Abstract:
3-Carene and limonene cannot be separated from each other by rectification because of the closeness of their boiling points. They are readily separated by azeotropic distillation. Effective agents are: cyclopentanol, 2-nitropropane, ethyl formate amyl acetate dimethyl carbonate, tetrahydrofuran, acetic acid and 2-amino-amethyl-1-propanol.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of separating 3-carene, limonene and phellandrene using certain organic liquids as the agent in azeotropic distillation. 
     DESCRIPTION OF PRIOR ART 
     Azeotropic distillation is the method of separating close boiling compounds or azeotropes from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid, said liquid forming an azeotrope with one or two of the compounds to be separated. Its presence on each plate of the rectification column alters the relative volatility 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 azeotrope forming agent is introduced with the feed to a continuous column. The azeotrope forming agent and the more volatile component are taken off as overhead product and the less volatile component comes off as bottoms product. The usual methods of separating the azeotrope former from the more volatile component are cooling and phase separation or solvent extraction. 
     The usual method of evaluating the effectiveness of azeotropic 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    99      49  34   28  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 which produce complex mixtures of terpenes, e.g. turpentine. A process to separate this mixture into its pure components would enhance its value. Three of the commonest close boiling compounds in one of these are 3-carene, B.P.=167° C., phellandrene, B.P.=175° C. and limonene, B.P.=178° C. The relative volatility among these three is as low as 1.05 which makes it impossible to separate by conventional rectification. Azeotropic distillation would be an attractive method of effecting the separation of these three if agents can be found that (1) will create a large apparent relative volatility among these three and (2) are easy to recover from the azeotropic agent. Table 2 shows the relative volatility required to obtain 99% purity. With an agent giving a relative volatility of 1.75, only 23 actual plates are required. 
     
                       TABLE 2______________________________________Theoretical and Actual Plates Required vs. RelativeVolatility for Terpene SeparationRelative  Theoretical Plates Required                    Actual Plates RequiredVolatility  At Total Reflux, 99% Purity                    75% Efficiency______________________________________1.4    28                381.6    20                271.75   17                23______________________________________ 
    
     OBJECTIVE OF THE INVENTION 
     The object of this invention is to provide a process or method of azeotropic distillation that will enhance the relative volatility of 3-carene, limonene and phellandrene 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 the terpenes and recycled to the column with little decomposition. 
     SUMMARY OF THE INVENTION 
     The objects of this invention are provided by a process for separating 3-carene, limonene and phellandrene which entails the use of certain organic compounds as the agent in azeotropic distillation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     I have discovered that certain organic compounds will greatly improve the relative volatility between 3-carene, limonene and phellandrene and permit the by rectification when employed as the agent in azeotropic distillation. Table 3 lists the compounds that I have found to be effective in separating 3-carene from limonene in the presence of phellandrene. They are amyl acetate, ethyl acetate, acetonitrile, acetal, methyl t-butyl ether, anisole, t-amyl methyl ether, isopropyl ether, dioxolane, propyl formate, ethyl acetoacetate, methyl formate, ethyl isobutyrate, methyl propionate, methyl lactate, propyl propionate, butyl propionate, 
     
                       TABLE 3______________________________________Effective Azeotropic Distillation Agents For Separating 3-CareneFrom Limonene and Phellandrene                        Rel. Vol.Agent              Temp., °C.                        3-Car/Lim______________________________________Amyl acetate       146       1.75Ethyl acetate      86        1.75Acetonitrile       78        1.4Acetal             112       1.35Methyl t-butyl ether              70        1.5Anisole            153       1.55t-Amyl methyl ether              106       1.3Isopropyl ether    84        1.4Dioxolane          82        1.5Propyl formate     91        1.8Ethyl acetoacetate 158       1.35Methyl formate     36        1.4Ethyl isobutyrate  131       1.3Methyl propionate  84        1.35Methyl lactate     138       1.55Propyl propionate  128       1.45Butyl propionate   151       1.8Ethyl isovalerate  144       1.35Ethyl formate      59        1.55Dimethyl carbonate 94        1.52-Butanol          100       1.351-Butanol          118       1.45t-Amyl alcohol     107       1.35n-Amyl alcohol     134       1.3Cyclohexanol       153       1.33-Pentanone        109       1.43-Methyl-2-butanone              108       1.352-Octanone         165       1.35Butyronitrile      118       1.4Triethyl amine     106       1.4Ethanolamine*      146       1.35Butyl amine        91        1.352-Butanone         82        1.45Acetone            57        1.55Diethyl amine      71        1.35Dipropyl amine     125       1.3Pyridine           123       1.62-Methoxyethanol   121       1.5Diethylene glycol methyl ether              166       1.3Tetrahydrofuran    80        1.45Acetic acid        115       1.4Butyric acid       155       1.3Methyl pivalate    108       1.45Methyl ethyl ketoxime              147       1.3Cyclopentanol      131       1.32-Amino-2-methyl-1-propanol              150       1.32-Nitropropane     120       1.352-Butoxyethanol    159       1.35______________________________________ *Two phase 
    
     ethyl isovalerate, ethyl formate, dimethyl carbonate, 2-butanol, 1-butanol, t-amyl alcohol, n-amyl alcohol, cyclohexanol, 3-pentanone, 3-methyl-2-butanone, 2-octanone, butyronitrile, triethyl amine, ethanolamine, butyl amine, 2-butanone, acetone, diethyl amine, dipropyl amine, pyridine, 2-methoxyethanol, diethylene glycol methyl ether, tetrahydrofuran, acetic acid, butyric acid, methyl pivalate, methyl ethyl ketoxime, 2-amino-2-methyl-1-propanol, 2-nitropropane, 2-butoxyethanol and cyclopentanol. 
     Table 4 lists the compounds that are effective in separating 3-carene from limonene. They are amyl acetate, 1-butanol, anisole, isopropyl ether, dioxolane, ethyl formate, methyl acetate, methyl propionate, methyl formate, ethyl acetate, propyl propionate, n-butyl propionate, dimethyl carbonate, t-amyl alcohol, 3-pentanone, 2-octanone, 2-pentanone, 3-methyl-2-butanone, 2,3-butanedione, cyclohexanone, acetonitrile, butyronitrile, 2-butanone, diethylene glycol methyl ether, butyl amine, dipropyl amine, triethyl amine, 2-methoxyethanol, acetone, p-cresol, pyridine, tetrahydrofuran, 2,6-dimethyl phenol, propylene carbonate, 2-methyl-2,4-pentanediol, 1,1,3,3-tetramethyl urea, 4-hydroxy-4-methyl-2-pentanone, methyl ethyl ketoxime, 2-nitropropane, butyraldehyde oxime, 1,2-Methylenedioxybenzene, 1-methoxy-2-propanol, 2-amino-2-methyl-1-propanol, 2-butoxyethanol, propoxypropanol, 4-fluoro benzaldehyde and cyclopentanol. 
     Table 5 lists the compounds that are effective in separating phellandrene from 3-carene and limonene. They are dimethylformamide, ethyl lactate, cyclopentanol, 4-hydroxy-4-methyl-2-pentanone, formic acid, butyraldehyde oxime, 1,2-methylene dioxybenzene, 1-methoxy-2-propanol, 2-dimethylamine-2-methyl-2-propanol and 2-nitropropane. 
     THE USEFULNESS OF THE INVENTION 
     The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 3, 4 and 5. All of the successful agents show that 3-carene, limonene and phellandrene can be separated from each other by means of azeotropic distillation in a rectification column and that the ease of separation as measured by relative volatility is considerable. 
     
                       TABLE 4______________________________________Effective Azeotropic Distillation Agents For Separating 3-CareneFrom Limonene                        Rel. Vol.Agent              Temp., °C.                        3-Car/Lim______________________________________Amyl acetate       153       1.651-Butanol          120       1.55Anisole            152       1.4Isopropyl ether    91        1.45Dioxolane          78        1.4Ethyl formate      58        1.7Methyl acetate     56        1.65Methyl propionate  83        1.35Methyl formate     31        1.75Ethyl acetate      83        1.3Propyl propionate  138       1.5n-Butyl propionate 133       1.3Dimethyl carbonate 92        1.3t-Amyl alcohol     107       1.353-Pentanone        119       1.352-Octanone         162       1.353-Methyl-2-butanone              104       1.352,3-Butanedione    93        1.452-Pentanone        110       1.4Cyclohexanone      150       1.3Acetonitrile       80        1.5Butyronitrile      117       1.72-Butanone         90        1.35Diethylene glycol methyl ether              165       1.3Butyl amine        86        1.4Dipropyl amine     119       1.3Triethyl amine     99        1.32-Methoxyethanol   120       1.4Acetone            56        1.5p-Cresol           156       1.4Pyridine           114       1.5Tetrahydrofuran    88        1.42,6-Dimethyl phenol              146       1.42-Methyl-2,4-pentanediol              166       1.31,1,3,3-Tetramethyl urea              163       1.35Propylene carbonate              166       1.34-Hydroxy-4-methyl-2-pentanone              131       1.55Methyl ethyl ketoxime              145       1.45Cyclopentanol      127       1.6Butyraldehyde oxime              142       1.41,2-Methylene dioxybenzene              164       1.31-Methoxy-2-propanol              120       1.352-Amino-2-methyl-1-propanol              147       1.52-Nitropropane     120       1.552-Butoxyethanol    160       1.3Propoxypropanol    149       1.54-Fluoro benzaldehyde              164       1.65______________________________________ 
    
     
                       TABLE 5______________________________________Effective Azeotropic Distillation Agents For SeparatingPhellandrene From 3-Carene and Limonene                          Rel. Vol.Agent                Temp. °C.                          Lim/Phl______________________________________Dimethylformamide    127       1.6Ethyl lactate        146       1.45Cyclopentanol        137       2.04-Hydroxy-4-methyl-2-pentanone                148       1.45Formic acid          103       1.3Butyraldehyde oxime  145       1.351,2-Methylene dioxybenzene                164       1.351-Methoxy-2-propanol 126       1.452-Dimethylamine-2-methyl-2-propanol                150       1.82-Nitropropane       120       1.5______________________________________ 
    
    
    
     WORKING EXAMPLES 
     1. One hundred grams of a crude turpentine mixture containing principally 3-carene, limonene and phellandrene and 100 grams of amyl acetate were charged to the stillpot of five theoretical plate glass perforated plate rectification column and operated at total reflux for nine hours. The overhead composition was 94% 3-carene, 4% limonene and 2% phellandrene; the stillpot composition was 48% 3-carene, 32.1&amp; limonene and 19.9% phellandrene. This indicates a relative volatility of 3-carene to limonene of 1.65 and limonene to phellandrene of 1.04. 
     2. Twenty grams of 3-carene, 80 grams of limonene and 100 grams of cyclopentanol were charged to the five theoretical plate perforated plate rectification column and operated at total reflux for nine hours. The overhead composition was 74.9% 3-carene, 25.1% limonene; the stillpot composition was 21.6% 3-carene, 78.4% limonene. This indicates a relative volatility of 1.6. 
     3. One hundred grams of the crude turpentine mixture of 3-carene, limonene and phellandrene and 100 grams of dimethylformamide were charged to the five theoretical plate rectification column and refluxed for nine hours. The overhead composition was 88.9% 3-carene, 8.3% limonene and 2.8% phellandrene; the stillpot composition was 51.6% 3-carene, 13.7% limonene and 34.7% phellandrene. This indicates a relative volatility of 3-carene to limonene of 1.24 and of limonene to phellandrene of 1.5.