Infrared characterization of small molecule adsorption on zeolite

Because zeolites have unique adsorption properties, they are widely used as selective adsorbents in industrial applications. Traditionally, quantitative zeolite properties such as adsorption isotherms or adsorption kinetics have been determined using gravimetric or volumetric methods. These methods have limited capacities when attempting to study adsorption from samples containing mixture of potential adsorbates. Further, they do not provide any structural information concerning the adsorbent or the adsorbed species.; 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 a multivariate calibration method called principal component analysis (PCA).; 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. FTIR combined with PCA has been demonstrated to be a powerful method for the study of the adsorption kinetics of water on zeolite surfaces. Adsorption isotherms can also be derived from infrared data. Factors (e.g., gas flow rates, water vapor concentration, etc.) that affect the kinetics and equilibrium mass of adsorbed water on zeolite are discussed in Chapter three.; A competitive adsorption process will result in the case where water and carbon dioxide are simultaneously present in a gas sample in contact with a zeolite. A study of carbon dioxide adsorption and simultaneous adsorption of carbon dioxide and water on zeolite 3A is discussed in Chapter 4. One of the advantages of IR spectroscopy is that it provides information concerning both adsorbates and adsorbents. Analyses of the IR spectra reveal that carbon dioxide is both chemisorbed and physisorbed on zeolite 3A. FTIR combined with PCA also can yield quantitative adsorption information about carbon dioxide adsorption on zeolite 3A. The results show that the carbon dioxide adsorption on zeolite is diffusion-controlled and thus different from that of water. In order to determine the effects of carbon dioxide on water adsorption properties, a series of coadsorption experiments with different carbon dioxide to water ratios were performed. It was found that water adsorbs more strongly than carbon dioxide and can replace most of the adsorbed carbon dioxide, however, the presence of carbon dioxide does affect the water adsorption capacity on zeolite 3A.; Chapter five contains a discussion of studies about water and carbon dioxide adsorption on zeolite 4A and 5A. Zeolites 4A and 5A have pore sizes that are larger than zeolite 3A due to different cations in the zeolite structures. Experimental results show that adsorption of carbon dioxide on both zeolites 4A and 5A is much faster than on zeolite 3A. The pore size plays a critical role in adsorption kinetics and this further suggests carbon dioxide adsorption on zeolite 3A is diffusion controlled. On zeolite 5A, more chemisorbed species were found during CO2 adsorption processes presumably due to higher Ca2+ content. Adsorption of water and the effects of carbon dioxide on the adsorption of water on zeolite 4A and 5A are similar to those on zeolite 3A.