JP7820811B2 - Porous silica, method for producing porous silica, metal honeycomb circulation body, and method for producing metal honeycomb circulation body - Google Patents

Description

The present invention is an effective porous silica technology that enables the absorption and concentration of large amounts of heavy VOCs consisting of high-boiling point solvents with a boiling point of 150°C or higher. Furthermore, the present invention provides a metal honeycomb flow-through body coated with the porous silica of the present invention, which can be used to highly efficiently absorb and concentrate the heavy VOCs, then heat, purify, regenerate, and cool repeatedly.

Among VOCs (volatile organic compounds), high-boiling solvents with boiling points of 150°C or higher have a slow evaporation rate, strong dissolving power, and high compatibility with solutes such as resins, preventing precipitation. As a retarder for paint solvents, they can improve the smoothness of painted surfaces, prevent whitening, and add gloss.

In recent years, there has been growing demand for high-capacity, miniaturized electronic components for fifth-generation smartphones, laptops, and autonomous and connected vehicles.

Capacitors, in particular, are electronic components with the function of temporarily storing electricity, and are used in all devices that handle electricity and radio waves in various ways within electronic circuits, for purposes such as removing noise contained in electric current, extracting only necessary signals, and cutting off direct current and allowing only alternating current to pass. There are approximately 800 capacitors per smartphone, approximately 900 per laptop, and approximately 1,000 per automobile.

Traditionally, capacitors have been made from other materials such as tantalum and aluminum electrolytic capacitors, but today, dielectric multilayer ceramics have become mainstream due to their compact size, low profile, high capacitance, high reliability, low loss, and environmental friendliness, and the number of ceramic capacitors used worldwide each year has reached approximately 2 trillion units.

Increasing the capacitance of multilayer ceramic capacitors requires multi-layering, and both the dielectric ceramic layer and the electrode layer must be 0.8 μm thin and precisely multi-layered to avoid misalignment or structural defects.

To create multilayer ceramic capacitors, a conductive paste consisting of binder resin (methacrylic resin), polar organic solvent, and metal powder (Ni, Al, Ag, Cu, Pd, Cr, Fe, and Co, or an alloy selected from these) is applied to a ceramic green sheet using screen printing or other methods, and then laminated.

An example of an application in which heavy VOCs consisting of high-boiling point solvents with a boiling point of 150°C or higher are used in the manufacturing process is the polar organic solvent contained in the conductive paste. High-boiling point solvents such as hexyl acetate and terpineol are used because they have a difference in solubility parameter of 0 to 3 (J/cm ³ ) from the binder resin, thereby achieving smoothness of the coating film.

Therefore, VOC separation using absorption methods necessarily involves a process of separating VOCs from air, which requires the use of absorbents in the presence of oxygen. However, while activated carbon and molecular sieving carbon (MSC) have high absorption capabilities and can absorb larger amounts of VOCs than inorganic oxides such as silica, alumina, silica-alumina, and zeolite, their flammability makes their use in the presence of oxygen undesirable from a safety perspective. Rather, from a safety perspective, non-flammable inorganic oxide absorbents, such as silica, alumina, zeolite, and silica-alumina, are preferable. Furthermore, the necessity to use inorganic oxide absorbents with lower VOC absorption capacity than activated carbon and MSC presents a bottleneck in the development of VOC processes. Therefore, to recover VOCs using absorption methods, a non-flammable inorganic oxide absorbent, particularly one with a novel composition that has a high dynamic absorption capacity suitable for heavy VOCs composed of high-boiling-point solvents with a boiling point of 150°C or higher, is required; however, such an absorbent has not yet been established.

Porous silica is expected to be used as an absorbent for removing harmful volatile organic compounds. When used in a typical application, such as exhaust gas treatment, it must absorb target components from the flowing gas, requiring strong absorption capacity. For this purpose, the absorbent preferably has a pore diameter 1 to 1.2 times the VOC kinetic molecular diameter. Medium VOCs, which are medium-boiling point solvents below 150°C, have a kinetic molecular diameter of approximately 0.62 nm, for example, toluene and methylcyclohexane. Meanwhile, many heavy VOCs, which are high-boiling point solvents above 150°C, have a larger kinetic molecular diameter of 0.8 to 1 nm. Therefore, it is preferable for the absorbent to have many micropore diameters of approximately 0.8 to 1.15 nm. Furthermore, thin pore wall thickness and large micropore volume contribute to the absorption capacity.

Cationic surfactants made from quaternary ammonium salts are highly toxic and have a high environmental impact, so from a safety perspective, triblock copolymers containing polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO) are preferred. To achieve an average micropore diameter of approximately 0.8 to 1.15 nm, it is necessary to control the diameter of the associated micelles to 0.8 to 1 nm and synthesize porous silica with many micropores.

Because the absorption/separation and catalytic activity of porous materials depends heavily on the chemical surface properties of the pores, their shape, size, and uniformity, porous materials are classified by the IUPAC according to the size of their pores (pore diameter).

Patent Document 1 proposes a method for producing porous silica in which an alkoxysilane and a low-molecular-weight cationic surfactant are mixed directly without using an alcohol-based solvent, and water is added as a reactant to adjust the pH. The resulting precursor solution is then gelled to form silica.

According to Patent Document 1, among the cationic surfactants, octadecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and tetradecyltrimethylammonium bromide, which have 18 to 14 carbon atoms, have been confirmed to have mesopores, while dodecyltrimethylammonium bromide, decyltrimethylammonium bromide, octyltrimethylammonium bromide, hexyltrimethylammonium bromide, and butyltrimethylammonium chloride, which have 12 or fewer carbon atoms, have been confirmed to have micropores.

Furthermore, it has been shown that porous silica with micropores obtained using the cationic surfactants with 12 or fewer carbon atoms has improved toluene absorption performance. Among these, hexyltrimethylammonium bromide with 6 carbon atoms has the highest toluene absorption performance, and it has also been reported that the addition of an organic silane further enhances toluene absorption performance.

However, in the examples of Patent Document 1 having the presence of micropores, the example having 6 carbon atoms has an average micropore diameter of 1.12 nm, and in the range of 0.80 nm to 1.15 nm, the maximum total pore volume was 0.32 cm ³ /g. Naturally, the micropore volume is a part of the total pore volume, and therefore is less than 0.32 cm ³ /g.

On the other hand, in the example with 8 carbon atoms to which organic silane was added, the average micropore diameter was 0.99 nm, and the maximum total pore volume was 0.25 cm ³ /g in the range of 0.80 nm to 1.15 nm.

In Patent Document 1, porous silica primarily having micropores is obtained using the cationic surfactant with 12 or fewer carbon atoms. However, the micropore volume is not shown in the range of 0.80 nm to 1.15 nm, the average micropore diameter optimal for heavy VOCs. However, the total pore volume, which is the sum of the micropore volume and mesopore volume, is small, and the examples suggest that the optimal micropore volume for heavy VOCs is not obtained.

Patent Document 2 proposes a method for producing fibrous porous silica particles, which comprises mixing a mixed solution containing an acidic aqueous solution, a nonionic surfactant, a silicic acid ester, and water in the presence of a metal salt, stirring the mixture at 30°C or higher but lower than 50°C for 30 minutes to 2 hours, aging the resulting reaction suspension at 30 to 100°C for 30 minutes to ¹⁰ hours, filtering the resulting fibrous silica precursor, and then removing the nonionic surfactant from the precursor, thereby obtaining fibrous porous silica particles having a micropore volume of 0.10 to 0.25 cm 3 /g, uniform length, and high monodispersity.

According to Patent Document 2, it is desirable for nonionic surfactants, particularly triblock copolymers (PEO-PPO-PEO), to have a weight-average molecular weight of approximately 4,000 to approximately 8,000. In the examples, only Pluronic P123, which has a weight-average molecular weight of 5,800 and 30% PEO of the total molecular weight, is suggested.

It is stated that the larger the micropore volume, the higher the absorption capacity, but looking at the examples, the total pore volume is 0.70 to 0.90 cm ³ /g, while the micropore volume is 0.10 to 0.17 cm ³ /g, so the proportion of micropores is small, and the pore diameter is 6.07 to 7.22 nm, meaning that the porous silica is mainly composed of mesopores.

There has been no suggestion of using triblock copolymers (PEO-PPO-PEO) to produce porous silica primarily composed of micropores.

Patent Document 3 proposes spherical micropore silica porous particles characterized by having micropores with a pore diameter of 2 nm or less and a pore volume of 0.25 cm ³ /g or more, a BET specific surface area of 600 m ² /g or more, a C constant measured by BET analysis of 450 or more, and a particle diameter of 20 to 500 μm.

According to Patent Document 3, there is provided a method for producing spherical microporous silica particles by mixing and stirring an aqueous alkali silicate solution and a mineral acid in the presence of a nonionic surfactant, carrying out a reaction at a temperature of 5°C to 35°C, and removing the nonionic surfactant from the resulting spherical particles, wherein the mineral acid is used in an amount equivalent to 3.5 to 10 moles per mole of the alkali silicate in terms of _SiO2 , and the nonionic surfactant is a triblock copolymer of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) or polyethylene oxide-polybutylene oxide-polyethylene oxide (PEO-PBO-PEO), having a molecular weight of 4,500 to 16,000, with the proportion of the hydrophilic portion (PEO) relative to the total molecular weight being 75% or more.

In the examples, the micropore volume is 0.328 cm ³ /g to 0.367 cm ³ /g, and the average micropore diameter is 0.66 nm to 0.76 nm. The average micropore diameter is small, and the porous silica of the present invention does not have an average micropore diameter sufficient for dynamic absorption of heavy VOCs.

Patent Document 4 proposes a component that absorbs medium-boiling organic solvents such as toluene and xylene, which have boiling points of 100°C or higher but lower than 150°C, and then purifies the medium-boiling VOCs using an oxidation catalyst during desorption and regeneration. The proposed component configuration includes an absorbent material made of beta zeolite or mordenite zeolite, which supports silver and palladium, and a palladium-containing oxidation catalyst supported on the surface of a paper honeycomb.

Beta zeolite has a maximum pore size of 0.73 x 0.71 nm, while mordenite zeolite has a maximum pore size of 0.70 x 0.65 nm. While these zeolites are suitable for absorbing the medium VOCs mentioned above, their pore sizes were too small for the heavy VOCs with boiling points of 150°C or higher used in the present invention, resulting in insufficient absorption.

Due to the above issues, industrial applications of dynamic absorption and concentration of heavy VOCs have been extremely limited.

Patent No. 5647669 Patent No. 5051512 Patent No. 4484193 JP 2007-21363 A

The object of the present invention is to provide porous silica that can achieve highly efficient dynamic absorption and concentration performance for heavy VOCs composed of high-boiling polar organic solvents at 150°C or higher, as well as purification performance during VOC desorption, or to provide a heavy VOC absorbent material that incorporates a metal catalyst into the porous silica.

The objective is to provide a metal honeycomb flow-through body coated with the heavy VOC absorbent material.

In order to solve the above problems, the porous silica of the present invention is characterized by having micropores that are identified by the classification of IUPAC absorption isotherms, a micropore volume of 0.35 cm ³ /g or more and 0.55 cm ³ /g or less, and an average micropore diameter of 0.80 nm to 1.15 nm.

The average diameter of the micropores may be 0.88 nm to 1.12 nm.

The micropore volume (B) of the porous silica may account for 90% or more of the total pore volume (A).

The porous silica may contain at least one precious metal selected from platinum, palladium, and rhodium.

The content of the precious metal may be 0.5 to 1.5 mass%.

In order to solve the above-mentioned problems, the method for producing porous silica of the present invention is a method for producing porous silica from a nonionic surfactant and an alkoxysilane without using a cationic surfactant consisting of a quaternary ammonium salt, and includes the following steps: (A1) adding the nonionic surfactant, an acidic catalyst, a metal salt, and the alkoxysilane to water as a solvent, and forming associated micelles of the nonionic surfactant at 50°C to 60°C while simultaneously causing a hydrolysis reaction with the alkoxysilane to produce a silica sol; (B1) after the hydrolysis reaction, maintaining the silica sol at 80°C to 100°C for 2 to 5 hours to age the silica sol and obtain a gel substance; and (C1) separating the silica sol by solid-liquid separation through filtration. and a post-treatment step of separating the gel substance, washing the gel substance with water, drying the gel substance, and then calcining the gel substance at 500 to 600°C. The nonionic surfactant is a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO), the weight-average molecular weight of the triblock copolymer is greater than 1500 and less than 3000, and the polypropylene oxide (PEO) accounts for greater than 10% by mass and less than 50% by mass of the total molecules of the triblock copolymer. In step (A1), the molar ratio of the starting materials is alkoxysilane:nonionic surfactant:acidic catalyst:water:metal salt=1:0.02-0.05:2-3:10-40:0.5-0.8.

Furthermore, to solve the above-mentioned problems, the metal honeycomb flow-through body of the present invention is formed by coating the surface of a metal honeycomb having a specific heat of 500 (J/kg·°C) or less and a thermal conductivity of 15 (W/m·°C) or less with the porous silica of the present invention.

The material composition of the metal honeycomb may be 73 to 80 mass% Fe, 17 to 21 mass% Cr, and 3 to 6 mass% Al.

In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a metal honeycomb flow-through body, which is a method for manufacturing a metal honeycomb flow-through body formed by coating the surface of a metal honeycomb with porous silica, and includes the following steps: (A2) preparing a slurry containing the porous silica, an inorganic sol liquid, and water; (B2) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder; (C2) coating the cell surfaces of the metal honeycomb with the slurry obtained after step (B2); and (D2) drying and firing the metal honeycomb after coating with the slurry.

In addition, in order to solve the above-mentioned problems, the method for manufacturing a metal honeycomb flow-through body of the present invention is a method for manufacturing a metal honeycomb flow-through body by coating the surface of a metal honeycomb with porous silica containing a precious metal catalyst, and includes the following steps: (A3) preparing a slurry consisting of the porous silica, an inorganic sol liquid, and water; (B3) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder; (C3) coating the cell surfaces of the metal honeycomb with the slurry after step (B3); (D3) drying and firing the metal honeycomb after coating with the slurry to obtain a metal honeycomb flow-through body; (E3) preparing a precious metal liquid consisting of a precious metal salt solution and water; (F3) immersing the metal honeycomb flow-through body in the precious metal liquid; and (G3) drying and firing the metal honeycomb flow-through body after immersion in the precious metal liquid.

In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a metal honeycomb flow-through body, which is a method for manufacturing a metal honeycomb flow-through body formed by coating the surface of a metal honeycomb with porous silica containing a precious metal catalyst, and includes the following steps: (A4) preparing a slurry containing the porous silica, an inorganic sol liquid, a precious metal salt solution, and water; (B4) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder; (C4) coating the cell surfaces of the metal honeycomb with the slurry obtained after step (B4); and (D4) drying and firing the metal honeycomb after coating with the slurry.

Furthermore, the heavy VOCs composed of high-boiling point solvents with a boiling point of 150°C or higher are ester-based VOCs such as hexyl acetate, heptyl acetate, octyl acetate, dodecyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, benzyl acetate, butyl butyrate, butyl benzoate, benzyl benzoate, and dihydroterpineol acetate; ether-based VOCs such as anisole, phenetole, benzyl ethyl ether, diphenyl ether, dibenzyl ether, and ethylene glycol diethyl ether; and alcohol-based VOCs such as n-octanol, n-decanol, n-dodecanol, α-terpineol, and dihydroterpineol. The metal honeycomb flow element of the present invention is characterized by absorbing and concentrating at least one of the heavy VOCs with the porous silica, and purifying and regenerating the porous silica that has absorbed and concentrated the heavy VOCs.

The porous silica and precious metal-containing porous silica of the present invention, the metal honeycomb flow bodies coated with them, and the devices equipped with them can achieve more than twice the dynamic absorption capacity of heavy VOCs consisting of high-boiling polar organic solvents at temperatures above 150°C compared to conventional technology. Furthermore, by enabling the purification performance during heavy VOC desorption to be approximately 30°C lower, they can provide a technology with a highly efficient cycle of absorption, purification, regeneration, and cooling.

1 is an SEM image (×100 magnification) of Example 2 as an example of the VOC absorption and purification material of the present invention. 1 is an SEM image (×500 magnification) of Example 2 as an example of the VOC absorption and purification material of the present invention. IUPAC classification of nitrogen absorption isotherms. 1 shows the relationship between the proportion of hydrophilic moieties in the total molecules of surfactants in Examples and the weight average molecular weight. 1 shows the relationship between the proportion of hydrophilic moieties in the total molecule of surfactants in Examples and the molecular weight of the hydrophobic moieties. 1 is an example of a comparison [I] of nitrogen absorption isotherms between the present invention and the prior art. 1 is an example of a comparison [II] of nitrogen absorption isotherms between the present invention and the prior art. 1 is an example of a comparison of micropore diameter distributions [I] in the examples. 1 is an example of a comparison of micropore diameter distributions [II] in the examples. 1 shows the relationship between the average diameter and pore volume of micropores in the examples. 1 shows a performance test method for dynamic absorption, purification and regeneration in the examples. 1 shows the results of a cycle test of VOC absorption, VOC purification and regeneration, and cooling for Example 2M. Example 7: Results of cycle tests of PM VOC absorption, VOC purification and regeneration, and cooling. Example 8 shows the results of a cycle test of VOC absorption at 8 ppm, VOC purification and regeneration, and cooling. 1 shows the results of a cycle test of VOC absorption, VOC purification and regeneration, and cooling for Comparative Example 15M. 10 is a comparison of heat generation due to purification and regeneration of metal honeycomb flow bodies coated with VOC absorbents of Example 2M, Example 7PM, and Example 8PPM. 1 is a comparison of the hexyl acetate decomposition and purification performance of Example 2M, Example 7PM, and Example 8PPM.

Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments.

The present inventors have conducted extensive research into porous silica that can efficiently achieve both dynamic absorption performance for heavy VOCs consisting of high-boiling polar organic solvents at 150°C or higher and purification performance during VOC desorption, and as a result have discovered an absorbent material that is mainly composed of micropores, has a micropore volume of 0.35 cm ³ /g or more, and an average micropore diameter of 0.80 nm to 1.15 nm.

Heavy VOCs consisting of high-boiling point solvents of 150°C or higher that are the subject of this invention include hexyl acetate and α-terpineol, and have a dynamic molecular diameter of 0.8 nm to 1 nm.

On the other hand, medium-boiling solvents with a boiling point of 100°C or higher but lower than 150°C, which are not the subject of this invention, include toluene and methylcyclohexane, and have a dynamic molecular diameter of approximately 0.62 nm.

The former of the present invention has a larger kinetic molecular diameter than the latter, and therefore, it is preferable that the absorbent have a pore diameter that is 1.0 to 1.2 times the kinetic molecular diameter of the VOC.

The absorbent material of the present invention is made of porous silica and is characterized by having many micropores with diameters of about 0.8 nm to 1.15 nm and a large micropore volume of 0.35 cm ³ /g or more.

Below, the means for solving the problems of the present invention are specifically described.

(Molecular weight of nonionic surfactant)
The heavy VOC absorbent of the present invention is a porous silica having micropores synthesized from a nonionic surfactant and an alkoxysilane, without using a cationic surfactant made of a quaternary ammonium salt, and is characterized in that the nonionic surfactant has a weight-average molecular weight of more than 1,500 and less than 3,000.

(PEO content ratio of nonionic surfactant)
The heavy VOC absorbent of the present invention is characterized in that the nonionic surfactant is a triblock copolymer containing polyethylene oxide (PPEO)-polypropylene oxide (PPO)-polyethylene oxide (PPEO), and the polypropylene oxide (PPEO) accounts for more than 10% and less than 50% of the total molecule.

(Mean Micropore Diameter and Micropore Volume)
The material for absorbing, concentrating, and purifying heavy VOCs of the present invention is a porous silica synthesized from the nonionic surfactant and an alkoxysilane, characterized in that the porous silica has micropores identified by the IUPAC absorption isotherm classification, a micropore volume of 0.35 cm ³ /g or more, and an average micropore diameter of 0.80 nm to 1.15 nm.

(precious metal catalyst)
The material for absorbing, concentrating and purifying heavy VOCs of the present invention is characterized in that the porous silica contains at least one noble metal selected from the group consisting of platinum, palladium and rhodium.

(Precious metal catalyst content)
The material for absorbing, concentrating and purifying heavy VOCs of the present invention is characterized in that it contains 0.5 to 1.5 mass % of the noble metal.

(Porous silica manufacturing method)
A method for producing porous silica from a nonionic surfactant that is a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO), the weight-average molecular weight of which is greater than 1,500 and less than 3,000 and the content of the polypropylene oxide (PEO) in the total molecules is greater than 10% and less than 50%, and from an alkoxysilane, comprising the following steps (A1) to (C1):

(A1) The method includes a step of adding the nonionic surfactant, acid catalyst, metal salt, and alkoxysilane to a water solvent, raising the bath temperature to 50°C to 60°C, and then slowly cooling the mixture to 35°C to 40°C to form associated micelles of the nonionic surfactant and simultaneously carry out a hydrolysis reaction of the alkoxysilane. In step (A), the molar ratio of the starting materials is alkoxysilane: nonionic surfactant: acid catalyst: water: metal salt = 1: 0.02-0.05: 2-3: 10-40: 0.5-0.8.

(B1) After the hydrolysis reaction, the mixture is aged at 80°C to 100°C for 2 to 5 hours.

(C1) After filtering, washing with water, and drying, the product is calcined at 500-600°C.

(Physical properties of metal honeycomb material)
The metal honeycomb flow-through body of the present invention is characterized by having a specific heat of 500 (J/kg·° C.) or less and a thermal conductivity of 15 (W/m·° C.) or less.

(Composition of metal honeycomb material)
The metal honeycomb flow-through body of the present invention is characterized by comprising 73 to 80 mass % of Fe, 17 to 21 mass % of Cr, and 3 to 6 mass % of Al.

(Heavy VOC Absorbent Coating Method)
The metal honeycomb flow-through body of the present invention coated with an absorbent for heavy VOCs is characterized by being produced by the following steps (A2) to (D2).

(A2) A process of preparing a slurry consisting of a material that absorbs, concentrates, and purifies heavy VOCs, an inorganic sol liquid, and water. (B2) A process of adjusting the slurry to an average particle size of 1 to 10 μm using a wet grinder. (C2) A process of coating the slurry on the cell surface of the metal honeycomb. (D2) A process of drying and firing the coated slurry.

(Absorbent coating method for heavy VOCs containing precious metal catalysts)
The metal honeycomb flow-through body of the present invention, which is coated with a heavy VOC absorbent containing a precious metal catalyst, is characterized by being produced by the following steps (A3) to (G3).

(A3) A process for preparing a slurry consisting of a material that absorbs, concentrates, and purifies the heavy VOCs, an inorganic sol liquid, and water. (B3) A process for adjusting the average particle size of the slurry to 1 to 10 μm using a wet grinder. (C3) A process for coating the slurry on the cell surface of the metal honeycomb. (D3) A process for drying and firing the coated slurry. (E3) A process for preparing a precious metal liquid consisting of a precious metal salt solution and water. (F3) A process for immersing the metal honeycomb flow body coated with the heavy VOC absorbent in the precious metal liquid. (G3) A process for drying and firing the coated precious metal liquid.

(Absorbent coating method for heavy VOCs containing precious metal catalysts)
The metal honeycomb flow-through body of the present invention, which is coated with a heavy VOC absorbent containing a precious metal catalyst, is characterized by being produced by the following steps (A4) to (D4).
(A4) A process of preparing a slurry consisting of a material that absorbs, concentrates, and purifies heavy VOCs, an inorganic sol liquid, a precious metal salt solution, and water. (B4) A process of adjusting the slurry to an average particle size of 1 to 10 μm using a wet grinder. (C4) A process of coating the slurry on the cell surface of the metal honeycomb. (D4) A process of drying and firing the coated slurry.

(Target heavy VOCs)
The metal honeycomb flow-through body of the present invention is characterized by absorbing, concentrating and purifying heavy VOCs made of high-boiling point solvents such as esters, ethers and alcohols, as shown below.

(Esters) Hexyl acetate, heptyl acetate, octyl acetate, dodecyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, benzyl acetate, butyl butyrate, butyl benzoate, benzyl benzoate, dihydroterpineol acetate (Ethers) Anisole, phenetole, benzyl ethyl ether, diphenyl ether, dibenzyl ether, ethylene glycol diethyl ether (Alcohols) n-octanol, n-decanol, n-dodecanol, α-terpineol, dihydroterpineol

(Embodiment 1) Porous Silica In the present invention, an alkoxysilane, a metal salt, and a mineral acid are used as a silica source, and a block polymer of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO), a non-toxic, low-tolerance, inexpensive nonionic surfactant, is used as an organic structure-directing agent (OSDA), having a weight-average molecular weight of 1500 to 3000 and in which the proportion of the hydrophilic portion PEO in the total molecule is more than 10% but less than 50%.

The researchers found that the higher the PPO content (lower PEO content) of the nonionic surfactant in the total molecule, the lower the critical micelle concentration (cmc) and critical micelle temperature (cmt), making it easier to form micelles. Furthermore, they found that by raising the reaction bath to a high temperature of 50°C to 60°C, the hydrophobicity increases, the size of associated micelles decreases significantly, and intermolecular associations are formed.

The nonionic surfactant has a low weight-average molecular weight of 1500 to 3000, which, combined with the fact that the micelle size is extremely small and the micelle structure can be controlled uniformly, has made it possible to produce porous silica with an unparalleled large pore volume, with an average micropore diameter of 0.8 nm to 1.15 nm and a micropore volume of 0.35 cm ³ /g or more, representing a significant inventive step.

The porous silica particles of the present invention do not necessarily have a fibrous shape, but must have an average micropore diameter of 0.8 nm to 1.15 nm and a micropore volume of 0.35 cm ³ /g or more, and have an irregular shape as shown in Figures 1 and 2.

Specific embodiments of the porous silica particles of the present invention are described below.

(Porous silica manufacturing method)
A method for producing porous silica from a nonionic surfactant that is a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO), the weight-average molecular weight of which is greater than 1,500 and less than 3,000 and the content of the polypropylene oxide (PEO) in the total molecules is greater than 10% and less than 50%, and from an alkoxysilane, comprising the following steps (A5) to (C5):

(A5) The method includes a precursor (sol) preparation step in which the nonionic surfactant, the acid catalyst, the metal salt, and the alkoxysilane are added in this order to a water solvent, and association micelles of the nonionic surfactant are formed at 50°C to 60°C while simultaneously causing a hydrolysis reaction of the alkoxysilane, and in the step (A5), the mixing molar ratio of the starting materials is alkoxysilane:nonionic surfactant:acid catalyst:water:metal salt=1:0.02-0.05:2-3:10-40:0.5-0.8.
(B5) After the hydrolysis reaction, the mixture is aged at 80°C to 100°C for 2 to 5 hours (dehydration condensation gelation) step. (C5) After filtering, washing with water and drying, the mixture is baked at 500 to 600°C.

(Nonionic surfactant)
The nonionic surfactant of the present invention is preferably a block polymer having a weight-average molecular weight of 1500 to 3000 and a hydrophilic portion PEO content of more than 10% to less than 50% of the total molecule, and more preferably a block polymer having a weight-average molecular weight of 1500 to 2000 and a hydrophilic portion PEO content of 20% to 40%.

If the weight-average molecular weight exceeds 3,000, the average micropore diameter will be 1.15 nm or greater, the number of micropores will decrease, and the number of mesopores will increase, making it difficult for heavy VOCs to condense within the pores or be absorbed by single molecules, resulting in reduced dynamic absorption capacity. On the other hand, if the weight-average molecular weight is less than 1,500, the average micropore diameter will be less than 0.8 nm, which is equal to or smaller than the dynamic molecular diameter of heavy VOCs, reducing condensation within the pores and absorption by single molecules.

When the proportion of the hydrophilic portion PEO in the total molecule of the nonionic surfactant of the present invention is 10% or less, the hydrophobicity becomes excessive, the associated micelle structure becomes too large, and the average micropore diameter becomes 1.15 nm or more, which is undesirable. On the other hand, when the proportion of the hydrophilic portion PEO in the total molecule is 50% or more, the hydrophobicity is insufficient, making it difficult to form an associated micelle structure, resulting in an average micropore diameter of less than 0.8 nm, which is undesirable.

In the precursor preparation step (A5) in which associated micelles of the nonionic surfactant of the present invention are formed and simultaneously the alkoxysilane is hydrolyzed, the temperature of the reaction bath is increased to 50°C to 60°C, then slowly cooled and maintained at 35°C to 40°C, thereby increasing hydrophobicity and converting the associated micelles to a compact form. In order to produce the porous silica of the present invention having an average micropore diameter of 0.8 nm to 1.15 nm and a micropore volume of 0.35 ^cm3 /g or more, it is preferable to increase the temperature of the reaction bath to 50°C to 60°C, then slowly cool, and maintain the temperature at 35°C to 40°C with continuous stirring for 2 to 20 hours, and more preferably to increase the bath temperature to 50°C to 55°C, then slowly cool, and maintain the temperature at 35°C to 40°C with continuous stirring for 3 to 18 hours.

If the temperature of the reaction bath is increased by less than 50°C, hydrophobicity does not increase, micelle aggregation is low, and the average micropore diameter is less than 0.8 nm, which is undesirable. On the other hand, if the temperature of the reaction bath is increased by more than 70°C, not only hydrolysis but also dehydration condensation reactions will proceed, forming siloxanes, resulting in a non-uniform pore distribution, which is undesirable.

When stirring the reaction bath in the precursor preparation (A5) step, it is important to stir the precursor (sol) solution uniformly throughout so that the alkoxysilane is hydrolyzed and absorbed around the formed associated micelles. The stirring method is not particularly limited as long as it can stir the precursor (sol) solution uniformly throughout, but it is preferable to use baffle plates or rods that account for 10-20% of the diameter of the reaction vessel, and stirring blades that account for 40% or more.

Then, in the aging (B5) step, aging is preferably carried out at a bath temperature of 80°C to 100°C for 2 to 5 hours. It is even more preferable to carry out aging at 90°C to 98°C for 3 to 4 hours. Stirring may or may not be performed during aging, but if stirring is performed, it is preferable to perform uniform stirring in the same manner as in the precursor preparation (A) step described above.

In the post-treatment step (C5), after filtering, washing with water, and drying, the sample is preferably calcined at 500 to 600°C, although this depends on the number of samples and the calcination time. Calcination at 550 to 600°C is particularly preferred.

As acid catalysts, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc., and organic acids such as acetic acid can be used. Inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are preferred, with hydrochloric acid being particularly preferred from the standpoint of catalytic properties and the fact that it is less likely to remain as a residue like nitrate, sulfate, and phosphate radicals.

The alkoxysilane used in the present invention may be tetramethoxysilane, tetraethoxysilane, tetraisopropylsilane, etc. However, tetraethoxysilane (hereinafter abbreviated as TEOS) is preferred due to the toxicity of tetramethoxysilane resulting from the production of methanol and the slow reaction rate of tetraisopropylsilane.

The molar ratio of the starting materials is alkoxysilane: nonionic surfactant: acidic catalyst: water: metal salt = 1: 0.02-0.05: 2-3: 10-40: 0.5-0.8.

Preferred metal species in the metal salt of the present invention are Na, K, Li, Cs, etc., and among these, Na and K are preferred because increasing the concentration lowers the cmc and cmt of the nonionic surfactant, allowing associated micelles to grow. As salts of the metal, chlorides, sulfates, nitrates, etc. can be used as starting materials. Chlorides are preferred because they are less likely to remain as residual salts of nitrate or sulfate groups.

(Embodiment 2) Metal honeycomb flow body The metal honeycomb flow body of the present invention is made of ferritic stainless steel and has a smaller specific heat capacity (Table 5) than the conventionally used glass fiber honeycomb flow bodies. As a result, VOCs absorbed in the VOC absorption and concentration zone can be circulated through the VOC purification and regeneration zone by circulating heated air, and the VOCs can be purified and regenerated in a short period of time. Thereafter, the VOCs can be cooled in a short period of time by blowing air in the cooling process. This is advantageous in that it increases the cycle efficiency of absorption and concentration, purification and regeneration, and cooling, allowing a large amount of VOCs to be treated per hour.

On the other hand, the metal honeycomb flow body of the present invention is made of ferritic stainless steel, which has a lower thermal conductivity (Table 5) than general-purpose stainless steels such as austenitic stainless steel (e.g., SUS304) and martensitic stainless steel (e.g., SUS410). This means that the heat from the heated air in the VOC purification and regeneration zone is less likely to be transferred to the VOC absorption and concentration zone and cooling zone, making it preferable in that it has little impact on the VOC absorption and concentration amount and cooling efficiency.

(Physical properties of metal honeycomb material)
The metal honeycomb flow-through body of the present invention is preferably made of ferritic stainless steel Fe-20Cr-5Al (JFE20-5USR, manufactured by JFE Steel Corporation) or ferritic stainless steel Fe-18Cr-3Al (JFE18-3USR, manufactured by JFE Steel Corporation), which has a specific heat of 500 (J/kg·°C) or less and a thermal conductivity of 15 (W/m·°C) or less (Table 5).

(Composition of metal honeycomb material)
The metal honeycomb flow-through body of the present invention uses ferritic stainless steel Fe-20Cr-5Al (JFE20-5USR, manufactured by JFE Steel Corporation) or ferritic stainless steel Fe-18Cr-3Al (JFE18-3USR, manufactured by JFE Steel Corporation) containing 73 to 80 mass% Fe, 17 to 21 mass% Cr, and 3 to 6 mass% Al (Table 6).

The metal honeycomb flow body of the present invention is formed by overlapping and winding a flat sheet and a pleated sheet of ferritic stainless steel Fe-20Cr-5Al (JFE20-5USR, manufactured by JFE Steel Corporation) foil (thickness 20 μm to 40 μm) made of ferritic stainless steel Fe-18Cr-3Al (JFE18-3USR, manufactured by JFE Steel Corporation) with a brazing filler material sandwiched between the two sheets. The honeycomb roll is then manufactured by melting the brazing filler material in a heating furnace to bond the honeycomb roll to its outer periphery. The outer periphery of the honeycomb roll is not particularly limited, but is typically a stainless steel (thickness 1 mm to 3 mm) outer cylinder, which is heated and bonded to the honeycomb roll with brazing filler material in the same manner as the honeycomb.

From the viewpoint of VOC absorption and pressure loss, the metal honeycomb flow-through body of the present invention preferably has a cell number of 200 to 400 cells/inch ² , and more preferably 250 to ³⁵⁰ cells/inch ^{2 .}

(Embodiment 3) Coating of porous silica The porous silica of the present invention is obtained by mixing an inorganic binder with water, adjusting the particle size using a ball mill or the like to form a slurry, coating the metal honeycomb with the slurry, and then drying and firing the slurry.

The inorganic binder is preferably a material with a similar coefficient of linear expansion so that the porous silica and metal honeycomb of the present invention can maintain sustained adhesion during the heating and cooling cycles that occur during purification and regeneration. From this perspective, alumina sol is preferred.

The mixing of the slurry materials is preferably such that the mass ratio, calculated on a solids basis (excluding water), is the porous silica of the present invention: alumina sol: water = 1:0.1-0.2:2-4.

From the viewpoint of adhesion to the metal honeycomb flow-through body, the porous silica of the present invention in the slurry preferably has an average particle size _D50 of 1 μm to 10 μm, and particularly preferably 2 μm to 5 μm. If the average particle size _D50 is less than 1 μm, the viscosity of the slurry increases, causing clogging of the inner cell surfaces of the metal honeycomb flow-through body, resulting in a decrease in VOC absorption and concentration performance and/or an increase in pressure loss, which is undesirable. On the other hand, if the average particle size _D50 exceeds 10 μm, adhesion between the porous silica particles of the present invention and between the layers of the metal honeycomb flow-through body decreases, leading to a decrease in VOC absorption and dust generation, which is undesirable.

The porous silica of the present invention is preferably coated on the inner cell surfaces of the metal honeycomb in an amount of 80 g/L to 150 g/L per volume (L) of the metal honeycomb, with 90 g/L to 140 g/L being particularly preferred. A coating amount of less than 80 g/L is undesirable because the coating amount is insufficient and VOC absorption and concentration performance is reduced. A coating amount of more than 150 g/L is undesirable because the inner cell surfaces of the metal honeycomb flow element become clogged, reducing VOC absorption and concentration performance and/or increasing pressure loss.

(Embodiment 4) Noble Metal Catalyst The material for absorbing, concentrating and purifying heavy VOCs of the present invention is characterized by comprising the porous silica of the present invention and at least one noble metal selected from the group consisting of platinum, palladium and rhodium.

When porous silica and precious metals are supported on the inner cell surfaces of a metal honeycomb flow element, purification begins when the metal honeycomb inlet gas temperature reaches approximately 170°C during heated air regeneration, and the metal honeycomb outlet gas temperature rises to over 300°C due to the exothermic oxidation reaction of heavy VOCs. In contrast, when porous silica is used alone, purification begins when the metal honeycomb inlet gas temperature reaches approximately 200°C, and the metal honeycomb outlet gas temperature only rises to 220°C. (Figure 11)

When porous silica and precious metals are supported on the inner surface of the cells, the purification start temperature shifts to a lower temperature by approximately 30°C compared to when only porous silica is supported on the inner surface of the cells, thereby shortening the purification and regeneration cycle time and further contributing to energy savings in heated air.

The inventors discovered that, among precious metals, platinum has high oxidation activity in the low temperature range of 150°C to 250°C, while palladium and rhodium have high oxidation activity in the higher temperature range of 250°C or higher.

It is more preferable to load platinum on the inner surface of the cell at 0.5 g/L to 1.0 g/L, and palladium and/or rhodium at a total loading of palladium and rhodium of 0.25 g/L to 0.5 g/L.

(Precious metal catalyst content)
The material for absorbing, concentrating and purifying heavy VOCs of the present invention is characterized in that the noble metal is contained in an amount of 0.5 g/L to 1.5 g/L per volume (L) of the metal honeycomb.

From the standpoint of the amount of heavy VOCs purified by oxidative decomposition, shortening of regeneration time, and cost, it is preferable that the precious metal content be 0.7 g/L to 1.2 g/L. If it is less than 0.5 g/L, the amount of heavy VOCs purified by oxidative decomposition and shortening of regeneration time will be insufficient, which is undesirable. On the other hand, if it exceeds 1.5 g/L, the cost will be high and it is undesirable.

The following examples further illustrate the present invention. However, the present invention is not limited to these examples. The obtained porous silica was evaluated using the following equipment.

(Observation by electron microscope)
Analytical equipment: A scanning electron microscope, JSM-6610LA, manufactured by JEOL Ltd., was used, and the sample was fixed directly onto the sample stage with double-sided carbon tape and images were observed in low vacuum mode at an acceleration voltage of 15 kV.

(specific surface area, total pore volume, micropore volume, average micropore diameter)
The sample was pretreated in advance in a vacuum at 200°C for 3 hours, and the IUPAC classification and BET specific surface area were determined from the nitrogen absorption isotherm measured at liquid nitrogen temperature (-196°C) using a BELSORP-max manufactured by Microtrac-Bell Corporation. The total pore volume was calculated from the maximum absorption amount at relative pressure (P/P ₀ = 0.980) as the sum of the mesopore volume and micropore volume. The micropore volume and average micropore diameter were calculated from the intercept of the second straight line using the t-plot method, and the average micropore diameter (2t) was calculated from the inflection point. The micropore volume and average micropore diameter were then shown as a micropore distribution using the MP method, which differentiates the curvature near the inflection point of the t-plot.

(Example 1) L-64
In Example 1, porous silica was synthesized using a nonionic surfactant consisting of a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide (PEO)-polyethylene oxide (PEO), with a weight-average molecular weight of 2900 and 40% ethylene oxide (PEO) in the total molecule. The obtained porous silica was synthesized.

Specifically, 245 g of ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, 40% ethylene oxide (PEO) in total molecules) and 1540 g of ion-exchanged water were placed in a glass container (5 L) while stirring. Next, 130 g of salt (99% or more sodium chloride) and 290 g of concentrated hydrochloric acid (37%) were added. Stirring was then continued at 35-40°C for 4 hours to fully dissolve the ADEKA (registered trademark) Pluronic L-64 and form associative micelles.

711 g of tetraethoxysilane (TEOS) was added to the solution as an alkoxysilane, and the bath temperature was raised to 50-55°C. The bath was then slowly cooled and maintained at 35-40°C with continuous stirring to hydrolyze the alkoxysilane. This liquid was used as the precursor solution.

The precursor liquid was then heated to 90-100°C and held there for 3-4 hours to mature, completing the gelation process, and the entire solution turned into a visually colorless gel-like solid.

Next, the gel-like solid was filtered and repeatedly washed with water until the pH of the wash water reached 5-6. It was then transferred to a fireproof container, dried, and calcined at 550°C for 3 hours to obtain porous silica.

(Example 2) L-34
In Example 2, porous silica was synthesized in the same manner as in Example 1, except that the nonionic surfactant ADEKA (registered trademark) PLURONIC L-34 (weight average molecular weight 1700, ethylene oxide (PEO) 40% in total molecules) was used instead of ADEKA (registered trademark) PLURONIC L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) used in Example 1.

(Example 3) L-72
In Example 3, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic L-72 (weight average molecular weight 2750, ethylene oxide (PEO) content 20% in total molecules) was used instead of ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) content 40% in total molecules), a nonionic surfactant used in Example 1.

(Example 4) L-62
In Example 4, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic L-62 (weight average molecular weight 2500, ethylene oxide (PEO) 20% in total molecules) was used instead of the nonionic surfactant ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) used in Example 1.

(Example 5) L-42
In Example 5, porous silica was synthesized in the same manner as in Example 1, except that the nonionic surfactant ADEKA (registered trademark) PLURONIC L-42 (weight average molecular weight 1630, ethylene oxide (PEO) 20% in total molecules) was used instead of ADEKA (registered trademark) PLURONIC L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) used in Example 1.

(Example 6) L-44
In Example 6, porous silica was synthesized in the same manner as in Example 1, except that the nonionic surfactant ADEKA (registered trademark) PLURONIC L-44 (weight average molecular weight 2200, ethylene oxide (PEO) content in total molecules 40%) was used instead of ADEKA (registered trademark) PLURONIC L-64 (weight average molecular weight 2900, ethylene oxide (PEO) content in total molecules 39.7%) used in Example 1.

(Comparative example 1) P-123
In Comparative Example 1, a nonionic surfactant triblock copolymer PEO-PPO-PEO (Pluronic P-123, weight-average molecular weight 5800, manufactured by BASF) and hydrochloric acid were stirred at approximately 550 rpm at 45°C. After 10 minutes, sodium chloride was added, and after another 10 minutes, a mixed solution of TPEOS and water was added. In this example, the amount of sodium chloride added was varied, and the molar ratio of the mixed solution was TPEOS:P123:HCl: _H2O :NaCl = 1:0.017:5.85:199:1.495. After stirring this mixed solution for another hour, stirring was stopped and the solution was transferred to a thermostatic water bath preheated to 80°C and aged for 3 hours. The solid product was filtered from the reaction suspension, thoroughly dried at 60°C, and then heated at 600°C for 1 hour to remove organic components and obtain fibrous mesoporous silica particles. Comparative Examples 1 to 5 correspond to Examples 1 to 5 of Patent Document 2.

(Comparative example 2) P-103
In Comparative Example 2, mesoporous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic P-103 (weight average molecular weight 4900, ethylene oxide (PEO) content in total molecules 30%) was used instead of the nonionic surfactant ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) content in total molecules 40%) used in Example 1.

(Comparative example 3) L-61
In Comparative Example 3, mesoporous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic L-61 (weight average molecular weight 2000, ethylene oxide (PEO) content in total molecules 10%) was used instead of the nonionic surfactant ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) content in total molecules 39.7%) used in Example 1.

(Comparative Example 4) P-65
In Comparative Example 4, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic P-65 (weight average molecular weight 3400, ethylene oxide (PEO) content in total molecules 50%) was used instead of ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) content in total molecules 40%), a nonionic surfactant used in Example 1.

(Comparative Example 5) L-31
In Comparative Example 5, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) PLURONIC L-31 (weight average molecular weight 1100, ethylene oxide (PEO) 10% in total molecules) was used instead of ADEKA (registered trademark) PLURONIC L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) as the nonionic surfactant used in Example 1.

(Comparative Example 6) L-35
In Comparative Example 6, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic L-35 (weight average molecular weight 1900, ethylene oxide (PEO) 50% in total molecules) was used instead of ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) as the nonionic surfactant used in Example 1.

(Comparative Example 7) L-23
In Comparative Example 7, porous silica was synthesized in the same manner as in Example 1, except that ADEKA (registered trademark) Pluronic L-23 (weight average molecular weight 1055, ethylene oxide (PEO) 30% in total molecules) was used instead of ADEKA (registered trademark) Pluronic L-64 (weight average molecular weight 2900, ethylene oxide (PEO) 40% in total molecules) as the nonionic surfactant used in Example 1.

(Comparative Example 8)
A sodium silicate aqueous solution prepared by diluting commercially available JIS No. 3 sodium silicate with water was added to a solution of Pluronic F88 (weight average molecular weight 11,400, hydrophilic portion PEO ratio 80%, manufactured by BASF) consisting of a triblock copolymer PEO-PPO-PEO dissolved in 2N hydrochloric acid while stirring at 600 rpm. The molar ratio of the mixed solution was _SiO2 :Pluronic F88: _Na2O :HCl: _H2O = 1:0.0064:0.312:3.93:152. The _H2O contained water derived from all raw materials. The reaction temperature was 25°C to 27°C, and the reaction was stirred for 2 hours. The solid product was then filtered, washed with warm water at 60°C, and thoroughly dried at 50°C. Finally, the mixture was calcined in an electric furnace at 600°C for 1 hour to remove organic components, yielding spherical, regular-shaped porous silica particles. Comparative Example 8 corresponds to Example 8 of Patent Document 3.

(Comparative Example 9)
A polypropylene container was charged with 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) as a silica source, followed by dispersion and stirring of 0.2 to 1.2 eq (0.038 mol x 0.2 to 0.038 mol x 1.2) of cationic surfactant. At this stage, the TPEOS and surfactant do not mix; in other words, a homogeneous mixture is not formed. Dodecyltrimethylammonium bromide was used as the cationic surfactant to synthesize porous silica.

Next, approximately 2 to 4 eq (0.038 mol x 2 to 0.038 mol x 4) of water, the pH of which had been adjusted to approximately 0 to 2 using hydrochloric acid, was added to the above mixture and stirred at room temperature. After stirring for approximately one hour, the hydrolysis of TEOS progressed, resulting in a nearly uniform solution. This solution (precursor solution) was kept at room temperature or 60°C and continued to be stirred or allowed to stand. Gelation was completed within 12 hours to several days, and the entire solution appeared visually to be a colorless, transparent gel. This gel was dried at 60°C and calcined at 600°C for 3 hours to remove the surfactant. This resulted in colorless, transparent, monolithic porous silica.

(Comparative Example 10)
In Comparative Example 10, porous silica was obtained in the same manner as in Comparative Example 9, except that decyltrimethylammonium bromide was used instead of dodecyltrimethylammonium bromide as the cationic surfactant.

(Comparative Example 11)
In Comparative Example 11, porous silica was obtained in the same manner as in Comparative Example 9, except that decyltrimethylammonium bromide was used instead of dodecyltrimethylammonium bromide as the cationic surfactant.

(Comparative Example 12)
In Comparative Example 12, porous silica was obtained in the same manner as in Comparative Example 9, except that hexyltrimethylammonium bromide was used instead of dodecyltrimethylammonium bromide as the cationic surfactant.

(Comparative Example 13)
In Comparative Example 13, porous silica was obtained in the same manner as in Comparative Example 9, except that butyltrimethylammonium chloride was used instead of dodecyltrimethylammonium bromide as the cationic surfactant.

(Comparative Example 14)
[Pore size control by adding organic silane]
In Comparative Example 14, porous silica was obtained in the same manner as in Comparative Example 9, except that triethoxyvinylsilane was added to the precursor solution of Comparative Example 11.

Specifically, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) and 8 g x 5% (0.038 mol x 5%) of triethoxyvinylsilane (TEVS) were mixed in a polypropylene container as a silica source. 0.2 to 1.2 equivalents of a surfactant were then added and stirred. To this mixture, 2 to 4 equivalents of water adjusted to a pH of 0 to 2 using hydrochloric acid were added and stirred at room temperature. After approximately 1 hour of stirring, hydrolysis of the TPEOS progressed, resulting in a nearly homogeneous solution. This solution (precursor solution) was then maintained at room temperature or 60°C and stirred or allowed to stand. Gelation was complete within 12 hours to several days, with the entire solution visually appearing as a colorless, transparent gel. This gel was dried at 60°C and baked at 600°C for 3 hours to remove the surfactant. The surfactant used was a cationic surfactant consisting of octyltrimethylammonium bromide.

(Comparative Example 15)
In Comparative Example 15, porous silica was obtained in the same manner as in Comparative Example 14, except that hexyltrimethylammonium bromide was used instead of octyltrimethylammonium bromide as the cationic surfactant.

(Comparative Example 16)
In Comparative Example 16, porous silica was obtained in the same manner as in Comparative Example 14, except that butyltrimethylammonium chloride was used instead of octyltrimethylammonium bromide as the cationic surfactant in Comparative Example 14.

Tables 5 to 7 show the raw material types, blending ratios, and synthesis conditions for the porous silica of Examples 1 to 6 and Comparative Examples 1 to 16. Furthermore, Figure 4 shows the relationship between the proportion of hydrophilic moieties in the total molecule and the weight-average molecular weight, and Figure 5 shows the relationship between the proportion of hydrophilic moieties in the total molecule and the molecular weight of the hydrophobic moiety.

The pore analysis results for the porous silica of Examples 1 to 6 and Comparative Examples 1 to 16 are shown in Table 8, including the IUPAC classification of the absorption isotherm, BET specific surface area, total pore volume (A), average micropore diameter, micropore volume (B), and the percentage of micropore volume (B) in the total pore volume (A).

(Nitrogen absorption isotherm)
Fig. 6 shows nitrogen absorption isotherms for porous silica in Examples 1 and 2 as examples of the present invention and Comparative Examples 2, 4, 5, and 7 as examples of the prior art. Similarly, Fig. 7 shows nitrogen absorption isotherms for porous silica in Examples 1 and 2 as examples of the present invention and Comparative Examples 12 and 15 as examples of the prior art.

(Micropore size distribution)
Fig. 8 shows the micropore size distributions of the porous silica of Examples 1 and 2 as examples of the present invention and Comparative Examples 4 and 7 as examples of the prior art. Similarly, Fig. 9 shows the micropore size distributions of the porous silica of Examples 1 and 2 as examples of the present invention and Comparative Examples 12 and 15 as examples of the prior art.

(Relationship between average diameter of micropores and pore volume)
FIG. 10 shows the relationship between the average diameter and pore volume of the micropores in the porous silica of Examples 1 to 6 and Comparative Examples 1 to 16.

(Embodiment 2) Preparation of Metal Honeycomb Flow Body The metal honeycomb flow body of the present invention was prepared by using a metal foil of ferritic stainless steel Fe-20Cr-5Al (JFE20-5USR, manufactured by JFE Steel Corporation, thickness 30 μm, width 120 mm), and winding a metal honeycomb portion around a 122 mm diameter roll with a wavy cell pattern of 300 cells/ ^inch² while inserting a brazing filler material between the foil and on the top surface of the flat foil, while maintaining a constant winding tension.

For the outer cylinder, a stainless steel (SUS304, 1.5 mm thick, 140 mm wide) plate was prepared in advance, cut to a length that would result in a cylindrical inner diameter of 122 mm, and then the outer cylinder was curved using a roll bender.

Next, the metal honeycomb section was wrapped in a curved outer cylinder, brazing material was inserted between them, and the end faces of the outer cylinder were welded together. The brazing material was then heated and fused in a vacuum heating furnace to produce a metal honeycomb flow-through body (honeycomb diameter 122 mm x width 120 mm, volume 1.4 L).

(Embodiment 3) Porous Silica Coating Method First, 200 g of each sample was mixed with 800 g of ion-exchanged water and 200 g of Alumina Sol AS200 (alumina content 10 wt %, manufactured by Nissan Chemical Industries, Ltd.) to form a slurry in a ball mill. The slurry was then applied to a metal honeycomb (honeycomb diameter 122 mm, length 120 mm, volume 1.40 L, cell count 300/ ^inch2 , manufactured by ACR Corporation), dried, and fired at 500°C to prepare porous silica-coated metal honeycomb flow-through bodies (hereinafter referred to as Examples 1M to 6M and Comparative Examples 1M to 16M) with each sample loaded on the metal honeycomb to a loading of 100±15 g/L.

(Embodiment 4) Method for coating porous silica containing a precious metal catalyst (Example 7PM)
Example 7PM is an example of a metal honeycomb flow-through structure made of porous silica containing a platinum catalyst of the present invention, which absorbs, concentrates, purifies, and regenerates heavy VOCs. A platinum-supported solution was prepared by mixing 16.0 g of a platinum salt solution (dinitrodiammine Pt(II) nitrate solution, 8.368% Pt, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with 2,000 g of ion-exchanged water. Next, the metal honeycomb flow-through structure of Example 2M, coated with 92 g/L of porous silica, was immersed in the platinum-supported solution for 12 hours, so that the entire honeycomb portion was immersed. The structure was then dried and fired at 500 °C for 2 hours to produce the metal honeycomb flow-through structure of Example 7M, coated with porous silica containing 0.75 g/L of platinum.

(Example 8 PPM)
Example 8 PPM is an example of a metal honeycomb flow element made of porous silica containing platinum and palladium catalysts of the present invention, which absorbs, concentrates, purifies, and regenerates heavy VOCs. A palladium-loaded solution was prepared in advance by mixing 4.0 g of a palladium salt solution (palladium (II) nitrate solution, 8.300% Pd, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with 500 g of ion-exchanged water.

The metal honeycomb flow body of Example 7 PM was immersed in the palladium-loaded solution for 12 hours, up to a position 30 mm from the end of the honeycomb. It was then dried and fired at 500°C for 2 hours to produce the metal honeycomb flow body of Example 8 PPM, coated with porous silica containing 0.25 g/L of palladium.

(Embodiment 5) Cycle Test of Heavy VOCs Cycle tests of the absorption and concentration process, purification and regeneration process, and cooling process were conducted for Examples 1M to 6M, 7PM, and 8PPM and Comparative Examples 1M to 16M. Hexyl acetate (boiling point: 169.2°C, Chapman (2009)) was used as the heavy VOC.

(Adjusting the concentration of hexyl acetate volatilized gases by heating)
In a volatilizer, hexyl acetate was heated to 150°C to volatilize it and mixed with air to produce a 150 ppm hexyl acetate volatilized gas. The volume of the metal honeycomb flow body was 1.4 L, and the space velocity was adjusted to 30,000 h ^-1 and the inlet gas temperature of the metal honeycomb flow body was adjusted to 60°C.

(Hexyl acetate absorption and concentration process)
Furthermore, the end point of absorption and concentration was determined to be the time when the leak concentration of xyl acetate reached 30 ppm as hydrocarbon at the outlet of the metal honeycomb flow body.

(Hexyl acetate purification and regeneration process)
Immediately after the end of the absorption concentration, heated air was introduced using a superheater at a space velocity of 22,000 h ⁻¹ so that the inlet gas temperature of the metal honeycomb flow body was 200° C., and hexyl acetate was desorbed and purified for 15 minutes.

(Cooling process of metal honeycomb flow body)
Immediately after 15 minutes of the hexyl acetate desorption purification, air at room temperature was introduced into the metal honeycomb flow body at a space velocity of 22,000 h ^-1 to cool the metal honeycomb flow body.

(Repeat cycle)
The three steps of absorbing and concentrating hexyl acetate, purifying and regenerating, and cooling were repeated again.

The test system is shown in Figure 11. The gas concentration detectors at the inlet and outlet of the metal honeycomb flow body were the Motor Exhaust Gas Analyzer MEXA-7100DEGR manufactured by Horiba, Ltd., which measured hydrocarbon concentration. Furthermore, the concentration of the purified and decomposed gas components was measured at the outlet using the FT-IR Motor Exhaust Gas Analyzer FAST-2100 manufactured by Databird.

Figures 12 to 14 show examples of cycle test results, and Table 9 shows the dynamic absorption of hexyl acetate.

(Purification and regeneration effect of hexyl acetate using precious metal catalyst)
FIG. 16 shows the results of a comparison of the inlet and outlet temperatures of the metal honeycomb flow bodies of Example 2M, Example 7PM, and Example 8PPM in the purification and regeneration of hexyl acetate by heating at 200° C.

For the metal honeycomb flow element of Example 2M, the outlet temperature reached approximately 220°C when the inlet temperature reached 200°C, shifting to a temperature approximately 20°C higher due to the exothermic reaction caused by the oxidative decomposition of hexyl acetate. On the other hand, for the metal honeycomb flow element of Example 7PM, the outlet temperature reached approximately 330°C when the inlet temperature was around 180°C, shifting to a temperature approximately 150°C higher due to the exothermic reaction caused by the oxidative decomposition of hexyl acetate. Furthermore, for the metal honeycomb flow element of Example 8PPM, the outlet temperature reached approximately 340°C when the inlet temperature was around 170°C, shifting to a temperature approximately 160°C higher due to the exothermic reaction caused by the oxidative decomposition of hexyl acetate.

The gas compositions detected by FT-IR analysis at the outlet of the metal honeycomb flow element when the inlet temperature of the metal honeycomb flow element reached 170 to 200°C are shown in Tables 10 to 12. Example 8 PPM can be purified to the most H ₂ O and CO ₂ by oxidative decomposition of hexyl acetate (Equation 1).

Figure 17 shows the change in hydrocarbon (HC) concentration over the purification and regeneration time when heated to 200°C. Example 8 PPM was found to purify and regenerate hydrocarbons (HC) in the shortest time.

Compared to Example 2M, Example 7PM, which contains platinum, is able to improve purification and regeneration performance due to the effect of the oxidation catalyst, requires less thermal energy for heating, shortens regeneration time, and enables highly efficient heavy VOC treatment. Furthermore, Example 8PPM, which contains platinum and palladium, is able to improve purification and regeneration performance due to the effect of the oxidation catalyst compared to Example 7PM, requires less thermal energy for heating, shortens regeneration time, and enables highly efficient heavy VOC treatment.

The present invention relates to, for example, a porous silica having a large micropore volume of 0.35 cm 3 /g or more and an average micropore diameter of 0.8 nm to 1.15 nm, which is obtained by using a safe, environmentally friendly nonionic surfactant as a template, which is a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide ( ^PPO )-polyethylene oxide (PEO), and which has a weight-average molecular weight of more than 1,500 but less than 3,000 and a hydrophilic moiety of more than 10% but less than 50% of the total molecule. This porous silica can absorb more than twice as much heavy VOC as conventional techniques, and furthermore, by using the metal honeycomb and/or oxidation catalyst of the present invention, it is possible to treat large amounts of heavy VOC in a short purification/regeneration cycle, and the present invention can be effectively used in industries such as finely laminated electronic components.

Claims (11)

Without using a cationic surfactant consisting of a quaternary ammonium salt,
A method for producing porous silica from a nonionic surfactant and an alkoxysilane, comprising the steps of:
(A1) a step of adding the nonionic surfactant, the acid catalyst, the metal salt, and the alkoxysilane to water as a solvent, and forming associated micelles of the nonionic surfactant at 50°C to 60°C while simultaneously causing a hydrolysis reaction with the alkoxysilane to produce a silica sol;
(B1) an aging step of aging the silica sol by maintaining the silica sol at 80°C to 100°C for 2 hours to 5 hours after the hydrolysis reaction to obtain a gel substance;
(C1) a post-treatment step of separating the gel substance by solid-liquid separation through filtration, washing the gel substance with water, drying the gel substance, and then calcining the gel substance at 500 to 600°C;
the nonionic surfactant is a triblock copolymer containing polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO);
The weight average molecular weight of the triblock copolymer is more than 1500 and less than 3000,
The polyethylene oxide (PEO) is contained in the total molecules of the triblock copolymer in an amount of more than 10% by mass to less than 50% by mass,
In the step (A1), the molar mixing ratio of the starting materials is the alkoxysilane: the nonionic surfactant: the acidic catalyst: the water: the metal salt=1:0.02-0.05:2-3:10-40:0.5-0.8. A metal honeycomb flow-through body having a specific heat of 500 (J/kg ° C) or less and a thermal conductivity of 15 (W/m ° C) or less , the surface of which is coated with porous silica ,
The metal honeycomb flow-through body is a porous silica having micropores identified by the IUPAC absorption isotherm classification, a micropore volume of 0.35 cm ³ /g or more and 0.55 cm ³ /g or less, and an average micropore diameter of 0.80 nm to 1.15 nm . 3. The metal honeycomb flow-through body according to claim 2 , wherein the material composition of the metal honeycomb is 73 to 80 mass % Fe, 17 to 21 mass % Cr, and 3 to 6 mass % Al. The metal honeycomb flow-through body according to claim 2, wherein the average diameter of the micropores is 0.88 nm to 1.12 nm. 4. The metal honeycomb flow-through body according to claim 2, wherein the micropore volume (B) of the porous silica accounts for 90% or more of the total pore volume (A). The metal honeycomb flow-through body according to claim 2 , wherein the porous silica contains at least one kind of precious metal selected from platinum, palladium, and rhodium. The metal honeycomb flow-through body according to claim 6, wherein the content of the noble metal is 0.5 to 1.5 mass%. A method for manufacturing a metal honeycomb flow-through body in which porous silica is coated on the surface of a metal honeycomb,
(A2) preparing a slurry containing the porous silica, an inorganic sol liquid, and water;
(B2) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder;
(C2) A step of coating the slurry after the step (B2) on the cell surface of the metal honeycomb;
(D2) drying and firing the metal honeycomb after coating with the slurry;
The method for manufacturing a metal honeycomb flow-through body according to claim 2 or 3 , comprising: A method for manufacturing a metal honeycomb flow-through body, which is formed by coating a surface of a metal honeycomb with porous silica containing a precious metal catalyst, comprising:
(A3) preparing a slurry containing the porous silica, an inorganic sol liquid, and water;
(B3) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder;
(C3) A step of coating the slurry after the step (B3) on the cell surface of the metal honeycomb;
(D3) drying and firing the metal honeycomb after coating with the slurry to obtain a metal honeycomb flow body;
(E3) preparing a precious metal solution comprising a precious metal salt solution and water;
(F3) a step of immersing the metal honeycomb flow-through body in the precious metal liquid;
(G3) drying and firing the metal honeycomb flow-through body after immersion in the precious metal liquid;
The method for manufacturing a metal honeycomb flow-through body according to claim 2 or 3 , comprising: A method for manufacturing a metal honeycomb flow-through body, which is formed by coating a surface of a metal honeycomb with porous silica containing a precious metal catalyst, comprising:
(A4) preparing a slurry containing the porous silica, an inorganic sol liquid, a noble metal salt solution, and water;
(B4) adjusting the average particle size of the porous silica in the slurry to 1 to 10 μm using a wet grinder;
(C4) A step of coating the slurry after step (B4) on the cell surface of the metal honeycomb;
(D4) drying and firing the metal honeycomb after coating with the slurry;
The method for manufacturing a metal honeycomb flow-through body according to claim 2 or 3 , comprising: Heavy VOCs consisting of high-boiling point solvents with a boiling point of 150°C or higher,
Ester-based VOCs: hexyl acetate, heptyl acetate, octyl acetate, dodecyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, benzyl acetate, butyl butyrate, butyl benzoate, benzyl benzoate, dihydroterpineol acetate,
ether-based VOCs, such as anisole, phenetole, benzyl ethyl ether, diphenyl ether, dibenzyl ether, and ethylene glycol diethyl ether; and alcohol-based VOCs, such as n-octanol, n-decanol, n-dodecanol, α-terpineol, and dihydroterpineol;
4. The metal honeycomb flow-through body according to claim 2 or 3 , wherein at least one of the heavy VOCs is absorbed and concentrated by the porous silica, and the porous silica having absorbed and concentrated the heavy VOCs is purified and regenerated.