Effect of SO<sub>2</sub> on the CO<sub>2</sub> Capture Performance of Self-Supported Branched Poly(ethyleneimine) Scaffolds
Pavithra Narayanan, Ryan P. Lively, Christopher W. Jones
Abstract
High Resolution Image Download MS PowerPoint Slide Self-supported branched poly(ethyleneimine) scaffolds with continuous and interconnected porosity are synthesized by crosslinking branched poly(ethyleneimine) (b-PEI) with poly(ethylene glycol) diglycidyl ether (PEGDGE) using ice templating at two different temperatures, −196 and −78 °C (PEI 196 and PEI 78, respectively). XPS and elemental analysis show that PEI 196 has a lower degree of crosslinking and retained more primary and secondary amines than PEI 78. As a result, PEI 196 experiences 32% more loss in CO 2 adsorption capacity when exposed to 200 ppm SO 2 since SO 2 irreversibly binds with primary amine sites. The SO 2 uptake for a given feed composition and flow rate depends on the adsorption cycle time. Hence, by varying the cycle time in alternate CO 2 –SO 2 adsorption–desorption cycles, it is demonstrated that the ideal CO 2 /SO 2 selectivity can be improved by a factor of 10 simply by taking advantage of the transient kinetic selectivity. The ideal CO 2 /SO 2 selectivity is defined as the ratio of gas uptake of CO 2 to that of SO 2 from a CO 2 /N 2 mixture and SO 2 /N 2 mixture at concentrations relevant to that of desulfurized flue gas. A cycle consisting of 5 min of adsorption has the best sorbent lifetime among the cycles studied. Desorption studies show a shift from strong CO 2 –amine interactions to weaker interactions with successive cycles. In situ IR spectroscopy further suggests the protonation of amines and the tethering of SO 2 to the oxygen atom of the β-amino alcohol formed during the crosslinking of PEI as a mechanism of adsorption of SO 2 .