Abstract:
Acetone cannot be separated from a mixture of isopropanol and water because of the closeness of their boiling points. Acetone can be easily separated from isopropanol and water by extractive distillation. Effective extractive agents are 1-nitropropane, 3-carene, dimethylsulfoxide and 3-pentanone.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating acetone from a mixture of acetone, isopropanol and water using certain organic compounds as the agent in extractive distillation. 
     DESCRIPTION OF PRIOR ART 
     Extractive distillation is the method of separating close boiling comnounds 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 Celcius degrees or more higher than the highest 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. 
     The usual method of evaluating the effectiveness of extractive distillation agents is the change in relative volatility of the compounds to be separated. Table 1 shows the degree of separation or purity obtainable by theoretical plates at several relative volatilities. Table 1 shows that a relative volatility of at least 1.2 is required to get an effective separation by rectification. 
     
                       TABLE 1______________________________________Effect of Relative Volatility on Theoretical StageRequirements.SeparationPurity,  Relative VolatilityBoth Products    1.02   1.1    1.2  1.3  1.4  1.5  2.0  3.0(Mole Fraction)    Theoretical Stages at Total Reflux______________________________________0.999    697    144    75   52   40   33   19   120.995    534    110    57   39   30   25   14   90.990    463    95     49   34   26   22   12   70.98     392    81     42   29   22   18   10   60.95     296    61     31   21   16   14   8    40.90     221    45     23   16   12   10   5    3______________________________________ 
    
     Acetone and the isopropanol--water azeotrope boil fourteen degrees apart and are difficult to separate by conventional rectification. Table 2 shows that to get 99% purity, with a relative volatility of 2, sixteen actual plates are required, with a relative volatility of 3, only ten actual plates are required. 
     
                       TABLE 2______________________________________Theoretical and Actual Plates Required vs. Relative VolatilityFor Acetone - Isopropanol - Water SeparationRelative Theoretical Plates Required                     Actual PlatesVolatility    At Total Reflux, 99% Purity                     Required, 75% Eff.______________________________________1.1      95               1272.0      12               163.0      7                10______________________________________ 
    
     OBJECTIVE OF THE INVENTION 
     The object of this invention is to provide a process or method of extractive distillation that will enhance the relative volatility of acetone to isopropanol and water in their separation in a rectification column. It is a further object of this invention to identify effective extractive distillation agents that are stable and can be recycled. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are provided by a process for the separation of acetone from isopropanol and water which entails the use of certain organic compounds when employed as the agent in extractive distillation. 
     
                       TABLE 3______________________________________Effective Extractive Distillation Gents For SeparatingAcetone From Acetone - Isopropanol - Water Mixtures                 RelativeCompound              Volatility______________________________________None                  1.07Dimethylsulfoxide     3.0Butyl acetate         3.0Hexyl formate         2.2Methyl pivalate       3.0Propyl butyrate       2.9Isopropyl phthalate   3.0Diethylene glycol     3.0Polyethylene glycol 300                 2.2Heptane               3.0Ethyl benzoate        2.0Methyl t-butyl ether  3.0Isopropyl ether       3.0Phenyl ether          2.2Formamide             2.0Anisole               2.0Polyethylene qlycol 400                 3.04-Methyl-2-pentanone  3.02-Heptanone           2.42-Octanone            2.82-Undecanone          2.7Dimethyl carbonate    2.62-Butanone            2.5Tetra methyl sulfone  2.1Butyl formate         3.0Butyl benzoate        2.0Butyl ether           2.8n-Pentyl propionate   2.7Dimethyl formamide    2.82-Methoxyethanol      2.6Propylene glycol phenyl ether                 2.51,1,3,3-Tetramethyl urea                 3.0Butyronitrile         2.02-Ethoxyethanol       3.01-Methoxy-2-propanol  3.0Diethylene glycol methyl ether                 2.8Diisobutyl carbinol   2.53-Ethoxy propionate   2.4Diethylene glycol ethyl ether                 2.4Diethylene glycol hexyl ether                 2.3Diethylene glycol butyl ether                 2.6Tripropylene glycol methyl ether                 2.83-Methyl-2-butanone   2.32-Pentanone           2.63-Pentanone           3.04-Methyl-2-pentanone  2.92,6-Dimethyl-4-heptanone                 2.55-Methyl-2-hexanone   2.51,3-Butanediol        2.11,4-Butanediol        2.1Ethylene glycol       2.32-Methyl-2,4-pentanediol                 2.12,3-Butanediol        2.1Methyl benzoate       2.6Ethyl acetate         2.3Isobornyl acetate     2.1Methyl propionate     2.5Isocetyl stearate     3.0Dioctyl phthalate     2.0Dibutyl sebacate      3.01-Methoxy-2-propanol  3.0Cyclohexanol          2.33-Methyl-2-butanol    3.0Amyl alcohol          2.14-Methyl-2-pentanol   2.7n-Hexanol             2.4n-Octanol             2.2n-Tetradecanol        3.0Sulfolane             2.3Tetraethyl silicate   3.01-Methyl piperazine   2.5Toluene               2.0Ethyl benzene         2.0o-Xylene              2.0m-Xylene              2.3p-Xylene              2.7Dipentene             2.5Cumene                2.8Cyclohexene           3.0Limonene              3.02,2,4-Trimethyl pentane                 2.74-Hydroxy-2-methyl-2-pentanone                 2.3Cyclohexane           2.73-Carene              3.0Methyl glutaronitrile 2.62,2-Dimethoxypropane  3.0Propylene glycol methyl ether                 2.62-Amino-2-methyl-1-propanol                 2.2Acetal                2.0Triethanolamine       2.8Ethanolamine          2.0N,N-Dimethyl aniline  2.11-(2-Hydroxyethyl-2-pyrrolidinone                 2.94-Ethyl morpholine    2.82,6-Diethyl morpholine                 2.4Cyclohexylamine       3.0Diethylamine          3.0Triethylamine         3.0Butyl amine           3.0Diisobutylamine       3.0N,N-Dimethyl ethanolamine                 2.33-Dimethyl aminopropylamine                 2.0Propiophenone         2.1Diaminocyclohexane    2.82-Dimethylamino-2-methyl-1-propanol                 3.0Hexamethylene imine   3.02-Methyl-1-butanol    2.43-Methyl-1-butanol    2.33-Methyl-2-butanol    2.31-Nitropropane        2.3______________________________________ 
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I have discovered that certain organic compounds will effectively increase the relative volatility between acetone and isopropanol--water during rectification when employed as the agent in extractive distillation. Table 3 summarizes the data obtained with these agents. They are dimethylsulfoxide, butyl acetate,hexyl formate, methyl pivalate, propyl butyrate, isopropyl phthalate, diethylene glycol, polyethlene glycol 300, polyethylene glycol 400, heptane, ethyl benzoate, methyl t-butyl ether, isopropyl ether, phenyl ether, formamide, anisole, 4-methyl-2-pentanone, 2-heptanone, 2-octanone, 2-undecanone, dimethyl carbonate, 2-butanone, tetramethyl sulfone, butyl formate, butyl benzoate, butyl ether, n-pentyl propionate, dimethyl formamide, 2-methoxyethanol, propylene glycol phenyl ether, 1, 1, 3, 3-tetramethyl urea, butyronitrile,2-ethoxyethanol, 1-methoxy-2-propanol, diethylene glycol methyl ether, diisobutyl carbinol, 3-Ethoxy propionate, diethylene glycol ethyl ether, diethylene glycol hexyl ether, diethylene glycol butyl ether, tripropylene glycol methyl ether, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone, 5-methyl-2-hexanone, 1,3-butanediol, 1,4-butanediol, ethylene glycol, 2-methyl-2,4-pentanediol, 2,3-butanediol, methyl benzoate, ethyl acetate, isobornyl acetate, methyl propionate, isocetyl stearate, dioctyl phthalate, dibutyl sebacate, 1-methoxy-2-propanol, cyclohexanol, 3-methyl-2-butanol, amyl alcohol, 4-methyl-2-pentanol, n-hexanol, n-octanol, n-tetradecanol, sulfolane, tetraethyl silicate, toluene, 1-methyl piperazine, ethyl benzene, o-xylene, m-xylene, p-xylene, dipentene, cumene, cyclohexene, limonene, 2,2,4-trimethyl pentane, 4-hydroxy-2-methyl-2-pentanone, cyclohexane, 3-carene, methyl glutaronitrile, 2,2-dimethoxypropane, propylene glycol methyl ether, 2-amino-2-methyl-l-propanol, acetal. triethanolamine, ethanolamine, N,N-dimethyl aniline, 1-(2-hydroxyethyl)-2-pyrrolidinone, 4-ethyl morpholine, 2,6-diethyl morpholine, cyclohexylamine, diethylamine, triethylamine, butyl amine, diisobutylamine, N,N-dimethylethanolamine, 3-dimethyl aminopropyl amine, propiophenone, diaminocyclohexane, 2-dimethylamino-2-methyl-1-propanol, hexamethylene imine, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol and 1-nitropropane. 
     THE USEFULNESS OF THE INVENTION 
     The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1, 2 and 3. All of the successful agents listed there show that acetone can be separated from isopropanol and water by means of extractive distillation and that the ease of separation as measured by relative volatility is considerable. 
    
    
     WORKING EXAMPLES 
     Example 1 
     Fifty grams of acetone, isopropanol and water mixture and 50 grams of 1-nitropropane as the extractive agent were charged to a vapor-liquid equilibrium still and refluxed for three hours. The vapor composition was 2.5% acetone, 76.5% isopropanol and 21.0% water; the liquid composition was 1.05% acetone, 65.4% isopropanol and 33.55% water. This is a relative volatility of acetone to isopropoanol of 2.0. 
     Example 2 
     Fifty grams of acetone, isopropanol and water mixture and 50 grams of 3-carene as the extractive agent were charged to a vapor-liquid equilibrium still and refluxed for three hours. The vapor composition was 4.1% acetone, 76.4% isopropanol and 14.5% water; the liquid composition was 1.5% acetone, 84.5% isopropanol and 14% water. This is a relative volatility of acetone to isopropanol of 3.0