JP5856524B2 - Method for producing silica membrane filter - Google Patents

Description

The present invention relates to a method for producing a silica film filter. More particularly, a method for producing a silica film filter that can be used to separate or concentrate only certain types of material out of the fluid being intermingled plural kinds of materials.

  A separation membrane may be used when only a specific type of material is separated or concentrated from a fluid in which a plurality of types of materials are mixed. An example of such a separation membrane is a silica membrane. The silica film is a porous film in which a plurality of pores are formed. The pores of the silica membrane are continuously formed from one surface to the other surface of the silica membrane, and the substance can be separated or utilized by utilizing the ability of a specific type of substance to pass through the pores. Concentrate. In general, the pores of a silica film have a characteristic that allows a substance having a small molecular diameter (for example, water, carbon dioxide, etc.) to easily pass therethrough. Utilizing such characteristics, silica membranes are used for applications such as separation of water from a mixture of water and ethanol, and separation of carbon dioxide from combustion exhaust gas.

  On the other hand, for the purpose of improving the permeability of a silica membrane, a membrane obtained by hybridizing a silica membrane and an organic compound has been studied (see, for example, Patent Documents 1 and 2 and Non-Patent Documents 1 and 2). Specifically, it has been proposed to use a raw material containing an organic functional group in silicon alkoxide as a raw material for producing a precursor of a silica film. By firing the precursor produced using such a raw material, a part of the organic functional group contained in the raw material is lost, and pores are formed in the silica film. Note that the above-described permeability means a performance that allows only the above-described “specific type of substance” to pass through the pores of the silica membrane.

  Further, as described above, when a raw material containing an organic functional group is used for silicon alkoxide, an affinity effect due to the organic functional group partially remaining in the silica film is also expected. Furthermore, in such a silica membrane, there is an expectation for an application for separating an aromatic component and alcohol from an organic mixed compound.

JP 2001-212401 A International Publication No. 2012/002181

Journal of Membrane Science, 380 (2011) 41-47 Separation and Purification Technology, 16 2 (1999) 139-146

  However, the conventional silica membrane as described above has a problem that the permeability is not sufficient in alcohol separation from the organic mixed compound. For this reason, development of a silica membrane effective for the separation of alcohol from an organic mixed compound is desired.

  The present invention has been made in view of the above-described problems, and a silica membrane filter that can be used to separate or concentrate only a specific type of substance from a fluid in which a plurality of types of substances are mixed, And a method for manufacturing the same. In particular, a silica membrane filter particularly effective for separating alcohol from an organic mixed compound and a method for producing the same are provided.

According to the present invention, the following sheet production method of silica film filter is provided.

[ 1 ] A silica raw material containing a silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more is hydrolyzed and polycondensed to obtain a precursor solution containing a precursor sol. The precursor solution is prepared by bringing the precursor solution into contact with the surface of the porous substrate, and the precursor solution contained in the precursor solution is flowed by the dead weight of the precursor solution. possess a covering step of adhering onto the surface of wood, the porous drying the precursor sol adhered to the surface of the substrate and then the drying and heat treatment step of heat-treating at 300 to 600 ° C., and It said precursor the number of carbon atoms for use in the solution preparation step and the molecular weight at least 8 over 120 organic functional group includes a functional group containing at least one of a portion to an oxygen atom and a nitrogen atom Siri Method of manufacturing a membrane filter.

[ 2 ] The silica according to [ 1 ], wherein the organic functional group having 8 or more carbon atoms and having a molecular weight of 120 or more contained in the silicon alkoxide is decomposed by 40 to 100% in the drying / heat treatment step. Membrane filter manufacturing method.

  The silica membrane filter of the present invention includes a porous substrate and a silica membrane provided on the surface of the porous substrate. The silica film in the silica film filter of the present invention includes a functional group containing at least one selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, and oxygen atoms. Further, this silica film is obtained by heat-treating a precursor sol made of a silica raw material containing silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more.

  In the silica membrane filter of the present invention, part of the “organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more” contained in the above-described silicon alkoxide forms pores of the silica membrane by the heat treatment. ing. The pores of the silica film formed by such “organic functional groups having 8 or more carbon atoms and a molecular weight of 120 or more” have larger pore diameters than the pores of the silica film of the conventional silica film filter. It is. And by forming such large pores in the silica membrane, it becomes possible to express extremely good permeability in alcohol separation from the organic mixed compound.

  Further, in the method for producing a silica membrane filter of the present invention, a silica membrane is formed using "a silica raw material containing a silicon alkoxide having at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120". I am making it. For this reason, the silica membrane filter of this invention mentioned above can be manufactured simply.

It is a perspective view showing typically one embodiment of a silica membrane filter of the present invention. It is a mimetic diagram showing an example of a covering process in one embodiment of a manufacturing method of a silica membrane of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the present invention.

(1) Silica membrane filter:
First, an embodiment of the silica membrane filter of the present invention will be described. FIG. 1 is a perspective view schematically showing one embodiment of the silica membrane filter of the present invention. As shown in FIG. 1, the silica membrane filter 100 of this embodiment includes a porous substrate 1 and a silica membrane 3 provided on the surface of the porous substrate 1.

  The silica film 3 of the silica film filter 100 of this embodiment includes a functional group including at least one selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, and oxygen atoms. Further, the silica film 3 is obtained by heat-treating a precursor sol made of a silica raw material containing silicon alkoxide having at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more. . In FIG. 1, reference numeral 2 denotes a cell. Reference numeral 11 denotes one end face of the porous substrate 1, and reference numeral 12 denotes the other end face of the porous substrate 1.

  In the silica membrane filter of the present embodiment, part of the “organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more” contained in the silicon alkoxide described above forms pores of the silica membrane by the heat treatment. doing. The pores of the silica film formed by such “organic functional groups having 8 or more carbon atoms and a molecular weight of 120 or more” have larger pore diameters than the pores of the silica film of the conventional silica film filter. It is. And by forming such large pores in the silica membrane, it becomes possible to express extremely good permeability in alcohol separation from an organic mixed compound (for example, organic mixed liquid).

  For this reason, the silica membrane of the silica membrane filter of the present embodiment can be particularly suitably used as a separation membrane that selectively permeates the alcohol from an organic mixed liquid containing alcohol. Hereinafter, the ability to selectively separate alcohol from an organic mixed compound containing alcohol may be referred to as “alcohol selection performance”. Moreover, in the silica membrane filter of this embodiment, although there is no restriction | limiting in particular about the kind of alcohol isolate | separated from an organic mixed compound, A C1-C4 alcohol can be mentioned as a suitable example.

  When the silicon alkoxide contained in the silica raw material does not contain an organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more, the pores formed in the silica film are reduced and good alcohol selection performance is obtained. Not expressed. For example, when the carbon number of the organic functional group contained in the silicon alkoxide is 7 or less or the molecular weight of the organic functional group is less than 120, the permeation resistance of the pores formed in the silica film is large. As a result, the alcohol permeability deteriorates.

(1-1) Silica film:
As described above, the silica film used in the silica film filter of the present embodiment includes a functional group including at least one selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, and oxygen atoms. Further, this silica film is obtained by heat-treating a precursor sol made of a silica raw material containing silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more. Hereinafter, “functional group containing at least one selected from the group consisting of carbon atom, hydrogen atom, nitrogen atom, and oxygen atom” actually contained in the silica film is referred to as “functional group contained in silica film”. There is. Moreover, the organic functional group contained in the silicon alkoxide contained in the silica raw material may be referred to as “organic functional group contained in silicon alkoxide”. Further, “an organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more” contained in silicon alkoxide is referred to as “specific organic functional group contained in silicon alkoxide” or simply “specific organic functional group”. is there. The “functional group contained in the silica film” may be a functional group containing at least one selected from the group consisting of a carbon atom, a hydrogen atom, a nitrogen atom, and an oxygen atom, as described above. That is, it may be a functional group containing a carbon atom or a functional group containing no carbon atom. For example, it may be a hydroxy group or a hydrogen atom.

  The functional group contained in the silica film is a functional group containing at least one selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, and oxygen atoms. This functional group may be one in which a part of the organic functional group contained in the silicon alkoxide contained in the silica raw material described above remains without being decomposed in the heat treatment. Further, some of the organic functional groups contained in the silicon alkoxide contained in the silica raw material may be other functional groups generated after being decomposed in the heat treatment.

The specific organic functional group contained in the silicon alkoxide is an organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more. The shape of the specific organic functional group is not particularly limited, and examples thereof include those containing a linear or branched alkyl group, a cyclic saturated hydrocarbon, and an aromatic hydrocarbon. Further, in a part thereof, that contain a functional group containing an oxygen atom or a nitrogen atom. The shape of the functional group containing an oxygen atom or nitrogen atom is not particularly limited, and examples thereof include a hydroxyl group, an epoxy group, a carboxyl group, an aldehyde group, an amino group, an amide group, and the like.

  The specific organic functional group contained in the silicon alkoxide preferably has 8 to 20 carbon atoms, more preferably 8 to 18 carbon atoms, and particularly preferably 8 to 15 carbon atoms. By setting the number of carbon atoms of the specific organic functional group within the above numerical range, it is possible to produce a silica film having alcohol selectivity and excellent alcohol permeability. When the number of carbon atoms exceeds 20, the specific organic functional group may become too large, and the specific organic functional group may disappear due to heat treatment to generate too large pores. Therefore, although alcohol permeability becomes high, alcohol selectivity may fall.

  In the specific organic functional group contained in the silicon alkoxide, the molecular weight is preferably 120 to 300, more preferably 120 to 250, and particularly preferably 120 to 200. By setting the molecular weight of the specific organic functional group in the above numerical range, it is possible to produce a silica membrane having alcohol selectivity and excellent alcohol permeability. In addition, when the molecular weight exceeds 300, the specific organic functional group becomes too large, and the specific organic functional group disappears by heat treatment and the generated pores may become too large. Therefore, although alcohol permeability becomes high, alcohol selectivity may fall.

  Specific organic functional groups contained in silicon alkoxide include decyl group, dodecyl group, octadecyl group, 2- (3,4-epoxycyclohexyl) ethyl group, N-phenyl-3-aminopropyl group, and N-cyclohexylaminopropyl group. , Etc.

  Moreover, it is preferable that the specific organic functional group contained in the silicon alkoxide does not contain an organic functional group of acenes. The organic functional group of acenes is an organic functional group containing a compound in which a plurality of benzene rings are linearly condensed. The boiling point of the organic functional group of acenes is significantly higher than that of an organic functional group containing a hydrocarbon having the same molecular weight. For this reason, in the heat treatment step, the specific organic functional group is hardly decomposed, and pores derived from the specific organic functional group are hardly formed. Similarly, the specific organic functional group contained in the silicon alkoxide preferably does not contain an organic functional group having a polycyclic aromatic hydrocarbon. Such an organic functional group having a polycyclic aromatic hydrocarbon also has a significantly higher boiling point than an organic functional group containing a hydrocarbon having the same molecular weight. As a result, it is difficult to form pores derived from this specific organic functional group.

  In general, an organic functional group having a large molecular weight has a higher boiling point, and the temperature of heat treatment necessary for removing it from the silica film (hereinafter also referred to as “heat treatment temperature”) becomes high. Further, it is generally known that the silica structure becomes denser as the heat treatment temperature becomes higher, and there is a concern that the permeability of the silica film may be lowered due to the higher heat treatment temperature. In order to remove an organic functional group having a large molecular weight from the silica film without increasing the heat treatment temperature of the silica film, it is not preferable that the organic functional group has a structure that is difficult to thermally decompose. That is, it is preferable that the organic functional group has a structure that is easily thermally decomposed. For this reason, the specific organic functional group is an organic functional group other than the organic functional group of acenes and the organic functional group having polycyclic aromatic hydrocarbon, thereby suppressing the high temperature of the heat treatment of the silica film. it can.

  In the silica membrane filter of the present embodiment, the “organic functional group having 8 or more carbon atoms and 120 or more molecular weight (ie, a specific organic functional group)” contained in the silicon alkoxide contained in the silica raw material, It is preferable that it is decomposed by 40 to 100%. By comprising in this way, the pore which expresses alcohol permeability favorably will fully be formed in a silica membrane.

  The silica membrane of the silica membrane filter of this embodiment is produced as follows. First, a precursor sol is prepared by hydrolyzing and polycondensing a silica raw material containing a silicon alkoxide containing at least one specific organic functional group. Next, the precursor sol is disposed in a film shape on the porous substrate. A precursor sol disposed in a film shape on a porous substrate is heat-treated to produce a silica film. Here, the silica raw material for producing the precursor sol may contain a substance other than silicon alkoxide. For example, the silica raw material may contain a metal element other than silicon.

  Examples of the silicon alkoxide containing at least one specific organic functional group include decyltrimethoxysilane, dodecyltrimethoxysilane, octadecyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and N-phenyl-3. -Aminopropyltrimethoxysilane, naphthalyltrimethoxysilane, N-cyclohexylaminopropyltrimethoxysilane, etc. can be mentioned. The above-mentioned “silicon alkoxide containing at least one specific organic functional group” may be used alone or in combination of two or more. Further, the silica raw material for producing the silica film may contain a silicon alkoxide other than the above-described “silicon alkoxide containing at least one specific organic functional group”. Here, “silicon alkoxide including at least one specific organic functional group” is referred to as “silicon alkoxide (A)”, and “silicon alkoxide other than“ silicon alkoxide including at least one specific organic functional group ”is referred to as“ silicon alkoxide ( B) ". When both the silicon alkoxide (A) and the silicon alkoxide (B) are contained in the silica raw material for producing the silica film, the total amount of silicon alkoxide (A) relative to the total molecular weight of silicon alkoxide (B) The molecular weight ratio is preferably 1 or more. The ratio of the total molecular weight of the silicon alkoxide (A) to the total molecular weight of the silicon alkoxide (B) can be expressed as “total molecular weight of silicon alkoxide (A) / total molecular weight of silicon alkoxide (B)”.

  In the silica membrane filter of the present embodiment, the silica membrane becomes hydrophobic when a part of the specific organic functional group remains in the silica membrane even by the heat treatment described above. That is, when the specific organic functional group is not decomposed 100% by the heat treatment described above, the silica film becomes hydrophobic. As a result, since the silica film is difficult to adsorb water vapor, the silica film is more durable against water vapor.

  When silicon alkoxide is hydrolyzed and polycondensed when the precursor sol is produced, silicon alkoxides are successively bonded to each other to form a chain in which structural units derived from silicon alkoxide are linked. Also, this chain is made up with occasional branching. As a result, a chain of structural units derived from silicon alkoxide forms a network structure. The mesh with this network structure is the prototype of the pores. When silicon alkoxides are bonded to each other to form a network structure, the specific organic functional group prevents the three-dimensional structure from becoming a small network, or the specific organic functional group It is inferred that the angle between the chain and the chain acts to be a predetermined angle. By the action of such specific organic functional groups, it is presumed that the size of the mesh or the shape of the mesh that is the prototype of the pores is suitable for passing alcohol.

  By heat-treating the precursor sol thus produced, the mesh of the network structure described above becomes pores. By this heat treatment, some specific organic functional groups contained in the precursor sol are decomposed. In particular, when the specific organic functional group that was inside the mesh that is the prototype of the pore is decomposed, a space is created in a place that would have occupied if the specific organic functional group did not decompose. It is inferred that the hole becomes larger. Alternatively, it is assumed that the shape of the pores changes due to the decomposition of the specific organic functional group. It is inferred that such changes in the size and shape of the pores make the pores more suitable for passing alcohol. The reason why only alcohol permeates selectively in the silica membrane of the silica membrane filter of the present embodiment is unknown, but the following is presumed. In other words, the pore size and shape are more suitable for permeation of alcohol than permeation of organic compounds other than alcohol, and it is assumed that alcohol can selectively permeate from organic mixed compounds containing alcohol. The

(1-2) Porous substrate:
The silica membrane filter of this embodiment is provided with a porous substrate. A silica film is provided on the surface of the porous substrate. When the silica film is provided on the surface of the porous substrate, the strength of the silica film can be reinforced. The porous substrate has a large number of pores passing therethrough. Therefore, the fluid can pass through the porous substrate.

  As a porous substrate that can be used in the silica membrane filter of the present embodiment, a porous substrate made of a porous ceramic mainly composed of at least one of alumina, titania, silica, cordierite, zirconia, mullite, and the like is used. Is preferred. When alumina or the like listed here is a main component, the porous substrate is excellent in heat resistance, chemical resistance, impact resistance, and the like.

  In the porous substrate, pores having an average pore diameter of 0.0005 to 5 μm are preferably opened on the surface of the portion where the silica film is provided. By comprising in this way, the permeation | transmission flux of the substance which permeate | transmits a silica membrane can be made high. Further, when the average pore diameter of the porous substrate is within the above numerical range, the silica membrane can be completely filled into the opening portions of the pores of the porous substrate.

  In the silica membrane filter of the present embodiment, the porous substrate may have a single layer structure or a multilayer structure. The single-layer structure means that the porous substrate is composed of one kind of porous substrate. The multilayer structure means that the porous substrate is composed of two or more kinds of porous substrates, and the two or more kinds of porous substrates are laminated.

  There is no restriction | limiting in particular about the shape of a porous base material. Examples of the shape of the porous substrate include a cylindrical shape (tube shape) such as a cylinder and a rectangular tube, and a column shape such as a column and a rectangular column. The shape of the porous substrate may be a plate shape such as a disk shape or a polygonal plate shape. In addition, since the ratio of the surface area of the silica membrane to the volume of the silica membrane filter can be increased, the shape of the porous substrate is preferably a monolith shape. "Monolith shape" is a lotus shape in which a plurality of cells (holes) extending from one end surface to the other end surface, which serve as a fluid flow path, are formed on a columnar base material having one end surface and the other end surface. This means the shape. When such a monolithic porous substrate is used, it is preferable to provide a silica film on the inner wall surface of the lotus-like hole.

  In the silica membrane filter of this embodiment, the silica membrane is provided in a state where it does not penetrate deeply into the pores from the surface of the porous substrate from the viewpoint of increasing the permeation flux of the substance that permeates the silica membrane. It is preferable that

(2) Silica membrane filter manufacturing method:
Next, an embodiment of a method for producing a silica membrane filter of the present invention will be described. The method for producing a silica membrane filter of the present embodiment includes a “precursor solution preparation step”, a “coating step”, and a “drying / heat treatment step”. The “precursor solution preparation step” includes a precursor sol obtained by hydrolyzing and polycondensing a silica raw material containing a silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more. In this step, a precursor solution is obtained. In the “coating step”, the precursor solution obtained in the precursor solution preparation step is brought into contact with the surface of the porous substrate, and the precursor contained in the precursor solution by flowing under the dead weight of the precursor solution. In this step, the sol is deposited on the surface of the porous substrate. The “drying / heat treatment step” is a step of drying the precursor sol adhering to the surface of the porous substrate and then heat-treating it at 300 to 600 ° C. Through these steps, a silica membrane filter can be manufactured. The silica membrane filter obtained by the method for producing a silica membrane filter of this embodiment is the silica membrane filter of the present invention described so far.

  In the precursor solution preparation step, the silica raw material is stirred at 40 to 150 ° C., and the silicon alkoxide is hydrolyzed and polycondensed to accelerate the polymerization of the silicon alkoxide, so that the precursor having an appropriate size for film formation is obtained. A body sol can be obtained. In addition, when the silica raw material is stirred, the size of the precursor sol can be adjusted by adjusting the temperature of the silica raw material, the time for stirring the silica raw material, and the like. When the precursor sol is large, it becomes difficult for the precursor sol to enter the pores from the surface of the porous substrate in the subsequent coating step. As a result, the thickness of the silica film that has entered the pores from the surface of the porous substrate can be reduced. Therefore, it is possible to produce a thin silica film by using a large precursor sol. When the silica film is thinned in this way, it is possible to increase the permeation flux when the substance is permeated through the silica film.

  The silica raw material contains silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more. Hereinafter, “a silicon alkoxide having at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more” may be referred to as “specific silicon alkoxide”. The silica raw material preferably contains an organic solvent. Although it does not specifically limit as this organic solvent, Alcohol, ethers, ketones, amides, aromatics, etc. which are miscible with a silica raw material and water can be mentioned. For example, ethanol, isopropanol, N-methyl-2pyrrolidone, etc. can be mentioned. Moreover, you may mix not only one type but 2 or more types of organic solvents.

  The precursor solution prepared in the precursor solution preparation step preferably contains a catalyst in order to promote hydrolysis of the specific silicon alkoxide. Examples of the catalyst contained in the precursor solution include an acid catalyst and an alkali catalyst. Specifically, examples of the acid catalyst include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid. Moreover, as an alkali catalyst, sodium hydroxide, potassium hydroxide, ammonia etc. can be mentioned, for example.

  The silica raw material used in the precursor solution preparation step can be prepared by a method in which the specific silicon alkoxide and the organic solvent are mixed and stirred, and then an acid catalyst and water are further added and stirred. .

  In the coating step, the precursor sol contained in the precursor solution is deposited on the surface of the porous substrate by flowing down due to the weight of the precursor solution (this coating method is hereinafter referred to as the flowing-down method). When the precursor sol is deposited on the porous substrate by the flow-down method, the precursor sol receives an appropriate stress compared to the case where the precursor sol is deposited by the dip method or spin coat method described later. While closing the pores of the porous substrate in a short time. As a result, the thickness of the resulting silica membrane becomes thin, and the pore diameter of the obtained silica membrane becomes a size suitable for expressing the alcohol selection performance.

  When the precursor sol is deposited on the porous substrate by the dip method, the thickness of the resulting silica film tends to be thicker than in the case of the flow-down method. At this time, since the precursor sol freely enters the pores of the porous substrate, the precursor sol is excessively filled in the pores of the porous substrate. The pore diameter of the silica membrane obtained by the dip method is slightly smaller than the size suitable for expressing the alcohol selection performance. In addition, when the amount of the precursor sol attached is reduced in order to reduce the thickness of the silica film, it is difficult to completely block the pores of the porous substrate with the precursor sol. For this reason, pores having a pore size of several nm or more may be formed in the obtained silica film. When such a pore having a pore diameter of several nanometers or more is formed in the silica membrane, a substance other than the separation object passes through the pore. That is, the pore having a pore diameter of several nm or more becomes a defect in the silica film.

  When the precursor sol is deposited on the porous substrate by the spin coating method, the thickness of the silica film can be reduced as in the case of the flow-down method. However, in the case of the spin coating method, the precursor sol is densely filled in the pores of the porous base material due to excessive stress during the spin coating rotation. Therefore, like the dip method, the pore diameter of the obtained silica membrane is smaller than the size suitable for expressing the alcohol selection performance. Here, if the rotation speed of the spin coat is decreased in order to reduce the stress at the time of spin coat rotation, the thickness of the silica film is increased. Further, when the rotation speed of the spin coat is reduced, it becomes difficult to completely block the pores of the porous substrate with the precursor sol. For this reason, pores having a pore size of several nm or more may be formed in the obtained silica film. As described above, pores having a pore diameter of several nm or more become defects in the silica film.

  When the silica film is formed not by the sol-gel method but by the vapor phase method such as the CVD method, the precursor sol freely enters the pores of the porous substrate as compared with the flow-down method. End up. Therefore, the precursor sol is excessively filled in the pores of the porous substrate. As a result, the pore diameter of the obtained silica membrane tends to be smaller than the size suitable for expressing the alcohol selection performance.

  FIG. 2 is a schematic view showing an example of a coating step in one embodiment of the method for producing a silica film of the present invention. Prior to the precursor sol coating step, at least a part of the outer peripheral surface of the porous substrate 33 is masked with the masking tape 41. Subsequently, as shown in FIG. 2, the porous base material 33 is held in a state where the extending direction of the cells 35 is aligned with the vertical direction, and the cells of the porous base material 33 are formed from the upper end surface of the porous base material 33. The precursor solution 31 is poured into 35. Reference numeral 37 in FIG. 2 indicates a partition wall of the porous substrate 33.

  At this time, first, the precursor sol contained in the precursor solution 31 adheres to the inner wall surface 39 of the cell 35 around the upper end surface of the porous substrate 33. Subsequently, the precursor sol flows down by its own weight while adhering to the inner wall surface 39, thereby covering the inner wall surface 39 in a film shape while spreading from the upper side to the lower side. When the precursor sol completely covers the inner wall surface 39 to the lower end surface, the precursor sol that cannot adhere to the inner wall surface 39 is discharged out of the cell 35 from the lower end surface of the porous substrate 33. .

  According to this flow-down method, the precursor sol does not easily enter the pores of the porous base material 33, and an excessive amount of the precursor sol does not easily adhere to the inner wall surface 39. As a result, a thin film of the precursor sol can be formed on the inner wall surface 39. Thus, when a thin film of the precursor sol is formed, a silica film filter having a high permeation flux can be obtained.

  Moreover, some organic functional groups derived from the specific silicon alkoxide can be decomposed by drying the precursor sol attached on the surface of the porous substrate and then heat-treating it at 300 to 600 ° C. As a result, a silica membrane having high alcohol selection performance can be obtained. When the heat treatment temperature is lower than 300 ° C., the organic functional group is not sufficiently decomposed and sufficient permeability cannot be obtained. On the other hand, when the heat treatment temperature is higher than 600 ° C., the silica structure is densified, so that the pores formed by removing the organic functional group are reduced, and the permeability is reduced. Note that the heat treatment step can be performed in the air, in an inert gas, in a vacuum, or the like. In the method for producing a silica membrane filter of the present embodiment, the organic functional group having 8 or more carbon atoms and 120 or more molecular weight contained in the specific silicon alkoxide is decomposed by 40 to 100% in the drying / heat treatment step. It is preferable. Thereby, a silica membrane with high alcohol selection performance can be obtained satisfactorily. For example, when the decomposition of the organic functional group is less than 40%, pores formed by the organic functional group are reduced, and the permeability may be reduced.

  Moreover, in the manufacturing method of the silica membrane filter of this embodiment, it is not necessary to limit the coating process and the drying / heat treatment process once. That is, it is only necessary that the pores of the porous substrate are finally closed by the silica film. Therefore, by repeating the coating process or by repeating both the coating process and the drying / heat treatment process, the pores of the porous substrate are gradually closed with the precursor sol, and finally the fineness of the porous substrate is reduced. It is also possible to make the hole completely closed. By performing the coating process a plurality of times, the amount of the precursor solution used in one coating process can be reduced. As a result, since the amount of the precursor sol flowing down on the surface of the porous substrate is also reduced, it is possible to prevent the precursor sol from excessively entering the pores.

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

(1) Production of silica membrane filter:
( Reference Example 1)
In Reference Example 1, a silica membrane filter was prepared using dodecyltrimethoxysilane as a silicon alkoxide containing a specific organic functional group. The organic functional group of dodecyltrimethoxysilane has 12 carbon atoms and a molecular weight of 169.

In Reference Example 1, first, this dodecyltrimethoxysilane and ethanol were mixed and stirred at 4 ° C. to prepare a mixed solution in which dodecyltrimethoxysilane and ethanol were sufficiently mixed. Next, an aqueous nitric acid solution was added little by little for hydrolysis, and the mixture was further stirred for 1 hour at 4 ° C. Next, the obtained mixed solution was brought to 50 ° C. and stirred for 3 hours. If separation occurred during stirring, hexane was added as needed. Thereafter, the mixed solution was diluted by adding a solvent. Note that when adding a solvent, the concentration of silica sol in the mixed solution was adjusted to the amount of solvent so as to be 2.0 wt% in terms of SiO _2. In this way, a precursor sol containing dodecyltrimethoxysilane was obtained.

  160 ml of the obtained precursor sol is weighed, and the precursor sol flows down into the cell formed on the monolithic ceramic substrate by the method shown in FIG. A sol was deposited. A monolithic ceramic substrate having a diameter of 30 mm and a length of 160 mm was used. In addition, when attaching the precursor sol, both ends of the ceramic substrate were sealed with glass.

  Next, after drying the precursor sol adhered to the inner wall surface of the cell, the dried precursor sol was heat-treated at 500 ° C. for 1 hour. By this heat treatment, a silica film made of the precursor sol is formed. The steps from the coating of the precursor sol to the heat treatment were repeated 3 to 6 times, and the pores of the monolithic ceramic substrate were blocked by the silica film on the inner wall surface of the cell of the monolithic ceramic substrate. It was confirmed.

( Reference Example 2)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that the heat treatment was performed at 450 ° C.

( Reference Example 3)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that octadecyltrimethoxysilane was used as a silicon alkoxide containing a specific organic functional group.

Example 4
A silica membrane filter was produced in the same manner as in Reference Example 1 except that 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane was used as the silicon alkoxide containing the specific organic functional group.

(Example 5)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that N-phenyl-3-aminopropyltrimethoxysilane was used as a silicon alkoxide containing a specific organic functional group.

( Reference Example 6)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that naphthalyltrimethoxysilane was used as a silicon alkoxide containing a specific organic functional group.

Table 1 shows the types of silicon alkoxides used in Reference Examples 1 to 3, 6 and Examples 4 and 5 , the number of carbon atoms of the organic functional group, the molecular weight of the organic functional group, and the heat treatment temperature.

(Comparative Example 1)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that tetramethoxysilane was used as the silicon alkoxide for producing the precursor sol.

(Comparative Example 2)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that phenyltrimethoxysilane was used as the silicon alkoxide for producing the precursor sol.

(Comparative Example 3)
A silica membrane filter was produced in the same manner as in Reference Example 1 except that octyltriethoxysilane was used as the silicon alkoxide for producing the precursor sol.

  Table 2 shows the types of silicon alkoxides used in Comparative Examples 1 to 3, the carbon number of the organic functional group, the molecular weight of the organic functional group, and the heat treatment temperature.

(2) Pervaporation test of mixed organic liquid:
The pervaporation test of the mixed organic liquid was performed with respect to the silica membrane filters of Reference Examples 1 to 3, 6 and Examples 4 and 5 and Comparative Examples 1 to 3 by the following method.

First, a mixed liquid of ethanol, o-xylene and n-octane having a temperature of 50 ° C. was circulated in the cells of the silica membrane filters of the respective reference examples, examples and comparative examples. The mass ratio of ethanol, o-xylene, and n-octane was ethanol: o-xylene: n-octane = 33: 33: 33. Then, the pressure was reduced at a vacuum degree of about 1.33 kPa from the side surface of the monolith type ceramic base material, and the permeated vapor from the side surface of the monolith type ceramic base material was collected by a trap cooled with liquid nitrogen. The total permeation flux (fluid that permeated the membrane of the unit area per unit time) was calculated from the mass of the collected permeated vapor. Moreover, the liquid substance of the permeate vapor was analyzed by gas chromatography to determine the composition of the permeate vapor. Tables 1 and 2 show the ethanol permeation flux (kg / m ² · hr) and the permeate ethanol concentration (mass%).

The silica membrane filters of Reference Examples 1 to 3, 6 and Examples 4 and 5 have a high ethanol permeation flux, and selectively separate ethanol from a fluid in which ethanol, o-xylene, and n-octane are mixed. Had excellent performance. The silica membrane filters of Comparative Examples 1 to 3 had a lower ethanol permeation flux than the silica membrane filters of Reference Examples 1 to 3, 6 and Examples 4 and 5 . This is because the silicon alkoxide for producing the precursor sol does not contain an organic functional group, or even if it contains an organic functional group, the number of carbon atoms is less than 8 or the molecular weight is less than 120. This is presumed to be because the pores of the film have become smaller.

  INDUSTRIAL APPLICABILITY The present invention can be used as a silica membrane filter that can be used to separate or concentrate only a specific type of substance from a fluid (liquid or gas) in which a plurality of types of substances are mixed, and a method for manufacturing the same. In particular, the silica membrane filter of the present invention can be suitably used as a separation membrane that selectively permeates alcohol from an organic mixed compound containing alcohol.

1: porous substrate, 2: cell, 3: silica film, 11: one end surface, 12: the other end surface, 31: precursor solution, 33: porous substrate, 35: cell, 37: partition wall, 39 : Inner wall surface, 41: masking tape, 100: silica membrane filter.

Claims (2)

Precursor solution for obtaining a precursor solution containing a precursor sol by hydrolyzing and polycondensing a silica raw material containing a silicon alkoxide containing at least one organic functional group having 8 or more carbon atoms and a molecular weight of 120 or more A preparation process;
The precursor solution is brought into contact with the surface of the porous substrate, and the precursor sol contained in the precursor solution is deposited on the surface of the porous substrate by flowing under the dead weight of the precursor solution. A coating process;
Said porous drying the precursor sol adhered to the surface of the substrate and then possess a drying and heat treatment step of heat-treating, the at 300 to 600 ° C.,
Silica membrane filter in which the organic functional group having 8 or more carbon atoms and 120 or more molecular weight used in the precursor solution preparation step includes a functional group containing at least one of an oxygen atom and a nitrogen atom. Manufacturing method. 2. The production of a silica membrane filter according to claim 1 , wherein the organic functional group having 8 or more carbon atoms and having a molecular weight of 120 or more contained in the silicon alkoxide is decomposed by 40 to 100% in the drying / heat treatment step. Method.

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