Clathrate hydrate formation in the system methane + 3-methyl-1-butanol + water: equilibrium data and crystallographic structures of hydrates

Abstract

Clathrate hydrate formation in the system methane + 3-methyl-1-butanol + water is demonstrated. The data of four-phase-equilibria for methane + 3-methyl-1-butanol + hydrate + water equilibria are determined in the temperature range of 273–282K. The equilibrium pressures at temperatures below 279K are lower, by 0.4MPa at most, than those of structure I hydrate formed in the methane + water system without 3-methly-1-butanol, suggesting the formation of a hydrate different from structure I methane hydrate. Conversely, at temperatures above 279K, the equilibrium pressures are higher by 0.2MPa than those of the methane structure I hydrate, suggesting the thermodynamically inhibited formation of structure I methane hydrate. To confirm the crystallographic structures of the hydrates, X-ray diffraction and Raman-spectroscopy measurements were performed with hydrate crystal samples prepared at two conditions: at 274.0K and 2.55MPa, and at 279.5K and 6.30MPa. The measurements revealed a structure II hydrate formation at the lower temperature, contrary to the expectation of the structure H hydrate formation. The hydrate formed at the higher temperature was determined to be of structure I.