EP1907506A1 - Method of converting a synthesis gas into hydrocarbons in the presence of sic foam - Google Patents

Abstract

The invention relates to a method of converting carbon monoxide into hydrocarbons C2+ in the presence of hydrogen and a catalyst containing a metal (optionally with added promoter) which is placed in a multitubular reactor in which the tubes contain the catalyst which is supported by a support that is based on a hard cell foam of silicon carbide.

Description

 PROCESS FOR TRANSFORMING A SYNTHESIS GAS TO HYDROCARBONS IN THE PRESENCE OF SiC FOAM

TECHNICAL AREA

The present invention relates to a process for converting synthesis gas to C ₂ ⁺ hydrocarbons by Fischer-Tropsch synthesis, on an SiC foam in particular beta, and in particular a rigid foam. PRIOR ART

Numerous documents describing Fischer-Tropsch (FT) synthesis using metal catalysts supported on various catalytic supports are known.

WO-A-0112323 and WO-A-0154812 (Battelle) generically refer to carbides as a support or interfacial layer of catalytic systems for FT synthesis. There is no mention of the type of carbide that can be used and more particularly the crystalline phases and / or the nature of the recommended shaping.

The patents US-P-5648312, US-P-5677257 and US-P-5710093 (Intevep) describe a particular catalytic support suitable for FT synthesis (capable of being implemented in a fixed bed, a boiling bed or in "slurry"). The catalytic species in these documents is a Group IVB or VIII metal, or a mixture, especially zirconium and cobalt.

The support used in the above patents is obtained in particular by the formation of a suspension of silica and silicon carbide in a basic solution, the formation of drops and their separation into spheres, then the passage of the spheres in an acidic solution. to lead to a catalyst support comprising a substantially homogeneous mixture of silica and SiC. The processes for synthesizing hydrocarbons from synthesis gas use this catalytic support, which is in the form of spheres. It is also sought to significantly increase reactor flows and productivity. In particular, it is sought to increase the rate of gaseous mixture CO + H ₂ to be converted into hydrocarbon in the reactor as well as the productivity. SUMMARY OF THE INVENTION

The invention therefore provides a process for converting carbon monoxide to C ₂ ⁺ hydrocarbons in the presence of hydrogen and a catalyst comprising a metal in a reactor containing said catalyst supported on a support based on silicon carbide foam, implemented under the following operating conditions:

WH (GHSV) ranging from 100 to 5000 h ^-1 and

- WHSV ranging from 1 to 100 IT ¹ .

It is recalled that the GHSV and WHSV are defined (and calculated in the examples) as follows (the gas comprises for GHSV and WHSV both CO and H ₂ , under normal conditions of temperature and pressure):

GHSV = Total flow rate gas (rpm) x 60 / reactor volume occupied by the catalyst (grain or foam) (ce) This is the opposite of the contact time.

WHSV = Mass flow rate gas (CO + H ₂ ) (g / min) x 60 / mass of main catalytic metal (g).

The invention also provides a process for converting carbon monoxide to C ₂ ⁺ hydrocarbons in the presence of hydrogen and a catalyst comprising a metal in a multitubular reactor containing said support supported catalyst containing a silicon carbide foam.

The new synthesis method FT uses a new catalytic support comprising (preferably consisting of) a foam (monolith) of SiC, in particular SiC β. The foam is preferably rigid. This support generally has a macroscopic structure controllable at will consisting of an interconnected network of cells of micrometric or millet size with a porosity in general meso- and macroporous. Preferably, the size of the cells is between 0.3 and 5 mm. The macroscopic structure, in particular the alveolar structure, is generated directly during the synthesis of the material without the need for any additional shaping as is generally the case with supports based on α-SiC where post-synthesis shaping is necessary to give the macroscopic structure, the latter being however useful in the invention even though they are not preferred. Thus, compared with the supports of the prior art, a support is particularly suitable for the exothermic reaction of the FT synthesis. This support offers many advantages, especially in terms of operating parameters. This is in fact a chemically inert carrier, different from alumina, consequently unsuitable for the formation of ^one metal aluminates which are often regarded as the cause of the deactivation of the catalysts. It is also a support consisting of a good thermal conductor material, thus perfectly capable of transferring the reaction heat formed within the catalytic mass. In addition, its shaping as a rigid structure-related foam gives it better heat conduction properties than if it were simply grain-shaped, which are used stacked against each other within the reactor . The thickness of the solid bridges constituting the rigid foam is relatively small compared to that of a grain or an extrusion. This favors the diffusion of the reagents towards the active sites and the evacuation of the liquid and gaseous products out of the active sites, thus favoring a better activity per site. In the case of granular or extruded media, diffusion of the reaction products through the porous network of greater thickness is lower and could lead to problems of clogging of the sites reducing the efficiency of the catalyst. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an enlarged view of a beta SiC foam used in the invention, more particularly a rigid foam;

FIG. 2 is an enlarged view of a catalyst useful in the invention;

Figures 3 to 8 give the results of the yields of the different fractions in flow time function for Examples 1 to 6, respectively.

Figures 9a to 9d are schematic representations of reactors used in the context of the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The Sic a. is widely known in the art, in various forms including the foam form. Such a foam is available, for example, from Ultramet, Pacoima, CA, USA.

SiC β is prepared by a gas / solid reaction between SiO in vapor form generated in situ and solid carbon intimately mixed (without liquid). For more details on the β-SiC, reference may be made to the following patent applications and patents, incorporated by reference in the present application: EP-AO 313480, EP-A-0 440569, US-P-5217930, EP-AO 511919, EP-AO 543751 and EP-AO 543752. Compared to the α-form, generally obtained in the form of a powder thus requiring the presence of binders for final macroscopic shaping, the β-SiC synthesized by the process described above is obtained in various macroscopic forms directly after synthesis without the need to add binders (binders which could significantly modify the thermal conductivity of the material but also its microstructure which would be detrimental to the catalytic process envisaged). SiC alpha foam, although not preferred, is also useful. The crystals are generally cubic face-centered type, for the variety β. In general, the specific surface area of β SiC is between 5 and 50 m ² / g, more particularly between 5 and 40 m ² / g and preferably between 10 and 25 m ² / g. The porosity (that is to say the porosity of the material constituting the foam) essentially consists of meso- and macropores substantially without (less than 5% by volume) presence of micropores which can cause diffusion problems of the reagents and products which are therefore detrimental to the selectivity to products useful in the intended process. SiC β is prepared in the form of foam (alveolar). For example, reference may be made to EP-A-0543752, US-P-5449654 and US-P-6251819.

The foam has variable pore openings, between 300 and 5000 microns, preferably between 1000 and 3000 microns. The open porosity (macroporosity) of the SiC foam can vary from 30 to 95%, preferably from 30 to 90%, especially from 50 to 85%.

More precisely, the foam has two levels of porosity: 1) a so-called "cellular porosity" porosity with diameters of millimeter aperture of between 0.3 and 5 mm (advantageously between 1 and 3 mm), this alveolar porosity of the foam ranging from 30 to 95%, preferably from 30 to 90%, especially from 50 to 85%; 2) SiC porosity constituting the foam with pore diameters corresponding to the specific surface area mentioned above. It should be noted the existence of another porous network inside the rigid bridges of the support.

The open structure makes it possible to use much higher space velocities without suffering a loss of charge through the catalytic bed. A low pressure drop can reduce compression or recycling in the process. Furthermore, the SiC foam, in particular SiC β, has a reagent diffusion time which is very low, especially less than the second. The foam therefore makes it possible to obtain very high productivities, especially at high space velocity.

More precisely, the honeycomb structure makes it possible to use superficial gas velocities (ratio between the total flow rate of gas entering the reactor and the straight section of the same reactor considered empty) which are much higher without suffering excessive pressure drop across the reactor. of the catalytic bed. A low pressure drop has the advantage of reducing the cost of compression or recycling of fluids in the process. If we compare this rigid foam of β-SiC impregnated on its surface (eggshell or egg-shell impregnation) active catalytic metal to a stack of mm-sized grains impregnated in mass of the same proportion of catalytic metal, it can be demonstrated that the superficial deposition of the catalytic metal deposited on the foam will be more effectively used than the same amount of this metal core impregnating grains of SiC β. Indeed, it is known that the Fischer Tropsch reaction has a productivity limited by the intraparticular diffusion of the gaseous reactive species (CO and H ₂ ). The small thickness of the location of the active sites with respect to the surface of the catalyst also makes it possible to increase the evacuation rate of the products, liquid and gaseous reaction, thus favoring the frequency of transformation of the reagents by active site.

The foam can also be used in milled form, which considerably reduces the apparent volume of the catalyst (with a significant gain in weight relative to the volume). The reduction ratio may for example be between 2 and 10, in particular between 4 and 6.

This SiC β has very good mechanical properties making it possible to envisage its use as a catalyst support in fixed bed or "fixed slurry" processes. Because of its very good thermal conductivity, generally much higher than that of metal oxides, the hot spots are limited to the surface of the catalyst. This improves the selectivity towards the useful products. The foam structure synthesized according to the methods described above is interconnected throughout the structure of the material. This thus promotes the transfer of heat throughout the material due to the absence of insulating areas as could be the case of a structure shaped in the presence of inorganic non-conductive binders.

Due to the connectivity of the rigid foam structure and the high thermal conductivity of the SiC material (alpha or beta), the appearance of hot spots due to the exothermicity of the reactions is less than with the bulk granular catalysts deposited on oxide supports or the like. The greatest spatial uniformity of temperature obtained by the best heat transfer is on the one hand local, from the catalytic site towards the support SiC, on the other hand global, over the extent of the rigid foam, and this, whatever the reactor employed. The heat release per unit volume of foam (that is to say reactor) is also lower as the foam's porosity is higher; thus the heat released and then discharged in contact with a wall (exchanger, reactor ...) can be adjusted by means of this cellular porosity.

These characteristics give the rigid foam of the invention properties far superior to those of a fixed bed random stack (dense or not) well-known catalyst grains of the prior art, and which is more subject to points. because of: 1) low thermal conductivity at the points of contact between grains and 2) an intergranular porosity set at about 0.35-0.40. In addition to these thermal advantages, overall mechanical strength is better than that of conventional catalyst grains which can undergo mutual frictional wear either during charging in the reactor or during operation of the process.

This SiC beta has thermomechanical properties making it possible to envisage its use as a catalytic phase support in various other high-temperature processes.

Moreover, the absence of binder makes it possible to maintain the thermal conductivity of the support at all points of the support. The absence of binder avoids a reaction with the catalytic species (which otherwise could lead to a loss of activity over time).

According to one embodiment, the catalyst support contains more than 50% by weight of silicon carbide in beta form. According to a preferred embodiment, the catalyst support contains from 50 to substantially 100% by weight of beta-silicon carbide foam, and preferably substantially 100% of said silicon carbide.

According to one embodiment, the rigid foam is made of silicon carbide, the latter being predominantly in beta form, and the complement in alpha form, to which are added manufacturing residues such as carbon or silicon or compounds thereof . The catalytic properties of the material are conferred by surface and / or deposition of chemically and / or physically active phases.

The catalyst of the invention consists of said previously defined support to which one or more metals optionally added with promoters, conferring the catalytic activity, are added. As the main catalytic metal (main active catalytic metal), Group VIII metals can be used conventionally, for example cobalt, iron or ruthenium, cobalt being particularly preferred. Iron is also particularly preferred. It is also possible to use a promoter at the same time, in a conventional manner. Among the promoters, mention may be made of another metal of group VIII or else the metals selected from the group consisting of Zr, K, Na, Mn, Sr, Cu, Cr, W, Re, Pt, Ir, Rh, Pd, Ru , Ta, V, Mo and mixtures thereof. Of these, Mo and Zr are preferred.

The main metal content -or catalytic species, that is to say active catalytic species- (especially of the group consisting of cobalt, iron or ruthenium), and in particular cobalt, is generally from 1 to 50% preferably from 3 to 20% of the final weight (total weight) of the catalyst, in particular up to 10%. The content of promoter, in particular molybdenum or zirconium, is conventionally between 0.1 and 15% of the final weight of the catalyst, in particular between 2 and 10% by weight. A primary metal / promoter weight ratio is typically from 10: 1 to 3: 1, which is a preferred range.

The deposition of the catalytic metal is in a conventional manner. For example, the impregnation of the pore volume (the pore volume of the SiC foam material) with a salt of the metal, for example cobalt nitrate, can be used. It is also possible to use the evaporated drop method (also known as "egg shell"), by drop of a solution of metal salt at room temperature on a high temperature support (that is to say the foam support previously raised to high temperature), leading to a deposit (ie a metal precursor deposit) essentially at the surface, for example a solution of cobalt nitrate in air on a surface. support at 250 ^° C. Another variant of the impregnation method could be done by completely immersing the support based on SiC foam in a solution containing the precursor salt (s) of the active phase (s) desired (s) then take out the impregnated foam then for drying in air (draft). The operation may be repeated several times until the solution containing the salt of the active phase is exhausted. The operation can also be repeated several times until the desired level of impregnation of the support is obtained. The thus impregnated support is then dried.

The supports impregnated by the various methods described above can then be treated in the following manner: drying in air at 100 ^° C. for 2 hours and then calcining in air at 350 ^° C. for 2 hours in order to transform the salt or the precursor salts in its or its corresponding oxides. The product after calcination is reduced under hydrogen flow at 400 ^° C. (or between 300 and 550 ^° C.) for 2 hours in order to obtain the metallic form of the constituents of the active phase or at least a part of the constituents of the phase. active. It should be noted that the reduction could also be carried out according to another variant, namely by replacing the flow of hydrogen with a reducing flow which could be the reaction flow itself, ie CO and H ₂ , with CO: H ratios. ₂ variables (adjustable). The reduction temperature could also be varied over a relatively wide range around 400 ⁰ C as well as the reduction pressure which could be equal to or greater than the atmospheric pressure.

The Fischer-Tropsch synthesis reaction is generally carried out under the following operating conditions:

total pressure: 10 to 100, preferably 20 to 50 atmospheres;

reaction temperature: 160 to 260, particularly 160 to 250, preferably 180 to 250 and more particularly 180 to 230 ^° C .;

- H ₂ / CO ratio of the synthesis gas starting between 1.2 and 2.8, preferably between 1.7 and 2.3. Special operating conditions are provided, which allow to obtain very good results:

WH (GHSV) ranging from 100 to 5000 h ^-1 , preferably from 150 to 3000 h ^-1 , and

WHSV ranging from 1 to 100 h ^-1 , preferably 1

(advantageously 5) at 50 h ^-1 .

The method according to the invention makes it possible to obtain productivity (or Space Time Yield, STY) which are very high, whether for all the hydrocarbon species or only for the C ₄₊ cut. Productivity (or Space

Time Yield, STY) are expressed in moles of CO converted into product per mole of catalytic species and per hour, that is to say: STY = molar feed rate of CO

(mol / min) x conversion / mole number of catalytic species

(mol) x 60.

The unit can be expressed simply in h ^"1 .

According to one embodiment, the method according to the invention is implemented under the following operating conditions:

- hydrocarbon productivity greater than 3 h ^"1

(or moles of CO converted per mole of catalytic species per hour), in particular between 1 and 100 h ^-1 , preferably between 5 and 100 h ^-1 (or moles of CO converted per mole of catalytic species and by hour), and

- productivity of C ₄₊ hydrocarbons exceeding 3 h ^"1

(or moles of CO converted per mole of catalytic species per hour), especially between 1 and 50 h ^-1 , preferably between 5 and 50 h ^-1 (or moles of CO converted per mole of catalytic species and by hour) .

Typically, the STY values in hydrocarbons are greater than 3 moles of CO converted per mole of catalytic species and per hour, and in particular between 1 (advantageously 5) and 100 moles of CO converted per mole of catalytic species and per hour. , and the STY values for the C ₄₊ cut are in particular between 1 (advantageously 5) and 50 moles of CO converted per mole of catalytic species and per hour.

In particular, the contact time (= 3600 / WH) in the invention may even be less than 2, or even 1 second (ie a WH greater than 1800 h ^-1 , or even greater than 3600 h ^-1 ).

It will be recalled that the GHSV, WHSV & STY (productivity) are defined (and calculated in the examples) as follows (the gas includes for GHSV and WHSV both CO and H ₂ ) (under normal temperature and humidity conditions). pressure):

GHSV = Total gas volume flow (cc / min) / apparent catalyst volume (ce) x 60. This is the opposite of the contact time.

WHSV = Mass flow rate gas (CO + H ₂ ) (g / min) / mass catalytic species (g) x 60.

STY = CO gas (mol / min) molar flow rate x conversion / mole number catalytic species (mol) x 60.

The process according to the invention is especially carried out in a multitubular reactor, comprising for example more than 10, preferably more than 100, preferably from 1000 to 100000 tubes, in particular from 2000 to 10000 tubes. Each tube contains coaxial cylindrical elements of rigid foam of SiC β, which have been previously impregnated with the catalytic metal species or species.

Such a reactor, equipped with SiC foam as a catalyst support, is effective for the Fischer-Tropsch synthesis reaction. It can be equipped with an integrated heat exchanger, in order to evacuate the heat generated by the exothermic reaction. It is generally designed and realized as a multitubular heat exchanger, which allows to evacuate in the calender the heat generated within the tubes where the synthesis reaction (exothermic) takes place.

The process according to the invention can be carried out upwards in the reactor or downwardly, that is to say with a reactive gas flow upwards or downwards in the reactor.

In the case of implementation upwards, it is possible to adjust the flows so that the reaction is implemented under conditions that are close to a "slurry". In a normal "slurry", the liquid is obtained by overflow or withdrawal at the bottom in the case of recirculation, with entrainment of particles, the injected gas being brought into contact with liquid at the level of the catalyst elements. Thus, still in a conventional "slurry" reactor, the liquid produced by the reactor is maintained in natural internal recirculation within the reactor and contains the catalyst in the form of fine particles that must be separated within the liquid flow that is withdrawn from the reactor. reactor, the injected gas being simply introduced into contact with the liquid by a conventional dispensing member.

The present invention makes it possible to adjust the conditions to obtain an effect equivalent to a "slurry" mode (with controlled gas / liquid contacts), but without the disadvantages of driving catalyst particles. This last point is a particularly significant advantage insofar as on the one hand the catalyst is very expensive, and on the other hand the separation of the entrained particles from the liquid drawn downstream (filtration) and the particle recovery require the implementation. delicate processes and they too expensive. It is also possible to have a larger flow.

More specifically, the conventional slurry reactor principle has two advantages and two major disadvantages. The advantages are that the catalyst used is a fine powder (dp50 of between 30 and 200 μm) whose catalytic performance is in principle not likely to be limited by the transfer of internal material. The other advantage is that the continuous phase within the reactor is liquid and thus the transfer capacity of the reaction heat within this reactor is relatively good and in particular much better than in the case of an implementation. fixed bed reactor with continuous downward gas flow. A major drawback of the conventional slurry type reactor is that it is absolutely necessary to prevent this (very expensive) fine powder catalyst from being entrained - thus lost - with the withdrawal of the liquid phase from the reactor, which is essential since this Liquid phase is precisely the product of Fischer Tropsch synthesis. The second disadvantage is the "back-mix" of the gas-induced liquid-solid suspension that limits the conversion per unit volume, and the coalescence of the gas bubbles that limits gas-liquid transfer and hence productivity.

The implementation of the process according to the invention using an ascending reactive gas flow in the reactor makes it possible to retain one of the advantages of the conventional slurry, that is to say the good capacity to evacuate the heat of the reactor. reaction since the continuous phase of the reactor is also liquid. In the case where the main active catalytic metal deposited on the foam is maintained in a thin layer (less than 100 μ), the risk of limitation by the internal transfer of material is very low as in the case of the conventional slurry reactor. But in doing so, the disadvantage of the latter due to the risk of losing the catalyst by driving in the withdrawal of liquid no longer exists since the catalyst is fixed on the rigid SiC β foam which fills the tubes of the reactor. In addition, the honeycomb structure of the rigid foam limits the size of the gas bubbles and is thus favorable to a high gas-liquid interfacial area, thus favoring gas-liquid transfer and therefore productivity. The modest average size (less than about cm) of the cells of the rigid foam limits the back mixing of the liquid induced by the bubbles, which is generally favorable to productivity.

In addition, if it is expected to use a pump to promote the recirculation of the liquid from the upper to the lower part of the reactor, it becomes possible to choose and impose a superficial velocity of the liquid which is impossible in a conventional bubble column type system for which the liquid recirculation rate is closely dependent on the rising velocity of the reactant gas. To implement this forced recirculation of the liquid, it can provide a gas / liquid separation device, such as an overflow, upstream of the supply line of the pump. This limits the recirculation of the bubbles, which limits the back mixing, approaching the conditions of a piston flow (which is advantageous for all chemical reactions in terms of conversion and selectivity to intermediate products such as petroleum liquids, distillates, kerosene or naphtha are sought).

Still in the case of the embodiment with an ascending reactive gas flow, the mechanical wear of the support / catalyst assembly (stationary in this case) is reduced compared to a conventional "slurry" system, in which the fine particles of support / catalyst (mobile in this case) are subjected to severe mechanical stresses, therefore attrition wear due in particular to the bursting of the gas bubbles. Catalyst costs are therefore reduced.

The downward implementation corresponds to what is generally practiced during fixed-bed reactions which lead to the formation of liquids from gases.

More specifically, the implementation of the process of the invention with a downstream reactive gas flow reactor corresponds to what is generally practiced with fixed bed catalytic reactors and for highly exothermic reactions. It is indeed well known that in these cases the use of conventional multitubular reactors whose design and operation are very similar to those of a tube and shell heat exchanger is used. The chemical reaction then takes place in the tubes, which are filled with granular catalysts, the calender being itself fed with a coolant or water that turns into vapor. In the case of this reactor, the heat removal potential of the reaction generated within the catalytic tubes depends on the speed of the gas but also on the effective thermal conductivity of all the catalyst grains packed together in each tube.

However, the present invention differs from the conventional multitubular reactor concept in that the tubes are not filled with catalyst grains but rigid Sic foam. This forms a solid phase continuum in each reactor tube, whereas the use of a catalyst bed in the form of grains induces a weak interface of thermal contact between grains (discontinuities between elements solid phase). This has the consequence that the thermal conductivity of the rigid SiC foam impregnated with catalyst is better than that of a set of catalyst grains. The use of foam thus makes it possible to improve the efficiency of the heat transfer from the catalytic tubes to the heat transfer fluid or the steam and to eliminate any risk of hot spots within the catalytic mass which are well known are the cause of loss of selectivity and possible loss of control of reactor safety. However, the efficiency of heat transfer is traditionally a limiting factor for the diameter of the reactor tubes. Consequently, the invention makes it possible to carry out the reaction in tubes of greater diameter than according to conventional methods, and consequently to reduce the number of tubes per reactor for equivalent production, hence clear advantages in terms of ease of realization and cost of these reactors.

In the same vein, increasing the cellular porosity of the foam reduces the reaction heat evolution per unit reactor volume. The same effect can be obtained in conventional granular fixed bed by diluting the catalyst grains with an inert granular solid. The decisive advantage of the rigid foam of the invention is to achieve the same result without solid diluent and without increasing the pressure drop on the catalytic reactor.

As in a conventional fixed bed system, the internal diffusion in the support / catalyst phase is a limiting factor due to the millimetric size of the grains used. A parade consists of depositing the active metal at the periphery of the grains. An advantage of the invention is that the same peripheral impregnation technique can be used with the rigid foam. Another advantage of the invention over the conventional fixed bed system is that the pressure drop is determined by the cellular porosity of the rigid foam, and that it is adjustable independently of the superficial velocity of the reactive gas. .

According to another embodiment of the process according to the invention, the reactor still of multitubular design and downward reactive gaseous flow contains tubes filled with activated carbon impregnated SiC β foam in one part and grain catalyst similarly impregnated in another part.

It appears advantageous to provide for filling the lower part of the tubes of the reactive gaseous reactor descending support grains / catalyst (the support may be SiC, preferably beta, and the grain size may be millimeter), and the upper part of these same tubes with rigid SiC foam (impregnated with catalyst) as described above, in the form of rigid blocks. It is known that most of the heat is produced at the beginning of the reaction, so at the top of the tube, because of the kinetics of the latter. Thus, the presence of foam in the upper part provides the benefits mentioned above in terms of heat transfer, while the presence of grains in the lower part can save money by limiting the amount of foam (more expensive) to implement.

According to a more particularly preferred embodiment, the linear foam / grain distribution can vary from 1: 3 to 1: 1, and is advantageously about 1: 2, which means that the grains occupy about two-thirds of the useful portion of each tube and foam about one-third. When the support is in the form of grains, this support may be conventional, for example alumina or silicon carbide (advantageously in beta form).

A uniform foam may be used in the reactor, or according to one embodiment use a pore size gradient or cells (along the tubes of the reactor in particular). In particular, it is possible to vary the size of the pores (or cells) of the foam along the flow of gas (in the direction of gas flow), the size decreasing. For example, one can define three sections of similar length, and load these three sections with foams having pore sizes ranging from 2500-3000, for example 2700 microns, to 1200-1800, for example 1500 microns, and finally 700- 1200 for example 1100 μm. It is thus possible to optimize the reaction taking into account the products which are formed progressively along the axis of flow of the catalytic bed.

Examples of possible reactor schemes for carrying out the invention are shown in Figures 9a to 9d.

Fig. 9a is an example of upward mode operation. The reactor 1 comprises, at the bottom, a syngas supply line 2 which is terminated by a distribution member 3. The syngas, or synthetic gas, is the mixture of hydrogen and carbon monoxide which feeds the reaction of Fischer-Tropsch synthesis. The reactor 1 is filled with a liquid 4. The syngas forms bubbles in the liquid 4 at the dispensing member 3. The syngas bubbles back into the liquid 4 along tubes 5 containing catalyst blocks on a SiC beta foam support. It is therefore within the tubes 5 that the Fischer-Tropsch reaction takes place. Between the different tubes is provided a heat exchange system 6. A heat transfer fluid supply pipe 7 and a heat transfer fluid withdrawal pipe 8 are provided at the inlet and outlet of the heat exchange system 6 for the circulation of the coolant. The reactor further comprises, at the head, a withdrawal line 9 for gaseous effluents resulting from the Fischer-Tropsch reaction and, at the bottom, a line 10 for withdrawing liquid effluents resulting from the Fischer-Tropsch reaction.

Figure 9b corresponds to an operating variant in ascending mode. According to this variant, the reactor is provided with a liquid overflow 11. The liquid is taken by a withdrawal pipe 12 connected to the level of the overflow 11. A pump 13 ensures the forced recirculation of a portion of the liquid , by sucking the liquid taken from the withdrawal line 12 and by reinjecting a portion of the liquid at the bottom of the reactor 1 via a liquid supply line 14, while the other part of the liquid is withdrawn via the line of liquid. withdrawal 15.

Figure 9c shows an example of down-mode operation. In this configuration, the reactor 21 is equipped with a supply line 22 of syngas at the reactor head. The syngas goes down along tubes 23 containing catalyst blocks on a SiC beta foam support. It is therefore within the tubes 23 that the Fischer-Tropsch reaction takes place. Between the different tubes is provided a heat exchange system 24. A heat transfer fluid supply pipe 25 and a heat transfer fluid withdrawal pipe 26 are provided at the inlet and outlet of the heat exchange system 24 for the circulation of the coolant. The reactor further comprises, in the foot, a withdrawal line 27 for collecting all the products of the Fischer-Tropsch reaction.

According to the operating variant in downward mode shown in FIG. 9d, the tubes 23 contain in their lower part (on about 2/3 of the useful length) of the catalyst supported on SiC grains, and in their upper part (about 1/3 of the useful length) of the catalyst supported on a beta SiC foam.

In the process according to the invention, the hydrocarbon effluent may contain more than 70 mol% of a mixture comprising from 50 to 90 mol% of C ₆ to C ₁₂ hydrocarbons and from 10 to 50% of hydrocarbons. of Cχ ₃ -C _24. The effluent may contain more than 80, preferably more than 90 mol% of a mixture of C ₆ to C ₂₅ .

In the process according to the invention, the hydrocarbon effluent may generally contain not more than 10 mol% of olefins and branched hydrocarbons, and / or less than 2 mol% of C ₁ -C ₂₀ alcohol.

In the process according to the invention, in the hydrocarbon effluent, the content of methane and CO ₂ may be less than 20 mol%.

In the process according to the invention, the hydrocarbon effluent may contain not more than 10 mol% of olefins and branched hydrocarbons, and / or less than 2 mol% of C _x to C ₂₀ alcohol.

In the process according to the invention, the hydrocarbon effluent may contain more than 80%, preferably more than 90% by mole of a mixture of C ₆ to C ₂₅ . In the process according to the invention, the hydrocarbonaceous effluent may contain levels above 6% for C7, C _8, C _9, C _10, C _X1, C ₂ and C _3.

In the process according to the invention, the hydrocarbon effluent may contain levels greater than 8% for

In the process according to the invention, the hydrocarbon effluent may contain a concentration of olefinic hydrocarbons of less than 1%.

In the process according to the invention, the hydrocarbon effluent may have a content of methane and CO _{2 of} less than 20 mol%.

Finally, the method according to the invention may also include a step of upgrading, in particular for the production of fuel. This upgrading step can include isomerization, cracking, etc.

In the application, the ratios are molar unless otherwise stated. EXAMPLES

The following examples illustrate the invention without limiting it. Example 1 (comparative).

In this example, the SiC-based support, in the form of monolithic foam (rigid cellular foam) with an average cell opening size or pore of about 500 μm and a specific surface area of 11 m ² / g, is impregnated with the porous volume method with an aqueous solution containing the cobalt salt in nitrate form. The weight of the precursor salt is calculated to have a final cobalt load of 30% by weight based on the weight of catalyst after calcination and reduction. The impregnated product is then dried under air at 100 ^° C. for 2 h and then calcined under air at 350 ^° C. for 2 hours in order to convert the precursor salt into its corresponding oxide. The product after calcination is reduced under hydrogen flow at 400 ^° C. for 2 hours to obtain the metallic form of the active phase.

The Fischer-Tropsch synthesis reaction is carried out under the following conditions: - total pressure: 40 atmospheres

- reaction temperature: 220 ° C

- catalyst volume: 20cc

- catalyst mass (support + active phase): 5.0g

mass of the active phase: 1.5g

- 50cc / min H ₂ + CO (NTP)

- dilution 50cc / min Ar (NTP)

- molar ratio H ₂ / CO of 2.

reactive contact time / catalyst: 12 sec (WH 300 h ^-1 ).

- WHSV: 0.95 hr ^"1

Productivity in hydrocarbons and C ₄₊ hydrocarbons is obtained as follows:

STYHC = 1.58 hr ^-1

STY ₀₄₊ = 1.14 hr ^-1 Example 2 (Invention)

In this example, the SiC-based support, in the form of monolithic foam (rigid cellular foam) with an average cell opening size or pore of about 1500 μm and a specific surface area of 15 m ² / g, is impregnated with the method indicated in Example 1. The mass of the precursor salt is calculated to have a final cobalt load of 10% by weight relative to the weight of catalyst after calcination and reduction. Figure 1 shows a view of a support while Figure 2 shows an enlarged view of the foam thus obtained.

The Fischer-Tropsch synthesis reaction is carried out under the following conditions:

- total pressure: 40 atmospheres

reaction temperature: 220 ^° C.

- catalyst volume: 18cc

catalyst mass (support + active phase): 4.0 g

- active phase mass: 0.4 g

- 200cc / min H ₂ + CO

- no dilution with Ar

- molar ratio H ₂ / CO of 2.

reactive contact time / catalyst: 5.5 sec (WH 660 h ^-1 ). - WHSV: 14, 3 hrs ^"1

Productivity in hydrocarbons and C ₄₊ hydrocarbons is obtained as follows:

STYHC = 7.0 hr ^-1

STYc ₄₊ = 6.58 hr. ¹ Example 3 (Invention).

The procedure is as in Example 2, but under the following conditions:

- total pressure: 40 atmospheres

reaction temperature: 230 ^° C.

- catalyst volume: 18cc

catalyst mass (support + active phase) 3.48 g

active phase: 0.34 g

- 200cc / min H ₂ + CO

molar ratio H ₂ / CO of 2.

reactive contact time / catalyst: 5.5 sec (WH 660 h ^-1 ).

- WHSV: 16.4 hrs ^"1

Productivity in hydrocarbons and C ₄₊ hydrocarbons is obtained as follows:

STYHC = 7.25 hr ^-1

STY _{C4 +} = 5.41 h ^-1 Example 4 (Invention)

The procedure is as in Example 2, but under the following conditions:

- total pressure: 40 atmospheres

reaction temperature: 240 ^° C.

- catalyst volume: 18cc

- catalyst mass 3.48g

- 350cc / min H ₂ + CO

- molar ratio H ₂ / CO of 2.

reactive / catalyst contact time: 3.1 sec (WH 1160 h ^-1 ).

- WHSV: 28.7 hrs ^"1

One obtains productivities of hydrocarbons and hydrocarbons C ₄₊ as follows: STYHC = 40 h ^"1 STY _{+ C4} = 14 ^{h -1.} Example 5 (Invention)

The procedure is as in Example 2, but the catalyst is this time doped with 2% Zr. The impregnation procedure is the same as in Example 1, the zirconium salt being ZrO (NO ₃ ) ₂ .

The procedure is as in Example 2, but under the following conditions:

- total pressure: 40 atmospheres

reaction temperature: 220 ^° C.

- catalyst volume: 36cc

- catalyst mass 8.35g

- 200cc / min H ₂ + CO

- molar ratio H ₂ / CO of 2.

reactive contact time / catalyst: 10.9 sec (WH 330 h ^-1 ).

- WHSV: 6, 8 hrs ^"1

Productivity in hydrocarbons and C ₄₊ hydrocarbons is obtained as follows:

STY _H C = 6, 35 h ^"1

STYc ₄₊ = 6.0 h ^-1 Example 6 (Invention).

The procedure is as in Example 2, but the catalyst is this time ground and not in the form of a macroscopic foam. The foam before grinding is impregnated by the immersion method as previously described with a solution containing an adequate amount of a cobalt salt (cobalt nitrate). After drying followed by heat treatments, the foam containing the active phase based on cobalt is milled and then tested in the FT reaction. The volume reduction factor is between 4 and 6. The procedure is as in Example 2, but under the following conditions:

- total pressure: 40 atmospheres

reaction temperature: 220 ^° C.

- catalyst volume: 37 cc

catalyst mass (support + active phase): 22.7 g

active phase mass: 2.3 g

- 400cc / min H ₂ + C0

- molar ratio H ₂ / CO of 2. reactive contact time / catalyst: 5.5 sec (WH 650 h ^-1 ).

- WHSV: 5.0 hrs ^"1

Productivities are obtained in hydrocarbons and hydrocarbons C ₄₊ as follows: STY = _HC 3,71 h ^"1 ₀₄₊ STY = 2.69 ^{h" 1.}

Claims

A process for converting carbon monoxide to C ₂ ⁺ hydrocarbons in the presence of hydrogen and a catalyst comprising a metal in a reactor containing said catalyst supported on a support based on silicon carbide foam, implemented in the following operating conditions:

WH (GHSV) ranging from 100 to 5000 h ^-1 and

- WHSV ranging from 1 to 100 hr ^"1.

2. A process for converting carbon monoxide to C ₂ ⁺ hydrocarbons in the presence of hydrogen and a catalyst comprising a metal in a multitubular reactor containing said supported catalyst on a support containing a silicon carbide foam.

3. Method according to claim 2, implemented under the following operating conditions:

WH (GHSV) ranging from 100 to 5000 h ^-1 and

- WHSV ranging from 1 to 100 hr ^"1.

4. Method according to one of claims 1 to 3, wherein the silicon carbide foam comprises more than 50% by weight of silicon carbide in beta form.

5. Method according to one of claims 1 to 4, wherein the catalyst support contains from 50 to substantially 100% by weight of beta-silicon carbide, and preferably substantially 100% of said silicon carbide.

6. Method according to one of claims 1 to 5, wherein the foam has pore openings, between 300 and 5000 microns, preferably between 1000 and 3000 microns.

7. Method according to one of claims 1 to 6, wherein the foam is rigid.

8. Method according to one of claims 1 to 7, wherein the open porosity of the SiC foam ranges from 30 to 90%, especially from 50 to 85%.

9. Method according to one of claims 1 to 8, implemented under the following operating conditions:

WH (GHSV) ranging from 150 to 200Oh ^-1 ;

WHSV ranging from 1, advantageously 5, to 50 h ^-1 .

10. Method according to one of claims 1 to 9, implemented under the following operating conditions:

- hydrocarbon productivity greater than 3 h ^-1 , and

- productivity in C ₄₊ hydrocarbons greater than Sh ^"1 .

11. Method according to one of claims 1 to 10, implemented under the following operating conditions:

- hydrocarbon productivity between 5 and 10Oh ^-1 , and

- productivity in C ₄₊ hydrocarbons between 5 and 5Oh ^"1 .

12. Method according to one of claims 1 to 11, implemented under the following operating conditions:

total pressure: 10 to 100 atmospheres;

reaction temperature: 160 to 260 ^° C., preferably 160 to 250 ^° C. and

- H ₂ / CO ratio of the synthesis gas starting between 1.2 and 2.8.

13. Method according to one of claims 1 to 12, implemented under the following operating conditions:

- total pressure: 20 to 50 atmospheres;

reaction temperature: 180 to 230 ^° C .;

- H ₂ / CO ratio of the synthesis gas starting between 1.7 and 2.3.

Process according to one of Claims 1 to 13, in which the reactor contains a part in which the catalyst is supported on a support based on rigid silicon carbide foam and a part in which the catalyst is supported on a substrate. support in the form of grains or extrusions.

15. Method according to one of claims 1 to 14, implemented in an upward manner in the reactor.

16. Method according to one of claims 1 to 14, implemented downwardly in the reactor.

17. Process according to one of claims 1 to 16, in which the catalyst contains from 1 to 50%, more particularly from 3 to 30% by weight, advantageously from 3 to 20% by weight, of one or more metals. of the group consisting of cobalt, iron or ruthenium.

18. The method according to one of claims 1 to 17, wherein the catalyst further contains a promoter selected from the group consisting of Zr, K, Na, Mn, Sr, Cu, Cr, W, Re, Pt, Ir, Rh, Pd, Ru, Ta, V, Mo and mixtures thereof, preferably Mo and Zr.

19. Method according to one of claims 1 to 18, wherein the reactor is a multitubular reactor containing more than 10 and preferably more than 100 tubes, in particular from 1000 to 100000 tubes.

20. The method according to one of claims 1 to 18, wherein the foam has a pore size gradient.

21. Method according to one of claims 1 to 20, wherein the foam is ground.

22. Method according to one of claims 1 to 20, wherein the reactor is provided with an integrated heat exchanger.

3. Method according to one of claims 1 to 22, comprising a step of upgrading for the production of fuel.