INDUSTRIAL A N D ENGINEERING CHEMISTRY
Hudson, B. E., Jr., and Hauser, C. R., I b i d . , 63, 3156 (1941). Kuta, W. M., and Adkins, H., I h i d . , 52, 5391 (1930). McElvain, S. M., Ibicl., 51, 3124 (1929). MoElvain, S. SI.,“Organic Reactions,” Vol. Is’, p. 256, New York, John Wiley 8: Sons, 1948. National Distillers Chemical Co., Division of National Distillers Products Corp., Cincinnati, Ohio, Tech. BUZZ.101, 104 (1952). Pierce, 0. R., Purdue Cniversity, unpublished studies. Roberts, D. C., and hicElvain, S. AT., J . Am. Chem. S o c , 59,
Claisen, L., Ber., 20, 651,655, 2178, 2188, 2191, 2194 (1887). Fisher, N., and McElvain, 8 . M., J. Am. Chem. SOC.,56, 1766 (1 934).
Gilman, H., “Organic Syntheses,” Vol. I , p. 230, h-ew York, John Wiley & Sons, 1932. Gilman, H., and Blatt, A. H., “Organic Syntheses,” 2nd ed., Vol. I, p 235, New York, John TWey & Sons, 1941. Hanslev. V. L.. I N D .E N G . CHEM..39., 55 (1947) . Ibid.,
43,1759 ’(1951).
Hansley, V. L., J. Am. C”hem.Soc., 57, 2303 (1935). Ransley, V. L. (to E. I. du Pont de Nemours & C o . ) , U. S. Patents 2,394,608 (Feb. 12, 1 9 4 6 ) ; 2,487,333 (h-ov. 8, 1949); 2,487,334 (Nov. 8 , 1949). Hauser, C. R., and Hudson, B. E., Jr., “Organic Reactions,” Vol. I, pp. 266, 278, 290, 291, New York, John Wiley & Sons,
2007 119371. , I
Siggia, S., “Quantitative Analysis via Functional Groups,” p. 17, i i e v York, John Wiley & Sons, 1949. Snell, J. M., and McElvain, 8. M., J. Am. C h e m SOC.,53, 750 (1931 1.
Zbid., p. 2310.
Titerlu. -4.W..J . Chem.
1942.
Soc.. 81. 1520 (1900): Ber., 35, 2321
(1902).
Hauser, C. R., and Renfrew, T T . B., Jr., J . Am. Chem. Sac., 59,
Weygand, C., “Organic Preparations,” Interscience Publishers. 1945.
1823 (1937).
Hudson. B. E.. Jr.. Dick, R. H., and Hauser. C. R., Ibid., 60, ’
Vol. 45, No. 2
RECEIVED for review -4pril 2 5 , 1952.
1960 (1938).
p. 410,
h-ew York,
ACCEPTED October 7, 1952.
Pyrolysis of Propane and Butanes at Elevated Pressure H. J. HEPP AND F. E. FREY Research Division, Phillips P e t r o l e u m Co., Bartlesville, Okla.
R
EACTIONS taking place and products formed when paraffin hydrocarbons are subjected to the action of heat at loiv pressure have been extensively investigated, but only in a few instances has the effect of higher pressures been explored. Egloff, Thomas, and Linn (6)investigated the pyrolysis of propane and the butanes at atmospheric and 100 pounds per square inch pressure under nonliquid-forming conditions and found t h a t pressure decreased olefin formation and increased reaction rate, Second-order decomposition reactions with a lower activation energy than the first-order reactions were postulated t o explain the observed kinetics. Tropsch, Thomas, and Egloff (9) pyrolyzed propane and t h e butanes at 250 and 725 pounds per square inch. From this work it was concluded that bimolecular decomposition reactions of the types proposed b y Frey and Smith ( 3 ) :
2C3H8 --+ become important a t the higher pressures. T h e yield of olefins was decreased and the yield of liquid products increased as pressure was increased. Pearce and Nemome ( 6 ) studied the thermal decomposition of n-hexane at 15,000 pounds per squareinch gage and found t h a t products boilingabove, as well as below, hexane were formed. Very little olefin survived in the gaseous products. T h e commercial application of high pressure pyrolysis of low boiling hydrocarbons
C3H6
+ Cz& + CH,
CRACKING b-
EXPANSION
TAR
FLOW h
Figure 1.
has been described by Keith and Ward (& 5 ) and by Bogk Ostergaard, and Smoley ( 1 ) . The present investigation had as its principal object the determination of gas and liquid products formed when propane and the butanes are pyrolyzed at 1500 and 2500 pounds per square inch. Gaseous products were rather completely analyzed, and the liquids as completely as circumstances would permit. ‘
APPARATUS
T h e apparatus employed is shown in Figure 1. The electrically heated tube furnace was 36 inches long and had a bore of 1.25 inches. It was mounted with a small downward slope in the direction of flow. The reaction tubes proper were made of 18 chrome, 8 nickel alloy steel and had inside diameters of ‘/a and 1 1 4 inches, Since this alloy has some carbon-forming tendency, close-fitting, thin-walled copper tubes were telescoped within the alloy tubes and soldered a t both ends t o prevent hydrocarbon flow outside the liner. Reaction tubes of small internal diameter and comparat i v e l y great length were chosen t o avoid convection and to give FURNACE a fair linear velocity. MERCURY RESERVOIR A close-fitting twisted copper ribbon was inserted into the quarterinch tube t o prevent convection. I n order t o ensureeven tempera’LE CONTAINER t u r e s , the reaction Ek tubes were t i g h t l y 3ESSURE C Y L I N D E R wound with copper sheet bo a diameter that would just slide -4pparatus
3
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1953
O F BUTANE TABLE I. PYROLYSIS
AT
41 1
2500 LB./SQ. INCH GAGE
Expt. No. Av. temp., ' F. Av. pressuSe, lb./sq. in. gage Exposure time, min.
28 972 2530 2.4
31 977 2330 5.45
30 977 2725 13 0
9 1024 2530 0.42
18 1026 2517 1.56
7 1018 2370 2.2
8 1020 2310 4.0
Butane reacted, % IC X lo-*, sec. Composition of products, wt. % H2 CHI CeH4 CzHe CaHe CEH~ C4H8 CdHio Gasoline Residue Coke
18.0 1.4
40.2 1.6
60.0 1.2
11.3 4.8
42.0 5.8
57.0 6.4
62.5 4.1
0.01 2.58 0.57 2.38 3.21 1.34 1.29 82.03 6.51 0.08
0.02 5.0 0.3 6.7 3 2 3.9 2 4, 59.8 15.43 3.1 0.15
100.00
100.00
100.00
8.0 11.5 4.8 18.3 3.7 15.5 38.2
8.5 13.9 5.4 17.0 3.9 10.0 41.3
Total
Nil ___
Composition of total liquid product, wt. %a 11.1 Pentenes 7.9 Pentanes 7.7 Hexenes 29.9 Hexanes 6.5 Heptenes 23.5 Heptanes 12.4 Heavier Total
__
-
__
100.0
100.0
100.0
Densit of 400' F. end point 0.70 gaeofne at 60' F., g./ml. Density after olefin removal Olefin content, liquid vol. % a Fractions include cyclics and aromatics.
... ...
0.72
into the furnace, I n all of the experiments subsequent t o 12, a fairly close-fitting copper rod was inserted into the exit end of the reaction tube, extending just into the reaction zone, for the purpose of speeding up the withdrawal of reaction products into the cold end of the tube. This rapid cooling of reaction products was considered necessary to arrest uncontrolled reaction t h a t might have occurred had temperature drop been slow. Temperatures were determined by means of four calibrated thermocouples placed at 6-inch intervals between the reaction tube and the copper sheeting. Temperatures were usually kept constant t o about f 9" F. during a run. The flow rates were low enough t o ensure t h a t the true temperature of the gases undergoing reaction was essentially the same as t h a t of the reaction tube. As shown in the diagram, the pressure on the system was supplied b y compressed nitrogen. Nitrogen pressure was transmitted t o a mercury reservoir, and the mercury in turn forced the sample into the reaction tube. A weighing device was used t o give warning when the remaining charge volume was low. Presaures were measured by two Bourdon tube gages a t the mercury reservoir and the furnace exit. During an experiment the pressure decreased 50 to 200 pounds per square inch depending upon the quantity of material processed. The initial and final pressures were averaged to obtain the pressure of the run. PROCEDURE
With the furnace a t slightly above operating temperature and the reaction tube filled with nitrogen a t atmospheric pressure, the valve on t h e charge sample container was slowly opened. As soon as t h e exit gage showed full pressure, the expansion valve was cracked t o establish a predetermined differential on the flow meter following the tar trap, and the gas vented. As soon as furnace temperature became constant and sufficient product passed t o ensure t h a t all "off-condition" starting material had been vented, the trap was changed and the gas from the flowmeter led directly into the kettle of a low temperature fractionating column which previously had been cooled t o liquid nitrogen temperature. The experiment was terminated b y bringing the pressure in t h e t a r trap t o atmospheric, disconnecting from the expansion valve, and plugging of the tar trap. The charge container valve was then closed, products in the reaction tube vented, the tube flushed with nitrogen, and cooled quickly by removing from the furnace.
tKi%
0.71
... ...
-
__
___
100.00
100.00
100.00
.
.
0.06 12.43 0.26 12.18 3.61 7.55 2.26 37.51 20.79 3.31 0 04 100.00 . . I
I
...
...
...
... ... ... . I .
__
... ... ... ...
100.0 0.662 0.666 39
...
0.72
...
...
...
...
0.707 0.687 28
I n the case of the n-butane runs a t 1022' F., the procedure was varied somewhat. After operating conditions had been established as outlined above, the effluent sample was collected by displacing mercury from a sample receiver at full operating pressure. Flow rate was maintained a t the same value as employed in establishing operating conditions by releasing mercury through an accurately calibrated flowmeter. The sample was later transferred by mercury displacement t o the low temperature analytical column and sufficient pressure, about 500 pounds per square inch, was maintained to ensure t h a t no weathering took place during transfer. ANALYSISOF PRODUCTS. I n all cases t h e reactor effluent, comprising gases, gasoline, and the portion of trap liquid distillable at 1 t o 2 mm. of mercury and room temperature, was condensed in a low temperature analytical column. The sample waa fractionated and the individual gaseous fractions analyzed by combustion or absorption methods. The olefin content of the Cd fraction from the butane runs and of higher boiling fractions was determined by titration with a 1% solution of bromine in carbon tetrachloride. The pentanes and heavier fraction, which included hydrocarbons boiling to about 300' F., were distilled into a weighed glass bulb, sealed off, and reweighed. This fraction, plus the hydrocarbons distilled from the t a r trap liquid t o about 400" F. were combined and called gasoline. The maximum error in gasoline values is not more than 10% and usually is much less. Gasoline was analyzed by fractionating into C5,C g , C,, and C8 and heavier cuts. The olefin content of the individual fractions was then determined by titrating with a 1%solution of bromine in carbon tetrachloride. Because of the small size of fractions available, t h e error in separations is probably 5 t o 10%. I n Run 31 (Table I V ) a larger sample was available, and the accuracy is better. I n some instances, the olefin content of the full-range gasoline was determined by reacting with mercuric acetate in glacial acetic acid at 50' C. for 12 hours, and recovering the unreacted hydrocarbons by steam distillation. The resulting distillate contained 4 t o 8% olefins as determined by bromine titration, and this was added to the mercuric acetate value. The tar remaining in the trap after distilling at 1 to 2 mm. of
412
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 2
IC0
into lower molecular weight olefins, paraffins, and hydrogen. This decomposition is follored very closely by synthesis reactions involving the olefins, which yield higher boiling products, ii-ormally liquid products appear a t an early reaction stage, f o l l o ~ e dby tar and finally by coke as reaction time is prolonged. The gaseous products were largely saturated, with only small concentrations of olefins surviving. As previously noted by Tropsch et al. (Q), pressure decreased the yield of low molecular weight olefins. The concentration of olefins was increased as temperature was raised, or pressure lowered. Hox-ever, a t a given temperature-pressure condition, olefin concentration tended to reRACTICAL OPERATING C O N D I T I O N P R A C T I C A L OPERATING C O N O l T l O N main stationary over a wide butane decomposition range. Olefin production and consumption were substantially balanced in this region. I The Cd and lighter primary products formed by iso- and n-butane at 2500 pounds per square I inch gage were determined by plotting the experimental data of Tables I and VIII, expressed as moles per 100 moles butane reacted, against the per cent decomposed, and extrapolating to zero I I conversion ( 7 ) . The results are listed in Table I I11 along with the primary decomposition prodI I I ucts as determined by Steacie et al. (8) at atmosI I pheric pressure. I I The primary decomposition of n-butane was not appreciably affected by pressure or by temperature in the range covered. Since n-butane decomposes mainly by carbon-carbon bond scission, this perhaps was to be expected. The dehydrogenation of isobutane to isobutene was retarded. There is not enough data for propane to permit this sort of analysis, since olefin yields are sensitive t o temperature at the drastic conditions required for propane pyrolysis. The total number of moles of butene and lighter Figure 2. n-Butane Pyrolysis a t 2500 Pounds per Square Inch Gage products a t 2500 pounds per square inch pressure was 160.7 for n-butane, and 176 for isobutane per 100 moles butane reacted. A carbon balance indicates that only about 85% of the reacted butane formed mercury a t room temperature was transferred to a small flask light products. The 15% which did not form light products and distilled a t atmospheric pressure to a vapor temperature of reacted t o form higher boiling products either in the primarv 390" to 400" F. The weight of the distillate was included in the process, or by a rapid secondary reaction which was not diagasoline fraction, and the residue in the tar fraction. tinguished from the primary process in the present work. The tar values reported are the sum of the residue boiling The effect of increasing reaction time on the composition of above about 390" F. and tar recovered from the reaction tube the normally liquid products made a t 2500 pounds per square after the run. Tar was recovered from the reaction tube by flowing 20 to 40 cc. of chloroform through the reactor, filtering to remove carbon, and evaporating the chloroform. TABLE 11. PYROLYSIS O F n-RCTANE AT 1500 LB./SQ.I N C H Coke was determined by scraping out the dried reaction tube GAGE with a copper brush and weighing. Some additional coke was 5 51 49 50 E x p t . No. occasionally recovered from the chloroform washings. The coke 1112 1022 1022 1022 -4v.temp. ' F. A v . press&, lb./?q. in. gage 1740n 1450 1533 1470 determination was difficult because of the small bore of the tubes 1.2 1.5 2.1 Exposure time, min. 0.04 and the small amount of coke usually present. The results are Butane reacted, % ' 17 1 47.4 49 0 60.5 78 0 8.9 7 5 7 4 not particularly accurate when coke is small. IC x 1 0 - 3 , see. MATERIALS USED. The hydrocarbons emploved were sepaComposition of products, wt. 70 Hz 0.09 0.03 0.02 0.04 rated from natural gasoline by exhaustive fractionation and con8.97 12.64 2.43 8.51 CHa 0.48 1.11 0.90 0.34 CZF4 tained less than 1% homologs and other impurities. lj.59 3.42 7.56 8.85 cas I'
q t
I
DISCUSSION OF D A T A
n-BUTANE.n-Butane was reacted at pressures of 1500 and 2500 pounds per square inch gage, and temperatures of 977", 1022", and 1112" F. The summarized data are listed in Tables I and 11, and the 2500-pound data are plotted in Figure 2. The general course of the reaction is illustrated by the data on n-butane, plotted in Figure 2. The butane first decomposes
C3H6 CaHs C4Hs C4HlO Gasoline Residue Coke
6.14
1 13 0.72 82.91 2.78 0.27 0.0
6.81 5.24 3.07 52.60 13.84 1.44 0.0
6.55 4.58 2.96 51.00 14.89 1.84 0.0
0.36 6.98 3.00
39.50 16.02 3.62
0.77 ___-__-Total 100,oo 100.00 100,oo 100.00 a The feed was diluted with nitrogen; this is the partial pressure of the n-butane.
10
9 -
TABLE 111. INITIAL DECOMPOSITION PRODUCTS AT ATMOSPHERIC AND 2500 LB./SQ.INCH GAGEPRESSURE
Hydrocarbon CHd CSHB CaHs
Primary Products, Mole % n-Butane Isobutane 2500 Lb./sq. Atm. 2590 Lb./sq. Atm. in. gage pressure (8) in. gage pressure ( 8 )
.
31.9 31.8 4.0
33.9 33 9
CeHi CeHa
11.6 15.3
15 2 14.1
0.5 ...
HZ
0.7 4.7 100.0
2.9
11.9 11 .9 100.0
CIHB Total
39.3 36.4
14 14
...
...
... 100.0
.
S
I
0 9 0.9 35 35 99.8
-
-
8 -
7 6 e 5 -
7
4 .
X
.'
3 2 -
8
Lo
B
1 9 -
%
a
8 -
*5x
;-
6R L3 3
/
-
2 5 0 0 P.S.I. D I T A
-
2:
3 -
inch gage pressure is shown in Table I. I n run 28, where the reaction was stopped after 2.4 minutes, hexanes and heptanes were the most abundant products formed. These are the expected products from the alkylation of ethylene and propylene, the main olefins resulting from the initial decomposition, with the excess of n-butane present. Increasing the time t o 5.45 minutes resulted in a large increase in products boiling above heptane. Pentane was also increased while other fractions were decreased. At 13 minutes these same trends were continued, except t h a t there was no further decrease in olefins. Increasing the temperature from 977" to 1018O F. (experiments 7 and 30) under otherwise equivalent conditions, resulted in an increase in olefins and decrease in products boiling above C,. All of these samples gave a positive test for aromatics upon nitra-
olefins and paraffins were present. Cyclohexane was present in a relatively large amount. Benzene and toluene amounts were small. More drastic cracking produces larger yields of cycloparaffins and aromatics.
TABLE IV.
COMPOS~TION O F GASOLINE FROM BUTANE R u n 31 Amount,
Wt. %
Component Low boiling pentenes 2-Methylbutene-2 Pentene-2 Isopentane n-Pentane
1.2
4.1 4.2 3.1 10.7
Hexenes Hexanes Cyclohexane Benzene Heptenes Heptanes : Boiling point,
5.7 8.8
11.7 1.5 C., 80-90
90-97 97-105 Toluene Octanes-octenes-toluene Residue a t 200' C.
Properties Indexof refraction, 250 c.
Density, des
...
... ... ...
...
0:752
... ...
4.5
...
1.6
0.693
9.8 5.6
1.7 8.4 17.4
... ...
... ...
... 1:3 i 5 2
.. .. ..
... ...
1,392
0 775 0.826
1:437
:
... ...
.g'f
2 -
Q
;-
d
E
~
6 --
b 1500 ?SJ. D 4 T A
1
4 x 3 -
2 -
1 975 1000 1025 1050 1075 1100 1125 1150 1175
liquids a t low percentage decompositions, to dark brown or black viscous products at extensive reaction. T a r formation began slowly after gasoline formation was initiated, and increased rapidly with increasing conversion. The per-pass yield of normally liquid products increased with increasing reaction time up t o the longest times studied. However, in practice, coke formation limits the per-pass destruction of n-butane t o about 5oy0. At 2500 pounds per square inch pressure and 5oy0destruction, the yield of gasoline boiling range products was about lSyo by weight. This is about 36y0 based on butane reacted. I n recycle operation, with complete retention of Ca's and C4's in the cycle, the ultimate yield at these reaction conditions is about 48% by weight. The single-pass yield of gasoline range products is affected by temperature, pressure, and conversion level as shown in Table V. PROPANE. Propane was reacted at temperatures of 977", 1022O, and 1112O F. at 2500 pounds per square inch pressure,
TABLE V.
...
The cracking and synthesis reactions occur simultaneously in the reaction zone, and involve not only the normally gaseous components, but also the gasoline and higher boiling products. As a result, when reaction time is prolonged, part of the gasoline is converted into tar and the tar is partly converted into coke. Coke deposition starts rather sharply when sufficient high boiling tar has been formed t o reach its dew point, and begins to condense on the walls of the reactor. The products boiling above gasoline varied from mobile, yellow
0
Hydrocarbon Propane n-Butane
Isobutane
EFFECTOF REACTIONCONDITIONS O N SINGLE-PASS GASOLINE YIELD
Gasoline Yield, Wt. % of Hydrocarbon Reacted 2500 Lb./sq. in. gage 1500 Lb./sq. in. gage % Reacted 977' F. 1022' F. 1112' F. 1022" F. 1112' F. 20 42.4 37.4 26.6 24.9 30 34.7 32.4 32 2
40
26.0
30 50
60
38.1 37.6 35.0 28.5
20 30
... ...
40
40 50
.. .. ..
...
27.9
36.'2
... ...
35.9 33.7 27.6 31.2 30.3 25.0
22.1
...
... ...
31.3 29.2 26.0
...
...
...
...
...
...
...
...
.. ..
.. ..
...
... ... ...
INDUSTRIAL AND ENGINEERING CHEMISTRY
414
TABLEVI. Expt. No. Av. temp O F. Ay. preeszre, lb./sq. in. gage Exposure time, min. Propane reacted, Yo k X 10-4,sec. Inside diameter reaction tube, in. Vol. reaction zone, CC.
Flow rate, g./min.
Properties of gasoline Density dm Density'after olefin removal, dzo Olefin content. liquid vol. % a Estimated.
PYROLYSIS OF PROPANE AT 2600 LB./SQ. INCH GAGE
25 979
26 976
27 982
12 1022
10 1022
11 1063
13 1108
2700 10.4 14.5 2.4
2645 24.1 27.2 2.2
2445 53.3 48.6 2.1
2650 3.06 14.9
2575 10.0 31.5 6.4
2700 7.9 49.6 16.7
2490 0.67 35.2
8.8
2910 0.69 37.2 112.5
2900 1.9 52.6 66.0
0.23
0.23
0.11
0.11
0.11
0.11
0.11
0.11
14.7 0.072
14.7 0.0275
3.14 0.118
3.14 0.034
3.14 0.0414
2.88 0.378
2.88 0.557
2.88 0.186
0.02 7.50 0.19 4.18 0.84 72.78 1.22 2.15 10.02 0.93 0.17
0.05 17.62 0.41 10.61 0.88 51.53 1.30 2.78 8.24 3.07 3.51
0.02 2.99 0.43 2.85 1.07 85.10 0.71 0.85 5.91 0.07
0.04 9.62 0.21 7.29 0.81 68.48 1.27 2.86 8.74 0.62 0.05
0.06
0.07 11.48 1.03 6.59 2.44 62.81 2.32 2.37 10,OG 0.83
0.07 21.78 0.43 11.22 1.38 47.42 0.93 2.45 6. 60 4.24 3.50a
100.00
100.00
...
...
... ...
... ...
100.00
...
100.00
40 1112 1450 0.45 26.3
Composition of products, we. % H2 C H4 CZH4 CzHo C3H6 CaHs i-CnHs n-CaHs i-CnHio n-CdHm Gasoline Residue Coke
38 1112 1465 0.72 41.2
1.1
1 .o
0.11 2.52 0.194
6.59 1.30 4.98 3.47 73.74 0.43 1.22 1.15
...
6.90 0.16 Nil
~
100 00
...
...
0.11 2.52 0.32 0.06
100.00
... ,..
...
PYROLYSIS OF PROPASE AT 1500 LB./SQ. ISCH GAGE
Expt. 3-0. Av. temp., F. Av. pressure, lb./sq. in. gage Exposure time, min. Propane reacted, % k X 10-2, seo. Inside diameter reaction tube, in. Val. reaction zone, cc. Flow rate, g./min.
Total
21 1110
0.23
and a t 1112' F. a t 1500 pounds pressure. The data are listed in Tables VI and VII. The reaction is similar to the n-butane reaction, except that reaction conditions for a given per cent decomposition are considerably more drastic. This results in lower per-pass yields of gasoline range products, and tar and coke appear earlier in the reaction. TABLEVII.
108.0
19 1103
14.7 0.169
Composition of products, wt. % 0.02 HP 2.72 CHI 0.29 CzHa 1.51 CPHE 0.74 C5HE 85.46 CsHs 0.80 C4Hs 0.65 C4H10 Gasoline 7.53 Residue 0.28 0.0 Coke Total
Vol. 45, No. 2
0.09 12.29 1 81 8 45 5.09 58.86 0 54 1.28 1 96
...
8 65
0 99
39 1112 1445 1.9 64.7 0.9 0.11 2.52 0.067 0.12 22.86 1.07 14.28 3.33 35.28 0.62 0.79 2.01 1.82 13.77 1.89 2.13
__
0 0
-
100 00
100 00
The gasoline range products were not subjected to detailed analysis. However, as shown in Table VI, the gasoline contained 20 t o 3070 of unsaturates. Paraffins, cycloparaffins, and aromatics were present, and the content of ring compounds increased with increasing propane conversion. The single-pass yield of gasoline range products passed through a maximum of about 10 weight % a t 30 to 40% conversion as shown in Table VI. Coke formation limits per-pass propane conversion to about 30y0. At this condition gasoline range products yield is about 10% by weight, corresponding to about 33% of the propane reacted. The influence of operating variables on per-pass yield is shown in Table V. The results of four experiments in which isoISOBUTAKE. butane was reacted a t 1022' F. and 2500 pounds per square inch
0.06
18.68 0.16 12.36 1.30 50.42 1.00 3.78
9.35 2.05 0.84a
8.42 0.99 6.32 3.31 64.83 1.90 1.75 11.96 0.39 0.07
...
__
__
___
__
100.00
100.00
100.00
100.00
0.715
0.752
...
0.710
0.770
...
...
...
21
32
28
0.770
gage pressure are listed in Table VIII. The courbe of the reaction is much the same as previously detailed for n-butane. Table VI11 lists the composition of the gasoline formed at, an early stage in the reaction. Heptanes were the most abundant product, but hexanes %-erealso present in substantial quantity, despite the small amount of ethylene generated from isobutane. At least part of the heptanes may have been formed by propylene-isobutane alkylation. The hexanes may have resulted from polymerization of propylene with hydrogen transfer, or by reaction of isobutane with ethylene formed by secondary cracking. The gasoline yield on a once-through basis v a s intermediate between propane and n-butane. However, in recycle operation there is little difference in the yield from the two butanes.
TABLEVIII.
.--.
PYROLYSIS OF ISOBUTANE AT 2500 LB./SQ. ISCH GAGE
Exnt. -No.~
~~
Av. temp.,
22 lOZ2 25aO 1.33
23 1022 2440 2.01
13.0 1.75
21 5 2.02
~~
F.
-477. pressure, lb./sq. in. gage
ExDosure time, min.
Isobutane reacted, % k X 1 0 - 3 , sec. Val. reaction zone, cc. Charging rate, g./min.
3.29 0.355
3.29 0,209
Composition of products, w t . yc Hz CHa
0.05 2.58
0.05
C2H4
CZHE C3HE CsHs C4HS C4Hl0 Gasoline Residue Coke Total Composition of gasoline, wt. % a Psntenss Pentines Hexenes Hexanes Heptenes Heptanes Octenes Octanes Heavier
0.06
0.22 3.22 1.36 2.28 87.05 3.06 0.12
...
4.46 0.09 0.56 3.17 3.37 3.34 78.45 6.03
0.48
24 1024 2910 4.18
1022 2535 5.07
43 1 2 25
49.5 2.23
3 29 0 116
0.06 11.22 0.13 2.95 2.13 8.64 2.66
56.93 13.17 2.06 0 05
32
2.52 0.064
0.06 14.23 0.07 4.04 1.78 9.83 3.16 50.54 12.42 3.25 0.62
____
... __
___
___
100.00
100.00
100.00
100.00
...
... ,
.
... .. ... ... ..
...
8.0
11.1 53 11.9 6.9 34.3 4 2 9.2 9.1
Total ... 100.0 a Density, dzo: C Ecut, 0.686; C I cut, 0.704; Cs cut, 0.735
...
...
... ...
... ... ...
. .
February 1953
INDUSTRIAL A N D ENGINEERING CHEMISTRY
As would be expected from the somewhat more refractory nature of isobutane compared with n-butane, carbon appears somewhat earlier in the decomposition. The maximum per-pass decomposition with reasonable freedom from coking is about 43% for isobutane compared with about 50% for n-butane a t the 2500 pounds per square inch gage level. KINETICS
The first-order reaction velocity constants are plotted in Figure 3. For comparison, the reaction velocity constants for propane and n-butane (8)at atmospheric pressure are also shown. While the present experiments were not aimed especially at obtaining kinetic data, and pressure and temperature were not controlled as closely as might be desired, it i s believed that the data are sufficiently accurate t o indicate the relative magnitude pf the effect of high pressure on reaction velocity. Despite the complex reactions occurring, the data plot on a reasonably straight line for both propane and n-butane. However, activation energies calculated from the slope of the lines are higher than a t atmospheric pressure. It is not known whether this is real or is the result of experimental errors. Both
415
compounds reacted at substantially higher rates under pressure. The reaction velocity of isobutane was intermediate between propane and n-butane. LITERATURE CITED
(1) Bogk, J. E., Ostergaard, P., and Smoley, E. R , Proc. Am. Petroleum Inst., I I I , 21, 17 (1940). (2) Egloff, G., Thomas, C. L., and Linn, C. B., IND.ENQ.CHEM., 28, 1283 (1936). (3) Frey, F. E., and Smith, D. F., Ibid., 20, 948 (1928). (4) . . Keith. P. C.. Jr.. and Ward. J. T.. Chemistru & Industru. -~ 55. 532 (1936). (5) Keith, P.C., Jr., and Ward, J. T., Refiner Natural Gasoline M f r , , 14,506 (1935). (6) Pearce, J. N.,and Newsome, J. W., IND.ENG.CHEM.,30, 588 (1938). (7) Schneider, V.,and Frolich, Per K., Ibid., 23, 1405 (1931). (8) Steaoie, E. W. R., and Puddington, I. E., Canadian J. Research, 16B, 176,260, 411 (1938). (9) Tropsch, H.,Thomas, C. L., and Egloff, G., IND.ENQ.CHEM., 28, 324 (1936). RECEIVED for review June 9 , 1952. ACCEPTED September 20, 1962. Presented before the Division of Petroleum Chemistry at the 121st Meeting of the AMBRICAN CHEMICAL SOCIETY, Milwaukee, Wis.
Preparation of Carotene Concentrates from Dehydrated Alfalfa Meal H. Lt MITCHELL, W. G. SCHRENK, AND RALPH E. SILKER Kansas Agricultural Experiment Station, Manhattan, K a n .
UCH consideration has beengiven to methods of preparing carotene concentrates from chlorophyll-containing plant tissues. Such concentrates have potential use as a means of supplying vitamin A potency to feeds. Their preparation would be of importance to the alfalfa dehydration industry because it would expand the present market for dehydrated alfalfa meal. Numerous procedures have been devised for preparing carotene concentrates. I n the more recent methods adsorbents have been employed for the removal of chlorophyll and xanthophylls. Thus, calcium hydroxide (6) and activated carbon black (4) have been advocated for this purpose. The ideal adsorbent should adsorb the carotene weakly, or not a t all, it should have a strong adsorptive affinity for chlorophyll and xanthophylls, it should be inexpensive, and it should be regenerated easily for further use. I n this laboratory, tricalcium phosphate was found t o meet these requirements. TESTS O F ADSORBENTS
Primary consideration was given to the search for an adsorbent which would not adsorb carotdne but wouldadsorb chlorophyll and xanthophylls. The first screening test consisted of pouring a Skellysolve B extract of alfalfa meal on a 25 X 150 mm. column of the adsorbent being tested and observing the resulting separation of pigments. The substances tested were sodium carbonate, calcium hydroxide, magnesium oxide, basic magnesium carbonate, aluminum sulfate, magnesium sulfate, calcium sulfate, barium carbonate, tricalcium phosphate, and portland cement. By the column technique it was readily seen t h a t sodium carbonate, aluminum sulfate, calcium sulfate, and cement did not adsorb
the chlorophyll tightly enough to permit separation. On the other hand, magnesium oxide and calcium hydroxide adsorbed all pigments, and it was necessary to wash the column with a mixed solvent t o elute the carotene. Basic magnesium carbonate, barium carbonate, and tricalcium phosphate gave good separation of the pigments, although carotene moved more slowly on the magnesium and barium carbonates than it did on the tricalcium phosphate. Mann (5) used steamed bone meal as an adsorbent in the quantitative determination of carotene in plant tissue. Although bone meal is considered to be essentially calcium phosphate, it actually has a more complex structure, which appears t o be similar t o the apatite minerals (1). Tricalcium phosphate appeared to fit more nearly the requirements listed above for a good adsorbent, and i t was chosen for further tests. Because of its limited capacity, an ordinary adsorption column is not suitable for processing large amounts of plant extract i n the laboratory. If the carotene is not adsorbed appreciably by the adsorbent, it should be possible t o increase the amount of extract which can be processed by stirring the adsorbent with the plant extract in a large container and removing the adsorbent by filtration. Finely powdered tricalcium phosphate was added with stirring to a Skellysolve B extract of alfalfa contained in a large beaker. Phosphate was added until upon settling no green color was apparent in the supernatant liquid. An aliquot of the supernatant liquid was chromatographed on activated magnesia (Westvaco No. 2641) and the carotene was eluted with a solution of 4y0 acetone in Skellysolve B (6). The carotene concentration of this eluate was measured with a Beckman
