Methane–propane hydrate formation and memory effect study with a reaction kinetics model

Abstract

Although natural gas hydrates and hydrate exploration have been extensively studied for decades, the reaction kinetics and nucleation mechanism of hydrate formation is not fully understood. In its early stage, gas hydrate formation can be assumed to be an autocatalytic kinetic reaction with nucleation and initial growth. In this work, a reaction kinetics model has been established to form structure II methane–propane hydrate in an isochoric reactor. The computational model consists of six pseudo-elementary reactions for three dynamic processes: (1) gas dissolution into the bulk liquid, (2) a slow buildup of hydrate precursors for nucleation onset, and (3) rapid and autocatalytic hydrate growth after onset. The model was programmed using FORTRAN, with initiating parameters and rate constants that were derived or obtained from data fitted using experimental results. The simulations indicate that the length of nucleation induction is determined largely by an accumulation of oligomeric hydrate precursors up to a threshold value. The slow accumulation of precursors is the rate-limiting step for the overall hydrate formation, and its conversion into hydrate particles is critical for the rapid, autocatalytic reaction. By applying this model, the memory effect for hydrate nucleation was studied by assigning varied initial amounts of precursor or hydrate species in the simulations. The presence of pre-existing precursors or hydrate particles could facilitate the nucleation stage with a reduced induction time, and without affecting hydrate growth. The computational model with the performed simulations provides insight into the reaction kinetics and nucleation mechanism of hydrate formation.

Investigation of the Influence Mechanism of CO2 Hydrate Formation in Seawater Systems in the Presence of Solid Promoters by Combining In Situ Raman Analysis with Macroscopic Experiments

“…Therefore, when conducting CO 2 hydrate formation experiments using the secondary water as a solution, the acidity of the secondary water on one hand inhibited the dissolution of CO 2 , and on the other hand, the ion effects of H + and HCO 3 – together with other salt ions in the secondary brine water jointly inhibited the CO 2 hydrate formation. This was clearly different from the reported findings that the secondary water was more conducive to CH 4 hydrate formation. , The results also indicated that it was not recommended to recycle secondary brine water for the purpose of considering material loss when using the brine water as a solution for hydrate-based CO 2 capture.…”

“…This was clearly different from the reported findings that the secondary water was more conducive to CH 4 hydrate formation. 40,41 The results also indicated that it was not recommended to recycle secondary brine water for the purpose of considering material loss when using the brine water as a solution for hydrate-based CO 2 capture.…”

Improved industrial induction time-based technique for evaluating kinetic hydrate inhibitors

“…This considered hydrate formation as an autocatalytic kinetic reaction, including nucleation and early growth. It found that the facilitation of the nucleation stage was indicated by a reduced induction time ( Ke et al, 2020 ). However, it was reported that water-hydrate memory enhanced the number of moles of gas by hydrate formation compared to fresh water ( Pallipurath et al, 2019 ).…”