Design and Construction of an X-ray Diffraction Cell for Hydrate Studies at Elevated Pressures

This work describes the setup and operation of an X-ray diffraction (XRD) cell for hydrate studies at elevated pressures (hereon we call it ‘‘high-pressure cell’’ for convenience). Most hydrate XRD measurements have been performed at low temperatures to ensure hydrate stability at atmospheric pressure. As a result, extrapolation has been required to determine hydrate volume at in situ conditions. With high pressure capabilities, however, this system can extend current structural knowledge without extrapolation, leading to less error in predictive modeling and a more accurate view of in situ hydrates. The cell has both low- and high-temperature capabilities, operating from 77 to 300 K using liquid nitrogen boil-off as a means of refrigeration, and can maintain pressures from 14 kPa to 7 MPa. Preliminary measurements of carbon dioxide hydrates at in situ conditions have been obtained and lattice parameters are comparable to those in the literature.