JPH0764542B2 - Method for producing silica gel for liquid chromatography - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silica gel for liquid chromatography.

Silica gel has higher mechanical strength than polymer-based fillers such as cross-linked dextran and polyacrylamide.
It is widely used as a packing material for liquid chromatography because it hardly swells or shrinks due to changes in pH, ionic strength, eluent composition, etc.

[Prior art]

Conventionally, as silica gel, spherical silica gel and crushed silica gel are known. Spherical silica gel is superior to crushed silica gel in its performance and use characteristics.

Further, when used as a packing material for liquid chromatography among spherical silica gel, it is required to strictly control physical properties such as surface area, average pore diameter, pore volume and the like.

That is, spherical silica gel having a surface area of 300 to 500 m ² / g, an average pore diameter of 80 to 120 Å and a pore volume of 0.8 to 1.2 ml / g is desired.

Furthermore, in order to increase the separability of the packing material for liquid chromatography, it is necessary to reduce the particle size, and in order to realize more rapid and highly accurate separation in recent years, the average particle size is 1 to 20 μm. Microspherical silica gel is desired.

However, such silica gel is not easy to manufacture and expensive.

The following methods are conventionally known as methods for obtaining fine spherical silica gel.

(1) JP-A-60-71515 describes a method of emulsifying a water glass sol in an organic solvent containing a first surfactant and then adding a second surfactant to gelate the same. ing.

In this method, since the organic solvent used for emulsification is separated from silica gel, a distillation step is required, which is economically disadvantageous.

The obtained gel has an average particle size of 11.3μ from that example.
However, other physical properties are not specified, and its utility as a packing material for liquid chromatography is unknown.

(2) Japanese Patent Application Laid-Open No. 54-9588 describes a method of forming fine spherical particles of 0.5 to 50 μm by using a polymerizable organic material having miscibility with water as a binder. There is.

What is obtained by this method is a mixture of silica sol particles and an organic material, and in order to obtain silica gel, it is necessary to remove the polymerized organic material by a sintering process at 500 ° C. or higher and for 4 hours or longer. Further, the physical properties of the obtained gel are determined by the kind of the colloidal silica as the raw material, and it is difficult to control the desired gel physical properties.

(3) A spray drying method is known as a method for obtaining a spherical gel without using the above-mentioned organic solvent or organic material.

JP-A-53-65293 proposes a method of spray drying silica sol. However, when the present inventors carried out this method, it was found that the product was likely to be silica gel having a spherical shape but a hollow or a large depression.

When silica gel having such hollows or large dents is used as a packing material for liquid chromatography, its strength is not sufficient, and it is likely to break or spread the separated sample, which is not preferable.

Japanese Examined Patent Publication (Kokoku) No. 43-7012 discloses that a sodium silicate solution is gelled with gaseous carbon dioxide, thermally formed, further treated with sulfuric acid, and then spray-dried to give a surface area of 300 to 1000 m ² / g.
A method for obtaining silica gel with a pore volume of 0.5 to 1.25 cc / g is described.

In this method, since gaseous carbon dioxide is used, it is difficult to control the reaction and it is difficult to control the physical properties of the resulting silica gel.

JP-B-47-3446 discloses that an aqueous solution of an alkali metal silicate and a mineral acid are reacted to form a silica hydrosol having a pH of 9.6 to 10.9, which is gelled and further reacted with a mineral acid to form an acidic silica gel slurry by spray drying. A method for obtaining microspheres of 10-80μ is described.

In this way, according to the example, silica gels with very large surface areas of 740 m ² / g to 965 m ² / g are obtained. Such high surface area silica gels are generally
They often have micropores of 50Å or less. When the liquid is intended for use as a packing material for chromatography, such micropores are not very effective for separating sample components, and also cause a decrease in the strength of silica gel.

Further, in Japanese Examined Patent Publication (Kokoku) No. 47-35676, sodium silicate and sulfuric acid are mixed at 23 to 50 ° C. to prepare a mixed solution having a pH of 9.8 to 10.4, in which a hydrogel slurry is formed and the pH after aging is set to 3
A method is described below in which the pH is lowered to below, the pH is raised to 8 to 10.2 after aging, and the aging and spray drying are performed.

The silica gel obtained in this way is according to the examples
It has a pore volume of 0.9-1.15 ml / g with a surface area of 194-560 m ² / g, but the average pore size is not specified.
Further, as described above, there are many aging steps and the operation is complicated.

JP-B-43-7012, 47-3446, 47-35676 In any method, it is an essential requirement to carry out the gel-forming step on the alkaline side, but the present inventors likewise on the alkaline side. Using a gel-formed slurry, the cause is unknown, but often very brittle gel,
It was also found that it is easy to obtain particles having many irregularities on the surface or particles having irregularly shaped particles other than spherical particles. Such silica gel does not pose a problem as a usual desiccant, but when it is considered to be used as a packing material for liquid chromatography, packing efficiency is lowered, which is not preferable.

[Problems to be solved by the invention]

The object of the present invention is a simpler and cheaper method than the above-mentioned prior art, a method for producing fine spherical silica gel having a smooth surface and high performance as a packing material for liquid chromatography which does not contain irregular particles. To provide.

[Means for solving problems]

The gist of the present invention is a method for obtaining silica gel by spray-drying a silica hydrogel slurry obtained by reacting an aqueous solution of an alkali metal silicate with an aqueous solution of a mineral acid. A. To produce active silicic acid having a SiO ₂ concentration of 6.5 to 11.5 wt% at pH 3.0 to 4.0 b. Gelling the silicic acid under stirring c. Reacting with an aqueous ammonia solution, Washing with water d. Wet-grinding the obtained hydrogel e. Spray-drying with a two-fluid nozzle method, which is a method for producing silica gel for liquid chromatography, which will be described in detail below.

Examples of the alkali metal silicate used in the present invention include sodium silicate and potassium silicate, and sodium silicate is generally used. As the mineral acid, sulfuric acid, hydrochloric acid, nitric acid or the like can be used.

Any method may be used as a method of generating active silicic acid, but a method of dropping an alkali metal silicate into a mineral acid under stirring is preferable.

At this time, it is necessary to adjust each concentration and mixing ratio of the alkali metal silicate and the mineral acid so that the final pH is 3.0 to 4.0 and the SiO ₂ concentration is 6.5 to 11.5 wt%.

The pH value has a great influence on the gelation time, and if the pH value is less than 3.0, it takes a long time for the gelation to be impractical.If the pH value exceeds 4.0, the gelation proceeds rapidly to stabilize the silicic acid. Difficult to prepare.

The SiO ₂ concentration of the produced silicic acid has a significant effect on the average pore size of the finally obtained silica gel. That is, the SiO ₂ concentration is
If it is less than 6.5 wt%, the average pore size of silica gel obtained is 80.
When it is less than Å and the SiO ₂ concentration exceeds 11.5 wt%, the average pore diameter of the obtained silica gel exceeds 120 Å and the gel has low strength.

The active silicic acid production temperature can be carried out in the range of 5 to 60 ° C,
Particularly, 30 to 50 ° C is preferable and practical. Generation temperature is 5
When the temperature is lower than ℃, it takes a long time to gel, and when the temperature exceeds 60 ℃, the gelation proceeds rapidly, and it becomes difficult to stably generate active silicic acid. The aqueous solution of active silicic acid thus obtained is gelled under stirring to form a silica hydrogel slurry.

The temperature of gelation is not particularly limited, but at low temperature it takes a long time to complete gelation, and at high temperature, gelation progresses rapidly and uniform stirring becomes difficult, so 20-50 ° C is suitable. Is. In general, the lower the gelation temperature is, the slower the gelation speed is and the easier the stirring is. Therefore, for example, the method of starting the gelation at 20 ° C., making it into a slurry state, and then raising the temperature to 80 ° C. to complete the gelation is also possible. It is possible.

The stirring means may be any as long as it can crush the hydrogel generated when the activated silicic acid is gelated to generate a slurry of the hydrogel, and an ordinary paddle type stirring blade can be used, but it is necessary. A high-speed stirrer, a kneader or the like can be used depending on the requirements.

An aqueous ammonia solution is added to the produced silica hydrogel slurry to cause a reaction. At this time, the concentration of the slurry is not particularly limited, but a high concentration has a high viscosity and stirring is difficult, and a low concentration is economically disadvantageous. Therefore, a SiO ₂ concentration of 5 to 10 wt% is suitable.

The larger the pH of the ammonia-treated liquid, the larger the average pore size of the final silica gel and the smaller the surface area. For example, by adjusting this pH to 8.0 to 9.0, they can be adjusted to 80 to 120Å and 300 to 500 m ² / g, respectively.

The reaction temperature is not particularly limited, but 60 to 90 ° C. is appropriate because a low temperature requires a long time to complete the reaction.

After completion of the reaction, the product is washed with water and excess water to remove by-produced alkali metal salts. If spray drying is performed without removing this by-product, pores are likely to be non-uniform because the salt crystallizes and precipitates in the obtained silica gel.

The obtained overcake is dispersed in water and then wet-milled.

This grinding process has a great influence on the particle surface state and shape of the final silica gel. That is, the surface is smooth,
The pulverization treatment is indispensable in order to obtain silica gel in which irregular shaped particles are not mixed. Any pulverizing method may be used as long as it is a wet method, and for example, a ball mill, a vibration mill, a stirring ball mill, a rod mill, a friction disk mill, a stone mill colloid mill, or the like can be used.

By spray-drying the pulverized silica hydrogel slurry thus obtained by a two-fluid system, fine spherical silica gel can be obtained.

As a conventional spraying method, a pressure nozzle method, a rotary disk method, and a two-fluid method are known, but a pressure nozzle method and a rotary disk method are widely adopted in terms of power consumption.

In the above-mentioned JP-A-53-65293, JP-B-43-7012, 47-3446, 47-35676, there is no particular limitation on the spraying method, and there is no provision in JP-A-53-65293. The examples only describe a spray-drying method by means of a rotating disc method.

The inventors of the present invention have conducted various studies to obtain silica fine particles by spray drying, and the shape, physical properties and particle size of the obtained particles greatly vary depending on the combination of the properties of the liquid or slurry to be sprayed and the spraying method. It was not easy to obtain silica fine particles with the same shape, physical properties and particle size. For example, as mentioned above, silica gel with hollow or large dents, very brittle gel or those with many irregularities on the surface or mixed particles other than spheres Small pore size, large surface area, large pore size and low strength Was often obtained.

Therefore, in order to obtain fine spherical silica gel with an average particle size of 1 to 20μ having surface area of 300 to 500m ² / g, average pore diameter of 80 to 120Å, and pore volume of 0.8 to 1.2ml / g, It is necessary to spray-dry the above slurry by a specific spraying method.

That is, as described above, an aqueous solution of an alkali metal silicate is reacted with an aqueous solution of a mineral acid to generate active silicic acid having a SiO ₂ concentration of 6.5 to 11.5 wt% at pH 3.0 to 4.0, and the silicic acid is gelled under stirring. The above object can be achieved by spray drying the silica hydrogel slurry produced by wet pulverizing the obtained hydrogel after reacting with the aqueous ammonia solution and then washing with water.

When the two-fluid method in the method of the present invention is changed to a spraying method using a pressure nozzle method and a rotating disk method, the particle size distribution is 3 to 100 µ, the average particle diameter is 30 µ or more, and fine particles of 1 to 20 µ are efficiently obtained. Was not easy.

The conditions for spray-drying by the two-fluid method are not particularly limited, but the spray pressure is preferably 4 kg / cm ² or more. If the spray pressure is less than 4 kg / cm ² , the average particle size may increase, and the yield of fine particles of 1 to 20 μ may decrease.

The hot air temperature for drying may be 100 to 300 ° C.

According to the method described above, it is possible to obtain high-performance fine spherical silica gel as a packing material for liquid chromatography, which has a smooth surface and does not contain irregularly shaped particles.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, without using an organic solvent or an organic material, the surface is smooth and the irregular-shaped particles can be mixed at a low cost by a simple method without requiring a complicated operation. High performance micro spherical silica gel can be obtained as a packing material for liquid chromatography.

Next, the present invention will be described more specifically by way of examples.

Example 1 500 g of a sulfuric acid aqueous solution having a concentration of 15 wt% was supplied to a reaction tank installed in a 50 ° C. constant temperature tank. While stirring the sulfuric acid aqueous solution with a paddle type stirring blade, a sodium silicate aqueous solution with a SiO ₂ concentration of 12 wt% is approximately 1260
g was added to prepare active silicic acid having a SiO ₂ concentration of 8.6 wt% at pH 3.5. After about 10 minutes, the aqueous silicic acid solution thickened and gelation started. At this time, stirring was continued to complete gelation while crushing the hydrogel to obtain silica and a rogel slurry.

Pure water and an aqueous ammonia solution having a concentration of about 8 wt% were added to the silica hydrohydrogel slurry to adjust the SiO ₂ concentration to about 6 wt% and pH 8.0, and then reacted at 80 ° C. for 2 hours.

After completion of the reaction, the product was washed with excess water, dispersed in water, wet-milled with a Dyno-Mill (Willie A. Bakofen), and then the inlet hot air temperature was 200 ° C, the outlet hot air temperature was 100 ° C, and the spray pressure was set to 5 kg / cm ² . It was spray-dried with a two-fluid spray dryer.

The obtained silica gel was spherical with a size of 20 μm or less, the surface was smooth, and irregular particles were hardly mixed.

Regarding the physical properties, as shown in Table 1, it was suitable as a packing material for liquid chromatography.

Example 2 100 g of a sulfuric acid aqueous solution having a concentration of 15 wt% was supplied to a reaction tank installed in a 20 ° C. constant temperature tank. About 285 g of sodium silicate having a SiO ₂ concentration of 12 wt% was added while stirring the sulfuric acid aqueous solution with a huddle type stirring blade.
An active silicic acid having a SiO ₂ concentration of 8.9 wt% was prepared at pH 4.0. about
After 50 minutes, the silicic acid aqueous solution started to gel.

The hydrogel is crushed by stirring and gelled.
The temperature was raised to 80 ° C. to complete gelation.

Pure water and a concentration of about 8w in the resulting silica hydrogel slurry
Add t% aqueous ammonia solution, SiO ₂ concentration approx. 6 wt%, pH 8.0
Then, the mixture was reacted at 77 ° C overnight. After the reaction,
It was washed with excess water, wet-milled with a ball mill, and then spray-dried with a two-fluid spray dryer set at an inlet hot air temperature of 200 ° C. and an outlet hot air temperature of 100 ° C. and a spray pressure of 7 kg / cm ² .

The obtained silica gel was 20 μm or less in size and had a smooth surface, and almost no irregular particles were mixed.

Regarding the physical properties, as shown in Table 1, it was suitable as a packing material for liquid chromatography.

Comparative Example 1 To 200 g of a sulfuric acid aqueous solution having a concentration of 15 wt%, 341 g of a sodium silicate aqueous solution having a SiO ₂ concentration of 20 wt% was added, and the SiO ₂ concentration was 12.6 w at pH 4.0.
It carried out on the same conditions as Example 2 except having obtained t% activated silicic acid.

The silica gel obtained had a spherical shape and a smooth surface, and there was no mixture of irregularly shaped particles, but as shown in Table 1, the average particle diameter and pore size were large, and the pore volume was large and relatively weak.

Comparative Example 2 In the same manner as in Example 2, except that 446 g of an aqueous sodium silicate solution having a SiO ₂ concentration of 7.5 wt% was added, and the SiO ₂ concentration was 6.1 at a pH of 4.0.
A wt% active silicic acid was prepared and carried out.

The obtained silica gel was fine spheres of 20 μm or less, the surface was smooth, and irregular particles were not mixed, but the pore size was small and the pore volume was small as shown in Table 1.

Comparative Example 3 As in Example 2, but without adding ammonia,
The treatment was carried out at pH 6 overnight at 80 ° C.

The obtained silica gel was 20 μm or less in microspheres and had a smooth surface, and almost no irregular particles were mixed.
As shown in the table, the pore size was small.

Comparative Example 4 It was carried out in the same manner as in Example 1, but without wet grinding.

Although the obtained silica gel was spherical, it had irregularities on the surface and had irregular-shaped particles mixed therein.

Comparative Example 5 The procedure of Example 1 was repeated, except that spray drying was performed using a rotary disk type spray dryer.

The silica gel obtained had a spherical shape and a smooth surface, and there was no mixture of irregularly shaped particles, but the average particle size was 40μ and the number of fine particles of 20μ or less was small.

Comparative Example 6 The procedure of Example 1 was repeated, except that spray drying was performed using a pressure nozzle spray dryer.

The silica gel obtained had a spherical shape and a smooth surface, and there was no mixture of irregularly shaped particles, but the average particle size was 80μ, and there were almost no fine particles below 20μ.

Claims (1)

[Claims] 1. A method for obtaining silica gel by spray-drying a silica hydrogel slurry obtained by reacting an aqueous solution of an alkali metal silicate with an aqueous solution of a mineral acid. A. To produce active silicic acid having a SiO ₂ concentration of 6.5 to 11.5 wt% at pH 3.0 to 4.0 b. Gel the silicic acid under stirring c. React with an aqueous ammonia solution and wash with excess water D. The obtained hydrogel is wet-ground and e. Spray-dried by a two-fluid nozzle method. A method for producing silica gel for liquid chromatography.