Comparative Study of Molecular Basket Sorbents Consisting of Polyallylamine and Polyethylenimine Functionalized SBA-15 for CO Capture from Flue Gas.

Polyallylamine (PAA)-based molecular basket sorbents (MBS) have been studied for CO capture in comparison with polyethylenimine (PEI)-based MBS. The characterizations including N physisorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and thermogravimetric analysis (TGA) showed that PAA (M =15 000) is more rigid and has more steric hindrance inside SBA-15 pores than PEI owing mainly to its different polymer structure. The effects of temperature and PAA loading on the CO sorption capacity of PAA-based MBS have been examined by TGA by using 100 % CO gas stream and compared with PEI/SBA-15. It was found that the capacity of the PAA/SBA-15 sorbent increased with increasing temperature. The optimum capacity of 88 mg  g was obtained at 140 °C for PAA(50)/SBA-15 whereas the optimum sorption temperature was 75 and 90 °C for PEI-I(50)/SBA-15 (PEI-I, M =423) and PEI-II(50)/SBA-15 (PEI-II, M =25 000), respectively. The capacity initially increased with the increase of PAA loading and then dropped at high amine contents, owing to the increased diffusion barrier. The highest CO capacity of 109 mg  g was obtained at a PAA loading of 65 wt %, whereas the PAA(50)/SBA-15 sorbent gave the best amine efficiency of 0.23 mol  mol . The effect of moisture was examined in a fixed-bed flow system with simulated flue gas containing 15 % CO and 4.5 % O in N . It was found that the presence of moisture significantly enhanced CO sorption over PAA(50)/SBA-15 and greatly improved its cyclic stability and regenerability. Compared with PEI/SBA-15, PAA/SBA-15 possesses a better thermal stability and higher resistance to oxidative degradation. However, the CO sorption rate over the PAA(50)/SBA-15 sorbent was much slower.