U.S. patent application number 10/686716 was filed with the patent office on 2004-12-16 for reactor or an apparatus for production of aromatic compounds in a moving bed.
Invention is credited to Brunet, Francois-Xavier, Clause, Olivier, Deves, Jean-Marie, Hoffmann, Frederic, Sanchez, Eric.
Application Number | 20040253154 10/686716 |
Document ID | / |
Family ID | 9552825 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040253154 |
Kind Code |
A1 |
Brunet, Francois-Xavier ; et
al. |
December 16, 2004 |
Reactor or an apparatus for production of aromatic compounds in a
moving bed
Abstract
A moving bed process for producing aromatic compounds comprises
at least a first step in which principally naphthene
dehydrogenation is carried out in the presence of hydrogen in a
mole ratio (H.sub.2).sub.1/(HC), said step being followed by at
least one subsequent step carried out at a mole ratio
(H.sub.2).sub.2/(HC).sub.2, the process also comprising reducing
the catalyst with hydrogen in a ratio (H.sub.2).sub.red/(HC). In
accordance with the invention,
(H.sub.2).sub.1/(HC)+(H.sub.2).sub.red/(HC-
).ltoreq.(H.sub.2).sub.2/(HC).sub.2, (HC) representing the molar
quantity of feed in the first step and (HC).sub.2 that of the
subsequent step, or
(H.sub.2).sub.1/(HC)+(H.sub.2).sub.red/(HC)>(H.sub.2).sub.2/(HC).sub.2-
, but where (H.sub.2).sub.1/(HC) is less than
(H.sub.2).sub.2/(HC).sub.2. Particular application to
reforming.
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: |
9552825 |
Appl. No.: |
10/686716 |
Filed: |
October 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10686716 |
Oct 17, 2003 |
|
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09725510 |
Nov 30, 2000 |
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6660895 |
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Current U.S.
Class: |
422/600 ;
422/234 |
Current CPC
Class: |
C10G 35/12 20130101;
B01J 8/12 20130101 |
Class at
Publication: |
422/188 ;
422/189; 422/234 |
International
Class: |
B01J 008/00; B01J
010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1999 |
FR |
99/15 227 |
Claims
1. A reactor for treating a hydrocarbon cut using a catalyst
circulating in a moving bed, comprising at least one line for
introducing a catalyst to the top of the reactor and at least one
line for withdrawing catalyst located at the bottom of the reactor,
and comprising at least one zone for treating the cut by a
dehydrogenation reaction, said zone being provided with at least
one line for introducing the cut, at least one line for withdrawing
said treated cut and gaseous effluent, said zone further comprising
at least one line for introducing a hydrogen-containing gas,
wherein said zone for treating is located in the lower portion of
the reactor, the upper portion comprising at least one catalyst
reduction zone provided with at least one line for introducing
hydrogen-containing gas.
2. A reactor according to claim 1, comprising a means for
separating said zones to prevent the gases entering said zones from
mixing.
3. A reactor according to claim 1, comprising, at the reduction
zone, at least one line for withdrawing gaseous effluent from the
reduction step, the reactor also comprising at least one means for
separating said zones to prevent the gaseous effluents from the
reduction step and the treatment zone from mixing.
4. An apparatus for producing aromatic compounds from a hydrocarbon
cut using a catalyst circulating in a moving bed, comprising: at
least one zone, the first zone, for the treating the cut involving
a naphthene dehydrogenation reaction, said zone being provided with
at least one line for introducing the cut and at least one line for
introducing a hydrogen-containing gas, and also comprising at least
one gaseous stream withdrawal line; at least one subsequent
treatment zone located after said first zone and comprising at
least one line for supplying feed to said subsequent zone, and at
least one line for withdrawing a gaseous effluent; at least one
zone for separating catalyst, liquid product and gaseous
hydrogen-containing effluent located after said treatment zones; at
least one catalyst regenerating zone; at least one zone for
reducing regenerated catalyst connected to said zone carrying out
naphthene dehydrogenation such that the reduced catalyst enters
said dehydrogenation zone, said reduction zone being provided with:
at least one line for introducing hydrogen-containing gas; and at
least one line for extracting a gas stream; at least one line for
recycling at least a portion of the gaseous hydrogen-containing
effluent from said separation zone to said zone carrying out the
dehydrogenation reaction; in which apparatus the line for
withdrawing a gaseous stream from the reduction step is connected
to at least one line supplying feed to the subsequent zone.
5. An apparatus according to claim 4, also comprising at least one
line for recycling at least a portion of the gaseous
hydrogen-containing effluent obtained from the separation zone to
said reduction zone.
6. A reactor according to claim 1, comprising at the reduction
zone, at least one line for withdrawing gaseous effluent from the
reduction step, the reactor also comprising at least one means for
separating said zones to prevent the gaseous effluents from the
reduction step and the treatment zone from mixing.
7. An apparatus for producing aromatic compounds from a hydrocarbon
cut using a catalyst circulating in a moving bed, comprising: at
least one zone, the first zone, for treating the cut involving a
naphthene dehydrogenation reaction, said zone being provided with
at least one line for introducing the cut and at least one line for
introducing a hydrogen-containing gas, and also comprising at least
one gaseous stream withdrawal line; at least one subsequent
treatment zone located after said first zone and comprising at
least one line for supplying feed to said subsequent zone, and at
least one line for withdrawing a gaseous effluent; at least one
zone for separating catalyst, liquid product and gaseous
hydrogen-containing effluent located after said treatment zones; at
least one catalyst regenerating zone; at least one zone for
reducing regenerated catalyst connected to said zone carrying out
naphthene dehydrogenation such that the reduced catalyst enters
said dehydrogenation zone, said reduction zone being provided with:
at least one line for introducing hydrogen-containing gas, and at
least one line for extracting a gas stream; at least one line for
recycling at least a portion of the gaseous hydrogen-containing
effluent from said separation zone to said zone carrying out the
dehydrogenation reaction; wherein the line for withdrawing a
gaseous stream from the reduction step is connected to at least one
line supplying feed to the subsequent zone, further comprising a
reactor according to claim 1.
Description
[0001] The invention relates to moving bed processes for producing
aromatic compounds from hydrocarbons, in which a hydrocarbon feed
supplemented by a hydrogen-rich gas is transformed. More
specifically, it relates to continuous reforming or still more
specifically to BTX (butene, toluene, xylene) production with
continuous catalyst regeneration
[0002] More particularly, it relates to the step in which
principally the naphthenes contained in the feed are
dehydrogenated, i.e., the step carried out in the first reforming
reactor, or to the production of aromatic compounds.
[0003] The catalyst generally comprises a support (for example
formed from at least one refractory oxide, the support also
possibly including 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 alkalis, alkaline-earths,
lanthanides, silicon, group IVB elements, non noble metals, group
IIIA elements, etc.). As an example, such catalysts contain
platinum and at least one other metal deposited on a chlorinated
alumina support. In general, such catalysts are used to convert
naphthenic or paraffinic hydrocarbons which can be transformed by
dehydrocyclisation and/or dehydrogenation, in reforming or for the
production of aromatic hydrocarbons (for example production of
benzene, toluene, or ortho-, meta- or para-xylene). Such
hydrocarbons originate from fractionating crude oil by
distillation, or from other transformation processes such as
catalytic cracking or steam cracking.
[0004] Such catalysts have been widely described in the
literature.
[0005] Many chemical reactions occur during the reforming process.
They are well known; reactions which are beneficial for the
formation of aromatic compounds and improving the octane index
which can be cited are naphthene dehydrogenation, cyclopentane ring
isomerisation, paraffin isomerisation, paraffin dehydrocyclisation;
the deleterious reactions include paraffin and naphthene
hydrogenolysis and hydrocracking. The reaction rates of such a
variety of reactions are very different and are highly endothermic
for dehydrogenation reactions and exothermic for the other
reactions. For this reason, the reforming process is carried out in
a plurality of reactors which are subjected to varying temperature
drops.
[0006] Experience has shown that naphthene dehydrogenation
reactions occur in the first reactor or reactors.
[0007] Thirty years ago, reforming processes or aromatic production
processes were carried out at 40 bars, while twenty years ago, it
was 15 bars, and today's reforming reactors operate at pressures
below 10 bars, in particular in the range 3 to 8 bars.
[0008] However, such a reduction in the hydrogen pressure is
accompanied by more rapid catalyst deactivation by coking. Coke, a
compound with a high molecular weight and primarily based on carbon
and hydrogen, is deposited on the active sites of the catalyst. The
H/C mole ratio of the coke formed is in the range about 0.3 to 1.0.
The carbon and hydrogen atoms form condensed polyaromatic
structures with a variable degree of crystallinity depending on the
nature of the catalyst and the operating conditions employed in the
reactors. While the transformation selectivity of hydrocarbons to
coke is very low, the amount of coke which accumulates on the
catalyst can be large. Typically, for fixed bed units, such amounts
are in the range 2.0 to 20.0 or 25.5% by weight. For slurry reactor
units, these amounts are in the range 3.0 to 10.0% by weight at the
outlet from the last reactor. The coke is mainly deposited in the
last or in the last two reactors.
[0009] Coke deposition, which is faster at low pressure,
necessitates more rapid catalyst regeneration. Currently,
regeneration cycles are as short as 2-3 days.
[0010] Many patents concern processes for reforming or producing
aromatic compounds with continuous or sequential catalyst
regeneration.
[0011] The processes employ at least two reactors in which a moving
bed of catalyst circulates from top to bottom traversed by a feed
composed of hydrocarbons and hydrogen, with the feed being
re-heated between each reactor.
[0012] Experience has shown that the first reactor is the home of
rapid reactions producing large amounts of hydrogen.
[0013] The Applicant's French patent FR-A-2 657 087 describes such
a reforming process.
[0014] FIG. 1 reproduced in this document (corresponding to FIG. 2
of FR-A-2 657 087) employs 4 reactors. An initial feed composed of
hydrocarbons and hydrogen is circulated through at least two
reaction zones disposed in series, side by side, each of these
reaction zones being of the moving bed type, the feed circulating
successively in each reaction zone, and the catalyst also
circulating in each reaction zone and flowing continuously in the
form of a moving bed from top to bottom in each zone, the catalyst
being withdrawn from the bottom of each reaction zone and being
transported in a stream of hydrogen to the top of the next reaction
zone, the catalyst that is continuously withdrawn from the bottom
of the last reaction zone traversed by the feed then being sent to
a regeneration zone.
[0015] Referring to FIG. 1, the feed composed of hydrocarbons and
hydrogen in a set H.sub.2/HC ratio traverses reactor 1 (29) and is
re-heated, traverses reactor 2 (42), is re-heated, traverses
reactor 3 (55a), is re-heated, traverses reactor 4 (55), and is
sent to a separation section.
[0016] The catalyst drops into reactor 1 (29), is traversed by the
feed and is withdraws from (29) via lines (31) and (32). It is
recovered in a hopper (34a), lifted to the upper surge drum (39) of
reactor 2 via a lifting means (34) and (36); it flows from the
surge drum (39) via lines (40) and (41) towards reactor 2 (42); it
is withdrawn from (42) via lines (44) and (45), is recovered in a
hopper (47a), lifted to upper surge drum (52a) of reactor 3 via a
lifting means (47) and (49a); it flows from the surge drum (52a)
via lines (53a) and (54a) towards reactor 3 (55a); it is withdrawn
from (55a) via lines (62a), is recovered in a hopper (47b), lifted
to upper surge drum (52) of reactor 4 via a lifting means (47c) and
(49); it flows from the surge drum (52) via lines (53) and (54)
towards reactor 4 (55); it is withdrawn from (55) via lines (62),
is recovered in a hopper, lifted to upper surge drum (7a) of
regenerator (10) via a lifting means (60a), (6a) and (6b); it flows
from this surge drum (7a) via line (9) towards regenerator (10); it
is withdrawn from (10) via lines (16) and is recovered in a hopper
(17a), lifted to upper surge drum (63) of reactor 1 via a lifting
means (17) and (19); it flows from this surge drum (63) via line
(66) to a reduction drum (20) where the catalyst at least partially
regains it metallic form; finally, it flow via lines (27) and (28)
towards reactor 1 (29).
[0017] The feed in the reactor(s) for reforming Or producing
aromatic compounds is generally treated at pressures of 0.1 to 4
MPa, preferably 0.3-0.8 MPa. 400-700.degree. C., preferably
480-600.degree. C., at space velocities of 0.1 to 10 h.sup.-1,
preferably 1-4 h.sup.-1, and with recycled hydrogen/hydrocarbon
(mole) ratios of 0.1 to 10, preferably 3-10, more particularly 3-4
for regenerative reforming and 4-6 for the aromatic compound
production process.
[0018] Traditionally after the last reactor, a first separation is
carried out between the hydrocarbons and a recycled hydrogen which
is re-injected into fresh feed.
[0019] The non-recycled effluent undergoes a separation process to
produce hydrogen known as exported hydrogen, which may contain up
to 10% by volume or preferably 4% by volume of light hydrocarbons
such as ethane and propane. By comparison, recycle hydrogen can
contain more than 10%, generally more than 12% or 15% by volume of
C.sub.2.sup.+, C.sub.2H.sub.4 to C.sub.10 aromatic compounds.
[0020] The coked catalysts are regenerated.
[0021] The catalyst is generally regenerated in three principal
steps:
[0022] (a) a combustion step wherein the coke is eliminated by
burning with an oxygen-containing gas;
[0023] (b) a halogenation step wherein the catalyst is flushed with
a halogenated gas to re-introduce halogen into the catalyst and
re-disperse the metallic phase;
[0024] (c) a drying or calcining step, which eliminates the water
produced by coke combustion from the catalyst.
[0025] It is completed by a reduction step wherein the catalyst is
reduced prior to introducing the feed, which is generally carried
out between the regenerator (where steps a, b, c are carried out)
and the first reactor where the reaction takes place.
[0026] Reduction consists of chemical transformation of the
metallic phase contained in the catalyst. After preparing the
catalyst or after the calcining step undergone by the catalyst
undergoing regeneration, the metal or metals are present on the
catalyst surface in the form of the oxide or the oxychloride, which
are practically inactive, catalytically speaking. Before injecting
the hydrocarbon feed to be treated, it is thus vital for the
catalyst to be reduced.
[0027] In practice, such reduction is carried out at high
temperature (between 300-800.degree. C., more generally 450.degree.
C. to 550.degree. C.) in the presence of exported or purified
hydrogen, and for periods generally in the range from a few minutes
to a few hours. The purified hydrogen originates from an exported
hydrogen purification unit. It generally contains less than 1% by
volume of C.sub.2.sup.+.
[0028] Thus a purified or exported hydrogen gas is supplied for
reduction and which is then withdrawn and lost once the reduction
operation is complete, and a (non purified) recycle hydrogen is
supplied for the reaction in a H.sub.2/HC ratio which is unique to
the reforming unit.
[0029] More precisely the present invention concerns a process for
producing aromatic compounds from a hydrocarbon cut using a
catalyst circulating in a moving bed, the process comprising at
least the following successive steps:
[0030] a first step for treating the cut employing a naphthene
dehydrogenation reaction carried out in the presence of hydrogen in
a ratio (H.sub.2).sub.1/HC, where (H.sub.2).sub.1 represents the
molar quantity of pure hydrogen introduced into said first step and
HC represents the molar quantity of feed introduced into said first
step;
[0031] followed by at least one subsequent treatment step carried
out in the presence of hydrogen in a mole ratio
(H.sub.2).sub.2/(HC).sub.2, where (H.sub.2).sub.2 represents the
molar quantity of pure hydrogen introduced into said subsequent
step and (HC).sub.2 represents the molar quantity of feed entering
said subsequent step;
[0032] separating the gaseous hydrogen-containing effluent from the
liquid product and from the catalyst, recycling at least a portion
of the gaseous hydrogen-containing effluent, termed the recycle as,
to said first treatment step,
[0033] regenerating and reducing the catalyst then re-introducing
the catalyst into said first treatment step, reduction taking place
in the presence of hydrogen in a mole ratio (H.sub.2).sub.red/HC
where (H.sub.2).sub.red represents the quantity of pure hydrogen
introduced into the reduction step;
[0034] in which process the slim of the mole ratios
(H.sub.2).sub.1/HC+(H.sub.2).sub.red/HC is less than or equal to
the mole ratio (H.sub.2).sub.2/(HC).sub.2, or
(H.sub.2).sub.1/(HC)+(H.sub.2).sub.r- ed/(HC) is greater than
(H.sub.2).sub.2/(HC).sub.2, but where (H.sub.2).sub.1/(HC) is less
than (H.sub.2).sub.2/(HC).sub.2.
[0035] In the present invention, it is also possible to use recycle
hydrogen for reduction. This disposition can increase the available
quantity of exported hydrogen--a product with a high added
value--and can also if necessary do away with purifying the
hydrogen from the reforming process.
[0036] The reduction step is generally carried out at
300-800.degree. C., preferably 400-600.degree. C., with the
catalyst residence time being 15 min to 2 bouts, preferably 30 min
to 1 hour 30 minutes.
[0037] The aromatic compound production process (and more
particularly the zone in which the naphthene dehydrogenation
reaction is principally accomplished) is carried out at
400-700.degree. C. at 0.1-0.4 MPa, with space velocities of 0.1-10
h.sup.-1, with H.sub.2/HC mole ratios of 0.1 to 10.
[0038] Advantageously reforming is carried out at 0.3-0.8 MPa, at
480-600.degree. C., with space velocities of 1-4 h.sup.-1 and with
preferred H.sub.2/HC ratios of at most 4 or even at most 2 in the
step involving dehydrogenation.
[0039] BTX aromatic compounds are advantageously produced at
0.3-0.8 MPa, at 480-600.degree. C. with space velocities of 1-4
h.sup.-1 and with preferred H.sub.2/HC ratios of at most 6 or even
at most 3 in the step involving dehydrogenation.
[0040] The treatment step can be conducted in one or more zones;
thus for the reforming shown in FIG. 1, four treatment zones are
used.
[0041] The invention thus pertains to the naphthene dehydrogenation
step essentially carried out in the first zone (or first reactor)
of the treatment step. A plurality of sections (or zones or
reactors) can be used to carry out each step.
[0042] The invention will be better explained with reference to
FIG. 2.
[0043] The catalyst circulates from regenerator (106) to the upper
surge drum (101) of the first reactor (103) via a transfer means
(107) which, for example, is a lift (107); it falls under gravity
via lines (108) towards the reduction zone (109). This reduction
zone can be axial or radial and can comprise one or more sections.
The catalyst leaving the reduction zone passes via line(s) (109)
into the first reactor (103) from which it is withdrawn via lines
(110); it is then sent to the upper surge drum (104) of the second
reactor (105) via a transfer means (111), advantageously a
lift.
[0044] The hydrogen-containing gas used for the reduction step is
supplied via line (112). Advantageously, it is supplied at the
temperature of the reduction step, via at least one heating means
(113). The resulting stream (114) reduces the catalyst in chamber
(102). A stream (115) leaves
[0045] A hydrogen-containing gas supplied via at least one like
(117) is added to the feed supplied via at least one line (116) and
the resulting stream enters the first reactor via line (119), in
which reactor the naphthene dehydrogenation reactions principally
take place.
[0046] Define (H.sub.2).sub.1 as the quantity in moles of hydrogen
(expressed as pure hydrogen) supplied to the first reactor (103)
(excluding any hydrogen which may originate from reduction) via
line (119);
[0047] (H.sub.2).sub.red as the quantity in moles of hydrogen
(expressed as pure hydrogen) provided to reactor (102) via line
(114);
[0048] (H.sub.2).sub.2 as the quantity in moles of hydrogen
(expressed as pure hydrogen) supplied to reactor (105) in which the
subsequent step occurs (not principally including naphthene
dehydrogenation reactions);
[0049] (HC) as the quantity in moles of feed entering the first
reactor:
[0050] (HC).sub.2 as the quantity in moles of feed entering the
reactor for the subsequent step (105).
[0051] In FIG. 2 (HC).sub.2 is equal to HC since all of the
effluent from the first reactor is treated in the second reactor.
It is possible to envisage the case where only a portion of the
effluent from the first step is treated in the subsequent step, and
the case where feed is added to the effluent from the first step
prior to the reactor for the subsequent step.
[0052] In accordance with the invention, the quantity
(H.sub.2).sub.1 is such that: 1 ( H 2 ) 1 HC + ( H 2 ) red HC ( H 2
) 2 ( HC ) 2 1 )
[0053] and preferably, the gaseous effluent from the reduction step
is introduced into said first step and/or into at least one
subsequent step following dehydrogenation, 2 or ( H 2 ) 1 HC + ( H
2 ) red HC > ( H 2 ) 2 ( HC ) 2 but where ( H 2 ) 1 HC < ( H
2 ) 2 ( HC ) 2 2 )
[0054] In general, at least a portion of the gaseous effluent from
the reduction step is extracted from the unit without passing
through ally of said steps. Preferably, the gaseous effluent from
the reduction step is introduced into said first step and/or into
at least one subsequent step following dehydrogenation.
[0055] In general, (H.sub.2).sub.1/HC is at most 10, preferably 0.1
to 10.
[0056] All quantities awe expressed in moles. The quantity
(H.sub.2) is expressed as pure hydrogen but the hydrogen-containing
gas used may be based on purified hydrogen, exported hydrogen or,
as is preferable, recycle hydrogen.
[0057] The quantity of hydrogen supplied to the reduction step
(calculated as pure hydrogen) is selected such that the HSV with
respect to the catalyst is in the range 1 to 10 kg of hydrogen/kg
of catalyst/h, preferably in the range 2 to 6 kg of hydrogen/kg of
catalyst/h. The flows rate of the gas is sufficient to eliminate
the heat supplied by any C.sub.2.sup.+ hydrocarbon cracking
reactions contained in the reduction gas.
[0058] The quality of the hydrogen is less critical than in the
prior art. Thus advantageously, a gas can be used for reduction
which may contain large quantities of impurities, for example 15%
by volume of C.sub.2.sup.+ (recycle hydrogen) However, the use of
purified or exported hydrogen is also included in the scope of the
invention.
[0059] It should be noted that the ratio (H.sub.2).sub.2/(HC).sub.2
defined above is the ratio conventionally used in the treatment
process, more particularly that used in the prior art in the first
zone. Thus preferably, it is 2-4 for reforming and 3-6 for aromatic
compound production.
[0060] This means that the ratio (H.sub.2).sub.1/HC, in the
treatment zone where the naphthene dehydrogenation reaction occurs,
is lower to the ratio H.sub.2/HC of the prior art when (FIG. 2) the
hydrogen supplied for reduction is withdrawn from the reduction
step and does not pass into said zone (except for the small amount
that passes along with the moving catalyst bed). Clearly iu this
case, hydrogen is generally added to the feed entering said
subsequent step.
[0061] Thus when implementing the invention, the ratio
(H.sub.2).sub.1/HC in said zone has been able to be reduced and as
a result, the naphthene dehydrogenation reaction is favoured.
[0062] Advantageously, stream (118) is supplied at the reaction
temperature of the first reactor (103) by at least one heating
means (120). The resulting stream (119) reacts in reactor (103) and
produces an effluent (121).
[0063] Preferably, the gas streams (115) and (121) are mixed in a
line (122) and constitute the feed for the net reactor (105), which
is advantageously supplied at the reaction temperature by means of
at least one heating means (123). L this preferred disposition,
mixing the reduction hydrogen effluent with the effluent from the
first reactor can produce a ratio (H.sub.2).sub.2/(HC).sub.2 at the
inlet to the second reactor that may be higher than in the prior
art, thus encouraging hydrocarbon transformation after
dehydrogenation.
[0064] Thus the gaseous effluents from reduction and the step
implementing dehydrogenation are introduced into at least one step
following dehydrogenation. This includes arrangements in which a
portion of the effluent is introduced into a subsequent step (for
example the second reactor), a further portion of the effluent (or
the remaining portion) being introduced into a further subsequent
step (for example a 3.sup.rd reactor).
[0065] It is even possible to add recycle gas (or any other
hydrogen) to said step following dehydrogenation.
[0066] More generally, at least a portion of the gaseous effluent
from reduction can be introduced in the step implementing
dehydrogenation and/or at least one step following
dehydrogenation.
[0067] The effluent leaving reactor (105) via line (124) is then
treated in a conventional treatment process; for example, it is
sent to a third treatment zone, or it may be withdrawn, etc. . . .
The same is true for the catalyst.
[0068] The invention thus consists of diminishing the supply of
hydrogen via line (119) in the first zone of the treatment step, if
compared with the prior art and increasing the quantity of hydrogen
in the reduction step. In all cases, the quantity of hydrogen used
for reduction is controlled.
[0069] This quantity of hydrogen used for reduction can be adjusted
to the operator's requirements. It may correspond to maintaining
the global H.sub.2/HC ratio (reduction+1.sup.st reactor). It may
reach a globally higher H.sub.2/HC ratio while maintaining a
hydrogen deficit in the first reactor. This results in maintaining
the H.sub.2/HC ratio (with respect to the prior art) in the second
reactor (after major dehydrogenation of the naphthenes), or in an
increase in this ratio, favouring other reactions. Supplemental
hydrogen can also be injected.
[0070] This provides major advantages:
[0071] (a) a large flow rate of hydrogen with respect to the
quantity of catalyst in the reduction zone which limits deleterious
thermal effects of hydrogenolysis and hydrocracking of
C.sub.2.sup.+ hydrocarbons which may be present in the hydrogen
used for reduction, such that the process of the invention can
function with recycle hydrogen and in the absence of
purification
[0072] (b) The first reactor is the primary seat of naphthene
dehydrogenation reactions (for the reforming units or for the
production of aromatic compounds) which are strong hydrogen
producers; a reduction in the quantity of hydrogen introduced into
the feed for this first reactor favours these dehydrogenation
reactions which are more rapid. Despite these reactions that are
more favourable to coking, it has been shown that coking has no
time to develop in a manner which is substantial with respect to
the prior art situation.
[0073] From the operator's viewpoint the advantages of the
invention result from:
[0074] (a) the possibility of using a less pure hydrogen for
reduction and limiting the residence time in the reduction
zone;
[0075] (b) limiting dechlorination and metallic sintering in the
reduction zone, and thus increasing the service life of the
catalyst;
[0076] (c) optimising die H.sub.2/HC ratio in the first reactor
which reduces the quantity of catalyst necessary in this first
reactor for naphthene dehydrogenation.
[0077] A preferred apparatus for carrying out the process of the
invention is an apparatus for producing aromatic compounds from a
hydrocarbon cut using a catalyst circulating in a moving bed,
comprising:
[0078] at least one zone, the first zone, for treating the cut
involving a naphthene dehydrogenation reaction, said zone being
provided with at least one line for introducing the cut and at
least one line for introducing a hydrogen-containing gas, and also
comprising at least one gaseous stream withdrawal line;
[0079] at least one subsequent treatment zone located after said
first zone and comprising at least one line supplying feed to said
subsequent zone, and at least one line for withdrawing a gaseous
effluent;
[0080] at least one zone for separating catalyst, liquid product
and gaseous hydrogen-containing effluent located after said
treatment zones;
[0081] at least one catalyst regenerating zone;
[0082] at least one zone for reducing regenerated catalyst
connected to said zone carrying out naphthene dehydrogenation such
that the reduced catalyst enters said dehydrogenation zone, said
reduction zone being provided with:
[0083] at least one line for introducing hydrogen-containing
gas;
[0084] and at least one line for extracting a gas stream;
[0085] at least one line for recycling at least a portion of the
gaseous hydrogen-containing effluent from said separation zone to
said zone carrying out the dehydrogenation reaction;
[0086] in which apparatus the line for withdrawing a gaseous stream
from the reduction zone is connected to at least one line supplying
feed to the subsequent zone.
[0087] Preferably, the apparatus also comprises at least one line
for recycling at least a portion of the gaseous hydrogen-containing
effluent obtained in the separation zone to said reduction
zone.
[0088] In the case of the production of aromatic compounds
envisaged here, the line for withdrawing the treated cut from any
of the treatment zones is the same as the line for withdrawing
gaseous effluents, the reaction talking place in the gas phase.
[0089] Clearly, since the catalyst bed circulates in a moving bed,
each zone is provided with a means for supplying catalyst and a
means for withdrawing it.
[0090] Advantageously, the line for introducing a
hydrogen-containing gas is also connected to a line supplying
recycled gaseous effluent.
[0091] Particularly advantageously, the invention provides an
apparatus for carrying out the process of the invention. This
apparatus is a vessel (reactor) comprising a reduction zone
followed (in the direction of flow of the catalyst) by a zone for
dehydrogenation.
[0092] More precisely, the invention concerns a reactor for
treating a hydrocarbon cut using a catalyst circulating in a moving
bed, comprising at least one line for introducing a catalyst to the
top of the reactor and at least one line for withdrawing catalyst
located at the bottom of the reactor, and comprising at least one
zone (103) for treating the cut by a dehydrogenation reaction, said
zone being provided with at least one line (119) for introducing
the cut, at least one line (121) for withdrawing said treated cut
and gaseous effluent, said zone further comprising at least one
line (117, 119) for introducing a hydrogen-containing gas, in which
reactor said treatment zone is located in the lower portion of the
reactor, the upper portion comprising at least one catalyst
reduction zone (102) provided with at least one line (114) for
introducing hydrogen-containing gas.
[0093] FIG. 3 shows such a reactor. The figure shows a radial bed
apparatus.
[0094] Because of the importance of the hydrogen flow rate and the
pressure drop resulting in an axial bed, a radial bed may be
preferred, but axial bed arrangements are also encompassed within
the scope of the invention.
[0095] The catalyst circulates front regenerator (106) to the upper
surge drum (101) of the first reactor (125), via a transfer means
(107) which, for example, is a lift (107); it falls under gravity
via lines (108) towards the reduction zone (102). This reduction
zone can be axial or radial and can comprise one or more sections.
The catalyst leaving the reduction zone passes into the zone
carrying out dehydrogenation (103) located in reactor (125) from
which it is withdrawn via lines (110); it is then sent to the upper
surge drum (104) of the second reactor (105) via a transfer means
(111), advantageously a lift.
[0096] The hydrogen-containing gas used for idle reduction step is
supplied via line (112). Advantageously, it is supplied at the
temperature of the reduction step, via at least one heating means
(113). The resulting stream (114) reduces the catalyst in zone
(102). After radially traversing the catalytic bed from the
exterior to the interior of the reactor, the gaseous effluent is
collected in the central collector (127).
[0097] A hydrogen-containing gas supplied via at least one line
(117) is added to the feed supplied via at least one line (116) and
the resulting stream enters the first reactor via line (119), in
which reactor the naphthene dehydrogenation reactions principally
take place.
[0098] Advantageously, stream (118) is brought to the reaction
temperature of zone (103) by at least one heating means (120). The
resulting stream (119), traversing the bed front the exterior to
the interior of the reactor, reacts in zone (103).
[0099] The resulting gaseous effluent is collected in the central
collector (127).
[0100] The gaseous effluents from reduction zone (102) and the
treatment zone carrying out dehydrogenation (103) are withdrawn as
a mixture via line (121), and constitute the feed for the next
reactor (105), which feed is advantageously brought to the reaction
temperature by at least one heating means (123).
[0101] Mixing of the gases entering into each zone is
advantageously avoided by using a means (126) (for example a plate)
for separating said zones.
[0102] In the arrangement shown in FIG. 3, the gaseous effluents
are mixed in the central collector (127). In a variation, their
mixing in the reactor is avoided by using a means for separating
said zones located in the collector. The gaseous effluents are then
separately withdrawn from each zone, the reactor then including at
least one line for withdrawing the gaseous effluent from the
reduction step.
[0103] We have described radial circulation of the gas over the
catalytic bed from the exterior to the interior of the reactor, but
circulation in the reverse direction is also encompassed within the
scope of the invention.
[0104] Preferred applications are reforming and BTX production.
[0105] The apparatus comprising said reactor also forms part of the
invention.
[0106] Advantageous embodiments are as follows
[0107] (1) the whole of the gaseous effluent from the reduction
step is sent to said first step and the whole of it is sent to said
subsequent step;
[0108] (2) the gaseous effluents from the reduction step and said
first step are separately withdrawn then sent as a whole to said
subsequent step (FIG. 2);
[0109] (3) a portion of the gaseous effluent from the reduction
step is sent to said first step; the other portion is sent to said
subsequent step, mixed with the gaseous effluent from said first
step (the gaseous effluent from the reduction step can be sent to
one or more subsequent steps);
[0110] (4) a portion of the gaseous effluent from the reduction
step is sent to at least one subsequent step and/or to the first
step, the remainder being withdrawn from the unit without passing
through any of said treatment steps;
[0111] (5) all of the gaseous effluent from the reduction step is
withdrawn without passing through any of said treatment steps;
hydrogen is added to the feed entering said subsequent step.
[0112] It should be noted that for all of these arrangments, the
ratio (H.sub.2).sub.1/HC in the first step is always lower than
that in said subsequent step.
[0113] It should also be noted that, in general, at least a portion
of the gaseous effluent from the reduction step is introduced into
at least one treatment step of the process (first step, subsequent
step).
[0114] In all of the advantageous arrangements cited above,
hydrogen can always be added outside the process.
[0115] The following example illustrates the invention without
limiting its scope.
[0116] A catalyst circulated at 800 kg/l and 90839 kg/h of feed
were treated. Redaction was carried out with 18294 kg/h of an 83.7%
by volume pure hydrogen-rich gas with a molar mass of 9.6 kg/kmole,
with an 112 HSV of 4 h.sup.-1, and with a catalyst residence time
of 1 hour. The (H.sub.2).sub.red/HC ratio was 2.07. In the first
treatment zone (first reactor), 9976 kg, of a 83.7% by volume pure
hydrogen-rich gas with a molar mass of 9.6 kg/kmole was injected
into a 90839 kg/h feed. Thus the (H.sub.2).sub.1/HC ratio was
1.13.
[0117] In the prior art, for the same feed and catalyst flow rate,
a recycle gas with a molar mass of 9.6 kg/kmole containing 83.7% by
volume of hydrogen was injected into the first reactor at a flow
rate of 28270 kg/h. All of the effluent passed into the second
reactor, The resultant mole ratio (H.sub.2).sub.2/HC was 3.2.
Reduction was carried out with a 92.1% by volume hydrogen-rich gas,
with a molar mass of 4.4 kg/mole at a flow rate of 600 kg/h, with a
residence time of 2 hours for the 1.5 catalyst.
[0118] It can be seen that using the process of the present
invention, a non-purified hydrogen containing more than 10% by
volume of impurities, and generally more than 15% by volume, can be
used both in the present reforming reactor and in the reducing
reactor; and the flow rate of the hydrogen-rich gas injected into
the feed for the first reactor is less than the quantity added for
reduction.
[0119] These conditions can be adjusted.
[0120] When a (H.sub.2).sub.1/HC ratio of less than 1.1 is desired,
the remaining hydrogen-rich gas (which has not been injected into
the feed that enters the first reactor) has to be injected into the
effluent from the first reactor before it enters the second
reactor.
[0121] If a higher (H.sub.2).sub.1/HC is desired in the first
reactor, it is possible to reduce the flow rate of the reduction
H.sub.2. Thus with an H.sub.2 HSV in the reduction zone of 2
h.sup.-1, for example, it is possible to operate under the
conditions of the example with a (H.sub.2).sub.1/HC ratio of 1.4 in
the first reactor.
[0122] It is possible to have a residence time and a reduction
H.sub.2 HSV and a (H.sub.2).sub.1/HC ratio in the first reactor
such that the case of the example is not applicable. It is possible
for the quantities of reduction hydrogen and hydrogen injected into
the feed not to be sufficient to have a suitable (H.sub.2).sub.1/HC
ratio at the inlet to the second reactor. In this case, it is
possible to provide for supplemental injection of a hydrogen-rich
gas into effluents leaving the first reactor, or at least into the
feed for the second reactor.
* * * * *