CO2/ethane extractive distillation with n-decane

CO2 and ethane are close-boiling (both around 195 K at 1 atm) and form a near-azeotropic VLE at NGL-processing pressures, a known problem for straight distillation in CO2-flood-associated gas and acid-gas-rich NGL streams. A heavy n-decane solvent shifts CO2's relative volatility enough to take it overhead in far fewer stages than an ordinary deethanizer would need; a second column then strips the solvent from the ethane bottoms for recycle. The extractive column runs at a moderately high reflux (R=4.5) — the operating point a genuinely close-boiling pair needs to hold a sharp CO2/ethane split with a heavy solvent — and both columns converge.