Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LAYERED RESXDVA TREATMENT CATALYST
-PROCESS AND TEMPERATURE PROFILE
05 BACK~ROUND OF THE_INVENTION
This inverition relates to hydrodemetalation and
hydrodesulfurization of feedstocks, particularly hydro-
demetalation and hydrodesulfurization processes that use
multiple beds.
The world supply of petroleum is shrinking,
thereby forcing the utilization of feedstocks that are not
considered to be readily refinable into lighter products.
Examples of such heavy feedstocks are Maya Crude, Arabian
Heavy Crude, California San Joaquin Crude and various
venezuelan Crudes. These crudes are characterized by low
hydrogen to carbon ratios and high nonhydrocarbon con~ami-
nant content. These contaminants include sulfur, nitrogen
and metals, in particular, iron, nickel and vanadium, in
the form of various soluble organometallic compounds, such
as porphrins and asphaltenes.
It is preferred that sulf~r and metals be
removed as early as possible in the processing of con-
taminated feedstocks since both sulfur and metals tend to
lessen the activity of downstream catalysts. In the case
of metals, this deactivation tends to be irreversible.
Also, when burned, products that contain less contaminants
tend to require less post combustion treatment to provide
an environmentally acceptable exhaust.
Many processes are known to remove metals and
sulfur from feedstocks. Simple distillation will remove
most of the lighter hydrocarbons, and solvent extractions
can remove the asphaltene fraction which contains high
concentrations of sulfur and metals. ~ydroconversion
processes are used extensively for desulfurization, and
such processes will remove metals as well. The metals
tend to deposi~ on the surface of the desulfurization
catalyst, deactivating it. There has recently been great
effort placed in hydrodemetalation. Catalysts have been
made that remove most metals from the feedstock. Various
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catalysts supported on alumina Eor demetalation of feedstocks are known.
United States Patent No. 3,876,523 to Rosinski et al discloses a catalyst
useful for demetalation and desulfurization of residual petroleum oil,
carried out with hydrogen and with an alumina base catalyst incorporating
a Group VIB and a Group VIII metal. The catalyst has at least 60 percent
of its pore volume in pore diameters within the range of 100 to 200 Angstroms,
at least 5 percent of its pore volume is in pore diameters greater than
500 Angstroms, at least 5 percent of its pore volume is in pore diameters
less than 40 Angstroms and the surface area of the catalyst is 40 to 150
meters2/gram, preferably a surface area up to abou-t 110 meters2/gram.
Ano~ther alumina demetalation catalyst is disclosed in United
States Patent No. 4,257,922 to Kim et al. The catalyst support is
characterized by bimodal pore distribution with the average diameter of
the smaller pores ranging from about 100 to 200 Angstroms and preEerably
120 to 140 Angstroms, and average diameter of the larger pores being in
excess of 1,000 Angstroms.
United States Patent No. 4,196,102 to Inooka et al discloses
a catalyst for hydrotreatment of hydrocarbons comprising one or more of
metals selected from the group consisting of transition metals and metals
of Group IIB of the Periodic Table supported on sepiolite, a fibrous
magnes:Lum silicate clay.
A variety oE multiple bed processing schemes are known to
remove sulfur and metals before further processing. United States
Patent No. 4,212,729 to Henslet et al discloses a two-stage catalytic
process Eor hydrometalation and hydrodesulEurization of heavy hydrocarbon
streams containing asphaltenes and a substantial amount of metals. The
first stage o~ this process comprises contacting the feedstock in a Eirst
reaction zone with hydrogen and a demetalation catalyst comprising
hydrogenation metal selected from Group VIB and/or Group VIII deposed on
a large-pore,
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high surface area inorganic oxide support; the second
stage of the process comprises contacting the effluent
05 from the first reaction zone with a catalyst consisting
essentially of hydrogenation metal selected from Group VIB
deposited on a smaller pore, catalytically active support
comprising alumina, said second stage catalyst having a
surface area within the range of about 150 meters2/gram to
about 300 meters2/gram, having a majority of its pore
volume in pore diameters within the range of about 80
Angstroms to about 130 Angstroms, and the catalys~ has a
pore volume within the range of about 0.4 cubic
centimeters/gram to about 0.9 cubic centimeters/gram~
U.S. Patent No. 4,166,026 to Fukui et al dis-
closes a process for hydrodesulfurization of heavy
hydrocarbon oil containing asphaltenes and heavy metals.
The heavy oil is hydrotreated in a continuous two-step
process. In the first step the heavy oil is subjected to
hydrodemetalation and selective cracking of asphaltenes by
the use of a catalyst having a unique selectivity there-
for. In the second step the effluent from the flrst step
is subjected to hydrodesulfurization to produce desul-
furized oils of high ~rade by the use of a catalyst having
a pore volume and pore size distribution particularly
adapted for the hydrodesulfurization of the effluent.
It has been discovered that ln a two-stage
hydrodemetalation/hydrodesulfurization catalytic process
where the feedstock is first contacted with a catalyst
tailored for demetalation, and then is contacted with a
catalyst tailored for desulfurization, if the first
catalyst zone is kept at a higher average temperature than
the second zone, the product from the second zone has less
contaminants and the entire system has a longer life than
if both catalyst zones are kept at the same average
temperature.
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_ MMARY OF THE INVENTION
A process is provided for hydroconversion of
hydrocarbonaceous feedstocks containing both sulfur and metals
by passing the feeds-tock through multiple catalyst beds. An
inverse temperature profile is maintained in the beds.
A process for removing contaminants from a feedstock
containing both me-tals and sulfur is provided. The feedstock
is contacted with catalysts in two zones, the first zone
containing a demetalation catalyst and the second zone con-
taining a desulfurization catalyst. The average temperatureof the first zone is at least 15C higher than the average
temperature of the second zone.
Thus in its broadest aspect this invention provides
a process for hydrotreating a hydrocarbonaceous feedstock
containing both sulfur and metal comprising:
contacti.ng said feedstock with molecular hydrogen in the
presence of a first catalyst having subs-tantial demetalation
activity, said first catalyst being contained in a first
catalytic zone, said first catalytic zone being maintained
at a first average temperature and at an elevated pressure,
thereby producing a first effluent;
contacting said first effluent with a molecular hydrogen
quench, thereby producing a second effluent;
contacting said second effluent with a second catalyst
having substantial desulfurization activity, said second
catalyst being contained in a second catalytic zone, said
second catalytic zone being maintained at a second average
temperature, said second average temperature being at least
15C less than said first average temperature, and at an
elevated pressure, thereby producing a product; and
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wherein the molecular hydrogen quench produces a
dif~erence in temperature between said first effluent and
said second effluent which is greater than the difference
between said first average temperature and said second average
temperature.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graphical representation of a conventional
temperature profile through a reaction vessel with multiple
quenches.
FIG. 2 is a graphical representation of a temperature
profile of this invention.
DETAILED DESCRIPTION
The feedstocks for the present invention are
hydrocarbonaceous feedstocks that contain sulfur and metal.
Frequently hydrocarbonaceous feedstocks will contain .5 percent
sulfur, up to 4 percent sulfur and in extreme cases, over 6
percent sulfur, and 35 ppm metals, up to 200 ppm metals and in
extreme cases, over 1,000 ppm metals. Unless specifically
denoted to the contrary, as used herein, "percent sulfur," or
"percent," refers to weight percent based on total elemental
sulfur in the feedstock. Such feedstocks include crude oils,
topped crudes, atmospheric and vacuum residua, solvent deas-
phalted oil, liquids from oil shales and tar sancls and coal-
derived liquids. The feedstocks of the present invention
have boiling points that will frequently exceed 400F and may
exceed l,000F.
The feedstock of the present invention will contact,
in a first zone, a catalyst tailored for hydrodemetalation,
and then will contact, in a second zone, a
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catalyst tailored for desulfurization. The "first and
second zonest" as used herein r refer to temperature con-
05 trolled zones; that is, the first ~one will have anaverage temperature~at least 15C higher than that of the
second zone~ The catalyst in the first 20ne may be the
same as the catalyst in the second ~one, and each ~one may
contain more than one catalyst.
The catalyst of the first zone can be any of a
class of well-known and defined hydrodemetalation
catalysts. Catalysts supported on alumina are known and
are generally characterized by the presence of macropores,
herein defined as pores larger than 1,000 Angstroms in
diameter, and an average calculated micropore diamet~r of
over 100 Angstroms when calculated by the formula:
Average Micropore Diameter = 4 x PV x 104
SA
where PV is micropore volume expressed in cubic
centimeters/gram of catalyst where micropores are those
pores of less than 1,000 Angstroms in diameter, and SA is
surface area expressed in meters2/gram of catalyst.
Such catalysts may contain catalytic metals, in
particular, metals from the group consisting of Group VIB
and Group VIII Transition metals of the Periodic Table of
Elements, particularly, molybdenum, tungsten, nickel and
cobaltO The Group VI metals may be present in quantities
3U ranging from 1.5 weight percent to 20 weight percent. The
Group VIII metals may be present in quantities up to 15
percent. There may be no Group VIII metals at all on some
alumina-supported hydrodemetalation catalysts.
Clay-supported demetalation catalysts may also
be the catalyst of the first zone~ Such catalyst supports
may be made from æepiolite, attapulgite, polygorskite, and
similar fibrous magnesium silicate clays or halloysite and
similar fibrous or rod-like aluminum silicate clays.
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These catalysts are physically characterized by large cal-
culated average pore diameters, frequently over 200
05 Angstroms, and few macropores. These catalysts may con-
tain catalytic meta~ls, and in particular, those selected
from the group consisting of Group VI and Group VIII
Transition metals, particularly, molybdenum~ tungsten,
nickel and cobalt and various combinations of these
metals
Any other catalyst that shows substantial hydro-
demetalation activity can be used in the first zone of
this invention. "Substantial hydrodemetalation activity"
- is herein defined as the ability to remove at least 25
percent of the metals content of a feedstock continuously
for a period of time not less than 500 hours under hydro-
processing conditions.
The catalyst of the second zone can be any cata-
lyst that shows substantial hydrodesulfurization activity.
These catalysts, frequently supported on alumina or alu-
mina in combination with silica, boria, titania, magnesia,
or other refractory inorganic oxides, are characterized by
calculated average pores diameters of greater than 50
Angstroms and few macroporesO Typical:Ly, desulfurization
catalysts have more catalytic metals, giving them higher
intrinsic activities. The catalytic me~als are selected
from the group consisting of Group VI and ~roup VIII
Transition metals.
Any catalyst that shows substantial de~ulfuriza-
tion activity can be used. "Substantial desulfurization"is herein defined as the activity required to remove at
least 25 percent of the sulfur content of a feedstock for
at least 500 hours under hydroprocessing conditions.
As used herein, hydroprocessing conditions are
those conditions that are known to the art to give cata-
lytic hydroconversion of hydrocarbonaceous feedstocks.
Typical conditions for the present invention are 355C to
450C for the first zone average temperature, and 340C to
450C for the second zone average temperature, while
maintaining at least a l5~C temperature difference. Space
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velocity of feedstock is between 0.1 and 1.5. Total pres-
sure is between 500 and 3~000 psig, and partial pressure
05 of hydrogen is between 300 and 2,800. Recycle rate for
hydrogen is between`2,000 and lO,000 SCF/BBL. Normally as
the activity of the catalysts decrease, the temperature of
the reaction vessels will be adjusted upward to maintain a
specified quality in the product, usually a maximum toler-
able amount of contaminants.
It is possible that the same catalyst might be
used both` for demetalation and desulfurization. The cata-
lyst charge of the first zone would tend to lose activity
for desulfurization relatively rapidly, but could maintain
lS demetalation activity for some time. Desulfurization
reactions are believed to be reactions where sulur is
hydrogenated to hydrogen sulfide and thereafter passes out
of the reaction zone. Demetalation deposits metals on the
outer surface or inner pore surface of the catalyst. It
has been observed that a catalyst can therefore lose the
property of catalytically hydrogenating sulfurl but still
deposit metals.
It may be desirable to shape both the hydrode-
metalation and desulfurization catalyst particles in some
shape other than the conventional rouncl cylinder. ~f such
shaped catalysts are used, it is preferred that the
diameter of the smallest circle that can be circumscribed
around the particle be 1/64 to l/2 inches~
Another embodiment of the present invention is
,having more than one catalyst in either or both of the
zones. For example, a macroporous, large pore demetala-
tion catalyst can be used in the first zone, at high
temperature, the second zone can be charged with firstly,
a large pore desulfurization catalyst that can also remove
metals and then secondly, a smaller pore desulfurization
catalyst that has poor metals capacity, both catalysts
maintained at a temperature of at least 15C les~ than the
first zone.
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The present invention re~uires at least a 15C
temperature diference between the first zone and the
05 second zone. Referring to FIG. 1, the temperature profile
of a conventional m~ltiple catalyst bed reaction vessel is
shown. Bed 1 would be the first bed the feedstock would
contact, and, in the opera~ion shown, the coolest. Three
temperature zones are shown, separated by hydrogen
quenches. The average temperature for each zone is de-
noted by Tl ave, T2 ave and ~3 ave. At each quench point
there is~a drop in temperature, for examplel Ql In this
way the temperature increase of the exothermic catalytic
hydrogenation reactions of each zone are controlled. In
lS operation, the average temperatures of each catalyst bed
tend to rise, for example, Tl ave will frequently be 10C
cooler than T2 ave. Economic operation of the reactor
dictates using less quench gas than is necessary to
achieve Tl ave = T2 ave. The change in temperature (~T)
for any bed in commercial operation will frequently be
from 10C to 20C.
FIG. 2 shows an example of the present inven-
tion, a reactor containing 3 catalyst beds in which the
first bed operates at ~ higher temperature than the down~
stream beds. Bed 1 is the first. catalyst bed the feed-
stock contacts, but unli]ce conventionaL operation, it is
the hottest bed the feedstock contacts. The change in
average temperature in the operation of the present
invention is at least 15C. T2 ave and T3 ave are pref-
erably held closer together than typical in conventionaloperation. In FIG. 2 the first zone comprises Bed 1 and
the second ~one comprises Beds 2 and 3. It will be noted
that ~T ave is much greater in the operation of this
invention than it is conventionally, thereby providing a
second, cooler temperature zone.
The temperature profile will be observed to have
several sharp drops at various points along the length of
the reaction vessel. These correspond to gaseous hydrogen
quenches inside the reaction vessel. For the maintenance
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of the desired temperature profile of the present inven-
tion, more hydrogen must be used at the junction of the
05 first and second bed than at any other quenching point.
It should~be appreciated that although the tem-
peratures of FIG. 1 are of a single reactor, multiple
temperature controlled reactors can be used. For example,
guard bed reactors in separate vessels, at a temperature
15C hotter, could be substituted. The temperature of the
catalyst beds generally increases during the life of the
catalysts of the beds to maintain a preselected quality of
productl The temperature cannot increase beyond certain
limits dictated by metallurgic constraints of the reaction
vessel. When the first zone, the hottest, reaches the
maximum temperature which the reaction vessel can toler-
ate, the temperature of that zone must be held at a
constant value, allowing the temperature of the second
zone to eventually equal that of the first zone. When the
two zones are at the same temperature, the end of run of
that catalyst charge has been reached.
Although Applicants do not wish to be bound to
any particular theory of operation, it is believed that
the demetalation catalyst of the first zone has contami-
nation removal activity similar to the desulurizationcatalyst of the second zone, which has more metals than
the demetalation catalyst, even though the demetalation
catalyst has less intrinsic activity, because of the
temperature differential. More metals are removed in the
first zone, which does not lose activity rapidly, and the
catalyst of the second zone does not lose activity for
desulfuri~ation as rapidly. The total catalyst system,
therefore, has longer life than otherwise would be
possible.
EXAMPLE
The followiny catalysts were prepared to use in
a reactor with the inverse temperature profile of the
present invention. Catalyst A is prepared as follows:
Eight milliliters of 88 percent formic acid
(specific gravity 1.~) was added to 300 milliliters of
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distilled water. This solution was added to 500 grams of
Kaiser alumina at about 50°C and about 50 milliliters
every minute shile mixing. The mixing continued for 20
minutes after all the solution had been added. A second
solution made from 6 milliliters of 58 percent ammonium
hydroxide, 45 milliliters of molydbenum solution, and
200 milliliters of distilled water was added at a rate of
50 millilters per minute while stirring. The molybdenum
solution was prepared by dissolving 17.4 grams of MoO3 in
17.2 millilters of 30 percent NH4OH and 26 millilters of
distilled water. The temperature during the second addi-
tion was approximately 60°C. to 65°C. The doughy mixture
was extruded with a trilobal fluted die and dried on a
screen tray in a preheated oven at 120°C for 2 hours and
then at 200°C for 2 hours. The dried extrudate was
calcined at 680°C in a steam stmospher. After one hour,
fresh dry air replaced the stream and the extrudate was
calcined for another half an hour at 680°C.
Catalyst B is prepared according to the
procedure described in U.S. Patent No. 4,113,661 issued to
P. W. Tamm, September 12, 1987, entitled "Method for
Preparing a Hydrodesulfurization Catalyst." An 80/20 by
weight mixture of Catapal*, made by Conoco, alumina and
Kaiser alumina are sized in the range below about 150
microns and treated by thoroughly admixing the mixed
powders with a aqueous solution of nitric acid, were for
each formula weight of the alumina (Al2O3) about 0.1
equivalent of acid is used. The treated alumina powder is
in the form of a workable paste. A sample of this paste
completely disperses when one part is slurried in four
parts by weight of water. The pH of the slurry is in the
range of about 3.8 to about 4.2, usually about 4.0 After
hydroxide is thoroughy admixed into the paste in an amount
equivalent to about 80 percent of the ammonium hydroxide
theoretically required to completely neutralize the nitric
acid; that is, about 0.08 equivalent of the hydroxide is
*Trade Mark
added to the paste per formula weight of the alumina present. The
ammonium hydroxide used i5 desirably about an 11 percent by weight
solution because the volatile material evolved during drying and cal-
cination content of the treated and neutralized solids should be in the
range of 50 to 70 weight percent. With the addition and thorough
admixing of ammonium hydroxide, the paste changes to a free-flowing
particulate solid suitable as a feed to an extruder. The extruder has
a die plate that will extrude the shaped particles of -the present invention.
The extrudate precursor is freed of loosely-held water by an initial
moderate drying step, for example, at a temperature in the range of 75C
to 250C. The preparation of the carrier is then completed by calcining
the dried extrudate at a temperature between 250C to 800C in a dry or humi~
atmosphere, The resulting carrier has a pore volume o~ about 0.7 cubic
centimeters/gram, of which at least about 85 percent is furnished by
pores having a diameter in the range between about 80 and 150 Angstroms.
Less thcan about 1.0 percent of pore volume is furnished by pores larger
than 1,000 Angstroms. By calcining the catalyst in a 100 percent
steam atmosphere at 450C to 600C, larger pores, for example, 160
Angstroms to 190 Angstroms, may be obtained~
A ractor was charged with two layers of catalyst. The first
layer and first zone was Catalyst A and the second layer and second zone
was Catalyst B. An Arabian Heavy Atmospheric residue of 4.~ weight
percent sulfur, 26 ppm nickel and 89 ppm vanadium was contactecl with
Catalysts A and B in series. Initially, conditions were 2,200 psig,
about 1,800 psig average pressure of hydrogen and about 0.35 hr 1 space
velocity, with the first catalyst kept at about 1~C hotter than the
second catalyst. The -temperature of the two beds was increased to maintain
a constant sulfur concentration of 0.6 we:ight percent in the effluent from
the second zone. At mid-run, the length oE the run possible for this
system was extrapolated. End of run for this system is the metallurgical
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limit of the reaction vessel. The temperature difference
between the first and second zone was increased to 2~C.
05 The temperature of the vessel was increased until the
first zone was 427~, the metallurgical limit of the reac-
tion vessel and the temperature of the first ~one was held
constant as the temperature of the second zone was
increased to 427C, the end of the run. The actual time
of this run was about 25 percent better than the length of
run estimated from mid-run extrapolations. The increase
in catalyst life is believed to be a function of the
larger difference in average temperature.
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