Resin–Paraffin Aggregation Processes in Waxy Oil Revealed by Vanadyl Porphyrin Spin Probe

The work demonstrates the great potential of using a vanadyl porphyrin probe to study resin–paraffin aggregation processes in oils. The dynamics and polarity of the local environment of vanadyl octaethylporphine (VOOEP), used as a spin probe, specially introduced into oil with a high content of paraffins and resins, have been studied. It has been found that VOOEP does not enter into paraffin crystallites even at temperatures 25 K below the wax appearance temperature but forms aggregates composed of resin molecules that can be adsorbed onto the surface of paraffins. The proposed approach to the precise simulation of experimental ESR spectra based on the Monte Carlo method in the temperature range in which partial averaging of anisotropic interactions is observed showed that as the temperature decreases from 320 to 200 K, the fraction of aggregates that capture the spin probe increases from 10 to 80%. It has been found that the incorporation of VOOEP into the aggregates is accompanied by an increase in the polarity of the local environment of the spin probe, which is consistent with the proposed mechanism of resin–paraffin aggregation processes in waxy oils.