| Abstract
| - Natural fatty alcohols are one of the major oleochemicals and can be produced by catalytichydrogenation of fatty acid methyl esters. In the commercial multiphase process, the hydrogenavailability to the solid catalyst limits the reaction rate. By adding propane to the reactionmixture, we can utilize the unique properties of supercritical fluids, properties between those ofgases and liquids. Using propane, a substantially homogeneous supercritical phase is created,whereby hydrogen has complete access to the solid catalyst. At high substrate concentrations,a rapid fall of the reaction rate was observed, and the benefits of the propane addition werecompletely lost. This fall depends on a split of the supercritical reaction mixture into two phases(a substrate-rich and a hydrogen-rich phase). If this phase split occurred using small catalystparticles (≤32 μm), the pressure drop over the catalyst bed increased sharply because the formedliquid droplets blocked the void space in the porous catalyst bed. These two phenomena wereused to deduce the product and substrate solubility in the reaction mixture. The product showedthe most unfavorable solubility which increased with higher pressure. Under our processconditions (150 bar, 280 °C, and 11 mol % hydrogen), a single phase was observed up to 2 mol% (i.e., 15% by mass) product. Besides the minimum pressure in the catalyst bed, substratetransport limitation could be shown to be an important factor in process optimization. Therefore,egg-shell catalysts or fine catalyst particles (100−300 μm) should preferably be used in thecontinuous supercritical reactors.
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