Macroporous Silica with Thick Framework for Steam‐Stable and High‐Performance Poly(ethyleneimine)/Silica CO₂ Adsorbent

Abstract

Poly(ethyleneimine) (PEI)/silica has been widely studied as a solid adsorbent for post-combustion CO capture. In this work, a highly macroporous silica (MacS), synthesized by secondary sintering of fumed silica, is compared with various mesoporous silicas with different pore structures as a support for PEI. The silicas with large pore diameter and volume enabled high CO adsorption kinetics and capacity, because pore occlusion by the supported PEI was minimized. The steam stability of the silica structures increased with the silica wall thickness owing to suppressed framework ripening. The silicas with low steam stability showed rapid leaching of PEI, which indicated that the PEI squeezed out of the collapsed silica pores leached more readily. Consequently, MacS that had an extra-large pore volume (1.80 cm g ) and pore diameter (56.0 nm), and a thick wall (>10 nm), showed the most promising CO adsorption kinetics and capacity as well as steam stability.

Oxidation-stable amine-containing adsorbents for carbon dioxide capture

“…Generally, the low adsorbent stability necessitates the continuous addition of fresh adsorbents, which significantly increases the material cost for CO 2 capture. Amine-containing adsorbents are known to degrade via various chemical pathways including the oxidative degradation of amines 15 – 22 , 30 – 33 , urea formation under the CO 2 -rich atmosphere 21 – 25 , 33 – 35 , steam-induced degradation of the porous supports 20 , 26 – 28 , and irreversible adsorption of SO 2 29 , 37 , 38 . Aside from the oxidative degradation of amines, various solutions have been proposed for suppressing the degradation pathways.…”

“…For instance, urea formation can be inhibited by selectively using secondary amines rather than primary amines 24 , 34 or injecting steam during adsorbent regeneration 14 , 22 , 23 , 28 . Steam-induced degradation can be solved by using porous supports with enhanced hydrothermal stability 26 – 28 . In addition, the amine poisoning by SO 2 can be avoided by employing advanced desulfurization unit before CO 2 capture 41 .…”

Exploring steam stability of mesoporous alumina species for improved carbon dioxide sorbent design

“…Once the CO2 is desorbed, the steam is then condensed, leaving a stream of high purity CO2 for sequestration [42][43][44]. It is also noted that even if an alternative regeneration technique is used, the flue gas emitted from industrial plants, and other point sources, is not dry, containing between 3 -10 % H2O [44]. Thus, regardless of the regeneration technique employed, steam stability is still fundamental to practical sorbent design.…”

“…Thus, regardless of the regeneration technique employed, steam stability is still fundamental to practical sorbent design. Several studies have focused on the stability of the amine species under these simulated steam stripping conditions [41][42][43][44]. We have previously shown that amine-functionalized mesocellular foam (MCF) is susceptible to structure degradation on steaming.…”

“…However, Choi et al suggest that silicas with thicker walls, larger pore volumes and pore diameters could be more resilient to steam stripping. They showed that macroporous silica impregnated with PEI can retain 90 % CO2 uptake after 14 days of steaming, whereas PEI impregnated MCM-41, SBA-15 and MCF could only retain 38 %, 50 % and 58 % respectively [44]. Despite these studies, few have focused on the stability of the support in isolation.…”