ANIMAL GLUE

Bones Used i n Consolidated’s Plant Are Obtained from South America and Local Sources and Stockpiled until Needed

A Staff-Industry CoRRaborantive Report ,. e WILLIAM Q . HULL Associate Editor

J

.

e

WALTER G. BANGERT i n collaboration with

UST when it was discovered that a strong adhesive could be produced when piehes of hide or animal bones are cooked in water is not known, but historians agree that, like many other discoveries, the find was probably accidental. It may have been a result of an observation t h a t stews, especially those containing bones or skins, yield a sticky solution, and gelatinize when allowed t o cool. Or it may have followed closely behind techniques developed for tanning and preserving hides and pelts. Since man was quick to use skins for protection against cold and for construction of crude shelters, and also appreciated cooked over raw meat a t a rather early date, it is a safe assumption that glue has been known and used from the earliest periods of civilization. Recorded history goes back as far as 3300 years and stone carvings from the ancient Egyptian city of Thebes of t h a t period depict cabinetmakers gluing rare woods t o more common sycamore for veneer furniture (6). Originating from the old French glu and the Latin glutem or glus meaning glue, the word has been used in the literature since 200 A. D., and among the many references is one by Lanfranc, who in the year 1400 wrote, “As it were two bordis weren ioyned togidere with cole or with glu”

Consolidated Chemical Industries, Inc., Sun Francisco, Cal;,f.

( 1 ) . The first glue patent, issued t o one Peter Zomer in England in 1754, described the process of: “Making from the tails and fins of whales and from such sediment, trash, and undissolved pieces of the fish as are usually thrown away as useless, after t h e boiling of the blubber, a sort of train oil, and after the remains of such tails, fins, sediment, and undissolved pieces a kind of glue called fish glue” (16). For many centuries glue was produced by individual artisans in small quantities for their own use. It was not until 1690 during the reign of William I11 in Holland that the first commercial animal glue plant was erected (6). At the beginning of the eighteenth century the industry sprang up in England and since t h a t time has advanced steadily throughout the world. Germany soon appreciated the production of glue and gelatin as an important key industry, and one company established in 1895 with three plants had within 17 years grown t o 17 plants with producing facilities in Austria, Russia, Belgium, Switzerland, and France. First commercial production of glue in the United States was in 1808 but detailed information about the industry before 1860 is not readily available. First factories were in the New England states and later in Ohio, and in addition to glue manufacturers,

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INSTRUMENTS

WWHITlbpp)

CONTAINUO

many tanners produced glue from their own stock. By 1880 $here were 82 plants in the United States producing glue either m a principal or by-product, and the total production in 1886$7 was approximately 38,000,000 pounds. Of this, 28,000,000 pounds were made from hide and neat’s-foot stock and 10,000,000 pounds from bone, bone liquor, and pigs’ feet. In spite of the long history of the animal glue industry in the United States, its maximum potentialities were not realized until more recent times when certain fundamentals about its technical nature were developed. Progress in protein and colloid chemistry and development of explicit analytical and testing procedures have established gluemaking as one of our nation’s basic industries. I n addition t o its many uses as a n adhesive, numerous applications depending on the properties of animal glue as a sizing and coating medium and in compositions and colloidals have resulted (Figure 1). In 1950, there were 36 plants producing animal glue in the United States. These were owned by 26 companies and produced over 150,000,000pounds of product in t h a t year. Total investment in glue-producing plants exceeds S100,000,000 (10). Chemical Distinction between Glue and Gelatin Is One of Degree of Purity Only

Corresponding t o cellulose, the principal structural material that gives strength t o plants, collagen, a simple protein of the albuminoid class, is present in the bones and connective tissues of vertebrate animals. It comprises a large part of the organic materials of the bones, tendons, and skin, and when obtained from the different tissues, i t varies slightly in composition. When heated in water t o 80” or 90° C., collagen is converted slowly into gelatin, another albuminoid protein, as expressed by the reaction: CiozHicgOasNa~ Ha0 +C10~H161030Nn Collagen Gelatin

+

Gelatin is a nearly colorless, transparent, and amorphoue substance, retaining about 16 t o 18% water. It is naturally of

a slightly yellow cast but is pure white and water-free when precipitated from alcohol or salts. The chemical distinction between gelatin and glue is one of degree of purity only, glue being an impure gelatin. Commercially, gelatin is of higher gel strength, lighter in color, and gives solutions t h a t are clear and sweet. Too, certain chemicals used in gluemaking are not permissible in production of gelatin inasmuch as gelatin is used as a food product and produced under conditions acceptable t o the Federal Food and Drug Administration. Gelatins obtained from different sources vary slightly in their chemical compositions (Table I).

TABLEI. ELEMENTARY COMPOSITIONOF COLLAGENA N D GELATINFROM VARIOUS SOURCES (7) Carbon, Hydrogen, Nitrogen, Material Collagen Gelatin from bone Gelatiii $FOGligalnents Gelarin from tendons Gelatin from isinglass Gelstin (commercial) Gelatin, ash-free

%

%

50.75

6.47 6.50 6.71

50.00

50,49 50.11 48.69 49.38 50.52

6.56 6.76 6.80

6.81

.

% 17.86 17.50 17.90 17.81 17.68 17.97 17.53

Sulfur,

Oxygen,

%

%

0.57 0.26

24.92 26.00 24,33 25,26

... ...

0.70

...

25 i 3 25.15

Gelatin swells t o several times its normal volume when added t o cold water or dilute acids or alkalies. A slightly acid solution results in maximum swelling and the degree of acidity or alkalinity determines the extent of swelling. The gel goes into solution when the temperature is increased t o 35” C. Gelatin is a colloid of the emulsoid type and the viscosity of i t a solutions is high and varies widely with temperature changes, concentration, and hydrogen ion concentration. While collagen is the basic constituent of animal and &h skins and forms the basic raw material for gelatin and glue, there is no tissue that consists exclusively of the one protein. Whether obtained from the skin, sinews, bone, or fish parts, collagen is

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INDUSTRIAL AND ENGINEERING CHEMISTRY

always found associated with other proteins, including keratin, elastin, mucin, chondrine, and other materials. Nonprotein organic materials and inorganic salts are also present. I n the process of making glue, some of these proteins become hydrolyzed and are removed during washing of the stock. Gelatin is the first product formed from the hydrolysis of collagen. If operating conditions are not properly controlled, hydrolysis proceeds beyond the gelatin-forming stage and the protein becomes progressively less useful as it breaks down step by step into proteoses, peptones, polypeptides, amino acids, and finally ammonia. The gluemaker is constantly striving t o recover the greatest possible amount of glue a t the lowest permissible temperature in order t o limit degradation beyond gelatin. Animal Glues Are Graded on the Basis of Comparative Gel and Viscosity Values

%

The two principal types of animal glue are hide glues and bone glues. Bone glues are further divided into extracted bone glues, which are made from bones after the extraction of grease, as contrasted with green bone glues which are made from fresh, or green, bones. Hide glues are produced from the collagen in hide pieces and connective tissues associated with the hide. Packing and tanning industries are the principal sources of these materials. Hide glues are the strongest and most versatile of animal glues in so far as broad industrial usages are concerned. Extracted and green bone glues are derived from collagen present in bones principally of cattle origin. Extracted bone glues, which are made from clean, dry, degreased bones, are bright in color and moderate in strength. Glues made from green bones are lower in strength. Bone glues are not as versatile as hide glues but find many uses and wide acceptance where glues of lower and medium strength are desired. Animal glues are generally graded on the basis of comparative gel and viscosity values. All other things being equal, a glue of higher gel value has a higher bond strength than a glue of lower gel value. The gel strength is expressed in grams and is the number of grams required t o produce a 4-mm. depression in a gel sample prepared under specified conditions. Gel strength measurements range from about 30 grams for weak glues t o 500 grams for exceptionally strong jellies. Viscosity measurements are expressed in millipoises and range from 25 t o approximately 200. The gelometer and pipet-form viscometer adopted by the National Association of Glue Manufacturers aa well as all test conditions and procedures have been described (11, 19). In addition t o grading of glues on basis of gel strength and viscosity, consideration must be given t o the pH, ash content, grease content, type of glue, and processing methods. Specifications for bone and hide glue are shown in Table 11.

TABLE 11. ANIMALGLUESPECIFICATIONS Gel value, grama Viscosity millipoises Water content, % Ash content, % p H (jn water solution) Specific gravity Color Physical form

Bone Glue

Hide Glue

67-222 38-70 11-14 2 .O-3.0

135-520 50-200 11-14 2.5-3.5 6.5-7.4 1.27

5.8-6.8

1.27

Light yellow to brown Flake, pearl, ground

Light yellow t o brown Flake, pearl, ground

Gluemaking can be briefly summarized: The stock, whether bone or hide, is given preliminary treatment t o remove foreign matter and t o physically condition the collagen for rapid conversion. It is then heated in water and the insoluble collagen is hydrolyzed into gelatin. Repeated cooks, each using fresh water and higher temperatures, yield glue solutions containing lower gel-testing glues. After filtering, the glue is concentrated in vacuum pans, bleached, dried, ground, and sacked.

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Consolidated Chemical Industries, Inc., Plant at San Francisco, Calif., Produces 10,000,000 Pounds of Hide and Bone Glue Yearly

Animal glue has bccn produced a t the Consolidated Chemical Industries plant ncar Sari Fransisco, Calif., since 1890. Originally established as Pacific Bone Coal and Fertilizing Co., founded in 1878 and incorporated tvio years later, the original company became a part of a holding company, Consolidat,ed Chemical Go., in 1927. The holding company was reorganized in 1937 and Consolidated Chemical Industries, Inc., which in the nicantime had acquired or built plants in Texas, Louisiana, hlassachusetts, and Argentina, became an operating company. At the present time, plants are located in Sari Fran 0 , Houston, Ft. Worth, Baton Rouge, Bastrop and Springhill, La., Little Rock, Ark., Woburn, Mass., and Buenos Aires. Principal products include various types of animal glues, gelatin, sulfuric and hydrochloric acid, ammonium sulfate, aluminum sulfate, grease, tallow, fccding bone meal, bone black, and ammonium and potash alum. The San Francisco plant, Tvhich has undergone ninny expaneions and modernizations since its establishment over 70 yems ago, is now the only large animal glue industry in the West and one of the largest and most modern plants in the United States. Current production tot.als 10,000,000 pounds of hide and bone glue per year. Utilitx rcquirements of this plant, are listed in Table 111.

TABLE 111. U‘TILITICS REQCIREMEKT~ (Per day of operation) 12,000 Electricity, kx.-hr. Water, gallons 700,000 Gas cu. ft. 1,500,000 Ste’itn, thousand lb. pcr day 800

Animal glues include all glues produced from the skins and bones of cattle, goats, shccp, horses, pigs, rabbits, and other animals. There ie thus a variety of diffcrent types of glue stock based on, first, the animal source and, secondly, the method of preservation t o which the material has been subjected. Smith ( I S ) lists 14 market classifications of hide stocks which, he points out, is by no means complete and Bogue (8)lists 17 classifications of bone stocks. Hovever, commercial glues are derived chiefly from cattle hides and bones which yield superior products. Consolidated’s plant in San Francisco produces hide glues and extracted bone glues. Hide glue raw materials include cattle skins and fleshings and a small proportion of sheep skins. These materials are obtained chiefly from California tanneries and meatpacking industries within a radius of 50 miles of the plant. Bones are secured from the western states and also imported from the company’s plants in South Smerica. As late as World War 11, large amounts of bones were imported from Canada and, until a few years ago, from India. At the present time, bones are obtained from Consolidated’s South American plants M ith bones from local sources representing approximately 50% of the plant’s to tal requirements. Preliminary Treatment of Hides Includes Water Washing to Kemove Previously Added Chemicals and Liming to Swell the Protein Content

Raw materials vary considerably in water, grease, and glue content. All hides, fleshings, and bones are bought on a tonnage basis, the cost varying with glue content established from experience for each stock type. Hide glue raw materials have either been salted, limed, pickled, or in the case of chrome stock, tanned prior to delivery to the glue plant. Preliminary treatment involves washing of stock with large quantities of water to remove chemicals previously added to preserve or treat the stock and a liming treatment to “plump” or swell the protein content in order that extraction during cooking will proceed efficiently and rapidly (Figure 2).

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Fleshings and trimmings togctlicr rcpresent approximately 75% of the t,otal hide glue stock uscd in Consolidated’s plant. Fleshings, which contain approsimat,cly 7 to 10% glue, 7 to toyo grease, 3 t o 5% hnkage or hair, and the balance water, have been limcd prior to delivery t o the plant to prevent putrefaction. These arc immediately prepared for U ~ C First . preliminary treatment is washing to reniovc alkalies and other soluble salts and soluble degradation products and t’o swell the protein. Washing is acconiplished in one of 12 standard cone-type hide wash mills. These arc wood tubs 50 inches high and 18 feet in diarnetcr and madc of 3-inch. fir. Each has a capacity of 8000 gallons. To a, central upright! popt is attached t h r apex of a cleated, 17-oodcn cone approximat’ely 7 feet in length. The cone rcvolves a,uound the tank at, a, speed of approximately 12 r.p.m. wit,h a rolling motion. Stock is feci into the wash mill to approximately t,he level of the revolving cone by a 21/2-ton overhead crane with a 1-yard bucket, which is used t o convey all material in the n-ashing and liming depart>mcnts. Water is fed continuously into the mill a t a rate of spproxiniately 120 to 150 gallons per minute from an overhead linc. Kastc Tvater is discharged to the sc~vcrthrough a drainage scrc.cn,42 X 144 inches, madc of copper and containing l/ls-inch perforations, n-hich is located in the lower side of the mill. Fleshing6 are gcncrally washed for 10 hours a,nd finally neutralized through addition of sulfurous acid. .4 second 2-hour washing rcmovcs any cxcees acid. Thc stock is t,hen ready for cooking. Trimmings, second of thc tiyo important hide glue raw materials, include all part,s of thc hide trimmed off in preparing the hide for the tanner and consist, of noses, pates, ears, tails, and other pieces. The trimmings are generally received in a salted condition and must be limed prior t,o cooking. The salted pieccs are first washed for 2 t.o 3 hours in onc of the wash mills previously described to remove salt and extraneous matter, Free wat,er is then drained, and 5 % lime solution is addcd t,o the wash mill to covor the stock. The mixture is then “rolled” for 2 hours. The limed material is then transferred to one of 24 concrete liming vats, average size of which is 10 X 22 X 12 feet. Limewater ( 5 % ) is added to cover the trimmings and 60 days are allowed for complete liming. During this period, the va.ts are drained several times and fresh limewater is added. In sonie cases, the limed st.ock is transferred t o another vat in order to ensure complete exposure. At the end of this period, the stock is given a 10-hour washing in the n-ash mills, is neutralized with sulfurous acid, and after a 2-hour final washing is ready for cooking. The 5% lime solution for all processing is made in a fir tank 12 feet in diameter and 9 feet high equipped with a propeller agitator t h a t rotat,es a t 100 r.p.m. Approximately 1 ton of lime is consumed daily. Large amounts of chrome wastes are used in gluemaking but in this case the stock must be detanned prior t o processing. Total hide glue stock from all of the mentioned sources is 600 t,ons per month. Water requirements for the glue plant are large and total 700,000 gallons per day. Packer Bones Are Degreased w i t h Solvent Kaphtha i n a Batch, Rotary Extractor

Bones vary in their glue and grease content. Green bones contain 12% glue, 15% fat, 33% mineral matter, and the balance water. Dry bones collected from different sources contain 15 to 20% glue, 4 t o 10% fat, 40 to 60% mineral matter, and the balance water. Packer bones, from freshly slaughtered cattle and sheep, are treated a t the packing house .for removal of a part (approximately 50%) of the grease content and all adhering tissue. They are then dried and delivered t o glue plants. Degreasing is accomplished by solvent extraction. Consolidated’s plant uses approximately 50% imported bones which have been degreased prior t o shipment. The balanceconsisting of dry bones, packer bones, etc.-must be degreased

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prior t o extraction of glue, or otherwise some of the grease is extracted with the glue product. A batch, rotary extractor using solvent naphtha is employed. The extractor is essentially a horizontal steel cylinder 8 feet in diameter and 16 feet long and geared a t one end for rotating for discharging. A charge of 15 tons of crushed bone is fed by gravity through three manholes from a storage bin above. Manholes are closed and 2000 gallons of solvent naphtha, previously heated to approximately 215" F., are added. The naphtha used has a boiling point of 178" t o 218" F. and flash point below 60" F. Steam a t 60 pounds per square inch (308' F.) is circulated through longitudinal coils, 1 1 / ~inches in diameter, t o provide heat. Vaporized naphtha is percolated through the extractor in amounts varying from 4000 t o 8000 gallons depending on moisture and grease contents of the bone. The flow of naphtha is then stopped and the solution of grease in the solvent is drained off. The grease-containing solvent is referred t o as a "miscella" and generally 2 t o 6 miscella are withdrawn before all grease has been removed. This generally requires from 4 to 16 hours. Sfter the last miscella, a 25-inch vacuum is applied on the extractor for 1 hour to remove the last traces of naphtha. The solvent vapors containing moisture pass through a condenser and then a water separator, and naphtha is recycled. The miscellas are pumped t o one of three cylindrical steel storage tanks, each with a capacity of 2000 gallons. From the storage tanks, the miscella passes t o a distiller where the naphtha is evaporated from the grease. The solvent is then condensed and recycled. After complete removal of grease and naphtha, the extractor is rotated until the manholes are at the bottom and the bones are dropped t o a n apron feed and then t o a bucket elevator which conveys them t o an extracted bone storage tank. From this point on, treatment of all bones is the same. Extracted bones are crushed t o -11/2 inch in a hammer mill, and the crushed bone is elevated t o a vibrating screen with 9mesh openings (723). Fines pass t o bags for bone meal; tailings are conveyed t o storage bin. Prior t o cooking, the bones are treated with dilute sulfurous acid t o bleach the bones and t o facilitate removal of foreign matter in subsequent washings. Acidulation is carried out in one of eight open fir tanks, each of which has a capacity of approximately 2000 cubic feet. Forty tons of extracted bones are fed into a tank and 0.25% sulfurous acid is added until the bones are covered, usually requiring approximately 8000 gallons. Three times during an 8-hour period the acid solution is drained and fresh acid added, and the following morning t h e bones are conveyed t o wash reel. The sulfurous acid is produced from sulfur dioxide from one of two sulfur burners and two coke-packed wood absorption towers (223). From the acidulation tanks, the bones, from which the acid has been drained, are picked up by an overhead crane and delivered t o a hopper which feeds t o a rubber conveyor belt going t o the bone wash reel. This is an inclined cylindrical rotary reel. An inner sleeve cylinder contains l/d-inch perforations and the outer cylinder contains 10-mesh openings. Water at 120" F. is sprayed into the washer and the bones fed a t t h e upper end. Speed of rotation is 10 r.p.m. and feed rate is approximately 80 tons over a 31/pho~r period. All material not passing through 10-mesh screen as the bones move down the washer, pass t o an elevator and then t o a drag chain conveyor that feeds the cooking tanks. Fines ( - 10 mesh) pass t o settling basin and are used in making bone meal fertilizer. Glue Is Extracted i n Fractions with Stock and Extracted Liquor Kept at High Temperatures for the Shortest Possible Time

The term "extraction" in gluemaking refers t o the process by which the gelatinous material or collagen from prepared hide and bones is dissolved in water and removed from the balance of the stock. The process is often called cooking or boiling.

INDUSTRIAL AND ENGINEERING CHEMISTRY

October 1952

..

The general principles of extraction from fleshings, hide pieces, or bones are much the same. The gluemaker is principally concerned with keeping both the stock and the extracted liquor at peak temperatures for the shortest possible period of time, The glue is usually extracted in fractions-those removed, first and which have been less exposed to high temperature producing glues of higher gel values and later fractions producing progressively products of lower gel values because of repeated periods of cooking. Within limits, the precise temperatures of extraction are not of prime importance inasmuch m similar products are obtained by extraction at near boiling point for a short time or lower temperatures for longer periods. Fractional extraction is carried out in both open vats as well as pressure tanks. Several processes involving continuous extraction have been devised. One of these makes use of the Archimedian screw in a steam-jacketed cylinder from which both glue solutions and remaining stock is removed continuously. A second continuous system employs a battery of digesters connected by pipes (4). These processes are not in general use at the present time. Hide Stock. Consolidated has 12 kettles in which hide stock is cooked. These are rectangular open vats, 9 X 14 X 6feet high and made of 3-inch fir, The vats are equipped with a 8/4-inch perforated false bottom made of wood under which 2inch copper coils for providing heat are located. Steam at 50 pounds' pressure (298 " F.) is used. Hide glue stock from the wash mill pit is conveyed by a crane t o one of the kettles which is filled t o within a foot or so of the top. Sufficient fresh water is added t o nearly cover the stock and steam turned into the coils until the desired temperature is reached. The temperature of cook is maintained through regulation of steam feed. The first run of top quality glue is cooked at 155" to 165" F. for 4 t o 5 hours, Hydrometer tests taken at irregular intervals show when solution is sufficiently concentrated for removal. The first fraction, containing 4 t o 5% glue, is drawn off, fresh water is added, and another run or boiling is made. Subsequent runs are at higher temperatures and produce glue solutions of concentrations as tabulated: Fraction

No.

Temp., O F.

1 2 3 4 5

155-165 160-180 165-185 200-205 212

Cooking Time, Hours 4-5

6 6 6 6

Concn

% Glug 4-6 4-4'/z 3'/& 2-2 1/l 1-11/2

Most of the high quality glue is removed in the first three runs. The remaining glue, of lower gel value, is removed in the fourth and fifth fractions. Grease, amounting t o 8 t o 10% of stock charged t o kettle, comes t o the top during extraction and is skimmed off for further processing. Approximately 4 tons are recovered daily. From the kettle, the glue solutions flow by gravity t o liquor-receiving boxes below, from which they are pumped through %inch mild steel pipe t o the filtration plant. The residual tankage in the kettles consists of hair, grease, and insoluble lime soaps of fatty acids. It is boiled overnight with sulfuric acid solution, arrproximately 300 pounds per kettle, in open wood tanks containing open steam coils. The grease is floated off the top; the remaining tankage is first passed through an hydraulic press for removal of water and any remaining grease and is then processed for fertilizer. Bone Stock. Extraction of glue from degreased acidulated bones is normally conducted in pressure tanks. Several processes are practiced. The bones are sometimes boiled in water at pressures ranging from 10 to 20 pounds per square inch. I n the English process, hot water is added a t the top at the same time that steam enters at the bottom. In other processes, water is provided entirely by condensation of live steam on the charge ( 8 ) .

2281

Successive run8 are generally more concentrated than those from open tanks but the gel values of the glue are lower. The tanks are operated independently or in groups using the countercurrent principle. The plant being described has nine pressure tanks or digcsters. These are cylindrical vessels with convex ends, 8 feet in diameter and 12 feet in over-all height, and are constructed of 1/2-inch boiler plate. A false bottom, made of mild carbon steel and containing l/a-inch perforations, is located at the bottom of the cylindrical section. This is covered with a layer of burlap before the charge is added. The tanks are generally operated in two batteries of four tanks each. Approximately 10 tons of bones are charged t o each of the four tanks in a battery through a manhole at the top of each vessel. The tanks are sealed and the bones are subjected t o varying pressures t o convert the collagen t o glue which is then extracted in batches with hot water. This procedure is repeated until all the glue is removed. Glues made from the first runs have higher gel values and those from succeeding Tuns have progressively lower gel values, Each of the leachings consists of approximately 2000 gallons of glue liquor. The glue concentrations are determined with a special hydrometer that gives values in per cent glue. It requires 18 hours t o run a complete battery of four tanks, which generally is scheduled t o begin at 8 A.M. of one day and be completed by 2 A.M. of the following day. Each bone charge of 10 tons produces approximately 4000 pounds of glue and 5'/2 t o 6 tons of dry steamed bone. Glue liquors are pumped t o one of seven 2500-gallon liquor boxes or tanks made of Douglas fir. Steam bones, which have shrunk approximately 25% of their former size during pressurizing, contain approximately 5% crude protein and are subsequently processed into steamed bone meal. Consolidated Uses Plate-and-Frame and Leaf Filters to Remove Fine Particles and Collodial Matter from the Glue Solutions

The coarser particles in glue solutions are effectively removed by filter presses. Finer particles and colloidal matter, however, are not soeasily removed, because of the protective action of glue, and render the glue turbid unless additional clwification techniques are employed. Many methods have been used, including removal by mechanical means, settling, and centrifuging; adsorptive processes, using filter-mass or bone black; and formation of precipitates through the use of blood albumin, phosphoric acid, alum, and many other substances ( 3 ) . Some methods require boiling of the glue solutions, and, while rendering a very clear product, seriously lower the strength of the glue. Consolidated employs both plate-and-frame and leaf filters. Two of the former have been used for many years. They contain 30 X 30 inch aluminum frames and employ a standard cottonweave duck cloth (6E). Each filter has 500 square feet of filter area. Diatomaceous earth is fed t o the solution a t a rate of 0.25% of the total feed. The filters will clarify 75 gallons of glue solution per minute each. For extra clarity or in the cme of unusually turbid feeds, two filtrations are made. A recent addition t o the plant is a stainless steel leaf filter which is used at all times when operations permit. The filter has 510 square feet of filter surface, 21 leaves, and 45 feet of cake space ( 3 8 ) . All construction is of Type 304 stainless steel. The tank diameter is 48 inches and over-all height is 106 inches. Maximum operating pressure is 65 pounds per square inch and capacity is over 100 gallons per minute. While comparative installation cost is high, increased capacity and low operating cost suggest additional installations in the future. As in the plate-and-frame filter, diatomaceous earth is used as a filtering aid and is added in amounts equal t o 0.25% by weight of feed. The clarified solution is pumped t o one of five 8400-gallon evaporator storage boxes. T o each liquor, 10 pounds of zinc sulfate are added as a preservative.

INDUSTRIAL AND ENGINEERING CHEMISTRY

2282

All glue solutions are concentrated by evaporation before the product is dried. I n older processes, evaporation was accomplished through the use of steam-jacketed kettles. Multipleeffect evaporators are used in all modern plants.

Water 1s Removed f r o m Wet Pearls in a 90-FooL 'I'wo-Stage A i r Dryer

Consolidated has a four-bodied, thiee-efl'ect,vertical tube vacuum rvaporator system ( 6 E ) . The units are 24 feet in over-all height. The shells and heads are constructed of cast iron. Each effect rontains 250 tubes 16 feet long whirh vary in dimension from 1 1 / 4 to 2 inches and which are made of copper in three of the units and of Type 304 stainless steel in t,he fourth. The condenser contains 880 7/8-i1ich tubes 10 feet long, or a total area of 2050 square feet. Approximately 60,000 gallons of bone glue liquors (500,000 pounds) containing 6.5gb glue are fed to the evaporators daily. Discharge liquor totals 59,200 pounds a t 0.55% concentration. Evaporation from bone glue Ptoclc totals 52,800 gallons per day. Hide glue liquor feed totals 24,000 gallons at 5%, and discharge liquor 2700 gallons a t 35%. The evaporators are normally operated two thirds of the tiihe 011 bone glue and one third on hide glue. The concentrated glue solution is pumped t o one of seven 6 X 12 feet cylindrical fir "finishrd glue" storage .boxes or tanks. These are equipped with propeller-t,ype agitators and 2-inch steam coils for either heating or cooling to maintain the solution a t a temperature of 125' F. The coils are made of copper in five of the tanks and of Type 304 stainless steel in the others. To each of the tanks are added the following chemicals when needed foi, the function indicated: Chemical Zinc sulfate Hvdiulren ueroxide Hide gyeask emulsion Zinc oxide (white or opaque glue only)

A4~nonnt Added, % by Weight 1-2 2 2 10

Purpose Preservative Bleachine azent

Defoaminlg agent Pigment

I!nt,il fairly recent timrs, final drying of the glue was accomplished in slab sheet form in tunnel dryers. The concentrated solution from evaporators m-as run into an endless rubber belt t>oa depth of 1/4 inch and the belt run through a refrigerated compartment. Here the glue gelled and, on coming out of refrig-

Vol. 44, No. 10

erated compartment, was removed from the belt in a gel form as a continuous sheet. The cooled slabs were then cut into pieces about 5 feet long, placed on mesh screen, and dried in a tunnel dryer. After drying, the sheets of flake glue were stripped from the wire screen and crushed to desired keness. This drying process was slovi and expensive and many processes have been developed t o eliminate tunnel drying. Consolidated converts the glue into "pearl" form before drying. This is accomplished by dropping the liquid glue a t 125" F. into a cylindrical vessel containing base spirits which have been precooled t o 32" F. by a W t o n ammonia refrigerating system. In the bottom of the 24-inch inside diameter cylinder called a pearl head is a perforated plate containing 3/32-inch holes. The glue solidifies as its drops through the chilling bath and emanates from the holes in small bead-shaped pellets called pearls. There are four of these pearlers, each of which has a capacity of 225 gallons per minute. The base spirits used has a flash point of 120" F. and a boiling point range from 330" t o 380" F. The mixture of base spirits and pearls flows to the middle of a rotating octagonal-shaped screen containing 0.04-inch openings. The base spirits passes through the screen and is recycled. The pearls travel down the screen to a belt conveyor a t the end which carries them t o the dryer. A two-stage air dryer is used t o remove water from the glue pearls (423). Stage A, which is located over stage B, consists of five compartments each 18 feet long, 10 feet wide, and 8 feet high. Stage B has five compartments of similar size. The pearls are fed by an oscillating feeder belt to a 10-foot wide continuous wiremesh belt made of Type 304 stainless steel 12-mesh wire which travels through Stage A a t a rate of 0.8 foot per minute for normal operation. The 3-inch layer of pearls a t feed end has decreased to 2 inches a t discharge, the moisture content of the glue having been reduced from 45 to between 20 and 25% as the glues pass through the five compartments in which the temperatures aremaintained a t 74", 78", 84", go", and 94" F., from feed to discharge of A stage. The temperatures are maintained by hot air fed to each section over the traveling belt; the air is exhausted after picking up the water from the pearls. The layer is maintained uniform in thickness by a system of rotating levelers and agitators. At the discharge end of stage ,4,the pearls drop to a belt of the same type which travels through stage B in the opposite direction. This belt carries a 4-inch layer of pearls and normally travels through the dryer a t a rate of 0.4 foot per minute. Temperatures are maintained a t 110", 125", 1 3 j 0 , 150°, and 150" F. in the five compartments and the pearls, which contain 20 t o 25% moisture a t feed end are 100% glue (which retains 1201, moisture) a t discharge end. Temperature of the hot pearls is reduced to near room temperature during the last 3 feet on the belt by cold air fan. Drying time is 6 to 8 hours in comparison with 1to 3 dags for flake-drying systems. The dry glue pearls are conveyed t o one of eight 20,000-pound storage bins. 4 s desired, the glue from these tanks may be blended t o give a product with a desired gel value. A blower removes the pearls from the bottom of any one of the tanks to tanks from which they are elevated to a mixer. This is a large cylindrical vessel in the middle of which is a 12-inch casing containing a revolving screw which runs from the bottom t o top of the mixer. Pearls from storage bins are fed to top of the mixer and circulated from bottom to top by the screw giving complete mixing. From the mixer, the pearls can be conveyed to the bagging machineor ground. Approximately75'% is ground beforeshipment. A cage mill, similar t o the one previously described, is used and particles larger than 8 mesh are removed by vibrating screen and returned to the cage mill feed. In the making of very fine powdered glue, a typical milk dryer is used to dry glue from the finish glue tanks. Two rotating drums heated with steam which rotate toward each other, pick

INDUSTRIAL AND ENGINEERING CHEMISTRY

October 1952

up a thin layer of glue from pans underneath. Knife blades remove the dried film from the drums. An attrition mill reduces the glue to 90 t o 98% through a 200-mesh screen and 5001, smaller than 325 mesh. This type of glue is used in making cold-water paints. By-products of Glue Manufacture Include Steamed Bone Meal, Fertilizers, and Grease

The glue content of both hides and bones is comparatively small, and large scale production of glue requires handling of enormous amounts of raw materials with large tonnages of nonglue-containing materials remaining. Use is made of practically all the animal stocks coming into a glue plant, however, and disposal problems are those connected with the sale of usable by-products and not of waste. The most important by-product of bone glue production is steamed bone meal. The product is processed from the residue of bones remaining in the pressure tanks after removal of the collagen content. It is a valuable stock feed additive. Bones from the pressure tanks are removed with forks from doors located in the lower sides of the vessel and dropped t o a pit. These bones contain 38% moisture, most of which must be removed before the bones can be ground. An overhead crane conveys the bones to a steamed bone dryer, which is essentially a chamber with perforated beds on which the bones are placed and through which hot air is blown for removal of water. The room is 28 feet wide and 88 feet long and perforations are inch. The wet bones are scattered over the perforated roof and dried overnight with 250" to 300" F. air from an 80,000cubic-foot-per-minute blower. The moisture content is reduced t o 4%. D r y bones are conveyed by vacuum through a 400foot pipe t o the grinding department. A cage mill, the outer ring of which is 50 inches in outside diameter and inner ring 37 inches in outside diameter is used for grinding. A Hummer screen removes all +lO-mesli particles and recycles them t o the cage mill. All -10-mesh particles are bagged in 100-pound multiwall paper bags. The steamed bone meal is marketed as a sterile product without admixture of other substances and has the following specifications: Crude rotein content (min.), yo Crude fat content (min.), % Nitrogen-free extract (max.), % Crude fiber Imax.). LT, Moisture ( m i x ) % Bone phosphatk'of lime, Caa(PO$n, (min.) % Ash (max.), % 'I

5

0 2

2

7 72 87

Consolidated produces steamed bone meal a t a rate of approximately 50 tons per day. Bone char, the carbonaceous residue obtained from the destructive distillation of bones, is used in the decolorization and refining of sugar. Consolidated uses bone stock from South America in its bone char plant. The bones have been prepared and ground t o 8 to 12 mesh before shipment. Three gas-fbed furnaces with 14 vertical retorts per furnace are used. Each retort is filled from the top and emptied at the bottom by gravity flow. 100 pounds are withdrawn at the bottom and added a t the top every 2 hours. Temperatures are 750" to 950" C. The bone char yield is approximately 60 t o 65% of the charged bones and is sacked in 100-pound bags. Consolidated produces approximately 3500 tons of bone char per year. Fumes from the retorts include 3 t o 5y0 bone oil, 5 t o 6% bone tar, and 8 to 10% ammonia. The bone oil is recovered in an absorption tower and sold for use as a blowfly repellent. Other fume products are not recovered. The treated tankage from the hide kettles, consisting of hair and other organic matter, is used in making fertilizer. Certain quantities of scrap leather, from local shoe factories, as well as

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INDUSTRIAL A N D ENGINE RING CHEMISTRY

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search which have already resulted in the numerous uses of animal glue shown in Figure 1 seem to spell continued prospcrity for the animal glue industry.

TABLE IV.

U. S. ANIMALGLUEPRODUCTION (14) (In thousands of pounds)

Year 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 Not available.

Bone 66,337 66,466 74,243 70,689 65,969 89,415

. . .a

. . .a . . .n ...

Hide 72,914 62,213 63 498 63:311 62,438 67,861 69 ,670 57,619 65,115 67,342

Literature Cited (1) Alexander, J., “Glue and Gelatin,” pp. 1-19, New York, The Chemical Catalog Co., Inc., 1923.

Finished Glue Is Stored and Shipped in 100-Pound Bags

hoofs and horns, the latter being reccived expressly for this usc or removed from glue stock, arc also used for fertilizer making. T h e product normally contains 6 t o 10% ammonia. Approximately 5 tons per day are produced. Approximately 1 ton of the raw materials described is charged t o one of four rendering cookers and subjected to a pressure of 40 t o 60 pounds per square inch for 30 minutes to 1hour (1E). This treatment breaks down fibrous content eo t h a t it can be more easily ground and also degrades the organic compounds present so t h a t the fertilizer vi11 be readily available to plants from the soil. The “cooked” tankage is ground by a hammer mill t o 10 to 12 mesh with oversized particles being rerouted t o the hammer-mill feed. A total of 10 tons of grease per day is produced in Consolidated’s plant. This is skimmed from the kettles as it rises during cooking from the tankage remaining in t h e kettle after the glue solution has been drained off and from the naphtha solvent from the bone grease extractor. The grease is boiled with dilute sulfuric acid t o split the lime soaps and washed with hot water t o settle out foots. It is sold for use in soapmaking. Numerous Uses of Animal Glue Point to Continued Prosperity for the Industry

In the last few years, a big scale synthetic resin adhesive industry has developed. During the past generation, casein adhesives and vegetable adhesives have become products of great commercial value. However, in spite of the development of these vegetable and synthetic adhesives, animal glue production in the United States has not reached a point of decline (Table XV). I n fact, programs centering on chemical and applied re-

(2) Ibid., pp. 1 6 2 4 . (3) Ibid., pp. 164-6. (4) Bennett, H. G., “Animal Proteins,” pp. 230-3, Xew York, D. Van h‘ostrand Co., 1921. (5) Bogue, R. H., “The Chemistry and Technology of Gelatin and Glue,” pp. 1-12, Sew Sork, McGraw-Hill Book Co., Inc., 1922. (6) Ibid., p. 5 , (7) Ibid., p. 50. ( 8 ) Ibid., p. 275. (9) National Association of Glue Manufacturers, Inc., “Animal Glue in Industry,” facing p. 1, New York 18, National Association of Glue hlanufacturers, Inc., 1951. (10) Ibid., pp. 1-7. (11) National Association of Glue Manufacturers, IND.EKG.CREM., 16,310-15 (March 1924). (12) National Association of Glue Manufacturers, IND.ENG.CHEM., ANAL.ED.,2,348-51 (July 15, 1930). (13) Smith, P. I., “Glue and Gelatine,” pp. 9-10, Brooklyn, K . Y., Chemical Publishkg Co., Inc., 1943. (14) U. S. Dept. Commerce, “Facts for Industry,” Series M19M. 2a-12. (15) Zomer, Peter, Brit. Patent 691 (May 23, 1764). Processing Equipment (1E) Allbright-Ne11 Co., The, Chicago, Ill., Laabs rendering cooker. (2E) Glens Falls Machine U‘orks, Inc., Glens Falls, N. Y . , 14 inch X 3 foot rotary sulfur burner. (3E) Siagara Filter Corp., Buffalo, S . Y . ,Model 510-28 leaf filter. (4E) Proctor &- Schwarta, Philadelphia, Pa., 10-unit 2-stage air dryer. (5E) Shriver, T., & Co., Harrison, K, J., 30 X 30 inch plate-andframe filter presses. (6E) Swenson Evaporator Co., Harvey, Ill., 4-body, 3-effect vertical tube evaporators. (7E) Tyler, W. S., Co., Cleveland 14, Ohio, Type 38, Hum-mer screen. RECEIVED for review August 20, 1952.

ACCEPTED August 25, 1952.