Powdered activated carbon is an indispensable product particularly in the removal of polycyclic aromatic hydrocarbons (PAHs). A mixture of bleaching earth and powdered carbon combines the strong sides of the two substances. Bleaching earth removes soap residues, phospholipids and mucilages and these substances interfere with the working
of
activated carbon. Activated carbon, on the other hand, is perfect for adsorbing natural coloring matter and PAHs. For oils with high concentrations of contaminants, such as soap residues, phosphates and resins, it can be advisable to add the bleaching earth to the edible oil before purification with activated carbon takes place.
Boyce Carbon has developed a number of grades of
powdered activated carbonsthat have been optimized for specific contaminant removal and also filterability, responding to a demand from the market. The carbon can be added on its own or mixed with bleaching earth for the treatment of edible oils such as:
palm oil
coconut oil
sunflower oil
soybean oil
Fish oil.
Process of Decoloration
The best decoloration takes place using a ratio of 60 percent bleaching earth and 40 percent
powdered carbon. Bleaching takes place as a rule at higher temperatures (between 75-115C). This is done in a vacuum, so that the oil and the coloring matter are not able to oxidize. The dosing of the carbon/bleaching earth mixture lies between 0.5 and 1.5 percent by mass. For the removal of PAHs, the usual powdered carbon dosage is 0.25 percent by mass. For seriously contaminated edible oil, the dosing necessary may be 1.5 percent by mass. Where normal bleaching times can take twenty to thirty minutes, the process time for removing PAHs can rise to about 45 minutes. Although chemically
activated carbon gives good decoloration, the preference goes to steam activated carbon. This provides a better compromise between the desired decoloration and the unwanted oil loss in the filter cake. Steam-activated carbons are also outstanding at removing light and heavy polycyclic aromatic hydrocarbons. The Boyce Steam activated carbon is used worldwide for the bleaching of edible oils. This type offers a good compromise between the desired adsorption and the unwanted oil loss.
