CRYSTALLIZATI0N JOSEPH A. PALERMO Colgute-Palmolive Co., Jersey Cify, N. J.
C . S. GROVE, Jr.,
HERBERT M. SCHOEN Syrucuse University, Syracuse 70, N. Y.
K
AISHEV (49) has derived Wulfl’s law for the equilibrium form of crystals in a homogeneous phase by a thermodynamic method. Expressions were also derived for the n ork necessary for the isothermal building of crystals in terms of crystal &e and saturation. Salli (89) derived an equation for the rate of growth of crystals as a function of the diffusion coefficient, degree of supersaturation, crystal radius, thickness of the depleted zone, surface tension, molecular weight,, and molecular volume. Lemmelein (54) has discussed the expcrimcntal production of crystals with equilihrium forms and the crystal-vapor equilibrium of hexamethylenetetramine. Iinacke and Stranski (61) have reviewed the theory of crystal yronth. Birman ( 7 ) has discussed the calculation of the average potential of an infinite nonionic crystal. He has shorn that the Frenkel-Bethe formula can be obtained from the Fourier representation of the total crystal potential. Roberts and Mandelkern (85) have reported on the thcrmodynamics of crystallization in high polymers. Sirota (97) has discussed the general problem of the development of an isothermal invariant transformation in time as applicable to crystallization. He has pointed out that for this problem the magnitude of the appearing nuclei, diinensions of growth, and the peculiarities of the transformation process are important. .4 growth rate equation is given and the effect of additives and the growth rate are discusscd. Litunovskii and Todes (66) have derived equations for the rate of crystal growth in the region of pure molecular diffusion in supersaturated solutions. The measured rate of crystal groxth in supersaturated potassium dichromate solution was in good agreement with the theoretically calculated values. Litunovskil (65) has developed a semiempirical equation expressing the linear diinension of a crystal as a function of supersaturation. He studied the rate of change of the linear dimensions of potassium dichromate crystals during crystallization and solution for values of initial supersaturation, dimensions of seed crystals, and rates of agitation. Pohl (80) has solved the time-dependent diffusion equation by transformation calculus to obtain the solute concentration in a solvent after a segrcgating liquid-solid interface is passed through the materlal. Graphical and tabulated results for typical esperxmental conditions are presciited. Gondshira (36) has presented a statistical explanation of isothermal recrystallization. A theoretical and mathematical analysis of the kinetics of the crystallization process made by Todes (10s)shows a strong dependence on the initial relative supersaturation. Burton, Prim, and Slichter (11) have examined the incorporation of solute elements into single crystals of germanium gromu from the melt in terms of a simple model. The theory accounts for the contribution of solute transport in the melt oxving to diffusion and Auid motlon, to the over-all process of impurity incorporation during steady state crystallization. NUCLEATION A N D GROWTH
Van Hook and MacInnes (107,108) have made a study of the graining of sugar solutions hy sonic irradiations. They ob486
AND
served that the extent of nucleation i s dependent on frequency, power input, time of treatment, nature of the container, and supersaturation of the solution. They reported on the crystallization of sucrose, arabinose, fructose, sorbitol, gulose, melibiose, glycerol, m-cresol, diglpcerjrlaldehyde, brucine, salol, and others. Ogawa (74) has reported a reduction in the precipitation time of aluminum hydroxide from 3 days to 5 hours by exposure of the sodium aluminate solution to 620-kilocycle ultrasonic wavee. Polotskir, Benieva, and Khodev (81) have studied the effect of supersonic waves on the crystallization of o-chloronitrohenzene, and on the pure mptals, cadmium, zinc, and tin. Kobayashi (52) has studied the nucleus formation and growth of si!ver chloride. Johnson and O’Rourke (47) have reported on the kinetics of barium sulfate precipitate formation. Turnbull (IO$) studied the rate of precipitation of barium sulfate from aqueous solution by the conductometric technique. Christiansen (18, 19) has niade a study of the steady-state nucleation and growth of crystalline precipitates. Supplementing this study with a treatment that takes the time of attainment of the steady state of nucleation into account, he shows that the steady state is attained almost instantaneously. Pound (53) has reported on the heterogeneous nucleation of crystals from a vapor. IIirano and Tsunoda (43) made a study of the timc required for the nucleus formation of urea adducts of paraffins under a microscopc in the presence of methanol, ethanol, propanol, butanol, and water as activators. Xielsen (72) studied the mechanism of the origin of recrystallization nuclei . Chretien, IIeubel, and Trimole (17) studied the temperature variations accompanying crystallization of sodium chloride and potassium chloride solutions by photographically recording the temperature-time curve. The velocity of crystallization varies with diffusion, the area of the crystals, the number of seeds, their granulation, and the square of the supersaturation. Neurnann and hIicus (70) have studied the linear speed of crystallization of salol in thin layers. JZorris and Strickland-Constable (67) studied the growth of the (110) faces of benzophenone crystals from a melt and reported
JOSEPH A. PALERMO of the research and development staff of Colgate-Palmolive Co. works primarily on spray drying of detergents, H e received his B.S.Ch.E. (1942) and M.Ch.E. (1943) from the University of Arkansas ; his Ph.D. dissertation (1952) from Syracuse University, was carried out on crystallization. Palermo is a member of AIChE, ACS, Phi Lambda Upsilon, and Sigma Xi.
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
Vol. 40, No. 3
that the rates of growth of the individual faces normally reniaiiied constant a t constant supercooling and constant stirring rates, even when the face area was increased considerably. Matusevich (67) has reported on the effect of the rate of cooling on the size of the rcsultant crystals. FigurovskiI and Komarova (50) studied the rates of crystallization of potassium aluminum sulfate and cuprous sulfate from their supersaturated solutions. They point out that the correlation of the growth rate with time indicates that crl stallization is a second-order process for these two materials. Fiillman (34) has explained the phenomena of crystal growth, dislocations, and spiral growth. Excellent photographs of the spiral gron%h patterns of paraffin and silicon carbide are given dmelinckx (1) has presented photograms to support his previous contention that cross-laced growth patterns of crystals of normal long-chain alcohols are real. Mergault and Branche (6'4) have reported on the crystallization of anhydrous titania dissolved in cryolite in the form of rutile. The smaller crystals obtained were colorless, while the larger sizes were bluish in color. Baur (6) has crystallized triacetin from liquid triacetin and from a 50% solution in 00% ethyl alcohol.
VARIABLES AFFECTING CRYSTALLIZATION
Sadovyi (87, 88) has related the rate of crystallization of glucose to basic physical factors. A t moderate supersaturation and proper seeding, crystallization of glucose monohydrate proceeded below 35" C. This is important because the rapid drop in solubility with temperature permits a greater yield. The erg-stallization rate was found to be directly proportional to superssturation, independent of temperature, but a poiver function of the ratio of viscosities of pure and impure saturated solutions. Seifert (92) has comprehensively discussed the basic principles of crystal structure, changes in shape and their causes, changes due to surrounding factors, uniformity of grain size of industrial products, problems in nucleation, ammonium sulfate crystallization, effect of purity upon erystallization, storage and the caking problem, and crystal formation in the vapor phase. Hirano (42) has observed that the crystal growth is accrlerxted in the supersaturated solutions of several inorganic salts under the action of super-high-frequency waves of wave lengths of 20 to 30 em The TiTave length of 20 is effective for potassium chloride, potassium nitrate, potassium dichromate, and amnionIum oxalate and the wave length of 30 for lead nitrate, copper sulfate, and potassium aluminum sulfate. Chatterjee (15) has studied the crystallization of saturated potassiuni chloride and barium chloride solutions during cooling from 80" to 45' C. at the rate of 10' per hour a t different stirring rates. Matuserich (58) has studied the effects of the rates of cooling and stirring on unsceded crystallization of saturated solutions of potassium nitrate and potassium ferrocyanide and has determinrd the temperature of initial crystallization as a
function of stirring. Llatusevich and Shabalin (60)have studied the effect of stirring upon crystal growth of potassium nitrate and potassium frrrocyanide and have discussed in detail the results on the basis of the theoiy of eusting ultramicroscopic crystal formations 1x1 saturated solutions. Matusevich and Shabalin (59) have also reported on the effect of the intensity of stirring solutions on the size of the resultant crystals. Chatterji and Rastogi (16) investigated the effect of foreign substances on the limits of supcr saturation of potassium chloride The foreign substanccs studied included octyl alcohol, caprylic acid, linoleic acid, methylene blue, Congo red, malachite green, Bismark broivn, e o m , crystd violet, sodium chloride, potassium nitrate, potassiiim chlorate, magnesium chloride, glass wool, and glass powder. The inorganic substances produced no eff& while the dyes had a tendency to stabilize the supersaturatrtf solution after repezted heatings. Shirasaki and Muroya ( C i C ) have reported that larger crjstals of ammonium sulfate ma) be
C. S. GROVE, JR., is a graduate of Lenoir-Rhyne College ; he received his B.S. in chemical engineering from N. C. State College in 1928; his M.S. from M.I.T. in 1934; and Ph.D. from the University of Minnesota in 1942. Grove is professor chemical engineering and director of engineering research at Syracuse ; previous positions were with N. C. State College, University of Minnesota, State University of Iowa, and Du Pont.
HERBERT MARTIN SCHOEN received his B.Ch.E. from Syracuse University in 1952. H e worked as research associate on protein hydrolyzates and received his M.Ch.E. from Syracuse University in 1953. At present Schoen is employed by the Syracuse University Research Institute; his previous position was with the United States Rubber International Carp. We is a member of Alpha Chi Sigma and several technical societies.
March 1956
COURTESY BRUSH ELECTRONIZS LO.
Crystal bar storage vaults
INDUSTRIAL AND ENGINEERING CHEMISTRY
4137
UNIT OPERATIONS REVIEW
Single crystal growth
. . . virtually a new field in itself
obtained from solution by addition of small amounts of stilfurir acid and sodium hexametaphosphate. The effect on the crystallization of many other inorganic substances is described. Cavallaro and Mantovani (18, I S ) have studied the crystallization of sucrose in the presence of some organic nonsugars. The effects of glycine, asparginine, spartic acid, gdacturonic acid, and glutamic acid on sucrose crystallization were reported. ltircev and Sandera (66) conducted a series of experiments in which they determined the effect of sodium sulfite, calcium chloride, sodium hydroxide, calcium nitrate, and aluminum sulfate on raw sucrosc yield during crystallization of low grade massccuites. The best yields were obtained a i t h sodium sulfite and calcium chloride. Suzuki (101) has eyamined the effect of cotsaltous and manganous ions on the yield and growth in the crystallization of sucrose SINGLE CRYSTALS
Kalker (111) has investigatrd the h>drothermal growth of qudrtz crystals with the welded chamber type of vertical stationary autoclave of improved design. Large, brilliantly clear, single quartz crystals have been g r o m to mights of the order of 1 pound each in about 2 months. Sobek and Hale (99) have patented an apparatus for growing single quartz crystals which consists of a pressure vessel which includes a silica dissolving region for containing crystalline quartz, and a quartz growing region, arranged to hold one or more quartz seeds. A channel made up of a plurality of pipes connects the two regions. The whole system is disposed to contain a fluid for dissolving and redepositing the quartz and is rockrd mechanicaUy t o effect fluid transfer. It is operated a t elevated temperatures and pressures. The crystals produced are 10 to 20 times more valuable in terms of usable volume of oscillator gi nde quartz than the average raw electronic quartz of commerce. Sohek (98) has also patented an apparatus for growing single quartz crystals of desired shape and size. Broge and Iler (9) have described in a patent the growth of quartz crystals from seeds suspended in a continuously replenished silica solution containing initially Si03,NazO, and 0.005% of sodium oleate a t a piessure of 1000 atin. and a t temperatures of 450' and 360" C. a t the bottom and top of the autoclave. Tanenbaum and Valdcs (102) have descrihed the grosth of single crystals of n-type silicon containing up to five p-regions from 0.0005 to 0.002 inch 15 ide which are sdtnble for the production of n-p-n junction transistors. Stanley (100) has studied the hydrothermal growth of large ammonium phosphate crystals by single-cycle and multicycle processes t o produce a siibatitute for natural quartz in communication equipment. Eversole and Drost (28) have patented a process for the >J nthcsis of monocrystalline rutile. A black singlc crystal is produced by fusion of a mixture of powdered titanium dioxide and 0.1% chromic oxide in a Verneuil furnace a t 600" to 1300" C. Conversion to red occurs mhen the boule is fired in an oxidizing atmosphere for 10 hours a t 1150' C. A mixture of titanium dioxide and 0.01yo vanadium pentoxide similarly treated also produces red rutile. IIonigmann (44) has described the growth of large platelike hexamethylenetetramine single crystals without iniperfections from the vapor phase. Estes (26) has patented a crystallizer designed for growing clear and flawless lithium sulfate piezoelectric crystals. Mohorcic (66) has described the growth of large naphthalene crystals Industrial Practice. Uemura and others (105) have described i n a Japanese patent a process for producing ammonium chloride
crl stdq The mother liquor containing sodium chloride, ammonium chloride, and ammonium bicarbonate, after separation of sodium bicarbonate, is treated with calcium hydroxide. The precipitate is filtered and the filtrate is treated with sodium chloride and cooled to crystallize the ammonium chloride. Yasuda (113) has obtained a Japanese patent for the crystallization of ammonium chloridc from the sodium bicarbonate-free mother liquor in the Schreiber process. Shirasaki (95) patented a process for the crystallization of ammonium chloride from its solution containing sodium polyphosphate. Felio (29) has described a novel two-stage crystallization process for the production of ammonium nitrate. Enoksson and Enohson (92) have described in a Swedish patent how the tendency to lump formation of ammonium nitrate is reduced by incorporation of 0.005 to 5% of an alkyl sulfate, alkyl sulfonate, alkylaryl-sulfonate, or alkyl phosphate having eight to 30 carbon atoms per molecule with a t least four in an aliphatic chain. These materials may be added either before or after crystallization. Nylander (73) patented the treatment of ammonium nitrate with polymetaphosphate to prevent lump formation. Okada and others (76) obtained a Japanese patent for an ammonium thiosulfate recovery process. A solution containing arnmonium thiosulfate, arsenic oxide, and ammonia is treated with liquid ammonia and cooled to produce ammonium thiosulfate having 97.2% purity. Gol'dshtein (55) has described the throry and practice of the ammonia soda process and the mechanism of growth of sodium bicarbonate crystals. Johnson ( $ 6 )described in a patent, a process for crystallization of alumina hydrate from a caustic liquor supersaturated with sodium and aluminum oxides. Deryabina and Rfishchenko (21) have studied the crystallization process of gypsum for different values of supersaturation. The solutions were prepared by reaction between solutiolis of calcium chloride and sodium sulfate, potassium sulfate, or magnesium sulfate. Oliver (76) described a process for the purification of native commercial salt to produce a first grade salt of 99.92% piirity and a second grade salt of 97.68% purity M-ith a total recovery of 89.1%. Pfann (79) has recently described a simple method of obtaining multistage batch Reparations by crystallization. Known as zone-refining, it consists of passing short molten zone8 through a solid charge. This technique can now be used on a continuous basis by means of the zonc-void method. Feed enters a t an intermediate point in a column down which the molten zones travel: waste and product leave at the ends. Materials move in the column through the agency of voids, which are introduced a t the ends and travel tovc.ard the feed inlet. The voids and molten zones arc moved by external heaters in a simple manner, and the principle of reflux is utilized. Jo\- and Pajne (48) have discussed the fractional crystallization of similar substances, such as radium and barium, wlitw thc concentration of one substance is very small. Mathematiral relationships are developed for fractionation systems. Escher ( 2 5 ) has patented an evaporating apparatus designed to produce courbe granular salt. Ayres (2) has described in a patent an evaporative crystallization process to prevent salting up and to maintain crystal size somewhat more uniform. Badger and Standiford (3) have described the improvrnieii ts in the design and operation of convcntional salt plants. They discussed the design improvements, economics, grainers, salt handling, vacuum pans, materials of construction, salt removal, product purity, scale removal, evaporator cleaning, evaporator economy, and fuel costs. Badger and Standiford ( 4 ) have also
CRYSTALLIZATION
Top view of 35-gallon experimental crystallizer showing hollow fin cooling elements and stirring helix COURTESY SUGAR & C H E M I C A L M A C H I N E R Y I h C .
Heat exchange and stirring element used in FletcherBlanchard crystallizers; geometry of coils equalizes heat exchange throughout crystallizer
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C r y s ta I I i z e r s
COURTESY H. AMARO. SAL TEdO L D A . PORTUGAL
Salt production by solar evaporation
Front or drive end of Lafeuille crystallizer Cooling water i s introduced and discharged through piping at right; spur gear and iron ring bearing surface are visible, center COURTESY DORR.OLIVER
Zdanky Schwingcrystallizer COURTESY GIOVANOLI\ FRERES S . A
SWITZERLAND
Cooling medium flows thr ough coils countercurrent to solution; pneumatic hammer, a t top, sets freely suspended coils into vibration, thereby minimizing crust formaticin
March 1956
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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UNIT OPERATIONS REVIEW
“Crystallization remains the cheapest method of separation and purification in quantity-thus its continued importance in long established industries and its promise for future processes, such as the production o f fresh water. Currently, stimulated largely by demand for large, pure, single crystals of many substances, we are experiencing a revival o f interest and activity in the theory and practice o f the crystallization process. ” ANDREW VAN HOOK College of the Holy Cross
described and compared some of the less orthodox salt manufacturing processes which include the Flake salt process, the Alberger process, the Morton process, the International process, the granulated salt process, and the Richards process. Flow diagrams of these processes are given. Hester and Diamond (40) have collaborated in editing an excellent staff-industry collaborative report on salt manufacture. The Morton process and the Grainer process are described and illustrated with flow sheets and a materia1 balance of a IO-tonper-hour vacuum pan system is given. Discussions on construction and operation of brine wells, purification of brine, multiple effect evaporation in vacuum salt, salt evaporation problems, drying dewatered salt, screening, and packaging are included. Silin (96) has discussed the variations in the operation of crystallizers for low grade massecuitrs giving a number of examples. Nichik (72) has studicd the effect of temperature and concentration of the crystallization of sucrose. Higbie (42) has tabulated the partial enthalpies of sucrose and water in solution and has described the methods by which sugar technologists and process engineers may compute the thrrmal effects attending the process of solution, vaporization, and crystallization in aqueous sucrose solutions. The partial enthalpies are tabulated for 0 to 65% sucrose from 32‘ to 200’ F., and the procedures for computing, which are thermodynamically exact, are illustrated. Findlay (31) has described in a patent a continuous crystallization process in which organic crystals of high purity are obtained from a binary or multicomponent eutectic-forming liquid mixture. Nakajima (69) has patented a process for the crystallization of hcxachlorocyclohexane high in gamma isomer. Zar and Rlusicant (113) have developed and patented a process for producing crystals of truns-stilbene of exceptional stability which are useful as scintillating detectors for nuclcar radiations. Haines, I’owers, and Bcnnett (38) have published a staffindustry collaborative report on the crystallization aspects of p-xylene production. Coats (20) has patented a process for the separation of p-xylene by crystallization in which heavy depositions of p-xylene on the cooling coils are prevented by making the coils a part of a high-amperage circuit and heating it periodically. Broriillard and Mutaffis (10) have discussed the factors causing crystallization of phthalocyanine blue Varlamov and Starose1’ski1 (109) constructed an apparatus for producing crystals of nitrosylsulfuric acid of a definite composition with a predetermined sulfuric acid and dinitrogen trioxide content. The Ethyl Gorp. ( g 7 ) has described in a British patent a process in which gammabenzene hexachloride is crj llized having a 92% purity with a yield of 83%. EQUIPMENT FOR CRYSTALLIZATION
Apparatus and equipment used in crystallization processes arc described in scveml papers and patents. In some cases, these pieces of equipment are designed for crystallization of spccific substances, but in other cases the apparatus has a more general application.
Hamada (39) has obtained a Japanese patent for a vacuum evaporator for the concentration and crystallization of sodium sulfate using the waste liquor from a rayon plant. A vacuum crystallizer has been described by Nakai (68) and an evaporation crystallizer for producing comsc grained salt has been patented by Escher (24). Pepinsky, Baecklund, and others (78) have described a device for preparing single crystal spheres. Shiba (93) has developed an apparatus for hot filtration, extraction, and reerystallization with volatile and flammable solvents. Other patents have described various types of crystallization equipment. These include a sugar-crystallizer (45), a dewaxing apparatus with a scraper.arrangement (SO), an apparatus for sodium sulfide recrystallization (8W),crystallizere for growing large piezoelectric or optical crystals (23, 77), and an improved crystallization tube (8). Freve (33) has patented a fractional crystallizer for the purification of cyclohexane and Rush (86) has described a continuous centrifugal crystal purifier. BOOKS AND REVIEWS
A numbcr of books and papers reviewing various phases of crystallization have been published recently. Books have becn written by Kuznetsov (53), Read (84, Verma (110), Gonzales ( 3 1 ) ,Klug and Alexander (50),and Matz (63). Frank-Kamenetskil (3%’)has written a historical survey of the field of crystallography and of the men prominent in this field. Van Hook (106) has summarized sucrose crystallization. Chatelain (14) has reviewed liquid crystals covering the past 20 years. Bamforth (,5) has discussed crystallization, crystal growth, fractional crystallization, production of sodium sulfate, nitrogenous salts, potash, sugar, etc., and a crystallizing plant in a review giving 75 references. Matz (62) has reviewed the literature of 1952 and 1953. In another review (61) he has discussed basic principles, as well as cooling, evaporative, vacuum, and classifying crystallizer types. Schuur ( S I ) has reviewed the crystallization of high polyniers and has discussed spherulites, thc mechanism and rate of crystallization, the continuity of crystal lattice, and the melting range of high polymers.
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