an
/I/ECj unit Operations Review
Mixing by J. Henry Rushton, Purdue University, Lafayette, I d .
Mixing for liquid-liquid mass transfer operations and for continuous processing is being studied intensively
CONT~NUOUS
PROCESSING is making it imperative that mixer performance be well understood and that scale-up techniques be developed. Increasing attention is being given to the mixing of dry solids and to an understanding of the performance of industrial equipment. This review covers the period from October 1959 to January 1961.
and Vosnick (45). An oscillating impeller, by which the impeller blades have a straight-path motion, was described by Eck (75). A Venturi-type mixer for continuous blending of liquids was described by Molyneux (28), and Bartok and others (4) gave data on mixing in a reaction vessel by jet flow. Schulze-Bergkamen (42) described an agitator drive of small height.
General Two comprehensive reviews on mixing, one by Rushton and Oldshue on the mixing of liquids (47)and the other by Weidenbaum on the mixing of solids (46); brought u p to date the present theory and practice of the various types of mixing. Items to consider in specifying mixing equipment for various applications were discussed by Bates ( 6 ) , who also gave (5) some of the important factors about mixing to be considered in bench scale experimentation. Ackley (7) reviewed all published material on heat transfer as a function of mixing. Oldshue (36) described the application of mixers to the manufacture of cosmetics. Experimental work on the mixing of flour doughs was described by Earle (74)as an example of the mixing of plastic materials. H e found that the logarithm of his criterion for mixing was proportional to time of mixing a t constant mixer speed.
Mixer Types Most publications deal with the common types of fluid mixing impellersmarine propellers, standard flat-blade turbines, and paddles-but six articles were devoted to other types. The use of anchor-type impellers was discussed, and data were given by Uhl
Theoretical Aspects Available information on the entrainment of surrounding fluid into a turbulent jet stream was reviewed and discussed by Donald and Singer (73). Mixing of two thin parallel flow streams was studied by Ting ( 4 4 , and Yen (51) gave results of another study of the mixing of two parallel flow streams. Longitudinal mixing of fluids in packed beds was the subject of a report by Cairns and Prausnitz (8). A degree of mixing was defined by Hobler and Strek (22), who used it to evaluate flat-blade turbine performance. Flow velocities were measured in mixing tanks by Gzovski (27).
Mixing of Continuous Flows The use of mixing impellers in relatively small tanks in continuously flowing systems to smooth concentration fluctuations is frequently overlooked as an economical means of “pipeline” mixing. Gutoff (20) gave a theoretical discussion of this useful technique. The “degree of mixing” in continuous flow systems was defined and discussed (53), and Cholette and others (9) showed how mixing can affect the performance of flow reactors. Automatic continuous blending of gasoline was de-
scribed by Butler (7). Pawlowski (39) described a mixing tube for a multistage reactor.
Flow Patterns Of particular interest in this area are the effects of viscosity and of nonNewtonian liquids, because the proper use of mixing impellers for such liquids depends upon producing a fluid motion which will bring together all portions of tank fluid as quickly as possible. Metzner and Taylor (26) and Norwood and Metzner (35) have studied patterns and neutralization rates in various viscous conditions using standard flatblade turbines. A detailed study of flow directions throughout cylindrical mixing vessels, both with and without baffles, was reported by Nagata and others (34). The same authors (33) have studied flow patterns in the viscous and transition flow range of mixing. These were the first data relating flow, power consumption, and pattern for the transition range. Information on preparing fluorescent particles for tracer work in fluid flow was presented by Allen (2) ; he had previously described their use in observing flow patterns in mixing vessels.
liquid-liquid Contacting For purposes of mass transfer, the contacting of immiscible liquids, usually in a continuous fashion, is of growing importance. A large amount of experimental work is being done in this field. Nagata and Yamaguchi (30) studied the effect of mixers in tanks on the rate of mass transfer between two phases followed by chemical reaction. VOL. 53, NO. 9
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T h e results give valuable information on mass transfer coefficients in standard types of mixing installations. Gardner and others (78) gave performance data for a multiple impeller column for a countercurrent organic extraction. More data are available on the performance of a column using rotating disk impellers in an article by Davies and others (72). Chemical molecules which will scintillate can be dissolved in one phase of a two phase liquid system and used to determine interfacial area of the drops resulting when mixed with a n impeller. Mitsis and others (27) gave drop area measurements obtained by the use of this method. Pavlushenko and Yanishevskii (38) measured the area of drops dispersed by paddle mixers and correlated the arca with the fluid properties of the liquids and the motion of the mixer. Areas of drops produced by- flowing two liquid phases through an orifice were measured and related to orifice-pip? ratios, flow velocities, and fluid properties by Mcnonough and oth?rs (25). A photographic technique was used by Nagata and others (31) to measur? drop size and interfacial area. They also measured mass transfer rates under conditions wherein the internal motion of the drop could be varied and thr cffect studied.
Solid-liquid The suspension of solids in liquid by paddle impellers was studied by Weisman and Efferding (67). They evaluated the effect of some of the variables involved. Mass transfer coefficients were given for solution of solids in water and sucrosc solutions using standard type mixing turbines in cylindrical vessels by Barker and Treybal (3). .4 large amount of‘ data on solution of solids and hydration reactions involving solids and liquids has been correlated by Nagata and others (29, 32). Geometrically similar s).stems were used, and the data are of great valur theoretically and for practical design purposes. .4 method for mixing solids, recommended by Comyn (70). involves putting them into suspension and mixing in a !iquid; after this, they may be agglomerared, the liquid drained off, and rhe solid9 dried.
Gas-liquid ‘The use mentation the mass liquid and
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of mixing impellers in ferprocesses to promote both transfer between air and between liquid and solids
was described by Oldshue and others (37). Scale-up of commercial equipment was d;scussed. Mixing impeller size, speed, and air flow rates were correlated by Yoshida and others (52) with the transfer coefficient for oxygen in the oxygen-sulfite reaction.
Mixing Dry Solids I n the past few years, increasing interest has been apparent in the development and understanding of the mixing of solids. T h e mechanism has been discussed by Fischer ( 1 7 ) , who defined theoretical limits of blends and the sizing of equipment. Yano and others (49) gave results of solids mixing and related them to the velocity coefficient. Sterrett (43) discussed methods of scaleup of mixers and sifting of solids. Various types of equipment have been evaluated : Rathmell (40) and Gayle and Gary (79) discussed horizontal drum-type mixers and the advantages and disadvantages of horizontal and vertical mixers. LVeydanz (48) described a tetrahedral tumbler mixer and gave results therefrom. Ribbon-type mixers have been studied for solids mixing by Yano and others (50). Iiyama and Aoki (24) analyzed the behavior of paddle-type mixers for solids and reported on the power required for rotating the paddles in finely divided solids. Mixing by means of fluidization with air was discussed by D’arcy-Smith ( 7 7 ) . The use of radioactive materials as tracers in solids mixing to determine optimum mixing time and other mixing criteria was explained by Hoffman (23).
Effect of Other Operations Mixing of liquids and vapors on the platrs of distillation columns is an important factor on column performance; the effect of mixing on plate efficiencies has bren vtudied by Equchi and Nagata (76).
literature Cited (1) Ackley. E. J., Chem. Eng. 67, No. 17.
133 (1960). (2) Allen, M., Zbid.: 67,No. 13, 136 (1960). (3) Barker, J. J., Treybal, R. E., A.Z.Ch.E. Journal 6, 289 (1960). (4) Bartok, W., Heath, C. E., Weiss, M. A., Ibid., 6, 685 (1960). (5) Bates, R. L., IND.END. CHEM.51, 1245 (1959). (6) Bates, R. L., Petrol. Refiner 39, No. 11, B. B., No. i8)7) Butler, Cairns, (1960). Prausnitz, Sci. 20 (1960).
Zbid., 39, 8 , 97 (1960). 243 E. J., .J. M., Chem. 12, Eng. (9) Cholette, A,, Blanchet, J., Cloutier, L., Can. J . Chem. Eng. 38, 1 (1960). (10) Comyn, R. H., Marcus, I. R., McIntyre, R. E., IND.ENG. CHEM.52,
995 (1960). (11) D’arcy-Smith, F. E., Brit. Chem. Eng. 4, 652 (1959).
INDUSTRIAL AND ENGINEERING CHEMISTRY
(12) Davies, J. T., Ritchie, I. M., Southward, D. C., Trans. Znst. C h m . Engrs. (London) 38, 331 (1960). (13) Donald, M. B., Singer, H., Zbid., 37, (lt:52!J2,9k. L., Zbid., 37, 297 (1959). (15) Eck, B., Chem.-In,gr.-Tech. 32, 94 (I 9 m . \ - - --,-
(16) Eguchi, W., Nagata, S., Chem. Bng. (Japan) 24, 142 (1960). (17) Fischer, J. J., Chem. Eng. 67, No. 16, 107 (1960). (18) Gardner, F. H., Ellis, S. R. M., Hughes, J. G., Dechema Monograjh. 32, 199 (19591. (19) Gayle,’J. B.? Gary, J. H., IND.ENG. CHEM.5’2, 519 (1960). Gutoff, E. B., A.Z.Ch.E. Journal 6, (1960). Gzovski, S. Ya., Khim. Mashinostroenie 6 , 13 (1959). Hobler, T., Strek, F., Chem. Stosuwana 43 (1959). Hoffman, A. M.,IND.ENG. CHEM. ’ 52, 781 (1960). (24) Iiyama, E., Aoki, R., Chem. Eng. (Japan) 24, 205 (1960). (25) McDonough, J. A., Tomme, W. S., Holland, C. D., A.Z.Ch.E. Journal 6, 615 (1960). (26) Metzner, A. B.: Taylor, J. S., Zbid., 6, 109 (1960). (27) Mitsis, G. J., Plebuch, R. R., Gordon, K. F., Zbid., 6, 505 (1960). (28) Molyneux, F., Brit. Chem. Eng. 5 , 136 (1960). (29) Nagata, S., Yamaguchi, I., Chem. Eng. (Japan) 24, 726 (1960). (30) Zbid., p. 736. (31) Nagata, S., Yamaguchi, I., Harada, M., Zbid., 24, 742 (1960). (32) .Nagata, S., Yamaguchi, I.; others, Zbzd., 24, 618 (1960). (33) Nagata, S., Yamamoto, K., others, Zbid., 24, 99 (1960). (34) Nagata, S., Yamamoto, K., others, Kagaku (Kikai), 23, 595 (1959). (35) Norwood, K. W., Metzner, A. B., A.I.Ch.E. Journal 6, 432 (1960). (36) Oldshue, J. Y., J . SOC.Cosmetic Chemists 10, 332 (1959). (37) Oldshue, J. Y., IND.ENG.CHEM.52, 60 (1960). (38) Pavlushenko, I. S., Yanishevskii, A. V., Zhur. Priklad. Khim. 32, 1495 (1959). (39) Pawlowski, J., Chem.-Zng~.-Tech. 32, 820 (1960). (40) Rathmell, C . , Chem. Eng. Progr. 56 No. 4. 116 (1960’1. (41) Ru’shton,’ J. ’H., Oldshue, J. Y., Chem. En?. Progr. Symposium Ser. 55, NO. 25, 181 (19591. (42) ~Schulze-Bergkamen, J., Chem.-Zngr.Tech. 32. 45 11960). (43) Sterrett, K. R.: Chem. Eng. 66, No. 19, 155 (1959). (44) Ting, L., J . Math. and Physics 38, 98 (November 1959). (45) Uhl, V. W., Vhsnick, H. P., Chem. Eng. Progr. 56, No. 3, 72 (1960). (46) Weidenbaum, S. S., Chem. En,?. Progr. Symposium Ser. 55, No. 25, 199 (1959). (47) Weisman, J., Efferding, L. F., A.Z.Ch.E. Journal 6. 419 (19601. (48) Weydanz, W.,‘ Chem‘.-Zngi.-Tech. 32, 343 (1960). (49) Yano, T., Kanise, I., Sano, Y.: Chem. Ene. (Jaban1 24, 198 (1960). (50) -Yano; T:, Sano, Y . . others, Zbid., 24, 219 (1960). (51) Yen, K. T., Trans. Am. SOC.Mech. Engrs. Ser. E 27, 390 (September 1960). (52) Yoshida, F., Ikeda, A , , others, IND. ENG.CHEDI.52, 435 (1960). (53) Zwietering, T h . N., Chem. Eng. 8 i . 11, 1 (1959). )
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