Formation of Methane Hydrate from Polydisperse Ice Powders

Abstract

Neutron diffraction runs and gas-consumption experiments based on pressure-volume-temperature measurements are conducted to study the kinetics of methane hydrate formation from hydrogenated and deuterated ice powder samples in the temperature range of 245-270 K up to high degrees of transformation. An improved theory of the hydrate growth in a polydisperse ensemble of randomly packed ice spheres is developed to provide a quantitative interpretation of the data in terms of kinetic model parameters. This paper continues the research line of our earlier study which was limited to the monodisperse case and shorter reaction times (Staykova et al., 2003). As before, we distinguish the process of initial hydrate film spreading over the ice particle surface (stage I) and the subsequent hydrate shell growth (stage II) which includes two steps, i.e., an interfacial clathration reaction and the gas and water transport (diffusion) through the hydrate layer surrounding the shrinking ice cores. Although kinetics of hydrate formation at stage II is clearly dominated by the diffusion mechanism which becomes the limiting step at temperatures above 263 K, both steps are shown to be essential at lower temperatures. The permeation coefficient D is estimated as (1.46 +/- 0.44) x 10(-12) m2/h at 263 K with an activation energy Q(D) approximately 52.1 kJ/mol. This value is close to the energy of breaking hydrogen bonds in ice Ih and suggests that this process is the rate-limiting step in hydrate formation from ice in the slower diffusion-controlled part of the reaction.

A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

“…Kuhs et al (2006) calculated E a and find a value (92.8 kJ mol −1 ) two times greater than the ones of Staykova et al (2003) and Genov et al (2004) for the formation of CH 4 and CO 2 clathrates respectively. In the case of CO 2 -clathrate, Genov et al (2004) estimated the activation energies to be 5.5 kJ mol −1 at low temperatures and 31.5 kJ mol −1 above 220 K, indicating that water molecule mobility plays a considerable role in the clathration reaction.…”

“…Conventionally, two main stages of the clathrate formation process are distinguished (Kuhs et al 2006). The first stage, relatively rapid, corresponds to the formation of a clathrate film over the crystalline ice surfaces (stage I), and the second, wich dominates when the whole ice grain is covered by a clathrate layer, is the growth of the shell of clathrate A82, page 12 of 24 phase around ice grains (stage II).…”

“…The second, much slower, stage of grain growth by diffusion of water molecules and gas through the clathrate shell is then neglected. For the first stage, determined values between 3 × 10 −13 and 10 −12 mol m −2 Pa −1 s −1 for the formation rate of CO 2 clathrate from CO 2 gas and crystalline water ice at temperatures around 200 K. and Kuhs et al (2006) determined values of the kinetics parameter of methane clathrate formation between 245 and 272 K starting from hydrogenated and deuterated ices. They showed a temperature dependence with values ranging between about 9 × 10 −14 mol m −2 Pa −1 s −1 at 245 K and 5 × 10 −13 mol m −2 Pa −1 s −1 at 263 K. These authors and others (Wang et al 2002;Staykova et al 2003;Genov & Kuhs 2003) assumed that the value of the kinetics parameter of formation/dissociation of clathrates follows an Arrhenius-type function of temperature:…”

From stellar nebula to planetesimals

“…The kinetic conditions of clathrate formation from crystalline water ice and gas species x are, however, poorly constrained at low temperature and very few values exist only for CO 2 and CH 4 molecules and for temperatures greater than 180 K (Schmitt 1986;Staykova et al 2003Staykova et al , 2004Kuhs et al 2006;Wang et al 2002;Genov & Kuhs 2003;Falenty et al 2011). The physical parameters that may affect the kinetics are multiple: temperature, total pressure of the gas, activity of the water ice surface (mobility of water molecules), type of volatile molecule trapped, thickness of clathrate formed, and thermal history (Schmitt 1986).…”

Systematic kinetic studies on mixed gas hydrates by Raman spectroscopy and powder X-ray diffraction

“…Kuhs and co-workers have developed and continuously ed-ited an own complex mathematical description for the formation of structure I gas hydrates from ice powder based on the finding that some hydrate crystals showed a porous microstructure in the nanoscale [8][9][10][11][12][13]. From the attempt to treat hydrate formation and decomposition in similar ways Genov [11] suggested a combined Avrami-Erofeev and Ginstling-Brounshtein model.…”