Asphaltene nickel

In the heaviest fractions such as resins and asphaltenes (see article 1.2), metal atoms such as nickel and vanadium are found. They belong in part to molecules in the porphyrine family where the basic pattern is represented by four pyrrolic rings, the metal being at the center of this complex in the form Wi - or V0+ (< 3)... 

Asphaltenes have high concentrations of heteroelements sulfur, nitrogen, nickel and vanadium. Their content varies widely in petroleum oils (Table 1.5). They cause a number of problems throughout the petroleum industry. 

Physical methods of fractionation of tar sand bitumen usually indicate high proportions of nonvolatile asphaltenes and resins, even in amounts up to 50% wt/wt (or higher) of the bitumen. In addition, the presence of ash-forming metallic constituents, including such organometaUic compounds as those of vanadium and nickel, is also a distinguishing feature of bitumen. 

The presence of asphaltenes, originating in the fuel, acts as a trap for vanadium, nickel, and sodium (which promote slagging and sulfur corrosion)-, these asphalthenes often contain sulfur compounds, which simply add to the contaminant load. Additionally, asphaltenes act as precursors to spherical stack solids (cenospheres), which are exhausted with the flue gases as stack emissions. 

An additional mechanism affects the deposits formation from the H-Oil reactor, rejection of vanadium and nickel sulfides from the catalyst. In the vacuum tower, asphaltene precipitation was found to be the prevalent fouling mechanism. In asphaltene... 

Mogollon, L. Rodriguez, R. Larrota, W., et al., Biocatalytic removal of nickel and vanadium from petroporphyrins and asphaltenes. Appl Biochem Biotechnol, 1998. 70-72 pp. 765-777. 

Another current development in the use of F-T chemistry in a three-phase slurry reactor is Exxon s Advanced Gas Conversion or AGC-21 technology (Eidt et al., 1994 Everett et al., 1995). The slurry reactor is the second stage of a three-step process to convert natural gas into a highly paraffinic water-clear hydrocarbon liquid. The AGC-21 technology, as in the Sasol process, is being developed to utilize the large reserves of natural gas that are too remote for economical transportation via pipelines. The converted liquid from the three-step process, which is free of sulfur, nitrogen, nickel, vanadium, asphaltenes, polycyclic aromatics, and salt, can be shipped in conventional oil tankers and utilized by most refineries or petrochemical facilities. 

Brunnock et al. [67] have also determined beach pollutants. They showed that weathered crude oil, crude oil sludge, and fuel oil can be differentiated by the n-paraffin profile as shown by gas chromatography, wax content, wax melting point, and asphaltene content. The effects of weathering at sea on crude oil were studied parameters unaffected by evaporation and exposure are the contents of vanadium, nickel, and n-paraffins. The scheme developed for the identification of certain weathered crude oils includes the determination of these constituents, together with the sulfur content of the sample. 

In Section II, the nature of the metal compounds in petroleum oils is discussed to establish a basic understanding of the targeted reactants. The chemical composition of the host petroleum and residuum is described, including a discussion of the two classes of metal compounds (1) metal-loporphyrins and (2) nonporphyrin metals. The troublesome asphaltenes will also be described. Comparison is made between the characteristics of vanadium and nickel complexes and their distribution in residua. 

Nickel and vanadium in petroleum exist as soluble organometallic complexes that fall into two categories metal porphyrins and nonporphyrin metal complexes. Both the porphyrins and the nonporphyrins may be distributed over a wide boiling range (350-650°C+), reflecting significant variations in molecular weight, structure, and polarity. Metal porphyrins and nonporphyrin metal complexes also tend to precipitate as part of the asphaltene materia] to an extent that varies with the source of the crude oil. 

Crude oil origin Asphaltenes (wt. %)d Nickel Vanadium Iron... 

A spectrum of metal compound reactivities in petroleum could arise for several reasons. Nickel and vanadium exist in a diversity of chemical environments. These can be categorized into porphyrinic and non-porphyrinic species vanadyl and nonvanadyl or associated with large asphaltenic groups and small, isolated metal-containing molecules. Each can be characterized by unique intrinsic reactivity. Reaction inhibition which occurs between the asphaltenes and the nonasphaltenes, as well as between Ni and V species, can also contribute to reactivity distributions. The parallel reaction interpretation of the observed reaction order discrepancy is therefore compatible with the multicomponent nature of petroleum. Data obtained at low conversion could appear as first order and only at higher conversions would higher-order effects become obvious. The... 

Vanadyl and nickel reactivity differences resulting from the chemistry of the oxygen ligand on vanadium were discussed in Section IV,A,l,c. Enhanced V reactivity could also arise from molecular size constraints. Beuther and co-workers (Beuther and Schmid, 1963 Larson and Beuther, 1966) speculate that nickel concentrates in the interior of asphaltene micelles while vanadium concentrates on the exterior. Thus a combination of stronger adsorption due to the oxygen ligand and inhibition of Ni reaction, coupled with the exposed position at the periphery of the asphaltene, may all contribute to the enhanced vanadium reactivity relative to nickel. 

A linear relationship is often observed between vanadium removal and sulfur removal, whereas the relationship between nickel and sulfur removal is linear but of smaller slope (Massagutov et al., 1967). For asphaltene-containing stocks, this phenomenon is interpreted on the basis of heteroatom distribution within the asphaltene micelles (Beuther and Schmid, 1963). Sulfur and vanadium are concentrated on the exterior, whereas nickel is concentrated in the interior. Conversion of the asphaltene generally leads to simultaneous removal of sulfur and vanadium, whereas nickel removal is more difficult. 

The distinguishing features of resid feedstocks are (1) the presence of asphaltenes or pentane-insolubles, (2) high carbon residues, (3) the presence of metals, mainly nickel and vanadium, and (4) unknown endpoints insofar as boiling range is concerned. 

The removal of metals with the asphaltenic sulfur is observed in Figure 4. This response is consistent with an asphaltene model in which vanadium and nickel are buried as porphyrins or sandwich compounds (9). The slightly higher removal of vanadium reflects a general tendency for vanadium to deposit on the catalyst more readily than nickel. 

Metals distribution, which in some degree should relate to asphaltene distribution, are shown for the actual equilibration temperatures in Table IX. Nickel showed the expected enrichment at all temperatures. Vanadium responded similarly except at 403 and 603°F. Progressive sulfiding (0.6, 0.7, 1.4% S) and coke lay-down (0.8, 1.5, 7.8% C) were observed for the used catalysts and hence represent an experiment complication. 

Asphaltenic sulfur is the most refractory specie in re-sids and the removal of metals, particularly nickel, correlates well with removal of asphaltenic sulfur. 

The exclusion of asphaltenes is matched by the distribution of nickel inside and outside the catalyst pore structure. Vanadium distribution is inconsistent, probably influenced by coke deposition at the higher temperatures. 

Distillation concentrates the metallic constituents in the residua (Table 3-5) some can appear in the higher-boiling distillates but the latter may, in part, be due to entrainment. Nevertheless, there is evidence that a portion of the metallic constituents may occur in the distillates by volatilization of the organometallic compounds present in the petroleum. In fact, as the percentage overhead obtained by vacuum distillation of reduced crude is increased, the amount of metallic constituents in the overhead oil is also increased. The majority of the vanadium, nickel, iron, and copper in residual stocks may be precipitated along with the asphaltenes by low-boiling alkane hydrocarbon solvents. Thus, removal of the asphaltenes with n-pentane reduces the vanadium content of the oil by up to 95% with substantial reductions in the amounts of iron and nickel. 

Catalyst bed plugging can arise in a variety of ways, but the overall effect of bed plugging is always the same expensive shutdowns and possibly complete renewal of the expensive catalyst. Thus, the deposition of rust, coke, or metal salts (e.g., sodium chloride) from heavier and dirtier feedstock may all contribute to the plugging of a catalyst bed. Vanadium and nickel may also be deposited onto the surface of the catalyst as well as into the pore system. Asphaltene deposition from residua and heavy oils is also a potential means of bed plugging— coagulation of the asphaltenes becomes appreciable at temperatures above 420°C (790°F) with the formation of hard, coke-like materials on the catalyst. 

Such a sulfur-type polymer might also be expected to lose much of the sulfur by treatment with Raney nickel (36). However, these particular (Athabasca) asphaltenes are difficult to desulfurize with Raney nickel (26) as compared with a variety of aromatic/aliphatic thioether polymers of the... 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Samples. Table I lists the six residua studied and their sulfur, nickel, vanadium, and weight percent asphaltenes data. The Arabian Light is a vacuum (1000 + °F) residuum, while the other five are atmospheric (650 -f °F) residua. The samples were analyzed as received from the refinery distillation tower. 

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