(461e) Catalytic Conversion of Carbon Dioxide with Solar Hydrogen Under Supercritical Conditions

Energy storage technologies are of great interest at the present time. Excess electricity generated from wind parks and/or photovoltaic can be used to produce so called solar-hydrogen via electrolysis of water. This offers a high potential for the chemical storage of energy [1]. The solar-hydrogen can be converted with carbon dioxide to many different hydrogenation products, such as methane, methanol, dimethyl ether or hydrocarbons [2].

A favorable hydrogenation product and subject of current research is methanol. Compared with hydrogen the liquid state of methanol allows an easy storage and transportation. Methanol has excellent combustion properties making it suitable as fuel for combustion engines [3]. Furthermore, methanol can be used as commodity chemical in the chemical industry or as feedstock for intermediates such as formaldehyde, MTBE or acetic acid.

In this contribution a process for the carbon dioxide hydrogenation under supercritical conditions will be presented. Herein, the reaction equilibrium is shifted to the product side and high space-time-yields and therefore low investment costs could be achieved.

Experimental

Cu/ZnO/Al₂O₃-catalysts were used for the hydrogenation of carbon dioxide to methanol. The catalysts were prepared by a co-precipitation method of the corresponding metal nitrates using potassium hydroxide. The performance of these catalysts was examined in dependence of the temperature. The experiments were carried out in a tubular reactor at a pressure of 150 bar and temperatures between 200 and 380 °C. The liquid phase was analyzed via GC-analysis and the gas composition via FTIR-spectroscopy.

Results

In the hydrogenation of carbon dioxide over Cu/ZnO/Al₂O₃-catalysts methanol is the main product. In dependence of temperature the methanol yield and selectivity is increasing up to 300 °C. At higher temperature methanol selectivity is decreasing as expected from thermodynamics because of endothermic reverse watergas-shift-reaction. The highest methanol yield was achieved at a temperature of 300 °C. The results are compared to a commercial available methanol-synthesis-catalyst.

At lower temperatures (<230 °C) high selectivity to methanol and high CO₂ conversion could be achieved due to phase separation. To achieve this goal a more active catalyst is needed.

References

[1] F. Ausfelder, A. Bazzanella, Chem.-Ing.-Tech. 2009, 81 (10), 1565-1573.

[2] W. Wang, S. Wang, X. Ma, Chem. Soc. Rev. 2011, 40, 3703-3727.

[3] API Report No. 4261, 1988, Alcohols and Ethers â?? A Technical Assessment of Their Application as Fuels and Fuel Components