Separation Process Principles- 2n - Seader & Henley - Solutions Manual

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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 n-Hexane 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 (W-C) 1.89 x 10-5 0.98 x 10-5 2.03 x 10-5 4.00 x 10-5 DA,B (Expt.) 1.69 x 10-5 1.50 x 10-5 1.92 x 10-5 3.70 x 10-5 Except for ethanol, the Wilke-Chang equation makes good predictions. The applicable Hayduk-Minhas equation, Eq. (3-42), 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, n-Hexane, 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 (H-M) DA,B (Expt.) Methanol 88.8 37.0 0.57 2.55 x 10-5 1.69 x 10-5 Ethanol 125.3 59.2 1.17 1.70 x 10-5 1.50 x 10-5 -5 Benzene 205.3 96.0 0.60 1.96 x 10 1.92 x 10-5 n-Hexane 271.0 140.6 0.32 3.05 x 10-5 3.70 x 10-5 Except for methanol and n-hexane, the predictions by the Hayduk-Minhas 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 10-5 cm2/s for the diffusivity of B at infinite dilution in A. Find: Diffusivity by the Hayduk-Minhas equation, (3-42). Analysis: The applicable H-M 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 10-5 and the predicted value of 2.15 x 10-5 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. (3-42) of Hayduk-Minhas 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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