Hybrid Ionic Liquid Capsules for Rapid CO2 Capture | Industrial

May 24, 2019 - Particle size distribution of (a) [EMIM][TFSI] capsule (b) [HMIM][TFSI] capsule. CO. 2. uptake of neat ILs. Within the pressure range s...
0 downloads 0 Views 3MB Size
Download PDF
Article pubs.acs.org/IECR

Cite This: Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Hybrid Ionic Liquid Capsules for Rapid CO2 Capture Qianwen Huang,† Qinmo Luo,‡ Yifei Wang,‡ Emily Pentzer,*,‡ and Burcu Gurkan*,† †

Department of Chemical Engineering Biomolecular Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States ‡ Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States

Downloaded via BUFFALO STATE on July 22, 2019 at 11:04:30 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: The CO2 absorption by ionic liquids (ILs) were enhanced by the use of hybrid capsules composed of a core of IL and shell of polyurea and alkylated graphene oxide (GO). These composite structures were synthesized using a Pickering emulsion as a template, and capsules of two different ILs were prepared. The contribution of the encapsulated IL on the CO2 absorption of the capsules is consistent with agitated neat IL, but with an improved mass transfer rate of absorption across different pressures. This novel materials design allows for CO2 to be absorbed significantly faster compared to neat IL and provides insight into improved carbon capture technologies.

■

tions.28−32 In gas separations, encapsulation of IL can increase the active surface area of the IL, improving the kinetics of uptake compared to bulk (i.e., neat) ILs. Parlomar et al.19 prepared carbon capsule shells from phenol-formaldehyde resin and then soaked the capsules in an IL solution to impregnate them with imidazolium-based ILs. The obtained capsules showed a drastic increase in the rate of NH3 gas uptake compared to the IL itself. With a similar material, Lemus et al. demonstrated the capture-and-release of NH3,18 as well as CO2,22 as did Moya et al.20 Encapsulation of an IL containing an aprotic heterocyclic anion was also demonstrated, and thermodynamically favorable CO2 uptake under high pressure with enhanced mass transfer rate was shown.21 Recently, ILs have been confined in a laminated graphene oxide (GO) membrane33 primarily to improve high-pressure stability against leaching of the IL out of the support during CO2 separation. These reports illustrate that the encapsulation of ILs is promising for overcoming current limitations for their use in CO2 separations, and that facile and scalable access to such systems is required. In this paper, we report encapsulated ILs, synthesized via a one-pot synthetic, benign, and scalable route with a permeable polymer composite shell for CO2 capture, illustrating enhanced mass transfer in gas uptake compared to agitated and unagitated neat IL. The distinction in these encapsulated ILs compared to previous studies is the polyurea shell that keeps GO reinforcement sheets in place while providing permeability to CO2. Additionally, here we show the effective uptake at low

INTRODUCTION Carbon capture is a pressing need in modern society since the primary energy source continues to be fossil fuel burning, which generates CO2 waste, a greenhouse gas. There are various technologies for CO2 capture such as absorption,1 adsorption,2 membrane separations,3 and electrochemical separations;4 each method takes advantage of a high-CO2affinity solvent or a functional material.5,6 Absorption-based technologies that utilize a CO2-absorbing fluid such as aqueous amines7 have been used in the utility sector, specifically in post-combustion flue gas treatment.8 However, CO2 capture with aqueous amines is an energy intensive process9 since it requires elevated temperatures for the desorption of CO2 and the recycling of the absorbing fluid. Ionic liquids (ILs) have been investigated as alternative solvents to aqueous amines as they present unique properties that are well suited for CO2 capture, such as high CO2 solubility, negligible volatility, wide liquidus range, and tunable reaction enthalpy with CO2.10−13 The main challenge to utilizing ILs for CO2 capture is the high viscosity which results in severe mass transfer limitations,14 in addition to the cumbersome handling of liquids compared to solids on the small scale and in closed systems in terms of system complexity and maintenance (e.g., for applications requiring CO2 filtration in spacecraft and submarines). To overcome these challenges, ILs have been loaded onto porous solid supports such as fumed silica,15 carbon,16 and polymeric membranes3,17 which removes the necessity of pumping the absorbing liquid in a conventional absorber−desorber separation unit. Encapsulated ILs have been reported as effective gas uptake materials18−22 and have also found utility beyond gas separations such as electrode materials,23 microreactors,24,25 compartmentalized catalysis,26,27 and structures for extrac© 2019 American Chemical Society

Received: Revised: Accepted: Published: 10503

January 17, 2019 April 6, 2019 May 24, 2019 May 24, 2019 DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research

(0.50 mL) was added to dilute the prepared emulsion. Next, a heptane solution of HDI (1.33 mol/mL, 1.25 mL) was added dropwise while the vial was gently swirled by hand. The mixture was left unagitated for 72 h, and the capsules were isolated by gravity filtration and washed thoroughly with hexanes. The capsules were dispersed in hexanes (100 mL) and propylamine (5 mL) was added. Then, the solution was allowed to stand for 3 h to quench any residual isocyanate groups. Of note, if the propyl amine step is not performed, the capsules aggregate and cross-link and cannot be redispersed. The solid particles were collected by gravity filtration and washed with hexanes to neutral pH (as determined by litmus test), then dried under reduced pressure to yield a light brown powder. The same procedure was followed for the preparation of [HMIM][TFSI] capsules, except that (1) 0.4 mg/mL C18GO was used as the oil phase and (2) the volumes of IL, EDA, and HDI were halved (these changes were made to account for higher viscosity of the IL).35 Isolation of Capsule Shell. The capsule shell is isolated by extracting IL from capsules three times with acetone washing followed by centrifugation. Each time the supernatant was discarded, and after the last wash, the obtained solid pellet was dried under a vacuum. Analytical Methods. To prepare samples for optical microscopy, the capsules were dispersed in dodecane, and then the suspension was drop cast onto a glass slide. Pressing of capsules was accomplished by placing capsules between two glass slides; then pressure was applied manually, followed by separating two glass slides, which were then ready for optical microscopy imaging. To quantify the content of IL in the capsules, 20 mg of capsules was mixed with an acetone-d6 solution containing mesitylene as an internal standard (0.8 mL of 0.047 M). The extracted solution was then analyzed by 1H NMR spectroscopy and the wt % of IL determined by the relative integration of signals for the IL and mesitylene. Samples for analysis by SEM were prepared by spreading isolated capsules on double sided tape, followed by blowing away loose particles with a nitrogen gas stream. CO2 Measurements. The CO2 uptake capacities were measured by CO2 absorption isotherm in IL-based materials, including GO-IL capsules (2−3 g), neat ILs (same IL equivalent as the IL content of the corresponding capsule), and GO-IL capsule shells (same equivalent mass as the shell content of the corresponding capsule), using a Micrometritics TriStar II analyzer (pressure range 0 to 950 mmHg, resolution 98%) were purchased from Acros Organics. Heptane and dodecane were purchased from Fisher. Instrumentation. Centrifugation was accomplished with an Eppendorf 5804. Fourier transform infrared (FTIR) spectroscopy was performed using an Agilent Cary 630 FTIR in ATR mode. The hand-held emulsifier used was from BioSpec Products, Model 985370. Optical microscopy images were taken using an AmScope M150C microscope with an AmScope MU500-CK 5.0 MP USB microscope camera. 1H NMR measurements were collected using a Bruker Ascend III HD 500 MHz. Nova NanoLab 200 FEG-SEM/FIB was used for individual capsule images under secondary electron scattering mode. Preparation of Alkylated GO (C18-GO). Graphene oxide (GO) was prepared using a modified Hummer’s method as reported in the literature34 and described in detail in our previous work.35 Briefly, natural graphite (1.0 g) was oxidized in concentrated H2SO4 (134 mL) at room temperature with KMnO4 (1.0 g, 0.063 mol) for 24 h; equimolar KMnO4 was repeatedly added every 24 h, with a total of 4 batches (4 g in total). Then, the mixture was diluted with ice−water (0.70 L), and aqueous H2O2 was added carefully until the pink color disappeared. Solid GO was collected by centrifugation and washed repeatedly with 2-propanol until the supernatant was neutral. GO was dried under reduced pressure at room temperature. To prepare alkylated GO, GO (100 mg) and octadecylamine (1.0 g) were suspended in DMF (100 mL) at 50 °C until a dark precipitate formed. This precipitate was isolated by centrifugation and then redispersed in toluene (100 mL) with an addition of octadecylamine (2.0 g). The reaction vessel was loosely capped and stirred overnight at 50 °C. The product, a dark brown solid, was isolated by centrifugation, then washed with toluene and octane thoroughly and dried under reduced pressure. Preparation of IL Capsules. The preparation of IL capsules was accomplished similarly to our previous report23,32 For [EMIM][TFSI] capsules, the oil phase consisted of C18GO in heptane (5 mL, 1 mg/mL standardized by parental GO), and the IL phase was a mixture of [EMIM][TFSI] (1.00 mL) and ethylenediamine (0.090 mL, 1.33 mol). These two solutions were combined in a vial and agitated by three cycles of emulsifying (20 s each) with a hand-held emulsifier at the highest energy level, with 15 s rests in between. Then, heptane

where P1/P2 is the system manifold pressure before/after dosing He onto the sample (mmHg), TSTD is the standard temperature (273.15 K), TMAN is the system manifold temperature before dosing He onto the sample (K), VMAN is the manifold volume (cm3), and VFS is the volume of free space (cm3 at standard temperature). About 4 h of vacuum was applied after free space measurement to release He absorbed in the samples. 10504

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research

Figure 1. (a) [EMIM][TFSI] capsules: (i) Optical microscopy image (inset shows image after pressing), (ii) SEM image, (iii) FTIR spectra of neat [EMIM][TFSI] and [EMIM][TFSI] capsules. (b) [HMIM][TFSI] capsules: (i) Optical microscopy image (inset shows image of expelled liquid droplets resulted from pressing), (ii) SEM image, (iii) FTIR spectra of neat [HMIM][TFSI] and [HMIM][TFSI] capsules.

The free space of the sample tubes with neat ILs was calculated with eq 2 VFS = VEM − VS

PPCPI = 100

P = Hx

(6)

where x is the mole fraction of CO2, H is the Henry’s law constant in units of pressure, and P is the equilibrium pressure.

■

RESULTS AND DISCUSSION IL capsules were prepared using an IL-in-oil Pickering emulsion as a template and interfacial polymerization between an IL-soluble diamine and oil-soluble diisocyanate; alkylated GO was used as the particle surfactant.23,39,40 Figure 1ai and bi show the optical microscopy images of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([HMIM][TFSI]) capsules, respectively. Spherical, individual capsules were observed for each, with a diameter of about 10−50 μm for [EMIM][TFSI] capsules and about 5− 25 μm for [HMIM][TFSI] capsules (see Figure S1 for particle size distribution analysis). The permeable shell (∼1 μm thick) of these materials provides a large gas−liquid surface area, as we previously reported.23,38 Upon applying pressure to the capsules with a top glass slide, droplets of IL were expelled, as observed by optical microscopy (see insets). Figure 1aii and bii show the SEM images of representative capsules, showing a

PAVG = [ − 36(P11 + P1) + 9(P10 + P2) + 44(P9 + P3) (3)

PCHG = [5(P11 − P1) + 4(P10 − P2) + 3(P9 − P3) + 2(P8 − P4) + (P7 − P5)] /110

(5)

where PAVG is the average pressure (mmHg), PCHG is the change in pressure (mmHg), PPCPI is the percent change per interval, and Pi is the ith pressure reading taken at equilibrium intervals (i = 1 to 11 mmHg). From the measured pressure change and free head space in the sample chamber, the amount (moles) of CO2 absorbed was calculated via the ideal gas law. The physically absorbed CO2 in neat ILs was expressed in terms of Henry’s law constant:

(2)

in which VFS is the calculated free space, VEM is the free space of the empty tube with a stir bar, and VS is the sample volume that is obtained by the measured mass divided by known density of the liquid sample (1.372 g/cm3 for [HMIM][TFSI] at 25 °C36 and 1.524 g/cm3 for [EMIM][TFSI] at 20 °C37). The measurement of CO2 uptake was conducted after the determination of free space. For the measurement of CO2 uptake capacity in neat ILs, a stir bar was used to agitate the IL (1000 rpm). As a comparison, the CO2 of neat ILs was also measured without agitation. Isotherms were obtained at 19.5 ± 1°C and at a pressure range of 0−950 mmHg. The amount of CO2 absorbed by the ILs was calculated from the pressure change between the CO2 injection and equilibrium. Equilibrium was assumed to be reached when the pressure change per equilibration time interval (first derivative) was less than 0.01% of the average pressure during the interval (10 s). The time between each data recorded is the equilibrium time at a certain pressure. Both pressure change and average pressure were calculated using the Savitzky-Golay38 method with eqs 3 to 5:

+ 69(P8 + P4) + 84(P7 + P5) + 89(P6)] /429

PCHG (%) PAVG

(4) 10505

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research

Figure 2. (a) CO2 absorption capacity for agitated [EMIM][TFSI] (red squares), [EMIM][TFSI] capsules (purple circles), and a capsule shell (blue triangles). (b) Gravimetric CO2 uptake for agitated [EMIM][TFSI] (red squares), still [EMIM][TFSI] (yellow diamonds), and encapsulated IL (purple circles).

Figure 3. (a) Equilibrium time between each pressure set point for agitated [EMIM][TFSI] (red squares) and [EMIM][TFSI] capsules (purple circles) as pressure is increased. (b) Total elapsed time for equilibration of [EMIM][TFSI] (red squares) and [EMIM][TFSI] capsules (purple circles) as pressure increased in about 0.066 bar steps. Solid lines are to guide the eye. For these studies, the sample sizes were 2.9 g for agitated IL and 2.8 g for capsules; Figure S7 shows the impact of the amount of IL.

with the gas. A detailed analysis of the capsule shell morphology through the corresponding N2 adsorption− desorption isotherms is in Figure S4, and a pore size distribution is in Figure S5. Accordingly, the surface area of the capsule shells (without IL core) is 75 m2/g (Table S1) while that of the IL-filled capsules is minimal, about 0.2 m2/g, according to our previous publication.35 This implies the IL capsules do not have significant porosity; however, they are permeable to CO2. Figure 2b compares the gravimetric CO2 uptake of still [EMIM][TFSI], agitated [EMIM][TFSI], and the encapsulated [EMIM][TFSI] (subtraction of the contribution of the shell from the total uptake of the capsule sample). The molar CO2 uptake of still [EMIM][TFSI] and agitated [EMIM][TFSI] is presented in Figure S2. The isotherm of the agitated IL indicates the thermodynamic equilibrium, whereas the isotherm of the still IL reflects diffusion-limited capacity for a given time, obtained with a limited gas−liquid surface area. The Henry’s law constant for CO2 was calculated from the isotherm of agitated [EMIM][TFSI] as 39 bar (Figure S2a), in agreement with the literature.41 The CO2 capacity of encapsulated IL is consistent with the agitated IL; compare purple circles and red squares in Figure 2b within the uncertainty of the measurements (about 10%; see Supporting Information for error analysis). Therefore, these results demonstrate that (i) the GO-IL capsule shell is permeable to CO2 such that the IL absorbs the gas and (ii) the increased active surface area of the IL afforded by encapsulation suppresses mass transfer limitations of un-

single capsule with a slightly rough surface. The FTIR spectra of [EMIM][TFSI] capsules and neat [EMIM][TFSI] are shown in Figure 1aiii: the fingerprint regions of the spectra both show distinctive stretching frequencies of the IL at 1347 cm−1, 1345 cm−1, 1178 cm−1, and 1131 cm−1. The spectrum of the capsules also includes absorption bands at 1616 and 1579 cm−1, attributed to CO and N−H structures of the polyurea, not present in the spectrum of the neat IL. Similar results were observed for the [HMIM][TFSI] capsules, with characteristic IL stretching frequencies for neat [HMIM][TFSI] and capsules, and the identifying polyurea peaks for the capsules (Figure 1biii). For both types of capsules, extraction of the encapsulated IL with an organic solvent containing an internal standard revealed that both are ∼80 wt % IL. To test our hypothesis if the emulsion-templated encapsulation of IL could overcome the limitations of CO2 uptake, the CO2 capacities of neat [EMIM][TFSI] (either still and agitated at 1000 rpm), [EMIM][TFSI] capsules, and capsule shells after extraction of the IL were measured. This was accomplished by performing CO2 absorption isotherms at 19.5 ± 1 °C barometrically from 0 to 1.26 bar of CO2 using a calibrated volume cell, following complete evacuation by vacuum. The measured CO2 uptake of the IL (red squares), IL capsules (purple circles), and capsule shell (blue triangles) are shown in Figure 2a, illustrating that the capsules have a higher gravimetric CO2 capacity compared to neat [EMIM][TFSI]. The capsule shell composed of alkylated GO and polyurea has appreciable CO2 capacity, suggesting favorable interactions 10506

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research

Figure 4. (a) Gravimetric CO2 capacity for agitated [HMIM][TFSI] (red open squares), still [HMIM][TFSI] (yellow open diamonds), and encapsulated [HMIM][TFSI] (purple open circles). (b) Equilibrium time for agitated [HMIM][TFSI] (red open squares) and [HMIM][TFSI] capsules (purple open circles) as pressure is increased. (c) Total elapsed time for equilibration of [HMIM][TFSI] (red open squares) and [HMIM][TFSI] capsules (purple open circles) as pressure is increased in about 0.066 bar steps. Solid lines are to guide the eye. For these studies, the sample sizes were 2.2 g for agitated IL and 2.1 g for capsules; Figure S7 shows the impact of the amount of IL.

measured gravimetric CO2 capacity per gram of IL for agitated [HMIM][TFSI] (red open squares), still [HMIM][TFSI] (orange open diamonds), and the encapsulated [HMIM][TFSI] (purple open circles). The average Henry’s law constant for CO2 was calculated from the repeated isotherms of agitated [HMIM][TFSI] as 30.5 bar (Figure S2b), in agreement with the literature.39 Again, within the uncertainty of our measurements, the CO2 capacity of the encapsulated and agitated IL are similar, and both are superior to still IL which is far from the thermodynamic equilibrium. This again illustrates that the capsule shell of polyurea and alkylated GO is permeable to CO2 and that the encapsulation of the IL has removed the need for agitation. Similar to the [EMIM][TFSI] capsules, Figure 4b and c suggest an improved rate of CO2 uptake of the [HMIM][TFSI] capsules over the agitated IL: equilibration at 1.26 bar occurred after a total of 271 min for agitated [HMIM][TFSI], but only 59 min for [HMIM][TFSI] capsules. These results suggest the synthesized IL capsules are promising CO2 separation materials for packed bed type reactors and may offer energy savings over traditional absorber−desorber type separation technologies due to their improved gravimetric CO2 capacity and enhanced mass transfer rate.

agitated IL. This demonstrates that the scalable and facile Pickering emulsion-templated encapsulation of [EMIM][TFSI] removes the necessity to agitate IL to reach the thermodynamic equilibrium for CO2 uptake. We then sought to understand how the rate of CO2 uptake differed between agitated and [EMIM][TFSI] capsules, as these metrics directly impact the design of separation technologies. Figure 3a shows the equilibrium time for agitated IL and encapsulated IL as a function of pressure where the pressure is increased by about 0.066 bar after each equilibration step. These data show that after application of 0.3 bar of CO2, the time for the IL capsules to equilibrate decreases drastically, whereas the time for the agitated IL sample to equilibrate remains constant (compare red and purple spectra in Figure 3a). Figure 3b further highlights the improved performance of the IL capsules, showing that the agitated IL equilibrates at 1.26 bar of CO2 pressure after a total of 271 min, whereas the IL capsules equilibrate at the same pressure after a total of only 97 min. This result illustrates the enhanced mass transfer rate of CO2 absorption by the IL capsules compared to agitated neat IL. To determine if our strategy to encapsulate ILs for enhanced performance in CO2 uptake is applicable to other ILs, we evaluated the performance of similar [HMIM][TFSI] capsules. The [HMIM] cation has a similar structure to [EMIM] but bears a hexyl chain in place of an ethyl chain and is thus more hydrophobic and is known to have higher CO2 capacity.42,43 The anion for the two ILs evaluated is the same ([TFSI]). The measured CO2 uptakes of the IL, IL capsules, and capsule shell are shown in Figure S3. In a similar vein to the [EMIM][TFSI] capsules discussed above, the encapsulated IL demonstrates higher CO2 capacity compared to the agitated IL (Figure S3), with contribution from the capsule shell. Figure 4a shows the

■

CONCLUSIONS We have prepared hybrid capsules containing about 80 wt % ionic liquid in a shell of polyurea and alkylated graphene oxide using a Pickering emulsion as a template and studied the CO2 uptake of these materials across low CO2 pressures. The capsule shell itself contributes to CO2 uptake and the contribution of the encapsulated IL is competitive with agitated neat IL. This demonstrated that the capsule shell 10507

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research

(5) D’Alessandro, D. M.; Smit, B.; Long, J. R. Carbon Dioxide Capture: Prospectes for New Materials. Angew. Chem., Int. Ed. 2010, 49, 6058−6082. (6) Bara, J. E.; Camper, D. E.; Gin, D. L.; Noble, R. D. RoomTemperature Ionic Liquids and Composite Materials: Platform Technologies for CO 2 Capture. Acc. Chem. Res. 2010, 43, 152−159. (7) Du, Y.; Yuan, Y.; Rochelle, G. T. Capacity and Absorption Rate of Tertiary and Hindered Amines Blended with Piperazine for CO2capture. Chem. Eng. Sci. 2016, 155, 397−404. (8) Liang, Z.; Rongwong, W.; Liu, H.; Fu, K.; Gao, H.; Cao, F.; Zhang, R.; Sema, T.; Henni, A.; Sumon, K.; et al. Recent Progress and New Developments in Post-Combustion Carbon-Capture Technology with Amine Based Solvents for CO2 Capture and Storage (ICCS), Provincial Hunan Key Laboratory for Cost-Effective Utilization of Fossil Fuel Aimed at Reducing Carbon-Dioxide. Int. J. Greenhouse Gas Control 2015, 40, 26−54. (9) Dutcher, B.; Fan, M.; Russell, A. G. Amine-Based CO2capture Technology Development from the Beginning of 2013-A Review. ACS Appl. Mater. Interfaces 2015, 7 (4), 2137−2148. (10) Shiflett, M. B.; Maginn, E. J. The Solubility of Gases in Ionic Liquids. AIChE J. 2017, 63 (11), 4722−4737. (11) Gurkan, B.; Goodrich, B. F.; Mindrup, E. M.; Ficke, L. E.; Massel, M.; Seo, S.; Senftle, T. P.; Wu, H.; Glaser, M. F.; Shah, J. K.; et al. Molecular Design of High Capacity, Low Viscosity, Chemically Tunable Ionic Liquids for CO2capture. J. Phys. Chem. Lett. 2010, 1 (24), 3494−3499. (12) Bara, J. E.; Carlisle, T. K.; Gabriel, C. J.; Camper, D.; Finotello, A.; Gin, D. L.; Noble, R. D. Guide to CO2 Separations in Imidazolium-Based Room-Temperature Ionic Liquids. Ind. Eng. Chem. Res. 2009, 48 (6), 2739−2751. (13) Shiflett, M. B.; Drew, D. W.; Cantini, R. A.; Yokozeki, A. Carbon Dioxide Capture Using Ionic Liquid 1-Butyl-3-Methylimidazolium Acetate. Energy Fuels 2010, 24 (10), 5781−5789. (14) Aghaie, M.; Rezaei, N.; Zendehboudi, S. A Systematic Review on CO2 Capture with Ionic Liquids: Current Status and Future Prospects. Renewable Sustainable Energy Rev. 2018, 96 (July), 502− 525. (15) Mirzaei, M.; Mokhtarani, B.; Badiei, A.; Sharifi, A. Improving Physical Adsorption of CO2 by Ionic Liquids-Loaded Mesoporous Silica. Chem. Eng. Technol. 2018, 41 (7), 1272−1281. (16) Santiago, R.; Lemus, J.; Moreno, D.; Moya, C.; Larriba, M.; Alonso-Morales, N.; Gilarranz, M. A.; Rodríguez, J. J.; Palomar, J. From Kinetics to Equilibrium Control in CO2 Capture Columns Using Encapsulated Ionic Liquids (ENILs). Chem. Eng. J. 2018, 348, 661−668. (17) Cowan, M. G.; Gin, D. L.; Noble, R. D. Poly(Ionic Liquid)/ Ionic Liquid Ion-Gels with High “Free” Ionic Liquid Content: Platform Membrane Materials for CO2/Light Gas Separations. Acc. Chem. Res. 2016, 49 (4), 724−732. (18) Lemus, J.; Bedia, J.; Moya, C.; Alonso-Morales, N.; Gilarranz, M. A.; Palomar, J.; Rodriguez, J. J. Ammonia Capture from the Gas Phase by Encapsulated Ionic Liquids (ENILs). RSC Adv. 2016, 6, 61650−61660. (19) Palomar, J.; Lemus, J.; Alonso-Morales, N.; Bedia, J.; Gilarranz, M. A.; Rodriguez, J. J. Encapsulated Ionic Liquids (ENILs): From Continuous to Discrete Liquid Phase. Chem. Commun. 2012, 48, 10046−10048. (20) Moya, C.; Alonso-Morales, N.; Gilarranz, M. A.; Rodriguez, J. J.; Palomar, J. Encapsulated Ionic Liquids for CO2 Capture: Using 1Butyl-Methylimidazolium Acetate for Quick and Reversible CO2 Chemical Absorption. ChemPhysChem 2016, 17, 3891−3899. (21) Moya, C.; Alonso-Morales, N.; De Riva, J.; Morales-Collazo, O.; Brennecke, J. F.; Palomar, J. Encapsulation of Ionic Liquids with an Aprotic Heterocyclic Anion (AHA-IL) for CO2Capture: Preserving the Favorable Thermodynamics and Enhancing the Kinetics of Absorption. J. Phys. Chem. B 2018, 122, 2616−2626. (22) Lemus, J.; Da Silva F, F. A.; Palomar, J.; Carvalho, P. J.; Coutinho, J. A. P. Solubility of Carbon Dioxide in Encapsulated Ionic Liquids. Sep. Purif. Technol. 2018, 196, 41−46.

material is permeable to CO2, thus allowing CO2 to reach the inner IL core efficiently. We illustrate that this structure− property relationship is consistent for two different ILs: [EMIM][TFSI] and [HMIM][TFSI]. Both encapsulated ILs have enhanced CO2 absorption rates owing to the increased gas−liquid surface area interface, compared to neat ILs. This design overcomes the need for agitation of the system and opens opportunities for practical applications. Ongoing work focuses on tailoring the chemical composition of the shell, as well as evaluating the impact of particle diameter and IL identity to further improve the performance of the composite capsules and the incorporation of these tailored structures as the active material in packed bed columns.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.9b00314.

■

CO2 isotherms for neat ionic liquids and propagation of error analysis for CO2 capacity measurements (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Qinmo Luo: 0000-0003-4269-2642 Emily Pentzer: 0000-0001-6187-6135 Burcu Gurkan: 0000-0003-4886-3350 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS E.P., Q.L., and Y.W. thank NSF CAREER Award #1551943 for financial support, NSF MRI-1334048 for NMR instrumentation, and Mr. Hobart Chen for help in preparing large amounts of the capsules. SEM images were taken at the Swagelok Center for the Surface Analysis of Materials (SCSAM) at CWRU. Q.H. and B.G. would like to acknowledge NASA Early Career Faculty Award #80NSSC18K1505 for the CO 2 measurements.

■

REFERENCES

(1) Sreedhar, I.; Nahar, T.; Venugopal, A.; Srinivas, B. Carbon Capture by Absorption − Path Covered and Ahead. Renewable Sustainable Energy Rev. 2017, 76, 1080−1107. (2) Trickett, C. A.; Helal, A.; Al-Maythalony, B. A.; Yamani, Z. H.; Cordova, K. E.; Yaghi, O. M. The Chemistry of Metal-Organic Frameworks for CO2 Capture, Regeneration and Conversion. Nat. Rev. Mater. 2017, 2 (8), 1−16. (3) Dai, Z.; Noble, R. D.; Gin, D. L.; Zhang, X.; Deng, L. Combination of Ionic Liquids with Membrane Technology: A New Approach for CO2separation. J. Membr. Sci. 2016, 497, 1−20. (4) Gurkan, B.; Simeon, F.; Hatton, T. A. Quinone Reduction in Ionic Liquids for Electrochemical CO2 Separation. ACS Sustainable Chem. Eng. 2015, 3 (7), 1394−1405. 10508

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509

Article

Industrial & Engineering Chemistry Research (23) Luo, Q.; Wei, P.; Huang, Q.; Gurkan, B.; Pentzer, E. B. Carbon Capsules of Ionic Liquid for Enhanced Performance of Electrochemical Double Layer Capacitors. ACS Appl. Mater. Interfaces 2018, 10, 16707−16714. (24) Weiss, E.; Abu-Reziq, R. Ionic Liquid-Based Polymeric Microreactors and Their Applicability. J. Mater. Sci. 2017, 52, 10637−10647. (25) Zhang, X.; Cai, Y. Octadecyltrichlorosilane (OTS)-Coated Ionic Liquid Drops Micro-Reactors for Homogeneous Catalytic Reactions at Designated Interfaces.Pdf. Beilstein J. Nanotechnol. 2012, 3, 33−39. (26) Sahiner, N.; Yasar, A. O.; Aktas, N. Dicationic Poly(4-Vinyl Pyridinium) Ionic Liquid Capsules as Template for Co Nanoparticle Preparation and H2production from Hydrolysis of NaBH4. J. Ind. Eng. Chem. 2015, 23, 100−108. (27) Weiss, E.; Dutta, B.; Kirschning, A.; Abu-Reziq, R. BMImPF6@SiO2Microcapsules: Particulated Ionic Liquid as a New Material for the Heterogenization of Catalysts. Chem. Mater. 2014, 26 (16), 4781−4787. (28) Elizarova, I. S.; Luckham, P. F. Layer-by-Layer Encapsulated Nano-Emulsion of Ionic Liquid Loaded with Functional Material for Extraction of Cd2+ions from Aqueous Solutions. J. Colloid Interface Sci. 2017, 491, 286−293. (29) Vincent, T.; Parodi, A.; Guibal, E. Immobilization of Cyphos IL-101 in Biopolymer Capsules for the Synthesis of Pd Sorbents. React. Funct. Polym. 2008, 68, 1159−1169. (30) Archana, V.; Meera, K. M. M. S.; Anantharaman, N. Studies on Removal of Phenol Using Ionic Liquid Immobilized Polymeric MicroCapsules. Arabian J. Chem. 2016, 9, 371−382. (31) Lakshmi, D. S.; Cundari, T.; Furia, E.; Tagarelli, A.; Fiorani, G.; Carraro, M.; Figoli, A. Preparation of Polymeric Membranes and Microcapsules Using an Ionic Liquid as Morphology Control Additive. Macromol. Symp. 2015, 357, 159−167. (32) Luo, Q.; Wang, Y.; Chen, Z.; Wei, P.; Yoo, E.; Pentzer, E. Pickering Emulsion-Templated Encapsulation of Ionic Liquids for Contaminant Removal. ACS Appl. Mater. Interfaces 2019, 11, 9612− 9620. (33) Ying, W.; Cai, J.; Zhou, K.; Chen, D.; Ying, Y.; Guo, Y.; Kong, X.; Xu, Z.; Peng, X. Ionic Liquid Selectively Facilitates CO2 Transport through Graphene Oxide Membrane. ACS Nano 2018, 12 (6), 5385−5393. (34) Dimiev, A.; Kosynkin, D. V.; Alemany, L. B.; Chaguine, P.; Tour, J. M. Pristine Graphite Oxide. J. Am. Chem. Soc. 2012, 134, 2815−2822. (35) Luo, Q.; Wang, Y.; Yoo, E.; Wei, P.; Pentzer, E. Ionic LiquidContaining Pickering Emulsions Stabilized by Graphene Oxide-Based Surfactants. Langmuir 2018, 34, 10114−10122. (36) Zhang, S.; Sun, N.; He, X.; Lu, X.; Zhang, X. Physical Properties of Ionic Liquids: Database and Evaluation. J. Phys. Chem. Ref. Data 2006, 35 (4), 1475−1517. (37) Makino, T.; Kanakubo, M.; Masuda, Y.; Umecky, T.; Suzuki, A. CO2 Absorption Properties, Densities, Viscosities, and Electrical Conductivities of Ethylimidazolium and 1-Ethyl-3-Methylimidazolium Ionic Liquids. Fluid Phase Equilib. 2014, 362, 300−306. (38) Savitzky, A.; Golay, M. J. E. Smoothing and Differentiation of Data by Simplified Least Squares Procedures. Anal. Chem. 1964, 36 (8), 1627−1639. (39) Wei, P.; Luo, Q.; Edgehouse, K. J.; Hemmingsen, C. M.; Rodier, B. J.; Pentzer, E. B. 2D Particles at Fluid-Fluid Interfaces: Assembly and Templating of Hybrid Structures for Advanced Applications. ACS Appl. Mater. Interfaces 2018, 10, 21765. (40) Rodier, B. J.; de Leon, A.; Hemmingsen, C.; Pentzer, E. Polymerizations in Oil-in-Oil Emulsions Using 2D Nanoparticle Surfactants. Polym. Chem. 2018, 9, 1547. (41) Cadena, C.; Anthony, J. L.; Shah, J. K.; Morrow, T. I.; Brennecke, J. F.; Maginn, E. J. Why Is CO2 so Soluble in Imidazolium-Based Ionic Liquids? J. Am. Chem. Soc. 2004, 126 (16), 5300−5308.

(42) Liu, H.; Huang, J.; Pendleton, P. Experimental and Modelling Study of CO2 Absorption in Ionic Liquids Containing Zn (II) Ions. Energy Procedia 2011, 4, 59−66. (43) Anderson, J. L.; Dixon, J. K.; Brennecke, J. F. Solubility of CO2,CH4,C2H6, C2H4,O2, and N2 in 1-Hexyl-3-Methylpyridinium Bis(Trifluoromethylsulfonyl)Imide: Comparison to Other Ionic Liquids. Acc. Chem. Res. 2007, 40 (11), 1208−1216.

10509

DOI: 10.1021/acs.iecr.9b00314 Ind. Eng. Chem. Res. 2019, 58, 10503−10509