JP2009255031A - Treatment method of ceramic porous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of a ceramic porous film, capable of substantially shortening the time until a ceramic porous film reaches a resolution performance which can be finally developed by the lapse of timer, and preventing damages with the possibility of lowering film characteristics such as dissolution from being easily generated. <P>SOLUTION: In the treatment method of the ceramic porous film, to the ceramic porous film 1 formed by attaching ceramic sol onto a porous base material 10, drying the ceramic sol and then calcining it, the treatment of bringing carboxylic acid molecules into contact is executed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a treatment method for improving separation performance when a ceramic porous membrane is used as a separation membrane.

  Separation of specific components from mixed liquids containing multiple liquid components, such as separation membranes (filters) used for separation of water from mixed liquids containing water obtained from biomass and ethanol, etc. A ceramic porous film made of a ceramic material having excellent corrosion resistance such as erlite, mullite, silicon carbide and the like is used.

  Such a ceramic porous membrane is formed by adhering a ceramic sol on a porous substrate, drying the ceramic sol, and firing it, and is usually integrated with the porous substrate serving as a support. Used.

  Incidentally, as described above, when a ceramic porous membrane is used as a separation membrane, it is known that the separation performance changes with time. Specifically, the separation factor α of the ceramic porous membrane increases with the passage of time, and after rising to some extent, the separation factor α is maintained. That is, the ceramic porous membrane has a problem that the separation factor α is low in the initial state just produced, and the original separation performance cannot be obtained until the separation factor α is finally expressed. is there.

  In Patent Document 1, a siliceous porous membrane is immersed in water, brought into contact with water vapor of 100 ° C. or higher, or exposed to an environment having a humidity of 30% or higher and a temperature of 0 ° C. or higher in advance. A treatment method is disclosed in which a predetermined amount of water is adsorbed on the wall surfaces of the pores. By performing such treatment, it is possible to slightly shorten the time until the final separation performance is developed. However, in addition to not expecting a significant reduction in the time taken to develop the final separation performance, there are variations in the effect. Furthermore, dissolution of the siliceous porous membrane may occur due to contact with water or water vapor during the treatment, and the membrane characteristics as a separation membrane may be deteriorated.

JP 2001-276586 A

  The present invention has been made in view of such conventional circumstances, and the purpose of the present invention is to determine the time until the ceramic porous membrane finally reaches the separation performance that can be developed over time. An object of the present invention is to provide a method for treating a ceramic porous membrane, which can be greatly shortened and can suppress the possibility of deteriorating membrane characteristics as a separation membrane by dissolution.

  In order to achieve the above object, according to the present invention, the following ceramic porous membrane treatment method is provided.

  [1] A ceramic porous membrane that is subjected to a treatment of bringing a carboxylic acid molecule into contact with a ceramic porous membrane formed by attaching a ceramic sol on a porous substrate, drying the ceramic sol, and then firing the ceramic sol. Processing method.

  [2] The ceramic porous membrane according to [1], wherein the ceramic porous membrane is a porous silica membrane formed by adhering a silica sol on a porous substrate, drying the silica sol, and then firing the silica sol. How to treat the membrane.

  [3] The method for treating a ceramic porous membrane according to [1] or [2], wherein after the treatment for bringing the carboxylic acid molecule into contact, the surface of the ceramic porous membrane is further subjected to a heat treatment.

  [4] The method for treating a ceramic porous membrane according to any one of [1] to [3], wherein as the treatment, a carboxylic acid aqueous solution is circulated on the surface of the ceramic porous membrane.

  [5] As the treatment, while allowing the carboxylic acid aqueous solution to flow on the surface of the ceramic porous membrane, the surface of the ceramic porous membrane opposite to the surface through which the carboxylic acid aqueous solution flows is in a reduced pressure state, The method for treating a ceramic porous membrane according to any one of [1] to [3], wherein the carboxylic acid aqueous solution is treated to permeate the ceramic porous membrane.

  [6] The ceramic porous membrane according to [4] or [5], wherein a linear velocity on the membrane surface of the carboxylic acid aqueous solution circulated on the surface of the ceramic porous membrane is 0.5 to 100 cm / sec. Processing method.

  [7] In any of the above [4] to [6], in the treatment, the pH of the aqueous carboxylic acid solution to be used is 6 or less, the treatment temperature is 20 to 110 ° C., and the treatment time is 2 to 500 hours. A method for treating a ceramic porous membrane according to claim 1.

  [8] The method for treating a porous ceramic membrane according to any one of [1] to [7], wherein the carboxylic acid molecule is at least one of an acetic acid molecule and a citric acid molecule.

  [9] The method for treating a ceramic porous membrane according to any one of [1] to [8], wherein the carboxylic acid molecule is a citric acid molecule.

  When the treatment method of the present invention is carried out, the separation performance (separation coefficient α) in the initial state of the ceramic porous membrane is improved, and until the ceramic porous membrane finally reaches the separation performance that can be developed over time. Since the time can be greatly shortened, high separation performance can be exhibited in a short time after the production of the ceramic porous membrane. In addition, since the aqueous solution of carboxylic acid having a lower pH value than that of water can be used for the treatment for contacting the carboxylic acid molecules, the ceramic porous membrane to be treated can be used in a high pH environment such as a silica porous membrane. Even if it is easy to dissolve, it is difficult for dissolution to occur, and it is possible to suppress the possibility that the membrane characteristics as a separation membrane deteriorate.

  Hereinafter, the present invention will be described based on specific embodiments, but the present invention should not be construed as being limited thereto and based on the knowledge of those skilled in the art without departing from the scope of the present invention. Various changes, modifications, and improvements can be added.

  In the present invention, the ceramic porous membrane to be treated is formed by attaching a ceramic sol on a porous substrate, drying the ceramic sol, and then firing it.

  Preferred examples of the material for the porous substrate serving as the support for the ceramic porous membrane include alumina, silica, cordierite and the like. The porosity of the porous substrate is preferably about 25 to 55% from the viewpoint of the strength and permeability of the substrate. Moreover, it is preferable that the average pore diameter of a porous base material shall be about 0.005-5 micrometers. What is necessary is just to select the thickness of a porous base material in the range which does not impair the permeability | transmittance of a separation component while satisfy | filling intensity | strength required as a support body.

  In addition, the porous base material is composed entirely of the same material, and may be a base material having a single-layer structure in which the average pore diameter and porosity of each part are uniform, or the material, average pore diameter, porosity, etc. May be a base material having a multilayer structure in which a plurality of different layers are laminated. As a porous substrate having a multilayer structure, for example, as shown in FIG. 2, a substrate body 11 having a predetermined average pore diameter and a substrate body 11 formed on the substrate body 11 are smaller. A porous substrate 10 composed of an ultrafiltration membrane (hereinafter referred to as “UF membrane”) 14 having an average pore diameter is preferred. As shown in FIG. 1, when the ceramic porous membrane 1 is formed on the UF membrane 14 of the porous substrate 10 having such a structure, a high-separability ceramic porous membrane 1 with few defects such as cracks is obtained. It is easy to be done. When the porous substrate 10 is composed of the substrate body 11 and the UF membrane 14, it is preferable to use titania as the material of the UF membrane 14.

  There is no restriction | limiting in particular about the shape of a porous base material, According to the intended purpose of using a ceramic porous membrane, it can select suitably. For example, the porous substrate 10 shown in FIG. 3 has a monolithic shape in which a plurality of cells (through holes) 23 serving as fluid flow paths are partitioned by partition walls 22. When a ceramic porous film is formed on the inner wall surface of the cell 23 of the porous substrate 10 having such a shape, and the mixed liquid is introduced into the cell 23, the ceramic porous film is formed among the components constituting the mixed liquid. Only the specific component which can permeate | transmit can permeate | transmit a ceramic porous membrane, and also permeate | transmit the porous base material 10, and is discharged | emitted from an outer wall surface. The porous substrate 10 having such a shape can be produced by an extrusion molding method or the like. In addition, it is preferable that the inner wall surface of the cell 23 of the porous base material 10 is comprised by the UF film | membrane as mentioned above.

  Suitable materials for the porous ceramic film 1 formed on the porous substrate 10 include silica, titania, zirconia, alumina, cordierite, mullite, silicon carbide, and the like. Among these, a porous film made of silica is particularly preferable because the average pore diameter can be easily controlled.

  In forming the ceramic porous film, first, a ceramic sol (coating liquid) containing the components of the ceramic porous film to be obtained is prepared. For example, when forming a porous silica membrane, tetraethoxysilane is hydrolyzed at 50 ° C. for 5 hours in the presence of nitric acid to obtain a sol solution, and the sol solution is 1.0% by mass in terms of silica. A silica sol is prepared by diluting and adjusting with ethanol so as to be. Although it is possible to dilute with water instead of diluting with ethanol, diluting with ethanol can form a thin film in one film formation, and a film with a high permeation rate can be formed. Here, silica sol is used as a component of the ceramic sol, but sol of other components such as titania and zirconia can be used instead of silica sol.

  Next, the prepared ceramic sol is deposited on the porous substrate. For example, when the porous substrate is monolithic, as shown in FIG. 4, the outer peripheral surface of the porous substrate 10 is masked with a masking tape 41, and the ceramic sol 40 is removed from the upper part of the porous substrate 10. The ceramic sol is deposited on the inner wall surface of the cell 23 by pouring and passing through the cell 23. Thereafter, if necessary, excess ceramic sol is removed by shaking the porous substrate 10 by hand several times. The method of attaching the ceramic sol on the porous substrate is not limited to such pouring, and may be performed by other methods such as a dip method.

  Next, the ceramic sol attached to the porous substrate is dried. The drying method is not particularly limited. For example, as shown in FIG. 5, it is preferable to dry the cell 23 by sending air into the cell 23 using a dryer 25 or the like. Thus, by drying by ventilation, the ceramic sol can be densely formed into a film. The temperature of ventilation is preferably 10 to 80 ° C. When the air is blown at a temperature lower than 10 ° C., the ceramic sol attached to the inner wall surface of the cell 23 does not easily dry, and thus a dense ceramic porous film cannot be obtained, resulting in a film having a large average pore diameter. There is. Further, when the air is blown at a temperature higher than 80 ° C., cracks are likely to occur on the ceramic porous membrane surface. The speed at which the blast passes through the cell 23 is preferably 0.1 to 100 m / sec. If the speed at which the blast passes through the cell is less than 0.1 m / sec, the time required for drying may become too long. On the other hand, if the speed at which the blast passes through the cell exceeds 100 m / sec, cracks are likely to occur on the surface of the ceramic porous membrane.

  The ceramic sol thus deposited on the porous substrate is dried and then fired. Firing can be performed, for example, by raising the temperature at 100 ° C./hr, holding at 500 ° C. for 1 hour, and then lowering the temperature at 100 ° C./hr.

  The series of operations described above for attaching, drying, and firing the ceramic sol may be repeated a plurality of times as necessary.

  In the present invention, the ceramic porous film thus formed on the porous base material is subjected to a treatment for bringing carboxylic acid molecules into contact therewith. As a result of extensive studies by the present inventors, the separation performance (separation coefficient α) in the initial state of the ceramic porous membrane is improved by bringing the carboxylic acid molecule into contact with the ceramic porous membrane in this way, and the ceramic porous It was found that the time until the membrane reaches the separation performance that can be finally expressed over time can be greatly shortened. The reason why the separation performance of the ceramic porous membrane is improved by the treatment is considered to be that the hydrophilicity of the pore wall is improved by contacting the carboxylic acid molecule with the pore wall.

  In the present invention, as the carboxylic acid molecule to be brought into contact with the ceramic porous membrane, at least one of acetic acid molecule and citric acid molecule is preferable because it has a high effect of improving the separation performance (separation coefficient α). Is more preferable because a higher effect can be obtained than when acetic acid molecules are contacted.

  Specific methods for bringing the carboxylic acid molecules into contact with the ceramic porous membrane include a method of circulating a carboxylic acid aqueous solution on the surface of the ceramic porous membrane (hereinafter referred to as “circulation method”), a carboxylic acid aqueous solution. Is passed through the ceramic porous membrane surface, and the surface of the ceramic porous membrane opposite to the surface through which the carboxylic acid aqueous solution circulates is reduced in pressure so that the carboxylic acid aqueous solution permeates the ceramic porous membrane. (Hereinafter referred to as “transmission method”) and the like. In particular, the treatment by the permeation method is preferable because the effect of improving the separation performance (separation coefficient α) is high. In these methods, the carboxylic acid aqueous solution may be vaporized and distributed on the surface of the ceramic porous membrane.

  Thus, since the carboxylic acid aqueous solution having a pH lower than that of water can be used for the treatment for bringing the carboxylic acid molecules into contact with each other, the ceramic porous membrane to be treated has a high pH such as a silica porous membrane. Even if it is easy to dissolve in the environment, dissolution is less likely to occur and deterioration of the film characteristics can be suppressed as compared with the above-described treatment for adsorbing water.

  The pH of the carboxylic acid aqueous solution used for the permeation method and the distribution method is preferably 6 or less, and more preferably 1 to 4. When the pH exceeds 6, when the ceramic porous membrane to be treated is easily soluble in a high pH environment such as a silica porous membrane, the possibility of dissolution increases. In addition, when the pH of the carboxylic acid aqueous solution to be used is about 1-4, even if it changes the temperature of carboxylic acid aqueous solution, the separation factor (alpha) which reaches | attains by performing the said process hardly changes.

  The treatment temperature, that is, the temperature of the aqueous carboxylic acid solution is preferably 20 to 110 ° C, and more preferably 20 to 50 ° C. If the treatment temperature is less than 20 ° C., the treatment may take too long. Moreover, when processing temperature exceeds 110 degreeC, when pH, such as carboxylic acid aqueous solution used for a process, is high, possibility that a ceramic porous membrane will melt | dissolve will increase.

  The treatment time, that is, the time for allowing the aqueous carboxylic acid solution to flow over the ceramic porous membrane surface or for allowing the aqueous carboxylic acid solution to pass through the ceramic porous membrane is preferably 2 to 500 hours, and preferably 24 to 500 hours. More preferably, it is time. If the treatment time is less than 2 hours, the effect of improving the separation performance may not be sufficiently obtained. Further, even if the treatment is performed for more than 500 hours, it is difficult to obtain a further improvement effect of separation performance.

  In the flow method and the permeation method, the linear velocity at the film surface of the carboxylic acid aqueous solution to be circulated on the surface of the ceramic porous film is preferably 0.5 to 100 cm / second. As for the linear velocity, a higher speed is preferable because the contact efficiency of the carboxylic acid molecule is increased. However, if the linear velocity exceeds 100 cm / sec, it is difficult to obtain an effect of further improving the contact efficiency of the carboxylic acid molecule.

  In addition, after contacting the carboxylic acid molecules by the flow method or the permeation method, the effect of improving the separation performance is further improved by sending air to the cell for 2 to 100 hours to heat-treat the surface of the ceramic porous membrane. Get higher. The temperature of the air blowing is preferably 10 to 200 ° C., and the time until the separation performance that can be finally expressed can be shortened by increasing the temperature. This is presumably because carboxylic acid molecules are fixed to the surface of the ceramic porous membrane by heat treatment, and high separation performance (separation coefficient α) is improved.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

Example 1
A monolithic substrate body (outer diameter 30 mm, length 80 mm, cell inner diameter: 2.5 mm, number of cells: 55) made of alumina having an average pore diameter of 0.2 μm, and each cell of the substrate body A porous silica membrane was formed on a porous substrate formed of a titania UF membrane having an average pore diameter of 0.8 nm formed on the wall surface. Note that both ends of the porous substrate are sealed with glass.

  As a specific method for forming the porous silica membrane, first, tetraethoxysilane is hydrolyzed in the presence of nitric acid at 50 ° C. for 5 hours to form a sol solution, and the sol solution is 0.7 mass in terms of silica. The silica sol (coating solution) was obtained by diluting and adjusting with ethanol so as to be in%. Next, the porous base material is fixed with a jig so that the axial direction thereof is the vertical direction, and about 80 mL of silica sol whose temperature is controlled from the upper part of the porous base material is poured into the cell and allowed to pass through the cell. As a result, silica sol was deposited on the inner wall surface of the cell. Thereafter, ventilation was performed from the top of the porous substrate for about 5 seconds to remove excess silica sol. In addition, it confirmed that the silica sol adhered (film-forming) to the whole inner peripheral wall of a cell by this process.

  Subsequently, the silica sol adhering to the inner peripheral wall of the cell was air-dried for 1 hour so that air at room temperature passed through the cell of the porous substrate. The amount of air to be ventilated was adjusted so that the outlet air speed of the porous substrate cell was 3 to 4 m / sec. After drying, the entire porous substrate was heated at 100 ° C./hr in an electric furnace, held at 500 ° C. for 1 hour, and then cooled at 100 ° C./hr. The above series of operations (attachment of silica sol, drying, firing) was repeated four times to form a porous silica film on the porous substrate.

  Next, the formed porous silica membrane was subjected to a treatment for bringing carboxylic acid molecules into contact therewith. Specifically, an aqueous acetic acid solution having a pH of 1 and a liquid temperature of 70 ° C. is circulated at a linear velocity of 300 cm / sec in a cell of a porous base material on which a porous silica film is formed. A process of allowing the aqueous acetic acid solution to permeate through the porous silica membrane by reducing the pressure from the side of the material at a vacuum of about 10 Torr was performed for 2 hours.

  Thus, after contacting a carboxylic acid molecule with the porous silica membrane, a water-ethanol separation test was conducted. In this test, an aqueous solution having an ethanol concentration of 94% by mass was decompressed at a vacuum degree of about 10 Torr from the side surface of the porous substrate while circulating an aqueous solution at a temperature of 70 ° C. through the cell at a feeding rate of 15 L / min. The permeate discharged from the side surface was collected by a liquid nitrogen trap, and the separation factor α was calculated from the ethanol concentration of the collected permeate and the raw solution before permeation. The separation factor α calculated by the test is shown in Table 1.

(Examples 2 to 20)
As a treatment for bringing a carboxylic acid molecule into contact with the porous silica membrane formed in the same manner as in Example 1, the pH and liquid shown in Table 1 were placed in the cell of the porous substrate on which the porous silica membrane was formed. A warm (treatment temperature) acetic acid aqueous solution or citric acid aqueous solution was circulated over the time (treatment time) shown in the same table at the linear velocity shown in the same table. After contacting carboxylic acid molecules with the porous silica membrane in this manner, a water-ethanol separation test was conducted in the same manner as in Example 1. The separation factor α calculated by the test is shown in Table 1.

(Comparative Example 1)
The silica-porous membrane formed in the same manner as in Example 1 was subjected to a water-ethanol separation test without being subjected to a treatment for bringing a carboxylic acid molecule into contact therewith. The separation factor α calculated by the test is shown in Table 1.

(Comparative Example 2)
The silica porous membrane formed in the same manner as in Example 1 was treated with a nitric acid aqueous solution. Specifically, a nitric acid aqueous solution with a liquid temperature of 70 ° C. and a pH of 1 is circulated for 500 hours at a linear velocity of 50 cm / second in a cell of a porous substrate on which a porous silica membrane is formed. It was. After contacting nitric acid molecules with the porous silica membrane in this manner, a water-ethanol separation test was conducted in the same manner as in Example 1. The separation factor α calculated by the test is shown in Table 1.

  As shown in Table 1, Examples 1-17 which performed the process which contacts a carboxylic acid molecule with respect to a silica porous membrane have a higher separation coefficient (alpha) than the comparative example 1 which did not perform the said process, and the said process It can be seen that the separation performance is improved. This is presumably because the pores of the porous silica membrane were reduced in size by contacting with carboxylic acid molecules, or the water selectivity was improved by contacting with a highly hydrophilic carboxylic acid aqueous solution to improve water selectivity. . In particular, Example 1 treated by the permeation method exhibited an effect of improving the separation performance in a short time. Further, from the results of Examples 2, 3, 5 and 7, when the pH and other conditions of the aqueous carboxylic acid solution are the same, it is possible to obtain a higher separation performance improvement effect by bringing the citric acid molecule into contact with the acetic acid molecule. I understand that Further, from the results of Examples 2, 9 and 10, in the carboxylic acid aqueous solution having a pH of about 1, the silica does not dissolve and the value of the separation factor α does not change depending on the liquid temperature (treatment temperature). It can be seen that the higher the temperature is, the more the reaction is promoted, and the time it takes for the separation membrane to reach the separation performance that can finally be expressed over time. Furthermore, as the results of Examples 3, 11 and 12 show, even in the carboxylic acid aqueous solution having a pH of about 4, no change in the value of the separation coefficient α due to the liquid temperature (treatment temperature) was observed. However, as the results of Examples 4, 13, and 14 show, when the pH of the carboxylic acid aqueous solution is about 5, dissolution of silica is promoted and the effect of improving the separation performance decreases as the liquid temperature increases. Moreover, as the results of Examples 6 and 15 to 17 show, the higher the linear velocity of the aqueous carboxylic acid solution flowing on the membrane, the higher the contact efficiency of the carboxylic acid molecules, and the higher separation performance improvement effect is obtained. When the linear velocity exceeds about 100 cm / sec, it is difficult to obtain a further improvement effect. The comparative example 2 which processed using the nitric acid aqueous solution has a low separation performance improvement effect, but this is considered to be because the separation membrane is not hydrophilized by the processing.

  Moreover, as the results of Examples 6 and 18 to 20 show, it can be seen that a high separation performance improvement effect can be obtained by applying a heat treatment to the surface of the porous silica membrane after contacting the carboxylic acid aqueous solution. The higher the heat treatment temperature, the faster the time until the separation performance that can be finally expressed is reached. This is considered to be because the carboxylic acid molecules are fixed to the surface of the porous silica membrane by heat treatment, and the effect of improving the separation performance is enhanced.

  The present invention can be suitably used as a treatment method for improving the separation performance when using a ceramic porous membrane as a separation membrane.

It is sectional drawing which showed typically an example of the structure of the ceramic porous membrane formed on the porous base material. It is sectional drawing which showed typically an example of the structure of the porous base material. It is a perspective view which shows an example of the shape of a porous base material. It is explanatory drawing which shows an example of the method of forming (film-forming) a ceramic porous film | membrane on a porous base material. It is explanatory drawing which shows an example of the method of forming (film-forming) a ceramic porous film | membrane on a porous base material.

Explanation of symbols

1: Ceramic porous membrane, 10: Porous base material, 11: Base material, 14: Ultrafiltration membrane (UF membrane), 22: Partition wall, 23: Cell, 25: Dryer, 40: Ceramic sol (coating solution) ), 41: Masking tape.

Claims (9)

Ceramic porous film formed by attaching a ceramic sol on a porous substrate, drying the ceramic sol, and then firing it,
A method for treating a ceramic porous membrane, wherein a treatment for contacting carboxylic acid molecules is performed.   The ceramic porous membrane according to claim 1, wherein the ceramic porous membrane is a porous silica membrane formed by adhering a silica sol on a porous substrate, drying the silica sol, and then firing the silica sol. Method.   The method for treating a ceramic porous membrane according to claim 1 or 2, wherein after the treatment for bringing the carboxylic acid molecules into contact, a surface of the ceramic porous membrane is further subjected to a heat treatment.   The processing method of the ceramic porous membrane as described in any one of Claims 1-3 which performs the process which distribute | circulates carboxylic acid aqueous solution on the said ceramic porous membrane surface as said process. As the treatment, while circulating an aqueous carboxylic acid solution on the surface of the ceramic porous membrane,
The process of making the said carboxylic acid aqueous solution permeate | transmit the said ceramic porous membrane by making into a pressure reduction state the surface on the opposite side to the surface through which the said carboxylic acid aqueous solution distribute | circulates of the said ceramic porous membrane. The processing method of the ceramic porous membrane as described in any one of Claims.   The method for treating a ceramic porous membrane according to claim 4 or 5, wherein a linear velocity at the membrane surface of the carboxylic acid aqueous solution circulated on the surface of the ceramic porous membrane is 0.5 to 100 cm / sec.   The said process WHEREIN: The pH of the said carboxylic acid aqueous solution to be used is 6 or less, process temperature is 20-110 degreeC, and process time is 2-500 hours, It is any one of Claims 4-6 A method for treating a ceramic porous membrane.   The method for treating a ceramic porous membrane according to any one of claims 1 to 7, wherein the carboxylic acid molecule is at least one of an acetic acid molecule and a citric acid molecule.   The method for treating a ceramic porous membrane according to any one of claims 1 to 8, wherein the carboxylic acid molecule is a citric acid molecule.

Images