Recent Research activities:

Phase Equilibrium Measurements and modelling of ionic liquids

A systematic research in the field of ionic liquids takes place only the last few years, where ionic liquids are examined more and more instead of the conventional organic solvents not only in chemical reactions but also in separation methods.

A systematic research in the field of ionic liquids has taken place only the last few years, where ionic liquids are examined more and more instead of the conventional organic solvents not only in chemical reactions but also in separation methods.

With a view of a better understanding of the usage of ionic liquids for chemical reactions or separation processes, the knowledge of thermodynamic properties and, especially, phase equilibrium data is needed. Such data in the case of mixtures containing antioxidants are almost inexistent.

More information and detailed results can be found in:

• E. Alevizou, G. Pappa, E. Voutsas, Prediction of phase equilibrium in mixtures containing ionic liquids using UNIFAC, Fluid Phase Equil., 284(2) 2009, 99.

Phase equilibrium of natural gas mixtures.
(The project is financially supported by STATOIL, Norway)

One of the gas quality specifications used for ensuring safe transport of natural gas is the dew point of the mixture. Avoiding hydrocarbon condensation is crucial since the presence of liquids in the pipelines increases the pressure drop and introduces operational problems resulting from the two phase flow in pipelines designed for single phase transportation. Thus, accurate prediction of hydrocarbon dew point temperatures and pressures are of great importance to obtain a safe and effective utilization of the natural gas pipelines.

Cubic equations of state (EoS), such as the Peng-Robinson (PR) and Soave-Redlich-Kwong, coupled with the classical van der Waals mixing rules, are routinely used by the oil and gas industry for the design of recovery and processing operations of natural gases.

Previous studies have pointed out that currently all thermodynamic models have difficulty in representing correctly the whole phase envelope with both the cricondentherm and the cricondenbar.

In the framework of this project the performance of the UMR-PRU model that has been developed in our laboratory is tested in the prediction of experimental dew point data of synthetic and real natural gases.

The Universal Mixing Rule (UMR) is a mixing rule for cubic equations of state (CEoS) applicable to all type of system asymmetries. For the cohesion parameter of the CEoS the mixing rule involves the Staverman-Guggenheim part of the combinatorial term and the residual term of the original UNIFAC Gibbs free energy expression. For the co-volume parameter of the CEoS the quadratic concentration dependent mixing rule is used with the combining rule for the cross parameter. The UMR is applied to the Peng-Robinson equation of state leading to what is referred to as the UMR-PRU model.

In this project the applicability of UMR-PRU was extended to natural gas mixtures. Very satisfactory predictions were obtained for both the cricondentherm and the cricondenbar.

More information and selected results can be found in:

• E. Voutsas, K. Magoulas and D. Tassios, Universal Mixing Rule for Cubic Equations of State Applicable to Symmetric and Asymmetric Systems:? Results with the Peng?Robinson Equation of State, Ind. Eng. Chem. Res., 2004, 6238-6246.
• Skylogianni E, Novak N, Louli V, Pappa G., Boukouvalas C., Skouras S., Solbraa E., Voutsas E., Measurement and prediction of dew points of six natural gases, Fluid Phase Equilibria 424, 2015, 8-15

Phase equilibrium in associating mixtures.

The Cubic Plus Association (CPA) is an equation of state (EoS) developed in our laboratory that is suitable for describing associating fluids. The equation combines the simplicity of a cubic equation of state (Soave-Redlich-Kwong or Peng-Robinson), which is used for the physical part and the theoretical background of the perturbation theory employed for the chemical (or association) part. Excellent description is obtained of both vapor pressures and saturated liquid volumes of pure associating compounds such as alcohols, phenols, glycols, acids and water.

More information and selected results can be found in:

• Voutsas E., Perakis Ch., Pappa G., Tassios D., An Evaluation of the Performance of the Cubic-Plus-Association Equation of State in Mixtures of non-Polar, Polar and Associating Compounds: Towards a Single Model for non-Polymeric Systems, Fluid Phase Equilibria, 261(1-2), 2007, 343-350.
• Pappa G., Perakis C., Tsimpanogiannis I., Voutsas E., Thermodynamic Modeling of the vapor-liquid equilibrium of the CO₂/H₂O mixture, Fluid Phase Equilibria, 284(1), 2009, 56-63.

Experimental measurements and modelling in acid gas-alkanolamine-water solutions.

The most mature acid gas (CO₂, H₂S) capture processes rely on the use of amine solvents to wash acid gases out of a gas mixture, such as flue gas. The accurate design of acid gas treatment processes requires the knowledge of vapor-liquid equilibrium (VLE) of aqueous alkanolamine solutions containing acid gas.

This project involves:

Experimental VLE measurements of aqueous solutions containing N-methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP)

Thermodynamic modelling of acid gas-alkanolamine-water systems. To this purpose, a thermodynamic framework for representing chemical and vapor-liquid equilibria in acid gas-alkanolamine-water systems has been developed, where the vapor-liquid equilibrium is calculated through a new EoS/G^E model called the electrolyte-LCVM model.

More information and detailed results can be found in:

• Pappa G., Anastasi Ch., Voutsas E., Measurement and Thermodynamic Modeling of the Phase Equilibrium of Aqueous 2-amino-2-methyl-1-propanol Solutions, Fluid Phase Equilibria, 243, 2006, 193-197.