Yutaek Seo

One-dimensional approaches for methane hydrate production by CO2/N2 gas mixture in horizontal and vertical column reactor

The recovery of methane gas from methane hydrate bearing sediments was investigated by using a continuous stream of a CO2 and N2 gas mixture. A long cylindrical high-pressure reactor was designed to demonstrate the recovery of methane from methane hydrate bearing sediments, and the injection rate of the gas mixture was controlled to monitor the amount of recovered methane from methane hydrates. The recovery efficiency of methane gas from methane hydrates is inversely proportional to the flow rate of the CO2 and N2 gas mixture. Methane hydrates were synthesized by using two different sediments, having particle size distributions of 75 to 150 μm and 45 to 90 μm with the same porosity, and the recovery efficiency of methane from methane hydrates was also monitored. We confirmed that there is no significant difference in the replacement characteristics by using these two different sediments. Horizontal and vertical flows of the CO2 and N2 gas mixture were applied to monitor the effect of flow direction on replacement characteristics. We also confirmed that a similar amount of methane was recovered in horizontal and vertical flows of the CO2 and N2 gas mixture at the same flow rate. The present study may help in establishing the process variables for recovering methane gas from methane hydrate bearing sediments in offshore conditions.

Thermoresponsive Microcarriers for Smart Release of Hydrate Inhibitors under Shear Flow

The hydrate formation in subsea pipelines can cause oil and gas well blowout. To avoid disasters, various chemical inhibitors have been developed to prevent or delay the hydrate formation and growth. Nevertheless, direct injection of the inhibitors results in environmental contamination and cross-suppression of inhibition performance in the presence of other inhibitors against corrosion and/or formation of scale, paraffin, and asphaltene. Here, we suggest a new class of microcarriers that encapsulate hydrate inhibitors at high concentration and release them on demand without active external triggering. The key to the success in microcarrier design lies in the temperature dependence of polymer brittleness. The microcarriers are microfluidically created to have an inhibitor-laden water core and polymer shell by employing water-in-oil-in-water (W/O/W) double-emulsion drops as a template. As the polymeric shell becomes more brittle at a lower temperature, there is an optimum range of shell thickness that renders the shell unstable at temperature responsible for hydrate formation under a constant shear flow. We precisely control the shell thickness relative to the radius by microfluidics and figure out the optimum range. The microcarriers with the optimum shell thickness are selectively ruptured by shear flow only at hydrate formation temperature and release the hydrate inhibitors. We prove that the released inhibitors effectively retard the hydrate formation without reduction of their performance. The microcarriers that do not experience the hydration formation temperature retain the inhibitors, which can be easily separated from ruptured ones for recycling by exploiting the density difference. Therefore, the use of microcarriers potentially minimizes the environmental damages.

Hydrate formation in water-laden microcapsules for temperature-sensitive release of encapsulants

Microcapsules have been widely used to store and release active materials for various purposes. In this work, we design microcapsules that separate an inner water phase from guest molecules in the surrounding medium with a polymeric shell. The water and guest molecules are brought into contact within the shell, where a hydrate is formed when the temperature is lower than the hydrate formation condition. A steady supply of water and guest molecules through the shell matrix into the hydrates yields local cracks in the shell. As the hydrates continue to grow in the absence of external shear flow, the cracks slowly propagate along the whole shell. In contrast, in the presence of external shear, the cracks formed by the hydrate formation are rapidly widened by the shear. This is the first direct evidence presenting the effects of hydrate formation on water-laden microcapsules. We believe that the microcapsules can be further engineered to produce temperature-sensitive microcarriers for controlled delivery of specialty chemicals.