1012
Energy & Fuels 1996, 10, 1012-1016
Inverse Size Exclusion Chromatography Using Extraction Residues or Extracts of Coals as a Stationary Phase Mitsuru Morino, Hiroyuki Kaneko, Toshimasa Takanohashi,* and Masashi Iino Institute for Chemical Reaction Science, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-77, Japan Received March 6, 1996. Revised Manuscript Received April 26, 1996X
Coals were extracted with a carbon disulfide-N-methyl-2-pyrrolidinone (CS2-NMP) mixed solvent at room temperature. The extraction residue was packed into a column, and inverse liquid chromatography (ILC) was carried out for standard polystyrenes with a wide range of molecular weight, using this column. The retention volume of polystyrenes was smaller than that of chloroform or benzene which was used as a carrier solvent except in a few cases and decreased with an increase in their molecular weight, suggesting that polystyrenes were separated by size exclusion mechanism. The extraction residue with high extraction yield (63 wt %) from Zao Zhuang coal separated the polystyrenes with molecular weight of 102-107 and that with low extraction yield (5 wt %) did not separate well polystyrenes higher than 104 molecular weight, suggesting that relatively large pores, which separate high molecular weight polystyrenes, would not be formed for the residue with low extraction yield. An extract fraction from Zao Zhuang coal, which is the CS2-NMP-soluble and pyridine-insoluble fraction (PI), also could separate polystyrenes by size exclusion mechanism. The size exclusion mechanism for this ILC was discussed.
Introduction Hsieh and Duda1 reported that sorption occurs when a coal contact with vapor solvents, i.e., adsorption on the coal external and pore surfaces and diffusion into the coal bulk. Green et al.2 also measured a similar sorption for the extract as that for the residue, although the extract has few pores. Diffusion of a solvent into the coal bulk is carried out through the coal macromolecular network, depending on the affinity between a solvent and a coal. A diffused solvent may interact with the specific sites in the coal bulk. When such diffusion of a solvent occurs in the coal bulk, swelling can be observed, and a solvent is absorbed until an equilibrium is attained. The molecular space into which a solvent can diffuse is called “swelling pore”. The swelling pores form from instantaneous fluctuation of cross-link structure in the coal bulk. On the other hand, when a solvent enters into the physical (permanent) pores, a coal usually does not swell. Several radical probes have been used in liquid phase to investigate the internal pores of coals,3 and the size and shape of pores have been reported from the measurements of radical concentration of the retained probes at an equilibrium. Recently, the inverse gas chromatography (IGC)4,5 and the inverse liquid chromatography (ILC)6-9 tech* To whom correspondence should be addressed. E-mail:
[email protected]. X Abstract published in Advance ACS Abstracts, June 1, 1996. (1) Hsieh, S. T.; Duda, J. L. Fuel 1987, 66, 170. (2) Green, T. K.; Selby, T. D. Energy Fuels 1994, 8, 213. (3) Spears, D. R.; Kispert, L. D.; Piekara-Sady, L. Fuel 1992, 71, 1003. (4) Glass, A. S.; Larsen, J. W. Energy Fuels 1993, 7, 994. (5) Glass, A. S.; Larsen, J. W. Energy Fuels 1994, 8, 284. (6) Winans, R. E.; Goodman, J. P.; Neill, P. H.; McBeth, R. L. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1985, 30, 427.
S0887-0624(96)00037-0 CCC: $12.00
niques were applied to the study on interactions between probes and coals; i.e., coals are packed into a column and various probes are injected into the column. In the IGC technique, the adsorption of probe gases on coal pore surface is measured. In general, the gases do not diffuse into the coal bulk, since the contact time is too short to reach an equilibrium, although Larsen and Warnett10 reported that Illinois No. 6 coal has only internally isolated pores into which a probe can reach only through diffusion in the coal bulk. On the other hand, in the ILC technique, the interactions between probes dissolved in a carrier solvent and coal swollen with the carrier solvent are measured. When a solvent contacts with solid coal, it will take significant time to diffuse into the bulk of coal, while, in ILC, the diffusion of a solvent into a rubbery swollen coal may be fast. The diffusivity of a solvent depends on the diffusion rate and the flow rate of a carrier solvent and the cross-linking density of coal. The ILC using the extraction residue or the extract as stationary phase was carried out using aromatic compounds as probe.11 The sorption mechanism, which involves absorption (diffusion) into the coal bulk, in addition to usual adsorption on the coal pore surface, is discussed. When probes with large molecular size such as polymer are used in the ILC, another separation mechanism, i.e., size exclusion mechanism, is expected to dominate. (7) Kwon, K. C.; Finseth, D. H.; Lai, R. W. Sep. Sci. Technol. 1990, 25, 1871. (8) Hayashi, J.; Amamoto, S.; Kusakabe, K.; Morooka, S. Energy Fuels 1993, 7, 1112. (9) Hayashi, J.; Amamoto, S.; Kusakabe, K.; Morooka, S. Energy Fuels 1995, 9, 1035. (10) Larsen, J. W.; Warnett, P. Energy Fuels 1988, 2, 719. (11) Kaneko, H.; Morino, M.; Takanohashi, T.; Iino, M. to be submitted for publication.
© 1996 American Chemical Society
ILC Using Extracts of Coals
Energy & Fuels, Vol. 10, No. 4, 1996 1013 Table 1. Ultimate and Proximate Analyses of Coals ultimate analysis, wt % (daf)
proximate analysis, wt % (db)
coal
C
H
N
S
Oc
VM
ash
FC
Beulah Zapa Illinois No.6b Lower Kittanningb Zao Zhuang Pocahontas No.3a
71.6 80.0 82.3 86.9 90.6
4.8 5.0 5.2 5.1 4.3
1.0 1.6 1.7 1.5 1.1
0.9 2.9 3.9 1.6 0.7
21.7 10.5 6.9 4.9 4.0
42.2 38.9 31.5 28.6 21.5
9.6 10.4 12.1 7.4 4.8
48.2 20.2 56.4 64.0 77.6
a
Argonne Premium Coal Samples. b The Pennsylvania State University Coal Bank. c By difference. Table 2. Extraction Yield of Raw Coals, Retention Volume of Carrier Solvent, and Volume of Extraction Residue (
