EP1289937A1

EP1289937A1 - Method for separating a hydroxybenzonitrile-type compound

Info

Publication number: EP1289937A1
Application number: EP01945416A
Authority: EP
Inventors: Jean-Francis Spindler; Roland Jacquot; Michel Alas
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 2000-06-14
Filing date: 2001-06-13
Publication date: 2003-03-12
Also published as: FR2810317B1; US20060149093A1; FR2810317A1; WO2001096284A1; AU2001267641A1; JP2004503524A

Abstract

The invention concerns a method for separating a hydroxybenzonitrile-type compound obtained by an amination/dehydration process. More particularly, the invention concerns 2-hydroxybenzonitrile, also called 2-cyanophenol. The inventive method for separating a hydroxybenzonitrile compound from a reaction gas flow comprising it wholly or partly in the form of an ammonium salt is characterised in that it consists in displacing the ammonium ions, through a physical treatment carried out on the reaction gas flow derived from its preparation or from the solid previously recuperated from said flow or according to a chemical treatment carried out on the reaction gas flow, after liquefaction.

Description

PROCESS FOR SEPARATING A HYDROXYBENZONITRILE COMPOUND.

The subject of the present invention is a process for the separation of a hydroxybenzonitrile type compound obtained according to an amination / dehydration process. It relates more particularly to 2-hydroxybenzonitrile, also called 2-cyanophenol.

The invention also relates to a process for the separation and purification of a compound of hydroxybenzonitrile type contained in a gaseous reaction flow.

Hydroxybenzonitriles are products of great industrial interest because they are used as colorants and as intermediates in the preparation of active materials such as herbicides, fungicides, insecticides.

One of the access routes to hydroxybenzonitriles consists in carrying out the amination of an alkyl hydroxybenzoate followed by a dehydration reaction. Thus, it is described according to DE 2,020,866 more particularly a process for the preparation of 4-hydroxybenzonitrile, in the gas phase, by reaction of ammonia and of the methyl ester of 4-hydroxybenzoic acid, in the presence of a catalyst which is phosphoric acid deposited on a support such as silica gel. A process of the same type is described in FR 2 332 261 and CA 2 177939, except that the catalyst is respectively boron phosphate or boron phosphate doped with a transition metal from the group Va, Via, llb, lllb, of the periodic classification of the elements published in the Bulletin of the Chemical Society of France, n ° 1 (1966). The problem which arises when it is desired to separate the hydroxybenzonitrile type compound obtained according to this type of process which consists in reacting in the gas phase in particular methyl 2-hydroxybenzoate and ammonia, in the presence of a dehydration catalyst is that we are faced with a difficulty resulting from the fact that the product obtained solidifies as soon as it condenses, which implies difficult isolation.

Other difficulties lie in the formation of by-products due to two types of side reactions. Thus, the product obtained is trimerized into S-triazine all the more quickly the higher the temperature of the reaction medium. Thus, it has been found that from 140 ° C., the trimerization was immediate and that it was due to an auto catalytic phenomenon. Another type of secondary reaction which occurs is the hydrolysis of 2-hydroxybenzonitrile obtained into 2-hydroxybenzamide due to the water released during the preparation of 2-hydroxybenzonitrile, reaction accentuated by the presence of ammonia.

There is a real industrial problem of obtaining 2-hydroxybenzonitrile from the reaction gas stream comprising it.

It has now been found, and this is what constitutes the object of the present invention, a process for the separation of a hydroxybenzonitrile type compound from a gaseous reaction stream comprising it in whole or in part in the form of an ammonium salt characterized in that it consists, in order to obtain a hydroxybenzonitrile type compound, of displacing the ammonium ions:

- according to a physical treatment carried out on the reaction gas flow resulting from its preparation or according to a physical treatment of the solid recovered beforehand from the reaction gas flow after liquefaction or on this same solid put in solution,

- Or according to a chemical treatment carried out on the reaction gas flow after liquefaction.

In the following description of the present invention, the term “hydroxybenzonitrile type compound” means an aromatic compound carrying at least one hydroxyl group and one nitrile group and / or the hydrated form of said compound, that is to say the nitrile group is replaced by all or part by an amido group.

According to a first embodiment of the present invention, the displacement of the ammonium ions takes place by a physical treatment and more precisely by a heat treatment.

According to a second embodiment of the invention, the displacement of the ammonium ions takes place according to a chemical treatment and more precisely according to an acid treatment. It has been found that the hydroxybenzonitrile compound is present in the reaction gas stream in a form in which the OH group is salified, that is to say it is in the form of an ammonium salt and that the content of Free OH represented less than 10% by mol, preferably less than 5%. In order to separate the hydroxybenzonitrile compound, it has been found that a displacement of the ammonium ions is necessary.

At the end of the vapor phase reaction for preparing the hydroxybenzonitrile type compound according to an amination / dehydration process of an alkyl hydroxybenzoate type compound, the gas reaction flow is at an elevated temperature generally above 200 ° C. preferably between 200 ° C and 600 ° C, and even more preferably between 350 ° C and 450 ° C

In accordance with the process of the invention, it has been found that it is possible to obtain a compound of the benzonitrile type with a free OH group, by heat treatment of the salified compound without there being any development of side reactions such as trimerization and hydrolysis of the nitrile group.

A first variant of the process of the invention consists in thermally treating the gas flow comprising it.

A second variant of the process of the invention consists in liquefying the reaction gas stream, then in recovering in solid form, the compound of the hydroxybenzonitrile type salified from said stream then in heat treating the solid product obtained either directly or after dissolving .

Another variant of the process of the invention consists in liquefying the gaseous reaction flow, then in treating it with an acid thus leading to the production of a compound of the 2-hydroxybenzonitrile type then in recovering it in an organic phase which is separated .

The method of the invention is applicable to any aromatic compound comprising at least one aromatic ring of 6 carbon atoms and carrying at least one nitrile group and a whole or part OH group, salified.

The invention relates to benzene, naphthalene rings or a chain of benzene rings separated by a valence bond, an alkyl or alkylidene group having from 1 to 4 carbon atoms, an atom (for example, oxygen or a functional group (for example CO The invention relates more particularly to compounds which can be symbolized by the following formula:

in said formula, R symbolizes one or more substituents.

The hydroxybenzonitrile of formula (I) can carry one or more substituents insofar as it does not interfere with the process of the invention. The number of substituents present on the cycle depends on the carbon condensation of the cycle and on the presence or not of unsaturations on the cycle.

The maximum number of substituents likely to be carried by a cycle, is easily determined by a person skilled in the art. In the present text, the term "several" is generally understood to mean less than 4 substituents on an aromatic ring.

Examples of substituents are given below, but this list is not limiting. We can cite in particular:

- linear or branched alkyl groups preferably having from 1 to 6 carbon atoms and even more preferably from 1 to 4 carbon atoms,

- linear or branched alkenyl groups preferably having from 2 to 6 carbon atoms and even more preferably from 2 to 4 carbon atoms,

linear or branched haloalkyl groups preferably having from 1 to 6 carbon atoms and from 1 to 13 halogen atoms and even more preferably from 1 to 4 carbon atoms and from 1 to 9 halogen atoms,

- the hydroxyl group,

- group N0 ₂ ,

- the alkoxy groups R- | -O- or thioether R S- in which R 1 represents a linear or branched alkyl group having from 1 to 6 carbon atoms and even more preferably from 1 to 4 carbon atoms or the phenyl group; alkenyloxy groups, preferably an allyloxy group,

- the acyloxy or aroyloxy groups R CO-0- in which the group Ri has the meaning given above,

- the acyl or aroyl groups R- | -CO- in which the group R ₁ has the meaning given above,

- a halogen atom, preferably a fluorine atom,

- a CF ₃ group.

The invention is particularly applicable to the separation and purification of 4-hydroxybenzonitrile and 2-hydroxybenzonitrile. In the following description of the present invention, the process of the invention applied to the preparation of 2-hydroxybenzonitrile is described for the purpose of simplification, but it can be transposed to all the above-mentioned compounds.

In accordance with the process of the invention, the starting point is a reaction gas flow (FJ comprising essentially 2-hydroxybenzonitrile, all or part, salified. By this is meant that the amount of 2-hydroxybenzonitrile expressed in molar% relative to to the committed alkyl 2-hydroxybenzoate is at least 50%, preferably at least 75% and even more preferably between 80 and 95%.

The gas flow (FJ also includes ammonia at a rate of 200 to 600 mol%,, nitrogen, at a rate of 5 to 200 mol%, of the alcohol liberated by the starting ester, the more often methanol in an amount of 50 to 100% by mol, water formed during the reaction, about 50 to 100%.

The reaction gas flow (FJ can optionally comprise from 0 to 5 mol% of phenolic compounds for example phenol, from 0 to 5 mol% of the starting hydroxybenzoate ester, and of products resulting from secondary reactions, such as hydrolysis or trimerization, in particular from 0 to 10 mol% of 2-hydroxybenzamide optionally N-alkylated by the alcohol released, for example N-methyl- (2-hydroxybenzamide) and less than 3 mol% of S-triazine.

The different concentrations of the components of the flux are given by way of illustration and without limitation.

It should be noted that this reaction flow is essentially gaseous, but the invention also includes the case of the aerosol, that is to say that part of the gas flow can be condensed so that there is the presence of particles. liquids, preferably, less than 10% by volume. This reaction gas flow can originate in particular from an amination / dehydration process of an alkyl hydroxybenzoate.

Thus, it can be symbolized by the following formula:

(II) in said formula, R has the meaning given above in formula (I) and R1 generally represents an alkyl group having from 1 to 4 carbon atoms, preferably a methyl or ethyl group.

Among the hydroxybenzoates used more preferably, there may be mentioned methyl 2-hydroxybenzoate, ethyl 2-hydroxybenzoate or ethyl 4-hydroxybenzoate. Preferably, methyl and ethyl 2-hydroxybenzoates are used.

The compound of formula (II) is therefore reacted with ammonia, in the vapor phase, in the presence of a heterogeneous catalyst.

As examples of catalysts, mention may be made in particular of boron phosphate optionally doped as mentioned in CA 2 177939 or else phosphoric acid deposited on a support which may be silica and / or alumina and / or titanium oxide. Preferably, a silica gel or kieselguhr type support is used: phosphoric acid representing from 50 to 75% of the weight of the catalyst.

Although the quantity of ammonia used may be equal to the theoretical quantity determined by the stoichiometry of the reaction (i.e. one mole of ammonia per mole of hydroxybenzoate), it is preferable to conduct the amination using an excess of ammonia. In general, it is preferred to use at least two moles and more particularly from 2 to 5 moles of ammonia per mole of hydroxybenzoate. The excess ammonia present in the gas stream resulting from the amination reaction can be recycled.

The apparent contact time of the gas flow with the catalyst defined as the time in seconds during which a unit volume of gas mixture (measurement under normal pressure and temperature conditions) is in contact with the unit volume of catalyst can be between 0.001 sec and 10 min and preferably between 0.01 sec and 2 min.

The reaction is generally carried out under atmospheric pressure, at a temperature ranging from 200 ° C to 600 ° C, preferably between 350 ° C and 450 ° C. At the end of the reaction, a reaction gas flow is obtained (FJ comprising as light gases, ammonia, water and an alcohol originating from the starting alkyl hydroxybenzoate compound ((preferably, methanol)) and as heavy gases essentially all or part of the salified 2-hydroxybenzonitrile and the by-products mentioned above. The process of the invention which makes it possible to obtain a hydroxybenzonitrile type compound with a free OH group, from a benzonitrile type compound, all or part in the form of an ammonium salt, can also be applied to a compound of the benzonitrile type in hydrated form, that is to say a compound of the hydroxybenzamide type corresponding to the formula (I) in which the group CN is replaced by a CONH ₂ group, all or part in the form of an ammonium salt.

It is therefore not departing from the scope of the present invention to apply the process of the invention to a compound of the hydroxybenzonitrile type in hydrated form. Said compound being obtained in a known manner according to an amination reaction of a compound of alkyl hydroxybenzoate type, by reaction with ammonia, in the presence of a conventional catalyst: glass beads, silica, silica-alumina . Physical treatment of the reaction flow comprising 2-hydroxybenzonitrile in salified form.

According to the process of the invention, it has been found that in order to separate the 2-hydroxybenzonitrile from the reaction gas flow, the ammonium salt has to be displaced.

To this end, the temperature of the hot reaction stream is lowered to a temperature such that a liquid phase is condensed essentially comprising salified 2-hydroxybenzonitrile while allowing the decomposition of the ammonium salt leading to the release of ammonia.

According to a first variant of the process of the invention, this operation is carried out, by bringing the gaseous reaction flow into contact with a solvent

(organic solvent and / or water) then the whole is cooled to a temperature below 200 ° C, preferably between 200 ° C and 100 ° C so as to obtain a liquid phase essentially comprising 2-hydroxybenzonitrile.

The gas stream is placed in the presence of a solvent (S ^.

Several imperatives govern the choice of solvent.

A first is that the solvent is stable under the reaction conditions.

A second characteristic is that this solvent is vaporized in the chosen temperature zone, that is to say its boiling point must be less than 250 ° C.

The solvent advantageously has a boiling point between 100 ° C and 250 ° C, preferably between 100 ° C and 200 ° C.

A preferred variant of the invention is to choose a solvent which also makes it possible to carry out the purification of the 2-hydroxbenzonitrile obtained, by crystallization. It is therefore a solvent which dissolves it hot but which is a poor solvent when cold, most often at room temperature, preferably between 15 and 25 ° C.

A polar or nonpolar solvent can be used. As examples of suitable solvents, mention may be made of water, water / alcohol mixtures, for example methanol, ethanol: aromatic hydrocarbons, halogenated or not, for example, toluene, xylenes, ethylbenzene, monochlorobenzene; ethers for example, anisole or 2-ethylhexanol.

In the case of water / alcohol mixtures, these generally comprise less than 50% of alcohol, preferably from 1 to 50%, and more preferably, from 1 to 25% of alcohol and from 50 to 99%, preferably 75 to 99% water.

The amount of solvent involved represents from 30 to 500% of the weight of the reaction gas flow. From a practical point of view, the hot gas flow is generally brought into contact with the vaporized reaction solvent.

Light (FJ comprising ammonia, alcohol (most often methanol), water and in some cases an azeotropic water / organic solvent mixture) and on the other hand, heavy (FJ essentially 2-hydroxybenzonitrile and the solvent (organic solvent and / or water) and in the minority other products such as phenolic compounds for example phenol, the starting hydroxybenzoate ester, 2-hydroxybenzamide optionally N-methyl - (2-hydroxybenzamide) and S-triazine.

The invention also relates to a process for the separation and purification of 2-hydroxybenzonitrile.

The first step is carried out according to the preceding description and the heavy fraction (F ^ comprising essentially 2-hydroxybenzonitrile and the solvent) is treated.

The purification is then carried out by distilling the products with lower boiling points and then distilling the 2-hydroxybenzonitrile.

The first fraction recovered between 20 ° C and 40 ° C at 0.4 mbar, corresponds to the solvent. The second fraction obtained between 40 ° C and 110 ° C at 0.4 mbar, corresponds to the phenol and the starting hydroxybenzoate.

The third fraction obtained at 110 ° C under 0.4 mbar, consists of 2-hydroxybenzonitrile.

Salicylamide, N-methylsalicylamide and S-triazine are recovered at the bottom.

The 2-hydroxybenzonitrile thus purified by distillation has a purity of at least 95%, preferably at least 98%.

Another purification technique consists in carrying out a crystallization of 2-hydroxybenzonitrile then a solid / liquid separation of the crystallized product. We start with the fraction (FJ from the separation step. Then, by cooling to a temperature between 100 ° C and - 10 ° C, preferably between 10 ° C and 0 ° C, crystallization is caused 2-hydroxybenzonitrile, then the crystallized product is separated by conventional solid / liquid separation techniques, preferably by filtration. A solid is recovered which is essentially 2-hydroxybenzonitrile and a liquid phase (F ^ comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products.

The solid can be subjected to a drying operation carried out at a temperature between 30 ° C and 80 ° C, preferably between 40 ° C and 50 ° C.

The 2-hydroxybenzonitrile has a very good purity greater than 90%, preferably greater than 95%.

Another purification technique that can be used is purification by refining.

We start with the fraction (FJ from the separation step. We start by cooling it to a temperature between 100 ° C and 30 ° C.

An aqueous phase (F ₇ ) and an organic phase F are obtained which are separated after decantation.

The organic phase consists essentially of 2-hydroxybenzonitrile and of the solvent (S ^.

The water and / or the solvent are separated by distillation at a temperature of 90 ° C to 100 ° C and under a reduced pressure of between 1mbar and 1 bar. A crude reaction mass is obtained essentially comprising 2-hydroxybenzonitrile.

A purification operation by refining is then carried out. Refining is carried out discontinuously using devices allowing liquid / solid separation (draining, zone fusion) and dimensions depending on the volume to be treated and their number. The choice of device type is also not critical. They may, for example, be conventional drainers or other refining apparatus, for example those sold under the name PROAPT (registered trademark). Drainers of the vertical cylindrical tubular heat exchanger type can for example be used. The processing of the fraction (F in one or more devices is essentially carried out according to the following 4 phases:

- phase 1 corresponds to the slow crystallization of the charged mixture

- phase 2 corresponds to cold draining of the eutectic (2-hydroxybenzonitrile mixture + impurities such as the starting hydroxybenzoate, phenol, salicylamide and N-methylsalicylamide)

- phase 3 corresponds to the hot drainage recovered during the reheating phase until the desired purity is obtained - phase 4 corresponds to the fusion-recovery of the product at the desired purity.

Obtaining fractions of substantially constant compositions also makes it possible to automate the progress of this refining. The fraction (Fg) comprising 2-hydroxybenzonitrile is sent to one or more refining apparatus (es).

Before phase 1, the device is heated above the melting point of 2-hydroxybenzonitrile (98 ° C), ie for example between 100 ° C and 120 ° C.

During phase 1, the mass is cooled, e.g. to a temperature between 10 and 50 ° C, over several hours, e.g. within 5 to 15 hours, which induces slow crystallization of the charged mixture.

After phase 1, the product remaining liquid is withdrawn from the device (phase 2) before proceeding to phase 3.

Phase 3 consists in the slow heating of the refining apparatus, possibly started during phase 2, eg up to a temperature between 94 ° C and 98 ° C, in several hours, eg in from 8 to 15 h.

The end of phase 3, which conditions the purity of the product, can be determined - either by measuring the crystallization point, or by any other physico-chemical analysis technique. Phase 4 provides for heating the device to a temperature above 95 ° C so as to melt the 2-hydroxybenzonitrile, which is drawn off in the molten state (F „.

The eutectic fractions recovered (F _{1 (} during refining can be recycled as a mixture or separately with hot draining, preferably in the previous step.

A 2-hydroxybenzonitrile is obtained having a purity of at least 98%, preferably at least 99%.

Physical treatment of ammonium cyanophenate. According to another embodiment of the invention, the 2-hydroxybenzonitrile is separated from the gas reaction stream (FJ which contains it in salified form, according to a variant process which comprises the steps of liquefaction of the reaction gas stream, crystallization of the 2-hydroxybenzonitrile in the form of an ammonium salt, hereinafter called "ammonium cyanophenate", solid / liquid separation of the crystallized product then heat treatment of the separated solid making it possible to release ammonia, water, an alcohol ( preferably methanol) and recover the 2-hydroxybenzonitrile. Another variant of the invention consists in thermally treating the ammonium cyanophenate, not in the form of a solid but in thermally treating the ammonium cyanophenate in solution in an organic solvent S ^ j. Thus, the reaction gas flow is liquefied, then the ammonium cyanophenate is crystallized, and a solid / liquid separation is carried out, then the solid product obtained is solubilized in an organic solvent, preferably polar finally treated thermally the organic solution obtained. More precisely, we start by liquefying the reaction gas flow (FJ, by cooling from 90 ° C - 100 ° C, to a temperature of 40 ° C - 30 ° C and contacting with water which allows on the one hand, to eliminate light (ammonia and water) and to recover an aqueous phase comprising ammonium cyanophenate and ammonia. The amount of water used represents from 50 to 500% of the weight of

(F

In a next step, in a first step, the crystallization of ammonium cyanophenate is carried out.

By cooling the liquefied stream F ₁₂ to a temperature between 0 ° C - 30 ° C, the ammonium cyanophenate crystallizes.

The separation of the crystallized product is then carried out according to conventional solid / liquid separation techniques, preferably by filtration.

The separation is carried out at a temperature between 0 ° C and 20 ° C.

A solid which is essentially ammonium cyanophenate and a liquid phase (F ₁₃ ) comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products are recovered.

The recovered product can be represented by formula (III):

(III) in said formula, R has the meaning given above. The heat treatment is then carried out at a temperature between 80 ° C and 20 ° C, under a pressure between 1 mbar and 1 bar, preferably between 1 mbar and 500 mbar.

A light fraction (F comprising ammonia, the solvent (S) is removed and the 2-hydroxybenzonitrile is recovered, in solid form. According to another alternative embodiment of the invention, the heat treatment is carried out on ammonium cyanophenate which is dissolved in an organic solvent (S _a ).

We start by solubilizing the solid ammonium cyanophenate obtained as above by liquefying the gas stream, crystallization and separation leading to ammonium cyanophenate in solid form and a liquid phase (F _1S ).

The ammonium cyanophenate is dissolved by adding an aprotic polar organic solvent. As examples of suitable solvents, there may be mentioned dimethylformamide or N-methylpyrrolidone.

Preferably, dimethylformamide is chosen.

The amount of solvent used represents from 30 to 500% of the weight of the ammonium cyanophenate. An organic solution of ammonium cyanophenate is obtained which is subjected to a heat treatment at a temperature between 80 ° C and 20 ° C, under a pressure between 1 mbar and 1 bar, preferably between 1 mbar and 500 mbar.

A light fraction F is comprising ammonia, the solvent is eliminated and _recovery is obtained (F ₁₇ ) which is 2-hydroxybenzonitrile in solution in a solvent (S ₂ ) and it is possible to classically isolate it by distillation or by cooling on a scaly machine.

Chemical treatment of the flux comprising 2-hydroxybenzonitrile in salified form.

According to another embodiment of the invention, the 2-hydroxybenzonitrile is separated from the gas reaction flow (FJ which contains it in salified form, by effecting a chemical displacement of the ammonium ions.

This variant of the process consists in liquefying the reaction gas flow, in treating it with an acid thus leading to the production of 2-hydroxybenzonitrile, in carrying out a liquid / liquid separation allowing the 2-hydroxybenzonitrile to be recovered in the organic phase.

More precisely, we start by liquefying the reaction gas flow (FJ, by cooling from 90 ° C - 100 ° C, to a temperature of 40 ° C - 30 ° C and contacting with water which allows one hand, to eliminate light

(ammonia and water) and recover an aqueous phase comprising ammonium cyanophenate and ammonia. The amount of water used represents 50 to 700% of the weight of

(Ft).

The neutralization of the ammonium ions is then carried out using an acid.

Use is made of a Brônsted acid having a pka measured in water, less than 6, preferably, between - 1 and 4.

As more specific examples, mention may be made of sulfuric acid, hydrochloric acid, phosphoric acid or acetic acid.

The concentration of the acid solution is indifferent: it can vary between 30 and 100%. The amount of acid used is such that the pH obtained is between 6 and 1, preferably between 4 and 3.

The neutralization operation is carried out at a temperature advantageously between 90 ° C and 30 ° C.

The reaction mixture obtained is subjected to decantation making it possible to separate an aqueous phase F _r3 . comprising excess acid and ammonium salts and an organic phase (F _2C ) comprising 2-hydroxybenzonitrile.

The latter can be purified according to the purification techniques such as distillation, crystallization and refining, described above.

The present invention also relates to installations making it possible to implement the various variants of the method of the invention.

Physical treatment of the reaction flow comprising 2-hydroxybenzonitrile in salified form. The present invention also relates to an installation allowing the implementation of the process of the invention which comprises at least one unit making it possible to separate the 2-hydroxybenzonitrile from the gas reaction stream and optionally a unit for purifying the 2-hydroxybenzonitrile. The separation unit comprises: - a first column (1) designed to bring the gaseous reaction flow into contact with the solvent (water and / or organic solvent), - a second column (2) whose inlet is connected to the base of the column (1), this column (2) being designed to obtain at the head of the column a light fraction comprising ammonia, water and an alcohol (preferably, methanol) and at the bottom of the column a heavy fraction comprising essentially 2-hydroxybenzonitrile, the solvent (water and / or organic solvent), some traces of ammonia and secondary products in minority quantities. Figure 1 shows the diagram of a separation unit according to the invention.

The installation allowing the separation comprises a first column (1) ensuring good gas / liquid contact, for example a washing tower. It comprises at the top of the column means for admitting the reaction gas flow (F to be treated and means for admitting the solvent (S ^, for example a pump and a vaporization device (nozzles) of the latter. its lower part, the column comprises means for discharging the heavy phase (liquid and / or gas) connected to a second column (2) which is supplied at mid-height.

The column (2) allowing gas / liquid separation is a column comprising cooling means (condenser). It is provided in its upper part with means for evacuating the gas phase including the light ones (FJ and in its lower part, with means for withdrawing the liquid phase (F ^.

According to a preferred embodiment of the invention, the installation comprises a separation unit and a purification unit.

Thus, the separation unit is completed by means ensuring the purification of the 2-hydroxybenzonitrile contained in the heavy fraction (FJ recovered at the outlet of the separation unit.

Figures 2 to 4 illustrate the different means that can be implemented.

According to a first preferred embodiment which consists in carrying out the purification by distillation (FIG. 2), the installation further comprises a distillation column (3) fed by the heavy fraction (FJ coming from the previous column (2) and designed to get :

- at the top of the column, different fractions, under a pressure of 0.4 mbar:

- light fractions with a boiling point below 40 ° C at atmospheric pressure,

- a fraction between 40 ° C and 110 ° C corresponding to phenol and methyl salicylate

- a fraction at 110 ° C corresponding to 2-hydroxybenzonitrile (FJ,

- And at the bottom of the column, the various impurities (F _ε ) whose boiling point is greater than 110 ° C: salicylamide, N-methylsalicylamide and S-triazine.

From this information, the skilled person is perfectly able to choose the means to be implemented according to the starting mixture. We will simply recall the following. The size (especially the diameter) of the distillation columns depends on the circulating flow and the internal pressure. Their dimensioning will therefore be mainly based on the flow of mixture to be treated. The internal parameter that is the number of theoretical stages is determined in particular by the composition (ratios) of the incoming mixture and the purity or the composition of the mixture to be obtained at the top and bottom of the distillation. It will be noted that the columns may be packed with ordered packing, as is perfectly known to those skilled in the art. The installation being determined, the skilled person adjusts the operating parameters of the columns.

Thus, the distillation column (3) could advantageously, but not be limited to, a column having the following specifications:

- number of theoretical stages: from 5 to 40, preferably from 10 to 30;

- reflux rate R between 1 and 10; - low residence time, preferably less than 30 min.

According to a second embodiment which consists in carrying out the purification by crystallization (FIG. 3), the installation comprises a crystallization reactor (4) provided with means for admission of the fraction (FJ as well as a withdrawal device necessary for This reactor is equipped with stirring means, a temperature regulation device (hot / cold): cooling can be ensured by circulation of cold water in a double jacket or by means of packing. interior (coils).

It is connected to a solid / liquid separation device, (5), such as a wringer, agitated filter, filter press, candle filter.

It allows a solid consisting essentially of 2-hydroxybenzonitrile and an aqueous phase to be recovered (FJ comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products.

The separation device (5) is optionally associated with drying means (6) such as a rotary dryer or agitated dryer, thus making it possible to recover the 2-hydroxybenzonitrile in the form of powder (P).

According to a third embodiment (FIG. 4) which consists in carrying out purification by refining, the installation comprises a cooling tower (7) provided with means for admitting the fraction (F ^ as well as a withdrawal device necessary to its operation.

It is connected to a liquid / liquid separation device, (8), such as a decanter. It makes it possible to separate an aqueous phase (F ₇ ) from an organic phase consisting essentially of 2-hydroxybenzonitrile (FJ.

This organic phase is directed into a reactor (9) equipped with stirring means, a temperature regulation device (hot / cold). It is surmounted by a distillation column and provided with a reduced pressurization system which makes it possible to separate by distillation Fg), the organic solvent and / or the remaining water.

The organic phase (F is conveyed in a device (10) allowing the refining (draining, zone fusion) and dimensioned according to the volume to be treated and their number. The choice of the type of device is not critical either They can be, for example, conventional drainers or other refining devices, for example those sold under the name PROAPT (registered trademark). It is possible, for example, to use drainers of the vertical cylindrical tubular exchanger type. different fractions containing impurities (F _1C ) and a fraction of 2-hydroxybenzonitrile F „.

Physical treatment of ammonium cyanophenate.

In accordance with another variant of the invention which consists in thermally treating not the gaseous reaction flow comprising 2-hydroxybenzonitrile but ammonium cyanophenate, the process is carried out in an installation comprising a separation unit illustrated in the figures

5 or 6.

The installation shown in FIG. 5 comprises a washing tower (11) fitted with a gas intake system (FJ and a device for introducing water via a pump making it possible to recovering at the bottom a liquid phase (F ₁₂ ) comprising water, crude ammonium cyanophenate and ammonia; the mixture being transferred to the reactor (12),

In the reactor (12) in which crystallization of the ammonium cyanophenate is carried out and which is provided with means for admitting the fraction (F ₁₂ ); said reactor being equipped with stirring means, a temperature regulation device (hot / cold).

It has in its lower part, a withdrawal device making it possible to connect it to a solid / liquid separation device, (13), such as a wringer, agitated filter, filter press, candle filter.

It allows a solid consisting essentially of ammonium cyanophenate and an aqueous phase (F ₁₃ ) comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products to be recovered. The separation device is associated with drying means (14) such as a stirred dryer in which it is subjected to a temperature and pressure cycle so as to decompose the solid ammonium cyanophenate into 2-hydroxybenzonitrile, thus allowing recovering the 2-hydroxybenzonitrile in powder form (P) while removing the solvent and the remaining ammonia (F, J.

According to another variant illustrated by FIG. 6, the installation comprises, as in FIG. 5, a washing tower (11) and a reactor (12) in which crystallization of the ammonium cyanophenate is carried out and which is equipped with means admission of fraction F _t2 ; said reactor being equipped with stirring means, a temperature regulation device (hot / cold).

It has in its lower part, a withdrawal device making it possible to connect it to a solid / liquid separation device, (15), such as a wringer, agitated filter, filter press, candle filter and equipped with a means of admission of a solvent (S ^ thus allowing the solubilization of the ammonium cyanophenate. It makes it possible to recover the ammonium cyanophenate in organic solution and an aqueous phase F _ia ) comprising the solvent (S ^, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products.

The mixture is sent to a reactor (16) equipped with stirring means, a temperature regulation device (hot / cold), surmounted by a distillation column and provided with a reduced pressure system. which allows the organic solvent and / or the remaining water F ₆ to be separated by distillation and the thermal decomposition of the ammonium cyanophenate into 2-hydroxybenzonitrile is carried out by joint application of the temperature and the pressure.

Recovering (F ₁₇ ) which is 2-hydroxybenzonitrile in solution in a solvent (Sg) and it is possible to isolate it conventionally by distillation or by cooling on a scaly machine.

Chemical treatment of the flux comprising 2-hydroxybenzonitrile in salified form. The separation unit shown in Figure 7 includes:

- a washing tower (17) provided with a gas intake system (FJ and with a device for introducing water via a pump making it possible to recover a liquid phase at the bottom (F ₁₈ ) comprising water, crude ammonium cyanophenate and ammonia which is transferred into the reactor (18), a neutralization reactor (18) being equipped with stirring means, with a regulating device temperature (hot / cold), a reagent introduction device (acid) and a pH regulation device (electrode): said reactor comprising in its lower part, a withdrawal device making it possible to connect it to a device (19),

- A liquid / liquid separation device (19) such as a decanter making it possible to separate an aqueous phase (F _{1 £} ). comprising excess acid and ammonium salts and an organic phase (F _2O comprising 2-hydroxybenzonitrile. The latter can be purified according to purification techniques such as distillation, crystallization and refining illustrated in FIGS. 2 to 4.

Thus, the process of the invention makes it possible to obtain a 2-hydroxybenzonitrile of high purity. The invention will now be described in more detail using embodiments of the invention taken by way of nonlimiting examples.

Example 1

Chemical treatment of the flow comprising the 2-hydroxybenzonitrile salified in the form of ammonium according to FIG. 7.

The crude reaction flow from the reactor comprising 0.52 mol of salified 2- hydroxybenzonitrile (2-HBN) and 1.7 mol of ammonia (F- _t ) is dissolved in 72 g of water at 60 ° C. in the tower washing (17).

The stream (F ₁₈ ) is then transferred to a stirred reactor (18), where 35.1 g of 98% sulfuric acid are added, maintaining a temperature of 60 ° C.

The final pH must be between 3 and 4, at the end of the addition of the sulfuric acid.

The crude 2-hydroxybenzonitrile, upper phase, (F ₂₀ ) is recovered after decantation at 60 ° C, in a decanter (19).

The crude 2-hydroxybenzonitrile is 61% by weight.

The recovery yield is 96% (0.506 mol).

Example 2 In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to example 1 is purified by crystallization at a temperature of 0 ° C. in a solvent which is toluene. The results obtained are as follows:

- 2-hydroxybenzonitrile purity = 95%, - isolated yield = 74%.

Example 3 In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to Example 1 is purified by crystallization at a temperature of 0 ° C. in a solvent which is chlorobenzene.

The results obtained are as follows: - purity of 2-hydroxy benzonitrile = 99%, - isolated yield = 55%.

Example 4

Physical treatment of the ammonium cyanophenate according to FIG. 6. The crude reaction flow coming from the reactor comprising 0.52 mol of salified 2- hydroxybenzonitrile (2-HBN) and 1.7 mol of ammonia (F) is dissolved in 216 g of water at 60 ° C in the washing tower (11).

This flow is loaded into a reactor (12) where it is subjected to crystallization by cooling to 15 ° C. The precipitated ammonium 2-cyanophenate is recovered by filtration in the filter (15), where it is washed with 50 g of ammonia at 5% by weight.

The precipitate is drained, then redissolved in the filter in 70 g of dimethylformamide.

The solution of ammonium 2-cyanophenate in dimethylformamide is transferred to the reactor (16) where the water and then the ammonia are removed by heating at 60 ° C under 100 - 50 mbar.

The isolation yield of 2-hydroxybenzonitrile is 72% and the purity (excluding DMF) of 2-hydroxybenzonitrile is 99.5%.

Example 5

Physical treatment of the reaction flow comprising 2-hvdroxybenzonitrile salified in the form of ammonium, according to FIG. 1.

The crude reaction flow from the reactor comprising 0.52 mol of salified 2-hydroxybenzonitrile (2-HBN) and 1.7 mol of ammonia at 420 ° C ((Fi) is brought into contact with 200 g of xylene, in the washing tower (1).

The flow is then transferred to a column (2), where the mixture is cooled to 110 ° C by an exchanger.

The ammonium 2-cyanophenate decomposes and the ammonia is eliminated at the top of the column. The crude 2-hydroxybenzonitrile in solution in xylene (F is recovered at the bottom of the column.

The crude 2-hydroxybenzonitrile is 89% by weight (excluding solvent). The recovery yield is 94% (0.49 mol). Example 6

In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to Example 5 is purified by crystallization from a solvent which is xylene.

The results obtained are as follows:

- purity of 2-hydroxybenzonitrile = 92%,

- isolated yield = 68%.

Example 7

The crude reaction flow from the reactor comprising 0.52 mol of salified 2-hydroxybenzonitrile (2-HBN) and 1.7 mol of ammonia at 420 ° C ((F _ή ) is brought into contact with 200 g of xylene, in the washing tower (1).

The ammonium 2-eyanophenate decomposes and the ammonia is eliminated at the top of the column. The crude 2-hydroxybenzonitrile in solution in xylene (F ₃ ) is recovered at the bottom of the column.

The crude 2-hydroxybenzonitrile is 89% by weight (excluding solvent). The recovery yield is 94% (0.49 mol).

Example 8

In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to Example 7 is purified by crystallization at a temperature of 0 ° C. in a solvent which is xylene. The results obtained are as follows: - purity of 2-hydroxybenzonitrile = 92%,

- isolated yield = 68%.

Example 9

In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to Example 7 is purified by crystallization at a temperature of -10 ° C. in a solvent which is a xylene / methanol mixture (95: 5, w / w%).

The results obtained are as follows: - purity of 2-hydroxybenzonitrile = 98%,

- isolated yield = 85%.

Example 10 Physical treatment of the reaction flow comprising salified 2-hvdroxybenzonitrile in the form of ammonium, according to FIG. 1.

The crude reaction flow from the reactor comprising 0.52 mol of salified 2-hydroxybenzonitrile (2-HBN) and 1.7 mol of ammonia at 420 ° C (FJ is brought into contact with 180 g of xylene and 20 g of DMF in the washing tower (1) The flow is then transferred to a column (2), where the mixture is cooled to 110 ° C by an exchanger.

The ammonium 2-cyanophenate decomposes and the ammonia is eliminated at the top of the column.

The crude 2-hydroxybenzonitrile dissolved in xylene + DMF (F ₃ ) is recovered at the bottom of the column.

The crude 2-hydroxybenzonitrile is 88% by weight (excluding solvent). The recovery yield is 97% (0.49 mol).

Example 11 In an apparatus illustrated in FIG. 3, the crude 2-hydroxybenzonitrile obtained according to Example 7 is purified by crystallization at a temperature of -10 ° C. in a solvent which is a xylene-DMF mixture (90: 10, w / w%).

The results obtained are as follows: - purity of 2-hydroxybenzonitrile = 99%,

- isolated yield = 85%.

It should be understood that the invention defined by the appended claims is not limited to the particular embodiments indicated in the description above, but encompasses variants thereof which do not depart from the scope or the spirit of the present invention.

Claims

1 - Process for separating a compound of the hydroxybenzonitrile type from a gaseous reaction flow comprising it entirely or partly in the form of an ammonium salt characterized by the fact that it consists, with the aim of obtain a compound of the hydroxybenzonitrile type, to displace the ammonium ions:

- according to a physical treatment carried out on the reaction gas flow resulting from its preparation or according to a physical treatment of the solid previously recovered from the reaction gas flow after liquefaction or on this same solid put into solution,

2 - Process according to claim 1 characterized in that the hydroxybenzonitrile type compound corresponds to the following formula:

in said formula, R symbolizes one or more substituents.

3 - Process according to claim 2 characterized in that the hydroxybenzonitrile type compound corresponds to formula (I) in which R is chosen from

- linear or branched alkenyl groups preferably having 2 to 6 carbon atoms and even more preferably 2 to 4 carbon atoms,

- linear or branched haloalkyl groups preferably having 1 to 6 carbon atoms and 1 to 13 halogen atoms and even more preferably 1 to 4 carbon atoms and 1 to 9 halogen atoms,

- the hydroxyl group, - the N0 ₂ group,

- the alkoxy groups R O- or thioether R ₁ -S- in which R- _| represents a linear or branched alkyl group having from 1 to 6 carbon atoms and even more preferably from 1 to 4 carbon atoms or the phenyl group; alkenyloxy groups, preferably an allyloxy group, - acyloxy or aroyloxy groups R _r CO-O- in which the group R- _\ has the meaning given previously, - the acyl or aroyl groups R CO- in which the group R- _\ has the meaning given previously,

- a halogen atom, preferably a fluorine atom,

- a CF ₃ group.

4 - Process according to claim 1 characterized in that the hydroxybenzonitrile type compound is 4-hydroxybenzonitrile or 2-hydroxybenzonitrile.

5 - Method according to claim 1 characterized in that the compound of the hydroxybenzonitrile type is all or part, in hydrated form.

6 - Method according to one of claims 1 to 5 characterized in that the reaction gas flow (Fi) essentially comprises 2-hydroxybenzonitrile, all or part, salified; preferably, the quantity of 2-hydroxybenzonitrile expressed in molar % relative to the alkyl 2-hydroxybenzoate used is at least 50%, preferably at least 75% and even more preferably between 80 and 95%. .

7 - Method according to claim 6 characterized in that the gas flow (F) also comprises ammonia at a rate of 200 to 600% by mol, nitrogen, at a rate of 5 to 200% by mol, the alcohol released by the starting ester, preferably methanol in an amount of 50 to 100% by mol, of the water formed during the reaction, approximately 50 to 100%, optionally 0 to 5% in mol of phenolic compounds preferably, phenol, from 0 to 5% by mol of the starting hydroxybenzoate ester, and products resulting from secondary reactions, such as hydrolysis or trimerization, in particular from 0 to 10% by mol of 2 - hydroxybenzamide optionally N-alkylated by the alcohol released, for example N-methyl-(2-hydroxybenzamide) and less than 3% by mol of S-triazine.

8 - Process according to one of claims 1 to 4 characterized in that the reaction flow comes from an amination/dehydration process of an alkyl hydroxybenzoate consisting of reacting it with ammonia, in the gas phase , in the presence of a heterogeneous catalyst, preferably phosphoric acid deposited on a silica gel or kieselguhr type support.

9 - Method according to one of claims 1 to 8 characterized in that the reaction gas flow has a temperature ranging from 200°C to 600°C, preferably between 350°C and 450°C.

10 - Method according to claim 1 characterized in that it consists of thermally treating the gas flow comprising 2-hydroxybenzonitrile, all or part, salified.

11 - Method according to claim 10 characterized in that the gaseous reaction flow is brought into contact with a solvent (organic solvent and/or water) then the whole thing is cooled to a temperature below 200°C, preferably , between 200°C and 100°C so as to obtain a liquid phase essentially comprising 2-hydroxybenzonitrile.

12 - Method according to one of claims 10 and 11 characterized in that the solvent (Si) is a polar or apolar solvent, preferably chosen from: water, water/alcohol mixtures preferably, methanol, ethanol : halogenated or non-halogenated aromatic hydrocarbons, preferably toluene, xylenes, ethylbenzene, monochlorobenzene; ethers, preferably anisole or 2-ethylhexanol.

13 - Method according to one of claims 10 to 12 characterized in that the hot gas flow is generally brought into contact with the vaporized reaction solvent and that the light (F _∑ ) is recovered on the one hand. comprising ammonia, alcohol (most often methanol), water and in certain cases, an azeotropic water/organic solvent mixture and on the other hand, heavy substances (F ₃ ) essentially 2- hydroxybenzonitrile and the solvent (organic solvent and/or water).

14 - Process according to one of claims 10 to 13 characterized in that the heavy fraction (F ₃ ) essentially comprising 2-hydroxybenzonitrile and the solvent is purified by distillation.

15 - Process according to one of claims 10 to 13 characterized in that the heavy fraction Fg) essentially comprising 2-hydroxybenzonitrile is purified by crystallization.

16 - Process according to claim 15 characterized in that the heavy fraction (F ₃ ) is cooled to a temperature between 100°C and - 10°C, preferably between 10°C and 0°C, which causes the crystallization of 2-hydroxybenzonitrile; we then carry out the separation of the crystallized product according to conventional solid/liquid separation techniques, preferably by filtration; a solid is recovered which is essentially 2-hydroxybenzonitrile and a liquid phase Fg); the solid is subjected to a drying operation carried out at a temperature between 30°C and 80°C, preferably between 40°C and 50°C.

17 - Process according to one of claims 10 to 13 characterized in that the heavy fraction (F ₃ ) essentially comprising 2-hydroxybenzonitrile is purified by refining.

18 - Process according to claim 17 characterized in that the heavy fraction (F ₃ ) is cooled to a temperature between 100°C and 30°C; an aqueous phase (F ₇ ) and an organic phase (Fg) are separated, essentially 2-hydroxybenzonitrile and the solvent (S^; the organic phase is treated so as to separate the water and/or the solvent by distillation under reduced pressure to recover a crude reaction mass essentially comprising 2-hydroxybenzonitrile which is subjected to a purification operation by refining.

19 - Method according to claim 18 characterized in that the reaction mass is cooled to a temperature between 10 and 50°C; the temperature is raised between 94°C and 98°C, making it possible to separate the eutectic fractions including the impurities; it is heated to a temperature above 98°C so as to melt the 2-hydroxybenzonitrile, which is withdrawn in the molten state (F ₁₁ ).

20 - Process according to claim 1 characterized in that it consists of liquefying the reaction gas flow, then crystallizing the ammonium cyanophenate, then carrying out a solid/liquid separation then thermally treating the solid product obtained.

21 - Process according to claim 20 characterized in that one begins by liquefying the reaction gas flow (F), by cooling from 90°C - 100°C, to a temperature of 40°C - 30°C and putting in contact with water which allows, on the one hand, to eliminate light particles and to recover an aqueous phase comprising ammonium cyanophenate and ammonia.

22 - Method according to claim 20 characterized in that the liquefied flow (F _i2 ) is cooled to a temperature between 0°C - 30°C, which causes the crystallization of ammonium cyanophenate and the crystallized product is separated according to conventional solid/liquid separation techniques, preferably by filtration making it possible to recover a solid which is essentially ammonium cyanophenate.

23 - Method according to one of claims 20 to 22 characterized in that the heat treatment is then carried out at a temperature of between 80°C and 20°C, under a pressure of between 1 mbar and 1 bar, of preferably, between 1 mbar and 500 mbar allowing the 2-hydroxybenzonitrile to be recovered in solid form.

24 - Process according to claim 1 characterized in that it consists of liquefying the reaction gas flow, then crystallizing the ammonium cyanophenate, then carrying out a solid/liquid separation, solubilizing the solid product obtained in an organic solvent , preferably polar, then heat treating the organic solution obtained.

25 - Process according to claim 24 characterized in that it consists of liquefying the reaction gas flow, then crystallizing the ammonium cyanophenate, then carrying out a solid/liquid separation as described in one of claims 21 to 23 .

26 - Process according to claim 24 characterized in that the solid product obtained is solubilized in an organic solvent, preferably polar, aprotic and preferably dimethylformamide or N-methylpyrrolidone.

27 - Process according to claim 26 characterized in that the organic solution of ammonium cyanophenate is subjected to heat treatment at a temperature of between 80°C and 20°C, under a pressure of between 1 mbar and 1 bar, preferably between 1 mbar and 500 mbar making it possible to eliminate a light fraction F _?6 ) and to recover (F ₁₇ ) which is 2-hydroxybenzonitrile in solution in a solvent (S ₂ ).

28 - Process according to claim 1 characterized in that it consists of liquefying the reaction gas flow, treating it with an acid thus leading to obtaining 2-hydroxybenzonitrile, carrying out a liquid/liquid separation making it possible to recover the 2-hydroxybenzonitrile in the organic phase. 29 - Process according to claim 28 characterized in that the reaction gas flow (Fi) is liquefied by cooling from 90°C - 100°C to a temperature of 40°C - 30°C and brought into contact with water which allows, on the one hand, to eliminate light particles and to recover an aqueous phase comprising ammonium cyanophenate and ammonia.

30 - Method according to claim 28 characterized in that the neutralization of the ammonium ions is carried out using a Brônsted acid having a pka measured in water, less than 6, preferably between - 1 and 4.

31 - Process according to claim 30 characterized in that the acid is sulfuric acid.

32 - Method according to one of claims 30 and 31 characterized in that the quantity of acid used is such that the pH obtained is between 6 and

1, preferably between 4 and 3.

33 - Process according to claim 28 characterized in that the reaction mixture obtained is subjected to decantation making it possible to separate an aqueous phase (F ₁₉ ) comprising the excess acid and ammonium salts and an organic phase ( F ₂₀ ) comprising 2-hydroxybenzonitrile.

34 - Process according to one of claims 20 to 33 characterized in that the 2-hydroxybenzonitrile is purified according to the purification techniques described in one of claims 14 to 19.

35 - Installation for separating 2-hydroxybenzonitrile from a gaseous reaction flow comprising 2-hydroxybenzonitrile, in salified form characterized by the fact that it comprises: - a first column (1) designed to bring the reaction flow into contact gaseous and the solvent (water and/or organic solvent),

- a second column (2) whose inlet is connected to the foot of the column (1), this column (2) being designed to obtain at the head of the column a light fraction comprising ammonia, water and an alcohol ( preferably methanol) and at the bottom of the column a heavy fraction essentially comprising 2-hydroxybenzonitrile, the solvent (water and/or organic solvent), some traces of ammonia and secondary products in minor quantities. 36 - Installation according to claim 35 characterized in that the first column (1) is a washing tower comprising at the head of the column means for admitting the reaction gas flow (F) to be treated and means for admitting the solvent (S^, a vaporization device (nozzles) and means for evacuating the heavy phase (liquid and/or gaseous) connected to a second column (2) supplied at mid-height, comprising cooling means ( condenser) and provided in its upper part with means for evacuating the gas phase including the light ones (F _∑ ) and in its lower part, with means for withdrawing the liquid phase (F ₃ ).

37 - Installation according to claim 36 characterized in that the separation unit is supplemented by a purification unit which is a distillation unit comprising a distillation column (3) supplied with the heavy fraction (F ₃ ) coming from the previous column (2) and designed to obtain: - at the top of the column, different fractions, under a pressure of 0.4 mbar:

- light fractions whose boiling point is less than 40°C at atmospheric pressure,

- a fraction between 40°C and 110°C corresponding to phenol and methyl salicylate - a fraction at 110°C corresponding to 2-hydroxybenzonitrile (FJ,

- and at the bottom of the column, the various impurities (F ₅ ) whose boiling point is greater than 110°C: salicylamide, N-methylsalicylamide and S-triazine.

38 - Installation according to claim 37 characterized in that the distillation column (3) has the following specifications: number of theoretical stages: from 5 to 40, preferably from 10 to 30; reflux rate R between 1 and 10; low residence time, preferably less than 30 min.

39 - Installation according to claim 35 characterized in that the separation unit is supplemented by a purification unit which is a crystallization unit comprising:

- a crystallization reactor (4) provided with means for admitting the fraction (F ₃ ) as well as a withdrawal device connected to the separation device (5) and equipped with stirring means, a regulation device of the temperature,

- a solid/liquid separation device (5), preferably a spin dryer, stirred filter, filter press, candle filter making it possible to recover a solid made up of essentially by 2-hydroxybenzonitrile and an aqueous phase (Fe) comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products,

- optionally drying means (6), preferably a rotary dryer or stirred dryer, thus making it possible to recover the 2-hydroxybenzonitrile in powder form (P).

40 - Installation according to claim 35 characterized in that the separation unit is supplemented by a purification unit which is a refining unit comprising:

- a cooling tower (7) provided with means for admitting the fraction (F ₃ ) as well as a withdrawal device connected to a separation device (8),

- a liquid/liquid separation device (8), preferably a decanter, making it possible to separate an aqueous phase (F ₇ ) from an organic phase consisting essentially of 2-hydroxybenzonitrile (F ₈ ),

- a reactor (9) provided with means for admitting the organic phase and equipped with stirring means, a temperature regulation device (hot/cold), a distillation column and provided with a reduced pressure system which makes it possible to separate by distillation (F ₉ ), the organic solvent and/or the remaining water and to recover a crude 2-hydroxybenzonitrile,

- one or more refining devices, preferably of the drainer type, which makes it possible to eliminate impurities (F ₁₀ ) and recover a liquid fraction of 2-hydroxybenzonitrile (F _ή1 ).

41 - Installation for separating 2-hydroxybenzonitrile by physical treatment of ammonium cyanophenate comprising:

- a washing tower (11) provided with a gas admission system (F- _t ) and a device for introducing water via a pump making it possible to recover a phase at the bottom liquid (F ₁₂ ) comprising water, crude ammonium cyanophenate and ammonia; the mixture being transferred into the reactor (12),

- a crystallization reactor (12) of ammonium cyanophenate and provided with means for admitting the fraction (F ₁₂ ) and a withdrawal device making it possible to connect it to a separation device (13); said reactor being equipped with stirring means, a temperature regulation device,

- a solid/liquid separation device (13), preferably a spin dryer, agitated filter, filter press, candle filter making it possible to recover a solid consisting essentially of ammonium cyanophenate and an aqueous phase (F ₁₃ ) comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products,

- drying means (4) preferably, an agitated dryer in which it is subjected to a cycle of temperature and pressure so as to decompose the solid ammonium cyanophenate into 2-hydroxybenzonitrile, thus making it possible to recover the 2-hydroxybenzonitrile in powder form (P) while eliminating the solvent and the remaining ammonia (F ₁₄ ).

42 - Installation for separating 2-hydroxybenzonitrile by physical treatment of ammonium cyanophenate comprising:

- a washing tower (11) provided with a gas admission system (Fi) and a device for introducing water via a pump making it possible to recover a liquid phase at the bottom ( F _i2 ) comprising water, crude ammonium cyanophenate and ammonia; the mixture being transferred into the reactor (12),

- a crystallization reactor (12) of ammonium cyanophenate and provided with means for admitting the fraction (F ₁₂ ) and a withdrawal device making it possible to connect it to a separation device (13); said reactor being equipped with stirring means, a temperature regulation device, - a solid/liquid separation device (13), preferably a spin dryer, stirred filter, filter press, candle filter allowing recovery a solid consisting essentially of ammonium cyanophenate and an aqueous phase (F ₁₃ ) comprising the solvent, a little 2-hydroxybenzonitrile (less than 5% by weight) and by-products and equipped with an admission means a solvent (S ₂ ) thus allowing the solubilization of ammonium cyanophenate,

- a reactor (16) provided with a device for admitting the organic solution of ammonium cyanophenate, equipped with stirring means, a temperature regulation device surmounted by a distillation column and provided with a system of reduced pressure which makes it possible to separate by distillation the organic solvent and/or the remaining water _{? 6} ) and to carry out the thermal decomposition of ammonium cyanophenate into 2-hydroxybenzonitrile.

43 - Installation for separating 2-hydroxybenzonitrile by chemical treatment of the gaseous reaction flow comprising 2-hydroxybenzonitrile, in salified form characterized by the fact that it comprises:

- a washing tower (17) provided with a gas admission system (F) and a device for introducing water via a pump making it possible to recover at the bottom a liquid phase (F^ comprising water, crude ammonium cyanophenate and ammonia which is transferred to the reactor (18),

- a neutralization reactor (18) equipped with stirring means, a temperature regulation device, a reagent (acid) introduction device and a pH regulation device (electrode): said reactor comprising in its lower part, a withdrawal device allowing it to be connected to a device

(19),

- a device (19) for liquid/liquid separation, preferably a decanter making it possible to separate an aqueous phase F _/ g, comprising excess acid and ammonium salts, and an organic phase (F _2Q ) comprising 2- hydroxybenzonitrile.

44 - Installation according to claims 41 to 43 characterized in that it is supplemented by a purification unit described in one of claims 37 to 40.

45 - Compound of the hydroxybenzonitrile type in the form of ammonium salt corresponding to formula (III):

(HO in said formula, R has the meaning given in one of claims 2 and 3.

46 - Ammonium 2-cyanophenate of formula: