Solvent Extractor Product

Overview

A solvent extractor for oil is a continuous processing system that uses organic solvent—typically hexane (C₆H₁₄)—to dissolve residual oil from flaked oilseed. After the Oilseed Expeller Press has recovered 35–50% of seed oil mechanically, the remaining pressed cake contains 8–15% oil. Solvent extraction recovers 98–99.5% of this residual oil, making the process economically essential in large-scale oilseed crushing.

The process operates in three stages: extraction (mixing flakes with hexane), miscella separation (crude oil recovery), and desolventization (removing hexane). The entire loop is closed to minimize solvent loss and fire risk.

Extraction principle

Hexane is an excellent solvent for triglyceride oils because of its low polarity and high selectivity—it dissolves oil but not protein or carbohydrate. The Extraction Tower is a vertical tower where flakes descend on a slow Extraction Conveyor while hexane spray enters from the top, creating a countercurrent contact. As the flake bed descends through fresh solvent zones, extraction proceeds in stages: initially high concentration gradient, then progressively dilute solution until the flakes exit nearly oil-free at the bottom.

The residence time in the tower is typically 30–60 minutes, allowing equilibration between solid (flake) and liquid (hexane) phases. Oil-loaded hexane, called miscella, is collected on perforated decks and flows to the Miscella Collection.

Miscella processing

The Miscella Tank receives crude miscella containing 10–25% oil and 75–90% hexane. A Miscella Pump recirculates it through a Miscella Heater that raises temperature to 50–60°C. This gentle heating causes hexane to volatilize preferentially—hexane has a lower boiling point (69°C) than water in the oil. The vapors are drawn off by vacuum and condensed for recycling. What remains in the tank is crude oil containing 0.5–1.0% residual hexane.

A Miscella Filter removes fine seed particles before the crude oil moves to refining.

Desolventization

The Desolventizer-Toaster is a jacketed vessel where the extracted crude oil undergoes final solvent removal under vacuum and steam heat. The Desolv Agitator maintains slow mixing to expose maximum surface area to the vaporous hexane. The Vacuum Pump draws pressure down to 50–100 mbar absolute, dramatically lowering hexane boiling point. Indirect steam heating (via the jacket) raises temperature to 100–110°C, causing hexane to flash off. The desolventized oil exits with typically < 500 ppm hexane—well below food safety thresholds.

Solvent recovery and recycling

This is the economic and safety heart of the system. Hexane vapors from the tower, miscella tank, and desolventizer flow into the Condenser, a water-cooled heat exchanger. The vapors condense to liquid at 25–35°C.

The condensed hexane collects in the Hexane Recovery Loop tank, a settling vessel with a baffle that separates water and impurities (that have accumulated) from clean hexane. A Recovery Pump circulates recovered hexane through a Recovery Filter to remove oxidized hexane and particulate, then through a Recovery Cooler that brings it back to 20–25°C, ready for reuse in the tower spray headers.

Recycling efficiency is typically 95–98%, with the 2–5% loss attributable to volatilization and entrainment. Fresh hexane is added to maintain inventory.

Safety and environmental considerations

Hexane is flammable (flash point −23°C) and requires tight process control. All vessels and ducts operate at slightly positive pressure or under vacuum to prevent air ingress and explosive atmospheres. Electrical equipment is classified for hazardous areas. The closed loop minimizes worker exposure and environmental release.

Regulatory limits on hexane residue in food oils are strict: EU allows < 10 ppm, USA < 100 ppm. The desolventizer design must reliably achieve these targets.

Integration with other processes

The solvent extractor typically follows the Flaking Mill. Flakes enter the tower; desolventized oil proceeds to Oil Degumming System (in the refining train) and then to storage or bleaching. Spent flakes, now nearly oil-free (< 2% oil), exit the conveyor's discharge end. These are valuable as animal feed or protein ingredient.

In smaller operations, a Oilseed Expeller Press alone may suffice for premium cold-pressed positioning. In commodity crushing, the mechanical-solvent combination is standard.

Performance indicators

Oil recovery at 98%+ is standard. Hexane cost is typically 20–30% of operating cost. Energy for heating (steam) and vacuum (electricity) is the next major input. Modern extractors aim for energy efficiency of 1000–1200 kWh per ton of feed processed. Capital cost is high—€500k–€2M for a plant processing 5 tons per hour—but unit economics are strong at scale.