the propyl and butyl derivates, branching of the chain increased the volatility. The isopentyl derivative was eluted before the n -pentyl, analogously with the butyl derivatives; however, the sec -pentyl derivative was eluted after the n pentyl derivative. Good separation was obtained except for the propyl derivatives where isopropyl emerged as a shoulder on the n-propyl peak. The see-pentyl derivative was not properly separated from the n -hexyl derivative. The oxazolin-5-ones could also be identified by their mass spectra which were fairly simple. The most prominent ions were rnle 175, 161, 105, and 7 7 . The relative intensities of the fragments are given in Table I. Only the two lowest homologs had molecular ions. The size of the higher homologs could be determined from the (M - 28)-+ fragment which resulted from loss of the carbonyl group. This fragment was further cleaved between the first and second carbon of the side chain to give the very abundant rnle 161 fragment. The compounds with branching a t the first carbon of the side chain did not give the M - 28 fragmentation, and they did also lack the rnle 161 fragment. The ( M - 28).+ fragment of the ethyl derivative had a mass of 175. Since the (M - 28).+ ion in all the other derivatives was accompanied with the rnle 161 fragment but not here, it is most likely that the (M - 28).+ fragment in this ~ the case was not due to loss of CO but to loss of C S H from side chain. The cleavage of the side chain as an olefin fragment very likely occurred via a McLafferty rearrangement ( 7 ) . Thus, all homologs with a hydrogen on the second carbon of the side chain had abundant fragments of m/e 175. The only exception was the tert-butyl derivative where
sterical factors probably hindered this fragmentation. The oxazolin-5-ones with secondary carbons a t the first position of the side chain, i.e. isopropyl and sec-pentyl, gave rnle 175 fragments of higher intensity than the unbranched homologs, i.e., 65% for isopropyl us. 10% for n-propyl, and 100% for see-pentyl us. 10% for n-pentyl. Branching a t the second carbon of the side chain also gave differences in the intensity of the rnle 175 fragment, i.e., 18%for isobutyl us. 6% for n-butyl. This was the only significant distinction between the mass spectra of these two derivatives. Branching further out in the side chain did not affect the McLafferty cleavage, i . e . , the isopentyl derivative had 9% intensity of the mle 175 fragment and the n -pentyl derivative 10%. In fact, it was impossible to distinguish the mass spectra of those two pentyl derivatives. The benzoyl fragment with rnle 105 was the base peak in all spectra. The phenyl ion of rnle 77 also was abundant in all spectra.
LITERATURE CITED (1) Y. Wolman, W. J. Haverland, and S. L. Miller, Proc. Nat. Acad. Sci. USA, 69, 809 (1972). (2) 0. Grahl-Nielsen and E. Solheim, Chern. Cornrnun., 1972, 1093. (3) P. A. Levene and R. E. Steiger, J. B i d Chem., 76, 299 (1928). (4) R. E. Steiger, J. Org. Chem., 9, 396 (1944). (5) H. Rodriguez, C. Chuaqui, S. Atala, and A. Marquez, Tetrahedron, 27, 2425 (1971). (6) 0. Grahl-Nielsen, J. Chrornatogr., 93, 229 (1974). (7) D. G. I. Kingston, J. T. Bursey, and M. M. Bursey, Chem. Rev., 74, 215 (1974).
RECEIVEDfor review July 15, 1974. Accepted September 30, 1974.
Characterization of Oil Shales by Laser Pyrolysis-Gas Chromatography Ray L. Hanson and
N. E. Vanderborgh
Department of Chemistry, The University of New Mexico, Albuquerque, N.M. 8713 1
Douglas G. Brookins Department of Geology, The University of New Mexico, Albuquerque, N.M. 8713 1
Oil shales occur in large quantities in the North American continent. They represent a large proportion of the known hydrocarbon reserves ( I , 2 ) . Currently work is being done on these materials to find new methods for their rapid characterization. Here we report initial studies on laser pyrolysis monitored by gas chromatography. Shales, like coal where considerably more analytical information exists, contain complex mixtures of high molecu‘lar weight hydrocarbons. It is of economic interest to know the amount of hydrocarbon in the rock; likewise moisture, ash, and particular elements have been determined in shales (3-5). Certainly much work will be done to improve these analyses in the immediate future. The standard method for oil shale characterization centers around combustion in oxygen. The evolved C 0 2 is measured volumetrically (6 1. Inorganic carbon (C03’-) is determined by an acidimetric procedure ( 7 ) . Other methods include the Fisher assays where shale samples are heated in a standard retort; the oil and other hydrocarbons
given off are collected and,weighed (8). This method has been used for years and most of the existing analytical data result from studies of this sort. More recent studies have looked a t the individual constituents obtained with solvent extraction followed by separation and identification (9, 1 0 ) . A. Giraud applied pyrolysis-gas chromatography to the geochemical characterization of kerogen in sedimentary rock. Low temperature cracking patterns showed products rich in aromatics. The mass of low molecular weight gases can be estimated from the C1-C3 hydrocarbons evolved while the C4-Cll alkanes serve as a reliable measure of the oil that can be produced. High temperature pyrolysis (here 500 “C) shows much more extensive cracking. Results indicate a series of cracking processes with the time dependence that one might predict for this type of analysis. Giraud indicated that pyrolysis must be of brief duration with minimal secondary reactions ( I 1 ). These requirements lead to the consideration of laser py-
A N A L Y T I C A L CHEMISTRY, V O L . 4 7 , NO. 2, F E B R U A R Y 1975
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viously described ( 1 5 ) .Product gases were swept directly onto the gas chromatograph column. A Varian Model 940 GC was used; separations were done on columns of a 6-in. (?&-in.stainless steel) precolumn of Poropak S (100-120 mesh) followed by a 6-foot column of Carbosieve B (80100 mesh). Data were obtained isothermally a t 100 "C. Helium carrier gas flow was 25 ml/minute. The instrument was equipped with a FID (flame ionization detector) (as supplied) and with a BILD (beta-induced luminescence detector), constructed in our laboratory (16). Effluents were split and fed simultaneously to each detector. Characterized Samples. Samples were supplied by J. P. Biscar (University of Wyoming). Samples as supplied were powders. Care was taken to make these as homogeneous as possible. Individual samples were pelletized at 20,000 psi; thin sections of these resulting pellets were then cut, placed in the quartz tubes, and pyrolyzed under a flowing helium stream.
b
RESULTS AND DISCUSSION A representative laser pyrogram is shown in Figure 1.
F ID
A 1 Figure 1. Laser pyrogram from oil shales
Representative results from a 1-joule normal burst zap. Upper trace, output from beta-induced luminescence detector. Lower trace FID. Arrow represents pyrolysis event. Peak identification (from retention volumes). ( a ) = Hz. ( 6 )= CO, ( c ) = CHI. ( d ) = COz, ( e ) = C2H2, ( f ) = CZH+ Water when present appears between COz and CZHZon the BILD
rolysis. Ruby laser radiation couples effectively with shale material and lasers deposit large amounts of power into the shale sample. Biscar initially reported utilization of a laser source for oil shale characterization (12, 13). His results, with a pulsed ruby system, clearly showed that the acetylene yield could be correlated with Fisher assay results, i.e., the amount of acetylene produced by pyrolysis is a measure of the hydrocarbon content of the shale. These results were done with an on-line gas chromatograph. More recently Biscar has suggested that a flame ionization detector be used directly to give an integrated total hydrocarbon quantification without the initial separation caused by the GC column (14). We report here additional work using laser pyrolysis-gas chromatography. Considerable additional information can be obtained from a quantitative measurement of the gaseous effluents.
EXPERIMENTAL Instrumentation. The laser used in these studies was a TRG 104A, pulsed ruby. Output energy is approximately 1 joule/pulse. Studies were made in the normal pulse mode fired by an Xenon flash lamp. A 21-cm focal length quartz lens was used to focus the beam on shale samples contained in the sample container pre336
Two separate traces are shown. The upper is the data taken from the BILD while the lower is the more usual FID output. Pyrolysis was initiated a t the arrow and then time is shown from right to left. The hydrocarbon peaks, methane, acetylene, and ethylene are obvious on both traces. Of interest is the mixture of low molecular weight gases that appear in the BILD output. Included here are hydrogen, the carbon oxides, and water. Hydrocarbons represent only about 20% by volume of the total gases in the effluent. Separation of the low molecular weight hydrocarbons is obtained using a carbosieve column, Poropak Q. Analyses using a Poropak S column a t 150 "C reveal that over 75% by volume of the organic product gases are low molecular weight hydrocarbons. Some C4-Cll hydrocarbons and aromatics are produced. These low concentration products will be studied in the future to obtain information about the quality of the oil that can be obtained from the shale samples (9-11). These results can be rationalized using the previously reported mechanisms of plume quenching and thermal blowoff (17). The low molecular weight gases (H2, CO, CO2, H20, CH4, C2H2, CzH4, C2H6) are the products from plume quenching and contain information about the atomic composition of the material. The kinetics of the heat soaking process reduces the fraction of product formation from the thermal blowoff route. One can easily explain this by assuming that the material has a high heat capacity due to the large inorganic carbonate content (typically 78-86%). Shales are also thought to contain methane, absorbed and entrapped in the material. This may be part of the methane peak although the amount contributed to the total peak may be small because of possible losses in grinding and handling the samples. Thus, we are concerned with the product gases from the plume quenching pathway. Five separate characterized shale samples were used for these tests. These were supplied with Fisher assay results (gallons/ton), water content, and weight percent carbon and hydrogen. Results from the laser induced pyrolysis are tabulated in Table I. Also included are the analytical data as received. (Oil shale samples and analytical data were obtained from J. P. Biscar, The University of Wyoming. They represent shales from the Green River formation.) The column for nonwater hydrogen simply represents the amount (here in a weight percentage) of the total hydrogen that is not in the water. This should then be characteristic of that hydrogen contained in the hydrocarbon constituents. The ratio of this value to the carbon is also shown. This falls close to 1.60 f 0.10 except for the first sample. Hydrogen to carbon ratios for shales in this formation have been reported a t a similar value ( I O , 1 8 ) . The first possible correlation with this information is that shown in Figure 2. Here the intensity of the acetylene
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 2, FEBRUARY 1975
Table I. Selected D a t a for Laser Pyrolysis of Green River Oil Shales BID
FID integrator Cil
IVater
yields
content
a
6.0 18.0 27.4 36.9 39.7
(-
)b
4.0 1.2 6.0 9.1 0.8
Total
Organic
Nonwater
iydrogen,
carbon,
hydrogen
wt 5/rb
Wt % *
W t %C
0.63 1.12 2.14 2.80 2.41
7.17 8.25 13.08 16.91 18.00
0.44 1.06 1.86 2.38 2.37
I total
organic
C2HZs c2H4
for CH4, C2H2,
% of total
*
productse
C2H4e
125 502 585
n. a. 888
Fisher assay results. D a t a s u p p l i e d b y J . P. Biscar. C a l c u l a t e d from a n a l y t i c a l d a t a ( t o t a l gen/carbon. Results from t h i s s t u d y . E a c h result is t h e average of 3 replicate analyses. a
BILD
COUntS
for CH4,
HI@
0.73 1.54 1.61 1.69 1.59
-I Io
H
2.76 5. 28 6. 5 1 5.79 7. 98
0.146 0.405 0.671 0.786 0. 712
- water H). R a t i o of nonwater h y d r o -
___
'I
0
4
12
8
H20 GallonrlTon
,';
1C
Figure 3. Water yield produced by laser pyrolysis compared to gravimetric water data
60
0 ' 1 Gallonrr-o"
Figure 2. Acetylene yield produced by laser pyrolysis of oil shales compared to Fisher assay results
Data taken from the BILD, lo is the signal proportional to light intensity with no signal quenching. I is the maximum peak intensity as a result of quenching. Error bars show standard deviation found on replicate results on each samole
peak (taken from the BILD) is shown plotted us. data from Fisher assay information. Representative standard deviations are shown on the error bars. We have no way of assuring that the samples are completely homogeneous. Reproducibility of laser power is similar to the relative standard deviation, &5%. Currently work is in progress to monitor the power of each laser pulse. This will permit normalization of the data for variation in laser power from pulse to pulse. Even so, the data shown in Figure Z do show the correlation found by Biscar and adequately reproduces the Fisher assay results.
Data taken from the BILD detector. (FID not sensitive to water.) Data here are plotted logarithmically since BILD detector shows such response over wider ranges of concentration
Another result is shown in Figure 3. Here the water content, again data from the BILD detector, is shown plotted us. water data obtained gravimetrically. The correlation clearly shows the applicability of this method. One can also rapidly determine the amount of nonwater hydrogen by a quantification of the hydrogen produced in the laser pyrolysis event. These data are shown in Figure 4 where the hydrogen yield is shown us. the "nonwater hydrogen", the difference between the total hydrogen and that which can be attributed to the hydrogen in the water contained in the shales. This correlation is also quite clear. Laser pyrolysis even in these simple experiments shows good promise to additionally characterize oil shales. The information that can be obtained from a quantification of the plume quenching products is large. First, as these re-
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*
337
briefly before. Investigations under way will explore ways to improve precision. It might be pointed out that current methods for the task of oil shale characterization are not particularly precise. The obvious advantage of LPGC is the rapidity of these analyses and the ease of automation. Depending upon the amount of separation required (and as Biscar suggests the total pyrolysis products can be fed directly into a FID for a determination of the hydrocarbon content), analysis time can be in the order of minutes. This is a marked improvement in the methodology for oil shale characterization.
T
CONCLUSION In conclusion, laser pyrolysis gas chromatography permits a rapid and sensible method for the characterization of shales. The total analysis time is but ten minutes. Moreover, the method permits easy automation and shows good promise as a routine analytical procedure. The laser pyrogram also gives data for CO and COz. This information should lead to a characterization of the carbonate content of the shale and also the extent of oxidation of the organic material.
LITERATURE CITED
2
1 NOn-Watev
Hyorogen
3 w:
i
Figure 4. Hydrogen yield produced by laser pyrolysis Compared to nonwater hydrogen. Data taken from the BlLD detector and plotted linearly as ( l o / ) I /
-
(1) (2) (3) (4)
(5) (6) (7) (8) (9) (10)
sults have indicated and as first shown by Biscar, Fisher assay results are duplicated. One can also determine the hydrogen/carbon ratio. This can be done in several ways. The ratio of CH4/C2H2 strongly suggests a C:H ratio of 1:6; or one can determine the "nonwater hydrogen" (19). From these data and the hydrocarbon content (C2H2 yield) the C/H ratio can be determined. Last, the amount of water contained in the shale can be rapidly assayed. The reproducibility of these data has been mentioned
(11) (12) (13) (14) (15) (16) (17) (18) (19)
M. T. Atwood, Cbem. Techno/., 3, 617 (1973). G. L. Cook, J. Petrol. Techno/., 24, 1325 (1972). F. L. Hartley, Cbem. Eng. News, 52, 15 (1974). R . J. Cameron, J. Petrol. Techno/., 21, 253 (1969). E. W. Cook, Fuel, 53, 16 (1974). A. E. Foscolos, and R. R. Barefoot, Geological Survey Can., Pap. No. 70-11, 1-8 (1970). J. W. Wimbereley, Anal. Cbim. Acta, 48, 419 (1969). A. E. Hubbard, U.S. Bur. Mines R e p . Invest., 6676, 1965, 19 pp. D. E. Anders and W. E. Robinson, Geocbim. Cosmochim. Acta, 35, 661 (1971). W. E. Robinson, in "Organic Geochemistry," G. Eglington and M. T. Murphy, Ed., Springer-Verlag, New York, N.Y., 1969, Chap. 6 and 26. A. Giraud, Amer. Ass. Petrol. Geol. Bull., 54, 439 (1970). J. P. Biscar. Anal. Cbem., 43, 982 (1971). J. P. Biscar, J. Chromatogr., 56, 348 (1971). J. P. Biscar. University of Wyoming, Laramie, Wyo.,personal correspondence, 1974. W. T. Ristau and N. E. Vanderborgh, Anal. Chem., 42, 1848 (1970). W. T. Ristau and N. E. Vanderborgh, Anal. Cbem., 44, 359 (1972). W. T. Ristau and N. E. Vanderborgh, Anal. Cbem., 43, 702 (1971). E. W., Cook, Fuel, 53, 16 (1974). N. E. Vanderborgh, and W. T. Ristau, Amer. Lab., 5, 41 (1973).
RECEIVED for review August 2, 1974. Accepted October 7, 1974.
Methylmercury Species and Equilibria in Aqueous Solution Dallas L. Rabenstein, Christopher A. Evans, M. Coreen Tourangeau, and Mary T. Fairhurst Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
The solution chemistry of methylmercury has become a subject of interest with the recognition of its importance in environmental pollution by mercury. The aqueous solution model most widely used (1-4)is that of Schwarzenbach and Schellenberg ( 5 ) , although some uncertainty exists as to the nature of methylmercury species in solution (4,6, 7). In the Schwarzenbach and Schelienberg model, which was developed from p H titration data for solutions containing 5.85 X 10d4M to 2.19 X 10-2M methylmercury, CH3HgOH2+ reacts with hydroxide ion to form CH3HgOH and with CHBHgOH to form (CH3Hg)zOH+. 338
CH3HgOHZ'
+
K -
OH-
CHSHgOH
[ CH,HgOH]
' - [ CH,HgOH,'][
CH,HgOH,+
+
+ HZO
CH,HgOH
OH']
e (CH,Hg),OH+ +
[(CH Hg) OH']
Kz = [ C H , H g O H , " , H g O H ]
(1) H,O (2 1
Woodward and coworkers (I, 8, 9 ) identified the species CHsHgOH2+ and CH3HgOH in aqueous solution by
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