Efficient Capture of CO₂from Simulated Flue Gas by Formation of TBAB or TBAF Semiclathrate Hydrates

Abstract

Capturing CO 2 by forming hydrate is an attractive technology for reducing the greenhouse effect. The most primary challenges are high energy consumption, low hydrate formation rate, and separation efficiency. This work presents efficient capture of CO 2 from simulated flue gas (CO 2 (16.60 mol %)/N 2 binary mixtures) by formation of semiclathrate hydrates at 4.5 and 7.1 °C and feed pressures ranging from 2.19 to 7.31 MPa. The effect of 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) and tetra-n-butyl ammonium fluoride (TBAF) on the hydrate formation rate, reactor space velocity, and CO 2 separation efficiency was studied in a 1 L stirred reactor. The results showed the hydrate formation rate constant increased with increasing feed pressure and reached the maximum at 2.82 × 10 -7 mol 2 /(s • J) with TBAB and 8.26 × 10 -7 mol 2 /(s • J) with TBAF. The space velocity of the hydrate reactor increased with increasing feed pressure and reached a maximum of 13.46 h -1 with TBAB and 25.96 h -1 with TBAF. CO 2 recovery was about 50%, and the optimum CO 2 separation factor with TBAF was 36.98, which was about 4 times higher than that with TBAB in the range of feed pressure. CO 2 could be enriched to 90.40 mol % from simulated flue gas under low feed pressure by two stages of hydrate separation with TBAF. The results demonstrated that TBAB, especially TBAF, could accelerate hydrate formation. The space velocity of the hydrate reactor with TBAB or TBAF was higher than that with THF. CO 2 could be easily enriched in the hydrate phase by two stages of hydrate separation under gentle conditions.

A new apparatus to enhance the rate of gas hydrate formation: Application to capture of carbon dioxide

“…As seen in the figure, the CO 2 recovery is higher in the new apparatus compared to the laboratory scale apparatus and also higher than experiments conducted with TBAB and TBAF Li et al, 2009). Fan et al (2009) reported a final gas consumption (calculated based on pressure drop data) of 0.14-0.32 moles for experimental pressures between 3.4 and 7.3 MPa in the presence of TBAB and 0.063-0.191 moles for experimental pressures between 2.2 and 6.8 MPa in the presence of TBAF. Taking into account the amount of water report 600 cm 3 of liquid contents) taken for experiments, gas consumption on a water free basis is 0.004-0.010 mol of gas per mol of water for experimental pressures between 3.4 and 7.3 MPa for TBAB containing system and 0.002-0.006 mol of gas per mol of water for experimental pressures between 2.2 and 6.8 MPa for TBAF containing system.…”

“…The normalized rate of gas supply calculated by taking into account of the volume of water (Eq. (3)) for the experiments conducted in the presence of 1.0 mol% THF in the lab-scale apparatus and the new large scale apparatus (this work) and data available in Fan et al (2009).…”

Equilibrium Conditions for Semiclathrate Hydrates Formed with CO2, N2, or CH4 in the Presence of Tri-n-butylphosphine Oxide

“…In other words, SCHs are capable of selectively incorporating small gas guest molecules within the small cavities of the SCHs. Unlike ordinary hydrates having well defined structures (Structure I, Structure II, and Structure H), SCHs have diverse structures and have hydrogen-bonding interaction between guests and hosts molecules, which is much stronger than the van der Waals force in ordinary hydrates 5 SCHs have drawn increasingly more interest from researchers for their potential applications in hydrogen storage 8 , carbon dioxide storage 9 , and gas separation [10][11][12][13][14] . The thermodynamic data of SCHs are limited, and the majority of them are for TBAB 8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] .…”

Phase equilibrium measurements for clathrate hydrates of flue gas (CO2+N2+O2) in the presence of tetra-n-butyl ammonium bromide or tri-n-butylphosphine oxide

“…Despite the satisfactory separation efficiency of current CO 2 capture methods, a challenge remains as to how to reduce the cost and achieve high regenerability [3,4]. One of the most promising attempts for addressing this challenge is CO 2 hydrate formation [5][6][7][8][9][10][11][12]. CO 2 hydrate is one of gas hydrates that are inclusion compounds with cages formed by the hydrogen-bonded water molecules and guest species [13].…”