition slightly increased. When temperature varied from 540 to 600 °C, whisker carbon was produced and its activity increased with temperature. As temperature exceeded 600 °C, carbon deposition slightly increased that can be attributed to formation of pyrolytic carbon. The minimum of carbon deposition was occurred in low pressure, high S/C and at 600 °C. So, the kinetic rate of carbon deposition was suggested in these conditions using generalized reduced gradient nonlinear method. The proposed kinetic rate of methane decomposition reaction can accurately predict the experimental rate data.