Fzgure 7.
Polybutodiene
resistance, qood resistance to oxidation and low tciiiperatures, low hysteresis-and thus relatively low I i c L i i t buildup. As time proqresses, rubber companies are worliinq hard to increase the percentage of PBD in tii.cLs. Goodrich-Gulf has already developed a 1007, pol!.butadiene tire, from a preprocessed elastomer, 11.i(11 claims that these tires last iwice as long as oncs inac!r of natural rubber. Nontire markets for PBD have hardly been scratclwl. and account for about 4y0 of the use pattern as sho\\.ii below. Only a small percentage of polyisoprene is consumed in tires; this use pattern ma); n o t change substantially if prices for natural rulllxr continuc downward.
Polydiene consumpfzon
0 Polyisoprene
a
Polydiene Use Pattern (In per cent ) Polybutadiene Polyisopt ene 7 YO2 1967 7 962 7967
Tire Nontire
96 4
75 25
10
90
10 90
Plants for Everyone
Yeor'1961
1962
1963
1964
1965
1966
1967
Figure 2. Polydiem capacity polybutadiene
0 Polyisoprene
250
200
c 0 Ln
-P
150
0
L
0
G
s
100
-c I-
50
0 ~~~
Year 1959
1960
19kl
1962
1963
1964
All SBR producers except two (Copolymer Rubller gL Chemical and United Rubber & Chemical) are now manufacturinq a t least one of the two polydienes, either coinmerciall!. or in pilot plants. And C . S. Rubber's Naugatuck Chemical Di\ision, now sho\vinq considerahle interest in ethylene-prop)-lene elastonier, may also join the polybutadiene ranks; it has made trans-polyhutadiene in its pilot plant at Baton Rouye, La. Phillips moved into polybutadiene ahead of c\w-yone. during 1960, by converting existiiig SBK facilities ( 7 ) . Shell launched commercial polyisoprene production the same year, using similar tactics. . h e r i c a n Rubber, Firestone, and Goodyear are now producing polybutadiene commercially ; Goodrich-Gulf expects to have converted SBR facilities in operation later this year (Table I ) . Texas-U. S., with a plant noiv under construction, will produce polybutadiene in 1964. Additional pol!.isoprene units are also scheclulcd for start-up this year, by Goodyear and Shell. Pilot plants have been operated hy American Rul)l)er. Firestone, Goodrich-Gulf, Goodyear, Phillips, and Shell. Last year General Tire completed its polyllutadiene pilot plant, presumably to test processes it ma!- eventually license; Texas-U. S. also has its polylmtadienc pilot plant in operation. Naugatuck completed a semiworks unit, earlier this year, to produce ethylene-propylene (EPR), and polybutadiene and polyisoprene elastomer . h i entirelb. new catalyst system is involved, it says. By 1964, polydiene plant capacity should amount to 221,000 long tons, or better than 250,000 lonq tons if General Tire and Naugatuck reach an earl!. decision to build commercial units. American Rubi)er officials claim their facility can readily produce an additional 20,000 tons when needed. Last year the industry had a coml)incd (po1yl)utacliciie plus polyisoprene) excess capacity of 250°;& durinq VOL. 5 4
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initial start-up and marketing periods. This year excess capacity will dwindle to 75%, a comfortable margin, and drop to 20% by 1764-requiring additional plants. Thus, the rubber people seem to have a reasonably good grip on the supply and demand situation, and a firm grip on polybutadiene, even though considerable oversupply is predicted for polyisoprene through 1967.
TABLE 1. Company
American Rubber & Chemical Louisville, Ky. Firestone Tire & Rubber Orange, Tex. General Tire & Rubber Mogadore, Ohio Goodrich-Gulf Chemicals Institute, W. Va. G o o d y e a r Tire & Rubber Beaumont, Tex.
Rapid Overseas Growth
With the notable exception of EP rubber, pioneered in Italy by Montecatini, most elastomer technology has originated in the United States and then dribbled overseas. SBR is a good example. But polydianes have moved abroad at a much faster clip. Within a year or so, Canada, Great Britain, Europe, South America, and Japan will have a minimum potential of 200,000 long tons-almost equal to American capacity (Table 11). Of the 1 2 plants planned, under construction, or in operation, 6 units are slated to operate under a Goodrich-Gulf license. Some hedging is under way for polyisoprenere garding installation of two-way units: Shell Chemical and Asahi Chemical. Time will tell whether anyone overseas has the courage to specialize solely in polyisoprene, other than Shell Nzderland.
Long Tons
-_ PBD
PI
Naugatuck Chemical Baton Rouge, La. Phillips Petroleum Borger, Tex. Shell Chsrnical Marietta, O h i o Torrance, Calif.
40,000
1962
30,000
Canada England France
Germany Hol!and Italy
Japand
1961
10,000
1962
20,000
1961 1962
2,000
1962
25,000
1960 18,000" 18,000
1962 1960 1964
Capacity to be doubled during 7963.
PBD
=
polybutadiene; PI = polyisojrene.
FOREIGN POLYDIENE PLANTS"
Company
PBD
PI
Both
Process License
Fish International Corp.b Fabric0 de Borracha Sintetica de
10,000
U. S.
Pernambuco Polymer Corp. Shell Chemical Co., Ltd. Firestone International Michelin Societe des Elastomeres d e Synthese Chemische W e r k e Huels Shell N e d e r l a n d Chemische, N. V. Azienda N a z i o n a l e ldrogenazione Combustible Montecatini Asahi Chemical Bridgestone Tire
28,000 20,000
Firestone Goodrich-Gulf Goodrich-Gulf Firestone Phillips
Japanese G e o n Ube Industries
20,000 15,000 12,000 25,000 20,000
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Rubber
Goodrich-Gulf Goodrich-Gulf Unannounced
15,000 20,000 20,000 20,000 Pilot plant Pilot plant Pilot Plant
n Existing or planned. * Comprising Fish International, Continental O i l , Cities Serum, U. S. Rubber, and Witco Chemical. Shell, Texas Butadiene, and French, tire producers. ti It is generally belicved that M I T I will approve only one or t u ' o units. PBD = polybutadiene; PI = polyisoprrnc.
18
1961
Pilot Plant
Long T o n s
Argentina Brazil
Yeur
Texas-U. S. Chemical Port Neches, Tex. 20,000
Some Americans are also hedging polyisoprene markets with two-way units, notably Firestone. Only Goodyear and Shell are committed to polyisoprene
Country
Bolh
20,ooc
low Cost Monomers
TABLE II.
DOMESTIC POLYDIENE PLANTS
Phillips Montecatini Firestone Goodyear Goodrich-Gulf Goodrich-Gulf Comprisinp Saint-Cobain,
units; both firms will manufacture captive monomer supplies. Polybutadiene started out with an introductory price of 35 cents a pound-polyisoprene a t 30 cents on a dry basis (Table 111). With volume production, prices are now down to 27'/2 and 23 cents, dry basis, respectivcly. Meanwhile, natural rubber (tire grade) prices have dipped to 271/2 cents, dry basis, and may well go considerably lower. I n fact, a big economic battle is shaping up between polydienes and natural rubber as the latter moves into a worldwide oversupply situation. Currently, SBR lists at 23 cents a pound, dry basis, while oil-extended materials sell in the range of 17 to 19 cents. Meanwhile, butadiene and styrene are listed a t l Z 3 / , cents per pound. Styrene is the only monomer that has dropped in price since 1960, when it was quoted at 141/2cents. One of the big problems with polyisoprene is monomer cost. At least 5 processes have been carefully evaluated, three synthetic and two bssed on refinpry streams: methyl ethyl ketone-formaldehyde; acetone-acetylene; isobutylene-formaldehyde ; isopentane or isoamylenes dehydrogenation ; and propylene dimer pyrolysis. Most Americans have concluded that refinery-based
TABLE Ill. POLYDIENE PRICES (Dry basis) Cents per Pound Year Poly butadiene Polyisoprene
1959 1960 1961 1962
35 31 ' / z
301/2 27'/z
30 27 25
23
processes are the lowest cost routes, although some foreign activity is taking the synthetic path. Goodyear decided to go with propylene dimer and Shell picked isoamylenes dehydrogenation. It's hard to visualize that isoprene can be made as cheaply as butadiene, but a ceiling can be established from one well known fact: Goodyear publicly stated it had rejected alternate routes costing as much as 15 cents. A number of companies have researched isoprene, including Continental Oil, Ethyl Gorp., Gulf and Sinclair-Some firms are ready to build units if they can find a customer a t the right price. Rubber companies in general don't want to pay the prices suggested by the potential suppliers. Lower natural rubber prices could put polyisoprene in a bind, which requires a monomer-to-polymer conversion cost estimated roughly a t 7 to 9 cents a pound. The industry is also watching new technology coming around the corner from Badische Anilin und Soda Fabrik, currently investigating solvent extraction for separating butadiene from C* hydrocarbon fractions. Heretofore, solvent extraction (other than cuprous ammonium acetate) has not led to a suitable process and conventional fractional distillation gives only a
Figure 3. Crawford and Russell reactor
partial separation. According to BASF claims, N-methylpyrrolidone works well and gives extracts containing 20 to 30% butadiene. The butadiene is SO pure, it says, that it can be used for stereospecific polymerization. It's really a question as to whether solvent extraction can compete with extractive distillation. Existing methods of extractive distillation, and cuprous ammonium acetate (CAA) extraction, are reported not to produce a stereo-grade monomer-it almost always contains too much acetylenics, well above the average 50 p.p.m. tolerance level. Hence, producers must
AUTHOR Harry W . Haines, Jr., i s a consulting chemical engineer and owner of Haines &? Associates in Houston, Tex. VOL. 5 4
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Polydiene catalysts are closely guarded industrial secrets presumably resort to additional processing steps such as hydrogenation with the Dow catalyst developed for this purpose. I n France, Societe des Elastomers de Synthese is building a 37,000 ton-per-year butadiene plant reported to be using a new “iodine” process developed by Shell. Details have not been revealed, but the process is presumed to have attractive capital and operating costs. Catalyst Systems
\
Catalyst systems employed in diene polymerizations are probably the most closely guarded secrets in the rubber industry. Occasional, official statements say Ziegler-type, Ziegler-Natta, or lithium systems are used, with no mention of the solvents employed. Numerous authors (6, 8, 74) have published reasonable guesses, based on the patent literature and trade opinions circulating in the rubbzr and catalyst manu. facturing industries. But no one can say, authoritatively, who is correct. During a recent countdown, the systems shown (Table IV) seem to be hitting close to home. Where does the industry stand on solvents? Most producers seem to prefer normal paraffins (in the pentane to heptane range) or benzene. Recently, Humble Oil launched a new line of isoparaffins (Isopar), claimed to play a n important role in butadiene and isoprene polymerizations. cis-Contents of the various elastomers are also subject to question, depending on the analyst and his methods. Other factors are probably more important, such as cold flow properties and ease of milling on standard equipment, all of which may be related to 1,2-addition and 3,4-addition structure, and truns-1,4 content. Certain generalizations can be drawn from specific
TABLE IV.
systems, however (72). All of the Ziegler-Natta catalysts produce truns-l,4 or 1,2-addition structures of butadiene except the Ti14 AIR3 combination. With isoprene the TiC1, A1R3 and TiClr CdRz combinations provide cis-1,4 orientation. This is an interesting sitbation because both of these combinations produce trans-1,4-polybutadiene and the Ti14 AIR3 system is not active in isoprene polymerization. Effective Ziegler-Natta catalysts produce about 90 to 95% cis-l,4-polybutadiene and 95 to 97y0 cis-1,4polyisopren e. n-Butyl lithium and sec-butyl lithium have been tested for butadiene and isoprene polymerization. These compounds, without a cocatalyst, produce 35 to 45% czs-1,4polybutadiene and 90 to 94% cis-l,4-polyisoprene. n-Butyl lithium is usually chosen because it is more readily available (in pentane, hexane, and heptane solvents), more stable in storage, and cheaper-even though it is slightly less reactive. I t is generally conceded that butyl lithium catalyzes the polymerization of isoprene to a higher molecular weight than that of natural rubber, and thus requires additional Banbury milling time. Ziegler-catalyzed polyisoprene is said to have almost exactly the same molecular weight distribution as ,natural rubber and requires minimum pretreatment. A cobalt system, similar to that employecl by GoodrichGulf, has been studied extensively by Gippin (7). Diethyialuminum chloride in combination with cobaltous chloride, or cobaltous chloride pyridinates produce 98y0cis-l,4-polybutadiene- in a benzene solvent. Conclusions regarding the effect of. AlC13, when added to the system, would seem to indicate that CoCl:, AlEtLCl AlEtClz is also a n active combination.
+
+
+
+
POLYDIENE CATALYST SYSTEMS
Catalyst System
Company
+
+
Approximate cis-Content, yo PBD PI
System
American Rubber & Chemical
Titanium iodide, AI alkyl
95
Phillips
Firestone Tire & Rubber
Butyl lithium
40
Firestone
93
Butyl lithium
Firestone
95-98
G e n e r a l Tire & Rubber
Proprietary“
G o o d ric h - G uI f C h emica Is
98
Goodrich-Gulf
G o o d y e a r Tire & Rubber
Co halides, AI alkyl halides Titanium iodide, AI alkyl Titanium tetrachloride, AI alkyl
95
Phillips
Naugatuck Chemical
Proprietary
95
95
Phillips Petroleum
Titanium iodide, AI alkyl
Shell Chemical
Butyl lithium
Texas-U. S. Chemical
Proprietary
a
It i s generally believed that General Tire will license from Goodrich-Gulf or Phillips. polybutadiene; PI
PBD
=
20
INDUSTRIAL A N D ENGINEERING CHEMISTRY
= polyisoprene.
95
U. S. Rubber Phillips
92-93
95
Goodyear
Shell Texas-U. S.
reactor during solution polymerization-about 200/, . This philosophy of reducing solvent-recycle load was tied to operation in a total hydrocarbon system ( 9 ) . Solvent was removed from the elastomer in a “solventremoval” extruder. The first extruders developed for this purpose employed vacuum. They were expensive to operate and generally did not perform satisfactorily. Reactor heat transfer coefficients, at high solids content, were seldom more than 5 B.t.u./hr./sq. ft./” F. This led to the development, by Crawford and Russell, of a scraped wall reactor (Figure 3) which reportedly gave heat transfer coefficients of 25 to 30 B.t.u./hr./sq.
Goodrich-Gulf says its cobalt system produces polybutadiene which can be used in tire manufacture without the addition of other elastomers. However, Goodrich-Gulf‘s material does contain up to 14% of “preprocessing aids.” Bus tires made with a 1 0 0 ~ o polybutadiene tread wear more than twice as long as those made from natural rubber, they claim.
201
ft./” F.
I
I
I
I
2
4
6
I
I
10 20 Plant capacity, thousand long tons Year
I
I
40
Figure 5. Polydiene plant capital investment
Reaction mechanisms of the various catalyst systems have been discussed by Kuntz (70). Safe methods of handling pyrophoric organometallics, titanium trichloride, and butyl lithium have been described in the literature (2, 77, 73),and instructions are available from the various catalyst suppliers : Continental Oil, Ethyl Corp., Texas Alkyls, American Potash & Chemical, Foote Mineral, and Lithium Corp. of America. Manufacturing Technology
If catalysts systems are considered an industry trade secret, production technology is even more so. None of the rubber companies have published comprehensive flowsheets of their processes. While most war-time SBR plants were designed similar to one another as an expediency, the opposite is true of polydiene units. New catalyst systems and solution polymerization techniques have given the ritblier companies an opportunity to exercisc a great deal of manufacturing ingenuity. Some polydiene plants today are an adaptation of retired SBR facilities; other processes were developed from scratch through the pilot plant and semiworks stages. Early development efforts were aimed at producing the highest possible solids (elastomer) content in the
I
Today, a number of plants are known to employ the philosophy of keeping reactor solids content to 10% or less, for the purpose of operating at lower viscosities. And many operators form a crumb-water slurry as soon as possible in the plant (Figure 4). However, the industry still has diverse and strong opinions about the best methods for drying polydienes. Most plant operators would like to avoid costly maintenance associated with the tunnel dryers commonly employed in SBR plants. Some have installed Banhury dewatering systems to achieve the desired result ; others have used an expeller-extruder combination. Competition is keen among equipment manufacturers on these drying systems. Most of the new polydiene facilities have required a . . capital investment ranging from $8 to $12 million (Figure 5 ) , while semiworks plants cost in the neighborhood of $1 to $2 million. EP Rubber I s Here
Almost before the industry can digest polydienes, another newcomer is on the scene-ethylene-propylene elastomer. These new materials, although not stereospecific, can also he made in facilities designed to produce stereo-regular rubbers. Humble Oil started this trend when it began commercial production in converted butyl rubber facilities at Baton Rouge, La. Recently, Du Pont announced it would build a 15,000 ton-per-year unit at Beaumont, Tex., scheduled for completion next year. Canada’s Polymer Corp. at Sarnia, Ont., has been pilot plantiny EPR for some time and now says it will also go commercial “in the very near future.” Earlier this year Avisun announced it would expand the company’s pilot plant at Marcus Hook, Pa., to make semiconimercial quantities; U. S. Rubber’s Naugatuck Chemical Division is also makiny semicommercial quantities at Baton Rouge, La.; Hercules Powder has been operating a pilot plant for more than a year. Most of the emphasis on EPR is coming from chemical companies. ’Within five years EPR consumption may exceed 70,000 long tons per year. Its initial use is aimed at nontire applications-wire and cahle coatings, conveyor belts, steam hoses, O-rings, tank liners, and (Continued on page 23) VOL. 5 4
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FIGURE 4.
POLYDIENE PROCESSING SCHEME
Frequently the catalyst is a two-component system, but it may also consist of one o r three components. These materials a r e dissolved o r slurried in the polymerization Cor other suitable) solvent, in o n e o r more propelleragitated vessels. Catalyst makeup i s a batch operation, but catalyst feeding is continuous. Purified and dried diene (butadiene o r isoprene) a n d cotalyst a r e pumped as liquids t o the plant polymerization section which contains four o r more agitated vessels a r ranged f o r series u p f l o w o f reactants. A t moderate viscosities the reactors may b e turbine-agitated; higher viscosities require special equipment such as screw-type agitators and scraper blades. U p f l o w allows the reactors t o operate full, with front-end pumping of l o w viscosity feed, rather than intermediate pumping of high viscosity product. Some reactors have been designed with draft tubes, others with banks of c o o l i n g coils which a c t as baffles. At moderate viscosities where high heat transfer coefficients a r e encountered, internal c o o l i n g coils and jacketed vessels a r e commonly employed. Scraped-surface reactors, of the type d e v e l o p e d by C r a w f o r d and Russell, must b e used f o r high viscosity materials. The reactor effluent leaving the polymerization section may contain from 7.5 t o 20y0 solids (polymerized diene). Some plants a d d a short stop a t this point t o deactivate the catalyst and "kill" the reaction. Polydienes a r e produced a t temperatures ranging from 40' to 140' F. and pressures up to several atmospheres. Residence time in the reactors may vary from 2 t o 6 hours for most catalyst systems. A solvent, t w o carbon atoms 22
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
heavier than the monomer, keeps polymerization pressure low and facilitates separation of unreacted monomer. The reactor cement, as it is commonly called, flows t o a b l o w d o w n tank where, b y a reduction in pressure and o c casionally the introduction of heat, unreacted diene i s flashed t o the diene cleanup system. Solvent vapors leaving the b l o w d o w n tank are condensed and recycled, o r the liquid can b e sent directly to the solvent cleanup system. Antioxidant is n o w added t o the polymer cement, on the w a y to the surge tank, t o prevent product degradation. In those plants which d o n o t employ a total hydrocarbon system, one o r more flash tanks a r e used t o produce a crumb-water slurry and t o remove the polymerization solvent by steam stripping. I f the catalyst system i s watersoluble, most of the catalyst fragments will be removed from the elastomer in the flash tanks. The exact techniques f o r removing nonsoluble catalyst particles a r e closely guarded trade secrets. After dewatering, the w e t polydiene crumb is washed, dried, and packaged as bales. W e t solvent from the flash tank decanters is pumped t o a solvent cleanup system. Some plants may use a single distillation column, whereas others employ t w o columns in series f o r removal o f a heads and tails cut. Following distillation, the solvent is dried. Gaseous diene from the b l o w d o w n tank is recompressed, purified in a distillation column, and transferred to storage o r to the diene-drying system. Monomer-to-polymer conversion cost should b e about 7 t o 9 cents p e r pound.
similar products. EPR will compete with natural and reclaimed rubber in these markets, as well as other synthetics, including SBR, butyl rubber, and neoprene. Du Pont holds patents covering various catalyst systems, including Tic14 $. LiAl alkyl, and VCld 4A1Cl3 A1(C4H9)a. U. S. Rubber is known to have worked with soluble systems derived from alkyl aluminum halides and vanadium oxytrichloride, or vanadium tetrachloride. Interest in EPR runs high because of low monomer costs-about 5 cents a pound. The product itself has some highly desirable properties : outstanding ozone resistance, excellent electrical properties, and it can be oil-extended. How soon, and to what extent, EPR can penetrate tire markets is still a debatable question.
+
Future Prospects
No one seems to question that polydienes will create far-reaching changes in the domestic and foreign rubber industry. I t seems to be only a matter of the degree of penetration. But how far can they go? Some experts say that, in a decade or so, polydienes could steal up to one half of the existing domestic markets for natural rubber and SBR. They may eventually become the basic elastomers of the industry. The future of polybutadiene may well hinge on a trend toward 50% SBR and 50% PBD tire treads, or a trend toward 1 0 0 ~ oPBD tire treads. Polyisoprene’s future is linked closely with isoprene monomer costs and natural rubber prices, because this elastomer can be used in most or all of natural rubber’s applications. Although a number of new plants have been constructed, it is significant that some companies moved rapidly into polydienes by converting a t least a part of their SBR facilities: Goodrich-Gulf at Institute, W. Va. : Phillips Petroleum at Borqer, Tex. ; and Shell Chemical at Torrance, Calif. When polydienes make further inroads into SBR markets, additional SBR plants may get a face-lifting. Polydienes are definitely puttin? a squeeze un natural rubber prices which, in a few years, may drop to a range of 20 to 25 cents per pound ( 3 ) . For the future, a continuoiis world wide oversupply of natural rubber is expected. U. S. State Department officials, in a more pessimistic note, think that prices could go well below 20 cents a pound. Last year, an zstimated 70y0 of polybutadiene consumption was combined with SBR. But this percentage can decrease as more PBD is blended with natural rubber. Although rubber companies have been slow about developing nontire uses, this market should account for about 25% of the use pattern within 5 years. Polyisoprene is in a state of flux, primarily because it is not developing outlets in the tire market as expected. However, PI latexes will probably make substantial inroads into the natural latex business, because their purity and solids content can be carefully controlled. Several companies have now moved trans-l,4-polybutadiene up to the semicommcrcial level-Phillips
Petroleum and Naugatuck Chemical. High transpolybutadiene resembles natural trans-polyisoprene rubbers (balata and gutta-percha) in many ways. U. s. Rubber recently revealed the advantages of using rhodium salt catalysts, which need no cocatalyst. These catalysts seem to work in emulsion polymerization with water, using dodecylbenzene sulfonate as a catalyst solvent. U. S. Rubber is also actively studying trans-l,4polyisoprene (synthetic balata). A tenfold increase in efficiency of the Natta catalyst (VCla+A1Et3) was obtained by supporting the vanadium trichloride on clay to increase its surface area. Researchers at U . S. Rubber say efficiency of either the supported or unsupported catalyst can be increased substantially (50fold) by addition of a third component-titanate ester or an alkyl titanium trialkoxide- which produces an active soluble system instead of a heterogeneous system. These examples clearly indicate the rubber trade will have a number of tailor-made elastomers available within the next few years, in addition to PBD, PI, and EPR. Research emphasis seems to be headed in the direction of soluble catalyst systems, and emulsion polymerization. Supporting segments of the industry are also .joining the parade of new products. United Carbon recently introduced an oil furnace black, made a t Ivanhoe, La., claimed to have “outstanding processing advantages” for stereo-rubbers, especially polybutadiene. This carbon black is designed to keep wear resistance up when polybutadiene content of the tire is increased. Its use permits 100% polybutadiene to be handled on roll mills without crumbling or sticking. Earlier this year, Nalco Chemical came out with.a new bridging agent-a polyalkanolpolyamine-aimed at solving the filler-matrix adhesion problem. This material apparently increases the tack of cis-l,4-polybutadiene. It’s a safe bet that rubber processors will have to step lively to keep up with the changing trends.
SUGGESTED READING (1) Crouch, W. W., Kahle, S. R., Petrol. Refner 37, 187-94 (November 1958). (2) Dezmelyk, E. W., Reed, R. S., IND.ENG.CHEM.53, 68A-71A (June 1961). 3) D’Ianni, Jgmes D., Petrol. ReJner 41,169-70 (January 1962). 4) D’Ianni, James D., Chem. Eng. Progr. 58, 73-4 (March 1962). 5) Fedor, Walter S., Chem. Eng. News 40, 88-104 (March 12,
i
__
1962) -,
(6) Gkshinowitz, Harold, Evans, T. W., Todd, David B., IND. END.CHEM.54, 23-32 (April 1962). (7) Gippin, Morris, I H E C Prod, Rer. and Develop. 1, 32-9 (March
--
1962) -,
(8) Gdckone, Eugene, Chem. Eng. 69, 93-106 (April 2, 1962). (9) . , Kuchinski, F. L., Muraski, F. T., Chem. Ene. Proer. 57. 62-6 (August 1961). (10) Kuntz, Irving, A.1.Ch.E. 47th Natl. Meeting, Baltimore, Md., May 22, 1962. (11) Lerner, R. W., IND.ENG.CHEM.53, 70A-71A (December 19611 _,_.
(12) Mark, H. F., Atlas, S. M., Chem. Eng. 68, 143-52 (Dec. 12, 1961). (13) Mirviss, S. B., Rutkowski, A. J., Seelbach, C. W., Oakley, H. T., IND.END.CHEM.53, 58A-60A, 62A (January 1961). (14) Piombino, Anthony J., Chem. Week 90, 48-52, 55, 58, 60 (April 14, 1962). VOL
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