Surface-to-Volume Ratio of Ganglia Trapped in Small-Pore Systems Determined by Pulsed-Field Gradient Nuclear Magnetic Resonance.
Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) measurements of hydrocarbon diffusion are shown to provide a quantitative measure of the surface-to-volume (s/v) characteristics of slowly dissolving hydrocarbon ganglia, trapped in a water-saturated porous medium, for systems with pore sizes below the limit of spatial resolution of magnetic resonance imaging (MRI). The porous medium is in the form of a packed bed of glass ballotini. The PFG NMR approach is validated in two ways. First, both MRI and PFG analyses are performed on the same system containing ballotini with a diameter of 1 mm. The s/v ratio of the dissolving ganglia determined by the two methods is the same to within the accuracy of the experimental data. Second, below the spatial resolution limit of MRI, PFG NMR alone is used to characterize the s/v ratios of ganglia entrapped in two packings of ballotini with diameters 0.1 and 0.5 mm, respectively. The s/v data are then included into a one-dimensional advection-dispersion model of the ganglia dissolution process. The resultant mass transfer coefficients obtained are in agreement with those obtained, under the same conditions of aqueous superficial flow rate, following MRI analysis of hydrocarbon dissolution in larger pore structures. Copyright 2001 Academic Press.
Johns
M. L.
ML
Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, CB2 3RA, United Kingdom
Gladden
L. F.
LF