Decomposition Kinetics and Self-Preservation of Methane Hydrate Particles in Crude Oil Dispersions: Experiments and Theory

Abstract

The self-preservation phenomenon may be used for storage and transportation of natural gas in the form of gas hydrate. In this work, decomposition kinetics and self-preservation of methane hydrate dispersions in two types of crude oils were studied. Hydrate particle sizes in both dispersions did not exceed 30 μm. The experiments were performed at constant temperatures from −4 to −20 °C without preliminary deep-freezing of the samples. The kinetic curves of the methane hydrate decomposition were recorded as depending on methane pressure in the autoclave vs time. In the experiments with the first dispersion, it was shown that at the decomposition degree of 50%, the hydrate decomposition rates decreased by 1–2 orders of magnitude in comparison to the rates at the start of the decomposition process; therefore, hydrate self-preservation took place. Estimated thickness of the ice shell providing self-preservation did not exceed 1.3 μm at the decomposition degree of 50%. Self-preservation was less pronounced in experiments with the second dispersion. It may be explained by the presence of the surfactant in the second dispersion, which was added to stabilize the water-in-oil emulsion from which the dispersion was obtained. Possible mechanisms and the effect of various factors on the efficiency of self-preservation are discussed in this work. A mathematical model of hydrate decomposition process taking into account self-preservation of hydrate particles in the dispersion is suggested. A time-dependent (decreasing) diffusion coefficient of methane in ice shell was used in the model.

Modeling of Freon 134a Gas Hydrate Synthesis via Boiling and Condensation of Gas in a Volume of Water

“…where M w = 18 g/mol and M j = 102 is the molar mass of the water and freon, respectively, N w = 136 is the number of water molecules per gas molecule in the hydrate, N A is the Avogadro number, and a = 1.7 • 10 −7 cm is the length of the edge of the cubic lattice of structure II as freon is included only in type I cavities (Y 2 v 2 = 0.9 • 8) [35]. Thus, the density of the formed hydrate is 1.079 g/cm 3 . The graph (Fig.…”

“…Gas hydrates are of great interest to specialists all over the world because they have a lot of interesting and useful properties. For example, due to their ability of self-preservation [1][2][3][4], hydrates can be used for storage and transportation of significant amounts of natural gas, as well as disposal of harmful and greenhouse gases. Even under non-equilibrium external conditions, but at a slightly negative temperature, the gas hydrate will be in a stable state.…”

Non-Isothermal Kinetic Model of the Methane Hydrate Dissociation Process at Temperatures Below Ice Melting Point

“…In [49], [65][66][67][68], the phenomenon of self-conservation is considered as a diffusion process with a damping diffusion coefficient (see also simplified diffusionkinetic model with apparent mass transfer coefficient [69]). The author constructed an isothermal theory of self-preservation for particles of different geometries.…”

“…It seems reasonable to use the available models for the inverse process associated with narrowing and blocking of pores [74,75]. For example, exponent in time damping function used in [66], [68] is to have a (triangles-with gas burning, circles-without gas burning).…”

Study of Enhancement of Synthesis of Freon 134a Gas Hydrate During Boiling of Liquefied Gas with Its Simultaneous Stirring with Water

“…This opens up great opportunities for transportation and storage of various gases, especially so for storage of hydrogen and natural gas. A particular effect can be achieved due to the ability of gas hydrates to stay in the stable state beyond the thermobaric region of hydrate stability at low temperatures [1][2][3][4], which enables storage and transportation of natural gas with less power expenses as compared, for example, with the liquefied state (the temperature of transportation of liquefied natural gas is −162 • C). Next, each original gas has distinct thermobaric conditions of hydrate formation, and thus a specific gas can be transformed from a mixture to the hydrated state with subsequent decomposition of the resulting hydrate for gas release and separation from the original mixture.…”