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Solubilities of carbon dioxide in the eutectic mixture of levulinic acid (or furfuryl alcohol) and choline chloride
J. Chem. Thermodynamics 88 (2015) 72–77
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Solubilities of carbon dioxide in the eutectic mixture of levulinic acid (or furfuryl alcohol) and choline chloride Meizhen Lu, Guoqiang Han, Yaotai Jiang, Xudong Zhang, Dongshun Deng ⇑, Ning Ai Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
a r t i c l e
i n f o
Article history: Received 14 November 2014 Received in revised form 2 April 2015 Accepted 15 April 2015 Available online 22 April 2015 Keywords: Renewable deep eutectic solvents Levulinic acid Furfuryl alcohol Choline chloride Carbon dioxide Solubility
a b s t r a c t The solubilities of carbon dioxide (CO2) in the renewable deep eutectic solvents (DESs) containing levulinic acid (or furfuryl alcohol) and choline chloride were determined at temperatures (303.15, 313.15, 323.15, and 333.15) K and pressures up to 600.0 kPa using an isochoric saturation method. The mole ratios of levulinic acid (or furfuryl alcohol) to choline chloride were fixed at 3:1, 4:1 and 5:1. Standard Gibbs free energy, dissolution enthalpy and dissolution entropy were calculated from Henry’s law constant of CO2 in the DESs. Results indicated that levulinic acid based DESs are more effective to capture CO2 than furfuryl alcohol based ones. The solubility of CO2 in the DESs increased with increasing mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride as well as pressure and decreased with increasing temperature. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Serious greenhouse effect and resulting environmental problems has raised public attention worldwide [1,2]. CO2, identified as the main greenhouse gas, is inevitably produced in large qualities from the burning of fossil fuels. Therefore, carbon capture and sequestration (CCS) have been the focus of many researches in recent years [3]. The principal technologies for CO2 capture include absorption, adsorption, membrane separation, and cryogenic separation [4]. Currently, the industrial and commercial amine-based absorbents for carbon capture at post-combustion conditions have several inherent drawbacks, including the solvent loss, equipment corrosion, and high energy requirements for regeneration [4–8]. Thus, the development of economic and environmentally-friendly absorbents for CO2 capture has always been desirable. Ionic liquids (ILs) are extensively reported as a kind of new and ‘‘promising’’ absorbent for CO2 in the past two decades due to their unique properties, such as high thermal stability, extremely low volatility, diversity, and tuneable properties [9–11]. However, ionic liquids still have several shortcomings including high price, complicated technology for production and purification, uncertain toxicity and poor biodegradability [12]. Hopefully, the emerging deep eutectic solvents (DESs), known as an advanced generation of ILs, seem to be good candidates [13]. The DESs were found to have ⇑ Corresponding author. E-mail address: [email protected] (D. Deng). http://dx.doi.org/10.1016/j.jct.2015.04.021 0021-9614/Ó 2015 Elsevier Ltd. All rights reserved.
many interesting solvent properties that are similar to conventional ILs. Moreover, DESs have the advantages such as acceptable cost, good biodegradability, renewability, and low-toxicity [14]. DES is easy to prepare by directly mixing hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), which form a eutectic mixture with lower melting point than its original precursors through hydrogen-bond network [15,16]. Since Abbott adopted the term of ‘‘deep eutectic solvents’’ (DESs) in 2003 [17], DESs have attracted increasing attentions over the past ten years. The scope of HBD has been expanded to include alcohols [18], sugars [19], organic acids [20], and amides [21], while HBA merely focuses on quaternary ammonium salts [22,23] and quaternary phosphium salts [24]. DESs were also widely used as media in chemical reaction [25–27], electro-deposition [28,29] and extraction separation [30–33] with encouraging results. Recent works explored the possibility of DESs as the absorbents for CO2 capture. For example, Li’s group [34–36] have measured the solubility of CO2 in 1:2 mol choline chloride–urea DES (commercial name: reline), aqueous DES (choline chloride/ethylene glycol, choline chloride/glycerol, choline chloride/malonic acid) systems, aqueous blends of (reline + monoethanolamine). Francisco et al. [12] reported the CO2 capture using natural 1:2 mol (choline chloride + lactic acid) DES. Li et al. [37] reported the solubility data of CO2 in the eutectic mixture of choline chloride and urea at temperatures (313.15, 323.15, and 333.15) K under pressures up to 13 MPa. In our previous works [38,39], the solubility of CO2 in the DESs composed of choline chloride and HBDs like phenol, 1,4-butanediol, 2,3-butanediol,
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1,2-propanediol, diethylene glycol, and triethylene glycol were determined. As a continuation of our study, we will present new measurements on the solubility of CO2 in the renewable DESs containing levulinic acid (or furfuryl alcohol) and choline chloride at temperatures (303.15, 313.15, 323.15, and 333.15) K and pressures up to 600 kPa by the isochoric saturation method. The mole ratios of levulinic acid (or furfuryl alcohol) and choline chloride were fixed at 3:1, 4:1 and 5:1. For the better understand of dissolution behaviour of CO2 in the DESs, Henry’s law constant, standard Gibbs free energy, dissolution enthalpy, and dissolution entropy were further calculated from the solubility of CO2 in the DESs.
2. Experimental 2.1. Chemicals The CO2 (mass fraction purity >0.9995) was supplied by Jingong Special Gas Co., Ltd. Choline chloride (mass fraction purity >0.985) was supplied by Jinan Hualing Pharmaceutical Co., Ltd. Levulinic acid (mass fraction purity P0.985) and furfuryl alcohol (mass fraction purity P0.982) were obtained from Shanghai Aladdin Chemical Reagent Co., Ltd. The summary of the chemicals used, their purities, and sources are listed in table 1. The DESs were prepared by directly mixing choline chloride and levulinic acid (or furfuryl alcohol). The water mass fraction of each DES was determined by Karl Fischer analysis (SF-3 Karl-Fischer Titration, Zibo Zifen Instrument Co. Ltd.) with the result of less than 9.6 104 in all cases. The density of the DESs was carefully measured at temperatures (303.15, 313.15, 323.15, and 333.15) K under 101.3 kPa using pycnometer (its volume was first calibrated with double-distilled water at each experimental temperature) immersed in a thermostatic oil-bath. The mass of the DESs was weighed by electronic balance (Mettler-Toledo AL204) with an estimated uncertainty of ±2 104 g. A DSC (differential scanning calorimeter, NETZSCH 200 F3) was used to measure the melting points of present DESs. In the DSC experiment, the samples were continuously purged with 50 mL min1 of dried nitrogen. The temperature was calibrated using indium (mass fraction purity >0.99999,
TABLE 1 Description of chemicals used in the study. Chemical
Source
Mass fraction purity
Carbon dioxide Choline chloride Levulinic acid Furfuryl alcohol
Jingong Special Gas Co., Ltd. Jinan Hualing Pharmaceutical Co., Ltd.
>0.9995 >0.985
Shanghai Aladdin Chemical Reagent Co., Ltd. P0.985 Shanghai Aladdin Chemical Reagent Co., Ltd. P0.982
Tm = 429.76 K). About (10 to 25) mg of the DES were crimped in an aluminium standard sample pan and analysed under a nitrogen atmosphere by cooling-heating (2 K min1) cycles between T = (173.15 and 283.15) K. The temperature-dependent thermal curves were recorded (figures S1 and S2). The first curve transition temperature was selected as the melting point, which corresponded to the solidus of the DES (beginning of melting). The melting points of DESs are listed in table 2. 2.2. Apparatus and procedures A stainless apparatus as illustrated in our previous work [38] was used to measure the solubility of CO2 in the DESs. It was mainly composed of gas equilibrium cell (EC) and gas reservoir (GR) with the volumes of (141.61 and 370.99) cm3, respectively. The temperature was carefully controlled using thermostatic water baths with a precision of ±0.05 K. The pressure was monitored by pressure transmitter (Fujian WIDEPLUS Precision Instruments Co., Ltd, WIDEPLUS-8, 0-600.0 kPa) with an accuracy of ±0.1% full-scale. The solubility of CO2 in the DESs was determined using an isochoric saturation method [40]. The detailed experimental procedures were described in our previous works [38,39]. In a typical run, the temperature of GR was kept at 303.15 K. After a known mass of DES (about 60 to 80 g, the accurate mass of the DES, w, was weighted by electronic balance) was added into the EC, the air in the whole system was evacuated to pressure p0. Keeping the valve needle between GR and CO2 cylinder open, GR was charged with CO2 up to pressure p1. The temperature of EC was set at T using a thermostatic water bath. Keeping the needle valve between GR and EC open, CO2 was transferred into EC to contact with DES. (Gas + liquid) equilibrium was supposed to be reached if the pressure of EC kept unchanged within 2 h. The final pressures were recorded as p2 for GR and p3 for EC. Then, the partial pressure of CO2 at equilibrium was calculated as following,
ps ¼ p3 pv
ð1Þ
where ps is the partial pressure of CO2 at equilibrium state. pv represents the saturated vapour pressure of DES at the experimental temperature. In present work, the values of pv are indirectly determined using the TGA analysis according to literature method [41]. In brief, the evaporation rates of DES and reference substance (RS) were recorded under the same conditions, respectively. Levulinic acid and furfuryl alcohol were selected as reference substances for (levulinic acid + choline chloride) and (furfuryl alcohol + choline chloride) mixtures, respectively. The saturated vapour pressures of two reference substances were taken from literatures [42,43]. The pv of DES was calculated as the produce of following two parts, pv of reference substance and the evaporation rate ratio of DES to RS. The values of pv for two DESs are listed in Table 2. The absorbed CO2 (nCO2 ) was calculated by the following equation,
TABLE 2 Physical properties of the deep eutectic solvents studied (DESs) (expressed by mole ratio of levulinic acid or furfuryl alcohol to choline chloride, the same below): melting points (Tm, under p = 101.3 kPa), density (q, under p = 101.3 kPa) and saturated vapour pressure (pv) at different temperatures.a Solutions
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1 a
Tm/K
262.0 263.0 263.2 237.4 238.6 239.4
q/(g cm3)
pv/Pa
303.15
313.15
323.15
333.15
1.1346 1.1341 1.1337 1.1318 1.1315 1.1309
1.1276 1.1273 1.1270 1.1252 1.1243 1.1238
1.1209 1.1204 1.1202 1.1186 1.1171 1.1166
1.1138 1.1131 1.1130 1.1120 1.1099 1.1095
303.15
49 57 64
313.15
114 123 133
323.15
333.15
242 255 266
4.3 5.5 7.7 436 461 479
Standard uncertainties u are u(T) = 0.05 K, u(Tm) = 0.1 K, u(p) = 0.6 kPa, u(pv) = 1.0 Pa and the combined expanded uncertainty Uc is Uc(q) = 0.0008 g cm3 (0.95 level of confidence). The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
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nCO2 ¼ qg ðp1 ; TÞV GR qg ðp2 ; TÞV GR qg ðps ; TÞðV EC w=qDES Þ
ð2Þ
3. Results and discussion 3.1. Solubility of CO2 in the DESs
where qg ðpi ; TÞ denotes the density of CO2 in mol cm3 under pressure pi (i = 1, 2, s) and temperature T, and is obtained according to the reference [44]. VGR and VEC represent the volumes of GR and EC in cm3, respectively. qDES is the density of DES at experimental temperature in g cm3;the decrease of the DES’s density because of the CO2 solubility is very small and neglected. The mole fraction (xCO2 ) and molality (mCO2 ) of CO2 in the DESs mixture were calculated by the following equations,
xCO2 ¼ nCO2 =ðnCO2 þ nDES Þ
ð3Þ
mCO2 ¼ nCO2 =w
ð4Þ
The densities of the DESs at different temperatures under 101.3 kPa are listed in table 2. The densities of the mixtures of choline chloride and levulinic acid were slightly higher than those of choline chloride and furfuryl alcohol. The solubility of CO2 in the DESs was determined at temperatures ranging from (303.15 to 333.15) K in 10 K intervals and pressures up to 600.0 kPa. The mole ratios of levulinic acid (or furfuryl alcohol) to choline chloride were fixed at 3:1, 4:1 and 5:1. Values of the measured solubility of CO2 in the DESs (xCO2 , mole fraction; mCO2 , molality) at different temperatures (T) and partial pressure of CO2 (p) at the equilibrium state are listed in table 3. The measured solubility data of CO2 in 5:1 mole (levulinic acid + choline chloride) and (furfuryl alcohol + choline chloride) at four temperatures are plotted in figures 1 and 2, respectively. Figure 3 shows the solubilities of CO2 in levulinic acid (or furfuryl
where nCO2 is the mole number of CO2 absorbed in the DESs, nDES is the mole number of DES, and w is the mass of the used DES.
TABLE 3 Solubility of CO2 in the deep eutectic solvents (DESs) (xCO2 , mole fraction; mCO2 , molality) at different temperatures (T) and equilibrium pressure (p).a T = 303.15 K
a
313.15 K
323.15 K
p/kPa
xCO2
mCO2 /(mol kg1)
p/kPa
xCO2
mCO2 /(mol kg1)
0.0043 0.0111 0.0164 0.0215 0.0270 0.0302
0.0351 0.0919 0.1367 0.1800 0.2272 0.2549
69.8 202.5 306.8 410.9 508.5 579.8
0.0031 0.0090 0.0138 0.0182 0.0228 0.0259
nlevulinic 0.0255 0.0741 0.1146 0.1523 0.1914 0.2180
acid:
79.4 208.4 310.9 411.9 510.9 570.0
0.0039 0.0109 0.0167 0.0227 0.0281 0.0316
0.0321 0.0914 0.1402 0.1925 0.2396 0.2700
60.0 176.9 282.4 380.1 485.1 565.9
0.0029 0.0085 0.0135 0.0185 0.0231 0.0273
nlevulinic 0.0243 0.0712 0.1132 0.1562 0.1954 0.2319
acid:
72.5 201.2 305.3 410.6 508.4 574.9
0.0041 0.0112 0.0177 0.0237 0.0294 0.0333
0.0339 0.0944 0.1502 0.2023 0.2526 0.2869
73.1 200.1 308.4 412.2 511.4 573.7
0.0032 0.0096 0.0152 0.0200 0.0248 0.0281
nlevulinic 0.0271 0.0809 0.1282 0.1698 0.2115 0.2410
acid:
71.5 188.9 296.9 401.7 501.5 566.7
0.0029 0.0076 0.0114 0.0147 0.0179 0.0197
0.0263 0.0704 0.1060 0.1375 0.1676 0.1856
80.8 214.6 321.4 426.7 523.2 581.7
0.0024 0.0063 0.0095 0.0126 0.0155 0.0173
nfurfuryl 0.0217 0.0581 0.0881 0.1171 0.1454 0.1618
alcohol:
80.9 218.3 323.7 425.3 524.1 582.8
0.0032 0.0082 0.0126 0.0166 0.0205 0.0228
0.0306 0.0777 0.1195 0.1589 0.1964 0.2196
70.3 192.2 295.4 403.5 502.8 568.8
0.0025 0.0064 0.0099 0.0133 0.0165 0.0183
nfurfuryl 0.0232 0.0608 0.0941 0.1269 0.1571 0.1753
alcohol:
82.5 212.1 319.3 412.5 519.3 581.5
0.0031 0.0085 0.0125 0.0167 0.0207 0.0234
0.0300 0.0811 0.1201 0.1614 0.2015 0.2276
70.9 203.4 304.7 404.9 505.2 570.2
0.0025 0.0071 0.0106 0.0141 0.0176 0.0198
nfurfuryl 0.0237 0.0678 0.1024 0.1361 0.1707 0.1924
alcohol:
77.3 210.2 316.5 414.7 516.3 577.4
333.15 K mCO2 /(mol kg1)
p/kPa
xCO2
mCO2 /(mol kg1)
= 3:1 0.0027 0.0075 0.0113 0.0150 0.0186 0.0208
0.0221 0.0616 0.0934 0.1246 0.1553 0.1738
85.9 219.8 321.6 425.2 524.9 583.0
0.0025 0.0066 0.0102 0.0133 0.0163 0.0183
0.0205 0.0541 0.0841 0.1108 0.1359 0.1526
= 4:1 0.0032 0.0084 0.0125 0.0167 0.0205 0.0229
0.0266 0.0703 0.1050 0.1403 0.1731 0.1937
82.6 218.5 326.0 426.2 528.5 587.4
0.0024 0.0072 0.0103 0.0138 0.0168 0.0185
0.0201 0.0602 0.0859 0.1154 0.1414 0.1562
= 5:1 0.0030 0.0083 0.0128 0.0174 0.0213 0.0239
0.0254 0.0698 0.1084 0.1474 0.1817 0.2038
78.9 216.1 319.2 417.3 519.7 581.0
0.0027 0.0074 0.0110 0.0146 0.0179 0.0199
0.0225 0.0624 0.0923 0.1231 0.1522 0.1694
ncholine chloride = 3:1 81.5 0.0023 222.1 0.0056 329.6 0.0084 428.9 0.0110 528.6 0.0134 585.3 0.0148
0.0214 0.0518 0.0777 0.1024 0.1247 0.1383
86.3 224.4 330.3 430.4 530.6 586.4
0.0018 0.0047 0.0072 0.0095 0.0118 0.0129
0.0168 0.0438 0.0665 0.0883 0.1098 0.1208
ncholine chloride = 4:1 65.2 0.0021 188.1 0.0053 296.2 0.0085 399.3 0.0115 494.2 0.0143 565.8 0.0164
0.0173 0.0502 0.0805 0.1089 0.1362 0.1566
86.8 220.3 326.1 426.6 529.6 585.4
0.0022 0.0054 0.0080 0.0108 0.0131 0.0146
0.0203 0.0512 0.0757 0.1023 0.1250 0.1389
ncholine chloride = 5:1 71.3 0.0023 194.1 0.0061 301.0 0.0094 403.6 0.0126 502.8 0.0158 573.1 0.0180
0.0215 0.0579 0.0903 0.1219 0.1523 0.1743
74.9 204.2 315.2 409.6 511.7 577.2
0.0020 0.0054 0.0084 0.0111 0.0137 0.0154
0.0189 0.0517 0.0808 0.1064 0.1318 0.1486
p/kPa
ncholine
chloride
80.8 210.0 314.0 417.6 517.8 579.7 ncholine
chloride
83.0 219.6 321.1 423.5 523.8 584.2 ncholine
chloride
75.6 208.8 315.9 418.4 517.2 579.9
xCO2
Standard uncertainties u are u (T) = 0.05 K, u (p) = 0.6 kPa, ur (x) = 0.02, ur (m) = 0.02. The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
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b
600
a
500
500
400
400 p/kPa
p/kPa
600
300
300
200
200
100
100
0 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 xCO 2
0 0.00
0.04
0.08
0.12 0.16 0.20 -1 mCO /mol.kg 2
0.24
0.28
FIGURE 1. Solubility of CO2 (a, mole fraction; b, molality) in deep eutectic solvents (DES) of levulinic acid and choline chloride (5:1 mole ratio) at different temperatures: 5, 303.15 K; h, 313.15 K; 4, 323.15 K; s, 333.15 K; —, linear fit.
a
500
500
400
400
300
300
200
200
100
100
0 0.000
b
600
p/kPa
p/kPa
600
0.005
0.010
0.015 xCO 2
0.020
0 0.00
0.025
0.04
0.08 0.12 0.16 -1 mCO /mol.kg 2
0.20
0.24
FIGURE 2. Solubility of CO2 (a, mole fraction; b, molality) in deep eutectic solvents (DES) of furfuryl alcohol and choline chloride (5:1 mole ratio) at different temperatures: }, 303.15 K; 4, 313.15 K; s, 323.15 K; 5, 333.15 K; —, linear fit.
600
3.2. Henry’s law constant
500
Henry’s law can be used to describe the physical solubility of gas in the solvents [45]. Therefore, Henry’s law constant Hx based on mole fraction was used to quantitatively express the solubility of CO2 in the DESs as following [46],
p/kPa
400 300
liq
f 2 ðp; T; x2 Þ ; x2 !0 x2
Hx ðp; TÞ lim
200
where Hx is Henry’s law constant based on mole fraction,
100 0 0.00
ð5Þ
liq
0.04
0.08
0.12 0.16 0.20 -1 mCO /mol.kg 2
0.24
0.28
FIGURE 3. Solubility of CO2 (molality) in deep eutectic solvents (DESs) of levulinic acid (or furfuryl alcohol) and choline chloride at T = 313.15 K: s, nlevulinic acid: ncholine chloride = 5:1; h, nlevulinic acid: ncholine chloride = 3:1; 4, nfurfuryl alcohol: ncholine chloride = 5:1; 5, nfurfuryl alcohol: ncholine chloride = 3:1; —, linear fit.
f 2 ðp; T; x2 Þ is the fugacity of CO2, p and x2 are the partial pressure at the equilibrium state and mole fraction of CO2 in the liquid phase, respectively. When it reached the (vapour + liquid) equilibrium state, the fugacity of CO2 in the liquid phase should be equal to that in the vapour phase. So, v ap
liq
f 2 ðp; T; x2 Þ ¼ f 2 ðp; T; y2 Þ ¼ y2 p/2 ðp; T; y2 Þ; v ap
alcohol) and choline chloride (3:1 and 5:1 mole ratio) at T = 313.15 K. It can be seen that the solubility of CO2 in the DESs increases linearly with pressure and decreases with increasing temperature. Moreover, the solubility of CO2 gets the highest in the mixture of levulinic acid and choline chloride (5:1 mole ratio). Such behaviour illustrates that the dissolution of CO2 in the DESs is believed to be a physical process.
ð6Þ
where f 2 ðp; T; y2 Þ is the fugacity of CO2 in the vapour phase, y2 and /2 are the mole fraction and fugacity coefficient of CO2 in the vapour phase, respectively. In this work, the vapour pressure of the DESs was very small at the experimental temperatures, thus the gas phase was supposed to be pure CO2 and y2 was approximately equal to unity. It was also supposed that the fugacity coefficient /2 of CO2 at relatively low pressure could be calculated using two-term Virial equation. Thus, in the very diluent region of CO2 in
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M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
liquid phase, Hx is expressed as following by the combination of equations (5) and (6), liq
f 2 ðp; T; x2 Þ p/ ðp; T; y2 Þ p/2 ðp; TÞ ¼ lim 2 ffi x2 !0 x2 !0 x2 x2 x2
Hx ðp; TÞ ¼ lim
ð7Þ
. Similarly, Henry’s law constant Hm based on molality can be defined as following,
"
# liq f 2 ðp; T; m2 Þ p/ ðp; TÞ Hm ðp; TÞ lim ffi 2 m2 !0 ðm2 =m0 Þ ðm2 =m0 Þ
ð8Þ
where m0 = 1 mol kg1, and m2 is the molality of CO2 in the liquid phase. In this work, Hx and Hm were obtained by calculating the linear slope of fugacity vs mole fraction and molality of CO2, respectively. These Henry’s law constants were given in table 4. It is evident that the solubility of CO2 in the DESs of levulinic acid and choline chloride is higher than that of furfuryl alcohol and choline chloride at the same temperature and mole ratio. It also revealed that the carboxyl group in levulinic acid was more powerful to capture CO2 than the hydroxyl group in furfuryl alcohol, which was in good agreement with the results reported by Li et al. [47]. Moreover, the solubility of CO2 in the DESs increased with the increasing mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride. For further evaluation of these renewable DESs as CO2 absorbents, Henry constants Hm at T = 313.15 K in present DESs were compared with those in other DESs and several ILs reported in the literature. As shown in table 5, values of the solubility of CO2 in the DESs studied are higher than those in the ammonium-based ILs [48], such as 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium lactate ([hhemel]) and 2-hydroxy-N-(2-hydroxyethyl)-Nmethylethanaminium acetate ([hhemea]), but slightly lower than those in the imidazolium ILs [49–51], including 1, 3-Dimethylimidazolium dimethylphosphate ([dmim][Me2PO4]), 1-Ethyl-3methylimidazolium diethylphosphate ([emim][Et2PO4]), 1-hexyl3-methylimidazolium tetrafluoroborate ([hmim][BF4]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]). Moreover, values of the solubility of CO2 in DESs are higher than those in dihydric alcohols (or lactic acid) and choline chloride [38,12], but lower than those in urea (or glycerol) and choline chloride [34,37,52]. These differences of the solubility demonstrate that the interactions between the groups in HBDs (with the exception of glycerol) and CO2 follow the sequence of amide > carbonyl group > ether bond > hydroxyl group.
Ddis H ¼ R½@ lnfHðT; pÞ=p g=@ð1=TÞp
ð10Þ
Ddis S ¼ ðV dis H V dis G Þ=T
ð11Þ
where DdisGo, DdisHo, DdisSo are the standard Gibbs free energy, dissolution enthalpy and dissolution entropy for CO2 in DESs under pressure po = 0.1 MPa, respectively. The DdisHo reflects the strength of interaction between CO2 and DESs, and DdisS0 means the order degree of intermolecular structure in the solution of CO2 and DESs. The DdisGo, DdisHo, and DdisSo at different temperatures under pressure po = 0.1 MPa are calculated and listed in table 6.
TABLE 5 Comparison of Hm in present deep eutectic solvents (DESs) with some ILs and other deep eutectic solvents (DESs) at T = 313.15 K.a
Ddis G ¼ RT lnfHðT; pÞ=p g
ð9Þ
Hm/MPa
[hhemel] [45] [hhemea] [45] [dmim][Me2PO4] [46] [emim][Et2PO4] [46] [hmim][BF4] [47] [bmim][Tf2N] [48] nCC:nurea = 1:2.5 [37] nCC:nurea = 1:2 [34] nCC:nglycerol = 1:2 [49] nCC:nethylene glycol = 1:2 [35] nCC:nlactic acid = 1:2 [12] nCC: n2,3-butanediol = 1:4 [38] nCC: n1,4-butanediol = 1:4 [38] nCC:n1,2-propanediol = 1:4 [38] nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1
5.38 4.65 2.35 1.84 1.81 1.06 1.37 1.29 1.70 2.71 4.00 3.44 4.18 4.43 2.62 2.41 2.35 3.54 3.14 2.91
a
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
TABLE 6 Calculated standard Gibbs free energy (DdisGo), enthalpy (DdisHo) and entropy (DdisSo) of solutions at 0.1 MPa and T = 303.15 K.a
3.3. Thermodynamic properties Thermodynamic properties are helpful for quantitative description of CO2 dissolution into DESs and design of capture process. Three thermodynamic properties can be calculated from the correlation of Henry’s law constants as following,
Solvents
Solutions
DdisGo/ (kJ mol1)
DdisHo/ (kJ mol1)
DdisS0/ (J mol1 K1)
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1
13.16 13.05 12.89 14.25 13.89 13.85
15.35 14.75 14.46 11.67 14.47 9.45
94.05 91.70 90.20 85.49 93.53 76.84
a
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
TABLE 4 Henry’s law constants (Hx, based on mole fraction; Hm, based on molality) of CO2 in the deep eutectic solvents (DESs) at different temperatures.a Solutions
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1 a
Hx/(MPa)
Hm/(MPa)
303.15 K
313.15 K
323.15 K
333.15 K
303.15 K
313.15 K
323.15 K
333.15 K
18.54 17.76 16.61 28.54 24.73 24.31
21.91 20.39 20.12 33.11 29.95 28.14
27.37 25.07 23.83 38.68 34.04 31.32
31.46 30.86 28.47 44.64 39.49 36.79
2.20 2.09 1.93 3.05 2.58 2.50
2.62 2.41 2.35 3.54 3.14 2.91
3.28 2.97 2.77 4.14 3.57 3.24
3.74 3.67 3.36 4.79 4.15 3.81
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
Under all conditions, the values of DdisHo are negative, meaning that the absorption of CO2 in DESs is exothermic and the intermolecular interaction of CO2 with DESs is strong. The negative values of DdisSo imply that a more ordered structure is obtained with the dissolution of CO2 into DESs. As a result, all the DdisGo show positive values, meaning the dissolution of CO2 into DESs is not spontaneous. 4. Conclusions New solubility results for CO2 in the renewable DESs composed of levulinic acid (or furfuryl alcohol) and choline chloride were reported over the temperature range (303.15 to 333.15) K in 10 K intervals and pressures up to 600.0 kPa. Standard Gibbs free energy, dissolution enthalpy and dissolution entropy were deduced from Henry’s law constant. Results indicated that the levulinic acid-based DESs have higher absorption capacity for CO2 than furfuryl alcohol-based ones. And the solubility of CO2 in the DESs increases with the increasing pressure as well as mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride and decreased with increasing temperature. The dissolution of CO2 into DESs is not spontaneous. Acknowledgments The research was supported by the Natural Science Foundation of Zhejiang Province (Y4100699) and the National Natural Science Foundation of China (21476205). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jct.2015.04.021. References [1] H.Q. Yang, Z.H. Xu, M.H. Fan, R. Gupta, R.B. Slimane, A.E. Bland, I. Wright, J. Environ. Sci. 20 (2008) 14–27. [2] E.J. Maginn, J. Phys. Chem. Lett. 1 (2010) 3478–3479. [3] P.T. Anastas, M.M. Kirchhoff, Acc. Chem. Res. 35 (2002) 686–694. [4] J.D. Figueroa, T. Fout, S. Plasynski, H. McIlvried, R.D. Srivastava, Int. J. Greenhouse Gas Control 2 (2008) 9–20. [5] M.M. Taib, T. Murugesan, Chem. Eng. J. 181–182 (2012) 56–62. [6] D. Camper, J.E. Bara, D.L. Gin, R.D. Noble, Ind. Eng. Chem. 47 (2008) 8496–8498. [7] G.T. Rochelle, Science 325 (2009) 1652–1654. [8] M.L. Gray, Y. Soong, K.J. Champagne, H. Pennline, J.P. Baltrus, R.W. Stevens Jr, R. Khatri, S.S.C. Chuang, T. Filburn, Fuel Process. Technol. 86 (2005) 1449–1455. [9] C. Capello, U. Fischer, K. Hungerbühler, Green Chem. 9 (2007) 927–934. [10] J.E. Bara, D.E. Camper, D.L. Gin, R.D. Noble, Acc. Chem. Res. 43 (2010) 152–159. [11] G.N. Wang, W.L. Hou, F. Xiao, J. Geng, Y.T. Wu, Z.B. Zhang, J. Chem. Eng. Data 56 (2011) 1125–1133. [12] M. Francisco, A. Bruinhorsta, L.F. Zubeir, C.J. Peters, M.C. Kroon, Fluid Phase Equilib. 340 (2013) 77–84. [13] M. Francisco, A. Bruinhorst, M.C. Kroon, Angew. Chem. Int. Ed. 52 (2013) 3074– 3085.
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JCT 14-629
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J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct
Solubilities of carbon dioxide in the eutectic mixture of levulinic acid (or furfuryl alcohol) and choline chloride Meizhen Lu, Guoqiang Han, Yaotai Jiang, Xudong Zhang, Dongshun Deng ⇑, Ning Ai Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
a r t i c l e
i n f o
Article history: Received 14 November 2014 Received in revised form 2 April 2015 Accepted 15 April 2015 Available online 22 April 2015 Keywords: Renewable deep eutectic solvents Levulinic acid Furfuryl alcohol Choline chloride Carbon dioxide Solubility
a b s t r a c t The solubilities of carbon dioxide (CO2) in the renewable deep eutectic solvents (DESs) containing levulinic acid (or furfuryl alcohol) and choline chloride were determined at temperatures (303.15, 313.15, 323.15, and 333.15) K and pressures up to 600.0 kPa using an isochoric saturation method. The mole ratios of levulinic acid (or furfuryl alcohol) to choline chloride were fixed at 3:1, 4:1 and 5:1. Standard Gibbs free energy, dissolution enthalpy and dissolution entropy were calculated from Henry’s law constant of CO2 in the DESs. Results indicated that levulinic acid based DESs are more effective to capture CO2 than furfuryl alcohol based ones. The solubility of CO2 in the DESs increased with increasing mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride as well as pressure and decreased with increasing temperature. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Serious greenhouse effect and resulting environmental problems has raised public attention worldwide [1,2]. CO2, identified as the main greenhouse gas, is inevitably produced in large qualities from the burning of fossil fuels. Therefore, carbon capture and sequestration (CCS) have been the focus of many researches in recent years [3]. The principal technologies for CO2 capture include absorption, adsorption, membrane separation, and cryogenic separation [4]. Currently, the industrial and commercial amine-based absorbents for carbon capture at post-combustion conditions have several inherent drawbacks, including the solvent loss, equipment corrosion, and high energy requirements for regeneration [4–8]. Thus, the development of economic and environmentally-friendly absorbents for CO2 capture has always been desirable. Ionic liquids (ILs) are extensively reported as a kind of new and ‘‘promising’’ absorbent for CO2 in the past two decades due to their unique properties, such as high thermal stability, extremely low volatility, diversity, and tuneable properties [9–11]. However, ionic liquids still have several shortcomings including high price, complicated technology for production and purification, uncertain toxicity and poor biodegradability [12]. Hopefully, the emerging deep eutectic solvents (DESs), known as an advanced generation of ILs, seem to be good candidates [13]. The DESs were found to have ⇑ Corresponding author. E-mail address: [email protected] (D. Deng). http://dx.doi.org/10.1016/j.jct.2015.04.021 0021-9614/Ó 2015 Elsevier Ltd. All rights reserved.
many interesting solvent properties that are similar to conventional ILs. Moreover, DESs have the advantages such as acceptable cost, good biodegradability, renewability, and low-toxicity [14]. DES is easy to prepare by directly mixing hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), which form a eutectic mixture with lower melting point than its original precursors through hydrogen-bond network [15,16]. Since Abbott adopted the term of ‘‘deep eutectic solvents’’ (DESs) in 2003 [17], DESs have attracted increasing attentions over the past ten years. The scope of HBD has been expanded to include alcohols [18], sugars [19], organic acids [20], and amides [21], while HBA merely focuses on quaternary ammonium salts [22,23] and quaternary phosphium salts [24]. DESs were also widely used as media in chemical reaction [25–27], electro-deposition [28,29] and extraction separation [30–33] with encouraging results. Recent works explored the possibility of DESs as the absorbents for CO2 capture. For example, Li’s group [34–36] have measured the solubility of CO2 in 1:2 mol choline chloride–urea DES (commercial name: reline), aqueous DES (choline chloride/ethylene glycol, choline chloride/glycerol, choline chloride/malonic acid) systems, aqueous blends of (reline + monoethanolamine). Francisco et al. [12] reported the CO2 capture using natural 1:2 mol (choline chloride + lactic acid) DES. Li et al. [37] reported the solubility data of CO2 in the eutectic mixture of choline chloride and urea at temperatures (313.15, 323.15, and 333.15) K under pressures up to 13 MPa. In our previous works [38,39], the solubility of CO2 in the DESs composed of choline chloride and HBDs like phenol, 1,4-butanediol, 2,3-butanediol,
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M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
1,2-propanediol, diethylene glycol, and triethylene glycol were determined. As a continuation of our study, we will present new measurements on the solubility of CO2 in the renewable DESs containing levulinic acid (or furfuryl alcohol) and choline chloride at temperatures (303.15, 313.15, 323.15, and 333.15) K and pressures up to 600 kPa by the isochoric saturation method. The mole ratios of levulinic acid (or furfuryl alcohol) and choline chloride were fixed at 3:1, 4:1 and 5:1. For the better understand of dissolution behaviour of CO2 in the DESs, Henry’s law constant, standard Gibbs free energy, dissolution enthalpy, and dissolution entropy were further calculated from the solubility of CO2 in the DESs.
2. Experimental 2.1. Chemicals The CO2 (mass fraction purity >0.9995) was supplied by Jingong Special Gas Co., Ltd. Choline chloride (mass fraction purity >0.985) was supplied by Jinan Hualing Pharmaceutical Co., Ltd. Levulinic acid (mass fraction purity P0.985) and furfuryl alcohol (mass fraction purity P0.982) were obtained from Shanghai Aladdin Chemical Reagent Co., Ltd. The summary of the chemicals used, their purities, and sources are listed in table 1. The DESs were prepared by directly mixing choline chloride and levulinic acid (or furfuryl alcohol). The water mass fraction of each DES was determined by Karl Fischer analysis (SF-3 Karl-Fischer Titration, Zibo Zifen Instrument Co. Ltd.) with the result of less than 9.6 104 in all cases. The density of the DESs was carefully measured at temperatures (303.15, 313.15, 323.15, and 333.15) K under 101.3 kPa using pycnometer (its volume was first calibrated with double-distilled water at each experimental temperature) immersed in a thermostatic oil-bath. The mass of the DESs was weighed by electronic balance (Mettler-Toledo AL204) with an estimated uncertainty of ±2 104 g. A DSC (differential scanning calorimeter, NETZSCH 200 F3) was used to measure the melting points of present DESs. In the DSC experiment, the samples were continuously purged with 50 mL min1 of dried nitrogen. The temperature was calibrated using indium (mass fraction purity >0.99999,
TABLE 1 Description of chemicals used in the study. Chemical
Source
Mass fraction purity
Carbon dioxide Choline chloride Levulinic acid Furfuryl alcohol
Jingong Special Gas Co., Ltd. Jinan Hualing Pharmaceutical Co., Ltd.
>0.9995 >0.985
Shanghai Aladdin Chemical Reagent Co., Ltd. P0.985 Shanghai Aladdin Chemical Reagent Co., Ltd. P0.982
Tm = 429.76 K). About (10 to 25) mg of the DES were crimped in an aluminium standard sample pan and analysed under a nitrogen atmosphere by cooling-heating (2 K min1) cycles between T = (173.15 and 283.15) K. The temperature-dependent thermal curves were recorded (figures S1 and S2). The first curve transition temperature was selected as the melting point, which corresponded to the solidus of the DES (beginning of melting). The melting points of DESs are listed in table 2. 2.2. Apparatus and procedures A stainless apparatus as illustrated in our previous work [38] was used to measure the solubility of CO2 in the DESs. It was mainly composed of gas equilibrium cell (EC) and gas reservoir (GR) with the volumes of (141.61 and 370.99) cm3, respectively. The temperature was carefully controlled using thermostatic water baths with a precision of ±0.05 K. The pressure was monitored by pressure transmitter (Fujian WIDEPLUS Precision Instruments Co., Ltd, WIDEPLUS-8, 0-600.0 kPa) with an accuracy of ±0.1% full-scale. The solubility of CO2 in the DESs was determined using an isochoric saturation method [40]. The detailed experimental procedures were described in our previous works [38,39]. In a typical run, the temperature of GR was kept at 303.15 K. After a known mass of DES (about 60 to 80 g, the accurate mass of the DES, w, was weighted by electronic balance) was added into the EC, the air in the whole system was evacuated to pressure p0. Keeping the valve needle between GR and CO2 cylinder open, GR was charged with CO2 up to pressure p1. The temperature of EC was set at T using a thermostatic water bath. Keeping the needle valve between GR and EC open, CO2 was transferred into EC to contact with DES. (Gas + liquid) equilibrium was supposed to be reached if the pressure of EC kept unchanged within 2 h. The final pressures were recorded as p2 for GR and p3 for EC. Then, the partial pressure of CO2 at equilibrium was calculated as following,
ps ¼ p3 pv
ð1Þ
where ps is the partial pressure of CO2 at equilibrium state. pv represents the saturated vapour pressure of DES at the experimental temperature. In present work, the values of pv are indirectly determined using the TGA analysis according to literature method [41]. In brief, the evaporation rates of DES and reference substance (RS) were recorded under the same conditions, respectively. Levulinic acid and furfuryl alcohol were selected as reference substances for (levulinic acid + choline chloride) and (furfuryl alcohol + choline chloride) mixtures, respectively. The saturated vapour pressures of two reference substances were taken from literatures [42,43]. The pv of DES was calculated as the produce of following two parts, pv of reference substance and the evaporation rate ratio of DES to RS. The values of pv for two DESs are listed in Table 2. The absorbed CO2 (nCO2 ) was calculated by the following equation,
TABLE 2 Physical properties of the deep eutectic solvents studied (DESs) (expressed by mole ratio of levulinic acid or furfuryl alcohol to choline chloride, the same below): melting points (Tm, under p = 101.3 kPa), density (q, under p = 101.3 kPa) and saturated vapour pressure (pv) at different temperatures.a Solutions
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1 a
Tm/K
262.0 263.0 263.2 237.4 238.6 239.4
q/(g cm3)
pv/Pa
303.15
313.15
323.15
333.15
1.1346 1.1341 1.1337 1.1318 1.1315 1.1309
1.1276 1.1273 1.1270 1.1252 1.1243 1.1238
1.1209 1.1204 1.1202 1.1186 1.1171 1.1166
1.1138 1.1131 1.1130 1.1120 1.1099 1.1095
303.15
49 57 64
313.15
114 123 133
323.15
333.15
242 255 266
4.3 5.5 7.7 436 461 479
Standard uncertainties u are u(T) = 0.05 K, u(Tm) = 0.1 K, u(p) = 0.6 kPa, u(pv) = 1.0 Pa and the combined expanded uncertainty Uc is Uc(q) = 0.0008 g cm3 (0.95 level of confidence). The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
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nCO2 ¼ qg ðp1 ; TÞV GR qg ðp2 ; TÞV GR qg ðps ; TÞðV EC w=qDES Þ
ð2Þ
3. Results and discussion 3.1. Solubility of CO2 in the DESs
where qg ðpi ; TÞ denotes the density of CO2 in mol cm3 under pressure pi (i = 1, 2, s) and temperature T, and is obtained according to the reference [44]. VGR and VEC represent the volumes of GR and EC in cm3, respectively. qDES is the density of DES at experimental temperature in g cm3;the decrease of the DES’s density because of the CO2 solubility is very small and neglected. The mole fraction (xCO2 ) and molality (mCO2 ) of CO2 in the DESs mixture were calculated by the following equations,
xCO2 ¼ nCO2 =ðnCO2 þ nDES Þ
ð3Þ
mCO2 ¼ nCO2 =w
ð4Þ
The densities of the DESs at different temperatures under 101.3 kPa are listed in table 2. The densities of the mixtures of choline chloride and levulinic acid were slightly higher than those of choline chloride and furfuryl alcohol. The solubility of CO2 in the DESs was determined at temperatures ranging from (303.15 to 333.15) K in 10 K intervals and pressures up to 600.0 kPa. The mole ratios of levulinic acid (or furfuryl alcohol) to choline chloride were fixed at 3:1, 4:1 and 5:1. Values of the measured solubility of CO2 in the DESs (xCO2 , mole fraction; mCO2 , molality) at different temperatures (T) and partial pressure of CO2 (p) at the equilibrium state are listed in table 3. The measured solubility data of CO2 in 5:1 mole (levulinic acid + choline chloride) and (furfuryl alcohol + choline chloride) at four temperatures are plotted in figures 1 and 2, respectively. Figure 3 shows the solubilities of CO2 in levulinic acid (or furfuryl
where nCO2 is the mole number of CO2 absorbed in the DESs, nDES is the mole number of DES, and w is the mass of the used DES.
TABLE 3 Solubility of CO2 in the deep eutectic solvents (DESs) (xCO2 , mole fraction; mCO2 , molality) at different temperatures (T) and equilibrium pressure (p).a T = 303.15 K
a
313.15 K
323.15 K
p/kPa
xCO2
mCO2 /(mol kg1)
p/kPa
xCO2
mCO2 /(mol kg1)
0.0043 0.0111 0.0164 0.0215 0.0270 0.0302
0.0351 0.0919 0.1367 0.1800 0.2272 0.2549
69.8 202.5 306.8 410.9 508.5 579.8
0.0031 0.0090 0.0138 0.0182 0.0228 0.0259
nlevulinic 0.0255 0.0741 0.1146 0.1523 0.1914 0.2180
acid:
79.4 208.4 310.9 411.9 510.9 570.0
0.0039 0.0109 0.0167 0.0227 0.0281 0.0316
0.0321 0.0914 0.1402 0.1925 0.2396 0.2700
60.0 176.9 282.4 380.1 485.1 565.9
0.0029 0.0085 0.0135 0.0185 0.0231 0.0273
nlevulinic 0.0243 0.0712 0.1132 0.1562 0.1954 0.2319
acid:
72.5 201.2 305.3 410.6 508.4 574.9
0.0041 0.0112 0.0177 0.0237 0.0294 0.0333
0.0339 0.0944 0.1502 0.2023 0.2526 0.2869
73.1 200.1 308.4 412.2 511.4 573.7
0.0032 0.0096 0.0152 0.0200 0.0248 0.0281
nlevulinic 0.0271 0.0809 0.1282 0.1698 0.2115 0.2410
acid:
71.5 188.9 296.9 401.7 501.5 566.7
0.0029 0.0076 0.0114 0.0147 0.0179 0.0197
0.0263 0.0704 0.1060 0.1375 0.1676 0.1856
80.8 214.6 321.4 426.7 523.2 581.7
0.0024 0.0063 0.0095 0.0126 0.0155 0.0173
nfurfuryl 0.0217 0.0581 0.0881 0.1171 0.1454 0.1618
alcohol:
80.9 218.3 323.7 425.3 524.1 582.8
0.0032 0.0082 0.0126 0.0166 0.0205 0.0228
0.0306 0.0777 0.1195 0.1589 0.1964 0.2196
70.3 192.2 295.4 403.5 502.8 568.8
0.0025 0.0064 0.0099 0.0133 0.0165 0.0183
nfurfuryl 0.0232 0.0608 0.0941 0.1269 0.1571 0.1753
alcohol:
82.5 212.1 319.3 412.5 519.3 581.5
0.0031 0.0085 0.0125 0.0167 0.0207 0.0234
0.0300 0.0811 0.1201 0.1614 0.2015 0.2276
70.9 203.4 304.7 404.9 505.2 570.2
0.0025 0.0071 0.0106 0.0141 0.0176 0.0198
nfurfuryl 0.0237 0.0678 0.1024 0.1361 0.1707 0.1924
alcohol:
77.3 210.2 316.5 414.7 516.3 577.4
333.15 K mCO2 /(mol kg1)
p/kPa
xCO2
mCO2 /(mol kg1)
= 3:1 0.0027 0.0075 0.0113 0.0150 0.0186 0.0208
0.0221 0.0616 0.0934 0.1246 0.1553 0.1738
85.9 219.8 321.6 425.2 524.9 583.0
0.0025 0.0066 0.0102 0.0133 0.0163 0.0183
0.0205 0.0541 0.0841 0.1108 0.1359 0.1526
= 4:1 0.0032 0.0084 0.0125 0.0167 0.0205 0.0229
0.0266 0.0703 0.1050 0.1403 0.1731 0.1937
82.6 218.5 326.0 426.2 528.5 587.4
0.0024 0.0072 0.0103 0.0138 0.0168 0.0185
0.0201 0.0602 0.0859 0.1154 0.1414 0.1562
= 5:1 0.0030 0.0083 0.0128 0.0174 0.0213 0.0239
0.0254 0.0698 0.1084 0.1474 0.1817 0.2038
78.9 216.1 319.2 417.3 519.7 581.0
0.0027 0.0074 0.0110 0.0146 0.0179 0.0199
0.0225 0.0624 0.0923 0.1231 0.1522 0.1694
ncholine chloride = 3:1 81.5 0.0023 222.1 0.0056 329.6 0.0084 428.9 0.0110 528.6 0.0134 585.3 0.0148
0.0214 0.0518 0.0777 0.1024 0.1247 0.1383
86.3 224.4 330.3 430.4 530.6 586.4
0.0018 0.0047 0.0072 0.0095 0.0118 0.0129
0.0168 0.0438 0.0665 0.0883 0.1098 0.1208
ncholine chloride = 4:1 65.2 0.0021 188.1 0.0053 296.2 0.0085 399.3 0.0115 494.2 0.0143 565.8 0.0164
0.0173 0.0502 0.0805 0.1089 0.1362 0.1566
86.8 220.3 326.1 426.6 529.6 585.4
0.0022 0.0054 0.0080 0.0108 0.0131 0.0146
0.0203 0.0512 0.0757 0.1023 0.1250 0.1389
ncholine chloride = 5:1 71.3 0.0023 194.1 0.0061 301.0 0.0094 403.6 0.0126 502.8 0.0158 573.1 0.0180
0.0215 0.0579 0.0903 0.1219 0.1523 0.1743
74.9 204.2 315.2 409.6 511.7 577.2
0.0020 0.0054 0.0084 0.0111 0.0137 0.0154
0.0189 0.0517 0.0808 0.1064 0.1318 0.1486
p/kPa
ncholine
chloride
80.8 210.0 314.0 417.6 517.8 579.7 ncholine
chloride
83.0 219.6 321.1 423.5 523.8 584.2 ncholine
chloride
75.6 208.8 315.9 418.4 517.2 579.9
xCO2
Standard uncertainties u are u (T) = 0.05 K, u (p) = 0.6 kPa, ur (x) = 0.02, ur (m) = 0.02. The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
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M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
b
600
a
500
500
400
400 p/kPa
p/kPa
600
300
300
200
200
100
100
0 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 xCO 2
0 0.00
0.04
0.08
0.12 0.16 0.20 -1 mCO /mol.kg 2
0.24
0.28
FIGURE 1. Solubility of CO2 (a, mole fraction; b, molality) in deep eutectic solvents (DES) of levulinic acid and choline chloride (5:1 mole ratio) at different temperatures: 5, 303.15 K; h, 313.15 K; 4, 323.15 K; s, 333.15 K; —, linear fit.
a
500
500
400
400
300
300
200
200
100
100
0 0.000
b
600
p/kPa
p/kPa
600
0.005
0.010
0.015 xCO 2
0.020
0 0.00
0.025
0.04
0.08 0.12 0.16 -1 mCO /mol.kg 2
0.20
0.24
FIGURE 2. Solubility of CO2 (a, mole fraction; b, molality) in deep eutectic solvents (DES) of furfuryl alcohol and choline chloride (5:1 mole ratio) at different temperatures: }, 303.15 K; 4, 313.15 K; s, 323.15 K; 5, 333.15 K; —, linear fit.
600
3.2. Henry’s law constant
500
Henry’s law can be used to describe the physical solubility of gas in the solvents [45]. Therefore, Henry’s law constant Hx based on mole fraction was used to quantitatively express the solubility of CO2 in the DESs as following [46],
p/kPa
400 300
liq
f 2 ðp; T; x2 Þ ; x2 !0 x2
Hx ðp; TÞ lim
200
where Hx is Henry’s law constant based on mole fraction,
100 0 0.00
ð5Þ
liq
0.04
0.08
0.12 0.16 0.20 -1 mCO /mol.kg 2
0.24
0.28
FIGURE 3. Solubility of CO2 (molality) in deep eutectic solvents (DESs) of levulinic acid (or furfuryl alcohol) and choline chloride at T = 313.15 K: s, nlevulinic acid: ncholine chloride = 5:1; h, nlevulinic acid: ncholine chloride = 3:1; 4, nfurfuryl alcohol: ncholine chloride = 5:1; 5, nfurfuryl alcohol: ncholine chloride = 3:1; —, linear fit.
f 2 ðp; T; x2 Þ is the fugacity of CO2, p and x2 are the partial pressure at the equilibrium state and mole fraction of CO2 in the liquid phase, respectively. When it reached the (vapour + liquid) equilibrium state, the fugacity of CO2 in the liquid phase should be equal to that in the vapour phase. So, v ap
liq
f 2 ðp; T; x2 Þ ¼ f 2 ðp; T; y2 Þ ¼ y2 p/2 ðp; T; y2 Þ; v ap
alcohol) and choline chloride (3:1 and 5:1 mole ratio) at T = 313.15 K. It can be seen that the solubility of CO2 in the DESs increases linearly with pressure and decreases with increasing temperature. Moreover, the solubility of CO2 gets the highest in the mixture of levulinic acid and choline chloride (5:1 mole ratio). Such behaviour illustrates that the dissolution of CO2 in the DESs is believed to be a physical process.
ð6Þ
where f 2 ðp; T; y2 Þ is the fugacity of CO2 in the vapour phase, y2 and /2 are the mole fraction and fugacity coefficient of CO2 in the vapour phase, respectively. In this work, the vapour pressure of the DESs was very small at the experimental temperatures, thus the gas phase was supposed to be pure CO2 and y2 was approximately equal to unity. It was also supposed that the fugacity coefficient /2 of CO2 at relatively low pressure could be calculated using two-term Virial equation. Thus, in the very diluent region of CO2 in
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M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
liquid phase, Hx is expressed as following by the combination of equations (5) and (6), liq
f 2 ðp; T; x2 Þ p/ ðp; T; y2 Þ p/2 ðp; TÞ ¼ lim 2 ffi x2 !0 x2 !0 x2 x2 x2
Hx ðp; TÞ ¼ lim
ð7Þ
. Similarly, Henry’s law constant Hm based on molality can be defined as following,
"
# liq f 2 ðp; T; m2 Þ p/ ðp; TÞ Hm ðp; TÞ lim ffi 2 m2 !0 ðm2 =m0 Þ ðm2 =m0 Þ
ð8Þ
where m0 = 1 mol kg1, and m2 is the molality of CO2 in the liquid phase. In this work, Hx and Hm were obtained by calculating the linear slope of fugacity vs mole fraction and molality of CO2, respectively. These Henry’s law constants were given in table 4. It is evident that the solubility of CO2 in the DESs of levulinic acid and choline chloride is higher than that of furfuryl alcohol and choline chloride at the same temperature and mole ratio. It also revealed that the carboxyl group in levulinic acid was more powerful to capture CO2 than the hydroxyl group in furfuryl alcohol, which was in good agreement with the results reported by Li et al. [47]. Moreover, the solubility of CO2 in the DESs increased with the increasing mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride. For further evaluation of these renewable DESs as CO2 absorbents, Henry constants Hm at T = 313.15 K in present DESs were compared with those in other DESs and several ILs reported in the literature. As shown in table 5, values of the solubility of CO2 in the DESs studied are higher than those in the ammonium-based ILs [48], such as 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium lactate ([hhemel]) and 2-hydroxy-N-(2-hydroxyethyl)-Nmethylethanaminium acetate ([hhemea]), but slightly lower than those in the imidazolium ILs [49–51], including 1, 3-Dimethylimidazolium dimethylphosphate ([dmim][Me2PO4]), 1-Ethyl-3methylimidazolium diethylphosphate ([emim][Et2PO4]), 1-hexyl3-methylimidazolium tetrafluoroborate ([hmim][BF4]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]). Moreover, values of the solubility of CO2 in DESs are higher than those in dihydric alcohols (or lactic acid) and choline chloride [38,12], but lower than those in urea (or glycerol) and choline chloride [34,37,52]. These differences of the solubility demonstrate that the interactions between the groups in HBDs (with the exception of glycerol) and CO2 follow the sequence of amide > carbonyl group > ether bond > hydroxyl group.
Ddis H ¼ R½@ lnfHðT; pÞ=p g=@ð1=TÞp
ð10Þ
Ddis S ¼ ðV dis H V dis G Þ=T
ð11Þ
where DdisGo, DdisHo, DdisSo are the standard Gibbs free energy, dissolution enthalpy and dissolution entropy for CO2 in DESs under pressure po = 0.1 MPa, respectively. The DdisHo reflects the strength of interaction between CO2 and DESs, and DdisS0 means the order degree of intermolecular structure in the solution of CO2 and DESs. The DdisGo, DdisHo, and DdisSo at different temperatures under pressure po = 0.1 MPa are calculated and listed in table 6.
TABLE 5 Comparison of Hm in present deep eutectic solvents (DESs) with some ILs and other deep eutectic solvents (DESs) at T = 313.15 K.a
Ddis G ¼ RT lnfHðT; pÞ=p g
ð9Þ
Hm/MPa
[hhemel] [45] [hhemea] [45] [dmim][Me2PO4] [46] [emim][Et2PO4] [46] [hmim][BF4] [47] [bmim][Tf2N] [48] nCC:nurea = 1:2.5 [37] nCC:nurea = 1:2 [34] nCC:nglycerol = 1:2 [49] nCC:nethylene glycol = 1:2 [35] nCC:nlactic acid = 1:2 [12] nCC: n2,3-butanediol = 1:4 [38] nCC: n1,4-butanediol = 1:4 [38] nCC:n1,2-propanediol = 1:4 [38] nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1
5.38 4.65 2.35 1.84 1.81 1.06 1.37 1.29 1.70 2.71 4.00 3.44 4.18 4.43 2.62 2.41 2.35 3.54 3.14 2.91
a
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
TABLE 6 Calculated standard Gibbs free energy (DdisGo), enthalpy (DdisHo) and entropy (DdisSo) of solutions at 0.1 MPa and T = 303.15 K.a
3.3. Thermodynamic properties Thermodynamic properties are helpful for quantitative description of CO2 dissolution into DESs and design of capture process. Three thermodynamic properties can be calculated from the correlation of Henry’s law constants as following,
Solvents
Solutions
DdisGo/ (kJ mol1)
DdisHo/ (kJ mol1)
DdisS0/ (J mol1 K1)
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1
13.16 13.05 12.89 14.25 13.89 13.85
15.35 14.75 14.46 11.67 14.47 9.45
94.05 91.70 90.20 85.49 93.53 76.84
a
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
TABLE 4 Henry’s law constants (Hx, based on mole fraction; Hm, based on molality) of CO2 in the deep eutectic solvents (DESs) at different temperatures.a Solutions
nlevulinic acid: ncholine chloride = 3:1 nlevulinic acid: ncholine chloride = 4:1 nlevulinic acid: ncholine chloride = 5:1 nfurfuryl alcohol: ncholine chloride = 3:1 nfurfuryl alcohol: ncholine chloride = 4:1 nfurfuryl alcohol: ncholine chloride = 5:1 a
Hx/(MPa)
Hm/(MPa)
303.15 K
313.15 K
323.15 K
333.15 K
303.15 K
313.15 K
323.15 K
333.15 K
18.54 17.76 16.61 28.54 24.73 24.31
21.91 20.39 20.12 33.11 29.95 28.14
27.37 25.07 23.83 38.68 34.04 31.32
31.46 30.86 28.47 44.64 39.49 36.79
2.20 2.09 1.93 3.05 2.58 2.50
2.62 2.41 2.35 3.54 3.14 2.91
3.28 2.97 2.77 4.14 3.57 3.24
3.74 3.67 3.36 4.79 4.15 3.81
The standard uncertainty of mole ratio of levulinic acid or furfuryl alcohol to choline chloride is 0.001.
M. Lu et al. / J. Chem. Thermodynamics 88 (2015) 72–77
Under all conditions, the values of DdisHo are negative, meaning that the absorption of CO2 in DESs is exothermic and the intermolecular interaction of CO2 with DESs is strong. The negative values of DdisSo imply that a more ordered structure is obtained with the dissolution of CO2 into DESs. As a result, all the DdisGo show positive values, meaning the dissolution of CO2 into DESs is not spontaneous. 4. Conclusions New solubility results for CO2 in the renewable DESs composed of levulinic acid (or furfuryl alcohol) and choline chloride were reported over the temperature range (303.15 to 333.15) K in 10 K intervals and pressures up to 600.0 kPa. Standard Gibbs free energy, dissolution enthalpy and dissolution entropy were deduced from Henry’s law constant. Results indicated that the levulinic acid-based DESs have higher absorption capacity for CO2 than furfuryl alcohol-based ones. And the solubility of CO2 in the DESs increases with the increasing pressure as well as mole ratio of levulinic acid (or furfuryl alcohol) to choline chloride and decreased with increasing temperature. The dissolution of CO2 into DESs is not spontaneous. Acknowledgments The research was supported by the Natural Science Foundation of Zhejiang Province (Y4100699) and the National Natural Science Foundation of China (21476205). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jct.2015.04.021. References [1] H.Q. Yang, Z.H. Xu, M.H. Fan, R. Gupta, R.B. Slimane, A.E. Bland, I. Wright, J. Environ. Sci. 20 (2008) 14–27. [2] E.J. Maginn, J. Phys. Chem. Lett. 1 (2010) 3478–3479. [3] P.T. Anastas, M.M. Kirchhoff, Acc. Chem. Res. 35 (2002) 686–694. [4] J.D. Figueroa, T. Fout, S. Plasynski, H. McIlvried, R.D. Srivastava, Int. J. Greenhouse Gas Control 2 (2008) 9–20. [5] M.M. Taib, T. Murugesan, Chem. Eng. J. 181–182 (2012) 56–62. [6] D. Camper, J.E. Bara, D.L. Gin, R.D. Noble, Ind. Eng. Chem. 47 (2008) 8496–8498. [7] G.T. Rochelle, Science 325 (2009) 1652–1654. [8] M.L. Gray, Y. Soong, K.J. Champagne, H. Pennline, J.P. Baltrus, R.W. Stevens Jr, R. Khatri, S.S.C. Chuang, T. Filburn, Fuel Process. Technol. 86 (2005) 1449–1455. [9] C. Capello, U. Fischer, K. Hungerbühler, Green Chem. 9 (2007) 927–934. [10] J.E. Bara, D.E. Camper, D.L. Gin, R.D. Noble, Acc. Chem. Res. 43 (2010) 152–159. [11] G.N. Wang, W.L. Hou, F. Xiao, J. Geng, Y.T. Wu, Z.B. Zhang, J. Chem. Eng. Data 56 (2011) 1125–1133. [12] M. Francisco, A. Bruinhorsta, L.F. Zubeir, C.J. Peters, M.C. Kroon, Fluid Phase Equilib. 340 (2013) 77–84. [13] M. Francisco, A. Bruinhorst, M.C. Kroon, Angew. Chem. Int. Ed. 52 (2013) 3074– 3085.
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JCT 14-629