U.S. patent application number 10/402152 was filed with the patent office on 2003-11-27 for process for the production of hydrocarbons with low sulfur and mercaptan content.
This patent application is currently assigned to Institut Francais du Petrole. Invention is credited to Marchal-George, Nathalie, Picard, Florent, Uzio, Denis.
Application Number | 20030217951 10/402152 |
Document ID | / |
Family ID | 27839409 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030217951 |
Kind Code |
A1 |
Marchal-George, Nathalie ;
et al. |
November 27, 2003 |
Process for the production of hydrocarbons with low sulfur and
mercaptan content
Abstract
Process for desulfurization of a cut containing hydrocarbons
comprising sulfur compounds and olefinic compounds comprising at
least the following successive steps: a first desulfurization in
the presence of hydrogen and a hydrodesulfurization catalyst under
conditions leading to a desulfurization rate of said cut strictly
higher than 90%; separation of most of the hydrogen sulfide from
the effluents resulting from the first desulfurization; a second
desulfurization of the effluents, with the hydrogen sulfide
removed, resulting from the separation step, in the presence of
hydrogen and a hydrodesulfurization catalyst, and under conditions
leading to a desulfurization rate of said effluents less than that
of the first desulfurization.
Inventors: |
Marchal-George, Nathalie;
(Saint Genis Laval, FR) ; Picard, Florent; (Saint
Synphorien D'O zon, FR) ; Uzio, Denis; (Marly Le Roi,
FR) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
Institut Francais du
Petrole
Rueil Malmaison Cedex
FR
|
Family ID: |
27839409 |
Appl. No.: |
10/402152 |
Filed: |
March 31, 2003 |
Current U.S.
Class: |
208/210 ;
208/217 |
Current CPC
Class: |
C10G 65/04 20130101 |
Class at
Publication: |
208/210 ;
208/217 |
International
Class: |
C10G 045/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2002 |
FR |
02/04.108 |
Claims
1. Desulfurization process for a cut containing hydrocarbons
comprising sulfur and olefinic compounds and having at least the
following successive steps: a first desulfurization in the presence
of hydrogen and a hydrodesulfurization catalyst under conditions
leading to a desulfurization rate of said cut strictly higher than
90%, separation of most of the hydrogen sulfide (H.sub.2S) from the
effluents resulting from the first desulfurization, a second
desulfurization of the effluents, with the hydrogen sulfide
removed, resulting from the separation step, in the presence of
hydrogen and of a hydrodesulfurization catalyst and under
conditions leading to a desulfurization rate of said effluents less
than that of the first desulfurization.
2. Process according to claim 1, wherein at least one of the
hydrodesulfurization catalysts has at least one element from group
VIII of the periodic table.
3. Process according to claim 2, wherein at least one of the
catalysts further has at least one element from group VIB of the
periodic table.
4. Process according to claim 1, comprising at least one element
from group VIII of the periodic table selected from the group
consisting of nickel and cobalt and at least one element from group
VIB from the periodic table selected from the group consisting of
molybdenum and tungsten.
5. Process according to one of the preceding claims, wherein the
first desulfurization is performed at a temperature between
250.degree. C. and 350.degree. C., under pressure between 1 and 3
MPa, at an hourly spatial liquid speed between 1 h.sup.-1 and 10
h.sup.-1, and with an H.sub.2/HC ratio between 50 l/l and 500
l/l.
6. Process according to one of the preceding claims, wherein the
second desulfurization is performed at a temperature between
200.degree. C. and 300.degree. C., under pressure between 1 and 3
MPa, at an hourly spatial liquid speed between 1 h.sup.-1 and 10
h.sup.-1 and with an H.sub.2/HC ratio between 50 l/l and 500
l/l.
7. Process according to one of the preceding claims, wherein the
desulfurization rate of the second desulfurization is strictly
greater than 80%.
8. Process according to one of the preceding claims, wherein the
difference between the desulfurization rates of the first and the
second desulfurization is at least one percent in absolute
value.
9. Process according to one of the preceding claims, further
comprising a supplementary step of selective hydrogenation of the
diolefins contained in the cut, said step being performed before
the first desulfurization.
10. Process according to one of the preceding claims, further
comprising a supplementary step of making the light sulfurous
compounds heavy, said step being performed before the first
desulfurization.
11. Process according to one of the preceding claims, further
comprising at least one supplementary separation step for said cut
into at least two fractions: a light fraction containing a small
amount of the sulfurous compounds, a heavy fraction containing most
of the sulfurous compounds, at least said heavy fraction then being
processed according to the first desulfurization step.
12. Application of the process according to the preceding claims to
gasolines resulting from catalytic cracking or coking of a heavy
batch containing hydrocarbons or steam cracking.
Description
[0001] This invention relates to a process for the production of
hydrocarbons with low sulfur content. This fraction of hydrocarbons
contains an olefin fraction generally higher than 5% by weight and
most often higher than 10% by weight. The process makes it possible
notably to valorize an entire gasoline cut containing sulfur by
reducing the sulfur and mercaptan content of said gasoline cut to
very low levels, without reducing the gasoline yield, and while
minimizing the reduction in the octane rating during said process.
The invention is applicable particularly when the gasoline to be
processed is a gasoline from catalytic cracking with a sulfur
content greater than 500 ppm by weight or even higher than 1000 ppm
by weight, even 2000 ppm by weight, and when the desired sulfur
content in the desulfurized gasoline is less than 50 ppm by weight,
even 20 ppm by weight or even 10 ppm by weight.
PRIOR ART
[0002] Future specifications for automobile fuels are expected to
show a great reduction in the sulfur content of these fuels,
notably in gasolines. This reduction is intended to limit notably
the sulfur oxide content in the exhaust gases of automobiles.
Current specifications for sulfur contents are on the order of 150
ppm by weight and will be reduced in the coming years to achieve
contents lower than 10 ppm after a transition to 30 ppm by weight.
The evolution of specifications for sulfur content in fuels thus
requires the development of new processes for extensive
desulfurization of fuels.
[0003] The principal sources of sulfur in gasoline bases are fuels
from so-called cracking, and mainly the gasoline fraction resulting
from a catalytic cracking process of a residue from atmospheric or
vacuum distillation of a crude petroleum. The gasoline fraction
resulting from catalytic cracking, which represents an average of
40% of gasoline bases, in fact makes up more than 90% of the amount
of sulfur in gasolines. Consequently, the production of low-sulfur
gasolines requires a step of desulfurization of gasolines from
catalytic cracking. This desulfurization is conventionally
performed by one or several steps of placing the sulfurous
compounds contained in said gasolines in contact with a
hydrogen-rich gas in a process called hydrodesulfurization.
[0004] Further, the octane rating of such gasolines is very
strongly tied to their olefin content. The preservation of the
octane rating of these gasolines thus requires that the
transformation reactions of olefins into paraffins, which are
inherent to hydrodesulfurization processes, be limited.
[0005] Further, gasolines have corrosive properties because of the
presence of mercaptans. To limit the corrosiveness of gasolines, it
is generally necessary greatly to lower the mercaptan content to
values at least lower than 10 ppm and ideally 5 ppm. The mercaptans
measured in desulfurized gasolines are called recombination
mercaptans, i.e., resulting from the addition reaction of hydrogen
sulfide (H.sub.2S) produced during the desulfurization step and of
the olefins present in the gasoline. The solution usually used to
eliminate these mercaptans consists in hydrogenating the olefins
present in the gasoline. However, for the reasons already
described, this hydrogenation results in a latent octane loss in
gasolines from catalytic cracking.
[0006] Numerous solutions have been proposed to selectively
eliminate sulfurous compounds in gasolines by limiting undesirable
hydrogenation reactions of the olefins, generally evaluated by one
skilled in the art in the form of an olefin saturation rate at the
exit of the reactor. Among these processes there are processes in
which the gasoline is processed in one or two reactors in series
without intermediate separation of H.sub.2S. These processes make
it possible partially to resolve the problem of the octane and
mercaptan index in batches with a sulfur content not exceeding
generally 1000 ppm, and for which the desired desulfurization rates
are low, typically less than 90%.
[0007] The processing of sulfur-rich gasolines (i.e., containing
more than 1000 ppm or even more than 2000 ppm of sulfur) aimed at
ultimately reaching sulfur contents less than 50 ppm, even 20 ppm
or even 10 ppm, can optionally and preferably require the use of a
process comprising hydrodesulfurization in at least two
hydrodesulfurization reactors in series, and intermediate
elimination of the H.sub.2S formed during the first
hydrodesulfurization step. This type of plan is preferably intended
to achieve high desulfurization rates, for example rates of 99%, to
bring a gasoline with sulfur concentrations on the order of 2000
ppm to sulfur concentrations on the order of 10 ppm.
[0008] For example, patent EP 0755995 proposes a plan consisting of
at least two hydrodesulfurization steps and a step for eliminating
the H.sub.2S between two hydrodesulfurization reactors. The
hydrodesulfurization rate must, at each step, be between 60% and
90%. But such a process does not make it possible to expect to
achieve desulfurization rates higher than 99% at industrial scale.
To reach a more extensive desulfurization, it would appear
necessary to add at least one supplemental step, which greatly
limits the economic attractiveness of the process.
[0009] U.S. Pat. No. 6,231,753 proposes the processing of highly
sulfurous gasolines with a plan also comprising 2
hydrodesulfurization steps and an intermediate elimination of the
H.sub.2S formed. The operating conditions are such that the
desulfurization rate and temperature of the gasolines of the second
hydrodesulfurization step are greater than those of the first
step.
SUMMARY OF THE INVENTION
[0010] Generally, this invention relates to a new process
comprising 2 steps of hydrodesulfurization and intermediate
elimination of H.sub.2S which simultaneously makes it possible
to:
[0011] achieve future specifications for automobile gasolines,
i.e., sulfur contents on the order of 30 ppm or even 10 ppm,
depending on the country.
[0012] to control the olefin hydrogenation process during said
process.
[0013] to limit the loss of octane rating connected with
hydrodesulfurization processes,
[0014] to decrease the mercaptan content for a given sulfur and
olefin content in desulfurized gasolines.
[0015] More specifically, the invention relates to a
desulfurization process for a cut containing hydrocarbons
comprising sulfur and olefinic compounds comprising at least the
following successive steps:
[0016] a first desulfurization in the presence of hydrogen and a
hydrodesulfurization catalyst under conditions leading to a
desulfurization rate of said cut strictly higher than 90%,
[0017] a separation of most of the hydrogen sulfide (H.sub.2S) from
the effluents resulting from the first desulfurization,
[0018] a second desulfurization of the effluents, with the hydrogen
sulfide removed, resulting from the separation step, in the
presence of hydrogen and of a hydrodesulfurization catalyst and
under conditions leading to a desulfurization rate of said
effluents less than that of the first desulfurization.
[0019] Thus, this process of desulfurization proposes a solution
for achieving high desulfurization rates, typically higher than 95%
and more specifically higher than 99%, while limiting the octane
loss through hydrogenation of the olefins, as well as the formation
of recombination mercaptans. The result is the production of a
gasoline low in sulfur and mercaptans and with a high octane
rating.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The invention relates to a process of desulfurization of a
cut containing hydrocarbons comprising sulfur and olefinic
compounds comprising at least the following successive steps:
[0021] a first desulfurization in the presence of hydrogen and a
hydrodesulfurization catalyst under conditions leading to a
desulfurization rate of said cut strictly higher than 90%,
[0022] separation of most of the hydrogen sulfide (H.sub.2S) from
the effluents resulting from the first desulfurization,
[0023] a second desulfurization of the effluents, with the hydrogen
sulfide removed, resulting from the separation step, in the
presence of hydrogen and of a hydrodesulfurization catalyst and
under conditions leading to a desulfurization rate of said
effluents less than that of the first desulfurization.
[0024] In the process according to the invention, preferably at
least one of the hydrodesulfurization catalysts comprises at least
one element from Group VIII of the periodic table and, more
preferably, at least one of the catalysts further has at least one
element from group VIB of the periodic table.
[0025] Very preferably, said hydrodesulfurization catalysts include
at least one element from Group VIII of the periodic table,
selected from the group consisting of nickel and cobalt and at
least one element from Group VIB of the periodic table, selected
from the group consisting of molybdenum and tungsten.
[0026] Preferably, the first desulfurization of the process
according to the invention is performed at a temperature between
250.degree. C. and 350.degree. C., under pressure between 1 and 3
MPa, at an hourly spatial liquid speed between 1 h.sup.-1 and 10
h.sup.-1 and with an H.sub.2/HC ratio between 50 l/l and 500 l/l,
and preferably the second desulfurization is performed at a
temperature between 200.degree. C. and 300.degree. C., at a
pressure between 1 and 3 MPa, at an hourly spatial liquid speed
between 1 h.sup.-1 and 10 h.sup.-1 and with an H.sub.2/HC ratio
between 50 l/l and 500 l/l.
[0027] Preferably, the desulfurization rate of the second
desulfurization is strictly higher than 80% and, more preferably,
the difference between the desulfurization rates of the first and
second desulfurization is at least one percent in absolute value.
Such a difference can be obtained notably thanks to a temperature
difference and/or in hourly volume speed between the first and
second desulfurization, and/or by different catalytic activity of
the catalysts used in the first and second hydrodesulfurization
step, for example due to a difference in the composition or
preparation of these catalysts.
[0028] The process according to the invention can optionally
further comprise a supplemental step of selective hydrogenation of
the diolefins contained in the cut containing hydrocarbons, said
step being performed before the first desulfurization. It can more
preferably further comprise a step of making the light sulfurous
compounds heavy increasing the boiling point of the light sulfur
compounds by combining them with another compound, said step being
performed before the first desulfurization, and very preferably
further comprise at least one supplemental separation step of said
cut into at least two fractions:
[0029] a light fraction containing a small part of the sulfurous
compounds,
[0030] a heavy fraction containing most of the sulfurous compounds,
at least said heavy fraction then being processed according to the
first desulfurization step.
[0031] The process according to the invention is preferably applied
to batches such as gasoline cuts resulting from catalytic cracking
or from coking a heavy batch containing hydrocarbons, or from steam
cracking.
[0032] The invention will be better understood from reading the
following embodiment, given purely by way of nonlimiting
example.
[0033] According to the preferred but nonobligatory embodiment of
the invention that follows, the batch to be desulfurized is
preferably processed optionally in a series of reactors for
selective hydrogenation of the diolefins (step a) and of making the
light sulfurous compounds heavy (step b). The batch thus
pre-processed is then distilled and fractionated into at least two
cuts (step c): a light gasoline low in sulfur and high in olefins
and a heavy gasoline high in sulfur and low in olefins. The light
fraction resulting from the three preceding steps generally
contains less than 50 ppm of sulfur, preferably less than 20 ppm of
sulfur, very preferably less than 10 ppm of sulfur, and generally
does not require subsequent processing before being used as a base
gasoline. The heavy fraction resulting from the three preceding
steps in which most of the sulfur is concentrated is processed
according to the process that is the object of this invention. This
preferred embodiment offers the advantage of further minimizing the
loss of octane because the light olefins with 5 carbon atoms,
easily hydrogenated, are not sent to the hydrodesulfurization
section.
[0034] Generally, the experimental conditions of these
pre-processing steps a), b), and c) are the following:
[0035] 1) Selective Hydrogenation (Step a):
[0036] This optional step of pre-processing the gasoline to be
desulfurized is intended to eliminate at least partially the
diolefins present in the gasoline. The hydrogenation of dienes is
an optional but advantageous step that makes it possible to
eliminate practically all the dienes present in the cut to be
processed before the hydro-treating. The diolefins are precursors
of gums that polymerize in hydrotreatment reactors and thus limit
their lifetime.
[0037] This step is generally performed in the presence of a
catalyst comprising at least one metal from group VIII, preferably
selected from the group formed by platinum, palladium, and nickel,
and a support. A catalyst containing 1 to 20% by weight of nickel
deposited on an inert support, such as for example aluminum,
silicon, silica-aluminum, a nickel aluminate or a support
containing at least 50% aluminum will be used. This catalyst
generally operates at a pressure of 0.4 to 5 MPa, at a temperature
of 50 to 250.degree. C., with an hourly spatial liquid speed of 1
h.sup.-1 to 10 h.sup.-1. Another metal from group VIb can be
combined to form a bimetallic catalyst, such as for example
molybdenum or tungsten. This metal from group VIb, if it is
combined with the metal from group VIII, will be deposited at a
rate of 1% by weight to 20% by weight on the support.
[0038] The choice of operating conditions is particularly
important. Most generally the process is done under pressure in the
presence of an amount of hydrogen that is slightly higher than the
stoichiometric value necessary to hydrogenate diolefins. The
hydrogen and the batch to be processed are injected as ascending or
descending currents in a reactor that is preferably a fixed
catalyst bed. The temperature is most generally between 50 and
300.degree. C., preferably between 80 and 250.degree. C., most
preferably between 120 and 210.degree. C.
[0039] The pressure is selected so as to be sufficient to maintain
more than 80%, and preferably more than 95% by weight of the
gasoline to be processed in liquid phase in the reactor; it is more
generally 0.4 to 5 MPa and preferably higher than 1 MPa. An
advantageous pressure is between 1 and 4 MPa, those limits
included.
[0040] Under these conditions, the spatial speed is on the order of
1 to 12 h.sup.-1, preferably on the order of 4 to 10 h.sup.-1.
[0041] The light fraction from the gasoline cut from catalytic
cracking can contain up to several % by weight of diolefins. After
hydrogenation, the diolefin content is reduced to less than 3000
ppm, even to less than 2500 ppm and better to less than 1500 ppm.
In certain cases, a diene content less than 500 ppm can be
obtained. The diene content after selective hydrogenation can even
be reduced in certain cases to less than 250 ppm.
[0042] Simultaneously with the selective hydrogenation reaction of
the diolefins, there is an isomerization of the double external
olefin bond leading to the formation of internal olefins. This
isomerization results in the formation of olefins that are more
resistant to hydrogen saturation and leads to a slight gain in the
octane number (or a compensation of the octane number due to the
slight loss of olefin). This is probably due to the fact that
internal olefins have an octane rating generally higher than that
of terminal olefins.
[0043] According to an embodiment of the invention, the
hydrogenation step of dienes is performed in a catalytic
hydrogenation reactor that comprises at least one catalytic
reaction zone through which the entire batch, and the amount of
hydrogen necessary to perform the desired reactions, generally
pass.
[0044] 2) Making the Light Sulfurous Compounds Heavy (Step b):
[0045] This optional step consists in transforming the saturated
light sulfur compounds, i.e., the compounds whose boiling
temperature is less than that of thiophene, into saturated sulfur
compounds whose boiling temperature is higher than that of
thiophene. These light sulfurous compounds are typically mercaptans
with 1 to 5 carbon atoms, CS.sub.2, and sulfurs with 2 to 4 carbon
atoms. This transformation is preferably performed on a catalyst
comprising at least one element from group VIII (groups 8, 9, and
10 of the new periodic table) on an aluminum-type, silica or
aluminum silica, or nickel aluminate support. The choice of
catalyst is made notably so as to promote the reaction between the
light mercaptans and the olefins, which leads to mercaptans or
sulfurs with boiling temperatures higher than thiophene.
[0046] This optional step can be optionally performed at the same
time as step a), on the same catalyst. For example, it can be
particularly advantageous to operate, during hydrogenation of the
diolefins, under conditions such that at least some of the
compounds in the form of mercaptans are transformed.
[0047] In this case, temperatures are generally between 100 and
300.degree. C. and preferably between 150 and 250.degree. C. The
H.sub.2/batch ratio is adjusted between 1 and 20 liters per liter,
preferably between 3 and 15 liters per liter. The spatial speed is
generally between 1 and 10 h.sup.-1, preferably between 2 and 6
h.sup.-1, and the pressure is between 0.5 and 5 MPa, preferably
between 1 and 3 MPa.
[0048] 3) Separation of the Gasoline into at Least Two Fractions
(Step c)
[0049] This step is optional. When it is performed after steps a)
and b), it makes it possible to produce a light, desulfured
gasoline containing most often less than 50 ppm of mercaptans.
During this step, the gasoline is fractionated into at least two
fractions:
[0050] a light fraction with a limited residual sulfur content,
preferably less than about 50 ppm, preferably less than about 20
ppm, very preferably less than about 10 ppm, and making it possible
to use this cut without performing other treatment(s) intended to
reduce its sulfur content.
[0051] a heavy fraction in which most of the sulfur, i.e., all of
the sulfur initially present in the batch and that is not in the
light gasoline, is concentrated.
[0052] This separation is performed preferably using a conventional
distillation column. This fractionation column must make it
possible to separate a light gasoline fraction containing a low
sulfur fraction and a heavy fraction containing preferably most of
the sulfur initially present in the initial gasoline.
[0053] The light gasoline obtained after the separation generally
contains at least all the olefins with 5 carbon atoms, preferably
compounds with 5 carbon atoms and at least 20% of olefins with six
carbon atoms. Generally, this light fraction obtained after steps
a) and b)have a low sulfur content, i.e., it is generally not
necessary to treat the light cut before using it as fuel.
[0054] The gasoline processed using the variant of the process
according to the invention, which is described below, is a cracked
gasoline resulting directly from the cracking or pretreating unit
according to at least one of steps a), b), or c) described
above.
[0055] The process according to the invention comprises two
desulfurization steps d) and f) performed in two separate reaction
zones, as well as a step e) for H.sub.2S separation between the two
hydrodesulfurization zones.
[0056] The first hydrodesulfurization step (step d) consists in
passing the gasoline to be treated over a hydrodesulfurization
catalyst, in the presence of hydrogen, at a temperature between
250.degree. C. and 350.degree. C., preferably between 270.degree.
C. and 320.degree. C. and at a pressure between 1 and 3 MPa,
preferably between 1.5 and 2.5 MPa. The spatial liquid speed is
generally between 1 h.sup.-1, and 10 h.sup.-1, preferably between 2
h.sup.-1 and 5 h.sup.-1, the H.sub.2/HC ratio is between 50
liters/liter (1/1) and 500 l/l, preferably between 100 l/l and 400
l/l, more preferably between 150 l/l and 300 l/l. The H.sub.2/HC
ratio is the ratio between the hydrogen throughput at 1 atmosphere
and 0.degree. C. and the hydrocarbon throughput. Under these
conditions, the reaction takes place in the gaseous phase. The
desulfurization rate achieved during this step is strictly higher
than 90%, i.e., for example, a gasoline initially containing 2000
ppm of sulfur will be transformed into a gasoline containing less
than 200 ppm of sulfur. The operating conditions during this step
are thus adjusted depending on the characteristics of the batch to
be treated so as to achieve a desulfurization rate strictly higher
than 90%, preferably higher than 92%, and very preferably higher
than 94%. The effluents resulting from this first
hydrodesulfurization step are partially desulfurized gasoline,
residual hydrogen, and H.sub.2S produced by decomposition of
sulfurous compounds.
[0057] This step is followed by a step (step 3) of separating most
of the H.sub.2S from the other effluents. This step is intended to
eliminate at least 80% and preferably at least 90% of the H.sub.2S
produced during step d). The elimination of the H.sub.2S can also
be achieved in different ways, known for the most part by one
skilled in the art. For example, there is absorption of H.sub.2S by
a mass of metallic oxide, selected preferably from the group
consisting of zinc oxide, copper oxide, or molybdenum oxide. This
absorbent mass can preferably be regenerated and will be able to be
regenerated continuously or discontinuously by, for example,
thermal processing in an oxidizing or reducing atmosphere. The
adsorbent mass can be used in a fixed or mobile bed. Another more
conventional method consists in cooling the effluent of step d) to
produce a liquid and a gas that are rich in H.sub.2 and H.sub.2S.
The H.sub.2S can be separated from the H.sub.2 by means of a
washing unit with amines, whose operation is well known to one
skilled in the art.
[0058] A second desulfurization step f) is intended to achieve
extensive desulfurization of the gasoline resulting from step e) to
the desired sulfur content. This step consists in making the
gasoline resulting from step e), mixed with hydrogen, pass over a
hydrodesulfurization catalyst at a temperature between 200.degree.
C. and 300.degree. C., preferably between 240.degree. C. and
290.degree. C., at a pressure between 1 and 3 MPa, preferably
between 1.5 and 2.5 MPa. The liquid spatial speed is generally
between 1 h.sup.-1 and 10 h.sup.-1, preferably between 2 h.sup.-1
and 8 h.sup.-1, the H.sub.2/C ratio is between 50 liters/liter
(l/l) and 500 l/l, preferably between 100 l/l and 400 l/l, and most
preferably between 150 l/l and 300 l/l. Under these conditions, the
reaction takes place in the gaseous phase. The mixture of gasoline
and hydrogen processed during this step contains less than 100 ppm
of H.sub.2S and preferably less than 50 ppm of H.sub.2S. The
operating conditions of this step are such that the desulfurization
rate makes it possible to achieve the required sulfur content while
maintaining a desulfurization rate less than that of the first
step. The batch to be processed during this step is much less
sulfurous than the initial batch, and the desired desulfurization
rates are much less. Consequently, the necessary catalyst volumes
and the operating temperatures are likewise much lower. For
example, the VVH (hourly volumic speed) of desulfurization step f)
can be 1.5 times greater than the VVH of step d), and/or the
temperature of desulfurization step f) can, for example, be at
least 10.degree. C. and advantageously at least 20.degree. C. less
than that of step d). Most often, the catalyst volumes are fixed in
industrial units, the desulfurization rate of step f) is then
adjusted mainly by temperature. In any case, said difference can be
adjusted without going beyond the scope of the invention, by any
means known to act on the desulfurization rate of each step d) or
f), for example using, for step f), a catalyst that is less active
than that of step d). The difference in activity between the
catalysts of steps d) and f) can, for example, be obtained by
using, for step f), a catalyst containing a lower quantity of
metals or a support with a smaller specific surface area compared
to the catalyst of step d). Another solution can consist in using a
partially deactivated catalyst for step f).
[0059] The operating conditions during step f) are thus adjusted
depending on the characteristics of the batch to be processed to
achieve a desulfurization rate most often strictly greater than
80%, preferably greater than 85%, and very preferably greater than
92%, or even greater than 95%.
[0060] The difference between the desulfurization rates of the
first and second step of hydrodesulfurization is generally greater
than 1%, preferably greater than 2%, and very preferably greater
than 3% in absolute value.
[0061] Surprisingly, it was found by the applicant that such
constraints on the respective desulfurization rates of steps d) and
f) make it possible to minimize the mercaptan content of the
gasoline produced and thus to make any subsequent step of
sweetening the gasoline optional or less constraining.
[0062] According to a variant embodiment of this process, it is
also possible to inject fresh hydrogen into the second
hydrodesulfurization reactor, to separate the hydrogen from the
gasoline produced and to inject this hydrogen, which generally
contains less than 200 ppm of H2S, into the first
hydrodesulfurization step.
[0063] The catalysts used during steps d) and f) comprise at least
one element from group VIII and/or at least one element from group
VIB on an appropriate support.
[0064] The content of metal from group VIII, expressed as an oxide,
is generally between about 0.5 and 15% by weight, preferably
between 1 and 10% by weight. The content of metal from group VIB is
generally between 1.5 and 60% by weight, preferably between 3 and
50% by weight.
[0065] The element of group VIII, when it is present, is preferably
cobalt, and the element of group VIB, when it is present, is
generally molybdenum or tungsten. The support of the catalyst is
usually a porous solid, such as, for example, an aluminum, a silica
aluminum, or other porous solids, such as, for example, magnesium,
silica or titanium oxide, alone or mixed with aluminum or silica
aluminum. To minimize hydrogenation of the olefins present in heavy
gasoline, it is advantageous preferably to use a catalyst in which
the molybdenum density, expressed in % by weight of MoO3 per unit
of surface, is greater than 0.07 and preferably greater than 0.10.
The catalyst according to the invention preferably has a specific
surface area less than 190 m.sup.2/g, more preferably less than 180
m.sup.2/g, and very preferably less than 150 m.sup.2/g.
[0066] After introducing the element(s) and optionally formatting
the catalyst (when this step is performed on a mixture that already
contains the base elements), the catalyst is in a first stage of
activity. This activation can correspond to either an oxidation and
then a reduction, or to a direct reduction, or to a calcination
only. The calcination step is generally performed at temperatures
going from about 100 to about 600.degree. C., preferably between
200 and 450.degree. C., with air flowing through.
[0067] The catalyst is preferably used at least partially in its
sulfurous form. The introduction of sulfur can be done before or
after any activation step, i.e., calcination or reduction.
Preferably, no oxidation step of the catalyst is performed once the
sulfur or a sulfurous compound has been introduced onto the
catalyst. The sulfur or sulfurous compound can be introduced ex
situ, i.e., outside the reactor where the process according to
which the invention is performed, or in situ, i.e., inside the
reactor used for the process according to the invention. In this
latter case, the catalyst is preferably reduced under the
above-described conditions, then sulfured by passage of a batch
containing at least on sulfurous compound which, once decomposed,
leads to the fixation of sulfur on the catalyst. This batch can be
gaseous or liquid, for example hydrogen containing H.sub.2S, or a
liquid containing at least one sulfurous compound.
[0068] The significance and the advantages of this invention are
obvious from comparison of examples 1 and 2 according to the prior
art and example 3, according to the invention.
EXAMPLE 1
According to the Prior Art
[0069] Example 1 relates to a desulfurization process without
intermediate elimination of H.sub.2S and with a
hydrodesulfurization step.
[0070] A catalyst A for hydrodesulfurization is obtained by
impregnation "without excess solution" of a transition aluminum
available in the form of small balls with a specific surface area
of 130 m2/g and pore volume of 0.9 ml/g, with an aqueous solution
containing molybdenum and cobalt in the form of ammonium
heptamolybdate and cobalt nitrate. The catalyst is then dried and
calcined under air at 500.degree. C. The cobalt and molybdenum
content of this sample is 3% CoO and 10% MoO3.
[0071] 100 ml of catalyst A is placed in a fixed bed, tubular
hydrodesulfurization reactor. The catalyst is first sulfured by
processing for 4 hours under a pressure of 3.4 MPa at 350.degree.
C., in contact with a batch consisting of 2% sulfur in the form of
dimethyl disulfide in n-heptane.
[0072] The batch processed is a gasoline from catalytic cracking
whose initial boiling point is 50.degree. C. and final boiling
point is 225.degree. C. Its sulfur content is 2000 ppm by weight
and its bromine index (iBr) is 69 g/100 g, which corresponds to
about 36% by weight of olefins.
[0073] This batch is processed on catalyst A, under a pressure of 2
MPa bar, an H.sub.2/HC ratio of 300 l/l and a VVH of 2 h.sup.-1.
Table 1 shows the influence of the temperature on the
desulfurization and olefin saturation rates.
1TABLE 1 Sulfur Mer- Saturation Tem- content of captan Desulfuri-
iBr Of Rate of perature Desulfured Content zation Desulfurized
Olefins (.degree. C.) Gasoline (ppm) (ppm) Rate (%) Gasoline (HDO)
310 41 32 97.9 20.3 70.6 320 23 20 98.8 14.7 78.7 330 12 11 99.4 10
85.5
[0074] The operating conditions required to achieve 10 ppm of
sulfur with this type of highly sulfurous gasoline are high
temperature (>310.degree. C.) and low VVH (2 h.sup.-1). Under
these conditions, it is possible to achieve desulfurization rates
higher than 99%, but the olefin saturation rate then becomes very
high (greater than 85%), which acts negatively on the octane
rating.
EXAMPLE 2
According to the Prior Art
[0075] Example 2 relates to a desulfurization process with two
hydrodesulfurization steps and intermediate elimination of the
H.sub.2S formed, according to the prior art.
[0076] Catalyst A is used under gentler conditions than those of
example 1. According to the prior art, the desulfurization rate of
the second hydrodesulfurization step is higher than that of the
first step. The batch processed is the same as the batch of example
1.
[0077] The batch is sent into the reactor of example 1 on catalyst
A mixed with hydrogen. The operating temperature is 285.degree. C.
Other operating conditions are specified in table 2. The effluents
coming out of the reactor contain 239 ppm of sulfur. They are
cooled and stripped so as to separate the hydrogen and the H.sub.2S
from the hydrocarbon phase. The stripped effluents are then
reinjected into the reactor loaded with catalyst A mixed with fresh
hydrogen, according to the operating conditions of said second step
indicated in table 2. The batch throughput was multiplied by 1.5
with respect to the throughput of the first step. The experimental
device used has an online sulfur analyzer which makes it possible
continuously to measure the sulfur content of the effluents. The
reactor temperature during the second step was adjusted so as to
produce a gasoline containing 10 ppm of sulfur.
2 TABLE 2 First step Temperature 1 .degree. C. 285 VVH 1 h-1 4
Pressure 1 bar 20 H2/HC1 l/l 300 Sulfur at exit ppm 239 iBr at exit
49.9 HDS % 88.1 Second step Temperature 2 .degree. C. 292 VVH 2 h-1
6 Pressure 2 bar 20 H2/HC2 l/l 300 Sulfur at exit ppm 10 Mercaptans
at exit ppm 9 iBr at exit 36.9 HDS % 96.0 Overall HDS % 99.5
Overall HDO % 46.6
[0078] This example shows that the process comprising two
hydrodesulfurization steps with intermediate elimination of
H.sub.2S is much more selective than the process with one step used
in example 1. Indeed, the gasoline produced in example 2 has the
same sulfur content as the gasoline of example 1, but the olefin
saturation rate (HDO) here is 46.7%, compared to 85.5% for example
1. The process used in example 2 thus makes it possible to minimize
the processes leading to olefin saturation during
hydrodesulfurization.
EXAMPLE 3
According to the Invention
[0079] In this example, the desulfurization rate of the first step
is, in contrast to example 2, higher than that of the second
step.
[0080] The batch processed is the same as in examples 1 and 2.
[0081] The batch is sent into the above-described reactor on a
catalyst A mixed with hydrogen. The operating temperature is
300.degree. C. The other operating conditions are specified in
table 3. The effluents exiting the reactor contain, respectively,
117 ppm of sulfur. The operating mode is the same as for example 2:
the effluents are cooled and stripped so as to separate the
hydrogen and the H.sub.2S from the hydrocarbon phase, which is
reinjected into the reactor loaded with catalyst A, mixed with
fresh hydrogen, according to the operating conditions indicated in
table 3. The batch throughput was multiplied by 1.5 with respect to
the throughput of the first desulfurization step. As in example 2,
the temperature was adjusted so as to finally recover, at the exit
of the reactor, a gasoline containing 10 ppm of sulfur.
3 TABLE 3 First step Temperature 1 .degree. C. 300 VVH 1 h.sup.-1 4
Pressure 1 MPa 2 H.sub.2/HC1 l/l 300 Sulfur at exit ppm 117 iBr at
exit 43.4 HDS % 94.2 Second step Temperature 2 .degree. C. 264 VVH
2 h.sup.-1 6 Pressure 2 MPa 2 H.sub.2/HC2 l/l 300 Sulfur at exit
ppm 10 Mercaptans at exit ppm 6 iBr at exit 36.8 HDS % 91.2 Overall
HDS % 99.5 Overall HDO % 46.7
[0082] The process according to the invention, i.e., use of a
desulfurization rate of the first step greater than that of the
second step, makes it possible to achieve the same sulfur content
in desulfurized gasoline, as well as the same olefin saturation
rate as the prior art, illustrated by example 2. But the effluent
produced using the process according to the invention has 30% less
mercaptans than the gasoline resulting from example 2. The use of
the process according to this invention thus makes it possible not
only to greatly limit olefin saturation but also to greatly
decrease the mercaptan content and thus the corrosiveness of the
gasoline produced.
[0083] It is to be noted that the adjective "sulfurous" used in
this application is not limited to tetravalent forms of sulfur, but
instead is intended to include all forms of sulfur-containing
compounds and elemental sulfur.
[0084] 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.
[0085] 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.
[0086] The entire disclosure of all applications, patents and
publications, cited herein and of corresponding French application
No. 02/04.108, filed Mar. 29, 2003 is incorporated by reference
herein.
* * * * *