Countercurrent methods

Hydrolysis by Steam. High pressure steam, 4.5—5.0 MPa (650—725 psi), at 250°C in the absence of a catalyst hydroly2es oils and fats to the fatty acids and glycerol (20). The reaction is commonly carried out continuously in a countercurrent method. The glycerol produced during the reaction is continuously extracted from the equiUbrium mixture with water. A yield of 98% can be achieved. Currentiy, the preferred method to produce soaps is steam hydrolysis of fats followed by alkaU neutrali2ation of the fatty acids. 

A combined Merox process operation is also utilized to sweeten fuel. This countercurrent method involves feeding fuel into the bottom of a vertical reactor and feeding caustic and catalyst from the top. Mercaptans are extracted into the caustic and react to form disulfides. The caustic and disulfides are later separated. The following reactions occur during the Merox sweetening process ... 

Reserpine is isolated from its plant producers by using a nonaqueous solvent process, using, for example, boiling methanol extraction of the African root Rauwolfia vomitoria. Naturally, these extractions are carried out under countercurrent methods. The methanol extract is concentrated and acidified with 15% acetic acid and then treated with petroleum naphtha to remove impurities. Extraction is made using ethylene dichloride. The solvent is neutralized with dilute sodium carbonate, evaporated to drive off the ethylene dichloride, and further evaporated to crystallize the crude reserpine crystals that are then crystallized. 

Countercurrent Method of extraction such that the feed solution and the solvent flow in opposite directions. 

Phycoerythrin and phycocyanin were extracted from dried Asakusa-nori (Porphym tenera) and subjected to partition with an aqueous polymer phase system (Table 1) using the above standard countercurrent method. Fig. 4b shows the results of separation, where two components are well resolved. 

Because of its importance, only the continuous countercurrent method is discussed here. Also, since the stage method is normally used, the differential-contact method is not considered. In common with other stage cascade operations, leaching may be considered, first, from the standpoint of ideal stages and, second, from that of stage efficiencies. 

So far we have considered only the newer countercurrent methods for fractionating peptides. These will probably play a predominant role in the future, though the classical methods of fractional crystallization and precipitation should not be forgotten. They are still the most effective methods of fractionating proteins and probably larger polypeptides, such as the oxidation products of insulin (Sanger, 1949a). 

The simulated countercurrent method is a general idea that can be applied also to size exclusion... 

Any of the above can, of course, be single-stage or multi-stage and, for the latter, co-current or countercurrent. Methods 2 and 3 are similar in that both are based on diluting the solids in the wash liquid except that method 2 starts with a solid mass (filter cake or sediment) and method 3 starts with the solids... 

The solution is carried to the verge of precipitation by adding dilute acetic acid. Then it is flooded with more dilute acetic acid and mixed vigorously, so that the cellulose acetate comes out as a flake rather than a gelatinous mass or fine powder. The flake then is washed by standard countercurrent methods to remove the last traces of acid, and is dried in a suitable dryer. 

Extraction with solvent. The countercurrent method of contacting is used universally except for such special cases as the single contact sometimes used in propane deasphalting. 

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