Evaluation of the performance of the Twu - Coon - Cunningham cubic equation of state in predicting the speed of sound in high-pressure hydrocarbon systems

The newly developed Twu-Coon-Cunningham (TCC) cubic equation of state (CEOS) is used to determine the speed of sound for a series of hydrocarbon mixtures (both vapour and liquid) and pure liquid alkanes over the temperature and pressure ranges 100-454 K and 0.02-1000 bar, respectively. The data are then compared against experimental results as well as those predicted from the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) CEOS as a function of reduced temperature and pressure, T-r and p(r).All three CEOS perform poorly in predicting vapour speeds of sound near or at the critical region, while at p(r) > 3 the TCC CEOS consistently performs better than the other CEOS. Conversely, the TCC CEOS gives rise to relatively large errors at T-r < 0.6 in predicting speeds of sound for liquid alkanes. This is because the predicted values of (partial derivative/p/partial derivative V)(T) obtained from the TCC CEOS (where p is pressure, V is volume, T is temperature) are too large compared with the corresponding values calculated from the other CEOS. For the liquid mixture, all three CEOS perform reasonably well.