The present invention relates to a process for carrying out endothermic, heterogeneously catalyzed reactions.

Such a process, especially for the nonoxidative dehydroaromatization of

C1 -C4-aliphatics in the presence of zeolite-comprising catalysts, is known from US 2012/0022310. This US application relates to a process for carrying out endothermic, heterogeneously catalyzed reactions in which the reaction of the starting materials is carried out in the presence of a mixture of inert heat transfer particles, such as glass spheres, ceramic spheres and silicon carbide particles, and catalyst particles, where the catalyst particles are regenerated in a nonoxidative atmosphere at regular intervals and the heat of reaction required is introduced by separating off the inert heat transfer particles, heating the heat transfer particles in a heating zone and recirculating the heated heat transfer particles to the reaction zone. In the nonoxidative dehydroaromatization of C1 -C4-aliphatics (DHAM) the DHAM catalysts usually comprise a porous support and at least one metal applied thereto, i.e. at least one metal as active component and at least one further metal as dopant, wherein the active component is selected from among Mo, W, Re, Ru, Os, Rh, Ir, Pd, Pt, and the dopant is selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, V, Zn, Zr and Ga. A crystalline or amorphous inorganic compound is usually used as support. The mixture comprising catalyst particles and inert heat transfer particles is transferred from the reaction zone into a regeneration zone wherein both the catalyst particles and the inert heat transfer particles are regenerated in a nonoxidative atmosphere by introduction of a hydrogen-comprising regeneration gas stream.

WO 2009/105344 relates to a process for converting methane to higher hydrocarbons including aromatic hydrocarbons, the process comprising contacting a feed comprising methane with a dehydrocyclization catalyst in a reaction zone under conditions effective to convert said methane to aromatic hydrocarbons, said dehydrocyclization catalyst comprising molybdenum or a compound thereof dispersed on an aluminosilicate zeolite and the amount of aluminum present as aluminum molybdate. The dehydrocyclization reaction tends to deposit coke on the catalyst and hence, to maintain the activity of the dehydrocyclization catalyst, at least part of the catalyst is continuously or intermittently regenerated by withdrawing a portion of the catalyst from the or each reaction zone, either on an intermittent, or a continuous basis, and then transferring the catalyst portion to a separate regeneration zone. Since the dehydrocyclization reaction is endothermic, it is necessary to supply heat to the reaction by withdrawing part of the catalyst from the reaction zone, either on an intermittent or a continuous basis, supplying heat to the catalyst and then returning the heated catalyst back to the reaction zone.

US 2007/0249880 discloses a process for converting methane to higher hydrocarbon(s) including aromatic hydrocarbon(s) in a reaction zone, the process comprising : (a) providing to a reaction zone a hydrocarbon feedstock containing methane; (b) providing a quantity of catalytic material within the reaction zone; (c) maintaining the reaction zone with an inverse temperature profile; and (d) operating the reaction zone under reaction conditions sufficient to convert at least a portion of methane to a first effluent having said higher hydrocarbon(s).

In addition, the scientific article of K. Honda, X. Chen & Z.-G. Zhang. Catalysis Communications. Vol. 5, 2004, pp. 557-561 relates to the identification of the coke accumulation and deactivation of sites of Mo2C/HZSM-5 catalyst in CH4 dehydroaromatization. The authors suggest that the results of activity have revealed that the coking that seriously reduced the activity of bi-functional Mo2C/HZSM-5 catalyst in the CH4 dehydroaromatization might occur predominantly over the Bronsted acid sites of HZSM-5 component.

An aspect of the above discussed prior art is that coked catalyst needs to be regenerated outside of the methane dehydroaromatization (MDA) reactor with hydrogen. Coke burn-off with oxygen would convert catalytically active Mo carbide into Mo oxide being volatile at high temperature resulting in a significant loss. Another aspect is that the catalytically active Mo carbide moiety needs to be formed again during an induction period in the MDA reactor. In addition, regeneration with hydrogen does not supply enough heat such that the hot regenerated catalyst recirculated to the MDA reactor could be used as heat source for the endothermic MDA reaction requiring additional heating of the recirculated catalyst, e.g. by hot flue gases, when using the regenerated catalyst as heat source for the MDA reaction.

Another aspect is that recirculated coarse inert heat carrier particles occupy a significant part of the MDA reactor volume without effect beyond being heat source. Additional means are necessary for regenerating coked fine bifunctional catalyst either inside the MDA reactor, or in a second external recirculation loop for fine bifunctional catalyst. The denser and larger particles of the inert heat carrier may grind t e fine bifunctional catalyst particles, thereby creating dust and related problems.

An object of the present invention is to provide a process for carrying out endothermic, heterogeneously catalyzed reactions wherein the disadvantages of the prior art discussed above have been overcome or at least minimized.

Another object of the present invention is to provide a process for carrying out endothermic, heterogeneously catalyzed reactions wherein the heat necessary for the endothermic reaction is supplied by regenerated catalyst particles.

The process for carrying out endothermic, heterogeneously catalyzed reactions according to the present invention comprise the steps of:

a) Carrying out the reaction in a reaction zone in the presence of a mixture comprising two types of catalyst particles, comprising metal supported catalyst particles and aromatization catalyst particles,

b) Separating of the coked aromatization catalyst particles from said mixture present in said reaction zone,

c) Transferring of said separated coked aromatization catalyst particles into a regeneration zone,

d) Carrying out a regeneration of said coked aromatization catalyst particles in said regeneration zone,

e) Recirculating the thus regenerated aromatization catalyst particles to said reaction zone.

On basis of the above steps one or more of the above mentioned objects can be achieved. In the embodiment of the conversion of methane or other lower hydrocarbons into aromatics, i.e. benzene, by non-oxidative dehydroaromatization the reactor contains two types of catalyst particles. The present inventors assume that metal supported catalyst particles, e.g. molybdenum (Mo)carbide, especially Mo(oxy)carbide, on inert support activates methane to form intermediate species while aromatization catalyst particles, e.g. zeolite particles catalyze the aromatization of the intermediate species. Coking of zeolite occurs as undesired side reaction of the aromatization reaction. The present invention is principally based on the fact that the metal supported catalyst particles, e.g. supported Mo(oxy)carbide, stays in the reactor while the aromatization catalyst particles, e.g. partially coked zeolite particles are discharged from the reactor and decoked in a regenerator. In the present description the terms "Mo carbide" and "Mo(oxy)carbide" are used interchangeably. Air can be used for burning off coke because zeolites are not sensitive to oxygen. The combustion heat of removed coke heats up the zeolite particles which in turn are recirculated to the reactor at a temperature higher than the reaction temperature. The heated, regenerated catalyst particles supply the heat for the overall endothermic dehydroaromatization reactions. In a preferred embodiment the catalyst particles comprise supported metal catalyst particles and zeolite particles. According to another embodiment the catalyst particles comprise bifunctional catalysts, e.g. Mo carbide supported on zeolite particles, and zeolite particles.

Solid acid catalysts, such as zeolites, are inorganic or organic porous solids which provide Bronsted- and/or Lewis-acidic sites capable to catalyze aromatization reactions of lower aliphatic hydrocarbons.

The present inventor found that the two types of catalyst particles with the two different catalytic components/functions will undergo different treatments inside the process, e.g. for coke removal. If both catalytic functions/components are located on the same type of catalyst particle like in the discussed US 2012/0022310 and WO 2009/105344, the catalyst particles need to be treated such that none of the two catalytic functions/components is damaged.

According to the present invention one type of catalyst particles comprises a metal supported catalyst, i.e. molybdenum as catalytic component for methane activation and the second type of catalyst particle comprise zeolite as catalytic component for aromatization. The present inventor found that the first type (molybdenum) should not be treated with air because it will damage the catalytic function (as can be found in WO 2009/105344) while the second type (zeolite) can and should be treated with air. Since the second type (zeolite) accumulates coke much faster than the first type (molybdenum) it can be recirculated through an oxidizing regenerator, heated up during coke combustion and returned as heat carrier and regenerated second type-catalyst into the reactor. The present inventor is of the opinion that the first type (molybdenum) of catalyst particles cokes much less and is regenerated, if needed, in a separate, non-oxidizing regenerator, e.g. by hydrogen. According to the present method the mixture of catalyst particles is not regenerated (for coke removal) and reheated (for reaction heat supply) in a single step, as is the case in both WO 2009/105344 and US 2012/0022310, but preferably the second type (zeolite) of catalyst particles is regenerated and reheated. The afore mentioned reaction zone is chosen from the group of fluidized bed type reactor, fixed bed trickle flow type reactor and monolith trickle flow reactor. In case the reactor is a fluidized bed reactor the Mo carbide catalyst, especially Mo(oxy)carbide, on inert support forms a stationary bubbling bed and the zeolite powder is transported upwards by gas through the bubble and void volume. In case the reactor is a fixed bed trickle flow reactor the Mo carbide catalyst on inert support forms the fixed bed and zeolite powder trickles through the void space by gravity, or is transported upwards by gas through the void space. The sizes of the inert support particles for the Mo carbide catalyst and the zeolite particles are to be chosen such that the Mo carbide catalyst is fluidized in bubbling mode in the fluidized bed reactor, or forms a fixed bed in the fixed bed reactor. The zeolite is either kept in bubbling or fast fluidization mode by the gas feed flow in a fluidized bed reactor, or kept in trickle flow or in fast fluidization in a fixed bed or monolith trickle flow reactor. This means in general that the Mo carbide catalyst particles have a larger particle mean diameter, and the zeolite particles have a smaller particle mean diameter. The engineer skilled in the art will be able to select the diameters of Mo carbide catalyst particles and zeolite particles accordingly.

According to another embodiment the reactor is a monolith trickle flow reactor, in which the Mo carbide catalyst is immobilized on the monolith surface and the zeolite powder trickles downwards through the straight or zigzag shaped channels of the monolith, or is transported upwards by gas through the channels of the monolith.

The present inventors found that the reaction temperature can be chosen such that the coking rate is high enough that burning off the coke delivers the heat required by the overall endothermic dehydroaromatization reaction.

According to another embodiment both types of catalysts can be fluidized in bubbling mode together in the reactor, and recirculate between the reactor and a disengagement vessel, where the fine zeolite particles and the coarse particles of supported Mo carbide are separated by elutriation of the fine zeolite particles. In an embodiment the Mo carbide catalyst particles, especially Mo(oxy)carbide, are recycled directly to the reactor, or fed to a reducing regenerator in order to remove any potential traces of coke by hydrogasification, while the elutriated zeolite particles are decoked in an oxidative regenerator by coke burn-off. In that way, the Mo carbide catalyst can be regenerated or replaced independently on the zeolite catalyst. If a reducing regenerator is included into the present process for regenerating the Mo carbide catalyst particles separately from the zeolite catalyst particles, the Mo carbide catalyst may contain an acid function as well. In such an embodiment the dehydroaromatization reactor contains a mixture of bifunctional catalyst, e.g. Mo carbide supported on zeolite, and zeolite, of which the bifunctional catalyst particles are decoked in a reducing regenerator and the zeolite particles are decoked in an oxidative regenerator. In that way, the Mo carbide catalyst particles are more active for methane activation. Like in the previous discussed embodiments, the bifunctional catalyst particles have on average a larger particle size than the zeolite particles.

More heat additional to the combustion heat of coke burn-off can be supplied to the recirculating fine zeolite particles in an additional catalyst reheater. The flue gases of a burner heat the catalyst reheater and provide part of or the complete transport gas for transporting the fine zeolite catalyst through the reheater which is essentially a riser. In that way, the reactor temperature does not necessarily to be chosen such that the coking rate matches the heat requirements of the overall aromatization reaction, but can be chosen in a wider temperature range.

According to a preferred embodiment the fluidized bed reactor can be compartmented horizontally or vertically by baffles, weirs or trays in order to ensure a more uniform residence time distribution of the catalyst particles of both types, and especially of the fine zeolite particles. In that way, it is prevented that comparably fresh and not yet coked zeolite catalyst is withdrawn prematurely from the reactor. The regenerated hot zeolite particles can be recirculated to the compartmented reactor to different compartments in order to ensure a more homogeneous temperature profile.

According to a preferred embodiment the regeneration zone comprises a stripper unit and an oxidative regenerator, wherein the stripper is fed with natural gas as stripping gas, and the gaseous effluent comprising mainly natural gas components, lower olefins, benzene, toluene and naphthalene is sent to further processing units.

The effluent comprising coked particles from said stripper is preferably fed to said oxidative regenerator, said oxidative regenerator being fed with air.

As mentioned before, in an embodiment step b) comprises feeding the mixture of said two types of catalyst particles to a disengagement vessel, separating of the coked catalyst particles from the mixture present in said disengagement vessel and returning the other type of catalyst particles into said reaction zone, wherein said disengagement vessel is fed with natural gas.

The step of returning said other type of catalyst particles comprises especially feeding said other type of catalyst particles to a reducing regenerator and returning the thus regenerated other type of catalyst particles to said reaction zone, wherein said reducing regenerator is fed with a hydrogen containing gas.

The step of recirculating the regenerated catalyst particles comprises preferably a step of reheating the regenerated catalyst particles and returning the thus reheated, regenerated catalyst particles to said reaction zone, more preferably by passing the reheated, regenerated catalyst particles through a cyclone before returning to said reaction zone.

According to a preferred embodiment the present method further comprises positioning several reaction zones in series, wherein the oxidatively regenerated catalyst particles from a first reaction zone are fed to a second reaction zone, wherein the oxidatively regenerated catalyst particles from a second zone are fed to a third reaction zone, wherein preferably the coked catalyst particles from the third reaction zone are transferred to a regeneration zone and the thus regenerated catalyst particles are fed to the first reaction zone in order to ensure a more uniform residence time distribution of the catalyst particles of both types, and especially of the fine zeolite particles. In that way, it is prevented that comparably fresh and not yet coked zeolite catalyst is withdrawn prematurely from the dehydroaromatization reactor. The oxidatively regenerated catalyst particles transferred from a first to a second reaction zone, or from a second to a third reaction zone can be reheated with flue gas before entering a second or a third reaction zone. Even more heat can be supplied to the reaction zones for the endothermic overall reaction in that way. The regenerated hot zeolite particles can be recirculated to the reactor to different reaction zones in order to ensure a more homogeneous temperature profile. Such a method of positioning several reaction zones in series is however not restricted to a specific number of reaction zones.

While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention. The invention will now be more particularly described with reference to the accompanying drawings and the following non-limiting Examples.

Fig.1 shows an embodiment of the method according to the present invention.

Fig.2 shows another embodiment of the method according to the present invention.

Fig.3 shows an embodiment of the method according to the present invention.

Fig.4 shows another embodiment of the method according to the present invention.

Fig.5 shows another embodiment of the method according to the present invention.

Referring to Fig. 1 , the drawing illustrates a simplified design of a dehydroaromatization reactor system for converting methane or lower hydrocarbons into aromatics by non-oxidative dehydroaromatization according to one embodiment of this disclosure, wherein natural gas is used as feedstock. Molybdenum (Mo) carbide, especially Mo(oxy)carbide, on inert support stays in the reactor while the partially coked zeolite particles and product gas are discharged from the reactor and fed to a stripper. In the stripper natural gas is used as a stripping gas and CH4, lower olefins, lower paraffins, benzene, toluene, naphthalene are discharged from the top of the stripper. The zeolite particles are in a fluidized state in the stripper and discharged to an oxidative regenerator for decoking purposes. Air is used for burning off coke because zeolites are not sensitive to oxygen. The combustion heat of removed coke heats up the zeolite particles which in turn are recirculated to the reactor at a temperature higher than the reaction temperature. The heated, regenerated catalyst particles supply the heat for the overall endothermic dehydroaromatization reactions. The dehydroaromatization reactor can be a fluidized bed reactor, a fixed bed trickle flow reactor or a monolith trickle flow reactor. The Mo carbide catalyst on an inert support forms the fixed bed and zeolite powder trickles through the void space, wherein the Mo carbide catalyst is fluidized in bubbling mode (fluidized bed reactor), or forms a fixed bed in the fixed bed reactor, while the zeolite is either kept in bubbling or fast fluidization mode by the gas feed flow. In a monolith trickle flow reactor the Mo carbide catalyst is immobilized on the monolith surface and the zeolite powder trickles through the straight or zigzag shaped channels of the monolith. Fig. 2 is a schematic drawing illustrating a simplified design of a dehydroaromatization reactor system for converting methane or lower hydrocarbons into aromatics by non-oxidative dehydroaromatization according to another embodiment of this disclosure. The stripping section and oxidative regenerator, as discussed in Fig 1 above, are omitted for legibility reasons, but the person skilled in the art would immediately recognize that these process units are necessary as well. This simplification of the total process is also valid for the discussion of the processes shown in Figs. 3-5.

Both catalysts are fluidized in bubbling mode together in the dehydroaromatization reactor, and recirculate between the reactor and a disengagement vessel, where the fine zeolite particles and the coarse particles of supported Mo carbide are separated by elutriation of the fine zeolite particles. The Mo carbide catalyst particles can be recycled directly to the dehydroaromatization reactor. In the disengagement vessel natural gas is used as transport gas, and the coked zeolite particles, together with the natural gas, are sent to the stripping section and oxidative regenerator, as discussed in Fig. 1 above. The thus regenerated, hot zeolite particles are returned to the reactor at the bottom thereof. Product gas leaves the dehydroaromatization reactor at the top and is further processed elsewhere.

Fig. 3 is based on the principle of Fig. 2 discussed above, but the Mo carbide catalyst particles are fed from the disengagement vessel to a reducing regenerator in order to remove any potential traces of coke by hydrogasification, while the elutriated zeolite particles are withdrawn from said disengagement vessel and decoked in an oxidative regenerator by coke burn-off, as discussed above in Fig.2. In that way, the Mo carbide catalyst can be regenerated or replaced independently on the zeolite catalyst. Hydrogen is fed to the reducing regenerator in which regenerator the Mo carbide catalyst particles are present as a bubbling fluidized bed. Hydrogen and methane is discharged from the reducing regenerator, and the thus regenerated Mo carbide catalyst particles are recycled to the bottom of the dehydroaromatization reactor with the aid of a transport gas, for example natural gas.

Fig. 4 shows another embodiment of the present invention in which an additional catalyst reheater is used. Consequently, more heat additional to the combustion heat of coke burn-off is supplied to the recirculating fine zeolite particles in such an additional catalyst reheater. The flue gases of a burner heat the catalyst reheater and provide part of or the complete transport gas for transporting the fine zeolite catalyst through the reheater which is essentially a riser. The reheated catalyst particles are fed to a cyclone for separating the zeolite particles from the gaseous stream, and only the catalyst particles thus heated are fed to the dehydroaromatization reactor. In that way, the reactor temperature of the dehydroaromatization reactor does not necessarily to be chosen such that the coking rate matches the heat requirements of the overall aromatization reaction, but can be chosen in a wider temperature range.

Fig. 5 shows another embodiment of the present invention in which the fluidized bed dehydroaromatization reactor of the type fluidized bed is compartmented vertically by trays in three different compartments in order to ensure a more uniform residence time distribution of the catalyst particles of both types, and especially of the fine zeolite particles. In that way, it is prevented that comparably fresh and not yet coked zeolite catalyst is withdrawn prematurely from the dehydroaromatization reactor. The regenerated hot zeolite particles are recirculated to the top compartment of the compartmented reactor. Although in this embodiment according to Fig. 5 three compartments are present, the invention is in no way limited to any number of compartments and even five, six or ten compartments may be present.

The bottom or third compartment receives natural gas as feedstock and the product gas leaves the dehydroaromatization reactor at the top after passing through the second or middle compartment and the top or first compartment, respectively. In the top compartment the mixture of both zeolite particles and supported Mo catalyst is transported to a disengagement vessel in which the zeolite particles are separated from the supported Mo catalyst particles. The supported Mo catalyst particles are returned to the top compartment of the dehydroaromatization reactor, whereas the zeolite particles, together with the transport gas, are fed to a separation unit, e.g. a cyclone, and separated from the transport gas. The zeolite particles thus separated are fed to the middle or second compartment of the dehydroaromatization reactor.

In the middle or second compartment of the dehydroaromatization reactor the mixture of both zeolite particles and supported Mo catalyst is transported to a disengagement vessel in which the zeolite particles are separated from the supported Mo catalyst particles. The supported Mo catalyst particles are returned to the middle or second compartment of the dehydroaromatization reactor, whereas the zeolite particles, together with the transport gas, are fed to a separation unit, e.g. a cyclone, and separated from t e transport gas. The zeolite particles thus separated are fed to the bottom or third compartment of the dehydroaromatization reactor.

In the third or bottom compartment of the dehydroaromatization reactor the mixture of both zeolite particles and supported Mo catalyst is transported to a disengagement vessel in which the zeolite particles are separated from the supported Mo catalyst particles. The supported Mo catalyst particles are returned to the third or bottom compartment of the dehydroaromatization reactor, whereas the zeolite particles, together with the transport gas, are fed to a separation unit, e.g. a cyclone, and separated from the transport gas. The zeolite particles thus separated are fed to a stripping section and an oxidative regenerator (both not shown), as discussed in Fig. 1 above. The thus regenerated hot zeolite is returned to the top or first compartment of the dehydroaromatization reactor. According to a preferred embodiment the coked zeolite particles coming from the third or bottom compartment of the dehydroaromatization reactor are first sent to a stripper section and an oxidative regeneration section and then to a reheating section, similar to the embodiment as discussed above in Fig. 4.

The embodiment according to Fig. 5 shows that coarse particles of Mo carbide catalyst on an inert support are fluidized in bubbling mode in the different compartments of a vertically compartmented fluidized bed by upwards flowing gas feed of methane and lower hydrocarbons. Regenerated hot particles of fine zeolite catalyst coming from the bottom compartment of the dehydroaromatization reactor are fed to the top compartment and fluidized in bubbling mode together with the Mo carbide catalyst particles. Zeolite particles are separated from the Mo carbide catalyst particles in a disengagement vessel next to each reactor compartment and fed to the next lower reactor compartment. Zeolite catalyst deactivated by coke is collected in the disengagement vessel next to the bottom zone of the reactor and interstitial product gas is removed from the deactivated zeolite catalyst in the stripper by using methane as stripping gas.

The deactivated zeolite catalyst is regenerated by burning off coke with oxygen or air in a bubbling fluidized bed and thereby heated up. The regenerated zeolite catalyst is preferably further heated by burner flue gases in a riser to a temperature higher than the reactor gas outlet temperature and high enough to supply the heat of the endothermic overall aromatization reaction via the sensible heat of the regenerated zeolite catalyst particles.

Although the embodiment shown in Fig. 5 discloses a countercurrent flow of zeolite and feed/product gas, according to another preferred embodiment the regenerated hot zeolite is fed to the bottom compartment and coked zeolite is withdrawn from the top compartment.

Although the embodiment shown in Fig. 5 discloses the use of natural gas as transport gases to the disengagement vessels, according to another preferred embodiment hot flue gas is used as transport gas, thereby heating up the zeolite particles transferred from a previous to a subsequent compartment and supplying even more heat to the reactor compartments for the overall endothermic reactions. The above discussed Figs. 1 -5 clearly show that the use of two types of catalyst particles in a dehydroaromatization the reactor has a beneficial effect on the supply of the heat of reaction to the reactor. The supported Mo carbide catalyst stays in the reactor while the partially coked zeolite particles are discharged from the reactor and decoked in a separate process unit, i.e. a regenerator. The combustion heat of removed coke heats up the zeolite particles which in turn are recirculated to the reactor at a temperature higher than the reaction temperature. The heated, regenerated catalyst particles supply the heat for the overall endothermic dehydroaromatization reactions.

The following numerical references are used in Figures 1 -5;

1. air

2. Product gas

3. Flue gas

4. Coked zeolite

5. bubbling fluidized bed of zeolite particles

6. slide valve

7. regenerated, hot zeolite

8. natural gas as feedstock

9. natural gas as stripping gas

10. reactor with MoxCy catalyst

11. Oxidative regenerator

12. Transport gas

13. Natural gas as transport gas

14. Zeolite particles (fine

15. MoxCy Catalyst particles (coarse)

16. Bubbling fluidized bed of MoxCy catalyst particles

17. Disengagement vessel

18. Fluidized bed reactor

19. (Reducing) regenerator

20. Hydrogen

21. Methane

22. Coked MoxCy catalyst

23. Regenerated MoxCy catalyst

24. stripper

25. fuel 26. Burner

27. cyclone

28. Catalyst reheater (riser)

29. zeolite from middle to bottom compartment

30. zeolite from top to middle compartment

10