Granulation method for azo compounds and granules obtained

Abstract

The invention relates to a method for granulating azo compounds, comprising the following steps: a) a step of granulating by stirring an aqueous suspension of the azo compound in the presence of an organic binder, b) an optional step of recovering the granules obtained in step a), preferably by filtration; and c) an optional step of drying the particles recovered in step b). The invention also relates to particles obtainable using said method and to the use thereof.

Description

[0001] The present invention relates to a process for granulating azo compounds and to granules obtainable by this process and to their use.

[0002] Azo compounds, and more particularly 2,2'-azobis(isobutyronitrile), known as AZDN or AIBN, are known products. They are used as swelling agents, synthesis intermediates or initiators for polymerization reactions using free radicals. These reactions can be polymerization reactions in bulk, in solution, in suspension or in emulsion, and very different monomers can be used, for example (meth)acrylic acid or vinyl monomers, such as acrylamide, acrylonitrile, alkyl (meth)acrylates, styrene, vinyl chloride and vinyl acetate or vinylidene chloride. The fields of application are therefore very diverse and relate in particular (but not exclusively) to acrylic sheets or fibers, flocculants, coatings, coating resins, graft polyols, polystyrene, PVC, PVA or PMMA.

[0003] These azo compounds are conventionally obtained by oxidation of hydrazo derivatives or the corresponding aminonitriles, as described, for example, in documents US Pat. No. 2,515,628, WO 03 / 002521, US Pat. No. 3,390,146, CN 1309705 or EP 2821393. After oxidation, the resulting suspension is generally drained and then optionally dried to give a solid in the form of a powder.

[0004] However, azo compounds in powder form cause many problems.

[0005] In particular, they generate dusts that may present explosion risks and / or industrial hygiene risks. Indeed, after these dusts are accidentally suspended in the air, they may come into contact with the upper respiratory tract of the people who handle them. Such contact may occur to operators on site at industrial facilities, for example when manually loading powders into a reactor, or to operators collecting samples required for controlling the manufacturing process. It is desirable to limit any contact of this type to a minimum or even avoid it completely, in order to ensure the safety of the operators and guarantee the hygiene of the manufacturing site.

[0006] Furthermore, powders of this type are not easy to handle by operators. The flowability of powders is usually not sufficient to make them easy to transport and load into reactors. Azo compounds in powder form have poor flowability, often leading to agglomeration problems during their storage and loading.

[0007] There is therefore a need for improved forming of azo compounds, particularly so that they generate little or no dust and are easier to handle by operators.

[0008] It is therefore an object of the present invention to provide a granulation process which is easy to implement and preferably more environmentally friendly.

[0009] Another object of the present invention is to provide azo compound granules which avoid or reduce dust and / or which can be easily transported and handled.

[0010] It is an object of the present invention to provide strong, that is to say resistant, particles of azo compounds which retain their shape in particular during their storage and their handling.

[0011] Another object of the present invention is to provide particles of azo compounds having properties similar to those of powders.

[0012] The present invention meets all or part of the above objects.

[0013] The inventors have found that the granulation of azo compounds can be carried out by means of a process using aqueous suspensions of these compounds under stirring and in the presence of an organic binder. This process makes it possible in particular to avoid the use of large amounts of organic solvents, the suspension being aqueous. It also makes it possible to obtain granules without the use of surfactants or dispersants.

[0014] Mechanical granulation is known, for example, from document WO 00 / 24706. This involves compressing and then extruding a powder of an azo compound to form granules. However, controlling the forming temperature is important for this technology. However, such control is not evident at an industrial level. This type of process involves the risk of heating by friction or compression and therefore of severe thermal decomposition of the azo compound during granulation. In addition, the granules obtained by mechanical granulation are not very resistant to breakage and tend to disintegrate.

[0015] The process according to the invention avoids these risks of heating and decomposition by using mild granulation conditions, thereby making it possible to obtain granules of high purity. Thus, the application properties of the compound, in particular in polymerization, are preserved.

[0016] Furthermore, and surprisingly, the particles according to the invention are strong (resistant). More particularly, their resistance to crushing is significantly greater than that of other known shaped forms of azo compounds.

[0017] In particular, "resistance to crushing" refers to the maximum weight per unit surface consisting of particles that these particles can support before being crushed or disintegrating (i.e. losing their shape):

[0018] Resistance to crushing = load weight at the crushing point / particle surface area

[0019] To measure crush resistance, the compressive load required to cause the particle to break is usually measured.

[0020] The crushing resistance of the granules according to the invention is in particular greater than or equal to 25 g / cm 2, more preferably greater than or equal to 40 g / cm 2 .

[0021] They preferably have a g / cm 2 , preferably 95g / cm 2 , more preferably 100 g / cm 2 Or even 500g / cm 2 For example, their maximum crushing resistance is 50 to 200 g / cm 2 , preferably 55 to 95 g / cm 2 .

[0022] Therefore, they can be transported and handled without breaking or disintegrating.

[0023] Since they are preferably substantially spherical, they can be easily discharged from drums or storage bags and loaded into the reactor.

[0024] Therefore, the particles according to the invention are preferably substantially spherical, or even spherical, and they may have a diameter of 0.5 mm to 5 mm, preferably 2 to 3 mm. Therefore, their size is generally larger than dust, and in particular their size is much larger than respirable dust. In particular, "dust" refers to particles with a size of less than 100 μm. More particularly, the size of respirable dust is less than 20 μm, preferably less than 5 μm.

[0025] Surprisingly, the granules obtained have properties similar to those of the powders, and in particular similar dissolution times. The granules according to the invention are therefore fully suitable for industrial use, just like conventional powders.

[0026] Brief description of the invention

[0027] The present invention relates to a granulation method for an azo compound of the following general formula (I):

[0028] [Chemical formula 1]

[0029]

[0030] in:

[0031] ●Group R 1 , R 2 , R 3 and R 4 The same or different, independently selected from:

[0032] - a straight-chain or branched alkyl group, preferably a (C1-C6)alkyl group, which is optionally substituted by a hydroxyl group or an alkoxy group or by a halogen atom;

[0033] - cycloalkyl, preferably (C3-C6)cycloalkyl, which is optionally substituted by hydroxy or alkoxy or by halogen atoms;

[0034] - aryl, preferably phenyl or naphthyl, which is optionally substituted by hydroxy, alkyl or alkoxy or by halogen atoms;

[0035] - aralkyl, preferably benzyl or phenethyl, which is optionally substituted by one or more alkyl, alkoxy or hydroxyl groups or by one or more halogen atoms; or

[0036] -R 1 With R 2 and / or R 3 With R 4 At least one of the combination of forms a cycloalkyl group or a C(O) group with the carbon atom to which it (or they) are attached;

[0037] ●Group R 5 and R 6 The same or different, independently selected from CN or NH2;

[0038] The method comprises the following steps:

[0039] a) a granulation step carried out by stirring an aqueous suspension of the azo compound in the presence of an organic binder;

[0040] b) an optional step of recovering the particles obtained in step a), preferably by filtration; and

[0041] c) an optional step of drying the particles recovered in step b).

[0042] The invention also relates to particles obtainable or obtained or directly obtained by a process as according to the invention.

[0043] The invention also relates to particles comprising an azo compound of the general formula (I) and an organic binder as defined below.

[0044] The present invention also relates to a material having a thickness greater than or equal to 25 g / cm 2 , more preferably greater than or equal to 40g / cm 2 Crushing resistance of particles.

[0045] The invention relates to the use of such particles as swelling agents, initiators for polymerization reactions using free radicals or as synthesis intermediates, in particular in the preparation of pharmaceutical or agrochemical compounds. DETAILED DESCRIPTION OF THE INVENTION

[0047] The azo compound has the following general formula (I):

[0048] [Chemical formula 1]

[0049]

[0050] in:

[0051] ●Group R 1 , R 2 , R 3 and R 4 The same or different, independently selected from:

[0052] - a straight-chain or branched alkyl group, preferably a (C1-C6)alkyl group, which is optionally substituted by a hydroxyl group or an alkoxy group or by a halogen atom;

[0053] - cycloalkyl, preferably (C3-C6)cycloalkyl, which is optionally substituted by hydroxy or alkoxy or by halogen atoms;

[0054] - aryl, preferably phenyl or naphthyl, which is optionally substituted by hydroxy, alkyl or alkoxy or halogen atoms;

[0055] - aralkyl, preferably benzyl or phenethyl, which is optionally substituted by one or more alkyl, alkoxy or hydroxyl groups or by one or more halogen atoms; or

[0056] -R 1 With R 2 and / or R 3 With R 4 At least one of the combination of forms a cycloalkyl group (preferably a (C3-C6) cycloalkyl group) or a C(O) group with the carbon atom to which it (or they) are attached;

[0057] ●Group R 5 and R 6 Identical or different, independently of one another, are selected from CN (nitrile) or NH2 groups.

[0058] Preferably, R 5 and R 6 same.

[0059] In particular, when R 5 and R 6 When they are the same and represent NH2 groups, R 1 With R 2 and R 3 With R 4 Each forms a C(O) group with the carbon atom to which they are attached; or

[0060] When R 5 and R 6 When the groups R 1 , R 2 , R 3 and R 4 The same or different, independently selected from:

[0061] - a straight-chain or branched alkyl group, preferably a (C1-C6)alkyl group, which is optionally substituted by a hydroxyl group or an alkoxy group or by a halogen atom;

[0062] - cycloalkyl, preferably (C3-C6)cycloalkyl, which is optionally substituted by hydroxyl or by halogen atoms;

[0063] - aryl, preferably phenyl or naphthyl, which is optionally substituted by hydroxy, alkyl or alkoxy or by halogen atoms;

[0064] - aralkyl, preferably benzyl or phenethyl, which is optionally substituted by one or more alkyl, alkoxy or hydroxyl groups or by one or more halogen atoms; or

[0065] -R 1 With R 2 and / or R 3 With R 4 At least one of the combination of forms a cycloalkyl group with the carbon atom to which it (or they) are attached.

[0066] Most preferably, R 5 and R 6 represents a CN (nitrile) group. In particular, R 1 and R 3 Same and / or R 2 and R 4 same.

[0067] Preferably, the group R 1 , R 2 , R 3 and R 4 Selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclopropyl and phenyl.

[0068] In particular, the group R 1 , R 2 , R 3 and R 4 is selected from alkyl as defined above. In particular, when the substituents are alkyl and / or alkoxy, they contain 1 to 6 carbon atoms. Halogen includes in particular fluorine, chlorine, bromine and iodine.

[0069] Preferably, the compounds of general formula (I) are symmetrical.

[0070] Examples of the azo compounds of general formula (I) include:

[0071] 2,2'-Azobis(isobutyronitrile),

[0072] 2,2'-Azobis(2,4-dimethylvaleronitrile),

[0073] 2,2'-Azobis(2-methylhexanenitrile),

[0074] 2,2'-Azobis(2-cyclopropylpropionitrile),

[0075] 2,2'-Azobis(2-phenylpropionitrile),

[0076] 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(1-cyclohexanecarbonitrile), and azodicarbonamide.

[0077] The corresponding structures are given in the following table:

[0078] [Table 1]

[0079]

[0080] The preferred compound according to the invention is 2,2'-azobis(isobutyronitrile), commonly referred to as AZDN or AIBN. It corresponds to the compound wherein R 1 , R 2 , R 3 and R 4 is methyl and R 5 and R 6 A compound containing a CN group (CAS No. 78-67-1).

[0081] Before the azo compound of formula (I) is granulated, it is usually in a solid state, most commonly in the form of a powder. Thus, the azo compound is preferably in the form of a powder, the powder comprising particles having a size of 10 μm to 200 μm, preferably 40 μm and 150 μm. In particular, the powder has a particle size distribution (Dv50) of 10 μm to 200 μm, preferably 40 μm to 150 μm, more preferably 90 μm to 130 μm.

[0082] The particle size of a powder is usually defined as the statistical distribution of the particles that make up the powder according to their size (size and shape of the elementary particles). The particle size distribution (Dv50) is a known parameter. It corresponds to the particle size (μm) below which 50% of the particle volume on the distribution curve expressed as cumulative frequency is located. For example, if Dv50 = 100 μm, 50% of the sample particle volume has a diameter less than 100 μm, and 50% of the particle volume has a diameter greater than 100 μm. Two other characteristic diameters commonly used to describe the particle size distribution of powders are Dv10 and Dv90:

[0083] - Dv10: this corresponds to the diameter (μm) below which 10% of the volume of the particles lies; and

[0084] - Dv90: This corresponds to the diameter (μm) below which 90% of the particle volume lies.

[0085] In particular, AZDN (especially dried) is in the form of a powder having a Dv50 of 80 to 200 μm, preferably 90 to 110 μm.

[0086] In particular, AZDN (especially wet) is in the form of a powder having a Dv50 of 80 μm to 200 μm, preferably 110 μm to 130 μm.

[0087] Therefore, the azo compound powder may contain 0.1 to 10 wt %, preferably 5 to 10 wt % of water, relative to the total weight of the powder.

[0088] Preferably, the solubility of the compound of formula (I) in the organic binder is at least 10 g / L, preferably 10 g / L to 100 g / L, and more preferably 20 g / L to 70 g / L. Therefore, the azo compound is preferably soluble in the organic binder.

[0089] The solubility can be determined using standard methods. It can also be determined as follows:

[0090] 1.5 g of the compound of formula (I) are added to 10 g of an organic binder at 20° C. The bottle is shaken for a period of 1 to 10 hours, for example 6 hours. After decantation, the binder is analyzed to determine its content of the compound of formula (I): this content corresponds to the solubility of the azo compound in the organic binder in g / L. The analysis is performed by gas chromatography. A standard range of 0 to 150 g / l is produced by diluting the compound of formula (I) in acetone.

[0091] The azo compounds of the formula (I) according to the invention are known and commercially available, usually in powder form.

[0092] For example, there may be mentioned AZDN sold by Arkema, the products V-40, V-59, AIBN, V-65 sold by Fujifilm Wako or the products sold by Chemours 52. 64. 67 and 88.

[0093] It is also possible to use azo compounds that are directly recovered after their production. For example, it is possible to use azo compounds obtained in the form of wet powders after the corresponding hydrazine or aminonitrile compounds have been oxidized, drained, washed, and are obtained. In this case, the powder may contain 5 to 10 % by weight of water relative to the gross weight of the powder.

[0094] The same azo compound can be used after being drained, washed and then dried. In this case, the powder may contain 0.01 to 0.2% by weight of water relative to the total weight of the powder.

[0095] The granulation step a) of the azo compound is carried out in the presence of an organic binder which is preferably liquid (under the operating conditions of the process according to the invention).

[0096] In particular, the organic binder is poorly soluble in water. “Poorly soluble in water” particularly means that the solubility of the binder in water is less than or equal to 25 g / L, preferably 0.1 g / L to 20 g / L, more preferably 5 g / L to 15 g / L.

[0097] To measure the solubility of the organic binder in water, conventional methods can be used. 100 g of water and 20 g of binder can also be mixed with stirring at 20° C. for 1 hour. The aqueous phase is decanted and then analyzed by gas chromatography to determine the binder content (in g / L), corresponding to its solubility.

[0098] Preferably, the organic binder is selected from aliphatic acetates, aliphatic carbonates, non-halogenated aromatic hydrocarbons, aliphatic ketones and aliphatic ethers, or mixtures thereof.

[0099] Among the aliphatic acetates, alkyl acetates are preferred, the alkyl group being able to contain at least 4 carbon atoms, preferably 4 to 6 carbon atoms. They are especially of the following formula:

[0100] CH3-C(O)OR a , R a is an alkyl group containing at least 4 carbon atoms, preferably 4 to 6 carbon atoms.

[0101] Among the aliphatic carbonates, dialkyl carbonates are preferred, the alkyl group being able to contain at least 2 carbon atoms, preferably 2 to 3 carbon atoms. They are especially of the following formula:

[0102] R b -OC(O)-OR c , R b and R c are independently an alkyl group containing at least 2 carbon atoms, preferably 2 to 3 carbon atoms. b and R c same.

[0103] Non-halogenated aromatic hydrocarbons refer in particular to alkylbenzenes, and preferably toluene, xylene (o-xylene, m-xylene and p-xylene) and cumene. Alkylbenzenes refer in particular to benzene substituted by at least one alkyl group, the alkyl group containing at least 1 carbon atom, preferably 1 to 5 carbon atoms, more preferably methyl.

[0104] Among the aliphatic ketones, dialkyl ketones are preferred, which may contain at least 6 carbon atoms, preferably 6 to 8 carbon atoms. They are particularly of the formula: CH3-C(O)-R d , R d It is an alkyl group containing at least 4 carbon atoms, preferably 4 to 6 carbon atoms.

[0105] Among the aliphatic ethers, dialkyl ethers are preferred, which may contain at least 6 carbon atoms, preferably 6 to 8 carbon atoms. They are especially of the formula: CH3-OR f , R f The alkyl group is an alkyl group containing at least 5 carbon atoms, preferably 5 to 7 carbon atoms, and is preferably cyclic.

[0106] It should be understood that the alkyl group mentioned above may be linear, branched or cyclic.

[0107] Preferably, the organic binder is selected from the following:

[0108] Toluene, m-xylene, p-xylene, o-xylene, n-butyl acetate, isobutyl acetate, cyclopentyl methyl ether (CPME or methoxycyclopentane), diethyl carbonate, methyl isobutyl ketone and methyl amyl ketone.

[0109] Preferably, the organic binder is selected from the following:

[0110] Toluene, m-xylene, n-butyl acetate, isobutyl acetate, cyclopentyl methyl ether (CPME or methoxycyclopentane) and methyl isobutyl ketone.

[0111] Preferred organic binders are isobutyl acetate and cyclopentyl methyl ether, more preferably isobutyl acetate.

[0112] Prior to step a) granulation, the method may comprise the step of preparing an aqueous suspension of the azo compound (i.e. a heterogeneous mixture in which the liquid phase is water and the solid dispersed phase is the azo compound). For example, the azo compound is mixed with water in powder form (preferably as defined above), and preferably mixed under stirring. The suspension may be prepared by any conventional method by a person skilled in the art.

[0113] In the context of the present invention, it is also possible to use an acidic aqueous suspension of an azo compound obtained directly after an oxidation step of a hydrazo compound or of the corresponding aminonitrile (e.g., in the case of AZDN, after a chlorination step of hydrazo-bis-isobutyronitrile). This suspension may contain from 2 to 15% by weight of HCl relative to the total weight of the suspension.

[0114] In the suspension, the azo compound / water mass ratio may be 1 / 99 to 40 / 60, preferably 10 / 90 to 25 / 75; and more preferably 15 / 85 to 25 / 75.

[0115] The process according to the invention comprises the step a) of granulating an azo compound of the general formula (I) as defined above suspended in water under stirring and in the presence of an organic binder.

[0116] Preferably, the organic binder is added to the aqueous suspension. The organic binder may be added to the azo compound and then the water, or the three components may be placed in the reactor simultaneously, although these embodiments are not preferred.

[0117] The addition of the organic binder can be carried out by any means known to the person skilled in the art. It can be a one-time or continuous one, preferably a one-time one. In fact, it is not necessary to add the organic binder gradually: the total amount of the latter can be added to the aqueous suspension of the azo compound at one time. Therefore, it is preferred to carry out a rapid addition of the organic binder, for example for a duration of 1 to 30 minutes, more preferably 1 to 20 minutes, in particular 1 to 5 minutes.

[0118] The granulation step a) is carried out under stirring. The stirring can be carried out by any known stirring device or element, such as any type of blade (straight or inclined) or a spiral belt. The reactor can include one or more stages of stirring elements.

[0119] More particularly, the stirring speed (corresponding, for example, to the rotation speed of the stirring element) must be sufficient to obtain a uniform suspension of the azo compound in water and a uniform dispersion of the organic binder, but not to result in the formation of an emulsion. When operating in a reactor of 1 to 10 liters, speeds of 500 to 900 rpm are generally used, or when operating in a reactor of the order of 100 liters, speeds of 50 to 300 rpm may be used. For example, the stirring speed may be increased or decreased throughout step a), but it is preferably gradually reduced.

[0120] In general, the formation of particles occurs quickly, i.e., after stirring for a few minutes in the presence of the organic binder. In particular, particles are formed in a period of 1 minute to 30 minutes, for example 2 minutes to 10 minutes. Spherical (or substantially spherical) particles with a maximum diameter of about 0.5 to 5 mm, for example 1 to 5 mm, preferably 2 to 3 mm are usually obtained. Maintaining stirring after particle formation can serve to consolidate the particles obtained and / or reduce their dispersion.

[0121] Step a) may be performed for a period of 1 minute to 10 hours, preferably 30 minutes to 5 hours, more preferably 1 hour to 5 hours.

[0122] The granulation step a) may comprise or consist of the following two steps:

[0123] A1) adding an organic binder to an aqueous suspension of the azo compound under stirring to obtain a granulation medium; then

[0124] A2) Maintaining agitation of the granulation medium.

[0125] Preferably, step a) is carried out in the absence of surfactants and / or dispersants.

[0126] Preferably, step a) is carried out without adding surfactants and / or dispersants.

[0127] For example, step a) is carried out in the absence or without addition of sodium dioctylsulfosuccinate.

[0128] The granulation step a) is carried out in particular at a temperature which does not cause degradation of the azo compound. The temperature may be from 5° C. to 45° C., preferably from 10° C. to 40° C., for example from 10° C. to 20° C. This step is generally carried out at atmospheric pressure.

[0129] The azo compound / water mass ratio may be 1 / 99 to 40 / 60, preferably 10 / 90 to 25 / 75; and more preferably 15 / 85 to 25 / 75.

[0130] The organic binder / azo compound mass ratio may be 0.2 to 0.5, preferably 0.3 to 0.5, more preferably 0.3 to 0.4.

[0131] The method according to the invention optionally comprises a subsequent step of recovering and drying the particles obtained in step a). These steps can be carried out in a conventional manner. For example, the particles can be recovered by filtering. They can then be dried. In particular, they can be dried at a temperature of 10°C to 45°C, preferably 20°C to 40°C. They can be dried under reduced pressure, or more preferably dried under flushing with air, depleted air or an inert gas such as nitrogen. Drying can last for several hours, for example 1 to 10 hours, preferably 3 to 5 hours.

[0132] “Particles” refer in particular to solid and cohesive agglomerates of constituent particles, which particles can have a size of 10 to 200 μm, preferably 90 to 110 μm.

[0133] The present invention therefore relates to particles obtainable (or obtained or directly obtained) by the process according to the present invention. Such particles are novel.

[0134] The invention also relates to particles comprising an azo compound of formula (I) as defined above and an organic binder as defined above.

[0135] In particular, in the particles according to the invention, the binder is present in trace amounts; in particular when these particles are dried after recovery, this leads to evaporation of the organic binder. Thus, the particles according to the invention may contain 20 ppm to 3000 ppm, for example 20 ppm to 1000 ppm of organic binder. More particularly, they contain 20 ppm to 500 ppm of organic binder, more preferably 50 ppm to 300 ppm of organic binder, still more preferably 50 ppm to 200 ppm of organic binder, in particular after drying.

[0136] In particular, the particles according to the invention have a particle size greater than or equal to 25 g / cm 2 , more preferably greater than or equal to 40 g / cm 2 Crushing resistance.

[0137] They advantageously have a thickness of 90 g / cm 2 , preferably 95g / cm 2 , more preferably 100 g / cm 2 Or even 500g / cm 2 For example, their maximum crushing resistance is 50 to 100 g / cm 2 , preferably 55 to 95 g / cm 2 .

[0138] The particles according to the invention are generally substantially spherical or spherical in shape. They may have a diameter of 0.5 to 5 mm, and more preferably 1 to 5 mm, for example 2 to 3 mm.

[0139] The present invention also relates to particles comprising an azo compound of general formula (I) as defined above, having a particle size greater than or equal to 25 g / cm 2 , more preferably greater than or equal to 40 g / cm 2 Such particles may include one or more of the above-mentioned features.

[0140] One of the advantages of the particles according to the invention is their solidity, which allows them to be transported and handled very easily. They are also of high purity, with a low content of residual organic binders.

[0141] The invention relates to their use as swelling agents, initiators for polymerization reactions using free radicals or as synthesis intermediates, in particular for the preparation of pharmaceutical or agrochemical compounds. The polymerization reactions can be bulk, solution, suspension or emulsion polymerizations and can employ very different monomers, for example (meth)acrylic or vinyl monomers such as acrylamide, acrylonitrile, alkyl (meth)acrylates, styrene, vinyl chloride and vinyl acetate or vinylidene chloride. The fields of application are particularly (but not exclusively) acrylic sheets or fibers, flocculants, coatings, coating resins, graft polyols, polystyrene, PVC (poly(vinyl chloride)), PVA (polyvinyl acetate) or PMMA (polymethyl methacrylate).

[0142] In particular, the particles according to the invention can be used for the preparation of polyols grafted with a mixture of styrene and acrylonitrile, or for the preparation of polyacrylonitrile as a precursor for carbon fibers. Example

[0143] The particle sizes of dry AZDN used in the examples are 52.5 / 101 / 180 microns dv(10), dv(50) and dv(90), respectively. The particle sizes of wet AZDN are 61 / 119 / 203 microns dv(10), dv(50) and dv(90), respectively.

[0144] The particle size is measured using The measurement is performed using a drop of water and A surfactant (ethoxylated nonylphenol) was used as dispersant. The particle size measurement was performed after 10 minutes of circulation in the measuring cell.

[0145] Example 1: Granulation in a 500 ml reactor

[0146] 1- Operation Mode :

[0147] Granulation :

[0148] The reactor was a 500 ml double-walled glass reactor, the temperature of which was maintained at 15° C. by circulating cold water, and it was equipped with a mechanical stirrer.

[0149] 22.4 g of dry AZDN was weighed into a beaker, and then 100 mL of water was added. After the mixture was stirred evenly with a spatula, the aqueous suspension was transferred to a reactor. Then 100 mL of water was added to recover the residual AZDN in the beaker.

[0150] The suspension in the reactor was stirred at a speed of 1000-1100 rpm so that the AZDN remaining on the surface was entrained by stirring. After a few minutes, the organic binder was quickly added to the reactor. The stirring speed was then reduced to 850 rpm.

[0151] After stirring for about three hours, particle formation or other conditions were recorded.

[0152] The reactor is drained onto a filter. Optionally, a final rinse of the reactor is performed using an aqueous filter solution saturated with a binder.

[0153] The filtered granules were washed and allowed to dry in open air under ventilation for about 24 hours. The friability of the formed and dried granules was recorded via their resistance to manual crushing.

[0154] Measurement of Solubility of Organic Binders in Water :

[0155] The measurement is performed by contacting and stirring 100 g of water and 20 g of an organic binder at 20° C. for 1 hour. The aqueous phase is decanted and then analyzed by gas chromatography to determine the concentration of the organic binder.

[0156] Measurement of the Solubility of AZDN in Organic Binders :

[0157] The measurement is carried out by adding 1.5 g of AZDN to 10 g of organic binder at 20°C. The bottle is shaken for about 6 hours. After decanting, the organic binder is analyzed to determine its AZDN concentration. The analysis is carried out by gas chromatography, with the injector temperature set at 220°C (under these conditions, AZDN is essentially converted to tetramethylsuccinonitrile in the injector). A standard range of 0 to 150 g / l is produced by diluting AZDN in acetone.

[0158] Gas chromatography analysis :

[0159] The chromatographic column was an OV1701 wide-pore column (diameter = 0.25 mm, length = 30 m, film thickness = 0.25 μm), and the chromatographic apparatus was a Hewlett Packard HP 6890 apparatus equipped with a FID (flame ionization) detector.

[0160] 2- Results obtained :

[0161] The results obtained are presented in the following table:

[0162] [Table 2]

[0163]

[0164] *The solidity after drying is evaluated as follows:

[0165] - Positive: The dried particles did not break under slight pressure from the scraper;

[0166] - Negative: The dried granules were broken under slight pressure from the scraper and produced powder.

[0167] **Test B was performed using 5% aqueous HCl solution instead of water.

[0168] After granulation according to the invention, granules with a size of 1 to 3 mm are obtained which are strong enough for recovery, drying and handling.

[0169] Example 2: Granulation in a 2L reactor

[0170] 1- Granulation and drying :

[0171] Granulation :

[0172] A similar apparatus as in Example 1 was used, but with a 2-liter reactor. The quantities involved are given in the following table.

[0173] The stirrer was a pitched blade stirrer and the initial stirring setting was 800 rpm and then reduced to 600 rpm after the organic binder was introduced as in the previous example.

[0174] Drying of granules :

[0175] A porous glass filter with a diameter of 6 cm was used, which was equipped with a double jacket to allow heating of the filter wall by circulating hot water. 100 g of undried filtered particles were introduced into the filter. A constant nitrogen flow (2 liters / minute) was then injected through the bottom of the filter at different temperatures.

[0176] The particles obtained are given in the table below:

[0177] [Table 3]

[0178]

[0179] *10% HCl aqueous solution

[0180] ** Starting from 109 g wet AZDN containing 8.2% water, which is equivalent to 100 g dry AZDN

[0181] 2- Determination of residual organic binder content :

[0182] During the drying of the above granules, about one gram of the granules obtained with isobutyl acetate was taken out over time and analyzed by gas chromatography to determine the residual binder content.

[0183] The results obtained are presented in the following table:

[0184] [Table 4]

[0185]

[0186] Using CMPE, drying was faster at 30°C and a residual CPME concentration of 0.01% was observed after 3 hours with no significant change thereafter (5 hours drying).

[0187] Therefore, the preparation and drying of the granules can be carried out under satisfactory industrial conditions. After several hours of drying, the granules obtained have a residual organic binder content of 0.01 to 0.02% by mass, i.e., a residual organic binder of 100 to 200 ppm (i.e., 100 to 200 mg of organic binder per kg of granules).

[0188] 3- Crushing test on dried granules :

[0189] 20 g of AZDN granules obtained in Example 2 were placed and distributed evenly in a glass crystallizer with a diameter of 6 cm, and a flat-bottomed glass beaker with a diameter of 5 cm (whose empty mass was 200 g) was then placed on top of it. If no crushing or breaking of the granules was observed, additional weights of 200 g were gradually added above the beaker until the granules were observed to begin to be crushed, visible through the transparency of the bottom of the beaker or the sides of the glass crystallizer.

[0190] The surface area of ​​the beaker is S = πx(2.5) 2 =19.625cm 2 .

[0191] Crushing resistance is: [total weight at breakpoint (beaker + additional weight)] / [S]

[0192] Comparison test :

[0193] Granules were prepared by extrusion according to the procedure described in Examples 1 and 2 of the application WO 00 / 24706. The AZDN powder is the powder used in the previous examples of the present application. The diameter of the granules obtained is 5 mm and the average length is 1.5 cm (between 1 and 2 cm). Once dried, these granules appear very brittle when handled. They show very low resistance to the crushing test, much lower than the resistance obtained by the granules according to the invention.

[0194] The results obtained are presented in the following table:

[0195] [Table 5]

[0196]

[0197] *C13-C15 fatty alcohols condensed with ethylene oxide and propylene oxide

[0198] The granules according to the invention have a significantly improved resistance to crushing.

[0199] They are easy to handle and do not fall apart.

[0200] Example 3: Granulation in a 100 L reactor

[0201] 1- Granulation and drying :

[0202] A 100-liter enameled stainless steel AE100 reactor of the DE DIETRICH brand was used. The reactor vessel had an inner diameter of 508 mm and an effective height of 375 mm.

[0203] The stirring is ensured by an "impeller" type stirrer with a diameter of 300 mm, which has three straight blades to ensure radial stirring. The stirring speed can be varied from 0 to 200 rpm. The reactor is equipped with a ball-type bottom valve connected to the filter dryer. The filter diameter is 55 cm. The filter is equipped with a scraper stirrer with a diameter of 48 cm, which can be moved up and down in the filter, allowing, in a lowered position flush with the filter, mechanical evacuation of the dried product through a side opening. The stirring speed can be varied from 0 to 60 rpm. The filter cloth is a 20 micron mesh cloth.

[0204] The test was carried out at room temperature (19-20°C).

[0205] The reactor was maintained under nitrogen with a light flush of 50 l / h.

[0206] 43.1 kg of deionized water were introduced, stirring was set at 200 rpm and the temperature was 18° C., and 11.3 kg of wet AZDN powder with a water content of 8% were introduced within 5 minutes.

[0207] After 5 minutes, 4.1 kg of isobutyl acetate were added over two minutes. The formation of particles was visible in the first few minutes. After 5 minutes, the stirring was reduced to 100 rpm and these conditions were maintained for 5 hours.

[0208] The reactor then drains through a bottom valve into a filter. The particles are filtered by applying nitrogen pressure to evacuate and recover the aqueous liquid.

[0209] Then, at room temperature for 10 min 3 / h nitrogen flushing for 24 hours.

[0210] The granules, once dried, were solid and could be recovered by activating the mechanical scraper stirrer, the speed being set at 6 rpm. In this way, 10.2 kg of AZDN were recovered in the form of granules having a diameter of about 2 to 3 mm.

[0211] 2-Crushing resistance test :

[0212] The particles described in the previous examples were tested for crushing resistance, and the results showed that these particles had very good solidity, with a crushing resistance of at most 91.72 g / cm 2 .

[0213] 3-Dissolution test :

[0214] The particle dissolution test was performed at room temperature. A glass conical flask equipped with a magnetic stirring bar was placed on a magnetic stirrer. Stirring was stopped and 13 g of AZDN was introduced into the conical flask. Then 100 ml of acetone was quickly introduced and stirring was started (100 rpm). The time required for visual observation to no longer see undissolved AZDN crystals was recorded.

[0215] Commercial recrystallized AZDN (130-257-438 microns / dv 10-50-90), AZDN particles prepared and dried as above, and the dry powdered AZDN used in Example 1 were compared.

[0216] [Table 6]

[0217]

[0218] It can be seen that the spherical AZDN particles obtained according to the present invention dissolve as fast as the initial AZDN in powder form. On the other hand, the recrystallized AZDN crystals, although having a smaller average diameter than the spherical particles of the present invention, take longer to dissolve in acetone.

[0219] No visible insoluble material was recorded for each sample.

Claims

1. A method for granulating an azo compound of the following general formula (I): [Chemical formula 1] in: *Group R 1 , R 2 , R 3 and R 4 The same or different, independently selected from: - a straight-chain or branched alkyl group, which is optionally substituted by a hydroxyl group or an alkoxy group or by a halogen atom; - cycloalkyl, which is optionally substituted by a hydroxyl or alkoxy group or by a halogen atom; - aryl, which is optionally substituted by a hydroxyl, alkyl or alkoxy group or by a halogen atom; - an aralkyl group which is optionally substituted by one or more alkyl, alkoxy or hydroxy groups or by one or more halogen atoms; or -R 1 With R 2 and / or R 3 With R 4 At least one of the combination of forms a cycloalkyl or C(O) group with the carbon atom to which it (or they) are attached; *Group R 5 and R 6 are identical or different and are independently selected from CN or NH2 groups; The method comprises the following steps: a) carrying out a granulation step by stirring an aqueous suspension of the azo compound in the presence of an organic binder; b) an optional step of recovering the particles obtained in step a), preferably by filtration; and c) an optional step of drying the particles recovered in step b).

2. The granulation method according to claim 1, wherein the organic binder is added to the aqueous suspension.

3. The granulation method according to claim 1 or 2, wherein the azo compound of general formula (I) is selected from the following: 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylhexanenitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2-phenylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(1-cyclohexanenitrile) and azodicarbonamide; preferably 2,2'-azobis(isobutyronitrile).

4. The granulation process according to any one of the preceding claims, wherein the organic binder is selected from aliphatic acetates, aliphatic carbonates, non-halogenated aromatic hydrocarbons, aliphatic ketones and aliphatic ethers.

5. The granulation method according to any one of the preceding claims, wherein the azo compound / water mass ratio may be from 1 / 99 to 40 / 60, preferably from 10 / 90 to 25 / 75; and more preferably from 15 / 85 to 25 / 75.

6. The granulation method according to any one of the preceding claims, wherein the organic binder / azo compound mass ratio may be from 0.2 to 0.5, preferably from 0.3 to 0.5, more preferably from 0.3 to 0.

4.

7. Granules comprising an azo compound of the general formula (I) as defined in any one of claims 1 or 3 and an organic binder as defined in any one of claims 1 or 4.

8. The particle according to claim 7, characterized in that They are substantially spherical in shape, preferably with a diameter of 0.5 to 5 mm.

9. Granules obtainable by a process according to claims 1 to 6.

10. Use of the particle according to any one of claims 7 to 9 as a swelling agent, an initiator for polymerization reactions using free radicals, or as a synthesis intermediate, in particular in the preparation of pharmaceutical or agrochemical compounds.

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