An equation of state for methane in the gas and liquid phases

An equation of state was developed which represented experimental methane P‐V‐T data over the temperature range of 130 to 625° K. for pressures to 10,000 lb./sq. in. obs. with densities to 0.36 g./cc. For 598 experimental points the mean square percent deviation in the predicted pressures was 0.07% with only 10 points having deviations above 0.2%. The low density limit of the equation predicted second virial coefficients within 1 cc./mole of the accepted values for temperatures above 200° K. The equation was developed by first analyzing isochoric data from the saturation point to the high temperature or pressure limit. An expression was then obtained, reflecting qualitative behavior of the isochores, that reproduced experimental data along each isochore with an average pressure error of 0.02% and a maximum error of 0.08%. This expression had the form P = A + BT + C exp [E (T — T0)] + D exp (k—F/T) where k and T0 were normalizing constants and A through F were functions of density. From the density dependence of these parameters a single expression was obtained which fit the entire range of experimental data.