Chemical and Biomolecular Engineering - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemPromoted Direct Air Capture of Carbon Dioxide by Synergistic Water Harvesting( 2023-10)Adsorption-based direct air capture (DAC) of carbon dioxide has been widely recognized as a necessary measure to contain atmospheric CO2 concentrations. Chemisorbents like solid amines are effective in capturing ppm level CO2. However, because of the large heat of adsorption, the regeneration of solid amines requires high energy consumption and a significant driving force, compromising the economic viability and productivity of DAC. A vapor-promoted desorption (VPD) process was developed to recover the CO2 adsorbed on solid amines by in situ vapor purge using water harvested from the atmosphere synergistically. A double-layered adsorption configuration, sequentially packed with solid amines and water adsorbents, was used to perform direct air capture based on the VPD process. The desorption of CO2 was substantially enhanced in the presence of concentrated water vapors at around 100 degrees Celsius, resulting in the concurrent production of 97.7% purity CO2 and fresh water at ambient pressure. CO2 working capacities of 1.0 mmol/g could be achieved using a commercial amine-grafted resin. Furthermore, a solar-heating DAC prototype was demonstrated to power the regeneration, recovering over 98% of the adsorbed CO2 while consuming 10.4 MJ/kgCO2 thermal energy. PEI-impregnated sorbents have been extensively studied for DAC due to their high atmospheric CO2 adsorption capacities. However, efficient recovery of the adsorbed CO2 from PEI has received limited attention. The developed VPD process was employed to effectively regenerate PEI-impregnated sorbents, producing fresh water and 98% pure CO2 with a remarkable working capacity of 1.61 mmol/g at 105 degrees Celsius. The high CO2 working capacity was realized through a reduction in CO2 partial pressure inside the column caused by the increase of water vapor pressure. The in situ vapor purge allowed for the recovery of more than 95% of the CO2 adsorbed on PEI, with an energy consumption of only 8.9 MJ/kgCO2 for sorbent regeneration. While the VPD process has demonstrated excellent performance in regenerating PEI-impregnated sorbents, a significant concern arises from amine deactivation at high regeneration temperatures. To address this issue, a vapor-promoted temperature vacuum swing adsorption (VPTVSA) process was developed, reducing the temperature required for the in situ vapor purge. This VPTVSA process regenerated PEI-impregnated sorbents at temperatures as low as 60 degrees Celsius, producing 99% purity CO2 with a stable working capacity of 1.10-1.13 mmol/g over 45 cycles. The minimum work required for adsorbent regeneration was only 1.62 MJ/kgCO2, over 37% lower than temperature-vacuum swing desorption. This low-temperature regeneration process not only reduces the exergy demand but also has the potential to extend the lifespan of numerous low-cost PEI-impregnated sorbents, contributing to a reduction in the overall cost of DAC.