EA041871B1 - METHOD FOR PRODUCING MICRONIZED SILICA GEL - Google Patents

Description

Typically, silica gel is described as a non-depositable, bonded, rigid three-dimensional structure of adjacent and interconnected silica particles. Micronized silica gels can be used as adsorbents for various gases or liquids, as a stabilizing or clarifying agent in beer, wine, beverages or edible oils, as an opacifying agent and filler in paints and coatings, as an abrasive in toothpaste, as component of antifogging agents and as antiblocking agents in polymer films, as a functional or reinforcing filler in plastics, as an adsorbent in the manufacture of paper, plastic or textile coatings, as a carrier in the manufacture of catalysts, as a carrier for active ingredients in cosmetics or pharmaceutical industries, as well as an anti-caking agent in the production of powdered substances.

Three different types of processes are used to manufacture the most commonly used amorphous silica powder products, which are produced in quantities of several 100,000 tons per year.

1. Pyrotechnic production of silicon dioxide from tetrachlorosilane SiCl ₄ , hydrogen and oxygen in an oxy-hydrogen flame.

Essentially, the large-scale synthesis of silicon dioxide can be described as the continuous hydrolysis of silicon tetrachloride (SiCl ₄ ) in a flame at a temperature of about 1200°C (EP 097378 A1, DE 19530339 A1). In the described case, SiCl ₄ goes into vapor and then spontaneously and quantitatively reacts with water intermediately formed in the hot blast gas flame to form the target silicon dioxide. Because this process is carried out in a flame, the silica produced by these processes is also called fumed silica.

When the reaction is carried out in a flame, highly viscous particles of silicon dioxide with a diameter ranging from 5 to 50 nm are initially formed. The surface of these particles is not microporous, but smooth. These primary particles in the flame are densely fused into larger formations - the so-called aggregates. The sizes of these particles-aggregates are in the range from 100 to 500 nm. Upon cooling, the aggregates form tertiary structures in the form of scaly agglomerates. The size of these scaly agglomerates is in the range of 1-100 µm. Aggregates are characterized by the presence of pores, while the large accessible surface of aggregates and agglomerates leads to a relatively high BET specific surface area (up to 600 m ² /g). It should be noted that the total specific surface area, also called the BET specific surface area, is determined in accordance with the method proposed by Brunauer, Emmett, Teller, also called the BET method.

2. Chemical precipitation of alkali metal silicates with acids.

Large scale precipitation processes involve the partial neutralization of a solution of alkali metal silicates, typically a sodium silicate solution, from which the silica is precipitated by stirring at elevated temperature with the addition of acids (primarily sulfuric acid), whereby gel formation is avoided. Colloidal particles of silicon dioxide with low molecular weight grow to a certain size. The electrolytes formed during the neutralization process contribute to the coagulation of these particles into agglomerates. The final structures of the agglomerates (coagulates) flocculate with the formation of aggregates and strengthen (US Pat. No. 2819002, EP 0272380 A2).

Amorphous precipitated silica powders differ from micronized silica gels in that they have a more open structure and therefore lower internal porosity. Under certain conditions, a high total pore volume can be imparted to precipitated silica by targeted agglomeration into scaly tertiary structures.

3. Sol-gel transformation of alkali metal silicates with acids in acidic silica gels.

In industrial large-capacity processes, two sol-gel processes are predominantly carried out.

Silica gels can be prepared at low pH by acidifying an aqueous solution of a soluble metal silicate, usually sodium silicate, with acid. Acidification is usually carried out by treating the silica solution with a strong mineral acid, such as sulfuric acid or hydrochloric acid, to pH values at which the silica solution gels. The three-dimensional gel structure thus obtained includes the solvent used. The silica gel is then washed from the electrolyte using time- and energy-intensive washing processes. If necessary, the adjustment of the pore structure is carried out later by exposure to the post-treatment of the hydrogel (US Pat. No. 2759798, US 3501269 A).

Silica gels can also be prepared by bringing an aqueous solution of sodium silicate to a low pH (about 2.2) using an ion exchanger in the protonated form, where the silica is made by adding a base to reach pH values of 4 to 8, which initiates the formation of the silica gel. The final structure of the silica gel is almost completely free of electrolyte and can be immediately subjected to heat aging or, if necessary, further treatments to achieve a suitable porosity (DD 261586 A1, DD 279233 A1).

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Typical of such sol-gel conversion processes is the relatively low colloidal stability of the intermediate silica sols. Such silica sols, which polycondensate uncontrollably within only a few hours, are called unstable silica sols.

The disadvantage of incorporating an unstable sol results from the filamentous structure of the silica, which leads to a sterically hindered and hence disordered polycondensation. The silica chains are randomly connected, with the result that the required porous structure of this kind of silica gel can only be optimized in the next processing step.

The proposed approach represents a transition from a sol to a gel, in which a stable silica sol obtained by direct stabilization is used as the starting material. The sol-gel transition is initiated by bringing its pH to a value in the range of 4.0 to 7.0. Changing the pH value is achieved by adding a volatile acid and a volatile base, which means an acid and a base that can be removed from the composition by evaporation. The preferred version of this process uses formic acid and ammonium carbonate. The hardness of the thus obtained hydrogel is in the range of 20-520 N/m ² . Moreover, the resulting product is not homogeneous enough, and its hardness, measured at different points in the same batch, also varies significantly. Since silica gels for industrial use must have a high hardness of the intermediate hydrogel and the availability of large amounts of material, there is a need for improved methods for the production of micronized silica gels of this kind.

Therefore, the main technical problem is to provide methods for the production of micronized silica gel, characterized by a hardness of its intermediate hydrogel in excess of 600 N/m ² .

This technical problem is solved by the innovations proposed in the description and disclosed in the claims.

Thus, in a first aspect, the present invention relates to a method for the production of micronized silica gel, which includes:

(a) loading a stable silica sol with a silica content ranging from 5 to 50% by weight;

(b) adjusting the pH of the stable silica sol to a value in the range of 1.7 to 4.0 using an ion exchanger in at least partially, preferably fully protonated form;

(c) heating the silica sol obtained in (b);

(d) adding a fluid containing a volatile acid and a volatile base to the silica sol (c) and mixing to achieve the same pH value throughout the volume of the reaction mass in less than 5 minutes, while the pH value is in the range from 4.0 to 7 .0;

(e) product aging (d);

(f) drying the product (e) and (g) micronizing the silica gel thus obtained.

Here, the fluid is preferably defined as either a gas or a liquid. The fluid containing a volatile acid and/or a volatile base is preferably a volatile acid and/or a volatile base.

The term micronized silica gel refers to silica gel that has been micronized, which means that its average particle diameter has been reduced to values less than 1000 microns, preferably less than 500 microns, more preferably less than 100 microns. The particle size distribution is measured by dynamic light scattering. It is based on the observation that the angle of laser radiation refracted by a particle is related to the size of the particle. In a complex sample containing particles of various sizes, the diffraction of light results in a typical scattering pattern. By analyzing this chart, an accurate particle size distribution of the sample can be obtained. Here, the particle diameter of the dispersed phase refers to the volume median particle diameter, also referred to as d ₅₀ . Thus, unless otherwise noted, d ₅₀ preferably refers to the volume median particle diameter as measured by dynamic light scattering (DLS). It should be noted that one skilled in the art is capable of determining the volume median particle diameter based on DLS measurements.

The term is preferably used here to indicate that the specified feature is not inherent and may or may not be present, but that additional beneficial effects can be achieved if it is present.

A colloid is a composition in which one substance, which has particles of microscopic size, also called a dispersed phase, is distributed throughout the volume of another substance, called a dispersion medium. The dispersed phase particles typically have a diameter in the range from 1 to 1000 nm and can be measured, for example, using dynamic light scattering (DLS). It is typical that colloids are characterized by the fact that they do not settle, i. the dispersed phase does not separate from the dispersion medium, or a significant amount of time is required for separation, more than 1 hour, or more than 1 day. Both the dispersed phase and the dispersion medium can be a gas, a liquid, or a solid, except that no colloids are known in which both phases are ha

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A sol is a colloid in which the dispersed phase is a solid and the dispersion medium is a liquid at 25°C and a pressure of 1 atm. In other words, a sol consists of very small solid particles in a continuous liquid medium. The particle diameter of the dispersed phase in sols is typically in the range of 1 to 100 nm, which can preferably be measured by dynamic light scattering, also referred to as DLS. Here, the particle diameter of the dispersed phase is the volume median particle diameter, also referred to as d ₅₀ . Thus, unless otherwise indicated, d ₅₀ preferably refers to the volume median particle diameter measured by the DLS method. Under certain conditions, the sols are characterized by high stability, which means that the sols may not settle, i.e. the dispersed phase does not separate from the dispersion medium over a period of at least 6 months.

Silicasol is a sol in which the dispersed phase contains silica particles and the dispersion medium typically contains water. In other words, silicasol is a colloidal system consisting of finely dispersed, discrete amorphous silica particles and a solvent. The solvent is usually an aqueous solution containing salts and buffers.

Silicon dioxide is silicon oxide, corresponding to the general chemical formula SiO ₂ . Silicon atoms in various forms of silicon dioxide exhibit tetrahedral coordination, with (largely) in the crystal lattice each silicon atom is surrounded by four oxygen atoms. Thus, the general chemical formula of SiO ₂ reflects the stoichiometry of silicon dioxide, but not its molecular structure, which is not a single molecule containing two oxygen atoms and one silicon atom. It is understood that silicon dioxide can form large crystal lattices in which the oxygen atoms surrounding a particular silicon atom are bonded to other silicon atoms, with each silicon atom surrounded by successive oxygen atoms arranged in a tetrahedral structure around the silicon. This ability of silicon dioxide to form large structures allows it to exist in the form of discrete particles of various sizes or polymeric structures. It should be noted that the polymer structure of silicon dioxide is non-linear, but has cross-links, since each silicon atom can serve as a branching point of the structure. Thus, a typical silica polymer structure is a three-dimensional structure in which each silicon atom is tetrahedrally surrounded by four oxygen atoms and each oxygen atom is surrounded by two silicon atoms.

In accordance with the definition of the International Union of Pure and Applied Chemistry (IUPAC), a gel is a non-fluid colloidal structure or polymer structure that is impregnated throughout its volume with a fluid medium. In other words, gels are defined as highly dilute cross-linked systems that do not exhibit fluidity. A gel in which the fluid, also called swelling agent, is water is called a hydrogel. A gel in which the fluid is a gas is called a xerogel. The colloidal structure or polymeric structure is porous, which means that it contains spaces formed between the structures and these spaces are filled with fluid. Thus, a gel differs from a sol in that it is a two-phase system, wherein the individual solid phase contains a colloidal or polymeric structure, and the individual fluid phase is contained in the pores of the gel structure where the solid phase is not dispersed in the liquid phase.

Silica gel is a gel in which the solid phase is silicon dioxide, which forms a polymer structure through covalent bonds, as described above. Silica gel, in which the water content varies from 50 to 95 wt.%, preferably in the range from 65 to 95 wt.%, is called silicate hydrogel.

Under certain conditions, the sol can turn into a gel. In this process, called the sol-gel transition, a gel structure gradually begins to form in the sol, containing both a liquid phase and a solid phase. This process is also called gelation.

The diagram in Fig. 1 (reproduced from Her R., The Chemistry of silica, September 1979) shows the relationship between silica sol stability and its pH value. A sol is considered stable when its spatial composition does not change with time, which means that the particles of the dispersed phase of silicon dioxide do not settle or separate from the aqueous medium. The stability of the silica sol depends on the surface charge of the particle, which depends on the ions that are adsorbed on the surface of the sol particles. In turn, the surface charge determines whether there are repulsive forces between the particles that contribute to the stability of the silica sol. As can be seen from the diagram in Fig. 1, silica sol is stable under weakly basic conditions, at pH values ranging from 7.5 to 10.7. When salts such as sodium chloride are introduced, or when the conditions are changed to acidic (pH below 7.0), the stability of the silica gel is significantly reduced and a transition of the sol to the gel is observed.

The definition of a value between X and Y should be understood in such a way that the value can take on any value equal to or greater than X, but at the same time equal to or less than Y. In other words, this value must not be less than X and must not be greater than Y .

The preparation of stable silicasols is known to those skilled in the art. In one embodiment of the preparation method, an unstable silica sol is used as a starting point. IN

- 3 041871 According to the definition, an unstable silica sol is a silica sol that is not stable, which means that its composition can change over time as a result of settling of particles of dispersed silica and their separation from the aqueous medium, or through a sol-gel transition. An unstable silica sol can be converted to a stable silica sol by changing its pH to a value in the range of 7.5 to 10.7.

Alternatively, a stable silica sol can be prepared directly from an aqueous solution of sodium silicate, also called water glass.

This method consists in adding a silicate solution to a slurry of a weakly acid cation exchanger in H ⁺ form, the pH of the slurry being in the range of 2.0 to 6.0. Under these conditions, silicic acid is first formed, which is then converted to particles of the dispersed phase of silica in a process consisting in a long transition to slightly alkaline slurry pH values, more preferably, the slurry pH is in the range from 7.5 to 10.7. This production method makes it possible to obtain stable silica sols having a particularly narrow particle size distribution and a high silica content. Such stable silica sols obtained directly from the silicate and without the formation of an unstable sol at any stage are referred to as directly stabilized silica sols.

The directly stabilized silica sol is characterized by a high silica content. Preferably, the directly stabilized silica sol contains 5 to 50% silica. More preferably, the directly stabilized silica sol contains 15 to 50% silica.

An ion exchanger is a material capable of binding ions and exchanging the ions associated with it with another ion-containing solution or composition. Examples of materials that can be used as ion exchangers include, but are not limited to, ion exchange polymer resins, zeolites, montmorillonite, clay. Typical industrial processes preferably use ion exchangers containing polymeric resins. Ion exchangers are either cation exchangers, by which is meant ion exchangers capable of exchanging cations, or anion exchangers, by which are meant ion exchangers capable of exchanging anions. Certain cation exchangers are capable of binding H ⁺ ions and can adjust the pH of a solution or formulation by exchanging cations present in the solution or formulation with H ⁺ ions bound to the H ⁺ exchanger. Preferably, an ion exchanger having a strong acid functional group is used as the H ⁺ exchanger. The strongly acid functional group may be, but is not limited to, a sulfo group. A non-limiting example of an ion exchanger suitable for use in the process of the present invention is Lewatit MP S 108 H.

Ions H ⁺ related to this invention, usually correspond to the protonated form of the solvent. In the case of aqueous solutions, H ⁺ ions exist in the form of oxonium cations H ₃ O ⁺ .

For the production of silica gel in accordance with the present invention, a stable silica sol is used. Preferably the stable silica sol is a directly stabilized silica sol. One of the possibilities for the production of silica gel is the use of a stable silica sol as a starting material. Stable silicasol is a colloidal system consisting of finely divided discrete amorphous particles of SiO ₂ and a solvent, which does not undergo changes in the degree of dispersion over time - no coagulation of colloidal particles is observed. The colloids remain uniformly distributed in the dispersion medium, and no settling of particles under the action of gravity is observed. The silica particles of the stable sol are preferably spherical and in most cases have a diameter d ₅₀ ranging from 3 to about 100 nm, as determined by the DLS method.

One skilled in the art will recognize that if the pH of a stable silica sol is set between 3.5 and 7.0 and the system is heated to between 20 and 100°C, a sol-to-gel transition, also known as the process of gelation, with the formation of a hydrogel. However, such a hydrogel is characterized by insufficient mechanical strength, which makes further processing extremely difficult. A hydrogel characterized by a hardness below 520 N/m ² measured using the method previously disclosed in DE 102006022685B4, which results in a liquefaction effect unfavorable for further processing. Any mechanical stress of such a hydrogel leads to its transformation into a paste-like mass, which is not suitable for movement within an industrial enterprise, which is associated with the formation of syneresis water. Here syneresis water is defined as water displaced from the gel. The low mechanical stability of the hydrogel structure leads to structure contraction and subsequent collapse of the silica gel pores.

It will be noted that the product of step (d), ie the gelation product of the heated silica sol obtained in step (c), is also referred to as a hydrogel.

Surprisingly, it has been found that when the volatile acid and/or volatile base is evenly distributed throughout the silica sol in the ash for a short period of time, preferably less than 5 minutes, more preferably less than 1 minute, the resulting

- 4 041871 silicate hydrogels are characterized by hardness ranging from 600 to 2000 N/m ² . Preferably the volatile acid is an aqueous solution of formic acid and the volatile base is an aqueous solution of ammonium hydrogen carbonate. The change in pH value converts the stable silica sol to its metastable form, which can spontaneously gel into the corresponding silicate hydrogel. Surprisingly, it was found that the time scale of the gelation process coincides in order of magnitude with the time of diffusion of formic acid and ammonium carbonate into the silica sol. However, when a silicate hydrogel is formed, further diffusion of acid and base, preferably formic acid and ammonium carbonate, slows down, and gelation in subsequent portions of silica sol proceeds under suboptimal conditions, resulting in a hydrogel with lower hardness.

As demonstrated in the examples, immediate agitation results in hydrogels with significantly higher hardness compared to a situation where agitation is allowed to proceed more slowly, or when it is not applied and formic acid and ammonium hydrogen carbonate are distributed only by diffusion. When comparing the products described in Reference Example 2 and Example 2, it can be seen that in the latter case, a product with a significantly higher strength is formed if immediate mixing is carried out.

In order to form a hydrogel with a hardness in the range of 600 to 2000 N/m ^{2 ,} the addition and mixing of the formic acid solution and the ammonium carbonate solution in the silicate sol must be ensured so that the mixing proceeds faster than the gelation process. Embodiments of the invention provide a preferred means of achieving a uniform pH throughout the volume of the silica sol in a short time such that the gelation process can be initiated under optimal conditions simultaneously throughout the volume of the silica sol.

The optimal conditions for initiating the silica sol gelation process are determined by the pH value of the silica sol. Preferably, the pH of the silicasol is adjusted to between 4.0 and 7.0 in order to initiate gelation. More preferably, the pH of the silicasol is adjusted to between 5.0 and 6.0 in order to initiate gelation. Most preferably, the pH of the silicasol is adjusted to between 5.3 and 5.7 in order to initiate gelation.

It is considered that the pH value throughout the volume of silica sol is the same if it does not deviate throughout the volume of silica sol by more than 1.0 pH units from a certain value, while the determined value is preferably the average pH value of the entire volume of silica sol. More preferably, the pH value throughout the volume of silica sol is considered the same if it does not deviate throughout the volume of silica sol by more than 0.5 pH units from a certain value. Most preferably, the pH value throughout the volume of silica sol is considered the same if it does not deviate throughout the volume of silica sol by more than 0.25 pH units from a certain value. Therefore, if in a particular embodiment of this invention the pH value of the silica sol is set to 5.5 and is required to be the same throughout the volume of the silica sol, this will mean that at each location of the silica sol the pH will be in the range from 4.5 to 6.5 , more preferably this will mean that at each silica sol location the pH will be between 5.0 and 6.0, most preferably it will mean that at each silica sol location the pH will be between 5.25 and 5.75 . The pH value is preferably measured at 25°C.

The final structure of the silicate hydrogel is almost completely free of electrolytes and is subsequently maintained. If the silicate hydrogel is contaminated with electrolytes, in other words, contains electrolytes or is not free of electrolytes, these electrolytes should be washed with water. Here, electrolytes are defined as substances that exist in the form of positive and negative ions other than H ⁺ (also understood as H ₃ O ⁺ ) or OH ^- , such as salts such as sodium chloride NaCl. Volatile acid and base can be removed from the hydrogel structure by converting them to gases, and accordingly are not considered as electrolytes that can contaminate the silicate hydrogel, as disclosed in the description. It should be noted that both formic acid and ammonium bicarbonate are volatile and can be converted into a gaseous state.

As used herein, the term volatile, as in the case of a volatile acid or volatile base, preferably refers to substances or mixtures of substances (such as acids and/or bases) that can be evaporated at temperatures below 120°C, preferably below 105°C, and at a pressure of 1 atm, at least 95, preferably 99, most preferably 99.5 wt.%. The term evaporation includes, for example, evaporation of substances or mixtures of substances (i.e. transition from a liquid phase to a gaseous phase), sublimation of substances or mixtures of substances (i.e. transition from a solid phase to a gaseous phase), decomposition of substances or mixtures of substances, and evaporation of decomposition products and/or decomposition of substances or mixtures of substances and sublimation of decomposition products.

Preferably, a formic acid solution and an ammonium carbonate solution are used as the volatile acid and volatile base to bring the pH of the silica sol to between 4.0 and 7.0. However, this choice is not limiting and any acid and/or any

- 5 041871 a base which is volatile and suitable for adjusting the pH of the silica sol to a value in the range of 4.0 to 7.0 can be used in the method according to the present invention. Accordingly, the volatile acid may be selected from the group consisting of an aqueous solution of formic acid, pure liquid formic acid, pure gaseous formic acid, a gaseous composition containing formic acid, acetic acid, propionic acid and butyric acid. The volatile base may be selected from the group consisting of aqueous ammonium hydrogen carbonate, pure gaseous ammonia, gaseous compositions containing ammonia, aqueous ammonia, pure liquid or gaseous alkylamine, aqueous alkylamine, or gaseous compositions containing alkylamine, N,N-dialkylamine or N,N,Ntrialkylamine, in which each alkyl group is independently methyl, ethyl, propyl or butyl.

The product of the gelation process is maintained. During exposure, the silicate hydrogel is subjected to heat aging. The purpose of heat aging is to further strengthen the hydrogel structure, which leads to an increase in hardness as well as to control the porosity of the hydrogel. Porosity refers to the pore volume normalized to the mass of silica gel, which is expressed in cm ³ /g and can be obtained from the nitrogen adsorption isotherm by the method disclosed in the description. Preferably, the holding time is from 1 minute to 50 hours. More preferably, the holding time is from 1 to 20 hours.

The silicate hydrogel obtained in this way contains a significant amount of water. Depending on the silica sol used, the water content of the silicate hydrogel ranges from 50 to 95% by weight, preferably from 65 to 95% by weight. In this description, the water content of silica gel is expressed in wt.%, which is the ratio of the mass of water contained to the total mass of silica gel, expressed as a percentage. In order to ensure industrial applications, excess water is removed during the drying process. Any industrially applicable method for drying silica gel can be used in the present invention. As a non-limiting example, a vacuum drum dryer can be used to dry the resulting silicate hydrogel.

The last step in the production of micronized silica gel is micronization. Micronization is the process of grinding material so that the final volume median particle diameter d ₅₀ is in the range of 1 to hundreds of microns, preferably in the range of 1 to 100 µm, as measured by the DLS method. The type of mill used in the present invention is not limited, and any mill can be used. In certain embodiments of the present invention, a jet mill may be used.

In another implementation, this invention relates to the production of micronized silica gel, in which the volatile acid is an aqueous solution of formic acid, and in which the volatile base is an aqueous solution of ammonium hydrogen carbonate.

In another implementation of the invention, this method, at least in part, is carried out using a reactor consisting of: a reactor vessel with a cavity; at least one stirrer inside the cavity of the reactor vessel, rotating relative to the reactor vessel around the axis of rotation, while at least one stirrer contains at least one stirring nozzle; wherein at least one agitator and/or at least one mixing nozzle contains at least one outlet for adding fluid to the reactor vessel; and wherein at least one outlet is configured to be in fluid communication with one or more fluid supplies via at least one fluid connection. Silicasol is loaded into the cavity of the reactor vessel and the fluid is added to the reactor vessel through at least one outlet. At least one agitator is rotated during at least part of step (d).

The reactor may have the following features, as disclosed in this description. The advantages associated with the use of the reactor as described are disclosed below. For example, by means of a reactor it can be ensured that a fluid, such as a volatile acid and/or base, is more homogeneously, evenly and/or quickly added to the silica sol contained in the reactor cavity. The reactor may also form an independent embodiment of the present invention and may thus be claimed regardless of the method herein described.

Under conditions of industrial use, means must be provided for adding a volatile acid and/or a volatile base, preferably an aqueous solution of formic acid and an aqueous solution of ammonium hydrogen carbonate, to the silica sol from step (c) and mixing to achieve a uniform pH throughout the entire volume of the reactor in less than 5 min. In certain implementations of this invention, the reactor disclosed in this description can be used.

In another implementation, the present invention relates to a method for the production of micronized silica gel, where the silica sol obtained in stage (c) is heated to a temperature in the range from 20 to 100°C.

By adjusting the pH of the silica sol to values ranging from 1.7 to 4.0, a metastable silica sol is formed. The metastable silica sol is then heated to a temperature ranging from 20 to

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100°C. As previously demonstrated, the gelation of a heated metastable silica sol can be initiated by adjusting its pH values to between 4.0 and 7.0. Preferably, the silicasol obtained in step (c) is heated to a temperature in the range from 40 to 90°C. More preferably, the silica sol in step (c) is heated to a temperature in the range of 50 to 80°C.

Another implementation of this invention relates to a method for the production of micronized silica gel, where formic acid is used in a concentration in the range from 0.1 to 10 wt.%, preferably in the range from 0.1 to 1 wt.% more preferably in the range from 0.1 to 0.2 wt.%, based on the total weight of an aqueous solution of formic acid.

The concentration of formic acid in aqueous solution is given in wt.%, also denoted wt./wt. In order to calculate the concentration of the solution thus determined, the total dissolved mass of formic acid is divided by the total mass of the aqueous formic acid solution and expressed as a percentage (%). Preferably, formic acid is used in a concentration ranging from 0.1 to 10% by weight. More preferably, formic acid is used at a concentration ranging from 0.1 to 1% by weight. Most preferably, formic acid is used at a concentration in the range of 0.1 to 0.2% by weight.

The combination of formic acid and ammonium hydrogen carbonate is used to bring the pH of the metastable silica sol to between 4.0 and 7.0. The present invention is not limited to using only the combination of formic acid and ammonium hydrogen carbonate. However, the present invention requires that the combination of components be able to allow the pH value to be adjusted to between 4.0 and 7.0, and that all components are volatile, which means that they can be completely removed by evaporation without leaving any residual electrolytes in silicate ash.

Formic acid is used to stop the buffering action of ammonium bicarbonate used to adjust pH. On the other hand, formic acid is also used to maintain the stability of the metastable silica sol until the gelation process is initiated. Preferably, formic acid and ammonium hydrogen carbonate may be added simultaneously, or formic acid may be added first, followed by ammonium hydrogen carbonate.

Another implementation of this invention relates to a method for the production of micronized silica gel, where ammonium bicarbonate is used in a concentration in the range from 1 to 21 wt.%, preferably in the range from 5 to 15 wt.%, most preferably in the range from 8 to 12 wt.% based on the total weight of an aqueous solution of ammonium carbonate.

The concentration of ammonium bicarbonate in aqueous solution is given in wt.%, also denoted wt./wt. In order to calculate the solution concentration thus determined, the total dissolved mass of ammonium hydrogen carbonate is divided by the total mass of the aqueous ammonium hydrogen carbonate solution and expressed as a percentage (%). Preferably, ammonium hydrogen carbonate is used in a concentration ranging from 1 to 21% by weight in its aqueous solution. More preferably, ammonium hydrogen carbonate is used at a concentration ranging from 5 to 15% by weight in its aqueous solution.

Most preferably, ammonium hydrogen carbonate is used at a concentration ranging from 8 to 12% by weight in its aqueous solution.

Depending on the requirements for the porous structure, three different types of treatment can be applied. In certain embodiments of this invention, heat aging is carried out under atmospheric conditions. During thermal aging under atmospheric conditions, silica gels with a pore volume of 0.2 to 0.8 cm ³ /g are obtained using the method disclosed in the description. In further implementations of this invention, hydrothermal heat aging is carried out.

By hydrothermal heat aging, which can be carried out at a water vapor pressure of 3 bar (abs), silica gels with a pore volume of 0.7 to 1.5 cm ³ /g are obtained. In other implementations of the present invention, spend heat aging with treatment with gaseous ammonia. By treatment with gaseous ammonia, a pore volume of 1.0 to 2.8 cm ³ /g is achieved, where the pore volume can be adjusted by varying the ammonia pressure and the duration of the treatment.

Thus, another implementation of this invention relates to a method for the production of micronized silica gel, where the stage of aging is carried out in air. In other words, this embodiment of the invention relates to a method in which the thermal aging of the silicate hydrogel is carried out under atmospheric conditions, in contact with air at ordinary pressure.

Air refers to the gaseous composition that makes up the Earth's atmosphere. Typically, dry air is composed of about 21% oxygen, about 78% nitrogen, about 1% argon, and smaller amounts of other gases, predominantly carbon dioxide. In addition to these components, air can contain up to 1% water vapor. Here, the composition of the air is determined in vol.%. Assume that in this document, the air is not limited to the given composition. As the person skilled in the art knows, the composition of air varies with altitude and geographic location.

Thermal aging under atmospheric conditions is carried out by exposing the resulting silicate hydrogel to atmospheric air at ambient pressure and ambient temperature.

- 7 041871 Wednesday. Ambient pressure is understood as a pressure value ranging from 0.95 to 1.05 atm. By ambient temperature is meant a temperature in the range of 4 to 36°C, preferably in the range of 10 to 30°C, most preferably in the range of 18 to 26°C. It should be understood that these values are not limiting. In accordance with the implementation of the invention, for thermal aging, the silicate hydrogel is exposed to atmospheric air as it is, without further processing.

Another embodiment of this invention relates to a method for the production of micronized silica gel, where the aging step is carried out in air for a time ranging from 0.1 to 50 hours.

The resulting silicate hydrogel is usually air-cured for a time ranging from 1 to 50 hours. Preferably, the resulting silicate hydrogel is air-conditioned for a time ranging from 0.5 to 25 hours. in the range from 1 to 15 hours. By aging in air at atmospheric pressure, in other words, by thermal aging in atmospheric conditions, and subsequent drying and micronization, silica gels with a pore volume ranging from 0.2 to 0.8 cm ³ can be obtained /G.

Another implementation of this invention relates to a method for obtaining micronized silica gel, in which stage (e) is carried out in an inert atmosphere.

Alternatively, the resulting silica gel may be matured in an inert gas atmosphere. An inert gas atmosphere is defined as a composition of gases containing more than 90% inert gas. Inert gases are known to the person skilled in the art and include nitrogen and elements of group 18 of the periodic table of elements. Preferably, nitrogen, helium or argon is used as the inert gas in the method of the present invention.

The resulting silica gels can mature in air or in an inert gas atmosphere at pressures up to 9 bar. Preferably, the resulting silica gels can be matured in air or under an inert gas atmosphere at pressures up to 2 bar.

Thus, in another implementation, the present invention relates to a method for the production of micronized silica gel, where stage (c) is carried out in air or in an inert atmosphere and at pressures up to 9 bar.

Another implementation of this invention relates to a method for the production of micronized silica gel, where in stage (e) the product from stage (d) is steamed. Steam is understood as water vapor, in other words, H ₂ O above the boiling point under the available pressure. Steam may contain up to 20% of other gases, including but not limited to air components such as nitrogen, oxygen, carbon dioxide, argon. Preferably the steam is supplied under conditions where water exists in its vapor form. For this reason, steam is preferably supplied at a pressure of 1 bar and a temperature in excess of 100°C.

Steam treatment may also be referred to as hydrothermal treatment. It is understood that under such conditions, water molecules are more reactive than in the liquid state. During processing, water molecules in the gaseous phase fill the pores of the silicate hydrogel and hydrolyze some of the Si-O bonds. Thus, the pores expand. In other words, the pores get bigger. This process manifests itself through an increase in the porosity of the silica gel. Under processing conditions including steaming, in other words hydrothermal heat aging followed by drying and micronization, silica gels having a pore volume ranging from 0.7 to 1.5 ^cc /g can be obtained.

The porosity of the obtained silica gels is determined using adsorbing instruments such as Nova 3200 (manufactured by Quantachrome, Odelzhausen). Porosity measurements include the determination of various parameters, including BET (Brunauer, Emmett, Teller) total pore surface area, also called BET surface area, pore volume per unit mass of gel, also called pore volume, and/or average pore size, here understood as the average pore diameter. These parameters are determined during volumetric adsorption measurements. They are carried out using nitrogen gas at a relative pressure ranging from p/p ₀ =0 to p/p ₀ =1 bar at 77.2 K, where p and p ₀ are equilibrium and nitrogen saturation pressure at the adsorption temperature. To this end, nitrogen gas is brought into contact with the silica gel samples in the sample container. The temperature in the sample container is kept constant. The amount of adsorbed nitrogen is measured when equilibrium is established between the absorbate (in this case, nitrogen) and the adsorbent (porous silica gel). Using the resulting adsorption isotherms, the pore volume, pore diameter, and BET surface area are determined.

The total specific surface area, also called the BET surface area, is determined according to the method proposed by Brunauer, Emmett and Teller (BET), also called the BET method. The BET surface area calculations are carried out by linearizing the adsorption data using the BET equation, which represents the adsorbed volume as a function of the relative nitrogen pressure in the range p/p ₀ =0.05-0.3, where p and p ₀ are the equilibrium and nitrogen saturation pressure at temperature adsorption. The BET theory assumes multilayer gas adsorption on the surface. In accordance with the BET method, the adsorption isotherm can, under certain conditions, be represented as a linear function of the parameter p/p ₀ in accordance with the formula p / p ₀ s - 1 1

--and / but ₌ -----, _h -V 1 - p / Po V _m cv _m c where ν is the amount of absorbed gas;

p and p ₀ - equilibrium and nitrogen saturation pressure at the adsorption temperature;

vm is the amount of gas absorbed by the monolayer;

c - BET constant, determined by the formula

Ej-El c = e em where E1 is the heat of adsorption for the first layer;

EL is the heat of adsorption for the second and subsequent layers, which is equal to the heat of evaporation.

When plotting experimental data according to the formula, both parameters vm and c can be determined and used to calculate the BET surface area (SBET) according to the formula v _m Ns ^ _Β ετ- _Va where N is Avogadro's number;

s is the adsorption cross section of the adsorbing samples;

V is the molar volume of the gas and a is the mass of the solid sample of the adsorbent (in this case silica gel).

Pore radii are determined by the BDH (Barrett-Joyner-Halenda) method and can be calculated from both adsorption and desorption isotherms using the Kelvin equation. The Kelvin equation describes the influence of the curvature of the liquid-vapor meniscus surface on the vapor pressure and relates the pore diameter to the relative pressure (p/p ₀ )

JT(p(r/r ₀ ) = 't where p is the vapor pressure over the liquid-vapor meniscus surface curve with effective radius rm;

V L is the molar volume of the absorbent liquid;

γ is the surface tension of the liquid;

p ₀ is also the saturation vapor pressure, which corresponds to the vapor pressure at r _m x;

R is the universal gas constant and

T is the temperature.

This method is particularly suitable for mesoporous adsorbents such as silica gels.

The total pore volume P _V is determined directly from the nitrogen adsorption isotherm at a relative pressure p/p ₀ of about 1. The total amount of gas adsorbed can be converted to a liquid volume corresponding to the total pore volume P _V using the formula

Py = k V(N ₂ ~) where k is a conversion factor of 1.5468x10'3 kg/m ³ that is set for a liquid nitrogen density of 808.6 kg/m ³ ;

V (N2) is the total adsorbed volume of nitrogen.

In FIG. 3 shows an object of defined geometry, preferably used to measure the hardness of a silicate hydrogel. This method was previously disclosed in DE 102006022685 B4. The hardness of the hydrogel is determined using a Unimat 050 SV tensile tester and a PHYSIMETER® 906 MC multi-parameter system (manufactured by Erichsen, Reiner) as previously disclosed. In a specific embodiment of the present invention, 300 ml of a sol in a 600 ml beaker (DIN 12331, ISO 3819) is hydrogeled by the addition of ammonium hydrogen carbonate and formic acid. The hydrogel sample is thermostated at 70°C. The measurement is started 30 minutes after the addition of ammonium carbonate and formic acid. An object of a certain geometry with a relative feed rate of 20 mm/min is pressed into the hydrogel in the center of the beaker. Penetration depth - 10 mm. Force measurements are taken at intervals of 1 s and the values measured at the end of the measurement are expressed in N/m ² and taken as the hardness of the gel.

Another embodiment of the present invention relates to a process for the production of micronized silica gel, in which the steam in step (e) is supplied at an absolute pressure ranging from 1 to 100 bar for a time ranging from 1 to 50 hours.

In a particular embodiment of the present invention, the steaming is carried out at an absolute pressure ranging from 1 to 100 bar. Preferably, the steaming is carried out at an absolute pressure ranging from 1 to 3 bar. Absolute pressure is defined as the pressure relative to full vacuum. The steaming is carried out for a period of time ranging from 0.1 to 50 hours. Preferably, the steaming is performed for a period of time ranging from 1 to 20 hours.

During steaming, thermal aging of the silica structure occurs. During

- 9 041871 of this process, water vapor is evenly distributed among the pores of the silica gel and partially dissolves the particles of silicon dioxide, which leads to an increase in the pore size. Increased pore sizes can be measured as an increased average pore diameter.

A further implementation of this invention relates to a method for the production of micronized silica gel, where in stage (e) the product (d) is treated with gaseous ammonia.

The person skilled in the art knows that silica gel (including but not limited to silicate hydrogel) can be treated with an aqueous ammonia solution to increase the average pore diameter and total pore volume (DE 102006022685 B4). It has also been demonstrated that a similar effect can be obtained by fumigating the hydrogel with ammonia gas. Therefore, it is known to those skilled in the art that the heat aging process of the silicate hydrogel can be carried out using ammonia gas. Gaseous ammonia diffuses into the hydrogel and dissolves in water in the pores within the silica structure. Thus, when treated with ammonia, smaller particles of silicon dioxide are redistributed through repeated dissolution and precipitation to energetically more favorable positions. As a result, the porosity of the silicate hydrogel treated in this way is changed so that the total pore volume as well as the average pore diameter is higher than that of the silica gel before treatment. Moreover, due to the high diffusion rate of ammonia gas in the silicate hydrogel structure, the heat aging process is greatly accelerated.

The processing time can be optimized by varying the ammonia pressure.

The silicate hydrogel obtained in step (e) can be treated with ammonia gas for a time ranging from 0.1 to 50 hours. Preferably, the silicate hydrogel obtained can be treated with ammonia gas for a time ranging from 1 to 20 hours. The silicate hydrogel obtained can be treated with gaseous ammonia at an absolute pressure ranging from 1 to 100 bar. Preferably, the silicate hydrogel obtained in step (e) can be treated with gaseous ammonia at a pressure ranging from 1 to 10 bar.

Therefore, another embodiment of this invention relates to a method for the production of micronized silica gel, where the treatment with gaseous ammonia is carried out at an absolute pressure in the range of 1 to 100 bar for a time of 0.1 to 50 hours.

A further embodiment of the present invention relates to a method for the production of micronized silica gel, where the treatment with ammonia gas is carried out at an absolute pressure ranging from 1 to 10 bar for a time ranging from 1 to 20 hours.

The silicate hydrogel resulting from the gelation process in step (e) typically has a high water content. The silicate hydrogel contains mainly water and becomes suitable for industrial use only after drying, when excess water is removed. By drying, silica gel or silicate hydrogel is obtained. Any of the industrially applicable methods for drying silica gel can be used in the present invention. Here, the water content of silica gel is expressed in wt.%, which refers to the ratio of the mass of water contained to the total mass of silica gel, expressed as a percentage. The final product, micronized silica gel, has a water content ranging from 1 to 65% by weight. Preferably, the water content of the produced silica gel is in the range from 1 to 20 wt.%, More preferably, the produced silica gel contains water in the range from 1 to 8 wt.%.

Thus, another implementation of this invention relates to a method for the production of micronized silica gel, where the water content in the produced silica gel is in the range from 1 to 65 wt.%.

The dried silica gel is finely ground in the last step of the method of the present invention using a mill.

The type of mill for this invention is not limited, and any type of mill can be used. In certain embodiments of the present invention, a jet mill may be used. Through micronization, a volume median particle diameter d ₅₀ of 1 to 100 µm is achieved. More preferably, micronization achieves a volume median particle diameter of 1 to 20 µm.

Preferably, the processes of drying and grinding (micronization) of the resulting silicate hydrogel are combined and carried out in one apparatus. In other words, after exposure, the silicate hydrogel is subjected to simultaneous drying and micronization in a drying-grinding plant. There are several advantages to such an implementation. When smaller particles are dried, their available surface area becomes larger during grinding and, as a result, the drying process is faster. At the same time, more efficient grinding is achieved for silica gel that has been partially devoid of moisture content.

Therefore, another implementation of this invention relates to a method for the production of micronized silica gel, where stages (f) and (g) are carried out simultaneously.

In FIG. 4 shows an example of hardware design for the implementation of this method, while the equipment includes installations for drying and grinding. In this embodiment, the silica

- 10 041871 the sol turns into a silicate hydrogel and matures inside the reactor (which is shown in more detail in Fig. 2). Upon completion of the thermal aging of the hydrogel, it is transferred to a dosing tank, which feeds the drying-grinding plant for simultaneous drying and micronization.

Silica gels prepared in accordance with the method of this invention can be crushed in such a way that the desired particle diameter is achieved. The dried silica gels are pulverized, or, in other words, micronized so that the average particle size obtained is in the range of 1 to 100 µm. Preferably, the silica gels produced have an average particle diameter in the range of 1 to 12 microns.

Thus, another implementation of this invention relates to a method for the production of micronized silica gel, where silica gel is formed with an average particle diameter in the range from 1 to 100 microns.

Disclosed in the description of the method allows the production of silica gels, characterized by high hardness. Previously described processes for the production of micronized silica gels that use sol gelling, also referred to as the sol-gel process, do not produce silica gels with a hardness of 600 N/m ² . It should be noted that the hardness determined here is measured using a Unimat 050 SV tensile tester and a PHYSIMETER® 906 MC multi-parameter system (manufactured by Erichsen, Reiner) as previously indicated. It should also be noted that the hardness of the silicate hydrogel is measured before the silicate hydrogel is subjected to the drying and micronization steps. The method disclosed in the present invention allows the production of silicate hydrogels with a hardness ranging from 600 to 2000 N/m ² . Preferably, the process of this invention allows the production of silicate hydrogels with a hardness ranging from 600 to 1200 N/m ² .

Thus, a separate implementation of this invention relates to a method for the production of micronized silica gel, where the hardness of the product in stage (e) is in the range from 600 to 2000 N/m ² .

Another particular implementation of this invention relates to a method for the production of micronized silica gel, where the silica gel is characterized by an average pore radius from 1 to 100 nm.

Another particular embodiment of the present invention relates to a process for the production of micronized silica gel, wherein the silica gel has a pore volume of 0.2-2.8 ^cc /g.

Another particular embodiment of the present invention relates to a process for the production of micronized silica gel, wherein the silica gel has a BET surface area of 20 to 1200 m ² /g.

Another implementation of the invention relates to micronized silica gel obtained in accordance with the method disclosed in the description.

Another advantageous technical problem relates to the provision of a reactor that is optimized for the production of micronized silica gel with a hardness ranging from 600 to 2000 N/m ² .

In accordance with another implementation of the present invention, the mentioned technical problem is solved by providing a reactor that is capable of rapid and/or homogeneous and/or uniform addition of a volatile medium containing a volatile acid and/or base to a substance (preferably silica sol) contained in the reactor cavity. The term fast refers to a time scale of the order of 5 minutes or less, preferably 1 minute or less.

Another implementation of the invention relates to a reactor, preferably a reactor for the production of micronized silica gel. The reactor contains a reactor vessel with a cavity and at least one stirrer inside the cavity in the reactor vessel, capable of rotating relative to the reactor vessel around the axis of rotation. At least one stirrer contains at least one stirring nozzle. At least one stirrer and/or at least one stirring nozzle contains at least one outlet for adding a volatile medium to the reactor vessel. At least one outlet is configured to communicate in fluid with one or more fluid supplies through at least one fluid connection.

The reactor may be configured to produce micronized silica gel or an intermediate product for the production of micronized silica gel from silica sol.

The term reactor here refers to a device that is adapted to carry out a biological, chemical and/or physical reaction. The reactor consists of a reactor vessel with a cavity. The reactor vessel may substantially include a cavity. That is, the reactor vessel may include one or more openings through which substances can be added to or withdrawn from the cavity and/or through which a person can enter the cavity, for example, to service the reactor.

An agitator may also be referred to as an axle or a shaft. It is arranged in such a way that it rotates around the axis of rotation. Preferably, the stirrer is elongated along the axis of rotation. The term agitator refers to the structure that extends the agitator. For example, the stirring heads may be positioned radially on the stirrer and/or perpendicular to the stirrer and/or axis of rotation. If the agitator rotates, then at least one agitating head rotates with the agitator about the axis of rotation. The stirring head is preferably configured for homogeneous

- 11 041871 and/or uniform mixing of substances, such as silica sol contained in the cavity of the reactor vessel, when at least one stirrer and at least one stirring nozzle rotate.

The at least one outlet may refer to an opening located on the surface of at least one agitator and/or at least one agitator head. The term fluid connection may refer to a fluid supply line or conduit, which may, for example, be present in at least one agitator and/or at least one agitator head that is connected to at least one outlet with at least one inlet fluid. A fluid connection may consist of more than one fluid supply line or channels.

For example, the fluid supply may consist of a central channel within at least one agitator, with this central channel oriented along the axis of rotation, and subsequent channels branch off from said central channel. These subsequent channels may branch off to the surface of at least one agitator and/or to the surface of at least one agitator head.

Preferably, each of the at least one mixing nozzles contains at least one outlet, preferably at least 2, at least 3 or at least 4 outlets.

The liquid connection may extend from the outside of the reactor cavity to at least one outlet located on at least one stirrer and/or at least one stirring nozzle in the reactor cavity.

The fluid supply may include a pump configured to introduce a fluid, such as a volatile acid and/or base, through a fluid connection through at least one outlet into the cavity of the reactor vessel. The fluid supply may be located outside the reactor cavity.

Unexpectedly and not obviously, it was found that such a reactor has a structure similar to that of a paddle dryer or a paddle mixer. However, unlike a paddle dryer or a paddle mixer, in this reactor at least one agitator and/or at least one agitator nozzle contains at least one outlet, as described here. Through at least one outlet on at least one stirrer and/or at least one stirring head, a fluid, such as a volatile acid and/or base, can be homogeneously, evenly and/or quickly added to the silica sol contained in the cavity .

In accordance with another implementation of the present invention, the liquid connection is supplied through a channel that passes through the mixer, preferably along the longitudinal axis of the mixer, and if at least one outlet is in the stirring nozzle, then through the stirring nozzle.

Thus, it becomes unnecessary to place additional fluid supply lines along the agitator and/or agitator head. Moreover, such a solution also makes it possible to direct the fluid connection from outside the cavity into the cavity without the need to provide a separate line through the reactor vessel from outside the cavity into the cavity.

In accordance with the following implementation, at least one mixer contains at least one mixing nozzle per mixer, preferably at least 2 and at most 40, more preferably between 4 and 24.

With this approach, an improved, i.e. more homogeneous and/or uniform mixing of the substance, for example silicasol, in the cavity of the reactor vessel.

In accordance with another implementation of the invention, the reactor vessel has a volume of at least 50 liters, preferably at least 500 liters, more preferably at least 1000 liters.

In accordance with another embodiment of the invention, at least one stirring head has a length of at least 0.1 m, preferably at least 0.5 m.

With this approach, an improved, i.e. more homogeneous and/or uniform mixing of the substance, for example silicasol, in the cavity of the reactor vessel.

According to a further embodiment of the invention, the channel has a cross-sectional area of at least 3 mm ² , preferably at least 20 mm ² , more preferably 50 mm ² .

The cross-sectional area may refer to the cross-sectional area that is perpendicular to the length of the channel. Preferably, the cross-sectional area of the channel is such for at least 90% of the entire length of the channel, preferably the entire length of the channel.

With this approach, it can be guaranteed that the required amount of fluid is added to the reactor vessel cavity in 5 minutes or less, preferably 1 minute or less.

In accordance with the following implementation of at least one mixing nozzle is a blade in the form of an oar, with or without spokes, blades, separators and rods. Preferably, the supply of fluid occurs through these paddles, blades

- 12 041871 sti, separating device and/or rod.

With this approach, an improved, i.e. more homogeneous and/or uniform mixing of the substance, for example silicasol, in the cavity of the reactor vessel.

In accordance with the following implementation of the invention, the reactor vessel has an inlet for loading material into the reactor vessel.

For example, the inlet can be made to load a solid material, such as silica sol, into the reactor vessel and/or its cavity. Moreover, the reactor vessel may have an inlet for adding fluid to the cavity.

Preferably, the reactor vessel includes an outlet for discharging the silicate hydrogel or micronized silica intermediate.

In accordance with the following implementation of the invention, the reactor has an element for setting the desired temperature inside the cavity of the reactor vessel or the temperature of the material fed into the cavity of the reactor vessel. Preferably, this element is a steam heating system, which is designed so that water vapor is supplied to the cavity of the reactor vessel.

Preferably, this element is designed so that the temperature of the material loaded into the cavity, such as silica sol, can be brought to a predetermined temperature between 20 and 100°C, preferably from 40 to 90°C, even more preferably from 50 to 80°C.

With this approach, the reactor is designed in such a way as to stimulate the transition of the silica sol to the silicate hydrogel.

In accordance with the following implementation of the invention, at least one inlet hole contains a nozzle.

With this approach, the fluid can be more homogeneously and/or evenly added and/or introduced into the cavity of the reactor vessel. Thus, the fluid can be more homogeneously and/or evenly added to the silica sol within the cavity.

In accordance with the following embodiment of the invention, the fluid connection contains at least one active or passive valve to control the flow, prevent backflow and/or close holes.

With this approach, the supply of fluid through the fluid connection to the cavity of the reactor vessel can be effectively controlled, which allows you to effectively control the reaction inside the reactor vessel.

According to a further embodiment of the invention, the reactor vessel and/or at least one agitator is made of a non-reactive material, preferably metal, even more preferably stainless steel. Additionally, or alternatively, the inside of the reactor is lined with a non-reactive material, preferably rubber, plastic, enamel, or composites based on them, for example, the inside of the reactor vessel and/or the stirrer and/or the stirrer are coated as indicated.

With this approach, the negative impact of, for example, fluid, i. volatile acid and/or base on the reactor vessel can be reduced or completely prevented.

In accordance with the following implementation of the invention, the reactor contains a drive mechanism for rotating at least one stirrer. Preferably, the drive mechanism is configured to rotate at least one agitator at 1-200 rpm, more preferably at 1-120 rpm, even more preferably at 1-60 rpm.

With this approach, a homogeneous and/or uniform supply of fluid can be ensured, i.e. volatile acid and/or base, to silicasol for a short period of time, preferably within 5 minutes or less, more preferably within 1 minute or less.

According to a further embodiment of the invention, the fluid is a volatile acid and/or a volatile base, preferably an aqueous solution of formic acid and/or an aqueous solution of ammonium hydrogen carbonate.

The following implementation of this invention relates to the use of the reactor described here for the production of silica gel.

The following implementation of the invention relates to a method for the production of micronized silica gel in the reactor, here described, the method includes the following steps:

(a) loading silica sol into the cavity of the reactor vessel;

(b) rotating at least one agitator relative to the reactor vessel;

(c) introducing a fluid, preferably a volatile acid and/or a volatile base, more preferably an aqueous solution of formic acid and/or an aqueous solution of ammonium hydrogen carbonate, into the cavity of the reactor vessel.

Steps (c) and (b) can be carried out at least partially simultaneously.

In other words, at least one continuation of steps (c) and (b) is performed at the same time.

In accordance with the following implementation of the invention, the reactor contains the element described here, and the method further includes the stage (d) setting the temperature of the silica sol inside the cavity of the reactor to a predetermined temperature in the range from 20 to 100°C, preferably from 40 to 90°C, still

- 13 041871 more preferably from 50 to 80°C. Step (d) is performed after step (a) before step (c).

In accordance with the following implementation of the invention from 1 to 50 wt.% fluid is added to the cavity within 5 minutes or less, preferably within 1 minute or less. In addition, or alternatively, the agitator is rotated as the fluid is added to the cavity.

In other words, the agitator rotates for most or all of the time that fluid is added to the cavity.

Further implementation and/or exemplary embodiments of the present invention are disclosed in the following numbered paragraphs.

1. A method for the production of micronized silica gel, the method comprising:

(a) loading a stable silica sol with a silica content in the range from 5 to 50 wt.%;

(b) adjusting the pH of the stable silica sol to between 1.7 and 4.0 using an ion exchanger in at least partially protonated form;

(c) heating the silica sol obtained in step (b);

(d) adding a fluid containing a volatile acid and/or a volatile base to the silica sol obtained in step (c) and stirring until a uniform pH is reached throughout the reaction volume in less than 5 minutes, while the pH is in the range of 4.0 to 7.0;

(e) exposure of the product obtained in stage (d);

(f) drying the product obtained in step (e); and (g) micronizing the silica gel thus obtained.

2. The method of claim 1, wherein the volatile acid is an aqueous solution of formic acid, and wherein the volatile base is an aqueous solution of ammonium hydrogen carbonate.

3. The method according to claim 2, in which the method is carried out at least partially using a reactor consisting of a reactor vessel with a cavity;

at least one stirrer inside the cavity of the reactor vessel, made with the possibility of rotation relative to the reactor vessel around the axis of rotation;

wherein at least one stirrer contains at least one stirring nozzle;

wherein at least one agitator and/or at least one mixing nozzle contains at least one outlet for adding fluid to the reactor vessel;

wherein at least one outlet is connected downstream to one or more fluid supplies via at least one fluid connection;

wherein the silica sol is loaded into the cavity of the reactor vessel, and wherein the fluid is added to the reactor vessel via at least one outlet;

wherein at least one agitator rotates at least partially during step (d).

4. The method according to any one of paragraphs.1-3, in which the silicasol in stage (c) is heated to a temperature in the range from 20 to 100°C; preferably 40 to 90°C, even more preferably 50 to 80°C.

5. The method according to any one of claims 1 to 4, wherein the formic acid is used at a concentration in the range of 0.1 to 10% by weight, preferably in the range of 0.1 to 1% by weight, most preferably in the range of 0 .1 to 0.2 wt.%, based on the total weight of the aqueous solution of formic acid.

6. The method according to any one of claims 1 to 5, in which ammonium bicarbonate is used in a concentration in the range from 1 to 21 wt.%, preferably in the range from 5 to 15 wt.%, most preferably in the range from 8 to 12 wt. %, based on the total weight of the aqueous ammonium bicarbonate solution.

7. The method according to any one of claims 1 to 6, wherein step (e) is carried out in air.

8. The method according to any one of claims 1 to 6, wherein step (e) is carried out in an inert atmosphere.

9. The method according to claim 7 or 8, in which stage (e) is carried out for a time ranging from 0.1 to 50 hours.

10. Process according to any one of claims 1 to 6, wherein in step (e) the product from step (d) is steamed.

11. The method according to claim 10, wherein the steaming is carried out at an absolute pressure ranging from 1 to 100 bar for a time ranging from 0.1 to 50 hours.

12. Process according to any one of claims 1 to 6, wherein in step (e) the product from step (d) is treated with gaseous ammonia.

13. The method according to claim 12, wherein the treatment with ammonia gas is carried out at an absolute pressure ranging from 1 to 100 bar for a time ranging from 0.1 to 50 hours.

14. Process according to claim 12 or 13, wherein the treatment with ammonia gas is carried out at an absolute pressure ranging from 1 to 10 bar for a time ranging from 1 to 20 hours.

15. The method according to any one of claims 1 to 14, wherein steps (f) and (g) are carried out simultaneously.

16. A process according to any one of claims 1 to 15, wherein the silica gel produced contains water in the range of 1 to 65% by weight.

- 14 041871

17. The method according to any one of claims 1 to 16, wherein silica gel is formed with an average particle diameter in the range of 1 to 100 µm.

18. Process according to any one of claims 1 to 17, wherein the hardness of the product in step (e) is between 600 and 2000 N/m ² .

19. The method according to any one of claims 1 to 18, wherein the silica gel has an average pore radius of 1 to 100 nm.

20. A process according to any one of claims 1 to 19, wherein the silica gel has a pore volume of 0.2-2.8 ^cc /g.

21. The method according to any one of claims 1 to 20, wherein the silica gel has a BET surface area of 20 to 1200 m ² /g.

22. Micronized silica gel obtained in accordance with the method according to any one of claims 121.

23. Reactor (100) for the production of micronized silica gel, while the reactor contains a reactor vessel (102) with a cavity (104);

at least one stirrer (106) inside the cavity of the reactor vessel, made with the possibility of rotation relative to the reactor vessel around the axis of rotation;

wherein at least one agitator contains at least one mixing nozzle (108);

wherein at least one agitator and/or at least one mixing nozzle contains at least one outlet (110) for adding fluid to the reactor vessel;

wherein at least one outlet is connected downstream to one or more fluid supplies (112) via at least one fluid connection (114).

24. The reactor according to claim 23, characterized in that the liquid connection continues in the channel (116, 118) which extends in the mixer, preferably along the longitudinal axis of the mixer, and if at least one outlet is present in the mixing nozzle, then the channel continues in the mixing head.

25. The reactor according to claim 23 or 24, characterized in that at least one stirrer contains at least one stirring nozzle per stirrer, preferably from 2 to 40, more preferably from 4 to 24.

26. The reactor according to any one of claims 23 to 25, characterized in that the reactor cavity has a volume of at least 50 liters, preferably at least 500 liters, more preferably at least 1000 liters.

27. The reactor according to any one of claims 23 to 26, characterized in that at least one mixing nozzle has a length of at least 0.1 m, preferably at least 0.5 m.

28. Reactor according to any one of claims 23-27, when dependent on claim 24, characterized in that the channel has a cross-sectional area of at least 3 mm ² , preferably at least 20 mm ² , more preferably 50 mm ² .

29. The reactor according to any one of claims 23-28, characterized in that at least one mixing nozzle is a blade in the form of an oar (108), equipped or not equipped with spokes (120), blades, separators and rods, while preferably the fluid supply passes through these oar, blades, separating device and/or rod.

30. Reactor according to any one of claims 23 to 29, characterized in that the reactor vessel has an inlet (122) for loading material into the reactor vessel.

31. The reactor according to any one of claims 23-30, characterized in that the reactor is provided with an element for setting the temperature inside the cavity of the reactor vessel or the material loaded into the cavity of the reactor vessel, while preferably this element is a steam heating system, which is designed in such a way that that steam enters the cavity of the reactor pressure vessel.

32. Reactor according to any one of claims 23-31, characterized in that at least one outlet is provided with a nozzle.

33. Reactor according to any one of claims 23-32, characterized in that the fluid connection contains at least one active or passive valve to control the flow, prevent backflow and/or close the holes.

34. The reactor according to any one of claims 23-33, characterized in that the reactor vessel and/or at least one stirrer and/or at least one stirring nozzle is made of a chemically inactive material, preferably metal, even more preferably stainless steel; and/or wherein the reactor is internally coated with a chemically inactive material, preferably rubber, plastic, enamel or a composite based on them.

35. The reactor according to any one of claims 23-34, characterized in that it is also provided with a drive mechanism (136) for rotating at least one stirrer, while preferably the drive mechanism is designed so that it rotates at least one stirrer at 1- 200 rpm, more preferably at 1-120 rpm, even more preferably at 1-60 rpm.

36. The reactor according to any one of claims 23-35, characterized in that the fluid is a volatile acid

- 15 041871 this and/or a volatile base, preferably an aqueous solution of formic acid and/or an aqueous solution of ammonium bicarbonate.

37. The use of a reactor according to any one of claims 23-36 for the production of micronized silica gel.

38. A method for producing micronized silica gel using a reactor according to any one of claims 23 to 37, the method comprising the following steps:

(a) loading silica sol into the cavity of the reactor vessel;

(b) rotating at least one agitator relative to the reactor vessel;

(c) introducing a fluid, preferably a volatile acid and/or a volatile base, more preferably an aqueous solution of formic acid and/or an aqueous solution of ammonium hydrogen carbonate, into the cavity of the reactor vessel, wherein steps (c) and (b) are carried out at least partially at the same time.

39. The method according to p. 38, characterized in that the reactor contains an element according to p. C, even more preferably between 50 and 80° C., with step (d) being carried out after step (a) before step (c).

40. The method according to item 38 or 39, characterized in that from 1 to 50 wt.% fluid is added to the cavity within 5 minutes or less, preferably within 1 minute or less; and/or the stirrer is rotated while the entire amount of fluid is added to the cavity.

Brief description of the drawings

In FIG. 1 shows the correlation between silica sol pH and stability as well as gel time.

In FIG. 2 shows a reactor according to an embodiment of the invention.

In FIG. 3 shows a device used to measure the hardness of a silicate hydrogel.

In FIG. 4 shows the layout of the method for producing micronized silica gel of the present invention, including simultaneous drying and micronization of silica gel.

For a person skilled in the art, various modifications and variations of the invention are obvious within the scope of the invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, it is intended that various modifications of the described modes of carrying out the invention, which are obvious to a person skilled in the art, are relevant to this invention.

The following examples are solely illustrative of the present invention and should not be construed as limiting the scope of the invention, which is in any case defined by the appended claims.

Examples

Example 1

Silicasol (300 ml) with d ₅₀ 5 nm and a silica content of 15% and a pH value of 9.2 is adjusted to pH 2.0 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH- meters. The silica sol is then heated to 70°C. Subsequent addition of 0.3 ml of 0.1 wt.% aqueous formic acid solution and 12.0 ml of 10 wt.% aqueous ammonium hydrogen carbonate solution with direct stirring for less than 1 min leads to the adjustment of the pH value of the silica sol to a value of 5.5 and to initiating a rapid gelation process. The measured hardness of the obtained silicate hydrogel is 978.23 N/m ² . The resulting silica gel is then separated into several samples, to which various aging protocols are applied.

One portion of the silicate hydrogel thus obtained is kept for 3 hours under atmospheric conditions, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.95 cm ³ /g, the measured average pore radius is 5.0 nm, and the BET specific surface area is 625 m ² /g.

Another portion of the thus obtained silicate hydrogel is subjected to hydrothermal aging. The silicate hydrogel is aged for 3 hours, treated with steam at a pressure of 1.5 bar, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 1.55 cm ³ /g, the measured average pore radius is 6.0 nm, and the BET specific surface area is 415 m ² /g.

Another portion of the silicate hydrogel thus obtained is treated with gaseous ammonia at a pressure of 5 bar for 10 hours. The hydrogel is then dried to a residual water content of 2% and micronized to an average particle diameter of 8 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 2.75 cm ³ /g, the measured average pore radius is 14.4 nm, and the BET specific surface area is 341 m ² /g.

- 16 041871

Example 2

Silicasol (300 ml) with d ₅₀ 6 nm and a silica content of 22% and a pH value of 9.3 was adjusted to a pH value of 1.8 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH- meters. The silica sol is then heated to 70°C. Subsequent addition of 0.3 ml of 0.1 wt.% aqueous formic acid solution and 12.5 ml of 10 wt.% aqueous ammonium hydrogen carbonate solution with direct stirring for less than 1 min leads to the adjustment of the pH value of the silica sol to a value of 5.5 and to initiating a rapid gelation process. The measured hardness of the obtained silicate hydrogel is 815.11 N/m ² .

The silicate hydrogel thus obtained is treated with ammonia gas at a pressure of 2 bar for 10 hours. The hydrogel is then dried to a residual water content of 2% and micronized to an average particle diameter of 8 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 1.85 cm ³ /g, the measured average pore radius is 16.5 nm, and the BET specific surface area is 295 m ² /g.

Reference example 2.

Silicasol (300 ml) with d ₅₀ 6 nm and a silica content of 22% and a pH value of 9.3 was adjusted to a pH value of 1.8 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH- meters. The silica sol is then heated to 70°C. The subsequent addition of 0.3 ml of a 0.1 wt.% aqueous solution of formic acid and 12.5 ml of a 10 wt.% aqueous solution of ammonium hydrogen carbonate leads to a pH value of silica sol of 5.5 and initiation of the gelation process. The measured hardness of the obtained silicate hydrogel is 476.29 N/m ² .

Example 3

Silicasol (300 ml) with d ₅₀ 7 nm and a silica content of 30% and a pH value of 9.0 was adjusted to a pH value of 2.4 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH- meters. The silica sol is then heated to 70°C. Subsequent addition of 0.3 ml of 0.1 wt.% aqueous formic acid solution and 10.5 ml of 10 wt.% aqueous ammonium hydrogen carbonate solution with direct mixing for less than 1 min leads to the establishment of a silica sol pH of 5.5 and to the initiation of a rapid gelling process. The measured hardness of the obtained silicate hydrogel is 722.24 N/m ² . The resulting silica gel is then separated into several samples to which different aging protocols are applied.

One portion of the thus obtained silicate hydrogel is kept for 3 hours in contact with air at a pressure of 1 atm and a temperature of 25°C, then dried to a residual water content of 10% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.75 cm ³ /g, the measured average pore radius is 7.0 nm, and the BET specific surface area is 445 m ² /g.

Another portion of the thus obtained silicate hydrogel is subjected to hydrothermal aging, i. the silicate hydrogel is aged for 3 hours, treated with steam at a pressure of 1.5 bar, then dried to a residual water content of 10% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 1.35 cm ³ /g, the measured average pore radius is 9.0 nm, and the BET specific surface area is 326 m ² /g.

Another portion of the silicate hydrogel thus obtained is treated with gaseous ammonia at a pressure of 2 bar for 3 hours. The hydrogel is then dried to a residual water content of 10% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 2.05 cm ³ /g, the measured average pore radius is 14.0 μm, and the BET specific surface area is 295 m ² /g.

Example 4

Silicasol (300 ml) with a d ₅₀ of 15 nm and a silica content of 40% and a pH value of 9.0 is adjusted to a pH value of 1.7 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 H. The pH value is determined using a pH meter. The silica sol is then heated to 70°C. Subsequent addition of 0.32 ml of 0.1 wt.% aqueous formic acid solution and 12.0 ml of 10 wt.% aqueous ammonium hydrogen carbonate solution with direct mixing for less than 1 min leads to the establishment of a silica sol pH of 5.5 and initiation of a rapid gelling process. The measured hardness of the obtained silicate hydrogel is 682.31 N/m ² . The resulting silica gel is then separated into several samples to which different aging protocols are applied.

One portion of the thus obtained silicate hydrogel is kept for 3 hours in contact with air at a pressure of 1 atm and a temperature of 25°C, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.65 cm ³ /g, the measured average pore radius is 6.0 nm, and the BET specific surface area is 188 m ² /g.

- 17 041871

Another portion of the thus obtained silicate hydrogel is subjected to hydrothermal aging. The silicate hydrogel is aged for 3 hours, treated with steam at a pressure of 1.5 bar, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.95 cm ³ /g, the measured average pore radius is 10.0 nm, and the BET specific surface area is 185 m ² /g.

Another portion of the silicate hydrogel thus obtained is treated with gaseous ammonia at a pressure of 2 bar for 3 hours. The hydrogel is then dried to a residual water content of 10% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 1.07 cm ³ /g, the measured average pore radius is 20.0 nm, and the BET specific surface area is 121 m ² /g.

Example 5

Silicasol (300 ml) with d ₅₀ 3 5 nm and a silica content of 50% and a pH value of 9.2 is adjusted to a pH value of 2.0 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH -meter. The silica sol is then heated to 70°C. Subsequent addition of 0.3 ml of 0.1 wt.% aqueous formic acid solution and 12.0 ml of 10 wt.% aqueous ammonium hydrogen carbonate solution with direct mixing in less than 1 min leads to the pH value of the silica sol being adjusted to 5.5 and initiation fast gelling process. The measured hardness of the obtained silicate hydrogel is 607.92 N/m ² . The resulting silica gel is then separated into several samples to which different aging protocols are applied.

One portion of the thus obtained silicate hydrogel is kept for 3 hours in contact with air at a pressure of 1 atm and a temperature of 25°C, then dried to a residual water content of 3% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.25 cm ³ /g, the measured average pore radius is 35.0 nm, and the BET specific surface area is 129 m ² /g.

Another portion of the thus obtained silicate hydrogel is subjected to hydrothermal aging. The silicate hydrogel is aged for 3 hours, treated with steam at a pressure of 1.5 bar, then dried to a residual water content of 10% and micronized to an average particle diameter of 15 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.44 cm ³ /g, the measured average pore radius is 43.0 nm, and the BET specific surface area is 85 m ² /g.

Another portion of the silicate hydrogel thus obtained is treated with gaseous ammonia at a pressure of 2 bar for 3 hours. The hydrogel is then dried to a residual water content of 10% and micronized to an average particle diameter of 8 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.59 cm ³ /g, the measured average pore radius is 55.0 nm, and the BET specific surface area is 29 m ² /g.

Example 6

Silicasol (1500 L) with d ₅₀ 5 nm and a silica content of 15% and a pH value of 9.1 is adjusted to a pH value of 2.0 using the protonated form of the strongly acidic cationic ion exchange resin Lewatit MP S 108 N. The pH value is determined using pH- meters. The silica sol is then heated to 70°C. Subsequent addition of 1.5 L of 0.1 wt.% aqueous formic acid solution and 58.5 L of 10 wt. gelling process. The measured hardness of the obtained silicate hydrogel is 908.22 N/m ² . The resulting silica gel is then separated into several samples to which different aging protocols are applied.

One portion of the silicate hydrogel thus obtained is kept for 3 hours under atmospheric conditions, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 0.90 cm ³ /g, the measured average pore radius is 5.0 nm, and the BET specific surface area is 598 m ² /g.

Another portion of the thus obtained silicate hydrogel is subjected to hydrothermal aging. The silicate hydrogel is aged for 3 hours, treated with steam at a pressure of 1.5 bar, then dried to a residual water content of 3% and micronized to an average particle diameter of 4 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 1.47 cm ³ /g, the measured average pore radius is 6.0 nm, and the BET specific surface area is 396 m ² /g.

Another portion of the silicate hydrogel thus obtained is treated with gaseous ammonia at a pressure of 5 bar for 10 hours. The hydrogel is then dried to a residual water content of 2% and micronized to an average particle diameter of 8 μm. The porosity of the obtained silica gel is evaluated. The total pore volume is 2.69 cm ³ /g, the measured average pore radius is 15.4 nm, and the BET specific surface area is 322 m ² /g.

In FIG. 2 shows a reactor 100 in accordance with an exemplary embodiment of the invention. The reactor consists of a reactor vessel 102 having a predominantly cylindrical shape with respect to the axis of the reactor vessel. Reactor cavity 104 is enclosed in reactor vessel 102. Reactor cavity 104 is shaped to allow loading, for example, silica sol. The reactor cavity 104 may have a volume of at least 50 liters, more preferably at least 500 liters, even more preferably

- 18 041871 at least 1000 l.

Further, the reactor 100 includes a stirrer 106 having at least one, for example 8, stirring heads 108 extending from the stirrer 106. The stirrer 106 rotates about an axis of rotation, which in the present embodiment coincides with the axis of the reactor vessel. In the present exemplary embodiment, the mixing heads 108 are perpendicular to the axis of rotation and are in the form of a paddle containing spokes 120. The mixing heads 108 are at least 0.1 m long, more preferably at least 0.5 m long.

The reactor vessel 102 and/or at least one agitator and/or at least one agitator head is made of a non-reactive material, preferably metal, even more preferably stainless steel. Alternatively or in addition, the reactor 100, for example, the inner surface of the reactor vessel 102 and/or the stirrer 106 and/or the stirring head 108 is coated with a non-reactive material, preferably rubber, plastic, enamel or composites based on them.

In the present exemplary embodiment, each of the mixing nozzles 108 includes at least one outlet 110 connected in fluid flow to the fluid supply 112 via a fluid connection 114. Preferably, each of the outlets 110 is provided with a nozzle. However, as disclosed herein, outlets may also be located on the agitator 106. Fluid supply 112 includes a pump 128 for supplying fluid, such as a volatile acid and/or base, to fluid supply 114. Fluid connection 114 is represented by a central channel 116 inside the mixer 106. For each of the mixing nozzles 108, further channels 118 branch off from the central channel 116.

Fluid connection 114 may also include supply line 130 connecting conduit 116 to pump 128. Moreover, fluid connection 114 may also include supply lines 132 for supplying fluids other than those supplied by pump 128 to outlets 110. For example, a pump 128 can supply ammonium bicarbonate and/or formic acid while supply line 132 supplies ammonia. In addition or alternatively, the reactor vessel 102 may include at least one opening for supplying fluid to the cavity. The central channel 116 and/or the continuation of the channel 118 may have a cross-sectional area of at least 3 mm ² , more preferably at least 20 mm ² , even more preferably 50 mm ² .

Preferably, fluid connection 114 includes at least one active or passive valve to control flow, prevent backflow, and/or close openings.

In addition, the reactor vessel 102 includes an inlet 122 for loading, for example, silica sol into the cavity 104. The inlet 122 is connected to a supply line 124 and a pump 126 for supplying, for example, silica sol to the inlet 122 and into the cavity 104. The reactor vessel 102 is also contains an outlet 138 for discharging micronized silica gel or an intermediate product for the production of micronized silica gel. Outlet 138 may include a pneumatically operated butterfly valve to control unloading.

The reactor 100 also includes a drive mechanism 136 configured to rotate the agitator 106 and the agitating nozzles 108 about an axis of rotation. The drive mechanism may be configured to rotate at least one agitator at 1-200 rpm, more preferably at 1-120 rpm, even more preferably at 1-60 rpm.

In addition, the reactor 100 includes a heating element 134 for setting the desired temperature within the cavity 104 of the reactor vessel 102 and/or the temperature of the material, such as silica sol, within the cavity 104. Preferably, the heating element 134 is a steam heating system consisting of a steam supply and a steam inlet. 134 in the reactor vessel.

The reactor vessel 102 also includes a hatch 140 to allow a worker to enter the interior of the reactor vessel, for example, for maintenance.

Claims (13)

1. A method for the production of micronized silica gel, the method comprising: (a) loading a stable silica sol with a silica content in the range from 5 to 50 wt.%; (b) adjusting the pH of the stable silica sol to between 1.7 and 4.0 using an ion exchanger in at least partially protonated form; (c) heating the silica sol obtained in step (b); (d) adding a fluid containing a volatile acid and/or a volatile base to the silica sol obtained in step (c) and stirring until a uniform pH is reached throughout the entire reaction volume in less than 5 minutes, while the pH is in the range from 4.0 to 7.0; (e) exposure of the product obtained in stage (d); (f) drying the product obtained in step (e); and (g) micronizing the silica gel thus obtained, wherein the volatile acid is selected from the group consisting of an aqueous solution of formic acid, - 19 041871 pure formic acid in liquid state, pure gaseous formic acid, gaseous composition containing formic acid, acetic acid, propionic acid and butyric acid, and the volatile base is selected from the group consisting of an aqueous solution of ammonium bicarbonate, pure gaseous ammonia, gaseous compositions containing ammonia, an aqueous solution of ammonia, a pure liquid or gaseous alkylamine, an aqueous solution of an alkylamine, or gaseous compositions containing an alkylamine, N,N-diαalkylαmin or N,N,N-triαalkylαmin, in which each alkyl group is independently methyl, ethyl, propyl or butyl, and moreover, at least stage (d) is carried out in a reactor that contains a reactor vessel with a cavity; at least one stirrer inside the cavity of the reactor vessel, rotating relative to the reactor vessel around the axis of rotation; wherein at least one stirrer contains at least one stirring nozzle; wherein at least one agitator and/or at least one mixing nozzle contains at least one outlet for adding fluid to the reactor vessel; wherein the at least one outlet is fluidly connected to one or more channels within the agitator via at least one fluid supply line or channel. 2. The method according to claim 1, characterized in that the volatile acid is an aqueous solution of formic acid, and in which the volatile base is an aqueous solution of ammonium bicarbonate. 3. The method according to claim 1 or 2, characterized in that the silicasol in stage (c) is heated to a temperature in the range from 20 to 100°C; preferably 40 to 90°C, even more preferably 50 to 80°C. 4. The method according to any one of claims 1 to 3, characterized in that formic acid is used in a concentration in the range from 0.1 to 10 wt.%, preferably in the range from 0.1 to 1 wt.%, most preferably in the range from 0.1 to 0.2 wt.%, based on the total weight of the aqueous solution of formic acid. 5. The method according to any one of claims 1 to 4, characterized in that ammonium bicarbonate is used in a concentration in the range from 1 to 21 wt.%, preferably in the range from 5 to 15 wt.%, most preferably in the range from 8 to 12 wt.%, based on the total weight of an aqueous solution of ammonium bicarbonate. 6. Process according to any one of claims 1 to 5, characterized in that step (e) is carried out in air, or in which step (e) is carried out in an inert atmosphere. 7. The method according to claim 6, characterized in that stage (e) is carried out for a time ranging from 0.1 to 50 hours. 8. Process according to any one of claims 1 to 5, characterized in that in step (e) the product from step (d) is steamed. 9. The method according to claim 8, characterized in that the steam treatment is carried out at an absolute pressure ranging from 1 to 100 bar for a time ranging from 0.1 to 50 hours. 10. Process according to any one of claims 1 to 5, characterized in that in step (e) the product from step (d) is treated with gaseous ammonia. 11. Method according to claim 10, characterized in that the treatment with ammonia gas is carried out at an absolute pressure in the range of 1 to 100 bar for a time in the range of 0.1 to 50 hours, and in which the treatment with gaseous ammonia is preferably carried out at an absolute pressure in the range from 1 to 10 bar for a time in the range from 1 to 20 hours. 12. The method according to any one of claims 1 to 11, characterized in that steps (f) and (g) are carried out simultaneously. 13. The method according to any one of claims 1 to 12, characterized in that the produced silica gel contains water in the range from 1 to 65 wt.%, and in which silica gel is formed with an average particle diameter in the range from 1 to 100 μm, and in which the hardness of the product in step (e) is in the range of 600 to 2000 N/m ² , and in which the silica gel has an average pore radius of 1 to 100 nm, and in which the silica gel has a pore volume of 0.2-2.8 cm ³ / G; and wherein the silica gel has a BET surface area of 20 to 1200 m ² /g.