Novel Adsorbent Synthesis, Diffusion in Nanoporous Materials, and Adsorption System Optimization

Abstract

This research focuses three specific topics related to gas-phase adsorption: the synthesis and characterization of a novel carbon-silica composite adsorbent material, the diffusion of condensable vapors in single adsorbent particles, and an examination of pulse inputs and layered-bed optimization.

The first segment of the work details the synthesis of a carbon-silica composite (CSC) adsorbent derived from MCM-41 and polyfurfuryl alcohol. The novel material has a high surface area, and a narrow pore size distribution. Materials were also prepared using different furfuryl alcohol solvents and were polymerized and carbonized at different pressures. The surface area of the materials is affected by both solvent selection and the pressure at which carbonization takes place. The novel material is unique because the carbon pores are created from templating rather than from an activation process.

The next segment extends a concentration-swing frequency response method to examine mass transfer rates and concentration dependence for adsorption of condensable vapors in adsorbent particles. The adsorption kinetics of water and hexane in BPL activated carbon and the adsorption of water in silica gel are determined at several different concentrations. The mechanism that best describes the adsorption of water in BPL activated carbon is nanopore diffusion, and both models can be used to describe the diffusion of hexane in BPL activated carbon. The diffusion of water in silica gel is best characterized by the Glueckauf linear driving force model.

In the final segment of this work a mathematical model is developed to examine the sensitivity of fixed beds with respect to system parameters. The impact of mass and energy transfer effects and adsorbent layer thicknesses are determined by calculating the derivatives of the outlet concentration and outlet temperature. The adsorption of hexane on BPL activated carbon is contrasted with the adsorption of nitrogen on carbon molecular sieve, and combined mass and energy effects are considered by studying the adsorption of nitrogen on BPL activated carbon. The sensitivity data are then applied to determine the optimum bed layering of a two-layer, two-bed PSA system.