Hydrogen production by methane decomposition : catalyst design and thermodynamic optimization

Abstract

The thermo-catalytic decomposition of methane (TCD) is of great interest currently as it is a green, simple technology that yields hydrogen and carbon nanomaterials. It is not associated with the emission of carbon containing molecules: CO or CO2.The necessity to globalize this decomposition stems from the necessity to decrease the massive emissions of the greenhouse gases, and thus reaches its summit nowadays. This reaction retains an endothermic nature and thus the conversion rises with any increase of the reaction temperature. Therefore, to ensure high level of hydrogen, operating at a high temperature is necessary. The hydrogen obtained from this thermal decomposition acts as a recommended substitute for fossil fuels as combusting it gives water unlike other fuels. It can be produced using numerous ways and encompasses many applications since it holds large amounts of energy. The carbon that is also produced, can take many forms and can be used in many situations that require high thermal and electrical conductivity, strength and durability. The thermal decomposition of methane is original as it reduces the production of the oxides, consequently, eluding the need for carbon dioxide removal and the water gas shift steps which are obligatory in other conventional processes. TCD is generally studied over various types of catalysts, for instance it could be mono, bi, tri-metallic combination of metals, metal oxides, or even metal-doped carbon catalysts. The deactivation of the catalyst is a frequent problem accompanying the reaction. In this report, a first part was focused on the design of catalysts for TCD reaction, for instance, iron based catalysts dispersed on a mesoporous alumina support (Fe/Al2O3) due to the numerous vital aspects it presents as well as Ni/Al2O3 catalysts used for comparison purpose. In the second part of the report, the attention was shifted to executing a detailed thermodynamic study in order to assess different factors relating to the TCD reaction. It turns out that when water and hydrazine are introduced into our system, these compounds will meddle with the equilibrium and the side reactions to minimize the amounts of the produced carbon and amplify the in hydrogen yield. Ethylene, propylene and ethanol were dealt with and each reacted in an exclusive manner with our methane feed to either influence solely the carbon or both the hydrogen and carbon formation. The three substances that were added in the simulations performed, directly dissociated contributing to initial amounts of carbon and raising the quantities of methane. Pressure is considered to be a dominant factor in the thermodynamics of methane decomposition reaction and has a noticeable effect on the methane decomposition reaction progress, in which low pressures were favored for a smooth transition from the methane to the products to be maintained.