331
Asphaltene Constituents
It is therefore apparent that asphaltene removal from a crude oil is greatly facilitated by addition
of reactive metal salts, which remove the necessity of handling large volumes of solvents and the
like as in the conventional deasphalting process. Although the precipitated asphaltene materials
contain substantial amounts (10%–20% and even up to 30% w/w) of organically bound chlorine,
this is nevertheless not a disadvantage, as other work has shown that these materials lend themselves
to a variety of uses, especially thermal decomposition to good grade coke.
Reactions of asphaltenes with sulfur have also received some attention and have yielded interesting
results. For example, treatment of the asphaltenes with oxygen or with sulfur at 150°C–250°C
(300°F–480°F) yields a condensed aromatic product [H/C = 0.97; H/C (asphaltenes) = 1.20] containing very little additional sulfur. The predominant reaction here appears to be condensation between
the aromatic and aliphatic moieties of the asphaltene constituents caused by elemental sulfur, which
are in turn converted to hydrogen sulfide. Condensation appears to proceed in preference to molecular degradation, and treatment of the condensed products at 200°C–300°C (390°F–570°F) for 1–5 h
again affords good grade cokes (H/C = 0.54–0.56). In all instances, the final products contain only
very low amounts of elements other than carbon and hydrogen (ΣNOS <5% w/w), a desirable property of good grade coke.
Attempts to phosphorylate asphaltenes with phosphoric acid, phosphorous trichloride, or phosphorous oxychloride have been partially successful insofar as it is possible to introduce up to 3%
w/w phosphorus into the asphaltenes. However, application of these same reactions to oxidized
asphaltenes increased the uptake of phosphorus quite markedly since there is up to 10% w/w in the
product. Subsequent reaction of the phosphorus-containing products is necessary to counteract the
acidity of the phosphorus functions.
Other reactions of asphaltenes have also been performed, but the emphasis has mainly been on
the formation of more condensed materials to produce good grade cokes. For example, thermal treatment of the halogenated derivatives affords aromatic cokes (H/C = 0.58; coke from the thermal
conversion of asphaltenes at ∼460°C [860°F] has H/C = 0.77) containing less than 1% w/w halogen.
Other investigations also show that treatment of the haloasphaltenes with suitable metal catalysts—
copper at 200°C–300°C (390°F–570°F) for 1–5 h or sodium at 80°C–100°C (175°F–212°F) for 1–5 h
yields aromatic (H/C = 0.55–0.86, respectively) coke-like materials having 0.5%–3% w/w halogen.
Residual halogen may finally be removed by treatment at 300°C (570°F) for 5 h.
Other chemical modifications include metallation of the asphaltenes or halo-asphaltenes
using metal or metallo-organics, followed by carboxylation to yield acid functions in the product. Interaction of the asphaltenes with m-dinitrobenzene affords a product that, when treated with
hydroxylamine (NH 2 OH) or an amine (RNH 2 ), yields nitrogen-enriched products.
Reaction of asphaltenes with maleic anhydride and subsequent hydrolysis also yields a product
bearing carboxylic acid functions. Asphaltenes react with diazo compounds and the procedure may
be used to introduce functional groups into the asphaltene molecule to modify the properties of
these materials.
12.6 SOLUBILITY PARAMETER
The solubility parameter (Table 12.2) is a measure of the ability of the compound to act as a solvent
or nonsolvent and as well as a measure the inter- and intramolecular forces between the solvent
molecule and between the solvent and solute molecules (Barton, 1991). The solubility parameter
is also a major parameter in certain petroleum products, especially in material such as residua and
asphalt (Redelius, 2000, 2004).
Any change in the physical and chemical properties of crude oil can be a key factor in the stability
of the system. For example, as the degree of conversion in a thermal process increases, the solubility
power of the medium toward the heavy and polar molecules decreases due to the formation of saturated products (Speight, 1994). This is reflected in a relative change in the solubility parameters of the
dispersed and solvent phases leading to a phase separation (Speight, 1992, 1994; Wiehe, 1993, 1994).
Asphaltene Constituents
It is therefore apparent that asphaltene removal from a crude oil is greatly facilitated by addition
of reactive metal salts, which remove the necessity of handling large volumes of solvents and the
like as in the conventional deasphalting process. Although the precipitated asphaltene materials
contain substantial amounts (10%–20% and even up to 30% w/w) of organically bound chlorine,
this is nevertheless not a disadvantage, as other work has shown that these materials lend themselves
to a variety of uses, especially thermal decomposition to good grade coke.
Reactions of asphaltenes with sulfur have also received some attention and have yielded interesting
results. For example, treatment of the asphaltenes with oxygen or with sulfur at 150°C–250°C
(300°F–480°F) yields a condensed aromatic product [H/C = 0.97; H/C (asphaltenes) = 1.20] containing very little additional sulfur. The predominant reaction here appears to be condensation between
the aromatic and aliphatic moieties of the asphaltene constituents caused by elemental sulfur, which
are in turn converted to hydrogen sulfide. Condensation appears to proceed in preference to molecular degradation, and treatment of the condensed products at 200°C–300°C (390°F–570°F) for 1–5 h
again affords good grade cokes (H/C = 0.54–0.56). In all instances, the final products contain only
very low amounts of elements other than carbon and hydrogen (ΣNOS <5% w/w), a desirable property of good grade coke.
Attempts to phosphorylate asphaltenes with phosphoric acid, phosphorous trichloride, or phosphorous oxychloride have been partially successful insofar as it is possible to introduce up to 3%
w/w phosphorus into the asphaltenes. However, application of these same reactions to oxidized
asphaltenes increased the uptake of phosphorus quite markedly since there is up to 10% w/w in the
product. Subsequent reaction of the phosphorus-containing products is necessary to counteract the
acidity of the phosphorus functions.
Other reactions of asphaltenes have also been performed, but the emphasis has mainly been on
the formation of more condensed materials to produce good grade cokes. For example, thermal treatment of the halogenated derivatives affords aromatic cokes (H/C = 0.58; coke from the thermal
conversion of asphaltenes at ∼460°C [860°F] has H/C = 0.77) containing less than 1% w/w halogen.
Other investigations also show that treatment of the haloasphaltenes with suitable metal catalysts—
copper at 200°C–300°C (390°F–570°F) for 1–5 h or sodium at 80°C–100°C (175°F–212°F) for 1–5 h
yields aromatic (H/C = 0.55–0.86, respectively) coke-like materials having 0.5%–3% w/w halogen.
Residual halogen may finally be removed by treatment at 300°C (570°F) for 5 h.
Other chemical modifications include metallation of the asphaltenes or halo-asphaltenes
using metal or metallo-organics, followed by carboxylation to yield acid functions in the product. Interaction of the asphaltenes with m-dinitrobenzene affords a product that, when treated with
hydroxylamine (NH 2 OH) or an amine (RNH 2 ), yields nitrogen-enriched products.
Reaction of asphaltenes with maleic anhydride and subsequent hydrolysis also yields a product
bearing carboxylic acid functions. Asphaltenes react with diazo compounds and the procedure may
be used to introduce functional groups into the asphaltene molecule to modify the properties of
these materials.
12.6 SOLUBILITY PARAMETER
The solubility parameter (Table 12.2) is a measure of the ability of the compound to act as a solvent
or nonsolvent and as well as a measure the inter- and intramolecular forces between the solvent
molecule and between the solvent and solute molecules (Barton, 1991). The solubility parameter
is also a major parameter in certain petroleum products, especially in material such as residua and
asphalt (Redelius, 2000, 2004).
Any change in the physical and chemical properties of crude oil can be a key factor in the stability
of the system. For example, as the degree of conversion in a thermal process increases, the solubility
power of the medium toward the heavy and polar molecules decreases due to the formation of saturated products (Speight, 1994). This is reflected in a relative change in the solubility parameters of the
dispersed and solvent phases leading to a phase separation (Speight, 1992, 1994; Wiehe, 1993, 1994).