Surface enhanced nuclear magnetic resonance relaxation mechanisms and their significance in chemical engineering applications

Rates of nuclear magnetic resonance (NMR) relaxation have been utilized in the characterization of natural and synthetic porous media, effectively providing an alternate form of porosimetry. The physical basis for characterization is the enhancement in relaxation rate associated with fluid surface interactions with contributions from paramagnetism, dipolar coupling and diffusion. While paramagnetism dominates in most geological samples, recent interest has focused on surfaces with negligible content of paramagnetic centers, such as kerogen in shales or synthetic polymers. Here, dipolar coupling (intermolecular and/or intramolecular) has been demonstrated as an important relaxation mechanism. Following from fundamental insights, new applications are being developed to characterize fluid adsorption strengths relevant to catalysis and pore fluid compositions relevant to gas separations. NMR relaxometry will find growing application in a number of chemical engineering subdisciplines.