Solubility of benzene in methane + nitrogen mixtures at LNG conditions

One of the most common non-hydrocarbon components in natural gas, nitrogen, is thought to reduce the solubility of impurities such as benzene in liquefied natural gas. However, no data are available at LNG-relevant conditions to estimate the magnitude of this effect. This work presents optical measurements of the solubility of solid benzene in mixtures of methane and nitrogen using a stirred, high-pressure apparatus. These measurements were undertaken at industrially-relevant concentrations of benzene from (25 to 450) ppm at pressures from (3.8 to 13.5) MPa. The measured data suggest that benzene solids may form at temperatures up to 3.3 K higher than those predicted using the default models in the thermodynamic software package ThermoFAST. The measured data were used to tune the benzene-nitrogen binary interaction parameter, improving the accuracy of the prediction for the benzene-methane–nitrogen ternary system by up to 2.0 K in the solid–liquid equilibrium region. Together, these data and the resulting improvements to the thermodynamic model can help LNG plant operators and engineers avoid the formation of benzene solids from nitrogen-containing natural gas.