Effects of Large Guest Molecular Structure on Thermal Expansion Behaviors in Binary (C₄H₈O + CH₄) Clathrate Hydrates

Abstract

Investigating the thermal expansion of clathrate hydrates is essential for understanding their complex physicochemical properties. Although there have been various discussions on the thermal expansion, few studies have investigated the structural effect of each guest molecule. To compare the lattice expansion behaviors with cyclic and linear large guest molecules, cyclobutanol and butyraldehyde, having the same formula of C4H8O, were used as new sII hydrate formers with a help gas of CH4. In Raman spectra of the bonding characteristics, the peaks of the C–H stretching mode, O–H stretching mode, and O:H stretching phonon showed unique shift behaviors as the temperature rises. A crystallographic analysis using high-resolution powder diffraction showed that the (cyclobutanol + CH4) hydrate undergoes smaller lattice expansion than the (butyraldehyde + CH4) hydrate under thermal stimulations, and the phase equilibria showed that the cyclobutanol case involves milder formation conditions than the butyraldehyde case. These structural effects could be based on the different guest–host interactions, and molecular dynamics simulation results also show that the different thermal expansivity or molecular motion of the large guest in a hydrate cage causes these unique interactions. The results of this study provide insight into distinctive guest–host interactions depending on the guest structure and their effects on the hydrate lattice.

Phase Equilibria and Spectroscopic Identification of Structure II Hydrates with New Hydrate-Forming Agents (Cyclopropylamine and Cyclopentylamine)

“…In the past decades, several studies have investigated the effects of thermodynamic hydrate promoters on guest inclusion behavior, hydrate structure, hydrate phase equilibria, and kinetics of hydrate formation. − Recent investigations have revealed a distinctive phenomenon for the inclusion of guest molecules in hydrate cages. − Normally, clathrate hydrates can be constructed by a “host” water framework and “guest” molecules, and the host–guest chemistry in clathrate hydrates is stabilized by van der Waals interactions. , These types of clathrate hydrates are known as canonical clathrate hydrates. However, recent studies have reported the presence of various non-canonical clathrate hydrates.…”

“…However, recent studies have reported the presence of various non-canonical clathrate hydrates. Certain large molecules with hydroxyl or amine groups in their molecular structures, such as propanols, butanols, pentanols, cyclic alcohols, and some amine molecules, can form clathrate hydrates in the presence of a help gas. ,− In addition, hydroxyl or amine moieties of large molecules in the hydrate cages may have an interaction with “host” water frameworks via hydrogen bonding. Therefore, more research is still required to achieve a comprehensive understanding of the physicochemical properties of non-canonical clathrate hydrates.…”

A comprehensive review on molecular dynamics simulation studies of phenomena and characteristics associated with clathrate hydrates

“…Recently, the lattice expansion of CH4 sII hydrate in the existence of linear and cyclic guest molecules (cyclobutanol and butyraldehyde) with the identical formula of C4H8O was studied to figure out the effect of bonding characteristics on hydrate thermal expansion. Based on the results, less lattice expansion in the system consisting of cyclobutanol in comparison with butyraldehyde was observed but the promotion impact of cyclobutanol on hydrate equilibrium was found to be higher [376].…”

Temperature effects on the C–H symmetric stretching vibrational frequencies of guest hydrocarbon molecules in 512, 51262 and 51264 cages of sI and sII clathrate hydrates

“…21 In earlier studies, the temperature dependence of the C-H symmetric stretching frequencies of encapsulated CH 4 as a guest molecule were investigated using Raman spectroscopy. [22][23][24] In the case of sI CH 4 hydrate, the thermal variation in the frequencies of CH 4 in larger cages (sI 5 12 6 2 cages) is greater than that of frequencies of CH 4 in smaller cages (sI 5 12 cages). 24 In another earlier study, the neutron diffraction experiments for sI deuterated CD 4 hydrate showed that CD 4 in the sI 5 12 6 2 cage distributes longitudinally within the cage at temperatures higher than 80 K, whereas CD 4 in the 5 12 cage distributes spherically around the center of the cage even at higher temperatures.…”