WO2018167646A1

WO2018167646A1 - A process for preparing sodium silicate from rice husk ash

Info

Publication number: WO2018167646A1
Application number: PCT/IB2018/051633
Authority: WO
Inventors: Debabrata Rautaray; Prabhat PARIDA; Mayura LOLAGE; Ashwini ANGAL; Sunil ROKADE
Original assignee: Tata Chemicals Limited
Priority date: 2017-03-14
Filing date: 2018-03-13
Publication date: 2018-09-20

Abstract

A process for preparing sodium silicate from rice husk ash is disclosed. Said process comprises fusing the rice husk ash with trona at an elevated temperature ranging between 1200-1500 °C for a time period ranging between 2-4 hours to obtain sodium silicate.

Description

A P R OC E SS F OR PR E PA R ING SO DIU M SI L ICAT E F R O M RIC E H USK ASH

F ield of Invention A process for preparing sodium silicate from rice husk ash is disclosed. Particularly, a process for preparing silica from rice husk ash is disclosed.

Background Precipitated sil ica finds application as a catalyst carrier, absorbent for an active material, viscosity, texturizing or anti-caking agent element for battery separators, toothpaste or paper additive, reinforcing filler in silicone matrices or in compositions based on natural or synthetic polymer(s), in particular on elastomers), particularly diene elastomers. V arious methods are known for preparing silica. It is further known that the method used for prepari ng si I i ca also i nf I uences the physi cal and chemi cal properti es thereof. Typi cal ly, silica is prepared by a precipitation reaction between a silicate, in particular an alkali metal silicate, and an acidifying agent, followed by a filtration and a washing step and, then optionally a step for disintegrating the obtained filter cake.

T raditionally, sil icate required for production of silica was obtained by fusing sil ica sand with sodium carbonate. Presently, a major quantity of silicate is obtained from rice husk ash. Rice husk is an agricultural residue, available abundantly in rice producing countries. India alone produces approximately 12 million tons of rice husk annually. Silica is the major constituent of rice husk ash, making it economically feasible to extract silica, which has wide market. Using rice husk ash for production of silica, also addresses the issue of appropri ate di sposal of ri ce husk ash. To prepare si I i ca, si I i cate i s obtai ned from ri ce husk ash by fusing rice husk ash with sodium hydroxide. However, sodium hydroxide being expensive, increases the overall cost of the production of silica,

T here is therefore a need to devise an improved process which could reduce the overall cost of production of silica. It is also required that the such a process is able to produce silica having desired characteristics. Summary

A process for preparing sodium silicate from rice husk ash is disclosed. Said process comprises fusing the rice husk ash with trona at an elevated temperature ranging between 1200- 1500 eC for a ti me peri od rangi ng between 2-4 hours to obtai n sodi um si I i cate.

A process for preparing silica from rice husk ash is also disclosed. Said process comprises f usi ng the ri ce husk ash with trona at an el evated temperature rangi ng between 1200- 1500 eC for a time period ranging between 2-4 hours to obtain sodium silicate; dissolving the obtained sodium silicate in an aqueous medium to obtain sodium silicate solution at a temperature of 100-160eC; acidifying said sodium silicate solution to cause precipitation of silica.

Figure 1 illustrates the process of preparing silica in accordance with an embodiment of the present disclosure;

Figure 2 shows the X -ray Diffraction measurements of silica extracted from rice husk ash usi ng the process of the present di scl osure;

Figures 3 shows the Transmission E lectron Microscopy (TE M) analysis of silica extracted from rice husk ash using the process of the present disclosure; Figure 4 shows Field emission scanning electron microscopy analysis of silica extracted from rice husk ash using the process of the present disclosure.

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It wi 11 neverthel ess be understood that no I i mi tati on of the scope of the di scl osure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. It wi 11 be understood by those ski 11 ed i n the art that the f oregoi ng general descri pti on and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

Reference throughout this specification to "one embodiment" "an embodiment" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in one embodiment", "in an embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

In the broadest scope, the present di scl osure rel ates to a process for prepari ng si I i cate from rice husk ash. In particular, said process comprises fusing the rice husk ash with trona at an el evated temperature rangi ng between 1200- 1500 eC for a ti me peri od rangi ng between 2-4 hours to obtai n sodi um si I i cate.

T he present di scl osure al so rel ates to a process for prepari ng si I i ca from ri ce husk ash. S ai d process comprises fusing the rice husk ash with trona at an elevated temperature ranging between 1200- 1500 eC for a time period ranging between 2-4 hours to obtain sodium silicate; dissolving the obtained sodium silicate in an aqueous medium to obtain sodium silicate solution at a temperature of 100-160eC; acidifying said sodium silicate solution to cause precipitation of silica.

In accordance with an aspect, the above disclosed process results in obtaining precipitated silica having the foil owing physico-chemical characteristic data: a CT A B surface area i n a range of 80-350 n /g;

a B E T surface area i n a range of 90-400 n /g nr g;

a DBP oil absorption in a range of 70-350 ml/lOOg; a CDBP coefficient (DA) in range of 0.4-0.9; and

a sears number (V 2) i n a range of 12-30 ml/ (5g) .

In accordance with an embodiment, said precipitated silica alongside the parameters mentioned above has one or more of the following physico-chemical parameters, independently of one another:

- average primary particle size in a range of 10-100 nm;

- average particulate aggregate size (% of particles) in a range of 200-2000 nm;

- a mi era- pore area i n a range of 9-75 rrrVg;

- tapped density in a range of 0.08-0.5 g/cc;

- bul k density i n a range of 100-300 g/l;

- a mi era pore vol ume rangi ng from 0.005-0.025 cmBg;

- a pore diameter rangi ng from 100-350 i ;

- a moisture loss of 3-7% by weight, on drying for two hours at 105eC;

- a pH value of 5.5-7.5 (5 % in water);

- a Wk coefficient number less than 3.4;

- a S 1 O2 content of greater than 97 %; and

- sol ubl e salts content of I ess than 0.5%.

In accordance with an embodiment, trona comprises sodium carbonate and sodium bicarbonate. In accordance with an embodiment, trona comprises sodium carbonate in an amount ranging between 40-50% and preferably 44%. In accordance with an embodiment, trona comprises sodium bicarbonate in an amount ranging between 25-35%. Trona may also comprise 2-3 % Sodium fluoride, about 2% Sodium chloride and about 6%, insoluble impurities. The composition of trona is illustrated in table 1, below. In accordance with an embodiment, trona is processed to reduce the impurities. Any known process may be used to process trona so as to reduce the amount of impurities. The composition of said processed trona is illustrated below, in table 2. Table 1 : Composition of Trona

In accordance with an embodiment, the rice husk ash and trona are fused i n wA/v ratio ranging between 1 :0.8 to 1 :1.5. Preferably, the rice husk ash and trona are fused in w/w ratio in a range of 1 : 1. In accordance with a related embodiment, the rice husk ash and trona are fused under a pressure in a range of 1 to 6 atm. Preferably, the rice husk ash and trona are fused under a pressure in a range of 1 atm.

In accordance with an embodi ment, the sodi um si I i cate and the aqueous medi um are mixed in w/w ratio in a range of 1 :10- 1 :20. Preferably, sodium silicate and the aqueous medium are mixed in w/w ratio in a range of 1 :10. In accordance with a related embodiment, the aqueous medium is maintained at a temperature in a range of 90-150eC . In accordance with an embodi ment, the aqueous medi um is water.

In accordance with an embodiment, the acidification is carried out until silica is precipitated completely. In accordance with an embodiment, acidification is caused using a mineral acid selected from a group consisting of sulphuric acid, hydrochloric acid, nitric acid, organic acids like citric acid, acetic acid, oxalic acid. In accordance with a related embodiment, the mineral acid has a molarity in a range of 0.1 M to 2 M, and preferably around 0.625 M. In accordance with an alternate embodiment, the acidification is caused by passing carbon dioxide or sulphur dioxide. Such acidification is caused using carbon di oxi de and/or sul phur di oxi de i n an amount rangi ng between 3.5-5 gm of C 0₂ per 100 gm of sodium silicate having 5-7% Na₂0 and 5-8 gm of S0₂ per 100 gm of sodium silicate having 5-7% Na₂0. Preferably, 4.96 gm C0₂ and 7.5 gm S0₂ per 100gm of sodium silicate having 5-7% Na₂0 is used.

In accordance with an embodiment, the precipitated silica obtained upon completion of reaction is filtered followed by washing. Washing is done to eliminate the by-products, obtained as a result of reaction. Thus obtained precipitated silica is then subjected to a drying step. The drying step may be carried out by spray drying, spin flash drying, or vacuum tray dryi ng. A Iternatively, the wet cake is subj ected to short-term dryi ng, f ol I owed by addition of a dispersing agent in a suitable solvent. The dispersion may then be dried to obtain precipitated silica. In accordance with an embodiment, the dispersion of silica is prepared using a dispersing agent selected from a group consisting of metal salt of saturated and unsaturated fatty esters with long hydrocarbon chain/ fatty acids in an appropriate solvent selected from a group consisting of butanol, butanone, toluene and acetone.

T he si I i ca accordi ng to the present di scl osure can be used i n tyre rubber, ri ce rol I er rubber, shoe sole rubber or any other elastomers, cosmetic especially dental application, in environmental remediation, and in paints. Specifically, the silica disclosed herein is suitable for use as filler in vulcanizable or vulcanized elastomer compositions. The vulcanized elastomer composition can be used for the manufacture of tyre and other rubber products. In accordance with an embodi ment, sai d si I i ca may be used as a rei nf orci ng f i 11 er in a quantity in a range of 7 to 90 phr. Any conventional process may be used to form vulcanizable or vulcanized elastomer compositions using the above disclosed silica as reinforcing filler. E xamples:

E xample 1 : Precipitation of silica by preparing sodium silicate from R HA using sodium carbonate, T rona and Processed T rona

Three separate processes were carried out by mixing 12.5 grams of powdered RHA and 18.75 gm of powder trona, 12.5 grams of sodi um carbonate and 15 grams processed trona i n three beakers. T he mixture was heated at 1200eC for two hours i n a muff I e furnace. T he glassy solid sodium silicate was taken out and dissolved in hot water after grinding. The solution of sodium silicate was centrifuged to remove the impurities. Thereafter, preci pitated si I i ca was obtai ned by aci difyi ng the above sodi um si I i cate sol uti on by addi ng 1.25M sulphuric acid. The precipitate was washed twice with distilled water followed by drying. The silica obtained using the three processes was compared and the results have been tabulated in Table 3, below.

Table 3: Results

Further, silica extracted after calcination at different temperatures, was observed and tabul ated i n T abl e 4, bel ow. Table 4: Results after calcination

T he properti es of the preci pitated si I i ca obtai ned usi ng the processed trona i n accordance with the process described above have been tabulated in Table 5, below.

Table 5: Properties of precipitated silica

Industrial Applicability The process disclosed here in an inexpensive and easy process of preparing silica. The process enables using rice husk ash for production of commercially viable silica, which has otherwise not been obtained in any prior known processes. The silica according to the present disclosure can be used in tyre rubber, rice roller rubber, shoe sole rubber or any other elastomers, cosmetic especially dental application, environmental remediation and paints.

Trona is a cheaper source of sodium carbonate and hence reduces the cost of production of silica, as compared to prior known processes.

Claims

We C laim:

1. A process for prepari ng sodi um si I i cate from ri ce husk ash, the process compri si ng:

fusing the rice husk ash with trona at an elevated temperature ranging between 1200- 1500 eC for a ti me peri od rangi ng between 2-4 hours to obtai n sodi um si I i cate.

2. A process as cl ai med cl ai m 1 , wherei n the ri ce husk ash and trona are fused i n w/w rati o rangi ng between 1 : 1 to 1 : 1.5.

3. A process as claimed claim 1, wherein trona comprises 40-50 % sodium carbonate, 25-30% sodium bicarbonate, 2-3% sodium fluoride, 2% sodium chloride and 6% insoluble impurities.

4. A process as claimed claim 1, wherein trona is processed prior to fusion with the ri ce husk ash, to reduce the amount of i mpuriti es to about 0.5- 1 %.

5. A process for prepari ng si I i ca from ri ce husk ash, the process compri si ng:

fusing the rice husk ash with trona at an elevated temperature ranging between 1200- 1500 eC for a ti me peri od rangi ng between 2-4 hours to obtai n sodi um si I i cate; dissolvi ng the obtai ned sodi um si I i cate i n an aqueous medi um to obtai n sodi um si I i cate sol uti on at a temperature of 100- 160eC ;

aci difyi ng sai d sodi um si I i cate sol uti on to cause preci pi tati on of si I i ca.

6. A process as cl ai med cl ai m 5, wherei n the ri ce husk ash and trona are fused i n w/w rati o rangi ng between 1 : 1 to 1 : 1.5.

7. A process as claimed claim 5, wherein trona comprises 40-50 % sodium carbonate, 25-30% sodium bicarbonate, 2-3% sodium fluoride, 2% sodium chloride and 6% insoluble impurities.

8. A process as claimed claim 5, wherein trona is processed prior to fusion with the rice husk ash, to reduce the amount of impurities to about 0.5-1 %.

9. A process as claimed in claim 5, wherein sodium silicate and the aqueous medium are mixed i n wA/v rati o i n a range of 1 : 10 to 1 :20.

10. A process as claimed in claim 5, wherein acidification is caused using a mineral acid selected from a group consisting of sulphuric acid, hydrochloric acid, nitric acid, organic acids like citric acid, acetic acid, oxalic acid or by passing carbon dioxide or sulphur dioxide.

11. A process as cl ai med i n cl ai m 5, wherei n the preci pitated si I i ca has:

- a CTA B surface area in a range of 80-350 m2/g;

- a B E T surface area i n a range of 90-400 m2/g m2g

- a D B P oi I absorption i n a range of 70-350 ml/1 OOg;

- a C DBP coefficient (DA) in range of 0.4-0.9; and

- a sears number (V ₂) i n a range of 12-30.