June, 1931
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Summary of Present Knowledge Concerning Constitution of Paraffin Wax The general knowledge with regard to the constitution of paraffin wax may be summarized as follows: (1) Paraffin waxes from all sources are composed only of normal and isoparaffinic molecules. (2) The number of different normal molecules that may occur in any one wax is small (eight to ten), although as many as fourteen different molecules have been found in different waxes. (3) The relative proportions and types of molecules present, within the above classification, vary with the source of the wax. (4) The normal molecules present in any wax may vary from Cz& to Cs7Hue. ( 5 ) The nature of the isomeric paraffin hydrocarbons likely to be present is difficult to determine, as no data and no pure compounds are available for a study of the isomeric material of the indicated molecular weight.
The following conclusions are based on the present x-ray study: (1) From an x-ray examination, two normal paraffin molecules, C38H78 and Ca~Hss,which have never before been definitely recognized as being constituents of paraffin wax, have been identified in the wax studied. One of these molecules, CaHsc, never before recognized synthetically or naturally, helps to fill in the gap between the known molecules C38H78 (synthetic, natural) and C67Hllb (natural) and CqoHlz? (synfhetic). (2) From an x-ray examination it is evident that no fraction of either series studied can be a pure compound.
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(3) An x-ray investigation is an independent method of further corroborating the ideas that paraffin wax is composed only of normal and isoparaffinic hydrocarbons. (4) T h e x-ray diffraction method can be of considerable aid in evaluating the amounts of normal and isoparaffin molecules present in crude waxes. From this the properties of the wax may be deduced. ( 5 ) A research study of the individual crystals occurring in paraffin wax (I, 11,18) should prove very interesting and perhaps valuable. Literature Cited Buchler and Graves, IND.ENG.CHEM.,19, 718-24 (1927). Carpenter, J . Inst. Petroleum Tech., 12, 288-315 (1926). Clark, Science, 66, 136-7 (1927). Ferris, Cowles, and Henderson, IWD.END.CHEM.,21, 1090-92 (1929). Fischer and Schneider, Ges. .4 hhandl. Kenntnis Kohle, 5, 117-78 (1920). Francis, J . Chem. Soc., 121,496-513 (1922). Francis, Watkins, and Wallington. Ihid., 121, 1529-35 (1922). Francis, Watkins, and Wallington. Ihid.. 121, 2804-10 (1922). Francis and Wood, Ibid., 1946, 1420-3. Hengstenberg, Z . Krist., 67, 583-94 (1928). Katz, J . Inst. Petroleum Tech., 16, 870-88 (1930). Kraft, Ber., 40, 4 7 7 9 4 4 (1907). hfeyers and Stegeman. I A D . ENG.CHEM.. 20, 638-41 (1928). Muller and Saville, J . Chem. Soc., 127, 599-603 (1925). Piper, Brown, and Dyment, Ihid., 127, 2194-200 (1925). Piper, Malkin, and Austin, I b i d . , 1946, 2310-8. Saville and Shearer, I b i d . , 127, 591-8 (1925). Tanaka, Kobayashi, and Sadayuki. J . F a c u f t y Eng. Tokyo I m p . U n i r . . 17, 275-82 (1928). Thibaud, Comfit. rend., 184, 24, 96 (1927).
Recovery of Rubber and Cotton from Uncured Tire Ply Scrap' Extraction Process Charles S. Powell FIRESTONE TIRE & RUBBER COMPANY, AKRON,OHIO
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A new method for reclaiming uncured tire ply scrap The acid process for reis described. This is a n application of t h e familiar claiming cured tire scrap trims has always been solvent-extraction process. It possesses several adwas developed by Mitchell, a difficult p r o b l e m . vantages over the other methods of separating t h e b e t w e e n 1882 and 1889 (6) Composed of uncured rubber rubber and cotton fabric in t h e scrap, particularly and has been a d a p t e d for and long staple cotton, their from t h e standpoint of waste of materials, for both use with u n c u r e d t r i m s . value is considerable. Certhe cotton a n d t h e rubber are completely reclaimed The scrap as it comes from tain quantities, after b e i n g without deterioration. If t h e process is to have wide broken down on a mill, can the t i r e - b u i l d i n g room is application, however, means must be devised for t r e a t e d with 25 per cent be used in bead covers, flaps, utilizing t h e dilute rubber cement produced. s h o e soles, and mats withsulfuric acid in large wooden out detrimental effects. The vats. The temDerature is Dunlop Rubber Company ( 2 ) has been granted a patent raised to 110" C. in about 2 hours by passing steam into the covering a composition of uncured ply scrap, ground scrap, mixture or by means of steam coils. The acid is then drained etc., to be used in the manufacture of objects of fibrous rubber. from the scrap, which is then washed in the vats several times with water, and finally removed to a washing mill, where the Previous Methods remainder of the acid is removed. During the process the There are several methods in use for reclaiming the uncured cotton is entirely disintegrated and the rubber is practically tire ply scrap. I n one method the cotton is washed from the as good as the original skim stock, except that the accelerator rubber on a four-roll washer. The sheet of rubber passes and a large part of the zinc oxide have been destroyed. With between the four rolls, each passage exposing a fresh surface the advent of the very active acidic accelerators in recent t o the action of streams of water. A great deal of the cotton years, the acid process has been complicated by the necessity is removed from the rubber in this way, and the action of the of a preliminary treatment with caustic to remove the water is assisted by a wire buffing wheel, which is very effec- accelerator, to prevent the stock from curing during the acid tive in tearing the cotton away from the rubber. The rubber, treatment. The acid process is therefore wasteful and after being dried, is used over again as skim stock, while the expensive. cotton may be dried and sold. A patent has been granted to Development of Solvent-Extraction Process T. F. Furness on a modified form of this process (3). There is nothing new about a solvent-extraction process. 1 Received March 16, 1931. Presented before a meeting of the Akron Rubber Group, February 9, 1931. Extraction has been widely used in recovering oils and fats
HE utilization of tire
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Thl. 23, XO. ti
frmri various waste pniducta. A smiewliat rclatrd process was patcnted about ten years ago ( I ) for reclairnirii: cured tire scrap. 'l'lie tires arc immersed in solvent for 24 hours. A t t,iie end of this time tlie rubber is not dissolved, but swollen sufficiently to a l h a separation of the fabric and rnbber. I'erifokl (4)recommends treating uncured scrap by a solventextraction method. The stock is pressed into blocks and then cut into slabs an inch thick. Tliese slabs are then extracted twice with solvent and the cotton is centrifuged and dried. An extraction process is quite simple as applied to uncured trims. The scrap arid solvent are placed in IL coutainer and agitated. The rubber swells, goes into solution, and tlic wmetit, produced is drained off. The cott,on must then be
the heavy-cement tank. The riext two washes are drained into the tliin-cement tank and the lnst two waslies go t o the tank for very tliin ccment. Ily this time the &ton, which contains less tliati 1 per ceot of rubber, is quite white arid clean. However, it contains about 300 gallons (1134 liters) of betrzene, which does not drain off. 1:or that reason it is necessary to steam t.lie cotton after each run arid recover the solveilt. To assist in vaporizing the benzetie and to keep tlie terriyerature as low as possible, the system is providcd with a vacuum pump. Steam a t 50 pounds (3.51 kg. per sq. cm.) pressure is turned into the extractor through four nozzles a t the bottom of the outer shell. The benzene is vaporized and passcs over with the steam to the conclenmrs, where they are both c o n d e n s e d and drawn to the vacuum pump, which in turn delivers tliem to the water separator. I n the separator the water, being lieavier than tlie bcnaene, set.tles to the bottom, wliere it iu drawn off, while the benaene runs off tile tup into tbe pure-benzene tank. I n filling the cxtractor, instead of using pure benrene, thin ccCWP merit is used for the first four washes. For tire last two washe8 it has been found ne( preheat the benzene to 140' F. (60" C . ) before washing tile scrap. The use of tiot washes speeds up the process considerably and helps in obtainiug a cotton with a low rubber content. The cotton is removed tlirough tho lower doors of the extractor. It contains about 30 sieure ~ - ~ i s g r a r nof at^^ far sotvent ~ ~ t"f uncured ~ ~ l'im~ scrap t i por ~ cent ~ ml)iiture and must be dried before being used. This is done in large hot& driers, rinsr:d with fresh solvent to remove the rest of the rubber. siicli as are used for drying reclaimed rubber. After the nioistnrt! had limn rcnioved from the cotton. The difficulty in the process is in working out a safe, efficient nietfiod for removing ttie cotton from the cement. In tlie it was put tlirwigli a sliredder to remove any small knots and beginning an attempt was made to do this by putting the balls of fibers wliicli 11ad formed, Origiiially, tlic extract,ors were lined with a coarse cloth. mixture of ruhber cement and cotton into a liydraulic press and squeezing the cement tltrouglr a screen. Tlie screen soon which was rattier tightly w,veti. N o difficulties were enbecame clogged, however, and the resulting pressure caused ecn~nteredduring the first run, hut during the second run it the ceniont to spirt from the tnp of the press. Moreover, wa impossible to drain tlic cetneirt in a reasonable lengtli of it was rather diflicult to transfer the mixtitre of cement and cotton from tire niixer to the press. I+'urthermore,the pressed pulp had to be put back into the mixer and rinsed with fresh sillvent.. Experiments m r e also conducted using a centrifuge to remove the cement. This was satisfactory for a wliile, lntt the lioles in the centrifuge became clogged with dried rubber arid it was necessary to take it apart and burn out tiic ruhber. This process was also inefficient, slow, and darigerous. It would have been almost impossible to carry nut either of these processes on a large scale. Extraction equipment was then purchased,' and this is the plant, wit11 n~~nr(~rous altcratioris, which is in operation today. The extraction plant is sliown in Figures 1 and 2. T h e extractor is 5 feet (l.SL inetcrs) in diameter and 12 feet (3.65 meters) long and contains a revolving cage, lined with :Xt-rnesli wire screeti (wire diam. 0.013 inch). This cage revolves a t about I 1 r. p. m. and is provided with doors for eliargiiig arid discharging. To operate the rxtractra, it is rotated iint.il tlie dmm are Fimre 2 -.Solvmf-Ertracli~,nPlant for Reclaimlng 'Tire Scrap rtpposite the doors a t the top of the outer sliell. The cage is t,hen loaded with 1000 pounds of uncured tire ply scrap and time. Apparently, a thin film of rubber had cured on the both sets of doors are closed. 'l'bc extractor is t.lien filled with inside of the cloth during the steaming process. Tlie exbenzene throngli the charging litie and the cage started tractors were then lined with 8-ounce burlap. Much better rotating. At the cnd of ahout 2 hours the valve in tlie drain results were obtained, and therefore on the next run the exlitie is q)ened, with the cage still revolving, and the lieavy tractors were relined u-ith 18-niesligalvanized screen, similar tu cement is drained into the storagc tank for heavy cement. window screening. The cotton came through this screen, c(xThe extractor is tlien filled again and waslied for '/z liourp taminating the cement, and so a 30-mesh steel screen was subarid then drained as before. This second wash also goes to stituted. This mon rusted and was replaced wit11 one of inonel metal. So far these screens have performed very satisfactorily. 2 From Ernest Scott B Cu., Fall River, Ma-.
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IXDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1931
When the extraction plant was first put into operation the length of t h e for steaming varied from 3 to 6 hours. This was an excessive length of time for the evaporation of 300 gallons (1134 liters) of benzene. By the use of hot washes and wire screen lining instead of cloth, the average time of steaming was cut to about 60 minutes. Applications of Products
The two products obtained during the extraction process from uncured tire ply scrap are cotton, containing about 0.5 per cent rubber, and a 6 per cent rubber cement in benzene. From 1000 pounds (454 kg.) of scrap were obtained 1200 gallons (4536 liters) of cement and about 400 pounds (181 kg.) of cotton. The first problem was to dispose of the rubber cement. A rubber cement of about the same composition as the cement obtained from the tire ply scrap, but with a higher rubber content, is used in the impregnation of fabric. The problem resolved itself into producing a heavier cement from the 6 per cent extracted cement. The original process called for a still, or evaporator, which would concentrate the cement to the required rubber content, However, this idea was abandoned when it was realized that in evaporating the rubber cement the thin film of rubber next to the heating surface would be cured, and also the low conductivity of the rubber cement itself would make evaporation very difficult. The concentration of the cement was therefore increased by adding fresh stock in the cement mixer. Aside from a small application in rubber compounding, the cotton may be utilized in paper manufacture and as a filler in cheap felt compositions. It may also be finely ground and used as cotton floc, since the 1 per cent rubber it contains is not detrimental. Economics of Process
The actual cost of recovering the rubber and cotton by the extraction process is only 30 per cent of the cost of acid re-
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claiming. I n addition the cotton is saved and can be sold, thus increasing the savings effected. The cotton and rubber are both completely reclaimed without suffering any deterioration. I n the other methods for reclaiming uncured ply scrap, either a depreciated product results (acid process) or an incomplete separation of the rubber and cotton may occur (washing process). The power consumption and the labor cost of extracting with solvent are both low. Limitations of Process
There are several limitations to the extraction process, however. Scraps containing appreciable amounts of reclaim are unsuitable, because cement made from them cannot be used for fabric impregnation. Another difficulty is that it is not practical to mix scraps containing different accelerators, owing to the rapid set-up of the cement under the combined effect of certain accelerators. The process must therefore be operated on one kind of scrap a t a time. I n order economically to dispose of the cement produced, the extraction of the uncured scrap must operate in conjunction with fabric impregnation. In plants which do not do this the process would have limited applicability. Acknowledgment
Acknowledgment is made to N. A. Shepard, who initiated the process, and to F. W. Stavely and R. R. Jones, who, with the writer, developed it. Literature Cited (1) Chandeysson, British Patent 157,792 (Jan. 10, 1921); C Q O U ~ C 6’ ~O~C guffa-percha, 19, 11, 195 (1922). (2) Dunlop Rubber Co., French Patent 637,211 (July 7, 1927); Rev. gtn. caoutchouc, 6, No. 43, 25 (1928). (3) Furness, U. S. Patent 1,321,200 (Nov. 11, 1919). (4) Penfold, I n d i a Rubber J., 77, 337 (1929). (5) Weber, “Chemistry of Rubber Manufacture,“ Gri5n. p. 265 (1926).
An X-Ray Diffraction Study of Chicle’*z Charles W. Stillwell DEPARTMENT OF CIIEMISTRY, UNIVERSITY OF ILLINOIS, U R B A N AILL. ,
A comparative study of the x-ray diffraction patterns for whole chicle, both crude and refined, and for the several fractions into which it may be conveniently separated, brings out the following facts: (1) Whole crude chicle is a mixture of at least three crystalline constituents-the gutta, the resin, the “benzene insolub1e”and one or more amorphous fractions. (2) Refined chicle is essentially the same in structure as crude chicle, except that the gutta is probably highly dispersed and amorphous.
(3) Calcium oxalate monohydrate exists in chicle as such and is the crystalline constituent of the benzeneinsoluble fraction. (4) Chicle gutta is identical with gutta-percha and balata, its exact nature depending on how one interprets the facts relating to the last two. (5) The structural units of chicle do not assume a preferred orientation under tension, and chicle differs in this respect from rubber.
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v
ERY few data as to the nature of chicle are available in the literature. An average analysis is as follows (1): %
%
Water-soluble: Arabin., . . . . . . . . . 1 0 . 0 Calcium.. . . . . . . . 9 . 0 Sugar.. . . . . . . . . 5 . 0 Calcium salts. . . . 1.O
Alban . . . . . . . . . . . . . . . 33 75 Fluavil.. . . . . . . . . . . . 2 2 . 5 0 Gutta., . . . . . . . . . . . . . . 18.75
25.0
75 00
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1 Received January 17, 1931. Presented by C. W. Stillw-ell and G. L Clark before the Division of Rubber Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931. 2 This investigation was supported by the Beechnut Packing Co.
Dannerth ( 2 ) lists a typical analysis of chicle, and hazards the opinion that the chewing qualities of any gum are a function of the resin content and the melting point of the resin. The gutta is apparently polymerized isoprene, alban is a mixture of two or three compounds, and fluavil may be a mixture of two compounds. Separation into Fractions
Both crude and refined chicle were studied in the present investigation. Each was separated into the customary gutta and resin fractions as follows: The whole gum was dissolved
