No abstract

A comparative analysis of the composition of vanadyl porphyrins isolated from heavy oil using two different sulfocationites has been carried out. As a source of vanadyl porphyrins, heavy oil of Volga-Ural basin characterized by a high vanadium content was used. The N,N-dimethylformamide extract of asphaltenes was derived from this oil and subjected for isolation of primary vanadyl porphyrin concentrate on a SiO2 column, which was then chromatographically purified with sulfocationite by our improved method. Strongly acidic cation-exchange resin and asphaltene sulfocationite recently developed in our laboratory were used as sulfocationites. According to ultraviolet–visible spectroscopy, both sulfocationites showed excellent applicability for purification, providing isolation of a broad (>50%) fraction of vanadyl porphyrins with higher spectral purity compared to results of conventional methods. Results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis showed that composition of isolated vanadyl porphyrins depends upon the chemical nature of sulfocationite. Despite the same range of vanadyl porphyrin homologues (C26–C40, with maximum falling on C32) isolated by both sulfocationites, purification with asphaltene sulfocationite resulted in a 1.4-fold decrease in the content of the most abundant DPEP type of vanadyl porphyrins, with a corresponding 1.1–1.9-fold increase in the content of the rest of the types. It was also established that, when purification is accomplished, a significant part of the same vanadyl porphyrins still remains in the column, which can be explained by their associations with non-porphyrin components of the oil.

Extraction by N,N-dimethylformamide with further column chromatography allowed obtaining concentrate of vanadylporphyrins from asphaltenes of heavy sulfurous oils with high vanadium content. The prevailing types of vanadylporphyrins, their ratio, and molecular mass distribution were determined. The influence of obtained vanadylporphyrin concentrates on the stability of asphaltenes in the system “solvent/precipitator” was investigated. Kinetic studies using UV–vis spectroscopy have revealed that an increase in the content of vanadylporphyrins in asphaltenes leads to acceleration of their deposition from solution and destabilization of colloidal systems.

The chapter describes the opportunities of extracting porphyrins by polar solvents (acetone, N,N-dimethylformamide (DMF), isopropanol, and acetonitrile) and sulfuric acid from various highly molecular petroleum fractions and residues. It has been found that the predissolution of petroleum objects such as asphaltenes and resins in aromatic solvents allows improving the extraction of porphyrins by means of reducing their association with polycondensed heteroatomic structures. Based on the absorption spectra and mass spectra, primary types of porphyrins in obtained extracts were revealed. The distinctions between porphyrin extractions in resins and asphaltenes were revealed. Sulfuric acid extraction allows producing highly concentrated primary extracts of demetallated porphyrins. The share of porphyrin fractions in obtained extractions was 13.0-24.2 wt%, which depends on the concentration of metal porphyrins in initial asphaltenes and resins.

Comparative analysis of the composition and properties of heavy oils from various oil fields has revealed an inverse dependence of the asphaltene/resin ratio upon the vanadium content in resins. This indicates the diminishment of asphaltene precipitation ability with an increase in the content of vanadyl complexes in heavy oil resins. Experiments have shown that the addition of vanadyl porphyrins to resins enhances their inhibition activity toward asphaltene precipitation. For this purpose, vanadyl porphyrins have been concentrated by N,N-dimethylformamide extraction from resins and additionally purified by column chromatography. The obtained vanadyl porphyrin concentrate has been added to resins at the ratio of 1–5 wt %, and its influence on asphaltene stabilization has been further evaluated. Evaluation has been performed by measuring the optical density of deasphalted oil obtained by dilution of the crude oil with 20-fold excess of n-hexane, where resins with various contents of vanadyl porphyrins have been initially dissolved. The change in composition and properties of precipitated asphaltenes has been analyzed, and an increase in their absorbance, aromaticity, and degree of ring fusion with the growth of the vanadyl porphyrin content in resins has been demonstrated. Results have shown the efficiency of vanadyl porphyrins in resins as inhibitors of asphaltene precipitation.