Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to catalytic hydrotreating or
catalytic hydrocracking of hydrocarbon materials and, more
particularly, to catalytic hydrocracking of heavy
hydrocarbon oils, such as bitumen from tar sands.
Proven reserves of conventional crude oil supplies are
expected to diminish significantly within the next two
decades. As the available amount of relatively light
crude oil decreases, other sources which can be used as
raw materials to produce hydrocarbon fuels must be
utilized. Initially there will be a tendency to use
progressively heavier and heavier crude oils. These
substances must be refined to a greater extent in order to
make products which are equivalent to those which in the
past have come from conventional light crude oils. For
example, heavier crude oils tend to have higher
concentrations of asphaltenes and also larger values of
Conradson carbon residue, which is an indication of the
coke forming tendency of a particular hydrocarbon
material. Several changes must be made to these heavy
crude oils in order to transform them into usable fuel
products. The major change is the conversion of the
higher boiling larger molecules into lower boiling smaller
molecules,
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There are several potential processes for this
molecular weight reduction. For example, coking processes
have been used to a considerable extent in the past. The
:~ most undesirable feature of the coking processes is that
large quantities of coke are produced as an unusable
by-product. The coke originates in the asphaltenes and
- coke-precursors contained in the original crude oil.
The heavier crude oils contain larger quantities of
asphaltenes and coke precursors and, therefore, produce
larger quantities of by-product coke. This coke is high
in sulphur and also contains large concentrations of
metals, such as nickel, vanadium and frequently iron.
Disposal of this coke is a major problem. ThUs, it cannot
readily be used as a conventional fuel because the large
quantities of sulphur in the coke necessitates the use of
expensive stack gas scrubbing facilities to prevent
excessive dioxide emissions to the atmosphere and
consequent acid rains. This coke is also not well suited
to the production of electrodes such as those used in the
aluminum or related industries because the metal
concentrations within the coke are unacceptably high~ The
end result is that the coke by-product obtained from the
coking processes is at best very difficult to dispose of.
It is, of course, highly desirable to be able to
replace the coking processes with a process which is
capable of converting all of the high molecular weight
species in the heavy crude oils into usable liquid `
products. Hydrocracking is such a process and various
configurations of this process have been used
commercially. ~or example, there are fixed bed reactors
in which a heavy oil feedstock and hydrogen are combined
and passed through a vessel containing a fixed bed of
catalyst. Alternatively, fluidized beds or ebullating
beds of catalyst have been used in which the combination
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r of hydrogen and liquid hydrocarbon feedstock enters the
bottom of the vessel where small sized catalyst particles
are suspended in a fluidized state. Using the
hydrocracking process, virtually all of the feedstock is
converted into usable liquid fuels or into liquid products
for which conventional refining technologies are
available. However, the hydrocracking process also has
one operational deficiency. When these heavy crude oils
are processed in the presence of a catalyst, there is a
tendency for large quantities of coke and also large
concentrations of metals (which originate in the organo-
metallic compounds in the heavy crude oil) to deposit on
the catalyst surface. This catalyst deactivation has a
profound influence on the operation of the process, as the
conversion rate decreases substantially with time.
Initially, coke deposition is the predominant deactivation
mechanism. After longer periods of time, both coke
deposition and metals deposition are responsible for the
deactivation of the catalyst.
Studies have shown that catalysts contain at least two
kinds of coke. One type of coke acts as a reaction
intermediate which is subsequently converted into reaction
products. The other type of coke is an unreactive
material which blocks catalytic sites and decreases
activity of the catalyst. Ideally, the formation of coke
which blocks catalytic sites should be minimized.
The commonly used hydrocracking catalysts consist of
combinations of compounds containing group VI elements
(chromium, molybdenum and tungsten), group VIII elements
i`
(cobalt and nickel) and a catalyst support such as
alumina, silica or chemical or physical combinations of
silica-alumina. Such catalysts are expensive to produce
and deactivate rapidly at hydrocracking conditions, making
;` them poorly suited to catalytic hydrotreating or
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hydrocracking of large volumes of many types of heavy
hydrocarbon oils.
Other elements that have been used in catalysts for
the conversion of hydrocarbons are the alkali metals and
alkaline earth metals. For instance, S.P.S. Andrew I. &
E.C. Prod. Res. Dev. 8, 321 (1969) describes a steam
reforming catalyst which is a nickel catalyst containing
alkaline compounds as activators. In discussing the
function of such catalyst, the article states ""the
success of alkalized nickel reforming catalysts.O.is
primarily due to its ability to increase the rate of
removal of carbon residues from the nickel surface by
steam gasification." This represents but one example and
it has been known for many years that alkaline eompounds
have the ability to eatalyze the steam-carbon reaction.
Another example of the use of an alkaline earth metal
in a steam reforming catalyst is Canadian Patent 811,139
in which a large amount of alkaline earth metal is used in
a nickel, alumina catalyst.
~UMMARY OF THE INVENTION
Aecording to the present invention, it has been quite
surprisingly discovered that the alkali metals and
alkaline earth metals when present in small quantities in
the usual hydrocraeking eatalyst are highly effective in
preventing the deposition of earbonaceous materials on the
surface of the catalyst. Thus, the present invention in
its broadest aspect relates to an improvement in the
proeess for catalytically hydrotreating or catalytically
hydroeracking a hydrocarbon material in which a
hydrocarbon material and hydrogen are reacted under heat
and pressure in the presence of a catalyst comprising at
least one group VIb element and at least one group VIII
element on a silica, alumina or silica-alumina support,
the improvement being the presenee of a small amount of at
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least one group Ia element, whereby deposition of
carbonaceous materials on the surface of the catalyst is
substantially decreased.
As the group Ia elements there can be specifically
mentioned lithium, sodium, potassium, rubidium, cesium and
francium. The added materials interact with compounds in
the hydrocracking catalyst to produce a decreased rate of
formation of unreactive carbonaceous deposits which block
catalytic sites. By having fewer unreactive carbonaceous
deposits on the catalyst, it is possible for a higher prop-
ortion of the reactive sites to participate in reactions.
One function of the group Ia elements may be that they
affect the acid-base properties of the solid catalyst
support. Frequently the materials which are used as
; 15 catalyst supports, such as silica, alumina or their
mixtures, have acidic sites. Two types of acidic sites
have been described theoretically. Bronsted acids are
those which are hydrogen donors. Lewis acids are those
which are electron pair acceptors. Hydrocracking and
; 20 hydrotreating catalysts of the type used in the present
invention sometimes contain both types of acid sites.
. Adding the group Ia elements tends to make such catalyst
~` more basic. In principal this should involve the
elimination of some of the acidic sites, particularly of
the Lewis type. Any undesirable reactions which are
promoted by acid sites, such as coke deposition, are
believed to be hindered when the number of acid sites are
decreased and the basicity of the catalyst is increased.
The process of this invention can be carried out with
advantage ~or a variety of different purposes. For
instance, a heavy crude oil may be hydrocracked with the
object of reducing its molecular weight. .Other reactions,
such as sulphur removal, nitrogen removal, oxygen removal,
hydrogenation of aromatics, olefins and other unsaturated
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compounds will occur simultaneously. The process may also
be used to hydrotreat hydrocarbon feedstocks for sulphur
removal, nitrogen removal or hydrogen addition without
extensive molecular weight reduction.
Heavy hydrocarbon feedstocks which can be p~ocessed
can include such materials as petroleum crude oil,
atmosphere tar bottoms products, vacuum tar bottoms
products, heavy cycle oils, shale oils, coal derived
fluids, crude oil residuum, topped crude oils and the
heavy bituminous oils extracted from tar sands. Of
particular interest are the oils extracted from tar sands
which contain wide boiling range materials from naphtha
through kerosene, gas oil, pitch, etc., and which contain
a large proportion, usually more than about 40 to 50~ by
weight of materials boiling above 524C, equivalent
atmospheric boiling point.
~n a typical process in accordance with the invention,
the feedstock is heated to about 50-400C, preferably
75-250C, and mixed with hydrogen. After the hydrogen
addition, the mixture is heated further to about 250-550C,
preferably 375-~75C. This oil-hydrogen mixture enters
the reactor and flows through a catalyst bed. This
catalyst bed can be either a fixed bed or a fluidized or
ebullated bed. The hydrogen gas and oil feedstock contact
the catalyst in such a way that both reactants are present
and available and the reaction can occur. The reaction is
preferably carried out at a pressure of up to 3000 psig
and a hydrogen partial pressure in the range of 1 atm to
1000 psig. The liquid space velocity is conveniently in
the range 0.1 hr 1 to 35 hr 1, preferably 0.5 hr 1
to 20 hr 1.
Reaction pressures used are a function of the
properties of the feedstock, as characterized by molecular
type and boiling point range. Thus, for hydrocarbon
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feedstocks containing components boiling above 525C, a
pressure of 500-3000 psig is preferred. For gas oil
feedstocks containing components boiling between
200-525C, a pressure of 50-1500 psig is preferred, while
for naphtha feedstocks having components boiling between
room temperature and 250C a pressure of 20-1000 psig is
preferred. The reactor can be a downflow trickle bed
reactor or an upflow fixed bed reactor. Alternatively, it
may be a fluidized bed or ebullated bed reactor. After
the products leave the reaction vessel they are separated.
Either a single separation vessel or a series of
separation vessels may be used. When a series of
separation vessels are used, subsequent vessels are
maintained at decreasing pressures. The vapours leave
through the top of the separation vessel and the liquid
~ through the bottom. A hydrogen rich vapour stream can be
- recycled to the reactor after removing some of the H2S~
acid gases and light hydrocarbon gases.
The liquid product obtained can be used in a number of
different ways. Thus, the total liquid product may be fed
directly into a pipeline. Alternatively, the liquid
; product can be separated by fractionation, distillation or
other means and the resulting streams can be hydrotreated
separately. The highest boiling material, e.g. that
~oiling above about 525C, may be used on the site to
provide energy for the process. Alternatively, it may be
gasified and the gasification product may be used as a
source of process energy.
The alkali metal or alkaline earth metal compounds
used in the catalyst may conveniently be in the form of an
oxide, hydroxide or carbonate. ~ typical catalyst may
contain 0.5-35% by weight of a group VI element,
- preferably molybdenum or tungsten. It may also contain up
to 10% by weight, preferably 0.5-6~ by weight of a group
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VIII elementr preferably cobalt or nickel oxide. The
amount of group Ia element in the catalyst is usually
based on the amount of group VI element present and is
usually in an atomic ratio of 0.1:10, preferably 0.3:4~ to
the group VI elements.
The catalyst used in this invention may have a variety
of geometries. The catalyst typically have pore sizes,
from 2 to 1000 nm, preferably 8 to 60 nm and a surface
area greater than 50 m2/g. Small pore zeolites, such as
those having pore sizes smaller than 2 nm,are not normally
utilized in the present invention. The reason for this is
that the pores in the zeolites are so small that they do
not permit the entrance of the high molecular weight
hydrocarbon species involved in the hydrocracking or
hydrotreating reactions of this invention. The catalyst
supports are of the amorphous type and are not crystalline
when they contain pores of the sizes utilized in the
present invention. These pore sizes have several effects
on the reaction rate. In general, the larger the pore
size the laeger the size of the molecules which can enter
the pore and therefore react within the interior of the
catalyst. If the pores are relatively small, for example,
5-6 nm, some of the larger molecules are unable to enter
the pores. In other cases where the hydrocarbon molecules
a~e small enough to enter the pores, the rate of diffusion
of the molecule within the pore is quite slow. Larger
molecules quite often react predominently within the
surface region of pellets or extrudates of the catalyst.
On the other hand, if the catalyst contains pores of
larger sizes, for example 40 to 60 nm, the large
organo-metallic species are able to re-enter the pores and
penetrate throughout the catalyst form. When heavy crude
oils are processed, the metals are neither deposited at
the pore mouth exclusively nor predominantly within the
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exterior shell of the catalyst shape. Instead, they are
distributed more evenly throughout the entire catalyst.
This means that the reaction rate tends to be enhanced as
the metal deposits are uniform and therefore the whole
catalyst can be used. The catalyst life is extended and
the catalyst can be used for longer periods of time. When
distillate fractions are hydrotreated in catalysts having
large pores, the rates of molecular diffusion are higher
than in small pore catalysts. As a result, the reactants
diffuse further toward the center of the catalyst particle
so that reaction is not restricted to a thin shell on the
exterior of the catalyst particle.
Unfortunately, the effect of catalyst size is not
single valued. By making the catalyst pores larger it is
possible for large molecules to go to the interior of the
catalyst. Some of these large molecules are coke
precursors and as the pores increase in size, the amount
of coke per unit surface area of catalyst increases. This
tends to increase the rate at which the catalyst
deactivates.
The catalysts used in the process of this invention
can be prepared in a variety of different ways. For
example, a calcined catalyst support may be impregnated by
solutions contalning the desired components. As an
example, gamma alumina can be impregnated with solutions
containing cobalt ions, molybdate ions and group I metal
ions. The resulting material is then calcined again to
` produce the catalyst product. According to another
procedure, the catalyst may be prepared by adding
compounds containing the desired components into a gel
composed of water and the material which would become the
catalyst support. When the gel is dried and calcined, the
excess water is driven off and the metals converted to the
corresponding oxides. They may also be prepared by
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coprecipitation or mechanical mixing of components. These
all represent well known techniques in the industry.
Ceetain preferred embodiments of this invention will
now be further illustrated by the following non-limitative
examples. The results are shown on the attached drawings
in which:
Figure 1 is a series of plots showing +525C pitch,
oxygen, sulphur and nitrogen conversions v. lithium to
molybdenum atomic ratio;
Figure 2 is a series of plots showing surface area,
hydrogen to carbon ratio and coke content v. lithium to
molybdenum atomic ratio;
Figure 3 is a series of plots showing ~525C pitch,
oxygen, sulphur and nitrogen conversions v. sodium to
molybdenum atomic ratio;
Eigure 4 is a series of plots showing surface area,
hydrogen to carbon ratio and coke content v. sodium to
molybdenum atomic ratio;
Figure 5 is a series of plots showing +525C pitch,
oxygen, sulphur and nitrogen conversions v. potassium to
molybdenum atom ratios;
~igure 6 is a series of plots showing surface area,
hydrogen to carbon ratio and coke content v. potassium to
molybdenum atom ratio; and
Figure 7 is a series of plots showing specific gravity,
sulphur content and nitrogen content v. time on stream.
Example 1
A series of catalyst samples were prepared, each
` sample having a base consisting of 5 kg o~ alpha~alumina
monohydrate powder (a mixture of 20% by weight of Conoco
Catapal~ SB and 80% by weight of Catapal~N). This
powder was placed in a mix muller and solutions of cobalt
nitrate and ammonium paramolybdate were mixed into the
powder such that when calcined it contained 2.2% by weight
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of the molybenum trioxide and 1.1% by weight of the cobalt
oxide. The group la element was added to the catalyst in
the form of a solution of lithium carbonate. Four
catalyst samples were prepared in the above manner having
the same amounts of cobaltand molybdenum but with
increasing amounts of lithium carbonate at atomic ratios
of lithium to molybdenum of 1, 1.8, 4.2 and 8.5. These
were compaeed with one catalyst which did not contain a
group Ia element.
These materials were mixed in the muller and a small
amount of stearic acid was added before the mulled powder
was extruded into 3.18 mm diameter extrudates. These
extrudates were dried at 110C overnight and then calcined
at 500C for approximately 8 hours.
The samples of the catalysts were analyzed for cobalt
and molybdenum via a standard atomic absorption
technique. The lithium concentrations were determined by
a standard flame photometer approach after dissolving the
extrudates in hydrochloric acid.
As a feedstock for hydrocracking there was used an
" Athabasca bitumen obtained the from ~reat Canadian Oil
Sands Ltd. at ~ort McMurray, Alberta. This bitumen had
the general properties shown in Table 1 below
TABLE 1
_ General ProPerties of At~ !abaSca Bi tumen
Specific Gravity, 16/16C 1.009
As`h (wt.~) 700C 0.59
Iron (ppm) 358
Nickel (ppm) 67
Vanadium (ppm) 213
Conradson Carbon Residue (wt.%) 13.3
Pentane Insolubles (wt.%) 15 5
Benzene Insolubles (wt.%) 0 72
Sulphur (wt.%) 4.48
Nitrogen (wt.%) 0.43
Oxygen (wt.~) 0.95
Carbon (wt.%) 83.36
Hydrogen (wt.%) 10 52
+525C Residuum twt.%) 48 03
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Catalyst evaluation experiments were performed in a
fixed-bed reactor system using the above feedstock. The
reactor was filled completely with extrudates and the
bitumen, mixed with hydrogen (purity 99.9 wt.%), flowed
into the bottom of the reactor as a bottom feed. Each
; catalyst sample was evaluated at a pressure of 13.9 MPa
and a temperature of 450C with a liquid volumetric space
velocity of 0.29 ks based on the total empty reactor
volume. The hydrogen flow rate was set at 43.1 ml/s at
S.T.P. The reactor was kept at steady state for one hour
preceding and for two hours during the liquid product
collection period. Prior to the evaluation experiments,
each catalyst was presulphided in the presence of bitumen
and hydrogen for approximately 14.4 ks. The feedstock and
liquid products were analyzed for carbon, hydrogen,
sulphur, nitrogen, oxygen and the fraction boiling above
525C. Hydrogen and carbon elemental analysis were
performed using a Perkin Elmer model 240 analyzer. Oxygen
was determined via neutron activation analysis using a
neutron generator.
The coke concentration was determined on both a used
catalyst and on a ~resh catalyst which acted as a
` reference. The fresh reference catalyst was saturated
with the appropriately matched liquid product obtained
from the corresponding catalyst evaluation experiment.
During saturation, the fresh reference catalyst was
evacuated and then impregnated with liquid reaction
product for approximately 0.9 ks at 55.3 MPa and at room
temperature. Paired catalyst samples (i.e. reference and
used) were then deoiled in a flowing hydrogen stream (7.29
x 105 m3/s at S.T.P.) while the temperature was raised
over a one hour period to 600C. The samples were kept at
600C for 0.9 ks then allowed to cool to 200C in the
flowing hydrogen stream. The paired catalysts were then
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weighed and left overnight in a mufEle furnace at 600C.
The change in weight after oxidation in the muffle furnace
was ascribed to the coke being removed from the
catalysts. Each of the weight changes was expressed as a
percent of the final catalyst weight (i.e. coke free
catalyst basis). The amount of coke on the fresh
reference catalyst was ascribed to coke formed during
deoiling from the hydrocarbon product adhering to the
catalyst. The amount of coke on the reference catalyst
was subtracted from the amount of coke on the used
catalyst to obtain the coke values reported. This
empirical definition of coke is used to represent the
amount of coke on the used catalyst after removal from the
reactor but prior to the deoiling procedure.
The results of these tests are shown in Figures 1 and
2 of the drawings. In ~igure 1 the conversion results are
shown in solid lines and solid circles, while the amounts
of reaction per unit surface area are shown by the dotted
lines and open squares for catalysts containing lithium.
The conversion results generally go through a maximum as
additional lithium is added to the catalyst. The amount
- of reaction per unit area went through a maximum as
lithium was added to the catalyst.
Figure 2 shows the surface area, H/C ratio in the
liquid, and coke content of catalysts containing lithium.
The surface area of the fresh catalyst and hydrogen to
carbon ratio in the liquid product go through a maximum
and then decrease with increasing lithium content of the
catalyst. The coke content goes through a minimum and
then increases with increasing lithium content of the
catalyst. The decreased quantities of coke on catalysts
containing small quantities of lithium illustrate the
object of the present invention.
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Example 2
A new series of catalyst samples were prepared using
the same procedures and materials as in Example 1 except
that the lithium carbonate was replaced by sodium
carbonate.
The same feedstock was used as in Example l and the
same series of catalyst evaluation experiments were
carfied out in the fixed bed reactor.
The results of these tests were shown in Figures 3 and
4, with Eigure 3 showing the conversion results as solid
lines and solid circles and the amounts of reaction per
unit surface area as dotted lines and open squares for the
catalysts containing sodium. In this case, all the
conversion results decreased as the amount of sodium in
the catalyst increased. On a unit surface area basis, the
amounts of pitch removed and oxygen removed increased
slightly with increasing concentration of sodium in the
catalyst.
Eigure 4 shows the surface area, H/C ratio in the
` 20 liquid product and coke content of catalysts containing
sodium. All the quantities decreased with the addition of
sodium and the decreased coke content showed that there -
are smaller quantities of carbonaceous deposits on the
catalyst.
Example 3
The procedures of Example 1 were repeated once again
` and catalyst samples were once more prepared with the only
change being the replacement of lithium carbonate with
~- potassium carbonate. The catalyst evaluation experiments
were repeated again in the fixed bed reactor using the
~ same feedstock and conditions as in Example l. The
:~ results obtained are shown in Eigures 5 and 6 of the
~` drawings.
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Figure 5 shows the conversion results as solid lines
and solid circles and the amounts of reactions per unit
surface area as dotted lines and open squares for the
catalysts containing potassium. All of the conversion
results decrease as the amount of potassium in the
catalyst increases and on a unit surface area basis, the
amounts of pitch removed and oxygen removed increased
slightly with increasing concentration of potassium in the
catalyst. The amounts of sulphur removed and nitrogen
` 10 removed per unit area generally decreased with increasing
potassium content in the catalyst.
Figure 6 shows the surface area, H/C ratio in the
` liquid product, and coke content of the catalyst
containing potassium. All three quantities decreased with
the addition of potassium. The decreased coke content
shows that there are smaller quantities of carbonaceous
deposits in the catalyst of this invention.
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