Desolventizing

Solvent solubility. A low solubility of extrac tion solvent in the raffinate generally leads to a high relative volatihty in a raffinate stripper or a low solvent loss if the raffinate is not desolventized. A low solubility of feed solvent in the extract leads to a high relative separation and, generally, to low solute-recovery costs. 

Figure 17. Process flow scheme for continuous evaporation in a rubber desolventizing process.

More efficient procedures utilize expanders and extruders to convert the flakes into collets, or porous, spongelike material. Collets are larger and less fragile than soybean flakes aiding in the oil extraction and drainage process. This also minimizes the amount of hexane that needs to be recovered in the desolventizer. 

Kellor (32) points out that overheating adversely affects palatability. Precise control of heat for desolventizing and in subsequent processing steps is needed. Stott and Smith (33) showed no negative effects to lysine or methionine for a typical commercial desolventizing-toasting process. 

The most common form of extraction involves two immiscible liquids and a solute that is soluble in both and will be recovered. Liquid-liquid extraction requires (1) extraction, (2) medium recovery, and (3) raffinate desolventizing. The Udex process is a cost-effective liquid-liquid fractionation process for the separation of aromatics from aliphatics. The extraction solvent (diethylene or triethylene glycol) is recovered by steam distillation, and the raffinate and extract streams are desol-ventized by water extraction. 

Fig. 34.16. Schumacher type desolventizer-toaster-dryer-cooler (DTDC). (Courtesy of Crown Iron Works Company, Minneapolis, MN.)...

The liquid-and-solid mixture from the batch cookers is filtered, and the solid is desolventized to give a fish-meal product. 

All necessary storage tanks and receiving tanks The slurry tank complete with agitator Batch filter and meal desolventizer Decanter still Water still... 

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