SHAPED ARTICLES OF SILICA GEL AND POROUS, AMORPHOUS MIXED OXIDES

Abstract: The invention relates to shaped articles based on silica gel and/or porous, amorphous mixed oxides. The shaped articles have a specific pore volume of 0.3 to 2.0 ml/g, a BET surface in the range 20 to 800 m<2>/g and a compression strength of at least 40 N (determined according to the Chatillon method). At least 50% of the total pore volume consists of mesopores with a diameter of </= 50 nm. The invention also relates to processes for the production of shaped articles and the use thereof, as adsorbers or catalyst supports.

Description: SHAPED ARTICLES OF SILICA GEL AND POROUS, AMORPHOUS MIXEfi OXIDES The present invention relates to shaped articles having a high pore volume and simultaneously a high compression strength, as well as to processes for the production of such shaped articles and the use thereof. Silica gels and porous, amorphous mixed oxides are inter alia used as adsorbents and as catalysts or catalyst supports in industrial suspension, fixed bed or fluidized bed processes. For this purpose usually granular forms of the silica gels or porous, amorphous mixed oxides are used. A major disadvantage of the two aforementioned materials is their inadequate mechanical stability, which inter alia leads to the formation of fine fragments and dustline fines. These undesired finely divided components e.g. impair the operation of a fixed bed to a significant extent, because a high pressure loss occurs when gases and liquids flow through. The average service life of a reactor or adsorber bed is greatly reduced through the occurrence of large amounts of finely divided particles. A process for the production of silica-containing shaped articles is e.g. described in US patent 4,256,682. Silica xerogels or silica aerogels are pasted with an aqueous, ammoniacal medium and subsequently compressed and extruded. The shaped articles obtained are characterized either by a rela- tively high pore volume and low compression strength or by a relatively high compression strength and a low pore volume. European patent EP 309 048 Bl describes the production of extrudates starting from silica or silica/titanium dioxide or silica/zirconium dioxide mixtures and a binder comprising ammonia or an ammonia-releasing component. The pore system of the extrudate obtained is constituted by mesopores and macropores . A significant proportion of the pore volume and the BET surface of the starting components is lost during the extrusion process. A process for the production of silica catalyst supports is described US patent 4,937,394. Ultra-finely divided, precipitated silica is extruded with silica sol as the binder. The known processes are either based on the deformation of fumed silicas, precipitated silicas or pure silica gels. The shaped articles obtained are characterized either by a relatively high compression strength or by a relatively high pore volume. However, in connection with adsorbents catalyst supports and catalysts a combination of high pore volume and high compression strength is desired. In the above processes the deformation or extrusion step leads to a pore volume loss . Thus, the problem of the present invention is to make available mesoporous shaped articles not suffering from the indicated disadvantages and processes for the production thereof. According to the invention this problem is solved by shaped bodies based on silica gel and/or porous, amorphous mixed oxides and which are characterized in that (a) the specific pore volume is at least 0.3 ml/g and preferably in the range 0.3 to 2.0 ml/g, and in particularly preferred manner in the range 0.8 to 2.0 ml/g, (b) at least 50% of the total volume of the pores consists of mesopores with a diameter of < 50 run, (c) the BET surface is in the range 20 to 800 m /g and (d) the compression strength is at least 40 N (determined according to the Chatillon method) . The terms acropores , mesopores and icropores are used here in accordance with the corresponding IUPAC definitions . The shaped articles are obtainable by mixing (1) silica gel and/or porous, amorphous mixed oxides, (2) binders, (3) optionally plasticizers and/or lubricants and (4) polar solvents, and subsequent shaping, drying and calcining the mixture obtained. The term "drying" is understood to mean the removal of a solvent, such as e.g. water, whilst "calcining" includes a chemical reaction, such as e.g. a chemical modification of the binder . Both xerogels, aerogels and hpdrogels can be used as silica gels (1). In the present case a hydrogel is understood to mean an amorphous, porous product with a solids content between 30 and 80%, the remainder being water. In order to maintain and/or increase the pore volume the silica gels are preferably used in impregnated form. For impregnation purposes water, polyols, glycols, fatty acid amides, glycerol esters and waxes and more particularly erucic acid amide are suitable. Preferred mixed oxides are Si0 2 /Ti0 2 , Si0 2 /Zr0 2 , Si0 2 /Al 2 0 3 . These mixed oxides can be produced in per se known manner, e.g. according to the sol-gel process. The silica gel (1) and/or the porous, amorphous mixed oxide preferably has a BET surface in the range 100 to 1000 m /g and in particularly preferred manner 200 to 600 m /g, while the pore volume is preferably in the range 0.6 to 5.0 ml/g and in particularly preferred manner in the range 0.6 to 2.5 ml/g. Mixtures of said silica gel and mixed oxide types are also suitable. The particle size of the silica gel/mixed oxide is preferably 0.1 to 100 μm, particularly 0.1 to 10 μm. In order to be able to process the silica gel and amorphous mixed oxides to shaped articles, they are mixed in a compounding step (mixing) with additives, such as binders and plasticizers , which give the materials a certain plasticity, which is a prerequisite for the following shaping process. Preferred binders are tetraalkyl orthosilicates , silica sols, silica hydrogels, in particular ultra-finely divided, porous silica hydrogels, siloxanes and mixtures of these components, particularly silicone resins, ultra-finely divided, porous silica (so called submicron silica) or siloxanes of formula (I): in which R stands for substituted or unsubstituted alkyl, aryl, alkenyl, alkinyl, alkoxy or aryloxy, in which the R radicals can be the same or different, R' substituted or unsubstituted alkyl, aryl, alkenyl or alkinyl, in which the R' radicals can be the same or different and n is an integer from 1 to 10 (branched or unbranched), preferably 3 to 6 , and in particularly preferred manner 3 or 4. Preferred definitions, selectable independently of one another, for R and R' are: R substituted or unsubstituted C j to C 20 , preferably C : to C 10 and particularly C i to C 5 alkyl, C 6 to C 20 , preferably C 6 to C 15 and particularly C 6 to C 10 aryl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkenyl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkinyl, C x to C 20 , preferably C { to C 10 and particularly C : to C 5 alkoxy or C 6 to C 1Q , preferably C 6 to C 15 and particularly C 6 to C 10 aryloxy, preferably phenoxy and R' substituted or unsubstituted C x to C 20 , preferably C l to C 10 and particularly C L to C 5 alkyl, C 6 to C 20 , preferably C 6 to C 15 and particularly C 6 to C 10 aryl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkenyl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkinyl. In the present case the term "ultra-finely divided silica" is understood to mean a dispersion of porous silica particles in a polar or apolar solvent, preferably in water, with a solids content in the range 1 to 30 wt . % and an average particle size in the range 0.05 to 3.0 μm. The particles can be of precipitated silica or silica gel. They have an internal porosity leading to the dried particles having a nitrogen pore volume (BET measuring method) of at least 0.5 ml/g in pores with a size of 60 nm or smaller. The silicone resins also suitable as binders are preferably solvent-free and the particle size is preferably in the range 1 to 10 μm. The binders used according to the invention react during the subsequent drying and calcining, accompanied by the formation of solid bridges and consequently ensure a high mechanical stability of the shaped articles. Through the use of these hitherto undescribed binders, it is simultaneously possible to obtain shaped articles with a high pore volume. The optionally used plasticizers should be completely removed from the shaped articles produced following the end of shaping, e.g. by calcining, because even small amounts of extraneous materials can impair e.g. the catalytic properties and the ageing resistance of the shaped articles. Suitable plasticizers are known to the expert. Preferred plasticizers are cellulose ethers, polysaccharides, polyvinyl alcohols, starch and starch derivatives, as well as mixtures of these compounds. Particular preference is given to methyl cellulose. These plasticizers are soluble or swellable in polar solvents . In addition to or in place of the plasticizers it is possible to use a lubricant. Preferred lubricants are graphite, wax emulsions, fatty acids and/or fatty acid mixtures. The lubricants permit a precision adjustment of the rheological characteristics of the materials to be extruded. The use of a plasticizer or lubricant is optional and the process is preferably performed without the addition of plasticizers and/or lubricants. Preferred polar solvents are water, monohydric and polyhydric alcohols or mixtures of these components. The solvent can be used either in pure form or mixed with catalytically active components. Suitable catalytically active components are in particular aluminium acetyl acetonate, e.g. hardener F100 ( acker-Chemie GmbH) and other compounds able to speed up a crosslinking of the binder. The choice of solvent is also dependent on the binder used and optionally also the plasticizer and lubricant. It must be selected in such a way that a premature reaction of these components is avoided. The mixture used for producing the shaped articles according to the invention preferably contain: 1 to 97 wt.%, particularly 20 to 80 wt . % of silica gel and/or porous, amorphous mixed oxide, - 1 to 97 wt.%, particularly 5 to 75 wt.% binder and optionally 2 to 30 wt.%, particularly 5 to 15 wt.% plasticizer, in each case based an the total weight of the mixture without solvents . This mixture is compounded in a polar solvent, preferably water, i.e. is processed to a plastic material. Binders according to formula (I) are preferahly used in a proportion of 2 to 25, particularly 5 to 25 wt.%, ultra-finely divided amorphous silica preferably in a proportion of 2 to 25, particularly 5 to 25 wt.% and silica hydrogels preferably in a proportion of 2 to 85, particularly 5 to 75 wt.%, in each case based on the total reaction mixture without solvents . These quantity ranges also apply when using mixtures of these materials, the total binder quantity being within the above- defined, preferred ranges of 1 to 97 and particularly 5 to 75 wt.%. In the case of binders of formula (I) the Si0 2 content of the binder is preferably at least 50 wt.% and in particularly preferred manner at least 60 wt.%, based on the total binder weight. In the case of ultra-finely divided, porous silica the Si0 2 content is at least 5 wt.% and in the case of silica hydrogels at least 30 wt.%, in each case based on the total binder. These details relate to the composition of the binder prior to drying and calcining. The plasticizer quantity used is dependent on the binder used and the binder content, the sought pore volume and in particular the proportion of macropores. Through increasing the plasticizer proportion it is possible to increase the macropore proportion. The shaped articles are preferably produced in that (i) in a first step the silica gel and/or the porous, amorphous mixed oxide is impregnated with a substance suitable for maintaining the pore volume, preferably with water or another of the above-described components , (ϋ) the thus treated silica gel and/or mixed oxide is mixed in a second step with the binder and the polar solvent and optionally a plasticizer and/or a lubricant, (iϋ) said reaction mixture is subsequently shaped to shaped articles and (iv) in a fourth step the shaped articles obtained are dried and calcined. Preferably "the first and second steps of the process according to the invention are carried out in a kneader or mixer, e.g. a sigma paddle mixer. For performing the third process steps the reaction mixture is transferred into the deformation apparatus, preferably an extruder. Extrusion can take place both in a plunger extruder and in a single or twin-screw extruder. The subsequent drying preferably takes place at a temperature in the range 120 to 300 °C, calcining at at least 300 °C, preferably at a temperature in the range 300 to 1000 °C, particularly 300 to 600 °C. It is a particular advantage of the process according to the invention that it does not require the use of auxiliary agents or aids, such as e.g. waxes, oils or fatty acids. Such aids are usually used in small quantities, which increases the mixing costs in order to obtain a uniform distribution of these components within the overall material. This increases the production time and costs. The risk of introducing impurities is reduced, such impurities possibly having a disadvantageous action, e.g. on the ageing resistance of the shaped article. The shaped articles obtained are characterized by a combination of high compression strength and high pore volume. The compression strength determined according to the Chatillon method is at least 40 N, preferably at least 50 N and in particularly preferred manner at least 80 N. For measuring the compression strength use is made of a Chatillon measuring instrument of John Chatillon & Sons Inc. with planeparallel plunger faces. The compression strength is determined on solid cylindrical extrudates of identical length with a diameter of 5 mm and a length/diameter ratio of 1.5. The compression strength was determined over the circumferential surfaces at ambient temperature. The compression strengths measured over the end faces of the extrudates are above 5 N/mm , preferably above 10 N/mm , in particularly preferred manner above 20 N/mm and more especially preferred manner above 30 N/mm . For determining the compression strength over the end faces use is made of a tension/compression testing machine type UP 1455 of the Zwick firm. The measurement takes place on solid cylindrical extrudes with a diameter of 5 mm and a length of 7 mm. It must be ensured that the end faces of the extrudates are plane-parallel for precise, reproducible compression strength measurements . The measurement was carried out at ambient temperature. The preforce is 1 N. The measurements are performed at a testing speed of 1 mm/min. The testing force acts on the end faces. The shaped articles have pore volumes of at least 0.3 ml/g and in particular 0.3 to 2.0 ml/g. Advantageously using the above- described process, shaped articles can be produced with pore volumes in the range 0.8 to 2.0 ml/g. The pore volume is measured by the BET method. At least 50%, preferably at least 60% and in particularly preferred manner at least 70% of the total pore volume consist of mesopores with a diameter of < 50 run. The BET surface of the shaped articles is in the range 20 to 800 m /g, preferably 100 to 800 m /g, in particularly preferred manner 200 to 800 m /g and more especially preferred manner 400 to 800 mVg. The shaped articles can have any extrudable shape. Preferably they have a cylindrical or three-lobe shape or are in hollow ring form. The shaped articles are particularly suitable as adsorbents, catalysts or catalyst supports, as well as for the production thereof, particularly as catalysts or catalyst supports in industrial solid bed applications. Adsorbents are used as adsorbing agents in gas, liquid or steam drying, as adsorbers/desorbers in air conditioning systems and as adsorbing agents in hydrocarbon recovery. After use the adsorbents can be regenerated by heat treatment and/or pressure swing processes. For the production of catalysts the shaped articles are treated in per se known manner with catalytically active substances such as acids, bases, different metals, noble metals, metal salts and other catalytically active substances . For this purpose the desired catalytically active substance or a suitable precursor thereof can be added during process steps (i) to (iii), but preferably the finished shaped articles are impregnaced with said substances following onto step (iv). As a function of the catalytically active component the shaped articles are suitable as catalysts e.g. for alcohol synthesis, alkylation, epoxidation, hydrogenation, esterification, oxidation, carbonylation, oligomerization and rearrangement. The following examples further illustrate the invention. Example 1 In a sigma paddle mixer 1.5 kg of water-containing silica gel A are mixed and homogenized with 0.2 kg of ethyl silica-ethyl ester (SILREΞ (R) 43220), 0.1 kg of methyl cellulose (METHOCEL) and 0.15 kg of water. This mixture is extruded and the resulting extrudates are dried at a temperature of 200 °C and then calcined at a temperature of 350 °C. Example 2 As in example 1 a mixture consisting of 1.5 kg of silica gel B, 0.26 kg of alkyl silicone resin (silicone solid resin ML, Wacker-Chemie GmbH), 0.05 kg of methyl cellulose and 4.0 kg of water is produced and extruded to extrudate B. Drying takes place at 120 °C and calcining at 450 °C. Example 3 1.5 kg of silica gel C containing erucic acid amide (30% amide) are kneaded with 1.75 kg of an aqueous suspension of ultra- finely divided porous silica gel (solids content > 15%) and 0.2 kg of methyl cellulose and subsequently extruded to shaped article C. Drying takes place at 200 °C and calcining at 700 °C. The analytical data of silica gels A to C and the resulting extrudates A to C are given in the following table. Silica Pore Precharging Extrudate Pore Compression Compression gel volume with volume strength strength (ml/g) (ml/g) (N/mm 2 ) ' (N)"~ A 1.5 water A 1.4 8 50 B 1.2 B 0.8 13 80 C 1.8 erucic acid C 1.0 10 65 amide Determined by means of the tension/compression testing machine UP 1455 of Zwick Determined by the Chatillon measuring instrument of John Chatillon & Sons Inc.

Claims: Claims Shaped article, based on silica gel and/or porous, amorphous mixed oxide, characterized in that a) the specific pore volume is in the range 0.3 to 2.0 ml/g, b) at least 50% of the total volume of the pores consist of mesopores < 50 run, c) the BET surface is in the range 20 to 800 m /g and d) the compression strength is at least 40 N (determined according to the Chatillon method) . Shaped article according to claim 1, characterized in that the specific pore volume is in the range 0.8 to 2.0 ml/g. Shaped article according to claim 1 or 2 , obtainable by mixing (1) silica gel and/or porous, amorphous mixed oxide, (2) binders, (3) optionally plasticizers and/or lubricants and (4) polar solvents and subsequent shaping, drying and calcining of the mixture, characterized in that the binder contains tetraalkyl orthosilicate, silica sol, silica hydrogel, in particular ultra-finely divided, porous silica hydrogel, ultra-finely divided, porous silica, siloxane, silicone resin or a mixture thereof. Shaped article according to claim 3, characterized in that the binder contains ultra-finely divded, porous silica, silicone resin or siloxane according to formula (I) R R R RO -Si -O'-Si -O 1 Si- OR ' (H OR ' OR' j n OR' in which R stands for substituted or unsubstituted alkyl, aryl, alkenyl, alkinyl, alkoxy or aryloxy, in which the R radicals can be the same or different, R' stands for substituted or unsubstituted alkyl, aryl, alkenyl or alkinyl, in which the R' radicals can be the same or different and n is an integer from 1 to 10 (branched or unbranched) , or a mixture thereof. Shaped article according to claim 4, characterized in that R stands for substituted or unsubstituted C l to C 20r preferably C l to C 10 and particularly C { to C 5 alkyl, C 6 to C 20 , preferably C 5 to C 15 and particularly C 6 to C 10 aryl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkenyl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkinyl, Cj to C 20 , preferably C to C 10 and particularly C x to C 5 alkoxy or C 6 to C 20 , preferably C 6 to C 15 and particularly C 6 to C 10 aryloxy, preferably phenoxy and/or R' stands for substituted or unsubstituted C x to C 20 , preferably C x to C 10 and particularly C l to C 5 alkyl, C 6 to C 20 , preferably C 6 to C 15 and particularly C 6 to C 10 aryl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkenyl, C 2 to C 20 , preferably C 2 to C 10 and particularly C 2 to C 5 alkinyl and/ or n is equal to 3 to 6. 6. Shaped article according to claim 4 or 5 , characterized in that the binder comprises ultra-finely divided, porous silica, silicone resin or a siloxane of formula (I). 7. Shaped article according to one of the claims 3 to 6, characterized in that the silica gel (1) is a xerogel, aerogel or hydrogel and/or the mixed oxide is Si0 2 /Ti0 2 , Si0 2 /Zr0 2 or Si0 2 /Al 2 0 3 . 8. Shaped article according to claim 7, characterized in that the silica gel is impregnated with a polyol, glycol, fatty acid amide, glycerol ester, wax and/or in particular water. 9. Shaped article according to claim 3 or 8 , characterized in that the silica gel and/or the porous, amorphous mixed oxide has a BET surface in the range 100 to 1000 m /g. 10. Shaped article according to one of the claims 3 to 9, characterized in that the silica gel and/or the porous, amorphous mixed oxide has a pore volume in the range 0.6 to 5.0 ml/g. 11. Shaped article according to one of the claims 3 to 10, characterized in that the plasticizer contains one or more cellulose ethers, polysaccharides, polyvinyl alcohols, starch, starch derivatives or a mixture of these compounds. 12. Shaped article according to one of the claims 3 to 11, characterized in that it contains as lubricants graphite, a wax emulsion, a fatty acid and/or a fatty acid mixture. 13. Shaped article according to one of che claims 3 to II, characterized in that the polar solvent is water or monohydric or polyhydric alcohols or a mixture of these components . 14. Shaped article according to one of the claims 3 to 13, characterized in that the mixture of components (1), (2) and optionally (3) contains 1 to 97 wt.%, particularly 20 to 80 wt.% silica gel and/or porous, amorphous mixed oxide, 1 to 97 wt.%, particularly 5 to 75 wt.% binders and optionally 2 to 30 wt.%, particularly 5 to 15 wt.% plasticizers . 15. Shaped article according to one of the claims 3 to 14, characterized in that the mixture of components (1), (2) and optionally (3) and (4) is, after shaping, dried at 120 to 300 °C and calcined at 300 to 1000 °C. 16. Process for the production of shaped articles according to claims 1 to 15, characterized in that mixing takes place of (1) silica gel and/or porous, amorphous mixed oxide, (2) binders, (3) optionally plasticizers and/or lubricants and (4) polar solvents, subsequently shaping takes place to shaped articles, which are dried and calcined. 17. Process according to claim 16, characterized in that (i) silica gel and/or a porous, amorphous mixed oxide is impregnated with a suitable pore volume- maintaining substance, (ii) the thus treated silica gel and/or mixed oxide is then mixed with the binder, the polar solvent and optionally plasticizers and/or lubricants, (iii) said reaction mixture is then shaped to shaped articles and (iv) the shaped articles obtained are dried and calcined. 18. Process according to claim 17, characterized in that in step (iϋ) the reaction mixture is shaped to shaped articles by extrusion. 19. Process according to one of the claims 16 to 18, characterized in that the shaped articles in step (iv) are dried at a temperature in the range 120 to 300 °C and calcined at a temperature in the range 300 to 1000 °C. 20. Process according to one of the claims 16 to 19, characterized in that the shaped articles are treated with a catalytically active component. 21. Process according to claim 20, characterized in that the catalytically active substance is constituted by one or more acids, bases, metals, noble metals or metal salts. 22. Use of shaped articles according to one of the claims 1 to 15 as adsorbents for solid bed applications. 23. Use of shaped articles according to one of the claims 1 to 15 for drying gases, liquids or steam. 24. Use of shaped articles according to one of the claims 1 to 15 as adsorbers/desorbers in air conditioning systems. 25. Use of shaped articles according to one of the claims 1 to 15 as adsorbing agents in hydrocarbon recovery. 26. Use of shaped articles according to one of the claims 1 to 15 as catalyst supports for solid bed or suspension applications . 27. Use of shaped articles according to one of the claims 20 to 21 as catalysts for alcohol synthesis, alkylation reactions, epoxidation reactions, hydrogenation reactions, esterif ication reactions, oxidation reactions, carbonylation reactions, oligomerization reactions and/or rearrangement reactions .

Inventors: BRINKMANN ULRICH, HOEFER HANS H, SETZER CONSTANZE, TREFZGER CHRISTIAN, BRINKMANN, ULRICH, HOEFER, HANS, H., SETZER, CONSTANZE, TREFZGER, CHRISTIAN
Applicants: BRINKMANN ULRICH, GRACE GMBH & CO KG, HOEFER HANS H, SETZER CONSTANZE, TREFZGER CHRISTIAN, BRINKMANN, ULRICH, GRACE GMBH & CO. KG, HOEFER, HANS, H., SETZER, CONSTANZE, TREFZGER, CHRISTIAN
Application year: 2000
Main classification: B01J35
IPC codes: B01J20, B01J21, B01J35, B01J37, C01B33, C04B38