EP1448749A1

EP1448749A1 - Method for converting synthetic gas in series-connected reactors

Info

Publication number: EP1448749A1
Application number: EP02790546A
Authority: EP
Inventors: Ari Minkkinen; Reynald Bonneau; Alexandre Rojey
Original assignee: IFP Energies Nouvelles IFPEN; Eni SpA
Current assignee: IFP Energies Nouvelles IFPEN; Eni SpA
Priority date: 2001-11-20
Filing date: 2002-10-28
Publication date: 2004-08-25
Anticipated expiration: 2022-10-28
Also published as: CA2466938C; CA2466938A1; FR2832416A1; US20030096881A1; CN100354392C; FR2832416B1; RU2004118604A; NO20042077L; CN1612924A; US6921778B2; WO2003044127A1; EP1448749B1; RU2294913C2; AU2002365951A1

Abstract

The invention concerns a method for converting a synthetic gas into liquid hydrocarbons implemented in at least two reactors in series containing a catalytic suspension of at least a solid catalyst suspended in a liquid phase, wherein said reactors are substantially perfectly mixed, the last reactor is at least fed by at least part of at least the gas fractions collected at the output of one of the other reactors, at least one reactor is fed with a catalytic suspension current derived directly from another reactor, and at least a catalytic suspension current from another reactor is at least partly separated so as to obtain a substantially catalyst-free liquid product and a catalyst-enriched catalytic suspension, which is recycled.

Description

PROCESS FOR THE CONVERSION OF SYNTHESIS GAS IN REACTORS

SERIAL

PRIOR ART:

The production of liquid fuels by Fischer-Tropsch synthesis opens up significant prospects for the exploitation of gas fields far from major markets. These developments are conditioned by the need to reduce costs and in particular investment costs in order to improve the profitability of this sector.

One of the ways to achieve this objective is to play on a scale factor to reduce investment costs per tonne of liquid product obtained.

The use of the catalyst used to promote the synthesis reaction in the form of a suspension in the liquid phase (“slurry”) makes it possible to produce reactors of very large unit size and to achieve very high production levels, for example 10,000 barrels per day using a single three-phase reactor.

Such three-phase reactors comprising a catalyst in suspension in a solvent generally inert in the reaction. They are generally called slurry reactors. Among the different types of slurry reactors, there have been known in particular perfectly agitated autoclave type reactors, or else bubble column type reactors which operate under variable hydrodynamic conditions ranging from the perfectly agitated reactor to the reactor operated in piston mode without dispersion, this both for the gas phase and for the liquid phase.

Recently, such types of reactors have been considered for Fischer-Tropsch synthesis, rather than conventional fixed bed reactors which have the drawback of not dissipating the heat produced by the reaction as easily.

Thus, patents US 5,961,933 and US 6,060,524 describe a process and an apparatus making it possible to operate a slurry reactor of the bubble column type for the Fischer-Tropsch synthesis. In these patents, the slurry reactor includes an internal or external liquid recirculation system, which makes it possible to achieve higher productivities for each Fischer-Tropsch reactor. Patent application WO 01 / 00.595 describes a process for the synthesis of hydrocarbons from synthesis gas in a three-phase reactor, preferably of the bubble column type, and in which the hydrodynamic conditions of the liquid phase are such that the number Péclet of the liquid phase is greater than 0 and less than 10. Furthermore, the surface speed of the gas is preferably less than 35 cm.s-1.

Patent EP-B-450 860 describes a method for optimally operating a three-phase bubble column type reactor. This patent seeks to optimize the operation of a single reactor of this type, it is indicated that the performance depends essentially on the dispersion of the gas phase (number of Péclet for the gas phase) and on the suspension of the catalyst in the liquid phase. In particular, the number of Péclet for the gas phase must imperatively be greater than 0.2. Thus, this patent recommends not using a substantially perfectly stirred reactor with regard to the gas phase (number of gas Péclet close to 0), since this type of reactor leads to insufficient performance levels.

Thus, such a method comes up against certain limitations, linked in particular to the phenomena of axial mixing. To promote the gas-liquid and solid liquid mass transfer and the thermal transfer, it is advantageous to strongly stir the liquid and gaseous phases in presence, which increases the axial mixing. In addition, for large reactor diameters, for example from 8 to 11 m, large internal recirculation movements occur, which cause a very large mixture of the liquid phase. These phenomena are favorable in terms of gas-liquid and / or liquid-solid mass transfer and thermal transfer, but moreover a very strong mixture can be unfavorable for the degree of progress of the reaction.

The method according to the invention aims to overcome these problems by combining at least two three-phase reactors, preferably at least three three-phase reactors. It has in fact been observed that the use of reactors highly mixed in series makes it possible to obtain correct progress of the reaction, while promoting the evacuation of calories. This sequence makes it possible to achieve high productivities in desired products, that is to say essentially paraffins having essentially a carbon number greater than 5, preferably greater than 10, while limiting the formation of light products (C1-C4 hydrocarbons).

DESCRIPTION OF THE INVENTION:

The invention relates to a process for the synthesis of hydrocarbons preferably having at least 2 carbon atoms in their molecule and more preferably at least 5 carbon atoms in their molecule by contacting a gas containing essentially monoxide of carbon and hydrogen and in a reaction zone containing a suspension of solid particles in a liquid, which comprises solid particles of reaction catalyst. Said catalytic suspension is also called slurry. The process according to the invention is therefore implemented in a three-phase reactor. Preferably, the method according to the invention will be implemented in a three-phase reactor of the bubble column type.

The process according to the invention is a process for converting a synthesis gas into liquid hydrocarbons used in at least two reactors in series, preferably at least three reactors in series containing at least one catalyst in suspension in a liquid phase , in which said reactors are perfectly mixed, the last reactor is at least partly fed by at least part of at least one of the gaseous fractions collected at the outlet of at least one of said reactors, and the product mixture in phase liquid and catalyst leaving the last reactor is at least partly separated so as to obtain a liquid product substantially free of catalyst and a liquid fraction enriched in catalyst (catalytic suspension enriched in catalyst, or concentrated catalytic suspension), which is recycled

Each of the reactors used is a bubble column type reactor, with contacting the gas with a very divided liquid / solid mixture (“slurry” or “slurry bubble column” reactor according to English terminology)

The catalysts used can be of various natures and usually contain at least one metal preferably chosen from the metals of groups 5 to 11 of the new periodic classification of the elements. The catalyst can contain at least one activating agent (also called promoter) preferably chosen from the elements of groups 1 to 7 of the new periodic classification. These promoters can be used alone or in combination.

The support is generally a porous material and often a porous inorganic refractory oxide. By way of example, this support can be chosen from the group formed by alumina, silica, titanium oxide, zirconia, rare earths or mixtures of at least two of these porous mineral oxides.

Typically the suspension can contain from 10 to 65% by weight of catalyst. The catalyst particles have an average diameter usually between about 10 and about 100 microns. Finer particles can possibly be produced by attrition, that is to say by fragmentation of the initial catalyst particles. In the process according to the invention, each of the reactors is highly mixed and approaches the conditions for perfect mixing. The reactors according to the invention are therefore defined as being substantially perfectly agitated and the number of Péclet can be advantageously used as a criterion making it possible to measure the degree of agitation of said reactors.

Since the reaction takes place in the liquid phase, mastering the hydrodynamics of this phase is essential. The piston-dispersion model can be applied to each liquid phase, since it is well suited to continuous phases. The Peclet number linked to this model is Pe liq = VI ^* H / D _ax or VI is the speed of the liquid in the reactor, H the expansion height of the catalytic bed and D _ax the axial dispersion coefficient. It should preferably be less than 10, and more preferably less than 8. Such a model is less well suited to the representation of mixing phenomena in the gas phase. However, if it is nevertheless used to interpret a tracer experiment, by determining a Peclet number, for example from the variance of the output concentration profile, it appears that it is possible to reach preference values less than 0.2, preferably less than 0.18, very preferably less than 0.15 and even more preferably less than 0.1 or even less than 0.05 and in certain cases less than or equal to 0, 03.

These conditions are more easily met in the case of a reactor of very large diameter, for example greater than 6 m. However it is also possible to reach such conditions in the case of a reactor. smaller diameter by adjusting the hydrodynamic conditions to promote agitation, and therefore gas-liquid and liquid-solid mass transfers. This agitation can be obtained by any means known to those skilled in the art, and in particular for example by generating recirculation movements of the liquid phase by means of structures internal to the reactors or by means of external recirculation such as loops. recirculation.

The mixing effect in the gas phase will be increased if said gas phase is finely dispersed, in gas bubbles with a diameter not exceeding, for example, a few millimeters. Such a condition is moreover favorable to the reaction kinetics.

To promote the progress of the reaction, in the process according to the invention, reactors are used in series, at least two, but preferably at least three. This also makes it possible, and this is another object of the present invention, to stage the injection of synthesis gas. In this way it is possible to optimize the configuration of the reactors in series. In particular, when targeting high train capacities to benefit from a scale effect, one is generally limited by the maximum diameter of a reactor, for reasons of construction and transport by road. This diameter can be for example 11m. In this case, to maximize the production capacity, it is advantageous to use reactors of the same diameter and this can be done by adjusting the amount of synthesis gas sent to each of the reactors.

Each of the reactors is operated at a temperature preferably between 180 ° C and 370 ° C, preferably between 180 ° C and 320 ° C, more preferably between 200 ° C and 250 ° C, and at a pressure preferably comprised between 1 and 5 MPa (Megapascal), preferably between 1 and 3 MPa.

In summary, the process according to the invention is a process for converting a synthesis gas into liquid hydrocarbons used in at least two reactors in series containing at least one catalyst in suspension in a liquid phase, in which said reactors are substantially perfectly mixed, the last reactor is at least partly fed by at least part of at least one of the gaseous fractions collected at the outlet of at least one of said reactors, and the mixture of product in the liquid phase and the catalyst leaving the last reactor is at least partially separated so as to obtain a liquid product substantially free of catalyst and a liquid fraction enriched in catalyst, which is recycled. The process according to the invention preferably comprises at least 3 reactors in series. In the method according to the invention, the number of liquid peclet is preferably less than 8, and independently, the number of gas peclet is preferably less than 0.2 and more preferably less than 0.1.

According to a preferred mode of operation of the method according to the invention, at the outlet of each reactor the gas phase is separated from the liquid phase containing the catalyst in suspension. More preferably, the gaseous fractions leaving the first reactors are combined, treated and sent to the inlet of the last reactor and very preferably, the gaseous fraction leaving the last reactor is recycled at the inlet of the production stage synthesis gas.

According to a preferred mode of operation of the method according to the invention, the introduction of synthesis gas is distributed at the inlet of the reactors in series so that all the reactors are of identical size.

The catalyst of the process according to the invention is preferably formed from a porous mineral support and from at least one metal deposited on this support. The catalyst is preferably suspended in the liquid phase in the form of particles with a diameter preferably less than 200 microns.

Several possible embodiments of the invention are described below. In the figures presented, the references of the same flow or equipment are identical.

EXAMPLE 1:

Several embodiments of the invention are possible, one of these modes is presented in FIG. 1.

In this example of arrangement of the process according to the invention, 3 reactors are used in series. The synthesis gas arrives via the line 100. It is sent to the first reactor R1, in which it is dispersed within the liquid phase formed by the reaction products which are recycled. At the outlet of this first reactor R1, the mixture of liquid product formed containing the catalyst in suspension (catalytic suspension) as well as the unreacted gas is discharged through line 101. in the form of a dispersed phase. Via line 102 a second supply of synthesis gas is introduced and the resulting mixture is sent via line 103 to the second reactor R2. At the outlet of this second reactor R2, the mixture of liquid product containing the suspended catalyst and the unreacted gas are discharged via line 104, in the form of a dispersed phase. Via line 106 a third supply of synthesis gas is introduced and the resulting mixture is sent via line 107 to the third reactor R3. At the outlet of this third reactor R3, the mixture of liquid product containing the suspended catalyst and the unreacted gas are discharged via line 108, in the form of a dispersed phase. The gas phase is separated from the liquid phase in the separator SL. This gas phase is evacuated via line 111, treated and recycled. The liquid phase containing the suspended catalyst (catalytic suspension) is sent to the SC separation and filtration system. The liquid phase separated from the catalyst is discharged through line 110 while the liquid phase concentrated in catalyst (concentrated catalytic suspension) is recycled through line 109 to the first reactor R1.

EXAMPLE 2:

In the process according to the invention, intermediate separations can optionally be carried out. In particular; it is possible to separate the residual gas fraction at the outlet of each reactor, as shown in the diagram in FIG. 2.

The residual gas fractions are separated at the outlet of each of the reactors, by means of the separators, SL1, SL2 and SL3.

This avoids sending the inert gases and the water contained in the residual gas fractions leaving one reactor to the next reactor. The separators SL1, SL2, SL3 operate for example by decantation, by providing a sufficient residence time in the separation flask. The gaseous fractions thus collected by conduits 111, 112 and 113 are combined, treated and recycled.

The gaseous fractions collected by conduits 111, 112 and 113 contain water, carbon dioxide, light hydrocarbons as well as a mixture of carbon monoxide and hydrogen. It is advantageous to send the oxide mixture carbon and hydrogen collected at the outlet of a reactor at the following reactor (not shown).

The other flows or equipment are identical to those in FIG. 1.

EXAMPLE 3 In the case of the example of embodiment shown in FIG. 3, the gas fractions collected by the conduits 112 and 113 at the outlet of the reactors R1 and R2 are combined and treated. The gas mixture is first cooled in the exchanger-condenser C1, so as to condense the water. A mixture of three phases is thus obtained, which are separated in the separator S4: an aqueous phase which is discharged through line 114, a liquid hydrocarbon phase which is discharged through line 115, and a gaseous phase which is evacuated through line 116. The gas phase is sent to a treatment section T1, so as to at least partially separate the carbon dioxide which it contains. The gaseous fraction rich in carbon dioxide, which is thus separated is discharged through line 117. The treatment section T1 can implement the various known methods for separating the carbon dioxide. It is possible, for example, to use a washing process with a solvent, such as for example an amine, or else a physical solvent such as refrigerated methanol, propylene carbonate or tetraethylene glycol dimethyl ether (DMETEG). One can also use any other method based for example on a separation by adsorption or a separation by selective membrane. The gaseous mixture obtained, which is evacuated from the treatment unit T1 by the conduit 106, is enriched in carbon monoxide and in hydrogen. It still contains light hydrocarbons and in particular methane. It is sent to the inlet of the last R3 reactor. It can optionally be mixed with an additional mixture of carbon monoxide and hydrogen, coming from the synthesis gas production section (not shown). The light hydrocarbons which arrive via line 106 and which are not converted in the reactor R3 are evacuated through line 111 and can be recycled at the inlet of the synthesis gas production section. EXAMPLE 4:

Another example of possible arrangement is shown in FIG. 4: The synthesis gas is sent to the first reactor R1 via line 100. At the outlet of the reactor R1, the gas phase and the liquid phase are separated in the separator SL1. The gas phase leaving the separator SL1 is cooled in the exchanger C1. This refrigeration leads to the condensation of an aqueous phase and to the evacuation of this condensed phase through line 210, moreover a condensed phase of light hydrocarbons is evacuated through line 211. The resulting gaseous phase is evacuated through line 113 and sent to reactor R2, being mixed at the inlet of reactor R2 with an addition of synthesis gas arriving through line 102. At the outlet of reactor R2, the gas phase and the liquid phase are separated in the separator SL2 . The gas phase leaving the separator SL2 is cooled in the exchanger C2. This refrigeration leads to the condensation of an aqueous phase and to the evacuation of this condensed phase through line 212 and moreover of a condensed phase of light hydrocarbons which is evacuated through line 213. The resulting gaseous phase is evacuated via line 112 and sent to reactor R3, with an addition of synthesis gas arriving through line 106. At the outlet of reactor R3, the gas phase and the liquid phase are separated in the separator SL3. The gas phase leaving the separator SL3 is cooled in the exchanger C3. This refrigeration leads to the condensation of an aqueous phase and to the evacuation of this condensed phase through line 213; in addition, a condensed phase of light hydrocarbons is evacuated via line 214.

The liquid products leaving the separators SL1, SL2 and SL3 via the conduits 200, 201 and 202, containing the catalyst in suspension (catalytic suspensions) are sent as a mixture to the separator SC, in which the liquid products evacuated via the conduit 110 are separated a liquid phase concentrated in catalyst (concentrated catalytic suspension), which is recycled to reactors R1, R2 and R3.

In the diagram in FIG. 4, the separators SL1, SL2 and SL3 are shown as distinct from the reactors R1, R2 and R3. The gaseous phase leaving each reactor could, as an alternative, be separated from the liquid phase containing the catalyst in suspension in the reactor itself, the liquid phase containing the catalyst then being able to be removed under level control. EXAMPLE 5:

This example describes an embodiment allowing the circulation of the catalyst. between the various reactors. Figure 5 shows the corresponding diagram.

Each reactor being strongly mixed, the catalyst introduced at the base of each reactor is distributed homogeneously throughout the liquid phase occupying the reactor. In the embodiment shown diagrammatically in FIG. 5, the unconverted gas fraction disengages at the head of each reactor and the liquid phase containing the catalyst in suspension (catalytic suspension) flows by overflow and circulates towards the base of the following reactor by simple gravity. The transfer lines ensuring the passage from one reactor to the next reactor must be designed so as to present the most regular slope possible. The liquid phase collected at the outlet of the last reactor is at least partially separated from the catalyst that it contains and filtered. It is then discharged through line 110. The catalyst which remains in suspension in a residual liquid phase (concentrated catalytic suspension) is recycled with this liquid phase to the first reactor by the line shown in dotted lines.

Such an embodiment can also be implemented in cases where devices for separation and in particular for disengagement of the gas phase are implemented at the outlet of each of the reactors as is illustrated in examples 2, 3 and 4 .

It is also possible to carry out at the outlet of each of the reactors a separation between the liquid phase produced and a liquid phase concentrated in catalyst which is returned to the reactor. Instead of a single separation device SC, for example in such a case there will be as many separation devices as there are reactors.

FIGS. 6 and 7 present two diagrams of arrangement of reactors with circulation usable in the process according to the invention. These reactors include an internal exchanger, for example made up of preferably tubular cooling bundles. These reactors have a supply and an outlet, the water entering via line 1 and the generated steam leaving via line 2. A charge dispersion system 4 is also arranged inside the reactor. It can be a distributor plate of the gaseous charge (synthesis gas) supplied by line 3. The supply of liquid comprising the catalyst in suspension can optionally be carried out by the same line, the gas / liquid / solid mixture being produced upstream, like this is the case in FIGS. 6 and 7. It is also possible to use separate supplies, only the gas supplying the dispersion system 4. In FIG. 7, the internal recirculation is favored by the design of the reactor.

EXAMPLE 6

FIG. 8 represents another mode of arrangement of reactors according to the invention, with particular circulation of the catalyst: As in Example 3, the installation comprises two (first) reactors R1, R2 operating in parallel with synthesis gas supplied by lines 100 and 102, and a reactor R3 operating in series with R1, R2, using untransformed residual synthesis gas, coming from reactors R1 and R2 via lines 101 and 104. This residual synthesis gas, or the first stage is (advantageously) treated in the unit S1, in order to substantially eliminate the water, and possibly carbon dioxide, before supplying the reactor R3 via line 112. The section S1 can thus correspond to the equipment C1 and S4 of Figure 3, possibly with the addition of the processing section T1 shown in the same figure. The particular arrangement of the installation of FIG. 8, with respect to the installation of FIG. 3 relates to the circulation of the catalyst, that is to say of the catalytic suspension of at least one solid catalyst in a liquid phase typically composed of reaction products. This catalytic suspension circulates at least partly in counter-current between the different reactors, a current of catalytic suspension circulating from the last reactor R3 (last compared to the circulation of synthesis gas), to a first reactor R2 by line 221. Another stream of catalytic suspension flows from reactor R2 to reactor R1 via line 222. A third stream of catalytic suspension flows from reactor R1 to reactor R3, via line 223, the separation section SC, then line 109 in which circulates a (relatively more) concentrated catalytic suspension, a stream of purified liquid having been discharged via line 110.

Alternatively, the reactor R1 is not supplied by a catalytic suspension coming from R2, but by a catalytic suspension coming from R3, flowing in the start of line 221 then in the dotted line 224. the current of In this alternative, the catalytic suspension evacuated from the reactor R2 is sent to the section SC via line 222, then the dotted line 225, then line 223.

In these two configurations, a suspension current flows (directly, that is to say without passing through a separation section) from (or from) the last reactor R3, to a previous or first reactor R1 or R2 (relative to the circulation of synthesis gas), and a relatively concentrated suspension stream, coming from a separation section SC, feeds the or a last reactor R3.

An advantage of these configurations results from the fact that the last reactor R3 operates with a concentration of the catalytic suspension higher than that of the preceding reactors or first reactor (s) R1, R2. In fact, the average concentration (of catalyst) of the catalytic suspension in the reactor R3 is lower than that of the suspension supplying R3 via line 109, due to the production of liquid products in R3. More generally, a catalytic suspension leaving a reactor is less concentrated than the catalytic suspension feeding this same reactor. The advantage of having a relatively more concentrated catalytic suspension in the last reactor is that this makes it possible to compensate for less favorable operating conditions. On the one hand, the reactor R3 being downstream of R1 and R2, operates under a lower pressure than that (s) of R1, R2. On the other hand, the synthesis gas is depleted in reagents (H2 / CO) in the reactors R1, R2, and enriched in inert produced by the reaction, in particular in methane. Consequently, due to these two phenomena, the partial pressure of reactants (H2 / CO) is notably lower in the (or one) last reactor R3 than in a previous or first reactor R1, R2. The use of a relatively higher catalytic concentration in the (or one) last reactor makes it possible to compensate for the influence of this lower partial pressure and to be able to maintain a high conversion in the last step. The mass percentage of catalyst may for example be between 20 and 35% by weight, in particular between 25 and 32% by weight in the first reactors R1, R2. In the reactor R3, the mass percentage of catalyst can be multiplied by a factor K of between 1.03 and 1.25, in particular between 1.06 and 1.20 and for example between 1.08 and 1.18 relative to the (x) percentage (s) of one (or more) of the first reactors R1, R2.

Often, in one or other of the different configurations described in the previous figures, or in other configurations not described but obvious for the person skilled in the art, at least one reactor (R1, R2, or R3) is supplied (typically directly, that is to say without intermediate fractionation of the type of a liquid separation / catalytic suspension) by a stream of catalytic suspension originating from another reactor. In general, an installation for implementing the method according to the invention (according to one of the configurations in the preceding figures or other configurations obvious to the person skilled in the art), at least one reactor is supplied with a current of catalytic suspension coming directly from another reactor, and at least one catalytic suspension stream coming from a reactor is at least partly separated so as to obtain a liquid product substantially free of catalyst and a catalytic suspension enriched in catalyst (concentrated) , which is recycled. Typically, each of the reactors is in communication with at least one other reactor, via a suspension stream sent directly to this other reactor or coming directly from this reactor.

Often, the catalytic suspension enriched in catalyst is recycled to the last reactor (for example R3), so as to enrich the catalytic suspension of this last reactor compared to that (s) of the other reactors, for example of one or more reactors (R1, R2). The method can in particular comprise a first reaction stage carried out in several first reactors operating in parallel, in which the gaseous fractions leaving these first reactors are combined, treated and sent to the inlet of a last reactor. The conversion carried out in the first reactors can be determined so that all the reactors are of identical size. Various modifications, obvious to the person skilled in the art, can be implemented without departing from the scope of the invention: In particular, and by way of nonlimiting examples, the number of "first reactors" or "last (s) reactor ( s) "can be different, for example between 1 and 8. The number of reaction stages can be between 1 and 5. The reactors R1, R2, R3 previously described can be replaced by reaction zones, possibly integrated in a fewer reactors etc. EXAMPLE 7:

This example presents a material balance sheet of an embodiment according to FIG. 4.

Via line 100, a flow rate of 713 t / h of synthesis gas arrives, the molar composition of which is as follows:

Water 0.004

Hydrogen 0.672

CO 0.311

Methane 0.013

The process used comprises 3 reactors R1, R2, R3 substantially perfectly mixed and having the Péclet numbers between 0.02 and 0.03.

The reactor R1 operates at a temperature of 236 ° C. At the outlet of reactor R1, after separation, there is collected via line 200, 66 t / h of liquid products comprising 87% in molar fraction of constituents, the molecule of which comprises at least 10 carbon atoms. After cooling the gas phase, 234 t / h of water (line 210), 67 t / h of condensed hydrocarbons (line 211) and 347 t / h of synthesis gas are recovered at a pressure of 2.8 MPa. , which is sent to reactor R2 via line 113 while being mixed with 327 t / h of synthesis gas arriving through line 102.

At the outlet of reactor R2, after separation, 63 t / h of liquid products are collected via line 101. After the gaseous phase has cooled down, the pipe 212, 224 t / h of water is recovered, the pipe 213 76t / h of condensate and the pipe 112, 311 t / h of synthesis gas, which is sent to the reactor R3 by being mixed with 293 t / h of synthesis gas arriving via line 106.

At the outlet of reactor R3, liquid product is collected via line 202, 58 t / h. After cooling the gas phase, 205 t / h of water, 75 t / h of condensate and 266 t / h of synthesis gas are recovered.

The overall conversion yield reaches 91%.

It is possible to carry out this example with reactors of different sizes. It is also possible to use reactors of identical size, by adapting the temperatures and conversions to liquid products used for the reactors R1, R2, R3, associated with the distribution of the synthesis gas. Adaptation of the conditions for increasing the relative size of a given reactor allowing these conditions to be obtained, can be achieved by increasing the relative flow rate of synthesis gas at the inlet of this reactor, and / or by increasing the conversion in this reactor, and / or by reducing the temperature of this reactor. Preferably, only the first two parameters are used, the temperature of the three reactors remaining substantially identical. In the previous example, the conditions cited can be obtained with reactors of identical size, operating at similar pressures (differing only in pressure losses), and maintained at the same temperature of 236 ° C.

Claims

1. Method for converting a synthesis gas into liquid hydrocarbons used in at least two reactors in series containing a catalytic suspension of at least one solid catalyst suspended in a liquid phase, in which said reactors are substantially perfectly mixed , the last reactor is at least partly supplied by at least part of at least one of the gaseous fractions collected at the outlet of at least one of the other reactors, at least one reactor is supplied by a stream of catalytic suspension coming directly from another reactor, and at least one stream of catalytic suspension coming from a reactor is at least partly separated so as to obtain a liquid product substantially free of catalyst and a catalytic suspension enriched in catalyst, which is recycled.

2. Method according to claim 1, in which each of the reactors is in communication with at least one other reactor, by means of a suspension stream sent directly to this other reactor or coming directly from this reactor.

3. Method according to one of claims 1 or 2 wherein said catalytic suspension enriched in catalyst, is recycled to the last reactor (R3), so as to enrich the catalytic suspension of this last reactor compared to that (s) of the others reactors, for example one or more reactors (R1, R2).

4. Method according to one of claims 1 to 5, comprising a first reaction step carried out in several first reactors operating in parallel, in which the gaseous fractions leaving these first reactors are combined, treated and sent to the entry of a last reactor.

5. Method according to claim 4, in which the conversion carried out in the first reactors is determined so that all the reactors are of identical size.

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6. Method according to one of claims 1 or 2 wherein the number of liquid Péclet is less than 8.

7. Method according to one of claims 1 to 3 wherein the number of gas Péclet is less than 0.2.

8. Method according to one of claims 1 to 3 wherein the number of gas Péclet is less than 0.1.

9. Method according to one of claims 1 to 5 wherein at the outlet of each reactor the gas phase is separated from the liquid phase containing the catalyst in suspension.

10. Method according to one of claims 1 to 9, wherein the catalyst is formed of a porous mineral support and at least one metal deposited on this support, the catalyst being suspended in the liquid phase in the form of particles with a diameter of less than 200 microns.

11. Method according to one of claims 1 to 10, wherein the distribution of the introduction of synthesis gas at the inlet of the reactors in series is determined so as to allow the use of reactors of identical size.

12. Method according to one of claims 1 to 11, wherein the gaseous fraction leaving the last reactor is recycled to a stage of production of synthesis gas for the supply of said reactors.