ANALYTICAL CHEMISTRY, VOL. 51, NO. 11. SEPTEMBER 1979
LITERATURE CITED
Table IV. Comparison of Colored Acid Eluates from River and Tap Water
resin XAD- 1 XAD-2 XAD-4 XAD-7 XAD-8
(1) M. Schnitzer and S. V. Khan, "Humic Substances in the Environment", Marcel Dekker, New York. 1972. (2) J. J. Rook, Environ. Sci. Techno/., 11, 478 (1977). (3) G. A. Junk, J. J. Richard, M. D. Grieser, D. Witiak, J. L. Witiak, M. C. Arguello, R. Vick, H. J. Svec, J. S. Fritz, and G. V. Caider, J. Chromatcgr.. 99, 745 (1974). (4) E. M. Thurman, R. L. Malcolm, and G. R. Aiken, Anal. Chem., 50, 775, (1978). (5) M. D. Grieser and D. J. Pietrzyk, Anal. Chem., 45, 1348 (1973). (6) R. F. C . Mantoura and J. P. Riley, Anal. Chim. Acta, 76, 97 (1975). (7) D. H. Stuermer and G. R. Harvey, Deep-sea Res., 24, 303 (1977). (8) J. H. Weber and S. A. Wilson, Water Res., 9, 1079 (1975). 19) R. Kunin. Polvm. €no. Sci.. 17. 58 11977). (io) R. L. Malcolm, J . R e s , U.S.Geol. Surv.,'4, 37 (1976). (1 1) D. J. Pietrzyk, E. P. Kroeff, ard T. D. Rotsch, Anal. Chem.,50, 497 1978). (12) G. Sposito and K. M. Hobclaw, Soil Sci. Soc.Am. Proc.. 41, 330 1977). (13) D. J. Pietrzyk and C. H. Chu, Anal. Chem., 49, 860 (1977). (14) E. P. Kroeff and D. J. Pietrzyk. Anal. Chem., 50, 502 (1978). (15) R. L. Wershaw, D. J. Pinckney, and S.E. Booker, J . Res. U.S Geol. Surv.. 5. 565 119771. (161 Y . Chen'and~M.Schnitzer, Soil Sci. SOC.Am. Proc., 40, 866 (1976). (17) J. C. Huang and J. T. Garrett, Jr., Roc. hd Waste Conf.,30, 1111 (1975) (Pub. 1977). (18) T. R. Kressman and J. A. Kitchener, Discuss. Faraday Soc. 7, 90 (1949). (19) W. J. Weber and J. C. Morris, J . Sanit. Eng. Div., A m . SOC. Civ. Eng., 89. (SA-2), 3483 (1968). (20) J. R. Parrish, Anal. Chem., 49, 1189 (1977). (21) R. P. Scott and P. Kucera, J . Chromafogr., 142, 213 (1977). (22) J. March, "Advanced Organic Chemistry: Reactions, mechanisms and structure", McGraw Hill, New York, 1968, p 676. (23) R. L. Gustafson and J. Paleos, in "Organic Compounds in Aquatic Environments". S.J. Faust, Ed., Marcel Dekker, New York, 1971, p 312. (24) J. A. Leenheer, U. S. Geological Survey, Denver. Colo., 1975, unpublished data. (25) E. M. Thurman. G. R. Aiken, and R. L. Malcolm, Proceedings of the 4th Joint Conference on Sensing of Environmental Pollutants, 1977. (26) S. A. Wilson and J. H. Weber, Anal. Lett., 10, 75 (1977).
South Platte River Arvada tap eluate water eluate abs at abs at DOC, 460nm, 460nm, mgiL AU AUb 94 92 78 a
140
0.54 0.52 0.35 0.58 0.67
1803
0.38 0.42 0.34 0.45 0.49
DOC data for XAD-7 was meaningless owing to excessive bleed of this resin. Absorbance units.
a
hibited t h e highest recovery efficiency of the styrene divinylbenzene resins, was 80% as effective as XAD-8 based on visible absorbance data.
CONCLUSION T h e acrylic ester resins, XAD-7 and XAD-8, attain equilibrium more rapidly, have higher adsorption capacities, and are more efficiently eluted than their styrene divinylbenzene counterparts when fulvic acid is the solute of interest. For these reasons, and because it lacks the bleed problems possessed by XAD-7, XAD-8 is the resin of choice for t h e concentration and isolation of fulvic acid from natural waters. Practical usefulness of t h e styrene divinylbenzene resins, XAD-1, XAD-2, and XAD-4 for concentration of fulvic acid is limited, because of slow diffusion-controlled adsorption and a n inefficient elution process caused by charge-transfer complexation.
RECEIVED for review March 23, 1979. Accepted June 18, 1979. The use of the brand name in this report is for identification purposes only and does not imply endorsement by the US. Geological Survey.
Separation and Characterization of Synthoil Asphaltene by Gel Permeation Chromatography and Proton Nuclear Magnetic Resonance Spectrometry Irving Schwager,' Jonathan T. Kwan, Win Chung Lee, Shan Meng, and Teh Fu Yen" Chemical Engineering Department, University of Southern California, University Park, Los Angeles, California 90007
Synthoil has been fractionated on a preparative scale by gel-permeation chromatography on styrene-divinyl benzene packing (Bio-Beads S-XE). Five fractions were eluted in the order of high to low molecular weights: 3.2 & 1.O wt % , /@, = 1280; 31.6 f 1.7 wt %, M,, = 964 f 3; 32 f 2.1 wt %, M,, = 515 f 12; 20.5 f 1.1 wt %, M,, = 413 f 4; 12.7 f 1.8 wt %, M,, = 359 f 11. Aromatic molecules with large saturated substituents elute before smaller, more aromatic molecules. Structural characterization of the fractions was carried out using a modified Brown-Ladner proton nuclear magnetic resonance analysis. A plot of molecular weight vs. elution volumes for standards, and Synthoil coal liquid fractions affords a relatively smooth curve which may be used to determine approximate molecular weights of coal liquid products.
T h e work described in this paper is a continuation of our studies on the separation and characterization of coal liquids from major demonstration processes. We originally separated the coal-liquefaction products from five demonstration processes into five fractions by solvent fractionation ( I ) . We carried out structural characterization studies on the solvent fractions by proton nuclear resonance methods ( 2 ) . We then turned our attention to the asphaltene fraction of coal liquids, which is defined operationally as soluble in benzene and insoluble in pentane. This fraction, which consists of highly functionalized, highly aromatic, high molecular weight components, has been reported to be an intermediate in the conversion of coal to oil ( 3 , 4) and t o increase the viscosity of coal-derived liquids (5-7). We studied the molecular weight and association (8, 9), t h e determination of nitrogen and oxygen functional groups (IO), and t h e solvent elution chromatographic (SEC) separation and characterization of these coal-derived asphaltenes ( 2 1 ) . We now report on t h e
Present address: Filtrol Corp., Los Angeles, Calif. 90023. 0003-2700/79/0351-1803$01.00/0
C
1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 11, SEPTEMBER 1979 7
1
\
c-DFFERENTIAL REFRACTOMETER
\
4
WEIGHED SAMKES
I
180
1 240 270 300
210
ELUTION
330
VOLUMEImll
Figure 1. Preparative GPC chromatogram of Snythoil asphaltene; gel, 8% DVB, 200-400 mesh; THF flow rate, 2 mL/min; sample size, 3 mL,
0.33g/mL
further characterization of Synthoil asphaltene by gel-permeation chromatography and other techniques. GPC has been used to fractionate petroleum derived asphaltenes (12, 13), a n d coal hydrogenation products (14-19). We have used preparative scale G P C on Bio-Beads, SX-8 to obtain molecular-sized Synthoil asphaltene fractions for characterization, and we have used these narrow GPC fractions, SEC fractions, solvent fractions, a n d standard compounds to derive a plot of number-average molecular weight vs. retention time on analytical p-Styragel HPLC columns.
EXPERIMENTAL Materials Studied. Standard compounds used to obtain the reference GPC correlation curve were obtained from commercial sources. Synthoil centrifuged product oil was produced at 450 OC, 27.6 mPa (4000 psig) from West Kentucky, hvAb, Homestead Seams 9, 11, 12, 13 and solvent fractionated to obtain the coal-derived solvent fractions ( I ) . The asphaltene was further separated by exhaustive solvent elution chromatography on silica gel with benzene, diethyl ether, and tetrahydrofuran ( 2 2 ) . Analytical Scale GPC. Analytical scale high performance liquid chromatography (HPLC) was carried out using a Waters L.C. system comprised of the following equipment: (1)Waters Associates model 6000A solvent delivery system. (2) Waters Associates model 440 absorbance detector (254 nm). (3) Waters Associates model R401 differential refractometer, and (4) Houston Omniscribe 2-pen recorder. Three p-Styragel columns (two 100 A and one 500 A, 7 mm i.d. X 30 cm length, = 3000 plates each) were connected in series. Uninhibited T H F was used as solvent. Samples were prepared as 2% solutions in T H F which had been degased by sonic bath stirring. The samples were filtered across a 0.45-wm millipore filter, and the flow rate was adjusted to 1.0 mL/min. Preparative Scale GPC. Preparative scale GPC separations were carried out with an Alltech Associates 25 mm i.d. X 1 m glass column, slurry packed with Bio-Rad, S-X8, Bio-Beads (200-400 mesh, 8% cross-linked, styrene-divinyl benzene). The column
was connected to the Waters Associates HPLC system described previously. Tetrahydrofuran (THF) (freshly distilled from sodium) was used as a solvent. A typical GPC run is presented in Figure 1. Generally a 3-mL sample, containing = 1 g of asphaltene, was loaded onto the top of the column, and a flow rate of = 2 mL,/min was used to elute the sample. Pressures of 5-10 psig were sufficient to obtain reasonable flow rates. The progress of the chromatograph was generally followed by use of the differential refractive index detector, because UV absorption was too strong except at the beginning and final stages of elution. The fractionated GPC samples were stripped of solvent on a rotary evaporator and freeze dried to powders from benzene. The last trace of benzene was removed by heating the powders overnight in a vacuum oven. Elemental analyses were carried out with standard procedures by the ELEK Microanalytical Labs., Torrance, Calif., and Huffman Labs., Wheatridge, Colo. Molecular weights were determined in o w laboratory with a Mechrolab Model 301A Vapor Pressure Osmometer. In normal runs, 6-8 concentrations over the range 4-39 (g/L) were employed in the solvents benzene or tetrahydrofuran for extrapolation to infinite dilution (8). Proton NMR spectra were obtained on a Varian T-60 Spectrometer. The solvent used was 99.8% DCC13 with 1% TMS. NMR analysis was carried out using modified Brown-Ladner equations (2, 20). RESULTS AND DISCUSSION Characterization of Synthoil GPC Fractions. I n this part of the study, preparative scale GPC was used to separate Synthoil asphaltene according to molecular size distribution. T h e GPC eluent was arbitrarily divided into five fractions, and these fractions were characterized by elemental analyses, VPO molecular weight determination and Brown-Ladner structural characterization by proton NMR. T h e manufacturer reports Bio-Beads S-X8 to have a molecular weight exclusion limit of 1000. We found t h a t a polypropylene oxide standard of mol wt 2000 was excluded,
ANALYTICAL CHEMISTRY, VOL. 51, NO. 11, SEPTEMBER 1979
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I\
bI
r! ri
a
2L W
IW
n
01
N r(
0
8
16
24
ELUTION
40
32
VOLUME
48
(rnll
Figure 2. Analytical GPC chromatograms of Synthoil asphaltene and Synthoil asphattene fractions: gel, p-Styragel, two 1 0 0 4 and one 500-A columns, each 30-cm length: THF flow rate, 1.0 mL/min; UV, 1 A at 254 mm
whereas a similar standard of mol wt 800 was not excluded. A t the lower molecular weight separation range, anthracene could be separated from benzene, but tetralin and toluene could not be separated. In the mid-range aromatics such as 9,lO-diphenylanthracene could be separated (almost to base line) from 1,2-benzanthracene on our column. Reinjection of fraction two afforded only a relatively narrow peak indicating that the sample size was sufficiently small to avoid overloading the column. The weight fraction recovery and VPO molecular weights of the fractions are shown in Figure 1. The number average molecular weight of the fractions: %
9 ri
(where Ni= the number of molecules in the ith molecular weight stage) was calculated to be 548. This value is very close to the value of 561 calculated independently by VPO in the solvent THF. The average molar properties of the fractions, derived from elemental analyses, VPO molecular weight determination, and Brown-Ladner NMR analyses, are presented in Table I. The elution took place in the order of high to low molecular weight.
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 11, SEPTEMBER 1979
Table 11, Standard Compounds Used t o Obtain GPC Correlation Curve" standards mol wt 1, benzene 78 2. cyclohexane 84 3. naphthalene 128 4. pentamethylbenzene 148 5 . anthracene 178 6 . benzanthracene 228 254 7. 9-phenylanthracene 8. 1,l'-bis(acenaphtheny1idene) 304 9. 9 ,lo-diphenylanthracene 330 10. 1,2,8,9-dibenzpentacene 378 11. squalene 411 12. Pressure Chemical Standard 600 13. tetra-meso-4-methylphenylporphin 670 1 4 . polypropylene glycol 800 1 5 . tetra-meso-2-naphthylporphin 818 918 1 6 . tetra-meso-biphenylporphin 17. polypropylene glycol 1200 a
A,
Columns used: Waters Associates y-Styragel: 1 X 5 0 0 2 X 100 A (each 7.8 mm, 30-cm length).
c
saturated substituent, n, decreases from 2.5 to 1.5. The fraction of available aromatic edge atoms occupied by substituents, CT, also decrease from 0.69 to 0.37 as the elution volume increases. These results can be interpreted in terms of aromatic ring systems, with large saturated substituents eluting first. As the elution volume increases, the saturated substituents decrease in number and size resulting in the molecules becoming smaller and more aromatic. The size of the average aromatic ring system, as measured by the ratio of substitutable aromatic edge atoms to total aromatic atoms, HarU/CaT, appears to go through a minimum a t Cut 3. Correlation between Molecular Weights and GPC Retention Times. Representative GPC chromatograms of several asphaltenes, carried out on the above described series of p-Styragel columns, are shown in Figure 2. The elution volume corresponding to the maximum detector response was obtained for various Synthoil coal liquid fractions, Synthoil asphaltene SEC and GPC fractions, and a set of standard compounds (Table 11). These retention volumes were plotted vs. the known molecular weights, and the VPO number average molecular weights (Figure 3). The results show a relatively smooth curve which may be used for obtaining number average molecular weights rapidly for unknown coal liquid fractions.
ACKNOWLEDGMENT The authors thank the Pittsburgh Energy Research Center of the United States Department of Energy for generously supplying samples of their coal liquid product, and J. G. Miller who assisted with portions of the experimental work.
t
LITERATURE CITED
t
I
I
I8
I
20
I
22
Elution
I
1
26
24
Volume
[
28
I
30
ml 1
Figure 3. Molecular weights and GPC elution volumes for standards (0),and Synthoil coal liquid fractions (0, GPC; A, solvent)
T h e C / H ratio generally increases as the mol wt decreases, and the % oxygen shows a large decrease in Cut 5. The aromaticity, f a , shows a steady increase from 0.58 to 0.76 with fraction number, while the number of carbon atoms per
(1) I. Schwager and T. F. Yen, fuel, 57, 100 (1978). (2) I. Schwager, P. A. Farmanian, and T. F. Yen, Prepr., Div. Pet. Chem., Am. Chem. Soc., 22(2),677 (1977):ibid., in "Analytical Chemistry of Liquid Fuel Sources", P.C. Uden, S. Siggh, and H. B. Jensen, Eds., Adv. Chem. Ser., 170, Chapter 5 (1978). (3) S.Weller, M. G. Pelipetr, and S. Friedman, Ind. Eng. Chem., 43, 1572, 1575 (1951). (4) R . Yoshida, Y. Maekawa, T. Ishii, and G. Takeya, Fuel, 55, 337,341 (1976). (5) H. W. Sternberg, R . Raymond, and S. Aktar, Prepr., Div. Pet. Chem., Am. Chem. Soc., 20(3),711 (1975). (6) J. E. Schiller, B. W. Farnum, arid A. E. Sandreal, hepr., Div. FuelChem., Am. Chem. Soc., 22(6),33 (1977). (7) K. C. Tewari, N. Kan, D. M. Susco, and N. C. Li, Anal. Chem.,51, 182 (1979). (8) I. Schwager. W. C. Lee, and T. F. Yen, Anal. Chem., 49, 2363 (1977). (9) W. C. Lee, I. Schwager, and T. F. Yen, Prepr., Dlv. Fuel Chem., Am. Chem. Soc.. 23(2),37 (1978). (IO) I. Schwager and T. F. Yen, Anal. Chem., 51, 569 (1979). (11) I. Schwager and T. F. Yen, Fuel, 58, 219 (1979). (12) K. H. Akget, frepr., Div. Pet. Chem., Am. Chem. Soc.,10(3),29 (1965). (13) L. R. Snyder, Anal. Chem., 41, 1223 (1969). (14) Y. Maekawa, S.Ueda, Y. Hasegawa, Y. Nakata, S.Yokoyama, and Y. Yoshida, Prepr., Div. FuelChem., Am. Chem. Soc.. 20(3), 1 (1975). (15) S.Yokoyama, D.M. Bodily, and W. H. Wiser, Prepr., Div. FuelChem., Am. Chem. Soc., 21(7),77,84 (1976). (16) W. M. Coleman, D.L. Wooton, H. C. Dorn, and L. T. Taylor, Anal. Chem., 49, 533 (1977). (17) D. L. Wooton, H. M. Coleman, J. T. Taylor, and H. C. Dorn, Fuel, 57, 17 (1978). (18) c. D. Hathaway, C. W. Curtis, S. Meng, A. R. Tanar, and J. A. Guin, Prepr., Div. fuel Chem., Am. Chem. Soc.. 23(4), 185 (1978). (19) F. R . Mayo and N. A. Kirschen, Fuel, 57, 405 (1978). (20)J. K. Brown and W. R. Ladner, Fuel, 39, 87 (1960).
RECEIVED for review March 23,1979. Accepted June 7,1979. This research was supported by the United States Department of Energy under Contract No. EX-76-C-01-2031.
