Description:FIELD OF THE INVENTION
[0001] The present disclosure relates to a process of preparing precipitated silica for various industrial application from biorefinery multi-substrate boiler ash, using controlled precipitation of extracted sodium silicate solution. The present disclosure also relates to an apparatus for the preparation of precipitated silica.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Prior to this invention, attempts to study the effect of various reaction conditions such as reaction time, temperature, the concentration of reactants, etc. on structural properties of precipitated silica derived from biogenic sources, is studied and are summarize below.
[0004] WO 2004/073600 describes a process and apparatus for the manufacturing of precipitated silica from rice husk ash. The process also regenerates the chemicals used making a close loop operation. The silica particle produced from the invention has bulk density in a range of 80 – 500 kg.m3, specific surface area in range of 50-400 m2/gm and particles size in range of 1-30 microns. But the utilization of leftover black solid is not described & process is exclusively developed on rice husk ash also another drawback of the process was the blockade of the sparger hole during carbon dioxide addition at a certain minimum flow rate resulting in uneven properties of final precipitated silica.
[0005] US 20030118500 discloses a process for the preparation of precipitated silica which is used as reinforcing fillers for elastomers. The process involves the reaction of silicate with an acidifying agent to obtain suspension of precipitated silica. The precipitation includes the following steps (i) Preparation of stock silicate solution containing at least one electrolyte. (ii) Addition of acidifying agent to stock silicate solution until the pH of the solution reaches 7 to 8.5. (iii) The remaining silicate solution and acidifying agents are added to the reaction media until the final pH is obtained in the range of 4 to 6. The silica slurry is then filtered, washed, and dried to recover dry precipitated silica. The drawback of the process includes high energy input because of spray drying and the rate of acid and silicate solution addition is need to be controlled precisely.
[0006] WO 2001/074712 discloses a process for synthesis of precipitated silica from rice husk ash through precipitation technique. But the properties of final product does not have improved structure to match reinforcement for elastomers.
[0007] US Patent 7700062 describes a process of the production of precipitated silica from reaction medium of reduced ionic strength using silica acid. US Patent 7700062 also discussed the effect of surface modifying agent to improve surface properties, but invention fails to improve the structure of precipitated silica for reinforcement related applications.
[0008] Thus, there is a need to develop an efficient process for obtaining precipitated silica.

OBJECTS OF THE INVENTION
[0009] An objective of the present invention is to provide a process of preparing precipitated silica.
[0010] Another objective of the present invention is to provide an apparatus for the preparation of precipitated silica.

BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 showed Process flow diagram.
[0012] Figure 2 showed top view of acid pretreatment reactor (101).
[0013] Figure 3 showed side view of acid pretreatment reactor (101).
[0014] Figure 4 showed top view of digestion reactor (201).
[0015] Figure 5 showed side view of digestion reactor (201).
[0016] Figure 6 showed top view of precipitator reactor (301).
[0017] Figure 7 showed side view of precipitator reactor (301).
[0018] Figure 8 showed top view of regenerator reactor (401).
[0019] Figure 9 showed side view of regenerator reactor (401).
SUMMARY OF THE INVENTION
[0020] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0021] The present disclosure discloses a process of preparing precipitated silica having a) dissolving 5 to 15 % w/w of a biorefinery multi-substrate boiler ash in 2 to 15 % w/w of a first acid under condition to obtain a pretreated biorefinery multi-substrate boiler ash; b) digesting 5 to 15 % w/w of the pretreated biorefinery multi-substrate boiler ash with 1 to 10 % w/w of a base under condition to obtain a sodium silicate solution; c) adding 1 to 5 % w/w of a soluble alkali metal salt in the sodium silicate solution under condition to obtain a alkali metal salt treated sodium silicate solution; and d) adding 5 to 20 % w/w of a second acid in the alkali metal salt treated sodium silicate solution under condition to obtain precipitated silica.
[0022] The present disclosure discloses an apparatus for the preparation of precipitated silica having apparatus for the preparation of precipitated silica comprising: i) a pre-treatment reactor includes a novel draft tube first feed inlet for biorefinery multi-substrate boiler ash and second inlet for first acid; a two-paddle type agitator and baffles are incorporated in the reactor to ensure agitation; a draft to evenly distribute solid ash throughout the vessel; a first outlet for pretreated biorefinery multi-substrate boiler ash; ii) a digestor includes a first feed inlet for pretreated biorefinery multi-substrate boiler ash obtained from the first outlet of the pre-treatment reactor and second inlet for base; a two-paddle agitator with baffles are integrated to ensure optimal mixing; first outlet for sodium silicate solution; iii) a precipitator includes a first feed inlet for sodium silicate solution obtained from the first outlet of the digestor and second inlet with a spray nozzle throughout the vessel for second acid for uniform distribution of acid during precipitation reaction; a ribbon-like agitator with baffles are incorporated in the reactor to ensure optimal agitation; a first outlet for precipitated silica and sodium sulphate; and iv) a regenerator includes first feed inlet for sodium sulphate solution obtained from the first outlet of the precipitator and second inlet for calcium hydroxide; a two-paddle agitator with baffles are integrated to ensure optimal agitation; first outlet for recovering the calcium sulphate and sodium hydroxide solution.
[0023] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

DETAILED DESCRIPTION OF THE INVENTION
[0024] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0025] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0026] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0027] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0028] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it is individually recited herein.
[0029] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0030] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0031] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0032] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0034] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0035] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0036] An embodiment of the present disclosure discloses a novel process and apparatus for production of precipitated silica from biorefinery multi-substrate boiler ash.
[0037] In an embodiment of the present disclosure discloses a process of preparing precipitated silica comprising: a) a) dissolving 5 to 15 % w/w of a biorefinery multi-substrate boiler ash in 2 to 15 % w/w of a first acid under condition to obtain a pretreated biorefinery multi-substrate boiler ash; b) digesting 5 to 15 % w/w of the pretreated biorefinery multi-substrate boiler ash with 1 to 10 % w/w of a base under condition to obtain a sodium silicate solution; c) adding 1 to 5 % w/w of a soluble alkali metal salt in the sodium silicate solution under condition to obtain a alkali metal salt treated sodium silicate solution; and d) adding 5 to 20 % w/w of a second acid in the alkali metal salt treated sodium silicate solution under condition to obtain precipitated silica. The first acid in step a) is having normality in the range of 0.1 to 5 N. The base in step b) has normality in the range of 1N to 10N. Addition of second acid in step d) has normality in the range of 0.5 N to 5N.
[0038] In an embodiment of the present disclosure discloses that the biorefinery multi-substrate boiler ash is composed of rice straw, lignin cake and concentrated syrup.
[0039] In an embodiment of the present disclosure discloses that the first acid is selected from a group consisting of hydrochloric acid, sulfuric acid, nitric acid and combination thereof. The second acid is selected from a group consisting of sulfuric acid, hydrochloric acid and nitric acid and combination thereof. The base is selected from a group consisting of sodium hydroxide and sodium carbonate and combination thereof.
[0040] In an embodiment of the present disclosure discloses that the alkali metal salt is selected from a group consisting of sodium sulphate, sodium chloride, sodium nitrate and combination thereof.
[0041] In an embodiment of the present disclosure discloses that the condition in step a) includes temperature in the range of 70 ? to 95 ? for the period in the range of 0.5 to 3 hours. The condition in step b) includes temperature in the range of 90 ? to 150 ? for the period in the range of 0.5 to 3 hours. The condition in step c) includes temperature in the range of 60 ? to 90 ?. The condition in step d) includes temperature in the range of 65 ? to 95 ? for the period in the range of 0.5 to 3 hours.
[0042] In an embodiment of the present disclosure discloses that the step b) includes further processing to recover black carbon-rich solid.
[0043] In an embodiment of the present disclosure discloses that the step d) also produces sodium sulphate solution having concentration in the range of 2 to 8 gm Na2SO4/100 mL.
[0044] In an embodiment of the present disclosure discloses that the sodium sulphate is reacted with calcium hydroxide at a temperature in the range of 15 ? to 50 ? for the period in the range of 1 hr to 5 hr to recover calcium sulphate and sodium hydroxide solution.
[0045] In an embodiment of the present disclosure discloses that the step d) involve neutralization of the solution is carried out to achieve the pH of the solution in the range of 3 to 6.
[0046] Another embodiment of the present disclosure discloses an apparatus (1) for the preparation of precipitated silica comprising: i) a pre-treatment reactor (101) includes a first feed inlet (105a) for biorefinery multi-substrate boiler ash and second inlet (105b) for first acid; a two-paddle type agitator (120) and baffles (125) are incorporated in the reactor to ensure agitation; a draft (130) to evenly distribute solid ash throughout the vessel; a first outlet (150a) for pretreated biorefinery multi-substrate boiler ash; ii) a digestor (201) includes a first feed inlet (205a) for pretreated biorefinery multi-substrate boiler ash obtained from the first outlet (150a) of the pre-treatment reactor and second inlet (205b) for base; a two-paddle agitator (220) with baffles (225) are integrated to ensure optimal mixing; first outlet (250a) for sodium silicate solution; iii) a precipitator (301) includes a first feed inlet (305a) for sodium silicate solution obtained from the first outlet (250a) of the digestor and second inlet with a spray nozzle (360) throughout the vessel for second acid for uniform distribution of acid during precipitation reaction; a ribbon-like agitator (320) with baffles (325) are incorporated in the reactor to ensure optimal agitation; a first outlet (350a) for precipitated silica and sodium sulphate; and iv) a regenerator (401) includes first feed inlet (405a) for sodium sulphate solution obtained from the first outlet (350a) of the precipitator and second inlet (405b) for calcium hydroxide; a two-paddle agitator (420) with baffles (425) are integrated to ensure optimal agitation; first outlet (450a) for recovering the calcium sulphate and sodium hydroxide solution.
[0047] In an embodiment of the present disclosure discloses that the pre-treatment reactor (101), the digestor (201), the precipitator (301) and the regenerator (401) each include a primary reactor and a lid with a flange connected with a bolt.
[0048] In an embodiment of the present disclosure discloses that the pre-treatment reactor (101), the digestor (201), the precipitator (301) and the regenerator (401) each designated three slots for temperature (135, 235, 335, 435), pressure (110, 210, 310, 410) and pH (140, 240, 340, 440) measurement respectively.
[0049] In an embodiment of the present disclosure discloses that the each reactor vessels are fully insulated.
[0050] In an embodiment of the present disclosure discloses that the each reactor vessels have a second outlets (150b, 250b, 350b, 450b) for sampling purpose.
[0051] In an embodiment of the present disclosure discloses that the first outlet (150a, 250a, 350a, 450a) and the second outlet (150b, 250b, 350b, 450b) of each reactor are fitted with glove valves.
[0052] Biorefinery Multi-substrate boiler ash is generated from the ashes of various substrates such as rice straw, lignin and concentrated syrup. In the present invention a diluted mineral acid is used to extract metallic impurity from biorefinery multi-substrate boiler ash. A solution of sodium hydroxide is used to extract silica from pre-treated biorefinery multi-substrate boiler ash in form of sodium silicate solution along with generation of carbon rich black solid. Diluted sulphuric acid is used as precipitating agent to precipitate out silica from extracted sodium silicate solution. The sodium hydroxide solution is regenerated (from waste water generated during purification and washing of precipitated silica) using calcium hydroxide, along with generation of calcium sulphate, the carbon rich black solid is further utilize as soil enhancer. The precipitated silica derived from present invention has multiple applications in various industries such as filler in rubber and tires, anticaking agents in food, excipients in pharmaceuticals, thickening and abrasive agent in personal care products.
[0053] Biorefinery multi-substrate boiler ash is generated as a waste product in ethanol biorefineries. Biorefinery multi-substrate boiler ash is a mixture of rice straw, lignin and concentrated syrup in various proportions. The composition of individual components of biorefinery multi-substrate boiler ash is provided in table 1.
Table 1: Composition of individual components of biorefinery multi-substrate boiler ash.
Sr. No. Elements Unit Rice Straw Lignin Cake Concentrated Syrup
1 Alumina as Al2O3 % 0.5-0.6 0.2-0.3 0.1-0.2
2 Calcium as CaO % 3.1-3.2 5.5-6.0 1.6-1.7
3 Iron as Fe2O3 % 0.6-0.8 0.3-0.4 0.9-1.0
4 Potassium as K2O % 16-17 1.5-1.6 14 -15
5 Magnesium as MgO % 2.4-2.5 1.6-1.7 12-13
6 Sodium as Na2O % 15-16 2.4-2.5 23-24
7 Phosphorus as P2O5 % 0.9-1.0 1.0-1.1 7.8-7.9
8 Silica as SiO2 % 40-41 79 -80 2.8-2.9
9 Sulphate as SO3 % 2.4-2.5 2.9-3.0 24-25
10 Titanium as TiO2 % 0.05-0.06 0.02-0.03 0.01-0.02
11 Chloride as Cl % 3.19 0.38 3.43

[0054] Biorefinery multi-substrate boiler ash contains high amount of silica majorly in amorphous form, along with other impurities. The composition of biorefinery multi-substrate boiler ash is provided in Table 2.
Table 2: Composition of biorefinery multi-substrate boiler ash
Component Percentage/PPM
SiO2 67.1 %
Na2O 14.3 %
SO3 9.16 %
K2O 4.49 %
P2O5 4.20 %
CaO 2.87 %
Al2O3 1.43 %
MgO 0.918 %
Cl- 0.510 %
MnO 0.342 %
TiO2 0.202 %
Cr2O3 0.112 %
MoO3 363 ppm
NiO 233 ppm
CuO 194 ppm
ZnO 177 ppm
SrO 116 ppm
PbO 81.1 ppm
Rb2O 48.7 ppm
Br- 38.7 ppm
ZrO2 34.1 ppm
CoO 6.12 ppm
As2O3 2.03 Pm

[0055] Rice husk ash contains high amount of silica along with other impurities. Biorefinery multi-substrate boiler ash used in present invention is a mixture of different ashes and contains relatively less silica and high impurities than rice husk ash, which makes biorefinery multi-substrate boiler ash different from rice husk ash. The chemical composition of both rice husk ash and biorefinery multi-substrate boiler ash are summarized in Table 3.
Table 3: Composition of rice husk ash and biorefinery multi-substrate boiler ash.
Component Rice husk ash Biorefinery multi-substrate boiler ash
SiO2 96.7 67.1 %
Na2O 0.26 14.3 %
SO3 - 9.16 %
K2O 0.91 4.49 %
P2O5 - 4.20 %
CaO 0.49 2.87 %
Al2O3 1.01 1.43 %
MgO 0.19 0.918 %
Cl- - 0.510 %
MnO 0.37 0.342 %
TiO2 0.16 0.202 %
Cr2O3 - 0.112 %
MoO3 - 363 ppm
NiO - 233 ppm
CuO - 194 ppm
ZnO - 177 ppm
SrO - 116 ppm
PbO - 81.1 ppm
Rb2O - 48.7 ppm
Br- - 38.7 ppm
ZrO2 - 34.1 ppm
CoO - 6.12 ppm
As2O3 - 2.12 ppm

[0056] The present invention valorises biorefinery multi-substrate boiler ash into various grades of precipitated silica for industrial applications. The present invention also eliminates the cost and mitigates the environmental impact of waste ash disposal.
[0057] The present invention also recycles the waste water, regenerates the sodium hydroxide solution with the help of calcium hydroxide along with generation of calcium sulphate, resulting in reduction of the input cost along with value addition to the process. The process is as shown in Fig. 1.
[0058] In an embodiment of the present invention describes a novel process of manufacturing of precipitated silica from biorefinery multi-substrate boiler ash. The process design and optimization is carried out at laboratory scale to meet industrial requirements.
[0059] Various structural properties of precipitated silica can be controlled by manipulating silica polymerization reaction using various parameters such as: rate of nucleation of particles, growth of particles up to a desired size, pH for coagulation of aggregated particles, metal ion concentration and other reaction parameters.
Production of precipitated silica from biorefinery multi-substrate boiler ash
[0060] Biorefinery multi-substrate boiler ash contains 65 % to 70 % of silica, mostly in amorphous form. Silica can be extracted from biorefinery multi-substrate boiler ash in an economically feasible way through the process proposed in the present invention. The process consists of following steps:
Acid pre-treatment of biorefinery multi-substrate boiler ash
[0061] Acid pre-treatment of biorefinery multi-substrate boiler ash refers to removal of metallic impurities from ash in form of soluble salts. The required quantity of biorefinery multi-substrate boiler ash (5 % to 15 % solid loading) is dissolved in diluted solution of hydrochloric acid (0.1 N to 5 N) at an elevated temperature greater than 70 0C for the period of 0.5 to 3 hours. After completion of acid pre-treatment, then the treated biomass is washed with tap water to remove impurities.
Generation of sodium silicate solution and carbon rich black solid from acid pre-treated biorefinery multi-substrate boiler ash
[0062] The required quantity of acid pre-treated biorefinery multi-substrate boiler ash (5 % to 15 % solid loading) is added into the solution of sodium hydroxide (1 N to 10 N) at an elevated temperature of 90 0C to 150 0C for the period of 0.5 hours to 3 hours. After completion of digestion reaction sodium silicate solution is recovered from black solid using conventional press.
Controlled precipitation of silica from extracted sodium silicate solution
[0063] In the precipitation step, the extracted sodium silicate solution is heated at an elevated temperature ranging from 50 0C to 100 0C. The alkali metal ion concentration of the sodium silicate solution is regulated in the range of 10 gm/L to 40 gm/L using a soluble alkali metal salt (sodium sulphate). Diluted sulphuric acid (concentration ranging from 0.5 M to 5 M) is used to neutralize the alkali present in sodium silicate solution making silica precipitate out from the solution. The precipitation involves three steps, in the first step 10 to 40 % of the alkali present in the solution is neutralized in time ranging from 2 to 20 minutes. The second step involves the aging of the precipitated silica solution for the same amount of time. In the third step remaining alkali of the solution is neutralized until the final pH of the solution is in the range of 3 to 6 in time ranging from 20 minutes to 40 minutes. The precipitated silica slurry is then filtered, washed (until free from SO4-2), dried, and pulverized to obtain precipitated silica.
Recycling of waste water, regeneration of chemicals from waste stream, utilization of carbon rich black solid as soil enhancer
[0064] The waste water generated during washing and purification of precipitated silica is recycled back after treatment.
[0065] The sodium sulphate solution obtained after filtration of precipitated silica slurry is used to generate sodium hydroxide solution and calcium sulphate salt.
[0066] The carbon rich black solid is utilized as soil enhancers in agriculture fields.
Various Chemical reactions associated with the present invention
[0067] Digestion

[0068] Precipitation

[0069] Regeneration

APPARATUS
[0070] The apparatus (1) used for the reaction consist of four equipments: i) a pre-treatment reactor (101), ii) a digestor (201), iii) a precipitator (301), and iv) a regenerator (401). Each one is provided with a temperature and pH controlled baffled reactor system to provide maximum surface reaction and reaction sites. The baffle is also provided with a lid and a flange through which the agitator is placed. Continuous monitoring of pH of the reactor is also provided to improve process efficiency. The double paddle type agitator is provided to enhance the agitation. In precipitator additional spray nozzle with a ribbon helical agitator is also provided.
The detailed description of each reactor is given below:
i) Acid pretreatment reactor (101)
[0071] The arrangement includes a primary reactor vessel and a lid with a flange (115) and connected with bolts (155). Inside the reactor vessel, there is a two-paddle type agitator (120) setup attached to rotor shaft (145). Baffles (125) and the agitator (120) setup are incorporated in the reactor to ensure optimal agitation. Temperature, pressure, and pH measurements can be taken through three designated slots (135, 110 and 140) respectively. The reactor vessel is equipped with a draft tube (130) to evenly distribute solid ash throughout the vessel and avoid chocking and settling of solid particles in the reactor. Additionally, the reactor vessel is fully insulated. Two inlet points (105a and 105b) are available, one for feeding a solid multi substrate boiler ash and the other for feeding the acid solution. Two outlet points (150a and 150b) are provided: one for product recovery (pretreated biorefinery multi-substrate boiler ash) and the other for sampling. Both outlet points are fitted with globe valves. As shown in Fig 2 and Fig 3.
ii) Digestion reactor
[0072] The setup comprises a primary reactor vessel accompanied by a lid with flange (215) and connected with bolts (255). Within the reactor vessel, there is a two-paddle agitator (220) arrangement attached to rotor shaft (245), along with baffles (225), which are integrated to ensure optimal mixing. Three designated slots (235, 210 and 240) allow for the measurement of temperature, pressure, and pH respectively. Moreover, the reactor vessel is fully insulated. There are two points of feed inlet (205a and 205b), one for acid feeding pre-treated multi-substrate boiler ash obtained from the first outlet of the pre-treatment reactor and the other for feeding the sodium hydroxide solution. Additionally, two outlet points (250a and 250b) are provided: one for recovering the product (sodium silicate solution) and the other for sampling purposes. These details are illustrated in Figs. 4 and 5.
iii) Precipitation reactor
[0073] The arrangement includes a primary reactor vessel and a lid with a flange (315) and connected with bolts (355). Inside the reactor vessel, there is an agitator setup designed in a ribbon-like manner (320) attached to rotor shaft (345). Baffles (325) and the agitator (320) setup are incorporated in the reactor to ensure optimal agitation. The utilization of a ribbon-type agitator (320) facilitates the synthesis of precipitated silica with the desired specifications. Because during precipitation reaction the viscosity of the reaction mixture increases drastically, due to the formation of silica gel. The system with a ribbon-type agitator (320) effectively disrupts the gel formation, leading to an enhanced quality of the final precipitated silica.
[0074] The reactor vessel is equipped with a spray nozzle (360) to evenly distribute Sulphuric acid throughout the vessel. Additionally, the reactor vessel is fully insulated. The spray type nozzle helps in uniform distribution of acid during precipitation reaction, and avoiding the localized reaction. By controlled addition of acid, spray nozzle (360) also provides the controlled precipitation of silica from reaction mixture.
[0075] Temperature, pressure, and pH measurements can be taken through three designated slots (335, 310 and 340) respectively. The effective pH and temperature control also helps in achieving the controlled precipitation of the silica from sodium silicate solution.
[0076] Two inlet points (305a and 305b) are available, one for feeding the sodium silicate solution obtained from the first outlet of the digestor and the other with a spray nozzle for the acid solution. Two outlet points (350a and 350b) are provided: one for product recovery (precipitated silica and sodium sulphate) and the other for sampling. Both outlet points are fitted with globe valves. As shown in Fig. 6 and Fig. 7.
iv) Regenerator reactor
[0077] The arrangement includes a primary reactor vessel and lid with a flange (415) and connected with bolts (455). Inside the reactor vessel, there is a two paddle type agitator (420) setup attached to rotor shaft (445). Baffles (425) and the agitator (420) setup are incorporated in the reactor to ensure optimal agitation. Temperature, pressure, and pH measurements can be taken through three designated slots (435, 410 and 440) respectively. The reactor vessel is fully insulated. Two inlet points (405a and 405b) are available, one for feeding sodium sulphate solution obtained from the first outlet of the precipitator and the other for feeding the calcium hydroxide solution. Two outlet points (450a and 450b) are provided: one for product recovery (calcium sulphate and sodium hydroxide) and the other for sampling. Both outlet points are fitted with globe valves. As shown in Fig. 8 and Fig. 9.
Product characterization
[0078] Bulk density: To determine bulk density a method prescribed by the Indian Standard Specifications was adopted. A 250 ml measuring cylinder is used to measure the volume of the pre-weighted silica sample. After tapping 50 times taking 2 seconds for each tapping, the volume is used to calculate the bulk density

[0079] Loss on ignition: pre-weighted sample of silica is dried in a muffle furnace at 1000 for 2 hours. Loss on ignition is calculated using the following equation

[0080] Moisture content: pre-weighted sample of silica is dried in a muffle furnace at 105 for 2 hours. Moisture content is calculated using the following equation

[0081] Specific surface area: The method described by Brunauer, Emmet, and Teller is used to measure the specific surface area of the sample. The method involves the measurement of nitrogen absorbed at different partial pressures.
[0082] Average particle size: The laser diffraction method is used to determine the average particle size and particle size distribution.
[0083] Water absorption: Distilled water is added dropwise into the known weight of the sample (approx. 5 gm) until a stiff putty-like paste that does not break or separate has appeared. The following equation is used to calculate water absorption

[0084] pH : 5 grams of sample is dissolved into 100 ml distilled water. The powder is uniformly distributed using a glass rod. A calibrated pH meter is used to measure the pH of the slurry.
[0085] Description of precipitated silica derived from present invention
Appearance: White free flowing powder
Chemical formula: SiO2
Molecular weight: 60.0
Loss on ignition: 4 % - 7 %
Particle size distribution: 10 – 50 microns
pH: 6.2 – 7.4
Tapped bulk density: 90 – 320 kg/m3
Surface area: 32 – 241 m2/gm
Water absorptivity: 6.01-7.73 gm water/gm silica
APPLICATIONS OF PRECIPITATED SILICA
[0086] Precipitated silica derived from present invention is highly purified form of silica and has a wide range of applications in various industries such as:
1. Rubber and tires: as reinforcing fillers
2. Toothpaste and oral care: as thickening and abrasive agent
3. Food and beverage: as flow and anticaking agents
4. Pharmaceuticals: as excipient in tablets and capsules
5. Paint, adhesive and sealant: as rheology control agent to improve levelling properties
6. Battery and Electronic: as insulator
7. Agriculture: as anticaking agent for pesticides and herbicides to improve flowability

ADVANTAGES OF PRESENT INVENTION
[0087] Valorisation of waste biorefinery multi-substrate boiler ash into various valuable product.
[0088] A novel process of production of precipitated silica for various industrial applications.
[0089] Recycling of waste water and regeneration of sodium hydroxide solution.
[0090] A novel and economically feasible process of production of silica from renewable source.
[0091] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0092] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Examples 1
[0093] 100 grams of multi-substrate boiler ash is dissolved into 900 ml of 5N hydrochloric acid solution for the period of 4 hrs at elevated temperature of 70 The reaction mass is filtered, solid mass is washed with distilled water to make it chloride free and dried for further processing.
Examples 2
[0094] 100 grams of multi-substrate boiler ash is dissolved into 900 ml of 2N hydrochloric acid solution for the period of 4 hrs at elevated temperature of 85 The reaction mass is washed with distilled water to make it chloride free and dried for further processing.
Example 3
[0095] 900 grams of hydrochloric acid treated biorefinery multi-substrate boiler ash is further treated with 1N solution of sodium hydroxide for 1 hr at the temperature of 130 °C. The sodium silicate solution is recovered from digested reaction mass. The resulting sodium silicate solution exhibits a SiO2/ Na2O mole ratio equal to 3.61 with SiO2 7.0 wt% and Na2O 2.0 wt%.
[0096] Black carbon-rich solid was also recovered for further processing.
Example 4
[0097] 900 grams of hydrochloric acid treated biorefinery multi-substrate boiler ash is further treated with 1N solution of sodium hydroxide for 1.5 hr at the temperature of 100 . The sodium silicate solution is recovered from digested reaction mass. The resulting sodium silicate solution with SiO2/ Na2O mole ratio equal to 3.9 with SiO2 7.2 wt% and Na2O 1.9 wt%.
[0098] Black carbon-rich solid was also recovered for further processing.
Example 5
[0099] 900 grams of multi-substrate boiler ash is digested with a 1N solution of sodium hydroxide for 2hr at the temperature of 130 . The sodium silicate solution is recovered from digested reaction mass. The resulting sodium silicate solution exhibits a SiO2/ Na2O mole ratio equal to 3.59 with SiO2 8.0 wt% and Na2O 2.3 wt%.
[00100] Black carbon-rich solid was also recovered for further processing.
Example 6
[00101] 108 gm of sodium silicate containing SiO2 = 8.0 %, Na2O = 2.3 %; SiO2/Na2O = 3.59, was introduced into a 5 L beaker over a magnetic cum heating plate. The Na+ ion concentration of the solution was adjusted to 22.01 gm/L by adding soluble sodium salt. The sodium silicate solution was heated to 65 and 2 M sulphuric acid was added at controlled rate of 46.83 ml/min for the period of 5 minutes. After 5 minutes acid addition was interrupted for 5minutes. Then remaining acid of same concentration was added at the rate of 7.80 ml/min for 35 minutes till pH of the mixture reaches 4.2. The slurry is then filtered and washed until free from sulphate ion. The washed silica slurry is dried overnight in hot air oven at 80 . The properties of silica are (i) BET specific surface area = 169 m2/gm; (ii) Bulk density = 0.185 gm/ml; (iii) Moisture content = 1.5 wt%; (iv) pH (5% slurry) = 7.2.
Example 7
[00102] 200 gm of Sodium silicate containing SiO2 = 8 %, Na2O = 2.3 %; SiO2/Na2O mole ratio = 3.59 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 35.51 gm/L by adding soluble sodium salt. Solution was pre heated to 75 . 252.4 ml 2 M Sulphuric acid was added at the rate of 25.42 ml/min for 10 minutes. After first step of neutralization 10 minutes were provided for ageing. The remaining sulphuric acid was added in 25 minutes at the rate of 10.4 ml/min until final pH of the slurry is adjusted to 4.5. The washed silica slurry is dried overnight in hot air oven at 80 . The washed silica slurry is dried overnight in hot air oven at 80°C. (i) BET specific surface area = 240 m2/gm; (ii) Bulk density = 0.112 gm/ml; (iii) Moisture content = 1.7 wt%; (iv) pH (5% slurry) = 7.2.
Example 8
[00103] 2.5 Kg of Sodium silicate containing SiO2 = 8 %, Na2O = 2.3 %; SiO2/Na2O mole ratio = 3.59 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 49.71 gm/L by adding soluble sodium salt. Solution was pre heated to 85 °C. 2.71 L 2 M Sulphuric acid was added at the rate of 181.2 ml/min for 15 minutes. After first step of neutralization 15 minutes were provided for ageing. The remaining sulphuric acid was added in 15 minutes at the rate of 192.55 ml/min until final pH of the slurry is adjusted to 3.3. The washed silica slurry is dried overnight in hot air oven at 80°C. The washed silica slurry is dried overnight in hot air oven at 80°C. (i) BET specific surface area = 163 m2/gm; (ii) Bulk density = 0.148 gm/ml; (iii) Moisture content = 2.3 wt%; (iv) pH (5% slurry) = 6.2.
Example 9
[00104] 108 gm of sodium silicate containing SiO2 = 7.2 %, Na2O = 1.9 %; SiO2/Na2O = 3.91, was introduced into a 5 L beaker over a magnetic cum heating plate. The Na+ ion concentration of the solution was adjusted to 22.01 gm/L by adding soluble sodium salt. The sodium silicate solution was heated to 65°C and 2 M sulphuric acid was added at controlled rate of 63.3 ml/min for the period of 5 minutes. After 5 minutes acid addition was interrupted for 5 minutes. Then remaining acid of same concentration was added at the rate of 8.9 ml/min for 35 minutes till pH of the mixture reaches 4.24. The slurry is then filtered and washed until free from sulphate ion. The washed silica slurry is dried overnight in hot air oven at 80°C. The properties of silica are (i) BET specific surface area = 134 m2/gm; (ii) Bulk density = 0.215 gm/ml; (iii) Moisture content = 2.1 wt%; (iv) pH (5% slurry) = 7.5.
Example 10
[00105] 71 Kg of Sodium silicate containing SiO2 = 7.2 %, Na2O = 1.9 %; SiO2/Na2O = 3.91 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 35.51 gm/L by adding soluble sodium salt. Solution was pre heated to 75°C. 78.6 L 2 M Sulphuric acid was added at the rate of 7.86 L/min for 10 minutes. After first step of neutralization 10 minutes were provided for ageing. The remaining sulphuric acid was added in 25 minutes at the rate of 3.34 L/min until final pH of the slurry is adjusted to 3.5. The washed silica slurry is dried overnight in hot air oven at 80°C. The washed silica slurry is dried overnight in hot air oven at 80°C. (i) BET specific surface area = 183 m2/gm; (ii) Bulk density = 0.121 gm/ml; (iii) Moisture content = 1.9; (iv) pH (5% slurry) = 6.2.
Example 11
[00106] 3 Kg of Sodium silicate containing SiO2 = 7.2 %, Na2O = 1.9 %; SiO2/Na2O = 3.91 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 49.71 gm/L by adding soluble sodium salt. Solution was pre heated to 85°C. 4.64 L 2 M Sulphuric acid was added at the rate of 0.309 L/min for 15 minutes. After first step of neutralization 15 minutes were provided for ageing. The remaining sulphuric acid was added in 15 minutes at the rate of 0.319 L/min until final pH of the slurry is adjusted to 4.0. The washed silica slurry is dried overnight in hot air oven at 80°C. (i) BET specific surface area = 123 m2/gm; (ii) Bulk density = 0.238 gm/ml; (iii) Moisture content = 2.8 wt%; (iv) pH (5% slurry) = 6.9.
Example 12
[00107] 25 Kg of Sodium silicate containing SiO2 = 7.0 %, Na2O = 2.0 %; SiO2/Na2O mole ratio = 3.61 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 22.01 gm/L by adding soluble sodium salt. Solution was pre heated to 65 . 21.42 L 2 M Sulphuric acid was added at the rate of 4.12 L/min for 5 minutes. After first step of neutralization 5 minutes were provided for ageing. The remaining sulphuric acid was added in 35 minutes at the rate of 0.64 L/min until final pH of the slurry is adjusted to 3.7. The washed silica slurry is dried overnight in hot air oven at 80 . The properties of silica are (i) BET specific surface area = 163 m2/gm; (ii) Bulk density = 0.139 gm/ml; (iii) Moisture content = 0.8 wt%; (iv) pH (5% slurry) = 6.6.
Example 13
[00108] 2.5 Kg of Sodium silicate containing SiO2 = 7.0 %, Na2O = 2.0 %; SiO2/Na2O mole ratio = 3.61 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 35.51 gm/L by adding soluble sodium salt. Solution was pre heated to 75°C. 3.08 L 2 M Sulphuric acid was added at the rate of 300.4 ml/min for 10 minutes. After first step of neutralization 10 minutes were provided for ageing. The remaining sulphuric acid was added in 25 minutes at the rate of 121.1 ml/min until final pH of the slurry is adjusted to 3.5. The washed silica slurry is dried overnight in hot air oven at 80°C. The washed silica slurry is dried overnight in hot air oven at 80°C. (i) BET specific surface area = 211 m2/gm; (ii) Bulk density = 0.120 gm/ml; (iii) Moisture content = 1.9 wt%; (iv) pH (5% slurry) = 6.5.
Example 14
[00109] 3.2 Kg of Sodium silicate containing SiO2 = 7.0 %, Na2O = 2.0 %; SiO2/Na2O mole ratio = 3.61 was introduced in a stainless-steel vessel equipped with a stirrer. Na+ ion concentration was adjusted to 49.714 gm/L by adding soluble sodium salt. Solution was pre heated to 85 . 4.95L 2 M Sulphuric acid was added at the rate of 330.15 ml/min for 15 minutes. After first step of neutralization 15 minutes were provided for ageing. The remaining sulphuric acid was added in 15 minutes at the rate of 340.31 ml/min until final pH of the slurry is adjusted to 4.0. The washed silica slurry is dried overnight in hot air oven at 80 . The washed silica slurry is dried overnight in hot air oven at 80 . (i) BET specific surface area = 141 m2/gm; (ii) Bulk density = 0.178 gm/ml; (iii) Moisture content = 3.5 wt%; (iv) pH ( 5% slurry) = 7.3.
Example 15
[00110] 5L of recovered Sodium Sulphate solution reacted with 4N solution of calcium hydroxide at a temperature ranging from 15°C to 50°C, for a period of 1 hr to 5 hr. Recovered solution contains 0.4 N NaOH 5L solution. 150 gm of Calcium sulphate was recovered.
[00111] The obtained silica specification are as follows:
Table 4: Silica specifications
S. No. SiO2/Na2O ratio Temperature Precipitation time (minutes) Tapped Bulk Density (gm/ml) Surface area (m2/gm)
Stage 1 Aging Stage 2
1 3.59 65 5 5 35 0.185 169
2 75 10 10 25 0.112 240
3 85 15 15 15 0.148 163
4 3.91 65 5 5 35 0.215 134
5 75 10 10 25 0.121 183
6 85 15 15 15 0.238 123
7 3.61 65 5 5 35 0.139 163
8 75 10 10 25 0.120 211
9 85 15 15 15 0.178 141

[00112] A skilled artisan will appreciate that the quantity and type of each ingredient can be used in different combinations or singly. All such variations and combinations would be falling within the scope of present disclosure.

[00113] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

, Claims:1. A process of preparing precipitated silica comprising:
a) dissolving 5 to 15 % w/w of a biorefinery multi-substrate boiler ash in 2 to 15 % w/w of a first acid under condition to obtain a pretreated biorefinery multi-substrate boiler ash;
b) digesting 5 to 15 % w/w of the pretreated biorefinery multi-substrate boiler ash with 1 to 10 % w/w of a base under condition to obtain a sodium silicate solution;
c) adding 1 to 5 % w/w of a soluble alkali metal salt in the sodium silicate solution under condition to obtain a alkali metal salt treated sodium silicate solution; and
d) adding 5 to 20 % w/w of a second acid in the alkali metal salt treated sodium silicate solution under condition to obtain precipitated silica.
2. The process as claimed in claim 1, wherein the biorefinery multi-substrate boiler ash is composed of rice straw, lignin cake and concentrated syrup.
3. The process as claimed in claim 1, wherein the first acid is selected from a group consisting of hydrochloric acid, sulfuric acid, nitric acid and combination thereof.
4. The process as claimed in claim 1, wherein the base is selected from a group consisting of sodium hydroxide and sodium carbonate and combination thereof.
5. The process as claimed in claim 1, wherein the second acid is selected from a group consisting of sulfuric acid, hydrochloric acid and nitric acid and combination thereof.
6. The process as claimed in claim 1, wherein the alkali metal salt is selected from a group consisting of sodium sulphate, sodium chloride, sodium nitrate and combination thereof.
7. The process as claimed in claim 1, wherein the condition in step a) includes temperature in the range of 70 ? to 95 ? for the period in the range of 0.5 to 3 hours.
8. The process as claimed in claim 1, wherein the condition in step b) includes temperature in the range of 90 ? to 150 ? for the period in the range of 0.5 to 3 hours.
9. The process as claimed in claim 1, wherein the condition in step c) includes temperature in the range of 60 ? to 90 ?.
10. The process as claimed in claim 1, wherein the condition in step d) includes temperature in the range of 65 ? to 95 ? for the period in the range of 0.5 to 3 hours.
11. The process as claimed in claim 1, wherein the step b) includes further processing to recover black carbon-rich solid.
12. The process as claimed in claim 1, wherein the step d) also produces sodium sulphate solution.
13. The process as claimed in claim 11, wherein the sodium sulphate is reacted with calcium hydroxide at a temperature in the range of 15 ? to 50 ? for the period in the range of 1 hr to 5 hr to recover calcium sulphate and sodium hydroxide solution.
14. The process as claimed in claim 11, wherein the step d) involve neutralization of the solution is carried out to achieve the pH of the solution in the range of 3 to 6.
15. An apparatus (1) for the preparation of precipitated silica comprising:
i) a pre-treatment reactor (101) includes a first feed inlet (105a) for biorefinery multi-substrate boiler ash and second inlet (105b) for first acid; a two-paddle type agitator (120) and baffles (125) are incorporated in the reactor to ensure agitation; a draft tube (130) to evenly distribute solid ash throughout the vessel; a first outlet (150a) for pretreated biorefinery multi-substrate boiler ash;
ii) a digestor (201) includes a first feed inlet (205a) for pretreated biorefinery multi-substrate boiler ash obtained from the first outlet (150a) of the pre-treatment reactor and second inlet (205b) for base; a two-paddle agitator (220) with baffles (225) are integrated to ensure optimal mixing; first outlet (250a) for sodium silicate solution;
iii) a precipitator (301) includes a first feed inlet (305a) for sodium silicate solution obtained from the first outlet (250a) of the digestor and second inlet with a spray nozzle (360) throughout the vessel for second acid for uniform distribution of acid during precipitation reaction; a ribbon-like agitator (320) with baffles (325) are incorporated in the reactor to ensure optimal agitation; a first outlet (350a) for precipitated silica and sodium sulphate; and
iv) a regenerator (401) includes first feed inlet (405a) for sodium sulphate solution obtained from the first outlet (350a) of the precipitator and second inlet (405b) for calcium hydroxide; a two-paddle agitator (420) with baffles (425) are integrated to ensure optimal agitation; first outlet (450a) for recovering the calcium sulphate and sodium hydroxide solution.
16. The apparatus (1) as claimed in claim 15, wherein the pre-treatment reactor (101), the digestor (201), the precipitator (301) and the regenerator (401) each include a primary reactor and a lid with a flange connected with a bolt.
17. The apparatus (1) as claimed in claim 15, wherein the pre-treatment reactor (101), the digestor (201), the precipitator (301) and the regenerator (401) each designated three slots for temperature (135, 235, 335, 435), pressure gauge (110, 210, 310, 410) and pH (140, 240, 340, 440) measurement respectively.
18. The apparatus (1) as claimed in claim 15, wherein the each reactor vessels are fully insulated.
19. The apparatus (1) as claimed in claim 15, wherein the each reactor vessels have a second outlets (150b, 250b, 350b, 450b) for sampling purpose.
20. The apparatus (1) as claimed in claim 15, wherein the first outlet (150a, 250a, 350a, 450a) and the second outlet (150b, 250b, 350b, 450b) of each reactor are fitted with globe valves.