Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SLURRY HYDROPROCESSING STAGED PROCESS
BACKGROUND OF THE INVENTION
This invention relates to a process employing
a catalyst slurry for the hydrotreating of a heavy fuel
oil. More particularly, the process comprises a high
temperature hydrotreating stage followed by one or more
lower temperature stages.
The petroleum industry employs hydrotreating
to upgrade the quality of gas oils in order to make
them suitable as a feedstock to a fluid catalytic
cracker (FCC). Hydrotreating accomplishes the hydro-
genation of multi-ring aromatic compounds contained in
gas oils to one-ring aromatics or completely saturated
naphthenes. This is necessary to assure low coke and
high gasoline yields in the cat cracker. Multi-ring
aromatics cannot be cracked effectively to mogas (motor
gasoline) and heating oil products, whsreas partially
hydrogenated aromatics or naphthenes can be cracked to
premium products in the naphtha and heating oil boiling
range. Hydrotreating is further capable of removing
sulfur and nitrogen which is detrimental to the crack-
ing process.
Conventional processes for hydrotreating
heavy feeds, whether utilizing a fixed bed or a slurry
system, have inherent limitations. The catalyst
employed in the hydrotreater becomes poisoned by
organic nitrogen containing compounds in the feed being
treated, wherein such compounds are adsorbed onto the
catalyst and tie up its hydrogenation sites due to the
slow kinetics or turnover for hydrodenitrogenation.
Desirable hydrotreating reactions are thereby hindered.
For example, the catalyst becomes incapable of satu-
rating aromatic compounds in the feed fast enough.
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Higher temperatures are frequently needed to counter
the poisoning effect of such compounds. However, at
higher temperatures, thermodynamic equilibrium tends to
favor the preservation of undesirable multi-aromatic
compounds.
According to the present invention, a slurry
hydrotreating process employing temperature staging
provides a means to circumvent both the kinetic and
equilibrium limits conventionally encountered in either
fixed bed or slurry hydrotreating processes.
Hydrotreating processes utilizing a slurry of
dispersed catalysts in admixture with a hydrocarbon oil
are generally known. For example, Patent No. 4,557,821
to Lopez et al discloses hydrotreating a heavy oil
employing a circulating slurry catalyst. Other patents
disclosing slurry hydrotreating include U.S. Patents
Nos. 3,297,563; 2,912,375; and 2,700,015.
Staging of reactors in a hydrotreating
process is also generally known. For example, U.S.
Patents Nos. 3,841,~96 and 3,297,S63 disclose slurry
hydrotreating reactions that can be operated with a
plurality of stages. However, the advantages of
operating the subsequent stages at lower temperatures
were not recognized. U.S. Serial No. 009808, filed
February 2, 1987 (published EP application 277,718A)
discloses staged fixed bed reactors at successively
lower temperatures in order to promote equilibrium
limited aromatic saturation reactions in a hydrocarbon
oil. The advantages of temperature staging revealed in
this reference for fixed bed operations, however, are
minimal compared to the result~ obtained in the present
invention wherein temprature ~taging is utilized in a
slurry process.
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BRIEF DESCRIPTION OF THE INVENTION
The present invention teaches a method of
maximizing hydrogenation rates while avoiding equili-
brium limits in a slurry hydrotreating process, wherein
a hydrotreating catalyst of small particle size is
contacted with petroleum or synfuel feedstocks for
hydrogenation of aromatics and removal of organic
nitrogen. The slurry hydrotreating process employs a
high temperature stage followed by one or more low
temperature stages.
These and other objects are accomplished
according to applicants' invention, which comprises:
(1) contacting a gas oil feedstock with hydrogen
in a relatively high temperature first hydro-
treating zone in the presence of a hydro-
treating catalyst slurry such that substan-
tial hydrodenitrogenation and aromatics
saturation of the feedstock is carried out;
(2) contacting the effluent from the first
hydrotreating zone in the presence of a
hydrotreating catalyst slurry with further
hydrogen in a relatively low temperature
second hydrotreating zone; and
(3) separating hydrogen gas and catalyst from the
product of the second hydrotreating zone to
yield a hydrotreated product.
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BPIEF DESCRIPTION OF THE DRAWINGS
The process of the invention will be more
clearly understood upon reference to the detailed
discussion below upon reference to the drawings where-
in:
FIG. 1 shows a schematic diagram of one
process scheme according to this invention comprising a
two stage hydrotreating slurry reaction.
FIG. 2 shows a graph illustrating that
temperature staging can double the effectiveness of
slurry hydrotreating for improving the quality of the
hydrotreated product for use as catalytic cracker feed.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that hydrogenation
rates of a gas oil can be maximized and equilibrium
limits avoided by operating a slurry hydrotreating
process with two or more stages, preferably well mixed
isothermal stages. According to the present invention,
a relatively high temperature stage is followed by one
or more low temparature stages. For example, a two
stage process might process fresh feed in a 760F stage
and process the product from the first stage in a 720F
stage. Alternatively, several stages can be operated
at successively lower temperatures, such as a 780F
stage followed by a 740F stage foll~wed by a 700F
stage. Such an arrangement provides, in the first
stage, fast reaction rates and, in the final stage or
stages, lower equilibrium multi-ring aromatics levels
(hence greater kinetic driving forces).
The slurry hydrotreating process of the
present invention can be used to treat varlous feeds
from fossil fuels such as heavy catalytic cracking
cycle oils (HCCO), coker gas oils, and vacuum gas oils
(VGO), which contain high concentrations of aromatics.
Similar feeds derived from petroleum, coal, bitumen,
tar sands, or shale oil are also suitable.
Suitable feeds for processing according to
the present invention include those gas oil fractions
which are distilled in the range of 590 to 1200F,
preferably in the 650 to 1100F range. Above 1200F it
is difficult or impossible to strip all of the feed off
the catalyst with hydrogen and the catalyst kends to
coke up. Also, the presence of concarbon and
asphaltenes gum up the catalyst. The feed should not
be such that more than 10% boils above 1050F. The
nitrogen content is normally greater than 1500 ppm. The
2+ ring aromatics represent 50% or more and the 3+ ring
aromatics content of the feed should generally should
represent 25% or more by weight.
Suitable catalysts for use in the present
process are well known in the art and include, but are
not limited to, molybdenum (Mo) sulfides, mixtures of
transition metal sulfides such as Ni, Mo, Co, Fe, W,
Mn, and the like. Typical catalysts include NiMo, CoMo,
or CoNiMo combinations. In general sulfides of Group
VII metals are suitable. (The Periodic Table of
Elements referred to herein is given in Handbook of
Chemistry and Ph~sics, published by the Chemical Rubber
Publishing Company, Cleveland, Ohio, 45th Edition,
1964.) These catalyst materials can be unsupported or
supported on inorganic oxides such as alumina, silica,
titania, silica alumina, silica magnesia and mixtures
thereof. Zeolites such as USY or acid micro supports
such as aluminated ~AB-O-SIL can be suitably composited
with these supports. Catalysts formed in-situ from
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soluble precursors such as Ni and Mo naphthenate or
salts of phosphomolybdic acids are suitable.
In general the catalyst material may range in
diameter from 1 ~ to 1/8 inch. Preferably, the cata-
lyst particles are 1 to 400 ~ in diameter so that intra
particle diffusion limitations are minimized or elimi-
nated during hydrotreating.
In supported catalysts, transition metals
such as Mo are suitably present at a weight percent of
5 to 30%, preferably 10 to 20%. Promoter metals such
as Ni and/or Co are typically present in the amount of
l to 15%. The surface area is suitably about 80 to 400
m2/g, preferably 150 to 300 m2/g.
Methods of preparing the catalyst are well
known. Typically, the alumina support is formed by
precipitating alumina in hydrous form from a mixture of
acidic reagents in an alkaline aqueous aluminate
solution. A slurry is formed upon precipitation of the
hydrous alumina. This slurry is concentrated and
generally spray dried to provide a catalyst support or
carrier. The carrier is then impregnated with cataly-
tic metals and subseguently calcined. For example,
suitable reage~ts and conditions for preparing the
support are disclosed in U.S. patents Nos. 3,770,617
and 3,531,398, herein incorporated by reference. To
prepare catalysts up to 200 microns in average dia-
meter, spray drying is generally the preferred method
of obtaining the final form of the catalyst particle.
To prepare larger size catalysts, for example about
1/32 to 1/8 inch in average diameter, extruding is
commonly used to form the catalyst. To produce cata-
lyst particles in the range of 200 ~ to l/32 inch, the
oil drop method is preferred. The well known oil drop
method comprises forming an alumina hydrosol by any of
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the teachings taught in the prior art, for example by
reacting aluminum with hydrochloric acid, combining the
hydrosol with a suitable gelling agent and dropping the
resultant mixture into an oil bath until hydrogel
spheres are formed~ The spheres ars then continuously
withdrawn from the oil bath, washed, dried, and
calcined. This treatment converts the alumina hydrogel
to corresponding crystalline gamma alumina particles.
They are then impregnated with catalytic metals as with
spray dried particles. See for example, U.S. Patents
Nos. 3,745,112 and 2,620,314.
In the slurry hydrotreating process of the
invention, fresh or reactivated catalyst can be conti-
nually added while aged or deactivated catalyst can be
purged or regenerated. The reactivated catalyst is
preferably continuously recycled to the reactor.
Consequently, a slurry hydrotreating process can be
operated at more severe conditions than a fixed bed
hydrotreater, which typically operates for 1 or 2 years
before it becomes necessary to shut it down in order to
replace the catalyst.
Referring to FIG. 1, a feed stream 1, by way
of example consisting of a gas oil feed, is introduced
into a first slurry hydrotreating xeactor 2 operated at
a relatively higher temperature compared to a second
slurry hydrotreating reactor 3. Before being passed to
the hydrotreat~r reactor 2, the feedstream 1 is typi-
cally mixed with a hydrogen containing gas stream 4 and
heated to reaction temperature in a furnace or pre-
heater 5. A make-up hydrogen stream 6 may be intro-
duced into the recycle hydrogen supply stream 4 to the
hydrotreating reactor 2. The hydrotreating reactor 2
contains typically 10 to 70 percent catalyst, pre-
ferably about 40 to 60 percent solids by weight. The
feed may enter through the bottom of the reactor and
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bubble up through an ebulating or fluidized bed.
Recycle of the reactor effluent via a pump (not shown)
is optional to recycle a portion of the feed for
reactor mixing. The effluent stream 8 from the first
hydrotreating reactor 2 is suitably lowered in tempera-
ture by either introducing a guench feed stream 7
and/or passing the effluent through a cooler 16. In
addition, further hydrogen gas is suitably introduced
via stream 18 into the first hydrotreating reactor
effluent stream 8 before the latter is passed into the
second hydrotreating reactor 3. The effluent from this
second reactor is suitably passed via stream 9 through
a cooler 10, and into a gas-liquid separator or dis
engaging means 11 to take off gases, principally
hydrogen, before yielding a liquid product stream 12.
In many cases, the liquid products are given a light
caustic wash to assure complete removal of H2S. Small
quantities of H2S, if left in the product, will oxidize
to free sulfur upon exposure to the air, and will cause
the product to exceed pollution or corrosion specifi-
cations.
Depending on the size of the catalyst parti-
cles used therein, the hydrotreating reactors 2 and 3
may optionally have filters at entrance and/or exit
orifices to keep the catalyst particles inside the
reactors. The reactors may alternatively have a flare
(increasing diameter~ configuration such that when the
reactor is kept at minimum fluidization velocity, the
catalyst particles are prevented from escaping through
an upper exit orifice.
As indicated above, the hydrotreating reac-
tors ara arranged in descending temperature such that
the last reactor is between 650 and to 750F where
equilibrium is favorable for hydrogenation of aromatics
to one ring aromatics. The first stage is at a more
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elevated temperature, for example between 700 to 800F
where more rapid hydrodenitrogenation (HDN) can occur.
Referring again to FIG. 1, the gas-liquid
separator or disengaging means 11 separates the liquid
product from hydrogen gas along with ammonia and
hydrogen sulfide by-products of the hydrotreating
reactions and recycles them in gas stream 13 via
compressor 14 back for reuse in the recycle hydrogen
supply stream 4. An off gas stream 15 may be removed
from the gas stream 13. The gas stream 13 is usually
passed through a scrubber (not shown) to remove hydro-
gen sulfide and ammonia because of their inhibiting
effects on the kinetics of hydrotreating and also to
reduce corrosion in the recycle circuit.
The catalyst used in the hydrotreating
reactors 2 and 3 is preferably reactivated on a con-
tinuous basis as described in copending application
S.N. 414,166, herein incorporated by reference. Spent
catalyst may be removed from the reactors 2 and 3 via
streams 19 and 20, respectively. Fresh make-up cata-
lyst ma~y be introduced via streams 17 and/or 21 into
the feed stream 1.
The operating conditions in the hydrotreating
reactors depend to some extent on the particular feed
being treated. The first hydrotreating reactor is
suitably at a temperature of between 700 and 800F,
preferably between 750 and 780F and at a pressure of
800 to 4000 psig, preferably 1500 to 2500 psig. The
hydrogen treat gas rate is 1500 to 10,000 SCF/B,
preferably 2500 to 5000 SCF/B. The space velocity
(WHSV) or holding time is suitably 0.2 to 5, pre~erably
0.5 to 2.
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The second (low temperature) hydrotreating
reactor operates at a temperature between about 650 and
750F, preferably between 675 and 725F and a pressure
of 800 to 4000 psig, preferably 1500 to 2500 p5ig. The
hydrogen treat gas ratio is 1500 to 10,000 SCF/B,
preferably 2000 to 5000 SCF/B. The space velocity
(WHSV) is O.2 to 5, preferably 0.5 to ~.
COMPARATIVE EXAMPLE 1
For comparison to the present staged hydro-
treating process, sinyle stage runs were conducted as
follows. Commercial hydrotreating catalyst, KF-840,
was crushed and screened to 32/42 mesh size. Catalyst
properties are shown in Table I. This crushed catalyst
was then sulfided overnight using a 10~ H2S in H2 gas
blend. A 30.9 gram sample of the presulfided catalyst
was added to a 300 cc stirred autoclave reactor along
with 100 cc's of a heavy feed blend comprised of heavy
vacuum gas oils, heavy coker gas oils, coker bottoms
and heavy cat cracked cycle oil. Properties of the
feed are listed in Table II.
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Table I
Catalyst Properties
Nio, Wt% 3.8
MoO3, Wt% 19.1
P20s, Wt% 6.4
Surface Area, m2/gm 175.0
Pore/volume, cm3/gm 0.38
Table II
Feedstock Pro erties
Sulfur, Wt% 1.~3
Nitrogen, Wt% 0.39
Carbon, Wt% 87.63
Hydrogen, Wt% 9.60
Gravity, API 9.2
Wt~ Aromatics by HPLC
Saturates 26
1 Ring g
2 Ring 10
3~ Ring 43
Polar Aromatics 12
GC Distillation F
5% 665
20% 753
50% 882
80% : 1004
95% 1150
The autoclave was heated to 690F under 1200 psig
hydrogen pressure. The autoclave was operated in a gas
flow thru mode so that hydrogen treat gas was added
continuously while gaseous products were taken off.
This hydrogen was added over the course of the run and
the initial hydrogen charge plus make-up hydrogen was
equivalent to 3500 SCF/B of liquid charged to the
autoclave. After two hours at reaction conditions, the
autoclave was quenched or cooled quickly to stop
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reactions. The autoclave reactor was depressured and
the catalyst was filtered from the liquid products.
These products were then analyzed to determine the
extent of HDS, HDN, and aromatics hydrogenation. The
results are shown in Table III. Similar experiments
were conducted with the same catalyst and feed, but at
reaction temperatures of 720, 730, 750, and 780F. The
results of these experiments are shown in Table III.
Table III
1200 Psig, 31.5 wt% Catalyst on Feed,
2 Hours at Tem~erature 3500 SCF/B HYdroqen
Slurry Hydrotreating
Temperature, F 690 720 730 750 780
Slurry Product Quality
Wt% Sulfur .215 .065 .047 .019 .001
Wt% Nitrogen .122 .088 .086 .051 .028
Wt% Sats + lR AR 64 63 63 64 61
Wt% 3+ R AR & Polars 21 18 22 22 25
Wt% Polar AR 2.2 1.2 1.6 1.1 0.7
MAT Conversion 58.9 63.3 61.2 60.5 57.2
MAT Coke 2.87 3.12 3.00 2.95 2.67
The results of Table III show that product
sulfur, nitrogen and polar aromatics were all reduced
by hydrotreating at higher temperatures and that heavy,
3+ ring aromatics were reduced by increasing the
temperature from 690 to 720F. However, further
increases in temperature resulted in higher heavy
aromatics levels. This minimum 3+ ring aromatics
concentration at relatively low temperatures indicates
that aromatics saturation equilibrium limits heavy
aromatics saturation at temperatures above 720F.
Saturates plus 1 ring aromatics levels tend to remain
constant over a broad temperature range from 690 to
750F before falling as hydrotreating temperature was
increased from 750 to 780F. This indicates that
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equilibrium limits the production of compounds which
can be converted to mogas in an FCC unit at hydro-
treating temperatures of 750F or more.
The net effect of the impact of hydrotreating
temperature on FCC feed quality was evaluated by the
well known (MAT) Micro-activity Test which is de-
scribed, for example, in the oil Gas Journal, 1966,
Vol. 64, No. 39 at pages 7, 84, and 85; and the Novem-
ber 22, 1981 edition of the Oil and Gas Journal at
pages 60-68. An equilibrium cracking catalyst from a
commercial FCC unit was used in the MAT to crack each
of these hydrotreated products. High MAT conversions
to mogas and lighter products are desirable. Low MAT
coke yields are desirable. The highest conversion was
achieved by hydrotreating at 720F, but the lowest MAT
coke yields were achieved at the highest temperature
tested, 780F. Products with both high MAT conversion
and low MAT coke yields could not be produc~d at a
single hydrotreating temperature.
EXAMPLE 2
To illustrate the staged process according to
the present invention, an experiment similar to Com-
parative Example 1 above was conducted with the same
catalyst and feed. However, in this experiment the
autoclave was heated to 760F and held for one hour.
Then the autoclave was quickly (in 10 sec or less)
cooled to 720F and held for an additional hour before
quenching to halt all reactions. This temperature
staging experiment was repeated by heating to 750F and
holding for one hour, followed by one hour at 690F.
The rasults of these experiments are shown in Table IV.
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Table IV
1200 Psig, 31.5 wt% Catalyst on Feed,
3500 SCF/B Hydroqen
Slurry Hydrotreating 760/720 750/690 730
Temperature, F
Time on 1/1 1/1
Temperature, Hours 4
Slurry Product Quality
Wt% Sulfur .029 .065 .047
Wt% Nitrogen .054 .088 .086
Wt% Sats ~ lR AR 69 63 63
Wt% 3+ R AR & Polars 16 18 22
Wt~ Polar AR 0.6 1.2 1.6
MAT Conver~ion 63.5 59.9 64.1
MAT Coke 2.68 2.53 2.60
Comparing th2 results of the temperature
staging experiments with the experiments o~ Comparative
Example 1, which was run at a single temperature for 2
hours, it may be concluded that the temperature staging
experiments provide both the high HDS, HDN and polar
aromatics removal of the higher temperature experiments
and the high heavy aromatics removal/saturates and
ring aromatics production of the lower temperature
experiments. Referring to FIG. 2, it can be seen the
temperature staging experiments provided lower MAT coke
yields at any given MAT conversion. The lowest MAT
coke yields were observed for the product from the
750/690F temperature staging experiment. The
760/720F temperature staging experiment showed lower
heavy aromatics levels and higher saturates plus 1 ring
aromatics levels than any two hour, single temperature
experiment. In order to match the resul~s o~ the ~wo
hour temperature staging experiment, a single tempera-
ture, say 730F, would require four hours.
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EXAMPLE 3
To further illustrate the present invention,
a further experiment was conducted with the same
catalyst and feed as in Comparative Example 1. The
autoclave was heated to 720F under 1200 hydrogen
pressure, and after two hours at reaction conditions,
the autoclave was quenched. The catalyst was dis-
charged from the autoclave, filtered and recharged to
the autoclave with another 100 gms of the same feed.
The same catalyst charge was filtered and recycled in
the autoclave several times in order to line out
catalyst performance. The results of this experiment
along with a similar experiment at 760F are shown in
Table V. In the similar experiment, catalyst from a
temperature staging autoclave run, in which the auto-
clave was run at 760F for an hour and then 720F for
an hour, was discharged, ~iltered and recycled to
further autoclave temperature staging experiments. The
temperature staging conditions and results for this
experiment and a similar experiment at 800 and 720F
are shown in Table V.
Table V
1200 Psig, 31.5 wt% Catalyst on Feed,
3500 SCF/B Hydroqen
Slurry Hydrotreating 760/720 800/720 720 760
Temperature, F
Time on 1/1 1/1 2 2
Temperature, Hours
Slurry Product Quality
Wt% Sulfur .062 .036.126 .051
Wt% Nitrogen .144 .092.186 .092
Wt% Sats + lR AR 65 64 61 61
Wt~ 3+ R AR & Polars 20 20 23 24
Wt% Polar AR 1.8 1.4 2.7 1.5
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Comparing the results of the temperature staging
experiments with the experiments run at a single
temperature for 2 hours, the temperature staging
experiments with recycled catalyst provided both lower
heavy aromatics levels and higher saturates plus 1 ring
aromatics levels than any two hour, single temperature
experiment. HDS, HDN and polar aromatics removal in
the temperature staging experiments were as good or
better than at single temperature experiments at the
same average temperature.
The process of the invention has been des-
cribed generally and by way of example with reference
to particular embodiments for purposes of clarity and
illustration only. It will be apparent to those
skilled in the art from the foregoing that various
modifications of the process and materials disclosed
herein can be made without departure from the spirit
and scope of the invention.
