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Energy & Fuels 1989,3, 304-307
Quantitative Analysis of Kerosenes by Raman Spectroscopy Kathryn S. Kalasinsky, James P. Minyard, Jr., and Victor F. Kalasinsky Mississippi State Chemical Laboratory and Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762
J. R. Durig* Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208 Received December 2, 1988. Revised Manuscript Received January 9, 1989 ~
A quantitative analysis technique for carbon atom character of kerosenes was derived by using Raman spectroscopy. The results were obtained by ratioing the integrated areas of peaks associated with the vibrations of the particular carbon atoms of interest. The error limits range from 0.01% to 0.35% for the olefinic region, from 0.01% to 0.12% for the aromatic region, and from 0.01% to 0.46% for the saturated region. The results are compared to those obtained by other methods that have been approved as standard methods. Many samples have been tested, and all analyses have been found to be accurate to within 0.5%. Introduction I t is necessary for the oil industries to identify their kerosene products by reporting the percentage content of olefins, aromatics, and saturates. There are several approved American Society for Testing Materials (ASTM) methods that are generally used for this analysis,’ all of which leave considerable doubt with a wide margin of error. The search for a better, more accurate method has been pursued for quite some We have employed Raman spectroscopy with a new method that shows promise with very high accuracy measurements. In Table I is shown the analysis of one oil sample, determined by six different methods in any of five possible laboratories. The first three methods are those approved by ASTM. The ASTM D-1319 method employs column chromatography, the reproducibility varies widely, the results are in volume percent, and all aromatic olefins, some diolefins, and compounds containing sulfur, nitrogen, or oxygen are determined as aromatics. The ASTM D1019 method is a phase separation method that cannot distinguish the olefins from aromatics; the results are in volume percent, and all compounds containing sulfur, nitrogen, or oxygen are determined as olefins and aromatics. The method D-875 is one that determines the olefins and aromatics from bromine number and acid absorption, and the values are in volume percent with sulfur-, nitrogen-, or oxygen-containing compounds reducing the accuracy of the method. High-pressure liquid chromatography (HPLC) determines the values in weight percent but the reproducibility varies greatly (Table I). 13CNMR spectroscopy cannot distinguish the olefins from the aromatics. The reported values are in atom percent and the non-hydrocarbon materials do not interfere, but the accuracy of the experiment has not been tested with any known samples nor has the instrumental error been determined. The Raman method determines the values in atom percent and the non-hydrocarbon materials do not (1)1987 Annual Book of ASTM Standards; ASTM Philadelphia, PA, 1987, D-1319, D-1019, and D-875, Section 5, Vol. 05.01. (2) Heigl, J. J.; Black, J. F.; Dudenbostel, B. F., Jr. Anal. Chen. 1949, 21,554. (3) Shoolery, J. N.; Budde, W. L. Anal. Chem. 1976,48, 1458. (4) Miller, R. L.; Johansen, N. G. Presented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy,Atlantic City, NJ, March 1982; Paper 62. (5) Wooten, D. L.: Spectroscopy (Springfield, Oreg.) 1986,1(3), 14.
0887-0624/89/2503-0304$01.50/0
interfere. The accuracy of the experiment has been determined to be within 0.5% by known samples, and the reproducibility is very good. It was felt that the desired results could be obtained by ratioing the integrated areas of peaks associated with the vibration of the particular carbon atoms of interest. This quantitative analysis is an extension of the method published by Koenig for determining amounts of polymer material from the infrared spectra: and it is described in the following section.
Experimental Section The Raman spectra were obtained by using a Spex Ramalog DUV spectrometer equipped with a Spectra-Physics Model 171 argon ion laser operating at 4880 A. The solid samples were packed in Pyrex capillaries and sealed at both ends. The spectra for solutions were obtained from solutions made with either CS2 or C2C4 that were also sealed in Pyrex capillaries. Depolarization data were taken with the standard Spex accessory.‘ The Raman spectrometerwas interfaced to a Nicolet Model 1180 computer for signal averaging. Theoretical Derivation for Quantitative Analysis of a Three-Component System from Raman Data Infrared spectra can be described by the Beer-Lambert law
A = abc (1) where A is the absorbance, “a” is the specific absorptivity, “b” is the path length of the infrared beam through the sample, and “c” is the concentration of the sample. Similarly, Raman spectra can be described by A = Na2 (2) where ”N” is the number of molecules in the laser beam, and “a”is the polarizability tensor for the molecule. If we wish to measure the relative amounts of three different components in the Raman spectrum, we can follow the description given by Koenig for the infrared6 spectra. However, unlike this previously described method, we cannot use the Raman spectra themselves, but rather “simulated” spectra that put all intensities of component (6) Koenig, J. L.; Kormos, D. Appl. Spectrosc. 1979, 33, 349. (7) Schrotter, H. W. Raman Spectroscopy Theory and Practice; Szymanski, H. A., Ed.; Plenum Press: New York, 1970; Vol. 2, Chapter 3.
0 1989 American Chemical Society
Quantitative Analysis of Kerosenes
Energy & Fuels, Vol. 3, No. 3, 1989 305 Table I. Analysis of Unknown Oil Sample A
method ASTM D-1319
laboratory A
run no.
I I I
B C ASTM D-1019 ASTM D-875
HPLC
I1 I I I I1 I11 I I I1 I11
C C B
D
NMR Raman
E
olefins
aromatics
saturates
3.95 1.0 4.5 3.1
10.2 10.0 10.7 9.6
85.85 89.0 84.8 87.3 86.0 86.0 89.2 91.0 89.2 92.3 97.53 97.21 97.62
14.0 5.1 2.1 0.4 2.1
8.9 8.7 8.6 8.7 7.7
2.47 2.79 2.38
1together, all intensities of component 2 together, and all intensities of component 3 together? giving (3)
0.0 0.0 0.0
+ +
AI1 = Ai’ AIH = Ai”
+
+ A< + A C =
N l ” ( ~ 1+ ) 2N f l ( ( ~+~N)
