Determination of Satw rated Hydrocarbons in Heavy Petroleum Fractions by Mass Spectrometry H. E. LUMPKIN Technical and Research Divisions, Humble
Oil
and Refining Co., Baytown, Tex.
A procedure for the tjpe analysis by mass spectron:etrj of the saturate portion of petroleum materials of high molecular weight employs characteristic fragment masses of paraffins, noncondensed naphthenes, and condensed naphthenes containing two through six condensed rings per molecule to delineate these types. The sensitivity and interference coefficients are averages from purecompound spectra and extrapolateddata. The method is simpleand rapid, lending itself toinverted matrix and computer calculation. Any group Mith an instrument capable of resolving and pumping out high boiling petroleum materials should be able to use the method directlj.
I
X THE gasoline and lower distillate boiling ranges of petroleum, mass spectrometer methods of type analysis ( 1 , 2, 7 )
generally determine both saturate and aromatic compoiind types. The t,hree saturate types usually measured by these methods are paraffins, naphthenes, and condensed naphthenes. The condensed naphthenes in gasoline are primarily compounds containing two condensed naphthene rings per molec:ile, such as bicyclo-octane, hydrindane, and Decalin. I n the higher distillate boiling ranges of petroleum it becomes necessary to separate the saturate and aromatic portions of oil prior to mass spectrometric determinations. This can be accomplished fairly completely using solid adsorbent chromatographic techniques (4,6 ) . The two portions of oil are then examined separately by the methods available. The mass spectrometer has been employed to identif>- many of the hydrocarbon and nonhydrocarbon compound types present in the aromatic portion of a gas oil ( 6 ) , and methods have been published for the analysis of the saturate portion of lubricating oils and wax (3,11). The latter methods do not, honever, determine the degree of condensation of the naphthenes. -4s the more complex fractions of petroleum, such as heating oil, gas oil, cycle stock, and lubricating oil, contain condensed naphthene compounds made up of more than t v o condensed naphthene rings per molecule, additional types should be determined for more complete characterization of the samples. A procedure recently described by Melpolder and associates (9) does provide for the analysis of condensed naphthalenes as well as aromatic nuclei. .4 method has been developed in these laboratories which determines paraffins, noncondensed naphthenes, and condensed naphthenes containing two to six condensed rings per molecule. The development of this method and its application to pure compounds and to separated petroleum fractions are described. OBTAINING THE MATRIX
I n the development of the type analysis it was desirable to use a sound theoretical basis entailing a minimum of assumptions .4 simple, rapid method was sought, which would yield the maximum information concerning the extent of condensation of the naphthenes. It was also desirable t h a t the method lend itself to inverted matrix and electronic computer calculation. There are two major steps involved in the development of a type analysis by mass spectrometry: (1) the selection of a group of masses which are characteristic of the compound types to be determined; and (2) the determinai.ion of sensitivity and inter-
ference values of the types---i.e., the ion abundance (or peak height) on a relative or absolute k) ‘ of each type a t its selected group of characteristic masses and at the masses chosen for all the other compound types. I n surveying the literature of mass spectral data, 138 spectra of pure saturate compounds of high molecular weight were found. These had been submitted to 1ie;iearch Project 44 of the American I’ttroleum Institute by the laboratories of the Shell Oil Co., .4tlantic Refining Co., and Humble Oil and Refining Co. -4s there m r e several compounds available of each of the types being considered for inclusion in the procedure, except five and six condensed rings per molecule naphthenes, it was thought that these might provide sufficient data on which to base the method. I t was hoped that the averaging effect of the few compomids of each type employed in setting u p the procedure would give a result approaching that for the many thousands of compound$ making up each type in the high boiling ranges of petroleum. The mechanics of evaluating various selections of characteristic masses and computing the sensitivity and interference coefficients appeared to be so formidable that it \vas decided to employ high speed electronic calculators and sorters on the problem. Accordingly, the relative intensities (most abundant peak = 1OO.OOj of each of the masses beginning a t m/e 24 for each of the 138 spectra, as well as factors for computing absolute sensitivities in divisions per micron of reservoir pressure on a common sensitivity basis for each spectrum, were punched 011 data cards. Summation of the relative intensit,iee for the selected m / e groups and computation of the sensitivity and interference values viere made with a high speed computing machine. .4fter various selections of mass groupings had been tried with varying degrees of success as indicated by sample analyses, the masses characteristic of the compound types given in Table I were chosen.
Table I. Characteristic >lass Groupings Paraffins 71, 85, 99, 113 69.83. 97. 111. 125. 139 Noncondensed naDhthenes Condensed naphthenes 109, 123, 137, 151, 165, 179, 193 2 rings/molecule 149. 163, 177. 191, 205, 219, 233, 2-17 3 rinas/molecule 189,203 rings/molecule 4 --. , 217, 231. 215,259, 273, 287, JUI
5 ringsiniolecule
6 rings’molecule
229, 243, 257, 271, 285, 299, 313, 327, 341 - - -, 3.55 -- 269, 283, 297. 311, 325, 339, 363, 367, 381,395, 409
The paraffin masses are the usual ones employed in t j p e analyses and are the C5 through C, alkyl ions. The naphthene masses were chosen so that the lowest mass in each group represented the minimum nuclear molecular weight, assuming all C5 rings. The series advanced by 14 mass units (CH, groups) to the nuclear molecular weight corresponding to all CP, rings; then four additional peaks in the same C,H*,+, series were added in order t h a t alkyl substitution on the nucleus might contribute to the summation. .4fter computation, the sensitivity and interference values were tabulated by compound type and by source of spectra in each type. Simple averages of the coefficients of the compoiintis in each tvpe nere computed. iis there 1946
V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6
1947 divisions per micron they would contribute to the mass summations selected for the other types (interference values) from extrapolation of curves constructed from the data for the other types. I n plotting average divisions per micron for each summation against number of condensed naphthene rings per molecule (Figure l ) , it was found that the curves were regular, leading t o extrapolated values for the condensed naphthenes of five aiid ais rings per molecule, which appeared satisfactory. Data. from the curves for all the types were read and arranged in matrix form (Table 111). T h e method contains no provision for determining small amounts of aromatic impurities which might be present in the saturate portion of a separated oil. Alkyl benzenes and indanes would interfere with and be determined primarily as four- and five-ring condensed naphthenes.
were some rather large differences among the compound type sensitivities for the spectra from different laboratories, only the values from the Shell spectra, which represented the majority of those available, were employed further. I n Table I1 the number of compounds of each type used in determining the final coefficients are shown. Although the pure compound sensitivity values varied widely u-ithin each type, no dependence of sensitivity of molecular weight could be found. Because of the complete absence of pure compound spectra for condensed naphthenes having five and six rings per molecule, it was nece-sary to determine the sensitivity coefficients and the
Table 11. No. of Pure Compound Calibration Spectra Employed Paraffins 24 (S normal, 16 iso) Noncondensed naphthenes 28 Condensed naphthenes 2 rings/molecule 8 3 rings/molecule 6 4 rings ’molecule 6
APPLICATION TO PURE COMPObYD SPECTRA
-
Total
72
_________
.
~
~-
~
Table 111. Rlatrix for Saturate Type Analysis Noncondensed Condensed Xaphthenes ParafNaph23456fins thenes ring ring rmg ring ring 29 243 6: Y 71-113 5 O l n 13.4 7 4.4 235 120 72 49 35 93 1 Y 69-139 206 3 4 0 2
~109-193
X149-247 V189-301 Y229-355
0 1 0 1 5
1’269-109
48 0 0 0 0
7 9 1 3
130 75 410 88 4 1 245 7 . 6 165 0.9 0.4 2.7 0 4 0 0 0
50 50 50
~
a
~
~
38
33 28 35
127
a Divisions per micron of pressure vith n C x m;’e 226 divisions per niicron. . ~~.~ ~ ~ ~
Table IV.
An analytical method for comples mixtures may be put to an extreme test by applying it to pure compounds. This is clone regularly in the literature and in many cases is meaningful, T h e analyses of a few pure compounds by this method are given in Table IT’. T h e compounds were selected a t random, every second, or every third, in the tabulation of Shell data being chosen, according to the number of each type While . - available. some may view these data as indicating the probable accuracy of the method, they indicate, rather, the differences between each particular pure compound spectrum and the average spectra of those of that. type employed in arriving a t the matrix values. T h e analyses of the pure compounds further shorn that the masses chosen for each type are indeed characteristic of the type. ANALYSES OF LUBRICATING OIL FRACTIONS
T h e method has been applied to a series of “homogcnvoiis” saturate fractions of lubricating oil obtained from API Research
102 =
10.0
~
-
_
_
_
_
~ ~
..
-4nalyses of Pure Compounds Condensed Naphthenes. % V n-.. n.
Type and Name ,z-I’araffins n-Hexacosane n-Octacosane n-Hexatriacontane n-Dotriacontane n-Tetracosane IsoDaraffins 9-n-Biityldo
Parafcond. fin, 5% Naph., 99 47 91 98
2-ring
3-ring
0 2 9 7
99
0
0 0
0
0
Si 98
(3,5,5-trimethylhexsl)octadecane Soncondensed naphthenes
8.5
14
1
1 .I-Dicyclohexyltetradecane 1 I-Cyclohexylheneicosane 13-Cyclohexylpentacosane 7-Cyclohexyleicosane 1 ,5-Dicyclohexyl-S(2-cyclohexylethy1)pentane 1.7-Dicyclopentyl-4 (3-cyclopentylpropyl) heptane 1,4-Di-n-decylcyclohexane 12-Dicyclohexyiethane I-Cyclohexyldecane ?-ring condensed naphthenes 11-or-decalinheneicosane 1 ,I-Di(rr-decals1)hendecane Y-[~(cis-0,3,3-Bic~clooctyl)’ methyl lheptadecane I-a-Decalylhendecane I , 1-Di (a-decalyl) ethane 8-ling condensed naphthenes 9-n-Dodecylperhydroanthracene 9-n-Dodecylperhydrophenanthrene 1 f5-Perhydroacenaphthyl) pentadecane 9-C yclohexylperhydroanthracene +ring condensed naphthenes Cholestane 6-n-Ontylperhydrobenz (de)anthracene 9-n-Octylperhydronaphthacene
0 -11
93 59
7
30 37
fi7
0
n
n n
0 0
n
0 0
0
n
0
0
0
0 0
0
0
0
n
n n
n
0
0
0
93
7
0
0
93
7 0
0
0
ion ino 1 no
0
7
0
91
4
88
19 0 0
11
n
68 in0
0
100
0
0
n 0
0 0
1
1 0 0
0
98 85
0 10
100
n
n
n
0
0
20
69
0
3 11
96 88
n
0
0
n n 0
0 0 0
0 0
0
n
0
n 0 n
0
0
0
0 0
0
n
n
n
0 0
63
0
5-ring
n
1
98 88
4-ring
83
2
n
n
0 0 0
0 0
0
0
0
1948
ANALYTICAL CHEMISTRY
Project 6, on n hich a considerable body of analytical information is available ( 8 ) . This includes the normal measurements of physical properties, from which the average number of naphthene rings per molecule (R,)can be calculated employing van Xes and van IVesten’r n-d-11 correlations ( I O ) . B modified Coneolidated Model 21-103 analytical mass spectrometer \vas employed in obtaining the spectra of these samples and of those described later T h e niodifications made on the instrument and the heated inlet system used in this study have been discussed ( 6 ) . I n Table V the average number of naphthene rings per molecule (R., ) for -4PI-6 homogeneous lubricating oil fractions 1 through 5 are shovn. These value; were calculated from t h e n-d-11 method, from the k n o n n hydrogen content of the samples, and from a density correlation devised b y B. H. Johnson of these laboratorier. The R, values are compared n-ith the average number of r,ngs per condensed nucleus calculated from the mass fipectrometer analyses. T h e very good correlation between the mass spectrometer and the RY values may indicate t h a t most of the naphthene rings in the average molecule are condensed in one nucleus. Determination of the mass spectrometer value, which appears to correlate well with the important catalytic cracking feed stock characteristic, Rs, is possible from a type analysis only if a breakdoxn of the condensed naphthenes into number of rings per molecule is obtained.
I
:
ATVALYSES OF THERMAL DIFFUSION FRACTIONS
Analyses of some thermal diffusion fractions from t h e saturate portion of a dewaxed light motor oil distillate b y this method are shown in Table 1-1, As thermal diffusion is an analytical separation method knox-n t o concentrate paraffins in t h e top portion of t h e column and condensed naphthenes in the bottom of the column in the separation of saturates, t h e regularity of the calculated analyseq shown i. satisfying.
Table Y. Comparison of Ring kalues bj Mass Spectrometer with Number of Naphthene Rings per hlolecule Determined bj Sew era1 Methods \PI-6 Homogeneous Lubricating Oil Fraction KO 1 2 3 4 5 2 08 1 88 1 74 2 76 hlS 1 15 1 81 2 04 1 99 2 70 n-d-hI 0 96 1 00 2 00 2 00 2 00 3 00 % H 1 06 2 02 2 02 2 08 2 50 Densitj correlation
Table 1-1. .hal>-sesof Thermal Diffusion Diffusion column port No. 2 6 Paraffins 64 44 Noncondensed naphthenes 34 43 Condensed naphthenes 2 rings/molecule 2 9 3 rings/molecule 0 4 0 0 4 rings/molecule 5 rings/molecule 0 0 6 rings/molecule 0 0
Fractions 8
1
47
13 3
23 10
2 0 0
CONCLUSION
A mass spectrometric method for t h e analysis of saturate fractions of high molecular weight has been developed. Considering the complexity of the samples to which t h e method can be applied, it is very rapid. T h e calculation, including numbering the masses on the record, reading the peak height of 55 masses, summing the groups, and solving t h e equations with an inverted matrix, requires about 40 minutes. Any group with a n instrument capable of resolving and pumping out petroleum materials in
I :I
I
i/l
I
I
I
I
i
I A .
I
I
I
the boiling range from heating oils to lubricating oils should be ~ method directly in analyzing saturate fractions able to a p p l ~the ACKNOWLEDGMENT
T h e authoi {ti-he? to express his appreciation t o S. H . Hastings for his helpful advice and suggestions in selecting the masses used for the compound types, and to acknowledge the help of G. R. Taylor, C. R. Middleton, and R. W.Ewing in obtaining t h e spectra nnd in making many of the computations.
10 18
39 44
1 0 0
1
LITERATURE CITED
(1) Brown, R . A,.
. ~ A L CHEM. .
23, 430 (1951).
(2) Brown. R. A,. Doherty, F. W., Spontak, J., Consolidated Engineering Corp.. IIass Spectrometer Group Rept. 84 (1951). (3) Clerc, R . J.. Hood, d.,O’Neal, AI. J., Jr., AFAL.CHEX.27, 868
(1955) (4) Hibbard. R . R., I n d . Eng. Chem. 41, 197 (1949). (5) Lipkin, AI. R..Hoffecker, W.9.. hlartin, C. C., Ledley, R. E., .INAL. CHEM.20, 130 (1948). (6) Lumpkin, H. E., Johnson, B. H., Ibid., 26, 1719 (1954). (7) Lumpkin, H. E., Thomas, B. W.,Elliott, A., Ibid., 24, 1389 (1952) (8) RIair, B. J., Rossini, F. D., I n d . Eng. Chem. 47, 1062 (1955). (9) Melpolder. F. IV., Brown, R. h.,Washall, T. A , Doherty, F. W.,Headington, C. E . , ASAL. CHEY.28, 1936 (1956). (10) Nes, K., van, and Westen, H. A , van, ”Aspects of t h e Constitution of Mineral Oils,” Elsevier, Houston, Tex., 1951. (11) O’Keal, 11. J., Jr., Wier, T. P., Jr., A N ~ LCHEX . 23, 830 (1951). RECEIVED for review February 6. 1956. Accepted September 4, 1966. Fourth Conference on Mass Spectrometry, ASTM Committee E-14 on Mass Spectrometry, Cincinnati, Ohio, M a y 1956.
