DE2907942A1 - Hard porous mouldings or pellets contg. crystalline silica - made from silica flour and guanidine silicate soln., and used esp. as catalysts or catalyst carriers - Google Patents

Abstract

Silica flour is mixed with a soln. (I) of guanidine silicate and possibly with extra water. The mixt. is possibly predried, and is next moulded, dried and possibly also tempered. The silica flour is pref. 1-100 mu m, esp. 1-50 mu m, in size; whereas the aq. soln. (I) pref. has a wt. ratio of guanidine silicate:water of 1:2 to 4:1, esp. 1-2.6:1. The wt. ratio S/G, where S = SiO2 and G = guanadine silicate, is pref. 1.4-25/1, esp. 3-23/1. The total water content of the mixt. is pref. 3-50, esp. 4.4-30 wt.%. The mixt. may also contain 0-30%, esp. 1-23% addns. (II), esp. silica gel or powder or zeolites; or substances (II) low in alkali, esp. sawdust, cellulose-ether, active carbon or soot. The mouldings are employed esp. as catalysts or catalyst carriers with specific surface 1-30m2/g., and average pore widths 10-1000 nm, esp. contg. only 0.01-0.1% alkali calculated as Na2O.

Description

Process for the production of hard, porous,

Crystalline Silica-Containing Moldings The invention relates to a process for the production of hard, porous, crystalline silica containing Moldings and moldings of this type and their use.

Moldings of the type described are of great industrial importance. They are used as catalysts or carriers in catalytic processes, whereby they are adapted in shape and nature to the respective process. Products with high crystallinity and specific surfaces are particularly useful between 1 and a few 10 m2 / g and average pore sizes between about 10 and 1000 nm. A low alkali content may also be desirable for special applications be.

Known processes for the production of such moldings use as Starting material silica granules obtained by the sol-gel process, e.g. by precipitation from water glass solution with acid, and its alkali content in time- and costly washing stages is reduced.

For conversion into granules containing crystalline silica must then be tempered at temperatures above 1100 ° C, which with a large Consumption of energy is connected and also special, expensive burning apparatus presupposes.

It is possible to keep the temperature of the tempering stage by adding crystallization aids to lower. A well-known, good remedy is Nu20, when added to it, the temperature but still has to be above 8000C. In addition, included according to this procedure produced moldings inevitably larger amounts of alkali, which with special interfere with catalytic processes and are therefore undesirable.

Another method for the production of the moldings consists in To compress montmorillonite into balls and remove the undesirable components, such as alkali, Iron and aluminum can be extracted with acid in a complex process step.

The object of the invention is to provide a method for the production of hard, to provide porous, crystalline silica-containing moldings, which avoids the disadvantages of the known methods.

According to the invention, quartz powder and guanidine silicate solution, optionally mixed homogeneously with the addition of water, optionally predried and then deformed, dried and optionally tempered.

Quartz powder is understood as meaning particulate, crystalline silica. Although the selection of the particle size of the quartz powder is not critical and only the desired one Process product is limited, a particle size in the range from 1 to 100 μm is preferred. The best results are obtained with grain sizes from 1 to 50 p.

The guanidine silicate used is used as a solution. The relationship Guanidine silicate: H20 0 can be in the limits 1: 2 to 4: 1, preferably Vary 1: 1 to 2.6: 1.

Mixing the quartz powder and the guanidine silicate solution can take place with the addition of water and / or other additives. The order of The addition of the components to be mixed is irrelevant. It is best to look after Combine all components of the mixture, the mixture for another 5 to 60 minutes, preferably 10 to 40 minutes to homogenize by stirring, kneading or similar measures.

The finished homogeneous mixture has a total water content of 3 to 50% by weight, preferably from 4.4 to 30% by weight. The quotient q = S / G - in which S the SiO2 content of the mixture of the quartz powder and G the SiO2 content of the Mixture of the guanidine silicate mean (in each case in% by weight) - can mean values assume between 1.4 and 25. Values between 3.0 and 23 are preferred. which only contain quartz powder and guanidine silicate, q is a measure of the crystallinity of the molded body.

The finished mixture can be shaped in any way; the Shape of the molded body depends on its later intended use, the preferred type of deformation according to the flow properties of the finished mixture.

In addition to other methods, pressing into molded bodies, such as e.g. Tablets etc., pouring in forms, dripping, balls in the rotating cup as Types of deformation possible. The production of flat structures is also possible, e.g. by spreading on a smooth surface or between two plates.

The deformation can usually take place directly with the finished mixture be made. In a particular embodiment of the invention, however pre-drying is carried out. The moist mixture is used for 5 to 30 minutes long, preferably 10 to 20 minutes, with temperatures of 50 to 100, preferably 60 to 90 ° C. This drying is particularly recommended for the subsequent one Deformation with the help of a tablet press.

After molding, the water-containing moldings undergo drying subjected by 90 to 150, preferably 110 to 130 minutes at 70 to 150, preferably 110 to 130 ° C are dried. You can then the moldings are tempered at 100 to 700, preferably 300 to 600 ° C.

For special purposes, the mixture to be homogenized can be made from Quartz flour, guanidine silicate solution and possibly added water and other additives are mixed in.

The proportion of additives can be 0 to 30, preferably 1 to 23 wt .-% of the finished mixture. The type of additives depends on the purpose which is pursued with their addition. The following exemplary list is intended to Illustrate the usefulness and meaning of possible additions, but without limiting them to act: 1. To set a defined crystallinity of the molded body can a) SiO2-containing substances, such as SiO2 gels, powders, xerogels or zeolites, b) thermally stable "diluents" such as MgO, ZnO, SiC> Al 2 O 3 can be used.

2. To set the mean pore radius and / or the specific The surface of the molding can be volatile at dry or tempering temperature or decomposable substances such as wood flour, activated carbon, soot, cellulose ether, are used will.

3. To adjust the flow properties of the mixture to be dried Substances such as SiO2 gel, cellulose ether, modified phyllosilicates can be used will.

The method described is easy to carry out and works through Use of low temperatures saves energy and is very economical.

The products of the process are porous moldings, two of which are specific Surface is in the range from 1 to a few 10 m / g and its mean pore diameter be approx. 1 to 1000 nm. Surface and pore diameter are determined by the selection of the The particle size of the quartz powder and the type and amount of additives can be influenced.

The process products contain crystalline silica. The degree the crystallinity of the finished shaped body can be determined by the content of the shaped body on quartz powder can be adjusted very easily and reach values of more than 95% by weight.

Surprisingly, the process products have burst pressures good hardness over 3 kg. This hardness is particularly good with values above 9 kg Shaped bodies that only use quartz powder, guanidine silicate solution and possibly Addition of water and the products of a special process preferred type of method according to the invention. Especially surprising and it is by no means foreseeable that molded bodies of the last-mentioned type will also already be have a high hardness without tempering or even be harder than after tempering can and can thus be produced in a particularly energy-saving manner. In contrast, comparable moldings which do not contain any quartz powder have burst prints less than 3 kg does not have good hardness even after tempering. The hardness of moldings, which contain additives is between these two, depending on the type and amount of additives Extremes.

According to a further, particularly preferred embodiment of the method hard, porous shaped bodies containing crystalline silicic acids can be produced that contain only small amounts of alkali. So it is possible to have molded bodies produce, the alkali content of between 0 to 1 wt .-%, preferably between 0.01 to 0.1% by weight (the alkali content is calculated as Na 2 O and based on the Molded body related). For the production of such process products is only the alkali content of the raw materials as additional criteria to be considered for their selection. There is no need to use the starting materials subject to expensive cleaning operations, since quartz flour types with only 0.02 % By weight alkali and practically alkali-free guanidine silicate solutions are commercially easy Are available.

Examples Abbreviations used in the following section mean: Gua = guanidine silicate solution q = quotient of S and G (definition see p. 6) VT = information on predrying TE = Information on tempering B = bursting pressure in kg (mean value from 20 measurements) A = alkali content of the finished molding (in% by weight as Na2O) ZS = additive MS = molecular sieve Es The following three types of quartz powder are used: Type I Type II Type III SiO2 (% by weight) 99.77 88.06 99.35 Al203 (wt.) 0.12 8.45 0.30 Na2O (wt.%) - 1.01 0.03 K20 (wt.%) 0.02 0.04 Grain size (p) 1-50 1-50 1-50 Description quartz flour Westerwald crystal quartz flour V.Busch Quarzsand Company E. Kick Schnaittenbach Schnaittenbach as Two types of guanidine silicate solution are used. Both are practically alkali-free.

% Weight type *) SiO2 guanidine H2O L, liquid 25 25 50 F, solid 35 35 30 Supplier: SKW Trostberg The bursting pressure of the moldings (balls or granules with 6 mm diameter, tablets with 6 mm thickness) is in a burst pressure measuring device, Zwick company, measured the specific surface area according to Haul / Dümbgen (BET one-point method with nitrogen) and the mean pore diameter is derived from the specific surface area and pore volume calculated.

Test series 1 (see Table 1) 100 g of quartz flour is mixed with guanidine silicate solution Type F and water mixed, homogenized for 10 to 40 minutes and - if necessary after pre-drying - deformed. In No. 1 to 9, the deformation was carried out with a Tablet press, at 10 by hand and at 11 by rounding in the granulating cup.

120 minutes drying at 1200C and tempering below the specified Conditions gave moldings with very good bursting pressures and low alkali contents. The bursting pressures of the dried, non-tempered moldings were for No. 5 already 8.9 kg, for No. 11 20.1 kg and for No. 2, which was not tempered, 17.7 kg.

The specific surface areas of the finished moldings were 10 - 40 m² / g, the mean pore diameter 16 - 65 nm.

Table 1 Moldings made from quartz powder, guanidine silicate solution and water No. share VT TE BA Quartz Gua H2O q Min ° C Min ° C Type gg 1 I 20.0 1.25 14.3 10 60 120 500 19.0 0.019 2 I 20.0 2.5 """- - 17.7" 3 I 20.0 2.5 """120 300 18.6" 4 I 20.0 2.5 """" 400 17.5 " 5 I 20.0 2.5 """" 500 19.0 " 6 III 20.0 2.5 """" 600 15.2 0.065 7 III 17.5 1.25 16.3 20 | 80 "500 16., 3 0.066 8 | I | 17.5 | 1.25 | "| 10 | 70 |" | "| 18.4 | 0.019 9 I 12.5 1.25 22.8 15 90 "" 14.9 10 I 20.0 28.0 14.3 - - "|" 10.8 11 | I | 20.0 | 28.0 | "| - | - |" | "| 10.2 Test series 2 (see Table 2) 100 g of quartz powder are mixed with type F guanidine silicate solution and homogenized for 10 minutes.

The deformation takes place without pre-drying according to the following deformation techniques a) Powder droplets As a powder presented to collect and dry the droplets were used: quartz powder, fumed silica, wood flour, methyl cellulose, Soot, molecular sieve powder.

b) Dripping through a hot air-heated downpipe.

c) Dripping on inclined plates or foils.

d) pouring into molds.

e) Distribute between 2 plates (none of the resulting film can Burst pressure can be measured).

After drying for 2 hours at 1200C and tempering for 2 hours at 5000C, hard moldings with a specific surface area of 20 - 80 m2 / g and mean pore diameters of 11 - 67 nm.

Table 2 Moldings made from quartz powder and guanidine silicate solution No. Mixing components q BA Quartz gua Type 9 12 I 62.5 6.4) 0.017 13 III 31.3 12.8 9.2 to 0.065 14 1 31.3 12.8 17.0 0.019 15 II 55.6 6.3 0.887 Test series 3 (see Table 3) 100 g quartz powder type I is mixed with guanidine silicate solution type L (No. 23 and 24: type F), additives and optionally water and homogenized for 10 minutes. In tests 16 to 22, the deformation takes place by hand without predrying, in nos. 23 and 24 after 10 minutes / 60 ° C. predrying using a tablet press.

After drying for 120 minutes at 1200C and tempering for 120 minutes at 5000C (No. 22: 600 ° C), hard molded bodies with a specific surface area of 30 to 80 2 / g and mean pore diameters of 10 to 60 nm were obtained. Guanidine silicate solution and additives No. Mixing ingredients Gua H20 ZS q B 9 9 Art g 16 75.4 - MgO 8.7 5.3 6.2 17 75.0 - ZnO 16.7 5.3 3.4 18 125.0 6.3 MSA 100.0 3.2 8.3 19 125.0 6.3 MSX 100.0 3.2 7.7 20 | 66.7 | - | MSY | 3.3 | 6.0 | 10.1 21 64.5 2.5 MSA 2.5 6.2 6.1 + + Carbon black 1.8 22 64.5 2.5 MSA 2.5 6.2 5.6 + + Carbon black 1.8 23 20.7 20.0 SiO2 *) 25.0 13.7 6.7 24 | 25.0 | 30.0 | SiO2 *) | 40.0 | 11.4 | 7.2 *) jet-milled fines, grain size 1 - 6 µ test series 4 (no inventive design) For comparison, under otherwise identical conditions as in test series 3, nos. 16 to 22, moldings were produced from the following mixture components: a) 100 g SiO2 + 230.8 g Gua, type F + 100 g H20 b) 100 g SiO2 + 200 g Gua, type F + 120 g H20 c) 100 g SiC + 16.1 g Gua, type L d) 100 g SiC + 60.0 g Gua, Type L.

Moldings which did not contain any crystalline silica resulted and - even using SiC, which is known to be very hard - only burst pressures from 0.8 to 2.1 kg.

Claims (15)

Claims process for the production of hard, porous, crystalline Silica-containing moldings, characterized in that quartz powder and Guanidine silicate solution, if necessary mixed homogeneously with the addition of water, optionally pre-dried and then shaped, dried and optionally are tempered. 2. The method according to claim 1, characterized in that quartz powder with a grain size of 1 to 100, preferably 1 to 50 p is used. 3. The method according to any one of claims 1 or 2, characterized in that that as a guanidine silicate solution, an aqueous solution with a weight ratio Guanidine silicate: H20 from 1: 2 to 4: 1, preferably 1: 1 to 2.6: 1 used will. 4. The method according to any one of claims 1 to 3, characterized in that that for the finished mixture the quotient of the measured in percent by weight The SiO2 content of the quartz powder and the guanidine silicate has a value between 1.4 and 25, preferably 3 to 23. 5. The method according to any one of claims 1 to 4, characterized in that that the total water content of the finished mixture 3 to 50, preferably 4.4 to Is 30% by weight. 6. The method according to any one of claims 1 to 5, characterized in that that 0 to 30, preferably 1 to 23 wt .-% of the homogeneous mixture to be dried consist of further additives. 7. The method according to claim 6, characterized in that as additives SiO2-containing substances are used. 8. The method according to claim 7, characterized in that as additives SiO2 gel, powder or xerogel or zeolites can be used. 9. The method according to claim 6, characterized in that as additives Low-alkali, volatile or decomposable at the drying or tempering temperature Substances are used. 10. The method according to claim 9, characterized in that wood flour, Cellulose ether, activated carbon or carbon black can be used. 11. The method according to any one of claims 1 to 10, characterized in, that the mixture ingredients 0 to 1 wt .-%, preferably 0.01 to 0.1 wt .-% Contains alkali, calculated as Na2O and based on the finished molded body. 12. The method according to any one of claims 1 to 11, characterized in that that the water-containing moldings for 90 to 150, preferably 110 to 130 minutes be dried at 70 to 150, preferably 110 to 130 0C. 13. The method according to any one of claims 1 to 12, characterized in that that the dried moldings are tempered at 100 to 700, preferably 300 to 6000C will. 14. Use of the according to the method according to any one of claims 1 up to 13 produced SiO2 moldings as a catalyst or carrier. 15. Hard, porous, crystalline silica-containing moldings, characterized by an alkali content of 0 to 1 wt .-%, preferably 0.01 to 0.1% by weight, calculated as Na20.