Process for recovering silicates from polymer compositions comprising silica

Abstract

A process for recovering silicates from a polymer composition comprising silica is provided, the process being characterized by mild reaction conditions. The silicate may be recovered without degrading or depolymerizing the polymer composition.

Description

Technical Field

[0001] The present disclosure relates to a method for recovering silicate from a polymer composition comprising silica. Background Art

[0002] The following discussion of the prior art is provided to place the present disclosure in the proper technical context and to enable its advantages to be more fully understood. However, it should be understood that any discussion of the prior art throughout the specification should not be taken as an explicit or implicit admission that such prior art is widely known or forms part of the common general knowledge in the art.

[0003] The use of precipitated silica as a reinforcing filler in polymer compositions is known. In particular, it is known to use precipitated silica as a reinforcing filler in elastomeric compositions. This use is very demanding: the filler must be easily and effectively incorporated and dispersed in the elastomeric composition and, typically in combination with a coupling agent, form chemical bonds with one or more elastomers on one side and the silica on the other side, resulting in a high and uniform reinforcement of the elastomeric composition. In general, precipitated silica is used in order to improve the mechanical properties and the handling and abrasive properties of the elastomeric composition.

[0004] Polymer compositions comprising silicon dioxide, such as automobile tires, are typical examples of products derived from non-renewable petroleum resources. At present, thermal cracking is considered to be a useful industrial method for increasing the value of waste rubber compounds by recovering materials and energy. However, thermal cracking must use high temperatures. Generally speaking, the method of utilizing such non-renewable petroleum resources is inefficient. When the waste polymer composition is not properly disposed of and the residue is not easy to reuse, there is a risk of polluting the local environment. Silicon dioxide is almost never recycled in this way, and is often considered to be a "poison". Removing it before or after any additional treatment may be beneficial to re-evaluate (revalorising) other residues.

[0005] Therefore, there remains a need to develop a process for recovering silicates from polymer compositions comprising silica, in particular from scrap tires that may be off-specification (performance, size, etc.) or even from scrap process rubber formulations. Summary of the invention

[0006] It is therefore an object of the present disclosure to provide a process for recovering silicates from a polymer composition comprising silica, which process is characterized by mild reaction conditions.

[0007] Accordingly, the present disclosure relates to a method for recovering silicate from a polymer composition comprising silica, the method comprising the steps of:

[0008] (i) contacting a polymer composition comprising silica with a base in the presence of a solvent,

[0009] (ii) reacting the base with silicon dioxide to form a silicate, thereby obtaining a polymer composition which has lost at least part of the silicon dioxide and a solution comprising the silicate, and

[0010] (iii) separating the solution obtained in step (ii) from the polymer composition obtained in step (ii).

[0011] Other subjects and features, aspects and advantages of the present disclosure will become more clearly apparent upon reading the following detailed description and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Particle size distribution of tire powder prepared in the examples.

[0013] definition

[0014] In this specification, the terms "silicon dioxide" and "precipitated silica" are used as synonyms.

[0015] Throughout this specification, including the claims, unless otherwise indicated, the term "comprising one / an" should be understood to be synonymous with the term "comprising at least one / an", and "between..." should be understood to include the limit values.

[0016] As used herein, the term "(C n -C m )" (where n and m are both integers) indicates that the group can contain from n to m carbon atoms per group.

[0017] Use of the articles "a," "an," and "the" means that the grammatical object of the article is one or more than one (ie, to at least one).

[0018] The term "and / or" includes the meanings "and", "or" and all other possible combinations of the elements associated with this term.

[0019] It should be noted that, for the sake of continuity of description, limiting values ​​are included in the range of values ​​given unless otherwise indicated.

[0020] Ratios, concentrations, amounts and other numerical data may be presented in a range format herein. It should be understood that this range format is used only for convenience and brevity and should be flexibly understood to include not only the values ​​explicitly stated at the limits of the range, but also all individual values ​​or sub-ranges included within the range, just as if each value or sub-range was explicitly stated. DETAILED DESCRIPTION

[0021] The present disclosure provides a method for recovering silicate from a polymer composition comprising silica, the method comprising the steps of:

[0022] (i) contacting a polymer composition comprising silica with a base in the presence of a solvent,

[0023] (ii) reacting the base with silicon dioxide to form a silicate, thereby obtaining a polymer composition which has lost at least part of the silicon dioxide and a solution comprising the silicate, and

[0024] (iii) separating the solution obtained in step (ii) from the polymer composition obtained in step (ii).

[0025] The term "polymer composition" is used herein to refer to a composition comprising at least one polymer. When referring to the polymers in the composition, the phrase "at least one" is used herein to indicate that one or more than one polymer of each type may be present in the composition.

[0026] The expression "copolymer" is used herein to refer to a polymer comprising repeating units derived from at least two monomer units having different natures.

[0027] The at least one polymer may be selected from thermosetting polymers and thermoplastic polymers, the latter being preferred.

[0028] Notable non-limiting examples of suitable thermoplastic polymers include styrene-based polymers such as polystyrene, (meth)acrylate / styrene copolymers, acrylonitrile / styrene copolymers, styrene / maleic anhydride copolymers, ABS; acrylic polymers such as polymethyl methacrylate; polycarbonates; polyamides; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene ether; polysulfones; polyaryletherketones; polyphenylene sulfide; thermoplastic polyurethanes; polyolefins such as polyethylene, polypropylene, polybutene, poly-4-methylpentene, ethylene / propylene copolymers, ethylene / α-olefin copolymers; copolymers of α-olefins and various monomers such as ethylene / vinyl acetate copolymers, ethylene / (meth)acrylate copolymers, ethylene / maleic anhydride copolymers, ethylene / acrylic acid copolymers; aliphatic polyesters such as polylactic acid, polycaprolactone, and aliphatic diol / aliphatic dicarboxylic acid copolymers.

[0029] Silica can advantageously be present in the elastomeric composition as reinforcing filler.The notable non-limiting example of suitable elastomer is diene elastomer.For example, an elastomer derived from aliphatic or aromatic monomers can be used, which comprises at least one degree of unsaturation, such as, particularly, ethylene, propylene, butadiene, isoprene, styrene, acrylonitrile, isobutylene or vinyl acetate, polybutyl acrylate or their mixture.It can also be mentioned that functionalized elastomers are elastomers and halogenated polymers functionalized by chemical groups (for example, by being able to react with the surface of silica) along the macromolecular chain and / or at one or more of its ends.It can be mentioned that polyamide, ethylene homopolymer and copolymer, propylene homopolymer and copolymer.Other suitable elastomers are those comprising chloro-butyl monomer or bromo-butyl monomer (for example as bromo-butylene).

[0030] Among the diene elastomers, mention may be made, for example, of 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 related functionalized polymers (for example exhibiting pendant polar or reactive groups or polar groups at the chain ends which can interact or react with silica).

[0031] Mention may also be made of natural rubber (NR) and epoxidized natural rubber (ENR).

[0032] The polymer composition may be vulcanized with sulfur or crosslinked, in particular with peroxides or other crosslinking systems, such as diamines or phenolic resins.

[0033] The type of silica according to the present disclosure is not particularly limited. It can be conventional or highly dispersible silica, such as Premium SW, Premium200MP, 1165MP, 1115MP or 1085GR (commercially available from Solvay).

[0034] The surface area of ​​mesoporous silica (CTAB as template) according to the present disclosure can be 40 to 500 m 2 / g.

[0035] The BET surface area of ​​silica according to the present disclosure may be 40 to 500 m 2 / g.

[0036] The proportion by weight of silicon dioxide in the polymer composition can vary within a relatively wide range. It generally represents from 0.01% to 40%, in particular from 10% to 40%, especially from 20% to 40%, relative to the amount of polymer or polymers.

[0037] In the case of elastomeric compositions, the % is sometimes referred to as phr or per hundred parts of rubber. Preferably, the silica in the polymer composition may be from 5 to 200 phr, and more preferably from 5 to 150 phr.

[0038] Applicants have found that the higher the silica content in the polymer composition, the higher the silicate recovery efficiency.

[0039] In some embodiments, the polymer composition may additionally include other inorganic reinforcing fillers (such as nanoclay, alumina), or organic reinforcing fillers (such as carbon black, carbon black nanotubes, graphene, starch, cellulose, etc.).

[0040] Silica according to the present disclosure preferably constitutes at least 5% by weight, preferably at least 30%, more preferably 60%, indeed even at least 80% by weight of the total amount of reinforcing filler.

[0041] In a preferred embodiment, the polymer composition comprises silica and carbon black. The proportion of silica and carbon black by weight relative to the amount of the one or more polymers may be 1% to 50%.

[0042] Advantageously, the polymer composition comprising silica, in particular the polymer composition comprising silica recovered from tires, especially scrap tires, can be provided in powder form. The skilled person can determine measurement methods, such as scanning electron microscopy (SEM), particle size distribution analyzer (PSD) or vernier calipers, to obtain the average particle size and / or particle size distribution, depending on the processing process, such as cryogenic grinding, pulverization process and crushing process.

[0043] For SEM analysis, a ZEISS EVO-18 with a tungsten filament with a voltage of 20 kV equipped with a backscattered electron detector (BSD) or a secondary electron detector was used. Magnifications can reach up to 50K-100K. SEM is used to detect particle sizes between 200 nm and 1000 μm. The particles were deposited on a layer of graphite tape, coated with Pt for 40 seconds, and measured by SEM. The results obtained were analyzed using SmartSEM software. For each sample, approximately 10 photos were taken and a total of 100 particles were analyzed to obtain the size distribution described. From this size distribution, the average particle size of the particles was obtained. The software used to measure the size of the particles was ImageJ, whereby the particles were approximated to irregular shapes by measuring the longest distance. After setting the scale, the longest diameter of the particles was measured manually one by one until the total number of particles measured was 100. Each particle was measured 3 times to obtain the average size.

[0044] For particle size distribution analyzer (PSD), a Malvern Mastersizer 3000 with a range lens of 300 RF mm was used. PSD is used to detect a particle size range of 10 nm to 3.5 mm. The particles are dissolved in ethanol and the mixture is stirred for 10 min. The dispersed sample is passed through the measurement area of ​​the optical bench, where a laser beam irradiates the particles. Then, a series of detectors accurately measure the intensity of light scattered by the particles in the sample to both red and blue wavelengths and over a wide range of angles. Prepare and measure at least three parallel samples to obtain particle size distribution, such as D10, D50 and D90. Particle size distribution D10, D50 and D90 represent that 10%, 50% or 90% of the particles in the powder are less than the size within this range.

[0045] For ruler analysis, a vernier caliper is used to measure particle sizes greater than 1000 μm. The longest diameter of each particle is measured manually. Approximately 100 particles are measured to obtain an average value for the particle size distribution.

[0046] The method for preparing the powder is not particularly limited. For example, the technician can use mechanical forces like crushing (grinding, rolling and biting), grinding (with balls and rods) or even chopping to prepare the powder. In a preferred embodiment, the powder can be prepared by cryogenic grinding.

[0047] The silica-containing polymer composition, in particular the silica-containing polymer composition recovered from tires, especially scrap tires, may require pretreatment. The skilled person will appreciate that different parts of scrap tires may require different pretreatments.

[0048] For example, tire tread, which is a silica-rich fraction, can be removed from the tire by a machine having a blade system and then shredded and ground.

[0049] As another example, when pre-treating the non-tread portion of the waste tire or the entire waste tire, the technician can first powder the non-tread portion or the entire tire, and then remove the metal portion and the fiber portion in the tire. For example, the pre-treatment can be the method disclosed in US 2017 / 0043351, which includes the steps of pre-grinding, low-temperature freezing, grinding and heating of the feed material, ferrous metal and fiber removal, accumulation, screening and storage of micronized powder. The pre-treatment can also be a method including the steps of shredding, metal removal and fiber removal.

[0050] The term "base" is used herein to refer to one or more than one base. Any base can be used in the method as long as it can react with silicon dioxide to form a silicate. Non-limiting examples of suitable bases are inorganic bases such as alkali metal hydroxides, alkaline earth metal hydroxides and ammonia. Preferably, the base can be sodium hydroxide or potassium hydroxide.

[0051] The solvent according to the present disclosure is not particularly limited. Advantageously, the solvent is stable under alkaline conditions. It can be water, an organic solvent or a mixture thereof. The organic solvent preferably has a pH of less than 33 MPa. 1 / 2 , preferably between 15 and 29 MPa 1 / 2 Between, more preferably 20 to 25 MPa 1 / 2 The overall Hansen solubility parameters of

[0052] Preferably, the solvent may comprise water. In this case, when the base is an inorganic base, it may advantageously be dissolved in water to form an aqueous solution before contacting the polymer composition. The concentration of the base in the aqueous solution may advantageously be 4 wt.% to 50 wt.% and preferably 8 wt.% to 40 wt.% relative to the total weight of the aqueous solution.

[0053] In some embodiments, the solvent may consist of water.

[0054] In certain embodiments, the solvent can be a mixture of water and an organic solvent. The organic solvent can be selected from the group consisting of toluene, dimethylbenzene, acetone, DMSO and alcohol. Preferably, the organic solvent can be selected from the group consisting of DMSO, toluene, acetone, 1-propanol, 2-propanol, 2-butanol and the tert-butyl alcohol, more preferably selected from the group consisting of toluene, acetone, 1-propanol, 2-propanol, 2-butanol and the tert-butyl alcohol, and most preferably selected from the group consisting of 1-propanol, 2-propanol and 2-butanol.

[0055] In a specific embodiment, when the solvent is a mixture of water and an organic solvent, the volume ratio of water to the organic solvent may be 0.1:1 to 10:1, and preferably 0.2:1 to 3:1.

[0056] The molar ratio of base to silica may advantageously be from 40:1 to 1:1, preferably from 20:1 to 2:1, and more preferably from 5:1 to 2:1.

[0057] The reaction temperature in step (ii) may be 25°C to 180°C, preferably 40°C to 120°C, and more preferably 70°C to 100°C.

[0058] The reaction time in step (ii) may be 2 to 48 hours, and preferably 3 to 24 hours.

[0059] The reactor may preferably be made of a material resistant to the above-mentioned organic solvents and alkalis, such as Teflon and hastelloy.

[0060] The method for separating the solution and the polymer composition in step (iii) is not particularly limited. The method may be centrifugation and / or decantation, depending on the particle size.

[0061] Advantageously, by using methods according to the present disclosure, silicates can be recovered without degrading or depolymerizing the polymer composition.

[0062] Advantageously, at least 50 wt.%, preferably at least 60 wt.%, more preferably at least 80 wt.% of silica is recovered relative to the total weight of silica in the polymer composition, calculated on the silicon content in the solution obtained in step (iii).

[0063] Silicates recovered by the process according to the present disclosure may be advantageously used in the manufacture of silica, especially precipitated silica.

[0064] Precipitated silica can be manufactured from recovered silicates by processes well known to the skilled person. Such processes typically include reacting the recovered silicate with an acid in an aqueous solution to obtain a slurry containing precipitated silica particles. Such processes typically also include filtering, and if necessary, washing the slurry to obtain a suspension of silica particles ("filter cake"), and drying the filter cake to obtain precipitated silica in powder form. A suitable process among many other processes is described and illustrated in U.S. Patent No. 11,241,370, the entire contents of which are incorporated herein by reference for all purposes.

[0065] The term "acid" is used herein to refer to one or more than one acid that can be added during the process of the method of the invention. Any acid can be used in the method. Usually inorganic acids such as sulfuric acid, nitric acid, phosphoric acid or hydrochloric acid, or organic acids such as carboxylic acids, for example acetic acid, formic acid or carbonic acid are used. Good results have been obtained with sulfuric acid.

[0066] The skilled person will appreciate that when an acid is added, the pH of the solution decreases. Preferably, the pH may be reduced to a value below 6, and more preferably below 5.

[0067] Advantageously, the process according to the present disclosure can be used for the recycling of scrap tires, which aids in the production of silicates or precipitated silica.

[0068] The following examples are included to illustrate embodiments of the present disclosure. Needless to say, the present disclosure is not limited to the described examples.

[0069] Experimental Section

[0070] Material

[0071] - Simplified green tire tread formulation sheet (Solvay) containing 32 wt.% SiO2;

[0072] -Sodium hydroxide (CAS: 1310-73-2, >96%, Sinopharm);

[0073] - dimethyl sulfoxide (DMSO) (CAS: 67-68-5, 99%, J&K);

[0074] - tert-Butanol (CAS: 75-65-0, 99.5%, J&K);

[0075] - Ethylene glycol (CAS: 107-21-1, 99.5%, J&K);

[0076] -Acetone (CAS: 67-64-1, ≥99.5%, AR, Sinopharm Group);

[0077] -Toluene (CAS: 108-88-3, ≥99.5%, AR, Sinopharm Group);

[0078] -1-Propanol (CAS: 71-23-8, ≥96%, Sinopharm Group);

[0079] -2-Propanol (CAS: 67-63-0, ≥96%, Sinopharm Group);

[0080] -2-Butanol (CAS: 78-92-2, CP, Sinopharm Group);

[0081] -Ethanol (CAS: 64-17-5, ≥95%, Sinopharm Group).

[0082] Preparation of green tire powder

[0083] A simplified green tire tread formulation sheet prepared by Solvay was shredded and cut into powder. The particle distribution of the powder was determined by a particle size distribution analyzer (PSD) Malvern Mastersizer 3000. While stirring, the tire powder was dispersed in ethanol in a sample unit, and the sample was allowed to disperse evenly for about 10 minutes. Figure 1 As shown, the test was repeated 6 times to ensure consistent results. According to PSD, 90% of the particles had a diameter below 338 μm, 50% had a diameter below 190 μm, and 10% had a diameter below 94.5 μm.

[0084] Example 1

[0085] The tires were treated with an aqueous NaOH solution containing no organic solvent.

[0086] In a typical procedure, green tire powder (1.5 g) and NaOH aqueous solution (33 wt.%, 15 ml) were sequentially added to a Teflon reactor equipped with a Teflon condenser. The mixture was heated and stirred at 85°C for 22 hours. After the reaction, the mixture was transferred to a centrifuge tube. The reactor was washed with mixed EtOH and H2O (20 mL) to completely remove the solvent and residual tire from the reactor into the centrifuge tube. The mixture was centrifuged at 10000 rpm for 5 min to separate the tire from the liquid. The separated liquid was stored in a container, and then freshly mixed EtOH and H2O were added to the centrifuge tube to remove the residual NaOH from the tire. The procedure was repeated several times until the pH of the separated liquid was equal to 7. Finally, the wet tire was dried at 100°C under vacuum. All the separated liquid in the container was concentrated to 50 ml by evaporation at 40°C and 60 mbar. The silicon content in the liquid and the amount of silicon in the remaining tire were quantified by ICP. The amount of SiO2 extracted in the liquid, the amount of SiO2 remaining in the tire, and the mass balance of SiO2 before and after the reaction were calculated according to the following equations.

[0087]

[0088] Example 2

[0089] The tires were treated with aqueous NaOH and 2-propanol.

[0090] In a typical procedure, green tire powder (1.5 g), aqueous NaOH solution (33 wt.%, 15 ml) and 2-propanol (10 ml) were sequentially added to a Teflon reactor equipped with a Teflon condenser. The mixture was heated and stirred at 82°C for 22 hours. After the reaction, the mixture was transferred to a centrifuge tube. The reactor was washed with mixed EtOH and H2O (20 mL) to completely remove the solvent and residual tire from the reactor into the centrifuge tube. The mixture was centrifuged at 10000 rpm for 5 min to separate the tire from the liquid. The separated liquid was stored in a container, and then freshly mixed EtOH and H2O were added to the centrifuge tube to remove the residual NaOH from the tire. The procedure was repeated several times until the pH of the separated liquid was equal to 7. Finally, the wet tire was dried at 100°C under vacuum. All the separated liquid in the container was concentrated to 50 ml by evaporation at 40°C and 60 mbar. The silicon content in the liquid and the amount of silicon in the remaining tire were quantified by ICP.

[0091] Example 3

[0092] The tires were treated with aqueous NaOH and 1-propanol.

[0093] The reaction scheme was similar to Example 2 except that 10 ml of 1-propanol was added.

[0094] Example 4

[0095] The tires were treated with aqueous NaOH and 2-butanol.

[0096] The reaction scheme was similar to Example 2 except that 10 ml of 2-butanol was added.

[0097] Example 5

[0098] The tires were treated with aqueous NaOH and tert-butyl alcohol.

[0099] The reaction scheme was similar to Example 2 except that 10 ml of tert-butyl alcohol was added.

[0100] Example 6

[0101] The tires were treated with aqueous NaOH and toluene.

[0102] The reaction scheme was similar to Example 2 except that 10 ml of toluene was added and the reaction temperature was 105°C.

[0103] Example 7

[0104] The tires were treated with aqueous NaOH and acetone.

[0105] The reaction scheme was similar to Example 2 except that 10 ml of acetone was added and the reaction temperature was 105°C.

[0106] Example 8

[0107] The tires were treated with aqueous NaOH and dimethyl sulfoxide (DMSO).

[0108] The reaction protocol was similar to Example 2 except that 10 ml of DMSO was added and the reaction temperature was 105°C.

[0109] Example 9

[0110] The tires were treated with aqueous NaOH and ethylene glycol.

[0111] The reaction scheme was similar to Example 2 except that 10 ml of ethylene glycol was added.

[0112] Table 1 Effect of organic solvents

[0113]

[0114] The ICP analysis error can be ±3%.

[0115] Table 1 shows that various solvents combined with NaOH solution can be used to extract SiO2 from tires. Among them, 2-propanol is the most effective solvent.

[0116] Example 10

[0117] Tires were treated with aqueous NaOH and DMSO.

[0118] The reaction scheme was similar to that of Example 8 except that 15 ml of NaOH aqueous solution (concentration 18 wt.%) was added.

[0119] Example 11

[0120] The tires were treated with aqueous NaOH and tert-butyl alcohol.

[0121] The reaction scheme was similar to that of Example 5 except that 15 ml of NaOH aqueous solution (concentration 18 wt.%) was added.

[0122] Table 2 Effect of NaOH solution concentration

[0123]

[0124] The ICP analysis error can be ±3%.

Claims

1. A method for recovering silicate from a polymer composition containing silicon dioxide, the method comprising the following steps: (i) contacting a polymer composition comprising silica with a base in the presence of a solvent, (ii) reacting the base with silicon dioxide to form a silicate, thereby obtaining a polymer composition which has lost at least part of the silicon dioxide and a solution comprising the silicate, and (iii) separating the solution obtained in step (ii) from the polymer composition obtained in step (ii).

2. The method according to claim 1, wherein: The solvent is water, an organic solvent or a mixture thereof.

3. A method according to any one of the preceding claims, wherein: The solvent is a mixture of water and an organic solvent.

4. A method according to any one of the preceding claims, wherein: The organic solvent has a pressure less than 33 MPa. 1 / 2 , preferably between 15 and 29 MPa 1 / 2 Between, more preferably 20 to 25 MPa 1 / 2 The overall Hansen solubility parameters of 5. A method according to any one of the preceding claims, wherein: The organic solvent is selected from the group consisting of toluene, xylene, acetone, DMSO and alcohol.

6. A method according to any one of the preceding claims, wherein: The organic solvent is selected from the group consisting of DMSO, toluene, acetone, 1-propanol, 2-propanol, 2-butanol and tert-butanol.

7. A method according to any one of the preceding claims, wherein: The organic solvent is selected from the group consisting of toluene, acetone, 1-propanol, 2-propanol, 2-butanol and tert-butanol.

8. A method according to any one of the preceding claims, wherein: The organic solvent is selected from the group consisting of 1-propanol, 2-propanol and 2-butanol.

9. A method according to any one of the preceding claims, wherein: The molar ratio of the base to silica is from 40:1 to 1:1, preferably from 20:1 to 2:1, and more preferably from 5:1 to 2:

1.

10. A method according to any one of the preceding claims, wherein: The base reacts with silica at a temperature of 25°C to 180°C, preferably 40°C to 120°C, and more preferably 70°C to 100°C.

11. A method according to any one of the preceding claims, wherein: The proportion by weight of silica in the polymer composition is from 0.1% to 40%, in particular from 10% to 40%, especially from 20% to 40%, relative to the amount of polymer or polymers.

12. A method according to any one of the preceding claims, wherein: The silica-containing polymer composition is in the form of a powder.

13. The method according to any one of the preceding claims, further comprising recovering the silica-containing polymer composition from the tire.

14. A method for producing precipitated silica, the method comprising: - recovering silicate from a polymer composition comprising silica by the process according to any one of claims 1 to 12, and - Using the recovered silicates to produce precipitated silica.

15. The method of claim 14, further comprising recovering the silica-containing polymer composition from the tire.

16. Use of the method according to claim 13 or 15 for recycling waste tyres.

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