Activated alumina is an excellent desiccant, and the alumina use as a desiccant should have a large specific surface area. Spherical particles with diameters of 3-5 and 6-8mm are widely use. Activated alumina can adsorb a large amount of water vapor, and alumina saturated with water can easily reuse by drying to remove physically adsorbed water. In addition to dry air, activated alumina is also to remove moisture from various gases and organic liquids, such as for alcohol dehydration. Activated alumina is also a good adsorbent for the oxides of ammonia, hydrogen fluoride, and arsenic. It has been widely use as a defluoriner for high fluoride drinking water and in the acid production industry. So, how to produce and manufacture activated alumina?

There are two types of raw materials for the production of activated alumina, one is “fast powder removal” produced from trihydrate alumina or Bayer alumina, and the other is pseudo boehmite produced from aluminate or aluminum salt or both.

The Raw Material

Alumina is the main raw material for producing activated alumina balls, as FCA in foreign countries. In China, called “fast powder removal” because it is an alumina powder produced by rapid dehydration method. Fast powder removal “is a mixture of alumina and ρ – alumina, with varying concentrations due to differences in production conditions. The key technology of alumina lies in rapid dehydration, usually carry out in fluidized bed reactors, controlled by combustion gas or liquid to regulate the bed temperature. Using a conical reactor, dry and crushed aluminum hydroxide is added from the side and rapidly roasted in a fast dehydration furnace for 0.1-1 second to produce a mixture of aluminum oxide.

The production method of pseudo boehmite: Artificially produced monohydrate alumina and trihydrate alumina cannot be as desiccants, adsorbents, catalysts, and catalyst carriers due to their low specific surface area, small pore volume, and low activity. Therefore, it is necessary to process monohydrate alumina or trihydrate alumina into pseudo boehmite. Pseudo boehmite has high specific surface area, large pore volume, large pore size, and high activity, making it suitable for use as a desiccant, adsorbent, catalyst, and catalyst carrier in fields such as petrochemicals, fertilizers, and exhaust gases.

Four Production Method

1. Acid production of pseudo boehmite: pseudo boehmite obtain by adding precipitant ammonia water to a solution of aluminum trichloride, follow by precipitation, filtration, washing, and drying. Preparation of alumina using aluminum chloride and ammonia water as raw materials, with a focus on investigating neutralization temperature pH、 The influence of reactant concentration and aging conditions on pore structure. The advantage of this production method is that it can produce pseudo boehmite with high pore volume and high specific surface area, but the disadvantage is that the cost of producing pseudo boehmite is relatively high;
2. Production of pseudo boehmite by alkaline method: In order to cooperate with the replacement of catalysts in fertilizer plants, research and production of fertilizer catalysts have tackled. The technical specifications of the developed alumina carrier are: apparent density of 0.55-0.65kg/L, alumina mass fraction of 94.0% -95.5%, sodium oxide mass fraction of 0.01% -0.03%, specific surface area of 175-250m2/g, pore volume of about 0.50mL/g, pore size of 3-6nm, pore volume of 0.7-1mL/g, pore size distribution of 10-50nm, and a few pore sizes of 40nm. It is a superior product with multiple applications;

Production of Pseudo Boehmite

1. Production of pseudo boehmite by double aluminum method: The so-called “double aluminum method” uses aluminum sulfate and sodium metaaluminate to react in parallel to produce pseudo boehmite, and uses aluminum sulfate and sodium metaaluminate as raw materials to prepare macroporous pseudo boehmite and alumina. The battle team studied the concentration of raw materials, reaction temperature pH、 Experimental conditions such as aging time, aging temperature, and water washing. The pore volume, specific surface area, and pore size of the prepared pseudo boehmite are all superior to the technical indicators of the alkaline method. The double aluminum method for preparing pseudo boehmite is a widely-use method both domestically and internationally, which saves acid and alkali comparing to the alkaline method, and has a lower cost;
2. Preparation of pseudo boehmite by carbonization method: The preparation of pseudo boehmite by carbonization method relies on the sintering process to produce alumina, using intermediate products NaAlO2 solution and CO2 as reaction materials. The process is simple and relatively low-cost. The waste liquid in production can return to the alumina production process for reuse, with almost no waste discharged and minimal environmental pollution. It is a competitive and promising method. The quality, raw material concentration, and gelation temperature of the carbonized method for preparing pseudo boehmite products pH、 The aging temperature and time, as well as the drying temperature of the wet filter cake, are related to many production conditions. The shortcomings of the carbonization method for producing boehmite are the presence of impurities in the product, low purity, and high water consumption for sodium washing.