Emanuel A. Crespo

Soft-SAFT Equation of State as a Valuable Tool for the Design of new CO 2 Capture Technologies.

The design, simulation and/or optimization of new processes rely on the availability of robust and accurate models or equations of state (EoS). However, traditional cubic equations of state (EoS’s), traditionally used in many process simulators, fail on describing complex polar and associating behavior of some molecules, leading to unreliable results and hence, poor design and optimization. This problem can be overcome with the use of robust, reliable equations of state. This work belongs to a long term project assessing the performance and usefulness of an advanced EoS (soft-SAFT), as a valuable tool for the description of highly non-ideal systems and thus, for the reliable simulation/design of new technologies. We focus here on assessing the validity of soft-SAFT, a molecular-based EoS, for the development of novel technologies for CO2 capture using polyether blends as solvent. Within soft-SAFT polyether molecules are modeled as chains with end-groups having an association site, explicitly mimicking the hydroxyl end-groups. The study comprises polyethers, including glymes, and their mixtures with CO2 at different conditions. It is shown that soft-SAFT is able to successfully describe the thermodynamic behavior (e.g. vapor pressures and liquid densities) of these solvents in wide temperature and pressure ranges. Moreover, by explicitly considering the quadrupolar moment of CO2, and using one, temperature and pressure independent binary interaction parameter, an accurate description of the gas solubilities in several polyethers was achieved. For glymes, which among polyethers exhibit the highest CO2 solubilities, such parameter was found to correlate with the molecular weight of the solvent. Finally the equation was used to predict the thermal and pressure cycle capacities of the different solvents. Results presented here reinforce the use of soft-SAFT as a reliable tool for solvent screening, offering reliable predictions of phase equilibria and solubility behavior in a wider number of systems.

Vapor Liquid Equilibria of Binary Mixtures of 1-Butyl-3-methylimidazolium Triflate (C4mimTfO) and Molecular Solvents: n-Alkyl Alcohols and Water

Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C4mimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined in the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels ( p = 500 mbar, 700 mbar, and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the nonideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish the structure-property relationship between the C4mimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.