Direct Determination of C3 to Cs Hydrocarbons in Olefinic and Nonolefinic GasoIines by Gas-Liquid Chromatography D. D. ZAKAIB The British Americon O i l Co., ltd., Montreal, Conada
bA gas-liquid chromatographic method i s presented for the direct determination of light ends (C, to CS hydrocarbons) in gasolines on the basis of peak area measurement for both the light components and the backflush CB+hydrocarbon portion of the sample. Relative liquid volume response factors have been derived to convert peak area to liquid volumes. A singlestage column, a partitioning agent combination, and related retention times, suitable for resolving and identifying light end components in both olefinic and nonolefinic gasolines, are described. The need for calibration standardization, or special equipment has been eliminated. This method requires therefore less time to perform while maintaining good precision and accuracy.
T
HE ADVEXT of gas-liquid chroniatography (GLC) resulted in efforts to replace the lengthy and relatively inaccurate low temperature fractional distillation (LTFD) methods used for the determination of light ends in gasoline. The few chromatographic methods advanced to date are limited in speed and versatility by the necessary addition of internal standards t o the sample prior to analysis, the use of “bracketing” with mixtures of known composition, or the need for multistage columns and special equipment. Lichtenfels et al. ( 5 ) used modified equipment and multiple columns. An internal standard or bracketing technique was used for quantitative measurement. Favre et al. (4) and Dietz (8) developed techniques for nonolefinic gasolines only and calibration or internal standards were required. An attempt has been made to overcome these disadvantages by selecting a single-stage column (adaptable to commercially available instruments), rvhich will permit resolution of light end components found in commercial gasolines, and by using a backflushing technique, which will measure directly the total Cs+ portion of the sample. A series of relative liquid volume
response factors has been derived to convert the resultant chromatogram into the desired liquid volume pertentages. Elimination of the additional steps required for other chromatographic techniques results in speed and versatility. EXPERIMENTAL
Apparatus. A Burrell Corp. Model K-2 Kromotog equipped with a hot wire filament, a standard backflushing device n-hicli permits t h e backflush components t o be recorded, a flash vaporizer, and a n integrator was used. The preliminary n-ork was concerned with the development of a partitioning agent which would permit resolution of olefinic and nonolefinic hydrocarbons in the CBto C j range. Dinonyl phthalate and di-2-ethylhexyl sebacate were useful partitioning agents for the analysis of nonolefinic gasolines, but were not satisfactory for the desired resolution of light hydrocarbons found in olefinic gasolines. Finally, a partitioning agent combination m-hich gave the required separation to Ct to C j olefins and paraffins was selected. The carbon number resolution afforded by di-2-ethylhexyl sebacate
Table I.
Retention Times with 16-Foot Combination Column
Components Air Ethylene and ethane Propane Propylene Isobutane n-Butane Isobutene and 1-butene trans-2-Butene cis-2-Butene and butadiene Isopentane 3-Methyl-1-butene n-Pentane 1-Pentene 2-Methyl-1-butene Neohexane trans-2-Pentene cis-2-Pentene 2-Pllethyl-2-butene Unidentified hexene( 8) 2-Methylpentane 3-Methylpentane and unidentified hexene
Retention Times, Minutes 2.1
2.7 3.8 4.5 6.0 8.3
96 11.9 13.4 15.5 16.2 20.6 23.3 25.8 26.9 29.2 30.6 34.1 38.0 39.4 45.7
\vas combined with the olefin-retarding properties of tri-m-tolyl phosphate saturated with silver nitrate. These agents Were coated On 30- to firebrick (25% by lveight) and packed l/rinch stainless steel in a 16-foot column in the follolving proportions: 4 feet of di-2-ethylhexyl sebacate follovied by 12 feet of tri-m-tolyl phosphate (silver nitrate-saturated). This column is a modification of one suggested by Lichtenfels et al. ( 5 ) . h specially prepared blend containing all the Cz to Cs hydrocarbons of interest was run. Operating conditions were helium flow a t 60 ml. per minute measured at the column exit and the column temperature set a t 30’ C. Each eluted component was vollected by conventional fraction collection techniques and subsequently identified by mass spectrometry (AIS). The retention times measured under these conditions are listed in Table I. Procedure. Gasoline samples are refrigerated and stored in small serum bottles with aluminum-sealed skirttype rubber stoppers. Then 0.01 to 0.02 ml. of sample is withdrawn Kith a hypodermic microsyringe and injected into the column. Accuracy in sample volume measurements is not critical. T h e sample is eluted at a helium flow rate determined by t h e desired separation of the olefins (if present). When all the light end components, up t o and including CS hydrocarbons, have been eluted and their peak areas recorded, the helium flow through the column is reversed and the Ce+ portion eluted and recorded in the same manner. The peak areas are then measured by accepted techniques. These are corrected by multiplying with the relative liquid volume response factors of Table 11. The corrected areas are then normalized to obtain a direct liquid volume percentage of each component or group of components. Figures 1 and 2 show chromatograms of typical nonolefinic and olefinic gasolines, respectively. DISCUSSION
A series of relative , liquid volume response factors was derived from the molar response data reported by Messner, Rosie, and Argabright (6). These data consist of relative thermal VOL. 32, NO. 9, AUGUST 1960
1107
Figure 1. gasoline
Chromatogram of typical nonolefinic base stock
response per mole factors for a number of organic compounds, including many hydrocarbon isomers up to Clo nparaffin. Additional data were derived in thh laboratory to obtain the
Table II. Relative Liquid Volume Response per Unit Chromatographic Peak Area
Table 111.
L =
molecular weight B X density at 60' F.
where 2
L = relative liquid volume response per unit chromatographic peak area B: = relative peak area per mole ( 6 )
Figure 3 was constructed using this equation. The curves shown indicate that the responses converge and reach an area of relatively close upper and
Derivation of Liquid Volume Response Factors from Compound-Type Analyses for Depentanized Gasolines
Compound Types Paraffins Cycloparaffins Aromatics Dicycloparafiins Stabilized reformate Paraffins Cycloparaffins Aromatics Dieycloparaffins Commercial Paraffins Olefins Cycloparaffins Aromatics Codas Stabilized cat. cracked Paraffins Olefins Cycloparaffins Aromatics Codas a Cyclrjolefins, diolefins, and acetylenes. Gawline Stabilized light straight-run
1108
Chromatogram of a typical olefinic base stock
more detailed information requirtd for this work. The hydrocarbon data reported by hfessner et al. were confirmed except for values given for propane and propylene, which were both found to be 70, based on work conducted here. These corrections have been incorporated into the relative liquid volume response factors of Table 11. The following formula was used to derive the relative volume response factors :
~~~
Relative Component Response Propane 1.24 Propylene 1.15 Isobuhe 1.26 n-Butme 1.17 Isobutene 1.14 1-Butene 1.15 trans-%Butene 1.08 &-%Butene 1.03 Isopenbe 1.14 n-Pentane 1.09 Pentenea 1.06O Hexanes plus 1,026 a Estimated value. Used for routine work; a precise value should be derived for more accurate work.
Figure 2. gasoline
ANALYTICAL CHEMISTRY
Volume
yo
No. Carbon Atoms/Mol.
41.8 38.2 18.4 1.6 39.9 11.3 48.5 0.3 22.5 29.4 27.4 11.8 8.9 16.0 36.9 9.1 22.3 15.7
7.7 7.7 7.7 7.7 7.0 7.0 7.5 7.0 7.5 7.5 7.5 7.5 7.5 7.4 7.4 7.4 8.0 7.4
L 1.03
1.00
1.02
1.01
I
4
5
6
N U ~ B €OF~ C A ~ B O NATOMJ PH
7
a
Ho/eu/b
9
,a
fc-,
Figure 3. Correlation between relative liquid volume response and nurnber of carbon atoms per molecule
lower limits in the C7 to Clo range. Based on the knowledge of the various hydrocarbon-type distributions in gasolines (as determined by mass spectrometry), an average liquid volume response of 1.02 may be used for the Ce+ portion of most gasolines. Mass spectrometer hydrocarbon-type analyses were performed on three typical base stocks and one finished gasoline. Table I11 lists the results and the computed L factors. Molar response values were not available for the olefins in the Ce to Clo range, but it was assumed that these would follow the same pattern as those for the paraffins. Subsequent work on olefinic gasolines confirmed this assumption. In some cases complete resolution of isopentane-3-methyl-1-butene-and of 2-methyl-1-butene-neohexaneis not achieved. A slower flow rate, or a rerun on another column which separates these pairs, may be used for improved resolution. An alternative approach is the application of chemical thermodynamic data to compute the olefinic isomer dis-
tribution. The work of Rossini is an excellent source of distribution data (3). Generally, for routine control work in this laboratory, the amount of neohexane assumed present is on the order of 0.2% in commercial gasoline and is not usually reported. The amount of 3-methyl-lbutene is assumed to be approximately 10% of the amount of %methyl-%butene present. %Methyl-2-butene is eluted without interference. Variation of flash vaporizer temperature affected the analytical results to some degree. A flash vaporizer temperature of about 30" C. above column temperature gave optimum results, with further temperature increases having a negligible effect. The column combination is not recommended for those samples suspected of containing a-acetylenes. RESULTS
To check the validity of the technique, a synthetic blend was prepared using research grade n-butane, n-pentane, and Phillips Petroleum Co. Special .4STM Maspec. Mix (1). A volume response factor of 1.00 was computed for the Ce+ hydrocarbons on the basis of the known composition. Table I V gives results obtained on this blend using various column temperatures with other operating conditions held constant. The analytical technique was ap-
Component Propane Isobutane n-Butane Isopenbe n-Pentane Cs Total (lis.vol. %) +
1
Table IV.
GLC Analysis of a Gasoline of Known Composition
Blended Composition as Verified Component by MS n-Butane 6.9 n-Pentane 15.6 77.5 Hexanes
+
7.1 15.6 77.3
30'C. 7.0 15.6 77.4
Run 3, 70" C. 7.1 15.5 77.4
Run 4, 70' C. 7.1 15.6 77.3
-4v. 7.1 15.6 77.3
-0.2 0 +0.2
can be attributed mostly to limitations of the latter method in detecting and accurately measuring the first light end components distilled (because of holdup between column and receiver lines). Since the results are normalized, the low temperature fractional distillation Cs+values tend to be high. CONCLUSION
This new method allows the direct determination of light hydrocarbons of interest in gasolines. Most of the disadvantages associated with other methods have been overcome. The method was found to be precise and accurate. Results on nonolefinic gasoline may be obtained within 25 minutes. The more complex olefinic gasolines may be analyzed within 1 hour. Investigations are currently being carried out to develop techniques for the quantitative collection of the C6+
Table V. Nonolefinic Gasoline Analyses by GLC and LTFD Reformate Stabilizer Bottoms Light Straight Run Stabilizer Bottoms Diff. Diff. LTFC, between LTFD, between av. of methGLC av. of methGLC 4 Av. 3 r u n s o ds 2 3 4 Av. 3 runs ods 1 2 3
-----Table VI.
+0.1 f0.5 +0.4 -0.1 -0.2 -0.7
0.1 1.2
8.5 7.5 82.7 100.0
GLC
0.1 0.1 0.1 0.1 . . 1.4 1.1 1.1 1.2 0.7 8.4 8.4 8.4 8.4 8.0 7.6 7.5 7.5 7.5 7.7 82.5 82.9 82.9 82.8 83.6 100.0 100.0 100.0 100.0 100.0
+0.1 +0.5 $0.4 -0.2 -0.8
Olefinic Gasoline Analysis by GLC and LTFD
A Commercial Gasoline
Cat. Cracked Stabilizer Bottoms Diff.
LTFD,a begken av. of meth3 runs ods
Components 1 2 3 4 Av. Propane Butenes 0 7 0.8 0.8 0.8 0.8 0.6 Isobutane 1.5 1.4 1.4 1.3 1.4 1.5 n-Butane 4.5 4.5 4.4 4.5 4.5 44 Pentenes 4.3 4.3 4.3 4.3 317 4.3 Isopentane 9.7 9.6 9.6 9.6 9.6 9.9 n-Pentane 6.3 6.5 6.4 6.4 6.4 6.1 73.0 72.9 73.1 73.1 73.0 73.8 Ca Total (liquid vol., yo) 100.0 100.0 100.0 100.0 100.0 100.0 * Lightends cut analyzed by mass spectrometry. +
Run 2,
plied to several typical petroleum-base stocks and blended gasolines and results were compared with those obtained by low temperature fractional distillation. Tables V and VI summarize the results on two groups of gasolines which are typical of those encountered in petroleum refining. The assumed liquid volume response value of 1.02 is valid because of the complex composition of the C6+ portion for these samples. Rather wide discrepancies did occur when this value was applied to a butylene polymer gasoline (predominantly Ce olefins). This emphasizes that this factor must be applied cautiously to hydrocarbon liquids composed mainly of a specific hydrocarbon or group of isomers. I n such cases, an empirical response factor should be derived. The bias between the Ce+ values listed in the tables in the GLC and low temperature fractional distillation results
0.1 0.1 0.1 0.1 ... 0.1 1.0 1.6 1.5 1.5 1.5 1.4 5.5 6.0 6.0 5.9 5.9 5.9 6.0 5.8 5.9 5.9 5.9 5.8 5.6 5.6 5.8 5.5 5.7 5.6 81.1 81.0 80.9 8 1 . 0 81.0 81.7 100.0 100.0 100.0 100.0 100.0 100.0
-
Run 1, 30" C.
Diff. between MS and GLC
------
+0.2 -0.1 +OI
+0:6 -0.3 f0.3 -0.8
Diff. LTFD" between av. of meth1 2 3 4 Av. 3 runs ods 0 . 1 -0.1 Trace Trace Trace Trace Trace GLC
3.3 0.6
0 7
3.4 0.5 n 7
3.4 0.6
n _ .7.
3.5 0.6 n 7
14.6 14.9 14.6 14.7 7.7 7.7 7.7 7.8 1.3 1.3 1.4 1.3 71.5 -71.7 _ _71.5 - - -71.6 100.0 100.0 100.0 100.0
3.4 3.1 0.6 0.5 0 7 0_ .7. 14.7 13.2 8.3 7.7 1.3 1.4 71.6 72.7 100.0 100.0
VOL. 32, NO. 9, AUGUST 1960
+0.3
+O.l 00 fl.5 -0.6 -0.1 -1.1
1109
portion of the gasoline sample for subsequent hydrocarbon-type analysis by mass spectrometry. ACKNOWLEDGMENT
The author acknowledges the valuable assistance rendered by Albert Paquette and Hank Alak of the laboratory staff.
LITERATURE CITED
(1) Am. Soc. Testing Materials, Phil-
adelphia, Pa., “Proposed Method of Test for Hydrocarbon Types in Low Olefinic Gasoline by Mass Spectrometry,’’ ASTM Committee D-2, Research Division IV, Section M. (2) Dietz, W. A., Coates, V. J., et al., “Gas Chromatography,” Academic Press, Sew York, 1958. (3) Farkas, A., “Physical Chemistry of Hydrocarbons,” Vol. 1, p. 363, Academic Press, New York, 1950.
( 4 ) Favre, J. A., Hines, W. J., Smith, D. E., Petrol. Refiner 37,251 (1968). ( 5 ) Lichtenfels. D. H.. Fleak. S. A.. Burrow, F. H.,Coggeshall, K.D., ANAL: >
,
CHEM.28, 1376 (1956). (6) Messner, A. E., Rosie, D. M., Argabright, P. A., Ibid., 31, 230 (1969).
RECEIVED for review December 10, 1959. Accepted June 3, 1960. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., February-March 1960.
Gas Chromatographic Determination of C b , C7, and Ce Olefins According to Their Carbon Structures KURT H. NELSON, WILLIAM J. HINES, M. D. GRIMES, and D. E. SMITH Research & Development Department, Phillips Petroleum Co., Bartlesville, Okla. ,Because of the large number of olefin isomers, considerable work will be required to develop gas chromatographic methods capable of determining the Ci. and CS olefins. As a substitute, a procedure for determining these olefins according to their carbon structures has been developed. This consists of first analyzing by gas chromatography the saturates portion from the original sample, then performing a similar analysis on the saturates from a hydrogenated sample. After calculating the data to a whole sample basis, the differences between the two analyses represent the sums of the various olefins having the same carbon structures. In this manner, all the olefins hydrogenating to form a particular paraffin or naphthene are reported as a group. On the basis of synthetic blends, the accuracy of the determination of a group of olefins is on the order of f6% of the amount present.
R
gas chromatography has come into widespread use in determining the Cs and lighter hydrocarbons in petroleum distillates. Gas chromatographic methods for determining the isomeric hexenes and hexanes have been reported (4,6, 7, 9, 12-14), but the analytical separation of some isomeric hexenes is still a problem. Very little work on the analysis of petroleum distillates for the individual C7 or higher olefins and saturates has been reported (4, 8). If the number of structural isomers is considered, there are only five Cg, nine C;, and 18 Cs paraffins. By comparison, there are 13, 27, and 68 structural isomers of the Cs,Ci, and C8 monoolefins, respectively. These do not in-
clude all the possible cis- and transisomers of these olefins. I n addition to these mono-olefins, numerous diolefins, cyclo-olefins, alkenylcyclo-olefins, and acetylenes may be present in a petroleum distillate. Because the development of gas chromatographic methods for the determination of the individual C7 and C8 olefins will require considerable work, an acceptable substitute procedure for determining the olefins according to their carbon structure would provide considerable information about the structural composition of the components in petroleum distillates. I n the procedure reported here, the olefin carbon structure analysis is carried out by determining the amounts of the individual parafKns and naphthenes present in a sample before and after hydrogenation. The differences betn-een the two analyses reprePent the olefins having the carbon structures of the corresponding paraffins and naphthenes. Thus, all the olefins having a particular carbon structure are reported as a sum.
ECENTLY,
1 1 10
*
ANALYTICAL CHEMISTRY
APPARATUS
Chromatograph. A custom-made chromatograph similar t o t h e PerkinElmer Model 154-A Vapor Fractometer in design and performance was used in this work. Silicone Column. The column consisted of 20 feet of coiled copper tubing, 1/4-inch diameter, which was filled with 35- to 80-mesh Chromosorb (Johns-hlanville, Manville, K. J.) impregnated with 17 weight yo Dow Corning 703 silicone oil. T h e column packing was prepared by pouring 10.3 grams of silicone oil onto 50.0 grams of Chromosorb in a n 8-ounce bottle. The Chromosorb was then shaken until it was dry enough to pour into the copper tubing. After filling
and plugging the column ends with glass wool, the column was placed in the chromatograph and flushed nTith helium. The newly prepared column was ready for use in about 30 minutes when a stable base line was indicated by the recorder of the chromatograph. The operating conditions for this column are listed in Table I.
Table
I.
Operating Conditions
Carrier gas Exit flo; rate, ml./min. Copmn temperature, C. Sample size, microliters
Silicone Squalane Column Column Helium Helium 60
60
88
77 10
10
Squalane Column. The column consisted of 14 feet of coiled copper tubing, 1/4-inch diameter, which was filled m-ith 35- to 80-mesh Chromosorb impregnated with 25 weight % squalane. This column packing was prepared in t h e same manner as the silicone column packing, except 16.7 grams of squalane was substituted for t h e silicone oil. The operating conditions for this column are listed in Table I. PROCEDURE
Remove the olefins and aromatics from an aliquot of the sample by acid absorption, employing ASTM Method D 1019-58T ( I ) , to obtain the raffinate (saturates portion) which contains only the paraffins and naphthenes. Next, hydrogenate the olefins in a second aliquot of the sample by any suitable procedure, and isolate the raffinate from the hydrogenated sample with ASTM Method D 1019-58T. This second raffinate contains the original saturates plus those created by hydro-
