Fractionation of Trans from Partially Hydrogenated Soybean Oil Fatty Acids

A multi-stage, low temperature solvent fractional crystallization process was developed in this work for the removal of trans fatty acids (TFA) and saturated fatty acids in free fatty acids (FFAs) obtained from hydrolysis of partially hydrogenated soybean oil (PHSO). The effects of host solvents, concentration of FAs, crystallization temperature and time on separation of TFA and SFA were studied. Among all the three solvents examined namely acetone, hexane and ethanol, acetone proved to be promising solvent. By employing acetone as a solvent TFA can be reduced to 11.6% from an initial content of 19.5% and SFA can be drop down to 3% from an initial content of 20%, by applying stepwise crystallization temperatures from 5ºC to -20ºC. Crystallization temperatures lower than -30ºC such as -35ºC and -40ºC can further lower the TFA content in liquid fraction down to 5-8% by employing acetone as a solvent. TFA content can be reduced down to 12.2% and 14%; and SFA content could be reduced to 3.3% and 3.1% from an initial content of 20% when hexane and ethanol were employed as solvents, respectively. Optimum FAs to solvent ratio was 1:5 (w/v) and with a time period of 12 h for each step of crystallization. The crystallization behavior of TFA strongly depends on the type of solvents employed and crystallization temperature, while SFA crystallization depends mostly upon temperature rather than nature of solvent. Even though total removal of TFA could not be achieved in the present study, a road map has been developed for a fractionation of TFA and SFA from partially hydrogenated oil FFAs.