Desorption processes: Supercritical fluid regeneration of activated carbon

Abstract

Models are developed for isothermal desorption in a fixed bed of adsorbent particles. While more general models require numerical solution of the governing equations, two practically important cases have analytical solutions: 1) an equilibrium desorption model where the rate of desorption is controlled by external and intraparticle mass transfer; and 2) a kinetic model where external and intraparticle mass transfer and a first-order irreversible desorption step control the overall process.Recent experimental data (Tan and Liou, 1988) for the desorption of ethyl acetate from activated carbon with supercritical carbon dioxide are found to fit the local-equilibrium model. Data for the effect of temperature on fractions desorbed indicate a reversal of the temperature dependence of the adsorption isotherm as the supercritical pressure is increased. This phenomenon is analogous to the observed cross-over region for the effect of temperature on the solubility of a solid at supercritical conditions.

Modeling of supercritical extraction of organics from solid matrices

“…However, caution has to be exercised when generalizing this result to other systems and particle Reynolds numbers have to be compared. As reported by Srinivasan et al (1990) and Recasens et al (1989), if the flow rate of supercritical carbon dioxide is very low (low particle Reynolds number), mass transfer may play an important role in the desorption process. The particle Reynolds numbers used in our experiments were at least an order of magnitude greater than those used in the experiments of Srinivasan et al (1990), and the external mass-transfer coefficients evaluated from Eq.…”

“…Tan and Liou (1989b) investigated the desorption of ethyl acetate from carbon and proposed a single parameter model assuming linear desorption kinetics to interpret their regeneration data. Recasens et al (1989) modeled the data of Tan and Liou (1989b) by two different parameter models: (1) an equilibrium model where the rate of desorption is controlled by external and intraparticle mass transfer; (2) a kinetic model where the external and intraparticle mass transfer and a first-order irreversible desorption step control the overall process. Later, Srinivasan et al (1990) studied the desorption characteristics of the same system as a function of pressure, temperature, flow rate, and particle size.…”

Microporous Activated Carbons Prepared from Palm Shell by Thermal Activation and Their Application to Sulfur Dioxide Adsorption

“…At room temperature this maximum is in the range of 100 to 200 bar for different systems: methane on carbon adsorbents (16), nitrogen on alumina (17), and carbon monoxide on zeolites (18). Supercritical adsorption has wide applications in the regeneration of adsorbents (19), remedy of contaminated soil (20), separation and purification of hydrogen and light hydrocarbons (21), and storage of fuel gases (22). However, so far there are very few papers that present either data or discuss the mechanisms of physisorption of fluids above their critical temperatures.…”

What's New in Industrial Polymerization with Supercritical Solvents? A Short Review

“…3, the latter effects allow the recovery of a solute after extraction by means of controlled evolutions near the critical region [4]. These processes are favorable not only in solubilization of solids but also in the adsorption and desorption from porous plant matrices or in the regeneration of adsorbents [11,12,13]. …”