**3. Results and discussion**

**2. Materials and methods**

156 Phthalocyanines and Some Current Applications

The study objects were the oil and natural bitumens of various-age deposits of Tatarstan fields and heavy residues of oil refining: vacuum residue (VR) from TAIF-NK OJSC oil refinery; asphalt (A-1) after tar propane deasphalting at the ANK Bashneft OJSC refinery; asphalt (A-2) after tar propane deasphalting at the NK Rosneft refinery; atmospheric residues of heavy oils

All oils and natural bitumens were separated from emulsion water and mechanical impurities by centrifugal process. Organic solvents of hch and chda classes were additionally treated and

Asphaltenes were extracted by using a common methodology by means of diluting with 40× hexane excess with further flushing to remove sedimented resins and oils in a Soxhlet apparatus. Oils and resins were separated by means of column chromatography, using an activated granulated large-pore silica gel as an immobile phase, with the grain size of

Vanadium and nickel concentrations in oils and asphaltenes were measured by means of direct flame atomic absorption spectrometry using AAS-1N spectrophotometer, with approved

To extract asphaltenes by a boiling solvent, a 1 g sample of asphaltenes was placed into a roundbottom flask with back flow condenser, 200 mL of extractant was added, and the mixture was boiled for 1 h. After cool-down, the mixture was filtered. The resulted extract was dried in vacuum. To extract asphaltenes by sedimentation extraction, a 1 g sample of asphaltenes was diluted in 10 mL of benzene. A total volume of 100 mL of extractant was added to the resulting solution, which was then boiled with a back flow condenser for 10 min. After the solution

The concentration of vanadyl porphyrins in extracts from asphaltenes was calculated for the

where 0.187 is the conversion factor describing the medium absorption; h is the height of absorption α-band maximum for 575 ± 5 nm; m is the extract sample, g; V is the porphyrin

Matrix-assisted laser desorption/ionization (MALDI) mass spectra of extracts from asphaltenes were obtained by UltraFlex III TOF/TOF mass-spectrometer in linear mode. The data were processed by using FlexAnalysis 3.0 software. The sample was ionized by nitrogen laser radiation (wave length of 337 nm) with the energy of 19 eV. Positively charged ions were recorded. A metallic target was used. Sinapinic acid was used as a matrix. Molecular ions of VPs of various homotypes are presented as peaks with the weight of 373 + 14n amu and 375 + 14n amu (where n is the number of methylene groups in pendent groups). The share of each homotype was calculated by means of internal normalization by using the peak intensity of molecular ions.

Cvp = 0.187h·V/m·l (1)

from the Ashalchinskoe (AR-1) and Zyuzeyevskoe (AR-2) fields.

0.2–0.5 mm, as well as the hexane/benzene mixture at 85:15 as an eluent.

standard samples of metal concentration in oil products used as blank solutions.

cooldown, asphaltenes were filtered. The resulting extract was dried in vacuum.

absorption band of 575 nm according to the following formula:

extract volume to be reached, mL; l is the flask thickness, cm.

desiccated by employing widely known methods.

#### **3.1. Vanadyl porphyrin extraction with polar solvents**

The schemes applied to extract metal porphyrin complexes from oil objects have some disadvantages that do not allow using them on a large scale. When using liquid extraction, multiple extraction is needed to achieve high degree of extraction. If asphaltenes are used as extraction objects, the number of extraction steps is multiply increased, therefore, frequently the process is performed in Soxhlet apparatuses. Such extraction conditions are explained by the fact that in oil systems, asphaltenes are associated with oils and resins due to multiple intermolecular interactions, such as electrostatic, dipole, and dispersive ones. The molecular weight of resulted aggregates can be 10,000 amu and more. Metal porphyrins tend to establish strong associations with aggregates of such weight. Metal porphyrins can also be captured into the grid of asphaltenes by the type of molecular sieves. In this connection, it becomes difficult to extract metal porphyrin complexes. It is only possible to obtain concentrates enriched with these compounds. Previously, asphaltene extraction by various solvents was used to obtain metal porphyrin concentrates [24]. It occurred that no more than 60% of the total amount of vanadyl porphyrins is extracted during asphaltene extraction. The extraction process takes place at the solvent boiling temperature in order to increase the extractant solvability. This allows increasing the extraction degree of metal porphyrins, but it also contaminates the extract with highly molecular heteroatomic components.

To increase the extraction degree of metal porphyrins, we proposed using sedimentation extraction. Unlike the direct extraction from asphaltene, this approach suggests preliminary dissolution of asphaltene in a small amount of good solvent. Asphaltene dissolution allows the partial destroying of the intermolecular links inside aggregates that results in some metal porphyrins being liberated. This is followed by metal porphyrin extraction by the solvent excess having low solvability toward asphaltenes, but good solvability toward metal porphyrins. As a result, asphaltenes are sedimented, and metal porphyrins remain in the solution. Polar nonaromatic solvents have low solvability toward asphaltene-tarry components of oil and high solvability metal porphyrins.

To assess the efficiency of metal porphyrin extraction from an asphaltene solution by using sedimentation extraction, the obtained results were compared with the results of standard extraction of metal porphyrins from dry asphaltenes. Benzene was used as an asphaltene solvent; four solvents belonging to different classes of organic compounds were used as polar solvents: acetone, DMF, isopropanol, and acetonitrile.

As an extraction object, asphaltenes of the Ashalchnskoe field oil were used. The extracts obtained in the form of toluene solutions were spectrophotometered within the range of 400–630 nm. Absorption spectra show clear absorption bands at 530 (α-band) and 575 nm (β-band) typical of vanadyl porphyrins (**Figure 2**). A 550 nm band belonging to nickel porphyrins is not recorded in spectra.

When asphaltenes are treated with a boiling solvent, the maximum extract yield is obtained when using isopropanol (**Figure 3**). When using acetone and DMF, extract yields are lower, and in case of acetonitrile, no extract is formed. When using sedimentary extraction from asphaltene solutions, the maximum extract yield occurs with DMF. The sedimentary extraction used for all solvents under study allows reaching higher extract yields and concentrations of vanadyl porphyrins in them as compared to boiling solvent extraction (**Figure 4**).

The most common types of metal porphyrins in oil are etio- and desoxophylloerytroetioporphyrins (DPEP). To assess their ratio in the DMF extract from oil asphaltenes, matrix-assisted laser desorption/ionization (MALDI) is used. (Etio-type porphyrins have the molecular weight of 375 + 14n, and DPEP-type porphyrins – 375 + 14n.) Based on the intensity of peaks, the ratio of Σetio/ΣDPEP equaled 0.73.

MALDI can be used to assess the substitution nature in the porphyrinic ring (**Figure 5**). In both series of porphyrins, alkyl substitutes on the ring periphery contain 6–19 atoms of carbon. Porphyrins of etio-series contain C26–C39 homotypes with the maximum concentration at m/z = 529, which corresponds to C31 homotype that contains alkyl substitutes with

**Figure 2.** Visible absorption spectrum of asphaltene extract.

**Figure 3.** Yield of vanadyl porphyrin extracts from asphaltenes.

To assess the efficiency of metal porphyrin extraction from an asphaltene solution by using sedimentation extraction, the obtained results were compared with the results of standard extraction of metal porphyrins from dry asphaltenes. Benzene was used as an asphaltene solvent; four solvents belonging to different classes of organic compounds were used as polar

As an extraction object, asphaltenes of the Ashalchnskoe field oil were used. The extracts obtained in the form of toluene solutions were spectrophotometered within the range of 400–630 nm. Absorption spectra show clear absorption bands at 530 (α-band) and 575 nm (β-band) typical of vanadyl porphyrins (**Figure 2**). A 550 nm band belonging to nickel por-

When asphaltenes are treated with a boiling solvent, the maximum extract yield is obtained when using isopropanol (**Figure 3**). When using acetone and DMF, extract yields are lower, and in case of acetonitrile, no extract is formed. When using sedimentary extraction from asphaltene solutions, the maximum extract yield occurs with DMF. The sedimentary extraction used for all solvents under study allows reaching higher extract yields and concentrations of vanadyl porphyrins in them as compared to boiling solvent extraction (**Figure 4**).

The most common types of metal porphyrins in oil are etio- and desoxophylloerytroetioporphyrins (DPEP). To assess their ratio in the DMF extract from oil asphaltenes, matrix-assisted laser desorption/ionization (MALDI) is used. (Etio-type porphyrins have the molecular weight of 375 + 14n, and DPEP-type porphyrins – 375 + 14n.) Based on the intensity of peaks,

MALDI can be used to assess the substitution nature in the porphyrinic ring (**Figure 5**). In both series of porphyrins, alkyl substitutes on the ring periphery contain 6–19 atoms of carbon. Porphyrins of etio-series contain C26–C39 homotypes with the maximum concentration at m/z = 529, which corresponds to C31 homotype that contains alkyl substitutes with

solvents: acetone, DMF, isopropanol, and acetonitrile.

phyrins is not recorded in spectra.

158 Phthalocyanines and Some Current Applications

the ratio of Σetio/ΣDPEP equaled 0.73.

**Figure 2.** Visible absorption spectrum of asphaltene extract.

**Figure 4.** Concentration of vanadyl porphyrin in asphaltenes extracts.

**Figure 5.** MALDI mass spectrum of vanadyl porphyrin extract from asphaltenes.

high number of carbon 11 atoms. Porphyrins of DPEP-series contain C28–C41 homotypes with the maximum concentration at m/z = 529, which corresponds to C31 homotype that contains alkyl substitutes with high number of carbon 9 atoms.

#### **3.2. Porphyrin extraction with sulfuric acids from asphaltenes and resins**

Another methodological approach to the extraction of porphyrin complexes from oils and their components is acid extraction. Extraction methods described in the literature are adaptable and cannot be used for large-scale extraction. The extraction process also takes much time. Furthermore, all the above methodologies were developed for light oils with a low concentration of asphaltene-tarry substances. Meal porphyrin acid extraction from asphaltenetarry substances is almost not described.

At the first stage, it seems necessary to reveal the most efficient acid extractant with the maximum yield of porphyrin extract. Extraction conditions may have a heavy effect on the results; first of all, this refers to temperature and duration. For a preliminary assessment of acid extraction capabilities, heavy oil asphaltenes from the Zyuzeyevskoe field were used. Concentrated hydrochloric, phosphorous, and sulfuric acids were used as extractants. As in case of polar solvent extraction, a 10% solution in benzene was used to reduce the association of metal porphyrins with asphaltenes, and the process itself was maintained at the room temperature. For phosphorous and hydrochloric acids, asphaltenes do not develop into the acid phase. When treating asphaltene solutions with sulfuric acids, an extractant and a benzene-insoluble residue is formed. A difference from the method currently applied to produce metal-free porphyrin from asphaltenes consists in the fact that demetaling of metal porphyrins occurs simultaneously with their extraction from asphaltenes. The need for preliminary extraction of metal porphyrins is avoided. Due to slurry formation, a centrifugal process and further filtering in a Schott's funnel were used to segregate the extract and the residue. The obtained extract was neutralized with a 20% cooled-down solution of sodium hydrate until reaching a neutral reaction. Tetrachloromethane was extracted from the resulting water solution. The yield of the primary extract after solvent stripping was 9%.

There are no metal porphyrin bands of 530 and 575 nm in the absorption spectrum in the visible area for the primary extract, and there are bands typical of free porphyrin bases (**Figure 6**). This testifies that when sulfuric acid acts on metal porphyrins, they are demetaled and metalfree porphyrins are formed. In this manner, concentrated sulfuric acid is the most optimal extractant to extract and demetaleted porphyrin from oil asphaltenes and resins.

To define the composition of porphyrin extracts in case of sulfuric acid extraction, asphaltenes and resins of heavy oils from Ashalchinskoe (TN-1 asphaltenes and resins) and Zyuzeyevskoe fields (TN-2 asphaltenes and resins) were used. Extraction was carried out according to the scheme described above. In case of sulfuric acid extraction, as for asphaltene extraction, an extract of porphyrins and an insoluble residue are formed. The results obtained for the yield of extracts are summarized in **Table 1**.

The amount of porphyrin extracted from resins or asphaltenes of heavy oils with increased vanadium concentration varies within 7.9–13.0 wt%. If oils are compared individually, the

**Figure 6.** Visible absorption spectrum of sulfuric acid extract of asphaltenes from Zyuzeyevskoe oil field.

porphyrin extract yield from resins as compared to that from asphaltenes is 3–4 wt% higher in both cases. When the vanadium concentration both in resins and asphaltenes increases, the yield of extracts is also increased. If the vanadium concentration in asphaltenes differs by two times, the relative extract yield increase will be about 14% just as in resins where the vanadium concentration difference is even higher (3.33 times), and the extract yield is increased by relative 15% only. In this manner, for asphaltenes and resins where the vanadium concentration will exceed the values as compared to the objects under study, it is unlikely that the porphyrin extract yield will be significantly increased.

To obtain data for the composition and types of porphyrins in extracts, silica gel adsorption chromatographic separation was used. A mixture of 0.5% isopropyl alcohol and 99.5% of


**Table 1.** Yield of sulfuric acid extracts.

high number of carbon 11 atoms. Porphyrins of DPEP-series contain C28–C41 homotypes with the maximum concentration at m/z = 529, which corresponds to C31 homotype that

Another methodological approach to the extraction of porphyrin complexes from oils and their components is acid extraction. Extraction methods described in the literature are adaptable and cannot be used for large-scale extraction. The extraction process also takes much time. Furthermore, all the above methodologies were developed for light oils with a low concentration of asphaltene-tarry substances. Meal porphyrin acid extraction from asphaltene-

At the first stage, it seems necessary to reveal the most efficient acid extractant with the maximum yield of porphyrin extract. Extraction conditions may have a heavy effect on the results; first of all, this refers to temperature and duration. For a preliminary assessment of acid extraction capabilities, heavy oil asphaltenes from the Zyuzeyevskoe field were used. Concentrated hydrochloric, phosphorous, and sulfuric acids were used as extractants. As in case of polar solvent extraction, a 10% solution in benzene was used to reduce the association of metal porphyrins with asphaltenes, and the process itself was maintained at the room temperature. For phosphorous and hydrochloric acids, asphaltenes do not develop into the acid phase. When treating asphaltene solutions with sulfuric acids, an extractant and a benzene-insoluble residue is formed. A difference from the method currently applied to produce metal-free porphyrin from asphaltenes consists in the fact that demetaling of metal porphyrins occurs simultaneously with their extraction from asphaltenes. The need for preliminary extraction of metal porphyrins is avoided. Due to slurry formation, a centrifugal process and further filtering in a Schott's funnel were used to segregate the extract and the residue. The obtained extract was neutralized with a 20% cooled-down solution of sodium hydrate until reaching a neutral reaction. Tetrachloromethane was extracted from the resulting water solu-

There are no metal porphyrin bands of 530 and 575 nm in the absorption spectrum in the visible area for the primary extract, and there are bands typical of free porphyrin bases (**Figure 6**). This testifies that when sulfuric acid acts on metal porphyrins, they are demetaled and metalfree porphyrins are formed. In this manner, concentrated sulfuric acid is the most optimal

To define the composition of porphyrin extracts in case of sulfuric acid extraction, asphaltenes and resins of heavy oils from Ashalchinskoe (TN-1 asphaltenes and resins) and Zyuzeyevskoe fields (TN-2 asphaltenes and resins) were used. Extraction was carried out according to the scheme described above. In case of sulfuric acid extraction, as for asphaltene extraction, an extract of porphyrins and an insoluble residue are formed. The results obtained for the yield

The amount of porphyrin extracted from resins or asphaltenes of heavy oils with increased vanadium concentration varies within 7.9–13.0 wt%. If oils are compared individually, the

extractant to extract and demetaleted porphyrin from oil asphaltenes and resins.

contains alkyl substitutes with high number of carbon 9 atoms.

tarry substances is almost not described.

160 Phthalocyanines and Some Current Applications

of extracts are summarized in **Table 1**.

**3.2. Porphyrin extraction with sulfuric acids from asphaltenes and resins**

tion. The yield of the primary extract after solvent stripping was 9%.

benzene was applied as eluent [25]. A total volume of 10 mL of liquid was sampled during elution. To decrease the number of fractions analyzed against the absorption spectra in the visible band, the obtained solutions were combined visually according to the color change (**Table 2**). A further study of absorption spectra in the visible band confirmed that this approach can be applied, since the differences in spectra allow identifying the types of porphyrins. To all colored fractions, except for the first and the last one, there are four absorption bands registered, having various intensity at 620, 565, 535, and 500 nm (bands I–IV), according to which a specific spectral type can be assigned to porphyrins.

The first (oil-like) and the last (resin-like) colored fractions obtained after separation of asphaltene extracts do not show absorption bands of metal-free porphyrin. In resin extract separation, the resin-like fraction is the first to eluted, followed by the oil-like fraction. These fractions being present in the sulfuric acid extracts are related to occluded oils and resins in asphaltenes.

The data for the yield of fractions after chromatographic separation of the sulfuric acid extract of asphaltenes are given in **Table 3**. The total concentration of oil-like and resin-like fractions in the extract reaches 53.2 wt%. Some part of the extract is not eluted and remains on the silica gel. The concentration of porphyrin fractions in extracts of resins is higher than in those from asphaltenes.

Phyllo-type porphyrins are predominant in asphaltene extracts. Apart from etio- and phylloporphyrins, there are also rhodo- and DPEP found in asphaltene extracts. Reduced concentration of DPEP in asphaltene extracts as compared to solvent extraction allows suggesting the isocyclic ring destruction in the porphyrins of this type during acid extraction.

Unlike asphaltenes, the porphyrins of resin extracts contain only these etio- and phyllotypes, which is the primary difference in the composition of porphyrin extracts of resins and asphaltenes. Etio-type of porphyrins is predominant in resin extracts. No rhodo-type porphyrins contained in resins is probably related to co-sedimentation of porphyrins with asphaltenes during their extraction due to polar groups presented in them and, consequently, lower solubility in hexane. As for asphaltenes, the most probable reason for no DPEP in extracts from resins can be the isocyclic ring destruction during sulfuric acid extraction.


**Table 2.** Spectral types of petroleum demetalleted porphyrins.


**Table 3.** Yield of fractions after column chromatography of asphaltenes and resins porphyrinic extracts.

#### **3.3. Porphyrin extraction with sulfuric acids from the solution of heavy petroleum residues**

Since the extraction of individual resins and asphaltenes is a hard task, their industrial concentrates are used for porphyrin extraction—residual products of oil refining. First of all, these are the vacuum residue (tar) and asphalts from tar deasphaltizing with the total concentration of asphaltenes and resins being 50–70 wt% depending on the initial oil composition. For the vanadium concentration of 200–500 ppm in some heavy oils of Tatarstan, Samara, and Ulyanovsk region fields, the total concentration of vanadium and nickel in residual products of oil refining will be 1000 ppm and more.

As the objects of study, heavy petroleum residues of existing productions and atmospheric residues obtained in laboratory conditions (>350°C) from heavy oils with increased vanadium concentration were used. Density, component composition, and vanadium and nickel concentration were measured for all heavy petroleum residues (HPR) (**Table 4**).

Determining the concentration of these metals allows the preliminary assessing of the concentration of metal porphyrins in initial objects. The vanadium concentration in A1 and AR-2 is 9.2–9.3 times higher than that of nickel. V/Ni is also 9.8 times higher for A-2, but for


**Table 4.** Density and composition of HPR.

benzene was applied as eluent [25]. A total volume of 10 mL of liquid was sampled during elution. To decrease the number of fractions analyzed against the absorption spectra in the visible band, the obtained solutions were combined visually according to the color change (**Table 2**). A further study of absorption spectra in the visible band confirmed that this approach can be applied, since the differences in spectra allow identifying the types of porphyrins. To all colored fractions, except for the first and the last one, there are four absorption bands registered, having various intensity at 620, 565, 535, and 500 nm (bands I–IV), accord-

The first (oil-like) and the last (resin-like) colored fractions obtained after separation of asphaltene extracts do not show absorption bands of metal-free porphyrin. In resin extract separation, the resin-like fraction is the first to eluted, followed by the oil-like fraction. These fractions being present in the sulfuric acid extracts are related to occluded oils and resins in

The data for the yield of fractions after chromatographic separation of the sulfuric acid extract of asphaltenes are given in **Table 3**. The total concentration of oil-like and resin-like fractions in the extract reaches 53.2 wt%. Some part of the extract is not eluted and remains on the silica gel. The concentration of porphyrin fractions in extracts of resins is higher than in those from

Phyllo-type porphyrins are predominant in asphaltene extracts. Apart from etio- and phylloporphyrins, there are also rhodo- and DPEP found in asphaltene extracts. Reduced concentration of DPEP in asphaltene extracts as compared to solvent extraction allows suggesting the

Unlike asphaltenes, the porphyrins of resin extracts contain only these etio- and phyllotypes, which is the primary difference in the composition of porphyrin extracts of resins and asphaltenes. Etio-type of porphyrins is predominant in resin extracts. No rhodo-type porphyrins contained in resins is probably related to co-sedimentation of porphyrins with asphaltenes during their extraction due to polar groups presented in them and, consequently, lower solubility in hexane. As for asphaltenes, the most probable reason for no DPEP in extracts from resins can be the isocyclic ring destruction during sulfuric acid

**intensity of the absorption** 

**Spectral type of porphyrins**

**bands**

isocyclic ring destruction in the porphyrins of this type during acid extraction.

**Fraction number Solution color The order of decreasing** 

**Table 2.** Spectral types of petroleum demetalleted porphyrins.

 Cherry III→IV→II→I Rhodo Dark orange IV→I→II→III DPEP Dark red IV→II→II→I ETIO Red IV→II→III→I Phyllo

ing to which a specific spectral type can be assigned to porphyrins.

asphaltenes.

162 Phthalocyanines and Some Current Applications

asphaltenes.

extraction.

VR and A-1, the vanadium concentration is about five times higher than the nickel concentration. In this way, a potential share of nickel porphyrins for the selected HPRs can be about 10–20% of the vanadium porphyrin concentration.

During extraction, the most part of HPRs is transformed into an insoluble finely divided black product. As a result of sulfuric acid exposure, the composition is greatly altered primarily because of newly formed sulfonic and sulfoxide groups, which is represented by the absorption growth in the area of 1030 cm−1 and 1200–1400 cm−1 in IR bands as compared to initial objects.

The yield of primary porphyrin extracts for the selected HPRs varies within 6.9–12.9% equivalent to the weight of the initial oil stock (**Table 5**). The maximum extract yield is found for AR-2 where the vanadium and nickel concentration are also maximal. For AR-1, rather high yield of the primary extract is also found; however, the vanadium and nickel concentrations are relatively low. Thus, the total concentration of vanadium and nickel in HPRs is no determinant for forecasting the yield of porphyrin extracts in case of sulfuric acid extraction.

Based on absorption spectra analysis in the visible band, there are metal-free porphyrins found in all obtained extracts with simultaneous dissipation of characteristic absorption bands of vanadyl and nickel porphyrins, which testify demetallization of metal porphyrins during extraction. To characterize porphyrins in obtained extracts, adsorption chromatographic separation was used with further analysis of electronic spectra.

The results of adsorption chromatographic separation of primary porphyrin extracts (**Table 5**) show that about 70–75% include various oil-like and resin-like fractions containing no porphyrins, with some part of them not eluted by the recommended solvent mixture and remaining adsorbed on the silica gel.

A comparative analysis of IR spectra allowed identifying that oil-like and resin-like fractions have the same structural and group composition as resins and oils obtained when analyzing the composition of initial HPRs. The results of chromatographic separation of primary extracts show that the share of porphyrin fractions is 13.0–24.2%. The absorption spectrum analysis


**Table 5.** Yield of fractions after column chromatography of primary porphyrinic extracts.

in the visible band for all porphyrin fraction shows that there are all four types of porphyrins (**Figure 3**). Phyllo- and etio-porphyrins are predominant. In AR-1 and AR-2 extracts, the share of phyllo-porphyrins is significantly higher. One of the reasons for reduced concentration of DPEP in sulfuric acid extracts can be the isocyclic ring destruction when exposed to sulfuric acid. The total yield of porphyrin fractions for both the primary extract composition and inequivalent to the initial HPRs prove no unambiguous correlation with the total vanadium and nickel concentration in the initial feed.

Metal-free porphyrins have four absorption bands in electronic spectra whose intensity depends on the type of porphyrins, so it is complicated to precisely measure the concentration of metalfree porphyrin in the obtained fractions. As an indirect method to assess the concentration of porphyrins in the extract, a comparative analysis of vanadium and nickel concentration reduction in HPRs can be used by analyzing the vanadium and nickel concentration in the extract by means of atomic absorption spectroscopy. As a result, it has been found that the sulfuric acid extract composition is extracted from 62.4 to 81.1% of vanadium contained in initial HPRs, with full extraction of nickel. Probably, the vanadium extraction from asphaltenes is incomplete, since the share of vanadium in the extract is inversely proportional to the concentration of asphaltenes in HPRs. Correspondingly, some vanadyl porphyrins remain in the insoluble residue. Since the molecular weight of vanadyl and nickel porphyrins is 10 times higher as compared to the atomic mass of vanadium and nickel, the potential concentration of metal porphyrins in HRP can be assessed, which is approximately evaluated as the total concentration increased by ten times.

A similar level of porphyrin concentration in concentrates cannot be achieved when extracted by such polar solvents as DMF or acetone with further single chromatography. It is especially important that the maximum concentration of porphyrins in obtained concentrates is reached when using heavy petroleum atmospheric residue (AR-2) as a feed, with increased vanadium and nickel concentration and simultaneously minimal ratio of asphaltenes and resins. In perspective, it is possible that such oils can be regarded as a stock to produce cheap natural porphyrins for using primarily as dyes and catalysts.
