Soybean Oil Refining: Removing 4 Types of Impurities

Soybean oil is one of the world's top five edible oils and one of the edible oils we see most in our daily life. Soybean oil is commonly processed by two processes: pressing in oil presses and leaching in oil solvent extraction equipment. The soybean oil extracted from these two processes is called crude oil or gross oil in edible oil standards.

Eliminating 4 Impurities：Buying Soybean Oil Refining Line 

Crude oil generally refers to the extraction from the leaching or pressing process from vegetable oilseeds containing some impurities that are not suitable for food (or industrial use) of fats and oils, such as phospholipids, free fatty acids, water, pigments, odor substances, and other impurities can not be removed by simple filtration, these impurities in the edible oil will cause rancidity and deterioration of soybean oil, so the oil plant will also be used in the oil refinery equipment to further refine the soybean oil.

1. Suspended Impurities in Crude Oil

Suspended impurities are tiny particles present in crude oil and may include impurities, pigments, and other substances that are insoluble in the oil. Effective removal of these suspended impurities is critical to improving oil clarity and stability.

3 Ways to Remove Suspended Impurities

• 1. Soybean crude oil precipitation method

The sedimentation method is a commonly used method for removing suspended impurities. By adding an appropriate precipitant to the sedimentation tank, the suspended impurities settle to the bottom, thereby achieving the separation of impurities. This step requires careful control of precipitation conditions to avoid adverse effects on oil quality.

• 2. High-speed centrifugal separation method

Centrifugation is a method that uses a high-speed rotating centrifuge to quickly separate suspended impurities. This method is easy to operate and has remarkable effects, but the impact of centrifugal conditions on the oil needs to be considered to ensure product quality.

• 3. Membrane separation technology method

Membrane separation technology is an efficient suspended impurity removal method developed in recent years. It filters oil through a microporous membrane, thereby effectively trapping suspended impurities on the membrane. This method is efficient and environmentally friendly, but requires strict control of membrane selection and operating conditions.

2. Peptide-soluble Impurities

In the production process of edible oil, peptidic impurities are a type of substances in crude oil that are difficult to remove, such as phospholipids, proteins, mucilage and glycosyl diglycerides, etc., which have adverse effects on the stability and deep processing of oil. In the refining process, the removal of these peptizing impurities using physical or chemical methods is an indispensable step.

Degumming method selection and selection guide

Commonly used degumming methods include hydration degumming, acid refining degumming, adsorption degumming, thermal polymerization degumming and chemical reagent degumming. In the processing of edible oils and fats, hydration degumming and acid refining degumming are commonly used. Hydration degumming is suitable for refining edible oils and fats, while acid refining degumming is mainly used for refining industrial oils.

Detailed explanation of the operating steps of hydration degumming

Hydration degumming takes advantage of the hydrophilicity of peptized impurities, using hot water or dilute alkali, salt, phosphoric acid and other electrolyte aqueous solutions, and adding them to the hot crude oil under stirring. This allows the peptized impurities to absorb water and condense, and then complete the degumming process through sedimentation and separation. The main steps include:

• Heating the crude oil: Keep the crude oil at a suitable degumming temperature.

• Add aqueous solution: Slowly add the aqueous solution containing electrolytes to the stirred crude oil.

• Stirring and agglomeration: Stirring causes the peptizing impurities to combine with water molecules and agglomerate.

• Sedimentation separation: Stop stirring, allow the condensed impurities to settle to the bottom, and separate the clear degummed oil.

Selection of soybean crude oil degumming equipment

Soybean Oil Degumming Process

The main equipment for hydration and degumming includes hydrators, separators, dryers and desolvators. The hydrator is used to mix and stir the crude oil and aqueous solution, the separator is used to settle and separate the condensed impurities, the dryer is used to remove residual moisture, and the desolventizer is used to further remove residual peptizing impurities.

3. Efficiently Remove Fat-soluble Impurities

Fat-soluble impurities mainly include waxes, pigments, etc., which have a significant impact on the color and transparency of soybean oil. Therefore, the effective removal of these fat-soluble impurities is a necessary step to ensure the appearance quality of oil products.

How to remove wax

Wax is one of the important fat-soluble impurities that affects the transparency and stability of soybean oil. To effectively remove wax, you can use the following methods:

Low-temperature crystallization: Taking advantage of the properties of oil and fat to crystallize at low temperatures, the wax is precipitated by controlling the temperature. Subsequently, the wax in the oil is separated through steps such as filtration, thereby improving the transparency of the oil.

Solvent extraction: Use a specific solvent, such as n-hexane, to form a complex with the wax, and then extract the wax from the oil through distillation or other separation methods. This method is relatively efficient and can effectively remove wax in a short time.

Pigment removal techniques

Pigments are another important fat-soluble impurity that affects the appearance of soybean oil. To improve the clear appearance of your oil, the following methods can be used to remove pigments:

Activated carbon adsorption: Activated carbon has strong adsorption properties and can adsorb fat-soluble pigments in oil. Add activated carbon to soybean oil, and stir or filter to allow the pigment to be adsorbed by the activated carbon and separated.

Centrifugal separation: Using the principle of oil-water separation, the pigment particles in the oil are separated through high-speed centrifugation. This method has a better removal effect on granular pigments and can also improve the clarity of the oil.

4. Reduce free fatty acid content

• The content of free fatty acids is reduced, and the odor components are significantly reduced.

In the processing of edible oils and fats, the free fatty acid content in crude oil is closely related to the odor components. By effectively controlling free fatty acids, odorous components in the oil can be directly reduced. Normally, when the free fatty acid content drops to the range of 0.01%-0.03%, the odor can reach the qualified standard.

• The increase in high acid value and odor components directly leads to an increase in processing losses.

The high acid value and odorous components in the oil will not only directly lead to an increase in refining losses, but also require increased steam consumption, heat energy input, deodorization time, splash losses, etc. Reducing acid value and odor component content has become a key goal to effectively control deodorization loss.

• Take effective measures to reduce the formation of odor components

In order to reduce the content of odor components, a series of measures need to be taken. Choose high-quality raw oils and avoid oils containing large amounts of free fatty acids. During processing, control operating conditions to prevent excessive temperatures and long processing times. Using appropriate deodorization technology and equipment, such as steam deodorization, can help effectively remove odor components and improve oil quality.

Through the above means, the content of free fatty acids and odor components can be effectively controlled, deodorization losses can be reduced, and the quality and economic benefits of edible oils and fats can be improved.