Introduction
Introduction
- Gas hydrates
- Crystal structures
- Trend of applications
The host structure of gas hydrates is classified as structure I (sI), structure II (sII) and structure H (sH). 22] also investigated the semiclathrate-based fuel gas separation at milder condition than the gas hydrate formation condition.
Thermodynamic hydrate promotion
- sII hydrates
- Semiclathrates
Adding THF and CP to the hydrate formation system can significantly decrease the equilibrium pressure of the gas hydrate at a given temperature and pressure condition because they are confined in large cages with sII hydrates, resulting in significant thermodynamic stabilization. Compared to water-miscible promoters, the liquid phase of CP requires more vigorous stirring to increase the gas–liquid contact area for gas hydrate formation due to its immiscibility with water, indicating a higher energy requirement for the actual application.
As observed in the double CH4 + TBAF semiclathrate [35], the slight downward shift of the NMR peak for the CH4 molecules trapped in the double CH4 + TBAC semiclathrate is the result of deshielding caused by the presence of electronegative chloride (Cl). Both CO2 and N2 molecules are enclosed in the cages of the clathrate was confirmed from the Raman spectra.
Experimental section
Experimental
- Materials
- TiAAB synthesis
The solvent was evaporated by heating under vacuum, and the crystals were then dissolved in ethyl acetate.
Experimental apparatus & procedure
- Stability condition measurements
- Differential scanning calorimeter (DSC)
- Gas uptake and CO 2 composition measurements
The CO2 selectivity of the TBAC semiclathrate phase was comparable to that of the pure clathrate. Clathrate-based CO2 capture from combustion gas was investigated in the presence of TBAC.
Introduction
Quaternary ammonium salts (QASs), including tetra-n-butylammonium bromide (TBAB), fluoride (TBAF), chloride (TBAC), and tetra-isoamylammonium bromide (TiAAB) form semiclathrates under atmospheric pressure [1-6]. Moreover, as a thermodynamic promoter, TiAAB is expected to have high thermodynamic stability than other quaternary ammonium salts.
Results and discussion
- Phase equilibria of QAS semiclathrates and spectroscopic analysis
- Phase equilibria of TiAAB semiclathrates and spectroscopic analysis
The onset temperature of TBAC hemi-clathrate at 3.3 mol% was identical to the equilibrium temperature shown in (Figure 3.2.), which was measured in the conventional reactor. As observed in (Figure 3.2), maximum stabilization occurred at 3.3 mol% TBAC, which is also the stoichiometric concentration of TBAC·29.7H2O hemiclathrate. The thermodynamic stabilization of N2 + TBAC hemiclathrate was found to be highest in TBAC solution (3.3 mol%), which corresponds to the stoichiometric concentration of TBAC·29.7H2O.
13C NMR spectra of pure CH4 hydrates, pure TBAC semiclathrate and double CH4 + TBAC semiclathrates. The stability conditions of double semiclathrates CO2 + TiAAB with a concentration of 3.7 mol% TiAAB are shown in (Figure 3.14).
Conclusions
Subsequently, semiclathrate-based CO2 capture from post-combustion flue gas was investigated in the presence of TBAB, TBAC and TBAF. The TBAC (3.3 mol%) semiclathrate at 8.0 MPa had the highest gas uptake and the sharpest changes in CO2 concentration in the vapor phase. Both CO2 and H2 molecules are trapped in the cages of the clathrates, was confirmed from the Raman spectra.
5] Kim, S., Choi S-D., Seo, Y., "CO2 capture from flue gas using clathrate formation in the presence of thermodynamic promoters", Energy (In press). Semiclathrate hydrate phase equilibria for CO2 in the presence of tetra-n-butylammonium halide (bromide, chloride or fluoride).
Post-combustion CO 2 capture using QAS semiclathrates formation
Introduction
The gas uptake in the TBAC semiclathrates and CO2 composition changes in the vapor phase were measured according to reaction time in order to investigate selective distribution of gas molecules, gas distribution and cage filling properties. Furthermore, the gas molecules trapped in the semicloth rate gratings were analyzed by means of Raman spectroscopy. The gas uptake and CO2 concentration changes in the vapor phase during QAS semi-clathrate formation were measured to investigate the preferential occupancy of CO2 in the semiclathrate phase.
CO2 concentrations in the vapor and semiclathrate phases after completion of semiclathrate formation were measured to elucidate CO2 selectivity based on the types of QAS semiclathrate used. Enclustering of guest molecules in semiclathrate lattices was confirmed by micro Raman spectrometer and time-dependent in situ Raman spectrometer.
Results and discussion
- Stability conditions of the QAS semiclathrates
- Gas uptake and composition measurements of QAS semiclathrates
- Raman spectroscopic analysis
The accumulated amount of gas consumed during the semiclathrate formation reaction is equal to the total amount of gas trapped in the cages of TBAC semiclathrate. However, in the 1.0 mol% TBAC solution, smaller amounts of TBA + and Cl − are available for semiclathrate formation. After confirming the completion of the TBAC semiclathrate formation reaction, the CO2 concentration in the vapor phase was measured, and then the concentration of recovered CO2 from the semiclathrate phase was analyzed.
The final CO2 compositions in the vapor and semiclathrate phases for the TBAB, TBAC and TBAF semiclathrates are shown in (Figure 4.11.) and were compared with those of the gas hydrate. The Raman spectra of the TBAC semiclathrate and CO2 + N2 + TBAC semiclathrate were obtained after the completion of semiclathrate formation in the experiments shown in (Figures 4.15 and 4.16.).
Conclusions
Because the formation of gas hydrate requires high pressure and low temperature, clathrate-based CO2 capture from a flue gas is difficult to apply in the actual process. Clathrate-based CO2 capture from flue gas was investigated in the presence of thermodynamic promoters such as TBAB, TBAC, TBAF, THF and CP. In Chapter 5, clathrate-based CO2 capture from the simulated flue gas mixture was investigated in the presence of tetrahydrofuran (THF) as a water-soluble sII hydrate former, cyclopentane (CP) as a water-insoluble sII hydrate former, and tetrabutylammonium chloride (TBAC). ) as a semi-clathrate former.
Tetra-n-butyl ammonium bromide hemi-clathrate hydrate process for the post-combustion capture of carbon dioxide in the presence of dodecyl trimethyl ammonium chloride. 6] Kim, S., Choi S-D., Seo, Y., "CO2 capture from flue gas using clathrate formation in the presence of thermodynamic promoters", Energy (In press).
Post-combustion CO 2 capture using THF, CP, TBAC clathrates formation
Introduction
This indicates that the clathrate-based CO2 capture is eco-friendly through solution recovery and heat recovery between the clathrate formation and dissociation units [18]. This former stabilizes a clathrate structure at low pressure or high temperature conditions, although the gas storage capacity is lower compared to the gas hydrate by adding these promoters, since the clathrate former is occupied in the lattice cavities. In addition, the clathrate formers are operated in the liquid phase, this means that the final gas product does not pollute as it will remain with the liquid phase when the clathrate is dissociated.
The gas uptake and changes in CO2 concentration in the vapor phase during clathrate formation were measured to analyze the preferential gas occupancy in the clathrate phase. The inclusion of guest molecules in the clathrate lattices was confirmed with a micro-Raman spectrometer.
Results and discussion
- Stability conditions of clathrates
- Gas uptake and composition measurements of clathrates
- Raman spectroscopic analysis
However, in the presence of clathrate former, the equilibrium pressure of the gas hydrate can decrease significantly at a given temperature. To investigate the gas storage capacity and CO2 selectivity in the clathrate phase, gas uptake in clathrates and changes in CO2 composition during clathrate formation were measured. As shown in Figure 5.2, both the THF and CP solutions showed higher CO2 concentrations in the clathrate phase at 1.0 mol% than at 5.6 mol%.
The TBAC solutions showed the highest CO2 selectivity in the clathrate phase for both the 1.0 mol% and the stoichiometric (3.3 mol%) concentrations. CP (5.6 mol%) hydrate dissociation has been expected to have similar behavior in the gas separation process.
Conclusions
Hydrate-based combustion process for carbon dioxide capture in the system of tetra-n-butylammonium bromide solution in the presence of cyclopentane. Tetra-n-butylammonium bromide semi-clathrate hydrate process for post-combustion capture of carbon dioxide in the presence of dodecyltrimethylammonium chloride. Experimental measurements of hydrate phase equilibria for carbon dioxide in the presence of THF, propylene oxide and 1,4-dioxane.
Semiclathrate hydrate phase equilibria for CO2/CH4 gas mixtures in the presence of tetrabutylammonium halide (bromide, chloride or fluoride). Hydrate-based combustion capture of carbon dioxide in the presence of a thermodynamic promoter and porous silica gels.
Pre-combustion CO 2 capture using TBAC semiclathrates formation
Introduction
The most promising options for clathrate-based CO2 capture from the fuel gas mixture is clathrate formation, because CO2, whose hydrate equilibrium state is extremely milder than H2, is expected to be enriched in the clathrate phase, resulting in in the high selectivity of CO2 in the class phase. The phase equilibrium of the clathrate in the presence of the hemiclathrate former would be greater than that of the CO2 and H2 hydrate, since CO2 and H2. The concentrations of CO2 in the vapor and clathrate phases after the completion of clathrate formation were measured to ensure CO2 selectivity.
The inclusion of guest molecules in the clathrate lattices was confirmed with a micro-Raman spectrometer. In addition, the semi-clathrate stability conditions and dissociation heat values in the presence of TBAC with fuel gas will be determined using a high-pressure micro-differential scanning calorimeter (HP μ-DSC).
Results and discussion
- Stability conditions of TBAC semciclathrates
- Gas uptake and composition measurements of QAS semiclathrates
- Raman spectroscopic analysis
- Differential scanning calorimeter (DSC) measurements
After the completion of each clathrate formation with CO2 (40%) + H2 (60%), the final CO2 concentration in the vapor phase was first measured and then, the CO2 composition of the gas obtained from the clathrate phase was measured. The experimental results clearly show that TBAC (3.3 mol%) clathrate had greater gas uptake than TBAC (1.0 mol%) semiclathrate form- formation. Figure 6.6.) shows changes in the composition of CO2 in the vapor phase during clathrate formation. The CO2 concentrations in the vapor phase continued to decrease during clathrate formation because CO2 is captured more selectively in the clathrate phase than H2.
The change in CO2 concentration in the vapor phase is strongly influenced by the type and concentration of the promoter. In the pressure range from 0.1 to 10 MPa, the dissociation enthalpies of the CO2 + TBAC (3.3 mol%) semiclathrate were higher than that of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate and increased with increase in pressure of H2.
Conclusions
Thermodynamic and spectroscopic identification of guest gas quenching in tetra-n-butylammonium double fluorine hemiclathrates. Seo, Thermodynamic and spectroscopic identification of guest gas enclathration in double tetra-n-butylammonium fluoride hemiclathrates, J. 6] Kim, S., Kim, Y., Lee, Y., Kim, E., Seo, Y ., "Guest gas enclathration in tetra-n-butyl ammonium chloride (TBAC) semi-clathrates: Thermodynamic and spectroscopic analyses", Korean Institute of Chemical Engineers (KIChE) Autumn Meeting, October 2013.
16] Lee, J., Lee, D., Lee, Y., Kim, S., Kim, E., Seo, Y., "Thermodynamic and Spectroscopic Analyzes of Cyclopentane Hydrates in the Presence of Small Guest Molecules", Korean Institute of Chemical Engineers (KIChE) Autumn Meeting, Oct.2014, Daejeon. 17] Lee, Y., Kim, S., Kim, E., Seo, Y., “Experimental Verification of the CH4 Flue Gas Replacement in Structure H Hydrate System”, Korean Institute of Chemical Engineers (KIChE) Fall Meeting, Oct. 2014, Daejeon.
Conclusion
