Unit Operations in Crude Oil Refining: Process and Methods

In the process of refining crude oil, several unit operations are undertaken to transform the raw substance into marketable petroleum products. Four key operations, namely degumming, neutralization, bleaching, and deodorization, play a crucial role in achieving this goal. This article delves into the details of these operations and their role in the broader refining process.

1. Degumming

Degumming is a process aimed at removing gums from the oil. Gums are substances that can interfere with the stability and quality of the final product, so their removal is essential. There are two primary types of gums, hydrated and unhydrated, and each requires a different approach.

Hydrated Gums are removed using water. This method is straightforward and relies on the natural tendency of hydrated gums to dissolve in water. By adding water to the oil, the gums can be separated and removed through a process called liquid-liquid extraction. This method is efficient and effective for hydrated gums.

Unhydrated Gums, on the other hand, are more challenging to remove. They require the use of citric acid. During the degumming process, the oil is mixed with citric acid, which reacts with the gums. The resulting solution is then separated using a centrifuge. The gums are then removed, leaving a purer form of oil.

2. Neutralization

Neutralization is a critical step in refining crude oil, particularly in eliminating free fatty acids (FFAs), which are known as soaps. FFAs can affect the quality and stability of the final product, so their removal is necessary. This process involves the reaction of the FFAs with a caustic solution, typically sodium hydroxide (NaOH).

During neutralization, the FFAs react with the caustic solution, forming a salt called soap, which is insoluble in oil. This reaction is exothermic and produces heat, which can be used to maintain the temperature of the system. Once the reaction has taken place, the soaps are separated from the oil, typically using a settling tank or a centrifuge. The resulting product is a significantly purer form of oil.

3. Bleaching

Bleaching is a process designed to remove color and some phospholipids from the oil. This is achieved by using bleaching earth, a natural clay-like material that acts as an absorbent. Bleaching earth has a high affinity for colored molecules and phospholipids, allowing it to remove these impurities effectively.

The bleaching process typically involves the following steps:

The oil is mixed with bleaching earth in a high temperature environment to promote the adsorption of impurities. The mixture is then filtered to remove the bleaching earth, leaving the purified oil behind. The bleaching earth is washed to remove any traces of oil that might contaminate it for future use. The washed bleaching earth is dried and can be reused in subsequent cycles.

The result is a product that is not only free from unwanted pigments and phospholipids but also has a less bitter taste and a better texture.

4. Deodorization

Deodorization is an advanced process that focuses on the elimination of odors, free fatty acids, gums, and volatile impurities from the oil. This can significantly improve the sensory qualities of the final product, making it more desirable for various applications. The process typically involves the use of vacuum distillation.

In the deodorization unit, the oil is heated and vaporized under a high vacuum. The vapor is passed through a series of towers or columns containing a series of absorbents. These absorbents, often composed of various metals, adsorb the odorous compounds, leaving the oil free from unwanted volatiles. The vapor is then condensed and recovered for possible reuse or disposal.

The process is carefully regulated to ensure that the temperature and vacuum conditions are optimal for the effective removal of volatiles without causing damage to the oil. Deodorization can be further categorized into two types:

Primary Deodorization involves the removal of odors and some odorous impurities from the oil. This is typically the initial step in the deodorization process. Secondary Deodorization focuses on the removal of remaining odors and impurities. This step is more intensive and may be required for oils that still have noticeable odors.

Conclusion

The refinement of crude oil involves a series of unit operations designed to purify and enhance the quality of the final product. Each operation plays a crucial role, and the removal of gums, neutralization of FFAs, bleaching of color and impurities, and deodorization to eliminate odors are essential steps in this process. Mastering these operations ensures that the refined oil meets the high standards required for various industrial and consumer applications.