towards the potential of cyano and amino acid-based ionic liquid mixtures for facilitated co2...

8/18/2019 Towards the Potential of Cyano and Amino Acid-based Ionic Liquid Mixtures for Facilitated CO2 Transport Membranes

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facilitated CO2 separation [22 ,23] . In particular, special attention has

been paid to amino acid-based ionic liquids (AAILs) since naturallyoccurring AA not only combine reactive amine groups that can actas CO2 carriers but also are biodegradable, biocompatible, and veryversatile compounds in IL's synthesis. Kasahara et al. [24] rst de-monstrated the potential of AAILs, namely [P 4444 ][Gly] and[C2mim][Gly], to actively transport the CO 2 through SILMs. In con-trast to what was found for the conventional [C 2mim][NTf 2] SILM,signi cant enhancement of both the CO 2 permeabilities and CO 2 /N2selectivities with decreasing feed pressure and also with increasingtemperature were observed for SILMs containing AAILs. The sameresearch group further investigated the in uence of using AAILscomposed of cations with different sizes, [P 2225 ][Gly], [P4444 ][Gly]and [P 66614 ][Gly] [25] , as well as the effect of diverse AA-basedanions, [P 4444 ][Gly], [P4444 ][Ala], [P4444 ][Pro] and [P 4444 ][Ser] [26] ,on the CO 2 facilitated transport and separation from N 2 using SILMs.Moreover, Kasahara et al. [27] studied the in uence of IL viscosityon the CO 2 permeation properties through SILMs of [P 4444 ][Gly],[P4444 ][mGly] and [P 4444] [2-CNpyr], and showed that the majorfactor controlling the CO 2 permeability is the viscosity of the CO 2 -IL complex.

Although signi cant progress has been achieved in improvingthe CO 2 separation of SILMs by task-speci c AAILs, their high visc-osity is undoubtedly a key limitation for their practical industrialapplication, since the CO 2 diffusion is strongly compromised. Tocircumvent this shortcoming, in this work we propose the use of IL mixtures, so that one IL component provides the desired chemicalcharacteristics for the active transport of CO 2 while the othermaintains the low viscosity. Our recent studies have shown that theuse of binary IL mixtures with specially tailored properties is aneasy and powerful strategy to ne-tune the gas permeation prop-erties and the CO 2 separation performance of SILMs [28 ,29] .

In this work, binary IL mixtures were studied by xing the 1-ethyl-3-methylimidazolium cation ([C 2mim]

þ ) and researchingdifferent anion chemical structures. Taking into account that ILscomprising AA-based anions can effectively act as CO 2 carriers [24]and also that ILs with cyano-functionalized anions present re-markably low viscosities [30] and both high CO 2 permeabilities andpermselectivies [29] , ve AAILs, namely 1-ethyl-3-methylimidazo-lium 2-aminoacetate ([C 2 mim][Gly]), 1-ethyl-3-methylimidazolium(S)-2-aminopropanoate ([C 2mim][ L -Ala]), 1-ethyl-3-methylimida-zolium 2-aminoethanesulfonate ([C 2mim][Tau]), 1-ethyl-3-methy-limidazolium (S)-2-amino-3-hydroxypropanoate ([C 2mim][ L -Ser])

and 1-Ethyl-3-methylimidazolium (S)-pyrrolidine-2-carboxylate

([C2mim][ L -Pro]), were mixed with 1-ethyl-3-methylimidazolium

tricyanomethane ([C 2mim][C(CN) 3]) and SILMs were prepared.Their CO 2 and N 2 permeation properties were determined at a xedtemperature and different trans-membrane pressure differentials.

2. Experimental section

2.1. Samples

The 1-ethyl-3-methylimidazolium tricyanomethane ([C 2mim][C(CN)3 ]) ( 4 98 wt% pure) was supplied by IoLiTec GmbH. Thepure amino acid-based ILs, 1-ethyl-3-methylimidazolium 2-ami-noacetate ([C 2mim][Gly]), 1-ethyl-3-methylimidazolium (S)-2-aminopropanoate ([C 2mim][ L -Ala]), 1-ethyl-3-methylimidazolium2-aminoethanesulfonate ([C 2mim][Tau]), 1-ethyl-3-methylimida-zolium (S)-2-amino-3-hydroxypropanoate ([C 2mim][ L -Ser]) and1-ethyl-3-methylimidazolium (S)-pyrrolidine-2-carboxylate ([C 2mim][ L -Pro]) were synthesized in our lab via a two-step anionexchange reaction [31] , according to a procedure proposed byOhno et al. [32] . The chemical structures of the ILs used in thiswork are presented in Fig. 1. To reduce the water and other volatilesubstances content, all the pure ILs were dried under vacuum(10 3 kPa) and subject to vigorous stirring at a moderated tem-perature ( E 318 K) for at least 4 days immediately prior to use.

The IL mixtures were prepared using an analytical high-preci-sion balance with an uncertainty of 7 10 5 g by syringing knownmasses of each IL component into glass vials. Good mixing wasassured by magnetic stirring for at least 30 minutes. Subsequently,the prepared IL mixtures were dried under vacuum (10 3 kPa) at amoderate temperature ( E 318 K) for another 4 days. The sampleswere prepared immediately prior to the measurements. Thecomposition descriptions of the prepared IL mixtures, as well astheir water contents, which were determined by Karl Fischer ti-tration (831 KF Coulometer, Metrohm), are presented in Table 1 .Given that all the IL mixtures were prepared at 0.5 of mole fractionand that the only difference among them is the amino acid anion,we will use acronyms as depicted in Table 1 .

2.2. Gas permeation measurements

Porous hydrophilic poly(tetra uoroethylene) (PTFE) membranesprovided by MerckMillipore, with a pore size of 0.2 μm and an

average thickness of 65 μm, were used to prepare all the SILM

[C 2mim][L-Ser]

[C 2mim][C(CN) 3]

[C 2mim][Gly]

[C 2mim][L-Ala]

[C 2mim][L-Pro]

[C 2mim][Tau]

Fig. 1. Chemical structures and short names of the ionic liquids used in this work.

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con gurations according to our previously reported procedure [28] .Ideal (i.e., single gas) CO 2 and N 2 permeabilities and diffusivitiesthrough the prepared SILMs were measured using a time-lag ap-paratus. Details on the construction and operation of this experi-mental setup are entirely described elsewhere [33] . In this work, allthe prepared SILMs were degassed under vacuum inside the per-meation cell during 12 h before testing, in order to remove en-trained gases and traces of water. The single gas permeation ex-periments were performed at T ¼ 318 K with different trans-mem-brane pressure differentials (2.5, 5, 10, 25, 50 and 100 kPa) andvacuum ( o 0.1 kPa) as the initial downstream pressure (permeate).At least three separate experiments of each gas on a single SILMsample were carried out. Between each run, the permeation celland lines were evacuated on both upstream and downstream sidesuntil the pressure was below 0.1 kPa. No residual IL sample wasfound inside the permeation cell at the end of the experiments,which indicates that the SILM mass remained approximately con-stant throughout the experiment. The thickness of the SILMs wasassumed to be equivalent to the membrane lter thickness.

The gas permeability ( P ) values were determined from thesteady-state volume ux through the SILM ( J ), the SILM thickness(ℓ ) and the pressure difference across the SILM ( Δ p) according to:

= ℓ

∆ ( )P J

p 1

The gas diffusivity ( D) values were obtained according to Eq.(2) . The time-lag parameter ( θ ), which can be obtained beforeachieving steady state ux, was deduced by extrapolating theslope of the linear portion of the pd vs. t curve back to the timeaxis, where the intercept is equal to θ [34] .

θ =

ℓ( )

D6 2

2

It was also possible to calculate the gas solubility since the gastransport through supported liquid membranes occurs accordingto a solution – diffusion mass transfer mechanism, where perme-ability ( P ) is the product of solubility ( S ) and diffusivity ( D) asfollows [35] :

= × ( )P S D 3

The ideal permeability selectivity (or permselectivity), α i/ j, wasobtained by dividing the permeability of the more permeablespecie i to the permeability of the less permeable specie j. Asshown in Eq. (4) , the permselectivity can also be expressed as theproduct of the diffusivity selectivity and the solubility selectivity.

α = = ×( )

⎛

⎝⎜

⎞

⎠⎟

⎛

⎝⎜

⎞

⎠⎟

P P

DD

S S 4

i ji

j

i

j

i

j/

3. Results and discussion

The chemical structures of the pure ILs used and the

composition description of the prepared IL mixtures are shown inFig. 1 and Table 1 , respectively. The water contents (wt%), as wellas the viscosity ( η), density ( ρ), and molar volume ( V m ) values of the IL phases used in the preparation of the studied SILMs, namelythe pure [C 2mim][C(CN) 3 ] and its mixtures with the different AA-ILs, are also summarized in Table 1 . It is well known that the highviscosity of the pure amino acid-based ILs promotes low sorptionand desorption rates. As a result, extremely long experiments andvery low CO 2 gas permeabilities are obtained under dry gas con-ditions. Thus, for practical purposes, the measured gas permeationproperties of the IL mixtures were only compared to those of [C2mim][C(CN) 3 ], which has both very high permeabilities andpermselectivies [29] . A thorough analysis regarding the effect of mixing ILs with structurally different anions on the gas perme-ability, diffusivity and solubility, as well as on the CO 2 facilitatedtransport through the prepared SILMs, will be presented in thenext subsections.

The single CO 2 and N 2 permeation experiments through theSILMs containing [C 2mim][C(CN) 3 ] and AA-based IL mixtures werecarried out using a time-lag apparatus, which allows for the si-multaneous determination of permeability and diffusivity. As-suming that the gas transport occurs via a solution-diffusion me-chanism, the solubility was estimated from the measured per-meability and diffusivity data using Eq. (3) . Both the in uence of mixing diverse AA-based ILs with [C 2mim][C(CN) 3 ] and the effectof the trans-membrane pressure differential on the gas transport,as well as on the CO 2 /N2 permselectivity properties were studied.Furthermore, a comparison between the CO 2 permeabilities andCO2 /N2 permselectivities obtained in this work and those of otherSILMs reported in literature will be performed in order to under-stand the potential of the proposed strategy in the preparation of advanced liquid phases for CO 2 separation.

3.1. Effect of mixing ILs with [C(CN) 3] and different [AA] anions

Since, in general, similar trends of gas permeability, diffusivityand solubility were observed among the prepared SILMs for eachone of the trans-membrane pressure differences studied (dataprovided in Supporting Information, Tables S1 – S3 and Figs. S1– S3),the in uence of mixing the [C 2mim][C(CN) 3] with the diverseamino acid-based ILs on the gas permeation properties is discussedherein at the xed trans-membrane pressure differential of 50 kPa.

3.1.1. Gas permeabilityThe experimental gas permeabilities ( P ) values through the

prepared SILMs, measured at T ¼ 318.15 K with a trans-membranepressure differential of 50 kPa, are presented in Fig. 2.

The obtained CO 2 permeability values vary from 562 to 60 Bar-rer, while N 2 permeabilities differ from 7 to 19.1 Barrer. In fact, thepermeability of N 2 is one or two orders of magnitude lower thanthat of CO 2 , indicating the SILMs ’ aptitude to ef ciently separatethese gases. The pure [C 2mim][C(CN) 3] SILM presents the highestCO2 and N 2 permeabilities, 562 and 19.1 Barrer, respectively.

As expected, mixing [C 2 mim][AA] ILs with [C 2 mim][C(CN) 3 ] has

Table 1Composition description, acronym, physical properties (at T ¼ 318.15 K), and water contents of [C 2mim][C(CN) 3 ] and IL mixtures used to prepare the SILMs studied.

IL sample Acronym wt% of water M (g mol 1 ) η a (mPa s) ρ a (g cm 3 ) V m a (cm 3 mol 1 )

[C2 mim][C(CN) 3 ] [C2mim][C(CN) 3] 0.01 201.23 8.20 1.067 188.46[C2 mim][C(CN) 3 ]0.5 [Gly]0.5 [C(CN)3 ][Gly] 0.65 193.23 18.69 1.102 175.33[C2 mim][C(CN) 3 ]0.5 [L -Ala] 0.5 [C(CN)3 ][L -Ala] 0.10 200.24 24.90 1.086 184.39[C2 mim][C(CN) 3 ]0.5 [Tau] 0.5 [C(CN)3 ][Tau] 0.05 218.27 27.27 1.148 190.09[C2 mim][C(CN) 3 ]0.5 [L -Ser] 0.5 [C(CN)3 ][L -Ser] 0.29 208.24 41.25 1.125 185.09

[C2 mim][C(CN) 3 ]0.5 [L -Pro] 0.5 [C(CN)3 ][L -Pro] 0.17 213.26 44.93 1.100 193.86

a Values taken from Gouveia et al. [31] .

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and co-authors showed that AAILs, containing phosphonium ca-tions combined with AA-based anions such as [Gly] , [Ala] ,[Pro] and [Tau] , have high CO 2 absorption capacities, between0.80 and 1.26 mol of CO

2 per mole of IL, indicating the pre-

dominance of 1:1 mechanism [51 ,19].From Fig. 3, it can be seen that the CO 2 solubilities of the SILMs

containing IL mixtures increase in the order [C(CN) 3 ][Tau] o[C(CN)3 ][Gly] [C(CN)3 ][L -Ala] o [C(CN)3 ][L -Pro] o [C(CN)3 ][L -Ser].The SILM made of the [C(CN) 3 ][Tau] mixture exhibits the lowestCO2 solubility (621 10 6 m 3 (STP) m 3 Pa 1 ), meaning that theAA-based anion having a sulfonate group ( – −SO 3 ) instead of a car-boxylate ( – COO ) promotes lower CO 2 solubilities. Similar CO 2solubilities values were obtained for [C(CN) 3 ][Gly] and [C(CN) 3 ][L -Ala] SILMs, 778 10 6 and 804 10 6 m 3 (STP) m 3 Pa 1 re-spectively, probably due to similarity of the chemical structure of [Gly] and [ L -Ala] anions ( Fig. 1). On the other hand, the pre-sence of [ L -Ser] anion, which only has an extra hydroxyl group ( –OH) compared to the [ L -Ala] - anion, allowed the [C(CN) 3 ][L -Ser]SILM to exhibit the highest CO 2 solubility (1180 10 6 m 3 (STP)m 3 Pa 1 ) amongst all the SILMs studied.

Considerable efforts have been made to develop and understandthe relationship between CO 2 solubility and the intrinsic propertiesof ILs. In 2006, Camper et al. introduced a model for low pressureCO2 solubility and selectivity in imidazolium-based ILs at 298.15 K,313.15 K, and 323.15 K. The model, based on regular solution theory(RST) relates gas solubility (on a molarity basis) to IL molar volume[53] . On the other hand, Carvalho and Coutinho [54] developed acorrelation for solubility of CO 2 in ILs with validity up to 5 MPa andtemperatures ranging from room temperature up to 363 K. Al-though many ILs signi cantly deviate from the curve proposed byCarvalho and Coutinho [54] , the in uence of the IL molecularweight on the CO 2 solubility can be seen. Moreover, a correlationbetween free volume and CO 2 solubility and selectivity was recentlyproposed by Shannon et al. [55] , who suggested that the IL freevolume ( V f ) and fractional free volume (FFV, i.e. V f /V m ) can be cor-related to molar volume, providing better insight into CO 2 solubilityand selectivity trends of imidazolium-based ILs. In sum, all thesemodels recognize that CO 2 solubility increases with increasing IL molar volume, molecular weight and free volume [56] .

Looking at the CO 2 solubility results obtained in this work(Fig. 3), and regardless of the narrow range of molar volume andmolecular weight of the IL phases used ( Table 1 ), deviations fromthe mentioned recognized trends can be observed for the SILMsbased on the IL mixtures containing [Tau] , [L -Ser] , and [Pro] .Although the [C(CN) 3 ][L -Pro] IL mixture has a higher molar volume(193.9 cm 3 mol 1), the highest CO 2 solubility was obtained in the

[C(CN)3][L -Ser] SILM. Another outlier is [C(CN) 3 ][Tau] SILM, which

presents the lowest CO 2 solubility, albeit it has the highest mole-cular weight (218.27 g mol 1 ) among the IL phases tested. Thus, theCO2 solubility in the prepared IL mixtures containing AA-basedanions cannot be entirely described by IL molar volume or mole-cular weight as single parameters. In fact, the CO 2 solvation in AA-based ILs occurs through a chemisorption scheme [16] , which is themainly responsible for their improved CO 2 solubilities, and thiscontrasts with the physical solubility scheme observed for the ILs

(mostly having non-coordinating anions such as [NTf 2] , [BF4] ,[PF6 ] , [SCN] , [DCA] , [OTf] , among others) used in the estab-lishment of the previously mentioned correlations [53 – 55] . Despitethese correlations provide useful approximations to predict CO 2solubility trends for many ILs, diverse studies have also showeddeviations to these tendencies [28 ,29 ,37,57 – 59] . All these evidencesshow that the proposed correlations are certainly limited by theanion nature of the ILs used in their derivations or, in other words,limited to ILs where only CO 2 physical solubility occurs.

3.2. Effect of the trans-membrane pressure differential

The effect of the trans-membrane pressure differential on thegas permeation properties and the CO 2 /N2 permselectivity was

investigated in order to understand the gas transport mechanismthrough the prepared SILMs.

3.2.1. Gas permeationThe gas permeability, solubility and diffusivity values of the

[C(CN)3 ][Tau] SILM measured at T ¼ 318.15 K and different trans-membrane pressure differentials (2.5, 5, 10, 25, 50 and 100 kPa)are shown in Figs. 4– 6, respectively.

The values obtained through the pure [C 2mim][C(CN) 3] SILMare also plotted in these gures for comparison. The data de-termined for the remaining SILMs are only provided in SupportingInformation ( Tables S1-S3 and Figs. S1-S3 ) since similar behaviorsto those revealed by the [C(CN) 3 ][Tau] SILM were observed.

As it can be seen in Fig. 4, the N 2 permeability almost does notchange along the several trans-membrane pressure differentials stu-died, meaning that N 2 permeation through both the [C(CN) 3][Tau] and[C2mim][C(CN) 3] SILMs can be described using conventional solution-diffusion mechanism. Regarding the CO 2 permeability, it is well knownthat the CO 2 partial pressure across the membrane markedly in u-ences the CO 2 permeability of facilitated transport membranes be-cause of carrier saturation. Fig. 4 shows CO 2 permeability of the sup-ported [C(CN) 3][Tau] mixture signi cantly increases from 109 to 733Barrer when the trans-membrane pressure differential decreases from100 to 2.5 kPa, while the CO 2 permeability through the pure[C2mim][C(CN) 3]-based SILM does not signi cantly change (556 – 539Barrer). Accordingly, the transport of CO 2 molecules through thesupported [C(CN) 3][Tau] mixture can be attributed to both chemicalreaction and Fick diffusion. This evidence is further supported by thelarger solubility of CO 2 in [C(CN)3][Tau] ( Fig. 5) and the reduced CO 2diffusivities through [C 2mim][C(CN) 3] under low trans-membranepressure differentials ( Fig. 6).

Likewise, as the trans-membrane pressure differential de-creases, the CO 2 permeability through the SILMs containing the[C(CN)3 ][AA] mixtures approaches or even surpasses that in thepure [C 2 mim][C(CN) 3]-based SILM ( Fig. S1, Supporting Informa-tion). For instance, at 2.5 kPa of partial pressure, the CO 2 perme-ability in the [C(CN) 3 ][Tau] is 36% higher than that obtained in thepure [C 2mim][C(CN) 3 ]. Therefore, and as expected, it can beclaimed that the [C(CN) 3 ][AA] mixtures have the ability to act asCO2 carriers under low trans-membrane pressure differentials,facilitating the permeation of CO 2 through the SILMs.

3.2.2. CO 2 /N 2 permselectivity

The ideal CO 2 /N2 permselectivities of all the prepared SILMs are

0

200

400

600

800

1000

1200

1400

C O

2 S o l u

b i l i t y x

1 0 6 ( m 3 ( S T P ) m - 3 P a -

1 )

Fig. 3. CO2 solubility values (m 3 (STP) m 3 Pa 1) through the prepared SILMs atT ¼ 318.15 K and a trans-membrane pressure differential of 50 kPa.



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depicted in Fig. 7 as a function of the trans-membrane pressuredifferential (kPa) tested.

The CO2 /N2 permselectivity of the pure [C 2mim][C(CN) 3 ] SILMslightly decreases with decreasing the trans-membrane pressuredifferential. On the other hand, the CO 2 /N2 permselectivity of theSILMs containing the [C(CN) 3 ][AA] mixtures signi cantly increasesas the trans-membrane pressure differential decreases, with morepronounced effect for the [C(CN) 3 ][L -Ala] and [C(CN) 3 ][Tau] SILMs.For example, at 2.5 kPa of partial pressure, the CO 2 /N2 perms-electivity of the prepared SILMs can be ordered as: [C(CN) 3 ][L -Pro](18.5) o [C2mim][C(CN) 3] (21.2) o [C(CN)3 ][Gly] (27.0) o [C(CN)3 ][L -

Ser] (33.9) o [C(CN)3 ][L -Ala] (45.1) o [C(CN)3 ][Tau] (69.1). This

means that only the [C(CN) 3 ][L -Pro] IL mixture exhibits lowerCO2 /N2 permselectivity (at 2.5 kPa) compared to that of the pure[C2mim][C(CN) 3 ], which can be attributed to the quite low CO 2permeability through the [C(CN)

3][L -Pro] SILM (see Table S1 ).

It is worthy to note that the effect of the trans-membranepressure differential on the CO 2 /N2 permselectivity accounts forsimilar variation trend of CO 2 permeability in [C(CN) 3 ][L -Ala] (765Barrer) and [C(CN) 3][Tau] (733 Barrer). In view of both large CO 2permeabilities and high CO 2 /N2 permselectivities at low trans-membrane pressure differentials, the [C(CN) 3 ][L -Ala] and[C(CN)3 ][Tau] mixtures are promising candidates as ef cient liquidphases for facilitated CO 2 separation through SILMs.

4. Conclusions

In this work, equimolar IL mixtures containing [C(CN) 3 ] anddifferent AA anions are proposed as new liquid phases to prepareadvanced facilitated SILMs for ue gas separation (CO 2 /N2 ). TheCO2 and N 2 permeabilities, diffusivities, and solubilities of these IL mixtures were measured using SILM con gurations, at a xedtemperature and several trans-membrane pressure differentials,using a time-lag apparatus.

The results obtained showed that CO 2 permeability decreaseswith increasing IL viscosity, with the exception of the[C(CN)3 ][Gly] mixture. Conversely to what would be expected, gasdiffusivity does not present an inversely proportional relationshipwith IL viscosity, with the exception of [C(CN) 3 ][L -Ser] and[C(CN)3 ][L -Pro] mixtures and the pure [C 2mim][C(CN) 3 ]. Moreover,IL mixtures displayed a dramatical increase in CO 2 solubilitycompared to the pure [C 2mim][C(CN) 3 ] due to the addition of theAA-based anions. Besides physical solubility, the presence of amine and carboxylic acid groups also provided a chemical solu-bility mechanism. Although the best CO 2 /N2 permselectivities andCO2 permeabilities were obtained at low trans-membrane pres-sure differentials, the [C(CN) 3][AA] mixtures have the ability to actas CO2 carriers, facilitating the permeation of CO 2 through theSILMs. In sum, the results of this work highlight that using mix-tures of ILs to tailor the properties of ILs is a promising strategy todesign improved liquid phases for facilitated CO 2 separation fromN2 through SILMs.

Acknowledgments

Liliana C. Tomé is grateful to FCT ( Fundação para a Ciência e a

Tecnologia ) for her post-doctoral research grant (SFRH/BPD/

0

20

40

60

80

100

120

140

160

180

200

0

100

200

300

400

500

600

700

800

900

2.5 5 10 25 50 100

N 2 P e r m e a

b i l i t y

( B a r r e r

)

C O

2 P e r m e a

b i l i t y

( B a r r e r

)

Pressure (kPa)

Nitrogen

Carbon Dioxide

Fig. 4. Gas permeability values at T ¼ 318.15 K as a function of the trans-membranepressure differential (kPa): [C 2 mim][C(CN) 3 ] (CO2 ) ( light gray bars),[C2 mim][C(CN) 3 ] (N2) ( ), [C(CN)3 ][Tau] (CO 2 ) (dark gray bars), [C(CN) 3][Tau] (N 2 )( ).

0

250

500

750

1 000

1 250

1 500

1 750

2 000

2.5 5 10 25 50 100

C O

2 S o

l u b i l i t y

( x 1 0 6 ) ( m 3 ( S T

P ) m - 3 P a -

1 )

Pressure (kPa)

Fig. 5. CO2 solubility values at T ¼ 318.15 K as a function of the trans-membranepressure differential (kPa): [C 2 mim][C(CN) 3 ] ( ), [C(CN)3 ][Tau] ( ).

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0

10

20

30

40

50

60

70

80

90

100

2.5 5 10 25 50 100

C O

2 D i f f u s i v

i t y

( x 1 0 1 2 ) ( m 2 · s - 1 )

C O

2 D i f f u s i v

i t y

( x 1 0 1 2 ) ( m 2 · s - 1 )

Feed Pressure (kPa)

IL Mixture

Pure IL

Fig. 6. CO2 diffusivity values at T ¼ 318.15 K as a function of the trans-membranepressure differential (kPa): [C 2 mim][C(CN) 3 ] ( ), [C(CN)3 ][Tau] ( ).

0

10

20

30

40

50

60

70

80

2.5 5 10 25 50 100

C O 2 / N

2 P e r m s e

l e c t

i v i t y

Pressure (kPa)

Fig. 7. CO2 /N2 permselectivity values of all the studied SILMs as a function of thetrans-membrane pressure differential (kPa): [C 2mim][C(CN) 3] ( ), [C(CN)3 ][Gly](□ ), [C(CN)3 ][L -Ala] ( ), [C(CN)3][Tau] ( ○ ), [C(CN)3][L -Ser] ( ), [C(CN) 3][L -Pro] ( ).



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101793/2014). Isabel M. Marrucho acknowledges FCT/MCTES(Portugal) for a contract under Investigador FCT 2012. This workwas partially supported by FCT through Research Unit GREEN-it“ Bioresources for Sustainability ” (UID/Multi/04551/2013).

Appendix A. Supplementary material

Supplementary data associated with this article can be found in theonline version at http://dx.doi.org/10.1016/j.memsci.2016.03.008 .

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towards the potential of cyano and amino acid-based ionic liquid mixtures for facilitated co2...

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