MODIFIED REDLICH-KWONG EQUATIONS OF STATE FOR CH4 AND CH4-H2O FLUID MIXTURES

Modified Redlich-Kwong (MRK) equations of state are proposed for CH4 a nd CH4 - H2O fluid mixtures, expressing the parameters a and b as func tions of temperature and pressure. For CH4 the new MRK was obtained by fitting 2,831 P - V - T-data for temperatures 150 K less-than-or-equa l-to T less-than-or-equal-to 623 K and pressures up to 10.3 kbar. In t he P - T range of investigation, calculated volumes relative to experi mentally determined volumes have an average percent deviation of 0.2 ( for T > 210 K the average percent deviation is 0.08). Extrapolation to high pressures and temperatures has been tested with shockwave data s o that the MRK should yield good results to 2000 K and at least 200 kb ar and is therefore really useful for geochemical conditions. The MRK for the binary CH4-H2O is obtained using the new MRK for CH4 and a sim ilar MRK for H2O, proposed by GREVEL & CHATTERJEE (1992), assuming con ventional mixing rules for the parameters a(mix) and b(mix) and introd ucing adjustable corrective factors epsilon and tau for the cross coef ficients. These factors were fitted to three existing sets of P - V - T - X(CH4)-data (WELSCH, 1973; BAZAEV et al., 1974; SRETENSKAYA et al. , 1986). As an independent proof of the validity of the MRK for the bi nary the accuracy of reproducing H(m)ex measurements of WORMALD & COLL ING (1984) was investigated and showed a good agreement between measur ed and calculated data.