Cracking of a rapeseed vegetable oil under realistic FCC conditions
A rapeseed vegetable oil, pure and blended with conventional FCC feedstock, has been catalytically cracked with a commercial equilibrium catalyst under realistic FCC conditions. The rapeseed oil can be converted into gasoline- and diesel-range hydrocarbons that are low in sulfur and nitrogen. The triglycerides are predominately converted within 50 ms at 485–585 °C into fatty acids through radical cracking reactions. Relatively high amounts of coke are formed. The high aromatisation rate of the fatty acids causes the formation of large amounts of aromatics of up to 30–40 wt.% in the gasoline fraction. Due to the high aromaticity the product is hardly subject to serial cracking reactions and the lower olefins yield (C3 and C4) remains low. The rate of aromatisation is highly dependent on the olefinicity of the fatty acid and the reaction temperature. The catalytic conversion of the carbon–carbon bond saturated stearic acid results in a higher gasoline yield (57 wt.% versus 34 wt.% for the rapeseed oil) with a much lower aromaticity (13 wt.% in gasoline versus 32 wt.% in gasoline for the rapeseed oil). Due to the lower aromaticity the serial cracking reactions to the lower olefins are much better (7 wt.% C3 and 7 wt.% C4). In all cases, the oxygen from the fatty acids is evolved predominantly as water. Other oxygenates have not been observed in significant quantities.