Multivariate analysis of infrared spectra for monitoring and understanding the kinetics and mechanisms of adsorption processes.

摘要

The in situ and in real-time monitoring of the adsorption of multiple species of small gas molecules onto zeolites is a challenge faced by many researchers. The aim of this dissertation research is to develop a method that can be used to both quantitatively and qualitatively monitor adsorption processes on zeolites, especially when more than one adsorbate is present. The method used in the research is to couple Fourier transform infrared spectroscopy (FTIR) with multivariate calibration methods such as principal component analysis (PCA) and multivariate curve resolution (MCR).; Chapters one and two contain an introduction and the experimental details of the chapters that follow. Chapter three contains a discussion of a study involving the quantitative characterization of water adsorption on zeolite 3A. Factors (e.g., wafer mass, water vapor concentration, etc.) that affect the kinetics and equilibrium mass of adsorbed water on zeolite are discussed.; A study of CO2 adsorption and simultaneous adsorption of CO 2 and water on zeolite 3A is discussed in Chapter four. Adsorption CO 2 onto zeolite 3A has been investigated as a function of time, zeolite mass, and CO2 partial pressure using infrared spectroscopy coupled with PCA. Simultaneous CO2 and H2O co-adsorption is investigated with the kinetics of H2O and CO2 resolved from each other. The kinetics of CO2 adsorption is found to follow a combined barrier resistance diffusion model.; Chapter five contains a discussion of studies about ammonia adsorption and water/ammonia simultaneous co-adsorption onto zeolite 3A. In contrast to water adsorption, ammonia adsorption is very weak but still detectable. The water adsorption capacity of the zeolite is decreased by about 5% as a result of concurrent, or prior, ammonia adsorption.; Chapter six contains a discussion of studies about H2O/CO 2/NH3 simultaneous co-adsorption onto zeolite 3A. The desorption process was investigated as well, and we have observed the formation of nitrile and transient presence of ammonium carbonate (or ammonium bicarbonate) species during the course of zeolite wafer temperature increasing.; FTIR combined with PCA and MCR has been demonstrated to be a powerful method to study the kinetics of simultaneous co-adsorption of multiple species onto surfaces.