Nuclear magnetic resonance studies of porous media

Nuclear Magnetic Resonance (NMR) is becoming an increasingly popular measurement technique in chemical engineering research because of its ability to probe both microscopic and macroscopic phenomena. In this paper an overview of ongoing research projects in the area of characterization of porous solids, and the adsorption and transport phenomena associated with molecular species sorbed within porous materials is given. NMR allows us to probe many processes non-invasively for the first time; these data give us new information which can then be used to design or optimize processes. Research in this area has followed two main themes. Firstly, a combination of NMR Imaging, PGSE and relaxometry methods in combination with numerical simulation techniques are used to study structure-transport relationships in amorphous, porous catalyst pellets. These studies emphasize the importance of characterizing structural heterogeneities within a porous medium if the transport characteristics of the macroscopic sample are to be adequately modelled. Secondly, deuterium spectroscopy studies of single and binary component adsorption in zeolites are presented. These experiments allow us to explore effects such as adsorption heterogeneity and molecular traffic control and to yield a physical understanding of otherwise anomalous adsorption behaviour in zeolites. The insight into adsorption phenomena gained by this technique suggests the possibility of optimizing adsorption-separation and catalytic processes by co-adsorbing specially selected species within the pore structure of the zeolite.