Pressure dependence of gas hydrate formation in triple systems water-2-Propanol-methane and water-2-Propanol-hydrogen

The compositions of the cubic structure II double hydrates of 2-propanol and methane have been determined. The hydrates have been prepared at 274.2 K, under methane pressure of 10.0 +/- 0.3 MPa from solutions with 2-propanol content varying from 4.2 to 18.1 wt%. The combination of thermovolumetric measurements, powder X-ray diffraction and Raman spectroscopy has given evidence that the double hydrate formed is a substitutional solid solution in the whole range of studied 2-propanol concentrations in the starting aqueous solutions. It has been shown that the maximal extent of substitution of 2-propanol by methane grows with the increasing pressure of the synthesis. The composition of the double hydrate with the largest gas content prepared under methane pressure of 10.0 +/- 0.3 MPa corresponds to (3.0pA+5.0CH(4))(H)center dot(12.6CH(4))(D)center dot 136H(2)O (PA - 2-propanol, indexes H and D denote molecules situated in H and D cavities, respectively). When the synthesis is carried out at methane pressure of 5.2 MPa, the composition of the double hydrate with the largest gas content is (4.3PA+3.7CH(4))(H)center dot(13.3CH(4))(D)center dot 136H(2)O. In addition, high-pressure DTA has been employed to demonstrate that the double hydrate of 2-propanol and water is formed only at hydrogen pressure exceeding 50 MPa. (C) 2016 Published by Elsevier B.V.