(381ag) Enhanced CO2 Adsorption Rate in Polyammonium Protic Ionic Liquids Functionalized SBA-15

Enhanced CO₂ adsorption rate in
polyammonium protic ionic liquids functionalized SBA-15

Wei
Zhang, Yi He*, Yao Shi*

Key Laboratory of Biomass Chemical Engineering of Ministry of
Education, Institute of Industrial Ecology and
Environment, College of
Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027,
China

Abstract:

The development of cost-effective and
high-efficiency adsorbents for CO₂ capture from flue gas deriving
from the large-scale burning of fossil fuels represents one of the most
significant scientific and technological challenges since the industrial
revolution to face the global warming and anthropogenic climate change.
Compared with conventional ionic liquid (IL) like imidazole ILs and amino
acid-based ILs, polyammonium protic ionic liquids (PILs) possess the advantages
of low-cost, simple-synthesis and high absorption capacity, but the same
drawbacks of high viscosity and CO₂ diffusion limitation. To
overcome these challenges, we develop mesoporous silica SBA-15 supported
triethylenetetrammonium nitrate sorbents with excellent CO₂ uptake
rate and great adsorption capacity. The CO₂ capture performance of
the hybrid sorbents was evaluated under
conditions mimicking a combustion flue gas (15% CO₂) at the temperature range of 298-348 K. The
breakthrough experiments revealed that S15-66PIL (the mass ratio of PIL to
carrier is 2:1) exhibited the highest CO₂ adsorption capacity of
2.11 mmol/g at 333 K. In order to better understand the adsorption kinetics and
the rate-controlling step of the sorbent, the CO₂ adsorption
capacity was plotted against t^0.5 using the intra-particle diffusion
model (IPDM). The results demonstrated that S15-66PIL reached the fastest CO₂
adsorption rate and the adsorption rate of rate-controlling step
was 131*10^-3
mmol g^-1 s^-0.5, approximately five times higher than bare
support and two times higher than
previously reported ILs-functionalized and amine-modified support systems. The
high CO₂ adsorption rate of the adsorbent can be explained by the
large surface area of the support which favors the diffusion of PIL and CO₂
molecules in its pores. In addition, the thermostability of S15-66PIL was
comparable to other ILs-functional molecular sieve and was better than
TEPA-modified porous materials. The long-term operating performance of the
sorbent evaluated by 10 times cyclic adsorption/regeneration experiments and
the results showed that 92% of original CO₂ capture capacity was
reversible. FT-IR analysis coupled with isosteric heat and DFT calculation
revealed that the adsorption nature of the samples was chemisorption and CO₂
preferentially interacted with the primary amine -N(3)H2 in [TETA][NO₃]
to form carbamate due to the highest binding energy. Overall, [TETA][NO₃]
impregnated SBA-15 sorbent provide a low-cost, high adsorption capacity
alternative with fast adsorption kinetics, and desirable regenerability.
Therefore, it may serve as a promising candidate for CO₂ capture in
industrial applications.

Keywords: CO₂
adsorption; polyamine-based protic ionic liquids; SBA-15; Nanopore confinement;
DFT calculation

Fig.
1. CO₂ adsorption diagram, IPDM kinetic plots of S15-xPIL and comparison
of diffusion rate constant of rate-controlling step for these sorbents