Modelling a kinetic deviation of the magnesium hydrogenation reaction at conditions close to equilibrium

Marcus Adams,David M Grant,Alastair Stuart,Gavin S Walker

doi:10.1016/j.ijhydene.2019.04.036

Marcus Adams, David M Grant + Show 2 more

Open Access

https://doi.org/10.1016/j.ijhydene.2019.04.036

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Abstract

A model has been derived for the magnesium hydrogenation reaction at conditions close to equilibrium. The reaction mechanism involves an adsorption element, where the model is an extension of the Langmuir adsorption model. The concept of site availability (σs) is introduced, whereby it has the capability to reduce the reaction rate. To improve representation of σs, an adaptable semi-empirical equation has been developed. Supplement to the surface reaction, a rate equation has been derived considering resistance effects. It was found that close to equilibrium, surface resistance dominated the reaction.

Highlights

Research efforts to store surplus energy for concentrated solar power (CSP) plants have looked beyond latent heat technologies, to a potentially cheaper and more effective technology, thermochemical energy storage (TCES). [1,2], A potential TCES system is based on utilising the enthalpy of reaction of a reversible metal hydride reaction, where metal hydrides are selected based on several governing factors, such as operating temperature, enthalpy of reaction, plateau pressure and cost
Many hydrides have been identified for a TCES system, in part due to their versatility, for example combining magnesium with a transition metal such as nickel or iron enables the tuning of the operating temperatures at a reasonable cost [3]
At conditions close to equilibrium, the analysis suggests that the reaction is surface resistance dominating with a reaction order of 5/3

Summary

Introduction

Research efforts to store surplus energy for concentrated solar power (CSP) plants have looked beyond latent heat technologies, to a potentially cheaper and more effective technology, thermochemical energy storage (TCES). [1,2], A potential TCES system is based on utilising the enthalpy of reaction of a reversible metal hydride reaction, where metal hydrides are selected based on several governing factors, such as operating temperature, enthalpy of reaction, plateau pressure and cost. [1,2], A potential TCES system is based on utilising the enthalpy of reaction of a reversible metal hydride reaction, where metal hydrides are selected based on several governing factors, such as operating temperature, enthalpy of reaction, plateau pressure and cost. Many hydrides have been identified for a TCES system, in part due to their versatility, for example combining magnesium with a transition metal such as nickel or iron enables the tuning of the operating temperatures at a reasonable cost [3]. A key challenge with the design of this system are the reaction kinetics, where sufficient understanding is needed to facilitate an efficient energy store [2]. This paper focuses on the kinetics, the hydrogenation reaction

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