Liquid-Vapor Equilibria in the Acetvlrnethvlcarbinol-Water Sv stern J J
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R. H.BLOM AND AARON EF'RON Northern Regional Research Laboratory, U . S . Department of Agriculture, Peoria, I l l .
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CETYL M E T H Y LLiquid-vapor equilibrium data have been determined for from reservoir A was fed a t the acetylmethylcarbinol-water system at atmospheric CARBINOL is proa constant rate to heater B pressure. The acetylmethylcarbinol which was used in duced by the action of cerwhere t h e glycol w a s this work was prepared by the vapor-phase oxidation of tain bacteria on fermentavaporized and mixed with a 2,S:butylene glycol. The purification of the carbinol is ble substrates. I n particm e a s u r e d stream of air. also described. Composition and boiling point of the aceular, Aerobacter aerogenes The hot gases were then tylmethylcarbinol-water azeotrope at a pressure of 760 mm. produces substantial quanp a s s e d t h r o u g h catalyst of mercury have been established. tities of the carbinol when tube C which was packed t h e f e r m e n t i n g mash is with clean copper turnsubjected to intense aeraings and maintained a t a tion (6, fd). A process has been developed through the cotemperature exceeding 270' C. Thermometer D, immersed in operative efforts of the Northern Regional Research Laboratory the gas stream, and thermocouples E, placed on the outside of the and Joseph E. Seagram & Sons, Inc., for the production of 2,3catalyst tube, were used to measure the temperature of the vapor butylene glycol by the fermentation of grain mashes with A . during its passage through the apparatus. After oxidation, the aerogenes. By carefully controlling the aeration during fervapor was cooled and condensed. The product from the oxidamentation, it is possible to limit the formation of acetylmethyltion apparatus was then analyzed for acetylmethylcarbinol, dicarbinol. For example, a typical beer would contain butylene acetyl, and butylene glycol. Operating data and analytical reglycol and acetylmethylcarbinol in quantities equivalent to sults for a few of the runs are given in Table I. For preferential 14.0 and 0.5 pound, respectively, per bushel of grain fermented. production of acetylmethylcarbinol, low oxygen-glycol ratios Consideration has been given to the recovery of the by-product were used. Glycol which was oxidized or lost in one pass over carbinol and to its interference in the butylene glycol recovery the catalyst averaged 26 to 30%. I n general, combined yields process. I n these deliberations, liquid-vapor equilibrium data of carbinol and diacetyl, based on glycol disappearance, amounted for the acetylmethylcarbinol-water system were of the utmost to 70 to 80%. The average ratio of acetylmethylcarbinol to diimportance. The purpose of this paper is to present these data. acetyl in the product was approximately 4. With higher oxygenBecause pure acetylmethylcarbinol is not readily obtainable, the glycol ratios, more g.ycol is oxidized per pass, but the ratio of preparation and purification of the compound will be described. carbinol to diacetyl in the product is much less. Acetylmethylcarbinol was recovered from the glycol oxidation product by fractional distillation. The fraction which boiled PROPERTIES AND PREPARATION from 139' to 145' C. was redistilled, and a heart cut was taken. Acetylmethylcarbinol is an alpha keto-alcohol and has the This material was dimerized in the presence of zinc a t approxiformula CHsCHOHCOCH,. A colorless liquid a t ordinary mately 4' C. The crude dimer was filtered from undimerized temperatures, it is miscible with water in all proportions and is material, washed with diethyl ether, and vacuum-dried over calsoluble in most other common solvents. Values for the boiling cium chloride. It was found that, if the liquid carbinol was expoint of the carbinol, ranging from 140' to 145' C., have been posed to the atmosphere for 12 to 24 hours before it was dimerreported by various investigators (1, 6, If). Acetylmethylized, an acetylmethylcarbinol dimer resulted which was crystalcarbinol solidifies over a period of several days, at temperatures line, white, and very stable. The finished material was stored a t approximating 0 ' C., to form a white crystalline compound which room temperature with no apparent reversion to the monomer. has been proved to be a dimer of the carbinol (2). Zinc catalyzes It was analyzed for carbon and hydrogen: found 54.7% carbon, the reaction. The dimer has no definite melting point. Acetyl9.21 % hydrogen; theoretical 54.5% carbon, 9.15% hydrogen. methylcarbinol dimer is a stable material and is an excellent The refractive index of the melted dimer was n2: = 1.4190. source of pure monomer. The preparation of the dimer is a simple method for the purification of crude distilled carbinol. EQUILIBRIUM' DETERMINATIONS No liquid-vapor equilibrium data for the acetylmethylAn equilibrium still similar to the one described by O t h e r carbinol-water system are available in the literature. It has been (10)was used in this work. To prevent oxidation of the acetylobserved a t this laboratory and by Fulmer and co-workers (3) methylcarbinol, an atmosphere of carbon dioxide was maintained that it is difficult to recover acetylmethylcarbinol from weak in the still during distillation. Air was swept from the apparatus water solutions by distillation methods; i.e., it has not been with the inert gas, and a stream of carbon dioxide was. passed possible to make quantitative separations of water and carbinol across the vent during the distillation. A thermometer with 1' by atmospheric fractional distillation. subdivisions was used to determine the temperature of the vapor. The carbinol was prepared by catalytic vapor-phase oxidation The still was charged with distilled water and acetylmethylof 2,3-butylene glycol. Butylene glycol has been catalytically carbinol dimer in amounts calculated to make a solution of the oxidized in the vapor phase by McAllister and de Simo (9) and approximate desired composition. When the mixture was Kolfenbach (7) to produce diacetyl as the principal product. heated, the dimer was converted to the monomer (3, 1I) which XlcAllister and de Simo reported the formation of acetylmethyldissolved to form a clear solution. All distillations were concarbinol by the oxidation. ducted for 2 hours with an evaporation rate of approximately 200 The oxidation apparatus is shown in Figure 1. Butylene glycol 1237
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interference of acetylmethylcarbinol in the method, and the corrected values were deducted from 100 to give the carbinol content. Table I1 gives results of the equilibrium determinations, and Figure 2 shows the equilibrium diagram. Figure 3 presents the phase diagram for the acetylmethylcarbinol-water system a t 750 mm. COMPOSlTION AND BOILING POINT OF AZEOTROPE
Several mixtures of carbinol and water, each mixture of approximate aeeotropic composition as deduced from the previous work, were boiled a t total reflux under a 1 X 48 inch Stedman fractionating column. An atmosphere of carbon dioxide was provided to minimize oxidation of the acetylmethylcarbinol. The still-head pressure was kept constant at 762 mm. of mercury by venting the still through a water-sealed bubbler. A Beckmann differential thermometer, graduated t o 0.01' C., was used to measure the boiling temperature at the top of the column. The thermometer had been standardized at the boiling point of xvater a t 762 mm. of mercfiry. The distillation was conducted until steady-state conditions were established as indicated by constancy of the temperature. A small sample of overhead con-
Figure 1.
Oxidation Apparatus
cc. of liquid per hour. Since the distillate receiver had a capacity of 25 cc., the rate of circulation was approximately eight cycles per hour. Samples of the liquids in the boiler and distillate receiver were taken at the end of the distillation period. Those samples containing less than 93% acetylmethylcarbinol were analyzed for their carbinol content by a periodic acid-oxidation method used for the determination of butylene glycol. One mole of acetylmethylcarbinol is oxidized by the acid to one mole of acetaldehyde and one mole of acetic acid. The acetaldehyde is distilled into a solution of sodium bisulfite to form the stable addition compound. Excess bisulfite is destroyed with iodine, and the combined bisulfite is then liberated with alkali and determined by titration with iodine. A sample of acetylmethylcarbinol dimer was dried at room temperature for several days over anhydrous magnesium perchlorate. The loss in weight, presumed to be water, was determined to be 0.270. Analysis of dilute solutions of this dried sample by the periodic acid method, by the direct titration method of Johnson ( 4 ) and by the iodoform method of Langlykke and Peterson (8) indicated that the method used in this work gave slightly low results. The factor of 1.027 was calculated and used t o convert analytical values for acetylmethylcarbinol to the reported values. The carbinol contents of those samples containing acetylmethylcarbinol in cxccss of 93% were obtained by difference; Le., water was determined by the method of Karl Fischcr, the water values were corrccted for the
ACETILMETHYLCARBI~IOL IN
LIOUID,
WEIGHT %
Figure 2. Liquid-Vapor Equilibrium Diagram for the Acetylmethylcarbinol-Water System at 750 M m . of
mercury
TABLE I.
VAPOR-PHASE
OXIDATION OF 2 , 3 - B U T Y L E N E
Run hTo. Average glycol rate g./hr. Average air rate l./rnm. Tern t o catalyit C. CataPyst temp., 0 Feed, moles oxygen/mole glycol Space velocitya Product rate, d h r . Product analysis, % ' Butvlene elvcol Aceiylmet?lylcarbinol Diacetyl Glycol oxidized oq lost,.% of feed Acetylmethylcarbinol yield, % b Diacetyl yield, % b Glycolunaccounted for, % of feede Acetylmethylcarbinol-diacetyl weight ratio
.
'c.
GLYCOL
3 4 9 1 0 1 207 230 325 815 180 0.57 1.16 1.17 1.16 1.13 298 291 290 295 297 358 314 374 319 307 0.142 0.252 0.228 0.160 0.161 1240 1870 1970 2340 2280 202 220 326 304 174 76.3 17.4 0.65 26.5 64.9 2.5 8.6
79.1 9.53 4.9 23.1 41.1 21.9 8.5
75.1 14.8 4.1 28.2 51.3 14.4 9.7
79.6 12.5 3.5 20.0 64.3 18.3 3.5
72.0 19.6 3.1 30.5 63.2 10.2 8.1
28.7
1.9
3.6
3.6
6.3
Volume of gas a t standard conditions passed in contact with 1 volume of catalyst per hour. b Per cent of,theory, based on glycol which disappeared during oxidation. e Most of this loss was as fog from the condensing system.
December, 1945 150
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TABLE11. LIQUID-VAPOR EQUILIBRIUM DATA FOR ACETYLMETHYLCARBINOL-WATW SYSTEMAT 750 MM. OF MERCURY Observed" -Smoothedoa, Temp., 2, 1/. Temp.. wt.% w?$& O C. Wt.% wt.% c. 0.0454 0.0594 99.8 0.2 0.27 99.8 2 0.0482 0.115 0.5 0.67 b 0.127 0.0933 3 1 .o 1.35 ... b 4 0.167 0.0987 2.0 2.6 b 0.262 0.184 5 5.0 6.2 ... b 0.270 0.230 6 8.3 7.0 b 0.469 7 0.651 10.0 11.1 b 0.471 8 0.599 13 0 13.5 b 1.26 0.882 9 15.0 15.0 (99:87)c b 1.22 10 0.960 17.0 16.3 b 5.65 11 4.48 20.0 18.2 b 9.91 8.88 12 25.0 21.2 100:0 b 13.7 13 13.4 30.0 23.8 100.1 14.9 14 15.1 99.8 40.0 28.3 100.4 17.0 16.8 15 50.0 32.4 100.8 10.5 16 17.4 100 0 60.0 30.3 101.2 22.4 19.8 17 70.0 40.5 101.8 b 27.8 22.8 18 80.0 46.7 102.7 b 34.1 25.5 19 85.0 51.3 104.8 100.5 40.9 28.7 20 90.0 60.1 109.5 b 32.1 49.2 21 95.0 76.7 119.8 56.9 22 101.0 35.5 98.0 89.6 131.2 60.9 39.0 101.7 23 99.0 94.8 137.3 72.8 42.2 24 102.0 81.2 47.9 25 103.0 87.6 54.7 100 0 26 92.2 04.2 112 5 27 93.4 75.9 119.0 28 97 .O 84.3 29 124.0 96.8 30 98.9 140.5 0 a! acetylmethylcarbinol in liquid. y acetylmethylcarbinol in vapor. b Neither the apparatus nor the tdermometer was sensitive enough to detect the small temperature changes in these regions. At 760 mm. Hg. Detn.
No. 1
... ...
... ... ...
ACETYLMETHYLCARBINOL,
WEIGHT
%
Figure 3. Phase Diagram for AcetylmethylcarbinolWater System at 150 M m . of Mercury
densate was then slowly withdrawn. This sample and a sample of the liquid in the boiler were analyzed for acetylmethylcarbinol by the periodic acid method. Table I11 gives analytical results and observed temperatures. The boiling points at 760 rnm. of mercury are based on the assumption that AT/ AP for the azeotrope is equal t o A T / AP for water. The results show that the azeotrope contained 15.0% by weight of acetylmethylcarbinol, which is in agreement with the value obtained from the equilibrium determinations The boiling point of the azeotrope at 760 m a . of mercury was 99.87' C. DISCUSSION OF RESULTS
The unusual behavior of dilute acetylmethylcarbinol-water solutions during atmospheric distillation is caused by the formation of a minimum constant-boiling mixture which has a boiling point close to that of water. It is apparent from consideration of the liquid-vapor equilibrium data that dilute solutions of acetylmethylcarbinol will distill practically unchanged in composition. Simple distillation was utilized by Langlykke and Peterson (8) in their method for determining carbinol in fermentation liquors. They report that, for solutions containing up t o 0.1 % carbinol, the distribution of acetylmethylcarbinol during simple distillation is constant and independent of the concentration in the solution. I n order that the distribution may be independent of concentration, the equilibrium relation between IC
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-
the liquid and vapor composition must be linear. That the relation is linear for concentrations of acetylmethylcarbinol in the liquid up t o 1.0% by weight is shown in Figure 4. The equilibrium line is straight and follows the equation y = 1.345~ where x and y represent the concentrations of carbinol in the liquid and vapor, respectively. Table IV compares a portion of Langlykke's data and calculated data based on liquid-vapor equilibrium. The calculated results were obtained by the Rayleigh equation with the relation between x and y as given above, The two sets of values are in good agreement. It is estimated that the application of Langlykke's method can be safely extended to fermentation liquors containing up t o l.Oyo acetylmethylcarbinol. Figure 2 shows t h a t it is difficult t o separate water and the azeotrope by fractional distillation at atmospheric pressure.
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TABLE111. BOILINGPOINTAND COMPOSITION OF ACETYLMETHYLCARBINOL-WATER AZEOTROPE Beck-
Run No. standardization 1 2 3 Av. 1, 2, 3
TABLE IV.
ACETYLMETHYLCIRBINOL
IN
LIQUID,
WEIGHT
%
Figure 4. Equilibria of Acetylmethylcarbinol-Water System at Low Concentrations of Carbinol (7SO RZm. of Mercury)
2,",9,Boiling Point, C. 5.24 5.11 6.12
...
...
762 mm. 100.07 99.84 99.96
... 99.94
C. 760 mm. 100.00 99.87 99.88
...
99.87
Acetylmeth lcarbinol, W t . k in: Boiler Overhead
...
13.0 14.6 15.9
...
ii.0
14.8 16.2 15.0
OBSERVED AND CALCULATED VOLATILITY OF ACETYLMETHYLCARBINOL IN Aauzous SOLUTIONS
Acetylmethylcarbinol in Distillate, % of Carbinol in Total Distilled Fractions % of T o d l Langlykke's CalcuDifference, Distilled obsvd. (av.") latedb hased on obsvd. 0.63 32.0 31.8 25 1.67 60.7 59.7 50 1.32 84.7 83.6 75 a For solutions contailring
