Porphyrins in crude oils

The detection of vanadium, nickel, and porphyrins in crude oils were analyzed by high-temperature gas chromatography-atomic emission spectroscopy (HT-GC-AES), presenting characteristic metal distribu-... 

Quimby, B.D, Diyden, P.C. Sullivan, J.J. (1991), A selective detection of volatile nickel, vanadium and iron porphyrins in crude oils by gas chromatography atomic emission spectroscopy, /. High Res. Chromatogr., 14,110-116. 

Spectroscopic and chemical studies of vanadyl OEP have been reported, including m 50-substitution to form nitro-, chloro-, and benzoyloxy-derivatives trans-alkylation occurs when the vanadyl porphyrin is heated on clay and other supports, thus providing a model for the generation of homologous polyalkyl-porphyrins in crude oil and bitumen. m sa-Tetraferrocenyl-porphyrin and its copper complex have been prepared, and spectroscopic and other studies carried out on mixed-valence oxidation products, as models for the study of thermal electron-transfer processes in cytochrome-c. X-Ray crystal structures have been reported for diaquo and perchlorate complexes of Fe" TPP, " dichloro-molybdenum complexes of OEP and TPP, and for the bis-[(R5)-l-phenyl-ethylamine] complex " of Co TPP. Oxomolybdenum complexes TPP-... 

Many metals occur in crude oils. Some of the more abundant are sodium, calcium, magnesium, aluminium, iron, vanadium, and nickel. They are present either as inorganic salts, such as sodium and magnesium chlorides, or in the form of organometallic compounds, such as those of nickel and vanadium (as in porphyrins). Calcium and magnesium can form salts or soaps with carboxylic acids. These compounds act as emulsifiers, and their presence is undesirable. 

The presence of vanadium and nickel in crude oils, especially as metal porphyrin complexes, has focused much attention in the petroleum refining industry on the occurrence of these metals in feedstocks (Reynolds, 1997). Only a part of the total nickel and vanadium in crude oil is recognized to occur in porphyrin structures (Table 3-5). In general, it is assumed that about 10% w/w of the total metal in a crude oil is accommodated as porphyrin complexes although as much as 40% of the vanadium and nickel may be present as metal porphyrin complexes in petroleum. 

Vanadium is present in crudes mainly in the +4 state (58). In fact, up to 50% of the total vanadium in crude oil can be found as V02+ in organometallic compounds such as porphyrins and naphthenates (59-63). During the cracking reaction in a FCCU, these compounds deposit V (probably in the form of VO+2 cations) on the catalyst surface. Then, after steam-stripping and catalyst regeneration, formation of V+5 surface phases occur. The effects of vanadium on FCC properties are more severe than any of the other metals present in petroleum feedstocks. In fact, vanadium causes an irreversible loss of cracking activity which is the result of a decrease in crystallinity, pore volume and surface area of the catalyst, Figure 5. 

In this paper, we present the results of an experimental study on the phase behavior of well-characterized binary mixtures which represent the more complex mixtures that arise in SCF extractions of petroleum residua and coal liquids. These binary mixtures consist of pentane and toluene with meso-tetraphenylporphyrin (TPP). Porphyrins occur naturally in crude oils (11,12) and represent an important class of high molecular-weight constituents of these oils, including those which contain heavy metals, such as nickel and vanadium. 

AAA-alumina (75% Si02/25% AI2O3 aluminosilicate gel provided by Davison) was used without further pretreatment. Benzene solutions of either vanadyl porphyrin (5, 10, 15, 20-tetraphenyl-21H, 23H-porphine vanadium oxide) or vanadyl naphthenate were impregnated by incipient wetness onto the EuY or the gel to generate a loading of 1.0 wt % vanadium. Vanadyl naphthenate has been widely utilized as a model V-contaminant and metalloporphyrins have been identified as metallic species in crude oil (29-30). The solvent was removed under... 

The presence of this and other materials presents potential problems in industrial processing, and there is great interest in characterization of the chemical nature of the vanadium species present. EPR is most widely used in these studies since the metal is in the oxo-vanadium(IV) state. Optical spectroscopy in the visible region can also be used on extracts since oxo-vanadium(IV) porphyrins, which absorb at around 572 nm and 534 nm 116,119), can readily be detected. However, it has been shown (120-122) that the total amount of vanadium present in crude oils and tar sand bitumen is higher than can be accounted for by the presence of oxo-vanadium(IV) porphyrins. It has therefore been suggested that the vanadyl may be bound to a range of different tetra-dentate ligands in crude oils (120-123). 

The amazing richness of vanadium complexes in crude oil and shale raises the obvious questions of where these vanadium complexes come from and what their biogenic source is. It is generally believed that the vanadium porphyrins result from the incorporation of vanadium in porphyrin structures originating from chlorophyll. (The reader is re-... 

Petroleum always contains nitrogen, sulphur and phosphorous in the form of organic compounds like porphyrin. Porphyrins are formed from the green coloring matter (chlorophyll), or from the red coloring matter (hemin) of blood. They occur in crude oil as complex hydrocarbons which oxidize readily. 

In crude oil, the vegetable porphyrins are more abundant than the animal porphyrins. Bays, gulfs, coastal lagoons, enclosed seas and submarine basins with poor water circulation would enable petroleum deposits to form. 

The heavy metals in crude oil residues are agglomerated, first of all, in asphaltenes in the form of porphyrin compounds. One example of this compound is presented in Figure 8.2 ... 

Neither of these metalloporphyrins has been found in crude oil, however. Mercury forms porphyrin complexes with mesoporphyrin but the complexes are decomposed by water. The extraction of crude oil C-1 with distilled water removed insignificant amounts of Hg, thus indicating that Hg is not present in the oil as a porphyrin complex. Arsenic also shows a higher concentration in the low-molecular-weight fraction than in the 1000-4000 fraction. This is consistent with the previous conclusion that part of the As in crude oil is present in low-molecular-weight compounds such as alkyl or aryl arsines. 

The association of the typical porphyrin absorption spectra with high-molecular-weight compounds in crude oil has led to the assiamption that... 

The porphyrin metallo complexes in crude oils, asphaltenes and other natural bitumens are chiefly those of vanadium and nickel although copper, iron and even uranium have been suggested. Recently in a Precambrian shale, porphins were found to chelate with iron, zinc and copper in addition to vanadium and nickel.The origin of these complexes is still uncertain, although several theories have been advanced. Some of these theories could be verified or possibly even disproved if the porphyrin type bound to each metal was known. Furthermore, since these heavy metals are harmful to both health and catalysts, a systematic study of demetallation of metalloporphyrins should prove useful. 

Among the porphyrins encountered in the crude oils, etioporphyrins (etio) and dexophylloerithroetioporphyrin (DPEP), and their homologues are more frequently observed (Baker and Louda, 1988), (Barwise and Roberts, 1984). The complexity of porphyrin mixtures have made the isolation of these pigments difficult, but the improved chromatographic and spectroscopic techniques have made possible the separation and identification of a number of metalloporphyrins (Les Ebdon et al.,1994). The identification of Ni and V porphyrin was quite earlier (Treibs et al., 1936) but the organic forms of other metals in crude oils was achieved only later, with the advent of hyphenated techniques, e.g. HPLC or GC coupled to AAS or ICP-MS for elemental detection. The porphyrins of Co, Cr, Ti and Zn were identified in oil shales by HPLC-ICP-MS (Les Ebdon et al.,1994). 

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