Recovery of CO₂ from Flue Gas Using Gas Hydrate:  Thermodynamic Verification through Phase Equilibrium Measurements

Abstract

The main purpose of this study was to develop a new hydrate-based gas separation (HBGS) process especially for recovering CO2 from flue gas. Temperature and pressure conditions for hydrate formation have been closely examined at the various CO2 concentrations of flue gases. Tetrahydrofuran (THF) chosen as a hydrate promoter can also participate in forming hydrates and produces a mixed hydrate together with CO2. The hydrate stability region was greatly expanded by using THF for lowering the equilibrium formation pressure. To confirm thermodynamic validity of the HBGS process, the three-phase equilibria of hydrate, liquid, and vapor were measured for the systems comprising CO2, N2 and water with or without THF in the temperature range of 272−295 K. In addition, two phase equilibria of hydrate and vapor were experimentally investigated for the same systems at several temperatures. Through close examination of the overall experimental results, it was firmly verified that the HBGS process makes it possible to recover more than 99 mol % of CO2 from the flue gas. The key unit operations of the HBGS lie in hydrate formation and subsequent dissociation similarly to gas absorption and desorption using the sterically hindered amines. The HBGS provides several advantages over the conventional ones. First, the operational temperature is moderate in the range of 273−283 K, and continuous operation allows this process to treat a large amount of gaseous stream. Second, only a small amount of THF is needed together with water and therefore severe corrosion problem can be avoided. Third, the aqueous solution containing THF after dissociation can be easily recycled to the hydrator.

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

“…The dry molar (%) gas compositions of the binary gas mixtures were determined by gas chromatography and are as follows: CO 2 (17.0)/N 2 (83.0) for the model flue gas and CO 2 (40.0)/H 2 (60%) for the model fuel gas mixture. Since N 2 and O 2 form hydrate at approximately the same pressure/temperature conditions, the above CO 2 /N 2 mixture is considered a suitable model flue gas (Kang and Lee, 2000;Linga et al, 2007a). THF was supplied by Fisher Scientific with 99% purity.…”

“…Capture of CO 2 from power plant flue gases from conventional power plants or from fuel gases from gasification plants is a technological application of gas hydrates under consideration (Aaron and Tsouris, 2005;Kang and Lee, 2000;Klara and Srivastava, 2002;Kumar et al, 2009;Linga et al, 2008Linga et al, , 2007aSeo et al, 2005). Post-combustion CO 2 capture involves separation of CO 2 from the flue gas mixture emitted from a power plant.…”

Thermodynamic promotion of carbon dioxide–clathrate hydrate formation by tetrahydrofuran, cyclopentane and their mixtures

“…Several publications are available in the literature, presenting THF as a possible promoter in pre- Linga et al, 2007aLinga et al, , 2007bZhang et al, 2009) or post combustion ( Giavarini et al, 2010, Kang andLee, 2000;Kang et al, 2001;Linga et al, 2010;Linga et al, 2007bLinga et al, , 2008 hydrate-based CO 2 capture processes. However, only a few publications provide detailed phase equilibrium data for the ternary system of water, THF and CO 2 , especially at low temperatures and THF concentrations of approximately 17.4 mass percent (5 mole percent) in the aqueous phase (Delahaye et al, 2006;Sabil et al, 2010;Seo et al, 2008).…”

“…In separation attempts applied to gas mixtures containing CO 2 and nitrogen, one of the main conclusions was that the selectivity of CO 2 over N 2 in the hydrate phase is lowered by the presence of THF compared to the non-promoted systems (Kang and Lee, 2000). The highest CO 2 selectivities were obtained when operating at low temperatures.…”

Resolving CO2 and methane hydrate formation kinetics

“…Many workers (Lee et al 1997) have assumed formation of a mixed hydrate. A previous study based on exhaust gas seemed to assume that mixed hydrates would be formed (Kang and Lee 2000). However, more recent work does indicate that ''pure'' hydrates would be formed (Kang et al 2001).…”