Grafted propyldiethanolamine for selective removal of SO2 in the presence of CO2

• Grafted-diethanolamine adsorbs selectively, quantitatively and reversibly ppm SO2 in CO2.
• Material with 1.75 mmol/g amine adsorbs 2.84 at 23 °C in the presence of 1% SO2/N2.
• The SO2 adsorption capacity is unchanged in the presence of oxygen under dry condition.
• The SO2 uptake increased significantly in the presence of water vapor.

Propyldiethanolamine-grafted pore-expanded mesoporous silica was developed for selective adsorption of SO2 in the presence of CO2. With 1.75 mmol/g amine loading, the adsorption capacity in the presence of 1% SO2/N2 under dry condition was found to be 2.84 and 2.14 mmol/g at 23 and 50 °C, corresponding to SO2/N ratios of 1.63 and 1.30, respectively. Not only the material did not capture any CO2 under typical adsorption conditions, but the presence of CO2 did not affect SO2 uptake under dry or humid condition. Moreover, the SO2 adsorption capacity remained unchanged in the presence of 10% O2/N2 under dry condition. The presence of water vapor improved the SO2 adsorption capacity of the material at room temperature by ca. 50% at 83% relative humidity. The SO2-saturated adsorbent under dry condition was regenerated completely by flowing N2 at 130 °C, and the SO2 working capacity remained unchanged in consecutive adsorption/regeneration cycles. Based on earlier FTIR and 15N NMR data using similar grafted tertiary amine, it is suggested that the adsorption takes place by charge transfer complexation between SO2 and the tertiary amine nitrogen. Nonetheless, consistent with literature data, it is speculated that SO2 adsorption also occurs through zwitterion formation involving interaction between OH groups and SO2.