Pyrolysis of Propane and the Butanes Olefin Concentrations, Yields, and Related Factors GUSTAV EGLOFF, CHARLES L. THOMAS, AND CARL B. LINN Universal Oil Products Company, Chicago, Ill.
N THE effort to utilize better the paraffin hydrocarbons in natural or refinery gases, considerable work has been directed toward producing the more chemically active olefins from these gases. The pyrolytic method of effecting such a change was the basis of the many experiments which Egloff, Schaad, and Lowry (7) have reviewed. Many of these studies were made to determine the reactions which take place and their mechanisms (5, 9, 12, I S , 14, 16, 18, 20, 93). Still others were concerned with the larger scale application of these reactions
sessed a catalytic activity which decomposed the hydrocarbon gas into sooty carbon and hydrogen. This action was eliminated by pickling the tube in hot 17 per cent hydrochloric acid and treating with hydrogen sulfide at room temperature and then at 600" C. After such treatment neither sooty carbon formed nor did the tubes regain their activity after being burned out with oxygen. During their use the tubes did not become brittle. The reaction zone was considered to be the 50.8 X 1.58 cm. section of the tube, with a volume of 9 5 CC. (1-.6,11,15,91,25). Figure 1 illustrates the apparatus used in the pyrolysis of proWith the improvements in experimental technic now availpane, n-butane, and isobutane. The gas was passed from a cylinable, i t is possible to determine with greater accuracy the der, through a pressure-regulating valve, into the reaction factors which play important parts in the pyrolysis reactions. tube. After passing through the reaction zone, the pressure was released through a needle valve, the liquid product collected in Such data as the maximum olefin concentrations obtainable a graduated receiver, and the gas with the yields, the amount of passed through a meter into the samoriginal hydrocarbon reacted, and pling bottles for analysis. A flowthe effect of temperature, reaction meter in the exit line gave evidence of variations in the exit gas rate. The Propane and the butanes time, and pressure are available in feed rate was calculated from the exsome cases, but there seem to be no were studied in A l l e g h e n y pansion of the gas during the heating. data correlating all of these factors In experiments where n-butane or m e t a l t u b e s at atmospheric under strictly comparable c)ondiisobutane was pyrolyzed, each was and 7 kg. per sq. cm. prescharged from a cylinder surrounded tions. The present study supplies by a steam jacket in order to obtain s u r e s in the range 600" to these data for propane b e t w e e n the required operating pressure. 700" C. Increasing the reac600" and 700" C. a t 1 kg. and 7 kg. In the experiments carried out at per sq. cm. Similar data are given 1 kg. per sq. cm., the gas was passed tion time increased the conthrough a calibrated flowmeter into for n-butane at 600" to 650" and centration of olefins in the the reaction tube. The exit gas was isobutane a t 650" C. collected in a gasometer where the exit reacted gas to a maximum, rate was measured. At feed rates after which the concentration Experimental Procedure above 15 litera per hour the gas was metered into the reaction tube by a d e c r e a s e d with further inTwo f u r n a c e s of the same type wet test meter. were used at 1 and 7 kg. per sq. cm. crease in time. Increasing the pressure, respectively. They conpressure increased the reacsisted of electrically heated aluminum Analytical Methods bronze blocks, 61 cm. long, containtion rate at 600" C. A t higher ing a single hole, 2.85 cm. in diameDETERNINATION OF EXPA4XSIOS. temperatures this effect disapter, and equipped with an automatic The molecular weights of the gas temperature control. peared. Apparently, then, a charged and the exit gas were deThe temperature was measured by portion of t h e r e a c t i o n i s an iron-constantan thermocouple used termined by the Dumas method, with a potentiometer. The thermoThe ratio, molecular weight of the second-order, and its activacouple was placed in a well in the gas charged divided by molecular tion energy is less than the block with the hot junction midway weight of the exit gas, gives a in the block. There was no thermofirst-order r e a c t i o n or reaccouple in the reaction tube, since it quantity defined as the Dumas extions. Increasing the pressure was assumed that the temperature in pansion, which theoretically is equal the reaction zone was the same as that also decreased the maximum to the volume of exit gas divided measured in the block. by the volume of gas c h a r g e d . concentration of olefins obThe reaction tubes were of 18-8 chromium-nickel steel and were conWhen carbon or liquid polymer is tainable in the reacted gas. structed as indicated in Figure 1. The formed, the D u m a s e x p a n s i o n Conditions for m a x i m u m welds in the reaction tube were antends to be higher than the true nealed by heating to 1040" C. for 30 yields of olefins are given in value. Under the condibions of minutes and quenching in w a t e r detail. after annealing. The tubes Iposthese experiments, however, the 1283
1284
INDUSTRIAL AKD ENGINEERIZG CHEMISTRY FIG. I
APPARATUS
FOR PRESSURE
PYROLYSIS
A
M
A - F R O M CHARGING 5 T O C K . 8 -AUTOMATIC TEMPERATURE CONTROL. C -THERMOCOUPLE. D -INSULATION. E A L U U I N U U BRONZE BLOCK. 762 C U O.D. X Z.65CM. L O . X 8 D 9 6 ~ LONG. ~ . ? -ELECTRIC HEATING ELEMENT. 0 - A L L E G H E N Y METAL REACTION TUBE 21.34UM 0.0. X 1 5 . 7 9 M M . I D . X 1 O . ~ C U . L O N G . H - A L L E G H E N Y M E T A L INLET L O U T L E T T U B E 5 le26 MM. 0 0 X 5.46 MU. 1.D.X 211 CM. LONG J NELOLE VALVE. K WELDS L LIQUID R E C E I V E R . U - T O G A S METER I SAMPLE B O T T L E
both in method and in operating technic of the Podbielniak method, such variations were obtained. For this reason the results reported in this paper have been confined as far as possible to data obtained by the other methods described (absorption analyses and expansion). The analyses by lowtemperature fractionation plus absorption were used only to obtain a relation between the expansion and percentage paraffin converted. I n this case it was possible to use three or four analyses so that errors in one particular analysis were not so serious, Table X shows that considerable quantities of +butylene are reported as being present as a pyrolysis product of isobutane. So far it has not been proved that the analysis is wrong; however, the result seems improbable a t this time. Until further evidence is available, all of the C, fraction is considered to be isobutylene.
Definition of Terms
-
-
formation of carbon and liquid occurred to such a slight degree relative to the gas processed that the Dumas expansion equaled the true expansion within the experimental error involved in its determination. GAS ANALYSIS. During an experiment, gas samples were taken a t a number of feed rates in order to obtain the olefin us. contact time values. These samples were analyzed for olefins by passing into the usual reagents. In the experiments where isobutane was charged, 63 per cent sulfuric acid was used to remove isobutylene. The concentration of propene plus n-butenes was determined by passing into 87 per cent sulfuric acid, and the ethylene by bromine water. The concentration of total olefins was checked by passing a fresh sample into bromine water. In addition to the methods described, several complete analyses were made a t various percentage conversions of paraffin hydrocarbons under the same conditions of temperature and pressure. These were made by low-temperature fractionation according to the Podbielniak method ($1) in addition to a combination absorption and combustion analysis of the fractions. The olefin concentrations found by these two methods were in fair agreement, although in most cases the discrepancy was greater than the experimental error of the absorption method. However, excellent agreement was obtained in the concentration of total olefins. One of the chief sources of error in the method of low-temperature fractionation plus absorption has been the determination of the olefins in the fractions from the low-temperature distillation. Such fractions often contain 50 per cent olefins. Fractions containing large amounts of isobutylene were particularly difficult to analyze accurately. Some difficulty was also noticed in separating the Cf fraction when there was hardly enough present t o give reflux a t the top of the column. These errors and possibly others in the Podbielniak method lead to some confusion in the results, For example, in Table IV a t 600" C. two analyses are reported, one showing 45.4 and the other 44.4 per cent propane conversion. Even though some error may exist in the contact time and even in the temperature, such close percentage conversions should give product concentrations which agree much more closely than the results indicate. The same situation is observable in Table IV a t 650' where there are two analyses indicating 42 per cent propane conversion; yet the analyses differ widely. I n spite of the attempt to eliminate as far as possible errors
VOL. 28, h-0.11
To avoid any misunderstanding it seems advisable to define some of the terms to be used: OLEFINCONCEZ~TRATION is the concentration of the designated olefin in volume per cent in the gas as it leaves the reaction tube. OLEFIWYIELDis the number of volumes of olefin formed when 100 volumes of the original hydrocarbon react. CONVERSION PER PASSor per cent reacted per pass is the percentage of the original hydrocarbon which has reacted in one passage through the reaction zone. CONTACT TIMEOR REACTION TIMEis the arithmetical average time in seconds that the hydrocarbon remains in the reaction volume of the tube under the experimental conditions used. It was calculated from the formula: where CT = contact time, sec.
V E = vol. at reaction temp., cc. t = total time of expt., sec. V o = cc. gas (standard conditions) charged to apparatus in time t V1 = cc. gas (standard conditions) removed from apparatus in time t P = o erating pressure, atm. (1.035 kg. per sq. cm.) T = aEs. temp.
Since V R comes:
=i
95 cc. in these experiments, the formula beFIG.,? P Y R O L Y S I S O F PROPANE A T 6 0 0 . AN0 IKG.PER CM?
1
I
OM 110
lM
4 0
w W
UO W
M
uo lwO
IO
20 30 40 50 %PROPANE R E A C T E D PER PASS
60
70
INDUSTRIAL AZD ENGISEERING CHEMISTRY
ZOVERIBER, 1936 CT
5.187tP X lo4 T(V1 1'0)
FIG. 3
+
= -
1285
0
PYROLY515 OF PROPANE A T BSO'AND
IKG.
PER CM?
U
PRODUCTION RATEis the number of volumes of a product formed in one volume of reaction space per hour. This factor has little theoretical interest but is important practically since it determines the size of the reaction equipment necessary for a desired amount of product. IOi
Propane
1
I
I
II
II
I
IO
20
I
I
1
I
I
I
I
01
I
II
w
m
Propane was studied in detail a t 600°, 650°, and 700" C., both a t 1 and 7 kg. per sq. cm. Tables I and I1 give the results obtained a t 1 kg.; Tables I11 and IV give the corresponding results a t 7 kg.
TABLEI. OLEFIN CONCENTRATIONS, YIELDS, AND RELATED FACTORS IN THE PYROLYSIS OF PROPANE AT 1 Kct. PER SQ. CM. Concn.
Contact Time See.
Expansion
C2H1in Exit Gas
%
Vol. C ~ H I / Vol. CsHd 100 Vol. 100 Vol. Conon. Calcd. C3Ha CaHs C3H6in % CaHs Reacted Exit Gas Reacted" Reacted
%
170
.It,600' C. 34 2.4 7.5 38 2.6 6.3 10 39 3.3 12 37 4.1 12.5 41 5.2 25 35 7.9 35 33 9.5 42 29 9.8 11.7 49 36 11.9 46 33 11.4 56 29 A t 650' C. 15 45 40 1.12 5.3 6.0 3.3 44 22 45 8.4 8.2 1.1s 6.4 40 42 34 11.3 10.8 1.27 12b 42 3s 38 12.0 11.8 1.34 16 52 36 40 14.8 13.2 1.42 23 32 41 67 17.8 13.8 1.54 44 6 .. .. .. 12.1 1.68 19.5 83 b .. .. .. 9.0 1.96 18.0 150 .. .. .. 5.6 2.11 15.7 286 .It 700' C. 46 49 1.7 3.8 1.03 1.8 0.5 34 44 8.8 3.6 2.8 1.07 0.7 43 41 11 4.3 4.1 1.09 0.9b 49 50 16 1.13 7.1 6.9 1.4 36 30 38 8.8 9.5 1.24 1.7 42 37 42 13.3 11.6 1.34 2.8b 40 48 35 13.1 10.9 1.2s 2.9 56 36 38 1 4 . 6 1 4 . 0 1.45 5.4 29 43 76 20.4 13.5 1 61 6.7b . . . . ,. 2 1 . 6 1 3 . 6 1 , 7 3 9.7 23.1 6.4 2.06 35b 2 3 . 9 1 1 . 7 1 . 8 6 19 23.4 8.0 1.94 36 3.7 2.21 19.6 66 0 Per cent conversion = 125 (expansion -1) when expansion < 1.65. b Experiments in which t h e gases were also analyzed by low-temperature fractionation (Table 11). 7.1 7.26 14 19 28b 54 103 105b 196 198b 383
1.06 1.05 1.08 1.10 1.10 1.20 1.28 1.23 1.39 1.37 1.45
2.4 2.3 3.6 4.0 4.7 7.4 9.0 10.0 12.6 11.2 11.3
The data in Tables I and I11 were compiled from absorption analyses and expansion., Within certain limitations, the expansion was found to be proportional to the amount of paraffin hydrocarbon reacting. This would seem reasonable if a certain volume of propane in decomposing yielded a fixed ratio of reaction products which, in turn, would give a definite increase in the expansion. Using the data in Tables I1 and IV, it was possible to establish this relation. The equation, TABLE 11.
H2 CHI C2H4 CZHB CzHa C3Hs Calod. expansion Obsvd. expansion yo conversion
I
I
I
I
G z
i? Y x
0
x
m
PROPANE
40
RLACTLD
LO
rcn
PASS
Per cent propane reacted = 125 (expansion-l), expresses this relation best for the present data. After the pyrolysis has proceeded so far that secondary reactions occur t o an appreciable extent, this relation no longer holds. Just where this relation becomes so inaccurate as to produce appreciable errors is not known. In the present work the relation has not been used in experiments where liquid products were formed or where the expansion was greater than 1.65, This last figure may be somewhat too high so that the percentage propane reacted is reported as being higher than it actually is. On the whole, it does not seem that this error will be larger than the experimental error. Using this relation to calculate the percentage propane reacted, it was then possible to calculate the yields of ethylene and propylene under various conditions. These values are also included in Tables I and 111. To portray better the trends in the reactions, the data in Tables I and I11 are plotted in Figures 2 to 7 . The highest concentration of propylene (14 per cent) is obtpined a t 700" C. and 1 kg. per sq. cm. with 35 per cent of the reacting propane being converted into propylene a t 5.4 seconds contact time. The highest ethylene concentration in the exit gas is 23.9 per cent (Table I) a t 700" and 1 kg. per sq. cm. with a contact time of 19 seconds. The ethylene yield under these conditions is not known but is estimated to be about 50 per cent of the propane reacting. At 7 kg. per sq. cm. the highest propylene concentration
CONCESTRATIONS OF PRODUCTS IN EXITGASFORMED BY PYROLYSIS OF PROPANE AT 1KG. PER SQ.CM. (IN VOLUMEPERCENT)
7 2 sec. 2.2 2.9
...
1.6 3.3 89.3 1.05 1.05 6.2
600' C. 28 seo. 105 sec. 4.7 7.3 14.9 5.5 9.2 3.6 1.6 4.9 10.0 6.7 77.8 53.7 1.11 1.27 1.22 1.10 31.8 13.3
199 sec. 5.4 20.2 9.5 9.0 14.4 38.8 1.32 1.35 48.9
-650' 12 see. 7.8 7.3 9.7 7.4 11.1 56.7 1.23 1.27 30.4
C.44 sec. 12.1 22.7 12.6 6.4 16.4 29.8 1.50 1.54 55.3
83 sea. 11.0 28.9 19.6 6.2 9.0 25.3 1.62 1.68 58.9
-
0.9 sec. 3.9 1.6 2.9 5.3 4.6 81.8 1.09 1.09 11.3
~
700' C.-2.8 sec. 6.7 sec. 10.4 15.6 12.1 4.4 12.2 45.3 1.35 1.35 38.6
12.8 27,l 20.3 4.8 17.0 18.0 1.61 1 61 70.4
~ 35 sec. 13.8 43.1 25.5 6.5 6.1 5.0 2.06 2.06 89.5
VOL. 28, NO. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
1286 I
There is considerable error in making this extrapolation,
TABLE111. OLEFINCOXCENTRATIONS, YIELDS,AND RELATED especially since the analyses a t low concentrations are subject IN PYROLYSIS OF PROPANE AT 7 KG. PER SQ. CM. FACTORS to considerable experimental error. Consequently it is a Contact Time
Expansion
Vol. C%H4/Vol. CaHs/ Concn. Concn. Calcd. 100 Vol. 100 Vol. C1H4 in C3Hain % CsHs CaHs CaHa Exit Gas Exit Gas Reacteda Reacted Reacted
%
SeC.
1.04 1.06
7.0 10 14 22 31 54 59b 128 1356 l66b 267 303 646
1.14 1.18 1.26 1.20 1.45 1.37 1.39 1.59; 1.780
2.0 2.8 3.2 5.1 7.2 8,Q 8.4 9.7 10.2 10.6 8.7 8.0 6.4
5.7 7.3 9.7 12b 15 19b 21 27b 32 41 5Ob 56
1.14 1.20 1.22 1.30 1.31 1.38 1.42 1.48 1.52C 1.58C 1.63C 1.70C
6.8 7.6 9.9 11.6 12.3 13.0 12.4 12.7 13.3 13.5 12.9 12.1
1.8 2.2 2.7b 4.0b 4.4 5.4 6.0b 6.8 7.1 7.9 9.6 9.9b 11 12 14
1.07 1.13 1.17 1.30 1.33 1.43 1.45 1.52 1.46 1.56 1.63 1.67 1.65 1.66 1.69
3.4 5.6 6.2 11.4 12.5 13.5 14.1 14.9 15.1 15.4 15.0 15.3 17.1 16.2 16.2
1.08
1.58
% At 600' C. 2.0 2.7 3.2 5.2 7.0 8.8 8.2 10.0 10.0 9.9 9.0 9.3 5.8 At 650" C. 5.7 7.3 8.7 9.9 11.0 11.7 13.0 11.9 12.4 11.8 10.5 10.2 At 700' C. 2.8 4.9 6.3 10.2 11.0 12.7 13.0 13.0 12.4 13.6 13.5 13.0 12.5 12.7 12.3
6.0 7.5 10 17 22 32 25 56 46 45
41 3s 34 34 38 35 40 25 30 32 19 17
.. ..
..
.
17 25 27 38 39 48 52 60
41 40 34 35 37 35 39 26 30 30 19 20
..
I
..
46 36 45 40 41 37 34 31 31 26 27
29 26 22
8.7 16 21 38 41 54 56 65 57 70 79
42 40 38 39 40 36 37 35 39 34 31
34 35 38 35 36 34 34 30 32 30 28
..
.. ..
.. ..
..
..
..
38 35 39 34 37 34 35 29
..
n-Butane The pyrolysis of n-butane was studied s t 600" and 650" C., a t 1and 7 kg. per sq. cm. The relation between expansion and percentage n-butane reacted was established in the same way as for propane. At 1 kg. per sq. cm:
..
..
..
little surprising that independent workers, using different reaction systems (quartz and 18-8 chromium-nickel steel) and different methods of analysis, should obtain results which agree so closely with those of the present study. Figures 2 t o 7 show that the olefin concentrations are consistently lower a t 7 than a t 1 kg. per sq. cm. This probably occurs because the higher pressure favors reactions between the olefins produced, giving other products such as liquid, which was found in some cases. That the propylene maxima both a t 1 and a t 7 kg. per sq. cm. occur a t shorter contact times than the maxima for ethylene is probably due to the greater tendency of propylene to undergo secondary reactions. At 600" C. the concentrations of ethylene and propy'ene were equal. As the temperature was raised to 700" C., the concentration of ethylene increased more rapidly than that of propylene. An explanation for this is offered in the section on "Kinetics."
Per cent n-butane reacted
Per cent n-butane reacted
..
Hr CHI CrH4 CzHs CnHa CIHE Cslcd. expansion Obsvd. exqansion conversion 0
-
166 sec. 0.2 25.0 8.0 12.1 12.2 42.5 1.31 1.36 44.4a
12 see. 8.8 9.4 10.5 17.8 9.7 43.8 1.325 1.30 42.0"
=
115 (expansion-1)
Having established a way to estimate the percentage conversion, it became necessary t o devise means for estimating the percentage n-butylenes in the exit gas. From the lowtemperature fractionations which were made (Tables VI and VIII), it was found that the percentage n-butylenes in the
TABLE-IV. CONCENTRATION OF PRODUCTB IN EXITGASFORMED BY ~ O L (IN VOLUME PERCENT) C.135 sec. 5.7 20.4 10.8 12.6 10.6 39.9 1.37 1.37 45.4"
100 (expansion-1)
At 7 kg. per sq. cm:
5 Per cent C3Hs reacted = 125 (expansion -1) when expansion < 1.65. b Experiments in which the gases were also analyzed by low-temperature fractionation (Table IV). c A liquid product was also formed.
-----600° 59 see. 0.9 19.6 7.4 3.9 9.0 59.2 1.21 1.20 28.5
=
650' C. 19 sec. 27 seo. 5.7 6.7 17.8 20.3 11.3 9.0 8.7 16.6 11.0 15.3 34.0 44.4 1.423 1.305 1.48 1.38 51.6 42.0''
Y S I SOF
50 see. 6.6 40.6 13.1 15.4 7.4 16.8 1.93 1.63 67.6
PROPANE AT 7 KG. PER SQ. CM.
-
2.7sec. 3.7 17.8 7.5 3.0
7.0 60.8 1.238 1.17 24.8
700' C.
4.0 sec. 6.9 15.3 16.1 5.1 11.8 44.8 1.32 1.30 40.7
6.0mc. 8.3 22.4 13.3 8.5 12.4 31.7 1.45 1.45 54.0
9.9 sec. 8.4
17.6 16.7 12.4 15.8 26.9 1.475 1.67 60.3
Section on "Analytical Methods" discusses these inconsistencies.
was 13.5 per cent a t 700' C., giving a yield of 30 per cent of the reacted propane a t a contact time of 8 seconds. The highest ethylene concentration was 17 per cent a t 700" C. with an estimated yield of 35 per cent a t a contact time of 10 seconds. (Because of the large percentage of propane reacting a t the ethylene maxima, it was not possible to determine the yields by the expansion method. For this reason the ethylene yields have been estimated from the nearest low-temperature fractionation analysis.) It is also of interest to compare the yields (volumes of olefin per 100 volumes of propane reacted) obtained by extrapolation to zero per cent decomposition. This comparison follows: 650" 725' Temp., O C. 1 'Pressure (kg./sq. om.) 1 48 CaH4 39 50 42 .CsHa a Schneider and Frolich (85).
600 1 41 41
650 1 49 49
700 1 50 46
600 7 42 42
650 7 51 42
700 7 44 35
exit gas varied between 2 and 5 per cent. Further, a curve could be drawn giving a relation between the percentage conversion and the percentage n-butylenes which is probably as accurate as the experimental method. From this curve and the values for the percentage propylene plus n-butylenes found by the absorption analyses, i t was possible to determine the individual percentages of propylene and n-butylene. These values with the contact time are given in Tables V and VI1 and have been plotted in Figures 8 to 11. In the curves showing the ~olumesof olefins per 100 volumes of n-butane reacted, a few of the points do not lie on the curves drawn. This is usually in the region of small percentage conversion-i. e., isobutane > n-but'ane. Egloff and Parrish (6) gave a summary of the evidence on relat,ive thermal stability. In the present work this same relat'ive stability obtains. If a more stable substance requires a longer time to undergo a given percentage conversion a t a given temperature than some less stable sui stance, then it is interesting to note (Table XIII) that propane a t 600" C. and 1 kg. per sq. cm. is more stable than at 600" and 7 kg. Similarly, n-butane a t 600" and 1 kg. is more stable than n-but'ane at' 600" and 7 kg. This effect of pressure on the apparent stability can be carried still further, as shown in Table XV. Table XV indicates that it takes propane longer to give 39.8 per cent conversion a t 600" C. and atmospheric pressure than at, 585" C. and 51 kg. per sq. em. Similarly n-butane at 555' and 51 kg. per sq. em. seems to react faster than a t 600" C. and atmospheric pressure under the conditions indicated in Table XV. These data indicate rather plainly that pressure plays an important role in the apparent stability of the hydrocarbons under consideration. At present it seems that any absolute measure of the stability must take into
1292
ISDUSTRIAL ASD ENGINEERING CHEMISTRY
VOL. 28, NO. 11 FIG, I 3
P Y R O L Y 4 1 S OF i - B U T A N E AT O O ' A N D
I h C . P E R CM2
0
c
Y L w
2 ?
$ 8
7 n
d
I
20
IS
-im
I
1.0
'
I50
0 5 z
140
:la0 w
IO
IM 1%
140
130
uo
Lzo
I IO
I10
UIO 0
IO
20
30
%I-NTANL
SO 60 R L A C T C D P E R PASS 40
70
100
10
0
LO
30 40 50 60 5 i d U T A N L R L A C T L O PER PASS
?O
consideration not only the temperature but also the pressure and percentage conpersion of the hydrocarbon whose stability is being measured. As long as relative stabilities are measured under strictly comparable conditions, the above factors disappear.
in Table XVI. The A Fo298values are given for 298" K. with both starting material and products at unit activity. At 600" to 700" C. the absolute values of A F" will be quite different, but it seems possible that the differences between the several reactions will be of the same order of magnitude. It seems significant that the bimolecular reactions (3,7,8,12,and TABLEXV. TIMEREQUIRED TO EFFECT A GIVENPERCEXTAGE 13) are among the most probable if these data may be used as criteria. CONVERSION UNDER DIFFERENT CONDITIONS Conversion
%* 21.5 39.8
At 585O C., 51 kg./sq. cm. See." 52.2 86.8 7
At 550' C., 5 1 kg./sq. om.
a
Propane At 600' C . ,
7 kg./sq. cm. 30 80
pressure Sec. 40 142
n-Butane At 600' C.,
At 600' C., a t m .
Sec.
7 kg./sq. cm. See. 33
43.4 47 55.3 82 50 From Tropsch, Thomas, and Egloff ( $ 5 ) .
Kinetics
A t 600' C., a t m .
pressure See.
57
In the preceding paragraphs on the effect of temperature and pressure certain apparently anomalous effects of these factors are mentioned. For example, increasing the reaction CHANGES FOR PYROLYTIC TABLEXVI. FREEEXERGY REACTIOXS~
105
~~~~
Energetics of t h e Reactions It is interesting to tabulate the possible reactions taking place in the present study and to calculate the free energy changes. Tropsch, Thomas, and Egloff (16)gave the reactions which probably occur. Using the recent data for the A F O m values of the hydrocarbons published by Parks (19), it is possible to calculate the free energy changes. The equations and the calculatcd A F O mvalues for the reactions are given
4F0m C3Hs --f CaHe f Hz CzHa CHI CzH4 2CaHs -+DCHI f CiHs f CaH6 n-CbHio CiHa f HZ n-CaH~o CHI CaHs CzHa CZHE n-CaHio 2n-CaHio CH4 f CaHs n-CiHs 2C2He f n-CdHa 2n-C4Hio Iso-C4Hlo +iso-CiHs i- H Z Iso-CIHio ----f CHI 4- CaHe Iso-C~Hio CzH4 CzHs 2 iso-CdHlo CH4 CsHa iiso-CdHa 2 iso-CiHio 2CzHe iso-C~Hs a Calculated from Parks d a t a ( 1 9 ) .
+ + + + + + + + +
--+ + +
++ +
+
Cal./rnol. 21040 9740 6700 19080 7100 12140 5140 7840 18960
7240 12280 5160 7360
Reaction No.
1 2 3 4
5 6 7 8
9 10 11 12 13
NOVEMBER. 1936
INDUSTRIAL AKD ENGINEERING CHERIISTRY
1293
temperature increases the reaction rate roughly 7 to 8 fold a t 1 kg. per sq. cm. but only 4 fold a t 7 kg. The other effect was that increasing the reaction pressure from 1 to 7 kg. per sq. cm. a t 600" C. increased the rate of reaction. .4t 650" and 700' this effect diminished or disappeared. An explanation for both of these effects may be obtained from a study of the kinetic behavior of the second-order reactions 3, 7, 8, 12, and 13 shown in Table XVI. .4n increase in pressure accelerates these reactions because of the increase in concentration of the substance undergoing reaction (10, Zdl $6). An increase in pressure a t 600" C. increases the reaction rate of the second-order reaction, and the rate of the firstorder remains about the same with the result that the total rate has been increased by increasing the pressure. If we assume that these reactions have a lower energy of activation than that of the first-order reactions, then the effects are explicable. Increasing the temperature increases the reaction rates of the first-order reaction more than it does of the second-order, owing to the larger activation energies of the first-order reactions. Since the reactions a t 1 kg. per sq. cm. are dominated by the first-order reaction, this rate is increased more than the reactions a t 7 kg. per sq. cm. where the second-order reactions play a major role. This explains the observation that increasing the temperature increases the reaction rate more a t 1 kg. than a t 7 kg. per sq. cm. Following this reasoning it seems that, if the temperature is increased enough, the rate of the first-order reactions will be increased to such an extent that the second-order again plays a minor role even a t 7 kg. This situation seems to have been reached in the present experiments a t 650" C. for the butanes and a t 700" for propane, and explains the observation that increasing the pressure to 7 kg. per sq. cm. does not increase the reaction rate a t 700" C. This same assumption s e e m to explain the effect of temperature on the relative concentrations of ethylene and propylene in the reactions of propane. The ethylene and propylene concentrations were equal a t 600" C. As the temperature increased to 700", the ethylene concentration was consistently larger than the propylene. Table XVI shows that propylene is formed in reactions 1and 3, ethylene in reaction 2. If reactions I and 2 are accelerated in about the same ratio by the temperature increase a t the expense of reaction 3, then ethylene will tend to increase in concentration (and yield) over propylene until reaction 3 plays only a negligible part in the system. For reactions 1 and 2 to be accelerated in about the same ratio by a temperature increase, their activation energies should be similar. According to Marek and Neuhaus (17) the reaction velocity constant for dehydrogenation (reaction 1) is greater than that for demethanation (reaction 2) between 550' and 675" C. From the Marek and Neuhaus data the authors have calculated that the average energy of activation of reaction 1 is 75,600 calories per mole and 75,800 for reaction 2. In other words, the activation energies are equal between 550" and 675" C. so far as is known.
concentration of propylene was 16.5 t o 17.5 per cent at both temperatures and pressures studied, with a yield of 42 to 44 per cent. The shortest contact time required t o produce this concentration and yield was 18 seconds a t 650" and 7 kg. per sq. cm. The maximum concentration of ethylene was 21 per cent a t 650", 1 kg., and 142 seconds. The olefin production rates at 7 kg. are 8 t o 10 times those a t atmospheric pressure. 3. Isobutane was studied a t 650" C. under I and 7 kg. pressure. The maximum isobutylene concentration was 21 per cent a t 1 kg. and 21 seconds, with a yield of 50 per cent. A t 7 kg. the maximum isobutylene concentration was 17 per cent with a yield of 45 per cent a t a contact time of 12 seconds. The maximum propylene concentration was 12 per cent a t 1 kg., giving a yield of 22 per cent a t a contact time of 39 seconds. Isobutylene was produced about 1.7 times as fast a t 1 kg. as a t 7 kg. and the production rate of propylene a t 7 kg. was 6 times as fast as a t 1 kg. 4. In all the experiments studied, the effect of increasing the reaction time was t o increase the amount of hydrocarbon reacting and to increase the concentration of olefins to a maximum, after which an increase in time produced a decrease in olefin concentration. When two or more olefins were produced simultaneously, their maxima usually occurred a t different times; the propylene maxima took place a t shorter contact times than those of ethylene. 5. Increasing the temperature increased the maximun concentrations of olefins obtainable from a given gas. A temperature increment of 50 " increased the reaction rate roughly 7 t o 8 fold a t 1kg., but a t 7 kg. per sq. cm. the increase was only 4 fold. 6. Increasing the pressure from 1 to 7 kg. per sq. cm. increased the reaction rate a t 600" C., but this effect disappeared a t 650" with n-butane and a t 700" with propane. The same pressure change increased the production rates of the olefins by 6 t o 8 fold with the exception of isobutane which was actually decreased 1.7 fold by the application of 7 kg. per sq. cm. pressure. 7. By taking into consideration certain second-order reactions resulting from pyrolysis and assuming that they have a lower energy of activation than the first-order readtions, it is possible to explain these apparently anomalous effects of temperature and pressure. Thermodynamic evidence is presented t o indicate that these second-order reactions are a t least as probable thermodynamically as others that are known t o take place. 8. The stabilities of the hydrocarbons studied decrease in > isobutane > n-butanethe following order-propane when tested under comparable conditions. The apparent stability of these hydrocarbons is decreased considerably by the application of pressure under certain temperature conditions.
Summary
for carrying out the lowtemperature Podbielniak fractionations used in this work.
1. Propane was pyrolyzed a t 600", 650", and 700" C. under 1 and 7 kg. per sq. cm. pressure. The highest concentration of propylene was 14 per cent, obtained a t 700" C., 1 kg. per sq. cm, contact time of 5.4 seconds, and 35 per cent yield. The highest ethylene concentration was 23.9 per cent a t 700°, 1 kg., and 19 seconds, with a yield of 50 per cent based upon reacted propane. At 7 kg. per sq. cm. the olefin concentrations and yields were slightly lower but the production rate of the reaction equipment was 5 to 8 times that a t 1 kg. 2. n-Butane was studied a t 600" and 650' C. a t 1 and a t 7 kg. per sq. om. The n-butylene concentration in the exit gas varied between 2.5 and 4.8 per cent. The maximum
Acknowledgment Acknowledgment is made to M. J. Strauss and J. B. Grutka
Literature Cited (1) Cambron, Can. J. Research, 7, 646 (1932). (2) Cambron and Bayley, Ibid., 9, 175, 583, 591 (1933). ( 3 ) Cooke, Swanson, and Wagner, ,VatZ. Petroleum News, 27, No. 47, 33 (1935). (4) Dunstan, Hague, and Wheeler, IND.ESG. CHmf., 26, 307 (1934). (5) Ebrey and Engelder, Ibzd., 23, 1033 (1931). (6) Egloff and Parrish, paper presented before Division of Petroleum Chemistry a t 13th Midwest Regional Meeting, Louisville, Ky., Oct. 31 to Nov. 2 , 1935. (7) Egloff, Schaad, and Lowry, J. Phys. Chem., 34, 1617 (1930). ( 8 ) Egloff and Wilson, IXD. ENG.CHEW,, 27, 917 (1935).
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Frey and Hepp, Ibid., 25, 441 (1933). Frey and Smith, Ibid., 20, 948 (1928). Frolich and Wiesevich, Ibid., 27, 1055 (1935). Hague and Wheeler, J . Chem. Soc., 1929, 378. Hurd, Parrish, and Pilgrim, J . Am. Chem. Soc., 55, 5016 (1933). Hurd and Spence, Zbid., 51, 3353 (1929). Keith and Ward, Natl. Petroleum News,27, N o . 47, 52 (1935). Lang and Morgan, IND. ENQ.CHEX.,27, 937 (1935). Marek and Neuhaus, Ibid., 25, 516 (1933). Neuhaus and Marek, I b i d . , 24, 400 (1932). Parks, Chem. Reo., 18, 325 (1936). Pease, J. Am. Chem. Soc., 50, 1779 (1928).
A n industrial waste survey was made covering the most highly industrialized area of New Jersey. Using as units the employees of each industry, the results were integrated a n d e s t i m a t e s made for the entire waste p r o d u c t i o n of t h e state. The quantities of wet sludge produced by the industries amounted to 700,000 tons a year, as compared to 900,000 tons of sewage sludge. The settleable solids amounted to nearly 100,000 tons a year as c o m p a r e d with 450,000 tons of sewage sludge. The estimated “population equivalents’’ for the indust r i e s a m o u n t e d t o over 300,000 tons or about twothirds of the total domestic waste produced by the entire population of the state.
VOL. 28, NO. 11
(21) Podbielniak, IND. ENQ. CHEM.,Anal. Ed., 5, 119, 135, 172 (1933). (22) Podbielniak, Oil Gas J., 29, No. 52, 22, 140 (1931). ENG.CHEM.,23, 1405 (1931). (23) Schneider and Frolich, IND. (24) Steacie, Hatcher, and Rosenberg, J . Chem. Phys., 4, 220 (1936). (25) Sullivan, Ruthruff, and KuentzeI, ISD. ENG. CHEM.,27, 1072 (1935). (26) Tropsch, Thomas, and Egloff, Ibid., 28, 324 (1936).
RECEIVED July 3, 1936. Presented before the Division of Orgsnic Chemistry a t the 91st Meeting of the American Chemical Society, Kansai City, Mo., April 13 t o 17, 1936.
STREAM POLLUTION
HE problem of stream pollution in New Jersey is intensified by the density of population and industrial development. Fully two-thirds of the population resides in the northern part of the state, where manufacturing is of primary importance and greatly diversified. Textile dyeing and finishing, chemical, silk manufacturing, tanning, and steel plants and power laundries are among those producing large quantities of waste. Some of the waste is highly putrescible, some is poisonous, and some contains large quantities of suspended solids capable of settling in the streams. Investigations of the major streams produced a fair idea of the condition and the degree of pollution caused by domestic and industrial waste. The sewage pollution of the interstate stream amounts to a sludge production (met) of over 900,000 tons a year, and the oxygen required for stabilization (bday B. 0. D.) is more than 750,000 pounds of oxygen daily. Since the pollution load put upon the streams by domestic sewage is only a part of the total load, and very little information was available t o indicate the part played by industrial wastes, studies were undertaken to estimate the volume, type, and strength of the industrial wastes discharged.
IN NEW JERSEY Importance
of Industrial Waste WILLEM RUDOLFS New Jersey Agricultural Experiment Station, New Brunswick, N. J.
The survey was conducted with the aid of a number of chemists and engineers employed under the C. W. A. and E. R. A., and of employees of the P. W. A., covering nine counties of the most highly industrialized area of the state. During the survey, 1792 industries were visited, and definite information and samples were obtained from 1213 of them. Since many industries were of the same type, samples of wastes were gathered from 401 industries, 251 of which were completely analyzed and 150 partly analyzed for confirmation. The water consumption of the industries from which samples were collected amounted to 54,600,000 gallons daily; the liquid wastes discharged amounted to 43,651,000 gallons a day. Rather complete analyses were made, consisting of different types of suspended solids, sludge volume, oxygen consumed, acidity, alkalinity, chlorides, pH, etc.
Analytical Results The large volume of analytical results’ was grouped more or less arbitrarily, following, in general, the national census of industries. This classification made possible the determination of stream pollution by groups of industries and of the general effect on localized conditions, and permitted the calculation of the gross pollution caused by all industries in the state. A total of 205 different industries from which samples v-ere collected were selected for calculations to determine the volume and strength of the waste produced per employee per day. 1 Detailed results will be published in a bulletin from the N. J. Agricultural Experiment Station.
