# Ammonia Gas Adsorption in Fixed Bed and Fluidized Bed Using Bentonite Particles
## 3 Results and Discussion
### Ammonia Adsorption
#### 3.3.2 Adsorption Kinetics  
According to the dynamic particle studies from previous publications [46; 47; 48; 49; 50; 51; 52; 53; 54; 55], the minimum fluidization velocity (\(U_{m\!f}\)) is considered to be equal to 0.27 m/s for the particle size \(\overline{\mathrm{d}}_{\mathrm{p}}=750\,\upmu\)m, and the minimum fluidization velocity (\(U_{m\!f}\)) is equal to 0.67 m/s for the particle size \(\overline{\mathrm{d}}_{\mathrm{p}}=1500\,\upmu\)m, in order to highlight the influence of the gas velocity formed from ammonia and air. The first ammonia absorption took place in a fixed bed (\(U_{g}=0.6\,\times\,U_{m\!f}\)) and the following ammonia retentions in fluidized bed conditions, i.e., at the initial fluidization, when \(U_{g}=U_{m\!f}\), and at the fluidization with small bubble gas, when \(U_{g}=1.4\,\times\,U_{m\!f}\). The ammonia adsorption capacity on bentonite particles was measured until bed saturation, \(C/C_{0}\)-1. Ammonia adsorption tests were performed on sodium bentonite particles previously prepared in small particles and characterized under different gas-particle contact conditions, as illustrated in Figure 9.  
Analyzing the ammonia adsorption curves (Figure 9a), an increase in the adsorption capacity can be observed, recorded by the sodium bentonite particles, with the increase in the gas velocity (\(U_{g}\)) under the conditions mentioned above. At equilibrium, in the case of particle sizes with \(\overline{\mathrm{d}}_{\mathrm{p}}=750\,\upmu\)m, the ammonia adsorption capacity varies at saturation from 0.326 mmol NH\({}_{3}\)/g in a fixed bed to 0.436 mmol NH\({}_{3}\)/g in incipient fluidization and to 0.553 mmol NH\({}_{3}\)/g in a homogeneous fluidized bed. In a fixed bed, it can observe that the bed saturation occurs after 455 s, and in a fluidized state, the bed saturation occurs immediately, after 115 to 154 s.  
A similar variation of the ammonia adsorption capacity occurs in the case of particle sizes with \(\overline{\mathrm{d}}_{\mathrm{p}}=1500\,\upmu\)m (Figure 9b); in a fixed bed, the value is 0.357 mmol NH\({}_{3}\)/g with bed saturation after 514 s. Under incipient fluidization (\(U_{g}=U_{m\!f}\)), the ammonia adsorption capacity is 0.518 mmol NH\({}_{3}\)/g and particle bed is saturated after 150 s.  
\begin{table}
\begin{tabular}{c c c c} \hline
**No. ** & **Adsorbent Particles** & **Average Particle Size** (\(\overline{\mathrm{d}}_{\mathrm{p}}\), \(\upmu\)m)** & **Gas Velocity, (\(U_{g}\), m/s)** & **Total Flow Rate, (\(Q_{T}\), L/s)** \\ \hline
1. & & & 0.6 \(\times\,U_{m\!f}\) & 0.3341 \\ \hline
2. & & 750 & \(U_{m\!f}\) & 0.5436 \\ \hline
3. & & & 1.4 \(\times\,U_{m\!f}\) & 0.7525 \\ \hline
4. & Sodium bentonite & & 0  
In a homogeneous fluidization bed, when \(U_{S}=1.2\times U_{m\!f}\), the ammonia adsorption capacity is 0.763 mmol NH\({}_{3}\)/g and the bed saturation happens immediately, after 125 s.  
The influence of ammonia adsorption capacity depending on the gas-particle contact technique for aluminum bentonite particles is shown in Figure 10.  
The kinetic curve shows that the particles with \(\overline{\mathrm{d}}_{\mathrm{p}}=750\,\mathrm{\upmu m}\) (Figure 10a) exhibit, in the fixed bed, a lower value of ammonia adsorption capacity of 0.409 mmol NH\({}_{3}\)/g at bed saturation after 742 s. In the case of incipient fluidization, the ammonia adsorption capacity is 0.572 mmol NH\({}_{3}\)/g and the particle bed saturation occurs after 245 s. When \(U_{S}=1.4\times U_{m\!f}\), the ammonia adsorption capacity registered is 0.804 mmol NH\({}_{3}\)/g and the bed saturation happens after 235 s.  
The aluminum bentonite particles with \(\overline{\mathrm{d}}_{\mathrm{p}}=1500\,\mathrm{\upmu m}\) (Figure 10b) exhibited the highest values for ammonia adsorption capacity at saturation.