DESC:
FIELD OF THE INVENTION
The present invention relates to a process for preparation of precipitated silica having high surface area (HSA) high dispersibility (HD). The HD Silica (HDS) obtained is suitable for use in various applications in preparation of rubber components and tyres.

BACKGROUND OF THE INVENTION
Precipitated silica is in high demand in a variety of applications. It is also useful in preparation of rubber components and tyres. For these applications, one needs precipitated silica with high surface area in the range of 250-350 m2/g, CTAB 170 to 230 m2/g, sears number in the range of 15-20 ml/1.5 g.

Reference may be made to a US patent publication number 2020/0115246 A1, dated 16 April 2020, by Rautaray Debabrata, wherein specification of precipitated silica is described exhibiting high dispersibility in elastomers, for its use as filler in vulcanising rubber without specific method and application.

Reference may be made to a US patent publication number 2020/0115245 A1, dated 16 April 2020, by Rautaray Debabrata, a process for preparation of the precipitated silica having high dispersibility, medium surface area BET and CTAB is described. The process employs an organic surfactant which makes the process complex, expensive and handling organic laden effluent.

There is a need to develop a process for preparing precipitated silica having desirable properties useful in variety of applications for example in preparation of rubber components and tyres.

The present inventors have surprisingly developed an efficient process for preparing precipitated silica having high surface area, high CTAB, and high sears number exhibiting high dispersibility which is not reported hitherto.

The present inventors have developed a process for preparing precipitated silica which does not employ any organic substance in the process. The process operates at moderate temperature and aging time. The product obtained is suitable for its application in preparation of rubber component and tyres

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a process for preparing precipitated silica having desirable properties.

It is an object of the present invention to provide silica useful in preparation of rubber components and tyres.

It is another object of the present invention to provide precipitated silica having high surface area.

It is another object of the present invention to provide precipitated silica having high dispersibility.

It is another object of the present invention to provide precipitated silica having high CTAB.

It is another object of the present invention to provide precipitated silica having high sears number.

It is another object of the present invention to provide precipitated silica with simple method without employing any organic substance in the process.

SUMMARY OF THE INVENTION
According to an aspect of the present invention there is provided a process for the preparation of precipitated silica comprising the steps of,
(i) Adding water to the jacketed reactor;
(ii) Adding sodium silicate having Na2O:SiO2 ratio in the range of 1:3.2-3.4 into the reactor;
(iii) Heating the reactor content to a temperature in the range of 55-85ºC;
(iv) Adding simultaneously sodium silicate, sulfuric acid and water to the reactor within a period of 90-150 minutes;
(v) Monitoring alkali number and maintaining the alkali number in the range of 10-20;
(vi) Aging the reactor content for 15-30 minutes;
(vii) Adjusting the pH of the reactor content to a range of 3.0 to 4.5;
(viii) Filtering the reactor content;
(ix) washing the wet cake until the conductivity of wash water reaches 1000-5000;
(x) Drying the wet cake; and
(xi) Granulating the dried powder in the roller compacter.

DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the scope of the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, steps or components but does not preclude the presence or addition of one or more other features, steps, components or groups thereof.

The present invention relates to a process for preparation of precipitated silica having high surface area (HSA) high dispersibility (HD). The HD Silica (HDS) obtained is suitable for use in various applications in preparation of rubber components and tyres.

In an embodiment of the present invention, there is provided a process for preparation of highly dispersible precipitated silica having high BET, high CTAB, and high sears number.

In an embodiment of the present invention there is provided a process for the preparation of precipitated silica comprising of the following steps,
(i) Adding water to the jacketed reactor;
(ii) Adding sodium silicate having Na2O: SiO2 in the ratio in the range of 1:3.2-3.4 into the reactor;
(iii) Heating the reactor content up to 55-85ºC;
(iv) Adding simultaneously sodium silicate, sulfuric acid and water to the reactor within 90-150 minutes;
(v) Monitoring alkali number maintaining the alkali number in the range of 10-20;
(vi) Aging the reactor content for 15-30 minutes;
(vii) Adjusting the pH of the reactor content from 3.0 to 4.5;
(viii) Filtering the reactor content;
(ix) Washing the wet cake till 1000-5000 conductivity of wash water;
(x) Drying the wet cake;
(xi) Granulating the dried powder in roller compacter.

In an embodiment of the present invention, water is added in the reactor to create a water pool.

In another embodiment of the present invention, sodium silicate having Na2O: SiO2 in the ratio in the range of 1:3.2-3.4 is added in the reactor water pool. The reactor content is heated to 55-800C.

In another embodiment of the present invention, sodium silicate, sulfuric acid and water streams are added into the reactor in 90-150 minutes.

In another embodiment of the present invention, alkali number is monitored and maintained in the range of 10-20.

In another embodiment of the present invention, on completion of addition of reactants, the reactor content is aged for 15-30 minutes.

In another embodiment of the present invention, the pH of the reactor content is brought down to 3.5-4 by addition of sulfuric acid.

In another embodiment of the present invention, the reactor content is filtered.

In another embodiment of the present invention, the filter cake is washed with water till wash water conductivity is 1000-5000.

In another embodiment of the present invention, the washed cake is dried.
In another embodiment of the present invention, the dry product is granulated in roller compactor at a pressure of 25-30 bar.

The product obtained in the present invention was characterized and arrived at the following product specification.

Sr. No. Parameters Unit Range
1 Appearance -- White granule
2 BET Surface Area m2/g 250 -350
3 CTAB Surface Area m2/g 170 - 230
4 Sears Number ml/1.5g 14 - 18
5 Loss on Drying (105°C for 2h) % 4 -8
6 pH (5% in water.) - 5.5 – 7.5

ADVANTAGES OF THE PROCESS AND PRODUCT OF THE PRESENT INVENTION
The present process is energy efficient, economically attractive, less polluting and produces product having high application in preparation of rubber component and tyres. The product obtained also improves dynamic properties of the rubber component and tires.

EXAMPLES
The present invention is described below with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the invention in any manner.

Example-1
7.82 kg of water is taken in a ss jacketed reactor equipped with stirrer having 22 L of holding capacity. 0.644 kg of Sodium silicate having Na2O:SiO2 weight ratio of 1:3.21 and SiO2 content of 22.10% (w/w) is added into the reactor. The reactor content was heated to 720C and stirring was initiated at 500 rpm. Simultaneous addition of sodium silicate having Na2O: SiO2 weight ratio of 1:3.21 and SiO2 content of 22.10% (w/w), sulfuric acid having concentration of 20.29 % (w/w), and water was started in the reactor. The rate of addition was kept at 38 ml/min of sodium silicate, 16.6 ml/min of sulfuric acid and 25 ml/min of water for the three streams respectively. The addition was continued for 120 minutes. The alkali number was monitored and maintained at about 15-18. After addition is completed, the content of the reactor is aged for 20 minutes. After aging, the pH was brought down from 10.4 to 4 pH by addition of sulfuric acid. The content of reactor was filtered using vacuum filter, washed with water till wash filtrate exhibits conductivity of 3000 µs/cm. The wet cake was dried in an oven at 1100C. The dry material is passed through 325 mesh sieves. The characterisations of the product is given in the following table-1

Table-1
Sr. No. Parameters Unit Value obtained Test method
1 Appearance -- White powder -
2 BET Surface Area m2/g 288.5 ASTM- D1993
3 CTAB Surface Area m2/g 196.4 ASTM- D6845
4 Sears Number ml/1.5g 16.20 ASTM-D8016-15
5 Loss on Drying (105 °C for 2 h) % 4.9 ISO 787-2
6 pH (5% in water.) - 6.63 ISO 787-9

Example-2
7.73 kg of water is taken in a ss jacketed reactor equipped with stirrer having 22 L of holding capacity. 0.763 kg of Sodium silicate having Na2O:SiO2 weight ratio of 1:3.24 and SiO2 content of 22.29 % (w/w) is added into the reactor. The reactor content was heated to 710 C and stirring was initiated at 500 rpm. Simultaneous addition of sodium silicate having Na2O: SiO2 weight ratio of 1:3.24 and SiO2 content of 22.29 % (w/w), sulfuric acid having concentration of 20.48 % (w/w), and water was started in the reactor. The rate of addition was kept at 37 ml/min of sodium silicate, 15 ml/min of sulfuric acid and 27 ml/min of water for the three streams respectively. The addition was continued for 120 minutes. The alkali number was monitored and maintained at about 18-20. After addition is completed, the content of the reactor is aged for 20 minutes. After aging, the pH was brought down from 10.5 to 3.56 pH by addition of sulfuric acid. The content of reactor was filtered using vacuum filter, washed with water till wash filtrate exhibits conductivity of 2910 µs/cm. The wet cake was dried in an oven at 1100C. The dry material is passed through 325 mesh sieve. The characterisations of the product is given in the following table-2

Table-2
Sr. No. Parameters Unit Value obtained Test method
1 Appearance -- White powder -
2 BET Surface Area m2/g 304.9 ASTM- D1993
3 CTAB Surface Area m2/g 203.1 ASTM- D6845
4 Sears Number ml/1.5g 17.6 ASTM-D8016-15
5 Loss on Drying (105 °C for 2 h) % 5.6 ISO 787-2
6 pH (5% in water.) - 6.7 ISO 787-9

Example-3
36600 kg of water is taken in a ss reactor equipped with stirrer having 80 kl of holding capacity. 3201 kg of Sodium silicate having Na2O:SiO2 weight ratio of 1:3.26 and SiO2 content of 22.48 % (w/w) is added into the reactor. The reactor content was heated to 650 C and stirring was initiated at 42 rpm. Simultaneous addition of sodium silicate having Na2O: SiO2 weight ratio of 1:3.26 and SiO2 content of 22.48 % (w/w), sulfuric acid having concentration of 98.5 % (w/w), and water was started in the reactor. The rate of addition was kept at 11736 kg/hrs of sodium silicate, 491 litter/hrs of sulfuric acid and 8481 litter/hrs of water for the three streams respectively. The addition was continued for 120 minutes. The alkali number was monitored and maintained at about 16-18. After addition is completed, the content of the reactor is aged for 20 minutes. After aging, the pH was brought down from 10.7 to 3.51 pH by addition of sulfuric acid. The content of reactor was filtered in a filter press, washed with water till wash filtrate exhibits conductivity of 2700 µs/cm. The wet cake was slurried with 17% solids and adjust slurry pH to 3.0 by addition of sulfuric acid. Silica slurry was dried in spray dryer (inlet temperature 550-570 0C and out let temperature 90-95 0C. The dry powder material is passed through roll compacting machine and made granules at pressure of 25-30 bar The characterisations of the product is given in the following table -3

Table-3
Sr. No. Parameters Unit Value obtained Test method
1 Appearance -- White granules -
2 BET Surface Area m2/g 319.8 ASTM- D1993
3 CTAB Surface Area m2/g 215.6 ASTM- D6845
4 Sears Number ml/1.5g 15.73 ASTM-D8016-15
5 Loss on Drying (105 °C for 2 h) % 6.30 ISO 787-2
6 pH (5% in water.) - 6.54 ISO 787-9

Example-4
7.92 kg of water is taken in a ss jacketed reactor equipped with stirrer having 22 L of holding capacity. 0.515 kg of Sodium silicate having Na2O:SiO2 weight ratio of 1:3.24 and SiO2 content of 22.60 % (w/w) is added into the reactor. The reactor content was heated to 720C and stirring was initiated at 500 rpm. Simultaneous addition of sodium silicate having Na2O: SiO2 weight ratio of 1:3.24 and SiO2 content of 22.60 % (w/w), sulfuric acid having concentration of 20.96 % (w/w), and water was started in the reactor. The rate of addition was kept at 38 ml/min of sodium silicate, 18.3 ml/min of sulfuric acid and 27 ml/min of water for the three streams respectively. The addition was continued for 120 minutes. The alkali number was monitored and maintained at about 10-11. After addition is completed, the content of the reactor is aged for 20 minutes. After aging, the pH was brought down from 10.3 to 3.90 pH by addition of sulfuric acid. The content of reactor was filtered using vacuum filter, washed with water till wash filtrate exhibits conductivity of 3320 µs/cm. The wet cake was dried in an oven at 1100C. The dry material is passed through 325 mesh sieve. The characterisation of the product is given in the following table -4

Table-4
Sr. No. Parameters Unit Value obtained Test method
1 Appearance -- White powder -
2 BET Surface Area m2/g 272.0 ASTM- D1993
3 CTAB Surface Area m2/g 192.40 ASTM- D6845
4 Sears Number ml/1.5g 15.4 ASTM-D8016-15
5 Loss on Drying (105 °C for 2 h) % 5.30 ISO 787-2
6 pH (5% in water.) - 6.44 ISO 787-9

Rubber Compound Properties

Properties Regular HD silica with medium surface area (160-180 m2/g) Example -3 HD silica high surface area
Rheometer (MDR @ 160 °C, 30 Minutes)
ML (Inch Pounds) 3.69 4.11
MH (Inch Pounds) 13.32 14.35
MH-ML (Inch Pounds) 9.63 10.24
TS1 (Minutes) 1.05 0.95
TS2 (Minutes) 1.39 1.34
Tc90 (Minutes) 13.25 9.56
Mooney Viscosity (ML 1+4 @ 100 °C)
Mooney Viscosity 57.81 64.43
Physicals (Slabs Cured at 160 °C for 30 Minutes)
Tensile strength (MPa) 8.02 7.66
100% Modulus (MPa) 2.04 2.07
300% Modulus (MPa) 5.15 4.83
Tear Strength (MPa) 3.54 3.86
Elongation @ break % 522 535
Abrasion Loss(mm3) 81.2 72.9
Hardness (shore A) 70 69

High surface area silica (HSA) is used in lower phr (45 to 65 phr ) compared to regular HD Silica (65 to 85 phr) in the model recipe of a passenger car tread compound.

With the similar hardness of both the compounds, HSA Silica one proves to be better in abrasion resistance property, Also the rate of vulcanization with HSA silica found to be faster as compared to regular silica.

It is to be understood that the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention.
,CLAIMS:
1. A process for the preparation of precipitated silica comprising the steps of,
(i) Adding water to the jacketed reactor;
(ii) Adding sodium silicate having Na2O : SiO2 ratio in the range of 1:3.2-3.4 into the reactor;
(iii) Heating the rector content to a temperature in the range of 55-85ºC;
(iv) Adding simultaneously sodium silicate, sulfuric acid and water to the rector within a period of 90-150 minutes;
(v) Monitoring alkali number and maintaining the alkali number within the range of 10-20;
(vi) Aging the reactor content for 15-30 minutes;
(vii) Adjusting the pH of the reactor content to a range of 3.0 to 4.5;
(viii) Filtering the rector content;
(ix) washing the wet cake until the conductivity of wash water reaches 1000-5000;
(x) Drying the wet cake; and
(xi) Granulating the dried powder in the roller compacter.

2. The process as claimed in claim 1, wherein in step (i) the water is added in the reactor to create a water pool.

3. The process as claimed in claim 1, wherein in step (ii) the sodium silicate having Na2O: SiO2 ratio in the range of 1:3.2-3.4 is added in the rector water pool.

4. The process as claimed in claim 1, wherein in step (iii) the reactor content is heated to 55-80ºC.

5. The process as claimed in claim 1, wherein in step (iv) sodium silicate, sulfuric acid and water streams are added into the reactor in 90-150 minutes.

6. The process as claimed in claim 1, wherein in step (v) the alkali number is monitored and maintained in the range of 10-20.

7. The process as claimed in claim 1, wherein in step (vi), upon completion of addition of reactants, the reactor content is aged for 15-30 minutes.

8. The process as claimed in claim 1, wherein in step (vii) the pH of the reactor content is brought down to 3.5-4 by addition of sulfuric acid.

9. The process as claimed in claim 1, wherein in step (viii) the reactor content is filtered.

10. The process as claimed in claim 1, wherein in step (ix) the filter cake is washed with water till the wash water conductivity is 1000-5000.

11. The process as claimed in claim 1, wherein in step (x) the washed cake is dried.

12. The process as claimed in claim 1, wherein in step (xi) the dry product is granulated in roller compactor at a pressure of 25-30 bar.

13. The process as claimed in claim 1, wherein the product obtained exhibits the following characteristics.
Sr. No. Parameters Unit Range
1 Appearance -- White granule
2 BET Surface Area m2/g 250 -350
3 CTAB Surface Area m2/g 170 - 230
4 Sears Number ml/1.5g 14 - 18
5 Loss on Drying (105 °C for 2 h) % 4 -8
6 pH (5% in water.) - 5.5 – 7.5