Aqueous nonelectrolyte solutions. Part XIX. Congruent dissociation melting point and the formula of structure II methane hydrate

• Published in: Canadian Journal of Chemistry
• Main Author: Glew, David N
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2003
• Subjects: Organic Chemistry; General Chemistry; Catalysis; Methane hydrate
• Online Access: http://dx.doi.org/10.1139/v03-004; http://www.nrcresearchpress.com/doi/pdf/10.1139/v03-004

Twenty-four equilibrium pressures, P(h 2 l 1 g), of structure II methane hydrate h 2 with water l 1 between 27.0 and 46.9°C are well represented by a four-parameter equation, which indicates a standard error (SE) of 1.95% on a single pressure measurement. Forty equilibrium constants K p (h 2 [Formula: see text]l 1 g) for dissociation of structure II methane hydrate into water and methane between 27.0 and 47.7°C and at pressures up to 784 MPa at 45.0°C are best represented by a three-parameter thermodynamic equation, which indicates an SE 1.25% on a single K p (h 2 [Formula: see text]l 1 g) determination. The congruent dissociation melting point C(h 2 l 1 gx m ) of structure II methane hydrate is at 47.71°C with SE 0.03°C and at pressure 533 MPa with SE 5 MPa. The congruent K p (h 2 [Formula: see text]l 1 g) is 102.9 with SE 0.3 MPa, ΔH° t (h 2 [Formula: see text]l 1 g) is 61 531 with SE 244 J mol –1 , and the congruent formula is CH 4 ·5.670H 2 O with SE 0.061H 2 O. At congruent point ΔV(h 2 [Formula: see text]l 1 g) = 0 and its estimate is 1.0 with SE 1.6 cm 3 mol –1 . Stability range of structure II methane hydrate with water extends from quadruple point Q(h 1 h 2 l 1 g) at 26.7°C and 55.5 MPa up to quadruple point Q(h 2 h 3 l 1 g) at 47.3°C and 620 MPa. The metastability range of structure I methane hydrate with water is discussed.Key words: methane hydrate, clathrate structure II, stability range, dissociation equilibrium constant, formula, congruent melting point, metastability of structure I hydrate.