CS217020B1 - Process for preparing spherical silica gel - Google Patents

Abstract

After sorting out the appropriate particle size, the silica gel in the spherical form finds application as an adsorbent in high-performance liquid chromatography. It can also be a starting material for adsorbents and chemically bound phases, which are also widely used in liquid chromatography. The spherical silica gel with a particle size of 0.001 to 0.1 mm and a pore volume of more than 1 cm^.g"^· is prepared according to the invention by dispersing ammonia-based silica hydrosol in cyclohexanol with the addition of acid, optionally with the addition of dispersion stabilizers of the alkylarylsulfonate and/or polyethylene glycol and/or polypropylene glycol type, gelling the silica hydrosol into a hydrogel, aging the hydrogel optionally in the presence of fluoride salts, treating the hydrogel with water and organic solvents, drying into silica gel and stabilizing its porous structure by boiling in an aqueous solution of an inorganic acid.

Description

BACKGROUND OF THE INVENTION The present invention relates to the preparation of a spherical eelilegel having a particle size of 0.001 and 0.1 mm and a volume greater than 1 aP < ^-1 >

The preparation of silica gel and aluminosilica gel in spherical form has been known for several decades. In earlier times it was all relatively larger spheres, of the order of millimeter, as catalysts and catalyst supports. Slys were prepared by dispersing droplets of an aqueous solution of silicic acid, i.e., silica hydrosol, in oil. In this way, it was not possible to prepare the particles required for modern high performance liquid chromatography, where particles of the order of microns to tens of microns find use. The particles could only be formed by dispersing a sol or solution of alkali metal silicate in liquids with non-miscible or limited mixing, vigorous stirring or shaking.

One group of methods is based on aqueous solutions of alkali metal silicas, for example water glass, from which, after dispersion in an orgenic liquid, the sol is liberated by the addition of an acid. The second group of methods is based on sol, most often prepared by acidifying the diluted waterglass, or less often by removing the cstions from the diluted waterglass by kstex treatment.

The organic environment in which the gel forming solution caps are formed are most often mineral, vegetable or animal oils, lower liquid hydrocarbons and lower halogenated hydrocarbons. A variety of other organic liquids can be used as dispersion media in the literature. They are esters such as amyl acetate, ethyl acetate, dibutyl phthalate; ketones such as methyl ethyl ketone, diethyl ketone; aldehydes, e.g. butyleldehyde, furfural; nitriles, not propionitrile, ecrylonitrile; acids such as velic acid, oleic acid; nitro compounds such as nitromethane, nitrobenzene; ethers such as diethyl ether, dibutyl ether; amines such as aminobenzene, butylamine, amylamine and alcohols such as butenol.

Furthermore, a mixture of a polar solvent such as alcohol and liquid paraffin was used. A mixture of 20 to 60 percent by volume of aliphatic alcohols up to liquid paraffin has proven to be spherical. Liquid polytoers or their solutions, such as polyorgsnosiloxane oils, have also been used as dispersing media, the advantage of which is a higher viscosity, retarding the reduction of the droplets of the aqueous solution, so that the gelatin can be rendered at rest without disturbing the gel particles by stirring.

A particular case is the use of aqueous solutions of organic solvents miscible with water such as alcohols, ketones, aldehydes, esters or dimethylformemide, starting from an aqueous solution of silicas, which is converted into gel after dispersion by treatment with sodium bicarbonate and / or acid.

In order to avoid the coalescence of the droplets of the dispersed aole or silicate solution, use! dispersion stabilizers. For example, silicone oil, octadecylemine, diethylene glycol oleate have been used.

The dispersed silica gel gels to the silicalhydrogel by adjusting its pH to a neutral point or by raising its temperature. The organic dispersion medium is roughly separated by decentation, filtration or centrifugation, the remainder being washed with organic solvents.

On drying, the hydrogel is converted to silica gel and its porous structure is stabilized by annealing at higher temperatures, for example at 450 to 900 ° C, or by repeated annealing at 300 to 900 ° C, alternating with boiling silica gel in water. Annealing ae also incinerates any residues of organic substances sorbed on silica gel from the dispersion medium.

A disadvantage of the processes using oily substances and polymers is their difficulty in removal from the hydrogel or silica gel, and these processes generally do not require the final annealing of the product. Annealing is disadvantageous for the adsorption utilization of silica gel and for its use as a starting material for chemical phase binding, as it dehydrates the surface of the silica gel. A disadvantage of low molecular weight organic solvent processes is the poor stability of the sol or gel particles in this environment and the formation of bead deformation due to inelastic collisions at the sol-gel transition stage and at the early gel stage when it is plastic and sticky.

The above drawbacks are overcome by a process for preparing spherical silica gel having a particle size of 0.001 to 0.1 mm and a pore volume of greater than 1 cnP. g ^- ^ silikahydrosolu dispersion in an organic liquid immiscible with water or sparingly miscible, characterized in that for 1 part silikahydrosolu adding 0.001 to 0.01 parts of ammonia in aqueous solution or gas, from 0.0001 to 0.015 parts hexemethyltetrtaminu optionally in the form of an aqueous solution, cyclohexanol or cyclohexanol are added as an organic liquid with an addition of 0.001 to 0.025 parts of acid relative to 1 part of silicahydrosol, the silicahydrosol is dispersed into droplets in organic medium, optionally in the presence of alkylarylsulfonate and / or polyethylene glycol of polypropylene glycols in an amount of 0.001 to 10 based on the weight of cyclohexanol, the silica hydrosol is allowed to gelatinize nt the hydrogel or it is ironed by adding the above amount of acid preferably in the form of a cyclohexanol solution, the hydrogel is aged in dispersed medium for 0.5 hours 6 days at a temperature of 15 to 120 ° C, optionally from the addition of ammonium and / or sodium and / or potassium fluoride in an amount of 0.0001 to 0.005 parts per 1 part of hydrogel, after which the hydrogel is washed with water and / or a water-miscible organic solvent and / or a water-immiscible organic solvent, the material is dried at a temperature of 20 to 160 ° C and stabilized by heating in a 1 to 30% fragrant inorganic acid solution at a temperature of 30 to 110 ° C.

The advantage of the process for preparing the spherical silica gel of the present invention is the very good stabilizing effect of the dispersion medium on silica hydrosol so that gelatinization of the 3-cananyl-gel can take place at rest or in the case of supplying the acid to the finished dispersion under gentle agitation. The warming stage of the soft, plastic hydrogel passes through completely. The result is a good spherical particle shape. The low molecular weight dispersed medium and its good solubility in organic solvents, possibly in a mixture of polar solvents and water, allow it to be thoroughly washed off, preventing its sorption to the silica gel surface and thereby eliminating the need for silica gel annealing.

A further advantage of the process according to the invention is a gelling system based on a green sol, which is sufficiently stable so that it does not gelatinize spontaneously in the acid present in cyclohexanol or added to the dispersion preferably in the form of a cyclahexanol solution with hexamethylenetetraamine present in the sol. Due to the varying acidity of the starting sol, prepared for example from dilute waterglass on the cation exchange column, it is not necessary to select exactly the amount of acid to neutralize the free ammonia and it is advisable to add more since any excess of acid is neutralized by hexamethylenetetraamineB Indeed, for optimal rapid gelation, it is important that the pH of the sol be around the neutral point, preferably in the pH range of 6.0 to 7.5. ^if not, uncontrolled and extends the gelatinization time, that solubles may bind together in the sediment for longer periods of time after dispersion. Furthermore, the plastic stage of the hydrogel, characterized by its adhesive properties, is extended.

Another advantage of the process according to the invention is the possibility of controlling the particle size of the sol and hence the silica gel to a certain extent by selecting the type of stabilizer and its amount under constant dispersion conditions. Using polyethylene glycol alone or polypropylene glycol alone produces coarser particles and, on the other hand, using only alkylsulfonate produces fine particles. The mixture of both types of stabilizers achieves an optimum yield of the desired grain. In the examples, liquid stabilizers of polyethylene glycols, polypropylene glycols having a molecular weight of less than 1,000 K and a liquid electrolylaryl sulfonate, soluble in distilled water to a cloudy solution and well soluble in organic solvents, were used. The process according to the invention can be carried out without any stabilizer. In this case, the size of the beads is determined only by the intensity of dispersion, i.e., agitation or shaking, which, however, does not have the same range of efficacy as the stabilizers.

Another advantage of the process according to the invention is the possibility of selecting the pore volume of the resulting silica gel. A pore volume of about 1 cm @ 2 is achieved with the use of alkali metal fluorides or ammonium fluoride. As a result of the use of these fluorides, a larger pore volume of, for example, 1.7 cm @ 3 can be achieved within certain limits by the amount of fluorides, the duration of their action and the temperature.

A further advantage of the process according to the invention is the simpler stabilization of the porous structure of silica gel by boiling in an aqueous acid solution and no disadvantageous annealing is required.

The choice of acid to neutralize ammonia in the sol is unlimited in terms of effect. Both inorganic acids such as sulfuric acid, phosphoric acid, nitric acid or organic acids such as acetic acid or trichloroacetic acid can be used. Acids having a higher water content, such as hydrochloric acid, are less preferred, since non-functional water is introduced with them into the dispersion system, although such acids can also be used. ^For stabilizing the porous structure of silica gel, strong inorganic acids such as hydrochloric acid, nitric acid or sulfuric acid are suitable.

With respect to silica hydrosol, any silica hydrosol that has the ability to gel the gel around a neutral pH point can be used. can be prepared from dilute solutions of alkali metal silicates or dilute waterglass and acid, or more preferably, by removing cations from the dilute waterglass by cation exchange, since the aol contains less salts and less polluting cations. The silica or hydrated silica content of the silica hydrosol is not particularly limited. Its lower concentration limit is determined by the ability to gelatin around the neutral pH point and the upper concentration limit is determined by the technical possibilities for its preparation. For example, silica hydrosol containing 5 to 20 weight percent silica is suitable.

The bead silica gel according to the invention is, after screening with a suitable particle size, suitable as an adsorbent for liquid chromatography, in particular for high performance liquid chromatography. It can also serve as a suroyin for adsorbents with chemically bonded phases, which also find use in liquid chromatography.

Example 1

In _a 2 liter reactor, a 5 minute stirring dispersion of droplets of silikehydrosol from an organic phase feed consisting of 1000 ml of cyclohexanol, 12.5 g of polyethylene glycol 400 and 0.95 g of alkylarylsulfonate and an aqueous phase consisting of 250 ml of silicahydrosol at pH = 2.9 containing 7.5% by weight of silica, 3 ml of 25% aqueous ammonia and 1.7 ml of a 50% aqueous hexamethyltetraamine solution. The dispersion was poured into 250 ml of cyclohexanol containing 0.95 ml of 96% sulfuric acid, allowed to stand for 16 hours, refluxed for 1 hour, and then refluxed for 2 hours after addition of 3 g of ammonium fluoride. The bead hydrogel was isolated by filtration and washed under suction with 1.5 L of 50% aqueous methanol, 3 L of acetone and 0.9 L of toluene. It was then vacuum-dried at 110 ° C ε stabilized by boiling in 7.5% aqueous hydrochloric acid for one hour. After washing the acid with water, the silica gel was dried at 110 ° C. The product had a median particle size from 0.010 to 0.015 mm and a pore volume of 1.3 cm .g ^J.

Example 2

In a 5 liter flask, a twenty second shake dispersion of silica hydrosol droplets was formed from an organic phase feed consisting of 1250 ml cyclohexanol, 6.5 g polyethylene glycol, 0.97 g alkylarylsulfonate and 0.46 ml 96% sulfuric acid and an aqueous phase consisting of 250 ml of silica hydrosol, pHP3 > 1, containing 7.2% silica, 1.75 ml of a 25% aqueous ammonia solution and 1.6 ml of a 50% aqueous hexamethylenetetraamine solution. The dispersion was allowed to stand for 24 hours, refluxed for one hour, and refluxed for 2 hours after the addition of 3 g of ammonium fluoride. The slurry was filtered and the bead hydrogel was processed to silica gel as in Example 1. The product had a mean particle size of 0.008 to 0.012 mm and a pore volume of 1.35 cm @ 3.

Example 3

The procedure was the same as in Example 2, except that the reflux time was 4 hours without fluoride addition and 1 hour with fluoride addition. The product had a pore volume of 1.7 eAr ¹ .

Example 4

The procedure was as in Example 2, except that the reflux time in the presence of fluoride was 4 hours, the product having a pore volume of 1.75 cnP.g -1.

Example 5

The procedure of Example 1 was followed except that the addition of alkylarylsulfonate was omitted. The product had a median particle size from 0.02 to 0.03 mm and a pore volume of 1.6 cm \ g ^- l · prior to the stabilization of the porous structure by boiling in acid, the volume of pores of 2.0 cm .g ^ ^- ^.

Example 6

Proceeding as in Example 2, except that the additions of both dispersion stabilizers were omitted, the product had a wider particle size distribution with the largest particle size in the range of 0.015 to 0.040 µm.

Example 7

The procedure of Example 1 was followed except that the addition of ammonium fluoride and washing the hydrogel with 50% aqueous methanol was omitted. The product had a pore volume of 1.05 cm 2 / g. ¹ Example 8

The procedure of Example 2 was followed except that an equimolar mixture of potassium fluoride and sodium fluoride was used instead of ammonium fluoride. The product had a pore volume of 1.25 cm ^ .g ^'1.

Example 9

The procedure was as in Example 1, and the difference was that the amount of ammonium fluoride was increased from 3 g to 4.5 g ε before the hydrogel was washed with 50% aqueous methanol and the hydrogel was washed with 1 liter of distilled water. The product had a pore volume of 1.62 cm \ ^_1 g.

Example 10

The procedure of Example 2 was followed except that the poly-ethylene glycol site used was polypropylene glycol having a molecular weight of about 1000 H. The average particle size of the product was 0.009 to 0.014 mm.

Example 11

The procedure of Example 4 was followed except that the addition of polyethylene glycol was omitted, washing with 50% aqueous methanol and acetone washing was omitted. The product had a median particle size from 0.004 to 0.010 mm and a pore volume of 1.48 mm ^ .g ^'1.

Claims (1)

A process for the preparation of spherical silica gel having a particle size of 0.001 to 0.1 mm and a pore volume of greater than 1 cm @ 2 .g @ ^{-1 by} dispersing silica hydrosol in an organic liquid with unmixed or limited mixing. add 0.001 to 0.01 parts of emonisk in the form of an aqueous solution or gas with 0.0001 to 0.015 parts of hexamethylenetetrsemin, optionally in the form of an aqueous solution, cyclohexanol or cyclohexsol with an addition of 0.001 to 0.025 parts of acid based on 1 part of silicahydrosol , ailicahydrosol ae dispersed in the organic medium into droplets, optionally from the presence of dispersion stabilizers of the alkylarylaulfonate type and / or polyethylene glycols and / or polypropylene glycols in an amount of 0.0001 to 10% based on the weight of cyclohexanol; gelling is carried out by the addition of the abovementioned amount of aforesaid In an amount of acid, preferably in the form of a cyclohexanol solution, the hydrogel is aged in the dispersed medium for 0.6 hours to 6 days at 15 to 120 ° C, optionally with the addition of 0.0001 ammonium and / or sodium and / or potassium fluoride. up to 0.005 parts, based on 1 part of hydrogel, after which the hydrogel is washed with water and / or a miscible organic solvent and water and / or a water-immiscible organic solvent, dried at 20 to 160 ° C and stabilized by heating at 1-30 % aqueous solution of inorganic acid at 30 to 110 ° C.