Palm oil is the world's second largest edible vegetable oil, and it plays an extremely important role in cooking and food manufacturing. However, crude palm oil contains many colloidal impurities, pigments, and odorous substances that can impact both its quality and safety. Some of these substances are harmful to people's health, and to ensure its suitability for consumption, crude palm oil undergoes a rigorous refining process.
The palm oil purification process
The typical refining process of palm oil is physical refining. The main process flow is: crude palm oil→degumming→deacidification→decolorization→deodorization→refined palm oil. The purpose of palm oil refining is to remove various impurities in crude palm oil. After deodorization, the impurities in the crude palm oil are removed and refined palm oil can be obtained.
Palm oil decolorization
Among them, decolorization is the most important part of palm oil refining process, and it is also a key factor in determining palm oil refining cost and quality. At present, for the most effective method of palm oil decolorization method, activated carbon and activated clay are commonly used together to promote decolorization and purify oil. Activated carbon can effectively remove polycyclic aromatic hydrocarbons of macromolecules that cannot be adsorbed by clay (while the deodorization process, activated clay can only remove polycyclic aromatic hydrocarbons containing 4 or less low molecular weight). Activated carbon has a particularly strong adsorption effect on polycyclic aromatic hydrocarbons. Even if the activated carbon filter cake is pressed, the filtered oil does not contain polycyclic aromatic hydrocarbons.
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Activated carbon's superior adsorption properties ensure that even after filtration, the refined oil remains free from harmful polycyclic aromatic hydrocarbons. This dual approach of using activated carbon and activated clay enhances the overall purification process of palm oil, meeting stringent quality standards for consumption.
Glycidyl fatty acid esters removal
Beyond decolorization and PAH removal, a growing concern in the palm oil industry is the presence of glycidyl fatty acid esters (GEs), which are process contaminants formed during high-temperature refining. GEs can hydrolyze into glycidol, a compound classified as a probable carcinogen, making their control a critical quality and food-safety priority.
Based on our field experience, palm oil after conventional refining typically carries GE levels in the range of 3–4 mg/kg. When treated with activated carbon under optimized conditions, the GE content can be reduced to as low as 0.15–0.2 mg/kg—a reduction of over 90%—bringing the oil well within current regulatory thresholds and buyer specifications.
Through repeated trials, we have identified the following window as the most effective for GE removal:
Activated carbon-to-oil ratio: 2–3% (w/w)
Contact temperature: 85–90 °C
Filtration: Use a screen mesh smaller than half the average particle size of the lower-layer activated carbon to prevent carry-over into the finished oil.
For best results in GE removal, we recommend walnut-shell-based or apricot-shell-based powdered activated carbon. These raw materials yield a highly developed mesoporous structure that is especially effective at trapping the larger GE molecules while maintaining the decolorization performance you already rely on.
Conclusion
Southeast Asian countries lead global palm oil production, driving significant demand for decolorizing agents such as activated clay and activated carbon in the refining industry. This sector imports nearly 3.6 million tons annually to purify palm oil, ensuring compliance with safety and quality standards. Zhulin activated carbon plays a pivotal role in this process, guaranteeing effective decolorization and purification. For more information on how Zhulin carbon enhances palm oil refining, please contact us today.
