Thermophysical properties of the liquid organic hydrogen carrier system based on benzyltoluene considering influences of isomerism and dissolved hydrogen

Abstract

The benzyltoluene (BT)-based liquid organic hydrogen carrier (LOHC) system currently considered for large-scale applications represents a mixture of regioisomers. To characterize this complex system, a comprehensive experimental database for various thermophysical properties of synthesized BT isomers and their mixtures without and with the presence of hydrogen (H2) close to vapor-liquid equilibrium is established using optical and conventional techniques at process-relevant temperatures and pressures up to 573 K and 6 MPa. The surface tension varies by less than 4% among the dehydrogenated (H0-BT) or hydrogenated (H12-BT) isomers. The density and viscosity of mixtures of H0-BT or H12-BT isomers can be described by simple mixing rules with average absolute relative deviations of 0.022% and 0.38%. With increasing H2 pressure, the viscosity remains nearly constant, while the interfacial tension decreases by up to 5%. The thermal and mutual diffusivity of H12-ortho-BT containing dissolved H2 at 6 MPa decrease and increase with increasing temperature.