Simultaneous capture of SO
2
and NO
x
from flue gas is critical for coal-fired power
generation.
In this study, environmentally friendly and high-performance deep
eutectic solvents based on ethylene glycol and ammonium bromide were
designed to capture SO
2
and NO
2
simultaneously.
The SO
2
and NO
2
absorption performances and
absorption mechanisms were systematically investigated by
1
H NMR and Fourier transform infrared (FT-IR) spectroscopy in combination
with ab initio calculations using Gaussian software. The results showed
that EG-TBAB DESs can absorb low concentrations of SO
2
and
NO
2
from the flue gas simultaneously at low temperatures
(≤50 °C).
1
H NMR, FT-IR, and simulation results
indicate that SO
2
and NO
2
are absorbed by forming
EG-TBAB-SO
2
–NO
2
complexes, Br
–
is the main active site for NO
2
absorption, and NO
2
is more active in an EG-TBAB-NO
2
–SO
2
complex than SO
2
. EG-TBAB DESs exhibit outstanding
regeneration capability, and absorption capacities remain unchanged
after five absorption–desorption cycles. The fundamental understanding
of simultaneous capture of SO
2
and NO
2
from
this study enables DES structures to be rationally designed for efficient
and low-cost desulfurization and denitrification reagents.
New ternary deep eutectic solvents (DESs), including imidazole (Im), ethylene glycol (EG), and methyltriphenyl phosphonium bromide (MTPB), were synthesized at different molar ratios to absorb SO 2 in flue gas. Excitingly, the EG−Im−MTPB (1:2:1) DES has achieved the unexpected achievement of its absorption capacity being greatly improved to 0.65 g of SO 2 /g of DES (4.43 mol/mol) at 3000 ppm and 30 °C, which is the best performing DES for capturing SO 2 under the same conditions ever reported. The aftereffects of thermodynamic investigation demonstrate that there is a solid compound communication between EG−Im−MTPB (1:2:1) DES and SO 2 . In particular, the enthalpy change (Δ r H m ), entropy change (Δ r S m ), and Gibbs free energy change (Δ r G m ) were plainly determined as −50.45 kJ/mol, −114.57 J mol −1 K −1 , and −16.20 kJ/mol, separately. The Fourier transform infrared, 1 H nuclear magnetic resonance, and quantum chemistry calculation results confirm that multiple active sites, including the N atom of Im and the Br atom of MTPB, are the main factors by which DES effectively absorbs SO 2 . Further, a UNIQUAC method by Aspen Plus V12 is set up for the SO 2 absorption process with 6000 m 3 /h flue gas, indicating that the EG− Im−MTPB (1:2:1) DES can completely absorb SO 2 in the flue gas when the consumption of DES is 26.8 m 3 /h.
NO absorption by using deep eutectic solvents (DESs) from flue gas has become one of great research interest. In this work, different DESs were prepared with acetylcholine chloride as a hydrogen‐bond acceptor. The effect of molar ratio of the hydrogen‐bond acceptor and different hydrogen‐bond donor, temperature, and different hydrogen‐bond donors on NO absorption by acetylcholine chloride DESs was investigated systematically. The absorption experiment of NO by acetylcholine‐methyl urea DES at an absorption capacity of 0.119 (g NO/g DES) when the molar ratio of acetylcholine chloride to methyl urea was 1 : 2 at 30–40 °C. The absorption mechanism of NO by acetylcholine chloride DESs was determined by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance combined with quantum chemical calculation. The results indicated that NO with acetylcholine‐methyl urea DESs by chemical absorption to form NONO structure, nitrogen‐oxygen double bonds (N=O), nitrogen‐oxygen single bonds (N−O), and nitrogen‐nitrogen single bonds (N−N). The simulation results showed that nitric oxide formed two hydrogen bonds with N atoms on methyl urea: C−N⋅⋅⋅N and O=N⋅⋅⋅N=O. Thermodynamic properties showed that the ▵rHom for NO absorption in acetylcholine‐chloride‐type DES was −15.39 kJ/mol, which was more efficient for NO absorption/desorption.
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