Separation
of Active Amyl
Isoamyl Alcohol
Alcohol
and
Zhou Rongqi
(Department of Chemical Engineering , Tsinghua University ,Beijing 100084)
Abstract
Factors affecting the separation of isoamyl alcohol and active amyl alcohol ,such
as reflux ratio, vapor velocity, temperature automatic control and feed
composition ,have been are studied. The operational condition are also discussed.
Active amyl alcohol product with a concentration of more than 95% and a yield of 30%
is obtained.
Keywords: active amyl alcohol, isoamyl alcohol, fusel oil, distillation
1
Introduction [1-3]
Fusel oil is a by-product of alcohol distillation. In China about two million tons of
alcohol are produced every year , 0.3%of which is fusel oil. isoamyl alcohol and
active amyl alcohol are contioned in fusel oil with a totel amount of 50% or so.
Active amyl alcohol , also called 2-Methyl-1-Butanol, and Isoamyl alcohol ,or
3-Methyl-1-Butanol, have the same molecular formulas. The difference of
configuration between them is methyl location. This leads to their completely differnt
optical rotation properties,that is , the former is left-hand rotation, optical rotation of
-5.9(25℃),which the latter isn’t optically active.
It is comparatively easy to obtain the mixture composed of them from fusel oil by
the ordinary distillation. However, in this case the concentration of active amyl alcohol
at most would be 20%-30%, the remaining70%-80%would be isoamyl alcohol.So it is
difficult to reach a concentration of 95% for them respectively because of the small
boiling point difference(2.8℃).
In the industry both of them have commercial value, especially the high price of
active amyl alcohol. So active amyl alcohol belongs to fine chemical products with
high additional value。
Liquid crystal synthesized with active amyl alcohol is used extensively for the
sake of good stability and wide temperature range. So far this product has not been
produced .domestically. If imported from abroad, active amyl alcohol with a
concentration of 95% Costs more than1000 RMB, per kilogram(.above 3000 RMB/kg
for 99% grade)
2
Selection of Separation Methods
The current methods for separating active amyl alcohol and isoamyl alcohol are
listed below:
(1) Ordinary distillation
This method can reach the target.But it is unsatisfactory in some respects, It needs
100 theoretical plates and a period of several days to separate them,while the yield
is as low as 10%.
1
(2) Extractive distillation
German researchers used 2,3-dichloropropanol and 2,3-dibromopropanol as the
solvents to separate them by extractive distillation[5] and got some success. But this
method is limited by the expensive cost, solvent toxicity and low resistance to high
temperature .
(3) Gas chromatography separation[5]
This method is good for separation them. But it isn’t easy to industrialize due to
the low throughput and yield.
(4) Chemical separation[5]
Active amyl alcohol and isoamyl alcohol are combined with barium bisulfate ,
then on the basis of different solubilities they can be separated .
Based on the situation in China, we have improved the ordinary distillation in
order to meet the needs of industrialization. A set of separation methods by salting
out-special precise distillation with certain adaptability has been established .
3. Experiment
3.1 properties of the system
Fusel oil is a mixture of several components . The typical compositions and physical
properties are listed in Tables1 and 2.
Table 1 Physical properties of fusel oil
Component
active amyl alcohol
isoamyl alcohol
butanol
propanol
ethanol
water
Boiling point
Density
Heat capacity
Composition
g·ml-1
Enthalpy of
vaporization
J·g-1
℃
J·(g·K)-1
%
128.0
130.8
107.9
97.2
78.5
100
0.809
0.8094
0.802
0.804
0.789
1.0
535.9
485.7
574
6807.7
389.3
2256.6
2.98
2.87
2.38
2.45
2.42
418.6
11.8
31. 1
6.2
1. 7
19.5
29.7
The optical rotation of active amyl alcohol is -5.91.
Table 2
Alcohol
Azeotropes between fusel oil
Azeotropic temperature
components and water(ambient pressure)
℃
Alcohol %(wt)
Water %(wt)
ethanol
78.7
96.0
4.0
propanol
87.7
71.7
28.3
isopropyl alcohol
80.3
87.4
12.6
isobutanol
89.92
66.8
33.2
butanol
92.7
57.5
42.5
isoamyl alcohol
95.15
50.4
49.6
The difference of boiling points between active amyl alcohol and isoamyl alcohol is 2.8℃,
relative volatility α= 1.078.
2
3.2 Experimental apparatus
The initial fusel oil contains about 29% water and 10% active amyl alcohol. By means
of salting out, the content of water will decrease to15% with active amyl alcohol up to
15% or so. 97% active amyl alcohol is obtained by precise distillation in the column
having 40 theoretical plates. The characteristics of this column are : 1) the partition on
the reflux ratio is very standard because gas partition is used instead of liquid
partition .2) automatic control system is equipped . The top temperature of the column
can be accurately controlled to ensure the quality of top product. 3) It is competent for
keeping heat well, and the vapor velocity is high and stable.
A new-type column used for batch distillation is employed in the experiments with a
height of 1.2m, diameter of 30mm and a mesh packing section of 1.1m. Autocontrol
meter controls the top product temperature. In the meantime the oil-bath temperature at
the bottom controls the vapor velocity. We use the yield of active amyl alcohol and
factorεexpressing separation ability to show the experimental results.εis defined as :

x i  x0
ε=
x0

Heve x 0 stands for the initial mole fraction of active amyl alcohol, x i is the average
mole fraction of active amyl alcohol at the top of the column.
3.3 The influence of reflux ratio on the separation
It can be seen from Figure 1 that as reflux ratio Rt increases, the yield of active amyl
alcohol also goes up. For the same yield, the factorεunder lower reflux ratio is
evidently less than that of higher reflux ratio.
The more reflux ratio, the better are separation results. But it takes longer time to
higher reflux ratio. to accomplish the separation process. Thus the optimum reflux ratio
is around 20based on30 sets of data.
0.70
Rt=20
0.60
ε
0.50
Rt=15
0.40
0.30
0.20
0.10
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Active amyl alcohol yield
Fig.1 The influence of reflux ratio on the separation
3.4 The influence of vapor velocity on the separation
Vapor velocity is controlled by the oil-bath temperature. In certain range , high oil3
bath temperature means that velocity vapor fluid is considerable, and factor εand
the yield also rise correspondingly. In the first period of heating, factor εrises quickly,
but when oil temperature reaches certain point ,factor εlevels off.
In the process of production we should select suitable vapor velocity so as to make
quality and yield high, and low energy consumption. Thus the optimum temperature is
170-180 ℃based on 21 sets of data.
1.40
180℃
1.00
170℃
ε
162℃
0.60
Rt=20
0.20
0.00
0.20
0.40
0.60
0.80
1.00
Active amyl alcohol yield
Fig.2 The influence of oil_-bath temperature on the separation
3.5 The influence of automatic temperature control at the top of the
column
Automatic temperature control at the top of the column is to control the concentration
of active amyl alcohol in the product. It is showed by experiments that with regard to
εor yield, automatic control has significant effect. But it needs longer operation time.
Automatic
temperature
control
0.40
No control
ε
0.30
oil-bath temperature
170℃
Rt=50
0.20
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Active amyl alcohol yield
Fig.3 The influence of temperature control on the separation
3.6 The influence of feed concentration on the separation
4
It is verified by experiments that as the concentration of the feed increases and the
yield rises , εdecreases gradually. The curve is very steep when the concentration
is low. When the concentration reaches certain amount, the curve becomes level.
So it is advisable that reflux ratio should be changed when the concentration is
high, that is, in the first period of distillation reflux ratio is small, and later reflux
ratio should be increaced. Through experiments the following optimum
operational conditions are obtained: oil-bath temperature 170 ℃; reflux ratio
100/5 for low concentration; temperature control; changing reflux ratio for high
concentration; whole reflux and batch distillation.
1.20
33.2%
1.00
ε
0.80
44.4%
0.60
0.40
0.20
0.00
0.20
oil-bath temperature
170℃
feed concentration 81.8%
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Active amyl alcohol yield
Fig.4 The influence of feed composition on the separation
4
Conclusion
Based on the ordinary distillation , the separation of active amyl alcohol is
improved in terms of operational process and conditions. Compared with the ordinary
distillation , the yield rises from 10.8% to 30% and the concentration of active amyl
alcohol in the product can be as high as 97.9%.
This process may provide some helpful hints for similar separation processes of
isomer-couple mixtures.
References
[1] Cheng Linneng,Hu Shengwen, “Solvent Handbook”,
Chem.Eng.Press,Beijing,1986,
p.300( in Chinese)
[2]“Chemical Engineering Handbook”, Vol.1,Foundational Data and Physical
Properties, Chem.Eng.Press,Beijing,1979( in Chinese)
[3]“Chemical Engineering Handbook”,Vol.13,Equipment of Vapor-Liquid Mass
Transfer,Chem.Eng.Press,Beijing,1979(Chinese)
[4 ] Kortum G. , Faltusz E., Chemie Ing Techn., 1961; 33(9): 599
[5] Frankc, Whitmore ,Hrrjsulewine J., J .Amer. Chem. Soc., 1938; 60:2569
5