for Efficient Adsorptive Desulfurization - ACS Publications - American

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Maximizing the Density of Active Groups in Porous Poly(Ionic Liquid)s for Efficient Adsorptive Desulfurization Lu Peng, Fangyuan Guo, Cui Zhang, Jian Xu, Sheng Xu, Changjun Peng, Jun Hu, and Honglai Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04873 • Publication Date (Web): 24 Mar 2017 Downloaded from http://pubs.acs.org on March 28, 2017

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Industrial & Engineering Chemistry Research

Maximizing the Density of Active Groups in Porous Poly(Ionic Liquid)s for Efficient Adsorptive Desulfurization Lu Peng,a Fangyuan Guo,a Cui Zhang,a Jian Xu,b Sheng Xu,a Changjun Peng,a Jun Hu,*a Honglai Liu*a a.State Key Laboratory of Chemical Engineering and School of Chemistry & Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PC China. b.Shanghai Institute of Measurement and Testing Technology, 1500 Zhangheng Road, Shanghai, 201203, PC China. ABSTRACT: Porous poly(Ionic Liquids) (PPILs) with both advantages of ionic liquids (ILs) activities and porous properties have caused great interests in adsorptive desulfurization. High density of active functional groups and large surface area in PPILs are two critical factors for enhancing the desulfurization performance; however, there is usually a trade-off between them. In this work, a novel PPIL of poly(bipropargylimidazolium chloride) (P[BPPIM]) was fabricated through a single-step cyclotrimerization homopolymerization. Through this full-atomic utilization method, the mass density of active imidazolium groups were maximized; meanwhile, the introduction of rigid benzene rings within imidazolium rings propped up the porous structure in P[BPPIM], with a surface area of 160.8 m2·g-1 and pore volume of 0.39 cm3·g-1. Based on the density function theory calculation, the binding energies of dibenzothiophene (DBT) over P[BPPIM] were significantly increased due to the synergistic effect of imidazolium ring and benzene ring, resulting in an enhanced saturated DBT adsorption capacity of 37.13 mgS·g-1, which was the best one among all the reported PILs according to our knowledge.

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1. Introduction Desulfurization of liquid fuels has attracted worldwide concerns due to the heavy air pollution in nowadays.1,2 The current technology implemented in industry is hydrodesulfurization (HDS). For HDS, the main limitation is the difficulty to remove aromatic sulfur including thiophenic compound and its derivatives. Therefore, many alternative technologies such as adsorptive desulfurization (ADS), extractive desulfurization (EDS) and oxidative desulfurization (ODS) have been explored in recent years.3-8 Possessing distinctive functional properties, ionic liquids (ILs) have been reported as good solvents for EDS9 and catalysts for ODS.10-12 However, their applications are greatly limited due to the removal difficulty after the extraction and severe ventures of the secondary pollution. The solidification of ILs through polymerization13-17 has been approved as a good solution.18-20 Especially, porous polymeric ILs (PPILs) have attracted much more attentions since they can provide space for host guest molecules, and enhance the activity of ionic liquid (IL) monomers. Kuzmicz et al.21 reported PPILs by the radical polymerization of divinylbenzene and IL monomers. Copolymerization of ionic liquid monomers with the rigid aromatic vinyls ensured their high specific surface area, but the mass density of active IL groups in PPILs was low. Li et al.22 synthesized a cross-linked PPILs through a two-step approach, in which the linear polymer was firstly obtained by the free radical polymerization of 1-vinylimidazolium, and followed by a quaternized cross-linking with 1,4-bis(chloromethyl) benzene. However, its specific surface area (99.6 m2·g-1) were not large enough for good desulfurization performance. Currently, based on the available synthesis methods of the radical copolymerization with aromatic vinyls19,21,23 or delicately designed IL monomers with aromatic phenyl groups24-26, a trade-off between the high density of active IL groups and the good porosity usually limits further applications of PPILs.


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Therefore, novel methods for successfully constructing PPILs with both sufficient active IL groups and good porosity are highly demanded. Surveying various construction methods of functionalized porous organic polymers, the cyclotrimerization is one of the most elegant and successful method.27-31 Through the cyclotrimerization, rigid phenyl groups can be generated, and hence unique porous structures can be constructed in a single-step.32,33 Rendering this bond-forming reaction through homopolymerization, i.e. without any other co-reactant monomers, it can be a rather atomefficient way to maximize their most advantages of IL activities. Meanwhile, the introduced aromatic phenyl groups can provide a guarantee of rigid units to prop up porous skeleton. More importantly, aromatic phenyl groups can also be benefit for enhancing the desulfurization of aromatic sulfurs through the π-stacking interaction. However, no work concerning about the construction of PPILs through the cyclotrimerization reaction has been reported so far. With

these

considerations

in

mind,

we

produced

a

novel

porous

PILs

of

poly(bipropargylimidazolium chloride) (P[BPPIM]) through a single-step cyclotrimerization homopolymerization for the first time. The obtained P[BPPIM] exhibited a high dibenzothiophene (DBT) saturated adsorption capacity of 37.13 mgS·g-1. Then, we calculated the molecular interaction between DBT and the designed IL of bipropargylimidazolium chloride ([BPPIM]Cl), as well as the segments of P[BPPIM]) through the density function theory (DFT). The increased binding energy (BE) revealed there would be a great synergistic effect between imidazolium ring and benzene ring. Additionally, the full-atomic molecular simulation by using grand canonical Monte Carlo (GCMC) method further revealed its porosity formation mechanism and high density of active groups at the surface of pores. The enhanced BEs and the chain molecular morphology revealed that by increasing the density of active IL groups and


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introducing benzene rings through the cyclotrimerization, it can significantly enhance the desulfurization performance. 2. Experimental Section 2.1 Materials. All chemicals were used as received without further purification except cupric(II) chloride (CuCl2·2H2O, 99%) which was heated at 110 °C for 2 h to remove the coordinated water. N-trimethylsilyl-imidazole (C6H12N2Si, 98%), propargyl chloride (C3H3Cl, 97%), and bis(triphenylphosphine)palladium(II) dichloride (Pd(PPh3)2Cl2, 98%) were obtained from TCI (Shanghai) Development Co., Ltd. Dibenzothiophene (DBT, 98%) was purchased from J&K Chemicals (Shanghai, China). Benzothiophene (BT, 99%) and 4,6-Dimethyldibenzothiophene(4,6-DMDBT) were purchased from Adamas Reagent Co.,Ltd. Dimethyl formamide, diethyl ether, toluene, cupric chloride and n-octane were obtained from Shanghai Chemistry Reagents Co., Ltd. 2.1.1 Synthesis of bipropargylimidazolium chloride ([BPPIM]Cl). The synthesis procedure

of

ILs

of

[BPPIM]Cl

was

based

on

the

work34

that:

N-

trimethylsilylimidazolium and propargyl chloride, with the molar ratio of 1:2, were dissolved in toluene (70 wt %), and refluxed at 60°C for 24 h. The resulting product was washed with diethyl ether (10 mL×3), then dried at 100 °C for 12 h (yield=98%). [BPPIM]Cl: 1H NMR (400 MHz, D2O, δ): 9.02 (s, 1H), 7.57(s, 2H), 5.02 (d, J = 2.8 Hz, 4H), 3.00 (t, J = 2.8Hz, 2H); 13C NMR (100 MHz, D2O, δ): 135.8, 122.5, 77.6, 74.3, 39.4; Anal. Calcd for C9H9ClN2: C 59.84, H 5.02, N 15.51, Cl 19.63. 2.1.2 Preparation of bipropargylimidazolium chloride (P[BPPIM]). P[BPPIM] was obtained through a one-step cyclotrimerization catalyzed by bis(triphenylphosphine)palladium(II) dichloride. In a typical synthesis, [BPPIM]Cl (0.36 g, 2 mmol),


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bis(triphenylphosphine)-palladium(II) dichloride (0.07 g, 0.1 mmol) and anhydrous cupric chloride (0.54 g, 4 mmol) were mixed with dimethyl formamide (10 mL) in a 50 mL autoclave reactor and reacted at 200 °C for 12 h. The resulting solid was filtered and washed with hot water for several times to remove the catalyst and reactant residues, then dried under vacuum overnight, which was denoted as P[BPPIM]. 2.2 Characterization. The morphology of samples was characterized by Field-emission scanning electron microscope (FESEM, Nova Nano SEM 450) and transmission electron microscope (TEM, JEOL JEM-2100). Elemental analysis was conducted on an elemental analyzer (Vario EL III). The chlorine content was determined by ion chromatography using a Dionex DX-600 apparatus. The FTIR spectra were recorded on a Nicolet iS10 FTIR spectrometer using the KBr pellet technique. Solution

1

H nuclear magnetic

resonance (NMR) spectrum was obtained in a D2O solution with a Bruker 400MHz Advance spectrometer. Solid state 13C crosspolarization (CP)/magic-angle spinning (MAS) NMR spectrum was recorded with a Bruker Avance III-600MHz spectrometer at a frequency of 100.62 MHz with 13 kHz spinning rate and 1024 scans were signal averaged. The chemical shifts of

13

C NMR spectra were referenced to tetramethylsilane. N2

adsorption-desorption isotherms at 77 K were measured by volumetric adsorption analyzer ASAP 3020. X-ray photoelectron spectroscopy (XPS) measurement was conducted with a PHI 5000C ESCA spectrometer (Perkin-Elmer, USA). The thermal decomposition behavior was performed on a NETZSCH STA 499 F3 thermogravimetric analyzer (TGA), and the sample was heated at a rate of 10 oC min-1 under N2 gas flow at a rate of 40 mL min-1.


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2.3 Desulfurization experiments. The desulfurization performance of PILs adsorbents were tested by the batch experiment. The model oil was prepared by dissolving DBT with different initial concentrations (ranging from 50 mgS·L-1 to 500 mgS·L-1) in n-octane. In a typical desulfurization experiment, 20 mg of adsorbent was mixed with the model fuel (5 mL) under stirring at room temperature in dark. Then, the adsorbents were separated by the centrifugation. The concentrations of sulfur in the model oil before and after desulfurization process were determined by a gas chromatography-flame photometric detector (GC-950, Haixin Chromatography), which was equipped with a HP-5 capillary column (15 m×0.53 mm×1.5 lm film thickness). The inherent error and uncertainties of the chromatography measurement were no more than 5%. The adsorption amount was calculated by Equation 1. qi = V (C0 − Ci )×10−3 m

(1)

where qi is the amount of sulfur compounds adsorbed on the adsorbent (mgS·g-1 adsorbent), V is the volume of the model oil (mL), m is the mass of the adsorbent used (g), and C0 and Ci (mgS·L-1) are the concentrations of sulfur in the model oil before and after desulfurization, respectively. The adsorption isotherms can be obtained by plotting the amount of sulfur compounds adsorbed at equilibrium (qe) against the equilibrium concentration of sulfur in the model oil (Ce), and the results were fitting by the Langmuir adsorption model, which can be described as Equation 2 . Ce Ce 1 = + qe q0 q0b

(2)


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where q0 is the amount of sulfur compounds adsorbed corresponding to the complete monolayer coverage (mgS·g-1), b is the Langmuir constant (L·mg-1). Therefore, the maximum complete adsorption amount q0, can be obtained from the reciprocal of the slope of the plot of Ce/qe against Ce. The kinetic was studied based on the pseudo-second-order model as Equation 3. t 1 t = 2 + q t kq e qe

(3)

where t is the adsorption time, qt is the amount of sulfur compounds adsorbed at any time t, (mgS·g-1), qe is the amount of sulfur compounds saturated adsorbed (mg·g-1), k is the pseudosecond-order-rate constant (g·[mg·h]-1). The rate constant k can be obtained from the slope and the intercept of the plot of t/qt versus t. The desulfurization performance of P[BPPIM] for BT, DBT, and 4,6-DMDBT was investigated in the model oil (500 mgS·L-1). And the desulfurization performance was tested in the same way as above. The selectivity of desulfurization performance against aromatic compounds was investigated by adding specific amount of toluene into the model fuels, such as in the presence of 5 wt.% or 10 wt.% toluene in the model oil (500 mgS·L-1). And the desulfurization performance was tested in the same way as above. The regeneration of PILs adsorbents was achieved by the extraction. For each recycle, the adsorbent was extracted by toluene for three times to remove the adsorbed sulfur compounds, and then dried at 120 °C under vacuum overnight. The stability of the desulfurization performance of the regenerated adsorbent was tested by repeating the desulfurization test. In above experiments, we repeated the tests in quintuplicate, each resulted data was the average value, the corresponding deviation was calculated by the mean standard deviation


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(STDEVP function), and expressed as the error bar on each data in the corresponding plotting curves. 2.4 Calculation details. The geometrical structures of DBT, IL monomer of [BPPIM]Cl, and the segments of P[BPPIM] were optimized using gradient corrected (GGA) correlation functional of Perdew and Wang (PW91) with the double numerical plus (DNP) polarization basis set.35 The BE between DBT and different segments were calculated to evaluate the adsorption strength. In this work, the atomistic model of [BPPIM]Cl was constructed using a modified rotational isomeric state method.36 Three lowest energy configurations were selected for equilibration by a 21-step MD compression and relaxation scheme.37,38 All the theoretical calculations were performed by the Dmol3 module in Materials studio 6.0. 3. Results and Discussion 3.1 Construction of P[BPPIM]. A convenient one-step cyclotrimerization was used to realize the construction of P[BPPIM]. The chemical reactions were illustrated in Scheme 1, and the proposed formation mechanism39 can be found in Supporting Scheme S1. By opening triple C-C bonds of [BPPIM]Cl monomers, the benzene rings were cyclized through closing the ring step by step. With the continuous addition of [BPPIM]Cl, P[BPPIM]

was

obtained

by

this

cyclotrimerization

reaction.

Although

the

cyclotrimerization has been well applied in constructing porous aromatic polymers, as far as we know, it was the first time to be tried in the fabrication of PPIL. The element analysis results for C, H and N, and ion chromatograph analysis for Cl showed that the contents of C, H, N, and Cl in P[BPPIM] were 58.6, 6.9, 15.2, and 19.2%, consistent with the theoretical mass percentage of each element in [BPPIM]Cl monomer, respectively.


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Therefore, the cyclotrimerization homopolymerization can maximize the density of the active imidazolium rings and introduce the functional benzene rings in P[BPPIM], simultaneously.

Scheme 1. Chemical reaction of the synthesis of P[BPPIM].

Figure 1. Characteristics of the formation of benzene rings in P[BPPIM] (a) solid-state 13

C MAS NMR spectrum, 13C NMR spectrum of [BPPIM]Cl was taken as the reference

and (b) FTIR spectrum. According to the formation mechanism of P[BPPIM], the existence of the benzene rings in product can be a good proof of the successful cyclotrimerization reaction. As shown in Figure 1a, compared the

13

C NMR spectrum of [BPPIM]Cl monomer with the

solid-state 13C MAS NMR spectrum of P[BPPIM] polymer, it was found that the peaks of the propargyl at 78 ppm and 75 ppm disappeared and the peaks of the benzene ring at 132


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ppm and 129 ppm40 outstood remarkably. The FTIR spectra (Figure 1b) also revealed the formation of benzene ring through its characteristic skeleton vibration peak at 1628 cm1 19

.

Whereas the peak of carbon-carbon triple bond at 2100 cm-1 which originally existed

in the spectrum of [BPPIM]Cl monomer disappeared, indicating that the propargyl groups in [BPPIM]Cl almost completely cyclotrimerized into benzene rings. Additionally, the existence of the adsorption peak of imidazolium skeleton at 1512 cm-1,41 the deformation vibration of C-H bond in the imidazolium ring at 1437 cm-1, and the C–N stretching band of imidazolium ring at 1105 cm-1 implied imidazolium rings were retained commendably after the cyclotrimerization.42 Moreover, C1s XPS spectra of P[BPPIM] (Supporting Figure S1a) showed that the bonding energies of the simulated curves, centering at 284.7, 286.0 and 286.5 eV, were assigned to benzene carbon and imidazolium carbon, respectively.43 And N1s XPS spectra (Supporting Figure S1b) suggested the bands at 399.8 and 400.6 eV, were typically aroused from the imidazolium ring,44 which were consistent with results of

13

C NMR and FTIR spectra. Therefore, by introducing benzene

rings among imidazolium rings through this cyclotrimerization homopolymerization, P[BPPIM] was successfully fabricated.

Figure 2. SEM image (a) and TEM images b) of P[BPPIM].


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Figure 3. N2 adsorption isotherm and its corresponding pore distribution curve of P[BPPIM]. 3.2 Porosity of P[BPPIM]. As shown in Figure 2a, SEM image revealed that P[BPPIM] powder was composed of nanoparticles, which aggregated into nano-flakes. From its TEM images (Figure 2b), large amounts of random interstitial pores can be observed among the nanoparticles. The high resolution TEM image in the insert further suggested that these nanoparticles were full of amorphous micropores. The textural properties of P[BPPIM] was characterized by N2 adsorption at 77 K. The isotherm is type IV with a clear hysteresis loop of type H4 at the high relative pressure (P/P0) ranging from 0.9 to 0.99 (Figure 3), reflecting a typical mesostructure. The Brunauer-EmmettTeller (BET) surface area and total pore volume (calculated at P/P0=0.99) are as high as 160.8 m2·g-1 and 0.39 cm3·g-1, respectively. The majority of pore size distribution in mesopores appears at 4nm and 35nm (Figure 3, inset). Therefore, through cyclotrimerization, P[BPPIM] not only retained the whole characteristic properties of [BPPIM]Cl monomer, but also exhibited quite good porosity.


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Figure 4. For P[BPPIM], (a) DBT adsorption isotherm and the corresponding plot based on the Langmuir model, (b) Kinetic adsorption curve of DBT (500 mgS·L-1) and the corresponding fitting plot of the pseudo-second-order dynamic model. 3.3 DBT adsorption performance on P[BPPIM]. When we used DBT in n-octane as the model fuel, the desulfurization performance of P[BPPIM] was shown in Figure 4a. All the original experimental data and the corresponding standard deviations were listed in Supporting Table. S2, with the standard deviations no more than 0.89. We can see the adsorption capacity increased with the concentration of DBT. Fitting with the Langmuir adsorption isotherm (Equation 2), a good linear relationship was obtained between Ce/qe vs. Ce (standard deviation R2>0.98). Calculated from the reciprocal of the slope, the saturated DBT adsorption capacity on P[BPPIM] reached as high as 37.13 mgS·g-1. According to our knowledge, it was the best one among the reported PILs,22-23, 45-47 and even larger than several typical porous materials, such as MCM-41, activated carbon and MIL-10048-50 (Supporting Table. S3). When we fixed DBT concentration at 500 mgS·L-1, the kinetic desulfurization behavior of P[BPPIM] in the model fuel was investigated at 293 K, all the original experimental data and the corresponding standard deviations were listed in Supporting Table. S4. As shown in Figure 4b, DBT uptakes increased rapidly in the initial 1 h to reach 15.43±0.48


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mgS·g-1. When the adsorption time was prolonged to 4 h, the adsorption almost reached the equilibrium with the uptakes of 30.05±0.82 mgS·g-1. And it was observed that the adsorption of DBT can be described quite well by a pseudo-second-order kinetic model with the standard deviation R2>0.99, suggesting the strong affinity of DBT with P[BPPIM] due to the high density of imidazolium rings and benzene rings. 3.4 Mechanism of the enhanced desulfurization performance. The molecular interaction between DBT and IL monomer of [BPPIM]Cl, as well as the segments of P[BPPIM] were calculated by DFT to illustrate the mechanism of the enhanced desulfurization performance. As shown in Figure 5, the BE of DBT to the pristine imidazolium ring in [BPPIM]Cl (Figure 5a) was calculated as -23.48 kJ·mol-1. After the cyclotrimerization, [BPPIM]Cl can be polymerized into P[BPPIM] with the structure unit of one newly-formed benzene ring linked by three imidazolium rings. Accordingly, two configurations of segments of P[BPPIM], focusing on the imidazolium ring linked with two benzene rings (Figure 5b) and the benzene ring linked with three imidazolium rings (Figure 5c) were constructed and optimized, respectively. The BEs of DBT to the imidazolium ring in P[BPPIM] was enhanced to -49.5 kJ·mol-1, and that to the benzene ring dramatically increased to -84.1 kJ·mol-1. Both enhanced BEs revealed that there would be a great synergistic effect between imidazolium ring and benzene ring, and the introduction of benzene rings into PIL chains would show a significant benefit for desulfurization.


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Figure 5. BEs of DBT over (a) the monomer [BPPIM]Cl, (b) and (c) the segment of P[BPPIM] calculated by DFT. In which C is in green, N is in blue, S is in orange, H is in white. The dark green sphere is Cl anion. Moreover, the configuration of the molecular chain arrangement, the porosity of the network, and the distribution of the active functional groups in the network were further demonstrated by a full-atomic molecular simulation by GCMC method (detailed method was provided in Supporting Information). As shown in Figure 6a, composing of 30 units, the main chain of P[BPPIM] in pink color expended randomly in a three-dimensional cubic simulation box. Instead of twinning closely with each other, the chain formed a loose structure, and interconnected intrinsic porosity was naturally produced (Figure 6b). Because imidazolium rings were connected to benzene rings through a short CH2 group, the backbone of P[BPPIM] chains were relatively rigid, and hence propped up the porosity. The surface area of the simulated P[BPPIM] was estimated as 294 m2·g-1, slightly different with the experimental results. From an arbitrary enlargement of the chain segments near the pore, we can see imidazolium rings and benzene rings were surrounded and exposed at the surface of pores, which ensured to their functional activities. Accordingly, combining both advantages of the good porosity and the synergistic activities of imidazolium rings and benzene rings, the desulfurization performance of P[BPPIM] were highly enhanced.


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Figure 6. Simulated morphologies of P[BPPIM] (a) random arrangement of the chain (b) free volume, denoted as pink regions. The enlargements are the distributions of the segments of the chain near the pores.

Figure 7. BEs of DBT over (a) the monomer [BPPIM]Cl, (b) and (c) the segment of P[BPPIM] calculated by DFT. In which C is in green, N is in blue, H is in white. The dark green sphere is Cl anion. 3.5 Influence of the sulfur substrates. To study the desulfurization performance of P[BPPIM] for different sulfur compounds, benzothiophene (BT), DBT, and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were chosen as the representative sulfur compounds. The results in Table 1 displayed that sulfur removal of BT, DBT and 4,6-DMDBT were 10.13±0.29 mgS·g-1, 30.50±0.52 mgS·g-1 and 6.32±0.10 mgS·g-1, respectively. The sulfur removal is at the following order: DBT > BT > 4,6-DMDBT. As calculated by Otsuki et al.,51 the electron density on the


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sulfur atom was 5.758 for DBT, 5.739 for BT, and 5.760 for 4,6-DMDBT. For DBT and BT, the desulfurization performance improved with increasing aromatic electron density. Whereas, relatively low sulfur removal of 4,6-DMDBT was mainly affected by the steric hindrance of the methyl groups, which made 4,6-DMDBT molecules difficult to approach to the active species of P[BPPIM]. Table 1. Desulfurization performance of different sulfur substrates

a

Substrate

q0 (mgS·g-1) a

Electron density b

Deviation

BT

10.13

5.739

0.29

DBT

30.50

5.758

0.52

4,6-DMDBT

6.32

5.760

0.10

Experiment conditions: Sulfur contents of BT, DBT, 4,6-DMDBT in model oil were 500

mgS·L-1 in n-octane, V(model oil) = 5 mL, m(adsorbent) = 20 mg; b

Data from the reference by Otsuki et al. 51 3.6 Selectivity and recyclability of P[BPPIM]. Usually, the introduction of benzene

rings in the networks would also increase the affinity with aromatic hydrocarbons due to the enhanced π-complexation interaction. Since aromatic hydrocarbons are main components in fuel, the selectivity between the aromatic thiophenic sulfurs and aromatic hydrocarbons should be taken into account. When toluene was chosen as the aromatic representative, the calculated BEs of toluene with the imidazolium ring enhanced from 20.7 kJ·mol-1 in [BPPIM]Cl to -25.7 kJ·mol-1 in P[BPPIM], and even high as -42.5 kJ·mol-1 with the benzene ring in P[BPPIM], respectively (Figure 7). Accordingly, the DBT adsorption capacity of P[BPPIM] inevitably decreased in the presence of aromatic hydrocarbons. As shown in Figure 8a and Supporting Table. S5, without adding toluene,


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the DBT adsorption capacity from the model oils (500 mgS·L-1) was 30.50±0.32 mgS·g-1, it decreased by 20.2% and 29.4% in the presence of 5 wt.% and 10 wt.% toluene, respectively. Anyhow, the DBT adsorption capacity of 23.98±0.68 mgS·g-1 or 21.21±0.75 mgS·g-1 were still quite acceptable. More importantly, because the BEs of DBT with P[BPPIM] were enhanced much more significantly than those of toluene, the selectivity of DBT to toluene held as high as 5.1 and 4.8 in the presence of 5 wt.% and 10 wt.% toluene, respectively. (Supporting Figure S2, and the calculation details can be found in Supporting Information).

Figure 8. For P[BPPIM], (a) DBT adsorption capacities from the model oils (500 mgS·L1

) in the presence of toluene with different concentrations, (b) the recycle adsorption

performance in the model fuel (500 mgS·L-1). Since the thermo-decomposition temperature of P[BPPIM] was lower than 250 oC (Supporting Figure S3), we used the extraction method to regenerate the adsorbent. The recycling performance of P[BPPIM] (Figure 8b, Supporting Table. S6) suggested the adsorption capacity of DBT decreased a little after each cycle. After 5 cycles, the adsorption capacity still maintained at 24.24±1.32 mgS·g-1. 4. Conclusions


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In this work, a single-step cyclotrimerization was successfully used to synthesize novel PPIL with both high density of active functional groups and good porosity. The obtained porous P[BPPIM] showed a BET surface area of 160.8 m2·g-1 and pore volume of 0.39 cm3·g-1. It exhibited a high DBT saturated adsorption capacity of 37.13 mgS·g-1, and a good selectivity of DBT/toluene of 5.1 from the model oils (500 mgS·L-1) in the presence of 5 wt.% toluene. The introduction of benzene rings in P[BPPIM] provided relatively rigid units to prop up the porous skeleton, and also exhibited a synergistic effect with the imidazolium ring to enhance the affinity with DBT. Therefore, this cyclotrimerization method can provide a convenient and promising strategy to establish novel PPILs for further applications. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. *E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work is supported by the National Key Basic Research Program of China (2013CB733503) and the Natural Science Foundation of China (Nos. 91334203, 21376074， U1362111). Shanghai


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Table of Contents Maximizing the Density of Active Groups in Porous Poly(Ionic Liquid)s for Efficient Adsorptive Desulfurization Lu Peng,a Fangyuan Guo,a Cui Zhang,a Jian Xu,b Sheng Xu,a Changjun Peng,a Jun Hu,*a Honglai Liu*a Keyword: porous poly(ionic liquid), cyclotrimerization, desulfurization, density function theory, full-atomic molecular simulation. Porous poly(ionic liquid) of propargylimidazolium chloride (P[BPPIM]) has been fabricated by a single-step cyclotrimerization. Based on the density function theory calculation, the binding energies of dibenzothiophene (DBT) over P[BPPIM] were significant increased due to the synergistic effect of imidazolium ring and benzene ring, resulting in an enhanced saturated DBT adsorption capacity of 37.13 mgS·g-1.


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Figure 1. Characteristics of the formation of benzene rings in P[BPPIM] (a) solid-state 13C MAS NMR spectrum, 13C NMR spectrum of [BPPIM]Cl was taken as the reference and (b) FTIR spectrum.



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Figure 3. N2 adsorption isotherm and its corresponding pore distribution curve of P[BPPIM].


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Figure 4. For P[BPPIM], (a) DBT adsorption isotherm and the corresponding plot based on the Langmuir model, (b) Kinetic adsorption curve of DBT (500 mgS·L-1) and the corresponding fitting plot of the pseudosecond-order dynamic model.



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Figure 5. BEs of DBT over (a) the monomer [BPPIM]Cl, (b) and (c) the segment of P[BPPIM] calculated by DFT. In which C is in green, N is in blue, S is in orange, H is in white. The dark green sphere is Cl anion.


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Figure 7. BEs of DBT over (a) the monomer [BPPIM]Cl, (b) and (c) the segment of P[BPPIM] calculated by DFT. In which C is in green, N is in blue, H is in white. The dark green sphere is Cl anion.



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Figure 8. For P[BPPIM], (a) DBT adsorption capacities from the model oils (500 mgS·L-1) in the presence of toluene with different concentrations, (b) the recycle adsorption performance in the model fuel (500 mgS·L1).


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