阅读说明：本技术 沉淀二氧化硅及其制造方法 (Precipitated silica and method for producing same ) 是由 E.奥兰奈曼 C.法尔奥-马丁 P.加伯 L.居伊 S.内沃 C.菲奥勒 于 2018-05-03 设计创作，主要内容包括：一种以在其表面上存在特定的酸性位点为特征的沉淀二氧化硅以及一种用于其制造的方法。(A precipitated silica characterized by the presence of specific acidic sites on its surface and a process for its manufacture.)

1. A precipitated silica characterized by:

-the amount of at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof is in the range of from 0.5 to 30.0 mol%;

infrared absorption spectra having wavelengths between 1538 and 1559cm^-1At least one peak in between 1612 and 1635cm^-1One peak in between, the spectrum having been measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum, with the ratio (at 1538 to 1559 cm)^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.80.

2. The precipitated silica of claim 1 wherein the concentration is between 1538 and 1559cm^-1The area under the peak in between is at least 0.02cm^-1。

3. The precipitated silica of any one of the preceding claims, wherein the concentration is between 1612 and 1635cm^-1The area under the peak in between is at least 0.03cm^-1。

4. The precipitated silica of any of the preceding claims, wherein the at least one element M is selected from the group consisting of Al and Ga.

5. The precipitated silica of any one of the preceding claims, wherein the amount of the at least one element M is in the range of from 0.7 to 25.0 mol%, even 0.8 to 25.0 mol%.

6. The precipitated silica of any of the preceding claims, wherein from 40 to 800m²A/g, preferably from 50 to 450m²BET surface area S in g_BET。

7. A process for the preparation of the precipitated silica of any one of claims 1 to 5, comprising reacting a silicate with an acid to produce a suspension of precipitated silica, said reaction comprising at least one step wherein silicate or at least one compound of element M is added to a reaction medium while the reaction medium is at a pH of from 2.0 to 6.0, preferably from 3.0 to 5.0, and wherein the at least one compound of element M is added to the reaction medium after at least 50% by weight of the total amount of silicate required for the reaction has been added to said reaction medium.

8. The method of claim 6, comprising the steps of:

(i) providing a starting solution having a pH equal to or greater than 7.0;

(ii) reducing the pH of the reaction medium to a value below 7.0 by simultaneously adding silicate and acid to the starting solution or by adding acid to the starting solution; and

(iii) simultaneously adding silicate and acid to the reaction medium such that the pH of the reaction medium is maintained in the range of from 2.0 to 6.0 to obtain a suspension of precipitated silica,

wherein at least one compound of the element M is added to the reaction medium during steps (ii) and/or (iii), with the proviso that this addition is carried out after at least 50% by weight of the total amount by weight of silicate required for the reaction has been added to the reaction medium.

9. The method of claim 6, comprising the steps of: the method comprises the following steps:

(i') providing a starting solution having a pH equal to or greater than 7.0;

(ii') reducing the pH of the reaction medium to a value below 7.0 by simultaneously adding silicate and acid to the starting solution or by adding acid to the starting solution; and

(iii) simultaneously adding to the reaction medium an acid and at least one compound of the element M, so that the pH of the reaction medium is maintained in the range from 2.0 to 6.0 to obtain a suspension of precipitated silica, with the proviso that this addition is carried out after at least 50% by weight of the total amount of silicates required for the reaction have been added to the reaction medium.

10. The process according to claim 7 or 8, wherein, when M is B or Ga, the following additional steps are performed after steps (iii) and (iii'):

(iv) stopping the addition of the acid and increasing the pH of the reaction medium to a value of from 7.0 to 10.0;

(v) simultaneously adding an acid and a silicate to the reaction medium in such a way that the pH of the reaction medium is between 7.5 and 9.5; and

(vi) the addition of the silicate is stopped while the addition of the acid to the reaction medium is continued to reach a pH of the reaction medium of less than 6.0 to obtain a suspension of precipitated silica.

11. A composition comprising the precipitated silica of any one of claims 1 to 5 and at least one polymer.

12. The composition of claim 10, wherein the at least one polymer is selected from the group of elastomers.

13. An article comprising the composition of claim 10 or 11.

14. The article of claim 12 in the form of: sole, floor covering, gas barrier, cableway roller, seal for a household appliance, seal for a liquid or gas duct, brake system seal, duct, sheath, in particular cable sheath, cable, engine mount, battery diaphragm, conveyor belt, or conveyor belt.

15. A catalyst, catalyst support, insulating material, resorcinol-formaldehyde/silica complex, absorbent for active materials, additive for toothpaste, concrete or paper comprising the precipitated silica of any one of claims 1 to 5.

Technical Field

The present invention relates to precipitated silica and to a method for the manufacture thereof.

Background

The use of precipitated silica as a reinforcing filler in polymer compositions, as a catalyst carrier, as an anti-caking agent, as a rheology modifier or as an abrasive in toothpaste compositions is known.

In particular, there is a continuing need for precipitated silicas that can be successfully used in a variety of applications such as reinforcing fillers and catalysts or catalyst supports in polymer compositions.

Disclosure of Invention

A first object of the present invention is to provide a novel precipitated silica which can be used in a variety of applications, for example as a catalyst or catalyst support and as a reinforcing filler in polymer compositions. A second object of the invention is a method for producing the precipitated silica of the first object.

The precipitated silicas of the invention are characterized inter alia by the presence of specific acid sites on their surface. The silicas of the invention are defined in detail in the description which follows and in the claims and examples.

Detailed Description

The precipitated silica of the present invention is characterized in that:

-the amount of at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof is in the range of from 0.5 to 30.0 mol%;

-infrared absorption spectrum having at 1538cm^-1And 1559cm^-1At least one peak in between 1612 and 1635cm^-1Has been measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum, with the ratio (at 1538 and 1559 cm)^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.80.

The use of pyridine adsorption for studying the properties of silica surfaces by infrared techniques has been previously described, see e.g. Nikiel, l.; zerda, t.; chem. [ journal of physico-chemistry ], 1991, 95, 4063 and Zaho, x.s. et al; j.phys.chem.b [ journal of physico-chemistry B ], 1997, 101, 6525. This technique allows discrimination between different SiOH sites in the silica structure.

Precipitated silicas containing aluminum have previously been described, for example in WO 2015/128404 a1 and in WO 2011/117400 a 1. The infrared spectra (measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum) of the precipitated silicas disclosed in these prior art documents are at 1538 and 1559cm^-1Without exhibiting any peaks in between.

Advantageously, the precipitated silica of the invention is characterized in that:

-the amount of at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof is in the range of from 0.5 to 30.0 mol%;

infrared absorption spectra having wavelengths between 1538 and 1559cm^-1At least one peak in between 1612 and 1635cm^-1At least one peak in between, the spectrum having been measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum; and wherein at 1538 and 1559cm^-1The area under the peak in between is at least 0.02cm^-1And the ratio (at 1538 to 1559cm^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.80.

In this specification, the terms "silica" and "precipitated silica" are used as synonyms.

The silica of the present invention contains at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof. The at least one element M is present in an amount ranging from 0.5 to 30.0 mol%. The amount of element M is defined herein as the amount of at least one M in moles relative to the moles of silica.

The element M is preferably selected from the group consisting of Al and Ga. More preferably, the element M is Al. Other elements may be included in the silica of the present invention.

The amount of at least one element M in the silica of the invention may be at least 0.7 mol%, at least 0.8 mol%, even at least 1.0 mol%. The amount of the at least one element M is typically not more than 25.0 mol%, preferably it is not more than 20.0 mol%, more preferably it is not more than 15.0 mol%.

The precipitated silica of the invention is characterized by the presence of acidic sites on its surface, which are capable of forming bonds with pyridine and which can still be detected by infrared spectroscopy after treatment at 25 ℃ under vacuum as detailed below.

Thus, the precipitated silica of the invention is characterized by having a molecular weight of 1538 and 1559cm after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum^-1At least one peak in between 1612 and 1635cm^-1Infrared absorption spectrum of at least one peak in between. The endpoints are included in the definition of the range of the infrared absorption spectrum.

The expression "in X and Ycm^-1At least one peak in between "is used herein to indicate that X and Ycm are^-1There is a maximum of one absorption band in the region of the infrared absorption spectrum in between.

For the avoidance of doubt, except at 1538 and 1559cm^-1And between 1612 and 1635cm^-1In addition to the peaks in between, the infrared absorption spectrum of the precipitated silica of the present invention contains other peaks.

The peaks in the infrared absorption spectrum were determined on a silica sample subjected to the following conditions: under vacuum (10)^-5Pa) at 25 ℃ for 1 hour; under vacuum (10)^-5Pa) at 180 ℃ for 2 hours; gaseous pyridine (at 670Pa) was introduced at 25 ℃ for 5min to reach saturation; at 25 ℃ under vacuum (10)^-5Pa) for a period of 30 min.

At 1541cm^-1The presence of a nearby peak was associated with the formation of protonated pyridinium species at 1622cm^-1The presence of a nearby peak is related to the coordination of pyridine to the silica surface. Both absorption bands are indicative of the presence of silica on the surfaceThe specific acid sites present.

The distance between 1538cm and 1559cm^-1The area under the peak in between is at least 0.02cm^-1. It is typically at least 0.03cm^-1Generally at least 0.04cm^-1。

At 1612 and 1635cm^-1The area under the peak in between is at least 0.01cm^-1. It is typically at least 0.03cm^-1At least 0.04cm^-1Overall at least 0.05cm^-1And even at least 0.10cm^-1. In any case, the ratio (at 1538 to 1559cm^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.80.

Ratio (at 1538 and 1559cm-¹Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) may be less than 0.70, even less than 0.65. Ratio (at 1538 to 1559cm^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is at least 0.01, typically at least 0.02, preferably at least 0.04.

Ratio (at 1538 to 1559cm^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is typically between 0.02 and 0.80, preferably between 0.04 and 0.80. This ratio may even be between 0.05 and 0.80.

The silicas of the invention are further characterized by a BET surface area S_BETIn the range of from 40 to 800m²In the range of/g. BET surface area S_BETIs at least 50m²(ii) in terms of/g. BET surface area S_BETCan conveniently be greater than 60m²(ii) in terms of/g. BET surface area S_BETCan be less than 700m²A/g, preferably less than 500m²A/g, more preferably less than 450m²/g。

Advantageously, the precipitated silicas of the invention may have a particle size ranging from 50 to 450m²G, preferably from 60 to 400m²BET surface area S in the range of/g_BET。

In an advantageous embodiment, the precipitated silica of the invention is characterized in that:

at the slave40 to 800m²BET surface area S in the range of/g_BET；

-the amount of at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof is in the range of from 0.5 to 30.0 mol%;

infrared absorption spectra having wavelengths between 1538 and 1559cm^-1At least one peak in between 1612 and 1635cm^-1Has been measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum, with the ratio (at 1538 and 1559 cm)^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.80.

Preferably at 1538 and 1559cm^-1The area under the peak in between is at least 0.02cm^-1. More preferably, at 1538 and 1559cm^-1The area under the peak in between is at least 0.02cm^-1And at 1612 and 1635cm^-1The area under the peak in between is at least 0.03cm^-1。

In another advantageous embodiment, the precipitated silica of the invention is characterized in that:

-in the range from 50 to 450m²BET surface area S in the range of/g_BET；

-at least one element M selected from the group consisting of Al and Ga in an amount in the range of from 0.7 to 25.0 mol%, 0.8 to 25.0 mol%, even from 1.0 to 25.0 mol%;

infrared absorption spectra having wavelengths between 1538 and 1559cm^-1At least one peak in between 1612 and 1635cm^-1Has been measured after chemisorption to saturation with pyridine followed by treatment at 25 ℃ under vacuum, wherein at 1538 and 1559cm^-1The area under the peak in between is at least 0.02cm^-1And the ratio (at 1538 to 1559cm^-1Area under the peak in between)/(at 1612 and 1635cm^-1The area under the peak in between) is less than 0.70.

Preferably at 1538 and 1559cm^-1The area under the peak in between is at least 0.03cm^-1And at 1612 and 1635cm^-1Has an area under the peak of at least 0.03cm^-1。

A second object of the invention is a process for preparing the precipitated silica of the invention. The process comprises reacting a silicate with an acid to produce a suspension of precipitated silica, said reaction comprising at least one step wherein the silicate or at least one compound of element M is added to a reaction medium while the reaction medium is at a pH in the range of from 2.0 to 6.0, preferably from 3.0 to 5.0, and wherein the at least one compound of element M is added to the reaction medium after at least 50% by weight of the total amount of silicate required for the reaction has been added to the reaction medium. The total amount of at least one compound of at least one element M is added to the reaction medium after at least 50% by weight of the total amount of silicate required for the reaction has been added thereto.

The total amount of silicate used to obtain a given final silica amount can be determined by the person skilled in the art at the start of the process according to common general knowledge.

The reaction comprises adding a silicate and at least one compound of element M to the reaction medium, with the proviso that the silicate or the at least one compound of element M is added to the reaction medium at a pH of from 2.0 to 6.0, preferably from 3.0 to 5.0.

It has been found that an important condition for promoting the formation of acidic sites on the surface of the silica of the invention is the presence of a step process carried out at an acidic pH, i.e. at a pH of from 2.0 to 6.0, preferably from 3.0 to 5.0. On the other hand, the distribution of acid sites (through 1538 and 1559 cm)^-1The sum of the peaks in between 1612 and 1635cm^-1Those identified in the introduction) is influenced by the stage of introduction of the element M into the reaction medium.

In an advantageous embodiment of the process of the invention, at least one compound of the element M is added to the reaction medium while the pH is in the range from 2.0 to 6.0, preferably from 3.0 to 5.0.

In certain embodiments of the process of the present invention, at least one compound of the element M is added to the reaction medium at the time the total amount of silicate required for the reaction has been added to the reaction medium.

In other embodiments, the at least one compound of the element M is added to the reaction medium after 60%, 70%, 80%, 90% by weight of the total amount of silicate required for the reaction has been added to the reaction medium.

The term "silicate" is used herein to refer to one or more than one silicate that may be added during the process of the present invention. The silicate is selected from the group consisting of alkali metal silicates. Advantageously, it is selected from the group consisting of sodium silicate and potassium silicate. The silicate may be in any known form, for example a metasilicate or disilicate.

In the case where sodium silicate is used, the latter generally has SiO₂/Na₂The O weight ratio is between 2.0 and 4.0, in particular between 2.4 and 3.9, for example between 3.1 and 3.8.

The silicate may have a concentration (in SiO) of between 3.9 and 25.0 wt.%, for example between 5.6 and 23.2 wt.%, in particular between 5.6 and 20.7 wt.%₂Representation).

The term "acid" is used herein to refer to one or more than one acid that may be added during the process of the present invention. Any acid may be used in the process. Usually, inorganic acids, such as sulfuric acid, nitric acid or hydrochloric acid, or organic acids, such as acetic acid, formic acid or carbonic acid, are used.

The acid can be metered into the reaction medium in diluted or concentrated form. Different concentrations of the same acid may be used at different stages of the process.

In a preferred embodiment of the process, sulfuric acid and sodium silicate are used at all stages of the process.

The element M is selected from the group consisting of B, Al, Ga and mixtures thereof. The element M is preferably selected from the group consisting of Al and Ga. More preferably, the element M is Al.

Any compound of element M may be used in the process of the invention, as long as it is soluble in water. Typically, at least one compound of the element M is added to the reaction medium in the form of a solution (typically an aqueous solution).

Notable examples of suitable compounds include, but are not limited to, nitrates, chlorides, and sulfates.

When the element M is Al, suitable compounds are, for example, aluminum sulfate, aluminum nitrate and alkali metal aluminates. Preferably, the compound is selected from the group consisting of alkali metal aluminates, in particular potassium aluminate or more preferably sodium aluminate.

The definitions and preferences provided above apply equally to the specific embodiments of the method described below.

In a first embodiment, the method of the present invention comprises the steps of:

(i) providing a starting solution having a pH equal to or greater than 7.0;

(ii) reducing the pH of the reaction medium to a value below 7.0 by simultaneously adding silicate and acid to the starting solution or by adding acid to the starting solution; and

(iii) simultaneously adding silicate and acid to the reaction medium such that the pH of the reaction medium is maintained in the range of from 2.0 to 6.0 to obtain a suspension of precipitated silica,

wherein at least one compound of the element M is added to the reaction medium during steps (ii) and/or (iii), with the proviso that this addition is carried out after at least 50% by weight of the total amount by weight of silicate required for the reaction has been added to the reaction medium.

During step (ii), the at least one compound of the element M may be added to the reaction medium. Alternatively, during step (iii), a compound of the element M may be added to the reaction medium. In yet another embodiment, during steps (ii) and (iii), a compound of element M may be added to the reaction medium.

In all embodiments, the entirety of the at least one compound of the element M is added to the reaction medium after at least 50% by weight of the total amount by weight of silicate required for the reaction has been added thereto.

In step (i) of the first embodiment of the method, a starting solution having a pH equal to or greater than 7.0 is provided in a reaction vessel. The starting solution is an aqueous solution, i.e. the solvent is water.

Typically, the starting solution has a pH between 8.0 and 13.0, in particular between 8.0 and 12.0.

The starting solution may be obtained by adding a base (e.g. NaOH) to water to obtain a pH value as detailed above.

Alternatively, the starting solution may comprise silicate. In this case, it can be obtained by adding an acid to a mixture of water and silicate to obtain a pH equal to or greater than 7.0.

The starting solution may also contain preformed silica particles at a pH equal to or greater than 7.0.

The starting solution of step (i) may comprise one or more electrolytes. Preferably, the starting solution contains an electrolyte. The term "electrolyte" is used herein in its accepted sense, i.e., to designate any ionic or molecular species that decomposes or dissociates when in solution to form ionic or charged particles. Mention may be made of salts selected from the group consisting of alkali metals and alkaline earth metals. Advantageously, the electrolyte used in the starting solution is a salt of the metal of the starting silicate and a salt of the acid used in the process. Notable examples are sodium chloride, for example in the case of the reaction of sodium silicate with hydrochloric acid, or preferably sodium sulfate in the case of the reaction of sodium silicate with sulfuric acid. The electrolyte does not contain the element M.

Preferably, when sodium sulphate is used as the electrolyte in step (i), its concentration in the starting solution is between 8 and 40g/l, in particular between 10 and 35g/l, for example between 13 and 30 g/l.

In step (ii), the pH of the reaction medium is lowered to a value below 7.0 by simultaneously adding silicate and acid to the starting solution or by adding acid to the starting solution.

In one aspect of this first embodiment, step (ii) comprises simultaneously adding the acid and the silicate to the starting solution to lower the pH of the reaction medium to less than 7.0. The rate of addition of acid and silicate during step (ii) is controlled in such a way that the average pH of the reaction medium is reduced to less than 7.0. The pH of the reaction medium is preferably between 7.0 and 2.0, in particular between 6.0 and 2.0.

In this aspect of the process, step (iii) is a continuation of step (ii) and it may be carried out under the same or different reaction conditions, such as different pH, different rates of addition of reagents.

In a second aspect of said first embodiment, step (ii) of the process comprises adding an acid to the starting solution to lower the pH of the reaction medium to less than 7.0, typically to a pH value between 7.0 and 2.0, typically between 6.0 and 2.0.

Step (iii) then comprises the simultaneous addition of the acid and of the silicate to the reaction medium obtained at the end of step (ii). The rate of addition of acid and silicate during step (iii) is controlled in such a way that the average pH of the reaction medium is maintained between 2.0 and 6.0. In certain embodiments of the method of the present invention, the pH is maintained at a constant value or it may be varied during step (iii).

During stage (ii)/(iii), the pH of the reaction medium is preferably maintained between 2.5 and 5.5, in particular between 3.0 and 5.0. In certain embodiments of the method of the present invention, the pH is maintained at a constant value or it may be varied during step (iii).

In a second embodiment, the method of the present invention comprises the steps of:

(i') providing a starting solution having a pH equal to or greater than 7.0;

(ii') reducing the pH of the reaction medium to a value below 7.0 by simultaneously adding silicate and acid to the starting solution or by adding acid to the starting solution; and

(iii) simultaneously adding an acid and at least one compound of the element M to the reaction medium so that the pH of the reaction medium is maintained in the range from 2.0 to 6.0 to obtain a suspension of precipitated silica.

Steps (i ') and (ii') of the second embodiment of the method are carried out under the same conditions as described for steps (i) and (ii) of the first embodiment.

During step (iii'), the acid and the at least one compound of the element M are added simultaneously to the reaction medium in such a way that the pH of the reaction medium is maintained in the range from 2.0 to 6.0, preferably from 3.0 to 5.0. No silicate is added to the reaction medium during step (iii'). Typically, all silicate required for the reaction has been added at the end of step (ii').

It should be noted that the method of the present invention may comprise additional steps. For example, one or more curing steps may be performed between the different steps as detailed above.

When M is B or Ga, the method according to the first and second embodiments may additionally include:

-a step (iv) carried out after step (iii) or (iii') comprising stopping the addition of acid and raising the pH of the reaction medium to a value from 7.0 to 10.0;

-a step (v) carried out after step (iv) comprising the simultaneous addition of an acid and a silicate to the reaction medium in such a way that the pH of the reaction medium is between 7.5 and 9.5; and

-a step (vi) comprising stopping the addition of the silicate while continuing the addition of the acid to the reaction medium to reach a pH of the reaction medium of less than 6.0 to obtain a suspension of precipitated silica.

The pH of the reaction medium may be increased during step (iv) by the addition of a base (e.g. NaOH) or a silicate.

When the element M is B or Ga, the method according to the first embodiment may therefore comprise the following steps as detailed above: (i) (ii), (iii), (iv), (v) and (vi), wherein at least one compound of B or Ga is added to the reaction medium during at least one of steps (ii), (iii) and (iv), with the proviso that the totality of at least one compound of B or Ga is added after at least 50% by weight of the total amount of silicates required for the reaction have been added to the reaction medium.

Regardless of the stage at which the compound of the element M is added, the cumulative amount of said compound metered into the reaction medium is such that the amount of M in the precipitated silica is between 0.5 and 30.0 mol%, even between 0.7 and 25.0 mol%. The rate of addition of the at least one compound of the element M may be adapted to obtain the desired M content in the precipitated silica by means known to the person skilled in the art.

The reaction vessel in which the reaction of the silicate with the acid is carried out is generally equipped with suitable stirring and heating equipment.

The entire reaction of the silicate with the acid is generally carried out at a temperature of between 40 ℃ and 96 ℃, in particular between 80 ℃ and 95 ℃.

According to one variant of the invention, the entire reaction of the silicate with the acid is carried out at a constant temperature, generally between 40 ℃ and 96 ℃, in particular between 80 ℃ and 95 ℃.

According to another variant of the invention, the temperature at the end of the reaction is higher than the temperature at the beginning of the reaction: thus, the temperature at the start of the reaction is preferably kept between 40 ℃ and 80 ℃ and then, preferably, the temperature is increased up to a value between 80 ℃ and 96 ℃, the temperature being kept at this value until the end of the reaction.

At the end of the step just described, a suspension of precipitated silica is obtained, which is subsequently subjected to separation (liquid/solid separation). Thus, the process in all its embodiments typically comprises the further step of filtering the suspension of precipitated silica and drying the precipitated silica.

Separation typically involves filtration followed by washing (if necessary). Filtration is carried out according to any known method, for example by means of a belt filter, a rotary filter, for example a vacuum filter, or, preferably, a filter press.

The filter cake is then subjected to a liquefaction operation. The term "liquefaction" is herein intended to indicate a process in which a solid (i.e. a filter cake) is converted into a fluid-like substance. After the liquefaction step, the filter cake is in a flowable, fluid-like form and the precipitated silica is in the form of a suspension.

The liquefaction step may comprise a mechanical treatment which results in a reduction of the particle size (granulometric) of the silica in the suspension. The mechanical treatment may be performed by passing the filter cake through a high shear mixer, a colloid mill, or a ball mill. Optionally, the liquefaction step may be performed by subjecting the filter cake to a chemical action, for example by adding water or acid. Both mechanical and chemical treatments may be performed. The suspension of precipitated silica obtained after the liquefaction step is subsequently dried.

Drying may be carried out according to means known in the art. Preferably, the drying is carried out by atomization. For this purpose, any type of suitable atomizer may be used, in particular a turbine, a nozzle, a hydraulic or a two-fluid spray dryer. In general, when filtration is performed using a pressure filter, a nozzle spray dryer is used, and when filtration is performed using a vacuum filter, a turbine spray dryer is used.

When the drying operation is carried out using a nozzle spray dryer, the precipitated silica which may then be obtained is generally in the form of substantially spherical beads. After this drying operation, optionally, a step of grinding or micronization may be carried out on the recovered product; the precipitated silica which may then be obtained is generally in the form of a powder.

When the drying operation is performed using a turbo spray dryer, the precipitated silica that may then be obtained may be in the form of a powder.

Finally, the dried, milled or micronized product as previously indicated may optionally be subjected to an agglomeration step comprising, for example, direct compression, wet granulation (i.e. using a binder such as water, silica suspension, etc.), extrusion or, preferably, dry compression.

The precipitated silica which can then be obtained by this agglomeration step is generally in the form of particles.

The precipitated silicas of the invention can be used in many applications, such as catalysts, catalyst supports, absorbents for active materials (in particular for carriers for liquids, especially for foodstuffs, such as vitamins (vitamin E or choline chloride)), as viscosity regulators, texturizers or anti-caking agents, or as additives for toothpaste, concrete or paper. The silica of the invention can also be conveniently used for the manufacture of thermal insulation materials or for the preparation of resorcinol-formaldehyde/silica composites.

The precipitated silicas of the invention are particularly advantageously employed as fillers in polymer compositions. The at least one polymer may be selected from thermosetting polymers and thermoplastic polymers. Notable non-limiting examples of thermosetting polymers include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, and cyanate ester resins.

Notable non-limiting examples of suitable thermoplastic polymers include styrene-based polymers such as polystyrene, (meth) acrylate/styrene copolymers, acrylonitrile/styrene copolymers, styrene/maleic anhydride copolymers, ABS; acrylic polymers such as polymethyl methacrylate; a polycarbonate; a polyamide; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene ether (polyphenylene ether); polysulfones; a polyaryletherketone; polyphenylene sulfide (polyphenylene sulfide); a thermoplastic polyurethane; polyolefins such as polyethylene, polypropylene, polybutylene, poly-4-methylpentene, ethylene/propylene copolymers, ethylene/alpha-olefin copolymers; copolymers of alpha-olefins and various monomers, such as ethylene/vinyl acetate copolymers, ethylene/(meth) acrylate copolymers, ethylene/maleic anhydride copolymers, ethylene/acrylic acid copolymers; aliphatic polyesters such as polylactic acid, polycaprolactone, and aliphatic diol/aliphatic dicarboxylic acid copolymers.

The silicas of the invention can be advantageously used as reinforcing fillers in elastomer compositions. A preferred object of the present invention is therefore a composition comprising the silica of the invention and one or more elastomers, preferably exhibiting at least one glass transition temperature between-150 ℃ and +300 ℃, for example between-150 ℃ and +20 ℃.

A notable non-limiting example of a suitable elastomer is a diene elastomer. For example, elastomers derived from aliphatic or aromatic monomers comprising at least one unsaturation, such as, in particular, ethylene, propylene, butadiene, isoprene, styrene, acrylonitrile, isobutylene or vinyl acetate, polybutyl acrylate, or mixtures thereof, may be used. Mention may also be made of functionalized elastomers, which are elastomers functionalized by chemical groups located along the macromolecular chain and/or at one or more of its ends (for example by functional groups capable of reacting with the silica surface), and halogenated polymers. Mention may be made of polyamides, ethylene homo-and copolymers, propylene homo-and copolymers.

Among the diene elastomers that may be mentioned are, for example, polybutadienes (BR), polyisoprenes (IR), butadiene copolymers, isoprene copolymers, or mixtures thereof, and in particular styrene/butadiene copolymers (SBR, in particular ESBR (emulsion) or SSBR (solution)), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR), isoprene/butadiene/styrene copolymers (SBIR), ethylene/propylene/diene terpolymers (EPDM), and also related functionalized polymers (for example presenting pendant or terminal polar groups capable of interacting with silica).

Mention may also be made of Natural Rubber (NR) and Epoxidized Natural Rubber (ENR).

These polymer compositions can be vulcanized with sulfur or crosslinked, in particular with peroxides or other crosslinking systems (for example diamines or phenolic resins).

Generally, the polymer compositions additionally comprise at least one (silica/polymer) coupling agent and/or at least one capping agent; they may also contain, among other things, antioxidants.

Notable non-limiting examples of suitable coupling agents are, for example, "symmetrical" or "asymmetrical" silane polysulfides; mention may be made more particularly of: bis ((C1-C4) alkoxy (C1-C4) alkylsilyl (C1-C4) alkyl) polysulfides (in particular, disulfides, trisulfides or tetrasulfides), such as, for example, bis (3- (trimethoxysilyl) propyl) polysulfide or bis (3- (triethoxysilyl) propyl) polysulfide, such as triethoxysilylpropyl tetrasulfide. Mention may also be made of monoethoxydimethylsilylpropyl tetrasulfide. Mention may also be made of silanes comprising masked or free thiol functions.

The coupling agent may be pre-grafted to the polymer. It can also be used in the free state (that is to say without prior grafting) or grafted onto the surface of the silica. This is also done for the optional masking agent.

The coupling agent may optionally be combined with a suitable "coupling activator", that is to say a compound which, when mixed with the coupling agent, increases the effectiveness of the latter.

The weight ratio of the silicas of the invention in the polymer composition can vary within a fairly wide range. It generally represents an amount of polymer(s) from 10% to 200%, in particular from 20% to 150%, especially from 20% to 80% (e.g. from 30% to 70%) or from 80% to 120% (e.g. from 90% to 110%).

The silica according to the invention may advantageously constitute the entirety of the reinforcing inorganic filler and even of the reinforcing filler of the polymer composition.

Compositions comprising the precipitated silicas of the present invention may be used to manufacture a variety of articles. Non-limiting examples of finished products comprising at least one of the above-described polymer compositions are, for example, shoe soles, floor coverings, gas barriers, flame retardant materials and also engineering components, such as cableway rollers, seals for household appliances, seals for liquid or gas conduits, brake system seals, conduits (flexible), sheaths (especially cable sheaths), cables, engine supports, tires, battery membranes, conveyor belts, or conveyor belts.

If the disclosure of any patent, patent application, and publication incorporated by reference herein conflicts with the description of the present application to the extent that terminology may become unclear, the description shall take precedence.

Analytical method

The physicochemical properties of the precipitated silica of the present invention were determined using the method described below.

BET surface area

The BET surface area was determined according to the Brunauer-Emmett-Teller (Brunauer-Emmett-Teller) method as detailed in standard NF ISO 5794-1, appendix E (6 months 2010), with the following adjustments: the samples were pre-dried at 160 ℃. + -. 10 ℃ for the partial pressure measured (P/P)⁰) Is between 0.05 and 0.20.

CTAB surface area

The CTAB surface area was determined according to standard NF ISO 5794-1, appendix G (6 months 2010).

Determination of the content of element M

The sample is exposed to hydrofluoric acid (e.g., 0.2-0.3g SiO with 1mL of 40% hydrofluoric acid₂) After the medium digestion, the content of the element M was determined by ICP OES (inductively coupled plasma optical emission spectroscopy). The clear solution is diluted in 5% aqueous nitric acid (e.g. by a factor of 1500 for an amount of 0.3%) according to the expected concentration of element M. The intensity measured at a specific wavelength of element M (e.g. 396.152nm for A1; 249.773nm for B and 233.527nm for Ga) is compared to a calibration curve in the range of 0.05 to 2.00mg/L for standards obtained under similar analytical conditions. The amount in the solid was obtained by calculation using the dilution factor and the measured dry extract of silica.

Determination of residual sulfate in silica

Sulfate is determined by measuring the sulfur in silica by ICP OES (inductively coupled plasma optical emission spectroscopy) after digestion of the sample in hydrofluoric acid (e.g., 0.2-0.3g of silica with 1mL of 40% hydrofluoric acid). The clear solution is diluted in 5% aqueous nitric acid (e.g., for 0.5% 8O) according to the expected sulfur concentration₄Diluted by a factor of 1500). The intensity measured at a specific wavelength of sulfur (e.g., 180.672 and 181.975nm) is compared to a calibration curve in the range of 0.05 to 2.00mg/L for sulfur standards obtained under similar analytical conditions to measure the amount of diluted solution. The amount of sulphur in the solid was obtained by calculation using the molecular weight ratio between sulphur and sulphate, the dilution factor and the dry extract of silica.

Infrared spectroscopy

Between 0.2% and 0.6% by weight of Na₂SO₄Content and amount of other anions (e.g. Cl) not exceeding 0.015% by weight for each individual anion^-、Br^-、I^-、NO₃ ^-、PO₄ ^3-) On a silica sample. Contains high content of Na₂SO₄The sample of (a) should be washed with water to reduce the amount of salt to a level of 0.2% -0.6% by weight. Samples containing other salts (e.g., chlorides, nitrates, etc.) in an amount greater than 0.015% by weight (measured on the anion) should be washed to reduce the residual anion content to 0.015% by weight and Na should be added₂SO₄To obtain a value between 0.2% and 0.6% by weight. An appropriate amount of Na should be added₂SO₄Added to the wash water to obtain a value between 0.2% and 0.6% by weight after drying. The pure product should be suspended in Na with a suitable concentration₂SO₄To obtain a value between 0.2% and 0.6% by weight after drying.

Equipment and sample preparation: the surface infrared analysis (by absorption) was performed on a Bruker Equinox 55 FTIR spectrometer on pellets of pure product. The pellets were silica ground (as received) in an agate mortar and at 2T/cm²Obtained after 10 seconds of pelletization. The diameter of the pellets was generally 17 mm. The weight of the pellets was between 10 and 20 mg.

Spectrum collection

The pellets are placed in a high vacuum chamber (10) of a spectrometer^-5Pa) is added. The collection was carried out under high vacuum (collection conditions: from 400 cm)^-1To 6000cm^-1(ii) a The scanning times are as follows: 100, respectively; resolution ratio: 2cm^-1). A background spectrum was recorded, and a spectrum was recorded after each step 1 to 5 was performed at the temperature and pressure as described below:

1.25 ℃ under atmospheric pressure;

2.25 ℃ under vacuum (10)^-5Pa) for 1 hour (desorption of residual water);

3.180 deg.C under vacuum (10)^-5Pa) for 2 hours.

4. Introducing gaseous pyridine (670Pa) at 25 ℃ for 5min to reach saturation;

5. at 25 ℃ under vacuum (10)^-5Pa) for a period of 30 min.

The spectra were normalized using the instrument software, version OPUS 7.2, supplied by Bruker Optik GmbH, as follows: correcting a baseline; at 1870cm^-1SiO of (2)₂The fingerprint peak scale was 0.2 absorbance units (to normalize the spectra of different samples to the same mass of SiO₂)。

At 1538 and 1559cm^-1And 1635 and 1612cm^-1Determination of the area under the peak in between

The infrared spectrum considered is from 1700cm^-1To 1400cm^-1。

As detailed above, the determination of the area under the peaks in the identification region of the IR spectrum was performed on the spectrum obtained at the end of step 5 using the integration function of the software version OPUS 7.2, supplied by Bruker Optik GmbH: in the menu "set points", method B is selected and at 1538 and 1559cm respectively^-1And 1612 to 1635cm^-1The integral is calculated between the values in between. The values obtained by the software are recorded.

Outline the operation at 1538 and 1559cm^-1Calculation of the integral under the peak in between: identification of the value on the infrared absorption curve corresponding to 1538cm^-1And 1559cm^-1And they are connected by a straight line passing through the two points. Absorption spectrum and including at the straight line and at 1538cm^-1And 1559cm^-1The area of the region between the absorption spectra in between is considered as the area under the peak.

Examples of the invention

Example 1

An aqueous suspension of silica was prepared by introducing 2160g of the filter cake (equal to 24.09% of the dry extract) into 3041g of deionized water following the procedure described in example 1 of EP 520862 a1, from the initial stage until the separation of the filter cake.

The silica suspension was placed in a 5L reactor with stirring and the temperature was then adjusted to 60 ℃. The pH of the suspension was adjusted to 3.5 by adding sulfuric acid (concentration ═ 7.7 wt%).

204g of aluminum sulfate Al dissolved in water and having a concentration of 22.4g/L of aluminum₂(SO₄)₃The solution was added to the suspension. The pH of the reaction medium is maintained at a value of 4.5 throughout the addition of the aluminium sulphate solution (solution using sodium hydroxide NaOH 1M). The reaction medium is allowed to mature for 300 s. The resulting slurry was dried by NIRO spray to obtain precipitated silica S1. The separated product was washed with deionized water to remove residual Na₂SO₄In an amount ranging from 0.2 to 0.6 wt% and then dried.

The properties of the precipitated silica S1 are reported in table I.

TABLE I

Comparative example 1

Example 3 of WO 96/30304 is reproduced essentially as described. The properties of the precipitated silica CS1 are reported in table I. As in comparative example 1, the addition of an aluminum compound at a pH of 7.7 provided a pH of 1559cm at 1538-^-1Precipitated silica without any peaks in the region.

Comparative example 2

Example 1 of EP 520862A 1 was reproduced essentially as described, wherein an aluminum compound with a pH > 6.0 was added. The precipitated silica CS2 was characterized at 1538-1559cm^-1There were no peaks in the region and therefore the ratio (at 1538 to 1559 cm)^-1Area of peak in between)/(1612 and 1635cm^-1Peak area in between) equals zero. The precipitated silica CS2 had an Al content of 0.7 mol% and a CTAB surface area of 154m²/g。

Examples 2 and 3-comparative examples 3 and 4

Compared to silica CS2, an elastomeric composition was prepared using silica S1 of the present invention. These compositions, expressed in parts by weight per 100 parts of elastomer (phr), are described in table II below:

TABLE II

The process for preparing the rubber composition is carried out in two successive preparation stages: a first stage of high temperature thermomechanical working followed by a second stage of mechanical working at a temperature of less than 110 ℃ to introduce a vulcanization system.

This first stage was carried out using a Brabender brand internal mixer type mixing device (capacity 70 mL). The initial temperature and the speed of the rotor are set so as to achieve a mixture drop temperature between 130 ℃ and 160 ℃.

In the first procedure of this first stage, the elastomer and the reinforcing filler (introduced in portions) are mixed with the coupling agent, the oil and the stearic acid. The duration is between 5 and 8 minutes.

After cooling the mixture (temperature below 100 ℃), the second procedure enables incorporation of zinc oxide and a protective/antioxidant agent. The duration of this procedure is between 2 and 5 minutes.

After cooling the mixture (temperature less than 100 ℃), a vulcanization system is added during the second stage. It is carried out on an open mill preheated to 50 ℃. The duration of this phase is between 2 and 6 minutes.

Each final mixture was then calendered in the form of a sheet with a thickness of 2 to 3 mm.

Characteristics of the vulcanized product

The measurements were carried out at 160 ℃ after vulcanization. Uniaxial tensile tests were carried out on an Instron 5564 apparatus at a speed of 500mm/min according to the specification of standard NF ISO 37 with test specimens of the H2 type. The 300% modulus corresponds to the stress measured at 300% tensile strain, and the tensile strength is expressed in MPa; elongation at break is expressed in MPa and energy at break is expressed in joules.

After crosslinking, the Z values were measured according to ISO 11345 according to the method described by S.Otto et al in Kautschuk Gummi Kunststoffe, 58 Jahrgarg, NR 7-8/2005.

The percentage "undispersed area" was calculated using a camera viewing the sample surface at 30 ° incident light. Bright spots are associated with charge and agglomerates, while dark spots are associated with the rubber substrate. Digital processing converts the image to a black and white image and allows the determination of the percentage "undispersed area" as described in the documents cited above. The higher the Z score, the better the dispersion of the charge in the elastomeric matrix (a Z score of 100 corresponds to complete dispersion and a Z score of 0 has moderate dispersion).

The calculation of the Z value is based on the percentage area in which the charge is not dispersed, as supplied by the machine by Mono-Nisco (Dynisco) company together with its operating mode and its operating software DisperData1000 is measured according to the following equation:

z is 100- (undispersed percent area)/0.35

The vulcanized sample (parallelepipedal test specimen: 8 mm) is recorded²Cross section and height of 7 mm) and the amplitude of the dynamic shear modulus of elasticity (Δ G'). The samples were subjected to a double alternating sinusoidal shear strain at a temperature of 40 ℃ and a frequency of 10 Hz. The strain amplitude sweep process is performed according to an out-return (out-return) cycle, going out from 0.1% to 50% and then returning from 50% to 0.1%. These values reported in table III are obtained from the return strain amplitude scan and are related to the maximum value of the loss factor (tan δ max) and the amplitude of the elastic modulus (Δ G') between the values of 0.1% and 50% strain (payne effect).

TABLE III

The silica according to the invention is a highly dispersible silica which allows to reduce the low energy dissipation (lower Δ G' and tan δ max) at 40 ℃ without negatively affecting the reinforcement.