December 1948
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
hydrocarbon allowed a reduction in the maleic anhydride value of the feed from 22.5 to 2.5 mg. per ml., while treatment with 65% sulfuric acid a t 40" C. allowed a reduction to 6.4 mg. per ml. Little or no polymer was formed during hydrogenation, while 4% of polymer was formed in the acid pretreatment and redistillation for polymer removal was required prior to alkylation. Alkylation runs comparing the hydrogenated and acid-treated Cg fractions are summarized in Table VI, which shows that similar increases in acid life were obtained by the two methods. However, a yield advantage, due to conversion of dienes to monoolefins and the absence of polymer formation during hydrogenation, is indicated for the hydrogenation case. This advantage would, of course, be amplified with Cg fractions containing higher concentrations of diolefins. PROCESS CONSIDERATIONS
The simplified flow diagram shown in Figure 11roughly outlines the essential features required in the design of a commercial selective hydrogenation unit based on the above experimental work. For this scheme it is assumed that the feedstock contains sufficiently low concentrations of diolefins so that an adiabatic reactor can be employed. The exothermic heat of hydrogenation of a diolefin to a mono-olefin is about 28 kilocalories per gram mole, and an initiating temperature of 220" C. and a maximum temperature of around 300" C. are considered as safe limits for adiabatic operation with C4 or C6 fractions. The use of an isothermal reactor or the incorporation of a product to feed recycle would probably be required for feedstocks containing high concentrations of diolefins. Sufficient data are not available to place limits on the hydrogen purity, but satisfactory results have been obtained using a 1 to 1 mole ratio of hydrogen t o hydrocarbon. I n view of the high degree of selectivity of the nickel sulfide catalyst for diolefin hydrogenation, olefins, paraffins, and light hydrocarbon impurities in the hydrogen all function as inert diluents in the system. Satisfactory results should be obtained with dilute hydrogen
230 1
streams, provided that the partial pressure of hydrogen is maintained in a suitable operating range. Depending on the operating pressure and the temperature t o which the effluent product stream from the hydrogenation unit is cooled, varying proportions of hydrocarbon would be present in the hydrogen recycle stream and in the vented hydrogen. Within limits, the operating pressure could be adjusted to keep the hydrocarbon content of these streams to a minimum and refrigeration could also be employed for control. While pressures of over 150 pounds per square inch gage have not been investigated, the use of higher pressures should offer no difficulties with feedstocks of moderate diolefin content. I n the diagram in Figure 11 provision is shown for catalyst sulfiding and regeneration in place, but in view of the long operating cycles anticipated, external facilities may prove more desirable. Temperatures of around 300' to 400" C. are believed suitable for burning and sulfiding the catalyst. ACKNOWLEDGMENT
The authors wish to express appreciation to their colleagues in the Shell Development Company who assisted in the experimental work. LITERATURE CITED
(1) Anglo-Iranian Dil Co., Ltd., Humble Oil and Refining Go., Shell Development Go., Standard Oil Development Go., and Texas CO., Oil GUSJ.,38, NO.27, 104-8 (1939). (2) Gerhold, Iverson, Nebeck, and Newman, Trans. Am. Inst. Chem. Engis., 39, 793 (1943). (3) Ipatieff and Pines, J. 07gqChem., 1, 464 (1936). (4) McAllister, Anderson, Ballard, and Ross, I b i d . , 6, 647 (1941). (5) McA!lister, Anderson, and Ross, U. 5. Patent 2,399,240 (April 30, 1946). (6) Ormsndy and Craven, J. Inst. Petroleum Tech., 13, 311 (1927).
(7) Young, Meier, Vinograd, Bollinger, Kaplan, and Linden, J. Am. Chem Soc., 69,2046 (1947).
RECZIVED February 27, 1948. Presented before t h e Division of Petroleum Chemistry, Symposium on Modern Motor Fuels, a t the 113th Meeting of t h e AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
BUTADIENE FROM ETHANOL Utilization of By-Product Ethyl Acetate E. E. STAHLY, H. E. JONES, AND B. B. CORSON Mellon Institute of Industrial Research, Pittsburgh, Pa. I t was-shown that butadiene results from the reaction of ethyl acetate with acetaldehyde in the presence of a tantala-silica catalyst at 325" to 350' C. Therefore, it is pos-
sible to increase the efficiency of the ethanol process for the manufacture of butadiene by recycling the by-product ethyl acetate. The first step in the utilization of ethyl acetate probably is the formation 'of ethanol by hydrolysis. The steady-state concentration, at which the amount of ethyl acetate formed per pass equaled the amount consumed, was determined for the commercial operating conditions.
T
HE Carbide and Carbon Chemicals Corporation's process for manufacturing butadiene from ethanol (8) comprises passing a mixture of approximately 62.7 mole yc ethanol, 22.8 mole % acetaldehyde, and 14.5 mole % water over a tantalum pentoxide (2%)-silica (98%) catalyst. A number of by-products are formed in this process. During World War 11, when the process was applied extensively, some of these by-products were recovered as marketable chemicals, others were recycled with recovered
ethanol and acetaldehyde, but most of them, including a major Dart of the ethvl acetate, were burned as fuel. Part of this byproduct ethyl acetate was formed in the acetaldehyde converters (in the dehydrogenation of ethanol) and part in the butadiene converters. This acetate-corresponding t o about 3 weight % of the ethanol lost in by-reaction-regardless of its point of formation was separated azeotropically with a by-product oil fraction boiling intermediate to the ethanol and acetaldehyde fractions and thus was not fed t o the butadiene converters. This paper presents experimental evidence that ethyl acetate can be converted to butadiene under the conditions employed in the commercial plants. The utilization of ethyl acetate n~ould increase butadiene production 2y0: this would have amounted t o an increase in butadiene production of 14,000,000 pounds in 1944, or a saving of 43,000,000 pounds of 92 weight Ycethanol. EXPERIMENTAL
APPARATUS AND PROCEDURE. The laboratory apparatus is shown diagrammatically in Figure 1. The premixed ethanol-acetaldehyde feed was pumped for &hour periods through a 12-inch
2302
INDUSTRIAL AND ENGINEERING CHEMISTAY
I : r
A - Feed Reservoir 8 - Pump C- Vaporizer
- Gas Collection System
J I
D - Furnace E- Product Flask F - Dry Ice Trap 6 - Wet Test Meter Figure 1.
H
Manometer Catalyst Tube
K
-
L
- Temperature
Thermocouple K'- Thermocouple M
- Nitrogen
Regulator
Line
Laboratory Apparatus
catalyst bed containing 125 cc. of catalyst. The products were condensed in a dry-ice receiver and subsequently distilled through an 18-plate packed column to separate butadiene from unreacted feed. Three fractions were collected: initial boiling point to 13' C.; 13' to 30" C.; 30" to 95' C.; and bottoms. These fractions were analyzed for the follon-ing components: fraction 1, butadiene and acetaldehyde; fraction 2, acetaldehyde; fraction 3, ethanol, acetaldehyde, acetal, and ethyl acetate; and bottoms, acctic acid. Using the commercial feed composition and operating conditions, and fresh commercial tantala-silica catalyst for each run, the laboratory unit gave a 36% conversion per pass and a 64% over-all efficiency. CALCULATION OF RESULTS.The yield values were calculated as follows:
Vol. 40, No. 12
The value derived from titration, however, was always coiihi i n t d by determining the ethyl acetate in the feed and in the product. EFFECTOF ADGITIONALWATER. Inasmuch as little water can be dissolved in feed stocks rich in ethyl acetate, the experimental procedure was to pump the water and the nonaqueous feeds t o the reactor in separate streams. Representative experimental data are presented in Table 11. The additional water had little effect on the production of butadiene, but the ester hydrolysis was increased from 41 to 58%. EFFECT OF OMISSIONOF WATER. One laboratory experiment was made at the Kobuta plant ( 3 ) of Koppers Company with a m-ater-free feed containing acetaldehyde and ethyl acetate in the mole ratio of 1 to 2.83. The conversion of ethyl acetate was 18 mole 7oat 350" C. and 0.5 liquid hourly space velocity (1.h.s.v.). These data do not disprove the hydrolysis mechanism because water was present in the reaction zone, although the initial feed x a s dry. For example, water is produced by the condensation of acetaldehyde to crotonaldehyde and by the reaction of ethanol with crotonaldehyde to form butadiene. Also, the catalyst always contains a small amount of water. STEADY-STATE CONCENTRATION OF ETHYL ,!!CETATE. Experiments were made (Table 111) to determine the steady-state concentration of ethyl acetate under operating conditions. At steady state the concentration of ethyl acetate in the reactor is constant because the amount of ethyl acetate formed equals the amount hydrolyzed. An effort was made to maintain commercial feed composition n i t h respect t o water (about 16 mole clo) and acetaldehyde (about 22.8 mole yo). Three runs with average
TABLE
ACETATE-ALDEHYDE FEEDS 1. DATAO S ETHYL Standard EthanolAcetaldehyde Feed
Ethyl Acetate-Acetaldehyde Feed
Composition of feed, inole 70 27.2 27.2 27.2 26.9 14.5 Water 47.2 52.0 0 52.0 52.0 Ethyl acetate 2.6 2.6 2.6 0.9 62.7 E t h anol 18.2 18.2 18.2 25.0 22.8 Acetaldehyde 0.56 0.42 0.40 0.40 0.38 Feed rate, l.h.s.v.5 351 328 327 326 350 Catalyst temperature, ' C. 2.95 2.97 4.25 2.73 0 Ethyl acetate in, moles 1.88 1.95 3.12 1.58 0.044 Ethyl acetate out, moles 0.16 5.13 0.15 0.21 0.15 Ethanol in, moles 0.37 2.84 0.59 0.72 0.62 Ethanol o u t moles 1.12 1.14 1.03 0.01 1 10 Acetic acid jound, moles 14 20 36 19 19 Conversion t? C4H6, mole % 43 b 64 59 56 58 Over-all efficiency, mole % 35 37 41 27 18 Hydrolysis of ester, mole % ' a Volume of liquid feed per volume of catalyst per hour. b Low efficiency is attributed primarily to low ratio of ethyl acetate t o acetaldehyde i n the feed (about 1.9 moles ester per mole of acetaldehyde), t
Conversion, mole
7'
Moles of C4Hs formed X 200 - Moles of feed (CzH60H CHaCHO)
+
Over-all efficiency, mole yo = Moles of C4He formed X 200 bloles of CZHSOII reacted
+
-
reacted 0.92
T o conform with plant practice the over-all efficiency of the process was based on ultimate alcohol consumption; the moles of acetaldehyde consumed were divided by 0.92 because the commercial dehydrogenation of ethanol to acetaldehyde operated a t 92% efficiency. The calculations of efficiencies for feeds containing ethyl acetate were made in similar manner and a mole of ethyl acetate was regarded as a mole of ethanol. The factor 0.92 was omitted in calculating conversions, again to conform with plant practice.
TABLE11. EFFECTO F jTrAT13R ON ETHYT, ACETATEACETALDEHYDE FEEDAT 350" C. Composition of nonaqueous feed, mole % ' Ethyl acetate Ethanol Acetaldehyde Mole ratio, water t o ethyl acetate Feed rate, 1.h.s.v. Ethvl acetate in. moles Ethyl acetate out, moles Acetic acid formed, moles Conversion t o CaHe, mole % Over-all efficiency, mole c/c Hydrolysis of ester, mole %
71 .O 4.2 24.8 4.5 0.4 2.96 1.19 1.72 20 60 58
71.5 3.5 25.0 0.5 0.4 2.96 1.75 1.22 20 60 41
DISCUSSION OF RESULTS
ETHYLACETATE-ALDEHYDE FEEDS.The outcome of initial runs with ethyl acetate-acetaldehyde feeds (Table I) compared favorably with the data for standard feed runs. It was shown that the product from feed containing ethanol, acetaldehyde, and ethyl acetate contained acetic acid equivalent to the ethyl acetate consumed. Evidently, the first step in the utilization of ethyl acetate in the production of butadiene is hydrolysis of the ester. Experimentally, the consumption of ester was easily followed by titrating the product for acetic acid.
CONDITIONS WITH ETHYL ACETATETABLE111. STEADY-STATE ACETALDEIIYDE FEED (Liquid hourly space velocity, 0.4; Composition of feed, mole % 16.7 14.5 Water 2.1 0 Ethyl acetate 62.7 57.6 Ethanol 22.8 23.7 Acetaldehyde 0.16 Ethyl acetate in, moles 0 0.044 0 . 2 0 Ethyl acetate out, moles 0.05 Acetic acid formed, moles 0.01 18 31 Hydrolysis of ester, moles %
350' C.) 16.1 3.4 58.5 22.0 0.26 0.25 0.05 20
15.0 4.9 55.0 25.1 0.40 0.36 0.09 23
23.6 13.3 43.6 19.5 1.08 0..65 0.26 24
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948
steady-state concentrations of 3.4% ethyl acetate showed 36% conversion and 6670 over-all efficiency; this compares with 36% and 64%, respectively, for average standard operation. This agreement is within the limits of experimental duplicability. The fact that the efficiency was not lowered by replacing part of the ethanol with an equivalent amount of ethyl acetate demonstrated that the ester was as efficientlv utilized as the ethanol. Apparently, 3.4 mole yo of ester was the steady-state concentration. The amount of ester recovered (column 3) was equal to that charged, and the acetic acid in the product was equivalent to about 2o % Of the ester fed. Therefore, the acetate utilized at steady-state corresponded to about 1.2 mole % (2.2 weight %) of the alcohol content of the commercial feed. lunS was made in which A series Of five successive to by-products and unconsumed reactants were recovered and re-
'-
2303
cycled. The catalyst was just as active in the fifth cycle as it was in the first cycle. Ethyl acetate is equivalent, mole per mole, for the production of butadiene, as shown by the following-equations: . CHoCHO
+
+
CHICHO CzHjOH +C4Hs 2Hz0 ( I ) CHBCOOC~HE +CaHe HzO 4-CHaCOOH
+
+
LITERATURE CITED
(1) Quattlebaum, Toussaint, and Dunn, J. Am. Chem. sot., 69, 593 (1947).
(2) Toussaint, Dunn, and Jackson, IND. ENG.CHEM., 39, 120 (1947). (3) Winans. C. F.. arivate communication. RECIDIVED September 19, 1947. A contribution of the Multiple Fellowships on Catalysia (Office of Rubber Reserve) and Tar Synthetics (Koppers Company, I ~ ~ . ) .
Decomposition of Elastomers at High Temperatures GLENN S. SKINNER AND JAMES H. MCNEAL University of Delaware, Newark, Del.
AI1 of the selected elastomer compositions from natural rubber, GR-S, butadiene-acrylonitrile copolymer, and neoprene were found to undergo exothermic decomposition when heated rapidly. The exothermic action is characterized by the formation of products requiring loss of hydrogen by the stocks such as hydrogen chloride, hydrogen cyanide, and saturated hydrocarbons. Phosgene could not be detected in the smoke from neoprene. The effects of compounding agents and of preheating below the exothermic decomposition temperatures are reported. The evolution of smoke is not essentially a characteristic of the exothermic action. A column of smoke 22 inches long causes 50% extinction of the maximum beam of a standard sealed-beam headlight before the exothermic action begins. Moreover, the smoke just above some of the stocks disappears entirely during the exothermic action, whereas zinc and magnesium oxides cause the evolution of much denser smokes at this stage. The outside heating temperatures at which the smoke and gases flash are similar for gum stocks of the four elastomers. The smoke from neoprene then extinguishes the pilot light, but the other samples are igni'ted and continue to burn.
v
ULCANIZED elastomer stocks made from neoprene, 1,3butadiene-acrylonitrile copolymer, GR-S, and natural rubber are employed in the manufacture of products which, in use, may be subjected to heat or fire. Selected vulcanized compositions of those elastomers have therefore been examined at high temperatures for comparison as to thermal behavior, density of smoke formed, and flammability of volatile products. Previous studies (6) showed that definite and sometimes large differences in the decomposition temperature of eIastomer stocks may result from compounding, even with very small amounts of materials such as accelerators. With respect to decomposition products the examination of the liquid portion from the destructive distillation of crepe rubber (2) revealed no fully saturated compound. It was also found that the presence of magnesium and zinc oxides during the distillation increases volatile liquids other than isoprene and dipentene and also the amount of aromatics at the expense of chain compounds.
Midgley and Henne assigned relative cleavage tendencies of the different linkages in the chain from the yields of the liquid cleavage products and attributed the modifying effect to the action of magnesium oxide upon the double bonds. The C-C bond 4-5 in the following formula was represented as being cleaved approximately 150 times as frequently as bonds 1-2 or 3-4, whereas in the presence of magnesium oxide this ratio dropped to 80 times as much: 6 H CHsH H H I
I
H 1
2
. . b-G=c-c-c
H €I 4 6
3
The cleavage of the C-C bond 2-6 should lead to methane, which would not be detected among the liquid products. Such a reaction would be expected since the needed hydrogen at position 1 is in the reactive 1-3 position, counting both carbon atoms of the double bond. Similarly neoprene and 1,3-butadiene-acrylonitrile copolymer would be expected to yield hydrogen chloride and hydrogen cyanide, respectively. The structure of neoprene is definitely known from its oxidation to succinic acid ( I ) , and it may be considered to be predominantly a 1-4 addition polymer of 2-chloro-I,3-butadiene. Although other substances, such as cyclic polymers (6),may be present, this structure is relatively satisfactory as a basis for understanding the chemical behavior of neoprene:
c1
8'
I . . . . . CHn-C=CHCHzCHg 1
2
3
4
5
6
=CHCHs, 7 8
..
A large part of a butadiene-acrylonitrile copolymer is probably as depicted by the following chain segment: C=Y I
. . . . . CHGH=CH-CHdHCH2. 1
2
3
4
5
6
.. . .
I n the neoprene chain hydrogen atoms 1 and 5 are in the reactive 1-3 position to the double bonds at 3-2 and 7-6, respectively. I n the butadiene-acrylonitrile chain the hydrogen atom at posi.
