Controlling the kinetics of gas hydrate formation using surface-active particles and identification of their behaviors at the water-guest interfaces = 표면활성입자를 이용한 가스 하이드레이트의 성장속도 조절 및 물-객체 계면에서의 거동 현상 분석
Gas hydrate is one of crystalline compounds which is consisted of encaged small guest molecules and host crystal lattices, constructed by hydrogen-bonded water molecules. This thesis deals with the study on the promotion effect of hydrate seed crystals on hydrate formation for natural gas storage, and the inhibition effect of hydrophobic particles on hydrate formation at the oil-water interface to resolve flow assurance problem in subsea pipeline.
In chapter 2, rapid sI $CH_4$ hydrate formation is induced by the injection of sII cyclopentane (CP) hydrate seeds. CP hydrate crystals were used as seeds for $CH_4$ hydrate formation to induce rapid hydrate nucleation and continuous crystal growth because CP hydrates can be easily prepared without any pressurization. Also, the metastable zone width of $CH_4$ hydrate is significantly diminished with the addition of CP hydrate seeds, and the effect of CP hydrate seeds on the $CH_4$ hydrate nucleation was analyzed using the hydrate nucleation theory.
In chapter 3, two hydrophobic particles, activated carbon particles (AC) and hydrophobic fumed silica nanoparticles (SiNPs), delay the kinetics of gas hydrate formation at the interface between water and oil phases. Small sized particles move to interface of two immiscible liquid phases, and they gather to form a particle layer, which prevents the contact between water and hydrate particles. However, the rate of hydrate formation can be accelerated at higher particle concentrations in the water-in-oil emulsion system. This can be explained that modified surface of emulsion droplets induces the rapid hydrate formation, and it is the reason why the role of hydrophobic particles changes from inhibitors to promoter on gas hydrate formation in water-in-oil emulsion; the high concentration of hydrophobic particles can induce the local supersaturation at the water-particle interfaces, and the capillary water bridges expands the contact area between water and oil phases.