CA1213262A

CA1213262A - Spherical micro-porous silica gel and a production process thereof

Info

Publication number: CA1213262A
Application number: CA000433775A
Authority: CA
Inventors: Junji Arika; Eiji Shiota; Kazuaki Yamamoto
Original assignee: Toyo Soda Manufacturing Co Ltd
Current assignee: Tosoh Corp
Priority date: 1982-08-04
Filing date: 1983-08-03
Publication date: 1986-10-28
Also published as: FR2531417B1; JPS5926911A; GB2127002B; JPH0323486B2; GB2127002A; DE3328267C2; FR2531417A1; GB8320491D0; DE3328267A1; US4554211A

Abstract

Abstract of the Disclosure A novel spherical micro-porous silica gel having a mean diameter of 3 - 20 µm, a bulk density of 0.28 - 0.41 g/cm3, a pore size of 18,000 -100,000 and a specific surface area of 1,000 - 1,400 m2/g, useful as a packing material for gas or liquid chromatography or as a support for catalysts used in catalytic reactions, is produced by gelling an aqueous solution containing (a) SiO2 and (b) stearic acid or a mixture of stearic acid and a non-ionic surface active agent of which HLB ranges from 3.5 to 6.0 as an emulsifier which solution is dispersed as aqueous droplets in an oil phase, wherein the primary particle diameter is not larger than 6 nm and the molar ratio of SiO2 to Na2O is not larger than 5.5, with an organic acid as a gelling agent.

Description

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This invention relates to a spherical micro-porous silica gel and a production process thereof. Particularly, this invention pertains to an , efficient spherical micro-porous silica gel having an extremely large specific surface area and especially useful as a support for liquid chromatography and a process for producing that spherical micro-porous silica gel.
A silica gel is used not only as a packing material for the I columns for gas or liquid chromatography but also as a support for catalysts used in various catalytic reactions In order to meet such demands, a silica gel is required to have a certain particle size, micro-porous structure and large specific surface area 3 Among other things, when used as a support for high speed liquid I chromatography, a silica gel has to satisfy many strict requirements. Briefly, the silica gel need (1) to be fine particles having a mean diameter of about m, (2) to be fully spherical in shape and uniform in size, (3) to have a certain pore size and specific surface area large enough to separate con-stituents present in the sample compounds and (4) to have sufficient strength unlikely to collapse or to be broken by moving layers which exert pressures or permeate into it.
Silica gels produced in conventional processes commonly have a specific surface area of 200 - 50~ mug For this reason, development ox a new silica gel having Nash larger specific surface area, together with greater retention capacity has been long awaited. silica gels used for high speed liquid chromatography have been produced by hydrolysis of organic Solon compounds. But this process has a disadvantage that organic Solon compounds are expensive and the process itself is very complex ; It has also been known that silica gels may be manufactured by causing sodium silicate or silica sol to form a gel while they are suspended in an oil phase as aqueous droplets. However, compared with the above process .

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starting from organic Solon compounds, the gelatin process has proved to be more disadvantageous because the produced silica gel is mostly deformed and ) inferior in capacity ox making chemical bond with other compounds.
Under the circumstances, the present inventors have studied intensively to eliminate the above-described drawbacks of such conventional process and have finally discovered a spherical silica gel having very large specific surface area and a process for producing the same with ease at low } costs.
I` Accordingly, the present invention provides a spherical micro-Jo 10 porous silica gel having a mean diameter of 3 - 20Jlm, a bulk density of 0~28 - 0.41 g/cm3, a pore size of 18,000 - 100,000, and a specific surface area of 1,000 - 1,400 mug The present invention also provides a process for producing a sphere teal micro-porous silica gel having a mean diameter of 3 - 20 my a bulk i density of 0.28 - 0.~1 g/cm3, a pore size of ]8,000 - 100,00~, and a specific surface area of 1,000 - 1,400 mug which process comprises subjecting to gel~tion a water-in-oil type emulsion which an aqueous droplets contains Sue dispersed in an oil phase wherein (a) in the aqueous droplets containing ` Sue the primary particle diameter of Sue is not larger than 6 no and the I molar ratio of Sue to Noah is not larger than 5.5, (b) either Starkey acid or a mixer of s~earlc acid and a non-ionic surface active agent whose HUB
ranges from 3.5 to 6.0 is employed as an emulsifier and I an organic acid is employed as a golfing agent.
Figure 1 shows a typical calibration curve of polystyrene deter-mined through liquid chromatography in which polystyrene molecular weight is plotted against its effluent amount in the logarithmic scale.
Figure 2 shows comparative figures of k' which indicates capacity ' factor of each kind of the micro-porous silica gal against anisole, vitro-

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Bunsen, methyl bonniest, and acetophenone.
1. Anisole, I Nitrobenzene, 3. Methyl buoyancy 4. Acetophenone The silica gel according to the present invention is fully spherical micro-porous and has a mean diameter of 3 - 20 m, a bulk density of 0.2~ - 0.41 glaucoma, a pore size of 18,000 100,000, and a specific surfacearea of 1,000 - 1,400 mug The term "pore size" (hereinafter may be abbreviated as PUS), as employed in this specification, is specified by the PUS value which represents a certain magnitude of polystyrene molecular weight and expressed by the point A, an intersection of two lines drawn tangentially to a calibration curve as shown in Figure 1. Hereupon the calibration curve is made up through liquid chromatography by the plotting ox effluent amounts ox various classes of polystyrene from the column against their corresponding molecular weight deter-mined in advance, where the column, 4 mm in diameter and 300 mm long is packed previously with the silica gel in question.
The production process of the silica gel according to the invention comprises preparing a water-in-oil type emulsion from an aqueous solution containing Sue and an organic solvent, and producing a fine particle through gelatin of the emulsion by the addition of a golfing agent, whereby the size and shape of the emulsion particle are maintained as they stand In this process, an aqueous solution containing Sue is used as one of the starting materials; in this aqueous solution, the primary particles of Sue should not be larger than 6 no in diameter and the molar ratio of Sweeney should not ye larger Han 5.5.
In contrast with a known method in which an aqueous solution containing primary silica particles, the mean diameter of which extends from several no to several tens no or a soluble component is employed in this I

I) invention, if the mean diameter of the primary silica particles exceeds 6 no, it becomes difficult to produce a silica gel having a specific surface area of at least 450 m go likewise if the molar ratio of Sweeney exceeds 5.5, the soluble component can no longer remain stable in the aqueous solution containing Sue. As a result, it becomes impossible that the soluble component dissolved in the aqueous solution precipitates and the desired silica gel with large specific surface area are produced consequently In this invention, as the aqueous solution containing Sue, an aqueous solution containing silica sol and/or sodium silicate may be used far this purpose. The water-in-oil type , 10 emulsion may be prepared by dispersing the aqueous solution described above into an organic solvent which contains as an emulsifier Starkey acid or a ', mixture of Starkey acid and a non-ionic surface active agent whose HUB ranges from 3~5 to 6Ø
i So far it has been believed that a stable water-in-oil type emulsion can be prepared by merely adding a non-ionic surface active agent whose HUB is in the range 3.5 - I However, with only such a non-ionic surface active agent, silica gel particles tend to aggregate each other upon ;`, gelatin. Besides, they tend to grow into such a deformed shape that their packing density is reduced consequently. Therefore in this in~ent~on, Starkey I acidulous used singly or in combination with the non-ionic surface active agent to facilitate formation of a fully spherical silica gel practically without an aggregation or deformation by taking advantage that Turk acid has a strong affinity with silica gel . The term non-ionic surface active agent, employed in this invention, includes sorbitan menstruate, sorbitan moonlit, propyleneglycol moo-Stewart and the like, all of which are familiar to those who are skilled in the art. however, sorbitan nostearate is the most preferred among the ` compounds mentioned above.

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Although the amount of the above emulsifier to be used is not particularly important, the emulsifier will little effect the stability of the prepared emulsion if the amount is extremely small. In addition, if the amount of the emulsifier is too small, the gel particle tends to aggregate on Jo gelatin. To the contrary, when the amount of the emulsifier exceeds a certain limit, the effect of the emulsifier will stay almost unchanged.
Taking these into account, the desirable amount of the emulsifier is in the range of 0.5 - 1% by weight based on the total emulsion in this invention.
Various kinds of organic solvents may be used and there is practically no restriction of the solvent if it dissolves at least 1% by weight of the emulsifier. Among them, aromatic hydrocarbons, such as Bunsen, Tulane? zillion, ethyl Bunsen, etch, are particularly useful in this in-mention.
Meanwhile, in this invention any common types of stirrers can be used to make up the emulsion. However, since ordinary paddled stirrers are sometimes ineffective in reducing the mean diameter of the emulsion particles to below 30J~m and with such type of stirrers the particle size distribution ; most likely becomes road, it is considerably difficult to produce a silica gel having a desired size of about 10 elm in plenty. From this standpoint, in this invention it is recommended to use a homogenizer type stirrer The thus prepared emulsion is subjected to gelatin by adding a golfing agent whereby a slurry containing the desired spherical silica gel particles is produced. An organic acid or an android thereof is used as the golfing agent. Such lower fatty acids or androids thereof as formic acid, acetic cold, prop ionic acid and the like can be favorably used, but acetic android is particularly preferred for this purpose In relation to this step, according to this invention it is also possible to vary the PUS value by varying the rate of adding the golfing agent Separation of the spherical fine particles from the thus produced slurry can be made by any conventional means. or example, the slurry contain-in the spherical silica gel is added to alcohol; after being kept standing for a little while, the supernatant alcohol solution is decanted and the no-mining slurry is washed with an acidic aqueous solution like dilute sulk fork acid, etc., water, and alcohol in succession before the silica gel is dried.
In the process as described above, the desired silica gel having a large specific surface area and efficient capacity required for a support for high speed liquid chromatography can be produced easily at low costs.
This invention will be explained in more detail in the following examples.
-Example 1-An oil phase was prepared by dissolving 1.08 g of sorbitan moo-Stewart of a HUB 4.7 and 1.08 g of Starkey acid in about 250 ml of Tulane.
A homogenizer type stirrer commercially available under the trade mark TO
Auto Home mixer, manufactured by Tokushu Cook Cage Kabushiki Couch, was used to make up an emulsion. The stirrer was rotated at a rate of 6,000 rum and 80 ml of a silica sol of which the primary particle size was below 6 no and I the molar ratio of Sweeney was 5, which was manufactured by Shokubai Casey Cage Kabushiki Couch under the trade mark Cataloid SUE, was added to the oil phase and stirred for about 16 minutes.
Thus, the silica sol turned to spherical fine particles having a diameter of 5 to 20 em. After that, 10 ml of acetic android was poured into the emulsion over about 30 seconds to cause gelatin and the gel was kept standing overnight for aging.
The silica gel slurry prepared in this way was dispersed in ` methanol and left to stand for a little while. After that, the Tulane and ~2~2~
`'' i the emulsifier previously added were removed by decanting the supernatant .,.,,~
methanol solution.
Next, the silica gel slurry was rinsed with a dilute sulfuric acid of pi 2.5 until the pi of the slurry reached 2.5, and then rinsed with deionized water until the pi of the slurry became equal to the deionized water's.
The deionized water contained in the silica gel was replaced with ethanol.
After that, the silica gel was dried overnight at 60C under a reduced Jo pressure.
Table l shows the data of the physical properties of the silica Jo 10 gel obtained in this example hereinafter referred to as Gel-l. For the in-formation, the data of the physical properties of a silica gel used as a support for high speed liquid chromatography, which is produced by Toy Soda manufacturing Co., Ltd. under the trade mark LS-320, were also given in Table 1 for the sake of comparison.

Table 1 Jo Physical Properties Jollily LS-320 ¦ Specific surface area mug 1,379 500 lo Pore size PUS 19,000 14,000-16,000 Bulk density (g/cm3) 0.41 0.51 Shape Spherical Spherical I` Mean diameter em) 10 10 Content of the particle having '; the size distribution 5 - 15~m 95 to by weight) remark 1: the specific surface area was determined by the BET method.
remark 2: The particle size distribution was measured by means of a COTTER

I` Counter.

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-Example 2-A spherical micro-porous silica gel thereinafter referred to as Gel-2) was produced quite similarly to the process of Example 19 except that ; the total amount of the acetic android was poured into the emulsion over one hour, The physical properties of the silica gel are shown in Table 2.
-Example 3-Sodium silicate (Sue content: 13.9~ by weight, Noah content: 4.2%
by weight, Molar ratio of Sweeney in place of silica sol was emulsified in the same way as in example 1. The emulsion was caused to gel by adding lo 10 ml ox acetic android over 45 seconds. After that, the gel was treated similarly to Example 1 to produce a spherical micro-porous silica gel (herein-aster referred to as elm The physical properties are given in Table 2.

Table 2 Nlysical PropertiesGel-2 Gel-3 Specific surface area (m go 1,132 1,013 Pore size (PUS) 60,000 100,000 Bulk density (g/cm3) 0.32 0~28 Shape Spherical Spherical Jean diameter my 10 3 - 5 example 4-In order to study efficiency required for a support for liquid chromatography, each kind of the spherical micro-porous silica gel obtained was packed into a 4 my x 300 mm column to compare their retention capacity against a mixture composed of Tulane, anisole, nitrobenzene, methyl bonniest, and acetophenone. Hexane, which contains 0.5% of ethanol, was used as a moving phase.

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Jo The retention capacity was assessed with the capacity ratio k', which is expressed by the following equation.

k = (OR - V0)/VO
where V0 stands for the effluent amount of Tulane and OR stands for effluent amounts of other samples mentioned above.
As best seen from Figure 2, each kind of the spherical micro-7' porous silica gel showed the retention capacity 1.2 - 1.7 times as much as the retention capacity of LS-320 with the increase of their specific surface ; area.
As described above, it is obvious that the silica gel produced according to this invention brings about an excellent capacity.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A spherical micro-porous silica gel, which is characterized by having a mean diameter of 3-20µm, a bulk density of 0.28-0.14 g/cm3, a pore size of 18,000-100,000, and a specific surface area of 1,000-1,400 m2/g.

2. A silica gel according to claim 1, which contains at least 95% by weight of particles having a diameter of 5-15µm.

3. A process for preparing a spherical micro-porous silica gel which has a mean diameter of 3-20µm, a bulk density of 0.28-0.41 g/cm3, a pore size of 18,000-100,000 and a specific surface area of 1,000-1,400 m2/g, which process comprises subjecting to gelatin a water-in-oil type emulsion having an aqueous solution containing SiO2 as aqueous droplets dispersed in an oil phase, wherein (a) in the aqueous solution containing SiO2 the primary particle diameter is not larger than 6nm and the molar ratio of SiO2/Na2O is not larger than 5.5, (b) stearic acid or a mixture of stearic acid and a non-ionic surface active agent whose HLB ranges from 3.5 to 6.0 is employed as an emulsifier, and (c) an organic acid or anhydride thereof is employed as a gelling agent.

4. A process according to claim 3, in which the said aqueous solution containing SiO2 is an aqueous solution which contains a silica sol and/or sodium silicate.

5. A process according to claim 3, in which the gelling agent is a lower fatty acid or anhydride thereof.

6. A process according to claim 3, in which the gelling agent is acetic anhydride.

7. A process according to claim 5, in which the oil phase is an aromatic hydrocarbon solvent.

8. A process according to claim 1, 4 or 6, in which the emulsifier is sorbitan monostearate, sorbitan monooleate or propylene glycol monostearate.

9. A process for preparing a spherical micro-porous silica gel which has a mean diameter of 3-20µm, a bulk density of 0.28-0.41 g/cm3, a pore size of 18,000-100,000 and a specific surface area of 1,000-1,400 m2/g, which process comprises:
(1) preparing a water-in-oil type emulsion comprising an aqueous solution as aqueous droplets dispersed in an oil phase, an emulsifier selected from stearic acid or a mixture of stearic acid and a non-ionic surface active agent having HLB of 3.5 to 6.0, wherein the aqueous solution contains primary silica particles having a mean diameter of not larger than 6nm, silica sol or sodium silicate and the molar ratio SiO2/Na2O in the aqueous solution is not larger than 5.5, (2) adding a lower fatty acid or anhydride thereof as gelling agent to the water-in-oil type emulsion, thereby a slurry contain-ing the desired spherical silica gel particles is produced, and (3) separating the silica gel particles from the slurry.

10. A process according to claim 9, in which acetic anhydride is used as gelling agent.

11. A process according to claim 10, in which the emulsif-ier is used in an amount of 0.5 - 1% by weight based on the total emulsion.

12. A process according to claim 9, 10 or 11, in which a mixture of stearic acid and sorbitan monostearate is used as the emulsifier.

13. A process according to claim 9, 10 or 11, in which the silica gel particles are separated from the slurry by first adding an alcohol to the slurry, decanting the supernatant, and washing with an acidic aqueous solution.

14. A process according to claim 9, 10 or 11, in which the water-in-oil type emulsion has aqueous droplets having a mean diameter of below 30 nm.

15. A method for separating a mixture into its components, which method comprises subjecting the mixture to a gas or liquid chromatography comprising as a support the spherical microporous silica gel as defined in claim 1 or prepared by the process of claim 3.

16. A silica gel according to claim 1, having a specific surface area of from about 1,013 m2/g to 1,379 m2/g.