Study On Effects Of Additive On Hydrate-Based CO₂/N₂ Separation

Carbon dioxide capture, utilization and storage is an efficient method of CO2 emission reduction. It has caused much attention that applying the hydrate technology into gas separation. Hydrate-based CO2 capture is considered as the most promising long-term CO2 capture method. In this study, we investigated hydrate thermodynamic properties and separation efficiency using hydrate physical properties test system. The high resolution magnetic resonance imaging (MRI) experiment platform was also used to study the hydrate formation and dissociation properties in the process of gas flow, which can provide a fundamental data for the industrial application of hydrate-based CO2 capture from flue gas under the action of additive mixture.Hydrate phase equilibrium and induction time of CO2/THF/TBAB/H2O system were tested in this study. The simultaneous use of THF and TBAB can mitigate hydrate formation conditions.1% THF mixed with TBAB have little effect on CO2 hydrate phase equilibrium condition (except 1%THF+5%TBAB); when THF concentration is 5%, increasing TBAB concentration can efficiently reduce hydrate phase equilibrium pressure. The additive mixture of 5%THF+5%TBAB is better than other concentrations used in this study on the aspect of decreasing hydrate phase equilibrium pressure and formation induction time.Through the study of CO2/N2 hydrates phase equilibrium conditions and gas separation characteristics under the condition of additive mixture (THF+TBAB), it is found the hydrates phase equilibrium pressure of 5%THF+5%TBAB and 5%THF+10%TBAB are almost the same, which are lower than 10%TBAB used alone. The additive mixture has a remarkable effect on gas separation characteristics; with the increase of THF and TBAB concentrations, both the gas consumption and CO2 recovery significantly increase. In addition, the gas consumption, CO2 recovery and CO2 separation factor all show a rising trend when the initial pressure increases, so high pressure is beneficial for gas separation. Considering hydrate phase equilibrium and gas separation efficiency as a whole,5%THF+10%TBAB and 6MPa operating pressure is the optimal condition of hydrate-based CO2/N2 separation in this study.The CO2/N2 hydrates formation and dissociation properties in the process of gas flow was also study using MRI. In the experiment of CO2/N2 hydrates generating under constant pressure, it was found the solution after hydrate dissociation can make hydrate generate easily, and high pressure above 5 MPa make hydrate generate more.In the experiment of CO2/N2 hydrates formation in the flow, slower flow rate is more conducive to hydrates formation. The pressure has little effect on hydrates formation above 5 MPa. Due to the displacement function of gas in the flow, the solution in the vessel decreased gradually, which caused hydrates generation rarely after three cycles.