Patent Publication Number: US-6042697-A

Title: Separation of 9,11-Diene C18 fatty acid from 10,12-Diene C18 fatty acid by azeotropic distillation

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating 9,11-diene C18 fatty acid from 10,12-diene C18 fatty acid by azeotropic distillation. 
     DESCRIPTION OF PRIOR ART 
     Azeotropic distillation is the method of separating close boiling compounds or azeotropes from each other bv carrying out the distillation in a multiplate rectification column in the presence of an added liquid, said liquid forming an azeotrope with one or more of the compounds to be separated. Its presence on each plate of the rectification column alters the relative volatility in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The azeotrope forming agent is introduced with the feed to a continuous column. The azeotrope forming agent and the more volatile component are taken off as overhead product and the less volatile component comes off as bottoms product. The usual method of separating the azeotrope former from the more volatile component are cooling and phase separation or solvent extraction. 
     The usual method of evaluating the effectiveness of azeotropic distillation agents is the change in relative volatility of the compounds to be separated. Table 1 shows the degree of separation or purity obtainable by theoretical plates at several relative volatilities. Table 1 shows that a relative volatility of at least 1.2 is required to get an effective separation by rectification. 
     
                       TABLE 1                                                     
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Effect of Relative Volatility on Theoretical stage Requirements.          
Separation Purity,                                                        
          Relative Volatility                                             
Both Products                                                             
          1.02    1.1    1.2  1.3 1.4  1.5 2.0  3.0                       
(Mole Fraction)                                                           
          Theoretical Stages at Total Reflux                              
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0.999     697     144    75   52  40   33  19   12                        
0.995     534     110    57   39  30   25  14   9                         
0.990     463     95     49   34  26   22  12   7                         
0.98      392     81     42   29  22   18  10   6                         
0.95      296     61     31   21  16   14   8   4                         
0.90      221     45     23   16  12   10   5   3                         
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     9,11-Diene C18 Fatty Acid and 10,12-Diene C18 Fatty Acid boil only about a degree apart, have a relative volatility of 1.05 and are impossible to separate by conventional rectification. Table 2 shows that with an agent giving a relative volatility of 1.85 only 20 actual plates are required, 
     
                       TABLE 2                                                     
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Theoretical and Actual Plates Required vs. Relative Volatility for        
9,11-Diene C18 Fatty Acid vs. 10,12-Diene C18 Fatty Acid                  
Relative Theoretical Plates Required                                      
                          Actual Plates                                   
Volatilty                                                                 
         At Total Reflux, 99% Purity                                      
                          Required, 75% Eff.                              
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1.65     19               26                                              
1.75     16               22                                              
1.85     15               20                                              
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     OBJECTIVE OF THE INVENTION 
     The objects of this invention are to provide a process for the separation of 9,11-Diene C18 fatty acid from 10,12-Diene C18 fatty acid which entails the use of certain organic compounds when employed as the agent in azeotropic distillation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     I have discovered that certain organic compounds will effectively increase the relative volatility between 9,11-Diene C18 fatty and 10,12-Diene C18 fatty acid during rectification when employed as agent in azeotropic distillation. They are isopropyl acetate, 3-methyl-2-butanone, nitroethane, 2-nitropropane,N,N-dimethylformamide, amyl acetate, ethyl acetoacetate, 1-decene, propyl formate, butyl ether, butyraldehyde, ethylene glycol dimethyl ether, methyl pivalate, hexyl formate, cyclopentanone and nonane. 
     
                       TABLE 3                                                     
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Effective Azeotropic Distillation Agents For Separating                   
9,11-Diene C18 Fatty Acid From 10,12-Diene C18 Fatty Acid                 
Compounds          Relative Volatility                                    
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None               1.1                                                    
Isopropyl acetate  1.2                                                    
3-Methyl-2-butanone                                                       
                   1.45                                                   
Nitroethane        1.25                                                   
2-Nitropropane     1.25                                                   
N,N-Dimethylformamide                                                     
                   1.55                                                   
Amyl acetate       1.55                                                   
Ethyl acetoacetate 1.4                                                    
1-Decene           1.65                                                   
Propyl formate     1.75                                                   
Butyl ether        1.25                                                   
Butyraldehyde      1.35                                                   
Ethylene glycol dimethyl ether                                            
                   1.3                                                    
Methyl pivalate    1.45                                                   
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                       TABLE 4                                                     
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Effective Azeotropic Distillation Agents For Separating                   
10,12-Diene C18 Fatty Acid From 9,11-Diene C18 Fatty Acid                 
Compounds      Relative Volatility                                        
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None           1.1                                                        
Hexyl formate  1.5                                                        
Cyclopentanone 1.85                                                       
Nonane         1.25                                                       
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     THE USEFULNESS OF THE INVENTION 
     The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1, 2, 3 and 4. All of the successful agents show that 9,11-Diene C18 fatty acid can be separated from 10,12-Diene C18 fatty acid by means of azeotropic distillation and that the ease of separation is considerable. 
    
    
     WORKING EXAMPLES 
     Example 1 
     Fifty grams of 9,11-Diene C18 fatty acid--10,12-Diene-C18 fatty acid mixture and fifty grams of propyl formate as the azeotrope forming agent were charged to a vapor--liquid equilibrium still and refluxed for two hours. The vapor composition was 55% 9,11-Diene C18 fatty acid, 45% 10,12-Diene C18 fatty acid; the liquid composition was 41% 9,11-Diene C18 fatty acid, 59% 10,12-Diene C15 fatty acid, Thie is a relative volatility of 1.75. 
     Example 2 
     Fifty grams of 10,12-Diene C18 fatty acid--9,11-Diene-C18 fatty acid mixture and fifty grams of cyclopentanone as the azeotrope forming agent were charged to vapor--liquid equilibrium still and refluxed for two hours. The vapor composition was 77% 10,12-Diene C18 fatty acid, 23% 9,11-Diene C18 fatty acid, the liquid composition was 64.5% 10,12-Diene C18 fatty acid, 35.5% 9,11-Diene-C18 fatty acid. This is a relative volatility of 1.85.