Lf Lawien Zubeir

Hydrophobic deep eutectic solvents as water-immiscible extractants

Hydrophobic deep eutectic solvents (DESs) are presented for the first time. They consist of decanoic acid and various quaternary ammonium salts. The effect of the alkyl chains on the hydrophobicity and the equilibrium of the two-phase DES–water system were investigated. These new DESs were successfully evaluated for the recovery of volatile fatty acids from diluted aqueous solutions.

Enhanced CO2 Capture in Binary Mixtures of 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids with Water

Absorption of carbon dioxide and water in 1-butyl-3-methylimidazoliun tricyanomethanide ([C4C1im][TCM]) and 1-octyl-3-methylimidazolium tricyanomethanide ([C8C1im][TCM]) ionic liquids (ILs) was systematically investigated for the first time as a function of the H2O content by means of a gravimetric system together with in-situ Raman spectroscopy, excess molar volume (V(E)), and viscosity deviation measurements. Although CO2 absorption was marginally affected by water at low H2O molar fractions for both ILs, an increase of the H2O content resulted in a marked enhancement of both the CO2 solubility (ca. 4-fold) and diffusivity (ca. 10-fold) in the binary [C(n)C1im][TCM]/H2O systems, in contrast to the weak and/or detrimental influence of water in most physically and chemically CO2-absorbing ILs. In-situ Raman spectroscopy on the IL/CO2 systems verified that CO2 is physically absorbed in the dry ILs with no significant effect on their structural organization. A pronounced variation of distinct tricyanomethanide Raman modes was disclosed in the [C(n)C1im][TCM]/H2O mixtures, attesting to the gradual disruption of the anion-cation coupling by the hydrogen-bonded water molecules to the [TCM](-) anions, in accordance with the positive excess molar volumes and negative viscosity deviations for the binary systems. Most importantly, CO2 absorption in the ILs/H2O mixtures at high water concentrations revealed that the [TCM](-) Raman modes tend to restore their original state for the heavily hydrated ILs, in qualitative agreement with the intriguing nonmonotonous transients of CO2 absorption kinetics unveiled by the gravimetric measurements for the hybrid solvents. A molecular exchange mechanism between CO2 in the gas phase and H2O in the liquid phase was thereby proposed to explain the enhanced CO2 absorption in the hybrid [C(n)C1im][TCM]//H2O solvents based on the subtle competition between the TCM-H2O and TCM-CO2 interactions, which renders these ILs very promising for CO2 separation applications.

Low Transition Temperature Mixtures as Innovative and Sustainable CO2 Capture Solvents

The potential of three newly discovered low transition temperature mixtures (LTTMs) is explored as sustainable substituents for the traditional carbon dioxide (CO2) absorbents. LTTMs are mixtures of two solid compounds, a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), which form liquids upon mixing with melting points far below those of the individual compounds. In this work the HBD is lactic acid and the HBAs are tetramethylammonium chloride, tetraethylammonium chloride, and tetrabutylammonium chloride. These compounds were found to form LTTMs for the first time at molar ratios of HBD:HBA = 2:1. First, the LTTMs were characterized by determining the thermal operating window (e.g., decomposition temperature and glass transition temperature) and the physical properties (e.g., density and viscosity). Thereafter, the phase behavior of CO2 with the LTTMs has been measured using a gravimetric magnetic suspension balance operating in the static mode at 308 and 318 K and pressures up to 2 MPa. The CO2 solubility increased with increasing chain length, increasing pressure, and decreasing temperature. The Peng-Robinson equation of state was applied to correlate the phase equilibria. From the solubility data, thermodynamic parameters were determined (e.g., Henrys law coefficient and enthalpy of absorption). The heat of absorption was found to be similar to that in conventional physical solvents (-11.21 to -14.87 kJ·mol(-1)). Furthermore, the kinetics in terms of the diffusion coefficient of CO2 in all LTTMs were determined (10(-11)-10(-10) m(2)·s(-1)). Even though the CO2 solubilities in the studied LTTMs were found to be slightly lower than those in thoroughly studied conventional physical solvents, LTTMs are a promising new class of absorbents due to their low cost, their environmentally friendly character, and their easy tunability, allowing further optimization for carbon capture.

PC-SAFT Modeling of CO2 Solubilities in Deep Eutectic Solvents

Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), a physically based model that accounts for different molecular interactions explicitly, was applied to describe for the first time the phase behavior of deep eutectic solvents (DESs) with CO2 at temperatures from 298.15 to 318.15 K and pressures up to 2 MPa. DESs are mixtures of two solid compounds, a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), which form liquids upon mixing with melting points far below that of the individual compounds. In this work, the HBD is lactic acid and the HBAs are tetramethylammonium chloride, tetraethylammonium chloride, and tetrabutylammonium chloride. Two different modeling strategies were considered for the PC-SAFT modeling. In the first strategy, the so-called pseudo-pure component approach, a DES was considered as a pseudo-pure compound, and its pure-component parameters were obtained by fitting to pure DES density data. In the second strategy, the so-called individual-component approach, a DES was considered to consist of two individual components (HBA and HBD), and the pure-component parameters of the HBA and HBD were obtained by fitting to the density of aqueous solutions containing only the individual compounds of the DES. In order to model vapor-liquid equilibria (VLE) of DES + CO2 systems, binary interaction parameters were adjusted to experimental data from the literature and to new data measured in this work. It was concluded that the individual-component strategy allows quantitative prediction of the phase behavior of DES + CO2 systems containing those HBD:HBA molar ratios that were not used for k(ij) fitting. In contrast, applying the pseudo-pure component strategy required DES-composition specific k(ij) parameters.

Low viscosity highly conductive ionic liquid blends for redox active electrolytes in efficient dye-sensitized solar cells

Mixtures of ionic liquids were prepared and used for the development of composite redox electrolytes by blending a standard low viscosity ionic liquid solvent (EMimDCA, 1-ethyl-3-methylimidazolium dicyanamide) with various iodide-based ionic liquids based on the methylimidazolium cation (DMII, EMII, PMII, BMII and HMII). The novel electrolytes based on the [CnC1im]I–EMimDCA double salt ILs show interesting physicochemical properties including low viscosity (10–110 MPa s) and high diffusion coefficient of triiodides , respectively, characteristics that promise increased performance in DSC devices. Their electrochemical properties along with the conductivity were also tuned and optimized; values as high as 2–4 mS cm−1 were estimated for the conductivity. Solar cells based on these composite electrolytes attained efficiencies over 4% under 1 sun with the highest being 5.5%, attained by the EMimDCA–DMII mixture. Quite notably, these efficiencies further increased up to 6.5%, when the cells were illuminated by 0.1 sun.

Microscopic study of the corrosion behaviour of mild steel in ionic liquids for CO2 capture applications

Three 1-alkyl-3-methylimidazolium tricyanomethanide (TCM) ionic liquids (ILs) (alkyl = ethyl, butyl and hexyl) and one butyrolactam cation-based IL with a fluorinated anion were synthesised and tested in contact with mild steel (MS) at temperatures up to 80 °C. The corrosion behaviour was evaluated by monitoring the morphological changes on the steel surface after testing. Exposure of MS to the IL results in two main types of degradation that depend on the IL type. General etching over the macroscopic surface of the alloy was revealed for the IL with the fluorinated anion. The 1-alkyl-3-methylimidazolium TCM ILs promoted dissolution of MnS inclusions present in the steel. In the ILs with a shorter alkyl chain in the cation (alkyl = ethyl, butyl), the dissolution of MnS was accompanied by generation of corrosion products around the inclusion sites, which are mainly identified as magnetite and maghemite ferrites by micro-Raman spectroscopy. The rest of the macroscopic steel surface remains unaffected. Etching resulted in significant weight loss due to removal of material, whereas no significant weight loss was revealed following MnS dissolution. Butyrolactam cation-based IL severely attacks MS with the formation of a plethora of corrosion products including ferrites (mainly hematite), zinc oxide, sulphates and carbonates. Addition of 500 ppm sodium molybdate to the butyrolactam cation-based IL resulted in efficient inhibition of etching at both room temperature and 60 °C due to adsorption of molybdate on the alloy surface. A side effect of MS degradation is that the CO2 absorption capacity of the ILs can be severely reduced through the transfer of metal ions and corrosion products from the metallic surface to the liquid phase. Therefore, gravimetric CO2 absorption capacity and kinetic measurements on the selected 1-alkyl-3-methylimidazolium tricyanomethanide ILs before and after their contact with MS were also conducted with the purpose to unveil and study these side effects. Moreover, CO2 absorption experiments of the butyrolactam cation-based IL before and after contact with MS, as well as in the presence of a sodium molybdate inhibitor, showed that sodium molybdate has the capacity to limit significantly the etching rate without affecting the CO2 capture performance of the IL.

Carbon Dioxide Solubilities in Decanoic Acid-Based Hydrophobic Deep Eutectic Solvents

The solubility of CO2 in hydrophobic deep eutectic solvents (DESs) has been measured for the first time. Six different hydrophobic DESs are studied in the temperature range from 298 to 323 K and at CO2 pressures up to 2 MPa. The results are evaluated by comparing the solubility data with existing hydrophilic DESs and currently applied physical solvents and fluorinated ionic liquids. The DESs are prepared by mixing decanoic acid with a quaternary ammonium salt with different halide anions and alkyl chain lengths. The measured CO2 solubilities are similar to those found in renowned fluorinated ILs, while the heats of CO2 absorption are in the range of nonpolar solvents. The presented DESs show good potential to be used as CO2 capture agents.