2014 Volume 93 Issue 2 Pages 142-150
Three asphaltenes recovered from the vacuum residue of Middle East crude oil mixture (ME), the atmospheric residues of Minas crude oil (MI) and Cold lake oil sand bitumen (CL), were separated into 5 fractions (Fr1-Fr5) according to average molecular weight (Mn) and a fraction from effluent (Fr6) by preparative gel permeation chromatography (GPC), with >95 wt% of the total recovery. The original asphaltene and the fractions were analysed by elemental analysis, 1H-NMR and analytical GPC to obtain the input data for an average molecular structural analysis (H/C, N/C, S/C atomic ratios, and atomic ratios of hydrogen types). The dependencies of those parameters on Mn were represented using 1 or 2 linear fitting equations, respectively. Using the equations, the parameters were calculated followed by the estimation of carbon aromaticity (fa) from those parameters. An average molecular structural analysis was applied to Fr1-Fr5 fractions at several Mns to estimate the numbers of units (condensed aromatic ring systems) and aromatic rings per molecule (M and Ra). M was 1.0 at low Mn range, then increased with increasing Mn. Ra increased linearly with increasing Mn. The numbers of aromatic rings per unit (Ra/M) were about 8-10 at M=1.0 in every original asphaltene, and then increased up to 13-15 for ME and MI, but kept about 9 for CL. An average molecular structural analysis was also performed for every original asphaltene and Fr6 fraction. In the case of ME and MI, Ra/M for Fr6 was larger than that for original asphaltene, and MI had larger unit size than ME. On the other hand, Fr6 fractions for CL had almost the same Ra/M as original asphaltene, while Fr6 fraction contained more hetero atoms.
