RU2161124C1 - Method of preparing rice husk for high-pure silicon dioxide producing - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: invention relates to production of amorphous silicon dioxide. Method of preparing rice husk for production of high-pure amorphous silicon dioxide involves rice husk sifter, collection and removal of floated particles after each husk washing out in cold and hot water, husk squeezing under pressure 0.01-10 MPa after washing out in hot water or after washing out in acid solution. Then after squeezing washing out in cold water, acid solution and then in hot and cold distilled water is carried out. Method provides the complete removal of husk from organic components. EFFECT: improved method of preparing. 1 tbl

Description

 The invention relates to the field of production of amorphous silicon dioxide.

 Known methods for the preparation of rice husks upon receipt of amorphous silicon dioxide from it (see application N 86-104705, C 01 B 33/113, China; Indian patent N 159017; German patent N 1532398 from 15.11. 1978; French patent N 2356595 A1 dated 03.03.1978; RF patent N 1699918 A1 dated 12.23.1991), in which rice husk is washed with cold water and processed in solutions of organic or inorganic acids. According to these patents, amorphous silicon dioxide is obtained with a purity of 82 - 90.0%.

 The closest is the method described in the patent of the Russian Federation 2061656 C1 dated 06/10/1996, in which rinsing with hot water and / or mineral acid is additionally applied, and then rinsing with deionized water. Get silicon dioxide with a purity of 99.9%, not more.

 According to the above patents, it is impossible to obtain amorphous silicon dioxide with a purity of more than 99.9%, since the final product always contains impurities of oxygenated particles of the organic components of the husk.

 The aim of the proposed method for the preparation of rice husk is to more thoroughly clean it from organic components before subsequent operations to obtain amorphous silicon dioxide with a purity of more than 99.95%.

 This goal is achieved by the fact that in addition to the well-known operations described in the above patents - washing in cold and hot water, processing in acid solutions, additional operations are performed: sifting husks; collection and removal of floating particles after each washing in cold and hot water; crimping rice husk at a pressure of 0.01 - 10 MPa after washing in hot water or after washing in an acid solution, followed by washing in water and an acid solution; rinsing compressed husks in hot and cold distilled water.

The need for these operations is due to the following:
- in the initial mass of husk, supplied from elevators and cereal plants, is inorganic dust and flour, large inclusions in the form of straw stalks that are easy to clean by sieving, for example, on grain vibrating screens;
- in the light, floating in rice husk fractions, there is the largest number of organic components that are coked during the preliminary firing and do not completely burn out during high-temperature oxidative firing and are present in the final product in the form of black inclusions;
- in the husk processed in cold and hot water, with acid solutions, in the skeletal structure formed by silicon-containing fibers there are still hardly washed away organic residues, which can be squeezed out mechanically and then removed by additional washing;
- in order to obtain the purest product, the final washing operations must be performed in distilled water, which does not contain ions of chlorine, potassium, sodium and other impurities.

 The indicated additional operations to clean rice husks make it possible to obtain the final product - amorphous silicon dioxide with a purity of 99.99 - 99.999%.

 Examples of carrying out the invention.

1. Optimal conditions. Screening of incoming husk on a set of sieves from dust and large foreign particles; rinsing in cold water; collection and removal of floating particles of rice husks and foreign particles; washing in hot water (water temperature 85-90 ^o C, duration 1.5-2.0 hours); rinsing in cold water; collection and removal of floating particles; washing with a 10% aqueous solution of sulfuric acid at a temperature of 85-95 ^o C for 2 hours; washing in hot water (T = 85-95 ^o C, τ = 10-15 minutes); rinsing in cold water; crimping the husk at a pressure of 0.1 MPa in a press-pressing apparatus; rinsing in cold water; washing in a 5% aqueous solution of sulfuric acid (deionized water) at T = 85-95 ^o C, τ = 1.5-2.0 hours; washing in hot deionized water, T = 85-95 ^o C, τ = 20-30 minutes; 4x washing in cold deionized water. The organic content in the husk is 0.025%.

This is followed by heat treatment operations to obtain silicon dioxide (drying at 80-100 ^o C (or centrifugation and drying), preliminary burning, grinding, oxidative burning (final).

 The content of silicon dioxide in the final product is 99.995%, see table.

 2. Boundary conditions for crimping pressure. All operations are the same as in example 1, and the crimp pressure is minimal - P = 0.01 MPa.

 The organic content in the husk increases to 0.05%, and the carbon content in the final product to 0.005%, and the silicon dioxide content in the final product decreases to 99.99%.

 3. Overseas conditions for crimping pressure. All operations are the same as in example 1, and the crimp pressure P = 0.005 MPa.

 A decrease in crimping pressure of less than 0.01 MPa worsens the conditions for removing organics from rice husk and its content reaches 0.2%; the carbon content in the final product in this case increases to 0.05%, and the content of silicon dioxide in the final product decreases to 99.9%.

 4. Boundary conditions for crimping pressure. All operations are the same as in example 1, and the maximum crimp pressure is 10 MPa.

 The organic content in the husk is reduced to 0.005%, the carbon content in the final product is reduced to 0.0005%, and the silicon dioxide content in the final product is increased to 99.999%.

 5. Overseas conditions for crimping pressure. All operations are the same as in example 1, and the pressure rises to 15 MPa.

 An increase in pressure above 10 MPa does not lead to a noticeable improvement in the quality of the washed husk and the final product.

 6. Overseas conditions for the collection and removal of pop-up particles. The collection and disposal of pop-up particles is not performed; crimp pressure P = 10 MPa, and all other operations are the same as in example 1.

 In this case, the maximum organic content in the peeled husk is 0.6%, the maximum amount of carbon in the final product is 0.1% and the minimum amount of silicon dioxide in the final product is 99.3%.

 7. Foreign conditions for sifting rice husks. Screening is not performed; all other operations are the same as in example 1.

 In this case, the organic content in the peeled husk is 0.15%, the carbon content in the final product is 0.03%, and the silicon dioxide content in the final product is 99.92%.

 The last two examples show the necessity of performing the operations of screening the husk and collecting and removing pop-up particles.

 Table. Rice husk preparation conditions and product quality.

 The sequence of crimping operations can be changed and, for example, you can crimp the husk after the first hot washing with water; the operation of collecting and removing pop-up particles can be performed after each washing.

Claims (1)

 A method of preparing rice husk to obtain high-purity amorphous silicon dioxide, including washing in cold and hot water, washing in an acid solution, characterized in that the rice husk is sieved, after each washing with water, pop-up particles are collected and removed after washing in hot water or after washing in an acid solution followed by washing with water, the rice husk is crimped at a pressure of 0.1 - 10 MPa, after the crimp, the husk is washed in cold water, in an acid solution, and then in cell and cold distilled water.

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