PROCESS FOR GRANULATING AZO COMPOUNDS AND OBTAINING GRANULES

Abstract

The present invention relates to a process for granulating an azo compound comprising the following steps: a) a granulation step by stirring an aqueous suspension of said 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 granules recovered in step b). It also relates to granules that can be obtained by the process according to the invention and their uses.

Description

Title of the invention: PROCESS FOR GRANULATING AZO COMPOUNDS AND OBTAINING GRANULES

[0001] The present invention relates to a process for granulating azo compounds, as well as the granules that can be obtained by this process and their uses.

[0002] Azo compounds, and more specifically 2,2'-azobis(isobutyronitrile), known as AZDN or AIBN, are well-known products. They are used as blowing agents, synthesis intermediates, or initiators of polymerization reactions involving free radicals. These reactions can be bulk, solution, suspension, or emulsion polymerization reactions and can involve a wide variety of monomers, for example, (meth)acrylic or vinyl monomers, such as acrylamide, acrylonitrile, alkyl (meth)acrylate, styrene, acetate, and vinyl chloride or vinylidene chloride. Their applications are therefore very diverse and include, but are not limited to, acrylic sheets or fibers, flocculants, paints, coating resins, grafted polyols, polystyrene, PVC, PVA, and PMMA.

[0003] These azo compounds are classically obtained by oxidizing the corresponding hydrozoic derivatives or amino-nitriles as described for example in documents US 2,515,628, WO 03 / 002521, US 3,390,146, CN 1309705 or EP 2 821 393. After oxidation, the resulting suspension is generally dewatered, then possibly dried, to give a solid in powder form.

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

[0005] In particular, they generate dust that may present a risk of explosion and / or industrial hygiene. This dust can come into contact with the upper respiratory tract of those handling it after being accidentally released into the air. Such contact can occur with operators present at the industrial installation, for example, during the manual loading of powder into reactors or with operators taking samples necessary for monitoring the manufacturing process. It is advisable to minimize, or even completely avoid, any such contact in order to ensure the safety of operators and guarantee the hygiene of the manufacturing premises.

[0006] Furthermore, this type of powder is not easily handled by operators. The powder is generally not sufficiently flowable to allow for easy transport and loading into reactors. Azo compounds in powder form exhibit poor flowability, often resulting in problems with clumping during their storage and loading.

[0007] There is therefore a need for an improved shaping of azo compounds, in particular one that does not generate little or no dust and that is easily handled by operators.

[0008] Thus, an objective of the present invention is to provide a granulation process that is easy to implement, and preferably more environmentally friendly.

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

[0010] An objective of the present invention is to provide azo compound granules that are solid (i.e., resistant), in particular that retain their shape during storage and handling.

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

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

[0013] The inventors discovered that the granulation of azo compounds can be achieved using a process employing an aqueous suspension of these compounds, under agitation and in the presence of an organic binder. This process notably avoids the need for large quantities of organic solvents, as the suspension is aqueous. It can also produce granules without the use of surfactants or dispersants.

[0014] For example, mechanical granulation is known from document WO 00 / 24706. This involves compressing and then extruding powders of azo compounds to form granules. However, this technique requires precise control of the shaping temperature. Such control is not readily achievable on an industrial scale. This type of process carries risks of overheating due to friction or compression, and consequently, risks of violent thermal decomposition of the azo compounds during granule formation. Furthermore, granules obtained by mechanical granulation are not very resistant to crushing and disintegrate easily.

[0015] The process according to the invention avoids these risks of overheating and decomposition by using gentle granulation conditions, which makes it possible to obtain granules of good purity. The application properties of the compounds, particularly in polymerization, are thus preserved.

[0016] Moreover, and surprisingly, the granules according to the invention are solid (resistant). More specifically, they exhibit a crush resistance significantly greater than other known forms of azo compounds.

[0017] In particular, "crush resistance" means the maximum weight per unit of a surface composed of granules that these granules can withstand before crushing or disintegrating (i.e., losing their shape):

[0018] Crushing resistance = weight of the load at the breaking point / surface area of ​​the granules

[0019] To measure crush resistance, one generally measures the compressive load required to cause the granule to break.

[0020] The crush resistance of the granules according to the invention is in particular greater than or equal to 25 g / cm2, preferably even greater than or equal to 40 g / cm2.

[0021] They preferably have a maximum crush resistance of 90 g / cm², preferably 95 g / cm², more preferably 100 g / cm² or even 500 g / cm², inclusive. For example, their maximum crush resistance is between 50 and 200 g / cm², preferably between 55 and 95 g / cm².

[0022] They can therefore be transported and handled without breaking or disintegrating.

[0023] Being preferably substantially spherical, they can flow easily from storage drums or bags and the loading of reactors is facilitated.

[0024] Thus, the granules according to the invention are preferably substantially spherical, or even spherical, and may have a diameter between 0.5 mm and 5 mm, preferably between 2 and 3 mm. They are therefore generally larger than dust particles and, in particular, much larger than inhalable dust. "Dust" is understood to mean particles smaller than 100 µm. In particular, inhalable dust particles are smaller than 20 µm, preferably smaller than 5 µm.

[0025] Also surprisingly, the granules obtained exhibit properties similar to those of powders, and in particular a similar dissolution time. The granules according to the invention are therefore perfectly suited for industrial use, like conventional powders.

[0026] BRIEF DESCRIPTION OF THE INVENTION

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

[0028] [Chem.l]

[0029] in which: • The radicals R1, R2, R3 and R4, whether identical or different, are chosen independently hanging from each other among:

[0030] - a linear or branched alkyl group, preferably a (Ci-C6) group )alkyl, possibly substituted by a hydroxy, alkoxy group or by a halogen atom;

[0031] - a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, even typically substituted by a hydroxy group, alkoxy group or by a halogen atom;

[0032] - an aryl group, preferably phenyl or naphthyl, possibly substituted by a hydroxy, alkyl, alkoxy group or by a halogen atom;

[0033] - an aralkyl group, preferably benzyl or phenethyl, possibly substituted by one or more alkyl, alkoxy, hydroxy group(s) or by one or more halogen atoms; or

[0034] - at least one of the combinations of R1 with R2 and / or of R3 with R4 form, with the carbon atom to which it (or they) is / are attached, a cycloalkyl radical or a C(O) group; • the radicals R5 and R6, identical or different, are chosen independently of each other from among the CN or NH2 groups;

[0035] said process comprising the following steps: a. a granulation step by stirring an aqueous suspension of said azo compound, in the presence of an organic binder; b. a possible step for recovering the granules obtained in step a), preferably by filtration; and c. a possible drying step for the granules recovered in step b).

[0036] The present invention also relates to granules that can be obtained or obtained or directly obtained by the process according to the invention.

[0037] The present invention also relates to granules comprising an azo compound of general formula (I) and an organic binder, as defined below.

[0038] The present invention also relates to granules having a crush resistance greater than or equal to 25 g / cm2, preferably even greater than or equal to 40 g / cm2.

[0039] The present invention relates to the use of such granules as swelling agents, initiators of polymerization reactions involving free radicals, or as synthetic intermediates, particularly in the preparation of pharmaceutical or agrochemical compounds. DETAILED DESCRIPTION OF THE INVENTION

[0040] Azo compounds have the following general formula (I):

[0041] [Chem.l]

[0042] in which: • The radicals R1, R2, R3 and R4, identical or different, are chosen independently of each other from among:

[0043] - a linear or branched alkyl group, preferably a (Ci-C6) group )alkyl, possibly substituted by a hydroxy, alkoxy group or by a halogen atom;

[0044] - a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, even typically substituted by a hydroxy group, alkoxy group or by a halogen atom;

[0045] - an aryl group, preferably phenyl or naphthyl, possibly substituted by a hydroxy, alkyl, alkoxy group or by a halogen atom;

[0046] - an aralkyl group, preferably benzyl or phenethyl, possibly substituted by one or more alkyl, alkoxy, hydroxy group(s) or by one or more halogen atoms; or

[0047] - at least one of the combinations of R1 with R2 and / or of R3 with R4 form, with the carbon atom to which it (or they) is / are attached, a cycloalkyl radical (preferably a (C3-C6)cycloalkyl) or a C(O) group; • the radicals R5 and R6, identical or different, are chosen independently of each other from among the CN (nitrile) or NH2 groups.

[0048] Preferably, R5 and R6 are identical.

[0049] In particular, when R5 and R6 are identical and represent an NH2 group, then R1 with R2, and R3 with R4 each form with the carbon atom to which they are attached, a C(O) group or;

[0050] when R5 and R6 are identical and represent a CN group, the radicals R1, R2, R3 and R4, identical or different, are chosen independently of each other from:

[0051] - a linear or branched alkyl group, preferably a (Ci-C6) group )alkyl, possibly substituted by a hydroxy, alkoxy group or by a halogen atom;

[0052] - a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, even typically substituted by a hydroxy group or by a halogen atom;

[0053] - an aryl group, preferably phenyl or naphthyl, possibly substituted by a hydroxy, alkyl, alkoxy group or by a halogen atom;

[0054] - an aralkyl group, preferably benzyl or phenethyl, possibly substituted by one or more alkyl, alkoxy, hydroxy group(s) or by one or more halogen atoms; or

[0055] - at least one of the combinations of R1 with R2 and / or of R3 with R4 form, with the carbon atom to which it (or they) is / are attached a cycloalkyl radical.

[0056] Preferably, R5 and R6 represent a CN (nitrile) group. In particular, R1 and R3 are identical and / or R2 and R4 are identical.

[0057] Preferably, the radicals R1, R2, R3 and R4 are chosen from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclopropyl, phenyl.

[0058] In particular, the radicals R1, R2, R3, and R4 are chosen from among the alkyl groups as defined above. In particular, when the substituent(s) are alkyls and / or alkoxys (also referred to as alkoxys), they comprise between 1 and 6 carbon atoms. Examples of halogens include fluorine, chlorine, bromine, and iodine.

[0059] Preferably, the compounds of general formula (I) are symmetrical.

[0060] As an example of azo compounds of general formula (I), we can cite:

[0061] 2,2'-azobis(isobutyronitrile),

[0062] 2,2'-azobis(2,4-dimethyl-valeronitrile),

[0063] 2,2'-azobis(2-methylhexylonitrile),

[0064] 2,2'-azobis(2-cyclopropylpropionitrile),

[0065] 2,2'-azobis(2-phenylpropionitrile),

[0066] 2,2'-azobis(2-methylbutyronitrile),

[0067] the l,l'-azobis(l-cyclohexanecarbonitrile), and

[0068] azodicarbonamide.

[0069] The corresponding structures are given in the table below:

[0070] [Tables 1] Denomination Structure 2,2'-azobis(isobutyronitrile) CH, CH, Oh-CNNC-CW CN CN 2,2'-azobis(2,4-dimethyl-valeronitrile) Œh CIL CH, CH, ! " 1 ' ï ■' HC- C- N - NC-CH,— CH * " î ' i: CH, CN CN CIL 2,2'-azobis(2-methylhexylonitrile) CH, CH, CH^ZH^Ç- N ” N - C-pH^CH3 CN CN ' 2,2'-azobis(2-cyclopropylpropionitrile) YY ' 1 1 CN CN 2,2'-azobis(2-phenylpropionitrile) x 2,2'-azobis(2-methylbutyronitrile) CH, —CHC-N = N—C—CH-7-CH □ - !- CN CN 1,1 '-cyclohexanecarbonitrile e) \ ) \_X-N™NC—7 1 l CN CN azodicarbonamide O h c. \nn nh?

[0071] The preferred compound according to the invention is 2,2'-azobis(isobutyronitrile), gen commonly called AZDN or AIBN. It corresponds to the compound for which R1, R2, R3 and R4 are a methyl group and R5 and R6 are a CN group (CAS No. 78-67-1).

[0072] Before its granulation, the azo compound of formula (I) is generally in the state solid, most often in powder form. Thus, said azo compound is preferably in the form of a powder comprising particles having a size between 10 µm and 200 µm, preferably between 40 µm and 150 µm. In particular, said powder has a particle size distribution (Dv50) between 10 µm and 200 µm, preferably between 40 µm and 150 µm, and more preferably between 90 µm and 130 µm.

[0073] The particle size distribution of a powder is generally defined as the statistical distribution of the particles that compose the powder according to their dimensions (size and shape of the elementary particles). The particle size distribution (Dv50) is a known parameter. It corresponds to the particle diameter (pm) below which 50% of the particle volume lies on the distribution curve expressed as a cumulative frequency. For example, if Dv50 = 100 pm, 50% of the particle volume in the sample has a diameter less than 100 pm and 50% of the particle volume has a diameter greater than 100 pm. The two other characteristic diameters commonly used to describe the particle size distribution of powders are Dv10 and Dv90: - DvlO: this corresponds to the diameter (pm) below which 10% of the particle volume lies; and - Dv90: it corresponds to the diameter (pm) below which 90% of the particle volume is located.

[0074] In particular, AZDN (especially dry) is in the form of a powder with a Dv50 between 80 pm and 200 pm, preferably between 90 pm and 110 pm.

[0075] In particular, AZDN (especially wet) is in the form of a powder with a Dv50 between 80 pm and 200 pm, preferably between 110 pm and 130 pm.

[0076] Said azo compound powder may thus comprise between 0.1% and 10%, preferably between 5% and 10% by weight of water, relative to the total weight of the powder.

[0077] Preferably, said compound of formula (I) has a solubility in the organic binder of at least 10 g / L, preferably between 10 g / L and 100 g / L and more preferably between 20 g / L and 70 g / L. Said azo compound is therefore preferentially soluble in said organic binder.

[0078] This solubility can be determined using conventional methods. It can also be determined as follows:

[0079] 1.5 g of compound of formula (I) is added to 10 g of organic binder at 20°C. The bottle is shaken for a period of between 1 h and 10 h, for example 6 h. After settling, the binder is analyzed to determine its content of 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 curve is prepared between 0 and 150 g / L by diluting compound of formula (I) in acetone.

[0080] The azo compounds of formula (I) according to the invention are known and are dis- commercially available, usually in powder form.

[0081] Examples include AZDN marketed by Arkema, V-40, V-59, AIBN, V-65 products marketed by Fujifilm Wako or Vazo®52, Vazo®64, Vazo®67 and Vazo®88 products marketed by Chemours.

[0082] An azo compound recovered directly after its production can also be used. For example, the azo compound can be used after it has been drained, washed, and obtained as a wet powder following oxidation of the corresponding hydrazo or amino-nitrile compound. In this case, the powder may contain between 5% and 10% water by weight, relative to the total weight of the powder.

[0083] This same azo compound can be used after being wrung out, washed and then dried. In this case, the powder may contain between 0.01% and 0.2% by weight of water, relative to the total weight of the powder.

[0084] The granulation step a) of the azo compound is carried out in the presence of an organic binder. Said organic binder is preferably liquid (under the operating conditions of the process according to the invention).

[0085] In particular, said organic binder is sparingly soluble in water. By "slightly soluble in water", we mean in particular a binder which has a solubility in water less than or equal to 25 g / L, preferably between 0.1 g / L and 20 g / L, preferably again between 5 g / L and 15 g / L.

[0086] To measure the solubility of the organic binder in water, conventional methods can be used. Alternatively, 100 g of water and 20 g of binder can 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.

[0087] Preferably, the organic binder is chosen from aliphatic acetates, aliphatic carbonates, non-halogenated aromatic hydrocarbons, aliphatic ketones and aliphatic ethers, or mixtures thereof.

[0088] Among aliphatic acetates, alkyl acetates are preferred, said alkyl comprising at least 4 carbon atoms, preferably between 4 and 6 carbon atoms. They are notably of the following formula:

[0089] CH3-C(O)O-Ra, Ra being an alkyl comprising at least 4 carbon atoms, preferably between 4 and 6 carbon atoms.

[0090] Among aliphatic carbonates, dialkyl carbonates are preferred, said alkyls comprising at least 2 carbon atoms, preferably between 2 and 3 carbon atoms. They have, in particular, the following formula:

[0091] Rb-OC(O)-O-Rc, Rb and Rc being independently of each other an alkyl comprising at least 2 carbon atoms, preferably between 2 and 3 carbon atoms. Preferably Rb and Rc are identical.

[0092] Non-halogenated aromatic hydrocarbons are understood to mean, in particular, alkylbenzenes and preferably toluene, xylene (o-, m- and p-xylenes) and cumene. In particular, alkylbenzene is understood to mean a benzene substituted by at least one alkyl group comprising at least one carbon atom, preferably between one and five carbon atoms, and preferably methyl.

[0093] Among aliphatic ketones, dialkyl ketones are preferred, which may comprise at least 6 carbon atoms, preferably between 6 and 8 carbon atoms. They are in particular of the following formula: CH3-C(O)-Rd, Rd being an alkyl comprising at least 4 carbon atoms, preferably between 4 and 6 carbon atoms.

[0094] Among aliphatic ethers, dialkyl ethers are preferred, which may comprise at least 6 carbon atoms, preferably between 6 and 8 carbon atoms. They are in particular of the following formula: CH3-O-Rf, Rf being an alkyl comprising at least 5 carbon atoms, preferably between 5 and 7 carbon atoms, and preferably cyclic.

[0095] It is understood that the aforementioned alkyls may be linear, branched or cyclic.

[0096] Preferably, the organic binder is chosen from the group consisting of:

[0097] toluene, m-xylene, p-xylene, o-xylene, n-butyl acetate, isobutyl acetate, cyclopentyl methyl ether (CPME or methoxycyclopentane), diethyl carbonate, methyl isobutyl ketone and methylpentyl ketone.

[0098] Preferably, the organic binder is chosen from the group consisting of:

[0099] toluene, m-xylene, n-butyl acetate, isobutyl acetate, cyclopentyl methyl ether (CPME or methoxycyclopentane) and methyl isobutyl ketone.

[0100] Preferred organic binders are isobutyl acetate and cyclopentyl methyl ether, more preferably isobutyl acetate.

[0101] Before step a) of granulation, the process may include a step of preparing the aqueous suspension of the azo compound (i.e., the heterogeneous mixture in which the liquid phase is water and the dispersed solid phase is the azo compound). For example, the azo compound in powder form, preferably as defined above, is mixed with water, preferably under stirring. A person skilled in the art can prepare this suspension by any conventional method.

[0102] In the context of the present invention, the acidic aqueous suspension of azo compound obtained directly after the oxidation step of the corresponding hydrazo compound or amino-nitrile (for example, after the chlorination step of hydrazo-bis-isobutyronitrile, in the case of AZDN) can also be used. Such a suspension may comprise between 2% and 15% by weight of HCl, relative to the total weight of the suspension.

[0103] In said suspension, the mass ratio of azo compound / water can be understood to be between 1 / 99 and 40 / 60, preferably between 10 / 90 and 25 / 75; and more preferably between 15 / 85 and 25 / 75.

[0104] The process according to the invention includes a step a) of granulating an azo compound of general formula (I) as defined above, in suspension in water, by agitation, and in the presence of an organic binder.

[0105] Preferably, the organic binder is added to the aqueous suspension. It is possible to add the organic binder to the azo compound and then add water, or to place all three components in the reactor at the same time, although these embodiments are not preferred.

[0106] The organic binder can be added by any means known to those skilled in the art. It can be added at a single point or continuously, preferably at a single point. Indeed, it is not necessary to add the organic binder gradually: the entire quantity can be added all at once to the aqueous suspension of the azo compound. It is therefore preferable to add the organic binder rapidly, for example, over a period of between 1 and 30 minutes, preferably between 1 and 20 minutes, and in particular between 1 and 5 minutes.

[0107] Step a) of granulation is carried out under agitation. This agitation can be achieved by any known means or agitator, for example any type of blade (straight or inclined) or helical ribbon. The reactor may comprise one or more stages of agitator(s).

[0108] In particular, the stirring speed (corresponding, for example, to the rotational speed of the stirring impeller) must be sufficient to obtain a homogeneous suspension of the azo compound in water and a homogeneous dispersion of the organic binder, without, however, causing the formation of an emulsion. A speed of 500 to 900 rpm is generally used when operating in a reactor of 1 to 10 liters, or a speed of 50 to 300 rpm can be used when operating in a reactor of approximately 100 liters. The stirring speed can, for example, be increased or decreased throughout step a), but it is preferable to decrease it gradually.

[0109] Generally, granule formation occurs rapidly, within a few minutes of stirring in the presence of the organic binder. In particular, the granules form over a period ranging from 1 to 30 minutes, for example, between 2 and 10 minutes. Spherical (or nearly spherical) granules are generally obtained, with a maximum diameter of approximately 0.5 to 5 mm, for example, between 1 and 5 mm, preferably between 2 and 3 mm. Continued stirring after their formation can help consolidate the granules and / or reduce their dispersion.

[0110] Step a) can be carried out for a period of between 1 minute and 100, preferably between 30 minutes and 5 hours, preferably again between 10 and 5 hours.

[0111] Step a) of granulation may comprise or consist of the following two steps:

[0112] A1) adding the organic binder to the aqueous suspension of azo compound to obtain a granulation medium, under agitation; then

[0113] A2) maintaining agitation of the granulation medium.

[0114] Preferably, step a) is carried out in the absence of surfactants and / or dispersing agents.

[0115] Preferably, step a) is carried out without the addition of surfactants and / or dispersing agents.

[0116] For example, step a) is carried out in the absence or without the addition of sodium dioctylsulfosuccinate.

[0117] Step a) of granulation is carried out in particular at a temperature that does not cause the degradation of the azo compound. It can be between 5 °C and 45 °C, preferably between 10 °C and 40 °C, for example between 10 °C and 20 °C. It is generally carried out at atmospheric pressure.

[0118] The mass ratio of azo compound / water can be between 1 / 99 and 40 / 60, preferably between 10 / 90 and 25 / 75; and more preferably between 15 / 85 and 25 / 75.

[0119] The organic binder / azo compound mass ratio may be between 0.2 and 0.5, preferably between 0.3 and 0.5, more preferably between 0.3 and 0.4.

[0120] The process according to the invention optionally includes subsequent steps of recovering and drying the granules obtained in step a). These steps can be carried out conventionally. For example, the granules can be recovered by filtration. They can then be dried. In particular, they can be dried at a temperature between 10 °C and 45 °C, preferably between 20 °C and 40 °C. They can be dried under reduced pressure or, more preferably, under a purge of air, depleted air, or an inert gas such as nitrogen. The drying can last a few hours, for example, between 1 and 10 hours, preferably between 3 and 5 hours.

[0121] The term “granules” refers in particular to solid and cohesive agglomerates of constituent particles, said particles having a size between 10 pm and 200 pm, preferably between 90 pm and 110 pm.

[0122] Thus, the present invention relates to granules that can be obtained (or obtained or directly obtained) by the process according to the invention. Such granules are novel.

[0123] The present invention also relates to granules comprising an azo compound of general formula (I) as defined above and an organic binder as defined above.

[0124] In particular, in the granules according to the invention, said binder is present in trace amounts; especially when these are dried after recovery, which results in a evaporation of the organic binder. The granules according to the invention can thus comprise between 20 ppm and 3,000 ppm, for example between 20 ppm and 1,000 ppm of organic binder. More particularly, they comprise between 20 ppm and 500 ppm of organic binder, preferably between 50 ppm and 300 ppm of organic binder, and even more preferably between 50 ppm and 200 ppm of organic binder, especially after drying.

[0125] In particular, the granules according to the invention have a crush resistance greater than or equal to 25 g / cm2, preferably even greater than or equal to 40 g / cm2.

[0126] They advantageously have a maximum crush resistance of 90 g / cm², preferably 95 g / cm², more preferably 100 g / cm² or even 500 g / cm², inclusive. For example, their maximum crush resistance is between 50 and 100 g / cm², preferably between 55 and 95 g / cm².

[0127] The granules according to the invention are generally substantially spherical or spherical in shape. They may have a diameter between 0.5 and 5 mm and more preferably between 1 and 5 mm, for example between 2 and 3 mm.

[0128] The present invention also relates to granules comprising an azo compound of general formula (I) as defined above and having a crush resistance greater than or equal to 25 g / cm2, preferably greater than or equal to 40 g / cm2. Such granules may comprise one or more of the characteristics mentioned above.

[0129] One of the advantages of granules such as those according to the invention is their solidity, which makes them very easy to transport and handle. They are also of good purity, with a low content of residual organic binder.

[0130] The present invention relates to their use as blowing agents, initiators of polymerization reactions involving free radicals, or as synthetic intermediates, particularly in the preparation of pharmaceutical or agrochemical compounds. The polymerization reactions can be bulk, solution, suspension, or emulsion polymerization reactions and can involve a wide variety of monomers, for example, (meth)acrylic or vinyl monomers, such as acrylamide, acrylonitrile, alkyl (meth)acrylate, styrene, vinyl acetate and chloride, or vinylidene chloride. Areas of application include, but are not limited to, acrylic sheets or fibers, flocculants, paints, coating resins, grafted polyols, polystyrene, PVC (polyvinyl chloride), PVA (polyvinyl acetate), and PMMA (polymethyl methacrylate).

[0131] In particular, the granules according to the invention can be used in the preparation of polyols grafted by a mixture of styrene and acrylonitrile or in the preparation of polyacrylonitriles precursors of carbon fibers. EXAMPLES

[0132] The particle size distribution of the dry AZDN used in the examples is 52.5 / 101 / 180 microns respectively dv(10), dv(50) and dv(90). That of the wet AZDN is 61 / 119 / 203 microns respectively dv(10), dv(50) and dv(90).

[0133] This particle size measurement is performed using a Masterziser® S device. The measurement is carried out using water and a drop of Igepal® (nonylphenol ethoxylated) surfactant as a dispersant. The particle size measurement is performed after 10 minutes of circulation in the measuring cell. EXAMPLE 1: Granulation in a 500 ml reactor 1- Operating procedures:

[0134] Granulation:

[0135] The reactor is a 500ml double-walled glass reactor, maintained at 15°C by a cold water circulation. It is equipped with mechanical stirring.

[0136] 22.4g of dry AZDN are weighed into a beaker and then 100mL of water are added. After After homogenizing the mixture with a spatula, the aqueous suspension is transferred to the reactor. 100 mL of water are then added to recover the AZDN remaining in the beaker.

[0137] The suspension in the reactor is stirred at 1000–1100 rpm so that the AZDN remaining on the surface is carried along by the stirring. After a few minutes, the organic binder is rapidly added to the reactor. The stirring speed is then reduced to 850 rpm.

[0138] After approximately three hours of agitation, the formation or not of granules is noted.

[0139] The reactor is drained over a filter. Optionally, the aqueous filtration solution, saturated with binder, is used to finish rinsing the reactor.

[0140] The filtered granules are washed and left to air dry under ventilation for approximately 24 hours. The fragility of the formed and dried granules is noted by their resistance to manual crushing.

[0141] Measurement of the solubility of the organic binder in water:

[0142] The measurements were carried out by bringing 100g of water and 20g of organic binder into contact under stirring at 20°C for 1h. The aqueous phase was decanted and then analyzed by gas chromatography to determine the concentration of organic binder.

[0143] Measurement of the solubility of AZDN in the organic binder:

[0144] The measurements were carried out by adding 1.5 g of AZDN to 10 g of organic binder at 20°C. The bottle was shaken for approximately 6 hours. After settling, the organic binder was analyzed to determine its AZDN concentration. The analysis was performed by gas chromatography with an injector temperature set at 220°C (in Under these conditions, AZDN is essentially transformed into tetramethylsuccinonitrile in the injector. A standard curve is prepared between 0 and 150 g / l by diluting AZDN in acetone.

[0145] Gas chromatographic analyses:

[0146] The chromatographic column is a macrobore OV1701 column (diameter = 0.25mm, length = 30m, film thickness = 0.25 microns), the chromatographic apparatus is a Hewlett Packard HP 6890 apparatus equipped with a FID (flame ionization) type detector. 2- Results obtained:

[0147] The results obtained are presented in the following table:

[0148] [Tables2] Binder Test Binder Solubility in Water (g / b) AZDN Solubility in Binder (g / b) Mass Ratio Binder* AZDN Granule Formation Granule Size (mm) Drying Strength A Meta-Xylene <0.5 25 0.30 YES 1-3 positive B*' 0.30 YES 1-3 positive c 0.35 YES 1-3 positive D Toluene < 0.5 ® 0.23 YES 1-3 positive E 0.40 YES 1-3 positive F 0.47 QUI 1-3 positive G 0.40 YES 1-3 positive H 0.30 YES 1-3 positive ! Mètf^ 20 75.5 0.42 YES 1-3 positive J 45 0.35 YES 1-3 positive K lylèftoxycy^^ (CRMEf * " 12.5 30.5 0.30 YES 1-3 positive L 0.40 YES 1-3 positive M 0.43 YES 1-3 positive N n-Butyl acetate 7 59 0.30 YES 1-3 positive O 0.38 YES 1-3 positive P Isobutyte acetate 7 59 0.38 YES 1-3 positive Q 0.38 YES 1-3 positive R 0.40 YES 1-3 positive S 0.40 YES 1-3 positive T 0.37 YES 1-3 positive U piggiyi. carbonate 19 85 0.47 YES 1-3 positive

[0149] * The strength after drying was evaluated as follows:

[0150] - positive: the dried granule does not crush under light pressure from the spatula;

[0151] - negative: the dried granule crushes under light pressure from the spatula and gives powder.

[0152] ** Test B carried out with an aqueous solution of 5% HCl instead of water.

[0153] Following granulation as per the invention, granules of size are obtained between 1 and 3 mm, which are strong enough to be recovered, dried and handled. EXAMPLE 2: Granulation in a 2L reactor 1- Granulation and drying:

[0154] Granulation:

[0155] Apparatus similar to that of Example 1 is used, but with a two-litre reactor. The quantities involved are given in the table below.

[0156] The agitator is an inclined blade agitator and the initial agitation is set at 800 revolutions per minute and then lowered to 600 revolutions per minute after introduction of the organic binder as in the previous example.

[0157] Drying of the granules:

[0158] A 6 cm diameter porous glass filter with a double jacket is used, allowing the filter walls to be heated by circulating hot water. 100 g of filtered, undried granules are introduced into the filter. A constant flow rate of nitrogen (2 L / min) is then injected from the bottom of the filter at different temperatures.

[0159] The production of the granules is given in the table:

[0160] [Tables3] Organic binder Water (g) AZDN (g) Mass ratio Uant / AZDN Granule formation Granule size obtained (mm) meta:Xylene 900 100 0.30 OUi 2-4 900* 100 0.30 OUi 2-4 iM é >en ta ne |CPME) 900 100 0.45 OUI 2-4 n-Butyl acetate 900 100 0.36 OUi 2-4 d-Gobytyl acetate 900 100 0.40 OUI' 2-4 900 109** 0.40 OUI 2-4 'Aqueous solution HC! 10% ** We start with 109g of moist AZDN containing 8.2% water, which is equivalent to 100g of dry AZDN

[0161] 2- Determination of the residual organic binder content:

[0162] During the drying of the granules described above, approximately one gram of granules obtained with isobutyl acetate is taken over time and analyzed by gas chromatography to determine the residual binder content.

[0163] The results obtained are presented in the following table:

[0164] [Tables4] Residual binder content (% by mass) 40°C 30°C 0 22 22.22 1 11.65 15.17 2 1.59 7.80 3 0.02 0.30 6 0.02 0.02 9 0.02 0.01

[0165] With CMPE, at 30 °C, drying is faster and after 3h a residual CPME concentration of 0.01% is observed which does not change significantly thereafter (5 h drying).

[0166] The preparation and drying of the granules can therefore be carried out under satisfactory industrial conditions. After a few hours of drying, granules are obtained with a residual organic binder mass content of between 0.01% and 0.02%, i.e., between 100 ppm and 200 ppm of residual organic binder (i.e., between 100 and 200 mg of organic binder per kg of granules). 3- Crushing test of dried granules:

[0167] 20g of AZDN granules obtained in Example 2 are placed and distributed uniformly The mixture is formed in a 6cm diameter glass crystallizing dish, then a 5cm diameter flat-bottomed glass beaker (with an empty mass of 200g) is placed on top. If no crushed or broken granules are observed, additional 200g weights are gradually added on top of the beaker until the granules begin to break down, visible through the beaker or on the sides of the glass crystallizing dish.

[0168] The surface area of ​​the beaker is S = ir x (2.5)2 = 19.625 cm2

[0169] The crushing resistance is: [total weight (beaker + additional weight(s)) at breaking point] / [S]

[0170] Comparative test:

[0171] Granules were prepared by extrusion according to the procedure described in WO 00 / 24706, Examples 1 and 2. The AZDN powder is that used for the preceding examples in this application. The granules obtained have an average diameter of 5 mm and a length of 1.5 cm (between 1 and 2 cm). Once dried, these granules appear very fragile when handled. They exhibit very low resistance in the crush test, much lower than that obtained for the granules according to the invention.

[0172] The results obtained are presented in the following table:

[0173] [Tables5] Organic agent Total mass applied at the breaking point (g) Crush resistance (g / cm²) m-xylene 1200 61.15 δ-Spbutyl acetate n-Butyl acetate >= 1200 61.15 CPME >= 1200 61.15 Comparative test according to WO 00 / 24706: Granule without surfactant ~ example 1 200 10.19 Granule with surfactant - example 2 400 20.38

[0174] The granules according to the invention exhibit a significantly improved resistance to crushing.

[0175] They are easily handled without falling apart. EXAMPLE 3: Granulation in a 100 L reactor 1- Granulation and drying:

[0176] A 100-litre AE100 enamelled stainless steel reactor from the DE DIETRICH brand is used. The internal diameter of the reactor vessel is 508 mm, the usable height is 375 mm.

[0177] Agitation is provided by a 300 mm diameter impeller-type agitator with three straight blades, ensuring radial agitation. The agitation speed can vary from 0 to 200 revolutions per minute. The reactor is equipped with a ball-type bottom valve connected to a filter dryer. The filter diameter is 55 cm. The filter is equipped with a 48 cm diameter scraper agitator that can move up or down within the filter and, when lowered flush with the filter, allows for mechanical discharge of the dried product through a lateral opening. The agitation speed can vary from 0 to 60 revolutions per minute. The filter cloth is a 20-micron mesh.

[0178] The test is carried out at room temperature (19-20°C).

[0179] The reactor is maintained under nitrogen by a slight sweep of 50 l / h.

[0180] 43.1 kilograms of demineralized water are introduced. The agitation is set to 200 revolutions per minute, the temperature is 18°C. 11.3 kilograms of wet AZDN powder with 8% water content are introduced over 5 minutes.

[0181] After 5 minutes, 4.1 kilograms of isobutyl acetate are added over two minutes. Granule formation is visible within the first few minutes. After 5 minutes, the stirring speed is reduced to 100 rpm and these conditions are maintained for 5 hours.

[0182] The reactor is then drained through the bottom valve into the filter. The granules are filtered by applying nitrogen pressure in order to remove and recover the aqueous liquids.

[0183] A nitrogen sweep of 10 m3 / h is then set up for 24h at ambient temperature.

[0184] Once dried, the granules are solid and can be recovered by starting the mechanical scraper agitator set at a speed of 6 revolutions per minute. This yields 10.2 kilograms of AZDN in the form of granules approximately 2 to 3 millimeters in diameter. 2- Crush resistance test:

[0185] A crush resistance test of the granules as described in the previous example was carried out and shows very good strength of these granules with a resistance of up to 91.72 g / cm2. 3- Dissolution test:

[0186] A dissolution test of the granules is carried out at room temperature. A glass Erlenmeyer flask fitted with a magnetic stir bar is placed on a magnetic stirrer. With the stirring stopped, 13 g of AZDN are introduced into the Erlenmeyer flask. 100 mL of acetone is then rapidly added, and the stirring is started (100 rpm). The time taken until no undissolved AZDN crystals are visible is recorded.

[0187] Commercial recrystallized AZDN (130-257-438 microns / dv 10-50-90), prepared and dried AZDN granules as obtained above, and dry powdered AZDN used in Example 1 are compared.

[0188] [Tableauxô] Dry AZDN powder (Dv 50 = 100 microns) Spherical AZDN (2-3 mm granules) According to the invention Recrystallized AZDN (Dv 50 = 247 microns) Dissolution time (seconds) 15 15 35

[0189] It can be seen that the spherical AZDN granules obtained according to the invention dissolve as rapidly as the initial AZDN in powder form. On the other hand, the crystals Recrystallized AZDN, although of smaller average diameter than the spherical granules of the invention, take much longer to dissolve in acetone.

[0190] It is noted that there is no visible insoluble material for each of the samples.

Claims

1. Demands Granulation process for an azo compound of the following general formula (I): [Chem 1]

2.

3. in which: * The radicals R1, R2, R3 and R4, identical or different, are chosen independently of each other from among: - a linear or branched alkyl group, possibly substituted by a hydroxy, alkoxy group or by a halogen atom; - a cycloalkyl group, possibly substituted by a hydroxy, alkoxy group or by a halogen atom; - an aryl group, possibly substituted by a hydroxy, alkyl, alkoxy group or by a halogen atom; - an aralkyl group, possibly substituted by one or more alkyl, alkoxy, or hydroxy group(s) or by one or more halogen atoms; or - at least one of the combinations of R1 with R2, and / or of R3 with R4 forms, with the carbon atom to which it is (or they are) attached, a cycloalkyl radical or a C(O) group; * The radicals R5 and R6, identical or different, are chosen independently of each other from among the CN or NH2 groups; said process comprising the following steps: a) a granulation step by stirring an aqueous suspension of said azo compound, in the presence of an organic binder; b) a possible step for recovering the granules obtained in step a), preferably by filtration; and c) a possible drying step of the granules recovered in step b). Granulation process according to claim 1, wherein said organic binder is added to said aqueous suspension. Granulation process according to claim 1 or 2, wherein the azo compound of general formula (I) is selected from the group consisting of: 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethyl-valeronitrile), 2,2'-azobis(2-methylhexylonitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2-phenylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), l,r-azobis(l-cyclohexanecarbonitrile) and azodicarbonamide; preferably 2,2'-azobis(isobutyronitrile).

4. 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. Granulation process according to any one of the preceding claims, wherein the mass ratio of azo compound / water can be between 1 / 99 and 40 / 60, preferably between 10 / 90 and 25 / 75; and more preferably between 15 / 85 and 25 / 75.

6. Granulation process according to any one of the preceding claims, wherein the organic binder / azo compound mass ratio can be between 0.2 and 0.5, preferably between 0.3 and 0.5, more preferably between 0.3 and 0.

4.

7. Granules comprising an azo compound of 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, in an amount between 20 ppm and 1000 ppm.

8. Granules according to claim 7, characterized in that they are substantially spherical in shape, preferably with a diameter between 0.5 and 5 mm.

9. Use of the granules according to any one of claims 7 or 8, as blowing agents, initiators of polymerization reactions involving free radicals, or as synthetic intermediates, particularly in the preparation of pharmaceutical or agrochemical compounds.