Oil deacidification is one of the key steps in the oil refining process, which aims to remove free fatty acids (FFA) in oil and improve the quality and stability of oil. The presence of free fatty acids will affect the flavor, shelf life and food safety of oil, so the deacidification process is crucial to the production of edible oil.
Main methods of deacidification process:
1. Alkali refining deacidification method (chemical deacidification)
Principle: By adding alkali solution (usually sodium hydroxide solution) to neutralize the free fatty acids in the oil, soap stock (sodium fatty acid) is generated, thereby separating fatty acids from the oil.
Scope of application: Mainly used for refining vegetable oils, especially oils with higher free fatty acids, such as palm oil, soybean oil, etc.
Steps:
Add an appropriate amount of alkali solution to the oil to neutralize with the free fatty acids to generate soap stock.
Use water washing or steam treatment to remove soap stock.
Separate oil from soap stock and impurities by centrifugal separation.
Advantages: Suitable for processing oils with high acid value, obvious deacidification effect, and relatively simple operation.
Disadvantages: Alkali refining and deacidification will lose some neutral oil, and the treatment of the generated soap stock waste liquid is more complicated and prone to environmental pollution.
2. Physical deacidification method (distillation deacidification)
Principle: Using steam distillation under high temperature and vacuum conditions, the free fatty acids in the oil are evaporated and removed before triglycerides due to their high volatility, achieving the purpose of deacidification.
Scope of application: Suitable for processing high-quality oils or oils that need to maintain the nutritional components of oils, such as sunflower oil, olive oil, etc. It is particularly suitable for oils with low free fatty acid content.
Steps:
The oil is heated under vacuum conditions, and the free fatty acids are vaporized at high temperature.
The steam takes away the free fatty acids and collects them after condensation.
After the oil is cooled, it enters the next refining step (such as decolorization and deodorization).
Advantages: The deacidification process does not require the addition of chemical agents, avoiding oil loss and environmental pollution, and maintaining the natural quality of the oil.
Disadvantages: It requires higher equipment investment and energy consumption, especially when processing oils with high free fatty acid content, the efficiency is low.
3. Esterification deacidification method
Principle: Using acid or enzyme catalysis, free fatty acids react with glycerol to form triglycerides (i.e. neutral oil), thereby reducing the free fatty acid content in oils and fats.
Scope of application: Esterification deacidification is usually used for the refining of high-end oils or special-purpose oils and fats, especially in situations where it is desired to minimize the loss of neutral oils.
Steps:
Add esterification catalysts (acids or enzymes) to the oils and fats to react with free fatty acids and glycerol.
After the reaction is completed, remove the catalyst and the generated by-products by washing with water or other methods.
Advantages: Small oil loss, can effectively reduce the acid value of high acid value oils and fats.
Disadvantages: Complex process, long reaction time, and large equipment investment.
Detailed introduction of deacidification equipment:
1. Alkali refining deacidification equipment
Mixing reactor:
Used for the full mixing reaction of oils and fats with alkali solution to ensure the neutralization of free fatty acids and alkali solution.
The reactor is usually equipped with a stirrer and a heating device to ensure the uniformity and efficiency of the reaction.
Centrifuge:
After alkali refining and deacidification, a centrifuge is required to separate the oils and fats from the generated soap stock. The centrifuge rotates at high speed to deposit the heavier soap stock and leave the lighter oil in the center.
Washing device:
It is used to wash the oil after deacidification to remove the residual soap stock and impurities. It is usually multi-stage washing, using soft water or steam cleaning.
Soap stock separator:
The soap stock separator is used to further separate the soap stock to ensure that it does not remain in the oil.
2. Physical deacidification equipment
Distillation tower:
The core of the distillation deacidification equipment is the distillation tower. The oil in the tower is distilled at high temperature (about 200-260°C) and vacuum conditions, and the free fatty acids are vaporized. The tower is designed with a multi-stage tray structure to increase the contact area between the oil and steam and improve the deacidification efficiency.
Vacuum system:
During the distillation deacidification process, in order to avoid oxidation and excessive thermal decomposition of the oil, it must be operated under high vacuum conditions. The vacuum system usually includes a multi-stage vacuum pump and a condenser to maintain a low pressure state in the tower.
Condenser:
After the free fatty acids are taken away from the distillation tower by steam, they need to be condensed into liquid and collected. The function of the condenser is to cool the steam back to liquid.
Heater:
Oil needs to be deacidified at high temperature. The heater usually uses a heat transfer oil heating system to ensure the stability and uniformity of the oil temperature.
3. Esterification deacidification equipment
Esterification reactor:
The reactor is used for the reaction of oil and oil with esterification catalyst. The reactor is usually equipped with a temperature control system and a stirring device to ensure the uniformity and effect of the reaction.
Catalyst feeding system:
It is used to accurately control the amount of catalyst added in the esterification reaction to ensure the reaction efficiency.
Post-processing equipment:
Oil after esterification reaction needs to be filtered or washed to remove the catalyst and by-products generated by the reaction. Filters and washing devices are used to purify oil.
Selection of deacidification process and equipment:
Oil types: Different types of oils (such as soybean oil, palm oil, sunflower oil, etc.) contain different amounts of free fatty acids and are suitable for different deacidification processes. Oils with high free fatty acids are usually deacidified by alkali refining, while high-quality oils are more suitable for physical deacidification.
Production scale: Large-scale production enterprises usually choose equipment with a high degree of automation to ensure production efficiency and quality; small-scale production enterprises may choose equipment with simpler processes.
Product requirements: High-end edible oils and special-purpose oils (such as medicinal oils and cosmetic oils) have higher requirements for deacidification effects, and usually choose physical or esterification deacidification.
The selection of oil deacidification process and equipment has an important impact on oil quality and production cost. Modern oil refineries optimize the process and equipment combination to maximize the refining efficiency of oils and ensure the high quality of the final product.