Pyridinium Containing Amide Based Polymeric Ionic Liquids for CO2

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Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Pyridinium Containing Amide Based Polymeric Ionic Liquids for CO2/CH4 Separation Sonia Zulfiqar,*,†,‡ Daniele Mantione,§,‡ Omar El Tall,∥ Fernando Ruipeŕ ez,⊥ Muhammad Ilyas Sarwar,# Alexander Rothenberger,∇ and David Mecerreyes⊥,¶ †

Department of Chemistry, School of Sciences & Engineering, The American University in Cairo, New Cairo 11835, Egypt Laboratoire de Chimie des Polymères Organiques, Université Bordeaux/CNRS/INP Allée Geoffroy St-Hilaire, Bâtiment B8, 33615 Pessac Cedex, France ∥ Core Laboratories, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia ⊥ POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 72, 20018 Donostia-San Sebastián, Spain # Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan ∇ Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia ¶ Ikerbasque, Basque Foundation for Science, E-48011 Bilbao, Spain

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S Supporting Information *

ABSTRACT: Herein, we describe the design and synthesis of novel pyridinium containing amide based poly(ionic liquid)s (PAPILs) for CO2 capture and separation. Additionally, a new and unique crystal structure of pyridinium containing diamine monomer [MDAP][TFSI] is also presented. PAPILs reveal potential for CO2/CH4 separation and isosteric heat of adsorption in the physisorption range. KEYWORDS: Poly(ionic liquid)s, CO2 capture, CO2/CH4 separation

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INTRODUCTION

solid adsorbents are of growing interest because they address the drawbacks posed by a conventional absorption process using alkanolamine solutions.1−3 In this context, many attempts have already been made with various solid sorbents; however, polymeric ionic liquids (PILs), an emerging family of sorbents, have not been studied considerably for their CO2 capturing potential.1,4−13 Recently, we have reported that just by suitably tailoring the PILs structure (cation, anion, backbone, alkyl chain substituents), promising results for CO2 capture can be obtained.1 Keeping in view the importance of amide functionality having dual interaction sites (NH and CO)

Climate change is one of the pressing global problems in the spotlight nowadays.1 Carbon dioxide (CO2) is a leading greenhouse gas held accountable in this respect and its mitigation is of paramount importance. Presently, combustion of fossil fuels is the world’s principal energy source and there is a dire need of technologies for carbon capture from such sources. Carbon capture and storage (CCS) is a promising way for the remediation of CO2 from the atmosphere.2,3 There already exist several technologies to capture CO2 emanating from point sources such as solvent absorption, membrane separation, cryogenic fractionation, chemical looping and physical adsorption.1 Solvent absorption is the most extensively used process at the industrial level, but it is often discouraged because of many associated limitations. On the other hand, © XXXX American Chemical Society

Received: April 6, 2019 Revised: May 24, 2019

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DOI: 10.1021/acssuschemeng.9b01903 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Letter

ACS Sustainable Chemistry & Engineering Scheme 1. Synthesis Protocol of [MDAP][TFSI] and PAPILs

crystals of [MDAP][TFSI] were subjected to single crystal Xray diffraction analysis, which revealed the chiral crystal structure of [MDAP][TFSI]. The structure crystallizes in the orthorhombic P212121 space group with crystal cell parameters a = 11.21892(11) Å, b = 11.41336(11) Å, c = 47.0823(4) Å, α = 90°, β = 90°, γ= 90°, V = 6028.68(10)(Å3), Dcalc = 1.782 g/cm3, and Z = 16, Z′ = 4 (Figure 1 and Table S1). PAPILs were synthesized by the reaction of diamino monomer [MDAP][TFSI] with isophthaloyl chloride (IPC) and 2,6-pyridinedicarbonyl chloride (PDC) in tetrahydrofuran as the reaction medium and in the presence of triethylamine to quench HCl produced during the polyamidation reaction. The reaction was carried out at low temperature to avoid side reactions. The chemical structures of PAPILs were confirmed using Fourier-transform infrared (FTIR) spectroscopy, 13C CP/MAS NMR, 19F MAS NMR (MAS NMR: magic-angle spinning nuclear magnetic resonance), and elemental analysis (Figures S1−S3). The characteristic bands of amide NH and CO stretching vibrations and those related to the TFSI anion were observed in both the synthesized polymers. The 13C CP/ MAS NMR spectrum of PAPIL-1 showed typical CO, CN, and NCH3 signals at 164.79, 141.75, and 35.25 ppm, respectively. The 19F MAS NMR spectrum of PAPIL-1 also

and slightly basic nature, we purposely designed pyridinium containing amide based PILs. To the best of our knowledge, this is the first report on amide based PILs for CO2 capture and separation. In general, PILs have not been extensively exploited for CO2 capture, but there exist some reports on PILs containing imidazolium and ammonium cations.5,9−20 However, PILs with a pyridinium cation have not been paid enough attention for such applications.21,22 Herein, we also present a new X-ray single crystal structure of pyridinium containing diamine monomer [MDAP][TFSI] used in the synthesis of PAPILs.

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RESULTS AND DISCUSSION The synthesis routes of ionic diamino monomer [MDAP][TFSI] and PAPILs are outlined in Scheme 1, and the detailed experimental procedure is given in the Supporting Information. Typical synthesis involves the reaction of 2,6-diaminopyridine (DAP) with methyl trifluoromethane-sulfonate in dichloroethane yielding methyl-diaminopyridinium trifluoromethanesulfonate [MDAP][TFMS], which subsequently undergoes anion exchange resulting in the formation of methyldiaminopyridinium bis(trifluoromethanesulfonyl)imide [MDAP][TFSI]. The colorless rectangular prism shaped B


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ACS Sustainable Chemistry & Engineering

supporting the SEM results and illustrating more porous structure of PAPIL-2. CH4 gas isotherms of PAPILs were probed at 273 K (Figure 4B) while CO2 adsorption−desorption isotherms of PAPILs were recorded at 273 and 298 K (Figure 4C,D), respectively. PAPIL-2 exhibited higher CO2 uptake (13.9 mg/g) at 273 K and 1 bar compared to PAPIL-1 (8.1 mg/ g) owing to its more porous nature. The sorption values achieved for PAPILs are still better than for many PILs reported in the literature with TFSI anions (Table S5). On the other hand, the CO2 sorption values of PAPILs at 298 K are in fact lower compared to 273 K, demonstrating the exothermic nature of the binding (Table 1).24 The narrow hysteresis of CO2 adsorption−desorption isotherms especially at 273 K suggests weak interactions between PAPILs and CO2 molecules, indicating a lower energy penalty for regeneration.25 In order to calculate the interaction of CO2 and CH4 gas molecules with PAPILs, two theoretical models have been defined in each case. Figure 5A,B shows the interaction of a CO2 molecule with PAPIL-1 and PAPIL-2, whereas Figure 5C,D illustrates the interaction of a CH4 molecule with PAPIL1 and PAPIL-2, respectively. The binding energy of CO2 with PAPIL-2 (−18.33 kJ/mol) is more negative than that with PAPIL-1 (−15.68 kJ/mol), thus showing stronger affinity of PAPIL-2 for CO2, and hence supporting the experimental results. (Tables S2−S4). The results of quantum chemical calculations are presented in Table 2. In the PAPIL-1/CO2 complex, the CO2 molecule locates in a parallel plane over the region where the interaction between cation and anion of ionic polymer takes place, at around 3.20 Å from the nitrogen of the pyridinium. Since the interaction is rather weak, the CO bond lengths change slightly as compared to the CO2 free molecule (R = 1.165 Å) and a small deviation of the OCO angle is observed (177.7°) (Table 2). In the PAPIL-2/CO2 complex, the CO2 molecule is displaced with respect to the pyridinium cation and is able to interact with both the nitrogen of the amide (3.41 Å) and the nitrogen of the adjacent pyridine (3.28 Å). Therefore, the calculated binding energy for PAPIL-2 is greater than that of PAPIL-1. Accordingly, one of the CO bonds of CO2 is a bit more stretched (1.169 vs 1.165 Å of free CO2) and the other one is shortened (1.161 Å). The bond angle slightly deviates from linearity (177.6°). On the other hand, the interaction of PAPILs with CH4 is notably weaker as compared to CO2,1 although somewhat greater affinity was observed for PAPIL-2. The geometry of CH4 remains unchanged, with C−H bond distances of 1.092 ± 0.001 Å. In both complexes, the CH4 molecule is located in a plane over the pyridinium cation, at 3.367 and 3.337 Å of the nitrogen for PAPIL-1 and PAPIL-2, respectively. The distances with respect to the amide group are 3.984 and 3.952 Å for PAPIL-1 and PAPIL-2, correspondingly. The increase in the

Figure 1. Molecular diagram of [MDAP][TFSI] showing a chiral crystal structure.

revealed the presence of a peak at −83.79 ppm due to the TFSI anion (Figure S2 and Figure S3). The 13C CP/MAS NMR spectrum of PAPIL-2 displayed CO and CN signals at 164.4 and 146.98, respectively, while the signal of NCH3 revealed two peaks at 36.3 and 42.4 ppm. This observation was further validated by 19F MAS NMR, which also shows the appearance of two peaks for the TFSI anion at −83.93 and −86.77 ppm, respectively. This suggests that there are two kinds of NCH3 and TFSI anion signals present in the PAPIL2 structure. This observation is strikingly unique, and we propose an equilibrium between the two possible structures given in Scheme 2. This type of transalkylation exchange was also observed by Drockenmuller et al.23 in the case of triazolium dynamers. Elemental analysis also confirmed the successful formation of PAPILs and the calculated chemical compositions for PAPILs are consistent with the measured values. PAPILs are amorphous, as revealed by the PXRD patterns (Figure 2A). Thermograms also showed that both PAPILs are thermally stable and exhibit weight loss above 225 °C (Figure 2B). Scanning electron microscopy (SEM) imaging of PAPIL-1 displayed the particulate morphology and a compact structure; conversely, PAPIL-2 demonstrated the presence of agglomerated porous particles, which is also evident from its high surface area value as compared to PAPIL-1 (Figure 3A,B). High resolution transmission electron microscopy (HR-TEM) images of PAPILs also indicated the formation of core−shell nanoparticles. This unique morphology of PILs may be attributed to the presence of cationic and anionic moieties in the structure (Figure 3C,D). The porosity of PAPILs was measured using N2 adsorption−desorption isotherms at 77K (Figure 4A). The surface area of PAPIL-2 was found to be higher (22 m2/g) in contrast to PAPIL-1 (1.9 m2/g), thus Scheme 2. Possible Structures of PAPIL-2

C


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Figure 2. (A) Powder X-ray diffraction (PXRD) patterns of PAPILs. (B) Thermogravimetric analysis curves of PAPILs.

Figure 3. SEM images of (A) PAPIL-1 and (B) PAPIL-2. HR-TEM images of (C) PAPIL-1 and (D) PAPIL-2

PAPIL-1 and PAPIL-2 selectively capture 6−7 times more CO2 than CH4 in a binary gas mixture containing 50% CO2 and 50% CH4 owing to the interactions between CO2 and heteroatoms present in the PAPIL structures (Figure 4F). It is well-known that the presence of heteroatoms in polymers has a strong influence on the resulting CO2 sorption and selectivity.27,28

interaction energy with PAPIL-2 can be ascribed to the smaller methane−IL distances observed. The binding affinity between PAPILs and CO2 molecules can also be seen from isosteric heat of adsorption (Qst,CO2), calculated using the Clausius−Clapeyron equation (Figure 4E). The Qst values of PAPILs are in accordance with physisorption and typical for many physisorptive solids.26 For separation of CO2, which is a principal contaminant found in natural gas, high selectivity of CO2 over CH4 is crucial. For this reason, CO2/ CH4 selectivity of PAPILs was determined at 273 K (Table S6).

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CONCLUSION We have successfully synthesized pyridinium containing amide based PILs for the first time. The highest CO2 uptake of 13.9 D


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Figure 4. (A) N2 gas isotherms for PAPILs measured at 77K (Inset: Differential pore size distribution curves from BJH method). (B) CH4 gas adsorption−desorption isotherms of PAPILs at 273 K. (C and D) CO2 gas adsorption−desorption isotherms of PAPILs at 273 and 298 K. (E) Isosteric heat of CO2 adsorption for PAPILs. (F) CO2/CH4 selectivity calculated by IAST method for CO2:CH4 gas mixture of 0.5:0.5.

Table 1. Surface Area, Pore Size, CO2 and CH4 Adsorption Data at 1 bar, Isosteric Heat of Adsorption (Qst), and CO2/CH4 Selectivity of PAPILsa CO2 Uptake (mg/g) PAPILs

SABET (m2/g)

SALangmuir (m2/g)

Pore size (nm)

PAPIL-1 PAPIL-2

1.9 22.0

3.3 32.4

9.3 16.5

T = 273K T = 298K 8.1 13.9

3.5 6.5

Qst,CO2 (kJ/mol)

CH4 Uptake (mg/g) T = 273 K

CO2/CH4 Selectivity T = 273 K

37.15 38.04

0.6 1.2

6.9 6.2

a

Brunauer−Emmett−Teller (BET) surface area from N2 adsorption isotherms, average pore size from Barrett−Joyner−Halenda (BJH) adsorption, isosteric heat of adsorption (Qst) obtained from CO2 isotherms data at 273 and 298 K using the Clausius−Clapeyron equation at initial loading. CO2/CH4 selectivity was calculated by the IAST method for CO2:CH4 gas mixture of 0.5:0.5. E


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Figure 5. Molecular models for (A) PAPIL-1/CO2 (B) PAPIL-2/CO2 (C) PAPIL-1/CH4, and (D) PAPIL-2/CH4 complexes.

ORCID

Table 2. Binding Energy of CO2 and CH4 with PAPIL-1 and PAPIL-2 (ΔECP)a CO2

Sonia Zulfiqar: 0000-0002-5692-6334 Fernando Ruipérez: 0000-0002-5585-245X Muhammad Ilyas Sarwar: 0000-0002-3943-3538 David Mecerreyes: 0000-0002-0788-7156

CH4

PAPILs

ΔECP

R1

R2

α

ΔECP

PAPIL-1 PAPIL-2

−15.68 −18.33

1.168 1.169

1.162 1.161

177.7 177.6

−8.84 −9.97

Author Contributions ‡

These authors contributed equally.

a

In kJ/mol. CO bond length (Ri), in Å, and OCO angle (α), in degrees, of the CO2 molecule. Data obtained at the ωB97XD/631+G(d,p) // ωB97XD/6-311++G(2df,2p) level of theory.

Notes

The authors declare no competing financial interest.

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mg/g was obtained for PAPIL-2 at 273 K and 1 bar, which is superior in contrast to many PILs reported in the literature with a TFSI anion, thus exhibiting potential application in CO2 capture.1 The improvement in surface area and porosity of PILs may aid in enhancing the CO2 sorption values. Furthermore, variation of cation and anions would also lead to a significant impact on CO2 sorption performance of PILs; such work is ongoing in our group.

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ACKNOWLEDGMENTS Dr. Sonia Zulfiqar is highly grateful for the financial support provided by Marie Curie IIF grant “NABPIL” (No. 629050) from the European Commission under the seventh Framework Programme (FP7-PEOPLE-2013-IIF). Dr. Fernando Ruipérez thanks the technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ, ERDF, and ESF) for generous allocation of computational resources. Dr. Daniele Mantione is highly thankful for the support provided through EU project FP7-PEOPLE-212-ITN 316832-OLIMPIA. CCDC 1402084 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http:// www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336033.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.9b01903. Detailed experimental section including synthetic procedures of the monomers and PAPILs, FT-IR spectra, CP/MAS 13C NMR spectra, 19F MAS NMR spectra, BET linear plots, Cartesian coordinates of CO2, CH4, PAPILs, PAPILs/CO2, and PAPILs/CH4 complexes, calculation methods and IAST fitting curves and parameters, ln P vs 1/T graphs for PAPILs, and comparison of CO2 adsorption data with other PILs reported in the literature (PDF) Crystallographic data (CIF)

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*Email: sonia.zulfi[email protected], soniazulfiqar@yahoo. com. Fax: +20 2 2795 7565. Tel: +20 2 2615 2562. F


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Pyridinium Containing Amide Based Polymeric Ionic Liquids for CO2

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