Development of a high pressure automated lag time apparatus for experimental studies and statistical analyses of nucleation and growth of gas hydrates

Abstract

Nucleation in a supercooled or a supersaturated medium is a stochastic event, and hence statistical analyses are required for the understanding and prediction of such events. The development of reliable statistical methods for quantifying nucleation probability is highly desirable for applications where control of nucleation is required. The nucleation of gas hydrates in supercooled conditions is one such application. We describe the design and development of a high pressure automated lag time apparatus (HP-ALTA) for the statistical study of gas hydrate nucleation and growth at elevated gas pressures. The apparatus allows a small volume (≈150 μl) of water to be cooled at a controlled rate in a pressurized gas atmosphere, and the temperature of gas hydrate nucleation, T(f), to be detected. The instrument then raises the sample temperature under controlled conditions to facilitate dissociation of the gas hydrate before repeating the cooling-nucleation cycle again. This process of forming and dissociating gas hydrates can be automatically repeated for a statistically significant (>100) number of nucleation events. The HP-ALTA can be operated in two modes, one for the detection of hydrate in the bulk of the sample, under a stirring action, and the other for the detection of the formation of hydrate films across the water-gas interface of a quiescent sample. The technique can be applied to the study of several parameters, such as gas pressure, cooling rate and gas composition, on the gas hydrate nucleation probability distribution for supercooled water samples.

Probability distributions of gas hydrate formation

“…Heneghan and Haymet and Maeda et al described the process of how the survival curves can be obtained using the data collected by an ambient pressure ALTA and by an HP-ALTA, respectively. 9,11 Hydrate formation was found to occur over a temperature range from 278 to 289 K at P 5 10.7 MPa. The equilibrium hydrate dissociation temperature (T eq ) at P h 5 10.7 MPa is 296.1 K. 13 The T f distribution curves obtained from the first mode of operation were used to make initial estimates of the range of temperatures at which the "isothermal induction time" measurements should be carried out (the second mode of operation).…”

“…For a detailed description of the modes of operation of the HP-ALTA, see Maeda et al 11 Briefly, the water sample was placed in a glass sample cell ("boat") about 30 mm in length and 4 mm in width. The sample cell was placed in a stainless steel chamber and a light beam was passed through the sample vertically ("interfacial transmittance configuration").…”

Fuel Gas Hydrate Formation Probability Distributions on Quasi-free Water Droplets

“…10 As a consequence, the experimentally measured hydrate formation temperature (T f ) distributions are functions of not only the usual physical parameters, such as gas pressures, but also the heterogeneous nucleation properties of the walls that contain the sample.…”

“…10 Because measurements of induction times are experimentally time-consuming and challenging, we typically use HP-ALTA to measure the maximum achievable subcooling temperature (ΔT) distributions in lieu of induction time distributions or nucleation rate distributions. 11 The driving force for nucleation linearly increases with increasing subcoolings.…”

The TTT Curves of the Heterogeneous and Homogeneous Crystallization of Lithium Disilicate – A Stochastic Approach to Crystal Nucleation

“…Later probability distribution functions in the formation of the first supercritical nucleus have been studied for other liquid metals, such as niobium and zirconium (Morton et al, 1994), aluminum (Uttormark et al, 1997), gold and copper (Wilde et al, 2006(Wilde et al, , 2009, and tin (Yang et al, 2009(Yang et al, , 2011(Yang et al, , 2013 but also in water (pure and seeded) (Barlow and Haymet, 1995;Heneghan et al, 2001Wilson et al, 2005) and in gas hydrates (Maeda et al, 2011(Maeda et al, , 2012. In all these experiments, a single sample was repeatedly undercooled from above the melting temperature, while either the time (at an isothermal hold) or the temperature (at an isochronal cooling) of crystallization was detected.…”