Modern Analytical Distillation of Crude Petroleum J. A. LOCKWOOD, R. L. LETOURNE\U, ROBERT MATTESON, A N D F R i N K SIPOS California Rerenrrh Corp., Richmond, Calif.
AI though many petroleum companies employ their own methods of assaying crude oil, a review of the literature reveals very little information on this subject and practically nothing involving the ninm modern types of distillation equipment. The new equipment desorihed consists essentially of a spinning hand column for atmospheric and vacuum distillation, a spinning auger still (a truly novel molecular still) for fractionations that would normally he performed in a molecular still, and an nil-glass
F
OIt many years the need for a standardized mean8 of wsayinK crude petroleum has heenevident. .4nalytical dataobtaincd by standardized equipment and operating procedures are required as a basis for the selection of refinery processing schemw and their evaluation, to provide data for design or altcration o i process equipment, and as a hask far contractual rdiitionshipP involving the sale or exchange of crude petroleum. To satisfy this wide range in requirementfi, the scope of crude oil analysis extends from a simple two-product breakdown t o the preparation and inspection of several gasolines, middle distillates, and residua. It may include a gas fraotional analysis and a true hoiling point distillation, as well as equilibrium Aash vaporization data. on the whole oil and one or more residua. Mctnv analvtioal methods currently in use have been designed by petroleum refiners and engineering firms to meet their own specific requirements. These methads differ markcdly in the distillation e q u i p ment and degree of fractionation employed, and in the nature of the products prepared for inspection. To date no specific method or combination of methods has been widely adopted by industry. In 1922 Dean and caworkers at the U. S. Bureau of Mines made a great contribution (2) toward standardization of crude oil analysis based upon a single, straightFigure 1. Spinning Band forward atmospheric and Column
equilibrium flash vaporization unit. Typical data illustrative of the results obtained are included. A combination of these stills permits obtaining a wide variety of data to seme as a basis for the selection and evaluation of refinery processing schemes for the design or alteration o f pmeeas equipment, and as a hasis for contractual relationships involving the sale or exchange of crude petroleum. The stills are recommended to the industry as a suitable basis for standard testing methods in these important fields.
vacuum distillation. This is commonly known 8 s the Wempel distillation. The method has p r o v d very satisfactory in cases where it is unnecessary to produce cuts in sufficient volumc t,o perform a wide variety of tests on the frmtiom, and \$-hero moderate depth of di8tillation into the crude suffices. In 1941 Mithoff, MaePherson, and Sipos presented a pertinent discussion (S) before the San Francisco meeting of the Ameriosn Petroleum Institutc. This study Wi16 concerned primarily a i t h the characteristics of California. crude oils, but it contained a complete description of the snalytiwl distillation procedures cmployed. Over the past tcn years further refinements have been made in these methods and the analytiosl procedures now employ more modern typeR of equipment. Although these methods are more claboratc than those of the Bureau of Mines, they yield considerably more information. This paper describes thc equipnient for analysis of orude oil a8 currently employed in the l&txxatorimof the California Researoh Chrp. The appamt.us hns provcd to he versatile. rapid, and
r
Figure 2. 1398
Arrangement of Equipment for True Boiling Point Distillation
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1399
Table I A
B
Method C D
E
Gasdines
210' F. end point 260O F. end mint 320° F. end L i n t
340' F. end point 390' F. end point
X
X
X
X X X
X
X
~ ~ ~ ~ ~ . ~ . ~ ~ ~ .
437O F. end noint ~~~
~~
Heart out, 260° to 390- F. end point Kerosene distillate 360 viscositv'after 340' F. end point gasoline 400 visoosity. after 390' F. end mint gasoline 525O end point after 320' F. end mint ecLsoline Gas oil 35 viscositybafter 3Y09 F. end
X
x x
X
~
X
point gasoline 40 visooaity'aftcr 390° F. end point gasoline Heavy, after 40 viscosity' gas oil
Residuum After 390' F. end point gasoline X After 525- F. end point kerosene distillate After 400 viscosity' kerosene distillate After 40 viscosit9 gas oil After heaw gas oil Approni-te still charge, liters 2-5 Saybolt therrnovisoosity. S.R.C. viseosity at looe F.
X
hqhly satlrfactory in more than three years of routine laboratom operation. It is believed that these factors, together with the advanced design, answer the industry's need for a standardized apparatus far distillation of crudo oil. The principal still employs a spinning band column 0.5 inch in diameter and 3 feet long, in which almost the entire distillation of a crude oil is performed. The distillation is carried ta a bottoms temperature of 650' F. a t 1 mm. of mercury pressure. One of the great advantages is that only one distillation column, instead of two or three, need be used. A simple laboratorymolecular still of new design is used t o extond the distillation of the residua far beyond anything heretofore possible without going to more complicated molecular stills. An all-glass equilibrium flash vaporization still requiring only modest quantities of feed stack covers a wide variety of operating conditions. Selected data
X
X X
X
X X
X
1'
X 4 8
6-8
t
X X 8-10 15-18
I
14'
Figure 3.
Spinning Auger Still
Figure 4.
Equilibrium Flash Vaporization Still
A N A L Y T I C A L CHEMISTRY
1400 on California crudes illustrate the use of the equipment in preparing analyses of typical crude oils.
A
W 2 0 PRESSURE RCCULATOR
CY
CONDENSER
TYPES OF CRUDE PETROLEUM ANALYSES
Several standardized procedures are employed by the CaliPRLSLURL RCGULATION SYSTEM fornia Research Corp. These are of three principal types: product breakdown, true boiling point analysis, and equilibrium flash vaporization. The standardized product breakdowns employed have been designated a8 Methods A, B, C, D, and E. The prodSYSTLM ucts prepared are shown in Table I. In the true boiling point analysis the crude oil is distilled into well fractionated cuts of 4 volume % ' and inspections are obtained. The CUT PRESSURE distillation may be conducted RCCULATION SYSTEM independently, in which case a 1500-ml. charge is used, or it may be combined with a RUIBER STOPPC RUBIER STOPPER product breakdown of the type shown above, using charges as Figure 5. Arrangement of Equipment for Equilibrium Flash Distillation large as 18 liters. The equilibrium flash vaporization tireakdowns are of the standard type required for use heptane and methylcyclohexane; atmospheric pressure; total in the design and operation of commercial atmospheric and reflux; boilup rate of 2 liters per hour. It will handle as much as vacuum distillation units. 4 liters per hour under these conditions with a drop in theoretical plates to about 15. The boilup rates of about 2 liters per hour a t SPINNING B 4 Y D COLUMN 10 mm. of mercury, and about 1 liter per hour a t 1 mm. are exceptionally high for these pressure regions. Column holdup The spinning band column developed in these laboratories is is less than 5 ml., including liquid held up in the head. Although similar in many respects to that described by Birch, Gripp, and this type of column does not have the small height equivalent of a Nathan ( 1 ) . There are, however, several important differenres theoretical plate of many types of packed columns, it is more than in the mechanical features, which allow routine operation of adequate for crude evaluation, as is shown by the fact that most these columns. Figure 1 shows the details of the glass part of of the distillations are carried out at a reflux ratio of 5 to 1 or less, the column assembly unsilvered and without the band installed. which means only one third or less of the column's fractionating Figure 2 is a schematic diagram shoxing the column mith its porn-er is used. principal accessories. h typical procedure illustrates hofi the equipment may be used The column consists of heavywalled borosilicate glass tubing to determine a true boiling point curve and a t the same time to 0.5 inch in inside diameter and 3 feet long. It is vacuumprepare a large number of cuts which may be blended to form jacketed and silvered t o ensure adiabatic operation. The vacuum jacket is further encased in a tubular heating mantle to stocks desired in a Method D analysis. minimize heat losses and strains on the column in high temperature operation. The band is a strip of 18-gage stainless steel 44 A 10-liter charge of the crude is introduced into an evacuated inches long and approximately 16/92 inch wide. Clearance of 12-liter still pot fitted to the column. Ice water is circulated inch, only enough to prevent binding, is allowed. The band through the still-head condenser in order to preserve the light is twisted through a spiral of 720' throughout its length. The ends of the crude. As a further safeguard against losses, two additional length of the band extends into the still pot, where it 500-ml. traps, cooled with a bath of carbon dioxide and alcohol, serves the important function of a stirrer. The top of the band is and a &gallon gas bottle filled with salt water are connected in attached to a rod by a flexible link. This rod extends through a series to the still-head condenser vent. Heat is applied to the glass bearing in the head assembly, and a rubber nipple lubristill pot, and rotation of the band is started to provide stirring cated with castor oil serves as a vacuum-tight gland, permitting rotation of the band. The column head is also vacuum-jacketed and so prevent the building up of water pockets in the still pot. and equi ped with an electrically operated reflux controller. The column is set for total reflux, and this condition is mainThe h i n t i s rotated within the column a t a speed of about 3000 tained until no more material is collected in the traps and all the r.p.in., co as t o oppose the rising action of the vapors. A variwater in the crude is rejected from the system. With fresh traps able-speed driving motor is used in order to allow smooth operainstalled, the distillation is allowed to proceed to a cut point of tion of each column at the optimum band speed near 3000 r.p.m. 110" F. at a reflux ratio of 20 t o 1. On a dried crude, it is posAt the end of the low pressure distillation, rotation is reversed, sible to debutanize quantitatively by operating initially at a thus causing the band to operate as a vapor pump. reflux ratio of 20 t o 1 with alcohol chilled to -30" F. circulated through the condenser. The column is then operated at a reflux The column shows an efficiency equivalent to 20 theoretical ratio of 5 to 1, and 4'% cuts are taken to a vapor line temperature slates under the following operating conditions: test mixture, 1 ~ of 320" F., followed by 1% cuts during the reminder of the dis-
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 tillation. However, during distillation of the middle portion of the wide range gas oil the reflux ratio may be reduced to 2.5 to 1 and 4y0 cuts taken. The distillation is performed at atmospheric pressure up to a bottoms temperature of 625"F., a t which point the operation is stopped, the still pot is cooled, the pressure is reduced to 10 mm. of mercury, and the distillation is continued to a 625" F. bottoms temperature. Again the distil!ation is interrupted, the still pot is cooled and the pressure is reduced to 1.0 mm. of mercury, and then continued to 650" F. bottoms temprrature.
1401 drops in either the column or the still pot. to prevent return of water t o the still pot.
The head is designed
SPINNING AUGER HIGH VACUUM STILL
As the result of observations made on thc performance of the spinning band column operated with the band turning so as to function as a vapor pump, a smaller $till JTith a pump in the form of an auger was developed.
Cuts from thc distilltition :we blended to provide the products required for inspection. If a fractional analysis of the gas in the crude is desired, the carbon dioxide trap condensate and the first cut thereafter are analyzcd by means of a mass spectrometer. They may be analyzed separately o r combined, depending upon whether gasoline blends arc to be inspected on a stabilized or unstabilized basis. Several features of this still make it particularly valuable in assay of crude oil. Precise control of reflux provides greater reproducibility in the yields and characteristics of products. The boilup rate a t reduced pressures is much highrr t h m is obtainable with packed columns. Use of the same distillation for the product breakdown and the true boiling point analysis saves time and reduces the possibility of inconsistencies. Production of all cuts for the true boiling point analyais from :t single charge t o the still eliminates transfer losses, A small difference in vapor and bottoms temperatures results from the very low pressure drop across the column. This permitR a greater overhead yield for a given bottoms temperature. The effrctivc shortening of the column toward the end of the distillation by changing direction of rotation of the band also increases the yield of distillate obtainable. Wet crude oils are handled without difficulty because the high degree of agitation by the band prevents formation of large water
Figure 7.
True Boiling Point Distillation of San Joaquin Valley Crude 33.6O API composite
This still, shown in Figure 3, has a rolumn8inches longand about 1.25 inches in diameter, fitted nith itn ordinary wood bit which has been machined t o fit snugly within the column. This column, like the band column, is vacuum-jacketed and further protected from temperature strains by an exterior heating mantle. No reflux controller is employed, but internal reflux in the column is considerable. The still is operated a t pressures of about 1 micron, and the auger is rotated a t a speed of 5OOO r.p.m., thus acting as a vapor pump. h stirrer attached to the auger aids in the disengagement of the vapor from the liquid a t these low pressures. Overhead rates as high as 200 ml. per hour are achieved, even at a pressure of 1 micron. The charge to this still is a residuum prepared on the spinning band column under the conditions described in the preceding section. Seventy or more per cent of the residuum stock may be distilled into fractions on this device, bringing the total over-all distillation yield on the crude to over 95%. (The characteristics of this new still will be described in more detail in a subsequent publication. .4 patent has been applied for.)
ST -1
2
~001
50 I
25
l
l 30
/
I
/
35
] 40
VOL. % DISTILLED Figure 6. Analysis of San Joaquin Valley Crude 33.6O API composite Gasoline breakdown
With this still, lubricating oil fractions as heavy as those produced by deaaphalting or deresinification of residua have been obtained by distillation. Figure 9 illustrates the extension of the viscosity-yield relationship possible by use of this still. EQUILIBRIUM FLASH VAPORIZATION STILL
This apparatus is an all-glass device which performs an isothcrnial equilibrium vaporization of crude oils or residuum stocks
ANALYTICAL CHEMISTRY
1402
a t a feed rate of 3 to 6 ml. per minute. It covers the range from atmospheric temperature to 750' F. and pressures from atmospheric down to approximately 1 mm. of mercury. Its principle of operation is identical to that of a much larger all-metal device recently described by Smith ef al. (4). Th? apparatus, shonn in Figure 4, is constructed of borod i c a t r glass and insulated t)>means of an integral, silvered vacuum jacket. Heat is supplird by saturated va or from a boiler a t the base o r the apparatuq. The entire apparatus is 39.5 inches high. Commonly used heat tranrfer liquids are uped to :each temperatures up to 400 F.: above this choice of liquids is MID X DISTILLED more critical. Bromonaohthalene True Boiling Point Distillation of San .Joaquin Valley Crude Figure 8. is satisfactory up to i i ~atmospheric boiling point (640" F,), 33.6" API composite Inspections of 45% cuts US. mid 90' distilled but organic (alkyl aiyl) dicatcx esters are effective up to 750" I: without decompwition n-hen blanketed with dry nitrogen. This permita distillation to lie performed considerably beyond niended t o the industry as B basis for a standardized ryrtem of the atmospheric boiling point of mercury. Because of its analyticd crude oil distillation. high density and toxicity, mercury has been found to be unsuitable for use as a boiling fluid in glaw apparatus, especially in TYPICAL CRUDE ANALYSIS work employing nontechnical personnel xvhere even an occasional failure of the eauiDment niav not br tolrrated. Typical results of crude oil assays made on the equipment Feed to the column is preheated in a borosilicate glass coil described above are presented in tabular and graphical form in consi$ting of 16 feet of double-coiled tubing 8 mm. in inside Table I1 and Figures 6 to 13. Table TI presents a Method D diameter located in the same vapor bath that surrounds the flash analysis of a San Joaquin Valley, Calif., crudc. Method A, B, chamber. The preheated feed is introduced about 50 mm. from and (' analyses are usually subniit,ted siinilaily in tabular form. the bottom of the flash chiimlm, n hich consists of a tube 22 mm. in inside diameter and 300 mni. long. The accessory equipment Results of Method D or E analyses, efipecially if obtained in conused with this device is Phon 11 scheiiiaticdly in Figure 5 . junction with a true boiling point analysis, map also be presented graphically, as illustrated in Figures 6 to 11. This permits ready estimation of the yields and inspections of products other than Adequate data for design and operation of commercial dihti1l:ition units are readily ohtainable from this apparatus. About 300 ml. of charge are rrquired in a IO.& 9.0. single equilibrium flash vaporization 8.0. run to provide sufficient stoch fol 7.0 the desired inspection-. Thus, a *e0 5.0. five-point equilibrium distillation Ibreakdown on a crude or I esiduuni 4.0. may be obtained with approsiY 3.0 mately 1500 ml. of charge (FigG ures 12 and 13). c_ The equipment described above 8 2.0. V has been used in essentiallv its ? present form for over threr Y years, either as single units 0 1 1.0 in combination. Operation has y 0.9: been placed on a routine hasih z 0.0' 0.7. employing nontechnical person0.6 nel. O u t s t a n d i n g among t h e 0 .5 characteristics of the method employed is the wide variety of products that can be made froin many different types of crude oils $11 three pieces of equipnwnt vic*ld desired products more 1 apidly than apparatus formerly used. With this background of Figure 9. True Boiling Point Distillation of San Joaquin Valley Crude experience, the stills and general 33.6' API composite Viscosity US. m i d % of cut methods presented are recomL
A
I
3
E s
=
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1403 ACKNOWLEDGMENT
The design of the glass portions of the various apparatus could not have been accomplished satisfactorily without the assistance
30
40
50
0
70
80
90
I00
RESIDUUM YIELD; Hx.X FROM CRUDE Figure 10.
Analysis of San Joaquin Valley Crude 33.6' API c o m p o s i t e I n s p e c t i o n s of r e s i d u u m From M e t h o d D analysis
30
40
50
60
70
80
BO
100
RESIDUUM YIELD, VOL. % FROM CRUDE Figure 11. Analysis of San Joaquin Valley Crude
those made directly in the analysis. The graphical presentation of the results of a series of equilibrium flash distillations of another California crude is illustrated in Figures 12 and 13.
33.6' API composite. Viscosity of res i d u u m . From M e t h o d D a n a l y s i s
Table 11. Method D Analysis of 33.6 API San Joaquin Valley, Calif., Crude Composite Kerosene Residuum Distillate Gas Oil, After After Afte; after .liter 400 340: 390 3900 390° vis. 437' e n d p o m t e n d p o i n t end point end point kerosene end point gasoline gasoline gasoline gasoline distillate
Gasolines
Yield From crude as received From butane-free crude Butanes a n d lighter Range from crude as received Gravity, OAPI Flash, closed Tag, OF. Flash, Pensky-Martens OF. Flash, Cleveland open ;up, O F . Viscosity, Saybolt thermo S.S.U. a t 70° F. S.S.U. a t looo F. S.S.U.a t 130° F. S.S.U. a t 210° F. Pour point, F. Sulfur, wt. yo Wax (Holde), % Sediment a n d water, % Vapor pressure, Reid, lb. Conradson carbon % ' s a p . NO., mg. K o H / ~ . Characterization pravity Neut. N o mg. KOH/g. Aniline point F. Smoke t e n d e k y IaGp. mm. Cetane No. Octane KO.b y ASTM D 357-48. After 1 ml. TEL/gal. After 2 ml. TEL/gal.
ASThl distillation method Start 5%
10% 20% 30% 40% 50% 60% 70%
E%
95% E n d point % recovered yo loss
Crude
340° end point
100.0
28.9
...
...
2.4Q ... 0 to 0 to 100.0 28.9 33.6 61.1
... ...
... ...
...
... ...
50.2 41.2
...
+25 0.32 3.1 0 2 4.2
...
0.35
... ... ... ... ... ... ... ...
D-86 124 160 215 300 375 480 564 a t 504/, distilled
390° E n d Point UnButanerect. free 34.3
... ...
0 to 34.3 57.6
...
... , . . , . .
,..
...
... 0:010
,..
... ... ... ... ... ...
...
... 0:012
.. ... , . .
... ... ...
... ... ... ...
... ... ., , ...
61.2 72.4 77.5
D-86 82 120 147 182 203 220 235 260 267 286 311 340 340 95.0 4.0
D-86 93 131 160 194 218 238 257 278 300 325 356 390 390 95.0 4.0
66.4
~
31.95 32.80
... ...
... , . .
...
38.9
...
...
Oto
38.9 54.5
... ...
15.0
...
28:9'to 43.9 39.5 139 ,..
... ...
...
...
, . .
...
...
...
...
... ... ... ,
..
... ... ...
...
...
... ... ...
...
... ...
... 01015
... ... ...
... ... ...
... I
.
.
... ... ...
55.8
... D-86 98 138 167 202 227 251 272 297 325 356 39 1 421 437 96.0 3.0
D-86 357 371 380 390 398 406 416 426 438 454 477 493 519 98.0 1.o
7.0
...
3413'to 41.3 38.5 162
... ,..
360"
...
... 01041
... ... ... ... ... ... ... ... 23 ... ... ...
400
...
... ...
...
6:649
... ... ...
...
... ...
0.07 135 23
... ...
...
... ...
D-86 394 402 407 412 416 420 425 430 437 445 457 468 492 98.0 1.0
D-158 442 470 480 499 518 538 560 582 606 633 662 681 708 99.0
...
After gas oil
34.4
65.7
58 7
31.3
34:i'to 68.7 32.3
34:3'to 100.0 23.9
41:3'to 100.0 22.2
68,;I'to 100.0 15.5
...
...
213
...
...
47.9 40.0
... +30 0.34
...
... ...
... ... ...
0.13 153 50 '
...
... ... ...
260
...
...
...
...
295
... ...
140 80.6 42.6 +70 0.48 4.7
245 120 48.3 +80 0.53 5.2
... 3.2 ...
...
...
...
...
3.5 0.50 28.2
...
... ...
465
... ...
...
1910 205 4-105 0.64 9.6
...
...
6.6 ,.. , . .
OEstimated.
... ...
,..
Approx. Composltlon of Crude Vol. ?& (Ercene) 53 Riverdale Raisin City Kettleman Guijarral Hills
12 19 16 100
1404
ANALYTICAL CHEMISTRY
VOL. % DISTILLED
Figure 12. Analysis of Sail Joaquin Valley Crude 30' API Equilibrium flash distillation a t atmospheric pressure
of W. R. Doty, head glassblower of the California Research Corp. The helpful cooperation of G. R. MacPherson in the preparation of this paper is gratefully acknowledged. LITERATURE CITED
(1) Birch, S. F., Gripp, V., and Kathan, W. S., J . SOC.C h m . I?kd.,
66,33 (1947). (2) Dean, E. W.. Hill. H. H.. Smith, K. A. C.. and Jacobs, W. A.. U.S. Bur. Mines, Bull. 207 (January 1922).
IO
i
30
40
50
60
70
VOL. X DISTILLED Figure 13. Analysis of Sun Joaquin Valley Crude 30' API Equilibrium flash distillation Viscosity of bottoms
(3) Mithoff, R. C., MacPherson, G. R., and Sipos, F., Oil Gas J . , 40, S O . 26, 81-5, 187 (1941). ( 4 ) Smith, R. B., Dresser, T., Hopp, H. F., and Paulsen, T. H., I ? d Eng. Chem., 43, 766 (1951). RECEIVEDMay 14, 1951.
Direct Determination of Oxygen in Organic Compounds Carbon Reduct ion-Manometric Met hod JOSEPH HOLOWCHAK AND G. E. C. WEAR Esso Laboratories, Research Division, Standard Oil Development Co., Linden, N . J .
A
T THE present time, there is no entirely satisfactory method
for the direct determination of oxygen in organic substances, especially in samples of low oxygen content. The most promising method, currently used by most laboratories in this country and exclusively in European countries (16), is based on the thermal decomposition of the organic compound over carbon, first proposed by Schdtze ( 16) and later improved by Unterzaucher (20). Elving and Ligett ( 4 ) in their review of the direct determination of oxygen critically examined the available methods and presented a complete literature survey on the subject. Since this review was written, practically all the publications on the direct determination of oxygen have been based on the Unterzaucher carbon-reduction procedure, Among these are the excellent papers by Aluise et a[.(I), Dinerstein and Klipp (S),and Maylott and Lewis ( l a ) of this country, Deinum and Schouten ( 2 ) of the Netherlands, and Kirsten (9) of Sweden. A recent publication by Grosse el al. (6) describes an entirely new procedure, an isotopic method, which does not require the quantitative separation and quantitative recovery of the ouygen-containing compound 01 any of its reaction products.
-
Considerable difficulties are encountered by many laboratories in adapting the titrimetric Unterzaucher method to the direct determination of oxygen. The major cause of the uncertainty of the method has not been established. At present, it is not known exactly what reactions the iodine pentoxide undergoes under varying conditions. It has been the experience of this and other laboratories that hydrogen, produced during the pyrolysis of the organic compound, reacts with iodine pentoxide, as shown in Table I, with liberation of iodine, which leads to high results. This effect, coupled with the variation in the operating blank, makes it extremely difficult to obtain reliable results on substances of low oxygen content, especially petroleum product8. I t is particularly desirable, however, to have a reliable method for the determination of small amounts of oxygen in petroleum materials, as a sninll amount of oxygen may represent an appreciable quantity of an oxygenated impurity of high molecular weight in the petroleum fraction. Knowledge of the oxygen content is important, because trace amounts of oxygen may affect the stability of petroleum materials during storage and use.
