U.S. patent application number 10/921301 was filed with the patent office on 2005-03-17 for use of a catalyst comprising a beta silicon carbide support in a selective hydrodesulphurization process.
Invention is credited to Bouchy, Christophe, Diehl, Fabrice.
Application Number | 20050056568 10/921301 |
Document ID | / |
Family ID | 34043783 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056568 |
Kind Code |
A1 |
Bouchy, Christophe ; et
al. |
March 17, 2005 |
Use of a catalyst comprising a beta silicon carbide support in a
selective hydrodesulphurization process
Abstract
The invention concerns the use of supported catalysts comprising
at least one metal or metallic compound of a metal from group VI
and/or group VIII deposited on a support essentially constituted by
.beta. silicon carbide in a process for selective
hydrodesulphurization of an olefinic hydrocarbon feed that is
substantially free of polynuclear aromatics and metals. The
invention can be used to carry out deep desulphurization of
catalytically cracked gasoline cuts with very limited saturation of
olefins and thus a minimum loss of octane number.
Inventors: |
Bouchy, Christophe; (Rueil
Malmaison, FR) ; Diehl, Fabrice; (Rueil Malmaison,
FR) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Family ID: |
34043783 |
Appl. No.: |
10/921301 |
Filed: |
August 19, 2004 |
Current U.S.
Class: |
208/216R ;
208/217 |
Current CPC
Class: |
B01J 23/882 20130101;
C10G 45/06 20130101; C10G 2300/104 20130101; B01J 37/0203 20130101;
C10G 2300/202 20130101; C10G 2400/02 20130101; B01J 27/224
20130101; C10G 45/10 20130101; C10G 2300/1044 20130101; B01J 23/74
20130101; C10G 2300/301 20130101; B01J 23/85 20130101; B01J 23/24
20130101; B01J 37/20 20130101; B01J 37/0205 20130101 |
Class at
Publication: |
208/216.00R ;
208/217 |
International
Class: |
C10G 045/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2003 |
FR |
03/10.027 |
Claims
1. Use of supported catalysts comprising at least one metal or
metallic compound of a metal from the group formed by elements from
group VIII and/or group VIB of the elements periodic table
deposited on a support essentially constituted by .beta. silicon
carbide, in a process for selective hydrodesulphurization of an
olefinic hydrocarbon feed that is substantially free of polynuclear
aromatics and metals.
2. Use according to claim 1, in a process for selective
hydrodesulphurization of a feed with an end point of less than
260.degree. C., comprising at least 5% by weight of olefins.
3. Use according to claim 2, in a process for selective
hydrodesulphurization of a feed boiling in the gasoline range.
4. Use according to claim 3, in a process for selective
hydrodesulphurization of a feed comprising at least 50% by weight
of pyrolysis gasoline and/or fluid catalytic cracking gasoline.
5. Use according to claim 1, in which the support has a specific
surface area in the range 5 to 300 m.sup.2/g.
6. Use according to claim 1 in a process for selective
hydrodesulphurization carried out under temperature conditions in
the range 200.degree. C. to 400.degree. C., a pressure in the range
0.5 to 4 MPa, with a H.sub.2/feed ratio in the range 100 to 600
(litre/litre) and with an hourly mass flow rate of feed with
respect to catalyst (WHSV) in the range 1 to 15 h.sup.-1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the oil refining industry,
more particularly to the production of gasoline bases from
different units for converting oil cuts, in particular cracking
units.
[0002] Thermal cracking units, for example for visbreaking or
cokefaction, or catalytic cracking, for example for fluidized bed
catalytic cracking, produce unsaturated gasoline cuts comprising
large quantities of aromatics and olefins. Such gasoline cuts
generally have substantial levels of sulphur, for example in the
range 200 to 3000 ppm by weight, which is incompatible with general
specifications for gasoline fuel. Thus, such cuts have to be deeply
desulphurized to reduce the sulphur content to less than 30 ppm by
weight or even 10 ppm by weight in accordance with current
specifications, or to satisfy future specifications. Industrial
processes that are in current use to carry out said operation are
catalytic hydrodesulphurization processes.
[0003] Said cuts typically have an end point of 260.degree. C. or
less. Thus, they are substantially free of heavy aromatics. Said
fractions are also substantially free of metals such as nickel,
vanadium or mercury which may poison the catalyst and/or prevent
its regeneration. Deep hydrodesulphurization of said fractions,
however, is very difficult because of a specific technical problem:
those fractions have to be efficiently desulphurized without,
however, substantially hydrogenating the olefins that are present.
A reduction in the olefin content and thus a correlative increase
in the paraffin content would result in an unacceptable drop in the
octane number of the gasoline fuel, an essential parameter for
selling price. Thus, a method for selective hydrodesulphurization
of the treated fractions is sought, i.e. hydrodesulphurization
which can eliminate sulphur with minimum hydrogenation of the
olefins in the feed.
PRIOR ART
[0004] Catalysts used industrially for that operation are typically
based on alumina, typically comprising at least one metal or
metallic compound of a metal from group VIII of the elements
periodic table (group including nickel, iron and cobalt, by which
the version of the elements periodic table which is used can be
identified) and/or at least one metal from group VIB of that table
(group comprising molybdenum and tungsten). A variety of techniques
have already been employed to increase the hydrodesulphurization
selectivity: modifying the operating conditions in which
desulphurization is carried out and/or modifying the
hydrodesulphurization catalyst to improve selectivity. Several
methods have been proposed to improve the selectivity of the
catalyst. Non exhaustive examples which can be cited are:
[0005] U.S. Pat. No. 4,140,626, concerning a process for
hydrotreating cracked naphtha using a catalyst containing a metal
from group VIB and from group VIII deposited on a support composed
of at least 70% by weight magnesium oxide;
[0006] U.S. Pat. No. 3,957,625, for a process for selective
desulphurization of cracked gasoline using a
cobalt-molybdenum/alumina type catalyst with a promoter selected
from barium, magnesium, cadmium and rare earths;
[0007] U.S. Pat. No. 5,348,928, concerning a method for preparing
and formulating a selective hydrotreatment catalyst comprising a
metal from group VIB containing 4% to 20% oxide equivalent by
weight and a metal from group VIII containing 0.5% to 10% oxide
equivalent by weight. The support contains 0.5% to 50% oxide
equivalent by weight of magnesium and 0.02% to 10% oxide equivalent
of an alkali with respect to the total catalyst mass.
[0008] However, known prior art catalysts consume quantities of
olefins which remain substantial and prejudicial to selling price
of the fuel. This consumption depends on the treated feed, the
hydrotreatment conditions, but also on the required degree of
desulphurization. One aim of the invention is to use particular
catalysts that can improve the hydrodesulphurization selectivity
for light cuts comprising olefins. A further aim of the invention
is to propose a process for selective hydrodesulphurization
employing said catalysts.
DESCRIPTION OF THE INVENTION
[0009] Catalysts comprising a support constituted by .beta. silicon
carbide are already known: European patent EP-B1-0 313 480
describes a catalyst for hydrotreating oil distillation cuts, said
catalyst comprising a support constituted by .beta. silicon carbide
(SiC).
[0010] That support is described as advantageous in that it is
resistant to poisoning by both coke and metals. Coke accumulation
is described as being linked to the presence of high molecular
weight aromatics, and the presence of metals (principally nickel
and vanadium) is described as the result of the presence of said
metals in heavy oil cuts. The desulphurizing activity is measured
by comparison with other catalysts (comprising a catalyst with an
alumina support with a specific surface area of 220 m.sup.2/g) in
the case of thiophene. Such a comparison shows that the
desulphurizing activity (moles of thiophene transformed per gram of
catalyst and per second) of the catalyst with a SiC support is
substantially lower than that of the catalyst with an alumina
support by a factor of close to 2 to 6 depending on the surface
areas of the SiC support used and close to that of a catalyst based
on alumina.
[0011] The technical teaching of that patent is that the SiC
support can overcome problems connected with the presence of high
molecular weight aromatics or metals in the feed. That patent, in
contrast, does not indicate the advantage of using a SiC support in
place of alumina with respect to hydrodesulphurization activity.
Further, it neither mentions nor suggests any advantages in using
such a catalyst for selective hydrodesulphurization of olefinic
feeds in accordance with the invention (feeds substantially free of
the undesirable compounds already mentioned).
[0012] In contrast, the Applicant has surprisingly discovered that
for the selective hydrodesulphurization of olefinic feeds, the use
of catalysts with a support essentially constituted by .beta. has
substantial advantages over known catalysts. It appears that the
use of SiC is advantageous as it can produce a catalyst with
improved selectivity, and can minimize the start up time for said
catalyst by limiting the initial hydrogenating overactivity. Such a
problem has been reported for commercial catalysts supported on
alumina, and U.S. Pat. No. 4,149,965 teaches prior deactivation of
the catalyst prior to its use in hydrotreating an olefinic feed,
the deactivation treatment being selected so as to limit the
hydrogenating activity of the catalyst.
[0013] Without wishing to be bound to a particular theory, this
effect could be considered to derive from the properties of the
support, which could be both substantially non acidic and
substantially non basic. It is known that the hydrogenating
properties of catalysts are enhanced by the acidity of the support.
The absence of acidity could contribute to explaining the results
obtained, thanks to a relatively low hydrogenating activity of the
catalyst with a .beta. SiC support as regards olefins. This could
encourage the hydrodesulphurization selectivity as regards olefin
hydrogenation. It cannot be excluded that the nature of the
sulphide phase and thus its catalytic properties could be
different, depending on whether it is formed on an alumina support
or on a .beta. silicon carbide support.
[0014] The .beta. silicon carbide used in the invention typically
has a specific surface area (measured by the BET technique) that is
over 5 m.sup.2/g, preferably in the range 5 to 300 m.sup.2/g, and
more preferably in the range 10 to 250 m.sup.2/g. The pore volume
of the support is typically in the range 0.20 cm.sup.3/g to 1.0
cm.sup.3/g, preferably in the range 0.3 cm.sup.3/g to 0.8
cm.sup.3/g, and more preferably in the range 0.35 cm.sup.3/g to
0.65 cm.sup.3/g.
[0015] The amount of group VI metal, in moles per gram of support,
is typically in the range 6.94.times.10.sup.-5 to
1.40.times.10.sup.-3, preferably in the range 8.34.times.10.sup.-5
to 6.95.times.10.sup.-4 and highly preferably in the range
1.04.times.10.sup.-4 to 5.50.times.10.sup.-4. The amount of group
VIII metal, in moles per gram of support, is generally in the range
4.0.times.10.sup.-5 to 1.1.times.10.sup.-3, preferably in the range
5.34.times.10.sup.-5 to 5.34.times.10.sup.-4, and highly preferably
in the range 6.0.times.10.sup.-5 to 4.0.times.10.sup.-4. The
catalyst can also advantageously contain phosphorus the content of
which, in moles per gram of support, can be in the range
1.64.times.10.sup.-5 to 1.64.times.10.sup.-3, preferably in the
range 8.2.times.10.sup.-5 to 1.31.times.10.sup.-3, and highly
preferably in the range 8.2.times.10.sup.-5 to
6.6.times.10.sup.-4.
[0016] The manufacture of silicon carbide type supports which can
be used in heterogeneous catalysis is already known and disclosed
in patents such as EP-B1-0 440 569 or in U.S. Pat. No.
B1-6,184,178, although this list is not exhaustive. That type of
support is manufactured on an industrial scale, for example by
SICAT Sarl (France).
[0017] The catalysts of the invention can be prepared using any
standard preparation method that is known to the skilled person,
the different metals of the active phase also possibly being
deposited sequentially or simultaneously on the support. Non
exhaustive examples which can be cited are dry impregnation
preparation methods, exchange methods, or surface organometallic
chemical methods.
[0018] The catalysts can be presulphurized in situ or ex situ prior
to use in the selective hydrodesulphurization process.
Sulphurization can be carried out using any method that is known to
the skilled person. As an example, the catalyst can be placed in an
atmosphere of H.sub.2S diluted with a stream of hydrogen at a
predetermined temperature for a predetermined period.
[0019] In general, the invention concerns the use of supported
catalysts comprising at least one metal or metallic compound of a
metal from the group formed by elements from groups VIII and/or VIB
of the periodic table, deposited on a support essentially
constituted by .beta. silicon carbide, in a process for selective
hydrodesulphurization of an olefinic hydrocarbon feed substantially
free of polynuclear aromatics and metals.
[0020] Typically, the feed has an end point of less than
260.degree. C., and comprises at least 5% by weight of olefms.
Generally, said feed boils in the gasoline range, i.e. in the ASTM
boiling point range of about 30.degree. C. to 230.degree. C. As an
example, the feed comprises at least 50% by weight of pyrolysis
gasoline and/or fluid catalytic cracking gasoline, and may even be
constituted by more than 90% by weight, or even entirely
constituted by gasoline fractions or gasoline deriving from a steam
cracker and/or a fluid catalytic cracker (FCC).
[0021] Usually, the selective hydrodesulphurization process is
carried out under temperature conditions in the range 200.degree.
C. to 400.degree. C., at a pressure in the range 0.5 to 4.0 MPa,
with a H.sub.2/HC ratio in the range 100 to 600 (litre/litre under
normal conditions) and with an hourly mass flow rate of feed per
unit weight of catalyst (WHSV) in the range 1 to 15 h.sup.-1.
EXAMPLES
Example 1
Preparation of a Catalyst A for Use in Accordance with the
Invention
[0022] A catalyst A was obtained by using a synthesis method termed
the OrganoMetallic Surface Chemical method (OMSC). Silicon carbide
SiC extrudates (2 mm diameter) were supplied by SICAT Sarl; their
principal characteristics are summarized in Table 1.
1TABLE 1 Characteristics of SiC support Form Surface area:
S.sub.BET m.sup.2/g Pore volume (Hg) cm.sup.3/g Extrudates 53 0.4 2
mm
[0023] An aqueous solution of ammonium heptamolybdate was
impregnated using the pore volume method into the silicon carbide.
The molybdenum (Mo) concentration in the solution was calculated to
obtain the desired Mo content on the support, then the solid was
left to mature for 12 hours. The solid was then oven dried at
120.degree. C. for twelve hours, and calcined for two hours at
500.degree. C. in a stream of dry air (1 l/h.g of catalyst). The
solid was then sulphurized in a stream of gaseous H.sub.2S in
hydrogen (15% by weight of H.sub.2S, total gas flow rate 1 l/h.g of
catalyst) from ambient temperature to 400.degree. C. (5.degree.
C./min ramp-up). The temperature was kept at 400.degree. C. for two
hours, then the system was cooled to 200.degree. C. (ramp-down
5.degree. C./min) and maintained at that temperature for an
additional two hours in pure hydrogen, then finally cooled to
ambient temperature, still in pure hydrogen. The pretreated solid
was transferred into a reactor suitable for OMSC synthesis (Schlenk
tube). This reactor had already been filled with solution so that
the volume of the solution was 10 cm.sup.3/g of catalyst, then
purged with argon to eliminate all traces of oxygen from the
medium. The solution was constituted by an organometallic Co
complex, cobalt biscyclopentadienyl Co(C.sub.5H.sub.5).sub.2
diluted in n-heptane. The concentration of organometallic complex
was selected to obtain a Co/(Co+Mo) atomic ratio of 0.4. The solid
was left in solution for two hours at ambient temperature and
hydrogen bubbled through, then washed in pure heptane and dried in
a stream of argon at ambient temperature overnight. Finally, the
solid was sulphurized by applying the same treatment as above. The
characteristics of the catalyst following sulphurization are shown
in Table 2.
2TABLE 2 Characteristics of catalyst A (in accordance with use in
the invention) Mo content Co content Co/(Co + Mo) atomic ratio (wt
%) (wt %) (atom/atom) 3.1 0.7 0.37
Example 2
Preparation of a Catalyst B (Comparative)
[0024] Catalyst B was obtained using the same synthesis protocol as
for catalyst A, with an industrial alumina type support from Axens.
The characteristics of the support are given in Table 3:
3TABLE 3 Characteristics of industrial alumina support Form Surface
area: S.sub.BET m.sup.2/g Pore volume (Hg) cm.sup.3/g Beads 60 0.6
2.4-4 mm
[0025] The characteristics of the catalyst after sulphurization are
shown in Table 4:
4TABLE 4 Characteristics of catalyst B (comparative) Mo content Co
content Co/(Co + Mo) atomic ratio (wt %) (wt %) (atom/atom) 3.2 0.7
0.36
[0026] Thus, catalyst B is essentially distinguished from catalyst
A in the nature of the support used, and also by the dimensions of
the grains.
Example 3
Comparison of Use of Catalyst A with that of Catalyst B on a First
Olefinic Feed
[0027] In order to overcome diffusional limitation problems, the
catalysts were ground to the 300-500 micrometre fraction in the
absence of air. The solids were then passivated in air at ambient
temperature for 4 hours and loaded into the catalytic reactor. The
catalyst was then sulphurized in situ using a synthetic feed (6% by
weight of dimethyldisulphide in n-heptane) under the following
conditions: Total pressure=2.0 MPa, H.sub.2/feed=300 (litre/litre),
mass flow rate of feed with respect to catalyst per hour (WHSV)=3
h.sup.-1. A constant temperature stage for sulphurization was
carried out for 4 hours at 350.degree. C. (temperature ramp-up
20.degree. C./hour). After sulphurization, the temperature was
reduced to 150.degree. C. and the sulphurization feed was replaced
with FCC gasoline to be treated, and the operating conditions were
adjusted. In this example, the two catalysts were tested on a first
olefinic feed constituted by a moderately sulphurized total FCC
gasoline with the characteristics shown in Table 5.
5TABLE 5 Characteristics of first olefinic feed Total S: 460 ppm by
weight Density (25.degree. C.): 0.76 PONA analysis (wt %):
Paraffins: 28.4 Naphthenes; 8.1 Aromatics: 29.3 Olefins: 34.2
[0028] The test conditions were as follows: total pressure: 1.5
MPa;
[0029] H.sub.2/feed=300 (litre/litre), mass flow rate of feed with
respect to catalyst per hour (WHSV)=9 h.sup.-1.
[0030] The temperature was varied between 280.degree. C. and
310.degree. C. Each operating condition (temperature) was kept
constant for at least 48 hours, and a reversal point ensured that
the loss of desulphurizing activity of the catalyst was very small
or even zero. The degrees of HDS and HDO are calculated
respectively using the following formulae:
HDS=100.times.(1-S.sub.f/S.sub.o), in which S.sub.o and S.sub.f
respectively represent the concentrations in the feed and effluent
(ppm);
HDO=100.times.(1-C.sub.f/C.sub.o) in which C.sub.o and C.sub.f
represent the concentrations of olefins in the feed and in the
effluent respectively (wt %).
[0031] The hydrodesulphurization and hydrogenation activities were
calculated by assuming an order of 1 (sulphur-containing compounds
) and 0 (olefinic compounds) respectively for the reactants:
A.sub.HDS=Ln(100(100-HDS));
A.sub.HDO=C.sub.c.times.HDO/100.
[0032] Table 6 shows the results obtained for catalysts A and B. It
appears that the catalyst supported on silicon carbide was much
more selective than the catalyst supported on alumina since
catalyst A was systematically less hydrogenating than catalyst
B.
6TABLE 6 selective hydrodesulphurization of a first olefinic feed
Test HDS HDO Catalyst T (.degree. C.) duration (h) (%) (%)
A.sub.HDA A.sub.HDO A 280 96 74.5 12.1 1.37 0.040 B 280 96 73.3
15.2 1.31 0.051 A 290 144 86.8 19.2 2.02 0.063 B 290 144 86.2 24.3
1.97 0.081 A 300 192 94.0 29.4 2.81 0.097 B 300 192 93.2 33.3 2.66
0.111
[0033] More precisely, the use of a silicon carbide support in
place of alumina can reduce the hydrogenating activity of the
catalyst while its desulphurizing activity remains constant or may
even be slightly improved.
Example 4
Start Up Operation of Catalyst A and Catalyst B in Selective
Hydrodesulphurization of a First Olefinic Feed
[0034] The changes in hydrodesulphurization and hydrogenation
during the first 96 hours of the test of Example 3 for catalyst A
and catalyst B are shown in Table 7 and in FIG. 1.
7TABLE 7 Change in degree of hydrodesulphurization and
hydrogenation during start up of catalysts A and B during selective
hydrodesulphurization of a first olefinic feed HDS HDO Catalyst
Test duration (h) (%) (%) A 10 75.0 12.8 B 12 74.5 20.1 A 24 74.8
12.5 B 24 74.5 18.2 A 36 74.6 12.2 B 38 73.9 17.1 A 48 74.5 12.1 B
48 73.5 16.3 A 72 74.2 12.3 B 72 73.2 15.4 A 96 74.5 12.1 B 96 73.3
15.2
[0035] During the first hours of the test, catalyst B (not in
accordance with the catalyst used in the invention) exhibited
hydrogenating overactivity compared with its stabilized state,
while its desulphurizing activity was essentially stable. Then, to
achieve a similar sulphur content, catalyst B (not in accordance)
resulted in hydrogenation of a surplus of olefins in the feed at
the start of the test, and the quality of the gasoline obtained at
the start of the cycle on catalyst B was thus lower in terms of
octane number than that obtained for the same catalyst after
stabilization. For this type of catalyst, a partial deactivation
treatment such as that proposed in U.S. Pat. No. 4,149,965 is thus
recommended to limit its hydrogenating activity prior to passing
the feed. In contrast, this phenomenon is substantially reduced on
catalyst A (in accordance with the use of the invention), which had
no substantial hydrogenating overactivity at the start of the test
and very rapidly reached its steady state. Thus it was not
necessary to partially deactivate catalyst A prior to bringing it
into contact with the feed.
Example 5
Comparison of Catalyst A with Conventional Catalyst B on a Second
Olefinic Feed
[0036] In this example, the two above catalysts were tested on a
depentanized olefinic feed (Table 8) more sulphurized as above.
8TABLE 8 Characteristics of second olefinic feed Total S: 2297 ppm
by weight Density (25.degree. C.): 0.77 PONA analysis (wt %):
Paraffins: 24.5 Naphthenes; 8.4 Aromatics: 37.0 Olefins: 30.1
[0037] The test conditions were as follows: total pressure: 1.8
MPa; H.sub.2/feed=350 (litre/litre), WHSV=7 h.sup.-1. The
temperature was varied between 280.degree. C. and 310.degree. C. to
vary the degree of desulphurization. Table 9 shows the results
obtained for catalysts A and B:
9TABLE 9 Selective hydrodesulphurization of a second olefinic feed
Test HDS HDO Catalyst T (.degree. C.) duration (h) (%) (%)
A.sub.HDA A.sub.HDO A 280 96 77.9 13.7 1.51 0.046 B 280 96 77.1
16.7 1.47 0.056 A 290 144 87.3 18.0 2.06 0.060 B 290 144 86.7 20.5
2.02 0.068 A 300 192 92.9 22.2 2.65 0.074 B 300 192 92.5 25.0 2.59
0.083 A 310 240 95.8 26.5 3.17 0.088 B 310 240 95.6 30.1 3.12
0.100
[0038] For this feed again, the catalyst supported on silicon
carbide proved to be more selective. The best selectivity for
catalyst A was again due to a lower hydrogenating activity for
catalyst A, while the desulphurization activity of the two
catalysts was substantially identical.
[0039] Without further elaboration, it is believed that one skilled
in the art can, using the preceding description, utilize the
present invention to its fullest extent. The preceding preferred
specific embodiments are, therefore, to be construed as merely
illustrative, and not limitative of the remainder of the disclosure
in any way whatsoever.
[0040] In the foregoing and in the examples, all temperatures are
set forth uncorrected in degrees Celsius and, all parts and
percentages are by weight, unless otherwise indicated.
[0041] The entire disclosure[s] of all applications, patents and
publications, cited herein and of corresponding French application
No. 03/10.027, filed Aug. 19, 2003 is incorporated by reference
herein.
[0042] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0043] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *