Catalysis of Organic..

422 Production of Biodiesel10080Selectivity (mol%)604020Stearic acid (SA)HeptadecaneUnsaturated Et-SAΣC17-productsBy-products00 10 20 30 40 50 60 70Ethyl stearate conversion (%)Figure 6. Product selectivity versus ethyl stearate conversion for the non-pretreatedcatalyst in the deoxygenation of ethyl stearate. Reaction conditions: 5 mol% ethylstearate in hexadecane, T=270 ˚C, p=1 bar, m cat =0.4 g and V’=0.1 ml/minThe mass of catalyst was varied in order to achieve higher conversions andinvestigate diffusion limitations (Figure 7). The experiments over 0.2 g of catalyst at270˚C (residence time: 4 min) gave an initial conversion of 16% while doubling themass of catalyst (residence time: 8.2 min) the initial conversion increased to 23%. Athree time increased catalyst mass (0.6 g, residence time: 12 min) converted 58% ofethyl stearate, however the catalyst was rapidly deactivated within 10 minutes fromthe initial conversion of 58% to 32% of conversion. The non-linear relationshipbetween the catalyst mass and the initial conversion gave additional indication thatthe catalyst bed was partially deactivated, thus concluding that mechanistic studies ofthe initial rates should take into account the very fast deactivation. Experimentscarried out with different catalyst masses at 300˚C showed similar tendencies, thehigher catalyst mass, 0.6 g, deactivated more rapidly then 0.4 g of catalyst. Thedeactivation could be caused by coke formation, the concept which is alsostrengthened by the observed loss of initial surface area, however, the similardecrease of surface area for the three catalyst mass does not explain the non-lineartrend appearing. Thus, concluding that the deactivation is additionally affected bycatalyst poisoning and/or sintering. Furthermore reproducibility was proven to begood by repeating the experiment over 0.4 g of catalyst at 270˚C. The completeconversion of ethyl stearate was achieved over 0.6 g of catalyst with the volumetricflow of 0.07 ml/min (residence time: 17.2 min) at 270˚C and at 300˚C over 0.6 g ofcatalyst. The effect of catalyst mass on conversion and selectivity is shown in Figure7.