Adsorption kinetics and equilibria: Theoretical analysis, computer simulation and applications

Xuezhi Steve Jin, Purdue University

Abstract

Adsorption is of great interest in various fields of science and engineering. It is widely used for separation and purification, and is a crucial step in heterogeneous catalysis. In another example, the blood compatibility of medical devices is directly related to adsorption of plasma proteins. An understanding of the adsorption rate, the approach to equilibrium and the binding mechanism, and our ability to model and predict the process are key issues in these applications. Many adsorption models have been proposed. Most of them do not consider steric blocking effects which, however, are significant in many adsorption systems. As a consequence, the model predictions fail to represent the adsorption behavior accurately.^ The Random Sequential Adsorption (RSA) model properly accounts for the blocking effects in irreversible adsorption. In this study, the concept of the RSA is generalized to include both irreversible (RSA) and reversible (RRA) adsorption either on a continuous surface (CS) or a random site surface (RSS) for single and multicomponent systems. With this extension a total of eight corresponding model systems are established. The models are studied via computer simulation and theoretical analysis, and equations are developed for applications. An exact mapping between the RSA-RSS and RSA-CS has been established, so that all properties of the former can be derived from a knowledge of only the behavior of the latter process. A new concept, the random reversible adsorption jamming coverage, $\theta\sbsp{\infty}{RRA},$ is introduced and clearly defined. This newly defined $\theta\sbsp{\infty}{RRA}$ is an indispensable reference state for the RRA process and provides a link between theory and experiment. Corresponding simulation algorithms are developed to evaluate $\theta\sbsp{\infty}{RRA}$ on the CS and on the RSS. In terms of the contribution to the simulation methodology, efficient algorithms are devised to generate jammed RSA-CS configurations, and evaluate the available surface functions of all the eight model systems. For the RRA, the new algorithm produces a speed-up of several orders of magnitude compared with the conventional one. A number of interesting kinetic phenomena are observed for the first time with the new algorithm. The equations developed for the one component systems have been applied to the correlations of both experimental adsorption kinetics and equilibrium isotherm data. In all cases, accurate correlations are obtained, and the resulted fitting parameters are found to be consistent with the physical and chemical properties of the systems. ^

Degree

Ph.D.

Advisors

Major Professors: Julian Talbot, Purdue University, N.-H. Linda Wang, Purdue University.

Subject Area

Engineering, Chemical

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