Vapor-Phase Cracking
c
H. P. A. GROLL, Shell Development Company, Emeryville, Calif. The pyrogenetic conversion of gaseous and liquid hydrocarbons into aromatics has been investigated, and vapor-phase cracking of gas oil studied at almos-. pheric pressure over a wide range of temperatures and rates of throughput. Of all gaseous hydrocarbons, propylene gives the highest yields of aromatics. Striking regularities are found in the pyrolysis of all hydrocarbons. These are believed to contribute essential data to the theory of cracking, especially with respect to the formation of aromatic hydrocarbons at temperatures around 800” C., the mechanism of which appears to be much simpler than for lowtemperature cracking. At all temperatures “demethanization” is found to prevail over dehydrogenation, provided carbon formation is prevented. The
T
HE work described in this paper was carried out in this
laboratory in 1929 and 1930. Publication was determined upon at the present time because of the growing interest in vapor-phase cracking and because theories have recently been advanced, which, in the opinion of the author, cannot be completely reconciled with their experimental results. The present investigation includes the pyrolysis of several gaseous hydrocarbons of higher molecular weight than methane. The pyrolysis of propylene became of particular interest when this gas was found to give higher yields of aromatic hydrocarbons than any of the other gases. This behavior should be a clue to the mechanism of aromatic formation. Certain regularities, found to be common to the pyrolysis of all hydrocarbon gases, suggested extension of these experiments to the cracking of oil under similar conditions. A California gas oil, highly refined for use as spray oil, was chosen as raw material because, being Edeleanu-treated, it is typical of a purely nonaromatic gas oil, and, therefore, all aromatics appearing in the cracked products must have been synthesized by the reactions involved. Good yields of aromatic hydrocarbons were obtained from this oil. The growing interest in processes for the production of high-antiknock fuel and the possible increased demand for gaseous olefins for chemical raw materials led to the development of this inyestigation to a general study of vapor-phase cracking. The results obtained over a wide range of conditions permit the prediction of products obtainable under various operating conditions of vapor-phase cracking. CHEMISTRY O F VAPOR-PHASE CRACKING
PREVIOUS WORK Several complete literature reviews on cracking have appeared, including one by Lomax, Dunstan, and Thole (15), and recent ones by Egloff, Schaad, and Lowry (7). Vapor-phase cracking of oils has been under investigation since the latter part of last century. Many important features, such as the production of aromatic hydrocarbons and the use of steam in the cracking tubes recently shown to prevent carbon formation, were suggested in early patents (16, 17). Catalysts, such as scrap iron, iron oxide, coke,
nature and yield of products are functions of temperature and rate of throughput, and these two variables are f o u n d to be connected by a simple function over a comparatively wide range. A method is shown by which the throughput of commercial vapor-phase cracking processes can be increased considerably. Owing to patent considerations most of these processes include certain specific features, m a n y of which are of doubtful advantage and have created a good deal of confusion and prejudice. T h e chief purpose of this paper is to contribute to overcoming these prejudices by showing the natural limitations of a n y vapor-phase cracking process and by trying to p r e d k t what result m a y be expected f r o m changing the conditions i n any given plant. clay, and the like, for packing in the tubes or retorts were tried as early as 1886 ( 3 ) . The art was then more or less forgotten until the war. Shortage of toluene and benzene in the countries of Allies led to new developments in production of aromatics by cracking of oils (12, 19). Since then the interest in vapor-phase cracking has never ceased although i t was not until recently that commercial cracking processes, such as the Gyro, the Leamon, and “true vapor-phase” cracking (Knox process), were established. I n spite of commercial development, little systematic work appears to have been published on the subject. The pyrolysis of hydrocarbon gases has been investigated recently by several workers-e. g., Piotrowski and Winkler (18) and especially Wheeler and co-workers (11, 20, g2). The mechanism of cracking has been discussed in many publications since Berthelot’s classic studies (2) in which he postulates an intermediate formation of acetylene in the pyrogenetic synthesis of aromatic hydrocarbons. The most comprehensive theoretical investigations on cracking are those of Haber (10) and of Dunstan, Wheeler, and co-workers ( 5 , 1 1 , 2 0 , 2 2 ) . While all the theories developed in the references mentioned agree generally as to the mechanism of low-temperature cracking where longer hydrocarbon chains break to shorter ones with the formation of olefins and either a paraffin or hydrogen, there is considerable disagreement between various theories which attempt to account for the formation of aromatic hydrocarbons. While Haber and others assumed with Berthelot that acetylene plays an important role as intermediate product, Hague and Wheeler, in agreement with developed a theory in which they assume that Davidson (4, ethylene is the intermediate product which is subsequently polyherized to butylene. The latter is dehydrogenated to butadiene which, with another molecule of ethylene, forms cyclohexene, this in turn being dehydrogenated to benzene. Recently Frey and Hepp (8) have investigated the pyrolysis of ethane, propane, butane, and ethylene. Most of their observations could be corroborated by the work reported here. Geniesse and Reuter (9)have investigated the effect of time and temperature on the cracking of oils and have undertaken to calculate the velocity constants of cracking reactions of various hydrocarbons.
784
~
-
July, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY MECHAXISM OF REACTIONS INVOLVED
The work described here is concerned with cracking nonaromatic hydrocarbons a t temperatures between 500" and 850" C. While the lower limit is given by the nature of the cracking reactions which practically cease around 400" C., the upper limit was chosen because most materials now used in the construction of practical cracking units will not stand higher temperatures, and because the mechanism of cracking becomes entirely different a t temperatures where any hydrocarbon (even methane) will crack with hydrogen formation either to carbon or, a t high velocities in very narrow reaction spaces, to acetylene. Within the temperature range of this investigation little hydrogen is formed except in the presence of active dehydrogenation catalysts. These a t cracking temperatures, however, effect a rapid decomposition of all hydrocarbons to carbon and hydrogen and actually catalyze partial dehydrogenation only a t lower temperatures. The simplest type of cracking prevailing a t low temperatures consists in the splitting of hydrocarbon chains-e. g., one molecule of olefin and one of paraffin hydrocarbon may be formed from a paraffin: C n + m&(n + rn) + 2 = Cr&n
+ CrnH~rn+
2,
(n
=
2)
(1)
This reaction will result in high gasoline yields if the raw material consists of large enough molecules, and but little gas will be formed. It will be shown below that up to about 625" (2. no appreciable condensation of the chain fragments takes place, a t least none to form heavy tar. The residue of cracked distillate after distilling off gasoline is similar to the original cracking stock. A more intensive cracking takes place a t higher temperatures when, in general, the following reactions occur. The formation of any olefin from a paraffin of higher molecular weight can be expressed as follows, if direct dehydrogenation is excluded,
for example, C18H28 = 3C4" or Cl8H28 = 4CsHs
+ CH4 + CH4
6C2H4
+ CH4
and from an olefin of higher molecular weight, (3)
Diolefins occur in considerable amounts in the product, and their formation can be explained in a similar way: n-1 CnH2n + 2 = 7CPHzp- 2
+ (+n
+ 1) CHI,
(P = m - 1; n
> m L 2)
(4)
These diolefins, being very susceptible to condensation and polymerization, complicate considerably the mechanism of pyrolysis for the temperature range 650' to 750' C. They, as well as the large number of other components, are able to react among each other in almost an infinite number of ways; any attempt therefore to formulate a mechanism could but incompletely express the true state of affairs. One fact, however, must be emphasized: there is a consistent preponderance of methane over hydrogen in the reaction gases a t all temperatures of the cracking range. While there is no doubt that some direct dehydrogenation takes place in such a complicated maze of reac,tions, and while it may even be assumed that a part of the hydrogen formed is again consumed in con-
785
current hydrogenation, the assumption that dehydrogenation plays an indispensable role in vapor-phase cracking, especially in the formation of aromatics, needlessly complicates the explanation of the process. The optimum temperature for the formation of aromatic hydrocarbons by cracking is around 800' C. At this point the mechanism of the pyrolysis appears to become much simpler and the final liquid and gaseous products are more uniform in character than those obtained a t lower temperatures. The simplest mechanism for the formation of aromatic hydrocarbons by splitting methane from hydrocarbon chains is a primary formation of low-molecular olefins according to Equations 2 and 3 followed by reactions 6 and 7 : R-CH=CH-R' 3R-C=CH-
I
= =
R-C=CH-
1
+ R'H
(6)
CsHsRa
(7)
The investigation of the products from the pyrolysis of aliphatic hydrocarbons shows that R and R' are usually not larger than CHa. Especially a t high temperatures we will find that R is H and R' is CHI. I n this case the olefin of Equation 6 is propylene, and it appears that the intermediate formation of propylene plays an important part in the series of reactions producing aromatic hydrocarbons. This assumption agrees well with the fact that propylene forms aromatic hydrocarbons more readily and with higher yields than ethylene or butylene, an observation which can also be made from Wheeler's experiments (5), though he did not arrive a t this conclusion. According to Dunstan and Wheeler's theories one would expect just the opposite. Within the temperature range of 650" to 750" C. the ratio of hydrogen to methane formed decreases with the cracking temperature while the sum of both gases increases. This phenomenon again speaks against any dehydrogenation theory, whereas it can be easily explained by assuming that a t lower temperatures either the radicals R' in Equation 6 are larger than CH, and decompose to olefin and hydrogen or they unite with each other instead of with hydrogen. Above 800" C. the ratio increases rapidly with the temperature as would be expected. However, the following questions which might seem to contradict the mechanism shown above remain to be answered: (1) Why is acetylene never found in more than traces in the products of vapor-phase cracking, although the intermediate product of Equations 6 and 7 is obviously an acetylene? (2). How can the formation of polycyclic hydrocarbons be exulained for which Wheeler assumes condensation of butadiene wfih benzene? (3). How can the formation of aromatics from ethylene be explained, as demethanization of ethylene would leave only carbon?
The author thinks that satisfactory answers can be given to all of these questions: (1) It is conceivable that the divalent radicals, R-C-CH
I
I
and HC=CH ("nascent" acetylene), are polymerized to benzene
/
\
rings more readily than they would form an acetylene hydrocarbon. This assumption is also made by Berl and Forst ( 1 ) . But, even if such an assumption were not made, there is no reason for expecting free acetylene t o be present in the gas. It is well known that the polymerization velocity of acetylene is great a t temperatures as low as 600" t o 700" C. whereas at 800' with concentrated acetylene this exothermic reaction becomes so violent that it causes decomposition to carbon. Therefore it is probable that in combination with the highly endothermic cracking reaction, polymerization proceeds smoothly and instantaneously, so that practically no ree acetylene appears in the final product.
I N D U S T R I A L A N D E NG I NE E R I NG C H E M I S T R Y Thermocouple Connecfion
2
1- Gus 5furug? Cyknder 2- Reduciq Wve 3 - Rqu/uting hive
-
4 F/owmcfer 5- By-RtSs fir Checking flawmefer 6 -Sofefy Vulve (hj)
7 - R m d o n Tube 8 - €/ecfric furnace
I2 - ice 5ufh
9 FOgSeNhng Chamber IO - Conden5ers ll fir Rccewers
13- COz t Alcohol Condensers 14- Gus Nefer 15- Churcou/ Absorpfion rube
(NO. 1) FOR FIGURE1. APPARATUS
CRACKING HYDROCARBOS
GASES
(2) Polycyclic aromatic hydrocarbons are formed by direct polymerization of acetylene, which shows that there is no need to assume an intermediate formation of butadiene. The presence of considerable amounts of styrene in the product from propylene pyrolysis gives a clue as to the mechanism. (The xylene cut was found to contain more than 60 per cent of styrene.) Styrene is probably formed by addition of nascent acetylene to benzene:
Similarly, the formation of naphthalene would be as follows:
Thermocouple Connecfinn
I - Oil Feed Reservmr
The reactions discussed can be completely expressed by the following equations:
9- Fcg&ff/fng Chumbrr IO - Condensers I/ - fir Receivers iz ice Bufb 13- 602 t Alcohol Condensers I4 Gas Mefer 15- Chorcoa/ Absorpfion Tuba
4 - Rcgu/ofing Valves 5 - Pressure Rqu/uior&) 6 - flush Evupmfor 7 - Reucfion Tube 8 - €/ectric furnuce 2 Wuier feed Reservoir 3 Wuier feed Regdofor
-
FIGURE 2. APPARATUS (No. 3) FOR CRACKING OILS IN VAPOR PHASE
for the formation of aromatics from a paraffin hydrocarbon, and
for formation from an olefin.
These equations were evolved from the empirical results of this investigation and have proved to be valid for any hydrocarbons-gaseous or liquid, aliphatic as well as naphthenicexcepting those which already contain aromatics such as Edeleanu extract from California oils. The formation of benzene from Edeleanu extract which originally contains considerable amounts of aromatic hydrocarbons is due to the mere splitting off of side chains from the original benzene rings. The olefins formed in this splitting reaction, of course, may be pyrolyzed further with formation of more aromatics. These reactions can be formulated as fO11OTYs: Ar-CHZ-CH2-R
For the formation of anthracene, phenanthrene, etc., the same mechanism would apply. Incidentally, the hydrogen which would be formed a t 800" C. by these reactions is closely in agreement with the amount of hydrogen actually found in the gas. (3) The formation of aromatic hydrocarbons from ethylene is the only reaction which needs an additional assumption. Wheeler assumes a polymerization of ethylene to butylene as an essential step for benzene formation. This is based on the observation that butylene can be obtained from ethylene. Such a reaction, which Fould certainly be of high practical value if it were quantitative, was investigated by Edlund ( 6 ) of this laboratory. He observed, however, that, above 500" C. and increasing with the temperature, propylene prevails increasingly over butylene in the products obtained by heat treatment of ethylene. Thus the polymerization of ethylene can no longer be an argument in favor of the butylene-butadiene theory and we may assume the intermediate formation of propylene with more justification. It is of interest that Lenher ( 1 4 ) confirms that propylene, rather than butylene, is the principal thermal polymerization product of ethylene. Such an assumption has the advantage of correlating all other experimental results without any further ad hoc theories.
1-01. 25, No. 'i
=
ArH
+ CHz=CH-R
(12)
The aliphatic olefins formed may react further according to Equations 3, 6, and 7 . This would account for the higher yield of tar obtained from Edeleanu kerosene extract. It also explains the fact that the aromatic hydrocarbons formed by pyrolysis of this extract have larger proportions of benzene homologs with aliphatic side chains. These side chains do not appear to be limited to one carbon atom as in the case of those from the cracking of aliphatic hydrocarbons. There is apparently no tendency for polycyclic aromatics to depolymerize to benzene. On the contrary, more intensive cracking increases the polycyclic ring compounds. Thus a heavy aromatic petroleum distillate yields a heavy tar, the light aromatic content of which depends greatly on the structure of the compounds in the raw material. I n general, the heavier the raw material the lower is the yield of light aromatics. The molecular weight of aliphatic cracking stock, for reasons explained above, has not much influence on the nature of the aromatics formed. APPARATCS Apparatus KO.1 used for the pyrolysis of gases is shown in Figure 1. The gases pass from the storage cylinder through a flowmeter to the reaction tube heated by an electric furnace. The tube has a diameter of 22 mm. and is heated to the reaction temperature for a length of about 15 cm.; thus the heated space is about 55 cc. From the tube the gas passes through a fog-settling bulb to
1l:BI.: >IATI.:RIAI'
I.
1
the tar coniierrper arid receiver. The 1%-t receiver is cooled with cariron dioxide in ;rlcohol. The non~nndensi~l~le gm goes through Tlic first experirrients wit11 propylene were carried out in it ehnrcaiii nhanrption tulle to the stnck, but its flow is mei~sured occmiorially in nn aspirator, which is placed before the ehnrconl silica tubes. Iron tubes xerc tried but imniediately became t,uhr t o m i k e t h e readings indrpenilent, of gas nbsolption in the plugged tip carbon, tlie forination of wliieli iron catalyzes. 16.5 19.6 to increase the yield of gasoline by recirculating the residue. Nil Acetylene Nil Nil N-il Trace 0.6 4 . 3 13.0 1 6 . 2 21.2 24.6 Ethylene 23.4 From 725" to 825" C. the yields are fairly constant. The Ethane 1.6 3.8 4.3 5.1 3.2 4.2 only changes brought about by further increase of temperaPropylene 3 . 7 1 1 . 2 13.4 1 1 . 3 1 1 . 3 4.3 ProDane 0.4 2.9 1.9 1.6 0.7 0.4 ture are the gradual disappearance of the aliphatic hydroBucylene 1.7 6.4 5.3 2.9 0.0 0.0 0.2 Butane 0.9 0.5 0..3 0.0 0.0 carbons and the splitting of side chains from the alkylated Total unsatd. 9 . 7 30.6 34.9 3 5 . 6 3 5 . 9 28.3 aromatics. Both of these changes are clearly shown by the increasing sharpness of the breaks in the distillation curves and cracked distillate. The gasoline in this tar amounts to about by the increase in the benzene plateau a t the expense of those 17 per cent of the cracking stock and a good deal of the residue of toluene and xylene. The content of aromatics in the benis unchanged gas oil which may be recirculated to the cracking zene and in the toluene cuts shown in Table IX is further evitube. dence of these changes. TABLEx. Experiment Max. temp. in tube, I:, Fresh spray oil or rerun from expt. R a t e of flow of gas oil, cc./min. Gal./hour/cu. f t . space Heated space cc. Total oil cha&ed, grams Rate of flow of water, grams/min. Yield of zar 70b y weight 205' C. enb. point gasoline. % of cracking stock Yield of gas, % by weight of cracking stock Yield of gas, cu. ft./gal. charged
LrAP0R-PH.4SE CRACKIXQ O F S P R A Y OIL WITH
(Apparatus N o . 4) K-7 K-8 K-1 650 650 675 Fresh K-7 Fresh 11.9 11.7 9.5 35.5 34.9 28.4 150 150 150 4274 1223.5 835 1.0 1.0 2.1 81.3 82.0 74.0
K-11 550 Fresh 10.0 29.9 150 si 1 1.0 98.0
K-10 600 Fresh 10.0 29.9 150 1495 1.0 93.3
2.3
8.2
21.0
22.4
(2.o)a 1.8
6.7 6.4
(18.7) 19.3
(18.0) 20.1
HIGHRATESO F FEED
K-9 675 Fresh 12.0 35.8 150 1498.5 1.0 74.4
K-3 700 Freeh 19.6 58.5
1457.5 1.2 70.5
20.1
22.4
22.3
25.1
23.4
20.2
20.3
(26.0) 23.3
(25.6) 23.9
29.5 28.7
(42.3) 37.9
(46.0) 46.0
(31.8) 31.7
(57.9) 48.5
K-4 700 Fresh 12.0 35.8 150 1480 1.1 57.7
150
K-5 K-2 K-6 705 700 770 Fresh K-4 & 5 Fresh 11.8 11.4 11.8 35.2 35.2 34.1 150 150 150 1541.5 722 1515.5 1.2 1.6 0.8 54.0 68.2 42.1
CHEYICAL
GAS
PODBIELNIhK AXALYSIS
.~NALSSI~
%, mJ
CHEMICAL GAS ANALSSIS
weaoht oJ
Oi
Val. % crackof ins,
Or
gad stock Hydrogen 11.5 7.6 0.1. ... 10.0 Methane 22.2 26.3 1.1 ... 19.5 Ethylene 33.5 2.3 , . 40.0 Ethane 1813 9.2 0.7 ... 13.8 Propylene .. 16.2 1.7 ... 16.7 Propane ,. 3.6 0.4 .,. ... Butylene .. 2.3 0.3 ... ... Butane 0 . 5 0 . 1 . . . ... Total unsatd. 48:O 52.0 4.2 . .. 56.7 Figures in parentheses are not measured b u t calculated b y difference.
PODBIELNIAH -kNALYSIS 7 C H E b l I C A L GAS .4NALSSIS-%.by weaght
'
Val. % crack-
of
8.6 30.0 32.7 7.0 13.4 1.8 6.0 0,s
52.1
... ... ... ... ... ... ... ... ...
gas 8.3 30.0 34.0 7.3 15.8 1.9 2.5 0.2 52.3
an0 stock 0.2
5.5 11.0 2.5 7.6 1.0 1.6 0.1 20.2
4.5 28.1 1017
.. .. ..
5617
... ... .... ..
... ... ... ... ...
13.0 27.5
6.7 36.3
l0:3
.. ..
.. .. .. ..
49:2
57:O
7 94
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 23. NO. 7
144
im
W
60
LO
Expt. Temp., O C. Spray oil gai./hrl/cu. f t .
Figure 18 1-20 650
Figure 19 1-17 700
Figure 20
600
750
Figure 21 1-19 800
Figure 22 1-22 850
13.5
13.5
13.5
13.5
13.5
13.5
Figure 17 1-2 1
1-18
8
8
E
3
82
FIGURES 17 TO 25. DISTILL~TIO\ C U R ~ E S , UITH EFFICIENT FR.4CTIONATING COLUMN, OF 205 c. END POIXTGASOLINE FROM VAPOR-PHASE CRACKIVG OF cALIFORVI4 SPRAY OIL (REFINEDGAS O I L ) AT VARIOCSTEMPERATURES A \ D RATES OF FEED
2
I
h Expt. Temp., O C. Spray oil gal /hrl/cu. ft.
Figure 23 K-7 650
Figure 24 K-4 700
Figure 25 K-2 770
3 5 . 5 (cf. Figure 26)
3 5 . 8 (cf. Figure 27)
35.2
The increase in total liquid and solid products towards temperatures above 800" C. is due to increasing formation of asphalt and carbon. Small amounts of acetylene appear a t these temperatures probably to increase a t higher temperatures. The theoretical limits of these curves a t very high temperatures are free carbon and hydrogen in amounts corresponding to that in which they are present in the cracking stock. YIELDCURVESOF GASEOCSP R O D U C T S . The curve for total yield of cracked gas, also shown as percentage by weight of the cracking stock, is complementary to the curve for the tar yield; i. e., as no carbon is formed in the tubes, the sum of tar plus gas must be 100 per cent of the cracking stock, the handling losses being eliminated in a manner described above. Thus the course of the curve is fully defined by the characteristics of the tar curve already described. The composition of the gas is given in Table I X and is also shown in the large diagram of Figure 16 as percentage by weight of the cracking stock. The amount of methane and hydrogen formed increases steadily with the temperature, both as percentage in the gas and yield in percentage of the cracking stock. The amount of total gaseous olefins formed increases rapidly up to 675" C. after which it increases but slowly to its maximum of 36 per cent by weight of the cracking stock a t 800' C . ; after this point it decreases rapidly. This is not surprising, considering, as has been already demonstrated, that gaseous olefins are converted to aromatics at these temperatures. The slow increase in total olefins from 675" to 800" C. is due only to the increase in ethylene yield, whereas the yields of higher olefins are declining during this interval. The maximum olefin content in the cracked gas is obtained around 650' C., when butylene formation is a t its maximum, The maximum yield of propylene occurs somewhat higher a t 700" C. I n the method of analysis described above, some loss of butylene is always likely to occur; consequently, the yields shown for this compound are minimum figures.
EFFECT OF RATE
OF
THROUGHPUT
The rate of throughput was studied in a series of experiments shown in Table X . As may be expected from the results of Geniesse and Reuter, the yields obtained with increased throughput do not correspond to the yields for the same temperature a t the standard rate in Figure 16, but to those for some lower temperature. This becomes clearer if the distillation curves for the 205" C. end point gasoline distilled from the tar formed in the experiments of Table X are compared with the distillation curves for the products of Table IX made a t the standard rate of throughput. The distillation curves are shown in Figures 17 t o 30. Here it may be seen that the distillation curves of the products made a t high throughputs correspond to those of products from standard rate of throughput in the manner shown in Table X I . COMP~RISOS OF DISTILLATION CURVE3 OF GASOMADEi~ F'BRIOUSRATESOF FLOW
TBBLEXI
LINES
TEUP C 650 675 700
zoo
(00
770
R-\TE GaZ/hr,'cu ft 35.5 28.4 58.5 35.8 34.1 35.2
S I ~ L PRODUCT ~ R AT 13 5 GAL/ H R / c C FT
.
c.
600 600-650 600-650 650 650 Little above 700
ESTD TEUP DEVI4TION
c.
++ 2505 ('0 +75 50 +50
+
+60 (7)
XII.
COMPARISOX O F REACTION TEMPERATURES AND RATESOF THROUGHPUT CORRESPOSDISG RhTF OF TEMP.F O R TEMP. EXPT. TEMP. FLOW 13.5 GAL./HR./CU.FT. DEVIATION C. Gal./hr./eu. ft. c. c. 009 4-41 35.5 K-7 650 -11 661 11.0 1-16 650 624 +51 28.4 K-1 675a 630 +70 58.5 K-3 700 655 +45 35.8 700 K-4 664 +41 35.2 K-5 705 - 10 720 10.2 1-12 710 731 39 35.2 K-2 770 a Another experiment at 675' gave a value fitting into the curve of Figure 32 TABLE
+
July, 1933
I N DU STR IA L A N D EN G I N EER IN G CHE MISTR Y
795
These obvious regularities can be analyzed more exactly by the method shown in Figure 31. The results in Table X and some of those in Table T'II (only those experiments w e r e considered in which no excessive amount of steam was used) were p l o t t e d as in the s c h e m e of c u r v e s of Figure 16. The location of the abscissa for the group of results for each experiment was found empirically by trial. Table XI1 gives the results of this method. These values are plotted in Figure 32 and give a smooth curve. The curve surprisingly is the Finure 26 Finure 27 Finure 28 Eupt. K-8 (rerun of residue K-6 (rerun of residue K-3 same for a fairly wide range of reaction temperafrom K-4 a n d 5) from K-7) tures. This makes possible the construction of T e m p , ' C. 650 700 700 Spray oil, a conversion slide which may be applied to the gal /hr./cu. ft. 3 4 . 9 (cf. Figure 23) 3 4 . 1 (cf Figure 24) 58.5 atscissa of the diagram in Figure 16. The con\-ersion slide is shown in Figure 32. As the slide is used for converting measured r e a c t i 011 temperatures a t various velocities back to the temperature of Figure 16, the negative values of the deviations gi\,en in Table XI are plotted on the abscissa. The following examples will explain the use of the slide which, in effect, serves to transpose the temperature coijrdinates in such a way as t'o correct for variat'ion in rate of throughput: (1) The apparatus is operated at a maximum temperature of 750" C. measured in the center of the tube. The rate of throughput is 42 gallons per hour per cubic foot tube space. Khat will the product be under these conditions? The arrow of the slide (13.5 gallons per hour per cubic foot) is pointed to 750" on the abscissa of PFR CENT DISTILLED Figure 16; 42 gallons on the slide will then be oppoeite 697" on the chart and the composition of prodFigure 30.-0 Experiment K-1, 670 C., 28.4 ucts will correFpond to the intersection points of gal./hr./cu. it. the curves with a line dram-n parallel to the ordinate through the point of 697". (2) The apparatus is to run with a throughput of 25 gallons per hour per cubic foot, and a product Per Cenf Disfilled corresponding to that for 800" C. in Figure 16 is Figure 29. Experiment K-9, 6i5O C., desired. At what indicated temperature should the 35.8 gal./hr./cu. it., check on fraction method: two curves obtained in two independent disapparatus be operated? ti!lations of same material by two different The slide is placed on the abscissa at 25 gallons operators per hour per cubic foot opposite 800". The arrow FIGURES 26 TO 30. DISTILL.4TION CURVES, WITH EFFICIENT points to 825", the temperature at which the reac-, FRACTIOSATING COLUMN. OF 205 c. ESD POIST G ~ S O L I N EFROM tion should be carried out FrAPOR-PH.4SE CRACKING OF CALIFORX1.4 S P R A Y OIL (REFINED (3) The auuaratus is to he run at hiehest UOSGAS OIL) AT V~4RIOUSTEMPERATURES .4ND RATES OF FEED sib1ethrough;;t and the maximum yield Gf gasdline in one pass is desired--i. e., 25 per cent by weight of the cracking stock. The highest t e m p e r a t u r e permissible in the tube for safe working is, say, 775' C. The maximum gasoline yield is obtained at 675" in the chart. sisting partly of aromatic hydrocarbons, does not crack in the The arrow of the slide is set opposite 775". Then 675" on the manner of aliphatic oils, yields more tar and less gasoline chart is opposite 95 gallons per hour per cubic foot, the through- than the fresh spray oil in the first cracking. Gas formation put necessary to produce the desired product. is also markedly decreased. These results conform with the Table X shows the results of two experiments (K-6 and observations made in cracking Edeleanu extract. However, K-8) in which the charging stock consists of once-cracked the distillation curves of the gasolines produced from fresh residue. The yields and nature of products of experiment oil (Figure 24) and from rerun residue (Figure 27) show no K-8 are the same as those of K-7 in which fresh spray oil differences. Table VI shows the Engler distillations of the cracked resiwas cracked under the identical conditions, a t 650" C. and around 35 gallons per hour per cubic foot which corresponds dues of the experiments described above. This in connection to 608" to 610" C. a t 13.5 gallons per hour per cubic foot, the with Table IX shows that recirculation of the cracked residue TI ill improve the gasoline yield materially under conditions standard velocity of Figure 16. The distillation curves for the gasoline fractions of both of experiments K-7 and K-8, but not as much under those of experiments are shown in Figures 23 and 26. The curves are experiments K-4, K-5, and K-6. To what extent the ideal curve of Figure 32 and the slide nearly identical, which is further evidence that fresh oil and rerun residue give the same products and yields. The cracked for Figure 16 may be generally applied is not known a t residue of experiments K-4 and K-5 behaved differently when present. I t may be necessary either to construct a special recracked in experiment K-6. These experiments were car- slide for each different plant or to obtain a different set of ried out a t TOO" C. with a rate of flow of about 35 gallons per curves like that of Figure 16 for radically different cracking hour per cubic foot corresponding to 658" to 660" C. in Figure stocks. The latter is not likely to be necessary as long as 16 a t the standard velocity. chiefly aliphatic or naphthenic oils are used. This is probable Under these conditions onre-cracked residue, which, con- from the rerun experiments discussed above. The boiling I
I
796
INDUSTRIAL AND ENGIXEERING CHEMISTRY
FIGURE 31. ESTIMATIOKS
OF
LOCATIONS IN FIGURE 16
OF
Vol. 25, No. 7
EXPERIMENTS WITH DIFFERENT FEEDRATES
range of the residue of experiment K-7 differs widely from firmation is had by the suppression of the reaction of steam that of fresh spray oil (Table VI). with hydrocarbons to give carbon monoxide, carbon dioxide, However, the method for predicting results used in Figure and hydrogen a t 800" to 850" C. This reaction has not time 16 can apparently be widely applied to cracking and other to occur under the conditions of the experiments described, endothermic reactions. For instance, Wheeler and the Im- although steam was used in almost all of the experiments perial Chemical Industries ($21)heated ethvlene to 800" C. between 800" and 850" C. gas volume " The advantages of applying higher temperatures with with a space velocity of 1 tube volume minutes and obtained higher throughputs are the following: 29 per cent tar. A yield of 30 per cent is claimed a t 1100" C. (a temperature a t which carbon and hydrogen are formed a t (1) The capacity of a plant of given size can be greatly ingas volume . creased. slow flow) and a space velocity of 6400 tube volume minutes ( 2 ) The heat regulation is simple. I t is very difficult in practice t o keep the temperature of B furnace constant within a few This is an illustration of the validity of the principle for very degrees. Therefore it appears simpler to let the furnace rise t o extreme conditions. The yield of 32 per cent of tar obtained some much higher temperature which need not be so carefully controlled and regulate the feed so as to here checks with Wheeler's (Table 111). give the desired product. The rate of Further c o n f i r m a t i o n has been enfeed can be varied instantly to meet recountered in this laboratory with the quirements without the time lag inherent catalytic dehydrogenation of secondary in all temperature regulation. alcohols to ketones. (3) A rapid s t r e a m of gas or vapor through a tube tends t o equalize local It appears, therefore, that considerirregularities in t u be t e m p e r a t u r e . able technical advantage can be achieved Moreover, an endothermic reaction itself in any process involving endothermic provides a thermostatic control, because its velocity will be greatest at the hottest reactions by applying much higher tems ots of the reaction space; consequently, peratures than correspond to the equilibtge greatest amount of heat will be withrium value of products desired, but by drawn from the hottest zone. subjecting the m a t e r i a l to the action These general principles are not new of heat a t this temperature for a much and have been utilized in other experishorter time. The velocity of throughments here and elsewhere. The present put necessary for each temperature can work is an excellent illustration of the be determined empirically. Up to the principle. p r e s e n t a number of cases have been found in this 1a b o r a t o r y where side 20 650' NATURE AND YIELDS OF r e a c t i o n s k n o w n to take p l a c e a t PRODUCTS elevated temperatures do not occur if the time of heating is short enough, Although the character of most of w h e r e a s other reactions occurring a t the products has been described in the discussion of the e x p e r i m e n t s , t h e lower temperatures proceed to a point properties of the products of practical which appears to c o r r e s p o n d to an FIGURE32. COXSTRUCTION OF SLIDE equilibrium or pseudoequilibrium a t lower temperatures. Not only are the curves, Figure 16, favorable evidence in behalf of this principle, but further concracking only can be fully described. OF FIGURE 16 '
July, 1933
I N D U S T R 1.4 L A K D E N G I N E E R I N G C H E M I S T R Y
They are aromatic hydrocarbons, gaseous olefins, and methane which may be separated from each other without difficulty. At lower temperatures, however, the complex nature of the products prohibits practical separation of chemical individuals except from the gaseous fractions. Consequently, such products can be classified only with respect to general properties such as degree of unsaturation, antiknock value, gravity, etc.
able raw material for dyestuffs should be greatly reduced. The yield of anthracene may be increased by recracking the alkyl anthracenes in the manner previously discussed for alkyl benzenes and naphthalenes. Kaphthalene is, unfortunately, a by-product of little value. TABLE XIV.
PRODUCTS O F HIGH-TEMPERATURE CRA(’K1SG
Cracking a t high temperatures yields principally aromatic products. The yields from aliphatic cracking stock for the higher members of the series are likely to be independent of the nature of the cracking stock since the ratio of carbon to hydrogen changes but little in this region. The lower members-for example, the gaseous hydrocarbons-give the varied yields shown in detail in Table IV. Pyrolysis of high-boiling oils a t the same temperature yields products similar to those from the pyrolysis of gases, but the proportions are somewhat changed, more aromatic hydrocarbons with side chains being formed. The optimum yield of toluene, which is one of the most valuable aromatic hydrocarbons under present market conditions, is obtained a t a somewhat lower temperature, when the aromatic hydrocarbons recovered begin to be mixed with some aliphatic (mainly olefinic and diolefinir) substances. These olefins may be slightly detrimental to the quality of the products. Table XI11 showe the properties of the principal products of high-temperature cracking. TABLE
XIII.
TAR.4ND GAS OBTAINED HIGH-TEMPERATURE CRACKINQ
COMPOsITION O F
Cracking stock Temp., C. Composition of t a r , yo by weight: Olefins below 75’ C. Benzene Toluene Xylenes styrene Trimethylbenzenes Higher alkyl benzenes Total below 205’ C.
+
Naphthalene .41kyl naphthalenes Anthracene, phenanthrene Alkyl anthracenes, etc. Heavy t a r residue Aromatics: I n benzene fraction I n toluene fraction Bromine number: Benzene fraction Toluene fraction Composition of gas, % by vol.: Hydrogen Methane Ethylene Ethane Propylene Propane Butylene Butane Total unsatd.
.
HYDROCARBOl GA0EB
800 1.0 36 7.0 4.0 ”
48:O 18.0 3.0 10.0 12.0 9.0 93.3 92.9
BY
EDELEABU KEROSENE S P R A Y OIL EXTRACT 750 800 800 4.4 18.4 10.5 6.3
i7.’} 47.4
._ .. ..
..
.. ..
..
6.0 .. 2.8 .. (Average) 20.0 l0:6 50-60 39.0 20-25 29.6 0-5 6.7 2-7 10.5 ., . . 21 .. 04 0.2 20130 42.1
4.5 23.2 8.8 4.5 3.7 3.0 47.7 10.0 6.9 6.0 3.1 26.3
0.65 4.9 4.75 7.2 8.7 5.1 31.30 13.6 21.3 5.7 5.1 23.0
94.2 96.9
92.7 90.1
11.6 7.9 1.3:2
33.4 32.6 ,5.2 10.0 11.0 0.6 10.0
42.6
12.0 22.3 (Arerage) 20.0
48.0 20.0 4.0 7.5 0. . 5 2+:5
The yields of various products obtainable per barrel (42 gallons) of cracking stock are shown in Table XIT’. The material cost of producing aromatic hydrocarbons can be calculated from the data of this table. It is not possible to estimate the operating costs for a high-temperature cracking unit with any degree of accuracy, because such a process had never been worked satisfactorily, commercial attempts heretofore having been frustrated by carbon formation* A method for overcoming this difficulty and developing a process capable of working with high productivity per unit of plant has been shown. The operation cost should be reasonable. The anthracene formed is easily separated and purified; therefore, the present principal costs of refining for this valu-
797
YIELDS O F PRODUCTS FROM HIQH-TEMPERATURE
CRACKINGO
Charging s t o c i Temperature, C. Yields, gal./bbl. of charge: Olefins boiling below 75’ C . Benzene Toluene Xylenes styrene Trimethylbenzenes Higher alkyl benzenes Total below 205’ C. Yield, lb./bbl. of charge: Naphthalene Alk 1 naphthalenes Antgracene phenanthrene Alkyl anthracenes, eto. Heavy t a r residue Yield of gae, cu. ft./bbl. Olefins, % by vol. of gas For yields from gases, Bee Table IV.
+
+
a
SPRAY OIL 750 800 0.90 3.03 1.73 1.06 1.32 8.04
. . 2677
42.1
0.95 3.87 1.49 0.77 0.53 0.62 8.23 12.4 8.53 7.35 3.82 32.6 2830 42.6
KEROSENE EXTRACT 800 0.20 1.27 1.24
1.91
2.33 1.35 8.30
25.8 40.3 10.85 9.60 43.5 1900 ( 8,V.) 20-30
PRODUCTS OF VAPOR-PHASE CRACKIKG AT MODERATE TEMPERATURES
This type of cracking is illustrated by experiments 1-21 and 1-20 of Table I X and especially by the experiments of Table X. Table XV shows the products obtained a t 600’ and 650” C. a t the standard rate of flow. The yields in the first pass are calculated from Figure 16 and the yields upon recirculation are carefully estimated from the results of experiments K-4 t o K-8, Table X. TABLE xv.
YIELDS O F PRODUCTS FROM VAPOR-PHASE CRACKIKQ SPRAY O I L 4 T MODERATE TEMPERATURES
(Standard rate of flow) Temperature in Figure 16, C. Yields in first pass per bbl. of charge: Gasoline, gallons Recycling stock (distillable), gallons Gas, cu. i t . Estd. yield per bbl. of cracking stock with total recirculation: Gasoline, gallons Heavy t a r residue, pounds Gas, cu. ft. Olefins in gas yo by vol. Aromatics in ’ asoline, % Bromine num%er Antiknock value, benzene equivalent, %
600
650
8 28 534
12.5 13 1590
24 22 1600 52 6.2 164 80
16 30 2500 53 21.4 107 92
Although refined spray oil was used in these cracking experiments, a few experiments indicated that there is no substantial difference in yields or type of products when a straight-run California stove oil is substituted for the spray Oil’ LkCKXOWLEDGJfENT
This paper is published through the courtesy of the Shell Development Company t o whose research director, E. C. Williams, the author makes grateful acknowledgment. The author’s thanks are further due to G. Hearne who carried out a great deal of the experimental work and to other colleagues for their advice and assistance.
LITERATURE CITED (2) (3) (4)
(5)
Berl and Forst, z. Angew. Chem,, 44, 193-7 (1931), Berthelot, Bull. SOC. chim., [2] 6, 272-4 (1866); Ann. chim. phys., [4] 9, 451 (1866); “Les carbures d’hydrogene,” Vol. 11, p. 15, Gauthier-Villars et Cie, Paris, 1901. Burns, British Patent 14,958 (1886). Davidson, IND.ESG. CHEM., 10, 901-10 (1918). Dunstan, Hague, and Wheeler, J. SOC.Chem. Ind., 50, 313-1ST (1931).
INDUSTRIAL AND ENGINEERING CHEMISTRY Edlund, K. R., unpublished work. Egloff, Schaad, and Lowry, J . Phys. Chem., 34, 1617-1740 (1930); J . Inst. Petroleum Tech., 16, 133-246 (1930). Frey and Hepp, IND. EKG.CHEM.,24, 282 (1932). Geniesse and Reuter, Ibid., 22, 1274 (1930); 24, 219 (1932). Haber, “Experimental-Untersuchungen uber Zersetaung und Verbrennung von Kohlen~vasserstoffen,”Habilitationsschrift, Munich, 1896. Hague, E. K,,and Wheeler, R. V.,J . Chem. SOC.,1929, 37893; Fuel, 8, 560-87 (19’29). Hall, U. S. Patent 1,194,289 (1916); British Patent 1594 (1915). Hofmann, K. A., “Lehrbuch der anorganischen Chemie,” 5th ed., P. 326, F. J&weg &z Sohn A-G., Brunschweig, 1924. Lenher, J. Am. Chem. Soc., 53, 3752-65 (1931).
Vol. 25, N o . 7
(15) Lomax, Dunstan, and Thole, J . Inst. Petroleum Tech., 3, 36-120 (1916). (16) Meffert, German Patent 99.254 (1897). (17) Meikle, British Patent 23,649 (1896). (18) Piotroivski and Winkler. Petroleum Z., 26, 763-80 (1930). (19) Rittman, British Patents 9162 and 9163 (1915). (20) Wheeler, R. V., and Wood, W. L., Fuel, 7, 535-9 (1928) ; J. Chem. Soc., 1930, 1819-28; F u d , 9, 567-74 (1930). (21) Wheeler, T. S., and Imp. Chem. Ind., Ltd., British Patent 332,998 (June 4, 1929). (22) Williams-Gardner, Fuel, 4, 430-40 (1925). RECEIVED N w e m b e r 21, 1932. Presented before t h e Division of Petroleum Chemistry a t t h e 84th Meeting of the American Chemical Society, Denver, colo., August 22 t o 26, 1932.
Production of 2,3-Butylene Glycol by Fermentation Effect of Sucrose Concentration ELLISI. FULMER,L. h4. CHRISTENSEN, AND A. R. KENDALL, Iowa State College, Ames, Iowa
T
H E purpose of this study was to determine in a quantitative manner the influence of the concentration of sucrose, in a synthetic medium, upon the production of 2,3-butylene glycol by bacterial action, in order to find the optimum conditions for maximum yields of the glycol. The data show yields in the neighborhood of 50 grams of the glycol per 100 grams of sugar fermented under the optimum conditions described. These yields are of such a magnitude as to point t o industrial production. The research is being extended to increase these yields further, to speed up the rate of fermentation, to develop methods of recovery, and t o study the chemical properties of the glycol and its uses in the synthesis of other organic substances. There are many papers in the literature involving the determination of 2,3-butylene glycol and acetylmethyl carbinol; most of these determinations were qualitative and incidental. Hence, there will be briefly reviewed only those communications in which quantitative data were obtained under standardized conditions. One of the earliest references is that of PBr6 (28) who identified acetylmethyl carbinol as produced from mannitol by B. subtilis and B. naesentericics vdgatus, and from dextrose and glycerol by Tyrothrix tenuis. Grimbert ( 6 ) identified this chemical as produced from various sugars by B. tartiicus. Desmots (3)proved this material to be produced from various substrates by several bacteria including B. mesentericus vulyatus, B. fuscus, B. pauua, B. ruber, B. subtilis, and Tyrothrix tenuis. Harden and Walpole (9) were the first to prove the production of acetylmethyl carbinol and 2,3-butylene glycol by bacterial action on sugars. They found that about 27.2 per cent of the dextrose fermented by B. lactis aeroyenes, under anaerobic conditions, was converted into 2,3-butylene glycol. Walpole (26), using B. lactis aeroyenes in a nutrient medium containing 5 per cent sugar (dextrose or levulose), under anaerobic conditions, obtained yields of two optically active forms of the glycol, the diphenylurethan derivatives melting a t 199.5’ and 157’ C., respectively, with the former composing about 90 per cent of the mixture. Harden and Norris (8)found that 6 . coli communis converted 33 per cent of the dextrose into the glycol, calculated on the basis of sugar carbon.
Lemoigne (12, 13) found that the relative amounts of 2,3butylene glycol and acetylmethyl carbinol varied with the time of fermentation. The ratio of carbinol to glycol was 860 to 1718 at the end of 3 days, and a t the end of the seventh day was 5772 t o 3371. Harden and Xorris ( 7 ) found that Aerobacter avogenes converted 9.9 per cent of the glycerol used into 2,3-butylene glycol. Lemoigne (14-1 7 ) reported the action of three strains of the Bacillus proteus group upon dextrose. The amounts of the carbinol and glycol in milligrams produced after various time intervals were: 3 Days 16 60
Acetylmethyl carbinol 2,3-Butylene glycol
6 DAYS 60 140
18 DAYS 110 60
Breden and Fulmer (1) studied the fermentation of sucrose and xylose by Aerobacter faeni. The yields of glycol and carbinol may be summarized as follows in terms of grams of each chemical produced per 100 grams of sugar fermented: XYLOSF
2 3-Butylene glycol
&etylmethyl carbinol
Aerobic 10 5 2 6
Anaerobic 13 7 0 2
S~CROTE Aerobic Anaerotic 16 7 15 0 6 4 0 5
F’erhave (25) found the organisms Clostridium polyrnyxa and Aerobacter aerogenes to be especially active in the production of 2,3-butylene glycol from carbohydrates. The production of 2,3-butylene glycol and acetylmethyl carbinol by the action of yeast upon various substrates has been studied especially by Neuberg and Reinfurth (19), Neuberg and Rosenthal (ZO), Kluyver and Donker ( I O ) , Seuberg and Gorr (18), Seuberg and Simon ( a l ) , Kluyver, Donker, and visser’t Hooft (11), Elion (0, and others. hIE DIUM
AABD
BACTERIA
In developing synthetic media for the growth of yeast, Fulmer, Kelson, and Shermood ( 5 ) and Sherwood and Fulmer (84) systematically varied the concentrations of the salts used in order t o determine optimum conditions for growth a t the given temperature. The same procedure was adopted here in developing the medium optimum for the maximum production of the 2,3-butylene glycol by Aerobacter pectinouorum a t 37.5” C . The best medium contained, per 100
