Oilseed leaching applies the principle of like‑dissolves‑like, so that oil contained in oilseeds can dissolve in a selected solvent. During leaching, both oil molecules and solvent molecules migrate from regions of higher concentration to regions of lower concentration: oil molecules pass into the solvent and solvent molecules pass into the oil, until the solute concentrations in the two phases are fully equal. Therefore, sufficient contact time between solvent and material must be guaranteed to extract as much oil as possible from the feedstock. Nevertheless, longer leaching time does not always mean better performance. This article introduces how leaching duration affects leaching results and final products.
I. Impacts on Leaching Performance
1. Insufficient leaching time
Oil transfer rates vary for different feedstocks, or for the same feedstock with different pretreatment processes. Insufficient leaching time prevents adequate diffusion and dissolution between oil molecules and solvent molecules. This reduces oil extraction rate, raises residual oil content in meal, and increases cost losses. Furthermore, lower oil yield leads to dilute mixed oil, which increases steam consumption for mixed‑oil treatment and raises overall production costs.
2. Excessively long leaching time
During leaching, oil molecules migrate from high‑concentration feedstock into low‑concentration solvent to form mixed oil. As leaching time increases, the oil proportion in mixed oil rises while oil content in meal keeps decreasing. After a certain duration, the decline of residual oil in meal slows down. Once dynamic equilibrium of molecular transfer is reached — the leaching limit — further extending time cannot lower meal residual oil any more. It merely increases energy consumption, cuts production efficiency and drives up manufacturing costs significantly.
II. Impacts on Crude Leached Oil
As mentioned above, leaching dissolves oil into solvent based on the like‑dissolves‑like principle. Along with oil, the solvent also dissolves phospholipids, pigments, free fatty acids, waxes and other substances. Prolonged leaching raises the content of these impurities in crude leached oil, degrading oil quality indicators such as high phosphorus and wax content, elevated acid value and dark color. It increases consumption of acid, alkali and bleaching earth in subsequent refining processes, causes higher refining loss, lower refining yield and higher production costs.
III. Impacts on Meal
Solvent retained in wet meal exists mainly in three forms: chemical bonding, physicochemical bonding and mechanical entrapment. Solvents bound chemically or physicochemically to wet meal are difficult to remove. Extended leaching time increases the fraction of chemically‑ and physicochemically‑bound solvent. This makes desolventization of wet meal harder, resulting in higher solvent retention in meal or excessive protein denaturation.
