Interplay between Reaction and Phase Behaviour in Carbon Dioxide Hydrogenation to Methanol

• Published in: ChemSusChem Vol. 10; no. 6; pp. 1166 - 1174
• Main Authors: Reymond, Helena, Amado‐Blanco, Victor, Lauper, Andreas, Rudolf von Rohr, Philipp
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 22-03-2017
• Subjects: Aluminum Oxide - chemistry; Behavior; Carbon dioxide; Carbon Dioxide - chemistry; Catalysis; Catalysts; Copper - chemistry; heterogeneous catalysis; high pressure; Hydrogenation; Methanol - chemistry; Methyl alcohol; Optimization; raman spectroscopy; Reaction kinetics; Selectivity; Transition Temperature; Zinc - chemistry; raman spectroscopy; carbon dioxide; heterogeneous catalysis; hydrogenation; high pressure
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201601361

Condensation promotes CO2 hydrogenation to CH3OH beyond equilibrium through in situ product separation. Although primordial for catalyst and reactor design, triggering conditions as well as the impact on sub‐equilibrium reaction behaviour remain unclear. Herein we used an in‐house designed micro‐view‐cell to gain chemical and physical insights into reaction and phase behaviour under high‐pressure conditions over a commercial Cu/ZnO/Al2O3 catalyst. Raman microscopy and video monitoring, combined with online gas chromatography analysis, allowed the complete characterisation of the reaction bulk up to 450 bar (1 bar=0.1 MPa) and 350 °C. Dew points of typical effluent streams related to a parametric study suggest that the improving reaction performance and reverting selectivities observed from 230 °C strongly correlate with (i) a regime transition from kinetic to thermodynamic, and (ii) a phase transition from a single supercritical to a biphasic reaction mixture. Our results advance a rationale behind transitioning CH3OH selectivities for an improved understanding of CO2 hydrogenation under high pressure.
Finding the balance: A parametric study of the hydrogenation of CO2 to CH3OH is performed to assess the dependence of reaction performance on a broad range of operating conditions over a commercial Cu‐based catalyst. The beneficial effects of high pressure, temperature and prolonged contact times on CO2 conversion are confirmed. Phase separation as a function of operating pressure and temperature, as well as of extent of reaction, is also demonstrated. Reaction conditions should hence combine kinetic optimum with phase optimum for the reaction performance to profit from a synergistic effect.