Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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H'~DROTREA'TING PROCESS
The present invc:.ntion relates to a process for hydrotreating
in a sing7_e reactor v:~elssel comprising at Least an upper and a lower
catalyst tied a hydrocarbon oil which is substantially liquid at
process conditions azad to a reactor vessel suitable for carrying
out such process.
It is. foreseen t:.hat the amount, of contaminating compounds,
such as sulphur' and aar°omatics, allowed to be present in hydrocarbon
oils according to en~,~i.rorunental legislation, wiL1 continuous7_y
decrease i.n thc=_ futu~.-e. _'herefore, there is much interest in
processes with the hf:l.p of which the content of ~>uch compounds in
hydrocarbcm oils can be reduced to a l.ow level in a commercially
attractive way.
In some c<3.talyti:c desulphurization processes, such as
described in e.g. Br:i:t:isa patent specification :irr20248, use is made
of two or more fixed-bed catalytic reaction systems, each
consisting, of one or more> react:ic>n vessels. The ~~ap:ital investment
needed for such procEesse_==; utilizing several reacr_ion vessels, is
higher than the capital investment nee-ded for th~~ present single
reactor vessel process .
The present invE:rat ion relatE:s to a process For hydrotreating
in a single reactor ~~essel comprising at least an upper and a lower
catalyst bed, a hydr<~carhon oil which is substantially liquid at
process conditi_ons,.~,r1-,i<:h process comprises:
(i) contacting partly hydrotreated.hydrocarbon oil
at elevated l~emperature and pressure in the upper catalyst
bed with a hydrotreating catalyst in the presence of clean
hydrogen containing gas,
(ii) separating the effluent of step (i) into
hydrotreated hydrocarbon oil and used hydrogen containing
gas, which hydrot::reated hydrocarbon oil is removed from
the process,
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(iii) contacting i-resh hydrocarbon oil at elevated
temperature and pressure with a hydrotreating catalyst in
the lower cat:alyst bet in the p:z:esence of used hydrogen
containing gas obtained in step (ii), wherein hydrogen
partial pressure in the upper catalyst bed is higher than
hydrogen partial pressure in the lower catalyst bed,
(iv) separating the effluent of step (iii) into partly
hydrotreated hydrocarbon oil and contaminated hydrogen
containing gas, which contaminated hydrogen containing gas
lc) is removed from the pz:-ocess, and
(v) transporting partly hydrotreated hydrocarbon oil
obtained in step (iv) to step (;i.) .
In the process according to the present invention,
the final hydrotreating step is carried out in the presence
of hydrogen which may contain a relatively small amount of
hydrogen sulphide, which leads t:o good hydrotreating
results.
The present hydrotreating process differs from
conventional hydrotreating processes, such as described in
2() US patent specification 4,243,5:L9, in the sequence of the
process steps. In the process according to the present
invention the final hydrotreating step is carried out in the
upper catalyst bed. Whereas, on the contrary, in the
conventional process, the final hydrotreating step is
2S carried out in a lower catalyst bed, which is situated
further downstream the hydrogen gas flow. By operating the
final hydrotreating step in the upper catalyst bed, one has
the advantage of operating it at the highest hydrogen
partial pressure maintained in t:he vessel, due to the
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pressure drop over thEy vessel. A higher hydrogen partial
pressure gives better hydrotreating results.
Further, they use of a feedstock which is
substantially liquid at process conditions makes that the
'S separation of hydrocarbon oil and hydrogen containing gas
can be attained without the need to cool down the partly
hydrotreated oil, separate gas from liquid and to heat the
partly hydrot.reated oi.l up again, which is dis-advantageous
from an economical point of view.
It. is now possible to obtain the same good results
as in a countercurrent. mode of operation without suffering
from the
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inherent disadvantages of countercurrent operation, such as
restrictions on the gas and liquid space velocity.
The present invention relates furthermore to a reactor vessel
suitable for hydrotreating a hydrocarbon oil according to the
invention, in which vessel:
(a) above the upper zone for retaining a catalyst bed is situated
an inlet for gas and an inlet for liquid,
(b) between the upper and lower zones for retaining a catalyst bed
is situated a separating means for separating liquid and gas,
(c) between the upper zone for retaining a catalyst bed and the
separating means is situated an outlet for liquid,
(d) between the separating means and the lower zone for retaining
a catalyst bed is situated an inlet for liquid,
(e) below the lower zone for retaining a catalyst bed is present
an outlet for gas and an outlet for liquid, or an outlet for
liquid and gas,
to which vessel a means is attached for transporting liquid
obtained from the outlet for liquid situated below the lower zone
for retaining a catalyst bed to the inlet for liquid situated above
the upper zone for retaining a catalyst bed.
The process according to the present invention suitably
comprises a hydrodesulphurization process in step (iii) followed by
a further hydrodesulphurization process in step (i). In this way a
very low sulphur level can be attained in a commercially attractive
way. Other contaminants, such as nitrogen containing compounds, can
also to a certain extent be removed in a hydrodesulphurization
process. Further, the process suitably involves a hydrodesul-
phurization process in step (iii) followed by a hydrogenation
process in step (i). In that way both the sulphur and the aromatics
content of the fresh hydrocarbon oil can be diminished in a
commercially attractive way.
The hydrocarbon oil subjected to the present process is
substantially liquid at process conditions. The liquid phase of the
hydrocarbon oil makes that the separation of the hydrotreated
hydrocarbon oil from the hydrogen containing gas in step (ii) can
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be attained in a simple way. Suitably this separation is carried
out with the help of one or more separating trays consisting of a
conventional liquid draw-off tray as used in distillation units.
The separation of step (iv) can be carried out outside or
inside the reactor vessel. In the first case, the hydrocarbon oil
will usually be cooled down and needs heating up before it can be
used in step (i). Therefore, separation inside the reactor,
preferably with the help of a separating tray as described above,
is preferred.
The pressure drop over the reactor vessel will generally be
between 0.2 and 10 bar, more specifically between 0.5 and 5 bar. It
is possible to add hydrogen to the lower catalyst bed. However, in
general the hydrogen partial pressure will be higher in the upper
catalyst bed than in the lower catalyst bed. The pressure drop will
generally make that the hydrogen partial pressure in the upper
catalyst bed is between 0.1 and 9 bar, more specifically between
0.4 and 4.5 bar higher than in the lower catalyst bed.
With the expression "clean hydrogen containing gas" is meant a
gas containing less than 3$ by volume of hydrogen sulphide,
preferably less than l~ by volume, more preferably less than 0.5 $
by volume, most preferably less than 0.1 ~ by volume. Suitably,
contaminated hydrogen containing gas obtained in step (iv) is
cleaned, e.g. by treating it with an amine, and subsequently used
in step (i) as clean hydrogen containing gas.
A hydrocarbon oil which is substantially liquid at process
conditions, is understood to comprise a hydrocarbon oil of which a
major amount, for example more than 70 ~ by weight suitably more
than 80 $ by weight, and preferably more than 95 ~ by weight, is in
the liquid phase. Hydrocarbon oils which can be suitably treated in
the process according to the present invention, comprise any
hydrocarbon which is substantially liquid at process conditions,
for example kerosene fractions. A hydrocarbon oil which could be
suitably treated in the process would be a gas oil, as the
environmental constraints on this oil fraction have become quite
strict. A suitable gas oil would be a gas oil substantially, e.g.
_ 5 _ ~, Q ,
more than 75$ by weight, boiling in the range between 150 and
400 °C.
If a gas oil is hydrotreated in the process according to the
present invention, steps (i) and (iii) are suitably carried out at
a temperature of between 150 and 450 °C, suitably between 300 and
400 °C, preferably between 325 and 390 °C, more preferably
between
340 and 385 °C, and step (i) is suitably carried out at a pressure
of between 20 and 85 bar, preferably between 30 and 65 bar, and
step (iii) is suitably carried out at a pressure of between 15 and
80 bar, preferably between 25 and 60 bar.
Further, in the present process suitably a lubricating oil can
be hydrotreated, such as a lubricating oil substantially, e.g. more
than 958 by weight, boiling in the range between 320 and 600 °C.
If a lubricating oil is hydrotreated in the process according
to the present invention, steps (i) and (iii) are suitably carried
out at a temperature of between 300 and 400 °C, preferably between
325 and 390 °C, mare preferably between 340 and 385 °C, and a
pressure of less than 250 bar, preferably less than 200 bar, more
preferably less than 175 bar.
The hydrotreating catalyst employed in the process according
to the present invention, suitably comprises one or more metals
from Group 1b, 2a, 4b, Sb, 6b, 7b and 8 of the Periodic Table of
the Elements in the Handbook of Chemistry and Physics, 63rd
edition, on a solid carrier. The carrier can optionally comprise a
zeolite.
As described above, the hydrotreating process according to the
present invention preferably involves in step (i) a hydrogenation
process and in step (iii) a hydrodesulphurization process, or in
both steps a hydrodesulphurization process.
In the first mode, in step (i) a hydrogenation catalyst is
applied at hydrogenation conditions which include a temperature of
between 150 and 350 °C, and in step (iii) a hydrodesulphurization
catalyst is applied at hydrodesulghurization conditians. In such
case, the hydrodesulphurization of step (iii) must in general be
carried out such that a sulphur content is attained which is such
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that the specification of the sulphur tolerance of the
hydrogenation catalyst of step (i) is met, as otherwise this
hydrogenation catalyst could be poisoned. Suitably, the
hydrocarbon oil obtained in step (iv) contains not more that
15% by volume of sulp~uur containing compounds, based on
volume of sulphur containing compounds present in the fresh
hydrocarbon oil, preferably not more than 10%.
In the second mode, in both step (i) and (iii) a
hydrodesulphurization catalyst is applied at
hydrodesulphurization conditions. In that case, the partly
hydrotreated hydrocarbon oil obtained in step (iv) suitably
contains between 1 anc~ 30% by volume of sulphur containing
compounds, based on volume of sulphur containing compounds
present in the fresh hydrocarbon oil.
The present invention can suitably be carried out
in a reactor vessel as shown in Figure 1.
The upper catalyst bed 6 can contain either a
hydrodesulphurization or a hydrogenation catalyst; the :Lower
catalyst bed 7 contains a hydrodesulphurization catalyst.
Clean hydrogen containing gas is fed to the reactor via line
2, while partly hydrotreated hydrocarbon oil is introduced
in the upper part of the reactor via line 1. The inlet for
gas and the inlet for liquid can be combined. However, it
is preferred to have separate inlets. The hydrotreated
effluent from the upper catalyst bed 6 is separated from gas
with the help of a draw-off tray (separating tray) 8. ~.Che
separated hydrotreated hydrocarbon effluent is removed from
the reactor via line 3, while used hydrogen containing gas
passes the separating tray 8 and reaches the lower catalyst
bed 7. Via line ~, fresh hydrocarbon oil is introduced
between the separating tray 8 and the lower catalyst bed 7.
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The partly hydrotreated effluent obtained after passing the
fresh hydrocarbon oil over the lower catalyst bed 7, is
removed from the reactor via line 5 and separated into
partly hydrotreated hydrocarbon oil which is sent to line 1,
and contaminated hydrogen containing gas. The contaminated
hydrogen containing gas is suitably cleaned by treating it
with an amine, so-called scrubbing. The cleaned gas
obtained can then, optionally together with make-up
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hydrogen, be recycled to line 2 and be used again.
The advantages of the present invention will be illustrated by
the following example.
EXAMPLE
The process was carried out in a set-up as described in
Figure 1. The catalyst present both in the upper and the lower
catalyst bed was a hydrodesulphurization catalyst, comprising 3.1$
by weight of cobalt and 12.4$ by weight of molybdenum, based on
total amount of catalyst, on alumina. The catalyst particles were
in the shape of 1.2 mm trilobes.
A gas oil feedstock of which according to the ASTM
distillation curve more than 78$ by volume is in the gaseous phase
at 383 °C, more than 50$ by volume is in the gaseous phase at
345 °C and more than 208 is in the gaseous phase at 300 °C was
led
to the reactor via line 4. The overall process conditions comprise
a temperature of 360 °C and a weight hourly space velocity of
2.0 kg/l.h and a hydrogen to oil ratio of 200 N1/kg. The hydrogen
partial pressure at the outlet of the upper catalyst bed was
24.4 bar, while the hydrogen partial pressure at the outlet of the
lower catalyst bed was 23.1 bar. At these process conditions about
7 8 by weight of the gas oil feedstock was in the gaseous phase.
The sulphur content of the feed, the partly hydrotreated feed and
the hydrotreated feed are shown in Table 1, in amount of elemental
sulphur on total amount of feed.
Table 1
partly hydrotreated
feed hydrotreated feed
feed
Sulphur content ($ by weight) 1.64 0.21 0.06
Not according to the invention, fresh feedstock as described
hereinabove was processed in a set-up similar to the one of
Figure 1, at process conditions substantially as described
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hereinabove. No intermittent hydrogen separation took place between
the catalyst beds; no hydrocarbon oil was added or removed between
the catalyst beds. The hydrogen partial pressure at the reactor
outlet was 23.1 bar. The hydrotreated hydrocarbon oil obtained had
a sulphur content of 0.11$wt.
