# Ammonia Gas Adsorption in Fixed Bed and Fluidized Bed Using Bentonite Particles
## 2 Materials and Methods
### Ammonia Adsorption and Desorption Procedure  
The study of ammonia adsorption isotherms and kinetics in a fixed bed [35] and in a fluidized bed [33] on sodium bentonite particles and aluminum pillared bentonite particles has been carried out in an experimental installation shown in Figure 1a. After the adsorption process, the materials were subjected to the desorption of ammonia molecules from the particles with the help of nitrogen vapors by thermo-desorption. The particles saturated in ammonia were found in the column in a fixed bed to verify the recycling possibility and regeneration without major structural damage. The experimental thermo-desorption installation is shown in Figure 1b. The experimental installations used for ammonia adsorption-desorption are composed of a Pyrex transparent column with internal diameter of 5 \(\times\) 10\({}^{-2}\) m provided with a graduated scale for measuring the particle bed height. On the inlet of the mixed gases, a  
Figure 1: Experimental installations. 1—adsorption column; 2—graduated scale; 3—particle bed; 4—porous support; 5—mixed ammonia and air; 6—nitrogen gas; 7—desorption column; 8—electrical resistance. porous plate can be found with pore size diameter of 60-100 \(\upmu\)m for the uniform distribution of gases, which plays a supporting role for the particle bed. At the top of the column, a filter is placed with a pore size diameter of 0.44 \(\upmu\)m to avoid fine particle transport during fluidization. The adsorption installation, as shown in Figure 1a, is equipped with three gas routes, one for ammonia gas with 99.95 purity grade, one for compressed air and the last route for gases mixing (ammonia and air). Two gases passed separately through two Brooks Sho-Rate flow meters: one for ammonia gas from the bottle with flow range from 0 to 2.5 L/min and another for compressed air with flow range from 0 to 60 L/min, which passes through a granular drierite column to absorb the humidity from the air. The gases meet in a mixing system to obtain the known initial ammonia concentration (C\({}_{0}\)) before starting the adsorption tests. Concentrations are expressed in parts per million (ppm). Ammonia adsorption capacity was measured until saturation of the bed particles on inlet/outlet of the adsorption column using an Agilent Technologies 3000A 4-Channel Micro GC G2802A, Markham, ON, Canada. The non-adsorbed ammonia was removed and neutralized into a gas scrubber that contained an acid solution and the saturated particles were placed in the desorption installation for regeneration. Ammonia test results were determined by reference to the calibration curve made before starting the adsorption experiments. Adsorption ammonia capacity in a fixed bed and fluidized bed under saturation conditions was calculated using specific equations [17; 35; 44] and expressed in mmol NH\({}_{3}\)/g of bentonite. The variable parameters for testing the ammonia adsorption capacity are average particle diameter, \(\overline{d}_{p}\), gas velocity, \(U_{g}\), and total gas flow (ammonia and air), \(Q_{T}\). The parameters kept constant during the adsorption tests and their approximate values are adsorbent mass at 200 g, geometric ratio (\(L_{0}/D\)) at 2 and initial ammonia concentration at 3800 ppm. All ammonia adsorption experiments were carried out at ambient temperature in different gas-particle contact conditions: in a fixed bed or packed bed, under incipient fluidization and homogeneous fluidization with small gas bubbles in the bed. The desorption installation is composed of a Pyrex transparent column with an internal diameter of 3.5 \(\times\) 10\({}^{-2}\) m, a porous support, one trace for nitrogen gas and cylindrical electrical resistance for heading the particle bed, as presented in Figure 1b. The experimental parameters in ammonia desorption tests are the following: bed particles height: 1, heating temperature: 300 \({}^{\circ}\)C, time contact: 2 h and the dry nitrogen flow: 0.1 L/min.