For the conditions and results of Example 8.4, determine the following when using a six-flat-bladed turbine impeller in a closed vessel with baffles and with the extract phase dispersed, based on the properties given below: 

(a) minimum rate of rotation of the impeller for complete and uniform dispersion; 

(b) agitator power requirement at the minimum rotation rate; 

(c) Sauter mean droplet diameter;
(d) interfacial area; 

(e) overall mass-transfer coefficient, K_OD;
(f) overall transfer units, N_OD; 

(g) Murphree efficiency, E_MD; and
(h) fractional benzoic acid extraction. Interfacial tension = 22 dyne/cm, and distribution coefficient for benzoic acid = cD/cC=21.

Data From Example 8.4

Benzoic acid is to be continuously extracted from a dilute solution in water using toluene in a series of discrete mixer-settler vessels arranged for countercurrent flow of 500 gpm of feed and 750 gpm of solvent. Assuming a residence time, tres, of 2 minutes in each mixer and a settling vessel capacity of 5 gal/min-ft₂, estimate:

Transcribed Image Text:

Density, g/cm³ Viscosity, CP Diffusivity of benzoic acid, cm²/s Raffinate Phase 0.995 0.95 2.2 x 10-5 Extract Phase 0.860 0.59 1.5 x 10-5