(451d) Comparison of the Vapor-Liquid Equilibria and Solubility Predictions of Various Gas Mixtures Using the Cpa , SAFT and PC-SAFT  Equations of State

Reliable phase equilibria calculations are vital for the design of several hydrate applications, including flow assurance, and desalination and gas separation technologies using hydrates. The fundamental technical and economic feasibility of these latter processes are dependent on the accurate assessment of phase equilibria behavior of the fluid and hydrate phases. In order to calculate accurate phase equilibria behavior of hydrates, the fluid models need to be corrected for pure component properties and binary vapor-liquid equilibria over a range of temperatures and pressures. Five parameters (a, b and c for the cubic EoS part, and two for the association volume and strength) of the cubic plus association equation of state were optimized for the associating components by simultaneous minimization of absolute errors in saturated liquid densities and vapor pressures with comparison to experimental data and DIPPR (Design Institute of Physical Properties) correlations .Various other equations of state, which include the cubic plus association (CPA-EoS), Soave Redlich Kwong (SRK), Peng Robinson (PR), Statistical Associating Fluid Theory (SAFT), and Perturbed-Chain SAFT (PC-SAFT), have been applied in this work to predict vapor-liquid equilibria of various binary systems (Hydrate Former (HF) + hydrocarbons). SAFT and PC-SAFT equation of state parameters were adopted from ^1,2. Model accuracies were compared with and without using binary interaction parameters for various binary systems containing C₁-nC₃/CO₂/H₂S/N₂/MEG/MeOH/EthOH/H₂ + hydrocarbons (low to medium molecular weight). Furthermore, absolute errors (AADx, AADy) were calculated and compared for combinations of binary mixtures, including self associating systems. In predicting the vapor part of phase envelope, all equations of state gives comparable accuracy. However, predictions of the liquid part of the phase envelope show significant errors without using BIP for all EoS (SRK, PR, cPA, SAFT and PC-SAFT EOS). Moreover appropriate mixing rules for cPA, SAFT and PC-SAFT equations of state are required to reduce the deviations from experiment when these models are applied to polar molecules. The association energy and volume of interaction are treated with mixing rules developed by ³, to investigate the effect of various mixing rules on model accuracies.