Adsorption of ammonia using mesoporous alumina prepared by a templating method

Abstract

Ammonia, NH3, is a key chemical widely used in chemical industries and a toxic pollutant that impacts human health. Thus, there is a need for the development of effective adsorbents with high uptake capacities to adsorb NH3. An adsorbent with a high surface area and a small pore size is generally preferred in order to have a high capacity for the removal of NH3. The use inorganic nanoporous materials as gas adsorbents has increased substantially and emerged as an alternative to zeolite and activated carbon. Herein, mesoporous alumina (MA) was prepared and used as an NH3 adsorbent. MA showed good pore properties such as a uniform pore size and interlinked pore system, when compared to commercial adsorbents (activated carbon, zeolite, and silica powder). MA has free hydroxyl groups, serving as useful adsorption sites for NH3. In an adsorption isotherm test, MA exhibited 4.7-6.5 times higher uptake capacities for NH3 than commercial adsorbents. Although the larger surface areas of adsorbents are important features of ideal adsorbents, a regular and interlinked adsorbent pore system was found to be a more crucial factor to adsorb NH3.

Bead-Shaped Mesoporous Alumina Adsorbents for Adsorption of Ammonia

“…For the ammonia adsorption, NH 3 (5000 ppm balanced with N 2 ) and dried N 2 (99.999%) were used as an adsorbate gas and a carrier gas, respectively. Adsorption experiments were conducted by using a home-made adsorption system using a fixed-bed adsorbent column [18]. The experimental apparatus consisted of a stainless-steel adsorption column with adsorbent bed, mass-flow controller, six-port valve connected with a sample loop, and an ammonia gas detector (GAS TIGER 6000, Wamdi; China) for detecting the outlet NH 3 concentration.…”

“…Kim and co-workers also compared the adsorption capacity of mesoporous alumina, commercial silica, zeolite and activated carbon. The mesoporous alumina showed the highest calculated equilibrium capacity (214 mg/g) of ammonia adsorption at room temperature while other adsorbents, such as commercial silica (33 mg/g), zeolite (43.3 mg/g), and activated carbon (45.8 mg/g) showed relatively low values [18].…”

“…Kim and co-workers also compared the adsorption capacity of mesoporous alumina, commercial silica, zeolite and activated carbon. The mesoporous alumina showed the highest calculated equilibrium capacity (214 mg/g) of ammonia adsorption at room temperature while other adsorbents, such as commercial silica (33 mg/g), zeolite (43.3 mg/g), and activated carbon (45.8 mg/g) showed relatively low values [18].In order to achieve high performance of NH 3 adsorption, adsorbent materials must have favorable physicochemical characteristics, such as large surface area and acidic adsorption sites, since a large amount of basic ammonia should be adsorbed on the surface of adsorbents [21]. Mesoporous alumina, as it has a large surface area, large pore size, and high acidity, should be a candidate as an adsorbent for ammonia removal.…”

“…Among the above techniques, the adsorption of ammonia on solid adsorbents has been widely studied because of the simple operation of the whole process and the easy regeneration of this valuable gas. To date, various porous materials, including activated carbon, zeolite, alumina, and a metal-organic framework (MOF), have been demonstrated as adsorbents for efficient ammonia removal, and there has been remarkable progress on adsorption of ammonia in terms of either adsorption capacity or adsorption kinetics [5,6,[15][16][17][18][19]. Helminen et al studied the ammonia adsorption capacities of traditional inorganic adsorbents including activated carbon, alumina, silica gel, and zeolite materials.…”

“…They obtained better adsorption capacity of porous alumina (3.13 mmol/g) and observed that both the porous structure and the acidic surface of alumina are beneficial for the adsorption of base ammonia molecules. Kim et al also synthesized mesoporous alumina and compared its adsorption capacity with those of other adsorbent materials in a lab-scale adsorbent column [18]. The mesoporous alumina had the highest capacity among the other adsorbents, including commercial silica, zeolite, and activated carbon.When people developed new adsorbent materials, they tested adsorbents as a fine powder for evaluating their intrinsic adsorption capacity [22], although a practical adsorption column consisted of shaped adsorbent pellets.…”