(28f) Kinetics of Tetra-n-Butylammonium Bromide + Hydrogen Semi-Clathrate Hydrate Formation

Hydrogen (H₂) is regarded as a promising alternative to fossil fuels, because it offers a solution for three main global challenges: (i) reduction of greenhouse gas emissions, (ii) fulfillment of energy requirements, and (iii) reduction of local air pollution. However, due to the difficulty in finding an effective storage medium, the application of H₂,for example in the automotive sector, is currently limited.

Single H₂ clathrate hydrates have been considered as potential future H₂ storage material. Their profitability, safety, fast and high reversibility and efficient production make them more suitable for this application than other H₂ storage materials. However the main disadvantage of single H₂ clathrate hydrates is the high pressure (200 MPa at 273K) required for formation. Recently, it has been reported that tetra-n-butyl ammonium bromide (TBAB) can be used as an additive to form H₂-TBAB semi-clathrate hydrates with water, which are stable at much more practical conditions (atmospheric pressure and close to room temperature). Similar to clathrate hydrates, semi-clathrate hydrates have empty small cavities that can be filled by H₂ molecules. Moreover, the TBAB molecule is non-volatile which means there is no contamination of the H₂ released. These favorable conditions make the H₂-TBAB semi-clathrate hydrates particularly attractive as a potential H₂ storage media.

In order to elucidate the potential of H₂-TBAB semi-clathrate hydrates for H₂ storage, kinetic data and in situ Raman spectroscopy measurements were obtained for two TBAB concentrations (2.56 mol% and 3.7 mol% in the liquid solution) in a pressure range of 5 – 16 MPa. In order to prove or disapprove the stochastic nature of hydrate growth, two approaches were applied: (i) isochoric temperature cycle method and (ii) temperature constant method. To the best of our knowledge, these are the first results of time-dependent kinetic conditions of H₂-TBAB semi-clathrate hydrates using in situ Raman spectroscopy in an aqueous solution. Results will be presented at the conference.