Measurement of carbon dioxide freezing in mixtures of methane, ethane and nitrogen

There have been minimal solid-vapor-equilibrium (SVE) studies for mixtures of light natural gas constituents containing carbon dioxide. In this work, frost points for the methane-carbon dioxide binary were determined for mixtures containing 1.00%, 1.91% and 2.93% carbon dioxide at pressures ranging from 140 psia to 435 psia and temperatures ranging from -156°F to -121°F. The effect on the carbon dioxide frost point due to the addition of ethane and nitrogen was also examined. A non-sampling visual observation apparatus that avoided problems involved while sampling a saturated mixture in equilibrium was constructed to collect SVE data at low temperatures. Frost points collected for the methane-carbon dioxide binary were within a reasonable range of existing data. Frost point temperatures were higher with increased ethane content as well as increased nitrogen content at higher pressures. The Peng-Robinson EOS was used to correlate the methane-carbon dioxide SVE data using a temperature dependent interaction parameter.