PNNL

Abstract

Direct air capture (DAC) technologies extract CO2 from the atmosphere for CO2 storage, or utilization. Capturing CO2 from the air is the most expensive application of carbon capture because CO2 in the atmosphere is very dilute. There are limited number of CO2 capture technologies for DAC application. This project aims at developing an energy efficient technology for DAC, leveraging two PNNL’s chemistries (solid and liquid CO2 capture). Three CO2 capture sorbents consisting of amine based CO2BOLs immobilized in mesoporous silica were designed, synthesized, and tested. These sorbents had ~ 19-23 wt.% amine loadings which is lower than typical amine-based silica sorbents. The surface area and pore volumes of these solid supported CO2BOLs are lower compared to those of the pristine silica support. The CO2 capture performance of these materials was significantly lower than the typical silica supported amines due to low amine loading and higher molecular weight with low amine density. These results show that immobilize CO2BOLs in silica are not viable materials for removing CO2 from ambient air. This project also designed, synthesized at tested liquid solvents for DAC application. Solvent properties that is vapor pressure, CO2 uptake capacity, kinetics, and viscosity for three novel solvents were evalauted. The CO2 uptake capacity for one of the most promising amine-based solvent BEPBEGDA was the highest at 13.2 wt% corresponding to 97 mol%. The vapor pressure of the BEPBEGDA solvents were very low at 80 °C compared to other solvents making them suitable for DAC application. The effect of humidity on the CO2 capture performance of these solvents was evaluated which shows that presence of moisture doesn’t have a negative effect on the CO2 uptake performance but makes it slightly better. The performances of these solvents were slightly below that of the 0.1M NaOH solution tested under similar conditions. Despite of the slightly lower CO2 uptake, it is expected that these liquid solvents will have lower regeneration temperature and minimum evaporative losses due their low vapor pressure. Future work will focus on optimization of the liquid solvents for DAC application to improve both CO2 capture efficiency and capacity without viscosity and vapor pressure increase. Testing of these solvents under DAC conditions using a gas liquid contactor that mimic industrial applications is needed. Solvent cost projection, techno-economic analysis and life cycle analysis are required to evaluate economic viability of this technology.