U.S. patent application number 10/703546 was filed with the patent office on 2005-09-29 for process and device for the production of aromatic compounds including a reduction of the catalyst.
Invention is credited to Brunet, Francois-Xavier, Clause, Olivier, Deves, Jean-Marie, Hoffmann, Frederic, Sanchez, Eric.
Application Number | 20050214176 10/703546 |
Document ID | / |
Family ID | 9552826 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050214176 |
Kind Code |
A1 |
Brunet, Francois-Xavier ; et
al. |
September 29, 2005 |
Process and device for the production of aromatic compounds
including a reduction of the catalyst
Abstract
The invention relates to a process for the production of
aromatic compounds from a hydrocarbon fraction with a catalyst that
preferably circulates in a moving bed, a process that comprises at
least the following successive stages that take place in at least
one zone: treatment of the fraction in the presence of hydrogen and
implementing at least one reaction for dehydrogenation of
naphthenes; separation of the gas effluent that contains hydrogen,
the liquid product and the catalyst; regeneration of the catalyst;
reduction of the catalyst; and reintroduction of the catalyst for
the treatment stage; recycling in the treatment stage of at least a
portion of the gas effluent that contains the hydrogen that is
called recycling gas; process in which the reduction stage is
carried out in the presence of recycling gas that is introduced in
an amount such that the amount of pure hydrogen that is provided is
between 1-10 kg/kg of catalyst, whereby the effluent that is
obtained from the reduction is then separated from the catalytic
bed. The invention also pertains to the related device.
Inventors: |
Brunet, Francois-Xavier;
(Istres, FR) ; Clause, Olivier; (Chatou, FR)
; Deves, Jean-Marie; (Vernouillet, FR) ; Sanchez,
Eric; (Rueil Malmaison, FR) ; Hoffmann, Frederic;
(Paris, FR) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Family ID: |
9552826 |
Appl. No.: |
10/703546 |
Filed: |
November 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10703546 |
Nov 10, 2003 |
|
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|
09725931 |
Nov 30, 2000 |
|
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6677494 |
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Current U.S.
Class: |
422/141 ;
422/139; 422/145 |
Current CPC
Class: |
C10G 35/12 20130101;
B01J 8/12 20130101 |
Class at
Publication: |
422/141 ;
422/139; 422/145 |
International
Class: |
B01J 008/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1999 |
FR |
99/15228 |
Claims
1-11. (canceled)
12. An apparatus for the preparation of an aromatic compounds from
a hydrocarbon fraction with a catalyst that circulates in a moving
bed, comprising: at least one zone for treating the fraction that
implements a reaction for dehydrogenation of naphthenes, wherein
said zone is equipped with at least one pipe for introducing the
fraction, at least one pipe for drawing off a treated fraction, at
least one pipe for introducing the catalyst at the top of said
zone, and at least one pipe to output the catalyst that is located
at the bottom of said zone, at least one pipe for introducing a gas
that contains hydrogen, and at least one pipe to extract a gas
flow; at least one zone for separating the catalyst, the liquid
product and the gas effluent that contains hydrogen; at least one
zone for regenerating the catalyst; at least one zone for reducing
regenerated catalyst connected to the zone that implements the
dehydrogenation of naphthenes in a manner that the reduced catalyst
enters the dehydrogenation zone via the pipe for the introduction
of the catalyst, wherein said reduction zone is equipped with at
least one pipe for introducing a gas that contains hydrogen, and at
least one pipe for extracting a gas flow; at least one pipe for
recycling at least a portion of the gas effluent that contains
hydrogen from said separation zone to said zone that implements the
dehydrogenation reaction; and at least one pipe for recycling at
least a portion of the gas effluent that contains hydrogen in the
pipe for the introduction of gas into the reduction zone.
13. An apparatus according to claim 12, further comprising at least
one reaction zone that is located after the zone that implements
the dehydrogenation reaction, wherein the at least one reaction
zone comprises at least one pipe to input the catalyst and one pipe
to output the catalyst, at least one pipe to introduce a gas that
contains hydrogen, at least one pipe to output a gas effluent, at
least one pipe to input the reaction effluent that is obtained from
the preceding zone, and a pipe for the reaction effluent that is
obtained from this zone, wherein the pipe to introduce a gas that
contains hydrogen is connected to pipes for the extraction of gas
flows that are obtained from the dehydrogenation zone and the
reduction zone.
14. An apparatus according to claim 13, wherein the pipe for the
introduction of a gas that contains hydrogen is connected to a pipe
that provides the recycled gas effluent.
Description
[0001] The invention relates to the processes (preferably in a
moving bed) for the production from hydrocarbons of aromatic
compounds, in which a hydrocarbon feedstock that is treated by a
hydrogen-rich gas is transformed. It pertains more specifically to
the regenerative reforming or to the more specific production of
BTX (butene, toluene, xylenes) with continuous regeneration of the
catalyst.
[0002] It relates more particularly to the stage of reduction of
the catalyst and optionally also to the first reactor in which the
reactions for dehydrogenation of the naphthenes that are contained
in the feedstock for the most part take place.
[0003] The catalyst generally comprises a substrate (for example
formed by at least one refractory oxide; the substrate can also
include one or more zeolites), at least one noble metal (preferably
platinum), and preferably at least one promoter metal (for example
tin or rhenium), at least one halogen and optionally one or more
additional elements (such as alkalines, alkaline-earths,
lanthanides, silicon, elements of group IV B, non-noble metals,
elements of group III A, etc.). The catalysts of this type contain,
for example, platinum and at least one other metal deposited on a
chlorinated alumina substrate. In a general way, these catalysts
are used for the conversion of naphthenic or paraffinic
hydrocarbons that can be transformed by dehydrocyclization and/or
dehydrogenation, in reforming or for the production of aromatic
hydrocarbons (for example production of benzene, toluene, ortho-,
meta- or paraxylenes). These hydrocarbons are obtained from the
fractionation of crude petroleums by distillation or other
transformation processes such as catalytic cracking or
steam-cracking.
[0004] These catalysts are extensively described in the
literature.
[0005] The chemical reactions that are involved in the reforming
process are numerous. They are well known; for the reactions that
are beneficial to the formation of aromatic compounds and to the
improvement of the octane number, it is possible to cite the
dehydrogenation of naphthenes, the isomerization of cyclopentanoic
cycles, the isomerization of paraffins, and the dehydrocyclization
of paraffins; and for the harmful reactions, it is possible to cite
hydrogenolysis and hydrocracking of paraffins and naphthenes. These
various reactions have very different speeds and are strongly
endothermic for the dehydrogenation reactions, exothermic for the
other reactions. This is why the reforming process takes place in
several reactors that undergo more or less significant temperature
drops.
[0006] Experience shows that the dehydrogenation reactions of
naphthenes occur in the first reactor or reactors.
[0007] The processes for reforming or for production of aromatic
compounds were carried out at 40 bar 30 years ago; at 15 bar 20
years ago, and today, it is common to see reforming reactors that
operate at pressures of less than 10 bar, in particular between 3
and 8 bar.
[0008] This drop in hydrogen pressure, however, is accompanied by a
faster deactivation of the catalyst by coking. The coke that
consists of a high molecular weight and a primarily carbon and
hydrogen base is deposited on the active sites of the catalyst. The
H/C molar ratio of the coke that is formed varies from about 0.3 to
1.0. The carbon and hydrogen atoms form condensed polyaromatic
structures whose percentage of crystalline organization is variable
based on the nature of the catalyst and operating conditions of the
reactors. Although the selectivity of transformation of the
hydrocarbons into coke is very low, the contents of coke
accumulated in the catalyst can be significant. Typically, for the
fixed-bed units, these contents are between 2.0 and 20.0 to 25.5%
by weight. For the circulating-bed units, these contents are spread
from 3.0 to 10.0% by weight at the outlet of the last reactor. The
coke is deposited for the most part in the last two reactors.
[0009] The coke deposition, faster at low pressure, also imposes a
faster regeneration of the catalyst. The current regeneration
cycles can drop up to 2-3 days.
[0010] Numerous patents deal with the processes for reforming or
for production of aromatic compounds with continuous or sequential
regeneration of the catalyst. The diagrams of processes use at
least two reactors, in which a catalytic moving bed, through which
passes a feedstock that consists of hydrocarbons and hydrogen, a
feedstock that is reheated between each reactor, circulates from
top to bottom.
[0011] Experience shows that the first reactor is the center of
highly productive and fast hydrogen reactions.
[0012] Patent FR-2,657,087 of the applicant describes such a
reforming process.
[0013] In FIG. 1 that is reproduced here (corresponding to FIG. 2
of Patent FR-2,657,087), four reactors are used. An initial
feedstock that consists of hydrocarbons and hydrogen is circulated
through at least two reaction zones that are placed in series, side
by side, whereby each of these reaction zones is of moving-bed
type, the feedstock circulates successively in each reaction zone,
and the catalyst also circulates in each reaction zone by flowing
continuously, in the form of a moving bed, from top to bottom of
each of them, whereby the catalyst that is drawn off at the bottom
of each reaction zone is transported in a hydrogen stream to the
top of the next reaction zone, and whereby the catalyst,
continuously drawn off from the bottom of the last reaction zone
through which the feedstock passes, is then sent into a
regeneration zone.
[0014] In referring to FIG. 1, the feedstock that consists of
hydrocarbons and hydrogen, according to a well-defined H2/HC ratio,
passes through reactor 1 (29), is reheated, passes through reactor
2 (42), is reheated, passes through reactor 3 (55a), is reheated,
passes through reactor 4 (55) and is sent to a separation
section.
[0015] The catalyst drops into reactor 1 (29) by the feedstock
passing through it, the catalyst is drawn off from (29) via pipes
(31) and (32), is collected again in a hopper (34a), and is raised
to upper buffer flask (39) of reactor 2 via a lifting means (34)
and (36); it flows from this buffer flask (39) via pipes (40) and
(41) to reactor 2 (42); it is drawn off from (42) by pipes (44) and
(45), is collected again in a hopper (47a), and is raised to upper
buffer flask (52a) of reactor 3 via a lifting means (47) and (49a);
it flows from this buffer flask (52a) via pipes (53a) and (54a) to
reactor 3 (55a); it is drawn off from (55a) by pipes (62a), is
collected again in a hopper (47b), and is raised to upper buffer
flask (52) of reactor 4 via a lifting means (47c) and (49); it
flows from this buffer flask (52) via pipes (53) and (54) to
reactor 4 (55); it is drawn off from (55) via pipes (62), is
collected again in a hopper, and is raised to upper buffer flask
(7a) of regenerator (10) via a lifting means (60a), (6a) and (6b);
it flows from this buffer flask (7a) via a pipe (9) to regenerator
(10); it is drawn off from (10) via pipes (16), is collected again
in a hopper (17a), and is raised to upper buffer flask (63) of
reactor 1 via a lifting means (17) and (19); it flows from this
buffer flask (63) via pipes (66) to a reduction flask (20), where
the catalyst at least partially regains its metallic form; finally,
it flows via pipes (27) and (28) to reactor 1 (29).
[0016] The treatment of the feedstock in the reactor(s) for
reforming or production of aromatic compounds generally takes place
under pressures of 0.1 to 4 MPa and preferably 0.3-0.8 MPa,
400-700.degree. C. and preferably 480-600.degree. C., volumetric
flow rates from 0.1 to 10 h.sup.-1 and preferably 1-4 h.sup.-1 and
with recycled hydrogen/hydrocarbon ratios (mol.) of 0.1 to 10 and
preferably 3-10, and more particularly 3-4 for regenerative
reforming and 4-6 for the process for the production of aromatic
compounds.
[0017] Traditionally, a first separation is carried out after the
last reactor, between the hydrocarbons and a recycling hydrogen
that is reinjected into the fresh feedstock.
[0018] The non-recycled effluent undergoes a separation process
that makes it possible to obtain a so-called exported hydrogen,
which can contain up to 10% by volume, or at best 4% by volume, of
light hydrocarbons such as ethane and propane. In comparison, the
recycling hydrogen can contain more than 10%, generally more than
12% or 15% by volume of C2+, C2H4 to C10 aromatic compounds.
[0019] The coked catalysts are regenerated.
[0020] Generally, the regeneration of the catalyst is carried out
mainly in three stages:
[0021] (a) a combustion stage where the coke is eliminated by
burning with a gas that contains oxygen,
[0022] (b) a halogenation stage where the catalyst is flushed by a
halogenated gas, which makes it possible to reintroduce the halogen
in the catalyst and to redisperse the metallic phase,
[0023] (c) a stage for drying or calcination that eliminates from
the catalyst the water that is produced by the combustion of the
coke.
[0024] It is completed by a reduction stage where the catalyst is
reduced prior to the introduction of the feedstock, which is
generally carried out between the regenerator (where stages a, b,
and c are used) and the first reactor where the reaction takes
place.
[0025] The reduction consists of a chemical transformation of the
metallic phase that is contained in the catalyst. At the end of the
preparation of the catalyst or the calcination stage that the
catalyst undergoes in regeneration, the metal or metals are present
at the surface of the catalyst in oxide form, or oxychloride form,
virtually catalytically inactive. Before the hydrocarbon feedstock
that is to be treated is injected, it is therefore essential to
initiate the reduction of the catalyst.
[0026] In practice, this reduction is carried out at a high
temperature (between 300-800.degree. C. and more generally 450 and
550.degree. C.) in the presence of exported or purified hydrogen
and for periods of generally between several minutes to several
hours. Purified hydrogen is obtained from an exported hydrogen
purification unit. It generally contains less than 1% by volume of
C2+.
[0027] A purified or exported hydrogen gas was thus provided for
the reduction, and said gas was then drawn off and lost, once the
reduction operation ended, and a recycling (non-purified) hydrogen
was provided for the reaction in a single H2/HC ratio for the
reforming unit.
[0028] This invention proposes using the recycling hydrogen in
reduction and optionally combining the reduction zone and the first
reactor when the process operates with a catalytic moving bed. This
arrangement makes it possible in particular to increase the amount
of exported hydrogen--produced with high added value--that is
available. The invention also makes it possible, if necessary, to
make it unnecessary to purify the hydrogen that is obtained from
the reforming process.
[0029] More specifically, the invention relates to a process for
the production of aromatic compounds from the hydrocarbon fraction
with a catalyst (preferably circulating in a moving bed), a process
that comprises at least the following successive stages that take
place in at least one zone: treatment of the fraction in the
presence of hydrogen and implementing a reaction for
dehydrogenation of naphthenes; separation of the gas effluent that
contains hydrogen, the liquid product and the catalyst;
regeneration of the catalyst; reduction of the catalyst and
reintroduction of the catalyst for the treatment stage; and
optionally preferably recycling in the treatment stage using
dehydrogenation of at least a portion of the gas effluent that
contains hydrogen that is called recycling gas; process in which
the reduction stage is carried out in the presence of recycling gas
that is introduced in an amount such that the amount of pure
hydrogen that is provided is between 1-10 kg/kg of catalyst,
whereby the gas effluent that is obtained from the reduction is
then separated from the catalytic bed.
[0030] The invention thus proposes an additional stage to the
process that consists of recycling in the reduction stage at least
a portion of the gas effluent that contains hydrogen (called
recycling gas) that was separated from the liquid and the
catalyst.
[0031] Advantageously, in the treatment zone where the reaction for
dehydrogenation of naphthenes takes place, the amount of recycling
gas is such that the H2/HC molar ratio is at most 10, whereby H2
represents the amount that is expressed in moles of pure hydrogen
provided to the zone of the treatment stage in which primarily the
dehydrogenation reaction takes place, and whereby HC represents the
amount, expressed in moles, of hydrocarbons in the fraction that
enters said zone.
[0032] The reduction stage is generally carried out between
300-800.degree. C., preferably between 400-600.degree. C., whereby
the dwell time of the catalyst is 15 minutes to 2 hours, and
preferably 30 minutes to 1 hour and 30 minutes.
[0033] The process for the production of aromatic compounds (and
more particularly the zone in which primarily the reaction for
dehydrogenation of naphthenes is carried out) is conducted at
400-700.degree. C., 0.1-4 MPa, with volumetric flow rates of 0.1-10
h.sup.-1, and H2/HC molar ratios of 0.1 to 10.
[0034] Advantageously, the reforming is carried out under 0.3-0.8
MPa, at 480-600.degree. C., with volumetric flow rates of 1-4
h.sup.-1 and with preferred H2/HC ratios of at most 4, even at most
2, in the stage that implements the dehydrogenation.
[0035] A production of BTX aromatic compounds is advantageously
carried out under 0.3-0.8 MPa, at 480-600.degree. C., with
volumetric flow rates of 1-4 h.sup.-1 and with preferred H2/HC
ratios of at most 6, even at most 3, in the stage that implements
the dehydrogenation.
[0036] The treatment stage can be carried out in one or more zones;
thus four treatment zones are used for the reforming shown in FIG.
1.
[0037] The invention therefore focuses on the reduction stage that
is carried out in the catalyst and optionally in the first zone (or
first reactor) of the treatment stage.
[0038] The invention will be better understood from FIG. 2.
[0039] The catalyst circulates from regenerator (106) to upper
buffer flask (101) of first reactor (103) via a transfer means
(107) that is, for example, an elevator or lift (107); it drops
under the action of gravity via pipes (108) to reduction zone
(102). This reduction zone can be axial or radial and can comprise
one or more sections. The catalyst that leaves the reduction zone
passes through pipe(s) (109) into first reactor (103), from which
it is drawn off via pipes (110); it is then sent to upper buffer
flask (104) of second reactor (105) via a transfer means (111),
advantageously an elevator.
[0040] The gas that contains the hydrogen that is used for the
reduction stage is provided via pipe (112). Advantageously, it is
provided at the temperature of the reduction stage, by at least one
heating means (113). Resulting flow (114) reduces the catalyst in
chamber (102). A flow (115) emerges therefrom.
[0041] To the feedstock, conveyed via at least one pipe (116), is
added a gas that contains hydrogen via at least one pipe (117), and
the resulting flow enters via pipe (119) into the first reactor in
which the dehydrogenation reactions of the naphthenes primarily
take place.
[0042] (H2).sub.1 is the amount in moles of hydrogen (expressed in
pure hydrogen) that is provided to first reactor (103) (whereby the
optional hydrogen that is obtained from the reduction is excluded)
via pipe (119)
[0043] (H.sup.2).sub.red is the amount in moles of hydrogen
(expressed in pure hydrogen) that is provided to reactor (102) via
pipe (114)
[0044] (H2).sub.2 is the amount in moles of hydrogen (expressed in
pure hydrogen) that is provided to reactor (105) in which the
subsequent stage takes place (not comprising primarily the
reactions for dehydrogenation of naphthenes)
[0045] (HC) the amount in moles of feedstock that enters the first
reactor
[0046] (HC).sub.2 the amount in moles of feedstock that enters the
reactor of the subsequent stage (105).
[0047] In FIG. 2, (HC).sub.2 is equal to HC since the entire
effluent of the first reactor is treated in the second reactor. It
is possible to envisage the case where only a portion of the
effluent of the first stage is treated in the subsequent stage, and
the case where the feedstock is added to the effluent of the first
stage before the reactor of the subsequent stage.
[0048] According to the process, the amount (H2).sub.1 is such that
1 ( H 2 ) 1 H C ( H 2 ) red H C ( H 2 ) 2 ( H C ) 2
[0049] In a general way, 2 ( H 2 ) 1 H C
[0050] is at most 10, and preferably 0.1 to 10.
[0051] All of the amounts are expressed in moles.
[0052] The amount of hydrogen that is provided in the reduction
stage (calculated in pure hydrogen) is selected such that the PPH
relative to the catalyst is between 1 and 10 kg of hydrogen/kg of
catalyst/h, preferably between 2 and 6 kg of hydrogen/kg of
catalyst/h. The gas flow rate is adequate to eliminate the calories
that are provided by optional cracking reactions of hydrocarbons
into C2+ contained in the reduction gas.
[0053] The quality of the hydrogen is less critical than in the
prior art. It thus is advantageously possible to use in reduction a
gas that can contain large amounts of impurities, for example 15%
by volume of C2+.
[0054] With regard to the first reactor (primarily dehydrogenation
reactions of naphthenes), recycling hydrogen is very advantageously
used, but purified hydrogen and exported hydrogen could be used
although this solution is not very advantageous economically.
[0055] It will be noted that the H2/HC ratio that is expressed
above is the ratio that is conventionally used in the treatment
process and more particularly in the first zone. It is thus
preferably 2-4 for the reforming and 3-6 for the production of
aromatic compounds.
[0056] This means that the (H2).sub.1/HC ratio, in the zone of the
treatment stage where the reaction for dehydrogenation of the
naphthenes takes place, is less than the H2/HC ratio of the prior
art when (FIG. 2) the hydrogen that is provided for the reduction
is extracted from the reduction stage and does not pass into said
zone (except the small portion that passes with the catalytic
moving bed).
[0057] Thus, by using the process, it was possible to reduce the
(H2).sub.1/HC ratio at said zone, and consequently the reaction for
dehydrogenation of naphthenes is promoted.
[0058] Advantageously, flow (118) is brought to the reaction
temperature of first reactor (103) by at least one heating means
(120). Resulting flow (119) reacts in reactor (103) and provides an
effluent (121).
[0059] Gas flows (115) and (121) are preferably mixed in a pipe
(122) and constitute the feedstock of the following reactor (105),
which is advantageously provided at the reaction temperature by at
least one heating means (123). In this preferred arrangement, the
mixture of hydrogen effluent for reduction with the effluent of the
first reactor makes it possible to obtain an (H2).sub.2/(HC).sub.2
ratio at the inlet of the second reactor that can be higher than in
the prior art, thus promoting the transformation of the
hydrocarbons after dehydrogenation.
[0060] The gas effluents that are obtained from the reduction and
the stage that implements the dehydrogenation thus are introduced
into at least one stage following the dehydrogenation.
[0061] It is even possible to add recycling gas in said stage that
follows the dehydrogenation.
[0062] More generally, at least a portion of the gas effluent that
is obtained from the reduction can be introduced into the stage
that implements the dehydrogenation and/or at least one stage
following the dehydrogenation.
[0063] The effluent that leaves reactor (105) via pipe. (124) is
then treated according to the standard treatment process, for
example, it is sent to a third treatment zone, it can be drawn off,
etc. . . . The same holds true for the catalyst.
[0064] The invention therefore consists in reducing the supply of
hydrogen via line (119) in the first zone of the treatment stage,
if it is compared relative to the prior art, and in increasing the
amount of hydrogen in the reduction stage. In all cases, the amount
of hydrogen that is used in reduction is controlled.
[0065] This amount of hydrogen that is used in reduction can be
modulated according to the needs of the user. It may correspond to
maintaining the overall H2/HC ratio (reduction+1st reactor). It may
result in a higher overall H2/HC ratio but while maintaining a
hydrogen deficit in the first reactor. At the level of the second
reactor (after predominant dehydrogenation of the naphthenes), this
leads to maintaining the H2/HC ratio (relative to the prior art) or
to increasing this ratio that promotes other reactions. An
additional injection of hydrogen can also be made.
[0066] This leads to very important advantages:
[0067] (a) A significant flow rate of the hydrogen relative to the
amount of catalyst in a reduction zone that limits the harmful
thermal effects of hydrogenolysis and hydrocracking of C2+
hydrocarbons that are optionally present in the hydrogen that is
used for the reduction, such that the process of the invention can
operate with recycling hydrogen and without purification,
[0068] (b) the first reactor is essentially the center of
dehydrogenation reactions of naphthenes (for the reforming units or
production of aromatic compounds) that are highly productive in
hydrogen; a reduction of the amount of hydrogen that is introduced
into the feedstock of this first reactor promotes these
dehydrogenation reactions that are faster. Despite these conditions
that are more favorable to coking, it was noted that the coking
does not have the time to develop in a sensitive manner relative to
the prior situation.
[0069] For the user, the invention is reflected by significant
gains that result from:
[0070] (a) The possibility of using a less pure hydrogen in
reduction and of limiting the dwell time in the reduction zone,
[0071] (b) the limiting of the dechlorination and the metallic
sintering in the reduction zone and thus increasing the service
life of the catalyst,
[0072] (c) the optimization of the H2/HC ratio in the first reactor
which makes it possible to reduce the amount of catalyst that is
necessary in this first reactor for the dehydrogenation of
naphthenes.
[0073] The invention also relates to a device for aromatic compound
production that implements the process according to the
invention.
[0074] Said device for production of aromatic compounds from a
hydrocarbon fraction with a catalyst that circulates in a moving
bed comprises:
[0075] at least one zone for the treatment of the fraction that
implements a reaction for dehydrogenation of naphthenes, whereby
said zone is equipped with at least one pipe for the introduction
of the fraction, at least one pipe for drawing off said treated
fraction, at least one pipe for the introduction of the catalyst at
the top of said zone, and at least one pipe for the output of the
catalyst and located at the bottom of said zone, whereby said zone
also comprises at least one pipe for the introduction of a gas that
contains hydrogen and also comprises at least one pipe for the
extraction of a gas flow;
[0076] at least one zone for the separation of the catalyst, the
liquid product and the gas effluent that contains hydrogen;
[0077] at least one zone for the regeneration of the catalyst;
[0078] at least one zone for the reduction of the regenerated
catalyst connected to said zone that implements the dehydrogenation
of naphthenes such that the reduced catalyst enters said
dehydrogenation zone via said pipe for the introduction of the
catalyst, whereby said reduction zone is equipped
[0079] with at least one pipe for the introduction of gas that
contains hydrogen,
[0080] and at least one pipe for the extraction of a gas flow;
[0081] at least one pipe for the recycling of at least a portion of
the gas effluent that contains hydrogen from said separation zone
to said zone that implements the dehydrogenation reaction;
[0082] the device also comprises at least one pipe for the
recycling of at least a portion of the gas effluent that contains
hydrogen in the pipe for the introduction of gas into said
reduction zone.
[0083] Advantageously, the device comprises at least one reaction
zone that is located after said zone that implements the
dehydrogenation reaction, whereby said reaction zone comprises at
least one pipe for the input of catalyst and a pipe for its output,
at least one pipe for the introduction of a gas that contains
hydrogen and at least one pipe for the output of a gas effluent,
and at least one pipe for the input of the reaction effluent that
is obtained from the preceding zone and a pipe for the reaction
effluent that is obtained from this zone, device in which the pipe
for the introduction of a gas that contains hydrogen is connected
to pipes for the extraction of gas flows that are obtained from the
dehydrogenation zone and the reduction zone.
[0084] Advantageously, the pipe for the introduction of a gas that
contains hydrogen is also connected to a pipe that provides the
recycled gas effluent.
[0085] The following example illustrates the invention without
limiting its scope.
[0086] The catalyst circulates at 800 kg/h, and 90,839 kg/h of
feedstock is treated. The reduction is carried out with 18,294 kg/h
of a hydrogen-rich gas with a purity of 83.7% by volume of
hydrogen, with a molar mass of 9.6 kg/kmol, with a PPH of H2 of 4
h.sup.-1, and a dwell time of the catalyst of 1 hour. In the first
treatment zone (first reactor), 9,976 kg/h of hydrogen-rich gas
with a purity of 83.7% by volume of hydrogen, a molar mass of 9.6
kg/kmol, is injected into the feedstock at 90,839 kg/h. An H2/HC
ratio that is equal to 1.13 is then obtained.
[0087] In the prior art, for the same flow rate of feedstock and
catalyst, a hydrogen recycling gas of molar mass 9.6 kg/kmol that
contains 83.7% by volume of hydrogen at the flow rate of 28,270
kg/h was injected into the first reactor. All of the effluent
passed into the second reactor. The resulting H2/HC molar ratio was
equal to 3.2. The reduction was carried out with a rich gas with
92.1% by volume of hydrogen, a molar mass of 4.4 kg/kmol, under a
flow rate of 600 kg/h, and for a dwell time of the catalyst of 2
hours.
[0088] It can be noted that with use of the process according to
this invention, it is possible to use non-purified hydrogen, i.e.,
containing more than 10% by volume of impurities, and generally
more than 15% by volume, both with regard to this reforming reactor
and to the reducing reactor; and the flow rate of hydrogen-rich gas
that is injected into the feedstock of the first reactor is reduced
by the amount that is added in reduction.
[0089] These conditions can be adjusted.
[0090] Actually, in the case where an H2/HC ratio that is lower
than 1.1 is desired, it will be necessary to inject the remaining
hydrogen-rich gas (which then had not been injected into the
feedstock that enters the first reactor) in the effluent of the
first reactor before its input into the second reactor.
[0091] If a higher (H2).sub.1/HC ratio in the first reactor is
desired, it is possible to reduce the flow rate of hydrogen H2 by
reduction. Thus, with a PPH H2 in a reduction zone equal to 2
h.sup.-1 for example, it then is possible to operate, under the
conditions of the example, an (H2).sub.1/HC ratio that is equal to
1.4 in the first reactor.
[0092] It is possible to have a dwell time and a PPH H2 in
reduction, and an H2/HC ratio in the first reactor, such that the
case of the example is not applicable. It may be that the amounts
of reduction hydrogen and injected hydrogen in the feedstock are
not adequate to have a suitable H2/HC ratio at the inlet of the
second reactor. In this case, it is possible to install an
additional injection of hydrogen-rich gas in the effluents that
leave from the first reactor, or at least in the feedstock of the
second reactor.
[0093] The use in reduction of the recycling gas for a moving-bed
process was described here. It may also relate to a fixed-bed
process, however.
[0094] It will be noted that this use in a moving bed is very
advantageously linked to the use of a reduced H2/HC ratio in the
first reactor, but that all higher values of the H2/HC ratio in
this reactor are possible, in particular those of the prior
art.
[0095] 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. Also, the preceding specific embodiments are to
be construed as merely illustrative, and not limitative of the
remainder of the disclosure in any way whatsoever.
[0096] The entire disclosure of all applications, patents and
publications, cited above and below, and of corresponding French
application 99/15.228, are hereby incorporated by reference.
[0097] 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.
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