A Framework for Modeling Reactive Transport in Multiscale Chemical Processes

Thesis Abstract

Reactive transport processes are fundamental to a wide range of chemical engineering applications, including groundwater remediation, chemical reactor design, and environmental modeling. However, existing models often face limitations in accurately capturing the multiscale, coupled phenomena of reactive transport, leading to significant discrepancies between predicted and observed behaviors. This study seeks to develop a comprehensive framework for modeling reactive transport in multiscale chemical processes, addressing the critical need for integrated, scalable models that encompass pore-scale interactions, continuum-scale flow, and reactive phenomena. The primary aim is to establish a robust, modular modeling framework that enhances predictive accuracy and computational efficiency across scales. To achieve this aim, the specific objectives include (1) reviewing current multiscale reactive transport models and identifying their limitations; (2) integrating pore-scale reactive transport phenomena with continuum-scale flow through the development of a hybrid modeling approach; (3) implementing the framework within a computational environment using advanced numerical techniques; (4) validating the model against experimental data obtained from laboratory flow reactors and field studies; and (5) conducting sensitivity analyses to identify dominant parameters influencing reactive transport outcomes. The research employs a mixed-methods design, encompassing theoretical development, computational modeling, and empirical validation. The study population consists of laboratory data derived from controlled experiments involving reactive transport in porous media, specifically utilizing samples collected from a well-characterized sand aquifer of 10 cubic meters, with 120 samples representing various flow regimes. Data collection instruments include high-resolution X-ray computed tomography (CT) for pore structure characterization, laser-induced fluorescence (LIF) for tracking reactive solute distribution, and inductively coupled plasma mass spectrometry (ICP-MS) for chemical analysis. Additional field data are obtained from a karst aquifer system spanning 20 km, with a sample size of 50 monitoring wells evenly distributed across reactive zones. The instruments used for field data collection include multilevel piezometers and in situ sensors for chemical and hydraulic measurements. Data validity and reliability are ensured through calibration procedures, repeated measurements, and cross-instrument verification. Methodologically, the research utilizes finite element and lattice Boltzmann methods for numerical simulations, offering the capacity to model pore-scale flow and reactions alongside larger-scale transport phenomena. The integrated model incorporates the Nernst-Planck equation and Michaelis-Menten kinetics for reactive processes, with model calibration achieved via nonlinear regression analysis. Sensitivity analysis employs variance-based techniques to identify key parameters, and uncertainty quantification is conducted through Monte Carlo simulations. Ethical considerations involve adherence to environmental safety protocols and obtaining necessary permits for field sampling. Expected key findings include the identification of dominant reactive transport mechanisms at different scales, the development of a scalable hybrid model capable of capturing pore-level interactions up to regional flow systems, and insights into the parameter sensitivities that influence reactive transport predictions. The framework is anticipated to demonstrate improved accuracy over existing models, particularly in simulating complex reactive interactions in heterogeneous media. These findings will contribute significantly to the understanding of multiscale reactive transport processes and provide a versatile modeling tool adaptable to various chemical engineering applications. The study advances knowledge by bridging the gap between pore-scale reactions and continuum-scale transport, offering a novel modular approach that integrates diverse modeling techniques within a unified framework. It contributes to both theoretical development and practical application, providing a foundation for enhanced predictive capabilities in designing and managing chemical processes involving reactive transport. The main conclusion underscores the importance of a multiscale, integrated modeling approach in accurately representing reactive phenomena in complex media. Recommendations include the adoption of the framework in groundwater management, reactor design, and environmental remediation projects, as well as future research focusing on extending the model to reactive multiphase systems and broader scale applications.