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240
able, whether this be accomplished by centralization in large corporations, or by farming out the problems to specialized laboratories on the industrial fellowship plan. The study of metallurgical research tendencier throughout the world, made in the course of preparing this paper, only strengthens the satisfaction the writer had last fall when President Hoover broadcast the plea, mentioned above, for more specialized research laboratories and more support for research. It was indeed a satisfaction to know that a t the
Vol. 22, No. 3
moment of his talk Battelle Memorial Institute was just beginning actually to do fundamental research, as well as to ser've industry by industrial research in metallurgy and fuels. The writer is proud to be connected with an institute whose founder several years ago envisaged the need President Hoover has so well expressed, and whose trustees have been working in the last few years on the planning of the building, and the plans for operation, of a research laboratory that. should be a real factor in meeting this need.
Formation of Butadiene b y Cracking of Hydrocarbons' Per K. Frolich,*R. Simard, and A. White DSPAPTMBNT OF
CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE
OF T E C H N O L O G Y , C A M B R I D G E ,
MASS.
Experiments are described which show that butadiene OKSIDERABLE interoxidation to acetaldehyde, may be formed from propane, butane, and cyclohexane condensation to aldol, reest in the problem of by cracking at high temperature, thus substantiating synthesizing r u b b e r duction to butylene glycol, the claims made in recent patents. like amorphous materials is and finally dehydration t o In the case of propane the highest yield obtained butadiene. revealed in the recent patent corresponds to about 1 mol of butadiene per 100 mols The present paper describes literature. Although natural of propane, and the indications are that this is close experiments made to study rubber has the empirical forto the maximum conversion obtainable by simple butadiene formation b y mula (CsHs). and hence may cracking. With propylene and butane the highest simultaneous cracking and be considered a polymer of yields observed are slightly more than 3 mols of the polymerization of propane, isoprene, other diolefins, pardiolefin per 100 mols of hydrocarbon, but in view of the butane, ethylene, propylene, ticularly butadiene, have also incomplete survey of the experimental conditions and cyclohexane. been used as raw material for there still remains a possibility of increasing these the synthetic product (3, &, Apparatus and Experimenconversion figures. A single experiment on the crack5 , 8, 11). Granting that a tal Procedure ing of cyclohexane gave 20.6 mols of butadiene per cheap source of diolefins is 100 mols of cyclohexane reacting. The gaseous hydrocarbons essential for the ultimate sucThe results also throw light on the mechanism of t o be cracked were passed cess of any process of this production of aromatics from paraffins in that they from a storage cylinder type, it may be advantageous point to the formation of diolefins as intermediates in under pressure through a to base the synthesis on the process. reducing valve to the crackbutadiene provided it can be ing chlmber. The exit gas obtained in large quantities from the chamber was conducted first through an ice-cooled a t a lower cost than isoprene. Brooks (1) states that butadiene is present in gases ob- and then through a carbon dioxide-cooled condenser, the tained by the cracking of hexane and higher petroleum hydro- uncondensed gas being expelled into the atmosphere. The carbons. I n studying the thermal decomposition of gaseous inlet gas rate was measured by means of an orifice flowparaffins, Davidson ( 2 ) found that butadiene was formed meter between the reducing valve and the inlet end of the when ethane and propane were cracked with simultaneous reactor. I n the case of cyclohexane, which is a liquid at polymerization of the resulting olefins t o aromatics. On the room temperature, the hydrocarbon was vaporized at a conbasis of this observation he suggested that diolefin formation stant rate into the reactor. The cracking chamber consisted of a 2-foot (61-cm.) length might possibly represent an intermediate step in the production of aromatics by cracking a t high temperature. Other of I-inch (2.5-cm.) quartz tubing, 15 inches (38 cm.) of which methods discussed in the literature use ethanol, acetaldehyde, were wound with nichrome resistance ribbon. The temperabutyric aldehyde, and phenol as raw materials for production ture was measured a t the center of the reactor by means of of butadiene. However, these compounds do not seem to a calibrated chromel-alumel thermocouple enclosed in a quartz offer so cheap and abundant a source of the diolefin as do the well. Although the temperatures thus recorded are probably high owing to radiation from the walls of the tube, they are petroleum hydrocarbons. Recent patents (4, 6, 6, 7 , 9) claim the production of diole- nevertheless comparable in all the experiments reported here. The ice-cooled trap condensed out most of the higher boiling fins by carefully controlled cracking of liquid paraffin, olefin, and cyclic hydrocarbons a t elevated temperatures and re- products, such as tar, benzene, naphthalene and, in the case duced or ordinary pressure. Steam and catalysts may or of cyclohexane, any undecomposed hydrocarbon. The butamay not be used. Cyclohexane (?) is mentioned specifically diene was condensed along with the lower boiling materials, as yielding considerable quantities of butadiene when heated such as propylene and butylene, in the carbon dioxide snow to high temperatures. Methane (8) is also mentioned as cooler. Gas samples were taken from time to time after the a starting material for the production of butadiene by way of ice cooler and analyzed for total unsaturateds by absorption cracking to acetylene in the electric arc, followed by catalytic in bromine water. The product collected in the carbon dioxide-cooled con1 Received December 26, 1929. denser was distilled, the fraction boiling above -30" C. being 2 Present address, Standard Oil Development Co.,Elizabeth, N. J.
C
I S D C S T R I A I , A S D E S G I S E E R I S G CHEMISTRY
RIarch, 1930
pa,sied through a train of glass-bead-packed absorbers containing a concentrated solution of bromine in carbon tetrachloride. I n this way the olefins and diolefins were brominated and remained in the solution. The bromine and carbon tetrachloride were distilled off while the residue present after the distillation had bc'en carried up t o 90" C. was evaporated to dryness on a steam bath. The solid remaining was mostly butadiene tetrabromide, having a melting point just under that of the pure compound (m. p. 118" (3.). From the weight of the tetrabromide the yield of diolefin was calculated. Results and Discussion The accompanying table shows that butadiene may be produced from propane, butane, propylene, and cyclohexane. The yields from propane and butane are on a b a a s of cracked as well as entering gas, considering that a t the conditions of the experiments practically all of the propane and butane were decomposed. The propylene conversion is based on entering olefin while the cyclohexane conversion is calculated from the hydrocarbon actually cracked. I n the case of propane the maximum conversion t o butadiene is 0.90 mol per cent, but the yield increases considerably when butane, propylene, and cyclohexane are used as raw materials, the conversions being 3.12, 3.31, and 20.60 mol per cent, respectively. In view of the incomplete survey of experimental conditions, however, there is no reason why these results should represent the maximum yields of butadiene obtainable from the hydrocarbons in question.
Tmw C. 690 709 72i m--
,a,
736 716 716 i27 739 i39 734 i78
816
INLET KATE Lilers per h o w
Data on B u t a d i e n e P r o d u c t i o n (Pressure = 1 atmosphere) TOTAL YIELD UNSATDS I N OF CRACKED BuT.4GAS DIEKE REXI4 R K S M o l % of To hydrocarbon PROPANE
27 27 27 27 49 27 20
34.3 36.7 3i.2 34.6 36.3 36.9 36.3
27
43 0 42 6 41 8
"7 20 ETHYLENE 20 20 20 PROPYLEKE
728
20
654
4 1 8 cc. per hour
2 7 . 3 PER
23.3
..
.. 1 3 6 PER
0.0 0 77 0.90 0.0 0.0 0.43 0.66 BDTASE 3 12 2.08 2 31
Propane a l n o s t completely cracked
.. .. C E N T . NITROGEN
3 31 CYCLOHEXANE 50 5 20.60
thalene and unidentified tarry compounds. The complete reaction scheme may therefore, in the case of the simple hydrocarbons, be represented by the following four steps: (1) cracking of the paraffin to olefin; (2) formation of butadiene from two olefin molecules; (3) formation of benzene (or a benzene derivative) from butadiene and a n olefin, as originally suggested by Davidson ( 2 ) ; and finally (4) further polymerization of benzene with butadiene or olefins to form more complex, higher boiling compounds. Using propane as an illustration, it is well laown that the primary cracking reactions are: There are three possible reactions by which butadiene may be formed from the resulting mixtures of ethylene and propylene:
On account of the disturbing influence of other reactions taking place simultaneously, it was not possible from blank experiments with the pure olefins to decide whether any one of these reactions goes in preference to the others. It was shown, however, t8hatbutadiene could be obtained both from ethylene and propylene when these olefins mere employed separately. Although this has not been definitely proved, the indications thus far are that benzene is formed, a t least in part, by either one of the reactions:
+
+
C& CnH4 = C& 2H2 C& f C3H6 = C6H6 f CHI
72.7
P E.R
C E. X T
No condensate in CO? snow coolers; small a m o u n t of condensables carried off i n exit gas a6.a
PER
CEXT
10 6
Based on cyclohexane decomposed
In the experiments with ethylene and propylene, nitrogen was used as a diluent to give a partial pressur(' of the olefin corresponding t o that in the gas mixture resulting from the cracking of propane. KO condensate was collected in the carbon dioxide cooler in the ethylene experiments. This was probably due t o the fact that the large amount of nitrogen and ethylene present carried off the condensables, such as butadiene, since in duplicating the work Schneider (10) recovered butadiene froin the exit gas by using hexane as a scrubbing medium in the carbon dioxide trap. When propylene and nitrogen were passed through the reactor, most of the condensable material was recovered by employing butane as a scrubbing liquid. I n the case of propane and butane the aniount of condensable material was so large that it acted itself a5 a scrubbing liquid. I n all experiments with propane, butane, ethylene, and propylene some high-boiling material was formed. This consisted largely of benzene with smaller amounts of naph-
(3a)
(311)
3C2H4 = CaHin
or 2C3Hs = CsH12 = CsH6
Butane almost completely cracked
+ Ha
The difficulty of obtaining a good material balance to serve as a proof of the mechanism lies in the marked tendency for heiizene to react further. While it might be interred that benzene could be formed with cyclohexane as an intermediate,
followed by
C E. S T .. N I T R O G E N
..
24 1
+ 3H2
the chief objection to this mechanism is that cyclohexane is exceedingly unstable a t the temperature of operation. Furthermore, the writers have never been able to synthesize cyclohexane with any appreciable yield directly from olefins a t atmospheric pressure and in the absence of catalysts. I n fractionating the liquid products the boiling point usually rises sharply after the benzene is taken off and only occasionally are small amounts of toluene and other simple benzene derivatives present. It stands to reason that the higher boiling tarry materials are formed by progressive polymerization of intermediately formed benzene with further amounts of olefins or diolefins, since other experiments showed that a tar of the same general type was formed in large quantities by reaction of benzene with ethylene under the same general conditions. Literature Cited (1) Brooks, "Chemistry of Non-Benzenoid Hydrocarbons," pp. 36, 42, Chemical Catalog, 1922. ( 2 ) Davidson, J. IND.EXG. CHEM., 10, 907 (1918). (3) Farbenfabriken vorm. F. Bayer & Co., U. S. Patents 1,069.951, 1,070,259 (1910); British Patent 15,254 (1910). (4) Hultman, U. S. Patent 1,704,194 (1927). (5) I. G., British Patent 298,584 (1927). (6) I. G., British Patents 303,323 (1928): 303,998 (1928). (7) I. G., British Patent 307,945 (1927). (8) I. G., British Patent 307,808 (1928). (9) Marks and Clerk, British Patent 297,231 (1927). (10) Schneider, Private communication (thesis for Sc.D. degree a t Massachusetts Institute of Technology, in progress). (11) Staudinger and Bruson, U. S. Patent 1,720,929 (1927).
