FR2655351A1 - Device for converting hydrocarbons in a reactor heated by a fluidised bed of particles, and its use - Google Patents

Abstract

Device for converting hydrocarbons and its use in the production of aromatic hydrocarbons. It comprises a vessel 1 with an upper face, a lower face and a side enclosure 2 and it contains a leakproof reactor filled with a catalyst, this reactor being partly immersed in a fluidised bed of hot and preferably inert particles; the reactor additionally comprises a plurality of reaction tubes 3 substantially parallel to each other, means 9 for feeding feedstock, connected to one end of the tubes 3, and means 8 for recovering the effluent, connected to the other end. The side enclosure 2 comprises at least one means 18, 19 for feeding hot gas. Application to the production of benzene, toluene and xylenes.

Description

This invention relates to a hydrocarbon conversion device and its use in particular in the production of aromatic hydrocarbons from a charge of aliphatic hydrocarbons of 2 to 12 carbon atoms in the presence of a zeolitic crystalline catalyst composition. It relates more particularly to the synthesis of a mixture comprising mainly benzene, toluene and xylenes, products which are capable in particular of improving the octane number of gasolines.

The promotion of low boiling aliphatic cuts such as LPG justifies the interest that can be brought to the implementation of conversion processes of these hydrocarbons which are efficient, selective and economical while also contributing to the formation of hydrogen as a by-product.

The reaction for the production of aromatic hydrocarbons has been described, in particular in patents US Pat. No. 3,760,024, US Pat. No. 3,756,942 and US Pat. optionally with a metal such as gallium in the frame or in the presence of a zeolitic catalyst containing a metal outside the frame as described in patents FR 2374 283 and US 4175 057.

The elementary processes involved in the transformation of aliphatic hydrocarbons into aromatic hydrocarbons are mainly the dehydrogenation of paraffins, the oligomerization of the unsaturated hydrocarbons obtained and the cyclization of the oligomers.

Overall, the reaction is highly endothermic, the reaction rate is sensitive to temperature variations and these successive reactions are accompanied by a deposit of coke on the catalyst and a reduction of the metal oxides contained in the catalyst, which deactivates it. very quickly and reduces cycle time.

It is known from US Pat. No. 4,224,298 to use a fluidized bed of particles to heat the tubes in which the reforming of hydrocarbons is carried out in order to obtain synthesis gas at a temperature of 750 to 800 OC. In this case the external skin temperature of the reaction tubes is around 9750C. The fluidized bed is heated by combustion of a fuel directly in the particle bed. This device has in particular the disadvantage of being able to operate only at high temperatures, therefore of lacking flexibility in order to be able to be used in the context of all types of reforming. On the other hand, it suffers from all the disadvantages which result fluidized bed combustion - First there may be problems with dispersion of the
fuel within the bed, especially when the diameter of this
bed is more than three meters for example and when occupied
by a large number of tubes. Under these conditions, the distribution
heat on the tubes is no longer homogeneous, and there may be
risks of post-combustion beyond the fluidized bed.

- Then, the control of the bed which operates at more than 10000C, may prove
delicate, especially during transient phases. In that case,
there is a risk of solidification of the entire bed due to
local overheating in poorly fluidized areas. For example,
emergency stop of the device, if the oxidant flow has not
not completely stopped, the oxidation of the fuel present in
the bed can continue in a fixed bed. This results in an elevation
important of the temperature of the bed by absence of exchange with the
bed fusion tubes.

One of the problems to be resolved therefore consists in ensuring uniformity
heating the reaction zone around 500 to 6000C
to obtain the flattest possible temperature profile
in it knowing that the catalyst is sensitive to a
increase in temperature and that it can be destroyed when the
critical temperature is exceeded.

Furthermore, another problem to be solved relates to the regeneration of the catalyst which must be rapid, and of variable frequency depending on the temperature of the reaction directly dependent on the charge to be treated. This regeneration must be gentle enough to preserve the performance of the catalyst and minimize its renewal rate.

The object of the invention is to respond to the problems raised above, so as to improve the conversion rates into aromatic hydrocarbons and the lifetime of the catalyst.

More particularly, the process for producing aromatic hydrocarbons comprises a step of bringing a charge of at least one aliphatic hydrocarbon of 2 to 12 carbon atoms into contact with a zeolitic catalyst composition optionally containing at least one metal in a reaction zone under suitable reaction conditions such that a mixture comprising aromatic hydrocarbons is recovered and that a used zeolitic catalyst is obtained with a minimum of coke deposited during the reaction, said reaction zone being heated by immersion in less partial in an enclosure containing a fluidized bed of particles. In addition, the particle bed is at least partially heated by the addition of heat produced outside said enclosure.

According to a characteristic of the process, the reaction zone can comprise at least one reaction tube arranged vertically or horizontally in the enclosure containing the fluidized bed.

This fluidized bed generally comprises particles with a particle size usually between 20 and 5000 micrometers, preferably between 50 and 200 micrometers and a density between 1000 and 6000 kg / m3, preferably between 1500 and 3000 kg / m3.

Their shape can be arbitrary but advantageously spherical.

The bed generally comprises inert particles, for example sand at least in part and, generally consisting of sand, is generally heated to a temperature substantially higher than the temperature of the reaction in the tubular reaction zone, for example from 4800 to 6000C, under heating conditions such that the temperature difference between the heating fluidized bed and the catalyst is usually between 5 and 1000C and advantageously between 20 and 400C.

According to another characteristic of the invention, the particle bed is usually fluidized by means of a fluidizing gas injected for example by tubes provided with orifices known to those skilled in the art, located at the base of the preferably cylindrical enclosure.

The fluidization gas flow rates are such that the surface speed is between 0.01 and 1.00 m / s and preferably between 0.1 and 0.3 m / s. Under these conditions, the quasi isothermicity of the bed is ensured and due to the good heat transfer coefficients between the bed and the internal wall of the tube, the lifetime of the catalyst is increased and the selectivity of the reaction improved.

These fluidization gases can be recovery fumes from an oven or a boiler, preheated air or even turbine effluents.

The fluidized bed of particles can be heated in part by the fluidization gases injected at a sufficiently high temperature, and preferably by injections of hot gases directly into the bed. It is also possible to recycle at least a portion of the particles withdrawn from the enclosure then reheated outside the enclosure, for example during the regeneration of the catalyst if it takes place outside the enclosure where the reactions leading to flavoring.

According to a characteristic of the process, the regeneration step of the catalyst can be carried out in the same reaction tube placed in the enclosure containing the fluidized bed, where the reaction step took place.

At least part of the heat released during this regeneration by the combustion reaction is then exchanged with the fluidized bed. The catalyst regeneration reaction which is exothermic then contributes significantly to the thermal balance of the process since it compensates at least in part for the heat loss due to the endothermicity of the aromatization reaction.

Any combination of supply of calories to the fluidized bed as described above can be envisaged. This is how the supply of heat due to the regeneration of the catalyst and at least one injection of gases heated to a temperature between 12,000 and 22,000C by gas oil burners for example and introduced directly into the fluidized bed, preferably at the side wall have given excellent results.

According to a preferred embodiment of the method according to the invention, the reaction zone can comprise a plurality of reaction tubes arranged in parallel and grouped in bundles, these being able to be fed in parallel. At least part of these is adapted to carry out the flavoring of the feedstock while the other part is adapted to carry out the catalyst regeneration step. The regeneration being substantially completed, the tubes previously operating in regeneration then operate in an aromatization reactor. This alternating operation by the set of valves is very flexible.

The catalyst can be in a moving bed or in a fixed bed, preferably in a fixed bed. Under these conditions in a fixed bed, the mechanical wear phenomena due mainly to the circulation of the catalyst are reduced, which lead to the formation of fines in large quantities, to disturbances in the operation of the unit, to the training of these fines by the reaction products resulting in degradation of the downstream processing units of the products, and an increase in the consumption of catalyst.

The advantages of the process according to the invention are as follows:
Thanks to its temperature uniformity and the excellent heat exchange coefficients which characterize it, the fluidized bed ensures a substantially constant temperature over the entire length of the tube as well as on all the tubes constituting the reaction zone, even if the beams comprise several hundred , or even several thousand tubes. The radial temperature profile is then found to be substantially flat. Thanks to this temperature uniformity over the entire volume of catalyst, this results in a better use of the latter.

The temperature uniformity of the bed is also an advantage during the regeneration of the catalyst in the enclosure. It makes it easy to start the oxidation of coke and to carry out this regeneration more quickly than in other implementations, since the calories released by the controlled oxidation are quickly transferred to the bed.

The temperature difference between the heating medium and the catalyst being preferably between approximately 20 and 400C, the catalyst will be found at bed temperature in the event of partial or total blockage of one of the tubes by an excessive coke deposit, by example and therefore under conditions which do not lead to its destruction.

When several bundles of tubes are immersed in the same fluidized bed, part of the calorific intake can come from regeneration when the bundles operate alternately, the process then becoming more energy efficient.

The technology thus described also makes it possible to reduce the passage time between the reaction cycle and the regeneration cycle since the temperature of the bed is the same in both cases.

For a given capacity, the size of the beam is much smaller than that required by radiant ovens for example. This greater compactness obviously leads to lower investments.

This technology, of very flexible design thanks to the modular aspect of its implementation, can be adapted to both small and large capacities. It can also be designed as well with a cyclic regeneration of the catalyst as with a continuous regeneration.

Generally the inert particles used as a fluidized bed are chosen from refractory materials such as aluminum oxides, silicon oxides (sand), natural magnesium or calcium carbonates or their mixture. Preferably, sand is used because of its availability and its low price.

The reaction is generally carried out in an inert atmosphere at a pressure between 0.2 and 10 bars and at a temperature of 400 to 6000C depending on the nature of the charge, the temperature being advantageously from 480 to 5500C for LPG cutting and from 450 to 5300C for the naphtha cut, and under a preferred pressure 1 to 5 bars absolute. Preferably this temperature is from 500 to 5300C for the LPG cut and from 480 to 5100C for the naphtha cut.

The catalyst used is generally a crystalline zeolite of the MFI type, such as the ZSM zeolites, for example ZSM5, ZSM8, ZSM11, ZSM12 and ZSM35 described in US Pat. No. 3,970,544.

These zeolites may advantageously contain at least one metal.

By way of example, mention may be made of zinc, gallium, preferably gallium.

These metals can be in the frame or outside the frame.

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

The catalyst is preferably used in the form of a fixed bed, which reduces attrition phenomena.

The recommended space velocities are usually 0.5 to 5h 1 and preferably 1.5 to 2.5h
The charge of aliphatic hydrocarbons generally comprises from 2 to 12 carbon atoms, it advantageously contains LPG or naphtha, the operating conditions possibly being different depending on the nature of the charge. For example, with a filler like LPG, we can operate at a temperature higher than the temperature at which we would operate with a filler like naphtha. The unit thus allows very quickly and by easy control of the temperature of the fluidized bed, to accept loads of variable composition.

In general, the operating conditions are optimized so as to convert at least 60% of the charge, particularly with the
LPG and advantageously at least 80% with an aromatic hydrocarbon content of at least 65% compared to the initial charge.

Consequently, it is possible to recycle, after separation of the effluents, the part of the charge that has not been converted.

Higher conversion rates can be obtained, with heavier loads, for example at least 95%.

The regeneration is generally carried out after a purging step in the presence of a gas containing oxygen according to a known technique (for example an N2 + 02 mixture). We usually operate at a temperature between 450 and 6500C and preferably between 480 and 5600C.

The invention therefore relates to the device for converting hydrocarbons, in particular for implementing the method.

It comprises an enclosure coated with an insulating material with an upper face, a lower face and a lateral envelope and it contains a reactor filled with an appropriate catalyst, said reactor being at least partly immersed in a fluidized bed of hot particles and preferably inert, the bed exchanging heat with said reactor, means for fluidizing the bed connected to the underside of said enclosure. The reactor further comprises a plurality of reaction tubes which are substantially parallel to one another and fed in parallel, means for supplying charge connected to one end of said tubes and means for recovering the effluent containing aromatic hydrocarbons connected to the end. opposite of these tubes, and said lateral envelope comprises at least one means for supplying hot gas.

According to a characteristic of the device, the enclosure can be cylindrical and the plurality of tubes constitutes a volume of generally cylindrical or generally polygonal shape.

According to another characteristic, the hot gas supply means has an entry from its transfer line into the lateral envelope, the distance of which to the upper face of the enclosure is generally between a quarter and half the height of the 'side cover, which promotes temperature uniformity in the bed.

According to another characteristic, complementary fluidization means connected to the underside of the enclosure can be added so as to fluidize the volume of the fluidized bed of particles located between the lateral envelope of the enclosure and the fictitious envelope determined by the plurality of reaction tubes with a greater fluidization speed than that delivered by the fluidization means of the bed at the level of the reaction tubes. This arrangement promotes the circulation of particles from the peripheral ring towards the center and therefore a better distribution of heat and a better heat exchange.

According to another characteristic, the device usually comprises regeneration means adapted to regenerate the used catalyst in the same tubes where the reaction for producing aromatics took place. These regeneration means generally comprise a supply of regeneration gas at one end of the bundle of tubes and an evacuation of the regeneration effluent at the other end.

The device may also include means adapted to connect the reaction tubes alternately to the regeneration means and then to the means necessary for carrying out the reaction, in particular to connect one end of the tubes to the load supply means and the other end to the means of evacuation of the effluent produced.

The method can be implemented according to another variant of the device according to the invention, described below
The device comprises a plurality of reaction tubes and a plurality of regeneration tubes immersed in the fluidized bed and adapted to regenerate the used catalyst. These regeneration tubes are connected at one end to a supply of regeneration gas and at the other end to an outlet for a regeneration effluent.

The device further comprises means suitable for connecting the reaction tubes alternately to the feed means for charging with their first end and to the means for recovering the effluent at their second end, then to the supply of regeneration gas by their first end and the evacuation of the regeneration effluent through their second end. In addition, these same means are adapted to connect the regeneration tubes alternately to the supply of regeneration gas by their first end and to the evacuation of the regeneration effluent by their second end and then to the load supply means. by their first end and to the means for recovering the effluent of aromatic hydrocarbons by their second end. These reaction tubes operate in the so-called reaction phase (production of aromatics) while the regeneration tubes operate in the so-called regeneration phase, in firstly and the reaction tubes then become regeneration tubes while the regeneration tubes become reaction tubes, in a second step.

The invention will be better understood in the light of the figures below schematically illustrating the method and the device according to the invention, among which - FIG. 1 shows the device in longitudinal section, - FIG. 2 represents a cross section of a zoned
reactive and regenerative in the same enclosure of a bed
fluidized, - Figure 3 illustrates an example of modular assembly where the
tubular reactors as well as tubular regenerators are
arranged in the same enclosure.

According to FIG. 1, a reaction vessel 1 of cylindrical shape having a wall 2 coated with an insulating material) comprises a sealed reactor 40 immersed in a fluidized bed of sand 13. This reactor comprises a plurality of tubes 3 made of stainless steel (100 for example), cylindrical or of generally cylindrical shape arranged vertically and held by support elements 22. Their internal diameter is between 10 and 200 mm, preferably between 50 and 100 mm and their length is from 2 to 20 m, of preferably 3 to 10 meters.

The tubes can be fitted internally with transverse fins in order to increase the heat transfer to the catalyst. These tubes are generally parallel to the axis of the enclosure and are grouped in bundles of cylindrical shape with a distance between axes of between 1.5 and 6 times the external diameter of the tube and preferably between 2 and 3 times the external diameter. . At their ends, the tubes are connected via upper and lower tubular plates 4 and 5 to a chamber 6 supplying the tubes with a charge introduced by the line 9 controlled by a valve 10 and to a chamber 7 recovering the effluent from the reaction discharged through line 8 controlled by a valve 17. These tubular reactors contain a fixed bed of zeolitic catalyst, for example ZSM5 which may contain gallium in the frame and outside the frame. This catalyst is introduced into the tubes according to methods known to those skilled in the art.

The charge, for example an LPG, is introduced via line 9 at the top of the reactor 40. It has been preheated for example by the smoke from the reactor in a convection zone located downstream of the outlet 11 of the enclosure 1 .

The volume occupied by the tubes represents from 10 to 35% of the total volume of the expanding fluidized bed.

The fluidized bed consists of sand particles of about 0.1 mm for example. The fluidization gas is introduced at the base of the enclosure 1 by fluidization tubes 14 suitably and substantially horizontally arranged over the entire base of the reactor and of the enclosure 1, substantially at the level of the lower end. tubes 3 through which the reaction effluents are evacuated. These fluidization tubes pierced with orifices directing the flow of fluidization gas towards the bottom of the reactor are in the form of an easily removable comb which is slid between the tubes 3 containing the catalyst. The fluidization tubes are connected to a manifold 15. The number and the shape of the orifices are such that there are no defluidized zones where the heat transfer between tubes and bed could no longer be ensured.

The reactor effluents pass through the diffusers 16 located at the base of the tubes 3 before leaving the reactor via line 8 and a control valve 17 which direct them to a separation unit, not shown in the figure.

The peripheral part 13a of the reactor not occupied by the reaction tubes generally represents between 5 and 40% of the total volume of the bed.

This crown of the bed directly in contact with the heating gases described below is driven by a higher fluidization speed, which makes it possible to more quickly balance the temperature of the bed, due to an intense circulation of particles induced by differences in the apparent density of the medium between the center and the periphery.

This circulation of particles from the periphery towards the center of the enclosure 1 can be accentuated at will by fluidization means 14a disconnected from the means 14 and arranged at its base, which make it possible to fluidize the particles at a higher speed at the periphery than in the center.

The heating of the fluidized bed is essentially carried out by injections of hot gases at a temperature between 1200 and 22000C coming from burners 18 with fuel oil for example and arranged in at least one hearth 23 coated internally with refractory materials. These are located outside the enclosure 1, preferably on the cylindrical lateral envelope, and are arranged in such a way that the flow of hot gases is introduced by a transfer line 19 against the current of the fluidization gases in a point located between the half and the upper third of the height of the fluidized bed. This transfer line is usually inclined towards the bottom of the reactor so as to avoid the accumulation of particles.

A protection device 24 prevents direct contact of hot gases with the tubes.

This leads to better heat-particle contact and to maintain the fluidized bed at a temperature determined according to the type of charge, which is substantially the same throughout the volume of the reaction zone, for example close to 5200C with a difference of temperature between the sand bed and the catalyst of around 200C.

The fumes formed by the mixture of fluidization and heating gases are recovered in the upper part of the reactor and evacuated by line 11 in order to recover the available heat.

Obviously, they are never in contact with the load. Likewise, the load or the effluents are never in contact with the fluidized bed.

A device 21 at the base of the reactor is a sand joint which allows the tube bundle to expand downward during the expansion of the tubes.

When the catalyst is deactivated, the regeneration stage thereof is carried out directly in the tubes where the reaction has taken place, without modifying the operating conditions of the fluidized bed. To this end, the supply of the load is stopped by the valve 10 and the tubes are supplied with regeneration gas introduced by the line 12 provided with a valve 60. The temperature of the fluidized bed being at an appropriate level, the regeneration starts instantly. The effluent regeneration gases are evacuated by the line 61 controlled by the valve 62.

Before each passage from the reaction phase to the regeneration phase and from the regeneration phase to the reaction phase, a stream of inert gas is generally circulated to purge the device.

The apparatus thus operates discontinuously, sometimes in the reaction phase, sometimes in the regeneration phase with phase durations which may be different or equal.

According to Figure 2 illustrating an example of reaction and regeneration of the catalyst in the same fluidized bed, the enclosure 1 contains the fluidized bed of sand 13 heated by the heating means 18 described above.

This enclosure contains a plurality of vertical tubes like those described above according to Figure 1, supplied in parallel. These tubes are adapted to be alternately, by suitable supply means, reactors for the production of aromatics 40, 41, 42, 43, 44 according to the process and regenerators 45 and 46 of spent catalyst after the reaction.

Reactors 40, 41, 42 and regenerators 45 and 46 are shown in FIG. 3. A set of open valves 70, 71, 72 makes it possible to supply the reactors with the load in parallel, while another set of closed valves 73 and 74 prohibits the circulation of the charge in the regenerators 45 and 46, but allows the supply of a regeneration gas such as nitrogen and air. The function of the discharge valves 31, 32, 33, 34 and 35 of the two types of effluent is identical to that of the preceding valves.

The heat given off by the combustion of the used catalyst in the tubes operating in regeneration provides part of the energy consumed by the reaction. All of these supply and outlet valves are controlled by control means 50 which allow the bundles of tubes 40, 41 and 42 to be alternately reactors for the production of aromatic hydrocarbons then regenerators and to the bundles 43 and 44 regenerators and reactors for the production of aromatics after a purge period.

These regenerators become reactors after the regeneration period, while other reactors become regenerators.

Illustratively shown are five bundles of tubes operating in a reactor and two operating in a regenerator. Any other combination is obviously possible and remains within the scope of the invention.

Claims (10)

1) Hydrocarbon conversion device comprising an enclosure  (1) with an upper face, a lower face and an envelope  side (2) and containing a sealed reactor (40) filled with a  suitable catalyst, said reactor being at least partly  immersed in a fluidized bed (13) of hot particles of  preferably inert, the bed exchanging heat with said  reactor, fluidization means (14) of the bed connected to the face  bottom of said enclosure, the reactor further comprising a  plurality of substantially parallel reaction tubes (3) between  them and supplied in parallel, supply means (9) in one  load connected to one end of said tubes and means of  recovery (8) of an effluent connected to the opposite end  said tubes (3), said lateral envelope comprising at least one  means for supplying hot gas (18,19). 2) Device according to claim 1, wherein the length of  tubes is 2 to 20 m and their internal diameter is 10 to 200 mm. 3) Device according to claim 1 or 2, wherein the tubes  are grouped into at least one beam, the distance between the axis of  each tube being between 1.5 and 6 times its diameter  external. 4) Device according to one of claims 1 to 3, wherein the  means (18, 19) for supplying hot gas is adapted to direct the  hot gas flow against the flow of the fluidizing gas flow. 5) Device according to one of claims 1 to 4 wherein  the enclosure is cylindrical and the plurality of tubes constitutes a  envelope of generally cylindrical shape or globally  polygonal. 6) Device according to one of claims 1 to 5 wherein the  hot gas supply means is located at a distance from the  upper face of the enclosure between a quarter and a half  the height of the side envelope. 7) Device according to claims 1 to 6, wherein the volume of the  fluidized bed located between the lateral envelope of the enclosure and  the envelope determined by the plurality of tubes is fluidized by  complementary fluidization means (14a) connected to the face  lower of the enclosure (1) and adapted to deliver a speed of  more fluidizing gas than that delivered by the  fluidization means (14) of the bed at the level of the tubes. 8) Device according to one of claims 1 to 7 characterized in that  that it includes means for regenerating (12, 61) the catalyst  used adapted to regenerate the catalyst in said tubes and which  are connected to the reaction tubes and means (50) adapted to  connect the reaction tubes alternately to the means  supply (9) under load and recovery means (8) of  the effluent and then to said regeneration means (12,61). 9) Device according to one of claims 1 to 7 comprising a  plurality of reaction tubes (40, 41, 42) and a plurality of  regeneration tubes (45, 46) immersed in the fluidized bed and  adapted to regenerate the catalyst, these regeneration tubes being  connected at one end to a regeneration gas supply  (12) and at the other end to an outlet (61) of an effluent from  regeneration and further comprising means (50) adapted to  connect the reaction tubes alternately to the means  supply (9) under load and recovery means (8) of  the effluent, then to the regeneration gas supply (12) and to  the evacuation of the regeneration effluent (61), these means (50)  being adapted to further connect the regeneration tubes  alternatively to the regeneration gas supply (12) and to  the evacuation of the regeneration effluent (61), then by means  supply of charge (9) and recovery means (8) of  aromatic hydrocarbon effluent, reaction tubes  operating in the so-called reaction phase while the tubes of  regeneration operate in the so-called regeneration phase in a first  time and the reaction tubes then becoming tubes of  regeneration while the regeneration tubes become  reaction tubes in a second step. 10) Use of the device in a production process  aromatic hydrocarbons from a charge of at least one  aliphatic hydrocarbon from 2 to 12 carbon atoms.