JP2808479B2 - Method for producing acid-resistant composite separation membrane - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an acid-resistant composite separation membrane, and particularly to a method for producing an acid-resistant composite separation membrane capable of selectively separating water from an aqueous solution containing an organic acid. It relates to a manufacturing method.

[Conventional technology]

Examples of the acid-resistant separation membrane capable of selectively separating water from an aqueous solution containing an organic acid include an organic polymer membrane (polyimide-based and Teflon-based) and an inorganic porous membrane. The former has a large separation factor but a low permeation rate, and has poor heat resistance, so it can be used only at relatively low temperatures.
The latter has a disadvantage that the permeation rate is large and the heat resistance is high, but the separation coefficient is small.

As an inorganic porous membrane, there is a membrane having an inorganic porous body as a base material and an inorganic membrane having a separation function supported on the surface thereof. As an example, there is an inorganic film manufactured by a method announced by Professor Masashi Asaeda of the Faculty of Engineering, Hiroshima University at the 54th Annual Meeting of the Chemical Engineering Association. This manufacturing method is as follows.

There are various inorganic porous bodies as shown in FIG. However, if the pore size of the inorganic porous material is large, the required amount of silica sol, which is a precursor of silica gel, is required to be large, and cracks are likely to occur, and if the pore size is too small, the permeation performance is reduced. 100-1
It is preferable to use an inorganic porous body of about 0,000 °.
In particular, foamed silica, sintered alumina, mullite, etc. having a pore diameter of 1,000 mm or more are preferably used.

Generally, the following method is used as a method for producing silica gel.

(1) water glass solution into a large amount of NaCl, were added salts such as Na ₂ SO _4, precipitation method (2) from the water glass solution to obtain a white powdery silica gel neutralized with further acid SiCl ₄ vapor It is burned in the flow to produce a SiO ₂ gas, which SiCl ₄ combustion method for collecting (3) SiO ₂ is evaporated in the vicinity of 1,700 ° C. the, SiO ₂ vapor aggregation method to condense it, however, by these methods The obtained SiO ₂ particles are coated on a thin film of about several tens μm, and
It is extremely difficult to obtain a porous material of about Å.

The method proposed by Asada et al. Is a method for producing silica gel by hydrolyzing silica sol. As the silica sol which is a precursor of silica gel, for example, a silica sol obtained by hydrolyzing an alkoxysilane containing an ethoxysilane group, a methoxy group or the like is used.

Examples of these alkoxysilanes include tetraethoxysilane {ethyl silicate, SiO (C ₂ H ₅ ) ₄ }, tetramethoxysilane {methyl silicate, SiO (OCH ₃ ) ₄ }, and any of these. Since the separation performance differs depending on the organic acid mixture to be separated, they are used properly.

The silica gel membrane used as the separation membrane is separated by hydrolyzing the raw material, tetraethoxysilane, etc., with water, stopping the polycondensation reaction halfway without completion, and gelling with -OH remaining as the active group. It is characterized by being used as a membrane.

 An example of the reaction of tetraethoxysilane is shown below.

Heating to 800 ° C. or more after hydrolyzing tetraethoxysilane or the like results in complete disappearance of —OH groups, resulting in glass having a —Si—O— crystal structure. This production method is already known.

The degree of progress of the polycondensation reaction can be apparently determined by the viscosity of the sol. For example, the sol (1-A) in FIG.
It is possible to control the pore size of the gel by selecting (1-B) and (1-C) and supporting them appropriately.

Generally, when a hydrolyzed sol is left at room temperature,
It gels completely in 0 hours, and gels in about 40 to 120 minutes at 80 ° C. Therefore, in order to produce a stable film, it is necessary to freeze this gelling reaction (polycondensation reaction). Then, the inorganic porous body after supporting the sol is fired at 200 ° C. or higher. If this calcination is insufficient,
C ₂ H ₅ groups remain, resulting in a film having unstable acid resistance.

Although any method can be adopted as a method for supporting the silica sol in the pores of the inorganic porous material, there are appropriate operating conditions for making the silica sol a stable silica sol film. One example is "Separation of organic acid / aqueous mixture by inorganic porous thin film" announced at the 54th Annual Meeting of the Society of Chemical Engineers, Japan. The method is as follows.

A silica sol is prepared by adding tetraethoxysilane and an acid catalyst to water at room temperature. The composition is shown in Table 1.

A tube made of an inorganic porous material is immersed in the silica sol, and a gel is formed in the pores of the porous material and the outer wall of the tube by a polycondensation reaction.

After the polymerization is completed, the porous body is taken out of the silica sol solution and left at room temperature to dry the surface.

 The porous body is dried in a dryer at 200 ° C.

The above operation was repeated for silica sols 1 and 2 respectively.
Repeat ~ 3 times.

[Problems to be solved by the invention]

Using the separation membrane produced by the method proposed in "Separation of organic acid / aqueous mixture by inorganic porous thin film" presented at the 54th Annual Meeting of the Chemical Engineering Society, a separation experiment of acrylic acid aqueous solution was performed. Was. The results are shown in FIG. As the elapsed time increases, the separation performance α decreases.

The present invention has been made in view of the above-mentioned technical level, and aims to provide a separation membrane having properties which are practically satisfactory in both of the conventional separation membranes, having no acidity, heat resistance and pressure resistance, and having a permeation rate and a separation coefficient. Is what you do.

[Means for solving the problem]

The present invention relates to a method for producing an acid-resistant composite separation membrane comprising silica gel obtained by hydrolyzing an alkoxysilane containing an ethoxy group or a methoxy group in pores of an inorganic porous material. In the preparation conditions of a plurality of types of silica sols produced by changing the mixing ratio of the raw material alkoxysilane, water and acid catalyst, the raw material mixing ratio of the silica sol to be supported is classified into two types, silica sol 1 and silica sol 2. (2) The weight ratio of water to alkoxysilane as the raw material for silica sol 1 is 0.5 to 2.0, and the reaction catalyst is
The weight ratio of the acid catalyst to the alkoxysilane is 0.01 to 0.1.
(3) The weight ratio of water to alkoxysilane as the raw material for silica sol 2 is set to 2.0 to 50, and as a reaction catalyst,
The weight ratio of the acid catalyst to the alkoxysilane is 0.01 to 0.5.
(4) maintaining the raw material for the silica sol 1 in a boiling state,
About 25 minutes, about 20 minutes and about 15 minutes of liquid after the start of boiling, respectively
1-A, 1-B and 1-C liquids; (5) The raw material for silica sol 2 was stirred and mixed at room temperature for 30 to 90 minutes to produce silica sol 2, (6) Surface of porous substrate After supporting the silica sol 1-A liquid thereon, the porous substrate is baked for 5 to 15 minutes in an electric furnace set at about 200 ° C., and then the porous body is set in an electric furnace set at about 300 ° C. Baking for 5 to 15 minutes in an electric furnace, and then baking the porous substrate in an electric furnace set to about 400 ° C. for 5 to 15 minutes, and then setting the porous substrate to about 500 ° C. in an electric furnace. Within 5 to 15
(7) After the silica sol 1-A liquid is further supported on the surface of the porous substrate supporting the silica sol 1-A liquid, the operation of the above (6) is repeated two to three times, (8) Next, on the surface of the porous substrate supporting the silica sol 1-A liquid, the same treatment as in the above (6) to (7) is further performed using the silica sol 1-B liquid, and (9) (6) using the silica sol 1-C liquid on the surface of the porous substrate supporting the silica sol 1-B liquid
(10) Next, the above silica sols 1-A, 1-B and 1-C
The above-mentioned silica sol 2 liquid is supported on the surface of the porous base material supporting the liquid, and the porous body is baked for 5 to 15 minutes in an electric furnace set at about 200 ° C. Is fired in an electric furnace set at about 300 ° C. for 5 to 15 minutes, and then the porous substrate is fired in an electric furnace set at about 400 ° C. for 5 to 15 minutes, and then the porous substrate 5 to 15 in an electric furnace set to about 500 ° C
(11) After the silica sol 2 liquid is further supported on the surface of the porous base material supporting the silica sol 2 liquid, the operation (10) is repeated two to three times. This is a method for producing a separation membrane.

 Table 2 shows the composition of the drug for preparing the silica sol.

The silica sol 1 has the properties shown in FIG. 4 depending on the retention time after boiling. The polycondensation of the sol progresses with time, and the pore diameter of silica gel formed after the sol is supported on a substrate and heated is reduced. Therefore, the characteristics of the separation membrane can be changed by selecting the degree of polycondensation.

As shown in FIG. 5, the silica sol 2 has a small change in viscosity (at 25 ° C.), but polycondensation proceeds rapidly after several thousand hours to form a high viscosity liquid.

According to the present invention, a plurality of silica sols 1 are produced. In the embodiment shown in FIG. 4, (1-A), (1-B) and (1-C)
By adjusting the pore size by sequentially supporting the silica sol 1 on the surface of the porous substrate, and further supporting the silica sol 2 having a selective separation function on the surface,
A method for producing a stable acid-resistant composite separation membrane is proposed.

 That is, in the present invention, a film is formed by the following method.

Using the chemicals of the composition of silica sol 1 in Table 2
Prepare sols of several viscosities (pore diameters) as shown in the figure. As an example, the raw material for silica sol 1 is kept in a boiling state,
About 25 minutes, about 20 minutes and about 15 minutes of liquid after the start of boiling, respectively
1-A, 1-B and 1-C liquids.

Next, silica sol 2 is manufactured by stirring and mixing at room temperature for about 30 to 90 minutes using a chemical having the composition of silica sol 2 shown in Table 2.

After supporting the silica sol 1-A liquid on the surface of a porous substrate (see FIG. 1), the porous substrate is baked for about 5 to 15 minutes in an electric furnace set at about 200 ° C. The porous body is fired in an electric furnace set at about 300 ° C. for about 5 to 15 minutes, and then the porous body is fired in an electric furnace set at about 400 ° C. for about 5 to 15 minutes. The porous substrate is fired in an electric furnace set at about 500 ° C. for about 5 to 15 minutes.

After the silica sol 1-A liquid is further supported on the surface of the porous substrate supporting the silica sol 1-A liquid, the above operation is repeated two to three times.

Next, a silica sol 1-B solution was further used on the surface of the porous base material supporting the silica sol 1-A solution,
The same processing is performed.

Next, on the surface of the porous substrate supporting the silica sol 1-B liquid, the same treatment as described above is performed using the silica sol 1-C liquid.

Next, the silica sol 2 liquid is supported on the surface of a porous base material supporting the silica sol 1-A, 1-B and 1-C liquid, and the porous body is placed in an electric furnace set at about 200 ° C. For about 5 to 15 minutes, and then the porous substrate is fired for about 5 to 15 minutes in an electric furnace set to about 300 ° C., and then the porous substrate is heated to about 400 ° C. Bake for about 5 to 15 minutes in the furnace,
Next, the porous substrate was placed in an electric furnace set at about 500 ° C. for 5 to 1
Bake for 5 minutes.

After further supporting the silica sol 2 liquid on the surface of the porous substrate supporting the silica sol 2 liquid,
Repeat several times.

The above-mentioned optimum conditions such as the processing temperature, time, and number of times differ depending on the state of the silica sol. For example, the rate of hydrolysis depends on the ratio of water to tetraethoxysilane (H ₂ O / Si
(OC ₂ H ₅ ) ₄ = r). For example, FIG. 6 shows the effect of r on the viscosity of silica sol 1 at 80 ° C. For silica sol 1, r = 0.5 to 2.0 is a condition that can be applied industrially, and preferably 1.0 to 2.0.

FIG. 7 shows the amount of acid that affects the particle size of the gel. A porous substrate having a pore size of about 0.01 to 1.0 μm is used. Therefore, when the particle size of the silica gel 1 produced by calcining the silica sol 1 is smaller than the pore diameter of the substrate, the gel is filled in the pores of the porous substrate to reduce the pore volume,
As a result, the permeation amount as the separation membrane is reduced, and the performance is reduced. Therefore, the weight ratio of acid catalyst to ethoxysilane should be between 0.01 and 0.1. On the other hand, silica sol 2
After being carried on the uppermost surface of the porous substrate and firing and gelling, the fine pores are involved in the separation performance, and are approximately 0.
It is necessary to set the pore diameter to 001 to 0.01 μm. Therefore, in order to control the particle size of the silica gel, the weight ratio of the acid catalyst to ethoxysilane should be 0.01 to 0.5, particularly preferably 0.2 or less.

In this example, nitric acid HNO ₃ was used as the acid.
Similar effects can be obtained by using an acid such as hydrochloric acid.

As described above, the hydrolysis rate and the polycondensation rate change depending on the composition. Therefore, it is possible to produce silica gel with a composition other than those in Table 2, but it is considered that the conditions according to the present invention are appropriate in view of the film formation time on an industrial scale, the pore size required for the separation performance as a silica gel membrane, and the like. Can be

Also, the firing temperature changes from about 100 ° C to about 500 ° C.
There is no problem if the temperature is raised step by step and the temperature is not stepwise but is raised continuously with a holding time.

Furthermore, as the inorganic porous material used in the present invention, the first
Although any of those shown in the figure can be used,
Foamed silica, sintered alumina, mullite, etc. of 000 mm or more can be preferably used.

The differences between the present invention and the conventional technology are summarized as follows.

1) Relaxation of Polycondensation Reaction Rate In the preparation of the silica sol 1, the proportion of an acid catalyst, for example, nitric acid, is reduced to promote the polycondensation reaction gently and to stabilize the film forming conditions.

2) Acceleration of hydrolysis rate In the preparation of the silica sol 2, the film formation time in which the ratio of an acid catalyst, for example, nitric acid is increased, is shortened.

3) Increase the firing temperature of the silica sol. Gradually increase the temperature of the silica sol from 100 ° C and finally 500 ° C.
In improving the acid resistance by eliminating the residual -C ₂ H ₅ group by baking.

[Action] The structure of the silica gel membrane is as follows.

Here, H ₂ O is selectively adsorbed to the —OH group, and other components are prevented from entering the pores of the silica gel membrane. On the other hand, H ₂ O adsorbed to the —OH group moves in the pores and evaporates in vacuum on the side where the pressure is reduced.

As described above, H ₂ O in the organic acid is selectively separated and removed by the —OH group of the silica gel membrane. FIG. 2 shows a schematic diagram of this state.

 Hereinafter, an example of the present invention will be described.

〔Example〕

The following treatment was performed using a ceramic tube (average pore diameter 0.5 μm, outer diameter 10 mm, length 500 mm) manufactured by NGK Insulators, Ltd. as the inorganic porous body of the substrate.

(1) Preparation of silica sol 1 A drug having the composition shown in Table 4 was placed in a beaker, and rapidly stirred and mixed at room temperature with a stirrer. While stirring is continued, 80
Exothermic reaction starts when preheated to ℃ (boiling state)
The viscosity rises rapidly in 25 minutes. 25 minutes after boiling starts, 20 minutes,
The liquids for 15 minutes are cooled to obtain liquids 1-A, 1-B and 1-C. The 1-C liquid has a slightly higher viscosity, and the 1-B liquid has a higher viscosity and is a jelly-like liquid when cooled to room temperature. The 1-A liquid is in a state of being solidified by cooling at room temperature.

(2) Preparation of silica sol 2 A drug having the composition shown in Table 4 was placed in a beaker, and stirred and mixed at room temperature with a stirrer for 60 minutes to obtain silica sol 2.

(3) Supporting method of silica sol 1) Supporting of one solution of silica sol A tube made of an inorganic porous material was placed in the silica sol (1-A).
The porous body was immersed in a liquid to carry a silica sol on the surface of the porous body.

The porous body was fired in an electric furnace set at 200 ° C. for 10 minutes.

Next, the porous body was fired in an electric furnace set at 300 ° C. for 10 minutes.

Next, the porous body was fired in an electric furnace set at 400 ° C. for 10 minutes.

Next, the porous body was fired in an electric furnace set at 500 ° C. for 10 minutes.

 The above operations-were repeated twice.

Next, the above processes 1 to 3 were performed using the 1-B solution.

Next, the above processes 1 to 3 were performed using the 1-C solution.

2) Carrying of silica sol 2 liquid Next, the above-mentioned treatments 1 to 2 were performed using silica sol 2 liquid.

An organic acid / water separation experiment was performed using a ceramic tube supporting silica gel manufactured by the above method and using the apparatus shown in FIG.

350 c of organic acid aqueous solution in a circulating glass container 1 with an inner diameter of 30 mm
The temperature was raised by the heater 3 while the liquid was circulated by the rotation of the motor 2 and the temperature was controlled by the temperature controller 5 while measuring the temperature with a thermocouple.

After reaching a predetermined temperature, a vacuum pump (not shown) is operated to evacuate the inside of the ceramic tube 6 supporting the gel by 1 Torr.
Aspirated to r. The gas passing through the ceramic tube 6 was condensed in a glass container 7 cooled with liquid nitrogen, and the separation performance was measured by measuring its weight. In FIG. 3, reference numeral 8 denotes a capacitor.

 The results are shown in FIGS.

Here, separation coefficient α = {(1-y) / y} / {(1-x) / x} x: composition of solvent in raw material (mol%) y: composition of solvent in permeated gas (mol%) ) In the case of a membrane comprising only an inorganic porous material, there was no separation performance.

(Experimental example 1) Separation experiment of acetic acid / water Fig. 8 shows the concentration of acetic acid and water
FIG. 9 is a chart showing the correlation between the amount of acetic acid permeated and the concentration of acetic acid in the permeated gas, and FIG. 9 is a chart showing the correlation between the concentration of acetic acid on the upstream side and the separation coefficient in the acetic acid / water system.

(Experimental example 2) Separation experiment of acrylic acid / water FIG. 10 is a table showing the correlation between the concentration of acrylic acid on the upstream side in the acrylic acid / water system, the permeation amount of water / acrylic acid, and the concentration of acrylic acid in the permeated gas. FIG. 11 is a chart showing the correlation between the upstream acrylic acid concentration and the separation coefficient in the acrylic acid / water system.

(Experimental Example 3) Separation experiment of propionic acid / water FIG. 12 is a chart showing the correlation between the concentration of propionic acid on the upstream side in the propionic acid / water system, the permeation amount of water / propionic acid, and the concentration of propionic acid in the permeated gas. FIG. 13 is a chart showing the correlation between the concentration of propionic acid on the upstream side and the separation coefficient in a propionic acid / water system.

(Experimental Example 4) FIG. 14 is a chart showing the results of a long-term (110 hours) continuous separation experiment of an acrylic acid / water system. In the figure, the circles indicate the results of experiments performed using the separation membranes manufactured by the method presented at the 54th Annual Meeting of the Society of Chemical Engineers, and the squares indicate the separation membranes manufactured by the method described in Examples of the present invention. The results of a separation experiment performed using the experimental apparatus shown in FIG. 3 are shown.

As a result, it is clear that the separation membrane manufactured by the method shown in the example of the present invention shows no change in the membrane performance.

〔The invention's effect〕

The acid-resistant composite separation membrane produced by the method of the present invention comprises an organic acid /
The present invention is extremely useful industrially because water can be separated from a water mixture with high separation performance and high permeation flux, and the method for producing the separation membrane of the present invention is easy.

[Brief description of the drawings]

FIG. 1 is a table showing the relationship between the types of inorganic porous materials usable in the present invention and the pore diameter thereof, and FIG. 2 is a schematic diagram illustrating the principle of selective separation of water in an acid-resistant composite separation membrane produced by the present invention. FIG. 3 is a schematic view of an experimental apparatus used for selectively separating water from an aqueous solution containing an organic acid by an acid-resistant composite separation membrane produced by the present invention, and FIGS. FIG. 14 is a table showing separation characteristics in acetic acid / water, acrylic acid / water, and propionic acid / water systems using the acid-resistant composite separation membrane produced in the example. FIG. 14 shows the results of a long-term continuous experiment of the acrylic acid / water system. 4 is a table comparing an acid-resistant separation membrane manufactured in an example of the present invention with an acid-resistant separation membrane manufactured by a method presented at the 54th Annual Meeting of the Society of Chemical Engineers of Japan.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-145414 (JP, A) JP-A-59-22927 (JP, A) JP-A-57-3735 (JP, A) JP-A-2- 31824 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 71/02 C01B 33/141 C08J 9/00

Claims (1)

(57) [Claims] 1. A method for producing an acid-resistant composite separation membrane comprising silica gel obtained by hydrolyzing an alkoxysilane containing an ethoxy group or a methoxy group in pores of an inorganic porous material, comprising: In the preparation conditions of a plurality of types of silica sols produced by changing the mixing ratio of the alkoxysilane, which is a raw material of the silica sol, water and an acid catalyst, the raw material mixing ratio of the silica sol to be supported is reduced to two types for silica sol 1 and silica sol 2. (2) The weight ratio of water to alkoxysilane as the raw material for silica sol 1 is 0.5 to 2.0, and the reaction catalyst is
The weight ratio of the acid catalyst to the alkoxysilane is 0.01 to 0.1.
(3) The weight ratio of water to alkoxysilane as the raw material for silica sol 2 is set to 2.0 to 50, and as a reaction catalyst,
The weight ratio of the acid catalyst to the alkoxysilane is 0.01 to 0.5.
(4) maintaining the raw material for the silica sol 1 in a boiling state,
About 25 minutes, about 20 minutes and about 15 minutes of liquid after the start of boiling, respectively
1-A, 1-B and 1-C liquids; (5) The raw material for silica sol 2 was stirred and mixed at room temperature for 30 to 90 minutes to produce silica sol 2, (6) Surface of porous substrate After supporting the silica sol 1-A liquid thereon, the porous substrate is baked for 5 to 15 minutes in an electric furnace set at about 200 ° C., and then the porous body is set in an electric furnace set at about 300 ° C. Baking for 5 to 15 minutes in an electric furnace, and then baking the porous substrate in an electric furnace set to about 400 ° C. for 5 to 15 minutes, and then setting the porous substrate to about 500 ° C. in an electric furnace. Within 5 to 15
(7) After the silica sol 1-A liquid is further supported on the surface of the porous substrate supporting the silica sol 1-A liquid, the operation of the above (6) is repeated two to three times, (8) Next, on the surface of the porous substrate supporting the silica sol 1-A liquid, the same treatment as in the above (6) to (7) is further performed using the silica sol 1-B liquid, and (9) (6) using the silica sol 1-C liquid on the surface of the porous substrate supporting the silica sol 1-B liquid
(10) Next, the above silica sols 1-A, 1-B and 1-C
The above-mentioned silica sol 2 liquid is supported on the surface of the porous base material supporting the liquid, and the porous body is baked for 5 to 15 minutes in an electric furnace set at about 200 ° C. Is fired in an electric furnace set at about 300 ° C. for 5 to 15 minutes, and then the porous substrate is fired in an electric furnace set at about 400 ° C. for 5 to 15 minutes, and then the porous substrate 5 to 15 in an electric furnace set to about 500 ° C
(11) After the silica sol 2 liquid is further supported on the surface of the porous substrate supporting the silica sol 2 liquid, the operation (10) is repeated two or three times. A method for producing a separation membrane.