New NMR Methods for Characterizing Nanoporous Structures and Nanoconfined Shale Gas

Abstract

Nanoporous materials, such as activated carbons and gas shale rocks, play crucial roles in both industry and daily life. Activated carbons have been used in various areas, such as water filtration, supercapacitors, and catalysis carriers, and shale gas has contributed more than 50% of the annual natural gas production in the United States. In all those areas, the performance of nanoporous materials is controlled by the properties of nanopores. However, both accurate characterization of micropores in activated carbons and evaluation of adsorption capability of high-pressure nature gas in shale rocks are challenging problems. We first introduce a room temperature method for determining micropore size distribution of activated carbons based on 1H nuclear magnetic resonance (NMR) of adsorbed water under magic angle spinning (MAS). The observed NMR peak shift comes from the nucleus-independent chemical shift (NICS). The density functional theory computation of NICS yields a quantitative relationship between the observed peak shift and the micropore size. This relationship provides a direct link between the 1H MAS NMR lineshape and micropore size distribution. The NICS NMR porometry technique is shown to be useful for characterizing micropore structures of highly carbonized activated carbons. In the second part, we develop a novel method for the evaluation of the gas storage capability of gas shale based on NMR T2 contrast. The FT-NMR spectral lineshape of gas stored inside pores, which reveal the properties of nanopores, are also studied by experiments. The combined information from spectra, longitudinal relaxation, and transverse relaxation not only offers a powerful tool for the evaluation of gas storage quantity but also provides valuable information for gas storage mechanisms.Doctor of Philosoph