Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Chemical Engineering

First Advisor

James A. Ritter

Abstract

It is now generally accepted that the increasing global temperatures over recent decades are due to the increasing atmospheric concentrations of greenhouse gas such CH4, N2O and most especially CO2. A viable technology that economically and efficiently captures and concentrates CO2 from various stack and process streams is highly needed. Various cyclic adsorption processed are showing some promise as economic feasible options for CO2 capture. To this end, hydrotalcite-like compounds (HTlcs), when promoted with metal carbonate, such as K2CO3, have attracted considerable attention in the literature due to their reversible adsorption capacity for CO2 at elevated temperatures.

The focus of this research was two-fold: the first objective was to obtain an in-depth understanding of the CO2 uptake and release processes in K-promoted HTlc, and the second objective was to further develop a non-equilibrium kinetic model to account for both temperature and pressure dependencies to make the model useful for cyclic adsorption process modeling and design. The temperature dependence was established by correlating a series of experiments over a wide range of temperatures and adsorption/desorption cycle times. The pressure dependence was established similarly by correlating a series of experiments over a wide range of temperatures and CO2 pressures during adsorption and desorption cycling. This temperature and pressure dependent version of the non-equilibrium kinetic model made it applicable for modeling both pressure swing adsorption (PSA) and temperature swing adsorption (TSA) processes. This model was compared to three different CO2 uptake and release models in the literature and found to be superior to all of them for PSA process modeling. Thermogravimetric analysis (TGA) and in situ Fourier transform infrared (FTIR) spectroscopy were also carried out to investigate the behavior of CO2 during its uptake in and release from K-promoted HTlc at high temperature with and without water vapor present. The IR spectra confirmed the existence and transformation of different carbonate species during adsorption and desorption. The TGA and FTIR results also confirmed the positive effect of water on the CO2-HTlc system.

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