2-4-1 CO₂ + N₂ mixed gas separation by ionic clathrate hydrates

Abstract

This paper reports an experimental study of CO₂ + N₂ mixed gas separation based on tetra-n-butylammonium bromide (TBAB) hydrates with TBAB aqueous solution of 40 mass%. The composition of a mixed gas simulated flue gas is CO₂ : N₂ = 0.15 : 0.85. We used a high-pressure cell having 800 cm³ inner volume for hydrate formation. We used three different pressure levels: 1, 3 and 5 MPa with 2.5 K of subcooling temperatures. We analyzed the gas compositions in gas phase before and after the hydrate formation by a gas chromatograph and calculated the gas compositions in hydrate phase. The CO₂ mole fractions in hydrate phase were higher in lower pressure conditions, i.e., 0.40–0.45 with 1 and 3 MPa and 0.30 with 5 MPa. The results suggest that TBAB hydrates have a tendency to form tetragonal and orthorhombic structures at low and high pressure conditions, respectively.