Abstract:
Tetrachloroethylene cannot be completely separated from methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol or t-amyl alcohol by conventional distillation or rectification because of the minimum boiling azeotropes. Tetrachloroethylene can be readily separated from these alcohols by extractive distillation. A typical effective agent is dimethylsulfoxide.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating tetrachloroethylene from the lower alcohols using certain organic compounds as the agent in extractive distillation. 
     DESCRIPTION OF PRIOR ART 
     Extractive distillation is the method of separating close boiling compounds or azeotropes 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 agent 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. When the compounds to be separated normally form an azeotrope, the proper agents will cause them to boil separately during the extractive distillation and thus make possible a separation in a rectification column that cannot be done at all when no agent is present. The extractive agent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive agent is introduced a few plates from the top of the column to insure that none of the extractive agent is carried over with lowest boiling component. This usually requires that the extractive agent boil twenty Centigrade degrees or more than the lowest boiling component. 
     At the bottom of a continuous column, the less volatile components of the close boiling mixtures and the extractive agent are continuously removed from the column. The usual methods of separation of these two components are the use of another rectification column, cooling and phase separation or solvent extraction. 
     Tetrachloroethylene, B.P.=121° C. forms minimum boiling azeotropes with the lower alcohols. With methanol, azeotrope boils at 63.7° C. and contains 37.5% tetrachloroethylene; with ethanol, the azeotrope boils at 76.7° C. and contains 37% tetrachloroethylene; with 1-propanol, the azeotrope boils at 94° C. and contains 52% tetrachloroethylene; with isopropanol, the azeotrope boils at 81.7° C. and contains 30% tetrachloroethylene; with 1-butanol, the azeotrope boils at 110° C. and contains 68% tetrachloroethylene; with 2-butanol, the azeotrope boils at 97° C. and contains 43% tetrachloroethylene; with isobutanol, the azeotrope boils at 103° C. and contains 60% tetrachloroethylene; with 1-pentanol, the azeotrope boils at 117° C. and contains 85% tetrachloroethylene; with 2-pentanol, the azeotrope boils at 113° C. and contains 66% tetrachloroethylene; with 3-methyl-2-butanol, the azeotrope boils at 116° C. and contains 81% tetrachloroethylene and with t-amyl alcohol, the azeotrope boils at 101° C. and contains 27% tetrachloroethylene. 
     Extractive distillation would be an attractive method of effecting the separation of tetrachloroethylene from these alcohols if agents can be found that (1) will enhance the relative volatility between tetrachloroethylene and these alcohols and (2) are easy to recover, that is, form no azeotrope with tetrachloroethylene or the alcohols and boil sufficiently above tetrachloroethylene and these alcohols to make separation by rectification possible with only a few theoretical plates. 
     Extractive distillation typically requires the addition of an equal amount to twice as much extractive agent as the tetrachloroethylene-alcohol mixture on each plate of the rectification column. The extractive agent should be heated to about the same temperature as the plate into which it is introduced. Thus, extractive distillation imposes an additional heat requirement on the column as well as somewhat larger plates. However this is less than the increase occasioned by the additional agents required in azeotropic distillation. 
     Another consideration in the selection of the extractive distillation agent is its recovery from the bottoms product. The usual method is by rectification in another column. In order to keep the cost of this operation to a minimum, an appreciable boiling point difference between the compound being separated and the extractive agent is desirable. We recommend twenty Centigrade degrees or more difference. It is also desirable that the extractive agent be miscible with the tetrachloroethylene and the alcohols otherwise it will form a two phase azeotrope with it and some other method of separation will have to be employed. 
     
                       TABLE 1______________________________________Effect of Relative Volatility on the Separation ofTetrachloroethylene From Alcohols at 99% PurityRelative   Theoretical             Actual Plates                         Actual PlatesVolatility   Plates    75% Efficiency                         75% Eff., Min. Reflux______________________________________1.2     50        67          871.5     23        31          402.0     13        17          223.0      9        12          16______________________________________ 
    
     The advantage of employing an effective extractive distillation agent is shown in Table 1. Tetrachloroethylene forms minimum boiling azeotropes with the lower alcohols which possess a relative volatility of 1.0 and cannot be separated by rectification. If extractive distillation is employed with an agent yielding a relative volatility of 2.0, a rectification column of only 22 actual plates will be required 
     OBJECTIVE OF THE INVENTION 
     The objects of this invention are to provide a process of method of extractive distillation that will enhance the relative volatility of tetrachloroethylene to methanol, ethanol,1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol and t-amyl alcohol in their separation in a rectification column. It is a further object of this invention to identify organic compounds that are stable, can be separated from tetrachloroethylene or the alcohols by rectification with relatively few plates and can be recycled to the extractive distillation column with little decomposition. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are provided by a process for the separation of tetrachloroethylene from methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol and t-amyl alcohol which entails the use of certain organic compounds as the agent in extractive distillation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     We have discovered that certain organic compounds will effectively increase the relative volatility between tetrachloroethylene and methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol or t-amyl alcohol when employed as the agent in extractive distillation. 
     The data in Tables 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18, 20, 21, 23, 25, 26, 28, 29, 31 and 32 was obtained in a vapor-liquid equilibrium still. In every case, the starting mixture was the tetrachloroethylene-alcohol azeotrope. The relative volatilities are listed for each of the agents. 
     Table 2 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from methanol. They are dimethylsulfoxide, acetophenone, 2-heptanone, 3-heptanone, 5-methyl-2-hexanone, adiponitrile, 2-octanone, isophorone, 3,3-dimethyl-2-butanone, diisobutyl ketone, isobutyl heptyl ketone, 2,4-pentanedione, acetonyl acetone, methyl benzoate, methyl salicylate, hexyl formate, isobutyl butyrate, hexyl acetate, amyl propionate, ethyl n-valerate, ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, phenyl acetate, propoxypropanol, butoxypropanol, dipropylene glycol methyl ether acetate, benzyl acetate, ethyl caproate and diethylene glycol diethyl ether. 
     Table 3 lists the compounds that were found to be ineffective agents for separating tetrachloroethylene from methanol. 
     
                       TABLE 2______________________________________Effective Agents For SeparatingTetrachloroethylene From Methanol                   RelativeCompounds               Volatility______________________________________Dimethylsulfoxide       1.45*Acetophenone            1.62-Heptanone             1.83-Heptanone             2.25-Methyl-2-hexanone     1.7Adiponitrile            1.2*2-Octanone              2.83,3-Dimethyl-2-butanone 1.65Diisobutyl ketone       1.85Isobutyl heptyl ketone  1.952,4-Pentanedione        1.4Isophorone              3.7Acetonyl acetone        1.75Methyl benzoate         1.6Methyl salicylate       2.1Hexyl formate           4.2Isobutyl butyrate       3.8Hexyl acetate           3.2Amyl propionate         3.4Ethyl n-valerate        1.85Ethylene glycol butyl ether acetate                   1.55Ethylene glycol ethyl ether acetate                   1.6Diethylene glycol ethyl ether acetate                   1.3Propoxypropanol         1.3Butoxypropanol          1.4Phenyl acetate          1.55Dipropylene glycol methyl ether acetate                   1.2Benzyl acetate          1.3Ethyl caproate          2.1Diethylene glycol diethyl ether                   1.75______________________________________ *Brings tetrachloroethylene out as overhead 
    
     
                       TABLE 3______________________________________Ineffective Agents For SeparatingTetrachloroethylene From Methanol______________________________________Sulfolane         Dimethylformamide3-Octanone        DimethylacetamideEthylene glycol diacetate             Glycerol triacetatePropylene carbonate             1-Methoxy-2-propanol acetate______________________________________ 
    
     One of the agents, methyl benzoate, whose relative volatility had been determined in the vapor-liquid equilibrium still, was then evaluated in a glass perforated plate rectification column and the results listed in Table 4. Methyl benzoate gave a relative volatility of 1.44 after one hour and 1.62 after two hours of operation. 
     
                       TABLE 4______________________________________Data From Run Made In Rectification Column           Time   Weight % Weight %                                   RelativeAgent  Column   hrs.   CCl.sub.2 --CCl.sub.2                           Methanol                                   Volatility______________________________________Methyl Overhead 1      2.2      97.8    1.44benzoate  Bottoms         24.4     75.6Methyl Overhead 2      0.6      99.4    1.62benzoate  Bottoms         17.7     82.3______________________________________ 
    
     Table 5 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from ethanol. They are dimethylsulfoxide, acetophenone, 5-methyl-2-hexanone, diisobutyl ketone, 2-heptanone, 3-heptanone, isobutyl heptyl ketone, 4-heptanone, 2,6-dimethyl-4-heptanone, 2-undecanone, 2,4-pentanedione, 2-octanone, 3-octanone, ethylene glycol methyl ether, diethylene glycol butyl ether, propoxypropanol, butoxypropanol, isophorone, methyl salicylate, diethylene glycol diethyl ether, 4-methyl-2-pentanol, n-decanol, methyl benzoate, amyl acetate, hexyl acetate, benzyl acetate, ethyl hexyl acetate, isobornyl acetate, amyl propionate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, isobutyl propionate, propyl caproate, ethyl valerate, diethyl malonate and hexyl formate. 
     Table 6 lists the compounds that we found to be ineffective agents for separating tetrachloroethylene from ethanol. 
     One of the agents, diisobutyl ketone, whose relative volatility had been determined in the vapor-liquid equilibrium still, was then evaluated in a glass perforated plate rectification column and the results listed in Table 7. Diisobutyl ketone gave a relative volatility of 1.35 after one hour and 1.62 after 1.5 hours of operation. 
     Table 8 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 1-propanol. They are dimethylsulfoxide, sulfolane, dimethylformamide, dimethylacetamide, 3-heptanone, 5-methyl-2-hexanone, adiponitrile, 2-octanone, diisobutyl ketone, 3-octanone, 2,4-pentanedione, isophorone, methyl benzoate, hexyl formate, isobutyl butyrate, hexyl acetate, amyl propionate, ethyl n-valerate, ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, butoxypropanol, phenyl acetate, dipropylene glycol methyl ether acetate, benzyl acetate, ethylene glycol diacetate, glycerol triacetate, triethylene glycol diacetate, diethylene glycol diethyl ether and propylene carbonate. 
     Table 9 lists the compound that we have found to be ineffective agents for separating tetrachloroethylene from 1-propanol. 
     
                       TABLE 5______________________________________Effective Agents For SeparatingTetrachloroethylene From Ethanol                 RelativeCompounds             Volatility______________________________________Dimethylsulfoxide     1.4*Acetophenone          1.655-Methyl-2-hexanone   1.55Diisobutyl ketone     1.62-Heptanone           1.553-Heptanone           1.5Isobutyl heptyl ketone                 1.84-Heptanone           1.62,6-Dimethyl-4-heptanone                 1.82-Undecanone          2.02,4-Pentanedione      1.32-Octanone            1.33-Octanone            1.5Ethylene glycol methyl ether                 1.4*Diethylene glycol butyl ether                 1.2Propoxypropanol       1.3Butoxypropanol        1.2Isophorone            1.45Methyl salicylate     1.6Diethylene glycol diethyl ether                 1.34-Methyl-2-pentanol   1.3n-Decanol             1.2Methyl benzoate       1.4Amyl acetate          1.7Hexyl acetate         1.75Benzyl acetate        1.3Ethyl hexyl acetate   1.5Isobornyl acetate     1.3Ethylene glycol butyl ether acetate                 1.3Diethylene glycol ethyl ether acetate                 1.4Amyl propionate       1.7Isobutyl butyrate     1.9Propyl caproate       1.4Ethyl valerate        1.7Diethyl malonate      1.25Hexyl formate         1.8______________________________________ *Brings out tetrachloroethylene as overhead 
    
     
                       TABLE 6______________________________________Ineffective Agents For SeparatingTetrachloroethylene From Ethanol______________________________________Sulfolane         DimethylformamideDimethylacetamide AdiponitrileEthylene glycol ethyl ether             Ethylene glycol butyl etherEthylene glycol phenyl ether             Diethylene glycol methyl etherIsoamyl alcohol   Diethylene glycol ethyl etherPropylene carbonate             Isooctyl alcoholTridecyl alcohol  Benzyl alcoholButyl-acetate     Tetrahydrofurfuryl alcoholPropylene glycol phenyl ether             1-Methoxy-2-propanol acetateDiethyl maleate   1-Methyl-2-pyrrolidinone______________________________________ 
    
     
                       TABLE 7______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % %      RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            Ethanol                                   Volatility______________________________________Diisobutyl   Over-    1      4.5      95.5   1.35ketone  head   Bottoms         29.7     70.3Diisobutyl   Over-    1.5    1.4      98.6   1.62ketone  head   Bottoms         32.7     67.3______________________________________ 
    
     One of the agents, diisobutyl ketone, whose relative volatility had been determined in the vapor-liquid equilibrium still, was then evaluated in a glass perforated plate rectification column and the results listed in Table 10. Diisobutyl ketone gave a relative volatility of 1.15 after one hour and 1.46 after two hours of operation. 
     Table 11 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from isopropanol. They are dimethylsulfoxide, acetophenone, diisobutyl ketone, 5-methyl-2-hexanone, 2-heptanone, 3-heptanone, 4-heptanone, isobutyl heptyl ketone, 2-octanone, 2,6-dimethyl-4-heptanone, methyl benzoate, 2-undecanone, 2,4-pentanedione, propiophenone, 3-octanone, acetonyl acetone, methyl salicylate, amyl acetate, 2-ethyl hexyl acetate, hexyl acetate, ethylene glycol butyl ether, benzyl acetate, dipropylene glycol methyl ether acetate, ethylene glycol phenyl ether, ethyl caproate, propyl butyrate, isobutyl butyrate, hexyl formate, ethyl isovalerate, isophorone, propoxypropanol and butoxypropanol. 
     Table 12 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from isopropanol. 
     One of the agents, diisobutyl ketone, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 13. Diisobutyl ketone gave a relative volatility of 1.37 after one hour and 1.72 after 1.5 hours of operation. 
     
                       TABLE 8______________________________________Effective Agents For SeparatingTetrachloroethylene From 1-Propanol                   RelativeCompounds               Volatility______________________________________Dimethylsulfoxide       2.6Sulfolane               2.1Dimethylformamide       2.0Dimethylacetamide       1.93-Heptanone             1.2*5-Methyl-2-hexanone     1.7*Adiponitrile            1.62-Octanone              1.25Diisobutyl ketone       1.453-Octanone              1.22,4-Pentanedione        2.2Isophorone              1.3Methyl benzoate         1.25Hexyl formate           1.9Isobutyl butyrate       1.55Hexyl acetate           1.6Amyl propionate         1.3Ethyl n-valerate        1.25Ethylene glycol butyl ether acetate                   1.35Ethylene glycol ethyl ether acetate                   1.45Butoxypropanol          1.35Phenyl acetate          1.55Dipropylene glycol methyl ether acetate                   1.55Benzyl acetate          1.8Ethylene glycol diacetate                   1.2Glycerol triacetate     1.2*Triethylene glycol diacetate                   1.55Diethylene glycol diethyl ether                   1.55Propylene carbonate     1.3*______________________________________ *Brings 1propanol out as overhead 
    
     
                       TABLE 9______________________________________Ineffective Agents For SeparatingTetrachloroethylene From 1-Propanol______________________________________Acetophenone      2-Heptanone3,3-Dimethyl-2-butanone             Isobutyl heptyl ketoneAcetonyl acetone  Methyl salicylatePropoxypropanol   Diethylene glycol ethyl ether1-Methoxy-2-propanol acetate             acetate______________________________________ 
    
     
                       TABLE 10______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % 1-Pro-                                   RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            panol  Volatility______________________________________Diisobutyl   Over-    1      26.5     73.5   1.15ketone  head   Bottoms         51.4     48.6Diisobutyl   Over-    1.5    5.6      94.4   1.46ketone  head   Bottoms         48.7     51.3______________________________________ 
    
     Table 14 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 1-butanol. They are propoxypropanol, butoxypropanol, mesityl oxide, 1-methoxy-2propanol acetate, dipropylene glycol methyl ether, diethylene glycol ethyl ether, 1-methoxy-2propanol, ethylene glycol methyl ether, ethyl 3-ethoxypropionate, diethylene glycol methyl ether, ethylene glycol butyl ether, ethylene glycol ethyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol isobutyl ether, 4-methoxy-4-methyl pentanone-2, ethylene glycol phenyl ether, dimethylsulfoxide, dimethylformamide, dimethylacetamide, acetophenone, adiponitrile, isophorone, hexyl acetate, hexyl formate and ethyl n-valerate. 
     Table 15 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from 1-butanol. 
     One of the agents, dipropylene glycol methyl ether, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 16. Dipropylene glycol methyl ether gave a relative volatility of 1.2 after one hour and 1.72 after two hours of operation. 
     Table 17 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 2-butanol. They are ethyl valerate, ethyl butyrate, isobutyl butyrate, ethyl isovalerate, isobornyl acetate, hexyl acetate, isobutyl isobutyrate, ethylene glycol ethyl ether acetate, dipropylene glycol methyl ether acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol hexyl ether, diethylene glycol hexyl ether, 4-methyl pentyl acetate-2, hexyl formate, diethylene glycol methyl ether, 4-methyl-2-pentanone and isophorone. 
     Table 18 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from 2-butanol. 
     One of the agents, isobornyl acetate, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 19. Isobornyl acetate gave a relative volatility of 1.39 after one hour of operation. 
     
                       TABLE 11______________________________________Effective Agents For SeparatingTetrachloroethylene From Isopropanol                   RelativeCompounds               Volatility______________________________________Dimethylsulfoxide       1.3*Acetophenone            1.75-Methyl-2-hexanone     1.55Diisobutyl ketone       1.62-Heptanone             2.13-Heptanone             1.4Isobutyl heptyl ketone  1.44-Heptanone             1.42-Octanone              1.52,6-Dimethyl-4-heptanone                   1.42-Undecanone            1.42,4-Pentanedione        1.3Propiophenone           1.43-Octanone              1.2Acetonyl acetone        2.0Methyl benzoate         2.1Methyl salicylate       1.5Amyl acetate            1.82-Ethyl hexyl acetate   1.6Hexyl acetate           1.4Ethylene glycol butyl ether                   1.3Dipropylene glycol methyl ether acetate                   1.5Ethylene glycol phenyl ether                   1.4Benzyl acetate          1.4Ethyl caproate          1.8Propyl butyrate         1.6Isobutyl butyrate       1.5Hexyl formate           1.3Ethyl isovalerate       1.8Isophorone              1.4Propoxypropanol         1.3Butoxypropanol          1.3______________________________________ *Brings tetrachloroethylene out as overhead 
    
     
                       TABLE 12______________________________________Ineffective Agents For SeparatingTetrachloroethylene From Isopropanol______________________________________Sulfolane      DimethylformamideAdiponitrile   DimethylacetamideEthylene glycol phenyl ether          4-Methoxy-4-methyl          pentanone-2Ethylene glycol methyl ether          Diethylene glycol methyl etherDiethylene glycol ethyl ether          Propylene glycol phenyl etherEthylene glycol ethyl ether          1-Methyl-2-pyrrolidinone______________________________________ 
    
     
                       TABLE 13______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % Iso- RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            propanol                                   Volatility______________________________________Diisobutyl   Over-    1      3.1      96.9   1.37ketone  head   Bottoms         24.3     75.7Diisobutyl   Over-    1.5    0.6      99.4   1.72ketone  head   Bottoms         23.7     76.3______________________________________ 
    
     
                       TABLE 14______________________________________Effective Agents For SeparatingTetrachloroethylene From 1-Butanol               RelativeCompounds           Volatility______________________________________Propoxypropanol     1.5*Butoxypropanol      1.3*1-Methoxy-2-propanol acetate               1.9Mesityl oxide       1.25Dipropylene glycol methyl ether               1.8Diethylene glycol ethyl ether               1.51-Methoxy-2-propanol               2.2Ethyl 3-ethoxypropionate               2.8Diethylene glycol methyl ether               1.8Ethylene glycol butyl ether               1.35Ethylene glycol methyl ether               2.4Ethylene glycol ethyl ether               2.2Diethylene glycol butyl ether               1.65Propylene glycol methyl ether               2.1Propylene glycol isobutyl ether               1.754-Methoxy-4-methyl pentanone-2               1.5Ethylene glycol phenyl ether               1.45Dimethylsulfoxide   3.6Dimethylformamide   3.0Dimethylacetamide   2.7Acetophenone        1.3Adiponitrile        1.2Isophorone          1.4*Hexyl acetate       1.3Hexyl formate       1.2Ethyl n-valerate    1.5______________________________________ *Brings 1butanol out as overhead 
    
     
                       TABLE 15______________________________________Ineffective Agents For SeparatingTetrachloroethylene From 1-Butanol______________________________________Hexyl acetate    Dipropylene glycol methyl ether            acetateMethyl isoamyl ketone            Ethylene glycol ethyl ether            acetateEthylene glycol methyl ether            4-Methoxy-2-pentanoneDiisobutyl ketone            2,6-Dimethyl-4-heptanoneSulfolane        2-Heptanone3-Heptanone      2-OctanoneAmyl acetate     Ethyl phenyl acetateBenzyl acetate   Methyl benzoate______________________________________ 
    
     
                       TABLE 16______________________________________Data From Run Made In Rectification Column                             Weight Rela-             Time   Weight % % 1-But-                                    tive Vola-Agent    Column   hrs.   CCl.sub.2 --CCl.sub.2                             anol   tility______________________________________Dipropylene    Over-    1      85.1     14.9   1.2glycol   headmethyl ether    Bottoms         60.4     39.6Dipropylene    Over-    2      98.9     1.1    1.72glycol   headmethyl ether    Bottoms         62.2     37.8______________________________________ 
    
     
                       TABLE 17______________________________________Effective Agents For SeparatingTetrachloroethylene From 2-Butanol                   RelativeCompounds               Volatility______________________________________Ethyl valerate          1.3Ethyl butyrate          1.35Isobutyl butyrate       1.5Ethyl isovalerate       1.85Isobornyl acetate       1.4Hexyl acetate           1.35Isobutyl isobutyrate    1.55Ethylene glycol ethyl ether acetate                   1.4Dipropylene glycol methyl ether acetate                   1.2Ethylene glycol methyl ether                   1.3*Ethylene glycol ethyl ether                   1.2*Ethylene glycol hexyl ether                   1.2*Diethylene glycol hexyl ether                   1.254-Methyl pentyl acetate-2                   1.25Hexyl formate           1.3Diethylene glycol methyl ether                   1.75*4-Methyl-2-pentanone    1.2*Isophorone              1.2*______________________________________ *Brings tetrachloroethylene out as overhead 
    
     
                       TABLE 18______________________________________Ineffective Agents For SeparatingTetrachloroethylene From 2-Butanol______________________________________Ethylene glycol butyl ether            Diethylene glycol ethyl etherDiethylene glycol butyl ether            Dipropylene glycol methyl etherPropylene glycol methyl ether            Tripropylene glycol methyl etherPropylene glycol isobutyl ether            1-Methoxy-2-propanol acetatePropoxypropanol  ButoxypropanolCyclohexanol     2-Ethyl hexyl acetateMethyl benzoate  Ethyl benzoateDiethyl maleate______________________________________ 
    
     
                       TABLE 19______________________________________Data From Run Made In Rectification Column           Time   Weight % Weight %                                   RelativeAgent  Column   hrs.   CCl.sub.2 --CCl.sub.2                           2-Butanol                                   Volatility______________________________________Isobornyl  Over-    1      6.1      93.9    1.39acetate  head  Bottoms         41.5     58.5______________________________________ 
    
     Table 20 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from isobutanol. They are ethyl valerate, ethyl isovalerate, ethyl butyrate, amyl acetate, hexyl formate, 4-methyl pentyl acetate-2, ethyl hexyl acetate, methyl caproate, methyl benzoate, ethyl benzoate, ethylene glycol butyle ether acetate, isobutyl butyrate, isobutyl isobutyrate, 1-methoxy-2-propanol acetate, 3-heptanone, isobutyl heptyl ketone, dimethylsulfoxide, dimethylformaide, acetophenone, dimethylacetamide and sulfolane. 
     Table 21 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from isobutanol. 
     One of the agents, dimethylsulfoxide, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 22. Dimethylsulfoxide gave a relative volatility of 2.2 after one hour and 2.3 after two hours of operation. Table 23 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 1-pentanol. They are dimethylsulfoxide, sulfolane, dimethylformamide, dimethylacetamide, acetophenone, adiponitrile, 2-heptanone, 3-heptanone, 3-methyl-2-hexanone, 2-octanone, diisobutyl ketone, isobutyl heptyl ketone, 2,6-dimethyl-4-heptanone, 2,4-phentanedione, isophorone, acetonyl acetone, methyl benzoate, methyl salicylate, n-hexyl formate, hexyl acetate, isobutyl butyrate, amyl propionate, ethyl n-valerate, ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, propoxypropanol, butoxypropanol, phenyl acetate, ethyl isovalerate, ethyl caproate, diethylene glycol diethyl ether, propylene carbonate and diethyl maleate. 
     One of the agents, diisobutyl ketone, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 24. Diisobutyl ketone gave a relative volatility of 1.45 after one hour and 1.36 after 1.5 hours of operation. 
     Table 25 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 2-pentanol. They are dimethylsulfoxide, sulfolane, dimethylformamide, dimethylacetamide, adiponitrile, diethylene glycol ethyl ether, diethylene glycol diethyl ether, 2,4-pentanedione, ethylene carbonate, propylene carbonate, 1-methyl-2-pyrrolidinone, triethylene glycol diacetate, diethylene glycol methyl ether, diethylene glycol butyl ether and propylene glycol isobutyl ether. 
     Table 26 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from 2-pentanol. 
     
                       TABLE 20______________________________________Effective Agents For SeparatingTetrachloroethylene From Isobutanol                 RelativeCompounds             Volatility______________________________________Ethyl valerate        1.4Ethyl isovalerate     1.55Ethyl butyrate        2.9Amyl acetate          1.3Hexyl formate         1.34-Methyl pentyl acetate-2                 2.6Ethyl hexyl acetate   1.25Methyl caproate       1.5Methyl benzoate       1.3Ethyl benzoate        1.25Ethylene glycol butyl ether acetate                 1.25Isobutyl butyrate     1.55Isobutyl isobutyrate  1.251-Methoxy-2-propanol acetate                 1.55*3-Heptanone           1.25Isobutyl heptyl ketone                 1.35Dimethylsulfoxide     2.3*Dimethylformamide     2.3*Dimethylacetamide     1.7*Acetophenone          1.4Sulfolane             1.2*______________________________________ *Brings tetrachloroethylene out as overhead 
    
     
                       TABLE 21______________________________________Ineffective Agents For SeparatingTetrachloroethylene From Isobutanol______________________________________n-Decanol       Nonyl alcoholn-Octanol       IsophoroneBenzyl alcohol  Ethylene glycol ethyl ether acetateHexyl acetate   Isobornyl acetateEthyl acetoacetate           Ethyl 3-ethoxypropionateEthylene glycol diacetate           5-Methyl-2-hexanone2-Octanone      2-UndecanoneNitromethane______________________________________ 
    
     
                       TABLE 22______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % Iso- RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            butanol                                   Volatility______________________________________Dimethyl-   Over-    1      99.5     0.5    2.2sulfoxide   head   Bottoms         33.9     66.1Dimethyl-   Over-    2      99.6     0.4    2.3sulfoxide   head   Bottoms         38.0     62.0______________________________________ 
    
     
                       TABLE 23______________________________________Effective Agents For SeparatingTetrachloroethylene From 1-Pentanol                 RelativeCompounds             Volatility______________________________________Dimethylsulfoxide     2.0Sulfolane             1.8Dimethylformamide     2.2Dimethylacetamide     1.65Acetophenone          2.3Adiponitrile          2.12-Heptanone           2.13-Heptanone           1.73-Methyl-2-hexanone   1.82-Octanone            1.8Diisobutyl ketone     1.4Isobutyl heptyl ketone                 1.42,6-Dimethyl-4-heptanone                 1.52,4-Pentanedione      1.7Isophorone            1.4Acetonyl acetone      1.6Methyl benzoate       1.7Methyl salicylate     1.8n-Hexyl formate       1.7Hexyl acetate         1.9Isobutyl butyrate     1.5Amyl propionate       2.0Ethyl n-valerate      1.8Ethylene glycol butyl ether acetate                 1.3Ethylene glycol ethyl ether acetate                 1.2Diethylene glycol ethyl ether acetate                 1.3Propoxypropanol       1.7Butoxypropanol        1.3Phenyl acetate        1.6Ethyl isovalerate     2.1Ethyl caproate        1.3Diethylene glycol diethyl ether                 1.2Propylene carbonate   1.7Diethyl maleate       1.7______________________________________ 
    
     
                       TABLE 24______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % 1-Pent-                                   RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            anol   Volatility______________________________________Diisobutyl   Over-    1      98.9     1.1    1.45ketone  head   Bottoms         86.7     13.3Diisobutyl   Over-    1.5    98.6     1.4    1.36ketone  head   Bottoms         88.3     11.7______________________________________ 
    
     
                       TABLE 25______________________________________Effective Agents For SeparatingTetrachloroethylene From 2-Pentanol               RelativeCompounds           Volatility______________________________________Dimethylsulfoxide   2.5Sulfolane           1.35Dimethylformamide   2.0Dimethylacetamide   1.9Adiponitrile        1.2Diethylene glycol ethyl ether               1.25Diethylene glycol diethyl ether               1.252,4-Pentanedione    1.3Ethylene carbonate  1.55Propylene carbonate 1.251-Methyl-2-pyrrolidinone               1.7Triethylene glycol diacetate               1.35Diethylene glycol methyl ether               2.1Diethylene glycol butyl ether               1.8Propylene glycol isobutyl ether               1.7______________________________________ 
    
     
                       TABLE 26______________________________________Ineffective Agents For SeparatingTetrachloroethylene From 2-Pentanol______________________________________Acetophenone   2-Heptanone3-Heptanone    Diisobutyl ketoneIsophorone     Ethylene glycol ethyl ether acetateHexyl formate  Methyl benzoateAmyl propionate          Ethylene glycol diacetateTriacetin      2-UndecanoneEthyl n-valerate          Hexyl acetateMethyl salicylate______________________________________ 
    
     
                       TABLE 27______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % 2-Pen-                                   RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            tanol  Volatility______________________________________Dimethyl-   Over-    1      99.4     0.6    2.5sulfoxide   head   Bottoms         17       83Dimethyl-   Over-    1.5    99.6     0.4    2.6sulfoxide   head   Bottoms         15.7     84.3______________________________________ 
    
     One of the agents, dimethylsulfoxide, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 27. Dimethylsulfoxide gave a relative volatility of 2.5 after one hour and 2.6 after 1.5 hours of operation. Table 28 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from 3-methyl-1-butanol. They are dimethylsulfoxide, sulfolane, acetophenone, dimethylformamide, dimethylacetamide, adiponitrile, 2-heptanone, 3-heptanone, diisobutyl ketone, 2,6-dimethyl-4-heptanone, isophorone, acetonyl acetone, isobutyl butyrate, ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, propoxypropanol, butoxypropanol, ethyl caproate, diethylene glycol diethyl ether and propylene carbonate. 
     Table 29 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from 3-methyl-1-butanol. 
     One of the agents, diethylene glycol diethyl ether, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 30. Diethylene glycol diethyl ether gave a relative volatility of 1.24 after one hour and 1.31 after 1.5 hours of operation. 
     Table 31 lists the compounds that we have found to be effective extractive distillation agents to recover tetrachloroethylene from t-amyl alcohol. They are dimethylsulfoxide, sulfolane, adiponitrile, dimethylformamide, dimethylacetamide, 2-heptanone, diisobutyl ketone, methyl salicylate, hexyl acetate, amyl propionate, ethyl n-valerate, ethylene glycol ethyl ether acetate, 2-undecanone, 2,4-pentanedione, ethylene glycol diacetate, 1-methyl-2-pyrrolidinone, propylene carbonate and ethylene carbonate. 
     Table 32 lists the compounds that we have found to be ineffective agents for separating tetrachloroethylene from t-amyl alcohol. 
     One of the agents, dimethylsulfoxide, whose relative volatility had been determined in the vapor-liquid equilibrium still was then evaluated in a glass perforated plate rectification column and the results listed in Table 33. Dimethylsulfoxide gave a relative volatility of 1.74 after one hour and 2.0 after 1.5 hours of operation. 
     THE USEFULNESS OF THE INVENTION 
     The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 2 to 33. All of the successful agents show that tetrachloroethylene can be separated from methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-methyl-1-butanol and t-amyl alcohol by means of extractive distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable. 
     
                       TABLE 28______________________________________Effective Agents For SeparatingTetrachloroethylene From 3-Methyl-1-butanol                 RelativeCompounds             Volatility______________________________________Dimethylsulfoxide     2.7Sulfolane             1.6Dimethylformamide     2.1Dimethylacetamide     2.6Acetophenone          1.7Adiponitrile          1.8*2-Heptanone           1.553-Heptanone           1.9Diisobutyl ketone     1.25*2,6-Dimethyl-4-heptanone                 1.25Isophorone            1.45Acetonylacetone       1.8Isobutyl butyrate     1.3*Ethylene glycol ethyl ether acetate                 2.15Diethylene glycol ethyl ether acetate                 1.35Propoxypropanol       1.5Butoxypropanol        1.7Ethyl caproate        1.45*Diethylene glycol diethyl ether                 1.9Propylene carbonate   1.8______________________________________ *Brings 3Methyl-1-butanol out as overhead 
    
     
                       TABLE 29______________________________________Ineffective Agents For SeparatingTetrachloroethylene From 3-Methyl-1-butano______________________________________2-Octanone     5-Methyl-2-hexanoneMethyl benzoate          Isobutyl heptyl ketoneMethyl salicylate          n-Hexyl formateHexyl acetate  Amyl propionatePropyl acetate Ethylene glycol butyl ether acetateEthyl valerate Diethyl maleate______________________________________ 
    
     
                       TABLE 30______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % 3-Me-                                   RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            1-BuOH Volatility______________________________________Diethylene   Over-    1      93.0     7.0    1.24glycol di-   headethyl ether   Bottoms         73.2     26.8Diethylene   Over-    1.5    95.3     4.7    1.31glycol di-   headethyl ether   Bottoms         73.9     26.1______________________________________ 
    
     
                       TABLE 31______________________________________Effective Agents For SeparatingTetrachloroethylene From t-Amyl Alcohol                 RelativeCompounds             Volatility______________________________________Dimethylsulfoxide     2.0Sulfolane             1.45Dimethylformamide     1.7Dimethylacetamide     1.55Adiponitrile          1.3*2-Heptanone           1.25*Diisobutyl ketone     1.2*Methyl salicylate     1.2*Hexyl acetate         1.2*Amyl propionate       1.2*Ethyl n-valerate      1.2*Ethylene glycol ethyl ether acetate                 1.2*2-Undecanone          1.25*2,4-Pentanedione      2.6*Ethylene glycol diacetate                 1.35*1-Methyl-2-pyrrolidinone                 1.45Propylene carbonate   1.35Ethylene carbonate    1.5______________________________________ *Brings tAmyl alcohol out as overhead 
    
     
                       TABLE 32______________________________________Ineffective Agents For SeparatingTetrachloroethylene From t-Amyl Alcohol______________________________________Acetophenone    3-Heptanone5-Methyl-2-hexanone           2-Octanone4-Heptanone     IsophoroneMethyl benzoate Hexyl formatePhenyl acetate  Ethylene glycol butyl ether acetatePropoxypropanol ButoxypropanolIsobutyl heptyl ketone           Triethylene glycol diacetateTriacetin______________________________________ 
    
     
                       TABLE 33______________________________________Data From Run Made In Rectification Column                            Weight            Time   Weight % % t-Amyl                                   RelativeAgent   Column   hrs.   CCl.sub.2 --CCl.sub.2                            Alcohol                                   Volatility______________________________________Dimethyl-   Over-    1      83       17     1.74sulfoxide   head   Bottoms         7.7      92.3Dimethyl-   Over-    1.5    90.1     9.9    2.0sulfoxide   head   Bottoms         5.3      94.7______________________________________ 
    
    
    
     WORKING EXAMPLES 
     EXAMPLE 1 
     Seventy grams of the tetrachloroethylene-methanol azeotrope and 30 grams of methyl salicylate were charged to a vapor-liquid equilibrium still and refluxed for four hours. Analysis indicated a vapor composition of 27.3% tetrachloroethylene 72.7% methanol; a liquid composition of 44% tetrachloroethylene, 56% methanol which is a relative volatility of 2.1. 
     EXAMPLE 2 
     A solution comprising 250 grams of the tetrachloroethylene-methanol azeotrope was placed in the stillpot of a 7.3 theoretical plate glass perforated plate rectification column. When refluxing began, an extractive agent comprising methyl benzoate was pumped into the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the top of the column was 65° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-methanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed by gas chromatography. The overhead analysis was 97.8% methanol 2.2% tetrachloroethylene and the bottoms analysis was 75.6% methanol, 24.4% tetrachhloroethylene. This gives an average relative volatility of 1.44 for each theoretical plate. Analysis after two hours of operation gave an overhead of 99.4% methanol, 0.6% tetrachloroethylene and a bottoms of 82.3% methanol, 17.7% tetrachloroethylene which is a relative volatility of 1.62 for each theoretical plate. This data is presented in Table 4. 
     EXAMPLE 3 
     A solution comprising 250 grams of the tetrachloroethylene-ethanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began and extractive agent comprising diisobutyl ketone was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 70° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-ethanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 95.5% ethanol, 4.5% tetrachloroethylene and the bottoms analysis was 70.3% ethanol, 29.7% tetrachloroethylene. This gives an average relative volatility of 1.35 for each theoretical plate. After 1.5 hours of operation, the overhead analysis was 98.6% ethanol, 1.4% tetrachloroethylene, and the bottoms analysis was 67.3% ethanol, 32.7% tetrachloroethylene which is a relative volatility of 1.62. This data is presented in Table 7. 
     EXAMPLE 4 
     A solution comprising 250 grams of the tetrachloroethylene-1-propanol azeotrope was placed in the stillpot of a 7.3 theoretical plate glass perforated plate rectification column. When refluxing began, an extractive agent comprising diisobutyl ketone was pumped into the column at a rate of 15 ml/min. Tje temperature of the extractive agent as it entered the top of the column was 68° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-1-propanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed by gas chromatography. The overhead analysis was 73.5% 1-propanol, 26.5% tetrachloroethylene and the bottoms analysis was 48.6% 1-propanol, 51.4% tetrachloroethylene. This gives an average relative volatility of 1.15 for each theoretical plate. Analysis after 1.5 hours of operation gave an overhead of 94.4% 1-propanol 5.6% tetrachloroethylene and a bottoms of 51.3% 1-propanol, 48.7% tetrachloroethylene which is a relative volatility of 1.46 for each theoretical plate. This data is presented in Table 10. 
     EXAMPLE 5 
     A solution comprising 250 grams of the tetrachloroethylene-isopropanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began and extractive agent comprising diisobutyl ketone was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 65° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-isopropanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collecte and analysed. The overhead analysis was 96.9% isopropanol, 3.1% tetrachloroethylene and the bottoms analysis was 75.7% isopropanol, 24.3% tetrachloroethylene. This gives an average relative volatility of 1.37 for each theoretical plate. After 1.5 hours of operation, the overhead analysis was 99.4% isopropanol, 0.6% tetrachloroethylene and the bottoms analysis was 76.3% isopropanol, 23.7% tetrachloroethylene which is a relative volatility of 1.72. This data is presented in Table 13. 
     EXAMPLE 6 
     A solution comprising 250 grams of the tetrachloroethylene 1-butanol azeotrope was placed in the stillpot of a 7.3 theoretical plate glass perforated plate rectification column. When refluxing began, an extractive agent comprising dipropylene glycol methyl ether was put into the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the top of the column was 76° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-1-butanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed by gas chromatography. The overhead analysis was 14.9% 1-butanol, 85.1% tetrachloroethylene and the bottoms analysis was 39.6% 1-butanol, 60.4% tetrachhloroethylene. This gives an average relative volatility of 1.20 for each theoretical plate Analysis after two hours of operation gave an overhead of 1.12% 1-butanol 98.9% tetrachloroethylene and a bottoms of 37.8% 1-butanol, 62.2 % tetrachloroethylene which is a relative volatility of 1.27 for each theoretical plate. This data is presented in Table 16. 
     EXAMPLE 7 
     A solution comprising 250 grams of the tetrachloroethylene 2-butanol azeotrope was placed in the stillpot of a 7.3 theoretical plate glass perforated plate rectification column. When refluxing began, an extractive agent comprising isobornyl acetate was pumped into the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the top of the column was 71° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-2-butanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed by gas chromatography. The overhead analysis was 93.9% 2-butanol, 6.1% tetrachloroethylene and the bottoms analysis was 58.5% 2-butanol, 41.5% tetrachhloroethylene. This gives an average relative volatility of 1.39 for each theoretical plate. This data is presented in Table 19. 
     EXAMPLE 8 
     A solution comprising 250 grams of the tetrachloroethylene isobutanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began an extractive agent comprising dimethylsulfoxide was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 75° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-isobutanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 0.5% isobutanol, 99.5% and the bottoms analysis was 66.1% isobutanol, 33.9% tetrachloroethylene. This gives an average relative volatility of 2.2 for each theoretical plate. After two hours of operation, the overhead analysis was 0.4% isobutanol, 99.6% tetrachloroethylene and the bottoms analysis was 62% isobutanol, 38% tetrachloroethylene which is a relative volatility of 2.3. This data is presented in Table 22. 
     EXAMPLE  9 
     A solution comprising 250 grams of the tetrachloroethylene 1-pentanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began and extractive agent comprising diisobutyl ketone was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 78° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-1-pentanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 1.1% 1-pentanol, 98.9% tetrachloroethylene and the bottoms analysis was 13.3% 1-pentanol, 86.7% tetrachloroethylene. This gives an average relative volatility of 1.45 for each theoretical plate. After 1.5 hours of operation, the overhead analysis was 1.4% 1-pentanol, 98.6% tetrachloroethylene and the bottoms analysis was 11.7% 1-pentanol, 88.3% tetrachloroethylene which is a relative volatility of 1.36. This data is presented in Table 24. 
     EXAMPLE 10 
     A solution comprising 250 grams of the tetrachloroethylene 2-pentanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began an extractive agent comprising dimethylsulfoxide was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 76° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-2-pentanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 0.6% 2-pentanol, 99.4% tetrachloroethylene and the bottoms analysis was 83% 2-pentanol, 17% tetrachloroethylene. This gives an average relative volatility of 2.5 for each theoretical plate. After 1.5 hours of operation, the overhead analysis was 0.4% 2-pentanol, 99.6% tetrachloroethylene and the bottoms analysis was 84.3% 2-pentanol, 15.7% tetrachloroethylene which is a relative volatility of 2.6. This data is presented in Table 27. 
     EXAMPLE 11 
     A solution comprising 250 grams of the tetrachloroethylene-2-methyl-1-butanol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began, an extractive agent comprising diethylene glycol diethyl ether was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 75° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-2-methyl-1-butanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed by gas chromatography. The overhead analysis was 7% 2-methyl-1-butanol, 93% tetrachloroethylene and the bottoms analysis was 26.8% 2-methyl-1-butanol, 73.2% tetrachloroethylene. This gives an average relative volatility of 1.24 for each theoretical plate. Analysis after 1.5 hours of operation gave an overhead of 4.7% 2-methyl-1-butanol, 95.3% tetrachloroethylene and a bottoms analysis of 26.1% 2-methyl-1-butanol, 73.9% tetrachloroethylene which is a relative volatility of 1.31 for each theoretical plate. This data is presented in Table 30. 
     EXAMPLE 12 
     A solution comprising 250 grams of the tetrachloroethylene-t-amyl alcohol azeotrope was placed in the stillpot of the 7.3 theoretical plate rectification column. When refluxing began an extractive agent comprising dimethylsulfoxide was pumped into the top of the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 67° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-t-amyl alcohol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After one hour of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 17% t-amyl alcohol, 83% tetrachloroethylene and the bottoms analysis was 92.3% t-amyl alcohol, 7.7% tetrachloroethylene. This gives an average relative volatility of 1.74 for each theoretical plate. After 1.5 hours of operation, the overhead analysis was 9.9% t-amyl alcohol, 90.1% tetrachloroethylene and the bottoms analysis was 94.7% t-amyl alcohol, 5.3% tetrachloroethylene which is a relative volatility of 2.0. This data is presented in Table 33.