Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
108~ 6
- 2 -
The invention relates to a process for the catalytic
hydrodesulphurization of heavy hydrocarbons.
Heavy hydrocarbon oils such as residues obtained
in the distillation of crude petroleum oils at atmospheric
pressure (known as long residues) generally contain
a considerablequantity of sulphur compounds. In order
to reduce the sulphur content of the heavy oils they
may be subjected to a catalytic hydrodesulphurization
treatment. This treatment is carried out by contacting
the heavy oil, together with hydrogen, at elevated temperature
and pressure with a desulphurization catalyst. Suitable
catalysts for this purpose are those which contain nickel
and/or cobalt and in addition molybdenum and/or tungsten
supported on a carrier. One drawback to this direct
desulphurization route is that a fairly rapid deactivation
of the catalyst generally occurs. This catalyst deactivation
is caused because the above-mentioned heavy hydrocarbon
oils generally contain a considerable quantity of asphaltenes
and metal compounds such as nickel and vanadium compounds,
a considerable proportion of which metal compounds are
present bound to the asphaltenes in the oil. These compounds
are deposited on the catalyst during the desulphurization
process, as result of which the catalyst deactivates
rapidly. It has been found that the catalyst deactivation
which occurs in the hydrodesulphurization of heavy
hydrocarbon oils by the direct route can be partly
1~8~1)1~i
-- 3 --
compensated by carrying out the process in the presence
of a quantity of water corresponding with a water vapour
partial pressure in the process of 0.5-30 bar. It has
further been found that the favourable effect of steam
on the catalyst activity in the hydrodesulphurization
of the present heavy oils occurs both if the process
is carried out at high pressure (PH ~ 90 bar) and
if the process takes place at low pressure (PH < 90 bar).
In order to avoid the above-mentioned catalyst
deactivation caused by the deposition of asphaltenes
and metal compounds, the heavy oil can be deasphalted
before being subjected to the catalytic hydrodesulphuriz-
ation treatment. This indirect desulphurization route,
which is applied in practice inter alia for the desulphurization
of long residues, is effected by first separating the
long residue by distillation at reduced pressure into
a distillate fraction and a residual fraction, subsequently
deasphalting the residual fraction and mixing the deasphalted
oil with the distillate fraction, and finally desulphurizing
the resultant mixture. If desired, for example when
the heavy oil contains too few light components, the
distillation at reduced pressure may be omitted and
the deasphalting treatment may be directly applied to
the heavy oil to be d~ulphurized. Just as in the direct
desulphurization route, catalysts which contain nickel
and/or cobalt and in addition molybdenum and/or tungsten
supported on a carrier have also been found very suitable
for application in the indirect desulphurization route.
It has now been found that for the desulphurization at hydrogen
partial pressures below 90 bar of heavy hydrocarbon oils which consist at
least partly of deasphalted oils, the activity of catalysts which contain
nickel and/or cobalt and in an addition molybdenum and/or tungsten
supported on a carrier can be considerably increased by carrying out the
process in the presence of a quantity of water corresponding with a water
vapour partial pressure in the process of 0.1-10 bar.
This discovery may be regarded as surprising for two reasons.
In the first place it has been determined that the presence bf steam in
the hydrodesulphurization of hydrocarbon oil distillates with the application
of the present catalysts has no effect at all on their activity. This is
the case both if the process is carried out at high pressure (PH ~ 90 bar)
and if the process takes place at low pressure (PH ~ 90 bar). In the
second place, it has been determined that the favourable effect of steam in
the hydrodesulphurization of heavy oils consisting at least partly of
deasphalted oils with the application of the present catalysts does not
; occur if the process is carried out at high pressure.
The present invention therefore relates to a process for the
catalytic hydrodesulphurization of heavy hydrocarbon oils, in which process
a heavy hydrocarbon oil consisting of a mixture of a distillate obtained in
the distillation at reduced pressure of a long residue with a deasphalted
short residue is contacted at elevated temperature, a hydrogen partial
pressure below 90 bar and in the presence of a quantity of water corres-
ponding with a water vapour partial pressure during the process of 0.1-10
bar, with a catalyst which contains nickel, cobalt or a mixture thereof
and in addition molybdenum, tungsten or a mixture thereof supported on a
carrier.
In the process according to the invention the feed used must be
a heavy hydrocarbon oil consisting at least partly of deasphalted oil, for
~ - 4 -
-
80~6
example a deasphalted distillation residue of a crude oil. This distillation
residue may have been obtained both from distillation at atmospheric
pressure (long residue) and from distillation at reduced pressure (short
residue). Although in the process according to the invention it is in
principle possible to start from a feed consisting entirely of a deasphalted
oil, for example a deasphalted long or short residue, the feed chosen is
preferably a mixture of a distillate obtained in the distillation at reduced
pressure of a long residue and a deasphalted short residue. A very suitable
feed for the process according to the invention can be prepared by separating
a long residue by distillation at reduced pressure into a distillate and a
short residue, deasphalting the short residue and mixing the distillate with
the deasphalted oil, preferably in production ratio. If in the process
according to the invention use is made of a distillate obtained from the
distillation at reduced pressure
lt!~38~6
of a long residue as one of the components making up
the feed, a flashed distillate of a long residue is
preferably chosen for this purpose. ~ r
In the process according to the invention the
feed should consist at least partly of a deaaphalted
oil. Deasphalting of the oil is preferably carried
out at elevated temperature and pressure and in the
presence of an excess of a lower hydrocarbon as solvent,
such as propane, butane or pentane or a mixture thereof.
According to the invention the hydrodesulphurization
is carried out in the presence of a quantity of water
corresponding with a water vapour partial pressure
during the process of 0.1-10 bar. The quantity of water
used should preferably correspond with a water vapour
partial pressure during the process of 0.5-7.5 bar.
The requisite quantity of water can be added to the
gas and/or liquid stream which is passed over the catalyst.
The water may be added as such, for example to the heavy
oil to be desulphurized, or steam can be added to the
hydrogen stream which is supplied to the process. If
desired, instead of water, a compound can be added,
such as a lower alcohol, from which water is formed
under the prevailing reaction conditions.
The catalysts which are suitable to be used in
the process according to the invention contain nickel
and/or cobalt and in addition molybdenum and/or tungsten
supported on a carrier. Preferably, catalysts are used
which contain 0.5-20 parts by weight and in particular
1~8~
0.5-10 parts by weight of nickel and/or cobalt and 2.5-60
parts by weight and in particular 25-30 parts by weight
of molybdenum and/or tungsten per 100 parts by weight
of carrier. The atomic ratio between the nickel and/or
cobalt on the one hand and the molybdenum and/or tungsten
on the other may vary within wide limits, but is preferably
between 0.1 and 5. Examples of very suitable metal
combinations for the present catalysts are nickel/tungsten,
nickel/molybdenum, cobalt/molybdenum and nickel/cobalt/molybdenwn.
The metals may be present on the carrier in metallic
form or in the form of their oxides or sulphides. It
is preferred to use the catalysts in the form of their
sulphides. Very suitable carriers for the present catalysts
are oxides of elements from Groups II, III and IV of
the Periodic System, such as silica, alumina, magnesia
and zirconia, or mixtures of the said oxides such as
silica-alumina, silica-magnesia, alumina-magnesia and
silica-zirconia. It is preferred to use aluminas and
silica-aluminas as carrier for the present catalysts.
The preparation of the present catalysts is preferably
carried out by single-stage or multi-stage coimpregnation
of a carrier with an aqueous solution which contains
one or more nickel and/or cobalt compounds and one
or more molybdenum and/or tungsten compounds, followed
by drying and calcining of the composition. During
drying of the compositions, which is generally carried
out at temperatures between 100 and 150C, physically
10880~;
-- 8 --
bound water is removed from the compositions; during
the calcining of the compositions, which is generally
effected by heating the compositions to a final temperature
between 450 and 550C and maintanining the compositions
for some time at this final temperature, decomposition
of the metal salts with formation of the corresponding
metal oxides takes place. As nickel and cobalt compounds,
frequent use is made of the nitrates in preparing the
present catalysts. As molybdenum and tungsten compounds,
ammonium molybdate and tungstate are generally used.
It has been found that during the calcining of
the present compositions, considerable heat effects ;
may occur which can adversely affect the activity of
the ultimate catalysts. In order to prepare catalysts
having a high activity it is therefore important to
minimize these heat effects during the calcining. One
of the causes of strong heat effects during the calcining
is the combined decomposition of nitrates and ammonium
compounds. The heat effects connected with this decomposition
may be avoided by using formiates of nickel or cobalt
instead of nitrates during the preparation of the catalysts.
Another possibility to minimize the heat effects occurring
during the calcining is to carry out the calcining
very carefully, for example by applying a low rate
of heating up, by carrying out heating in steps, etc.
Local overheating of the composition during the calcining, ~ !
with all its adverse effects on the activity of the
ultimate catalysts, can be largely avoided by ensuring
i~88~16
proper heat removal during the calcining, for example
by passing, while calcining is taking place, a gas stream
at high speed over the material to be calcined and
by calcining the material in a comparatively thin layer.
The catalytic hydrodesulphurization of heavy hydrocarbon
oils according to the invention is preferably carried
out by passing the hydrocarbon oil together with hydrogen
at elevated temperature and a hydrogen partial pressure
below 90 bar in an upward, downward or radial direction
through one or more vertically arranged fixed catalyst
beds. The hydrocarbon oil to be desulphurized may be
entirely or partly saturated with hydrogen, and in
addition to the hydrogen phase and the catalyst phase
a hydrogen-containing gas phase may be present in the
reactor. The hydrodesulphurization according to the
invention may be carried out in a single reactor, containing
one or more catalysts beds, or in two or more reactors.
An attractive manner of introducing steam when using
several catalyst beds in the process according to the
invention, consists of adding steam between two or
more of the catalyst beds.
The reaction conditions used during the hydrodesulphurization
according to the invention may vary within wide limits,
provided that the hydrogen partial pressure is less
than 90 bar. The hydrodesulphurization is preferably
carried out at a temperature of 300-450C, hydrogen
partial pressure of 10-75 bar, a space velocity of
8016
-- 10 -- ' ~
0.1-10 parts by weight of feed per part by volu~e of
catalyst per hour and a hydrogen/feed ratio of 150-2000
NlH2 per kg of feed. Particular preference is given
to a temperature of 325-425C, a hydrogen partial pressure
of 20-60 bar, a space velocity of 0.2-5 parts by weight
of feed per part by volume of catalyst per hour and
a hydrogen/feed ratio of 250-1500 NlH2 per kg of feed.
As has been mentioned above, the process according
to the invention is suitable inter alia to be applied
10 to deasphalted oils produced after deasphalting of
distillation residues obtained from the distillation
at atmospheric or reduced pressure of crude petroleum.
The process according to the invention is also very
suitable to be applied to deasphalted crude petroleum
15 and to deasphalted oils obtained after the deasphalting
of distillation residues deriving from the distillation
of products prepared by thermal or catalytic cracking
of heavy hydrocarbon oils. Where the above-mentioned
deasphalted oils are used as feed for the process according
20 to the invention, these oils can~be used as such or
mixed with distillate oils.
The end product of the process according to the
invention is a heavy hydrocarbon oil with a low sulphur
content, which is very suitable to serve inter alia
25 as feed for a catalytic conversion process for the
preparation of light hydrocarbon oils such as gasoline
and kerosine. Examples of such conversion processes
10~8()16
-- 11 --
are catalytic cracking and hydrocracking. Another very
suitable application of the desulphurized heavy hydrocarbon
oils prepared according to the invention is their use
as residual fuel oil with low sulphur content or their
use as low-sulphur blending component for the preparation
of residual fuel oils. In the latter application, the
other components in the blend may be both distillate
and residual components. A very suitable blending component
for the low-sulphur heavy hydrocarbonril for the preparation
of a residual fuel oil is the asphalt obtained in the
preparation of the deasphalted oil which serves as
feed for the process according to the invention.
The invention will now be elucidated with reference
to the following example.
EXAMPLE
The influence of steam on the activity of the
present catalysts for the hydrodesulphurization of various
hydrocarbon oils was investigated for two catalysts
( catalysts I and II) and three hydrocarbon oils (feeds
A, B and C) in a catalyst testing test. In this test
the oil, together with hydrogen, was passed in downward
direction through a vertically arranged cylindrical
reactor in which a fixed bed of the catalyst concerned
was present in the form of 1.5 mm extrudates. The experiments
were carried out at a water vapour partial pressure
varylng from 0-20 bar, which was obtained by adding
various quantities of water to the feeds. The composition
1~8t~016
- 12 -
of the catalysts, which were used in the form of their
sulphides, is shown below.
CATALYST I
Co/Mo/A12O3, containing 4.3 parts by weight of
cobalt and 10.9 parts by weight of molybdenum per 100
parts by weight of alumina carrier.
CATALYST II
Ni/Mo/A1203, containing 4.3 parts by weight of
cobalt and 10.9 parts by weight of molybdenum per 100
parts by weight of alumina carrier.
The three hydrocarbon oils which were used in
the present experiment may be described as follows.
FEED A
Hydrocarbon oil with a sulphur content of 3.24
% by weight and a total vanadium and nickel content
of 5 ppmw`, which oil had been obtained as follows starting
from a long residue of a Middle East crude oil.
100 Parts by weight of this long residue were
separated by flashing into 47 parts by weight of flashed
distillate and 53 parts by weight of short residue.
The short residue was deasphalted with n-butane as
solvent at an average temperature of 125C, a pressure
of 40 bar and a solvent/oil weight ratio of 4:1. In
this manner 33 parts by weight of deasphalted oil and
20 parts by weight of asphalt were obtained from the
short residue. The flashed distillate was mixed in production
ratio with the deasphalted oil into 80 parts by weight
of a heavy hydrocarbon oil which was used as feed A.
1~18~)16
- 13 --
FEED B
Hydrocarbon oil with sulphur content of 3.9~ by
weight, a total vanadium and nickel content of 62 ppmw
and a C5 asphaltene content of 6.4% by weight, which
oil had been obtained as long residue in the distillation
at atmospheric pressure of a Middle East crude oil.
FEED C
Hydrocarbon oil with a sulphur content of 2.6%
by weight, which oil had been obtained as distillate
in the flashing of a long residue of a Middle East
crude oil.
A total of 12 desulphurization experiments we~e
carried out. Experiments 1-4 with feed A were carried
out at a temperature of 395C, a space velocity of
0.8 kg of feed per kg of catalyst per hour and an H2/feed
ratio of 1000 NlH2 per kg of feed.
Experiments 5-8 with feed B were carried out at
a temperature of 420C, a space velocity of 4.35 kg
of feed per kg of catalyst per hour and an H2/feed
ratio of 250 NlH2 per kg of feed.
Experiments 9-12 with feed C were carried out at
a temperature of 350C, a space velocity of 2 kg of
feed per kg of catalysti per hour and an H2/feed ratio
of 4000 Nl/H2 per kg of feed.
The results of the desulphurization experiments
are shown in the table.
108E~ 6
-- 14
Table --
Exp. Feed Catalyst PH bar PH O,bar Sulphur in product
No. No. No. 2 2 % b~ weight
__________ ________ ________ ________ ___ ____ _________
1 A I 35 ~ 0.20
2 A I 35 5 0.14
3 AII 95 - 0.06
4 AII 95 5 o.o6
5 BII 70 - 2.5*)
B II 70 10 1.8*)
7 BII 150 - 1.4*)
8 BII 150 20 1.1*)
9 C I 70 - 0.21
10 C I 70 7 0.21
11 C I 150 - 0.11
12 C I 150 10 0.11
==_===========_==============================_==================
*) These figures indicate the average sulphur content ln
product, measured over the entire lifetime of the catalyst.
Of the experiments 1-12 shown in the table only
experiment 2 (low pressure/use of steam/feed consisting
partly of deasphalted oil) is an experiment according
to the invention. The other experiments are included
for the sake of comparison.
The results shown in the table clearly demonstrate
that the use of steam in the hydrodesulphurization
of hydrocarbon oils using the present catalysts:
ta) in the case of hydrocarbon residues, has a favourable
effect on catalyst activity, both at high and
low pressure (compare experiments 5-8)c
(b) in the case of hydrocarbon oil distillates, has
no effect on catalyst activity, neither at high
nor low pressure (compare experiments 9-12).
(ç) in the case of hydrocarbon oils consisting at least
partly of deasphalted oi], has a favourable effect
on catalyst activity at low pressure, but no effect
on catalyst activity at high pressure (compare
experiments 1-4).
