Abstract:
A method of separating ethanol and ethyl acetate, and ethanol and water involves distilling a mixture of the components by an extractive distillation process in the presence of an extractive distillation solvent. The extractive distillation solvent may be an amine, an alkylated thiopene, and paraffins.

Description:
This is a continuation of International PCT Application Numbers PCT/IB00/00074 and PCT/IB00/00076, filed on Jan. 26, 2000. 
    
    
     Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent Is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture. The invention suggests a method of separation of ethanol and ethyl acetate, and ethanol and water by distilling a mixture of the components by way of an extractive distillation process in the presence of an extractive distillation solvent. 
     Separation of components from ethanol mixtures thereof by extractive distillation. 
     FIELD OF INVENTION 
     The present invention relates to the separation of components from ethanol mixtures thereof by extractive distillation. 
     BACKGROUND TO INVENTION 
     Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture. 
     The separation of ethanol and ethyl acetate is complicated due to the existence of an azeotrope. Trimethylbenzene has been proposed in the literature as extractive distillation solvents to produce ethanol as distillate. 
     The separation of ethanol and water is complicated due to the existence of an azeotrope. Azeotropic distillation using benzene or cyclohexane is commonly used to effect the separation. Membrane separation, such as pervaporation, may alternatively be used to break the azeotrope. Pressure swing distillation is another separation method that may be used to produce pure ethanol and pure water. All of these methods utilize two distillation columns. In the case of azeotropic distillation, a phase separation device is needed. In the case of membrane separation, membrane modules are needed. Extractive distillation can also be used to effect the desired separation. This method also uses a two column system but the operation is simple. Ethylene glycol has been proposed in the literature as an extractive distillation solvent for the system ethanol/water. 
     As has been stated in U.S. Pat. No. 5,800,681 (Berg) extractive 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 or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive distillation solvent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds 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 extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is Introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component. 
     It is an object of this invention to suggest at least one further extractive distillation solvent for the separation of components from ethanol mixtures thereof. 
     SUMMARY OF INVENTION 
     According to the invention, a method of separation of ethanol from a mixture of ethanol and another compound selected from a first group consisting of ethyl acetate and water, includes the step of distilling the mixture containing at least ethanol and another compound selected from a first group consisting of ethyl acetate and water by way of an extractive distillation process in the presence of an extractive distillation solvent selected from a second group consisting of an amine, an alkylated thiopene, a paraffin and a chlorinated carbon. 
     The mixture may contain ethanol and ethyl acetate and the extractive distillation solvent may be selected from the group consisting of an amine, an alkylated thiopene and a paraffin. 
     The ethanol and ethyl acetate mixture may contain only ethanol and ethyl acetate. 
     The amine may be selected from a group consisting of N,N′-dimethyl-1, 3-propanediamine, N-N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane. 
     The alkylated thiopene may be ethyl thiopene. 
     The paraffin may be at least one of the components selected from the group consisting of dodecane, tridecane and tetradecane. 
     The mixture may contain ethanol and water and the extractive distillation solvent may be selected from the group consisting of an amine and a chlorinated hydrocarbon. 
     The ethanol and water mixture may contain only ethanol and water. 
     The amine may be selected from a group consisting of diaminobutane, 1,3-diaminopentane and diethylene triamine. 
     The chlorinated hydrocarbon may be hexachlorobutadiene. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     The invention will now be described by way of example with reference to the accompanying schematic drawing. 
     In the drawing there is shown a schematic view of an experimental apparatus for testing an extractive distillation solvent for separating components from mixtures thereof in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawing there is shown a vapour-liquid equilibrium still  10  Including a bulb flask  12  having a tube  14  leading to a condenser  16  and terminating in an outlet  18 . The outlet  18  has an electromagnetic closure mechanism  20 . 
     A liquid phase sample conduit  22  leads into the flask  12 . 
     A further liquid phase sample conduit  24  leads into the tube  14 . 
     A first thermometer  26  is adapted to read the temperature of the liquid contained in the flask  12 , and a second thermometer  28  is adapted to read the temperature of the vapour in the tube  14 . 
     The flask  12  can be heated by a heating mantle  30 . 
     The extractive distillation procedure is as follows: 
     A liquid mixture is prepared consisting of the components to be separated and, an extractive distillation solvent. The liquid is introduced into the bulb flask  12  via conduit  22 . 
     The mixture in the bulb flask  12  is then heated by the heating mantle  30  and kept at boiling point. 
     During boiling the mixture separates into a liquid phase remaining in the bulb flask  12  and a vapour phase in the tube  14 . In the tube  14  the vapour phase is cooled by the condenser  16 , whereafter it condenses and returns as liquid to the bulb flask  12 . 
     The mixture is boiled and condensed for several hours, normally 5 to 6 hours. The process of evaporation and condensation is repeated until equilibrium is reached between the vapour and liquid phases. Thereafter, a liquid sample of the liquid phase in the bulb flask  12  is extracted through conduit  22  and a liquid sample of the condensed vapour phase in the tube  14  Is extracted through conduit  24 . 
     The temperature of the liquid phase in the bulb flask  12  is continuously monitored by the thermometer  26 , and the temperature of the vapour phase in the tube  14  is continuously monitored by the thermometer  28 . 
     Experiment 1 
     An ethanol/ethyl acetate mixture with a molar ratio of 1:1 has a relative volatility of 0.92. 
     The separation was effected by using a suitable amine as an extractive distillation solvent. 
     A mixture of ethanol (16.8 g), ethyl acetate (31.2 g) and di-ethylene-triamine (289.8 g) was charged into the flask  12  of the vapour-liquid equilibrium still  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.103 
                 0.725 
               
               
                   
                 Ethyl Acetate 
                 0.100 
                 0.275 
               
               
                   
                 Di-ethylene-triamine 
                 0.797 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.56 for the system ethanol/ethyl acetate in the ternary system shown above, the ethanol being the distillate. 
     Experiment 2 
     An ethanol/ethyl acetate mixture with a molar ratio of 0.7:1 has a relative volatility of 1.05. 
     The separation was effected by using a suitable substituted thiophene as an extractive distillation solvent. A mixture of ethanol (2.3 g), ethyl acetate (6.0 g) and ethyl thiophene (24.7 g) was charged into the flask  12  of the vapour-liquid equilibrium  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.148 
                 0.690 
               
               
                   
                 Ethyl Acetate 
                 0.202 
                 0.295 
               
               
                   
                 Ethyl Thiophene 
                 0.651 
                 0.015 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 3.19 for the system ethanol/ethyl acetate in the ternary system shown above, the ethanol being the distillate. 
     Experiment 3 
     An ethanol/ethyl acetate mixture with a molar ratio of 1:1 has a relative volatility of 0.91. 
     The separation was effected by using a suitable paraffin as an extractive is distillation solvent. A mixture of ethanol (9.7 g), ethyl acetate (17.7 g) and dodecane (238.2 g) was charged into the flask  12  of the vapour-liquid equilibrium still  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.116 
                 0.707 
               
               
                   
                 Ethyl Acetate 
                 0.111 
                 0.280 
               
               
                   
                 Dodecane 
                 0.773 
                 0.013 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.41 for the system ethanol/ethyl acetate in the ternary system shown above, the ethanol being the distillate. 
     An ethanol/water liquid mixture with a molar ratio of 1.25:1 has a relative volatility of 1.71. 
     The separation was effected by using a suitable amine as an extractive distillation solvent. 
     A mixture of ethanol (23.7 g), water (7.4 g) and diethylenetriamine (330.7 g) was charged into the flask  12  of the vapour-liquid equilibrium still  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.125 
                 0.750 
               
               
                   
                 Water 
                 0.100 
                 0.250 
               
               
                   
                 Diethylenetriamine 
                 0.776 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.4 for the system ethanol/water in the ternary system shown above, the ethanol being the distillate. 
     Experiment 5 
     An ethanol/water liquid mixture with a molar ratio of 4:1 has a relative volatility of 1.12. 
     The separation was effected by using a suitable amine as an extractive distillation solvent. 
     A mixture of ethanol (11.1 g), water (1.1 g) and 1,3-diaminopentane (197.7 g) was charged into the flask  12  of the vapour-liquid equilibrium still  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.108 
                 0.732 
               
               
                   
                 Water 
                 0.027 
                 0.242 
               
               
                   
                 1,3-diaminopentane 
                 0.865 
                 0.026 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 1.33 for the system water/ethanol in the ternary system shown above, the water being the distillate. 
     Experiment 6 
     An ethanol/water mixture with a molar ratio of 0.9:1 has a relative volatility of 2.07. 
     The separation was effected by using a suitable chlorinated hydrocarbon as an extractive distillation solvent. 
     A mixture of ethanol (16.34 g), water (7.1 g) and hexachlorobutadiene (372.2 g) was charged into the flask  12  of the vapour-liquid equilibrium still  10  and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Ethanol 
                 0.163 
                 0.682 
               
               
                   
                 Water 
                 0.181 
                 0.311 
               
               
                   
                 Hexachlorobutadiene 
                 0.656 
                 0.007 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.43 for the system ethanol/water in the ternary system shown above, the ethanol being the distillate.