Polyether Production Cost
Preliminary cost calculations were made for a plant designed to produce 10,000,000 pounds per year of polyether from cornstarch based on the procedures described above and the flowsheet as outlined in Figure 1. For the production of two batches of polyether per day for 300 working days per year, a single reactor of 2700-gallon capacity would be adequate. T h e reactor and all necessary auxiliary equipment (such as rectifiers to recover ethylene glycol, dilution tanks, ion exchange columns, and thin-film evaporator) could be housed in a 40 X 40 X 50 foot high steel frame building of explosionproof design and constructed of corrugated Transite siding. Estimated fixed capital investment is $375,000 for design engineering, procurement, and construction of the production unit a t an existing plant site with normal services and facilities available. Accuracy range of the estimate is 10 to +25%, so the actual fixed capital investment is expected to be between $340,000 and $470,000. Plants at present equipped for propoxylation of polyols would require only a nominal conversion cost for adaptation to the new process. Based on currently published prices, the estimated raw material cost for polyethers produced from cornstarch in such a plant is 12.81 cents per pound. Plant operating cost is estimated at 2.17 to 2.33 cents per pound, based on $375,000 and $470,000 fixed capital investments, respectively (Table V). "Out-the-gate" cost of polyethers would be 14.98 to 15.14 cents per pound. Since these polyethers are 60 to 6570 propylene oxide, any reduction in the price of propylene oxide, below the current published price of 14*/2 cents per pound, would significantly reduce the cost of the finished polyether.
-
Conclusions
The successful preparation of glycol glycoside polyethers in 1000-pound lots and use of the polyethers in making foams
demonstrate their good potential as a new industrial poly01 for the production of urethane foams. Because of the many objectives of this study, it was impractical to investigate each area in detail. I t is evident that experiments could be designed to cover a wider range of conditions and formulations. Also, more experience with the process and products should lead to smoother operation and better product uniformity. Acknowledgment
We thank H. S. White, H. J. Richards, S. M. Baker, N. D. Farel, C. C. Peloza, and W. J. Luckow of Archer Daniels Midland Co. for their assistance with laboratory synthesis, physical testing, pilot-plant laboratory scale-up, and foam preparation. literature Cited
(1) Otey, F. H., Bennett, F. L., Zagoren, B. L., Mehltretter, C. L., IND.ENC.CHEM.PROD.RES.DEVELOP. 4,228-30 (1965). ( 2 ) Otey, F. H., Mehltretter, C. L., Rist, C. E., J . Am. Oil Chemists' SOC. 40, 76-7 (1963). (3) Otey, F. H., Zagoren, B. L., Bennett, F. L., Mehltretter C. L., IND.ENC.CHEM.PROD.RES.DEVELOP. 4,224-7 (1965). (4) Ote F. H., Zagoren, B. L., Mehltretter, C. L., Zbid., 2, 256-9 (19637: for review March 14, 1966 RECEIVED ACCEPTEDJune 15, 1966
Division of Organic Coatings and Plastics Chemistry, 152nd Meeting, ACS, New York, N. Y., September 1966. A report of work done under contract with the U. S. Department of Agriculture and authorized by the Research and Marketing Act of 1946. The contract was supervised by the Northern Utilization Research and Development Division of the Agricultural Research Service, Peoria, Ill. Mention of names of equipment or specific industrial products does not constitute endorsement by the U. S. Department of Agriculture over similar equipment or products not mentioned.
NOVEL PROCESS FOR P R E P A R A T I O N OF INORGANIC FOAMS M A R C 0 W I S M E R A N D JOSEP..
F.
ss
Coatings and Resins Division, Pittsburgh Plate Glass Co., Springdale, Pa. Alumina and silica refractories possessing densities of less than 30 pounds per cubic foot have been produced using aromatic, unsaturated polyester resins as the foamable polymer system. The polyester system developed can support inorganic fillers over a temperature range of 25' to 1950' C. (77' to 3500' F.). Although foamed shapes undergo considerable shrinkage in that temperature range, this method produces low density refractories without internal cracks and without substantial change in the original foamed shapes. The fact that aromatic, unsaturated polyester foams perform better than other foamable polymer systems can b e explained through the kinetics of the thermal degradation of these polyesters. HE behavior of various polymers at elevated temperatures Thas been investigated, with special attention to the strength of polymeric materials in their carbonized form. This relates to the relationship of flame retardancy and char formation during the exposure of a polymer to heat. During this investigation the possibility of improving the fire retardancy of organic foams by the incorporation of inorganic materials was also explored. This work led into the field of inorganic foams. The insulating properties of a refractory material from 1500' to 1900' C. (2800' to 3400' F.) are improved a t lower densi-
282
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
ties. Many approaches for the production of low density, high heat-resistant refractories have been explored. However, refractories in a density range of 20 to 25 pounds per cu. foot have not been easily obtained. One of the methods for preparing refractories is a gradual application of heat u p to temperatures of 1900' C. (3400' F.), which will convert a mixture of organic and inorganic materials into an inorganic refractory. The idea of preparing inorganic refractories starting with organic foams containing inorganic fillers is not entirely new. Patent literature and government reports describe processes
which claim to produce inorganic refractories from organic foams containing large amounts of inorganic filler. These foams were fired either in a n inert atmosphere or in the presence of oxygen. Several polymers were investigated as organic binders. A complex mixture of phenol-formaldehyde resin, epoxy resin, and polyaryl isocyanate has been used to prepare a titanium carbide foam ( 4 ) . Another approach has been the use of resole resins as organic binders ( 3 ) . Low density ceramic products have been made from combustible organic materials such as cork, sawdust, peat, and charcoal dust (2). None of the inorganic foams obtained by published methods showed appreciable strength along with a cellular structure that could classify them as suitable refractory foams of low density. Therefore, a series of organic foams containing inorganic fillers was prepared ( 5 ) . The preparation of inorganic foams from organic materials loaded with inorganic fillers places severe performance requirements on the organic material during the temperature ranges in which it is being oxidized, volatilized, and carbonized. Most of the organic foams that are heavily loaded with inorganic materials will burn and yield a powdered mixture of inorganic materials and carbon a t temperatures in the range of 420' to 700' C. (800' to 1300' F.). Therefore, the objective of this work was to find organic materials which provided charred structures that maintained strength in a temperature range of 260' to 1100' C. (500' to 2000' F.) and shrank without internal cracking or change in shape. Experimental
Several foamable polymer systems were used to prepare refractory-filled foamed objects. Alumina and silica were the oxides used, but other inorganic materials such as zirconia can be incorporated. All foams contained about 60% by weight refractory fillers and were foamed a t room temperature or, if necessary, a t elevated temperature.
The mixture was poured into a mold. Foaming occurred within 4 minutes and gelling occurred within 22 minutes, producing a foamed object with a density of about 35 pounds per cu. foot. Foaming results from the liberation of C O z formed by the reaction of maleic anhydride with water and sodium bicarbonate. EPOXYRESINS.Several methods of foaming epoxy resins were investigated. The most suitable catalyst was found to be triethylenetetramine. The use of liquid blowing agents (Freon 11, toluene) and chemical blowing agents which decompose to evolve CO1 and NH3 was satisfactory. A typical formulation consisted of a basic mixture of 158 grams of Epon 828 (diglycidyl ether of bisphenol A), 236 grams of refractory fillers, and 6 grams of Freon 11. The stoichiometric amount (20 grams) of triethylenetetramine was added and this mixture was stirred with a mechanical stirrer for 2 minutes, then poured into a mold. Foaming occurred within 6 minutes and gelling occurred within 25 minutes. The exothermic reaction of the amine with the epoxy groups causes the Freon 11 to vaporize, thus foaming the mixture. URETHANERESINS.One-shot and prepolymer-type urethane foams using polyisocyanates such as toluene diisocyanate (TDI), polymethylene polyphenyl isocyanate (PAPI), and diphenylmethane diisocyanate (MDI) were investigated. Only the polyaryl isocyanates showed promise for preparing the refractory products. A typical formulation consisted of 2 components, one (component A) containing 77 grams of a polyether polyol resin and 114 grams of refractory fillers, and the other (component B) containing 85.5 grams of PAPI and 124 grams of refractory fillers. Both components were cooled to 15' C. (59' F.). A tertiary amine was added (lye by weight based on polyol) to component A as catalyst and 6 grams of Freon 11 were added to component B. Component B was then added to component A and the mixture was stirred with a mechanical stirrer for 30 seconds, and poured into a mold. Foaming occurred within 3 minutes and gelling occurred within 12 minutes. Little difference in properties between polyester polyol- and polyether polyol-based urethane foams was observed.
RESOLERESINS. Resole resins, which are base-catalyzed Resins Used and Foaming Techniques. UXSATURATED phenol-formaldehyde resins, were also used to prepare rePOLYESTERRESINS.An unsaturated polyester resin prefractory-filled foamed objects. Phosphoric acid proved to be pared by the reaction of 9.4 moles of triethylene glythe best of numerous catalyst systems tried. Freon 11 and col, 6.0 moles of maleic anhydride, and 4.0 moles of isomethylene chloride are by far the best blowing agents for this phthalic acid was thinned with 16.5y0 styrene. The foamed object was obtained by mixing the three components shown foaming system containing the refractory fillers. in Table I. The cobalt octoate, maleic anhydride, and A typical formulation consisted of 158 grams of resole resin, water were added to the base mixture and stirred with a 236 grams of refractory fillers, and 6 grams of methylene chlomechanical stirrer for 11/2 to 2 minutes, after which methyl ride. T o this mixture were added 16 grams of a 50% aqueous ethyl ketone peroxide was added and stirred for 1 minute. solution of H3POa. The mixture was stirred with a mechanical stirrer for 1 minute and then poured into a mold. Foaming occurred within 5 minutes and gelling occurred within 18 minutes. I t was difficult to control density and cell structure Table 1. Refractory Formulation of the foamed object with this system. Weipht, Materials
Base mixture
Polyester-monomer mixture Emulsifier ( Tween-40) Cellulose acetate butyrate Styrene (to reduce viscosity) Refractory grade AI203 NaHC03 1. Blend well 2. Organics, 36.6Yc 3. Inorganics, 63.4Yc 4. Total styrene, 14.2Yc Foamable mixture Base mixture Cobalt octoate Maleic anhydride \Yater
Stir 1 1 / 2 to 2 minutes Methyl ethyl ketone peroxide 1. Stir 1 minute 2. Pour into mold
Grams
125.0 0.6 2.5 52.0 308.0 4.0
400.0 0.8
4.0 7.3
1.
Final additive
0.8
UREA-FORMALDEHYDE RESINS.Urea-formaldehyde resins modified with furfuryl alcohol were also used as a foamable polymer system for producing refractory-filled foamed objects. Freon 11 proved to be the best blowing agent for this system using an aqueous solution of H3P04 and p-toluenesulfonic acid as catalyst. A typical formulation consisted of 158 grams of ureaformaldehyde resin modified with furfuryl alcohol, 236 grams of refractory fillers, and 6 grams of Freon 11. T o this mixture were added 9 grams of a Soy0aqueous solution of Hap04 and p-toluenesulfonic acid. The mixture was stirred for 1 minute with a mechanical stirrer and poured into a mold. Foaming occurred within 5 minutes and gelling occurred within 15 minutes. I t was difficult to control density and cell structure of the foamed object with this system. PHENOLIC-EPOXY RESINS.A foaming system containing a resole resin in admixture with Epon 828 was also used to VOL. 5
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prepare a refractory-filled foamed object. This system was crosslinked with PAPI. A typical formulation consisted of two components, one (component A) containing 73 grams of resole resin, 34 grams of Epon 828, 18 grams of dimethyl formamide, and 185 grams of refractory fillers, and the other (component B) containing 39 grams of PAPI and 57 grams of refractory fillers. Component B was added to component A and the mixture was stirred with a mechanical stirrer for 30 seconds. The mixture was poured into a mold and put into an oven at 150' C. (300' F.) for 3 hours, after which time the material had foamed and gelled. Foaming resulted, with the evolution of water vapor present in the resole resin and CO,. I t was difficult to control density and cell structure of the foamed object using this system. The thermal conductivity of an alumina refractory having a density of 28 pounds per cu. foot was measured at 1100' C. (2000' F.) and found to be 3.7 B.t.u./hr./sq. ft./' F./inch (Figure 1). Materials of lower density and alumina refractories of higher purity produced even lower thermal conductivities. The linear reheat shrinkage a t 1650' C. (3000' F.) was 1 to 2%, whereas a t 1725' C. (3140' F.) it was 2 to 4.7% (Table 11). The linear reheat shrinkage of an alumina refractory having a density of 40 pounds per cu. foot, aged 5 hours at 1675' C. (3050' F.), was found to be 2.0% a t 1850' C. (3200' F.). Reheat properties a t 1.65y0 shrinkage and a density of 40 pounds per cu. foot after 24 hours at 1620' C. (2950' F.) are well within the ASTM (2-155-57 specification which also requires that the density be less than 68 pounds per cu. foot. The room temperature flexural strength was 645 p.s.i. Discussion
The preparation of organic foams containing large amounts of inorganic metal oxides requires a special technique. Many foaming systems do not develop enough gel strength to prevent collapse during rise \Then heavily loaded with inorganic fillers. Therefore, it was necessary to modify foaming techniques, catalysts, and blowing agents in order to achieve foam stability and gel strength.
Table 11.
Physical Prope~iesof Alumina Refractory at Two Densities Tests Bulk Density, Lb./Cu. Ft. 35 28 Modulus of rupture, p.s.i. 520 140
Cold crushing strength, p.s.i. Apparent porosity Reheat shrinkage, yo 3000" F. (1650" C . ) , 5-hr. hold Linear change, width Linear change, length Volume change (sample size 1 X 1 X 6 inches) 314OOF. (1725'C.), 5-hr. hold Linear change, width Linear change, length K factor 2000" F. 2400 F. Flexural strength, p.s.i.
560 85.9
270 85-90
2.1
1.2
1.1 2.1
5.5
4.8
2.1 4.7
...
...
3.7 4.6 345
All the completely cured foams which had fairly uniform cell structures were then subjected to temperatures u p to 1650' C. (3000" F.) in a conventional oven or kiln with no attempt to exclude air. When lower melting fillers such as silica were used, the maximum temperatures were around 985' to 1100' C. (1800' to 2000' F,). I n the temperature range between 260" and 875' C. (500' to 1600' F.), no substantial sintering of the inorganic materials occurs and the organic material vanishes, leaving a carbon structure behind. The performance of silica-containing foams was evaluated by subjecting them to temperatures up to 650' C. (1200' F.) in presence of air for 1 hour. A comparison of the strength properties of the resulting charred foam structures shows that the unsaturated polyester resins have about 3 to 20 times the compressive strengths of the epoxy-phenolic, epoxy, and polyurethane chars after being subjected to 650' C. (1200' F.) (Figure 2). The toughness of the polyester-derived chars is
POLYESTER
* Ct
.)cy
IO0
87
-. %
EPOXY
POLYURETHANE EPOXY-PHENOLIC
26
0
soo
1000
MEAN TEMPERATURE-
ISOO
2000
2400
DEGREES FAHRENHEIT
Figure 1 . Thermal conductivity of an alumina refractory (28 pounds per cu. foot density) at various temperatures 284
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
TEMPERATURE
"E
Figure 2. Compressive strength loss of foamed objects during formation of char structures
also far superior to that of the other chars, as measured by a char friability tumble test based on ASTM C-421-61 (Figure 3). The strength properties of the polyester foam during firing as well as the changes in density were measured. Density and flexural strength decreased gradually to a minimum a t a temperature range of 480' to 540' C. (900' to 1000' F.) and then increased to a maximum near the sintering temperature of the particular refractory filler used (Figures 4 and 5). The strength properties of the chars and of the refractory materials do not give the full picture, since the uniformity of cell structure is important. After exposure to 650' C. (1200' F.), the most uniform cell structure was found in the polyester char. The cell structures of the epoxy-urethane, epoxyphenolic chars were poor. After the superiority of the polyester system had been demonstrated, the reason why polyesters exhibited such outstanding properties was sought. The properties of solid cured castings of the resin systems used to produce the foams described above were compared. The heat distortion point of the polyester resin used, with the exception of the epoxy resin, is lower than the heat distortion points of the epoxy-phenolic, polyurethane, and phenolic resins. Obviously this does not give the desired clue. One could speculate that the more aromatic groups or ring structures there are in the polymer, the stronger the resulting char. Here again, polyesters, with the exception of urea resins, have the lowest content of aromatic groups. Therefore, this does not explain the extraordinary behavior of the polyesters either. Another possible explanation for the stronger char formation and stronger final refractory could be the different internal temperature reached in the brick during firing. This in turn could be explained by the difference in the heat of combustion of the polymers used. The heat of combustion data obtained, however, showed no significant difference in the heat of combustion of the polymers. The fact that the refractories in the process used were fired in an oxygen-starved atmosphere further diminishes the effect of heat of combustion. The thermogravimetric analyses of the cured resins determined in the presence of air or helium showed the first major differences between the thermal degradation of cured unsaturated polyesters and the other resins (Figures 6 and 7). I n the temperature range of 300' to 420' C. (570' to 790' F.) the
40 I
I
I
I
I
I
I
I
#-
>
L
10 5 50
TEMPERATURE
'E
Figure 4. Density gradient of polyester-derived foamed objects during formation of inorganic foams 600
I
x,
I
400
800
1200
TEMPERATURE
1600
1800
I
2000
OF:
Figure 5. Change in flexural strength of polyester-derived foamed objects during formation of inorganic foams
polyester resin loses about 80% of its weight. The other resins lose weight much more gradually over a much broader temperature range. Further evidence of the unique thermal degradation of cured unsaturated polyesters was obtained by differential thermal analysis. Only the polyester resin showed an endotherm in the temperature range of 300' to 420' C. (570' to 790' F.) (Figure 8) ; all the other polymer systems showed an exotherm in the same temperature range. The endothermic reaction indicates distillation of low molecular weight polymer fractions which result from bond rupture. I t was suspected that these fractions could be low molecular weight polystyrene. Anderson and Freeman suggested the following mechanism for the thermal degradation of polyesters in the presence of
CHAR FRIABILITY BASED ON AS.T.M, TUMBLE TEST (C-421-61 I
3.EPOXY
15. POLYESTER
Figure 3. Percentage weight loss of char structures subjected to ASTM Tumble test (C-42 1 -6 1) VOL. 5
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Figure 6. Programmed thermogravimetric curves (in air) of polymer systems used to prepare foamed objects
Figure 7. Programmed thermogravimetric curves (in helium) of polymer systems used to prepare foamed objects
650 600
550 500 450
# 400 W 350
a
2 300
100 50 0
Figure 8. Programmed differential thermal analysis curves (in nitrogen) of polymer systems used to prepare foamed objects 286
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
oxygen (7). The reaction appears to involve hydroperoxidation a t the alpha-carbon of the styrenated branch of the polymer. -CH-
-CH-
I I
CsHbCH f 0
I I
2 + C6HbCOOH
CHz
(1)
CHz
-CH-
-CHRearrangement follows : -CH--
-CH-
CHz
CHz
I
-CH--
-CH-
(3)
Cleavage may occur between carbonyl carbon and alphacarbon, followed by hydrogen transfer from the beta-carbon to the benzoyl radical.
(4)
T o elucidate the mechanism of the thermal degradation of polyesters further, the cured polyester was subjected to destructive distillation. The polyester coreacted originally with 32y0 monomeric styrene, shows, when subjected to destructive distillation, a weight loss of 65Y0 in the temperature range of 280' to 390' C. (535' to 735' F.), The over-all weight loss
Table 111.
Carbon Content of Refractory-Filled Samples Charred at 1200' F. Carbon, % Polymer Systems
Table IV.
Silica
23.4
7800"F. 37.7
Volume shrinkage, 70 Linear shrinkage, 70 Length Width
5.0 8.0
14.0 14.6
By a novel method of producing low density inorganic refractories, alumina and silica refractories possessing densities of less than 30 pounds per cu. foot have been produced by foaming the metal oxides in unsaturated polyester resins and firing the foamed objects u p to 1900' C. (3400' F.). The foamed objects undergo considerable shrinkage in that temperature range, but this method produces low density refractories without cracks and without substantial change in the original foamed shapes. The fact that unsaturated aromatic polyester foams perform better than other foamable systems has been explained through the kinetics of the thermal degradation of the unsaturated polyesters. Acknowledgment
The authors thank the Alcoa Research Laboratories, East St. Louis, Ill., and the Harbison-Walker Refractories Co., Pittsburgh, Pa., for the physical testing data on the alumina refractories.
(1959).
Per Cent Shrinkage during Formation of Inorganic Foam 7200' F.
Conclusions
literature Cited (1) Anderson, D. A., Freeman, E. S., J. Appl. Polymer Sci. 1, 192
0.43 1.88 2.02 6.76
Polyester EPOXY Epoxy-phenolic Polyurethane
was 81%, which corresponds to the thermogravimetric results. A large percentage of the fraction obtained between 280' and 390' C. (535' to 735' F.) was low molecular weight polystyrene as determined by infrared analysis. The pot residue solidifies to a tough solid char which becomes somewhat brittle upon cooling. The other resin systems which were fractionally distilled did not yield low and high molecular weight fractions. Rather than two distinct fractions, a gradual increase of the molecular weight of the fractions was observed. The rapid formation of a solid, high melting residue in the thermal degradation of unsaturated polyesters prevents distortion and excessive flow of the foam structure during the burning process. Since large parts of the polyester molecule escaped the refractory structure before complete combustion occurs, the charred foams obtained from polyesters would be expected to contain less carbon than the other foam systems. The polyester chars contained 5 to 15 times less carbon (Table 111). This may explain their higher strength, since larger amounts of carbon will insulate the surface of the refractory particles and prevent their' sintering. The final inorganic content of the alumina refractory as determined by spectrochemical analysis was 99.9%. T h e original foam contained about 5070 open cells and the char 95% open cells. The essentially open cell structure allowed the rapid evolution and burning of low molecular weight substances without rupturing the foam structure during firing. Considerable volume shrinkage also occurred (Table IV) during firing, but the foam objects neither ruptured nor changed shape.
Alumina, 2900"
F.
26.5 8.55
( 2 ) Fernhof, S., U.S. Patent 2,996,389 (Aug. 15,1961). (3) Kohn, S. (to Office National d'Etudes, et de Recherches ACrospatiales), Zbid., 3,124,542 (March 10, 1964). (4) Logan, I. M., Wise, D. C., McGahon, J. J., von Doenhoff, C.,
"Development of Non-Oxidic Refractory Foams," WADD (Wright Air Development Division), Clearinghouse for Federal and Technical Information, Springfield, Va., Tech. Rept. 60-124 (April 1960). (5) Wismer, M., Rood, L. D., Bosso, J. F. (to Pittsburgh Plate Glass Co.), Can. Patent 694,095 (Sept. 8, 1964); Brit. Patent 1,012,478 (Dec. 8, 1965).
7.13
RECEIVED for review April 21, 1966 ACCEPTEDJune 24, 1966
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