Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 63
64 Chapter 3 Ionic Liquids as an Extraction Media in Ternary Systems
[TDTHP][Phosph]+Butanol H2O
C3H7-CH2-OH
Figure 3.9: Extract phase1H NMR spectra for the system: [TDTHP][Phosph] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
C3H7-CH2-OH
[TDTHP][DCA]+Butanol
H2O
Figure 3.10: Extract phase 1H NMR spectra for the system: [TDTHP][DCA] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
Chapter 3 Ionic Liquids as an Extraction Media in Ternary Systems 65
[TDTHP][DEC]+Butanol
C3H7-CH2-OH
H2O
Figure 3.11: Extract phase 1H NMR spectra for the system: [TDTHP][DEC] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
H2O
C3H7-CH2- OH
[TDTHP][Phosph]+Butanol
66 Chapter 3 Ionic Liquids as an Extraction Media in Ternary Systems
C3H7-CH2-OH H2O
[TDTHP][DCA]+Butanol
Figure 3.13: Raffinate phase1H NMR spectra for the system: [TDTHP][DCA] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
[TDTHP][DEC]+Butanol H2O
C3H7-CH2-OH
Figure 3.14: Raffinate phase1H NMR spectra for the system: [TDTHP][DEC] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 67 were labelled [110] as 0.79-0.85 (m, 12 H), 1.2-1.3 (m, 32 H), 1.4-1.5 (m, 16 H); and 2-2.3 (m, 8 H), 0.79-0.96 (m, 15 H), 1.2-1.3 (m, 46 H), 1.4-1.5 (m, 16 H) and 2-2.3 (m, 10 H) ppm respectively (Figs. 3.10-3.11, 3.13-3.14). Thus for the estimation of mole fraction, 48 hydrogen atoms of [TDTHP][DCA] and 62 hydrogen atoms of [TDTHP][DEC] all lying in the range of 1.2-1.5 ppm were taken as reference peaks. The uncertainty of the mole fraction measurements has been conducted in a similar manner as performed for aliphatic-aromatic separation. For both phases, the uncertainty obtained in mole fraction composition was±0.001.
3.4.2 Results and Discussions
Experimental ternary data for four systems namely [TDTHP][Phosph] (1)- 1-propanol (2) - water (3), [TDTHP][Phosph] (1)- 1-butanol (2) - water (3), [TDTHP][DCA] (1)- 1-butanol (2) - water (3) and [TDTHP][DEC] (1)- 1-butanol (2) - water (3) were measured at 298.15 K and 1 atm (Tables 3.5-3.8and Figs.3.15-3.18). The extraction effectiveness are represented by distribution coefficient (β) and Selectivity (S) for equilibrium biphasic systems. Eqs. 3.2-3.3can be rewritten as,
S= xEb xRb xEw
xRw (3.2)
β= xEb
xRb
eq
(3.3)
Here, xb and xw are the molefraction of butanol and water, respectively.
Large value of distribution coefficient is desirable since it indicates lesser solvent
68 Chapter 3 Ionic Liquids as an Extraction Media in Ternary Systems Table 3.5: Experimental tie line data for the system [TDTHP][Phosph] (1) -
1-Propanol (2) - Water (3) atT=298.15 K andp=1 atm.
Sr.
No.
Extract Phase Raffinate Phase Distribution coefficient (β)
Selectivity xIL xp xw xIL xp xw (S)
1 0.353 0.448 0.199 0.000 0.028 0.972 16.000 78.151 2 0.418 0.388 0.194 0.000 0.014 0.986 27.714 140.857 3 0.189 0.63 0.181 0.000 0.038 0.962 16.579 88.116 4 0.063 0.744 0.193 0.000 0.067 0.933 11.104 53.681 5 0.275 0.531 0.194 0.000 0.03 0.97 17.700 88.500 6 0.517 0.297 0.186 0.000 0.009 0.991 33.000 175.823 7 0.65 0.179 0.171 0.000 0.008 0.992 22.375 129.801 8 0.685 0.144 0.172 0.000 0.003 0.997 48.000 278.233 Table 3.6: Experimental tie line data for the system [TDTHP][Phosph] (1) -
1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
Sr.
No.
Extract Phase Raffinate Phase Distribution coefficient (β)
Selectivity xIL xb xw xIL xb xw (S)
1 0.672 0.151 0.177 0.000 0.000 1.000 - -
2 0.568 0.276 0.156 0.000 0.007 0.993 39.429 250.978 3 0.403 0.415 0.182 0.000 0.007 0.993 59.286 323.465 4 0.341 0.456 0.203 0.000 0.008 0.992 57.000 278.542 5 0.289 0.503 0.208 0.000 0.011 0.989 45.727 217.424 6 0.251 0.541 0.208 0.000 0.026 0.974 20.808 97.436 7 0.16 0.612 0.228 0.000 0.032 0.968 19.125 81.197 8 0.092 0.724 0.184 0.000 0.038 0.962 19.053 99.612
Chapter 3 Ionic Liquids as an Extraction Media in Ternary Systems 69 Table 3.7: Experimental tie line data for [TDTHP][DCA] (1) - 1-Butanol (2) - Water
(3) atT=298.15 K andp=1 atm.
Sr.
No.
Extract Phase Raffinate Phase Distribution coefficient (β)
xIL xb xw xIL xb xw
1 0.631 0.369 0.000 0.000 0.000 1.000 - 2 0.250 0.750 0.000 0.000 0.011 0.989 68.182 3 0.167 0.833 0.000 0.000 0.013 0.987 64.077 4 0.055 0.945 0.000 0.000 0.017 0.983 55.588 5 0.093 0.907 0.000 0.001 0.037 0.962 24.514 6 0.731 0.269 0.000 0.000 0.000 1.000 - 7 0.523 0.477 0.000 0.000 0.005 0.995 95.400 8 0.355 0.645 0.000 0.000 0.009 0.991 71.667
Table 3.8: Experimental tie line data for [TDTHP][DEC] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
Sr.
No.
Extract Phase Raffinate Phase Distribution coefficient (β) xIL xb xw xIL xb xw
1 0.524 0.476 0 0.000 0.003 0.997 158.667 2 0.249 0.751 0 0.001 0.007 0.992 107.286 3 0.104 0.896 0 0.001 0.045 0.954 19.911 4 0.065 0.935 0 0.001 0.054 0.945 17.315 5 0.69 0.31 0 0.001 0.002 0.997 155.000 6 0.376 0.624 0 0.001 0.006 0.993 104.000 7 0.296 0.704 0 0.000 0.007 0.993 100.571
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 70
Figure 3.15: Experimental tie lines for the system: [TDTHP][Phosph] (1) - 1-Propanol (2) - Water (3) atT=298.15 K and p=1 atm.
distribution coefficient for butanol extraction (19-59) than propanol recovery (11-48) (Tables 3.5-3.6). This is due to the higher polarity of propanol as compared to butanol resulting in more solubility in water. The distribution coefficient varied in the range of 25-95 and 17-173 for ternary systems namely [TDTHP][DCA]
and [TDTHP][DEC] respectively (Tables 3.7-3.8). These values are much higher than 0.7-2.2 as obtained by Ha et al. [21] for different imidazolium based ILs containing tetrafluoroborate, trifluoromethanesulfonate, hexafluorophosphate, and bis(trifluoromethylsulfonyl)imide anions. Further the positive sloping of the tie lines indicate butanol favorably partitions into the IL phase (Figs. 3.16-3.18).
The distribution coefficient for [TDTHP][DCA] is twice as compared to the ILs reported by Nann et al. [49] that is, 1-decyl-3-methylimidazolium, tetracyanoborate
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 71
Figure 3.16: Experimental tie lines for the system: [TDTHP][Phosph] (1) - 1-Butanol (2) - Water (3) atT=298.15 K and p=1 atm.
([Im10.1][TCB]), 4-decyl-4-methylmorpholinium tetracyanoborate ([Mo10.1][TCB]), 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl) ([Im10.1][Tf2N]), and 4-decyl-4-methylmorpholinium bis-(trifluoromethylsulfonyl)imide ([Mo10.1][Tf2N]).
Further it was also observed that the distribution coefficients for [TDTHP][Phosph]
and [TDTHP][DEC] are twelve and seven times respectively higher as compared to the same IL’s [49]. Thus we can conclude that [TDTHP][Phosph] and [TDTHP][DEC] more favorably extract butanol from aqueous streams. The distribution coefficient for the present three systems are compared with literature data [49] in Fig.3.19.
It should be noted that the ternary diagram is wider than that obtained in case of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by Chapeaux et al. [23].
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 72
Figure 3.17: Experimental tie lines for the system: [TDTHP][DCA] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
the solvent requirement or the solvent-feed ratio will be less as compared to imidazolium based ILs for a particular degree of separation.
Selectivity is the ability to separate 1-butanol from water. Higher values of selectivity indicate better selective separation of 1-butanol. For ternary system containing [TDTHP][Phosph], the mole fraction of butanol in raffinate phase is very low resulting in higher selectivity (Table 3.6). For the other two systems, the molefraction of water in extract phase is nearly zero, hence selectivity approaches infinity as per Eq.3.2. Also Tables 3.7-3.8 and Figs. 3.17-3.18 represent negligible concentration of IL and water in either phase. It implies [TDTHP][DCA] and [TDTHP][DEC] are completely immiscible with water in ternary system. This confirms the findings of Cascon and Choudhary [111] for the IL: [TDTHP][DCA] where SILM-based pervaporation of 1-butanol indicated
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 73
Figure 3.18: Experimental tie lines for the system: [TDTHP][DEC] (1) - 1-Butanol (2) - Water (3) atT=298.15 K andp=1 atm.
high affinity for the alcohol. This is due to the strong hydrogen bonding between the dicyanamide anion and 1-butanol. Hydrogen bond energy [112] between dicyanamide ion with butanol (60.8 kJ/mole) is more as compared to that with water (53.9 kJ/mole).
This is contrary to the measurements by Freire et al. [17] where [TDTHP][DCA] and [TDTHP][DEC] were found to be more miscible with water. However hydrogen bond between the anions and butanol alters the miscibility of the ILs with butanol and water.
It can be seen from Figs.3.16-3.18that the amount of water content in [TDTHP][Phosph]
is more as compared to [TDTHP][DCA] and [TDTHP][DEC]. This is attributed to the more electronegative atoms (1 Phosphorous and 2 Oxygen atoms) in [Phosph]
anion thereby forming a strong bond with water [112]. In the subsequent section, the
Chapter3: Ionic Liquids as an Extraction Media in Ternary Systems 74
Figure 3.19: Comparison of Distribution Coefficient with imidazolium based cations at ambient conditions
based COSMO-SAC model.