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.
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