Land animal waxes (Woolwax)

Wool grease is secreted by the sebaceous glands in sheepskin; its prime function is to create a coat that protects both skin and fleece against exposure to the elements. The crude wool wax is refined to produce lanolin and derivatives from lanolin, such as lanolin alcohol, lanolin oil, ethoxylated lanolin, etc. These substances are commonly used as moisturizing ingredients in cosmetic and medical formulations. Lanolin also has industrial applications, as lubricants or protective preparations for ferrous metals.

When the wool is obtained, it then is turned out clean with moisture content of 16% of the weight of the clean, dried wool. If the wool is washed before shearing, the result, freed from yolk, will consist of 73% clean wool, 13% water, 5% soil, 4% fat, 2% potassium salts or equivalent and 2% of foreign organic matter. In contrast, unwashed wools contain 45 to 62% clean wool, 9 to 13% water, 9 to 16% soil, 10 to 24% grease, 4 to 6% potassium salts or equivalent and 4 to 8% foreign organic matter. In wool grease, the “suint” is the saponified portion that contains the potassium salts. The wool fat, which is recovered form the unsaponifiable, is the anhydrous lanolin (adeps lanae) or lanolin (adeps lanae hydrosis).

To determine wool grease in greasy wool, the sample is placed in an extraction thimble, after conditioning to a constant weight at 21.5°C and 70% relative humidity, dried over sulfuric acid for at least 12 hours at 70°C under a vacuum of 25 mm, weighed and placed in a Soxhlet extractor with petrolic ether. The extract is then freed from ether, and dried to a constant weight in a vacuum desiccator. For the determination of "suint," the degreased wool is extracted with hot water in a Soxhlet apparatus; the extract is evaporated on a water bath, dried in a vacuum desiccator, and the residue weighed.

Wool grease (yolk) and suint (water-soluble soaps) are estimated on the basis of percentages of the weights of the clean dry wool.

English merino yields 24 per cent, and Australian merino 42 per cent of woolwax on the clean dry wool basis. Lewkowitsch states that the commercial yield of fully refined woolwax from New Zealand wool is 16.8 per cent, from Australian wool 16 per cent, from South American wool 13.2 per cent, and from Russian wool 6.6 per cent. South American wools are· rick in yolk and require preliminary washing, while Australians do not. Washing is done with tepid water (45°C).

Wool grease of merino wool, Union of South Africa, has a refractive index of 1.4814 to 1.4681, average 1.4753 at 50ºC, which is known to be best for the n readings on wool grease. If the grease is extracted from raw unwashed wool by benzene it will have an acid number of about 93, saponification number 98.6, iodine number (Wijs) 41.8, and unsaponifiable 48.8%. The same wool grease when refined to anhydrous lanolin will have an acid number of 0.2-5.6, saponification number 88 to 96, iodine number 43 to 47, and 40 to 46.6% unsaponifiable.

Wool scouring and processes of grease recovery

The scouring of raw wool is done with the aid of warm soda (or potash) lye and a considerable amount of water. Scouring of wool by the soap-soda process necessitates treating it with dilute aqueous sodium carbonate at 20 ºC and then with all aqueous soap solution (pH of 10) at 40 to 50 ºC, for effective removal of the wax. The addition of 1 to 2% of an organic solvent, such as benzene, to the soap solution is said to permit operating at below 40 ºC, thus avoiding danger of felting and attack of wool by alkali. In England the recognized type of merino wool-washing machine has been the forked-frame bowl. Three to five of these machines as a unit are employed for steeping, scouring, rinsing, etc. The emulsion method of scouring is universal in England; but in North America the solvent method is largely in use, the solvent being recovered by distillation procedure for reuse. The following processes have been used to recover the grease after wool scouring:

1) The Acid cracking process – for recovering wool grease alone.

2) The Steeping process – for potash recovery and combined with acid treatment for grease recovery.

3) The Battage process – in this, the effluent is kept agitated by continuous beating with hand paddles, or bats, and the grease is caused to rise to the surface in a froth, the wool grease being recovered from the foam in a yield of only 25%.

4) The Barber jet process – it is a combination of jets designed to give very thorough mixing for the separation of wool wax from scour liquors. Compressed air and the liquor are pumped at high velocity though a battery of the Barber jets. The particles of grease coalesce, and this way they get separated from the water phase as a froth, which floats onto a trough, where it is washed with water sprays as it floats to the heating tanks. The process originated in France but has been working in England for a number of years.

5) The Solvent process – uses benzin or other solvent to extract the grease. Direct solvent extraction of wool was introduced in Europe around 1900, but the wool resulted from the process was harsh and brittle. It was then found that if the solvent extraction was regulated, the wool retains around .5 to .8% of wax, the fiber gets no damage and it can be washed to free it from suint.

6) The Flue gas treatment – waste liquors are treated with SO2 or CO2 from purified flue gas.

7) The Smith-Leach process – the scouring liquor is evaporated to a small bulk, the grease recovered in a centrifugal machine and the residue is incinerated for potash recovery.

8) The Scouring liquor recovery process - removes grease from the waste liquor and the scouring liquor is used over and over again until it is rich enough in potash salts to evaporate profitably.

9) The Supercentrifuge process – the warm liquor is settled to remove dirt, and is then passed through a Sharples supercentrifuge to separate the grease. In the Duhamel process the wool is treated in a succession of bowls, in the first of which most of the wool-fat is removed by the scouring action of recovered suint liquor. The spent solution from this bowl is pumped to a centrifuge designed to separate sediment from the grease-laden liquor, which then passes to ordinary separators. These discharge high-grade lanolin and degreased suint. In the "Adams centrifigal process," the machine is a simple disc separator, with an extended bowl hood which has jets placed in its periphery through which the mud escapes. The effluents from the scouring plant are passed through settling tanks, usually continuously, to remove sand, and then through a screen to remove burrs and fibers; the effluent is then heated and passed to the Adams centrifuge. The feed-rate, according to Gillespie, is about 7000 gallons per hour, with a mud production of about 110 gallons per hour. A greasy emulsion is obtained, which is reheated and passed to standard centrifugal purifiers. This process originated in 1928, but in the United States it has been improved upon. Centrifugal methods are used for the recovery of approximately 90% of the wool wax produced in Australia.

10) The Frosted wool process – removes dirt from grease wools of inferior quality. It is used on a large scale in the United States. The wool is passed through a freezing chamber, and cooled to between -30 and -50°F, at which temperature the grease is congealed to a brittle solid; thus subsequent opening and dusting within the freezing chamber shakes off all the impurities, leaving a clean dry wool. About 86 to 90% of the earthy, vegetable, and other foreign matters are removed from the fleece, and 33% of the wax. The wool is then lightly scoured, and finally dried.

Recovery of wool grease by the Acid-cracking process

Yorkshire Grease. The acid cracking process is commonly employed in England for the recovery of wool grease, for example: "Yorkshire Brown Grease". The wool-scouring suds arc collected in large tanks and treated with sufficient mineral acid, usually sulfuric, to "crack" the suint and scouring soaps present. The drained residue is then heated and pressed by wrapping in canvas bags to recover the crude wool grease. Yorkshire grease is distilled to obtain "spirit oil" (4 %), and "distilled grease" (45.5 %) which may be pressed for liquid oleic acid, and solid stearine (m. 48-53°C), "green oils" (15.5%), and pitch (14%, still residue). Water and loss are 21%. Distilled grease has 55% free fatty acids, 7% combined fatty acids, and 39% unsaponifiable matter.

Recovered Grease. In the larger works at Bradford Corporation, compressed air and "concertina" presses are employed. The residue remaining in the press is known as "sud-cake." This by-product is rich in wool fibers, and still contains about 16 per cent of fat. The sud-cake produced in England was formerly sold in France, where it was extracted with solvent to recover the so-called wool fat, and the fat-free residue was sold as a rich fertilizer. Such grease is called "Recovered Grease" and has a more consistent composition than "Yorkshire Grease." It is obtained from the combined sewage from approximately 50 wool-scouring concerns. Such greases have various technical uses but are too impure for the preparation of lanolin.

Recovery of woolwax by the Steeping process

There are three steps in the ordinary practice of degreasing wool, namely (1) steeping or washing with tepid water; (2) cleansing or scouring proper with weak alkaline solutions; (3) rinsing or final washing with water. The waste from the potash scouring of wool is run into large, shallow settling cisterns, where (a) the dirt settles out in the course of 24 hours; or (b) the waste liquor or lye is passed through a centrifugal machine where dirt and grease are separated. The dirt is rich in both nitrogen and potash (K2O). The liquor freed from dirt is siphoned into larger wooden vats which serve for the acidulation and recovery of the raw woolwax, or straight grease. In these vats the liquor is agitated by blasts of air from the bottom, and the sulfuric acid is sprayed evenly and gradually. When thoroughly mixed, the contents are left standing for 12 hours, and the raw wax is heated by live steam, or to a temperature of 49-52°C, so that the water can be drawn off for filtering and pressing. It is again run into settling cisterns to remove water, or it may be centrifuged to remove water from oil, depending upon which method is employed. The thoroughly cleansed product is anhydrous lanolin, an excellent emulsifying agent.

Anhydrous lanolin is comprised of about 60% alcohols, and 43.5% mixed fat acids (m, 41°C, iodine no. 17, m. wt. 327). The mixed alcohols have the following constants: m. p. 33°C, iodine no. 26-36, acetyl value 144, m. wt. 239.

Preparation of hydrous lanolin from straight grease

The product of the wool combers, or straight grease, if of good grade, is worked up into hydrous lanolin. The woolwax obtained by the steeping process above described, or by the modern “supercentrifuge” process, is kneaded with water for a long time, or until a water-white, colorless ointment, lanolin, is obtained. In the centrifugal recovery of woolwax, which came into extensive use in 1910, the liquors from the scouring bowls are mixed to give a content of wax approaching 2 %. At a temperature of about 60°C (140°F) the liquor is settled to remove dirt, and it is then passed through a “Sharples supercentriuge”, which operates at a rate of about 25,000 pounds of liquor per day as a maximum. The liquid wax containing about 10% of water, together with water containing the dissolved detergents and soluble materials of raw wool, are discharged continuously. The water which does not contain more than 0.1% of emulsified wax is acidified and again passed through the centrifuge. The waste liquor is discharged to a sewer, or treated for the recovery of potash compounds. The wax is further purified by a combination of washing and chemical bleaching agents, of which sulfur dioxide and chlorine compounds give the best results. Lanolin usually contains about 25% of adsorbed moisture; the best grade is marketed as lanolin, USP.

Solvent Processes for Extraction of Woolwax

In the ordinary solvent process the greasy wool is treated with solvent naphtha in closed kiers, and the resulting solution of wool grease is transferred to stills, where the naphtha is recovered and the wool grease is obtained as a by-product. The degreased wool is next treated with a dilute tepid green-soap solution to remove the suint and dirt. The process is said to leave the fiber in much better condition, and the recovered grease may be further purified for the preparation of lanolin compounds. The finer-stapled goods usually contain the largest proportion of grease, and the amount of grease recovered is of sufficient value to retire the cost of scouring.

Hypochlorite Process for Treatment of Wool-Scouring Wastes

The objectionable organic matter of wool-scouring wastes is oxidized by calcium hypochlorite, so that a marketable clean grease with a high yield is obtained. In this process, which was installed in a process plant, the wool-scouring waste is mixed, aerated, and then settled with calcium hypochlorite agent in an amount equal to that of the alkali used in the scour. The resulting sludge of calcium carbonate and insoluble soaps is permitted to separate by 8 hours settling, and the clear supernatant liquid is discharged to the sewer. The sludge and scum are acidified with sulfuric acid to a pH of 4-5, producing a concentrated sludge liquor and a supernatant liquor, which is discharged. The sludge from this process is heated to 190°F and filter pressed. Steam is applied to the presses until 70 to 75% of the grease is recovered. The cake may be disposed of on land and dries without odor. The grease is steamed, treated with mineral acid, and separated; it contains 2% moisture and 5 to 10% free fatty acid.