Abstract:
Isopropanol is difficult to separate from 2-butanone by conventional distillation or rectification because of the proximity of their boiling points. Isopropanol can be readily separated from 2-butanone by extractive distillation. Effective agents are o-cresol, ethylene glycol and nitroethane.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for separating isopropanol from 2-butanone using certain organic liquids 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 Celcius 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. 
     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.Separation Purity,      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______________________________________ 
    
     There are a number of commercial processes that produce complex mixtures of oxygenated compounds, e.g. the Fischer-Tropsch process. Two of the commonest oxygenated compounds usually present are 2-butanone, B.P=80° C. and isopropanol, B.P.=82° C. The relative volatility between these two is 1.35 which makes it difficult to separate them by conventional rectification. Extractive-distillation would be an attractive method of effecting the separation of 2-butanone from isopropanol if agents can be found the (1) will create a large apparent relative volatility between 2-butanone and isopropanol and (2) are easy to recover from the 2-butanone. Table 2 shows the relative volatility required to obtain 99% purity. With no agent, 42 actual plates are required. With an agent giving a relative volatility of 2.3, only 15 actual plates are required. 
     
                       TABLE 2______________________________________Theoretical and Actual Plates Required vs. RelativeVolatility for 2-Butanone - Isopromanol SeparationRelative  Theoretical Plates Required                    Actual Plates RequiredVolatility  At Total Reflux, 99% Purity                    75% Efficiency______________________________________ 1.35  31                421.7    17                232.3    11                15______________________________________ 
    
     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 2-butanone from isopropanol in their separation in a rectification column. It is a further object of this invention to identify organic compounds which in addition to the above constraints, are stable, can be ,separated from 2-butanone and recycled to the extractive column with little decomposition. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are to provide a process for separating 2-butanone from isopropanol 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 greatly improve the relative volatility of isopropanol from 2-butanone and permit the separation of isopropanol from 2-butanone by, rectification when employed as the agent in extractive distillation. Table 3 lists the compounds that I have found to be effective. They are phenol, o-cresol, m-cresol, 3-ethyl phenol, 4-ethyl phenol, o-sec. butyl phenol, 2-tert. butyl phenol, 2,4-dimethyl phenol, 3,5-dimethyl phenol, 2-isopropyl phenol, butyl amine, triethyl amine, cyclohexyl amine, 
     
                       TABLE 3______________________________________Effective Extractive Distillation Agents ForSeparating Isopropanol From 2-Butanone              RelativeCompounds          Volatility______________________________________None               1.35Phenol             1.55o-Cresol           1.7m-Cresol           2.13-Ethyl phenol     1.6o-sec. Butyl phenol              1.752-tert. Butyl phenol              1.552,4-Dimethyl phenol              1.52-Isopropyl phenol 2.44-Ethyl phenol     3.33,5-Dimethyl phenol              1.6Butyl amine        2.0Triethyl amine     1.6Cyclohexyl amine   1.6Dimethylsulfoxide  1.5*Dimethylacetamide  1.7*2-Nitrotoluene     1.6Ethylene carbonate 1.65Nitrobenzene       1.7Ethyl acetoacetate 1.5Methyl acetoacetate              1.5Isobutyl isobutyrate              1.5*2-Hydroxy acetophenone              1.55Ethylene glycol    2.2*1,2-Propanediol    1.6*1,3-Butanediol     1.75*5-Methyl-2-hexanone              1.52,4-Pentanedione   1.55Propiophenone      1.61,4-Butanediol     1.8*2-Methyl-1,3-propanediol              1.55*1,5-Pentanediol    1.6*1,6-Hexanediol     1.55*Glycerine          1.6*Nitromethane       2.5Nitroethane        2.3**1-Nitropropane     2.42-Nitropropane     2.3Butyronitrile      1.75______________________________________ *Brings 2Butanone out as overhead product **Data determined in multiplate rectification column 
    
     dimethylsulfoxide, dimethylacetamide, 2-nitrotoluene, nitrobenzene, ethyl acetoacetate, methyl acetoacetate, isobutyl isobutyrate, 2-hydroxy acetophenone, ethylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 5-methyl-2-hexanone, 2,4-pentanedione, propiophenone, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, glycerine, nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, butyronitrile and ethylene carbonate. Isomers or homologs that might be expected to be effective but which are not are p-cresol, 3-nitrotoluene and propyl butyrate. 
     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 show that isopropanol can be separated from 2-butanone by means of extractive distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable. 
    
    
     WORKING EXAMPLES 
     1. Fifteen grams of isopropanol, 20 grams of 2-butanone and 30 grams of o-cresol were charged to a vapor-liquid equilibrium still and refluxed for four hours. Analysis indicated a vapor composition of 47.6% isopropanol, 52.4% 2-butanone; a liquid composition of 34.7% isopropanol, 65.3% 2-butanone. This is a relative volatility of 1.7. 
     2. Fifteen grams of isopropanol, 20 grams of 2-butanone and 30 grams of ethylene glycol were charged to a vapor-liquid equilibrium still and refluxed for 13 hours. Analysis indicated a vapor composition of 58% isopropanol, 42% 2-butanone; a liquid composition of 75.2% isopropanol, 24.8% 2-butanone. This is a relative volatility of 2-butanone to isopropanol of 2.2. 
     Example 3 
     A solution comprising 50 grams of isopropanol and 150 grams of 2-butanone was placed in the stillpot of a 5.6 theoretical plate glass perforated plate rectification column. When refluxing began, an extractive agent comprising nitroethane 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 isopropanol-2-butanone 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 composition was 94.9% isopropanol, 5.1% 2-butanone and the bottoms composition was 15.2% isopropanol, 84.8% 2-butanone. This gives a relative volatility of isopropanol to 2-butanone of 2.3 for each theoretical plate.