kinetic tailing resulting from highly active adsorption sites. The infrequency of such sites on graphitized carbon would lead to more complete desorption of the solute molecules. The other supports may differ from graphitized carbon and each other only in the degree of heterogeneity of their surfaces. The efficiencies of the columns with respect to H E T P and resolution of a series of alcohols (ethanol, propanol, butanol) appear in Table 11. With experimentally obtained data, the resolution and H E T P were calculated using the following equations:
L
HETP= V2 16
Y b
where Ay = difference between retention volumes y1.2 = base-line peak widths V , = retention volume of peak i y E = base-line peak width of peak i ' L = column length, millimeters
The greater adsorption on graphitized carbon is beneficial a t this column loading, inasmuch as it aids in resolution. The values presented in parentheses are
those obtained with columns packed at constant weight ratio (5%) rather than constant film thickness and are included merely to indicate the increase in efficiency with increase in column loading of the other columns. The H E T P values are the means of the individual H E T P for ethanol, propanol, and butanol. CONCLUSIONS
The advantages of using Sterling FT-2700' C. graphitized carbon as a stationary support include the elimination of prior chemical treatment to prevent tailing even in the presence of low loadings of nonpolar stationary phases, excellent efficiency, and the absence of temperature limitations with respect to the support itself. The principal disadvantage is the necessity of sieving the coated support and the care necessary in packing columns to obtain normal gas velocities by preventing large pressure differentials. ACKNOWLEDGMENT
The author expresses his appreciation to S. Ross, Rensselaer Polytechnic Institute, Troy, N . Y., for discussions which helped to initiate this study and t o W. R.Smith, Godfrey L. Cabot Co., Cambridge, Mass., for supplying the author with Sterling FT-2700' C. graphitized carbon.
LITERATURE CITED
(1) Bevilacqua, E. M., English, B. S., Gall, J. S., AKAL.CHEM.34, 861 (1962). ( 2 ) Chem. Eng. S e w s 40, 50 (July 16, 1952). (3) Cieplinski, B. W., ANAL.CHEY.35, 2n6 119631. (4) u a l Sogare, S., Chin. S. J., Zbid., 34, 890 (1962). ( 5 ) Giddings, J. C., I b i d . , 35, 1999 (1963). (6) Halitsz, I., Horvath, C., .Yature 197, 71 (1963). (7) K'arrneri, A,, PvlcCaffrey, I., Bowman, R., Zbid., 193,575 (1962).
(8) Kiselev, -4.V., Gazo. Khrom., Tr. 1-02 (Peruoi) Vses. Konf., A k a d . .Yauk SSSR L~Ioscow1959, 45 (1960). ( 9 ) Landault, C., Guiochon, G., J . Chromatog. 9, 133 (1962). (10) Pefrett, R. H., Purnell, J. H., Zbid., 7 , 4 x 1 (1962). (11) Polley, M. H., Shaeffer, W. D., Smith, W. P., J . Phys. Chem. 57, 469
(1953). (12) Pope, C. G., A x . 4 ~ .CHEM.35, 654 (1963). (13) Purnell, H., "Gas Chromatography," p. 235, Wiley, New York, 1962. (14) Ross, S., Saelens, J. K., Olivier, J. P., J . Phys. Chem. 66,696 (1962). (15) Sams, J. R., Jr., Constabaris, G., Halsey, G. D., Jr., I b i d . , 64, 1689 (1960j. (16) I b i d . , 65, 367 (1961). (17) Sanford, C:, Ross, S., Ibid., 58, 288 i1964). (18) Sawyer, D. T., Ben, J. K., A x . 4 ~ . CHEM.34, 1518 (1962). (19) Smith, B. D., Radford, R. D., Zbid., 33, 1160 (1961). (20) Sze, Y. L., Borke, M. L., Ottenstein, D. SI., Zbtd., 35, 240 (1963). (21) Reinstein, A. W., I b z d . , 33,18(1961). RECEIVEDfor review July 29, 1963. Accepted hpril 16, 1964.
Simultaneous Determination of Crude Oil Boiling Range Distribution and Hydrocarbon-Type Distribution by Gas Chromatography V. F. GAYLOR, C. N. JONES, J. H. LANDERL,' and E. C. HUGHES Research Departmenf, Sfandard Oil Co. (Ohio), 4440 Warrensville Center Road, Cleveland 28, Ohio
b A rapid crude oil analysis procedure yielding both boiling range distribution and hydrocarbon type composition in less than 2 hours has been devised. Distil1a:ion-type yields up to 725' F. are calculated from gas chromatographic peak areas. Relative concentrations of aromatics and naphthenes in fractions boiling to about 390" F. are calculated from peak height measurements. Analytical procedures and computations are readily adaptable to routine refinery use. Crude oil chromatograms are obtained from a '/r-inch packed column with a thermal conductivity detector. A timeof-flight mass spectrometer was used for preliminary characterization of chromatographic separations and 1606
ANALYTICAL CHEMISTRY
showed that the poorly resolved peaks representing the lower boiling fractions of crude oil could be related to hydrocarbon-type composition. Quantitative calibration was effected by chromatographing naphtha fractions of known composition. The gas chromatographic technique for composition analysis has also been applied to reformer feed naphthas and is a reliable replacement for more expensive methods.
T
HE NUMEROUS APPLICATIONS of gas chromatography to analysis of petroleum streams are well known. Widespread routine uses have, however, been generally limited to the relatively
simple C1 through C7 hydrocarbons. Outstanding successes in analyzing more complex mixtures have been achieved, using specialized techniques and equipment, which often involve increased costs and analysis time. Methods which retain the speed and simplicity features of the original chromatographic technique may require a new approach to interpretation of complex chromatograms. This paper describes such an approach to crude oil analysis, based on research with a mass spectrometer used as a chromatographic detector. Previously reported applications of gas chromatography to quantitative Deceased.
crude oil analyses were limit'ed in scope. Webb (17') injected whole crude oil directly into a n analytical column and measured C1 through Ce hydrocarbons. Martin and Winters (13) and Rysselberge (16) used a short precolumn to retain heavy ends and quantitatively determined Cp through Ci and Cz through C5 hydrocarbons, respectively. A temperature programmed gas chromatography column was used by Barras andBoyle (1) for predicting jet fuel freezing point from crude oil analysis. The temperature programming technique vastly extends the useful molecular weight range of a single chromatographic analysis. Calculation of crude oil boiling range distribution from a temperature programmed chromatogram seemed feasible. Eggertsen, Groennings, and Holst ( 7 ) converted programmed chromatographic analyses of petroleum fract'ions to distillation type curves which closely approximated a 60-plate distillat,ion; Barras and Boyle ( I ) used analysis on an uncoated Chromosorb column to predict yield points on a 1-plate distillation column. While distillation type curves were of obvious value, determination of chemical composition from crude oil chromatograms was equally desirable. Chromatographic procedures were designed to optimize both molecular weight range and separation efficiency in a single analysis. Xormal tricosane was eluted in about 35 minutes while considerable resolution of low molecular weight hydrocarbons was retained. .is many as 50 distinct peaks and shoulders were obtained in the C B through Cil range, constituting a fingerprint profile qualitatively useful for characterizing crude oil. Quantitative int'erpretation in terms of single compounds or overall hydrocarbon type distribution required some knowledge of composition of each single peak. Identification of the Cs through Ci peaks presented no particular problems. Identification and determination of single compounds in the cS-c11 range are more difficult because of increasing complexity of composition. Desty, Goldup, and Swanton (4) identified more than half of 122 peaks resolved from the C3-C9 portion of the hmerican Petroleum Institute's Ponca City crude in a 20-hour run on a coated capillary column. Polgar, Holst, and Groennings (16) accomplished complete analysis of Ci and Cs alkanes, cyclopentanes, and cyclohexanes with two successive analyses on a 300-foot capillary column totalling about 3 hours; 80y0 of the possible compounds were quantitat'ively accounted for as individuals. Lindeman and .innis ( 1 2 ) used a magnetictype mass spectrometer for complete qualitative and quantitative analysis of chromatographic peaks of a 440" F. endpoint naphtha on a packed column;
over 60 single compounds were identified and general structure assignments were reported for many Clo and C11 compounds. It was unrealistic to expect that single compound analyses could be achieved chromatographically from the 30 poorly separated peaks representing the hundreds of CS through Cl1 compounds likely present in crude oil. Consistency of the peak pattern, however, and large variations in peak size distribution from sample to sample suggested that gross hydrocarbon-type distribution analyses might be computed directly from the chromatogram. Peak height measurements were preferred for this purpose since apparent separation even between discrete peaks was usually poor. Qualitative composition analysis a t each peak maximum was thus desired. A time-of-flight mass spectrometer, which produces 10,000 spectra per second, had the required speed and sensitivity for monitoring chromatographic column effluent ( 2 , 6, 8, 1 1 ) , though other reported techniques (6, 10) might also have been applicable. Photographic recording of spectra permits qualitative composition determination a t any single instant during elution of the chromatographic peak. Mass spectra obtained in this way were used to estimate relative hydrocarbon-type distribution a t each peak maximum. EXPERIMENTAL
Equipment and Procedures. A commercial gas chromatography unit (Model K-2 Kromo-Tog) employing a filament-type thermal conductivity detector, and equipped with temperature programmer, flow controller, a n d precolumn assembly, was used (Burrell Corp., Pittsburgh, Pa.). Primary elements of the chromatographic equipment are adequately described in the manufacturer's literature. The hairpin-shaped analytical column was 250 cm. long and 0.5-em. i.d. The '/,-inch precolumn was 1 foot long and contained packing identical to the anaiytical column. Valving in the flow system was such that the precolumn could be manually switched
Table
I.
from "in-stream" to "by-pass" position. Primary helium carrier was directed through the precolumn during sample injection and maintained until desired portions of crude oil had been flushed into the analytical column. Carrier flow was then switched to precolumn bypass position. Crude oil heavy ends trapped in the precolumn were backflushed and vented to atmosphere a t the flash vaporizer inlet port. The molecular weight split made by the precolumn was more sensitive to operating temperature than to flush time. Optimum precolumn temperature (Table I) a t a preselected flush time was determined by trial and error, using a representative crude oil and a second flush from the precolumn to determine fractionation point. The fractionating properties of precolumn packing used routinely for over 6 months did not change detectably. Eventual build-up of asphalt, evidenced by increased pressure drop, was corrected by replacing the upper l/z inch of packing. Two different column packings and corresponding experimental parameters were used (Table I). Highest molecular weight range was achieved with Procedure I1 while Procedure I was preferred for resolution of low molecular weight hydrocarbons. Resolution of C1-C5 hydrocarbons was optimized in either procedure by holding column temperature a t 25' C. until n-C5 was eluted. Column packings were temperature stabilized before use by heating for 24 hours under helium flow. Columns I and I1 were programmed to 250' C. and 300' C., respectively, without detectable liquid phase bleeding. Masimum molecular weight determined was C1, for Procedure I and C23 for Procedure 11. Chromatograms were recorded on a 1.O-mv. potentiometer recorder (Minneapolis-Honeywell Regulator Co., Philadelphia, Pa.), equipped with Disc integrator (Disc Instrument Co., Santa Ana, Calif.) for peak area determination. The time-of-flight mass spectrometer (18, 19), Model 12-100 (The Bendix Corp., Cincinnati, Ohio), was attached to the chromatographic equipment a t the detector vent (Figure 1). The variable leak (Model 9101-31, Granville-Phillips Co., Pullman, Wash.)
Chromatographic Operating Parometers
Column packing
Analytical column temperature : Initial temperature Initial temperature hold Heating rate Final temperature Precolumn temperature Precolurnn flush time Flow rate Sample size
Procedure I 5 . 0 wt. % Apiezon L on 30-60 mesh Chromosorb P 25" C.
3 0 minutes 7" C. per minute
250" C. 200" C. ' 3 minutes 115 cc. per minute 0 012ml.
Procedure I1 1.0 wt. % D.C. 710 Fluid and 3.0 wt. % Apiezon L on 40-50 mesh Chromosorb P 25" C.
2 0 minutes
11" C. per minute 300" C. 300" C. 1 minute 230 cc. per minute 0 024 ml.
VOL. 36, NO. 8, JULY 1964
1607
53
2 lo 20 ELVTDN TIME, MIN,
Figure 1.
Crude oil chromatogram;
40
30
0
(Procedure
II)
X '
-- -*-.?--f
a
was adjusted to raise internal spectrommm. mercury eter pressure to 2 X with pure helium effluent. Temperature of the 2.5-foot, 1/8-inch line connecting the leak to the spectrometer inlet port was maintained a t 170" C. and the spectrometer source chamber was heated to about 175" C. The ionizing source was operated a t 2.5 amperes filament current, 0.125 microamperes trap current and 70-e.v. energy level. Spectra were viewed on the screen of a Type 541 X oscilloscope, equipped with Type C.4 preamplifier (Tektronix, Inc., Cleveland, Ohio) and photographed with a Polaroid camera. Relative mass line intensities were estimated from peak heights measured on a Microcard Reader (Microcard Reader Corp., R e s t Salem, Wis.). Preparative scale gas chromatographic separations were effected on a Megachrom (Beckman Instruments, Inc., Fullerton, Calif.) equipped with j/,-inch, stainless steel columns, each 6 feet long. The eight columns were packed with 30% Xpiezon L on 30-60 mesh Chromosorb P and were pressure balanced according to the manufacturer's instructions. Ten milliliters of a naphtha boiling in the range 150400' F . were charged to the 225" C. flash vaporizer, with the separating columns at 120' C. Temperature of the column bath was subsequently increased at the rate of about 2" C. per minute over a period of about 30 minut,es and appropriate fractions were collected in liquid nitrogen cooled traps. DISCUSSION
Boiling Range Distribution Analysis. Normal paraffin peaks in the crude oil chromatograms were readily identified by either relative size or elution time (Figure 1) and were employed for boiling range yield point calibrat,ion. The columns described separated paraffins essentially by boiling point and exhibited only slight selectivity for naphthenes and aromatics. Naphthenes were retarded, relative to paraffins, by about one peak width and aromatic selectivity was only slightly greater. Chromatographic analyses of carefully fractionated disM a t e s of both highly aromatic and napht,henic crude oils showed that error due to column selectivity was negligible. Consequently, normal paraffin boiling point-elution time plots were used for yield point calibration. Liquid volume per cent distillation 1608
a
ANALYTICAL CHEMISTRY
yields were calculated directly from summed peak areas. Messner (14) showed that thermal conductivit,y molar area response for hydrocarbons is a function of both molecular weight and structure. Quantitative analysis for single compounds thus requires accurate knowledge of relative response of each compound. ;iveraging structure effects seemed permissible, however, when summing areas of peaks composed of many hydrocarbons likely including most possible structures. Quantitative calibration with normal paraffin standards was a ready means of compensating for molecular weight effects. Normal paraffin area response per unit liquid volume sampled also tended to average out structure effects a t each carbon number level (Figure 2). Liquid volume per cent yields were therefore calculated from area/volume constants experimentally determined for each Cj-C23 normal paraffin. Constants for Ca and lighter paraffins were obtained by extrapolating linear molar response curves. The molar response, relative to benzene, of any s:ngle normal paraffin was not necessarily identical to that reported earlier (14), a compilation of values measured under isothermal conditions. The slope of the normal paraffin molar response curve determined with temperature programming was found to be a function of flow rat'e, a t least a t rates exceeding 100 cc. per minute. This is believed to be due to failure to achieve temperature equilibration in the detector cell block, under flow and temperature conditions which exceeded equipment design limitations. Molar response curve slopes were, however, repeatable under constant operating condit,ions. Relatively large changes in flow rate, lOyoor more, were needed to produce a significant change in molar response slope. Composition of Light Naphtha and Off-Gas. Resolution of low boiling hydrocarbons was sufficient to obtain considerable composition information from the crude oil chromatogram. Complete separation of propane, isobutane, and normal butane was not achieved; resolution was, however, adequate for estimating concentrations with a reasonable degree of accuracy. Octane number of light naphtha boiling 55-200" F. was estimated from relative concentrations of normal
a H
X
O
-- -e x
I 5
6
7
B
9
D
II
12 I3
14 I5
16
C A W N NUhBER
Figure 2. Effect of hydrocarbon type on liquid volume response
paraffins and summed isoparaffins, naphthenes and benzene. Weighted average blending octane numbers of 45.0 for normal paraffins and 79.5 for isoparaffins, naphthenes, and benzene, calculated from pure compound octane numbers determined by the American Petroleum Institute's Project 45, were used for octane number prediction. Values estimated in this way were a t least as accurate as values calculated similarly from single compound analyses. Peak Labeling. As many as 30 major peaks and shoulders were obtained in the n-C7 to n-Cll portion of the chromatogram. Peak pattern could be considerably altered by relatively small changes in column packing, as, for example, Column I us. Column 11. However, column packing could be reproduced well enough to reproduce peak pattern. Further, the pattern on any one column was consistent for many different crude oil types. ;ill of the chemical composition analyses described herein, including peak identification data, were obtained from Column I, though the same procedures and principles were also effective for Column 11. Chromatographic peaks eluted between n-Cs and n-CI1were labeled for data handling purposes. Xajor group numbers were assigned to each series of peaks eluted between successive normal paraffins. Group 8 peaks included all peaks eluted between n-C; and n-C8, Group 9 peaks were eluted between n-C8 and n-Cg, etc. (Figure 4). Single peaks in each group were further identified by elution order within the group. .I partial relative retention t'ime, P R R T , was calculated for each peak :
PRRT of peak X = RT of n-P, - R T of Peak X RT of n-p2 - RT of n-PI where peak X is eluted between n-PI and n-Pp. The peak number identification included both group number and PRRT
mh
mh I
mh
Figure 3.
Mass spectral characterization of adjacent peaks
and thus defined exact location on the chromatogram. For example, peak 8-0.50 was eluted exactly halfway between n-C; and n-Cs. Group number does not necessarily define carbon number. The peaks immediately preceding a normal paraffin of carbon number A; usually contained both 9 and S - 1 naphthenes and aromatics, and isoparaffins largely of N carbon number. M a s s Spectrometer Analyses. Useful mass spectra of single peaks were achieved only by minimizing lag time between chromatographic and spectrometer units. Careful attention to length and temperature of low pressure inlet lines produced virtually simultaneous response from both detection systems. Overall spectrometer speed and sensitivity were sufficient to permit qualitative characterization of small shoulders immediately following or preceding major peaks. For example, spectra of peak 9-0.69 showed the peak probably contained a large amount of 3-methyl octane while the 9-0.75 shoulder was largely composed of ethyl benzene and one or more Cgnaphthenes (Figure 3). Contribution of 3-methyl octane to spectra of the 9 4 . 7 5 shoulder was small. Similarly, the naphthenic character of the 10-0.45 shoulder was not obscured by paraffin contribution from the larger 10-0.61 peak. Spectral comparisons of most poorly separated peaks showed chromatographic column efficiency to be a good deal better than was superficially apparent, Expected nonhomogeneity was detected and often explained occasional anomalous peaks resulting from large variations in single compound concentration. Xylene and Cg naphthene, for example, were often detected spectrally in the leading edge of n-Cg peaks, though not evident chromatographically. .\ shoulder on the n-Cg peak, iometimes observed in chromatograms of more aromatic crude oils, was largely composed of xylene with smaller amounts of normal nonane and Cg nalihthene.
Figure 4.
Qualitative
Mass spectra of comparable chromatographic peaks were qualitatively identical from sample to sample. Comparat,ive spectra contained the same mass lines though relative intensities varied somewhat with differences in single compound or compound-type distribut,ion within a peak. Spectra of the 9-0.12 peak in paraffinic crude oils, for example, indicated approximately equal concentrations of paraffinic (isoalkanes) and naphthenic (cycloalkanes) compounds while naphthenes predominated in the same peak in naphthenic crudes (Figure 4). Many of the chromatographic peaks were, however, consistently "pure" in hydrocarbon-t,ype composition. Mass spectra of 9-0.62 peaks were predominantly paraffinic and 10-0.10 shoulder spectra were highly naphthenic in both paraffinic and naphthenic-type crude oils (Figure 4). I n general, isoparaffins were concentrated in the chromatographic PRRT ranges of 0.6 to 0.7 and 0.2 to 0.3 in each peak group. Conversely, in the PRRT ranges 0.1 to 0.2, 0.4 to 0.5, and 0.8 to 0.9, isoparaffin levels were minimum and naphthenic spectra were usually observed. This PRRT distribution of isoparaffins in each peak group is consistent' with boiling point relations between branched and normal paraffins of the same carbon number. Identification of single compounds, though possible in many instances, was not a primary aim. Xass spectra were used semiquantitatively to estimate hydrocarbon-type distribution a t each peak and shoulder maximum. Spectral analysis could not necessarily define absence of either naphthenic or paraffinic hydrocarbon, as was the case for aromatics. A p p r e n t detection of small amounts of paraffin in a predominantly naphthenic peak, or conversely, could have resulted from spectral inaccuracy, contamination from an adjacent' poorly separated peak, or could have been real. Hydrocarbon-type distribution estimates were used only for qualitative
comparison of
two crude
oils
guidance and inaccuracy was of no particular concern. Quantitative Hydrocarbon Type Distribution. Accurate naphthene contents of peak group fractions, collected from a preparative scale gas chromatography unit, were determined by conventional mass spectrometry (3). Direct comparisons of composited analytical data showed that the chromatographic peak profile could be related to gross hydrocarbon-type distribution. Relative heights of predominantly naphthenic peaks were directly proportional to total naphthene content in each group (Figure 5). The major naphthenic peak was larger than the major isoparaffin peak in each group fraction of the Illinois crude oil; specifically, 7-0.27 > 7-0.74, 8-0.30 > 8-0.64, 9-0.47 > 9-0.62, 10-0.45 > 10-0.61, and 11-0.48 > 11-0.62. The reverse was true for t'he more paraffinic East Texas crude; 7-0.27 < 7-0.74, 8-0.30 < 8-0.64, 9-0.47 < 9-0.62, 10-0.45 < 10-0.61, and 11-0.48 < 110.62. Quantitative chromatographic analysis was effected by correlating peak height ratios with volume per cent naphthenes. The peak height, ratio was calculated from summed heights of the most naphthenic peaks and of all measurable peaks in each group. The method assumes that single peak, or psuedo compound, distribution within either major hydrocarbon-type class does not vary appreciably from crude to crude-i.e., that concentrations of naphthenes contributing to summed naphthenic peak heights are a constant proportion of total naphthene content, and that isoparaffins contributing to summed naphthenic peak heights are a constant proportion of total paraffin content. Estimation of aromatic concentration through Group 11 peaks also proved feasible. The aromatic elution pattern was such that only peaks 8-0.81, 9-0.75, 10-0.86, 11-0.32, and 11-0.87 were sufficiently sensitive to aromatic VOL. 36, NO. 8, JULY 1964
1609
EAST
TWAS CRUDEOIL TOF SPEClW. ESllMAlES:
were prepared by liquid phase chromatography on silica gel, and quantitative peak distribution was determined by gas chromatography analysis. Peak height ratios, measured from whole naphtha chromatograms, were correlated with single peak aromatic contents, where the latter was expressed as a volume per cent ratio:
+
Peak height (aromatic saturate X ) Peak height (saturate Y ) vol. yo aromatic cy vol. % saturate Y vol. Yo saturate X vol. yo saturate Y
ILUNOlS CRUDE OIL
Figure 5.
+
Composite qualitative and quantitative analyses
content and homogeneous in saturate content to reflect aromatic concentration. Direct calibration was effected by comparing heights of aromatic-saturate peaks and appropriate aromatic freesaturate peaks, where composition of the two saturate peaks were similar for each comparison. Peak height ratios were correlated with volume per cent ratios, assuming a constant concentration ratio for each pair of saturate peaks. Amounts of nonmeasured aromatics were predicted from regression equations calculated from quantitative distribution analyses.
were correlated with volume per cent naphthenes. Naphthenic peaks were 7-0.27, 7-0.88, 8-0.30, 8-0.43, 8-0.50, 9-0.12, 9-0.47, 10-0.45, 10-0.86, 110.32, 11-0.48, and 11-0.91. Calibration for Aromatic Analysis. Naphthas boiling about 200-400' F. were analyzed for total aromatics by quantitative mass spectrometry ( 3 ) . Pure aromatic fractions of the naphthas
Aromatic peak height ratios were calculated for 8-0.81/8-0.43, 9-0.75/90.47, 10-0.86/10-0.34, 11-0.32/11-0.48, and 11-0.91/11-0.48. Regression equations were calculated from similar quant'itative distribution analyses. Peak 11-0.16 aromatic was predicted from 8-0.81 aromatic; 100.68 and 10-0.54 from 9-0.75; 9-0.91, 10-0.19, 10-0, 11-0.68 and 11-0.48 from 10-0.86; 11-0.62 from 11-0.32; and 11-0 from 11-0.91. RESULTS
Boiling Range Distribution. Chromat,ographic boiling range yields of paraffinic crudes were essentially identical to distillation curves from a n
CALIBRATION PROCEDURES
Boiling Range Distribution Yields. Equation coefficients relating peak area per lov8 mole to carbon number were determined by chroinatographing standard solutions of pure normal paraffins in the range Cs-Cna. Calculated peak area per mole values for C1-CZ3were converted to peak area per ml., using the appropriate specific gravity-molecular Wright constant for earh normal paraffin. Calibration for Naphthene Analysis. Fractions containing hydrocarbons equivalent to each of Group 7 , Group 8 , Group 9, Group 10, and Group 11 peaks were prepared from naphthas of low to high naphthene rontent by large scale gas chromatography. Hydrocarbon-type distribution within each fraction was determined by quantitative mass spectrometry ( 3 ) and single peak heights were meawred from analytical scale chromatograms. Peak height ratios ( P I I R ) for each set of peak group fractions, and calculated as follow-s: 2 heights ~ of naphthenic peaks ~ _ PHR = Z heights of all peaks
1610
ANALYTICAL CHEMISTRY
/' 1 //"
500ooo-
/'
/'
,
1''
/
0 10mo4050607080900 I 0 2 0 3 3 4 0 5 0 6 0 voL% OF CRUE \Ax.% OF CRUDE
Figure 6. _
_
Comparison of distillation curves
0 0 0 0
.. . .
Gas chromatography 50-Plate distillation 5-Plate distillation
volume per cent of crude. Predicted light naphtha octane numbers averaged 2.3 octane numbers lower than measured values; bias correction allowed predictions accurate to 1 0 . 5 Octane Number. Heavy Naphtha Composition. No significant nonlinearity was detected in naphthene calibration curves in the range 15-55 vol. yo naphthenes and correlation coefficients were all significant a t the 99% confidence level. T h e naphthas used for calibration represented a wide variety of crude types which maximized scatter caused by variations in single compound distribution. Iverage deviations from fitted lines were 1.4, 1.3, 3.3, 1.0, and 2.4 yo naphthenes for Groups 7 through 11 peaks, respectively. Significant correlation coefficients (99yo level) for the primary aromatic calibration data verified the technique for direct measurement. Scatter was least for peaks averaging highest aromatic contents but was tolerable for all measured peaks. Total aromatic content of Groups 8 through 11 peaks could be accurately predicted from experimentally measured peaks; single 1701.
to 970
to ISo
to 218O
to 2620
to to So3500
to 388O
BOILING RANGE Y Figure 7. Typical naphtha analysis
efficient fractionating column. Highly aromatic and/or naphthenic crude oils were subject to some bias due to inadequacy of the calibration technique. T h e amount of positive bias caused by extreme aromatic concentrations was approximately equal t'o the distillation curve displacement in a low efficiency fractionating column-Le., about 10% of yields. For example, in the boiling range 200-600" F., chromatographic yields for Bradford crude oil were essentially identical to highefficiency distillation, Conroe yields were similar to low-efficiency distillation, and Hastings yields were intermediat'e between the two distillations (Figure 6). .lromatic contents in t'he same boiling range were about lo%, 30%, and 2Oyo',, respectively (9). Volume per cent calibration constants may be corrected for ext'reme variations in composition. However, hydrocarbon type bias was not detected in analyzing a number of more average crude oils containing moderate amount's of aromatics and napht,henes. Calculated recovery from chromatographic analysis of distillates from crude oils of intermediate hydrocarbon type composition averaged 99.5 vol. yo and yields were essentially identical to those from a 50-plate distillation column. Relative standard deviation of distillation yields estimated from gas chromatographic analyses was about over the range 200" to 725" F. and about &5yobelow 200" F. G a s and Light Naphtha Composition. Itepeatahility of propane, isobutane, and n-butane analyses was relatively poor due to sampling problems, as wvcll as incomplete resolution. S o sy-tcmatic error was tletec*ted lvhen rhromatographic gas a n d > x e r e c-ornl)ared to mass spectrometer
analyses of distillate fractions; normal butane contents, for example, averaged within +0,1% of mass spectrometer values over the range 0.1 to 1.7 liquid Table II.
TIU-1-5 LR-5-1 TIC-2-27 LR-4-12 61-4046 59- 1697 59-1665 59-1128 LR-2-24 61-1858 LR-4-26
Heavy Naphtha Composition Analyses
Vol. % naphthenes Gas Mass chrom. spect. (3) Diff. 43 9 43 5 0 4 47 6 48 5 0 9
45 1 39 7 55.3 47.8 32.5 35.5 48.3 49.4 38.9
Table Ill.
Vol.
Gas chrom. 8 9 8 5 8 2 7 9 9.8 9.4 7.6 7.8 8.1 9.9 8.0
0 9 0 5 1.6 0.7 3.6 1.4 1.4 1.7 0.8
44 2 39 2 53.7 48.5 28.9 34.1 46.9 47.7 39.7
% aromatics
Mass spect. ( 3 ) 8 1 7 8 8 0 9 4 10.6 8.0 7.8 8.1 7.8 9.2 9.1
Off-gas composition to (55" F.) Liq. vol. yo
O
350 400 450 500 550 600 650 700 725 Iiq. vol. % of crude 2.75 3.37 3.09
3 74 3 28
1.1
Typical Crude Oil Analysis
Boiling range dist. Cum. liq. F. vol. 70 55 100 150 200 250 300
Diff. 0 8 0 7 0 2 1 5 0.8 1.4 0.2 0.3 0.3 0.7
9.6 11.1
34.0 45.3
I .I
10.5 16.2 20.0 25.5 31.4 38.9 44.2 50.4 57.8 59.8
Light naphtha composition (55-200" F.) Liq. vol. 70
i-C6 n-Cs
9.1 15.8 18.7 14.1 42.3 69.2
i-ce + CP n-Ce
naphthenes, benzene Est. O X . (F-1 Clear) Heavy naphtha composition Boili2g range, Vol. % Vol. F. arom. naphthenes 156-210 2.3 29.2 2 1O-260 6.2 51.0 260-305 7.9 57.1 305-350 9.2 59.0 350-3 90 15.0 61.3
Vol. %
paraffins -68.5 42.8 35.0 31.8 23.7 ~~
VOL. 36,
NO. 8, JULY
1964
161 1
aromatic peak prediction was also possible but with increased error. Overall scatter in the calibration data n-as about 0.9 vol. yo aromatics, calculated as yo of naphtha boiling about 150-390" F. Standard deviation of replicate chromatographic hydrocarbon-type analyses was 1 0 . 2 vol. Yo naphthenes and rt0.1 vol. % aromjtics. Routine analyses over a period of several months averaged within 1.3 vol. % naphthenes and 0.7 vol. yo aromatics of mass spectrometer analyses (Table 11). Applications. An impressive amount of information was derived from a single chromatographic analysis of crude oil (Table 111). The chromatogram yields boilingrangr distribution dataneeded for refinery crude tower control and composition analysis adequate for stream value prediction. Hydrocarbon-type distribution analyses are directly applicable to units processing low boiling stocks and are also useful for prediction of quality of higher boiling streams. The entire crude oil analysis, including computations, can be completed in less than 2 hours by technician-level personnel. The chromatographic technique can be used routinely to guide crude oil purchases, for quality control of crude
oil receipts a t the refinery gate, to check crude oil blending facilities and for feed forward control on refinery units. The method has also been advantageously used for steam analysis (Figure 7 ) where speed and low cost are prerequisites for quality control. ACKNOWLEDGMENT
The authors gratefully acknowledge the contributions of Harrison M.Stine for initiating this work, Jean K. Evans for technical assistance, Richard Thutt' for the quantitative mass spectrometer analyses, and C. B. McKinney of the Bureau of Mines for supplying samples of Bradford, Conroe, and Hastings crude oils. LITERATURE CITED
( 1 ) Barras, R. C., Boyle, J. F., 27th
Midyear Meeting of the American Petroleum Institute's Division of Refining, San Francisco, Calif., May 16, 1962. ( 2 ) Bassette, R., Whitnah, C. H., J. Dairy Science, 44, S o . 6, 1164 (June 1961). (3) Brown, R. A,, ANAL. CHEM.23, 430 (1951). (4) Desty, D. H., Goldup, A,, Swanton, W. T., ISA Proceedings, 1961 Internatjonal Gas Chromatography Symposium of Instrument Society, of America, p. 83, Michigan State University, June 1961.
(5) Dorsey, J. A., Hunt, R. H., O'Neal, M. J., ANAL.CHEM.35,511 (1963). (6) Ebert, A. A., Jr., Ibid., 33, 1865 i1961). ( 7 ) Eggertsen, F. T., Groennings, S., Holst, J. J., Ibid., 32, 904 (1960). (8) Gohlke, R. S.,Ibid., 31, 535 (1959). (9) Holliman, R. C., Smith, H. M., McKinney, C. M., SDonsler. C. R.. Cnited States Department of the In: terior, Bureau of Mines Technical Paper 722 (1950). 10) Levy, E. J., Doyle, R. R., Brown, R. A,, Melpolder, F. R., ANAL.CHEM. 3 3 . 6- 9- -8 i\ -l -R- -6, .l ) li, Levy, E. J., Miller, E. D., Beggs, W. S.,Ibid., 35, 946 (1963). 12) Lindeman, L. P., Annis, J. L., Ibid., 32. 1742 11960). 13) 'Martin, R. 'L., Winters, J. C., Ibid., 31, 1954 (1959). 14) Messner, A. E., Rosie, D. M., Argabright, P. A., Ibid., 31, 230 (1959). (15) Polgar, A. G., Holst, J. J., Groennings, S.,Ibid., 34, 1226 (1962). (16) Rvsselberee. J. van. Znd. Chim. Belge24, 1023 (1959). ' (17) Webb, T. P., 7th Detroit Anachem I
Conference, Wayne State Cniversity, Detroit, Mich., 1959. (18) Wiley, W. C., Science 124, 817 (1956). (19) Wiley, W. C., McLaren, I. H., Rev. Sci. Inst. 26, 1150 (1956).
RECEIVEDfor review August 21, 1963. Resubmitted April 27, 1964. Accepted April 27, 1964. Sixth World Petroleum Congress, Frankfurt, Germany, June 1926, 1963.
Chromatographic Separation of Polycyclic Aromatic Hydrocarbons on Columns Containing s- I rinitrobenzene 'C..
0 .
I
RUSSELL TYE and ZEB BELL' Kettering Laboratory, Department o f Preventive Medicine and industrial Health, College o f Medicine, University of Cincinnati, Cincinnati, Ohio
b The presence of Lewis acids has a marked effect upon the distribution of Lewis bases between a polar and a nonpolar liquid. This principle has been investigated with respect to polynitro aromatic compounds in each of three glycols, as stationary phases, with isooctane as the mobile phase, for use in liquid-liquid partition chromatography. Mixtures of polycyclic aromatic hydrocarbons which are refractory to other separation methods may be separated by using 0.258M s-trinitrobenzene in a polyethylene glycol (Carbowax-400), supported on 100-200 mesh Columpak. The chromatographic retention volumes agree with volumes calculated from distribution coefficients. This aids in the identification of compounds and may permit making useful advance estimates of the adequacy of a given column in separating two compounds if their distribution coefficients can be measured. 1612
ANALYTICAL CHEMISTRY
T
HE SEPARATION AKD IDENTIFICATIOS of polycyclic aromatic hydro-
carbons (PAH) in such complex mixtures as coal tars or residua from the refining of petroleum have received considerable attention, especially because these mixtures may be carcinogenic, and they may be encountered environmentally. Many combinations of compounds are very difficult to separate by adsorption chromatography, the method most commonly used, and other methods, including paper chromatoggraphy, have been applied (6). The formation of complexes of P I H with polynitro aromatic compounds has long been used as a means of purification and identification ( I ) . McCaulay and Lien have utilized the differences in basicity of the alkyl benzenes for their selective extraction from n-heptane (4). I n a series of papers, Hammick and coinvestigators have reported extensive experimentation on the acidbase interaction between polynitro aro-
matic compounds and various others including P.IH ( 2 ) . This paper describes a liquid-liquid chromatographic method based on the format,ion of complexes of PA\H and s-trinitrobenzene (TNB) xithin the chromatographic column. The complexes, being more polar t,han the hydrocarbons, are selectively partitioned into the polar stationary phase with a corresponding increase in the chromatographic retention volume. Compounds, which in the absence of T S B have identical distribution coefficients, may have such differences in the stability of their complexes with TKB that, marked differences in their distribution coefficients and great ease of separat,ion result. Pyrene and fluoranthene are two such compounds, and the effects on their distribution coefficients of the addition of varying 1 Present address, Kaiser Steel Corp., Fontana, Calif.
