The role of carbon in oil refining
Edible oil refining involves several sequential steps: degumming, neutralisation, bleaching, deodorisation, and sometimes fractionation. Activated carbon is used in the bleaching step — to remove colour compounds, residual soaps, trace metals, and oxidation products that would otherwise affect the colour, flavour, and shelf life of the final product.
The bleaching step typically involves activated carbon and bleaching earth used together. Bleaching earth removes chlorophyll and carotenoids; activated carbon targets darker, more stubborn colour compounds — polycyclic aromatic hydrocarbons, oxidised fatty acids, and dark pigments — that bleaching earth alone cannot remove.
Which oils benefit from carbon treatment?
- Palm oil — dark carotenoids and oxidation products in crude palm
- Rice bran oil — high colour and wax content requiring intensive treatment
- Sunflower and rapeseed — primarily for polycyclic aromatic hydrocarbon removal
- Coconut oil — colour and flavour polishing for food-grade applications
- Used cooking oil for biodiesel — heavy colour bodies and contamination
Rajindra’s AC 200E and AC 325E grades are purpose-developed for edible oil applications — water-washed to remove impurities, with pH adjusted to avoid affecting the oil’s acid value.
Key specification requirements
For edible oil applications, the carbon must be food-contact certified and low in ash and heavy metals. Acid washing is important for oil processing — uncontrolled ash can introduce metals that catalyse oxidation and reduce shelf life. The carbon’s particle size (mesh) is also important for filtration efficiency — finer grades provide better contact but are harder to remove; coarser grades filter more cleanly but may leave colour compounds behind.
PAC vs GAC in oil processing
Powdered carbon (PAC or PAC with bleaching earth) dominates edible oil treatment because the small particle size maximises surface contact with the viscous oil. After contact time, the carbon is removed by pressure filtration. GAC has limited applicability in oil refining because of the difficulty of achieving adequate contact between the viscous oil and a packed bed.