AU656183B2 - Method of producing aromatic hydrocarbons in a chamber heated by radiant heating means with a variable heat flow - Google Patents

Abstract

A process is described for production of aromatic hydrocarbons from a charge of aliphatic hydrocarbons containing 2 to 12 carbon atoms, in an enclosure 1 comprising a plurality of pipes 3 which are filled with a catalyst and which are parallel and arranged in rows. A stage called reaction stage and a regeneration stage of the catalyst in the pipes of the enclosure are carried out. Heating of the pipes is produced by suitable radiant heating means 6, situated between two successive rows and arranged in sheets which are substantially perpendicular to the pipes. These sheets heat a first part of the pipes (feed side) with a heat flow greater than the mean heat flow of the heating means and a subsequent second part with a mean flow no greater than the mean heat flow, so that the isothermal condition (isothermicity) of the catalyst is substantially maintained, by virtue of suitable control means. Application to the production of benzene, toluene and xylenes. <IMAGE>

Description

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AUSTRALIA

Patents Act 1990 656183

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: METHOD OF PRODUCING AROMATIC HYDROCARBONS IN A CHAMBER HEATED BY RADIANT HEATING MEANS WITH A VARIABLE HEAT FLOW.

r r *r r ~r ~r ail The following statement is a full description of this invention, including the best method of performing it known to me:- *0Ct 4 4 ci t *r C tic *1 itt r:- I 1 1 it t i i 1 1 **i~r:i-fe.

lA The invention concerns a method, an apparatus for converting hydrocarbons and its use, particularly in producing aromatic hydrocarbons from a charge of aliphatic hydrocarbons with 2 to 12 carbon atoms in the presence of a zeolitic crystalline catalyst composition.

It more especially concerns the synthesis of a mixture containing a major proportion of benzene, toluene and xylenes, materials which are particularly well adapted to improve the octane number of petrols.

The upgrading of aliphatic cuts with a low boiling point oo, such as the LPGs explains the importance which may be 00 attached to using hydrocarbon conversion methods which are efficient, selective and economic and which also contribute to the formation of hydrogen as a by-product.

The reaction producing olefinic hydrocarbons has been described especially in patents US 3760 024, US 3756 942 0 and US 3855 980, in the presence of a crystalline zeolitic catalyst based on silica and alumina of the MFI type such as ZSM5 or ZSM12, possibly with a metal such as i, 20 gallium in the framework, or in the presence of a S. zeolitic catalyst containing a metal outside the framework as described in patents FR 2374 283 and US 4175 057.

The basic processes used in converting aliphatic S 1 25 hydrocarbons to aromatic hydrocarbons are chiefly dehydrogenation of paraffins, oligomerisation of the unsaturated hydrocarbons obtained and cyclisation of the oligomers. Taken as a whole, the reaction is highly endothermic, the reaction speed is sensitive to temperature variations and the successive reactions are accompanied by deposition of coke on the catalyst and 0 i,0 2 reduction of the metal oxides contained in the catalyst, with the result that the catalyst is deactivated rapidly and the cycle is shortened.

One of the problems to be solved is thus how to ensure uniform heating of the reaction zone in the region of 500 to 6000C so as to obtain the flattest possible temperature profile therein, in the knowledge that the catalyst is sensitive to a temperature increase and may be destroyed when the critical temperature is exceeded.

i0 It has in fact been found that the heat requirement does os o::o not remain constant as the endothermic reaction producing aromatic hydrocarbons progresses.

00 o 0000 Another problem to be solved relates to regeneration of the catalyst: it must be rapid and of variable frequency 5 according to the reaction temperature, which is directly odependent on the charge to be treated, but regeneration is generally carried out e.g. every 12 hours. It must be gentle enough to maintain the performance of the catalyst and to minimise its replacement rate.

During the used catalyst regenerating phase, on the other hand, it is preferable to reach the coke combustion temperature as rapidly as possible, in order to maintain a substantially constant temperature level right along the tube, in order to keep the catalyst active for as long as possible.

Prior art describes a method of heating with burners arranged on the walls of a cell which contains tubes filled with catalyst. For example patent US-A-4 973 778 describes the use of burners and the use of the combustion gases as the gas for regenerating the i 1:.

l"el 3 catalyst. This solution has the disadvantage of requiring a large number of conventional radiant burners to distribute and control the heat flows along the tubes.

Moreover only one row of tubes can be provided per cell; this involves having a large number of burners and cells, in view of the number of tubes required. Furthermore these types of burners and cells lead to great thermal inertia, which may cause deterioration of the tubes and the catalyst contained therein, should the feeding of the charge be stopped accidentally.

Finally, prior art is illustrated by patent JP-A-63197534 (Patent Abstracts of Japan vol.12, No. 482 (c-553) 3329, Dec.1988).

The object of the invention is to deal with the problems raised above so as to improve the rates of conversion to aromatic hydrocarbons and the durability of the catalyst.

Another object is to use appropriate radiant heating means for the aromatic hydrocarbon- produc i ng reaction and the catalyst-regenerating reaction in the same tubes.

More particularly, the invention concerns a method of producing aromatic hydrocarbons from a charge of aliphatic hydrocarbons with 2 to 20 carbon atoms in at least one reaction chamber, the chamber having a plurality of substantially parallel tubes arranged in rows and containing a fixed bed of a catalytic composition, characterised in that: a) a reaction phase producing aromatic hydrocarbons is carried out, during which the possibly preheated charge is circulated in the tubes containing the catalytic

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*0 0 0 00 0 00*0 0 0a 0000 0000 S00 0 0 .i u a00 000000 0 0 900004 0 BB, composition under appropriate conditions, and an effluent rich in aromatic hydrocarbons is collected: b) a phase of purging the tubes with at least one appropriate gas is carried out, after the reaction phase and after a catalyst-regenerating phase defined below, and a purge effluent is collected: c) and a phase of regenerating the catalyst is carried out in the tubes of the chamber under appropriate regenerating conditions, the catalyst being in a fixed bed and having had coke deposited on it during the reaction phase, and a regeneration effluent is recovered, the method further being characterised in that the tubes are heated during the reaction phase by a plurality of appropriate radiant heating means located between pairs of successive rows and arranged in layers which are substantially parallel, independent of one another and substantially perpendicular to the tubes, the heating means being adapted to heat a first part (the feed side) of the tubes with a heat flow greater than the mean heat flow of the reaction chamber, and adapted to heat a second part of the tubes, downstream of the first part, with a heat flow no more than equal to the mean heat flow of said chamber, so that the isothermicity of the catalyst is substantially maintained; the effluent rich in aromatic hydrocarbons is recovered and any combustion fumes emanating from the heating means are/distharged from the chamber.

One feature of the process is that 0.01 to 50% of the length of the reaction tubes, at the feed side, may be heated with a heat flow from 101 to 500% of the mean heat 14 -j flow of the chamber, and the remaining part of the tubes with a heat flow from 10 to 100% of the mean heat flow of the chamber.

The mean heat flow of the reaction chamber is defined by the ratio of the power absorbed by the set of tubes for a given reaction to the total external area of the tubes of the chamber.

From 0.01 to 40% and preferably 0.01 to 35% of the length o* of the reaction tubes at the feed side may advantageously 0 be heated with a heat flow from 120 to 300% and o 0 preferably 150 to 200% of the mean heat flow, and the remaining part of the tubes with a heat flow from 20 to and preferably 40 to 75% of the mean heat flow.

Under these conditions the temperature profile right :o *15 along the tube is substantially flat, allowing for a higher heat demand in the first part of the tube than in the remaining part. In this case use of the catalyst may 0"o0.. be optimised relative to the quasi maintenance of its i activity for the longest possible time.

The heating means used may advantageously be those described in patent US 4 664 620, comprising burners of substantially cylindrical, elongated shape with a matrix of ceramic fibre, which burn a mixture of gaseous fuel and air, without a flame, in the interstitial spaces between the fibres and transfer the heat by radiation.

The use of these ceramic fibre burners is thus one of the subjects of the invention.

They further have the advantage of liberating little i 1 1 ^I 6 NO., little CO and few hydrocarbons during combustion.

Their use is also very flexible, since the quantity of heat liberated may be controlled. In addition they have very little inertia. This is important in the event of inopportune termination of the feeding of the charge, or an excessive coke deposit on the catalyst which may interrupt the feeding of the charge.

Another feature of the process is that a purging phase is normally carried out between the phase producing aromatic :10 hydrocarbons and the phase regenerating the used catalyst. For this purpose the feeding of the charge to the tubes is stopped, the heating of the tubes is reduced or stopped, for example by interrupting the supply of oxidant and fuels to the burners, and the tubes are purged at least once with an inert gas such as nitrogen, under flow and temperature conditions such that the s o temperature of the catalyst remains substantially constant. This purging phase may be repeated between a I° regenerating phase and a reaction phase, with the result 20 that the catalyst is in an inert gas atmosphere before being put into contact either with oxygen in its regenerating phase or with hydrocarbons during the reaction phase.

Another feature of the process is that the catalyst regenerating phase is generally carried out by injecting preferably heated inert gas and air into the tubes, so as to obtain a gas containing 0.05 to 3% by volume, preferably 0.4 to 0.8% by volume of molecular oxygen (relative to the total gas) and heating 0.01 to preferably 0.01 to 35% of the length of the tubes at the feed side with a heat flow from 5 to 100% of the mean heat flow used during the reaction phase, under 01C~ 7 conditions such that the exothermicity of the coke combustion reaction is controlled.

The passage from the regenerating phase to the hydrocarbon producing phase is obviously made generally by carrying out a purging phase, e.g. as described above.

This brings the catalyst from an oxidising atmosphere to an inert atmosphere.

;o a° In a preferred embodiment of the method of the invention, the reaction chamber may comprise at least one module *oo: which has two sets of tubes disposed in substantially parallel rows. The reaction phase generally takes place in one of these sets of tubes while the catalyst regenerating phase is taking place in the other. When regeneration is substantially over, after the purging period, the tubes which were previously used for .o.j regeneration may then be used as the reactor producing aromatics. This alternating action, produced by a set of valves controlled by appropriate means, is found to be very flexible.

j The fact that the temperature level of the bed of catalyst during the hydrocarbon producing phase is substantially the same as that required during the regeneration phase has at least two advantages: The method thus described reduces the time of passage between the reaction cycle and the regeneration cycle, since the temperature is substantially the same in both cases and the method is carried out in the same tubes.i It also reduces the cycles of thermal stresses on the I /f tubes and on the catalyst.

i 8 The reaction generally takes place at an absolute pressure of 0.2 to 10 bar (1 bar 105 Pa) and a temperature of 400 to 600*C according to the nature of the charge. The temperature is advantageously from 480 to 550 0 C for the LPG cut and 450 to 530'C for the naphtha cut, at a preferred absolute pressure of 1 to 5 bar. The temperature is preferably from 500 to 540 0 C for the LPG cut and 480 to 510'C for the naphtha cut.

The catalyst used is generally a crystalline zeolite of the MFI type such as the ZSM zeolites, e.g. ZSM5, ZSM8, ZSM11, ZSM12 and ZSM35 described in patent US 3970 544.

These zeolites may advantageously contain at least one metal.

.t Some examples are zinc and gallium, preferably gallium.

r15 These metals may be in the framework or outside it.

It is also possible to use zeolites synthesised in a S: fluoride medium with or without metal.

The catalyst is preferably used in fixed bed form, thereby reducing attrition.

and preferably 1.0 to 3.0 h The aliphatic hydrocarbon charge generally has 2 to 12 carbon atoms. It advantageously contains LPG or naphtha, the operating conditions varying according to the nature of the charge. With a charge such as LPG, for example, one can operate at a higher temperature than with a a" charge such as naphtha. The unit thus enables charges of i -r i, .i 9 varying composition to be accepted very rapidly, through easy control of the temperature of the chamber.

Operating coiditions are generally optimised to allow at least 60% of the charge to be converted, particularly in the case of LPG to obtain an aromatic hydrocarbon ratio of at least 60% relative to the initial charge converted.

The non-converted part of the charge may be recycled when the effluent has been removed.

Higher conversion rates can be obtained with heavier :io charges such as a naphtha, e.g. at least V 4 *o Regeneration is generally effected at a temperature from 450 to 650°C and preferably 480 to 560°C.

The method of the invention may be carried out by a hyrocarbon converting apparatus provided with at least one chamber 1 containing at least one reactor 2, which i has a plurality of tubes 3, substantially parallel with one another and fed in parallel, the tubes being filled it with at least one catalyst in a fixed bed, chargefeeding means 4 connected to one end of the tubes and effluent- recovering means 5 connected to the tubes, the tubes being disposed in substantially parallel rows, i;| between which a plurality of radiant heating means 6 such as ceramic fibre gas burners are arranged in substantially parallel layers independent of one another, the heating means being substantially perpendicular to the tubes and adapted to heat them under appropriate conditions.

The apparatus further comprises means 9, 28 for regenerating the spent catalyst, including means for purging the tubes, means 9a, 9b for supplying 4 i u9 /r **jI I y^I W ,J _1 'ii regenerating gas and means 10, 32 for discharging the regeneration effluent, adapted to regenerate the spent catalyst in the tubes, these regenerating means being connected to the tubes, and alternate displacement means 20 adapted to connect the tubes alternately to the charge feeding means 4 and effluent recovery means 5, then to the catalyst-regenerating means 9, 28, the apparatus further comprising means 50 for checking and regulating the temperature of the tubes, connected to the layers of heating means.

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•o 0The heating means generally comprise a fuel anid oxidant feed and means for discharging combustion fumes, connected to a convection section which is itself connected to a chimney. The convection section may have a heat exchanger adapted to preheat the charge and the purging and regenerating gases.

°ai The tubes used in the method generally have a length of 2 to 20 m and an inside diameter of 10 to 200 mm. They are arranged in substantially parallel, advantageously vertical rows, and each row may contain one or more lines of tubes. The distance between the axes of the tubes is Cfrom 1.5 to 6 times its inside diameter. In a preferred embodiment the tubes are suspended and connected to the charge feed and the effluent discharge at one and the same end.

Another feature is that the apparatus normally comprises regenerating means adapted to regenerate the spent catalyst in the same tubes as where the aromaticproducing reaction took place. These regenerating means generally have a regenerating gas feed at one end of the bundle of tubes and discharge means for the regeneration 6 r' f t b s h i t n e b t w e h x s o h u e si h6-t f

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0Q 0 a a 10 043~ *a S *44$ a a a a 1- 11 effluent at the other end. This latter end may be located at the same side, e.g. ,;th the suspended tubes.

The apparatus may also comprise means adapted to connect the reaction tubes alternately to the regenerating means then to the means for carrying out the reaction, and particularly to connect one end of the tubes to the charge-feeding means and the other end to the means for discharging the effluent produced; in the case of suspended tubes this end may be at the same side.

In a preferred embodiment the apparatus may comprise at least one chamber with a first reactor containing a plurality of reaction tubes and a second reactor provided with a plurality of regenerating tubes adapted to regenerate the catalyst; the first and second reactor communicating through a passage with a convection section which is connected to the outside by appropriate means (chimney); the regenerating tubes being connected at one end to a regenerating gas feed and at the other end to means for discharging a regeneration effluent; and further comprising alternate displacement means adapted to connect the reaction tubes alternately to the chargefeeding means and effluent-recovery means then to the regenerating gas feed and the means for discharging the regeneration effluent; the alternate displacement means being adapted further to connect the regenerating tubes alternately to the regenerating gas feed and regeneration effluent discharge then to the charge-feeding means and the means for recovering the aromatic hydrocarbon effluent; the reaction tubes operating in so-called reaction phase while the regenerating tubes operate in so-called regeneration phase during a first stage, and the reaction tubes then becoming regeneration tubes while

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h U r lr-L- 1 L'i (I~illl--* L- ~~-iltC-ll c) a phase of regenerating the catalyst is carried 2 12 the regeneration tubes become reaction tubes during a second stage.

The design technology is very flexible owing to the modular nature of its application, and may be adapted either to large or small capacities. The flexibility with which the heating can be used at short notice is an additional asset.

Another feature of the apparatus is that the control and oj c regulation means may comprise at least one temperature second, subsequent portion of the tubes, the two probes 0: which can control the means for heating the first and i -00 second portions of the tubes.

ram The invention will be understood better if the accompanying drawings are studied These illustrate the :20 method and apparatus of the invention diagrammatically, and in them: Fig. is a longitudinal section through the reaction chamber, containing a reaction section and a regeneration section separated by a convection chamber, and Fig.2 shows the means for heating the tubes and the control and regulation means which control them.

Referring now to Fig.l, a reaction chamber 1 with walls clad with an nisulating matei comprises a reactor 2 j provided with a plurality of stainless steel tubes 3 of rma 'T 0 "-10 probe conce to- id f1T~-.~1.i rst polrion of th tube, a -wood 4 it 1 *0 0 S0 Ce 0 0 0** 00 .41400: 0 *00* *06* 0 o 00 ~.20 0 0 *04S*4

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4.~ $000 CA o C substantially cylindrical shape, which contain a fixed bed of a catalyst adapted to produce aromatic hydrocarbons. The tubes are spaced apart by a length equal to about twice their diameter, measured from the axis. They are substantially vertical and are arranged in substantially parallel rows containing two lines of tubes. A plurality of elongated, substantially cylindrical burners 6 with a ceramic fibre mnatrix are located between the rows. They can burn a mixture of gaseous fuel and air, supplied by a feed 7, without a flame. The burners are arranged in substantially parallel layers which are independent of one another and substantially perpendicular to the reaction tubes. The layers may comprise one or more burners, and the distance between burners is generally from 0.5 to 2.0 m. The distance between burners and tubes is generally from 0.2 to 0.8 m and advantageously from 0.3 to 0.5 mn. These radiant burners are adapted to heat a first portion of the tubes (at the feed side) with a heat flow of about 180% of the mean heat f low over a length of about 30% of the length of the tubes, which may be up to 8 m. The remaining part of the tubes is heated with a heat f low equal to about 70% of the mean heat flow.

The combustion fumes from the burners are discharged through a passage 14 to a convection section 13 in which the charge may be heated. Heat recovery means 19 may also be incorporated there. The fumes are discharged through a chimney 16.

The tubes of the reactor are fed in parallel with a charge of aliphatic hydrocarbons, e.g. LPG, which is, supplied through lines 17a and 4 by means of a pump 17.

The charge may be heated by a heat exchanger 11 upstream of its passage into the convection section,' the heat

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7 o 0~0 0 0 0~ *00* 0*010 o 0 00*0 00 0 00 0 04100 010 0010* 0400 0100 0 10 00-10 *#000 0 20 0 0010 exchanger receiving heat from the reactor effluent, which is discharged in parallel through a line 5 connected to the heat exchanger. The effluent is then directed by a set of appropriate valves 29 to a cooling tower 67, then to a gas/liquid separating flask 68 and finally to a fractionating section 70 which makes it possible to collect, on the one hand, aromatic hydrocarbons and, on the other hand, a gas enriched with hydrogen and a gas enriched with non-aromatic hydrocarbons, as well as the non-converted charge which may be recycled.

The reaction chamber has a reaction cell, as shown in Fig.l described above. It also has a regeneration cell arranged substantially symmetrically relative to the axis of the chamber passing through the convection section.

The regeneration cell is in fact substantially identical with the hydrocarbon-producing cell, since the two reactors operate alternately, with one operating in hydrocarbon-producing phase while the other operates in catalyst-regenerating phase.

The cell 8 operating in regeneration thus comprises the plurality of tubes 3 described above, arranged in rows with the burners 6 between them. ,The burners 6 are disposed in layers and adapted to heat-the tubes under the regenerating conditions described above. The tubes contain the catalyst on which coke has been deposited during the preceding, hydrocarbon- produc ing phase. First the gas used for the purge (nitrogen), supplied through the line 9a, then a mixture of nitrogen and air of oxygen by volume), supplied through the lines 9a and 9b, are introduced after being compressed, at the inlet of the regenerator 8 through the line 9 and the valve 28.

The tubes are fed in parallel. The fixed bed catalyst is at least partly regenerated under appropriate conditions

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and the combustion effluent is discharged through a line and passes through the heat exchanger 12, which partially preheats the purging gas and regenerating gas.

Additional preheating of these gases is carried out in the convection section.

The regeneration effluent is then directed by a set of valves 32 to a treatment and separation section (not shown in the figure).

0 In the embodiment already described, one cell operates in hydrocarbon production while the other operates in rregeneration phase. After the time required for the o hydrocarbon-producing reaction (about 12 hours) appropriate alternating displacement means 20 allow an alternation to take place, with the reactor 2 passing into regeneration phase while the regenerator 8 passes into hydrocarbon-producing phase.

000During the phase required for purging, valves 26 and 28, 0 which together supply the circuit with nitrogen, are t open, valves 25 and 27 are closed and valves 30 and 32 20 for recovering the purge effluent are open while valves 29 and 31 are closed.

After the purging phase the alternating displacement means open the valve 25 to feed the reactor with the charge and close the valves 26 and 27. These same means close the valves 30 and 31 to let the effluent be discharged through the valve 29, which is open towards the fractionating section Similarly, the alternating displacement means 20 let the i N2 air mixture pass through the open valve 28 to the regeneration cell 8 with the valve 27 closed, while the jf

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regeneration effluent is directed to the treatment section through the opening of the valve 32 and the closing of the valve 31.

After another purging phase the displacement means make the reactor 2 become a regenerator. The line 9 for the regenerating gas mixture supplies the reactor through the open valve 26, with the valves 28 and 29 closed, while the regeneration effluent is discharged through the line 5 with the valve 30 open and the valves 29 and 32 closed. The alternating displacement means similarly make the regenerator 8 become a reactor. For this purpose the charge is passed through the line 17b and the open valve 27 with the valves 25 and 28 closed to the line 9 supplying the reaction tubes, and the effluent from the reaction producing aromatic hydrocarbons is passed to the treatment section 70 through the line with the valve 31 open and the valves 29 and 32 closed.

The alternating displacement means 20 are of course connected to the means 50 for regulating the heating layers, which adjust the heating and thus the fuel feed differently during the aromatic-producing, purging and regenerating phases.

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~Tg LL~ The heating means are regulated and checked as follows (Fig.2).

Temperature probes 51, 56 and 57, arranged on the reaction tubes substantially at the level of the various heating layers 6, measure the temperature and pass an electric signal respectively through electric lines 52, 58 and 59 to the checking and regulating means 50, which are themselves connected the the alternating displacement I. A *t 17 means 20. For a specific phase of the aromatic-producing reaction for example, the electric signals transmitted by the probes are compared with previously recorded reference values. The means 50 then send response signals through the lines 53, 62 and 63, which respectively regulate the valves 54, 60 and 61 for feeding the fuel supplied, through the lines 55, 65 and 66, which are in turn connected to the fuel feed line 7.

These valves feed the heating means 6 according to the reference values and the temperature measured.

The chamber shown has one module containing a reactor or 0o cell operating in hydrocarbon-producing phase and another :o0 reactor operating in regeneration phase, the two reactors 1, being linked by a convection section. The chamber may of course contain a plurality of modules, for example with the two adjacent convection sections having one chimney to discharge the combustion effluent.

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Claims (9)

1. A method of producing aromatic hydrocarbons from a charge of aliphatic hydrocarbons with 2 to 12 carbon atoms in at least one reaction chamber, the chamber having a plurality of substantially parallel tubes arranged in rows and containing a fixed bed of a zeolitic crystalline catalyst composition, wherein: a) a reaction phase producing aromatic hydrocarbons is carried out, during which the charge, optionally preheated, is circulated in the tubes containing the o catalytic composition under conditions for producing o aromatic hydrocarbons, and an effluent rich in aromatic o hydrocarbons is collected; o: 0b) a phase of purging the tubes with at least one o o 15 inert purge gas is carried out, after the reaction phase and after a catalyst-regenerating phase defined below, and a purge effluent is collected; and 0444 0• c) a phase of regenerating the catalyst is carried out in the tubes of the chamber under regenerating conditions, the catalyst being in a fixed bed and having 4 had coke deposited on it during the reaction phase, and a regeneration effluent is recovered, characterised in that the tubes are heated during the reaction phase by a plurality of radiant heating means 25 located between two successive rows and arranged in layers which are substantially parallel, independent of one another and substantially perpendicular to the tubes, the heating means being adapted to heat a first part, representing 0.01 to 50% of the length of the tubes, at the feed side, with a heat flow equal to 101 to 500% of the mean heat flow of the reaction chamber, and adapted to heat i J0 0 h 5 i ert urg ga is arr ed ut, fte th rea tio ph se 0 L and afe aays-eeeaig hs eiedblw n L 19 part, with a heat flow equal to 10 to 100% of the mean heat flow of the chamber, so that the isothermicity of the catalyst is substantially maintained, the effluent rich in aromatic hydrocarbons is recovered and any combustion fumes emanating from the heating means are possibly discharged from the chamber.

2. The method of claim i, wherein 0.01 40% of the length of the reaction tubes at the feed side is heated with a heat flow from 120 to 300% of the mean heat flow of the chamber, and the remaining part of the reaction tubes with a heat flow from 20 to 85% of the mean heat flow. *o 0

3. The method of claim 1, wherein from 0.01 to of the length of the reaction tubes at the feed side is e heated with a heat flow from 150 to 200% of the mean heat 15 flow of the chamber, and the remaining part of the reaction tubes with a heat flow from 40 to 75% of the mean heat flow.

4. The method of claim 1, 2 or 3, wherein the charge feed and the regenerating gas feed are respectively stopped 20 -between each reaction phase and each regeneration phase and :0 between each regeneration phase and each reaction phase, and wherein the fuel and oxidant feed to the burners may be stopped, and the reaction tubes are purged at least once i with an inert gas such as nitrogen, under flow and temperature conditions such that the temperature of the catalyst is substantially constant.

The method of any one of claims 1 to 4, wherein the reaction chamber comprises at least one module of two sets of tubes, characterised in that the reaction phase is carried out in one of these sets of tubes while the catalyst-regenerating phase is carried out in the other set of tubes and vice versa. 00 0 0 ~b4 h~. T 20

6. The method of any one of claims 1 to characterised in that the catalyst-regenerating phase comprises injecting an inert gas such as nitrogen and air, both possibly preheated, so as to obtain a gas containing from 0.05 to 3% of molecular oxygen relative to the total gas in said reaction tubes, and heating from 0.01 to 50% of the length of the reaction tubes at the feed side with a heat flow equal to 5 to 100% of the mean heat flow of the chamber, under conditions such that the exothermicity of the coke combustion reaction is controlled. 0 ir 00 0 0000 0 0 o a a CCC *0 CCC

7. f rom f eed heat The method of claim 6, which comprises heating 0.01 to 35% of the length of the reaction tubes at the side with a heat flow equal to 5 to 100% of the mean flow of the chamber.

8. The method of any one of claims 1 to 7, wherein the heating means are burners with a ceramic fibre matrix.

9. The method of claim 8, wherein the distance between burners is 0.5 to 2 metres. The method of any one of claims 1 to 9, wherein 20 the isothermicitN., of the catalyst is checked and regulated by processing and control means connected to the radiant heating means, to at least one first temperature probe connected to the first part of the tubes and to at least one second probe connected to the remaining part of the tubes. DATED THIS 17TH DAY OF OCTOBER 1994 INSTITUT FRANCAIS DU.PETROLE By its Patent Attorneys: GRIFFITH HACK CO Fellows institute of Patent Attorneys of Australia. 0 CIL" -11 -4 1 4, METHOD OF PRODUCING AROMATIC HYDROCARBONS IN A CHAMBER HIEATPED DY RADIANTI HEATING MEANS WITH A VARIABLE BEAT FLOW I nvefltorrs Pierre RBNARD, Arl MINKK]NEN and Didier '4, ABSTRACT 99 4 o 99 94,, 9 99 te 1.0 r 9.4 4 9944 C. 4 ft 9 4 *944 *tC 4 9 20 Thite specification describes a method of producing aromatic hydrocarbons from a charge of aliphatic hydrocarbons with'2 to 12 carbon atoms, in a chamber 1 comprising a plurality of parallel tubes 3 filled with a catalyst and arranged in rows. A so-ca)lled reaction phase and a catalyst-regeneratipg phase are carried out in the tubes of the chamber. The tubes are heated by appropriate radiant heating means 6, located betw,,een two successive rows and arranged in layers substantially per-pendicular to the tubes. These layers heat a first part of the tubes (at the feed side) with a heat flux greate~r than the. moan heat flux of the heating means, and a sevond, subseq~uent part with a mean flux no more than equal to the mean heat flIux, so that the J sotherniicity of the cata) yst is substant iall Iy maintained, using appropriate control means. Can be, app)lied to the production of benzene, toluene and xyl cees. FIgure I to be. published.