JP2011000548A - Gas adsorbing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas adsorbing agent which is incombustible and excellent in adsorptivity, in which an adsorbed gas molecule is diffused easily, which can be regenerated excellently by purging/desorbing the gas adsorbed on the gas adsorbing agent by using an inert gas under normal pressure or in vacuum without heating the gas-adsorbed gas adsorbing agent, the absorption/desorption capacity of which are restrained from being deteriorated even in the coexistence of steam and consequently which can be applied to various purposes.SOLUTION: The gas adsorbing agent characterized in that ≥85% of the amount of a volatile organic compound (VOC) gas to be adsorbed can be desorbed is obtained, in porous silica which has connected micropores and mesopores in a primary particle thereof, by high temperature aging at synthesis or heat treatment after synthesis to enhance the hydrophobicity of the surfaces of these pores, and by circulating the inert gas at ≤35°C under normal pressure, after the VOC gas breaks and reaches a saturated/adsorbed state in a dynamic breakthrough curve measurement of the VOC gas.

Description

  The present invention is a gas that utilizes adsorption / desorption ability to a volatile organic compound (VOC) gas based on a binary pore structure caused by micropores and mesopores in which the pore surfaces present in primary particles are hydrophobized. More particularly, the present invention relates to a gas adsorbent having a high desorption ability under a normal pressure inert gas purge by controlling the chemical properties of the pore surface.

  In recent years, volatile organic compound (VOC) gas has been closed up as an environmental pollutant, and emission reduction measures have become an urgent issue (hereinafter, volatile organic compound (VOC) gas is simply abbreviated as “VOC”). ). In particular, the 1999 Act on the Promotion of Improvements in Management and Management of Specific Chemical Substances to the Environment (PRTR Law) was promulgated, and the handling amount and discharge of hazardous chemical substances including VOCs at each business site. Volume reporting is required. Furthermore, it is considered to regulate the VOC emission, and the emission control technology has become an urgent issue.

For this VOC removal process, it is necessary to select a suitable one depending on the target substance and concentration range, but it is generally divided into two methods, the combustion method and the adsorption method. Combustion and catalytic combustion are well known.
In recent years, the adsorption method has attracted attention in place of the combustion method from the viewpoint of the global warming problem associated with CO ₂ emissions. The adsorption method uses an adsorbent such as activated carbon, silica gel, or zeolite to remove VOC in exhaust gas.
The main feature of the adsorption method is that it can recover and reuse the VOC that is desorbed during regeneration of the adsorbent. The regeneration method uses heat (TSA), pressure reduction (PSA), and a combination of both. There are other methods. In general, since the regeneration operation is performed while alternately switching between adsorption and regeneration, the adsorbent is required to be able to be quickly desorbed at the same time as having a high adsorption capacity in constructing a VOC removal and recovery system.

As described above, the adsorbent used for VOC removal and adsorption / recovery is activated carbon, silica gel, zeolite, and the like.
Activated charcoal includes granular and fibrous materials, and has excellent adsorption performance. Generally, it is used in the case of large air volume and low concentration, but it is flammable, and depending on the type of VOC, Since different catalysis occurs, care must be taken in its use. In particular, when a ketone or aldehyde-based substance is used as a target, there is a risk of ignition due to heat generated by oxidation / polymerization at a high concentration. In addition, TSA is generally applied for regeneration in a steam distribution system. Therefore, it is unsuitable for recovery of water-soluble VOC, and finally, it is necessary to consider wastewater treatment.
As described above, activated carbon is inexpensive and is the most commonly used adsorbent, but there are difficulties in combustibility, heat of adsorption (heat generation), regeneration cost, etc. Depending on the type of VOC to be used, silica gel and zeolite are It is used as an alternative (Non-Patent Documents 1, 2, 3, etc.).

Silica gel is suitable for small air volumes and high concentrations, and can be regenerated by the PSA method. Also, zeolite has a higher adsorption capacity than silica gel at low concentrations, and the outlet concentration is severely regulated. It is effective and has an advantage not available with activated carbon such that both TSA and PSA can be used in the regeneration method.
However, in the case of silica gel, the adsorption ability is lower than that of activated carbon or zeolite, and there is a problem that the pore surface must be chemically modified, in particular, in order to improve the water vapor property. Furthermore, the adsorption capacity increases as the micropore volume increases, but the desorption capacity decreases, and the desorption process requires a heating operation in addition to vacuum and purging with an inert gas. Has become a major issue.

  In addition, in the case of zeolite, since the pore diameter is 1 nm or less, it is impossible to adsorb large molecules, and therefore, it is difficult to apply to the removal of high boiling point substances. In addition, a heating operation is required for desorption, and the development of a hydrophobic zeolite with better desorption characteristics is expected.

  As described above, current VOC adsorbents have their merits and demerits. To overcome various problems associated with future gas regulations, especially VOC regulations, and to realize removal, recovery and reuse of VOCs, There is a strong demand for the development of a VOC adsorbent that is easy to regenerate, in addition to its high adsorbability in the presence of coexistence.

The inventors of the present invention have described that a fibrous silica porous body synthesized using an inexpensive alkali silicate as a silica source and using the self-ordering ability of a non-toxic nonionic surfactant has mesopores and micropores. The unique adsorption / desorption phenomenon due to the binary pore structure of the above was recognized, and it was found to be particularly effective as an adsorbent for toluene, which is a VOC having a high use ratio (Patent Document 1). Furthermore, continuous research and development have been carried out, and it has been clarified that the fibrous silica porous material exhibits physical adsorption ability with respect to benzene or trichlorethylene (Non-patent Document 4).
Therefore, VOC has various gaseous substances having different molecular diameters, molecular structures, and physicochemical properties. However, as with commercial adsorbents such as activated carbon, zeolite, and silica gel, It is clear that the fibrous silica porous material can be used not only as toluene but also as a wide variety of gas adsorbents (Non-patent Documents 5 and 6).

  Specifically, fibrous silica having a binary pore structure, which is the gas adsorbent of Patent Document 1, exhibits a unique VOC adsorption ability, and is compared with silica gel having various pore characteristics. At the same time, even if the pore volume is about 1/2, it has the same adsorption capacity, and at the same time, after adsorption of toluene gas, 50% to 97% or more of the total adsorption is desorbed under an inert gas flow at 40 ° C. It was also clarified that "it is possible to desorb 98% or more of the total adsorbed amount under an inert gas flow at 60 ° C after adsorption of toluene gas".

Japanese Patent No. 4061408 Japanese Patent No. 4099811 JP 2004-182492 A JP 2004-143026 A JP 2006-151798 A JP 2006-151799 A JP 2007-204288 A Japanese Patent Application No. 2009-078051 Japanese Patent Application No. 2009-079589

PETROTECH, 2001, Vol. 24, No. 2, pp.145 Chemical equipment, October 2002 issue, special feature article "Latest trends in adsorbent technology and application development") Separate volume of September 2002 issue of Chemical Equipment Kosuge, K. Kubo, S. Kikukawa, N. Takemori, M. Langmuir, 2007, 23, 3095. Properties of porous materials and their applied technology, 1999, Fuji Techno System Co., Ltd. Porous adsorbent handbook, 2005, Fuji Techno System Co., Ltd.

However, in the fibrous silica having the above-mentioned binary pore structure, in order to achieve a desorption rate of 85% to 90% or more, a process of heating at a temperature higher than the adsorption temperature is indispensable. There has been a problem that it cannot be achieved by normal pressure inert gas purge. Furthermore, no evaluation has been made regarding the relationship between the chemical properties of the pore surface depending on the synthesis conditions of the fibrous silica porous material and the heat treatment temperature of the composite, and the VOC adsorption / desorption ability in the presence or absence of water vapor. It was.
In order to develop a system that can further promote the energy saving of VOC removal and adsorption / recovery treatment equipment, it is essential to develop an adsorbent that not only has a high adsorption capacity but also surpasses the conventional adsorbent desorption performance. . In addition, there are many different types of VOC use industries, and VOCs to be processed are often mixed gases with water vapor, and it is extremely important to develop a silica-based adsorbent that can suppress the decrease in VOC adsorption / desorption ability in the presence of water vapor. It is. That is, there is no significant difference in adsorption / desorption ability depending on the presence or absence of water vapor, and further, no heating operation is required in the desorption / regeneration process, and it is efficient by inert gas purging at normal pressure or vacuum near normal temperature. The development of adsorbents that can be desorbed directly will lead to the development of energy-saving VOC adsorption / recovery treatment equipment in the future.

  The present invention has been made in view of such circumstances, and is nonflammable, excellent in adsorption capacity, easy to diffuse adsorbed gas molecules, and particularly inert under non-heated atmospheric pressure or vacuum. An object of the present invention is to provide a gas adsorbent that is applicable to a wide range of applications by being excellent in desorption / regeneration ability by gas purge and suppressing a decrease in adsorption / desorption ability even in the presence of water vapor.

  The inventors of the present invention have prepared a porous silica porous material synthesized using an inexpensive alkali silicate as a silica source and using the self-ordering ability of a non-toxic nonionic surfactant, having mesopores and micropores. Based on the unique VOC adsorption / desorption behavior that occurs due to the organic linkage structure, we are conducting consistent research with the aim of developing a silica adsorbent with even better desorption ability. That is, the fibrous silica porous material produced by the synthesis method of Patent Document 2 has high adsorption ability and desorption ability based on the organic connection structure of mesopores and micropores, but particularly from the viewpoint of desorption ability. Sufficient performance was not obtained.

The inventors of the present invention have developed a porous silica body whose shape is controlled, including a novel fibrous silica porous body, and published several patents regarding its production method and application (Patent Documents 3, 4, 5, 6, 7) and two more patent applications (Patent Documents 8 and 9). In these patent documents, it is extremely effective for development of an efficient production method of a new fibrous or rod-shaped silica to be aged at a higher temperature after stirring the raw material solution for a certain period of time. It was clarified that it is excellent as control of
However, as described above, the VOC adsorption / desorption characteristic evaluation is limited to the fibrous or rod-shaped silica porous body synthesized only by the stirring process at relatively low temperatures in Patent Documents 1 and 2.

The present inventors have evaluated the VOC adsorption / desorption characteristics of the fibrous silica porous material obtained by the aging method under hydrothermal conditions and the heated product and the VOC adsorption / desorption characteristics in the presence or absence of water vapor so far. Found a VOC desorption effect that was completely unexpected and succeeded in developing a new VOC adsorbent.
That is, the pore surface of the fibrous silica porous material obtained by aging under hydrothermal conditions is more hydrophobic even with the heat-treated product at 600 ° C. than that obtained only by the low temperature stirring step. It was revealed that once adsorbed VOC was desorbed by approximately 90% or more by inert gas purge under non-heating conditions, and the desorption rate reached 65% to approximately 90% even when adsorbed in the presence of water vapor. In the fibrous silica porous material obtained by low-temperature stirring, the desorption rate is about 80% at the maximum, and when water vapor coexists, it decreases to 50%.
There are many studies on the modification of the silica surface under hydrothermal conditions, but there has been no report on the pore surface and VOC adsorption / desorption characteristics adjusted by the synthesis conditions of the silica mesoporous material.

In the present invention, as described in detail in the examples, the properties of the pore surface formed by heating and removing the surfactant filled in the pores are sensitive to hydrothermal synthesis conditions, and the VOC adsorption / desorption characteristics Has been found to improve significantly.
Furthermore, the silica porous body having mesopores and micropores in the primary particles is not limited to the fiber shape, and rod-like, spherical and lamellar silica and their aggregates can be used at a high temperature of 700 ° C. or higher. By heating, the pore surface becomes hydrophobic, regardless of the presence or absence of water vapor, once adsorbed VOC is desorbed by 89% or more by an inert gas purge under non-heating conditions, and the difference between the desorption rates is 10%. It became clear that

When porous amorphous silica is heated to a high temperature, silanol groups (Si-OH) are converted to siloxane bonds (O-Si-O) by dehydration / condensation of the silanol groups (Si-OH), resulting in improved hydrophobicity on the pore surface. Is well known. However, in a general commercial silica gel in which the interparticle gap functions as pores, the specific surface area (pore volume) is significantly reduced when heated simply to a high temperature. In order to use it as an adsorbent, the filling amount is bulky and increasing the size of the processing apparatus is a big problem.
As described above, the present invention improves the hydrophobicity of the pore surface by a simple method, and is particularly effective for energy saving development of the adsorption recovery system. For the first time, a new silica adsorbent with mesopores and micropores was successfully discovered.

The present invention has been made based on such knowledge.
That is, according to the present invention, the following inventions are provided.
[1] After having reached saturation adsorption through breakthrough in dynamic breakthrough curve measurement of volatile organic compound (VOC) gas, comprising a porous silica body having micropores and mesopores connected in primary particles A gas adsorbent characterized in that 85% or more of all adsorbed components can be desorbed by circulating an inert gas of 35 ° C. or lower under normal pressure.
[2] It consists of a porous silica material having micropores and mesopores connected in the primary particles, and in the dynamic breakthrough curve measurement of the mixed gas of volatile organic compound (VOC) gas and water vapor, A gas adsorbent characterized in that 80% or more of the total adsorbed amount can be desorbed by passing an inert gas of 35 ° C. or lower under normal pressure after reaching saturated adsorption.
[3] In the dynamic breakthrough curve measurement of both the volatile organic compound (VOC) gas alone and the mixed gas of the volatile organic compound (VOC) gas and water vapor, breakthrough reached saturation adsorption. Then, when comparing the total desorption amount through which an inert gas was circulated under an atmospheric pressure of 35 ° C. or lower, the desorption ratio of the volatile organic compound (VOC) gas mixed with water vapor was volatile organic compound (VOC). The gas adsorbent according to [1] or [2] above, wherein the gas adsorbent is 90% or more of the desorption ratio of the gas alone.
[4] The gas according to any one of [1] to [3] above, wherein the surfaces of the micropores and mesopores are hydrophobized by a high temperature aging step at the time of synthesizing the silica porous body or a heat treatment after the synthesis. Adsorbent.
[5] A heat treatment at 600 ° C. has a specific surface area of 700 m ² / g or more, a total pore volume of 0.55 ml / g or more, and a micropore volume of 0.05 ml / g or more. When compared with the heat treatment product at 60 ° C., 40% or more of the pore characteristic value at 600 ° C. is maintained, and even when heated to 800 ° C. or higher, the pore characteristics evaluation of the nitrogen adsorption isotherm clearly The gas adsorbent according to any one of [1] to [4] above, wherein the coexistence of water and mesopores can be confirmed.
[6] The gas according to any one of the above [1] to [5], wherein the primary particles are in the form of a fiber, rod, thin plate, or sphere. Adsorbent.

  The gas adsorbent of the present invention can desorb VOC once adsorbed with a high efficiency of 85% or more by an inert gas purge at normal pressure in a non-heated state, and further, under environmental conditions where water vapor coexists. Also, the desorption ability is 80% or more, which is extremely effective for the construction of an energy-saving VOC removal and adsorption recovery system. In addition, the adsorbent of the present invention is not limited to an inert gas purge at a normal pressure in a non-heated state, but a vacuum inert gas purge in a non-heated state, a normal pressure in a heated state, or a reduced pressure inert gas in the regeneration process. Of course, it is possible to apply a purge, and any of these can be employed to improve the performance of the adsorption recovery system.

Furthermore, since the gas adsorbent of the present invention can be synthesized in a short time under mild reaction conditions using an inexpensive raw material, it can be applied to new industrial applications. Utilizing a micron-sized particle form, it can be used as a nanocomposite adsorbent alone or in combination with various materials such as various silica gels, zeolites, activated carbon, clay minerals or resins, paints, and papers.
Furthermore, since the adsorbent of the present invention has a uniform pore size, not only VOC but also any gas molecule that can pass through the micropores, such as oxygen, nitrogen, carbon dioxide, carbon monoxide, freon, methane, It can be applied as an adsorbing / separating agent for hydrogen and the like.

It is a SEM image which shows the particle | grain form of the gas adsorbent of this invention, respectively, (a) Fibrous silica particle (Example 1), (b) Rod silica (Example 7), (c) Thin plate shape SEM images of silica (Example 5) and (d) spherical silica (Example 8). The conceptual diagram which shows the basic structural unit (primary particle) corresponding to each particle | grain form of the gas adsorbent of this invention. The FE-SEM image which shows the fine structure of the fibrous silica of this invention (Example 1). Toluene breakthrough curve and desorption behavior of fibrous silica of the present invention (600 ° C. heat-fired product of Example 1) and conventional (600 ° C. heat-fired product of Comparative Example 1) Comparison chart of (a) toluene breakthrough curve with and without coexistence of water vapor and (b) desorption behavior of VOC adsorbent of the present invention (800 ° C. heat-fired product of Example 1) Nitrogen adsorption isotherm of VOC adsorbent of the present invention (Example 1) Pore distribution curve of VOC adsorbent of the present invention (Example 1) T-plot of VOC adsorbent of the invention (Example 1) Nitrogen adsorption isotherms of Comparative Examples 3 and 4 T-plot of Comparative Examples 3 and 4

  The gas adsorbent composed of the porous silica according to the present invention has mesopores in the primary particles and micropores connected to the mesopores, and maintains this binary pore structure arrangement. By hydrophobizing the pore surface by a high temperature aging step or heat treatment after synthesis, it has VOC adsorption ability regardless of the presence or absence of water vapor, and at the same time has high desorption ability at non-heated atmospheric pressure. It is a great feature to demonstrate.

Initially, the particle | grain form of the silica porous body of this invention and its binary pore structure are demonstrated using figures.
(A) thru | or (d) of FIG. 1 are the scanning electron microscope images (SEM image) which show the particle | grain form of the gas adsorbent which consists of the silica porous body of this invention obtained in the Example mentioned later, 3 is an SEM image of fibrous silica obtained in Example 1, rod-like silica obtained in Example 7, thin-plate silica obtained in Example 5, and spherical silica obtained in Example 8. FIG.
The macro form of the porous silica of the present invention observed in the SEM images of FIGS. 1 (a) to 1 (d), respectively, corresponds to the corresponding basic structural unit, that is, a regular aggregate or irregular aggregate of primary particles. It is a collection.
FIG. 2 is a conceptual diagram simplified to explain the basic structural unit (primary particle) corresponding to each particle form. Hereinafter, each particle form will be described.

The fibrous silica particles in FIG. 1A have a length of 10 to 500 μm, and the pore characteristic values such as fiber length and mesopore diameter can be controlled by the synthesis conditions.
FIG. 3 is a scanning electron micrograph showing the microstructure of the fibrous silica obtained in Example 1, in which elongated rod-shaped particles are chained and stretched to one fibrous particle, and simultaneously stretched. It shows that a plurality of fibrous particles are gathered in a bundle.
Accordingly, the actual fibrous silica particles in FIG. 1A are an aggregate of fiber bundles composed of a plurality of fibrous particles.
FIG. 2A shows the basic structural unit of one fibrous particle, and clearly shows that rod-shaped particles are linked. However, although only three rod-like particles are drawn here, it is actually several tens to several hundreds of linked bodies.

In addition, the rod-like silica particles in FIG. 1 (b) can be recognized in the SEM image that rod-like particles having a length of about 1 to 2 μm exist individually, but in the actual composition, they are completely dispersed. It is difficult to achieve this state, and it is a secondary particle in which a large number of rod-shaped particles are aggregated, and is a massive particle having a size of several tens of μm.
FIG. 2B corresponds to one rod-shaped particle constituting the rod-shaped silica of FIG. 1B and shows a basic structural unit. Moreover, the basic structural unit of the fibrous particle in FIG. 2A is a chain of rod-shaped particles that are the basic structural unit in FIG. Further, FIG. 2C shows a rod-like basic structural unit in which the length of the basic structural unit in FIG. 2B is short, that is, the aspect ratio is small. The aspect ratio is obtained by dividing the particle length in the one-dimensional mesochannel direction by the particle width in the vertical cross section.

The thin silica particles shown in FIG. 1 (c) are strong aggregates of the thin rod-like primary particles shown in FIG. 2 (c). That is, the composite of FIG. 1C is agglomerated particles in which thin rod-shaped primary particles having a thickness of 0.3 μm or less are aggregated, and a peak value of the particle size distribution exists at about 20 mm.
Furthermore, the spherical silica particles in FIG. 1 (d) grow into spherical particles having a size of several tens of μm by strongly gathering small spherical particles (FIG. 2 (d)) of the order of submicron as primary particles. The spherical particles are aggregated particles of several hundred μm.

Next, the “pore structure in which micropores and mesopores are connected” in the present invention in each particle of the present invention will be described with reference to FIG.
In the fibrous silica (a), the rod-like silica (b), and the thin-plate silica (c), hollow portions (mesochannels) formed by passing through hexagonal columns extending in one direction are formed by the silica skeleton. Further, the basic units are regularly arranged in a honeycomb shape and exist as individual rod-like particles. The aspect ratio of the rod-like particles depends on the synthesis conditions, and can be controlled as thin plate-like particles as shown in FIG. The difference in the adsorption / desorption behavior of the present invention and the conventional fibrous and rod-like particles as VOC adsorbents is caused in particular by the pore diameter of the one-dimensional mesochannel and the degree of hydrophilicity / hydrophobicity of the pore surface.
When the basic structural unit is spherical as shown in FIG. 2D, the mesopores are three-dimensionally connected and the regularity of the arrangement structure is low, but the micropores connect the mesopores. It is thought that. Note that the mesopores can be controlled to the size of the micropores, which corresponds to the spherical microporous material of Comparative Example 1 described later.

In the gas adsorbent of the present invention, each mesopore (black hexagon in FIG. 2) is a large number of micropores (pores having an effective diameter of 2 nm or less) penetrating through the silica skeleton. The micropores and mesopores that are connected to each other by the black line and communicate with the outside world.
The “primary particles” in the present invention are particles corresponding to the basic structural unit shown in FIG. 2 and having mesopores and micropores regularly arranged in the basic structural unit. In general, commercially available silica gel has no pores in the primary particles, and the interparticle gaps formed by the primary particles or aggregates contribute to the adsorption. The pore diameter is controlled by the size of the aggregate.
Therefore, from the viewpoint of pore arrangement and pore diameter, the gas adsorbent comprising the porous silica of the present invention is commercially available due to the presence of pores in the primary particles and the extremely uniform pore size distribution. There are significant differences from silica gel.

  In order to improve the desorption ability of fibrous silica, which is a conventional gas adsorbent, the present inventors maintain a pore structure in which one-dimensional mesochannels and micropores connecting the channels are organically connected. It was found by measuring the dynamic breakthrough curve and desorption curve of VOC gas that it is effective to hydrophobize the pore surface and expand the mesopores.

The gas adsorbent of the present invention preferably has a clear and constant holding time until it breaks in the gas breakthrough curve and exhibits a sharp rise after breakthrough in all porous silica materials including fibrous silica. .
The “gas breakthrough curve” means a continuous curve showing a change in the outlet concentration with respect to the circulation time when a certain concentration of gas is circulated through the adsorbent. "There is a clear constant holding time" means that the gas is completely adsorbed by the adsorbent for a certain period of time from the start of flow and the gas concentration shows a value of zero. In addition, “showing a steep rise after breakthrough” means that the adsorbed gas component diffuses easily in the particle, and that the steeper the gas component, the better the diffusion in the particle. .

  More specifically, the shape of the breakthrough curve naturally depends on the gas to be measured, and even with the same gas type, the diameter and height of the adsorption tower, the amount of adsorbent, the particle size, and the packing It depends on density, gas concentration and flow rate. Unifying these conditions as much as possible, allowing a constant concentration of VOC to continuously flow through the sample, evaluating the adsorption capacity by the length of time (breakthrough time) during which the outlet concentration is maintained at zero, and the breakthrough time The longer it is, the higher the adsorption capacity. After the breakthrough, the measurement of the VOC concentration was continued, and when the outlet concentration became the same as the inlet concentration, a dynamic saturated adsorption state was reached, and the breakthrough curve from the distribution start point to the saturated adsorption arrival time The amount of dynamic adsorption can be calculated from the area. At this time, it is not completely adsorbed in the particles after breakthrough, and the VOC concentration increases. The steeper curve of this increase makes the adsorbed VOC easier to diffuse in the particles and has higher desorption ability. It suggests.

  In order to specifically evaluate the desorption ability, the VOC that was dynamically saturated and adsorbed was purged with nitrogen for a certain period of time in the non-heated state, i.e., near the same room temperature as during adsorption, to remove the VOC component that is relatively easy to desorb. After the separation, the temperature-programmed desorption (TPD) curve is measured until the temperature is further desorbed by heating at a constant temperature. The area of the TPD curve corresponds to the amount of VOC adsorbed relatively strongly on the adsorbent, and the amount obtained by subtracting this desorption amount from the dynamic adsorption capacity is desorbed by atmospheric pressure nitrogen purge, and is the amount of VOC that is easy to desorb. . The desorption operation time is set within 5 times the VOC circulation time to reach saturated adsorption, and the desorption ability in a short time is evaluated.

On the other hand, in actual VOC generation sites, it is often a mixed gas with water vapor, and the evaluation of the dynamic adsorption / desorption ability of VOC in the presence of water vapor is an essential issue.
In the present invention, the breakthrough curve in the presence of water vapor and the atmospheric pressure nitrogen gas purge and TPD measurement were performed in the same procedure as described above, and the dynamic adsorption / desorption amount was evaluated.
In this dynamic adsorption / desorption ability evaluation, the breakthrough curve was measured up to the saturated adsorption state in all cases, but the dynamic adsorption measurement was stopped at any stage before the saturated adsorption, and the desorption process Even if it shifts to, it is well known that the desorption rate of the gas adsorbent in the present invention is not deviated and rather the desorption rate becomes higher.

First, it will be explained that it is effective to increase the reaction temperature without changing the arrangement of the pore structure as one means for improving the VOC adsorption / desorption capability by hydrophobizing the pore surface.
FIG. 4 shows a dynamic breakthrough curve (a) and a desorption curve (b) of toluene of fibrous silica which is a conventional and VOC adsorbent of the present invention. The conventional fibrous silica was prepared by stirring the raw material reaction solution for 6 hours at a reaction temperature of 38 ° C., and corresponds to the 600 ° C. heat treatment product of Comparative Example 1 in Table 1.
The fibrous silica of the present invention shown in FIGS. 1 (a) and 3 is the same reaction raw material composition as before, stirred at 38 ° C. for 1 hour, and then aged at 80 ° C. and produced at 600 ° C. by heat treatment. It is a thing.

Comparing two fibrous silicas, it can be seen from FIG. 4 that the breakthrough time is longer for the fibrous silica of the present invention, and the rise after breakthrough is sharper for the fibrous silica of the present invention. It can be seen that diffusion is easy. Furthermore, the fibrous silica of the present invention is more strongly desorbed by temperature-programmed desorption (TPD), has a small amount of adsorbed toluene, has a higher rate of desorption by atmospheric pressure nitrogen purge, and has excellent desorption ability. I understand that
The adsorption / desorption phenomenon equivalent to that in Example 1 is observed in all the fibrous silicas of the present invention (Examples 2 to 4). In the fibrous silica of the present invention, as shown in Table 2, it is clear that almost 90% of the total dynamic adsorption amount is desorbed by the atmospheric pressure nitrogen purge, and the desorbability is extremely high.
As for the rod-like silica, the amount of adsorption is larger in the rod-like silica (Example 5) to which the aging method of the present invention is applied, compared to the rod-like particles in the conventional method (Comparative Example 2). 85% of the target adsorption amount is desorbed by atmospheric pressure nitrogen purge.

Unlike the prior art, the fibrous silica and rod-shaped silica of the present invention are not continuously stirred or ripened at a low temperature, but once the stirring reaction is stopped, the resulting suspension is ripened at a temperature higher than that during stirring. It is made by.
Furthermore, when water vapor coexists, the breakthrough time is shorter in all examples than in the case of toluene alone, but the degree of shortening is the fibrous silica of the present invention produced by aging at a higher temperature than during stirring and The rod-shaped silica is remarkably suppressed as compared with the case where it is produced by the conventional method. Specifically, for the heat-treated product at 600 ° C., the rate of desorption by atmospheric pressure nitrogen purge after toluene adsorption is R, and the desorption rate in the case of only toluene that does not coexist with water vapor and in the case of coexistence of water vapor, respectively. Let R (T600) and R (TW600).
As shown in Table 1, it is clear that R (TW600) is 10% or more higher than R (T600) in both fibrous silica and rod-like silica.
Therefore, the silica wall of the porous silica precursor is dehydrated and condensed by a aging reaction at high temperature, and is further heat-treated to connect the one-dimensional mesochannels having hydrophobic pore surfaces and the channels. Thus, a binary pore structure in which micropores coexist is formed. Furthermore, the VOC desorption rate is increased by inert gas purging under normal temperature and normal pressure because mass transfer is facilitated by aging at high temperature and by increasing the mesochannel diameter simultaneously with the hydrophobization of the pore surface. It is thought that it has contributed.

Next, as another method for hydrophobizing the pore surface, it is effective to heat the product at a temperature at which the surfactant, which is a pore-forming agent, is removed or once the surfactant has been removed. Explain that.
FIG. 5 shows a dynamic breakthrough curve (a) and a desorption curve (b) of toluene that clearly show the influence of water vapor coexistence of an example of fibrous silica that is a VOC adsorbent of the present invention prepared by heat treatment at 800 ° C. ). From FIG. 5A, it can be seen that even if water vapor coexists, the breakthrough time is only slightly reduced, and there is no difference in the shape of the breakthrough curve. What is particularly characteristic is that the amount of strongly adsorbed toluene that is desorbed by temperature-programmed desorption regardless of the presence or absence of water vapor is extremely small (FIG. 5B).

  This dynamic adsorption / desorption behavior related to the presence or absence of water vapor is observed in all the fibrous silicas of the present invention obtained by heat treatment at a high temperature. Furthermore, the porous particles obtained by heat treatment at high temperature, not only fibrous silica but also rod-like silica or aggregated particles of spherical particles, have the same dynamic adsorption / desorption behavior as above, and the present invention In the case of the gas adsorbent, the desorption rate by the atmospheric pressure inert gas purge under non-heating shows 85% or more when water vapor does not coexist and 80% or more when water vapor coexists.

It can be considered as follows that the gas adsorbent obtained by heat treatment at a high temperature of the present invention has a high VOC adsorption ability even in the presence of water vapor, and is particularly excellent in desorption ability.
In general, when silica gel is heated, siloxane bonds are formed by dehydration / condensation of silanol groups and the hydrophobicity of the pore surface is well known.
The major difference between the porous silica of the present invention and the commercially available silica gel is thermal stability, and the regular arrangement structure of the pores in the particles of the porous silica of the present invention is maintained even at a high temperature of 800 ° C. For example, as shown in Table 1, the specific surface area and total pore diameter volume of the porous silica obtained by heat treatment at 600 ° C. are maintained at 60% or more even at 800 ° C., and the micropores are also maintained at 40% or more. .

On the other hand, the commercially available silica gel (Comparative Example 4) in which mesopores and micropores are formed by interparticle gaps is destroyed by high-temperature heat treatment because of the three-dimensional irregular pore array structure formed by interparticle gaps. It is considered easy. For example, as shown in Table 1, in Comparative Example 4, when heated at 800 ° C., the specific surface area is remarkably reduced and falls from 725 m ² / g to 159 m ² / g.
However, in the case of a porous silica material synthesized by the present inventors and having only micropores although the degree of regularity in the particles is low (Comparative Example 3), the specific surface area is 600 ° C. and 800 ° C., which are 760 and 368 m, respectively. ² / g, and even when heated to 800 ° C., the specific surface area is only halved.

FIG. 9 shows the adsorption isotherms of Comparative Examples 3 and 4, and FIG. 10 shows a corresponding t-plot of the 800 ° C. heat-fired product. As can be seen from FIG. 9, the adsorbed amount greatly decreases at 800 ° C., but the amount of reduction is larger in Comparative Example 4. Moreover, in Comparative Example 4, it is clear from the t-plot that the shape of the adsorption isotherm changes and the cause is caused by the disappearance of the micropores, that is, the change in the pore arrangement structure. On the other hand, although Comparative Example 3 has only micropores, the pore volume is only halved even at 800 ° C., and the porous silica of Comparative Example 4 in which micropores are formed with interparticle gaps is obtained. Comparison shows that the thermal stability is high.
The reason why the gas adsorbent of the present invention is excellent in thermal stability is that the pores are present in the primary particles, so that the arrangement structure is maintained even at a high temperature, and the decrease in the adsorption amount is mainly due to the shrinkage of the wall. This is thought to be due to the accompanying decrease in pore width.

In this way, when the mesopores regularly arranged in the particles and the micropores connecting the mesopores coexist, dehydration / condensation of the silicate skeleton proceeds as the heat treatment temperature increases, and the pore diameter and pore volume are Although the mesopore arrangement structure in FIG. 2 is stably maintained even at a high temperature, a binary pore structure having a hydrophobized pore surface is formed, and a high VOC desorption rate is achieved. Can be considered.
In the case of the porous silica precursor having a binary pore structure in which the mesopores and the micropores connecting the mesopores coexist in the particles, the above is the formation under the high temperature hydrothermal condition or the heat treatment at the high temperature. In any case, it is shown that a hydrophobic surface of the pore is formed by maintaining the mesopore arrangement structure.

The porous silica preferably used in the present invention has a specific surface area of 700 m ² / g or more, a total pore volume of 0.55 ml / g or more, and a micropore volume of 0.05 ml / g or more in heat treatment at 600 ° C. In comparison with the 800 ° C. heat-treated product, 40% or more of the pore characteristic value of 600 ° C. is maintained, and even when heated to 800 ° C. or higher, the nitrogen adsorption isotherm is fine. It is characterized in that the coexistence of micropores and mesopores can be clearly confirmed by analyzing the pore characteristics by the t-plot method.

  The silica porous body preferably used in the present invention has regularly arranged mesopores having a diameter of 3 to 10 nm and has 2 nm or less micropores connecting the mesopores, and the micropores are 0.05 ml / g. This accounts for 10% or more of the total pore volume.

FIG. 6 shows adsorption isotherms of the porous silica material heat-treated at 600 ° C. and 800 ° C. in Example 1 of the present invention. FIG. 7 shows a pore size distribution curve of the porous silica corresponding to FIG.
In FIG. 6, the rise of the adsorption isotherm due to capillary condensation in the mesopores is recognized at a relative pressure of 0.6 to 0.7, and in the porous silica heated at 800 ° C., the adsorption amount decreases, It is clear that the shape of the adsorption isotherm of the silica porous body is the same, and the mesostructure is not destroyed. Further, the sharper the rise of the adsorption isotherm due to capillary condensation, the sharper the pore size distribution of the mesopores. As shown in FIG. 7, the mesopores are slightly narrowed in the porous silica heated at 800 ° C. However, it can be seen that both porous silicas have a uniform diameter.
Furthermore, a t-plot demonstrating the presence of micropores is shown in FIG. After adsorbing to the micropores, there are linear portions (M, M ′) indicating adsorbing to the mesopores, and the micropore volume can be determined from the intersection with the vertical axis by searching for that portion. The intersection between the straight line portion (N, N ′) and the vertical axis is a value obtained by removing the contribution due to the pores due to the particle gap, and is the sum of the mesopores and the micropore volume existing in the particles. Yes, corresponding to the total pore volume described in Table 1 described later. All the gas adsorbents of the present invention have the same results as in FIGS.
On the other hand, commercially available silica gel differs greatly from the porous silica of the present invention, and pores are formed by inter-particle gaps, so the pore size distribution is broad, and mesopores and micropores coexist. Are also difficult to identify by t-plots.

  In addition, the porous silica preferably used in the present invention is synthesized by utilizing the self-ordering ability of the polymer surfactant, so that the primary particles have a regular shape as shown in FIG. is doing. Further, the VOC adsorbent includes particles or aggregates composed of primary particles having a binary pore structure in which mesopores and micropores linked to mesopores coexist, and other substances such as clay minerals. It is possible to use as a mixture of these or a pellet-like molded body thereof.

Unlike the conventionally known adsorbents, the porous silica of the present invention is composed of a pure silica component, but the pore surface is controlled to be hydrophobic by a simple procedure, so that the two different sizes can be obtained. Due to the arrangement structure of the pores formed, the VOC high adsorption / desorption ability and the adsorption / desorption phenomenon are exhibited particularly in the presence of water vapor.
Further, in the case where the porous silica of the present invention does not coexist with water vapor, after adsorption of the VOC gas, in an unheated inert gas flow, “85% or more of all adsorbed components can be desorbed”, more preferably “90% or more of all adsorbed components can be desorbed”.
In addition, the porous silica of the present invention is also capable of desorbing 80% or more of the total adsorbed amount under non-heated inert gas flow after VOC gas adsorption even when water vapor coexists. Preferably, “90% or more of all adsorbed components can be desorbed”. Furthermore, the above desorption characteristic value is 85% or more, more preferably 90% or more, compared with the case where water vapor does not coexist.

  The gas adsorbent of the present invention has the advantages of conventional silica-based adsorbents such as nonflammability and the ability to recover and reuse gas with easy desorption ability, and is a major feature that it is easier to regenerate and VOC desorption. It enables the construction of a practical system that takes into account the recovery and reuse of gases that are not essential conditions for heat treatment in the process, and is considered an extremely useful adsorbent for the development of energy-saving VOC recovery equipment. Compared to the method of using a silica-based adsorbent, it has a remarkable inventive step. This is because regularly arranged mesopores are connected by micropores and have a hydrophobic pore surface by a simple operation, so that adsorbed VOC molecules can be easily diffused even in the presence of water vapor. It has completely different characteristics from the adsorption / desorption behavior of conventional silica-based adsorbents, such as the development of a cooperative action of adsorption / desorption phenomena of high adsorption capacity and high desorption capacity.

As described above, the gas adsorbent of the present invention has been found that the fibrous silica obtained by the new synthesis method by the inventors has VOC adsorption / desorption characteristics superior to those of conventional fibrous silica. It has been clarified that a silica porous body having not only silica but also mesopores and micropores having hydrophobic surface characteristics can exhibit good VOC adsorption / desorption characteristics even in the presence of water vapor. Successful development.
Table 1 shows the pore characteristic values obtained from the nitrogen adsorption isotherm of the porous silica adsorbent according to the present invention. In the same table (*), Comparative Examples 1 and 2 are 600 ° C. heat-fired products of Examples 6 and 7, respectively. Moreover, the spherical microporous material and the commercially available silica gel are listed as Comparative Examples 3 and 4, respectively. In addition, about the production method of a synthetic silica porous body, it describes in the latter Example.

In the table, S _BET is the specific surface area, V _micro is the micropore volume, _Vtotal is the total pore volume (the sum of the mesopore volume and the micropore volume), and D is the mesopore diameter.

Table 2 shows the dynamic adsorption / desorption characteristic values obtained from the breakthrough curve for toluene.

As described above, in the gas adsorbent of the present invention, it is important that mesopores and micropores are connected in the particles. Hydrophobization of the pore surface is performed by two methods, aging reaction conditions and heat treatment. Can be achieved.
Furthermore, the gas adsorbent of the present invention, which has a high desorption ability with an inert gas, can be improved by incorporating a heating operation or a vacuum operation together with an inert gas purge in the desorption process in the practical application of various VOC adsorption / recovery systems. It can be used as an adsorbent for efficient energy-saving adsorbers.

  The gas adsorbent comprising a porous silica material having micropores and mesopores according to the present invention has a high adsorption ability due to the presence of micropores, and a higher intraparticle diffusion ability has a mesopore connected to the micropores. It is thought to be expressed by pores. In particular, the high desorption rate due to the normal pressure inert gas purge is due to the hydrophobization of the pore surface based on the aging reaction after a certain stirring step. The degree of hydrophobization can be controlled by aging conditions, for example, reaction mixture ratio, addition of salts, control of reaction time and reaction temperature, temperature increase rate when removing the surfactant and holding treatment temperature, etc. . If the situation of the target VOC generation site, in particular, the condition that coexistence of water vapor is not a problem, the heat treatment at a high temperature becomes unnecessary only by adjusting the aging reaction conditions.

  Among the gas adsorbents of the present invention, the gas adsorbent composed of fibrous particles exhibits a micron order fiber shape, and can be formed into a filter or a felt shape, and can be applied to various applications. In addition, among the gas adsorbents of the present invention, rod-like particles and spherical particles including fibrous particles can be used in a wide variety of adsorbers as molded articles such as pellets using clay minerals as molding aids regardless of their shapes. It is possible to incorporate. In particular, it can be used under conditions where activated carbon fibers cannot be used as a gas adsorbent such as VOC in an oxidizing atmosphere where VOC is generated, and a wide range of applications can be expected. Furthermore, a new adsorbent is expected to be developed by supporting a transition metal or noble metal in the form of a metal element or oxide in a highly dispersed state on the pore surface.

EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited by this Example.
In addition, each test method performed in the Example was performed by the following method.

(Measurement method)
(1) Shape: A scanning electron microscope JSM5300 manufactured by JEOL Ltd. was used, and observed with an acceleration voltage of 10 kV and a WD of 10 mm. Furthermore, morphology observation was performed using a Hitachi field emission scanning electron microscope S-4700F.
(2) Specific surface area / pore size distribution: BELSORP MINI manufactured by Nippon Bell Co., Ltd. was used to determine the BET specific surface area from the nitrogen adsorption isotherm measured at the liquid nitrogen temperature, and the pore size distribution was analyzed by the BJH method. Furthermore, the total of the micropore volume and the mesopore volume, which is the total pore volume, and the micropore volume was determined by the t-plot method.
(3) Toluene adsorption / desorption test using a flow-through method: Using a dynamic breakthrough curve measuring device, 500 ppm of toluene diluted with nitrogen gas was used to place the adsorbents of Examples and Comparative Examples in U-tube sample tubes. About 0.03 g was taken and flowed at a flow rate of 100 ml / min at room temperature, and a breakthrough curve of toluene was measured to evaluate the adsorption ability. The breakthrough curve in the presence of water vapor was measured by mixing 500 ppm toluene and 2% water vapor at the same flow rate of 100 ml / min. After the breakthrough, the outlet concentration gradually increased, and after reaching dynamic saturation adsorption (total dynamic adsorption amount A), only nitrogen gas was allowed to flow for 2 hours and the desorption curve by atmospheric pressure nitrogen purge was measured. (Desorption amount B). Further, a temperature-programmed desorption spectrum was measured at 10 ° C./min in order to completely desorb the remaining VOC component (desorption amount C).
The desorption amount (B) is an adsorbed component that is desorbed only by flowing nitrogen gas under normal pressure out of the total dynamic adsorption amount A, and the larger the desorption amount, the better the adsorbent is. it can. The desorption amount (B) was calculated as the VOC amount obtained by subtracting the adsorbed component (C) removed by the temperature-programmed desorption from the dynamic adsorption capacity (A).

Example 1
Triblock copolymer Pluronic P123 (EO ₂₀ PO ₇₀ ) in which commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water was dissolved in 2N hydrochloric acid. EO ₂₀ , manufactured by BASF, average molecular weight 5800, hydrophilic portion EO ratio 30%) was added to the solution with stirring. Both raw material solutions were adjusted in advance to a predetermined temperature of 38 ° C. and mixed, and stirring was stopped one hour after mixing both raw material solutions. The open mouth of the glass reaction vessel containing this mixed solution was closed with a glass plate, quickly transferred to a constant temperature water bath adjusted to 80 ° C., and allowed to stand for 300 minutes for aging. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.88: 202. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is separated by filtration, washed, sufficiently dried at 65 ° C., and baked in an electric furnace at 600 ° C. and 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. In this example, synthesis was performed according to the method described in JP-A-2007-204288.
FIG. 1 (a) is an SEM image of this example, and the microstructure is as shown in FIG. 3, indicating that elongated rod-like particles of about 1 μm are chained.
The fibrous silica (Examples 1 to 4 and Example 6), which is the gas adsorbent of the present invention, all have the same microstructure. Table 1 shows the BET specific surface area, total pore volume, and micropore volume of silica particles of other examples and comparative examples including this example.

(Example 2)
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. Both raw material solutions were adjusted in advance to a predetermined temperature of 38 ° C. and mixed, and stirring was stopped 20 minutes after mixing both raw material solutions. This mixed solution was transferred to a Teflon (registered trademark) reaction vessel, sealed in a simple stainless steel vessel, and allowed to stand for 300 minutes in a constant temperature and constant temperature bath adjusted to 100 ° C. for aging. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.88: 202. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is separated by filtration, washed, sufficiently dried at 65 ° C., and baked in an electric furnace at 600 ° C. and 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. In this example, as in Example 1, the synthesis was performed according to the method described in JP-A-2007-204288.

(Example 3)
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. Both raw material solutions were adjusted in advance to a predetermined temperature of 38 ° C. and mixed, and stirring was stopped one hour after mixing both raw material solutions. This mixed solution was transferred to a Teflon (registered trademark) reaction vessel, sealed in a simple stainless steel vessel, and allowed to stand for 300 minutes in a constant temperature and constant temperature bath adjusted to 100 ° C. for aging. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.88: 202. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is separated by filtration, washed, sufficiently dried at 65 ° C., and baked in an electric furnace at 600 ° C. and 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. In this example, as in Example 1 and Example 2, the synthesis was performed according to the method described in JP-A-2007-204288.

Example 4
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. Both raw material solutions were adjusted in advance to a predetermined temperature of 38 ° C. and mixed, and stirring was stopped 2 hours after the mixing of both raw material solutions. The wet reaction product obtained by filtering and washing the reaction suspension is put in a Teflon (registered trademark) reaction vessel, and the suspension with pure water added is sealed in a simple stainless steel airtight vessel. Then, the mixture was allowed to stand for 300 minutes in a constant temperature and constant temperature bath adjusted to 100 ° C. in advance, and aging was performed. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.88: 202. H ₂ O contains water derived from all raw materials. For aging, 83 mol of water was used per 1 mol of SiO ₂ . After the aging reaction, the solid product is filtered off, washed, sufficiently dried at 65 ° C., and baked in an electric furnace at 600 ° C. and 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. . In this example, synthesis was performed according to the method of Japanese Patent Application No. 2009-078051.

(Example 5)
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. In this example, it is important to crystallize the white reaction product in a short time before aging, and when both raw material solutions adjusted in advance to a predetermined temperature of 38 ° C. are mixed, a white solid precipitate is obtained within 3 minutes. Was recognized. Stirring was stopped after 20 minutes after mixing, and the reaction suspension was transferred to a Teflon (registered trademark) reaction vessel, sealed in a simple stainless steel vessel, and pre-adjusted to 80 ° C. for 300 minutes. Aged and allowed to stand. In this example, the molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.0131: 0.312: 4.3: 151. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is filtered off, washed and sufficiently dried at 65 ° C. Finally, the organic component is removed by baking in an electric furnace at 600 ° C. for 1 hour to obtain porous silica particles. In this example, synthesis was performed according to the method of Japanese Patent Application No. 2009-079589.
FIG. 1C is an SEM image of this example. As shown in FIG. 2C, thin plate-like rod-like silica having a thickness of about 0.3 μm aggregates, and the particle size distribution peak reaches about 20 μm. Is recognized.

(Example 6)
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. Both raw material solutions were previously adjusted to a predetermined temperature of 38 ° C. and mixed, and stirring was stopped 6 hours after the mixing of both raw material solutions. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.88: 202. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is separated by filtration, washed, sufficiently dried at 65 ° C., and baked in an electric furnace at 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. In this example, synthesis was performed according to the method described in Japanese Patent No. 4099881. Table 1 shows the pore characteristic values of the fibrous particles obtained by heat treatment at 600 ° C. for 1 hour as Comparative Example 1.

(Example 7)
While stirring a commercially available JIS No. 3 sodium silicate (SiO ₂ : 23.6%, Na ₂ O: 7.59%) diluted with water in a triblock copolymer Pluronic P123 solution dissolved in 2N hydrochloric acid, the mixture was stirred. Added. Both raw material solutions are adjusted and mixed in advance at a predetermined temperature of 30 ° C., and after mixing both raw material solutions, stirring is stopped 30 seconds later, and the reaction is allowed to stand at 30 ° C. for 6 hours. The molar ratio of the mixed solution is SiO ₂ : Pluronic P123: Na ₂ O: HCl: H ₂ O = 1: 0.017: 0.312: 5.90: 203. H ₂ O contains water derived from all raw materials. After the reaction, the solid product is separated by filtration, washed, sufficiently dried at 60 ° C., and baked in an electric furnace at 800 ° C. for 1 hour to remove organic components and obtain fibrous porous silica particles. This example was synthesized according to Japanese Patent No. 40998811. In Table 1, the rod-like particles obtained by heat treatment at 600 ° C. for 1 hour are shown as Comparative Example 2 and their pore characteristic values are shown in Table 1.
FIG. 1 (b) is an SEM image of this example, and elongated rod-like particles of about 1 μm are gathered to obtain an aggregate of several tens of microns.

(Example 8)
Commercially available JIS No. 3 sodium silicate (SiO ₂ : SiO ₂ :) in a triblock copolymer Pluronic P104 (EO ₂₇ PO ₆₁ EO ₂₇ , manufactured by BASF, average molecular weight 5900, hydrophilic part EO ratio 40%) dissolved in 12% nitric acid. 23.6%, Na ₂ O: 7.59%), and a water-diluted aqueous sodium silicate solution is added with stirring at 400 rpm. The molar ratio of the mixed solution is SiO ₂ : Pluronic P104: Na ₂ O: HNO ₃ : H ₂ O = 1: 0.0138: 0.312: 4.06: 202. H ₂ O contains water derived from all raw materials. The reaction temperature is 35 ° C., and after stirring for 3 hours, the solid product is filtered and washed, dried sufficiently at 60 ° C., and baked for 1 hour in an electric furnace at 600 ° C. and 800 ° C. The component is removed to obtain porous silica particles.
FIG. 1D is an SEM image of the present example, which is a massive particle of several hundred microns, in which small spherical particles are strongly aggregated to grow into spherical particles of several tens of microns, and a plurality of spherical particles are aggregated.

(Comparative Example 3)
To a commercially available JIS No. 3 sodium silicate (SiO ₂ : SiO ₂ : Triblock copolymer Pluronic F88 (EO ₃₉ PO ₁₀₃ EO ₃₉ , manufactured by BASF, average molecular weight 11400, hydrophilic part EO ratio 80%) dissolved in 12% nitric acid. 23.6%, Na ₂ O: 7.59%) and a diluted sodium silicate aqueous solution added with water is added with stirring at 600 rpm. The molar ratio of the mixed solution is SiO ₂ : Pluronic F88: Na ₂ O: HNO ₃ : H ₂ O = 1: 0.0075: 0.312: 3.72: 146. H ₂ O contains water derived from all raw materials. The reaction temperature is 35 ° C., and after stirring for 4 hours, the solid product is filtered and washed, dried sufficiently at 60 ° C., and baked for 1 hour in an electric furnace at 600 ° C. and 800 ° C. By removing the components, the monodispersed spherical porous silica particles having a diameter of about 100 mm of Comparative Example 3 are obtained. In Comparative Example 3, the synthesis was performed according to the method described in JP-A No. 2004-182492.

(Comparative Example 4)
The silica particles of Comparative Example 4 are spherical silica gel particles having micropores and mesopores of a private company that produces and develops representative silica in Japan. The measurement results of the sample pretreated at 0 ° C. are described.

FIG. 9 shows adsorption isotherms of Comparative Examples 3 and 4, and FIG. 10 shows a corresponding t-plot of the 800 ° C. heat-fired product.
As can be seen from FIG. 9, the adsorbed amount greatly decreases at 800 ° C., but the amount of reduction is larger in Comparative Example 4. Moreover, it is clear from the t-plot that the shape of the adsorption isotherm changes in Comparative Example 4 and the cause is caused by the disappearance of the micropores, that is, the change in the pore arrangement structure. In the t-plot of Comparative Example 4, the amount of adsorption turned slightly upward with respect to the straight line from the origin, which is recognized as a characteristic shape of the mesopore porous body. On the other hand, although Comparative Example 3 has only micropores, the pore volume is only halved even at 800 ° C., and the porous silica of Comparative Example 4 in which the pores are formed with interparticle gaps is used. Comparison shows that the thermal stability is high. The reason why the adsorbent of the present invention is excellent in thermal stability is that the pores are present in the primary particles, so that the arrangement structure is maintained even at high temperatures, and the decrease in the amount of adsorption is mainly caused by the shrinkage of the wall. This is thought to be due to a decrease in the pore width.

Example 9
An example of a dynamic breakthrough curve and a desorption curve are shown in FIGS. 4A and 4B for Example 1, respectively. The same data is accumulated for all the adsorbents of the present invention, and in the dynamic breakthrough curve corresponding to FIG. 4 (a), the breakthrough time T for adsorbing all circulating toluene and maintaining the concentration at zero is 600. Table 2 shows the cases where water vapor does not coexist and coexists with respect to the heat-treated products at 800C and 800C. Further, the total dynamic adsorption capacity (A) and the adsorbed part (C) removed by the temperature-programmed desorption are obtained from the areas of the respective data curves, and the desorption can be performed only by flowing nitrogen gas under normal pressure from the difference (AC). In order to calculate the adsorbed content (B) to be released and to evaluate the desorption ability from the B / A (%) value, it is described as the desorption rate R in Table 2. In addition, as described above, the R value of the heat treatment product at 600 ° C. is represented as R (T600) in the case of toluene alone, and R (TW600) in the case of a mixed gas of toluene and water vapor, and this notation at 800 ° C. According to

Moreover, about the 800 degreeC heat baked material of Example 1, the influence on the VOC dynamic breakthrough curve and desorption curve with respect to the presence or absence of water vapor | steam is shown to Fig.5 (a) and (b), respectively. The data curves corresponding to the adsorbents of the other examples were also measured, and the breakthrough time T and the desorption rate R are shown in Table 2 as in the case of Example 1. In addition, about Example 8, only the 800 degreeC heat processing product was made into the measuring object. Furthermore, the corresponding measured value was also shown about the comparative example.
In Table 2, Comparative Examples 1, 2, and 3 are porous silica materials that were prepared without applying the aging step, and the desorption rate of the 600 ° C. heat-treated product was as low as 80% or less even when no water vapor coexists. The adsorbent does not represent 85% or more of the present invention. On the other hand, the desorption rate of the heat-treated product at 800 ° C. is 85% or more when water vapor does not coexist with all the adsorbents including Examples 6, 7, and 8 and 80% or more even when water vapor coexists. The specified adsorbent of the present invention is satisfied.

Based on Table 1 and Table 2, the following is clear regarding the relationship between the pore structure and surface characteristics of the adsorbent of the present invention and the desorption rate R.
The adsorbent of the present invention, fibrous silica (Examples 1 to 4), and rod-like silica (Example 5) obtained by aging at a temperature higher than the stirring temperature following the stirring reaction, do not apply the aging step (Example 6). Compared with Example 7), the desorption rate R (T600) is largely 85% or more. Furthermore, when comparing the desorption rate in the presence or absence of water vapor, the R (TW600) / R (T600) of the adsorbent of the present invention obtained by aging at a stirring temperature or higher is larger than when the aging step is not applied. The pore surface of the porous silica obtained by aging at high temperature is considered to be more hydrophobic.
More generally, the surface of the pores of the porous silica material can be hydrophobized by heat treatment at a high temperature, and in the case of silica gel in which pores are formed by inter-particle gaps and a large proportion of micropores is present, the temperature becomes 800 ° C or higher. When heated, the specific surface area and pore volume are significantly reduced, and the adsorption function as a porous body is inevitably lowered. This is clear from the heat treatment result of the commercially available silica gel of Comparative Example 4 in the above “Comparative Example”, and the change in the silicate skeleton structure due to dehydration condensation accompanying the heat treatment at 800 ° C. is significant, and the specific surface area and pore volume are It will decrease about 75% from the maximum value.
However, in Comparative Example 3 in which micropores are present in the particles, the specific surface area and pore volume are only halved from the value of 600 ° C. even at 800 ° C., and a marked difference from Comparative Example 4 is observed. However, it can be said that the micropores present in the particles have a more thermally stable structure than the micropores caused by the interparticle gaps. , VOC desorption becomes difficult. Therefore, in Comparative Example 3, not only the 600 ° C. heat treatment product but also the 800 ° C. treatment product in which the pore surface is hydrophobized has a low desorption rate, and R (T800) <65%. This is considered to be due to the remarkable decrease in the diffusibility within the particles due to the reduction of the micropore diameter, and the effect of hydrophobizing is difficult to appear.

On the other hand, for the silica adsorbent of the present invention in which mesopores and micropores coexist, when comparing the calcined products at 800 ° C. and 600 ° C., the micropore volume is reduced by 30 to 60% as in Comparative Example 3. The reduction in surface area is only 35%. This clearly shows that the mesopores are contracted by heating, but the mesoregular arrangement structure is maintained even at a high temperature.
Therefore, the adsorbent of the present invention in which a meso-micropore organic connection structure having a hydrophobic pore surface, which is a heat treatment product at a high temperature, is formed in all the examples (implementation). The desorption rates of the porous bodies obtained by heat treatment at 800 ° C. in Examples 1 to 8) were R (T800)> 85%, R (TW800)> 80%, and R (TW800) / R (T800 )> 90%.

  As described above, the adsorbent of the present invention adjusted at the time of synthesis so that the pore surface is hydrophobized has a high adsorption ability and a high desorption ability particularly in a non-heated state. It is effective for the development of adsorption recovery system. Furthermore, the adsorbent of the present invention obtained by hydrophobizing the surface of the pores by high-temperature treatment is highly desorbed by an inert gas purge near normal temperature or under vacuum without performing a heating operation in the VOC desorption process. Since it exhibits a separation rate, it is effective for developing a VOC gas adsorption and recovery system under a wide range of environmental conditions regardless of the presence or absence of water vapor. In the present invention, the desorption characteristics are evaluated by normal pressure nitrogen purge at normal temperature, but vacuum nitrogen (air) purge is generally employed in practical systems. The evaluation method of the present invention is carried out under normal pressure, which is less likely to desorb than a vacuum inert gas purge, and directly reflects the desorption characteristics of the adsorbent itself, and is considered extremely useful in constructing a practical system.

Claims (6)

  It consists of a porous silica body with micropores and mesopores connected in the primary particles. In the dynamic breakthrough curve measurement of volatile organic compound (VOC) gas, it breaks down and reaches saturated adsorption, and then under normal pressure A gas adsorbent characterized in that 85% or more of all adsorbed components can be desorbed by circulating an inert gas at 35 ° C. or lower.   It consists of a porous silica body with micropores and mesopores connected in the primary particles, and it breaks through to saturated adsorption in dynamic breakthrough curve measurement of a mixed gas of volatile organic compound (VOC) gas and water vapor. A gas adsorbent characterized in that 80% or more of the total adsorbed content can be desorbed by passing an inert gas of 35 ° C. or lower under normal pressure after reaching.   In a dynamic breakthrough curve measurement of both a volatile organic compound (VOC) gas alone and a mixed gas of the volatile organic compound (VOC) gas and water vapor, after breaking through and reaching saturated adsorption, 35 When comparing the total desorption amount through which an inert gas was circulated under normal pressure of ℃ or less, the desorption ratio of the volatile organic compound (VOC) gas mixed with water vapor is that of the volatile organic compound (VOC) gas alone. The gas adsorbent according to claim 1 or 2, wherein the gas adsorbent is 90% or more of a desorption ratio.   The surface of the said micropore and a mesopore is hydrophobized by the high temperature aging process at the time of the synthesis | combination of a silica porous body, or the heat processing after a synthesis | combination, The any one of Claims 1-3 characterized by the above-mentioned. Gas adsorbent. It has a specific surface area of 700 m ² / g or more in heat treatment at 600 ° C., a total pore volume of 0.55 ml / g or more, and a micropore volume of 0.05 ml / g or more. When compared with the product, 40% or more of the pore characteristic value at 600 ° C. is maintained, and even when heated to 800 ° C. or higher, the pore characteristics of the nitrogen adsorption isotherm are clearly evaluated as micropores and mesopores. The gas adsorbent according to any one of claims 1 to 4, wherein coexistence of the gas can be confirmed.   The gas adsorbent according to any one of claims 1 to 5, wherein the primary particles have a fibrous form, a rod form, a thin plate form, or a spherical form.