Dynamic nuclear polarization in suspensions of asphaltenes obtained from asphalt cements

Abstract

Nuclear Magnetic Resonance (NMR) and the Overhauser Effect (OE) type Dynamic Nuclear Polarization (DNP) have been used to study some colloidal asphaltene suspensions, in a weak magnetic field. Our approach is based on the idea that diffusing nuclear spins in the suspending fluid medium interact with unpaired electron spins in the asphaltene micells. The asphaltenes were extracted from asphalt cements with penetration grades 60 and 183 and were precipitated in petroleum ether. The percentage of asphaltenes thus obtained were 30 % and 10 % in weight. Toluene, benzene, chlorobenzene, nitrobenzene, pyridine, tetralin and quinoline were used as the suspending fluid medium with a viscosity range of six to one. The EPR spectra and the DNP parameters were obtained and the results are discussed.