JP2008062164A - Adsorbent for organic compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new adsorbent which is excellent in pore utilizing efficiency, can adsorb/remove a harmful organic compound such as VOCs to be mixed in a contaminated sample containing the harmful organic compound of not only ordinary concentration but also extremely low concentration in high efficiency particularly in a liquid phase system, and exhibits high treatment efficiency. <P>SOLUTION: The adsorbent for the organic compound is hydrophobic silica obtained by hydrophobizing binary porous silica having two types of pores simultaneously of a continuous pore (a macro through-hole) having a nanometer-sized pore diameter and another pore (a nanopore), which is connected directly to the macro through-hole and has a nanometer-sized pore diameter, so that the surface of the hydrophobized binary porous silica is modified to have an organic functional group without destroying a binary-porous structure. The average diameter of the nanopore of the hydrophobized binary porous silica is 2-15 nm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a novel adsorbent for adsorbing organic compounds typified by volatile organic substances (VOCs). Specifically, the organic compound is composed of hydrophobic silica obtained by modifying the surface of silica having both macro-through pores having continuous pores in the micrometer region and nanopores in the nanometer region with an organic functional group. The present invention relates to an adsorbent having excellent adsorption characteristics.

  Various environmentally harmful organic compounds are contained in environmental water including waste water and environmental samples such as soil and air. In general, the initial concentration of these organic compounds in a large volume of environmental samples is low. However, while it is present in the environmental sample for a long period of time, the concentration is increased by in-vivo concentration and the like, which greatly affects the ecosystem. Therefore, it is a serious problem to leave these in a large amount of environmental samples even in a low concentration state.

  Among these highly harmful organic compounds, volatile organic compounds (VOCs) such as trichlorethylene, which are used in large quantities in various industrial processes, are substances that are pointed out to be carcinogenic. It has been leached into the soil, causing pollution. Furthermore, some of these VOCs are also used in construction materials and the like due to their antiseptic effects, and adverse effects on residents such as sick house syndrome are problematic. Polycyclic aromatic hydrocarbons such as benzopyrene are substances that are pointed out to be carcinogenic in exhaust gases from various combustion devices for household and industrial use, especially automobile exhaust. The presence of concentration is regarded as a problem. Since these substances have serious direct effects on the human body, they must be removed during the discharge process and removed from the environment.

  On the other hand, some of the steroid hormones and chemical substances derived from the living body or synthesized and discharged into the environment show a hormone-like action when taken into the living body. These chemical substances are called endocrine disrupting chemical substances and are known to have adverse effects on the reproductive function of animals even in extremely small amounts. In the water environment, they act at extremely small amounts of ppb to ppt levels. It has been reported.

  These steroid hormones and hormone-like active substances are industrially produced and used in a wide range of resin materials, plasticizers, surfactants, dyes and their raw materials, agricultural chemicals, chemical manufacturing processes and garbage. Since these substances are often derived from artificial emissions such as those unintentionally generated in the process of incineration, it is necessary to efficiently remove these substances in the process of emission.

  Generally, adsorbents that adsorb harmful organic compounds in various environmental samples include inorganic adsorbents such as zeolite and silica gel, carbon adsorbents typified by activated carbon, and organic synthetic polymer systems composed of synthetic polymers. Adsorbents are used. Among these adsorbents, inorganic adsorbents have been actively developed because of their chemical stability and characteristic pore structure. Among these, silica gel has been attracting attention as an adsorbent, and it has been proposed to use it for the purpose described above by making it hydrophobic (see Patent Document 1).

  When the hydrophobic silica gel is used as an adsorbent, the sample is usually filled in a cylindrical container such as an adsorption tower and made of a liquid or gas such as water mixed with harmful organic compounds (hereinafter referred to as a contaminated sample). )) To adsorb and remove harmful organic compounds.

  However, the hydrophobic silica gel has a small pore volume in the nanometer region that becomes an adsorption site, and as a result, the diffusion of the contaminated sample into the pore is slow and it is difficult to reach the deep part of the pore. When processing low-concentration contaminated samples, the concentration of harmful organic compounds in the pores does not occur sufficiently, so a large amount of adsorbent is required to give the processing equipment sufficient adsorption and removal performance. Thus, there is a problem that the adsorbent cost increases.

JP 2004 1970018 A

  Therefore, the present invention adsorbs the mixed organic compound with high efficiency even on a contaminated sample made of a liquid or gas such as water mixed with an organic compound, particularly a contaminated sample containing an extremely low concentration of an organic compound. An object is to provide an adsorbent that can be removed.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, there are two types of pores: continuous pores with a pore size in the micrometer region (macro-through holes) and pores with a nano-meter region pore diameter (nano-pores) directly connected to the macro-through holes Hydrophobic binary pore silica obtained by subjecting the binary pore silica particles having both pores to a hydrophobic treatment and modifying the silica surface with organic functional groups without destroying the binary pore structure. Shows that when the nanopore after hydrophobization is in the range of 2 to 15 nm, it exhibits extremely excellent performance in the adsorption of the organic compound in a contaminated sample, particularly a contaminated sample of a system using water as a fluid. The headline and the present invention were completed.

  That is, the present invention is a hydrophobic silica hydrophobized by modifying the surface of silica having both macro-through pores having continuous pores in the micrometer region and nanopores in the nanometer region with an organic functional group. The adsorbent for organic compounds is characterized in that the average diameter of the nanopores after hydrophobization is 2 to 15 nm.

  The present invention also provides an adsorbent of the following aspect.

  1) An adsorbent in which the hydrophobic silica has a degree of hydrophobicity (M value) in the range of 30 to 80.

  2) An adsorbent in which the macroscopic pores of the hydrophobic silica are in the range of 0.1 μm to 100 μm.

3) wherein is a suction subject adsorbent organic compound nanopores volume after adsorbent 4) hydrophobic volatile organics (VOCs) is 0.2cm ³ /g~1.5cm ³ / g, adsorbents that are within the volume of macro-holes is 0.3cm ³ /g~1.5cm ³ / g.

  The adsorbent for organic compounds of the present invention has a continuous through hole (macro through hole) having a pore size in the micrometer region and a pore (nano pore) having a pore size in the nanometer region directly connected to the macro through hole. In addition, it exhibits excellent adsorption characteristics in adsorbing organic compounds by being composed of hydrophobic dual pore silica whose surface is modified with an organic functional group to be hydrophobized. That is, in the use of adsorbents of harmful organic compounds such as VOCs, the macro through-holes increase the diffusion rate of the fluid containing the organic compound as the adsorbed material into the nanopores, and the nanopores as the adsorption sites. Can adsorb organic compounds at high efficiency. In particular, in a liquid phase system in which the fluid is water or the like, even in a contaminated sample in which the concentration of the organic compound is extremely low, it is possible to adsorb and remove the mixed harmful organic compound with high efficiency.

  Hereinafter, the present invention will be described in detail.

(Adsorbent for organic compounds)
The adsorbent for organic compounds of the present invention is a hydrophobic dual-pore silica having specific nanopores, and is directly connected to the macro through-hole caused by the original dual-pore silica and the macro through-hole. It has a structure that has both nanopores.

  In the adsorbent for organic compounds of the present invention, it is important that the average diameter of the nanopores after being hydrophobized is in the range of 2 to 15 nm, preferably 5 to 13 μm. That is, when the average diameter of the nanopores is less than 2 nm, the nanopores are small, so that the hydrophobization treatment cannot be performed uniformly to the depth of the pores. descend. Moreover, when the average diameter of nanopores exceeds 15 nm, a sufficient surface area for adsorption cannot be ensured, resulting in a decrease in the adsorption performance of the organic compound.

  In the adsorbent for organic compounds of the present invention, the degree of hydrophobicity is represented by the M value defined in detail later. Briefly, put the sample and methanol / water mixture in a glass beaker, stir, let stand for 12 hours, and then suck the sediment and liquid part to leave the suspended matter. This is a method of measuring the weight of the suspended matter after drying, changing the above methanol / water ratio, examining the amount of suspension, and determining the volume fraction (%) of methanol where the sample is 50% suspended. Value. This M value indicates that the larger the value, the higher the degree of hydrophobicity in the sample.

  In the adsorbent for organic compounds of the present invention, the degree of hydrophobicity is not particularly limited, but is preferably made hydrophobic so that the M value is 30 to 80. That is, when the M value is less than 30, since the affinity with the organic compound is weak, the adsorption of the organic compound tends to be insufficient. In addition, when the M value is higher than 80, the affinity with the organic compound is improved. For example, when the fluid of the contaminated sample is water, the diffusion of the contaminated sample into the nanopore becomes insufficient, and There is a tendency for adsorption to be insufficient.

  In the adsorbent for organic compounds of the present invention, the organic functional group for modifying silica is not particularly limited as long as it has hydrophobicity, and any known group may be used. Specific examples of the organic functional group include, for example, a linear or branched alkyl group such as a methyl group, an ethyl group, a propyl group, a hexyl group, and an octadecyl group; a cyclic group such as a cyclopentyl group and a cyclohexyl group. Alkyl group; alkenyl group such as vinyl group, allyl group, isopropenyl group, octadecynyl group; substituted or unsubstituted aryl group such as phenyl group, naphthyl group, tolyl group, styryl group, xylyl group, mesityl group; benzyl group, Examples thereof include an aralkyl group such as a phenethyl group, and a fluorinated alkyl group in which hydrogen of these hydrocarbon groups is optionally substituted with fluorine.

  The M value can be arbitrarily changed by selecting an organic functional group for modifying the surface, the amount thereof, and the like.

  The macro through-holes of silica constituting the adsorbent for organic compounds of the present invention are continuous through-holes having an average diameter in the micrometer region, and the average diameter is in the range of 0.1 to 100 μm. preferable. That is, when the average diameter of the macropores is less than 0.1 μm, the pressure loss when the contaminated sample is circulated increases, and it is difficult to sufficiently diffuse the contaminated sample into the nanopores. In addition, when the average diameter of the macro through-holes exceeds 100 μm, the contaminated sample does not diffuse into the nanopores, and the opportunity to pass increases, and the adsorption performance tends to decrease.

In the organic compound adsorbent for the present invention, the volume of nanopores after ^{hydrophobization,} 0.2cm ^{3 /g~1.5cm} 3 / ^g, the volume of macro-through holes 0.3 cm ³ / g to 1. It is preferable that it is 5 cm < ³ > / g. That is, in the nanopore, when the volume is less than 0.2 cm ³ / g, the amount of adsorption per unit weight tends to be low, and the adsorption ability tends to be insufficient. On the other hand, when the volume of the nanopore exceeds 1.5 cm ³ / g, the physical strength as an adsorbent is lowered, and the binary pore structure may not be retained.

Moreover, in the macro through-hole, when the volume after hydrophobization is less than 0.3 cm ³ / g, the function as a bypass becomes insufficient, the diffusion of the contaminated sample into the nanopore becomes insufficient, and the adsorption efficiency Tends to decrease. On the other hand, when the volume of the macro through-hole exceeds 0.5 cm ³ / g, the physical strength as an adsorbent is reduced, and the ratio of contaminated samples passing through the nanopores is increased, resulting in a reduction in processing efficiency. Tend to invite.

  The form of the adsorbent for organic compounds of the present invention is not particularly limited, and examples thereof include powdery bodies, granular bodies, granular bodies, and structural bodies. Moreover, as for the shape, the powdery body is often obtained by forming a lump-like gel body by the method described later and crushing it, and is generally indefinite. In addition, the granular body and the granular body are generally indefinite and spherical. Of these, a spherical shape is particularly preferable. The granular and granular amorphous particles can be obtained by pulverizing the massive gel, and the granular and granular spherical particles or structures can be obtained by the method described below. It can be obtained by generating a gel body to have the above shape.

(Application of adsorbents for organic compounds to adsorption of contaminated samples)
The adsorbent for organic compounds of the present invention is an adsorbent that efficiently adsorbs hydrophobic substances, particularly harmful organic compounds, and easily desorbs them. Therefore, it can be beneficially used for all applications including a step of adsorbing a hydrophobic substance. For example, it is possible to remove harmful organic compounds by filling a fixed bed type, moving bed type, fluidized bed type or suspension tank type processing apparatus according to the shape of the filler and bringing it into contact with a contaminated sample. .
Moreover, the distribution method and distribution conditions of the contaminated sample at the time of processing may be appropriately selected depending on the type of apparatus and the type of the removal target. However, in the liquid phase system, the flow rate of the contaminated sample with respect to the amount of the adsorbent, and in the gas phase system, the treatment temperature and the pressure in the apparatus strongly affect the adsorption performance, so optimization is necessary.
On the other hand, the regeneration of the adsorbent is carried out in a liquid phase system by using, for example, a solvent such as dichloromethane, hexane, acetone, toluene, chloroform, methanol, acetonitrile, polychlorinated trifluoroethylene as a desorbing solvent. Examples thereof include a method for desorbing a compound, a method using acid treatment or alkali treatment, and a method using some of these methods in combination. In the gas phase system, a method of desorbing harmful organic compounds by changing the pressure (pressure swing adsorption: PSA, etc.) can be suitably used.

(Method for producing adsorbent for organic compounds)
The adsorbent for organic compounds of the present invention has continuous pores (macro-through holes) having a pore size in the micrometer region, and pores (nano-pores) in the nanometer region directly connected to the macro through-holes. ) And the two types of pores can be obtained by subjecting the silica surface to modification with organic functional groups without destroying the binary pore structure. .

  Although the manufacturing method of hydrophobic binary pore silica which is an adsorbent for organic compounds of the present invention is not particularly limited, it can be typically manufactured by the following method.

1. Method for Preparing Hydrophobic Treatment Base In the present invention, as the hydrophobization treatment base, continuous pores (macro-through holes) having a pore diameter in the micrometer region and nanometer-region fine pores directly connected to the macro-through holes are used. Dual-pore silica having two types of pores, a pore having a pore size (nanopore), is used.

  The binary porous silica which is the active ingredient is obtained by a method utilizing phase separation, for example, a method described in JP-A-3-8729 using silicon alkoxide, or WO2002 / 85785 using water glass. It can be produced by the method described.

  Specifically, a sol solution containing a silica source, a water-soluble polymer, and an acid catalyst is gelled and fixed in a phase-separation transient structure to thereby fix nanopores and macrofine cells having a structure in which the silica skeleton is intertwined. A gel body in which pores are formed can be obtained, and then the gel body can be produced by aging in a basic solvent as necessary, followed by drying and baking.

  As the silica source, silicon alkoxides such as methoxysilane and ethoxysilane, and water glass are used without particular limitation. Among them, water glass is generally a concentrated aqueous solution of alkali silicate, and the type and concentration thereof are not particularly limited, but JIS standard water glass sodium silicate JIS3 or equivalent is handled as a silica source. easy.

  In order to produce a wet gel by causing phase separation and gelation at the same time, a means for promoting gelation in the presence of a water-soluble polymer and an acid catalyst in a solution containing a silica source is effectively used.

  The water-soluble polymer is an organic polymer that can form a solution having an appropriate concentration when water is used as a solvent, and can be dissolved uniformly in a solution containing a silica source. The For example, sodium or potassium salt of polystyrene sulfonic acid which is a polymer metal salt, polyacrylic acid which is a polymer acid and dissociates to become a polyanion, polyacrylamine or polyethyleneimine which is a polymer base and generates a polycation Polyethylene oxide which is a neutral polymer and has an ether bond in the main chain, polyvinyl alcohol having a hydroxyl group in the side chain, or polyvinyl pyrrolidone having a carbonyl group.

  Of these, polyacrylic acid and polyvinyl alcohol are preferred because they are easy to handle. Polyacrylic acid having a molecular weight of 15,000 to 300,000, preferably 20,000 to 150,000 is suitable.

  The acid catalyst serves as a catalyst for the hydrolysis reaction of the silica source and is added to promote gelation. Usually, a mineral acid such as sulfuric acid, hydrochloric acid, nitric acid, or an organic acid is used. The concentration of the acid catalyst in the reaction system is in the range of 0.1 to 5 mol / L, preferably 1 to 4 mol / L.

  In the method for producing the dual pore silica, the sol solution is prepared by using a polar solvent such as water as a solvent and containing a predetermined amount of a silica source, a water-soluble polymer, and an acid catalyst. Moreover, the method of fixing the transient structure of the phase separation of the sol solution by gelation is to put the sol solution in a closed container or the like, and at 0 to 80 ° C., preferably at 10 to 30 ° C. for 10 minutes to 1 week, Preferably, it can be carried out by leaving for 1 to 24 hours.

  Here, the phase separation starts gradually by allowing the sol solution to stand. Here, by controlling the gelation time by adjusting the amount of the acid catalyst, the standing temperature, and the standing time, the phase separation is completed. The transient state of the phase separation, that is, the transient structure of phase separation, is fixed by gelation. In such a transient structure, a silica polymer and a solvent phase are mixed together in an intertwined state, whereby a gel body having nanopores and macropores formed of a structure in which a silica skeleton is intertwined is formed. It is formed.

  In addition, the mesopore diameter can be controlled by subjecting the wet gel prepared by the above method to aging treatment. This aging treatment is performed by impregnating the wet gel after washing with a basic solvent and leaving it to stand. This aging treatment is preferably performed in a basic aqueous solution of 0.01 to 10 N in a range of 0 to 80 ° C. The treatment time for aging is usually carried out in the range of 1 hour to 3 days, and can be determined by appropriately selecting the desired average pore diameter of the nanopores.

  The conditions for these aging treatments may be carried out by obtaining the time required for obtaining the desired average pore diameter of the nanopores by experiments in advance and selecting them appropriately. In addition, since the nanopore diameter may be reduced by hydrophobization treatment, it is possible to control the nanopore diameter after hydrophobization by calculating the reduced amount and preparing the nanopore of the silica raw material It becomes.

  Further, the control of the macropore diameter can be appropriately performed according to a known method. For example, it can be controlled by changing the composition weight ratio of the silica source or changing the standing temperature of the sol solution.

  In the above method for obtaining a gel body from a sol solution, when water glass is used as the silica source, it is necessary to wash the prepared wet gel before drying. This is because when the wet gel from water glass is dried as it is, the gel collapses as the drying proceeds. Therefore, it is necessary to remove the alkali metal salt by washing to remove alkali metal such as sodium in the wet gel before drying.

  Washing is performed by immersing the gel in water and allowing the gel having a thickness of about 1 cm to stand at room temperature for 12 hours or more. However, if the gel is thinner than this, the gel can be washed in a shorter time.

  The gel after washing with water is dried by leaving it at 30 to 80 ° C. for several hours to several tens of hours. After drying, firing is performed to remove organic substances and maintain the macro through-hole structure. The firing temperature is preferably 500 to 1100 ° C.

2. Hydrophobic treatment method In the present invention, the surface of the silica is modified with an organic functional group to be hydrophobized by subjecting the binary pore silica prepared based on the above-described method to a surface treatment with a known treatment agent. Hydrophobic binary porous silica is obtained. The method of hydrophobizing the two-pore silica silica that is the base material by the surface treatment is not particularly limited, and a known surface treatment method may be adopted. Specifically, a silane coupling agent, a titanate coupling agent, a method of treating with silicone oil, cyclic siloxane, hexaalkyldisilazane, or a hydrophobized silica obtained by the above-mentioned method, a styrenic or Examples thereof include a method of coating a cross-linked polymer typified by acrylic.

  Of these, treatment with a silane coupling agent is the most common. Examples of typical silane coupling agents include linear or branched alkyl groups such as methyl group, ethyl group, propyl group, hexyl group and octadecyl group; cyclic alkyl groups such as cyclopentyl group and cyclohexyl group; vinyl group, Alkenyl groups such as allyl group, isopropenyl group and octadecynyl group; substituted or unsubstituted aryl groups such as phenyl group, naphthyl group, tolyl group, styryl group, xylyl group and mesityl group; aralkyl groups such as benzyl group and phenethyl group And alkoxysilanes or chlorosilanes having a fluorinated alkyl group in which hydrogen of these hydrocarbon groups is optionally substituted with fluorine.

When the hydrophobization treatment is performed using the silane coupling agent, it is preferable to use the method described in JP-A 2006-96641. In this method, first, silica is put into a reaction vessel, dried at 120 ° C. to 180 ° C. in advance, and the inside of the vessel is replaced with an inert gas such as N ₂ gas and sealed. Subsequently, a silane coupling agent mist transported with a carrier gas such as N ₂ gas is allowed to flow through and contact with silica in a stirred state or fluidized bed, and heated at 120 ° C. to 300 ° C. for 5 minutes to 3 hours. Moreover, the hydrophobization process by hexaalkyldisilazane is also known widely. Specific examples of hexaalkyldisilazane used in the treatment include the following general formula:

(In the above formula, R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently an alkyl group having 1 to 18 carbon atoms.)
The thing shown by is mentioned. In the above formula, examples of the alkyl group represented by R ^{2 to} R ⁷ include the same groups as those exemplified as R ¹ in the cyclic siloxane. In order to obtain high processing efficiency, the R ^{2 to} R ⁷ are preferably a linear alkyl group having 1 to 3 carbon atoms. R ^{2 to} R ⁷ may be different from each other, but are preferably the same group from the standpoint of availability and surface treatment efficiency.

  Specific examples of particularly preferred hexaalkyldisilazane include hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane and the like.

  When the treatment with hexaalkyldisilazane is performed, it is preferable to employ the methods described in Japanese Patent No. 2886037 and the above-mentioned Japanese Patent No. 2886105. In this method, powder of inorganic particles is introduced into a container, and the container is sealed so that the partial pressure of hexamethyldisilazane is about 25 to 150 kPa in an inert gas atmosphere at a temperature of about 200 to 300 ° C. And is maintained for a certain period of time, preferably about 0.5 to 2 hours. At this time, water vapor is present in the container at a partial pressure of about 30 to 100 kPa, and a basic gas such as ammonia is allowed to coexist at a partial pressure of about 10 to 100 kPa as necessary.

  It is also possible to perform a hydrophobic treatment with a cyclic siloxane. Specific examples of the cyclic siloxane used include the following general formula in that the strain is large and the cleavage is easy and the reactivity is high.

(Wherein R ¹ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, a hydrogen atom or a hydroxyl group, Me is a methyl group, and n is an integer of 3 to 6)
It is preferable to treat with a cyclic siloxane represented by

In the above formula, R ¹ is a hydrocarbon group having 1 to 18 carbon atoms. The hydrocarbon group is not particularly limited as long as it has 1 to 18 carbon atoms, and may be any known group. Specific examples of the hydrocarbon group include straight chain or branched alkyl groups having 1 to 18 carbon atoms such as a methyl group, an ethyl group, a propyl group, a hexyl group, and an octadecyl group, a carbon such as a cyclopentyl group and a cyclohexyl group. A cyclic alkyl group having 4 to 6 carbon atoms; an alkenyl group having 2 to 18 carbon atoms such as vinyl group, allyl group, isopropenyl group, and octadecynyl group; phenyl group, naphthyl group, tolyl group, styryl group, xylyl group, mesityl group, etc. A substituted or unsubstituted aryl group having 6 to 18 carbon atoms; an aralkyl group having 7 to 9 carbon atoms such as a benzyl group and a phenethyl group;

  Among the hydrocarbon groups, a linear alkyl group having 1 to 3 carbon atoms, a phenyl group, and a phenethyl group are particularly preferable. Moreover, in said formula, n is 3-6, Most preferably, it is 3-4.

  Specific examples of such cyclic siloxanes include octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, tetramethyltetraphenylcyclotetrasiloxane, trimethyltriphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, trimethyltrivinyl. Examples thereof include cyclotrisiloxane, tetramethylcyclotetrasiloxane, and trimethylcyclotrisiloxane.

  Examples of the method of treating with cyclic siloxane include the following methods. First, in an inert gas atmosphere such as nitrogen or argon, while stirring the particles with a high-speed stirring device such as a Henschel mixer, cyclic siloxane or the like is added in a gaseous or liquid state thereto, and a predetermined temperature is set in a sealed reaction system. It can manufacture by heating to. The method of adding cyclic siloxane or the like to the particles may be either liquid or gaseous, and when added in liquid form, it may be added dropwise or by spraying. It is particularly preferable to add it in the form of a gas from the viewpoint that it can be uniformly processed. The heating temperature is not particularly limited as long as the particle surface can be hydrophobized by cyclic siloxane or the like, but in general, it is preferably not less than the boiling point of the cyclic siloxane to be used, and usually about 100 to 300 ° C. It is. In addition, the stirring speed at the time of stirring is not particularly limited, but if the stirring speed is too slow, the stirring efficiency is low, and heating unevenness may occur. Since the particles may be finely pulverized by contact or the like, and the binary pore structure may be destroyed, about 50 to 500 rpm is desirable.

  In addition, for the purpose of improving the degree of hydrophobicity to silica whose surface has been hydrophobized by the above method, a crosslinkable monomer and a polymerization initiator are arbitrarily added to a polymerizable monomer typified by a styrene-based or acrylic polymer. It is also possible to coat the surface of the crosslinked copolymer by adsorbing the treatment liquid mixed at a ratio of 1 to the silica surface and polymerizing it by heating.

  Specific examples of polymerizable monomers, crosslinkable monomers, and polymerization initiators that can be used include the following.

  i) Polymerizable monomer; monofunctional aromatic such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, p-tert-butylstyrene, chloromethylstyrene, p-chlorostyrene, vinylnaphthalene Vinyl monomers. Methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, tritridecyl (meth) acrylate, (meth) acrylic acid Benzyl, phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxy (meth) acrylate Monofunctional non-fluorine (meth) acrylic monomers such as ethyl, diacetone methacrylamide, methacrylonitrile, methacrylolein and the like. Perfluoroalkyl esters of (meth) acrylic acid such as trifluoromethyl (meth) acrylate, pentafluoroethyl (meth) acrylate, perfluorobutyl (meth) acrylate, and perfluoro-2-ethylhexyl (meth) acrylate. Vinyl acetate, methyl vinyl ketone, vinyl pyrrolidone, ethyl vinyl ether, divinyl sulfone, diallyl phthalate, etc.

  ii) Crosslinkable monomers; aromatic vinyl monomers such as polyfunctional aromatic vinyl compounds such as divinylbenzene, divinylbiphenyl, trivinylbenzene, and divinylnaphthalene. Ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylol methanetri (meta ) Polyfunctional non-fluorinated (meth) acrylic monomers such as acrylate, tetramethylolmethanetetra (meth) acrylate, methylenebis (meth) acrylamide, hexamethylenedi (meth) acrylamide and the like.

  iii) polymerization initiator: octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxylaurate, t -Organic peroxides such as hexyl peroxybenzoate and di-t-butyl peroxide, 2,2, -azobisisobutyronitrile and 2,2, -azobis- (2,4, -dimethylvaleronitrile Azobis-based polymerization initiators such as

As a method for coating the surface with the cross-linked copolymer, for example, the method disclosed in JP-A-2005-60668 is preferably employed. In this method, hydrophobized silica is put into a reaction vessel, dried at 120 ° C. to 180 ° C. in advance, and the inside of the vessel is replaced with an inert gas such as N ₂ gas and sealed. Subsequently, the mist of the treatment liquid in which the polymerizable monomer, the crosslinkable monomer, and the polymerization initiator, which are conveyed by a carrier gas such as N ₂ gas, are mixed in an arbitrary ratio is mixed with the hydrophobic state of the fluidized bed. This is a method in which an arbitrary amount is sprayed onto silica, the treatment liquid is adsorbed on the surface, and the mixture is heated at 50 ° C. to 180 ° C. for 30 minutes to 3 hours. However, when this method is used, the nanopores may be clogged even if the amount of the treatment liquid is small. Is preferred.

  Each treatment method may be repeated, and different treatment methods may be performed in multiple stages as long as the surface treatment layer is not altered by heat or the like.

  EXAMPLES Hereinafter, although an Example is shown and this invention is shown more concretely, this invention is not restrict | limited at all by these Examples.

(Measurement of macropore size, nanopore size, and pore volume)
A measurement sample dried in advance at 120 ° C. for 12 hours was measured for the pore size of the macropores, the pore size of the nanopores, and the pore volume by mercury porosimetry (manufactured by Cantachrome, POREMASTER-60). In the pore size distribution obtained by measurement, the maximum peak pore size appearing in the micrometer region was defined as the macro pore size. In the pore size distribution obtained by measurement, the maximum peak pore size appearing in the nanometer region was defined as the pore size of the nanopore. In the pore size distribution obtained by the measurement, the pore volume was determined by integrating all the differential values with respect to the pore size obtained in the measurement range.

(Measurement of hydrophobicity (M value))
In a 200 ml beaker made of glass, 0.5 g of a sample for measurement and 100 cm ³ of a methanol / water mixed solution are put in a magnetic stirrer using a bar-shaped Teflon (trade name: manufactured by DuPont) coat stirrer having a length of 20 mm and a diameter of 7 mm. The mixture was stirred at a rotational speed of 500 rpm for 30 minutes and allowed to stand for 10 hours, and then the sediment and liquid part were sucked to leave a floating part. It dried at 120 degreeC for 6 hours, and measured the weight of the floating part. The amount of floating was examined by changing the methanol / water ratio, and the methanol concentration where the measurement sample floated 50% was determined. The volume fraction (%) of methanol at this time was taken as an M value and used as an index representing the degree of hydrophobicity.

(Measurement of VOCs recovery rate)
Chloroform was selected as VOCs, and the recovery rate was measured using the sample as an adsorbent. The measurement was performed by the following method. A glass chromatograph tube (diameter 20 mm) was filled with 5 g of a sample for measurement, and the top and bottom were fixed with quartz wool. Then, 1000 cm ³ of chloroform-containing water having a predetermined concentration was circulated as a contaminated sample. Thereafter, the chloroform concentration of the contaminated sample after treatment was quantified by a gas chromatography mass spectrometer (GC / MS). Here, the recovery rate of chloroform was calculated by the following formula.

(Measurement of average particle size)
The particle size of the sample was measured with a laser diffraction / scattering particle size distribution analyzer (LS-230, manufactured by Coulter). The dispersion for measurement was prepared in accordance with “Particle Measurement Technology” (powder engineering society, 1994, published by Nikkan Kogyosha, page 23). For the calculation of the average particle diameter, the particle diameter at which the weight integrated distribution under the sieve is 50% was taken as the average particle diameter.

(Measurement of carbon content)
The carbon content of the hydrophobic silica was measured by heating the sample to 1350 ° C. in an oxygen atmosphere using a trace carbon analyzer (EMIA-511 type manufactured by Horiba, Ltd.). The amount of carbon obtained by this measurement is shown by converting per 1 g of the sample. As a pretreatment for measuring the coating amount, the sample was heated at 80 ° C. and the system was depressurized to remove moisture adsorbed in the air, and then the carbon content in the sample was determined.

Example 1
In the presence of polyacrylic acid having an average molecular weight of 25,000 (hereinafter referred to as HPAA), biporous silica was produced from water glass (No. 3 silica). The charged composition was water: concentrated nitric acid: HPAA: water glass = 97: 37: 6.5: 55 by weight ratio, and stirred at room temperature to obtain a uniform sol solution. At this time, the specific gravity of the sol solution was 1.2.

  After stirring, the sol solution was transferred to a plastic container and allowed to stand at 35 ° C. for 1 day to gel. Thereafter, the wet gel was washed with water to remove sodium, then immersed in 0.1 N ammonia and aged at 50 ° C. for 1 day. Then, it dried at 50 degreeC and baked at 600 degreeC for 2 hours. The calcined sample was pulverized with a mortar and sieved to obtain a dual pore silica powder.

200 g of the above-mentioned dual pore silica powder was charged into a stainless steel autoclave having a capacity of 1000 cm ³ . After the inside of the autoclave was replaced with nitrogen gas, 20 g of autoke, 1,3,5,7-octamethylcyclotetrasiloxane (hereinafter referred to as D4) was atomized with a two-fluid nozzle and sprayed onto the silica powder. It was. The autoclave was then sealed and heated at 280 ° C. for 1 hour. Subsequently, the system was depressurized while being heated, and unreacted D4 was removed to obtain a hydrophobic dual pore silica powder.

  The obtained hydrophobic binary porous silica powder had a nanopore diameter of 7.3 nm. Other physical properties are shown in Table 1. Moreover, the pore distribution measured by the mercury intrusion method is shown in FIG. 1, and an electron micrograph is shown in FIG. Table 2 shows the results of treating a chloroform-contaminated sample with a concentration of 1 ppm and the results of treating a chloroform-contaminated sample with a concentration of 100 ppm in the recovery rate of chloroform measured by the “measurement of recovery rate of VOCs”. Table 3 shows.

Example 2
Hydrophobic binary porous silica powder was obtained by the same composition and method as in Example 1 except that the aging step was performed using 1 N ammonia for the purpose of expanding the nanopore diameter.

  The obtained hydrophobic binary porous silica powder had a nanopore diameter of 12.1 nm. Other physical properties are shown in Table 1. Tables 2 and 3 show the chloroform recovery rates measured by the above-mentioned “Measurement of VOCs recovery rate”.

Comparative Example 1
A binary porous silica powder was obtained by the same composition and method as in Example 1 except that the hydrophobic treatment was not performed. Table 1 shows the physical properties of the obtained binary porous silica powder. Moreover, the pore distribution measured by the mercury intrusion method is shown in FIG. Tables 2 and 3 show the chloroform recovery rates measured by the above-mentioned “Measurement of VOCs recovery rate”.

Comparative Example 2
Hydrophobized silica powder was obtained in the same manner as in Experimental Example 1 except that a commercially available silica gel (manufactured by Fuji Silysia Co., Ltd., trade name: CARiACT Q-10; hereinafter referred to as Q-10) was used. Table 1 shows the physical properties of the obtained powder. Tables 2 and 3 show the chloroform recovery rates measured by the above-mentioned “Measurement of VOCs recovery rate”.

Comparative Example 3
As a measurement sample, Q-10 was used as it was. Table 1 shows the physical properties of Q-10. Tables 2 and 3 show the chloroform recovery rates measured by the above-mentioned “Measurement of VOCs recovery rate”.

  From the carbon content and the degree of hydrophobicity in Table 1, it can be seen that the surface of the silica is modified with an organic functional group and has hydrophobicity by performing surface treatment. From FIG. 1 and FIG. 3, the hydrophobic dual pore silica obtained by the present invention is a binary having both a micrometer region through hole (macro through hole) and a nanometer region pore (nanopore). It turns out that it has a pore structure.

  From the results of Table 2 and Table 3, the recovery rate of chloroform of hydrophobic dual pore silica (Examples 1 and 2) having nanopores after hydrophobization of several nanometers to several tens of nanometers is shown as hydrophilic samples ( It can be seen that it is very high compared to Comparative Example 1). In addition, the hydrophobized binary pore silica (Examples 1 and 2) has a higher chloroform recovery rate than the commercially available hydrophobized silica gel (Comparative Example 2). In the low-concentration contaminated sample, a significant difference was observed in the recovery rates of both. Therefore, it can be seen that the hydrophobic dual pore silica has very high performance as an adsorbent for organic compounds such as VOCs. This is because the affinity between the hydrophobic surface and the organic compound is high and it is in a state of being easily adsorbed, and the presence of macro through-holes improves the utilization efficiency of nanopores, which are adsorption sites, and has high adsorption capacity. It is thought that was expressed.

Hydrophobic binary pore silica and pore distribution in binary pore silica Electron micrograph of hydrophobic dual pore silica

Claims (5)

Hydrophobic silica, which has been made hydrophobic by modifying the surface of silica having both macro-through pores with continuous micropores in the micrometer region and nanopores in the nanometer region with an organic functional group. An adsorbent for organic compounds, wherein the average diameter of the nanopores is 2 to 15 nm. The adsorbent according to claim 1, wherein the hydrophobic silica has a degree of hydrophobicity (M value) of 30 to 80. The adsorbent according to claim 1, wherein the macro through-hole is 0.1 μm to 100 μm. The adsorbent according to claim 1, wherein the organic compound is a volatile organic substance (VOCs). Nanopores volume 0.2cm ³ /g~1.5cm ³ / g after hydrophobization, the volume of macro-through hole according to claim 1, wherein a 0.3cm ³ /g~1.5cm ³ / g Adsorbent.

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