A METHOD FOR MANUFACTURING A SUPPORT MATERIAL FOR CATALYSIS

Abstract: A mineral fibre paper is formed to a body with fine through channels, the body being impregnated with a dispersion of a filling material, a sol and a dispersion medium. A gelating medium is provided to the body to gelate the sol so that the whole sol is polymerized or gelated.

Description: A METH O D FOR MANUFACTURING A SUPPORT MATERIAL FOR CATALYSIS The present invention relates to a method for manufacturing a support material for catalysts, here a paper of mineral fibres, such as a paper of glass fibres is formed to a body with fine through channels, whereafter a gel is provided on the body. It is already known to use bodies manufactured in this way in form of blocks, rotors or similar as a support material for catalysts. In such methods to manufacture the support material the body is impregnated with a dispersion of a filling material and a silica sol. By means of drying the impregnated body at a low temperature a gelating of the sol is achieved. This implies a tideous process being very critical as to achieve the right deposition of the gel. Thus it is usual that the channels are clogged by the sol accumulated at the ends of the channels. This provides a far too high temperature during the following calcination of the body possibly resulting in burned-out portions of the body. The already known methods for manufacturing a support material are therfore providing a large rejection in manufacturing. To handle the stresses created on the cell body and the gel properties such as a strong, even and non-cracking gel are aimed at. The main object of the invention is to achieve a support material for catalysts providing these desired qualities. This object is according to the invention achieved in a way as stated in the claims to follow. The method according to the invention will be described more in detail here below. A block, a rotor or any other body is manufactured in that two tracks or bands of a paper of mineral fibres, one of which is folded or corrugated, is connected to a so-called single well in using any convenient adhesive. The paper contains artificial, e.g. spun or extruded fibres of various minerals, here glass fibres. The folded or corrugated paper track has a wave height of 1 to 7 mm. The single well produced in such a way is placed into blocks to form a stationary body with the desired shape and the desired dimensions or are wound into a cylindric rotor with a desired size. Various body shapes are depending on the application possible such as square, rectangular or even triangular or similar forms. The produced structure is from one end surface of the body to the corresponding opposite end surface provided with parallel through channels, laterally separated from each other by contact points between the plane and the folded layers. The cell body of glass fibre paper been manufactured in this way an impreganation of the body is provided in that a dispersion of a filling substance, a silica so and a dispersing medium is applied to it. The application might be provided by means of dipping, the body then being placed into the dispersion for a certain period. The dispersion can be mixed in a mixer before it is transferred to an impregnating bucket where the dipping is provided. The dispersion has a tendency to form a skin when remaining untouched for some period, but this problem can be avoided by means of some kind of circulation in the impregnating bucket. Another alternative is that this part of the process is performed with a flushing of the cell body by means of a so-called liquid curtain. When manufacturing the catalysts support according to the invention the silica sol is as previously mentioned mixed with a filling substance to a dispersion. This procedure is made to increase the dry content of the impregnating sol over 50 % being considered to present the upper limit for a silica sol. Together with a dispersing medium a dry content of 60 to 65 % can be achieved for the entire dispersion. This is necessary, as the glass fibre paper to be impregnated is very porous and usually has blanks of 90 to 95 %. An alternative method could be to impregnate several times in a sol and gelate it. Besides that the process costs would increase the sol is in most cases more expensive than a filler substance, this also increasing the costs for the raw materials. During gelation also a shrinking is performed. If the distances then are comparatively large as they are in a glass fibre paper the stresses on the gel become very large and weakening crack formations are obtained. To have a filling medium dispersed in the sol is a way to decrease these distances and thereby any crack formations. The support will thus be stronger, tougher and have increased form stability than without any filler medium. Moreover, if a temperature resistent filling medium is used the support will with preserved properties resist higher temperatures. Preferably a non fibrous filler medium is according to the invention used and examples of such preferred filler media are kaolin and other clay materials, silica, mica, talcum, felspar. After the impregnation a gutting of the cell body can be performed with e.g. air to clean the channels from the dispersion sol. The sol being a silica sol consists of small particles of silicic acid not sedimenting in water. The silicic acid is thus not solved in the water but so to say finely distributed. The particles can be 5 to 150 n large. With such small particles and contents of about 15 to 50 % their total area will be extremely large. The system will physically decrease its boundary, i.e. the particles will converge to fewer and essentially larger aggregates. Thus, a minor boundary is obtained. To prevent this the sol is generally stabilized by means of sodium hydroxide. The negative hydroxide iones settle on the particles surface and make these repellant to each other thus preventing any aggregation. If the sol is dried, i.e. the water is removed, the particles will finally approach each other so much that the stabilising effect is partly overcome and a gelation is performed. As described in the beginning such a drying procedure is however a tedious and sensitive process resulting in a large rejection of the manufactured support material due to clogged channels, as the impregnating sol will accumulate after some time due to gravitation. According to the present invention a gel medium is instead provided, e.g. a salt. The effect of the hydroxide iones on the sol particle area will be abolished due to a higher charging density in the sol. The effect of the hydroxide iones is overcome and the silicic acid particles are approaching each other sufficiently so that the whole sol is polymerized (gelated), i.e. obtains the minor boundary to be achievable between the silicic acid and the water. In practice however, the water will be locked into the structure and is there bound capillarily. Most soluble salts can perform as a gelating medium. According to the invention chlorides might thus be used such as sodium chloride, calcium chloride, magnesium chloride, aluminium chloride, zinc chloride and litium chloride, sulphates such as ammoniumsulphate, sodium sulphate, aluminium sulphate and aluminium-potassium sulphate, nitrates such as ammonium nitrate, aluminium nitrate and potassium nitrate and acetates such as ammonium acetate, calcium acetate and sodium acetate. Even other gelating media might be used such as e.g. acids, bases and alcolhols. Like salts they can disturb the fine balance existing in a stabilized silica sol and provide a strong gel structure. The stronger gel structure provides the possibility to manufacture a stronger support inspite of that fibrous materials are not used as a filler material. Previously such metarials have been used to achieve some kind of reinforcement. These material are however questionable in respect to health considerations. Examples of such fibrous materials now being avoided are: attapulgite, halloysite, sepiolite and wollastonite. Thereafter a drying of the body is performed at a temperature below 100 ° C to remove capillarily bound water without creating any crack formations. The cautious drying achieves that the excess salt leaves the structure and is deposited on the surface, where it is easily flushed off. A flushing or a washing of the cell body is thereafter performed to remove residues of the gelating medium from the cell body surfaces. These residues might possibly form dangerous gases during a following calcination of the cell body. To avoid such gases as an air pollution the cell body is therefore washed under e.g. a water curtain. Thus, even the cristallized gelating medium is solved and can be returned to a recovering system to recover the gelating medium. After the flushing and another drying of the body a calcination of the body can be performed at a high temperature to achieve a body form stability for a further treatment. In cases where organic materials exist in it this material will be burned off. To achieve the right structure for the supporting body surface depending on the application a final treatment is then performed, in which the the supporting body is coated (by means of an already known technology) with a Si0 ■*-< surface or a y-AU ___>O, surface. Here below an example of a method for manufacturing a support material for catalysts will be described. A cell body manufactured from glass fibre paper according to the procedure described in the beginning is impregnated e.g. by means of dipping or flushing with a dispersion of 25 to 35 % kaolin or any other filling material of the kind mentioned above, 65 to 75 % silica sol with a concentration (dry content) above 40 % (a silica sol with various particle size can be mixed) and a small amount, e.g. 0.5 % of a dispersing medium. Before any gelating is performed the body is gutted with air to clean the channels from any excess of dispersing sol. The gutted body is then provided with a gelating medium, here a sol with 10 % ammonium sulphate up to a saturated sol or a combination of the salts (NHΛ^SC and Na ^ SC , performed by means of dipping during about 30 minutes. At the end of the gelation the body is dried to remove capillarily bound water in an air stream with a temperature below 100 ° C until the body is completely dry. Thereafter, a washing or flushing av the body is performed to remove residues of the ammonium sulphate formed on the body surfaces during the gelation and the drying. These residues would during a following burning or calcination disintigrate into NH and SO-,, these gases performing as air pollutions during the burning. The washing is provided in that the body is e.g. flushed under a water curtain. During the following step a drying by means of air is performed at maximum 140 ° C and thereafter the temperature is raised either for a burning or a calcination at a temperature of about 240 to 300 C and with a dwelling period of 30 to 60 minutes to achieve a proper burning of possibly existing organic material and/or a raising of the temperature to e.g. 550 to 600 C at the end of the burning to achieve a good form stability of the body for a following treatment. Another impregnation of the body is thereafter provided with a sol with a dry content of 5 to 15 % and with an inner specific surface depending on the application, whereafter a drying is performed at a temperature below 100 C. This method provides a SiC surface. After a possible cutting of the body to obtain the desired dimensions and/or clean end surfaces on the body a catalyst supporting material has been obtained with the good properties indicated in the beginning. The invention is obviously not limited to the embodiment here described but can be modified within the scope of the claims to follow.

Claims: Claims 1. A method for manufacturing a support material for catalysts, in which a mineral fibre paper is formed to a body with fine through channels and where the body is impregnated with a dispersion of a filling material, a sol and a dispersing medium, characterized in that a gelating medium is applied to the body to gelate the sol so that the complete sol is polymerized or gelated. 2. A method according to claim 1, characterized in that a non fibrous material is used such as kaolin or other clay materials, silica, mica, talcum, felspar. 3. A method according to claim 1 or 2, characterized in that the gelating medium is a salt such as a chloride, a sulphate, a nitrate or an acid, a base or an alcohol. 4. A method according to anyone of the claims 1 to 3, characterized in that the body is dried at a temperature below 100 ° C to remove capillarily bound water and to force any excess of salt to protrude to the surface. 5. A method according to claim 4, characterized in that a washing or a flushing of the body is performed after the gelation and the drying to remove any possible excess of gelating medium. 6. A method according to anyone of the claims 1 to 5, characterized in that after the gelation a drying with air up to 140 C is performed and that the temperature thereafter is raised for burning off possibly existing organic material as well as a further raise of the temperature to about 550 to 600 ° C to bum the body to achieve a good form stability for it. 7. A method according to claim 3, characterized in that as a gelating medium is used a chloride such as sodium chloride, calcium chloride, magnesium chloride, aluminium chloride, zinc chloride and litium chloride. 8. A method according to claim 3, characterized in that as a gelating medium is used a sulphate such as ammonium sulphate, sodium sulphate, aluminium sulphate and aluminium- potassium sulphate. 9. A method according to claim 3, characterized in that as a gelating medium is used a nitrate such as ammonium nitrate, aluminium nitrate and potassium nitrate. 10. A method according to claim 3, characterized in that as a gelating medium is used an acetate such as ammonium acetate, calcium acetate or sodium acetate. 11. A method according to claim 3, characterized in that as a gelating medium is used an acid, a base or an alcohol. 12. A method according to anyone of the claims 1 to 11, characterized in that a blowing of the body channels is performed after the impregnation to clean the channels from the dispersing sol.

Inventors: SCHEFTE THOMAS, SCHEFTE, THOMAS
Applicants: MUNTERS AB CARL, SCHEFTE THOMAS, AB CARL MUNTERS, SCHEFTE, THOMAS
Application year: 1997
Main classification: B01J20
IPC codes: B01J21, B01J32, B01J35, B01J37, C01B33