Abstract:
Tetracholorethylene cannot be completely separated from n-butanol, isobutanol or 2-butanol by conventional distillation or rectification because of minimum boiling azeotropes. Tetrachloroethylene can be readily separated from n-butanol, isobutanol or 2-butanol by extractive distillatiion. Typical effective agents are: for n-butanol, dipropylene glycol methyl ether; for isobutanol, dimethylsulfoxide and isobutyl butyrate; for 2-butanol, ethylene glycol methyl ether and isobornyl acetate.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating tetrachloroethylene from the butyl 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 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 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. 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 the lowest boiling component. This usually requires that the extractive agent boil about twenty Centigrade degrees or more higher 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 three of the butyl alcohols. With n-butanol the azeotrope boils at 109° C. and contains 71 weight percent tetrachloroethylene; with isobutanol the azeotrope boils at 103° C. and contains 60% tetrachloroethylene and with 2-butanol the azeotrope boils at 97° C. and contains 68% tetrachloroethylene. There is no azeotrope with t-butanol. 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, n-butanol, isobutanol or 2-butanol and boil sufficiently above these four compounds 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-butanol 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 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 Butanols at 99% Purity.Relative  Theoretical            Actual Plates,                         Actual Plates,Volatility  Plates    75% Efficiency                         75% Eff., Min. Reflux______________________________________1.2    50        67           871.3    35        47           611.4    27        36           471.5    23        31           401.6    20        27           351.7    17        23           29______________________________________ 
    
     The advantage of employing an effective extractive distillation agent is shown in Table 1. Tetrachloroethylene forms minimum boiling azeotropes with the butyl 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 1.7 or higher, a rectification column of only 29 actual plates will be required. 
     OBJECTIVE OF THE INVENTION 
     The objects of this invention are to provide a process or method of extractive distillation that will enhance the relative volatility of tetrachloroethylene to n-butanol, isobutanol or 2-butanol 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 the 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 n-butanol, isobutanol or 2-butanol which entails the use of certain organic compounds as the agent in extractive distillation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I have discovered that certain organic compounds will effectively increase the relative volatility between tetrachloroethylene and n-butanol, isobutanol or 2-butanol by rectification when when employed as the agent in extractive distillation. Table 2 lists the compounds that I have found to be effective extractive distillation agents to recover tetrachloroethylene from n-butanol. The data in Tables 2,3,5,6,8 and 9 was obtained in a vapor-liquid equilibrium still. In every case, the starting mixture was the tetrachloroethylene-butanol azeotrope. The relative volatilities are listed for each of the agents. The compounds which are effective extractive distillation agents to remove tetrachloroethylene from n-butanol are dipropylene glycol methyl ether, diethylene glycol ethyl ether, 1-methoxy-2-propanol, ethyl 3-ethoxypropionate, butoxypropanol, diethylene glycol methyl ether, 1-methoxy-2-propanol acetate, ethylene glycol butyl ether, ethylene glycol methyl 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, propoxypropanol and mesityl oxide. 
     Table 3 lists the agents that were found to be ineffective agents for separating tetrachloroethylene from n-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 possessing 7.3 theoretical plates and the results listed in Table 4. Dipropylene glycol methyl ether gave a relative volatility of 1.72 after two hours of operation. 
     Table 5 lists the compounds that I have found to be effective extractive distillation agents to recover tetrachloroethylene from isobutanol. The effective agents are ethyl valerate, ethyl isovalerate, ethyl butyrate, n-amyl acetate, hexyl formate, 4-methylpentyl acetate-2, 2-ethyl hexyl acetate, methyl caproate, methyl benzoate, ethyl benzoate, ethylene glycol butyl ether acetate, isobutyl butyrate, isobutyl isobutyrate, 1-methoxy-2-propanol acetate, 3-heptanone, isobutyl heptyl ketone, dimethylsulfoxide, dimethylformamide, dimethylacetamide, sulfolane and acetophenone. The starred compounds in Table 5 bring the tetrachloroethylene out as overhead product; the others bring out isobutanol as overhead. 
     
                       TABLE 2______________________________________Effective Agents For SeparatingTetrachloroethylene From n-Butanol                RelativeCompounds            Volatility______________________________________Diethylene glycol ethyl ether                1.51-Methoxy-2-propanol 2.2Ethyl 3-ethoxypropionate                2.8Butoxypropanol       1.45Dipropylene glycol methyl ether                1.7Diethylene glycol methyl ether                1.81-Methoxy-2-propanol acetate                2.0Ethylene 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                1.45Propoxypropanol      1.2Mesityl oxide        1.25______________________________________ 
    
     
                       TABLE 3______________________________________Ineffective Agents, Tetrachloroethylene - n-Butanol______________________________________Hexyl acetate        Dipropylene glycol methyl ether acetateMethyl isoamyl ketone        Ethylene glycol ethyl ether acetate2-Methoxy-2-propanol        4-Methoxy-2-pentanoneacetate2,6-Dimethyl-4-hep-        Diisobutyl ketonetanone3-Heptanone  Ethyl isovalerate2-Methoxyethyl ether        Ethylene glycol hexyl etherDipropylene glycoldimethyl ether______________________________________ 
    
     
                       TABLE 4______________________________________Data From Run Made In Rectification Column             Time   Weight Weight %                                   RelativeAgent    Column   hrs.   % C.sub.2 Cl.sub.4                           n-Butanol                                   Volatility______________________________________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 5______________________________________Effective Agents For Separating TetrachloroethyleneFrom Isobutanol                 RelativeCompounds             Volatility______________________________________Ethyl valerate        1.4Ethyl isovalerate     1.55Ethyl butyrate        2.9n-Amyl 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*Sulfolane             1.2*Acetophenone          1.4______________________________________ *Brings out tetrachloroethylene as overhead 
    
     
                       TABLE 6______________________________________Ineffective Agents, Tetrachloroethylene - Isobutanol______________________________________n-Decanol      Nonyl alcoholn-Octanol      IsophoroneBenzyl alcohol Ethylene glycol ethyl ether acetateHexyl acetate  Ethyl-3-ethoxypropionateIsobornyl acetate          Ethylene glycol diacetateEthyl acetoacetate          5-Methyl-2-hexanone2-Heptanone    Ethyl phenyl acetate2-Octanone     2-UndecanoneNitromethane   Nitroethane______________________________________ 
    
     
                       TABLE 7______________________________________Data From Run Made In Rectification Column            Time   Weight %                           Weight %                                   RelativeAgent   Column   hrs.   C.sub.2 Cl.sub.4                           Isobutanol                                   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 6 lists the agents that were found to be ineffective agents for separating tetrachloroethylene from isobutanol. 
     Dimethylsulfoxide, whose relative volatility had been determined in the vapor-liquid equilibrium still, was evaluated in the perforated plate rectification column and the results listed in Table 7. Dimethylsulfoxide gave a relative volatility of 2.3 after two hours of operation. 
     Table 8 lists the compounds that I have found to be effective extractive distillation agents to recover tetrachloroethylene from 2-butanol. The effective agents are ethyl valerate, ethyl isovalerate, isobutyl butyrate, isobutyl isobutyrate, ethyl butyrate, hexyl formate, isobornyl acetate, diethylene glycol hexyl ether, ethylene glycol ethyl ether acetate, 4-methyl pentyl axetate-2, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol hexyl ether, diethylene glycol methyl ether, 4-methyl-2-pentanone, isophorone, dipropylene glycol methyl ether acetate and hexyl acetate. The starred compounds in Table 8 bring out tetrachloroethylene as overhead product; the others bring out 2-butanol as overhead product. 
     Table 9 lists agents that were found to be ineffective for separating tetrachloroethylene from 2-butanol. 
     Isobornyl acetate, whose relative volatility had been determined in the vapor-liquid equilibrium still, was evaluated in the perforated plate rectification column and the results listed in Table 10. Isobornyl acetate gave a relative volatility of 1.39 after one 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 10. All of the successful agents show that tetrachloroethylene can be separated from n-butanol, isobutanol or 2-butanol by means of extractive distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable. 
     WORKING EXAMPLES 
     EXAMPLE 1 
     Seventy grams of the tetrachloroethylene-n-butanol azeotrope and 30 grams of dipropylene glycol methyl ether were charged to a vapor-liquid equilibrium still and refluxed for six hours. Analysis indicated a vapor composition of 64.6% tetrachloroethylene, 35.4% n-butanol; a liquid composition of 50% tetrachloroethylene, 50% n-butanol which is a relative volatility of tetrachloroethylene to n-butanol of 1.8. 
     
                       TABLE 8______________________________________ Effective Agents For SeparatingTetrachloroethylene From 2-Butanol                   RelativeCompounds               Volatility______________________________________Ethyl valerate          1.85Isobutyl butyrate       1.5Ethyl isovalerate       1.85Isobutyl isobutyrate    1.55Ethyl butyrate          1.35Hexyl formate           1.3Isobornyl acetate       1.4Diethylene glycol hexyl ether                   1.25Ethylene glycol ethyl ether acetate                   1.44-Methyl pentyl acetate-2                   1.25Ethylene glycol methyl ether                   1.3*Ethylene glycol ethyl ether                   1.2*Ethylene glycol hexyl ether                   1.2*Diethylene glycol methyl ether                   1.2*4-Methyl-2-pentanone    1.2*Isophorone              1.2*Dipropylene glycol methyl ether acetate                   1.2*Hexyl acetate           1.35______________________________________ *Brings out tetrachloroethylene as overhead 
    
     
                       TABLE 9______________________________________Ineffective Agents, Tetrachloroethylene - 2-Butanol______________________________________Ethylene glycol butyl ether            Diethylene glycol ethyl etherDiethylene glycol butyl ether            Dipropylene glycol methyl etherPropylene glycol methyl ether            Propylene glycol isobutyl etherPropoxypropanol  Tripropylene glycol methyl etherButoxypropanol   1-Methoxy-2-propanol acetateCyclohexanol     2-Ethyl hexyl acetateMethyl benzoate  Diethyl maleateEthyl benzoate______________________________________ 
    
     
                       TABLE 10______________________________________Data From Run Made In Rectification Column            Time    Weight Weight %                                   RelativeAgent  Column    hrs.    % C.sub.2 H.sub.4                           2-Butanol                                   Volatility______________________________________Isobornyl  Overhead  1        6.1   93.9    1.39acetate  Bottoms           41.5   58.5______________________________________ 
    
     EXAMPLE 2 
     A solution comprising 140 grams of tetrachloroethylene and 60 grams of n-butanol was placed in the stillpot of a 7.3 theoretical plate rectification column. When refluxing began, an extractive agent comprising dipropylene glycol methyl ether was pumped into the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 85° C. After establishing the feed rate of the extractive agent, the heat input to the tetrachloroethylene-n-butanol in the stillpot was adjusted to give a total reflux rate of 40 ml/min. After two hours of operation, overhead and bottoms samples were collected and analysed. The overhead analysis was 98.9% tetrachloroethylene, 1.1% n-butanol and the bottoms analysis was 62.2% tetrachloroethylene, 37.8% n-butanol. This gives an average relative volatility of 1.72 for each theoretical plate. This data is presented in Table 4. 
     EXAMPLE 3 
     Seventy grams of the tetrachloroethylene-isobutanol azeotrope and 30 grams of dimethylsulfoxide were charged to the vapor-liquid equilibrium still and refluxed for five hours. Analysis indicated a vapor composition of 59.1% tetrachloroethylene, 40.9% isobutanol; a liquid composition of 36.6% tetrachloroethylene, 63.4% isobutanol which is a relative volatility of tetrachloroethylene to isobutanol of 2.5. 
     EXAMPLE 4 
     A solution comprising 180 grams of tetrachloroethylene and 120 grams of isobutanol was placed in the stillpot of a 7.3 theoretical plate rectification column. When refluxing began, an extractive agent comprising dimethylsulfoxide was pumped into the column at a rate of 15 ml/min. The temperature of the extractive agent as it entered the column was 85° 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 two hours of operation, the overhead and bottoms were collected and analysed. The overhead analysis was 99.6% tetrachloroethylene, 0.4% isobutanol and the bottoms analysis was 38% tetrachloroethylene, 62% isobutanol. This gives an average relative volatility of 2.3 for each theoretical plate. This data is presented in Table 7. 
     EXAMPLE 5 
     Seventy grams of the tetrachloroethylene-2-butanol azeotrope and 30 grams of isobornyl acetate were charged to the vapor-liquid equilibrium still and refluxed for seven hours. Analysis indicated a vapor composition of 72.5% 2-butanol, 27.5% tetrachloroethylene; a liquid composition of 65% 2-butanol, 35% tetrachloroethylene which is a relative volatility of 2-butanol to tetrachloroethylene of 1.7. 
     EXAMPLE 6 
     A solution comprising 150 grams of tetrachloroethylene and 100 grams of 2-butanol was placed in the stillpot of a 7.3 theoretical 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 column was 85° 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, the overhead and bottoms samples were collected and analysed. The overhead analysis was 93.9% 2-butanol, 6.1% tetrachloroethylene and the bottoms analysis was 58.5% 2-butanol, 41.5% tetrachloroethylene. This gives an average relative volatility of 2-butanol to tetrachloroethylene of 1.39 for each theoretical plate. This data is presented in Table 10.