Solubility Limitations in the Determination of Molecular Mass Distributions of Coal Liquefaction and Hydrocracking Products:  1-Methyl-2-pyrrolidinone as Mobile Phase in Size Exclusion Chromatography

Abstract

The use of tetrahydrofuran (THF) as mobile phase in size exclusion chromatography (SEC) has been found to lead to partial loss of sample and to give anomalous results in the characterization of a liquefaction extract and its hydrocracking products. The problem has been resolved by using NMP (1-methyl-2-pyrrolidinone) as mobile phase in SEC, showing significant fractions of sample eluting at the exclusion limit of an identical SEC column. This fraction has not previously been observed in SEC chromatograms obtained in THF. Comparison of SEC chromatograms obtained by UV-absorption and UV-fluorescence detection (in NMP) suggests that the material observed at the exclusion limit of the column corresponds to larger, more complex polynuclear aromatic ring systems than those present in material separated by the column. In NMP, samples produced during progressively higher temperature hydrocracking experiments eluted, as expected, at longer times, indicating progressive molecular size reduction with increasing intensity of the reaction. These data are consistent with the UV-fluorescence spectra and TGA-derived boiling point distributions of the set of samples. A twofold mechanism for loss of material in THF-based SEC may be proposed: (i) not all the sample dissolves in THF and (ii) some of the larger/more polar molecules apparently soluble in THF tend to deposit on column packings and do not elute through the column. Considerable caution therefore appears necessary in using THF as mobile phase in SEC work for the characterization of complex coal-derived liquids.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of kerogen extracts: effect of interactions between sample structure and matrix

“…As noted above, the perceived absence of high-MM materials by Lafleur and Nakagawa 29 could reasonably be interpreted in terms of the inherent limitations of evaporative and ionisation processes of the heated proble-MS technique, compared to laser desorption. In our work on coal derived samples, we have reported the magnitudes of 'excluded' peaks 28 to correlate with the presence of very large-MM material (at times extending to above 100,000 u), as indicated by MALDI-MS. 1,3,4 Taken together, the evidence suggests that the polarity of some molecules may cause shifts in their elution times to shorter values, and may overlap with signal from large-MM material in a manner probably also dependent on column operating temperature.…”

“…28 In particular we have considered relative increases in the magnitude of the excluded peak as signalling an increase in the abundance of material in the MM range above 1,000-2,000 u, and probably at much larger MM values. In view of other SEC work on coal derived liquids, suggesting that the magnitude of the excluded peak would be determined by the presence of polar material with MMs below 250 u, our interpretation requires some justification.…”

Asphaltene fractionation based on adsorption onto calcium carbonate: Part 1. Characterization of sub-fractions and QCM-D measurements

“…Earlier works [24,25] were based on tetrahydrofuran (THF) as mobile phase, but partial loss of asphaltene samples as well as material precipitation from solution in THF based SECs have been reported. [26] Another solvent employed as eluent is N-methyl-2-pyrrolidinone (NMP). [27][28][29][30] However, while NMP is a good solvent for coal derivatives, the solvency of NMP has been found to be limited for petroleum asphaltenes.…”

Choice of Extraction Voltage and Matrix in the Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry of Coal Tar Pitch — Pyridine Insolubles

“…The use of NMP as an eluent in SEC has nevertheless served to remove the severe solubility limitation encountered in the use of THF and has allowed the observation of a whole new range of large-MM materials near the exclusion limits of SEC columns. 13 fractionation 14 (pyridine solubles/insolubles) and by planar chromatography. 15 Good qualitative agreement was obtained between MALDI-TOF mass spectrometry and SEC where NMP was used as eluent: greater MMs were found by mass spectrometry in samples identified by SEC (in NMP) to give larger peaks at short elution times.…”