Unformatted text preview: B 7.4 × 10 −8 φ B M B
=
0
µ Bυ A.6 1/ 2 T (1) From Table 3.3, υA = 14.8 + 4(21.6) =101.2 cm3/mol
Using Eq. (1) with the following parameters, values of diffusivity are computed.
Solvent, B
Methanol
Ethanol
Benzene
nHexane MB
32
46
78
86 φΒ
1.9
1.5
1.0
1.0 µB , cP
0.57
1.17
0.60
0.32 DA,B (WC)
1.89 x 105
0.98 x 105
2.03 x 105
4.00 x 105 DA,B (Expt.)
1.69 x 105
1.50 x 105
1.92 x 105
3.70 x 105 Except for ethanol, the WilkeChang equation makes good predictions.
The applicable HaydukMinhas equation, Eq. (342), is,
DA,B = 155 × 10 −8
. T 1.29 PB0.5 / PA0.42 (2)
µ 0.92υ 0.23
B
B
where, for the nonpolar solute, CCl4 , with methanol and ethanol solvents, both P B and υB must
be multipled by 8µB in cP. Parachors for methanol and benzene are obtained from Table 3.5.
Parachors for ethanol, nHexane, and carbon tetrachloride are obtained by structural
contributions from Table 3.6. Using Eq. (2) with P A= 229.8 and the following parameters,
values of diffusivity are computed.
Solvent, B
PB
υB
µB , cP DA,B (HM) DA,B (Expt.)
Methanol
88.8
37.0
0.57
2.55 x 105
1.69 x 105
Ethanol
125.3
59.2
1.17
1.70 x 105
1.50 x 105
5
Benzene
205.3
96.0
0.60
1.96 x 10
1.92 x 105
nHexane
271.0 140.6
0.32
3.05 x 105
3.70 x 105
Except for methanol and nhexane, the predictions by the HaydukMinhas equation are good. Exercise 3.12
Subject: Estimation of the diffusivity of benzene (A) at infinite dilution in formic acid (B) at
25oC and comparison to the experimental value for B at infinite dilution in A.
Given: Experimental value of 2.28 x 105 cm2/s for the diffusivity of B at infinite dilution in A.
Find: Diffusivity by the HaydukMinhas equation, (342).
Analysis: The applicable HM equation is,
DA,B = 155 × 10
. −8 T 1.29 PB0.5 / PA0.42
µ 0.92υ 0.23
B
B (1)
From Table 3.5, parachors for A and B are 205.3 and 93.7, respectively.
From Table 3.3, The molar volume of the solvent, B, is 2(3.7)+14.8+7.4+12.0 = 41.3 cm3/mol.
From Perry's Handbook, the viscosity of B at 25oC is 1.7 cP.
Using Eq. (1), DA,B = 1.55 × 10 −8 2981.29 ( 93.7 0.50 / 205.30.42 )
(1.7) 0.92 (41.3) 0.23 = 6.5 × 10−6 cm 2 /s This is significantly less than the experimental value of 2.28 x 105 and the predicted value of
2.15 x 105 cm2/s for the diffusivity of formic acid at infinite dilution in benzene. Exercise 3.13
Subject: Estimation of the liquid diffusivity of acetic acid at 25oC (298 K) in dilute solutions of
benzene, acetone, ethyl acetate, and water, and comparison with experimental values.
Given: Experimental values.
Find: Infinite dilution diffusivities for acetic acid (A) in the four solvents using the appropriate
equation.
Analysis: For benzene, acetone, and ethyl acetate, Eq. (342) of HaydukMinhas applies:
DA,B = 155 × 10
. −8 T 1.29 PB0.5 / PA0.42 (1) µ 0.92υ 0.23
B
B From Table 3.5, the parachor for acetic acid = P A = 131.2. For all three solvents, this value is
multiplied by 2 to give 262.4. Parachors for benzene and acetone are obtained from Ta...
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 Spring '11
 Levicky
 The Land

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