803
INDUSTRIAL AND ENGINEERING CHEMISTRY
- 4 5 6 7 8 9 3 4 5 G 7 6 Q PH OF fATLIOUOR FIGURE 13. EFFECT OF OIL CONCENTRATION, EMULSIFICATION, AND PH VALUEOF OF FINISHED LEATHER
FAT LIQUORS ON STRENGTH
EFFECT OF MOISTURE IS LEATHER Chrome-tanned calfskin may be either fat liquored and then colored, or the reverse, depending upon the individual manufacturer. In either case the skin contains a definite amount of water a t the time of fat-liquoring. Figure 14 shows the oil adsorbed when chrome-tanned calfskin containing varying amounts of moisture is fat-liquored in various oils. From this figure it is seen that, in the cases of moellon, raw cod oil, cod oil and emulsifier, and moellon and emulsifier, the oil adsorbed decreases as the moisture of the leather increases. I t is also seen that for sulfonated cod oil or for sulfonated oils in general, as the moisture of the leather increases, the oil adsorbed increases also. This fact is to be expected, since the
sulfonated oils emulsify readily with water, and the water present in the leather has no effect upon this emulsification. From Figure 1.2 it would a p p e a r t h a t salted egg yolk is adsorbed as readily a t a n y moisture content. T h e a d d i t i o n of emulsifier to a f a t liquor containing moellon materially aids oil adsorption, giving a m a x i m u m adsorption a t a b o u t 50 per cent moisture. For p r a c t i c a l purposes, ,,hrome-tanned
Vol. 24, No. 7 I
s
g, ; 2
2
; e SALTED EGG YOLK
'
20 30 40 50 60 70 PER CENT nOlSTURL i N LEATHER
FIGURE 14. EFFECT OF
h b I S T U R E IN CHROME SKIN ON O I L ADSORPTION DURING FAT-LIQUORING
c a l f s k i n , just after s h a v i n g , will attain between50 and BO per cent moisture when drummed for 30 minutes; thus, reading off values for the various oils a t 50 per cent moisture will give an indication of the oil adsorbed under practical conditions. AC riNOWLEDGMEST
The writers wish to acknowledge gratefully the support given this work by the Hunt-Rankin Leather Company, of Peabody, Mass., and to acknowledge their permission to publish the results of the investigation. The writers also wish to express their appreciation of the analytical work of Robert Stafford of the Hunt-Rankin Leather Company. RECEIVED February 10, 1932. Presented before the Divmos of Leather and Gelatin Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 to September 4, 1931.
Vapor-Phase Cracking of Gasoline A Study of Optimum Conditions for Production of Unsaturated Gases from Gasoline H . ~ R O LA.D CASSAR,Organic Chemistry Department, Massachusetts Institute of Technology, Cambridge, Mass.
T
HE work described in this paper was undertaken to determine what was involved in the vapor-phase cracking of gasoline a t atmospheric pressures so as to yield unsaturated gases whose value is steadily increasing in the chemical 'ndustry. The gasoline selected was an untreated straight-run distillate made from Pennsylvania crude. Its Engler distillation showed 34 per cent off a t 212' F. (100' C.), and an end point of 410' F. (210' C,). The aniline point was 60" C.; hence it consisted mainly of paraffin hydrocarbons. This was also shown by its very low knock rating which was characteristic of straight-run distillates from this kind of crude. This type of gasoline was selected since its low kncck rating makes it less valuable for use in automobiles than most gasolines.
EXPERIMENTAL PROCEDURE The apparatus used consisted of a %foot (0.9-meter) length of 1-inch standard iron pipe, packed with pumice stone (1300
pieces per 100 grams) and heated for a length of 30 inches (76.2 cm.) by 1 kw. running through chrome1 A wire, gage.18; the whole was suitably heat-insulated by magnesia covering. The mercury positive displacement method of feeding the gasoline i t o the apparatus was used. Temperatures were read by means of a thermocouple loosely slipped into a thermometer pocket a t the exit of the tube; the gases and vapors produced were sent through a spiral condenser and receiver, the noncondensable gases being collected in two 20-liter glass carboys, graduated in liters and filled with water. The temperatures experimented with ranged from 500" to 700' C., and the feed rates ranged from 40 to 240 cc. per hour. Standard Pyrex and combustion tubes were found unsuitable for the higher temperatures. The volume of the 30 inches (76.2 cm.) of tube is 340 cc. A11 rates are reported as liquid time of contact, which figure takes care of the volume of the cracking tube used and the rate a t which the gasoline was fed. Liquid time of contact is
July, 1932
803
I R D G S T R I A L AND E N G I N E E R I Z G C H E M I S T R Y
CONSTANT-RATE RESULTD The constant-rate results are plotted in Figure 1. TOTAL GAS. The volume of the gas evolved, in liters per liter of gasoline charged, is plotted against temperature in " C. (curve A , Figure 1). Within the range examined, the total gas evolved increases directly with the temperature and is a linear function of it. The empirical equation is G =: (7' - 480) 2.38 volume gas evolved per unit volume charge T = temperature, O C.
where G
FIGURE 1. CONSTANT-RATE RESULTS (Liquid time of contact, 5.66 hours) Distillate a8 Deraentage of charge (upper scale) ........ _ . Total gas (loker-soaie) C. Percentage olefins in gas upper scale) D. Percentage aromatics in distillate (upper scale) E . Percentage olefins in distillate (upper scale) A.
(1)
=
This simple empirical linear relationship seems to be generally true. Curves A , B , C, and D in Figure 2 show how some of Gault and Hessel's results on hexadecane form straight lines too.
~~
B.
equal to the volume of the hot tube (in liters) divided by the rate of feed (in liters per hour); since the figure has one dimension (that of time) cubic feet or centimeters can be substituted for liters and give the same figures. This method of reporting rates facilitates comparison with other investigations, as it does not involre the dimensions of the cracking tube used. Thus Gault and Hessel ( 1 ) cracked hexadecane in a quartz tube, 2 X 64 cni., at the rate of 1 cc. per minute, corresponding to a liquid time of contact of 3.29 hours. At this rate they obtained 126 liters of gas per liter of feed a t 615" C. Under similar conditions, Pennsylvania straight-run gasoline gave 230 liters. A better index of rate from a theoretical standpoint would be the vapor time of contact. Unfortunately this involves the average molecular weight of the gasoline (a comparatively uncertain figure) and the percentage gasified a t different points in the tube; consequently, for purposes of comparison with different apparatus and different stocks, its value is problematical. The olefin content of the gas was determined by absorption in bromine water. The unsaturates in the distillate were approximately determined by absorption in 88 per cent sulfuric acid, and the aromatics by the aniline point method on the reqidue, checked by the nitric plus sulfuric method.
LITCW Gw PERlrreu or HEXRDECRNC. FIGURE 2. GASEVOLVED DURING CRaCKING OF HEXlDECANE (1) Curve A B C D
Liquid time of contact Hours
0.825 1.65 2.47 3.29
Two main series of runs were made: one at constant rate (60 cc. per hour, or 5.66 hours liquid time of contact) and at temperatures ranging from 500' to 700" C.; and the other at a constant temperature of 600" C. and at rates varying from 1.4 to 8.6 hours liquid time of contact.
600
u2 J8 400
so0
P
2
4 c 300
s" P
b
2t 200
4
0
J 6 9 iz L J Q U J OTMC or CONT#LT i~ HOJRS
is
FIGURE 3. CONST4NT-TE\IPER4TURE R E S C L T ~ A . Total gas (scale on left) 5. Distillate as percentage of charge (scale on right)
DISTILLATECHARGE. The percentage of the charge that appears as distillate is plotted against temperature as curve B in Figure 1, and here, too, the relationship is linear. UNSATURATES I N GAS. The percentage of olefins in the gas are plotted against the temperature in Figure 1, curve C; the olefins reach a maximum (around 600' C.) of 47 per cent, and diminish at both the higher and lower temperatures. This fact is almost certainly due to the polymerization of the unsaturates that occurs at the higher temperatures. AROMATICS IN DISTILLATE The aromatic content of the distillate increases rapidly with temperature, and a t 700 O C. has reached a figure of 60 per cent of the distillate, corresponding with 7.8 per cent of the charge (Figure 1, curve D ) . UNSATURATES I?; DISTILLATE. The olefin content of the distillate rises from 3 per cent at 500" c. to 35 per cent a t 700" c. From the above it follows that, if a maximum gas volume is required, a temperature of above 700" C. should be adopted s3 that all the gasoline will be changed into gas-650 volumes per volume of gasoline. These conditions also "hold for maximum olefins-220 volumes per volume of feed (Figure 1, curve E ) . If a maximum olefin content in the gas is required-i. e., a gas as rich as possible in olefins (a condition sometimes demanded for economic treatment of the gas)-a temperature of GOO" C. should be maintained, giving 45 per cent unsaturates or 135 volumes per volume of feed. CONSTANT-TEMPERATURE RESULTS The constant-temperature results are plotted in Figure 3. At a temperature of 600" C. the total gas evolved has been plotted against time of liquid contact in hours on semilogarithmic paper; in curve A , Figure 3, the points lie on a straight line. The empirical equation is:
I N DU STR I A L A N D E N GI N EER I N G C H E M I STR Y
a04
+
(2)
0.0758 G
(3)
In, G = H 0.0758 5.18 where G = volume of gas per unit volume of feed H = liquid time of contact, hours
Differentiating, dH dx
or the gas formed per unit time is proportional to the quantity of gas already formed; this characterizes the reaction as autocatalytic. This would mean that a partially gasified stock should crack more readily than a virgin stock, and that cracked or recycle stock should be preferable to straight-run stock for producing gas. The liquid-phase cracking of gas oil runs in the same direction as far as the production of gas is concerned, although in the opposite direction, where the production of gasoline is examined, Gault and Hessel's results ( 1 ) with a single compound give a linear relationship between gas formed and time of contact. Equations 1 and 2 can be combined to give a tentative general empirical formula for gas evolved as a function of temperature and rate a t atmospheric pressure from gasoline : G = (T - 480) 0.0085 G = (T - 480) 1.5
whence
6.1s
Vol. 24, KO. 7
Assuming this equation to hold, it follows that the rate of reaction doubles for every 70" C. between 500" and 700" C. Three hundred liters of gas are produced from 1 liter of gasoline in 7 hours liquid time of contact at 600" C. and therefore are produced twice as fast, or in 3.5 hours a t a temperature T,which is found to be 670" C. from Equation 4. The figure 70" C. is fairly reasonable, since gas reactions are known to double in rate every 10" at 0" C . and every 100" at 1000" C. Finally, since the gas formation goes on a t the expense of the feeding stock, the nongasified portion, which a p pears as distillate, should follow a law with respect to the feed similar to that followed by the gas in Equation 2. The distillate as percentage of charge has been plotted in Figure 3, curve B , and the logarithm of the distillate charge is a linear function of the time of contact, which is what one would expect from the autocatalytic nature of the gas formation. Numerous metallic oxides were tried as catalysts to modify the reaction but no marked effects were produced. LITERATURE CITED (1) Gault a n d Hessel, Ann. chim.,[lo] 2, 319-77 (1924).
RECEIVED January 6, 1932. The author's present address is Research
(4)
Department, Sun Oil Co., Marcus Hook, Pa.
Explosive Gaseous Reactions in a Dynamic System I.
The Reaction of Oxygen and Propane
S. P. BURKE,West Virginia University, Morgantown, W. Va., C. F. FRYLING,S t a t e of Illinois Geological Survey, Urbana, Ill., AND T. E. W. SCHUMANN, Fuels Research Institute, Union of South Africa
I
N THE course of an extended investigation on the oxidation of hydrocarbons conducted over a period of several years, certain observations were made which appeared to offer a means by which the mechanism of chain reactions or thermal explosions might be further elucidated. As a result special experiments were conducted with this object in view. These experiments and the deductions which followed therefrom are the subject of this paper. An incomplete but valuable bibliography on the subject of the oxidation of hydrocarbons is appended (1, 4). PART I. EXPERIMENTAL METHOD AND RESULTS I n the majority of the experiments, mixtures of oxygen or air and a gaseous hydrocarbon were passed through a long tube of nahow diameter coiled in a molten bath. Commercial propane (99 per cent C a s ) was the hydrocarbon employed in general. During the course of any experiment, the
+
n
pressure of the system, the composition of the ingoing gas mixture, and the rate of gas flow were maintained constant. I n most cases, the reaction was conducted in Shelby steel tubes, although other materials were also employed. The length of the tube immersed in the heating bath was 350 cm. unless otherwise noted. The course of the reaction was followed by analyzing the gases leaving the system. The amount and rate of disappearance of free oxygen was taken as the criterion of the amount and rate of reaction. I n Figure 1 a schematic drawing of the reaction system is shown. Figure 2 is a photograph of the more important apparatus. To secure the exact maintenance of the desired experimental conditions and the constant analysis of the ingoing and outgoing gases, the service of at least two operators was required. The experimental procedure was as follows: The flows of the hydrocarbon and air were governed by valves which were set a t the start of the experiment and across which a constant pressure difference was held throughout the run. To insure uniform initrial conditions, the hydrocarbon was evaporated
0
PRCIldRf G 4 U G t S PRFSSURI VALVE5
0
v
U
FIGURE 1.
E THERMOMETER F THIRWDSTATIC IONTROLLLO
STOP C O C K S
A
AIR
B
klTROGEN
C
LlPUlFlED PRDPANE
p
PRESSURE FLOWMIltR
OR OXYGEN
S C H E M A T I C DIAGR.4.M OF .4PP.4R4TL-S
0
PROPANE WAPORhTOR VENTURI MIXING TUBt
H REACTIONSALTS MOLTEN BATHCONOF TAININC REACTION
TUBE, STIRRLR,AND WERMOCOUPLE
I
POTLNT'OMETER
J
WATER C O D l l h C J A C e T
".
EXPANIION VALVE
L MOISTURE SEPARATOR M FLDWMElER N
ORSAT APPARATUS
0
WET METER
P
GASOMETER
,
