JP7784286B2 - Method for producing porous silica-alumina particles - Google Patents

Description

The present invention relates to a method for producing amorphous porous silica-alumina particles with a high specific surface area and a high pore volume.

Methods for preparing silica-alumina compositions are well known in the art, with representative methods including the neutralization reaction method and the pH swing method.

Examples of neutralization reaction (coprecipitation, cogelation) methods include those described in Patent Documents 1 to 4, in which silica hydrogel and a metal salt solution are mixed to produce amorphous silica-alumina that contains the metal salt uniformly throughout.

The pH swing method (immersion method), as described in Patent Documents 5 and 6, includes a preparation method that enables the production of amorphous silica-alumina in a single vessel by changing the pH of the reaction mixture, thereby precipitating silica and alumina.

Special Publication No. 27-3989 Special Publication No. 31-1862 Special Publication No. 30-5963 Special Publication No. 32-413 Special Publication No. 2010-537808 Special Publication No. 2016-502971

However, in the prior art, the porous silica-alumina obtained by the preparation methods described in Patent Documents 1 to 6 tend to have a relatively small specific surface area, i.e., much smaller than 400 m ² /g, and have the problem that the particle strength may be low.

Furthermore, there was a problem that the pore volume tended to be smaller than 1.0 mL/g.

The object of the present invention is to provide a method for producing porous silica-alumina particles that have a high specific surface area, a high pore volume, and increased particle strength.

Under such technical background, the inventors have conducted extensive research to solve the above problems, and as a result, have discovered a manufacturing method that can obtain porous silica-alumina particles having a large specific surface area, a large pore volume, and increased particle strength, and have developed the present invention.
The present invention, which has been developed to solve the above problems and achieve the above objects, is as follows. That is, the present invention is a method for producing porous silica-alumina particles, comprising:
a. Obtaining an aqueous solution containing pseudoboehmite alumina hydrate;
b. Obtaining an aqueous solution containing silica powder;
c) mixing the aqueous solution containing the pseudoboehmite alumina hydrate with the aqueous solution containing the silica powder, and promoting the reaction of the resulting slurry at a pH of 7.0 to 9.0 and at a temperature of 40 to 95°C for 10 minutes to 10 hours to obtain an aqueous solution containing a silica-alumina mixture;
d. A step of drying the aqueous solution containing the silica-alumina mixture to obtain porous silica-alumina particles;
The present invention proposes a method for producing porous silica-alumina particles, comprising:
However, porous silica alumina particles are
The specific surface area SA measured by the BET method is in the range of 400 to 600 m ² /g,
The pore volume PV measured by the BJH method is in the range of 1.0 to 2.0 mL/g,
The average pore diameter PD measured by the BJH method is in the range of 6 to 30 nm,
The mass ratio of silica to alumina is in the range of 2/98 to 70/30.

In the method for producing porous silica-alumina particles of the present invention, it is considered to be a preferable embodiment that the silica powder used in the step b has a Na ₂ O content of 0.4 mass% or less and a sulfate ion content of 0.5 mass% or less.

It is believed that a preferred embodiment of the method for producing porous silica-alumina particles of the present invention includes a step of filtering out the solid content in step d, followed by washing and drying to obtain silica-alumina particles.

The present invention makes it possible to obtain amorphous porous silica-alumina particles that have a high specific surface area, a high pore volume, and increased particle strength. These porous silica-alumina particles not only have high thermal insulation properties, but also contain solid acid, making them suitable for use as catalysts for petroleum refining, optical materials, or as additives to cosmetics, resin fillers, and surface coating materials (for purposes such as optical scattering and refractive index adjustment).

Preferred embodiments of the present invention will now be described in detail.
[Porous silica alumina particles]
_The porous silica-alumina particles of the present invention (hereinafter also simply referred to as "silica-alumina particles") are porous particles made of silica ( _SiO2 ) and alumina ( _Al2O3 ), and are configured as oxides having a high specific surface area and a large pore volume.

The porous silica-alumina particles of the present invention are amorphous. Therefore, crystalline silica-alumina such as zeolites are not included in the silica-alumina of the present invention. Whether the silica-alumina of the present invention is amorphous can be determined from its X-ray diffraction pattern. Specifically, if the X-ray diffraction pattern obtained by X-ray diffraction measurement of the silica-alumina of the present invention does not show a diffraction peak with a full width at half maximum of less than 1.0° in the range of 5°≦2θ≦50°, the silica-alumina of the present invention can be determined to be amorphous.

The silica-alumina particles obtained by the present invention have a silica to alumina ratio S/A, calculated as a mass ratio of _{SiO2 and Al2O3} , in the range of 2/98 to 70/30, preferably 5/95 to 65/35. If the alumina ratio is lower than S/A: 70/30, the solid acidity tends to decrease, and when the particles are used as a cracking catalyst, the required cracking rate cannot be achieved. On the other hand, if the silica ratio is lower than S/A: 2/98, the specific surface area SA tends to decrease.

The specific surface area SA of the obtained silica-alumina particles, as measured by the BET method, is in the range of 400 to 600 m ² /g, preferably 420 to 550 m ² /g. The reason for setting a lower limit is that when used as a cracking catalyst, a moderately high specific surface area SA is advantageous in terms of contact with and reactivity with hydrocarbons. On the other hand, if the specific surface area SA exceeds the upper limit, the pore diameter PD becomes too small, becoming smaller than the molecular size of the hydrocarbon reactant, and therefore unable to diffuse within the pores, which may prevent an effective reaction from occurring.

Furthermore, the pore volume PV measured by the BJH method is in the range of 1.0 to 2.0 mL/g, preferably 1.10 to 1.90 mL/g. If the pore volume PV is smaller than the lower limit, there will be fewer sites for effective reaction with hydrocarbon molecules. On the other hand, if the pore volume PV exceeds the upper limit, the crushing strength or abrasion resistance of the molded product will be weakened when used as a cracking catalyst, and powdering may occur when packed into a reactor, making operation impossible.

The average pore diameter PD, measured using the BJH method, is in the range of 6 to 30 nm (60 to 300 Å), preferably 7 to 18 nm (70 to 180 Å). The reason for setting a lower limit is that if the average pore diameter PD is too small, there will be many pores smaller than the hydrocarbon molecular size of the reactants, which may prevent them from diffusing within the pores and prevent an effective reaction from occurring. On the other hand, the reason for setting an upper limit is that the specific surface area will decrease, resulting in fewer active sites for the decomposition reaction and possibly a decrease in crushing strength.

The silica-alumina particles of the present application are also characterized by a low residual amount of positive and negative impurity ion components. Examples of residual cations include alkali metal ions such as residual sodium ions and potassium ions. The amount of these alkali metal ions (M ⁺ ) is 0.1 mass% or less, preferably 0.05 mass% or less, calculated as _M2O . Furthermore, the residual amount of inorganic acid ions such as sulfate ions and nitrate ions is 1.0 mass% or less, preferably 0.5 mass% or less. The reduction in impurity ion components suppresses the poisoning of solid acid sites and active metals.

[Method of manufacturing porous silica-alumina particles]
<a. Step of obtaining an aqueous solution containing pseudoboehmite alumina hydrate>
a-1. Blending process
Methods for preparing pseudoboehmite alumina particles are widely known, and among them, a method of neutralizing an aluminum salt and/or aluminate solution to precipitate pseudoboehmite alumina particles is preferred. The aluminum salt may be any aluminum salt, such as aluminum sulfate, aluminum chloride, or aluminum nitrate. The aluminate may be any aluminate, such as sodium aluminate or potassium aluminate. The neutralization reaction may be carried out by adding an alkaline aqueous solution, such as sodium hydroxide, potassium hydroxide, or ammonia water, to an aluminum salt aqueous solution; adding an acidic aqueous solution, such as sulfuric acid, hydrochloric acid, or nitric acid, to an aluminate aqueous solution; or mixing an aluminum salt aqueous solution with an aluminate aqueous solution. However, from the viewpoint of production costs, the method of mixing an aluminum salt aqueous solution with an aluminate aqueous solution to obtain an aqueous solution containing pseudoboehmite alumina hydrate is preferred.

《a-2. Aging process》
After mixing the two liquids to carry out the neutralization reaction, the reaction to form pseudo-boehmite alumina hydrate can be accelerated by adjusting the pH of the solution to a range of 7.0 to 10.0 and the temperature to a range of 30 to 70°C to accelerate the reaction (hereinafter also referred to as "aging") to obtain pseudo-boehmite alumina hydrate. If the pH exceeds 10.0, a bayerite phase with a small specific surface area is formed, which may reduce the activity of the final catalyst. Furthermore, if the pH is lower than 7.0, the pore volume of the final pseudo-boehmite alumina particles tends to decrease, making it difficult to produce pseudo-boehmite alumina particles suitable for use as a catalyst.

The aging temperature is preferably in the range of 30 to 70°C. If the temperature is below 30°C, the particles tend to aggregate strongly, which may reduce the pore volume of the powder obtained after the aging and drying process. Temperatures above 70°C are undesirable because bayerite tends to precipitate. The aging time is preferably in the range of 5 to 120 minutes, preferably 10 to 100 minutes, and more preferably 10 to 90 minutes. If the aging time is outside this range, the pore volume of the pseudo-boehmite alumina particles obtained in the end may be 0.8 mL/g or less, making them unusable as pseudo-boehmite alumina particles for catalysts. There are no particular restrictions on the aging time, but from the perspective of production efficiency, a time of 120 minutes or less is preferable. If the aging time is too long, the specific surface area of the pseudo-boehmite alumina particles obtained in the end tends to be small.

<<a-3. Cleaning process>>
The pseudo-boehmite alumina hydrate obtained in step a-2 is filtered off to obtain a pseudo-boehmite alumina cake. The boehmite alumina cake is transferred to a washing container and washed with water at 50 to 70°C to remove unreacted raw materials and impurity ions, etc., to obtain a pseudo-boehmite alumina cake. Pure water is added to the boehmite alumina cake and the mixture is stirred to obtain an aqueous solution containing pseudo-boehmite alumina hydrate.

<b. Step of obtaining an aqueous solution containing silica powder>
Methods for preparing silica powder are widely known, among which the pH during preparation can be controlled by adjusting the feed rates of the aqueous silicate solution and acid, and the _SiO2 concentration can be controlled by using a pre-calculated aqueous silicic acid solution and acid of specified concentrations.
The reaction can be carried out by feeding an aqueous silicate solution and an acid into a reactor maintained at 10 to 100°C, preferably 20 to 95°C, with stirring, to obtain an aqueous solution containing silica powder.

The silicate that can be used may be any of sodium silicate No. 1, No. 2, No. 3, potassium silicate, other soluble silicates, and diatomaceous earth.
The acid may be an inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid or phosphoric acid, or an organic acid such as formic acid, but an inorganic acid is preferred.

The silica powder used here preferably contains as little impurities as possible, such as contaminating ions, and preferably has an Na ₂ O content of 0.4% by mass or less and a sulfate ion content of 0.5% by mass or less, more preferably an Na ₂ O content of 0.10% by mass or less and a sulfate ion content of 1.0% by mass or less.

According to the above preparation method, an aqueous solution containing silica powder having a specific surface area measured by the BET method in the range of 190 to 800 m ² /g can be easily obtained.

<c. Step of obtaining an aqueous solution containing a silica-alumina mixture>
(An aqueous solution containing pseudoboehmite alumina hydrate and an aqueous solution containing silica powder are mixed to obtain an aqueous solution containing a silica-alumina particle mixture.)
An aqueous solution containing a silica-alumina mixture can be obtained by mixing the aqueous solution containing the pseudo-boehmite alumina hydrate, the solid content of which has been adjusted to 5 to 15% by mass, with the aqueous solution containing the silica powder, the solid content of which has been adjusted to 10 to 30% by mass, adjusting the pH to a range of 7.0 to 9.0, more preferably a range of 7.5 to 9.0, and aging the mixture at a temperature of 40 to 95° C. for 10 minutes to 10 hours. When mixing these two liquids, the aqueous solution containing the silica powder may be added to the aqueous solution containing the pseudo-boehmite alumina hydrate, or the aqueous solution containing the pseudo-boehmite alumina hydrate may be added to the aqueous solution containing the silica powder.

<d. Drying process>
The aqueous solution containing the silica-alumina mixture obtained in the step c is dried to obtain silica-alumina particles.

To dry and obtain silica-alumina particles, a spray dryer or other commonly used drying equipment can be used. There are no particular restrictions on the drying temperature, but temperatures that are too high are undesirable because they cause a phase transition from pseudoboehmite alumina to gamma-alumina. For this reason, an inlet temperature of 500°C or less and an outlet temperature of 200°C or less are preferred. In other words, drying is preferably performed at an inlet temperature of 300 to 500°C and an outlet temperature of 130 to 200°C.

<e. Cleaning step 2>
The silica-alumina particles obtained in the step d are suspended in water as needed and stirred, and then filtered and washed to obtain a cake of silica-alumina particles.

To reduce the residual alkali metal ion concentration in the silica-alumina particles obtained in step d, the temperature of the suspension is preferably in the range of 40 to 70°C, and the suspension is preferably filtered using an aqueous solution containing a water-soluble acidic substance. Examples of water-soluble acidic substances used here include ammonium sulfate, ammonium nitrate, and ammonium chloride.

Furthermore, after filtration, in order to remove residual salts, etc., the product is washed with warm water containing a water-soluble basic substance and then filtered to obtain a silica-alumina particle cake. The temperature of the washing water is preferably higher than room temperature, in the range of 50 to 70°C, in order to increase the efficiency of removing unreacted raw materials, impurity ions, etc. Examples of the water-soluble basic substance used here include ammonia water, hydroxide salts, carbonates, and hydrogencarbonates (the term "salt" used here refers to alkali metal salts and alkaline earth metal salts).
Depending on the amount of remaining impurities such as contaminating ions, step d may be repeated, and step e may be carried out again as necessary.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

<Measurement method or evaluation method>
The measurement and evaluation methods used in the examples are as follows.

(Method for measuring the content of each element, compound, and metal component (Si, Al, Na, SO ₄ ^2- ))
3 g of the measurement sample was collected in a 30 mL zirconia bowl with a lid, heat-treated (200°C, 20 minutes), and baked (700°C, 5 minutes). Then, 2 g of Na ₂ O and 1 g of NaOH were added and melted for 15 minutes. Furthermore, 25 mL of H ₂ SO ₄ and 200 mL of water were added and dissolved, and the mixture was diluted with pure water to 500 mL to obtain a sample. The content of each component in the obtained sample was measured on an oxide-equivalent mass basis using an inductively coupled plasma (ICP) optical emission spectrometer (Shimadzu Corporation, ICPS-8100, analysis software ICPS-8000).

(Method for measuring pore volume PV and average pore diameter PD)
The pore volume PV and average pore diameter PD were measured using a BELSORP-mini Ver. 2.5.6 manufactured by Microtrac-Bel Co., Ltd. Specifically, nitrogen gas was adsorbed onto a sample that had been heat-treated at 500°C for 2 hours while evacuating to a vacuum, and the pore volume PV (mL/g) and average pore diameter PD (nm) were calculated from the desorption isotherm of the relative pressure (P/P ₀ =0.99) according to the BJH method.

(Method for measuring specific surface area SA)
To measure the specific surface area (SA), approximately 30 mL of the sample was placed in a porcelain crucible (B-2 type), heated at 500°C for 2 hours, and then cooled to room temperature in a desiccator to obtain a measurement sample. Next, 1 g of this sample was taken and the specific surface area (SA) of the sample (m ² /g) was measured by the BET method using a fully automatic surface area measuring device (Multisorb 12 type, manufactured by Yuasa Ionics Co., Ltd.).

(Method for measuring average particle size)
The particle size distribution of the particles in the examples and the like was measured using a laser diffraction/scattering particle size distribution analyzer (LA-300) manufactured by Horiba, Ltd. Specifically, the sample was placed in a solvent (water) so that the light transmittance was in the range of 70 to 95%, and measurement was performed under the conditions of a circulation rate of 2.8 L/min, ultrasonic irradiation for 3 minutes, and repetition number of 30 times. From the obtained particle size distribution, the median diameter (D50) was adopted as the average particle diameter.

(Method for measuring loss on ignition (LOI: ignition loss, loss of ignition; hereinafter, also simply referred to as "LOI"))
The particles used as the measurement sample were fired at 1000°C for 1 hour, and the mass loss due to firing was calculated as a percentage.

(Wear resistance (attrition) test conditions)
Abrasion resistance
The wear resistance was measured using the apparatus described in Catalyst and Chemical Formation Techniques, Vol. 13, No. 1, p. 65, 1996, by flowing microspherical particles through a catalyst tube constituting the apparatus at an air linear velocity of 30 m/s, measuring the amount of wear for one hour after the start of the flow, and expressing it as the wear ratio (CAI). A CAI of less than 10 is preferred.

(X-ray diffraction measurement conditions)
X-ray diffraction of the silica alumina particles was measured using a MiniFlex manufactured by Rigaku Corporation. The measurement conditions were as follows: the operating axis was 2θ/θ, a CuKα source was used, and the measurement was performed continuously at a voltage of 40 kV and a current of 15 mA, from a start angle of 2θ = 5° to an end angle of 2θ = 50°, with a sampling width of 0.020°, and a scan rate of 10,000°/min.
The criterion for determining whether a sample is amorphous is that it does not exhibit a diffraction peak with a full width at half maximum of less than 1.0° in the range of 5°≦2θ≦50°.

[Example 1]
(Step a-1) Step of obtaining an aqueous solution containing pseudoboehmite alumina hydrate 60 kg of water was charged into a 200 L steam-jacketed stainless steel tank, and while stirring, 24 g of a 25% by weight aqueous sodium gluconate solution was added, followed by 885 g of a 22.6% by weight Al ₂ O ₃ and 17.3% by weight Na ₂ O sodium aluminate solution, and then 1408 g of a 24% by weight aluminum sulfate solution was added over 2 minutes to prepare a pseudoboehmite alumina seed slurry with a pH of 7.2. To this seed slurry, a 22.6% by weight Al _{2 O 3} and 17.3% by weight sodium aluminate solution was added at a flow rate of 275 mL/min, and a 23.6% by weight aluminum sulfate solution was added at a flow rate of 488 mL/min, respectively, and the temperature was maintained at 60 ° C. for 20 minutes. The pH of the finished slurry was 7.2. After stirring for 5 minutes, the pH was adjusted to 8.8 with 642 g of an aqueous sodium aluminate solution containing 22.6 mass % Al ₂ O ₃ and 17.3 mass % Na ₂ O, and stirring was continued for 2 hours at 60° C. Since the pH of the slurry had dropped to 7.05, the pH was again adjusted to 8.8 with 15% aqueous ammonia to obtain a pseudoboehmite alumina slurry.

(Step a-2) Washing Step The pseudo-boehmite alumina slurry of step a-1 was filtered, and the resulting pseudo-boehmite alumina cake was washed with 105 L of water at 60° C. to remove sulfate ions and sodium ions.
The washed pseudo-boehmite alumina cake had a weight of 38.4 kg and a solids concentration of 8.6% (the impurity contents at this stage were 0.1% by mass in terms of Na ₂ O and 1.0% by mass in terms of SO ₄ ^2- on a dry basis).
14.3 kg of pure water was added to 38.4 kg of pseudoboehmite alumina cake and stirred to obtain an aqueous solution containing pseudoboehmite alumina hydrate.

(Step c-1) Step of obtaining an aqueous solution containing a silica-alumina mixture The aqueous solution containing the pseudo-boehmite alumina hydrate and silica powder A (Sylysia 780, manufactured by Fuji Silysia Chemical Ltd.) in Table 1 are mixed to obtain an aqueous solution containing a silica-alumina particle mixture.
To the aqueous solution containing the pseudoboehmite alumina hydrate, 2.21 kg of silica powder A in Table 1 was added on a dry basis, and then the pH was adjusted to 8.2 with 260 mL of 15% aqueous ammonia.

(Step c-2) Aging Step The aqueous solution containing the silica-alumina particle mixture from step c-1 was transferred to a stainless steel steam-jacketed tank and aged with stirring at 50° C. for 2 hours.

(Step d) Drying Step The aqueous solution containing the silica-alumina particle mixture of step c-2 was treated with an emulsifier, and then spray-dried to obtain silica-alumina particles 1. The yield was calculated from the weight and moisture of the product after drying, and the properties of the product are shown in Table 2.

[Example 2]
Silica-alumina particles 2 were obtained under the conditions described in Example 1, except that silica powder B (Sylysia 250, manufactured by Fuji Silysia Ltd.) shown in Table 1 was used in place of silica powder A (other conditions were the same as in Example 1).

[Example 3]
Under the conditions described in Example 1, 200 mL of 15% ammonia water was used in (step c-1) the step of obtaining an aqueous solution containing a silica-alumina mixture to adjust the pH to 7.8, and the mixture was aged and dried under the same conditions as in Example 1 to obtain silica-alumina particles 3.

[Example 4]
Under the conditions described in Example 1, 340 mL of 15% ammonia water was used in (step c-1) the step of obtaining an aqueous solution containing a silica-alumina mixture to adjust the pH to 8.5, and the mixture was aged and dried under the same conditions as in Example 1 to obtain silica-alumina particles 4.

[Example 5]
Under the conditions described in Example 1, 1400 mL of 15% ammonia water was used in (step c-1) the step of obtaining an aqueous solution containing a silica-alumina mixture to adjust the pH to 9.5, and the mixture was aged and dried under the same conditions as in Example 1 to obtain silica-alumina particles 5.

[Example 6]
Under the conditions described in Example 1, 1.35 kg of silica powder A was added in (step c-1) in a dry amount, and then 260 mL of 15% aqueous ammonia was used to adjust the pH to 8.2. The mixture was then aged and dried under the same conditions as in Example 1 to obtain silica-alumina particles 6.

[Example 7]
Under the conditions described in Example 1, 3.15 kg of silica powder A was added in (step c-1) on a dry basis, and then 300 mL of 15% aqueous ammonia was used to adjust the pH to 8.2, followed by aging and drying under the same conditions as in Example 1 to obtain silica alumina particles 7.

[Example 8]
Under the conditions described in Example 1, 3.15 kg of silica powder A was added in (step c-1) on a dry basis, and then 160 mL of 15% aqueous ammonia was used to adjust the pH to 7.2, followed by aging and drying under the same conditions as in Example 1 to obtain silica alumina particles 8.

[Comparative Example 1]
Under the conditions described in Example 1, the silica powder used in (step c-1) was replaced with silica hydrogel prepared by the following method, and (step c) and thereafter were changed to (step c') to prepare a silica-alumina powder.

<Method for preparing silica hydrogel>
A 40-liter plastic tank was charged with 4.72 kg of 25% by weight sulfuric acid and 2.0 kg of pure water, and the temperature was adjusted to 30°C. While stirring this sulfuric acid solution, a sodium silicate solution with an 8.5% by weight _SiO2 concentration and an _SiO2 / _Na2O molar ratio of 3.2, adjusted to 45°C, was added dropwise at a flow rate of 0.56 kg/min over 45 minutes. The flow rate was then reduced to 0.1 kg/min, and the sodium silicate solution was added dropwise over 30 minutes until the pH reached 4.0. After the dropwise addition, stirring was continued for 165 minutes to obtain an aqueous silica hydrogel solution. 400 mL of 15% aqueous ammonia was added to this silica hydrogel, the pH was adjusted to 7.0, and the mixture was aged for 1 hour to obtain a silica hydrogel.

(Step c')
78,191 g of the aqueous solution containing the pseudoboehmite alumina hydrate and 893 g of the aqueous silica hydrogel solution were mixed by stirring, and then the pH was adjusted to 8.8 with 15 mass % ammonia water, and the mixture was aged at a temperature of 40 to 60°C for 10 minutes to obtain an aqueous solution containing a silica-alumina mixture.

(Step d') First washing step: The aqueous solution containing the silica-alumina mixture obtained in step c' was filtered, and the filtered silica-alumina mixture cake 1a was washed with 105 L of water at 60°C to remove sulfate ions and sodium ions. (The impurity content at this stage was 0.1% by mass in terms of Na ₂ O and 2.1% by mass in terms of SO ₄ ^2- on a dry basis.)

(Step e') Step of obtaining silica-alumina gel slurry 7 kg of 60 ° C. warm pure water was added to 23.0 kg of the silica-alumina mixture cake 1a obtained in the step d', and the silica-alumina concentration was adjusted to 10 mass%, and then stirred to form a slurry. The temperature of this slurry was 45 ° C. and the pH was 8.7. 1.8 L of 15 mass% ammonia water was added to this slurry to adjust the pH to 10.8, and then the slurry was transferred to a 50 L sealed tank equipped with a steam jacket and aged at 95 ° C. for 10 hours.

(Step f') First drying step: The aged slurry obtained in step e' was homogenized in an emulsifier, and then dried at an inlet temperature of 300°C and an outlet temperature of 150°C in a spray dryer to obtain silica alumina particles 1a having an average particle size of 70 μm.

(Step g') Second washing step
300 g of the silica-alumina particles 1a obtained in the step f' was suspended in 3000 g of ammonium sulfate at 60° C. in a 10% by mass concentration, stirred for 20 minutes, and then subjected to solid-liquid separation using a vacuum filter. The remaining cake was resuspended by pouring 3000 g of warm pure water at 60° C. Subsequently, the pH was adjusted to 8.8 with 15% by mass of ammonia water, and the mixture was stirred for 20 minutes. Then, the mixture was subjected to solid-liquid separation using a vacuum filter to obtain a silica-alumina mixed cake 2a.

(Step h'). Second drying process
The silica-alumina particle cake 2a obtained from the filter was taken out into a stainless steel tray and dried overnight at 130°C to obtain the desired silica-alumina particles 9.

As is clear from Table 2, the invention examples have a higher yield than the comparative examples, and have excellent particle strength with a CAI of less than 10.

The porous silica-alumina particles according to the present invention have a large pore volume and a large specific surface area, and therefore are expected to have heat insulating properties. In addition to the above properties, since they are made of silica-alumina and have solid acidity, they can be used as catalysts for petroleum refining, optical materials, or as additives for cosmetics, resin fillers, and surface coating materials (for the purposes of optical scattering, refractive index adjustment, etc.).

Claims (4)

A method for producing porous silica-alumina particles, comprising:
a. Obtaining an aqueous solution containing pseudoboehmite alumina hydrate;
b. Obtaining an aqueous solution containing silica powder;
c) mixing the aqueous solution containing the pseudoboehmite alumina hydrate with the aqueous solution containing the silica powder, and promoting the reaction of the resulting slurry at a pH of 7.0 to 9.0 and at a temperature of 40 to 95°C for 10 minutes to 10 hours to obtain an aqueous solution containing a silica-alumina mixture;
d. A step of drying the aqueous solution containing the silica-alumina mixture to obtain porous silica-alumina particles;
A method for producing porous silica-alumina particles, comprising:
However, porous silica alumina particles are
The specific surface area SA measured by the BET method is in the range of 400 to 600 m ² /g,
The pore volume PV measured by the BJH method is in the range of 1.0 to 2.0 mL/g,
The average pore diameter PD measured by the BJH method is in the range of 6 to 30 nm,
The mass ratio of silica to alumina is in the range of 2/98 to 70/30. The specific surface area is 420 to 550 m ² The method for producing porous silica-alumina particles according to claim 1, wherein the SiO 2 content is in the range of /g. The method for producing porous silica-alumina particles according to claim 2, wherein the average pore diameter PD is in the range of 7 to 18 nm. The method for producing porous silica-alumina particles according to any one of claims 1 to 3, characterized in that the silica powder used in step b has a Na ₂ O content of 0.4 mass% or less and a sulfate ion content of 0.5 mass% or less.