Catalyst preparation method
Source: | Author:weitongch | Published time: 2019-05-09 | 868 Views | Share:
Each method of manufacturing a catalyst is actually composed of a series of operating units. For convenience, people have named the key and distinctive operating unit as the name of the manufacturing method
Each method of manufacturing a catalyst is actually composed of a series of operating units. For convenience, people have named the key and distinctive operating unit as the name of the manufacturing method. The traditional methods are mechanical mixing method, precipitation method, dipping method, solution evaporation method, hot melting method, leaching method (leaching method), ion exchange method, etc. The new methods currently developed are chemical bonding method, fiberization method, etc. .

1. Mechanical mixing method
Add two or more substances into the mixing equipment and mix. This method is simple and easy to implement, for example, the manufacture of conversion-absorption desulfurization agent is to measure 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) Continuously add to a turntable with adjustable rotation speed and inclination, at the same time, spray the metered water and powder to mix and form a ball with a uniform diameter. The ball is then dried and roasted to be 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 the product composition and to manufacture high-quality catalysts. A common method is to add a precipitating agent (such as sodium carbonate and calcium hydroxide) to one or more metal salt solutions, and then obtain the final product after precipitation, washing, filtering, drying, shaping, and roasting (or activation).

3. Dipping method
Immerse the 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, the solution enters the pores of the carrier. The carrier is drained, and after drying and calcination, a layer of solid metal oxide or its salt is attached to the inner surface of the carrier.

4. Spray steam drying
It is used to prepare catalyst for fluidized bed with particle diameter of tens to hundreds of microns. For example, in the manufacture of metaxylene fluidized bed ammonia oxidation catalyst for m-dicarbonitrile, firstly mix the aqueous solution of metavanadate and chromium salt with a given concentration and volume, then mix it with a quantitative amount of newly prepared silica gel and pump it in In the spray dryer, after being atomized by the spray head, the moisture is evaporated to dryness under the action of the hot air flow, and the material forms a microsphere catalyst, which is continuously led out from the bottom of the spray dryer.

5. Hot melt method
The hot melting method is a special method for preparing certain catalysts. It is suitable for a few catalysts that have to go through the smelting process. In order to smelt each component by means of high temperature conditions, it is called a uniformly distributed mixture. With the necessary subsequent processing, it can be prepared. A catalyst with excellent performance.

6. Dipping method
From a multi-component system, a suitable liquid agent (or water) is used to remove part of the material to make a catalyst with a porous structure. For example, in the manufacture of skeleton nickel catalysts, a certain amount of nickel and aluminum are melted in an electric furnace, and the molten material is cooled to become an alloy. The alloy is broken into small particles and soaked with an aqueous solution of sodium hydroxide, and most of the aluminum is dissolved (sodium meta aluminate is generated ), that is, to form porous highly active framework nickel.

7. Ion exchange
Some crystalline materials (such as synthetic zeolite molecular sieve) metal cations (such as Na) 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 the other metal ions with Na under the controlled concentration, temperature, and pH conditions.

New methods in development
① The chemical bond is legal. This method is now widely used in the manufacture of polymerization catalysts. The purpose is to solidify the homogeneous catalyst. The carrier that can be chemically bonded to the transition metal complex has certain functional groups on the surface (or the functional groups are connected after chemical treatment), such as -X, -CH2X, and -OH groups. This kind of carrier is reacted with phosphine, arsine or amine to make it phosphonated, 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 It is possible to prepare chemically bonded solid-phase catalysts, such as the support of Ziegler-Natta catalysts for propylene bulk liquid phase polymerization.
② Fibrosis method. Used in the manufacture of precious metal-containing supported catalysts. For example, borosilicate is drawn into glass fiber wire, corroded with concentrated hydrochloric acid solution to become a porous glass fiber carrier, and then impregnated with chloroplatinic acid solution to carry platinum component. According to the practical situation, the fiber catalyst is pressed into various shapes and the 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 the cost is high.