JP2006069864A - Nanoporous body and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an almost spherical nanoporous body having high regularity and having fine pores with a small pore size distribution, to provide a method for efficiently producing the nanoporous body at a low cost where the average pore size of the fine pores in the obtained nanoporous body can be selected in a wide range. <P>SOLUTION: In the almost spherical nanoporous body, many fine pores with pore sizes on a nanometer level are formed in a skeleton structure composed of an inorganic material. The method for producing a nanoporous body comprises: a stage (a) where, in a reaction solution containing a metal alkoxide and/or the polycondensate thereof, a surfactant and a solvent, the metal alkoxide and/or its polycondensate is hydrolyzed, so as to obtain a hydrolyzate solution; and a stage (b) where the hydrolyzate solution is atomized on a gas of 50 to 170°C flowing to a fixed direction, so as to volatilize the solvent, and, after a metal salt is incorporated into the hydrolyzate solution, the metal salt-containing hydrolyzate solution is atomized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nanoporous body having nanometer-scale micropores, which can be used as an adsorbent, a separation membrane, a separation reaction membrane, a catalyst, and a catalyst carrier, and a method for producing the same.

  In recent years, it has been clarified that a porous body having a structure in which micropores having a uniform pore size of nanometer level are regularly arranged has excellent gas adsorbability and also has a function of separating various substances. For this reason, various methods for producing such a porous body have been proposed.

  For example, “J. Am. Chem. Soc., 114, 10834-10843 (1992)” (Non-Patent Document 1) uses a set of surfactants composed of alkyltrimethylammonium as a template (template), precipitated silica, Using colloidal silica, water glass, alkoxysilane, etc. as a raw material, a three-dimensional highly ordered composite of inorganic material and surfactant is formed by hydrothermal synthesis, and the composite is naturally dried and then fired. Describes a method for producing an inorganic porous material by removing organic substances contained in the material. The concentration of the surfactant was higher than the critical micelle concentration and lower than the liquid crystal phase formation concentration, for example, 25% by weight, and the pH of the solution was 10 to 13 on the alkali side. The standard reaction temperature was as high as 100 ° C. or more, and the reaction took about 2 days at the shortest.

  Such a hydrothermal synthesis method has been mainly used for the production of a porous body using a surfactant. The porous body obtained by the hydrothermal synthesis method has a structure in which micropores having a remarkably uniform pore diameter are regularly arranged as compared with porous bodies obtained by other production methods. However, it has been found that in order to obtain a porous body having sufficient gas adsorption properties, it is necessary to have a narrower pore size distribution and a high three-dimensional regularity. Further, from the viewpoint of gas adsorption, a spherical porous body having a large surface area is desired, but there is also a problem that a spherical porous body cannot be obtained by hydrothermal synthesis. Furthermore, since silica, surfactant, etc., which are raw materials, remain in the reaction solution used for hydrothermal synthesis, it is possible to obtain a porous body having a desired component ratio even when accurately weighed materials are charged into the reaction solution. There is a problem that you can not. In addition, the hydrothermal synthesis method needs to be kept at a high temperature of 80 ° C. or higher for a long time, and is costly. In addition, it is indispensable to separate and wash the product by solid-liquid separation means, and the operation is complicated. There is also the problem of being.

  In US Pat. No. 5,922,299 (Patent Document 1), an aqueous solution of a precursor of silica, a surfactant having ammonium ions, and an acid are mixed, and the surfactant and silica are regularly arranged. A method for producing mesoporous silica having a step of volatilizing the solvent of the solution is described. In order to volatilize the solvent, for example, the precursor solution is sprayed from a water-cooling nozzle of a spray dryer, and the generated water droplets are allowed to flow down in heated air. When the non-volatile residue obtained by volatilization of the solvent is calcined, mesoporous silica can be obtained.

  However, when producing mesoporous silica by the method described in Patent Document 1, not only the porosity of the product but also the regularity of the product greatly depends on the molar ratio of the surfactant / silica precursor used as a raw material. There is. For example, if an attempt is made to obtain mesoporous silica having a large porosity, the regularity of the pore structure is low and the pore size distribution becomes large. Such nanoporous silica cannot be said to be preferable as an adsorbent or a separating material. Further, only mesoporous silica having an average pore diameter of 4 nm or less and a wall thickness of about 1 nm can be produced, and there is a problem that the obtained mesoporous silica is very limited.

US Pat. No. 5,922,299 JS Beck et al., “A new family of mesoporous molecular sieves prepared with liquid crystal templates”, J. Am. Chem. Soc. 114, 10834-10843 (1992 )

  Accordingly, an object of the present invention is a substantially spherical nanoporous body having high regularity and fine pores with a small pore size distribution, and a method for producing such a nanoporous body efficiently and at low cost, and the obtained nanoporous body It is to provide a method capable of selecting an average pore diameter of micropores in a wide range.

  As a result of diligent research in view of the above object, the present inventors have obtained a solution containing (a) a metal alkoxide and / or a polycondensate thereof, a surfactant, and a solvent in a reaction solution, and the metal alkoxide and / or Alternatively, after hydrolyzing the polycondensate, (b) when the obtained hydrolyzate solution is spray-dried to a gas of 50 to 170 ° C. flowing in a certain direction, the hydrolyzate solution contains a metal salt. As a result, it was discovered that a substantially spherical nanoporous body was efficiently produced, and the present invention was conceived.

  That is, the method for producing a nanoporous body of the present invention produces a substantially spherical nanoporous body in which micropores having a nanometer-level pore diameter are formed in a skeleton structure made of an inorganic material. (A) Metal alkoxide and / or Or a step of hydrolyzing the metal alkoxide and / or the polycondensate in a reaction solution containing a polycondensate thereof, a surfactant, and a solvent to obtain a hydrolyzate solution, and (b) constant A step of volatilizing the solvent by spraying the hydrolyzate solution in a gas flowing in a direction of 50 to 170 ° C., and after the hydrolyzate solution contains a metal salt, the metal salt-containing hydrolysis The product solution is sprayed.

  It is preferable that at least a part of the solvent of the hydrolyzate solution is volatilized and the resulting concentrated liquid is sprayed with an inert gas. It is preferable to use a liquid which is water-soluble and has a boiling point of 170 ° C. or lower as a solvent for the reaction solution and the hydrolyzate solution. More preferred solvents are methanol, ethanol, n-propyl alcohol, i-propyl alcohol, hexanol, n-butyl alcohol, t-butyl alcohol, i-butyl alcohol, tetrahydrofuran, dioxane, dimethoxyethane, 4-methyldioxolane, acetonitrile, It is at least one selected from the group consisting of 2-methyltetrahydrofuran, 2-ethoxyethanol, propylene glycol-1-monomethyl ether acetate, propylene glycol-1-monomethyl ether, and 2-methoxy-1-propyl acetate.

  The surfactant is preferably a polyethylene oxide-polypropylene oxide polycondensate and / or a monoalkyl-polyethylene oxide polycondensate.

  As the metal alkoxide and / or polycondensate thereof, it is preferable to use an alkoxide of at least one metal selected from the group consisting of Si, Al, Ti, Zr and Ge and / or a polycondensate of alkoxide. And / or a polycondensate thereof is more preferably used, and tetraalkoxysilane is particularly preferably used.

  It is preferable to adjust the pH of the reaction solution to 1.0 to 5. The metal salt is at least one salt selected from the group consisting of Mn, Co, Ni, Fe, Cr, Mg, V, Sn, W, Ta, Nb, Hf, Pt, Pd, Ru, Rh and Ir. It is preferable to use it.

The nanoporous body of the present invention has a substantially spherical shape in which a large number of micropores having nanometer-level pore sizes are formed in a skeleton structure made of an inorganic material, and has an average particle size of 0.5 to 50 μm and a BET surface area of 300 m ² or more. The pore diameter of the pores in the pore size distribution obtained from the nitrogen adsorption isotherm is 2.5 to 10 nm, and at least one peak in the X-ray diffraction pattern Has a surface interval of 1.5 nm or more, and the half width of the maximum peak is 2 ° or less.

The nanoporous body has the following formula (1)
M ¹ _a M ² _b O _h・ ・ ・ (1)
(However, a represents a positive number of 1 or less, b represents a number of 0 or more and less than 1, a + b = 1, h represents a number of 1 to 2.5, M ¹ represents Si, Al, At least one selected from the group consisting of Ti, Zr and Ge, M ² is Mn, Co, Ni, Fe, Cr, Mg, V, Sn, W, Ta, Nb, Hf, Pt, Pd, Ru, It is preferably represented by at least one selected from the group consisting of Rh and Ir.

  In the method for producing a nanoporous body of the present invention, a metal alkoxide and / or its polycondensate, a surfactant, and a hydrolyzate obtained by hydrolyzing the metal alkoxide and / or its polycondensate in a solution containing an acid. Spray the product solution containing metal salt. By this manufacturing method, a substantially spherical nanoporous body can be obtained. Prior to spray drying, it is preferable to concentrate the hydrolyzate solution to some extent by reducing the pressure while forcing the hydrolyzate solution to flow. By concentrating the hydrolyzate solution, the spray drying process can be performed at a low temperature, so that a nanoporous body having excellent three-dimensional regularity can be obtained.

  Since the nanoporous body is in the form of a powder or a particle consisting of substantially spheres, it has a large surface area and does not require a step such as granulation in order to obtain a powder or a particle. Such a nanoporous body has an excellent adsorptivity, and is suitable as an adsorbent for organic substances such as water and benzene, and a catalyst carrier.

Hereinafter, the present invention will be described in detail by the best mode for carrying out the invention.
The “nanoporous body” in the claims and in the present specification has 20 or more micropores in 1 cm ³ , and 90% or more of the micropores have a diameter of 10 ⁻¹ to 10 ³ nm. It is a porous material belonging to the range. Therefore, “nanometer level pore diameter” refers to a pore diameter in the range of 10 ⁻¹ to 10 ³ nm.

[1] Method for producing nanoporous body In the method for producing a nanoporous body of the present invention, a hydrolysis solution containing a metal alkoxide and / or a polycondensate thereof as a starting material of an inorganic material, and a surfactant as a template. Is used.

(1) Metal alkoxide and / or polycondensate thereof Metal alkoxide and / or polycondensate thereof are starting materials for the nanoporous body. Specific examples of preferable metal alkoxides include alkoxides of metal elements of groups IVA and IVB of the periodic table. Of these, alkoxides of at least one metal selected from the group consisting of silicon, aluminum, titanium, and zirconium are more preferable. Particularly preferred are metal alkoxides mainly composed of silicon, such as alkoxysilanes, and mixtures of alkoxysilanes and alkoxides of metals other than silicon. When a silicon-based metal alkoxide is used as a starting material, a nanoporous body having excellent uniformity can be obtained. Nanoporous bodies with excellent uniformity show a prominent peak in X-ray diffraction. Examples of alkoxides of metals other than silicon include alkoxyaluminum.

As the alkoxysilane, tetraalkoxysilane represented by Si (OR ₁ ) ₄ (wherein R ₁ represents an alkyl group having 1 to 6 carbon atoms), and the following formula (2)
Si (OR ₂ ) _c (R ₃ ) _d (R ₄ ) _e (R ₅ ) _f・ ・ ・ (2)
_{(Wherein, R 2, R 3, R} 4 and R ₅ represents an alkyl group having 1 to 6 carbon atoms, c is an integer of 1 to 3, d, e and f represents an integer of 0 to 3, c + d + e + f = 4)), and mixtures thereof are preferred. Of the tetraalkoxysilanes, tetramethoxysilicate [Si (OCH ₃ ) ₄ ] and tetraethoxysilicate [Si (OC ₂ H ₅ ) ₄ ] are particularly preferable. When alkylalkoxysilane is used as a starting material, mesoporous silica having an alkyl group can be produced.

As the alkoxyaluminum, those represented by Al (OR ₆ ) ₃ (wherein R ₆ represents an alkyl group having 1 to ₆ carbon atoms) are preferable, and in particular, Al (OCH ₃ ) ₃ , Al (OC ₂ H ₅ ) ₃ , Al (O-iso-C ₃ H ₇ ) ₃ , and Al (OC ₄ H ₉ ) ₃ are preferred. Di-s-butoxyaluminoxytriethoxysilane is also preferred.

As the alkoxytitanium, those represented by Ti (OR ₇ ) ₄ (wherein R ₇ represents an alkyl group having 1 to 6 carbon atoms) are preferred, and in particular, Ti (OCH ₃ ) ₄ , Ti (OC ₂ H ₅ ) ₄ , Ti (O-iso-C ₃ H ₇ ) ₄ and Ti (OC ₄ H ₉ ) ₄ are preferred.

Zirconium alkoxide is preferably represented by Zr (OR ₈ ) ₄ (wherein R ₈ represents an alkyl group having 1 to 6 carbon atoms), and particularly Zr (OCH ₃ ) ₄ , Zr (OC ₂ H ₅ ) ₄ , Zr (O-iso-C ₃ H ₇ ) ₄ and Zr (OC ₄ H ₉ ) ₄ are preferred.

As an example of a preferred metal alkoxide polycondensate, the following formula (3)
(C ₂ H ₅ O) ₃ Si [Si (C ₂ H ₅ O) ₂ ] _n (C ₂ H ₅ O) (3)
(However, n represents an integer of 1 or more.)
An ethyl silicate condensate represented by the following formula (4)
(CH ₃ O) ₃ Si [Si (CH ₃ O) ₂ ] _m (CH ₃ O) (4)
(However, m represents an integer of 1 or more.)
The methyl silicate condensate represented by these is mentioned. Commercially available polycondensates of metal alkoxides may be used as starting materials. Examples of commercially available products include silicate 40 (ethyl silicate condensate, average n = 5), silicate 45 (ethyl silicate condensate, average n = 6), silicate 48 (ethyl silicate condensate, average) manufactured by Tama Chemical Co., Ltd. n = 7), M silicate 51 (methyl silicate condensate, average m = 4).

(2) Surfactant A surfactant is a template (template) for dissolving in a solvent together with a metal alkoxide and / or a polycondensate thereof (hereinafter simply referred to as “metal alkoxide etc.”) to form fine pores of an inorganic porous material. ). Any surfactant may be used as long as it forms a liquid crystal structure in a solution containing alcohol, metal oxide, metal alkoxide, and the like. A preferable surfactant is a nonionic surfactant. As shown in FIG. 1, those arranged in a column with three-dimensional high regularity in a solution are more preferable.

The nonionic surfactant is preferably a polyethylene oxide-polypropylene oxide polycondensate or a monoalkyl-polyethylene oxide polycondensate. Specific examples of polyethylene oxide-polypropylene oxide polycondensates include Pluronic (registered trademark) P123 manufactured by BASF: (EtO) ₂₀ (PrO) ₇₀ (EtO) ₂₀ (where EtO represents ethylene oxide and PrO represents propylene oxide) And Pluronic P103 and Pluronic P85. Specific examples of the monoalkyl-polyethylene oxide polycondensate include Pierj's Brij (registered trademark) 56: C ₁₆ H ₃₃ (EtO) ₁₀ (where EO represents ethylene oxide).

(3) Solvent The solvent of the hydrolysis solution is preferably water-soluble. If the solvent is not water-soluble, the starting metal alkoxide and / or the polycondensate thereof is difficult to mix with water and cannot be sufficiently hydrolyzed, which is not preferable. It preferably has a boiling point of 170 ° C. or lower. If a solvent having a boiling point of more than 170 ° C is used, it is difficult to volatilize the solvent at 50 to 170 ° C.

  Examples of preferred solvents are methanol, ethanol, n-propyl alcohol, i-propyl alcohol, hexanol, n-butyl alcohol, t-butyl alcohol, i-butyl alcohol, 2-ethoxyethanol, tetrahydrofuran, dioxane, dimethoxyethane, 4- Examples include methyldioxolane, acetonitrile, 2-methyltetrahydrofuran, propylene glycol-1-monomethyl ether acetate, propylene glycol-1-monomethyl ether and 2-methoxy-1-propyl acetate. A more preferable solvent is a monovalent alcohol having 5 or less carbon atoms. When such an alcohol is used, the surfactant can be easily dissolved, and the solvent can be efficiently volatilized. Specific examples of particularly preferred solvents include methanol, ethanol, n-propyl alcohol, i-propyl alcohol, and n-butyl alcohol. These alcohols have excellent volatility and handleability and are inexpensive.

  The water / solvent molar ratio is preferably 0.1 to 10, more preferably 0.2 to 10. If the water / solvent molar ratio is less than 0.1, hydrolysis is insufficient. If it exceeds 10, the amount of water is too large, so that the surfactant is hardly dissolved and the uniformity of the solution is too low. Further, when spray drying, it is not preferable because the temperature in the dryer must be set high. A particularly preferred molar ratio of water / solvent is 0.5-5.

(4) Hydrolysis solution
(a) Composition of hydrolyzing solution The composition of the hydrolyzing solution has a great influence on the pore diameter and three-dimensional high regularity of the resulting nanoporous body.

(i) Molar ratio of water / metal alkoxide (or water / metal alkoxide polycondensate) When metal alkoxide is used as the starting material, the molar ratio of water / metal alkoxide is preferably 1 to 40, and 2 to 20 Is more preferable. If the molar ratio of water / metal alkoxide is more than 40, too much water will cause the metal alkoxide hydrolysis reaction to be too fast, and the metal oxide before the surfactant is regularly arranged as the solvent evaporates. Precipitates. Moreover, since there is too little water as it is less than 1, the polycondensation reaction of a hydrolyzate is too slow.

  When a metal alkoxide polycondensate is used as a starting material, the ratio of the number of moles of water to the number of monomer units contained in the metal alkoxide condensate (water / number of monomer units of metal alkoxide condensate) The molar ratio is preferably the same as that of the metal alkoxide. In other words, when the number of condensation of the metal alkoxide condensate is n, the water / metal alkoxide condensate molar ratio is preferably 1 / n to 40 / n, and preferably 2 / n to 40 / n. More preferred.

(ii) Surfactant / solvent molar ratio The preferred surfactant / solvent molar ratio depends on the surfactant used. When the surfactant / solvent molar ratio is less than the lower limit of the preferred range, hydrolysis of the metal alkoxide proceeds before the surfactant is regularly arranged, and fine pores with high three-dimensional regularity are obtained. I can't. If it exceeds the upper limit, the concentration is too high and the surfactant precipitates from the solution.

  When the alkylpolyethylene oxide polycondensate is used, the molar ratio of the alkylpolyethylene oxide polycondensate / solvent is preferably 0.002 to 0.1. A specific example of a particularly preferred alkyl polyethylene oxide polycondensate / solvent molar ratio is 0.014 when Brij56 is used as the surfactant, 0.05 when Brij30 is used, and Brij35 is used. In this case, it is 0.0043, and when using Brij58, it is 0.0046.

  When a polyethylene oxide-polypropylene oxide polycondensate is used, the polyethylene oxide-polypropylene oxide polycondensate / solvent molar ratio is preferably 0.0005 to 0.05. A specific example of a particularly preferred polyethylene oxide-polypropylene oxide polycondensate / solvent molar ratio is 0.002 when using Pluronic P123 as the surfactant, and 0.0022 when using Pluronic P103, 0.001 when using Pluronic P85.

(iii) Molar ratio of surfactant / metal alkoxide or surfactant / metal alkoxide polycondensate The preferred molar ratio of surfactant / metal alkoxide and surfactant / metal alkoxide polycondensate depends on the surfactant used. Different. If the surfactant / metal alkoxide molar ratio is less than the lower limit of the preferred range, the amount of the surfactant is too small, so that a nanoporous body having a sufficient three-dimensional highly ordered structure cannot be obtained. If it exceeds the upper limit, the nanoporous body will not take a hexagonal structure, and the three-dimensional regularity will deteriorate.

  When using an alkylpolyethylene oxide polycondensate and a metal alkoxide, the molar ratio of alkylpolyethylene oxide polycondensate / metal alkoxide is preferably 0.02 to 1. A specific example of a particularly preferred alkyl polyethylene oxide polycondensate / metal alkoxide molar ratio is 0.14 when Brij56 is used as a surfactant, 0.5 when Brij30 is used, and Brij35 is used. In the case of using Brij58, it is 0.043.

  When polyethylene oxide-polypropylene oxide polycondensate and metal alkoxide are used, the molar ratio of polyethylene oxide-polypropylene oxide polycondensate / metal alkoxide is preferably 0.005 to 0.5. A specific example of the particularly preferred polyethylene oxide-polypropylene oxide polycondensate / solvent molar ratio is 0.02 when using Pluronic P123 as the surfactant, and 0.0215 when using Pluronic P103, When using Pluronic P85, it is 0.01.

  When a metal alkoxide polycondensate is used as a starting material, the ratio of the number of moles of surfactant to the number of monomer units contained in the metal alkoxide condensate (surfactant / number of monomer units of metal alkoxide condensate) is The preferred molar ratio of surfactant / metal alkoxide should be the same. That is, when the average condensation number of the metal alkoxide condensate is n, the molar ratio of the alkyl polyethylene oxide polycondensate / metal alkoxide polycondensate is preferably 0.02 / n to 1 / n, and the polyethylene oxide-polypropylene oxide polycondensate The molar ratio of condensate / metal alkoxide polycondensate is preferably 0.005 / n to 0.5 / n.

(b) Acid addition An acid is added to a solution containing a metal alkoxide or the like and a surfactant, and the metal alkoxide or the like is hydrolyzed by mixing uniformly at a low temperature. There are no particular limitations on the type of acid, and mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid and tartaric acid can be used. It is preferable to use hydrochloric acid because it can be completely removed by calcination. It is preferable to add an acid so that the pH of the solution is 0-6. A pH exceeding 6 is not preferable because the hydrolysis reaction and the condensation polymerization reaction are difficult to proceed. When the pH is less than 0, the metal salt and / or the hydrolyzate is easily precipitated in the solution. When the pH of the solution is in an acidic state of 0 to 6, a nanoporous body having three-dimensional high regularity can be obtained.

  When using a metal alkoxide as a starting material, the pH of the more preferred solution is 1 to 4.5. When a metal alkoxide polycondensate is used, the pH of the more preferable solution is 0.5 to 4, and the particularly preferable pH is 1.5 to 3.5.

(c) Other hydrolysis conditions After the acid is added, when the mixture is stirred at room temperature and normal pressure for about 10 to 60 minutes, the hydrolysis reaction of metal alkoxide and the like proceeds, and a transparent hydrolyzate solution is obtained. Although hydrolysis of a metal alkoxide etc. can be performed without heating, you may heat at low temperature (65 degrees C or less). The preferred hydrolysis temperature is 23-60 ° C. A more preferred hydrolysis temperature is 23 to 40 ° C.

(5) Addition of metal salt Prior to volatilization of the solvent, the hydrolyzate solution should contain a metal salt. Specifically, the metal salt is added to the hydrolysis solution or the hydrolyzate solution. When adding a hardly soluble salt, it is preferable to dissolve the salt in hydrochloric acid before hydrolysis. When adding a metal salt to the hydrolyzate solution, it is preferable to sufficiently stir (for example, 10 to 30 minutes) after the addition. If the hydrolyzate solution does not contain a metal salt, even if the hydrolyzate solution is sprayed into the flowing gas, (a) the hydrolyzate / surfactant complex is liquid (or oily) It does not become a solid as it is, or (b) a substantially spherical nanoporous body cannot be obtained as an aggregate of highly viscous white solids. By volatilizing the solvent in a state where the hydrolyzate solution contains metal ions, a substantially spherical nanoporous body having three-dimensional high regularity in the skeleton structure can be produced.

  The ratio between the main component and the metal salt in the skeleton of the nanoporous body is equal to the molar ratio between the metal alkoxide and the like in the hydrolysis solution and the salt. Therefore, by making the hydrolyzing solution contain metal-containing ions, a nanoporous body containing an element other than the main component in a desired amount in the skeleton structure can be produced. Since elements other than the main component are regularly incorporated into the skeleton, the three-dimensional high regularity of the nanoporous body is not inhibited.

  Examples of metal salts include Ti, Ge, Si, Al, Cr, Zr, Mn, Co, Ni, Fe, Mg, V, Sn, W, Ta, Nb, Hf, Pt, Pd, Ru, Rh and Ir And at least one salt selected from the group consisting of: Specific examples of more preferable metal salts include aluminum nitrate and zirconium nitrate.

(6) Aging and concentration of hydrolyzed solution While maintaining the hydrolyzate solution substantially uniform, a part of the solvent is volatilized to obtain a concentrated solution. Here, “substantially uniform” means that the solution is uniform to such an extent that the self-assembly (three-dimensional high ordering) of the surfactant is substantially maintained. Specifically, it means that the concentration distribution and temperature distribution of the solution are kept small enough not to hinder the three-dimensional high ordering of the surfactant.

  A method for making the hydrolyzate solution substantially uniform is not particularly limited, and a general method can be adopted. For example, it may be performed by a stirring means such as a stirring blade or a stirring bar, or may be performed by rotating a container containing a hydrolyzate solution.

  The temperature of the hydrolyzate solution is preferably 0 to 70 ° C, more preferably 10 to 60 ° C. If it is less than 0 ° C., the solubility of the surfactant is too small and the surfactant is precipitated. If it exceeds 70 ° C., the partial pressure of the metal alkoxide or the like is too high, and the yield of the nanoporous body decreases. Further, the molecular motion of the surfactant and the hydrolyzate is too large, and the three-dimensional high regularity of the nanoporous body is lost.

(7) Spray drying Spray the hydrolyzate concentrate into a gas at 50 to 170 ° C flowing in a certain direction. If the gas temperature exceeds 170 ° C., the volatilization of the solvent is too fast and the three-dimensional high regularity of the nanoporous body is lost too much. If the temperature of the gas is less than 50 ° C, the solvent cannot be removed sufficiently. The recovery rate is too low. The temperature of the gas is more preferably 50 to 100 ° C, and particularly preferably 80 to 100 ° C.

  It is preferable to flow the gas in a certain direction in a drying chamber having an inlet and an outlet, and spray the concentrate from a nozzle installed in parallel with the flow. The temperature in the drying chamber can be adjusted, and the gas temperature near the outlet is preferably set 30 to 80 ° C. lower than the vicinity of the inlet. In the vicinity of the inlet, the gas temperature greatly decreases due to the heat of vaporization of the solvent, but the influence is small in the vicinity of the outlet. For this reason, if the gas temperature near the outlet is lowered by 30 to 80 ° C. near the inlet, the temperature near the outlet and the temperature near the inlet become close to each other.

  It is necessary to keep the oxygen concentration low in the drying chamber. If the oxygen concentration in the drying chamber is too high, ignition and / or explosion may occur depending on the solvent, which is not preferable. Also, it is preferable to always keep the concentration of the solvent vapor below the lower limit of explosion. For example, when ethanol is used as a solvent and the temperature in the chamber is 170 ° C., the oxygen concentration needs to be 5% by volume or less, and the ethanol vapor concentration is preferably 4.3% by volume. As a method of keeping the concentration of the solvent vapor low, there is a method in which the inside of the drying chamber is made an inert gas atmosphere prior to spraying of the concentrated liquid, and the concentrated liquid is sprayed together with the inert gas. Furthermore, in order to prevent a flammable accident caused by electric sparks, it is necessary to make the electrical contacts have a protective specification.

  The nozzle is not particularly limited as long as the concentrate and the inert gas can be ejected in a mist state in a gas-liquid mixed state. A general nozzle is a thin tube having an inner diameter of about 0.3 to 1 mm. The nozzle back pressure is preferably 0.05 to 0.3 MPa. When the nozzle back pressure is more than 0.3 MPa, the flow rate balance between the concentrate and the inert gas is excessively disturbed, and droplets having a certain size range cannot be stably sprayed. When the nozzle back pressure is less than 0.05 MPa, the spray amount is too small and the production efficiency of the nanoporous body is too bad.

  The solvent contained in the sprayed concentrated liquid droplets volatilizes within several hundred msec. The three-dimensional highly ordered arrangement of surfactant and metal oxide is completed in the concentration process, and this structure is not easily lost even when sprayed or dried. For this reason, the three-dimensional highly regular structure hardly collapses during volatilization. Therefore, a dry nanoporous body having three-dimensional high regularity is generated by spray drying.

(8) Firing The nanoporous body is fired for a sufficient time to completely remove organic substances contained in the fine pores. The firing temperature is preferably 350 to 800 ° C, more preferably 400 to 650 ° C. The firing time is preferably 1 hour or longer, more preferably 1.5 to 14 hours, and particularly preferably 2 to 10 hours. The regularly arranged surfactant completely disappears, so that part becomes regularly arranged vacancies. In this way, a nanoporous body having three-dimensional high regularity is obtained as shown in FIG.

[2] Nanoporous body
(1) Inorganic material Nanoporous body is represented by the following formula (6)
M ¹ _a M ² _b O _h・ ・ ・ (6)
(However, a represents a positive number of 1 or less, b represents a number of 0 or more and less than 1, a + b = 1, h represents a number of 1 to 2.5, M ¹ represents Si, Al, At least one selected from the group consisting of Ti, Zr and Ge, M ² is Mn, Co, Ni, Fe, Cr, Mg, V, Sn, W, Ta, Nb, Hf, Pt, Pd, Ru, It is preferably represented by at least one selected from the group consisting of Rh and Ir. For example, when only silicon alkoxide is used as a starting material and only aluminum nitrate is used as a metal salt, a is 1 and M ² is not added. h represents the ratio of oxygen to the sum of Si and Al.

(2) Shape The nanoporous body has a substantially spherical shape or a shape in which a plurality of substantially spherical particles are combined. The “substantially spherical shape” means a shape that can be approximated to a spherical shape, and includes, in addition to the spherical shape, a distorted spherical shape, a partially broken spherical shape, and a flat spherical shape. A photograph of an example of the nanoporous body of the present invention is shown in FIG. The diameter of the approximate sphere is 0.5 to 50 μm. Of the nanoporous body, 40% by mass or more is preferably substantially spherical, and more preferably 80% by mass or more is substantially spherical.

Nanoporous bodies have a BET surface area of 300 m ² or more, and preferred nanoporous bodies have a BET surface area of 500 m ² or more. A nanoporous body having a BET surface area of 300 m ² or more has excellent adsorptivity. The BET surface area can be estimated based on the nitrogen gas adsorption amount and the like.

(3) Three-dimensional high regularity The metal oxide forming the nanoporous body preferably has a nanometer-level ordered structure (periodic structure). Examples of a preferred ordered structure include a hexagonal structure schematically shown in FIG. 1 and a cubic structure having pores connected in three dimensions. A nanoporous body having a hexagonal structure or a cubic structure has pores having a uniform pore diameter. In addition, as long as it has the skeleton structure which consists of inorganic materials, the component which comprises the nanoporous body of this invention is not limited, You may contain organic substance in parts other than skeleton.

  The three-dimensional regularity can be evaluated by the X-ray diffraction pattern of the nanoporous body. Since a nanoporous body having high regularity has a periodicity on the order of nanometers, the peak of the X-ray diffraction pattern usually appears at a small angle (2θ is approximately 5 ° or less). Among the obtained X-ray diffraction peaks, if the full width at half maximum of the maximum peak [the first peak and the (100) plane X-ray diffraction peak of the nanoporous body] is 2 ° or less, the three-dimensional regularity is excellent. I can say that. The full width at half maximum is preferably 1.5 ° or less, and more preferably 1 ° or less.

(4) Micropore
(a) Pore size The nanoporous body obtained by the method of the present invention is a microporous porous body and / or a mesoporous porous body. According to IUPAC, porous bodies are classified into microporous solids having a pore diameter of 2 nm or less, mesoporous solids having a pore diameter of 2 to 50 nm, and macroporous solids having a pore diameter of 50 nm or more. In the present specification, the “nanoporous body” refers to those having micropores and / or mesopores and having a skeleton made of an inorganic substance. The pore size of the nanoporous body is 2 to 10 nm, and preferably 2 to 4.0 nm. In the present specification, the pore size of the nanoporous body is defined as the pore size at the peak of the pore size distribution obtained from the following formulas (7) and (8) by the gas adsorption method. Gas adsorption measurement is performed at −196 ° C. after the nanoporous body is dried under reduced pressure (vacuum degassing) at 300 ° C. for 8 hours. Vacuum drying pressure during preferably not more than 10 ^-1 Pa, more preferably between 10 ^-2 Pa or less.

[R _c : critical radius of micropore where capillary condensation of adsorbate occurs,
t: thickness of the adsorbate multimolecular adsorption layer,
p / p ₀ : the ratio (relative pressure) between the adsorbate pressure p and the saturated vapor pressure p ₀ at the measurement temperature,
γ _∞ : Interfacial tension in the bulk liquid state of the adsorbate,
V _m : molar volume of adsorbate in bulk liquid state,
δ: a constant representing the displacement of zero adsorption relative to the interfacial tension surface, and
F (t) = RT [A / t ² −B] x ln C (A, B, and C are constants determined by the system)]

  Equation (7) was proposed by Broekhoff and de Boer (Broekhoff, J. C. P., and de Boer, J. H., J. Catal. 10, 377 (1968)). Equation (8) is a modification of the Kelvin equation and is called the GTKB-Kelvin-Cylindrical equation. This is a modified kelvin equation for Gibbs-Tolman = koening-Buff when the surface tension is considered to be a function of the curvature of the pores. In the formula of F (t), the constants A, B, and C are respectively determined by the nanoporous body system. For example, in the case of nanoporous silica, A = 0.1399, B = 0.034, and C = 10. The aforementioned pore size distribution evaluation method is described in detail in Miyata, T, Endo, A, Ohmori, T, Akiya, T, Nakaiwa, M, Journal of Colloid and Inerface Science, 262, p116, 2003.

(b) Thickness of the partition wall The nanoporous body not only has micropores having extremely small pore diameters, but also has very thin partition walls. The partition wall thickness is about 0.5 to 3 nm. Because of such thin partition walls, the nanoporous body obtained by the production method of the present invention has high porosity.

(5) Applications Since the nanoporous body has excellent adsorptivity, it can be used as an adsorbent for water and organic matter. For example, 0.15 to 0.80 g of benzene can be adsorbed per 1 g of nanoporous body. It can also be used as a catalyst support. For example, a nanoporous material carrying a sulfonic acid compound can be used for acetal reaction of aldehydes and ketones, and Fries transfer reaction of phenyl acetate. Since the nanoporous body is powdery or granular, there is no need for granulation or the like when used as an adsorbent or catalyst carrier, and it can be used as it is after firing. Therefore, since the production of the adsorbent and the catalyst is simple, the cost is low, and there is no possibility that the granulating agent (binder) is clogged in the micropores and the adsorbing ability is not lowered.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
Surfactant (Brij56) 14.14 g and ethanol (purity 99.5% by volume or more) 69 g were placed in a 200 mL glass beaker and stirred at room temperature for 15 minutes using a magnetic stirrer. Next, 29.64 g of tetraethylorthosilicate (purity 98%) and 2.81 g of aluminum nitrate (Al (NO ₃ ) ₃ · 9H ₂ O) are dissolved, and then 27.0 g of hydrochloric acid (1N) is added, and 20 at room temperature is added. Stir for minutes to obtain a clear hydrolyzate solution.

  This hydrolyzate solution was transferred to a 500 mL eggplant-shaped flask, and the solvent was volatilized by holding it at a temperature of 25 ° C. and a reduced pressure of 70 hPa for 1 hour 50 minutes using a rotary evaporator (38 rpm). A concentrate of the decomposition product was obtained.

  The concentrated solution was spray-dried with nitrogen gas using a spray dryer (GS310, manufactured by Yamato Kagaku) to obtain a white powder. In the spray drying process, the spray nozzle of the dryer uses a 0.7 mmφ nozzle, the spray rate is 4.8 g / min, the nozzle back pressure is 0.075 MPa, the chamber inlet temperature is 80 ° C., and the nitrogen gas wind pressure Was 0.5 MPa.

  The obtained white powder was baked at 600 ° C. to remove the surfactant. The obtained porous silica (fired body) was observed with a scanning electron microscope (SEM). A scanning electron micrograph of porous silica is shown in FIG. From FIG. 3, it was found that the porous silica has a spherical shape or a shape in which spherical objects are bonded.

The structural regularity of the pore structure was evaluated by an X-ray diffraction pattern (XRD) of porous silica and an adsorption isotherm by nitrogen gas. The X-ray diffraction pattern and nitrogen adsorption isotherm of nanoporous silica are shown in FIGS. 4 and 5, respectively. In FIG. 5, ● indicates adsorption, and ◯ indicates desorption. In the X-ray diffraction pattern, since a peak appeared at a position where 2θ was 2 to 6 °, it was found that porous silica has a high structural periodicity on the nanometer order. The BET surface area and pore diameter (mode value of the pore distribution curve obtained from the desorption amount) were calculated from the nitrogen adsorption isotherm. The BET surface area was 706 m ² / g and the pore size was 2.6 nm. From the BET surface area and pore diameter, it was confirmed that the porous silica has a nanometer level pore structure.

Example 2
Surfactant (Pluronic P123) 3.45 g and ethanol (purity 99.5 vol% or more) 13.8 g were placed in a 100 mL glass beaker and stirred, then tetraethylorthosilicate (purity 98%) 5.928 g, aluminum nitrate ( Al (NO ₃ ) ₃ · 9H ₂ O) (0.562 g) was dissolved, hydrochloric acid (1N) (5.4 g) was added, and the mixture was stirred for 10 minutes to obtain a transparent hydrolyzate solution.

  This hydrolyzate solution was transferred to a 100 mL eggplant-shaped flask, and the solvent was volatilized by using a rotary evaporator (78 rpm) at a temperature of 40 ° C. and a reduced pressure of 150 hPa for 1 hour to volatilize the solvent. A concentrated solution was obtained.

  The concentrated solution was spray-dried with nitrogen gas using a spray dryer (GS310, manufactured by Yamato Kagaku) to obtain a white powder. In the spray drying process, a 0.7 mmφ dryer spray nozzle is used, the spray rate is 4.6 g / min, the nozzle back pressure is 0.075 MPa, the chamber inlet temperature is 80 ° C., and the nitrogen gas wind pressure is 0.5. MPa.

The obtained white powder was fired at 600 ° C. to remove the surfactant, and porous silica (fired body) was obtained. A scanning electron microscope (SEM) photograph of porous silica is shown in FIG. From FIG. 6, it was found that the porous silica has a spherical shape or a shape in which spherical objects are bonded. The X-ray diffraction pattern and nitrogen adsorption isotherm of porous silica are shown in FIGS. 7 and 8, respectively. In FIG. 8, ● indicates adsorption, and ○ indicates desorption. In FIG. 7, since a peak appeared at a position where 2θ was approximately 1 °, it was found that porous silica has a high structural periodicity on the order of nanometers. The BET surface area and pore diameter (mode of the pore distribution curve obtained from the desorption amount) were calculated from the nitrogen adsorption isotherm, and were 311 m ^{2 /} g and 5.29 nm, respectively. From the BET surface area and pore diameter, it was confirmed that the porous silica has a nanometer level pore structure.

Example 3
A hydrolyzate solution was obtained in the same manner as in Example 2 except that 3.68 g of a surfactant (Pluronic P103) was mixed with ethanol, tetraethylorthosilicate, aluminum nitrate and hydrochloric acid, and concentrated and spray dried.

The obtained white powder was baked at 600 ° C. to remove the surfactant, and nanoporous silica (baked product) was obtained. The X-ray diffraction pattern of nanoporous silica is shown in FIG. From FIG. 9, it was found that nanoporous silica has a spherical shape or a shape in which spherical objects are bonded. FIG. 10 shows a nitrogen adsorption isotherm of nanoporous silica (fired body). In FIG. 10, ● represents adsorption, and ○ represents desorption. In FIG. 9, since a peak appeared at a position where 2θ is approximately 1 °, it was found that porous silica has a high structural periodicity on the order of nanometers. Further, the BET surface area and the pore diameter (mode value of the pore distribution curve obtained from the desorption amount) were calculated from the nitrogen adsorption isotherm, and were 276 m ^{2 /} g and 5.09 nm, respectively. From the BET surface area and pore diameter, it was confirmed that the porous silica has a nanometer level pore structure.

Comparative Example 1
The surfactant was put in ethanol and stirred, and then a hydrolyzate solution was obtained in the same manner as in Example 1 except that 31.26 g of tetraethylorthosilicate (purity 98%) and hydrochloric acid were mixed.

  The hydrolyzate solution was concentrated by reacting for 1 hour and 20 minutes at a temperature of 25 ° C. and a reduced pressure of 70 hPa, and then spray-dried under the same conditions as the spray-drying process of Example 1. A paste adhered. This is considered that the product which did not fully dry was aggregated without becoming powdery. A white solid adhering to the inner wall was collected, fired at 500 ° C. to remove the surfactant, and the obtained fired body was observed with a scanning electron microscope. A scanning electron microscope (SEM) photograph of the fired body is shown in FIG. As can be seen from FIG. 11, the nanoporous body prepared without adding aluminum nitrate did not have a substantially spherical shape.

Comparative Example 2
17.25 g of a surfactant (Pluronic P123) and 69 g of ethanol (purity 99.5% by volume or more) 69 g were placed in a 200 mL glass beaker and stirred, and then 31.67 g of tetraethylorthosilicate (purity 98%) and hydrochloric acid (1 Regulation) A transparent hydrolyzate solution was obtained in the same manner as in Example 1 except that 27.0 g was added and stirred. This hydrolyzate solution was transferred to a 500 mL eggplant-shaped flask and reacted at a temperature of 40 ° C. and a reduced pressure of 145 hPa for 1 hour using a rotary evaporator (78 rpm) to obtain a concentrated hydrolyzate solution. .

  When the concentrated solution was spray-dried under the same conditions as in the spray-drying process of Example 2, a white paste adhered to the inner wall of the spray dryer. This white solid was calcined at 500 ° C. to remove the surfactant, and the obtained calcined product was observed with a scanning electron microscope. A scanning electron microscope (SEM) photograph of the fired body is shown in FIG. As can be seen from FIG. 12, as in Comparative Example 1, this nanoporous body also did not have a substantially spherical shape.

Comparative Example 3
Referring to “Jornal of Physical Chemistry” (JMKim et al., 99, 45, 16742, 1995), mesoporous silica was synthesized as follows. Cataloid SI-30 is used as the silica source, sodium hydroxide and 25% by mass aqueous ammonia are used as the alkali source, cetyltrimethylammonium bromide is used as the surfactant, silica source: NaOH: NH ₃ : surfactant : An aqueous solution was prepared so that water was 6: 1.5: 0.15: 2: 250. When this aqueous solution was stirred at room temperature for 1 hour and stirred at 97 ° C. for 1 day, a gel was formed in the aqueous solution. The aqueous solution containing the gel was cooled to room temperature, and then a 30% by mass acetic acid aqueous solution was added to adjust the pH to 10.2. The step of stirring the gel-containing aqueous solution at 97 ° C. for 1 day and the step of adjusting the pH by adding an aqueous acetic acid solution were repeated three times, and then the product was filtered off and washed with pure water. The obtained white powder was dried and baked at 550 ° C. to remove the surfactant.

  SEM observation of the obtained fired powder was performed. A SEM photograph is shown in FIG. This powder was found to be non-spherical.

Comparative Example 4
With reference to “Jornal of the American Chemical Society” (Chao et al., 120, 6024-6036, 1998), mesoporous silica was synthesized as follows. Surfactant (Pluronic P123) 2.08 g, water 15.6 mL and hydrochloric acid (2N) 62.4 g were placed in a flask and stirred. Then, tetraethylorthosilicate (purity 98%) 4.73 mL was added and added at 40 ° C for 20 minutes. The mixture was stirred for 24 hours and allowed to stand at 80 ° C. for 24 hours. The product in the aqueous solution was filtered off and washed with pure water. The obtained white powder was dried and baked at 500 ° C. to remove the surfactant.

  SEM observation of the obtained fired powder was performed. A SEM photograph is shown in FIG. This powder was found to be non-spherical.

It is a schematic process drawing which shows the manufacturing principle of a nanoporous body. It is a microscope picture which shows an example of the nanoporous body of this invention. 2 is a micrograph showing nanoporous silica of Example 1. FIG. 2 is a graph showing an X-ray diffraction pattern of nanoporous silica of Example 1. FIG. 2 is a graph showing a nitrogen adsorption isotherm of nanoporous silica of Example 1. 2 is a photomicrograph showing nanoporous silica of Example 2. 4 is a graph showing an X-ray diffraction pattern of nanoporous silica of Example 2. 4 is a graph showing a nitrogen adsorption isotherm of nanoporous silica of Example 2. 4 is a graph showing an X-ray diffraction pattern of nanoporous silica of Example 3. 4 is a graph showing a nitrogen adsorption isotherm of nanoporous silica of Example 3. 2 is a photomicrograph showing porous silica of Comparative Example 1. 5 is a photomicrograph showing porous silica of Comparative Example 2. 4 is a photomicrograph showing mesoporous silica of Comparative Example 3. 6 is a photomicrograph showing mesoporous silica of Comparative Example 4.

Claims (11)

  A method for producing a substantially spherical nanoporous body in which fine pores having a nanometer-level pore diameter are formed in a skeleton structure made of an inorganic material, comprising: (a) a metal alkoxide and / or a polycondensate thereof, and a surfactant; A step of hydrolyzing the metal alkoxide and / or the polycondensate in a reaction solution containing a solvent to obtain a hydrolyzate solution, and (b) a gas of 50 to 170 ° C. flowing in a certain direction. A method comprising volatilizing the solvent by spraying the hydrolyzate solution, and spraying the hydrolyzate solution containing the metal salt after the hydrolyzate solution contains the metal salt. .   The method for producing a nanoporous body according to claim 1, wherein at least a part of the solvent of the hydrolyzate solution is volatilized, and the obtained concentrated liquid is sprayed together with an inert gas.   3. The method for producing a nanoporous body according to claim 1, wherein a solvent that is water-soluble and has a boiling point of 170 ° C. or lower is used.   The method for producing a nanoporous body according to any one of claims 1 to 3, wherein the solvent is methanol, ethanol, n-propyl alcohol, i-propyl alcohol, hexanol, n-butyl alcohol, t-butyl alcohol, i- Butyl alcohol, tetrahydrofuran, dioxane, dimethoxyethane, 4-methyldioxolane, acetonitrile, 2-methyltetrahydrofuran, 2-ethoxyethanol, propylene glycol-1-monomethyl ether acetate, propylene glycol-1-monomethyl ether and 2-methoxy-1- A method comprising using at least one selected from the group consisting of propyl acetate.   The method for producing a nanoporous body according to any one of claims 1 to 4, wherein a polyethylene oxide-polypropylene oxide polycondensate and / or a monoalkyl-polyethylene oxide polycondensate is used as the surfactant. .   The method for producing a nanoporous body according to any one of claims 1 to 5, wherein the metal alkoxide and / or polycondensate thereof is at least one metal alkoxide selected from the group consisting of silicon, zirconium, titanium and aluminum. And / or using a polycondensate of an alkoxide.   The method for producing a nanoporous body according to any one of claims 1 to 5, wherein an alkoxysilane and / or a polycondensate thereof is used as the metal alkoxide and / or the polycondensate. The method for producing a nanoporous body according to any one of claims 1 to 7, wherein the pH of the reaction solution is adjusted to 1.0 to 5.   The method for producing a nanoporous body according to any one of claims 1 to 8, wherein the metal salt is Ti, Ge, Si, Al, Cr, Zr, Mn, Co, Ni, Fe, Mg, V, Sn, W, A method characterized by being at least one salt selected from the group consisting of Ta, Nb, Hf, Pt, Pd, Ru, Rh and Ir. A substantially spherical nanoporous body in which a large number of micropores having a nanometer level pore diameter are formed in a skeleton structure made of an inorganic material, having an average particle diameter of 0.5 to 50 μm and a BET surface area of 300 m ² or more, The partition wall thickness of the micropores is 0.5 to 3 nm, the pore diameter at the peak of the pore size distribution obtained from the nitrogen adsorption isotherm is 2.5 to 10 nm, and at least one peak in the X-ray diffraction pattern is 1.5 nm or more. A nanoporous body having a surface spacing and a maximum half-value width of the maximum X-ray diffraction peak of 2 ° or less. The nanoporous body according to claim 10, wherein the following formula (1)
M ¹ _a M ² _b O _h・ ・ ・ (1)
(However, a represents a positive number of 1 or less, b represents a number of 0 or more and less than 1, a + b = 1, h represents a number of 1 to 2.5, M ¹ represents Si, Al, At least one selected from the group consisting of Ti, Zr and Ge, M ² is Mn, Co, Ni, Fe, Cr, Mg, V, Sn, W, Ta, Nb, Hf, Pt, Pd, Ru, A nanoporous body represented by: at least one selected from the group consisting of Rh and Ir.