from Alcohol
W . J. T O U S S A IN T , J. T . DUNN, AND D . R . J A C K S O N 1
Carbide and Carbon Chem icals Corporation, S outh C harleston, W. Va.
c h3—c h2o h + c h3—c h=c h—c h o —
>-c h2= c h— C H = C H 2 + CH3— CHO + H20 (1) The Ostromislensky process depended upon the conversion of acetaldehyde to crotonaldehyde (Equation 2) and the Lebedev process further required the formation of acetaldehyde from ethanol (Equation 3):
2CH3— CHO — > CH3— C H = C H — CHO + H20 (2) CH3— CH20H — 9- CH3— CHO + H2 (3) After this theory was presented, attention was concentrated on a study of Equation 1, and silica gel was eventually found to be a good catalyst for that reaction. In an attempt to improve the characteristics of this catalyst, it was found that certain metal oxides not only produced butadiene from the crotonaldehyde but also converted acetaldehyde and ethanol to butadiene wii/i con
siderable improvement over other known catalysts. It w ¡s found further that the addition of copper gave good results in the Lebe
dev type of process, if sufficient acetaldehyde were maintained in
U
N TIL the necessity arose of replacing our supply of natural rubber, investigation of the production of butadiene for synthetic rubber was of relatively minor importance in this country. In Russia where this eventuality was more apparent, the Lebedev process (#) for producing butadiene from ethanol was developed, and many details of the operations were published, exclusive of the specific nature of the catalyst. Much earlier Ostromislensky had obtained butadiene, in small but in
teresting amounts, from ethanol and acetaldehyde over catalysts which might be broadly described as having dehydrating proper
ties. Moreover, much information of more or less pertinence had accumulated in both the academic and patent literature on the reaction of alcohols and carbonyl compounds over various catalysts; but little progress was indicated in the preparation of diolefins by these reactions.
Intermittently over a long period the authors and others in this laboratory worked on the project of making butadiene. A significant advance was made when Quattlebaum (1) found that crotonaldehyde and ethanol gave butadiene more readily than did ethanol and acetaldehyde, and concluded that Ostromislen- sky’s process, and Lebedev’s also, had as the key step the reac
tion of ethanol and crotonaldehyde according to the following scheme:
1 Present address, W y a n d o tte C hem icals C orpora tion , W y a n d o tte , M ich . 120
February 1947 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 121
During the war em ergency a substantial part o f the butadiene for m an u faetu rin g syn th etic rubber was pro
duced from ethanol. T h e developm ent o f this process was facilitated by the recogn ition that crotonaldehyde is the interm ediate in the Ostrom islensky reaction, in which ethanol and acetaldehyde arc converted to butadiene.
Initially a process was developed for converting cro to n - aldeliyde and ethanol to bu tadien e with a catalyst o f silica gel, bu t suitable m odification o f t h e ‘ catalyst afforded equally efficient prod u ction o f butadiene from acétaldé
hyde and eth an ol. Further, by in corporating d ch ydro- genating com p on en ts in th e catalyst, the Lebedev type o f process was effected for converting ethanol m ore directly to butadiene. T he preferred catalyst for the acctaldehyde- ethanol reaction consisted o f silica gel im pregnated with
tantalum oxide. W ith this catalyst efficiencies o f abou t 67% from ethanol as th e u ltim ate raw m aterial were o b tained in the laboratory, and the results were substantially reproduced in plant operation. Zirconia supported on silica gel was considered as a possible replacem ent catalyst, since zirconia was m ore readily available and the yield o f butadiene was only som ew hat less than that obtained w ith the tantalum catalyst. T h e b y -p rod u cts from the process com prise a m u ltip licity o f h ydrocarbons, ald e
hydes, ketones, esters, ethers, a lcoh ols, etc. T h e m ore im p o rta n t o f these— nam ely, ethylene, b u tcn cs, ethyl ether, and bu ta n ol— were recovered on a plan t scale in a quality suitable for u t iliz a t io n .~ ~ T h e p h otograph on the opposite page shows a still used for the recovery o f b u ta
diene and o f reactants.
the feed to inhibit, hydrogenation of the butadiene. Most atten
tion, however, was given to the development of the Ostromislcn- sky process, since it seemed to offer greater certainty of success
ful large-scale operation within the limited time which then re
mained available for study.
B U T A D IE N E F R O M E T IIA N O L A N D C R O T O N A L D E H Y D E
At one time during these investigations the most promising method for the commercial production of butadiene seemed to be the reaction of ethanol and crotonaldehyde over a catalyst of purified silica gel. In laboratory scale experiments the results bad been improved to the point where butadiene was obtained from crotonaldehyde with an efficiency of 63%. In order to confirm these results in commercial types of equipment and to gain further information on the process, the study was continued in a large laboratory scale converter and still. The converter was a 3-inch by 24-foot stainless steel tube heated by boiling Dow- therm; it contained 18 feet of silica gel purified by treatment with nitric acid. The still consisted
of a 6-inch, 22-tray bubble cap column , on a 17-gallon kettle.
From these studies data are pre
sented in Table I from two series of ex
periments: one (experiments 17-21) in which the molar ratio of ethanol to cro
tonaldehyde in the feed material was 3 to 1, and the other (experiments 22-28) in which the ratio was 6 to 1. The effect of the larger excess of ethanol was to conserve the more valuable reactant, crotonaldehyde, although with some sacrifice in the efficiency from ethanol.
The calculations of efficiency and single
pass yield were made on the assumption that the butadiene was derived solely from the crotonaldehyde introduced, and the acetaldehyde solely from the ethanol, according to Equation 1.
( Single-pass yield” is used to denote the per cent yield of product based on a specific reactant or reactants fed;
efficiency” refers to the per cent yield based on the reactant consumed.) This gave an efficiency from ethanol to acet
aldehyde in one scries in excess of 100%, which is accounted for by hy
drolysis of the crotonaldehyde. The other items in the efficiency were
calcu-lated approximately; the gas consisted largely of propylene and ethylene, and the high boiling oils and tar were considered to be condensation products of crotonaldehyde; the percentage un
accounted for includes by-products of intermediate boiling point as well as loss.
In experiments 17 to 21, inclusive, with a 3 to 1 molar ratio of ethanol to crotonaldehyde, the approximate composition of the feed in mole per cent was: ethanol, 36-39; crotonaldehyde, 12- 13; water, 52-48. The feed rate varied between 3.84 and 4.04 gallons per hour per cubic foot of catalyst. At 360-370° C. the average single-pass yield of butadiene from crotonaldehyde was 27.6%, and of acetaldehyde from ethanol, 12.4%. The molar ratio of acetaldehyde to butadiene in the products varied be
tween 1.24 and 1.53. For the five runs the material balance on a carbon basis was 97.6%.
For experiments 22 to 28 ethanol and crotonaldehyde were employed in a molar ratio of 6 to 1 in a feed of the following ap
proximate composition, in mole per cent: ethanol, 42;
croton-A p p a r a t u s f o r M a k in g B u t a d ie n e in th e L a b o r a t o r y
122 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 39, No. 2
aldehyde, 7; water, 51. The feed rate was substantially the same for all experiments, 3.60 to 3.72 gallons per hour per cubic foot acetaldehyde to butadiene was 1.28. For these runs the material balance on a carbon basis was 98.2%.
In all of these experiments the ratio of acetaldehyde to buta
diene in the products was greater than unity, largely because of hydrolysis of crotonaldehyde rather than dehydrogenation of ethanol. The addition of acetaldehyde to the feed mixture was feasible for each experiment, and for this reason a wide fraction co n ta in in g these materials was recycled with make-up reactants in succes either as obtained or after hydrogenation, although isomeric dihydrotolualdehydes were indicated as present.
Most of our studies were made at approximately atmospheric pressure, the pressure drop through the catalyst and distillation system being about 8 to 16 pounds gage. However, a few experi
ments were made with a converter pressure of 50 pounds gage.
The feed mixture contained ethanol and crotonaldehyde in a molar ratio of 6 to 1. Thd product ion ratio was increased about 55%
over that obtained at atmospheric pressure, other conditions being the same, but the ultimate efficiency from ethanol to buta
diene was decreased appreciably. There was an excessive increase in oil formation as well as an indication of greater hydrolysis of crotonaldehyde to acetaldehyde.
Butadiene from the large sca.le experiments was refined in the still system modified to provide cooling of the condenser by methanol, which circulated through a carbon dioxide-acetone mixture. The make was passed through a scrubber supplied with 10% aqueous caustic soda to remove acetaldehyde. The follow
ing fractions were taken off in sequence: fraction 1, 4.7 pounds;
fraction 2, 7.9 pounds; and fraction 3, 9.S pounds. Fraction 1 contained 94% of butadiene by determination as the tetrabro- mide, and fractions 2 and 3 had a purity of 98.5% as indicated by freezing point, if the impurity is assumed to be butene. The incorporating certain metal oxides, notably those of tantalum, zirconium, and columbium, much smaller amounts of acctalde- hydc and correspondingly larger amounts of butadiene resulted.
With a catalyst of 2.4% tantalum oxide on silica gel at 325° C., a space velocity of 0.7 liter of liquid feed per hour per liter of cata
lyst, and a molar ratio of 6 moles of ethanol to 1 mole of croton
aldehyde in the feed, all but 7 % o f the crotonaldehyde was re
acted. The product contained only 0.3 mole of acetaldehyde for each mole of butadiene produced and 1.25 moles of butadiene for each mole of crotonaldehyde fed, and the production ratio was 5.5 pounds of butadiene per hour per cubic foot of catalyst.
Such results indicated that these catalysts were capable not only of producing butadiene from ethanol and crotonaldehyde, but also of converting acetaldehyde to crotonaldehyde. It therefore seemed likely that acetaldehyde could be used in the feed mixture instead of crotonaldehyde, and this was found to be t he case. The use of such catalysts with ethanol and
February 1947 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 123
hyde demonstrated an increasing efficiency in the order colum- bium, zirconium, and tantalum; a minimum expectancy of 61% efficiency from ethanol was established for the over-all
■ process, in which acetaldehyde would be produced from ethanol by the conventional copper catalyst, and the butadiene sepa
rately from ethanol and acetaldehyde over a tantalum oxide- silica gel catalyst. Because of extensive plant experience in pro
ducing acetaldehyde, the investigation could fortunately be limited, to a large extent, to the step of producing butadiene.
Much of this work was in laboratory scale equipment, which enabled more rapid progress in attacking many of the questions to be answered. Here again the analytical problems in determin
ing the efficiency were complex; while confidence was gradually acquired in the data of single experiments, more satisfying as
surance could be placed in a series of experiments in which the recovered reactants were repassed several times over the catalyst with make-up feed materials.
Data from a series of such experiments with a catalyst of 2.5%
tantalum oxide on silica gel are given in Table II. The butadiene fraction, after refining by distillation and treatment with aqueous hydroxylamine to remove acetaldehyde, contained the following:
propylene, 1.8%; butene, 2.2% ; • vinylacetylene, 0.011%;
butadiene, 96%. Based on four-carbon materials only, the buta
diene purity was about 98%. The efficiencies from ethanol and acetaldehyde to butadiene are calculated for the individual ex
periments of the series on the basis of the following equation:
CII3— GHiOH + CII3— CHO — >
CH2= C H — C H = C H 2 + 211,0 (4) The average ultimate efficiencies from ethanol are calculated from the amounts of ethanol consumed as such, and of acetalde
hyde referred to ethanol; acetaldehyde is obtainable at 92%
efficiency from ethanol.
Experiments of this nature established the possibility of ob
taining an efficiency of 65-70% without credit for the by
products. They formed a basis for the conditions which were recommended for the operation of the butadiene plants. These conditions were intentionally mild with regard to presumed or known deteriorating effects on the catalyst, while sufficient pro
ductivity was maintained.
A difficult problem involved the amount of tantalum oxide to use in the catalyst. The supply of ore was limited, and careful conservation was further necessitated because of other impor
tant wartime uses. Fortunately only a low percentage on the silica gel was required to give catalysts of good activity; how
ever, the activity varied with concentration as did the decline of activity with use. Variation of promoter concentration did not cause large effects in the efficiency of utilizing ethanol (Table III); but in view of the tremendous quantities of alcohol in
volved, it was necessary to be as economical as possible in the use of this raw material. It was decided that all of these factors were best satisfied by a catalyst of about 2% tantalum oxide, and this was generally installed in the plants.
The molar ratio of ethanol to acetaldehyde and the tempera
ture were highly significant and were, to some extent, compen
sating factors affecting the efficiency, the operating cycle, and the nature of the by-products. As shown in Table IV, the ef
ficiency was better at 325° C. with a feed mixture of 3 moles of ethanol to 1 of acetaldehyde than it was at 300° or 350° C.;
with a mixture of 2 moles of ethanol to 1 of acetaldehyde it was better at 350° than at 325° C. With the latter proportion of re
actants and the same space velocity the efficiency was inferior at 375° C.
The effect of molar ratio and temperature on decline in activity with use—a factor of much importance in determining the oper
ating cycle—was even more striking, as shown by Figure 1.
Sam ple o f Catalyst after R eaction Period (left) and Sam ple after R eac
tivation by O xidation o f the Carbonaceous D eposit w ith Air (right)
124 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 39, No. 2 hyde, the decline in production ratio with time was very slow at a temperature of 325° C. (curve 3, Figure 1 A) but was consider
ably accelerated at 300° C. Correlation with pilot plant produc
tion is shown by curve 4. Good agreement was reached, al
though recovered feed, containing diluents, was used in part of the pilot plant run. With a molar ratio of 2.5 to 1, similar ef
fects were noted, except that somewhat higher temperatures were required for best results (Figure IB).
With a molar ratio of 2 to 1 a considerable increase was noted in initial productivity due to the higher aldehyde concentration.
This also resulted in a rather rapid loss of activity through foul
ing, even at 350° C. (curve 3, Figure 1C). The addition of 10%
of water to the feed lowered the rate of decrease and the initial production ratio, so that the average produc
tivity was hardly affected. The addition of ---water did not prevent rapid fouling at 325° C.
High temperatures (375° and 400° C.) were even less satisfactory at the space velocity used.
In securing the maximum over-all produc
tivity, the time spent in burning off carbonaceous deposits must also be taken into consideration.
Further, the larger the amount of this deposit the longer would be the time required for its removal, since this step is highly exothermic and the catalyst is very sensitive to temperatures in excess of 500° C. In practice it was considered undesirable to exceed a temperature of 400° C.
By using steam as a diluent during much of the burn-off period and by operating with
ethylene,
feed mixtures containing ethanol and acetalde- hyde in a minimum molar ratio of about 2.5 to 1, excessive thermal deterioration of the catalyst was avoided.
The possibility was investigated of employ
ing pressure as a means of increasing produc
tion. At 80 pounds gage in experiments of about 30-hour duration, the average produc
tion ratios for the period were about equal to those from similar experiments at atmospheric pressure, but the subsequent carbon, burn- off was about ten times as large. At the elevated pressure the amount of carbonaceous deposit was reduced by increasing the ratio of ethanol to acetaldehyde in the feed, al
though it remained greater relative to the butadiene production than at atmospheric pressure. Similar effects were noted for a smaller increase in pressure (15 pounds gage).
Because of the large number of by-products, only the more significant and readily isolable ones were determined in the laboratory experi
ments. Knowledge of the other components progressed with the larger scale operations, which provided increased facilities, man
power, and quantities of material for such in amounts of butyraldéhyde, methyl ethyl ketone, ethyl acetate, and acetic acid, which are made in the formation of acetaldehyde, arc included in the values in Table V.
The major by-products comprise ethyl ether, hexenes and hexadienes, ethyl acetate, pentenes and
Ta b l e III. Ef f e c t o f Co n c e n t r a t i o n o f Ta n t a l u m Ox i d e
February 1947 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 125
Carbon dioxide 0 .0 3 H exenes-hexadienes 3 .9 7
Ethylene 3 .9 1 E th y l acetate 1 .1 7
Pentadienes 0 .4 6 U nidentified products 3 .8
Ethyl ether 8 .0 Loss 5 .1 Single-pass yield to butadiene from
55 37 45
pentadienes, acetic acid, and butanol. The hoxadienes consist mainly of 1,3-cyclohexadiene, 2,4-hexadiene, and 3-methyl-l,3- pentadiene with small amounts of 1,3-hexadiene. The hexenes were not identified but are believed to be both branched and straight-chain isomers. The pentadienes comprise bothpiperylene and isoprene in a ratio of about 6 to 1. The pentenes isolated and identified thus far consist of 2-pentene, 2-methyl-2-butene, and 2- methyl-l-butene, and the presence of 1-pentene and 3-methyl-l- butene is indicated. The butene mixture contained about 35%
of 1-butene, 44% of ¿rans-2-butene, 21% of as-2-butcne, and 0 to 3% of isobutene. Equilibrium apparently does not exist among the straight-chain butenes, since these values do not cor
respond with those of Voge and May (3). The presence of an excess of 1-butene indicates that this isomer is formed preferen
tially on the catalyst.
Several of the by-products were utilized. These included ethylene, butene, ethyl ether, and butanol (and crotyl alcohol);
they correspond to about 15% of the alcohol consumed. The de
tails of the operations were worked out through the cooperation of many individuals connected with the project. Isolation of the other components in a practical manner was more difficult ; the high boiling oils, in particular, seemed of importance only as fuel, but fortunately they were relatively small in amount.
Other oxides supported on silica gel which are capable of pro
moting the formation of butadiene from ethanol and acetaldehyde are those of zirconium, columbium, thorium, uranium, and
titanium, in order of decreasing activity. Zirconia on silica gel, the second most favorable catalyst, gave results of intermediate character between those of columbium and tantalum oxides.
It was considered as a replacement catalyst for the butadiene plants in case the supply of tantalum became inadequate. The maximum efficiency obtained was 59% from ethanol to butadiene.
A few selected experiments are given in Table VI. Butene forma
tion was somewhat greater than with catalysts of tantalum oxide, and the purity of the butadiene in the Ci fraction ranged from 91 to 95%. A favorable synergistic action was sought from combina
tions of the oxides of tantalum, columbium, and zirconium, but such effect was not definitely established.
B U T A D IE N E F R O M E T H A N O L
There is considerable fascination in the idea of passing ethanol alone into a converter and obtaining butadiene as the major product without the use of supplementary equipment for pro
viding acetaldehyde. This is apparently what was originally in
tended in the Lebedev process, in which improved results were subsequently obtained by recycling acetaldehyde.
tended in the Lebedev process, in which improved results were subsequently obtained by recycling acetaldehyde.