Abstract:
We use a stochastic approach to show how Taylor dispersion is affected by kinetic processes of adsorption and desorption onto surfaces. A general theory is developed, from which we derive explicitly the dispersion coefficients of canonical examples like Poiseuille flows in planar and cylindrical geometries, both in constant and sinusoidal velocity fields. These results open the way for the measurement of adsorption and desorption rate constants using stationary flows and molecular sorting using the stochastic resonance of the adsorption and desorption processes with the oscillatory velocity field.

Abstract:
In this work we have analyzed the adsorption-desorption kinetics in the framework of the lattice gas model. We have shown that the coefficients representing the transition probabilities must be carefully chosen even when they fulfill the principle of detailed balance, otherwise the observables arising from the kinetics present anomalous behavior. We have demonstrated that when the adsorption $A_i$ and desorption $D_i$ coefficients are linearly related through a parameter $\gamma$, there are values of lateral interaction, $V$, that lead to bad behavior in the kinetics. We have shown a phase diagram for the allowed values of $V$ and $\gamma$, concluding that detailed balance does not guarantee a correct physical behavior of the observables obtained from the rate equations like adsorption isotherms, sticking coefficients and thermal desorption spectra. Alternatively, we have introduced a description of the adsorption-desorption processes based in a simple but consistent energetic argument that leads to a correct behavior of the observables without physical inconsistencies.

Abstract:
Four different types of adsorbents, SBA-15, MCM-41, NaY and SiO2, were used to study the dynamic adsorption/desorption of toluene. To further investigate the influence of pore structure on its adsorption performance, two SBA-15 samples with different microspores were also selected. It is shown that microporous material NaY has the largest adsorption capacity of 0.2873 mL/g, and the amorphous SiO2 exhibits the least capacity of 0.1003 mL/g. MCM-41 also shows a lower break through capacity in spite of the relatively small pore diameter, because it can not provide the necessary small geometric confinement for the tiny adsorbates. However, the mesoporous SBA-15 silica with certain micropore volume shows relatively higher adsorption capacity than that of MCM-41 silica. The presence of micropores directly leads to an increase in the dynamic adsorption capacity of toluene. Although NaY has the highest adsorption capacity for toluene, its complete desorption temperature for toluene is high (> 350 degrees C), which limits its wide application. On the contrary, mesoporous silica materials exhibits a good desorption performance for volatile organic compounds at lower temperatures. Among these materials mesoporous SBA-15 samples, with a larger amount micropores and a lower desorption temperature, are a potentially interesting adsorbent for the removal of volatile organic compounds. This behavior should been related with the best synergetic effect of mesopores and micropores.

Abstract:
The physical and chemical texture of tectonically deformed coals produced by various formational mechanisms are different from those of primary coals, thus resulting in major differences among the physical properties of the reservoirs of these coals. We have studied the adsorption/desorption behavior of tectonically deformed coals by the use of isothermal adsorption/desorption experiments under equilibrium moisture condition. Experiments of isothermal adsorption/desorption of methane or multi-component gases have indicated that, the adsorption curves of coals with a low degree of tectonic deformation conform to the type of isothermal adsorption curve described by the Langmuir equation; the methane adsorption curves of coals with strong tectonic deformation cannot be described by the Langmuir equation. The adsorption/desorption process of methane and multi-component gases in the deformed coals is not consistent with primary coals, which form an effect of hysteresis in different kinds of tectonically deformed coals. With the change of pore structure of tectonically deformed coals at reservoir condition, the added adsorbed CH4 in the experiments is desorbed on the pore surface of coals during the pressure reduction process. Thus, the result shows that the adsorption volume in the process of desorbing is greater than that in adsorbing. Because of the deformation, structural change, and transformation of the adsorption potential field of coals, it is essential to form a new kind of isothermal adsorption curve and the hysteresis effect of the desorption process.

Abstract:
We propose an adsorption-desorption model for a deposit growth system, in which the adsorption and desorption of particles coexist. By means of the generalized rate equation we investigate the cluster (island) size distribution in the dynamic equilibrium state. The results show that the evolution behaviour of the system depends crucially on the details of the rate kernels. The cluster size distribution can take the scale-free power-law form in some cases, while it grows exponentially with size in other cases.

Abstract:
A reversible adsorption-desorption parking process in one dimension is studied. An exact solution for the equilibrium properties is obtained. The coverage near saturation depends logarithmically on the ratio between the adsorption rate, $\k_+$, and the desorption rate, $\k_-$, \hbox{$\req\cong 1-1/\log(k_+/k_-)$}, when $\k_+\gg\k_-$. A time dependent version of the reversible problem with immediate adsorption ($k_+=\infty$) is also considered. Both heuristic arguments and numerical simulations reveal a logarithmically slow approach to the completely covered state, \hbox{$1-\rho(t)\sim 1/\log(t)$}.

Abstract:
Many experimental studies of protein deposition on solid surfaces involve alternating adsorption/desorption steps. In this paper, we investigate the effect of a desorption step (separating two adsorption steps) on the kinetics, the adsorbed-layer structure, and the saturation density. Our theoretical approach involves a density expansion of the pair distribution function and an application of an interpolation formula to estimate the saturation density as a function of the density at which the desorption process commences, $\rho_1$, and the density of the depleted configuration, $\rho_2$. The theory predicts an enhancement of the saturation density compared with that of a simple, uninterrupted RSA process and a maximum in the saturation density when $\rho_2={2/3}\rho_1$. The theoretical results are in qualitative and in semi-quantitative agreement with the results of numerical simulations.

Abstract:
Adsorption and desorption of gold on the magnetic activated carbon (MAC) were investigated The adsorption rate of gold is higher than that of conventional coconut carbon in cyanide leach solution The loading gold can be easily desorbed as coconut carbon. Crushed fine magnetic carbon can be selected by a magnetic separator, It is suggested that the MAC can be used in carbon-in-pulp (CIP)process for increasing the recovery rate of gold

Abstract:
The time dependency of the diffusion coefficient of particles in porous media is an efficient probe of their geometry. The analysis of this quantity, measured e.g. by nuclear magnetic resonance (PGSE-NMR), can provide rich information pertaining to porosity, pore size distribution, permeability and surface-to-volume ratio of porous materials. Nevertheless, in numerous if not all practical situations, transport is confined by walls where adsorption and desorption processes may occur. In this article, we derive explicitly the expression of the time-dependent diffusion coefficient between two confining walls in the presence of adsorption and desorption. We show that they strongly modify the time-dependency of the diffusion coefficient, even in this simple geometry. We finally propose several applications, from sorption rates measurements to the use as a reference for numerical implementations for more complex geometries.

Abstract:
A solid-on-solid growth model for dimer adsorption and desorption is introduced and studied numerically. The special property of the model is that dimers can only desorb at the edges of terraces. It is shown that the model exhibits a roughening transition from a smooth to a rough phase. In both phases the interface remains pinned to the bottom layer and does not propagate. Close to the transition certain critical properties are related to those of a unidirectionally coupled hierarchy of parity-conserving branching-annihilating random walks.