FI71774B - FOERFARANDE FOER GRANULERING AV PARTIKLAR - Google Patents

Description

1 71774

Method for granulation of particles - Förfarande för granulering av particle

The present invention relates to a method for granulating particles, which comprises the step of mixing the particles, whereby they are brought into contact with each other at short intervals while spraying the mixed particles with an aqueous binder solution, after which the product is dried.

European Patent 27693 to Interox Chemicals Limited discloses and claims protection for certain magnesium salts useful, inter alia, as bleaching agents, being: in solid form, the magnesium salt of the following classes of compounds: Class (1) - aromatic carboxylic compound introduced around the aromatic moiety with a carboxylate group and a peroxycarboxylic acid group, both groups being separable from the corresponding aromatic carbocyclic anhydride by reaction with hydrogen peroxide and wherein said aromatic carboxylic compound is optionally further substituted with at least one of carboxyl, nitro -, chlorine and bromine groups or a class (2) - cycloaliphatic compound substituted around the cycloaliphatic ring by a carboxylate group and a peroxycarboxylic acid group, both groups being separable from the corresponding cycloaliphatic group. an aliphatic carbocyclic anhydride by reaction with hydrogen peroxide, and wherein said cycloaliphatic carboxylic compound is further optionally substituted with at least one group selected from alkyl, carboxylate, sulfonate, nitro, chloro and bromo groups, or a class (3) olefin is substituted with a carboxylate group and a peroxycarboxylic acid group, wherein the carbonyl group of the carboxylate substituent is conjugated to the carbonyl group of the peroxycarboxylic acid via olefinic unsaturation via an olefinic acid to the aliphatic compound, and wherein both substituents are separable

Said publication also describes the preparation of such salts by the reaction of anhydride, aqueous hydrogen peroxide and a magnesium base in an inert organic reaction medium such as ethyl acetate. In many cases, the average particle size of the solid product obtained directly by this method is smaller than would be advantageous in powdered detergent compositions.

Similarly, Interox Chemicals Limited EP-A-0 066 992 discloses an alternative process for the preparation of magnesium salts according to classes (1) and (3) as defined above, in which process the solid salt is precipitated from a substantially aqueous medium. In many cases, a product with an average particle size larger than that obtained from an inert organic reaction medium is obtained. Although this is advantageous in that the product is easy to add to the detergent compositions and does not disperse therein, the measured degree of solubility of the salt was found to decrease with increasing average size.

In this case, the possibilities and methods for granulating or agglomerating small particles of magnesium salts to produce granules that also contain agglomerates began to be investigated. Given the superior solubility of magnesium salts over conventional solid peroxygen bleaches, e.g., sodium perborate tetrahydrate and sodium percarbonate at ambient or near ambient temperatures, it could be assumed that agglomeration can be readily performed using water alone, the solubility of the product deteriorates.

3,71774

It is clear that many inorganic and organic compounds have been proposed in the past as granulating agents or coating agents for solid peroxygen compounds. Inorganic compounds include a solution of the peroxygen compound itself or the like, and organic glycol polymers are included in the organic compounds. When compounds of these classes, such as magnesium phthalate and polyethylene glycol, were tested as granulating agents for granulating magnesium salts using a fluidized bed, the product obtained generally differed little from that obtained using water alone, i.e. very little or no granulation. This indicated that only a very small amount of product with an acceptable particle size was obtained and even this product was too brittle to be acceptable. A similar poor result was obtained using dextrin or gelatin or a gum such as gum arabic described as a coating in French Patent 893115.

In addition, when a commonly used coating agent for inorganic persalts, namely, for example, the sodium silicate solution disclosed in Japanese Patent Publication No. 78/15716 in combination with dextrin, considerable decomposition of magnesium persalts occurred. Other materials, such as sodium or magnesium sulfate, have been described as coatings for phthalic acids in U.S. Patent 3,493,787, but in fact have very little or no positive effect on the brittleness of the product. This indicates that it is not possible to transfer the granulation technique directly from one group of peroxygen compounds to the magnesium salts described herein so that the effects are even reasonably foreseeable. For this reason, all these many published patents, starting with French patent 8931115, H. Guiot, only provide references to experiments on other family compounds and do not directly indicate what should be done with the magnesium persalts in question.

4,71774

According to the present invention, there is provided a process for granulating particles of one or more magnesium salts of the organic peroxyacid carboxylates described above, wherein the particles are one or more magnesium salts of an aromatic carboxylic compound having a carboxylate group anhydride by reaction with hydrogen peroxide, a binder consisting of polyvinyl alcohol or a carboxylated derivative thereof having an average degree of polymerization of 500 to 4000 and used as at least 0.1% of the polymer as a dry product, and the temperature of the particles being maintained at 65 ° C.

The invention will be explained in this connection with particular reference to the magnesium salt of monoperoxyphthalic acid, which is a hydrated salt and has the following empirical formula:

B

C

HCl-C ° C 3 H Mg 2+ .6H 2 O (I) HCl cc> 2 C 2

B

Other magnesium salts of classes (1), (2) and (3) may be used mutatis mutandis in the invention.

Polyvinyl alcohol (PVA) or a carboxylated derivative thereof is used as a binder. The average degree of polymerization of the PVA polymer is 500-4000. It will be appreciated that a blend of two or more PVA polymers may also be used, e.g., one containing a small amount of a lower molecular weight polymer, such as 5-15% by weight of a polymer having a degree of polymerization of 500-1000 and a degree of polymerization of 1500-2500 , wherein said mixture also contains, if desired, a small amount of 5,71774 PVA with an even higher degree of polymerization. As an alternative to using the preformed mixture, two or more polymer solutions may be added separately, either simultaneously or sequentially, with preferably a lower molecular weight polymer being added first. The PVA polymer used is typically one that has been hydrolyzed to more than 80%, and most successfully that has been hydrolyzed to 87-90%. It has been found that carboxylated derivatives of PVA polymers can also be used successfully.

The polymer is usually used in an aqueous solution with a concentration selected so that the solution can be sprayed using the selected device. Of course, the maximum strength used will depend on the molecular weight of the polymer and the temperature of the solution. Typically, the concentration of polymer is selected in the range of 1-12% by weight. When a polymer with a degree of polymerization of about 2000 is used, the very effective concentration of the polymer is then about 4-5% by weight. The solution may conveniently be used at ambient temperature, but if desired the solution may be sprayed at temperatures up to 65 ° C.

The amount of agglomerating agent used is normally selected from 0.1 to 5 L of polymer, often at least 0.2 L and in many cases at least 0.5 L, with the percentages of polymer used herein being by weight based on dry products. In practice, it is preferred to use up to about 2.5% of the polymer and often the amount is selected between 0.8 and 2.0 of the polymer. It is clear that the general rule is that the more agglomerating agent added, the larger the average particle size of the dry product obtained, but to some extent existing agglomerates tend to grow instead of forming new agglomerates. Of course, the amount of aylomerizing agent is selected taking into account the average size of the feed particle and the desired size of the product. The applicant has stated that it is appropriate to select an amount in the range from 0.3% to 2.0% and in particular from 0.8% to 1.5% by weight of the dry product when it is desired to produce an agglomerate with a substantial particle size in the range of 0.15 to 1 .0 mm using a feed of 6,71774 containing at least 75% by weight of particles with a diameter of less than 0.2 mm, the feed preferably containing at least 80% by weight of particles with a diameter of less than 0.15 mm.

After the agglomerate has been dried, it is often advantageous to screen it to isolate a fraction having a certain particle size range, whereby the particle size may be in the above-mentioned range or narrower, e.g. 0.2 mm to 0.85 mm. Undersized particles (fine) can be recycled to the agglomerator. The oversized particles can preferably be crushed or ground to such an extent that a substantial proportion of agglomerates are obtained over a given particle size range and the remaining fine particles are recycled again.

In the agglomeration process of the present invention, substantially all of the feed material has a particle size of less than 0.5 mm and in practice a large proportion of the particles are usually less than 0.2 mm, in many cases this proportion is 75-90% by weight or even greater. It is most preferred to use a feed having a weight-measured geometric mean particle diameter of 75 to 100 uni. The particles can be obtained from the methods described in the above-mentioned patent applications. Where they would otherwise be larger than the preferred size, they may be crushed or ground. If desired, the feed can be either dry or wet, in which case the actual operating conditions are adjusted so that the free water content of the particles is taken into account. It may be advantageous to use, for example, a moist solid obtained from a filter or centrifuge as described in EP-A 66992, optionally first carefully crushing or alternatively or additionally using dry and, if necessary, ground magnesium salt particles. It is clear that some of the feed particles may be particles of the same size as materials compatible with the above-mentioned magnesium salts according to classes (1), (2) and (3). Such materials can be advantageously selected from the compounds described in said European patent publication 27693, which form a particularly important class of desensitizing diluents and include 7,71774 halogen-free acid time 1 mammalian or alkaline earth metal salts with a first dissociation constant of at least -3 x 10 10, e.g. sodium and magnesium sulphate or various sodium phosphates. It is further understood that due to their method of preparation, the magnesium salt particles can often contain an additive, such as the magnesium salt of the corresponding non-oxygenated day, which in the case of magnesium monoperoxyphthalate is magnesium phthalate, and / or possibly various crystal transformers.

In an important embodiment of the invention, a particular feature is the use of an inert gas for mixing the particles, the gas being used in particular to fluidize the layer formed by the particles. By acting in this way, it is possible to obtain agglomerates of magnesium salt particles with a slightly lower free-flowing apparent bulk density than when using, for example, rotary pan or drum granulators. This can be a particular advantage when the agglomerates are intended to be added to powdered detergent compositions, the advantage being that the bulk density can more closely correspond to the bulk density of spray-dried products, the latter generally forming a substantial part of these compositions, minimizing bleach / detergent separation during processing. Therefore, according to an embodiment of the invention, an agglomerate of one or more of the magnesium salts described above, and in particular of magnesium magnesium peroperoxyphthalate, having a particle size in the range of 0.2 to 1.0 mm, a weight-concentrated particle size in the range of 0.4 to 0.65 mm and a free-flowing apparent bulk density are provided. in the range 0.3 to 0.6 kg / l, in particular when obtained by agglomeration of magnesium salt feed particles, of which at least 75% by weight is less than 0.2 mm and preferably at least 80% by weight is less than 0.2 mm. Such agglomerates can be prepared in particular by using a fluid bed granulator in combination with a hydroxyl-substituted organic polymer, especially PVA and carboxylated PVA described herein.

71774

The inert gas used to mix the particles is preferably air, but may be nitrogen or some other gas that does not react with the magnesium salt or agglomerating agent under contact conditions. In practice, the inert gas is naturally unsaturated with respect to the water vapor, an effect which naturally occurs when the gas is heated and / or dried before it is used to mix the particles.

In the fluidized bed process, a layer of magnesium salt particles is fluidized throughout by drawing up an inert gas, typically air, and the gas flow is adjusted according to conventional particle sizes and weights to keep the particles in suspension in the fluidization chamber. often using, for example, backflow or return blow filters, where such control and use of the fluidized bed is well known and need not be further elucidated here.

In batch or single treatment granulation of a fluidized bed, there are steps of first adding a layer of magnesium salt feed particles to the fluidization chamber and then bringing the particle layer to the desired temperature, spraying the agglomeration agent as an aqueous solution onto or preferably over the bed, drying and generally cooling. It is clear that different steps can be performed in the same or different chambers and that alternatively the process can be performed continuously using a segmented chamber or several chambers in which e.g. feed particles and / or agglomerates move from one segment or chamber to another, e.g. over a threshold or dam .

The inert gas is preferably used at an inlet temperature of 40 to 80 ° C, in particular at least 50 ° C and most preferably 60 to 65 ° C in the pre-cooling steps. During the cooling step, the temperature of the gas at the inlet end can be reduced progressively or immediately below 30 ° C, preferably to a temperature of 5 to 25 ° C and most preferably to ambient temperature.

9,71774

The particle layer is preferably brought to a temperature of 35 to 50 ° C, often to a temperature of 40 to 45 ° C before being sprayed. During the spraying or atomizing step, the bed is maintained at a temperature of at least 25 ° C and usually at most 50 ° C by means of a fluidizing gas and optionally heat generated in or around the fluidization chamber, preferably at a temperature of at most 65 ° C. As is well known in the art, the rate of addition of an aqueous solution of agglomerant to a fluidized bed is controlled according to the flow of fluidizing gas and other bed parameters so that the bed remains in a fluidized state and thus avoids a state known as "hydrogenation." Such adjustment or control is controllable by a person skilled in the art and takes into account external conditions such as ambient temperature and humidity. In practice, the applicant has found it suitable in many situations to gradually add the agglomerating agent solution over a limited period of at least 20 minutes and often 20 to 30 minutes and to maintain the temperature at about 30 ° C, typically between 28 and 33 ° C. Alternatively, the solution may be added in small portions instead of continuous addition. The solution is added in the form of a spray and, as is known, a certain variability in the particle size of the granulate can be achieved by varying the size of the spray droplets. According to the invention, it has been found particularly advantageous to spray from a nozzle having an orifice diameter selected in the range of 1.2 mm to 2.4 mm and a spray air pressure selected in the range of 1 to 4 bar, said readings being in particular about 1.8 mm at a spray air pressure of 1, 8 bar, but other equivalent orifice / spray pressure combinations are possible depending on, among other things, the dimensions of the operation.

The agglomerates are very preferably dried in a fluidized bed to avoid the formation of cakes, which could occur if the agglomerates were emptied wet from the bed. Drying is preferably continued until the exhaust gas has reached a constant temperature, the exact value of which, of course, depends on the inlet gas temperature and the device itself. When an inlet gas temperature of 60 to 65 ° C is used, the temperature of the gas from the filters, usually the return filter, is at most about 55 to 60 ° C. The drying time is usually between 5 and 20 minutes when drying in a bed. Subsequent cooling with cool gas still takes 5 to 10 minutes, and thus the overall granulation process normally takes 40 to 80 minutes, often 45 to 60 minutes from the start of the agglomeration addition.

By using a fluid bed granulation process and, if necessary, suitable screening thereafter, in particular to remove the remaining fine particles, a granular product can be obtained which meets the requirements for particle size and bulk density described above. The product produced by such a method is preferably free-flowing and its abrasion resistance can be judged by its resistance to the abrasive conditions in the fluidized bed, but the product can be further improved by providing a refiner in the bed if necessary. Furthermore, the product generally causes less color damage when washed than a product of similar particle size but higher density made using a ball mill granulator. Finally, it has been found that the product obtained by rapid fluid bed granulation as described herein loses only a very small part of its predominant oxygen (avox), which in many cases is less than 5% and often leaves a product containing at least 6% avox, which is the same as syöttöhiukkasissa.

The product of the present invention can be easily added to bleach and detergent compositions. Having now described the invention in general terms, some specific embodiments thereof will now be described, by way of example and without limitation. These may be modified as described above or on the basis of the skills and knowledge of a person skilled in the art without departing from the spirit and scope of the invention.

11 71 774

In the examples, the feed particles were obtained by grinding through a fluffing machine equipped with a 2 mm sieve to obtain a dry sample of magnesium monoperoxyphthalate in substantially the same manner as in the larger scale version of Example 17 of EP-A 66992. The analysis found that about 90% by weight of the feed particles had a diameter of less than 212 after grinding.

In each batch, a compact test fluidized bed chamber was filled with about 15 kg at the ambient temperature of the feed particles, and then the bed was fluidized by hot air draft, maintaining the inlet air temperature in the range of 60-65 ° C. The temperature of the bed was monitored and when it reached 40 ° C, the addition of a polyvinyl alcohol premix having an average molecular weight of about 2400 to 2500 (ambient temperature about 20 ° C, 4% by weight) was started and passed through a nozzle with a nominal orifice size. was 1.8 mm and the pressure was 1.8 bar. 2000 ml of solution was sprayed over the next 20-30 minutes. The temperature of the bed decreased slightly during spraying mainly due to evaporation, but was kept close to 30 ° C throughout. Fluidization with warm air continued for about 15 minutes after the addition of the polyvinyl alcohol solution was complete, at which point the temperature of the bed had risen to 55-57 ° C and the exhaust air had reached a constant temperature of about 40 ° C indicating that the bed was substantially dry. The layer was then fluidized for a few minutes with ambient air, and after the granules had cooled to 30-40 ° C, the product was emptied and then coarsely screened. Typically, the product yield in the nominal range of + 212 μm to 710 μm was about 7.5 kg, the yield of -212 μm was about 4.5 kg, and the yield of + 710 μm was about 3 kg. The oversized material was ground in said mill and the yield was 40% more of the product in the range of + 212 to -710 μm and the undersized material was recycled.

The free flowing apparent flow density of the product in the preferred size range was measured essentially according to the method and apparatus disclosed in British Patent No. 1,71774 to 1600106 and when the product was substantially free of undersized particles, said bulk density was in the range of 0.35 to 0.41 kg / l. The solubility of the product was measured by stirring 0.25 g of solid at 50 rpm in 25 ml of water at 20 ° C in a tube for 15 seconds, after which the tube was spun for 30 seconds and finally the supernatant was peeled or decanted and its proximal oxygen content (avox) was measured. By comparing the dissolved avox to the known avox of the solid product, the solubility of the active oxygen can then be calculated. Typically, the product of the invention in the preferred particle size range had a solubility of 70 to 90% by weight, while performing the same experiment on a ball mill granulated material had a solubility of just over 50% by weight, which is clearly worse. This same ball mill granulated product also tended to have a higher apparent transfer density, generally 0.6 to 0.7 kg / l.

Substantially the same results were obtained by repeating the example using the same fluidized bed apparatus and the same conditions except that the magnesium monoperoxyphthalate feed particles had a weight geometric mean of about 90 and several other polyvinyl alcohol sources were used with similar degrees of polymerization of about 1700 to 2400. than before in aqueous solution and giving a polymer weight loading of 1% by weight on the dry product. In addition to acceptable degrees of solubility, these products also had acceptable wear resistance.

In one variation, the example was repeated using an additional sample of the latter batch of magnesium salt feed particles and an aqueous solution of a carboxylated derivative of PVA was used as a binder. With a load of 2% on the dry product, the oversized product tended to form, but had excellent abrasion resistance and good solubility. This indicates that the carboxylated derivative of PVA is substantially as effective a binder for the present purpose as PVA itself.

13 71 774

For comparison, the example was also repeated using the same apparatus and conditions and the latter feed particles, but using other binders in aqueous solution. Gum arabic, gelatin, magnesium phthalate, sodium sulfate, methylcellulose, and dextrin were all able to granulate only a small fraction of the feed particles, and even these granules rubbed or wore easily.

Claims (10)

71774 A method for granulating particles, comprising the step of mixing the particles intermittently by spraying the mixed particles with an aqueous binder solution, after which the product is dried, characterized in that the particles are one or more magnesium salts of the aromatic carboxylic compound a carboxylate group and a peroxycarboxylic acid group, both groups derived from the corresponding aromatic carboxylic anhydride by reaction with hydrogen peroxide, a binder consisting of polyvinyl alcohol or a carboxylated derivative thereof as a dry matter having an average degree of polymerization of 500 to 4000 and used and the temperature of the particles is maintained at a maximum of 65 ° C during the process. Process according to Claim 1, characterized in that the magnesium salt is magnesium monoperoxyphthalate. Process according to Claim 1 or 2, characterized in that the polyvinyl alcohol has an average degree of polymerization of 1000 to 3000, preferably 1500 to 2500, Process according to one of the preceding claims, characterized in that the polymer is used as an aqueous solution at a concentration selected in the range from 1 to 12% by weight. Process according to one of the preceding claims, characterized in that the amount of polymer used is selected in the range from 0.5 to 2.5% and preferably from 0.8 to 2.0% by weight, based on the dry granular product. 717 74 Method according to one of the preceding claims, characterized in that at least 75% of the feed particles have a diameter of less than 0.2 mm, and preferably have a geometric mean diameter of 75 to 100 μm. Process according to one of the preceding claims, characterized in that the particles are mixed and fluidized with an inert fluidizing gas, the layer being kept at a temperature of at least 25 ° C during the addition of the aqueous polymer solution, Process according to Claim 7, characterized in that the inlet temperature of the fluidizing gas is from 50 to 60 ° C. Process according to Claim 7 or 8, characterized in that the agglomerates formed are then dried in a fluidized bed, preferably until the effluent fluidizing gas has reached a substantially constant constant temperature, and then the dried agglomerates are cooled to below 40 ° C by fluidizing with a cool fluidizing gas before emptying them from the layer. Method according to one of the preceding claims, characterized in that a fraction of the product with a particle size of 0.5 to 1.0 mm is then isolated. Patentkrav 717 7 4