Why focus on Trace Elements?
Each step in vegetable oil refining plays a critical role in improving oil quality. The bleaching stage is the final opportunity in the refining process to remove non-volatile contaminants. Trace elements such as phosphorus, calcium, magnesium, and iron are naturally present in crude soybean oil and can significantly impact the quality of the final product. Elevated levels of these contaminants can lead to off-flavors, reduced shelf life, increased color and limits its end use as a feedstock for renewable diesel.
Key adjustments made during the bleaching stage can dramatically increase oil quality, resulting in a better product for consumers. The table below demonstrates how soybean oil changes before and after the bleaching process under standard conditions (215°F, 20 minutes, 25 mmHg vacuum). The data in the table demonstrates that despite a significant reduction in phosphorus and other metals during bleaching, further optimizations can be applied to improve oil quality.
Key Adjustments for Element Removal
A few strategic changes can be made during the bleaching stage to improve the refining process.
- Increase Moisture Addition: Adding up to 0.4% w/w water during bleaching can help facilitate the removal of trace elements.
- Incorporate Citric Acid: Citric acid (100-1000 ppm) can chelate element ions, enhancing their removal during bleaching.
- Use Highly Activated Clay: Choosing an acid activated bleaching clay increases the adsorption of trace elements.
- Employ Pretreatment Products: Pretreatments like Select 350 can be used before bleaching to target specific impurities, further improving the oil’s quality.
Example of Adjustments on Trace Element Removal
| Description | Ca (ppm) | Fe (ppm) | Mg (ppm) | P (ppm) | % FM |
| SBO before bleaching | 5.96 | 0.43 | 2.85 | 11.79 | 0.13 |
| SBO after bleaching (RB) | 3.8 | 0.1 | 2.1 | 2.5 | 0.01 |
| Increasing Moisture to 0.4% from 0.1% | 3.1 | 0.1 | 1.5 | 2.1 | 0.01 |
| Highly activated clay (Perform 5000) | 2.9 | 0.1 | 1.2 | 1.84 | 0.01 |
| P5000 with Select®|350 Pretreat | 0.2 | 0.1 | 0.1 | 0.31 | 0.01 |
Bleaching is an essential step in the refining process that ensures high-quality soybean oil. By fine-tuning parameters such as clay dosage, moisture addition, and pretreatment strategies, refineries can significantly reduce the presence of trace elements. These optimizations lead to improved efficiency and oil quality.