MXPA98008479A

MXPA98008479A - Method for preparing particles that include unnucleum and sil protection

Info

Publication number: MXPA98008479A
Application number: MXPA/A/1998/008479A
Authority: MX
Inventors: Amiche Frederic
Original assignee: Rhone Poulenc Chimie
Priority date: 1996-04-22
Filing date: 1998-10-14
Publication date: 1999-04-06

Abstract

The present invention relates to: invention for a method for preparing particles comprising a dense silica protection and a core of another material, by rapid precipitation of active silica from a solution of aqueous alkali metal silica with a pH adjusted by a acidifying agent, on a support material other than silica, the separation of the silica suspension formed and dried from the coated silica suspension. These particle compounds consist of a protection formed by dense silica and a core of organic material without a polymer with particular phytosanitary biological activity, which can be used for the slow release of such solid organic material without polymer with particular phytosanitary biological activity by slow diffusion through the protection of síli

Description

METHOD FOR PREPARING PARTICLES THAT COMPRISE A NUCLEI AND A SILICA PROTECTION DESCRIPTION OF THE INVENTION The subject matter of the present invention is a method for preparing particles comprising a dense silica shield and a core composed of a support made of a material other than silica by precipitation on the active silica core through of an aqueous alkali metal silicate solution. Another subject matter of the invention, as novel industrial products, are composite particles made of a shield formed of dense silica and a core made of an organic material without a polymer having biological activity. The particles obtained according to the method of the invention can be used as fillers for rubber, polymers, concretes or papers or as vehicles for solid active materials or active principles, in particular that have biological activity, which constitute the nucleus or they are included in the nucleus; with rapid or slow release of the active material or the active principle or through the destruction of the protection go. edur.te mechanical or chemical action or by diffusion. It is known to prepare heterogeneous particles composed of dense silica protection deposited on a core composed of one; to r g a different from silica through the slow precipitation of active silica on the core from an aqueous alkali metal silicate solution, with pH adjustment using an acid (US-A-2,885,366). According to this document, the precipitation operation can be carried out in a medium of low ionic strength with an addition rate lower than a certain parameter S (expr s as silica weight that will be added per hour) with respect to the weight of the core which will be coated '!, defined by the following equation: S = (A / 200) 2n n_ being equal to (T-90) / 10 A representing the specific surface, expressed in m2 / g, of the support that is coated and T is the temperature in ° C, considering the formation of the core of dense silica particles.

For this reason, the active silica precipitation operation is long; In this way, the deposition of the order of 20 parts in [• of silica over 100 parts by weight of calcium carbonate at a temperature of the order of 80 to '"U ° C requires a precipitation reaction lasting 3 days. at 5 hours The Applicant Company has found a novel method that makes it possible to quickly precipitate dense active silica on a core composed of a charge other than silica, without the risk of the formation of nuclei of silica particles. "dense" means that it means a silica protection formed by a continuous layer composed of a network of crystalline structure of silica, in contrast to a box composed of a porous assembly of individual silica particles.The present invention of this nera consists of a method for preparing particles comprising a dense silica protection through the active silica precipitation of an alkali metal M silicate solution non-aqueous, with a Si02 / Na20 ratio of at least 2, preferably of the order of 2.5 to 4, with the adjustment of the pH using an acidifying agent, on a support made of a material other than silica, the separation of the formed silica suspension and the drying of the recovered silica suspension, the method is characterized in that the operation of forming silica suspension by precipitation is carried out in accordance with the following steps: a first step consisting of using a residue of initial vessel with a pH of 8 to 10 comprising water, at least one organic or inorganic support other than silica, which is insoluble in water under the pH and temperature conditions of the suspension forming operation, a salt of electrolyte of the group of metals at 1 ca 1 i no s, the amount of electrolyte present being approximately 0.4 mol, preferably in the order of 0.4 to 1.5 mol, of alkali metal ion not p or liter of container bead, and optionally a pH regulator or basic agent, at a temperature of the order of 80 to 98 ° C; a second step consisting of introducing to the container residue, the silicate containing at least about 100 grams of SiO2 / liter, preferably of the order of 100 > 1 330 grams of SiO2 / liter, and the acidifying agent, under conditions such that the kinetics K of active silica formation expressed in grams of silica / hour / grams of s or p - > r t- e, corresponds to a value K > 3 (A / 200) 2", preferably K> 4 (A / 200) 2" and very particularly K > 6 (A / 200) 2"n being equal to (T-90) / 10 A representing the specific surface, expressed in m2 / g, of the support to be coated and T is the temperature in ° C, the mixture gives reaction exhibiting a substantially constant pH of the order of 8 to 10 and maintained at a temperature of the order of 80 to 98 ° C, until it forms, the desired amount of active silica. The choice of silicate and acidifying agent to carry out the method of the invention is made in a manner well known per se. The alkali metal silicate is advantageously a sodium or potassium silicate. Particular mention may be made of sodium silicate. Generally, use is made as agent acidification, of an inorganic acid, such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or carbonic acid. Preferably this is sulfuric acid. The latter can be used in the diluted or concentrated form, preferably in the form of an aqueous solution exhibiting a concentration of the order of 60 to 400 g / 1. If it is carbonic acid, the latter can be introduced into the gas phase. Mention may be made, among the materials that may constitute the support for the implementation of the method of the invention, any inorganic or organic, solid or liquid compound of any shape (spherical, acrylic, and the like), which is inert with respect to silica active (hydroxylated silica) and which is insoluble in water under the pH and temperature conditions of the suspension-forming operation. The material is preferably in solid form. "The compound which is inert with respect to the silica" is understood to mean any compound that remains stable under the conditions of silica precipitation. "The compound which is insoluble in aqua" is understood to mean any compound that exhibits a solubility in water of less than about 0.5% by weight at 25 ° C. Mention may be made, as an example, of ma ferials: solid inorganic metal salts, such as calcium carbonate, zirconium carbonate, barium carbonate, lead carbonate, zinc sulphide, silver chloride, barium sulfate. , aluminum phosphate, titanium phosphate and the like, metal powders, such as iron, nickel, aluminum or copper powders, and the like, - solid metal oxides or hydroxides, such as aluminum oxides, chromium, iron, titanium , zirconium, zinc, titanium or cobalt, nickel hydroxide, and the like, natural or synthetic solid silicates, such as magnesium, aluminum or zinc silicates and the like, kaolin, atapuljite, bentonite, mica and the like, fiberglass and imides , porous solid silicates (bentonite, atapuljite, and the like) comprising an active material which is stable and insoluble in water under the conditions of pH and temperature of the suspension forming operation; it could be mentioned, as examples of active materials, those that possess biological activity (pharmaceutical, plant protection, and the like), solid organic polymers such as polyethylenes, polyesters and the like, organic materials without solid polymers, which may or may not be crystalline , which possess biological activity (pharmaceutical, plant protection and the like). The support used can have any size depending on the desired applications, for example in the order of 20nm to 30μm, preferably of the order of 50nm to 20μm. Particular mention is made, among the electrolytes, to the salt of the starting silicate metal and the acidification agent; preferably it is sodium sulfate; however, sodium chloride, nitrate or acid carbonate may be preferred if the presence of residual sulfate ions is not desired. The first stage consists in preparing the initial container waste.

If the support used is a solid material, the latter can be introduced as it is or, preferably, in the form of an aqueous dispersion. If it is a liquid, the latter is preferably used in the form of an aqueous emulsion. The amount of support that can be used is such that the container formed contains the order of at least 10% of its weight of solid support or the order of at least 10% of its volume of liquid support; the container bead can generally contain up to 50% of its weight or its volume of solid or liquid support. A pH regulator or basic agent can be used in the initial agent residue in order to ensure a pH of the container residue of the order of 8 to 10. It can be mentioned, as a pH regulator or basic agent, metal hydroxide. alkali, such as sodium hydroxide, dissolved alkali metal silicates, alkali metal phosphates, alkali metal acid carbonates, and the like. The obtained container residue is brought to a temperature of the order of [lagoon] 80 to 98 ° C. The second stage consists of adding the silicate solution and the acidifying agent simultaneously to the container residue, which is maintained with agitation. The respective amounts of the alkali metal silicate of the acidifying agent are selected in order to obtain the kinetics K of active silica formation mentioned above and in order to keep the pH of the reaction mixture at a substantially constant value of the order of 8 through 10 through the introduction of the two reagents. These two solutions are introduced while maintaining the mixture at a temperature of the order of 80 to 98 ° C. The introduction of the silicate solution is interrupted when the desired amount of silica is formed. The desired minimum amount of silica is that corresponding to a deposition of the order of 1 to 150 parts by weight of SI02 per 100 parts by weight of s or else. This second stage generally lasts at least 30 minutes to 2 hours. The pH of the mixture obtained at the end of the second stage, after stopping the introduction of the reagents, is subsequently carried out, if necessary, a value of less than 7, preferably of the order of 4 to 5. The mixture obtained at the end of the stage, after stopping the introduction e - > Reactants, optionally, are allowed to mature for approximately 10 to 30 minutes under the; n i s m ---. s temperature conditions. This optional maturing operation can be performed either before or after putting the p-H of the mixture to a value less than 7, preferably of the order of 4 to 5, if this pH correction is necessary. To conclude the operations described above, a suspension of silica is obtained, said suspension is subsequently sep a a (liquid / solid separation); This operation generally consists of a filtration (for example, separation through sedimentation, use of a rotary vacuum filter), followed by washing with water. The silica suspension thus recovers (filter cake) is subsequently dried (oven, stove, atomization). The particles thus obtained can exhibit a dense silica protection thickness of rd n from 2 to 200 nm, preferably of the order of '> at 50 nm, for a support core size of from 20 nm to 30 μm, preferably of the order of VJ n: n at 20 μm. The method that forms the subject matter d? The invention is well suited for preparing dense silica particles exhibiting a protective thickness of the order of 2 to 200 nm, preferably of the order of 5 to 50 nm, for a core size of the order Je 20 nm to 30 μm, preferably of the order of 50 nm to 20 μm. It becomes possible to obtain, according to the desired application, both particles with a dense silica protection which is brittle and easily broken by mechanical action and particles with a dense silica protection that resist mechanical actions. Particles with dense silica protection, which is mechanically brittle, may exhibit a protective thickness less than about 20 nm, preferably less than 10 nm, particularly if the core size is greater than 10 μm, very particularly greater than 15 μm. These particles generally exhibit a BET surface [lagoon] of the order of 0.1 to 200 m / g; the latter depends on the initial BET of the support. The specific surface of BET e determines in accordance with. the method of B r u n a u c r -Emme t -T e 11 e r, described in "The Journal J t: J American Chemical Society ", Vol. 60, page V" 1, February 1938, which corresponds to the NFT Standard 45007 (November 1987). The thickness of the protection is determined through an electron microscope. According to an alternative embodiment of the invention, the silica protection of the particles present in the suspension additionally contains traces of polyvalent cations, such as Mg 2 + Ca 2 + Ba 2+ or Pb 2+, preferably introduced into the aqueous solution formed during the suspension operation, in the first stage in the container bead, or in the second stage, during the simultaneous addition of the reagents. The presence of traces of polyvalent cations, which can be removed in the next stage, for example through the action of an acid (in this case in particular of Ca2 +, and the like), is particularly advantageous for micro-porosity. to the dense silica protection. This is because a microporous structure (J V. dense silica protection is advantageous, 11-release or an improvement in release with -> the material time that constitutes the core through diffusion through the protection of silica A second subject matter of the invention consists of, as novel industrial products, composite particles comprising a pellet of dense precipitated silica and a core made of an organic material without solid polymer, which may or may not be crystalline, which possesses biological activity (pharmaceutical, plant protection and the like) and which is insoluble in an aqueous medium with a p H of the order of 8 to 10 at a temperature of less than 100 ° C. Said composite particles can preferably be prepared from According to the method described above, they can also be obtained through any precipitation method that makes possible the deposition of dense silica through the precipitation of an alkali metal silicate on a support (for example, according to the method described in US-A-2,885,366). They can exhibit a dense silica protection thickness of the order of 2 to 200 n: r ?, preferably in the order of 5 to 50 nm, for a support core size, the support having biological activity of the order of 20 nm to Mμm, preferably of the order of 50 nm to 20 μm. The dense silica protection of the composite particles can also be brittle and can easily break through mechanical action or be resistant to mechanical actions. The particles that form the subject matter of the invention or that are obtained according to the method of the invention, composed of a dense silica protection as covering a support core, the support is made of a material other than silica, can have multiple applications. Particles that are resistant to mechanical action and with a core composed of a low cost solid material can be used as fillers for rubber or polymers, fillers for concrete or paper and the like. Particles with a protection that is sensitive to mechanical or chemical action can be used, as such or in a solid or liquid formulation, as vehicles for solid active materials or active principles, in particular having biological activity, (pharmaceutical, protection of plants, and the like) that constitute the nucleus or are included in the nucleus, with the release of the active material or the active principle through the destruction of the protection through mechanical or chemical action. Particles resistant to mechanical action can also be used for delayed release of active solids or active substances that possess biological activity, in particular protection activity of particular plants, constituting the nucleus or included in the nucleus through the slow diffusion Through the protection of silica, it being possible for this diffusion optionally, if desired, to be accelerated by the presence of my creativity in the protection of silica. The following examples are presented by way of illustration.

Example 1 A container residue was prepared through the introduction, into a 15 liter reactor, of 5 liters of water, of 0.43 moles / liter of sodium vessel bead in the form of sodium sulfate, of 1500 g of precipitated calcium carbonate (Sturcal H, sold by Rhonone - Po u 1 enc, exhibiting a particle size of 11 μm and a specific surface area of BET of 4 rrJ / gV v ^ e sodium silicate, with a ratio of S? 02 / Na O of 3.5 (aqueous solution containing 130g of S? O_ per liter), in an amount corresponding to a concentration of 5g of S? 02 per liter of the container bead. 8.5, it was brought to 90 ° C and kept under stirring The following was introduced subsequently and simultaneously: - an aqueous sodium silicate solution with a S 2 / Na 2 ratio of 3.5, the concentration of which is of 130 g of S? 02 per liter of the solution, and a solution of aqueous sulfuric acid containing 80 g of ac gone by book, with the f.-n to form 300g of silica in 50 minutes. After maturing for approximately 20 minutes, the obtained suspension was filtered; the filter cake was washed with water and then dried by atomization. The analysis of the product through electron microscopy (TEM) showed that the layer of silica deposited is of the order of 20nm. The BET surface [lagoon] of the final particles is 3.2 m2 / g.

The kinetics of addition of the silicate to t_-sodium was 0.24 g (SiO2) / h / g (C to COJ, cna 0.02 g (SiO2) / h / g (CaCO3) according to the t • • n --- previous ca (US-A-2, 885, 366).

EXAMPLE 2 A container bead was prepared through the introduction of, to a 15 liter reactor, 5 liters of water, 0.43 mol / liter of sodium vessel bead in the form of sodium sulphate, of 1150 g of precipitated calcium carbonate (Sturcal H, sold by Rhóne-Poulenc, exhibiting a particle size of 11 μm and a BET specific surface area of 4m2 / g) and sodium silicate, with a Si de 2 / Na 20 ratio of 3.5 (solution containing 130g of SiO2 per liter) in a quantity corresponding to a concentration of 2g of SiO per liter of container bead. The bead of the vessel with a pH of 9 was brought to 90 ° C and kept stirring. The following was introduced subsequently and simultaneously: an aqueous sodium silicate solution with a SiO2 / Na2 ratio of 3.5, the concentration of which. is 130g of SiO per liter of solution, - and gaseous CO2, in order to form 230 g of silica in 90 m 1 nu * "> After ripening for approximately ten minutes, the suspension obtained is filtered, - The suspension cake was washed with water and then dried in an oven at 80 ° C. Analysis of the product by electron microscope (TEM) showed that the thickness of the deposited silica layer is of the order of 20 nm The BET surface of the final particles is 3.7 m2 / g.The kinetics of the addition of the sodium silicate was 0.34 g (SiO2) / h / g (C to COJ, with 0.02 g (Si02). ) / h / g (CaCO) according to the previous technique (US-A-2, 885, 366).

Claims

1. A method for preparing particles comprising dense silica protection through the precipitation of active silica from an aqueous alkali metal silicate solution, with a SiO2 / NaO ratio of at least 2, preferably of the order of 2.5 to 4. , with an adjustment of the pH using an acidifying agent, on a support made of material other than silica, separation of the silica suspension formed and drying of the recovered silica suspension, the method characterized in that the operation of suspension formation of Silica through precipitation is carried out according to the following steps: a first step consisting of using an initial container residue with a pH of 8 to 10 comprising water, at least one organic or inorganic support other than silica, which is insoluble in water under the conditions of pH and temperature of the operation of suspension formation, an electrolyte salt of the group of such alkalines, the amount of electrolyte present being about 0.4 moles, preferably in the order of 0.4 to 1.5 moles, of alkali metal ion per liter of container residue, and optionally a regulator or basic agent, at a temperature of the order of 80 to 98 ° C; a second step consisting of the introduction, to the container residue, of the alkali metal silicate in the form of an aqueous solution containing at least about 100 grams of SiO2 / liter, preferably of the order of 100 to 330 grams of SiO2 / liter, and the acidifying agent, under conditions such that the kinetics K of active silica formation expressed in grams of 1 s / hr / hr / g of support, corresponds to a value K > 3 (A / 200) 2n, preferably K > 4 (A / 200) 2n and very particularly K > 6 (A / 200) 2"n being equal to (T-90) / 10 A representing the specific surface, expressed in m2 / g, of the support to be coated and T is the temperature in ° C, the reaction mixture exhibiting a substantially constant pH of the order of 8 to 10 and maintained at a temperature of the order of 80 to 98 ° C, until the desired amount of active d-silica is formed.

2. The method according to claim 1, characterized in that the alkali metal salt is a sodium or potassium silicate.

3. The method according to claim 1 or 2, characterized in that the acidifying agent is an organic or inorganic acid.

4. The method according to claim 3, characterized in that the acidifying agent is sulfuric, nitric, hydrochloric, acetic, formic or carbonic acid.

5. The method according to claim 4, characterized in that the acidifying agent is C02 gaseous or sulfuric acid in the form of aqueous solution exhibiting a concentration of the order of 60 to 400 g / 1.

6. The method according to any of the preceding claims, characterized in that the material constituting the support is selected from solid inorganic metal salts, metal powders, solid metal oxides or hydroxides, natural or synthetic solid silicates, solid porous silicates which they comprise an active material, which is stable and insoluble in water under the conditions of pH and temperature of the operation of suspension formation, solid organic polymers, or organic materials without solid polymers, which may or may not be crystalline, which They possess biological activity.

7. The method according to claim 6, characterized in that the material constituting the support is calcium carbonate or organic materials without solid polymers, which may or may not be crystalline, possessing biological activity, in particular plant protection activity.

8. The method according to any of the preceding claims, characterized in that the material constituting the support has any shape and size in the order of 20 nm to 30 μm, preferably in the order of 50 nm to 20 μm.

9. The method according to any one of the preceding claims, characterized in that the electrolyte is sodium sulfate, chloride, nitrate or hydride or g a n a r b ona t.

10. The method according to any of the preceding claims, characterized in that the support is used in the form of an aqueous dispersion.

11. The method according to any of the preceding claims, characterized in that the amount of support which can be used is such that the container residue formed contains in the order of at least 10% of its weight or of its support volume.

12. The method according to claim 11, characterized in that the container waste contains more than 50% of its weight or support volume.

13. The method according to any of the preceding indications, characterized in that the second stage of suspension formation is carried out by the simultaneous introduction of the alkali metal silicate and the acidifying agent, until the formation of at least 1 to 150 parts by weight of Si02 per -.00 parts by weight of support.

14. The silica particles comprising an active silica protection and a core composed of a support made of another material than the silica which is obtained according to the method formed of the subject matter of any of the preceding claims, characterized in that they exhibit a protection of thin silica of the order of 2 to 230 nm, preferably of the order of 5 to 50 nm for a support of core size of the order of 20 nm to 30 μm, preferably of the order of 50 to 20 μm.

15. The particle composite according to claim 14, characterized in that they exhibit a thin silica shield of at least about 20 nm, preferably at least about 10 nm.

16. The composite of amber particles with claim 15, characterized in that they exhibit a support core size of greater than about 10 μm, preferably greater than about 15 μm.

17. The compound of particles composed of a protection of dense precipitated silica and a core made of a solid organic material without polymer, which may or may not be crystallized, which weighs biological activity, in particular plant protection activity, and which is insoluble in an aqueous medium, with a pH of the order of 8 to 10 at a temperature of at least 100 ° C.

18. The particle composite according to claim 17, characterized in that they exhibit a thin silica protection of the order of 2 to 200 nm, preferably of the order of 5 to 50 nm, by a core size support of the order of 20 nm to 30 nm. μm, preferably of the order of 50 nm to 20 μm.

19. The use of the particle compound formed of the subject matter of claim 1 by the delayed release of such solid organic material without polymer that weighs biological activity, n particular protection activity by dif'i; Slow ui through the protection of silica.