Abstract:
A method of separating aromatic hydrocarbons and non-aromatic hydrocarbons, and aromatic hydrocarbons and naphtenes 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 ester of a dibasic acid, an acetonyl acetone or morpholine.

Description:
This is a continuation of International PCT Application Numbers PCT/IB00/00075 and PCT/IB00/00078, filed on Jan. 26, 2000. 
    
    
     FIELD OF INVENTION 
     The present invention relates to the separation of components from aromatic hydrocarbon 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. 
     As an example, the separation of C7, C8-isomers (non-aromatic hydrocarbons) and toluene (aromatic hydrocarbons) is complicated due to low relative volatilitles or the existence of an azeotrope. Aniline or phenol have been proposed in the literature as extractive distillation solvents to produce C7, C8-isomers as distillate. 
     As an example, the separation of benzene (aromatic hydrocarbons) and cyclohexane (naphtenes) is complicated due to the existence of an azeotrope. Aniline has been proposed in the literature as extractive distillation solvents to produce cyclohexane as distillate. 
     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 mixtures thereof. 
     SUMMARY OF INVENTION 
     According to the invention, a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons, includes the step of distilling a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons containing at least aromatic hydrocarbons and non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent being an ester of a dibasic acid. 
     The aromatic hydrocarbons and non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons. 
     The non-aromatic hydrocarbons may be at least one of the compounds selected from a group consisting of C7-isomers and C8-isomers. 
     The aromatic hydrocarbons may be toluene. 
     The ester of a dibasic acid may be selected from a group consisting of dimethylmaleate and dimethylphtalate. 
     Also according to the invention, a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons includes the step of distilling a mixture of aromatic hydrocarbons excluding benzene and non-aromatic hydrocarbons containing at least aromatic hydrocarbons excluding benzene and non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent being N-methyl 2-pyrrolidone. 
     The aromatic hydrocarbons/non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons. 
     The non-aromatic hydrocarbons may be least one of the compounds selected from a group consisting of C7-isomers and C8-isomers. 
     The aromatic hydrocarbons may be toluene. 
     The non-aromatic hydrocarbons may be naphtenes and the extractive distillation solvent may be selected from the group consisting of a dione, an ester of a dibasic acid and a morpholine. 
     The aromatic hydrocarbons and naphtenes mixture may contain only aromatic hydrocarbons and naphtenes. 
     The aromatic hydrocarbons may be benzene. 
     The naphtenes may be cyclohexane. 
     The dione may be acetonyl acetone. 
     The ester of a dibasic acid may be selected from a group consisting of dimethylmaleate and dimethylphtalate. 
    
    
     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 
     A C7, C8-isomers/toluene liquid mixture with a molar ratio of 0.96:1 has a relative volatility of 1.41. 
     The separation was effected by using a suitable ester of a dibasic acid as an extractive distillation solvent. 
     A mixture of C7, C8-isomers (19.1 g), toluene (18.4 g) and Dimethylphtalate (266.2 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 1 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 C7, C8-isomers 
                 0.108 
                 0.868 
               
               
                   
                 Toluene 
                 0.113 
                 0.132 
               
               
                   
                 Dimethylphtalate 
                 0.778 
                 0.00  
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 6.89 for the system C7, C8-isomers/toluene in the ternary system shown above, the C7, C8-isomers being the distillate. 
     EXPERIMENT 2 
     A C7, C8-isomers/toluene mixture with a molar ratio of 1.1:1 has a relative volatility of 1.38. 
     The separation was effected by using N-methyl-2-pyrolidone (NMP) as an extractive distillation solvent. 
     A mixture of C7, CS-isomers (30.2 g), toluene (25.2 g) and NMP (208.8 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 2 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 C7, C8-isomers 
                 0.183 
                 0.874 
               
               
                   
                 Toluene 
                 0.166 
                 0.124 
               
               
                   
                 NMP 
                 0.651 
                 0.002 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 6.36 for the system C7, C8-isomer/toluene in the ternary system shown above, the C7, C8-isomers being the distillate. 
     EXPERIMENT 3 
     An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1:1.06 has a relative volatility of 1.38. 
     The separation was effected by using N-methyl-2-pyrrolidone as an extractive distillation solvent. 
     A mixture of 2,2,4-trimethylpentane (19.3 g), toluene (16.5 g) and NMP (130.4 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) 
               
               
                   
                   
               
             
             
               
                   
                 2,2,4-trimethylpentane 
                 0.102 
                 0.752 
               
               
                   
                 Toluene 
                 0.108 
                 0.198 
               
               
                   
                 NMP 
                 0.791 
                 0.050 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 4.04 for the system 2,2,4-trimethylpentane/toluene in the ternary system shown above, the 2,2,4-trimethylpentane being the distillate. 
     EXPERIMENT 4 
     An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1:1.16 has a relative volatility of 1.40. 
     The separation was effected by using a suitable ester of a dibasic acid such as dimethylmaleate as an extractive distillation solvent. 
     A mixture of 2,2,4-trimethylpentane (22.9 g), toluene (21.4 g) and dimethylmaleate (226.5 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) 
               
               
                   
                   
               
             
             
               
                   
                 2,2,4-trimethylpentane 
                 0.100 
                 0.750 
               
               
                   
                 Toluene 
                 0.116 
                 0.222 
               
               
                   
                 Dimethylmaleate 
                 0.784 
                 0.027 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 3.91 for the system 2,2,4-trimethylpentane/toluene in the ternary system shown above, the 2,2,4-trimethylpentane being the distillate. 
     EXPERIMENT 5 
     An 2,2,4-trimethylpentaneltoluene mixture with a molar ratio of 1:1.16 has a relative volatility of 1.40. 
     The separation was effected by using a suitable ester of a dibasic acid such as dimethylphtalate as an extractive distillation solvent. 
     A mixture of 2,2,4-trimethylpentane (18.9 g), toluene (14.9 g) and dimethylphtalate (246.8 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 5 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 2,2,4-trimethylpentane 
                 0.104 
                 0.763 
               
               
                   
                 Toluene 
                 0.101 
                 0.237 
               
               
                   
                 Dimethylphtalate 
                 0.795 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 3.15 for the system 2,2,4-trimethylpentane/toluene in the ternary system shown above, the 2.2,4-trimethylpentane being the distillate. 
     EXPERIMENT 6 
     A cyclohexane/benzene liquid mixture with a molar ratio of 1:1 has a relative volatility of 0.97. 
     The separation was effected by using a suitable dione as, an extractive distillation solvent. 
     A mixture of cyclohexane (34.8 g), benzene (33.2 g) and acetonylacetone (181.1 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 fractionss were determined to be as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Benzene 
                 0.175 
                 0.173 
               
               
                   
                 Cyclohexane 
                 0.171 
                 0.821 
               
               
                   
                 Acetonylacetone 
                 0.654 
                 0.006 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 4.87 for the system cyclohexane/benzene in the ternary system shown above, the cyclohexane being the distillate. 
     EXPERIMENT 7 
     A benzene/cyclohexane mixture with a molar ratio of 1:1 has a relative volatility of 0.97. 
     The separation was effected by using a suitable ester of a dibasic acid as an extractive distillation solvent. 
     A mixture of cyclohexane (24.9 g), benzene (24.6 g) and dimethylmaleate (339.0 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 7 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Cyclohexane 
                 0.100 
                 0.654 
               
               
                   
                 Benzene 
                 0.106 
                 0.335 
               
               
                   
                 Dimethylmaleate 
                 0.794 
                 0.011 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.06 for the system benzenelcyclohexane in the ternary system shown above, the cyclohexane being the distillate. 
     EXPERIMENT 8 
     A cyclohexanelbenzene mixture with a molar ratio of 0.63:1 has a relative volatility of 1.05. 
     The separation was effected by using morpholine as an extractive distllation solvent. 
     A mixture of cyclohexane (22.5 g), benzene (22.0 g) and morpholine (175.5 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 8 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Cyclohexane 
                 0.049 
                 0.585 
               
               
                   
                 Benzene 
                 0.077 
                 0.415 
               
               
                   
                 Morpholine 
                 0.874 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 2.21 for the system cyclohexanelbenzene in the ternary system shown above, the cyclohexane being the distillate. 
     EXPERIMENT 9 
     A benzenelcyclohexane mixture with a molar ratio of 1:1.37 has a relative volatility of 0.92. 
     The separation was effected by using a suitable ester of a dibasic acid as an extractive distillation solvent. 
     A mixture of benzene (13.5 g), cyclohexane (20.0 g) and dimethylphthalate (268.4 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 9 
               
               
                   
                   
               
               
                   
                   
                 Liquid (mole 
                 Vapour (mole 
               
               
                   
                 Component 
                 fraction) 
                 fraction) 
               
               
                   
                   
               
             
             
               
                   
                 Benzene 
                 0.099 
                 0.326 
               
               
                   
                 Cyclohexane 
                 0.136 
                 0.674 
               
               
                   
                 Dimethylphthalate 
                 0.764 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     This translates to a relative volatility of 1.50 for the system cyclohexane/benzene in the ternary system shown above, the cyclohexane being the distillate.