JPH1119507A - Adsorbent and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adsorbent capable of efficiently recovering a volatile organic compound(VOC) of low concentration and to provide a method for producing the adsorbent. SOLUTION: The adsorbent for volatile organic compound(VOC) gas consists of a porous granular body in which silica is a main constituent and specific surface area is 400-700 m<2> /g, average pore diameter is 0.4-3.0 nm and steam adsorption amount is 3-10 ml/g. In the method for producing the above- mentioned adsorbent, the molded pellets of silica, in which specific surface area is >=600 m<2> /g and pore volume is the range within 0.05-0.5 cm<2> /g and average pore diameter is the range within 0.4-3.0 nm, or silica gel is heated at the prescribed temperature of the range within 550-700 deg.C at temperature rise velocity within 1-20 deg.C/minute and held at this prescribed temperature at the prescribed time. In the adsorbent, VOC selectivity for steam is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volatile organic compound (VOC) gas adsorbent and a method for producing the same, and more particularly, to a pressure swing adsorption separation method. The present invention relates to an adsorbent which is optimal as an adsorbent when recovering a low-concentration VOC gas by the PSA method, and a method for producing the same. In particular, the adsorbent for VOC gas of the present invention is suitable as an adsorbent for recovering low-concentration VOC gas in the air at a gas station or an oil depot using the PSA method.

[0002]

2. Description of the Related Art Liquid organic compounds such as gasoline, organic solvents for coating, and chlorinated organic solvents for cleaning contain a large amount of various organic compound components having a high vapor pressure. Organic compounds having a high vapor pressure are easily referred to as volatile organic compounds (VOCs) because they are easily volatilized. Today, liquid organic compounds are used in large quantities in various fields such as painting, printing, and cleaning, in addition to the use of gasoline and the like as fuel for internal combustion engines. VOC gas (hereinafter simply referred to as VOC) is volatilized and diffused into the atmosphere on a daily basis. VOC is the state in which volatilized to and dissipated into the atmosphere, but has become much lower concentrations, NO _x, to become a main factor causing photochemical smog reacts with SO _x and the like, the VOC into the atmosphere It is necessary to suppress radiation.

[0003] However, it is technically extremely difficult to efficiently recover low-concentration VOCs that have volatilized during use so as not to emit them to the atmosphere.
The definitive capture technique for C has not yet been established. For example, as one of the VOC capture technologies, PS using an adsorbent
The A method has been studied, but there is no adsorbent that can efficiently adsorb and capture low-concentration VOCs when it is released into the atmosphere from gas stations or oil depots. It is an application issue.

Activated carbon, a typical adsorbent, is 1000
It has a large specific surface area of at least m ² / g and is the most suitable adsorbent as a VOC adsorbent in view of only the adsorption capacity. However, because activated carbon is flammable, it must be used in the area of safety management in order to use it as an adsorbent for VOC adsorption equipment by the PSA method in gas stations or oil depots where flammable gas is handled. Is difficult.

[0005] Therefore, inorganic oxide adsorbents such as zeolite are attracting attention as non-flammable adsorbents, and the pressure-temperature fluctuation adsorption separation method (Pressu) which has almost the same adsorption principle as the PSA method.
re and Temperature Swing Adsorption, hereinafter PTSA
Method) and temperature swing adsorption separation method (Temperature Swing Adsorp).
(hereinafter referred to as TSA method). These methods use a very common inorganic oxide-based adsorbent such as zeolite and incorporate a step of swinging the temperature in order to desorb moisture adsorbed together with VOC from the adsorbent. However, in these adsorption separation methods, the target of adsorption is a relatively high-concentration VOC, and an example of practical application for capturing a relatively low-concentration VOC released from a gas station or an oil depot is as follows. Not found so far. The reasons that these methods are difficult to apply to recovery of low-concentration VOCs are firstly that VOCs are hardly adsorbed due to their low concentration, and secondly, that saturated steam affects the adsorption of VOCs. is there.

It seems that the use of a high surface area inorganic oxide-based adsorbent makes it possible to efficiently adsorb and desorb low-concentration VOCs. However, the surface of the inorganic oxide-based adsorbent has a highly polar hydroxyl group ( Since a large number of OH) are present, only water molecules having a high dipole moment are selectively adsorbed, and the amount of adsorbed / desorbed VOC is extremely reduced. For example, zeolite has a large specific surface area,
Since the ratio of silica to alumina (SiO ₂ / Al ₂ O ₃ ) is low, it exhibits acid properties, has high affinity for water, and selectively adsorbs water. The issue of affinity with water is, in particular, V
It becomes remarkable when the OC concentration is low.

More specifically, silica (silicon oxide, Si
O ₂ ) itself shows strong water repellency, but the surface of silica showing a high surface area usually has hydrophilic silanol (Si—O
Many H) groups remain. VOC of VOC-PSA method
In the adsorption process, competitive adsorption between water vapor and VOC
ive adsorption) is progressing, and if a large number of hydrophilic groups are present, a large amount of water will be adsorbed.
The amount of adsorption decreases. In addition, since a large amount of water is absorbed, there is a problem that water invades the inside and cracks occur in the adsorbent.

In order to prevent silanol groups from remaining, for example, methoxytrimethylsilane (CH ₃ O-Si- (C
There is a method in which an organosilicon compound such as H ₃ ) ₃ ) is brought into contact with silica to couple with a silanol group on the surface. On the other hand, a high-silica zeolite (HS-Zeolite) that has been hydrophobized from zeolite without destruction of the zeolite crystal by dealuminization by acid extraction or the like so as to prevent the zeolite from crystal destruction without impairing excellent porous properties such as a large specific surface area ) Has attracted attention as a low-concentration VOC adsorbent.

[0009]

By the way, environmental preservation equipment is not limited to VOC recovery, and generally imposes a new cost burden on a company to be introduced. Therefore, an economical process with low cost is strongly required. For example, in the PSA process, the cost of the adsorbent has a large weight in the cost of the entire process, and it is extremely important to develop an inexpensive adsorbent. However, organic silicon-based organic compounds such as methoxytrimethylsilane are volatile, which makes the coupling reaction equipment complicated, and silicon-based organic compounds are expensive, so that the coupling method is used for industrial processes. There is a problem that the hydrophobic treatment is not economically favorable. Also, high silica zeolite has a problem that the cost of dealumination is high, and it is not economically suitable for use in industrial processes. As described above, an economical adsorbent that can efficiently capture low-concentration VOCs and is suitable for an industrial process is not found in conventional adsorbents.

Accordingly, an object of the present invention is to provide a low-concentration VOC
To provide an adsorbent capable of efficiently recovering water and a method for producing the same.

[0011]

Means for Solving the Problems Accordingly, the present inventors have:
In order to efficiently adsorb low-concentration VOCs and increase the cracking resistance to water, it is necessary to remove the hydrophilic groups to reduce the water adsorbing ability, that is, improve the hydrophobizing ability and increase the VOC adsorbing ability. Thought it was necessary. As a result of repeated experiments, it was found that an adsorbent composed of a porous molded body containing silica as a main component and having specific porous physical properties such as a specific surface area, a pore volume, and an average pore diameter has excellent hydrophobicity and VOC use. The inventors have found that the present invention has an adsorption ability, and have completed the present invention. Further, they have found that such an adsorbent can be produced by heat treatment under specific conditions, and have completed the method of the present invention.

In order to achieve the above object, the adsorbent according to the present invention contains silica as a main component and has a specific surface area of 400-7.
Volatile organic compound having 1 to 12 carbon atoms, comprising a porous molded body of 00 m ² / g, average pore diameter of 0.4 to 3.0 nm, and water vapor adsorption of 3 to 10 ml-water vapor / g-adsorbent. It is characterized by selectively adsorbing compound gas.
Here, “selectively adsorbing volatile organic compound gas having 1 to 12 carbon atoms” means that the volatile organic compound gas having 1 to 12 carbon atoms is selectively used in gas and gas components excluding water vapor. Means to be adsorbed.

[0013] The method for producing an adsorbent according to the present invention comprises:
A method for producing an adsorbent for selectively adsorbing a volatile organic compound gas having 1 to 12 carbon atoms, wherein the specific surface area is 600
m ² / g or more and pore volume of 0.05 to 0.5 cm ³ /
g and a silica or silica gel pellet having an average pore diameter of 0.4 to 3.0 nm are heated to a predetermined temperature of 550 to 700 ° C. at a heating rate of 1 to 20 ° C./min. It is characterized in that it is heated and kept at a predetermined temperature for a predetermined time. The adsorbent produced by the method of the present invention has a specific surface area reduction rate of 5 to 40% and a water vapor adsorption amount of 3 to 10 m.
1 / g.

The volatile organic compound of the present invention is an adsorbent for adsorbing volatile organic compound gas (hereinafter, simply referred to as an adsorbent). VOC generated from a medium or light fraction of gasoline, naphtha, kerosene, gas oil, etc. Hydrophobicity and V
Because of its high OC adsorption capacity, relatively low concentration VOC released from gas stations, oil tanks, etc. by the PSA method
It is suitable as an adsorbent when adsorbing. VO in the present invention
C means a volatile organic compound gas having 1 to 12 carbon atoms, and VOC adsorption ability means ability to adsorb VOC.
In addition, a volatile organic compound means hydrocarbon, halogenated hydrocarbon, and oxygen-containing organic compound. The oxygen-containing organic compound is an organic compound containing —O— and / or ＯO in a chemical formula, and examples thereof include alcohols, ethers, esters, carboxylic acids, ketones, and aldehydes. The specific surface area, the pore volume and the average pore diameter indicating the porous physical properties of the adsorbent of the present invention are BET.
It is a value measured by the method.

Raw Material of Adsorbent The raw material of the adsorbent of the present invention is obtained by using a nitrogen molecule as a probe.
The specific surface area measured by the ET method is 600 m ² / g or more, preferably 650 m ² / g or more, and the pore volume is 0.05 to 0.1 g / m ² .
5 cm ³ / g, preferably in the range from 0.1~0.3cm ³ / g, an average pore diameter of silica or silica gel in the range of 0.4～3.0Nm. Here, silica means a substance containing no water, and silica gel means a substance containing water. Further, as long as the object of the present invention is achieved, the adsorbent raw material and the adsorbent may contain an inorganic component other than silica or silica gel. The practical upper limit of the specific surface area of the silica gel material which can be obtained on an industrial scale is currently about 800 m ² / g, but as the specific surface area increases, the adsorption capacity increases.

The specific surface area of an average pore diameter of the adsorbent material is large, it means that a wide VOC molecular adsorption area per unit weight or per unit bulk volume of the adsorbent, so much adsorption capacity increases, higher concentrations When the VOC is to be adsorbed, an adsorbent having a large specific surface area may be used. On the other hand, when a low-concentration VOC that has been volatilized and diffused into air as in the present invention is used, in addition to the large specific surface area, It is important to provide the adsorbent with an optimum pore size in which VOCs are easily adsorbed. This is because VOC molecules are considered to be capillary condensed and adsorbed in relatively small pores. Therefore, it is important that the adsorbent has a large surface area, a high contact probability with VOC molecules, and a porous material having small average pore diameters in order for the condensation process to proceed efficiently. . From this viewpoint, the raw material silica gel or silica has an average pore diameter of 0.4 to 3.0.
A range of 0 nm is preferable, and a range of 0.6 to 1.5 nm is more preferable. In the BET method, since the lower limit of the measurement of the pore volume and the pore distribution is a gap or a pore in which nitrogen molecules can enter, a hydrogen molecule smaller than a single molecular element such as a rare gas or nitrogen is used. When used as a probe or compared with a numerical value measured by an analysis method other than the BET adsorption theory, for example, the T-plot method, normalization such as conversion is performed.
ize).

Pore volume of raw material In order to have an optimum average pore diameter, a preferable pore volume of the raw material silica or silica gel is 0.05 from the correlation between the specific surface area, the pore volume and the average pore diameter. ~ 0.5
cm ³ / g, more preferably 0.1-0.3 cm
³ / g. Above this, the pore diameter becomes too large and it becomes difficult to smoothly advance the adsorption of VOC molecules. Conversely, if it is less than 0.05 cm ³ / g, the pore diameter becomes too small, and it becomes difficult for VOC molecules to enter the pores.

Raw Material Pellet Shape The raw material of the adsorbent raw material of the present invention may preferably be of various shapes such as a sphere, a column and a tablet.
Silica powder or silica gel powder can also be used, but in this case, it is preferable to mold them into various shapes and use them. As a molding method, a general molding method such as compression molding and extrusion molding can be preferably used. Note that a binder may be appropriately added to facilitate molding. The size of the molded body is determined by factors such as the size of the packed bed of the adsorbent and the allowable differential pressure.
mm, and more preferably 3 mm to 8 mm. If it is less than this, the differential pressure becomes too large, and if it exceeds this,
The voids between the compacts are too large.

Heating Rate The adsorbent of the present invention can be obtained by subjecting a silica gel raw material or a silica raw material having the above physical properties to a predetermined hydrophobic treatment. In the hydrophobization treatment, the temperature is raised to a predetermined range of the predetermined heating temperature at a specified range of the heating rate, and is maintained at the predetermined temperature for a predetermined time. The predetermined heating temperature does not need to be constant during the predetermined time, and may fluctuate within the specified temperature range. The rate of temperature rise may be 1 to 20 ° C / min, and more preferably 5 to 15 ° C / min. If the rate of temperature rise is higher than this, the temperature difference between the surface and the inside of the raw material particles becomes too large, so that the raw material particles are likely to crack. Furthermore, a heating rate higher than 20 ° C./min is not preferable because there is a possibility that the temperature may exceed a predetermined temperature range (overshooting) when shifting from heating to holding the temperature. Conversely, there is no theoretical problem if the heating rate is low, but 1 ° C./min is a practical lower limit because of economic reasons such as low productivity.

Heating temperature and holding time After the temperature is raised to the specified heating temperature, for 2 to 5 hours,
The raw material particles are fired while maintaining this temperature range. During this time,
Careful attention must be paid to temperature control. The range of the heat treatment (firing) temperature is preferably from 550 ° C to 700 ° C, more preferably from 600 ° C to 700 ° C, and most preferably from 62 ° C to 700 ° C.
0 ° C to 700 ° C. The calcination time is not conditional as compared with the temperature condition, but is preferably 2 hours to 5 hours, more preferably 3 hours to 5 hours.

According to the following equations (1) and / or (2),
Hydrophobization is considered to proceed by decomposing / eliminating or condensing a large number of silanol groups (Si-OH) present on the surface of silica or silica gel. It is necessary to maintain a predetermined temperature within a temperature range for a predetermined time. (SiOH) _n → Decomposition and desorption of SiO ₂ (1) (SiOH) _n → (Si-O-Si) _{n / 2} condensation (2) When the upper limit of the specified temperature range is exceeded, sintering of silica or silica gel ( Sintering) proceeds remarkably, and the decrease in specific surface area exceeds 40%, so that desired porous properties cannot be obtained. Conversely, if the temperature is lower than the lower limit of the temperature range, the hydrophobizing treatment becomes insufficient, so that the possibility of the adsorbent cracking during the pressure swing cycle of the PSA method increases. Compared with the temperature range, the severity of the time range to be maintained is not high, but if it is less than 2 hours, the chemical reactions of the formulas (1) and (2) may not proceed sufficiently. Poor productivity.

In order to prevent cracking due to thermal expansion or the like, the temperature is raised at a predetermined heating rate, and the surface OH groups are removed at a temperature of 550 ° C. or more and 700 ° C. or less as shown in formulas (1) and (2).
The hydrophobizing ability is improved. If only the purpose of improving the hydrophobicity is to increase the temperature and sintering, it is sufficient. However, in order to recover a low concentration of VOC in the air, a high surface area is maintained and the excellent hydrophobicity is improved. Therefore, as described above, the physical properties of the adsorbent raw material (silica or silica gel) become important.

[0023] As the specific surface area decreasing rate adsorption isotherm in PSA method (adsoption-isotherm), instead of performing adsorption until a steady state, in order to swing the pressure for each step of the adsorption predetermined time, low partial pressure It is necessary to adsorb VOC molecules quickly, and the adsorption speed is one of the important factors. Therefore, VO
In order to effectively adsorb C molecules, it is important to have a specific specific surface area, an average pore diameter and a hydrophobizing ability. As a result, the adsorption speed increases. In order to realize a high adsorption speed, the specific surface area reduction rate is preferably small. When the specific surface area reduction rate is 40% or more, the pore diameter changes due to sintering, the VOC adsorption capacity decreases, and cracks and strains occur due to volume change. And the like. By performing the heat treatment for hydrophobization under the conditions shown above, the reduction rate of the specific surface area represented by the formula (3) remains at 40% or less,
In addition, the average pore size is close to that of the silica gel raw material. As a result, an adsorbent having both excellent hydrophobizing ability and VOC adsorbing ability and having a high adsorption speed is realized. Specific surface area reduction rate (%) = (specific surface area of raw material silica / specific surface area after heat treatment) × 100 (3)

In the case of equilibrium adsorption at a water vapor adsorption amount of 20 ° C. and a water vapor pressure of 2 mmHg, if the adsorbent adsorbs 10 ml or more of water vapor per g, cracks often occur in the adsorbent. In addition, by the hydrophobizing treatment of the method of the present invention, the water vapor adsorption amount of the adsorbent is 10 ml /
g or less, but it is difficult to make it less than 3 ml-water vapor / g-adsorbent.

Usage of Adsorbent When the adsorbent is actually used in the PSA system, the volume and number of adsorption towers, the VOC concentration in the inlet gas, the VO
The amount of the adsorbent, the height of the adsorbent, and the like are appropriately determined according to operating conditions such as the C capture rate and the operating temperature. This adsorbent may be used in combination with or mixed with a known adsorbent such as high silica zeolite or alumina. However, since the market price of other adsorbents is higher than that of the present adsorbent, if the mixing amount or combination amount of known adsorbents is large, the economic advantage of the adsorbent of the present invention is lost. No activation treatment is required prior to using the adsorbent of the present invention.
For example, when stored for a long time in an extremely high humidity state, a vacuum drying process at a temperature in a range of room temperature to 350 ° C.
What is necessary is just to implement suitably. The drying time under reduced pressure is not absolutely determined by the PSA apparatus, but is a realistic time of 1 to 24 hours.

VOC selectivity of adsorbent The VOC selectivity of the adsorbent referred to in the present invention is the ratio of the amount of volatile organic compound adsorbed to the amount of water vapor and volatile organic compound adsorbed by the adsorbent. The ratio is a value defined by the following equation. VOC selectivity = {(A) / (A + B)} × 100 Here, A is a value of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C., Equilibrium adsorption of volatile organic compounds (ml / g (stp))
It is. B is the equilibrium adsorption amount (ml / g (stp)) of water vapor on the adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C.
In the present invention, when defining the equilibrium adsorption amount of the volatile organic compound (VOC) in the adsorbent, not the saturated vapor pressure of VOC but the pressure of 1/10 of the saturated vapor pressure of VOC is used as the saturated vapor pressure. This is because most of the VOC is adsorbed on the adsorbent before the pressure becomes 1/10 of the pressure. That is, in practice, the amount of adsorption at the saturated vapor pressure / the amount of adsorption at 1/10 of the saturated vapor pressure. Also, in the actual operation of PSA by the pressure fluctuation method,
In the adsorption step, the adsorption step is performed without increasing the pressure to the saturated vapor pressure of the VOC, until the pressure reaches 1/10 of the saturated vapor pressure of the VOC, and then the process proceeds to the desorption step.

From the above, the VOC selectivity is PSA
Can be defined as a factor indicating the VOC adsorption efficiency at the time of operation. Physically, the larger the value of the VOC selectivity of the adsorbent, the more easily the volatile organic compound is adsorbed in the presence of water vapor, and it can be evaluated as an excellent adsorbent for VOC-PSA. Therefore, the VOC selectivity of the adsorbent is 80% or more,
It is preferably at least 85%. An adsorbent having a VOC selectivity of 80% or more requires a smaller amount of adsorbent as compared with an adsorbent having a low VOC selectivity, and is significantly advantageous in terms of PSA method economics and operating efficiency. It is.

In addition to the VOC selectivity described above, the amount of VOC adsorbed by the adsorbent is also an important factor. For example, even if the VOC selectivity of the adsorbent is high, if the amount of adsorbed VOC is small, there arises a problem that the amount of adsorbent necessary for separating and recovering a predetermined amount of VOC becomes too large. Therefore, V
It is necessary to show a high OC selectivity and a VOC adsorption amount equal to or higher than a predetermined level. VOC adsorption amount is 20 ℃
And the equilibrium adsorption amount (ml / g (stp)) of the volatile organic compound to the adsorbent at a temperature of 20 ° C. under a pressure of 1/10 of the saturated vapor pressure of the volatile organic compound in the above. The measuring method is the same as the method shown in the measuring method of VOC selectivity. 1 of saturated vapor pressure of volatile organic compounds at a temperature of 20 ° C
The equilibrium adsorption amount of the volatile organic compound to the adsorbent at a temperature of 20 ° C. under a pressure of / 10 is preferably 30 ml / g (stp) or more, and more preferably 35 ml / g (stp) or more. If the value of the VOC adsorption amount is smaller than this, the amount of the adsorbent required for the apparatus to obtain the same effect increases, so that the adsorption tower becomes large and the standard of the equipment attached to the apparatus becomes large. In addition, there is a high possibility that operating costs will increase, for example, the size of the entire apparatus will increase, and the power consumption will increase. Conversely, the upper limit is not particularly limited, but is 150 m
It is considered that about 1 / g (stp) is the current upper limit.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described by way of examples.
The embodiment will be described specifically and in detail. Perform the following
Porous physical properties, hydrophobizing ability and
VOC adsorption capacity was evaluated by the following measurement methods and evaluation methods.
Was.Measurement of porous physical properties such as specific surface area, pore volume and average pore diameter
Ordinary law Porous physical properties of adsorbent raw materials (hereinafter referred to as raw material physical properties) and hydrophobicity
Physical properties of the adsorbent obtained by the
) Is high purity N_Two(Takachiho Chemical, Research Grade)
Automated surface for probe molecule
Product / pore diameter measuring device (Belsorp28, manufactured by Bell Japan)
Was measured by In the measurement of porous physical properties, specific surface area and
Prior to the measurement of the pore size, first, as a pretreatment, the sample adsorbent
And heat treatment under reduced pressure of the adsorbent raw material, and then
The properties were measured. Approximately 200 mg
Of the sample into a glass sample tube, ^-1-10^-2mmHg
While maintaining the reduced pressure, from the room temperature at a heating rate of 6 ° C./min.
The temperature was raised to 350 ° C. and maintained at the same temperature for 3 hours. That
After that, it is maintained at normal pressure +5 mmHg by high-purity helium gas.
While cooling, cool down to room temperature at a cooling rate of 5 ° C / min.
A sample was obtained. The weight of the obtained sample is accurately weighed, and the
Was used for the measurement. Liquefied nitrogen automatic
Use an automatic dewar with an auto feeder
Liquefied nitrogen temperature (-196 ° C)
(Dead volume) 3 times or more with high purity helium
Then, after evacuation, the probe molecules (nitrogen) are introduced.
And measured the specific surface area according to the BET method. Then
An adhesion measurement was carried out, and the average pore diameter was determined.

Method for Evaluating Hydrophobicity of Adsorbent In order to evaluate the hydrophobicity of the adsorbent, the equilibrium adsorption of water vapor was measured at a temperature of 20 ° C. and a pressure of 2 mmHg. Before the measurement of the hydrophobizing ability, the sample adsorbent was subjected to the following reduced pressure heating treatment as a pretreatment. That is, about 100 mg of a sample is put into a glass sample tube, and the temperature is raised from room temperature to 350 ° C. at a rate of 6 ° C./min while reducing the pressure to 10 ⁻¹ to 10 ⁻² mmHg. Hold for hours. Next, the sample was cooled to room temperature at a temperature lowering rate of 5 ° C./min to obtain a sample adsorbent. The obtained sample adsorbent was accurately weighed and provided for a sample for measurement. The water used as the water vapor source is prepared by putting 50 ml of ion-exchanged water into a glass liquid reservoir, bubbling it with a reduced pressure line, and carefully cooling and freezing the liquid reservoir bottom with dry ice-methanol refrigerant. Dissolved gas was released while evacuating at about 10 ^-2 mmHg. Subsequently, it was heated and thawed. This process was repeated until no dissolved gas was released to obtain purified water.

In the measurement of the equilibrium adsorption amount, a high-precision vapor adsorption amount measuring apparatus (Belsorp18, manufactured by Bell Japan) was used.
A glass reservoir (reservoir, volume: 150 m) in which a saturated water vapor generated from the liquid pool is maintained at 50 ° C. ± 1 ° C. while a liquid pool of purified water is maintained at 50 ° C. ± 1 ° C. in an air thermostat.
l), and further, water vapor was gradually introduced from a reservoir through an automatic flow control valve into a glass adsorption tube in which only the portion containing the sample adsorbent was kept at 20 ° C ± 0.5 ° C.
The introduction was continued until an equilibrium pressure of 2 mmHg was reached. 2mmH
g when the equilibrium pressure is reached, that is, when the pressure fluctuation for 10 minutes is within 0.1 mmHg, the amount of water introduced is determined from the pressure measured by the capacitance manometer and the internal volume of the system. Further, the equilibrium adsorption amount per weight of the adsorbent was calculated based on the sample weight after the pretreatment. In addition, in order to evaluate the cracking resistance of the adsorbent to water as one of the hydrophobicity, the sample adsorbent is immersed in water at 20 ° C.
After two weeks, cracks were checked.

Evaluation Method of VOC Adsorption Capacity of Adsorbent In order to evaluate the VOC adsorption capacity of the sample adsorbent, the reversible adsorption amount of VOC was measured as follows. Prior to the measurement, the sample adsorbent was subjected to the following reduced pressure heat treatment as a pretreatment. In the heat treatment under reduced pressure, first, about 100 mg of a sample is put into a sample tube, and the temperature is increased from room temperature to 350 ° C. at a rate of 6 ° C./min while reducing the pressure to 10 ⁻¹ to 10 ⁻² mmHg. At 1
Hold for hours. Next, the sample was cooled to room temperature at a temperature lowering rate of 5 ° C./min to obtain a sample adsorbent. In the measurement of VOC adsorption capacity,
The required sample weight was accurately weighed from the obtained sample adsorbent and provided for measurement. Further, isopentane to be used for the measurement was purified as follows. First, isopentane (Tokyo Kasei Kogyo Co., Ltd., reagent grade) is placed in a liquid reservoir, and bubbling is performed in a decompression line. Then, the surface of the liquefied nitrogen in the dewar is carefully brought into contact with the bottom of the liquid reservoir, cooled, solidified, and dissolved. Vacuum evacuation was performed on the order of 10 ^-2 mmHg while releasing gas. Then, it was heated and melted. This operation was repeated until no dissolved gas was released, to purify isopentane. Water used as a water vapor source was purified in the same manner as in the evaluation of the hydrophobicity.

At the time of measurement, purified water and isopentane were put into respective liquid reservoirs, and kept at a constant temperature of 50 ° C. ± 1 ° C. in a thermostat. First, the saturated steam generated from the liquid pool was cooled to 50 ° C.
Glass reservoir maintained at a temperature of ± 1 ° C (reservoir
, A volume of 150 ml) up to a pressure of 30 mmHg, and only the portion containing the sample adsorbent is stored at 20 ° C. ±
Water vapor was gradually introduced from a reservoir through an automatic flow control valve into a glass adsorption tube maintained at a temperature of 0.5 ° C.
The introduction was continued until the equilibrium pressure reached 0 mmHg. Then
From the pressure measured by the capacitance manometer and the internal volume of the system, the amount of water adsorbed when the equilibrium pressure of 10 mmHg was reached was determined. Then, isopentane vapor generated from the liquid reservoir was introduced into a glass reservoir (volume 150 ml) maintained at a temperature of 50 ° C. ± 1 ° C. up to a pressure of 540 mmHg, and only the portion containing the sample adsorbent was stored at 20 ° C. ± 0 ° C. .5 ° C
Isopentane vapor was gradually introduced from the reservoir through an automatic flow control valve into the glass adsorption tube maintained at the temperature of
The introduction was continued until the equilibrium pressure reached 540 mmHg. The equilibrium adsorption amount was the adsorption amount when the pressure fluctuation for 10 minutes was within 0.1 mmHg. The adsorption amount of isopentane is
It was determined from the pressure change and the volume in the system measured by the capacitance manometer, and further, the amount of adsorption per weight of the adsorbent was calculated based on the sample weight after pretreatment. Water vapor adsorption and V
The OC adsorption amount is measured using a high-accuracy vapor amount measurement device (Belsorp1
8, Bell Japan Co., Ltd.), and the opening and closing and adjustment of the flow control valve, etc. are performed by a personal computer (PC9821, manufactured by NEC)
Was controlled on-line.

The adsorbent according to the present invention is an adsorbent capable of selectively and efficiently adsorbing VOC having a low concentration of VOC in the atmosphere around a gas station or an oil depot, that is, VOC mixed with air to some extent. A problem in the adsorption and recovery of such low-concentration VOCs is the effect of the moisture contained in the air.
That is, the adsorption ability is reduced. In other words, low concentration VO
An excellent adsorbent for C is an adsorbent that is not easily affected by moisture. When moisture and VOC coexist, the adsorbent usually absorbs VOC of the adsorbent in order to preferentially adsorb water.
Adsorption capacity decreases. In this evaluation method, first, moisture is adsorbed on the adsorbent, then VOC is adsorbed, and the adsorbing ability is evaluated. This means that the VOC adsorption capacity is evaluated in a state where the water content is large, that is, in a state similar to a state where the VOC is at a low concentration. If reduced, like this evaluation method,
By adsorbing moisture in advance, the adsorbent is in a low-concentration VOC atmosphere or under more severe conditions, so that a large amount of VOC can be adsorbed even after moisture adsorption. It is highly correlated with the excellent ability to adsorb low concentration VOCs.

Measurement method of VOC selectivity of adsorbent The measurement of equilibrium adsorption amount of water vapor (ml / g (stp)) on adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C. is described in the method of evaluating adsorbent's hydrophobicity. This is performed according to a method for measuring the equilibrium adsorption amount of the water vapor. Equilibrium adsorption of the volatile organic compound on the adsorbent at a temperature of 20 ° C. under a pressure of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C. (ml / g (stp))
Is measured as described below. The organic compound used for the measurement is purified in advance. For example, taking isopentane as an example, first place reagent-grade isopentane in a reservoir, bubbling in a vacuum line, and then carefully contact the liquefied nitrogen surface in a Dewar bottle with the bottom of the reservoir to cool the isopentane, While solidifying, the dissolved gas is released while evacuating with a vacuum of the order of 10 ^-2 mmHg.
Next, the solidified isopentane was heated and melted. Repeat this operation until no dissolved gas is released,
Isopentane was degassed and purified. In the case of volatile organic compounds that are hard to solidify at the temperature of liquefied nitrogen, molecular sieves (molecular sieves) that have been cooled to around the temperature of liquid nitrogen in advance
The volatile organic compound is adsorbed on the material and heated, and the gas first desorbed from the molecular sieve is accumulated in the gas reservoir.

A glass reservoir (volume: 15) in which the degassed and purified isopentane vapor was maintained at 50 ° C. ± 1 ° C.
0 ml) to about 540 mmHg, and further, isopentane vapor was introduced from the reservoir into a glass adsorption tube in which the reservoir containing the sample adsorbent was kept at 20 ° C ± 0.5 ° C. Of saturated vapor pressure of
Under a pressure of / 10, the pressure fluctuation for 10 minutes at a temperature of 20 ° C. is 1/10 of the vapor pressure at 1 atm.
The amount of adsorption (equilibrium adsorption amount) at the time when the pressure fluctuation per minute becomes 0.02 mmHg or less is determined by the equilibrium adsorption of isopentane at 20 ° C. under the pressure of 1/10 of the saturated vapor pressure of isopentane at 20 ° C. Volume (ml / g (stp)). In the above description, isopentane is described as an example of the volatile organic compound, but the volatile organic compound is not limited to isopentane.

Hereinafter, specific experimental results will be shown. Example 1 Specific surface area is 600 m ² / g, pore volume is 0.40 ml / g
And a silica gel powder having a raw material property having an average pore diameter of 2.5 nm was tablet-formed into a 3.2 mm (diameter) × 3 mm (height) cylindrical pellet. The pellets were then heated in a muffle furnace from room temperature to 550 ° C. at a rate of 1 ° C./min and subsequently held at 550 ° C. for 5 hours. Then, it cooled to room temperature and obtained the sample adsorbent of Example 1.

When the physical properties of the sample adsorbent of Example 1 were measured, the specific surface area was 570 m ² / g and the pore volume was 0.38 m
1 / g, and the average pore diameter was 2.5 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel powder was 5%. Further, the water vapor saturated adsorption amount at 20 ° C. and 2 mmHg measured according to the above-described method for evaluating hydrophobicity was 9.8 ml / g (stp).
stp stands for Standard Temperature and Pre
ssure), and indicates the adsorption amount converted to 0 ° C. and normal pressure. Also, even after immersion in water and lapse of two weeks, no crack was generated in the sample adsorbent. According to the above-described method for evaluating the VOC adsorption ability, water is 10 mmHg at 20 ° C.
The amount of adsorbed isopentane measured after equilibrium adsorption was 3.1 m
1 / g (stp). The physical properties of the raw material, the conditions of the hydrophobic treatment, the physical properties of the adsorbent, the hydrophobicity and the amount of VOC adsorbed in Example 1 are described in the column of Example 1 in Table 1, respectively. Hereinafter, the same applies to Examples 2 to 5.

[Table 1]

Example 2 Specific surface area is 660 m ² / g, pore volume is 0.10 ml / g
And a silica gel powder having a raw material property having an average pore diameter of 0.6 nm is tablet-formed into pellets having the same shape as in Example 1, and the temperature is raised from room temperature to 600 ° C. at a rate of 5 ° C./min in a muffle furnace.
, And then kept at 600 ° C. for 4 hours. Then, it cooled to room temperature and obtained the sample adsorbent of Example 2.
The specific surface area of the sample adsorbent of Example 2 was 581 m ² / g, the pore volume was 0.09 ml / g, and the average pore diameter was 0.6 nm.
Met. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 12%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 7.5 ml / g (stp) and 4.5 ml / g (stp), respectively. In addition, no crack was generated in the sample adsorbent two weeks after immersion in water.

Example 3 Specific surface area is 690 m ² / g, pore volume is 0.30 ml / g
And a particle diameter 2 having a raw material property of an average pore diameter of 2.0 nm.
３3 mm spherical silica gel was heated from room temperature to 650 ° C. in a muffle furnace at a rate of 10 ° C./min.
It was kept at a temperature of 50 ° C. for 3 hours. Then, it cooled to room temperature and obtained the sample adsorbent of Example 3. The specific surface area of the sample adsorbent of Example 3 was 448 m ² / g, and the pore volume was 0.20 m.
1 / g and the average pore diameter were 1.8 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material spherical silica gel was 35%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 5.3 ml / g (stp) and 4.1 m, respectively.
1 / g (stp). In addition, no crack was generated in the sample adsorbent two weeks after immersion in water.

Example 4 The specific surface area is 700 m ² / g and the pore volume is 0.30 ml / g
And a particle diameter 2 having a raw material property of 1.5 nm in average pore diameter
３3 mm of spherical silica gel was heated from room temperature to 700 ° C. in a muffle furnace at a heating rate of 20 ° C./min.
It was kept at 00 ° C. for 3 hours. Then cool to room temperature,
The sample adsorbent of Example 4 was obtained. The specific surface area of the sample adsorbent of Example 4 was 420 m ² / g, and the pore volume was 0.18 ml / g.
g and average pore diameter were 1.7 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 40%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 3.2 ml / g (stp) and 3.7 ml / g (s), respectively.
tp). In addition, no crack was generated in the sample adsorbent two weeks after immersion in water.

Example 5 Specific surface area is 780 m ² / g, pore volume is 0.30 ml / g
And a particle diameter 2 having a raw material property of 1.5 nm in average pore diameter
３3 mm spherical silica gel was heated from room temperature to 620 ° C. in a muffle furnace at a rate of 15 ° C./min.
It was kept at a temperature of 20 ° C. for 2 hours. Then, it cooled to room temperature and obtained the sample adsorbent of Example 5. The specific surface area of the sample adsorbent of Example 5 was 655 m ² / g, and the pore volume was 0.25 m
1 / g, and the average pore diameter was 1.5 nm. Accordingly, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 16%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 10.0 ml / g (stp) and 5.9 ml / g, respectively.
g (stp). In addition, no crack was generated in the sample adsorbent two weeks after immersion in water.

Comparative Example 1 The specific surface area was 450 m ² / g, and the pore volume was 0.69 ml / g.
g, a silica powder having an average pore diameter of 6.1 nm and having raw material properties is tablet-formed into pellets having the same shape as in Example 1,
From a room temperature to 650 at a heating rate of 10 ° C / min in a muffle furnace
C. and subsequently held at a temperature of 650.degree. C. for 3 hours. Thereafter, the mixture was cooled to room temperature to obtain a sample adsorbent of Comparative Example 1. The specific surface area of the sample adsorbent of Comparative Example 1 was 383 m ² /
g, the pore volume was 0.59 ml / g, and the average pore diameter was 6.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 15%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 7.5 ml / g (s
tp) and 1.5 ml / g (stp). Also,
Two weeks after immersion in water, no cracks occurred in the sample adsorbent. The physical properties of the raw material of Comparative Example 1, the conditions of the hydrophobic treatment, the physical properties of the adsorbent, the hydrophobicity and the VOC adsorption amount were as follows:
Each is described in the column of Comparative Example 1 in Table 2. Hereinafter, the same applies to Comparative Examples 2 to 6.

[Table 2]

Comparative Example 2 The specific surface area was 650 m ² / g and the pore volume was 0.40 ml / g
And a particle size 2 having a raw material property having an average pore diameter of 2.5 nm.
３3 mm spherical silica gel was heated from room temperature to 800 ° C. in a muffle furnace at a rate of 30 ° C./min.
It was kept at a temperature of 00 ° C. for 6 hours. Then, it cooled to room temperature and obtained the sample adsorbent of Comparative Example 2. The specific surface area of the sample adsorbent of Comparative Example 2 was 280 m ² / g, and the pore volume was 0.79 m.
1 / g, and the average pore diameter was 11.3 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 65%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 4.8 ml / g (stp) and 0.1 ml / g, respectively.
(Stp). Also, two weeks after immersion in water, the sample adsorbent had significant cracks.

Comparative Example 3 The specific surface area was 780 m ² / g and the pore volume was 0.30 ml / g.
g, particle diameter 2 having raw material properties with an average pore diameter of 1.5 nm
球状 3 mm spherical silica gel was heated from room temperature to 520 ° C. at a rate of 0.5 ° C./min from room temperature in a muffle furnace, and then kept at a temperature of 520 ° C. for 1 hour. afterwards,
After cooling to room temperature, a sample adsorbent of Comparative Example 3 was obtained. The specific surface area of the sample adsorbent of Comparative Example 3 was 760 m ² / g, the pore volume was 0.29 ml / g, and the average pore diameter was 3.0 nm. Accordingly, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 3%. The water vapor saturated adsorption amount and isopentane adsorption amount obtained in the same manner as in Example 1 were 26.6 ml / g (stp) and 0.1, respectively.
It was 3 ml / g (stp). In addition, the sample adsorbent was powdered two weeks after immersion in water.

Comparative Example 4 The specific surface area was 690 m ² / g and the pore volume was 0.30 ml / g.
g, spherical silica gel (2 to 3 mm diameter) having a raw material property having an average pore diameter of 2.0 nm is heated in a muffle furnace from room temperature at a heating rate of 10 ° C./min, heated to 800 ° C., and then at the same temperature for 3 hours. Held. Then, it cooled to room temperature and was set as the sample adsorbent of Comparative Example 4. The specific surface area of the sample adsorbent of Comparative Example 4 was 248 m ² / g, the pore volume was 0.32 ml / g, and the average pore diameter was 5.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 64%. In addition, it shows hydrophobicity, 20 ° C, 2m
The water vapor saturated adsorption amount at mHg is 4.8 ml / g (st
p), no cracks were observed 2 weeks after immersion in water. The isopentane adsorption amount after equilibrium adsorption of 10 mmHg of water at 20 ° C. was 0.2 ml / g (stp).

Comparative Example 5 The specific surface area was 780 m ² / g and the pore volume was 0.30 ml / g.
g, spherical silica gel having an average pore diameter of 1.5 nm and having physical properties as raw materials was heated in a muffle furnace from room temperature to a heating rate of 5 ° C./mi.
n, heated to 520 ° C., and maintained at the same temperature for 3 hours. Then, it cooled to room temperature and was set as the sample adsorbent of Comparative Example 5. The specific surface area of the sample adsorbent of Comparative Example 5 is 755 m
² / g, the pore volume was 0.29 ml / g, and the average pore diameter was 1.5 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 3%. In addition, the water vapor saturated adsorption amount at 20 ° C. and 2 mmHg, which shows hydrophobicity, was 25.8 ml / g (stp), and powdered two weeks after immersion in water. 10mm water at 20 ℃
Isopentane adsorption amount after Hg equilibrium adsorption is 0.2 ml / g
(Stp).

Comparative Example 6 The specific surface area was 650 m ² / g and the pore volume was 0.40 ml / g.
g, a spherical silica gel having an average pore diameter of 2.5 nm and having physical properties of a raw material was heated in a muffle furnace from room temperature to a heating rate of 30 ° C./m.
After heating to 700 ° C., the temperature was maintained at the same temperature for 3 hours. Then, it cooled to room temperature and was set as the sample adsorbent of Comparative Example 6. The specific surface area of the sample adsorbent of Comparative Example 6 was 390
m ² / g, the pore volume was 0.60 ml / g, and the average pore diameter was 6.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 40%. In addition, the water vapor saturated adsorption amount at 20 ° C. and 2 mmHg showing the hydrophobizing ability was 3.7 ml / g (stp), and cracks had occurred two weeks after immersion in water. 20
The isopentane adsorption amount after equilibrium adsorption of water at 10 mmHg at 1.5 ° C. was 1.5 ml / g (stp).

As can be seen from the comparison between the examples and the comparative examples, the VOC adsorption amounts of all the examples were at least twice the VOC adsorption amounts of the comparative examples. Further, the sample adsorbent of the comparative example was powdered or cracked. When the specific surface area of the sample adsorbent is 400 m ² / g or less, the VOC adsorption ability is extremely poor as in Comparative Examples 1 and 2. Conversely, when the specific surface area is 700 m ² / g or more, as in Comparative Example 3. In addition, cracks easily occur in the adsorbent. Further, when the specific surface area of the raw material silica gel is 600 m ² / g or less, the VOC adsorption ability of the sample adsorbent is extremely poor as in Comparative Example 1.

In Comparative Example 1, the hydrophobizing treatment was carried out under the conditions specified in the present invention, but the specific surface area, the pore volume, and the average pore diameter were out of the specific ranges of the present invention, respectively, although they exhibited good hydrophobicity. Therefore, the VOC adsorption ability is poor. In Comparative Example 2, although the raw material properties of the raw material silica gel were within the specific range of the present invention, the hydrophobizing treatment conditions, that is, the heating rate and the heat treatment temperature exceeded the upper limits of the ranges specified in the present invention, respectively. Sintering or distortion occurred in the silica gel, and as a result, although the water vapor adsorption amount was relatively low, the VOC adsorption ability was extremely poor, and cracks occurred in the sample adsorbent. In Comparative Example 3, although the raw material properties of the raw material silica gel were within the specific range of the present invention, the hydrophobizing treatment conditions, particularly, the heat treatment temperature was lower than the lower limit of the range specified by the present invention, and the hydrophobizing treatment was insufficient. Furthermore, the hydrophobizing ability is poor and the VOC adsorption ability is extremely poor.

In Comparative Example 4, although the raw material properties were the same as in Example 3, the hydrophobizing temperature was 800 ° C., which was higher than the upper limit of the temperature range specified in the present invention. Therefore, although the adsorption material is hydrophobized, the specific surface area reduction rate is significantly increased, and the specific surface area of the obtained sample adsorbent does not reach the lower limit of the range specified in the present invention, so that sufficient VO
The amount of C adsorbed was not obtained, and it was not suitable as an adsorbent. Comparative Example 5 has the same raw material properties as Example 5, but has a hydrophobizing treatment temperature of 520 ° C., which is lower than the lower limit of the temperature range specified in the present invention. As a result, the specific surface area reduction rate is small in order to maintain the raw material properties. However, since the temperature range is low, the hydrophobicity becomes insufficient, the amount of water vapor adsorbed is remarkably large, and the sample adsorbent immersed in water is remarkably powdered. As a result, the VOC adsorption amount was also extremely low. In Comparative Example 6, although the raw material properties were within the range specified in the present invention, the heating rate during the hydrophobizing treatment was 30 ° C./min, which was higher than the upper limit of the heating rate range specified in the present invention. For this reason, the adsorbent is in a state where distortion is likely to occur. Since the heat treatment temperature was within the specified value, the surface was hydrophobized in terms of the amount of water adsorbed, but cracks occurred when immersed in water because of large distortion. Further, the VOC adsorption amount was also an unsatisfactory value, and was unsuitable as an adsorbent.

The results of Examples 1 to 5 in Table 1 and Comparative Example 1
By comparing with the results of the above, the hydrophobizing ability was 5
The temperature is effectively increased by reaching a temperature in the range of 50 to 700 ° C. at a rate of temperature increase of 1 to 20 ° C./min and maintaining the temperature in the same temperature range for 2 to 5 hours. Further, by using silica gel whose raw material properties are within the specified range of the present invention, good hydrophobicity such as crack resistance against water and water repellency, and high VO
An adsorbent exhibiting C adsorption ability can be obtained.

Evaluation by VOC Selectivity As one of the factors indicating the VOC adsorption capacity, V of the sample adsorbent
The OC selectivity was measured. Tables 3 and 4 show the sample adsorbents of Examples 1 to 5 and Comparative Examples 1 to 6.
And VOC selectivity was measured according to the method described above, and the results shown in Tables 3 and 4 were obtained. For the sample adsorbent of Example 3, three types of VO
For C, the VOC selectivity was measured. As can be seen from the comparison between Tables 3 and 4, the sample adsorbents of Examples 1 to 5 have VOC selectivities of 85% or more and 74%.
Compared to the VOC selectivities of Comparative Examples 1 to 6 below,
It shows a significantly higher VOC selectivity. From the test using the sample adsorbent of Example 3, the sample adsorbent of Example 3 shows that V
It can be seen that even if the types of OC are different, almost the same VOC selectivity is exhibited.

[Table 3]

[Table 4]

The above examples are illustrative for illustrating the present invention, and do not limit the present invention. The porous physical properties of the raw material silica gel, the conditions for the hydrophobic treatment, and the adsorbent for volatile organic compound gas Porous physical properties and the like are not limited by the conditions of the above-described examples unless they depart from the gist of the present invention.

[0055]

According to the present invention, by forming an adsorbent from a porous molded body containing silica as a main component and having specific porous physical properties, it has good hydrophobizing ability and high VOC adsorbing ability, A volatile organic compound gas adsorbent that selectively adsorbs a volatile organic compound gas having 1 to 12 carbon atoms can be realized. Furthermore, by subjecting a silica or silica gel raw material having specific porous properties to hydrophobic treatment conditions under specific conditions, an adsorbent according to the present invention optimal for the adsorption of volatile organic compound gas is economically produced. be able to. In addition, the low-cost volatile organic compound gas adsorbent of the present invention is VO
When used in a C-PSA device, VOC vapor can be recovered at an economical adsorbent cost, and an economical VOC-PSA device that is effective for preserving the atmospheric environment can be realized. In addition, the VOC can be stably recovered for a long period of time due to the excellent hydrophobicity of the adsorbent for volatile organic compound gas of the present invention and the high cracking resistance to water.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Yoshizawa 1134-2 Gongendo, Satte City, Saitama Prefecture Inside the R & D Center, Kosmo Research Institute, Inc. (72) Tomohiro Yoshinari 1134- Gongendo, Satte City, Saitama Prefecture 2 Research and Development Center, Cosmo Research Institute, Inc.

Claims (4)

[Claims] 1. A silica-based material having a specific surface area of 400
７００700 m ² / g, average pore diameter is 0.4 to 3.0 nm,
An adsorbent characterized in that it selectively adsorbs a volatile organic compound gas having 1 to 12 carbon atoms, the adsorbent being made of a porous molded body having a water vapor adsorption amount of 3 to 10 ml-water vapor / g-adsorbent. 2. A method for producing an adsorbent for selectively adsorbing a volatile organic compound gas having 1 to 12 carbon atoms, wherein the specific surface area is at least 600 m ² / g and the pore volume is 0.05.
~ 0.5 cm ³ / g and average pore size is 0.4 ~
A molded pellet of silica or silica gel in the range of 3.0 nm is heated to a temperature of 550 ° C. to 70
A method for producing an adsorbent, comprising raising the temperature to a predetermined temperature in a range of 0 ° C. and maintaining the temperature at the predetermined temperature for a predetermined time. 3. An adsorbent produced by the method for producing an adsorbent according to claim 2, wherein the rate of decrease in specific surface area is 4%.
An adsorbent, which is 0% or less and has a water vapor adsorption amount of 3 to 10 ml-water vapor / g-adsorbent. 4. A VOC selectivity defined by the following equation:
% Or more. VOC selectivity = {(A) / (A + B)} × 100 Here, A is a value of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C., Equilibrium adsorption of volatile organic compounds (ml / g (stp))
It is. B is the equilibrium adsorption amount (ml / g (stp)) of water vapor on the adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C.