Supercritical methanol process of modifying oil byproduct for concentrating natural tocopherols

The distillate from the oil deodorizer unit, which is known as deodorizer distillate (DOD), is a type of byproduct from the soybean oil refining process; it is rich in high-value compounds, such as natural tocopherols (vitamin E) and sterols. Generally, DOD is a very complex system, and the DOD must be modified before the tocopherols can be concentrated. As the conventional pretreatment, methyl esterification and methanolysis are conducted separately with different catalysts, which converts most of the fatty acids and glycerides to fatty acid methyl esters (FAMEs). Such processes cause many problems, such as high energy consumption, long operating time, and large amounts of wastewater. Therefore, in this work, we have attempted to use a pretreatment method that involves supercritical methanol (SC-MeOH) without any catalyst. The batch experimental results show that the SC-MeOH process leads to more FAMEs and sterols than those with conventional pretreatment; moreover, there is no damage to the tocopherols at high temperature and pressure (573 K, 20.1 MPa) for relatively long periods (30-45 min) and with a sufficient amount of methanol present (4/2 DOD, v/v). In addition, the phase behavior for the methanol/modified DOD system was investigated at temperatures of 523-598 K and pressures of 8.2-24.5 MPa. Based on experiments and comparison, a SC-MeOH process for modifying DOD is presented.