Hydrogen Production via Methane Pyrolysis: Modelling of a Single Rising and Pyrolysing Methane Bubble within a Molten Catalyst Bath

Abstract

The global targets for carbon-neutral hydrogen production by 2050 demonstrate the need to develop methods to produce a low-cost, low-emission form of hydrogen. Methane pyrolysis within a molten metal bath is currently a potential technique to meet this need. Despite having great techno-economic potential, this technique has not yet been demonstrated at an industrial scale, partly because of the lack of understanding of the mechanism. Molten metals are typically opaque, corrosive, and hard to maintain and handle, especially at temperatures over 1300 K, as is needed in pyrolysis reactors. Moreover, the presence of explosive and combustible gases such as hydrogen and methane, make it technically very challenging to perform in-situ measurements. To optimise the methane pyrolysis within bubble column reactors and hence minimise the cost of their scaling up, there is a need to develop both understanding about the multi-way coupling phenomenon of methane pyrolysis in a molten bath and reliable mathematical models. The present investigation aims to meet these needs. In doing so, 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, has been developed. The model predicts both the behaviour of the rising bubble in the column and the chemical reactions within it, accounting for any variations in the bubble radius and rising velocity, which have previously been assumed to be constant. A systematic sensitivity analysis was also undertaken. The reliability of the model was assessed through comparing its predictions with the experimental data available from the literature and a reasonable agreement was found. Furthermore, the results attained from the current calculations show that for the assessed conditions, more than 97% of the overall conversion of methane occurs at the bubble-molten bath interface. Furthermore, the bubble size and rising velocity inversely influence the methane conversion.