Hydroesterification of crambe oil (Crambe abyssinica H.) under pressurized conditions

In this study the continuous production of esters from the hydroesterification (hydrolysis followed by esterification in two-step) of crambe oil was performed under pressurized conditions without a catalyst. For this purpose the effects of experimental variables were evaluated aiming to maximize the formation of free fatty acids (FFA) in the hydrolysis and the ester content in the esterification, keeping the pressure fixed at 15 MPa. Transesterification was also performed for comparative purposes. The results indicate that the combination of high temperature and the addition of a cosolvent (n-hexane), for a low oil to water mass ratio, favors the FFA formation. The kinetics reaction is fast and optimal conditions for the hydrolysis were identified as: temperature of 320 °C, water to oil mass ratio of 1:1, 75% of cosolvent and reaction time of 14 min. In the esterification step, increasing the temperature and molar ratio has a considerable effect and favors the FFA conversion and esters content for a residence time of ≤20 min, after which the thermodynamic equilibrium of the reaction was reached. The hydroesterification provided a higher esters content (∼98%) compared to transesterification (∼89%).