High-Pressure Phase Equilibria of Tertiary-Butylamine Hydrates with and without Hydrogen

Abstract

Thermodynamic stability boundaries of the simple tertiary-butylamine (<i>t</i>-BA) hydrate and <i>t</i>-BA+hydrogen (H₂) mixed hydrate were investigated at a pressure up to approximately 100 MPa. All experimental results from the phase equilibrium measurement, in situ Raman spectroscopy, and powder X-ray diffraction analysis arrive at the single conclusion that the <i>t</i>-BA hydrates, under pressurization with H₂, are transformed from the structure VI simple <i>t</i>-BA hydrate into the structure II <i>t</i>-BA+H₂ mixed hydrate. The phase transition point on the hydrate stability boundary in the mother aqueous solutions with the <i>t</i>-BA mole fractions (<i>x</i>_{<i>t</i>‑BA}) of 0.056 and 0.093 is located at (2.35 MPa, 267.39 K) and (25.3 MPa, 274.19 K), respectively. On the other hand, in the case of the pressurization by decreasing the sample volume instead of supplying H₂, the simple <i>t</i>-BA hydrate retains the structure VI at pressures up to 112 MPa on the thermodynamic stability boundary