WO2021093961A1

WO2021093961A1 - Modified precipitated silicic acid with reduced moisture content

Info

Publication number: WO2021093961A1
Application number: PCT/EP2019/081376
Authority: WO
Inventors: Torsten Gottschalk-Gaudig; Sebastian KRÖNER
Original assignee: Wacker Chemie Ag
Priority date: 2019-11-14
Filing date: 2019-11-14
Publication date: 2021-05-20

Abstract

The invention relates to a modified precipitated silicic acid with a moisture content of 2.5 wt.% or less, relative to the total mass of the modified precipitated silicic acid, and to a method suitable for producing the modified precipitated silicic acids and characterized by a combination of a homogeneous in-situ modification of the silicic acid together with dynamic drying.

Description

Modified precipitated silica with reduced moisture content

The invention relates to a modified one

Precipitated silica with a moisture content of 2.5% by weight or less, based on the total mass of the modified precipitated silica, as well as a process which is suitable for the production of these modified precipitated silicas and is made up of a combination of a homogeneous in-situ modification of the silica characterized by dynamic drying.

State of the art

Precipitated silicas are oxides of silicon (SiO ₂ ) that are produced on an industrial scale using precipitation processes and are used in a wide range of applications. Due to their structural properties and the associated reinforcing effect, they represent an elementary component of both organic rubbers, e.g. for use in tires, and in silicone rubbers or other polymeric materials. Depending on the necessary crosslinking temperature, a distinction is made between cold and room temperature ( RTV) and hot or high temperature curing (HTV)

Silicone rubbers.

In addition, they are also used, for example, as a free-flow additive, reinforcing filler, carrier, filter aid, for rheology control or because of their abrasive properties. Free-flow additives or anti-blocking agents (anti-caking agents) act as additives in powdery or granular materials to prevent the formation of lumps and thus enable easy packaging, transport and use.

Depending on the desired effect in the target application, certain property profiles must be achieved through production. In numerous patent applications it is described that through precise control of certain process parameters such as temperature, pH value, dosing speeds, silicas can be produced with a certain combination of product properties, which in turn have an advantageous effect in the target applications.

WO 2018/019373 A1 discloses a method for producing a modified precipitated silica, which is characterized by an in-situ modification of the silica.

WO 2019/161912 A1 discloses a modified one

Precipitated silica with little to no coarse fraction and good redispersibility. This is achieved by combining a homogeneous in-situ modification of the silica together with high-performance liquid grinding.

WO 2019/129607 A1 discloses a precipitated silica modified by alkyl groups for use as a filler and a method for its production.

However, the precipitated silicas produced by known methods have a very high moisture content of 5 percent by weight (% by weight) or more. Even commercial hydrophobic precipitated silicas such as SIPERNAT ^® D17 (Evonik), still have a moisture content of 3 wt .-% or more.

A low moisture content is of particular importance for a large number of applications. Precipitated silicas, however, as a result of their production process, have a high proportion of moisture, especially in the form of adsorbed water. This water is problematic for many applications. During the extrusion of moldings, this water evaporates, for example, and leads to Bubbles in the extrudate. The quality of the corresponding moldings is impaired.

In addition, applications with food contact require conformity with national regulations (e.g. stipulated for Germany by the Federal Institute for Risk Assessment). requires a low volatile content. Here, water can falsify the measurement result and thus lead to problems in meeting the requirements.

The precipitated silicas produced by known methods also have a high water absorption capacity on storage, in particular under the conditions of high atmospheric humidity. For example, a commercial hydrophilic precipitated silica SIPERNAT ^® 288 (EVONIK) absorbs 9.6% by weight of water over 48 hours at 94% relative humidity, and even a commercial hydrophobic precipitated silica such as SIPERNAT ^® D17 (Evonik) under the same conditions still 3 , 5% by weight of water.

In particular, in regions with high humidity, the above-mentioned disadvantages of a high moisture content are exacerbated, or the silicas have to be pre-dried, which is cost-intensive, before use.

It was an object of the present invention to provide a modified precipitated silica with improved processability, for example during extrusion, and improved storage stability at high atmospheric humidity, as well as a process for producing such a precipitated silica.

This object is achieved by a modified precipitated silica which has a moisture content of 2.5% by weight or less, and a method that is achieved by a combination a homogeneous in-situ modification of the silica together with dynamic drying.

Description of the invention

The invention relates to a modified precipitated silica, characterized in that it has a moisture content of 2.5% by weight or less, based on the total mass of the modified precipitated silica.

Another aspect of the invention relates to a process for the production of the modified precipitated silica mentioned above, wherein i) the modification in a reaction mixture comprising

1 . one or more acids and

2. one or more compounds selected from the group consisting of precipitated silica, alkoxysilane and alkali silicate and

3. one or more organosiliconates takes place as modifiers, the modification reaction taking place during or immediately after the preparation reaction of the precipitated silica, ii) the solid phase of the reaction mixture is then separated from the liquid phase, the solid phase being optionally washed, and iii) the solid phase is dynamically dried.

Since the modified precipitated silica according to the invention is preferably produced by the process according to the invention, the following description is to be understood in such a way that features described in the context of the precipitated silica are disclosed equally for the process and vice versa Features described in the process are also disclosed for the precipitated silica.

In contrast to the precipitated silicas available in the prior art, the modified precipitated silica according to the invention is distinguished by a low moisture content.

The moisture content of the modified precipitated silica according to the invention is 2.5% by weight or less, based on the total mass of the modified precipitated silica. The moisture content is particularly preferably 2.0% by weight or less, particularly preferably 1.8% by weight or less, very particularly preferably between 0.5 to 1.8% by weight.

The moisture content can be determined using a drying balance, with 1 g of the modified precipitated silica being dried to constant weight at 105 ° C. The moisture content results as follows:

Moisture content (in% by weight) = 100% * (initial weight of the sample - final weight of the sample) / initial weight of the sample.

In contrast to the precipitated silicas available in the prior art, the modified precipitated silica according to the invention is preferably distinguished by low water absorption during storage.

The modified silica according to the invention preferably has a maximum water absorption in the range of less than or equal to 2.75% by weight, preferably from less than or equal to 2.5% by weight to greater than or equal to 0.5% by weight and particularly preferably of less than or equal to 2.25% by weight to greater than or equal to 0.5% by weight, in each case based on the total mass of the modified precipitated silica. The maximum water absorption can be determined using an analytical balance with underfloor weighing and a hygrostat, whereby 500 mg of the modified precipitated silica is first pre-dried at 105 ° C for 2 h (pre-dried state) and then at a temperature of 22 ° C and a relative humidity of 94% is stored for 48 h. The maximum water absorption results as follows: maximum water absorption (in% by weight) = 100% * (final weight of the sample - initial weight of the sample in the pre-dried state) / initial weight of the sample in the pre-dried state.

The modified precipitated silica according to the invention is preferably characterized in that its specific BET surface area is preferably 50 m ² / g to 400 m ² / g, particularly preferably 100 m ² / g to 300 m ² / g and particularly preferably 150 m ² / g to 250 m ² / g.

The specific surface can be determined by the BET method according to DIN 9277/66131 and 9277/66132.

The modified precipitated silica according to the invention is preferably characterized in that its carbon content is preferably 0.1% by weight or more, particularly preferably 0.5% by weight or more to 15% by weight or less, very particularly preferably 1, 0% by weight or more to 10% by weight or less, based in each case on the total mass of the modified precipitated silica. The carbon content is essentially based on the modification of the precipitated silica with organic residues.

The carbon content can be determined by means of elemental analysis, ie in a combustion analysis in a suitable analyzer. The modified precipitated silica according to the invention is preferably characterized in that the conductivity of its 5% methanolic-aqueous dispersion is preferably at most 500 S / cm, particularly preferably at most 100 S / cm and particularly preferably at most 25 S / cm.

Since modified silicas are poorly or not at all wetted by water, the conductivity of a corresponding sample can be determined in a methanol / water mixture. For this purpose, a small amount of sample (5 g of the precipitated silica modified according to the invention) is mixed with 10 g of methanol and only then is diluted with 85 g of deionized water. To achieve a homogeneous mixture, the batch is alternately mixed well and left to stand for a long time. Before the conductivity measurement with a conductivity measuring cell, the batch is shaken up again. The conductivity can be measured with any conductivity meter. It is determined for a reference temperature of 20 ° C. Determining the conductivity of a sample is also a very sensitive method for quantifying soluble impurities.

The modified precipitated silica is preferably distinguished by a homogeneous surface modification. A homogeneous surface modification has proven to be particularly advantageous for achieving a low moisture content and a low water absorption capacity of the precipitated silica. Without being bound by theory, it is assumed that the high-energy surface areas present in the case of an inhomogeneous modification of the silica preferentially interact with and adsorb polar water molecules.

To evaluate the homogeneity of the surface modification, a wetting test in combination with a distribution test between an aqueous and an organic one has proven useful Phase proven. According to the invention, preference is given to using n-butanol as the organic phase. It is also preferred that water is used as the aqueous phase.

If a modified precipitated silica is largely wetted by water after intensive mixing with water and sinks into the water phase and makes it cloudy, the modified precipitated silica is hydrophilic. If this modified precipitated silica does not cloud the organic phase at the same time in a system consisting of a water and an organic phase, which can be butanol, for example, the modified precipitated silica, which is assessed as hydrophilic, is also lipophobic. In this case there is a homogeneous surface modification.

A homogeneous surface modification is also present if a modified precipitated silica is not wetted after intensive mixing with water, i.e. floats on the water phase and forms a separate phase, i.e. is hydrophobic, but at the same time the organic phase in a system consisting of a water and an organic phase Phase is cloudy, i.e. lipophilic.

A homogeneous surface modification is also present if a modified precipitated silica is not wetted after intensive mixing with water, i.e. floats on the water phase and forms a separate phase, i.e. is hydrophobic, but at the same time in a system of a water and an organic phase of both Phases is not wetted and forms a third phase rich in solids.

An inhomogeneous surface modification occurs when a modified precipitated silica is wetted with water after intensive mixing, that is, sinks into the water phase and makes it cloudy, that is, it is hydrophilic, but at the same time in a system from a water and an organic phase, the organic phase is cloudy, i.e. it is lipophilic.

A more precise assessment of the homogeneity of the boundary layer is possible with the help of inverse gas chromatography in finite dilution (IGC-FC). This method allows the determination of the energetic homogeneity of a surface via the adsorption energy distribution function (AEDF). The AEDF is a graphical representation of the energy distribution of a surface. For the silicas modified according to the invention, 3 peaks were found in the distribution function.

A homogeneous surface modification is preferably characterized in that the relative area fraction F (P3) of the peak P3, which is in the range of approx. 28-32 kJ / mol of the AEDF of the modified precipitated silica determined by means of IGC-FC, is less than 0.2, in particular is preferably less than 0.15 and particularly preferably less than 0.1. The relative area share F (P3) is defined as F (P3) = A (P3) / [A (P1) + A (P2) + A (P3)], where A (Px) with x = 1, 2 or 3 is the area of peaks P1, P2 and P3. This means that the relative area portion F (P3) of the high-energy peak P3 preferably has the lowest possible intensity.

The large-scale production of synthetic silicas takes place mainly through precipitation processes. Silicas produced in this way are called precipitated silicas.

Precipitated silicas are produced by methods known to the person skilled in the art, as described, for example, in US Pat. No. 2,657,149, US Pat. No. 2,940,830 and US Pat. No. 4,681,750, from condensable tetra- or higher-functional silanes, alkoxysilanes, alkyl or alkali silicates (water glasses) or colloidal silica particles or solutions. A great advantage of precipitated silicas is that, in contrast to the much more expensive pyrogenic silicas, they represent a cost-effective product. The reaction mixture according to the invention comprises

1. one or more acids and

2. one or more compounds selected from the group consisting of precipitated silica, alkoxysilane and alkali metal silicate and 3. one or more organosiliconates as

Modifying agents.

Precipitated silicas and / or [SiO _4/2 ] starting materials are used in the reaction mixture, with alkoxysilanes and / or alkali metal silicates being used _{as [SiO 4/2] starting materials.} In a preferred embodiment, alkoxysilanes are used as [S1O4 _/ 2] starting materials. In an alternatively preferred embodiment, alkali metal silicates are used as [SiO _4/2 ] starting materials.

The modification is preferably carried out comprehensively in a reaction mixture

1 . one or more acids and

2. one or more compounds selected from the group consisting of alkoxysilane and alkali metal silicate and

3. one or more organosiliconates as modifiers

[SiO _4/2 ] units denote compounds in which one silicon atom is bonded to four oxygen atoms, each of which in turn has a free electron for a further bond. Units with Si-O-Si bonds connected via the oxygen atom can be present. In the simplest case, the free oxygen atoms are bound to hydrogen or carbon or the compounds are present as salts, preferably alkali salts. According to the invention, alkoxysilanes or alkali silicates (water glasses) are used as starting material (precursor) for the formation of [SiO _4/2 ] units ([SiO _{4/2] starting material).} In the context of this invention, the [SiO _4/2 ] units denote the precipitated silica; Alkoxysilanes or alkali silicates serve as [S1O4 / 2] starting materials for their production.

In both cases, regardless of whether alkoxysilanes or alkali silicates are used as the [S1O4 / 2] starting materials, the first reaction step involves the formation of soluble and low molecular weight silicas. For the sake of simplicity, only monomeric structures are described in the following reaction equations, although soluble oligomeric structures can also be involved.

If alkoxysilanes are used as the starting material for the production of precipitated silicas, the hydrolysis in water can be catalyzed by acids or bases:

Si (OR) ₄ + 4 H ₂ O → Si (OH) ₄ + 4 ROH

The hydrolysis is preferably carried out in aqueous solutions of mineral or organic acids, particularly preferably in aqueous sulfuric acid solution, hydrochloric acid solution or carbonic acid.

The alkoxysilanes used are preferably tetramethoxysilane and particularly preferably tetraethylorthosilicate (TEOS).

Water glasses are particularly preferably used as the [SiO _4/2 ] starting materials. Water glass is the term used to denote solidified, glass-like, i.e. amorphous, water-soluble sodium, potassium and lithium silicates or their aqueous solutions. By reaction with acid, particularly preferably in aqueous sulfuric acid solution, hydrochloric acid solution or carbonic acid, low molecular weight soluble silicas are also formed here:

M ₂ O · z SiO _{2 +} HX → Si (OH) _{4 +} 2 MX where z is any positive number.

Especially the structures present in aqueous solution are in reality much more complicated than shown here.

Nevertheless, the common notation for water glasses was used here. The exact stoichiometry and the composition of the salt formed (MX) naturally depends on the quality of the water glass used and can only be shown schematically here.

It is also possible to use mixtures or hydrolysis products of the starting materials mentioned, in particular their hydrolysis products with water and / or alcohols.

The orthosilicic acid Si (OH) 4 or oligomeric compounds formed in this way react under suitable reaction conditions with condensation and form particulate solids which are essentially composed of SiO _4/2 units: z Si (OH) ₄ _→ SiO 4z / ₂ + 2n H ₂ 0 where z is any positive number.

The condensation is favored in an acidic or especially in an alkaline environment.

Mineral acids, organic acids and / or carbon dioxide can be used as the acid.

Further substances such as electrolytes and / or alcohols can be added to the reaction mixture. The electrolyte can be a soluble inorganic or organic salt. Preferred alcohols include including methanol, ethanol or i-propanol. In a preferred embodiment, only electrolytes and / or alcohols are added to the reaction mixture as further substances in addition to water, alkali silicate, acid and organosiliconate, particularly preferably only electrolytes and particularly preferably no further substances are added to the reaction mixture.

The reaction mixture preferably contains water, alkali silicate, acid and organosiliconate, particularly preferably water, alkali silicate, acid and methylsiliconate, particularly preferably water, sodium silicate (sodium water glass), sulfuric acid and sodium monomethylsiliconate. This composition has the advantage that, in addition to the product, only the salt sodium sulfate is obtained as a by-product. This readily water-soluble salt can be separated from the product relatively easily, using separation methods such as filtration, sedimentation and / or centrifugation.

The temperature of the reaction mixture is preferably between 50.degree. C. and 105.degree. C., particularly preferably between 75.degree. C. and 95.degree. C. and particularly preferably between 85.degree. C. and 95.degree. In a particularly preferred embodiment, the reaction temperature is kept constant in the further process.

The pH of the reaction mixture is preferably between pH = 8 to pH = 10, particularly preferably between pH = 8.5 to pH = 9.5 and particularly preferably pH = 9. In a particularly preferred embodiment, the pH is kept constant during the further process. For this purpose, further acid, particularly preferably sulfuric acid or hydrochloric acid and particularly preferably concentrated sulfuric acid, is preferably added to the reaction mixture in order to counteract the alkalinity of the waterglass that may have been added. The starting materials such as acid, [SiO _4/2 ] starting materials, modifiers and any other substances are preferably metered in at a constant metering rate. Constant dosing speed means that it changes in the course of the dosing time preferably by a maximum of 15%, particularly preferably by a maximum of 5% and particularly preferably by a maximum of 1% based on the average speed, which is calculated as the quotient of the total dosing amount and time.

The metering takes place preferably over a period of 30 minutes to 120 minutes, particularly preferably over a period of 45 minutes to 90 minutes and particularly preferably over a period of 60 minutes to 70 minutes.

The total amount of [SiO _4/2 ] starting materials metered in is preferably chosen so that the solids _{content, calculated as the mass of [SiO 4/2} ] units, is 20% by weight, particularly preferably 10% by weight, based on the total mass of the starting materials does not exceed. Most preferably, the solid content is calculated as mass [Si0 _{_4/2]} units between 4 wt .-% and 8 wt. ~%, Based on the total mass of the reaction mixture. The mass of the starting materials is determined gravimetrically.

The exact microstructure of the silicas formed depends heavily on the exact reaction conditions. This is most evident from the change in the BET surface area, which is essentially inversely proportional to the size of the particles of the precipitated silica produced.

In general, the reactants are mixed by simply stirring. Easily dispersible silica fillers with particularly uniform particle size, specific surface area and "structure" can also be produced by reacting alkali silicate solutions with acids and / or acidic substances, optionally in the presence of neutral salts produce that the precipitation of the silica by rapid and intensive mixing of the reaction components under the action of high shear forces that of a steep

Resulting speed gradient, is made. The high speed gradient is preferably generated by means of continuously operating dispersers, such as a colloid mill.

In the 1st process step (i) for producing a modified precipitated silica, the reaction for producing a precipitated silica and its modification takes place in the same batch, the modification reaction taking place during or immediately after the reaction for producing the precipitated silica. This means that the modification takes place in the reaction mixture described above, which is used to produce the precipitated silica. In the context of this invention, this process is also referred to as a one-pot process. The one-pot process is a clear difference to the state of the art, which generally works with multi-stage, separate processes.

The modification reaction takes place during or immediately after the reaction for preparing the precipitated silica. According to the invention, "directly" in this context means that the modification in the reaction mixture, which _{comprises 1. the acid and 2. the precipitated silica and / or [SiO 4/2} ] starting materials and 3. an organosiliconate as a modifier, takes place without prior notice the modification reaction, a process step for separating salts and / or other by-products is carried out. The term “immediately” does not refer to immediate temporal, stirring or allowing to stand between the reaction steps is not excluded. According to the invention before the

Modification reaction but no ion exchange, filtration, Washing, distillation or centrifugation step and no resuspension carried out.

Dispensing with a previous process step for separating salts and / or other by-products has the great advantage that energy costs, time and resources such as washing solution or washing water and solution or water for resuspension are saved. This procedure makes the use of further units superfluous. It is of particular economic interest since the method according to the invention saves time and thus reduces the system occupancy time. The other by-products include alcohols, among others.

In the modification or modification reaction, which in the context of this invention is also referred to synonymously with hydrophobization or hydrophobization reaction, the unmodified precipitated silica reacts with a modifier. Correspondingly, the modifying agent is also referred to synonymously in the context of this invention with modifying agent, covering agent, covering agent, water repellent or silylating agent. The modified precipitated silica of the present invention is also referred to synonymously with hydrophobized precipitated silica.

The degree of modification can be determined by the carbon content according to DIN ISO 10694. This is preferably 0.1% by weight to 15% by weight based on the total mass of the modified precipitated silica. Depending on the desired use of the modified precipitated silica, certain degrees of modification can be particularly preferred. For example, when used in silicone rubbers, the carbon content is particularly preferably 0.5% by weight to 4% by weight and particularly preferably 1% by weight to 2% by weight, based on the total mass of the modified Precipitated silica. When used as an antiblocking agent, it is particularly preferably 4% by weight to 10% by weight and particularly preferably 5% by weight to 7% by weight, based on the total mass of the modified precipitated silica.

The temperature of the reaction mixture during the modification is preferably furthermore between 50.degree. C. and 105.degree. C., particularly preferably between 75.degree. C. and 95.degree. C. and particularly preferably between 85.degree. C. and 95.degree. The reaction temperature is particularly preferably kept constant during process step i, i.e. it fluctuates by a maximum of ± 5 ° C, particularly preferably by a maximum of ± 2 ° C.

The pH of the reaction mixture is preferably furthermore between pH = 8 to pH = 10, particularly preferably between pH = 8.5 to pH = 9.5 and particularly preferably pH = 9. The pH value is particularly preferably kept constant during process step i, i.e. it fluctuates by a maximum of 0.5 units, particularly preferably by a maximum of 0.2 units. For this purpose, further acid, particularly preferably sulfuric acid or hydrochloric acid and particularly preferably concentrated sulfuric acid, is preferably added to the reaction mixture in order to counteract the alkalinity of any siliconate added.

This process step preferably takes place with stirring.

This process step preferably takes place under the action of high shear forces, which originate from a steep gradient in speed. The high speed gradient is preferably generated by means of continuously operating dispersants such as a colloid mill. This has the advantage that finely divided silica with good dispersing properties is obtained. The modifying agent in preparation of the reaction mixture is preferably added in parallel with the [SiO _{_4/2]} -Ausgangsstoffen and the acid to the reaction mixture. In this case, it is particularly preferred that the end point of dosing _{_[4/2} SiO] -Ausgangsstoffe of the modifying agent is carried out together with the end point of the dosage of the. In another preferred embodiment, the end point of the metering of the modifying agent goes beyond the end point of the metering of the [SiO _4/2 ] starting materials.

In the case of the parallel metering of the modifier and the [SiO _4/2 ] starting materials, it is possible regardless of whether the metering of the modifying _{agent ends at the same time as the metering of the [SiO 4/2} ] starting materials or goes beyond this to completely or partially dispense with a further separate, additional, later addition of the same or a further modifying agent to the reaction mixture. It is particularly preferred to completely dispense with a further separate addition of the same or a further modifying agent to the reaction mixture. If the modifying agent is metered into the reaction mixture directly when the reaction _{mixture is prepared with the [SiO 4/2} ] starting materials and the acid, the process according to the invention is particularly inexpensive, quick and simple.

In a particularly preferred embodiment, the dosage of the [SiO _4/2 ] starting materials is gradually reduced, whereas that of the modifier is gradually increased during the overlap period, ie the joint dosage of [SiO _{4/2] starting materials and modifying agents.} This procedure has the advantage that the modification reaction can be controlled by the controlled addition of the modifying agent. Following a theoretical model of thought on particle structure, the degree of modification in the core of the particles is lower and then increases. The use of the compared to the modifier, which is more costly to use with the [S1O4 / 2] starting materials, is particularly efficient in this case.

In another preferred embodiment, the modifying agent is added to the reaction mixture at different times. This means that acid and [SiO _4/2 ] starting materials are metered in in a targeted manner at a defined temperature and a defined pH value (preferred conditions see above) and the modifying agent is only then metered in sequentially, i.e. staggered in time. This means that the modifying agent is added to the reaction mixture only after the acid and [SiO _{4/2] starting materials have been metered in completely.} The reaction to produce the precipitated silica and its modification take place in the same approach (one-pot process), but it is a two-step process.

In this case of staggered addition of the modifying agent, the metering takes place preferably over a period of 5-120 min, preferably 5-90 min and particularly preferably 10-30 min.

In this case of staggered addition of the modifying agent, the modifying agent can be added to the reaction mixture in one step or in several small portions, it being possible to add it in each case at a constant metering rate or at a metering rate which is gradually increased.

The term "staggered in time" refers to the response. The modification reaction starts at a different time. When the reaction is carried out continuously, one speaks of spatially offset in relation to the system design (see below). In other words, in order to achieve a staggered addition, the infeed must be spatially offset. This procedure has the advantage that the addition of the modifier, and thus the modification reaction, takes place in a controlled manner.

As already described for the parallel dosing, it is conceivable that the core of the produced particles can be formed from the cheaper alkali silicate by this procedure, while the outer part of the particles (shell) may be increasingly modified, that is, a chemically bound, by the Has modifying agent-transferring group. In this way, primary particles can be produced that are built up in the form of a core-shell model. From an economic point of view, the advantage of this process is that it is predominantly the particle surface that has a major impact on subsequent use reacts with the more cost-intensive modifier.

In addition to the described parallel or staggered dosing of modifier and [SiO _4/2 ] starting materials, all mixed forms are conceivable, i.e. for example a partial amount of the modifying agent is dosed in parallel and, for example, with a gradually increasing dosing rate and a partial amount staggered in time and, for example, with a constant dosing rate . The dosage of modifying agent and [SiO _4/2 ] starting materials can thus be selected as desired for the production of the modified precipitated silica and the particle properties can thereby be controlled. In accordance with the theoretical model for particle structure (see above), not only particles built up according to the core-shell model with a degree of modification that increases suddenly or abruptly from the inside to the outside, but also particles built up according to the gradient model by continuously adding the modifier according to the gradient model inside out be produced gradually or gradually increasing degree of modification

The modifying agents can be added to the reaction mixture in liquid form or as a dry powder.

The modifying agents can be added in pure form or as solutions in water or known technically used solvents, for example alcohols such as methanol, ethanol or i-propanol, ethers such as diethyl ether, tetrahydrofuran or dioxane, or hydrocarbons such as hexanes or toluene.

In the present application, a modifying agent is understood to mean organosiliconates and their solutions.

According to the invention, organosiliconates denote compounds of the general formula (I)

R ¹ n-Si (OR ² ) 4-n where R ¹ , R ² and n have the following meanings:

R ¹ = independently of one another hydrogen, linear or branched, optionally functionalized _{C 1} -C ₃ o-alkyl, linear or branched, optionally functionalized C _{2 -C 30} -alkenyl, linear or branched, optionally functionalized C ₂ -C ₃₀ -alkynyl, optionally functionalized C ₃ -C ₂ o cycloalkyl, optionally functionalized C ₃ -C ₂ o cycloalkenyl, optionally functionalized C ₁ -C ₂₀ heteroalkyl, optionally functionalized C ₅ -C ₂₂ aryl, optionally functionalized C ₆ -C ₂₃ -alkylaryl , optionally functionalized C6-C ₂₃ -arylalkyl, optionally functionalized C ₅ -C ₂₂ -heterorayl, R ² = independently of one another hydrogen, linear or branched, optionally functionalized C ₁ -C ₃₀ -alkyl, linear or branched, optionally functionalized C ₁ -C ₃₀ -alkyl, linear or branched, optionally functionalized C ₂ -C ₃₀ -alkynyl, optionally functionalized C ₃ -C ₂₀ cycloalkyl, optionally functionalized C ₃ -C ₂₀ cycloalkenyl, optionally functionalized C ₁ -C ₂₀ heteroalkyl, optionally functionalized C ₅ -C ₂₂ aryl, optionally functionalized C ₆ -C ₂₃ alkylaryl, optionally functionalized C ₆ -C ₂₃ arylalkyl, optionally functionalized C ₅ -C ₂₂ heterorayl,

NR ¹ 4 ⁺ , where R ¹ independently of one another can have the meanings given above,

Group of the general formula 1 / (pn * y) M ^{p +} X ^n- _y , where M is a metal atom selected from the group consisting of metals from the main and subgroups of the Periodic Table of the Elements, X is an anion, p is the oxidation number of the metal atom M, n is a integer from 1, 2 or 3 and y denotes an integer from 0, 1 or 2, and / or

Group of the general formula (IIa)

-SiR ¹ _m (OR ² ) _3-m where R ¹ and R ² independently of one another have the meanings given above and m independently of one another can mean 0, 1, 2 or 3, n = 1, 2 or 3, and at least one solvent , at least one surface-active substance or a mixture thereof, where in the compound of the general formula (I) or in the group of the general formula (H a) at least one radical R ² NR ¹ ₄ ⁺ or a group of the general formula 1 / (pn * y) M ^{p +} X ^n_ _y with the Above meanings for R ¹ , p, n, y, M and X is.

If R ² in the compound of the general formula (I) has the meaning of a group of the general formula (H a) several times, for example more than once, then there are corresponding compounds which have two, three, four or more units with Si atoms wear. Therefore, in the event that R ² more than once denotes a group of the general formula (H a), there are polysiloxanes.

The rule is that an organosiliconate has at least one Si-C bond, i.e. at least one residue must be organic in nature.

The particular advantage of using organosiliconates as modifiers is that they are highly water-soluble and therefore particularly suitable for a homogeneous reaction in an aqueous medium. The use of an aqueous solution of the otherwise solid substances simplifies handling, since an exact dosage can be achieved comparatively easily by means of pumps.

Modifying agents typically used, on the other hand, are poorly or not at all water-soluble. Some of them react violently with water and generate a lot of heat, which makes it much more difficult to conduct the reaction safely, uniformly and in a controlled manner (this applies, for example, to the chlorosilanes that are often used).

Mixtures of different organosiliconates can also be used according to the invention. Mixtures are preferably used when functional groups (for example vinyl, allyl, or sulfur-containing groups such as, for example, C ₃ H ₆ SH) are to be introduced. A methyl siliconate, particularly preferably a monomethyl siliconate, is preferably used as the organosiliconate in the process according to the invention.

The use of monomethylsiliconates is particularly advantageous beyond what has been said above, because monomethylsiliconates are simple and in good yield from the easily available and inexpensive substances methyltrichlorosilane,

Methyltrimethoxysilane or methylsilanetriol can be obtained by reaction with alkaline substances, if necessary in an aqueous medium.

Aqueous solutions of monomethylsiliconates of the general form (CH ₃ ) Si (OH) _3-x 0M _x and their oligomeric condensation products are particularly preferably used, the counterion M preferably being potassium or sodium and preferably x = 0.5-1.5 , particularly preferably 0.8-1.3. In a particularly preferred embodiment, x = 0.8-0.9. x does not refer to 1 molecule, but to the entirety of the molecules present in the mixture.

The organosiliconate solution used preferably has a density of 1.2-1.4 g / cm ^3. The density can be determined in accordance with DIN 12791, for example.

The impurities in the organosiliconate solution in alcohols (eg ethanol or methanol) contained in the production process are preferably <1% by weight, particularly preferably <100 ppm, based on the total mass of the organosiliconate solution. The alcoholic impurities can be determined by quantitative gas chromatography (for example with the 6890 gas chromatograph from Agilent equipped with an FID detector and OV-1 separation column). The solids content of the aqueous organosiliconate solutions is preferably 20% by weight to 70% by weight, particularly preferably 30% by weight to 60% by weight, based on the total mass of the organosiliconate solution. The solids content can be determined with an IR moisture analyzer (for example with the IR moisture analyzer MA 30 from Sartorius) at a measuring temperature of 105 ° C.

The active ingredient content calculated as (CH ₃ ) SiO _3/2 in the reaction mixture is preferably 15% by weight to 40% by weight, particularly preferably 30% by weight to 35% by weight, based on the total mass of the reaction mixture.

The alkali metal content of the organosiliconate solution is preferably 5% by weight to 20% by weight, particularly preferably 9% by weight to 18% by weight, based on the total mass of the organosiliconate solution. The alkali content can be determined, for example, by titration with 0.1 molar hydrochloric acid against the indicator phenolphthalein. In organosiliconate solutions, the number of groups with a basic reaction corresponds to the number of alkali metal ions.

The silicas according to the invention can be modified with only one organosiliconate, but a mixture of two or more compounds from the group of organosiliconates can also be used.

The total amount of modifier metered is preferably chosen so that the solids content calculated as [SiO _4/2 ] _g [(CH ₃ ) SiO _3/2 ] j (with g and j independently of one another as any positive number), ie the solids content of modified [SiO _4/2 ] units in the modified precipitated silica produced does not exceed 25% by weight, particularly preferably 15% by weight, based on the total mass of the reaction mixture. Particularly preferred the solids content, calculated as [SiO _4/2 ] m [(CH ₃₎ SiO _3/2 ] n, is between 5% by weight and 10% by weight based on the total mass of the reaction mixture.

According to the invention, it is preferred that the concentration of modified groups in the primary particles increases from the inside out.

After the reaction time has ended, ie after process step i and before process step ii, it is preferred that the pH value is preferably less than pH = 5, particularly preferably to a value less than pH = 4 and particularly preferably to pH = 3, 5 is lowered.

In addition, after the reaction time has ended, i.e. after process step i and before process step ii, the reaction mixture is preferably cooled to a temperature of less than 55 ° C and particularly preferably to room temperature, preferably continuing to stir during cooling.

In the 2nd process step (ii) the solid phase of the reaction mixture is separated from the liquid phase, the solid phase being optionally washed. This process step serves, among other things, to separate salts that would interfere with the later use of the modified precipitated silica.

The solid phase is preferably separated off from the liquid phase by filtering, sedimenting, pressing or centrifuging, particularly preferably by filtering.

Water, polar organic solvents or mixtures thereof can be used for washing; washing is preferably carried out with water, particularly preferably with fully demineralized, deionized (VE) water, which is characterized by that it has a conductivity of <5 μS / cm, preferably of <3 μS / cm and particularly preferably of <0.1 μS / cm.

Washing can be done in several ways.

For example, the solid separated by filtration is rinsed with fresh water until a sufficiently low (preferably constant) conductivity value of the wash water of <500 μS / cm, preferably <100 μS / cm, particularly preferably <10 μS / cm is reached. The flow through can take place continuously or in portions. A particularly efficient form of washing is the redispersion of the filter cake in clean water followed by further filtration.

The conductivity of water can be measured with a commercially available conductivity meter. An example of a conductivity meter that can be used is given in the analysis methods.

An aftertreatment with reagents which are known in the prior art and are usually used for modification is possible, if necessary.

After washing, the separated solid phase, ie for example the filter cake of the reaction mixture, has a solids content of 50% by weight or less, based on the total mass of the separated solid phase, preferably 10% by weight or more to 35% by weight or less, based on the total mass of the separated solid phase, and particularly preferably 20% by weight or more to 30% by weight or less, based on the total mass of the separated solid phase. It should be noted here that despite the relatively high water content of the separated solid phase, it has a solid-like appearance. Furthermore, the separated solid phase of the reaction mixture, ie for example the filter cake, is dynamically dried in a further process step (iii).

Drying processes are generally differentiated according to the type of energy supply: contact dryers, in which the heat is introduced into the goods to be dried via a heated wall, and convection dryers, in which the heat is introduced into the goods to be dried via a warm to hot gas flow.

A convection dryer is preferably used in the method according to the invention.

A further distinction between the processes in static and dynamic drying according to the movement of the items to be dried is also often used. Dynamic drying is understood to mean drying processes with movement of the items to be dried. Due to the high exposed mass transfer surface and the resulting more intensive heat transfer, these generally lead to significantly higher drying speeds than with static drying processes in which the material to be dried is dried without active movement (e.g. drying cabinet, tray dryer, belt dryer, drum dryer). Typical dynamic drying devices are paddle dryers, flow dryers or fluidized bed dryers.

The drying can also take place continuously or in portions (batch drying). The drying is preferably carried out continuously.

A further acceleration of the drying speed and the avoidance of lump formation in the items to be dried can be achieved by using increased mechanical loads on the items to be dried. Form possibilities for this Impact baffles in the flight conveyor zone of electric or flight dryers or also rapidly rotating internals, e.g. chopper units in paddle dryers or high-speed mixing and dividing tools in dryers of a similar design such as Spin Flash dryers (SPX Flow company).

In the method according to the invention, a dryer is preferably used which has elements for the mechanical loading of the material to be dried.

Due to the mechanical stress, lumps, agglomerates or incrustations are broken up and new surfaces are exposed, which are then available for mass and heat transfer.

In addition, classifying elements with the return of relatively heavy (moist or agglomerated) particles can be integrated into the drying room. Examples of classifying elements are air separators, ascending pipe separators, cyclones, swirl separators or also deflector wheel separators.

In the method according to the invention, a dryer is preferably used which has classifying elements.

In the method according to the invention, it is particularly preferred to use a dryer which contains elements for the mechanical loading of the material to be dried and classifying elements.

In the method according to the invention, it is very particularly preferable to use a convection dryer which contains elements for the mechanical loading of the material to be dried and classifying elements. In particular, a flow pipe with a downstream cyclone dryer or a dryer with a spin flash dryer with a deflector wheel sifter is used in the method according to the invention.

Regardless of the selected drying technology, the following sub-steps generally take place at the level of the items to be dried:

1. Heating up the material to be dried and the liquid.

In particular in the case of contact drying, the material to be dried is exposed to temperatures above the boiling point of the liquid to be removed, so that it can evaporate once the boiling point has been reached (depending on the process pressure). If dry drying gas is used convectively, drying below the boiling point of the liquid is also possible in principle, since the substance of the liquid is also transferred into the gas phase by evaporation.

2. Evaporation / Evaporation of the free liquid

In this phase, the free liquid between the particles and on the particle surface of the material to be dried is drawn off. The drying speed is mostly only influenced to a small extent by the particulate material to be dried and shows its maximum value in this phase. The evaporation / evaporation is similar to that of the pure liquid.

3. Drying of the "inner capillary moisture" from porous solids

After the freely accessible liquid has been subtracted, the drying level in the pores drops and there are transport resistances for diffusive removal of the water vapor from the pores as well as conductive heat conduction relevant from the particle surface to the interior of the solid. The drying speed decreases steadily with increasing dryness.

4. Discharge of residual liquid

Depending on the temperature, the last remaining quantities of the liquid (e.g. water of crystallization) can usually only be removed with very small amounts in the last drying step

Drying speeds are deducted, since both transport resistances increase and mass transfer forces are reduced.

A common measure for characterizing a drying process is the surface-specific drying speed, which is maximum in the second drying section described above and which decreases with increasing dryness of the items to be dried. The surface-specific drying speed in batch drying processes is determined by:

m _Fl mass of evaporated liquid [kg]

A Surface of the dry material [m ² ] A _BET specific BET surface of the dry material [m ² / kg] X _o Moisture content at the beginning of drying [-] X _t Moisture content at the end of drying [-]

Δt drying time [s]

V surface-specific drying speed [kg / (m ² * s) j or [g / (m ² * h)]

To describe continuous drying processes, the masses are given by corresponding mass flows ([kg / h]) and the Replace the drying time with the mean residence time of the product in the drying area ([s]).

The surface-specific drying speed over the entire drying process (from the start of drying to the end of drying) is preferably

0.04 g / (m ² * h) or more up to 60 g / (m ² * h) or less, particularly preferably 0.4 g / (m ² * h) or more up to 40 g / (m ² * h) ) or less, very particularly preferably 1 g / (m ² * h) or more to 20 g / (m ² * h) or less.

The drying temperature is preferably 70 ° C. or more to 200 ° C. or less, particularly preferably 90 ° C. or more to 170 ° C. or less, very particularly preferably 100 ° C. or more to 150 ° C. or less.

In the case of convective drying, the drying temperature is understood to mean the hot gas temperature (supply air temperature to the dryer) and, in the case of contact drying, the temperature of the heating elements (for example, heating jacket, pipe coils, heating strips or similar).

The mean residence time (in the case of continuous drying) or drying time (in the case of batch drying) is preferably 5 s or more to 3,600 s or less, particularly preferably 10 s or more to 1,800 s or less.

In the case of continuous drying, the mean residence time is preferably 5 s or more to 600 s or less, particularly preferably 10 s or more to 300 s or less.

The mean residence time of the material to be dried in the continuous drying is calculated from the quotient of the dry matter mass hold-up in the dryer and the mass flow of dry product through the dryer. In a preferred procedure, the dry material can be ground after cleaning. Here, units such as pin mills, classifier mills, hammer mills, countercurrent mills, impact mills or devices for grinding classification can be used.

In a further preferred procedure, the silica is ground in the liquid phase before dynamic drying. All mills in which the ground material is in a liquid phase can be used for this purpose. Typical examples are horizontal or vertical ball mills and bead mills, in which grinding media are used to comminute the material to be ground. In addition to the crushing impacts between particles and grinding media, these types of mills also have a large number of grinding media-grinding media and grinding media-apparatus wall impacts that can cause undesirable abrasion and wear and the associated product contamination.

Other typical examples are dispersing units such as rotor-stator apparatus (colloid mill, toothed ring disperser), the crushing effect of which is essentially due to shear forces from the surrounding fluid, as well as high-pressure homogenizers, the dispersing effect of which can be attributed to stretching flow, shear flow, turbulence and possibly also cavitation is. Roller mills such as roller mills or pan mills are particularly suitable for comminuting more viscous dispersions. Impact or autogenous liquid mills (liquid jet dispersers) are preferred, in which dispersion jets containing the predispersed ground material are directed towards one another with high kinetic energy or are directed towards impact surfaces. The comminution is based on particle-particle impacts, particle-wall impacts as well as turbulence and possibly cavitation of the surrounding fluid. The individual process steps can be carried out as a discontinuous (batch process) or continuous process. For technical reasons, preference is given to carrying out the reaction batchwise. This procedure has the advantage that the systems are very simple and less prone to failure. Standard agitators can be used. From the nucleation of the particles to the finished product, there is a very well-defined, narrow distribution of the "growth time", an important prerequisite for the manufacture of homogeneous products.

For the batch process, water is provided and heated. Then the starting materials such as acid, [SiO _4/2 ] starting materials and, if necessary, other substances are metered in. The modifying agent is metered in in parallel or at different times. After process step i) has taken place, the entire reaction mixture is removed, the solid phase is separated from the liquid phase, the solid phase optionally being washed, (ii), the solid phase being dynamically dried (iii) and optionally grinding.

In an alternatively preferred embodiment, the method steps take place in a continuous process.

The continuous process includes:

(a) the continuous feeding of

1. one or more acids and

2. one or more compounds selected from the group consisting of precipitated silica, alkoxysilane and alkali metal silicate in a reaction zone through which a liquid medium flows;

(b) the continuous feeding of

3. one or more organosiliconates as modifiers in parallel with the starting materials from (a) or spatially offset with respect to the system (in order to achieve a time-delayed addition with respect to the reaction mixture) into the reaction zone;

(c) the continuous discharge of the reaction mixture;

(d) the continuous separation of the solid from the liquid phase of the reaction mixture, for example by filtering, and optionally washing the solid phase; and

(e) continuous, dynamic drying of the solid phase.

The simplest form of a reactor for carrying out continuous chemical processes is a tube or tank reactor. WO 2011/106289 describes, for example, the continuous production of silica in a loop reactor, which can also be used in this process. A Taylor-Couette reactor, as described, for example, in DE 10151777, is particularly preferably used. This usually consists of two coaxial concentrically arranged cylinders, the outer hollow cylinder resting and the inner solid cylinder rotating. The volume that is formed by the gap between the cylinders serves as the reaction space. As described in detail in DE 10151 777, in the steady state, ie the state of the reactor after start-up (when the reactor is completely filled with the reactants), the Taylor number is 50-50,000, preferably 500-20,000, particularly preferably 3,000-10,000, and the Reynolds number (axial) 0.0724 to 7.24, preferably 0.1348-2.69, particularly preferably 0.4042-1.35. The mean residence time in the Taylor reactor can be between 5 and 500 minutes. The reactor is preferably operated in a vertical position with a flow from bottom to top or top to bottom.

The advantage of the process according to the invention, in which the production and modification of the precipitated silica are carried out in one pot, is that the process is particularly inexpensive, quick and easy to use, as well as works in a way that conserves resources. A particular advantage of the method is that compositions can be produced which have a high chemical purity. Despite the modification of the silica, non-volatile water-soluble impurities such as sodium, potassium and sulfur can easily be removed in process step (ii). It is particularly advantageous that a good separation of ionic impurities can be achieved even under normal washing conditions, ie with small amounts of the washing medium or in a few washing steps, which is expressed, for example, in a constant low conductivity of the washing medium.

The invention is described in more detail below on the basis of exemplary embodiments, without being restricted thereby.

Examples

materials

Sulfuric acid was obtained in a concentration of 50% in technical purity from Brenntag. The aqueous sodium silicate solution used was commercial water glass 38/40 from Wöllner with a density at 20 ° C according to the manufacturer's instructions of approx. 1.37 g / cm ³ .

The potassium methyl siliconate solution was aqueous

Potassium methylsiliconate solution SILRES ^® BS16 from WACKER Chemie AG with an active ingredient content, calculated as CH ₃ Si (O) _3/2 , of approx. 34% by weight according to the manufacturer's instructions, was used.

The fully demineralized (deionized) water (deionized water) used had a conductivity of ≤ 0.1 μS / cm. Unless otherwise mentioned, the process steps up to the filtration and washing step are carried out with stirring. Analysis methods:

Determination of the BET surface area

The specific surface was determined by the BET method according to DIN 9277/66131 and 9277/66132 using an SA ™ 3100 analyzer from Beckmann-Coulter.

Determination of the carbon content (% C)

The elemental analysis for carbon was carried out in accordance with DIN ISO 10694 using a CS-530 elemental analyzer from Eitra GmbH (D-41469 Neuss).

Determination of the homogeneity of the surface modification

Experiment 1:

25 ml of deionized water were placed in a 50 ml snap-lid glass. 100 mg of the silica powder to be examined were then added, the glass was closed and shaken vigorously for 30 s.

Rating:

- Hydrophilic: The silica was mostly wetted and sank into the water phase.

- Hydrophobic: Most of the silica was not wetted and did not sink. It floated on the water phase and formed a separate phase.

Experiment 2:

15 ml of deionized water and 15 ml of butanol were placed in a 50 ml snap-lid glass. 100 mg of the silica powder to be examined were then added, the glass was closed and shaken vigorously for 30 s. After the phases had been separated, the distribution of the particles in both phases was visually assessed.

Rating:

- Lipophilic: The upper butanol phase was very cloudy, the lower

Water phase largely clear. - Lipophobic: The upper butanol phase was largely clear, the lower water phase was very cloudy.

Determination of the homogeneity:

*) In this case, a third one, rich in solids, is formed

Phase between the aqueous phase and the butanol phase.

Determination of the BET constant CBET and the adsorption energy distribution functions

The determination was carried out by means of inverse gas chromatography in finite dilution (IGC-FC). For this purpose, a stainless chromatography column with an internal diameter of 2 mm and a length of 15 cm was filled with the silica to be examined. The sample amount was approx. 190 mg. The two ends of the column were closed with silanized glass wool. The packed column was connected to the gas chromatograph using 1/8 'Swagelok connectors. The gas chromatograph was a common commercial device with an FID detector. As a carrier gas

Helium used. Before the measurement, the sample was degassed for 16 h at 110 ° C. and a gas flow rate of 12 ml / min. The subsequent measurement was carried out at 50 ° C. and a gas flow rate of 20 ml / min. For this purpose, 1.5 to 3.0 ml isopropanol (purity at least GC quality) were usually injected with a 10 ml syringe. The amount of sample injected had to be determined iteratively. The aim was to have a maximum peak height at a relative pressure of 0.1 to 0.25. This could only be determined from the overall chromatogram.

To determine the dead volume, methane was injected together with isopropanol.

The isotherm for determining the BET constant C _BET was calculated according to Conder ("Physicochemical measurement by gas chromatography". JR Conder and CL Young. Wiley (Chichester), 1979). The adsorption energy distribution functions (AEDF) were determined according to Balard (H. Balard; "Estimation of the Surface Energetic Heterogeneity of a Solid by Inverse Gas Chromatography"; Langmuir, 13 (5), pp 1260-1269, 1997). ^{Software from Adscientis, "In-Pulse" ®} and "FDRJ07.5.F" ^® , was used to calculate the isotherm and the physical parameters derived from it or the AEDF.

To determine the area proportion of the high-energy peak of the AEDF, the distribution function was broken down into the individual peaks by means of peak deconvolution. For this purpose, the raw data from the AEDF was read into the ORIGIN program and a deconvolution was carried out assuming a Gaussian distribution of the individual peaks. In all of the examples mentioned here, the best fit was obtained assuming 3 peaks with peak positions of PI approx. 17-19 kJ / mol, P2 approx. 21-25 kJ / mol and P3 approx. 28-32 kJ / mol. In Table 1, the area fraction of the high-energy peak is F (P3) =

A (P3) / [A (P1) + A (P2) + A (P3)] in the range 28 - 32 kJ / mol, where A (Px) with x = 1, 2 or 3 is the area of the peaks P1, P2 and P3 is.

Determination of the moisture content

The moisture content was determined by means of a drying balance using the HG63 moisture analyzer from Mettler Toledo. For the measurement, 1.0 g of silica are placed in aluminum sample pans and dried at 105 ° C. to constant weight. The moisture content is then derived from the following formula: Moisture content (in% by weight) = 100% * (initial weight of the sample - final weight of the sample) / initial weight of the sample

The initial weight corresponds to the initial weight and the final weight corresponds to the weight of the sample after it has been dried to constant weight.

Determination of the maximum water absorption during storage:

The water absorption during storage was determined using an analytical balance with underfloor weighing (Mettler Toledo LW1956). The scale is set up on a scale table with an integrated draft shield above a hygrostat (desiccator). The sample carrier is hung through the lock inside the hygrostat. A saturated KNO ₃ solution sets a constant relative humidity depending on the ambient temperature. To weigh the samples, the hygrostat can be lowered on a lifting table and the lock with the sample carrier is released. The construction of the suspension and the lock allows the hygrostat to be lowered for several hours and the balance to be kept engaged. The balance is read out by a computer via the interface built into the balance. The measured values are saved and their progress is shown in an Excel spreadsheet.

A temperature and humidity sensor in the hygrostat record the temperature and humidity curve during the measurement and output them in the Excel spreadsheet. The measuring device is set up in a climatic room with a constant temperature of 22 ° C (+/- 0.5 ° C).

For the measurement, the cleaned sample dish with holder is dried for 30 minutes at 105 ° C. and then cooled in a desiccator with a drying agent for 30 minutes. To tar the balance, the sample pan with holder is then placed in the hygrostat, the sample holder is attached and weighing is started. After reaching constant weight, the scale is set to tare. The silica sample to be determined is then weighed into the sample dish (approx. 500 mg), dried at 105 ° C in a drying cabinet with nitrogen flushing (300 l / h) for 2 h, cooled in a desiccator for 30 min for 30 min, placed in the measuring device and the measurement started.

Unless otherwise stated, all tests and analyzes were carried out in air at a temperature of 22 ° C and under normal pressure (1013 hPa).

Example 1 (according to the invention)

18 kg of deionized water were heated to 90 ° C. in a 401 universal stirrer (steel / enamel) equipped with a propeller blade stirrer. While stirring (250 min ^-1 ), 5.04 kg of water glass were metered in at this temperature over the course of 60 minutes at a constant metering rate. At the same time, 1.22 kg of 50% strength sulfuric acid were metered in in parallel, whereby the pH value was kept largely constant (pH = approx. 8.5). The mixture was stirred for a further 5 min at 9000 and then with stirring at 90 ° C. within 60 min 0.59 kg of an aqueous potassium methylsiliconate solution with a relative metering rate of 2.3 mmol / (min * 1) and 0.29 kg 50% sulfuric acid dosed (pH = approx. 8.5). The mixture was stirred for a further 1 hour at 90 ° C. and pH = 8.5 and then acidified to pH = 3.5 by adding 50% strength sulfuric acid while stirring. After cooling to 50 ° C., the mixture was filtered through a chamber filter press using K100 filter plates, washed pH-neutral and blown dry with nitrogen. The filter cake with 75% moisture content was brought to dryness by means of a flow tube and a downstream cyclone dryer at a temperature of 105 ° C., a gas flow rate of 15,000 m ³ / h and an average residence time of the dry material of 25 s. The circulating air flow implemented in the cyclone dryer by the built-in components ensures that heavy or residual moist particles are retained for further drying, so that only Silica particles with a moisture content of <2% by weight could leave the dryer. (:; Classifier 20,000 min- ^1: 16,000 min- ¹ mill) After cooling to room temperature, the product was ground to a ZPS50 separator mill from Hosokawa-Alpine. The solid was then analyzed as described in the analysis methods. The results are shown in Table 1.

Example 2 (not according to the invention)

18 kg of deionized water were heated to 90 ° C. in a 401 universal stirrer (steel / enamel) equipped with a propeller blade stirrer. While stirring (250 min ^-1 ), 5.04 kg of water glass were metered in at this temperature over the course of 60 minutes at a constant metering rate. At the same time, 1.22 kg of 50% strength sulfuric acid were metered in in parallel, whereby the pH value was kept largely constant (pH = approx. 8.5). The mixture was stirred for a further 5 min at 90 ° C and then with stirring at 90 ° C within 60 min 0.59 kg of an aqueous potassium methyl siliconate solution with a relative metering rate of 2.3 mmol / (min * 1) and 0, 29 kg of 50% sulfuric acid dosed (pH = approx. 8.5). The mixture was stirred for a further 1 hour at 90 ° C. and pH = 8.5 and then acidified to pH = 3.5 by adding 50% strength sulfuric acid while stirring. After cooling to 50 ° C., the mixture was filtered through a chamber filter press using K100 filter plates, washed pH-neutral and blown dry with nitrogen. The filter cake was statically dried to constant weight on metal sheets in a drying cabinet at 150 ° C. (:; Classifier 20,000 min- ^1: 16.000 min ¹ mill) After cooling to room temperature, the product was ground to a ZPS50 separator mill from Hosokawa-Alpine. The solid was then analyzed as described in the analysis methods. The results are shown in Table 1. Example 3:

18 kg of deionized water were heated to 90 ° C. in a 401 universal stirrer (steel / enamel) equipped with a propeller blade stirrer. While stirring (250 min ^-1 ), 5.04 kg of water glass were metered in at this temperature over the course of 60 minutes at a constant metering rate. At the same time, 1.22 kg of 50% strength sulfuric acid were metered in in parallel, whereby the pH value was kept largely constant (pH = approx. 8.5). The mixture was stirred for a further 5 min at 90 ° C and then with stirring at 90 ° C within 110 min 1.54 kg of an aqueous potassium methyl siliconate solution with a relative metering rate of 2.4 mmol / (min * 1) and 0, 77 kg of 50% sulfuric acid dosed (pH = approx. 8.5). The mixture was stirred for a further 1 hour at 90 ° C. and pH = 8.5 and then acidified to pH = 3.5 by adding 50% strength sulfuric acid while stirring. After cooling to 50 ° C., the mixture was filtered through a chamber filter press using K100 filter plates and washed pH neutral. The filter cake with a moisture content of 75% by weight was brought to dryness by means of a flow tube and a downstream cyclone dryer at a temperature of 105 ° C., a gas flow rate of 15,000 m ³ / h and an average residence time of the dry material of 25 s. The circulating air flow created in the cyclone dryer by the internals ensures that heavy or residual moisture particles are retained for further drying, so that only silica particles with a moisture content of <2% by weight could leave the dryer. After cooling to room temperature, the product was ground in a ZPS50 ^{classifier mill from Hosokawa-Alpine (mill: 20,000 min -1} ; classifier: 16,000 min ^-1 ). The solid was then analyzed as described in the analysis methods. The results are shown in Table 1.

Example 4 (not according to the invention):

In a 401 universal stirrer (steel / enamel) equipped with a propeller blade stirrer, 18 kg of deionized water were added 90 ° C heated. While stirring (250 min ^-1 ), 5.04 kg of water glass were metered in at this temperature over the course of 60 minutes at a constant metering rate. At the same time, 1.22 kg of 50% strength sulfuric acid were metered in in parallel, whereby the pH value was kept largely constant (pH = approx. 8.5). The mixture was stirred for a further 5 min at 90 ° C and then with stirring at 90 ° C within 110 min 1.54 kg of an aqueous potassium methyl siliconate solution with a relative metering rate of 2.4 mmol / (min * 1) and 0, 77 kg of 50% sulfuric acid dosed (pH = approx. 8.5). The mixture was stirred for a further 1 hour at 90 ° C. and pH = 8.5 and then acidified to pH = 3.5 by adding 50% strength sulfuric acid while stirring. After cooling to 50 ° C., the mixture was filtered through a chamber filter press using K100 filter plates, washed pH-neutral and blown dry with nitrogen. The filter cake was statically dried to constant weight on metal sheets in a drying cabinet at 150 ° C. After cooling to room temperature, the product was ground in a ZPS50 classifier mill from Hosokawa-Alpine (mill: 20,000 min ^-1 , classifier: 16,000 min ^-1 ). The solid was then analyzed as described in the analysis methods. The results are shown in Table 1.

Table 1:

Claims

1. Modified precipitated silica, characterized in that it has a moisture content of 2.5% by weight or less, based on the total mass of the modified precipitated silica.

2. Modified precipitated silica according to claim 1, wherein the modified precipitated silica has a moisture content of 2.0% by weight, based on the total mass of the modified precipitated silica.

3. Modified precipitated silica according to one or more of claims 1 to 2, its specific BET-

Surface area measured by gas chromatography is 50 m ² / g or more and 400 m ² / g or less.

4. Modified precipitated silica according to one or more of claims 1 to 3, its carbon content, measured by means of elemental analysis, being 0.1% by weight or more, based on the total mass of the modified precipitated silica.

5. Modified precipitated silica according to one or more of claims 1 to 4, its carbon content, measured by means of elemental analysis, being 15% by weight or less, based on the total mass of the modified precipitated silica.

6. Modified precipitated silica according to one or more of claims 1 to 5, wherein the modified precipitated silica is characterized by a homogeneous surface modification.

7. A process for the preparation of a modified precipitated silica according to any one of claims 1 to 6, wherein i) the modification in a reaction mixture comprising

1. one or more acids and

3. one or more organosiliconates takes place as modifiers, the modification reaction taking place during or immediately after the preparation reaction of the precipitated silica, ii) the solid phase of the reaction mixture is then separated from the liquid phase, the solid phase being optionally washed and iii) the solid Phase is dried dynamically.

8. The method according to claim 7, wherein potassium methyl siliconate is used as the organosiliconate.

9. The method according to one or more of claims 7 to 8, wherein the drying in step iii) is carried out at a drying temperature of 70 ° C or more.

10. The method according to one or more of claims 7 to 9, wherein the solid in step iii) is dried continuously with an average residence time of 5 seconds or more and 3,600 seconds or less.

11. The method according to one or more of claims 7 to 10, wherein the solid is dried in step iii) at a surface-specific drying rate of 0.04 g / (m ² * h) or more to 60 g / ( ² * h) or less becomes.

12. The method according to one or more of claims 7 to 11, wherein a convection dryer is used for the drying in step iii).

13. The method according to one or more of claims 7 to 12, wherein a dryer with classifying and dwell time-extending elements is used for the drying in step iii).

14. The method according to one or more of claims 7 to 13, wherein a dryer is used for the drying in step iii), which mechanically stresses the solid.