Integrated CO2 capture and methanation

Details

Supervisors

De Wilde, Juray

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

enThis thesis investigates integrated CO₂ capture and methanation (ICCM), a process concept in which CO₂ adsorption and catalytic hydrogenation are carried out sequentially on the same dual-function material (DFM), eliminating the intermediate steps that burden conventional Power-to-Methane chains. Both constituent functions are characterised independently on a Ni/Al₂O₃–MgO DFM before drawing the implications for the integrated process. The methanation kinetics are studied in a micro-fixed bed reactor under steady-state conditions. Four Langmuir–Hinshelwood–Hougen–Watson mechanisms are derived and discriminated against the experimental dataset. A hybrid associative–dissociative route, in which CO₂ undergoes molecular pre-adsorption on basic surface sites followed by hydrogen-assisted C–O bond cleavage at the Ni surface, is selected as the reference kinetic model. The estimated parameters are consistent with the surface chemistry expected from the MgO-rich support and provide a quantitative rationalisation of the strong temperature dependence of CH₄/CO selectivity. The CO₂ adsorption behaviour of the same material is characterised by pulse injection experiments. The measured capacity decreases monotonically with temperature, consistent with the exothermic character of CO₂ chemisorption on MgO basic sites. A one-dimensional transient fixed-bed model reproduces the outlet pulse sequences and reveals that the catalyst bed remains only partially saturated under the experimental conditions, a result of direct relevance for the sizing of the adsorption step in an ICCM cycle. Both campaigns reveal a fundamental thermal mismatch between the adsorption and catalytic functions of the material: significant CO₂ uptake is confined to temperatures well below the range required for catalytic activity, confirming that capture and conversion must operate in distinct, sequential half-cycles. This constraint constitutes the primary design variable for ICCM systems based on this class of DFM, and the kinetic descriptions developed in this work provide the quantitative foundation needed to inform the rational design of such cycles.