Successful application of spray drying is due in p a r t t o much improved knowledge and control of drop
i--
atomization, spray/air contact, and drop evaporatitin
,
1
SPRAY
DRYING
o decades of research and development have madr T”spray drying a highly competitive means of drying whether the situation is a delicate operation under sterile conditionsor a high tonnage production of chemical products. The range of chemical products suitable for spray drying (Table I) continues to expand. Unit sizes and capacities have increased substantially through advancements in technical know-how and an appreciation of spray-dryer mechanisms, especially in the atomization field. This survey reports the status of spray drying today through individual appraisal of the stages that make up the unit operation-namely, atomization, spray-air contact, evaporation, and product separation. Further sections describe applications, economics, and new developments. The atomization stage is carried out by nozzles, rotating disks, or cups, the mode of atomization being selected by the feed and dried product characteristics. The nature of the spray-air contact is determined by the drying chamber design. Manufacturers continue to offer a varied design range to achieve optimum evaporation rates and product quality for the widely differing feeds to which spray drying can be applied. Product separation is closely connected to chamber design, and pneumatic transport systems, cyclones, bag filters, and scrubbers are used. The topic of dried product handling is a subject in its own right, and it is not included in this survey. Spray-drying application is reported, with special reference given to the most recent work. Spray drying has been surveyed in biannual reviews of the over-all drying scene by McCormick (725, 726). Atomization The atomizer is the most important feature of a spray dryer. Its selection and operation are of supreme importance in achieving economic production of a highquality product. It must achieve maximum evaporation rates through a high spray surface-to-mas ratio; it must also be controllable to achieve the required spray characteristics-homogeneity and drop size. V O L 6 0 NO.
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Rotating disks. The f i n d i n g of Marshall and coworkers (1, 72, 87, 179, 762) continue to form the basic work for rotahg-disk atomization theory, prediction, and application. Other notable contributors to the theory have been Frazer (66, 67),and Walton and Prewett (789). Hege (85)more recently published results of a study of disk atomization, which included a prediction of performance for low disk speeds. A study into aqueous-spray characteristics beyond the peripheral speed range investigated by Marshall and coworkers is reported by Masters (720). This study of spray characteristics was conducted on a 5-in. straightvaned wheel at peripheral speeds between 300-450 ft/sec. The relationship between drop size and disk speed at constant feed rate conditions was found to change as disk speed increased. However, it was conduded that for low disk loadings, it is possible to predict spray characteristics at higher speeds without undue error by extrapolation of the already published data (72,87) or by use of modified forms of the existing correlations. Drop-size data on which disk selection is based is commented upon by Kozlovskii (705). The design and operati " ' atomizers have been reviewe? '- a
recent symposium (722), and the following discussion which centered upon the problem of air-pumping effects of vaned disks has been reported elsewhere (29). The range of disk designs is extensive, each being for a set application. Curved vanes are claimed to increase the bulk density, especially in dairy products (122). Wheels of small vane area or containing nozzles are used to minimize air-pumping effects where aeration of product is detrimental to dried product specifications. A special curve-shaped vane profile (86) to reduce turbulence within the disk is claimed to improve particle size uniformity. Use of Teflon vanes asymmetric to radius, to improve atomization characteristics, has also been suggested (176). Problems with excessive wear on disk surfaces when abrasive and corrosive materials are atomized have been overcome by incorporating resistant surfaces within the disk design. A further antiwear arrangement (734) features nozzles placed in the disk periphery and protruding into the inner disk chamber. These nozzles are of an abrasive-resistant material and their protrusion allows buildup of abrasive material on +ha -did antiprolongs abrasion surface. This simple layout gr
TABLE 1.
SOME SUBSTANCES THl
Ethylenediaminotetraocc Enzymes, sundry Excreta Fats (spray coolin! Ferrites Ferrous sulfc Fish solubles Flavoring mc Fungic Garlic Glands, sunc Glucose Glutamic ac Gluten, maii Wheat Glyoxal Ground glas Gypsu-
Herbic b
Iron oxide Kaolin
Lactos Latex rubbel lignin derivc
lithium chlor liver extraci Magnesium carbo1 Magnesium silicatt Maleic acid Malt extroci
A Russian patent (703)for reduced disk wear concerns the use of vanes rotating in a vertical plane by friction and feed flow but no details on suitable peripheral speeds are given. T h e use of low speeds to minimize wear but maintain uniformity of spray size-at such speeds is claimed (744)by employing multiconcentric annular walls containing circumferentially spaced slots. Atomizer disks, which receive up to three feed flows separately and discharge in a fine spray with maximum degree of mixing and dispersion of the multiple feeds into one another, are also reported (77). The existence of air-pumping effects is often considered detrimental to atomization performance (29) and dried product characteristics, but tests by Turba (780) suggest the contrary. The pumping effect and the resulting expanding spray doud are said to produce an increase of grain density in relation to drying chamber size. Rotating cups. The application of spinning cups to produce liquid sheets suitable for disintegration into sprays of uniform drop size has been investigated by Frazer ef ol. (63, 64). The use of impinging air streams on the liquid sheet, formed at the cup lip, to produce either fine or coarse sprays is also reported (68). Semi-
with sheet thickness are quoted for a wide range of operating conditions. The sheet breakdown for both spinning disks and cups has been commented upon by Eisenklam (52). The cup principle has been applied to paste atomization (53),where the cup stem comprises a screw which feeds the paste to the rotating cup lip. Atomization is completed by air directed a t the lip. No operating details are given. Pressure nozzles. With the pressure nozzle, the pressure energy applied to the liquid feed is converted into kinetic energy. The nozzle is designed to shape the liquid into a jet or sheet which disintegrates readily owing to instability. The basic theory of pressure nozzles has been widely reported (68, 779, 782), with little contribution to the established atomization mechanism during the past decade. The range of nozzle designs is extensive, each meeting a specific spray requirement. The classification (68) of pressure nozzles illustrates this extensive range with working drop-size data. The optimum operational conditions of a given pressure nozzle are limited, so selection of the most suitable nozzle for a given spray-dryer application requires careful consideration. Selection of nozzles is discussed by Tate and Wilcox (779).
Potassium acetate Potassium carbonai Potassium nitrate Potassium permanganate Potassium phosphate
Stickwater lfish
Sulfonated naphthalene Synthetic rubber (butadiene Tannin extracts, vegetable
Resins, melamine-forma Phenol-formaldehvda
Serum, human ste Silicon carbide Soap lsee Detergent Sodium acetate Sodium antimonite Sodium chloride Sodium chlorite Sodium cyanide Sodium fluoride Sodiym fluosilicate 'Sodium phosphates Sodium hypochloril Sodium silicates
Uranium oxide
Many data have been accumulated through investigation into the atomization characteristics of pressure nozzles (778)) liquid film properties (48),and the effect of physical properties and flow on the surface area of the resultant spray sheet (47). The extensive range of nozzles offered by manufacturers, in which each nozzle has an optimum feed rate and operating condition, has made direct approach to manufacturers the established practice for inquiries about nozzles for spray-dryer application. N o single correlation is appropriate to express the performance of such a varied range of nozzle designs. Many of the proposed correlations apply specifically to one nozzle design and one feed liquid. However, empirical equations are available for use with some confidence in initial design and performance calculations. Most quoted is the Lewis equation (7 74). The design of pressure nozzles is characterized by the way in which liquid rotation is imparted to the feed liquid. The internal design features determine the type of spray formed-e.g., hollow or solid cone, flat spray. Narrow feed channels and small orifices make such nozzles suitable for low-viscosity liquids containing no solids in suspension. However, a pressure nozzle design for pastes is claimed (97) that features feed rotation in two stages to give high capacity and uniform particle size from a solid cone spray. Two-fluid nozzles (pneumatic atomization). Pneumatic atomization results from the high frictional shearing forces between the liquid surface and a highvelocity gaseous medium. The theory and characteristics have been reported (87, 740). The gaseous medium may be expanded to greater than sonic velocity, where an apparent improvement in atomizer performance is attributed to shock wave effects. Air is rotated within the nozzle and contacted with the liquid within the nozzle (internal mixing) or as the liquid emerges from the orifice (62, 67) (external mixing). Two-fluid atomization is a successful technique for producing very small spray droplets. The amount of energy available for atomization is independent of feed rate, so spray characteristics can be adjusted over a wide range of feed rates. The most quoted empirical correlations for use in initial design and performance calculations have been proposed by Nukiyama (740), and Kim and Marshall (700). Two-fluid nozzles are widely applied in the spray drying of highly viscous solutions and heavy pastes. A nozzle design is claimed (794) for the atomization of highly viscous polyethylene (3000 cps) which incorporates internal mixing a t sonic gas velocities and pressures up to 200 psig. Other designs for highly viscous polyethylene incorporate a built-in heated mantle around the feed annulus ( 7 7 ) . Nozzle designs used for pastelike materials and featuring a screw feed to the nozzle head were proposed by Baran (72) and Turba (787). I n the Baran nozzle, air-feed mixing takes place within the nozzle head. A high feed:air operating ratio (8:l) is claimed to achieve complete atomization over a wide range of capacities. Conventional pneumatic nozzles require air :feed ratios as low as 0.5 : 1. Feed pressures of 100 56
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
psig are quoted as optimum, and the design allows easy scale-up. Liquids with viscosities of 100,000 cps have been atomized, and successful applications include titanium dioxide, calcium carbonate, clays, stearates, corn starch, and organic and inorganic pigments. Turba reports on tests conducted on a small spray dryer using 4oy0 calcium carbonate and 37.5y0 dihydrochlorite pastes. Data show the effect of nozzle annuli adjustments on air and feed rates, and over-all dryer performance. A further nozzle, claimed suitable for suspension atomization, features a feed annulus that is adjustable during operation (70). T o increase the energy needed to atomize liquids that form long strings of product from rotating disks and pressure nozzles, a pneumatic nozzle design incorporating two gaseous streams, one either side of the liquid stream, is used. Kim and Marshall (700) report a correlation that predicts drop size characteristics for this arrangement. Kirschbaum (702) went as far as to incorporate three air streams. The use of two streams for paste atomization is claimed (749) to be successful when the feed nozzle head rotates with the paste screw mounted on the head spindle. The use of a cool second air stream (772) can assist completion of the atomization mechanism of concentrated, highly viscous products-e.g., gelatin. Atomizing the solution into a cool zone prior to introducing the spray into the drying zone retards evaporation until the drops are fully formed. A further development of multihead pneumatic nozzles is described (764) where powder and liquid are fed to the nozzle lip in adjacent annuli. The lip is comprised of two air streams surrounded by two feed streams. Powder is fed by a screw conveyor which rotates a surface between the powder and liquid annuli. Kozzles containing both liquids and solids have been employed in the agglomerating process-e.g., instantizing of spraydried skim milk powder (137, 745). A comparison of disks, pressure, and two-fluid nozzles has been made (732) and illustrated by four typical spray-dryer applications. Sonic nozzles, Recently, attention has been drawn to the use of sonic nozzles for spray drying feed products that cannot be successfully atomized by pressure nozzles or rotating disks. The mechanism of atomization in sonic nozzles promotes the formation of uniform drop size. The energy transfer for atomization is greater than for conventional two-fluid nozzles, making atomization of highly viscous products more feasible. I n a sonic nozzle, high-frequency vibrations act on the feed liquid, causing the feed to oscillate with eventual instability and break-up. High-frequency vibrations are produced by high-velocity air by static generators-e.g., whistles-or by dynamic generatorse.g., sirens-or induced mechanically by transducers. For nozzles using high-velocity air, the static genAUTHOR Keith Masters is u Development Engineer on the
technical staff of Niro Atomizer, Ltd., in Cobenhagen, Denmark.
erator type is used in spray-drying applications. These nozzles feature the impaction of a high-velocity air stream into a resonance chamber situated close to the liquid distributor. The most common whistles include the Hartmann, Stemjet, and Vortex types (79). In each case, liquid is distributed around the resonance chamber as a thin symmetrical sheet from an annulus, or as fine spray jets from a ring of orifices. The Hartmann whistle features a jet nozzle facing the resonance chamber. The original concept dates from 1923 (84). The Stemjet is a development of the Hartmann type in which a cylindrical rod or stem forms the axis of the nozzle resonator system. The Stemjet can produce powerful vibrations at pressures below the critical pressure, the limit at which Hartmann types cease to function. The Vortex whistle incorporates high-velocity air tangentially entering a circular tube, thus forming a vortex. This creates sonic energy as the air emerges from the tube opening. Efficiency of the Vortex whistle is superior to the other two types. Airjet sonic generators are reviewed by Litsios (775). The fundamentals of ultrasonic atomization have been reported by Antonevich (6) from observations of liquid films excited ultrasonically. The prime cause of atomization is suggested to be rupture of capillary waves formed in the liquid film. Peskin and Raco (147) also review the fundamentals. However, the contribution of ultrasonic excitation of liquids to liquid spray formation, where whistle-type nozzles are used, is still open to question. Wilcox and Tate (797), investigating liquid break-up by high-intensity sound from Hartmann, Stemjet, and special elliptical deflector designs, did not substantiate the rupture mechanism. Atomization was satisfactory at low flow rates, but drop distribution was far from uniform, and increase in feed rate readily increased spray drop size. They concluded that no improvement in break-up could be attributed directly to liquid wave stability beyond that normally produced by high-friction air flow in conventional two-fluid nozzles of comparable air-liquid ratios. Experiments evaluating the performance of Vortex whistles are reported by Chanaud (35). While debate continues on the merits of sonic nozzles powered by high-velocity air jets, practical experience has found such types incapable of effective atomization of highly viscous feeds, the area in which application was considered most likely. Use of these nozzles in spray-drying operations is virtually negligible, although successful incorporation in small-diameter chambers has been reported (46). Development of sonic nozzles incorporating mechanically induced vibration devices appears to have been more successful. Data from Russian sources indicate that such nozzle types are applied in industrial spray drying. One nozzle type (26) features ultrasonic impulses generated by a magnetic generator up to 16 kHz, or with a piezoceramic generator employing 800 kHz. Drop-size data of sprays formed by nozzles with magnetic transducers are reported (757) ; the English translation is presented elsewhere (25). Further data
on the use of such a nozzle to atomize liquids and melts are given by Popov (752). Working equations for mean volume-surface diameter are proposed in terms of the operating parameters : liquid viscosity, surface tension and density, nozzle dimensions, frequency and amplitude of vibrations, and liquid feed rate. With the development of sonic nozzles, numerous patented designs have been claimed. A form of Stemjet which has a diverging outlet to allow controlled gas expansion is claimed to operate with spray size independent of viscosity (774). A working equation for drop size accompanies the claim. A compact, reverse high-velocity acoustic generator incorporated in a nozzle for spray-dryer application is also available (67). Piezoelectric crystals fed with suitable electrical signals have been used as devices for generating and delivering mechanical vibration to a nozzle (70). Generators in the form of a vibrating tube (49) or of oscillating plates (707) are also featured. Development of sonic nozzles for use in spray drying is still in an early stage. The advantage of sonic nozzles is low-pressure operation with no moving parts and with wide liquid channels. Suggested is their possible use for abrasive and corrosive materials, a further field where pressure nozzle and rotating disk atomizers are at a disadvantage. Perhaps the most immediate application of sonic energy in spray drying lies in the employment of ultrasonics for improved drying rates (80, 777). Smallsize chambers are employed and improvements in capacity offer great advantages. Spray-Air Contact and Flow Profile
The way in which spray is contacted with air is determined by the position of the atomizer in relation to the drying-air inlet. The actual flow profile is dependent upon the design of the air disperser incorporated into the dryer. Air flow within spray-drying chambers is a major consideration in obtaining optimum product quality at maximum evaporation capacities. The movement of air predetermines the rate and degree of evaporation by influencing the passage of spray drops through the drying zone, the concentration of product in the region of the chamber wall, and the extent to which semidried particles re-enter hot spots around the disperser (through eddy-flow effects). In spite of the importance of air flow to dryer performance, few published data are available covering the past few years. Air patterns and individual drop trajectories are difficult to analyze, as probing devices interfere with normal flow conditions. Masters ( 7 2 7 ) approached the problem by studying drop flow; he measured spray impingement at the wall of a small chamber (6 ft in diameter). The effects of feed rate, air rate, and disk speed on the extent of wall impingement were also recorded. The lack of rational analysis has led to industrial dryer designs based upon empiricial experience and to scale-up from inconclusive pilot-plant studies. Air flow is classified as cocurrent, countercurrent, or mixed flow (a combination of the former two), as reVOL. 6 0
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lated to the passage of product from the atomizer to the drying chamber outlet. General reference to the chamber designs incorporating these air flows is given in the Marshall monograph (779) and in more recent drying reviews (76,38, 54). Study of drop-air flow has been based on visual observations in model chambers and on the use of probes in pilot-plant spray dryers. Such studies have been accompanied by mathematical analysis of individual drop trajectory and velocity distributions in vortex and streamline flow. These flows are analogous to two common dryer designsi.e., chambers with rotating disks and nozzle towers. The calculation of drop flow is carried out in two stages. The first stage considers motion in the close vicinity of the atomizer. Here the drying-air profile has no influence on drop trajectory. The second stage considers drop trajectory to be that following the chamber air-flow profile created by the design of the air disperser. This last assumption is based on the drop deceleration’s being rapidly terminated, with the drops then fully influenced by the over-all chamber flow pattern. The calculation of drop trajectories from motion in a centrifugal flow profile is given by Lapple and Shepherd (777). Drop flow in dryer designs incorporating disk atomizers is illustrated by Charm (37). The radial distance of travel depends upon the disk peripheral speed, as does drop size. Since drop diameter is inversely proportional to disk speed, maximum distance is attained when the drag forces have increased to give a critical drop diameter. At higher speeds, the projection distance will decrease, even though the drops have greater initial velocities. The penetration of aqueous sprays into chambers with rotating disk atomizers is reported by Frazer (67). Drop motion for cocurrent streamline flow in nozzle towers has also been reviewed (767). Edeling (57) studied flow patterns in a cocurrent nozzle tower featuring tangential air inlet. Drop trajectories in upward motion have been calculated by Mori and Suganuma (732) who used dimensionless variables. Kessler (96) has investigated air-flow profiles in a cocurrent laboratory nozzle dryer (2.6 ft in diameter). A special air disperser was utilized to create both streamline and vortex motion in the dryer. The apparent advantages of such an air disperser have led to patented chamber designs (99, 784, 785). Buckham and Moulton (30) studied air-mixing effects in a cocurrent nozzle tower (12 ft X 4 ft in diameter). Arni (7) studied the effect of air-en;ry design on air flow in cocurrent and countercurrent nozzle dryers of similar dimensions. Place et al. (748) used helium as a tracer for air-flow investigation in a 50-ft countercurrent nozzle tower processing a detergent formulation. A pulse of tracer was injected into the inlet duct, and the concentration of helium at various positions in the system was recorded as a function of time. Results from the dryer were compared on a model (1 :80 scale) using water. The existence of a core of air with a high vertical velocity channeling along the axis of the dryer was suggested, but not substantiated by the tracer technique. Chaloud 58
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
et al. (34) reported on air-flow characteristics in an industrial cocurrent nozzle tower drying a detergent formulation. The vortex air pattern indicated large differences in the vertical and tangential velocities throughout the dryer width and the presence of an air core of high vertical velocity. The use of particle flow data to calculate spray-dryer dimensions is reported by Kessler (97). The use of general trajectory equations to predict performance of small dryers, whether employing rotating disks or nozzles, is illustrated by Gluckert (75). Spray-air contact is not restricted to a narrow range of operating variables for optimum moisture removal, With the ever-increasing variety of product applications, successful operation for certain materials necessitates low- or high-velocity air flows. Extremely low velocities have been employed in cool-air drying processes to prevent heat damage of highly sensitive products. Drying performed with low inlet temperature conditions requires chambers to be excessively large. Size can be reduced, while maintaining the advantage of cool-air drying, by fitting an after-dryer to the base of the chamber. Processing of tomatoes (78) and bananas (28) is an example of such design applications. The direct mounting of additional equipment under a dryer has been reported as advantageous in reducing space and dust problems of interequipment transfer. Combining a spray dryer and calciner in one housing is an example (704). Low-velocity spray-air contact has been adopted for the production of so-called “instant products.” Cool air passed around the atomizer retards the evaporation rate and increases the chance of particle agglomeration. Such units have large diameters, enabling sufficient residence time for complete moisture removal (92). High velocities can be used when the product can withstand rapid evaporation rates and the impact of air jets. The product is contacted as air is accelerated through a venturi from 25 to 1000 ft/sec (20). Successful operation on fine-mesh slurries of cement, lime, coal, and sand is claimed (777). Such a process has been termed jet spray drying. Similar advantages of high-velocity contact were achieved by locating the atomizer in an inverted cyclone (783). Evaporation
Studies and publications on evaporation in spray drying continue to be centered around academic projects. Few data have been made available by manufacturers. The complexity of the spray evaporation mechanism during the actual process is still as formidable as ever, with typical problem approaches continuing to be by study of the single- or dual-drop system in still air (94, 768). This is a highly simplified model of the evaporating conditions likely to be encountered in the turbulent air streams of the drying chamber. A general survey of evaporation is given in the Marshall monograph ( 7 79), which summarizes early contributions and the establishment of combinations of Nusselt, Reynolds, Prandtl, and Schmidt groups to describe heat
and mass transfer. Such relations have been found valid for forced and natural convection at low evaporation rates. Natural convection effects in spray drying have been recently studied theoretically and experimentally by Cornish (42). Calculation of forced and natural convection transfer followed by linear addition is a satisfactory procedure for determination of the over-all rate. High rates necessitate correction to the Nusselt number (76) as the temperature gradient in the air film surrounding the drop is complicated by diffusing vapor leaving the drop surface. The degree of correction required has been debated (778), and the problems of evaporation at high air temperatures have been noted (777). Studies (47) directed at spraydryer evaporation phenomena, and also at simplified systems, have indicated Nusselt numbers of 2 can be used in both cases. However, Bose and Pei (79) have found that relative motion between drop and air is significant in evaporation rates; this emphasizes the importance of spray-air contact. However, Kessler (98) drew opposite conclusions. Rowe et al. (757) reviewed published data on heat and mass transfer in the Reynolds number range of lo1 to lo4. The proposed exponents of the dimensionless groups are many and varied, the Ranz and Marshall (755) relations being considered most reliable. The evaporation rate is dependent upon the nature of the liquid, as this defines drop temperature. The drop temperature is dependent upon the nature of the evaporating liquid. For pure solvent, the wetbulb temperature of the surrounding air is used as close approximation, provided dynamic equilibrium has been attained and that the temperature of the surrounding air is not excessive. For drops containing dissolved solids, the presence of solute depresses the vapor pressure of the solvent. However, a saturated film is quickly established at the drop surface, and as long as this saturation is maintained, the drying rate is constant and the wet bulb temperature approximation is valid. The eventual formation of a dried crust at the drop surface disrupts the dynamic equilibrium and, during the resulting falling-rate drying period, drop temperature increases accordingly. For drops containing inert solids in suspension, the negligible lowering of vapor pressure enables drop temperature during the constant-rate drying period to be likened to a drop of pure liquid of identical size, evaporating under the same conditions. T o compute the evaporation characteristics of sprays, the fundamental heat and mass transfer mechanisms to single drops are assumed to be valid. Studies directed specifically at determining transfer rates in sprays decelerating from the atomizer have been reported by Manning and Gauvin (776). The treatment of the evaporation of a nonhomogeneous spray by a step-by-step method has been suggested by Marshall ( 7 77), rate determination being conducted for selected size ranges of spray distribution. Data on drop evaporation enable calculation of drop drying times. Such data are essential for sizing the dryer to minimize oc-
currence of wall deposits. The drying times for pure liquid sprays are given by Duffie and Marshall (50), and for drops containing dissolved solids by Charlesworth and Marshall (36). For drops containing solids in suspension, the constant and falling drying rates are considered separately. Data on the critical moisture content and drop diameter at the completion of the constant rate-drying period are required. The complete evaporation history of water sprays, where the size and location of the drops can be found at any given moment, is presented by Sjenitzer (169). A product having certain desired dried characteristics is the requirement of every spray-drying operation. Many products have properties that are influenced by the evaporation conditions--e.g., those having delicate structures which define special color, appearance, and aroma (756). Reineccius reports on the retention of volatile components during drying from studies of diacetyl, acetone, and acetoin addition to skim milk concentrates. The major variable affecting retention of the volatile compounds during spray drying was the total solids content of the skim milk. Virtually all spray-dried materials have requirements for moisture content, drop density, and drop size. Moisture content is dependent upon drying temperatures and residence time in the drying chamber. Bulk density depends on drying rate, spray characteristics, and product, Drop size is seldom constant throughout evaporation; hence the wet atomization spray characteristics cannot be equated to the dried drop-size distribution, Drop-size density and specific surface are variables of minor importance in terms of volatile retention (756). Crosby and Marshall (43) discuss the relation between dry drop-size distribution and the original wet spray. Over a range of operating temperatures and feed concentrations, the size distribution of dry product appears to be narrower than the original spray. The original spray corresponds to the square root normal law, but deviates from this law during drying. Only at low feed concentrations was this deviation minimized. Factors influencing dried product properties are comprehensively reviewed by Duffie and Marshall (50). The case of particle expansion is reported by Buckham and Moulton (30). The puffing of detergent particles has been established from an industrial spray-drying investigation by Moore (730). The volumetric expansion is expressed in terms of drop diameter (0.1 to 0.5 mm) over a temperature range of 120 to 180°F. Volume expansion ratios up to 3 were obtained within this temperature range. Product Applications
Substances that have been spray dried on the industrial or pilot-plant scale are given in Table I. The chemical industry continues to broaden the range of application. The dairy industry shows increased plant capacity with the domestic demand for instant products and the widespread utilization of milk products as constituents of animal feedstuffs. The food industry remains active, following the trend to food dehydration. VOL. 6 0
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The chemical industry already applies spray drying to high-capacity production. The spray drying of polyvinyl chloride (PVC) for plastics is a typical example. Of the two PVC forms, emulsion and suspension (each defined by the nature of its polymerization), the former can only be dried successfully by spray techniques. Emulsion PVC particles are colloidal, and the emulsion is fed to the dryer at 30 to 45% solids. Rotating disk or nozzle atomization can be employed. Excessive inlet temperatures are not used because of the product heat sensitivity. Gentle drying is essential as the “fish-eye” relation to PVC is due to heat damage. The dried product consists of hollow globules shaped from tiny cohesive particles. The degree of cohesion is regulated by the drying temperatures. The product is rather brittle in its dried form, and mechanical handling damage is minimized by using bag filters rather than cyclones for product-air separation. Suspension PVC consists of larger particles. Mechanical dewatering is possible in a centrifuge, from which an 80% solids suspension having a very loose consistency (PVC snow) is obtained. Spray drying is then conducted with a rotating disk atomizer specially designed for nonliquid feeds. Such a method is of great interest to firms having large capacity for emulsion PVC spray drying, but allows only limited suspension PVC production. PVC of very low moisture content results when a fluid bed dryer is used after the spray dryer. I n the field of agricultural chemicals, spray drying is applied to fungicides and herbicides. Disk atomization is preferred, as the resulting fine powder grain size enables even dosage distribution. Ethylenebisdithiocarbamates of zinc and manganese, colloidal sulfur, and copper oxychloride are examples of spray-dried fungicides. I n the production of herbicides, the sodium salts are usually spray dried. The sodium salt of dichloropropionic acid requires strict drying outlet temperature control as product burning is likely if variations of only 5 to 6°C occur. Automatic control and built-in water-spray safety devices are featured in the plant design. Further examples of spray-dried herbicides include the sodium salt of methyl chlorophenoxyacetic acid and the series of products having similar chemical structures. Both organic and inorganic dyestuffs are spray dried. There has been much recent interest in organic pigments or soluble dyestuffs. Dryer designs use rotating disk atomization as fine grain size is normally required, to less than 5p. Maximum inlet drying temperatures of 250°C are generally imposed. For coarser, nondusty specifications, nozzle atomization is applied. Dyestuffs are often produced in small quantities, and the cleaning aspects of dryer design receive careful consideration. I t is advantageous, however, to use one drying unit for one product. Dye-slurry drying with a rotating disk atomizer has been reviewed (4). Kirady (707) reports experimental spray drying of pigment slurries with pressure-nozzle atomization. The use of two-fluid nozzle atomization in the spray drying of aqueous acrylic polymer dispersion paints is 60
INDUSTRIAL A N D ENGINEERING CHEMISTRY
claimed to be of advantage (22). Feed solids up to 45y0 and outlet drying-air temperatures of 125’F result in a 4% moist product bearing the exact proportions of solid resin, pigment, pigment extender, and other water-soluble paint constituents. The use of high-velocity air in two-fluid atomization application is claimed to improve the final quality of aqueous dispersion paint compositions (27). For detergent manufacture, dryer design is dependent upon product type. Heavy-duty detergent units feature countercurrent air flow and pressure-nozzle atomization in tall and slender drying towers. Lightduty detergent units often feature cocurrent designs. Special product handling prevents particle fracture, Solid content of the feed can be up to 65%, and the powder is dried to 10 to lZyo moisture content. Inlet drying temperatures range to 350°C. Silvis (766) reports on all aspects of detergent drying. The adjustment of slurry formulations is reviewed in other articles (728, 770). Improved techniques for production of sodium tripolyphosphate for detergent slurries are based on a novel plant design featuring a combination of spray dryer and calciner (37). Further reference to slurry preparation includes improved dryer operation (32) and detergent processing (787). Moore (730) reports on the effect of drying variables on detergent powder characteristics. The ceramic industry widely utilizes spray drying, especially in the production of a ceramic press body following the wet process. The advantage of direct transformation of the slip into an immediately pressable material is in this instance particularly attractive. The physical properties of spray-dried material are ideal for pressing and firing operations, thus decreasing rejection percentage. The properties of materials that have been spray dried for dry pressing have been reviewed by Storm (175). With the development of abrasion-resistant surfaces, both rotating disk and nozzle atomization can be applied with equal success. Choice is dependent upon the most suitable particle size for the pressing operation. Disk atomization has been used in large-capacity units producing kaolin clay, ferrites, aluminum oxide, and wall-tile material. Nozzle atomization is widely applied to steatites and walltile material. Use of spray drying for ferrites has been reviewed (2, 3, 733). New applications of spray drying are reported for silicon carbide abrasive (33), superphosphate fertilizers (93), phosphorous-phosphoric acids (770), and latex toner (39). The successful application (747) to spent sulfite liquors, a by-product of the pulp and paper industry, has enabled powder to be marketed for such uses as dispersing agents in insecticides, gypsum-board manufacture, leather tanning, furnace clays, and animal-feed pelletizing. The conversion of crills from the pulp into a useful product can be accomplished by spray drying the crills in aqueous solution, using a special cellulose atomizer (735). Application of spray drying offers almost limitless possibilities for the food industry. Entwistle (54) and Patsavas (742) have reviewed spray drying from
the food industry’s viewpoint. Dairy products continue their rapid growth (55) through the diversity of specialized purposes for which powders can now be utilized. This has been accompanied by an increased demand for more stringent milk powder specifications. The spray drying of milk was the subject of a recent symposium organized by the Australian Society of Dairy Technology ( 8 ) . The definition of stable powder forms most suitable for specific production applications is reported in other literature (44, 737, 736), together with the development of processing techniques for high-tonnage production of premium-grade powder of special physical characteristics. The structure of milk powders and new forms of marketed powder are reviewed elsewhere (45). Instant powder forms the basis of a further review (44). Some recent patent claims for instant powder production include agglomeration during nozzle atomization (82, 708),lecithin dosage (792), and use of binding agents (60). The other main by-product of the dairy industry, apart from skim milk, is whey formed from cheese-making and from the manufacture of casein. Spray-dried whey powder is now utilized as a fodder additive and as a constituent in the confectionary industry. Three spray-drying processes for producing ordinary and nonhygroscopic whey are discussed by Galsmar and Bergmann (73). Two methods are reported for fresh whey, including virtually all types of cheese whey, where further bacterial acidification has been stopped by cooling. One method is reported for acid whey (pH < 4.6). Weber (790) reviews methods for whey utilization. Special techniques for the spray drying of other dairy products include drying of fat-containing milk products (758,793), ice cream mix (73), sour cream (739), cheese (7729, and dietetic products (729). The role of spray drying in the coffee industry is outlined by Sivetz (767). Recent literature is limited because, at present, more attention is being paid to freeze-drying techniques. However, improved extraction techniques which yield improved quality of sprayor freeze-dried products are reported (777). Improved flavor and aroma retention are claimed with a spraydrying process which includes coffee fines stabilization through encapsulation of fines with extract (750). The spray drying of coffee is covered in a patent (89). Adoption of the spray drying of citrus fruit (90)has led to improvements in the quality of fruit powders, reports Urbanek (786). The mechanism of spray drying is suited for such heat-sensitive products, and the use of a carrier gum and inert gas packing aid flavor retention and product handling of the hygroscopic powder. The production by spray-drying techniques of soluble citrus fruit powder free from preservatives results in the retention of natural fruit flavors (788). Successful application to raspberries (727) and to tomatoes is reported (74). The spray drying of tomatoes, apples, bananas, and vegetables, where skim milk is used as a carrier, is reported by Breene and Coulter (23). For flavoring materials, an imitation brown sugar processed by spray drying has been marketed
recently (59). There is news of the production of a low-calorie sweetener based on dextrin, and of at least one noncaloric sweetening agent (74). Pressure-nozzle atomization is employed with up to 6570 feed solids. The dried powder contains 6 to 10% moisture. An experimental investigation into the spray drying of flavoring materials is reported by Brooks (29). Measurements were made on the loss of ethyl caprylate dispersed in aqueous gum arabic. A process for the preparation of dry flavoring materials from crustaceans for human consumption is reported by Gray (78) to utilize a spray-drying stage. Dry, free-flowing glucose production from starch conversion also includes a spray dryer (706). The dryer features a special fines return system, whereby powder is returned to the atomization zone. The spray drying of molasses for animal fodder is described (773). Feed contains 3 to 8% kaolin, and is atomized by a rotating disk into a chamber having air-swept walls. The application of spray drying to potato processing has resulted in three patents (88,754, 765). A pneumatic paste nozzle is featured for atomizing the mashed potato; the process is claimed to prevent the breakage of the potato cells, which results in the formation of a glutinous mass on reconstitution. A 9-in. bowl atomizer, rotating at 4600 rpm in a cocurrent drying tower, is reported in the patent coverage (88, 754) where powder at 5 to 6.570 moisture (bulk density 0.5 to 0.6 g/cc) yields prime mashed potato flavor on reconstitution with water or milk. The bowl design and operation prevent cell rupture from excessive shearing effects. The spray drying of starch (both pregelatinized and cold-setting) is reported (707). High-pressure atomization is used to make pastry mixes (40). The modification of basic spray-dryer designs to meet sterile processing conditions is reported by Masters (723). The use of one- and two-stage units is described to deal with the low-feed solid contents usually dried. Blood serum application is referred to as an example. A laboratory dryer design for biological materials is described by Tschernitz (77). A thesis on enzyme spray drying has been presented by Shah (763). By utilizing spray drying, abattoir products formerly considered to be waste can be converted into highly profitable commodities. Abattoir by-products include blood, hair, glands, tissues, and organs. Bergsoe and Fakstorp (77) describe the production of dehydrated glands and tissues, and lay out the flow sheets for processing blood to give ordinary and soluble blood powder, blood cell powder, and blood albumin. The production of high-protein foodstuffs by spray drying of meat extract and hydrolyzate is noted (729). Economics
Spray drying has been accepted for the solution of conventional drying problems because the operation has proved not only efficient but economic. The economics of spray drying are discussed by Quinn (753). Over-all cost analysis illustrates how highly competitive spray drying is in comparison with other forms of drying, especially at high capacities. In a two-part article, VOL. 6 0
NO. i o O C T O B E R 1 9 6 8
61
Belcher et al. (75, 76) first discuss the reasons behind the greater acceptance of spray drying in the process industries, and then consider plant design in relation to the cost of spray drying. Bach-Xielsen and Rasmussen ( 9 ) analyze performance data of industrial spray dryers. Plant data form the basis of a comparison between spray and alternative drying methods. The economics of spray dryers utilizing high-inlet temperatures are discussed with reference to the drying of kaolin clays. Jury (95)discusses heat and power costs as related to the total solids content of the feed and drying temperatures. Factors for design consideration are described. Reduced operating costs result from inplace cleaning to cut downtime, which also improves the quality of spray-dried eggs (58),many types of which are produced on the same spray drier. New Spray-Dryer Developments
Developments recently have been reported in closedcycle operation (743), full plant automation (746, 759, 767), spray cooling (24, SS), and spray freezing (83). Use of sonics to promote increased evaporation rates has been reviewed in a previous section. Drying under pulsating vacuum also has been discussed (746). Moisture is flashed off by subjecting the product to hot air at atmospheric pressure, followed by evacuation. Closed-cycle operation leads spray-dryer application into fields where materials dispersed in solvents can be dried and the solvent can be recovered and reused. Evaporation in atmospheres other than air promotes possibilities for processing products that are explosive or chemically reactive in air. The closed-cycle principle has also been adopted to sterile operation. Any required drying pressure or vacuum can be applied. A fully automated spray dryer for milk is reported in operation in Scandinavia (737, 759). A single button initiates the start-up sequence which can be followed on the schematic control panel. Shut-down procedure is also automatic. The instrumentation diagram for the plant is given. The automation of both evaporator and spray dryer is reported from Scandinavia (760). Four automatic layouts illustrate how the two items of equipment can be coupled together, thus eliminating the need for intermediate storage. Plant control is based on the automatic measurement of milk solid content leaving the last stage of the evaporator. Better consistency of powder quality is reported. The possibility of automatic addition of additives to the milk concentrate is another advantageous feature. *4quadruple effect evaporator working in conjunction with an automatic spray dryer is also reported (738). The arrangement features low steam consumptions at increased powder capacity. Spray cooling features atomization of material that solidifies at atmospheric temperature. Such products, when processed by conventional techniques require substantial manual labor, but the development of suitable nozzles has opened up potential spray-cooling application. The need for refrigerating equipment to chill the air entering the unit is still considered an un62
INDUSTRIAL A N D ENGINEERING CHEMISTRY
favorable process feature. The use of spray cooling in the rationalization of the wax industry is reported by Andracek (5). A basis for the design of spray-drying towers is also given. Application of a new continuous spray-freezing process has been reported by Hansen (83). The process features liquid atomization into refrigerated air or nitrogen, forming free-flowing particles. The particles enter a degassing system and are fed at a uniform rate into heated filter tubes for quick vapor removal. Sublimation heat comes from the air-heated shell of the tubes. Coffee extract has been processed, and qualities comparable to normal freeze-dried coffee have been obtained. Development is still in the pilot-plant stage. The spray-freezing principle in a closed cycle has been used for coffee extracts and citrus fruit (57). The feed is atomized with a pressure nozzle into a vacuum freezing chamber. The resulting frozen droplets pass to a vacuum-drying section. Drying is conducted under a relatively high pressure. The system can operate continuously without the need for make-up air. REFER EN CES (1) Adler, C. R., and Marshall, W. R., Chem. Eng. Progr., 47 (lo), 515-27; (12), 601-8 (1951). (2) Allen, A . C., Ceram. Ind., 82 (Z), 45-8 (1964). (3) Ibid., 88 (3), 62-5 (1967). (4) Amer. D y e s t u j Reptr., 52 (5), 185 (1963). (5) Andracek, A,, Chem. Tech., 11, 646 (1965). (6) Antonevich, J. N., Proc. A‘atl. E h t r o n . Conj.,13, 798-807 (1957). (7) Ami, V. R. S., Ph.D. Thesis “ T h e Production Movement and Evaporation of Sprays in Spray Driers,” U n h . of Washington, ?959; Micrbfilm No, 59-5454, University Microfilms, Inc., Ann Arbor, Mich. (8) Austral. Soc. Dairy Technol., Tech. Publ., No. 16 (1965). ( 9 ) Bach-Nielsen, H., and Rasmussen, E., Inst. Chem. Eng. Symp Ser 4th Congr. of the European Federation of Chemical Engineering, Londbn, Nb. 20, 63-6 (1966). (10) Badische Anilin u. Sodafabrik AG., Brit. Patent 944,320 (Dec 11, 1963). (11) Badische Anilin u. Sodafabrik AG., Dutch Patent 6,517,098 (June 30, 1966). (12) Baran, S. J., IND.ENO.CHEM., 5 6 (lo), 34-6 (1964). (13) Bassett, H. J., U S . Patent 3,215,532 (Nov 2, 1965). (14) BeatriceFood Co., ibid., 3,353,969 (Nov 11, 1967). (15) Belcher, D . W., Smith, D. A., and Cook, E.-&$., Chem. Eng., 70 (201, 83-8 (Sept 30, 1963). (16) Ibid., pp. 201-8 (Oct 14, 1963). (17) Bergsoe, C., and Fakstorp, J., Food Industries of South Africa, 29 (May 1950). (18) Birs A . G., Brit. Patent 1,015,599 (Jan 5 , 1966). (19) Rose, A. K., and Pei, D. C. T . , Can. J . Chem. Eng., 42 (61, 259-62 (1964). (20) Bradford, P., and Briggs, S. W., Chem. Eng. Progr., 59 (3), 76-80 (1963). (21) Bray, W. J., U S . Patent 3,287,290 (Nov22, 1966). (22) Ibid., 3,325,425 (June 13, 1967). (23) Breene, W. M., and Coulter, S. T., J . Doiry Sci.,50 (7), 1049-54 (1967). (24) Brit. Chem. Eng., 11 (41, 236 (1966). (25) Ibid., (31, p 226. (26) Ibid., (9), p 1049. (27) Ibid., 12 (11, 87-91 (1967). (28) Ibid., (11), p 1754. (29) Brooks, R., Univ. Birmingham Chem. Engr. (Eng.),16 (I), 11-16 (1965). (30) Buckham, J. A . , and hloulton, R. IV., Chem. Eng.Progr., 5 1 (3), 126-33 (1955). (31) Buttner-Werke Ag., Brit. Patent 1,026,675 (April 20, 1966). (32) Casridy, J., Pals, R., and Harris, H. C., U S . Patent 3,054,656 (Sept 18, 1962). (33) Ceramics, 11, 15-16 (May 1960). (34) Chaloud, J. M., Martin, J. B., and Baker, J. S., Chem. Eng. Progr., 53, 593 (1957). (35) Chanaud, R. C., J. Acous. Soc. Anrer., 95 (5), 953-60 (1963). (36) Charlesworth, D . M., and hlarshall, W. R., A.I.Ch.E. J.,6 (l), 9-23 (1960). (37) Charm, S. E., “Fundamentals of Food Engineering,” Avi Publishing G o . , Westport, Conn., 1963. (38) Chem. Eng., 74, 173-9 (June 19, 1967). (39) Clements, C. F., and Lenhard, M. J., U S . Patent 3,326,848 (June 20, 1967). (40) Colby, E. E., ibid., 3,257,213 (June 21, 1966). (41) Consilio, J. A , , and Sliepcevich, C. M., A.I.Ch.E. J., 3 (3), 418-27 (1957). (42) Cornish, A , , Instit. Chem. Eng. (Student Sec.) Symp., “Spray Processes,” Bradford, England (Sept 1966). (43) Crosby, E. J., and Marshall, W. R., Chem. Eng. Progr., 54 (7), 56-63 (1958). (44) Dairy Eng., 80, 58 (Feb 1963). (45) Dairy Ind., 31 ( 8 ) , 634-5 (1966). (46) Demister, Ltd., Malmo 20, Sweden, Pamphlet: “Sound Sources for Tomor. row’s .4coustic Processing,” 1965.
(47) Dloughy, J., and Gauvin, W. H., A.Z.Ck.E. J., 6 (l), 29-34 (1960). (48) Doumas, M., and Laster, R., Ckem. Eng. Progr., 49 ( l l ) , 518-26 (1953). (49) Drayer, W. L., US. Patent Re. 25,744 (March 16, 1965); Original: U.S. Patent 3,123,302 (March 3, 1964). (50) Duffie J A andMarshall, W. R., Ckem. Eng. Progr., 49 ( 8 ) , 417-23 (1953); ibid., (9),’pp 4dO-6 (1953). (51) Edeling C “Untersuchungen zur Zerstrubungstrocknung,” Angcw. Chcm., und Ckem.-ing. ‘ikch. No. 57,l-53 (1949). (52) Eisenklam, E. P., Ckem. Eng. Sci., 19, 673-4 (1964). (53) Englberger, A,, and Zmyle, E., W. Ger. Patent 1,196,127 (March 10, 1960). (54) Entwistle,R. E., FoodEng., 38 (2), 82-6 (1766). (55). Fpod and Agriculture Or anization of United Nations (FAO): ‘‘Annual Statistics Milk Products,” 176f. (56) Food Eng., 39 ( l l ) , 109-10 (1967). (57) Food Machinery Corp., Brit. Patent 1,086,251 (Oct 4, 1967). (58) Food Process.-Marketing, 28 ( 8 ) , 34-6 (1967). (59) Ibid., (7) 52 (1967). (60) Foremost Dairies, Inc., Brit. Patent 1,072,816 (Jan 21, 1967). (61) Fortman, W. K., U S . Patent 3,297,255 (Jan 10, 1967). (62) Frazer, R. P., Brit. Patent 664,676 (Jan 9, 1952). (63) Frazer, R. P., Dombrowski, N., and Routley, J. H., Ckem. Eng. Sci., 18,315-21 (1963). (64) Ibid., pp 323-37. (65) Ibid., pp 339-53. (66) Frazer, R. P., and Eisenklam, E. P., Trans. Inst. Chem. Eng., 34, 294-315 (1956). (67) Frazer, R . P., Eisenklam, E. P., and Dombrowski, N., Brit. Chem. Eng., 2 ( 9 ) , 496-501 (1957). (68) Ibid., (lo), 536-543 (1957). (69) Zbid., ( I l ) , 610-613 (1957). (70) Freeland, W., and Freeman, R. R., U.S.Patent 3,317,139 (May 2, 1967). (71) Tschernitz, J. L., and Marshall, W. R., Biotech. Biochem., 6 (4), 473-90 (1964). (72) Friedman, S . J., Gluckert, F. A., and Marshall, W. R., Chem. Eng. Progr., 48 (4), 181-91 (1752). (73) Galsmar, I., and Bergmann, A,, J . Dairy Tech., 20 (Z), 106-10 (1967). (74) Gebhardt, H. T., U.S. Patent 3,320,074 (May 16,1967). (75) Gluckert, F. A., A.Z.Ck.E. J., 8 (3), 460-6 (1762). (76) Godsave, G. A. E., 4th International Combustion Symp. Proc., Cambridge, Mass. (Sept 1952). (77) Graham, W.A., U S . Patent 3,269,660 (Aug30,1966). (78) Gray, R.D., ibid., 3,264,116 (Aug 2, 1966). (79) Greguss, P., Ultrasonics, pp 5-10 (Jan/March 1964). (80) Zbid., pp 83-86, (April/June 1963). (81) Gretzinger, J., and Marshall, W. R., A.I.Ch.E. J., 7 (2), 312-18 (1961). (82) Hanrahan, F. R., U.S. Patent 3,185,580 (May 25,1965). (83) Hansen, O., Food Engrg., 39 (6), 73-5 (1967). (84) Hartmann, J., Phys. Rev., 20, 719 (1923). (85) Hege, H., Chem. Ins. Tech., 36 (l), 52-9 (1764). (86) Hege, H., U S . Patent 3,250,473 (May 10, 1966); ibid., 3,345,192 (Oct 10, 1967). (87) Herring, W. M., and Marshall, W. R., A.I.Ck.E. J., 1 (Z), 200-9 (1955). (88) Hollis, F., U.S. Patent 3,220,857 (Nov 30, 1965). (87) Huste, A,, Breza, R. J., and Kohler, R . B., US. Patent 3,345,182 (Oct 3, 1767). (90) Znd. Gas, 26,304 (Jan 1963). (91) Industrie-Werke, Karlsruhe, A. G., Dutch Patent 6,613,056 (June 19, 1967). (72) Industrie-Werke, Karlsruhe, A.G., Brit. Patent 1,044,268 (Sept 28, 1966). (93) Ingenipens Ugeblad, Copenhagen, No. 47 (Nov 20, 1965). (94) Johns, W. R., Instit. Chem. Eng. (Student Sec.) Symp., “Spray Processes,” Bradford, England (Sept 1966). (95) Jury, E., Interceram, No. 2, 1-3 (1966). (96) Kessler, H. G., Ckem. Zng. Tech., 96 (5), 479-84 (1964). (97) Ibid., 39 (lo), 601 (1767). (98) Kessler, H. G., D S c . Thesis, MIT, Cambridge, Mass. (1952). (97) Kessler, H. G., W. Ger. Patent 1,199,191 (March 10, 1966). (100) Kim K Y and Marshall, W. R., A.I.Ch.E., 58th Natl. Meeting, Philadclihia‘(Dez 1965). (101) Kirady, G., Brit. Ckem. Eng., 5 ( l l ) , 791 (1960). (102) Kirschbaum, E., W. Ger. Patent 857,924 (Oct 9, 1952). (103) Klimov, I. S., Russ. Patent 186,885 (Oct 3, 1960). (104) Kotelnikov, G. R., U.S. Patent 3,289,732 (Dec 6, 1966). (105) Kozlovskii, 0. V., T r . VoIo odsk Molockn. Inst., Tekknol Fak 49, Summarized in English: Dairy Sci. Abstr., 28 (lo), 547 (1967). (106) Kroyer, K. K. (to Niro Atomizer), Brit. Patent 1,075,161 (July 12, 1967). (107) Kuchinke, E., and Buchta, K., U.S. Patent 3,332,785 (July 25, 1967). (108) Laguilharre Co., Brit. Patent 1,071,850 (June 14, 1967). (107) Lang, R . J., U.S. Patent3,103,310 (Sept 10, 1963). (110) Lanham, W. M., ibid., 3,113,063 (Dec 3, 1963). (111) Lapple, C. E., and Shepherd, C. B., IND.ENG.CHEM.,32 (5), 605-17 (1940). (112) Laster, R., Bower, H. S., and Huste, A., U.S. Patent 2,824,807 (Feb 25, 1958). (113) Lespagnol, M. J., Fr. Patent 1,437,582 (March28, 1966). (114) Lewis, H. C., Edwards, D. G., Goglia, M . J., Rice, R. I., and Smith, L. W., IND.ENC. CHEM.,40, 67 (1948). (115) Litsios, J., I.E.E.E. Trans., “Ultrasonic Engineering,” No. 9, 71-5 (1963). (116) Manning, W. P., and Gauvin, W. H., A.Z.Ck.E. J., 6 (2), 184-90 (1960). (117) Marshall, W. R., Amer.Soc. Meck. Engrs., Trans., 77 ( l l ) , 1377-85 (1955). (118) Marshall, W. R., Chem. Can., 7, 57 (1955). (117) Marshall, W. R., Ckem. Engrg. Progr. Monograph Ser., 50 ( 2 ) (1954). (120) Masters, K., Brit. Chem. Eng., 12 (12), 1890-3 (1967). (121) Zbid., 13 (l), 88-9 (1768); (Z), 242-4 (1968). (122) Masters, K., Inst. Chem. Eng. (Student Sec.) Symp., “Spray Processes,” Bradford, England (Sept 1966).
(123) Masters,K., Proc. Biochem., 2 (6), 15-18 (1967). (124) Masters, K., Uniu. Birmingham Ckem. Engr., England, 17 ( l ) , 18-24 (1966). (125) McCormick, P. Y.,IND.ENC.CHEM.,5 6 (lo), 57-60 (1964). (126) Ibid., 58 ( l l ) , 59-60 (1966). (127) Meyer-Frohlick, H., W. Ger. Patent 1,225,952 (Sept 29, 1966). (128) Milwidsky B. M., Sodp Ckem. Specialities, 38 (lo), 59-62; ( l l ) , 56-60; (12), 73-6 (1962). (129) Mohler, H., and Menzi, R., W. Ger. Patent 1,084,557 (July 7, 1766). (130) Moore, H Inst. Chem. Eng. (Student Sec.) Sym “ S ray Processes,” Bradford, Englffnd (Sept 1966); Rev. in Brit. Chem. Eng., &’(l), i7-91 (1967). (131) Moore J. G Hesler W. F., Vincent, M. W., and Dubbels, E. C., Ckem. Eng. Progr., 60 63”6 (1964). (132) Mori, Y . , and Suganuma, A., Kagaku Kogaku (Japan) (abridged ed. in Ens.), 4 (Z), 228-31 (1966). (133) Motyl, E. J., Western EIec. Epgr., 7 (31, 2-10 (1963). (134) Neilsen, K., Fr. Patent 1,474,280 (Feb 13, 1967). (135) Niro Atomizer, Brit. Patent 1,026,177 (April 14, 1966). (136) Nord. Mejeri Tidsskr., 30 (4), 65-7 (1964). (137) Ibid., 32 (3), 53-5 (1966). (138) Ibid., 33 (4), 83-5 (1767). (139) Noznick, P. P., Brit. Patent 1,072,308 (June 14,1967). (140) Nukiyama, S and Tanasawa Y Trans. SOL.Mech. Eng. Japan, Rcpls. 1-6, 4-6 (1938-40). ?ram. Hooc-Defincd’Res. Board Dept. Natl. Defence, Canada 10, M-9-47 (39:) H.Q. 2-0-264-1 (March 18,1950). (141) Paper MiNs News (April 8, 1963). (142) Patsavas, A. C., Ckem. Eng. Progr., 59 (4), 65-70 (1963). (143) Patsavas, A. C.. and CAttrell, C. E., A.1.Ch.E. 58th Natl. Meeting, Philadelphia (Dec 1965). (144) Peebles, D. D., U.S. Patent 3,095,149 (June25,1963). (145) Ibid., 3,279,724 (Oct 18, 1766). (146) Pennsalt Chem. Corp., Brit. Patent 1,044,164 (Sept 28, 1966). (147) Peskin, R. L., and Raco, R. J., J. Acoust. Soc. Am., 35 (9), 1378-81 (1963). (148) Place, G., Ridgway, K., and Danckwerts, P. V., Trans. Inslit. Chcm. Eng., 37, 268-76 (1959). (149) Pochmiiller, E., W. Ger. Patent 1,154,400 (April 2, 1964). (150) Ponzoni, G. B., U S . Patent 3,261,689 (July 7, 1966). (151) Popov, V. F., Kkim. Prom. (Russ),No. 12,18-21 (1964). F., and Goncharenko, G. K., ibid., Trans. into English, Foreign n: Air Force Systems Command, Wright Patterson Air Force Base Ohio F.T.D. TT-65-1445.1.2.4. (153) Quinn, J. J., IND.END.CHEM.,57 ( l ) , 35-7 (1965). (154) Rainwater, J. H., and Beck, R. G., W. Ger. Patent Appl. 1,245,272 (July 20, 1967). (155) Ranz, W. E., and Marshall, W. R., Chcm. Eng. Progr., 48 (3), 141-6 (1952). (156) Reineccius, G. A., Coulter, S. T., and Breene, W. M., J . Dairy Sci., 50 (6), 937 (1967). (157) Rowe, P. N., Claxton, K. T., and Lewis, J. B., Trans. Inst. Ckem. Engrr. (London), 43, T14-T31 (1965). (158) Saslaw, M., and Brady, J. J., U.S. Patent 3,295,986 (Jan 3, 1967). (159) Scand. Galaxy, No. 2 Publ., P.O. Box 1648, Vanlpise, Denmark (1966). (160) Ibid., No. 3 Publ., P.O. Box 1648, Vanlpise, Denmark (Spring e d . , 1968). (161) Scott, R., Dairy Ind., 32 ( l l ) , 811 (1967). (162) Seltzer, E., and Marshall, W. R., Chem. Eng. Progr., 46 (lo), 501-8 (1950). (163) Shah, V. D., Ph.D. Thesis, Univ. of Wisconsin, “Spray Drying of Enzyme Rennen,” 1963. (164) Siegenthaler, K., and Wild, H., Brit. Patent 1,028,004 (May 4, 1966). (165) Sienkiewictz, B., U S . Patent 3,261,695 (July 19, 1966). (166) Silvis, S. J., J . Amer. OiI Ckrm. Soc., 41,4-6,36-45 (Dec 17, 1964). (167) Sivetz, M. S . , and Foote, H “Coffee Processing Technology,” Avi Publishing Co., Westport, Conn. (1963): (168) Sjenitzer, F., Chem. Eng. Sci., 1 (3), 101-17 (1952). (169) Ibid., 1 7 (5), 309-22 (1962). (170) Soap Chem. Specialties, 98 (2), 147-9, 157 (1962). (171) SOC.Des. Produit Nestlt, S.A., Fr. Patent 1,483,823 (June 9, 1967). (172) SOC. Latiere du Pays d’Auge, “Solaipa,” Fr. Patent 1,477,638 (April 21, 1967). (173) Soloff, R. S . , J . Acoust.Soc.Am., 36 (5), 961-5 (1964). (174) Sonic Devel. Corp. America, Brit. Patent 1,063,860 (March 30,1967). (175) Storm, J., Third Colloquium on Dry Pressing, Bologna, Italy (March 14, 1966). (176) Sweeten, J. L., and Paul, G. H., Fr. Patent 1,444,632 (May23,1965). (177) Tailor, J. P., U.S. Patent 3,275,063 (Sept27, 1766). (178) Tate, R. W., and Marshall, W. R., Chem. Eng. Progr., 49 (4), 169-74; (S), 226-34 (1953). (179) Tate, R. W., and Wilcox, R. L., MiIk Products J., 52 (Feb 8, 1961). (180) Turba J Magyl Kern L a j a 10 (121, 641 (Hun) (1965); Rev. in Eng., Brit. Chem.’EAi., 11 (4), 304 (1t6d). (181) Turba, J., andNemeth, J., Brit. Ckem. Eng., 9 (7), 457-60 (1964). (182) Turner, G. M., and Moulton, R. W., Chrm. Eng. Progr., 49 (4), 185-90 (1953). (183) Uhlmann, S., Petzold, K., Mucke, E., and Heyde, Sj., E. Ger. Patent 54,302 (Feb 20, 1967). (184) Uhlmann, S., and Riehmer, H., E. Ger. Patent 51,254 (Oct 20, 1966). (185) Uhlmann, S., and Riehmer, H., E. Ger. Patent 56,223 (May 20, 1967). (186) Urbanek, J., Canner/Pncker, 135 (l), 52-3 (1966). (187) Versen, R. R., U S . Patent 3,334,049 (Aug 1, 1967). (188) Villarreal, J. R., ibid., 3,298,838 (Jan 17, 1767). (189) Walton, W. M., and Prewett, W. C., Proc. Pky. Soc., 6 2 B, 341 (1749). (190) Weber, G., Molk. Zeit. (Ger.), 88 (25), 1051-6 (1967) (191) Wilcox, R. L., andTate, R. W., A.Z.Ch.E. J., 11 (l), 69-72 (1965). (192) Williams, A. W., and Busch, A. A,, U.S. Patent 2,378,310 (Oct 11, 1966). (193) Williams, A. W., and Busch, A. A., Can. Patent 749,902 (Jan 3, 1967). (194) Wright, J. F., and Sharan, N. D., Brit. Patent 1,033,647 (June 22, 1966).
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No, Kay-Fries does not make polymers, or even the standard monomers. But we do make unusual organics that can make polymers do the special things you want them to. Some of our ortho esters, for example, are adept at adding to double bonds, as in chain terminating reactions. Other ortho esters - unsaturated ones - are unusually interesting for cross-linking and stabilizing applications. Cross-linking
is also a potential of some of our inalonaldehyde acetals. Or take cyanoacetic acid and its many derivatives, in which Kay-Fries pioneered. Aside from their utility in making cyanoacrylics, they offer a reservoir of possibilities as intermediates for special resins. Our newest family - OctriP" (1, 3, 5pentanetricarboxylic) acid and its derivatives - will give you
some new thoughts on alkyd resins, epoxy curing agents, plasticizers and chelation-type applications. And there are still others, like Kay-Fries phthalate esters, crotononitrile and allyl cyanide. This extensive variety merely proves what we've said all along-if your special problem calls for an unusual organic, try Kay-Fries. Kay-Fries Chemicals, Inc., 360 Lexington Avenue, New York, N.Y. 10017.
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Kay-Fries Chemicals, Inc. the chemist's chemist
