# Ammonia Gas Adsorption in Fixed Bed and Fluidized Bed Using Bentonite Particles
## 1 Introduction  
Intense industrial activities are one of the most important current problems because large quantities of pollutants, coming from different sources, are generated in the atmosphere with a direct influence on environmental degradation and the population's health. One of the strategies in environmental protection consists of developing some adsorbentmaterials that allow the retention of such toxic gases before releasing them into the atmosphere [1]. High levels of harmful gases are present in the environmental medium from chemical factories such as carbon monoxide, hydrogen chloride, chlorine, hydrogen sulfide, nitrogen oxide, ozone, ammonia, etc. [2,3]. Ammonia is a relatively strong base and the most useful chemical in modern society. It can be used as a fertilizer (anhydrous ammonia, aqua ammonia and urea), as a precursor to nitrogenous compounds, as a cleaner, in plastic products, fuels, explosive production, etc. [4]. A large amount of ammonia has increased dramatically in the atmosphere due to these industrial exhaust emissions from livestock farming as domestic pollutants and from agriculture [5,6]. Ammonia is a very toxic, corrosive, flammable and explosive substance under certain conditions. Ammonia gas produces undesirable odors, which cause, in humans, severe burning of the eyes, skin and respiratory irritation at a concentration as low as 50-100 ppm [7], and at higher quantities, death is induced in a few minutes [7,8]. Adsorption is one of the techniques that can be used to capture ammonia gas and to control the concentration in the released gas flow [2]. Various adsorbents were developed for environmental remediation, including carbon-based adsorbent (lignite, biochar, activated carbon [8] and resin), metal-organic framework, mineral clays (bentonite, zeolite) and their modified forms (nanomaterials) [9]. In terms of the structural properties, adsorptive characteristics and environmental applications, bentonite and their derivatives [10, 11, 12] may be good candidates regarding gas-particle contact and to solve the problem of controlling the ammonia concentration in air [13]. Bentonites are mineral clays that are found in nature with no toxic effects on ecosystems and a low price of purification. These are components of soils, valuable in many branches of industries at the local level (chemicals, food processing, construction, pharmaceutical and cosmetic products, ceramics, etc.) [14], composed more precisely of at least 50% montmorillonite, a phyllosilicate of the smectites family. This smectite family consists of a 2:1 layer phyllosilicate constituted by an octahedral sheet containing Al\({}^{3+}\), Mg\({}^{2+}\) or Fe\({}^{2+/3+}\) ions between two tetrahedral silica sheets [1,15], which shows the ability to swell by incorporating water or other molecules in the interlayer regions, like ammonia molecules [16]. Sodium bentonite in its natural or chemically modified state is used in this research as an adsorbent because it has the following properties: adsorption and ion exchange capacity [17, 18, 19, 20], wide surface area and permanent porosity [21], acid-base character [12, 13, 14, 15, 16, 17, 18, 19, 20], and regeneration capacity after repeated adsorption processes [17]. Aluminum pillared bentonite is the modified adsorbent used for ammonia adsorption in different methods of gas-particle contact. This material was made in the laboratory by the pillaring method with the following steps: bentonite hydration and pillaring agent preparation by hydrolysis, bentonite suspension intercalation with the pillaring agent that contains aluminum polyhydroxocations [27, 28, 29], repeated washings and filtration, drying, calcination [30, 31, 32, 33], and trituration in small particles. However, gas-particle contact [34] involving sodium bentonite and aluminum pillared bentonite as adsorbents for ammonia adsorption capacity determination presents a major challenge in a static regime (in fixed bed or expanded bed) and in a dynamic regime (fluidized bed).