1 Department of Chemistry, Technical University of Denmark2 Sustainable and Green Chemistry, Department of Chemistry, Technical University of Denmark
This thesis describes the catalytic conversion of bioethanol into higher value chemicals. The motivation has been the unavoidable coming depletion of the fossil resources. The thesis is focused on two ways of utilising ethanol; the steam reforming of ethanol to form hydrogen and the partial oxidation of ethanol to form acetyl compounds. The steam reforming has been covered by a literature study of the research work done so far giving an introduction to the use of ethanol as a feedstock. The partial oxidation of ethanol has been studied experimentally using gold and vanadium based heterogeneous catalysts, and two different experimental methods, namely, a batch system and a continuous flow system. In the batch reaction the process was carried out in the liquid phase using a gold catalyst and atmospheric air as the oxidant. Experiments were conducted at moderate pressures and temperatures (90-200 °C, 30-45 bar) with an aqueous solution of ethanol. It was possible to produce acetic acid in yields above 90 %. Two different support materials were investigated (MgAl2O4 and TiO2) and there did not seem to be any significant effect in changing the support. The kinetics of the reaction was also investigated and a simple kinetic model proposed, which could be fitted nicely to the experimental data. By changing the concentration of ethanol, it was possible to shift the selectivity towards ethyl acetate instead of acetic acid. However a concentration above 60 wt% was required for the ester to become the major product. In the continuous flow system, the oxidation reaction was carried out as a gas phase reaction using a vanadium based catalyst. For this series of experiments, a 50 wt% aqueous ethanol was oxidized with a diluted gas stream of O2 in helium, the reaction temperature and pressure were kept at a moderate level (175-200 °C, 2-10 bar). It was found that the reaction product could be controlled by means of the temperature and the space velocity, making it possible to shift between acetaldehyde and acetic acid as the main products. It was possible to achieve both acetaldehyde and acetic acid with selectivities above 90 % at close to full conversion. It was furthermore found that the O2/ethanol ratio was of importance for the conversion as well as the selectivity, with the conversion decreasing when the ratio was lowered.