Kinetic studies of structure-H hydrate using a Langmuir adsorption model: Effects of methyl cyclohexane and methyl cyclopentane as large-molecule guest substances on methane hydrate

Abstract

The present study investigates the kinetics of structure-H hydrate formation in the presence of large molecule guest substances (LMGS), Methyl cyclohexane (MCH) and Methyl cyclopentane (MCP), as well as methane as a help gas. The experiments were done at the temperatures range of 274.1–277.1 K. For studying the effect of LMGS on the kinetics of the hydrate formation, the initial pressure of each experiment was considered to be higher than the equilibrium pressure of structure-I methane hydrate formation. The molar consumptions of the help gas and guest substances during hydrate formation were calculated by using an algorithm based on the Langmuir adsorption theory. It was found that first step of a two-step process of hydrate formation in the presence of MCH and MCP is more related to the structure-I methane hydrate formation, so that the transition of sI to sH occurs after that. The results showed that the molar consumption of methane in the presence of MCH is more than that of MCP, and more structure-H hydrate is formed at all operational conditions. MCH could lower the gas/water interfacial tension dramatically and also affect the rate of sI hydrate formation. However, the MCP is more effective LMGS on the rate of sH hydrate formation as having the higher equilibrium pressures at all conditions. Finally, the consumption of help gas depends on the consumption of LMGS that it causes a constant participation ratio.