What makes 1,3-dioxolane an efficient sII hydrate former?

Abstract

Clathrate hydrates are attractive materials for gas storage and transportation, and how to quickly form hydrate is an urgent problem. In this scenario, efficient hydrate promoters are needed. 1,3-dioxolane (DIOX) and tetrahydrofuran (THF), with similar molecular structure and comparable molar mass, are both found as appropriate hydrate promoters, but the former is more efficient than THF. To illustrate the key attributes required for sII hydrate promoters, we investigate what makes DIOX a more efficient hydrate former than THF with the aid of molecular dynamics simulations. Our results show that the growth rates of DIOX and THF hydrates firstly increase and then decrease with increasing temperature, and the maximum values appear at ∼260 K and ∼270 K for DIOX and THF hydrates at 12.3 MPa, respectively. The growth rates are identical between DIOX and THF hydrates at 230 K, but the growth rate of DIOX is larger than that of THF hydrate before the growth rate drops. It is found that the growth of hydrate at lower temperatures (i.e., 230 K) is dominated by water rearrangements. At higher temperatures, the growth rate is controlled by the mobility of guest molecules. Most importantly, our analysis indicates that DIOX can easily escape from the unproperly trapped location to the right place for the formation of 51264 cages owing to its higher mobility than that of THF, making it an efficient sII hydrate former. The present work gives molecular-level insights that the mobility of molecules is an essential property for them to perform as efficient hydrate promoters, which could be helpful to design better hydrate promoters.