Experimental Investigation of the Reactivity of Organic Acids in Geologic Environments

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

McCollom EAR-0073850 The proposed research is an experimental investigation of the reactivity of organic acids at conditions pertinent to geologic environments. Organic acids are frequently the most abundant dissolved organic compounds in geologic fluids, and have been implicated to play a significant role in a number of geologic processes including the generation and migration of oil and natural gas, transportation of metals in ore-forming solutions, evolution of porosity in sedimentary basins, weathering, and subsurface geomicrobial activities. Previous attempts to evaluate decomposition rates of acetic acid and other organic acids have left large uncertainties in the behavior of these compounds under geologic conditions. These uncertainties will be addressed in the proposed research through a new experimental approach that involves a better reaction apparatus and a more comprehensive analysis of reaction products. Specific issues to be addressed include: (1) the relative contributions of decarboxylation and oxidation to the thermal decomposition of acetate and longer chain carboxylic acids, (2) the impact of chemical environment (oxidation state, pH, presence of dissolved sulfur compounds) on which decomposition pathway predominates, (3) whether CO2 and acetate can attain a state of metastable thermodynamic equilibrium under some circumstances, (4) whether condensation of organic acids or their reaction products can lead to synthesis of longer chain hydrocarbons in aqueous solutions. We expect these experiments to resolve the outstanding uncertainties in the reactivity of organic acids and allow quantitative evaluations to be made of the role of organic acids in geologic processes.