JP2001122612A - Spherical silica particle, method of manufacturing the same, and catalyst carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain spherical silica particle low in strength, large in specific surface area, free from collapse or crack on its surface and particularly most suitable as a catalyst carrier for olefin polymerization. SOLUTION: The spherical silica particle is an aggregate of a silica particle and has <=39.2×exp(-0.03×d) MPa tensile strength measured about a particle having (d) μm particle diameter, 1-200 μm average article diameter and >=400 m2/g specific surface area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel spherical silica particle, a method for producing the same, and a high-yield catalyst carrier for olefin polymerization using the same.

[0002]

2. Description of the Related Art Spherical silica particles are widely used as catalysts, catalyst carriers, pigments, fillers, adsorbents, desiccants, etc. due to their various particle diameters, pore structures, and surface physical properties. For example, as a catalyst carrier, it is also used as a catalyst carrier for olefin polymerization. In this case, it is known that the polyolefin polymerized on the surface of the catalyst supported on the silica particles grows while collapsing the silica particles, and low-strength silica particles are desirable as the olefin polymerization catalyst carrier. Further, since the shape of the produced polymer is similar to the shape of the carrier, the shape of the carrier is preferably spherical.

Conventionally, low-strength spherical silica particles obtained by aggregating silica particles have been used as an olefin polymerization catalyst carrier. For example, the particle size is large, the specific surface area is relatively small, and the dispersion of the catalyst to be supported is large. There has been a demand for a low-strength, low-strength, high-specific-surface-area, solid, spherical support having no depression or cracks on the surface.

That is, as a general method for producing spherical silica particles, an emulsification method such as emulsifying an aqueous solution of sodium silicate or an alkyl silicate in an incompatible solvent and gelling with an acid, alkali, water or the like is known. Is well known. Although this method makes it possible to obtain spherical silica particles without any depressions relatively easily, it generally aims at obtaining particles having high strength. In addition, a method is known in which an alkali silicate aqueous solution is reacted with a mineral acid to form a silica sol, which is spray-granulated with a two-fluid nozzle or the like and dried to obtain spherical silica particles. Easily obtained,
Depressed particles and hollow particles are easily generated, and it is difficult to obtain solid silica particles having no depressed or cracked spherical particles. Thus, spherical silica was expected to be used as a catalyst carrier for olefin polymerization, but one satisfying desirable physical properties was not obtained due to production problems.

[0005]

SUMMARY OF THE INVENTION The present invention has a low strength,
It is an object of the present invention to provide a spherical silica particle having a large specific surface area, a solid silica particle having no depression or crack, a method for producing the silica particle, and a polymerization rate particularly when used as an olefin catalyst carrier. .

[0006]

Means for Solving the Problems The present invention has been made to solve such problems, and a first invention is an aggregate of silica particles having a particle diameter of d (μm). tensile strength was measured for S (MPa) is less than or equal to S _t given by the following equation 1 (MPa), average particle diameter of 1 to 200 [mu] m, spherical specific surface area is equal to or is 400 meters ² / g or more silica Particles. S _t = 39.2 × exp (−0.03 × d) Equation 1.

In a second aspect of the present invention, a mixed solution of an alkali silicate and an acid has an average particle diameter of 0.05 to 3.0 μm.
The silica gel particles are dispersed, and the resulting dispersion is sprayed to form droplets.The droplets are heated in a gas, and the mixed solution of alkali silicate and acid in the droplets is gelled to form a gel. Is substantially completed, the temperature of the gas in contact with the spherical particles is 60 to 200 ° C., and the relative humidity is 20% or more. The third invention is a catalyst carrier for olefin polymerization comprising the spherical silica particles of the first invention.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below,
The spherical particles of the present invention have a specified low strength, and the definition of their tensile strength is as follows. That is, the tensile strength S (MPa) of one specific particle is S = 27 × P / (π × d ² ) as shown in the Journal of the Japan Mining Association, Vol. 81, pp. 1024 to 1030 (1965). Given. Here, P is the load (N) when the particles collapse, d
Is the particle diameter (mm) of the measured particles.

Here, the method of measuring P and d is as follows. There are various types of measuring devices, and a micro compression tester MCTM-500 manufactured by Shimadzu Corporation is suitable. Measurement method of P: A load is applied to the particles to be measured through an indenter, correlation data with the displacement (μm) is collected while changing the load (N), and the load at which the displacement rapidly changes due to particle collapse is measured. Measurement method of d: The particle size is automatically measured by manually adjusting the two scales to both ends of the particle while observing the microscope with a microscope.

In the present invention, the tensile strength S as an aggregate of silica particles in such a measuring method is equal to or less than the value of _St given by the equation (1). This is because if it exceeds this value, when used as an olefin catalyst carrier, the particles hardly disintegrate, and the polymerization rate may be reduced. Desirable tensile strength S is 75% or less of S _t. On the other hand, since it is difficult to handle or too made too strength is intended preferably 20% or more of S _t.

As described above, the present invention aims at low-strength particles. As can be seen from the above-mentioned measurement method, the tensile strength can be reduced by increasing the particle size. On the other hand, due to the decrease in the outer surface area per unit weight of silica, the catalyst-carrying capacity per unit weight of silica decreases, and a sufficient polymerization rate cannot be obtained, so that the object of the present invention cannot be achieved.

Therefore, in the present invention, the particles are formed into spherical aggregates, the average particle diameter is 1 to 200 μm, and the specific surface area is 4 μm.
It is specified as not less than 00 m ² / g, and is provided as a completely new silica particle. Here, the spherical aggregate refers to an aggregate of a large number of silica particles. Such spherical aggregates are easily disintegratable and have good fluidity, and can provide novel silica particles having specific physical properties.

In the present invention, the average particle diameter is 1 to 200 μm
The silica particles referred to above are those in which aggregates of many silica particles are within this range. Average particle diameter is 1μm
If it is smaller, the strength of the particles becomes excessive, and when the catalyst is supported on the particles, the particles are hardly disintegrated. This is not preferable because the possibility of performing the process is increased. Average particle diameter of 20
If it is larger than 0 μm, the reduction in the outer surface area per unit weight of silica causes a decrease in the amount of the catalyst carried per unit weight of silica, and the possibility that a sufficient polymerization rate cannot be obtained is undesirably increased.

The average particle diameter can be appropriately selected depending on the polymerization method, polymerization apparatus, operation method and the like.
m is more desirable. If the individual particles themselves are too large, even if the average particle diameter is within this range, the particles may be crushed or pulverized during transportation or transportation, or surface defects caused by coarse particles when formed into a sheet. It is preferable that the thickness be 50 μm or less, since adverse effects such as generation of phenomena appear.

On the other hand, when the specific surface area is less than 400 m ² / g, the catalyst particles to be supported when used as a catalyst carrier are aggregated, and the polymerization rate may be reduced, which is not preferable. A more desirable range is 500 m ² / g or more.

Next, a method for producing such novel silica particles according to the second invention will be described. That is, such silica particles are obtained by dispersing silica gel particles having an average particle diameter of 0.05 to 3.0 μm in a mixed solution of an alkali silicate and an acid, and spraying the dispersion to form droplets. The droplet is heated in a gas, the portion of the mixed solution of the alkali silicate and the acid in the droplet is gelled, and the gas in contact with the spherical particles at the time when the gelation is substantially completed. It can be suitably manufactured by setting the temperature to 60 to 200 ° C. and the relative humidity to 20% or more.

The silica gel particles dispersed in the mixed solution of alkali silicate and acid have an average particle diameter of 0.05 to 3.0.
It needs to be 0 μm. If the average particle diameter of the silica gel particles is smaller than 0.05 μm, the resulting spherical silica particles are unsuitable because the mechanical strength of the particles is low and the particles are easily broken during the production to form amorphous particles. Similarly, when the average particle diameter of the silica gel particles is larger than 3.0 μm, the mechanical strength of the obtained spherical silica particles is low, and amorphous particles are easily generated, which is not suitable. A more preferred range of the average particle diameter of the silica gel particles is 0.1.
1 to 1.0 μm.

In the production method of the present invention, the mixed solution of an alkali silicate and an acid is hydrolyzed by heating, and the polymerization of the hydrolysis product, silicic acid, proceeds to gel. . In the spherical silica particles obtained by the production method of the present invention, a gel formed from a mixed solution of an alkali silicate and an acid serves as a matrix for binding the silica gel particles in the dispersion. Hereinafter, in this specification, a dispersion in which silica gel particles are dispersed in a mixed solution of an alkali silicate and an acid is referred to as a composite dispersion.

When a dispersion of silica gel particles alone is formed into droplets and dried without using a mixed solution of alkali silicate and acid, or a silica sol is used instead of the mixed solution of alkali silicate and acid. Also, when silica gel particles are mixed and formed into droplets and dried, spherical silica gel particles are obtained. In these methods, gelation occurs mainly by evaporation of the solvent, so if the conditions are not properly controlled, the silica gel particles in the dispersion liquid move to the droplet surface with the evaporation of the solvent, and the spherical silica particles are easily hollowed out. Prone to collapse and cracks.

On the other hand, in the present invention, gelation is caused by hydrolysis of alkali silicate and polymerization of silicic acid. At this stage, evaporation of the solvent may occur, but since the chemical reaction is mainly promoted by heating and gelation, without a large volume change, the spherical silica particles are hard to hollow,
The occurrence of depressions and cracks is suppressed.

Therefore, it is preferable to adopt a condition in which the gelation rate by heating is relatively faster than the evaporation rate of the solvent. That is, it is important to adjust the relative speed between the gelation speed by heating and the evaporation speed of the solvent. The evaporation rate of the solvent from the droplet increases as the heating temperature increases, and decreases as the solvent vapor pressure around the droplet increases.

The temperature at which the droplets of the composite dispersion are heated in a gas is such that the temperature of the gas in contact with the spherical particles is 60 to 200 ° C. when the gelation is substantially completed. Is preferred. The point in time when the gelation is substantially finished means the point in time when the mixed solution of the alkali silicate and the acid in the composite dispersion liquid has lost its fluidity. If the gas temperature is lower than 60 ° C., gelation by heating is insufficient, and the strength of the generated spherical particles may be weak, which is not preferable. If the gas temperature is higher than 200 ° C., it is not preferable because the energy use efficiency is reduced.

In the production method of the present invention, if the solvent rapidly evaporates while the droplets gel, the resulting silica particles may not be spherical. Therefore, when the solvent is water, it is preferable to increase the water vapor pressure in the gas when heating in the gas. When the gelation is substantially completed, the relative humidity of the gas in contact with the spherical particles is desirably 20% or more.

It is more preferable that the relative humidity at this time is 30% or more. From the viewpoint of the physical properties of the spherical silica particles, there is no upper limit of the relative humidity, but when the humidity is high, there is a possibility that problems such as inconvenient dew condensation in the manufacturing apparatus may occur. The relative humidity of the gas in contact with the spherical particles is preferably 80% or less.

Further, in order to control the evaporation of the solvent from the droplets of the composite dispersion, a substance which reduces the vapor pressure of the solvent can be contained in the dispersion. When the solvent is water, it is preferable to increase the coexisting salt concentration of the water or to mix an organic substance having a boiling point lower than that of water. In this case, the evaporation rate of water from the droplets can be adjusted by changing the coexisting salt concentration and the amount of the organic substance having a boiling point lower than that of water.

In particular, it is preferable that 5% by weight or more of an organic substance having a boiling point lower than that of water is dissolved in water as a solvent. When the amount of the organic substance is less than 5% by weight, the effect of lowering the vapor pressure is insufficient. It is preferable that this organic substance be completely dissolved in water at the concentration used.
Specifically, methanol, ethanol, 1-propanol, 2-propanol, acetone and the like can be suitably used.

The silica gel particles dispersed in the composite dispersion are:
Silica gel obtained by reacting an alkali silicate such as sodium silicate with an acid such as sulfuric acid, silica gel obtained by hydrolysis of alkyl silicate or polyalkyl silicate, and the like can be used. Silica gel synthesized by a gas phase method and hydrated silicic acid called white carbon can also be used. Although the silica gel particles are hydrogels in the composite dispersion, silica xerogels may be dispersed.

By adjusting the pH, the amount of coexisting ions, the temperature and the like in the step of synthesizing silica gel, silica gel particles having an average particle diameter of 0.05 to 3.0 μm can be produced.
In addition, silica gel with a larger particle diameter is wet-milled by a medium stirring mill, colloid mill, wet ball mill, etc.
The particle size may be adjusted by treating with a dry milling method such as a jet mill or a dry ball mill. In particular, it is preferable to use a medium stirring mill in that particles having the above particle diameter range can be easily obtained and impurities are less mixed. After forming the composite dispersion, the silica gel particles in the composite dispersion may be adjusted to a desired particle size by using the above-mentioned pulverizing means.

As the alkali silicate, sodium silicate is preferable, and various silicate-sodium molar ratios of sodium silicate can be used according to the desired properties. The acid to be mixed with the alkali silicate is not particularly limited, but it is preferable to use sulfuric acid.

In preparing the composite dispersion, silica gel particles may be dispersed after preparing a mixed solution of an alkali silicate and an acid, but the silica gel particles may be dispersed in an alkali silicate solution or an acid solution. After dispersing in either, the other mixed solution component may be mixed. These mixing ratios are obtained by converting the silicic acid component and silica gel particles in the mixed solution into SiO ₂ , respectively, and comparing the silicic acid component in the mixed solution with SiO Preferably, ₂ is 5 to 50% by weight. A more preferred range is that the silicic acid component in the mixed solution is 10 to 30% by weight.

The gelation rate of the mixed solution of alkali silicate and acid can be adjusted by heating by changing the concentration, pH, and coexisting salt concentration. Generally, the higher the concentration, the faster the gelation rate. When the pH is in the range of 0 to 6, the gelation rate around room temperature is not high, but in other pH ranges, the gelation rate is high. The higher the coexisting salt concentration, the faster the gelation rate. Under any conditions, the gelation rate increases as the temperature increases.

As a method of forming the composite dispersion into droplets, a known spraying device such as a rotating disk system, a two-fluid nozzle system, a pressurized nozzle system, a two-fluid pressurized nozzle system, or an electrostatic system can be used. The droplet diameter at this time is selected according to the particle diameter of the desired spherical silica particles and the solid concentration of the composite dispersion, but is preferably 1 to 200 μm. Means for heating the droplets include a method using hot air, a method of passing through a heated cylinder, infrared heating, and dielectric heating.

The spherical silica particles obtained according to the present invention are:
Since a salt generated by the reaction between the alkali silicate and the acid is included, it is preferable to remove the salt by washing. After the washing, it is dried and, if necessary, is baked. At an appropriate stage in the manufacturing process, for the purpose of controlling pore characteristics, etc.
An aging treatment can also be performed.

Next, the third invention will be described. The spherical silica particles of the present invention are suitable for use as a catalyst carrier because of their low strength and large specific surface area. The polymerization rate can be increased.

First, the spherical silica particles of the present invention can be used without any limitation as compared with known carriers supporting olefin polymerization catalysts. That is, as the olefin polymerization catalyst to be supported, known catalysts can be used, and examples thereof include chromium-based catalysts such as chromium oxide, Ziegler-based catalysts such as magnesium chloride and titanium chloride, and metallocene catalysts such as zirconocene. Also, as a polymerization method, a known slurry method, bulk method, gas phase method, solution method, and the like can be suitably used. Further, there are no restrictions on the polymerization conditions.

The silica particles of the present invention are most useful as a carrier for an olefin polymerization catalyst as described above. However, they can be used as fillers for cosmetics, paints and the like utilizing their easy disintegration and high specific surface area. Also, it can be widely used as silica particles having no depression or crack on the surface.

[0037]

EXAMPLES [Measurement Method] The average particle diameter of the silica particles in the dispersion liquid and the silica particles after the spray heat treatment were measured with Microtrac UPA and Microtrac HRA X100 manufactured by Nikkiso Co., Ltd., respectively. The particle shape was observed and evaluated with a scanning electron microscope and an optical microscope. The specific surface area was determined by analyzing the result of measurement at a nitrogen relative pressure of 0 to 0.99 by the nitrogen adsorption method by the BET method. For the measurement, Kantachrome Autosorb manufactured by Kantachrome Co., Ltd. was employed.

Example 1 (Example) A sodium hydrosilicate was reacted with sulfuric acid and washed to obtain a silica hydrogel dispersion. When this dispersion is dried at 120 ° C., a silica xerogel having a pore volume of 0.45 cm ³ / g and a specific surface area of 745 m ² / g is obtained. This silica hydrogel dispersion was wet-pulverized with a sand mill filled with 0.5 mm zirconia beads to obtain a silica dispersion having an average particle diameter of 0.3 μm. The solid content concentration was 12% by weight.

25 kg% by weight of 6.5 kg of this silica dispersion
182 g of sulfuric acid were added and SiO _TwoConcentration 23.36
%, Na_TwoSodium silicate 117 with an O concentration of 7.83%
g with slow stirring to obtain a composite dispersion.
Was.

The composite dispersion was applied to a rotating disk spraying system for 2 hours.
The mixture was sprayed and heated in hot air of 00 ° C., and when the gelation was substantially completed, the spherical silica particles were recovered. At the time when the gelation was substantially completed, the temperature of the hot air was 70 ° C. and the relative humidity was 50%. This was dispersed again in water, adjusted to pH 8 with aqueous ammonia, and kept at 60 ° C. for 1 hour for aging. After adjusting to pH 3 with sulfuric acid, washing with demineralized water, 120
Dried for 2 hours at ° C.

The silica particles obtained as a result were solid spheres in which many fine silica particles were aggregated, and no depressions or cracks were observed on the surface. The average particle diameter of the obtained silica particles is 41 μm, and the specific surface area is 620 m ^2.
/ G. Tensile strength S measured by selecting a particle having a particle diameter of 50 μm from silica particles is 4.31MP.
a. Note that the value of S _t when the particle diameter 50μm is 8.73MPa.

"Example 2 (Example)"
Silica gel having a pore volume of 0.55 cm ³ / g and a specific surface area of 750 m ² / g is dispersed in water so as to have a solid content of 40% by weight, and wet-milled with a medium stirring mill filled with zirconia beads having a diameter of 0.5 mm. Thus, a dispersion containing silica gel having an average particle diameter of 0.4 μm was obtained.

To 20 kg of this dispersion was added 1.88 kg of a 25% by weight sulfuric acid solution. Next, SiO ₂ concentration 23.
1.71 kg of a 36% sodium silicate solution having a Na ₂ O concentration of 7.83% was diluted with 600 g of demineralized water, and gradually added to the above-mentioned sulfuric acid-added dispersion with vigorous stirring to form a composite dispersion. A liquid was obtained. The pH of this composite dispersion is 2.4.
Met.

The composite dispersion was supplied to a two-fluid nozzle by
The mixture was sprayed and heated in hot air at 50 ° C., and when the gelation was substantially completed, the spherical silica particles were recovered. At the time when the gelation was substantially completed, the temperature of the hot air was 70 ° C. and the relative humidity was 40%. This was dispersed again in water, adjusted to pH 8 with aqueous ammonia, and kept at 60 ° C. for 1 hour for aging. After adjusting to pH 3 with sulfuric acid, washing with demineralized water, 120
Dried for 2 hours at ° C.

The resulting silica particles were solid spheres in which many fine silica particles were aggregated, and no depressions or cracks were observed on the surface. The average particle diameter of the obtained silica particles is 19 μm, and the specific surface area is 590 m ^2.
/ G. Tensile strength S measured by selecting particles having a particle diameter of 20 μm from silica particles is 15.7 MP.
a. Note that the value of S _t when the particle diameter 20μm is 21.5MPa.

Example 3 (Comparative Example) A composite dispersion was obtained in the same manner as in Example 2, except that the silica gel having an average particle diameter of 5 μm was used without pulverization using a medium stirring mill. The composite dispersion was formed into droplets under the same conditions as in Example 1 and heated. The obtained silica particles were not spherical but amorphous. Of hot air at the time when the gelation is substantially finished,
The temperature was 80 ° C. and the relative humidity was 30%.

The average particle diameter of the obtained silica particles is 22.
0 μm, and the specific surface area is 750 m ^Two/ G. Shi
Select 220μm diameter particles from Lica particles
The tensile strength S measured was 0.10 MPa. What
In addition, when the particle diameter is 220 μm, S_tIs 0.05M
Pa.

Example 4 (Comparative Example) The composite dispersion obtained in Example 2 was similarly formed into droplets, sprayed in hot air at 150 ° C. and heated, and when gelation was substantially completed, The spherical silica particles were recovered. At the time when the gelation was substantially completed, the temperature of the hot air was 110 ° C. and the relative humidity was 2%. Although the obtained silica particles were spherical, many hollow particles were present and cracks were present.

[Evaluation of Olefin Polymerization Rate] The evaluation of the olefin polymerization rate was carried out as follows in accordance with the method described in JP-A-52-48583. The spherical silica particles and the aqueous solution of chromic acid are mixed and dried so that Cr is 1.2% by weight based on the solid content. This is activated at 760 ° C. for 5 hours. The obtained supported catalyst and isobutane are charged into a reactor, kept at 110 ° C. and 35 atm, and ethylene gas is introduced to carry out polymerization. After reacting for 90 minutes, the weight of the produced polyethylene is measured to determine the polymerization rate of each catalyst.

With the polymerization rate of the olefin polymerization catalyst using the spherical silica particles of Example 1 as a carrier as 100, the polymerization rate of the catalyst using each silica particle as a carrier was determined. The spherical silica particles obtained in Example 1, the spherical silica particles obtained in Example 2,
Commercially available spherical silica particles A and commercially available spherical silica particles B
Table 1 shows a comparison of polymerization rates obtained according to the above-mentioned method for evaluating the polymerization rate of olefin.

[0051]

[Table 1]

Table 2 shows the average particle diameter, specific surface area, and tensile strength of the commercially available spherical silica particles A and B used for comparison. In Table 2, ()
Numerical inner is the particle diameters of the spherical silica particles when determining the S or S _t.

[0053]

[Table 2]

[0054]

The spherical silica particle aggregate of the present invention has a low strength, a large specific surface area, is solid, and has no depression or crack.
Therefore, it can be widely used not only as a catalyst and a catalyst carrier but also as a silica particle which is solid and does not have depressions or cracks on its surface, including fillers for cosmetics and paints. The production method of the present invention can preferably obtain such beneficial spherical silica particle aggregates.

When the spherical silica particle aggregate of the present invention is used as an olefin polymerization catalyst carrier, the polymerization activity of olefin is high, so that the polymerization rate is increased and the produced polymer particles are large. Further, it can be suitably used as a catalyst other than olefin polymerization and a catalyst carrier.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryo Kusaka 10 Goi Kaigan, Ichihara-shi, Chiba Prefecture Asahi Glass Co., Ltd. F-term (reference) 4G072 AA28 BB07 CC13 DD02 DD03 DD04 DD05 GG01 GG03 HH19 HH21 JJ13 JJ15 LL06 LL07 MM01 MM02 MM02 MM31 MM32 PP17 RR06 RR12 TT01 TT05 UU17 4J015 EA10

Claims (3)

[Claims] 1. A tensile strength S (MP) measured for an aggregate of silica particles having a particle diameter of d (μm).
a) is less than or equal to S _t given by the following equation 1 (MPa), average particle diameter of 1 to 200 [mu] m, a specific surface area of 400
m ² / g or more, spherical silica particles characterized by the above-mentioned. S _t = 39.2 × exp (−0.03 × d) Equation 1. 2. A silica gel particle having an average particle diameter of 0.05 to 3.0 μm is dispersed in a mixed solution of an alkali silicate and an acid, and the dispersion is sprayed to form droplets. The mixture is heated in the liquid to gel a portion of the mixed solution of the alkali silicate and the acid in the droplet, and when the gelation is substantially completed, the temperature of the gas in contact with the spherical particles is adjusted to 60 to 2
The method for producing spherical silica particles according to claim 1, wherein the temperature is set to 00 ° C and the relative humidity is set to 20% or more. 3. An olefin polymerization catalyst carrier comprising the spherical silica particles according to claim 1.