Experimental determination of methane hydrate stability in methanol and electrolyte solutions

In order to establish the effect of mixtures of inhibitors on the locus of the incipient hydrate–liquid water–vapor (H–Lw–V) curve, equilibrium data have been collected for the quaternary system methane+water+methanol+sodium chloride. Three-phase incipient hydrate data have been collected at eight different concentrations of sodium chloride and methanol. The datasets are obtained to cover a wide range of conditions: pressures varying from 2 to 70 MPa and relative concentrations of up to 4 mol% sodium chloride and 27 mol% methanol. Two independent experimental methods have been used to measure the data. The first technique uses a Cailletet apparatus; this way of measuring hydrate phase equilibria is well established. The second technique involves Raman spectroscopy, which has not been used before to measure hydrate data in complex systems. Results obtained from the two techniques differ at most 1 K and are usually consistent within 0.3 K. The experimental results show that the inhibiting effect of a mixture of methanol and electrolyte is larger than what would result from linear addition of the separate effects.