In the field of modern grain and oil processing, solvent extraction has become the mainstream technology in edible oil industry with its advantages of higher oil yield, continuous production and low cost. This paper will briefly introduce the four core steps of solvent extraction plant from raw materials to crude oil, which will help to quickly understand this technological process.

Step 1: Pretreatment of raw materials

Objective: To lay a foundation for the subsequent leaching process by destroying the oilseed cell structure and increasing the specific surface area.

Key processes include:

1. Cleaning: Remove impurities such as stones, metals and straws to protect the equipment.

2. Crushing/hulling: Crushing or hulling large-particle oilseeds for processing.

3. Softening: Adjust the moisture and temperature to make the oilseed material soft and suitable for flaking.

4. Flaking: Press the oilseed into thin sheets (0.3–0.4 mm) to increase the contact area.

5. Puffing (optional): Through high-temperature and high-pressure treatment, the leaching efficiency is improved, which is commonly used in soybeans and rice bran.

Step 2: Leaching to get oil.

Objective: With the help of food-grade hexane and other solvents, the oil was dissolved from the embryo.

Process principle: Countercurrent leaching is adopted to improve extraction efficiency by maximizing concentration gradient.

Common equipment: Rotary extractor, ring extractor and crawler extractor.

Outputs: Concentrated mixed oil (containing 20%-30% oil) and wet meal (containing 25%-35% solvent).

Step 3: Desolution of wet meal.

Objective: To recover the solvent from wet meal, while retaining the nutrients in the meal.

Wet meal undergoes three steps of pre-desolventization, steam distillation, drying and cooling in DTDC, and finally high-quality feed meal with water content of about 12%, residual oil rate of less than 1% and solvent residue of less than 500 mg/kg is obtained.

Step 4: Separation of mixed oil.

Objective: To separate the solvent from the concentrated mixed oil and obtain crude oil that can be further refined.

Through the “evaporation+stripping” process of evaporator and stripper, using the low boiling point of n-hexane, the solvent was vaporized and condensed for recovery (recovery rate > 95%), and finally the leached crude oil containing a small amount of impurities was obtained.

Through pretreatment, solvent extraction, desolventization and separation, the solvent extraction plant realized efficient extraction of edible oil. This process is an important pillar technology of modern grain and oil industry, which extracts oil physically without changing its chemical properties and maximizing the utilization rate of resources.