JPH0425226B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a porous glass membrane that does not contain gel-like silica in its pores. (Prior art) Conventionally, porous glass membranes are produced by forming borosilicate glass into a thin tube, separating the phases into a sodium borate-rich phase and a silica-rich phase, and eluting the sodium borate-rich phase with acid. It was manufactured by a method.
However, in this manufacturing method, the silica component contained in the sodium borate phase produced by phase separation becomes gel-like silica in the acid treatment step and is deposited in the pores of the porous glass membrane. Since this gel-like silica disturbs the porous structure derived from the phase separation structure, it has become a major obstacle when it is necessary to precisely control the pore characteristics of a porous glass membrane. In order to avoid such drawbacks, in Japanese Patent Publication No. 53-44580, porous glass tubes (with a film thickness of 5 to
30μm), add sodium hydroxide solution to the glass
A method is described in which the pores are enlarged from 26 Å to 164 Å by using 1 portion per 100 g and treating at 0° C. for 24 hours. However, when using this method to treat a thick porous glass membrane (for example, 400 to 600 μm thick), microscopic cracks often occur on the surface of the porous glass membrane after the alkaline solution treatment step.
This has become a major obstacle in the production of porous glass membranes. (Problems to be Solved by the Invention) The present invention solves the conventional drawbacks in the manufacturing method of porous glass membranes that do not contain gelled silica, namely, the occurrence of minute cracks on the surface of the porous glass membrane after the alkaline solution treatment step. This is an attempt to eliminate the drawbacks that occur. (Means for Solving the Problems) Therefore, as a result of intensive studies in order to solve the above-mentioned conventional drawbacks, the present inventors have found that the present inventors have found that the film can be deposited in the pores without causing minute cracks on the surface of the porous glass membrane. We have invented a method to remove gelled silica. That is, the present invention provides a method for producing a porous glass membrane using borosilicate glass as a raw material glass, in which the phases are separated into a sodium borate-rich phase and a silica-rich phase, and the sodium borate-rich phase is separated with an acid. A porous glass characterized in that the eluted porous glass membrane is heat-treated at 700°C to 800°C and then treated with an alkaline solution to elute gel-like silica and a part of the silica skeleton deposited in the pores. This is a method for manufacturing a membrane. In the method of the present invention, a raw material glass such as that described in US Pat. No. 2,286,275 can be used as the raw material glass. After forming this raw glass into a thin tube with an outer diameter of 1 to 3 mm, it is heat-treated at a temperature range that does not cause fusion or deformation to separate the phases into a sodium borate-rich phase and a silica-rich phase. The rich phase is eluted with acid to obtain a porous glass membrane. As the acid, sulfuric acid, hydrochloric acid, nitric acid, etc. are used. This porous glass is sintered by heat treatment in the air, and according to the present invention, the heat treatment temperature is
700°C to 800°C is preferred. If the heat treatment temperature is lower than 700℃, the effect of suppressing cracking on the surface of the porous glass membrane after the alkaline solution treatment process is small, and if the heat treatment temperature is higher than 800℃, the porous glass membrane after the alkaline solution treatment is This is not preferable because the permeability of gases (for example, hydrogen gas, carbon monoxide gas, etc.) decreases. A porous glass membrane is obtained by treating the heat-treated porous glass membrane with an alkaline solution to elute gel-like silica and part of the silica skeleton deposited in the pores. According to the present invention, the alkaline solution used in the alkaline solution treatment step is preferably a strong alkaline solution (eg, sodium hydroxide solution, sodium hydroxide solution, etc.). Further, the amount of gel-like silica deposited is determined from the change in the cumulative pore volume curve determined by the nitrogen adsorption method. In addition, when it is necessary to improve the thermal stability of the porous glass membrane or when it is necessary to increase the mechanical strength of the porous glass membrane, the porous glass membrane after the alkaline solution treatment step is treated with an acid. It is preferable to bake after cleaning. As the acid, sulfuric acid, hydrochloric acid, nitric acid, etc. are used. (Examples) Hereinafter, the present invention will be described in detail based on Examples. Example 1 A raw material glass consisting of 62.5% by weight of SiO ₂ , 27.3% by weight of B ₂ O ₃ , 7.2% by weight of Na ₂ O, and 3.0% by weight of Al ₂ D ₃ was formed into a thin tube with an outer diameter of 2 mm and an inner diameter of 1 mm. After heat treatment at ℃ for 5 hours to separate the phases, 1N sulfuric acid was added to the glass.
A porous glass membrane was obtained by using 1 portion per 100 g and treating at 95° C. for 24 hours. This porous glass membrane was treated in air at 725°C for 4 hours, treated with 1°C of 0.5N sodium hydroxide solution at 1°C for 20 hours, and then washed with ion-exchanged water at 20°C for 5 hours. A porous glass membrane was obtained. The pore characteristics and pore size distribution of the porous glass membrane measured by the nitrogen adsorption method are shown in Table 1 and FIG. 1 for Sample No. 1. The average pore diameter D in Table 1 is a value calculated by D=4V/S using the pore volume V (cm ³ /g) and the pore specific surface area S (m ² /g). Although it is outside the scope of the present invention, in order to compare the amount of gel-like silica deposited in the pores, the pore characteristics and pore size distribution of the porous glass membrane before the alkaline solution treatment step were measured as sample No. 3. It is shown in Table 1 and FIG.
Further, when the above-mentioned alkali treatment was performed on the porous glass membrane after the acid treatment, fine cracks were generated on the surface of the porous glass membrane. As shown in Figure 1, when alkaline solution treatment is performed, the cumulative pore volume curve does not increase in the micropore region derived from gel-like silica, and instead increases in the pore diameter region derived from the split phase structure. It can be understood that by increasing the number of particles, no gelled silica is included in the pores. Example 2 A porous glass membrane after the mineral acid treatment step described in Example 1 was treated at 750°C for 4 hours, and a 0.5N sodium hydroxide solution was used at 1 level per 1.6 g of glass.
After 24 hours of treatment at ℃, the
A porous glass membrane was obtained by washing for hours. The pore characteristics and pore size distribution of the porous glass membrane measured by the nitrogen adsorption method are shown in Table 1 and FIG. 1 for Sample No. 2. It can be seen from FIG. 1 that, like sample No. 1, sample No. 2 also does not contain gel-like silica.

[Table] (Effects of the Invention) According to the present invention, the following exceptional effects can be obtained. (1) Porous glass membranes that do not contain gel-like silica can be manufactured. (2) No microscopic cracks occur on the surface of the porous glass membrane after the alkali treatment process.

[Brief explanation of drawings]

FIG. 1 is a graph showing the pore size distribution of a porous glass membrane obtained by the method of the present invention.

Claims (1)

[Claims] 1. In a method for producing a porous glass membrane using borosilicate glass as a raw material glass, the phase is separated into a sodium borate-rich phase and a silica-rich phase, and the sodium borate-rich phase is separated with an acid. A method for producing a porous glass membrane, which comprises heat-treating the porous glass membrane from which the silica has been eluted, and then treating it with an alkaline solution to elute gel-like silica and part of the silica skeleton deposited in the pores. 2. The manufacturing method according to claim 1, wherein the heat treatment temperature is 700°C to 800°C.