# Efficient Adsorbent-Desiccant Based on Aluminium Oxide
## 2 Methods of Obtainment of Aluminium Oxide Used in Industry
### Methods of AO Otainment
#### 2.2.3 Rapid Calcination of Baeyer Hydrate (Gibbsite)  
Method of Thermochemical Activation (TCA)  
Gibbsite can be calcined rapidly by pulsed heating at the dehydration temperature in apparatuses (the method of thermochemical activation by flue gases--thermochemical activation and thermochemical decomposition in catalytic heat generators) or by mechanochemical activation (MCA) in mills with high power rating. The essence of the TCA method is that the initial material--gibbsite--is activated by heated air in the pneumatic transport mode within a few seconds. The best result is achieved when combining TCA with MCA, as the TCA product is subjected to additional fine grinding. The resulting amorphous product has a large specific surface and is characterised by high reactivity. In the presence of water, it hydrolyses easily, and is accompanied by the formation of pseudoboehmite in the neutral environment and bayerite in the alkaline environment. The amorphized powder can be formed in advance before the crystallisation stage by pelletising on plate granulators into spherical particles, which then crystallise in a steam-air medium into high-strength balls of pseudoboehmite and then into those of aluminium oxide of mainly the \(\gamma\)-phase [34; 35]. \[2\text{Al(OH)}_{3}\to\text{Al}_{2}\text{O}_{3}+3\text{H}_{2}\text{O}.\]  
The TCA method is widely used, including for the multi-tonnage production of the so-called flash product (thermally activated aluminium hydroxide), which is a raw material for the preparation of aluminium oxide materials of various applications. However, it has serious drawbacks:  
* Dusty gas emissions
* Probability of contamination of TCA products due to impurities in the fuel and products of its incomplete combustion
* Instability of the operating mode, resulting in poor reproducibility of the physical and chemical properties of the flash product
* Low efficiency of energy use of the heat carrier and, consequently, high specific energy consumption--more than 10 kJ/g of raw materials  
Centrifugal Thermal Activation (CTA)  
In the light of the disadvantages of the CTA method, a new energy-saving technology has been developed to increase the reactivity of powder materials under the action of centrifugal force in centrifugal flash reactors [36; 37; 38], which is called centrifugal thermal activation (CTA). The appearance of the centrifugal reactor \"TSEFLAR\({}^{\text{TM}}\)\" of the drum type is shown in Figure 2.  
The main difference between CTA and TCA processes is that, during thermal activation, the powder is in contact for 1-2 s with a rotating and heated solid heat-transfer agent under the action of centrifugal forces. Conditions of the CTA process such as temperature, contact time, etc. can be varied in a wide range, thereby changing the decomposition depth of gibbsite and the properties of the obtained products. CTA products have a developed surface and disordered and heterogeneous mesoporous structure from which hydroxides and oxides of aluminium of different modifications can be formed, including during its subsequent hydration and heat treatment. The authors of [39] showed that the flash product, calcined at 400 \({}^{\circ}\)C, represents an almost amorphous phase and contains only a small amount of crystallised boehmite. An increase in the temperature during processing of this material leads to the crystallisation of the amorphous phase, accompanied by the formation of \(\eta\)-Al\({}_{2}\)O\({}_{3}\), whose proportion increases and reaches 60% at 900 \({}^{\circ}\)C.  
The phase composition of the CTA product of gibbsite at T \(>\) 400 \({}^{\circ}\)C and the contact time of \(\sim\)1.5 s is approximately as follows: Gibbsite (0-20%) + boehmite (0-10%) + pseudoboehmite (0-20%) + amorphous phase (the rest is up to 100%). As a result of the thermal shock treatment, the content of chemically bound water in the samples decreases to 5-15%, and the specific surface increases from 2-5 to 100-250 m\({}^{2}\)/g (T = 300 \({}^{\circ}\)C) due to the formation of a branched system of micropores.