Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia



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Bog'liq
Efficient Adsorbent-Desiccant Based on Aluminium O

Appl. Sci.
2021
,
 11
, 2457 
19 of 23 
NaX adsorbent are higher than those of the aluminium oxide adsorbent, and the protec-
tive action time of the layers of these adsorbents is comparable. However, at a higher 
pressure (0.3 ÷ 0.6 MPa), the situation changes, and the adsorption capacity and protec-
tive action time of the developed Al
2
O
3
adsorbent become higher. Under these condi-
tions, the use of the developed aluminium oxide adsorbent, considering its higher re-
sistance to moisture, lower cost and lower regeneration temperature, is preferable as 
compared to zeolite-based analogues during dehydration under pressure. 
Along with the equilibrium characteristics of adsorbents (adsorption capacities), an 
important role belongs to the adsorption kinetics, which take into account the dynamics 
of adsorption and diffusion of water vapour in individual granules of the absorbent and 
the rate of filling the volume of these granules. Since the adsorbent granules used in in-
dustrial conditions are usually shaped like cylinders and spheres of various sizes, it is 
important to study the influence of the grain size on the adsorption kinetics. The exper-
imental results on the kinetics of water vapour adsorption on active aluminium oxide 
have been described by the authors of [84–86]. 
The influence of the granule size on the water vapour absorption kinetics for the 
fractions of the studied sample of highly efficient aluminium oxide (0.25–0.5 mm and 0.5–
1.0 mm and a granule size of 3.7 × 6.0 mm) was studied by the authors of [86]. It has been 
shown that when the fraction size is more than 0.25–0.5 mm, the rate of water vapour 
adsorption decreases, which is due to the influence of internal diffusion. This happens 
due to the presence of small mesopores (3 ÷ 7 nm) in the aluminium oxide adsorbent. 
Mathematical simulation of mass transfer rates based on a quasi-homogeneous model 
has been performed. The mathematical simulation made it possible to obtain a quantita-
tive assessment of parameters such as the absorption rate constants and to obtain the ef-
ficient water diffusion coefficient inside the grain, the value of which was 1.2·10


m
2
/s. 
The proposed mathematical model describes quite well the experimental data on the ki-
netics of water vapour adsorption on a highly active aluminium oxide adsorbent and can 
be used for modelling the absorber. 
In this way, the data presented in this section indicate the important role of the ac-
id-base sites of the surface of aluminium oxides in their adsorption characteristics. By 
means of methods such as heat treatment or chemical modification, it is possible to con-
trol the variations in the strength and concentration of active surface sites and other 
characteristics of AO. As a rule, this type of impact changes the specific surface value, 
pore size distribution, total pore volume and adsorption characteristics of the material. 
The adsorption capacity of aluminium oxide in relation to water vapour can be increased 
by introducing up to 3 mass.% of alkaline cations (Na, K), increasing the concentration of 
strong basic sites on the surface. 

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