Mar., 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
oils of Borneo, Sumatra and Java are relatively rich i n light aromatic compounds, b u t low i n nitrogen. The latter oils, however, are very light a n d fluid and very different from t h e heavy pitch-like oils of California a n d Mexico, and i t has been frequently suggested t h a t these light fluid oils have been purified b y filtration through porous strata. Such light, supposedly filtered, crudes are low in sulfur as well as
been satisfactorily standardized, a n d frequent complaints are heard t h a t t h e reports of different chemists often fail t o agree with each other and rarely agree with t h e results obtained in t h e refinery. One great reason for this seems t o lie in t h e fact t h a t knowledge regarding the fractionation of complex mixtures, like crude oil, is in a rather unorganized condition. The United States Bureau of Mines has undertaken a study. which, it is hoped, will serve ultimately to secure t h e desired standardization of conditions of distillation. Some preliminary experiments were conducted, at the request of t h e Bureau, by Professors PI.C. Whitaker and F. J. Metzger of Columbia University. CRUDE PETROLEUM BY TABLEI-PERCENTAGE ANALYSESOF OKLAHOMA VARIOUS METHODS(a)
E. OF M. S A M P L E
NO. 1470 Engler(b) Ubbelohde(c) Regnault(d) Nawratil(c)
Cutbelow 150a C . . . . . C u t 150’ t o 300’. .. Cut above 300’. . . . . .
. . .
9.5 32.7 52.9
5.2 32.3 56.0
3.7 34.8 56.0
2.8 31.0 57.5
E. O F M. SAMPLE N O . 1464
16.7 11.5 9.5 11.1 Cut below 150 28.3 30.8 31.2 30.2 C u t 150’to 3&?’.:::: 53.5 53.5 52.5 Cut above 300’. , , . . 50.5 (a) For the sake of comparison, the temperature ranges prescribed for the Engler method were used in all the distillations. (a) Allen’s “Commercial Organic Analysis,” 3 (1910), 48. (c) I b i d . , 1 f i o i n ) Gn ( d ) Redw;o~,”;-”Petroleum and I t s Products,” 2 (1906), 536 and 2 (1913),
. .
y y .
206.
FIG.V-FRACTIONALDISTILLATIONOF GASOLINEMADEBY CRACKING UNDER
100 LBS. PRESSURE
nitrogen. Thus t h e converse of t h e above statement does not hold, probably for t h e reasons just indicated. Another noteworthy feature of gasoline made by cracking under a pressure of IOO lbs. is t h a t normal p a r a f i n e hydrocarbons appear t o be t h e predominating constituents. T h e amount of isopentane exceeds t h a t of normal pentane b u t t h e hexane a n d heptane fractions appear t o consist chiefly of t h e normal paraffines. These facts are brought out by Fig. V, representing t h e results of seven fractional distillations. CALCULATED Per cent FOUNDFor C ~ H M For CaHia CARBON . . . . . . . . . . . . . . . . 85.06 8 3 . 7 2 85.72 H Y D R O G E N. ..... . ,.,.. . . . . ..... . 14.93 16.28 14.28
.........
.
..
.
Only a very small amount of naphthenes appears to be present. Some evidence of t h e presence of methyl cyclopentane was shown by t h e above combustion analysis of t h e fraction boiling from 6 8 ” to 70’ C. MELLOXINSTITUTE OF INDUSTRIAL RESEARCH UNIVERSITY O F PITTSBURGH PITTSBURGH
--____
THE ANALYTICAL DISTILLATION O F PETROLEUM’ By W. P. RITTMANAND
E. U’. DEAN
Received January 4, 1915
I n t h e study of petroleum a n d petroleum products one of t h e most important processes of examination is a quantitative distillation. The information obtained by this method is of t h e utmost value, both from a technical f n d from a purely scientific point of view. Unfortunately, distillation methods have never 1
Published with the permission of the Director of the Bureau of Mines.
An extended abstract of bulletin now in preparation on t h e above subject. This bulletin will contain full details of construction of apparatus, methods used, and experiments reported herewith.
Their report is summarized in Table I and shows a wide discrepancy in the amounts of the various products obtained b y t h e various methods of analysis in use among petroleum chemists, t h e greatest differences being in t h e c a w o f t h e “naphtha” (cut below 150° C.). SCOPE O F T H E P R E S E N T R E P O R T
It is not intended t o discuss here t h e advantages a n d disadvantages of specific methods nom in use.’ Abundant a n d satisfactory d a t a are available with regard t o t h e effects of t h e various methods of distillation on mixtures of t w o or three constituents.2 N o results of a similar nature seem t o haGe been obtained for crude petroleum, and i t would appear t o be of utmost importance t o secure such data in beginning a study like t h e present one. Results of distillations differ mainly on account of t h e variable amounts of condensation occurring in the spaces between t h e surfaces of t h e boiling liquids a n d t h e outlets of t h e flasks or retorts used. We have considered three general cases. 1--When condensation is nil. 2--When condensation is moderate. 3-When condensation occurs in large amount, a n d there i s thorough contact between vapors a n d condensed liquid. I n a n apparatus designed by Allen a n d Jacobs3 for the distillation of California crude oils, t h e first condition is fulfilled: vapors, as they leave t h e liquid surface, pass unchanged in composition t o the condenser. The Allen and Jacobs method is by no means 1 See Allen’s “Commercial Organic Analysis,” loc. cil.; Redwood, “Petroleum and Its Products,” lac. c i f . ; Holde, “Untersucbung der Kohlenwasserstoffole und Fette,” 4th ed., 1913, pp. 29-38. 2 See Sydney Young, “Fractional Distillation,” 1908, Chapters X and XI. 8 “Physical and Chemical Properties of the Petroleums of the San Joaquin Valley of California,” Irving C . Allen and W. A. Jacobs, Bull. 19, Department of the Interior, Bureau of Mines.
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T H E JOL-R-YAL 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 CHEMISTRY
86
t h e only one by vhich this end can be attained b u t on account of availability and convenience i t has been selected as representative of the general case. Each of the T-arious methods studied b y Whitaker a n d Metzger secures a moderate degree of separation. T h e Ubbelohde is most generally in use and has therefore been chosen as representative. T h e extreme maximum limit oE separation is a difficult and perhaps impossible one t o attain, on account of mechanical and chemical difficulties connected with the distillation of crude petroleum. T h e literature’ which discusses still-heads and dephlegmators is very profuse. -4s representative of t h e class of apparatus furnishing maximum condensation, a Hempel column of moderate height has been selected, chiefly on account of its availability and simplicity. I n t h e past, petroleum chemists have strongly favored methods of t h e Ubbelohde type, on account of their convenience, and because i t was thought t h a t t h e results obtained did not differ very greatly from those of distillations involving thorough fractionation. T h e unsatisfactcry behavior of California oils, when examined b y these methods, lead t o the derelopment of t h e ,411en and Jacobs still. UECHA’NISM O F T H E P R O C E S S O F DISTILLATIOX
T h e distillation of crude petroleum, while offering numerous difficulties from a mechanical point of view, is, nevertheless, free from complications due t o t h e formation of “binary” and “ternary” mixtures. These mixtures, which may be either of maximum or of minimum boiling point, are linoivn t o occur only n i t h constituents of differing chemical natures. The inherent resemblances among all the hydrocarbons of a n y one crude oil render negligible t h e possibility of a n y difficulty in this direction. T h e composition of the vapor leaving the liquid a t a n y time is, therefore, a simple function of t h e partial pressures of t h e con.. stituents present and of their relative quantities. T o prevent changes in the composition of t h e vapor i t is necessary only t o prevent t h e escape of heat through t h e walls of t h e distilling vessel. T h e ,411en and Jacobs method accomplishes this by warming t h e walls of the flask with an enclosing electric heater. I n a simple distilling flask t h e process of cooling is irregular and takes place b y conduction through t h e walls of the vessel. It seems perfectly possible t h a t a considerable current of vapor m a y pass practically unchanged from the surface of t h e liquid t o t h e outlet. T h e Hempel column is one of t h e simplest and most effective devices for bringing the vapor into contact with a conducting medium a n d with t h e condensed liquid n-hich is running back. F o r its efficiency relative t o t h a t of other still-heads and for its specific advantages and disadvantages, t h e discussions published b y Young2 a n d Golodetz2 furnish satisfactory information. 1 Sydney Young, “Fractional Distillation,” loc. c i L ; see also A. Golodetz, “Fractional Distillation in t h e Laboratory and N e w Rectifying Apparatus,” Chem. Ind., 35 (1912), 102 and 142
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Vol. 71
KO.3
GENERAL SCHEME O F EXPERIMENTAL PROCEDURE
A11 distillations were made with portions of a ten gallon sample of Pennsylvania crude oil, taken from one of t h e pipe-lines running into t h e city of Pittsburgh. Primary distillations were conduc’ced b y each of the three methods indicated above. Cuts were made a t intervals of 2 5 ’ C . a n d fractions between t h e same temperature limits in each series n-ere combined and reserved for redistillation. Specific gravities were measured for t h e individual cuts and also for the combined fractions, t h e latter figures representing a n average of all the single determinations. Redistillations were made with portions of t h e combined 2 j o fract,ions: so cuts were made in these cases over appropriate temperature ranges and individual specific gravities determined. The whole series of experiments represents some j o primary distillations and about 4 0 redistillations. Over 800 specific gravity determinations were made, I t is felt therefore t h a t t h e measurements have been sufficiently comprehensix-e t o establish conclusively the relative amounts of fractionation secured by t h e three types of general distillation methods selected for study. The procedure adopted for t h e study of degrees of fractionation is believed t o be one which will be found of much service for other similar cases. I t furnishes a very satisfactory means of estimating t h e degrees of homogeneity of distillation cuts obtained from complex mixtures containing constituents n-hich cannot be readily identified by chemical or physical measurements. GEKERAL DETAILS OF PROCEDURE
T h e mechanical details involved in quantitative distillation are of great importance and deserve considerable discussion, though they will probably be of b u t slight interest t o those who have not worked with the various methods now in \Togue. HEATERS--A heater of t h e t y p e shown in Fig. I was used with a 2 2 0 volt alternating current in series with a n ammeter and a water rheostat. I n some cases the temperature of t h e vapor in the Hempel PUN apparatus was carried u p t o 3 2 j oC. which required a current density of from 3 t o 4 amperes. COKDENSER-At y p e of condenser had been deSECTION veloped which meets in a satisfactory manner the FIG. I-ELECTRIC HEATER FOR O ~ FLASKDISTILLATIONS needs of the work a t present in progress. I n distilling a‘crude oil, volatile products come over a t first, and t o prevent their loss efficient cooling is necessary; uiz., a temperature of o o C. or lower. For t h e heavy lubricants driven over during a vacuum distillation. an air con-
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Mar., 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 CHEMISTRY
denser gives too much cooling a n d there is trouble on account of lag or even clogging. The remedy for t h e latter difficulty is, of course, t o raise t h e temperature of condensation a n d t h u s reduce t h e viscosity of t h e distillates. Allen a n d Jacobs1 used a vertical Liebig condenser (this .position minimizing lag) and ran through t h e
I
I
I
b
FIG.11-DISTILLING APPARATUSCOMPLETE a-Switch a t Electric Mains. b-Water Rheostat.
