Investigation of Kinetics of Methane and Carbon Dioxide Hydrates in the Presence of Biobased Additives

Gas hydrates offer a viable solution for many industrial-scale applications such as capture of greenhouse gases and transport and storage of energy-rich gases and gas mixtures. However, the slow formation kinetics, inefficient conversion of water to hydrate, and severe operating conditions limit the large-scale implementation of this technology. Amino acids and other biobased additives have been demonstrated to enhance the kinetics of methane hydrate formation at lower concentrations (<1 wt %). Unlike the conventional surfactants that result in characteristic foam formation during hydrate dissociation, bioadditives do not result in foam, thereby offering greater flexibility for gas storage and gas separation applications. However, the literature also lists certain amino acids at selected concentration ranges functioning as inhibitors for carbon dioxide and methane hydrate formations. In order to discern the roles of amino acids and a few other bioadditives in hydrate formation, we perform experiments to identify a suitable additive that can enhance methane and carbon dioxide hydrate formations. Specifically, we investigate the kinetics of carbon dioxide and methane gas hydrate formations in the presence of methionine and chitosan in the concentration range of 0.01-0.4 wt % at comparable driving force (T and P) conditions. Further, the effect of the driving force on methane and carbon dioxide hydrate formation kinetics was examined at varying additive concentrations. It was observed that methionine served as an effective promoter for both methane and CO2 hydrate formations. However, chitosan significantly inhibited methane hydrate formation resulting in lower gas uptake and hydrate formation rates, whereas there was kinetic promotion offered by chitosan for carbon dioxide hydrate formation under experimental conditions. Further, investigations of the dissociation kinetics of methane and carbon dioxide hydrates by thermal stimulation in the presence of these additives under comparable experimental conditions were performed and included. It was observed that dissociation kinetics increases with increases in the concentrations of bioadditives. Morphological observations during hydrate formation and dissociation are presented as well.