Activated Clay STRONGER 223C

Palm oil refining typically involves four main stages: degumming, deacidification (neutralization), decolorization (bleaching), and deodorization. Activated clay is central to the decolorization (bleaching) step. Its primary purpose is to remove color bodies (e.g., carotenoids, chlorophyll, and their degradation products), trace metals, residual soaps, phospholipids, oxidation products, and off-flavors/odors.

Specific Steps of the Activated Clay Decolorization Process:

1. Pre-treatment & Conditioning:
Feedstock Preparation: Decolorization usually follows deacidification (either alkali refining or physical refining). Oil entering the bleaching section should have completed degumming and deacidification, have low Free Fatty Acid (FFA) content (especially for physical refining), be low in moisture (dewatered and dried), and have minimal residual soaps and gums.
Preheating: Deacidified palm oil is pumped into the bleacher vessel. This is typically a closed, agitated tank equipped with heating coils/jacket and a vacuum system.
Drying & Deaeration: Under vacuum (typically 20-70 mbar absolute / 15-50 mmHg abs) and with moderate agitation, the oil is heated to 90-110°C (commonly 98-110°C) and held for a period (e.g., 15-30 minutes) to thoroughly remove trace moisture. Effective drying and maintaining vacuum are critical prerequisites for successful bleaching.
2. Addition of Activated Clay:
Dosage Calculation: The amount of activated clay is determined based on the crude oil quality (primarily color intensity, soap content, impurity levels) and the target color for the refined oil. For standard RBD palm oil, dosage typically ranges from 0.5% to 2.0% (w/w). Higher dosages (up to 3-5% or more) may be needed for red palm oil (where carotenoid retention is desired) or deeply colored crudes.
Addition Method: Under agitation and vacuum, the calculated amount of dry activated clay is evenly dispersed into the hot oil via a charging port or powder injection system. Clumping must be avoided to ensure thorough contact with the oil.
3. Bleaching Reaction:
Temperature Maintenance: The oil-clay mixture is maintained at the set bleaching temperature (98-110°C is standard).
Agitation: Moderate agitation continues (avoiding excessive shear that could damage clay structure or incorporate air) to ensure uniform dispersion of clay particles, maximizing the adsorbent surface area.
Vacuum Maintenance: High vacuum (20-70 mbar absolute) is continuously applied. This prevents oil oxidation at high temperatures and helps remove gases and volatile compounds released during adsorption.
Contact Time: The clay remains in contact with the oil under these conditions for typically 15 to 30 minutes. Excessive time risks oil hydrolysis/isomerization (forming trans fats), while insufficient time leads to incomplete adsorption.
4. Cooling & Discharge:
Agitation Stop: At the end of the contact time, agitation is stopped first to allow brief settling of clay particles (aids subsequent filtration).
Cooling (Optional): The mixture may sometimes be cooled to 70-90°C to reduce oxidation risk during filtration and lower oil viscosity, depending on the specific process design.
Discharge: The oil-clay slurry (bleached oil slurry) is discharged from the bleacher to the filtration system, typically using vacuum or a pump, maintaining vacuum during transfer.
5. Filtration & Separation:
Filtration Equipment: A leaf filter (most common) or plate and frame filter press is used.
Filter Aid: A pre-coat of filter aid (e.g., diatomaceous earth or perlite) is usually applied to the filter medium (cloth/paper/plates). A small amount of “body feed” filter aid is often added to the slurry just before discharge to improve flow rate and reduce filter cake compressibility.
Filtration: The bleached oil slurry is forced under pressure through the filter medium. Clear, decolorized oil passes through as the filtrate.
Blow-Down & Oil Recovery: After filtration, the filter cake is blown with steam (or inert gas like N₂) to recover trapped oil.
Cake Discharge: The filter is opened, and the spent clay cake (containing adsorbed impurities, color bodies, and residual oil) is removed. Spent clay typically contains 20-40% retained oil.
Safe Cake Handling: Spent clay is hot and oil-laden, making it extremely prone to spontaneous combustion! It must be cooled under inert atmosphere or handled with extreme care for immediate safe disposal (e.g., controlled incineration, treated landfill).
6. Post-Filtration Treatment:
Polish Filtration: Before proceeding to deodorization, the decolorized oil usually passes through a polish filter (e.g., bag filter or cartridge filter) to remove any trace fines that penetrated the main filter.
Storage (Buffering): The filtered, bleached oil is stored in a buffer tank, ready for the deodorization stage.

Key Influencing Factors:

Clay Quality: Activity, particle size distribution, free acidity, moisture content, filtration characteristics.
Oil Quality: Crude oil color, residual soap, phospholipid content, moisture, FFA level, oxidation state.
Process Conditions: Temperature, vacuum level, contact time, agitation intensity, clay dosage.
Filtration Efficiency: Filter type, filter aid usage, operating pressure, effectiveness of cake blow-down.

Summary:

Activated clay plays a vital role in palm oil refining for decolorization and impurity removal. The core process occurs under high temperature, vacuum, and agitation, ensuring the clay effectively adsorbs undesirable components. Efficient and reliable filtration then completely separates the spent clay cake from the decolorized oil, yielding clarified palm oil with significantly reduced color. This provides qualified feedstock for deodorization. Crucial aspects ensuring effectiveness and safety (preventing oxidation and fire hazards) are rigorous vacuum application, thorough drying, precise temperature control, optimal contact time, and highly efficient filtration.