Comparison of hydrocarbon composition in complex coal-liquid

analysis of the fleld-ionizatlon mass spectral data are pres- ented. Detailed compositional Information could be obtained by one approach, while with ...
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Anal. Chem. lQ85, 57,666-671

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Comparison of Hydrocarbon Composition in Complex Coal-Liquid Samples by Liquid Chromatography and Field- Ionization Mass Spectrometry Todd W. Allen and Robert J. Hurtubise*

Department of Chemistry, The University of Wyoming, Laramie, Wyoming 82071 Howard F. Silver

Chemical Engineering Department, The University of Wyoming, Laramie, Wyoming 82071

Low-pressure llquid chromatography, hlgh-performance liquid chromatography, and field-lonlzatlon mass spectrometry were used to obtain compositlonal data on the hydrocarbons In two nondlstlllable coal-llquld samples. Two approaches for analysls of the field-Ionization mass spectral data are presented. Detailed composltlonal lnformatlon could be obtained by one approach, whlle wlth another approach, a general comparlson of a large amount of mass spectral data could be made on the basis of weight percent and Z serles. The methods developed can generally be applied for the analysls of complex hydrocarbon samples, and they allow for relatively easy comparison of hydrocarbon composltlon between samples.

Considerable work has been done on the separation and characterization of coal liquids and related samples (1-22). Many of the methods developed give general information on the composition of these complex samples. This information is useful; however, there is a need for more compositional details in many situations such as in process control work, in environmental studies, and in understanding the chemistry of coal liquefaction. Recently, we described methods for the determination of hydrocarbon compositions in high-boiling and nondistillable coal liquids by liquid chromatography and field ionization mass spectrometry (FIMS) (8,9). The general approach involved a combination of low-pressure liquid chromatography, high-performance liquid chromatography (HPLC), and FIMS. In this work, the previous methods were used to compare hydrocarbons from subbituminous and bituminous nondistillable coal-liquid samples. In addition, the data are reported on a weight percent basis rather than a mole percent basis as done previously, and the hydrocarbon data are compared by a pseudo-three-dimensional computer graphing method. Although coal-liquid samples were used in this work, the general approach reported for hydrocarbon analysis should be applicable to a variety of different samples. EXPERIMENTAL SECTION Material Studied. The two coal-liquid samples studied were produced by direct liquefaction in an SRC-I process. The Wyodak sample, produced from a subbituminous coal from the Canyon Anderson seams in the Amax Coal Co., Belle AyrMine in Wyoming, was supplied by Catalytic, Inc., from the Southern Company Services, Inc., SRC pilot plant located at Wilsonville, AL. This sample had an ash content of 0.52 wt. % ash and represented nondistillable material boiling above 427 “C. The second sample was produced from a bituminous Kentucky 9/14 coal. It had an ash content of 0.09 w t % ash and represented nondistillable material boiling above 524 “C. The sample was supplied by the Pittsburgh and Midway Coal Mining Co. SRC pilot plant near Tacoma, WA. Both samples were used as received. Apparatus and Chemicals. The liquid chromatograph consisted of a Waters Associates Model 6000A pump, a Model

U6K injector, a Model ALC 201 differential refractometer, and a Model 440 UV absorbance detector in series, a strip chart recorder, and a Bascom Turner Model 8120 computerized recorder. A 10-pm particle size semipreparative pBondapak NH2 column (Waters Associates) with n-heptane (MCB Omnisolve) at 0.8 mL/min was used in the separation. MCB Omnisolve grade n-heptane was filtered through a Millipore type F-H 0.45-pm filter and degassed by helium sparging. Sample Separation. Hydrocarbon fractions were isolated from “oils” (hexane solubles) of the Wyodak and Kentucky samples using previously described procedures (5,6). The weight percents of the hydrocarbon fractions were determined by first removing most of the solvent with a rotary evaporator. Then the concentrate was transferred to preweighed vials, dried carefully with a stream of nitrogen gas, and weighed. The hydrocarbon fractions were then separated into various fractions based on the number of double bonds in the structure, using an HPLC procedure which was discussed earlier (8,9). The determination of weight percent of these fractions was similar to that for “oils”except the volumes of solvent encountered did not require the use of a rotary evaporator. Only the hydrocarbons isolated from “oils”were further separated by HPLC because of the small amounts of hydrocarbons found in “asphaltenes” (toluene soluble, hexane insoluble). Field-Ionization Mass Spectrometry. Field-ionization mass spectra of the HPLC fractions were obtained by SRI International in Menlo Park, CA. The field ionization mass spectrometer used in this study was designed and built at SRI International. It was interfaced to and controlled by a PDP 11/10 Computer System. An activated metal foil was used for field ionization, and mass analysis was performed with a 10-in. radius, 60” magnetic sector mass analyzer. The mass spectrometer was operated at a nominal resolving power of 800 (20% valley). The ion detector uses ioncounting electronics,and the data were collected in a multichannel analyzer with 4096 channels. Details of the mass spectrometer were described earlier (23). Typically, about 40-80 pg of the sample was introduced with a direct insertion probe. The sample was initially cooled to -78 “C, and the spectrometer was set to repeatedly scan the desired mass range, usually 100 to 800 amu, at a speed of 56 ms/amu. The sample was then slowly heated, and the mass spectra of the evolving materials were acquired. Care was taken so as not to overload any of the channels of the multichannel analyzer. If the signal became too intense, the sample was cooled. Cumulative data for every eight scans were stored as a spectrum in the computer, and the acquisition continued till there was no more evolution of the sample at the maximum temperature, generally set at 450 “C. Depending upon the sample, the distillation lasted anywhere from 40 min to 2 h. The various spectra acquired over the entire mass range were mass analyzed with a calibration curve obtained with known compounds under the same mass spectrometer operating conditions. The mass-analyzed spectra were added together, and conversion from ion counts to corrected intensity was automatically performed by the computer using the following equation:

I; =

20(ion counts)i

Mi

(1)

where (ion counts)i is the number of ion counts in the ith peak

0003-2700/85/0357-0666$01.50/00 1985 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985

Table I. Weight Percent of Double Bond Fractions in Kentucky and Wyodak Coal Liquid Samples

Table 11. Percent Volatility and Number Average Molecular Weight of Double-Bond Hydrocarbon Fractions

wt % in total sample”

hydrocarbon fraction

Kentuckyb

Wyodak’

saturates 3 double bonds 5 double bonds 6 double bonds 7 double bonds 8 double bonds 9 double bonds 10 and 11double bonds 212 double bonds

0.16 0.21 0.57 0.51 1.34 0.98 0.98 1.65

0.49 0.14 0.63 0.28 1.40 1.40 0.98 2.10 2.18

recovery

7.90

9.60

1.50

Average of duplicate runs. Total hydrocarbons isolated from “oils” is 7.9%. Total hvdrocarbons isolated from “oils” is 10.4%.

667

fraction saturates 3 double bonds 5 double bonds 6 double bonds 7 double bonds 8 double bonds 9 double bonds 10 and 11double bonds 212 double bonds a

% volatility” no. av mol wt” Kentucky Wyodak Kentucky Wyodak 100 100 99 97 94 100 90 100

92 100 99 100 100 100 100 99

395.7 476.5 316.3 333.8 277.3 298.6 348.8 382.1

339.0 396.3 307.9 285.7 319.4

95

100

446.4

417.7

285.1 329.4 351.6

Data reported by SRI International.

a

and Mi is the mass of the ith peak. These intensities were automatically normalized to 10000 for each spectrum according to 10000zi Rli = ZiIi where liis from eq 1and CiIi is the s u m of all Zi. The values which result from eq 2 are provided by SRI International for each analysis. An HP-87 computer with an HP Model 82901M flexible disk drive and an HP Model 82905B printer were used to evaluate the data in this work. Computer programs were devised which allow for correction of peak intensities for natural abundance of carbon-13, for subsequent conversion to weight percent of the total sample, and for plotting of the weight percent data. Elemental Analysis. Elemental analysis of the total hydrocarbons found in the Wyodak sample was performed in duplicate by Huffman Laboratories, Inc., in Wheatridge, CO.

RESULTS AND DISCUSSION Separation of Hydrocarbons from Nondistillable Coal-Liquid Samples. The separation procedures developed previously were shown to effectively separate hydrocarbons in high boiling and nondistillable coal-liquid samples from other compound class fractions (5, 6, 24). The results in Table I show that hydrocarbons isolated from “oils” (hexane solubles) account for 7.9 w t 70of the Kentucky coal-liquid sample and 10.4 wt % of the Wyodak coal-liquid sample. Hydrocarbons isolated from “asphaltenes” (toluene soluble, hexane insoluble) were 50.5 wt % and were not considered further. Some analytical data on hydrocarbons and other compound class fractions from the two samples have been reported (23). The averages of duplicate elemental analyses for hydrocarbons in the Wyodak sample were 91.6 wt % carbon, 7.1 wt % hydrogen, 0.1 wt % nitrogen, 1.4 wt % oxygen, and 0.1 wt % sulfur. Composition of hydrocarbons in the Kentucky sample is expected to be similar, although elemental analysis is needed to confirm this. Separation of Hydrocarbons by HPLC. Hydrocarbons isolated from “oils” of the two cod-liquid samples were further separated by HPLC. The HPLC approach was described previously, and was shown to be effective in separating hydrocarbon mixtures according to the number of aromatic double bonds present in a given hydrocarbon structure (8,9). Little or no effect of alkyl substitution was observed. Nine fractions were obtained by the HPLC method. These were a saturates fraction and double bond aromatic fractions containing 3, 5,6, 7, 8, 9, 10 and 11, and 112 double bonds. Results of the HPLC separation are presented in Table I. The data show that although the Kentucky sample contains less hydrocarbons than the Wyodak sample (7.9 wt % and 10.4 w t %, respectively), the Kentucky sample contains more of the 3 double bond, 6 double bond, and 7 double bond type

hydrocarbons. Amounts of the 9 double bond fractions are equal, and the Wyodak sample contains more of all the other fractions, especially the 10-11 double bond fraction and the 212 double bond fraction. The separation into double bond fractions is essential for the subsequent analysis by FIMS, because it prevents overlap of components with the same mass but different molecular structure. The implications of this have been discussed in more detail (8, 9, 25). Field-Ionization Mass Spectrometry. Field ionization mass spectrometry is unique in its ability to produce unfragmented molecular ions and their isotopic signals (26) and is ideally suited to the analysis of components in coal derived liquids (15, 21-23, 27-30). FIMS combined with HPLC provides detailed information on the composition of coal-liquid samples which previously was unavailable. The hydrocarbon double bond fractions, isolated from Kentucky and Wyodak samples, exhibited high volatility under the conditions of the FIMS analysis as shown in Table 11. Number average molecular weights (MW,) were provided with the analysis for each fraction, and were calculated by using

(3) where Ii is the intensity of the ith component according to eq 1and Mi is the mass of the ith component. Values for MW, are given in Table I1 for each fraction. In general, the Kentucky fractions yielded higher values for MW, than the Wyodak fractions, indicating greater amounts of material at higher masses. After correction of individual intensity values in the FI mass spectrum for natural abundance of 13C, it was possible to convert the individual relative intensity values in each double bond fraction to weight percent in the coal-liquid sample. The weight percent values can be calculated by using eq 4, a form of which was recently reported by Yoshida et al. (22) (4)

where wt%i is the weight percent of the ith component, wt7ohtd is the weight percent of the double bond fraction in

the coal-liquid sample, and M , and Zi are as before. However, eq 4 is awkward to use in that the term C , ( M i l J is tedious to calculate. After combining eq 2, 3, and 4 and introducing a term to account for percent volatility of the fraction, we obtained eq 5. This equation is easily used to find weight percent of any component in the total coal-liquid sample (5)

where wt%i, wt%,,d, and Mi are as before, RIi is the relative

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985

668

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Flaure 1. Selected Zseries in the F I mass soectra of the 6 double bond hydrocarbon fractlon isolated from Kentucky (K) and Wyodak (W) coal-llquid simples: (1) c ~ H ~ ~(2) - ,c ~~ ;H ~ ~(3) - , C~~;H ~ , , - , ~ .

(normalized) intensity of the ith component in the spectrum (corrected for 13C abundance), MW, is the number average molecular weight of the double bond fraction, and F is fractional volatility of the double bond fraction. It should be noted that eq 4 and 5 represent the limiting case, where mole sensitivities for field ionization of compounds in each fraction are assumed to be equal (31). For fractions composed of related compound types, this assumption has been shown to result in acceptable quantitative distributions in the field ionization analysis (21,31). Considering the high selectivity of sample separation obtained for the material in this study, which produces hydrocarbon fractions, the assumption is applicable in our work. In correcting peak intensities for the presence of 13C,the molecular formula and intensity at each even mass, along with the natural percentage of the 13C isotope, were used to calculate expected isotope intensities at only the next higher, adjacent odd mass. Results of the calculation generally reduced the intensities at odd masses to negligible levels, indicating very low levels of nitrogen-containing species. This is consistent with the low nitrogen content (0.1 wt %) found in the total hydrocarbon fraction by elemental analysis. Weight Percent of 2 Series in Double Bond Fractions. Total weight percent values of the various homologous 2 series present in each double bond hydrocarbon fraction from the Kentucky and Wyodak samples are presented in Table 111, where the 2 numbers refer to the formula CnHzn+~. In general, for each double bond fraction, decreasing 2 number corresponds to increasing hydroaromatic character. The more detailed information in Table I11 reveals that some conclusions

made from data in Table I can be misleading, illustrating the importance of FIMS analysis. For example, although the Kentucky sample was shown in Table I to contain more 7 double bond hydrocarbons than the Wyodak sample, the Wyodak sample actually contains more of the -22, -24, -26, and -28 2 series in this fraction (Table 111). Similarly, the Wyodak sample contains more 5 double bond and 8 double bond hydrocarbons overall (Table I),but the Kentucky sample contains more of some of the 2 series in both fractions (Table 111). The 9 double bond fraction, which overall represents equal amounts in the two samples (Table I), contains differing amounts of the various 2 series (Table 111). Detailed Comparison of Field-Ionization Mass Spectra. By use of methods developed previously by us and an adaptation of a program which aids in structural assignments, it was possible to carry out a detailed comparison of the hydrocarbon composition in two or more coal-liquid samples (8,9,25,32). Figure 1,for example, illustrates the -14, -16, and -18 2 series from the 6 double bond hydrocarbon fractions of both coal-liquid samples. The CnH2,+ hydrocarbon series can be composed of biphenyl ( m / z 154) and its alkyl-substituted homologues. However, biphenyl is a very weak band for the Wyodak sample or a nonexistent band for the Kentucky sample in Figure 1. Because no other parent (i.e., unsubstituted) 6 double bond hydrocarbons can appear in this series, and because of the large intensities at m / z 168, 182, and 196 compared to the intensity at m / z 154 (biphenyl), various furan types (C,Hz,-&) which also contain 6 double bonds are assumed to be prevalent in the CnH2n-14series. Generally, furans were found to behave as hydrocarbons under

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985

669

Table 111. Weight Percent of Various 2 Series in Hydrocarbon Fractions from Kentucky (K) and Wyodak (W) Coal-Liquid Samples saturates Z

K

4-2

0.027

0 0.023 -2 -4 -8

0.016 0.013 0.018 0.019

-10

0.011

-6 -12 -14 -16 -18 -20 -22 -24 -26 -28 -30 -32 -34 -36 -38

W

3 d.b.a

K

0.047 0.043 0.039 0.042 0.051 0.022 0.067 0.032 0.057 0.029 0.031 0.030 0.020 0.014

W

0.015 0.027 0.023 0.018 0.015 0.009 0.008

5 deb.

K

W

0.045 0.087 0.14 0.19 0.13 0.15 0.087 0.073 0.052 0.046 0.034 0.031 0.024 0.022

7 d.b.

6 d.b.

K

W

0.039 0.045 0.087 0.098 0.087 0.067 0.050

0.015 0.039 0.069 0.048 0.043 0.032 0.019

-40 -42 -44

K

W

0.051

0.050 0.12 0.33 0.38 0.21 0.12 0.070

0.29 0.38 0.29 0.17

0.11 0.065

8 d.b.

K

W

0.089 0.40 0.32 0.22 0.12 0.077 0.068

0.089 0.51 0.31 0.21 0.12 0.073 0.059

9 d.b.

K

W

0.069 0.13 0.16 0.17 0.14 0.098 0.073

0.058 0.20 0.21 0.18 0.14 0.092 0.059

10-11 d.b. K W

0.084 0.15 0.18 0.18

0.15 0.11 0.084

0.15 0.37 0.38 0.41 0.31 0.24 0.16

12+ d.b.

K

W

0.19 0.22 0.23 0.22 0.20 0.20 0.18

0.26 0.31 0.32 0.34 0.30 0.28 0.24

'd.b. = double bond.

conditions of the separation (6, 8, 9). Although elemental analysis of the total hydrocarbon fraction indicated the presence of some oxygen-containing species, high resolution mass spectrometry and/or elemental analysis of this fraction and other fractions would be necessary to confirm the presence of furans. Notice in Table I11 that this series (2= -14 from 6 double bonds) accounts for nearly the same amounts in both the Kentucky and Wyodak samples (0.045 wt % and 0.039 w t %, respectively), suggesting that this 2 series is similar in the two samples. However, the Kentucky sample is distinctly different from the Wyodak sample as seen in Figure 1. The Wyodak sample contains a large peak at m/z 168 (dibenzofuran) which is absent in the Kentucky sample. Also, more material in the Kentucky sample is distributed in the higher mass range (300-750). The CnH2n-16series in the 6 double bond fraction is composed of fluorene, dihydrophenanthrenelanthracene, phenylindan, phenyltetralin, and their alkyl-substituted homologues. The Kentucky sample contains more of this series overall (Table III). Figure 1reveals that the Kentucky sample actually contains greater amounts of components at m/z 208, 222, and all higher masses in this series, while the Wyodak sample contains greater amounts of components at m/z 166, 180, and 194. The CnH2n-18series in the 6 double bond fraction contains compounds such as tetrahydropyrene, tetrahydrobenzofluorene, hexahydrobenzophenanthrene/anthracene,cyclohexylfluorene, and their alkyl-substituted homologues as indicated in Figure 1. Again the Kentucky sample contains much more of this series (Table 111),but the Wyodak sample has slightly more material in the mass range 500-600. It is emphasized that such detailed analysis of each double bond fraction and its 2 series is important, but the data generated are extensive and can obscure the overall compositional picture. For example, while Figure 1 shows some dramatic differences between the selected 2 series, these 2 series are relatively minor components of the hydrocarbons as a whole (Table I and Table 111). General Comparison of Hydrocarbon Composition, Because of the large amount of data from the FIMS experi-

I

Flgure 2. Comparison of mass Z series In saturates, 3 double bond (D.B.), and 5 double bond hydrocarbons isolated from Kentucky (K) and Wyodak (W) coal-liquid samples.

ment, it becomes very difficult to compare the overall hydrocarbon composition of two or more samples. In this work, a pseudo-three-dimensional computer graphing method was developed for the rapid comparison of all the data from the double bond hydrocarbon fractions. Figures 2-4 show the comparison of the FIMS data. All 2 series present in all the double bond fractions are given for comparison. Many of the significant compositional differences between the two samples can be easily seen.

670 -12

5-K

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985 -14

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2-

- -K--1 6!i - -E -u-16

-20 -,

-I(_

-22

-u- - 5-K

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- -K_

_u 1

2

-20 K U

-22 K Y

-24 U U

-26 K

U

-28 K

U

-30 K

U

-32 K

U

Figure 4. Comparison of mass 2 series in 9 double bond (D.B.), 10 and 11 double bond, and 1 1 2 double bond hydrocarbons isolated from Kentucky (K) and Wyodak (W) coal-llquld samples.

Saturates in the Kentucky and Wyodak samples are present a t 0.16 wt % and 0.49 wt %, respectively (Table I), and the Wyodak sample dominates in every 2 series (Table 111). Figure 2 shows that in the CnH2n+2, CnHan,and CnH2n-2series the maxima are shifted to higher masses in the Kentucky sample. A prominent peak for a tricyclic terpane in the CnHzn-4 series from the Wyodak sample is absent in. the Kentucky sample. The Wyodak sample contains some lower molecular weight material in all 2 series which is absent in the Kentucky sample. Hydrocarbons containing 3 double bonds are present at 0.21 wt % and 0.14 wt % in the Kentucky and Wyodak samples, respectively, and the Kentucky sample has more material in every 2 series (Table 111). Figure 2 shows that the Kentucky sample generally has much more material at higher masses, which is reflected in the higher average molecular weight for the Kentucky 3 double bond fraction (Table 11). In the CnHzn+and CnH2n-10 series, the Wyodak sample contains some low molecular weight material (below 220) which is absent in the Kentucky sample (Figure 2). Hydrocarbons containing 5 double bonds are present at 0.57 wt % and 0.63 wt % in the Kentucky and Wyodak samples, respectively. Although Table I11 shows that the Wyodak sample does contain more material in some 2 series (Le. CnH2n-12 and CnHZn-14),the Kentucky sample has more material in the other five series, which are more hydroaromatic in nature. Furthermore, Figure 2 reveals that the Wyodak sample has more material in the higher mass range compared to the Kentucky sample. Interestingly, the CnH2n-12and CnH2n-14 series in Figure 2 for the 5 double bond fractions show prominent peaks at the beginning of the Wyodak series that are missing in the Kentucky series. Hydrocarbons containing 6 double bonds are present at 0.51 wt YO and 0.28 wt % in the Kentucky and Wyodak samples, respectively (Table I). The Kentucky sample dominates in every 2 series (Table 111). Significant differences for three of the 6 double bond series, CnHZn-14,CnHZn-16,and CnHzn-18, revealed in Figure 3, were discussed in detail earlier (Figure

1). Hydrocarbons containing 7 double bonds are present at 1.50 wt % and 1.40 wt 70 in the Kentucky and Wyodak samples, respectively (Table I). However, Table I11 shows that the Wyodak sample contains more of the CnH2n-22,CnH2n-24, C,,HZ~-~ and ~ , CnH2n-28series while the Kentucky sample contains more of the CnH2n-18and C,H, series. Differences in distribution are easily seen in Figure 3. The initial peak in the CnH2n-18series, representing phenanthrene and/or anthracene, is prominent in the Kentucky sample but is diminished in the Wyodak sample. This is true also of the next three peaks in the series, which represent the C, to C3 alkyl substituted homologues. Hydrocarbons containing 8 double bonds are present at 1.34 wt 70 and 1.40 wt % in the Kentucky and Wyodak samples, respectively (Table I). The CnH2n-22series (pyrenes, fluoranthenes, benzofluorenes, etc.) is dominated by the Wyodak sample, while the Kentucky sample has somewhat more material in the CnH2n-24, CnHzn-zs,CnH2n-m, and CnH2n-32series (Table 111). Figure 3 shows that the distribution of material in most 2 series from the 8 double bond fractions is similar for the two samples. Hydrocarbons containing 9 double bonds, present at 0.98 wt % in both samples (Table I), were discussed earlier and were seen to contain differing amounts of the various 2 series (Table 111). This is seen more clearly in Figure 4, which also shows slight differences in distribution in the 2 series. The most apparent difference is in the CnHZn-24series, where the initial peaks (representing chrysene and/or tetracene and their alkyl-substituted homologues) are prominent in the Wyodak sample and diminished in the Kentucky sample. Hydrocarbons containing 10 and 11 double bonds are present at 0.98 wt % and 2.10 w t % in the Kentucky and Wyodak samples, respectively (Table I). The Wyodak sample contains much more of every 2 series (Table 111). Differences in distribution of material within each 2 series are revealed in Figure 4, where the maxima in the Kentucky 2 series profiles are generally at higher masses than the Wyodak

ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985

maxima. Also, initial peaks that are prominent in the Wyodak series are generally diminished in the Kentucky series. Hydrocarbons containing 12 and greater double bonds are present a t 1.65 wt % and 2.18 wt % in the Kentucky and Wyodak samples, respectively (Table I), and the Wyodak sample dominates all Z series (Table 111). However, Figure 4 reveals interesting differences within the 2 series, many of which have a distinct bimodal profile. This strongly indicates the presence of two homologous 2 series in each profile, for example, CnHZn-32and CnH2n-46 or CnH2n-34 and CnHZn-48. In these series, the maxima of the Kentucky profiles are again at higher masses. Initial peaks in the CnH2n-34,CnH2n-36, CnHZn-38, and CnHZnd0series which are prominent in the Wyodak sample are diminished in the Kentucky sample. A major difference occurs in the CnHZn-42 series where the Wyodak series begins abruptly at mass 378 and has its maximum at mass 392, while the Kentucky series shows a smooth distribution with a maximum at mass 462. In Table I11 and Figures 1-4, some relatively low molecular weight material appears. This indicates that there is not a sharp distinction between distillable and nondistillable coal-liquid samples. Because of the complex nature of coal liquids, it may be difficult to establish true equilibrium in the simple distillation step used to obtain a distillable sample and a nondistillable sample. In addition, it is possible that some of the distillable material becomes physically entrapped in the complex nondistillable portion. The methods discussed in this paper allow for detailed comparison of complex hydrocarbon samples (Figure 1)and general comparison of a large body of hydrocarbon data (Figures 2-4). It was empirically estimated from the FIMS data that the smallest detectable amount of a hydrocarbon was approximately 1.1X wt %. In addition, the methods developed are such that they should be generally applicable to a variety of complex hydrocarbon samples.

ACKNOWLEDGMENT The authors thank Stuart E. Scheppele for his helpful comments on this manuscript and Ripudaman Malhotra for providing information on the experimental and instrumental conditions for the field-ionization mass spectrometer. LITERATURE CITED (1) Schiller, J. E. Anal. Chem. 1977, 4 9 , 2292. (2) Farcaslu, M. Fuel 1977, 56, 9.

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Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1977, 49, 2253. Hurtublse, R. J.; Allen, T. W.; Schabron, J. F.; Silver, H. F. Fuel 1981, 60, 385. Boduszynski, M. M.; Hurtubise, R. J.; Sllver, H. F. Anal. Chem. 1982, 54. 372. Boduszynski, M. M.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1982, 5 4 , 375. Felice, L. J. Anal. Chem. 1982, 5 4 , 869. Boduszynski, M. M.; Hurtubise, R. J.; Ailen, T. W.; Silver, H. F. Anal. Chem. 1983, 55, 225. Boduszynski, M. M.; Hurtubise, R. J.; Allen, T. W.; Silver, H. F. Anal. Chem .-1983, 5 5 , 232. Burke, F. P.; Winschel, R. A.; Pochapsky, T. C. Fuel 1981, 60, 562. Later, D. W.; Lee, M. L.; Bartie, K. D.; Kong, R . C.; Vassilaros, D. L. Anal. Chem. 1981, 53, 1612. Romanowski, T.; Funcke, W.; Grossman, I.; Konlg, J.; Balfanz, E. Anal. Chem. 1983, 55, 1030. Matsunaga, A. Anal. Chem. 1983, 55, 1375. White, C. M.; Li, N. C. Anal. Chem. 1982, 5 4 , 1570. Yoshida, T.; Maekawa, Y.; Higuchi, T.; Kubota, E.; Itagaki, Y.; Yokoyama, S. Bull. Chem. SOC.Jpn. 1981, 54, 1171. Holstein, W.; Severin, D. Chromatographia 1982, 75, 231. Swansiger, J. T.: Best, H. T.; Danner, D. A,; Youngiess, T. L. Anal. Chem. 1982, 5 4 , 2576. Wozniak, T. J.; Hltes, R. A. Anal. Chem. 1983, 55, 1791. Brown, R. S.; Taylor, L. T. Anal. Chem. 1983, 55, 723. Chmielowiec, J. Anal. Chem. 1983, 55, 2367. Scheppele, S.E.; Grizzle, P. L.; Greenwood, G. J.; Marriott, T. D.; Perrelra. N. E. Anal. Chem. 1978, 48, 2105. Yoshida, T.; Maekawa, Y.; Shimada. T. Anal. Chem. 1982, 54, 967. St. John, G. A.; Buttrill, S. E.; Anbar, M. "Organic Chemlstry of Coal"; Larson, J. W., Ed.; American Chemical Society: Washington, DC, 1978; ACS Symp. Ser. No. 71, Chapter 17. Boduszynski, M. M.; Hurtubise, R. J.; Silver, H. F. Fuel 1984, 63, 93. Boduszynskl, M. M.; Hurtubise, R. J.; Allen, T. W.; Silver, H. F. Fuel, in press. Beckey, H. D. "Field Ionlzation Mass Spectrometry"; Pergamon Press: Oxford, 1971. Scheppele, S. E.; Greenwood, G. J.; Benson, P. A. Anal. Chem. 1977, 49, 1847. Buttrili, S. E. Org. Coat. Plast. Chem. 1980, 43, 330. U.S. Department of Energy, Bartlesville Energy Technology Center, Quarterly Technical Progress Report, DOE/BETC/QPR-81/3 Section C, 1981. Buttrili, S. E. Final Technlcal Report, SRI Project PYU8903, 1981. Scheppele, S. E.; Benson, P. A.; Greenwood, G. J.; Grindstaff, Q. G.; Aczel, T.; Beier, E. F. I n "Chemistry of Asphaltenes"; Bunger, J. W., Ll, N. C., Eds.; American Chemical Society: Washington, DC, 1981; Adv. Chem. Ser. No. 195, Chapter 5. Holdsworth, D. K. J. Chem. Educ. 1980, 57,99.

RECEIVED for review July 30,1984. Accepted November 26, 1984. Financial support for the project was provided by the US. Department of Energy, Contract No. DE-AC2279ET14874 and DE-AC22-83PC60015. Partial support was also provided by Electric Power Research Institute, Contract NO. RP2147-3.