Pellet Adsorption Research Articles

Effective adsorption of phosphate from wastewaters by big composite pellets made of reduced steel slag and iron ore concentrate

In order to remove phosphate from wastewater, a large plastic adsorption column filled with big phosphate-adsorbing pellets with diameters of 10 mm, heated by electromagnetic induction coils, was conceived. It was found that the prepared big pellets, which were made of reduced steel slag and iron ore concentrate, contain magnetic Fe and Fe3O4. The thermodynamics and kinetics of adsorption of phosphate from synthetic wastewaters on the pellets were studied in this work. The phosphate adsorption on the pellets followed three models of Freundlich, Langmuir and Dubinin–Kaganer–Radushkevick. The maximum phosphate adsorption capacity Qmax of the pellets were 2.46, 2.74 and 2.77 mg/g for the three temperatures of 20°C, 30°C and 40°C, respectively, based on the Langmuir model. The apparent adsorption energies were −12.9 kJ/mol for the three temperatures. It implied that ion exchange was the main mechanism involved in the adsorption processes. The adsorbed phosphate existed on the pellet surface mainly in the form of Fe3(PO4)2. A reduction pre-treatment of the pellet precursor with H2 greatly enhanced pellet adsorption for phosphate. The adsorption kinetics is better represented by a pseudo-first-order model. The adsorbed phosphate amounts were similar for both real and synthetic wastewaters under similar adsorption conditions. The percentage of adsorbed phosphate for a real wastewater increased with increasing pellet concentration and reached 99.2% at a pellet concentration of 64 (g/L). Some specific phosphate adsorption mechanisms for the pellets were revealed and the pellets showed the potential to efficiently adsorb phosphate from a huge amount of real wastewaters in an industrial scale.

Analysis of Diffusion and Adsorption of Volatile Organic Compounds in Zeolites by a Single Pellet Moment Technique

AbstractThe diffusion and adsorption of two common volatile organic compounds, i. e., methanol and benzene, in different zeolite pellets were studied experimentally by using the single pellet moment technique. The experiments were conducted in a one‐sided single pellet adsorption cell at different temperatures in the range between 303 and 343 K. The results showed that both volatile organic tracers were adsorbed reversibly onto all zeolite samples. The overall adsorption equilibrium constants of both volatile organic compounds decreased with increasing temperature. The adsorption of the tracers onto the zeolite samples were found to increase in the order of NaY > clinoptilolite > 4A. In the range between 303 and 343 K, the adsorption constants of benzene range from 10.51 to 5.52 for zeolite 4A, from 11.90 to 6.37 for clinoptilolite and from 20.32 to 9.82 for NaY. The adsorption constants of methanol range from 19.05 to 8.26 for zeolite 4A, from 38.40 to 9.12 for clinoptilolite and from 74.21 to 14.70 for NaY at temperatures between 303 and 333 K. The effective diffusivities for benzene varied from 2.20·10–6 to 13.01·10–6 m2/s, whereas for methanol, they varied from 9.80·10–6 to 15.60·10–6 m2/s at the temperatures studied.

Dynamic Analysis of Diffusion and Adsorption of Water‐Miscible and Water‐Immiscible Organic Vapors in Soil

AbstractA dynamic analysis of the diffusion and adsorption of water‐miscible volatile organic compounds (methanol and acetone) and water‐immiscible volatile organic compounds (benzene and toluene) in a soil pellet has been performed experimentally by using the single pellet moment technique. The experiments were conducted in a one‐sided single pellet adsorption cell at a temperature of 30 °C and varying relative humidities (0, 20, and 40 %). The results obtained with dry and wet systems showed that volatile organic tracers were adsorbed reversibly onto the soil. The overall adsorption equilibrium constants of both water‐miscible and water immiscible volatile organic compounds decreased with relative humidity. The sorption of water‐immiscible VOCs (benzene) onto soil was found to be much less than that of water‐miscible VOCs (methanol). The effective diffusivity of water‐immiscible volatile organic vapor (benzene) in the soil did not show a considerable change with relative humidity. In contrast, there was an appreciable change in the effective diffusivity for water‐miscible VOCs (methanol) with moisture.

Adsorption of propane and propylene onto carbon molecular sieve

Equilibrium data for propane and propylene adsorption on a carbon molecular sieve (CMS) 4A from Takeda are presented in the temperature range 343–423 K and 0–300 kPa pressure. The pellet adsorption loading is 0.9 mol/kg for propane and 1.2 mol/kg for propylene at 100 kPa and 373 K. The equilibrium selectivity for propylene in the low-pressure range are 2.3 (343 K) and 1.7 (423 K). Experimental data were fitted with the Toth and Dubinin models. Zero length column (ZLC) technique has been used to determine the controlling mechanism and estimate the diffusivity parameters. Transport of both hydrocarbons in the pellets is controlled by micropore diffusion. Breakthrough curves were measured in the same temperature range and atmospheric pressure, at the low partial pressure of adsorbate (linear region of the isotherm). Simple models have been used in the simulation of breakthrough curves.

Adsorption of Propane and Propylene in Pellets and Crystals of 5A Zeolite

Equilibrium and kinetic data for propane and propylene adsorption in pellets (Grace Davison) and crystals (PQ Corp.) of 5A zeolite are presented in the temperature range 323−423 K. The pellet adsorption loading measured by gravimetry is 1.7 mmol/g for propylene and 1.3 mmol/g for propane at 100 kPa and 423 K. The selectivity for propylene increases with temperature and is in the range 1.08−1.35 at 100 kPa, being higher at lower pressures. The kinetic data measured by zero-length-column (ZLC) chromatography indicate that the transport of sorbate in the pellets is controlled by macropore diffusion; pore diffusivities are in the range 0.018−0.027 cm2/s for both gases. Crystal diffusivities are in the range (1.1−7.2) × 10-11 cm2/s for propane and (0.2−6.2) × 10-11 cm2/s for propylene.

Honeycomb monoliths of activated carbons for effluent gas purification

During the incineration of urban waste incomplete mineralisation of some organic species can give rise to effluents contaminated with VOCs, furans and dioxins. These units produce large volumes of gas to be treated, but with low contents of these toxic species, for which the pressure drop caused by passing through a conventional pellet adsorption bed can be considerable. Another solution is to spray activated carbon powder into the contaminated effluent gas, although this is an expensive method. Thus, to avoid the problems associated with pressure drop or high operation costs, commercial activated carbons have been conformed as open-channel honeycomb monoliths. Their adsorption capacities towards an aromatic probe molecule, o-dichlorobenzene, chosen to simulate dioxins have been tested in a static regime. The results were analysed together with the textural and mechanical properties of the monolith composites in order to establish criteria by which the most suitable honeycomb monolith composite material for industrial use could be prepared.

Single-Point Magnetic Resonance Imaging Study of Water Adsorption in Pellets of Zeolite 4A

The water uptake process in commercial type particles of zeolite 4A has been studied using a single-point MRI method. True proton density,T1,T2, andT*2relaxation times were obtained with submillimetric resolution, overcoming the restrictions of shortT*2signals. The molecular mobility in nonequilibrium conditions has been characterized by relaxation time mapping. A clear reduction of the water sorption rate was observed by comparing MRI profiles of a loosely packed bed and gravimetric measurements of spread particles from the same sieved zeolite batch.

A network model for diffusion and adsorption in compacted pellets of bidisperse grains

In this study, a geometrical model is combined with the network of pores analogue to yield a structural-phenomenological description for diffusion and adsorption in pellets compacted from bidisperse and non-porous grains. Simulation results from both steady-state (single-pellet) and transient (chromatographic column) systems demonstrate how grain size and relative proportion affect mass transport in the pellet. For the steady-state case, it is shown that the effective medium approximation (EMA) can be readily applied to predict effective diffusivities which are in excellent agreement with network model simulations. Some specific guidelines are then outlined which suggest how to develop improved catalysts in terms of pellet structure and performance.

Vacuum Sorption Pumping Studies of Argon and Oxygen on 4A Molecular Sieves

Cryosorption pumping is a method of evacuating enclosed volumes by adsorbing gas on a deep bed of sorbent, such as Davison 4A zeolite, at cryogenic temperatures. Modeling the dynamic behavior of these systems for air pumping requires information on two major constituents of air: oxygen and argon. Particle size variation was the major variable in determining the mechanism of the process. The model comprises a fluid-phase mass balance representing the dynamics of gas in the bed and a spherical, one-dimensional diffusion equation describing adsorption in pellets of 4A zeolite. The present model calculates effective pore diffusivity taking into account Knudsen diffusion, ordinary diffusion, and Poiseuille flow. The primary diffusional resistance appears to occur in the macropores formed by the pelletizing clay binder, rather than in the bed interstices or microporous zeolite crystals.

Influence of intraparticle total pressure change on pore mass transport

AbstractInfluence of intraparticle total pressure change on pore mass transport is investigated in physical gas phase adsorption of a single component from an inert carrier medium. The Dusty Gas Model is applied to quantify pore mass transport, assuming local equilibrium between pore fluid and adsorbed phase. Calculated results for single pellet adsorption kinetics of cyclohexane on activated carbon and CO2 on molecular sieve 5 Å are compared with experimental data. It is found that the total pressure drop in the pore system may be as much as 1% of the ambient total pressure. This results in a maximum viscous flow contribution of 13% for the cases studied. Since this contribution is obtained only under conditions of low overall transport rates of the adsorbed component, the assumption of isobaric conditions within the pore system of a porous adsorbent appears justified for most cases of practical calculations.

Henry characteristics for finite adsorption on single adsorbent pellets

A theoretical model is presented describing single component adsorption and desorption kinetics in non-isothermal gas phase adsorption systems which takes into account a finite exchange rate between pore fluid and adsorbed phase. For the exchange mechanism a Henry formulation is assumed, while the pore diffusion model is used to quantify intraparticle mass transport. Applying the model equations for the calculation of single pellet adsorption kinetics of water vapour on activated carbon it may be seen that the assumption of instantaneous establishment of adsorption equilibrium within the pore system is justified. Slight deviations from equilibrium preferentially occur in the initial adsorption period.