Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: POSTERS Single Molecules, Biopolymers, Membranes

CPP 9.19: Poster

Montag, 25. Februar 2008, 16:45–19:00, Poster A

Carbon dioxide hydrate formation at the carbon dioxide - water interface — •Felix Lehmkühler¹, Michael Paulus¹, Christian Sternemann¹, Daniela Lietz¹, Federica Venturini², and Metin Tolan¹ — ¹Technische Universität Dortmund, Experimentelle Physik I/DELTA, Maria-Goeppert-Mayer-Str. 2, 44221 Dortmund, Germany — ²ESRF, BP 220, 38043 Grenoble Cedex 9, France

The formation of gas hydrate at the water - carbon dioxide interface was studied by x-ray reflectivity and x-ray diffraction experiments. CO₂ forms under high pressures and low temperatures cubic water cages with a lattice constant of 12 Å (structure I hydrate) and a CO₂ molecule in the center. At a temperature of 0^∘C a minimum pressure of 12.5 bar is required for CO₂ hydrate stability. In nature this formation takes usually place at the water - gas interface due to a higher gas concentration in comparison with the water bulk. However, the microscopic formation process is still not understood.

The water - CO₂ interface was investigated at a temperature of 0^∘C and gas pressures up to the condensation pressure of CO₂ of 35 bar. A pressure dependent adsoprtion of thin CO₂ layers is observable, but no hydrate formation. In contrast, after rising the gas pressure to condensate a macroscopic thick CO₂ layer hydrate crystallites could be observed at the liquid-liquid interface using x-ray diffraction.

To investigate this formation more precisely diffraction patterns were measured at different height positions of the sample. Hydrate clusters were observable at all positions except the gas phase. However, the highest formation rate is found at the water - liquid CO₂ interface.