Synthesis of dibutyl-trimethylsilanylmethyl-amine and its application towards SO2absorption with phase change behaviors

Article abstract of DOI:10.1039/d0nj04500d

The enforcement of environmental law worldwide has attracted considerable attention in recent years towards capturing sulfur dioxide (SO2). The phase change absorption has turned out to be an effective way due to its industrially scalable characteristics. Herein, an aminosilane absorbent, namely dibutyl-trimethylsilanylmethyl-amine (DTSMA), was facilely synthesized by a substitution reaction of chloromethyltrimethylsilane and di-n-butylamine. The phase-change absorption performance of SO2 was systematically studied by using dimethyl silicone oil (DSO) as the solvent. The viscosity of pure DTSMA was only 1.29 mPa s, which is much lower than those of absorbents such as ionic liquids and deep eutectic solvents reported elsewhere, and the absorption product is found to be a charge transfer complex DTSMA SO2. The absorption capacity of DTSMA can reach 1.90 and 0.57 mol SO2 per mol DTSMA under 1 and 0.02 atm at 30 °C, respectively. In particular, the DTSMA/DSO solution can be not only almost regenerated within just 60 minutes at 100 °C, but also exhibited selective absorption towards SO2. All the results indicated that the synthesized DTSMA absorbent has enormous potential for application in capturing SO2 with benign circular desorption performance. This journal is

Full text of DOI:10.1039/d0nj04500d

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Synthesis of Dibutyl-trimethylsilanylmethyl-amine and Its Application Towards
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SO2 Absorption with Phase Change Behaviors
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Bo Hao, Wenbo Zhao*, Dong Feng, Shengchao Xu, Yuan Chen*
Faculty of Chemical Engineering, Kunming University of Science and Technology
650500, P.R.China
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E-mail:wenshuixing@126.com, 4916339@qq.com
ABSTRACT: The enforcement of environmental law worldwide has attracted
considerable attention in recent years towards capturing sulfur dioxide (SO2). The phase
change absorption has turned out to be an effective way due to its industrially scalable
characteristics.
Herein,
an
aminosilane
absorbent
namely
dibutyl-
trimethylsilanylmethyl-amine (DTSMA) was facilely synthesized by a substitution
reaction of chloromethyltrimethylsilane and di-n-butylamine. The phase-change
absorption performance of SO2 was systematically studied by using the dimethyl
silicone oil (DSO) as solvent. The viscosity of pure DTSMA was only 1.29 mPa·s,
which is much lower than the absorbents like ionic liquids and deep eutectic solvents
reported elsewhere, and the absorption product is found to be a charge transfer complex
DTSMA·SO2. The absorption capacity of DTSMA can reach to 1.90 and 0.57 mol
SO2/mol DTSMA under 1 and 0.02 atm at 30 °C, respectively. Especially, the
DTSMA/DSO solution not only can be almost regenerated within just 60 minutes at
100 °C, but also exhibited selective absorption towards SO2. All the results indicated
that the synthesized DTSMA absorbent processes enormous potential applications in
capturing SO2 with benign circular desorption performance.

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KEYWORDS: Dibutyl-trimethylsilanylmethyl-amine, SO2 capture, PhaseDOchI: 1a0n.1g03e9,/D0NJ04500D
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Circular desorption
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1. INTRODUCTION
SO2 is one of the main pollutants released as a result of the burning of fossil fuels.
As a colorless gas with a strong pungent odor, SO2 diffused in the air will causing
serious harm to human health, plants and the ecological environment[1-2]. The treatment
of SO2 has attracted increasing concerns in recent years. By far, wet desulfurization
(FGD) technology using calcium-based absorbents is the most effective way for
controlling SO2 emissions [3-5]. However, the disadvantages of this technology can not
be ignored, such as generating a large amount of waste water and by-products (i,e.,
CaSO3 and CaSO4). Thus, one potential approach by using amine as absorbent has been
implemented towards SO2 capture. Yet, this method still has many shortcomings, such
as toxicity, equipment corrosion, solvent loss and usually requiring a lot of energy to
regenerate solvents [6-8]
.
Over the past decades, ionic liquids (ILs) has achieved great progress in the field
of SO2 absorption due to its tunable molecular structure and excellent absorption
properties, such as non-volatility and thermal stability [9-13]. Han et al., firstly reported
SO2 capture by [TMG]L (1,1,3,3-tetramethylguanidinium lactate), which was
synthesized by direct neutralization of TMG and lactic acid (L) [14]. Latter, a series of
functional ILs have been developed to meet the demand for effective SO2 absorption,
such as increasing the absorption capacity of SO2 and reducing desorption enthalpy,

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designing greener ILs and improving its selectivity [15]. The non-volatility property of
ILs significantly reduced the energy consumption and environmental pollution during
SO2 capture, nevertheless, the high viscosity characteristic of ILs limited its practical
applications [16-17]. Therefore, some researchers used small molecular solvents such as
water and methanol to reduce the viscosity of ILs [18-19]. However, the addition of these
solvents inevitably reduced the mass absorption capacity of SO2 and increased the
desorption energy consumption. To address the above issue, a possible strategy called
phase change absorption has been proposed recently in the field of SO2 capture. The
phase change absorption system consists of two parts, one is the absorbent that can react
with SO2, and the other is the solvent that can adjust the viscosity, mass transfer and
reduce volatility of the system. By simply bubbling SO2 into the system, the
homogeneous solution becomes two phases: a SO2-lean phase and a SO2-rich phase. In
this way, only the SO2-rich phase needs to be heated for regeneration while the lean
SO2 phase can be used directly without further treatment, this leading to the energy
required for regeneration significantly reduced [20]. Some researchers found that
ethylenediamine and cyclic diamine can react with SO2 and water to form sulfites and
precipitate from organic solvents [21]. Tertiary diamine like tetramethylethylenediamine
(TMEDA), tetramethylpentanediamine (TMPDA) can react with SO2 to form an
electron transfer product, which further absorbs water from air to become pyrosulfite
[22]. However, the liquid-solid phase change solvent has problems in its practical
applications. The captured SO2 mainly existed in the solid phase and easily blocked the
pipeline, which have resulted in mass transfer problem during the SO2 absorption
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process. A number of liquid-liquid phase change SO2 absorption systems have been
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developed to tackle this problem. For example, N,N-dimethylcyclohexylamine/liquid
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[23]
paraffin
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N,N-dimethylaniline/liquid
paraffin[24],
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dimethylethanolamine/hexadecane [25], etc. Although these solvent systems could
solved the problem of mass transfer ability, some disadvantages occur, such as the
absorbent and solvent are volatile and flammable. Therefore, it is urgently required to
develop a low flammability, low volatility and low viscosity phase change absorption
system that can capture SO2 efficiently, reversibly and economically.
It should be noticed that organosilicon compound is a kind of low flammability
solvent with high resistance to thermal oxidation. It produces silica carbon with high
thermal stability in fire and will further forms a silicon oxide protective layer to
prevents further combustion of the substance [26]. Moreover, its surface tension is low,
which can effectively avoid emulsification and foaming during the absorption process
[27]. Therefore, we believe that the organosilicon compound not only can be served as
SO2 absorbent, but also as solvent owning to its low-flammability and low viscosity
properties.
In this work, a low viscosity absorbent referred as DTSMA was synthesized, and
the non-flammability DSO was used as solvent. The phase change absorption behavior
of SO2 in the mixture of DTSMA/DSO was studied. H, 13C NMR and FTIR
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characterizations were used to determine the phase change absorption products. The
absorption capacity under various absorption conditions and distribution of SO2 both in
upper and lower phases were studied comprehensively. Besides, the selective

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absorption behavior and cyclic desorption performance of the DTSMA/DSO system
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were also carried out.
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2. EXPERIMENTAL SECTION
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2.1 Materials
Chloromethyltrimethylsilane (98%), Di-n-butylamine (99%), Diethylamine (99%),
Dipropylamine (99%), Dimethyl silicone oil PMX-200 (viscosity about 20mPa.s) and
Deuterated chloroform (99.8%) were purchased from Aladdin Chemical Reagent Ltd.
All reagents is used as recieved. SO2 (99.99 mol%), CO2 (99.9 mol%), and N2 (99.999
mol%) were supplied by Chengdu Hongjin Chemical Company.
2.2 Characterizations
1H and 13C NMR spectra were recorded on a Bruker AVANCE III HD 600
spectrometer using CDCl3 as a solvent. FTIR data was obtained via a BrukerTENSOR
27 FTIR spectrometer at room temperature. Thermogravimetric analysis (TGA) was
measured on a NETZSCH STA-449 F3 under a flow of nitrogen at the heating rate of
10 °C/min from room temperature to 800 °C. The UV-visible spectrum was recorded
by using a UV-visible spectrophotometer from 400 to 800 nm. DTSMA/DSO vapor
pressure is performed on a vapor pressure measuring device. The temperature was
controlled by a constant temperature oil bath, and the pressure was measured by a
pressure sensor (JYB-KO-MAA1 type, Beijing Kunlun Coast Sensor Technology Co.,
Ltd., China) with an uncertainty of 0.1 kPa. The content of each components in the
absorption system was determined by using the gas chromatography (GC-2010,
Chengdu Shimadzu Instrument Equipment Co., Ltd., China). An apparatus for

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measurement on vapor pressures of DTSMA/DSO solution were constructed aDcOcIo: 1r0d.1i0n3g9/D0NJ04500D
to the principle of quasi static method. After the pressure in the four-neck flask is 0 kPa,
a sample of solution was placed in the four-necked flask. The equilibrium pressures
were recorded after equilibrium was reached. The temperature was measured by
mercury thermometer (±0.5 °C). The pressure was measured by a pressure transducer
(Model JYB-KO-MAA1, Beijing Kunlun Coast Sensor Technology Co., Ltd., China)
with an uncertainty of 0.1 kPa.
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2.3 Synthesis of DTSMA absorbent
Under nitrogen protection, chloromethyltrimethylsilane and di-n-butylamine with
a molar ratio of 1:2 were added to a 250 ml three-necked flask, and the mixture was
condensed and refluxed at a constant temperature of 100 °C for 24 h in an oil bath. Then
the mixture was extracted with a 5 wt% sodium carbonate solution, the upper phase
solution was washed three times with deionized water, dried over anhydrous sodium
sulfate, and distilled under reduced pressure to obtain DTMSA.
2.4 SO2 absorption and desorption experiments
The equipment of the SO2 absorption and desorption experiment was showed in
Figure S1. DTSMA/DSO solution with different DTSMA mass fractions were added
to the Gas-Wash Bottle with a magnet, then, the Bottle was placed in a thermostatic
water bath. Upon absorption of SO2 gas, the sample was weighed every 5 minutes via
an electronic balance with accuracy of ± 0.0001 g, and the added mass was considered
to be the mass of SO2 absorbed by the solution. During the test, the concentrations of
SO2 were adjusted by controlling the flow rates of N2 and SO2 The absorption

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experiment was carried out until the equilibrium was reached. The absorption
performance of CO2 was also carried out by using the same method as a comparasion.
The desorption experiment was performed under a constant temperature in the same
device, prior to the desorption test, the upper phase was separated by dumping. Pure
N2, at a flow rate of 30 mL/min, was bubbled through the lower phase to desorb SO2 at
100 °C under atmospheric pressure. After desorption, the upper phase was mixed with
the desorption component for the next absorption experiment.
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2.5 Determination of the component distributions
DTSMA/DSO solution with 40 wt% of DTSMA was added to a Gas-Wash Bottle
followed by bubbling SO2 gas at a rate of 50 ml/min. Then, the DTSMA/DSO solution
with a absorption capacity of 0.8-1.8 mol SO2/mol DTSMA was obtained. After waiting
for three days, the upper and lower phases were separated. The contents of SO2 and
DTSMA in the solution were measured by gas chromatography, and the mass of the
DSO was calculated by the subtraction method.
3. RESULTS AND DISCUSSION
3.1 Synthesis of the DTSMA absorbent
NMR and FTIR characterizations were performed to determine whether DTSMA
was successfully synthesized. H and 13C NMR spectra of the di-n-butylamine,
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chloromethyltrimethylsilane and DTSMA product were showed in Figure 1. After the
substitution reaction, the total NMR peaks number of di-n-butylamine and
chloromethyltrimethylsilane was the same as the number of DTSMA product, but there

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are some change in chemical shifts of NMR in DTSMA. The proton H-5 (2.76 ppm) of
the methylene group connected to Si moved to H-5' (1.90 ppm), this result suggested
that the Cl atom of chloromethyltrimethylsilane was replaced by the N atom of di-n-
butylamine. The electron-withdrawing ability of N atom is weaker than Cl, thus have
caused the protons on the C5 atom move to higher field due to the rising electron cloud
density of C5. Similarly, the H-1 (2.54 ppm) of the methylene group attached to N
moved to H-1' (2.32 ppm) after the reaction because the alkyl group belongs to the
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electron-donating group. This conclusion was also supported by C NMR spectra.
After Cl on chloromethyltrimethylsilane was substituted by (CH3CH2CH2CH2)2N-
group, the C atom on the methylene (C-5) and methyl group (C-6) attached to Si have
shifted towards lower field. This was because the CH3CH2CH2CH2)2N- was very large
[28]
and exhibited obvious stereo compression effects and strong deshielding effects
.
The C atom on the methylene group (C-1) attached to N has shifted to lower field could
be also attributed to the stereo compression effects.

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Figure 1. (a) 1H NMR (600 MHz, CDCl3) and (b) 13C NMR (600 MHz, CDCl3)
spectra for Di-n-butylamine (A), Chloromethyltrimethylsilane (B) and DTSMA (C).
In addition, the chemical structure of DTSMA was further confirmed by FTIR
spectroscopy (Figure 2). The N-H bond of di-n-butylamine at 3293 cm-1 disappeared
after the reaction, indicated the disappearing of the N-H bond. Besides, the C-N bond
of di-n-butylamine at 1139 cm-1 changed from a moderately strong peak to a weak peak
of the DTSMA, demonstrated that the tertiary amine was successfully synthesized from
a secondary amine [29-30]. Furthermore, the C-Cl bond of chloromethyltrimethylsilane
at 645 cm-1 disappeared after the reaction suggested that the C-Cl bond has disappeared.
The Si-C bond of chloromethyltrimethylsilane at 856 cm-1 also appeared in spectrum
of the product, proved that the Si-C bond was successfully introduced into DTSMA [31]
.
The DTSMA synthesis reaction can be seen in Scheme 1.
Figure 2. Infrared spectra of di-n-butylamine (A), Chloromethyltrimethylsilane (B)

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and DTSMA (C).
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Scheme 1. Synthetic equation for synthesis of DTSMA.
3.2 Comparison of SO2 absorption capacity of different aminosilanes
As a comparison of the absorption performance of DTSMA, different
aminosilanes (Dipropyl-trimethylsilanylmethyl-amine and Diethyl-
trimethylsilanylmethyl-amine) were synthesized by using dipropylamine and
diethylamine as the raw material with chemical structure analogous to di-n-butylamine.
The NMR and FTIR spectra showed in Figure S2-S4 have turned out that the both of
dipropyl-trimethylsilanylmethyl-amine and diethyl-trimethylsilanylmethyl-amine
were successfully synthesized. The SO2 absorption capacity of the three aminosilanes
were compared using a 20 wt% aminosilanes/DSO solution at 30 °C and 1 atm (Figure
3). The results showed that the absorption capacity of the three types of aminosilanes
(DTSMA, dipropyl-trimethylsilanylmethyl-amine and diethyl-trimethylsilanylmethyl-
amine) were 2.20, 2.24 and 1.92 mol SO2, respectively. Among them, diethyl-
trimethylsilanylmethyl-amine has the smallest absorption capacity, this could be
attributed to its volatile property. Moreover, it should be noted that the absorption
capacity of dipropyl-trimethylsilanylmethyl-amine and DTSMA is basically the same
due to the similar chemical structure. The SO2 absorption performances of DTSMA
were further studied in the following due to its higher yield in the synthesis process.

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Figure 3. Absorption capacity of different aminosilanes.
3.3 Properties of the DTSMA/DSO solution
In order to study the absorption stability of the DTSMA/DSO solution, pure
DTSMA (100 wt%) and DTSMA/DSO solution with 20 wt% of DTSMA were purged
with N2 at a flow rate of 50 mL/min under 30 °C (Figure 4) and 100 °C(Figure S5).
After 6 hours of treatment, the weight loss of pure DTSMA was about 0.9 wt% and 2.6
wt%, whereas the weight loss of the solutions with 20 wt% DTSMA solution was only
0.4 wt% and 1.5 wt%, indicated that the introduction of DSO was very beneficial to
reduce the volatility of the DTSMA. The relationship between vapor pressure and liquid
phase composition was also measured at a constant temperature (Figure S6), it can be
seen that the addition of the DSO can reduce the vapor pressure of the DTSMA/DSO
system. The saturated vapor pressure of the pure absorbent DTSMA was 1.93 kPa,
while the vapor pressure of the DTSMA/DSO solution with 20 wt% of DTSMA was
1.20 kPa. Furthermore, the thermal stability of the prepared solution was studied by

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TGA analysis in a pure N2 environment (Figure S7). The thermal staDbOilI:it1y0.10o39f/D0NJ04500D
DTSMA/DSO solution increased remarkably with the introduction of DSO. For
instance, a 10 wt % weight loss of pure DTSMA occurs at 77 °C, while 137 °C for the
latter.
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Under experimental condition (45 °C), the viscosity of pure DTSMA and solution
with 40 wt% of DTSMA were 1.29 and 2.63 mPa·s, respectively. In comparison with
the absorbents reported in the literature, pure DTSMA has the minimum viscosity.
These values were much lower than the viscosity of the most previously reported ILs
and deep eutectic solvents (Table 1). After SO2 absorption, the absorption capacity of
pure DTSMA solution was 1 mol SO2/mol DTSMA, and the viscosity was only 29.46
mPa·s. The low viscosity values could be attributed to the low polarity of DTSMA and
DSO, this feature might enable DTSMA a better mass transfer rate during the SO2
capture process compared to the high-viscosity ILs and deep eutectic solvents reported
elsewhere.

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Figure 4. Effects of DTSMA concentration on the weight loss rate.
Table 1 Viscosity of the reported absorbents.
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Absorbent
T (K)
η (before
absorption)
(mPa·s)
2.63
η (after
absorption)
(mPa·s)
Ref
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57
58
59
60
DTSMA/DSO solution
(40 wt% DTSMA)
DTSMA
318
This work
This work
298
318
318
338
338
303.1
5
2.01
1.29
1.30
418
29.46
9.51
5.67
810
This work
32
Im−H2O
TMGL
33
33
34
MEAL
794
2000
[N2222][FA]/PEG200
85.70
34
35
35
[Ch][FA]/PEG200
[Et2NEMim][SCN]
[C2OHMim][SCN]
303.1
5
143.79
1284.31
112.15
303.1
5
303.1
5
36
37
N4444Cl:Pyr (1:2)
[NH2emim][OAc]
298.2
298
106.40
2810

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[bmim][OH]
2-
298
125
118
38
298.2
8
9
hydroxyethylammoniu
m formate
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Im-Gly
338
293
293
303.1
5
149
470
[P4442][BTFA]
[P4442][TTFA]
EU/BmimCl (1:2)
803.30
1116.40
375.90
36
BmimCl:4CH3-Im(1:2) 298.2
195.40
3.4 Analysis of absorption product and phase change mechanism
In order to determine the SO2 absorption mechanism of DTSMA, the absorption
product was characterized by NMR and FTIR (Figure 5). After absorption of SO2, the
number of proton peaks did not change but shifted to lower field. Among them, the
protons H-1 (2.32 ppm), H-5 (1.89 ppm) in two methylene groups connected to N were
shifted to H-1' (2.68 ppm), H-5' (2.19 ppm), respectively. Protons in other locations
have smaller chemical shifts when compared to H-1 and H-5, due to their longer
distances to N atom. These results indicated that there was an N→S charge-transfer
interaction between DTSMA and SO2 [42]. SO2 is an electron-withdrawing group, and
could lead to reduction of the electron clouds density around N atoms, so the shielding
effect of around the proton was weakened. The 13C NMR spectrum also confirmed this
speculation. Due to the charge interaction, chemical shift of the C atoms (C-1, C-5) in

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the two methylene groups connected to N are moved. The C at other locations are far
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away from N atom, so their chemical shifts exhibited almost no change.
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Figure 5. (a) 1H NMR (600 MHz, CDCl3) and (b) 13C NMR (600 MHz, CDCl3)
spectra for DTSMA before and after absorption of SO2.
FTIR spectroscopy (Figure S8) further confirmed that the absorption product was
DTSMA·SO2 The asymmetric and symmetric stretching vibration modes of gaseous
SO2 appeared at 1351 and 1150 cm-1, respectively [43]. After absorption, these stretching
vibration modes of SO2 in complex shifted to lower wavenumbers. It showed
characteristic peaks of the charge transfer complex at 1189 and 1098 cm-1. The reaction
equation of the electron transfer product was showed in Scheme 2.
Scheme 2. Reaction between DTSMA and SO2 to form DTSMA·SO2 product.
The SO2 phase change mechanism of the switchable solvent was mainly attributed
to the polarity change of the solution before and after absorption, which has been

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reported in previously reported literature [23]. In order to determine whether tDhOeI:p10h.1a0s3e9/D0NJ04500D
change mechanism of this absorption solution was the same as with that in the literature,
the polarity of the solution before and after absorption of SO2 was studied by an UV
absorption method. As shown in Figure 6, the maximum absorption wavelength of the
solution before and after absorption (1 mol SO2/mol DTSMA) were 520 and 533 nm,
respectively. This indicated the change of polarity of the solution was the phase change
mechanism of this silicone system.
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Figure 6. UV spectra of Nile red in DTSMA before and after absorption of SO2.
3.5 Impact of absorption conditions on absorption capacity
The effects of temperature on absorption capacity were investigated by using a 40
wt% DTSMA/DSO solution under 1 atm (Figure 7a). The absorption capacity of SO2
gradually decreased from 2.26 to 1.39 mol SO2/mol DTSMA with the rising
temperature from 20 to 50 °C. It demonstrated that low temperature was beneficial to
achieving maximum absorption capacity of SO2. Besides, the SO2 absorption capacity
of the solution with various DTSMA mass ratio was also investigated (Figure 7b). The
absorption capacity of the solution with 20 wt% DTSMA can reach to 2.20 mol

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SO2/mol DTSMA, while the solution with 80 wt% DTSMA decreased to 1.76 mol
SO2/mol DTSMA. This is because DSO has a small amount of physical absorption
capacity. Moreover, the partial pressure also has a great impact on the absorption
capacity (Figure 7c), i.e., when the partial pressure was decreased from 1 to 0.002 atm,
the absorption capacity decreased from 1.90 to 0.17 mol SO2/mol DTSMA. In other
words, the absorption capacity of SO2 decreases with the decreasing of partial pressure.
It should be noted that the absorption capacity of the solution with 40wt% of DTSMA
can still reach to 0.57 mol SO2/mol DTSMA at just 0.02 atm.
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Figure 7. Effects of temperature (a), DTSMA mass fraction (b) and pressure (c) on the
absorption capacity of SO2.

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Table 2 listed the absorption capacity of different absorbents reported in the
literature. Although some ILs and Deep Eutectic Solvents exhibited high absorption
capacity under low SO2 pressure, the high viscosity of these absorbents also limited
their practical applications. For example, the absorption capacity of BmimCl:4CH3-
Im(1:2), EmimCl-NFM (1:1), [P4442][BTFA] and [P4442][TTFA] is 1.07mol/mol,
1.30mol/mol, 1.34 mol/mol and 1.26 mol/mol, but exhibited high viscosity of 195.40,
375.90, 803.30 and 1116.40 mPa·s, respectively. And it can be concluded that the
absorption capacity of DTSMA was better than some of the absorbents, for example,
the absorption capacity of Bet-EG (1:3), [TMG][Ac], [MEA][Ac] and [P4442][TFSI]
was 0.33mol/mol, , 0.49 mol/mol, 0.28 mol/mol and 0.01mol/mol. All these results
indicated that the low viscosity DTSMA might serve as a promising absorbent towards
SO2 absorption under various pressures.
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Table 2 Comparison of absorption capacities of various absorbents under low partial
pressure SO2.
Absorbents
T (K)
Pressure(atm)
Absorption
capacity(mol/mol)
0.57
Ref
DTSMA/DSO
solution
303
0.02
This
work
(40 wt% DTSMA)
BmimCl:4CH3-Im
(1:2)
36
44
293
0.02
0.01
1.07
0.90
EmimCl-NFM (1:1)
293.15

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Bet-EG (1:3)
EU/BmimCl (1:2)
[TMG][Ac]
313.20
0.02
0.02
0.03
0.03
0.03
0.01
0.01
0.01
0.03
0.03
0.33
1.30
0.49
0.70
0.28
0.01
1.34
1.26
0.87
1.32
41
46
46
46
40
40
40
47
47
293.15
323
323
323
293
293
293
313
313
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[TMG][PhCOO]
[MEA][Ac]
[P4442][TFSI]
[P4442][BTFA]
[P4442][TTFA]
[N2222]P]
[N2222]2[succinate]
3.6 The effects of SO2 absorption capacity on the distribution two phases
Under the absorption conditions of 30 °C and 1 atm, the DTAMA/DSO
(40wt%/60wt%) solution was selected to study the effects of SO2 absorption capacity
on the distribution of DTSMA, DSO, and SO2 in upper and lower phases, and the results
were analyzed by gas chromatography (Figure 8). With the absorption capacity of SO2
increased from 0.8 to 1.8 mol SO2/mol DTSMA, the mass fraction of DTSMA in the
upper phase decreased from 35.6 to 7.7 wt%, and the mass fraction of DSO increased
from 58.7 to 87.7 wt%. The mass fraction of SO2 in the upper phase was about 5 wt%
and remained almost no change with the increases of SO2 absorption capacity. On the
other hand, with the increases of the absorption capacity of SO2, the mass fraction of
SO2 in the lower phase solution increased from 12.0 to 22.6 wt%, and the mass fraction
of DSO mass fraction decreased from 30.3 to 21.3 wt%. It should be noticed that the

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mass fraction of DTSMA changed from 57.7 to 56.0 wt%, which remained essentially
unchanged. In a word, the phase separation phenomenon occurs with the increases of
absorption capacity of SO2, where DTSMA in the upper phase gradually moves to the
lower phase, and the DSO in the lower phase gradually moved to the upper phase until
the absorption process completed.
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Figure 8. (a) Upper and (b) lower phase distributions of 40% DTAMA+60% DSO
solution after absorption of SO2 at 30 °C and 1 atm.
3.7 SO2 desulfurization efficiency and DTSMA/DSO cyclic absorption capability
The desulfurization efficiency was measured in an apparatus similar to that of Xu et al's
work [25,48]. As shown in Figure 9a, the desulfurization efficiency was higher than 95%
within absorption capacity of 1 mol SO2/mol DTSMA, this illustrated the excellent SO2
absorption ability of the solution. Moreover, the selective absorption experiment was
performed at 30 °C and 1 atm by using an absorption solution with DTSMA mass
fraction of 40 wt% (Figure 9b). It can be seen from the figure that the absorption
capacity of CO2 was only 0.077 mol CO2/mol DTSMA, it means that the selectivity
coefficient towards SO2/CO2 mixture gases was 25. The cyclic SO2 absorption

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performance of the DTSMA/DSO solution was also studied to evaluate its practical use
in industrial applications. We performed 5 times absorption/desorption cycle
experiments under the conditions of 1 atm and 100 °C . The result was showed in Figure
9c, obviously, the absorption capacity after fifth times of absorption experiment was
close to the first absorption capacity, indicated that the absorbent has almost no mass
loss during the 5 times absorption experiments. With the increasing of the cycling
numbers, the time required for absorption and desorption became longer. The reason is
that the electron transfer product cannot be regenerated increased, which resulted in
that the mass transfer rate decreased.
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Figure 9. SO2 desulfurization efficiency (a), selective absorption performance (b) and
recyclability (c) of the DTSMA/DSO solution. (Absorption conditions: 30 °C, 1atm
with the SO2 flow rate of 50 mL/min; Desorption conditions: 100 °C, 1 atm with the

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N2 flow rate of 50 mL/min)
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4. CONCLUSIONS
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In summary, we reported a facile and eco-friendly approach in synthesizing a
novel SO2 phase change absorbent with low viscosity. Benefiting from this silicon-
containing organic substance, the DTSMA exhibited miscible with low-flammability
DSO solvent, the integration of low volatility and low viscosity properties of the
DTSMA/DSO system was very beneficial to capturing SO2 into SO2-lean (upper) and
SO2-rich (lower) immiscible two phases. The absorption capacity of individual
DTSMA was 1.9 and 0.57 mol SO2/mol DTSMA at 1 and 0.2 atm under 30 °C
conditions, and the absorption product was found to be an electron transfer complex.
Besides, the DTSMA/DSO solution system exhibited selective absorption property
towards SO2 and mild cyclic desorption performance upon N2. The proposed synthesis
approach is not only of profound significance to environmental protection, but also a
great promotion to the industrial SO2 pollutant treatment.
ACKNOWLEDGMENTS
We acknowledge the financial support from National Natural Science
Foundationof China (Grant No. 21666011), Yunnan province high level talents special
supportplan (YNWR-QNBJ-2018-369) and Analysis and Measure Foundation of
Kunming University of Science and Technology (2018M20162108016).

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New Journal of Chemistry
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DOI: 10.1039/D0NJ04500D
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