Adsorption thermodynamics and mass transfer of toxic volatile organic compounds in activated-carbon fiber-cloth for air pollution control

Toxic volatile organic compounds (TVOCs) constitute 69% of the total air toxics emitted by major industrial point sources. Adsorption is one of the most practical mechanisms that can be used to separate and recover TVOCs before they are discharged into the atmosphere. Research on new adsorbent materials and adsorption processes were performed to achieve this goal. In this research, thermodynamic and transient behavior of TVOC adsorption in activated-carbon fiber-cloth were modeled. Experiments included steady-state and transient adsorption of acetone, as a surrogate for TVOCs, at select temperatures and partial pressures. The Dubinin-Astakhov model was modified to provide the “Thermal Equation of Equilibrium Adsorption” (TEEA) model. Such model allowed for derivations of continuous functions describing adsorption thermodynamic parameters in the phase space of temperature, adsorbate partial pressure, and adsorption capacity. A new model was developed to define functionality of the relative pore filling pressure of vapors to the micropore size of the adsorbent using the classical thermodynamics and TEEA. Relative mesopore filling pressure was modeled by modifying the Kelvin equation. The Modified-Kelvin equation provided a convenient and reliable method to determine the mesopore size distribution of the adsorbent. Effective diffusivity of adsorbates into the fibers was then modeled as a function of temperature, adsorbate partial pressure and adsorbent pore size distribution. A non-dispersive finite difference analytical-numerical model was developed to define the local adsorption kinetics. The kinetic model was used to calculate the effective diffusivity of acetone from short length chromatography (SLC) experiments. A Lattice Boltzmann Method (LBM) was developed and used to model the longitudinal effective diffusivity of square matrices of fibers within miniature fixed beds. Reflective lattice boundary conditions were developed to define complex solid configurations and provide a second order accurate solution on the boundaries. The models developed for this research were then integrated into a numerical model to determine the adsorption dynamics of acetone through the ACFC adsorber. Results from this research provide predictive tools to characterize adsorption thermodynamics, kinetics, and dynamics of other TVOC-adsorbent systems.