(381d) Modeling Water+Hydrocarbons and Water+Oxygenates Phase Equilibrium with the GC-PPC-SAFT Equation of State

The use of lignocellulosic biomass derived from agricultural and forest residues is currently considered as a promising alternative for the production of so-called second-generation biofuels. One of the challenges in the design of processes for converting these feedstocks into valuable products is the description of phase equilibrium: due to the highly oxygenated nature of these products and the presence of large amounts of water, both vapour-liquid and liquid-liquid equilibria can occur. Moreover, the large variety of compounds involved in these processes and the lack of experimental data make the use of predictive thermodynamic models very interesting.

The present work is focused on improving the GC-PPC-SAFT parameterization of pure water and its mixture with hydrocarbons and oxygenates. A previous work with this model [1] has led to succesful modelling of the phase equilibrium of these mixtures, but large density deviations were observed for pure water. Here, we used the approach proposed by Held et al. [2], consisting in modifying the temperature dependence of the hard sphere diameter of water in order to improve the global phase behaviour of this compound in a wide temperature range. The deviations in water vapour pressure and especially liquid density are now significantly reduced compared to the previous model [1], to as low as 2.2% and 0.6% ARD respectively, over a temperature range from 0ºC to 550ºC. Four new parameters are introduced.

Mixtures of water with alkanes, aromatics, alcohols, aldehydes, ketones, ethers and esters are then investigated using the group-contribution concept for predicting their LLE and VLE. Results in terms of mutual solubilities are found to be similar or better than our previous works on these mixtures [3]. The VLLE of some water-alcohol heteroazeotropic mixtures are also investigated. A comparison is also made between our purely predictive approach and the one using fitted binary interaction parameters (k_ij). The results so far reflect that after employing our new modifications, the model moves closer to real behaviour and prediction accuracy is enhanced for water mixtures.

References

[1] N. H. Dong, J.C. de-Hemptinne, R. Lugo, J. P. Passarello, P. Tobaly. â??Modeling Liquid-Liquid and Vapor-Liquid enquilbria of Binary systems containing water with an Alkane, an aromatic hydrocarbon, an alcohol or a gas, using GC-PPC-SAFTâ? Industrial Engineering and Chemical Research, 2011, 50: 7467-7483.

[2] C. Held, L.F. Cameretti, G. Sadowski â??Modeling of electrolyte solutions Part 1. Fully dissociated electrolytesâ? Fluid Phase Equilibria, 2008, 270: 87-96.

[3] T.B. Nguyen, J.C. de Hemptinne, B. Creton, G.M. Kontogeorgis. â?? Improving GC-PPC-SAFT equation of state for LLE of hydrocarbons and oxygenated compounds with waterâ? Fluid Phase Equilibria, 2014, 372: 113-125.