Diffusion of gases in coals and chars: Final report, September 15, 1985--September 14, 1988

Abstract

Eight PSOC coals representing a wide range of rank and geographic origin have been subjected to a wide range of pore structure analysis methods as well as gas diffusion measurements. Pore structure analysis techniques employed included carbon dioxide and nitrogen adsorption, helium pycnometry, mercury porosimetry, and low-field NMR spin-lattice relaxation measurements. In principle, NMR pore structure analysis avoids many of the problems associated with conventional pore structure methods such as pore structure changes during drying, sample compression, network/percolation effects, pore shape assumptions, and a limited pore size range. Spin-lattice relaxation measurements were conducted at a proton frequency of 20 MHz and 303 K using water contained in the coal pores. Pore size distributions were obtained via deconvolution of the NMR relaxation measurements using the method of regularization and application of the ''two fraction-fast exchange'' model of pore fluid behavior. A qualitative comparison of the NMR pore size distributions and surface areas (CO/sub 2//N/sub 2/) yielded good agreement. Monodisperse and bidisperse pore size distributions were noted with pore volume in the size range of <0.5 nm to 0.5 ..mu..m. Effective diffusivities of methane and nitrogen were measured at 303 K and ambient pressure using a pulse tracer analysis method. 37 refs.,more » 14 figs., 5 tabs.« less