It was the purpose of this investigation to ascertain the qualitative nature of the interracial tension equilibrium characteristics of the systems hexane-acetone-water and toluene-acetone-water by studying the effect of drop velocity on drop weight through use of the modified drop weight procedure, and comparing these results with those obtained from systems known to have time dependent interfacial tension relationships; to then evaluate the effect of interfacial tension on the rate or mass transfer by obtaining extraction data for the above systems in a horizontal, countercurrent liquid-liquid extraction tube for a series of interfacial tension values achieved through variation of the total acetone concentration in the system; and finally, to attempt to obtain an equation correlating the overall mass transfer coefficient based on the solvent film with the physical and operational variables of the systems and extractor.
The observation that some three component, ternary systems containing high molecular weight solutes required time to reach interfacial tension equilibrium, prompted a more careful consideration of the assumption that determinations or this property obtained under static conditions represented the values existing under extracting conditions. The drop weight method was selected for comparison studies. An equation relating drop weight to drop velocity was derived, and took the form:
m = 2πrσØ/g - Aρv²/g
where:
m = drop weight, gm
2, π = constants
r = tip radius, cm
σ = interfacial tension, dynes/cm
g = acceleration due to gravity, cm
A = cross sectional area of capillary tube, sq cm
ρ = density of fluid flowing in capillary, gm/cu cm
v = drop velocity, drops/min
Ø = correction factor for non-ideal drop detachment from tip.
The equation predicted that if (σ') and (Ø) were constants, a plot or drop weight (m) versus the square or the drop velocity (v²) would result in a straight line. The systems used to test the validity of the above equation were arabic acid and acetone as solutes with each of the following liquid pairs: benzene-water, cyclohexane-water, and toluene-water.
From this study, it was concluded that
1. Adjustment of interfacial tension for the systems acetone in toluene, benzene, or cyclohexane with water was so rapid that equilibrium was reached as quickly as the drops could be formed.
2. The interfacial tension values of systems containing solutes having a molecular weight of 50 to 60 measured by equilibrium methods will be representative of the interfacial tension values for the systems under extracting conditions.
3. Equilibrium methods are not suitable for evaluating interfacial tension under extracting conditions for solutes having a molecular weight on the same order of magnitude as that for arabic acid.
4. The experimental method used in this investigation failed to show any transient values of interfacial tension less than the equilibrium values as postulated by Christiansen and Hixon.
Extraction tests were made on the systems toluene-acetone-water and hexane-acetone-water at 25 to 29 °C, in an effort to determine the effect of interfacial tension on the overall mass transfer coefficient. Phase flow rates covered a range of 1,000 to 10,000 pounds per hour per square foot for both phases. Concentration ranged from 35 to 5 weight per cent acetone in the inlet water stream, and 20 to zero weight per cent acetone in the inlet toluene stream. For the hexane system. the concentrations varied from 45 to 15 weight per cent in acetone in the inlet water phase, and 5 to zero per cent acetone in the inlet hexane phase. The results of this study led to the following conclusions:
1. The overall mass transfer coefficient for acetone from water to hexane based on the hexane film, increased from 0.012 to 0.060 with an increase in interfacial tension from 7.6 to 24.0 dynes per centimeter, as controlled by decreasing acetone concentration.
2. The overall mass transfer coefficient for acetone from water to toluene based on the toluene film, decreased from 0.145 to 0.048 with an increase in interfacial tension from 6.6 to 22.5 dynes per centimeter, as controlled by decreasing acetone concentration.
3. Because of the opposite effect of interfacial tension on transfer of acetone from water to hexane and to toluene, no generalization as to the effect of interfacial tension on the overall mass transfer coefficient could be made.
4. The mass transfer coefficient for acetone to toluene was 0.1 to 0.025 ot the transfer coefficient for acetone from water to toluene.
5. The overall mass transfer coefficient based on the solvent phase concentrations can be correlated with 67 percent accuracy with the physical properties of the system by the equation:
K<sub>s</sub>d/D<sub>s</sub> = 2.708 x 10⁻²¹(dσ/μ<sub>s</sub>D<sub>s</sub>)<sup>0.7227</sup>(μ<sub>w</sub>/μ<sub>s</sub>)<sup>4.0592</sup>(μ<sub>s</sub>/ρ<sub>s</sub>D<sub>s</sub>)<sup>5.4361</sup>(dG<sub>s</sub>/μ<sub>s</sub>)<sup>0.4701</sup>(dG<sub>w</sub>/μ<sub>w</sub>)<sup>0.3027</sup>
where:
K<sub>s</sub> = overall mass transfer coefficient based on solvent phase, lb/hr- sq ft-ΔC
d = diameter of horizontal extraction tube, ft
D<sub>s</sub> = diffusivity of solute in solvent, sq ft/hr
σ = interfacial tension, lb/hr²
ρ<sub>s</sub> = density of solvent phase, lb/cu ft
μ<sub>w</sub>, μ<sub>s</sub> = viscosity of water and solvent phases, respectively, lb/ft-hr
G<sub>w</sub>, G<sub>s</sub> = mass velocity of water and solvent phases, respectively, lb/hr-sq ft.
6. Equations correlating the individual film coefficients with physical properties of the system derived from binary extraction studies could not be used to predict ternary overall mass transfer coefficients. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/87182 |
| Date | January 1957 |
| Creators | Mote, Julian Francis |
| Contributors | Chemical Engineering, Chemical Engineering |
| Publisher | Virginia Polytechnic Institute |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xiii, 250 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 20538611 |
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