Marcos Millan

Chromatographic separations enabling the structural characterisation of heavy petroleum residues

Abstract Two petroleum residues from European crudes have been fractionated using solvent (heptane) separation and column chromatography. The residues and the separated fractions have been characterised by size exclusion chromatography (SEC) and by UV-fluorescence spectroscopy (UV-F). Matrix assisted laser desorption/ionisation-mass spectrometry of the whole residues and the heptane insoluble fractions indicated that the bulk of the residues covered the mass range m / z 300–2000, while the heptane insolubles (1–2% of the whole) contained material in the mass range from about m / z 300 to 10 000. The upper mass ranges indicated by SEC using polystyrene standards were higher; the earliest eluting material from both distillation residues eluted at times corresponding to polystyrene standards of MMs above 1.85 million u. Possible reasons for the different observations are given. Data from UV-F suggests that the heptane solubility separation method was the most successful for the separation of the largest molecular mass and also probably the most polar materials in these residues. However, all three fractionation methods produced similar trends, showing greater polarity of the fractions to correlate with increasing molecular mass. The shift of maximum intensity of fluorescence towards longer wavelengths (in UV-fluorescence) with increasing molecular size, as indicated by SEC, strongly suggests that the fluorescing molecules are large rather than aggregates of small molecules. Differences in comparison with American petroleum residues can be observed.

Positive-Ion Electrospray Ionisation Mass Spectrometry of Acetone- and Acetonitrile-Soluble Fractions of Coal-Derived Liquids:

The acetone-soluble fraction of a coal tar pitch has been examined using positive ion electrospray ionisation (ESI), by infusion into the ESI stream. The acetonitrile-soluble fractions of a coal tar pitch, a coal digest and a low temperature coal tar have also been studied by high performance liquid chromatography/ESI mass spectrometry. In contrast to positive-ion ESI of proteins, which gives rise to multiply charged ions, this application to fossil fuels, petroleum asphaltenes and humic acids, appears to only give singly-charged ions. The major components of these samples, polycyclic aromatics that could be detected by gas chromatography/mass spectrometry, formed no ions in positive-ion ESI. The only ions detected were formed from azaarenes. Ions up to only m/z 500 or so were detected, although these fractions are known to contain higher-mass species, up to at least several thousand mass units. Fractions of the three samples [coal tar pitch, coal digest and a low temperature coal tar], insoluble in acetonitrile gave no satisfactory ESI spectra. The nitrogen contents of the fractions indicate that azaarenes become more prominent with increasing mass. However, these larger species could not be observed in the ESI mass spectra. Only some of the minor components of these samples could be observed. Size-exclusion chromatography and matrix-assisted laser desorption/ionisation mass spectrometry both indicate considerably larger molecules than those found by ESI-MS.

Metal-ion pillared clays as hydrocracking catalysts (II): effect of contact time on products from coal extracts and petroleum distillation residues☆ ☆

Abstract Novel catalysts have been prepared, based on montmorillonite (a natural clay) and laponite (a synthetic clay) pillared with tin, chromium and aluminium pillars as well as layered double hydroxides based on polyoxo-vanadate and -molybdate as previously described. These novel catalysts were compared initially with a standard Ni/Mo catalyst supported on alumina and a dispersed catalyst, Mo(CO) 6 in hydrocracking a coal extract for a short contact time of 10 min at 440 °C in a microbomb reactor with tetralin solvent and hydrogen at a pressure of 190 bar. In the present work, the best of the novel catalysts, chromium montmorillonite calcined at 500 °C and tin laponite, have been compared with the supported catalyst and a dispersed catalyst (Mo(CO) 6 ) in the repeated hydrocracking of fresh coal extract over three sequential periods of 1 h. Also, the chromium montmorillonite calcined at 500 °C has been used in the hydrocracking of primary coal extracts, prepared in the flowing solvent liquefaction rig from Pittsburgh #8 and Illinois #6 coals, for reaction times of 10 min and 2 h. Further, the chromium montmorillonite calcined at 500 °C and tin laponite, have been compared with the supported catalyst and in the absence of a catalyst, in the hydrocracking of a petroleum distillation residue with 10 min and 2 h reaction times. Results were compared by size exclusion chromatography in NMP solvent and by UV-fluorescence and evaluated by the extent of the shift of the SEC profile to small molecules and by the shift of the synchronous UV-fluorescence profiles to shorter wavelengths. The performances of both catalysts at short, long or repeated reaction times are seen to be better than that of the conventional NiMo catalyst for the hydrocracking of coal-derived materials and a petroleum residue. Trials on a longer time scale are necessary in the next level of evaluation.