The low temperature oxidation of Athabasca oil sand asphaltene observed from 13C, 19F, and pulsed field gradient spin-echo proton n.m.r. spectra

Abstract

The low temperature oxidation of Athabasca oil sand asphaltene observed from 13C, 19F and pulsed field gradient spin-echo proton n.m.r. spectra Desando, Michael A.; Lahajnar, Gojmir; Ripmeester, John A.; Zupancic, Ivan AbstractCarbon-13 and fluorine-19 nuclear magnetic resonance spectra of chemically derivatized, by phase transfer methylation and trifluoroacetylation, Athabasca oil sand asphaltene, reveal a broad site distribution of different types of hydroxyl-containing functional groups, viz., carboxylic acids, phenols, and alcohols. The low temperature air oxidation of asphaltene, at ca. 130ЊC for 3 days, generates a few additional carboxyl and phenolic groups. These results are consistent with a mechanism in which diaryl methylene and ether moieties react with oxygen. Self-diffusion coefficients, from the pulsed field gradient spin-echo proton magnetic resonance technique, suggest that low temperature oxidation does not appreciably alter the average particle size and diffusion properties of asphaltene in deuterochloroform. ᭧

Chemical derivatization of Athabasca oil sand asphaltene for analysis of hydroxyl and carboxyl groups via nuclear magnetic resonance spectroscopy

“…50±65 ppm are in the methoxy chemical shift range, as observed for other asphaltic substances [2,21,38,39]. Integrated areas of the methoxy peaks suggest that of the different catalyst/solvent combinations studied, phase transfer methylation (PTM) with TBAH/THF yields the highest degree of O-methylation (Table 1).…”

“…1 min through a solution of AOSA (ca. 0.2 g), plus 1±3 drops of 2,6-lutidine (ALD), in 2 ml of deuterochloroform (MSD isotopes) in nitrogen at 255 8C in an iso-propanol/dry ice bath [21,26]. The mixture was warmed to room temperature and nitrogen was bubbled through the sample for ca.…”

“…There is also the possibility of S-, N-, and C-methylations of thiol, thiophene, amine, amide, imine, pyrrole, pyridyl,¯uorenyl, etc. groups appearing at 18±50 ppm [21,25,31,41]. Indeed, comparison to the aliphatic spectral regions before and after PTM reactions, particularly in toluene or THF (Fig.…”

“…Interpretation of lineshape changes necessitates consideration of structural and dynamic properties of asphaltene solutions. For instance, AOSA can aggregate in organic solvents, as shown from NMR self-diffusion measurements [21] and vapor pressure osmometry [1,17,19]. In addition, the association complexes are probably different in toluene, THF, dichloromethane, and chloroform owing to solvent effects.…”

“…di-ortho-substituted phenols at ca. 59±63 ppm [21,33,39,40]. Primary alcoholic methyl ether groups usually resonate in the narrow range at 58±59 ppm [40].…”