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Jul 5, 2016 - ABSTRACT: A hyper cross-linked polymer, HCPVIM, was prepared by copolymerization of vinylimidazole (VIM) and divinylbenzene (DVB), ...
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Effect of Quaternization on Structure and Adsorptivity of Hyper Cross-Linked Poly(vinyl imidazole) for Thiohenic Sulfurs in Model Oil Jing Zhang,†,‡ Chunhong Ma,†,‡ Xuexi Zhu,†,‡ Yingzhou Lu,‡ Hong Meng,‡ Chunxi Li,*,†,‡ Biaohua Chen,†,‡ and Zhigang Lei†,‡ †

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China

Ind. Eng. Chem. Res. 2016.55:8079-8086. Downloaded from pubs.acs.org by UNIV OF LOUISIANA AT LAFAYETTE on 10/14/18. For personal use only.

‡

S Supporting Information *

ABSTRACT: A hyper cross-linked polymer, HCPVIM, was prepared by copolymerization of vinylimidazole (VIM) and divinylbenzene (DVB), whereby three poly ionic liquids (PILs) were synthesized via quaternization of the imidazole ring by hydrochloric acid, n-butyl chloride and 1,4-bis(chloromethyl) benzene, respectively. Their composition, morphology, specific area and thermal stability were characterized, and their adsorptivity for thiophenic sulfurs was studied. The HCPVIM is a mesoporous sorbent with specific area of 675 m2 g−1, and shows much higher desulfurization ability than its monomer analogue, ethyl imidazole, being about 8.0 mg S g−1 for dibenzothiophene (DBT) at equilibrium S-concentration of 900 ppm. Its desulfurization ability follows the order of DBT > benzothiophene> thiophene, being the same order as alkyl imidazole and imidazolium based ionic liquids. Compared to HCPVIM, the PILs are also mesoporous materials but with negligible micropores, lower specific area of ∼180 m2 g−1, and lowering thermal decomposition temperature of about 150 K. The PILs show a complex adsorption behavior for different sulfur compounds. As a whole, quaternization of HCPVIM tends to decrease the desulfurization ability for all sulfur compounds except the protonated HCPVIM for thiophene, which manifests the combinative effects of the decreased porosity and specific area and the increased electrostatic interactions in the ionized sorbents.

1. INTRODUCTION Poly ionic liquids (PILs), as a special polyelectrolyte containing ionic liquids (ILs) structure unit, have dual nature of both ILs and polymers,1 and have developed to be a research frontier of ILs. Some reviews have been available for the recent advances of PILs.2−4 PILs can be synthesized via two approaches: (1) polymerization of the ILs monomer through vinyl substitute. This method is widely used. However, it is hard to get a PIL with desired structure and polymerization degree due to the limited knowledge about the polymerization process and the polymerizability of the ionic monomers with varying electrostatic interaction and steric hindrance. (2) Modification of the commercial polymer via grafting or ionizing the polymer substitute. This method is more viable to make desired PILs since the structure and property of the PILs are determined by the polymer precursors. PILs have been widely used in the study of CO2 capture.5−7 They show much higher adsorption rate and capacity than the corresponding ILs, because of the porous structure8 and the abundant micropores that enhance the adsorption rate and capacity greatly.9 PILs also show excellent performance in wastewater decoloring10 and phenol adsorption from coal tar.11 In contrast to the prosperous study on adsorptive desulfurization with novel functional materials12−14 and the extractive desulfurization of ILs,15−17 the usability of PILs in oil © 2016 American Chemical Society

desulfurization has been barely explored until now. Wang et al.18 studied the adsorptive desulfurization ability of some polystyrene-grafted metal chlorides PILs for thiophenic sulfurs in model oil, and a promising result was shown. However, the anions of the PILs are water sensitive, which will hinder their practical use due to the negative effect of the accumulative water from the oil stream. Until now, little is known about the relationship between desulfurization capability of PILs and their ionic constituents and porous structure, and thus preliminary research is necessary. On the basis of the above cognition, a hyper cross-linked poly(vinyl imidazole) (HCPVIM) was prepared, which was then ionized, respectively, by hydrochloric acid (HCl), n-butyl chloride (BuCl), and 1,4-bis(chloromethyl) benzene (BCmBn), forming the resultant PILs, viz., HCPVIM-HCl (PIL-1), HCPVIM-BuCl (PIL-2), and HCPVIM-BCmBn (PIL3). Their composition, morphology, pore structure, specific area, and thermal stability were characterized, and their adsorptive desulfurization performance for model oil was studied. On this basis, the influence of quaternization on Received: Revised: Accepted: Published: 8079

March 10, 2016 June 14, 2016 July 5, 2016 July 5, 2016 DOI: 10.1021/acs.iecr.6b00961 Ind. Eng. Chem. Res. 2016, 55, 8079−8086

Article

Industrial & Engineering Chemistry Research structure, specific area, and desulfurization ability of HCPVIM was elucidated. The result is of significance for the rational design of PILs sorbents for the deep desulfurization of fuel oils.

Scheme 2. Representative Structures of Three PILs

2. EXPERIMENTAL SECTION 2.1. Chemical Materials. Thiophene (T, >99%), benzothiophene (BT, >97%), dibenzothiophene (DBT, >99%), 4,6dimethyldibenzothiophene (DMDBT, >99%), and indole (IND, >99%) were purchased from J & K Sci. Ltd. 2,2Azobis(isobutyronitrile) (AIBN, AR) was from Tianjin Guangfu Fine Chem. Ind. Inst. DMF, ethyl acetate, toluene, and octane with analytical reagent (AR) grade were from Beijing Yili Fine Chem. Ltd. 1,4-Bis(chloromethyl)benzene (BCmBn, AR), n-butyl chloride (BuCl, AR), divinylbenzene (DVB, AR), and 1-vinyl imidazole (VIM, AR) were from Aladdin Chem. All reagents were used as received. 2.2. Material Synthesis and Characterization. 2.2.1. Synthesis of HCPVIM. DVB was pretreated before use with dilute NaOH aqueous solution to remove the phenolic stabilizer, and 4 wt % AIBN solution of DMF was prepared for instant use. In total, 3 g of VIM, 100 g of DMF, and specific amounts of DVB and AIBN were added to a conical flask with AIBN being 4 wt ‰ of the monomers. The mixture was heated in an oil bath at 70 °C for 20 h, and white precipitates were formed gradually. The HCPVIM was obtained through filtration, washing with ethyl acetate, drying in a vacuum oven at 100 °C, and then kept in a laboratory dryer. Three highly cross-linked polymers were made, viz., HCPVIM-1, HCPVIM, and HCPVIM-3, corresponding to the mole ratio of VIM/DVB of 1:0.3, 1:0.5, and 1:1, respectively. The copolymerization reaction is shown in Scheme 1.

2.3. Characterization and Desulfurization Test. The composition, structure, morphology, specific area, pore structure and thermal stability of HCPVIM and its ionized derivatives (PILs) were characterized by elemental analysis, gel permeation chromatography (GPC), infrared spectrum (IR), solid state 13C nuclear magnetic resonance (13CNMR), scanning electron microscopy (SEM), N2 adsorption analyzer, and thermogravimetric analysis (TGA), respectively. The desulfurization performance of as-prepared sorbents for thiophenic sulfurs in model oil was evaluated by static adsorption at specified temperature in terms of the adsorbance qe (mg S g −1) at varying equilibrium S-concentrations. The model oil was a mixture of octane with specific amount of thiophenic sulfurs. The S-concentration in the oil was determined by a sulfur nitrogen analyzer (KY-3000S, China).

Scheme 1. Preparation of HCPVIM via Copolymerization of VIM and DVB

3. RESULTS AND DISCUSSION 3.1. Influence of DVB Usage on the Structure of HCPVIM. The structure and property of the HCPVIMs, viz., HCPVIM-1, HCPVIM, and HCPVIM-3, were analyzed, and the results are provided in the Supporting Information. It is found that the mole ratio of VIM/DVB in the polymers is much lower than its feeding ratio and decreases with the increasing amount of cross-linking agent DVB. This may arise from the differing polymerizability of VIM and DVB or the stronger self-polymerization of DVB, which results in some dissolution loss of the polymers with lower cross-linkage. Besides, all the HCPVIMs are ultrafine particles of 30−50 nm, and their size decreases slightly with the increasing ratio of DVB, because of the termination effect of the precipitation for the solution polymerization reaction. Moreover, the amount of DVB used has a great influence on the porous structure and specific area of HCPVIMs. Specifically, all HCPVIMs are mesoporous materials with pore size of about 6 nm, and their specific area and micropore specific area follow the order of HCPVIM > HCPVIM-3 > HCPVIM-1. HCPVIM has the highest specific area of 675 m2 g−1 and microporous specific area of 126.6 m2 g−1, and the smallest pore diameter of 5.55 nm. Finally, all the cross-linked polymers have good thermal stability with their pyrolysis temperature above 400 °C. Therefore, HCPVIM was chosen as raw material for the preparation of three PILs here.

2.2.2. Synthesis of PILs. Three PILs, i.e., PIL-1, PIL-2, and PIL-3, were prepared by reacting HCPVIM with HCl, BuCl, and BCmBn, respectively, via quaternization of the imidazole rings, and their representative structures are shown in Scheme 2. The detailed synthesis process is as follows. Synthesis of PIL-1. In total, 5 g of HCPVIM and 10 mL of 36 wt % HCl solution was added into a 100 mL conical flask and stirred at room temperature for 2 h. Then the filter cake was dried for 12 h at 100 °C under reduced pressure. Finally, white powder of HCPVIM-HCl, noted as PIL-1, was obtained. Synthesis of PIL-2. In total, 2 g of HCPVIM was mixed with excessive BuCl (10 mL) in a 50 mL pressure reactor and reacted at 70 °C for 72 h. Then the filter cake was dried in a vacuum dryer at 100 °C for 2 h. Finally, a yellowish powder of HCPVIM-BuCl, noted as PIL-2, was obtained. Synthesis of PIL-3. In total, 2 g of HCPVIM, 1.054 g of BCmBn, and 20 g of DMF were mixed in a 50 mL vial and reacted at 70 °C for 72 h under magnetic stirring. The filter cake was washed three times with ethyl acetate, and dried in vacuum dryer at 100 °C for 2 h. Finally, a yellowish powder of HCPVIM-BCmBn, noted as PIL-3, was obtained. 8080

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Industrial & Engineering Chemistry Research Scheme 3. SEM Images of HCPVIM and the PILs

3.2. Effect of Quaternization on Structure and Adsorptivity of PILs. The SEM images of HCPVIM, PIL-1, PIL-2, and PIL-3 are presented in Scheme 3. In comparison with HCPVIM, the particle size of the PILs becomes larger along with heavier aggregation and lower fluffy degree. This may be attributed to the filling effect of the ionizing species to the micropores via chemical bonding, which results in a permanent loss of some micropores and specific area, as justified by the BET analysis that follows. Besides, strong electrostatic interaction among the charged particles also enhances the aggregation of the PILs powders. Further, BCmBn can form a secondary cross-linking of HCPVIM chains during the ionization process, resulting in an even larger particle size and hard aggregates. The difference of HCPVIM and the PILs originates from the quaternization of the imidazole ring that converts a neutral polymer to ionic ones, and introduces extra interactions via ionic species and accompanying substituents. Figure 1 shows

the IR spectra of HCPVIM and the PILs. Compared to HCPVIM, a weak peak occurs at 1168.7 cm−1 for PIL-1, belonging to the vibration of +N−H in the protonated imidazolium ring19,20 by HCl. Similarly, two sharp peaks occur at 1161.0 and 1155.2 cm−1, respectively, for PIL-2 and PIL-3, belonging to the C−H deformation vibration of the imidazolium plane, as it occurred frequently in various imidazolium based ILs.21 The solid state 13C NMR spectra of HCPVIM and the PILs are presented in Figure 2. It is noted that the spectra are

Figure 2. Solid state 13C NMR (75 MHz) spectra of HCPVIM and the PILs.

virtually the same except a unique peak at about 137 ppm for all three PILs, arising from the carbon atom (N−C−N) of the imidazolium.22,23 The peaks at 127 and 144 ppm are ascribed, respectively, to the tertiary and quaternary carbon of the benzene ring, and the peak at 42 ppm is assigned to tertiary carbon connected to the benzene ring. The N2 adsorption−desorption curves of HCPVIM and the PILs are presented in Figure 3, and the resulting specific area,

Figure 1. IR spectra of HCPVIM and the PILs. 8081

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Figure 4. TGA curves of HCPVIM and the PILs.

Figure 3. N2 adsorption−desorption curves of HCPVIM and the PILs.

[FeCl4]−.27,28 The desulfurization ability of these solvents is usually assumed to arise from the conjugated π−π interaction29 and dispersion interaction30 between imidazole/imidazolium and thiophene rings, and other interactions if appropriate, e.g., hydrogen bonding31 and Lewis acid−base interaction.32 Therefore, as a polymerized vinyl imidazole, HCPVIM is expected to have a higher or at least comparable desulfurization ability than ethyl imidazole (EIM) and relative ILs. As seen from Figure 5, HCPVIM shows excellent sulfur removal ability, being about 2−3 times that of EIM in terms of

pore volume, and pore size are listed in Table 1. The results show that the ionizing process makes the microporous structure Table 1. Pore Structure Parameter of HCPVIM and the PILs absorbent

HCPVIM

PIL-1

PIL-2

PIL-3

BET specfic area/m2 g−1 micropore specfic area/m3 g−1 total pore volume/cm3 g−1 micropore volume/cm3 g−1 average pore size/nm

675.0 126.6 0.94 0.05 5.6

181.1 17.8 0.32 0.006 7.0

199.9 45.2 0.52 0.015 10.4

175.9 7.7 0.50 0.0006 11.3

vanish virtually and the specific area decreased greatly. Specifically, the microporous specific area decreased from 126.6 m2 g−1 for HCPVIM to 7.7 m2 g−1 for PIL-3, and the specific area fell sharply from 675 m2 g−1 for HCPVIM to about 180 m2 g−1 for all PILs. The average pore size of the sorbents increased from 5.6 nm for HCPVIM to 7.0, 10.4, and 11.3 nm, respectively, for PIL-1, PIL-2, and PIL-3 due to the vanishing of micropores. This agrees well with the increasing size of the ionizing reagents, i.e., HCl < BuCl < BCmBn. As clearly shown in Figure 3, both microporous and mesoporous adsorption volume of PILs for N2 decrease greatly because of the filling effect of the ionizing reagents for the porous HCPVIM, making some micro- and meso-porous structure disappear permanently. As shown from the TGA curves in Figure 4, compared with HCPVIM, the pyrolysis temperature of PILs advances greatly and experiences a two-stage decomposition, viz., the decomposition of imidazolium salt at 250−350 °C and degradation of the polymer chain at about 400 °C.19,24 The first decomposition temperature of PILs is close to the pyrolysis temperature of majority of imidazolium based ILs,25 arising mainly from a reverse reaction of nucleophilic addition, forming volatile components. The stability of the imidazolium rings follows the order of PIL-2 > PIL-3 > PIL-1, as indicated by the weight loss rate before 300 °C. 3.3. Desulfurization Performance of HCPVIM and Its Ionic Derivatives. 3.3.1. Adsorptivity of HCPVIM for Thiophenic Sulfurs in Oil. As is known that alkyl imidazoles show good extraction capacity for thiophenic sulfurs from oil and even better performance than the imidazolium based ILs26 except those with strong Lewis acidic anion like [AlCl4]− and

Figure 5. Adsorption isotherms of HCPVIM and EIM for DBT, BT, and T. Experimental conditions: 15 g of oil, 0.3 g of sorbent, stirring 4 h at 8 °C.

the desulfurization capacity at similar conditions. This may be ascribed to the good porosity of HCPVIM, which makes the sulfur molecules can directly enter the micropores without additional Gibbs energy (ΔG1 = 0) for creating such pores and fixed there via interaction with the nearby imidazole groups (ΔG2 < 0). In contrast, for the extractive desulfurization process, micro cavities have to be created beforehand with additional Gibbs energy (ΔG1 > 0) to overcome the cohesive energy of the extractant, whereby the sulfur molecules can enter the cavities and remain there with a similar ΔG2. Therefore, the adsorption process of sulfur molecules on HCPVIM needs to 8082

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Industrial & Engineering Chemistry Research overcome a lower Gibbs energy barrier, which corresponds to a higher S-partition coefficient (KN) or a higher desulfurization capacity. Compared with alkyl imidazoles, ILs have much higher cohesive energy due to the strong electrostatic interaction among ionic species,33 which can partly explain why their extraction desulfurization ability is usually lower than the corresponding alkyl imidazoles. Besides, the adsorption behavior of HCPVIM is quite complex, compared to the linearly increased extractive desulfurization ability of EIM with the equilibrium Sconcentration. This may be attributed to the multiscale porous structure of the sorbent, i.e., the micropores for monolayer Langmuir adsorption, and the meso-pores for multilayer physical adsorption. Therefore, HCPVIM seems more suitable for deep desulfurization of fuel oil with low initial S-content. In contrast, in the extraction process, the Gibbs free energy to transfer a sulfur molecule from the oil phase to extraction phase is virtually constant considering the infinite dilution Sconcentration in both phases, which results in a constant KN value. Moreover, the adsorptivity of HCPVIM follows the order of DBT > BT > T, which is the same as all alkyl imidazoles and the corresponding imidazolium ILs. This implies the decisive role of the imidazole/imidazolium ring in the desulfurization mechanism. For real oil, many kinds of sulfur and nitrogenous compounds are present, e.g., DMDBT and indole, which may affect the adsorptive desulfurization ability of the sorbent. To elucidate their influence, adsorption isotherms of HCPVIM were made for DMDBT-oil with 1000 ppm S and DBT-indoleoil with 1000 ppm S and 500 ppm N. As shown from Figure 6,

Figure 7. Adsorption isotherms of PIL-1 for DBT, BT, and T. Experimental conditions: the same as Figure 5.

reversed from the lowest to highest, being thrice its precursor. This may be attributed to the least steric hindrance and strong Lewis acidity of [HVIM]+, which is helpful for a closer approach of sulfur to the protonated imidazole ring and a stronger interaction therein. It is the Lewis acid−base interaction that makes the protonated HCPVIM have much higher adsorptivity for T than BT and DBT.32 In contrast, PIL1 shows much lower adsorption for BT and DBT than HCPVIM, which may be ascribed to the vanishing microporous adsorption. As shown from Figure 8, PIL-2 shows quite different sulfur adsorptivity from PIL-1, being DBT > BT ≈ T. In fact, its pore

Figure 6. Adsorption isotherms of HCPVIM for DMDBT oil with 1000 ppm S and DBT-indole oil with 1000 ppm S and 500 ppm N. Experimental conditions: 15 g of oil, 0.3 g of sorbent, stirring 4 h at 30 °C.

Figure 8. Adsorption isotherms of PIL-2 for DBT, BT, and T. Experimental conditions: the same as Figure 5.

the adsorbance of DMDBT is much lower than DBT due to the steric hindrance of the substitutes for a closer approach to and efficient interaction with the imidazolium ring. Further, the coexistent indole can greatly lower the adsorptive desulfurization capacity of the sorbent due to its competitive adsorption. 3.3.2. Desulfurization Performance of PILs. The adsorption isotherms of PIL-1, PIL-2, and PIL-3 for DBT, BT, and T are shown in Figure 7 to Figure 9, respectively. Obviously, the sulfur adsorptivity of PIL-1 is different from that of HCPVIM, being T ≫ DBT > BT, and the adsorptivity for T is even

structure is slightly superior to PIL-1 in terms of specific area and pore volume, as seen in Table 1, and the sole difference is their imidazolium cations, i.e., [HVIM]+ for PIL-1 and [BVIM]+ for PIL-2. In comparison with [HVIM]+, [BVIM]+ shows a stronger dispersion interaction with a specific sulfur, but its higher steric hindrance may compromise its efficient π−π interaction with thiophenc sulfurs. Therefore, PIL-2 shows a lower overall desulfurization performance than PIL-1. 8083

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This may be associated with its least micropores and rich mesopores arising from the secondary cross-linking of HCPVIM by BCmBn. The former decreases the overall sulfur adsorbance while the latter increases the mesoporous adsorption for BT and DBT. 3.3.3. Performance Comparison of the Four Sorbents. The adsorbance of the four sorbents (HCPVIM, PIL-1, PIL-2, and PIL-3) for DBT, BT, and T was compared at the same equilibrium S-concentration of 600 ppm by using the experiment results presented in Figures 5, 7, 8, and 9. As shown in Figure 10, the four sorbents show varying trends for different thiophenic sulfurs. For DBT, the adsorptivity of HCPVIM is always higher than the PILs, and the sulfur adsorptivity follows the order of HCPVIM> PIL-3 > PIL-1 > PIL-2, being 5.2, 4.4, 1.9, and 1.5 mg S g−1, respectively. This means that quaternization or ionization is not helpful for enhancing the desulfurization ability of HCPVIM. From a physical point of view, this may be

related to the disappearence micropores and a drastic decrease of specific area in the PILs sorbents. Besides, the extraction desulfurization ability of imidazolium ILs is also lower than their corresponding alkyl imidazoles. For BT, all the PILs show much lower adsorptivity than HCPVIM, which may be caused by their drastically reduced porosity and specific area. The desulfurization ability of the PILs follows the order of PIL-3 > PIL-2 > PIL-1, which seems irrelevant with their specific area but accords well with the increasing pore size and the size of the substitutes, i.e., benzyl(PIL-3) > butyl(PIL-2) > H(PIL-1). This order is compatible with the desulfurization ability of the homologous ILs reported by Jiang et al.,30 i.e., the desulfurization capability of the phosphoric ILs enhances linearly with the carbon number of the substituents on the imidazolim ring due to the increasing dispersive interactions with sulfur compounds. In short, the adsorptivity of HCPVIM may represent the upper limit of the imidazolium based PILs for BT and DBT. For T, PIL-1 shows much higher but PIL-2 and PIL-3 show lower adsorptivity than HCPVIM. This implies that protonation of the imidazole group can greatly enhance its interaction with T, while quaternization of the imidazole ring with alkyl substitutes tends to decrease the interaction with T. The adsorption capacity of the PILs for T follows the order of PIL-1 ≫ PIl-2 > PIL-3, which is in line with their increasing steric hindrance of the substituting groups, i.e., H(PIL-1) < butyl(PIL-2) < benzyl(PIL-3), and accordingly decreasing interactions with thiophene. 3.3.4. Reusability of the Sorbents. In view of the best adsorptivity of HCPVIM for BT and DBT and PIL-1 for T, regeneration experiments were carried out for HCPVIM and PIL-1 sorbents. The adsorption experiment was conducted in a glass vial at 298 K under the condition of 0.1 g of sorbent, 5 g of oil, and 2 h stirring. When the adsorption finished, the oil was poured out, and the sorbent was mixed with 20 g of absolute ethanol and magnetically stirred 2 h for desorption. The regenerated sorbent was obtained by centrifugal separation and vacuum drying at 80 °C for 4 h. The adsorption efficiency of the regenerated HCPVIM for BT and DBT and PIL-1 for T is presented in Figure 11. It is seen that the adsorption efficiency of the sorbents decreases about 15% in the first two

Figure 10. Adsorptivity comparison of HCPVIM and the PILs for DBT, BT, and T. Note: The data are taken from Figures 5, 7, 8, and 9 at an equilibrium S-content of 600 ppm.

Figure 11. Adsorption efficiency of HCPVIM and PIL-1 for DBT, BT, and T. Regeneration conditions: 0.1 g of used sorbent and 20 g of ethanol, stirring 2 h, drying the centrifugal residue at 80 °C for 4 h.

As shown from Figure 9, the adsorption behavior of PIL-3 is quite different from PIL-1 and PIL-2 but similar to HCPVIM.

Figure 9. Adsorption isotherms of PIL-3 for DBT, BT, and T. Experimental conditions: the same as Figure 5.

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cycles and then decreases slightly in the following recycling. The decreased adsorptivity may arise from the permanent loss of the microporosity of the sorbents due to the irreversible desorption of the micropores, while the mesoporous adsorptivity may be applicable for recycling uses.

4. CONCLUSIONS HCPVIM with rich micro/mesoporous structure was prepared through copolymerization of VIM and DVB with a high specific area of about 675 m2 g−1, average pore size of 5−7 nm, and decomposition temperature above 400 °C. It shows much higher adsorptivity for thiophenic sulfurs, being 2−3-fold that of EIM and imidazolium based ILs and follows the order of DBT > BT > T. Three PILs were prepared by reacting HCPVIM with HCl, BuCl, and BCmBn, respectively, and their porous structure and property were changed greatly compared to the polymer precursor. The PILs always show lower adsorptivity for thiophenic sulfurs than HCPVIM except PIL1 for thiophene due to the disappeared micropores and drastically decreased surface area. In summary, quaternization of HCPVIM is not helpful for increasing its desulfurization ability for the thiophenic sulfurs, but protonation of HCPVIM can greatly enhance its adsorption for thiophene.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00961. Characterization results of three highly cross-linked poly(vinyl imidazole)s (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone/fax: +86-10-64410308. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support from the National Natural Science Foundation of China (Grant No. 21376011).

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REFERENCES

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