Noncatalytic Addition of Ethylene1 to Paraffin Hydrocarbons F. E. FREY A N D H. J. HEPP Phillips Petroleum Company, Bartlesville, Okla.
QR
ESEARCH in hydrocarbon
chemistry during recent years has proceeded actively in many directions, and the chemical reactions of the simple paraffins and olefins have received a liberal share of attention. Simple hydrocarbons lend themselves readily to the identification of the reactions they undergo and to a study of their reaction mechanism, since it is possible to determine accurately the composition of reactants and reaction products. The now familiar development of gas polymerizat,ion to produce motor fuel has furnished a profitable field of application and has intensified the interest of the petroleum industry in an intimate picture of the chemistry involved. An extensive literature now exists in the field of gas conversion to produce motor fuel, and a number of processes and process steps have been described. (Many recent bibliographies relating both to chemistry and applications are available; citations 2, 8, and 19 present reference lists.) These processes were classified by Keith and Ward (19): 1. High-temperature, low-pressure gas cracking into unsaturates. When such a process is carried out primarily for the manufacture of motor fuel, the cracking obviously must be followed by polymerization. Typical of this work has been that of Cambron and Bayley ( I ) , Dunstan (4), Frey (9), Frolich (I@, Hurd ( I 4 ) , Neuhaus (df),Pease (E2), Rice ($4,Sullivan (25), and their co-workers. 2. High-temperature, low-pressure pyrolysis of saturates and unsaturates primarily to produce aromatics. Typical of these methods is the work of Cambron and Bayley ( I ) , Dunstan ( 6 ) , Frey ( I O ) , Podbielniak (23), and Zanetti (29). 3. Noncatalytic olymerization of gaseous olefins, as reported by Dunstan &), Ipatieff ( I 5 ) , Sullivan (%), and Wagner (26).
4. Catalytic polymerization of gaseous olefins, as investigated by Gayer ( I S ) , Ipatieff (f6),Waterman (27), Dunstan (e), and their associates. ( 5 ) Methods such as alkylation for effecting the combination of saturates and unsaturates, as shown by the work of Ipatieff et al. (17).
In this list should be included: (6) Noncatalytic conversion under pressure of saturates into motor fuel, as described by Youker (28) and by Keith and Ward (19, 20).
Catalytic dehydrogenation (7, 11) of gaseous paraffins to produce olefins and the use of hydrogenation to produce saturated motor fuel hydrocarbons may be mentioned also. These process steps involve, from the chemical standpoint, two types of reaction-i. e., dissociation into smaller molecules and synthesis in which larger molecules are formed by juncture of smaller ones. Dissociation may be brought about by the heat alone; thus a paraffin of two or more carbon atoms per molecule will decompose into an olefin and the complementary paraffin or hydrogen. With the aid of a dehydrogenation catalyst, decomposition to the corresponding olefin and hydrogen can be effected. The synthesis reactions include polymerization and produce normally liquid hydrocarbons from gaseous hydrocarbons. Not only can motor fuel suitable for incorporating in regular gasoline
be produced but, by operations partaking more or less of the nature of controlled chemical synthesis, individual hydrocarbons of desired structure suited for special purposes can be synthesized from simpler hydrocarbons. Thus aviation fuels of high antiknock rating can be produced to meet exacting requirements. Process steps 2 and 6 involve both dissociation and synthesis reaction. Polymerization of simple hydrocarbons to form larger molecules comprises several types of reactions. Simple olefins undergo olefin-olefin juncture under heat and pressure without the aid of catalysts to produce olefins of higher molecular weight, accompanied by cyclic hydrocarbons and paraffins notably under drastic conversion conditions. Reduction in reaction pressure reduces the velocity of reaction, and complex secondary reactions play a larger part, leading to predominantly aromatic liquids under drastic conditions Catalysts may markedly decrease the temperature and pressure necessary to bring about olefin-olefin juncture. Paraffins are, in general, far less reactive than olefins, but paraffin-olefin juncture may be effected catalytically. The present investigation establishes that paraffin-olefin juncture can be effected noncatalytically and plays a part, sometimes dominant, in the conversion of hydrocarbons by heat and pressure. The thermal conversion of paraffinb under pressure (group 6), particularly propane and butane under 800 to 2200 pounds per square inch, has been the subject of extensive experimental study (19, 20). It was established that the conversion involved first the splitting of the paraffin into smaller molecules, partly olefins. By reason of the pressure, the olefins so formed were generated under rather high partial pressure and proceeded to polymerize to normally liquid hydrocarbons, the splitting of the original paraffin and the polymerization reactions taking place simultaneously, The propane and butane are not completely converted in a single thermal treatment, and a high partial pressure of paraffinic reactants is accordingly present throughout the conversion period. The gasoline produced was found to contain olefinic polymers and cyclic hydrocarbons such as have been shown to result in the noncatalytic polymerization of olefins under pressure (group 3), but rather complete analyses of the gasoline disclosed further that isoparaffins were present in CODsiderable amount, constituting the greater part of the gasoline when strictly paraffinic reactants were subjected to thermal conversion a t the higher pressures. It was also found that yields of gasoline obtained, based on propane and butane disappearing, were high; and it w~tsobserved that paraffins, when admixed with olefins, underwent concomitant conversion to produce polymers under conditions too mild for the familiar cracking decomposition. These observations pointed strongly to the juncture of o l e h s with paraffins as an important polymer-forming reaction under such thermal conversion conditions. Furthermore, thermodynamic calculations indicated that such reactions were possible under the existing conditions of temperature and of paraffin and olefin partial pressure. 14 39
1440
INDUSTRIAL AND ENGINEERING CHEMISTRY
For the purpose of studying the thermal paraffin-olefin juncture reaction, a laboratory investigation mas carried out with the aid of a conversion method designed to permit the alkylation (or paraffin-olefin juncture) reaction to overshadow the other reactions which may take place. An individual olefin, ethylene, and the paraffins propane and isobutane, were reacted together to determine the identity of the paraffins produced under conditions favorable to primary juncture. This suggested the use of high conversion pressures, ranging from 2500 t o 4500 pounds per square inch. FIG I - DIAGRAM bF RFCIPCULATION APPARATUS
U Since olefins can be expected to polymerize rapidly by olefin-ole& juncture a t high partial pressures, means were provided for dispersing the olefin reactant in low concentration in the paraffin reactant before subjecting the mixture t o reaction temperature a t high pressure. In order to obtain a reasonable extent of conversion, additional olefin was supplied during the reaction as it was consumed, always maintaining the concentration of unreacted olefin at a low lwei. This effect was obtained on a laboratory scale by charging all the paraffin to be reacted to a closed system consisting of reaction tube and a circulation pump, then circulating the paraffin while adding olefin during the reaction period, stopping the reaction after the desired amount of olefin had been added, and finally withdrawing the reaction products.
Experimental Procedure
In the experiments to be described, a measured portion of propane or isobutane was circulated by means of a highpressure pump through a heated tube. At predetermined time intervals small portions of olefin were injected into this stream to supply a steady, low concentration of olefins t o the reaction zone. The olefin additions were continued until the desired quantity of olefin had been added. In run 266-12, a high-pressure flowmeter was substituted for the portionwise olefin addition arrangement, and the olefins were added continuously throughout the run (a substant'ially equivalent method of operation), After the last olefin addition, the reaction was continued for a time sufficient to circulate the hydrocarbon in the system once through the reaction zone. The products were then withdrawn from the system and analyzed. Figure 1is a diagram of the apparatus used in these experiments : The sample passes from container C (capacity 120 CC.) through short, water-cooled tube to the Hills-McCanna type G. B. D. pump, B, from which it is forced through the straight reaction tube, A , situated in a tube furnace. These reaction tubes were made of 18 per cent chromium-8 per cent nickel, low-carbon steel in two sizes; a tube with a bore of ' / 8 inch was used for experiment 231-2, and of inch for the other experiments. A thin, close-fitting copper tube was telescoped inside t o eliminate possible catalytic surfaces, and in addition the '/&-inchtube cona
VOL. 28. NO. 12
tained a close-fitting twisted copper ribbon to eliminate undesired convection. Oxidation of the co per and subsequent reduction were avoided. The exit end o f both tubes contained a loose-fitting solid brass rod to effect the rapid cooling of the effluent gases. The heating coil \\as divide'd into three sections under independent control to facilitate maintaining an even reaction temperature. Temperatures were read by means of a chromel-alumel thermocouple at 6-inch intervals along the tube. The furnace was 36 inches in length and the effective conversion zone about 10 inches shorter. From the reaction tube the hydrocarbons passed through a water cooler t o expansion valve 2 where the pressure was reduced to 100-150 pounds per square inch and into container C , when the cycle was repeated. The time required to cause all the hydrocarbon in the system to flow through the reaction zone depended on the pump setting. Experiments were continued for a t'ime sufficient to permit ten such cycles. At intervals of two to four times a cycle, small definite quantities of olefin were admitted by means of calibrated tube F and valves 5 and 6, each increment being a little less than the volume held in the line between valves 5 and 6 at a cylinder pressure in D of about 500 pounds per square inch. To observe circulation rate, the flowmeter shown at E was employed. This consisted of a small heating coil (about 30 watts) with a sensitive ammeter in series to give close regulation of the heat generated. A six-junction copper-constantan thermocouple with the cold junctions on the upstream, and the hot junctions on the downstream side measured the increase in temperature, and therefore the mass velocity of the hydrocarbon. The whole was heavily lagged. This meter operated satisfactorily, and circulation rates were readily controlled to 10 per cent. In starting an experiment, a weighed quant'ity of propane or isobutane was placed in container C, and a weighed quant,ity of olefin in container D. These bombs were connected into the system and, with tube A at reaction temperature, the entire system was evacuated through valve 1. Valves 1 and 2 were then closed, valve 3 was opened, and connections were checked for leaks. Valve 4 was opened and the pump started. There was usually a delay of 30 to 60 seconds before the pump took hold and built up to react,ion pressure. Valve 2 was then cracked just to maintain the desired pressure while the paraffin circulated. When this was achieved, valves 5 and 6 were manipulated t o admit an addition of olefin. The time was taken as beginning with the, first olefin addition. Twenty t'o forty olefin additions a t uniform intervals were made. After the last olefin addition, the circulation was allowed to continue for a time equal to one cycle, when valve 4 was closed and valve 2 opened, allowing the pressure in t,he reaction tube to drop t o 100-150 pounds per square inch. Valves 3 and 4 were then closed, and the portion of the sample outside of container C passed through valve 1 direct t,o an analytical fractionating column where it mas condensed. The part of the sample in container C was forced from the bomb by mercury under 500 pounds per square inch pressure, to preclude the possibility of weathering, into the column previously mentioned. The combined sample, consisting of all t'he reacted material, was then analyzed by means of low-temperature fractional distillation in a close-cutting column, combined with Orsat analysis for hydrogen, methane, and olefin determination. Olefins in the larger fractions and in the gasoline fractions were determined by bromine titration. The separation of individual paraffin isomers, which differ in boiling point by small intervals, was effected by observing the usual precautions of analytical fractionation, and in addition by maintaining a steady reflux temperature and rate of heat input to the distilling bulb, while distilling very slowly. These separations are less precise than the separations between adjacent homologs, however. Leaks in the system were not entirely prevented. Small losses could not have greatly affected product composition. f
Discussion of Data Table I gives the data obtained in a series of three experiments. Operating conditions of reaction time and temperature were chosen rather arbitrarily but were such as would permit only slight cracking. The experiments give information primarily on the comparative yields and identity of the products obtained from the paraffin-olefin pairs reacted. Thermodynamic calculations show that considerably higher yields of alkylation product could have been developed by larger olefin additions, and somewhat lower pressures could have been used. The high pressures and moderate conversions were employed, however, in order to favor especially
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1936
the formation of primary products. K i t h the aid of catalysts, lower pressures and temperatures may be used to effect paraffin-olefin juncture, and a study of the catalyzed reaction is in progress. The conditions required to effect the thermal reaction are such as to shoK that alkylation must play an appreciable part in prwsure-cracking and naphtha-reforming operations.
Products The principal liquid product formed in the experimental conversions was a mixture of isomeric paraffins whose molecular weight was equal t o the sum of that of the paraffin and olefin reactants. The yield of this product under the experimental conditions employed was one-half to three-fourths of the liquid products formed. The principal alkylation products formed from the two olefin-paraffin pairs investigated are as follows: ETHYLENE AND PROPANE. Experiments 231-2 and 231-3 (Table I) show conversion conditions and product analyses. Table I1 gives the composition of liquid products. This is a particularly clean-cut example of alkylation, in that about 75 weight per cent of the liquid products were pentanes, the formation of which can be represented by the equation : Ci"
+ CaHs
+
CJL2
Replacement of secondary hydrogen of the propane by ethyl yields isopentane, replacement of primary hydrogen yields npentane. The pentane fraction was composed of about twothirds isopentane and one-third n-pentane, accompanied by very little pentene (4 per cent). It is certain that the yields of pentanes permitted in experiments 231-2 and 231-3 did not approach the thermodynamic limit; consequently the relative proportions of iso- and n-pentane found reflects the comparative rate of substitution of primary and secondary hydrogen by ethyl, secondary hydrogen replacement proceeding the more rapidly. Both hexanes and heptanes were formed in substantial amount. At least a part of the hexanes were formed from the reaction of propylene and propane, while the heptanes may have been formed either by secondary alkylation of pentanes with ethylene, or by reaction of butylenes from ethylene polymerization with propane, or both. ETHYLEKE AND ISOBUTANE. In experiment 231-5 (Table I) are shown the results of a run a t 4500 pounds per square inch where ethylene and isobutane were reacted together. The analysis of the liquid products is shown in Table 111. Unfortunately, a fairly large leak occurred during the first 25 per cent of the run near the point of addition of the ethylene, which made it necessary to use some caution in estimating ethylene consumption. I n general, the reactions occurring are similar to those already discussed. Hexanes are the chief product and constitute 56.9 weight per cent of the gasoline. Their formation can be represented by the equation: C2H4
+ iso-C4H1o
+
CaHlr
The substitution of tertiary hydrogen by ethyl yields 2,2dimethylbutane, and the substitution of primary hydrogen yields 2-methylpentane. These were the predominant hexanes identified. The fraction designated 2,a-dimethylbutane distilled almost entirely a t 49.5-50.5' C. (121 -123 O F.) a t 760 mm. mercury, and agreed closely in boiling point, refractive index, and density with the reported properties of the synthetic hydrocarbon. The fraction designated 2methylpentane distilled almost entirely a t 60-61 O C. (140 O141.8' F.) and agreed closely in these properties with the reported properties of this paraffin. Nearly 80 per cent of the hexane fraction consisted of 2,2-dimethylhutane.
1441
TABLEI.
PRODUCTS FORMED BY INTER.4CTIOX O F P A R A F F I N 8 AND ETHYLESE UNDER ALKYLATION CONDITIONS
Experiment No. Gases reacted, weight
%
Pressure, lh./sq. in. Temp., F. (', C.) Av. reaction time of paraffin reactant, min. No. of olefin additions Gasoline yield based on roducts recovere$, ut. % Products recovered:
231-2
{ 8:::: 4500
94::
947 (508) 3.8
--
---
7.2
11.2
16.3
Wt. % Mole % Wt. % Mole % Wt. % Mole %
...
Iso-C4Hs 2-GHr 1-CkHs
10.39
... . ..
0
2.87 0.64 0.21 91.29
0.004
0.72 1.23 0.53 0.16 84.40
0.09 2.09 2.07 0.81 0.17 86.60
0.013 0.94 1.68 0.81 0.56 2.09
0.39 3.30 3.54 1.59 0.78 2.77
0.21
0.18
0.30 0.34
0.31 0.35
0.55
0.42
...
0.Ob 0.70
0.54
0.54
75.60 0.54
0.18 3.76 1.67 0.12
0.11 2.33 1.04 0.07
0.29 6.20 1.87 0.22
0.19 4.00 1.18 0.12
0.81 0.53 0.80 0.49
0.67 0.44 0.65 0.34
0.22
0.81
0.44)
...
... ...
7.20 1.88 0.18
4.94 1.29 0.13
...
0.20 1.12 0.12 0.37 0.10
0.09 0.52 0.05 0.15 0.04
0.Ob
2,2-Dimethylbutane 2-Methylpentane 10.42 n-Hexane Intermediate ole' fins Intermediate para5ns
...
C7H14 CiHis CsHia CsHis C8 and heavier: Unsatd. (olefins) Satd. (paraffins)
4.0 32
30
1.77 0.34 0.16 89.59
ISO-C4Hio
231-5 CZHI 1 2 . 1 Iso-CIHi;, 87.9 4500 940 (504)
4.1
40
Hz CHI CZH4 CZH6 C3H6 C3H6
n-CIHl0
231-3 CzH4, 8 . 9 CsHs, 91.1 4500 950 (510)
...
...
...
...
... ...
.. . ,. .. ....
0.16
0.07C
,
...
...
0.08
0.05
0.31
0.18
0.31 0.43 0.63 1.57
0.19 0.25 0.33 0.81
0.38
0.16
100.00
100.00
0.88 0.38 0.68 0.28 - - ~
100.00 100.00
100.00
100.00
The methane determination was lost through an eccident. b Less than 10 per cent of the butanes. 0 Heptanes and heavier.
a
OF LIQTIDPRODUCTS, ETHYLENE TABLE11. COMPOSITION AND PROPANE
Experiment No. 231-2 Gases reacted, wt. %: CZH4 4.7 C3Hs 95.3 4500 Pressure lh /ss in. F.' (" 6.) 947 (508) Temp ~ v r k. k t i o n time of para511 reactant, min. 3.8 Gasoline yield, weight 7 0 of reactants 7.2
Composition of liquid products: C5HlO ISO-CoHlz n-CsHiz C6HlZ CnHir C7H14 ClHl6 C, and heavier: Unsatd. Satd. Ca and above: Unsatd. Satd.
Wt. % 2.5 52.4 23.2 51 .. 87
... ...
2.2 12.2
... ...
231-3 8.9 91.1 4500 950 (510) 4.1 11.2
Wt. %
5E:!} 16.4
;:! }
lA:y} ... ...
-
-
100.00
100.00
Density (25' C.)
Refractive Index (20' C.)
0.618 0.633 0.677
1.3551 1.3597 1.3952
0.706
1.3970
...
....
. . I
0.755
.... 1.4203
The rate a t which tertiary hydrogen of the isobutane is substituted by ethyl is far greater than the rate for primary hydrogen substitution, and the difference is more marked than in the case of secondary us. primary substitution described in connection with the ethylene-propane juncture-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1442
VOL. 28, NO. 12
pounds, the alkylation reaction proceeded in TABLE111. COMPOSITION OF LIQUIDPRODUCTS, ETHYLENE AND ISOBUTANE about the manner to be expected if the alkylaGasoline Composition tion reaction were of about the second order. Refractive The proportion of hexanes (primary alkylation Density index Wt. % (25' C.) (20' C.) products) in the gasoline was decreased some231-5 Test No. Pentenes 4.97 ... .... what by the lower pressure, but the composition Gases reacted, wt. %: 3.25 Isopentane . . . . . . . 12.1 C2H4 4.91 n-Pentane ... ... . of these hexanes was but little affected.
ISO-CPHIO Pressure lb /sq in. F.' ( " C.) Temp ~ v re'Action . time, min. Gasoline yield, wt. % of reactants Olefins in gasoline, %
87.9 4500 940 (505) 4.0 16.3 16.1
Hexenes 22-Dimethylbutane 2-Methylpentane n-Hexane Heptenes Heptanes Octenes Octanes Residue: Unsatd. Satd.
3.01 44,26 11.55
1.11
0:645 0.655
... ... ...
2.39 4.54
E: t
0.714
2.33 4.17
__
100.00
The rate of hydrogen replacement by ethyl in these two instances decreases in the order tertiary -+ secondary + primary, and it is probable that the comparative rates found will indicate what is to be expected in the thermal ethylation of other paraffins. The heptanes and octanes, which constitute the chief higher products, probably resulted both from the direct alkylation of isobutane with propylene and other secondary reactions.
Conversion Pressure Very high pressures as contrasted with low pressures can be expected to favor primary paraffin-olefin juncture; lower pressures can be expected to favor alkylation involving olefin polymers as well. I n experiment 266-12 (Table IV) ethylene and isobutane were caused to react at 2500 pounds per square inch; the liquid product analyses are given in Table V. For comparison the experiment a t 4500 pounds per square inch (231-5) is also included. Although the effects of thermal decomposition are evident, because of the more severe time-temperature conditions employed a t 2500 A,ND SINGLE-POINT OLEFIN TABLEIV. EFFECTOF PRESSURE ADDITION ON ETHYLENE-ISOBUTANE CONVERSION
Experiment No. 266-11 Gases reacted, wt. %: Ethylene 16.5 Isobutane 83.5 4700 Pressure lb /sq in. 941 (505) TemD.. Fa'(' 6.) Av. ieaction time, min. 5.1 Exptl. method Single pass Gasoline yield, wt. % ' of effluents 20.4
231-5
9.8 90.2 2500 968 (520) 4.3 Recirculation
12.1 87.9 4500 940 (505) 4.0 Recirculation
12.8
16.1
r____
Mole % Wt. % Wt' % 1.28 0.05 0.013 2.341 Methane Hydrogen {3.48 3.09 0.94 10.35 1.03 1.6s 1.97 0.28 0.13 Ethylene 4.64 2.62 0.81 2.68 Ethane 5.14 2.21 1.72 0.56 0.76 Propylene 1.05 3.71 3.12 2.09 2.98 ProDane 3.83 2.22 2.32 0.75 2.35 2.26 But y 1en e 65.35 72.53 76.34 66.14 67.97 Isobutane 0.71 0.54 0.64 0.44 0.45 kLButane0.73 0.81 0.56 0.73 0.89 Pentenes 0.48 0.66 0.53 0.68 0 . 5 3 Isopentane 4.18 1.17 1.54 0.80 3.32 n-Pentane 0.36 0.68 0.49 0.55 0.37 Hexenes 1.9s 3.22 7.20 1.0s 0.72 2,2-Dimethylbutane 1.15 1.88 2.06 1.65 2.50 Other hexanes 0.32 0.39 0.18 0.22 0.13 Heptenes 0.74 0.53 1.01 1.14 0.65 Heptanes 0.21 0.50 0.63 0.69 0.35 Octenes 0.48 1.03 1.57 Octanes 1.76 3.52 Nonanes 1.79 4.19 0.29 0.24 Residue 0.29 0.79b loo.0b 100.00 100.00 100.00 100.00 a The carbon-hydrogen ratio of products in tests 266-11 and 266-12 is low. This factor is sensitive t o small analytical errors and will not affeot largely the conclusions drawn from the analyses shown. h 0.15 weight per cent of carbon was found in test 266-11. Mole % Wt. %
+
,
266-12
0":;) --
1:36Q5 1.3750
....
Circulation us. Once-Through Conversion In Tables IV and VI are shown the results of
.... ....
1.3987
an experiment (266-11) where a mixture of ethylene and isobutane was passed, without recirculation, through a heated tube-that is, subjected to simde once-through conversion. For comoarison; experiment 231-5 a t 4500 pounds presiure, n-here the ethylene was added in small increments througho u t the experiment, is also shown in the tables. The time, temperature, pressure, and percentage gasoline produced are roughly similar. The quantity of liquid products formed is definitely greater than the ethylene contained in the hydrocarbons reacted in both cases. The proportion of high-boiling compounds in the liquid products is definitely the greater in the case of once-through conversion in comparison with circulation conversion, under conditions otherwise similar. The proportion of hexanes (primary alkylation products) in the gasoline formed in once-through conversion is only about one-third that formed in the recirculation experiment, and the content of 2,2-dimethylbutane in the hexanes is less. The high content of paraffins in the gasoline from once-through conversion indicates extensive alkylation, but not the primary alkylation of the circulation experiment. The high-boiling products (C8 and heavier) of once-through conversion are not only more abundant but more cyclic, as the high specific gravities show; dark colored tar and considerable carbon were formed, in contrast with the products of the circulation conversion experiment. This experiment will be further discussed.
..
..
Chemistry of Alkylation Conversion REACTION MECHANISM. An inspection of product analyses (Tables I to VI) shows that a number of reactions are involved. The dominant reaction products, however, are the paraffins which should result from juncture of the original paraffin and olefin reactants. The mechanism of the thermal paraffin-olefinjuncture reaction involves much the same considerations as the familiar thermal decomposition of paraffin hydrocarbons as exemplified by
CSHH---t CzH4
+ CaHs
which is essentially the reverse reaction. The Rice chain mechanism (94,as formulated for the decomposition, can be applied to the juncture reaction by assuming free alkyl radicals to be first produced which then take part in reaction chains. Such a representation in brief form is as follows :
+ +
C3Ha +CzHsCHIC2Hb- (or CHs-) CIHE+C J L (or CH,) CaHr CzH4 --f CbH11C3Hs +CIHU C3H7CsHii-
+ +
+ CsH-
+
C8H- may serve as a chain carrier for the repetition in a reaction chain of the last two reaction steps shown. I t is notable that the hydrogen transfer reaction CzHa
+ CaH8 +C2He + CaHs
DECEMBER, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
1443
must be a minor one, to judge from the low OF LIQUID PRODUCTS, ETHYLENE AND ISOBUTANE, TABLEV. COMPOSITION amount of ethane formed in the propane-ethylene AT 2500 POUNDS PER SQUARE INCH e x p e r i m e n t s . Mor eo ve.r, product analyses -----Composition of Liquid Productspresented show that the fraction containing the Density paraffins of primary alkylation contains only a Mole % Wt. % 25'C. small proportion of the corresponding olehs. Expt. N ~ . 266-12 Pentenes 7.3 5.7 ... 6.3 5.2 Isopentane This makes rather questionable such a mechaG%t;;;;;Fdp wt. %: 9.8 +Pentane 15.3 12.0 ... 90.2 Hexenes 4.7 4.5 nism as ordinary olefin-olefin juncture, followed Isobutane 25.9 25.2 0'.652 2,2-Dimethylbutane by h y d r o g e n a t i o n , t o account for the chief ~ ~ ~ ~ ~ P:{sdl e t : $e' d 2500 968 (520) Other hexanes 15.2 14.7 0,682 paraffinic alkylation products. Av. reaction time, min. 4.3 Heptenes 2'5 0.714 Heptanes 62 '. 49 S e c o n d a r y reaction involving altogether 1 Yi$~~>l'b4nu~r~;;~~ts Octenes "6; 0.741 paraffin and 2 olefin molecules is indicated by recovered), wt. % 12.8 Octanes Nonenes and heavier: the fact that ethylene-propane run 231-3 yielded Unsatd. 2.0 2.9 heptanes as the chief paraffin fraction, second to 3.3 5.01 0.798 Satd. Residue 1 . 6 2 .5 ... p e n t a n e s , and ethylene-isobutane run 231-5 iEY3 iCi5 yielded octanes as the chief paraffin fraction, second to hexanes. Two reaction paths appear to be involved, and both probably contribute. In the latter case, for example, the reactiops may be reprenumber of paraffin and olefin isomers, each having several sented as follows: paths of decomposition. Condensation and cyclization also enter. It is possible to simplify the problem and obtain a partial solution by setting to one side reactions so slow that CZH4 f C4HlO c6H141 (1) they do not affect equilibria under consideration, and this CZH4 C6Hl4 +CSHIS applies particularly to formation of cyclics. The present (2) CzH4 C2H4 +C4Hs data, together with other available data on thermal reacC4Hs C4Hio +CsHis tions, indicate what reactions proceed rapidly and dominate the situation, and this applies to olefin-olefin polymerizaTHERMODYNAMICS. The Ohennodynamic equilibria for tion reactions, olefin-paraffin juncture, and; as reaction beparaffin-olefin juncture reactions, which are essentially the comes extensive, to paraffin-splitting reactions. familiar paraffin-splitting reaction proceeding in the reverse In the initial stage of an alkylation conversion, olefin-olefin direction, have been computed by a number of investigaand olefin-paraffin juncture are rapid. As an example, 2 to 5 tors. Especially a t more or less elevated temperatures, mole per cent of ethylene dispersed in paraffin at, say, 5000 seemingly small errors in the available fundamental thermal pounds per square inch and 932" F. can be expected to be data introduce decided uncertainty in computed equilibrium polymerized by such over-all reactions as the following: constants. Disagreements in numerical values will have t o be resolved by future studies. Kassel (18) has computed CZH4 CZH4 +ClHs equilibria for a few reactions using entropies derived from 3CzH4 +2C3Ha spectroscopic data, and the constants for two reactions are to yield simple olefinic molecules, in a multiplicity of species. shown in Table VII. The alkylation reaction is favored by In a case of this kind only a limited extent of such polymerizaincrease in total Dressure or Dartial Dresswe of either paraffin or olefin reactant, and is abverseli affected by increase in temperature. ~_.__ At the temperatures required for OF LIQUIDPRODUCTS, ETHYLENE A N D ISOBUTANE TABLEVI. COMPOSITION thermal alkylation, in the general 266-11 23 1-6 Run KO. neighborhood of 500" C. (932" F.), Charge stock, wt. % : \ 12.1 1 6 . 5 Ethylene elevated pressures, exceeding 1000 83.5 Isobutane 4700 pounds per square inch, will be rePressure, Ib./so. in. 941 (505) Temp., ' F. ( " C.) quired in most cases to effect with 4.0 5.1 Av. reaction time, min. Recirculation Single pass Exptl. method low olefin content an extent of con20.4 16.3 Yield c>f liquid products v e r s i o n , predominantly primary - ~ ~ _ _ _ Composition of Liquid Products alkylation, exceeding a few per cent. That a pressure as high as 5000 . ,RefracRefracp o u n d s per square inch may be Dentive tive DenBoiling index sityo index sit% Range, highly favorable is shown by the C. Mole % Wt. % (200 Wt. % (60 (20' (60 computations in Table 1-11, based F.)Q F.) C.) C.) on the Kassel constants. At a given 4.97 . . . . . . . 4.35 ... .... 5.94 Pentenes .... 3.25 ....... 3.32 ... 4.31 Isopentane pressure and temperature, a con.... 4.91 . . . . . . . 20.48 27.00 ... n-Pentane . . . . 3 . 0 1 . . . . . . . 2 . 6 9 3 . 0 1 . . . ... Hexenes sideration of the kinetics of poly2,2-Dimethylmerization and alkylation reactions 5 . 2 8 0 . 6 6 7 . . . . 4 4 . 2 6 0 . 652 1.3695 47-52 5 . 8 6 butane 1 2 . 6 6 0 . 6 6 3 1.3750 . . . 12.26 0.691 13.44 52-80 Other hexanes shows that alkylation to produce a 2 . 3 9 . . . . . ...... 1 . 0 8 1 . 0 6 Heptenes 0.709 80-93 4.54 . . . . . . . 5.58 5.27 .... c o m p l e x m i x t u r e of paraffins Heptanes 1 . 4 1 . . . . . . . . . . . 1 . 7 0 Octenes 0 . 7 3 2 1.4108 93-108 associated with olefin polymer may 10.51 8.78 ........... Octanes 0 . 7 0 0 . 5 8 Octenes be considerably more extensive than : E:] 0 . 7 2 2 1.3987 0 . 7 4 6 1.4080 108-117 3.45 2.88 Octanes . . . . . . . . . 0.97 0.81 the conversion to a single primary Octenes 1 . 4 3 0 5 0 . 7 8 6 117-128 . . . . . . . . . 3.27 2.73 Octanes alkylation product. . . . . . . . . . 0 . 7 9 3 1.4416 2 0 . 5 0 14.56 Nonenes + { 128-205 Nonanes + THERMODYNAMICS AND KINETICS. 6.50b 3.86 ... .... . . . . . 2 . 3 6 __ Residue Alkylation reactions offer an interest100,00 100.00 100.00 ing field for bringing to bear thermoa T o convert to densities at 25' C subtract 0.008. dynamics but the problem is complib Residue boiling above 130' C. (6,and up). cated by the synthesis of a large . I .
+
+ +
1
+
I
~
O
INDUSTRIAL AND ENGINEERING CHEMISTRY
1444
tion can take place before the thermodynamic limit is reached. The alkylation reaction C2H4
+ CzHs +C4Hia
also takes place, and, since the partial pressure of the paraffin is high, the reaction could outrun olefin polymerization before the thermodynamic limit would be reached. TABLEVII. THERMODYNAMIC EQVILIBRI.~ KP
Reaction Loglo K (18) (500' C.Ia Examplesb (C~HI~)/(CZH~)(C~HI) 0.296 (700" K.) 0.497 CZH4, 2.6; CZH6 -0.602 (SOO' K.) 5.6; C4Hl0, 91.8 (CIH~~)/(CH~)(C~H~) IL,' 0.0832 CsHn 5.1; CHI, 1617; c4Hi0, 78.2 a Computed from the values of Kassel, fugacity corrections applied. b Compositions of equilibrium mixtures in weight per cent based on K p values shown: pressure 5000 lb. per sq. in., temperature 500' C.,olefin reaotant 5 mol. per cent of the equilibrium mixture.
-
~( (: ~ ~ i~~
~
Although these two reactions, olefin-olefin and olefinparaffin juncture, represent the major initial reactions, the multiplicity of olefins formed will react with the paraffin reactant, present in high partial pressure, to produce a series of paraffinic juncture products. Paraffins formed by alkylation may react with a second molecule of olefin reactant to yield a higher paraffin. Such secondary synthesis reactions lead to a complex mixture of paraffins and olefins. Splitting reactions of synthesized paraffins will also take place. These reactions will sometimes take the reverse path of the synthesis that produced them, but will take other paths as well. Altogether these secondary reactions will produce a complex mixture of paraffins associated with limited amounts of many olefins. It is to be expected that driving the reaction to the thermodynamic limit by continued olefin addition will usually lead to such a mixture rather than a true noticeable reversing tendency. A general tendency for the lowest paraffins and moderately high olefins to develop a t the expense of earlier products would also be expected on extensive reaction. Extensive alkylation conversion with adequate reaction time can be expected to produce a mixture of paraffins associated with a' limited amount of olefins; the higher the pressure, the lower the olefin content. Extremely high pressure should permit the addition of olefin a t a very low steady-state concentration and should give extensive conversion to quite pure primary alkylation products, and then higher paraffins also by secondary alkylation. Rather low pressures should require a not too low steady-state olefin concentration and generate larger amounts of polymeric olefins concurrently with paraffins, leading to a complex mixture of product paraffins and olefins before a very high extent of conversion is developed. From another viewpoint, the highest pressures may make for a fairly clean-cut synthesis by alkylation, and lower pressures may allow of fairly efficient utilization of olefin in alkylation but with the production of complex products; whereas low pressures of a few hundred pounds allow thermal alkylation to contribute some gasoline hydrocarbons while most of the polymer is olefin polymer and cyclics in the end. The indications are that ethylene is a somewhat better olefin for thermal alkylation than propylene or butylene in respect to reaction rate and thermodynamic driving force. Although the most efficient conversion method for effecting primary alkylation has been considered to be continuous olefin addition during reaction, experiment 266-11 (Tables IV and VI) shows a simple oncethrough conversion of ethylene plus isobutane which gave fairly extensive paraffin formation. The products are chiefly paraffinic, and they can probably be partly accounted for by assuming a rapid polymerization in the initial stage of the reaction by reason of the high ethylene concentration to produce a multi-
VOL. 28, NO. 12
plicity of olefinic polymers which later undergoes juncture with isobutane to yield a variety of paraffins. The foregoing discussion presents an all-aliphatic picture; however, cyclization and condensation to form aromatics and tar also take place. These reactions are very slow in the circulation experiments, though the pressure is high. It is significant that the olefin concentration is low. The formation of aromatics, tar, and finally carbon appears to depend on olefin concentration; it is rapid and extensive when partial pressure of olefins is high. Thus, the once-through experiment last described yielded cyclics, tar, and carbon to a greater degree than the portion-wise addition experiment (Table IT) which was similar in other respects. Paraffins of high molecular weight undergo splitting and not condensation as do aromatics and olefins when they are exposed to conversion temperatures, and this accounts for the virtual absence of tar under favorable alkylation conditions in which maintained concentration of olefin is low. It is probable that, in high-pressure alkylation, very high conversions per thermal treatment can be obtained with little carbon-forming tendency. High-pressure thermal conversion of propane and butane yields gasoline associated with very little tar, and this behavior can be ascribed to the alkylation-type conversion predominating; the continuous addition of olefin reactant is accomplished by continuous cracking of a part of the propane and butane. This is in contrast to the higher tar yields sometimes resulting in pressure conversion of olefin-rich stocks.
Aviation Gasoline While thermal polymerization of gaseous olefins to motor fuel ordinarily leads to the formation of a complex mixture of hydrocarbons, the use of favorable alkylation conditions makes possible the synthesis of isoparaffins of varying structure and molecular weight or volatility by the choice of suitable reactant paraffins and olefins. Such isoparaffins, particularly the more highly branched in structure, have high antiknock ratings and possess high stability, calorific value and lead susceptibility. These characteristics are particularly desirable in aviation fuel. Isooctane (2,2,4trimethylpentane) is a now familiar example. The 2,2,-dimethylbutane (a hexane) is such a paraffin. This hexane was the chief paraffin synthesized by reacting together ethylene and isobutane. By fractionating a quantity of the liquid product, a 2,2-dimethylbutane fraction was separated for motor fuel tests. The data are as follows: The fraction was essentially paraffinic, containing 1.9 per cent olefin, The A. S. T. M. octane number of the fraction was 94.5 (unleaded), a little below that of isooctane, and the volatility was somewhat higher.
A. 5. T. M. octane No. (unleaded) Gravity ' A. P. I. Reid vabor pressure, lb./sq. in. A. 9.T. &I. distn.:
94.5 84.9 9.5
2,3-Dimethylbutane, or diisopropyl, accompanied by 2methylpentane is formed in substantial amount from the reaction of propylene and propane.
Acknowledgment The authors are indebted to J. P. Jones and J. L. Richmond for assisting with the experimental work.
DECEMBER, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited Canihron a n d Rayley, (’an. J . Research., 9, 175-96 (1933): 10, 145-63 (1934). Cooke. Swanson, and W a g n e r , .Votl, P e t r o l e m i .Yezs, 2’7, 33 ( X o v . 20, 19:ISj. D n n s t a n , Haeiie, and Howes. (‘hi‘niie. 6: iridibetrie, 34, 273 (1935). Dunstan, Hague. and JYheeler. I S D . Esc;. C H m r . , 26, 307-14 (1934). D u n s t a n , H a g u e , a n d Wheeler, J . SOC.Cheiii. Ind , 51, 131-3T (1932). D u n s t a n and Howes. J . I m t . P r t i d e i m Tech., 22, :347 (1936). Egloff, Satl. Petroleum Sews,28, 25 (Oct. 14, 1 9 3 6 ) . Egloff a n d Wilson, IXD.ESG.CHEM.,27, 933 (1935:’. F r e y , I b i d . , 26, 198 (1934). P r e y a n d H e p p , Ibid.,24, 282-8 (1932). F r e y a n d H u p p k e , I b i d . , 25, 54 (1933). Frolich a n d Wiezevich, I h i d . , 27, 1055 (1935). G a y e r . Ihid., 25, 1122 (1983).
1445
(14) H u r d , “ P y r o l y s i s of Carbon C o m p o u n d s , ” A. C. S. Monograph 50, New Tork, Chemical Catalog Co., 1929. (15) Ipatieff, Ber., 44, 2978-87 (1911). (16) Ipatieff a n d Egloff, IND.ESG. CHEX, 27, 1077 (1935). (17) Ipatieff et al., J . .-In&.Chens. Soc., 58, 913 (1936). (18) Kassel, J . Cheni. Phys., 4, 435 (1936). (19) K e i t h a n d W a r d , Chemistry Le. I n d u s t r y , 532 ( J u l y 3, 1936). (20) K e i t h a n d W a r d , .Vat[. Petroleum S e w a , 27, 52 (Nov. 20, 1935). (21) N e u h a u s a n d M a r e k , ISD.ESG. CHEXI.,24, 400-2 (1932). (22) Pease a n d D u r g a n , J. A m . Chem. Soc., 50, 1779 (1928); 52, 1262 (1930). ( 2 3 ) P o d b i e l n i a k , O i l Gas J . , 29 (52), 22 (1931). (24) Rice, J . A m . Chem. Soc., 53, 1959 (1931); 55, 3036 (1933). ( 2 5 ) SulliT-an, R u t h r u f f , a n d K u e n t s e l , ISD.ESG. C H E M . ,27, 1072 (1936). (26) W a g n e r , Ibid.,27, 933 (1935). (27) W a t e r m a n , Over, a n d Tullevers, Rec. Irav. chim., 53, 699 (1934). (28) I’ouker, U. S. P a t e n t 1,800,586 (April 14, 1931). (29) Z a n e t t i e t al., J. IND.E N Q . CHEM.,8, 777 (1916); 9, 474 (1917).
.
RECEIVED October 23, 1936.
Xo. 72 in the Berolzheimer Series of Alchemical and Historical Reproductions is from a woodcut in Bninswig’s “Liber de arte Distillandi de Simplicibus,” printed in Strassburg in 1500 by Johannes Grueninger, and is presented by the courtesy of the Pierpont Morgan Library. The stills shown are much simpler than those shown in No. 66, from a later edition of the same famous book, while they antedate those in No. 10 of the series, as do also the costumes of the “chemists.” Additional title-page illustrations from one or another edition of this, “Das buch der rechten kunst zu distilieren die einzig ding,” also known as “Das grosse Distilierbuch,” will appear later in the series.
A detailed list of the first sixty reproductions, together with full particulars for obtaining photographic copies of the originals, ap eared in our issue for January, 1936, page 129, where also will be found Rsprofuction N o 61 Reproduction No. 62 appears on page 241 of our February issue, No. 6 3 on’page 280 of March, No. 64 on page 413 of April, No. 65 on page 572 of May, No. 66 on page 677 of June, No. 67 on age 788 of July, No. 68 on page 914 of August, No. 69 on page 1037 of Septemfer, No. 70 on page 1197 of October, and No. 71 on page 1315 of November.
