Every method of making catalysts is actually composed of a series of operation units. For convenience, people choose the name of the key and distinctive operating unit as the name of the manufacturing method. Traditional methods include mechanical mixing method, precipitation method, immersion method, solution evaporation method, hot melting method, leaching method (leaching method), ion exchange method, etc., and the new methods currently developed include chemical bonding method, fiberization method, etc. .
1. Mechanical mixing method
Add two or more substances to the mixing equipment and mix. This method is simple and easy to implement. For example, in the manufacture of conversion-absorption desulfurizer, the powder of active components (such as manganese dioxide, zinc oxide, zinc carbonate) and a small amount of binder (such as magnesium oxide, calcium oxide) is measured Continuously add it to a turntable with adjustable speed and inclination, and at the same time spray metered water and powder to roll and mix and bond to form a sphere of uniform diameter. The sphere is then dried and roasted to become the finished product.
2. Precipitation
This method is used to manufacture catalysts that require high dispersion and contain one or more metal oxides. When manufacturing multi-component catalysts, suitable precipitation conditions are very important to ensure the uniformity of product composition and to manufacture high-quality catalysts. The usual method is to add a precipitating agent (such as sodium carbonate, calcium hydroxide) to one or more metal salt solutions, and then precipitate, wash, filter, dry, shape, and roast (or activate) to obtain the final product.
3. Dipping
The carrier with high porosity (such as diatomaceous earth, alumina, activated carbon, etc.) is immersed in a solution containing one or more metal ions, and the temperature is maintained at a certain temperature. The solution enters the pores of the carrier. The carrier is drained, dried and calcined, and a layer of required solid metal oxide or its salt is attached to the inner surface of the carrier.
4. Spray evaporation
Used to prepare fluidized bed catalysts with particle diameters ranging from tens of microns to hundreds of microns. For example, in the manufacture of meta-xylene fluidized bed ammonification and oxidation of meta-dicarbonitrile catalyst, firstly mix a given concentration and volume of metavanadate and chromium salt aqueous solution, and then mix it with a new quantitative silica gel and pump it in In the spray dryer, after being atomized by the nozzle, the water is evaporated to dryness under the action of the hot air flow, and the material forms a microsphere catalyst, which is continuously drawn from the bottom of the spray dryer.
5. Hot melt method
The hot-melt method is a special method for preparing certain catalysts. It is suitable for a small number of catalysts that have to go through the smelting process, in order to melt each component into a uniformly distributed mixture with the help of high temperature conditions, and with the necessary subsequent processing, it can be prepared Excellent catalyst.
6. Leaching
From the multi-component system, use an appropriate liquid agent (or water) to extract part of the substance to make a catalyst with a porous structure. For example, in the manufacture of skeletal nickel catalyst, a certain amount of nickel and aluminum are melted in an electric furnace, and the molten material becomes an alloy after cooling. The alloy is broken into small particles, soaked in sodium hydroxide aqueous solution, and most of the aluminum is dissolved (to generate sodium metaaluminate ), namely the formation of porous and highly active framework nickel.
7. Ion exchange method
The metal cations (such as Na) of certain crystalline substances (such as synthetic zeolite molecular sieves) can be exchanged with other cations. Put it into a solution containing ions of other metals (such as rare earth elements and some precious metals), and exchange other metal ions with Na under controlled concentration, temperature, and pH conditions.
New methods under development
①Chemical bonding law. This method is now widely used in the manufacture of polymerization catalysts. Its purpose is to solidify the homogeneous catalyst. Carriers that can chemically bond with transition metal complexes have certain functional groups on the surface (or functional groups after chemical treatment), such as -X, -CH2X, and -OH groups. This kind of carrier is reacted with phosphine, arsine or amine to make it phosphine, arsine or aminated, and then use the lone electron of phosphorus, arsenic or nitrogen atom on the surface to coordinate with the central metal ion of the transition metal complex By combining, a chemically bonded solid phase catalyst can be obtained, such as the production of Ziegler-Natta catalyst, a carrier for the bulk liquid phase polymerization of propylene.
② Fibrosis method. Used in the manufacture of precious metal-containing supported catalysts. For example, the borosilicate is drawn into glass fiber filaments, corroded with concentrated hydrochloric acid solution to become a porous glass fiber carrier, and then impregnated with chloroplatinic acid solution to carry platinum components. According to the practical situation, the fiber catalyst can be pressed into various shapes and required tightness. For example, the catalyst used for the oxidation of automobile exhaust gas can be compressed in a short round tube. If it is not an oxidation process, carbon fiber can also be used. The manufacturing process of the fiber catalyst is complicated and costly.
