CAREER: Adsorption and Transport in Heterogeneous Porous Media

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

ABSTRACT CTS-9733086 Lastoskie/Michigan State U. Physical and chemical heterogeneities in porous media strongly impact the thermodynamic and transport properties of fluids confined within porous materials. To fully exploit engineering processes which involve porous materials, the effects of heterogeneity on the properties of fluids in porous media must be more completely understood. In this CAREER plan, a set of research activities will be undertaken to develop statistical thermodynamic methods for characterizing fluid properties in heterogeneous porous media. Three thematic areas will be investigated: (1) sorption and diffusion of fluids in porous solids; (2) chemical dilution in heterogeneous media; and (3) enhancement of cellular transport in porous media via chemotaxis. Adsorbed-fluid phase equilibria and diffusive transport in microporous solids will be investigated using density functional theory and molecular dynamics simulation, respectively. These models will be used to interpret sorptometer measurements of gas uptake on microporous adsorbents and soils. A statistical thermodynamic model of mixing, the spatial variability index, will be used to model the dilution of solutes transported through disordered porous media. The predictions of the mixing model will be compared with the results of tracer experiments in packed columns and with field tests at aquifer injection wells. Cellular transport through porous media will be examined using cellular dynamics computer simulation. Validation of the cellular dynamics transport models will be obtained from diffusion gradient chamber visualizations of cell migration through porous media. The three research thrust areas have a strong relevance to environmental concerns regarding the fate, transport and bioremediation of contaminants in soils and groundwater. The educational component of the CAREER plan will thus be directed toward application of chemical engineering thermodynamics to environmental engineering issues, through the d evelopment of an air pollution course and environmental design problems in undergraduate chemical engineering courses. Research experiences for undergraduates will also be provided. The thermodynamic and transport properties of fluids and cells confined within porous media originate from fundamental interactions between fluid-phase species and porous solid surfaces. As such, they are strongly impacted by the heterogeneity of the porous material. Traditional empirical thermodynamic correlations do not provide detailed insight into the relationship between the structure of the porous solid and the properties of the adsorbed fluid. Statistical thermodynamics and molecular simulation, by contrast, are well suited to examining fluid phase equilibria and transport coefficients in confined porous media. Similarly, the migration of bacterial species in the aqueous phase has been studied extensively by both theoretical and experimental means, whereas bacterial migration in disordered porous media is poorly understood. Cellular dynamics simulation provides a direct means of predicting cell transport coefficients in highly heterogeneous environments that are otherwise difficult to analyze experimentally. Molecular modeling methods have gained widespread acceptance in research applications in the core areas of chemical engineering, such as gas separations, supercritical reactions and polymer processing. The benefits of molecular simulation can soon be brought to bear upon environmental process modeling of contaminant transport in natural systems, once the additional heterogeneity present in "natural" porous materials (e.g. soils) is properly accounted for. There is much controversy currently surrounding the fate of groundwater and soil contaminants in natural systems and the processes by which pollutants are retained in the subsurface. The knowledge gained from molecular simulations of contaminant transport in porous media will address these uncertainties. Insufficient mass transfer of inject ed nutrients and inadequate distribution of microbial agents are two of the principal causes of failure in attempts to restore contaminated aquifers via in situ bioremediation. Studies of chemical dilution in porous media will suggest improved design strategies for delivery of injected nutrients at bioremediation sites. Bacterial motility is a major, often the dominant, component of overall cellular transport in porous aquifer media, and there is evidence that this motility can be strongly attenuated by chemotactic response to chemical gradients in acetate and other substances. Cellular dynamics simulations of bacterial transport in porous media will guide the engineering of chemotaxis into bioremediation systems.