(648g) Carbon Dioxide in Chemical Processes

Carbon dioxide is used as a reactive ingredient in many process industries and electrochemical applications. These include buffered carbonate, alkaline, and biochemical systems that depend on the solubility and reactivity of the reactants. CO2 gas is used in pH-control that facilitates dissolution and precipitation of carbonates as well as in preventing or facilitating bacterial growth in process mixtures. This work presents an up-to-date review of how thermodynamics is helpful for process design. Techniques for removing acid gases, like CO2, from flue gases by absorption are commonly used in coal-gasification and sweetening of natural gases. In these systems, aqueous alkanolamine mixtures or alkaline solutions have traditionally been used. Recently, new materials like ionic-liquid polymer systems have recently been studied for CO2 absorption and other industrial applications. For process design, we require knowledge of molecular interactions, speciation and solubilities as well as chemical equilibria in reactive multiphase systems. Modeling of both phase equilibia and chemical equilibria provides a rigorous tool for describing aqueous industrial and environmental processes that include chemical reactions, sources and sinks of CO2. For process optimization, chemical-equilibrium data are increasingly needed to interpret complex industrial and natural systems that contain aqueous electrolytes and precipitates. Thermodynamic analysis provides quantitative relations among chemical energy, chemical reactions, solubilities of gases and salts, and important online process parameters like pH, temperature and pressure. Supported by laboratory experiments, and by pilot- and mill-scale experience, models have provided applications in different industries where CO2 is a reactant. New industrial applications include cleaning waste- and process waters as well as recovering valuable or environmentally harmful metal ions as carbonates. The current trend toward using carbon dioxide is partly due to increased demand for making chemical processes environmentally friendlier energy-efficient process with ever-smaller input of chemicals, raw materials, and water.