Nov., 1915
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
expense, either, I desire to emphasize, of sacrificing that very essential of all mechanical training-fundamental general principles to specialized details. NIAGARA FALLS, ONTARIO, CANADA
CONTRIBUTIONS OF THE CHEMIST TO THE EXPLOSIVES INDUSTRY By CHARLESE. MUNROE Explosives Expert, George Washington University
The explosive industry is essentially a chemical industry and is most efficiently conducted under close chemical supervision. It is true that a large part of the explosives used or proposed for use in commerce are mixtures of various components, that variations in the proportions of the components or modifications of the physical conditions of the components, or of the product, may fit i t better for certain of the multifarious uses to which explosives are put, and that this has given large opportunities for the exercise of empiric ingenuity which practically controlled the industry for centuries; but modern developments have proven that these mixtures can be most economically, uniformly and satisfactorily produced when their manufacture is supervised by skilled chemists who prove the degree of purity of each ingredient and, by a systematic scientific series of tests, determine quantitatively the characteristics of the product. As a fact, while the empiricist has dominated the industry up to recent times he has nevertheless benefited from the altruistic services of the chemist, for gunpowder, the mixture which almost alone served man’s purpose as an explosive through five centuries, was brought to the attention of western nations by Roger Bacon, whom E. von hleyer includes as an alchemist in his history of chemistry, and it was brought to a higher state of usefulness and reliability through the researches of Lavoisier, Berthollet, Gay Lussac, Violette, Chevreul, Bunsen, Linck, Karoyli, Debus, and other chemists, and a variation in the oxidizer was wrought when Berthollet proposed in 1785 the substitution of a chlorate for the nitrate. With the discovery of picric acid by Woulfe in London in 1 7 7 1 , its confirmation by Hausmann in 1788, its identification
94 5
as trinitrophenol by Laurent in 1 8 4 3 and the demonstration of its explosiveness per se by Sprengel in 1873 began the era of strictly chemical explosives. This was followed in 1800 by the discovery of mercuric fulminate by Howard, and the elaborate investigations of the fulminates by Liebig and his students; by the discovery of guncotton and the cellulose nitrates in 1845 by Schonbein and in 1 8 4 6 by Bottger; by the discovery of nitroglycerin by Sobrero in 1 8 4 6 ; by the discovery of diazo compounds by Griess in 1 8 5 8 ; and by the discovery of hydronitric or triazoic acid and its salts by Curtius in 1 8 9 0 . With the demonstration by Berthelot of the explosiveness of other nitrosubstitution compounds than picric acid there came a widely extended and constantly increasing use for them; and the number of different compounds made use of is constantly growing for while the cellulose nitrates, with nitroglycerine, are playing the r61e of propellants, the nitrosubstitution compounds are the explosives which are being made use of in the high explosives shell now working such devastation in the present war. I believe I have said enough to make it obvious that only by the liberal employment of trained chemists can this industry be continued or extended, and in recent years this view has been accepted and followed by manufacturers. It may be worth while to recall here that when the Census of the Chemical Industries was taken in 1900 an inquiry was made as to the number of chemists employed, because it was then recognized that this afforded a criterion by which to determine the intelligence and foresight with which the businesses were conducted. As shown in Bulletin No. 2 1 0 of that Census there was reported but 276 chemists employed in 1740 establishments then reporting, and that but 32 chemists were employed in the 97 explosives works from which returns were secured. It is not known what effect, if any, this inquiry had but it is understood that a t present a single explosives company in the United States employs alone many times this number of chemists. This improvement is gratifying to record but it should serve only as an example to be emulated. WASHINGTON. D. C.
ORIGINAL PAPERS THERMAL REACTIONS OF PETROLEUM HYDROCARBONS IN THE VAPOR PHASE’ B y WALTERF RITTMAN Received Sept. 8 , 1915
One of t h e m o s t widely studied and i m p o r t a n t chemical problems of t h e present d a y is t h e t h e r m a l decomposition o r “cracking” of petroleum h y d r o carbons. A considerable n u m b e r of investigations h a v e been u n d e r t a k e n along t h i s line, most of which were conducted w i t h t h e p r i m a r y i n t e n t i o n of developing commercial processes. T h e d a t a t h u s obt a i n e d h a v e been necessarily of a r a t h e r special c h a r a c t e r and, i n addition, a r e n o t particularly available t o t h e scientific world. In view of t h e wides p r e a d need for clear-cut a n d comprehensive informat i o n concerning t h e “cracking” reaction a series of experiments has been outlined for t h e purpose of s t u d y i n g t h e problem consistently a n d impartially i n all its phases. T h e first experiments2 were c o n d u c t e d i n connect i o n with t h e problem of oil-gas production a n d were limited t o s u c h conditions as might a p p l y i n t h a t 1
Published with the permission of the Director of the Bureau of Mines. THISJOURNAL, 6 (1914), 383 and 472.
* Whitaker and Rittman,
field. A t t e n t i o n w a s given t o t h e influences of t e m p e r a t u r e , pressure a n d concentration o n t h e e n d p r o d u c t s of t h e reaction, a m a x i m u m of care being bestowed u p o n t h e properties of t h e evolved gases. Liquid p r o d u c t s were examined o n l y w i t h regard t o general physical a n d chemical properties. I n t h e present experiments it has been f o u n d u n necessary t o give more t h a n a m i n i m u m of a t t e n t i o n t o q u a n t i t a t i v e relations a m o n g gaseous products. T h e results of t h e earlier experiments were so definite a n d so exactly i n accord with theoretical considerations t h a t little h a s been a d d e d t o t h e m i n t h e present connection. It has been possible, however, t o l e a r n f a c t s of the greatest i m p o r t a n c e concerning liquid p r o d u c t s of t h e cracking reaction a n d , i n addition, valuable information h a s been o b t a i n e d regarding t h e course a n d mechanism of t h e process. T h e results a t h a n d h a v e led t o t h e following conclusions w i t h r e g a r d t o t h e cracking reaction: I-The n a t u r e , b o t h physical a n d chemical, of an oil is of secondary importance, compared w i t h t h e influence of t e m p e r a t u r e , t i m e , a n d pressure, i n controlling t h e p r o d u c t s of t h e cracking reaction. Under
946
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
like conditions approximately similar results have been obtained from five different oils a n d it has seemed t h a t t h e minor existing differences may as probably be due t o variation in r a t e of reaction as t o t h e actual production of unlike equilibrium products. a-From a n y oil it is possible t o make a n y desired t y p e of hydrocarbon b y adjusting properly t h e conditions of t r e a t m e n t . (a)-Most favorable conditions for gasoline production are temperatures of about j o o o a n d pressures higher t h a n 6 atmospheres. (b)-Low-boiling aromatic hydrocarbons are produced best a t temperatures between 600' a n d 700' with pressures above 4 atmospheres. (c)-Higher temperatures favor t h e production of carbon a n d gas a t t h e expense of t h e liquid reaction products. 3-The course of t h e cracking process is one of dehydrogenation. 4-The formation of aromatic compounds seems t o occur in either of three ways:l (a)-The original oil may be decomposed t o small molecule compounds of t h e acetylene series which subsequently polymerize t o form t h e larger aromatic nuclei. (b)-There m a y be a simple splitting of polycyclic (asphaltic) hydrocarbons. (6)-There may be a dehydrogenation of naphthene hydrocarbons. THEORETICAL
T h e characteristic feature of t h e present set of experiments is t h a t cracking has been conducted in t h e vapor phase. T h e advantages of this method of procedure are considerable a n d , as will be shown in a later connection, have as much importance from a commercial as from a purely scientific point of view. T h e primary advantage of t h e one-phase system is t h a t b o t h temperature a n d pressure may be controlled separately a n d a t will. I n a two-phase system each is a function of t h e other. T h e simple vapor pressure curve diagram for water (shown in Fig. I) illustrates t h e characteristic difference between a one-phase a n d a two-phase system. If liquid a n d vapor are in equilibrium with each other we are confined t o t h e line representing t h e variation of vapor pressure with t e m TEXPERArnY If a n a t t e m p t is FIG.I-VAPOR PRESSURE O F WATER perature. made t o change one of these variables a n d keep t h e other constant a phase disappears. T h u s a n y a t t e m p t t o heat water above 100' C. a t atmospheric pressure tends t o produce entire conversion t o t h e s t a t e of vapor. If, however, we deal with t h e vapor phase only we may obtain a n y 1 Lewes, Jour. SOC.Chem. Id., 11 (1892), 584; R. Meyer, Ber., 46 (1912), 1609; R. Meyer, and Tanzen, Ber., 46 (1913). 3183; Ipatiew, B e . , 44 (1911), 2978; Brooks, Bacon, Padgett and Humphrey, THIS JOURNAL, 7 (1915). 180.
Vol. 7 , No. I I
desired combination of temperature a n d pressure as long as conditions are avoided which cause condensation. T h e vapor pressure of petroleum, which is a mixture a n d not a simple chemical compound, is not exactly analogous t o t h a t of water as t h e liquid a n d vapor phases differ in composition and t h u s permit t h e establishment of various conditions of equilibr i u m ; if temperatures are raised sufficiently high, however, t h e liquid will disappear, as in t h e simpler case. As applied t o present needs t h e limitations of t h e two-phase system become evident. If it is desired t o heat t o 8jO' C. a n oil boiling belo3w 300' enormous pressure must be developed t o retain t h e liquid phase, more pressure, probably, t h a n apparatus of ordinary construction will withstand. Yet it is perfectly easy a n d simple t o pass oil vapor through a t u b e heated to 850' and a t the same time maintain i n t h e system a n y desired pressure from a fraction of a n atmosphere t o over t h i r t y atmospheres. Other advantages of t h e vapor-phase system for heat decomposition of petroleum hydrocarbons are more mechanical t h a n chemical. T h e influence due to differences among t h e physical properties of various original oils is eliminated. I n systems which involve cracking b y distillation under pressure t h e a m o u n t of pressure developed in getting a n oil u p t o decomposition temperature depends upon t h e volatility of t h e oil. T h e t o t a l conditions a n d range of applicability of a process may be controlled b y this factor. When, however, as in t h e vapor-phase system, t h e interdependence of t h e t w o variables, temperature a n d pressure, has been eliminated, t h e influence of volatility of t h e oil is a minor consideration. I t is controlled b y adjustment of t h e vaporizing device, through which t h e oil passes before entering t h e body of t h e cracking furnace. T h e vapor-phase cracking process, as here conducted, possesses another characteristic which is advantageous, both from a scientific a n d from a commercial point of view. I n t h e present work a n d in a majority of commercial cracking processes t h e production of gas is undesirable. I t will be noted t h a t t h e method here employed minimizes its formation. T h e mechanism by which this end is accomplished is as follows. I n t h e cracking furnace we have established a n equilibrium which may be represented b y t h e following equation: Condensable Original Hydrocarbons)
{ Ezyt}+ { Condensable Cracked Hydrocarbons
At t h e lower end of t h e cracking t u b e is a Liebig condenser which removes b y cooling t h e unreacting residuum of original hydrocarbon a n d t h e condensable products, b u t which does not affect t h e permanent gases (hydrogen, methane, etc.). AS a result when more of t h e original hydrocarbons enter t h e furnace a new equilibrium is established without a n y further production of gas. I n actual practice this condition is not attained i n absolute degree b u t t h e above description indicates a strong general tendency. The factor of safety is another important consideration. I n t h e course of t h e cracking reaction only a
,
T H E J O U R N A L OF I i V D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
NOT-.,191 j
small portion of oil is i n t h e zone of action a t a n y one t i m e a n d in case of failure of a p p a r a t u s t o remain t i g h t there is no large volume of h o t oil t o be discharged. Valuable indications of what m a y be expected a s products of t h e cracking reaction m a y be obtained b y considering equilibrium relations between a typical hydrocarbon a n d i t s possible decomposition products. T h e initial substance chosen for present purposes is a hydrocarbon of t h e paraffin series, representative of t h e kerosene cut m-hich modern commercial conditions h a v e rendered desirable of transformation. T h e comp o u n d C1ZH26, boiling a t a b o u t ZIS', has been employed a s a basis for a n u m b e r of typical reactions (Table I ) , i t being understood, however, t h a t with each of t h e major reactions is coincident a n u m b e r of minor reactions. It is also t o be understood t h a t present considerations do n o t neglect t h e possibility of cracking poly-
947
a s t h e transformations a r e accompanied b y increases in t o t a l volume. This consideration is, however, modified b y t h e necessity of t a k i n g account of t h e factor of reaction velocity. According t o t h e law of mass action, reaction velocity is proportional t o concentration, a n d concentration is a derived function which varies i n t h e s a m e direction a s pressure. If we allow reactions sufficient t i m e t o proceed t o completion low pressure is favorable f o r t h e transformations represented b y E q u a t i o n s 3 t o 14. When, however, t i m e is limited t o a fixed a m o u n t t h e effect of low pressure m a y be unfavorable unless t h e reaction occurs with considerable rapidity. All t h e reactions indicated, except t h e last t w o , t a k e place with absorption of h e a t a n d therefore are favored b y high temperature. This is indicated b y t h e magnitudes of t h e approximate equilibrium constants which a r e figured according t o t h e Nernst equation.'
OF EQUILIBRIA TABLE I-QU~NTITATIVE STUDY
APPROXIMATE
No.
H e a t of Volume reaction(a) change 500 2 t o 2
REACTION
6
2ClzH26 ) r CH4 -t C23Has.. . . . . . . . . . . . 000 ~ C I Z H I_ ZI C ~ Q H+ O C I ~ H ~ .Q. .. .. . . . . , zJ= . . . . . . - 16750 CIZH28 C H I 4- CiiHz?. . . C12HZ6 1 -C I Q H ~4-Z C2H4.. . . . . . . . . - 16100 CIZH24 + H z . . . . . . . . . . . . . . - 31800 CIZH26 CnHz6 If 5CzH4 + C2H8.. . . . . . . . . . . . - 80400
7
CizHza
1 2 3 4 5
, , ,
,
, ,
,
1 to 2
,
1 to 2
,
+ H z . . . . . . . . . . . . -111600 CzH? + 2CSH12.. . . . . . . . . . . - 47600
6CzH4
,
,
,
8
C1zH28
9
CI?H28
10
CnH?6
6C?Hz
4-
7Hz..
11
CI~H~G
JC?H2
t
6Hz
12
CizHco
~ C I H ? 4CH4 -k C2H4.. . , . -154400
s If
2 to 2
,
CZH4.. . . .
1 to 2 1 to 6
1 to 7 1 to 3
- 61 100
1 to 4
. . . . . .. . . . . .
-381000
1 t o 13
4- CzHa.. . . . , ,
-336800
1 to 12
C Z H ?4- 2C4HlO
1 to 8
(Formulas refer t o partial pressures) K6oo K = CH4 X CZ3H48 0.306 (C12HZ6)2 K = c~QH2z 1.0 (ClZH26)2 CH4 X C I I H ~ Z 645. K = -____ ClZHZ8 C~QHZ xZCZH4 K = __-1950. C12H28 CizH2a X Hn K = --__ 0.0044 CIZH26 K = OLX-CzH6 1.25 X C12HZ6 (C1H4)8 X Hz 1.2 X K = C12H2a CzHz X ( C ~ H I Z ) ~ 7.1 K = _ _ _ -C12H26 --~ CzHzX ( C I H I O ) ~ X C Z H ~ 7.4 X K = _______ CIZHZG (CzHdO X ( H z ) ~ 1.0 x K = _ C12H26 _ _ ~ (CZH?)'X(H2)eXCZH4 3 .5 X K = C1ZH26 ( C Z H Z ) ~(CHa)4XCzH4 X 1.1 X K = --CIqHnr
7
1.0
~
3CzHz
I- C6Hs
,...
... . .. . . . , . . . .. . . . CiHa.. . . . . . . . . ., . .
1
.o
2820.
15500.
8300.
43500. 1.02
0.0616 10'6
1.58 X 10'9
1014
2.0
x
io1*
1.6
102
4.0
x
104
3.9
108
1 . 4 X 100
10-r~
5.0
x
10-16
7.1
X lG-a
5.6
X IO'@
10"
10-7
10.2
0.89
15
0.309
0.308
x-c&?!O
x
Kno
K6QQ
6.3 X
x x
1022
1023 106
6 . 2 X 1011 1.2
x
2.9 X
109 1Ol1
2 . 4 X 102'
162.
5.6
X IO'
7.1
X 1013
7 . 8 X 1020
2.0
X 1020
6.3
X 101s
5 . 7 X 1010
COHG
+I30700
3 to 1
K = ___(C2H2)B
CiHe 6 . 3 X 1020 2 . 2 X 10'6 1 . 6 X 1011 K = (CzHz)~X C3H4 (a) Whenever possible heats of reaction (for constant pressure) are based on values obtained b y experimental methods. I n other cases calculated values are used, based on the empirical formulae given by Thornsen. ("Thermochemischer Untersuchungen," Part IV, Chapter XIV.) 16
7CnH2
- C~HI
+I31900
3 to 1
cyclic hydrocarbons directly i n t o aromatic compounds. Here t h e case m a y be one of simple splitting, such as occurs in t h e transformation of a paraffin molecule t o a paraffin a n d a n olefin. By s t a r t i n g with a paraffin t h e case is made inclusive a n d is therefore best suited t o purposes of illustration. T h e possibilities of decomposition m a y be classified under t h e foilowing four heads< I-Paraffin
formation formation 3-Acetylene formation 4-Aromatic formation n-Olefin
T h e list of typical equations includes all these cases, and the approximate point Out general tendencies of t h e various reactions. It is t o be noted t h a t for all reactions save paraffin rearrangemerit (Equations I and ') and aromatic O r mation ( E q u a t i o n s I j a n d 16) t h e effect Of pressure is inimical,
Here again it must be remembered t h a t t h e case is n o t a simple one a n d t h a t certain of t h e reactions t a k e place a t t h e expense of others. Especially is i t t r u e t h a t t h e formation of hydrogen a n d carbon, undesirable e n d products, is favored b y high t e m p e r a t u r e a n d i t cannot be said, therefore, t h a t t o obtain a maximum yield of such a substance a s acetylene (Equation 7 ) i t is desirable t o h e a t a s strongly a s possible. A f e w specific cases deserve a t t e n t i o n . It seems entirely reasonable t o assume t h a t olefin formation is intermediate t o acetylene formation. Likewise there are clear indications t o t h e effect t h a t aromatic compounds are polymerization products of acetylenes. Hence the following relations Seem to hold for the effects of t e m p e r a t u r e a n d pressure. Acetylenes a r e
formed at moderately high temperatures and being intermediate to aromatics ,.he latter are likewise high 1 Nernst, "Theoretical Chemistry;" also text-books of physical chemistry -Whitaker and R i t t m a n , L O C . 'it.
948
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
t e m p e r a t u r e products. Acetylene formation appears t o be favored b y low pressure b u t t h e polymerization is a reaction helped b y high pressure a n d this, i n addition t o t h e factor of reaction velocity, leads t o t h e expectation t h a t aromatic formation must b e favored b y pressure. T h e u l t i m a t e products of t h e cracking reaction are carbon a n d hydrogen, their formation being favored b y high temperature. Being inactive a n d undesirable e n d products t h e y should be minimized b y moderation in securing t h e l a t t e r condition. EXPERIMENTAL G E N E R A L S C H E M E O F PRoCEDuRE-A scheme Of procedure similar t o t h a t described i n a n earlier paper’ has been adopted for the present series Of though the study Of products has been conducted On a broader The Of a sing1e unit was as a quantity Of Oil, generally between 40° and 6oo grams, was run through a n electrically heated furnace i n which were maintained carefully regulated a n d measured conditions of t e m perature and pressure. After the Of the “ r u n ” t h e q u a n t i t y of resulting oil was determined and the deposited scraped Out Of the furnace and weighed. The gas was in a suitable receiver a n d its volume read a n d recorded, although no use has been made of t h i s information i n t h e present connection.
I n connection with each major experiment or r u n a number of Supplementary determinations Were neCeSSarY. Both uncracked a n d cracked Oils were subm i t t e d t o analytical distillations a n d specific gravities were measured for t o t a l oils a n d for distillation cuts. Viscosities were determined for original a n d recovered oils. A number of refractive indices were measured, though these, like gas volumes, a r e n o t recorded. Refractive indices have been found t o agree so exactly with specific gravitiesZ t h a t these constants furnished no additional information of value. I n some cases when t h e presence of aromatic hydrocarbons was indicated b y t h e gravity figures, chemical examinations were made a n d t h e reliability of t h e former determinations verified. T h e m a t t e r of chemical methods of separation has received consideration i n other communications.3 Samples of evolved gases were removed f r o m t h e holder a n d later analyzed. This work will be described later. The scheme Of procedure may be summarized a s follows: “RUN”
OR MAJOR EXPERIMENT
of 400 g. t o 600 g. of oil in furnace at regulated temperature and pressure. a-Determination of quantities of oil, gas and carbon reI-Cracking
sulting. SUPPLEMENTARY DETERMINATIONS
I-Distillations of: ( a ) uncracked oil, ( b ) cracked oil. a-Determinations of specific gravities of uncracked oil, cracked oil and individual distillation cuts. Whitaker and Rittman, Loc. c i t . R i t t m a n and Egloff, THIS JOURNAL, 7 (1915), 578. Rittman, Twomey and Egloff, Mef.Chem. E n g . , Oct. 1. 1915; R i t t m a n and Moore, Ibid., Oct. 15, 1915. 1
2
8
Vol. 7 , No.
11
3-Determinations of viscosity and refractive index. 4-Chemical tests on distillates. 5-Analyses of evolved gases. C R A C K I N G E X P E R I M E N T O R “Ru”’-The apparatus a n d general method used for making a r u n was t h e same a s t h a t described in a n earlier paper.’ T h e a p p a r a t u s consists essentially of a n electrically heated furnace body eighteen inches long a n d one a n d a half inches i n diameter. At t h e upper e n d is a t t a c h e d a n oil feed cup a n d a vaporizing device. Below t h e furnace is a Liebig condenser discharging i n t o a receiver which is connected with either a r o t a r y t y p e v a c u u m p u m p or a pressure release valve. A final connection is made with a gas holder of 1 2 cu. ft. capacity. The whole order of the apparatus was therefore: ( I ) oil feed cup, ( 2 ) vaporizer, (3) f u r n a c e proper, (4) condenser, ( j ) first receiver, (6) v a c u u m p u m p or pressure valve, (7) second receiver i n case of vacuum, a n d ( 8 ) gas holder. T h e system is a closed one a n d a n y desired pressure from a thirtieth of an atmosphere up to 3 o atmospheres has been maintained. The electrical heating equipment of the furnace body permits t h e regulation of temperature at any desired height u p to I o o o o c, The temperat u r e measurements were made b y means of a thermocouple inserted in t h e interior of t h e furnace body. DISTILLATIONS were made in flasks of 2jo cc. bulb capacity, with necks 5,,8 in. in diameter and in. long t o t h e outlet t u b e . I n each case t h e neck of t h e flask was equipped with a 5 in. column of t h e Hempel t y p e , filled with aluminum beads, Original charges of zoo grams were distilled i n most cases a n d cuts were made a t I o o o c. a n d therefore at intervals of 50~,
SPECIFIC GRAVITIES were determined either b y means of a Westphal balance with plummet of one cubic centimeter displacement or else with Drushel t y p e pycnometers,z VISCOSITIES were measured i n t h e Engler viscosimeter a n d results are expressed i n Engler degrees, which represent ratios between r a t e s of flow of oils a n d water. REFRACTIVE INDICES mere measured with t h e Pulfrich refractometer. GENERAL RESULTS O F EXPERIMENTS
T h e results of a large number of t h e cracking experiments appear i n Table 11. T h e necessary arrangement of figures does not render t h e m particularly easy t o interpret, a n d more readable tables are given i n connection with t h e various points set forth b y these experiments (see various sections of Table 111). I t will be noted, however, t h a t experiments were performed with five different oils, most a t t e n t i o n having been given to three, which were a pennsYlvania refined burning oil, a n Oklahoma fuel oil a n d a California Kern River crude. These oils were particularly suited t o t h e present experiments a s t h e y are devoid of low-boiling constituents; t h e y are, therefore, of t h e class least valuable commercially, which renders t h e m most promising a s starting material for cracking re1 2
Whitaker a n d Rittman, LOGcit. R i t t m a n and Dean, THIS JOURNAL, 7 (1915), 185.
Nov., 191j
T H E JOURNAL O F INDUSTRIAL A N D ENGINEERING CHEMISTRY
actions. T h e y are also typical of t h e t h r e e great fields of t h e c o u n t r y , t h e eastern, t h e mid-continent a n d t h e western. I n addition t o t h e above t h r e e hIexican a n d Russian crude oils were examined a n d sufficient d a t a obtained t o show t h a t , i n spite of their different chemical n a t u r e a n d physical properties, these do not v a r y radically in their behavior from t h e others. Figures for t h e Russian oil were so few t h a t t h e y have not been used i n t h e later tables prepared for purposes of comparison. I t will be noted t h a t t h e ranges of t e m p e r a t u r e a n d pressure are considerable, a n d t h a t t h e entire regions of importance in t h e cracking reaction have been covered thoroughly. T e m p e r a t u r e s loiver t h a n t h e ones used d o n o t produce decomposition with sufficient rapidity while those higher in t h e scale generate a s m a x i m u m e n d products undesirable carbon a n d gas. T h e range of pressure was as great a s could be managed with a p p a r a t u s of or dinar y construction . S T U D Y O F R E S U L T S (See Tables I11 a n d IVI C A R B O S FoRMATIos-The first factor t o be considered is one which, though of t h e greatest importance f r o m a commercial point of view, is of b u t minor theoretical interest. Carbon formation was determined b y t h e r a t h e r crude method of scraping t h e interior of t h e cooled cracking t u b e after each r u n a n d weighing t h e solid material t h u s removed. I n spite of t h e roughness of t h e method valuable indications were obtained a s t o general tendencies. A s t u d y of t h e d a t a in Table 111 shows first t h a t there are characteristic differences a m o n g t h e series r u n with t h e various original oils. These differences m a y be a t t r i b u t e d t o a combination of t w o causes, one chemical, t h e other physical. T h e chemical factor m a y in t u r n be subdivided. T h e four oils varied in their c a r b o n content, p a r t l y because t h e r e were differences i n t h e average sizes of t h e hydrocarbon molecules a n d p a r t l y because of chemical differences a m o n g t h e basic n a t u r e s of t h e oils. Those of a n asphaltic base h a v e a higher carbon percentage t h a n those of paraffin base. Hence t h e following o r d e r : T h e Pennsylvania oil, which deposited least carbon. was a “water-white” kerosene of purely paraffin base a n d boiling so t h a t 90 per cent came over below 2 5 0 ’ C. T h e Oklahoma oil was intermediate a n d was of mixed paraffin a n d asphaltic base; a so-called “fuel oil” of which only 2 2 per cent distilled below 3 0 0 ’ . Still more carbon was deposited b y t h e California oil, a h e a v y K e r n River crude of asphaltic base a n d giving a distillation c u t of only I ; per cent below 300’. T h e Mexican oil was lighter t h a n t h e California a n d gave a distillation cut of 37 per cent below 300’ b u t it h a d a peculiar physical property of causing much heavy t a r r y material t o be included in t h e . c a r b o n deposit. As a result t h e figures f o r carbon formation a r e high a n d t h e yields of recovered oil a n d t h e gravities of recovered oils low. A comparison of averages of irregular sets of figures showing such marked variations is necessarily inaccurate a n d is almost unscientific, yet i t happens t o show t h e result which would be expected from theo-
949
retical considerations. Carbon deposition is favored by b o t h t e m p e r a t u r e a n d pressure. VISCOSITY OF RECOVERED oIL-In a considerable n u m b e r of experiments i t was inconvenient t o m a k e measurements of viscosity on account of insufficiency i n t h e q u a n t i t y of recovered oil. It will be noted t h a t , although t h e r e are considerable differences among t h e viscosities of t h e original oils. t h e analogous figures for recovered oils show b u t moderate variations. This fact is one of a n u m b e r going t o show t h a t t h e conditions of t r e a t m e n t of a n oil are of much more influence t h a n a n y properties, physical or chemical, which i t originally possesses. A specific comparison brings this o u t clearly. T h e ratio of viscosities between t h e original Pennsylvania a n d Oklahoma oils was a b o u t I : 35. T h e ratio between averages of t h e t w o series of recovered oils is a b o u t I : 3, a n d , b y omitting t w o v a c u u m r u n s of Oklahoma oil, t h e ratio can be brought down t o I
:
1.j.
N o a t t e m p t has been made t o average t h e viscosity values, a s sufficiently instructive indications can be obtained b y a s t u d y of a n y one of t h e series. T h a t for t h e Oklahoma oil is most complete a n d i t has been selected for use i n T a b l e 111. Here i t appears t h a t for r u n s u p t o 750’ C . viscosity decreases with temperature a n d with pressure. It does not, however, seem probable t h a t this rule will hold for higher t e m peratures a n d t h e single figure obtained for 800’ goes t o prove t h e t r u t h of t h i s reasonable expectation. A similar figure for California oil indicates likewise a n increase in viscosity as t h e 8 0 0 ” mark is approached. SPECIFIC G R A V I T Y O F R E C O V E R E D OIL-The variation among t h e specific gravities of t h e different sets of recovered oils is likewise a f a c t o r of interest. Here, as in t h e case of carbon deposition, i t will be noted t h a t t h e r e are characteristic differences a m o n g recovered oils from t h e various sources a n d t h a t these are of t h e s a m e order a s t h e g r a v i t y differences among t h e original oils. Pennsylvania cracked oils are lightest, Oklahoma next a n d California heaviest. T h e Mexican, on account of t h e tendency of heavy constituents t o stick t o t h e carbon, are a little lighter t h a n t h e California, although t h e original oil was heavier. Here again average values are a n uncertain proposition a n d must be regarded with d u e caution. It appears definitely, however, t h a t gravities increase with temperature. It is t o be expected t h a t t h e y would likewise increase with pressure a n d there are indications t h a t such is t h e case. Most of t h e deviations can be explained on t h e basis of probable experimental error. P E R C E N T A G E O F O I L RECOVERED-The percentage O f oil recovered is a factor of t h e greatest importance b u t , unfortunately, t h e necessary conditions of t h e present experiments prevented its determination with a n y degree of accuracy, especially in t h e cases of reactions under pressure. T h e pressure i n each case was “built u p ” b y gas generation due t o cracking of original oil a n d t h e r e was therefore i n each experiment a considerable period during which pressure was n o t u p t o t h e prescribed mark. I n addition it was
950
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 7 , No.
II
Sov., 191j
. T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
necessary for t h e experiments a t lower temperatures t o ha\-e t h e furnace greatly superheated a t t h e s t a r t
in order t o get t h e system u p t o t h e desired pressure before t o o large a proportion of t h e original charge of oil h a d been r u n through. If a r u n a t jooo a n d 24 atmospheres is t a k e n a s a n example t h e following conditions obtained: t h e
magnitude. are distributed with perfect impartiality. T h u s t h e Pennsylvania recovered oils are liable t o show either a maximum or a minimum percentage recovery. I t is indicated with entire definiteness in t h e tabulntion of averages t h a t percentage recovery decreases with increase of temperature. It appears also t h a t
TABLE IIB-RESULTS OF EXPERIMENTAL RUNS WITH RUSSIANA N D MEXICAN OILS RUSSIAN TL: MEXIC.4N O I L : Temperature: 675' 500 Orig. 750 600 600' 600' 500 500 Pressure-.itmospheres 12 atmos. 12 atmos. oil Vac. 12 I at. Vac. 12 1 Oil used imams) . . . . . . . 443 387 ... 812 479 628 500 573 591 Oil recovered (per cent).. 28.3 77.3 ... 37.3 47.2 40.2 66.0 54.5 72.8 Carbon (per cent). , . , . . , 2 1.7 0.0 10.5 13.1 16.4 9.0 16.2 9.8 Sp. Gr. of oil recovered.. .965 .88: ,892 .99: ,941 .99: .94,2 .9y ,9.3,0 Viscosity. . . . . . . . . . . . . . . . . . 1.$4 11.92 2.70 ... 1.96 6.73 1.15 1.88 First droo . . . . . . . . . . . . . . 40' 30 ... ... 30' 40 70' 300 55' Temperature S. G. % S.G. % S.G. 50S.G. %S.G. %SS.G. % S . G . %S.G. %S.G. 1 0 0 . . . . . . . . . . . . . . 30.5 ,863 7.3 ,718 0.0 . . . . 8.3.822 13.3.765 13.0.802 2.3.751 13.5.721 7.0.739 1 5 0 . , . . . . . . . . . . . . . 16.1 ,867 7.8 ,796 0.0 . . . . 5.0.836 12.5.829 8.3.837 3.5.782 13.3.807 8.7.792 200 . . . . . . . . . . . . . . 4.7 ,891 5.7 ,829 1.5 . . . i.i.868 8.0.846 9.2.860 8.3.811 11.0.837 8.5.82.5 2 5 0 . . . . . . . . . . . . . . . 13.9 Solid 13.8 ,856 10.7 ,836 10.5 ,915 11.0 ,899 13.0 ,923 10.5 ,846 13.0 .884 12.5 ,875 3 0 0 . . . . . . . . . . . . . . . 5.9 ,964 16.5 ,881 16.3 ,859 14.5 ,941 11.7 ,943 12.5 ,968 15.5 ,880 12.2 ,945 11.7 ,902 150 . . . . . . . . . . . . . . . 46.6 ,865 15.1 ,761 . . . . . . . . 1 3 . 3 . 8 2 7 2 5 . 8 . 8 7 7 21.3.816 5 . 8 . 7 7 1 26.8.766 15.7.770 250 . . . . . . . . . . . . . . . 24.5 . . . . 19.5 ,846 12.2 ,836 18.2 ,897 19.0 ,797 22.2 ,909 18.8 ,829 24.0 ,862 21.0 ,854
s2
furnace was s t a r t e d a t 650' a n d atmospheric pressure a n d oil r u n in till t h e pressure reached t h e desired height while, a t t h e same time, t h e t e m p e r a t u r e was allowed t o fall. I n such a n experiment it was necess a r y t o r u n through from I jo t o 2 0 0 grams of t h e t o t a l 600-gram charge of oil before desired conditions were established. It must be understood therefore t h a t t h e percentage recoveries a r e invariably low for
95=
400 10-1 1 527 73.5 13.8 ,932 4.43 35 0
Orig. oil
... , . . , .
,986 Over 300°
YoS.G.
7cS.G 4.8.729 0.0 . , . . 6.0.789 1.1.759 7.0.8.16 2.5.798 11.0 ,856 8.3 ,843 13.7 ,898 25.2 ,871 10.8.762 1.1.759 18.0 ,843 10.8 ,833
vacuum recoveries are greater t h a n those a t atmospheric pressure. Indications for pressures above one atmosphere are not entirely correct on t h e basis of figures given here. I t was noted, f o r instance, t h a t in t h e case of a pressure reaction a t j O O o gas formation was practically nil after t h e initial period during which conditions were being established. I n this case there should have been a recovery of practically I O O
TABLE111-CARBON FORMATIOX, PHYSICAL PROPERTIESA N D PERCENTAGES OF OILS RECOVERED PROPERTIES O F OILS RECOVERED PERCEFTAGE PERCENTAGES CARBOSFOKMATIOS Viscosities (Engler degrees) Specific gravitie5 OF OIL RECOVERED Pa. O k l a Cal LIea Av P a . O k l a . Cal Alex. A v . Pa Okla Cal. Mea. Russ. Pa. Okla. Cal. Mea. .4v. OF
OIL: T e m p Pres. C. aim.
1,026
. . . 0:99i 1:hi5 . . . 0 . 9 6 3 1.017
0.910 0.965 1 . 0 2 7
1.010 1 . 0 4 0 1 . 0 2 s 1 . 0 1 2 1.039 1 . 0 9 2 0.905 0 . 9 2 5 0 . 9 6 3 i:ii
i:48
i:is
:.
1.00
1.08
1:64
1.27 7.29
1.15 1.98 1.96 . . . 6.73
0:9i
i:25
i.35
.:
0.98 i : i z 1.00 1.54 1 . 0 0 2.51 1 . 0 4 13.42
i:3j
1.15
ORICIFAL
. . . . . . . . . . . . . . . . . . . .
1.52 . 6.161.88
..
...
...
1.44 ,.
1,026 1.011
0.990 . , . 0.965 . . . 1.028 1.048 0:992 0.946
...
. . . 0.908
...
0.882 0.819
0:9is 0 . 8 8 0
0,868 0.799 0 . 8 7 2 0.939 0:930 0 . 8 8 5 0.802 0 . 9 0 1 0 950 . . 0.884 . , . 0.882 . . , . . 0.882
.,.
. . . . . . . . . . . . . . . . . . . . . . . .
Over 1 1 . 9 2 350
Average Percentages Carbon Formation Viscosities for Oklahoma Series Pres. 6 12 18 24 Vac. 1 6 12 18 24 atin. Vac. 1 Temp. 4.50' 2.5 0.0 . . 1.731.50 ,, 500" 519 3 : 6 3 : 8 8 . 0 0 . 0 4 , 8 1 3 : 4 2 21.51 1 : i 4 1 . 3 2 . . 1 . 2 5 ,550~ 7.0 15.1 1.05 600: i : 5 8 : i 9 : 4 10:7 1 5 . 3 1 7 . 1 ? : i s 1 : 2 7 1:OS 1 4 : s 1 : , . 650 2.2 . . . . . . . . . . . 13.1 8 . 3 2 3 : 8 2 9 : 2 1: i:44 ,. , . . ,. , . 800 5.5 _ . . . . . . . . 1.64 . . . . . . . . . . . 850' 6.4 , . 4 , . , . . , . , , , .. , , , ,. ,. .,
::
0:908 . . . 0:S.S 0 . 8 7 7 0.942 0.819 0 . 8 0 8 0 : s i o 0:92s 0 810 0 867 0 . 9 2 8
:. .: .:
. . . . . . . . 1.50 2.71 , . ,.. I : O ~ 1.73 '4 43 . , . 1 . 0 5 35.40 3 5 : i
...
...
0 : 9 6 2 1:oos 1 : o i o . . . 1:000 0.926 0 , 9 7 3 0 . 9 9 7 0.965 0 918 0,907 0 . 9 9 6 0:941 0 , 9 4 0 0.885 0 . 9 3 1 0 . 9 8 4 . . . 0 . 9 3 3 0.810 0 . 9 0 6 0 . 9 6 6 0 . 9 9 2 0.926 0.811 0.899 0 . 9 6 0 0.942 0.903 ... 0.991 , . . 0.991
::I
. . . . . . . . . . . . . .. 1.05 . . . . . . . .
n 96
...
::
pressure reactions a n d t h a t t h e error is considerable in t h e case of t h e lower temperatures. T h e first point t o be noted in t h e d a t a is t h a t t h e differences among original oils seem t o h a v e no marked influence over t h e magnitude of t h e percentage recoveries. There is a n exception in t h e case of t h e Mexican crude where a large a m o u n t of t h e liquid product of reaction was held b y t h e carbon deposit. Among t h e other oils t h e variations. though of some
Average Specific Gravities of Recovered Oils Vac.
1
6
12
18
Average Percentages of Oil Recovered 24
Vac.
1
6
12
18
24
0.868 0.882 . . . 0:88401885 0 : 8 6 8 0 . 8 8 0 0 . 8 1 9 0.882 0.908 0.991 0:903 01926 01933 0.440 0 . 9 6 5 1.000
::: :::
0:946 11048 11028 01965 0.990 . . . . . . . . . . . . . . . 1.011 1.026 . . . . . . . . . . . .
per cent as carbon is not formed in t h e absence of gas a n d t h e only possible products must have been liquid. T h e low yields here indicated were due t o t h e preliminary cracking period during which pressure was low a n d temperature high. T h e indications for t h e effect of pressure a t higher temperatures are u n doubtedly correct, being in accord with theory a n d not explainable on t h e basis of a n y known experimental error.
952 FORMATION
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y O F G A S O L I N E A N D AROMATIC H Y D R O CARBONS
G A S O L I N E FORMATION-From b o t h a scientific a n d a commercial point of view t h e most i m p o r t a n t factors t o be considered i n t h e cracking reaction are t h e physical a n d chemical relations between original a n d recovered oils. T h e chief commercial interest in t h e cracking reaction has of l a t e centered on t h e problem of gasoline production. I t is r a t h e r a difficult m a t t e r t o establish a satisfactory definition of gasoline a n d for present purposes i t is unnecessary, a s t h e differences obtained among reaction products have been so great t h a t no fine distinctions are necessary. I n t h e present connection t h e magnitude of t h e distillation c u t u p t o 1 5 0 " C. has been considered a measure of t h e "naphtha" or "gasoline." On t h i s basis t h e a m o u n t of gasoline production has been figured for t h e different runs a n d results listed in Table I V . T h e calculations from experimental figures were. conducted as follows. T h e a m o u n t of oil i n t h e original sample distilling below
Vol. 7 , No.
11
favored b y pressure a n d t h a t t h e o p t i m u m temperatures are in t h e neighborhoods of 500" a n d 600". It is not, however, sufficient t o limit our considerations t o t h e d a t a appearing in Table IV. There are v a s t physical a n d chemical differences between cuts of approximately t h e same magnitude formed respectively a t 500 a n d 600' as will be noted when a comparison is made of t h e figures for specific gravities. DIFFEREKCESIN SPECIFIC GRAVITYOF CUTS TO 150' FROM PRESSURES A R D TEMPERATURES 600 A N D 500 PennsylOklaCaliPressure vania homa fornia Vac . . . . . . . . . . . 0.009 1 . . . . . . . . . . . . . 0.032 0:046 0:043 0.042 0.081 0.051 0.070 0.061 0.056 18 . . . . . . . . . . . . . 0 . 0 8 6 24 . . . . . . . . . . . . . 0.088 0:iii O:O.t3
FUNS AT LIKE Mexican 0:046
0:032
... ...
T h e above is a list of these density differences between distillates obtained from r u n s a t t h e same pressures a n d a t temperatures respectively of 600 a n d j o o " . T h e gravities of t h e 600" products are invariably t h e higher. I t will b e noted also t h a t t h e 600" products represent a large percentage of a small TABLE IV-FORMATION OF GASOLINEAND AROMATICS FORMATION OF LOW-BOILING recovery while t h e reverse is t h e case for j o o " prodPERCENTAGE GASOLINEFORMATION T e m p . PresAROMATIC HYDROCARBONS ucts. I n a d d i t i o n it m u s t be remembered that the inOC. sure Pa. Okla. Cal. Mex. Av. P a . Okla. Cal. Mex. Av. 1 850 . . . 2.4 2.4 . herent error of operation m a d e low the a m o u n t s o j gasoline Vac. . . 4:1 4:4 , , . 4.3 Vac. 4.6 7.1 . . . 5 . 9 800 reconered f o r pressure runs. 8 . 0 . . . 7 . 1 12 5 : 6 7 . 7 750 6.8 5.9 7.9 .. 6.9 6 T h e obvious conclusion is t h a t t h e favorable con5.1 4.7 5.0 , . 4.9 1 ditions for producing gasoline, a s determined b y t h e 4.1 4.2 2 . 2 2.9 3 . 4 Vac. 1.4 . . . . . 1.4 650 Vac. comparison of results of t h e present series of experil2:4 11.2 9.7 . , . 11.1 600 24 1 3 . 4 1 4 . 0 1 2 . 3 , , . 13.1 18 ments, involve a moderate temperature a n d a high 13.4 6 . 9 8.8 4.1 8.3 12 6 7.1 9.812.2 . . . 9.7 pressure. 1 7.3 5 . 8 5.1 4.3 5.6 1.0 1.1 3.0 0.4 1.4 Vac F O R M A T I O N O F A R O M A T I C HYDROCARBONS-It has . . 4.7 7.7 _ . . 6.2 5 5 0 24 7.3 . . . 7.3 18 long been known t h a t aromatic hydrocarbons m a y I : o 2.1 4:2 . . . 4.4 5 00 24 result from t h e cracking of petroleum. A recent 18 5.6 . . 5.6 12 5.6 1.8 j:7 & ¶ 3.0 study' of t h e properties of gas oils a n d derived t a r s 5.4 . . . 4.0 2.6 . . 6 1 1 . 8 0 . 6 1.2 1.1 1.2 has demonstrated this fact again with entire definiteVac. 0,7 . . . 0.7 450 18 3'3 : : 3 3 ness, a n d t h e present experiments have served t o de219 1 . 3 1 . 1 : ; : 1 : 8 12 400 10 . . . . . . 0 . 2 0.2 termine only what are t h e most favorable conditions for t h i s t y p e of transformation. AVERAGEPERCENTAGES AVERAGE LOW-BOILING Pres. GASOLIXEFORMATION AROMATIC HYDROCARBONS As was indicated i n t h e preceding section the Vac. 1 6 12 18 24 a t m . Vac. 1 6 12 18 24 Temp. characteristic property of aromatic hydrocarbons is . . . . . . . . . 1.8 3.3 450° 7.5 9.4 . . 500; i : i 4:9 S : i 1 3 . 7 14.6 15.2 0.7 1 . 2 4 . 0 3.0 5.6 4:4 their great density. Benzene, which boils a t 8 0 . 5 " , . . . . . . . . . . . . 7.3 6.2 550 1 7 . 3 12.3 1.4 5 . 6 9 , 7 8.3 13.1 11.1 has a specific gravity of 0.883 a n d toluene, with a 6000 3 : ; 11.2 i i : 3 1219 1 5 . 1 1 2 . 3 1.4 . . . . . . . . . . . 650' 3 . 0 . . .. boiling point of III", has a gravity of 0 . 8 7 2 . Paraffin 3 . 4 4.9 6 . 9 7.1 , . 7 5 0 O 5 . 1 4.7 617 8:1 : ' 1: .. 5.9 . . . . . . . . . . . 800" 7 . 2 . . . . . . . . . . .. or olefin hydrocarbons of equivalent boiling points 4.3 2.4 . . . . . . . . 850° 4 . 5 2 . 3 . . . . . . . . possess much lower gravities. This is indicated b y t h e 1 5 0 " mark was deducted from t h e distillation t h e following figures for straight chain hydrocarbons figure for t h e recovered oil. This last corrected perboiling a t temperatures slightly higher t h a n those centage was reduced t o terms of t h e original oil, giving a percentage which represents i t s degree of transforma- required for benzene a n d toluene. HYDROCARBON Boiling point Specific gra\.ity tion into hydrocarbons boiling below 150" C. 98.0 0.712 Heptane . . . . . . . . . . . . . . . . . . . . . 125.5 0 . 708 Octane.. . . . . . . . . . . . . . . . . . . . . . Thus for example, in the case of an experiment a t 500' and 0,703 Heptylene.. . . . . . . . . . . . . . . . . . . 9 8 . 0
I 2 atmospheres with Pennsylvania oil the distillation cut given in Table I is 23.8 per cent up to 1 5 0 ~ . The original oil distilled 4.8 per cent up to the same temperature. The increase is therefore 1 9 . 0 per cent. But of the original oil only 84.2 per cent was recovered and the gasoline formation was therefore 84.2 per cent of 19.0, or 16.0 per cent.
An examination of t h e results shows first of all a remarkable agreement among t h e effects of t h e s a m e conditions of temperature a n d pressure on t h e different original oils. T h e comparison of t h e average percentages indicates t h a t t h e formation of a large percentage of hydrocarbons boiling below 1 5 0 " C. is
Octylene. . . . . . . . . . . . . . . . . . . . .
123 . O
0.721
T h e quantitative separation of t h e different groups of hydrocarbons is n o t a process which can be conducted with ease a n d accuracy. There are chemical methods which have been recommended a n d these have been tried with results which h a v e appeared in another communication. For present purposes t h e indications furnished b y specific gravity measurements have been found sufficiently clear-cut t o differentiate results with a satisfactory degree of accuracy. 1
Rittman and Egloff, THISJOURNAL, 7 (1915). 481
S O V . ,1 9 1 j
T H E JOURiYAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
A scheme has been devised for t h e approximate calculation of the percentage formation of hydrocarbons of the aromatic series, boiling below I j O o . T h e assumption has been made t h a t t h e average gravity of t h e mixed aromatics benzene, toluene a n d t h e three xylenes is 0 . 8 7 j . This figure is undoubtedly x-ery near t h e true value a n d is justified b y t h e results obtained through its use. By studying some results of a previous paper' it was learned t h a t with t h e methods of distillation here employed t h e ai-erage specific gravities of I s o o distillation cuts of uncracked oils are as follows: Pennsylvania 0.721
Oklahoma 0.734
California 0.742
Mexican 0.759
953
gravity hydrocarbons) is favored b y moderate t o low temperatures and b y high pressure. IT'-The results obtained b y t h e series of laboratory experiments indicate striking commercial possibilities. The experimental work connected with this paper was carried out in t h e laboratories-of t h e Department of Industrial Chemistry of Columbia University, New York. CHEMICAL S E C T I O X O F PETROLECM DIVISION L' s BUREAUO F M I N E S . P I T T S B U R G H
A QUANTITATIVE METHOD FOR T H E DETERMINATION OF T H E ADULTERATION IN CHINESE WOOD OIL' B y J. C. BRIER Received October 5, 1915
Using these figures in connection with a value of 0.875 for t h e mixed aromatics a series of calculations was conducted a n d values obtained for t h e percentage formation of low-boiling aromatic hydrocarbons. The following example is typical of one of the less favorable runs. For a California (Kern River) oil, cracked a t 600' and I Z atmospheres the percentage recovery was 5 2 . 5 per cent and this oil gave be'ow 150' a 2 2 . 5 per cent distillation cut of gravity 0.842. The last figure: according to the scheme indicated above represents a mixture containing 75 per cent of the aromatics. The total aromatic formation was therefore 7 j X 2 2 . 5 X 5 2 . 5 per cent or 8.3 per cent on the basis of the original oil. Figures obtained in this way are shown i n Table I V a n d again there appears a n excellent agreement among t h e different original oils. T h e variations are moderate a n d are not characteristic. I n bonsideration of t h e several approximations an$ t h e inherent experimental errors t h e agreement m a y b e considered as striking. Again there is proof t h a t t h e conditions of t r e a t m e n t are of such importance t h a t a n y original tendencies on t h e parts of t h e oils used are rendered of negligible importance. I t will be noted from t h e average figures for lowboiling aromatics in T a b l e IV, t h a t most farorable conditions for t h e formation of benzene, toluene a n d xylenes seem t o be 600' a n d above a n d a t pressures greater t h a n 4 atmospheres. S U M MA R Y
Results of experiments here described have indicated t h e following conclusions: I-Equilibrium products of t h e cracking reaction seem t o be independent of t h e influence of chemical a n d physical properties of t h e original oils or a t most are affected only in minor degree b y such tendencies. T h e m a t t e r of carbon formation is t h e one clear-cut exception. Carbon is a residual product a n d its formation is proportional t o t h e a m o u n t originally contained in the oil. Viscosities a n d specific gravities seem t o show in slight degree t h e influence of properties of original oils b u t t h e differences are so slight t h a t t h e y m a y well be explained on t h e basis of failure t o reach complete equilibrium. 11-The formation of aromatic hydrocarbons occurs best a t moderate t o high temperatures a n d under high pressure. 111-The formation of gasoline (low-boiling, low 1
R i t t m a n a n d Egloff, THISJOURIAL, 7 (1915), 578.
Examination of a large number of shipments of Chinese wood oil extending over a period of several years, each shipment being checked against its behavior in t h e varnish kettle, has convinced t h e writer t h a t t h e advocated methods of testing Chinese wood oil, while affording valuable indications in certain cases, can be used with a n y degree of accuracy only o n grossly adulterated oils. Hoffman2 reports t h a t t h e adulteration of wood oil with foreign oils was very common in China in former years a n d t h a t t h e oils, pressed in China, hardly ever leached t h e market in a pure state. According t o h i m , oil from the kernel of the vegetable tallow seed, especially, was employed for t h e fraudulent blending of wood oil. Boughton3 states t h a t Chinese wood oil is frequently adulterated with soya bean oil. F r o m numerous inquiries t h e writer believes t h a t the larger amount of intentional adulteration is confined to t h e use of these two oils, b u t t h a t frequent accidental adulteration happens with ground n u t oil, sesame oil, a n d occasionally, with t e a seed a n d perilla oils. Importers, who are familiar with t h e production of Chinese wood oil and t h e various stages and methods of its transportation until barreled ready for export, have informed t h e writer t h a t adulteration, although not nearly a s prevalent as a t t h e time a t which Hoffman wrote, is still exceedingly common. It is well known t h a t t h e oil is obtainedh-om a large number of small producers b y t h e middlemen or merchants, who transport it in baskets made of bamboo lined with oiled paper (the average capacity of these baskets being approximately I 7 gallons). The native boats, which transport t h e oil t o t h e export markets, frequently carry mixed cargoes of t h e oils occurring in t h a t section of China where Chinese wood oil is produced. T h e frail baskets being piled on top of each other often become leaky, t h u s allowing t h e oils from t h e upper baskets t o contaminate t h e contents in t h e others. Then, too, t h e oils t h a t drip on the floor are collected and distributed among t h e various baskets throughout t h e cargo. Such cases a s those just cited make it difficult for t h e Chinese wood oil importers t o be sure as t o t h e purity of t h e oil they are buying, 1 This method was developed in collaboration with Dr. C. D. Holley in the Research Laboratory of t h e Acme White Lead and Color Works. 9 Seifenseider-Zeit., 35 ( I Y O S ) , 169. 3 Drugs, Oils a n d Paints, 29, 252-256.
