A quantitative NMR imaging study of mass transport in porous solids during drying

Abstract The temporal transformations of the radial distribution of a liquid in a presoaked porous cylindrical catalyst support pellet detected by 1 H NMR microimaging technique in the course of the pellet drying are analyzed quantitatively in terms of the diffusion equation. The approach is shown to be adequate for evaluating the diffusivity and its dependence on the degree of pellet saturation with a liquid, provided that the NMR microimaging data are properly corrected for the relaxation weighting effects. It is demonstrated that for liquids characterized by a low surface tension, such as acetone, benzene and cyclohexane, transformations of the concentration profiles can be adequately modeled assuming a liquid content-independent diffusivity. In contrast, the diffusivity of water in titania and alumina pellets substantially decreases with the decrease of water content. For alumina pellets with a pronounced “bimodality” in the pore size distribution the water concentration dependence of diffusivity is shown to be non-monotonic. It is argued that for liquids with high surface tension, the shape of the concentration profiles and the behavior of diffusivity as a function of liquid content are both related to the shape of the cummulative pore size distribution of the porous solid under study due to the existence of efficient capillary flows induced by capillary suction.

[1]  J. Bear,et al.  Introduction to Modeling of Transport Phenomena in Porous Media , 1990 .

[2]  B. Balcom,et al.  Single-Point Imaging of Partially Dried, Hydrated White Portland Cement , 1995 .

[3]  Sun Joseph Chang,et al.  Nuclear magnetic resonance imaging: a noninvasive analysis of moisture distributions in white oak lumber , 1990 .

[4]  Simon J. Doran,et al.  NMR imaging of fluids in porous solids , 1990, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[5]  Arnold Eucken,et al.  Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik , 1950 .

[6]  W. Press,et al.  Numerical Recipes in Fortran: The Art of Scientific Computing.@@@Numerical Recipes in C: The Art of Scientific Computing. , 1994 .

[7]  L. Gladden,et al.  Nuclear magnetic resonance studies of porous media , 1993 .

[8]  P. Perré,et al.  Detailed study of a model of heat and mass transfer during convective drying of porous media , 1988 .

[9]  Inverse problem for a quasi-linear equation of diffusion , 1998 .

[10]  L. Gladden,et al.  Probing the structure of porous pellets: an NMR study of drying. , 1994, Magnetic resonance imaging.

[11]  D. Pei,et al.  DRYING OF HYGROSCOPIC CAPILLARY POROUS SOLIDS --A THEORETICAL APPROACH , 1973 .

[12]  A. V. Luikov,et al.  Application of irreversible thermodynamics methods to investigation of heat and mass transfer , 1966 .

[13]  Piet J. A. M. Kerkhof,et al.  Drying kinetics; a comparison of diffusion coefficients from moisture concentration profiles and drying curves , 1995 .

[14]  Hjp Harold Brocken,et al.  Determination of moisture diffusivity in porous media using moisture concentration profiles , 1996 .

[15]  Leo L Pel,et al.  Determination of moisture diffusivity in porous media using scanning neutron radiography , 1993 .

[16]  Arthur R Schmidt,et al.  NONDESTRUCTIVE MEASUREMENT of TRANSIENT MOISTURE PROFILES and the MOISTURE DIFFUSION COEFFICIENT IN A POTATO DURING DRYING and ABSORPTION BY NMR IMAGING , 1991 .

[17]  Wills,et al.  A Stray Field Magnetic Resonance Imaging Study of the Drying of Sodium Silicate Films. , 1996, Journal of colloid and interface science.

[18]  J. R. Philip,et al.  Moisture movement in porous materials under temperature gradients , 1957 .

[19]  T. Harmathy.  Simultaneous Moisture and Heat Transfer in Porous Systems with Particular Reference to Drying , 1969 .

[20]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[21]  K. J. Packer,et al.  Spatially resolved T1 relaxation measurements in reservoir cores , 1991 .

[22]  L. I. Kheifets,et al.  Theory of preparation of supported catalysts , 1981 .

[23]  The drying-induced deformations of a clay plate , 1992 .

[24]  G. Guillot,et al.  Drying of a porous rock monitored by NMR imaging , 1989 .

[25]  J. B. Litchfield,et al.  Three-dimensional microscopic MRI of maize kernels during drying , 1992 .

[26]  P. Mansfield,et al.  Diffusion in liquid-solid systems by NMR imaging , 1986 .

[27]  Ian Turner,et al.  Convective drying of a consolidated slab of wet porous material , 1989 .