Critical phenomena in a mixture of methane, carbon dioxide and hydrogen sulfide

Abstract

Ng, H.-J., Robinson, D.B. and Leu, A.-D., 1985. Critical phenomena in a mixture of methane, carbon dioxide and hydrogen sulfide. Fluid Phase Equilibria, 19:273-286. The two- and three-phase boundaries for a mixture containing nominally 0.50 mole fraction methane, 0.10 mole fraction carbon dioxide and 0.40 mole fraction hydrogen sulfide were determined experimentally for a range of temperatures from c. 29 to – 83°C at pressures up to c. 13 MPa. The two-phase boundary curve commences with a conventional hydrogen-sulfide-rich liquid dew point locus which passes through an upper retrograde region and terminates at a vapor-hydrogen-sulfide-rich liquid critical point at − 16.9°C and 11.03 MPa. The phase boundary then follows a bubble point locus which terminates at a hydrogen-sulfide-rich liquid-methane-rich liquuid critical point at −45.6°C and 8.79 MPa. After this the boundary turns sharply upwards to higher pressures at lower temperatures. This separates the single phase from a second retrograde-like two-liquid region. The three-phase boundary enclosing a hydrogen-sulfide-rich liquid-methane-rich liquid—vapor region terminates when the methane-rich liquid dew point locus and the three-phase bubble point locus meet at a third critical point occurring at −57.5°C and 6.62 MPa. The measurements and observations were made using a sapphire cylinder as an equilibrium cell. Phase compositions and phase volume percentages were measured under a number of selected conditions in both the two- and three-phase regions.