The processes of aggregation and dissolution in model systems resin-asphaltene by NMR

Abstract

The resin-asphaltene model samples are studied by nuclear magnetic resonance (NMR). According to the differences in spin-spin relaxation times, we are able to distinguish two components of the resin in the mixture. The first component with slower relaxation rate corresponds to the resin in bulk. The second component with the much higher relaxation rate conforms to the resin interacting with the asphaltene particles. The dependence of the ratio between the contributions of these functions on the particle size of asphaltenes is found. It is shown that the fraction of resin molecules interacting with asphaltenes is described by the power dependence on the particle size in terms of one particle. In this case, the proportionality to the volume is given by the value of the exponent (0.9) that is closer to unity, while this exponent is 1.33 for the particle surface. This result is not consistent with the conventional simple model of an asphalt particle surrounded by a solvate resin layer. A hypothesis is formulated about the partial dissolution of asphaltene molecules in the resin is formulated, which is also confirmed by the dependence in the NMR signal of the fraction of the solid component on the particle size of asphaltenes. It is shown that the kinetic dependences of the fraction of the solid component, as well as the fraction of the resin molecules in the state of interaction with asphaltenes, reflect in general the opposite processes, although they are characterized by a close time value of 20 days.