Method for producing precipitated silica from plant ash, precipitated silica and its use in tire applications

Abstract

The invention relates to a method for producing precipitated silica from plant ash. The plant ash is used directly in the process, preferably without subjecting it to any pretreatment such as washing and / or incineration. The invention further relates to precipitated silica obtainable by said method and to the use thereof for producing filled elastomeric compositions or tyre parts and / or tyres.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European applications 23305439.4 and 23305440.2 filed on 29 March 2023 and European applications 23185252.6 and 23185224.5 filed on 13 July 2023, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] This invention relates to a method for producing precipitated silica from plant ash. The method comprises alkaline digestion of the plant ash to obtain a silicate solution, which is then reacted with an acidifying agent to precipitate silica. The method is characterized by subjecting the plant ash directly to alkaline digestion, preferably without any pretreatment such as washing and / or incineration. The invention further relates to precipitated silica—preferably obtainable or acquired by the method described above—and its use in the manufacture of filled elastomer compositions, tire components, and / or tires. Background Technology

[0004] Silicon dioxide (SiO2), also known as silica, is a common silicon compound found in nature. Naturally occurring silicon dioxide exists in both amorphous and crystalline forms, such as cristobalite, tridymite, and quartz, the latter being the main component of sand.

[0005] Quartz sand is often used to produce silicates (especially sodium silicate), which can be obtained, for example, by hydrothermally treating the quartz sand with a strong alkali such as sodium hydroxide, or by melting the quartz sand with sodium carbonate at a high temperature of about 1400°C-1500°C.

[0006] Sodium silicate can be used as is or as a raw material for the preparation of various inorganic materials, notably silica gel and precipitated silica. Precipitated silica is a form of synthetic silica in an amorphous form.

[0007] Both silicates and precipitated silica are versatile materials with a wide range of applications in the most diverse technological fields, from construction to detergents, tires, adhesives, food and pharmaceutical industries, and their global demand continues to increase.

[0008] However, the above-mentioned methods for producing precipitated silica have the following main drawbacks: the sand used as raw material is not a renewable resource on a human timescale, as its replenishment is achieved through rock erosion or weathering processes during geological periods.

[0009] Moreover, the aforementioned conventional method for manufacturing silica by sand fusion requires high energy consumption, since this method requires heating the reactants to high temperatures.

[0010] Therefore, it is clear that there is still a need to find a method for producing precipitated silica that is not only more sustainable in terms of the environment, but also cost-effective.

[0011] One possible renewable source that can be envisaged is ash deriving from the combustion of plants or plant parts, and in particular plant ash deriving from the combustion of plants rich in silica. In this regard, one particularly abundant biogenic source of silica is ash deriving from rice husks.

[0012] Rice husks are agricultural residues of the rice milling industry and are abundant in rice-producing countries. When burned, about 20% by weight of the rice husks is transformed into ash containing up to 97 wt.-% of silica.

[0013] In view of the large amount of silica contained in these ashes and their intrinsically renewable nature, many efforts have been made to try to extract silica from them, since this can represent an economically viable option for obtaining precipitated silica, which can also solve the problem of proper disposal of rice husks, which, as mentioned earlier, are waste of the milling industry.

[0014] However, one of the key factors involved in the use of plant ashes and in particular rice husk ash (RHA) as starting material concerns the complex nature and variable composition of said ashes, which generally contain, in addition to SiO2, other elements such as carbon, K, Mn, P, S, etc. Since for many applications, a high-purity precipitated silica is generally required, many efforts have been made to try to purify said ashes with the aim of reducing the content of the above-mentioned elements before the alkaline digestion of the ash.

[0015] WO 2019 / 168690 describes a method for the preparation of silicates from RHA. In this method, clean water is used in order to remove the impurities contained in the ash to levels < 250 ppm (S and CI) before the alkaline digestion of the rice husk ash in order to obtain high-purity silicates.

[0016] The main drawback of this method is that the washing step uses very large amounts of water, which could be used for other needs. This fact has a negative impact not only on the overall cost and complexity of the method, but also on the environment, since it causes a scarcity of resources on Earth.

[0017] IN 2020 / 21056035 discloses a process for the preparation of precipitated silica from RHA, wherein the RHA is incinerated (re-combusted) at a temperature of 900°C to 1025°C to remove moisture, carbon and any other volatile materials to obtain precipitated silica with high purity, prior to the alkaline digestion of ash.

[0018] In addition, in this case, this pre-treatment of the ash is energy consuming and has a negative impact on the economy and ecology of the process.

[0019] Therefore, there is still a need to develop an easy, environmentally friendly and cost-effective novel process for the production of precipitated silica. SUMMARY

[0020] The present invention relates to a process for the production of precipitated silica from plant ash, the process comprising the following steps:

[0021] (I) reacting plant ash containing SiO2 and potassium, the weight amount of potassium being at least 12.5 ‰ based on the weight of SiO2 contained in the plant ash, with a sodium-containing alkali metal base, preferably sodium hydroxide, in an aqueous reaction medium at a temperature of at least 100°C, so as to obtain an aqueous silicate solution, the aqueous silicate solution comprising (i) SiO2 in the form of silicate anions, (ii) a weight amount of sodium cations (Na + ) of at least 1.0 ‰ based on the weight of SiO2 contained in the silicate solution, and (iii) a weight amount of potassium cations (K + ) of at least 5.0 ‰ based on the weight of SiO2 contained in the silicate solution,

[0022] and

[0023] (II) reacting the aqueous silicate solution with an acidifying agent in an aqueous reaction medium having a pH exceeding 7.0 during at least a part of the duration of the reaction, so as to achieve precipitation of silica and to produce an aqueous slurry comprising SiO2 in particulate form.

[0024] According to a preferred embodiment, the process according to the present invention comprises, prior to step (I), a step (A) of combusting a plant and / or plant parts containing SiO2 and potassium, the weight amount of potassium being at least 12.5 ‰ based on the weight of SiO2 contained in the plant and / or plant parts, so as to obtain a plant ash.

[0025] The process of the present invention can comprise step (A) and does not contain any step (B) comprising re-combusting the plant ash, wherein said step (B) is subsequent to step (A) and prior to step (I).

[0026] The method of the present application can comprise step (A) and be free of any step (B) comprising washing the plant ash with a liquid containing water or acidified water, wherein said step (B) is after step (A) and before step (I). The method of the present application can comprise step (A) and be free of any step (B) comprising acid leaching and / or acid wetting the plant ash, wherein said step (B) is after step (A) and before step (I). The method of the present application can comprise step (A) and be free of any step (B) comprising at least one of (i) washing the plant ash with a liquid containing water or acidified water and (ii) acid leaching and / or acid wetting the plant ash, wherein said step (B) is after step (A) and before step (I). Washing the plant ash with a liquid containing water or acidified water, acid leaching the plant ash and acid wetting the plant ash would otherwise typically result in an operation to partially or completely remove potassium from the plant ash.

[0027] According to a particularly preferred embodiment, the method of the present application comprises step (A) and is free of any step (B) to remove part or all of the potassium from the plant ash, wherein said step (B) is after step (A) and before step (I).

[0028] The method of the present application can comprise step (A) and be free of any step (B’) comprising washing the plant and / or plant parts with a liquid containing water or acidified water, wherein said step (B’) is before step (A). The method of the present application can comprise step (A) and be free of any step (B’) comprising acid leaching and / or acid wetting the plant and / or plant parts, wherein said step (B’) is before step (A). The method of the present application can comprise step (A) and be free of any step (B’) comprising at least one of (i) washing the plant and / or plant parts with a liquid containing water or acidified water and (ii) acid leaching and / or acid wetting the plant and / or plant parts, wherein said step (B’) is before step (A) and before step (I). Washing the plant and / or plant parts with a liquid containing water or acidified water, acid leaching the plant and / or plant parts and acid wetting the plant and / or plant parts would otherwise typically result in an operation to partially or completely remove potassium from the plant and / or plant parts.

[0029] According to another particularly preferred embodiment, the method of the present application comprises step (A) and is free of any step (B’) to remove part or all of the potassium from the plant and / or plant parts, wherein said step (B’) is before step (A).

[0030] According to a still more preferred embodiment, the process of the application (i) comprises a step (A), (ii) does not contain any step (B) of removing part or all of the potassium from the plant ash, and (iii) does not contain any step (B’) of removing part or all of the potassium from the plant and / or plant parts, wherein said step (B) is after step (A) and before step (I) and wherein said step (B’) is before step (A).

[0031] According to other embodiments, the process of the application further comprises the following steps:

[0032] (III) filtering the aqueous slurry obtained after step (II), preferably using a filter press, so as to obtain a filter cake comprising SiO2in particulate form;

[0033] (IV) optionally washing the filter cake with a liquid containing water, preferably with water;

[0034] (V) liquefying the filter cake into a flowable aqueous suspension comprising SiO2in particulate form by adding a liquid containing water to the filter cake and optionally additionally by subjecting the filter cake to mechanical and / or chemical treatment;

[0035] (VI) drying the flowable aqueous suspension, preferably by means of a spray dryer, so as to obtain a precipitated silica.

[0036] The process of the application advantageously does not contain any step (B”) after step (VI) comprising washing the precipitated silica with a liquid containing water or acidified water. The process of the application also advantageously does not contain any step (B”) after step (VI) comprising acid leaching of the precipitated silica and / or acid wetting of the precipitated silica. Washing the precipitated silica with a liquid containing water or acidified water, acid leaching of the precipitated silica and acid wetting of the precipitated silica would otherwise typically lead to partial or complete removal of potassium from the precipitated silica.

[0037] Preferably, the process of the application does not contain any step (B”) after step (VI) of removing part or all of the sodium and / or potassium from the precipitated silica.

[0038] The present application also relates to a precipitated silica, preferably obtainable by said process, comprising:

[0039] (i) SiO2in particulate form in a weight amount ranging from 80.0% to 99.0% based on the weight of the precipitated silica;

[0040] (ii) sodium in a weight amount of at least 1.00 ‰ based on the weight of the SiO2contained in the precipitated silica; and

[0041] (iii) a weight amount of potassium of at least 0.30 ‰, based on the weight of SiO2 contained in the precipitated silica,

[0042] The precipitated silica is substantially free of SiO2 particles having organic moieties covalently bound thereto by Si-C bonds.

[0043] Furthermore, the present application relates to the use of said precipitated silica for the manufacture of at least one of the following: (i) a precipitated silica-filled elastomer composition, (ii) a tire component comprising a precipitated silica-filled elastomer composition and (iii) a tire comprising at least one component comprising a precipitated silica-filled elastomer composition.

[0044] The present application further relates to a precipitated silica-filled elastomer composition comprising at least one elastomer and said precipitated silica, to a tire component comprising said precipitated silica-filled elastomer composition and to a tire comprising at least one component comprising said precipitated silica-filled elastomer composition.

[0045] The present application also relates to a vehicle comprising said tire. The vehicle can be a motor vehicle, such as a car, a van, a mobile home, a bus, a coach, a truck or a construction machine (such as a backhoe loader or a dump truck); alternatively, the vehicle can be a non-motorized vehicle (such as a trailer or a handcart).

[0046] The present application solves the above-mentioned problems of the prior art by providing a process for the preparation of precipitated silica from plant ash, which is not only environmentally friendly but also economically advantageous. Indeed, the process of the present application does not require any pre-treatment of the plants, plant parts and / or plant ash or any post-treatment and in particular any washing step of the precipitated silica to efficiently prepare a precipitated silica having the desired properties.

[0047] In fact, the precipitated silica of the present application is advantageously used for the manufacture of precipitated silica-containing elastomer compositions and tires having the desired characteristics in terms of performances as well as mechanical and dynamic properties. DETAILED DESCRIPTION

[0048] Before the problems of the present application are described in detail, the following should be considered:

[0049] It should be understood that the application is not limited to the particular embodiments described since such embodiments can of course vary. It should also be understood that the terminology used herein is not intended to be limiting since the scope of the present application will only be limited by the appended claims.

[0050] As used herein, the singular forms “a,” “an,” and “the” include both singular and plural referents unless the context clearly dictates otherwise. For example, “a” or “an” means one or more.

[0051] 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, unrecited members, elements or method steps. It will be appreciated that the terms “comprising,” “comprises” and “comprised of,” as used herein, include the term “consisting of,” “consists” and “consists of.”

[0052] 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.

[0053] As used herein, the term “average” is arithmetic mean, unless otherwise indicated.

[0054] As used herein, the terms “% by weight,” “wt.-%,” “percent by weight,” or “percent by weight” are used interchangeably. The same applies to the terms “% by volume,” “vol.-%,” “percent by volume,” or “percent by volume,” or “% by mole,” “mol-%,” “percent by mole,” or “percent by mole.”

[0055] As used herein, the terms “‰ by weight” or “wt.-‰” are used interchangeably to indicate an amount of “permille” (i.e., “per thousand”). The same applies to the terms “‰ by volume,” “vol.-‰,” or “‰ by mole,” “mol-‰.”

[0056] Numerical ranges recited herein are inclusive of the integers within the range and (where applicable) fractions thereof. Numerical ranges recited are inclusive of both endpoints (e.g., 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed therein.

[0057] The expression "X is essentially free of Y" (another term of art in patent law) is used herein in its usual, generally accepted meaning, allowing for the possible, unavoidable presence of trace amounts of Y in X, which should be avoided as much as possible.

[0058] The expression "X is essentially free of Y" (another term of art in patent law) is used herein in its usual, generally accepted meaning, allowing for the possible, unavoidable presence of trace amounts of Y in X, which should be avoided as much as possible.

[0059] For the avoidance of doubt, "X is free of Y" is intended to mean only that X is completely free of Y.

[0060] As used herein, the term "sodium" encompasses sodium comprised in the precipitated silica in any form, notably sodium in at least one form selected from the group consisting of sodium element, sodium at the surface of the Si02 particles, sodium intercalated in the Si02 particles, disodium oxide, inorganic sodium salt, and mixtures thereof. As possible inorganic sodium salts, sodium chloride, disodium sulfate, disodium hydrogen phosphate, trisodium phosphate, sodium silicate, and mixtures thereof can be enumerated, notably. The presence of sodium in precipitated silica, notably in precipitated silica according to the present invention, is generally caused by the involvement of at least one inorganic compound containing sodium in the process of producing the precipitated silica; the inorganic compound involved can be a reagent involved in the precipitation reaction of silica (e.g. sodium silicate), an electrolyte or a pH buffer present during the course of the precipitation reaction of silica (e.g. sodium dihydrogen phosphate), a reaction product of the precipitation reaction (e.g. sodium sulfate, which can also be used as an electrolyte), a Si02-containing plant ash used for the preparation of silicates involved in the precipitation reaction of silica (e.g. rice husk ash), a base used for the preparation of silicates involved in the precipitation reaction of silica (e.g. NaOH or Na2CC>3), or a combination thereof. On the other hand, the process of the present invention rarely involves organic compounds containing sodium and the precipitated silica of the present invention is generally essentially free, essentially free, or even free of any organic compound containing sodium.

[0061] For the purposes of the present invention, the weight amount of sodium is expressed throughout the specification as elemental sodium.

[0062] As used herein, the term "potassium" is intended to mean potassium comprised in the precipitated silica in any form, notably potassium element, potassium at the surface of Si02 particles, potassium intercalated in Si02 particles, dipotassium oxides, inorganic potassium salts and mixtures thereof. As possible inorganic potassium salts, one can notably cite potassium chloride, dipotassium sulfate, di-potassium hydrogen phosphate, tri-potassium phosphate, potassium silicate and mixtures thereof. The presence of potassium in precipitated silica, notably in the precipitated silica of the application, is generally due to the involvement of at least one inorganic compound containing potassium in the process for producing the precipitated silica; the involved inorganic compound can be a reagent involved in the silica precipitation reaction (e.g. potassium silicate), an electrolyte or a pH buffer present during the course of the silica precipitation reaction (e.g. potassium dihydrogen phosphate), a reaction product of the precipitation reaction (e.g. potassium sulfate, which can also be used as an electrolyte), a Si02-containing plant ash used to prepare silicates involved in the silica precipitation reaction (e.g. rice husk ash), a base used to prepare silicates involved in the silica precipitation reaction (e.g. KOH or K2CO3), or a combination thereof. On the other hand, the process of the application involves rarely organic compounds containing potassium and the precipitated silica of the application is generally substantially free, essentially free or even free of any organic compound containing potassium.

[0063] For the purposes of the present application, the weight amount of potassium is expressed as element potassium throughout the specification.

[0064] All references cited in this specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references specifically mentioned in this document are incorporated by reference.

[0065] Unless defined otherwise, all terms used in disclosing the application, including technical and scientific terms, have the meaning commonly understood by one of ordinary skill in the art to which this application belongs. By further guidance, term definitions are included to better define the present teachings.

[0066] In the following paragraphs, the different alternatives, embodiments and variants of the application are defined in more details. Each alternative and embodiment thus defined can be combined with any other alternative and embodiment, when the range of values of the same parameter is separated, and this applies to each variant, unless clearly indicated to the contrary or clearly incompatible. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature indicated as being preferred or advantageous.

[0067] Furthermore, in one or more embodiments, particular features, structures, or characteristics described in this specification can be combined in any suitable manner, as will be apparent to those skilled in the art from this disclosure. In addition, while some embodiments described herein include some features, other embodiments include other features which are not mentioned in the context of those embodiments. The combination of features of different embodiments is to be considered to be within the scope of the application and forms different embodiments that are also to be considered as included within the application, as will be apparent to those skilled in the art.

[0068] The present application relates to a process for producing precipitated silica from plant ash, wherein the process comprises the following steps:

[0069] (I) reacting plant ash containing Si02 and potassium, the weight amount of potassium being at least 12.5 ‰ based on the weight of Si02 contained in the plant ash, with a sodium-containing alkali metal base, preferably sodium hydroxide, in an aqueous reaction medium at a temperature of at least 100 °C, so as to obtain an aqueous silicate solution, the aqueous silicate solution comprising (i) Si02 in the form of silicate anions, (ii) a weight amount of sodium cations (Na + ) of at least 1.0 ‰ based on the weight of Si02 contained in the silicate solution, and (iii) a weight amount of potassium cations (K + ) of at least 5.0 ‰ based on the weight of Si02 contained in the silicate solution,

[0070] and

[0071] (II) reacting the aqueous silicate solution with an acidifying agent in an aqueous reaction medium having a pH of more than 7.0 during at least a part of the duration of the reaction, so as to achieve precipitation of silica and to produce an aqueous slurry comprising Si02 in particulate form.

[0072] According to a preferred embodiment, the plant ash contains a weight amount of potassium of at least 13.5 ‰, more preferably at least 14.0 ‰, and most preferably at least 15.0 ‰, based on the weight of Si02 contained in the plant ash.

[0073] Preferably, the plant ash contains a weight amount of potassium of at most 100.0 ‰, preferably at most 50.0 ‰, more preferably at most 30.0 ‰, even more preferably at most 20.0 ‰, based on the weight of Si02 contained in the plant ash.

[0074] According to a particularly preferred embodiment of the present application, the plant ash contains a weight amount of potassium of 12.5 ‰ to 100.0 ‰, preferably 13.5 ‰ to 50.0 ‰, more preferably 14.0 ‰ to 30.0 ‰, even more preferably 15.0 ‰ to 20.0 ‰, based on the weight of Si02 contained in the plant ash.

[0075] The aqueous silicate solution obtained in step (I) contains (ii) sodium cations (Na + ) in a weight amount of at least 1.0 ‰, based on the weight of Si02 contained in the aqueous silicate solution. The aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount of very often at least 2.0 ‰, possibly at least 5.0 ‰, based on the weight of Si02 contained in the aqueous silicate solution. The aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount of often at least 1.0 %, possibly at least 2.0 % or at least 5.0 %, based on the weight of Si02 contained in the aqueous silicate solution. The aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount of sometimes at least 10 %, or even at least 15 %, based on the weight of Si02 contained in the aqueous silicate solution.

[0076] Furthermore, the aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount of often at most 100 %, very often at most 50 %, often at most 30 % and sometimes at most 20 %, based on the weight of Si02 contained in the aqueous silicate solution. In some other cases, the aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount which is certainly lower, for example at most 10 %, at most 50 ‰ or at most 30 ‰, based on the weight of Si02 contained in the aqueous silicate solution.

[0077] In some preferred embodiments of the present application, the aqueous silicate solution contains (ii) sodium cations (Na + ) in a weight amount of 1.0 % to 100 %, preferably 2.0 % to 50 %, more preferably 5.0 % to 30 %, based on the weight of Si02 contained in the aqueous silicate solution.

[0078] The aqueous silicate solution obtained in step (I) further contains (iii) potassium cations (K + ) in a weight amount which can be at least 5.0 ‰, at least 10 ‰, at least 15 ‰, or even at least 20 ‰, based on the weight of Si02 contained in the aqueous silicate solution. In some particular embodiments, the aqueous silicate solution obtained in step (I) can contain (iii) potassium cations (K + ) in a weight amount which is certainly higher, for example at least 50 ‰ or at least 100.0 ‰, based on the weight of Si02 contained in the aqueous silicate solution.

[0079] Preferably, the aqueous silicate solution contains (iii) potassium cations (K+ ). The aqueous silicate solution contains (iii) potassium cations (K + ) in a weight amount of more preferably below 100 ‰, still more preferably at most 70 ‰, even more preferably at most 50 ‰ and most preferably at most 30 ‰, based on the weight of SiO2 contained in the aqueous silicate solution.

[0080] In some preferred embodiments of the present application, the aqueous silicate solution contains (iii) potassium cations (K + ) in a weight amount of 5.0 ‰ to 500.0 ‰, preferably 5.0 ‰ to less than 100 ‰, more preferably 10 ‰ to 50 ‰, still more preferably 15 ‰ to 30 ‰, based on the weight of SiO2 contained in the aqueous silicate solution.

[0081] According to embodiments of the present application, in step (I) the plant ash is reacted in the aqueous reaction medium at a temperature of at least 120 °C, preferably at least 140 °C, more preferably 140 °C to 220 °C, even more preferably 160 °C to 200 °C.

[0082] Preferably, the alkali metal base contains sodium, preferably sodium hydroxide.

[0083] According to particularly preferred embodiments, the process according to the present application comprises a step (A) of combusting a plant and / or plant parts, prior to step (I), in order to obtain the plant ash, wherein the plant and / or plant parts contain SiO2 and potassium in a weight amount of at least 12.5 ‰, based on the weight of SiO2 contained in the plant and / or plant parts.

[0084] In other words, the plant ash is obtained from the combustion of a plant and / or plant parts.

[0085] According to preferred embodiments, the plant and / or plant parts contain potassium in a weight amount of at least 13.5 ‰, more preferably at least 14.0 ‰, most preferably at least 15.0 ‰, based on the weight of SiO2 contained in the plant and / or plant parts.

[0086] Preferably, the plant and / or plant parts contain potassium in a weight amount of at most 100.0 ‰, preferably at most 50.0 ‰, more preferably at most 30.0 ‰, even more preferably at most 20.0 ‰, based on the weight of SiO2 contained in the plant and / or plant parts.

[0087] According to particularly preferred embodiments of the present application, the plant and / or plant parts contain potassium in a weight amount of 12.5 ‰ to 100.0 ‰, preferably 13.5 ‰ to 50.0 ‰, more preferably 14.0 ‰ to 30.0 ‰, even more preferably 15.0 ‰ to 20.0 ‰, based on the weight of SiO2 contained in the plant and / or plant parts.

[0088] Without wishing to be bound to a specific mechanism theory, it has been found that the weight amount of potassium contained in the plants and / or plant parts, and in turn in the plant ash, as described above, has no any negative effect on the preparation of the aqueous silicate solution and on the preparation of the precipitated silica and its properties.

[0089] Similarly, it has also been found that the presence of both potassium and sodium cations contained in the aqueous silicate solution has no effect on the preparation of the precipitated silica and its properties.

[0090] In addition, it has been found that, for the purposes of the present application, it is not necessary to treat the plants and / or plant parts or the plant ash to remove the potassium contained therein, since the presence of potassium in the above-mentioned weight amounts has no negative effect on the properties of the precipitated silica.

[0091] According to an embodiment, the method of the present application can comprise step (A) and be free of any step (B) comprising re-combusting the plant ash after step (A) and before step (I).

[0092] According to an embodiment, the method of the present application can comprise step (A) and be free of any step (B) comprising washing the plant ash with a liquid containing water or acidified water after step (A) and before step (I).

[0093] According to an embodiment, the method of the present application can comprise step (A) and be free of any step (B) comprising acid leaching and / or acid wetting the plant ash after step (A) and before step (I).

[0094] Preferably, said acid leaching and / or acid wetting is carried out with an acidifying agent, more preferably with HC1, even more preferably with a 1 N or 6 N HC1 solution.

[0095] According to an embodiment, said acid leaching can be carried out by treating the plant ash with said acidifying agent, preferably with HC1, even more preferably with a 1 N or 6 N HC1 solution, under reflux for at least 1 hour, preferably for at least 1.5 hours.

[0096] Said acid wetting is preferably carried out by soaking the plant ash in said acidifying agent, preferably HC1, more preferably a 1 N or 6 N HC1 solution, for at least 1 hour, preferably for at least 3 hours, more preferably for 3 to 7 hours.

[0097] According to an embodiment, the method of the present application can comprise step (A) and be free of any step (B) comprising at least one of the following: (i) washing the plant ash with a liquid containing water or acidified water and (ii) acid leaching and / or acid wetting the plant ash after step (A) and before step (I).

[0098] Washing plant ash with a liquid containing water or acidified water, acid leaching of plant ash and acid wetting of plant ash would otherwise typically result in an operation for partially or completely removing potassium from plant ash.

[0099] According to a particularly preferred embodiment, the method of the application comprises step (A) and is free of any step (B) for removing part or all of the potassium from plant ash after step (A) and before step (I).

[0100] According to the application, said step (B) according to any one of the above embodiments can be considered as a step for pre-treating plant ash.

[0101] According to another particularly preferred embodiment, the method of the application can comprise step (A) and is free of any step (B’) comprising washing of the plant and / or plant parts with a liquid containing water or acidified water before step (A).

[0102] According to an embodiment, the method of the application can comprise step (A) and is free of any step (B’) comprising acid leaching and / or acid wetting of the plant and / or plant parts before step (A).

[0103] Preferably, said acid leaching and / or acid wetting is as defined above for step (B).

[0104] According to an embodiment, the method of the application can comprise step (A) and is free of any step (B’) comprising at least one of (i) washing of the plant and / or plant parts with a liquid containing water or acidified water and (ii) acid leaching and / or acid wetting of the plant and / or plant parts before step (A).

[0105] Washing of the plant and / or plant parts with a liquid containing water or acidified water, acid leaching of the plant and / or plant parts and acid wetting of the plant and / or plant parts would otherwise typically result in an operation for partially or completely removing potassium from the plant and / or plant parts.

[0106] According to a particularly preferred embodiment, the method of the application comprises step (A) and is free of any step (B’) for removing part or all of the potassium from the plant and / or plant parts. According to the application, said step (B’) can be considered as a step for pre-treating the plant and / or plant parts.

[0107] According to the application, plant ash which has not been subjected to any step (B) according to any embodiment as described above is considered as untreated plant ash, preferably unwashed and / or unresidued plant ash.

[0108] Similarly, according to the present application, a plant and / or plant parts which have not been subjected to any step (B’) according to any embodiment as described above are considered as untreated plants and / or plant parts, preferably unwashed plants and / or parts.

[0109] Without wishing to be bound by a particular theory, it has been found that the method according to the present application does not necessarily require any pre-treatment of the plant, plant parts and / or plant ash to remove potassium contained therein. On the contrary, it has been surprisingly found that the presence of said potassium in the plant, plant parts and / or plant ash does not affect the synthesis of precipitated silica and, in turn, the precipitated silica thus obtained still has the desired mechanical and rheological properties which are particularly advantageous for tire applications.

[0110] According to the present application, the plant is preferably an angiosperm, more preferably a monocotyledon or a dicotyledon, most preferably a plant belonging to a family selected from the group consisting of Poaceae, Equisetaceae, Cyperaceae, Cucurbitaceae, Cannabaceae, Arecaeae, Brassicaceae, and combinations thereof.

[0111] According to an embodiment of the present application, the plant is a tree. Preferably, the tree is selected from the group consisting of pine, oak, birch, elm, and combinations thereof.

[0112] Preferably, the plant belonging to Poaceae is selected from the group consisting of rice, wheat, sugarcane, bamboo, oat, barley, rye, sorghum, triticale, reed canary grass, reed, corn, miscanthus, and combinations thereof.

[0113] Preferably, the plant belonging to Equisetaceae is wild field horsetail.

[0114] Preferably, the plant belonging to Cyperaceae is sedge.

[0115] Preferably, the plant belonging to Cucurbitaceae is selected from the group consisting of melon, watermelon, pumpkin, cucumber, and combinations thereof.

[0116] Preferably, the plant belonging to Cannabaceae is hemp.

[0117] Preferably, the plant belonging to Arecaeae is palm tree.

[0118] Preferably, the plant belonging to Brassicaceae is rapeseed.

[0119] It is preferred that the plant containing silica (SiO2-containing plant) is a plant selected from the group consisting of rice, wheat, rapeseed, barley, bamboo, wild field horsetail, sedge, watermelon, and combinations thereof.

[0120] Preferably, the plant parts are selected from the group consisting of roots, stems, leaves, flowers, fruits, husks, ear husks, stalks, wood, and combinations thereof.

[0121] According to the present application, the plant parts can also be derived from processing of plants, such as straw (e.g. grain straw), bagasse (e.g. sugar cane bagasse), oil (e.g. palm oil), sawdust (e.g. tree sawdust), and / or pellets.

[0122] Preferably, the plant parts are selected from the group consisting of rice husks, rice straw, wheat husks, wheat straw, barley straw, barley husks, sugar cane bagasse, sugar cane leaves, bamboo stems, bamboo leaves, corn cobs, palm oil, miscanthus stalks, miscanthus leaves, sedge leaves, watermelon fruits, tree wood, and combinations thereof.

[0123] In a particularly preferred embodiment of the present application, the plant is rice, and preferably, the plant part is a husk.

[0124] According to the present application, the combustion of the plant and / or plant parts (step A) above) is performed by conventional techniques by combusting the plant parts and / or plants containing silicon dioxide.

[0125] Preferably, the combustion of the plant and / or plant parts is performed at a temperature of 300 °C to 1500 °C, preferably 500 °C to 1000 °C. According to an embodiment, the combustion of the plant and / or plant parts is performed at a temperature of > 700 °C, preferably at a temperature of > 700 °C to 1000 °C. According to another embodiment, the combustion of the plant and / or plant parts is performed at a temperature of < 700 °C, preferably at a temperature of 500 °C to < 700 °C.

[0126] According to the present application, the acidifying agent of step (II) above is selected from the group consisting of inorganic acids, which are preferably selected from the group consisting of sulfuric acid (H2SO4), hydrochloric acid (HC1), nitric acid (HN03), phosphoric acid (H3PO4), and combinations thereof; and organic acids, which are preferably selected from the group consisting of acetic acid, formic acid, carbonic acid, and combinations thereof.

[0127] According to the present application, step (II) of the above process is carried out in an aqueous reaction medium having a pH exceeding 7.0 during at least a portion of the duration of the reaction, preferably during at least 25% of the duration of the reaction, more preferably during at least 28% of the duration of the reaction and still more preferably during at least 33% of the duration of the reaction. In some embodiments, step (II) of the above process is carried out in an aqueous reaction medium having a pH exceeding 7.0 during at most 66% of the duration of the reaction, preferably during at most 50% of the duration of the reaction; in some other embodiments, step (II) of the above process is carried out in an aqueous reaction medium having a pH exceeding 7.0 during more than 50% of the duration of the reaction, preferably during at least 90% of the duration of the reaction, more preferably during at least 95% of the duration of the reaction and still more preferably during the entire duration of the reaction.

[0128] Preferably, step (II) of reacting the aqueous silicate solution with an acidifying agent is carried out at a temperature of at least 40°C, more preferably at least 60°C, still more preferably at least 75°C and most preferably at least 80°C. Moreover, step (II) is advantageously carried out at a temperature of at most 150°C, preferably below 100°C and more preferably at most 95°C. Good results are obtained when step (II) is carried out at a temperature ranging from 60°C to below 100°C. Excellent results are obtained when step (II) is carried out at a temperature ranging from 75°C to 95°C.

[0129] Preferably, the aqueous reaction medium of step (I) and / or (II) of the process of the present application is water.

[0130] According to the present application, the process can further comprise the following steps:

[0131] (III) filtering the aqueous slurry obtained after step (II), preferably using a filter press, so as to obtain a filter cake comprising SiO2in the form of microparticles;

[0132] (IV) optionally washing the filter cake with a liquid containing water, preferably with water;

[0133] (V) liquefying the filter cake into a flowable aqueous suspension comprising SiO2in the form of microparticles by adding a liquid containing water to the filter cake;

[0134] (VI) drying the flowable aqueous suspension, preferably by means of a spray dryer, so as to obtain a precipitated silica.

[0135] According to an embodiment of the present application, step (V) comprises subjecting the filter cake to a mechanical and / or chemical treatment in addition to the addition of the liquid containing water.

[0136] According to an embodiment, the process of the application does not contain any step (B”) after step (VI) comprising washing the precipitated silica with a liquid containing water or acidified water.

[0137] According to an embodiment, the process of the application does not contain any step (B”) after step (VI) comprising acid leaching and / or acid wetting the precipitated silica.

[0138] Preferably, the acid leaching and / or acid wetting is as defined above for steps (B) and (B’).

[0139] According to an embodiment, the process of the application does not contain any step (B”) after step (VI) comprising at least one of: (i) washing the precipitated silica with a liquid containing water or acidified water and (ii) acid leaching and / or acid wetting the precipitated silica.

[0140] Washing the precipitated silica with a liquid containing water or acidified water, acid leaching the precipitated silica and acid wetting the precipitated silica would otherwise generally lead to the partial or complete removal of potassium from the precipitated silica.

[0141] According to a particularly preferred embodiment, the process according to the application does not contain any step (B”) after step (VI) for removing part or all of the sodium and / or potassium from the precipitated silica.

[0142] According to the application, said step (B”) can be considered as a step of post-treating the precipitated silica.

[0143] According to an embodiment, the process according to the application does not involve (i.e. does not contain) a step of forming a xerogel.

[0144] Without wishing to be bound by a particular theory or mechanism, for the purposes of the present application, said precipitated silica obtained at the end of the process described above can be considered as a modified precipitated silica. In particular, sodium and potassium can be considered as integral components of the precipitated silica rather than impurities. Indeed, it has been found that sodium and potassium can be inserted to a large extent in the Si02 network, thereby resulting in a modified Si02, without adversely affecting its properties.

[0145] According to the application, the precipitated silica can also contain other elements selected from the group consisting of Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, P, Pb, S, Sb, Ti, Zn, and combinations thereof (originating from the synthesis and in particular from the use of untreated plant ash and untreated plants and / or plant parts). For the purposes of the present application, these elements are considered as impurities, in contrast to sodium and potassium.

[0146] The present application also relates to a precipitated silica.

[0147] The precipitated silica according to the present application can be obtained by the above-mentioned process. Thus, the present application also relates to a precipitated silica obtainable or obtained by the above-mentioned process.

[0148] Preferably, the precipitated silica according to the present application obtainable or obtained by the above-mentioned process comprises:

[0149] (i) SiO2in the form of microparticles in an amount of from 80.0 to 99.0 wt.-%, based on the weight of the precipitated silica;

[0150] (ii) sodium in an amount of at least 1.00 ‰ wt.-%, based on the weight of the SiO2contained in the precipitated silica; and

[0151] (iii) potassium in an amount of at least 0.30 ‰ wt.-%, based on the weight of the SiO2contained in the precipitated silica.

[0152] The precipitated silica according to the present application is essentially free of SiO2particles to which organic moieties are covalently bound via Si-C bonds; the precipitated silica can be essentially free or even free of SiO2particles to which organic moieties are covalently bound.

[0153] Preferably, the precipitated silica according to the present application is essentially free, essentially free or even free of SiO2particles to which organic moieties are covalently bound (regardless of which covalent bond between the SiO2particles and the organic moieties can be).

[0154] More preferably, the precipitated silica according to the present application is different from any organically modified precipitated silica.

[0155] As used herein, the term “organically modified precipitated silica” denotes a precipitated silica comprising SiO2particles and a substantial amount of (i) organic compounds and / or (ii) organic moieties covalently bound to the SiO2particles. The organically modified precipitated silica can be a precipitated silica comprising a substantial amount of organic compounds (e.g. polyethylene glycol) which are not covalently bound to the SiO2particles. The organically modified precipitated silica can be a precipitated silica comprising a substantial amount of organic moieties covalently bound to the SiO2particles; such organically modified precipitated silica is typically produced from a chemical reaction between an organic compound (e.g. potassium methyl silicate) and the SiO2particles. Thus, the organically modified precipitated silica contains a substantial amount of carbon, notably in the form of organic compounds and / or organic moieties. The organically modified precipitated silica can contain at least 0.5 %, at least 0.75 % or even at least 1 % of carbon, based on the weight of the SiO2contained in the organically modified precipitated silica.

[0156] The carbon is carbon contained in the above-mentioned organic moieties covalently bound to the SiO2 particles via Si-C bonds.

[0157] In contrast, the precipitated silica according to the present application is advantageously essentially free, intrinsically free, or even free of carbon. The carbon content of the precipitated silica advantageously ranges from 0 to less than 0.5 %, preferably from 0 to 4000 ppm, more preferably from 0 to 3000 ppm, still more preferably from 0 to 2000 ppm and even more preferably from 0 to 1000 ppm, based on the weight of SiO2 contained in the precipitated silica, as determined by the C / S method.

[0158] In addition, in this case, the carbon is carbon contained in the above-mentioned organic moieties covalently bound to the SiO2 particles via Si-C bonds.

[0159] The precipitated silica according to the present application comprises at least 0.25 ‰ by weight of potassium, based on the weight of SiO2 contained in the precipitated silica. According to an embodiment, the precipitated silica according to the present application comprises at least 0.33 ‰, preferably at least 0.35 ‰, more preferably at least 0.37 ‰, still more preferably at least 0.39 ‰ and most preferably at least 0.40 ‰ by weight of potassium, based on the weight of SiO2 contained in the precipitated silica.

[0160] According to an embodiment, the precipitated silica according to the present application comprises at most 3.00 ‰, preferably at most 1.50 ‰, more preferably at most 0.80 ‰, still more preferably at most 0.60 ‰ and most preferably at most 0.50 ‰ by weight of potassium, based on the weight of SiO2 contained in the precipitated silica.

[0161] According to a particularly preferred embodiment, the precipitated silica comprises a weight amount of potassium ranging from 0.33 ‰ to 0.80 ‰, preferably from 0.35 ‰ to 0.60 ‰ and more preferably from 0.37 ‰ to 0.50 ‰, based on the weight of SiO2 contained in the precipitated silica.

[0162] The precipitated silica comprises at least 1.00 ‰, preferably at least 1.50 ‰, more preferably at least 2.00 ‰, still more preferably at least 3.00 ‰ and most preferably at least 4.00 ‰ by weight of sodium, based on the weight of SiO2 contained in the precipitated silica.

[0163] According to an embodiment, the precipitated silica comprises a weight amount of sodium ranging from 1.00 ‰ to 20.0 ‰, preferably from 1.50 ‰ to 15.0 ‰, more preferably from 2.00 ‰ to 10.0 ‰, still more preferably from 3.00 ‰ to 10.0 ‰ and most preferably from 4.00 ‰ to 8.00 ‰, based on the weight of SiO2 contained in the precipitated silica.

[0164] The precipitated silica according to the present application comprises potassium and sodium, the ratio of the weight amount of potassium to the weight amount of sodium is advantageously at most 2.00, preferably at most 1.00, more preferably at most 0.50, still more preferably at most 0.30, even more preferably at most 0.16 and most preferably at most 0.12.

[0165] The precipitated silica according to the present application comprises potassium and sodium, the ratio of the weight amount of potassium to the weight amount of sodium is advantageously at least 0.005, preferably at least 0.01, more preferably at least 0.02, still more preferably at least 0.03, even more preferably at least 0.04 and most preferably at least 0.06.

[0166] The precipitated silica according to the present application comprises potassium and sodium, the ratio of the weight amount of potassium to the weight amount of sodium is advantageously ranging from 0.005 to 2.00.

[0167] The precipitated silica according to the present application comprises potassium and sodium, the ratio of the weight amount of potassium to the weight amount of sodium is advantageously at most 2.00, preferably at most 1.00, more preferably at most 0.50, still more preferably at most 0.30, even more preferably at most 0.16 and most preferably at most 0.12.

[0168] The precipitated silica according to the present application can comprise water in an amount ranging from 0.0% to 15.0%, in particular from 3.0% to 12.0% and more particularly from 5.0% to 10.0% by weight based on the weight of SiO2 contained in the precipitated silica.

[0169] The precipitated silica according to the present application can comprise sulfate anions (typically in combination with sodium and / or potassium counterions as one or more salts) in an amount ranging from 0.0% to 3.5%, in particular from 0.3% to 1.7% and more particularly from 0.7% to 1.4% of sulfate anions (expressed as SO4 2- ) by weight based on the weight of SiO2 contained in the precipitated silica.

[0170] The precipitated silica according to the present application has a sulfur content ranging from 0.0% to 2.0%, very often from 0.10% to 1.0%, typically from 0.20% to 0.50% by weight based on the weight of SiO2 contained in the precipitated silica as determined by the C / S method.

[0171] Preferably, the precipitated silica according to the present application comprises SiO2 in a weight amount ranging from 90.0% to 97% by weight of the precipitated silica.

[0172] According to an embodiment of the present application, the precipitated silica of the present application has a BET specific surface area of at least 165 m 2 / g, preferably at least 180 m 2 / g and more preferably at least 200 m 2 / g. According to a preferred embodiment, the precipitated silica has a BET specific surface area of at most 290 m 2 / g, preferably at most 280 m 2 / g, even more preferably ranging from 165 m2 / g to 280 m2 / g.

[0173] According to another embodiment, the precipitated silica of the present application has a CTAB specific surface area of at least 155 m 2 / g, preferably at least 165 m 2 / g, more preferably at least 180 m 2 / g. According to a preferred embodiment, the precipitated silica has a CTAB specific surface area of at most 225 m 2 / g, preferably at most 220 m 2 / g, even more preferably ranging from 155 m2 / g to 220 m2 / g.

[0174] According to an embodiment, the precipitated silica of the present application has a d 50 ranging from 20 nm to 200 nm, preferably from 50 nm to 180 nm. According to the present application, said d 50 r is measured by centrifugal sedimentation, preferably using a centrifugal photosedimentometer (CPS) in a disc centrifuge.

[0175] As mentioned above, without wishing to be bound by any particular theory, for the purpose of the present application, the precipitated silica can be considered as a modified precipitated silica.

[0176] In particular, sodium and potassium can be considered as full components of the precipitated silica rather than impurities. Indeed, it has been found that sodium and potassium can be inserted to a large extent in the Si02network, resulting in a modified Si02, without adversely affecting its mechanical properties and surface reactivity, so that it can be advantageously used for the desired applications, in particular for the production of precipitated silica-filled elastomer compositions, tire parts and / or tires.

[0177] Without wishing to be bound by a particular theory, it has been found that in plant ash, potassium is believed to be present notably in one or more forms that are insoluble in alkaline media, that is to say that they cannot be dissolved by a sodium-containing alkali metal base such as NaOH. These forms can include potassium mixed oxides with aluminium and / or iron. It can thus be concluded that this can lead to a value of the potassium content in the aqueous silicate solution that is lower than the value of the potassium content in the plant ash.

[0178] Furthermore, in the aqueous slurry obtained after step (II), it is believed that only a small amount of potassium can be trapped / inserted in the precipitated silica skeleton. According to embodiments of the application, when the aqueous slurry is filtered according to step (III) to obtain a filter cake, a large amount of potassium is present in the filter cake in the form of one or more potassium salts, such as K2SO4 when H2SO4 is the acidifying agent. When the filter cake is washed, such salts do not remain inside the filter cake but are eliminated with the washing. Thus, without wishing to be bound by a particular theory, it can be concluded that this can lead to a value of the potassium content in the precipitated silica that is lower than the values of the potassium content in the aqueous silicate solution and in the plant ash. Similar explanations apply to the amount of sodium in the precipitated silica.

[0179] Furthermore, without wishing to be bound by a particular theory, it can be concluded that the value of the sodium content in the aqueous silicate solution according to embodiments of the application can be higher than the value of the sodium content in the plant ash is typically achieved when sodium hydroxide, i.e. the sodium-containing alkali metal base that is preferred according to embodiments of the application, is used during step (I), as this sodium hydroxide is the source of sodium ions in the silicate.

[0180] The present application thus also relates to the use of a precipitated silica as described above for the manufacture of a precipitated silica-filled elastomeric composition.

[0181] The present application also relates to a process for the preparation of a precipitated silica-filled elastomeric composition, said process comprising mixing at least one elastomer with a precipitated silica of the present application as described above.

[0182] The present application also relates to a precipitated silica-filled elastomeric composition comprising at least one elastomer and a precipitated silica as described above.

[0183] According to the present application, a precipitated silica is employed as a reinforcing filler within said precipitated silica-filled elastomeric composition.

[0184] Preferably, said at least one elastomer has at least one glass transition temperature in the range of -150°C to +300°C, for example in the range of -150°C to +20°C.

[0185] Notable non-limiting examples of suitable elastomers are diene elastomers. 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, can be used. Mention can also be made of functionalized elastomers, which are 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 Si02particles, and halogenated polymers. Mention can be made of polyamides, ethylene homopolymers and copolymers, propylene homopolymers and copolymers.

[0186] Among the diene elastomers, mention can be made of, for example, polybutadiene (BR), polyisoprene (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 associated functionalized polymers exhibiting, for example, polar side groups or polar groups at the chain ends, which can interact with the Si02particles.

[0187] Mention can also be made of natural rubber (NR) and epoxidized natural rubber (ENR).

[0188] The precipitated silica-filled elastomer composition can be vulcanized with sulfur (then a vulcanizate is obtained) or in particular crosslinked with peroxides or other crosslinking systems, for example diamines or phenolic resins.

[0189] The precipitated silica-filled elastomer composition according to the embodiments of the application can also comprise at least one coupling agent and / or at least one covering agent and / or at least one antioxidant.

[0190] As coupling agent, it is possible in particular to use “symmetrical” or “asymmetrical” silane polysulfides; mention can be made more particularly of bis((Ci-C4)alkoxy(Ci-C4)alkylsilyl(Ci-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.

[0191] Mention can also be made of monoethoxydimethylsilylpropyl tetrasulfide.

[0192] Mention can also be made of silanes comprising masked or free thiol functions.

[0193] The coupling agent can be grafted beforehand onto the elastomer. It can also be used in free state or grafted onto the surface of the Si02particles.

[0194] The coupling agent can optionally be combined with a suitable "coupling activator" (i.e. a compound which increases the effectiveness of the coupling agent when mixed with it).

[0195] The amount of precipitated silica that can be employed within the precipitated silica-filled elastomer composition can be within a fairly wide range. It generally 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, of the amount of the at least one elastomer. Alternatively, the weight proportion of the precipitated silica of the application in the precipitated silica-filled elastomer composition can be from 80% to 120% by weight, for example from 90% to 110% by weight, of the amount of the at least one elastomer.

[0196] The precipitated silica according to the application can advantageously constitute the totality of the reinforcing inorganic filler and even the totality of the reinforcing filler of the elastomer composition.

[0197] The precipitated silica according to the application can optionally be combined with at least one other reinforcing filler, such as, in particular, a commercial highly dispersible precipitated silica, for example like 1165、 1115 MP or 1085 MP precipitated silica (commercially available from Solvay); another reinforcing inorganic filler, for example like alumina, indeed even a reinforcing organic filler, in particular carbon black (optionally covered with an inorganic layer, for example Si02).

[0198] The precipitated silica according to the application then preferably constitutes at least 50% by weight, indeed even at least 80% by weight, of the total amount of reinforcing filler.

[0199] This precipitated silica-filled elastomer composition can be used to manufacture a tyre component. Thus, another object of the application is the use of a precipitated silica-filled elastomer composition as described above to manufacture a tyre component comprising said precipitated silica-filled elastomer composition.

[0200] The present application also relates to a method for manufacturing a tire component comprising said precipitated silica-filled elastomer composition, wherein said method comprises mixing at least one elastomer with the precipitated silica of the present application as described above in order to obtain the above-mentioned precipitated silica-filled elastomer composition and shaping the precipitated silica-filled elastomer composition thus obtained into a tire component.

[0201] Another object of the present application is said tire component comprising the precipitated silica-filled elastomer composition as described above. Preferably, said tire component is a tire tread.

[0202] The present application also relates to the use of the precipitated silica-filled elastomer composition as described above for manufacturing a tire comprising at least one component comprising the precipitated silica-filled elastomer composition as described above (i.e. a tire component according to the present application). The present application also relates to a method for manufacturing a tire comprising at least one component comprising the precipitated silica-filled elastomer composition as described above (i.e. a tire component according to the present application), wherein said method comprises mixing at least one elastomer with the precipitated silica of the present application in order to obtain the precipitated silica-filled elastomer composition as described above, shaping the precipitated silica-filled elastomer composition thus obtained into a tire component comprising the precipitated silica-filled elastomer composition, and assembling the tire component comprising the precipitated silica-filled elastomer composition thus shaped with at least one tire component other than the tire component comprising the precipitated silica-filled elastomer composition in order to obtain a tire.

[0203] The present application also relates to a tire comprising at least one component comprising the precipitated silica-filled elastomer composition as described above, and to a vehicle comprising said tire.

[0204] If the disclosure of any patents, patent applications, and publications, if any, that are incorporated herein by reference conflicts in any manner with the description of the present application, then the description of the present application shall prevail.

[0205] The present application will now be illustrated by the following examples, which are not intended to be limiting.

[0206] Example

[0207] Materials and methods

[0208] All starting materials used in the examples are commercially available.

[0209] Example 1

[0210] Potentiometric method for determining Rp

[0211] A Titrando 808 was used in order to determine the weight ratio (Rp) [% weight (Si02) / % weight (Na20)]. The device was equipped with a reference electrode Ag / AgCl in 3 M KCl and a tungsten working electrode. Each Rp was measured in duplicate and the Rp value presented is the average between the two measurements.

[0212] A 0.5 g sample was weighed and completed with 30 mL of demineralized water. The titrating solution was a 0.1 N HC1 solution. The volume Vi (mL) was determined as the equivalent point of the titration. After this equivalent point, 0.5 mL of titrating solution was added.

[0213] Then, 50 mL of KF solution (50 g / 1 of KF in water / ethanol (50 / 50) was added and allowed to react for 3 minutes. Then, 15 mL of 0.1 N HC1 solution was added. The excess of HC1 was titrated by a 1 N NaOH solution and the volume V2 (mL) is the equivalent point of the titration.

[0214] Rp was then calculated following the formula:

[0215] Rp = (0.31 * Vi) / (1.5 (15 * 1 - V2 * 1) + (0.5 * 0.1))

[0216] Determination of purity analysis for determining the SiO2 content

[0217] A 1 g sample was ignited at 1000°C for 1 hour in a tared platinum dish, cooled in a desiccator and weighed. The resulting solid was wetted with water, 10 mL of hydrofluoric acid was added in small increments. The mixture was then evaporated to dryness in a steam bath and then cooled. 10 mL of hydrofluoric acid and 0.5 mL of sulfuric acid were added slowly until all the acid was volatilized. The sample was then ignited at 1000°C, cooled in a desiccator and then weighed. The ratio between the difference between the final weight and the weight of the initial ignited portion on the one hand and the weight of the original sample on the other hand represents the weight percentage of Si02.

[0218] Carbon-sulfur analysis (C / S method) for determining the carbon content

[0219] A 200 mg sample was analyzed in a Horiba EMIA 320-V2. The following parameters were used: Iron and tin spheres were used as combustion accelerators. A CS26-3.19% calibration sensor was used.

[0220] Possible pre-treatment of precipitated silicas

[0221] When the precipitated silica is in the form of highly agglomerated particles such as pellets, it is pre-treated before applying the method for determining the CTAB surface area in order to de-agglomerate the pellets in order to obtain a sample of precipitated silica in the form of a powder.

[0222] The sample of precipitated silica in the form of highly agglomerated particles, especially in the form of granules, is smoothly ground using a hand-held agate mortar and a hand-held agate pestle, on which a smooth pressure and friction are manually exerted in order to cause the agglomerates and other lumps contained therein to be broken. The grinding is carried out for a duration sufficient for the sample to acquire a visually homogeneous consistency, i.e. that of a powder; this duration is generally a few tens of seconds and generally does not exceed 1 min.

[0223] When the precipitated silica is in the form of a powder or in the form of microbeads, this pre-treatment is not necessary.

[0224] N-cetyl-N,N,N-trimethylammonium bromide (CTAB) method for determining the specific surface area

[0225] The CTAB specific surface area (S CTAB ) value is determined according to the following method derived from standard NF ISO 5794-1, appendix G. This method is based on the adsorption of CTAB on the "external" surface of the Si02particles.

[0226] In this method, CTAB is allowed to adsorb on the precipitated silica under magnetic stirring. The precipitated silica and the residual CTAB solution are then separated. The excess of unadsorbed CTAB is determined using a potentiometric titrator (titroprocessor) by back-titration with bis(2- ethylhexyl)sulfosuccinic acid sodium salt (hereinafter "AOT"), the end point being given by the turbidity maximum of the solution and determined using an optrode.

[0227] Apparatus:

[0228] Metrohm optrode connected to a photometer 662 Metrohm (wavelength: 520 nm); Metrohm titrator: Titrino DMS 716; Metrohm titration software: Tiamo. Glass beaker (2000 mL); volumetric flask (2000 ml); sealed glass bottles (1000 and 2000 mL); disposable beaker (100 mL); micropipette (500-5000 μί); magnetic stirring bar with 25 mm disc end for adsorption (Ref VWR 442-9431); magnetic stirring bar (straight) for titration; polycarbonate centrifuge tube (at least 20 mL), centrifuge (allowing a speed of 10000 rpm); glass vial (30 mL); thermal balance.

[0229] Preparation of the solution:

[0230] - Preparation of a 5.5 g / L solution of CTAB (buffered at a pH of about 9.6). In a 2000 mL beaker containing about 1000 mL of distilled water, at 25°C, add: 54.25 g of boric acid solution ([c] = 4%), 2.60 g of KCl and 25.8 mL (± 0.1 mL) of sodium hydroxide. Stir the solution thus obtained for 15 min, after which add 11.0 g ± 0.01 g of CTAB powder (99.9% purity, purchased from Merck). After stirring, transfer the solution into a 2000 mL volumetric flask kept at 25°C and make up to 2000 mL with distilled water. Then transfer the solution into a 2000 mL glass bottle and keep it at a temperature not lower than 22°C to avoid CTAB crystallization (which occurs at 20°C).

[0231] - Preparation of the AOT solution. About 1200 mL of distilled water in a 2000 mL beaker is heated to 35°C under magnetic stirring. Add 3.7038 g of AOT (98% purity, purchased from Aldrich). Then transfer the solution into a 2000 mL volumetric flask and allow it to cool back to 25°C. Make up to 2000 mL with distilled water and transfer the solution into two 1000 mL glass bottles, which are stored in the dark at 25°C.

[0232] All the equipment and solutions are kept at 25°C during the analysis.

[0233] Procedure at the beginning and at the end of each experiment

[0234] Beginning of the experiment: stir the solution before use. Purge the dosing device before use. Pass at least 40 mL of AOT through the device to ensure that the device is clean and to remove all air bubbles.

[0235] End of the experiment: purge the dosing device in order to remove the AOT solution. Clean the optode and immerse it in distilled water.

[0236] Blank factor determination

[0237] The variation of the concentration of the AOT and CTAB solutions over time is corrected by the determination of a daily "blank factor" called ratio R1 = V1 / m1.

[0238] In a 100 mL disposable beaker: accurately weigh 4.9000 g ± 0.0100 g of the 5.5 g / L CTAB solution (m1). Set the tare and accurately add 23.0000 g ± 1.0000 g of distilled water (M 水). The solution is placed on the dosing device under stirring at 500 rpm using a magnetic stirrer and the titration is started. Throughout the titration the stirring speed must be strictly constant, without generating too many air bubbles.

[0239] V1 is the end point volume of the AOT solution needed to titrate the CTAB solution m1.

[0240] The determination of R1 is carried out at least in duplicate. If the standard deviation of R1 = V1 / m1 exceeds 0.010, the titration is repeated until the standard deviation is lower than or equal to 0.010. The daily ratio R1 is calculated as the average of 2 or 3 measurements.

[0241] After each measurement the photophore must be washed with distilled water and dried with absorbent paper.

[0242] Adsorption of CTAB on precipitated silica

[0243] The water content (% H2O) of each precipitated silica sample is determined before the adsorption step as follows using a thermo balance (temperature: 160°C): the balance with an aluminum cup is tared; about 2 g of precipitated silica is weighed and the powder is evenly distributed on the cup, the balance is closed; the percentage of moisture is noted.

[0244] In a 100 mL disposable beaker, 0.0100 g of precipitated silica (m0) is accurately weighed. Then 50.0000 mL + 1.0000 mL of the CTAB stock solution (V0) is added. The total mass is recorded. The suspension is stirred on a stir plate using a magnetic stir bar with a round end at 450 rpm for 40 minutes ± 1 minute. After 40 minutes the sample is removed from the stir plate.

[0245] Then 25 to 50 mL of the suspension is transferred into a centrifuge tube (volume depends on the centrifuge tube size) and it is centrifuged at 10000 rpm speed for 35 minutes at 25°C. After centrifugation the tube is gently removed from the centrifuge in order not to disturb the precipitated silica. 10 to 20 mL of the CTAB solution is transferred into a glass vial, then the glass vial is stoppered with a stopper and kept at 25°C.

[0246] Titration of the CTAB solution

[0247] In a 100 mL disposable beaker: 4.0000 g ± 0.0100 g of the CTAB solution of unknown concentration (m2) is accurately weighed. The taring is set and 19.4000 g ± 1.0000 g of distilled water (M 水 ) is added. The solution is placed on the dosing device under stirring at 500 rpm and the titration with the AOT solution is started.

[0248] V2 is the end-point volume of AOT required to titrate m2 of CTAB solution.

[0249] CTAB surface area S CTAB is calculated as follows:

[0250]

[0251] where:

[0252] S CTAB = surface area of precipitated silica (including water content correction) [m2 / g] 2 / g]

[0253] R1 = V1 / m1 ;

[0254] m1 = mass of CTAB stock solution titrated to blank (kg);

[0255] V1 = end-point volume of AOT required to titrate m1 of CTAB stock solution to blank (L)

[0256] R2 = V2 / m2;

[0257] m2 = mass of CTAB solution titrated after adsorption and centrifugation (kg);

[0258] V2 = end-point volume of AOT required to titrate m2 of CTAB stock solution after adsorption and centrifugation (L)

[0259] [CTAB]i = concentration of CTAB stock solution (g / L)

[0260] V0 = volume of CTAB stock solution used for adsorption on precipitated silica (L)

[0261] M ES = solid content of precipitated silica used for adsorption (g), corrected for water content as follows:

[0262] M ES = m0 x (100 - %H20) / 100

[0263] where m0 = initial mass of precipitated silica (g)

[0264] Determination of the specific surface area

[0265] BET specific surface area S is determined according to the Brunauer-Emmett-Teller (BET) method as detailed in standard NF ISO 5794-1, Appendix E (June 2010) BETwith the following adaptations: pre-drying of the sample at 160°C ± 10°C; partial pressure P / P 0 between 0.05 and 0.2.

[0266] Determination of the particle size distribution and particle size by centrifugal sedimentation in a disc centrifuge using a centrifugal photosedimentometer (CPS)

[0267] determined by centrifugal sedimentation in a disc centrifuge using a centrifugal photodensitometer "CPS DC 24000 UHR" type marketed by the company CPS Instruments in a disc centrifuge. 50 16 84 × FWHM and Ld. This instrument is equipped with the operating software supplied with the device (operating software version 1 lg).

[0268] Instrument used: for the measurement needs, the following materials and products were used: ultrasonic system: Sonics Vibracell VC1500 / VCX1500 generator type 1500 W equipped with a 19 mm probe (transducer: CV154 + booster (part number: BHNVC21) + 19 mm probe (part number: 630-0208)).

[0269] analytical balance with precision of 0.1 mg (for example Mettler AE260); syringes: 1.0 ml and 2.0 ml with 20 ga needle; 50 mL beaker of high form (SCHOTT DURAN: 38 mm diameter, 78 mm high); magnetic stirrer with 2 cm stir bar; vessel for ice bath during sonication.

[0270] Chemicals: deionized water; ethanol 96%; sucrose 99%; dodecane, all from Merck; PVC reference standard from CPS Instruments; the peak maximum of the reference standard used should be between 200 nm and 600 nm (for example 237 nm).

[0271] Preparation of the disc centrifuge

[0272] For the measurement, the following parameters were established (see Table 1). For the calibration standard parameters, the information of the PVC reference delivered by the supplier was used.

[0273] Table 1

[0274]

[0275]

[0276] × cps = centipoise

[0277] System configuration ​

[0278] The measurement wavelength was set to 405 nm. The following run time option parameters were established (Table 2):

[0279] Table 2

[0280]

[0281] All other options of the software were left as set by the instrument manufacturer.

[0282] Preparation of the disc centrifuge

[0283] The centrifuge disc was rotated at 24000 rpm for a period of 30 min. A density gradient of sucrose (CAS number 57-50-1) was prepared as follows:

[0284] In a 50 mL beaker, a 24% by weight aqueous solution of sucrose was prepared. In a 50 mL beaker, an 8% by weight aqueous solution of sucrose was prepared. Once both solutions were homogenized separately, a sample was removed from each solution using a 2 mL syringe, which was injected into the rotating disc in the following order:

[0285] Sample 1 : 1.8 mL of 24 wt% solution

[0286] Sample 2: 1.6 mL of 24 wt% solution + 0.2 mL of 8 wt% solution

[0287] Sample 3: 1.4 mL of 24 wt% solution + 0.4 mL of 8 wt% solution

[0288] Sample 4: 1.2 mL of 24 wt% solution + 0.6 mL of 8 wt% solution

[0289] Sample 5: 1.0 mL of 24 wt% solution + 0.8 mL of 8 wt% solution

[0290] Sample 6: 0.8 mL of 24 wt% solution + 1.0 mL of 8 wt% solution

[0291] Sample 7: 0.6 mL of 24 wt% solution + 1.2 mL of 8 wt% solution

[0292] Sample 8: 0.4 mL of 24 wt% solution + 1.4 mL of 8 wt% solution

[0293] Sample 9: 0.2 mL of 24 wt% solution + 1.6 mL of 8 wt% solution

[0294] Sample 10: 1.8 mL of 8 wt% solution.

[0295] Before each injection into the disc, the two solutions were homogenized in the syringe by sucking in about 0.2 mL of air and then simply manually agitating for a few seconds (ensuring not to lose any liquid).

[0296] These injections of a total volume of 18 mL were used to generate a density gradient that could be used to eliminate certain instabilities that can occur during the injection of the sample to be measured. To protect the density gradient from evaporation, 1 mL of dodecane was added in the spinning disc using a 2 mL syringe. The disc was then left spinning at 24000 rpm for 60 min before any first measurement.

[0297] Sample preparation

[0298] The samples were prepared and analyzed according to the current protocol, i.e.: PE = 3.2 g / 40 ml H20 - The suspension was subjected to ultrasound in a cold environment (ice bath) at 1500 W for 8 minutes - 100 μL of sample was removed - The disc was spun at 24000 rpm - Analysis time 20-25 minutes.

[0299] 3.2 g of precipitated silica was weighed into a 50 mL high form glass beaker (SCHOTT DURAN: diameter 38 mm, height 78 mm) and 40 mL of deionized water was added to obtain an 8 wt.-% precipitated silica suspension. The suspension was stirred with a magnetic stirrer (minimum 20 s) and then the beaker was placed in a crystallizing dish with ice and cold water. The magnetic stirrer was removed and the crystallizing dish was placed under an ultrasonic probe which was placed at a distance of 1 cm from the bottom of the beaker. The ultrasonic probe was set to 56% of its maximum amplitude and run for 8 min. At the end of the ultrasonic treatment, the beaker was again placed on a magnetic stirrer with a 2 cm magnetic stir bar stirred at a minimum of 500 rpm until after sampling.

[0300] The ultrasonic probe should be in proper working condition. At least one of the following checks should be performed, preferably both: (i) visual inspection of the physical integrity of the probe end (roughness depth less than 2 mm measured with a precision caliper); (ii) check of the commercial 1165 MP precipitated silica measured d 50 was 93 nm ± 3 nm. If the result is negative, a new probe should be used.

[0301] Analysis

[0302] Before analyzing each sample, the calibration standard is recorded. In each case, 0.1 mL of a PVC standard provided by CPS Instruments, whose characteristics are pre-entered into the software, is injected. Importantly, the measurement is initiated in the software simultaneously with this first injection of the PVC standard. By ensuring that the measurement is initiated at the same time as the injection, confirmation from the instrument should have been received before injecting 100 μL of the pre-sonicated sample.

[0303] These injections were performed using two clean 1 mL syringes. At the end of the measurement, the endpoint was reached, representing the time required for all smaller diameter particles (configured to 0.02 μm in the software) to settle, yielding the ratio for each diameter category. The resulting curve is referred to as the aggregate size distribution.

[0304] result

[0305] value d 50 d 16 d 84 Ld is based on a distribution plotted with a linear scale. The integral of the particle size distribution function of diameter allows for the acquisition of a "cumulative" distribution, which is the total mass of particles between the minimum diameter and the diameter of interest.

[0306] d 50 : At this diameter, it was found that 50% by mass of the SiO2 particle population is between or below this diameter. 50 It is called the median size, which is the median diameter of precipitated silica.

[0307] d 84 This is the diameter, and it was found that 84% of the total mass of the particles is below this diameter.

[0308] d 16 The diameter is such that 16% of the total mass of the particles is measured to be below this diameter.

[0309] Ld: Calculated according to the following formula: Ld=(d 84 -d 16 ) / d 50

[0310] Determination of the pore volume and pore size by mercury (Hg) porosimetry

[0311] Pore ​​volume and pore size distribution were obtained using Micromeritics. IV 9520 porosimeter; they were calculated by Washburn's relation using a contact angle Θ equal to 140° and a surface tension γ equal to 485 dynes / cm. Each sample was dried in an oven at 200°C under atmospheric pressure for 2 hours before the measurement. For good reproducibility of the measurement, the initial weight of the precipitated silica placed in the porosimeter of type 10 (accuracy of 0.001 g) was chosen in such a way that the "stem volume used" (i.e. the percentage of the volume of mercury (Hg) consumed to fill the porosimeter) was between 40 and 80%. The porosimeter was then slowly evacuated to 50 μιη of Hg and maintained at this pressure for 5 min.

[0312] Software version IV 1.09 was used for the operation Apparatus. No correction was made on the raw data. The measurement range was from 3.59 kPa (0.52 psi) to 413685 kPa (60000 psi) and at least 100 measuring points were used (19 measuring points from 3.59 kPa (0.52 psi) to 193 kPa (28 psi) with an equilibration time of 10 seconds and then 81 points from 1.93 kPa (0.28 psi) to 413685 kPa (60000 psi) with an equilibration time of 20 seconds). If the mercury intrusion volume increment was > 0.5 mL / g, the software introduced additional measuring points if appropriate. The intrusion curve was smoothed by means of the "smooth differential" function of the apparatus software.

[0313] The Log Differential Intrusion (mL / g) versus pore size data were analyzed in the pore diameter range from 3.5 nm to 5 μιη.

[0314] Example 1 - Precipitated silica, sand source (comparative)

[0315] The reference precipitated silica was produced from sodium silicate obtained from sand (sand source sodium silicate).

[0316] The characteristics of the sand source sodium silicate (S0) used for this reaction (impurity profile and elemental composition) are shown in Table 3 below. The Rp value of the sodium silicate was obtained by the potentiometric method described above.

[0317] 17 L of purified water and 0.260 kg of sand source sodium sulfate S0 were introduced into a 25 L stainless steel reactor. The solution thus obtained was heated to 92°C. The whole reaction was carried out at this temperature. 80 g / L of sulfuric acid were introduced under stirring (350 rpm, TT mixing stirring) until the pH reached 4.1.

[0318] A sodium silicate solution having a SiO2 / Na2O weight ratio equal to 3.5 and a concentration of 230 g / L and sulfuric acid having a concentration equal to 80 g / L were simultaneously introduced into the reactor over a period of 10 minutes, wherein the sodium silicate solution was introduced at a flow rate of 107 g / min and the sulfuric acid was introduced at an adjusted flow rate in such a way as to maintain the pH of the reaction medium at a value of 4.1.

[0319] At the end of 10 minutes, the sodium silicate flow rate was kept constant. Instead of 80 g / L sulfuric acid, a sulfuric acid having a concentration of 1710 g / L was introduced over a period of 16 minutes and at a flow rate which allowed to maintain the pH of the reaction medium at a value of 4.1.

[0320] The addition of sulfuric acid was then stopped. The sodium silicate was introduced at a flow rate of 107 g / min as long as the pH of the reaction medium was below 8.0.

[0321] The pH of the reaction medium was then maintained at 8.0 for 18 minutes by simultaneously adding sodium silicate at a flow rate of 167 g / min and sulfuric acid having a concentration of 1710 g / L at an adjusted flow rate which allowed to maintain the pH of the reaction medium at 8.0.

[0322] Finally, at the end of this simultaneous addition, the reaction medium was brought to a pH of 4.0 by adding sulfuric acid having a concentration of 1710 g / L. The medium was aged at this pH for 10 minutes.

[0323] The slurry thus obtained was filtered through a filter press and washed (20% dry cake extract). The resulting filter cake was then mechanically broken up and the resulting slurry was dried using a spray dryer. The precipitated silica thus obtained (precipitated silica P0) was characterized as shown in Tables 3 and 4 below.

[0324] Example 2 - Precipitated silica, RHA source washed (comparative)

[0325] The reference precipitated silica was produced from a sodium silicate obtained from washed rice husk ash (RHA) (RHA source washed sodium silicate).

[0326] Initial RHA characteristics:

[0327] A rice husk ash (RHA) having the following characteristics was used:

[0328] - SiO2 concentration measured by the purity determination method as described above: 88.3 wt.-%, relative to the total sample;

[0329] - Carbon content analyzed by C / S as described above: 4.9 wt.-%, relative to the total sample.

[0330] RHA washing:

[0331] A solution of 1000 g of sulfuric acid at a concentration of 0.05 wt.-% and 50 g of RHA were introduced into the reactor under stirring.

[0332] The mixture was kept under stirring and heated to 70°C for 30 minutes. At the end of the 30 minutes, the RHA and acidified water mixture was separated by Büchner filtration in order to concentrate the solids before dissolution.

[0333] RHA dissolution:

[0334] In a 5 L stainless steel 316L autoclave reactor, the following reagents were introduced:

[0335] - 290 g of soda solution at a concentration of 397 g / L;

[0336] - 1164 g of RHA, and

[0337] - 2560 g of demineralized water.

[0338] The reaction mixture was kept under stirring with a TT mixing stirrer at 500 rpm.

[0339] The temperature of the mixture was then raised to 160°C using a double jacket and maintained for 3 hours.

[0340] Once the reaction was completed, a solid / liquid separation was performed by centrifugation. The centrifugate was diluted to reach the target Si02concentration and density. The diluted product corresponds to the sodium silicate S1 used for the subsequent silica precipitation step described below.

[0341] The characteristics of the sodium silicate washed with RHA source (impurities profile and elemental composition) are shown in Table 3 below. The Rp of this sodium silicate was analyzed by the potentiometric method described above.

[0342] Silica precipitation:

[0343] 17 L of purified water and 0.260 kg of sodium silicate S1 were introduced into a 25 L stainless steel reactor. The solution was heated to 92°C. The whole reaction was performed at this temperature.

[0344] 80 g / L of sulfuric acid were introduced under stirring (350 rpm, TT mixing stirring) until the pH reached 4.1.

[0345] A sodium silicate solution at a Si02 / Na20 weight ratio equal to 3.5 and a concentration of 230 g / L and sulfuric acid at a concentration equal to 80 g / L were simultaneously introduced into the reactor over a period of 10 minutes, wherein the sodium silicate solution was introduced at a flow rate of 107 g / min and the sulfuric acid was introduced at an adjusted flow rate in such a way as to maintain the pH of the reaction medium at a value of 4.1.

[0346] At the end of 10 minutes, the sodium silicate flow rate was kept constant. Instead of 80 g / L sulfuric acid, a concentration of 1710 g / L of sulfuric acid was introduced over a period of 16 minutes and at a flow rate allowing the pH of the reaction medium to be maintained at a value of 4.1.

[0347] The addition of sulfuric acid was then stopped. Sodium silicate was introduced at a flow rate of 107 g / min, as long as the pH of the reaction medium was below 8.0.

[0348] The pH of the reaction medium was then maintained at 8 for 18 minutes by simultaneously adding sodium silicate at a flow rate of 167 g / min and adding sulfuric acid at a concentration of 1710 g / L at a regulated flow rate allowing the pH of the reaction medium to be maintained at 8.

[0349] Finally, at the end of this simultaneous addition, the reaction medium was brought to a pH of 4.0 by adding sulfuric acid at a concentration of 1710 g / L. The medium was aged at this pH for 10 minutes.

[0350] The slurry thus obtained was filtered through a filter press and washed (20% dry cake extract). The resulting filter cake was then mechanically broken up and the resulting slurry was dried using a spray dryer. The precipitated silica thus obtained (precipitated silica P1) was characterized as shown in Tables 3 and 4 below.

[0351] Example 3 - Precipitated silica, RHA source not washed

[0352] The precipitated silica according to the application is produced from sodium silicate obtained from unwashed rice husk ash (RHA) (RHA source sodium silicate).

[0353] Initial RHA characteristics:

[0354] Rice husk ash (RHA) having the following characteristics was used:

[0355] - Si02concentration measured by the purity determination method as described above: 88.1 wt.-%, relative to the total sample;

[0356] - Carbon content analyzed by C / S as described above: 11 wt.-%, relative to the total sample.

[0357] RHA dissolution:

[0358] In a 20 L stainless steel 316L autoclave reactor, the following reagents were introduced:

[0359] - 1682 g of soda solution at a concentration of 397 g / L;

[0360] - 3700 g of RHA, and

[0361] - 4628 g of demineralized water.

[0362] The reaction mixture was kept under stirring with a TT mixing stirrer at 800 rpm.

[0363] The temperature of the mixture was then raised to 160°C using a double jacket and maintained for 3 hours.

[0364] Once the reaction was completed, the solid / liquid separation was performed by centrifugation. The centrifugate was diluted to reach the target Si02concentration and density. The diluted product corresponds to the sodium silicate S2used for the subsequent silica precipitation step described below.

[0365] The characteristics (impurities profile and elemental composition) of the unwashed RHA-derived sodium silicate (S2) are shown in Table 3 below. The Rpof this sodium silicate was analyzed by the potentiometric method described above.

[0366] Silica precipitation:

[0367] 17 L of purified water and 0.260 kg of sodium sulfate S2were introduced into a 25 L stainless steel reactor. The solution was heated to 92°C. The whole reaction was carried out at this temperature.

[0368] 80 g / L of sulfuric acid was introduced under stirring (350 rpm, TT mixing stirring) until the pH reached 4.1.

[0369] A sodium silicate solution with a Si02 / Na20 weight ratio equal to 3.5 and a concentration of 230 g / L and a sulfuric acid with a concentration equal to 80 g / L were simultaneously introduced into the reactor over a period of 10 minutes, where the sodium silicate solution was introduced at a flow rate of 107 g / min and the sulfuric acid was introduced at an adjusted flow rate in such a way as to maintain the pH of the reaction medium at a value of 4.1.

[0370] At the end of the 10 minutes, the sodium silicate flow rate was kept constant. Instead of 80 g / L of sulfuric acid, a sulfuric acid with a concentration of 1710 g / L was introduced over a period of 16 minutes and at a flow rate that allowed to maintain the pH of the reaction medium at a value of 4.1.

[0371] The addition of sulfuric acid was then stopped. The sodium silicate was introduced at a flow rate of 107 g / min as long as the pH of the reaction medium was lower than 8.0.

[0372] The pH of the reaction medium was then maintained at 8.0 for 18 minutes by simultaneously adding sodium silicate at a flow rate of 167 g / min and sulfuric acid with a concentration of 1710 g / L at an adjusted flow rate that allowed to maintain the pH of the reaction medium at 8.0.

[0373] Finally, at the end of this simultaneous addition, the reaction medium was brought to a pH of 4.0 by adding sulfuric acid with a concentration of 1710 g / L. The medium was aged at this pH for 10 minutes.

[0374] The thus obtained slurry was filtered and washed through a filter press (20% dry cake extract). The resulting filter cake was then mechanically broken up and the resulting slurry was dried using a spray dryer. The characteristics of the precipitated silica thus obtained (precipitated silica P2) are shown in Tables 3 and 4 below.

[0375] Example 4

[0376] In the following table (Table 3), the characteristics of the sand source sodium silicate (S0), the RHA source washed sodium silicate (S1) and the unwashed RHA source sodium silicate (S2) employed in Examples 1-3 are reported in terms of impurity profile and elemental composition. The characteristics of the corresponding precipitated silicas (P0, P1 and P2) produced according to Examples 1-3 are also reported in terms of impurity profile and elemental composition.

[0377] The amounts in Table 3 are in ppm, unless otherwise stated.

[0378] The amounts in the precipitated silicas are based on the total weight of the precipitated silica.

[0379] In Table 3, the symbol * indicates that the amount in the silicate solution is based on the total weight of the silicate solution.

[0380] The symbol ** indicates that the amount in the silicate solution is based on the weight of Si02.

[0381] As can be seen from this table, the absence of a washing step has mainly an impact on the amount of K.

[0382] Table 3

[0383]

[0384] In the following table (Table 4), the characteristics of the precipitated silicas produced according to Examples 1-3 described above are reported.

[0385] Table 4 - CTAB, BET, CPS and Hg porosimetry surface properties of sand source, RHA source washed and RHA source unwashed precipitated silica samples.

[0386]

[0387] Example 5 - Rubber application performance

[0388] Preparation of a rubber composition suitable for the preparation of a tire or tire component: The process for the preparation of a rubber composition (i.e. a precipitated silica filled elastomeric composition) is carried out in three successive stages.

[0389] The first and second mixing stages (non-productive stages, NP1 and NP2) comprise a thermo-mechanical working at high temperature, followed by a third mechanical working stage (productive stage, P3) at a temperature lower than 110°C. The latter allows the introduction of the vulcanization system.

[0390] The first and second stages are carried out by means of an internal mixer (net chamber volume 380 mL) from Brabender with a filling factor of 0.62 and 0.6, respectively. The initial temperature and rotor speed are fixed each time in order to reach a temperature of the drop of the mixture of about 140-170°C.

[0391] The duration of the first mixing stage is between 2 and 10 minutes. After cooling the mixture (temperature lower than 100°C), the second mixing stage allows the introduction of the vulcanization system (sulfur and accelerators). It is carried out on an open two-roll mill preheated to 50°C.

[0392] The duration of this stage is between 2 and 6 minutes.

[0393] The final rubber composition is then calendered into a sheet of thickness 2-3 mm.

[0394] In table 5, the amount of each ingredient of the composition is expressed in phr (per hundred of rubber), that is to say that they are based on the total amount of rubber contained in the rubber formulation (here sSBR + BR).

[0395] Table 5: Rubber formulation

[0396]

[0397]

[0398] 21% of styrene, 49% of vinyl-functionalized SSBR (Sprintan SLR 4602 from Synthos)

[0399] BR: Buna CB 25 from Arlanxeo

[0400] TESPT: Bis-(triethoxysilylpropyl)-tetrasulfide, Si69 from Evonik

[0401] N330: Carbon black

[0402] TDAE (treated distillate aromatic extract), Vivatec 500 from Hansen & Rosenthal KG

[0403] 6-PPD: N-1,3-dimethylbutyl-N-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys)

[0404] CBS: N-cyclohexyl-2-benzothiazyl-sulphenamide (Rhenogran CBS-80 from Rhein Chemie)

[0405] DPG: Diphenyl guanidine (Rhenogran DPG-80 from Rhein Chemie)

[0406] Rheology of the uncured compound was evaluated to monitor the processability indicators. Once the vulcanization profile was determined, the uncured compound was vulcanized at the vulcanization optimum (T98) and the mechanical and dynamic properties were measured.

[0407] Viscosity of the uncured composition

[0408] The Mooney viscosity was measured at 100°C using a MV 200 rheometer according to the NF ISO 289 standard. The torque value was read at 4 minutes after one minute of preheating (ML1+4-100°C). From the curve of the torque as a function of time, the following were determined:

[0409] - the minimum torque (Tmin) which reflects the viscosity of the composition at the temperature considered;

[0410] - the maximum torque (Tmax);

[0411] - the delta torque (AT = Tmax-Tmin) which reflects the degree of crosslinking induced by the action of the crosslinking system and, if necessary, of the coupling agent;

[0412] - T.90% corresponding to the time necessary to reach 90% of the maximum torque;

[0413] - the scorch time TS2 corresponding to the time necessary to have a 2 point rise above the minimum torque at the temperature considered and which reflects the time during which it is possible to handle the raw mixture at this temperature without initiating vulcanization (the mixture cures from TS2).

[0414] The results obtained are shown in Table 6.

[0415] Mechanical properties of the cured composition

[0416] The Shore A hardness measurement of the cured composition (vulcanization time at 160°C T98) was performed according to the ASTM D 2240 standard. The value was measured after 3 seconds.

[0417] Uniaxial tensile tests were performed on H2 specimens at a speed of 500 m / min on an INSTRON 5564 according to NF ISO 37 standard. Moduli M100 and M300 (obtained at 100% and 300% strain, respectively) and tensile strength (TS) are expressed in MPa; elongation at break (EB) is expressed as a percentage. The reinforcement index (RI) was calculated, defined as the ratio between the modulus obtained at 300% strain and the modulus obtained at 100% strain.

[0418] The measured characteristics are reported in Table 7.

[0419] Dynamic properties of cured compositions

[0420] Dynamic properties were measured on a viscosity analyzer (METRAVIB DMA+1000) according to ASTM D5992.

[0421] The dynamic response of the composite cured under strain scanning conditions was determined by subjecting parallelepiped specimens (8 mm² cross-section and 4 mm height) to sinusoidal deformation under alternating double shear at a temperature of 40 °C and a frequency of 10 Hz, with the forward cycle ranging from 0.1% to 50% and the return cycle ranging from 50% to 0.1%. The values ​​of the maximum loss factor (Tanδmax), shear storage modulus (G'0.1% and G*12%), and Payne effect (G'0.1%–G50%) were recorded during the return cycle. The measured properties are reported in Table 8.

[0422] Dynamic response of compositions cured under temperature scanning conditions

[0423] The dynamic response of the vulcanized rubber composition was measured by stretching a parallelepiped specimen (8 mm² cross-section and 7 mm height) at 1% alternating double shear sinusoidal deformation and a frequency of 10 Hz under a temperature scan from -70 °C to 100 °C (heating rate of +5 °C / min). The maximum loss factor (Tanδmax) was then measured.

[0424] Table 6 - Uncured

[0425]

[0426] Table 7 - Mechanical Properties / Curing

[0427]

[0428] Table 8 - Dynamic Properties / Curing

[0429]

[0430]

[0431] The above results show that the rubber compositions comprising the precipitated silica according to the application (i.e. RHA source unwashed) advantageously show similar mechanical and dynamic properties to the rubber compositions comprising the precipitated silica obtained by prewashing of rice husk ash (i.e. RHA source washed).

Claims

1. A precipitated silica, comprising: (i) Based on the precipitated silica being SiO2 in particulate form, ranging from 80.0% to 99.0% by weight, (ii) Sodium in an amount of at least 1.00‰ by weight of SiO2 contained in the precipitated silica, and (iii) Potassium in an amount of at least 0.25‰ by weight of SiO2 contained in the precipitated silica. The precipitated silica is essentially free of SiO2 particles to which organic components are covalently bonded via Si-C bonds.

2. The precipitated silica according to claim 1, wherein, Based on the weight of SiO2 contained in the precipitated silica, the weight of potassium is at least 0.30‰, preferably at least 0.33‰, more preferably at least 0.35‰, even more preferably at least 0.38‰, and most preferably at least 0.40‰.

3. The precipitated silica according to claim 1 or 2, wherein, Based on the weight of SiO2 contained in the precipitated silica, the weight of potassium is at most 3.00‰, preferably at most 1.50‰, more preferably at most 0.80‰, even more preferably at most 0.60‰, and most preferably at most 0.50‰.

4. The precipitated silica according to claim 1, wherein, Based on the weight of SiO2 contained in the precipitated silica, the weight of potassium ranges from 0.33‰ to 0.80‰, preferably from 0.35‰ to 0.60‰, and more preferably from 0.37‰ to 0.50‰.

5. The precipitated silica according to any one of the preceding claims, wherein, Based on the weight of SiO2 contained in the precipitated silica, the weight of sodium ranges from 1.00‰ to 20.0‰, preferably from 1.50‰ to 15.0‰, more preferably from 2.00‰ to 10.0‰, even more preferably from 3.00‰ to 10.0‰, and most preferably from 4.00‰ to 8.00‰.

6. The precipitated silica according to any one of the preceding claims, wherein, The ratio of the weight of potassium to the weight of sodium ranges from 0.01 to 1.00, possibly from 0.06 to 0.60, preferably from 0.02 to 0.40, more preferably from 0.03 to 0.20, and even more preferably from 0.04 to 0.

15.

7. The precipitated silica according to any one of the preceding claims, having a carbon content as determined by the C / S method, ranging from 0 to less than 0.5% by weight, preferably from 0 to 4000 ppm, more preferably from 0 to 3000 ppm, even more preferably from 0 to 2000 ppm, and even more preferably from 0 to 1000 ppm.

8. The precipitated silica according to any one of the preceding claims, having a sulfur content of, as determined by the C / S method, ranging from 0.10% to 1.0% by weight of SiO2 contained in the precipitated silica, preferably from 0.20% to 0.50%.

9. A method for producing precipitated silica from plant ash, the method comprising the following steps: (I) Reacting plant ash containing SiO2 and potassium with a sodium-containing alkali metal base, preferably sodium hydroxide, in an aqueous reaction medium at a temperature of at least 100°C to obtain an aqueous silicate solution, wherein the weight amount of potassium is at least 12.5‰ based on the weight of SiO2 contained in the plant ash, and the aqueous silicate solution contains (i) SiO2 in the form of silicate anions and (ii) sodium cations (Na+) in the form of at least 1.0‰ based on the weight of SiO2 contained in the silicate solution. + (iii) a potassium cation (K) of at least 5.0‰ by weight based on the weight of SiO2 contained in the silicate solution. + ), and (II) The aqueous silicate solution is reacted with an acidifying agent in an aqueous reaction medium having a pH of more than 7.0 for at least a portion of the reaction duration in order to achieve the precipitation of silica and produce an aqueous slurry containing SiO2 in particulate form.

10. The method of claim 9, further comprising a step (A) prior to step (I): burning a plant and / or plant part containing SiO2 and potassium to obtain the plant ash, the amount of potassium being at least 12.5‰ by weight based on the weight of SiO2 contained in the plant or plant part, wherein the method does not include any step (B) after step (A) and before step (I) to remove some or all of the potassium from the plant ash.

11. The method of claim 10, wherein it does not contain any step (B') prior to step (A) of removing some or all of the potassium from the plant and / or plant parts.

12. The method according to any one of claims 9 to 11, further comprising the following steps: (III) Preferably, the aqueous slurry obtained after step (II) is filtered using a filter press to obtain a filter cake containing SiO2 in the form of particulate matter. (IV) Optionally, the filter cake may be washed with a liquid containing water, preferably water. (V) The filter cake is liquefied into a flowable aqueous suspension containing SiO2 in particulate form by adding a liquid containing water to the filter cake and optionally by subjecting the filter cake to mechanical and / or chemical treatment. (VI) Preferably, the flowable aqueous suspension is dried by means of a spray dryer in order to obtain the precipitated silica.

13. The method of claim 12, wherein the method does not include any step (B”) after step (VI) to remove part or all of the sodium and / or potassium from the precipitated silica.

14. The method according to any one of claims 9 to 13, wherein, The precipitated silica is as defined in any one of claims 1 to 8.

15. Use of precipitated silica according to any one of claims 1 to 8 in the manufacture of at least one of: (i) a precipitated silica-filled elastomer composition; (ii) a tire component comprising a precipitated silica-filled elastomer composition, preferably a tire tread; and (iii) a tire comprising at least one component comprising a precipitated silica-filled elastomer composition.

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