Towards Zero Carbon Emissions: Novel Low Pressure Molecular Natural Gas/CO2/H2 Storage and Separation using Semi-Clathrates

Recent work carried out in this laboratory has revealed that considerable volumes of low molecular weight gases, including methane, CO2 and hydrogen, can be incorporated into structural cavities of a class of little known clathrate hydrates (or 'gas hydrates'), namely the semi-clathrate hydrates of Quaternary Ammonium Salts (QAS, e.g. tetra-n-butylammonium bromide (TBAB) at very low pressures (to atmospheric) and ambient temperature (30 oC). In addition to favourable conditions of thermodynamic stability, QAS hydrates have numerous further advantageous properties, including:1. The relative ease with which they can be formed/dissociated (by modest pressure and/or gentle temperature change) 2. The potential capacity to store large volumes of gas (62 and 52 vol/vol achieved for CH4 and H2 respectively in our preliminary experiments)3. The capability to strongly discriminate between different gases during gas uptake/hydrate growth (controlled by QAS type and aqueous concentration)4. The ability to produce readily transportable (e.g. in batch reactors, pipelines) hydrate-water slurries5. A very low parent liquid vapour pressure (similar to common salt solutions), meaning gases released from hydrates are of a very high purity (unlike for other volatile organic hydrate promoters such as THF/tetrahydrofuran)6. A relatively low toxicity compared with other organic hydrate promoters (e.g., THF) and chemicals used in gas processing (e.g., amine solutions)These properties give QAS semi-clathrates significant potential as a novel tool for the industrial storage/transportation and separation of gases. Based on the strength of results to date, a patent for this technology has been filed (GB 0511546.4: A method for gas storage, transport, peak-shaving, and energy conversion (2005)). The aim of the work proposed here is to assess the potential of this family of hydrate formers through an intensive integrated experimental and theoretical study. The technology will be investigated using three gases chosen specifically for their current importance in the global energy industry, namely natural gas (NG)/methane (CH4), carbon dioxide (CO2) and hydrogen (H2).