226
The Chemistry and Technology of Petroleum
The only drawback to this particular scheme appears to be the use of hexane as the precipitating
medium. Use of this solvent does not completely precipitate the asphaltenes in a sample and perhaps
the fraction designated hard resins may contain considerable portions of asphaltenes.
A fractionation procedure was also devised using n-butanol and acetone as the solvents and
consists of (1) separation of an asphaltic fraction by n-butanol, and (2) separation of the butanol-soluble portion into a paraffinic fraction and a cyclics fraction by chilling an acetone solution of the two, but it has the unfortunate result that all three fractions obtained may contain
asphaltenes. It is difficult to compare the method with any other or even establish any correlation
with previous experience. Even precipitation of the asphaltenes with n-pentane and subtracting
the asphaltenes from the asphaltic, arriving at a fourth fraction (asphaltic resins), did not appear
to correct the faults of the method since the asphaltic fraction does not contain all the asphaltenes
of the specimen.
Another method of fractionation consisted of stepwise separation into the following fractions:
1. Asphaltene constituents, precipitated by n-pentane
2. Resin constituents, precipitated with propane and subdivided by fractionation with aniline
into soft resins and hard resins
3. Wax constituents, precipitated with methyl iso-butyl ketone
4. Oil constituents, remaining fraction separated with acetone into paraffinic oils and naphthenic oils
A strong feature of this method is the subdivision of the resins fraction by solubility in aniline and
the subdivision of the paraffinic fraction into the three components: wax, paraffinic oils, and naphthenic oils.
It is unfortunate that, with the exception of asphaltene precipitation, no standard method exists
for the fractionation of crude oil, residua, bitumen, by solvent treatment. The procedures described
here each have their own individual merits, but there has not been any serious effort to apply these
methods to a wide variety of carbonaceous liquids to assess their general applicability. Fractionation
by means of solvents alone (perhaps with the exception of propane, which requires pressure equipment) would be convenient indeed, provided that facile separation of the solvent and the products
could be achieved at a later stage.
Another all-solvent procedure involves the use of acetone, which discharges a resin fraction, and
dimethylformamide, which then discharges a saturates fraction.
The use of all-solvent methods for the separation of petroleum allows the fractionation of
feedstocks to be achieved without loss of material (on the adsorbent) and produces fractions of
varying polarity (Speight, 1989). The obvious benefit of the all-solvent techniques is the complete
recovery of material, thereby allowing a more quantitative and qualitative examination of the
feedstocks.
The disadvantages of an all-solvent separation technique are that, first, in some instances, low
temperatures (e.g., 0°C to −10°C and the like) are advocated as a means of effecting oil fractionation
with solvents (Speight, 1979). Such requirements may cause inconvenience in a typical laboratory
operation by requiring a permanently cool temperature during the separation. Second, it must be
recognized that large volumes of solvent may be required to effect a reproducible separation in the
same manner as the amounts required for consistent asphaltene separation (ASTM D2006, ASTM
D2007, ASTM D4124, ASTM D893, IP 143). Finally, it is also essential that the solvent be of sufficiently low boiling point so that complete removal of the solvent from the product fraction can
be effected. Although not specifically included in the three main disadvantages of the all-solvent
approach, it should also be recognized that the solvent must not react with the feedstock constituents. In addition, caution is still required to ensure that there is no interaction between the solvent
and the solute.
The Chemistry and Technology of Petroleum
The only drawback to this particular scheme appears to be the use of hexane as the precipitating
medium. Use of this solvent does not completely precipitate the asphaltenes in a sample and perhaps
the fraction designated hard resins may contain considerable portions of asphaltenes.
A fractionation procedure was also devised using n-butanol and acetone as the solvents and
consists of (1) separation of an asphaltic fraction by n-butanol, and (2) separation of the butanol-soluble portion into a paraffinic fraction and a cyclics fraction by chilling an acetone solution of the two, but it has the unfortunate result that all three fractions obtained may contain
asphaltenes. It is difficult to compare the method with any other or even establish any correlation
with previous experience. Even precipitation of the asphaltenes with n-pentane and subtracting
the asphaltenes from the asphaltic, arriving at a fourth fraction (asphaltic resins), did not appear
to correct the faults of the method since the asphaltic fraction does not contain all the asphaltenes
of the specimen.
Another method of fractionation consisted of stepwise separation into the following fractions:
1. Asphaltene constituents, precipitated by n-pentane
2. Resin constituents, precipitated with propane and subdivided by fractionation with aniline
into soft resins and hard resins
3. Wax constituents, precipitated with methyl iso-butyl ketone
4. Oil constituents, remaining fraction separated with acetone into paraffinic oils and naphthenic oils
A strong feature of this method is the subdivision of the resins fraction by solubility in aniline and
the subdivision of the paraffinic fraction into the three components: wax, paraffinic oils, and naphthenic oils.
It is unfortunate that, with the exception of asphaltene precipitation, no standard method exists
for the fractionation of crude oil, residua, bitumen, by solvent treatment. The procedures described
here each have their own individual merits, but there has not been any serious effort to apply these
methods to a wide variety of carbonaceous liquids to assess their general applicability. Fractionation
by means of solvents alone (perhaps with the exception of propane, which requires pressure equipment) would be convenient indeed, provided that facile separation of the solvent and the products
could be achieved at a later stage.
Another all-solvent procedure involves the use of acetone, which discharges a resin fraction, and
dimethylformamide, which then discharges a saturates fraction.
The use of all-solvent methods for the separation of petroleum allows the fractionation of
feedstocks to be achieved without loss of material (on the adsorbent) and produces fractions of
varying polarity (Speight, 1989). The obvious benefit of the all-solvent techniques is the complete
recovery of material, thereby allowing a more quantitative and qualitative examination of the
feedstocks.
The disadvantages of an all-solvent separation technique are that, first, in some instances, low
temperatures (e.g., 0°C to −10°C and the like) are advocated as a means of effecting oil fractionation
with solvents (Speight, 1979). Such requirements may cause inconvenience in a typical laboratory
operation by requiring a permanently cool temperature during the separation. Second, it must be
recognized that large volumes of solvent may be required to effect a reproducible separation in the
same manner as the amounts required for consistent asphaltene separation (ASTM D2006, ASTM
D2007, ASTM D4124, ASTM D893, IP 143). Finally, it is also essential that the solvent be of sufficiently low boiling point so that complete removal of the solvent from the product fraction can
be effected. Although not specifically included in the three main disadvantages of the all-solvent
approach, it should also be recognized that the solvent must not react with the feedstock constituents. In addition, caution is still required to ensure that there is no interaction between the solvent
and the solute.