**Isolation of Porphyrins from Heavy Oil Objects**

Makhmut R. Yakubov, Guzalia R. Abilova, Kirill O. Sinyashin, Dmitry V. Milordov, Elvira G. Tazeeva, Svetlana G. Yakubova, Dmitry N. Borisov, Pavel I. Gryaznov, Nikolay A. Mironov and Yulia Y. Borisova

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68436

#### **Abstract**

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.

**Keywords:** vanadyl porphyrins, asphaltenes, resins, extraction, heavy petroleum residues, vanadium

#### **1. Introduction**

Metal porphyrins in oils are primarily represented by vanadyl and nickel porphyrins [1]. The remaining metal-containing compounds of vanadium and nickel are present in the form of chelates with pseudo-porphyrin structures or with porphyrins having atypical substitutes [2]. Due to low concentration of porphyrins having atypical structure, efficient separation and massspectrometry with ultrahigh definition are required to determine their structure [3], and the

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structure of pseudo-porphyrin complexes is still not defined. The paper also reports of oil being present in insignificant amounts in iron and copper porphyrins [4].

The analysis of oil porphyrins in oils and their components by various instrumental methods is impossible due to their low concentration, so usually, fractions enriched with metal porphyrins are used for analysis. All concentration methods for oil porphyrins can be conditionally divided into three groups:


For light oils having a relatively low concentration of asphaltene-resin substances, the first group of methods is mostly suitable for extraction of oil porphyrins: complex formation with Lewis acids usually represented by waterless metal halides [1]. This method consists in the formation of molecular complexes of metal porphyrins with titanium and iron halides that are insoluble in hydrocarbon systems, with further extraction of these complexes, destruction, and regeneration of metal porphyrins. This method is advantageous because of complete extraction of metal porphyrins when they are contained in trace concentrations.

The second group of methods currently used to extract porphyrins from oil is based on treating oils and oil components with strong acids. When using acids in order to extract oil porphyrins, metal porphyrins are demetaled and transformed into acid phase.

As demetaling agents, acids are used, such as sulfuric [5] and sulfonic acids [6]. A disadvantage of extracting oil porphyrins by using acids is partial destruction of porphyrins (40–80%) and inability to separately measure the concentration and study metal porphyrin complexes of vanadyl and nickel. Acid extraction is also inefficient for oils having low concentration of porphyrins. The advantages of porphyrin extraction with acids include low labor input and an opportunity to directly produce relatively clean concentrates of porphyrin compounds.

The third group includes extraction methods by using solvents that cannot be mixed with oil, with further extract treatment. Extraction methods employing selective solvents are advantageous for soft process conditions, which completely present any chemical transformations. Methanol [7] and N,N-dimethylformamide (DMF) [8] are used as solvents for extraction of metal porphyrins.

The concentration of porphyrins in extracts obtained by any of the above methods allows using them for further analysis, but in some cases, additional treatment of concentrates is needed by means of column chromatography. To identify and measure the concentrations of oil porphyrins, visible and UV-band spectroscopy is used due to three characteristics of absorption bands [9]. The most intensive absorption band also referred to as the Soret band is located at the boundary between the visible and the UV area at 400 nm. Other two bands referred to as α and β bands are located in the area of 570 and 535 nm for vanadyl porphyrins and 575 and 540 nm for nickel porphyrins.

As compared with metal porphyrins, electronic absorption spectra of metal-free porphyrin carry much information on the structure. There are four main spectral types of oil porphyrins differing in the absorption peak intensity at 500, 535, 565, and 620 nm (bands IV, III, II, and I, respectively) [10]. This property is associated with the effects of substitutes at the porphyrin ring periphery. Each of the types is represented with a mixture of various porphyrins differing in the nature and position of substitution (**Figure 1**).

Another informative method to determine the structure of metal porphyrins is mass-spectrometry [11]. Metal porphyrins are present in oil in the form of a continuous series. Most common of them are porphyrins with alkyl substitutes called etioporphyrins (ETIO) with the molecular weight of 375 + 12n (M), and metal porphyrins containing an isocyclic ring, also called deoxophylloerythroetio porphyrins (DPEP) with the molecular weight of 373 + 12n (M-2) [12]. Their ratio in oil is the most important geochemical parameter showing the maturity of oil [13]. Other series (M-2, M-4 …) are present in oil in significantly lower concentrations and are called minor.

To study the concentrates of oil metal porphyrins other methods can be used, such as EPR spectroscopy [14, 15], LDI mass-spectrometry [16], Fourier transform ion cyclotron resonance mass spectrometry [17], and high definition inductively coupled plasma mass spectrometry [18].

Metal porphyrins in oils have a negative effect on catalysts of oil refining processes [19, 20], so currently, oil demetallization methods are used and developed [21–23]. Effective development of methods to remove vanadium and nickel from oil is impossible without having information on the structure and properties of metal porphyrins. Since the complete extraction of oil metal porphyrins from oil objects is complicated due to strong associations with asphaltene molecules, this may cause insufficiently full study of metal porphyrins. This chapter gives a new approach to the extraction of metal porphyrins from asphaltenes and heavy petroleum residues (HPR), which allows increasing the degree of extraction, and it also presents the results obtained in determining the composition and properties of concentrates obtained.

**Figure 1.** Spectral types of porphyrins.

structure of pseudo-porphyrin complexes is still not defined. The paper also reports of oil being

The analysis of oil porphyrins in oils and their components by various instrumental methods is impossible due to their low concentration, so usually, fractions enriched with metal porphyrins are used for analysis. All concentration methods for oil porphyrins can be condition-

• Complex formation, chemical adsorption, and ion-exchanging chromatography when sufficiently labile chemical bonding is formed between various compounds and oil porphyrins. • Chemical interaction between various compounds and oil components accompanied by

• Extraction, separation, and sedimentation by solvents based on various solvability of indi-

For light oils having a relatively low concentration of asphaltene-resin substances, the first group of methods is mostly suitable for extraction of oil porphyrins: complex formation with Lewis acids usually represented by waterless metal halides [1]. This method consists in the formation of molecular complexes of metal porphyrins with titanium and iron halides that are insoluble in hydrocarbon systems, with further extraction of these complexes, destruction, and regeneration of metal porphyrins. This method is advantageous because of complete

The second group of methods currently used to extract porphyrins from oil is based on treating oils and oil components with strong acids. When using acids in order to extract oil por-

As demetaling agents, acids are used, such as sulfuric [5] and sulfonic acids [6]. A disadvantage of extracting oil porphyrins by using acids is partial destruction of porphyrins (40–80%) and inability to separately measure the concentration and study metal porphyrin complexes of vanadyl and nickel. Acid extraction is also inefficient for oils having low concentration of porphyrins. The advantages of porphyrin extraction with acids include low labor input and an opportunity to directly produce relatively clean concentrates of porphyrin compounds.

The third group includes extraction methods by using solvents that cannot be mixed with oil, with further extract treatment. Extraction methods employing selective solvents are advantageous for soft process conditions, which completely present any chemical transformations. Methanol [7] and N,N-dimethylformamide (DMF) [8] are used as solvents for extraction of

The concentration of porphyrins in extracts obtained by any of the above methods allows using them for further analysis, but in some cases, additional treatment of concentrates is needed by means of column chromatography. To identify and measure the concentrations of oil porphyrins, visible and UV-band spectroscopy is used due to three characteristics of absorption bands [9]. The most intensive absorption band also referred to as the Soret band is located at the boundary between the visible and the UV area at 400 nm. Other two bands

extraction of metal porphyrins when they are contained in trace concentrations.

phyrins, metal porphyrins are demetaled and transformed into acid phase.

present in insignificant amounts in iron and copper porphyrins [4].

new chemically stable compounds being formed.

vidual compounds in various solvents.

ally divided into three groups:

154 Phthalocyanines and Some Current Applications

metal porphyrins.
