(15)M. A . Collins and M. G. Bigdeli, in “Alcohol Intoxication and Withdrawai:
Experimental Studies Ii”,
M. M. Gross,Ed.,
Plenum Press, New York, N.Y.,
1975.D 79. (16)G. Cotien, Biochem. pharmacol., 25, 1123 (1976). (17)J. Axelrod and J. Daly, Science, 150,892 (1965). (18) W. J. A. Vanderheuvel, V. F. Gruber, L. R. Mardei, and R. W. Walker, J. Chromatogr., 114, 476 (1975). (19)R. E. Shoup and P. T. Kissinger, Clin. Chem. ( Winston-Salem, N.C.),sub-
mitted.
(20) R. M. Riggin and P. T. Kissinger, Clin. Chem. ( Winston-Salem,N.C.),sub-
mitted.
RECEIVEDfor review November 11,1976. Accepted January 11, 1977, This work was supported by the National Institute Sciences, the Science Foundam tion, and the Showalter Trust Fund. Of
Preparative Gel Permeation Chromatographic Separation of Solvent Refined Coal W. M. Coleman, D. L. Wooton, H. C. Darn,* and L. T. Taylor* Department of Chemistry, Virginia Polytechnic institute and State Universlty, Blacksburg, Va. 2406 1
A preparative quantltatlve Separation of THF- and CHCIasoluble solvent reflned coal (Pittsburgh No. 8) has been demonstrated employlng gel permeatlon chromatographic techniques utlllzlng three column packlngs: a styrene-dlvlnyl benzene packlng (Blo-Beads S-X4), a cross-linked poly( Nacryloylmorphollne) polymer (Enzacryl Gel K-l), and a modlfled alkylated dextran (Sephadex LH-20). Each packlng material Is evaluated based on the extent and time of separatlon and the cost of materlals. The percent recovery In the Blo-Bead case Is greater than 95%. Average molecular weights vla vapor phase osmometry on the four slzed fractions of THF-soluble SRC from Blo=Beadssuggests that a separatlon accordlng to molecular welght has been achieved. The description of a short tapered glass column to economlcally carry out these preparatlve separatlons Is descrlbed.
The search for materials having pore sizes that would permit separation of high molecular weight substances by effective molecular size has been extensive and has given rise to the widely used technique of gel permeation chromatography (GPC) (1).A variety of materials from numerous manufacturers have been developed to effect separations via GPC (2). In many instances rather complex mixtures have been efficiently size-separated on an analytical scale (3).These separations are not without some problems, not the least of which is one related to cost ( 4 ) . One, therefore, is prohibited from even considering preparative-size separations in many situations. In this light we wish to report the results of an evaluation of three GPC packing materials for the separation of coal liquids. A preparative-size separation of a solvent refined coal ( 5 ) (SRC) is also described employing one of these packing materials at a cost of $&lO/column including column and packing material. The SRC process is one of several research pilot plant operations under way for converting coal to a low sulfur, high Btu content fuel (6). Samples from the pilot plant include solid SRC product, process solvent, and light organic liquid product. The solid product is the material under examination in this report.
EXPERIMENTAL The SRC solid product on which our separations were accomplished was obtained from an Electric Power Research Institute funded Southern Services Inc. pilot plant operated by Catalytic Inc. at Wilsonville, Ala. A bituminous coal, Pittsburgh No. 8, served as the SRC source. The liquid chromatograph used was a Spectra-Physics Model 3500 B equipped with a thermostated refractive index detector. Bio-Beads
S-X4 (200-400 mesh) and S-X4-400 (25 rm) were obtained from Bio-Rad Laboratories, Rockville Centre, N.Y. Enzacryl Gel K-1, medium, was obtained from Aldrich Chemical Co., Milwaukee, Wis. Sephadex LH-20 was obtained from Sigma Chemical Co., St. Louis, Mo. Each column was packed with either a THF or CHCls slurry of the material (Figure 1) using an occasional 20 psi Nz to facilitate packing. The glass column, Figure 2, was prepared by the glass fabrication facility of this Department. Tetrahydrofuran and chloroform were obtained from Burdick & Jackson Laboratories, Muskegon, Mich., and were used as received. Molecular weight determinations via vapor phase osmometry were performed by Galbraith Microanalytical Laboratories, Knoxville, Tenn.
RESULTS AND DISCUSSION Large scale pilot plants for the liquefaction of coal are currently in operation. Since coal liquids are expected to become commercially available during the next decade, it is important to establish their suitability as sources of petrochemicals and power generation fuels. A thorough characterization of such materials by a variety of physicochemical probes (Le., I3C NMR, lH NMR C-H-N-S and trace metal analysis, molecular weight analysis, mass spectrometric analysis, etc.) normally requires gram quantities of material. Since the number of compounds in a coal liquid sample is staggering, a preliminary separation of the material into numerous fractions based on functionality, polarity, or molecular size is highly desirable prior to any type of characterization. The scale for GPC separations varies widely. For analytical determinations, sample sizes are small (1-2 mg); whereas, for preparative-size separations, larger quantities may be employed (0.5-1.0 g). The application of GPC to polymer chemistry is rather routine (7);however, its use in coal research has been mostly limited to analytical separations (8). For example, a supercritical-gas (toluene) extract, comprising 17%of a low-rank coal, has been separated (9) by a combination of solvent fractionation and both silica-gel and gel permeation (Sephadex-LH20) chromatography. The n-hexane solubles extracted by Soxhlet extractor of a Yahari coal subject to mild hydrogenation conditions are reported to be separable into 15 fractions via GPC (IO);however, the elution did not occur in the order of high to low molecular weight. The THF-soluble product after two alkylation steps with an Illinois coal is reported to be separable into 40 fractions via GPC with quantitative recovery (11);however, these workers do not reveal the conditions under which the separation was achieved. It should be pointed out that the employment of GPC to separate petroleum-type products has been more extensive (12) both on an analytical and a preparative scale. ANALYTICAL CHEMISTRY, VOL. 49, NO. 4, APRIL 1977
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-+- 2 O p s i
o,troqen
~ “ r i n ps e a l
bottom flask
e,
-swagelock
Teflon union
Figure 2. Glass column design and dimensions Flgure 1. Column packing apparatus
In a typical study (13,14), asphaltenes from several types of asphalts of very diverse properties have been fractionated analytically by GPC on cross-linked polystyrene gels. Broad molecular weight distributions were found spanning approximately 40 000 amu. Under certain conditions, good separation of petroleum heavy ends has been reported with loads of 150 mg/100 mL of column volume and higher (15). A recent article (16) from this laboratory reported the separation of SRC (Illinois coal) solid product employing Bio-Beads S-X4 on a glass column with dimensions as follows: 8 mm 0.d. X 120 cm long. The quantities of “sized fractions” obtained from a typical run were on the order of 10 mg and the separation time was over 1h. In an attempt to introduce and separate larger amounts of SRC solid product, numerous glass column designs were studied. Glass was employed in that it offered several advantages such as easier column fabrication, a readily observed separation, and fewer contamination problems. The column design which proved to be most suitable for our purposes is shown in Figure 2. The SRC under examination possess 97-98% solubility in T H F (1 7).Figure 3 shows a typical separation of this THFsoluble portion obtained on the column described in Figure 2. Sample collection points are noted on the chromatogram. All samples were reinjected to refine their purity and these chromatograms are shown in Figure 4. Injections were normally made with a 50% T H F saturated solution. Injections of more dilute solution did not alter the parameters of the separation. The column overload point was -1.5 g/15 mL injection. Beyond a 1.5-g load, the chromatogram began to lose resolution. Such overload effects have been well documented in GPC (18).With packing materials of the type being used in this study, the tightness and regularity of the packed column is usually checked with respect to the HETP as measured from a benzene injection (12). Values of 534
ANALYTICAL CHEMISTRY, VOL. 49, NO. 4, APRIL 1977
800-3000 TP/foot are obtained on columns that function adequately. The H E T P was determined on the Bio-Bead S-X4 column and found to be 1024 TP/foot. Total accessible (VT 1 92 mL) and excluded ( V Or 35 mL) volumes were estimated from the raw chromatograms since the nature of the molecules of the coal liquid is not established. A comparison with an empty column volume of approximately 150 mL suggests a normal GPC separation mechanism. Since one of the factors determining column efficiency is the particle diameter of the packing material, a separation of the same THF-soluble SRC employing Bio-Beads S-X4-400 (
