F. Handan Tezel

Kinetic and equilibrium studies of cesium adsorption on ceiling tiles from aqueous solutions

A series of experiments were performed to quantify the adsorption of cesium on ceiling tiles as a representative of urban construction materials. Adsorption was carried out from solutions to mimic wet environmental conditions. Non-radioactive cesium chloride was used as a surrogate of the radioactive (137)Cs. The experiments were performed in the range of initial cesium concentrations of 0.114-23.9 mg L(-1) at room temperature (21°C) around three weeks. Solution samples were taken after set periods of time and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The quantity of adsorbed Cs was calculated by mass balance as a function of time. Two kinetic and three equilibrium models were employed to interpret the test results. Determination of kinetic parameters for adsorption was carried out using the first-order reaction model and the intra-particle diffusion model. Adsorption equilibrium was studied using Langmuir, Freundlich and three-parameter Langmuir-Freundlich adsorption isotherm models. A satisfactory correlation between the experimental and the predicted values was observed.

Adsorption of cesium on cement mortar from aqueous solutions.

The adsorption of cesium on cement mortar from aqueous solutions was studied in series of bench-scale tests. The effects of cesium concentration, temperature and contact time on process kinetics and equilibrium were evaluated. Experiments were carried out in a range of initial cesium concentrations from 0.0103 to 10.88 mg L(-1) and temperatures from 278 to 313 K using coupons of cement mortar immersed in the solutions. Non-radioactive cesium chloride was used as a surrogate of the radioactive (137)Cs. Solution samples were taken after set periods of time and analyzed by inductively coupled plasma mass spectroscopy. Depending on the initial cesium concentration, its equilibrium concentration in solution ranged from 0.0069 to 8.837 mg L(-1) while the respective surface concentration on coupons varied from 0.0395 to 22.34 μg cm(-2). Equilibrium test results correlated well with the Freundlich isotherm model for the entire test duration. Test results revealed that an increase in temperature resulted in an increase in adsorption rate and a decrease in equilibrium cesium surface concentration. Among several kinetic models considered, the pseudo-second order reaction model was found to be the best to describe the kinetic test results in the studied range of concentrations. The adsorption activation energy determined from Arrhenius equation was found to be approximately 55.9 kJ mol(-1) suggesting that chemisorption was the prevalent mechanism of interaction between cesium ions and cement mortar.

Determination of pure and binary isotherms for nitrogen and krypton

Abstract In this study, dealuminated H-mordenite and silicalite are investigated for the separation of a binary mixture of Kr and N 2 . Pure and binary isotherms are determined using the chromatographic method and polynomial fit to the experimental data. Corresponding X - Y diagrams and separation factors are calculated. These properties give a more detailed picture of the sorption of N 2 Kr binary mixture than the Henrys Law constants alone. The isotherms are compared with the statistical model and with the Ideal Adsorbed Solution Theory (IAST).

Pure and Binary Adsorption Equilibria of Methane and Carbon Dioxide on Silicalite

Abstract For the separation of CH4 and CO2 from landfill gas, pure and binary adsorption behavior of these gases were studied up to 5 atmosphere pressure at 40, 70, and 100°C for silicalite as the adsorbent. Pure and binary adsorption isotherms were determined experimentally and compared to predicted isotherms by several equilibrium models, as well as the other available data in the literature. Experimental binary isotherms at different concentrations were determined by using three concentration pulse methods (CPM). HT–CPM (Harlick‐Tezel CPM) was observed to be the best one to describe the behavior of this binary system. Equilibrium phase diagrams and separation factors were obtained from the experimental binary isotherms. For this system, the integral thermodynamic consistency tests were also shown and discussed.

Multicomponent adsorption modeling: isotherms for ABE model solutions using activated carbon F-400

Biobutanol has attracted significant interest in recent decades and is seriously considered as a potential biofuel to partly replace gasoline. However, some production challenges must be addressed to make butanol economically viable such as the low product concentration and product toxicity inhibiting the microorganism. To alleviate these limitations, several in situ or ex situ separation techniques have been investigated in view of their integration to the biobutanol production process to enhance its economic viability. One of these techniques is adsorption which is one of the most energy-efficient techniques used for biobutanol separation. Considering the number of chemical species present in the ABE fermentation broth, it is essential to develop multicomponent adsorption isotherms for all components as a first step to design a high performance adsorption process. Few multicomponent isotherm models have been proposed such as multicomponent Langmuir and Freundlich. In this study, these two models as well as artificial neural networks were used to model the isotherms of each component in an ABE fermentation broth as a function of the equilibrium concentrations of all components for activated carbon F-400. Results showed that the multicomponent Langmuir model was not accurate due to the many simplifying assumptions. The multicomponent Freundlich and feedforward neural network (FFNN) isotherm models were able to predict the behavior of multicomponent systems very well. Indeed, the predictive model of the experimental data had a coefficient of determination (R2) of 0.97 and 0.99, for multicomponent Freundlich and FFNN isotherm models, respectively.

ADSORPTION OF TETRAFLUOROMETHANE AND NITROGEN BY VARIOUS ADSORBENTS

Adsorption of tetrafluoromethane (CF4) and nitrogen (N2) was studied by various adsorbents for the possible separation of these gases by an adsorption process. Adsorbent screening was carried out for 13 different adsorbents by determining Henrys law constants at different temperatures and determining the adsorption selectivity for the separation of these gases. Heat of adsorption values were also determined for these adsorbents. This was accomplished by using the concentration pulse chromatographic technique. The adsorbents studied included one activated alumna, three different activated carbons, zeolites A, X, Y, and ZSM-5 at different SiO2/Al2O3 ratios. Among them, three ZSM-5 zeolites and three activated carbon adsorbents were chosen for the determination of pure component isotherms at 23°C, since they showed the highest selectivity for CF4–N2 separation. Furthermore, activated carbon F-400, ZSM-5-30 (with a SiO2/Al2O3 ratio of 30), and ZSM-5-280 (with a SiO2/Al2O3 ratio of 280) were chosen to be studied further. Pure adsorption isotherms for CF4 and N2 were determined for different temperatures between 23 and 100°C for these three adsorbents up to 140 kPa pressure. Standard volumetric technique was used for the determination of the adsorption isotherms. Freundlich isotherm equation was used to model the pure isotherms for N2. Temperature dependent Toth isotherm model was used for the pure isotherms for CF4 and using the parameters of the Toth isotherm, isosteres were determined for this adsorbate at different adsorption capacities. It was concluded that ZSM-5-280 was the best adsorbent for the separation of CF4 from N2 since it had the largest capacity for CF4 and the lowest capacity for N2 within the pressure and temperature range looked at in this study.

The release of lindane from contaminated building materials

The release of the organochlorine pesticide lindane (γ-hexachlorocyclohexane) from several types of contaminated building materials was studied to assess inhalation hazard and decontamination requirements in response to accidental and/or intentional spills. The materials included glass, polypropylene carpet, latex-painted drywall, ceramic tiles, vinyl floor tiles, and gypsum ceiling tiles. For each surface concentration, an equilibrium concentration was determined in the vapour phase of the surrounding air. Vapor concentrations depended upon initial surface concentration, temperature, and type of building material. A time-weighted average (TWA) concentration in the air was used to quantify the health risk associated with the inhalation of lindane vapors. Transformation products of lindane, namely α-hexachlorocyclohexane and pentachlorocyclohexene, were detected in the vapour phase at both temperatures and for all of the test materials. Their formation was greater on glass and ceramic tiles, compared to other building materials. An empiric Sips isotherm model was employed to approximate experimental results and to estimate the release of lindane and its transformation products. This helped determine the extent of decontamination required to reduce the surface concentrations of lindane to the levels corresponding to vapor concentrations below TWA.

Promising air purifications on clinoptilolite

Summary A natural clinoptilolite from Turkey [1] has been tested for a variety of potential air purification / separations. Henrys law constants for adsorption of CO 2 , CO, NO, and N 2 were measured on clinoptilolite, 4A and 5A zeolites, and H - Mordenite over various temperature ranges between 243 and 473 K. Equilibrium separation factors were calculated for CO/N 2 and NO/N 2 systems on the various zeolites. Low concentration separation factors for the CO/N 2 and NO/N 2 systems ranged from 5 to 20 for clinoptilolite. Pure component adsorption isotherms were determined for N 2 and CO 2 on clinoptilolite at 303 K and up to 1 atmosphere. Binary adsorption isotherms for the CO 2 / N 2 / clinoptilolite system were predicted using the extended Langmuir equation, the Ideal Adsorbed Solution Theory (IAST), and the Flory - Huggins and Wilson forms of the Vacancy Solution Theory (FH-VST and W-VST, respectively).

Description of butanol aqueous solution transport through commercial PDMS pervaporation membrane using extended Maxwell–Stefan model

ABSTRACT The mass transport of components during the pervaporation of binary butanol aqueous solutions using commercial PDMS membranes has been investigated. A simplified approach of the Maxwell–Stefan model was extended to include the effect of membrane swelling and temperature on the diffusion coefficients and sorption properties. Partial permeate fluxes obtained at different temperatures and concentrations have been fitted to determine the extended model parameters. The sorption properties and diffusion coefficients of components have been estimated using fitted parameters. Predicted values of the solubility and diffusivity were used to calculate and compare the permeability of the components under different operating conditions. Abbreviations: HPLC - High performance liquid chromatography; MS - Maxwell–Stefan; PDMS - Polydimethylsiloxane; SEM - Scanning electron microscope

CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

ABSTRACT CO2 and CO adsorption on MFI type zeolites with different SiO2/Al2O3 ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO2/Al2O3 ratios within ZSM-5. The adsorption of CO2 for decreasing SiO2/Al2O3 ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO2 within the widest range of pressures and temperatures tested.