Deoxygenation and cracking of free fatty acids over acidic catalysts by single step conversion for the production of diesel fuel and fuel blends

Abstract

Gas phase deoxygenation of oleic acid was accomplished over palladium containing acidic catalysts under solvent-free conditions. Aluminum oxide catalysts were prepared out of three different boehmite precursors by calcination at different temperatures between 500°C and 1100°C forming different aluminum oxide phases. All catalysts were impregnated with 1wt.% palladium and subsequently tested for their deoxygenation performance either batch wise in autoclaves or continuously in a fixed bed plug flow reactor or in a trickle bed reactor. Conversion of oleic acid and selectivity to the desired diesel-like C17 hydrocarbons heptadecane and heptadecenes were studied with the best aluminum oxide found in the catalyst screening at different reaction temperatures, catalyst amounts and palladium amounts on the catalyst. Using boehmite found as best alumina precursor, different mixtures of such aluminum oxide with zeolites were prepared in order to increase the catalyst acidity and thus the deoxygenation performance. The optimum reaction conditions found for aluminum oxide catalysts were applied for the screening of these composite catalysts. Using the best composite catalyst, the effect of hydrogen dilution with nitrogen, the addition of water and catalyst regeneration by thermal treatment was tested. In addition catalyst containing silica aluminates doped with 1wt.-% Pd were prepared and tested for their catalytic activity in deoxygenation and cracking of free fatty acids. Some reactions were conducted under elevated hydrogen pressure. The catalysts were characterized by nitrogen adsorption isotherms (BET), temperature programmed desorption of ammonia (TPD), X-ray powder diffraction (XRD), thermo gravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM).