Analysis of Fusel Oil by Azeotropic Distillation S. T. SCHICKTANZ, A. D. ETIENNE, AND W. I. STEELE Alcohol Tax U n i t Laboratory, Bureau of Internal R e v e n u e , Washington, D. C.
D
URING the process of fermentation as normally applied in the production of ethyl alcohol, the starting raw materials contain proteins and amino acids which by the action of enzymes and yeast (8) produce a product known as fusel oil. The major portion consists of alcohols boiling between ethyl and hexyl and small amounts of ethyl alcohol, water, acids, esters, furfuraldehydes, and higher boiling alcohols. In Table I are shown results of the analysis of fusel oil by previous investigators. TABLEI. ANALYSISOF FUSELOIL Mandya molasses (6) Water Acid Ethyl alcohol Isopropyl alcohol n-Propyl alcohol Isobutyl alcohol n-Butyl alcohol Active amyl alcohol Isoamyl alcohol n-Amyl alcohol
Type of ,Mash -7 Sweet poKaoling (6) Molasses ( 5 ) tatoes (6)
18 ~.
..
0.1 8
0.5 18
5.5
] 4: 3
, .
6:3 0.6
i:s
l7:5 66.7
l2:4 50.7
..
..
..
.. ,.
..
77: 4 12.9 0.5
These indicate that the qualitative and quantitative aspects of fusel oil depend on many factors and are not controlled alone by the type of mash used. The other factors may be (a) type of yeast or enzyme used for fermentation, (b) condition and environment under which fermentation proceeds, and (c) method of recovery of fusel oil from the rectifying column (3). These facts were corroborated by the results of the present investigation in which the fusel oil fractions used were produced from almost identical “mash bills” in two different distilleries. I n Table I1 are given the weight percentage amounts of the alcohols found in the two samples of fusel oil, produced from mash containing more than 93 per cent corn. The results, as given, are calculated on the total weight of alcohols present, and are not representative of the fusel oil fractions as received. The amounts of water and ethyl alcohol present depend on the method used for concentrating the fusel oil fraction and, therefore, should not be included in the calculations. The residues obtained during the initial distillation procedure were too small in volume to continue the distillation. However, upon combining them, about 60 per cent was re-
covered as isoamyl alcohol by further distillation. This indicates that if n-amyl alcohol was present its amount would be considerably below 1 per cent of the alcohol fraction.
Experimental Procedure
To rid them of the excess water and ethyl alcohol, the samples were treated with saturated salt solution, and the fusel oil was recovered by extraction with carbon tetrachloride. The extract thus obtained was subjected to atmospheric distillation in a modified 120-plate bubble cap column ( 2 ) . The presence of the carbon tetrachloride facilitated the removal of the small amounts of water and ethyl alcohol still present in the mixture, by virtue of the low-boiling ternary azeotrope formed by water, ethyl alcohol, and carbon tetrachloride (4). By continued azeotropic distillation all the n-propyl alcohol and isobutyl alcohol were removed, leaving in the pot the alcohols boiling above n-butyl alcohol. However, because of an insufficient amount of carbon tetrachloride some isobutyl alcohol remained behind and was distilled along with the active amyl and isoamjil alcohols. TABLE11. ALCOHOLS IN FUSELOIL Alcohol
Distillery A
Distillery B
Wt. %
Wt. %
n-Propyl Isobutyl Active amyl Isoamyl Residue
In Figure 1 is shown the separation occurring during the distillation according to boiling point (curve 2 ) , refractive index (curve l),and specific rotation (curve 3). On curve 2, A indicates the ternary azeotrope water-ethyl alcoholcarbon tetrachloride, B the binary azeotrope n-propyl alcoholcarbon tetrachloride, and C the binary azeotrope isobutyl alcohol-carbon tetrachloride. There was no indication of the presence of isopropyl alcohol. However, to be sure, pIateau A was subjected to further extraction and subsequent distillation procedure, the results of which indicated the absence of isopropyl alcohol. Curves 1 and 2 respond alike to change. The low dip of curve 1 located near 2900 ml. is due to the presence of some
VOLUME of DISTILLATE in ml.
FIGURE 1. SEPARATION DURING DISTILLATION 420
AUGUST 15, 1939
1460
I456
1452
1.448
6 $1.444
-
a
I440
ANALYTICAL EDITION
421
isobutyl alcohol, which remained in the residue in the pot because of insufficient quantities of carbon tetrachloride to form the azeotrope. The irregularities noted in curve 3 are due to the intermittent distillation procedure used. The still was not run continuously, and consequently on starting each day there were produced abnormal conditions which were most evident in the specific rotation determinations. It is interesting to note that one fraction was obtained which had the value [CX]’; -5.57. Accordingly, using the value for pure l-amyl alcohol of [ala”-5.78 the purity was calculated as 96.3 per cent (1). The alcohols-wpropyl, isobutyl, and isoamyl-were identified as the phenyl urethane derivatives. The urethanes were prepared directly from the azeotropic mixtures by refluxing. approximately 10 ml. of azeotrope with 1 ml. of phenyl isocyanate for 20 minutes. A small amount of sodium bicarbonate was added to aid the reaction. After refluxing, the carbon tetrachloride was removed by evaporating on the steam bath and the urethane taken up in hot petroleum ether from which it precipitated upon cooling. The melting point of some of the derivatives thus formed did not agree with the values given in the literature. However, the same melting points were obtained independent of either the method of preparation or the source of the alcohol. TABLE111. MELTING POINTS
1.436
I432
Phenyl Urethane Literature
Alcohol
Found
Ethyl Isopropyl n-Propyl Isobutyl n-Butyl Isoamyl
51-51.5
c.
87
51.5 85.5-86 59.5 55
O
c.
52
90
58
80
57
55
In Table I11 are given the melting points as found by experiment and those given in the literature ( 7 ) . Although the melting points of the urethanes obtained from ethyl and npropyl alcohols are the same, mixed melting points are definite proof that the derivatives are not the same. It is to 1424 k be noted also that the melting points of the urethanes of iso0 4 6 12 16 20 24 28 butyl and n-butyl alcohols are higher than the values given in COMPOSITION WT. % the literature. FIGURE 2 The amount of alcohol in the azeotropic m i x t u r e s was d e t e r mined by r e f r a c t i v e index m e a s u r e m e n t s . However, since the solutions formed by carbon tetrachloride with the alcohols are abnormal, it was necessary to determine experimentally the relation between refractive index and composition. T h e c u r v e s are given in Figure 2 and show the change of refractive index n2: with change in composition for ethyl, isopropyl, n-propyl, and isobutyl alcohols. From the weight of the distillate and its r e f r a c t i v e i n d e x the COMPOSITION WEIGHT PERCENT weight of alcohol present was obtained. CURVES OF ALCOHOLS WITH CARBON TEITRACHMIRIDEI FIQURE3. AZEOTROPIC L428
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Azeotropes
It was noted during the investigation that in certain mixtures, the molal composition and boiling point of the azeotrope did not check with the values as given in International Critical Tables. Consequently the composition and boiling points of the azeotropes of ethyl, isopropyl, n-propyl, and isobutyl alcohol with carbon tetrachloride were determined. TABLEIV. AZEOTROPE VALUES Alcohol Ethyl ‘Isopropyl n-Propyl Isobutyl
Experimental Values International Critical Tables B. P. Alcohol Pressure B. P. Alcohol Pressure C. Mole % M m . Hg C. Mole % M m . Hg 64.95 39 760 38.0 760.4 64.92 32.1 762.5 67.0 36.0 760 68.6 25 760 1 8 . 7 7 6 3 . 5 7 2 . 8 73.2 75.8 11 760 8.2 762.5 75.75
In Table IV is given a comparison of the values obtained with those given in International Critical Tables (4). The discrepancies between the observed and reference values may be assumed as real, and not totally dependent on the slight variation in pressures existing during the determinations. TABLEV. ALCOROLVOLUME Alcohol
Alcohol t o Produce 100 MI. of Azeotrope
Ethyl Isopropyl n-Propyl Isobutyl
M1. 26.9 27.3 l5,l 7.86
I n Figure 3 are shown the azeotropic curves of the alcohols with carbon tetrachloride. Because of the flatness of the curves, it was impossible to obtain the correct value for the composition of the azeotrope by visual inspection. Accordingly, the true values were obtained by subjecting the mixtures of the various alcohols and carbon tetrachloride to a distillation in a 90-cm. (%foot) column packed with small glass helices. The molal composition of the azeotrope was then determined by measuring the refractive index of the distillate, and referring to the curves in Figure 2.
Apparatus In Figure 4 is shown the Cottrell boiling point apparatus used in the determination of the azeotropes. The lower tube on the apparatus, A , is the boiler, and is coated on the inner surface with a layer of Carborundum fused into the glass. This ensures uniform and even boiling at a11 times. Heat is applied by means of a heating coil made of B. & S. gage No. 22 Nichrome wire wrapped directly on the tube itself. To obtain uniform heating conditions, the boiler is lagged with a 1.25-cm. (0.5-inch) layer of magnesia cement. The boiling points were determined by means of a 4-junction copper-constantan thermoelement and a Leeds & Northrup potentiometer No. 248,801.
Discussion By azeotropic distillation, the qualitative and quantitative estimation of alcohols boiling below n-butyl and present in fusel oil is simplified. The advantage of this procedure is threefold: The water present is removed a t the beginning and does not interfere with the distillation; efficient distillation units are not necessary for complete separation; and because of the low percentage of alcohols present in the azeotropes, it is possible to proceed with small samples of fusel oil. I n other words, the distillable volume is increased to the point where the factor of holdup of the distillation unit need not enter into the problem. In Table V are given the volumes of alcohols necessary to produce 100 ml. of azeotrope.
IlA
TI Literature Cited (1) Brauns, D. H., J. Research, Natl. BUT.Standards, 18, 315 (1937). (2) Bruun, J. H., and Faulconer, M. W. B., IND. ENQ.CHEM.,Anal. Ed., 9, 192 (1937). (3) Glim, E., and Stentzel, F., 2. ges. Brauw., 54, 49-70 (1931).
(4) International Critical Tables, Vol. 3, New York, McGraw-Hill. Book Co., 1928. (5) Kumamato, Shin, J. Chem. SOC.Japan, 53, 30 (1932). (6) Rao, F. N. R., Current Sci., 1, 53 (1938). (7) Shriner and Fuson, “Identification of Organic Compounds,’’ p. 86, New York, John Wiley & Bons, 1935. (8) Yamada, Nasakazu, J . Agr. Chem. SOC.Japan, 8, 428 (1932).
