1227
Ind. Eng. Chem. Res. 1992,31,1227-1231 Rard, J. A.; Miller, D. G. Isopiestic Determination of the Osmotic and Activity Coefficients of ZnClz at 298.15 K. J. Chem. Thermodyn. 1989,21,463-482. Sato, T.; Nakamura, T. The Stability Constants of the Aqueous Chloro-Complexesof Divalent Zinc, Cadmium and Mercury Determined by Solvent Extraction with Tri-n-octylphosphineOxide. Hydrometallurgy 1980,6, 3-12. Silvester, L.F.; Pitzer, K. S. Thermodynamics of Electrolytes. VIII. High Temperature Properties, Including Enthalpy and Heat Capacity, with Application to Sodium Chloride. J. Phys. Chen. 1977,81, 1822-1828. Silvester, L. F.; Pitzer, K. S. Thermodynamics of Electrolytes. X.
Enthalpy and the Effect of Temperature on the Activity Coefficients. J. Solution Chem. 1978, 7 (5), 327-337. Tanaka, M. Modelling of Solvent Extraction Equilibria of Copper(I1) from Nitric and Hydrochloric Acid Solutions with &Hydroxyoxime. Hydrometallurgy 1990,24, 317-331. Yamada, E.; Nakayama, E.; Kuwamoto, T.; Fujinaga, T. A. Thermodynamic Study of the Synergistic Solvent Extraction of a Series of Zinc(I1) and Cadmium(I1) Complexes. Bull. Chem. SOC. Jpn. 1982,55 (lo), 3155-3159. Received for review October 10, 1991 Accepted December 19, 1991
Solvent Effects on the Hydration of Cyclohexene Catalyzed by a Strong Acid Ion Exchange Resin. 1. Solubility of Cyclohexene in Aqueous Sulfolane Mixtures Henk-Jan Panneman and Antonie A. C. M. Beenackers* Department of Chemical Engineering, State University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
The solubility of cyclohexene in different water-sulfolane mixtures was measured between 313 and 413 K. The results demonstrate a sharp increase of the solubility of cyclohexene with increasing percentages of sulfolane in the solvent mixture. Without sulfolane the increase of the solubility with temperature is higher than in mixtures with sulfolane. From thermodynamic calculations, using UNIFAC to predict the activity coefficients of all components, the solubility of cyclohexene in various mixtures and a t different temperatures could be computed. The experimental and computed solubilities are of comparable magnitude and show the same temperature and mixture-composition dependence. The solubility of cyclohexene in a mixture of 90 mol 9% sulfolane and 10 mol 9% water is, depending on the temperature, between 100 and 200 times higher than in pure water.
Introduction The direct hydration of alkenes catalyzed by a macroporous strong acid ion exchange resin is a simple and cheap process for producing alcohols. A disadvantage is the low mutual solubility of alkenes and water. A possible alternative is the use of an organic cosolvent, which gives a single liquid phase and a greatly improved solubility of alkenes in the solvent mixture. For the conditions that have to be satisfied for a proper cosolvent see part 3 (Panneman and Beenackers, 1992). Addition of a cosolvent will not only increase the solubility of the alkene in the reaction mixture but also change the equilibrium conversion, the reaction rate constant, and the activity of the ion exchange resin. We have studied the hydration of cyclohexene and used sulfolane as a cosolvent. In this contribution, we present both experimentally measured and theoretically predicted solubilities of cyclohexene in solvent mixtures of water and sulfolane at various temperatures. Such data are necessary for designing a process for the synthesis of cyclohexanol from cyclohexene with sulfolane as a cosolvent. The solubility of cyclohexene in water at room temperature is 0.003 km01.m-~(McAuliffe, 1966). As far as the authors know, no literature data are available for the solubility of cyclohexene in water-sulfolane mixtures. Mixtures of cyclohexene with water or water-sulfolane are far from ideal, and as a consequence predicted solubilities, which can be obtained from thermodynamic models, are highly uncertain. In this paper experimentally obtained solubilities of cyclohexene are compared with predicted solubilities, calculated with UNIFAC. Experimental Section A dynamic method was applied to measure the solubility of cyclohexene as a function of solvent composition. A
schematic representation of the equipment used is given in Figure 1. The feed liquids, cyclohexene and a watersulfolane mixture, were stored in two displacement pumps (Model 314 ISCO pumps) with a maximum flow rate of 5.56 X m 3 d (200 mL-h-'). The flow rate could be adjusted a t any level below the maximum value. During an experiment, the two liquid feed streams were continuously fed to a static mixer (i.d. = 3 X m; L = 4 m; filled with glass beads, d = 0.25 X m) immersed in a thermostatic oil batk. As shown in the Appendix, conditions in the mixer were such that at the mixer outlet phase equilibrium was established. The two-phase stream leaving that mixer was fed to a separator, also immersed in the oil bath. This separator could be considered as a pair of communicating vessels, interconnected both at the top and the bottom. The two-phase stream entered the first vessel in the middle. The light and heavy phases passed through the top and bottom connections, respectively. Here, continuous sample streams could be withdrawn from either the light or the heavy phase and directed to a liquid injection valve of a gas-liquid chromatograph. The sample tubes were electrically heated to prevent phase separation. A needle valve behind the injection valve kept the sample stream at pressure. The analysis of the samples is described elsewhere (Panneman and Beenackers, 1992; Marsman et al., 1988). The two-phase stream from the second vessel of the separator left the system via a back-pressure valve, which kept the total pressure in the system at 2 MPa.
Results The solubility of cyclohexene has been measured in various mixtures of sulfolane and water at temperatures between 313 and 413 K and a pressure of 2 MPa. The water-sulfolane ratio is influenced by the amount of sul-
088S-5885/92/2631-1227$03.QO/O0 1992 American Chemical Society
1228 Ind. Eng. Chem. Res., Vol. 31, No. 4, 1992
k+,
4,
GLC
lo-31 ' I 2.3 2.5
SULFOLANE
Table I. Solubility Parameters and the Solubilities of Cyclohexene in Different Aqueous Sulfolane Solutions at 313 and 413 K, D = 2 MPa SO,
I
27
'
'
29
'
'
I
3.1
1
3.3
1000/T (K-')
Figure 1. Schematic representation of the equipment used for the measurements of the solubility of cyclohexene: (1,2)displacement pumps; (3)static mixer; (4)phase separator; (5)back-pressure valve; (6,7)sample streams.
mol % sulfolane 0 40 60 80 90 100
'
AH89
kmol~m-~ kJ-mol-l 0.54 11.6 5.3 3.08 8.90 6.6 7.2 16.93 12.86 5.7 6.2 17.55
s, kmol~m-~ T = 313 K T = 413 K 0.006 0.018 0.36 0.66 1.30 0.62 0.92 2.08 2.45 1.29 1.44 2.90
folane dissolved in the cyclohexene phase. The flow rate of cyclohexene was adjusted to the water-sulfolane ratio so that the excess of the light phase, after phase equilibrium was reached, was always small. The total mass flow and the composition of both feeds were accurately known. The equilibrium composition of both the heavy and the light phases were experimentally determined. With these data the total mass flow of the heavy and light phase could be computed and the sum could be compared with the total mass flow of the feed. In all experiments the deviation between both quantities was less then 3%. The results are shown in Figure 2. The solubility increases with increasing temperature and percentage of sulfolane in the mixture. The temperature dependence of the solubility, s, is represented by s = so exp(-AHJR!!")
(1)
The calculated values of so and -AH8 are given in Table I. The enthalpy of dissolution (A",) for cyclohexene in sulfolane-water mixtures is approximately 4 kJ-mol-'; the value in water is -12 kJ-mol-'. The dissolution of cyclohexene is an endothermic process. From Figure 2 and Table I, it is clear that addition of 90 mol % sulfolane leads to an increase of the solubility of cyclohexene by typically 2 orders of magnitude. For a more general usage it would be preferred if it was posaible to estimate the solubility of cyclohexene in every possible water-sulfolane mixture and at every temperature. One possibility is to correlate the experimental data with a well-known solubility model. The second possibility is to use a completely predictive model. We tried to correlate our experimental data with multicomponent Henry's law (Prausnitz et al., 1986). However, to get a good correlation for all mixture compositions, the water-sulfolane interaction parameter, which is normally solute independent, varies with a factor of 2. This will be caused by the very different natures of water and sulfolane,
o water 40 mol% sulfolane o 60 mol% sulfolane 0 80 mol% sulfolane 90 mol% sulfolane v sulfolane
A
Figure 2. Temperature dependence of the solubility of cyclohexene in different binary water-sulfolane mixtures at 2 mPa.
giving strong nonideal solutions. Also the temperature dependent solubility of cyclohexene is poorly estimated with the model. In another contribution (Panneman and Beenackers, 1992), we successfully applied the UNIFAC method to calculate equilibrium compositions of the hydration of cyclohexene in aqueous sulfolane solutions. Again we will use UNIFAC, now for predicting the solubility of cyclohexene in water-sulfolane mixtures as a function of temperature. The thermodynamic condition for phase equilibrium is that the compositions in each phase are such that the equilibrium criterion is satisfied for each species in the mixture. Introducing the concept of activity coefficients results in xtyt(T,p,xt) = xpyf(T,p,xf)
i = 1, 2,
a*.,
N
(2)
The compositions of both coexisting liquid phases now can be calculated by applying the UNIFAC method to predict the activity coefficients of each component in each phase. Both the UNIFAC procedures and the procedures for calculating phase equilibria (Fredenslund et al., 1977; Skold-Jargensen et al., 1979; Macedo et al., 1983) were incorporated in a computer program. The sulfolane molecule cannot be represented by the molecular subgroups available in UNIFAC. However, a solvent with the same solvation properties, and with almost identical excess Gibbs free energy of mixing in aqueous mixtures, is acetone (Marcus, 1985). Sulfolane was represented by two methylene-carbonyl groups (-CH2CO-). Calculated activity coefficients of water and the simulated sulfolane in binary mixtures at 25 "C were in good agreement with experimental values of the activity coefficients determined by Tomilla et al. (1969; Panneman and Beenackers, 1992). In our calculations of the solubilities with the UNIFAC group contribution method, the parameter base published by Gmehling et d. (1982) was used. In a revision by Macedo et al. (1983), a number of parameters were adjusted, because of the availability of a number of infinity dilution activity coefficients for alkane-alkene systems. These adjusted parameters gave considerably better results. The used UNIFAC parameter values are shown in Table 11. The only data necessary
Ind. Eng. Chem. Res., Vol. 31, No. 4, 1992 1229 Table 11. UNIFAC Group Volume and Surface-Area Parameters and UNIFAC Interaction Parameters Used in This Paper main group 1 2 7 9
subgroup -CHF -CH~HH20 -CH2CO-
Rk
no. 2 6 17 20
0.6744 1.1167 0.92 1.4457
Table 111. Total Amount and Composition of the Feed and of both the Cyclohexene (1) and the Water-Sulfolane (2) Phases at Equilibrium, Computed by UNIFAC, at 313 and 373 K, Respectively
~~
molar fractions total amount ENE water sulfolane A. 1.40 mol% Sulfolane and 60 mol% Water; Temperature, 313/373 K feed (1.15mol) 0.15 0.60 0.40 phase 1 (0.133mol) 0.922/0.861 0.020/0.035 0.058/0.104 phase 2 (1.017mol) 0.026/0.037 0.588/0.583 0.386/0.380 ~~
B.2.90 mol
% Sulfolane and 10 mol % Water;
Temperature, 313/373 K feed (2 mol) 1.0 0.10 0.90 phase 1 (0.90mol) 0.894/0.79 0.009/0.019 0.096/0.191 phase 2 (1.1mol) 0.178/0.271 0.083/0.074 0.739/0.655 0.4 0 Experiments at 313 K .
UNIFAC at 313 K.
A Experiments at 313 K.
Xene
0.2
/
Sulfolane
A,,
(Mol W )
Figure 3. Solubility of cyclohexene, as a function of the molar fraction sulfolane in the feed, both experimental and calculated with UNIFAC.
for the calculations are the temperature and the mole fractions of all components in the feed. The resulta of two different solvent mixtures at 313 and 373 K are shown in Table 111. The solubility of cyclohexene in water-sulfolane mixtures, in Table I11 the amount of cyclohexene in phase 2, increases with temperature and with the amount of sulfolane in the feed mixture. The ratio of the molar fractions of water and sulfolane is almost constant for both the feed and the equilibrium solution. Although the solubility of sulfolane in phase 1 is significantly higher than that of water, the total amount of sulfolane in phase 1is almost negligible as long as the total amount of phase 1is small. For feeds with high percentages of sulfolane, the ratio of water and sulfolane in cyclohexene is approximately the same as the ratio in the feed. In Figure 3 both the experimental and calculated mole fractions of cyclohexene at 313 and 373 K are presented as a function of the mole fraction of sulfolane in the feed. The figure shows that the calculated mole fraction of cyclohexene is always about 30-40% higher than the value experimentally obtained. This deviation is the same for all sulfolane percentages in the feed and is caused by the very nonideal solvent mixtures. Nevertheless, the general trends in the influence of both sulfolane addition and variation of temperature are correctly predicted.
Qk
0.54 0.876 1.400 1.180
1 0.00 -35.36 300.00 26.76
interaction Darameters 2 7 86.02 1318.0 0.00 270.6 496.10 0.0 42.92 472.5
~
9 476.4 182.6 -195.4 0.0
Table IV. Solubility Parameters of Aqeous Sulfolane Mixtures both from Experimental Data and from Data Predicted with UNIFAC mol % sulfolane 0 40 60 80 90
from experiments ro AHsL,kJ-mol-' 0.013 12.3 0.216 6.2 1.008 8.0 2.359 8.5 1.905 6.9
from UNIFAC AHs,, kJ-mol-l 0.015 10.4 0.197 5.2 0.707 6. 2.166 7.3 3.223 7.6 x,,
The temperature dependence of the equilibrium mole fraction cyclohexene in water-sulfolane mixtures, as represented by XENE = xo exp(-W,JRT) (3) is shown in Table IV, for both the experimental and the calculated values. Again we see that the trends in the influence of temperature and solvent composition on both xo and AHsJ are correctly predicted, though there remains some difference in the absolute values.
Discussion The strong increase of the solubility of cyclohexene in binary mixtures of water and sulfolane, especially between 0 and 40 mol % sulfolane in the reaction mixture, and the difference of the enthalpy of dissolution between pure water and any solution of water and sulfolane are caused by the specific interactions between water and sulfolane upon mixing. A simple but attractive model describes liquid water in terms of a dynamic two-state system, (H,O), a (H20)d, comprising hydrogen-bonded (bulky, subscript b) and non-hydrogen-bonded (dense, subscript d) states. It is convenient to classify binary aqueous mixtures on the basis of their thermodynamic properties, particularly their molar excess functions. We can distinguish the following types of mixtures (Blandamer and Burgess, 1975). Aqueous mixtures for which GE is positive and lTSEl> lHElare called typically aqueous, TA. Aqueous mixtures of acetone, dioxane, and ethanol are examples of TA mixtures, in which "structure-forming" actions take place upon mixing at low mole fractions. Aqueous mixtures where lTSElare called typically nonaqueous, TNA. In some of these mixtures, GE is negative, TNAN, e.g. DMSO + water. In such mixtures intercomponent association occurs, which leads to a breakdown of water-water interactions. Mixtures where GE is positive are called TNAP; an example is sulfolane + water (Benoit and Choux, 1968). In TNAP mixtures the cosolvent exerts a depolymerizing effect on water and is a structure breaker (Blandamer and Burgess, 1975). The low solubility of cyclohexene in water is a consequence of a large negative value of TAS,(ENE,ENE+W) and a positive value of the enthalpy M,(ENE,ENE-+W). The observed enthalpy of dissolution of cyclohexene in water has a value of 12 kJ-mol-'. In water cyclohexene enhances the water-water interactions and is a structure former. The solubility of cyclohexene in binary watersulfolane mixtures is much higher. Addition of sulfolane breaks the '
1230 Ind. Eng. Chem. Res., Vol. 31, No. 4, 1992
three-dimensional water structure so that for solvating cyclohexene in this mixture TASt,(ENE,W+S) will become much less negative than that for solvating in pure water. We see from Table IV that the enthalpy of dissolution, AHs,, is decreased by a factor of 2 in going from water to a mixture with 40 mol % sulfolane. This also can be explained by the solfolane-water interactions. As a consequence of the structure breaking of sulfolane, the water cyclohexene interactions are less strong and the small dipole moment of cyclohexene will be responsible for only weak sulfolanecyclohexene interactions. Both effects are responsible for the considerable decrease of the enthalpy of dissolution.
Conclusions Addition of sulfolane as a cowlvent to a reaction mixture containing water and cyclohexene causes a large increase of the solubility of cyclohexene in the water-sulfolane solvent mixture. Sulfolane breaks the three-dimensional water structure, resulting in a lower enthalpy of dissolution and a less negative entropy difference if cyclohexene is added. The solubility of cyclohexene in different watersulfolane mixtures can be predicted by thermodynamic calculations, using the UNIFAC model to predict the activity coefficients of all components in both phases. The prediction of the change of solubility both as a function of the mole fraction of sulfolane and as a function of temperature are correct for 0 Ix s I1and 298 IT I 373 K. The absolute values of solubilities of cyclohexene are about 30% lower than those calculated from UNIFAC. These deviations might originate from our alternative representation of sulfolane in UNIFAC and by the fact that the cyclic structure of cyclohexene, which certainly influences the solubility, is not taken into account within UNIFAC. Acknowledgment This work was part of the research program of the Netherlands Foundation for Chemical Research (SON) and was made possible by financial support from the Netherlands Organization for Scientific Research (NWO). We thank DSM for additional financial support.
Nomenclature a = interfacial mass-transfer area, m2-m-3 A = cross-sectional area of the mixer, m2 c = concentration, km~lam-~ d = particle diameter, m [kNE] = molar concentration of cyclohexene, kmol~m-~ G = Gibbs free energy, J-mol-' H = enthalpy, J-mol-l AH8 = enthalpy of dissolution, J-mol-l A",, = enthalpy of dissolution on molar fraction basis, J-mol-' J = molar flux, kmol.m-2.s-1 k = liquid-liquid mass-transfer coefficient, m d N = number of components in a mixture p = pressure, mPa Qk = group surface area parameter R = gas constant, J-mol-W-' Rk = group volume parameter s = solubility of cyclohexene, k m ~ l - m - ~ so = preexponential solubility factor, k m ~ l - m - ~ S = entropy, J.mol-l.K-l T = temperature, K v, = superficial velocity, ms-l W = water W S = transfer from water to a water-sulfolane mixture
-
W / S = water-sulfolane mixture x = liquid mole fraction x o = preexponentional solubility factor z = length of the static mixer, m
Greek Letters = porosity, m13-(mreactor)-3 y i = activity coefficient of species i @ = volumetric flow rate, m 3 d Superscripts 1, 2 = indicators of phases 1 and 2 E = thermodynamic excess property Subscripts E,ENE = cyclohexene concentration in the organic phase E,W/S = cyclohexene concentration in a water-sulfolane mixture i = component i i = interfacial concentration of cyclohexene in = concentration at the entrance of the mixer out = concentration at the outlet of the mixer S = sulfolane component s = solubility related parameter s = superficial value tr = transfer between two different solutions t
Appendix Calculation of the Dimensions of the Static Mixer. The diameter of the static mixer, a coiled copper tube, is 3X m, and it is filled with glass beads (d = 0.25 X m). At the outlet of the static mixer, t!e watersulfolane mixture (W/S) has to be saturated with cyclohexene. Experimental conditions were such that the excesa of cyclohexene after equilibrium was always small. The amount of W/S in cyclohexene is small, so that
-- CE,ENE
(AI) The rate of mass transfer of cyclohexene is limited by the transfer rate through the W/S interface: CE,ENE,i
=
kW/S(cE,W/S,i
- cE,W/S)
(A2)
or @w/s
-acE,W/S
= kW/Sa(cE,W/S,i - cE,W/S)
(A3)
The experiments show that the change in watemulfolane flow rate as a function of z is small. The total flow rate and CE,W/S,i/CE,ENE,i are independent of z too. Therefore eq A3 can be easily integrated:
In
(
CE,W/S,i - CE,W/S,out CE,W/S,i - CE,W/S,in
)=-
kw/saz @W/S/(A4
(A4)
=0 CE,W/S,out = O.ggcE,W/S,i A value of the volumetric mass transfer (kwlsa) could be estimated from experiments with a similar system (isobutene + water + resin). The minimal value of the mass transfer in experiments with very small amounts of organic phase (4% isobutene) was 0.04 s-l. The experiments were done with comparable superficial velocities ((1- 5) X CE,W/S,in
m.s-1).
Values for the other quantaties are @w/s = 4.1 X m3*s-l Ar = ~ ( X3 10-3)2/(4)(0.4) = 2.83
v, = 5.8
X
m.5-l
X
10" m2
Ind. Eng.Chem. Res., Vol. 31, No. 4, 1992 1231 Substitution gives z 2 1.67 m
Therefore, a static mixer with a length of 4.0 m gives wateraulfolane solutions saturated with cyclohexeneunder all circumstances. Regietry No. Cyclohexene, 110-83-8; sulfolane, 126-33-0. Literature Cited Benoit, R. L.; Choux, G. RBactions dans le sulfolane 111. Etude des interactions eau-sulfolane. Can. J. Chem. 1968,46,3215. Blandamer, M. J.; Burgess, J. Kinetics of Reactions in Aqueous Mixtures. Chem. SOC. Rev. 1975,4,55. Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibria Using Unifac; Elsevier: Amsterdam, 1977;p 39. Gmehling, J.; Rasmussen, P.; Fredenslund, A. Vapor-Liquid Equilibria by UNIFAC Group Contribution. Revision and Extension. 2. Znd. Eng. Chem. Process Des. Dev. 1982,21,118. Macedo, E. A.; Weidlich, U.; Gmehling, J.; Rasmussen, P. VaporLiquid Equilibria by UNIFAC Group Contribution. Revision and Extension. 3. Ind. Eng. Chem. Process Des. Dev. 1983,22,676. Marcus, Y.Ion Solvation; John Wiley & Sons: Chicester, U.K., 1985; pp 190-191.
Marsman, J. H.; Panneman, H. J.; Beenackers, A. A. C. M. Automated On-Line Gas Chromatographic Injection of Samples Completely Liquified by Pressure. Chromatographia 1988,26,383. McAuliffe, C. Solubility of Paraffin, Cycloparaffin, Olefin, Acetylene, Cycloolefin, and Aromatic Hydrocarbons. J. Phys. Chem. 1966, 70,1267. Panneman, H.J.; Beenackers, A. A. C. M. Solvent Effects on the Hydration of Cyclohexene Catalyzed by a Strong Acid Ion-Exchange Resin. 3. Effect of Sulfolane on the Equilibrium Conversion. Ind. Eng. Chem. Res. 1992,in press. Prausnitz, J. M.; Lichtenthaler, R. N.; Gomes de Azevedo, E. Molecular Thermodynamics of Fluid-Phase Equilibria, 2nd ed.; Prentice Hall: Englewood Cliffs, NJ, 1986;p 398. Skjold-Jmgensen, S.; Kolbe, B.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibria by UNIFAC Group Contribution. Revision and Extension. Ind. Eng. Chem. Process Des. Deu. 1979,18,714. Tommila, E.; Lindell, E.; Virtalaine, M.; Laakso, R. Densities, Viscosities, Surface Tensions, Dielectric Conshts, Vapour Presaures, Activities and Heats of Mixing of Sulpholane-Water, SulphlaneMethanol and Sulpholane-Ethanol Mixtures. Suomen Kemistilehti 1969,B42,95. Received for reoiew November 12, 1991 Accepted December 8, 1991
