Patent Publication Number: US-6039846-A

Title: Separation of 3-methyl-2-pentenal from n-butanol by azeotropic distillation

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating 3-methyl-2-pentenal from n-butanol by azeotropic distillation. 
     DESCRIPTION OF PRIOR ART 
     Azeotropic distillation is the method of separating close boiling compounds or azeotropes from each other by 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 methods 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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     3-Methyl-2-pentenal and n-butanol boil about two degrees apart, have a relative volatility of 1.1 and are difficult to separate by conventional rectification. Table 2 shows that with an agent giving a relative volatilty of 2.7, only twelve actual plates are required. 
     
                       TABLE 2                                                     
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Theoretical and Actual Plates Required vs. Relative                       
Volatility for 3-Methyl-2-pentenal-n-Butanol                              
Relative Theoretical Plates Required                                      
                          Actual Plates                                   
Volatilty                                                                 
         At Total Reflux, 99% Purity                                      
                          Required, 75% Eff.                              
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2.7       9               12                                              
2.5      10               14                                              
2.0      12               16                                              
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     OBJECTIVE OF THE THE INVENTION 
     The object of this invention is to provide a process or method of azeotropic distillation that will enhance the relative volatility of 3-methyl-2-pentenal from n-butanol in their separation in a rectification column. It is a further object of thie invention to identify effective azeotropic distillation agents that are stable and can be recycled. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are to provide a process for the separation 3-methyl-2-pentenal from n-butanol 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 3-methyl-2-pentenal and n-butanol during rectification when employed as the agent in azeotropic distillation. They are 2,3-dimethylbutane, decahydronapthalene, t-butyl methyl ether, triethanol amine, trimethylene sulfone, sulfolane 2-nitrotoluene, dimethoxymethane, petroleum ether, tetramethyl ortho silicate, 2,5-diethyl aniline and cyclopentane. 
     
                       TABLE 3                                                     
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Effective Azeotropic Distillation Agents For                              
Separating 3-Methyl-2-pentenal From n-Butanol                             
                  Relative                                                
Compounds         Volatility                                              
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None              1.1                                                     
2,3-Dimethylbutane                                                        
                  1.7                                                     
Decahydronapthalene                                                       
                  2.0                                                     
t-Butyl methyl ether                                                      
                  1.6                                                     
Triethanol amine  1.4                                                     
Trimethylene sulfone                                                      
                  1.9                                                     
Sulfolane         1.7                                                     
2-Nitrotoluene    2.2                                                     
Dimethoxymethane  2.3                                                     
Petroleum ether   2.7                                                     
Tetramethylortho silicate                                                 
                  2.9                                                     
2,5-Diethyl aniline                                                       
                  1.3                                                     
Cyclopentane      1.7                                                     
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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 and 3. All of the successful agents show that 3-methyl-2-pentenal can be separated from n-butanol by means of azeotropic distillation and that the ease of of separation is considerable. 
    
    
     WORKING EXAMPLE 
     Example 1 
     Fifty grams of 3-methyl-2-pentenal-n-butanol mixture and fifty grams of tetramethylortho silicate as the azeotrope forming agent were charged to a vapor-liquid equilibrium still and refluxed for two hours. The vapor composition was 69.9% 3-methyl-2-pentenal, 30.1% n-butanol; the liquid composition was 44.5% 3-methyl-2-pentenal, 55.5% n-butanol. This is a relative volatility of 2.9.