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Scientific Hydrogenation at Supercritical Single-Phase Conditions BackgroundMany common hydrogenation reactions involve gaseous hydrogen, a liquid substrate (or substrate solution), and a solid catalyst. In such systems the hydrogen concentration at the catalyst surface is crucial for rate and selectivity of the reaction. Hydrogen, however, is poorly soluble in liquids, there is a considerable transport resistance between the gas phase and the bulk liquid. Furthermore, there is also a transport resistance between the bulk liquid and the catalyst. Both factors limit the hydrogen concentration at the catalyst surface and consequently the reaction rate. This can also lead to unwanted side reactions like isomerization. For instance, in the food industry, the partial hardening of edible oils suffers from the formation of unwanted trans-fatty acids due to hydrogen deficiency at the catalyst surface. Supercritical fluids combine in a very favourable way gas and liquid properties - they have a low viscosity, low surface tension and high diffusivity. By addition of a suitable solvent a single-phase system with hydrogen, substrate and the solvent can be created. In this way the transport resistance between gas and liquid is eliminated. Even the resistance at the catalyst surface is reduced [1, 2]. Projects In our studies we have investigated the hydrogenation of palm oil and rape seed oil for food use[3], the hydrogenation of fatty acid methyl esters to fatty alcohols to be used as surfactants[4] and the removal of polyaromatic hydrocarbons (PAH), chlorine and sulphur from lubricant oil for cars. Propane or dimethylether have been used to create the single-phase conditions. The results are summarised below:
For an extensive description of the projects go to C=C in triglycerides, fatty alcohol or Pilotplant References [1] Härröd, M., van den Hark, S., Macher, M.-B., Møller, P. (2001), In High Pressure Process Technology: Fundamentals and Applications (eds Bertucco and Vetter) Elsevier, p 496-508. [2] Härröd, M., Møller, P. (1994) European Patent EP 0 791 041 B1. [3] Macher M.-B. (2001) Ph.D. Thesis, Chalmers Univ. of Technology, Göteborg, Sweden [4] van den Hark, S. (2000) Ph.D. Thesis, Chalmers Univ. of Technology, Göteborg, Sweden For an extensive list of references from the persons in Härröd Research, go to References Page maintained by svh@harrod-research.se Updated: 2002-10-17 |