Unsaturated hydrocarbons in the lakes of Titan: Benzene solubility in liquid ethane and methane at cryogenic temperatures

The solubility of benzene in liquid ethane has been measured using ultraviolet absorption. Spectra were recorded in the 200-1000 nm range. The secondary absorption band (1B2u) of benzene in the region 230-260 nm was recorded to determine the solubility of the sample. Ethane does not absorb in the benzene UV region but absorption bands are observed at 908 nm, 745 nm, and 634 nm corresponding to C-H vibrational overtone transitions of liquid ethane with Δυ=4, 5 and 6, respectively. Spectra were obtained at several concentrations and temperatures. The solubilities are: (26±6) ppm at 94 K, (39±6) ppm at 102 K, (48±8) ppm at 111 K, (72±10) ppm at 132 K, and (170±38) ppm at 162 K. With the solubility obtained at each temperature the enthalpy and entropy of solution were calculated from the experimental data. The spectra of solutions of benzene in liquid methane have been obtained to determine the solubility at 97 K. Thermodynamic parameters and solubility data from experimental measurements are important for more realistic simulations of the chemical composition of the lakes of Titan.