Nucleation curves of methane–propane mixed gas hydrates in the presence of a stainless steel wall

Abstract

Nucleation phenomena are important to many applications of gas hydrates and yet the nucleation curves of gas hydrate systems have rarely been measured, presumably due to the experimental difficulties involved. We measured the nucleation curves of Structure II (sII) forming methane–propane mixed gas hydrates in the presence of a stainless steel (SS) wall using the second generation High Pressure Automated Lag Time Apparatus (HP-ALTA MkII). The instrument can apply a large number of linear cooling ramps to a small volume of water under isobaric conditions and record maximum achievable subcooling distributions. The survival curves with respect to methane–propane mixed gas hydrate formation were constructed from the recorded data and then converted to nucleation curves using the novel protocol we had recently reported. The nucleation rates per unit length of the three-phase-line, where the guest gas, water and the stainless steel wall met, were derived as functions of system subcooling. We also extended the measurements of the nucleation curves of the same guest gas hydrate in the presence of a glass wall to lower cooling rates than previously studied, so that the nucleation curves of these two systems could be compared at the same cooling rates. Comparison of the nucleation curves of these two systems showed that the nucleation rates per unit length of the three-phase-line were broadly similar to each other. The same instrument and experimental protocols can be utilized for the derivation of nucleation curves of a guest gas of a different composition and/or in the presence of another solid wall.