547
Solvent Processes
to molecular weight but also to molecular type. In any crude oil residue, the lowest boiling and most
paraffinic components are those most soluble in the light paraffinic solvent.
20.2.2 oPtIons For HeAvy FeedstoCks
Solvent deasphalting is a separation process that represents a further step in the minimization
of residual by-product fuel. However, SDA processes, far from realizing their maximum potential for heavy feedstocks, are now under further investigation and, with on-going improvements
in energy efficiency, such processes are starting to display maximum benefits when used in
combination with other processes. The process takes advantage of the fact that the maltene
constituents are more soluble in light paraffinic solvents than asphaltene constituents. This
solubility increases with solvent molecular weight and decreases with temperature (Girdler,
1965). As with vacuum distillation, there are constraints with respect to how deep a SDA unit
can cut into the residue or how much DAO can be produced. In the case of SDA, the constraint
is usually related to DAO quality specifications required by downstream conversion units.
However, SDA has the flexibility to produce a wide range of DAO that matches the desired properties. The process has very good selectivity for asphaltene constituents (and, to a lesser extent, resin
constituents) as well as metals rejection. There is also some selectivity for rejection carbon residue
precursors, but there is less selectivity for sulfur-containing and nitrogen-containing constituents.
The process is best suited for the more paraffinic vacuum residua with a somewhat lower efficiency
when applied to high-asphaltene residua that contain high proportions of metals and coke forming
constituents. The advantages and disadvantages of the process are that it performs no conversion
and produces a very high-viscosity by-product deasphalter bottoms and, where high-quality DAO is
required, the process is limited in the quality of feedstock that can be economically processed. In
those situations, where there is a ready outlet r use for the bottoms, SDA is an attractive option for
treating heavy feedstocks. One such situation is the cogeneration of steam and power, both to supply
the refiner’s needs and for export to nearby users.
20.2.2.1 Deep Solvent Deasphalting Process
The deep solvent deasphalting process is an application of the LEDA (low-energy deasphalting)
process (Table 20.2; Figure 20.5; RAROP, 1991, p. 91) that is used to extract high-quality lubricating oil bright stock or prepare catalytic cracking feeds, hydrocracking feeds, hydrodesulfurization
unit feeds and asphalt from vacuum residue materials. The LEDA process uses a low-boiling
hydrocarbon solvent specifically formulated to insure the most economical deasphalting design
for each operation. For example, a propane solvent may be specified for a low DAO yield operation, while a higher boiling solvent, such as pentane or hexane, may be used to obtain a high DAO
yield from a vacuum residuum (Table 20.3). The deep deasphalting process can be integrated with
a delayed coking operation (ASCOT process; q.v.). In this case, the solvent can be low-boiling
naphtha (Table 20.4).
Low-energy deasphalting operations are usually carried out in a rotating disc contractor (RDC) that provides more extraction stages than a mixer-settler or baffle-type column.
Although not essential to the process, the RDC provides higher quality DAO at the same yield,
or higher yields at the same quality. The low-energy SDA process selectively extracts the more
paraffinic components from vacuum residua while rejecting the condensed ring aromatics. As
expected, DAO yields vary as a function of solvent type and quantity, and feedstock properties
(Figure 20.2).
In the process, vacuum residue feed is combined with a small quantity of solvent to reduce its
viscosity and cooled to a specific extraction temperature before entering the RDC. Recovered solvent from the high-pressure and low-pressure solvent receivers are combined, adjusted to a specific
temperature by the solvent heater–cooler, and injected into the bottom section of the RDC. Solvent
Solvent Processes
to molecular weight but also to molecular type. In any crude oil residue, the lowest boiling and most
paraffinic components are those most soluble in the light paraffinic solvent.
20.2.2 oPtIons For HeAvy FeedstoCks
Solvent deasphalting is a separation process that represents a further step in the minimization
of residual by-product fuel. However, SDA processes, far from realizing their maximum potential for heavy feedstocks, are now under further investigation and, with on-going improvements
in energy efficiency, such processes are starting to display maximum benefits when used in
combination with other processes. The process takes advantage of the fact that the maltene
constituents are more soluble in light paraffinic solvents than asphaltene constituents. This
solubility increases with solvent molecular weight and decreases with temperature (Girdler,
1965). As with vacuum distillation, there are constraints with respect to how deep a SDA unit
can cut into the residue or how much DAO can be produced. In the case of SDA, the constraint
is usually related to DAO quality specifications required by downstream conversion units.
However, SDA has the flexibility to produce a wide range of DAO that matches the desired properties. The process has very good selectivity for asphaltene constituents (and, to a lesser extent, resin
constituents) as well as metals rejection. There is also some selectivity for rejection carbon residue
precursors, but there is less selectivity for sulfur-containing and nitrogen-containing constituents.
The process is best suited for the more paraffinic vacuum residua with a somewhat lower efficiency
when applied to high-asphaltene residua that contain high proportions of metals and coke forming
constituents. The advantages and disadvantages of the process are that it performs no conversion
and produces a very high-viscosity by-product deasphalter bottoms and, where high-quality DAO is
required, the process is limited in the quality of feedstock that can be economically processed. In
those situations, where there is a ready outlet r use for the bottoms, SDA is an attractive option for
treating heavy feedstocks. One such situation is the cogeneration of steam and power, both to supply
the refiner’s needs and for export to nearby users.
20.2.2.1 Deep Solvent Deasphalting Process
The deep solvent deasphalting process is an application of the LEDA (low-energy deasphalting)
process (Table 20.2; Figure 20.5; RAROP, 1991, p. 91) that is used to extract high-quality lubricating oil bright stock or prepare catalytic cracking feeds, hydrocracking feeds, hydrodesulfurization
unit feeds and asphalt from vacuum residue materials. The LEDA process uses a low-boiling
hydrocarbon solvent specifically formulated to insure the most economical deasphalting design
for each operation. For example, a propane solvent may be specified for a low DAO yield operation, while a higher boiling solvent, such as pentane or hexane, may be used to obtain a high DAO
yield from a vacuum residuum (Table 20.3). The deep deasphalting process can be integrated with
a delayed coking operation (ASCOT process; q.v.). In this case, the solvent can be low-boiling
naphtha (Table 20.4).
Low-energy deasphalting operations are usually carried out in a rotating disc contractor (RDC) that provides more extraction stages than a mixer-settler or baffle-type column.
Although not essential to the process, the RDC provides higher quality DAO at the same yield,
or higher yields at the same quality. The low-energy SDA process selectively extracts the more
paraffinic components from vacuum residua while rejecting the condensed ring aromatics. As
expected, DAO yields vary as a function of solvent type and quantity, and feedstock properties
(Figure 20.2).
In the process, vacuum residue feed is combined with a small quantity of solvent to reduce its
viscosity and cooled to a specific extraction temperature before entering the RDC. Recovered solvent from the high-pressure and low-pressure solvent receivers are combined, adjusted to a specific
temperature by the solvent heater–cooler, and injected into the bottom section of the RDC. Solvent