Patent Publication Number: US-5250157-A

Title: Separation of toluene from methyl isobutyl ketone by azeotropic distillation

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating toluene from methyl isobutyl ketone using certain organic compounds as the agent in azeotropic distillation. 
     DESCRIPTION OF PRIOR ART 
     Azeotropic distillation is the method of separating close boiling compounds 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 both 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. 
     Toluene, B.P. 110.75° C. and methyl isbutyl ketone, B.P. 116° C. form a minimum azeotrope boiling at 110.7° C. and containing 3% methyl isobutyl ketone and therefore are impossible to separate by distillation or rectification. Azeotropic distillation would be an attractive method to break this azeotrope and separate toluene from methyl isobutyl ketone by rectification. 
     
                       TABLE 1                                                     
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Theoretical and Actual Plates Required vs. Relative Volatility            
for Toluene - Methyl Isobutyl Ketone Separation                           
Relative                                                                  
       Theoretical Plates Required                                        
                           Actual Plates                                  
Volatility                                                                
       At Total Reflux, 95% Purity                                        
                           Required, 75% Eff.                             
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1.12   52                  70                                             
1.20   33                  44                                             
1.25   27                  36                                             
1.30   23                  31                                             
1.40   18                  24                                             
1.60   13                  17                                             
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     The advantage of using azeotropic distillation in this separation can be seen from the data shown in Table 1. If an agent can be found that will increase the relative volatility to 1.6, only seventeen actual plates are required for 95% purity. 
     
                       TABLE 2                                                     
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Effective Azeotrope Formers to Separate Toluene                           
From Methyl Isobutyl Ketone                                               
                  Relative                                                
Compounds         Volatility                                              
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1-Propanol        1.27                                                    
1-Butanol         1.60                                                    
Isobutanol        1.32                                                    
2-Methoxyethanol  1.7                                                     
Methyl cyclohexane*                                                       
                  1.07                                                    
n-Heptane*        1.18                                                    
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 *Brings methyl isobutyl ketone out as overhead                           
 
    
     OBJECTIVE OF THE INVENTION 
     The objects of this invention are to provide a process or method of azeotropic distillation that will enhance the relative volatility of toluene to methyl isobutyl ketone in their separation in a rectification column. It is a further object of this invention to identify certain organic compounds which are effective as azeotropic distillation agents, that are stable and can be readily separated from toluene and can be recycled to the azeotropic distillation column with little decomposition. 
     SUMMARY OF THE INVENTION 
     The objects of the invention are provided by a process for the separation of toluene from methyl isobutyl ketone which entails the use of certain organic compounds as the agent in azeotropic distillation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     We have discovered that certain organic compounds will effectively increase the relative volatility between toluene and methyl isobutyl ketone by rectification when employed as the agent in azeotropic distillation. Table 2 summarizes the data obtained with these agents in a rectification column. The agents which are effective are 1-propanol, 1-butanol, isobutanol, 2-methoxyethanol, methyl cyclohexane and n-heptane. 
     THE USEFULNESS OF THE INVENTION 
     The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1 and 2. All of the successful agents show that toluene can be separated from methyl isobutyl ketone by means of azeotropic distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable. 
    
    
     WORKING EXAMPLES 
     EXAMPLE 1 
     One hundred grams of the toluene-methyl isobutyl ketone azeotrope and fifty grams of 1-butanol were charged to a glass perforated plate rectification column containing 7.3 theoretical plates. After five hours at total reflux, overhead and bottoms samples were taken and analysed by gas chroma tography. The overhead was 99.8% toluene, 0.2% methyl isobutyl ketone; the bottoms was 93.9% toluene, 6.1% methyl isobutyl ketone which is a relative volatility of 1.6. 
     EXAMPLE 2 
     One hundred grams of the toluene-methyl isobutyl ketone azeotrope and 100 grams of 2-methoxyethanol were charged to the glass perforated plate rectification column containing 7.3 theoretical plates. After six hours at total reflux, the overhead analysis was 99.6% toluene, 0.4% methyl isobutyl ketone; the bottoms analysis was 85.0% toluene, 15.0% methyl isobutyl ketone which is a relative volatility of 1.7. 
     EXAMPLE 3 
     One hundred grams of the toluene-methyl isobutyl ketone azeotrope and fifty grams of n-heptane were charged to the glass perforated plate column containing 7.3 theoretical plates. After five hours at total reflux, the overhead analysis was 11% methyl isobutyl ketone, 89% toluene; the bottoms analysis was 3.5% methyl isobutyl ketone, 96.5% toluene which is a relative volatility of 1.18.