Granulation process of azo compounds and resulting granules

Abstract

The present invention relates to a process for granulating azo compounds, comprising the steps of: (a) granulating by stirring an aqueous suspension of a particular azo compound in the presence of an organic binder; (b) optionally recovering the granules obtained in step (a), preferably by filtration; and (c) optionally drying the granules recovered in step (b). The present invention also relates to the granules obtainable by the process according to the invention and their uses.

Description

[Technical Field]

[0001] The present invention relates to a process for granulating azo compounds, as well as to the granules obtainable by this process and their uses. [Background technology]

[0002] Azo compounds, more specifically 2,2'-azobis(isobutyronitrile), also known as AZDN or AIBN, are well-known products. They are used as swelling agents, synthetic intermediates, or initiators for free-radical polymerization reactions. These reactions can be bulk, solution, suspension, or emulsion polymerizations, and can involve a wide variety of monomers, such as acrylamide, acrylonitrile, alkyl (meth)acrylates, styrene, vinyl chloride, and (meth)acrylic or vinyl monomers such as acetate or vinylidene chloride. The fields of application are therefore very diverse, particularly (but not exclusively) related to acrylic sheets or fibers, flocculants, paints, coating resins, grafted 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 U.S. Pat. No. 2,515,628, WO 03 / 002521, U.S. Pat. No. 3,390,146, CN 1 309 705, or EP 2 821 393. After oxidation, the resulting suspension is generally discharged and then, if desired, dried to obtain a solid in powder form.

[0004] However, azo compounds in powder form pose a number of problems.

[0005] In particular, they generate dusts that may pose an explosion risk and / or an industrial hygiene risk. These dusts may in fact accidentally become airborne and then come into contact with the upper respiratory tract of those who handle them. Such contact may occur, for example, to workers present in industrial installations when manually loading the powder into reactors, or to workers taking samples necessary for controlling the production process. To ensure the safety of workers and guarantee the hygiene of production sites, it is desirable to limit this type of contact to a minimum or even avoid it altogether.

[0006] Also, this type of powder is difficult for workers to handle. The powders are generally not sufficiently fluid for easy transportation and loading into reactors. Azo compounds in powder form have poor flowability and often cause caking problems during storage and loading.

[0007] Therefore, there is a need for improved formulations of azo compounds, particularly those that generate little or no dust and are easily handled by workers. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore one of the objectives of the present invention to provide a granulation process that is easy to implement and preferably more environmentally friendly.

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

[0010] The object of the present invention is to provide granules of azo compounds that are rigid (i.e. resistant) and in particular retain their shape during storage and handling.

[0011] Another object of the present invention is to provide granules of an azo compound having properties similar to those of a powder. [Means for solving the problem]

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

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

[0014] For example, mechanical granulation is known from WO 00 / 24706. This involves compressing a powder of an azo compound and then extruding it to produce granules. However, this technique requires control of the molding temperature. However, such control is not obvious at an industrial level. This type of process carries the risk of heating due to friction or compression, and therefore the risk of severe thermal decomposition of the azo compound during the formation of the granules. Furthermore, the granules obtained by mechanical granulation are not very resistant to crushing and easily crumble.

[0015] The process according to the invention avoids these risks of heating and decomposition by using mild granulation conditions and makes it possible to obtain granules of high purity, thus preserving the application properties of the compound, especially in polymerization.

[0016] Furthermore, surprisingly, the granules according to the invention are rigid (resistant), more particularly they have a significantly greater crushing resistance than other known forms of azo compounds.

[0017] In particular, "crush resistance" means the maximum weight per unit of surface made up of granules that these granules can support before they crush or disintegrate (i.e. lose their shape): Crushing resistance = Load weight at breaking point / Granule surface area

[0018] Crush resistance is typically measured by measuring the compressive load required to break the granules.

[0019] The crush resistance of the granules according to the invention is in particular 25 g / cm 2 More preferably, 40 g / cm 2 That's all.

[0020] They are preferably 90 g / cm including the end points. 2 , preferably 95 g / cm 2 , more preferably 100 g / cm 2 , or even 500 g / cm 2 For example, their maximum crush resistance is 50 to 200 g / cm 2 , preferably 55 to 95 g / cm 2 is.

[0021] They can therefore be transported and handled without breaking or disintegrating.

[0022] Preferably they are substantially spherical so that they can flow easily from drums or storage bags, facilitating reactor loading.

[0023] Thus, the granules according to the present invention are preferably substantially spherical, or even spherical, and may have a diameter of 0.5 mm to 5 mm, preferably 2 to 3 mm. Therefore, they are generally larger in size than dust, and in particular much larger in size than inhalable dust. In particular, "dust" refers to particles less than 100 μm in size. More particularly, inhalable dust has a size of less than 20 μm, preferably less than 5 μm.

[0024] Surprisingly, the granules obtained also have similar properties to those of the powder, in particular similar dissolution times, and are therefore perfectly suitable for industrial use, just like conventional powders.

[0025] Brief description of the invention The present invention relates to a process for granulating an azo compound of the following general formula (I): [General formula (I)] [ka] (In the formula, ·R 1 Group, R 2 Group, R 3 groups, and R 4 The groups are the same or different and, independently of one another, a linear or branched alkyl group, preferably a (C1-C6) alkyl group, optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; an aryl group, preferably phenyl or naphthyl, optionally substituted with a hydroxy group, an alkyl group, or an alkoxy group, or a halogen atom; an aralkyl group, preferably benzyl or phenethyl, optionally substituted with one or more alkyl, alkoxy, or hydroxy groups, or one or more halogen atoms; selected from; or R 1 and R 2 Combination with and / or R 3 and R 4 and at least one of the combinations with, together with the carbon atom to which it (or they) are attached, forms a cycloalkyl group or a C(O) group; ·R 5 Groups and R 6 The groups are the same or different and are selected independently from the CN group and the NH group. The following steps: (a) a granulation step by stirring an aqueous suspension of said azo compound in the presence of an organic binder; (b) optionally recovering the granules obtained in step (a), preferably by filtration; and (c) optionally drying the granules recovered in step (b). The granulation process comprising:

[0026] The present invention also relates to granules obtainable or obtained or directly obtained by the process according to the invention.

[0027] The present invention also relates to granules comprising an azo compound of general formula (I) and an organic binder as defined below.

[0028] The present invention also provides a method for manufacturing a 25 g / cm 2 More preferably, 40 g / cm 2 The present invention relates to granules having the above crush resistance.

[0029] The present invention relates to the use of such granules as swelling agents, initiators of polymerization reactions using free radicals or synthetic intermediates, in particular in the preparation of pharmaceutical or agrochemical compounds. DETAILED DESCRIPTION OF THE INVENTION

[0030] The azo compounds have the following general formula (I): [General formula (I)] [ka] (In the formula, ·R 1 Group, R 2 Group, R 3 groups, and R 4 The groups are the same or different and, independently of one another, a linear or branched alkyl group, preferably a (C1-C6) alkyl group, optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; an aryl group, preferably phenyl or naphthyl, optionally substituted with a hydroxy group, an alkyl group, or an alkoxy group, or a halogen atom; an aralkyl group, preferably benzyl or phenethyl, optionally substituted with one or more alkyl, alkoxy, or hydroxy groups, or one or more halogen atoms; selected from; or R 1 and R 2 Combination with and / or R 3 and R 4 and at least one of the combinations with, together with the carbon atom to which it (or they) are attached, forms a cycloalkyl group (preferably (C3-C6)cycloalkyl) or a C(O) group; ·R 5 Groups and R 6 The groups are the same or different and are independently selected from CN (nitrile) or NH groups.

[0031] R 5 and R 6 are preferably the same.

[0032] In particular, R 5 and R 6 are identical and represent an NH group, R 1 and R 2 , and R 3 and R 4 each together with the carbon atom to which they are attached form a C(O) group; or R 5 and R 6 are identical and represent a CN group, R1 Group, R 2 Group, R 3 groups, and R 4 The groups are the same or different and, independently of one another, a linear or branched alkyl group, preferably a (C1-C6) alkyl group, optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; a cycloalkyl group, preferably a (C3-C6)cycloalkyl group, optionally substituted with a hydroxy group or a halogen atom; an aryl group, preferably phenyl or naphthyl, optionally substituted with a hydroxy group, an alkyl group, or an alkoxy group, or a halogen atom; an aralkyl group, preferably benzyl or phenethyl, optionally substituted with one or more alkyl, alkoxy, or hydroxy groups, or one or more halogen atoms; selected from; or R 1 and R 2 Combination with and / or R 3 and R 4 At least one of the combinations of together with the carbon atom to which it (or they) are attached forms a cycloalkyl group.

[0033] R 5 and R 6 Most preferably, R represents a CN (nitrile) group. 1 and R 3 are identical, and / or R 2 and R 4 are identical.

[0034] Preferably, R 1 Group, R 2 Group, R 3 groups, and R 4 The groups are selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclopropyl, and phenyl.

[0035] In particular, R 1 Group, R 2 Group, R 3 groups, and R 4 The groups are selected from the alkyl groups defined above. In particular, when the substituents are alkyl and / or alkoxy, they contain 1 to 6 carbon atoms. The halogens include in particular fluorine, chlorine, bromine, and iodine.

[0036] Preferably, the compounds of general formula (I) are symmetrical.

[0037] Examples of azo compounds of general formula (I) include: 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylhexylnitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2-phenylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(1-cyclohexanecarbonitrile), and Azodicarbonamide Examples include:

[0038] The corresponding structures are shown in the table below:

[0039] [Table 1]

[0040] A preferred compound according to the present invention is 2,2'-azobis(isobutyronitrile), commonly referred to as AZDN or AIBN. 1 , R 2 , R 3 , and R 4 is a methyl group, and R 5 and R 6corresponds to the compound in which is a CN group (CAS number 78-67-1).

[0041] Before granulation, the azo compound of formula (I) is generally in a solid state, and in most cases in powder form. Therefore, the azo compound is preferably in the form of a powder containing particles having a size of 10 μm to 200 μm, preferably 40 μm to 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.

[0042] The particle size of a powder is generally defined as the statistical distribution of the particles that make up 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 (μm) below which 50% of the particle volume lies in the distribution curve, expressed as cumulative frequency. For example, if Dv50=100 μm, then 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 that are usually used to describe the particle size distribution of a powder are Dv10 and Dv90: Dv10: corresponds to the diameter (μm) under which 10% of the particle volume is located; and - Dv90: corresponds to the diameter (μm) under which 90% of the particle volume lies.

[0043] In particular, the AZDN (especially dry) is in the form of a powder having a Dv50 of 80 μm to 200 μm, preferably 90 μm to 110 μm.

[0044] In particular, the 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.

[0045] Therefore, the azo compound powder may contain 0.1% by weight to 10% by weight, preferably 5% by weight to 10% by weight of water relative to the total weight of the powder.

[0046] Preferably, the compound of formula (I) has a solubility in the organic binder of at least 10 g / L, preferably from 10 g / L to 100 g / L, more preferably from 20 g / L to 70 g / L, and therefore the azo compound is preferentially soluble in the organic binder.

[0047] The solubility can be determined using standard methods. It can also be determined as follows:

[0048] 1.5 g of the compound of formula (I) is added to 10 g of organic binder at 20°C. The bottle is shaken for 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 (g / L) of the azo compound in the organic binder. The analysis is carried out by gas chromatography. The compound of formula (I) is diluted with acetone to produce a standard range of 0 to 150 g / L.

[0049] The azo compounds of formula (I) according to the present invention are known and are commercially available, generally in powder form.

[0050] Mention may be made, for example, of AZDN sold by Arkema, the products V-40, V-59, AIBN, V-65 sold by Fujifilm Wako Pure Chemical Industries, or the products Vazo® 52, Vazo® 64, Vazo® 67 and Vazo® 88 sold by Chemours.

[0051] It is also possible to use azo compounds recovered immediately after their production. For example, it is possible to use azo compounds obtained in the form of wet powders that have been discharged and washed after oxidation of the corresponding hydrazo compounds or amino-nitrile compounds. In this case, the powder may contain 5% to 10% by weight of water, based on the total weight of the powder.

[0052] This same azo compound may be used, drained, washed, and then dried, in which case the powder may contain 0.01% to 0.2% water by weight, based on the total weight of the powder.

[0053] 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).

[0054] In particular, the organic binder is poorly soluble in water. "Poorly soluble in water" particularly refers to a binder having a solubility in water of 25 g / L or less, preferably 0.1 g / L to 20 g / L, and more preferably 5 g / L to 15 g / L.

[0055] A conventional method may be used to measure the solubility of an organic binder in water: 100 g of water and 20 g of binder may 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 (g / L) corresponding to its solubility.

[0056] The organic binder is preferably selected from aliphatic acetates, aliphatic carbonates, non-halogenated aromatic hydrocarbons, aliphatic ketones, and aliphatic ethers, or mixtures thereof.

[0057] Among the aliphatic acetates, alkyl acetates are preferred, the alkyl of which may contain at least 4 carbon atoms, preferably 4 to 6 carbon atoms. They have in particular the following formula: CH3-C(O)OR a (R a is alkyl containing at least 4 carbon atoms, preferably 4 to 6 carbon atoms).

[0058] Among the aliphatic carbonates, dialkyl carbonates are preferred, the alkyl of which may contain at least 2 carbon atoms, preferably 2 to 3 carbon atoms. They have in particular the following formula: R b-OC(O)-OR c (R b and R c are each independently an alkyl containing at least 2 carbon atoms, preferably 2 to 3 carbon atoms. b and R c are preferably the same.

[0059] By non-halogenated aromatic hydrocarbons is meant in particular alkylbenzenes, preferably toluene, xylene (o-xylene, m-xylene, and p-xylene) and cumene. By alkylbenzene is meant in particular benzene substituted with at least one alkyl, more preferably methyl, containing at least one carbon atom, preferably 1 to 5 carbon atoms.

[0060] Among the aliphatic ketones, preference is given to dialkyl ketones, which may contain at least 6 carbon atoms, preferably 6 to 8 carbon atoms. They have in particular the formula: CH3-C(O)-R d (R d is alkyl containing at least 4 carbon atoms, preferably 4 to 6 carbon atoms).

[0061] Among the aliphatic ethers, preference is given to dialkyl ethers, which may contain at least 6 carbon atoms, preferably 6 to 8 carbon atoms. They have in particular the formula: CH3-OR f (R f is alkyl containing at least 5 carbon atoms, preferably 5 to 7 carbon atoms, and is preferably cyclic).

[0062] It is understood that said alkyl as defined above can be linear, branched, or cyclic.

[0063] Preferably, the organic binder is selected from the group consisting of 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 pentyl ketone.

[0064] The organic binder is preferably selected from the group consisting of toluene, m-xylene, n-butyl acetate, isobutyl acetate, cyclopentyl methyl ether (CPME or methoxycyclopentane), and methyl isobutyl ketone.

[0065] Preferred organic binders are isobutyl acetate and cyclopentyl methyl ether, more preferably isobutyl acetate.

[0066] Before the granulation step (a), the process may include a 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, preferably in the form of a powder as defined above, is mixed with water, preferably with stirring. Those skilled in the art can prepare this suspension by any conventional method.

[0067] In the context of the present invention, it is also possible to use an acidic aqueous suspension of a hydrazo compound or an azo compound obtained immediately after the oxidation step of the corresponding amino-nitrile (for example, in the case of AZDN, after the step of chlorination of hydrazobisisobutyronitrile). Such a suspension may contain 2% to 15% by weight of HCl relative to the total weight of the suspension.

[0068] In the suspension, the mass ratio of the azo compound to water may be 1 / 99 to 40 / 60, preferably 10 / 90 to 25 / 75, and more preferably 15 / 85 to 25 / 75.

[0069] The process according to the invention comprises a step (a) in which an azo compound of general formula (I) as defined above, suspended in water, is granulated by stirring in the presence of an organic binder.

[0070] It is preferred to add the organic binder 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 simultaneously, but these embodiments are not preferred.

[0071] The addition of the organic binder can be carried out by any means known to those skilled in the art. It can be one-time or continuous, preferably one-time. In fact, it is not necessary to add the organic binder gradually: the entire amount of the organic binder can be added at once to the aqueous suspension of the azo compound. Therefore, it is preferable to add the organic binder quickly, for example, for a period of 1 to 30 minutes, more preferably 1 to 20 minutes, and especially 1 to 5 minutes.

[0072] The granulation step (a) is carried out with stirring. This stirring can be carried out by any known stirring means or stirring element, for example any type of blade (straight or inclined) or helical ribbon. The reactor may contain one or more stages of stirring elements.

[0073] More specifically, the stirring speed (e.g., corresponding to the rotational speed of the stirring element) must be sufficient to obtain a uniform suspension of the azo compound and a uniform dispersion of the organic binder in water without forming an emulsion. When operating in a 1-10 liter reactor, a speed of 500-900 rpm is generally used, or when operating in a reactor of about 100 liters, a speed of 50-300 rpm can be used. For example, the stirring speed can be increased or decreased throughout step (a), but it is preferable to decrease it gradually.

[0074] Generally speaking, granule formation occurs rapidly, i.e., after a few minutes of stirring in the presence of the organic binder. In particular, granules are formed over a period ranging from 1 minute to 30 minutes, e.g., from 2 minutes to 10 minutes. Spherical (or substantially spherical) granules having a maximum diameter of approximately 0.5 to 5 mm, e.g., 1 to 5 mm, preferably 2 to 3 mm, are generally obtained. Maintaining stirring after their formation can help to compact the resulting granules and / or reduce their dispersion.

[0075] Step (a) can be carried out for a period of 1 minute to 10 hours, preferably 30 minutes to 5 hours, more preferably 1 hour to 5 hours.

[0076] The granulation step (a) may comprise or consist of the following two steps: A1) adding an organic binder to an aqueous suspension of an azo compound while stirring to obtain a granulation medium; A2) Maintaining agitation of the granulation media.

[0077] Step (a) is preferably carried out in the absence of surfactants and / or dispersants.

[0078] Step (a) is preferably carried out without the addition of surfactants and / or dispersants.

[0079] For example, step (a) is carried out in the absence of dioctyl sodium sulfosuccinate or without the addition of dioctyl sodium sulfosuccinate.

[0080] The granulation step (a) is carried out at a temperature that does not cause decomposition of the azo compound, and the temperature may be 5° C. to 45° C., preferably 10° C. to 40° C., for example 10° C. to 20° C. The granulation step (a) is generally carried out at atmospheric pressure.

[0081] The mass ratio of the azo compound to water can be from 1 / 99 to 40 / 60, preferably from 10 / 90 to 25 / 75, and more preferably from 15 / 85 to 25 / 75.

[0082] The mass ratio of organic binder / azo compound may be 0.2 to 0.5, preferably 0.3 to 0.5, and more preferably 0.3 to 0.4.

[0083] The process according to the invention optionally subsequently comprises steps of recovering and drying the granules obtained in step (a). These steps can be carried out in a conventional manner. For example, the granules can be recovered by filtration. The granules can then be dried. In particular, the granules can be dried at a temperature between 10°C and 45°C, preferably between 20°C and 40°C. The granules can be dried under reduced pressure or, more preferably, under a stream of inert gas such as air, depleted air or nitrogen. Drying can last for several hours, for example, 1 to 10 hours, preferably 3 to 5 hours.

[0084] By "granules" is meant in particular solid and agglomerated masses of constituent particles, said particles having a size of between 10 μm and 200 μm, preferably between 90 μm and 110 μm.

[0085] The present invention therefore relates to granules obtainable (or obtained or directly obtained) by the process according to the invention. Such granules are novel.

[0086] 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.

[0087] In particular, the binder is present in trace amounts in the granules according to the present invention. In particular, drying of the granules after collection leads to evaporation of the organic binder. Thus, the granules according to the present invention may contain 20 ppm to 3000 ppm, for example 20 ppm to 1000 ppm, of organic binder. More specifically, the granules, especially after drying, contain 20 ppm to 500 ppm of organic binder, more preferably 50 ppm to 300 ppm of organic binder, and even more preferably 50 ppm to 200 ppm of organic binder.

[0088] In particular, the granules according to the invention have a density of 25 g / cm 2 More preferably, 40 g / cm 2 It has a crush resistance of more than 10 ...

[0089] They advantageously have a viscosity of 90 g / cm including the end point. 2 , preferably 95 g / cm 2 , more preferably 100 g / cm 2 , or even 500 g / cm 2 For example, their maximum crush resistance is 50-100 g / cm 2 , preferably 55 to 95 g / cm 2 is.

[0090] The granules according to the invention are generally substantially spherical or spherical. They may have a diameter of 0.5 to 5 mm, more preferably 1 to 5 mm, for example 2 to 3 mm.

[0091] The present invention also includes azo compounds of general formula (I) as defined above, 2 More preferably, 40 g / cm 2 The present invention relates to granules having the above crush resistance. Such granules may include one or more of the above-mentioned characteristics.

[0092] One of the advantages of the granules according to the invention is their rigidity, which makes them very easy to transport and handle. These granules are also of high purity and have a low content of residual organic binders.

[0093] The present invention relates to their use as swelling agents, initiators of free radical polymerization reactions, or synthetic intermediates, especially in the preparation of pharmaceutical or agrochemical compounds. The polymerization reaction can be bulk, solution, suspension, or emulsion polymerization, and a wide variety of monomers can be used, such as (meth)acrylic or vinyl monomers, such as acrylamide, acrylonitrile, alkyl (meth)acrylates, styrene, vinyl chloride, and acetate or vinylidene chloride. The application areas concern, in particular (but not exclusively), acrylic sheets or fibers, flocculants, paints, coating resins, grafted polyols, polystyrene, PVC (poly(vinyl chloride)), PVA (polyvinyl acetate), or PMMA (polymethyl methacrylate).

[0094] In particular, the granules according to the invention can be used for the preparation of polyols grafted with mixtures of styrene and acrylonitrile or for the preparation of polyacrylonitrile as precursors for carbon fibres.

[0095] <Example> The particle sizes of the dry AZDN used in the examples are 52.5 microns dv(10) / 101 microns dv(50) / 180 microns dv(90), respectively. The particle sizes of the wet AZDN are 61 microns dv(10) / 119 microns dv(50) / 203 microns dv(90), respectively.

[0096] The particle size measurement is carried out using a Masterziser® S instrument. The measurement is carried out using water and one drop of Igepal® surfactant (ethoxylated nonylphenol) as dispersant. The particle size measurement is carried out after 10 minutes of circulation in the measuring cell.

[0097] Example 1: Granulation in a 500 ml reactor 1-Operation mode: Granulation: The reactor is a 500 ml double-walled glass reactor maintained at 15° C. by circulating cold water, and is equipped with a mechanical stirrer.

[0098] 22.4 g of dry AZDN was weighed into a beaker, and then 100 mL of water was added. After homogenizing the mixture using a spatula, the aqueous suspension was transferred to a reactor. Then, 100 mL of water was added to recover the AZDN remaining in the beaker.

[0099] The suspension in the reactor is stirred at 1000-1100 rpm, which causes the remaining AZDN on the surface to be lifted. After a few minutes, the organic binder is quickly added to the reactor. The stirring speed is then reduced to 850 rpm.

[0100] After stirring for approximately 3 hours, the presence or absence of granule formation is noted.

[0101] The reactor is drained onto a filter. Optionally, an aqueous filtrate solution saturated with binder is used to complete the rinsing of the reactor.

[0102] The filtered granules are washed and allowed to dry outdoors under ventilation for approximately 24 hours. The friability of the formed and dried granules is recorded by their resistance to manual crushing.

[0103] Determination of the solubility of organic binders in water: The measurement was carried out by contacting 100 g of water and 20 g of organic binder with stirring for 1 hour at 20° C. The aqueous phase was decanted and then analyzed by gas chromatography to determine the concentration of the organic binder.

[0104] Determination of AZDN solubility in organic binders: Measurements were performed 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 decantation, the organic binder was analyzed to determine its AZDN concentration. Analysis was performed by gas chromatography with the injector temperature set to 220°C (under these conditions, AZDN is essentially converted to tetramethylsuccinonitrile in the injector). AZDN was diluted with acetone to produce a standard range of 0 to 150 g / L.

[0105] Gas Chromatography Analysis: The chromatographic column is an OV1701 macrobore column (diameter=0.25 mm, length=30 m, film thickness=0.25 microns) and the chromatographic apparatus is a Hewlett Packard HP 6890 apparatus equipped with an FID (flame ionization) detector.

[0106] 2-Results obtained: The results obtained are shown in the table below:

[0107] [Table 2]

[0108] After granulation according to the invention, granules of 1-3 mm size are obtained, which are rigid enough to be collected, dried and handled.

[0109] Example 2: Granulation in a 2 L reactor 1-Granulation and drying: Granulation: An apparatus similar to that of Example 1 is used, but with a 2 liter reactor, and the quantities involved are shown in the table below.

[0110] The agitator is equipped with pitched blades and the initial agitation is set at 800 rpm, then reduced to 600 rpm after the introduction of the organic binder as in the previous example.

[0111] Drying the granules: A 6 cm diameter porous glass filter was used, equipped with a double jacket, allowing the filter walls to be heated by circulating hot water. 100 g of undried filtered granules were introduced into the filter. A constant flow of nitrogen (2 L / min) was then injected through the bottom of the filter at different temperatures.

[0112] The granules shown in the table below are obtained:

[0113] [Table 3]

[0114] 2-Determination of residual organic binder content: During drying of the granules, approximately 1 gram of the granules obtained with isobutyl acetate is taken over time and analyzed by gas chromatography to determine the residual binder content.

[0115] The results obtained are shown in the table below:

[0116] [Table 4]

[0117] For CMPE, at 30°C, drying is faster, with a residual CPME concentration of 0.01% observed after 3 hours, which does not change significantly thereafter (5 hours drying).

[0118] Thus, the preparation and drying of the granules can be carried out under satisfactory industrial conditions. After several hours of drying, granules are obtained with a residual organic binder content of 0.01% to 0.02% by mass, i.e., 100 ppm to 200 ppm (i.e., 100 to 200 mg of organic binder per kg of granules).

[0119] 3- Crushing test of dry granules: 20 g of the AZDN granules obtained in Example 2 are placed in a 6 cm diameter glass crystallizer and then placed in a 5 cm diameter flat-bottom glass beaker (empty mass 200 g) and distributed evenly. If no crushed or broken granules are observed, an additional 200 g weight is gradually added to the top of the beaker until the onset of crushing of the granules is observed, visible through the transparency of the bottom of the beaker or the side of the glass crystallizer.

[0120] The surface area of ​​the beaker is S = π × (2.5) 2 =19.625cm 2 is.

[0121] Crushing resistance is: [total weight at breaking point (beaker + additional weight)] / [S].

[0122] Comparative Test: Granules were prepared by extrusion according to the procedure described in Examples 1 and 2 of WO 00 / 24706. The AZDN powder was that used in the previous examples of this application. The resulting granules averaged 5 mm in diameter and 1.5 cm (1-2 cm) in length. When dried, these granules appeared very brittle when handled. These granules exhibited very low resistance to crushing tests, much lower than that obtained for granules according to the present invention.

[0123] The results obtained are shown in the table below:

[0124] [Table 5]

[0125] The granules according to the invention have significantly improved crush resistance. These are easily handled without falling apart.

[0126] Example 3: Granulation in a 100 L reactor 1-Granulation and drying: A 100 liter DE DIETRICH brand AE100 enamelled stainless steel reactor is used, with an inner diameter of 508 mm and an effective height of 375 mm.

[0127] Agitation is ensured by an "impeller" type agitator with a diameter of 300 mm, equipped with three straight blades that ensure 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 scraper agitator with a diameter of 48 cm, which can move up and down within the filter, allowing mechanical discharge of the dried product through a side opening, flush with the filter in the lower position. The agitation speed can vary from 0 to 60 rpm. The filter fabric is a 20-micron mesh fabric.

[0128] All tests are performed at room temperature (19-20°C).

[0129] The reactor is kept under nitrogen by a light flush of 50 l / h.

[0130] 43.1 kilograms of demineralized water are introduced. The stirring is set at 200 revolutions per minute and the temperature is 18° C. 11.3 kilograms of moist AZDN powder with a moisture content of 8% are introduced over 5 minutes.

[0131] After 5 minutes, 4.1 kilograms of isobutyl acetate is added over 2 minutes. Granule formation is visible within the first few minutes. After 5 minutes, the stirring is reduced to 100 rpm and these conditions are maintained for 5 hours.

[0132] The reactor is then drained through the bottom valve into a filter. The granules are filtered by applying nitrogen pressure to drain and collect the aqueous liquid.

[0133] Next, 10m 3 / h nitrogen flush is carried out in place at room temperature for 24 hours.

[0134] The granules, which are solid when dry, can be recovered by starting a mechanical scraper agitator set at a speed of 6 revolutions per minute. In this way, 10.2 kilograms of AZDN are recovered in the form of granules approximately 2 to 3 millimeters in diameter.

[0135] 2- Crush resistance test: Crush resistance testing of the granules as described in the previous example showed a maximum of 91.72 g / cm 2 This shows a very good stiffness of these granules with a resistance of 0.1 to 0.25 mm.

[0136] 3-Dissolution test: The granule dissolution test is carried out at room temperature. A glass Erlenmeyer flask equipped with a magnetic stir bar is placed on a magnetic stirrer. With stirring stopped, 13 g of AZDN is introduced into the Erlenmeyer flask. 100 ml of acetone is then quickly introduced and stirring is started (100 rpm). The time taken until no more undissolved AZDN crystals are visible visually is recorded.

[0137] A comparison is made between commercially available recrystallized AZDN (130-257-438 microns / dv10-50-90), AZDN granules prepared and dried as obtained above, and the dry powdered AZDN used in Example 1.

[0138] [Table 6]

[0139] It can be seen that the spherical AZDN granules obtained according to the present invention dissolve as quickly as the initial powder form of AZDN, whereas the recrystallized AZDN crystals, although having a smaller average diameter than the spherical granules of the present invention, take much longer to dissolve in acetone. No visible insoluble material was recorded for each sample.

Claims

1. A process for granulating an azo compound of general formula (I): [General formula (I)] 【Chemical 1】 (In the formula, *R １ group, R ２ group, R ３ group, and R ４ The groups are the same or different and, independently of one another, linear or branched alkyl groups optionally substituted with hydroxy or alkoxy groups, or halogen atoms; a cycloalkyl group optionally substituted with a hydroxy group or an alkoxy group, or a halogen atom; an aryl group optionally substituted with a hydroxy group, an alkyl group, or an alkoxy group, or a halogen atom; an aralkyl group optionally substituted with one or more alkyl, alkoxy, or hydroxy groups, or one or more halogen atoms; or R １ and R ２ and / or R ３ and R ４ and at least one of the combinations with, together with the carbon atom to which it (or they) are attached, forms a cycloalkyl group or a C(O) group; *R ５ Groups and R ６ The groups are the same or different and are independently of one another a CN group and an NH ２ selected from the group The following steps: (a) a granulation step by stirring an aqueous suspension of the azo compound in the presence of an organic binder; (b) the optional step of recovering the granules obtained in step (a), preferably by filtration; and (c) the optional step of drying the granules recovered in step (b). The granulation process comprising:

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

3. 3. The granulation process according to claim 1 or claim 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-dimethylvaleronitrile), 2,2'-azobis(2-methylhexylonitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2-phenylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(1-cyclohexanecarbonitrile), and azodicarbonamide, preferably 2,2'-azobis(isobutyronitrile).

4. The granulation process according to any one of claims 1 to 3, wherein the organic binder is selected from aliphatic acetates, aliphatic carbonates, non-halogenated aromatic hydrocarbons, aliphatic ketones, and aliphatic ethers.

5. The granulation process according to any one of claims 1 to 4, wherein the mass ratio of the azo compound to water can be from 1 / 99 to 40 / 60, preferably from 10 / 90 to 25 / 75, more preferably from 15 / 85 to 25 / 75.

6. Granulation process according to any one of claims 1 to 5, wherein 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.

7. Granules comprising an azo compound of general formula (I) according to claim 1 or claim 3 and an organic binder according to claim 1 or claim 4.

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

9. Granules obtainable by the process according to any one of claims 1 to 6.

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

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