Phase Equilibrium and Calorimetric Properties of Mixtures Using the Mattedi-Tavares-Castier Equation of State

Abstract

Natural gas and oil processing, among many other applications in the chemical industry, depends on accurate predictions of the thermodynamic and transport properties for their accurate and reliable design. Especially in the energy sector, in which the flow rates of process streams are large and equipment is big, improper design can be costly, both in terms of investment and operating costs. Equations of state (EOS) enable the evaluation of thermodynamic properties over a wide range of temperature and pressures and are routinely used for chemical process design. Many EOS exist but relatively few have become widely used, most notably the Peng-Robinson EOS in the oil and gas industry. However, the Peng-Robinson EOS and most other cubic EOS are unsuitable for predicting the phase behavior of mixtures that contain polar compounds. Such mixtures occur even in industries normally associated with the processing of non-polar substances (e.g., hydrocarbons). For example, natural gas may be contaminated by small amounts of water, carbon dioxide, and hydrogen sulfide, often removed using amines and glycols. Modern models such as the SAFT (statistical associating fluid theory), and its variants, and the CPA (cubic plus association) EOS are suitable alternatives but require solving the association equations before computing any thermodynamic property. The Mattedi-Tavares-Castier (MTC) EOS is an entirely explicit model that avoids this drawback but is capable of predictions of accuracy similar to that of the SAFT and CPA EOS. In this paper, we show results of calculations of phase equilibrium and calorimetric properties with the MTC EOS for systems of interest to gas processing industries.