A method for preparing precipitated silica from carbon dioxide

Abstract

The invention relates to precipitated silica, a production method thereof and its applications, such as reinforcing filler material in polymer compositions.

Description

[0001] A Method for Preparing Precipitated Silica from Carbon Dioxide

[0002] TECHNICAL FIELD

[0003] The invention relates to precipitated silica, a production method thereof and its applications, such as reinforcing filler material in polymer compositions, or in oral care applications.

[0004] TECHNICAL BACKGROUND

[0005] Precipitated silica, also called white carbon black, is a widely used inorganic material with unique physical and chemical properties, such as superior stability, reinforcement, thickening and thixotropy. The use of precipitated silica as a reinforcing filler in polymeric compositions, especially in elastomeric composition, is well known in the art.

[0006] However, this use is highly demanding: the filler has to readily and efficiently incorporate and disperse in the elastomeric composition and, typically in conjunction with a coupling reagent, enter into a chemical bond with the elastomer(s), to lead to a high and homogenous reinforcement of the elastomeric composition. In general, precipitated silica is used in order to improve the mechanical properties of the elastomeric composition as well as abrasion performance. Therefore, the precipitated silica has to show a good balance between conflicting properties such as abrasion resistance and / or polymer reinforcement on one hand and reduced energy dissipation properties, which in turn provide for reduced heat build-up, on the other. Even though precipitated silicas are known in the art, there is still the need to provide a precipitated silica showing an improved balance between these properties.

[0007] Several methods for producing precipitated silicas are known in the art.

[0008] Traditionally the so-called sulfuric acid precipitation production process is used. This process is for example described in US5891949A or WO97 / 45366A1. However, this method requires a high concentration of sulfuric acid, which causes environmental problems.

[0009] Therefore, in recent years, other methods for producing precipitated silicas have been developed, especially to avoid environmental problems. One possibility is to prepare silicas by carbonization, for example by pressure carbonization or in a high-temperature melting process, as for example described in CN 117208920 or CN 117208919. However, these methods usually demand a comparable high equipment and energy expenditures and their CO2 footprint is also critical. US2012 / 041128A1 and US2003 / 219370A1, also describe the synthesis of silicas by carbonization and, in particular, by reaction of sodium silicate and CO2, followed by a subsequent acidification of the suspension obtained.

[0010] Therefore, there is also still the need to provide a process for producing precipitated silica, which overcomes the drawbacks of the production processes as known in the prior art.

[0011] SUMMARY OF THE INVENTION

[0012] The present invention refers to a precipitated silica characterized by its infrared absorption spectrum having at least one peak between 2500 and 3000 cm’1and one peak between 1736 and 2110 cm’1, wherein the infrared absorption spectrum is measured after a treatment of the precipitated silica under vacuum at 25°C for 1 hour, and wherein the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is at least 0.05.

[0013] Furthermore, the invention relates to a process for the manufacture of the precipitated silica according to the invention comprising the steps of: a) reacting a silicate, preferably an alkali metal silicate, with carbon dioxide in an aqueous liquid medium to obtain a first suspension comprising precipitated silica; b) separating the precipitated silica of the first suspension from the aqueous liquid medium of the first suspension to obtain a cake; c) optionally washing the cake; d) subjecting the cake to a disintegration operation in order to obtain a second suspension of precipitated silica; e) spray drying the second suspension in a spray drier with a drying gas to obtain a dried precipitated silica; f) optionally milling the dried precipitated silica; g) optionally agglomerating the optionally milled dried precipitated silica into granules; wherein all or part of the step a) is operated at a basic pH.

[0014] A further aspect of the invention concerns the use of the precipitated silica of the invention in a composition based on a matrix compound, which is preferably a polymer. In particular, the invention relates to the use of the precipitated silica as a reinforcing filler in a polymeric composition.

[0015] The composition including the precipitated silica of the invention can be used in a finished article such as a tire, or a part of a shaped article. The composition including the precipitated silica of the invention can be used in oral care applications.

[0016] A further aspect of the invention thus concerns an oral care composition, such as a toothpaste composition, comprising the precipitated silica of the invention.

[0017] DETAILED DESCRIPTION OF THE INVENTION

[0018] Before the issues of the invention are described in detail, the following should be considered:

[0019] As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0020] The terms "comprising", "comprises" and "comprised of as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of as used herein comprise the terms "consisting of, "consists" and "consists of.

[0021] Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0022] As used herein, the term "average" refers to number average unless indicated otherwise.

[0023] As used herein, the terms "% by weight", "wt.- %", "weight percentage", or "percentage by weight", and the terms "% by volume", "vol.- %", "volume percentage", or "percentage by volume", are used interchangeably.

[0024] The recitation of numerical ranges by end points includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0025] The term “silica” is used herein to refer to silicon dioxide, SiCh. The term “silica” is used throughout the text to refer to precipitated silica. The expression “precipitated silica” is used to refer to a synthetic amorphous silica obtained by a process wherein the silicate is reacted with an acid. The term “silicate” is used herein to refer to one or more silicate which can be added during the course of the inventive process.

[0026] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0027] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0028] In the following passages, different alternatives, embodiments and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0029] Furthermore, the particular features, structures or characteristics described in the present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0030] The present invention refers to a precipitated silica characterized by its infrared absorption spectrum having at least one peak between 2500 cm’1and 3000 cm’1and one peak between 1736 cm’1and 2110 cm’1, wherein the infrared absorption spectrum is measured after a treatment of the precipitated silica under vacuum at 25°C for 1 hour, and wherein the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is at least 0.05.

[0031] The treatment of the precipitated silica before measuring the infrared absorption spectrum is carried out to desorb the residual water from the precipitated silica. The surface infrared analysis can be obtained on a Bruker Equinox 55 FTIR spectrometer as described for example in WO 2018 / 202755 and in the examples below.

[0032] It has been surprisingly found by the inventors that such a precipitated silica, when incorporated as a filler in a composition, preferably in an elastomer composition, in replacement of a homologue precipitated silica having the same specific surface area (BET) and external specific surface area (CTAB) but no peak from 2500 to 3000 cm’1with an area ratio above 0.05, is capable of reducing the energy dissipation of the composition.

[0033] According to the invention, the area ratio, i.e., the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’x), is at least 0.05, preferably of at least 0.07, more preferably of at least 0.10 and still more preferably of at least 0.12. Additionally, it is preferred that the area ratio ((area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1)) is of at most 0.75, more preferably of at most 0.70, or of at most 0.60, even more preferably of at most 0.50.

[0034] In a particular preferred embodiment of the invention, the area ratio ((area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1)) is in a range of from 0.15 to 0.50.

[0035] The area under the peak from 2500 to 3000 cm’1of the infrared absorption spectrum is mainly attributed, i.e., in part or fully, by at least one carbonate species present in the precipitated silica. The carbonate species present in the precipitated silica is formed during the production of the precipitated silica, wherein the following chemical equitation is involved:

[0036] X2O nSiCE + CO2=X2CO3 + nSiCE, wherein X is an alkali metal, preferably sodium or potassium.

[0037] The area under the peak between 1736 and 2110 cm’1is mainly attributed, i.e., in part of fully, by the SiCE structure of the precipitated silica.

[0038] Preferably, the area under the peak between 2500 and 300 cm’1is preferably at least 2.5 cm’1, or at least 4.0 cm’1, more preferably at least 5.0 cm’1.

[0039] The area under the peak between 1736 and 2110 cm’1is preferably at least 10.0 cm’1, more preferably at least 12.0 cm’1.

[0040] In any event the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is at least 0.05.

[0041] It is preferred that the precipitated silica of the invention is at least partially in particle form. In particular, it is preferred that the precipitated silica of the invention is fully in particle form, more preferably in form of a powder, beads, or granules. The particles or beads may be in substantially spherical form. The term “particle” or “particle form” is used herein to refer to aggregate of primary silica particles. The term particle is used to refer to the smallest aggregate of primary silica particles that can be broken by mechanical action. In other words, the term particle refers to an assembly of indivisible primary particles.

[0042] Furthermore, it is preferred that at least a part of the carbonate species is on the surface of the precipitated silica particles, more preferably all of the carbonate species is on the surface of the precipitated silica particles.

[0043] The BET surface area of the precipitated silica of the invention is preferably in a range of from 10 to 400 m2 / g, more preferably of from 25 to 350 m2 / g, most preferably of from 50 to 300 m2 / g. The BET surface area of the precipitated silica of the invention may be in a range selected from the group consisting of from 80 m2 / g up to less than 140 m2 / g, from 140 m2 / g up to less than 190 m2 / g, from 190 m2 / g up to less than 240 m2 / g and from 240 m2 / g up to 300 m2 / g.

[0044] The specific surface area (BET) of the silica can be determined according to the Brunauer-Emmett-Teller method (BET method) described in “The Journal of the American chemical Society, 60, 309 (1938)”, and corresponding to the standard NF ISO 5794-1, Appendix E (June 2010).

[0045] Additionally, it is preferred that the precipitated silica of the invention has a CTAB surface area ranging from 10 to 400 m2 / g, more preferred ranging from 25 to 350 m2 / g, even more preferred ranging from 40 to 280 m2 / g. The CTAB surface area of the precipitated silica of the invention may be in a range selected from the group consisting of from 60 m2 / g up to less than 130 m2 / g, from 130 m2 / g up to less than 180 m2 / g, from 180 m2 / g up to less than 230 m2 / g and from 230 m2 / g up to 280 m2 / g. The CTAB surface area can be determined according to the method as described in the examples.

[0046] CTAB surface area can be a measure of external specific surface area and is determined according to the standard NF ISO 5794-1, Appendix G (June 2010).

[0047] The precipitated silica of the invention has preferably an aqueous extract pH of at least 6.0, more preferably in a range from 6.5 to 10.5, still more preferably in a range from 7.0 to 10.0, possibly from 7.0 up to less than 8.5. Even more preferably, the precipitated silica of the invention has a basic pH, that is to say a pH above 7.0, advantageously above 7.0 and of at most 10.5, possibly from 8.5 to 10.0. The pH of the precipitated silica of the invention or rather of the aqueous extract can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or SiO? powder”). The precipitated silica of the invention can be produced by any method as known in the technical field of the invention. However, it is preferred that the precipitated silica is produced by a process comprising the following steps: a) reacting a silicate with carbon dioxide in an aqueous liquid medium to obtain a first suspension comprising precipitated silica; b) separating, the precipitated silica of the first suspension from the aqueous liquid medium of the first suspension to obtain a cake; c) optionally washing the cake; d) subjecting the cake to a disintegration operation in order to obtain a second suspension of precipitated silica; e) spray drying the second suspension in a spray drier with a drying gas to obtain a dried precipitated silica; f) optionally milling the dried precipitated silica; g) optionally agglomerating the optionally milled dried precipitated silica into granules; wherein all or part of the step a) is operated at a basic pH.

[0048] In a particular preferred embodiment, the precipitated silica is produced by a process consisting of process steps a), b), d) and e), and optionally of c), f) and / or g) as defined above.

[0049] The process of the invention does not need a high equipment expansion and has a decreased CO2 footprint in comparison to processes as known in the prior art.

[0050] The silicate used in the production process of the invention can be sourced from diverse materials like sand, natural sources containing silica, either combusted (like RHA or Rice Husk Ash) or as such, and even from waste (from construction, mining, spent foundry sand etc.) and is preferably an alkali metal silicate, more preferably selected from the group of consisting of sodium and potassium silicate, most preferably the silicate is sodium silicate. The silicate may be in any known form, such as metasilicate or disilicate.

[0051] In the case where sodium silicate is used, the latter generally has a SiO2 / Na2O weight ratio of from about 2.0 to about 4.0, in particular of from about 2.4 to about 3.9, for example of from about 2.9 to about 3.8.

[0052] The silicate may have a concentration (expressed in terms of SiCh) of from about 3.9 wt.-% to about 25.0 wt.-%, for example of from about 5.6 wt.-% to about 23.0 wt.-%, in particular of from about 5.6 wt.-% to about 21.0 wt.-%.

[0053] It is preferred that process step a) is carried out such that the first suspension has a basic pH. In particular, it is preferred that no acidification is operated at the end of the step a), so that, upon completion of the step a), the first suspension has a basic pH. It is further preferred that all of the step a) of the invented process is operated at a basic pH, so that, upon completion of the step a), the first suspension has a basic pH. The pH of first suspension can be determined by any method usually used in the art; in particular, it can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or SiCh powder”).

[0054] According to the teaching of the invention, a basic pH is a pH of above 7.0. preferably of 7.5 or higher. Preferably the pH of the process step a) is operated at a pH ranging from 7.0 to 11.0 or at a pH ranging from more than 7.0 up to 11.0, more preferably at a pH ranging from 7.0 to 10.5 or at a pH ranging from more than 7.0 up to 10.5, even more preferably at a pH ranging from 7.5 to 10.0. In particular, the preferred ranges for the pH at which step a) is operated can be determined based on the examples described below, the preferred ranges encompassing the exemplified values of these examples.

[0055] The reaction in step a) is carried out by directly contacting carbon dioxide with the silicate in an aqueous liquid to obtain a first slurry comprising precipitated silica.

[0056] Preferably, during the step a), all or part, preferably all, of the carbon dioxide is added continuously in the aqueous liquid medium. Also preferably, during the step a), all or part, preferably all, of the silicate is added continuously in the aqueous liquid medium. More preferably, during the step a), all or part of the carbon dioxide and all or part of the silicate are added continuously and simultaneously in the aqueous liquid medium. Still more preferably, during the step a), all of the carbon dioxide and all of the silicate are added continuously and simultaneously in the aqueous liquid medium.

[0057] In a particular preferred embodiment of the invention, the process is carried out such that the process step a) comprises the following sub-steps: al) providing a liquid aqueous medium, preferably water, a2) adding the silicate and the carbon dioxide to the liquid aqueous medium, wherein, during the step a2):

[0058] - the carbon dioxide is added to the aqueous medium at gaseous state, and

[0059] - part or all of the silicate and part or all of the carbon dioxide are added continuously and simultaneously to the liquid aqueous.

[0060] According to the invention, it is preferred that before carrying out step a2) the pH of the liquid medium is adjusted to a value of between 7.0 and 11.0, more preferably between 7.0 and 10.5, even more preferably between 7.5 and 10.0. This can be done by adding carbon dioxide to the liquid aqueous medium and / or an acidifying agent. For this purpose, any suitable acidifying agent as known in the art can be used. Preferably, the acidifying agent is selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, carboxylic acids such as acetic acid, formic acid and carbonic acid.

[0061] At the beginning of process step a) or a2), the temperature of the reaction medium is preferably between 65 and 100 °C, more preferably between 68 and 95 °C, even more preferably between 70 °C and 90 °C.

[0062] During the step a) or a2), the carbon dioxide is advantageously added to the aqueous liquid medium at gaseous state. As the skilled person is familiar with, gaseous carbon dioxide, when added to a liquid aqueous, gets dissolved therein into carbonic acid, which itself is in equilibrium with ionic species (HCCh', CO32) in respective amounts that depend on the pH of the aqueous liquid medium. For example, when the pH of the aqueous liquid medium is about 8.0 to 9.0, HCCh' is the predominant ionic species in the aqueous liquid medium.

[0063] Furthermore, during the step a2), all or part, preferably all, of the carbon dioxide is added continuously in the aqueous liquid medium. Also preferably, during the step a2), all or part, preferably all, of the silicate is added continuously to the aqueous liquid medium. More preferably, during the step a2), all or part of the carbon dioxide and all or part of the silicate are added continuously and simultaneously in the aqueous liquid medium. Still more preferably, during the step a2), all of the carbon dioxide and all of the silicate are added continuously and simultaneously in the aqueous liquid medium.

[0064] It is preferred that after adjusting the pH value of the liquid medium the silicate and / or the carbon dioxide are added to the liquid medium in step a) or a2) at a temperature preferably between 65 and 100 °C, more preferably between 68 and 95 °C, even more preferably between 70 and 95 °C. In one preferred embodiment of the invention, the step a) or a2) is carried at a constant temperature, preferably between 70 and 92 °C. In another preferred embodiment, the temperature at the start of step a or a2) is preferably maintained between 70 to 75°C or 75 to 82 °C; then, the temperature is increased in few minutes, preferably up to a value of 80 to 85 °C or 90 to 95 °C, at which it is maintained until the end of step a) or a2).

[0065] It is preferred that the addition of the silicate and / or carbon dioxide to the aqueous liquid medium in step a) or a2) is carried out for 50 to 80 minutes, more preferably for 55 to 75 minutes, particular preferably for 60 minutes. The pH value of the reaction medium during the addition of the silicate and / or carbon dioxide should be remained at a value as given above with respect to the basic pH used in step a) or a2).

[0066] The carbon dioxide flow rate, the silicate flow rate and the pH of the aqueous liquid medium are controlled by appropriated systems, and, if needed, adjusted during part or all of the step a) or a2) to ensure that the obtained first suspension comprising precipitated silica has a basic pH.

[0067] When all or part, especially when all, of the carbon dioxide is added continuously in the aqueous liquid medium during the step a) or a2) at a flow rate, especially when all of the carbon dioxide is added continuously in the aqueous liquid medium during the step a) or a2) at a flow rate, keeping this flow rate at a constant value or in a range between a lower limit and an upper limit has been found advantageous to manufacture a precipitated silica exhibiting superior properties as discussed herein. So, to ensure that the carbon dioxide flow rate is kept at the desired constant value or within the desired limits of the range, it has been found advantageous to control said carbon dioxide flow rate and to adjust it, if needed, during part or all of the step a) or a2). Advantageous, the same applies, mutatis mutandis, to the silicate when all or part of it is added continuously in the aqueous liquid medium during the step a) or a2).

[0068] When all or part of the carbon dioxide and all or part of the silicate are added continuously in the aqueous liquid medium during the step a) or a2) in accordance with a flow rate ratio rf carbon dioxide flow rate /

[0069] / silicate flow rate, especially when all of the carbon dioxide and all of the silicate are added continuously in the aqueous liquid medium during the step a) or a2) in accordance with a flow rate ratio “rf ’ as previously defined, keeping this flow rate ratio “rf ’ at a constant value or in a range between a lower limit and an upper limit has been found much advantageous to manufacture a precipitated silica exhibiting superior properties. So, to ensure that the flow rate ratio “rf ’ is kept at the constant desired value or within the desired limits of the range, it has been found advantageous to control both the carbon dioxide flow rate and the silicate flow rate, and to adjust one or both of them, if needed, during part or all of the step a) or a2). Preferred ranges for the carbon dioxide flow rate can be determined based on the examples, the preferred ranges encompassing the exemplified values.

[0070] As above indicated, part or all of the step a) or a2), preferably all of the step a) or a2), of the invented process is operated at a basic pH as defined above. Keeping the pH basic during part or all, preferably during all, of the step a) or a2), especially keeping the pH basic at a constant value greater than 7.0 or in a range between a lower limit and an upper limit as mentioned above, the produced precipitated silica exhibiting superior properties as demonstrated in the examples.

[0071] In a particular preferred embodiment of the invention, the process step a) of the process according to the invention is conducted in the following manner:

[0072] (i) Forming initial heel at a temperature ranging between 70 and 100 °C, for example, between 80 and 92 °C, comprising a silicate, and an aqueous liquid medium, preferably water. It is further preferred that the concentration of silicate in said initial tank base, expressed in SiCh equivalent, being less than 100 g / L, more preferably less than or equal to 80 g / L, even more preferably equal to or less than 78 g / L.

[0073] (ii) Preferably completing said initial heel, at a temperature between 70 and 100 °C, for example between 80 and 92 °C, with the addition of an electrolyte, for example an anhydrous sodium sulfate or sodium carbonate or sodium bicarbonate, wherein the salt concentration in said initial heel, expressed as for example Na2SO4 or NaHCCh or Na2COs equivalent, is preferably less than or equal to 20 g / L, more preferably less than or equal to 15 g / L, while generally being greater than 6 g / L. The term “electrolyte” is understood herein as normally accepted, that is to say that it means any ionic or molecular substance which, when in solution, decompose or dissociates to form ions or charged particles. As suitable electrolytes mention may be made of alkali metals and alkaline earth metal salts, in particular the salt of the starting silicate metal and of the acidifying agent as defined above.

[0074] The aqueous liquid medium including the silicate is agitated, preferably with an agitation speed between 150 and 325 rpm, more preferably at 250 rpm, maintained throughout the synthesis. The tank feed from steps (i) and (ii) generally has a pH ranging from 9.0 to 13.0. The pH of the reaction medium is monitored in real time.

[0075] (iii) Adding to said initial heel, at a temperature between 70 and 100°C, for example between 80 and 92°C, carbon dioxide and water, so as to adjust the pH of the reaction medium to a value between 7.0 and 9.0, preferably between 8.0 and 8.3 (typically substantially equal to 8), and to maintain a silica concentration profile over time relative to the acidic pathway. The concentration of gaseous carbon dioxide is preferably 100% and can be injected via a diffuser (sparger). The diffuser may have an internal diameter of for example 2 to 3 mm. The flow rate of carbon dioxide in step (iii) is preferably from 10 to 50 L / min, more preferably from 10 to 15 L / min for approximately 20 to 30 minutes and then from 30 to 40 L / min for approx. 15 to 20 minutes.

[0076] (iv) Adding, in the resulting medium, at a temperature between 80 and 100°C, for example between 80 and 92°C, preferably simultaneously, a silicate, gaseous carbon dioxide as gaseous acidifying agent, and water, the respective quantities of silicate, acidifying agent, and water added over time being chosen so that, throughout the addition.

[0077] The pH of the reaction medium remains between 7.0 and 9.0, preferably between 8.0 and 8.3 (typically substantially equal to 8). The flow rate of carbon dioxide in step (iv) is preferably from 30 to 40 L / min for 20 to 30 minutes, and the silicate concentration in the medium, expressed as SiCh equivalent, is preferably less than or equal to 55 g / L, more preferably less than or equal to 52 g / L.

[0078] According to the invention, the gas liquid contactor, also known as gas liquid reactors, is advantageously a reactor adapted to the coexistence of these two phases. There are various gas liquid contacting reactors whose performance is dependent on interfacial contact area. In the context of the invention, gas is with bubble shape dispersion bubbling column reactor in the liquid phase or more preferably stirring bubbling tank reactor. The gas dispersion in the liquid may be achieved by different types of contactors: packed columns, spray column, tray column, bubble column, agitated reactors.

[0079] In the context of the invention, a continuous stirred-tank reactor is preferably used. The continuous stirred-tank reactor offers advantages as excellent mixing of the reactants, ensuring uniform contact between the carbon dioxide and liquid phases. It promotes efficient mass transfer enhancement between gas-liquid and reaction kinetics, leading to improved conversion rates. The continuous stirred- tank reactor allows precise control over reaction conditions such as temperature, pressure and residence time. This control is needed for optimizing reaction efficiency and product quality. The design of a continuous stirred-tank reactor is simple and scalable.

[0080] After carrying out process step a) or a2) as described above, the first suspension obtained in this process step is subjected to solid liquid separation process to obtain a solid product, also referred as cake (process step b)). The obtained cake may be washed, if necessary. According to the invention, the separation step b) and the optional washing step c) are preferably carried out such that the obtained solid product (cake) has a basic pH, more preferably are carried out such that the obtained solid product has the same pH as the first suspension obtained in process step a). The pH value of the solid product, also referred as cake, can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or SiCh powder”).

[0081] In addition to the cake aqueous sodium carbonate mother liquors are obtained in this process step. The separation of the mother liquor from the cake can be carried out by any appropriate mechanical separating means, for example by belt filter, a rotary filter, by centrifugation, or more preferably by press filtration. By using a filter, the obtained cake is also called “filter cake”.

[0082] The mother liquor collected from the mechanical separation consists of an aqueous sodium carbonate and sodium bicarbonate mother liquors. It may advantageously be used to concentrate the mother liquors solution into aqueous sodium carbonate. Therefore, the mother liquors are subjected to thermal decomposition process at an elevated temperature above about 60 °C, preferably at a temperature in the range of from 60 °C to 150 °C, at atmospheric pressure, more preferably at a temperature in the range of from 90 °C to 110 °C, for time sufficient to thermal decomposition process usually for about 5 minutes to about 10 hours, preferably for about 15 minutes to about 2 hours.

[0083] The aqueous sodium carbonate and sodium bicarbonate mother liquors from the sodium bicarbonate thermal decomposition process are substantially saturated aqueous solutions from which sodium carbonate and sodium bicarbonate crystals may be crystallized as stable crystal phases and recovered from the mother liquor. This is normally effected in an evaporator-crystallizer. The solution is passed in N series through crystallization units, preferably “multiple effect” evaporator crystallizers. N crystallizers are fed the aqueous sodium carbonate solution and the feed passes through the crystallizers. As the aqueous sodium carbonate solution passes through the crystallizers, a slurry of sodium carbonate precursor crystals is formed and passed to each succeeding crystallizer. The slurry, after removal from the last of the multiple effect crystallizers is separated into the sodium carbonate precursor crystals and the mother liquor, for instance by a centrifuge. The crystals are either dried and stored or passed to a dryer or calciner and converted to soda ash. The mother liquor is then recycled to the system passing through the first effect evaporator crystallizer.

[0084] According to the invention, subsequently to steps (b) and optionally (c), the cake is then generally subjected to a disintegration (liquefaction) operation. The term "liquefaction" describes a process that may comprise a step of disintegrating the cake obtained at the end of the compacting step (or the optional lump breaking step as indicated below). The disintegrating step is a fluidification or liquefaction operation, in which the cake is rendered liquid, the precipitated silica being again in suspension. In general, this operation in particular makes it possible to lower the viscosity of the suspension to be dried subsequently. This operation may thus be done by subjecting the cake to a chemical action for example, by adding an aluminium compound such as sodium aluminate, and / or acid, preferably coupled with a mechanical action (for example, by passing through a tub that is continuously agitated or in a colloid-type mill or in an extruder)

[0085] The expressions “liquification step”, “liquification operation” or “disintegration” are interchangeably intended to denote a process wherein the filter cake is transformed into a flowable suspension, which can be then easily dried. After the liquefaction step the filter cake is in a flowable, fluid-like form and the precipitated silica is in suspension.

[0086] The liquefaction step may comprise a mechanical treatment which results in a reduction of the granulometry of the silica in suspension. Said mechanical treatment may be carried out by passing the filter cake through a high shear mixer, an extruder, a colloidal-type mill or a ball mill. Alternatively, the liquefaction step may be carried out by subjecting the filter cake to a chemical action by addition for instance of an acid (mineral or organic) or an aluminum compound, for example sodium aluminate. Still alternatively, the liquefaction step may comprise both a mechanical treatment and a chemical action.

[0087] The filter cake subjected to the disintegration step may be a mixture of more than one filter cake each one obtained from the filtration of a silica suspension, or a part of the silica suspension, obtained from the precipitation step. The filter cake may optionally be washed or rinsed before the disintegration step.

[0088] According to the invention, it is preferred that the disintegration (liquefication) operation is conducted such that second suspension obtained in said step has a basic pH, more preferably has the same basic pH as the first suspension obtained in process step a). The pH of the second suspension can be determined by any method usually used in the art; in particular, it can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or Si O2 powder”).

[0089] Subsequently to step d), step e) is performed which spray is drying the second slurry by applying the method for spray drying an aqueous slurry comprising precipitated silica in a spray drier with a drying gas to obtain a dried precipitated silica. Preferably, the dried precipitated is in a form of powder or beads.

[0090] For drying the precipitated silica any suitable type of spray dryer may be used, especially a turbine, nozzle, liquid-pressure or two-fluid type spray dryer. In general, when the filtration is carried out by means of a filter press, a nozzle spray dryer is used, and when the filtration is carried out by means of a vacuum filter, a turbine spray drier is used. When drying is carried out by means of a nozzle spry dryer, the precipitated silica can then be obtained is usually in the form of approximately spherical beads.

[0091] Preferably, the drying step e) of the process of the invention is conducted such that the dried precipitated silica has a basic pH, which can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or SiO? powder”). More preferably, the dried precipitated silica has the same pH as the second suspension obtained in process step d).

[0092] After drying the precipitated silica, a milling step f) may then be carried out on the recovered precipitated silica. The precipitated silica that can then be obtained is generally in the form of a powder.

[0093] The dried and milled precipitated silica as indicated above may optionally subjected to an agglomeration step g). Said agglomeration step consists, for example, of direct compression, wet granulation (that is to say with the use of a binder such as water, a silica suspension, etc.), extrusion or, preferably, dry compacting. When the latter technique is used, it may prove opportune, before carrying out the compacting operation, for the pulverulent products to undergo deaeration to remove the air included in the products and to ensure that they are more uniformly compacted. The silica that can then be obtained by this agglomeration step is generally in the form of granules.

[0094] The optional milling step and the optional agglomeration step of the process of the invention are preferably carried out such that the pH of the obtained precipitated silica is basic, more preferably are carried out such that the pH of the dried precipitated silica obtained in step e) is maintained. The pH of the precipitated silica obtained in the optional milling step f) and in the option agglomeration step g) can be determined by the method as described in the examples below (see chapter 4.) entitled “pH measurement of a cake / slurry or SiCh powder”).

[0095] In a specific embodiment of the invention, it is preferred that the pH of the first suspension obtained in step a) is maintained throughout the whole process.

[0096] A very preferred process in accordance with the invention is a process for the manufacture of the precipitated silica as above described, said process comprising the steps of a) reacting a silicate with carbon dioxide in an aqueous liquid medium to obtain a first suspension comprising precipitated silica; b) separating the precipitated silica of the first suspension from the aqueous liquid medium of the first suspension to obtain a cake; c) optionally washing the cake; d) subjecting the cake to a disintegration operation in order to obtain a second suspension of precipitated silica; e) spray drying the second suspension in a spray drier with a drying gas to obtain a dried precipitated silica; f) optionally milling the dried precipitated silica; g) optionally agglomerating the optionally milled dried precipitated silica into granules; wherein all or part of the step a) is operated at a basic pH, wherein the process step a) is carried out such that the first suspension has a basic pH, wherein the separation step b) and the optional washing step c) are conducted such that the obtained cake has a basic pH, wherein the drying step e) is conducted such that the dried precipitated silica has a basic pH, and wherein the optional milling step f) and the optional agglomeration step g) are carried out such that the pH of the obtained precipitated silica is basic.

[0097] In a particular embodiment, said very preferred process consists of process steps a), b), d) and e), and optionally of c), f) and / or g) as defined above.

[0098] An even more preferred process in accordance with the invention is a process for the manufacture of the precipitated silica as above described, said process comprising the steps of a) reacting a silicate with carbon dioxide in an aqueous liquid medium to obtain a first suspension comprising precipitated silica; b) separating the precipitated silica of the first suspension from the aqueous liquid medium of the first suspension to obtain a cake; c) optionally washing the cake; d) subjecting the cake to a disintegration operation in order to obtain a second suspension of precipitated silica; e) spray drying the second suspension in a spray drier with a drying gas to obtain a dried precipitated silica; f) optionally milling the dried precipitated silica; g) optionally agglomerating the optionally milled dried precipitated silica into granules; wherein all or part of the step a) is operated at a basic pH, wherein the process step a) is carried out such that the first suspension has a basic pH, wherein the separation step b) and the optional washing step c) are conducted such that the obtained cake has a basic pH, wherein the disintegration operation step d) is conducted such that the second suspension has a basic pH, wherein the drying step e) is conducted such that the dried precipitated silica has a basic pH, and wherein the optional milling step f) and the optional agglomeration step g) are carried out such that the pH of the obtained precipitated silica is basic.

[0099] In a particular embodiment, said even more preferred process consists of process steps a), b), d) and e), and optionally of c), f) and / or g) as defined above.

[0100] The precipitated silica of the invention can be used in numerous applications, for example as catalyst support, in polymer, especially elastomer, compositions, as viscosifying, texturizing or anti-tacking agent, as battery separator component, or as additive for toothpaste, concrete or paper feedstock.

[0101] Preferably, the precipitated silica is used in a composition based on a matrix compound as a filler. The expression composition “based on” should be understood as meaning a composition comprising the precipitated silica of the invention on the one hand and a further compound, especially a matrix compound and / or one or more reaction product(s) of the matrix compound, on the other hand.

[0102] The matrix compound is preferably a polymer, more preferably an elastomer. The polymer preferably exhibiting at least one transition temperature of between -150°C and +300°C, for example between -150°C and +20°C.

[0103] The composition may be based on one or more polymers or copolymers.

[0104] The expression “copolymer” is used herein to refer to polymers comprising recurring units deriving from at least two monomeric units of different nature. Mention may in particular be made, as possible polymers, of diene polymers, in particular diene elastomers.

[0105] For example, use may be made of polymers or copolymers deriving 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 their mixtures; mention may also be made of functionalized elastomers, that is elastomers functionalized by chemical groups positioned along the macromolecular chain and / or at one or more of its ends (for example by functional groups capable of reacting with the surface of the silica), and halogenated polymers. Mention may be made of polyamides, ethylene homo- and copolymers, propylene homo- and copolymers.

[0106] The polymer (copolymer) can be a bulk polymer (copolymer), a polymer (copolymer) latex or else a solution of polymer (copolymer) in water or in any other appropriate dispersing liquid.

[0107] Among diene elastomers mention may be made, for example, of polybutadienes (BRs), polyisoprenes (IRs), butadiene copolymers, isoprene copolymers, or their mixtures, and in particular styrene / butadiene copolymers (SBRs, in particular ESBRs (emulsion) or SSBRs (solution)), isoprene / butadiene copolymers (BIRs), isoprene / styrene copolymers (SIRs), isoprene / butadiene / styrene copolymers (SBIRs), ethyl ene / propylene / diene terpolymers (EPDMs), and also the associated functionalized polymers (exhibiting, for example, pendant polar groups or polar groups at the chain end, which can interact with the silica).

[0108] Mention may also be made of natural rubber (NR) and epoxidized natural rubber (ENR).

[0109] The polymer compositions can be vulcanized with sulfur or crosslinked, in particular with peroxides or other crosslinking systems (for example diamines or phenolic resins). In general, the polymer compositions additionally comprise at least one (silica / polymer) coupling agent and / or at least one covering agent; they can also comprise, inter alia, an antioxidant.

[0110] Non-limiting examples of suitable coupling agents are for instance "symmetrical" or "unsymmetrical" silane poly sulfides; mention may more particularly be made of bis((Ci-C4)alkoxyl(Ci-C4)alkylsilyl(Ci-C4)alkyl) polysulfides (in particular disulfides, trisulfides or tetrasulfides), such as, for example, bis(3-(trimethoxysilyl)propyl) polysulfides or bis(3- (triethoxysilyl)propyl) polysulfides, such as triethoxysilylpropyl tetrasulfide. Mention may also be made of monoethoxy dimethyl silylpropyl tetrasulfide. Mention may also be made of silanes comprising masked or free thiol functional groups.

[0111] The coupling agent can be grafted beforehand to the polymer. It can also be employed in the free state or grafted at the surface of the silica. It is the same for the optional covering agent. The proportion by weight of the precipitated silica of the invention in the composition can vary within a fairly wide range. It normally represents from 10% to 200% by weight, in particular from 20% to 150% by weight, especially from 20% to 80% by weight (for example from 30% to 70% by weight) or from 80% to 120% by weight (for example from 90% to 110% by weight), of the amount of the polymer(s).

[0112] The precipitated silica according to the invention can advantageously constitute all of the reinforcing inorganic filler and even all of the reinforcing filler of the composition.

[0113] However, the precipitated silica according to the invention can optionally be combined with at least one other reinforcing filler, such as, in particular, a commercial highly dispersible silica, such as, for example, Zeosil® Premium, Zeosil® Z1165MP or Zeosil® Z1115MP (commercially available from Solvay), a treated precipitated silica (for example, a precipitated silica "doped" using a cation, such as aluminum); another reinforcing inorganic filler, such as, for example, alumina, indeed even a reinforcing organic filler, in particular carbon black (optionally covered with an inorganic layer, for example of silica).

[0114] The compositions comprising the precipitated silica of the invention may be used for the manufacture of a number of finishing articles.

[0115] Non-limiting examples of finished articles comprising at least one of the polymer compositions described above are for instance of a part of a shaped article, footwear soles, floor coverings, gas barriers, flame-retardant materials and also engineering components, such as rollers for cableways, seals for domestic electrical appliances, seals for liquid or gas pipes, braking system seals, pipes (flexible), sheathings (in particular cable sheathings), cables, engine supports, battery separators, conveyor belts, transmission belts or. In particular it is preferred that precipitated silica is used for tires or for a part of a shaped article, even more preferably for tire treads (especially for light vehicles or for heavy -goods vehicles, e.g. trucks).

[0116] The composition comprising the precipitated silica of the invention may be used in oral care applications, preferably as an additive for toothpaste.

[0117] The present invention thus further concerns an oral care composition, preferably a toothpaste composition, comprising the precipitated silica of the invention.

[0118] The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only and are not used to limit the present invention thereto. Examples

[0119] Measurement Methods

[0120] 1.) Infrared Absorption Spectrum

[0121] The infrared absorption spectrum of each sample as discussed below was obtained by surface infrared analysis.

[0122] The surface infrared analysis can be carried out on a Bruker Equinox 55 spectrometer on a pellet of the pure product.

[0123] The pellet is typically obtained after grinding the silica as is in an agate mortar and pelleting at 2 T / cm2for 10 seconds. The diameter of the pellet is generally 7 mm. The weight of the pellet is between 10 and 20 mg.

[0124] The obtained pellet was placed in a high vacuum chamber (10‘5mbar) of the spectrometer. Acquisition took place under high vacuum and the following conditions: wavelength: from 400 cm’1to 6000 cm’1; number of scans: 100; resolution: 2 cm’1;

[0125] - temperature / period: 1.) 25 °C at atmospheric pressure, and

[0126] 2.) 25 °C under vacuum (10‘5mbar) for 1 hour (desorption of the residual water).

[0127] The spectra were standardized using the instrument software OPUS version 7.5 supplied by Bruker Optik GmbH as follows:

[0128] Baseline correction: The baseline correction is carried out with the tool baseline in the OPUS software. In the baseline tag, used start interactive mode. Then, in the start interactive mode, choose straight lines program and 0 iteration because it is necessary to define the baseline manually. On the spectra up the window, right click to shift on the manual mode. Then select different points on the spectra (5500, 4000, 3800, 2500, 2200, 1800 & 1600 cm’1). After selection, push on store to save the baseline correction.

[0129] Normalization spectra: The SiCh fingerprint peak at 1870 cm’1was scaled to 0.2 absorbance units (to normalize the spectra samples to the same mass of SiCh) by using the tag spectrum calculator.

[0130] Determination of the area under the band between 2500 to 3000 cm1and the area band between 1736 and 2110 cm1: used the tag integration and then create two different methods with set-up method • Method 1 : select model B left edge: 2110 cm’1and right edge 1736 cm’1.

[0131] Then, save the method by clicking on store method

[0132] • Method 2: select model B left edge: 3000 cm’1and right edge 2500 cm’1Then, save the method by clicking on store method

[0133] To calculate each integration, the methodology to apply is the following: Select the tag integration and click on the load integration method. Select the method 1 or the method 2 and click on the open button. Then click on the integrate button. The result is obtained on the link “integ” below the name of the spectra.

[0134] Finally, the ratio between the value obtained on the range 2500 cm’1to 3000 cm’xand the value obtained on the range 1736 cm’1and 2110 cm’1is calculated.

[0135] According to the invention, the range in the infrared absorption spectrum taken into consideration was from 2500 cm’1to 3000 cm’1for the carbonates and from 1736 cm’1and 2110 cm’1for the SiCh structure band.

[0136] 2.) Specific surface area (BET)

[0137] The specific surface area (BET) of the silica was determined according to the Brunauer-Emmett-Teller method (BET method) described in “The Journal of the American chemical Society, 60, 309 (1938)”, and corresponding to the standard NF ISO 5794-1, Appendix E (June 2010) with the following adjustments: the sample was pre-dried at 160 °C ± 10 °C; the partial pressure used for the measurement P / P° was between 0.05 and 0.2.

[0138] 3.) CT AB surface area

[0139] The CTAB surface area was a measure of external specific surface area and is determined according to the standard NF ISO 5794-1, Appendix G (June 2010).

[0140] 4.) pH measurement of a cake / slurry or SiO 2 powder

[0141] Depending on the moisture content measured on the silica sample (cake, slurry or powder) an aqueous suspension is prepared containing 5 ± 0.5% silica. The final mass of the suspension should be equal to 200 grams z m (SiO2)to weiqh = — — — — —1-0- — —

[0142] 100 — % Humidity The measurement method is conducted at room temperature (typically about 20°C). It includes the following steps:

[0143] Taring the beaker;

[0144] - Weighing the desired quantity previously determined on the basis of its moisture content;

[0145] - Making up to 200+ / - 0.5 g with demineralized water;

[0146] - Mixing until the suspension is completely homogenized; dipping the pH electrode into the suspension after calibration with pH 4.01; and 10.2 buffer solutions;

[0147] - Waiting for measurement to stabilize; and Reading the pH value indicated.

[0148] 5.) Na2SO4 / Na2CO content

[0149] As used herein the “Na2SO4 / Na2CO3 content” does not refer to a ratio but to the amount of the salts, namely sodium sulfate and / or sodium carbonates, like Na2CC>3 and / or NaHCCh, present at the surface of the silica sample and estimated by conductivity measurements according to the following method.

[0150] Operating mode:

[0151] 1. Measure the dry extract of the product to be analyzed using a thermobalance following one of the dedicated procedures.

[0152] 2. Calibrate the conductivity probe according to the manufacturer’s recommendations.

[0153] 3. Calibrate the pH electrode with buffer solutions 7 and 4.

[0154] 4. Prepare at least 100 g of a 5 %wt. SiO2 suspension by adding purified water.

[0155] 5. Thoroughly deagglomerate the product by magnetic stirring or Ultraturrax until a homogeneous suspension is obtained.

[0156] 6. Perform the conductivity measurement, noting the temperature at which the measurement is taken.

[0157] 7. Perform the pH measurement.

[0158] Expression of the results:

[0159] It is assumed that the ionic conductivity of the suspension is solely due to the sodium sulfate or sodium carbonates present in the solution. In particular, the conductivity of silica or other ionic impurities is neglected. SAMPLES

[0160] SAMPLE 1: Preparation of a first precipitated silica

[0161] (Working example)

[0162] 17700 g of water and 10700 g of an aqueous solution of sodium silicate at 240 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade propeller.

[0163] The weight ratio (Rp) of SiCh / Na?© of the sodium silicate used being 3.45. After starting the agitation (250 rpm), the tank feed thus constituted was heated to 79°C, and the pH was adjusted to 8.15 in 36 minutes by adding pure gas, carbon dioxide (average flow rate of 23 L per minute), and water (average flow rate of 315 grams per minute).

[0164] After 20 minutes of acidification by carbon dioxide, the temperature rises from 79°C to 90°C in 15 minutes.

[0165] Once the pH of 8.15 was reached, 2515 g of an aqueous solution of sodium silicate (Rp = 3.45) at 240 g / L in SiO? equivalent were simultaneously added at a rate of 126 g / min (addition duration: 20 minutes), along with 1230 g of pure CO2 gas at a rate of 35 L / min and 2760 g of water at a rate of 138 g / min, to maintain the pH of the medium at a value equal to 8.25 (within 0.1 pH unit). The temperature is maintained at 90°C throughout simultaneous addition. After the 20- minute addition, the addition of silicate and water was stopped, and the gaseous introduction of CO2 was continued until the pH of the reaction mixture stabilized at 8.

[0166] The solution was allowed to mature under stirring for 5 minutes. The resulting slurry was then filtered on a flat filter, and the obtained filtration cake was disintegration with water and with the addition of dilute sulfuric acid at 80 g / L. The disintegration cake obtained has a loss on ignition at 160°C greater than 85%. It was then dried by atomization (spraying).

[0167] The physico-chemical characteristics of the precipitated silica obtained, in powder form, are as follows:

[0168] Aqueous extract pH: 9.2

[0169] Na2SO4 / Na2COs content: 1.20% (relative to the total mass of the material in the dry state)

[0170] CTAB specific surface area: 153 m2 / g

[0171] BET specific surface area: 151 m2 / g

[0172] IR area under peak 2500 cm’1and 3000 cm’1: 7.7 cm’1 IR area ratio: 0.35

[0173] SAMPLE 2: Preparation of a second precipitated silica

[0174] (Reference example)

[0175] 17616 g of water and 10800 g of an aqueous solution of sodium silicate at 238 g / L in SiCL equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade propeller.

[0176] The weight ratio (Rp) of SiCh / Na?© of the sodium silicate used being 3.42. After starting the agitation (250 rpm), the tank feed thus constituted was heated to 78°C, and the pH was adjusted to 8.15 in 34.4 minutes by adding pure gas, carbon dioxide (average flow rate of 24 L per minute), and water (average flow rate of 328 grams per minute).

[0177] After 20 minutes of acidification by carbon dioxide, the temperature rises from 78°C to 90°C in 15 minutes

[0178] Once the pH of 8.15 was reached, 2530 g of an aqueous solution of sodium silicate (Rp = 3.42) at 238 g / L in SiO? equivalent were simultaneously added at a rate of 126.5 g / min (addition duration: 20 minutes), along with 1657 g of pure CO2 gas at a rate of 47 L / min and 2753 g of water at a rate of 138 g / min, to maintain the pH of the medium at a value equal to 8.15 (within 0.1 pH unit). The temperature is maintained at 90°C throughout simultaneous addition. After the 20- minute addition, the addition of silicate and water was stopped, and the gaseous introduction of CO2 was continued until the pH of the reaction mixture stabilized at 8.15.

[0179] After the simultaneous addition, an acidification of 14888 g of a mineral agent, sulfuric acid at a mass concentration of 8.2%, was carried out at a flow rate of 878 g / min for 17 minutes.

[0180] After the acidification, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0181] The solution was allowed to mature under stirring for 5 minutes. The resulting slurry was then filtered on a flat filter, and the obtained filtration cake was disintegration with water and with the addition of dilute sulfuric acid at 80 g / L. The disintegration cake obtained has a loss on ignition at 160°C greater than 85%. It was then dried by atomization (spraying).

[0182] The physico-chemical characteristics of the precipitated silica obtained, in powder form, are as follows:

[0183] Aqueous extract pH: 7.5 Na2SO4 / Na2COs content: 0.80% (relative to the total mass of the material in the dry state)

[0184] CTAB specific surface area: 164 m2 / g

[0185] BET specific surface area: 169 m2 / g

[0186] IR area under peak 2500 cm’1and 3000 cm’1: 6.3 cm’1

[0187] IR area ratio: 0

[0188] SAMPLE 3: Preparation of a third precipitated silica

[0189] (Working example)

[0190] 22194 g of water and 670 g of an aqueous solution of sodium silicate at 238 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade impeller.

[0191] The weight ratio (Rp) of SiO2 / Na2O of the sodium silicate used being 3.47.

[0192] After starting the agitation (250 revolutions per minute), the tank base thus formed was heated to 72 °C, and the pH was adjusted to 8.75 in 5.2 minutes by adding a pure gas, carbon dioxide (average flow rate of 6.6 L per minute), and water (average flow rate of 137 grams per minute).

[0193] Once the pH of 8.75 was reached, a simultaneous addition of 18818 g of an aqueous solution of sodium silicate (Rp = 3.47) at 238 g / L in SiO2 equivalent was carried out, at a flow rate of 228 g / min (addition duration: 82.5 minutes), 1624 g of pure CO2 gas at a flow rate of 11.1 L / min, and 7293 g of water at a flow rate of 303 g / min (addition duration: 24.5 minutes), in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit).

[0194] After 17 minutes of simultaneous addition, the temperature changes from 72°C to 82°C in 8 minutes and then the temperature is maintained at 82°C throughout the simultaneous addition.

[0195] After the simultaneous addition, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0196] The obtained slurry was then filtered on a flat filter, and the filtration cake obtained was disintegration with water and with the addition of sulfuric acid diluted to 80 g / L.

[0197] The disintegration cake obtained has a loss on ignition at 160 °C greater than 84%. It was then dried by atomization (spraying).

[0198] The physico-chemical characteristics of the obtained precipitated silica, in powder form, are as follows:

[0199] Aqueous extract pH: 9.1 Na2SO4 / Na2COs content: 1.4% (relative to the total mass of the dry material)

[0200] CTAB specific surface area: 159 m2 / g

[0201] BET specific surface area: 173 m2 / g

[0202] IR area under peak 2500 cm’1and 3000 cm’1: 9.3 cm’1

[0203] IR area ratio: 0.39

[0204] SAMPLE 4: Preparation of a fourth precipitated silica

[0205] (Working example)

[0206] 22140 g of water and 670 g of an aqueous solution of sodium silicate at 240 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade impeller.

[0207] The weight ratio (Rp) of SiO2 / Na2O of the sodium silicate used being 3.45.

[0208] After starting the agitation (250 revolutions per minute), the tank base thus formed was heated to 76 °C, and the pH was adjusted to 8.75 in 5.2 minutes by adding a pure gas, carbon dioxide (average flow rate of 6.6 L per minute), and water (average flow rate of 139 grams per minute).

[0209] Once the pH of 8.75 was reached, a simultaneous addition of 18762 g of an aqueous solution of sodium silicate (Rp = 3.45) at 240 g / L in SiO2 equivalent was carried out, at a flow rate of 284 g / min (addition duration: 66 minutes), 1675 g of pure CO2 gas at a flow rate of 14.2 L / min, and 7380 g of water at a flow rate of 306 g / min (addition duration: 24.5 minutes), in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit).

[0210] After 17 minutes of simultaneous addition, the temperature changes from 76°C to 82°C in 8 minutes and then the temperature is maintained at 82°C throughout the simultaneous addition.

[0211] After the simultaneous addition, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0212] The obtained slurry was then filtered on a flat filter, and the filtration cake obtained was disintegration with water and with the addition of sulfuric acid diluted to 80 g / L.

[0213] The disintegration cake obtained has a loss on ignition at 160 °C greater than 85%. It was then dried by atomization (spraying).

[0214] The physico-chemical characteristics of the obtained precipitated silica, in powder form, are as follows:

[0215] Aqueous extract pH: 7.1

[0216] Na2SO4 / Na2COs content: 2.3% (relative to the total mass of the dry material) CTAB specific surface area: 161 m2 / g

[0217] BET specific surface area: 184 m2 / g

[0218] IR area under peak 2500 cm’1and 3000 cm’1: 5.2 cm’1

[0219] IR area ratio: 0.19

[0220] SAMPLE 5: Preparation of a fifth precipitated silica

[0221] (Reference example)

[0222] 22020 g of water and 680 g of an aqueous solution of sodium silicate at 233 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade impeller.

[0223] The weight ratio (Rp) of SiCh / Na?© of the sodium silicate used being 3.45.

[0224] After starting the agitation (250 revolutions per minute), the tank base thus formed was heated to 76 °C, and the pH was adjusted to 8.75 in 5.5 minutes by adding a pure gas, carbon dioxide (average flow rate of 6.7 L per minute), and water (average flow rate of 112 grams per minute).

[0225] Once the pH of 8.75 was reached, a simultaneous addition of 19044 g of an aqueous solution of sodium silicate (Rp = 3.45) at 233 g / L in SiO? equivalent was carried out, at a flow rate of 288 g / min (addition duration: 66 minutes), 1844 g of pure CO2 gas at a flow rate of 15.7 L / min, and 7306 g of water at a flow rate of 303 g / min (addition duration: 24.5 minutes), in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit).

[0226] After 17 minutes of simultaneous addition, the temperature changes from 76°C to 82°C in 8 minutes and then the temperature is maintained at 82°C throughout the simultaneous addition.

[0227] After the simultaneous addition, an acidification of 1808 g of a mineral agent, sulfuric acid at a mass concentration of 96%, was carried out at a flow rate of 91 g / min for 20 minutes.

[0228] After the acidification, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0229] The obtained slurry was then filtered on a flat filter, and the filtration cake obtained was disintegration with water and with the addition of sulfuric acid diluted to 80 g / L.

[0230] The disintegration cake obtained has a loss on ignition at 160 °C greater than 84%. It was then dried by atomization (spraying).

[0231] The physico-chemical characteristics of the obtained precipitated silica, in powder form, are as follows: Aqueous extract pH: 7.15

[0232] Na2SO4 / Na2COs content: 0.5% (relative to the total mass of the dry material)

[0233] CTAB specific surface area: 163 m2 / g

[0234] BET: 186 m2 / g

[0235] IR area under peak 2500 cm’1and 3000 cm’1: 3.7 cm’1

[0236] IR area ratio: 0

[0237] SAMPLE 6: Preparation of a sixth precipitated silica

[0238] (Reference example)

[0239] 28692 g of water and 17210 g of an aqueous solution of sodium silicate at 241 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade impeller.

[0240] The weight ratio (Rp) of SiCh / Na?© of the sodium silicate used being 3.5.

[0241] After starting the agitation (250 revolutions per minute), the tank base thus formed was heated to 79 °C, and the pH was adjusted to 8.15 in 37.4 minutes by adding a mineral acid, sulfuric acid at a mass concentration of 8.2% (average flow rate of 335 g per minute for 20 minutes then 582 g per minute for 17.4 minutes).

[0242] After 20 minutes of acidification with carbon dioxide, the temperature rises from 79°C to 92°C in 15 minutes.

[0243] Once the pH of 8.15 was reached, a simultaneous addition of 4051 g of an aqueous solution of sodium silicate (Rp = 3.5) at 241 g / L in SiO? equivalent was carried out, at a flow rate of 201 g / min (addition duration: 20 minutes), and 4860 g of a mineral acid, sulfuric acid at a mass concentration of 8.2% at a flow rate of 241 g / min, in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit). The temperature is maintained at 82°C throughout the simultaneous addition.

[0244] After the simultaneous addition, an acidification of 1916 g of a mineral agent, sulfuric acid at a mass concentration of 8.2%, was carried out at a flow rate of 185 g / min for 10 minutes.

[0245] After the acidification, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0246] The obtained slurry was then filtered on a flat filter, and the filtration cake obtained was disintegration with water and with the addition of sulfuric acid diluted to 80 g / L.

[0247] The disintegration cake obtained has a loss on ignition at 160 °C greater than 85%. It was then dried by atomization (spraying). The physico-chemical characteristics of the obtained precipitated silica, in powder form, are as follows:

[0248] Aqueous extract pH: 7.4

[0249] Na2SO4 / Na2COs content: 1.0% (relative to the total mass of the dry material)

[0250] CTAB specific surface area: 165 m2 / g

[0251] BET: 162 m2 / g

[0252] IR area under peak 2500 cm’1and 3000 cm’1: 0 cm’1

[0253] IR area ratio: 0

[0254] SAMPLE 7: Preparation of a seventh precipitated silica

[0255] (Reference example)

[0256] 35742 g of water and 1081 g of an aqueous solution of sodium silicate at 236 g / L in SiCh equivalent were introduced in a reactor equipped with a temperature and pH control system and a stirring system with a 3 -blade impeller.

[0257] The weight ratio (Rp) of SiCh / Na?© of the sodium silicate used being 3.45.

[0258] After starting the agitation (250 revolutions per minute), the tank base thus formed was heated to 72 °C, and the pH was adjusted to 8.75 in 5.3 minutes by adding a mineral acid, sulfuric acid at a mass concentration of 8.1% (average flow rate of 175 g per minute).

[0259] Once the pH of 8.75 was reached, a first simultaneous addition of 11484 g of an aqueous solution of sodium silicate (Rp = 3.45) at 236 g / L in SiO? equivalent was carried out, at a flow rate of 454 g / min (addition duration: 25.3 minutes), 11822 g of sulfuric acid at a mass concentration of 8.1% at a flow rate of 467.5 g / min, in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit).

[0260] The second simultaneous addition of 16400 g of an aqueous solution of sodium silicate (Rp = 3.45) at 236 g / L in SiCL equivalent was carried out, at a flow rate of 457 g / min (addition duration: 35.9 minutes), 1403 g of sulfuric acid at a mass concentration of 96% at a flow rate of 39 g / min, in order to maintain the pH of the medium at a value equal to 8.67 (within 0.1 pH unit).

[0261] After 17 minutes of simultaneous addition, the temperature changes from 76°C to 82°C in 8 minutes and then the temperature is maintained at 82°C throughout the simultaneous addition.

[0262] After the simultaneous addition, an acidification of 218 g of a mineral agent, sulfuric acid at a mass concentration of 96%, was carried out at a flow rate of 24 g / min for 20 minutes. After the acidification, maturation was carried out by leaving the solution under stirring for 5 minutes.

[0263] The obtained slurry was then filtered on a flat filter, and the filtration cake obtained was disintegration with water and with the addition of sulfuric acid diluted to 80 g / L.

[0264] The disintegration cake obtained has a loss on ignition at 160 °C greater than 85%. It was then dried by atomization (spraying).

[0265] The physico-chemical characteristics of the obtained precipitated silica, in powder form, are as follows:

[0266] Aqueous extract pH: 7.6

[0267] Na2SO4 / Na2COs content: 0.6% (relative to the total mass of the dry material)

[0268] CTAB specific surface area: 161 m2 / g

[0269] BET: 173 m2 / g

[0270] IR area under peak 2500 cm’1and 3000 cm’1: 0 cm’1

[0271] IR area ratio: 0

[0272] In the following table, it is shown the pH measured at the various steps during the process for the manufacture of the precipitated silica according to samples 1-7, described above:

[0273] In the samples produced according to the invention (samples from examples 1, 3 and 4 - working examples) the pH at the end of the synthesis of the precipitated silica (step a) is advantageously basic, and the drying step is also conducted such that the dried precipitated silica has a basic pH. The most preferred working examples are examples 1 and 3, wherein the samples of the second suspension obtained at the end of the disintegration step also have a basic pH. Preparation of silica-filled elastomeric compositions

[0274] Prior to their use in silica filled elastomeric composition the silicas of the samples as described above, in powder form, were granulated. The compositions, expressed as parts by weight per 100 parts of elastomers (phr), are described in Tables 1 and 2 below.

[0275] Table 1

[0276] Table 2

[0277] (1) Oil extended solution SBR, Buna VSL4526-2HM from Lanxess with 45% of vinyl units; 26% of styrene units; Tg of -30°C, 37.5phr of TDAE

[0278] (2) BR: Butyl Rubber Buna CB 25 from Lanxess

[0279] (3) TESPD: Bis[3-(triethoxysilyl)propyl] disulphide, Luvomaxx TESPD from Lehmann&Voss&Co

[0280] (4) Hydrocarbon resin SYLVATRAXX 4101 from Arizona Chemical

[0281] (5) 6PPD: N-(l,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6-PPD from Flexsys

[0282] (6) DPG: Diphenylguanidine, Rhenogran DPG-80 from RheinChemie

[0283] (7) CBS: N-Cyclohexyl-2-benzothiazolesulfenamide, Rhenogran CBS-80 from RheinChemie

[0284] Process for the preparation of the rubber compositions

[0285] The preparation of the rubber compositions was carried out in two successive preparation phases: a first phase of high-temperature thermomechanical working, followed by a second phase of mechanical working at temperatures of less than 110°C to introduce the vulcanization system. The first phase was carried out using a mixing device, of internal mixer type, of Brabender brand (capacity of 380mL).

[0286] In a first pass of the first phase the elastomers and the reinforcing filler (introduction in instalments) were mixed with the coupling agent, the plasticizers, the stearic acid, the 6-PPD, the DPG and then the ZnO. The duration was 4min 45 and the dropping temperature was about 160°C.

[0287] After cooling the mixture (temperature of less than 100°C), the vulcanization system was added during the second phase. It was carried out on an open mill, preheated to 50°C. The duration of this phase was between 2 and 6 minutes. Each final mixture was subsequently calendered in the form of plaques with a thickness of 2-3 mm.

[0288] Mechanical properties of the silica-filled elastomeric compositions (vulcanisates)

[0289] The measurements were carried out after vulcanization 40 min at 150° C

[0290] Uniaxial tensile tests were carried out in accordance with the instructions of the standard NF ISO 37 with test specimens of EE type at a rate of 500 mm / min on an Instron 68SC-5 device. The x% moduli, corresponding to the stress measured at x% of tensile strain, are expressed in MPa. The tensile strength is expressed in MPa; elongation at break is expressed in MPa.

[0291] A reinforcing index (RI) was determined which is equal to the ratio of the modulus at 300% strain to the modulus at 100% strain.

[0292] The measurement of the loss of mass by abrasion was performed according to the indications of standard DIN53516, using a Montech abrasimeter in which the cylindrical specimen is subjected to the action of an abrasive gauze of P60 grains and attached to the surface of a rotating drum at a contact pressure of 10 N and over a course of 40 meters. The value measured is a volume of loss of substance (in mm3) after abrasion wear; the smaller the value, the better the abrasion resistance.

[0293] The values for the loss factor (tan 5) and amplitude of elastic modulus in dynamic shear (AG’) were recorded on vulcanized samples (parallelepiped specimen: cross section 8 mm2and height 7 mm). The sample is subjected to a double alternating sinusoidal shear strain at a temperature of 40° C and at a frequency of 10 Hz. The strain amplitude sweeping processes were performed according to an outward-return cycle, proceeding outward from 0.1% to 50% and then returning from 50% to 0.1%. The values reported in are obtained from the return strain amplitude scanning and concern the maximum value of the loss factor (tan 5 max) and the amplitude of the elastic modulus (AG’) between the values at 0.1% and 50% of strain (Payne effect). Measurements were performed on a Metravib DMA+1000 according to standard ASTM D5992 (see Table 3).

[0294] Table 3

[0295] The results of the table above demonstrate that a polymer composition comprising a precipitated silica according to the invention shows better reinforcement (higher reinforcement index, higher modulus 300 %) and a lower energy dissipation at 40 °C in comparison to a composition that does not include the precipitated silica according to the invention.

Claims

CLAIMS1. A precipitated silica characterized by its infrared absorption spectrum having at least one peak between 2500 and 3000 cm’1and one peak between 1736 and 2110 cm’1, wherein the infrared absorption spectrum is measured after a treatment of the precipitated silica under vacuum at 25°C for 1 hour, and wherein the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is at least 0.05.

2. The precipitated silica according to claim 1, which is at least partially in particle form and which comprises at least one carbonate species, wherein at least a part of the carbonate species is on the surface of the precipitated silica particles.

3. The precipitated silica according to claim 1 or 2, of which the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is of at least 0.07, more preferably of at least 0.10 and still more preferably of at least 0.12.

4. The precipitated silica according to any one of claims 1 to 3, of which the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is of at most 0.75, preferably of at most 0.70, more preferably of at most 0.60, and still more preferably of at most 0.50.

5. The precipitated silica according to claim 4, of which the ratio (area under the peak between 2500 and 3000 cm’1) / (area under the peak between 1736 and 2110 cm’1) is in a range of from 0.15 to 0.50.

6. The precipitated silica according to any one of the preceding claims having a BET surface area ranging from 10 to 400 m2 / g.

7. The precipitated silica according to any one of the preceding claims having a CTAB surface area ranging from 10 to 400 m2 / g.

8. The precipitated silica according to any one of the preceding claims having an aqueous extract pH above 7.0, advantageously above 7.0 and of at most 10.5, possibly from 8.5 to 10.0.

9. A process for the manufacture of the precipitated silica according to any one of claims 1 to 8, said process comprising the steps of: a) reacting a silicate with carbon dioxide in an aqueous liquid medium to obtain a first suspension comprising precipitated silica;b) separating the precipitated silica of the first suspension from the aqueous liquid medium of the first suspension to obtain a cake; c) optionally washing the cake; d) subjecting the cake to a disintegration operation in order to obtain a second suspension of precipitated silica; e) spray drying the second suspension in a spray drier with a drying gas to obtain a dried precipitated silica; f) optionally milling the dried precipitated silica; g) optionally agglomerating the optionally milled dried precipitated silica into granules; wherein all or part of the step a) is operated at a basic pH, wherein the process step a) is carried out such that the first suspension has a basic pH, wherein the separation step b) and the optional washing step c) are conducted such that the obtained cake has a basic pH, wherein the drying step e) is conducted such that the dried precipitated silica has a basic pH, and wherein the optional milling step f) and the optional agglomeration step g) are carried out such that the pH of the obtained precipitated silica is basic.

10. The process according to claim 9, wherein the disintegration operation step d) is conducted such that the second suspension has a basic pH.

11. The process according to claim 9 or 10, wherein all of the step a) is operated at a basic pH, so that, upon completion of the step a), the first suspension has a basic pH.

12. The process according to claim 9 or 10 or 11, wherein the step a) comprises: al) providing a liquid aqueous medium a2) adding the silicate and the carbon dioxide to the liquid aqueous medium, wherein, during the step a2):- the carbon dioxide is added to the aqueous medium at gaseous state, and- part or all of the silicate and part or all of the carbon dioxide are added continuously and simultaneously to the liquid aqueous.

13. The process according to claim 12, wherein the carbon dioxide flow rate, the silicate flow rate and the pH of the aqueous liquid medium are controlled and, optionally adjusted during part or all of the step a2).

14. A precipitated silica obtained by the process according to any one of claims 9 to 13.

15. A composition based on a matrix compound, preferably an elastomer, and a precipitated silica according to any one of claims 1 to 8 or claim 14.

16. A finished article, preferably a tire, or a part of a shaped article, preferably a tire tread, comprising the silica according to any of claims 1 to 8 or claim 14 or the composition according to claim 15.

17. An oral care composition, preferably a toothpaste composition, comprising the silica according to any of claims 1 to 8 or claim 14.

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