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Chemical Composition
8.3.2.4 Metallic Constituents
Metallic constituents are found in every crude oil and the concentrations have to be reduced to
convert the oil to transportation fuel. Metals affect many upgrading processes and cause particular
problems because they poison catalysts used for sulfur and nitrogen removal as well as other processes such as catalytic cracking.
The trace metals Ni and V are generally orders of magnitude higher than other metals in petroleum, except when contaminated with coproduced brine salts (Na, Mg, Ca, and Cl) or corrosion
products gathered in transportation (Fe).
The occurrence of metallic constituents in crude oil is of considerably greater interest to the
petroleum industry than might be expected from the very small amounts present. Even minute
amounts of iron, copper, and particularly nickel and vanadium in the charging stocks for catalytic cracking affect the activity of the catalyst and result in increased gas and coke formation and
reduced yields of gasoline. In high-temperature power generators, such as oil-fired gas turbines, the
presence of metallic constituents, particularly vanadium in the fuel, may lead to ash deposits on the
turbine rotors, thus reducing clearances and disturbing their balance. More particularly, damage by
corrosion may be very severe. The ash resulting from the combustion of fuels containing sodium
and especially vanadium reacts with refractory furnace linings to lower their fusion points and so
cause their deterioration.
Thus, the ash residue left after burning of a crude oil is due to the presence of these metallic
constituents, part of which occurs as inorganic water-soluble salts (mainly chlorides and sulfates of
sodium, potassium, magnesium, and calcium) in the water phase of crude oil emulsions. These are
removed in the desalting operations, either by evaporation of the water and subsequent water washing or by breaking the emulsion, thereby causing the original mineral content of the crude to be substantially reduced. Other metals are present in the form of oil-soluble organometallic compounds as
complexes, metallic soaps, or in the form of colloidal suspensions, and the total ash from desalted
crude oils is of the order of 0.1–100 mg/L. Metals are generally found only in the nonvolatile portion
of crude oil (Altgelt and Boduszynski, 1994; Reynolds, 1998).
Two groups of elements appear in significant concentrations in the original crude oil associated
with well-defined types of compounds. Zinc, titanium, calcium, and magnesium appear in the form
of organometallic soaps with surface-active properties adsorbed in the water/oil interfaces and act
as emulsion stabilizers. However, vanadium, copper, nickel, and part of the iron found in crude oils
seem to be in a different class and are present as oil-soluble compounds. These metals are capable
of complexing with pyrrole pigment compounds derived from chlorophyll and hemoglobin and are
almost certain to have been present in plant and animal source materials. It is easy to surmise that
the metals in question are present in such form, ending in the ash content. Evidence for the presence
of several other metals in oil-soluble form has been produced, and thus zinc, titanium, calcium,
and magnesium compounds have been identified in addition to vanadium, nickel, iron, and copper.
Examination of the analyses of a number of crude oil for iron, nickel, vanadium, and copper indicates a relatively high vanadium content, which usually exceeds that of nickel, although the reverse
can also occur.
Distillation concentrates the metallic constituents in the residues (Reynolds, 1998), although
some can appear in the higher boiling distillates, but the latter may be due in part 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 of overhead obtained by vacuum distillation of a 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 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.
Chemical Composition
8.3.2.4 Metallic Constituents
Metallic constituents are found in every crude oil and the concentrations have to be reduced to
convert the oil to transportation fuel. Metals affect many upgrading processes and cause particular
problems because they poison catalysts used for sulfur and nitrogen removal as well as other processes such as catalytic cracking.
The trace metals Ni and V are generally orders of magnitude higher than other metals in petroleum, except when contaminated with coproduced brine salts (Na, Mg, Ca, and Cl) or corrosion
products gathered in transportation (Fe).
The occurrence of metallic constituents in crude oil is of considerably greater interest to the
petroleum industry than might be expected from the very small amounts present. Even minute
amounts of iron, copper, and particularly nickel and vanadium in the charging stocks for catalytic cracking affect the activity of the catalyst and result in increased gas and coke formation and
reduced yields of gasoline. In high-temperature power generators, such as oil-fired gas turbines, the
presence of metallic constituents, particularly vanadium in the fuel, may lead to ash deposits on the
turbine rotors, thus reducing clearances and disturbing their balance. More particularly, damage by
corrosion may be very severe. The ash resulting from the combustion of fuels containing sodium
and especially vanadium reacts with refractory furnace linings to lower their fusion points and so
cause their deterioration.
Thus, the ash residue left after burning of a crude oil is due to the presence of these metallic
constituents, part of which occurs as inorganic water-soluble salts (mainly chlorides and sulfates of
sodium, potassium, magnesium, and calcium) in the water phase of crude oil emulsions. These are
removed in the desalting operations, either by evaporation of the water and subsequent water washing or by breaking the emulsion, thereby causing the original mineral content of the crude to be substantially reduced. Other metals are present in the form of oil-soluble organometallic compounds as
complexes, metallic soaps, or in the form of colloidal suspensions, and the total ash from desalted
crude oils is of the order of 0.1–100 mg/L. Metals are generally found only in the nonvolatile portion
of crude oil (Altgelt and Boduszynski, 1994; Reynolds, 1998).
Two groups of elements appear in significant concentrations in the original crude oil associated
with well-defined types of compounds. Zinc, titanium, calcium, and magnesium appear in the form
of organometallic soaps with surface-active properties adsorbed in the water/oil interfaces and act
as emulsion stabilizers. However, vanadium, copper, nickel, and part of the iron found in crude oils
seem to be in a different class and are present as oil-soluble compounds. These metals are capable
of complexing with pyrrole pigment compounds derived from chlorophyll and hemoglobin and are
almost certain to have been present in plant and animal source materials. It is easy to surmise that
the metals in question are present in such form, ending in the ash content. Evidence for the presence
of several other metals in oil-soluble form has been produced, and thus zinc, titanium, calcium,
and magnesium compounds have been identified in addition to vanadium, nickel, iron, and copper.
Examination of the analyses of a number of crude oil for iron, nickel, vanadium, and copper indicates a relatively high vanadium content, which usually exceeds that of nickel, although the reverse
can also occur.
Distillation concentrates the metallic constituents in the residues (Reynolds, 1998), although
some can appear in the higher boiling distillates, but the latter may be due in part 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 of overhead obtained by vacuum distillation of a 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 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.