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Tauer, Georg ; Schmitt, Julia ; Kern, Christoph ; Jess, Andreas:
TransientCO2 methanation on a nickel catalyst.
2018
Veranstaltung: Jahrestreffen Reaktionstechnik 2018
, 07.-09.05.2018
, Würzburg.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
,
Poster
)
Abstract
Considering the worlds growing energy consumption the limitation of fossil energy and their market share (approx. 86 % in 2015) [1] it is necessary to develop new strategies to substitute these energy sources [2]. Furthermore, burning of coal, natural gas or crude oil leads to an increase in atmospheric greenhouse gas emission, namely carbon dioxide. Renewable energies, i.e. wind and solar power, biomass as well as hydropower are widely viewed as CO2 neutral alternative energy sources for the future. However, renewables still have – to the present day – the drawback of highly fluctuating energy generation combined with no long term and large capacity electricity storage [3]. For storing surplus energy, the Power-to-gas concept is a promising technology [4]. Here hydrogen and carbon dioxide play the key role. By electrolysis of water using renewable energy, hydrogen is produced. However, storage and transport of compressed or liquefied hydrogen is expensive. Thus, the formation of methane using hydrogen and carbon dioxide is much more convenient because it is easier to handle and the infrastructure for methane (natural gas) transport and storage is already in place. This process is well-known as the Sabatier reaction where methane catalytically forms according to the following reaction:
CO2 (g) + 4 H2 (g) → CH4 (g) + 2 H2O (g), ΔHR° = -165 kJ/mol.
An attractive source for CO2 biogas with an amount of 25-55 vol.-% CO2 seems attractive. Hereby, excess electricity can be stored, and biogas can be refined to synthetic natural gas (SNG) [5]. Since the Sabatier reaction is highly exothermic, temperature control is required to avoid thermal runaway at high conversion.
Because of the fluctuating surplus energy and hence a fluctuating production of renewable hydrogen, a transient operation of the methanation reactor is desirable to minimize hydrogen storage [6]. Therefore it is necessary to develop a transient kinetic model. In this contribution an already developed steady-state model is proved on its transient suitability.
Therefore a step-change of the H2-, CO-2 and H2O- concentrations was realized and the adjustment of the methane formation was observed. The investigations aim is to figure out the influence thereof on the reaction rate. At 220°C a reference composition (40 % H2, 10 % CO2, 50 % N2) was set and the share of the components is altered to
H2: 0-80 %; CO2 0-20 %; H2O: 0-20 %; rest N2 and backwards. For the temperature influence between 180°C - 220°C were executed in 20 K increments.
These results combined with an already existing steady-state kinetic model are fundamental for modeling a wall-cooled fixed bed reactor in a non-steady-state methanisation process.