Structure and composition of CO₂/H₂ and CO₂/H₂/C₃H₈ hydrate in relation to simultaneous CO₂ capture and H₂ production

Abstract

in Wiley InterScience (www.interscience.wiley.com).Gas hydrates from a (40/60 mol %) CO 2 /H 2 mixture, and from a (38.2/59.2/2.6 mol %) CO 2 /H 2 /C 3 H 8 mixture, were synthesized using ice powder. The gas uptake curves were determined from pressure drop measurements and samples were analyzed using spectroscopic techniques to identify the structure and determine the cage occupancies. Powder X-ray diffraction (PXRD) analysis at À110 C was used to determine the crystal structure. From the PXRD measurement it was found that the CO 2 /H 2 hydrate is structure I and shows a self-preservation behavior similar to that of CO 2 hydrate. The ternary gas mixture was found to form pure structure II hydrate at 3.8 MPa. We have applied attenuated total reflection infrared spectroscopic analysis to measure the CO 2 distribution over the large and small cavities. 1 H MAS NMR and Raman were used to follow H 2 enclathration in the small cages of structure I, as well as structure II hydrate. V The inset shows the expanded central region of the spectrum without spinning sidebands. The peak at 6.59 ppm is due to the proton impurity in D 2 O.

Recent advances in gas hydrate-based CO2 capture

“…It induces the formation of S II hydrates when it competes with CO 2 for occupancy of large cages (Adisasmito and Sloan, 1992). A study has shown that 57% of large cages are occupied by CO 2 when 2.5 mol% C 3 H 8 was added to the system (Kumar et al, 2009a). In most studies, the S II hydrate form of CO 2 hydrates was observed.…”

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

“…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.…”

Enhancing CO2 separation for pre-combustion capture with hydrate formation in silica gel pore structure

“…The X-ray diffraction pattern of the mixed hydrate identifies the crystal structure with a cubic unit cell parameter of 1.186 nm; the 13 C NMR spectra of mixed hydrate suggests that the CO 2 molecules occupy a large amount of 5 12 and 5 12 6 2 cages, while H 2 resides in 5 12 cages [12]. Quantitative estimates of cage occupancy are provided based on the analysis of the IR spectra and the knowledge of hydrate gas composition from the gas chromatograph [13,14]. Although 13 C NMR spectroscopy provides only the superimposed spectral pattern of CO 2 in small and large cages, it still provides important information on the molecular dynamics of CO 2 in hydrate cages, which can be distinguished with a chemical shift anisotropy induced by the cage symmetry [15].…”

“…Hydrate formation from 41 mol% CO 2 and balanced H 2 gas mixture showed that most of the cages are occupied by CO 2 molecules, and that a 98.7 mol% CO 2 and balanced H 2 gas mixture is retrieved from the dissociation of hydrate formed at ∼9.2 MPa and 274.15 K. When decreasing the pressure from 9.2 MPa to 6.0 MPa, the concentration of CO 2 in the hydrate phase decreases from 98.7 to 96.5 mol%, which is a tendency opposite to that in bulk water. 13 C NMR spectra suggest that major changes of CO 2 distribution happen in small cages, which may indicate the effect of pore structure on the formation of mixed hydrate. Current industrial concepts such as a series of fixed-bed reactors and a fluidized bed reactor are discussed as possible design options for a hydrate-based pre-combustion CO 2 capture process.…”