1. Interactions Between Small Hydrocarbons and Water:
Clathrate Formation and Inhibition
Mary Jane Shultz, Tufts University PRF AC6
Clathrates contain more carbon than all the oil so far identified on Earth. To probe the interactions responsible for cluster nucleation, propane clathrates were formed in an optical cell capable of withstanding 100 atm. pressure. These are stable on the bench top for short periods. Inclusion of the propane guest is shown by popping sounds as the gas is released and by the flame, photographed on the left, as the gas is burned.
Fundamental interactions leading to clathrate formation are probed by dispersing water and propane in supercritical Ar and using infrared spectroscopy. (Dispersion avoids the opacity of aqueous solutions.) Propane in Ar at 0 oC shows a characteristic broad envelope in the CH stretch region due to rotational motion and hot bands.
Burning clathrate on the laboratory bench.
In contrast, addition of water to propane in argon results in sharp features due to quenching of the rotational motion. The sharpened structure evolves over approximately five hours as the propane-water cluster gathers further water.
Studies of clathrate formation often begin with ice. Probing the guest-ice interaction, requires identification of ice modes. Vibrational modes on the ice surface due to dangling lone pairs (a) and to bilayer stiching OH bonds (b) have been identified. These probe interactions with acidic molecules and morphology disrupting interactions respectively. a b