LITERATURE CITED
J. I(. Faris, J . P., Buchanan, X. F., ANAL.&EM. 30, 1909 (1958).
; l j Brody,
(2) Duffendack, 0. S., Thompson, X. B., Proc. Am. SOC. Testing Muteriab 36,
?art 11, 301 (1936). ( 3 ) Duffendack, 0. S., Wolfe, R. A., IND. -ZNG. CHEM.,ANAL.ED.10. 161 (1938). '4) Fowler, C. A.. Atomic Energy of Canada Ltd.,
?DB 92 (1953).
Chalk River, Rept.
(5)Fred, M. S., Nachtrieb, N. H., Tomkins, F. S., J. Opt. SOC.Am. 37, 279 (1947). (6LK0, R. K.,V . S. Atomic EnergS. ,omm. Rept. HW-57873 (1958). (7) Reichreiber ;Rein), J. E., Langhorst, A. L., Jr., Elliott, M. C., Zbid., LA-1354 (1952). (8)Van Tuyl, H. H., Ibid., HW-28530 (1953). (9)Wilhelm, H. A., IND.ENG.CHEW, ANAL.ED.10, 211 (1938).
Anaiysis of Petroleum Products in the
(10)Zotov, G., Fowler, C. A., Atomic Energy of Canada LM., Chalk River Rept. PDB 45 (1951). (11)Ibid., PBD 91 (1953). RECEIVEDfor review December 10, 1958. Accepted July 10,1959. Presented in part at the Pittsburgh Conference on Analytical Chemist and Applied Spectroscopy, March 1959,?hsburgh, Pa. Vork done under AEC Contract No. AT(29-1)-1106.
C12
to
C20
Range
jOIpplication of FIA Separatory and Low Voltage Mass S pectromet ric Techniques 6.1. KEARNS, N. C. MARANOWSKI, and G. F. CRABLE Gulf Research & Development Co., Pittsburgh, Pa. ,A procedure has been developed The fluorescent indicator adsorption for determining the composition of (FIA) technique (2,6 ) was found to be petroleum products in the C12 to C ~ O the most satisfactory separatory tool {ange using FIA separations and standbecause of its availability in most petroard and low voltage mass spectroleum laboratories, the ease with wllich metric techniques. The variation of the hydrocarbon types can be identified, low voltage sensitivities of aromatics speed, and freedom of fractions from with the number of substituents is used eluents. The FIA column was evaluio determine the average number of ated with respect to repeatability, substitutions per benzene ring. sample recovery, and ability to separate
production of high quality and commercially valuable petroleum uroducts from low grade charge stocks :mi .become an increasingly important ;art of Tehing technology. Such prodeuures, t o be economically feasible, rewme detailed information concerning tne composition of the material and the :orrelation of composition with chemical m u physical properties. These results an be obtained only from analytical procedures capable of providing detailed .omposition data. Standard and the -ecently developed low voitage mass -oectrometric techniques in con~unction sath suitable separation procedures proide the means for obtaining the dexrea information. This report describes i n anaiytical scheme for materiais in ++e approxlmate carbon number range ,:to Cn,and the results of such anaiyses %muse of che complexity of products n this range, it is desirable to separate he samples chromatographically bc"ore performing mass spectroinetnc .na:vses. Zach separated fraction muid contain predominantly one hy.rocarbon type and &ompound types + .uch have the same molecular formula ,mid be resolved. Tse of these concentrated fractions also results in in:reased peak heights for the low ioniz'ng voltage analyses. HE
I
1646
0
ANALYTICAL CHEMISTRY
higher molecular weight compounds adequately and was found satisfactory for use with products in this range. The separated fractions are analyzed by mass spectrometric techniques. The compound types and the distribution of condensed cycloalkanes in the saturate fraction are determined using standard ruas spectral data and analyses (3,IO). Low ionizing voltage techniques are used to analyze the oiefin and aromatic fractions. Field and Hastings (8) showed the advantage of using low energy electrons to simplify the mass spectrum and Lumpkin (11) present4 calibration data for aroniatic hydrocarbons of higher molecular weight. These data showed that the sensitivity idcreased with the degree of condensation of aromatic nuclei and decreased with molecular veight. A study of the low voltage rnass spectra of a series of alkyl benzenes has resulted in a relationship between sensitivity and the number of substitutions on the benzene ring. This relationship can be applied to aromatic fractions to dekrmine approximately the average number of substitutions per aromatic molecule. This procedure. can be applied only to aromatic fractions free from olefins and saturates. The information so obtained. although of a semiquantitative nature, can be of considerable value in understanding refin-
ing processes and in correlating properties with composition. ANALYTICAL PROCEDURES
Fluorescent Indicator Adsorption.
T h e fluorescent indicator adsorption technique (2, 5 ) is used for the analysis and separation of total saturates, oIefins, and aromatics. This method is a simple procedure for the chromatographic separation of hydrocarbons using silica gel as the adsorbent and isopropyl alcohol as the displacing agent. Fluorescent dyes are used to make the hydrocarbon-type boundaries clearly visible under ultraviolet light. The technique used for this work diEers from the standard FXA procedure only in the e l i i tion of the capillary tubing between the charger and the separator sections. This modification not only facilitates glass blowing, but also permits the sample to pass more rapidly through the charger section without changing the effectiveness of separation. The three iractions are collected from the tip of the capillary constriction a t the bottom of the analyzer section. With the aid of an ultraviolet light source, the emerging colored droplets can be identified 85 olefinic or aromatic once the colorless saturate fraction has been collected. By this method, eight to ten samples can be processed by one operater per day without difficulty. The repeatability limits for this method as stated in the ASTM procedure are: aromatics, 2.0 volume yo;olefins, 2.0 volume %; and saturates, 1.5 volume yo. Euplicate and, in one caw, triplicate analyses of a Diesel fuel and four diEerent jet fuels showed that the data were well within these limits. A question of importance in the use of
an FIA column as a separatory tool is the amount of the charged sample which is recovered. The lack of essentially complete recovery of the sample from the column would indicate that certain compounds or compound types were retained by the gel. Without complete r e covery the separated fractions would not necessarily be representative of the compound distributionin the original sample. Listed in Table I are the data obtained by collecting the individual fractions in calibrated vials and measuring the volumes recovered. It is apparent that, very good recovery is possible using this FIA procedurc. In the molecular weight range considered, the major part of the aromatics and olefins will have long alkyl groups as a part of each molecule. If the alkyl groups make the adsorption properties of these molecules more like paraffins, a certain amount of trailing into an adjacent fraction might be expected. For example, dodecylbenzene with its long alkyl side chain might behave on a silica gel column as either an olefin or a saturate. An attempt was made to evaluate this factor by adding known amounts of pure compounds to Diesel fuel and separating the resulting blends. The results of these analyses are shown in Table 11. Of the compounds examined, only dodecylbenzene produced a serious difficulty. The long side chain on the aromatic ring apparently makes this molecule less aromatic as far as silica gel adsorption is concerned and permits it to move into the less strongly adsorbed olefin fraction. Because such compounds can, in general, be detected by subsequent analysis, they present little practical difficulty in the analytical system described here. Mass Spectrometric Analysis. The saturate fractions of the products separated on the FIA column were analyzed by two standard group type analyses modified by using calibration data expressed as fractional total ionization (4). The first procedure (3) determined the liquid volume percentages of alkanes, noncondensed cycloalkanes (this group refers to both monocycloalkanes and polycycloalkanes) , condensed cycloalkanes, alkyl benzenes, and naphthalenes. The latter two group types served as a check on the effectiveness of the separation p r o w dure. The second procedure (10) determined the distribution of condensed cycloalkanes by number of rings-i.e., the volume percentages of compounds having two, three, and higher condensed ring systems. The olefin and aromatic fractions were examined by low voltage mass spectrometric techniques (8, 11). Mass spectrometric data were obtained using a Consolidated Electrodynamics Corp. Model 21-103 mass spectrometer after modification by the addition of a high temperature inlet system
Table 1.
Product Volume charge, ml. Volume recovered, mi. Recovery, % Table 11.
Recovery from FIA Columns
Jet Fuel No. 2 No. 3
No. 1 0.80 0.80 100.0
0.80 0.79 98.8
Diesel
No. 4 0.80
0.80 0.77 06.3
Fuel 0.80 0.76 95.0
0.78 97.5
Separation of Blends of Pure Compounds in Diesel Fuel
Sample Diesel fuel Phenyl-%butenein Diesel fuel n-Butylbenzene in Diesel fuel Diisopropylbenzene in Diesel fuel Dodecylbenzene in Diesel fuel I-Dodecene in Diesel fuel 1-Hexadecene in Diesel fuel
Hydrocarbon Type Aromatic Olefin Saturate Aromatic Olefin Saturate Aromatic Olefin Saturate Aromatic Olefin Saturate Aromatic Olefin Saturate Aromatic Olefin Saturate Aromatic Olefin Saturate
and circuitry for operation with electron energies in the range of 5 to 70 volts. The low voltage circuit used is essentially that described by Lumpkin ( I I ) , escept that all the data were taken with the repellers connected together. The high temperature inlet system has been described (12). In standardizing the ion chamber operating conditions to be used for low voltage operation, it was desirable to find one set of conditions suitable for both olefins and aromatics. It was decided that it was not necessary to eliminate all fragment ions from the low voltage spectra. The ideal situation is to operate at the highest ionizing voltage and, consequently, the highest parent ion sensitivity without producing fragment ions which could be misinterpreted as molecular ions. A survey of mass spectra of olefins and aromatics showed that the most serious problem existed with the olefins. The spectra of olefins, in general, contain relatively large ion fragment peaks at m/e values corresponding to the parent or molecular ions of lighter olefins. The presence of such fragment peaks would result in the calculation of erroneously high concentrations of the lighter olefins. Thus, the operating conditions used must result in negligible olefin fragmentation in the molecular weight region of interest; in this case above 100. The aromatics are simpler to handle because the prominent ion fragments are usually of odd mass number not corre-
Biend,
Val.
70
FTA Analysis. voi. 9;)
25 4 1 E, 73 i 25.4 1.5 73.1 25.4 1.5 73 1 25 4 1 5 73 1 18.1 8.9 73.0 18.1 1 8.1 8.9 73.0
19.5 1.6 78.9 2s 1'. 72 s 25 0 1 8
73.2 25.3 1.: 73.0 19 2 1: 1
GI? 6 17.5 9 4 ( 6 .i 18.5 7.6 73.9 cc
sponding to m y particular molecular species. A s the ionization potentials of aroinnties arc lower than olefin ionization potentials, operating conditions suitable for olefins are satisfactory for aromatics. Instrument operating conditions were: inlet system temperature, 175' C.; repeller voltage, 1.5 volts; ionizing voltage, 8.0 volts. The operating conditions for repeller and ionizing voltages were chosen from a study of the low voltage spectra of ldecene and ldodecene as a function of these voltage settings. These values essentially eliminate the appearance of fragments other than the molecular ion above m/e 100. The use of these operating conditions for olefins above Clz requires the assumption that the appearance potentials of m/e 100 and higher ion fragments of higher molecular weight olefins are equal to or greater than those of a Clz olefin. AIthough not essential to the analysis of separated fractions, the chosen conditions are such as virtually to eliminate interference from saturated compounds. To increase the lower limit of detectitbility, a pipet having a voiume of 4.8 pl. (0.0046 ml.) was used for charging all samples into a %liter reservoir. This is an increase in sample size of approximately five times the usual quantity of sampie charged to a mass spectrometer. Multiple introductions of the calibration standards showed that the volume could be reproduced within 3%.
Low VOLTAGECALIBRATION.The VOL. 31, NO. 10, OCTOBER 1959
0
1647
hasic problem of caiibration for all high molecuiar weight work is obtaining a generalized approach which can be ext,rapoiated to compound types and mclecuiar weight ranges for which no pure compounds are available. The most complete group of compounds available is the alkyl benzenes. From a study of this group plus a limited amount of data for other aromatic types, a reasonable caiibration scheme was developed. Figure 1 shows plots of alkyl benzene and naphthalene molecular ion sensitivities as a function of 1idii, the inverse of nirilecular weight. Lumpkin's assumpti011 (1 1 ) that all sensitivities were zero at infinite mass (1/M = 0) was also ilsed here. The a1kyl benzene data a p pear to be well represented by a seriw of straight lines, each line corresponding to a specific number of substitutions per iienzene ring. These data show that sensitivities for benzenes increase rapidly with increasing degree of substitution on t.he ring, and decrease with increasing molecular weight of the molecule. T h e limited amount of naphthalene data available shows an increase in sensitivity with number of substitutions on thr ring. However, the rate of increase of smsitivity with substitution is smaller than observed for the alkyl benzenes. The naphthalenes have a sensitivity increase of about 20% per substitution as compared with an increase 01 approximately 50% for the alkyl benzenes. From these results it is reasonable to assuine that the effect of substitution on sensitivity decreases in the anthracene and more highly condensed aromatics. For calculation purposes the monosubstituted naphthalene curve was uscd to represent the naphthalenes. il!though neither Lumpkin (11) nor Field and Hastings (8) reported an effect ?i' substitution on sensitivities, certain 2ata of Field and Hastings are in good agreement with the results reported here. Their calibration data show the sensitivities of alkyl benzenes as a smooth function of boiling point when compounds of a particular carbon number are considered. Their report shows that the number of substitutions per 3enzene ring was also increasing with boiling point. I n tQe particular case of +ethyltoluene and 1,3,54rimethylbenzene, which have boiling points differing .qless than 0.8O F.. Field and Hastings obtained sensitivities of 1725 and 2510 divisions, respectively. This large sensitivity change becomes reasonable when interpreted as the effect of increased degree of substitution. Calibration data for the additional five aromatic types determined-the indanes, indenes, acenaphthyienes, ace naphthenes, and anthracenes-are based: on experimental data for the first memh r s of each series. Further, scnsitivities obtained from the straight line drawn through the single calibration
1648
ANALYTICAL CHEMISTRY
I
0 BENZENE
1 0 0 00 ~ MONOSUBSTIlUTED
L?
BENZENES 3 DISUBSTITUTED BENZENES I ,4" soo1 A TRISUBSTITUTED I BENZENES a V TETRASUBSTITUTED I
-
1
~
\
6 6
ln
4
6
E
2
\
4
BENZENES NAPHTHALENE METHYLNAPHTHALENE DIMETHYLNAPHTHALENE
Figure 1. Molecular ion sensitivities for substituted benzenes and naphthalenes
,
\
\
'
Y,
-
I
L a
400l
+-2
z
r
w
0
t
I
,
I
250 50C
75 100 150 MOLECULAR W E l G HT L
A
,014 012
1
'
,
1
J
010 .ooa ,006 004 ,002 ,000
I MOLECULAR WEIGHT
6
Figure 2. Low voltage calibration data for aromatic types
ANTHRACENES
-.. 75 I
100 150 2 5 0 500 MOLECULAR WEIGHT I
/
,
I
,
I
,014 ,012 ,010 ,008 ,006 ,004 ,002 I MOLECULAR WEIGHT
I
.OOO
datum and zero sensitivity at infinite molecular weight are assumed to be independent of degree of substitution. These data are shown in Figure 2 along with the monosubstituted benzene and a 0 naphthalene curves. The discussion of tthe naphthalenes shows that this asV U 4 sumption is reasonable for the anthraz cenes and acenaphthylenes. Because of 0 I3 the mixed ring systems of the acenapht thenes, indanes, and indenes, substitution + v) m effects observed for benwnes and naph3 v) thalenes cannot be extrapolated reliably. A substitution on the saturated rings of these types would be expected to pr+ duce less effect than a substitution on the aromatic ring. However, the use of the assumption of no substitution effect m k e s available useful semiquantitstive NUMBER OF SUBSTITUTIONS PER BENZENE RING information on these compound types. Figure 3. Graph for determining numOlefin calibration data were obtained ber of substitutions on the benzene ring from the work of Field and Hastings (8)
after instrument standardization using terminal olefin d a h . As is the case in most mass spectrometric techniques, certain compound types which have the same molecular iormula cannot be distinguished as separate types. Diolefins and cyciomono-olefins, indenes and dihydronaphthalenes, indanes and Tetralins, and anthracenes and phenanthrenes are a few of these ambiguous types. Whenever one such type is cited in this report, the other appropriate types are inferred.
studied make this problem relatively unimportant. Volume percentages of all components are based on V,. Before volume percentages are calculated, all alkyl benzene calculated volumes are multiplied by the inverse of the substitution factor. This step is simply the normalization of these volumes to the true volume of alkyi benzenes in the sample.
CALCULATION PRO-
The internal consistency of the overall procedure was tested by collecting successive cuts of the saturate fraction of a kerosine and the aromatic fraction of a fuel oil. Appropriate mass spectrometric analyses were made of each portion and the results are reported as volume percentages of the original samples in Tables I11 and IV. Also reported are the volume percentages for the total fractions obtained by summing the results of the individual cuts and by analyzing total fractions obtained on duplicate separations. The good agreement between the data for total fractions and the sum of cuts of the fractions indicates that the procedure is self-consistent. However, the rather large changes observed for the individual cuts show that considerable separation of compound types does occur within each fraction. It is important that analyses be per-
Low
VOLTAQE
The calculation of the olefin distribution of the olefin fraction is standard in all respects. However, because of the introduction of substitution effect into the alkyl benzene sensitivity data, the analysis of the aromatic fractions requires a modification of the ca:culation procedure. Processing an aromatic fraction consists of first introducing a known volume of sample into the spectrometer. Using the calibration data of Figure 2, liquid volumes of each component are caiculated. Because the calibration curve used for the alkyl benzenes represents monosubstituted alkyl benzenes, the liquid volumes calculated for the benzenes will be correct if the sample contains only monoalkyl benzenes. If the sample actually contains predominantly higher substituted benzenes, the calculated volumes will be larger than the actual volumes in the sample. The degree of benzene substitution is estimated by summing the calculated liquid volumes of all components and comparing the sum with the known volume of liquid sample. A calculated total volume greater than the known volume indicates a higher degree of benzene substitution than one per molecule. The degree of substitution of the benzenes is determined by applying the equation: CEDURE.
Vk
'Ib v.
=
substitution factor
(1)
where
V r = known sample volume V. = sum of calculated liquid volumes of all aromatics except
Vs=
alkyl benzenes sum of calculated liquid volumes of all alkyl benzenes
A factor of 1.0 indicates that the alkyl benzenes are monosubstituted. Higher factors are converted to average number of substitutions by referring to Figure n
6.
The use of Equation 1 assumes that the correct calibration data have been used for all compDund types other than the alkyl benzenes. Errors in this assumption will, of course, affect the accuracy of the results. However, the l q e alkyl benzene concdntrations in the aromatic fractions of the materials
CHECKS ON THE METHOD
formed on the complete fraction t.o obtain the correct composition of the original sampir. The high concentration of po!ynuclear compounds in this sample does nci permit a calculation of the degree oi s u t stitution of the alkyl benzenes. Focalculation purposes, the alkyl benzene" are assumed to be monosubstituteti The procedure was tested further b:, adding the same quantity (7.4% by volume) of a number of olefins and arcmatics to a D i e d fuel. The saaturat+. fractions of such biends should be unaffected by the particular compound added. Table V gives the caicuiakci volume percentages of saturztes anti tli: total saturate volume percentages i i C t i i ally determined by the ETA procedure. along with the concentrations C,-1 cor.pound types in each fractio:! 'Tilt. data shown for the original Diesel fw,' were normalized to a totai saturate coi:centration of i'2.3Y0 for ease of conipar.ing results. Good agreement was foun
