Separation of 2-pentanol, 3-methyl-2-butanol and 1-butanol by azeotropic distillation

3-Methyl-2-butanol, 2-pentanol and 1-butanol are difficult to separate by conventional distillation or rectification because of the proximity of their boiling points. Mixtures of these three can be readily separated from each other by azeotropic distillation. Effective agents are hexyl acetate, hexane and 3-methyl pentane.

FIELD OF THE INVENTION 
This invention relates to a method for separating 2-pentanol, 
3-methyl-2-butanol and 1-butanol 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 both 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 
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Effect of Relative Volatility on Theoretical Stage 
Requirements. 
Separation Purity, 
Relative Volatility 
Both Products 
1.02 1.1 1.2 1.3 1.4 1.5 2.0 3.0 
(Mole Fraction) 
Theoretical Stages at Total Reflux 
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0.999 697 144 75 52 40 33 19 12 
0.995 534 110 57 39 30 25 14 9 
0.990 463 95 49 34 26 22 12 7 
0.98 392 81 42 29 22 18 10 6 
0.95 296 61 31 21 16 14 8 4 
0.90 221 45 23 16 12 10 5 3 
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There are a number of commercial processes which produce complex mixtures 
of alcohols, e.g. the Fischer-Tropsch process which produces a series of 
homologous alcohols. Three of the commonest alcohols usually present are 
3-methyl-2-butanol, B.P.=112.degree. C., 2-pentanol, B.P.=120.degree. C. 
and 1-butanol, B.P.=118.degree. C. The relative volatility of 
3-methyl-2-butanol and 2-pentanol is 1.4, between 1-butanol and 2-pentanol 
it is 1.08 and between 3-methyl-2-butanol and 1-butanol it is 1.25. 
When these three occur together as a mixture, they are impossible to 
separate by conventional rectification. Azeotropic distillation would be 
an attractive method of effecting this separation if agents can be found 
that (1) will create a large apparent relative volatility between them and 
(2) are easy to recover from 2-pentanol. Table 2 shows the relative 
volatility required to obtain products of 99% purity. With no agent, the 
relative volatilities are 1.08, 1.4 and 1.25, see Table 3. Table 2 shows 
that with a relative volatility of 1.08, 160 actual plates would be 
required. With an agent giving a relative volatility of 1.4, only 36 
actual plates are required; with a relative volatility of 1.95, only 19 
actual plates are needed. 
TABLE 2 
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Theoretical and Actual Plates Required vs. Relative 
Volatility for 3-Methyl-2-butanol - 2-Pentanol - 
1-Butanol Separation 
Relative 
Theoretical Plates Required 
Actual Plates Required 
Volatility 
At Total Reflux, 99% Purity 
75% Efficiency 
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1.08 120 160 
1.4 27 36 
1.6 20 27 
1.95 14 19 
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OBJECTIVE OF THE INVENTION 
The object of this invention is to provide a process or method azeotropic 
distillation that will enhance the relative volatility between 
3-methyl-2-butanol, 2-pentanol and 1-butanol in their separation as a 
mixture 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 alcohols and recycled 
to the azeotrope column with little decomposition. 
SUMMARY OF THE INVENTION 
The objects of this invention are to provide a process for separating a 
mixture of 3-methyl-2-butanol, 2-pentanol and 1-butanol 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-methyl-2-butanol, 2-pentanol and 1-butanol 
and permit the separation of these alcohols by rectification when employed 
as the agent in azeotropic distillation. Table 3 lists the compounds that 
I have found to be effective. The agents that remove 2-pentanol as bottoms 
product are 2-pentanone, n-propyl acetate, heptane, acetal, 2,2-dimethoxy 
propane, butyl formate, ethyl acetate, benzonitrile, t-amyl methyl ether, 
isobutyl acetate, methyl amyl acetate, amyl acetate, hexyl acetate, 
dipentene, d-limonene, terpinolene, 2,3,4-trimethyl pentane, 
dicyclopentadiene, octane, cumene, hexane, p-xylene, m-xylene, o-xylene, 
TABLE 3 
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Effective Azeotropic Distillation Agents For Separating 
2-Pentanol From 3-Methyl-2-butanol And 1-Butanol 
Relative Volatility 
1-BuOH 3-Me-2-BuOH 3-Me-2-BuOH 
Compounds 2-PnOH 2-PnOH 1-BuOH 
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None 1.08 1.4 1.25 
3-Pentanone 1.17 1.9 1.6 
n-Propyl acetate 
1.25 1.36 1.07 
Acetal 1.17 1.53 1.32 
2,2-Dimethoxy 
1.25 1.6 1.32 
propane 
Butyl formate 
1.25 1.35 1.08 
Ethyl acetate 
1.17 1.4 1.17 
Benzonitrile 
1.17 1.32 1.15 
t-Amyl methyl ether 
1.17 1.34 1.14 
Isobutyl acetate 
1.17 1.36 1.14 
Methyl amyl acetate 
2.1 2.3 1.1 
Amyl acetate 
1.75 1.65 1.0 
** Ethylene glycol 
1.17 0.8 0.7 
ethyl ether acetate 
Hexyl acetate 
1.65 1.8 1.04 
Dipentene 1.3 1.65 1.23 
d-Limonene 1.3 1.35 1.0 
Terpinolene 1.4 1.4 1.0 
** Carane 1.65 1.0 0.6 
2,3,4-Trimethyl 
1.3 1.3 1.0 
pentane 
Dicyclopentadiene 
1.3 1.18 0.9 
Octane 1.3 1.35 1.0 
Cumene 1.3 1.4 1.05 
Hexane 1.43 1.63 1.13 * 
p-Xylene 1.3 1.43 1.05 
m-Xylene 1.3 1.32 1.0 
o-Xylene 1.3 1.43 1.08 
Toluene 1.3 1.38 1.06 
Ethyl benzene 
1.4 1.35 0.9 
Cyclopentane 
1.3 1.55 1.2 
Cyclohexane 1.35 1.42 1.1 
1-Hexene 1.3 1.6 1.25 
Heptane 1.3 1.3 1.0 
Methyl cyclohexane 
1.3 1.53 1.15 
** 3-Methyl pentane 
1.95 1.72 1.0 * 
2-Nitropropane 
1.3 1.4 1.15 
** Methyl ethyl 
1.6 1.0 0.6 
ketoxime 
1-Octene 1.4 1.4 1.0 
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* Data From Multiplate Rectification Column 
** Brings 1butanol out as overhead product 
toluene, ethyl benzene, cyclopentane, cyclohexane, 1-hexene, methyl 
cyclohexane, 2-nitropropane and 1-octene. The agents that remove 1-butanol 
as overhead product are ethylene glycol ethyl ether acetate, methyl ethyl 
ketoxime, carane and 3-methyl pentane 
THE USEFULNESS OF THE INVENTION 
The usefulness or utility of this invention can be demonstrated by 
referring to the data presented in Tables 2 and 3. All of the successful 
agents show that 3-methyl-2-butanol, 2-pentanol and 1-butanol can be 
separated one from another by means of azeotropic distillation in a 
rectification column and that the ease of separation as measured by 
relative volatility is considerable.

WORKING EXAMPLES 
EXAMPLE 1 
Forty grams of a mixture comprising 10% 3-methyl-2-butanol, 40% 2-pentanol 
and 50% 1-butanol and 40 grams of hexyl acetate were placed in a vapor 
liquid equilibrium still and refluxed for six hours. The vapor composition 
was 10.3% 3-methyl-2-butanol, 36.1% 2-pentanol and 53.6% 1-butanol; the 
liquid composition was 7.9% 3-methyl-2-butanol, 49.6% 2-pentanol and 42.5% 
1-butanol. This is a relative volatility of 1-butanol to 2-pentanol of 
1.65, 3-methyl-2-butanol to 2-pentanol of 1.8 and 3-methyl-2-butanol to 
1-butanol of 1.04. 
EXAMPLE 2 
One hundred grams of a mixture comprising 10% 3-methyl-2-butanol, 40% 
2-pentanol and 50% 1-butanol and 140 grams of hexane were placed in the 
stillpot of a 5.6 theoretical plate glass perforated plate rectification 
column and refluxed for 1.5 hours. The overhead composition was 10.5% 
3-methyl-2-butanol, 8.2% 2-pentanol and 81.3% 1-butanol; the bottoms 
composition was 3.5% 3-methyl-2-butanol, 42.3% 2-pentanol and 54.2% 
1-butanol. This is a relative volatility of 3-methyl-2-butanol to 
2-pentanol of 1.63; of 3-methyl-2-butanol to 1-butanol of 1.13 and 
1-butanol to 2-pentanol of 1.43. 
EXAMPLE 3 
Forty grams of a mixture comprising 10% 3-methyl-2-butanol, 40% 2-pentanol 
and 50% 1-butanol and 100 grams of 3-methyl pentane were placed in the 
stillpot of a 5.6 theoretical plate glass perforated plate rectification 
column and refluxed for three hours. The overhead composition was 7.7% 
3-methyl-2-butanol, 1.6% 2-pentanol and 90.7% 1-butanol; the bottoms 
composition was 8.7% 3-methyl-2-butanol, 39.3% 2-pentanol and 52.0% 
1-butanol. This is a relative volatility of 3-methyl-2-butanol to 
2-pentanol of 1.72; of 3-methyl-2-butanol to 1-butanol of 1.0 and 
1-butanol to 2-pentanol of 1.95.