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Liquid Extraction by Robert E. Treybal, Department of Chemical Engineering, New York University, New York 53, N . Y . In the research area, there is a trend away from studies on small laboratory towers and an increasing tendency to study liquid-liquid interfacial and drop phenomena
b
Most promising research involves problems of "interfacial turbulence"
b First detailed study of a vibrating-plate extractor and renewed interest in the rotating-cylinder extractor mark the year's progress
WHILE
the past year saw some important fundamental work in the field of liquid extraction, the actual progress toward understanding the underlying phenomena has been disappointingly slo\v. IVe shall probably have to expect this: since it is now realized that what !vas once thought to he a relativel). simple subject is in reality exceedingly complex. Practical applications, nevertheless. have not in the past, nor have they noby, \vaited upon technical understanding. \Vhile this review no longer includes detailed reference to these, a few major developments are nevertheless noteworthy. I n the field of petroleum chemistry, there have been important developments. Sinclair Petrochemicals will build a plant for purifying isoamylenes. destined ultimately to become isoprene through dehydrogenation. .4fter the isoamylenes are extracted from a distilled gasoline into aqueous HzS04 in the new process. they are then extracted into an aliphatic hydrocarbon: from which they are readily separated by distillation. rather than separated from the acid by dilution with water. Reconcentration of the acid is thus avoided. In the interest of satisfying gasoline octane number and sensitivity requirements, Humble Oil and Refining has done kvork on phenol extraction of catcracker gas oil to remove aromatics before recycling to hydrodesulfurizing. Texaco uses furfural extraction to upgrade cracking feed at Los -4ngeles and at Eagle Point, N. J.? thus removing aromatics which produce coke and gas on cracking. Humble is also installing a new unit for deasphalting heavy gas oil.
.neiv I SO, extraction plant a t the Lisbon refinery of S..4. Concessionhria d a Refinaqiio de Petroleos em Portugal, built by Edeleanu of Frankfurt, is characterized by its flexibility: It is capable of producing kerosine, gas oil. and lube oils. Fourteen petroleum refiners are either building or planning new facilities to produce benzene, o-xylene, and naphthalene. much of it through extraction separation. The impetus here is the short supply of coke-oven aromatics follo~vingreduced steel production. S e w qnthetic phenol plants by Do\v! Reichhold, Allied. Union Carbide, Hooker. and Xlonsanto will rapidly bring this product nearer to the billion-poundper-year production level. The most popular route is the Dow process, via chlorobenzene. which uses benzene extraction to isolate the phenol. Texas Power and Light and Alcoa have started to produce lignite tar fractions in a new pilot plant a t Rockdale, Tex. A fractional extraction, using hexane and aqueous methanol as solvents, separates 1000 gallons per day of crude tar from low temperature carbonization of lignite into five neutral oil and tar-acid fractions in a 3-foot-diameter R D C column. If the economics prove favorable, this can ultimately lead to a very large industry, possibly processing 50 million gallons of tar per year. Chiaya Solvent Works of Taiwan no\\. operates three plants, two in Taiwan and one in the Philippines, for submerged-fermentation acetic acid, producing glacial acid by ethyl acetate extraction in packed towers. De Lava1 Separator has developed a new process for continuous refining of babassu. coconut, and palm-kernel oils which
utilizes an agitated line mixer for contacting oil and lye, followed by rapid separation in a hermetic centrifuge. out of contact with air, Boivman Chemicals, in England, purifies lactic acid by isopropyl ether extraction. The Israel hlining Industries process for phosphoric acid has been licensed to Tokyo Soda Manufacturers Co. for exploitation in Tokyo. The process involves dissolution of phosphate rock in HCI? followed by extraction of the phosphoric acid into n-butyl alcohol or isoamyl alcohol! producing 5870,rather than 42%. PlO:. This \vi11 represent a n important expansion of extraction into the inorganic field. Another possibility for the future is the Texas -4. and M. College process for extraction of water from brackish streams. \I'ith triethyl- and methyldiethylamines as solvents, preliminary estimates indicate a cost of $1.50 per thousand gallons. Metal separations still dominate the extraction-process literature; 44% of the 265 references found, bvhich deal strictly with process applications, involved metal separations. About one third of United States uranium ore. 7385 tons per d a y o f 0.25% ore. is now processed by liquid extraction. Davison Chemical Co., at Erwin. Tex., separates thorium and uranium by pulsed-column extraction. L-anadium Corp., a t Durango, Colo., makes the uraniumvanadium separation by mixed aliphatic amine-alkyl phosphate extraction. T h e U. S. Bureau of Mines. a t Salt Lake City. has developed a process for separating nickel and cobalt from HCI solutions using triiso-octylamine as solvent. Do\v Chemical has a process for separating these from sulfate solutions VOL. 53, NO. 2
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using dinonylnaphthalene sulfonic acid in kerosine as solvent. Freeport Sulphur has a process involving extraction of the thiocyanate solutions. I n the field of rare earths, Ionics, Inc., is looking into the processing of California bastnasite bv liquid extraction, which is apparently cheaper than the conventional ion exchange processes. T h e Bureau of Mines has also worked on this ore by extraction. Meanwhile, Union Carbide Nuclear Co. has used the old stand-by, tributyl phosphate, to make very pure gadolinium and promethium from nuclear operations by-products. T h e literature has recorded some very interesting metal separations with new organo-phosphorus solvents. We have progressed to the point where a new machine program for extraction of heavy metals, uranium, zirconium, and lanthanum from aqueous feeds into diluted tributyl phosphate has been reported to the A.1.Ch.E. Machine Computation Committee. For the review of the unit operation aspects which follows, the literature search ended on Nov. 1 1960.
General Reviews
A brief review of the entire field, including theory and equipment characteristics. was offered by Beckmann (2%). I t is particularly valuable in that it points out the limitations of our knowledge of the fundamentals of the liquid extraction operation. T h e applications in inorganic chemistry were given a particularly comprehensive review (&I). Recent progress in the mixing of hvo liquids was included in a review by Baird ( 7 A ) . A very complete treatment of the methods of calculation. but relatively little on the performance of equipment, was presented by the members of the staff of the University of Birmingham ( 3 A ) in a text-book review. Although the present review no longer lists publications in the field of process applications, it would be remiss to omit reference to the very comprehensive review (5A) and text (6A) on the separation of tantalum and niobium by Miller, which treats the liquid extraction processes very extensively. Methods of Computation Generalized mathematical expressions have been developed for cross-current extraction, in cases where the distribution coefficient is constant (70B). Minimum solvent quantity required, for fixed feed and raffinate compositions and numbers of stages, and distribution to the stages may also be calculated (20B). Optimum solvent distribution to the stages for maximizing the profit
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realized in such cases, for constant distribution coefficient and immiscible solvents, is \.\-ell known to be equal portions of solvent in each stage. However, the methods of dynamic programming permit extending the principles, via computer, to cases of nonlinear distribution and variable solvent immiscibility with solute concentration to optimize all operating conditions such as number of stages, stage temperature, cost of solvent recovery, and the like ( 2 3 ) . A nomogram solution to the problem of estimating raffinate and extract compositions in single-stage extractions is quicker than the customary method (TSB), and extensions of the McCabeThiele methods to countercurrent extraction have been explained (5B). For distribution curves which have the form of the Langmuir adsorption isotherm, calculations have been made, via computer, for solute recovery as a function of solvent to feed ratio, for one through six and an infinite number of countercurrent stages; results are presented graphically (7B). Digital computers can be applied generally to extraction problems (6B). Response of these processes to randomly fluctuating input has been studied and exact solutions obtained for linear systems (78). For the case of two-solvent or fractional extraction, Frolov (8B) has derived a n expression for the ratio of solute concentrations a t the feed stage, assuming immiscible solvents and constant distribution coefficients. For extractions involving any number of components. Smith and Brinkley (77B) have developed a rigorous, stage-tostage calculation procedure for cases where the number of stages is fixed. The procedure is trial-and-error, but through a n expression relating the error in composition at one erid of the cascade, compared n.itli that specified, to the error in the assumed composition a t the other, the computations may be brought to a convergence reasonably quickly. The whole may be speeded u p by first applying a short-cut procedure which, for many situations, will provide an adequate solution directly. Fractional extraction of weak acids or bases can be enhanced if the organic solution of the undissociated acids or bases are contacted with a n aqueous solution of their alkali or mineral-acid salts. If this well-known principle is applied in a Craig-tube device, modified to permit solvent flow in both directions, S tubes can produce 2 s - 1 stages of extraction. Il’ith Craig extractors containing as many as 1000 tubes, separation possibilities are considerable (3B, 4B). Use of reflux in such operations has been studied mathematically and experimentally.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Likening the entrainment resulting from incomplete settling in mixersettler extractors to backmixing in continuous columns. Sleicher calculated the effect on over-all efficient!. for cases where mass transfer occurs only in the mixer and also in the settler (76B). The conclusion is that entrainments as large as 10% are rarely of consequence and that settlers for all but the final stages of an extraction train are probably frequently over-designed. If a homogeneous chemical reaction in liquid solution is carried out in the presence of a n extractive solvent which removes a product, yield and rate will be improved. Relationships among rate, volumetric efficiency. and degree of conversion for multivessel reactors? and concurrent, countercurrent? and cross-current flow of solvent have been developed (73B). 4 mass-transfer coefficient. based on a driving force measured by the difference between concentration in one phase and equilibrium concentration attained by adiabatic mixing and separation of bulk phases, has given satisfactory correlation of a limited number of extraction data (75B). Expressions have been developed (77B) for predicting the effect of a variety of equilibrium chemical reactions on the liquid-phase masstransfer coefficient for first and second order reactions, for film and surfacerenewal theory, first order only in the case of the latter. A rate equation fcr the case of extraction when the solute forms a dimer in the solvent was proposed by Raal and Johnson ( 7 d B ) > while Linde (SB) studied the kinetics of transfer of sodium sulfonate at the isoamyl alcohol-water interface. A general procedure for establishing the economic optimum solvent to feed ratio, raffinate concentration, recovered solvenr-solute concentrarion, and number of stages was worked out for simple cases (78B). This permitted development of a n economic optimum stage efficiency to be used in scaling u p mixer-settlers from knowledge of small-scale characteristics. A short-cut method (72B) provides the number of stages resulting in the least cost for an arbitrarily chosen solvent to feed ratio which is not necessarily the optimum.
Interfacial Phenomena Many puzzling observations have been noted in the extraction literature. These include the markedly different masstransfer coefficients resulting from interphase solute transfer in opposite directions, the great influence on the flooding capacity of packed extractors caused by extraction of certain solutes (but not others) in one direction (but not in the
an other), spontaneous motion a t liquidliquid interfaces, a n d the like. I n recent years these all have been ascribed to “interfacial turbulence.” A promising start on the ansvers to these problems has been made (72C), and a relatively simple picture of the interfacial phenomenon has led to a mathematical formulation which. qualitatively a t least, agrees Ivith many of the observations. As a continuation of this attack. an equation of motion for SeIvtoniansurface fluids has bern derived (77C). T h e thermodynamic effects of surface phenomena in liquid and other dispersions have also been analyzed (6C). Experimentally, spontaneous eruptions of the surface resulting from differences in interfacial tension during mass transfer have been photographed (9C, 70C), a n d particularly beautiful photographs of the influence of direction of mass transfer on drop coalescence have been made (7C). I n the latter case, it was possible to predict the observation qualitatively from interfacial tension data in the ternary system. T h e variation of interfacial tension with time for ne~vlyformed surfaces \vas studied with jets of a liquid injected into another (,5C). Coalescence of a drop with a bulk liquid may result in the eruption of a secondary drop. and this has been found to follow a modification of the Ralleigh unstable jet theory ( 3 C ) . .4n approximately Gaussian distribution was observed for the time of coalescence i n such cases ( J C ) , the average value of which was influenced by temperature, d r o p size, diffusing components, a n electrostatic field, and the presence of solid particles. Average time of coexistence of hydrocarbon drops of constant size a t glycolhydrocarbon interfaces has also been studied (8C). T h e stability of most petroleum+vater dispersions results from surface adsorption of oil-soluble substances, which may be counteracted by specific surface-active agents (7C). T h e controlling mechanism for extraction of C O ~ ( K O S and ) ~ HNOs across a \vater-tribut)-l phosphate interface is also apparently a t the surface (ZC). Transfer from organic to aqueous is first order xvith respect to solute concentration, while the aqueous-to-organic transfer is initially third order, with a decreasing rate constant as equilibrium is approached. (See also the discussion under Drops and Bubbles.) Drops and Bubbles Mass-transfer rates for both inside and outside of drops have been measured by using two-component systems, in this way ensuring that one or the other of the two mass-transfer resistances did not interfere. Johnson and Hamielec ( 7 0 )
measured effective diffusion coefficients inside falling drops, after correcting for end effects during drop formation and coalescence, a n d found them to be from 2.2 to 52 times higher than the molecular diffusivities. These factors are higher than those calculated by Kronig and Brink for Hadamard circulation but approach them a t low drop Reynolds numbers. T h e factors are substantially lo\ver than those predicted by Handlos and Baron, ivhich a r e approached? ho\iever by oscillating drops. Garner and Haycock ( 4 0 ) observed the circulation race inside drops a t low Reynolds numbers. They concluded that it does not exceed that predicted by Hadamard in the Stokes-lalv region and that no circulation is possible below a settling velocity of about 0.5 cm. per second. Outside mass-transfer coefficients were measured by Griffith (5D) for drops suspended a t rest in a flowing liquid. T h e data appear to agree with several theoretical expressions derived to account for mobility of the liquid surface, interfacial tension gradients Ivithin the drop surface: and the like. Even with very high mass-transfer Grashof numbers. no natural convection effects were observed, which is contrary to other observations made with solid spheres. When iodine or nitrophenol was extracted from \vater into drops of carbon tetrachloride, rates were about triple those for a solid sphere ( 3 0 ) . Surface-active agents affected drop oscillation a n d terminal velocity but not mass-transfer rates. These agents do, hoivever, reduce the rate of extraction of ethylamine from water into toluene by as much as 67y0
(170). T h e nonconstancy of the drag coefficients of drops falling in liquid media a t Reynolds numbers above 500 has been sho\vn by Harmathy ( 6 0 ) to be the result of their changing shape, in turn a function of the Eotvos number s A p d 2 / ~ , where Ap is the density difference, d the equivalent spherical diameter, and u the interfacial tension. H e has produced a n excellent correlation of the literature data a n d some new data, for high Reynolds numbers, including wall effects produced when d exceeds the tube diameter. I n India, several researchers ( 7 0 , 2 0 , 8 0 , 720) have developed correlations for terminal velocity in terms of the usual dimensionless numbers. T h e interfacial surface created by the presence of droplets in a stirred vessel has been measured by a scintillation technique in stirred beakers (SD). T h e method uses tritiated water with a n immiscible liquid containing a scintillator and is limited to cases of essentially complete immiscibility and, for studies in extraction, where the scintillator will not interfere. Shinnar a n d Church (70D) have applied the concepts of local
b w d Unit Operations Review
isotropy to show that the interfacial aear produced when tNo insoluble liquids are agitated together will follow different functions: drop coalescence is the controlling factor in concentrated dispersions, while drop break-up controls in dilute. T h e form of the resulting expressions agrees with the literature data.
Equipment Mixer-Settlers. T h e data for liquid extraction and other operations in stirred vessels and columns were reviewed by Kneule (ZZE), who pointed out the dependence of the mass-transfer rates upon the power expended per unit of volume of liquid. : Ivery extensive study of extraction in stirred vessels \vas reported by Nagata and Yamaguchi (37E), who used a variety of chemical systems, several baffle arrangements, and a paddle agitator hvith blades a t an angle to the vertical in a 10-cm. vessel. Density difference was varied over a \\-ide range, and both chemically reacting and nonreacting liquids were used. Drop sizes, measured by photographing a withdrawn sample of the dispersion, showed about a tenfold variation in size for a fixed set of operating conditions. Detailed conclusions cannot be revie\ved here, but the principal observations were that the major effect of agitation is on the drop size, that continuous-phase transfer coefficients are little affected by operating conditions, and that mixing inside the drops is important only for the large drops produced a t low agitator speeds. A three-stage ”air-lift” contactor, a n air-agitated mixing vessel for uranium extraction, was built ( 2 9 E ) . I t proved to be free of maintenance problems and very economical of power. .4s a followu p of earlier Soviet work reported upon in the 1959 review of this series (March 1960): large scale separation of erythromycin and tetracycline from their fermentation broths is now done in jet mixers, with excellent stage efficiency (46E). Cyclones were studied in England as extractors for uranium into tributyl phosphate-kerosine (74E). T h e conclusions paralleled those from ivork in this country (see 1958 review, March 1959, Pt. 11) that good extraction and phase separation cannot both be obtained with a single cyclone. Two cyclones arranged for recycle of the unclarified stream will, however, give both, and these permit a contact time benveen liquids as low as 1 second. Woodle a n d Vilbrandt (44E) used ultrasound to mix toluene and water in the extraction of methanol. Stage efficiencies were not exceptional, even a t very large potver expenditures per unit of liquids treated. Their report includes a good bibliography of the use of ultrasound for extraction. VOL. 53, NO. 2
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Kew equipment includes a pulsed mixer-settler ( 8 E ) ; a mixer fitted with double impellers, one driving the heavy liquid upward. the other driving the light liquid downivard ( 6 E ) ; and a pump-screen mixer, lvhere the liquids are mixed by passage through a screen (?-E).Successhl scale-up of a shrouded paddle for washing an organic solvent in a cylindrical vessel was demonstrated
(27E). Several new decanter designs have been published (17E, 35E, 39E). .4 description of the use of semipermeable membranes for phase separation, not wetted by the dispersed phase and hence impervious to this phase a t moderate pressure drops, was offered (43E). Addition of from 0.05 to 2% polyethylene to the dispersion produced in aromatic hydrocarbon separations decreases the settling time to roughly 70% of its value in the absence of the polymer (33E). A revieiv of use of centrifuges for separating liquid-liquid dispersions was offered
(36E). Spray Tower. T h e first of a series of reports by Elgin and his co\vorkers (42E) has been presented. which extends the principles developed for fluidized solids to liquid-liquid contacting. I n this report, the slip velocity-hold-up relation was shown to apply for a nonflowing continuous phase, provided that the terminal velocity of single drops is used instead of that for solid particles. This trill be most valuable when extended to countercurrent flow of continuous and dispersed phases. Perforated-Plate Towers. UsPULSED. A few new data from verv small columns, with the system acetic acid-benzene-water, lvere obtained at several plate spacings (38E). Pulsing improved the rate of extraction from two- to tenfold (37E). Agitation with impellers between the perforated plates increased the stage efficiency of perforated plates as much as 70y0 in the extraction of diethylamine between water and hexone (9E). A most interesting application involving a liquid-liquid exchange of deuterium and hydrogen. was described (73E). T h e gas-liquid exchange of these isotopes is evidently a better process. however. New designs of toxvers have been offered (75E, 30E), and a friction-fit, piston-type perforated tray of Teflon was described as regularly available (20E). PULSED. Pulsating jets of solvent extract a t u p to double the rate of continuous jets (28E). Phenol was extracted from water in a 2.3-inch-diameter pulsed perforated-plate column, and the height of transfer units correlates successfully with pulse frequency x amplitude’flow rate ( 4 7 E ) ; HTU’s ranged from 6 to 17 inches. T h e extraction efficiency of a n unpulsed plate column
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can be increased threefold by pulsing ( 3 E ) . Detailed data for extraction of uranium into tributyl phosphate-paraffin hydrocarbon solutions are available for 1.6-inch-diameter columns ( 7 E ) and for extraction of acetic acid between \rater and hexone in a 3-inch-diameter column ( 2 E ) . Efficiencies in uranium extraction, a t solvent to feed ratios of 100. are limited by backmixing (23E). .4 revie\r is available ( - E ) . I n conventional pulsed columns. improved efficiencies and flow capacities can be obtained if advantage is taken of the different fluid properties in various parts of the column. which result in different plate spacing. plate designs. and materials of construction in the Lvarious parts of the same column (7OE). A new Swedish design of perforated-plate pulsed extractor. the ASEA-column?uSes a series of relatively short columns. connected from the top of one to the bottom of the next (ILTE). T h e movement of liquids is carried out by low rreyuency. large amplitude pulsing. suppleinenred if desired by a superimposed higb-frequenc! , short-amplitude pulse for agitation. T h e horizontal type of pulse column ( % E ) showed advantagcs over other types of horizontal extractors \rith respect to construction and maintenance. A new pulsing device was described (27E). Reciprocatinq-Plate Column. .A column containing plates with 1arg.r perforations, or made with other fairlv open construction. was described (79E) in which the plates are moved by a vertical. reciprocating motion in a manner originally suggested by van Dijck. A 3-inchdiameter column showed high floir rates and heights of a theoretical stage from 4.3 to 9 inches, depending upon extraction system and operating conditions. Packed Columns. Flooding d a t a in a 2-inch-diameter column with ring. saddle. and sphere packings of 0.19- to 0.5inch sizes were correlated by an expression similar in form to the 1951 correlation of Dell and Pratt (40173). The DellPratt correlation has also been modified to handle data for 0.25-inch rings (72E). I n another review of data (32E). the Hoffing-Lockhart correlation (1954) was found most suitable. I n the extraction of acetic and benzoic acids bet\veen water and benzene, the over-all coefficient was found to be dependent upon the drop Reynolds number and independent of continuousphase flo\r rates or which phase was continuous ( 7 E ) . This is contrary to the previously recorded experience for this type of extractor. Data from small columns are also available for extraction of UOz(N03) 2 from aqueous solutions into methylcyclohexanone (34E) and tributyl phosphatehydrocarbon solutions (77E). I n the
INDUSTRIAL AND ENGINEERINGCHEMISTRY
latter case. extraction efficiency decreased with increased column diameter: better values were obtained in columns containing alternate packed and u n packed sections. Pulsing the packed column low.ers the height equivalent to a stage appreciably. owing to break-up of the droplets and to increase of the residence time (78E); in I-inch-diameter columns i t may increase the flooding capacity. I n the extraction of phenol bet\vem !rater and but11 acetate or benzene in a pulsed packed column (2.3-inch-diameter. 0.28-inch rings), the height of a transfer unit ivas from 4.4 to 24 inches but rose to as high as 67 inches a t low solute concentrations (48E). Comparisons over a limited range of conditions \rere made \vith larger packings. sieve-plate pulsed. and rotating-disk extractors. but the results are not conclusive. Rotating Disk Column. Several new design features were described (17E). Rotating Cylinder Column. Interest in this device. consisting of a rotating cylinder axially located within a stationary shell with extraction taking. place within the relatively narrow annular space. has apparently revived. It offers l o ~ rresidence time. which is important in extraction of radioactive solutions whose solvent degradation from radioactivity is to be minimized. Davis and \\’eber ( 5 E ) reported data on several sizes. u p to 6 inches in diameter. u i t h L T 0 2 ( N 0 3 )extracted ? between aqueous HNO, and tributyl phosphate-kerosine ; HETS as low as 2.5 to 3 inches are possible, depending principally upon rotor speed. but most of the data show higher values. Dispersed phase residence times were also given. Centrifuqal Extractors. The Luwesta (a three-staqe. vertical axis machine) shoJced a 97y0 extraction of tar acids from ammoniacal liquors Icith butyl acetate as solvent, for solvent to feed ratios as lo\s as 1 to 15 (.I.SE). A variant of the Podbielniak extractor is especially adapted to the refining and ivashing of vegetable oils (76E). literature Cited
Reviews (1.4) Baird, M. H. I., .Vf/g. Chemist 31, 141, 147 (1760). (22,) Beckmann, R . B., Chem. En,?.Progr. Sympo.tium Ser. 5 5 , No. 25, 95 (1759). (3+) Garner. F. H., Ellis, S. R . M., others. in “Chemical Engineering Practice.” Vol. 5 , H. W. Cremer and T. Davies, eds.. Scientific Publications. London, 1958.
(4.4) Martin. F. S.. Holt. R. J. W., Quart. Rew. (London) 13, 327 (1959). (5A) Miller, G. L., Znd. Chemist 35, 175,
341. 443 (1959). (6A) Miller, G. L., “Tantalum and Niobium. Metallurgy of the Rarer Metals,” No, 6, Academic Press, New York. 1960.
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(1B) Acrivos: A,, Chrtn. En,.. Sci. 12, 279
(1 960). (2B) .Ark. R.. Rudd. D. F.. Amundsen, N. R.: Chrrn. En?. Sei. 12, 8 8 (1960). (3B) Barker. J. A , , Beecham. A. F.: .4us:i-a/iati J . Chrm. 13, 1 (1 960). (4B) Beecham. A. F., Maslen, V. h'.,Ibid., 13, 18 (1960). (5B) Bl~ixnbrrg,R . , b r i t . C h ~ mEng. . 5, 172 ( 1960). (6Bj D h n . J. H.. C.S. Atomic Energy Lomm. UCRL-8787, 1959. (7B) Ellis. D. A , . ISD. ENG. CHEM.52, 251 (1960). (8B) Frolov. .A. F..Khini. .LfashinosiroPnir 1959, No..6. 29. (9B) Linde. H.: M o n a t s t f r . d ~ u t . .4kad. CI*iss. Berlin 1 , No. 11. 699 (1959). (10B) Mikhanov, V. :I.. Zzz,at. Sibir. C'tdd. ..lirod. .Vaz,k S.S.S.R. 1960, No. 4: 64
( l l B j Can. J . Chern. Eng. 38, 89 (1960). (21E) Kishbaugh, A. A, L. S. Atomic l h r r g y Comm. DP-333, 1959. (22E) Kneule, F., DPchrma .Ilono,qraph 32, ' 136 (1959). (23E) Krieg, J. T.. Holloway. N. G.. Siniecek. N.. I:. S. Atomic Enrrqy Comm. MCW-1438. 1959. (24E) Kunoshima Chemical Industry '20.. Ltd., Japan Patent 2418('59), April 14. (25E) Lindstrom, 0.. French Patrnt 1,234,638 (May 16, 1960). (26E) Logsdail. D.H., Thornton. J. B.. J . .Vuclear Enrrgy, Pt. B , Reactor Technol. 1 , 15 (1959). (271;) Mapes. D. B. (to Pan American Petroleum Corp.). U. S.Patent 2,919,978 (Jan. 5, 1960). (28E) Massimilla. L., Volpicelli, G., Chim. c. ind. (.\lilan) 41, 497 (1959). (29E) Mathers. W. G.. Cornett, L. C., Winter. E. E.. Atomic Energy Canada, L,td.. Chalk River, Cht., AECL-913, 1959. (30E) MiBek, T.. Sustek. J.. Czech. Patents 92,280; 92,282 (Oct. 15. 1959). (31E) Nagata, S., Yamaguchl. I . .L1~rn. Fac. En?. Kyoto 1 . n ~ ~22, . Pt. 2 . 249 (1 960). (32E) Naumowicz. J . . Przemysl Chrm 38, ' 415 (1959). (33E) Rausch, M. K . (to Sinclair Refining Co.), U. S. Patent 2,914,471 (Nov. 24. 1959). (34E) Srajer, V.,ColleCti071 Czrchosior . Chern. Comniuns. 25, 427 (1960). (35E) Thompson, H.A . (I/? to Coastguard Srnarators. Ltd.). U. S. Patrnt 2,942,733 (36E) ( J i nTrowbridge, e 28, 1960)." M. E. O., Brit. Ch~ni. En,?. 4, 29 (1959). (37E) Ueyama, K., Katayama. A , . B u l l . L,.nir.. Osaka Prefect. Ser. A 7, 133 (1959). 138E) Uevama. K.. Kobavaski. H., Ibid., ' 7, 313 (1959). (39E) Unthank, D. G., Bristow, L. ( l / a to Henry A. J. Silky). Lr. S. Patent 2,917.178 (Dec. 15, 1959). (40E) Venkataraman, G., Laddha. G. S.. A . I . C h . E . Journal 6, 355 (1960). (41E) Walley, K . H., Reman. G. H . (to Shell Development Co.), U. S. Patent 2,912,310 (Nov. 10,1959). (42E) Weaver, R . E. C., Lapidus. L.. Elgin. J. C., '4.I.Ch.E. J o u r n a l 5, 533 (1 959). (43E) Wegmann. K., Chemikrr Z f q . 83, 226 (1959).
(44C)-~oodleH . . A , . Vilbrandt. F. C., (15E) Jones. E. I;. (to Universal Oil A.I.Ch.E. Journal 6, 296 (1960). Products Co.). U. S. Patrnt 2,900,238 (45E) Zaheer, S. H.. Chari. K. S., others. (.Aue. 18. 1959\. ' Ghip chim. e2, No. 2, 43 (1959). (16~) 'Kaiser. H.'R.. ~ o y ~C. e .M., J . ~ m . (46E) Zhukovskaya, S. A . Annenkova. Oil Chemists' SOC.37, 4 (1960). L. .A,, Boiko. I. D.. .Wed. Prom. S . S . S . R . 13, (17E) Karpacheva. S. 'hi., ' Medvedev. No. 5,26 (1959). S.F.. others, Khim. .\fashinostromie 1959, (47E) Ziolkowski, Z . , Kubica. J., Chrm. No. 4.10. Stosoteana 3, 57, 461 (1959). (18E) Karpacheva. S. M., Rozen, .4.M.. (48E) Ziolkowski. Z.,Naumobvicz, J.. others, Ihid., No. 3. 6. Ibid., 2, 457 (1958); 3, 475 (1959).
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