Performance of Selected Adsorbents for CO2 Capture: Equilibrium and Column Dynamics Study
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In the last two decades, metal organic frameworks (MOFs) have emerged as promising materials for gas separation and storage. Majority of the literature on MOF materials for gas separation is limited to equilibrium measurements due to the complexity associated in dynamic measurements such as the column break through studies and development of process cycles. Other reasons contributing to this trend include, the challenges involved in scale up of the synthesis procedure and that in pelletization of the synthesized MOF powders. In this work, the metal organic frameworks UiO-66, MIL-101(Cr), Cu-BTC and MIL-53(Al) are systematically investigated for CO2/N2 separation. In the first part of work, the chosen MOFs are synthesized in 10 g level. Then the synthesized MOF powders are shaped into pellets using poly vinyl alcohol (PVA) as the binder. The effect of shaping on structural and functional characteristics of MOF are examined through the BET, FESEM, FTIR, TGA and XRD analysis. The pure component isotherms of CO2, N2 are measured on MOF powders and pellets. About 14-20% decrease in CO2 adsorption capacity is observed after pelletization. Although, a reduction in specific loadings is observed, the change in volumetric capacity is lower, due to the increase in bulk density after pelletization. A single column PVSA experimental set up is developed and experimentally validated using zeolite 13X adsorbent. The breakthrough experiments conducted using synthetic dry flue gas (15% CO2, balance N2) as feed in a column containing about 8 to 12g of the MOF pellets (at 1.3 bar and 300 K) reveal preferential adsorption of CO2 over N2 and the CO2 separation. The process performance of MOF pellets is evaluated in three different PVSA cycles using the single column. The inclusion of purge and rinse step result in an increase of N2 product purity and CO2 product purity respectively. The best performance achieved with the employed 5-step (pressurization, adsorption, CO2 rinse, blowdown and N2 purge along with evacuation) PVSA cycle on the four chosen MOFs is CO2 purity (35%-68%), CO2 recovery (54%-61%) and CO2 productivity (0.075-0.269 kgCO2/(kgads·h). The findings from PVSA suggest that these MOF materials are promising for CO2/N2 separation at low CO2 concentrations, however a multi-bed PVSA may be needed to meet the process performance parameters for industrial requirement (CO2 purity >95%, CO2 recover >95%).
Supervisor: Sasidhar gumma