Distribution of phenolic solutes between water and non-polar organic solvents

J. Chem. Thermodynamics 1975,7,61-72

Distribution of phenolic solutes between water and non-polar organic solvents D. S. ABRAMS

and J. M. PRAUSNITZ

Chemical Engineering Department, University of California, Berkeley, California 94720, U.S.A. (Received 4 April 1974) Experimental measurements are reported for the equilibrium distribution of phenol, o-cresol, m-cresol, 2,6-xylenol, 3,5-xylenol, and 2,3-xylenol between water and several non-polar organic solvents. These new results, as well as those previously published, are correlated within the framework of the theory of associated solutions. Theoretical analysis shows that while the distribution coefficient is essentially independent of solute concentration when that concentration is very low, the distribution coefficient rises with solute concentration at intermediate concentrations, especially when aromatic solvents are used. For phenolic solutes and non-polar solvents, the correlation can be used to estimate distribution coefficients for those systems or those operating conditions (temperature, concentration) where experimental results are not available.

1. Introduction Extraction with organic solvents provides one possible method for removal of offensive pollutants in wastewater from petroleum and petrochemical industry effluents. Becauseof their odor and toxic action on marine life, phenolic solutes are particularly offensive pollutants and, as a result, government regulations have given special attention toward enforcing removal of these solutes prior to final discharge of industrial wastewaters. This work presents new experimental results on the distribution of phenolics between water and non-polar solvents and correlates new as well as previously published data within a framework provided by the theory of associated solutions. (Distribution of phenolic solutes between water and polar solvents will be considered in a separateforthcoming publication.) Particular attention is given to the variation of distribution coefficients with phenolic-solute concentration. As indicated by theory, and as supported by experiment, the distribution coefficient is independent of phenolic-solute concentration when that concentration is low but increases when that concentration rises. The concentration where this increase becomes appreciable depends on the particular system and on the temperature.

2. Experimental Distribution coefficients were measured for phenol, o-cresol, m-cresol, 2,6-xylenol, 3$xylenol, and 2,3-xylenol. Solvents used were hexane, cyclohexane, 3-methyl pentane, methyl cyclohexane, iso-octane, 2-hexene, carbon tetrachloride, benzene,

62

D. S. ABRAMS AND J. M. PRAUSNITZ

toluene, and m-xylene. Analytic reagent-grade chemicals were used throughout without further purification. Distribution coefficients were determined by contacting a solution of phenolic solute of known concentration in distilled water with a known volume of organic solvent in 125 cm3 Erlenmeyer flasks sealed with 15 mm poly(ethylene-co-propylene) 0 rings. The flasks were shaken in a wristshaker thermostatted to within kO.05 K at 280.15, 298.15, and 333.15 K. About 24 h was allowed for equilibration. Samples of both phases (aqueous and organic) were removed for chemical analysis. The analysis was carried out with a Beckman D.U. spectrophotometer. The aqueous phase was treated with an aqueous solution of sodium hydroxide converting the phenol to the phenolate form. The organic phase was re-extracted with aqueous sodium hydroxide yielding a phenolate solution and a phenol&free organic phase, Both the phenolate conversion and the sodium hydroxide extraction were totally accomplished with a mole ratio of sodium hydroxide to phenol of at least 2. The phenolate ion absorbs strongly at 285 nm. The slit-width was 0.1 mm. Beer’s law was obeyed in the concentration range considered here. In aqueous basic solutions, a phenolic solute dissociates into a phenolate ion and a hydrogen ion; the distribution coefficient is thus pH-dependent. However, as shown by Beychok,“) at pH < 8 the distribution coefficient is essentially independent of pH. All experimental results reported here were obtained for aqueous solutions having pH < 7. 3. Results and discussion Tables 1 and 2 present the experimental data. Figure 1 shows distribution coefficients for phenol in three solvents plotted against aqueous-phaseconcentration of phenol. For each solvent, the distribution coefficient is constant at low concentrations but increases as phenol concentration rises. We estimate the precision of the reported distribution coefficients to be +2 per cent. THERMODYNAMIC

ANALYSIS

For a phenolic solute distributed between an aqueous phase (a) and an organic phase (0) the distribution coefficient is defined by K, = x0/Y',

(1)

where x is the stoichiometric solute mole fraction. The standard state, pure liquid solute, is the same for both phases. Therefore, at equilibrium, the activity of the solute is the same in both phases and K, can also be written : K, = r”lr”, (2) where y is the activity coefficient of the solute. An alternative deflnition of the distribution coefficient, in terms of concentration, is K, = co/f, where c is the solute concentration.

(3)

DISTRIBUTION TARLE

-

COEFFICIENTS

FOR PHENOLIC

63

SOLUTES

1. Experimental results for the distribution coefficients Kc of phenol, at concentration the aqueous phase, between water and a hydrocarbon at temperature T

c”/mol dmU3

Kc

T = 298.15 K

Benzene, 5.50 x 6.89 x 3.26 x 7.38 x 1.74 x 3.05 x

10-S 1O-3 lo-’ 1o-2 10-x 10-l

Iso-octane, 7.70 x 1.40 x 1.50 x 3.76 x 8.60 x 3.47 x 6.45 x

10-s 10-s 10-S 1O-3 1O-3 10-z 1O-2

2.28 2.27 2.53 2.73 3.4s 5.88

Toluene, 1.23 x 4.63 x 1.22 x 3.65 x 6.52 x 1.72 x 2.71 x

Kc

T = 298.15 K 1O-3 1O-3 10-Z 1O-2 1O-2 10-l 10-l

1.40 1.40 1.42 1.49 1.57 1.93 2.41

T = 298.15 K 0.096 0.091 0.10 0.098 0.097 0.11 0.11

Methyl cyclohexane, T=298,15K 8.10 x 10-a 0.13 1.32 x 1O-2 0.13 9.71 x 10-Z 0.13 6.14 x 1O-2 0.13 2-Hexene, 6.50 x 2.35 x 3.57 x 4.47 x

c”/mol drnT3

T = 295.15 K 1O-2 10-l 10-l 10-l

0.41 0.43 0.49 0.56

Cyclohexane, T = 280.15 K 4.37 x 10-Z 0.10 3.9s x 10-l 0.12 5.52 x 10-l 0.16 6.72 x 10-l 0.22

Carbon tetrachloride, 8.40 x 10-Z 8.90 x 10-Z 1.66 x 10-l 2.46 x 10-l 3.10 x 10-l 3.58 x 10-l

T = 298.15 K 0.50 0.51 0.61 0.68 0.93 1.31

3-Methyl pentane, T = 298.15 K 6.20 x 1O-4 0.11 2.93 x 10-l 0.12 6.06 x 10-z 0.13 6.52 x 10-l 0.13 Benzene, 1.2 x 1.9 x 2.2 x 6.2 x 1.7 x

T = 280.15 K 10-S 10-s 10-Z 1O-2 10-l

1.60 1.64 1.82 2.15 3.29

Benzene, T = 333.15 K 1.2 x 10-Z 3.01 1.1 x 10-2 3.06 6.7 x 1O-2 3.32 2.5 x 10-l 4.88

c”/mol dm+

ca in

Kc

Pn-Xylene, T = 298.15 K 4.90 x 10-2 1.07 1.31 x 10-l 1.20 2.01 x 10-l 1.31 1.57 3.10 x 10-I Cyclohexane, T = 298.15 K 5.10 x 10-b 0.18 1.60 x 1O-2 0.18 6.80 x lo-’ 0.18 0.18 3.11 x 10-l 0.20 5.83 x 10-l 7.24 x 10-l 0.22 Hexane, 1.80 x 2.70 x 5.70 x 1.02 x 1.73 x 2.90 x 9.27 x 1.61 x 3.04 x 4.33 x 4.67 x

T = 298.15 K 1O-3 1O-3 10-S 1o-2 1o-2 1O-2 1O-2 10-l 10-l 10-l 10-l

0.16 0.16 0.16 0.16 0.16 0.16 0.17 0.17 0.17 0.17 0.17

Cyclohexane, T = 333.15 K 2.53 x 1O-3 0.28 3.00 x 10-a 0.29 4.03 x 10-I 0.34 6.01 x 10-l 0.44

These two distribution coefficients are related by: K, = K, v”/va, (4) where V” and V” are the molar volumes of the aqueousand organic phases,respectively. For dilute solutions the pure-solvent molar volumes may be used. For dilute aqueous solutions the activity coefficient of the monomeric non-ionized solute is expressedby a 2-suffix Margules equation: In ya = D(1 -x~)~, (5) where D is a constant for any solute at a given temperature. Experimental values of B, given in table 4, are obtained from Tsonopolous’ (lo’ correlation, based on solidliquid and liquid-liquid equilibrium data. The variation of D with temperature in the range 273 to 333 K is small and to a good approximation may be neglected.

64

D. S. ABRAMS AND J. M. PRAUSNITZ

TABLE 2. Experimental results for the distribution coefficients Kc of various phenols, at concentration P in the aqueous phase, between water and a hydrocarbon at 298.15 K F/m01 dm+

K,

1.45 x 10-d

1.02

1.30 x 10-a

1.88

2.67 x 1O-5 9.73 x 10-4

10.91 11.81

o-cresol between water and benzene 9.93 x 10-4 11.42 9.31 x 10-s 12.68

6.03 x 10-a

17.03

1.80 x 10-d

0.73

o-cresol between water and iso-octane 6.42 x 1O-3 0.80

6.19 x 1O-2

0.89

3.91 x 1o-4

1.53

o-cresol between water and 2-hexene 3.80 x 1O-3 2.39

3.29 x 1O-2

2.66

1.10 x 10-a 1.21 x 1o-2

0.45 0.56

m-cresol between water and cyclohexane 6.21 x 10-a 0.66 1.37 x 10-l 1.78

1.63 x 10-l

4.47

2.23 x lo+ 5.72 x 1O-4

12.89 13.05

5.99 x 10-a

13.85

3.09 x 1o-4 3.23 x lo-*

8.67 8.94

2,6-xylenol between water and iso-octane 1.72 x 1O-3 9.05 4.53 x 10-a 9.10

2.06 x 1O-2

10.59

1.23 x 1O-4

1.37

2,3-xylenol between water and cyclohexane 6.75 x 1O-3 3.70

1.54 x 10-4

1.20

2,3-xylenol between water and iso-octane 1.37 x 10-S 2.78

9.50 x 1o-5 1.40 x lo-*

20.91 24.93

3,5-xylenol between water and benzene 1.21 x 10-a 24.17

1.23 x 1O-3

24.17

6.76 x lo-’

1.71

3,5-xylenol between water and cyclohexane 1.12 x 10-a 1.88

9.50 x 1o-3

2.12

1.32 x 1O-3

1.42

3,5-xylenol between water and iso-octane 2.22 x 10-S 1.49

5.25 x 1o-3

4.86

c”/mol dm- 3

Kc

o-cresol between water and cyclohexane 5.26 x IO-” 1.19

c”/mol dm - 3

KC

5.30 x 10-a

1.26

o-cresol between water and carbon tetrachloride 4.61 x 1O-3 1.91 2.35 x 1O-2

3.59

2,6-xylenol between water and cyclohexane 1.29 x 1O-3 13.15

The activity coefficient of the solute in the hydrocarbon phase is given by the theory of associated solutions. Kehiaian (‘) discussestwo fundamental models for associated solutions in an inert solvent, based on Flory’s lattice theory : the Mecke-Kempter (MK) and the Kretschmer-Wiebe (KW) models. Several investigators(3-6’ used the KW model to describe the thermodynamics of alcohol + hydrocarbon mixtures whereas Bagley and coworkers(‘-*’ used the MK model. In both models an expression is derived for the Gibbs energy of mixing solvent B with solute polymer species Ai (i = 1, 2, . . ., a). The polymer speciesare formed by reactions of the type: &+A, = A,+1. (6)

UlSl’KlJ3U

IIUN

CUlzl+~lCl~N

1 S l-UK

YHENULIC

SULUTES

65

The standard Gibbs energy of formation associatedwith this reaction is assumedto be a constant independent of 12.It follows that the equilibrium constant for the reaction is also independent of n. In the KW model the standard state, assumedto be independent of n, is the state in which solvent molecules and polymer molecules are all separate and oriented; in the MK model the separatebut disoriented state is chosen as the standard state. Thesetwo standard states are related by the disorientation entropy which depends on chain

Cyclohcxanc\ xnSt

I 1O-3

I

1 / I

/ l

r??

I

10-l 10-l c”/mol dmm3

I

-.a y A

IO0

FIGURE 1. Distribution coefficients Kc for phenol at 298.15 K between water and hydrocarbon plotted against the concentration c” of phenol in the aqueous phase; 0, this work; 0, Philip and Clark;(15) [7, Johnson et al. ;czOJV, Korenman;“l* 12) X, Buchowski;(lg) A, Philbrick; A, T, Saha et Al.; -, Kc calculated. Golumbric et Al.;

length.cg)The standard Gibbs energy of formation is more likely to be independent of chain length if the molecules are oriented and in a position to react; we therefore use the KW model as derived by Renon and PrausnitzC3’ The key assumptions in the derivation are: (1) the solute exists in solution in the form of linear, hydrogen-bonded polymers; (2) the molar volume of an n-mer is n times the molar volume of a monomer, and (3) the “physical” interactions between all the segments(polymer and solvent) can be characterized by expressions of the van Laar type. The activity coefficient of the associating solute in the organic phase is given by: ln f = ln14A,i+Z, XA)+~B(~-~~A/~~B)+K~{~A~A~-~~,)+~~A/A~/RT, (7) where VA and I’, are the molar volumes of solute and solvent, respectively; p is the physical interaction parameter; X, and +A are the overall (stoichiometric) mole fraction and volume fraction, respectively, and K, is the equilibrium constant of reaction (6) : &

= n+A”+l/(n

+ l)$A,,

~AI-

(W

66

D. S. ABRAMS AND J. M. PRAUSNITZ

For a fixed solute, the equilibrium constant is independent of the solvent; it is a function of temperature only. The “true” volume fraction of molecular speciesA, is given by h,

= (1+x,

h-0

+4wAPWKZ

(PA.

(8)

The “true” volume fraction of monomer A, in the pure solute is given by 42, = lim,_, +Al = (1+2K,-(1 +4K,)1’2}/2K,2. (9) For any solute+ solvent + water system at a given temperature, the theory requires only one physical interaction parameter B and one equilibrium constant K,. The equilibrium constant, however, depends only on the solute and is independent of the solvent. The thermodynamic analysis represented by equations (5) to (9) is restricted to solute concentrations below the solubility limit. If the solute-solvent physical interaction parameter fl is sufficiently large, limited miscibility between the solute and the solvent may result in a three-phase system. However, in this study we are concerned only with the lower concentration region where such regions of partial miscibility are absent. We now consider some results derived from the model. In the following illustrative examples we have set D (the solute-water Margules constant) equal to 3.9. Figures 2 and 3 show that while the distribution coefficient is independent of solute concentration at very low concentrations, it is strongly concentration-dependent at higher solute concentrations.

fo-'

10m4

IO-2 x"

1o-3

FIGURE3 2. Effect of equilibrium constant K, and mole fraction xB of solute in water on the distribution coefficient K, when BVJRT = 0 and &/VA = 1.

Figure 2 also shows the effect of equilibrium constant K, on the distribution coefficient ; in these calculations fi has been arbitrarily set at zero and (V,/V,) arbitrarily set at unity. Since K, decreaseswith temperature, figure 2 further shows implicitly the primary effect of temperature on the distribution coefficient. A second-order effect, not shown in figure 2, arises from the temperature dependenceof /3.

DISTRIBUTION

COEFFICIENTS

FOR PHENOLIC SOLUTES

67

FIGURE 3. Effect of physical interaction parameter B and mole fraction xa of solute in water on the distribution coefficient K, when K, = 8.06 and VB/VA = 1; /3’ = BVJRT.

Figure 3 shows the variation of distribution coefficient with mole fraction for several values of /?,when K, = 8.06 and (V&Q = 1. The distribution coefficient rises with decreasing/3. DATA REDUCTION Table 3 gives sources of distribution coefficients for phenolic solutes in non-polar solvents. For one solute at a fixed temperature, we require one value of K, (independent of solvent) and one value of /3 for each solvent. All the results at 298.15 K for phenol were fitted simultaneously for all solvents studied, giving one K, and 16 values of /?. Therefore, the K, obtained for phenol may be considered as a solvent-independent parameter which does not contain any bias to fit the data for one particular solvent. The objective function for the least-squaresfit was the sum of squared deviations in In yA in the organic phase. This objective function is linear in p, in the least-squares sense,thereby reducing the search to a one-dimensional non-linear search in K, space, and 16 one-dimensional linear fits in/3 space.The results for 3,5-xylenol were fitted in the sameway. Since experimental results for many of the ternary systemsare not plentiful, it is difficult to obtain. unambiguous values of K, and /?. To facilitate data reduction, a semi-empirical correlation for K, was used; experimentally-determined values of K, (at 298.15 IS) for phenol, 3,5-xylenol, and several normal aliphatic alcohols(3) were plotted against the reciprocal of the normal boiling temperature Tbon semi-logarithmic coordinates. The data defme a straight line given by: ln(K,(298.15 K)) = 6.21121x 103(K/TJ- 11.58796. (10)

D. S. ABRAMS AND J. M. PRAUSNITZ

68

TABLE 3. Sources of distribution coefficients for phenol Hexane Cyclohexane 3-Methyl peutane Methyl cyclohexane Heptane Octane Iso-octane Nonane 2-Hexene Carbon tetrachloride Benzene Toluene o-Xylene m-Xylene p-Xylene Ethyl benzene Mesitylene

o-cresol m-cresol p-cresol 2,3-xylenol2,4-xylenol

11,12, AP” 11, 12, 16, 18, 19, AP AP AP 11 11 21 11 AP 11, 12,14,19,20, AP 11,12,15,17,19,22,AP 11,17, 19,21, AP 11,19 11, AP 11 11 19

11 16,18,AP 16,18,AP 11 11 11 11 AP 11, AP 11,AP 11 11 11 11 11

16, 18

18, AP

16,18, AP

AP 11 11

11 11

11 11

a This work.

Equation (10) was used for all sterically unhindered phenols, i.e. for phenolics without substituents in the 2 and 6 positions in the benzene ring. For sterically-hindered phenols, we expect values of K, somewhat lower than those predicted by equation (10). Experimental results for o-cresol and for iso-alcohols’3) yield an equation with slope equal to that of equation (10) but with a lower intercept. For o&o-substituted phenols, therefore, we use: ln(K,(298.15 K)) = 6.21121x 103(K/T,)-12.43413.

(11) For di-ortho substituted phenols we have results only for 2,6-xylenol. Because of strong steric interference, K, for 2,6-xylenol is much smaller than that for 3,5-xylenol. For di-ortho substituted phenols we use: ln(K,(298.15 K)) = 6.21121x 103(K/T,) - 14.001.

(12)

With J&(298.15K) determined from equations (IO), (1l), or (12), the distribution coefficients were then used to determine p. TEMPERATURE

DEPENDENCE

OF K. AND

/3

The temperature dependenceof K, is d In K,/d(l/T)

= -AH”/R.

(13) we assume a constant value for the standard Following Renon and Prausnitz,(3) enthalpy of formation: AH” = - 7.5 kcal,, mol-l.T t Throughout this paper calra = 4.184 J.

DISTRIBUTION

COEFFICIENTS

FOR PHENOLIC SOLUTES

69

various phenols between water and an organic solvent 2,5-xylenol 2,6-xylenol3,4-xylenol3,5-xylenol 11 11,16,18

16,18, AP

18

16,18, AP

a-ethyl phenol

m-ethyl phenol

p-ethyl phenol

16,18

16,18

11 16, 17, 18

11

11 AP

AP 11

11 11 11 11 11 11 11 11

11 11

11 11, AP

11 :: 11 11 11 11

Hexane Cyclohexane 3-Methyl pentane Methyl cyclohexane Heptane Octane Iso-octane Nonane 2-Hexane Carbon tetrachloride Benzene Toluene o-Xylene m-Xylene p-Xylene Ethyl benzene Mesitylene

Due to the paucity of data at temperatures other than 298.15 K, we assumethat /I is a linear function of l/T, giving p(T) = p(298.15 K)+(l/T-l/298.15

K)d/Y/d(l/T).

(14) Within the accuracy of the data, the value for dj?/d(l/T) is independent of solvent; for phenol in hydrocarbon solvents it is -20 kcal,, K cmb3. OF DATA For any given solvent, the fitted values ofg do not vary significantly with solute; no trend with solute could be detected. For example, for 6 setsof results for cyclohexane +phenol the standard deviation in p was 2.5 Cal,, cme3 whereas for over 40 sets of results for cyclohexane + a phenol the standard deviation was 1.5 Cal,, cmm3; in other words, the scatter for phenol + cyclohexane alone was larger than that for the combined data for solute + cyclohexane. Similar discrepancieswere found for distribution coefficients with other solvents. Within the scatter of the experimental results, a constant value of /?for each solvent was assumed.These values are shown in table 5. Table 4 gives for the pure solute Tb, V*(298.15 K), E, and the solute-water interaction parameter D. The parameter E may be used to calculate V, at temperatures other than 298.15 K. The correlation schemepresented here makes it possible to calculate distribution coefficients as a function of solute concentration for the solutes listed in table 4 with any of the solvents listed in table 5 for the (approximate) temperature range 283 to 313 K. The fundamental relation is equation (2) with activity coefficients found from equations (5) and (7). To convert to concentrations, use equation (4). To illustrate the CORRELATION

70

D. S. ABRAMS AND J. M. PRAUSNITZ

TABLE 4. Values, for various phenols, Margules equation (5) for solute-water E where E = {M&“/K Values

of the normal boiling temperature Tb, the constant D of the interaction, the molar volume VA(298.15K) at 298.15 K, and - 298.15 K)){l/V,(298.15 K) - l/V&“)} in parentheses are estimates vA(298.15 K) -__ cm” mol-l

Tb

Solute

K

phenol o-cresol m-cresol p-cresol 2,3-xylenol 2,4-xylenol 2,5-xylenol 2,6-xylenol 3,4-xylenol 3,5-xylenol o-ethyl phenol m-ethyl phenol p-ethyl phenol o-propyl phenol m-propyl phenol p-propyl phenol p-isopropyl phenol m-isopropyl phenol o-isopropyl phenol 2,3,6-trimethyl phenol 2,4,5-trimethyl phenol 2-methyl5-ethyl phenol 2-methyl4-ethyl phenol 2-ethyl5-methyl phenol 3-ethyl2-methyl phenol 3-methyl5-ethyl phenol thymol p-butyl phenol m-butyl phenol o-butyl phenol p-tert-butyl phenol a From reference 23. b From reference 24. c From reference 18.

454.9b 464.1 b 475.46 475.1lJ 491.0b 484.7b 486.0 b 485.0 b 498.0b 492.7b 480.6b 491.06 491.0d 493.2d 505.86 511.2d 498.2” 5OOh 501.2h 493.8c 508.4C 500.90 500.5” 497.3c 500.2c 509Sh 506.7b 521.2d 521.2d 508.2* 512.15”

87.87” 103.57” 104.97a 105”

(120)

120.2f 120.95c (119.0) 119.W 120.65g I17.72g 119.1gg 120.839 140.25d 141.11d (142) 142.5” 138.3” 137.4”

::::; (136) I:;:;

(136) (136)

155.0 154.05d 154.05d 154.05d 153.1gd

d From reference 25. e From reference 26. f From reference 27.

10% g cm-” s.2a 8.4‘7 7.6” (87::; 8.2’ (k$ 7.8C 8.3C 8.49 (E; (8.0) :E; She 7.6” pi (8.0) g; (i0) W-9

D’

3.90 5.24 5.24 5.24 6.41 6.41 6.41 6.41 6.41 6.41 6.58 6.58 6.58 7.92 7.92 7.92 7.27 7.27 7.27 7.17 7.17 8.33 8.33 8.33 8.33 8.33 8.21 9.26 9.26 9.26 9.26

g From reference 28. h From reference 29. * From reference 10.

DISTRIBUTION

COEFFICIENTS

71

FOR PHENOLIC SOLUTES

TABLE 5. Molar volumes VB(298.15K) of the organic solvents at 298.15 K and the solvent-phenolic physical interaction parameter ,!Jat 298.15 K (cab, = 4.184 J) Solvent

I’B(298.15 K) cm3 mol - 1

2-hexene hexane cyclohexane heptane 3-methyl pentane methyl cyclohexane octane nonane 2,2,4-trimethyl pentane (iso-octane)

p(298.15 K) calth cm- 3

126 132 109 148 131 128 164 179.7

8.49 13.87 13.86 12.23 13.43 13.62 13.16 12.88

166

13.5

VB(298.15K) /3(298.15K) ~cm3 mol-l calth cm+

Solvent

carbon tetrachloride p-xylene m-xylene o-xylene ethyl benzene toluene mesitylene benzene

97 124 123 121 123 107 140 89

8.86 1.83 1.87 2.06 2.59 0.50 3.12 -1.56

TABLE 6. Calculated limiting distribution coefficients K, for selected phenols between water and five non-polar solvents at 298.15 K

phenol o-cresol 3,5-xylenol 2,6-xylenol o-ethyl phenol m-isopropyl phenol 2,3,6-trimethyl phenol

n-Heptane

Cyclohexane

Hexene-2

Benzene

Carbon tetrachloride

0.197 1.03 2.17 7.10 3.78 3.87 7.85

0.192 0.998 2.08 6.90 3.64 3.69 7.50

KC 0.381 1.84 5.36 12.44 9.36 10.9 21.8

2.26 12.31 21.7 80.2 108 179 342

0.444 2.29 6.62 15.3 11.6 13.8 27.6

results of such calculations, table 6 presentscalculated limiting distribution coefficients for seven phenols in five non-polar solvents. A limiting distribution coefficient refers to low solute concentration in the aqueous phase. Within 95 per cent confidence limits, we estimate the accuracy of this correlation to be + 15 per cent.

The authors are grateful to the Environmental Protection Agency and to the National Science Foundation for financial support, to the University of California Computer Center for the use of its facilities, and to PO Sun Lee for assistancein experimental work. REFERENCES 1. Beychok, M. R. Aqueous Wastesfrom Petroleum and PetrochemicaI Plants. John Wiley & Sons : London. 1967, p. 91. 2. Kehiaian, H.; Treczczanowicz, A. Bull. Acad. Pal. Sci. 1970, 18, 693; 1968, 16, 445. 3. Renon, H.; Prausnitz, J. M. Chem. Eng. Sci. 1967,22,299. Errata: Chem. Eng. Sci. 1967,22,1891. 4. Kretschmer, C. B.; Wiebe, R. J. J. Amer. Chem. Sot. 1949, 71, 3176, 5. Nagata, I. Z. Physik Chem.: Leipzig 1973, 252, 305.

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