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Hydrofluorocarbons (HFC) are fluorinated compounds used globally for refrigeration. These gases have been shown to contain a greenhouse potential of up to 22,000 times that of CO2. Thus, 1298 type-5 deep eutectic solvents (DES) were examined for the absorption and interaction mechanisms of difluoromethane (R32), due to their non-polar attributes. Of these solvents, quaternary ammonium salts mixed with various species of hydrogen bond donators (HBD) produced the most favorable interactions, with ln activity coefficients predicted to be as low as −1.39 at 1:1 compositional ratio. These DES were further studied for compositional analysis where pure tetrabutylammonium bromide showed the strongest interaction potential. The pressure study showed a linear solubility increase with a pressure increase reaching up to 86 mol/mol% in a methyltrioctylammonium bromide and polyethylene glycol mixture at 9 bar. The van der Waals interaction is the driving force of absorption with ~3x enthalpic release over hydrogen bonding. All chemicals contain strong potential for an environmentally friendly solution, as is evident through an environmental health and safety analysis.

 

In this study, carbon dots are synthesized hydrothermally from loblolly pine using top-down and bottom-up processes. The bottom-up process dialyzed carbon dots from hydrothermally treated process liquid. Meanwhile, hydrochar was oxidized into carbon dots in the top-down method. Carbon dots from top-down and bottom-up processes were compared for their yield, size, functionality, and quantum properties. Furthermore, hydrothermal treatment temperature and residence time were evaluated on the aforementioned properties of carbon dots. The results indicate that the top-down method yields higher carbon dots than bottom-up in any given hydrothermal treatment temperature and residence time. The size of the carbon dots decreases with the increase in reaction time; however, the size remains similar with the increase in hydrothermal treatment temperature. Regarding quantum yield, the carbon dots from the top-down method exhibit higher quantum yields than bottom-up carbon dots where the quantum yield reaches as high as 48%. The only exception of the bottom-up method is the carbon dots prepared at a high hydrothermal treatment temperature (i.e., 260 °C), where relatively higher quantum yield (up to 18.1%) was observed for the shorter reaction time. Overall, this study reveals that the properties of lignocellulosic biomass-derived carbon dots differ with the synthesis process as well as the processing parameters. 

Deep eutectic solvents (DES) are compounds of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) that contain a depressed melting point compared to their individual constituents. DES have been studied for their use as carbon capture media and biogas upgrading. However, contaminants’ presence in biogas might affect the carbon capture by DES. In this study, conductor-like screening model for real solvents (COSMO-RS) was used to determine the effect of temperature, pressure, and selective contaminants on five DES’ namely, choline chloride-urea, choline chloride-ethylene glycol, tetra butyl ammonium chloride-ethylene glycol, tetra butyl ammonium bromide-decanoic acid, and tetra octyl ammonium chloride-decanoic acid. Impurities studied in this paper are hydrogen sulfide, ammonia, water, nitrogen, octamethyltrisiloxane, and decamethylcyclopentasiloxane. At infinite dilution, CO2 solubility dependence upon temperature in each DES was examined by means of Henry’s Law constants. Next, the systems were modeled from infinite dilution to equilibrium using the modified Raoults’ Law, where CO2 solubility dependence upon pressure was examined. Finally, solubility of CO2 and CH4 in the various DES were explored with the presence of varying mole percent of selective contaminants. Among the parameters studied, it was found that the HBD of the solvent is the most determinant factor for the effectiveness of CO2 solubility. Other factors affecting the solubility are alkyl chain length of the HBA, the associated halogen, and the resulting polarity of the DES. It was also found that choline chloride-urea is the most selective to CO2, but has the lowest CO2 solubility, and is the most polar among other solvents. On the other hand, tetraoctylammonium chloride-decanoic acid is the least selective, has the highest maximum CO2 solubility, is the least polar, and is the least affected by its environment.