Kinetic aspects in the selectivity of deep hydrogenation of 2-ethylanthraquinone overPd/SiO2

The liquid phase hydrogenation of 2-ethylanthraquinone (eAQ) was carried out in a slurry reactor in the presence ofPd/SiO2 catalyst at atmospheric pressure of hydrogen in temperature range 18–62°C. 2-ethylanthrahydroquinone (eAQH2) was initially formed with a selectivity close to 100%. In the further process termed ‘deep hydrogenation’ 2-ethyltetrahydroanthraquinone (H4eAQ) was formed as the main product. eAQH2 was also partly converted into other products, which were chromatographically separated and partly identified. A plausible reaction pattern including competitive (hydrogenation and hydrogenolysis) as well as consecutive reactions is postulated. Depending on the catalyst amount, grain size and temperature, deep hydrogenation was controlled by chemical reaction, internal diffusion or external mass transport processes. The influence of such different reaction regimes on the course of reaction and especially the yield of H4eAQ has been discussed on the basis of the proposed reaction pattern. The highest yield of H4eAQ was observed when reaction kinetics was controlled by external mass transport processes.