Separation of N2/CO2 mixture using a continuous high-pressure density-driven separator

•A new high-pressure, density-driven separator is designed and fabricated for separation of N2/CO2 mixture under steady-state condition.•The effects of process variables are investigated on separation efficiency.•A dimensionless number (Es) is introduced to evaluate separation of N2/CO2 mixture.•Perfect separation of N2/CO2 mixture takes place while Ar × Es is more than 4.5 × 1030.

A mixture of 85% nitrogen and 15% carbon dioxide (N2/CO2) is separable at ambient temperature on a continuous basis. A high-pressure, density-driven separator (HDS) was designed and fabricated to explore the process. The effect of the fluid variables, including pressure and mixture flow rate, was assessed on a separation efficiency metric. An important design parameter, the length of the HDS, was also evaluated in the experimental design. Essentially perfect separation is observed over a wide-range of conditions. Separation efficiency is correlated with two dimensionless groups. The first is the Archimedes number. It is a ratio of buoyant force to viscous force. The second dimensionless group is defined in this work. The Espanani number is the ratio of the pressure force to the viscous force. Excellent correlation between separation efficiency and the product of the Archimedes number and the Espanani number is observed. This observation informs both process and equipment design.