RU2380315C1 - Method of preparing concentrated hydrosol of silicon oxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in production of different types of paper, film-forming compositions on metal and ceramics, as binding material in production of thermal protective material, shell moulds for precision casting and in production of construction materials. A sodium silicate solution is subjected to ion-exchange conversion to polysilicic acid, stabilisation with sodium hydroxide solution, thermal treatment at temperature not above 130° C for 2-3 hours with intense stirring without changing volume of the solution. The thermally treated hydrosol of silicon oxide is passed through a pre-filtration unit with subsequent concentration of the solution through ultra-filtration using a membrane unit with tangential distribution of the flow of liquid.

EFFECT: invention allows for increasing concentration of hydrosol of silicon oxide, its degree of purity, reducing deposits on reactor walls, increasing efficiency of the process.

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Description

The invention relates to the production of silica hydrosols, which can be used in the manufacture of various types of paper, film-forming compositions for metal and ceramics, as a binder in the manufacture of heat-protective materials, shell molds for precision casting.

A known method of preparing a solution of colloidal silica by stabilizing a dilute solution of polysilicic acid after alkalization to a pH of 7.5-8.5 by heating in an autoclave with a jacket to a boil while removing water by evaporation (Euler R. Chemistry of silica. M .: Mir, 1982, p .443.) The disadvantage of this method is the formation on the heated surface of the apparatus and the interface between the liquid and vapor phases of solid dispersed silica deposits, high energy consumption.

A known method of thermal stabilization of polysilicic acid, comprising heating a dilute solution of polysilicic acid and thermal stabilization of a colloid with growing silica particles while evaporating to a concentration of silicon oxide 5-15% of the mass and increasing the volume of the solution by 1.5-4.5 times by feeding sol -feeder followed by concentration by ultrafiltration (ed. St. USSR No. 833496, 1981). This method does not completely exclude the formation of a solid suspension of silica suspended in a solution. Solid silica forms on the inner metal surface, heated through the jacket of the apparatus, when the solution boils. The method requires significant energy consumption.

A known method of obtaining a time-stable hydrosol of silicon dioxide by ion exchange of solutions of sodium silicate on cation exchangers, stabilization of polysilicic acid with a solution of sodium hydroxide, followed by heat treatment in an autoclave at a temperature above 100 ° C (US patent 3012973, CL 252-313, 1961).

The disadvantage of this method is the complexity of the process, insufficient productivity and high energy consumption.

A known method of obtaining a stable hydrosol of silicon dioxide, including ion-exchange conversion of a solution of sodium silicate into polysilicic acid, stabilization with a sodium-containing solution, heat treatment of the obtained hydrosol of silicon dioxide at a temperature of 100 ° C and atmospheric pressure and concentration (ed. St. No. 1452789, class C01B 33 / 14, 1989). The disadvantage of this method is the low productivity, the formation of solid suspended in a solution of a precipitate of silicon oxide and high energy consumption.

The closest in technical essence is a method of producing a silica hydrosol, including ion-exchange conversion of a sodium silicate solution into polysilicic acid, stabilization with a sodium-containing solution, concentration of a silica hydrosol to 8-10 wt.%, Heat treatment of the obtained silica hydrosol with hot steam for 2 5-3 hours (RU (11) 2124474 (13) C1, publ. 1999.01.10).

The objective of the invention is to increase the concentration of the hydrosol of silicon oxide, its degree of purity, reduce deposits on the walls of the reactor, increase the productivity of the process.

This problem is solved by performing thermal stabilization with stirring and preserving the volume of the system, as well as eliminating solid suspended sediment from silica solution using a pre-treatment unit, using an ultrafiltration unit to concentrate silica sol with the tangential distribution of the fluid flow supplied to the membranes.

The method is as follows.

A solution of sodium silicate with a concentration of 4-5% sodium oxide is passed through KU-2-8 cation exchange resin. The resulting polysilicic acid is stabilized with a sodium hydroxide solution to a pH of 9.0-9.5, subjected to heat treatment with vigorous stirring at a temperature not exceeding 130 ° C for 2-3 hours without changing the volume of the solution. The silica hydrosol is passed through a pre-filtration unit, followed by concentration of the solution by ultrafiltration.

Mixing during the process of thermal stabilization does not allow a solid precipitate of silica to precipitate on the inner surface of the reactor.

The prefiltration unit allows you to remove particles of solid silica, which abrasion and damage the surface of the filtering membranes of the ultrafiltration unit, worsen the quality of commodity colloidal silica solution.

The use of an ultrafiltration unit for concentrating a hydrosol of silicon oxide with a tangential distribution of the fluid flow supplied to the membranes allows one to significantly increase the ultrafiltration rate and obtain a stable product with a concentration of 45% and higher.

Execution examples

Example 1

250 l of a solution of polysilicic acid obtained from a dilute solution of sodium silicate by ion exchange on KU-2-8 cation exchange resin stabilized with an alkali solution is subjected to thermal stabilization at a temperature not exceeding 130 ° C and stirring (P = 70 rpm). The resulting solution of silicic acid is filtered on a prefiltration unit.

For purification from suspended particles, pre-filters with pore sizes of 20 μm, 5 μm, 3 μm and 1.2 μm were tested.

A comparative evaluation of the obtained colloidal solution was carried out by the method of nephelometric determination of turbidity.

Membrane with a pore size of 20 microns - a turbidity of 71 FTU.

5 μm pore size membrane - 52 FTU turbidity.

Membrane with a pore size of 3 microns - a turbidity of 60 FTU.

Membrane with a pore size of 1.2 microns - a turbidity of 62 FTU.

The highest performance in terms of pre-filtration rate and cleaning quality is ensured by the use of a filter with a pore size of 3 microns.

After preliminary filtration, the silica hydrosol is ultrafiltered on a block with a tangential distribution of the liquid flow through a 0.2 micron polypropylene membrane.

For comparison, the concentration of the hydrosol of silicon oxide was carried out using once-through tubular ultrafilters. Using only direct-flow tubular ultrafilters does not allow to obtain sols of high concentration.

Indicators of concentrate and filtrate are presented in table 1.

Table 1 Characterization of silica sol before and after ultrafiltration Indicators membrane unit with tangential distribution of fluid flow tubular membrane filter unit silica sol before ultrafiltration silica after ultrafiltration silica sol before ultrafiltration silica after ultrafiltration The content of SiO ₂ , g / l 45.49 454.90 47.29 337.0 The content of Na ₂ O, g / l - 5.65 pH of the medium 9,4 10.26 10.54 10.27 The diameter of the micelles, nm 6.6 8.0 9.5 9.7 Turbidity, FTU 98 288 Average filtration rate (l / h) 67.0 35.6

Example 2

Silica sol (SiO ₂ 345 g / L content) obtained by ion exchange (Example 1) and concentrated by ultrafiltration using direct-flow tube ultrafilters is further concentrated on an ultrafiltration unit with a tangential distribution of the liquid flow through a 0.2 μm membrane. As a result of additional ultrafiltration, hydrosols of silicon oxide with a concentration of 450-480 g / l in silicon oxide were obtained.

table 2 Characterization of silica sol after pre-concentration on a block with a tangential distribution of fluid flow through a polypropylene membrane with a pore size of 0.2 μm The name of indicators Starting silica sol Concentrate after filtration The content of SiO ₂ , g / l 345.42 473.48 The content of Na ₂ O, g / l 4.43 5.49 Density, g / cm ³ 1,205 1,281 pH of the medium 10.03 10.0 The diameter of the micelles, nm 8.76 9.88

Thus, the advantages of the proposed method are as follows:

- the method allows to obtain sols of a sufficiently high concentration (450-480 g / l for silicon oxide);

- the use of a block of membranes with a tangential distribution of the fluid flow allows you to increase the rate of concentration of the colloidal solution;

- the use of prefiltration prevents the destruction of membranes by particles of a solid precipitate of silicon oxide and extend their life;

- the stage of thermal stabilization of a solution of polysilicic acid with vigorous stirring and a constant volume of the solution eliminates the formation of solid dispersed silica deposits on the inner surface of the reactor.

Claims (1)

A method of producing a silica hydrosol, including ion-exchange conversion of a sodium silicate solution into polysilicic acid, stabilization of polysilicic acid with a sodium hydroxide solution, heat treatment of a stabilized solution, characterized in that heat treatment of the stabilized solution is carried out at a temperature of not higher than 130 ° C for 2-3 hours with intensive stirring without changing the volume of the solution, the heat-treated hydrosol of silicon oxide is passed through a pre-filtering unit followed by a concentrate tion of the solution by ultrafiltration using a membrane with a tangential block fluid flow distribution.