Dynamic Adsorption Model Research Articles

Improvement of the model for surface process of tritium release from lithium oxide

Among the various tritium transport processes in lithium ceramics, the importance and the detailed mechanism of surface reactions remain to be elucidated. The dynamic adsorption and desorption model for tritium desorption from lithium ceramics, especially Li 2O was constructed. From the experimental results, it was considered that both H 2 and H 2O are dissociatively adsorbed on Li 2O and generate OH − on the surface. In the first model developed in 1994, it was assumed that either the dissociative adsorption of H 2 or H 2O on Li 2O generates two OH − on the surface. However, recent calculation results show that the generation of one OH − and one H − is more stable than that of two OH −s by the dissociative adsorption of H 2. Therefore, assumption of H 2 adsorption and desorption in the first model is improved and the tritium release behavior from Li 2O surface is evaluated again by using the improved model. The tritium residence time on the Li 2O surface is calculated using the improved model, and the results are compared with the experimental results. The calculation results using the improved model agree well with the experimental results than those using the first model.

The quantification of shifting adsorption equilibria of gold and base metals in CIP plants

Most dynamic models for the carbon-in-pulp (CIP) process incorporate single and constant isotherms without taking fouling, variation in cyanide levels and competition from base metals into account. In contrast with these simplified models, the fundamental dynamic multicomponent CIP adsorption model proposed here incorporates a shifting equilibrium isotherm. Also, an empirical model was developed for predicting the degradation of cyanide down the adsorption cascade as a function of the feed pH and feed cyanide concentration. The effect of fouling was represented by introducing an additional theoretical component which competes with gold for adsorption onto activated carbon. A shifting isotherm could have an important effect on model predictions and this was highlighted by the prediction of copper adsorption. The copper loading profile was highly dependent on changing cyanide levels and gradual displacement of copper cyanide complexes by competing species.

Chemical flooding of oil reservoirs Part 9. Dynamic adsorption of surfactant onto sandstone cores from injection water with and without polymer present

The effect of polymer on the adsorption of surfactant at the solid/liquid interface related to low tension polymer water flood (LTPWF) of sandstone oil reservoirs was studied by means of dynamic laboratory experiments. An alkylpropoxyethoxy sulfate was used as surfactant, xanthan and a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate (An 125) were used as polymers, crude oil and n-heptane were the soils, and synthetic seawater was used for brine. All experiments were conducted at 50°C and 1 atm. Long-term adsorption experiments were performed by circulating the chemical solution through clay-containing reservoir cores for several weeks, and short-term experiments were conducted by injecting chemical slugs of constant concentration, but different size, through model sandstone cores. Various adsorption regimes of the surfactant were detected at different contact times between the reservoir core material and the circulated chemical solution, and it was observed that xanthan behaves as a sacrificial adsorbate towards the surfactant by decreasing the surfactant adsorption. In the slug experiments, using model cores, xanthan appeared to decrease the surfactant adsorption when using small surfactant slug sizes, but no measurable effect of xanthan or AN 125 on surfactant adsorption was observed for large sizes. A dynamic reversible adsorption model appeared to predict the propagation of the surfactant slug through the porous medium, but the adsorption level was not fitted.

Model discrimination and estimation of the intraparticle mass transfer parameters for the adsorption of bovine serum albumin onto porous adsorbent particles by the use of experimental frontal analysis data

Experimental data from a chromatographic system involving the adsorption of bovine serum albumin (BSA) onto porous anion-exchange adsorbent particles packed in a column are presented. The parameters that characterize the mass transfer mechanisms of intraparticle diffusion and convection are estimated by fitting the predictions of dynamic mathematical models describing adsorption in column systems having spherical perfusive and purely diffusive adsorbent particles to the experimental breakthrough data obtained from the column adsorption system. Both linear and nonlinear expressions for the equilibrium isotherm are considered. The values of the transport parameters are estimated in the time domain for the nonlinear adsorption models and in the Laplace transform domain for the linear adsorption models. The capabilities of the different models to describe satisfactorily the dynamic behavior of the adsorption system are compared. The dynamic nonlinear adsorption model for purely diffusive particles is found to describe most appropriately the dynamic behavior of the experimental chromatographic system studied in this work.

Modeling of surface reaction in tritium release from lithium ceramics and its comparison with transient experiments

Abstract Among the various tritium transport processes in lithium ceramics, the importance and the detailed mechanism of surface reactions still remains to be elucidated. A dynamic adsorption and desorption model for tritium desorption from lithium ceramics, especially Li2O was constructed. This model was improved in order to simulate tritium release behavior during temperature and sweep-gas composition changes. The surface heterogeneity of HTO release was also included by introducing multiple activation energies for desorption, which are assumed to be related to the number of oxygen vacancies surrounding noted OH− and OT− on the surface. The kinetic coefficients required for calculation were also improved by using recent experimental and/or reported data. Calculation results for sweep-gas composition and temperature changes were compared with BEATRIX-II experiments. The tritium release transient behavior and the chemical form of the released tritium were discussed.

Competitive adsorption of solutes in saturated soil columns: Mathematical model and experiments

Abstract Results of competitive adsorption column experiments of Cadmiua (Cd) and Zinc (Zn) are discussed. A mathematical model termed as Competitive Dynamic Adsorption Model (CDAM) to predict the solute concentration in the multi‐solute system is presented. The CDAM is verified using concentration history curves of Cd and Zn obtained from saturated column experiments.

The pressure swing adsorption drying of compressed air

An experimental and theoretical study of the drying of compressed air by a granular silica gel adsorbent was carried out using pressure swing adsorptio This process uses a portion of the dried air expanded to a lower pressure to purge the saturated bed for regeneration purposes. The effect of the volum ratio purge flow/feed flow on the dry air humidity when the process has reached quasi-steady state was investigated over the range 0.85–1.48. These humidities were predicted successfully by a simplified dynamic adsorption model using previously determined equilibrium and rate data. The approach to this steady state was also predicted. The calculated values of the humidity of the outlet regeneration flow indicate the potential of this process for the enrichment of trace adsorbates.

A convective-dispersive-adsorptive flow model for solute transport in soils. II. Evaluation of single and two-component adsorption models for phosphate movement in soils

Comparisons have been made between experimental breakthrough curves for phosphate ions in soil columns and computer simulations of solute transport based on a number of different adsorption models. These include single component linear and non-linear, instantaneous and dynamic adsorption models; as well as the model incorporating a combination of instantaneous and time-dependent components suggested in Part I. While certain portions of the complete breakthrough curves for phosphate could be reasonably approximated using simple one-component models, these generally failed badly to describe the shape and position of the experimental data over the complete range of the breakthrough curve. This was even more evident when both adsorption and desorption phases were considered. On the other hand, the model described in Part I combining instantaneous linear and a simultaneous time-dependent (dynamic) Freundlich-type adsorption components provided a good simulation of the experimental data over the full range of the breakthrough curves for both adsorption and desorption phases. Of particular significance is the ability of the model to handle successive experimental breakthrough curves with different amounts of residual adsorption. A method for 'normalizing' the solute transport equations to facilitate computer simulations is presented.