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Handbook of Size Exclusion Chromatography and Related ...

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Figure 1 SEC analyses <strong>of</strong> an aged asphalt <strong>and</strong> its Corbett fractions (500/50 A ˚ ,60cm<br />

PLgel, THF at 1 mL/min, 100 mL, RI detector). The whole asphalt is analysed using a<br />

7 wt% solution; the Corbett fractions are adjusted according to their weight fraction.<br />

asphalt from a road core along with chromatograms <strong>of</strong> its Corbett fractions. It is<br />

seen that the saturates appear slightly larger than the naphthene aromatics. There is<br />

a shift to larger size with the polar aromatic fractions <strong>and</strong> a greater shift with<br />

asphaltenes, but it is these latter fractions that tend to associate, thereby giving a<br />

false impression <strong>of</strong> molecular size.<br />

Boduszynski et al. (107,108), using field ionization mass spectroscopy<br />

(FIMS), obtained average molecular weights from 873 to 1231 for the Corbett<br />

fractions, with asphaltenes actually the smallest molecules. The VPO value for<br />

asphaltenes was over 4000. The values obtained for polar aromatics was 1020 by<br />

FIMS <strong>and</strong> over 1400 by VPO. Results for naphthene aromatics <strong>and</strong> saturates were<br />

quite close by the two methods. It should be realized that the designation <strong>of</strong><br />

asphaltenes is arbitrary, depending on the precipitating solvent (109,110). Propane<br />

precipitates most <strong>of</strong> the polar aromatics, <strong>and</strong> pentane asphaltenes can be nearly<br />

twice the heptane asphaltenes.<br />

Many <strong>of</strong> the properties <strong>of</strong> asphalt are determined by the variety <strong>of</strong> chemical<br />

types <strong>and</strong> their divergent properties. The asphaltenes <strong>and</strong> saturates are immiscible.<br />

Mixtures <strong>of</strong> asphaltenes <strong>and</strong> naphthene aromatics are highly non-Newtonian at<br />

© 2004 by Marcel Dekker, Inc.

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