JPH0624867A - Heat resistant stratiform silica porous body and production thereof - Google Patents

Abstract

PURPOSE:To provide a heat resistant stratiform silica porous body having excellent performance as a catalyst carrier, excellent adsorptivity to organic compounds such as fuel and heat resistance and large specific surface area and the producing method thereof. CONSTITUTION:In the stratiform silica porous body, a plate-like sheet layer 91 is formed from a crystalline stratiform silicate, a plurality of the sheet layer 91 is laminated and the adjacent sheet layers 91 are partially bonded with each other at bonding points 93 by silicate bond. The stratiform silica porous body forms a honeycomb porous structure, the distance between the adjacent sheet layers 91 is reduced at the bonding points 93 and fine pores 92 are formed with enlarged width between the bonding points 93. The content of alkali metal contained in the crystalline stratiform silicate is <=0.2wt.% and specific surface area is >=1000m<2>/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant layered silica porous material used as a catalyst carrier and an adsorbent for organic substances, and a method for producing the same.

[0002]

2. Description of the Related Art In a cracking catalyst and an exhaust gas purifying catalyst, the catalyst is exposed to a relatively high temperature (700 ° C. or higher).
Therefore, it is desirable that the catalyst itself has a high specific surface area in order to maintain the dispersibility of the active ingredient even at high temperatures. However, conventionally used zeolite, silica-alumina, alumina, silica gel, etc. do not necessarily have good heat resistance, and even if they have excellent heat resistance, there is a problem in the pore size distribution. On the other hand, there is a demand for an adsorbent having a large adsorbing capacity for use as an adsorbent for evaporative fuel filled in a canister of an automobile.

Recently, a silica porous material having a uniform pore size distribution has been synthesized (Bull. Chem. Soc. Jpn.,
Vol. 63, 988-992 (1990)). This porous silica material is obtained by widening the layers of the crystalline layered silicate. In this silica porous body, the laminated plate-like silica layers are finely curved, so that the adjacent silica layers are partially bonded by a siloxane bond to form a three-dimensional skeleton, and a uniform pore size distribution is obtained. Since it has the micropores, it has a honeycomb structure in cross section.

In producing the above layered silica porous material, first, a crystalline layered silicate is synthesized. next,
The water content in the crystalline layered silicate is dried. Then, by ion exchange with organic cations and washing with water, the width of the crystalline layered silicate layer is widened and alkali metal ions such as Na ⁺ are removed.

[0005]

However, the crystalline layered silicate aggregates due to the above-mentioned drying, and alkali metal ions cannot be sufficiently removed by the above-mentioned ion exchange and washing. Therefore, the alkali metal ion
It remains between the layers of the sheet layer and reduces the specific surface area due to crystallization into crystals and the like.

That is, the specific surface area of these layered silica porous materials is 900 m ² / g at the maximum, and the surface area is remarkably reduced at a high temperature of 800 ° C. or higher, resulting in poor heat resistance (see FIG. 3). In view of such problems, the present invention aims to provide a heat-resistant layered silica porous body having a high specific surface area and excellent heat resistance, and a method for producing the same.

[0007]

A heat-resistant layered silica porous material of the present invention comprises a plurality of plate-like sheet layers of crystalline layered silicate laminated, and the adjacent sheet layers are reduced in width at a bonding point by a siloxane bond. However, in the layered silica porous body having a honeycomb porous structure in which fine pores are widened between the bonding points, the content of alkali metal ions contained in the crystalline layered silicate is 0. Below 2 wt%,
In addition, the specific surface area is 1000 m ² / g or more.

What is most noticeable in the present invention is that the content of alkali metal ions contained in the layered silica porous material is 0.2 wt% or less and the specific surface area is 1000 m ² /
The point is that it is g or more. If the content of alkali metal ions exceeds 0.2 wt%, the movement of atoms is promoted at a relatively low temperature and crystallization into cristobalite or the like occurs. Therefore, the specific surface area of the layered silica porous material is reduced, and further the heat resistance is reduced. When the specific surface area of the layered silica porous material is less than 1000 m ² / g,
When the catalyst is loaded on the layered silica porous material, the activity of the catalyst cannot be sufficiently exerted, and when it is used as an adsorbent, its adsorption ability for organic substances is low.

The layered silica porous material of the present invention is shown in FIG.
~ As shown in Fig. 1 (c), the composition of the skeleton is SiO ₂ ,
It has a structure in which plate-shaped sheets 91 are vertically stacked, and each sheet 91 is curved or bent in the vertical direction. The upper and lower sheets 91 are partially connected to each other to form a honeycomb-shaped skeleton. The diameter of the fine holes 92 of the honeycomb is 1 to 6
It is 0Å.

[0010] The seat layer is a silicate layer SiO ₄ tetrahedra are formed by two-dimensionally linked, because the point of attachment of the SiO ₄ tetrahedra are bendable, even curved as a whole sheet layer Or it can be bent.
The sheet layer does not include an octahedron such as magnesium ion (Mg ²⁺ ) or aluminum ion (Al ³⁺ ) that interferes with the flexibility of the sheet layer. Further, the above-mentioned sheet layers are laminated by sandwiching an alkali metal ion such as Na ⁺ and H ⁺ . Further, specifically, as the crystalline layered silicate,
For example, kanemite (NaHSi ₂ O ₅ .3H ₂ O) is preferable.

Further, as another crystalline layered silicate,
Sodium disilicate (Na ₂ Si ₂ O ₃ ), Macatite (Na ₂ Si ₄ O ₉ / 5H ₂ O), Iraite (Na
₂ Si ₈ O ₁₇ · XH ₂ O), Magadiite (Na ₂ S
i ₁₄ O ₂₉ · XH ₂ O), Kenyaite (Na ₂ Si ₂₀ O)
₄₁ · XH ₂ O) or the like are typically, but not limited to.

Regarding the method for producing the above layered silica porous material, the alkali metal ion existing between the layers in the crystalline layered silicate having a water content of 10 wt% or more is ion-exchanged with the organic cation, and the organic cation is intercalated. The step of widening the inter-layer, the step of removing the alkali metal ions released by the ion exchange, and the step of burning the washed crystalline layered silicate to burn the organic cations and thereby to obtain the porosity. The method for producing a heat-resistant layered silica porous body is characterized by including the step of forming a porous body of the layered silica porous body.

In the above synthesis step, a crystalline layered silicate is synthesized from an amorphous silicate. As the amorphous silicate, there are commercially available powdered sodium silicate, those obtained by drying water glass into powder, and the like. For example, in the case of synthesizing kanemite, which is a type of crystalline layered silicate, Na ₂ O
It is preferable to use amorphous sodium silicate having a composition as close as possible to / SiO ₂ = 2.

This amorphous sodium silicate was mixed with 6
When fired at 50 ° C to 750 ° C, δ type Na ₂ Si ₂ O ₅
Crystallize into. Β or γ type N at temperatures lower than 650 ° C
in a ₂ Si ₂ O _5, at temperatures above 750 ° C. alpha-type Na
Crystallized to ₂ Si ₂ O ₅ . In the α, β and γ forms, crystalline layered silicate does not form upon reaction with water. Next, disperse this δ-type Na ₂ Si ₂ O ₅ in 2 to 50 times water,
After stirring for ~ 5 hours, filter. As a result, δ-type Na
Part of Na ⁺ of ₂ Si ₂ O ₅ is replaced with H ^{+ in} water, and N
It becomes aHSi ₂ O ₅ .3H ₂ O, and kanemite which is a crystalline layered silicate is obtained.

The water content of the crystalline layered silicate is 10 wt% or more. If it is less than 10 wt%, the crystalline layered silicate aggregates, the dispersibility in water decreases in the next interlayer widening step, and ion exchange between organic cations and alkali metal ions becomes difficult to occur. When it is 10 wt% or more, the crystalline silicate is well dispersed in water in the next interlayer widening step, and the ion exchange between the interlayer alkali metal ion and the organic cation is smoothly performed in a short time. As a result, the specific surface area of the layered silica porous material is 1000
It is possible to obtain an excellent heat-resistant layered silica porous body having a m ² / g or more and a residual amount of alkali metal ions of 0.2 wt% or less.

In the interlayer widening step, alkali metal ions in the crystalline layered silicate are ion-exchanged with organic cations. Since organic cations are bulkier than alkali metal ions, the layers of crystalline layered silicate are widened. As a result, the sheet layer is curved so as to surround the organic cations.

At the same time, the silanol (Si- in the adjacent sheet layers, excluding the portion into which the organic cations are introduced, is removed.
OH) are dehydrated and condensed to form siloxane bonds (Si-O).
-Si) is formed. As a result, adjacent sheet layers are partially bonded by siloxane bonds to form a three-dimensional honeycomb layer structure.

Examples of the organic cations include alkyl trimethyl ammonium, dimethyl dialkyl ammonium, alkyl ammonium and benzyl trimethyl ammonium. During the ion exchange, it is preferable to adjust the pH to 8-9. Furthermore, after that, 30 ~ 90 ℃
It is preferable to heat at.

In the washing step, alkali metal ions liberated by the ion exchange, counterions of organic cations, or unreacted organic cations are removed.
Particularly, the released alkali metal ions are completely washed and removed. As a result, the content of alkali metal ions becomes 0.2 wt% or less.

In the above-mentioned porous body forming step, the organic cations taken in between the layers are burned to form fine micropores. It also stabilizes the three-dimensional skeleton of the siloxane bond. Firing is performed in an oxidizing atmosphere at a temperature of 600 to 1200.
It is desirable to carry out at ℃. If the temperature is lower than 600 ° C., or if the temperature is outside the oxidizing atmosphere, the organic cations cannot be sufficiently removed. On the other hand, when the temperature exceeds 1200 ° C, the sintering proceeds too much, the micropores are broken, and the specific surface area decreases.

[0021]

[Operation and effect] Since the layered silica porous material of the present invention has an alkali metal ion content of 0.2 wt% or less,
It is difficult to crystallize even at a high temperature of 800 ° C or higher, and the micropores are stable. Therefore, it has excellent heat resistance. Also, 100
Since it has a specific surface area of 0 m ² / g or more, it exhibits excellent adsorption performance for catalyst carriers, absorbent materials for organic substances such as fuel, and the like.

On the surface of the layered silica porous material,
The amount of isolated hydroxyl groups is smaller than that of commercially available silica gel. Generally, the hydrophobicity of the surface is inversely related to the amount of isolated hydroxyl groups, and therefore the surface of the layered silica porous material is considered to be hydrophobic. Therefore, the layered silica porous material of the present invention has excellent adsorptivity to organic substances such as octane and fuel.

Further, according to the above manufacturing method, it is possible to manufacture the excellent heat-resistant layered silica porous material as described above. As described above, according to the present invention, it is possible to provide a heat-resistant layered silica porous body having excellent adsorbability to organic substances such as fuel and heat resistance, and a method for producing the same.

[0024]

【Example】

Examples 1 and 2 Examples of the present invention will be described with reference to FIG. The layered silica porous body 9 of the present example has a skeleton composition of SiO ₂ as shown in FIG. 1 (a), and as shown in FIG. 1 (b), basically has a honeycomb shape in which plate-like sheet layers 91 are superposed. It has the structure of. As shown in FIG. 1C, the sheet layer 91 is thinly curved, and the upper sheet layer 91 and the lower sheet layer 91 are partially joined at a joining point 93 to form a three-dimensional shape. It forms the skeleton.

Micropores 92 are formed between the layers of each sheet layer 91 and the connecting points 93. The fine holes 92 are formed by widening the sheet layer 91. The content of the alkali metal ions in the layered silica porous material 9 of this example is 0.2 wt% or less. The specific surface area of the layered silica porous material is 1000 m ² / g or more.

A method for producing the above layered silica porous material will be described. First, in the synthesis process, powdered sodium silicate (N
a ₂ O / SiO ₂ = 2.00) in an electric furnace at 700 ° C., 6
Burned for hours. The obtained sample was δ-
It was a Na ₂ Si ₂ O ₅ crystal. This δ-Na ₂ Si ₂
150 g of O ₅ crystal was immersed in 1.5 liter of water and stirred for 3 hours.

Then, the solid content is filtered, and the solid content is reduced to 3
Divided into two petri dishes and dried naturally. Three samples with different water contents were prepared by changing the natural drying time. Its water content is 1 based on the vacuum dried sample.
03% (weight ratio; the same applies hereinafter) (for Example 2), 53.9
% (For Example 3) and 6.6% (for Comparative Example 1).
The dried sample was analyzed by X-ray diffraction to obtain kanemite (NaHS
i ₂ O ₅ .3H ₂ O) was confirmed.

Next, in the interlayer widening step, 10 g (dry weight) of the above-mentioned three kinds of kanemite having different water contents are dispersed in 1 liter of 0.1N hexadecyltrimethylammonium chloride aqueous solution, and 2NHC1 aqueous solution is added to adjust pH to 8. It was adjusted to 0.5 and heated at 70 ° C. for 3 hours with stirring. Next, in the cleaning process,
The solid content was filtered and washed 4 times with 1 liter of water.

Then, in the step of forming a porous body, the obtained sample was fired at 700 ° C. under air flow to synthesize three kinds of layered silica porous bodies. In this way, the water content is 10
Layered silica porous materials synthesized from 3%, 53.9%, and 6.6% kanemite were designated as Example 2, Example 3, and Comparative Example, respectively.

The relationship between the water content of kanemite and the specific surface area of the layered silica porous material is shown in FIG. The specific surface area of the layered silica porous material was evaluated by the nitrogen adsorption amount of the layered silica porous body. As is known from FIG. 2, the layered silica porous body produced using kanemite having a water content of 10% or more is 1000
It was confirmed to have a specific surface area of m ² / g or more. If it is less than 7%, the specific surface area of the layered silica porous material tends to decrease rapidly.

Next, a heat resistance experiment was conducted on the layered silica porous material (Example 2, Comparative Example 1). In the experiment, the layered silica porous body was heated in the air at 600 to 1000 ° C. for 6 hours, and then the specific surface area of the layered silica porous body was measured as in the previous example. The result is shown in FIG.

As is known from FIG. 3, at any firing temperature, the layered silica porous material obtained by the production method of Example 2 had a larger specific surface area than the layered silica porous body of Comparative Example 2. Further, the layered silica porous material in Example 2 maintained a specific surface area of 750 m ² / g even when fired at 1000 ° C. On the other hand, the layered silica porous material in Comparative Example 1 has a thickness of 10 m when fired at 1000 ° C.
The specific surface area was ² / g.

Next, after firing at 1000 ° C.,
Powder X-ray diffraction was performed on the layered silica porous body (Example 2, Comparative Example 1). The layered silica porous material of Example 2 retained the layered structure. On the other hand, in the layered silica porous body of Comparative Example 1, cristobalite crystals were partially formed.

Example 3 Next, the relationship between the residual Na amount and the specific surface area of the layered silica porous material was investigated. The residual Na amount was determined by the atomic absorption spectrophotometry. The specific surface area of the layered silica porous material was measured in the same manner as the above measurement. The result is shown in FIG.

The amount of Na remaining in the layered silica porous material was changed by changing the number of times of washing in the washing step of the manufacturing method of Examples 1 and 2. Others are the same as in the first and second embodiments. As is known from FIG. 4, the residual Na content is 0.2
In the case of less than wt%, the specific surface area of the layered silica porous material is 1000 m ² / g or more. It can be seen that when the content exceeds 0.2 wt%, the specific surface area of the layered silica porous body is rapidly reduced as the residual Na amount is increased.

Examples 4 to 6 In this example, the change in the number of times of cleaning during the cleaning process
Changes in the specific surface area of the layered silica porous material and changes in the amount of Na ⁺ remaining were evaluated. First, the method for manufacturing the layered silica porous material will be described. In the synthesis step, 3870 g of sodium silicate powder was fired at 700 ° C. for 6 hours in an electric furnace. 3000 g of the obtained δ-Na ₂ Si ₂ O ₅ crystal was added to 3
It was immersed in 0 liter of water and stirred for 3 hours. The solid content was filtered, and kanemite having a water content of about 100 wt% was obtained.

Then, in the interlayer widening step, 3000 g (dry weight) of this kanemite was dispersed in 60 liters of a 0.1N hexadecyltrimethylammonium chloride aqueous solution, and a 2HNC1 aqueous solution was added to adjust the pH to 8.5. The mixture was stirred as it was at 70 ° C. for 3 hours.

Next, in the washing step, the solid content was filtered and washed with 120 liters of water. Here, five kinds of samples having the number of cleaning times of 0 to 4 are prepared. Then, in the porous body forming step, these samples were respectively fired at 700 ° C. for 6 hours under air flow to synthesize five types of layered silica porous bodies (Comparative Example 2, Comparative Example 3, Example 4 to Example). Example 6).

The results of the above measurements are shown in FIG. In the figure, the horizontal axis represents the number of times the layered silica porous body is washed, the left vertical axis and ◯ represent the specific surface area of the layered silica porous body, and the right vertical axis and ● represent N.
a Remaining amount is shown. As is known from FIG. 5, the specific surface area is improved as the residual amount of Na ⁺ is decreased. That is, when the number of washings is two or more, the residual Na amount is 0.2 w
It was t% or less and the specific surface area was 1000 m ² / g or more. On the other hand, when the number of washings is 0 or 1, the residual Na amount is more than 0.2 wt% and the specific surface area is 900 m.
It was less than ² / g.

Example 7 In this example, the ability of the layered silica porous body to adsorb evaporated fuel and the micropore diameter of the layered silica porous body were measured. First,
The method for producing the layered silica porous material will be described. In the synthesis step, powdered sodium silicate (Na ₂ O / SiO ₂ =
2.00) is fired in an electric furnace at 700 ° C for 6 hours to obtain δ-N
An a ₂ Si ₂ O ₅ crystal was obtained. 15 g of δ-Na ₂ Si ₂ O ₅ crystal was immersed in 150 ml of water, stirred for 3 hours, and then filtered.

Next, in the interlayer widening step, 15 g (dry weight) of kanemite having a water content of about 100 wt% was added to 0.1 wt.
The solution was dispersed in 300 ml of an aqueous solution of N-hexadecyltrithymelammonium chloride, put into an autoclave made of Teflon as it was, and heated at 65 ° C. for one week.

Next, in the washing step, the solid content was then filtered and thoroughly washed. Then, in the step of forming a porous body, the obtained sample was fired at 700 ° C. for 6 hours under an air stream to obtain a layered silica porous body. The specific surface area of the obtained porous body was determined in the same manner as in Examples 1 and 2, and was 1450 m ² / g.
Met.

Next, the adsorption capacity of the porous body was measured. At this time, for comparison, the results of activated carbon (Kuraray Coal), silica gel (Fuji Davison # 923), and silica-alumina (JGC N631L) were also shown and shown together.

In measuring the adsorption capacity, the particle size of 1.
A sample formed into a granular body of 0 to 3.0 mm was used, and octane was used as an organic substance to be adsorbed. The obtained adsorption characteristic is represented as an adsorption isotherm (25 ° C.) of octane in FIG. In the above measurement, the adsorption octane was desorbed after adsorbing the maximum adsorption amount. And
The residual adsorption amount after desorption is shown by ● in the figure.

In the figure, the horizontal axis indicates the relative vapor pressure of octane (P / Po), and the vertical axis indicates the adsorption amount of octane (wt%).
Indicates. As is known from FIG. 6, there is not much difference in octane adsorption amount between the layered silica porous body and the activated carbon. However, the residual adsorption amount (● in the figure) after desorption was 0% for the layered silica porous material, silica gel, and silica-alumina.
On the other hand, activated carbon shows 8.4%. The maximum adsorption amount of activated carbon is 42%. Therefore, 20% of the maximum adsorption amount of activated carbon is not desorbed.

The micropore volume (cc / g) and BET surface area (m ² / g) of the above four kinds of adsorbents are shown in Table 1, and the micropore distribution curve is shown in FIG. As known from Table 1 and FIG. 7, the layered silica porous material has a larger BET surface area and a smaller micropore volume than the other three kinds of adsorbents. The differential micropore volume is a value (cc / gA) obtained by differentiating the micropore volume by the micropore diameter.

Example 8 As shown in FIG. 8, an absorbent container 79 was filled with the layered silica porous material 75 of the present invention, and the adsorption capacity of the canister 7 was measured. The canister 7 has an octane vapor introduction pipe 71 and a purge pipe 72 in the upper part, and an air inlet pipe 73 is connected in the lower part of the absorbent container 79.
The capacity of the absorbent container 79 is 1.4 liters. In this, 630 g of a layered silica porous material 75 molded to have a particle size of 1 to 5 mm was filled.

Next, in measuring the adsorption capacity, the canister 7 was left at room temperature for 1 hour in a state of RH (relative vapor pressure) of 100%. Then, octane vapor was introduced into the canister 7 through the introduction pipe 71, and the octane adsorption amount (adsorbent amount) was measured. The results are shown in Table 2.
This adsorption amount is the weight (g) of octane adsorbed on 630 g of the layered silica porous material. After the adsorption, purging air was fed through the air feeding pipe 73 to desorb the adsorbed octane.

Next, the same operation as above was repeated twice for the second and subsequent adsorption capacity measurements. And the first
Each octane adsorption amount (g / adsorbent amount) from the 3rd to 3rd measurements was measured and is shown in Table 2. For comparison, the canister 7 was filled with 560 g of activated carbon (Kuraray Coal) and the same measurement was performed. The results are shown in the table.

As can be seen from the table, the canister filled with the layered silica porous material according to the present invention has an excellent adsorption capacity even in the third adsorption, which is almost the same as that in the first adsorption, and the deterioration thereof. You can see that there is no. On the other hand, it can be seen that activated carbon shows only about 80% adsorption capacity in the first adsorption in the second adsorption, and the adsorption ability deteriorates with each repetition.

[0051]

[Table 1]

[0052]

[Table 2]

[Brief description of drawings]

FIG. 1 is an explanatory view of a layered silica porous material of Examples 1 and 2.

FIG. 2 is a graph showing the relationship between the water content of kanemite and the specific surface area of a layered silica porous material in Examples 1 and 2.

FIG. 3 is a diagram showing a change in specific surface area with firing temperature in Example 2.

FIG. 4 is a diagram showing the relationship between the residual Na amount and the specific surface area of the layered silica porous material in Example 3.

FIG. 5 is a graph showing the relationship between the specific surface area and the amount of Na ⁺ remaining with respect to the number of washings in Examples 4 to 6.

FIG. 6 is an adsorption isotherm diagram of octane in Example 7.

7 is a micropore distribution curve diagram of the layered silica porous material and each absorber in Example 7. FIG.

FIG. 8 is an explanatory diagram of a canister according to an eighth embodiment.

[Explanation of symbols]

 9. ． ． Layered silica porous body, 91. ． ． Sheet layer, 92. ． ． Micropores, 93. ． ． Connection point,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location B01J 35/04 311 D 7821-4G (72) Inventor Akane Okada Nagakute-cho, Aichi-gun, Aichi Prefecture 1st at Yokochi 41 Toyota Central Research Institute Co., Ltd. (72) Inventor Kazuhiro Fukumoto 1-chome, Nagakute Town, Aichi-gun, Aichi-gun 1st Toyota Central Research Institute (72) Inventor Kazuyuki Kuroda Shinjuku, Tokyo 3-4-1 Okubo, Ward, Faculty of Science and Engineering, Waseda University

Claims (2)

[Claims] 1. A plurality of plate-like sheet layers of crystalline layered silicate are laminated, and the layers of the adjacent sheet layers are narrowed at a bonding point by a siloxane bond and widened between the bonding points. In the layered silica porous body having a honeycomb-shaped porous structure having fine pores, the content of alkali metal ions contained in the crystalline layered silicate is 0.2 wt%.
A heat-resistant layered silica porous material having the following specific surface area of 1000 m ² / g or more. 2. An interlayer widening step of ion-exchanging an alkali metal ion existing between layers in a crystalline layered silicate having a water content of 10 wt% or more with an organic cation and introducing the organic cation between the layers. A porous body for obtaining a porous layered silica porous material by burning the organic cation by burning the washed crystalline layered silicate to remove the alkali metal ions released by ion exchange A method for producing a heat-resistant layered silica porous body, comprising: