Degumming and bleaching are the critical pre-treatment stages in physical palm oil refining. Before Crude Palm Oil (CPO) can be thermally deodorized under high vacuum, it must be cleared of gums (phosphatides), trace heavy metals, and natural carotenoid pigments. Incompletely removed impurities will char and decompose during deodorization, leading to color reversion, burnt odors, and poor shelf stability. This technical guide examines the chemical reactions, processing parameters, and filtration physics of degumming and bleaching in industrial refining.
Upstream Impurity Management
The efficiency of the degumming and bleaching steps depends entirely on the initial quality of the crude feedstock. Refiners work closely with a trusted crude palm oil supplier to obtain batches with low moisture, low iron levels, and high Deterioration of Bleachability Index (DOBI) values. Feedstock quality dictates the exact dose of acid and bleaching clay needed to yield a high-clarity output distributed by a registered RBD palm oil supplier.
📚 Upstream Milling Link
FFA and peroxide levels are established during fruit extraction at the mill site. Discover the mechanical processing sequence in our guide on the palm oil milling process.
The Physics & Chemistry of Degumming
Crude palm oil contains approximately 0.5% to 1.0% gums (phosphatides), primarily in the form of non-hydratable phosphatides. Because these compounds do not dissolve in water, they must be chemically modified to make them insoluble in oil.
In physical refining, refiners perform acid degumming (dry degumming) by heating the crude oil to 85°C–90°C and injecting food-grade phosphoric acid (85% concentration) at a ratio of 0.05% to 0.10% by weight. The acid reacts with the non-hydratable phosphatides, chelating the divalent metal ions (calcium and magnesium) that hold the gums in solution. This causes the gums to precipitate as insoluble agglomerates, which are easily absorbed by the bleaching earth in the next step. As an integrated global bulk palm oil supplier, PalmAzia maintains strict process controls to ensure complete gum precipitation.
The Bleaching Stage: Adsorption Kinetics
The degummed oil flows directly into a vacuum bleaching vessel, where it is mixed with activated bleaching earth (bentonite clay) at a concentration of 0.8% to 2.0% depending on feedstock DOBI levels. The mixture is agitated at 95°C to 105°C under a vacuum of 50 to 80 mbar for 20 to 30 minutes.
Under these conditions, several purification reactions occur simultaneously:
- Pigment Adsorption: The highly porous clay adsorbs red carotenoid pigments (carotenes) and green chlorophylls onto its active sites.
- Gum Capture: The precipitated phosphatide-phosphoric acid complex binds to the clay surfaces.
- Metal Deactivation: Heavy metals (such as iron and copper) that catalyze oxidation are chelated and trapped within the clay lattice.
- Oxidation Product Removal: Primary oxidation products (hydroperoxides) decompose and are adsorbed, preventing secondary oxidation.
This pre-treatment choice determines whether the oil can be physically or chemically refined. Learn more about alternative routes at our refined palm oil supplier comparison article.
Filtration & Separator Physics
The oil-clay slurry is pumped from the bleaching vessel into vertical leaf filters. The slurry passes through stainless steel mesh leaves, which retain the spent clay while allowing the clean, bleached palm oil (BPO) to pass through. Once a filter chamber is full of spent clay (forming a filter cake), it is dried with steam or air, and the dry spent earth is discharged.
The bleached oil is then passed through polishing bag filters (pore size 5 to 10 microns) to capture trace clay particles before deodorization. Sourcing properly filtered oils prevents quality issues during shipment. Importers should coordinate bulk deliveries with an experienced bulk palm oil supplier to plan flexitanks or ISO containers.
Sourcing Certified & Sustainable Pre-treatment
Modern pre-treatment facilities must balance refining efficiency with strict sustainability controls. To comply with international food safety standards, refiners must verify that no harmful chemical residues remain in the refined oil. Sourcing from a certified sustainable palm oil supplier ensures that all refining plants adhere to RSPO supply chain certification standards.
Additionally, seasonal temperature changes at destination ports dictate whether cloud point parameters must be adjusted. Coordinate export requirements with a reliable Malaysia palm oil supplier to manage shipments to cold regions.
Degumming & Bleaching Parameters
The table below summarizes the typical operating parameters and specification targets for a standard degumming and bleaching run:
| Process Parameter | Degumming Phase | Bleaching Phase |
|---|---|---|
| Operating Temperature | 85°C – 90°C | 95°C – 105°C |
| Pressure / Vacuum | Atmospheric | 50 – 80 mbar (Vacuum) |
| Reagent Added | Phosphoric Acid (85% conc.) | Activated Bleaching Earth (Clay) |
| Dosing Rate | 0.05% – 0.10% by weight | 0.8% – 2.0% by weight |
| Retention Time | 15 – 20 minutes | 20 – 30 minutes |
| Phosphorus Target | Reduced from ~20 ppm to <10 ppm | Reduced from <10 ppm to <5 ppm |
Frequently Asked Questions (FAQ)
Why must phosphoric acid be added during degumming?
Phosphoric acid reacts with non-hydratable phosphatides, breaking their solubility in the oil by binding the divalent calcium and magnesium ions. This causes the gums to precipitate so they can be captured by the bleaching clay.
What is spent bleaching earth and how is it managed?
Spent bleaching earth is the clay discharged from the leaf filters after refining. It contains approximately 20% to 30% absorbed palm oil. This spent clay is collected and recycled for industrial applications, such as brick manufacturing or eco-friendly soil conditioners.
How does DOBI value affect the bleaching process?
DOBI measures the ease of bleaching crude palm oil. A low DOBI value (<1.8) indicates oxidized oil containing degraded carotenes, which requires high doses of bleaching clay (up to 3.0%) and results in higher oil loss within the filter cakes.
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