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-biphenyl mixtures feature advantageous characteristics such as low melting points and large hydrogen storage capacities. For contributing to a reliable database of process-relevant thermophysical properties, the present study investigates the viscosity, surface tension, and density of the LOHC-system based on diphenylmethane, biphenyl, and benzophenone between (278 and 573) K. General agreement between the viscosity and surface tension results from surface light scattering and the data from capillary viscometry and pendant-drop tensiometry is found. Larger surface tension differences beyond 10% for systems containing benzophenone seem to originate from surface orientation effects. For the eutectic diphenylmethane-biphenyl mixture including its hydrogenated dicyclohexylmethane-bicyclohexyl analog, the densities, surface tensions, and viscosities are not significantly different from those of the corresponding pure compounds. By gradually replacing diphenylmethane by its oxidized form benzophenone in mixtures with biphenyl, an increase in density, surface tension, and especially viscosity is observed.