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J. D. MINFORD and
T.
S. HUMPHRIES I
Alcoa Research Laboratories, Aluminum Co. of America, New Kensington, Pa. I
Products I
Aluminum Alloy Equipment for Controlled Quality Production
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Aluminum offers special advantages in the processing of food, drugs, and chemicals when color, purity, and quality of product are a prime consideration J
S E L E C T I O N of a material of construction in the chemical industries is based on a number of factors, such as the service life of the equipment, its cost, and the effect of the material on the chemical product that it contacts. In selecting a material of construction for a given application, there is frequently one dominant characteristic of the material that is essential to satisfactory performance. Hence the material is chosen with primary consideration of the dominant characteristic and the best possible compromise is made with the other desirable characteristics. Some of these characteristics are good heat conductivity, availability, ease of working, forming, and welding, light weight, and adequate strength. Aluminum has these characteristics and, in addition, offers other advantages in the chemical and food industries where products of controlled quality are required. Some of these advantages are high resistance to corrosion, nontoxicity, and the fact that aluminum does not contribute to discoloration of product or catalyze oxidative sludging. inorganic Chemicals In the production and handling of inorganic chemicals, aluminum has high resistance to corrosion and does not contribute to discoloration of these products or catalyze oxidative reactions. Aluminum is used for pipes, spray nozzles, screens, ductwork, and in equipment for sizing operations in the handling of alum in the paper industry because it does not cause discoloration and reduces the acidity of the chemical. Ammonium thiocyanate is produced and shipped in aluminum to ensure purity of product. Aluminum-lined baskets are used for handling and aluminum equipment for drying calcium hypochlorite. Catalytic fluorophosphates are prepared in aluminum reactors to ensure a satisfactory product. Aluminum is used for distillation towers, heat exchangers, storage tanks, piping, drums, and tank cars to minimize decomposition of hydrogen peroxide. If
strength is an important requirement, certain aluminum magnesium alloys of controlled purity are used. Phosphor suspensions are handled in aluminum containers to avoid heavy metal contamination, and, for the same reason, potassium pyrophosphate is cast, crushed, and shipped in aluminum. The color quality of titanium dioxide, a paint pigment, is maintained when it is dried in aluminum equipment. Other important inorganic chemicals with which aluminum is used to advantage are ammonium carbamate and carbonate, aluminum formate, and calcium phosphate and carbonates. Cosmetics Among the organics used in the cosmetics industry are the natural and synthetic oils, fats, and waxes; liquid, semisolid, and solid hydrocarbons; soaps and synthetic surface active agents; starches, gums, and resins; dyes and pigments; and acids, alcohols, and esters. Proper clarity and purity of these products are maintained in aluminum storage containers because the reactivity of these compounds with aluminum is slight. Water-clear glycerol, ammonium thioglycollate, hydrogen peroxide, and high purity water are handled in aluminum to provide quality control. Essential Oils Although the volume of production of the essential oils is small by comparison with other industrial chemicals, the dollar volume is considerable and the purity requirements are stringent. These materials are employed primarily in the manufacture of perfumes, flavors for food, and in pharmaceuticals to make the product more acceptable for oral or external application. Aluminum serves well as the material of construction for process equipment and for subsequent transportation and storage, as shown in Table I. Storage is a difficult problem because the materials are often complex mixtures and rancidity readily occurs in the presence of some materials of construction.
Explosives The corrosion resistance and nonsparking characteristics and the inertness of compounds of aluminum have resulted in its use in the explosive industry. Nitroglycerine is stored in aluminum tanks. Aluminum hoods, ducts, wash tanks, and extractors are used in the manufacture of gun cotton. Gelatin dynamite is dried, mixed, and packaged in aluminum equipment. Because of its high resistance to corrosion, aluminum is a preferred material of construction for contact with ammonium nitrate. The rapid growth of the fertilizer industry has resulted in a large increase in ammonium nitrate production, and, as a result, increasingly large amounts of aluminum equipment are employed. The nonsparking characteristic of aluminum is important when ammonium nitrate is handled as an explosive.
Food Aluminum possesses several advantages that make it desirable for use in the food industry. Important is the fact
Table I.
Essential Oils Compatible with Aluminum
(Soap Sanit. Chemicals, Blue Book, Catalog ed., 1950)
Acetophenone Benzyl acetate Eugenol and isoeugenol Geranyl acetate Hydroxycitronellal Linalyl acetate Methyl acetophenone Methyl anthranilate Methyl phenyl acetate Methyl salicylate Oil bois de rose Brazilian (oil rosewood) Oil cedarwood and cedarwood Texas Oil citronella Ceylon Oil citronella Java
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Oil copaiba (copaiva oil, copaiva balsam oil) Oil of lavandine (wilo lavender, lavande grosse) Oil lemongrass Oil peppermint Oil petitgrain Paraguay (oil petitgrain South America Oil spike (oil lavender spike, oil lavender Spanish, oil Spanish, spike, oil aspic) Oil of wintergreen Terpineol Terpinyl acetate Safrol
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Aluminum is one of the few materials of construction recommended for the processing of edible gelatin because its use results in a high purity product. I t is commonly used for heating coils, cookers, piping, receiving tanks, filters, evaporators, drying tunnels and screens, conveyors, and storage tanks. Aluminum is used in culture vessels and storage and transportation containers for yeasts because of its nontoxicity for microorganisms. Household yeast is packaged in aluminum foil. Aluminum-lined steam tube dryer ( 1 0 ft. diam. X 100 ft. long) with extruded tubes with integral longitudinal fins in the wet end (top picture). Aluminum heat exchangers for processing of edible oils (bottom picture) that aluminum is found in all foods and ordinary drinking water; in many instances it is present in amounts greater than found in foods after the food is cooked or stored in aluminum equipment (report of Federal Trade Commission, Docket 3874, 1900). Aluminum does not accelerate the destruction of vitamins or other accessory food factors, does not promote hydrolysis or pro-oxidative reaction of fats and oils, and is a good conductor of heat. I n the processing, packing, and storage of foods, aluminum is used for steam-jacketed cookers, tanks and vats, linings for storage and transportation containers, collapsible tubes, rigid packages, drums, pails, trays, bottle caps, closure, and foil. Food products such as flour, sugar, cocoa, soluble coffee, and salt are handled in bulk containers made of aluminum to protect against change of color and flavor. The use of aluminum as a storage and packaging material for foods is increasing rapidly. Unique packages whereby rapid freezing, storing, heating, and serving are accomplished with one container utilize large quantities of heavy gage aluminum foil. In Norway, it is common practice to package fish,
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meat products, oils, fats, and certain vegetables, such as peas and asparagus, in rigid aluminum cans. The darkening of products such as fish is avoided by the use of aluminum. A host of bakery products not only are prepared but also are baked in aluminum utensils which enable an even distribution of heat that results in excellent texture, crisp crusts. and general improvement of quality. Disposable pie plates and cake pans of heavy gage aluminum foil recently have come into Tvidespread use. Aluminum is a standard material of construction for handling and storing dairy products, especially in Europe. In the United States, butter and cheese are produced in aluminum equipment and packaged in aluminum foil to aid in the marketing of high quality unaltered, commercially acceptable products. ,4luminum neither discolors nor catalyzes the oxidation of edible oils and fats and hence is used for rendering and storage of margarine, lard, and coconut, cottonseed, olive, soy bean, peanut, and palm oils. I t also is used in the margarine industry for equipment such as kneading machines, cooling and dropping vats, trolleys, pails, and foil packaging.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Microbiological Processes Because of its nontoxicity to microorganisms, aluminum is used for equipment in which chemicals are produced by microbiological processes. High yield and a product free of heavy metal contamination are the important reasons for use of aluminum in contact with mold cultures for producing citric acid and gluconic acid. Citric acid is produced in pans while the production of gluconic acid employs the rotating drum plus aeration technique for mold culture. An additional product derived from this process is calcium gluconate, an important pharmaceutical. Brewing yeast and malt beverages are processed and handled in aluminum brew kettles, fermenters, yeast tubs, culture tanks, carbonating tanks, coolers, storage tanks, and barrels to preserve flavor, aroma, and color of the product. T h e nontoxicity of aluminum is important in the production of antibiotics. Antibiotics in high yields are produced in aluminum equipment because it does not adversely affect mold growth. Aluminum is used for preseed media, media, slurry, and storage tanks.
Naval Stores Equipment such as evaporators, transfer lines, storage tanks, and rosin kettles
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SPECIAL METALS-EQUIPMENT-PRODUCTS are made of aluminum. Protection of color and clarity resulting in a higher grade product has been the incentive for aluminum applications in the naval stores industry. For example, wood rosin (abietic acid anhydride) brings premium prices when it is processed in aluminum equipment. Another chemical produced from wood rosin, hydroabietyl alcohol, is processed in aluminum equipment to avoid discoloration. Similar type equipment is used in the production of high quality turpentine.
Petrochemicals Since many petrochemicals serve as raw materials for the pharmaceutical and cosmetic industries, aluminum is used extensively in the production and storage of these chemicals, especially when high purity, minimal contamination, color preservation, nontoxicity, and general stability of the product are important to ensure premium prices (Table 11). Aluminum is used in processing and handling dry acetylene to avoid the formation of explosive, heavy metal acetylides. Aluminum stills, coolers, tubing, and shipping containers are used for handling acetaldehyde to maintain stability and minimal contamination. Paraldehyde is shipped in aluminum drums because of the stability of the polymer in these containers. The water whiteness of acetic acid and acetic anhydride is assured by the use of aluminum equipment. In the production of acetic acid, aluminum condensers, receivers, oxidizing kettles, and piping are used. Both the acid and the anhydride are stored and shipped in aluminum. A combination of resistance to corrosion, maintenance of color of product, and light weight resulted in the use of aluminum tanks installed in a barge for handling acetic anhydride. Aluminum is used in practically all phases of manufacture and storage of acrolein. High purity, water-clear alcohols required in pharmaceuticals are produced in aluminum decanters, heat exchangers, and storage tanks. Color and purity of benzaldehyde and glacial acrylic acid are maintained in aluminum shipping containers. Aluminum trays are used in the final crystallization of benzoic acid to produce a high quality material suitable for a food preservative or a pharmaceutical additive. Extensive use is made of aluminum for storage tanks to avoid darkening and discoloration of fatty acids such as propionic, butyric, oleic, and stearic. In the manufacture, handling, storing, and shipping of high purity formaldehyde, aluminum has become a standard material of construction. It has been used for distillation towers, storage tanks,
piping, and tank car scrvice for more than 20 years. The aluminum bundles in heat exchangers and condensers in one lube oil extraction plant employing the furfural process have minimized the coking and polymerization of furfural, resulting in a savings of about $3000 per year in cleaning costs. Additional savings resulted from reduction in downtime. To minimize catalytic polymerization, hydrogen cyanide is produced and handled in reaction vessels, scrubbers, stills, condensers, piping, and storage tanks of aluminum. The purity and color of nitroparaffins are maintained even a t elevated temperatures for extended periods of storage in aluminum. The natural color of paraffin waxes is not altered during processing, molding, and storage in aluminum. Aluminum condensers, separators, and piping are used in the processing of pyridine. Laboratory tests indicate that the desired color of pyridine is maintained under storage conditions in aluminum.
Pharmaceuticals Because of the nontoxicity of the metal and because desirable colors of the product are conserved, aluminum equipment is used in the manufacture and storage of pharmaceutical products and their raw materials. Aluminum tanks, pipe, valves, pumps, reflux condensers, vapor lines, heating coils, evaporators, and reaction vessels are used in the production of acetanilide because aluminum does not impart color to the product. The raw materials (acetic anhydride and salicylic acid) of aspirin and the final product are prepared, stored, and packaged in aluminum. Aspirin is prepared in allaluminum reaction kettles. High purity boric acid is made in aluminum or aluminum-lined equipment. Strict quality control necessary for the production of synthetic Chloromycetin is maintained in aluminum equipment. Quinoline is stored in aluminum because the color of the tar base is not significantly affected, and stable color indices of solvents such as alcohols, esters, and ketones are maintained by storage in aluminum.
Plastics The use of aluminum process equipment in the plastics industry results in minimal color change of the product during the production of raw materials for the industry as well as in the production and storage of the raw plastic. Polymethyl methacrylate resin (Lucite or Plexiglas) is an example of an acrylic resin that is cast as rod or tube in alu-
minum molds to ensure transparency. Aluminum reaction kettles have been used for 10 years at temperatures to 450' F. in the manufacture of waterwhite alkyd resins. Raw materials used for producirlg these resins, such as phthalic anhydride and glycerol, are handled and stored in aluminum. Unitrace, an aluminum alloy product, is used to carry solids such as phthalic anhydride in molten form. The desired degree of transparency of cellulose acetate for production of film fibers and wrapping materials is obtained with aluminum process equipment, such as acetylators, aging tanks, precipitators, water extraction tanks, conveyors, and rotary dryers, as well as for storage of raw materials. The hazard of discoloration is further reduced by the use of aluminum ducts and hoods. Aluminum equipment, such as stills, condensers and receivers, is used in the production of ester gum resin. Phenolformaldehyde plastics are manufactured in aluminum reaction kettles. In general, most plasticizers are esters or derivatives of esters which are maintained water-white in aluminum. Styrene is polymerized in aluminum equipment to ensure transparency of the product. The water-white color of the styrene is conserved in aluminum storage tanks, and aluminum vaporizers and condensers ensure purity and proper color in the production of ethyl benzene, a raw material for styrene manufacture. High purity isothiocyanates, which serve as raw materials for polyurethane plastics, have been processed in aluminum distilling pots and condensers for 10 years because isothiocyanates are corrosive to many other common materials of construction. Aluminum reaction kettles have been used to prepare
Table II. Petrochemicak for Which Aluminum Alloys Are Used for Processing and Handling Acetaldehyde Acetic acid Acetic anhydride Acetone Acetylene Acrolein Acrylic acid, glacial Acrylonitrile Alcohols-methyl, ethyl, propyl, and higher Ammonia-gas solutions Amyl mercaptan Benzaldehyde Benzyl alcohol Benzene Butane, propane, etc. Butyric acid Butyric acid anhydride
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Creosote o-Dichlorobenzene Diethanolamine Formaldehyde Glycols-ethylene, propylene Hydrogen cyanide Methyl ethyl ketone Monoethanolamine Naphthalene Naphtha solvent Nitroparaffinscrude and refined Paraffin Paraldehyde Phenol Pyridine Tar and tar products Toluene Waxes-petroleum, tar
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urea-formaldehyde plastics for more than 15 years with excellent results. Aluminum piping is used to handle vinyl chloride and vinyl acetate slurries in the processing of vinyl resins. Aluminum condensers and piping also are employed in the preparation of polyvinyl acetate (Vinylite) because contamination by certain other metals hinders polymerization. The final product is stored in aluminum.
Synthetic Fibers and Textiles As in the plastics industry, the principal reason for using aluminum in the production of synthetic fibers is the maintenance of color standards. The hazard of discoloration, resulting from corrosion because of the humid condirions existing in the weaving of textiles, is minimized by the use of aluminum. I n addition the use of aluminum effects saving in the high speed operations connected with spinning the fibers because of reduced inertia. Types of aluminum equipment used in this industry include pulleys, handwheels, machine beds, glazing bars, trolleys, pipes, and vats, rollers, and other moving parts of carding machines, yarn drawing poles and trays, cans and creping rolls, panels, and other parts of fiber and wool dryers. Hydrogen cyanide, produced and handled in aluminum, is one of the raw materials of acrylonitrile used by manufacturers of acrylic fibers. Wide application is made of aluminum hoods and ducts and in weaving and knitting machines to conserve the desirable color of the fibers. Aluminum ducts, hoods, and equipment such as spinning buckets, work bobbins, spinning bobbins. and numerous reciprocating parts in the weaving and knitting machines are used to reduce inertia and to avoid discoloration of cellulose acetate fibers. Aluminum piping, tankage, and shipping containers are used for handling the raw materials and in the production of nylon to ensure freedom from discoloration and stability of the product. Feed hoppers for spinning machines, as well as hoods and ducts over such areas of operation, are made of aluminum because of low over-all cost and freedom from discoloration of the product. Light weight and nonstaining characteristics make aluminum desirable for nylon staple shipping tanks. Aluminum is used in the rayon industry for equipment such as desulfurizing tanks, twisting machines, separator blades, reel frames, emulsion rolls, spinning buckets, and ducts and hoods for air-conditioning systems. Bibliography INORGANIC CHEMICALS Hydrogen Peroxide
Buffalo Electro-Chemical Co., “Concentrated Hydrogen Peroxide,” Bull. 46 (February 1953).
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Buffalo Electro-Chemical Co., “Equipment for Use with High Strength Hydrogen Peroxide,” Bull. 40 (March-April 1952). Chem. Eng. 54, 213 (April 1947). Cooley, R . A., Chem. Inds. 59, 957 (1946). Lee, J. A,, “Materials of Construction for Chemical Process Industries,” McGraw-Hill, S e w York, 1950. Shanley, E. S., J . Chem. Educ. 28, 260 (1951). Shanley, E . S., Greenspan, E. P., IXD. EKG. CHEM.39, 1536 (Dec. 1947). Fluoraphosphate
Chem. Inds. 67, 380 (1950). IND.ENG.CHEM.43, 246 (1951). Calcium Compounds
Chem. Eng. 60, 140 (1953). Light .Metals 14, 664 (1951) COSMETICS Binger, W. W., Marstiller, C. M.,“Aluminum Alloys for Handling High Purity LVater,” National Association of Corrosion Engineers Meeting, New York, March 1936. ESSENTIAL OILS Hughes, A. P., Oregon State College Engineering Experiment Station, Bull. 31 (August 1952).
Anti biotiec
Stefaniak, J. J., Gorley, F. B., Braun, C. S., Johnson, M. S., IND.ENG. CHEM.,38, 666 (1946). NAVAL STORES
Chem. Eng. 55,129 (November 1948). Lee, J. A., “Materials of Construction for Chemical Process Industries,” McGraw-Hill, New York, 1950. Light .l!fetais i ,483 (1 944). PETROCHEMiCALS Aluminum Co. of Canada, “Aluminum with Food and Chemicals,” p . 69, 1951. (Acerylene) Light Metals 7, 483 (1944). Sanders, H. J., Edmunds, R. T., Stillman, W .B., I N D . ENG. CHEM. 47,358 (1955). Verink, E. D., Jr., Chem. Enp. 53, 253 (1946). Zbid., 57,108 (1950). Water Tower, 39, 1, 4 (September 1952). Wood, LV. L., “Production of Acetaldehyde, Acetic Acid, Acetic .4nhydride a n d Acetone from Acetylene a t Bunawerke, Schkopair” Final Report, 7 5 , I t e m 22, British Intelligence Objectives Sub-committee, London, H. M. Stationery- Offices.
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EXPLOSIVES ( N H ~ N O Z )
Petroleum ReJner. 28, 145 (.4pril 1949). Shipbuilding and Shipping. Record 7 6 , 8 (July 1950).
FOOD Bryan, J. M., “Aluminum and Aluminum Alloys in the Food Industry,” Dept. Sci. I n d . Research, Food Investigation Spec. Rept. 50 (1 948). Federal T r a d e Commission, Report Docket 3874. Ziels, N. FV., Schmidt, TV. H., Oil and Soafl’, 22, 327 (December 1945). Bulk Handling
Food Eng., 23, 83 (September 1951). Lewis, F. A . , Ibtd., 24, 77 (February 1952). Wright, R. E . , IND.EKG.CHELI. 42, 79 (1950). Containers
Light M e t a l s 7, 483 (1944). Modern Metals 10, 43 (October 1954) Dairy Products
Burrell, L., Am. Creamery and Poultry Prod, Reu., p. 314 (December 1931). Goll, F. D., M i l k Planl .Monthly 25, 60 (1936). Riis, F. R., Aluminum 22, 563 (1940). Schwartze, E. W., Murphy, F. J., Cox, G . , J . ”Vutrition4, 211 (1931). Stuzzi, D., Modern Metals 10, 34 (April 1954). Trebler, H. A., Metals and Alloys 12, 735 (1940). Edible Oils
Chem. Eng. 54, 109 (August 1947). Light Metals 7, 483 (1944). Gelatin
Food Eng., 23, 109 (April 1951). Light Metals 1, 205 (1938); 7, 483 (1944); 8,622 (1945). Citric and Gluconic Acids
Clark, T. F., Aronovsky, S . I., IWD. ENG. CHEM. 33.1063 (1941). Herrick, H. T.; Hellbach, R., May, 0. E., Ibid., 27, 681 (1935). Prescott, F. J., Shaw, J. K., Associates, Ibid., 45,338 (1953). Wells? P. A,, Herrick, H. T., Zbid., 30,225 (1938). Wells. P . A,. Lynch, D. F. J., Herrick, H. T . , May, 0. E., Chem. ‘Met. Eng. 44, 189 (1938). ~~
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Brewing
Aluminum Co. of Canada, “Aluminum with Food and Chemicals,” p . 37, 1951. Federal T r a d e Commission Report, Docket 3874.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Acrolein
Anzilotte, \V. F., “Preparation and Reaction of Acrolein,” U. S. Dept. Commerce, Fiat Final Report 1157 (Jan. 21, 1948). Chem. Eng. 57,111 (November 1950). Benzaldehyde
Aluminum Co. of Canada, “Aluminum with Food and Chemicals,” p. 71, 1951. Fatty acids
Chem. Eqg. 56,243 (June 1949). Chem. Inds. 59, 8 (July 1946). Chem. Processing 14, 40 (1951). Kenyon, R. L., Stingley, D. V., Young, H. P., IKD.ESG. CHEM.42, 202 (1950). Teeple, H. O., Corrosion 8, 14 (1952). Formaldehyde
AlcanIngot 12, 5 (1953). Chem. Eng. A’ews 32, 1033 (1954). Chem. Inds. 63, 585 (April 1948). Claugli, H . , “Manufacture of Formaldehyde a t I . G. Farben,” Bios Final Report, Item 22, British Intelligence Objectives Sub-committee, H. M. Stationery Office (May 1948). Schueler, R . C., Corrosion 7 , 6 (1951). W d e r Tolcer 39, Nos. 5, 6 (1953). Miscellaneous
Kerns, E. E., Baker, LV. E., “Use of Aluminum in Petroleum Refinery Equipment,” A.P.I. Proceedings (May 1951). Carlisle, P. J., Trans. Am. Znst. Chem. Engrs. 29, 113 (1933). ( H C I i ) Chem. Eng. .Yeas 30, 2344 (1952). (Kitroparaffins) PHARMACEUTICALS C h m . Erig. 60, 116 (June 1953). (Aspirin) Light Metals 14, 663 (1951). (Salicylic acid)
PLASTICS
Chem. Eng. 60, 118 (August 1953). (Plasticizers). Light A4eials, i , 483 (1944). (Cellulose acetate) Wakeman, R . L., “Chemistry of Commercial Plastics,” Reinhold, S e w York, 1947. (Acrylics and vinyls)
RECEIVED for review July 18, 1956 ACCEPTED September 12, 1956
