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

Abstract

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.

Dynamics of Asphaltene Aggregates under High-Pressure CO2 Revealed by Pulsed-Field Gradient NMR

“…Indeed, there are three distinct types of paramagnetic species in asphaltenes that largely contribute to relaxation time shortening: ions of metals with partially filled d- and f-electronic shells (the most widely presented are vanadium and nickel), delocalized π-electrons of aromatic rings, and stable organic radicals of the side chains. The concentration of paramagnetic ions (e.g., VO 2+ in metalloporphyrins) varies in a wide range (tens and hundreds of ppm), depending on the oil source, and can reach up to 0.1%, − while the concentration of stable carbon radicals might be 3–9 times lower . However, despite this low content, the effect of paramagnetic species is enormous since the magnetic moment of the electron is ∼650 times larger than that of nuclei.…”

Features of Wax Appearance Temperature Determination of Waxy Crude Oil Using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy Under Ambient and High Pressure

“…Yet the bigger difference between WAT measured by different methods within a model solution and waxy oil can be caused by a complex structure of wax gel in an oil sample due to the presence of resin and asphaltenes, which interfere with the process of wax microcrystals in a complex way. 49 On the other hand, the values of WAT in waxy oil can be determined with great accuracy by the appearance of the 730 cm -1 band, though this might be a time-consuming procedure to record the spectra with a small temperature step.…”

“…A sample of waxy oil (Züünbayan oil field, Mongolia) was used for the study; the composition and main properties are listed in Table S1 (Supplemental Material). 49 In addition to the viscometry used by Morozov et al, 50 the WAT of waxy oil was determined using a polarized light microscope (Olympus BX51). Additionally, the molecular composition of waxy crude oil was determined using a Khromos GH-1000 chromatograph (Russia) equipped with a flame ionization detector and a DB-2887 column (10 m, 0.530 mm, and 3 mm).…”