ROLE OF PREPARATION IN THE PERFECT EXTRACTION

Success of the solvent extraction process depends on the following parameters;

• Unspoiled oilseed during harvest, drying, transporting and storing;
• Cleaning the oilseed out of impurities such as stone, dust, earth and metal;
• Cracking and dehulling;
• Flaking;
• Conditioning and cooking;
• Mechanical extraction with oil screw press;
• Cake crushing and cooling;
• Height of the cake bulk in the extractor;
• Miscella percolation and grain size of the cake bulk in the extractor;
• Quality, temperature and flow of the fresh solvent entering the extractor;
• Miscella temperature at the extractor stages and extractor outlet, miscella concentration and residue ratio;
• Residue ratio at the outlet of miscella filter;
• The solvent ratio at the meal outlet of extraction;
• The solvent gas pressure level in the extractor.

HOWEVER, if the cleaning, cracking, dehulling, flaking and conditioning processes are not carried out properly, no matter how healthy the other parameters are met, a successful result cannot be obtained. These four parameters are preparation processes. Preparation constitutes the basis of a successful solvent extraction.

A) CLEANING

The process is started by sending the correctly dried and stored oilseed to the cleaning unit. Cleaning of the oilseeds from impurities such as stone, earth, plant stalk and metal should be done with care to increase the percentage of protein in the meal which determines the meal’s value, and to prevent the equipment from operating inefficiently and being damaged.

B) CRACKING & DEHULLING

In order to make the dehulling process efficient, it is necessary to subject the oilseed to a good cracking process in order to do the subsequent flaking and other processes properly. It is necessary to use different types of crackers for each kind of seed. 

For example sunflower seeds should be crushed by impact; the soybean should be divided into at least 4-6 pieces by cracking with the intending roller crushers. The most important consideration in the cracking process is to keep dust formation at minimum levels.

Dehulling process directly affects the protein ratio of the final extraction meal. The more the hull is separated, the higher the amount of protein in the cake will be. However, it is not desirable to separate all of the hulls because it reduces the miscella percolation of the cake in the extractor.

For example, in the sunflower seed process, if the percentage of hull remaining in the kernel after dehulling is about 12%, a protein ratio of 36% can be achieved in the final meal. In the soybean process, if the percentage of the hull remaining in the kernel after dehulling is around 1%, a protein content of about 48.5% can be obtained in the final meal. Having no dehulling results in reduced capacity in the press unit and in the solvent extraction unit and excess oil in the cake, which is undesirable in terms of capacity and oil yield. In addition, the quality of the oil decreases because the substances that give the color, taste and odor in the hull also pass to the oil with solvent.

C) FLAKING

Flaker machine is used for flaking the oilseeds. The size and the thickness of the flake are the significant parameters of the oil yield in pressing, residual oil content in the cake and the final solvent extraction meal. The seed’s oil is kept in small cells, therefore it is important to weaken and expand these cells since this makes the extraction process more successful. As the flake thickness increases, there will be more oil content left in meal after extraction. Residual oil amount left in meal can be arranged by adjusting the flake thickness as preferred, which has to be 0.30 mm max. For oilseeds such as soybean or rapeseed; preheating to 60 oC and conditioning prior to flaking process would be beneficial and helpful.

D) COOKING & CONDITIONING

In the conditioning process prior to mechanical or solvent extraction, the oil in the cracked and flaked oilseed is removed from the cell by the diffusion method. Immediately thereafter, with the effect of increasing heat, the cell membranes are destroyed and the entire oil remaining in the cell is separated from the kernel. The internal moisture that goes out of the cell together with the oil is thrown out with the help of the aspiration fan and the funnel in the cooker, and the humidity of the kernel is reduced to about 3-3.5% at the exit of the cooker. Thus, in the mechanical extraction, it makes the kernel easier to move inside the press. In solvent extraction, film formation between the oil and the solvent, which is released in the cake bulk in the extractor, is prevented and the crude oil is transferred to the solvent phase by providing full contact of solvent and oil. In this case, the yield of crude oil is increased by minimizing the oil remaining in the solvent extraction.

No matter how satisfying the other parameters and operations are, a successful extraction operation cannot be obtained if the preparation processes outlined above are not performed properly. PREPARATION IS PRECONDITION.

Thank you for devoting your time,

Regards

Author: Mr. Mehmet Celebi- MSc. Chemical Engineer         

HUM Oil & Fat Technologies 

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