Bao-Zi Peng

Interfacial properties of methane/aqueous VC-713 solution under hydrate formation conditions.

The interfacial tensions between methane and aqueous solutions of different contents of VC-713 (a terpolymer of N-vinylpyrrolidone, N-vinylcaprolactam, and dimethylamino-ethyl-methacrylate) were measured at different temperatures and pressures in the hydrate formation region. The surface adsorption free energies of methane were calculated accordingly in order to investigate the effect of this kinetic inhibitor on the nucleation of hydrate. The results show that the presence of VC-713 lowers the interfacial tension, increasing the concentration of methane on the surface of the aqueous phase, and thus promotes nucleation of hydrate at the gas/liquid interface. Additionally, the measured interfacial tension data suggest that VC-713 tends not to form micelles in water. Subsequently, the lateral growth rate of hydrate film on the surface of a methane bubble suspended in the aqueous phase was measured at different pressures to investigate the effect of VC-713 on the growth of hydrate. The results show that the lateral growth rate of hydrate film from aqueous VC-713 solution is much lower than that from pure water, demonstrating that VC-713 significantly inhibits the hydrate growth. The mechanism of the inhibition is also discussed.

Studies on hydrate film growth

The hydrate film properties and growth law at the interface between water phase and hydrate former (guest) phase are of significance to the overall study of hydrate formation kinetics and for developing methods to promote or inhibit the hydrate formation with respect to different industrial applications. In recent years, the experimental tools have become available to qualitatively observe the morphological nature of the film and quantitatively measure the growth of hydrate film. In this review, we provide an overview of the current state-of-the-art in the observation of hydrate film morphology, measurement and modeling of hydrate film growth rate. First, we review the morphological observations of hydrate formation at hydrate former/water interfaces occurring in different cases, such as bulk hydrate former phase contacting bulk water phase, small hydrate former droplets being exposed to bulk water phase, small water droplets being exposed to bulk hydrate former phase, and gas bubbles being suspended in bulk water phase. In the second section, the experimental determination of the lateral growth rate along the guest/water interface, the vertical growth rate normal to the guest/water interface and thickness of hydrate film are summarized. The mechanism and modeling of lateral growth and vertical growth of hydrate film are reviewed in the third section.

Heat Transfer Related to Gas Hydrate Formation/Dissociation

Gas hydrates are ice-like crystalline compounds comprised of small guest molecules, such as methane or other light hydrocarbons, which are trapped in cages of a hydrogen-bonded water framework. It has drawn attention in the gas and oil industry since 1930s because it was found that the formation of gas hydrates may block oil/gas pipelines (Sloan and Koh, 2007). However, with the gradual discovery of huge reserve of natural gas hydrates in the earth as well as the understanding of the peculiar properties of gas hydrates, more and more studies have focused on how to benefit from gas hydrates in recent decades. The most important aspect of gas hydrates research is attributed to the exploration and exploitation of natural gas hydrates. Additionally, people also try a lot in the development of novel technologies based on hydrates, such as separation of gas mixture via forming hydrates, storage of natural gas or hydrogen in the form of solid hydrates, and sequestration of CO2, etc. As the formation of gas hydrates is an exothermic process, heat transfer always accompanies hydrate formation or dissociation. The understanding of heat transfer mechanism is critical to the modeling of formation/dissociation kinetic process of gas hydrates, which favors the best exploitation of natural gas hydrates and the best design of reactor for hydrate production or decomposer for hydrate dissociation with respect to different kinds of hydrate application objects. In recent years, a variety of experimental and theoretical works focused on heat transfer involved in formation/dissociation of gas hydrates have been reported. They are summarized in this chapter accompanying presentation of our new work relevant to this topic. This chapter is organized as follows. In section 2, we present progresses in experimental measurement of the thermal conductivities of different kinds of gas hydrates, including pure gas hydrates and hydrate-bearing sediments. The achievements on mechanism and modeling of heat transfer occurring in the growth of hydrate film at the guest/water interface, as well as its influence upon the hydrate film growth rate are summarized in section 3. Our new experimental study on heat transfer in stirring or flowing hydrate system is given in section 4. Section 5 presents our recent work on the experimental and modeling studies on heat transfer in quiescent reactors for producing or decomposing big blocks of hydrates, and the formulation of the influence of heat transfer upon the hydrate formation/dissociation rate. In section 6, the mechanism of heat transfer in hydrate