Experimental and Modelling Studies of Water Sorption Properties of Cellulosic Derivative Fibers.

The objective of this study was to understand the chemical modification impact on interactions between water and cellulosic fiber. In that respect, cotton (C), flax (F), viscose (V) and cellulose acetate (CA) were analyzed by using a dynamic vapor sorption analysis. The sorption and desorption isotherms and kinetic curves were modelled using the Park model and the “Parallel Exponential Kinetics” (PEK) model-which allowed an accurate fitting on the whole range of water activity. The obtained sorption properties were correlated to the accessibility and the amount of sorption sites and also to the crystallinity level of the fibers. It was found that V exhibited the highest water sorption capacity due to a higher hydroxyl groups accessibility and a high amorphous fraction, followed up by F, C and CA. In contrast, higher kinetic sorption rate was obtained for CA due to a decrease of the hydroxyl groups within the fibers. Regardless the fiber, the determination of characteristic times showed that the kinetic rate was higher for sorption than desorption.

Analytical model for coupled multispecies advective dispersive transport subject to rate-limited sorption

Mathematical models that analytically solve a set of simultaneous multispecies advection-dispersion transport equations coupled with a series of chemical reactions are cost-effective tools for predicting the plume migration of dissolved chlorinated solvents and nitrogen chains. However, few analytical solutions for coupled reactive multispecies transport equations have appeared in the literature. For convenience of mathematical derivation, most analytical models currently used to simulate multispecies transport assume instantaneous equilibrium between the dissolved and sorbed phases of the contaminant. However, research has demonstrated that rate-limited sorption process can have a profound effect upon solute transport in the subsurface environment. Making the instantaneous equilibrium sorption assumption precludes consideration of potential effects of the rate-limited sorption. This study presents a novel analytical model for simulating the migrations of plumes of decaying or degradable contaminants subject to rate-limited sorption. The derived analytical model is then applied to investigate the effects of the rate-limited sorption on the plume migration of degradable contaminants. Results show that the kinetic sorption rate constant has significant impacts on the plume migration of degradable contaminants. Increasing the kinetic sorption rate constant results in a reduction of predicted concentration for all species in the degradable contaminants while the equilibrium-controlled sorption model lead to significant underestimation of the concentrations of degradable contaminants under conditions with low sorption Damköler number, Dai = βiLν. The equilibrium-controlled sorption model agrees well with the rate-limited sorption model when the Damköler number is greater than 2 to 3 order of magnitude. The invalidity of the equilibrium-controlled sorption model of low Damköler number case implies that the health risk could be underestimated if such a model is used for assessing the concentrations of the degradable contaminants in the health risk model.

Sorption of Bisphenol A in Aqueous Solutions on Irradiated and as-Grown Multiwalled Carbon Nanotubes

In this study, non-irradiated and weathered multiwalled carbon nanotubes (MWCNTs) obtained through irradiation, were studied as adsorbents for BPA, both nanomaterials being characterized before and after the adsorption process. The objectives of our investigation were to compare the characteristics of non-irradiated and irradiated MWCNTs, to evaluate the adsorption capacity of BPA by pristine and irradiated MWCNTs and to determine the variation of the kinetic, sorption and thermodynamic parameters during sorption process using both sorbents.

Transient solute transport with sorption in Poiseuille flow

Previous work on solute transport with sorption in Poiseuille flow has reached contradictory conclusions. Some have concluded that sorption increases mean solute transport velocity and decreases dispersion relative to a tracer, while others have concluded the opposite. Here we resolve this contradiction by deriving a series solution for the transient evolution that recovers previous results in the appropriate limits. This solution shows a transition in solute transport behaviour from early to late time that is captured by the first- and zeroth-order terms. Mean solute transport velocity is increased at early times and reduced at late times, while solute dispersion is initially reduced, but shows a complex dependence on the partition coefficient $k$ at late times. In the equilibrium sorption model, the time scale of the early regime and the duration of the transition to the late regime both increase with $\ln k$ for large $k$. The early regime is pronounced in strongly sorbing systems ($k\gg 1$). The kinetic sorption model shows a similar transition from the early to the late transport regime and recovers the equilibrium results when adsorption and desorption rates are large. As the reaction rates slow down, the duration of the early regime increases, but the changes in transport velocity and dispersion relative to a tracer diminish. In general, if the partition coefficient $k$ is large, the early regime is well developed and the behaviour is well characterized by the analysis of the limiting case without desorption.