Investigation into the impact of solid surfaces in aqueous systems

Abstract

Global warming is upon us. The scientific community is searching for methods of slowing down, preventing and reversing its effects. Carbon dioxide have been at the center of attention the last few decades, being the main contributor to man-made global warming. Carbon capture and sequestration is one of the potential tools in this under- taking of mitigation. By capturing carbon dioxide and transporting it to injection sites for subsurface storage the amount released can be reduced. This thesis approaches several of the topics involved in transport and sequestration of carbon dioxide. Carbon dioxide transport to injection site will likely be by pipelines. In arctic regions the potential for ice-like structures known as clathrates, or hydrates, to form due to the high pressure and low temperature conditions is significant. Reducing the risks of hydrate formation calls for knowledge of the decisive factors. Thus, this work participates in the development of more robust strategies for hydrate prediction and consequently prevention. In pipelines, oxidized carbon steel surfaces are readily available. These have proven to be excellent adsorption sites for water in the gas stream. Carbon dioxide is an hydrate former, capable of stabilizing hydrate cavities of water molecules as a guest molecule. Here the chemical potential of water, carbon dioxide and hydrogen sulfide is examined under realistic pipeline conditions. These results are used to predict if, in which phase, and from which phases, hydrate will form. It was found that water will adsorb onto the hematite (rust) surface. The water layers closest to the hematite have too low chemical potential for hydrates to form. However, as the distance to the hematite increases, water regains more and more of its bulk properties, where hydrates are possible. Adsorbed impurities like hydrogen sulfide is shown to assist carbon dioxide in forming stable hydrates. We draw the conclusion that relying solely on dew-point calculations may underestimate the risk of hydrate formation. Reducing the risk of hydrate formation can also be done by gas dehydration. As the hydrate cavities consists of hydrogen bonded water molecules, reducing available water will serve as a method of hydrate prevention. Linde Type A zeolites is often used in processing industry for gas dehydration. However, detailed information on kinetics such as rate of loading, diffusion and poisoning can still be improved. This work investigates the interfacial termination of Linde Type A zeolites. Furthermore, the effects of partial atomic charges in the interface region on diffusion, flux and water orientation and structuring are determined. It was found that while the termination mattered, the charge distribution dominated and significantly affected the kinetics in the interface region. Likewise, improper bal- ancing of partial atomic charges led to disturbances in the inter-cavity motion of water molecules. Depending on the distribution of charges in the interface the rate of loading were reduced by as much as half.