Encapsulated Amino‐Acid‐Based Ionic Liquids for CO2 Capture

European Journal of Inorganic Chemistry Accepted Article Title: Encapsulated amino acid-based ionic liquids for CO2 capture Authors: Liliana P. Silva, Cristian Moya, Marco Sousa, Ruben Santiago, Tania E. Sintra, Ana R.F. Carreira, José Palomar, João A. P. Coutinho, and Pedro Carvalho This manuscript has been accepted after peer review and appears as an Accepted Article online prior to editing, proofing, and formal publication of the final Version of Record (VoR). This work is currently citable by using the Digital Object Identifier (DOI) given below. The VoR will be published online in Early View as soon as possible and may be different to this Accepted Article as a result of editing. Readers should obtain the VoR from the journal website shown below when it is published to ensure accuracy of information. The authors are responsible for the content of this Accepted Article. To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000364 Link to VoR: https://doi.org/10.1002/ejic.202000364 01/2020 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER Encapsulated amino acid-based ionic liquids for CO2 capture Liliana P. Silva[a], Cristian Moya[a, b], Marco Sousa[a], Ruben Santiago[b], Tania E. Sintra[a], Ana R.F. Carreira[a], José Palomar[b], João A. P. Coutinho[a] and Pedro J. Carvalho*[a] [a] [b] CICECO – Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal Corresponding author E-mail: [email protected] (http://www.ciceco.ua.pt/pcarvalho) Sección de Ingeniería Química (Dpto. Química Física Aplicada), Universidad Autónoma de Madrid, 28049 Madrid, Spain 13] Abstract: Ionic liquids have gathered special attention due to their potential for carbon dioxide capture, and their potential as solvents for climate changes mitigation. Following the scope of previous works, amino acid-based ionic liquids encapsulated (ENILs) into carbonaceous submicrocapsules are here proposed as a novel material for CO2 capture. The ENILs prepared using tetrabutylphosphonium acetate ([P4,4,4,4][Ac]), used as reference, (2hydroxyethyl)trimethylammonium L-phenylalaninate ([N1,1,1,2(OH)][LPhe]), (2-hydroxyethyl)trimethylammonium L-prolinate ([N1,1,1,2(OH)][LPro]) and tetrabutylammonium L-prolinate ([N4,4,4,4][L-Pro] were characterized by SEM, TEM, elemental analysis, TGA and BET to assess their morphology, chemical composition, porous structure and thermal stability. The absorption of CO2 on these materials was studied up to 0.5 MPa and 343 K. The desorption of CO2 from the saturated ENILs was evaluated, at mild conditions, evidencing these materials as promising agents for CO2 capture from post-combustion sources, with high sorption capacity and fast and complete regeneration. Task-specific ionic liquids (TILs), amino acid-functionalized ILs, IL-mixed solvents and eutectic solvents, are promising materials for this purpose. Within chemisorption driven solvents, those based on amino acids stand out due to their low cost, abundant availability, easy biodegradability. synthesis [11,13,22–26,14–21] and low toxicity and However, the use of chemisorption driven solvents present several drawbacks, such as corrosivity, high viscosity of the products resultant from the chemical reaction(s), solvent loss and the high energy requirement for the regeneration processes, leading to high operational costs and ultimately leading to uneconomical, and sometimes technical unfeasible, processes. These drawbacks have hampered the development of separation units and industrial processes capable of fulfilling industry demands. The correct selection of the solvent stands thus, as one of the main challenges for innovative technological development of acid gases post-combustion Introduction treatment.[27] Furthermore, envisioning the use of green solvents is indispensable for a clean energy production, anthropogenic Mitigation of climate changes and the use of renewable CO2 capture, transportation, and/or reconstitution into value- energy sources have been two of the most important societal added products. Nonetheless, if one aims at developing a challenges, particularly when considering the increasing energy technical and economically viable process for carbon capture, the demand and average global temperature due to greenhouse pursuit on improving CO2 solubility, viscosity, heat capacity and gases release. Regarding the increasing average global mass transfer of sorbents must be addressed from a process temperature, predominantly due to accumulation of CO 2 in the engineering perspective, as highlighted by Leclaire and atmosphere, innovative post-combustion technologies for CO2 Heldebrant[3] in their recent ‘call to arms’ perspective.[3] As capture stand as indispensable for a cleaner energy production. emphasized by the authors, the community should shift focus Post-combustion stands as the most appealing emission sources from just enhancing equilibrium capacity to focus on the principles due to an easy retrofit of existent and new technologies into of green chemistry and green engineering, to make Carbon existing power plants. Although gas separation has long been Capture, Utilization and Storage (CCUS) a reality. used in natural gas industry, counterbalanced by the increased Although amino acid-based ILs are a promising class of value of the post-treated streams, post-combustion is still seen as solvents, CO2 absorption in these solvents presents important a non-efficient, costly and, ultimately, unfeasible process. [1–4] kinetic limitations, resultant from their inherent high viscosity or Over the last decade, the research community has been the drastic viscosity, increase upon reaction with CO 2.[14] proposing several approaches for the improvement of CO2 Nonetheless, many have pursued different approaches aiming at absorption, aiming at developing novel separation technologies minimizing these limitations, while maintaining the enhanced gas suitable for industrial implementation. [5–10] Among these, chemical sorption capacity, such as using a solid phase to immobilize the absorption has attracted special interest due to the solvents’ high solvents and the use of gas-liquid membrane contactors for gas capacity, even at post-combustion low CO2 partial pressures.[10– 1 This article is protected by copyright. All rights reserved. Accepted Manuscript Supporting information for this article is given via a link at the end of the document. 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER Results and Discussion absorption processes.[17,28] Recently, the confinement of solvents in nano-porous matrices has been proposed as a promising ENILs Characterization technique for gas separation, with improved mechanical integrity capable of overcoming the major drawbacks of the bulk solvents, The carbon capsules (Ccap) with a micro/mesoporous shell such as high viscosity and slow gas diffusivity, and ultimately, the structure and hollow core were studied by SEM and TEM. As separation.[20,29–36] The encapsulated ionic liquids (ENILs) have depicted in Figure 1 spherical capsules were obtained containing shown to impose no loss of the solvent absorbent capacity with a high carbon content (~90%w/w) and homogeneous morphology reduced quantities of solvent to achieve (∼500 nm of diameter and ∼150 nm of shell thickness). Elemental drastic enhancement of the CO2 sorption rate, both for physical or analysis allowed quantifying the incorporation of IL in the C cap, by chemical sorption driven solvents. [20,31,36,37] Here, aiming at further enhancing the CO2 solubility and the measuring the percentage of N in the final material, which can be fast sorption and desorption kinetics, amino acid-based ILs related to the uptake of the cations and amino acid anions.[38] The encapsulated in hollow carbonaceous submicrocapsules are EA results, reported in Table 1, confirm the adequate evaluated for gas separation at temperatures ranging from 303 to incorporation of the ILs (50−62% in mass). 343 K, for CO2 partial pressures ranging from 0 to 0.5 MPa. Figure 1. SEM (a) and TEM (b), (c) images of the Ccap used for the ENIL preparation. Table 1. Characterization of the Ccap and ENILs prepared with different load of IL. Textural properties EA IL Load (% w/w) %C %H %N Ccap 87.67 1.8 0.0 [P4,4,4,4][Ac] 58.67 5.1 0.0 60.2 [N1,1,1,2(OH)][LPhe] 59.57 6.8 6.3 51.2 [N1,1,1,2(OH)][L-Pro] 60.83 6.4 5.7 58.9 [N4,4,4,4][L-Pro] 62.02 6.7 8.4 60.9 Material ABET (m2/g) 1721 Figure 2. Nitrogen adsorption−desorption BET isotherm of capsules used in this work. Adsorption–desorption isotherms of N2 at 77 K were used to They show a highly developed porous structure (ABET = analyse the porous structure of the Ccap. The results of the BET 1721 m2/g), with contributions of micro- and meso-porosity, as analysis are reported in Table 1 and Figure 2, showing a type IV indicated by the high amount of nitrogen adsorbed in the whole adsorption isotherm with an inflection (or Knee) with the relative monolayer formation. pressure range, which is completely lost after incorporation of the IL in the Ccap (Table 1); i.e., the IL besides de 2 This article is protected by copyright. All rights reserved. Accepted Manuscript requiring 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER capsule, also completely fills the pores of the capsule structure. the sorption mechanism well described and accepted, [42,43] Shi et As reported in previous publications, al.[41] have shown that for the tetrabutylphosphonium acetate IL [31,38] the amount of IL confined inside the carbon capsules can be determined through a the anion controls the large CO2 solubility by chemisorption, with linear regression between the percentage of elemental nitrogen, the cation contributing mostly for the physisorption regime. As obtained by EA, and the weight percentage of IL incorporated on depicted in Figure 3 and 4, the L-Prolinate-based IL, a secondary the support. amine, presents higher CO2 solubility than the L-Phenylalaninatebase IL, a primary amine, at pressures below 0.5 MPa – inverting CO2 solubilities the behaviour observed for higher CO2 pressures. Although, effective CO2 mass transfer rates than primary amines, the amine possible to be determined using the apparatus and methodology pKa, degree of sterical hindrance or hybridization are known to here adopted due to the high viscosity of the reaction product(s) present a significant impact on the gas absorption.[45][46,47] of the carbon dioxide and the ILs. In fact, the initial contact and Furthermore, secondary hindered amines present higher absorption of the CO2 in the IL lead to the formation of a solid-like absorption rates than most primary amines but, primary and interface, at the gas-liquid interface, that did not allow for secondary amines with similar pKa and hindrance tend to present additional CO2 to absorb and diffuse to the IL bulk. Nonetheless, similar CO2 solubility.[45] Here, the anion charge delocalization, when confined within the Ccap the ILs did not present the anion hinderance, and aromaticity, seem to impose additional behaviour observed in the neat IL solubility measurements, thus, complexity that translates into higher solubilities, in mole fraction, ENIL sorption measurements were feasible within all the pressure of the [N1,1,1,2(OH)][L-Pro] and [N4,4,4,4][L-Pro], compared to the and temperature ranges evaluated. The only exception was [N1,1,1,2(OH)][L-Phe] and [C4C1im][L-Pro] reported in a previous [P4,4,4,4][Ac] that is solid at temperatures below 333 K. The publication[20] (Figure S9). Moreover, the higher degree of sterical encapsulation of IL not only enhances the mass transport hindrance and higher charge delocalization of the [N 1,1,1,2(OH)][L- properties but also lets us use ILs that would not reach the Pro] cation translates into a lower CO2 sorption capacity, than that thermodynamic equilibrium under reasonable conditions due to of the [N4,4,4,4][L-Pro]. However, when the molecular weight effect the kinetic limitations.[20] This improvement is due to the large is removed from the analysis by comparing the solubility in increase of the contact surface area between the gas phase and molalities, the differences and trends of the solubilities change. the amino acid IL, upon dispersion of the absorbent in submicrodrops, in good agreement with As depicted in Figure 4, the [N1,1,1,2(OH)][L-Pro] presents the previous highest solubility, at 343 K, followed by the [P4,4,4,4][Ac], [N4,4,4,4][L- results.[20,34,35,39,40] Pro] and [N1,1,1,2(OH)][L-Phe]. Nonetheless, as one would expect, The sorption isotherms of CO2 in the ENILs were within the physisorption regime the molecular weight becomes the determined at five temperatures, namely 303, 313, 323, 333 and dominant factor with the higher molecular weight ILs presenting 343 K, for the amino acid-based ILs and at three temperatures, higher solubility.[6] The experimental data are reported in Table namely 333, 343 and 353 K, for the [P4,4,4,4][Ac], as depicted in S1 in SI. Figure 3 – with the CO2 mole fractions calculated based on the moles of IL encapsulated. The results reported indicate an initial To ensure a successful industrial application one must region with low equilibrium pressure, typical of chemical sorption, ensure an easy and low energy demanding regeneration. Thus, followed by physical absorption regime with a fast increase of the the sorption capability of ENILs prepared with [P4,4,4,4][Ac], equilibrium pressure with the CO2 content. Furthermore, the ILs [N4,4,4,4][L-Pro], [N1,1,1,2(OH)][L-Pro] and [N1,1,1,2(OH)][L-Phe], was not only remain liquid during CO2 sorption but also maintain a high evaluated during four cycles of sorption-desorption. The CO2 absorption capacity and kinetics (Figure 4) when desorption cycles were performed after each sorption cycle at 1 encapsulated. This approach of creating ‘microsolid’ droplets of IL Pa, 343 K during 2 h, while the sorption was performed with an allows to overcome the problems associated to the use of neat initial pressure of (0.2 ± 0.05) MPa. As depicted in Figure 5, the ILs. regeneration of the ENIL was successful with the solubility Acetate-based ILs are known to play an important role in essentially constant after the various regeneration cycles, the conditioning chemical reactions with CO2 with reaction products deviations observed being within the experimental uncertainty. with low viscosity, compared to most chemisorption solvents.[41– Furthermore, 1H and 44] cycles showing no degradation of the ILs either due to Although most of the work focus on the imidazolium cation, with 13 C NMR was performed after the sorption 3 This article is protected by copyright. All rights reserved. Accepted Manuscript secondary amines tend to present lower solubility and higher The sorption isotherms of CO2 in the neat ILs was not 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER immobilization, solvent evaporation or gas sorption/desorption Figure 3. Pressure-composition diagram of the binary systems CO2 + [N1,1,1,2(OH)][L-Pro], CO2 + [N1,1,1,2(OH)][L-Phe], CO2 + [N4,4,4,4][L-Pro] and CO2 + [P4,4,4,4][Ac]. The lines are guides for the eyes. Figure 4. Molality – absorption time diagrams of (left) CO2 + [P4,4,4,4][Ac] and (right) the studied ENILs. 4 This article is protected by copyright. All rights reserved. Accepted Manuscript cycles, as depicted in Figure S10 of the Supporting Information. 10.1002/ejic.202000364 European Journal of Inorganic Chemistry Figure 5. Pressure-composition diagram of the binary systems CO2 + [P4,4,4,4][Ac], CO2 + [N4,4,4,4][L-Pro], CO2 + [N1,1,1,2(OH)][L-Pro] and CO2 + [N1,1,1,2(OH)][L-Phe] (left) and sorption (333 K and 0.2 MPa for the phosphonium IL and 323 K and 0.2 MPa for the remaining ILs) and desorption (343 K and 1 Pa) cycles (right). The lines are guides for the eyes. following the procedure reported by Allen et al.[48] and Santis et al.[49] The Conclusion ionic liquids were synthesized by the neutralization of [N4,4,4,4][OH] or Encapsulated amino acid-based ionic liquids (ENILs) were [N1,1,1,2(OH)][OH] with the respective amino acid/organic acid, namely the L- prepared for CO2 capture from post-combustion and their phenylalanine, L-proline and acetic acid. performance evaluated by means of an isochoric pressure cell. Succinctly, [P4,4,4,4][OH] or [N4,4,4,4][OH] (1 equiv, 40 wt% in aqueous The confinement of specific ILs into the carbon submicrocapsules solution) were added dropwise to an aqueous solution of acetic acid or resulted in ENILs with high CO2 sorption capacities and thermal respective amino acid, with a molar excess of 1.1 equivalent, at room stabilities. Furthermore, contrary to the neat ILs, whose reaction temperature. The reaction mixture was constantly stirred at room with CO2 lead to the formation of a solid-like interface that blocked temperature for [P4,4,4,4][Ac] and for [N4,4,4,4][L-Pro], and protected from further gas sorption and diffusion to the IL bulk, the ENILs remain light for 2 hours, producing the respective ionic liquid and water as the by liquid and absorbing the CO2 within the pressure range studied product. The water was then removed under reduced pressure (2 kPa). with fast sorption kinetics. The incorporation of the ILs into the For [N4,4,4,4][L-Pro], the resultant residue was dissolved in acetonitrile and carbon submicrocapsules increases their performance when filtered to remove the unreacted amino acid. Finally, the acetonitrile was compared with the neat IL, due to the increase of the surface removed under reduced pressure and the obtained compound was dried under high vacuum for at least 48 h. The ILs were further dried under high contact area, promoting higher mass transfer rates. In addition, vacuum (0.1 Pa) and moderate temperature (303 K) for at least 48 hours ENILs were successfully regenerated at mild conditions and used in order to remove the remaining solvents. [N1,1,1,2(OH)][OH] (1 equiv, 45 in successive CO2 capture-desorption cycles. Therefore, these wt% in methanol solution) was added dropwise to an aqueous solution of results highlight ENILs as new separating agents with promising amino acid, with a molar excess of 1.1 equivalents, at room temperature characteristics capture for [N1,1,1,2(OH)][L-Pro] and at 333 K for [N1,1,1,2(OH)][L-Phe]. The reaction technologies, with good thermal stability, high CO 2 sorption mixture was stirred for 2 hours and protected from light. The solvents were capacities, and low energy demanding in regeneration steps. then removed under reduced pressure (2 kPa). A solution of for industrial application in CO 2 acetonitrile/methanol (9:1, v/v) was then added under vigorous stirring in order to precipitate the excess of amino acid. The mixture was left stirring for 1 hour and the excess of amino acid was then filtrated. In a final step, Experimental Section the acetonitrile and methanol were evaporated initially under reduced pressure (2 kPa) and then high vacuum (0.1 Pa) and moderate Materials temperature (303 K) for at least 48 hours. The water mass fraction of the ionic liquids was determined by coulometric Karl Fischer titration (Metrohm, The tetrabutylammonium L-prolinate, [N4,4,4,4][L-Pro], the (2- model 831) and shown to be less than 0.05 wt%. The structure of all hydroxyethyl)trimethylammonium L-phenylalaninate, [N1,1,1,2(OH)][L-Phe], compounds was evaluated by 1H and (2-hydroxyethyl)trimethylammonium L-prolinate, [N1,1,1,2(OH)][L-Pro], and purity higher to 99% for all the ionic structures, as reported in Figures S1 the tetrabutylphosphonium acetate [P4,4,4,4][Ac,] ILs were synthesized 5 This article is protected by copyright. All rights reserved. 13 C NMR spectroscopy, showing Accepted Manuscript FULL PAPER 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER to S8 in Supporting Information. The properties of four selected ILs in formaldehyde resin was used as carbon precursor to obtain the desired this work are present in Table 2. carbon microcapsules. A mixture of 0.374 g of phenol/g template was through a rotary evaporated. Then, 0.238 g of paraformaldehyde/ g of 40 wt%), the tetrabutylphosphonium hydroxide ([P4,4,4,4]OH, in aqueous template was added, and the temperature was increased to 403 K and solution at 40 wt%), the (2-hydroxyethyl)trimethylammonium hydroxide maintained under vacuum for 24 hours. The resulting material was heated ([N1,1,1,2(OH)]OH, in methanol solution at 45 wt%), L-phenylalanine (99 wt% under a nitrogen atmosphere for 5 hours at 433 K in a vertical furnace, and of purity) and acetic acid (99.99 wt% pure) were acquired from Sigma- then, pyrolyzed at 1123 K for 7 hours. The silica template was removed by Aldrich. L-proline (99 wt% of purity) was acquired from Acros Organics. washing it with hydrofluoric acid solution (48 %v/v). The resulting Ccap Methanol (HPLC grade) and acetonitrile (99.9 wt% of purity) were acquired support material was washed with deionized water until reach pH 7 and from VWR. The water used was ultrapure water, passed by a reverse dried at 373 K for 24 hours. Phenol (99%), paraformaldehyde (95-100%), osmosis system and further treated with a Milli-Q plus 185 water aluminium trichloride (95-100%), ammonia (38%), absolute ethanol (99%) purification apparatus. and hydrofluoric acid (48%) used were provided by Panreac. Tetraethylorthosilicate (98%, TEOS) and octadecyltrimethoxysilane (90%, C18TMS) were supplied by Sigma–Aldrich. Then, the ENIL materials were The sorption experiments were carried out using carbon dioxide prepared by incipient wetness impregnation with the corresponding ILs, (CO2) supplied by Air Liquide Portugal with a purity of 99.999%. dissolved in ethanol to reduce the viscosity and assure good dispersion. To ensure a homogeneous penetration, into the pores, the IL solution was Preparation of the ENILs added drop wise over the Ccap, followed by vacuum evacuation, to remove the solvent, at 333 K and 1 Pa over 24 h. The procedure followed allowed The carbon submicrocapsules (Ccap) were synthesized following the to impregnate ~60% of IL (wt., ENIL basis) in the ENIL. The amount of IL template method described in detail in previous works.[32,34,36,39,50,51] A loaded was determined by weight difference between the final ENIL and model of a silica sphere with a solid core and mesoporous shell were used the weight of Ccap. as template. A volume of 15 mL of tetraethoxysilane (TEOS) was added to a reaction medium of an ethanolic solution composed of 185 mL of Elemental analysis (EA) was used to validate the IL impregnation. ethanol, 20 mL of distilled water and 12 mL of ammonia and maintained The IL impregnation percentage was derived from the linear relationship, with vigorous stirring at 303 K for at least 1 hour. Then, a mixture proposed in a previous publication,[38] using the percentage of elemental containing 17.5 mL of TEOS and C18TMS (2.5:1 v/v) was added to nitrogen, in the supported-IL materials and the weight percentage of the IL previous solution to form the mesoporous shell around them. This step supported on porous carbons. All the ENILs prepared had the was repeated twice in order to increase the thickness of the mesoporous resemblance and behaviour of a powdered material, allowing one to infer shell. After 1 hour of reaction, the resulting material was filtered and that all the IL was encapsulated. calcinated in air at 823 K for 6 hours. The silica spheres were then impregnated by a solution consisting on 0.27 g of AlCl3·6H2O per gram of template and calcinated again under the same conditions. A phenol- Table 2. Name, acronym, chemical structure and molecular weight of the four ILs studied in this work. Chemical Structure Mw /g.mol-1 Name Acronym Tetrabutylphosphonium acetate [P4,4,4,4][Ac] 318.48 (2-Hydroxyethyl)trimethylammonium L-phenylalaninate [N1,1,1,2(OH)][L-Phe] 268.27 (2-Hydroxyethyl)trimethylammonium L-prolinate [N1,1,1,2(OH)][L-Pro] 218.32 Tetrabutylammonium L-prolinate [N4,4,4,4][L-Pro] 356.60 6 This article is protected by copyright. All rights reserved. Accepted Manuscript added to the template and maintained in agitation for 14 hours at 373 K Tetrabutylammonium hydroxide ([N4,4,4,4]OH, in aqueous solution at 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER is removed. The purged sample is transferred to the furnace and to ensure Characterization of the ENILs complete and rapid combustion (oxidation) of the sample the furnace The morphology and microstructure of Ccap and ENILs were studied environment is composed of pure oxygen with a secondary oxygen flow by scanning and transmission electron microscopy (SEM and TEM). SEM directed to the sample via a ceramic lance. The combustion gases are micrographs were obtained using a HITACHI SU-70 operating at 25 kV. swept from the furnace through a thermoelectric cooler or an anhydrone The samples were previously coated with a carbon film using an Emitech reagent, to remove moisture, and collected in a thermostatically controlled K950X carbon evaporator. TEM analyses were performed by means of a ballast volume. The gases equilibrate and mix in the ballast before a Philips 420 JEM-2000 FX microscope. The porous structure was representative aliquot of the gas is extracted and introduced into a flowing characterized in a Micromeritics apparatus (Tristar II 3020 model) by stream of inert gas for analysis. adsorption−desorption isotherms at 77 K using the Brunauer−Emmett−Teller (BET) equation using the methodology reported Thermogravimetric analyses (TGA) of ILs and ENILs were in a previous publication and equation 1 (detailed description is given in conducted in a Setaram SETSYS Evolution 1750 thermobalance under the Supporting Information).[32] nitrogen atmosphere. A dynamic method was used with a temperature range from (298–835) K at a heating rate of 10 °C min-1 under a nitrogen 𝑆𝑎 = 𝑣𝑚 𝑁𝑎 𝑎𝑚 flow of 200 ml min-1. The accuracy of temperature and mass (1) 𝑣𝑚 𝑚𝑆 measurements was 0.1 K and 10-3 mg, respectively. Aluminium pans were used to hold an initial mass between 4 and 12 mg. In all TGA runs, the where Sa is the specific surface area, Na is the Avogadro’s number, Vm is derivative curves (DTG) were obtained for more in-depth interpretation and the amount of gas adsorbed if a monolayer was formed, am is the effective DTG temperatures. TDTG (K) was assigned to IL decomposition in the cross-section area of one adsorbed molecule, 𝑣𝑚 is the molar volume of one adsorbed molecule (22400 mL of volume occupied by solid supports from the DTG curve. As depicted in Figure 6, the studied mol of ILs are thermally stable up to 380 K and afterwards a sharp decomposition adsorbate gas at STP conditions) and mS is the mass of adsorbent. was observed in the temperature range of 380– 680 K. The respective ENIL exhibits a weight loss with a similar pattern to the neat IL, however Elemental analyses (EA) of Ccap and ENILs were carried out in a the peak appears a somewhat lower temperatures, denoting worse LECO CHNS-932 analyser to obtain C, H and N content. A macro-sized thermal stability due to the encapsulation, similar to that reported in a sample is weighed (2-5 mg) into a ceramic boat, placed in the loader and previous publication.[31] transferred to a sealed purge chamber, where entrained atmospheric gas Figure 6. Thermogravimetric analysis (TGA) of the studied ILs. 0.2%, and valves that allow controlling the gas addition. The experimental CO2 Solubility setup, except for the pressure transducer, is placed inside an oven with a The CO2 solubility was evaluated using a constant temperature- temperature stability of 0.5 K. The pressure transducer is placed outside volume equilibrium cell made of stainless steel, reported in detail in the oven to assure no influence of the temperature on the pressure elsewhere.[31] The isochoric equilibrium cell consists of a fixed volume cell uncertainty. connected to a gas line, as depicted in Figure 7. The gas line, also with a known volume, consists of a large volume cylinder, a pressure transducer A fixed amount of ENIL, whose exact mass is determined by weight (Swagelok S Model), able to operate up to 1 MPa with an uncertainty of using a high weight/high precision balance (Sartorius LA200P) with an 7 This article is protected by copyright. All rights reserved. Accepted Manuscript nitrogen 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER accuracy of 1 mg, is introduced into the cell. The ENIL is then kept under Acknowledgements gases absorbed during manipulation. The gas is introduced on the gas This work was developed by Portugal 2020 through European Regional Development Fund (ERDF), in the frame of Operational Competitiveness and Internationalization Programme (POCI), in the scope of the project Smart Green Homes - BOSCH - POCI01-0247-FEDER-007678, project CICECO-Aveiro Institute of Materials (UIDB/50011/2020 & UIDP/50011/2020), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement, Ministerio de Economía y Competitividad (MINECO) of Spain (project CTQ2017-89441-R) and Comunidad de Madrid (PT2018/EMT4348). L.P.S., A.R.F.C and P.J.C. acknowledge FCT for PhD grant (SFRH/135976/2018) and (SFRH/BD/143612/2019) and contract under the Investigator FCT 2015 contract number IF/00758/2015, respectively. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project Nº 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). section (dashed blue section, Figure 7) up to the desired pressure. The amount of gas (number of moles) present in the gas line is calculated using the Peng-Robinson EoS knowing the gas-phase volume and system pressure once the temperature equilibration is reached. The initial temperature is set to 353 K and once the equilibrium is reached the valve that connects the gas section with the solvent containing cell is open, allowing the gas to get in contact with the ENIL. The pressure decay is then monitored and logged, until new pressure equilibrium is reached. Knowing the cell gas phase volume and pressure, at equilibrium, the number of moles is determined. The number of moles adsorbed into the ENIL is then calculated by the difference to those initial added. The temperature is then decreased to a new set point allowing for additional gas to adsorb in the ENIL. Once the new equilibrium is reached the number of moles adsorbed into the ENIL is again calculated. After the equilibrium pressure is determined for all temperatures, the IL is regenerated by applying reduced pressure (1 Pa) and moderate temperature (353 K) for a Keywords: Post-combustion • Carbon dioxide capture • Encapsulated ionic liquids • Amino acid-based ionic liquids period never shorter than 4 hours. Once regenerated the adsorption procedure is then repeated with a different initial pressure of the gas, allowing thus, to determine additional equilibrium points and better describe the system phase diagram. The determined equilibrium points [1] are remeasured, normally in triplicate, aiming to minimize, identify and [2] remove measurement and manipulation errors. For S. D. Bazhenov, E. S. Lyubimova, Pet. Chem. 2016, 56, 889–914. E. S. Rubin, H. Mantripragada, A. Marks, P. 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All rights reserved. 10.1002/ejic.202000364 European Journal of Inorganic Chemistry FULL PAPER The absorption of CO2 on amino acid-based ionic liquids, encapsulated (ENILs) into carbonaceous submicrocapsules are proposed as a novel promising agents for CO2 capture from post-combustion sources, with high sorption capacity and fast and complete regeneration. Key Topic: amino acid-based ionic liquids; IL encapsulation into carbonaceous submicrocapsules 10 This article is protected by copyright. All rights reserved. Accepted Manuscript Entry for the Table of Contents