Experimental and Computational Investigation of Ethylene Oxide Hydrate and Its Mixed Hydrates with Propane and Isobutane

Gas hydrates represent an important class of crystalline solids, where water molecules form cage-like frameworks that encapsulate gas molecules. They have garnered significant attention for their unique properties and diverse applications in energy and environmental science. This study investigates the formation and vibrational properties of the ethylene oxide (EO) hydrate (structure I, sI) and EO-seeded hydrates of propane and isobutane (structure II, sII) using matrix isolation Fourier-transform infrared (FTIR) spectroscopy, supported by Density Functional Theory (DFT) calculations at the B3LYP/6-311++G(d,p) level of theory. Under low-temperature and low-pressure conditions, EO hydrate was formed by co-depositing a premix of EO and argon with D2O onto a CaF2 window held at 50 K, followed by a gradual annealing to 120 K for 60 minutes, and subsequent cooling to 4 K. Diagnostic shifts in vibrational modes, along with the characteristic splitting of the C-H vibrational stretching modes of EO, provided clear evidence of hydrate formation. Furthermore, due to its polarity, EO was adopted as a seeding agent to induce the formation of the sII hydrates of propane and isobutane under similar conditions, as confirmed by vibrational frequency shifts observed in both D2O and the C-H vibrational stretching modes of EO and the hydrocarbons. DFT calculations showed reasonable consistency with experimental data, validating the structural and vibrational characteristics of these hydrates. This work demonstrates the catalytic role of polar guest molecule EO in promoting hydrocarbon hydrate formation under low-temperature and low-pressure conditions. The novelty of this study lies in the combined use of experimental and computational approaches to elucidate EO’s influence on hydrate nucleation and stability, with implications for gas transport and energy storage technologies.