Programmable Thermoresponsive Micelle-Inspired Polymer Ionic Liquids as Molecular Shuttles for Anionic Payloads

International audienceTo enable the programmable thermoresponsive transport of anions between two phases, multifunctional hyperbranched polymer ionic liquids (hyperPILs) exhibiting micelle-inspired architectures are tailored as molecular shuttles. These polyelectrolytes consist of a hyperbranched poly(3-ethyl-3-hydroxymethyloxetane) (PEHO) core, an inner polyionic imidazolium (Im+) and an outer thermoresponsive polyoxazoline (POx) shell, which exhibits lower critical solution temperature (LCST) behavior in aqueous medium. Key step of the hyperPIL synthesis is the efficient chain termination of the cationic ring-opening 2-oxazoline polymerization by addition of polyfunctional imidazole-terminated PEHO. The resulting covalent attachment of the LCST-polyoxazoline shell renders hyperPIL polyelectrolytes thermoresponsive. As a function of the polyoxazoline chain length and the oxazoline monomer type, the hyperPIL cloud points (TCP) vary over a wide temperature range. The inner imidazolium shell enables the immobilization and transport of various anionically charged organic and inorganic payloads via anion exchange. Due to the thermal switching of the hydrophilicity/hydrophobicity balance, hyperPILs function as programmable molecular shuttles for anionic payloads transported back and forth between the phases of ethyl acetate and water. Thus, switchable hyperPILs qualify for manifold potential applications like catalytic processes with facile recycling of homogeneous catalysts via phase transfer

Determination of hydrogen loading in the carrier system diphenylmethane/dicyclohexylmethane by depolarized Raman spectroscopy

During the processes of hydrogenation or dehydrogenation of liquid organic hydrogen carriers (LOHCs), knowledge of the current degree of hydrogenation (DoH) is often essential. The present study shows that depolarized Raman spectroscopy allows the accurate determination of the DoH of the model LOHC system diphenylmethane (H0-DPM)/dicyclohexylmethane (H12-DPM) at temperatures up to 573 K. Using two independent experimental setups and binary mixtures of H0- and H12-DPM, a temperature-independent calibration factor could be obtained by analyzing Raman bands characteristic for the aromatic and aliphatic carbon rings. The successful transfer of the calibration to technical mixtures is validated by DoH measurements of samples from deliberately stopped hydrogenation reactions containing also the intermediate cyclohexylphenylmethane (H6-DPM) and of pure H6-DPM. Here, the average absolute deviation of the DoHs obtained by depolarized Raman spectroscopy from those measured analytically is 0.018, which demonstrates the applicability of the method at arbitrary and process-relevant temperatures

Influence of dissolved hydrogen on the viscosity and interfacial tension of the liquid organic hydrogen carrier system based on diphenylmethane by surface light scattering and molecular dynamics simulations

In hydrogenation and dehydrogenation processes of liquid organic hydrogen carriers (LOHCs), molecular hydrogen (H2) is present, but its influence on the thermophysical properties of the LOHC compounds is still hardly known. This study provides experimental results from surface light scattering and predictions from molecular dynamics simulations on the influence of dissolved H2 on the liquid viscosity, interfacial tension, and liquid density of the LOHC system based on diphenylmethane at varying degree of hydrogenation, process-relevant temperatures up to 573 K, and pressures up to 7 MPa. First-time measurements of the viscosity of bicyclic hydrocarbon compounds in the presence of dissolved H2 at saturation conditions reveal a negligible effect of pressure. The interfacial tension decreases independently of the LOHC composition by about 6% at 7 MPa. The simulations can adequately represent the effect of H2 on the interfacial tension and evidence a weak enrichment of H2 at the interface

Viscosity and Surface Tension of Fluorene and Perhydrofluorene Close to 0.1 MPa up to 573 K

In the present study, the liquid viscosity and surface tension of fluorene (H0-F) and its fully hydrogenated counterpart perhydrofluorene (H12-F), representing process-relevant byproducts of the liquid organic hydrogen carrier (LOHC) system based on diphenylmethane and dicyclohexylmethane and potentially interesting LOHC compounds by themselves, were determined close to 0.1 MPa using different experimental methods. Besides surface light scattering (SLS) allowing for a simultaneous access to both properties up to 573 K, conventional methods in the form of capillary viscometry and pendant-drop tensiometry were applied up to (473 and 523) K, respectively. Furthermore, the liquid density of H12-F was measured by vibrating-tube densimetry from (283 to 473) K. While agreement of the viscosity and surface tension results obtained by SLS and the conventional methods is found in the case of H12-F, this is not given for H0-F, especially with respect to its surface tension, which seems to be caused by SLS-specific effects. H0-F exhibiting a melting point of about 384 K shows larger values for density, surface tension, and viscosity compared to H12-F being liquid at 283 K. The latter compound features stereoisomerism which appears to have a pronounced effect on the thermophysical properties. This could be deduced by comparison with the very limited amount of experimental data for the fluorene-based substances that are available in the literature so far. The extension of the thermophysical property database for H0-F and H12-F under process-relevant conditions can be useful for future studies, particularly in the field of chemical hydrogen storage

Viscosity, surface tension, and density of binary mixtures of the liquid organic hydrogen carrier diphenylmethane with benzophenone

The liquid organic hydrogen carrier (LOHC) diphenylmethane may react to benzophenone in the presence of air, especially at elevated temperatures. Therefore, information about the influence of benzophenone added to diphenylmethane on process-relevant thermophysical properties is required. In the present contribution, the liquid viscosity, surface tension, and liquid density of binary mixtures of diphenylmethane with benzophenone are determined between (283 and 573) K using complementary experimental methods. Investigations on the surface tension by the pendant-drop method and surface light scattering indicate molecular orientation effects of benzophenone at the vapor-liquid interface. With increasing benzophenone content, an increase in density, surface tension, and especially viscosity is found. For the latter property, a distinct change in the temperature dependence is observed at the transition from the liquid to the supercooled liquid state. Furthermore, water dissolved in benzophenone causes changes within 15% and 3% relative to the viscosity and surface tension of benzophenone, respectively

Viscosity, surface tension, and density of the liquid organic hydrogen carrier system based on diphenylmethane, biphenyl, and benzophenone

Liquid organic hydrogen carriers (LOHCs) relying on eutectic diphenylmethane-biphenylmixtures feature advantageous characteristics such as low melting points and large hydrogen storage capacities. For contributing to a reliable database of process-relevantthermophysical properties, the present study investigates the viscosity, surface tension,and density of the LOHC-system based on diphenylmethane, biphenyl, and benzophenonebetween (278 and 573) K. General agreement between the viscosity and surface tensionresults from surface light scattering and the data from capillary viscometry and pendantdroptensiometry is found. Larger surface tension differences beyond 10% forsystems containing benzophenone seem to originate from surface orientation effects.For the eutectic diphenylmethane-biphenyl mixture including its hydrogenateddicyclohexylmethane-bicyclohexyl analog, the densities, surface tensions, and viscositiesare not significantly different from those of the corresponding pure compounds. Bygradually replacing diphenylmethane by its oxidized form benzophenone in mixtures withbiphenyl, an increase in density, surface tension, and especially viscosity is observed.© 2022 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC