Green Extraction of Volatile Fatty Acids from Fermented Wastewater Using Hydrophobic Deep Eutectic Solvents

Volatile fatty acids (VFAs) are carboxylic acids mainly produced via the fermentation of organic waste streams. Being industrial platform chemicals, sustainable, green and economical recovery of VFAs is necessary. Herein, hydrophobic deep eutectic solvents (HDES), “a new generation of water-immiscible designer solvents”, were assessed for the recovery of VFAs via liquid–liquid extraction. The eutectic mixture of menthol-lauric acid exhibited the highest stability and hydrophobicity. The binary solubility of the pairs {VFA in water} and {VFA in HDES}—and the saturation of the HDES with water were measured. Furthermore, the influences of key parameters on the extraction efficiency were investigated. On multi-stage extraction, an efficiency of 88% was achieved in 4 stages, and the HDES was successfully regenerated using vacuum evaporation. The HDES performance was also compared to other reported relevant solvents. It was concluded that menthol-lauric acid HDES is a promising candidate for the green extraction of VFAs from fermented wastewater

Role of Hydrocarbon Building Blocks on Gas-to-Liquid Derived Synthetic Jet Fuel Characteristics

The role of typical hydrocarbon building blocks of gas-to-liquid (GTL) derived jet fuels on their physical and chemical properties have been investigated. The ultimate goal of our studies is to develop accurate composition–property relationships for synthetic fuels to be used in optimizing synthetic fuel properties as per the aviation industry standards. The composition–property analysis has been carried out through formulating in-house fuel blends using neat GTL fuel building blocks (<i>normal-</i>, <i>iso-</i>, and <i>cyclo-</i>paraffins). Typical properties of interest in this study are density, freezing point, flash point, and heat content, all of which are essential for jet fuel certification. The systematic approach developed in this study was to identify an optimized region, in which all major properties for aviation standards are met. Different techniques were used, including the development of ternary mapping of these aforementioned building blocks alongside their physical properties. This has been achieved through formulating 35 blends giving a broad spread across the ternary map and generating a database from the experimental results. The optimized region and the composition–property relationships were obtained through building a statistical model of artificial neutral networks (ANNs) using the data generated as its basis. The generated data show that some properties, such as freezing point, exhibit nonlinear results whereas others are strongly linear, such as density and heat content. Aromatics in jet fuels are impactful (and required) even though their environmental harms are evident, and as such, their role on certain properties was preliminarily investigated. Furthermore it has been observed that different crystal shapes exist within some areas in the freezing point ternary map. Finally, the use of mathematical models as predictive tools was investigated, and in most instances the model developed was accurate. The outcome of the current study has been used to develop a new visualization technique for the relationship between GTL synthetic paraffinic kerosene’s and their building blocks (i.e., paraffinic hydrocarbons)

Effect of the Type of Ammonium Salt on the Extractive Desulfurization of Fuels Using Deep Eutectic Solvents

In a previous work, we proved that the deep eutectic solvents (DESs) consisting of mixtures of tetraalkylammonium salts with polyols are promising candidates for oil desulfurization based on the obtained liquid–liquid equilibrium (LLE) data. In this study, the capability of DESs containing other salts (e.g., different alkyl chain lengths or different functional groups on the ammonium cation) for the extraction of thiophene from {<i>n</i>-hexane + thiophene} mixtures via LLE was evaluated. Therefore, four DESs composed of tetraethylammonium chloride or methyltriphenylphosphonium bromide as hydrogen bond acceptors and ethylene glycol or glycerol as hydrogen bond donors were prepared. Thereafter, the binary solubilities of the aliphatic hydrocarbon (<i>n</i>-hexane) and the thiophene in DESs were measured at 298.2 K and atmospheric pressure. Next, ternary liquid–liquid equilibrium (LLE) data for the four ternary systems {<i>n</i>-hexane + thiophene + DES} were measured at 298.2 K and atmospheric pressure. The conductor-like screening model for real solvents (COSMO-RS) was used to better understand the extraction mechanism of thiophene. Experimentally obtained solute distribution coefficients and selectivities were calculated and compared to relevant literature. All DESs were found to be good candidates for extractive desulfurization with higher selectivities but somewhat lower distribution coefficients as compared to conventional ionic liquids. It was found that longer alkyl chain lengths on the cation yield higher distribution coefficients but lower selectivities, and the replacement of an alkyl group by a phenyl group on the cation generally yields lower distribution ratios ratios but higher selectivities

Mercury Capture from Petroleum Using Deep Eutectic Solvents

Mercury capture is a major challenge in petroleum and natural gas processing. Recently, ionic liquids (ILs) have been introduced as mercury extractants from oil and gas. ILs yield very high mercury extraction efficiencies (>95%) from hydrocarbons, but their drawbacks include complex synthesis, toxicity, and difficult regeneration after mercury capture. In this work, a new technology using deep eutectic solvents (DESs) for elemental mercury (Hg⁰) extraction from hydrocarbons is demonstrated. DESs are an innovative class of designer solvents exhibiting similar properties as ILs, such as low vapor pressure and low flammability, but DESs are formed from inexpensive hydrogen-bond donor and acceptor compounds that are often biodegradable. In this work, four DESs were investigated including choline chloride:urea, choline chloride:ethylene glycol, choline chloride:levulinic acid, and betaine:levulinic acid, where the molar ratio is 1:2 in all cases. The DESs were tested for their thermal stability, density, and viscosity. Their performance for mercury extraction was assessed using saturated solutions in <i>n</i>-dodecane as the model oil. It was found that solvent to feed ratios of 1:1 and 2:1 at temperatures of 303.15 and 333.15 K and atmospheric pressure yield extraction efficiencies greater than 80% for all four DESs. First-principles molecular dynamics simulations probing the solvation in choline chloride:urea indicate a tight first coordination shell for mercury. Calculation of the Hg–Hg potential of mean force supports formation of a mercury–mercury polycation for a pair of Hg¹⁺ ions, but not for pairs of Hg⁰ and Hg²⁺ species. Geometric analysis of the speciation and Mulliken population analysis support a redox reaction involving Hg²⁺ + 2Cl^–