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.

中文翻译：

---

基于反应动力学模型的甲烷-丙烷水合物形成和记忆效应研究

尽管天然气水合物和水合物勘探已被广泛研究了几十年，但对水合物形成的反应动力学和成核机制尚未完全了解。在其早期阶段，天然气水合物的形成可以被假定为具有成核和初始生长的自催化动力学反应。在这项工作中，建立了反应动力学模型以在等容反应器中形成结构 II 甲烷-丙烷水合物。计算模型由三个动态过程的六个伪基本反应组成：（1）气体溶解到大量液体中，（2）水合物前体的缓慢积累以开始成核，以及（3）开始后快速和自催化的水合物生长。该模型是使用 FORTRAN 编程的，具有从使用实验结果拟合的数据导出或获得的起始参数和速率常数。模拟表明，成核诱导的长度主要取决于低聚水合物前体的积累达到阈值。前体的缓慢积累是整个水合物形成的限速步骤，其转化为水合物颗粒对于快速自催化反应至关重要。通过应用该模型，通过在模拟中分配不同初始量的前体或水合物种类来研究水合物成核的记忆效应。预先存在的前体或水合物颗粒的存在可以促进成核阶段，同时减少诱导时间，而不影响水合物的生长。