FI69408C - FARING REFRIGERATION FOR FUNCTIONAL RESISTANCE POROESASILIKAGRANULER MED MEKANISK HAOLLFASTHET - Google Patents

Description

1 69408

The present invention relates to a process for producing mechanically strong wettable porous silica granules by granulating a finely ground silica-containing raw material such as synthetic silica or silicate, such as synthetic silica or silicate, such as flogite. The granules prepared by the process according to the invention are well suited for the preparation of, for example, chemical adsorbents.

The fines can be agglomerated, i.e. granulated, in a wide variety of ways, such as by mixing, pressing, thermal treatment, spray and dispersion methods, and agglomeration from a liquid medium. The incorporation of small particles into agglomerates can occur by means of solid bridges, immobile or moving liquids, by internal and external forces of molecules, and by mechanical bonds. A variety of additives can be used to increase particle size, such as binders, lubricants, and wetting agents. Only adsorbents with a large internal surface area have a technical significance. As a result of the activation or a special method of preparation, many small pores and a large specific surface area are obtained in the adsorbent. In addition to surface area, pore size is crucial. Most of the active surface is in the micropores. The existence of macropores is important because of the diffusion rate. In addition to the surface properties, the mass must meet certain technical requirements, especially with regard to mechanical strength. The more porous the material, the more binder it usually requires to stay together. The high amount of binder in turn tends to clog the pores in the granule and reduce its specific surface area.

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Synthetic silicas are good builders of adsorbents when it comes to their chemical and physical properties. They are highly resistant to humidity, temperature and pressure changes, as well as most substances used in adsorption applications. They have a large specific surface area, a large pore volume and a micro-meso-macro porosity. However, for adsorption applications, they must first be granulated. The granulation method should be such as to have the least possible effect on the porosity of the starting product, but at the same time give the granules sufficient strength to withstand mechanical handling. The silica granulation methods described in the literature are such as to obtain either porous but too soft granules, or strong but too dense granules for adsorption applications. The strength of the porous granules can be improved by using more binder, however, the amount of the microporous adsorbent is reduced and its efficiency is reduced.

In addition to synthetic silica, the silica body separated from the silicate has a pore distribution suitable for adsorption applications. However, a binder must be used in its granulation in order for the granules to have a sufficiently good mechanical strength for their further use. Various methods for preparing silica granules have been reported in the literature, but have been found to be unsuitable for adsorption applications mainly for the following reasons: binders that provided sufficiently strong granules (e.g., lye, water glass and starch) either significantly reduced the use of the granule for adsorption applications, or the binder (starch) itself affected the chemicals used to impregnate the adsorption masses (starch is a reducing agent), thus limiting the use of the product. The reducing effect of starch can be eliminated by heat treatment, but then the manufacturing costs of the product also increase.

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Binders that did not significantly alter the porosity of the starting product (e.g., silica sol) did not produce sufficiently strong granules until more than 10% by weight of the silica was used. Again, the abrasion resistance of the granules was not good enough. Binder costs also became too high.

The object of the present invention is thus to provide an economical method for producing silica granules which are at the same time both very porous and mechanically strong and resistant to wetting. The object of the invention is in particular to provide a process for the preparation of silica granules suitable for adsorption masses.

The main features of the invention appear from the appended claims.

It has now surprisingly been found that the use of quicklime and / or cement as a binder results in highly porous amorphous slag granules made of finely divided synthetic silica and a silicate, e.g.

The slaked lime and / or cement is added in an amount of at least 2%, preferably about 5-10% by weight of the silica-containing raw material.

In particular, it has been found that by using quicklime as a binder, porous granules can be granulated from silica, for example with a disc granulator, and are highly resistant to mechanical treatment, so that the specific surface area of the silica to be granulated does not change significantly. When granulation is carried out on a paste, cement can be advantageously used as a binder in addition to or instead of quicklime. This procedure is a particularly advantageous alternative when the silica is not dried but granulation takes place from a slurry or filter-dry cake. Disc granulation is especially suitable for dried silica.

For the strength of the granules, it is important that they pre-dry slowly in the presence of air, for example for 1-2 days at approximately room temperature. The result is further improved if the pre-drying is carried out in carbon dioxide-containing air. The final drying can be carried out at an elevated temperature by keeping the granules, for example, for 1-2 hours at more than 100 ° C, preferably at 105-110 ° C. In this case, the impregnability of the granule becomes as large as possible.

The process according to the invention makes it possible to prepare granules which are well suited, for example, for adsorption applications. The pore and strength properties have been made desirable without altering the original preferred properties of silica. In addition, the mechanical strength of the granules produced is so good that they can be used for air purification applications. The strength of the granules also withstands impregnation, i.e. wetting. In addition, the granules dust very little.

The invention is described in more detail below by means of examples.

Comparative Example 1 To 25 g of a dried and ground silica body separated from phlogopite was mixed with a silica sol having a dry matter content of 15% by weight so that the silica sol content of the pulp, calculated as dry matter, became a) 5, b) 10, c) 15, d) And e) 30% by weight of silica. If necessary, enough water was added to the mixture to obtain a suitably moist paste (water about 60% by weight).

The pulps were formed into cylindrical granules (diameter 3 mm, height 4 mm) with a perforated plate, which were first dried for a few days at room temperature, then at 110 ° C overnight. The specific surface area of the prepared granules was determined by N 2 adsorption (BET). The compressive and abrasion resistance of the granules was felt by hand.

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Granules with a silica sol solids content of up to 10% by weight of silica broke easily when compressed. When shaken, a lot of dust came off their surface. When the binder was more than 10% by weight of the silica, the compressive strength of the granules was relatively good, but the abrasion resistance was still poor. The BET surface area of the granules decreased as the amount of binder increased from 2 2,205 m / g to 110 m / g, corresponding to 5 and 30% silica sol as dry matter by weight of silica.

Comparative Example 2 1.25 g of starch was mixed with 100 g of a silica slurry having a solids content of 25% by weight. With stirring with a magnetic stirrer, the temperature of the slurry was raised to close to 100 ° C, whereupon the mixture turned into a jelly. Cylindrical pieces (diameter 3 mm, height 4 mm) were formed from the cooled mass with a perforated plate. The granules were dried first at room temperature, then at 110 ° C. The compressive and abrasion resistance of the granules was felt by hand. The specific surface area was determined by N adsorption (BET).

When compressed, the granules felt durable and when shaken 2 of them very little dust came off. The BET surface area was 310 m / g.

When the granules treated as mentioned above were impregnated with the KMnO solution, the starch used as a binder reduced the per-4 manganate to runic stone. In this case, a significant part of the power of the pulp intended for the adsorption application was lost. The reducing effect of the starch was almost completely eliminated when the granules were heat-treated at 500 ° C.

Comparative Example 3 To 150 g of moist silica (H 2 O 3% by weight) were added 2-N NaOH solution 12.5, 35.5, 72.6 and 126 ml. The mass was mixed well and 69408 6 was dried to form a paste. Cylindrical pieces (diameter 3 mm, height o 4 mm) were made from the paste with a perforated plate. The pieces were dried at 110 ° C and the abrasion and strength resistance of the granules thus obtained was evaluated by hand. The specific surface area was determined by N adsorption. The results are shown in Table 1 below.

Table 1 2N NaOH solution BET Durability ml ^ / g a) 12.5 205 Fragile, easily crumbled b) 35.5 110 c) 72.6 25 Moderately durable, non-dusty d) 125 <5 Durable, non-dusty

A similar decrease in surface area and improvement in strength was observed when the corresponding sodium additions were made in the form of water glass. A water glass solution with a dry matter content of 25% by weight and SiO 2: Na 2 O = 2.5 (molar ratio) was used.

Example 4

The finely ground silica was mixed with 5% by weight of finely ground quicklime. This mixture was fed to a rotating granulation plate while being sprayed with water. The granulated solo ratios were controlled to obtain as many granules as possible in the size of 2-5 mm. The granules were dried at room temperature in the presence of air for 1-2 days and finally at 105 ° C for about 2 hours.

The pore distribution and specific surface area of the granules prepared in this way were analyzed by both Hg porosimeter and nitrogen adsorption. The Hg porosimeter gave a surface area of 158 m / g and a pore volume of 1.38 ml / g, and N 2 adsorption, respectively, gave a surface area of ✓ 2 7 69408 of 149 m / g. When hand-felt, the granules were durable and very little dust was released during screening. The granules were impregnated with KMnO solution. No changes were observed in the durability of the granules.

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It should be noted that when granules were made from both natural silicates and synthetic silicates using quicklime as a binder, the granules disintegrated upon impregnation.

Comparative Example 5 A wet slurry of phlogopite silica body was mixed with 5% finely ground cement based on the weight of silica. The tough paste thus obtained was formed into cylindrical pieces (diameter 3 mm, height 3-5 mm) with an extruder-type granulator. The granules were first dried in the presence of air for 2 days at room temperature and then at 110 ° C for 2 hours.

The pore distribution and specific surface area of the granules prepared in this way were analyzed by both Hg porosimeter and nitrogen adsorption. The Hg porosimeter gave an area of 70 m / g and a pore volume of 1.06 -1 / J., respectively, by nitrogen adsorption to an area of 220 m / g. When hand-felt, the granules were even more durable than those prepared in Example 4. The impregnation resistance was also good. Cement-bonded silicate granules could not withstand wetting.

The pore size distribution of the granules prepared in Examples 4 and 5 is shown graphically in Figure 1.

The difference between the areas measured by nitrogen adsorption and the Hg porosimeter describes the microporosity of the product. Compared to commercial adsorbents, the granules prepared by the process of the invention differ above all in terms of macroporosity (pore diameter over 200 nm). The macropore volume of commercial adsorbents (e.g., KMnO-impregnated Al 2 O 2 masses disclosed in U.S. Patent No. 3,226,332) is only 10-30% of the macroporosity of the granules prepared by the process of the invention.

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The pore volume of granules intended for adsorption masses is important both for their function and their impregnability (the larger the pore volume, the more impregnation liquid can be absorbed into the granules). Table 2 summarizes the properties of the granules prepared as described in the examples, which are crucial for adsorption applications.

Table 2

Compression- Abrasion- Characteristic- Pore- Suitability durability durability surface volume adsorption- M / g ml / g mass

Comparison example. 1 a) bad bad 205 no b) good bad 110 x) no "2 good good 310 xx) no" 3 a) bad bad 110 xxx) no b) good good <5 xxxx) no

E.g.

4 good good 173 1.32 yes "5 good good 220 1.03 x) too high binder cost, poor abrasion resistance xx) reducing properties of starch as a barrier xxx) mechanical resistance poor xxxx) too small surface area

Claims (6)

69408 A process for the production of wetting-resistant porous silica granules having mechanical strength by granulating a mixture of finely ground silica-containing raw material, binder and water and drying and optionally heat-treating the granules thus obtained, characterized in that lime and / or cement. Process according to Claim 1, characterized in that at least 2%, preferably about 5-10% by weight of the silica-containing raw material is added to the quicklime and / or cement. Process according to one of the preceding claims, characterized in that the silica granules are first dried for 1-2 days at approximately room temperature and, if necessary, finally for 1-2 h at more than 100 ° C, preferably at 105-110 ° C. Process according to Claim 3, characterized in that the silica granules are dried in air containing CC 2. Method according to one of the preceding claims, characterized in that the silica granules are prepared by spraying water on a rotating plate containing or fed a mixture of finely ground silica-containing raw material and quicklime. Process according to one of the preceding claims, characterized in that the silica granules are produced by compression of finely ground silica-containing raw material, quicklime and / or cement and water.