Solvent extraction process description

Solvent Extraction is a process involving the injection of Hexane into the oil bearing cells of seeds resulting in a mix of oil and solvent, the so called miscella. The Hexane will be evaporated later from the miscella resulting in unrefined oil. By condensing the Hexane it can be recycled and used over and over again.

The entire process is largely divided into three main sections as follows:

• Seed preparatory section
• Main extraction section
• Meal/cake treatment section

The main Extraction Section is again divided into the following subsections:

• Extraction of oil from prepared raw materials
• Desolventisation
• Distillation/evaporation of Hexane to recover oil from miscella
• Condensation of Hexane
• Final Solvent Recovery Section

Preparatory section

An efficient Extraction would need that every oil bearing cell of the seeds comes in contact with Hexane. A smaller material size, gives a better penetration of the solvent (Hexane) into the oil bearing cells, but once too small it will prevent the solvent from percolation through the mass. Hence an optimum size is absolutely essential for efficient extraction.

The method of material preparation does vary from material to material depending upon its oil content and physical properties. We group them as follows:

• Oil Cakes
• High Oil Content Materials (Soybean, Sunflower, Rape Seed, Canola)
• Floury Materials (Rice Bran)

The prepared material is transported to the Main Extraction Section via a Conveyor.

Main extraction

The prepared material as described above is received into the Extraction plant by a conveyor. The transport speed through the solvent Spraying Chamber can be varied easily.

This chamber contains of a number of solvent sprayers which sprays the solvent over the entire bed of raw material. To view the distribution of spray, a light and sight viewing glasses are provided.

The wet meal coming out of the spraying chamber is de-oiled material and absorbed solvent which is to be recovered in the Desolventizing section. The mixture of the oil and solvent called “Miscella” is pumped into the miscella tank, from where it will be transported by means of a special Conveyor to the desolventizer.

Desolventisation

The wet meal contains 20% to 35% solvent. The basic principal involved in Desolventisation is direct and indirect heating of the wet meal with steam to a temperature well above boiling point of the solvent to ensure that no solvent is left over in the meal. Solvent vapors are sent to the Condensers via a Scrubber where the solvent is washed from any fines.

The de-oiled and desolventised meal is transported to the bagging Section with the help of a conveyor.

A Meal Cooler provides proper cooling of the material for easy bagging and to keep the moisture down to 10-12%.

Distillation

Miscella contains 12% to 18% solvent in the case of oil cakes or rice bran but 25% to 35% in the case of sunflower seed or rapeseed. During distillation, solvent evaporates first due to its lower boiling point (64 to 67 °C) leaving clean oil behind.

Distillation is performed in three stages under vacuum to ensure that no oxygen is present when the oil is heated to a high temperature. Presence of Oxygen will make the oil rancid. First evaporation takes place in an Economizer and is followed by a Flasher leaving practically only oil behind. This oil is further treated with open steam to ensure that no solvent stays behind.

The solvent vapors thus produced passes through an Oil Vapor separator to separate out any oil particles trapped with the solvent vapors before passing on to a Condenser.

Condensation

Solvent vapors are formed both in the Desolventisation Section as well as in the Distillation Section and need to be condensed. Special floating head types help quick and easy removal of tubular bundles for periodical cleaning.

Final solvent recovery

The air that is being ejected out of the system contains traces of solvent. In order to recover these traces, a special final vent air stripping column has been provided. It comprises of a main Absorber to give a large contact surface. It is partly filled with groundnut oil to absorb the solvent vapors from the air. The oil and solvent mixture is distilled later to recover the solvent.

Meal/Cake treatment section

The extracted and desolventised meal is transported to the bagging section by means of a Conveyor fitted with cooling arrangements.

Pricing

The seed preparatory section as described above costs Euro 145,000. The equipment for Solvent Extraction consisting of Extraction, Meal Desolventisation, Distillation, Solvent Recovery System, Filter Press etc. costs Euro 242,500. The Meal/Cake treatment section including the bagging section costs Euro 57,500.

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Larger capacities up to 2500 t/day are available. For quotes and more information, please contact me.