A numerical investigation of methane pyrolysis in a molten catalyst Bath–A single bubble approach

Abstract

A dynamic one-dimensional numerical model of methane pyrolysis within a rising and pyrolysing bubble in a column of molten Ni0.27Bi0.73, as a molten catalyst, is presented. The model predicts both the behavior of the rising bubble in the column and the chemical reactions within it, accounting for any variations in bubble diameter and rising velocity, which have previously been assumed to be constant. The conservation equations of energy, mass and momentum are solved simultaneously using the implicit Gauss–Seidel numerical method. The model accounts for the main parameters contributing to the methane pyrolysis reaction. The reliability of the model was assessed by comparison with the available experimental data from the literature and a reasonable agreement was found. Considering the model assumptions, the results show that, for the assessed conditions, more than 97% of the overall conversion occurs at the interface of the bubble and the molten bath, while the reaction within the bubble contributes only <3% of the overall conversion. A sensitivity analysis was also undertaken to the variations in the bubble size, column height, molten bath temperature, pressure, gas composition and temperature. Calculations show that methane conversion is more sensitive to the molten bath temperature than the initial gas temperature. Furthermore, it decreases significantly with any increase in pressure. Also, at pressures of > 2 MPa, the equilibrium condition is achieved within the bottom one-third of the column for the assessed conditions.