DE2127649A1 - Process for the production of large pore silica gel bodies - Google Patents

Description

concerning:

"Process for the production of large-pored silica gel bodies"

The invention relates to a method for producing large-pored silica gel bodies with modified areas of the Porosity and pore volumes, by treating dried silica gels in an autoclave in ammoniacal reactive medium.

It is well known that silica gel body, or Bodies that mainly consist of silica gel, very much in various fields, for example for adsorption purposes, can be used for chromatography and for catalysis purposes.

These bodies must of course generally have the mechanical

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see properties of abrasion resistance and compressive strength have, which are the prerequisite for the various uses, but also certain pore properties, depending according to the particular use under consideration.

For a long time, efforts have also been made to develop methods which lead to a development of the pore properties the silica gels and in particular allow substances with a larger pore diameter to be obtained, than the freshly made gels possess.

It is also known that usually in the production of most industrially used silica gels of Alkali silicates, especially iJatriumsilicaten assumed for obvious reasons of economy. In general, these silica gels are obtained by drying highly water-containing hydrogels, which on acidification under certain conditions of alkali silicate solutions arise and are heavily contaminated with the alkali salts corresponding to the acids used and, moreover, a may have some residual alkalinity as a result of an incomplete Neutralization of these alkali silicates. These gels have different specific surfaces and also different pore volumes, which mainly depend on the conditions during precipitation and during washing of the hydrogels depend.

In the previous French Patent Nos. 1 473 240 and 1482867 it is stated that gels can be obtained by calcining silica gels having a defined content of alkali salts and defined residual alkalinity at temperatures from 400 to 1200 ⁰ G, the reproducible porosity of pores different diameters up to several 1,000 Å, while those simply dried under gentle conditions and used as starting material

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ten gels specific surface areas in the range of several

100 m ² / g bee

correspond.

100 m / g, which have porosities with very fine pores

However, the use of the silica gels obtained by this process is associated with disadvantages in some cases due to the presence of alkali compounds which have contributed to the pore development of these gels, however, only to a great extent difficult to remove with ordinary washing treatments. In addition, the silica gels produced in this way show with Large diameter pores at higher firing temperatures a development in the direction of crystalline forms of silica, which are undesirable for certain areas of application and also a noticeable reduction in the original Pore volume.

The general effects of ammoniacal treatment are also known, which in the case of fired silica gels Λ leads to the development of large-pored porosity and, in freshly prepared silica hydrogels, a rapid contraction of these hydrogels by separating off water and increasing the pore size. However, some of the described and known procedural measures do not reliably lead to the expected results; this is especially true for the treatment of freshly prepared hydrogels, the structure of which is very fragile and is in a state of rapid development. On the other hand, as a result of the ammoniacal treatment of fired gels, the structure of the products obtained is not sufficiently modified by this treatment due to excessive development of this structure which has taken place beforehand and is caused by the firing.

It has now surprisingly been found that washed off

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and dried hydrogels Großporige.Kieselsäuregelkörper with very different porosity ranges, ie pore diameters of about 100 to about 2000 K can be produced if the dried and washed hydrogels are treated in an autoclave under pressure in the presence of an aqueous ammoniacal reacting medium in the vapor phase or in the liquid phase; the structure is not destroyed and an increase in the mean pore diameter while maintaining the original pore volume is achieved under the condition that the mean pore diameter of the treated silica gel bodies is greater than about 40 p . These strongly changed porosity ranges are of particular importance for chromatographic applications; in addition, the high purity of these silica gel bodies, which is achieved by very thorough initial washing, is often a valued advantage.

In practice, the silicic acid hydrogels have to be dried in order to obtain gels which are suitable for development in the autoclave in the presence of an alkaline reacting medium, because contrary to what is known up to now, the treatment of hydrogels, as they are made from silicates according to the various processes in aqueous medium are obtained under pressure and in an ammoniacally reacting medium usually leads to their destruction. In practice, the drying of the hydrogels is carried out at fairly low temperatures, as these are often technically customary. and the later development of the gels thus obtained is most pronounced under these conditions; However, the hydrogels can also be dried at temperatures in the range from 400 to 500 ^° C. without serious disadvantage; only by drying at the upper limit of the specified temperature range a somewhat different distribution of four-pore pores is obtained than with hydrogen which has been dried at a lower temperature.

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The "when drying at different temperatures up to The results achieved within the specified limits differ very little from one another with regard to the mean pore diameter and the pore volume of the dry products obtained. However, this takes place in the subsequent treatment dry products in ammoniacal medium under pressure an increasing development of their organization takes place that of the temperature maintained during drying depends on; this development is faster, the higher the applied Temperature when drying was. This drying will in fact occur at temperatures above the stated limit Calcination, which results in a considerable reduction in the specific surface area. But it can be noticed that when Eieselsaurehydrogelen are gradually heated to higher temperatures, the loss of water is not linear the rising temperature takes place: the adsorbed water is quickly removed by drying at a low temperature; the residual water, which corresponds to the water bound to the dry gels thus obtained, increases with increasing temperature at first only slowly removed, then this dewatering process passes through a maximum speed, which is essentially lies in the temperature range from 400 to 500 ° C, which has been specified above as the limit for the drying temperatures to be maintained.

The pressures used in treating the silica gel bodies can be quite low, but development will proceed this body in an ammoniacally reacting medium the faster the higher the pressure is. In practice a pressure of a few tens of bars is considered sufficient, although pressures in the region of 50 bars are also exceeded

as
can, without any other disadvantage, that a more complex and therefore less economical apparatus is necessary.

The concentration of the aqueous ammoniacal medium exercises

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has a very great influence on the extent and speed with which the desired results are achieved be achieved; however, a concentration of more than 100 g / l of ammoniacally reacting substance in this medium is not effective more changes in the speed of the development process.

The treatment time for the silica gel body must be long enough so that the temperature in all points given mass of this body is practically the same; In practice, a treatment duration of a few hours is sufficient for technically important products.

The treatments according to the invention can be carried out in the vapor phase or in the liquid phase; often the work becomes in vapor phase preferred because the properties in terms of porosity of samples at different points are more significant Quantities are withdrawn, are not widely spread; the treatment in the liquid phase, on the other hand, gives wider ones Pore distributions that may be desirable for certain applications.

Of course, the various parameters listed must be taken into account together and the choice of Properties of the silica gel body, from which it is assumed, must be aimed at with regard to the respective predetermined Result. So must, since the treatments according to the invention, the original pore volume of the silica gel body change practically only a little, the choice of the production method of these bodies are made so that they are practically the same Have pore volumes as they should have the end products, while the other parameters then the determine different pore distributions.

In the following examples, the treatment according to the invention is

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treatment in the autoclave and in the ammoniacal medium Silica gel balls obtained by coagulating silica sols in a liquid immiscible with water were explained as well as in an example of extrudates. Of course, with other forms of training of silica gel bodies, the original properties of which are identical to those of the spheres or extrudates, the same Results achieved; other forms of training include fragments obtained by crushing, for example from set gels or agglomerates obtained by pressing or pressing in embossing.

Example 1

In this example it is shown that the initial drying the silica gel body should be done at a fairly low temperature, so that its ability to be in the autoclave and to develop into large-pored porosities in ammoniacal medium is not impaired.

Obtained from sodium sulfate. Silica hydrogel spheres were washed in such a way that their Na ~ O residue content was not more than 0.02% by weight, based on the silica. These balls were dried at a low temperature at about 100 ° C. and then had an average diameter of i

TE ™

100 to 200 / µm, a pore volume of 1.05 cnr / g, where the mean diameter of the pores was about 120 S.

Three other samples of similar hydrogel spheres were ^{dried at 400, 600 and 800 °} C. and then all four samples were treated in the vapor phase for 3 hours at a pressure of 40 bar in an aqueous solution containing 25 g / l ammonia.

The following table 1 shows the measurement data for the

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listed products, namely the pore volume V, the mean pore diameter 0 _M and the pore distribution

TABEL

temperature at the cnr / g 0M Pore distribution in Drying, ° C. 1.0 f 100 1.0 850 600 - 400 1.0 700 450 - 600 1.0 4-10 300 - 800 420 300 - - 1200 - 1100 - 700 - 700

The comparison clearly shows that the diameter of the pores obtained is greater, the lower the The temperature during drying of the gel is and that above 400 ° C. it is more difficult to enlarge the pores. Otherwise the pore volume practically does not change.

Example 2

This example describes an autoclave treatment in vapor phase under a pressure of 10 bar for 3 hours, in An aqueous ammonia solution containing 5 g / l · Me was treated with silica gel balls of diameter 40 to 350 / µm carried out by drying hydrogel balls had been obtained and a pore volume of

• 2

0.7 cm / g and an average pore diameter of 60 S. The balls had been dried at different temperatures; the results are summarized in Table 2 below ¹ .

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TAB V ELLE • 2 Pore distribution temperature cnr / g £ while drying
⁰ C 0.7 / 300 - 150 0.7 440 250 - 400 0.7 400 200 - 600 0.7 360 200 - 800 350 - 700. - 650 - 600 - 600

This example again shows that the gels dried at low temperatures more easily have a large-pored porosity form.

Example £

In this example, the effect of increasing ammonia concentration in the aqueous autoclave solution is examined. The experiments were performed with same Kieselsäuregelkugeln passed through as in Example 1 which had been dried at 100 ⁰ C. Various samples of these spheres were treated in the autoclave for 3 hours under a pressure of 10 bar with different NH, concentrations. The results are summarized in Table 3 below.

TABLE 3:

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0? A B E L L E

NH ₅ gel of Pore volume 1J0 Pore distribution solution V cmVg 360 Ä g / l 500 0.06 1.06 520 80-350 0.25 1.00 600 200-700 0.50 1.05 700 300-800 1.0 1.02 800 300-800 2.5 1.05 820 350-900 5 1.00 800 400-1000 10 1.05 840 400 -1100 25th 1.02 400 -1100 60 1.01 400 -1100 95 1.01 450 -1200

These results clearly show that above a certain NEW content of the aqueous solution increases the concentration only has a minor effect and that a concentration of 100 g / l is regarded as the upper limit which there is no further advantage to exceeding.

Example 4

In this example, ammonia was replaced by other substances that react ammoniacally, such as ethylamine and ethylenediamine replaces that in a concentration of 50 g / l and 100 g / l were used. The same balls dried at 100 ° C. as in Examples 1 and 3 were treated; the test duration was 3 hours, the pressure 40 bar. The results are in

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summarized in Table 4 below.

TABEL

Amine content of the V · 0 _M pore-aqueous solution division

g / l cm ³ / g Ä - 1 ■

Ethylamine

50 1.09 700 400 - 1400

Ethylenediamine

100 1.07 750 400 - 2000

The results show an analogy with the results obtained with ammonia.

Example J?

. .,,,.,. ". -,, -u Xp liquid phase This example describes an autoclave application / in ammoniacal medium at two different concentrations: 0.25 g / l and 25 g / l

The same balls as in Examples 1, 3 and 4, which had been dried at 100 ° C., were used. Ä

After 3 hours of treatment under a pressure of 40 bar Results obtained are in Table 5 below summarized:

TABLE 5

NH ₅ content of the V 0 _M pore size

Autoclave solution division

g / l cm ^ / g &&

0.25 0.98 210 100 - 300 25 0.80 720 350 -1700

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This example shows that development is in the liquid phase is also possible.

Example 6

In this example, extrusions obtained were mm of diameter and height 3 treated for 5 π ™ from silica hydrogel microspheres, which were dried at 120 ⁰ g and a pore volume of 1 cmVg and an average pore diameter of 125 Å had. Two samples were treated: the first in the vapor phase and the second in the liquid phase, each for 3 hours at 40 bar and with an EBL content of the aqueous solution of 50 g / l.

The results are summarized in the following table 6:

³ Js TAB 1 ELLE 6th Pore distribution
S. treatment
in cm , 00
, 01 5 800-1,200
100 - 800 Vapor phase 1
liquid phasei 030
350

This example shows that the development of the body in the liquid phase, although analogous to the development in the vapor phase, leads to different mean pore diameters and a different pore distribution.

The method according to the invention is not restricted to bodies made of pure silica gel; Silica gel body, which contain other oxides or hydroxides can undergo an analogous development. The presence of this

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other oxides do not prevent the development of the porosity properties of the silica gel; such bodies can mainly contain oxides or hydroxides of magnesium, Aluminum and zirconium contain and are widely used for catalysis purposes.

PATENT CLAIMS:

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Claims (6)

Claims 1. A process for the production of large-pored silica gel bodies with modified areas of the porosity and the pore volumes, in particular for catalysis and chromatography by ammoniacal treatment of silicic acid-containing hydrogels, characterized in that the treatment -in an ammoniacally reacting medium in the autoclave with silica gel-like bodies carries out the one have been mean pore diameter>"I have 40 and by drying siliceous hydrogels! maximum temperature of 50O ⁰ C was obtained. 2. The method according to claim 1, characterized in that the autoclave treatment in the vapor phase performs. 3 · The method according to claim 1, characterized in that the autoclave treatment in liquid phase. 4 ·. Method according to claims 1 to 3 »characterized that an aqueous ammonia solution is used as the ammoniacally reacting medium. 5 · The method according to claim 1 to 6, characterized in that the pebble-like hydrogels Silica hydrogels used. 6. The method according to claim 1 to 5, characterized in g e that one uses silicic acid hydrogels which also contain other oxides or hydroxides as components contained by catalysts. 7231 109850/1863