Abstract
ThermoCatalytic Decomposition of methane (TCD) is studied as a method to convert natural gas into hydrogen and functional carbon. In these processes the carbon typically formed on top of a catalyst phase leading to particle growth. Therefore, the development of a particle growth model is necessary to understand the limitations of thermocatalytic decomposition of methane and to assess optimal parameters and process conditions. In this paper, a particle growth model is presented to describe the growth of functional carbon on the catalyst particle. This coupled model requires kinetic equations and information on deactivation rates which have been studied from literature. The morphology of the particle changes due to carbon formation, which leads to eventual deactivation. Therefore, these kinetic expressions are coupled to a particle growth model based on the analogy with the growth of particles in polyolefin production. To combine the effects of particle growth, kinetics, and internal heat and mass transfer, the Multi-Grain Model (MGM) was used. Results confirm that with the currently available catalysts the carbon yield is not affected by heat and mass transfer limitations, however, with the availability of more active catalysts these limitations will become important. Temperature, however, has a significant role in that it regulates the kinetic rate and thus growth rate, which in turn influences the catalyst deactivation. The optimum temperature for the production of nano-carbon, within a reasonable process time, therefore sensitively depends on the choice of catalyst. • Development of a particle growth model for Thermocatalytic decomposition of methane. • Combined mass/heat transfer, kinetics and particle growth using a multi-grain model. • Assessment of transfer limitations and temperature using available kinetic models.
Highlights
Hydrogen can be produced through different processes from different feedstocks, such as steam methane reforming, water splitting, and thermocatalytic decomposition of methane
A Multi-Grain Model has been developed to model the heat and mass transfer inside macroparticles coupled with the decomposition reaction of methane
The reaction rate model and deactivation factor from Amin [7] are used, the model is suitable for the use of other kinetic models which can be accommodated
Summary
Hydrogen can be produced through different processes from different feedstocks, such as steam methane reforming, water splitting, and thermocatalytic decomposition of methane. For a rational reactor and process design, modeling and experimental studies can provide the required understanding and basic data for this This understanding facilitates identification of optimal process conditions for maximum carbon nanomaterial production. Modeling of the catalyst performance as function of equivalent process time is critical for understanding and predicting the product and catalyst evolution in the reactor This performance can be expressed with the ratio of the mass of produced carbon to the mass of fresh catalyst used, called carbon yield (Eq (2)) and the change in catalyst particle size and density. The model couples different phenomena involved inside the catalyst particle (which is called macroparticle in this study) such as heat and mass transfer and chemical reaction.
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