How does solvent extraction remove oil left in pressed seed meal?

Solvent extraction is a highly efficient method used to recover residual oil from pressed seed meal, which typically retains 3 to 15 percent of its oil content after mechanical pressing.12

The process functions through the following steps:

• Preparation: The pressed cake is often flaked between smooth rolls to increase surface area and facilitate solvent penetration.2
• Percolation: A volatile solvent—most commonly petroleum benzin (such as commercial hexane or heptane)—is percolated through the meal.12
• Dissolution: The solvent dissolves the remaining oil, creating a mixture known as miscella.2
• Separation and Recovery: The miscella is separated from the solid meal (marc). Finally, the oil is recovered by evaporating the solvent, which is then condensed and recycled for further use.12

This process is highly effective, often reducing the residual oil content in the meal to less than 1 percent. Modern industrial systems, such as the Bollman or Rotocell extractors, utilize continuous counterflow cycles to maximize efficiency.23