Solvent unit consumption is an important assessment indicator for leaching production. It mainly consists of residual solvent in meal, residual solvent in crude oil, solvent-containing wastewater, solvent-laden tail gas, and losses from leakage, spillage and seepage. Today we analyze the factors affecting residual solvent in leached crude oil.
- Evaporation Equipment Evaporation equipment exerts a critical influence on the desolventizing efficiency of leached crude oil. Equipment manufactured by different producers may appear similar externally, yet their internal structures differ drastically — even vastly so — which naturally results in inconsistent desolventizing performance. The commonly-used first- and second-stage evaporators are long-tube rising-film evaporators. Improper operation will greatly impair evaporation-desolventizing performance.
- Temperature Desolventizing of leached crude oil aims to separate solvent from crude oil. The principle lies in their different boiling points: solvent in miscella is vaporized for separation from crude oil. Different evaporation equipment requires different optimal operating temperatures. Take the conventional long-tube rising-film evaporator as an example. During miscella evaporation, low feed temperature prevents vaporization upon entering the evaporator; parts of the long tube merely heat the feedstock instead of achieving rising-film evaporation. Excessively high feed temperature causes vaporization at the inlet, readily triggering vapor lock that hinders feeding and liquid film formation, thus deteriorating evaporation efficiency.
- Vacuum The boiling point of pure solvent is approximately 68 °C. In practice, however, the vaporization temperature of solvent rises along with miscella concentration. When miscella concentration exceeds 80 %, far higher temperatures than 68 °C are required for further solvent-crude oil separation. This is because crude oil and solvent in high-concentration miscella are bonded by chemical bonds, and energy is needed to break such bonds.Vacuum primarily lowers the solvent vaporization temperature during crude-oil desolventizing, so as to reduce the overall desolventizing temperature and avoid high-temperature side-reactions that degrade crude-oil quality. Nevertheless, higher vacuum does not always mean better performance. Vacuum should be coordinated with temperature to obtain optimal process parameters for evaporation equipment and maximize desolventizing efficiency.
- Solvent Solvent selection significantly affects residual-solvent levels in crude oil. Pure n-hexane boils at 68 °C, whereas the solvent used in leaching production is a mixture dominated by n-hexane with a broad boiling-range distillation spectrum. Low-boiling fractions vaporize easily yet condense poorly; high-boiling fractions resist vaporization and tend to remain in materials, pushing up solvent consumption. For leaching-solvent selection, a narrower boiling-point range facilitates solvent recovery and lowers unit solvent consumption.
- Content and Types of Impurities in Miscella Affected by leaching process, equipment, raw-material condition and operation modes, miscella generated in leaching varies in impurity content and species, including solid meal fines, fat-soluble free fatty acids, colloid-soluble protein and phospholipids. These impurities bind with solvent via both physical and chemical interactions and differ in removal difficulty, thereby exerting variable impacts on residual-solvent content in leached crude oil.
Above are the common factors influencing residual solvent in leached crude oil. What other factors do you think may contribute to residual solvent in leached crude oil?
