Each method of catalyst manufacturing is actually composed of a series of operational units. For convenience, the names of key and distinctive operational units are used as the names of manufacturing methods. Traditional methods include mechanical mixing, precipitation, impregnation, solution evaporation, thermal fusion, leaching (leaching method), ion exchange, etc. New methods that have been developed include chemical bonding and fiberization.
1. Mechanical mixing method
Add two or more substances into a mixing device for mixing. This method is simple and easy to implement. For example, in the manufacture of conversion-absorption desulfurizers, powdered materials of active components (such as manganese dioxide, zinc oxide, and zinc carbonate) and a small amount of binder (such as magnesium oxide and calcium oxide) are metered and continuously added into a rotating disc with adjustable speed and inclination. At the same time, metered water is sprayed in, and the powdered materials are mixed and bonded by rolling to form spheres of uniform diameter. These spheres are then dried and calcined to produce the finished product.
2. Precipitation method
This method is used to manufacture catalysts that require high dispersibility and contain one or more metal oxides. When manufacturing multi-component catalysts, suitable precipitation conditions are crucial for ensuring the uniformity of product composition and producing high-quality catalysts. The usual method involves adding a precipitant (such as sodium carbonate or calcium hydroxide) to one or more metal salt solutions, followed by precipitation, washing, filtration, drying, shaping, and calcination (or activation) to obtain the final product.
3. Impregnation method
Immerse a carrier with high porosity (such as diatomaceous earth, alumina, activated carbon, etc.) in a solution containing one or more metal ions, maintain a certain temperature, and allow the solution to penetrate into the pores of the carrier. Drain the carrier, dry it, and calcine it, so that a layer of the desired solid metal oxide or its salt adheres to the inner surface of the carrier.
4. Spray evaporation method
Used for the manufacture of catalysts for fluidized beds with particle diameters ranging from tens to hundreds of micrometers. For example, in the manufacture of catalysts for the fluidized bed ammonoxidation of m-xylene to m-xylene cyanide, a solution of metavanadate and chromium salt with a given concentration and volume is first thoroughly mixed, and then mixed with a quantitatively prepared silica gel. The mixture is pumped into a spray dryer, where it is atomized by a nozzle. The water evaporates under the action of hot airflow, and the material forms microspherical catalysts, which are continuously discharged from the bottom of the spray dryer.
5. Hot melting method
The hot-melting method is a special technique for preparing certain catalysts, applicable to a limited number of catalysts that must undergo a melting process. The purpose is to utilize high-temperature conditions to melt the individual components into a uniformly distributed mixture. Coupled with necessary subsequent processing, this method can produce catalysts with excellent performance.
6. Immersion method
From a multi-component system, a portion of the material is removed using appropriate liquid reagents (or water) to produce 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 melt cools down to form an alloy. The alloy is crushed into small particles and soaked in an aqueous solution of sodium hydroxide, where most of the aluminum is leached out (to form sodium metaaluminate), thus forming a porous, highly active skeletal 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. When added to a solution containing ions of other metals (such as rare earth elements and certain precious metals), under appropriate conditions of concentration, temperature, and pH, the other metal ions can be exchanged with Na.