NO330368B1 - Process and apparatus for separating liquid products from a suspension containing a solid, in the presence of a diluent - Google Patents

Description

The present invention relates to an apparatus and a method for separating a liquid phase from a suspension containing a solid, for example a catalyst for chemical conversion. The solids and especially the catalysts used in a process for chemical conversion (these are referred to below as catalysts for chemical conversion) can work in a multiphase reactor (slurry reactor) where the catalyst is in suspension in a liquid phase, where the suspension is also called "slurry".

This liquid phase contains in particular a liquid which is also referred to as slurry solvent which allows the solid to be brought into suspension, as well as at least a fraction of the products arising from the reaction. The multiphase reactor most often consists of a reactor that works with an entrainment layer or also a bubble column ("bubble column reactor") according to English terminology.

The present invention relates more particularly, but not exclusively, to methods for chemical conversion which are most often exothermic, but sometimes endothermic, and are used in multiphase reactors, i.e. reactors containing at least two phases: a liquid phase and a solid phase, but preferably the invention involves three -phase reactors containing a suspension of solid particles in a liquid and where at least one gas, optionally reactive gas, is used to form at least one conversion product which is at least partially liquid under the chosen working conditions.

The present invention relates more particularly to exothermic reactions which produce a high temperature for example above lOCC and often above 130°C, generally under an absolute pressure above 0.1 megapascal (MPa) and often above 0.5 MPa.

STATE OF THE ART

Among the exothermic reactions can be mentioned dehydrogenations, hydrogenations, transhydrogenations, aromatizations, hydrodenitrogenations, hydrotreatments in particular hydrotreatments of residues, hydroformylation, alcohol synthesis, synthesis of polyolefins, isomerizations, oligomerizations, and especially dimerizations (such as the so-called "dimersol" processes), oxidations, hydrodesulphurisations and aliphatic or aromatic alkylations. These reactions are described, for example, in the book J. F. LePage, published by Technipforlag in 1987 under the title "Applied Heterogeneous Catalysis" and in Ullmann's Encyclopeadia of Industrial Chemistry (volume B4, 5th edition, pages 105-106) which are cited as references and where the descriptions shall be considered as actually included in the present description.

The reactors for chemical conversion that are used can be of several types, with the solid being used either in the form of an entrained layer, or in a reactor of the bubble column type ("bubble column reactor" or "slurry bubble column reactor" according to English nomenclature) where the gas is brought in contact with a mixture of liquid/very finely divided solid (or the mixture is called "slurry" according to English nomenclature). The term "slurry" shall be used in the following description to denote a suspension of solid particles in a liquid. The reaction heat is usually removed using a heat exchanger (cooler), usually in the interior of the reactor.

Within the scope of the present invention, the apparatus usually comprises a bubble column. The bubble columns comprise a liquid environment containing a suspension of solid particles, usually where the main amount is catalytic particles and where the apparatus comprises at least one means for introducing at least one gas phase comprising at least one reactive gas, by means of at least one means for distribution which produces gas bubbles with usually a relatively small diameter. The gas bubbles rise up the column and at least one reactive gas is absorbed by the liquid and diffuses towards the solid. When the solid is a catalyst, the reactive gases are converted by their contact into gaseous and/or liquid and/or solid products depending on the conditions of the conversion and the type of catalyst.

The gaseous products possibly comprise at least one reactive gas which has not been converted and the gaseous products which are possibly formed during the reaction are collected near the top of the column. The suspension containing the liquid serves to form the suspension of solids and the liquid products formed by the conversion are recovered by means of an outlet line generally located at a height near the top height of the suspension in the column.

The solid particles are then separated from the liquid by any known means known to those skilled in the art, for example by filtration. For the description of the operation of a bubble column, reference is made, for example, to the patent document EP-A-0 820 806 indicated as a reference and where the description is considered to be actually included in the present description.

The apparatus according to the invention otherwise comprises means for separation, means for the production of, on the one hand, a liquid fraction and, on the other hand, optionally gaseous residual products or gaseous products formed as by-products during the conversion and which optionally include inert gases, light gaseous compounds and the fraction of the reactive gas that has not reacted.

The apparatus for chemical conversion otherwise comprises means for the separation of, on the one hand, liquid hydrocarbons and, on the other hand, possibly gaseous residual products comprising inert gases, light gaseous hydrocarbons, water which may have been formed during the reaction, and possibly part of the gas which has not reacted .

These products must be separated almost completely from the solids, for example until the residual content of solids is lower than a few tens of parts per million, and even roughly from 1 to a few parts per million (ppm) in order to be used or processed in the final steps.

This separation of the products is difficult, complicated and expensive due to the working conditions (high pressures and temperatures) and the often very large amounts of fine solids present in the products, of micrometer or submicrometer size.

This difficulty is further enhanced in the case where a reactor works in the presence of gas and a suspension (slurry), such as a reactor of the bubble column type, due to the very high concentration of fine solid particles in the suspension.

Typically, it is actually possible for a suspension (slurry) to have a quantity of solid particles which generally make up 10 to 65% by weight in relation to the weight of the suspension. These particles usually have an average diameter of less than 100 micrometres and contain quite large amounts of very fine or ultra-fine particles with a size of less than 10 micrometres, even sub-micrometre size.

Several technical means are known which allow the liquid/solid separation to be carried out: either in the reactor, or in a slurry loop outside the reactor.

However, these technical means prove to be very difficult to use and require large investments as it involves separating very concentrated suspensions, containing up to 20 or 30% by weight or even more solid matter.

Thus, patent document US-A-5 527 473 describes a process which allows reactions to be carried out in a liquid-solid slurry under which a gas passes continuously in an ascending direction and which works at high temperature and high pressure. The filtering elements have openings of between 0.5 and 100 micrometers and are arranged in the reactor and are surrounded by the slurry suspension. They allow maintaining the solid matter in the reactor while extracting the formed liquid.

The patent application EP-A-0 609 079 describes a process and an apparatus of the aforementioned slurry type for producing a liquid and possibly gas from gaseous reaction components. This apparatus comprises a means of filtration included in the reactor. These filters can be washed or de-sludged after interruption of the filtration, using a fluid that circulates in the opposite direction (backwash type system).

The patent US-A-5 770 629 describes a process of hydrocarbon synthesis in slurry in which the slurry is sent into a zone for separation of gas and solids and which is located in the reactor, and is then sent to a zone for separation and filtration located outside the reactor. A means of filtration is arranged in contact with the slurry in this external separation zone. This separation zone allows to remove part of the gas and the solid in the suspension before filtration, and to increase the efficiency of the filters in particular while avoiding their clogging with sludge.

The patent application WO-A-97/31693 shows a method for the separation of a liquid from a liquid/gas/solid slurry. This method involves degassing the suspension and passing it through a filter with cross-flow flow (English term "cross-flow filter") placed outside the reactor and which allows extraction of liquid and a slurry with a higher solids concentration.

WO-A-98/27181 describes an apparatus for separating catalyst particles from paraffins (waxes) formed during the reaction. The device includes a dynamic decanter and does not need a pump.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to an apparatus for separating liquid products from a suspension containing a solid in a multiphase reactor of the bubble column type. The device includes

• at least one means (4) for extracting part of a suspension containing said solid; • means for condensing compounds entrained in the gaseous effluent from the reactor; • at least one agent (27) connected to said agents for condensation for adding a diluent to all or part of the suspension extracted via the agent or agents (4), this diluent is made up of the condensed compounds; • at least one means (29) for primary separation equipped with at least one means (28) for sending all or part of the diluted suspension towards said means for separation, further at least one means (33) for recovering the separated liquid, and at least one means (30) for extracting a more concentrated suspension; • at least one secondary separation means (34) to separate and then via at least one means (36) to recover a substantially purified liquid; • at least one means (6) for separating out gas contained in the suspension which is extracted from the reactor by means of the means (4); • means for recycling the more concentrated suspension to the reactor. The invention also relates to a method for separating liquid products from a suspension containing a solid.

The procedure includes at least the following steps:

a1) extraction from a type chemical conversion reactor bubble column, which works with at least one solid in suspension in a liquid phase, of a part of the suspension containing said solid.

a2) degassing of the suspension extracted in step a1).

b) mixing the suspension taken out in step a2) with another hydrocarbon fraction called a diluent, this diluent is made up of the condensed compounds obtained from the following step f);

c) primary separation of at least part of the suspension diluted in step b) using at least one separation method, to produce a liquid with a solids content below 5% by weight, and a more concentrated suspension; d) secondary separation of the liquid obtained in step c) from the residual solid which this liquid contains, by means of at least one separation method; e) recycling in said reactor the more concentrated suspension; f) condensation of the compounds entrained in the gaseous state

the effluent from said reactor.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention relates to an apparatus and a method for separating a suspension of the slurry type containing a solid, the suspension coming from a multiphase reactor for chemical conversion. The apparatus and method are reliable, more efficient and represent a better investment than previously known apparatus or processes.

The present invention is particularly suitable for reactors for chemical conversion which allow carrying out a reaction selected from the group consisting of hydrogenations, aromatizations, hydrodenitrogenations, hydrotreatments and in particular hydrotreatments of residues, hydroformylation, alcohol synthesis, synthesis of polyolefins, oligomerizations and especially dimerizations (such as for example the known "dimersol" processes), oxidations, hydrodesulfurizations and aliphatic or aromatic alkylations.

The present invention is well suited for chemical conversion reactors which allow to carry out a reaction selected from the group consisting of reactions with hydrogenation or reduction of chemical compounds such as hydrogenation of carbon monoxide, hydrogenation of carbon, hydrogenation of pitch or tar, hydrogenation of aromatic compounds and in particular of benzene, hydrogenation of various organic starting compounds and in particular nitrobenzenes, nitriles, nitronaphthalenes, oxidation reactions and in particular oxidation of xylenes and for example production of terephthalic acid by oxidation of para-xylene, aliphatic or aromatic alkylation reactions.

The method and apparatus according to the invention are thus, for example, particularly well suited to the aliphatic alkylation processes which are, for example, described in patent document FR-A-2 694 932.

The pressures used are generally from about 1 to about 300 bar absolute, often from about 5 to about 80 bar absolute and more often from about 10 to about 60 bar absolute (10 bar = 1 MPa), and the conversion temperatures are usually from about 20 to about 450oC, often from about 130<*>0 to about 350°C and most often from about 150 to about 300°C.

The method and apparatus according to the invention are particularly suitable for use in association with a slurry-type reactor (i.e. in which a solid substance is brought into suspension in a liquid phase), for example a reactor of the bubble column type ("slurry bubble column" in English terminology) ). The invention can likewise be used with a reactor that works with an entrained layer.

Such a bubble column is described, for example, in patent document US-A-5 252 613 as well as in patent applications EP-A-0 820 806 and EP-A-0 823 470.

Any type of solid can be used in the method and apparatus according to the invention. The solids that are particularly suitable for the method according to the invention are comprised of the group consisting of inert solids, solids that allow the calorimetric amount of heat from the reaction to be absorbed or released, further adsorbing agents, masses for capture and solid catalysts.

The reactor for chemical conversion can optionally be completed with equipment that allows the adsorption or capture of liquid or gaseous molecules, such as the capture of mercury in the liquid phase, for example.

The method according to the invention comprises several steps, and in particular at least the following steps: a1) extraction from a reactor for chemical conversion, which works with at least one solid in suspension in a liquid phase, of a part of the suspension containing said solid; a2) possible degassing of the suspension extracted in step a1); b) mixing the suspension extracted in step a1) or which is degassed in step a2) with at least one other hydrocarbon fraction called a diluent; c) primary separation of at least part of the suspension diluted in step b) by means of at least one separation method preferably selected from the group consisting of: filtration, decantation, hydrocyclone separation, and centrifugal separation, to produce a liquid with a solids content below 5 wt. %, preferably below 2% by weight, and more preferably below 1% by weight and most preferably below 0.5% by weight, and d) secondary separation of the liquid obtained from step c) and the main amount of residual solids that the liquid contains by means of at least one separation method, preferably selected from the group consisting of: filtration, centrifugal separation and magnetic separation. This step allows obtaining a liquid which is essentially free of solid matter or which contains only traces of this solid matter, either a few tens of ppm, or even just a few ppm or of the order of 1 ppm (parts per million by weight).

More preferably, the separation method in step c) is a decantation or a filtration and most preferably a decantation.

More preferably, the separation method in step d) is a filtration or a magnetic separation and most preferably a filtration.

The diluent used in step b) consists of any fraction of hydrocarbons with a low or medium boiling point. One uses, for example, a C3 fraction, or a C4 fraction or also a C4-C5 fraction, i.e. a fraction containing respectively hydrocarbons with 3 carbon atoms, 4 carbon atoms or 4 to 5 carbon atoms, or also a fraction selected from the group consisting of naphthas, kerosenes, gas oils or mixtures of naphthas with at least one kerosene or a gas oil.

Preferably, the diluent used in step b) is a fraction with large hydrocarbons. In a preferred variant of the method according to the invention, a fraction of large hydrocarbons where the largest part is made up of the group with C3 to C22 hydrocarbons (ie hydrocarbons with 3 to 22 carbon atoms) is used as diluent.

Such fractions can actually be easily produced from fractions within the petroleum industry or effluents therefrom. At least 80% by weight and more preferably at least 90% by weight of the hydrocarbons in the fraction used as diluent are C3 to C22 hydrocarbons. More preferably, the fractionation is carried out mainly by paraffins. The mentioned fraction very preferably contains at least 60% by weight of paraffins and even more preferably at least 70% by weight of paraffins.

For example, a fraction containing compounds entrained by the vapor pressure in the gaseous effluent from a reactor can be easily condensed. This fraction constitutes an effective diluent for the method according to the invention. During this condensation, the entrained water is also condensed in the form of steam, but the aqueous phase and the organic phase containing the hydrocarbons can be easily separated, for example by extraction at different levels. Such a diluent can also be obtained without fractionation of the products from the synthesis reaction.

This fraction, obtained by simple condensation of the gaseous effluents, can advantageously be reheated and stabilized by removing highly volatile compounds, before it is mixed into the suspension to be separated. The mixture of suspension extracted in step a1) with this diluent allows obtaining a diluted suspension with a reduced viscosity and concentration of solids, and which is then easier to handle. Otherwise, it unexpectedly turns out that application of the method according to the invention allows a particular improvement in the efficiency of the separation of liquid products contained in the suspension.

The solid or the concentrated suspension recovered in steps c) and d) can be sent to the reactor, optionally after dilution or to be resuspended in a hydrocarbon fraction. However, when the obtained solid has a very low granulometry (particle size), the solid is not reintroduced into the reactor.

In general, the amount of diluent that can be used in the method according to the invention is not limited. Preferably, an amount of diluent is used which represents at least approximately 5% by volume, even approximately 10% by volume in relation to the volume of suspension extracted in step a1). More preferably, the suspension is mixed with a volume of diluent which represents between 20 and 300% by volume in relation to the volume of the suspension extracted in step a1).

Any apparatus for separation known to the expert in the field can be used in steps c) and d) of the method according to the invention.

Among these means can be mentioned, among others:

• filtration, frontal or tangential, on filter media such as sintered or fibrous or woven porous materials of metallic, ceramic or polymeric type; • decanting; • centrifugal separation using hydrocyclones or centrifuges;

• magnetic separation.

Among the means for separation that can be used in the method according to the invention can be mentioned, for example, means for separation such as dynamic decanters or filtration systems with cross-flow flow manufactured in particular by Société MOTT or filtration systems comprising a mesh structure ("wire mesh type" according to English terminology) which for for example those manufactured by PALL FILTER Corp., or also filtration systems described in the Kirk-Othmer Encyclopedia of Chemical Technology (Kirk-Othmer Encyclopedia of Chemical Technology, 1993, volume 10, pages 841-847).

It is also possible to use hydrocyclones described in the encyclopedia Ullmann (Ullmann's Encyclopedia of Industrial Chemistry, 1988, 5th edition, volume B2, pages 11-19 to 11-23).

The apparatus according to the invention is an apparatus for separating liquid products from a suspension containing at least one solid substance used in a process for chemical conversion or adsorption or capture. The apparatus comprises in its more general form: • at least one means (4) which allows the extraction from a multiphase reactor of a part of a suspension containing the said solid; • at least one means (27) which allows extraction of a diluent from all or part of the suspension extracted via the means or means (4); • at least one means (29) for primary separation equipped with at least one means (28) that allows sending all or part of the diluted suspension towards said means or means for separation, further equipped with at least one means (33) that allows recovery of the separated liquid, and at least one means (30) allowing recovery of a more concentrated suspension;

at least one means (34) for secondary separation which allows to separate and then via at least one means (36) to recover a substantially purified liquid, i.e. essentially free of solids or containing only traces of said solids.

In a particular embodiment, the apparatus according to the invention further comprises at least one means (6) for separating the gas contained in the suspension which has been removed from the reactor by means of the means or means (4).

The said means are preferably placed between the reactor (2) and the means or means (29) for primary separation.

In this particular form of the apparatus, the separated gas is preferably recovered via at least one means (5) and the liquid which is extracted from the column and the degassed is preferably recovered via at least one means (7) and is then preferably sent towards the means or means (29) for primary separation, preferably via at least one agent (28) and preferably after diluent has been added via the agent (27).

In a further preferred variant of this form of the apparatus according to the invention, this comprises two special means which allow sending the suspension extracted from the reactor by means of the means (4) towards the means or means (29) for primary separation, namely: • A line (9) which opens into the line (28) after the diluent has been added via the line (27),

• A line (8) in which no diluent is added.

This variant allows only a diluent to be added to part of the liquid that is withdrawn from the reactor.

It is likewise possible, without going beyond the scope of this invention, to use the preceding preferred variant for degassing the liquid withdrawn from the reactor, using, for example, a degassing tank or any other means known to the person skilled in the art .

In a more preferred variant, the apparatus according to the invention further comprises a pump (31) which allows sending the concentrated suspension from the agent (29) for primary separation back to the reactor (2).

An example of a variant of the device according to the invention is shown in the figure.

The supply is introduced via the line (1) into the reactor (2) of the bubble column type ("slurry bubble column" in English terminology), partially filled by means of a hydrocarbon fraction in which a solid substance has been brought into suspension (slurry).

This part of the apparatus constitutes an example of a reaction zone where it is possible to adapt the separation device according to the invention. Any other reaction zone known to the person skilled in the art, such as a bubble column described in the patent applications EP-A-820 806 and EP A-823 470 or the patent document US-A-5 252 613 can easily replace the reaction zone shown in figure 1 , using certain adaptations within the professional knowledge of the specialist in the area.

The gas that is formed or that has not reacted during the reaction is separated in the separation zone located below the liquid level in the reactor (2) and is then extracted from the reactor through the line (3). A fraction of the suspension is led via line (4) to a degassing tank (6) to separate the gas sent via line (5) into line (3) on the one hand and the degassed suspension sent to the decanter ( 29) via the wire (7).

It is then possible to add a diluent to all or part of the degassed suspension. The line (7) can thus be divided into two lines (8) and (9), as only the liquid that arrives via the line (9) and which is then diluted with a hydrocarbon fraction arrives via the line (27) before it enters the decanter (29) via the wire (28). The suspension arriving via the line (8) is introduced directly into the decanter (without dilution) at a level which is preferably lower than the introduction level (28) for the diluted suspension.

However, it is possible to send the entire degassed suspension from the line (7) by means of the line (9) so that the degassed suspension is completely diluted before it enters the decanter.

The non-condensed gas that is extracted from the reactor via the lines (3) and (5) is mixed with each other and is then fed via the line (10) into a cooler (11) which allows the temperature to be reduced. Via the line (12), the cooled mixture is introduced into a separation tank (13) which allows extraction of the gas in the line (16), possibly an aqueous phase containing mainly water via the line (14) and an organic phase containing liquid hydrocarbons via the line (15) .

The non-condensed gas can optionally be further introduced into a cooler (17) for cooling and then via the line (18) into a further separation step (19) which optionally again allows the recovery of an aqueous phase at (20) and a liquid hydrocarbon-containing phase at (21). The latter, when available, can be combined with the liquid recovered via the line (15) and then sent together through the line (22) towards the reheating boiler (23) to reheat the mixture preferably to the reaction temperature, and then via the line (24) to a separator ( 25). This separation allows obtaining a gas (26) and a stabilized liquid which serves as a diluent and which is sent towards all or part of the suspension via the line (27).

The decantation in the decanter (29) of the undiluted suspension from the line (8) and of the diluted suspension supplied from the line (28) provides a more concentrated suspension in the line (30) and which is recycled towards the reactor (2) via the line ( 30), using the pump (31) and the line (32). At the top of the decanter (29) a liquid (33) is obtained which contains a small amount of solid matter which is easily separated using a separation method known to the person skilled in the field (for example filtration, centrifugation, magnetic separation) in the separator (34). A liquid which is essentially free of solid matter and which only contains traces of this, either a few tens of ppm, even just a few ppm or of the order of 1 ppm, is obtained continuously from the line (36). The solid is taken out through the outlet (35) either continuously or discontinuously, depending on the separation method used.

A further preferred device according to the invention consists, for example, in replacing the decanter (29) either with a filtering device or centrifugal separation device, or with a hydrocyclone.

Briefly, the apparatus according to the invention is then adapted to the separation of liquid products from a suspension, used in a chemical conversion process or adsorption or capture process, and which contains a solid substance. This device includes in its more general form:

• At least one means (4) which allows extraction from a multiphase reactor of part of a suspension containing a solid, • At least one means (27) which allows the addition of a diluent to all or part of the suspension extracted via the means or means 4, • At least one means (29) for primary separation equipped with at least one means (28) that allows sending all or part of the diluted suspension towards the means or means for separation, further at least one means (33) that allows recovery of the separated liquid, and at least one means (30) which allows

extraction of a more concentrated suspension,

• At least one means (34) for secondary separation which allows to separate and then recover a substantially purified liquid via at least one means (36).

The apparatus according to the invention may optionally additionally comprise at least one means (6) for separating the gas contained in the suspension which is extracted from the reactor by means of the means (4). The means for separation (6) is preferably placed between the reactor (2) and the means (29) for primary separation.

In a variant, the apparatus according to the invention may optionally include two means which allow sending the suspension which is extracted from the reactor by means of the device (4) towards the device (29) for primary separation in the form of: • A line (9) which opens into line (28) before the diluent is added via line (27),

• A line (8) in which no diluent is added.

Preferably, the apparatus further comprises a pump (31) which allows sending the concentrated suspension coming out of the device (29) for primary separation to the reactor (2).

The invention also relates to a method for separation. Briefly, the method relates to the separation of liquid products from a suspension containing a solid, the method comprising at least the following steps: extraction from a reactor for chemical conversion of the bubble column type, which working with at least one solid in suspension in a liquid phase, of a part of the suspension containing said solid.

a2) degassing of the suspension extracted in step a1).

b) mixing the suspension taken out in step a2) with another hydrocarbon fraction called a diluent, this

diluent is made up of the condensed compounds obtained from the subsequent step f);

c) primary separation of at least part of the suspension diluted in step b) using at least one separation method, to produce a liquid with a solids content below 5% by weight, and a more concentrated suspension; d) secondary separation of the liquid obtained in step c) from the residual solid which this liquid contains, by means of at least one separation method; e) recycling in said reactor the more concentrated suspension; f) condensation of the compounds entrained in the gaseous state

the effluent from said reactor.

Preferably, the diluent used in the method according to the invention is a C3 fraction or a C4 fraction or also a C4-C5 fraction. More preferably, at least 80% by weight of the hydrocarbons in the fraction used as diluent are C3-C22 hydrocarbons.

In a very preferred variant of the method according to the invention, the diluent is made up of a fraction comprising compounds entrained by the vapor pressure in the gaseous effluent from the reactor and which are then condensed. After the condensation, the aforementioned fraction can be reheated and stabilized by removing highly volatile compounds.

In a further variant of the method according to the invention, the suspension can be divided into two fractions where only one fraction is mixed with the diluent.

Claims (15)

1. Apparatus for separating liquid products from a suspension containing a solid in a multiphase reactor of the bubble column type, characterized in that: • at least one means (4) for extracting part of a suspension containing said solid; • means for condensing compounds entrained in the gaseous effluent from the reactor; • at least one agent (27) connected to said agents for condensation for adding a diluent to all or part of the suspension extracted via the agent or agents (4), this diluent is made up of the condensed compounds; • at least one means (29) for primary separation equipped with at least one means (28) for sending all or part of the diluted suspension towards said means for separation, further at least one means (33) for recovering the separated liquid, and at least one means (30) for extracting a more concentrated suspension; • at least one secondary separation means (34) to separate and then via at least one means (36) to recover a substantially purified liquid; • at least one means (6) for separating out gas contained in the suspension which is extracted from the reactor by means of the means (4); • means for recycling the more concentrated suspension to the reactor. 2. Apparatus according to claim 1, characterized in that the said agent is placed between the reactor (2) and the agent (29) for primary separation. 3. Apparatus according to claim 1, characterized in that it comprises two means which allow sending the suspension coming out of the reactor through the means (4) towards the means (29) for primary separation, comprising: • a line (9) which opens into the line (28) before the point of addition of diluent via line (27), • a line (8) in which no diluent is added. 4. Apparatus according to claim 1, characterized in that it additionally comprises a pump (31) which allows sending the concentrated suspension coming out of the means (29) for primary separation towards the reactor (2). 5. Process for separating liquid products from a suspension containing a solid substance, characterized in that it comprises at least the following steps: a1) extraction from a reactor for chemical conversion of the type bubble column, which works with at least one solid in suspension in a liquid phase, of a part of the suspension containing said solid. a2) degassing of the suspension extracted in step a1). g) mixing the suspension taken out in step a2) with another hydrocarbon fraction called a diluent, this diluent is made up of the condensed compounds obtained from the following step f); h) primary separation of at least part of the suspension diluted in step b) using at least one separation method, to produce a liquid with a solids content below 5% by weight, and a more concentrated suspension; i) secondary separation of the liquid obtained in step c) from the residual solid which this liquid contains, by means of at least one separation method; j) recycling in said reactor the more concentrated suspension; k) condensation of the compounds entrained in the gaseous effluent from said reactor. 6. Method according to claim 5, characterized in that the diluent is a C3 fraction or a C4 fraction or also a C4-C5 fraction. 7. Method as stated in claim 5 or 6, characterized in that the fraction used as diluent is a fraction selected from the group consisting of: naphthas, kerosenes, gas oils or mixtures of naphthas with at least one kerosene or a gas oil. 8. Method according to any one of claims 5 to 7, characterized in that the diluent consists of a fraction comprising compounds entrained by the vapor pressure in the gaseous effluent from the reactor and which is then condensed. 9. Method according to claim 8, characterized in that after condensation the said fraction is reheated and stabilized by removing highly volatile compounds. 10. Method according to any one of claims 6 to 9, characterized in that the primary separation in step c) is selected from the group consisting of: filtration, decantation, hydrocyclone separation and centrifugal separation. 11. Method according to any one of claims 5 to 10, characterized in that the secondary separation method in step d) is selected from the group consisting of filtration, centrifugal separation or magnetic separation. 12. The method according to any one of claims 5 to 11, characterized in that the suspension is divided into two fractions, one of which is mixed with the diluent. 13. Method according to any one of claims 5 to 12, characterized in that the solid is a catalyst for chemical conversion. 14. Method according to any one of claims 5 to 13, characterized in that the reactor for chemical conversion allows carrying out a reaction selected from the group consisting of hydrogenation, aromatization, hydrodenitrogenizations, hydrotreatments and in particular hydrotreatments of residues, hydroformylation, alcohol synthesis, synthesis of polyolefins , oligomerizations and especially dimerizations, oxidations, hydrodesulfurizations and aliphatic or aromatic alkylations. 15. Method according to any one of claims 5 to 14, characterized in that the reactor for the chemical conversion is completed with an equipment that allows adsorption or capture of liquid or gaseous molecules to be carried out.