Recent Research activities:

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

The knowledge of the hydrocarbon dew point is of great importance for the oil & gas industry as it is one of the gas quality specifications used for ensuring safe transport of natural gas. Avoiding hydrocarbon condensation is crucial as 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. Very satisfactory results are obtained using the existing interaction parameters of the Original UNIFAC model for fluid phase equilibrium predictions at low and high pressures for a wide range of system asymmetries including mixtures containing polymers.

More information and selected results can be found in:

• E. Voutsas, V. Louli, C. Boukouvalas, K. Magoulas and D. Tassios, Thermodynamic property calculations with the universal mixing rule for EoS/G^E models: Results with the Peng-Robinson EoS and a UNIFAC model, Fluid Phase Equilib. 241, 2006, 216-228
• V. Louli, C. Boukouvalas, E. Voutsas, K. Magoulas and D. Tassios, Application of the UMR-PRU model to multicomponent systems: Prediction of the phase behavior of synthetic natural gas and oil systems, Fluid Phase Equilibria 261, 2007, 351-358.
• 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

Applications in supercritical fluids.

Supercritical extraction: Recovery of high value added components from natural products

The objective of this project is the recovery of high valued components from natural products using supercritical CO₂. The CO₂ is considered as a "green solvent", is inexpensive, volatile, non-flammable, non-toxic, readily available and a very good and flexible solvent in supercritical conditions. Thus, the supercritical fluid extraction (SFE), despite its high investment cost mainly due to the high operation pressures, attracts more and more attention for the recovery of high valued, bio-active, and thermo labile products.

In the framework of this project, experiments were conducted in the bench scale apparatus of TTPL (SFE-500, Separex), in order to examine the effect of various process parameters (pressure, temperature, solvent flow rate and particle size) in the recovery of oil and antioxidants from various raw materials, e.g. celery, parsley, pepper, dittany, and red grape marc. In the last case, the study was financially supported by GSRT.

The modelling of the process was also studied by employing various mass transfer and empirical models. The results obtained were used for the scale-up and design of an industrial SFE unit in collaboration with VIORYL SA.

More information and detailed results can be found in:

• Papamichail I., Louli V. and Magoulas K., Supercritical Fluid Extraction of Celery Seed Oil, J. Supercrit. Fluids, 18, 2000, 213-226.
• Louli V., Folas G., Voutsas E., Magoulas K., Extraction of Parsley Seed Oil by Supercritical CO₂, J. Supercritical Fluids, 30, 2004, 163-174.
• Louli V., Ragoussis N. and Magoulas K., Recovery of Phenolic Antioxidants from Wine Industry By-Products, Bioresource Technology, 92, 2004, 201-208.
• Perakis C., Louli V., Magoulas K., Supercritical Fluid Extraction of Black Pepper Oil, Journal of Food Engineering, 71, 2005, 386-393.
• Perakis C., Louli V., Voutsas E., Magoulas K., Supercritical CO₂ extraction of dittany oil: Experiments and modelling, J. Supercritical Fluids, 55, 2010, 573-578.