Adsorption Equilibrium and Effective Diffusivity in Cylindrical Alumina Particles Impregnated with Calcium Chloride (original) (raw)
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Turkish Journal of Chemistry, 2013
The adsorption equilibrium of water vapor on different adsorbent materials has been studied. Small grains of commercial activated carbon and alumina, with a diameter of d g = 1.5 × 10 −3 m, were impregnated with a hygroscopic salt (calcium chloride) to improve the performance of these materials. The main characteristics of the new composite materials were obtained by adsorption/desorption of nitrogen at 77 K and salt distribution on the adsorbent surface was shown using scanning electron microscopy. The adsorption equilibrium isotherms of water vapor were measured by a gravimetric system at 2 different temperatures in the case of alumina and impregnated alumina (303 K and 313 K) and 1 temperature (303 K) in the case of activated and impregnated carbon. The impregnated material samples presented the highest adsorption capacity on the entire pressure range. The experimental points obtained for the activated carbon and alumina and the impregnated alumina were fitted with the Dubinin-Astakhov equation while the Langmuir equation was used to fit the impregnated carbon data.
Study the Feasibility of Alumina for the Adsorption of Metal Ions from Water
The present work describes the adsorption of Ba 2+ and Mg 2+ ions from aqueous solutions by activated alumina in single and binary system using batch adsorption. The effect of different parameters such as amount of alumina, concentration of metal ions, pH of solution, contact time and agitation speed on the adsorption process was studied. The optimum adsorbent dosage was found to be 0.5 g and 1.5 g for removal of Ba 2+ and Mg 2+ , respectively. The optimum pH, contact time and agitation speed, were found to be pH 6, 2h and 300 rpm, respectively, for removal of both metal ions. The equilibrium data were analyzed by Langmuir and Freundlich isotherm models and the data fitted well to both isotherm modes as indicated by higher correlation of determination R 2 > 0.87 in both single and binary systems. Pore diffusion model for batch adsorption was used to predict the concentration decay curve for adsorption of Ba 2+ and Mg 2+ onto activated alumina. There was a good agreement between the experimental data and the predicted decay curves using pore diffusion model.
Microporous and Mesoporous Materials, 2010
This paper reports a target-oriented synthesis of the compact layer of alumina and its modification by a calcium chloride. The layer preparation procedure with the use of binder has been developed which makes it possible to widely vary the layer porous structure. The effect of the layer structure and composition on water vapor transport in it has been studied by NMR imaging. The effects of the size of the primary alumina grains, the amounts of the binder and the guest salt on the porous structure of the layer and the mechanism of vapor transport in the layer have been investigated. Variation of these parameters has been shown to alter the relative contributions of the diffusional resistances in the intergrain macropores and in the intragrain mesopores and to permit an intentional transition between the different diffusional regimes of water sorption. If the sorption rate is limited by the diffusion of water in the intergrain voids, an adsorption front is formed in the sample and is propagating into the layer. The penetration depth depends on time as t 0.5 . If the water sorption in the primary grains is the slowest process, the water uptake uniformly increases over the entire layer.
Response Surface Modelling of Water Vapor Adsorption in Fixed Bed of Impregnated Alumina Grains
revistadechimie.ro
The experimental design methodology was applied for response surface modelling (RSM) of a packed-bed based pilot-scaled set-up for water vapour adsorption on impregnated alumina grains. Experimental breakthrough curves were determined. The variables considered were the ratio between the volume of adsorbent bed and air flow rate (residence time), a geometrical parameter, the ratio between adsorption column diameter and the bed height, and air relative humidity respectively. The Central Composite Design (CCD) allowed developing an empirical model as a functional relationship between breakthrough time and the considered independent variables. It was found that all considered factors have an important effect on the response. The suggested mathematical model was validated using experimental data other than those employed in the experimental design. The predicted values are in good agreement with experimental data. The present paper shows that RSM can be also employed to predict dynamic adsorption processes.
Metals, 2020
Smelter grade alumina (SGA) plays multiple roles in the Hall–Héroult process for primary aluminum production. Given its very porous nature, one major role of SGA is to adsorb toxic hydrogen fluoride (HF) in the dry scrubber. However, also because of its porous nature, SGA inevitably adsorbs ambient moisture. This paper discusses the influence of alumina properties, including pore size distribution and specific surface area, on the physical adsorption of water vapor on SGA, as well as the adsorption kinetics. The result shows that the adsorption enthalpy of moisture on SGA is in the range of 4–13 kJ/mol. The adsorption capacity increases significantly with the particle specific surface area and total pore volume. A higher adsorption temperature indicates a much faster adsorption rate but corresponds to a lower equilibrium adsorption capacity.
Journal of The Serbian Chemical Society, 2006
Active transition alumina powders were obtained by flash calcination of gibbsite in a reactor for pneumatic transport in the dilute, two-phase flow regime in the temperature interval from 883 to 943 K with a residence time between 0.4 and 0.9 s. The results of X-ray diffraction analysis confirmed that the activated alumina samples were either microcrystalline or amorphous. From nitrogen adsorption-desorption isotherms, the specific surface areas of all samples were calculated by the BET method. Using the sorption data, the fractal dimension of the surface of the alumina samples was calculated according to a modified FHH method. By application of fractal geometry, using the values of the fractal dimension of the surface and of the specific surface area, the effective surface areas of the active aluminas were calculated for the adsorption of molecules having a cross-section area greater than that of the nitrogen molecule
Equilibrium and kinetic studies of adsorption of silica onto activated alumina
Desalination, 2007
Among the treatment processes appropriate for the removal of silica, it seems that activated alumina presents more advantages than membrane separation and chemical processes. Silica removal from aqueous solution was investigated using activated alumina. The nature of silica in a solution has a significant influence on its removal. Optimization of pH for adsorption of silica was done by studying the uptake of silica over activated alumina as a function of pH. Studies were conducted to delineate the effect of adsorbent dose and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. The effect of foreign ions on adsorption such as sulfate, fluoride, nitrate and hydrogenocarbonate did not significantly decrease the amount of silica removed. Silica concentrations were obtained by absorbance measurement of the of yellow or blue-colored silicomolybdic acid. Anion species concentrations were determined by ionic chromatography.
Review of Alumina in Adsorption Processes for Emerging Pollutants
2021
Water pollution can be found in the oceans, seas, rivers and lakes which can be taken as organic pollutants or better known as emerging pollutants. Emerging pollutants (EP´s) are chemical substances that persist in the environment, these molecules are in the food chain causing risks and adverse effects for human health and the environment. EP´s are not they are discharged as effluents indiscriminately, for this reason is important to improve water treatment by the application of advanced techniques as adsorption. Adsorbents like alumina are known for their large surface area, high mechanical properties and good resistivity to thermal degradation. Aluminum oxide or alumina (Al2O3) is a solid white ceramic material which has been considered an efficient adsorbent for EP´s removal as advanced water treatment.
Journal of Colloid and Interface Science, 1978
The interaction of water vapor with highly dehydroxylated ~,alumina has been investigated at four adsorption temperatures (25, 100, 150, 200°C) by means of a mierocalorimetric-volumetric technique. A part of the water molecules irreversibly chemisorbed at room temperature became reversibly adsorbed at the higher temperatures. Three types of adsorption mechanisms were noted: physisorption, only at the lowest temperature, coordination of molecular water on the dehydroxylated surface, and dissociative adsorption, within a wide energy spectrum. The molecular process appeared to be instantaneous, while thermokinetic data showed that dissociative adsorption was always activated. Increasing temperature resulted in greater filling up of the more energetic sites in the first stages of adsorption. In particular, from 150°C on the molecules appear to possess sufficient energy to obtain the most ordered surface occupation. The equilibrium between the two chemisorbed species was displaced toward dissociation by a temperature increase: Sites available for reversible adsorption were reduced, and the total heat released at high coverage decreased. These findings are interpreted on the basis of classical thermodynamic considerations.
International Journal of Heat and Mass Transfer, 2003
A selective water sorbent (SWS) is a composite material consisting of a porous host matrix and a hygroscopic substance (commonly an inorganic salt) impregnated into its pores. This work presents an experimental investigation for the kinetics of water vapor sorption on two host materials; namely mesoporous silica gel and alumina in comparison with the two composites SWS-1L and SWS-1A formed by impregnating these two host matrices with CaCl 2 . Moreover, the kinetics of water vapor sorption on microporous silica gel have been also investigated. The measurements have been carried out on 3 g samples of loose pellets on an isothermal wall under three different operating conditions of sorption heat pumps. The results obtained evidence a remarkable increase in the differential water loading of both SWS-sorbents over their host materials. However, and due to the increased diffusion resistance to water sorption resulting from the salt impregnation, the kinetics of water sorption into the host matrices is faster than that into the two SWS-composites. Moreover, SWS-1L is found to be faster than SWS-1A in sorbing water vapor. The differential water loading on microporous silica is about twice that on mesoporous silica and alumina, but the sorption kinetics are a little bit slower.