Chemical Fate of Contaminants in the Environment: Chlorinated Hydrocarbons in the Groundwater

Chlorinated hydrocarbons (CHCs) are the most common contaminant found at hazardous waste sites and are the most prevalent contaminants on U.S. Department of Energy (DOE) weapons production sites. Many of the CHCs are either known or suspected carcinogens and thus pose health risks to the public and/or site workers. Unlike simple hydrocarbons, CHCs are resistant to biodegradation, but can degrade by abiotic processes such as hydrolysis, nucleophilic substitution, and dehydrochlorination. Unfortunately, few studies of the reactions of chlorinated hydrocarbons have been reported in literature, and disagreement still exists about the mechanisms and rates of many of the key reactions. In this work, we modeled the reactions involved in the degradation of CHCs in the groundwater. The goals of the research proposed are: • development of a computational approach that will allow reaction pathways and rate constants to be accurately calculated • development of more approximate approaches, evaluated against the more accurate approach, which will lay the groundwork for exploratory studies of more complex CHCs • application of these approaches to study the degradation pathways of CHCs in aqueous liquids • application of the more approximate approaches to study the mechanism of forming complex CHC polychlorinated benzene compounds and dioxins. We examined elementary reactions involved in the aqueous-phase chemistry of chlorinated methanes and ethylenes in an attempt to obtain a detailed understanding of the abiotic processes involved in the degradation of this important class of contaminants. We began by studying the reactions of CHnCl(4-n) and C2HnCl(4-n) with OH¯, as these are thought to be the dominant processes involved in the degradation of these chlorinated species. We used state-of-the-art theoretical techniques to model the elementary reactions of CHCs important in the groundwater. We employed high-accuracy electronic structure methods (e.g., perturbation theory and coupled cluster methods with correlation-consistent basis sets) to determine the energies of the various stable species, intermediates, and transition states involved in the elementary reactions of CHCs. Effects of solvation on the reaction energetics were studied by including small numbers of solvent molecules (microsolvation). Our own N-layered molecular orbital + molecular mechanics (ONIOM) method was used because it allows the number of solvent molecules to be increased, and hybrid quantum mechanical/molecular mechanics (QM/MM) methods and continuum solvation models were used to estimate the effects of bulk solvation. Rate constants for the gas-phase, microsolvated, and bulk-phase reactions were computed using variational transition state theory (VTST)

Chemical Fate of Contaminants in the Environment: Chlorinated Hydrocarbons in the Groundwater

Chlorinated hydrocarbons (CHCs) are the most common contaminant found at hazardous waste sites and are the most prevalent contaminants on (Department of Energy) DOE weapons production sites. Many of the chlorinated hydrocarbons are either known or suspected carcinogens and thus pose health risks to the public and/or site workers. Chlorinated hydrocarbons, unlike simple hydrocarbons, are resistant to biodegradation, but can degrade by abiotic processes such as hydrolysis, nucleophilic substitution, and dehydrochlorination. Unfortunately, few studies of the reactions of chlorinated hydrocarbons have been reported in the literature, and disagreement still exist about the mechanisms and rates of many of the key reactions

New landscape of science, technology and innovation

La Ingeniería Química Colombiana está inmersa en nuevos panoramas de Ciencia, Tecnología e Innovación que traen consigo grandes retos para la industria, la academia y el Estado. Las investigaciones multidisciplinarias en energía, materiales, ingeniería de procesos y bioprocesos han llevado a estrategias de emprendimiento e innovación que prometen ser base de desarrollo en el país. En los siguientes capítulos se presentan los resultados más relevantes de las investigaciones realizadas por 19 instituciones colombianas en cooperación con 7 universidades internacionales, así como las contribuciones científicas de numerosas empresas colombianas. Este libro compila 236 resúmenes de investigaciones clasificadas en las siguientes líneas temáticas:1. Bioprocesos - 2. Economía circular - 3. Educación en Ingeniería Química - 4. Emprendimiento e innovación en Ingeniería Química - 5. Energías alternativas - 6. Oil & Gas - 7. Procesos y ciencia - 8. Tecnología en Ingeniería Química y simulación - 9. Tópicos ambientales - 10. MaterialesColombian Chemical Engineering is immersed in new scenarios of Science, Technology and Innovation that bring great challenges for industry, academia and the State. Multidisciplinary research in energy, materials, process engineering and bioprocesses have led to entrepreneurship and innovation strategies that promise to be the basis for development in the country. The following chapters present the most relevant results of the research carried out by 19 Colombian institutions in cooperation with 7 international universities, as well as the scientific contributions of numerous Colombian companies. This book compiles 236 research summaries classified in the following thematic lines: 1. Bioprocesses - 2. Circular economy - 3. Education in Chemical Engineering - 4. Entrepreneurship and innovation in Chemical Engineering - 5. Alternative energies - 6. Oil & Gas - 7. Processes and science - 8. Technology in Chemical Engineering and simulation - 9 Environmental topics - 10. MaterialsUniversidad EA