Article pubs.acs.org/jced
Liquid−Liquid Equilibria of Polyvinylpyrrolidone + Several Ammonium Salts + Water Aqueous Two-Phase Systems: Experimental and Correlation Yun Wang,*,† Yingchun Wu,† Liang Ni,† Juan Han,† Jingjing Ma,‡ and Yutao Hu† †
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, P. R. China School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, 2 Mengxi Road, Zhenjiang, 212003, P. R. China
‡
ABSTRACT: Phase equilibrium behaviors of polyvinylpyrrolidone (PVP) + (NH 4 ) 2 HPO 4 , (NH 4 ) 2 SO 4 , (NH 4 ) 2 CO 3 , (NH 4 ) 2 C 4 H 4 O 6 , and (NH4)2HC6H5O7 + H2O aqueous two-phase systems (ATPS's) were determined at 298.15 K. A series of common phase-forming ammonium salts and the corresponding anions were discussed. Meanwhile, the temperature effect on phase equilibrium behavior for PVP (K30) + (NH4)2HPO4 + H2O ATPS was investigated at (288.15, 298.15, and 308.15) K. It was found that phase-forming abilities of the salts are in the order: (NH4)2HPO4 > (NH4)2SO4 > (NH4)2C4H4O6 > (NH4)2HC6H5O7 > (NH4)2CO3. Furthermore, a third-order polynomial equation was used to correlate the binodal data, while a simple two-parameter equation along with the Othmer−Tobias and Bancroft equations was used to correlate the tie-lines data. All equations used above were proved to be valid for the experimental data. At last, the data of critical points were obtained by an extrapolation method.
1. INTRODUCTION The aqueous two-phase system (ATPS), which can be formed by adding either two different hydrophilic polymers or one polymer with one salt under specific thermodynamic conditions, has been utilized as a favored method in many industries like biotechnology and biochemistry. It has been proved to be efficient, especially for the separation and purification of large biomolecules as proteins, enzymes, and nucleic acids over the past few decades.1−3 For many years, poly(ethylene glycol) (PEG), a hydrophilic polymer that can form a two-phase system with a suitable polymer or a salt, has been often used in two-phase partitioning studies.4−7 Recently, it was another water-soluble polymer, polyvinylpyrrolidone (PVP), which can be used as PEG for the separation of biomolecules, that has aroused the interests of researchers. Zafarani-Moattar and co-workers8−11 have reported the liquid−liquid equilibrium (LLE) data of PVP (K12) + K3PO4, K2HPO4, and NaH2PO4 + H2O and PVP (K15) + Na3PO4, Na2HPO4, K2C4H4O6, and K2C2O4 + H2O ATPS's. Other systems like PVP (K15) + K3C6H5O7, NaCO3, Na2SO4, Na2C2O4, and MgSO4 + H2O, PVP (K15) + K2HPO4, KH2PO4, (NH4)2HPO4, and (NH4)H2PO4 + H2O, and PVP (K17, K30, and K90) + Na2SO4 + H2O have also been published in previous papers.12−17 PVP is an alternative, inexpensive, and stable polymer. It has great potential for aqueous two-phase extraction (ATPE). A previous work about equilibrium phase behaviors composed of PVP with salt systems17 has revealed that, on one hand, © 2012 American Chemical Society
increasing the polymer weights results in an increase of the twophase area, while on the other hand, increasing the polymer weights causes higher viscosity of the polymer-rich phase which will be an disadvantage for the phase separation. In our present work, the intermediate molecular weight PVP (K30) was chosen as the research polymer. Due to the current lack of the compelling information about equilibrium phase behaviors composed of PVP with ammonium salts, here, the binodal data and tie-line data of PVP (K30) with several ammonium salts including common organic and inorganic electrolytes were reported for the first time as far as we know. To evaluate the influence of temperature on the liquid−liquid equilibrium behavior, PVP (K30) with (NH4)2HPO4 at (288.15, 298.15, and 308.15) K ATPS's were studied. Additionally, a third-order polynomial equation and a simple two-parameter equation together with Othmer−Tobias and Bancroft equations were applied to the correlation of the binodal data and tie-line data for the investigated systems, respectively. Finally, to verify the dependability of the calculated method in estimating the critical points, we have made a comparison between the experimental and the calculated critical point of the PVP + (NH4 ) 2 HPO 4 , (NH4)2SO4, and (NH4)2C4H4O6 + H2O systems. Received: July 4, 2012 Accepted: October 3, 2012 Published: October 12, 2012 3128
dx.doi.org/10.1021/je300740g | J. Chem. Eng. Data 2012, 57, 3128−3135
Journal of Chemical & Engineering Data
Article
2. EXPERIMENTAL SECTION 2.1. Chemicals. PVP (K30, average MW = 60 000, 95 %, moisture content < 5.0 % by mass fraction), (NH4)2HPO4,
99 %, and 40 % (calculated by NH3) minimum mass fraction, respectively. The PVP and salts were used as received, without any further purification. Double-distilled and deionized water was used for the preparation and dilution of solutions. 2.2. Apparatus and Procedure. The experimental apparatus employed is essentially similar to the one used previously.10,18 In this work, a titration method was carried out for the determination of the binodal curves. Small amounts of salt solution with known concentration were filled into a glass vessel (50 mL) which contains PVP (K30) solution. Until the mixture became turbid, water was added to make the solution clear again. Step by step, the procedure above was repeated. An electronic analytical balance (FA1104B, Shanghai Yueping Instrument Co., Ltd., China) with an accuracy of ± 0.0001 g is needed for the calculation of the mixture composition by mass. The system temperature was controlled to within ± 0.1 K by
Table 1. Parameter Values of eq 1 for Each ATPS at 298.15 K a0
a1
a2
1.3325
0.1805
0.1829 0.1929 0.1660 0.1916 0.1822
system PVP PVP PVP PVP PVP
(K30) (K30) (K30) (K30) (K30)
+ + + + +
(NH4)2C4H4O6 + H2O (NH4)2HPO4 + H2O (NH4)2SO4 + H2O (NH4)2HC6H5O7 + H2O (NH4)2CO3 + H2O
(NH 4 ) 2 SO 4 , (NH 4 ) 2 C 4 H 4 O 6 , (NH 4 ) 2 HC 6 H 5 O 7 , and (NH4)2CO3 were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) with 99 %, 99 %, 99 %,
Table 2. Binodal Data as Mass Fraction for PVP (w1) + Salt (w2) + Water ATPS'sa w1
a
w2
w1
w2
0.1049 0.1081 0.1114 0.1136 0.1167
0.2453 0.2339 0.2226 0.2138 0.2016
0.1194 0.1220 0.1243 0.1321 0.1337
0.1933 0.1845 0.1764 0.1472 0.1381
0.0303 0.0362 0.0423 0.0474
0.3466 0.3121 0.2834 0.2576
0.0522 0.0562 0.0607 0.0650
0.2374 0.2186 0.1996 0.1778
0.0308 0.0335 0.0390 0.0433 0.0474 0.0533
0.3428 0.3206 0.2890 0.2669 0.2473 0.2191
0.0595 0.0623 0.0678 0.0723 0.0772 0.0801
0.1876 0.1723 0.1490 0.1252 0.0988 0.0873
0.0272 0.0308 0.0369 0.0399 0.0433
0.3675 0.3357 0.3029 0.2825 0.2627
0.046 0.0497 0.0517 0.0560 0.0580
0.2448 0.2281 0.2128 0.1970 0.1813
0.0460 0.0494 0.0579 0.0615 0.0653
0.3185 0.2862 0.2536 0.2305 0.2109
0.0671 0.0709 0.0769 0.0793 0.0833
0.1962 0.1824 0.1503 0.1339 0.1187
0.1854 0.1892 0.1970 0.2011
0.1774 0.1666 0.1478 0.1333
0.2055 0.2096 0.2147 0.2197
0.1208 0.1098 0.0956 0.0835
0.1177 0.1213 0.1278 0.1338
0.2787 0.2601 0.2368 0.2134
0.1372 0.1411 0.1435 0.1467
0.1955 0.1797 0.1679 0.1472
w1
w2
w1
w2
PVP + (NH4)2C4H4O6 + H2O System at 298.15 K 0.1353 0.1303 0.1485 0.0892 0.1377 0.1216 0.1510 0.0820 0.1400 0.1133 0.1540 0.0713 0.1423 0.1064 0.1567 0.0620 0.1457 0.0967 0.1614 0.0488 PVP + (NH4)2HPO4 + H2O System at 288.15 K 0.0680 0.1588 0.0841 0.0828 0.0718 0.1410 0.0864 0.0739 0.0762 0.1239 0.0906 0.0573 0.0799 0.1039 0.0984 0.0318 PVP + (NH4)2HPO4 + H2O System at 298.15 K 0.0818 0.0823 0.0951 0.0244 0.0841 0.0711 0.0967 0.0202 0.0869 0.0586 0.0996 0.0079 0.0889 0.0513 0.0995 0.0073 0.0918 0.0417 0.1027 0.0030 0.0937 0.0344 0.1056 0.0015 PVP + (NH4)2HPO4 + H2O System at 308.15 K 0.0608 0.1677 0.0744 0.0936 0.0625 0.1555 0.0786 0.0756 0.0643 0.1449 0.0827 0.0567 0.0672 0.1328 0.0870 0.0435 0.0703 0.1122 0.0936 0.0152 PVP + (NH4)2SO4 + H2O System at 298.15 K 0.0901 0.0924 0.1054 0.0207 0.0929 0.0732 0.1110 0.0091 0.0954 0.0628 0.1149 0.0029 0.0974 0.0551 0.1186 0.0020 0.1023 0.0362 0.1186 0.0016 PVP + (NH4)2HC6H5O7 + H2O System at 298.15 K 0.2241 0.0727 0.2415 0.0410 0.2279 0.0638 0.2455 0.0349 0.2326 0.0554 0.2529 0.0249 0.2369 0.0482 0.2627 0.0127 PVP + (NH4)2CO3 + H2O System at 298.15 K 0.1508 0.1295 0.1667 0.0523 0.1553 0.1070 0.1701 0.0433 0.1591 0.0903 0.1720 0.0345 0.1633 0.0678 0.1740 0.0275
w1
w2
w1
w2
0.1654 0.1733 0.1763 0.1796 0.1824
0.0399 0.0181 0.0091 0.0034 0.0023
0.1880
0.0012
0.1070 0.1100 0.1129 0.1179
0.0090 0.0041 0.0014 0.0007
0.1222 0.1252 0.1296 0.1343
0.0003 0.0002 0.0001 0.0001
0.1062 0.1106 0.1141 0.1161 0.1217 0.1230
0.0012 0.0008 0.0004 0.0003 0.0002 0.0001
0.0954 0.0982 0.1028 0.1048 0.1078
0.0077 0.0035 0.0018 0.0012 0.0008
0.1105 0.1182
0.0002 0.0001
0.1194 0.1230 0.1233 0.1273 0.1283
0.0012 0.0008 0.0006 0.0003 0.0003
0.1313 0.1360 0.1402
0.0002 0.0002 0.0001
0.2654 0.2662 0.2693 0.2719
0.0082 0.0073 0.0043 0.0032
0.2744 0.2890 0.2929 0.2957
0.0022 0.0006 0.0003 0.0002
0.1772 0.1784 0.1799 0.1856
0.0176 0.0134 0.0100 0.0017
0.1909 0.1953 0.2009
0.0005 0.0001 0.0001
Standard uncertainties u are u(mass fraction) = 0.002, u(T) = 0.1 K. 3129
dx.doi.org/10.1021/je300740g | J. Chem. Eng. Data 2012, 57, 3128−3135
Journal of Chemical & Engineering Data
Article
using a thermostat water bath (DF-101S, Yu Hua Instrument Co., Ltd., China). To determine the tie-lines, about 10 g of feed samples was prepared by mixing appropriate amounts of PVP (K30), salt, and water in the 10 mL centrifugal tube. After sufficient mixing, the solution was centrifuged at 2000 rpm for 20 min. Then, the sample was allowed to settle at 298.15 K for 10 h. After complete phase separation, samples of both phases were carefully collected with a syringe and weighed with the electronic analytical balance. The PVP (K30) concentration in both phases was determined by refractive index measurements performed at 298.15 K using a refractometer (2W AB0003, Guiyang Xintian Optoelectronics Technology Co., Ltd. China), of which precision is ± 0.0003. The relation between the refractive index, n, and the mass fractions of polymer, w1, and salt, w2, is given by literature9,19 as follows: n = a0 + a1w1 + a 2w2 (1)
Figure 1. Binodal curves for the investigated systems: PVP + several ammonium salts + water ATPS's at 298.15 K. □, (NH4)2C4H4O6; ○, (NH4)2HPO4; ▼, (NH4)2SO4; ●, (NH4)2HC6H5O7; ▽, (NH4)2CO3.
The values of coefficients a0, a1, and a2 for the applied systems are given in Table 1. a0 stands for the refractive index of pure water (w1 = 0 % and w2 = 0 %) at 298.15 K. a1 stands for the refractive index coefficient of PVP solution which is determined only by the concentration of the PVP solution (w2 = 0 %) at 298.15 K. While a2 is the refractive index coefficient of salt solution which is determined only by the concentration of salt solution (w1 = 0 %) at 298.15 K. For different salt systems, a0 and a1 remain unchanged. a0 and a1 in Table 1 are for all systems investigated. However, it should be pointed out that the equation mentioned above is only valid with mass fractions of w1 ≤ 10 % and w2 ≤ 5 %, for which linear standard curves of the solution refractive index versus polymer and salt concentration are obtained. The salt concentration in both phases was evaluated by a conductivity meter (DDS-11A, Shanghai Dapu Instrument Co., Ltd., China), and calibration curves of salt concentration against conductivity were acquired with salt concentrations ranging from (0 to 3) % (w/w). It should be noted that the salt solution shows nearly the same conductivity in water compared with that in the diluted polymer solution only when the salt concentration is in the range of (0 to 3) % (w/w). So, before the refractive index and electrical conductivity measurements, the samples should be diluted to the mass fraction range (w1 ≤ 10 and w2 ≤ 3) % mentioned above. The precision of PVP (K30) (mass fraction) was better than ± 0.002 as reported previously,19 while the maximum uncertainty of salt (mass fraction) was less than 0.002. A system was prepared according to the composition of the point which is close to the calculated critical point on the binodal curve. A little of PVP (K30) solution was added to make the system turn cloudy. Small amounts of water was filled to make it clear again, and then a little high concentration of salt solution was added in. The procedure above was repeated for several times. The mixture was allowed to settle at 298.15 K until the phase separation is complete. If the volume of the top phase is approximately equal to that of the bottom phase, the composition point can be determined to the critical point. An electronic analytical balance with an accuracy of ± 0.0001 g is needed for the calculation of the mixture composition by mass.
Figure 2. Temperature effect for the PVP + (NH4)2HPO4 + H2O system determined at ■, 288.15; ●, 298.15, and ▲, 308.15 K.
systems investigated at 298.15 K are given in Table 2. The phase diagrams of investigated systems are shown in Figure 1. As can be seen from Figure 1, the salting-out ability in forming an ATPS for the investigated salts can be arranged as: (NH 4 ) 2 HPO 4 > (NH 4 ) 2 SO 4 > (NH 4 ) 2 C 4 H 4 O 6 > (NH4)2HC6H5O7 > (NH4)2CO3. Since the salts above share the same cation (NH4+), the effects of anions for these salts on forming an ATPS can be arranged as HPO42− > SO42− > C4H4O62− > HC6H5O72− > CO32−. It seems that the salting-out strength of the inorganic anions (HPO42− and SO42−) is larger than that of the organic anions (C4H4O62− and HC6H5O72−) except CO32−. In other words, the inorganic salts seem to be easier to form an ATPS than the organic salts. As described in the literature, the salting-out ability of the anions can be related to their Gibbs free energy of hydration (ΔGhyd), and it seems that better salting-out of polymer is observed when the anions of the salt have a more negative ΔGhyd value.10,20,21 The ΔGhyd value of the several anions which were reported in the previous literature were arranged as follows: ΔGhyd(HPO42−) = −1789 kJ·mol−1 < ΔGhyd(CO32−) = −1315 kJ·mol−1 < ΔGhyd(C4H4O62−) = −1090 kJ·mol−1
