Lee. R . E.. Goranson. S.S., Enrione. R. E.. Morgan, G. B.. ibid.. 6 (12) 1025-30 (1972). Lundgren. D. A , . A t m o s . Enciron.. 3 ( 8 ) . 645-51 (1971). Lundgren, D . A,, J . .-lirPol/ut. Contr. Ass.. l i , 225-8 (1967). McKay. H . A . C.. ibid.. p p 7-14. J . CoiNovakov. T.. Mueller. P. K.. Alcocer. A . E.. Otvos. ,J. W,, loid Interface Sei.. 38 (1).225-34 (1972) (also reprinted in Hidy. 1972). Plumb, R. C., Hornig, D. F., J . Chem. Ph\s., 23 is), 947-53 (1953). Pustinger, .J. V.. Cave. U'.T.. Nielsen. M . L.. Spectrochim. Acta. 11,909-25 11959). Ranz. W . E . . "Principles of Inertial Impaction." Engineering Research Bull. S o . 66. Penn S t a t e Univ.. 1956. Ranz. R. E.. CVong. .J. B., Ind. Eng. C h e m . . 14 ( 6 ) . 1371-81 (1952).
Sehmel. G . A , . Paper No. 73-162 presented at the 66th .i\nnual Meeting of' the Air Pollution Control Ass.. Chicago. Ill.. .June 1973. Tuesday. C . S.. E d . . "Chemical Reactions in C r h a n Atmospheres." pp 241-67. American Elsevier. S e w York. S . Y . . 1971. Vedder. LV..Hornig. D . F.. ./. Chrrn. P h p . . 3.5 ( 5 ) .1560-8 (1961). Wagner. E. L.. Hornig. D . F.. ibid , 1X ( 3 ) . 296-300 (1%0). Whitby. K. T.. Husar. R. B.. Liu. B. Y. H . . J C'oiioid Intcrfacc3 Sci.. 3 9 (11,177-204 (1972a) (also reprinted in Hidy. 19721. Whitby. K . T.. Liu, B. Y. H.. Husar. R . B.. Barsic. S . ,J., ibid.. p p 136-64 (1972b) (also reprinted in Hidy. 19721.
Receiced for recieic, Auguht Xi. 1973 rlcccptc~! October 26. 1 W i . Work performed under t h e auhpic'e,\ of t h c A t o m i c Enere). C'rimmi sion
Hydrolysis of Polyurethane Foam Waste Lee R. Mahoney,' Steven A. Weiner, and Fred C. Ferris Chemistry Department, Scientific Research Staff, Ford Motor Co., P. 0. Box 2053, Dearborn. Mich. 48121
w The reaction of polyurethane foam with superheated water has been investigated as a method for the volume reduction and possible material recovery from the increasingly large amounts of low-density scrap foam generated from junk car shredders. Upon reaction for 15 min with superheated water a t 200"C, the low-density foam is converted to a liquid more dense than water. A 65-8570 theoretical yield of toluene diamines and a 90% yield of liquid polypropylene oxide are isolatable from the liquid. A systematic kinetic study revealed t h a t the rates of formation of the toluene diamines, TDA, and polypropylene oxide in the temperature range 160-190°C are given by the pseudofirst-order rate expression
where
0
[NH-C-]
I1
represents the total amounts of unreacted urea and polyether-urethane linkages. The temperature dependence of the rate constant k' is given by the Arrhenius expression
log h'
=
12.7 -
29,000
4.6 T ( O K )
It is concluded t h a t the hydrolysis process represents a viable solution to the solid waste disposal problems associated with scrap polyurethane foam materials. A late 1960 model automobile contains nearly the same percentage by weight of plastic materials as does solid municipal waste, namely 2-3%. Although a good deal of discussion and some research have been directed toward the problems associated with the solid waste management of plastics in municipal waste (Warner et al., 1970b), no attention has been given to the unique problems which To whom correspondence should he addressed
may be involved in the disposal of waste plastic materials generated from the recycling of junk vehicles. In contrast to the plastic materials in municipal waste which are ultimately disposed of in some 20,000 sites in this country (Warner et al., 1970a), a high percentage of the plastics in automotive products will be transported and concentrated at approximately 100 sites in this country-i.e.. junk automobile shredders (Dean et al., 1973). These giant machines shred entire automobiles 50,000-200,000 units per year, into fist-size fragments. The ferrous and nonferrous metals are recovered and recycled while the nonmetallic fraction containing concentrated plastic materials are rejected and disposed of by landfill. This laboratory has carried out a n analysis of the quantities of plastic and polymeric materials to be generated annually as scrap from junk vehicles in the period 1971 through 1981 (Mahoney and Weiner, 1972). The results of the analysis revealed t h a t the weight (volume) of polyurethane foam material generated per average junk car will increase from 2.2 lb (0.032 yd3) in 1972-73 to 11 Ib (0.16 yd3) in 1976-77 to 23.4 Ib (0.345 yd3) in 1980-81. Carshredding experiments on late model cars confirm these projections and reveal that greater than 95% of this foam material is collected in pieces larger than %-in. in the airfraction collector a t the auto shredder (Dean et al., 1973). In urban areas, the disposal by landfill of this low-density material, which is resistant to biodegradation (Darby and Kaplan, 1968), will represent a n increasing cost item for the junk car processor and is thus an impediment to the economical collection and recycling of junk automobiles. A method of volume reduction and disposal of this waste foam material should be inexpensive. ecologically sound and technically simple enough to be carried out a t the auto shredder site. The present work describes the results of a systematic study of a hydrolysis method which potentially satisfies all of these requirements and which, in addition, offers the possibility of recovery of valuable materials from the hydrolysis products,
Materials and Methods
Foam Utilized for Study. Unless otherwise stated, all experiments were performed on samples of high-resiliency Volume 8, Number 2, February 1974
135
Table I. Composition of Reaction Mixture Utilized in Foam Preparation Parts
9
weight
Corn ponent
Pluracol polyol 443 L.D. 813
4.5
Water Accure C
2.7 1.0
Weax A - 1 Crude TDI (TCPA)
Rem a r k s
500 molecular weight Glytriol
100
(polypropylene oxide) with ethylene oxide cap Moca; chlorinated aromatic diamine
Alkylbenzene sulfonatetriethanol amine salt Amine catalyst Isomeric 2,4- and 2,6-toluene diisocya nates
0.2 42
polyurethane flexible foam (density equal to 2.1 lb/ft3), supplied by Wyandotte Chemical Co. in the form of a molded bucket seat. The composition of the mixture utilized in the foam preparation was specified by Wyandotte and is presented in Table I. By combining the known chemical reactions of these materials during foam preparation (Saunders and Frisch, 1967) with the data in Table I, it is possible to represent the chemical structure of the present foam as shown in Figure 1. In experiments where shredded material was utilized, weighed amounts of the foam were placed in a Waring Blendor with water and shredded to fine particles of diameter equal to -0.1 cm. The water was decanted from the particles, and the shredded particles were then dried in a vacuum oven to 50°C to a constant weight and densit y equal to 6.3 lb/ft3. The weight of this dried material agreed within a few percent with the weight of the original foam. A number of ancillary experiments were performed on samples of other polyurethane foam materials. These samples included both new foam materials present in headrests, dashpanels, and doorpanels and scrap foam collected a t auto shredder sites. The original composition of these materials were, of course, unknown. 0 -N
H
F N - C - ; H I'
CH3
0 d
0
II N-c-0 H
-
PolyetherI
0
CH,
I
c=o
+
Urea Linkages 10 U n i t s
I
Polyether-
2 Units
NH
Ck
0 II
ce
+ -
Mota Urea Linkages
I Units Foam structure types and realtive amounts of hydrolyzable linkages Figure 1.
136
Environmental Science & Technology
Product Studies. Product isolation experiments were carried out in a stainless steel pressure reactor of 300-ml capacity (American Instrument Co.). The reactor, glasslined or unlined. initially charged with 10.0 grams of foam (shredded or in single pieces) and 100 ml of water, was lowered via a pulley system into a large constant temperature (h0.5'C) oil bath. An independent study of the heating rate of the liquid contents of the reactor revealed that it required approximately 20 min to heat the system to within a few degrees of the temperature of the oil bath. At various time intervals after the heat-up time, the reactor was removed from the bath and air cooled to room temperature. The initial cooling rate was 25"C/min. When the reactor was opened. it was found that the low-density foam-water system had been converted to a two-phase liquid system. The upper phase was a n aqueous solution containing toluene diamines (TDA) while the lower phase was a dark water-insoluble liquid of density 1.01 which by gel permeation chromatograph was found to be Pluracol Polyol 443. Vacuum distillation of either the separated water phase or the combined water-polyol phases yielded a sharp liquid fraction a t 120°C and 0.1-mm mercury pressure. On cooling, the liquid fused to a pale yellow solid. At the melting point, 93-94°C. infrared and ultraviolet spectra of the solid were identical to those observed with a reference sample, consisting of 80% pure 2,4-toluene diamine and 20% pure 2,6-toluene diamine. Other polyurethane foam materials, including both virgin materials and scrap materials collected from auto shredder sites. manifested the same behavior; after reaction a t 200°C for 15 min, the low-density foam-water systems were converted to two-phase liquid systems. Upon vacuum distillation, the aqueous phases yielded toluene diamines. The yields of diamines varied considerably with the source of the material. Headrest material yielded up to 25% by weight diamines. while the dirt and oil saturated scrap foam. collected from auto shredder sites, yielded 7 1 2 % by weight toluene diamines. In the latter cases, the polyol phases were. of course, contaminated with dirt and oil. Rate Study, The rate of hydrolysis was studied by sealing 100-mg samples of shredded foam with 1.0 ml of water in glass tubes. The tubes were placed in a constant temperature oil bath (*0.02"C), then removed, and quenched to room temperature with cold water a t various time intervals. The quenched tubes were then placed in a hollow aluminum tube with an aluminum beaker as base and crushed by means of a steel rod. For the poly01 analysis, the inside of the tube. the steel rod, and the contents of the beaker were washed with dioxane, and the washings were transferred to a 25-m1 volumetric flask. Water was used as the solvent for the toluene diamine analysis. The formation of monomeric ether units was determined by gel permeation chromatographic analysis of the dioxane solution (Larsen. 1968). The starting material is cross-linked and, upon treatment with dioxane. yields a dioxane solution which has no detectable peaks on the chromatogram. Foam reacted for a n extended period of time yields a single peak on the chromatogram identical in shape and position to that obtained from J reference sample of the pure polyether (PP443) and used in the preparation of the foam. Infrared and nmr analyses of collected samples of the chromatographic peak from the reacted foam reveal that the product is identical with the pure polyether (PP443), as measured by these spectroscopic techniques. Samples reacted for short time periods yielded chromatograms composed of two peaks corresponding to monomeric and dimeric species. The relative yields of monomeric polyether units as a function of time
Table I I . Yield of Pure Diamines from Reaction of Polyurethane Foam Teomp, C
185 185 185 200 200 200 200 200 200 200
Time," min
30 60 60 15 30 60 60 60 360 15e
Surface of reactorb
Grams TheoretiMethod of diamine/100 c a l yield,d isolationC g r a m s f o a m %,
G G G G G G G S G S
DW DW DC DW DW DC DW DW DW DC
9.0 11.4 10.0
48
12.0 16.0
64 86
13.2 14.4
71
15.0 17.3 14.9
61 53
77 80 93 801
D o e s n o t i n c l u d e 20-min h e a t . u p t i m e . G r e f e r s t o a g l a s s - l i n e d a n d S t o air.lined stainless steel reactor. DW r e f e r s t o distillation of separation water p h a s e , DC t o distillation of c o m b i n e d p h a s e s . d T h e o r e t i c a l y i e l d e q u a l s 18.7 g r a m s of d i a m i n e s per 100 g r a m s of 'I
C
c
f o.a .m .
Single p i e c e s , n o l s h r e d d e d . ' Seven successive a d d i t i o n s of 6-gram s a m p l e s t o 50 m l of water, isolation a f t e r s e v e n t h a d d i t i o n .
and temperature were then estimated by integration of the area under the peak corresponding to the monomeric species. The results were expressed by the relationship, m g of m o n o m e r
,_
.-
100 m g o f f o a m a r e a of m o n o m e r i c p o l y e t h e r / 1 0 0 m g of f o a m
a r e a o f 100 m g of p u r e m o n o m e r i c p o l y e t h e r The spectra of dilute water samples of the solutions obtained from the crushed glass tubes were recorded by means of a Cary Model H spectrophotometer from 25003300 A. Reference samples of pure 2,4-toluene diamine and pure 2,6-toluene diamine obeyed Beers law in the range 2500-3300 A with t 2 9 3 0 , ~equal ~ ~ ~ to 2300 50 M - l cm-I for the 2,4 isomer and C2940,4max equal to 1170 f 20 M - I c m - l for the 2,6 isomer. The ratio of the 2,4 isomer to 2,6 isomer in the foam sample is 4 : l with a theoretical yield equal t o 18.7/100 mg of foam. Accordingly, for complete reaction, the calculated absorption at 2940 A, due to the 2,4 isomer/100 mg foam/ml of water and 2,6 isomer/100 mg foam/ml of water, are 278 and 33, respectively. The yields of diamine as a function of time were calculated from the expression,
*
p e r c e n t yield = a b s o r p t i o n / 1 0 0 m g f o a m i m l of w a t e r 3 11
x 100
Results The results of the study of the yield of isolated diamines as a function of temperature, time of reaction, method of isolation, and effect of the surface of the pressure reactor are summarized in Table 11. The reaction of the foam with water for 15-60 min a t 200°C results in a 65-80% theoretical recovery of pure diamines. Moreover, the yield of diamines is independent of the method of recovery and is not affected by the nature of the reaction vessel; the use of a glass-lined or unlined stainless steel vessel results in comparable yields of pure diamine. In one experiment, the foam was hydrolyzed for 360 min and the yield of diamines was 93%. We feel that this represents a limiting yield and corresponds to the hydrolysis of all simple urea linkages. The remaining few percent of diamines are involved in moca-urea linkages (Figure 1) which are very resistant to hydrolysis.
The final entry in Table I1 gives the results of an experimental sequence carried out to determine whether the accumulation of products inhibits the hydrolysis or changes the nature of the products. In that experiment seven successive additions of -6 gram (180 ml) pieces of foam to a single 50-ml sample of water was made until 45.23 grams of foam had been reacted. After each addition, the reactor was heated a t 200°C for 15 min, cooled, opened, and recharged with foam, and the process was repeated. After seven additions, the combined water-polyether liquid phases were vacuum distilled. The yield of isolated pure diamines, 6.74 grams, was comparable with t h a t obtained from a single cycle experiment-Le., 80% of theoretical. The residue from the distillation consisted of 27.96 grams of a liquid which by gel permeation chromatography was 98% monomeric polyether (PP443) and 3.3 grams of a solid, which gave a positive chlorine test and therefore contains moca units. The yield of monomeric polyether in the liquid residue amounts to 90.8% of theoretical. In Table I11 are presented the data obtained from the kinetic study of the formation of toluene diamines by means of the spectrophotometric technique at 160°C. At long reaction times the yield of diamines is 95% of the theoretical value. This result is in agreement with the results of the product isoiation study reported above. From Figure 2 we see t h a t semilog plots of [95 - (percent yield),] vs. time at 160, 175, and 190°C are fairly linear for over 80% reaction. The slight deviations a t 160°C from linearity a t low conversion-i.e., less than 20%-is likely to be meaningful since the isomeric diamines are formed from the hydrolysis of a variety of different chemical groups including polyether-urethane (15%) and urea (77%). Indeed, it would be fortuitious if all types of groups hydrolyze at the same rate. In any case, over the major portion of the reaction, the rate of formation of diamine product. TDA, may be represented by the psuedofirstorder rate expression,
0
+
d(TDA) __ =
dt
k'[--NH---CI
I1
where
0
I-
