There are many methods for preparing alumina

Alumina carrier is the most widely used catalyst carrier in the chemical industry. The current development trend is mainly reflected in: developing a low-cost, green and environmentally friendly preparation process, controlling the pore size and pore size distribution of alumina, and improving the thermal stability of alumina , the preparation of nano-alumina and so on.

Due to the wide application of activated alumina and the complex changes in structure and morphology, the research on the preparation and properties of γ-Al2O3 as a catalyst carrier is still an active field so far. The current research progress on alumina carrier is mainly reflected in the following aspects:

Develop a low-cost, green and environmentally friendly preparation process

There are many methods for preparing alumina. According to different raw materials, the following preparation methods are commonly used:

①　Preparation from aluminum salts or aluminates, including alkali precipitation (ie, acid method), that is, hydrated alumina is precipitated from aluminum salt solution with alkali and acid precipitation (ie, alkali method), that is, acid is used from aluminate. Alumina monohydrate is precipitated in the solution;

②　Prepared from aluminum alkoxide;

③　Prepared from aluminum amalgam. When the alumina is prepared by the acid method, the purity of the raw material aluminum salt is very high.

The preparation of pseudo-boehmite by carbonization is a relatively young method. It uses carbon dioxide and sodium metaaluminate to react to prepare alumina. This method is simple to operate, pollution-free and low-cost, and is a very popular method.

In fact, the carbonization method is also one of the methods for preparing alumina by the alkaline method, which is to pass CO2 into the NaA102 solution for precipitation, because this method uses the intermediate product NaA102 solution and CO2 waste gas as the reaction raw materials, which is the lowest cost process route, and It has less pollution to the environment and is a more promising method, so there are many studies on this method, so it is called the carbonization method. Alumina prepared with CO2 sodium carbide aluminate solution can be made into activated alumina with lower Na20. By controlling the conditions of carbonization temperature, carbonization speed and endpoint pH value, alumina with different pore volumes and pore sizes can be obtained. Moreover, the alumina prepared by the carbonization method also has the advantages of large specific surface area, high purity, good corrosion resistance and high catalytic activity.

    There are four kinds of reactions in the gel formation process of NaA102-CO2 method: the rapid neutralization reaction of NaOH and CO2, the NaA102

The neutralization reaction with CO2, the spontaneous hydrolysis reaction of NaA102 and the composite reaction of hydrated alumina and Na2CO3, namely

               2NaOH+CO2→Na2CO3+H20

               2NaA102+C02+3H20→2Al(OH)3+Na2CO3

               NaA102+2H20→Al(OH)3+NaOH

               Na2CO3+2C02+2A1(OH)3→2NaAl(CO3)(OH)2+H20