Solvent Extraction Method for Edible Oil Processing

As an experienced player in the edible oil processing industry, I understand the constant need for efficiency and high-quality outputs. One method that continues to dominate the edible oil extraction process is solvent extraction. With its high yield and effective oil recovery, it's a technique that has proven invaluable to oilseed processors worldwide. 

Why Solvent Extraction is Your Best Bet for Edible Oil Processing

Solvent extraction is a highly effective method of extracting oil from oilseeds like soybeans, canola, sunflower, and cottonseed. What makes this method so popular is its ability to recover more oil, especially when compared to mechanical pressing methods. If you’re in a large-scale production environment, the chances are that you are already using, or at least considering, solvent extraction for its excellent yield.

To help you understand how this method works and why it’s so effective, let’s break it down.

What is Solvent Extraction and How Does It Work?

Solvent extraction is a process that involves using a chemical solvent to dissolve and separate oil from raw materials such as oilseeds. The most commonly used solvent in this method is hexane. It's chosen because of its ability to efficiently dissolve oils and its relatively low boiling point (63–69 °C), which allows for easy recovery after the extraction process. 

The process of solvent extraction allows for extracting the maximum amount of oil from the seeds, making it particularly suitable for large-scale industrial applications.

Key Steps in the Solvent Extraction Process

Preparation of Seeds:

The first step in the solvent extraction process is preparing the seeds. This involves cleaning, cracking, and often flaking or grinding the seeds to increase the surface area. This ensures better penetration of the solvent. In some cases, pre-pressing is done on seeds with high oil content (over 23%) to extract some oil before applying solvent extraction.

Extraction:

The prepared seeds are then treated with hexane in an extractor. Hexane dissolves the oil, and the mixture of oil and solvent is known as miscella.

Desolventizing:

After extraction, the remaining solid residue, known as de-oiled meal, is heated in a toaster to evaporate any remaining hexane without damaging the nutritional quality of the meal.

Distillation:

The miscella undergoes a distillation process where heat is applied to separate the hexane from the extracted oil. The hexane vapor is condensed and recovered for reuse, ensuring minimal loss and maximizing efficiency. Recovery rates can exceed 95%.

Advantages of Solvent Extraction

High Oil Yield

The primary advantage of solvent extraction is the high oil yield. Unlike mechanical pressing, which typically yields 60-70% of the oil in seeds, solvent extraction can achieve yields exceeding 95%. This makes it an excellent choice for large-scale operations processing hundreds of tons of seeds daily.

Efficiency

Solvent extraction is highly efficient because it allows for the extraction of almost all residual oil from the seed material. This method can leave less than 0.5% residual oil in the meal, which is often used for animal feed or other purposes.

Cost-Effectiveness

Given its efficiency, solvent extraction is also cost-effective, especially for large-scale production. The ability to extract oil from large amounts of seed with minimal waste means lower operational costs and higher profitability.

Safety Considerations

While solvent extraction is highly effective, it does come with its own set of challenges, particularly in terms of safety. Hexane is highly flammable, so it’s essential to have strict safety protocols in place. Processing plants need to take measures such as proper ventilation systems, explosion-proof equipment, and regular maintenance checks to mitigate risks associated with solvent handling.

Environmental Considerations

There is also growing pressure within the industry to move away from hexane and explore greener alternatives. For example, supercritical CO2 extraction is an emerging technology, but it’s still in the experimental phase for many companies.

How Does Temperature Affect the Efficiency of Solvent Extraction?

Temperature plays a crucial role in the solvent extraction process. The effect of temperature on extraction efficiency is significant, and here’s why:

Increased Leaching Rate:

Higher temperatures generally enhance the leaching rate, allowing the solvent to extract more oil. When the temperature increases, the viscosity of both the oil and the solvent decreases, allowing the solvent to penetrate the oil matrix more effectively. This results in a faster and more efficient extraction process.

Optimal Temperature Range:

While higher temperatures can improve efficiency, it’s essential to operate within an optimal range. Typically, around 61-62°C is considered ideal for hexane extraction. Temperatures above this range can cause excessive solvent vaporization, complicating the process and increasing risks.

Impact on Oil Quality:

While higher temperatures increase yield, they can also degrade the quality of the extracted oil. Heat can damage sensitive compounds such as vitamins and antioxidants, and it can also lead to undesirable substances in the oil. Therefore, finding a balance between maximizing yield and maintaining quality is essential.

How to Remove Free Fatty Acids (FFA) from Oil?

Free fatty acids (FFAs) are one of the main contaminants that affect oil quality. There are two primary methods for removing FFAs:

 1. Chemical Neutralization

In this method, an alkaline substance such as sodium hydroxide (caustic soda) is added to the oil. This reacts with the FFAs to form soap, which is insoluble in oil and is referred to as soapstock. The soapstock is then separated from the oil through centrifugation or settling.

Advantages:

Effectively reduces FFA levels.

Can also help decolorize the oil.

Cost-effective and efficient for large-scale operations.

Considerations:

Some neutral oil may be lost due to saponification.

 2. Physical Refining

Physical refining involves using heat and vacuum distillation to remove FFAs without chemical agents. This method does not leave any chemical residues in the oil and can recover valuable fatty acids.

Advantages:

No chemical residues left in the oil.

Generally results in less yield loss than chemical methods.

Can recover valuable fatty acids for reuse or sale.

Considerations:

It may be less effective for oils with very high FFA content.

Conclusion

Solvent extraction remains a highly efficient and widely used method for edible oil processing due to its ability to achieve high oil yields with minimal waste. The process is highly cost-effective and suitable for large-scale industrial applications. However, it’s important to keep in mind safety concerns and temperature control to ensure maximum efficiency and oil quality.

If you’re in the edible oil processing industry, understanding the critical factors that influence solvent extraction, such as temperature and FFA removal methods, can help you optimize your operations for better results.

For more information on edible oil processing and how our turnkey solutions can support your business, feel free to explore Myande Group's extensive offerings, which have helped clients worldwide establish over 800 edible oil processing lines.