I n d . Eng. C h e m . Res. 1990.29, 882-891
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Fredenslund, Aa.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibria using UNIFAC; Elsevier Scientific: New York, 1977. Gmehling, J.; Onken, U. Vapor-Liquid Eyuilibrium Data Collection: DECHEMA Chemistry Data Series: DECHEMA: Frankfurt Ihf., 1977; Vol. I. High, M. S.; Danner, R. P. Prediction of Solvent Activities in Polymer Solutions. Presented at the AIChE Meeting. Washington, DC, Nov 1988. Holten-Andersen, J. Group Contribution Model for Phase Equilibria of Polymer Solutions. Ph.D. Thesis, The Technical C'niversity o: Denmark, Lyngby, 1985. Holten-iZndersen, J.; Fredenslund, Aa.; Rasmussen, P.; Carvoli, G. Phase Equilibria in Polymer Solutions by Group Contribution. Fluid Phase Equilih. 1986, 29, 357. Holten-Andersen, J.; Rasmussen, P.; Fredenslund, Aa. Phase Equi lihria of Polymer Solutions by Group Contribution. 1. VaporLiquid Equilibria. /rid. Eng. Chem. Res. 1987, 26. 1382. Lichtenthaler, R. N.: Liu, D. D.: Prausnitz. J. M. Mar.romolecui,. . 1978. 2 2 . 192. Oishi, T.; Prausnitz, J. M, Estimation of Solvent Activities in Polymer Solutions Using a Group Contribution Method. Ind. Eng. Chem. Process Des. Deu. 1978, 17, 333. Prigogine, I. The Molecular Theory of Solutions; North Holland. Amsterdam, 1967. Sandler, S. I. The Generalized van der Waals Partition Function. I . Basic Theory. Fluid Phase Eyuilih. 1985, 19, 233. Wen, H.; Elbro, H. S.; Alessi, P. Data Collection on Poiymer Containing Solutions and Blends; DECHEMA Chemistry Data Series: DECHEMA: Frankfurt/M.. preliminary version 1989.
PEO = poly(ethy1ene oxide) PIB = polyisobutylene PMA = poly(methy1 acrylate) PPO = poly(propy1ene oxide) PS = polystyrene PVA = polyivinyl acetate) PVC = poly(viny1 chloride) Registry No. PE, 9002-88-4;PEO, 25322-68-3; PIB, 9003-27-4; PMA, 9003-21-8;PPO, 25322-69-4;PS, 9003-53-6;PVA, 9003-20-7; PVC. 9002-86-2; MEK. 78-93-3;C&14, 110-54-3;CaH18, 111-65-9; C10H22, 124-18-5; C12H26, 112-40-3; C14H30, 629-59-4; C16H34, 544-76-3; C,,H,,, 593-45-3; C20H42, 112-95-8; C24H50, 646-31-1; C33H74, 630-06-8;C40H82, 4181-95-7;C48H98, 7098-26-2;CSoH102, 6596-40-3: C($,22, 7667-80-3; cyclohexane, 110-82-7; toluene, 108-88-3;acetone, 67-64-1;chloroform, 67-66-3;benzene, 71-43-2; ethyl acetate, 141-78-6;2,2,4-C8HI8, 540-84-1;heptane, 142-82-5; 4-methyl-2-pentanone. 108-10-1;1-hexene, 592-41-6:vinyl acetate, 108-05-3: ethanol, 64-17-5.
L i t e r a t u r e Cited Chen, F. Group-Contribution Model for Mixtures with Polymers. Ph.D. Thesis. The Technical University of Denmark. Lyngby, 1991. Delmas, G.; Patterson, D.; Somcynsky, T. J . Polym. Sci. 1962,57, 79. Elbro: H. S.; Fredenslund, Aa.; Rasmussen, P. A New Simple Equation for A Free Volume Activity Coefficient. Predictions of Solvent Activities in Polymer Solutions. SEP 8913; The Technical Lniversity of Denmark: Lyngby. Denmark. 1989, to he published in ,I.lnrromolecuies. Flory, P. J.,Orwoll. R. .4,; Vrij. pi. J . ilm. Chem. Soc. 1964. 86. 3507.
Rrceiced for reuieu October 10, 1989 Accepted ,January 25, 199Q
Effect of Surfactants on Three-phase Fluidized Bed Hydrodynamics' Rajeev L. Gorowarat and Liang-Shih Fan* Department of Chemical Engineering, The Ohio State 1 iniuersity, Columbus, Ohm 43210
Experiments were conducted t o discern t h e relationship between three-phase fluidized bed hydrodynamics and surfactant solution characteristics. T h e standard characteristic, equilibrium surface tension, is inadequate. A novel method for surface tension evaluation, a dynamic maximum bubble pressure technique, was found to differentiate t h e 12 different solutions studied. T h e surfactant solutions were categorized based upon a combination of the terminal bubble rise velocity reduction, the equilibrium surface tension, and the new bubble surface tension values. These surfactant solution categories were correlated with experimentally observed three-phase fluidized bed and bubble column hydrodynamic behavior. Specifically, empirical correlations for gas holdup are presented Much of the fundamental laboratory work on threephase fluidization hydrodynamics has involved ideal airwater-glass bead systems or, instead of water, another pure fluid. It could be expected that a solution would behave similarly to a pure fluid with the same physical properties. This is not the case for surface tension effects, where behavior has been contrary to that expectation (Kelkar et al., 1983; Saberian-Broudjenni et al., 1984; Tarmy et al., 1984; Fan et al., 1986a). Dramatic changes in system hydrodynamics can occur with the addition of a surfactant. Surfactants affect hydrodynamic behavior of three-phase fluidized beds (and two-phase bubble columns) in three ways. First, the bubble size is generally reduced, increasing the interfacial area. Second, surface tension gradients are
developed around the bubble surface, reducing internal circulation, and hence rise velocity, as well as surface turbulence. Third, bubble coalescence is inhibited. by a variety of proposed mechanisms. Better understanding of the mechanism of surfactant behavior in three-phase fluidized beds may lead to more readily generalized models and correlations developed from air-water-glass bead systems, which can be extended to the complex mixtures in active reactor systems. Ideally. from a sample of desired reactant mixture produced in a laboratory, such as a fermentation bioreactor, the behavior of a three-phase fluidized bed can be predicted. This study provides a methodology for predicting the hydrodynamic behavior and a framework for further study.
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Brief L i t e r a t u r e Review Three-phase fluidized bed fundamentals have been reviewed by Epstein (19811, Muroyama and Fan (19851, Darton (1985), and more recently by Fan (1989). Surface tension of a pure liquid does not Seem to significantly affect the hydrodynamic behavior observed in a three-phase
* To whom all correspondence should be addressed.
'Paper 22i presented at the AIChE Annual Meeting, Washington. DC, Nov 27-Dec 2, 1988. :Current address: E. I. du Pont de Nemours & Co., Inc ,
Chemic& and Pigments Department, Research and Development Division, Edgemoor, DE 19809 0888-5885/90/2629-0882$02.50/0
c
1990 American Chemical Societk
Ind. Eng. Chem. Res., Vol. 29, No. 5, 1990 883 fluidized bed a t ambient temperature conditions (Dakshinamurty et al., 1971; Kim et al., 1975; Saberian-Broudjenni et al., 1984, Sinha et al., 1984). Many bubble column gas holdup correlations consider surface tension, but conflicting reports have been noted (Kelkar e t al., 1983). The effect of surfactants in general has not been thoroughly studied, except for the effects of short-chain alcohols, C1-C5. Oels et al. (1978) found that bubble column gas holdup increased with solute alcohol carbon number, from one to four, and increased with increasing local energy dissipation of the aerator. Lee and Buckley (1981) studied the behavior of an n-octanol solution in a three-phase fluidized bed of large particles, 2-, 4-, and 6-mm glass beads, and used a form of the isotropic turbulence equations to correlate the reduced bubble size. Kelkar et al. (1983) found that bubble column gas holdup increased with increasing alcohol carbon chain length but that varying concentration from 0.5 to 2.4 wt % was insignificant. It was hypothesized also, by Davis and Acrivos (1966), that beyond a critical concentration the surfactant concentration effects become negligible. Morooka e t al. (1986) studied a long-chain surfactant, Triton X-405 (Rohm and Haas Co.), a t a low concentration, 100 ppm, in a slurry bubble column. The results obtained were dramatic, with gas holdup appearing to reach a maximum a t 0.8, U, N 5 cm/s. The liquid velocity was 0.2-1.0 cm/s, and the particles were small (dp = 44 pm) for those experiments. As larger particles (dp = 230 pm) were used and the liquid velocity changed to 0.6-4.0 cm/s, gas holdup decreased. At a Ugof 5 cm/s, the gas holdup was near 0.15, with negligible liquid velocity effects when the larger particles were used. No comments on foaming were made by Morooka et al. In an annular three-phase fluidized bed with glass beads, Fan e t al. (1986) studied the effect of two short-chain alcohols, tert-pentanol (t-PA) and n-butanol, each a t concentrations of 0.5 and 1.0 wt %. They observed that gas holdup was higher for the five-carbon alcohol but that surface tension and concentration effects were insignificant. Fan et al. (1986) found that Kelkar et al.’s correlation was not satisfactory for t-PA in a bubble column, underpredicting the gas holdup, and attributed this also to distributor design. Both used C, as a correlation parameter. Song et al. (1987) studied cylindrical particles in a t-PA system, modeling a hydrotreating reactor. They observed three regimes in surfactant operation a t low gas velocities (nonfoaming condition) and found the liquid velocity effects to be significant in the dispersed (small and large) bubble regimes but not in the transition regime. Nicol and Davidson (1988) compared the effects of n-octanol (0.2 mL/L, u = 50 dyn/cm) and bovine serum albumin (BSA) (0.1-0.3 g/L, u = 57 dyn/cm) in a circulating bubble column and found no large difference between gas holdups for the alcohol and protein surfactant solutions. In unbaffled systems, solutions behaved like water, except more bubbles were entrained in the circulation carryover. Baffled systems, with higher shear areas, caused a decrease in the bubble size and an increase in gas holdup. The gas holdup has been related to the terminal bubble rise velocity (e.g., Wallis, 1969; Lockett and Kirkpatrick, 1975). Kulkarni e t al. (1987) suggested that the bubble rise velocity retardation parameter, y (derived similar to that in Levich (1962)) can be determined from single bubble rise velocity experiments. Kulkarni et al. used the calculated values for retardation parameters and Marrucci’s (1965) relationship for gas holdup to compare gas holdup predictions with literature data. They compared
their calculated values of tg with the data reported by Oels et al. (1978), but only for two alcohols, methanol and ethanol, with a perforated plate distributor. Kulkarni et al. (1987) did not compare the gas holdup results from this model with those obtained by Kelkar et al. (1983) but calculated bubble rise velocities and retardation parameters for the Kelkar et al. work and gave no reason for the discrepancy between those values of y and those found in single bubble measurements. Experimental evidence did not always support the general transition in bubble rise velocity predicted by Levich (1962). The equations predict a smooth transition between the spherical regime and the ellipsoidal regime, which was not observed (Davis and Acrivos, 1966; Bond and Newton, 1928). Savic (1953) first attempted to explain this phenomenon in terms of an immobile cap on the bubble. Davis and Acrivos (1966) and Griffith (1962) also developed equations to predict the transition between circulating (Hadamard-Rybczynski) and noncirculating (Stokes-type) bubbles. Davis and Acrivos developed a criterion assuming that the supply of surfactant was not limited, similar to that developed by Bond and Newton (1928) but changed the surface tension dependence in the dimensionless group now known as the Bond number, or Eotvos number (Clift et al., 1978). As did Griffith (1962), Davis and Acrivos (1966) expressed the surface tension dependence as a surface tension difference. Davis and Acrivos expressed the surface tension dependence as umax- umin,where umaris the surfactant free value and umin is the minimum surface tension, at which the film collapses. The key idea is that a sharp transition between a circulating and noncirculating internal flow regime can be predicted. Davis and Acrivos give a criterion that the drag on a bubble will equal that of a solid sphere when the relationship
gmax
- “min
I1.5
is satisfied. Dynamic Measurement of S u r f a c e Tension: New Bubble S u r f a c e Tension, Ob. The surface tension of a liquid can be determined from the pressure inside a bubble. The Laplace-Young equation relates the pressure differential over a curved surface and the radii of curvature (Rl,R2) (Adamson, 1982)
This method can be performed a t flow rates of up to 6 bubbles/s, if a sensitive pressure transducer and computer are used (Woolfrey et al., 1986). Woolfrey et al. (1986) studied the effect of NaCl on the dynamic or new bubble surface tension of sodium dodecyl sulfate (SDS). SDS in pure water had a surface tension similar to that reported by Vijayan et al. (1977), and the surface tension change with bubble rate was not large (Aub/Abr (defined in the Results and Discussion section) 0.25-0.63 mN s/m). A dramatic decrease in surface tension was observed when a 0.5 M NaCl solution was used. For example, a 0.52 mM SDS solution in water had a zero bubble rate surface tension, (Tb(o),of about 69 mN/m, whereas for 0.52 mM SDS solution in 0.5 M NaC1, ab(0) was about 36 mN/m, and h b / A b r was 5.2 mN s/m. Although Aub/Abr approached the same value as the concentration of SDS was increased, the values of surface tension did not. Also, the equilibrium values of impure SDS in water as reported by Vijayan e t al. (and the values reported by Walter and
884 Ind. Eng. Chem. Res., Vol. 29, No. 5, 1990 -1 ~.
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Figure 1. Schematic diagram of large-scale three-phase fluidization apparatus. Table I. Operating Conditions superficial liquid velocity three-phase fluidized bed bubble column superficial gas velocity solid phase: glass beads particle size solid density VM (calc) total solid loading static bed height
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