Modified Method for Hydrocarbon Type Analysis by Mass Spectroscopy II. E. LCMPKIN, B. W. THOMAS, AND ANNELLE ELLIOTT Humble Oil and Rejining Co., Baytown, Tex.
A rapid determination of the niajor hj drocarbon types in the gasoline boiling range of petroleum naphthas is valuable in the characterization of crude naphthas and in the evaluation of pilot unit feeds and products in process development studies. The mass spectrometer compound typeanalysisdeveloped by Brown is modified for application to samples of low- olefin content. Paraffins, naphthenes, aromatics, and condensed-ring naphthenes are determined in a single mass spectrometer run by the abundance of specific groups of peaks which are distinctive for the various compound types. The four types can be determined in olefin-free samples in 1 hour with an accuracy of about &lo% of the amount of each type present. This procedure may be adopted by any group possessing an analytical mass spectrometer and saves laborious and timeconsuming separations, chemical reactions, and physical determinations in type analyses. Cmnsiderable amounts of condensed-ring naphthenes are found in certain fractions of petroleum naphtha by this method.
THE
development of a method for the determination of hydrocarbon types in the gasoline boiling range of petroleum has been a subject of intensive investigation in recent years. The majority of the work in this field has involved the use of rather laborious and time-consuming separatious, chemical reactions, and physical determinations. X recent procedure developed by Kurta et al. (3) requires about 24 man-houis for fractionation, acid treating, bromide-bromate titration, and determination of refractive indices on the distillation fractions. More recently, Rampton (7) has employed distillation, silica gel percolation, hydrogenation, and refractive indices in the determination of paraffins, naphthenes, aromatics, olefins, and cyclic olefins. A mass spectrometer method for the deterniination of hydrocarbon types in the gasoline boiling range has been deticribed by Bron n ( 2 ) . Certain peaks in the mass spectra of the hydrocarbons are grouped to provide distinctive coefficients for the determination of the types present A related method has been in usc in this laboratory for some time. Because the method differs considerably in some of its features from that of Brown, it is felt that a description of it would be a worth-while addition to the field of applied mass spectroscopy. The Brown procedure obtains data on total paraffins, total iiaphthenes and/or mono-olefins, total aromatics, and the cyclomono-olefin, diolefin, and acetylene, or "coda," group. The proccdure presented here is designed to handle only streams of Ion nlefin content and the coda group, essentially nonexistent in virgin naphtha, is omitted. Olefins are determined by bromidebromate titration ( 1 ) and removed in a small scale brominationsteam distillation apparatus prior to the maas spectrometer analy-is. An addition hydrocarbon compound type, condensed-ring naphthenes, which apparently reaches considerable concentrations in higher boiling naphtha fractions, has been included in the present method, however. Paraffine, naphthenes, aromatics, and condensed-ring naphthenes are determined by a single mass spectrometer run on a Ce-400' F. boiling range sample. In the Brown method, unweighted average coefficients are em4
ployed. Greater accuracy is realized when appropriately weighted coefficients can be used. This depends upon some knon.lcdge of compound distribution. In applying the present procedure, weighted average coefficients for paraffins and naphthenes were calculated from component analyses of typical heavy Coastal, heavy mixed, and light mixed crude naphthas. In applications of the type analyses to narrow boiling range fractions (10' to 26" F.) coefficients weighted for the specific compound8 occurring in those ranges were used. Time requirements are about 1 man-hour for the brominationsteam distillation (not required on samples of low olefin content such as straight-run gasolines or virgin naphthas) and about 1 man-hour for the mass spectrometer run and calculations. Thc method has been employed effectively in the analysis of virgin naphthas, naphtha fractions, and feeds and products from pilot unit and process research studies. APPARATUS AND PROCEDURE
The Conaolidatd Engineering Corp. Model 21-102 mass spectrometer employed in this study has been described adequate]?by Washburn etal. (8). Calibration compounds and samples for analysis were introduced by means of a constant volume pipet of the type describcd by Purdy and Harris (6). A mercurial orifice introduction system was used in conjunction with the pipet. Normal heptane was run daily to determine changes in the sensitivity of the instrument (sensitivity basis- one pipetful = 158 divisions of m/e 300). Spectra of 51 paraffins, 40 naphthenes, 36 aromatics, and 4 con-
Table 1. \lass Spectrometer Data for Specific Boiling Range Type Analyses Boiling Range,
F.
Paraffins
Naphthenes
23.7 1.5
1.9 19.7
26.1 2.5
3.4 13.0
29 8
2.2
3.9 14.4
23.2 1 7
15.0
Condensed-Ring Saphtbenes
200-~20
243 2558 220-235 243 255
235-249 243 255 245-260 213 255
2.5
0.3 4.6 10.6 0.3 4.6 10.6 0.3 4.6 10.6 300-325 243 255
267
a b c
1389
24.2 2.2 0.2
2.2 16.3 1.9
243 sum of peaks at masses 4 3 , 5 7 , and 71 i 100. 255 sum of peaks a t masses 55 69 and 83 + 100. 267 sum of peaks a t masses 67: 81: a n d 95 t 100.
0.3 4.6 10.6
1390
ANALYTICAL CHEMISTRY
densed ring naphthenes in the C& range were recorded for Calibration purposes. The mass abundances resulting from charging equal volumes of each of the calibration compounds are combined in groups and used as a single coefficient. The spectra of the paraffis are generally characterized by abundant peaks a t m/e ratios of 43, 57, and 71 while the naphthenes contribute largely to masses 55, 69, and 83. Although mass 41 is relatively large for the low boiling napthenes, it becomes less distinctive at higher boiling ranges where the paraffin m/e 41 becomes equivalent with that of the naphthenes. For this reason the inje 41 was not used. Total aromatic content and aromatic molecular -weight distribution are determined from the aromatic parent peaks according to a method previously developed in this laboratory (4). M~~~~~ 67. 81. and 95 were found t o be abundant in the mass sDectra of the limited number of condensed-ring naphthenes available. -4 simple average of the coefficients for cis- and trans-Decalin, hydrindane, and 0,3,&bicyclo-octane was used for the condensedring naphthene calibration. As no check method is available for the determination of this hydrocarbon type, no claim can be made concerning the accuracy of its determination. Holyever, considerable amounts of this type are indicated to be present in crude petroleum by the type analysis of 275' to 400" F. naphtha fractions. It is pointed out that noncondensed dicyclic naphthenes. such as cyclopentylcyclopentane, -would appear as this type in the analysis. The steps involved in the analytical procedure are: (1) olefin determination from bromine number, (2) olefin removal by bromination-steam distillation, and (3) mass spectrometer determination of aromatics, paraffins, naphthenes, and condensed-ring naphthenes from a single mass spectrometer run. The latter I
three hydrocarbon types are determined by applying the summation of the mass groups from the sample to a matrix containing the calibration coefficients and solving the resulting simultaneous equations. il typical matrix, applicable to C~-400"F. samples, is shown below, in which the sums of grouped peaks are divided by 100:
243 255 267
Paraffins 24 9 __ 2 3 0 1
Condensed-Ring Naphthenee 0 3 4 6 10 6 __
Piaphthene2 5 15 8 1 0
-
Typical calibration data for specific boiling ranges from 200' to 325" F. are given in Table I. The coefficients for boiling ranges about 257" F. represent simple averages of the data available in this laboratory and in the literature'
,
DISCZ'SSION AND RESULTS
During the development of the procedure the wide boiling type analysis was applied t o a light virgin naphtha whose composition was known from component analyses of distillation fractions. Type analyses were obtained on the original naphtha, on the naphtha after a known amount of aromatics and olefins had been added, after the olefins were removed by bromination-steam distillation, and after the aromatics were removed by silica gel percolation. Data from the type analysis are compared with the known compositions in the various steps in Table 11. Analyses have been normalized to 100%. Accuracies of better than 10% of the amount of each hydrocarbon type present are indicated. Application of this method of type analysis to naphtha fractions boiling above the range a t present accessible to component analysis has been helpful in naphtha characterization studies. Data for the paraffins and naphthenes normally occurring in specific 10" to 25" F. boiling range fractions have been incorpoTable IT. Analyses of a Light Virgin Naphtha rated into type analyses. These specific (Volume per cent) boiling range analyses have proved useful Naphtha with After BrominaAromatics and tion-Steam DisAfter Silica Gel in analyzing fairly narrow boiling range Original Naphtha Olefins .4dded __ tillation Percolation refinery streams and blends of distillation Component Type Type Type Type fractions for which component analyses analyanalySynthcan+Synthe- analvSynthrana!ywere not justifiable. An example of this SI6 F1S SlSO s1s s1s" s1s SISa 81s Parafins 63.9 61.7 48.0 47.3 53.2 51.3 65.3 63.8 application is shown in Table 111. The Naphthenes 33.9 35.7 25.4 25.3 28.2 30.2 34.7 36.5 wideboiling data were used for fractions Aromatics 2.1 2.5 16.6 17.2 18.3 18.4 0.0 0.0 Olefills 0.1 0.1 10.0 10.2 0.1 __ 0.1 0.0 0.0 boiling above 325 F. Another fertile field . __ __ 100.0 100.0 100 0 100.0 100.0 100.0 100.0 100.0 in which the mass spectrometer Based on component analysis. t w e analvsis has shown merit. particularly because of its short Table 111. Analyses of Fractions of a Heavy Virgin Naphtha time requirements, is in the Individual Component Type Analysis, Val. YC analysis of feeds and products Val. Yo OleAnalysis, Vol. "c Condensx Boilin! fins by BroNaphNaphring naphfrom pilot units engaged in procRange, F. mine No. Paraffins thenes Aromatics Paraffins thenes .Iromatics thenes ess research studies. 204-212 n i 61.0 38.4 0.5 62.5 37.0 0.4 The procedure is also being 2 12-216 0.0 20.6 76.0 3.4 20.8 76.1 3.1 216-227 21 3 42.2 36 1 0.4 19.9 45.6 34.1 employed t o supplement other 227-248 0.2 66.3 2.1 31.2 66.0 31.3 2.5 245-254 0.4 49 6 50.5 50 0 0.0 0.1 49.0 analytical methods. The 254--257 72 i 27.2 0.0 24.4 0.3 75.2 0.0 0.I catalytic selective dehydrogena0.3 257-272 12.8 54.1 32.4 0.4 272-277 0.4 29.5 39.6 26.9 3.6 tion procedure developed by 277-289 0.7 17.8 20.6 58.1 2.8 0.6 289-301 2.9 27.2 65.0 4.3 Rampton (6) and employed in 0.5 301-306 5.0 2.3 31.2 61.0 a modified form in this labora0.8 306-315 26.9 40.2 17.6 14.5 1.4 3 15-326 51.3 5.6 26.0 15.7 tory is aided by the type analysis 1.0 327-334 24.8 20.0 46.0 8.2 0.8 335-345 12.7 25.6 54.8 6.1 i n t h e c h a r a c t e r i z a t i o n of 1.3 346-360 15.0 20.7 47.0 16.0 naphthenes. From data such as 1.3 361-380 12.4 25,2 42.6 18.6 ~~
".
381-397
..
1.7
Table IV. Feed Boiling Range, F. Para5ns Naphthenes Aromatics Olefills
Feed 250-260 78.6 21.4 0.0
~0 . 0 100.0
Product 74.3 10.2 15.5 0_ .0 100.0
46.2
25.2
12.2
14.7
Analyses of Feeds and Products from Dehydrogenation Cnit Feed 260-275
Feed 275-280
Product 35.1 44.0 52.1 14.2 12.8 41.0 0.0 _ 0.8
1oo.o
1oo.o
28.9 41.6 29.5 0.0
loo.o ~
Product 23.6 21.1 53.4 --1 . 9 100 0
Feed 280-295 56.3 25.9 17.8 -~ 0.0 100.0
Prorilii.1
52.2 15.0 32.4 ~-0 . 4 100 0
Feed
61.2 35.9 2.9 0.0 100.0
__
Feed 305-315
Product 65.1 12.0
295-305
~
20.0 2 9 100 0
58.1 36.6 2.6 ~
...
100.0
Product 61.6 18.3 19.1 ___1 . 0 100.0
V O L U M E 24, N O . 9, S E P T E M B E R 1 9 5 2
1391 mass spectra of the hydrocarbon types. The method is rapid, having a time requirement of about 2 hours, and is accurate t o better than &lo% of the type present. Provisions are made for an approximate determination of condensed-ring naphthenes.
Table \-. Inalyses of Synthetic Mixtures
Paruffill.; Kaphtheiies Aromatics
Olefins
29.7 36.8 33.6 0.0
io0.0
29.6 39.9 30.5 0.0
1oo.o
51.3 16.6 12.9 19.2
52.3 17.0 11.2 19.5
67.7 13.6 14.9 3.8
68.9 14.8 12.1 4.2
ioo.0
1575
10o.O
lo0.0
those shown in Table IV, combined with unit yield figures, a Ca-Ce ring naphthene split may be determined. Further data on this type of combined analysis are in the process of preparation for publication. Analyses of synthetic mixtures prepared by adding known amounts of naphthenes and olefins to stocks of,knonm composition are presented in Table 5'. Only the single determination shown was obtained on each mixture. CONCLUSION
Determination of the major hydrocarbon types in the gasoline boiling range of petroleum, applicable principally to stocks of low olefin content, involves the uee of distinctive m / e ratios in the
ACKNOWLEDGMENT
The authors express their thanks t o the management of the Humble Oil and Relining Co. for permission t o publish this material. They are indebted to Frances Lander and Maydell Williams for analyzing the samples and making many of the computations. LITERATURE CITED
(1) Am. Soc. Testing Materials, D 875-461' (1946). (2) Brown, R. A., ANAL.CREM.,23,430 (1951). (3) Kurtz, S . S., Jr., Mills, I. W., Martin, C. C., Harvey, W. T , and Lipkin, hl. R., Ibid., 19, 175 (1947). (4) Lumpkin, H. E., and Thomas, B. W., Ibid., 23,1735 (1951). (5) Purdy, K. M., and Harris, R. J.,Ibid., 22,1337 (1950). (6) Rampton, H. C., Ibid., 21, 1377 (1949). (7) Rampton, H. C., J . Inst. PetToZeum, 3 5 , 4 2 (1949). (5) Washburn, H. R., Wiley, H. F., Rock, S. ill., and Berry. C. E., IND. ENQ.CHEM., AXAL.ED.,17,74 (1945). RECEIVEDfor review March 24, 1952.
.4ccepted June 16, 1952
ldent ificat ion of Thiophene and Benzene Homologs Mass Spectral Correlations 1. W. KINNEY, JR.', AND G. I,. COOK Petroleum and Oil-Shale Experiment Station, Bureau of Mines, Laramie. Wgo. A new method for the identification of unknown organic compounds has been developed, using correlations that relate mass spectra with molecular structure. No prior mass spectral data for the unknown compounds are necessary for identifications. The basis of the method is the use of mass spectral correlations to identify structural groups i n unknown compounds. Identifications are completed by the use of supplemental chemical and physical data. The identification procedure is illustrated by the identification of two thiophenes, isolated from Colorado shale-oil naphtha. Development of mass spectral correlations is illustrated for thiophene and benzene homologs. The use of mass spectra in qualitative identification of unknown compounds has ordinarily been limited to comparison of the spectra of the unknowns with those of reference samples. Mass spectral correlations broaden the scope of mass spectrometry, permitting establishmentof certain factors of molecular structure directly from mass spectra of unknown compounds.
I
iY THE course of an investigation of the composition of shale-
oil naphtha, a need arose for a method of identifling the thiophenes in the molecular weight range 126 t o 154. As only a few of the compounds in this range are available, classical methods (10) of identification by direct property comparison are not easily applicable. The use of mass spectra offered a promising method of attacking this problem, as the literature contains several articles (4-7, 11-15) indicating the possibility of correlations between mass spectra and molecular structure. From a consideration of the mass spectra of available thiophene and benzene homologs, correlations were developed that permit deter1
Present address, I. W.Kinney and Co., Champaign, Ill.
mination of the configuration of the alkyl substituents on the nucleus. For thiophenes, combination of this technique with the preparation of mercuric acetate derivatives (16), methylation (8),and hydrogenation ( 8 ) permits identification of any compound in the 126 to 154 molecular weight range. In the case of higher molecular weight thiophenes certain compounds may be identified, or a t least the number of possible compounds may be limited considerably. '4s the correlations for the benzenes were made primarily t o confirm the thiophene data, no extensive application of these correlations is reported in this paper. However, it should be possible to identify mono- and disubstituted benzene homologs in the 120 to 148 molecular weight range. The substituent groups could be identified by mas8 spectral correlations, and their relative positions could be found by use of infrared spectra ( 2 , 19, 2 1 ) or by oxidation to the carboxylic acid (15). EXPERIMENTAL
The mass spectra used to develop the correlations given in thia paper were obtained from published data (1)or were run in this laboratory. The spectra run in this laboratory were obtained on a Consolidated mass spectrometer, Model 21-102, equipped with automatic control of the electron current. The temperature of the ionization chamber was automatically controlled t o 300' C. The ionizing voltage used for all compounds was 70 volts, except tor the diisopropylbenzenes (50 volts), which were among the compounds not run in this laboratory. Relative intensities of mass peaks in a spectrum are expressed in terms of the largest peak, or base peak, taken as 100%. For thiophene and benzene homologs the base peak consists of the molecular fragment containing the ring as illustrated in Table I. ,is shown, these peaks result from the breaking of either an abond (C-C bond next to the ring) or a p-bond (C-C or C-H bond once removed from the ring).
