Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen

Sophie Badre, Cristiane Carla Goncalves, Koyo Norinaga, Gale Gustavson, Oliver C. Mullins

Research output: Contribution to journalArticlepeer-review

243 Citations (Scopus)


The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4-10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption [1]. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the 'giant' asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.

Original languageEnglish
Pages (from-to)1-11
Number of pages11
Issue number1
Publication statusPublished - Jan 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Organic Chemistry


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