V O L U M E 26, NO. 1 1 , N O V E M B E R 1 9 5 4 was determined from the known amount of water added with correction for the amount of water present in the original recrystallized sample. The samples for run 4 were made by adding random amounts of water to samples of the recrystallized salt weighing over 40.00 grams, after shaking frequently over a period of 48 hours. Small samples were then removed and dried in a desiccator until the pressure remained constant a t 11 cm. of mercury for 24 hours. Forty-gram samples were used from the remainders for extraction. This variation was added as a check on the vacuum drying method. I t is apparent that temperature compensation is not only possihle but very good. The maximum deviation was in the order of 1 pa., rrhich Tas within the mechanical reproducibility of the microammeter. This deviation represents an error of about 0.027, moisture in either of the two salts. The apparatus had excellent time stability characteristics and results could be readily reproduced over extended periods of time. Determinations could be made rapidly. With the initial gain already set, a single determination required less than 10 minutes, including the time for stirring the salt and the solvent. ACKNOWLEDGMENT
The authors wish to express appreciation to The Texas Co., n-hich supported this work.
1719 LITERATURE CITED
Blake, G. G., J. Sci. Instr., 22, 174 (1945). Boeke, J., Philips Tech. Re*., 9 ( l ) ,13 (1947). Dean, E. W., and Stark, D. D., J . Ind. Eng. Chem., 12, 486 (1920).
Guichard, Marcel, Compt. rend., 215,20 (1942). Jensen, F. W., and Parrack, -4.L., Texas A. & M. College Eng. Expt. Sta., Bull. 92, 1946; IND. ENG.CHEM.,ANAL.ED., 18, 595 (1946).
Jolson, L. AI., 2. anal. Chem., 108,321 (1937). Kelly, M. J., “A Linear, Temperature Compensated, High Frequency Salinity Neasuring Device,” thesis, A. &. AI. College of Texas, College Station, Tex., 1951. Kieselbach, R., ISD.ESG. CHEW,ANAL.ED., 18, 726 (1946). llitchell, John, Jr., and Smith, D. &I., “dquametry,” Kew York, Interscience Publishers, 1948. Muller, G. R. (to Allgemeine Elektricitats Gesellschaft), Ger. Patent 696,056 (Aug. 8, 1940). Sand, H. J. S., “Electrochemistry and Electrocheniical.-lnalysis,” 1-01. 111, p. 84, Brooklyn, Chemical Publishing Co., 1942. Suter, H. R., BNAL.CHEM.,19, 326 (1947). West, P. W., Senise, P., and Burkhalter, T. S.,ANAL. CHEM, 24, 1260 (1952). RECEIVED for review March 15, 1954 Accepted August 18, 1954 Presented at the Regional Conclave, .k\rzRIcas CHEMICAL SOCIETY, Xew Orleans, L a , December 10,1953.
Identification of Compound Types in a Heavy Petroleum Gas Oil H. E. LUMPKIN and B. H. J O H N S O N Humble
Oil and
Refining Co., Baytown, Tex.
.Inalytical methods for petroleum products have been extended from gas through gasoline, kerosine, and heating oil in recent years. One of the last major challenges in composition studies of petroleum lies in the gas oil and lubricating oil ranges. A combination of separation techniques and ultraviolet and mass spectrometric data on the separated materials has been applied to the identification of hydrocarbon and sulfur compound types in the aromatic portion of a heavy gas oil. The majority of the sulfur compounds in the sample of fairly high sulfur content investigated is shown to be of the condensed aromatic-thiophene type. Figures are given showing the compound type identifications and the order of removal of the types from alumina gel.
I
S .iSY business venture involving a raw material and a fin-
ished product, knowledge of the composition of the feed stock and of the materials derived therefrom is highly desirable. -4nalytical methods for petroleum products have been extended from gas through gasoline, kerosine, and heating oil in recent years. A single mass spectrometer or infrared scan yields all the data necessary for the analysis of many gaseous samples (20, 21). Simple distillation with the application of some instrumental method to a few fractions is sufficient for component analyses in the lower gasoline boiling range ( I , 7 , I?‘). -4s the boiling range is increased through the heavy gasoline to the kerosine and heating oil ranges, component analyses give way to compound type analyses ( 3 , 4 , 15) and the procedures are still not overly complex or time-consuming. In the gas oil and lubricating oil ranges, the literature has been concerned mostly with structural group analysis employing refractive indices, density, mean molecular weight, bromine number, specific dispersion, and ultimate analyEes for carbon and hydrogen content (6, I S , 14). Van S e s and
van Westen (18) have reduced the time requirements of their n-d-M method of structural group analysis to 1to 2 hours and have shown many applications to refining operations. It is the authors’ belief, however, that a true compound type analysis can have much more meaning in evaluating crudes, adjusting refinery operations, and elucidating the nature of the mechanisms involved in many refining processes. This paper describes experimental work and spectral interpretations which have led to the identification of the major hydrocarbon and nonhydrocarbon compound type present in the aromatic portion of a heavy (600’ to 1000° F.) gas oil. The oil contained CIS to C35 compounds with maximum concentrations in the C27 to Cpg region. Chromatographic separations, ultraviolet and mahs spectral data, and sulfur analyses have been employed in this investigation. EQUIPMENT
A Consolidated Model 21-103 analytical mass spectrometer mas modified by the installation of a narrow exit slit analyzer tube and a high field magnet, in order that ions up to about m/e 600 could be resolved. Ap ropriate changes in the scanning circuit to decrease the rate ofscan to a value commensurate with the amplifier speed were made. A high temperature inlet system, differing principally from that of O’Seal et al. (19) in the design of the valve, was fabricated. A diagram of this heated inlet system is shown in Figure 1. The 2-liter borosilicate glass reservoir, valve, frit, and leak line are heated to 575” F. with 1/2-inch flexible heating tape. Each section of tape is controlled with a Variac and thermocouple. The glass apparatus is insulated with various layers of asbestos tape and heavy aluminum foil in order to conserve the input heat and to prevent the presence of undesirable cold spots. The gallium valve has a 1-inch-diameter port and is designed to conserve the relatively expensive gallium. About 7 ml. of gallium was used in the valve shown. The leak line was heated through the cover plate to within about 6 mm. of the ionization chamber. Ultraviolet spectra were obtained on a Cary h4odel 11 doublebeam recording spectrometer.
ANALYTICAL CHEMISTRY
1720 METHODS AND TECHNIQUES
t,ification scheme employing mass spectral data must be based 011 t'he molecular weights of the molecule ions or of the fragment ions produced under electron bombardment. Even though data are obt,ained on carefully separated samples, there are still many compound types and a wide spread of molecular weight's of each type present in a given fraction in the gas oil range of pet,roleum. .4 reasonable scheme of gross classification is to assign molecular typm to a given series, based on their carbon to hydrogen ratio, or, in the case of nonhydrocarbons, to their equivalent carbon to hydrogen ratio. The simplest aromatic compound type, alkyl benzenes, form the C,Hz,-, series of parent masses. All of the aromatic types have been assigned to series progressing in unsaturation from C,Hz,-s to C,H,,-18. There are compounds which belong to the C,,Hzn-2o group, but as these form the same parent mass series as the C,,H*n-e type, they have been treated as the latter in the classification scheme. Both molecular Keight and abundance of the parent masse3 and of selected fragment ions have been used in identifying the major hydrocarbon and nonhydrocarbon compound types in the percolate fractions of the gas oil. Fragment ions characteristic of certain compound types have been employed in type analyses in the gasoline and light gas oil regions of petroleum ( 2 , 3, 16). In surveying the mass spectral literature of high molecular weight aromatic compounds, it was noted that abundant ions are formed for the nucleus plus one, two, or three CHI groups, depending on the degree of substitution on the nuclew, and that the ion abundance of this series generally decreases as additional methrlene groups are added. Kinney and Cook (11) have pointed out the similarity of spectral features of substituted benzenes and thiophenes and in 17 of the 26 thiophene compounds for which mass spectra were given, the nucleus plus one or two CH? groups forms the base peak. This feature of the mass spectra has been utilized to a high degree in the present study. The sum of the parent mass abundance in the parent mass range of each series was plotted for successive percolate fractions obtained by the chromatographic techniques described. Khcn a maximum in a parent 6 for example-was noted, fragment ions in mass series-C,Hg,the corresponding series, CZHzn-7)were examined in the same cut or cuts. A fragment was sought which reached a maximum in the same region of the percolation which was considerably more abundant than the C,H,,-, peak one or two carbon numbers lower. In this manner the nuclear molecular weight was determined, and with knowledge of the ultraviolet spectra and of
Separation of Compound Types Using Solid Adsorbents. The problem of identifying the major compound types in the heavy gas oil was simplified by percolating the total gas oil through rolumns packed with silica and alumina gels, using the elution method of development (6, 9, 10, 12, 16). Sufficient separation of compound types was achieved by this method so that each of the final percolation cuts, on which the identifications were made, contained no more than four major compound types.
...
fl ,SOFTIRON
MAGNETS
.A. --PYREX
ROD
CJ: ....
Figure 1. Diagram of Mass Spectrometer Inlet System The first separation was made using silica gel as an adsorbent. A vertical glass column consisting of an upper section, 5 feet by 2 inches, and a lower section, 1 foot by '/A inch, was packed with Davison 28- to 200-mesh silica gel. Fifty grams of the heavy gas oil, diluted with 10 ml. of benzene to reduce the viscosity of the sample, was added to the top of the packed column. A large volume of iso-octane was passed through the column to elute the saturate portion, 52.4 weight % of the sample. Most of the saturates were removed by the iso-octane before any aromatics began to come off the column. A 10% benzene-QO% iso-octane solution was then used as an eluent. The portion of the sample that could be removed with this eluent, 30.6 weight %, was collected as aromatic fraction A. All of the oil that could be eluted with 100% benzene, 14.3 weight %, was collected as aromatic fraction B. The remainder of the sample, 2.7 weight %, was displaced from the column with ethyl alcohol. The ultraviolet spectra of these fractions indicated that fraction A contained principally benzene and naphthalene types with some phenanthrenes. Fraction B appeared to contain phenanthrenes and more highly condensed aromatic types. The alcohol desorbed fraction was composed of nonaromatic compound types with relatively low intensity absorption in the ultraviolet spectrum and no attempt was made to separate further and identify the components in this fraction.
To preserve the separation obtained on the silica gel column, fractions A and B were charged separately to columns packed with Alcoa F-20 alumina gel. A series of graded solvents was used to elute the samples from the columns, beginning with iso-octane and followed with mixtures of benzene and iso-octane. I n each case a particular solvent was used until the rate of sample removal became very slow. Approximately Zyocuts, based on charge, were taken and ultraviolet and mass spectra and total sulfur were obtained on all fractions. Mass Spectrometer Identifications. Any iden-
'i
600
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Cn Hen-6 CnHen-8 Cn Hen-10 CnHzn-I2 -*-*-*Cn Hen-14 CnHen-I6 Cn Hen- 18
-.-.a-
0
10
Figure 2.
20
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WEIGHT PER CENT OIL OFF COLUM$O
90
100
Identification of Compound Types in Aromatic Fraction .4 of Cas Oil
1721
V O L U M E 26, NO. 11, N O V E M B E R 1 9 5 4
-
m/r 101 m/e 147 m/e 161
Figure 3.
------
tributein alarge degree to the 7 fragments below m/e 147, gives a large 161 and 175 (not plotted), and is adsorbed on alumina to a considerably higher degree than alkybenzenes. Benzothiophenes meet all of these prerequisites. Selected fragment ion abundances from the C,H2,- series are plotted in Figure 4. M /e 155, characteristic of compounds containing naphthalene as their major nuclei, attains a maximum at about 70% on the abscissa, and the corresponding molecule ion series of Figure 2 has been identified a8 naphthalenes. The fact that 7n/e 197 increases rapidly while m/e 183 is low a t 90% oil off the column indicates the presence of a compound type belonging to the C,H2,-,2 group and having a probable nuclear molecular weight of 184. With the addition of a CH, group the first large ion expected would be a t mass 197. Dibenxothiophenes (or thiophenonaphthalenes) are found to conform to these requirements; thus the quite abundant and well separated type a t the 90% position of the C,H,,-12 parent mass curve is shown to be dibenzothiophenes. In a similar manner, using
I
Selected Ifasses in CnH2n--7 Series .4romatic Fraction A of Gas Oil
the general adsorbabilitj- characteristics of the aromatic types, the identification of the compound type was made. Sulfur analyses by the modified Dietert method wew obtained on each fraction. Compound Types Identified in a Heavy Gas Oil. In Figure 2 the sums of the parent mass abundances for the C,HW 6 through C,,HS~-I~ series have been plotted versus the per cent oil off the column when percolating aromatic fraction .4 over alumina gel. The task a t hand then is to identify the compound types contributing to these peaks. The first 10 to 15yo of the oil contained some saturates. The absence of large parent peaks is due to the fact that the saturated compounds form relatively small parent masses compzred to the aromatics. In addition, m / e 43, 57, 71, 85-41, 55, 69, 83-67, 81, 95, generally known to be characteristic of paraffins, naphthenes, and condensed naphthenes (16),are quite abundant in these first fractions. The identification of the compound types indicated in Figure 2 was accomplished mainly by study of the fragment ions. In Figure 3 selected ions which would be expected from compounds belonging to the C,H,,- 6 series have been plotted. I n the 10 to 40y0 region on the abscissa, mass 105, a peak expected from alkylbenzenes, is quite large. M / e 91, 92, 119, and 133, which are also characteristic masses in the spectra of the alkylbenxenes, were also very abundant in this portion of the chromatogram. The C,H,,-6 parent mass curve goes through a maximum in the same region; therefore, the compounds contributing to this maximum are identified as alkylbenzenes. In the 55 to 75% region of oil off the column of Figure 3, mass 161 becomes quite large and m/e 147 shows a slight maximum while the 105 peak is a t a minimum. At the corresponding position in the parent mass curve for the C,H2,-6 series, there is a pronounced maximum. Therefore, a compound type is sought to be assigned to this beries, which does not con-
Figure 4.
Selected Masses in C,H,,-n Series Aromatic Fraction A of Gas Oil
I200
t o 1 I
0
IO
Figure 5.
I
I
20
x)
I
I
40
Ii 100
I
I
I
I
I
I
I
1
50
60
70
80
90
I
WEIGHT PER C E N T OIL OFF COLUMN
Identification of Compound Types in Aromatic Fraction B of Gas Oil
1722
ANALYTICAL CHEMISTRY
ultraviolet data t o indicate the regions in which the major nuclear types were present and characteristic ions in the mass spectra, as well as qualitative knowledge concerning the relative adsorbabilities of the various compound types, identification of phenanthrenes, pyrenes, thiophene condensed in a benzene and naphthalene structure or with a phenanthrene structure, benaophenanthi enes, and benzopyrenes have been identified in a heavy gas oil. Some of these latter compound types occur in fraction B, the back end of the silica gel percolation (repercolated over alumina), and are identified with the maxima of their respective parent mass series in Figure 5.
2
0
IO
20
30
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SO
60
70
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90 100
PER CENT OFF COLUMN
Figure 7.
thenes. However, considerable information has been gained concerning the types of sulfur compounds occurring in the heavy gas oil portion of petroleum and the relative adsorbability of the major compound types on alumina gel. As additional calibration compounds become available and better separation techniques evolve, the complexity of analytical problems in this challenging boiling range of petroleum should be reduced.
\
0 0
Sulfur C o n t e n t of Aromatic F r a c t i o n B of Gas Oil
IO
20
30
40
50
60
70
80
90 100
PERCENTOFFCOLUMN
Figure 6.
S u l f u r C o n t e n t of Aromatic Fraction A of Gas Oil
To substantiate further the sulfur compound identifications, total sulfur determinations on the cuts of percolations 4 and B were obtained and are shown graphically in Figures 6 and i . The major maxima in sulfur content fall under the regions assigned to the sulfur compounds and serve as excellent confirmation of the identifications made of these major components. In the benzothiophene region, calculations based on the sulfur content and the average molecular weight indicated a concentration of 65% sulfur compounds n-as attained in this portion of the chromatographic run. -1 concentration of i O % sulfur compounds \$-as achieved in the nsphthalenobenzothiophene (or thiophenophenanthrene) region of percolation B. The maximum in the sulfur curve in the 0 to 15% region of Figure 7 was found t o be due to the presence of sulfides. The ultraviolet iodine-complex method (8) developed in these laboratories indicated the presence of sulfides. This is a semiquantitative procedure and very good agreement between the sulfur detei mined as sulfide sulfur and the total by the Dietert method was observed. The observed ahsencc of abundant parent masses in the 0 to 20% region of Figure 5, and the presence of large fragment peaks normally attributable t o paraffins, naphthenes, and benzenes in the mass spectra are expected features in the spectra of mixed sulfide compounds. I n previous percolations of samples containing sulfides over silica gel it has been observed that the sulfides are more strongly adsorbed than the aromatic compounds. Therefore, an inversion in adsorbability characteristics of the sulfides with respect to the majority of the aromatic materials in fraction B appears to have occurred in changing from silica to alumina gel. All of the questions concerning the application of high resolution mass spectrometry to complex mixtures of hydrocarbons and nonhydrocarbons are obviously far from answered; indeed, some of the parent mass maxima in the present study are as yet unexplained. Some compound types expected to be presentauch as diphenyls and phenylnaphthalenes-have not been identified. I n addition, the authors have been unable to distingui-h between condensed and noncondensed aromatic-naph-
ACKNOWLEDGMENT
The authors wish t o express their appreciation to S. H. Hastings for his helpful advice and suggestions in the compound type identifications, and to acknowledge the help of C. S. Langford, G. R. Taylor, C. R. Middleton, and R. R. Burch in making the separations and providing the mass spectral data. LITERATURE C I T E D
Bell, hI. F., ANAL.CHEM..22, 1005 (1950). Brown, R. A., Ihid.. 23,430 (1951). Brown, R. A., Doherty, W.,and Spontak, J., Consolidated Engineer;ng Corp., Mass Spectrometer Group Report 84 (1950). Brown, R. A,. Ilelpolder, F. W., and Young, 15’. S., Petrolpum Processing, 7,204 (1952). Claesson, S . , AriZiz Kemi,M i n e r a l . Geol., 23A, S o . 1 (1946). Deanesly, R. A l . , and Carleton, L. T., IND.ESG. CHEM.,ASAL. ED.,14,220 (1942). Feldman, J., and Orchin, AI., I n d . Eng. Chem.., 44, 2852 (1952). Hastings, S. H., ANAL.CHEM.,25, 420 (1953). Hibbard, R. R., I n d . E n g . Chem., 41, 197 (1949). Hirschler, 4 . E., and Amon, S., I b i d . , 39, 1585 (1947). Kinney, I. W.,Jr., and Cook, G. L., .&KAL. CHEM.,24, 1391 (1952). Lipkin, 11. R., Hoffecker, W,A., Martin, C. C.. and Ledley, R. E.,Ibid.,ZO, 130 (1948). Lipkin, h1. R., and Alartin, C . C., IWD. ESG. CHELf., .&NAL. ED., 19,183 (1947). Lipkin, 11. R., Martin, C. C., and Kurtz, S. S., I b i d . , 18, 376 (1946). and Elliott, h.,ASIL. CHEW, Lumpkin, H. E., Thomas, B. W., 24,1389 (1952). Xlair, J. B., and Forziati, A. F., J . Research -Yati. Bur. Standards, 32,165 (1944). llelpolder, F. W., Brown, K. A,, Young, W-.S.. and Headington, C. E., I n d . E n g . Chem., 44, 1142 (1952). Nes, K., van, and Westen, H. A , , van, “Aspects of the Constitution of Mineral Oils,” Houston, Tex., Elsevier Press. Inc., 1951. O’Neal, 13. J., Jr., and Wer, T. P., Jr., ANAL.CHEM..23, 830 (1951). Seyfried, W. D., and Hastings, S. H., IWD.EWG.CHEM.,ANAL. ED.,19,298 (1947). Washburn, H. W., Wiley, H. F.. Rock, S. hl., and Berry, C. E., I b i d . , 17,74 (1945). RECEIVED for review M a y 24, 1954 Accepted July 9, 1954. Presented before the American Society for Testing Materials, Committee E-14, New Orleans, La , May 24 t o 28, 1954.
