Note: Descriptions are shown in the official language in which they were submitted.
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INTEGRATED SOLVENT DEASPHALTING AND
SLURRY HYDROCRACKING PROCESS
FIELD OF THE INVENTION
[0001] The present invention relates to methods for preparing distillate
hydrocarbons
using slurry hydrocracking (SHC) to upgrade high-boiling or heavy hydrocarbons
obtained
from refinery operations and particularly solvent deasphalting (SDA). The
integration of SHC
with SDA and optionally other processes such as crude oil fractionation and/or
hydrotreating
may be used to obtain a high quality (e.g., high API gravity and/or low
sulfur) distillate.
DESCRIPTION OF RELATED ART
[0002] Solvent deasphalting (SDA) generally refers to refinery processes that
upgrade
hydrocarbon fractions using an extraction process in the presence of a
solvent. The
hydrocarbon fractions are often obtained from the distillation of crude oil,
and include
hydrocarbon residues (or resids) or gas oils from atmospheric column or vacuum
column
distillation. Solvents used in SDA are typically lower-boiling paraffinic
hydrocarbons such as
propane, butane, and their mixtures, having the ability to extract a
deasphalted oil (DAO)
with relatively lower levels of contaminants such as sulfur- and nitrogen-
containing
compounds, metals, and Conradson carbon residue. The extraction usually occurs
in a
countercurrent extractor, with the solvent phase and its extracted components
flowing in an
upward direction. In addition to DAO, the other major product of SDA is pitch,
a highly
viscous hydrocarbon that contains significant portions of the (non-extracted)
contaminants
present in crude oil.
[0003] The yields and quality of both the DAO and pitch depend on the
composition of
the SDA feed, the type and amount of solvent, and the extraction conditions.
The DAO
produced from SDA is a generally nondistillable product requiring further
upgrading with
fluid catalytic cracking (FCC), hydrocracking, and/or hydrotreating.
Additionally, the
significant quantities of pitch from SDA make this process less economically
attractive
compared to alternative heavy oil conversion processes.
[0004] Further refinery process streams normally sent to conventional
conversion
processes such as FCC, in order to yield more salable products, include gas
oils and
particularly vacuum gas oil (VGO). VGO is produced in a number of refinery
operations,
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including slurry hydrocracking, coking, crude oil fractionation, and
visbreaking, which
process heavy hydrocarbon feedstocks. Because of their significant levels of
contaminants
(e.g., metals and sulfur compounds) that deactivate supported metal catalysts,
in addition to
coke precursors in these streams, gas oils are unfortunately not easily
processed according to
conventional catalytic conversion methods. The conversion of coker gas oils to
more salable
distillate and naphtha blending components for transportation fuels is
therefore associated
with a number of drawbacks.
[0005] Like SDA, slurry hydrocracking (SHC) is also used for the upgrading of
heavy
hydrocarbon feedstocks including those mentioned above. In SHC, these
feedstocks are
converted in the presence of hydrogen and solid catalyst particles (e.g., as a
particulate
metallic compound such as a metal sulfide) in a slurry phase. Representative
slurry
hydrocracking processes are described, for example, in US 5,755,955 and US
5,474,977. In
addition to the VGO normally present in the reactor effluent, SHC (like SDA)
produces a
low-value, refractory pitch stream that normally cannot be economically
upgraded or even
blended into other products such as fuel oil or synthetic crude oil, due to
its high viscosity
and solids content. Moreover, SHC has disadvantages relative to other heavy
hydrocarbon
conversion processes, including a significant catalyst consumption requirement
and a high
capital cost due to the comparatively larger reactor size and high operating
pressures.
[0006] Particular sources of synthetic crude oil of increasing interest, and
for which
blending components are sought to improve their flow characteristics, are
bitumen and oil
sands. Bitumen refers to the low-quality hydrocarbonaceous material recovered
from oil sand
deposits, such as those found in the vast Athabasca region of Alberta, Canada,
as well as in
Venezuela and the United States. Bitumen and oil sands are recognized as a
valuable sources
of "semi-solid" petroleum or synthetic crude oil, which can be refined into
many valuable
end products including transportation fuels such as gasoline or even
petrochemicals.
[0007] There is an ongoing need in the art for process in which heavy
hydrocarbons (e.g.,
atmospheric column and vacuum column resids as well as gas oils) are converted
or upgraded
with improved efficiency. There is also a need for such processes in which the
net production
of low-value end products, including gas oils and pitch, is minimized. There
is further a need
for overall crude oil refining processes that include the upgrading of crude
oil residues and
particularly those obtained in significant proportions from heavy crude oil
feedstocks.
Ideally, the products of such refining processes should be suitable as
transportation fuel (e.g.,
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diesel and/or naphtha) blending components or even for blending into synthetic
crude oils to
improve their properties (e.g., viscosity and/or specific gravity).
SUMMARY OF THE INVENTION
[0008] Aspects of the invention relate to the finding that slurry
hydrocracking (SHC) can
be effectively integrated with other refining processes and particularly
solvent deasphalting
(SDA), hydrotreating, and/or crude oil fractionation to produce a high value
distillate stream
while recycling low-value gas oils, preferably to extinction, as well as at
least a portion of the
SHC pitch. SHC is generally known in the art for its ability to convert vacuum
column
residues to lighter products. However, it has now been discovered that the use
of a
deasphalted oil (DAO) from SDA as a heavy hydrocarbon feedstock component or
incremental feed to SHC results in operating synergies having commercially
important
advantages.
[0009] The DAO products from SDA processes, and particularly those processes
that are
operated with relatively high recoveries of DAO and low recoveries of pitch,
have high levels
of metal contaminants and Conradson carbon residue, making such DAO products
difficult to
upgrade with conventional FCC or hydrocracking, using either a fixed bed or
ebullating bed
of catalyst. Embodiments of the invention are associated with the discovery
that DAO is
effectively processed as a hydrocarbon feedstock component of SHC, with
complete or
essentially complete overall conversion to an SHC distillate. This distillate
may be
fractionated to provide, for example, lower- and higher-boiling products such
as naphtha and
diesel fuel.
[0010] The use of a heavy hydrocarbon feedstock comprising DAO may be combined
with other SHC process features to obtain additional benefits. For example,
recycling (e.g., to
extinction) a portion of an SHC pitch and/or an SHC gas oil recovered from the
SHC effluent
allows for the complete or essentially complete overall conversion of these
recycle streams
(as well as the DAO) to the higher value SHC distillate. Moreover, the high
content of polar
aromatic compounds (e.g., mono- and multi-ring aromatics) in the recycle SHC
gas oil, such
as vacuum gas oil (VGO) obtained from vacuum column fractionation of a liquid
product
recovered from the SHC effluent, reduces the catalyst requirement of SHC.
Without being
bound by theory, it is believed that these recycled aromatics help solubilize
asphaltenes in
SHC recycle streams and thereby prevent the formation of precipitated
agglomerates of
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asphaltenes and the solid particulate catalyst, leading to coking in the
reactor or increased
catalyst requirements to limit this coking. The recycling of SHC pitch can
also help minimize
make-up requirements, as this pitch contains catalyst with activity comparable
to that of fresh
catalyst.
[0011] Overall, the use of DAO as a component of the heavy hydrocarbon
feedstock in
SHC results in a surprisingly high conversion of this component (both on a per-
pass and
overall basis). Compared to conventional SHC, processing a vacuum column
residue from
crude oil fractionation in the absence of DAO, integrated processes according
to the present
invention have significantly reduced catalyst requirements, smaller reactor
sizes, and/or lower
reactor operating pressures. Relative to fixed bed or ebullating bed
hydrocracking processes,
the catalyst make-up rates of SHC processes described herein are surprisingly
less adversely
impacted by the high metals content of the DAO feed components, known to
deactivate
catalysts used in these conventional conversion processes. In fact, the types
and amounts of
contaminants in DAO products renders these streams difficult, in general, to
further upgrade
using FCC, hydrocracking, or hydrotreating.
[0012] In a representative integrated process, DAO is utilized in combination
with
recycled SHC gas oil, recovered from downstream fractionation/separation of
the SHC
effluent, in the overall heavy hydrocarbon feedstock to SHC. While portions of
this feedstock
may also generally include conventional components such as vacuum column
resid, the
presence of DAO results in the improvements discussed above. Moreover, DAO
from solvent
deasphalting (e.g., of a crude oil vacuum column distillation residue) is
often readily
available in large quantities, particularly in the case of refineries
processing heavy crude oils.
[0013] The present invention is therefore associated with the effective
utilization of DAO
as an attractive incremental feedstock (e.g., in combination with a vacuum
column residue),
which is efficiently upgraded (e.g., cracked) using SHC to yield lighter and
more valuable
distillate and optionally naphtha products. According to some embodiments, the
integration
of SDA with SHC is carried out such that a portion of the SHC pitch and the
SHC gas oil
products, obtained from vacuum column fractionation of a high pressure
separator bottoms
liquid recovered from the SHC effluent, are recycled back to the SHC reactor
or reaction
zone.
[0014] In other embodiments, an integrated SDA/SHC process is combined with
hydrotreating of the SHC distillate. As a result of the low (or non-existent)
net yield of gas oil
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products such as VGO, due to recycling of heavy-boiling fractions back to the
SHC reaction
zone, the hydrotreated distillate has a sufficiently high API gravity (e.g.,
at least 20 ), making
it attractive for blending into a synthetic crude oil that is transported via
a pipeline. Thus, the
hydrotreated distillate, or even the SHC distillate without hydrotreating, may
be obtained as a
high quality transportation fuel blending component with only a minor amount
or essentially
no hydrocarbons boiling at a temperature representative of gas oils (e.g.,
greater than 343 C
(650 F)). The integration of SHC with an existing refinery hydrotreating
process,
conventionally used for sulfur- and nitrogen-containing compound removal from
distillates,
may involve hydrotreating a recovered SHC distillate product in conjunction
with a straight-
run distillate obtained from crude oil fractionation and/or other refinery
streams. This
integration may advantageously reduce overall capital costs of the complex. As
discussed
above, the integration of SDA with SHC, optionally hydrotreating, and
optionally other
conventional refinery operations has the potential to provide significant
benefits in terms of
improved processing efficiency and product yields, reduction or elimination of
low-value
refractory byproducts, and/or the associated capital cost reduction.
[0015] In other representative embodiments of the invention, a crude oil
vacuum column
bottoms residue stream is a feedstock to SDA, used to generate the DAO as a
component of
the heavy hydrocarbon feedstock to SHC. The DAO is then combined at the inlet
of the SHC
reactor with one or more recycle SHC liquid product streams, which may include
a recycled
portion of SHC pitch and/or SHC gas oil, as discussed above, as well as a
recycled portion of
an SHC high pressure separator bottoms liquid. In addition to DAO and recycled
liquid
products, other components of the heavy hydrocarbon feedstock to SHC include
straight-run
hydrocarbon fractions from crude oil distillation, such as straight-run gas
oils (e.g., straight-
run VGO) and vacuum column residues or portions of these streams that are not
sent to SDA.
[0016] These and other aspects and embodiments relating to the present
invention are
apparent from the following Detailed Description.
BRIEF DESCRIPTION OF THE DRAWING
[0017] The FIGURE depicts a representative, integrated solvent deasphalting
and slurry
hydrocracking process, which is incorporated into a typical refinery
flowscheme.
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DETAILED DESCRIPTION
[0018] Embodiments of the invention relate to the use of solvent deasphalting
(SDA) in
combination with slurry hydrocracking (SHC) to upgrade a heavy hydrocarbon
feedstock. A
representative heavy hydrocarbon feedstock to the SHC is a mixture of
deasphalted oil
(DAO), as a fresh feed component, and at least one liquid product recovered
from the SHC
effluent and recycled to an SHC reactor (or reaction zone). The DAO is often
obtained from
subjecting a crude oil vacuum distillation column residue to solvent
deasphalting in the
presence of a solvent. The heavy hydrocarbon feedstock to SHC may therefore
comprise all
or a portion of DAO produced from SDA, either directly from this process or
following one
or more pretreatment and/or fractionation steps. To reduce the overall costs
and complexity
of the integrated process, the DAO is usually not subjected to an additional
extraction (e.g.,
involving phase separation), prior to passing the DAO to SHC for use as a
heavy hydrocarbon
feedstock component in this process.
[0019] In addition to DAO, the SDA process also generates an SDA pitch stream
containing a large proportion of the metals, Conradson carbon residue, and
other impurities
present in the vacuum resid and/or other feed(s) to SDA. The SDA pitch may be
used as a
fuel oil blending component or in the production of asphalts or cement.
Advantageously, the
SDA upstream of SHC may be operated under conditions that favor a relatively
high
recovery/low purity of DAO, compared to conventional SDA processes that
produce DAO
for other conversion processes (e.g., hydrocracking) that require higher
quality feeds.
[0020] According to one embodiment, for example, the heavy hydrocarbon
feedstock
comprises DAO together with one or more liquid products recovered from the
effluent of the
SHC reactor or reaction zone (e.g., by separation and/or fractionation) and
recycled.
Representative liquid products include the high pressure separator bottoms
liquid, as well as
gas oil and pitch products, which may be partially or entirely recycled.
Combinations of these
liquid products and/or portions of these products, may also be recycled. For
example, in a
representative embodiment, the hydrocarbon feedstock comprises, as recycled
liquid
products, both an SHC gas oil (or a recycled portion thereof) and a recycled
portion of an
SHC pitch obtained from vacuum column distillation of an SHC high pressure
separator
bottoms liquid. The integration of SDA with SHC in this manner provides
important benefits
as discussed above.
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[0021] The heavy hydrocarbon feedstock, in addition to DAO and recycled liquid
products as discussed above, may contain further components that can benefit
from
conversion in the SHC reaction zone to decrease the overall molecular weight
of the heavy
hydrocarbon feedstock, and/or remove organic sulfur and nitrogen compounds and
metals.
According to various embodiments, SHC is improved (e.g., by the suppression of
coke
formation) when a significant portion of the heavy hydrocarbon feedstock boils
in a
representative gas oil range (e.g., from 343 C (650 F) to 566 C (1050 F)) and
only at most
60% by weight, and often at most 40% by weight, of the heavy hydrocarbon
feedstock are
compounds boiling above 566 C (1050 F), which generally originate from a
recycled portion
of SHC pitch.
[0022] Representative further components of the heavy hydrocarbon feedstock
include
residual oils such as a crude oil atmospheric distillation column residuum
boiling above
343 C (650 F), a crude oil vacuum distillation column residuum boiling above
566 C
(1050 F), tars, bitumen, coal oils, and shale oils. Other asphaltene-
containing materials such
as whole or topped petroleum crude oils including heavy crude oils may also be
used as
components processed by SHC. In addition to asphaltenes, these further
possible components
of the heavy hydrocarbon feedstock, as well as others, generally also contain
significant
metallic contaminants (e.g., nickel, iron and vanadium), a high content of
organic sulfur and
nitrogen compounds, and a high Conradson carbon residue. The metals content of
such
components, for example, may be 100 ppm to 1,000 ppm by weight, the total
sulfur content
may range from 1% to 7% by weight, and the API gravity may range from -5 to
35 . The
Conradson carbon residue of such components is generally at least 5%, and is
often from
10% to 30% by weight. Overall, many of the heavy hydrocarbon feedstock
components of the
SHC process, including DAO, have properties that render them detrimental to
other types of
catalytic conversion processes such as hydrocracking (both fixed bed and
ebullating bed) and
fluid catalytic cracking. A representative DAO, for example, has a metals
content of at least
500 ppm (e.g., from 500 ppm to 2000 ppm) and a Conradson carbon residue of at
least 10%
(e.g., from 10% to 30%) by weight.
[0023] Integrated methods or processes for preparing SHC distillates generally
involve
passing a heavy hydrocarbon feedstock comprising DAO through an SHC reaction
zone in
the presence of hydrogen to provide an SHC effluent. The heavy hydrocarbon
feedstock may
be, but is not necessarily, present in a heterogeneous slurry catalyst system
in the SHC
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reactor, in which the catalyst is in the form of a solid particulate. For
purposes of the present
disclosure, however, homogeneous catalyst systems, in which the catalytically
active metal is
present in the liquid phase and is dissolved in the heavy hydrocarbon
feedstock (e.g., as an
oil-soluble metal compound such as a metal sulfide), also fall within the
definition of an SHC
process, since homogeneous processes are equally applicable for upgrading the
same types of
heavy hydrocarbon feedstocks with the same advantageous results associated
with the
embodiments discussed herein.
[0024] The SHC reaction is normally carried out in the presence of a combined
recycle
gas containing hydrogen and under conditions sufficient to crack at least a
portion of the
heavy hydrocarbon feedstock to a lighter-boiling SHC distillate fraction that
is recovered
from the effluent of the SHC reactor. The combined recycle gas is a mixture of
a hydrogen-
rich gas stream, recovered from the SHC effluent (e.g., as an overhead gas
stream from a high
pressure separator) and fresh make-up hydrogen that is used to replace
hydrogen consumed in
the SHC reactor or reaction zone and lost through dissolution as well as in
purge or vent
streams. The recovery of SHC distillate typically involves the use of flash
separation and/or
distillation of the SHC effluent, or a lower boiling fraction or cut thereof
(e.g., a fraction
having a lower distillation endpoint), to separate the SHC distillate as a
lower boiling
component from the co-produced (or unconverted) liquid products, including SHC
gas oil
and SHC pitch, in the SHC effluent. As discussed above, portions or all of
these recovered
liquid products may be recycled to the SHC reactor or reaction zone.
[0025] A slurry formed with the heavy hydrocarbon feedstock is normally passed
upwardly through the SHC reaction zone, with the slurry generally having a
solid particulate
content in the range from 0.0 1% to 10% by weight. The solid particulate is
generally a
compound of a catalytically active metal, or a metal in elemental form, either
alone or
supported on a refractory material such as an inorganic metal oxide (e.g.,
alumina, silica,
titania, zirconia, and mixtures thereof). Other suitable refractory materials
include carbon,
coal, and clays. Zeolites and non-zeolitic molecular sieves are also useful as
solid supports.
One advantage of using a support is its ability to act as a "coke getter" or
adsorbent of
asphaltene precursors that might otherwise lead to fouling of process
equipment.
[0026] Catalytically active metals for use in SHC include those from Group
IVB, Group
VB, Group VIB, Group VIIB, or Group VIII of the Periodic Table, which are
incorporated in
the heavy hydrocarbon feedstock in amounts effective for catalyzing desired
hydrotreating
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and/or hydrocracking reactions to provide, for example, lower boiling
hydrocarbons that may
be fractionated from the SHC effluent as naphtha and/or distillate products in
the substantial
absence of the solid particulate. Representative metals include iron, nickel,
molybdenum,
vanadium, tungsten, cobalt, ruthenium, and mixtures thereof. The catalytically
active metal
may be present as a solid particulate in elemental form or as an organic
compound or an
inorganic compound such as a sulfide (e.g., iron sulfide) or other ionic
compound. Metal or
metal compound nanoaggregates may also be used to form the solid particulates.
[0027] Often, it is desired to form such metal compounds, as solid
particulates, in situ
from a catalyst precursor such as a metal sulfate (e.g., iron sulfate
monohydrate) that
decomposes or reacts in the SHC reaction zone environment, or in a
pretreatment step, to
form a desired, well-dispersed and catalytically active solid particulate
(e.g., as iron sulfide).
Precursors also include oil-soluble organometallic compounds containing the
catalytically
active metal of interest that thermally decompose to form the solid
particulate (e.g., iron
sulfide) having catalytic activity. Such compounds are generally highly
dispersible in the
heavy hydrocarbon feedstock and normally convert under pretreatment or SHC
reaction zone
conditions to the solid particulate that is contained in the slurry effluent.
An exemplary in situ
solid particulate preparation, involving pretreating the heavy hydrocarbon
feedstock and
precursors of the ultimately desired metal compound, is described, for
example, in US
5,474,977.
[0028] Other suitable precursors include metal oxides that may be converted to
catalytically active (or more catalytically active) compounds such as metal
sulfides. In a
particular embodiment, a metal oxide containing mineral may be used as a
precursor of a
solid particulate comprising the catalytically active metal (e.g., iron
sulfide) on an inorganic
refractory metal oxide support (e.g., alumina). Bauxite represents a
particular precursor in
which conversion of iron oxide crystals contained in this mineral provides an
iron sulfide
catalyst as a solid particulate, where the iron sulfide after conversion is
supported on the
alumina that is predominantly present in the bauxite precursor.
[0029] Conditions in the SHC reactor or reaction zone generally include a
temperature
from 343 C (650 F) to 538 C (1000 F), a pressure from 3.5 MPa (500 psig) to 21
MPa (3000
psig), and a space velocity from 1 to 30 volumes of heavy hydrocarbon
feedstock per hour
per volume of said SHC zone. Advantageously, the SHC conditions generally
include a
relatively high space velocity and low reactor pressure (or hydrogen partial
pressure), relative
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to conventional fixed or ebullating bed hydrocracking processes. The catalyst
and conditions
used in the SHC reaction zone are suitable for upgrading the heavy hydrocarbon
feedstock to
provide a lower boiling component, namely an SHC distillate fraction, in the
SHC effluent
exiting the SHC reaction zone. The SHC distillate is generally recovered from
the total SHC
effluent (optionally after the removal of a hydrogen-rich gas stream for
recycle to the SHC
reactor, as discussed above) as a fraction having a distillation end point
which is normally
above that of naphtha. The SHC distillate, for example, may be recovered as a
fraction having
a distillation end point temperature typically in the range from 204 C (400 F)
to 399 C
(750 F), and often from 260 C (500 F) to 343 C (650 F), with heavier boiling
compounds
being recovered as liquid products, discussed above, that are completely or
partially recycled
to the SHC reactor or reaction zone.
[0030] According to a particular embodiment, the SHC distillate and a higher-
boiling
SHC fraction may be recovered as an overhead and a bottoms stream,
respectively, exiting a
hot high pressure separator to which the SHC effluent is fed (optionally after
the removal of
the hydrogen-rich gas stream). Fractionation (e.g., in a vacuum distillation
column) of all or a
portion of the higher-boiling SHC fraction, namely the SHC high pressure
separator bottoms
liquid, can then provide the SHC gas oil and SHC pitch, all or portions of
which may be
recycled. According to representative embodiments of the invention, the yield
of SHC
distillate (having a distillation end point in these ranges), is generally at
least 30% by weight
(e.g., from 30% to 65% by weight), normally at least 35% by weight (e.g., from
35% to 55%
by weight), and often at least 40% by weight (e.g., from 40% to 50% by
weight), of the
combined SHC effluent weight (e.g., the combined weight of the SHC distillate
and SHC gas
oil), excluding the solid particulate.
[0031] Depending on the desired end products, the SHC distillate may itself be
fractionated to yield, for example, naphtha and diesel fuel having varying
distillation end
point temperatures. For example, a relatively light naphtha may be separated
from the SHC
distillate, having a distillation end point temperature from 175 C (347 F) to
193 C (380 F).
According to other embodiments, a relatively heavy naphtha may be separated,
having a
distillation end point temperature from 193 C (380 F) to 204 C (400 F). The
naphtha may be
fractionated into one or more naphtha fractions, for example light naphtha,
gasoline, and
heavy naphtha, with representative distillation end points being in the ranges
from 138 C
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(280 F) to 160 C (320 F), from 168 C (335 F) to 191 C (375 F), and from 193 C
(380 F) to
216 C (420 F), respectively.
[0032] Depending on the particular separation/fractionation conditions used to
recover
the SHC distillate, this stream will normally contain quantities of organic
nitrogen
compounds and organic sulfur compounds. For example, the amount of total
sulfur,
substantially present in the form of organic sulfur compounds such as
alkylbenzothiophenes,
in this stream is generally from 0.1% to 4%, normally from 0.2% to 2.5%, and
often from
0.5% to 2%. The amount of total nitrogen in the SHC distillate, substantially
present in the
form of organic nitrogen compounds such as non-basic aromatic compounds
including
cabazoles, will normally be from 100 ppm to 2%, and often from 100 ppm to 750
ppm. The
SHC distillate will also generally contain a significant fraction of
polyaromatics such as 2-
ring aromatic compounds (e.g., fused aromatic rings such as naphthalene and
naphthalene
derivatives) as well as multi-ring aromatic compounds. According to some
representative
embodiments, the combined amount of 2-ring aromatic compounds and multi-ring
aromatic
compounds is at least 50% by weight of the SHC distillate, whereas the amount
of mono-ring
aromatic compounds (e.g., benzene and benzene derivatives such as
alkylaromatic
compounds) typically represents only at most 20% by weight.
[0033] The heavy hydrocarbon feedstock to the SHC reactor or reaction zone, as
discussed above, comprises, in addition to the SHC gas oil, DAO produced from
subjecting a
vacuum column resid to SDA in the presence of a solvent. In addition to the
DAO and
recycled liquid components as discussed above, other representative gas oil
components that
may be present in the heavy hydrocarbon feedstock include straight-run gas
oils such as
vacuum gas oil, recovered by fractional distillation of crude petroleum. Other
gas oils
produced in refineries include deasphalted gas oil and visbreaker gas oil. Gas
oils, as well as
the combined heavy hydrocarbon feedstock to the SHC reaction zone that
comprises these
gas oils, can therefore be a mixture of hydrocarbons boiling in range from 343
C (650 F) to
an end point of 593 C (1100 F), with other representative distillation end
points being 566 C
(1050 F), 538 C (1000 F), and 482 C (900 F). A representative SHC gas oil has
a
distillation end point temperature from 427 C (800 F) to 538 C (1000 F). In
the case of a
straight-run vacuum gas oil, the distillation end point is governed by the
crude oil vacuum
fractionation column and particularly the fractionation temperature cutoff
between the
vacuum gas oil and vacuum column bottoms split. Thus, refinery gas oil
components suitable
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in heavy hydrocarbon feedstocks to the SHC reactor, such as straight-run
fractions, often
result from crude oil fractionation or distillation operations, while other
gas oil components
are obtained following one or more hydrocarbon conversion reactions.
[0034] The SHC may be beneficially combined with hydrotreating, such that the
recovered SHC distillate or a fraction thereof, (e.g., a naphtha fraction or a
diesel fuel
fraction) is catalytically hydrotreated in a hydrotreating zone to reduce the
content of total
sulfur and/or total nitrogen. According to specific embodiments, for example,
a hydrotreated
naphtha fraction may be obtained having a sulfur content of less than 30 ppm
by weight,
often less than 10 ppm by weight, and even less than 5 ppm by weight. A
hydrotreated diesel
fuel may be obtained having a sulfur content of less than 50 ppm by weight,
often less than
ppm by weight, and even less than 10 ppm by weight. Hydrotreating of SHC
distillates to
provide a hydrotreated distillate, or hydrotreating of fractions of the SHC
distillates, may
therefore provide low-sulfur products and even ultra low sulfur naphtha and
diesel fractions
in compliance with applicable tolerances. According to a preferred embodiment,
the SHC
15 distillate has a sufficient API gravity for incorporation into a crude oil
or synthetic crude oil
obtained, for example, from tar sands. Representative API gravity values are
greater than 20
(e.g., from 25 to 40 ) and greater than 35 (e.g., from 40 to 55 ).
[0035] In other embodiments, integration of the SHC process with hydrotreating
can
involve, for example, passing an additional refinery distillate stream, such
as a straight-run
20 distillate, to the hydrotreating zone or reactor. Whether or not one or
more additional streams
are hydrotreated in combination with the SHC distillate, the hydrotreating is
normally carried
out in the presence of a fixed bed of hydrotreating catalyst and a combined
recycle gas stream
containing hydrogen. Typical hydrotreating conditions include a temperature
from 260 C
(500 F) to 426 C (800 F), a pressure from 7.0 MPa (1000 psig) to 21 MPa (3000
psig), and a
liquid hourly space velocity (LHSV) from 0.1 hr_' to 10 hr-1. As is understood
in the art, the
Liquid Hourly Space Velocity (LHSV, expressed in units of hr-) is the
volumetric liquid
flow rate over the catalyst bed divided by the bed volume and represents the
equivalent
number of catalyst bed volumes of liquid processed per hour. The LHSV is
closely related to
the inverse of the reactor residence time. Suitable hydrotreating catalysts
comprise a metal
selected from the group consisting of nickel, cobalt, tungsten, molybdenum,
and mixtures
thereof, on a refractory inorganic oxide support.
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[0036] As discussed above, the SHC process is advantageously integrated with
SDA,
wherein a DAO produced from this process is passed to the SHC reaction zone
for upgrading.
Recycled liquid products, such as a combination of both a recycled portion of
an SHC gas oil
and a recycled portion of an SHC pitch, beneficially reduce SHC catalyst
consumption
requirements while providing a significant level of conversion the DAO, and
the heavy
hydrocarbon feedstock in general, to higher-value products. According to
representative
embodiments, the heavy hydrocarbon feedstock is converted completely or
substantially
completely (e.g., with at least 95% overall conversion) to hydrocarbons having
a boiling
point temperature of 538 C (1000 F) or less in the SHC reaction zone.
Conversion levels to
these hydrocarbons on a "per pass" basis are generally at least 75%, typically
at least 85%,
and often at least 90%.
[0037] A typical SHC pitch stream, all or a portion of which may be recycled
to the SHC
reaction zone as a component of the heavy hydrocarbon feedstock, may be
obtained, for
example, from vacuum column distillation of an SHC high pressure separator
bottoms liquid.
In particular, this vacuum column distillation results in, relative to the
separator bottoms
liquid fed to this column, a lower-boiling SHC gas oil (e.g., SHC VGO) and a
higher-boiling
SHC pitch, normally obtained as a slurry in combination with the solid
particulate.
Accordingly, in a representative embodiment, a higher-boiling SHC effluent
fraction is
recovered as a bottoms liquid, itself in the form of a slurry with the solid
particulate, exiting a
hot high pressure separator. A portion of this bottoms stream may be recycled
directly to the
SHC reactor or reaction zone, while a non-recycled portion may be fractionated
using
vacuum fractionation to yield the SHC gas oil, all or some of which may be
recycled to the
SHC reactor, and the heavier SHC pitch, as described above. As with the SHC
gas oil, all or a
portion of the SHC pitch may also be recycled to the SHC reactor or reaction
zone. In a
specific embodiment, the heavy hydrocarbon feedstock to the SHC comprises, as
recycle
components, (i) a recycled portion of the SHC high pressure separator bottoms
liquid, (ii) a
recycled portion of an SHC gas oil, and (iii) a recycled portion of an SHC
pitch, with (ii) and
(iii) being obtained from fractionation of a non-recycled portion of the SHC
high pressure
separator bottoms liquid.
[0038] A typical SHC pitch, recovered as a higher boiling component, by flash
separation
or fractionation of said SHC effluent, will comprise or consist essentially of
hydrocarbons
boiling at temperatures greater than 482 C (900 F), usually greater than 538 C
(1000 F), and
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often greater than 593 C (1100 F). While aspects of the invention are
associated with the
advantages obtained, particularly with respect to catalyst make-up
requirements, from
recycling the SHC pitch to the SHC reactor or reaction zone, it is often
desired to remove a
non-recycled portion of the SHC pitch as a drag stream containing solid
particulate. This
prevents the accumulation of unwanted solids and other contaminants to
unacceptably high
levels. In an exemplary process, the particulate drag stream represents less
than 70%,
normally less than 50%, and often less than 25%, of the total SHC pitch stream
obtained from
vacuum column distillation of the SHC high pressure separator bottoms. These
purge rates of
the solid particulate correspond to associated catalyst make-up rates that are
considerably less
than those required in the conventional processing of vacuum distillation
column resids using
SHC, but without DAO as a heavy hydrocarbon feedstock component, optionally in
combination with the other recycled liquid products described above.
[0039] The present invention therefore relates to overall refinery flowschemes
or
processes for upgrading heavy hydrocarbon feedstocks discussed above, and
especially those
comprising DAO. Due to the recycle of liquid products such as SHC gas oil and
SHC pitch,
or portions of these streams, substantially all of the net products are either
distillates or coke,
with a relatively minor production of low-value SHC gas oil and SHC pitch.
According to
representative embodiments of the invention, the yield of distillate products
(e.g., a
hydrotreated distillate as discussed above) accounts for at least 80% of the
SHC process yield
(e.g., from 80% to 99%), and often accounts for at least 85% of this yield
(e.g., from 85% to
95%).
[0040] Further aspects of the invention relate to utilizing the SHC processes
discussed
above for making a synthetic crude oil or synthetic crude oil blending
component. The
processes involve passing a DAO derived from solvent deasphalting, with
optional
integration of the process with a hydrotreater as discussed above. Depending
on the
fractionation conditions used for downstream processing of the SHC effluent,
an SHC
distillate may be obtained having hydrocarbons essentially all boiling in the
distillate range or
lower. In representative embodiments, less than 10% by weight, and often less
than 5% by
weight, of the SHC distillate are hydrocarbons boiling at a temperature of
greater than 343 C
(650 F).
[0041] The integrated SDA/SHC processes described herein may be further
integrated
with crude oil fractionation, such that a straight-run distillate from a crude
oil atmospheric
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distillation column is hydrotreated together the SHC distillate. Fractionation
of the bottoms
product from this distillation column in a separate vacuum distillation column
may then be
carried out to yield VGO and/or vacuum residuum (or resid) that is/are passed
to the SDA
extractor, as discussed above, to provide DAO used in the heavy hydrocarbon
feedstock to
SHC.
[0042] A representative process flowscheme illustrating a particular
embodiment for
carrying out the methods described above is depicted in the FIGURE. The FIGURE
is to be
understood to present an illustration of the invention and/or principles
involved. As is readily
apparent to one of skill in the art having knowledge of the present
disclosure, methods
according to various other embodiments of the invention will have
configurations,
components, and operating parameters determined, in part, by the specific
feedstocks,
products, and product quality specifications.
[0043] According to the embodiment illustrated in the FIGURE, a slurry
hydrocracking
(SHC) reactor or reaction zone 20 is integrated into a refinery flowscheme.
The heavy
hydrocarbon feedstock 1 to this reaction zone is a combination of (i) a
deasphalted oil (DAO)
2 produced from solvent deasphalting process 30, (ii) a recycled portion 3 of
the liquid (in
combination with solid particulate) obtained as a bottoms liquid product 8
from hot high
pressure separator (HHPS) 60, (iii) a recycled portion 9 of an SHC pitch
stream 4 that is
obtained as a heavier-boiling fraction or bottoms product of SHC vacuum
distillation column
70, and (iv) a recycled portion 17 of an SHC VGO stream 5 obtained as a
lighter-boiling
fraction or overhead product from this column. Both (iii) and (iv) are
therefore obtained from
fractionation, in vacuum distillation column 70, of non-recycled portion 6 of
bottoms liquid
product 8 from HHPS 60.
[0044] As a component of heavy hydrocarbon feedstock 1 to SHC reactor or
reaction
zone 20, DAO stream 2 is obtained as the solvent-extracted product from
upstream solvent
deasphalting (SDA) process 30 which also generates SDA pitch stream 7. The
SDA/SHC
process illustrated in the FIGURE is further integrated in an overall refinery
process
flowscheme, with the feed stream to SDA process 30 comprising vacuum column
residue
stream (or resid) 10 from crude vacuum column or tower 40, typically
containing
hydrocarbons boiling above (i.e., having a cutpoint temperature) of 566 C
(1050 F). As
shown in the FIGURE, atmospheric column 80 generates atmospheric residue or
reduced
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crude stream 11, with a typical cutpoint temperature of 343 C (650 F) that is
fractionated in
vacuum column 40.
[0045] The SHC process is therefore utilized in an integrated manner to
upgrade DAO
stream 2 from solvent deasphalting process 30, which, as discussed above, is
efficiently
processed in the SHC reactor or reaction zone, relative to other conversion
processes. The
total SHC effluent stream 13 is then subjected to downstream
separation/fractionation
operations to recover upgraded products, remove pitch, and recycle
intermediates. According
to the embodiment illustrated in the FIGURE, total SHC effluent stream 13 is
separated using
hot high pressure separator (HHPS) 60 to recover SHC distillate 14, generally
boiling in a
range above that of naphtha. A non-recycled portion 6 of higher-boiling
fraction 8 recovered
from SHC effluent stream 13, and in particular from the bottoms of HHPS 60, is
then
fractionated in SHC fractionator 70, typically operating as a vacuum column.
SHC
fractionator separates SHC VGO stream 5 from SHC pitch stream 4, with portions
17 and 9
of streams 5 and 4, respectively, being recycled back to SHC reaction zone 20.
Both of
recycled streams 17,9 benefit the SHC process, in terms of minimizing catalyst
requirements,
as discussed above. A non-recycled portion 16 of SHC pitch stream 4 is removed
as a solid
particulate-containing drag stream to prevent the accumulation of excessive
amounts of
impurities. The removed solid particulate (e.g., catalyst) is replaced with
fresh makeup
catalyst (not shown), where the makeup (and removal) rates of solid
particulate typically
represent less than 25% of the solid particulate flow rate in SHC pitch stream
4. A non-
recycled portion 18 of SHC VGO stream 5 is also removed.
[0046] Optionally, the heavy hydrocarbon feedstock 1 can further include a VGO
fraction
19 from vacuum column 40, which, for example, contains hydrocarbons boiling in
the range
from 343 C (650 F) to 566 C (1050 F). This VGO fraction 19 may optionally be
fed directly
to distillate hydrotreating process 50. Another stream optionally used as an
incremental
feedstock to hydrotreating process 50 is a straight-run distillate 21 obtained
as a distillate
fraction of crude oil stream 12, fractionated in crude atmospheric column or
tower 80. A
further stream which may be hydrotreated is a portion of the SHC VGO stream 5
or 18,
namely SHC VGO hydrotreater feed stream 22, from SHC vacuum distillation
column 70.
Thus, SHC distillate 14, optionally with any combination or all of these
streams 19, 21, or 22
is used to obtain hydrotreated distillate 15 as a product of the overall
process having reduced
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nitrogen compound and sulfur compound impurities and/or an API gravity as
discussed above
that may be utilized as a blending component for synthetic crude oil.
[0047] In the overall integrated SDA/SHC process illustrated in the FIGURE,
the SDA
process 30 is advantageously operated with a high recovery of DAO that cannot
be
economically processed using conventional fixed bed or ebullating bed
hydroprocessing.
Also, the integration of SDA process 30 with SHC produces essentially the net
products of
pitch streams 7,16 and hydrotreated distillate 15. As is apparent from this
description, overall
aspects of the invention are directed to the integration of solvent
deasphalting and slurry
hydrocracking to optimize refinery operations. In view of the present
disclosure, it will be
seen that several advantages may be achieved and other advantageous results
may be
obtained. In view of the present disclosure, those having skill in the art
will recognize the
applicability of the methods disclosed herein to any of a number of integrated
SHC processes.
It will also be appreciated that various changes could be made in the above
processes without
departing from the scope of the present disclosure.
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