Ind. Eng. Chem. Process Des. Dev. 1904, 23, 545-552
= linear gas velocity in the dense section, L/O
545
Fan, L-S.; Mlyanaml, K.; Fan, L. T. Chem. Eng. J . 1977, 13(1), 13. Fan, L-S. Chem. Eng. J . 1981, 21, 179. Fan, L-S.; Satlja, S.; Wllson, I.; Fee, D.; Myles, K. M.; Johnson, 1. “Sulfation Klnetlcs of Calcined Llmestones/Dolomltes In a Thermogravlmetrlc Analyzer: Experlment. Modeling and Slmulation”, presented at the AIChE 74th Annual Meetlng, New Orleans, LA, Nov 8-12, 1981; Chem. Eng. J . In D r e s s . Fan,-L-S.; Satija, S.; Kim, B. C.; Nack, H. AIChEJ. 1084, 30(1),21. Fee, D. C.; Wllson, W. 1.; Myles, K. M.; Johnson, I.; Fan, L A . Chem. Eng. Scl. 1083. 38(11).1917. Fee, D. C.; Wilson, W. I.; Shearer, I. A.; Lenz, J.; Fan, L-S.; Myles. K. M.; Johnson, I. “Sorbent UtWlratlon Prediction Methodology-Sulfur Control In FluMIzed Bed Combustors”, ANL/CEN/FE-80-10, Argonne Natlonal Laboratory, 1980; 484 pages. Gear, C. W. “Numerlcal Initial Value Problems In Ordinary Dlfferentlal Equatlons”; Prentlce-Hall: Englewocd, NJ. 1971; pp 102-221. Hartman. M.; Coughlln, R. W. AICh€ J . 1978, 22(3), 490. Marroquln, 0.; Fan, L-S.; Fee, D. C.; Myles, K. M. “An Analytical Model for Freeboard and In-Bed Limestone Sulfation In Fluidized Bed Coal Combustors”, presented at the 13th Annual Meeting of the Fine Partlcle Soclety, Chicago, IL, Aprll 12-14, 1982. Nack, H.; Felton, G. W.; Llu, K. T. “Battelle’s Multlsolid FluMizebBed Combustion Process”, paper presented at the 5th Internatlonal Conference on Fluldlzed Bed Combustion, Washington, DC, Dec 1977. Nack, H.; Kiang, K. D.; Lln, K. J.; Murphy, K. S.; Smlthson, 0. R., Jr.; Oxley, J. H. “Fluldlzatlon Technology”; Kearlns, D. L.. Ed.; Hemisphere: Washington, DC, 1976; Vol. 2, p 739. Peterson, V.; Daradlnos. 0.;Serbent, H.; Schmldt, H-W. “Combustion in the Circulating FluM Bed: An Alternetlve Approach In Energy Supply and Environmental Protection”, Proceedings of the Sixth International Conference on Fluldlzed Bed Combustlon, 1980 Vol. 11, p 212. Setterfield, C. N. “Mass Transfer In Heterogeneous Catalysis”; MIT Press: Cambrldge, MA, 1969. Slncovec, R. F.; Madson, N. K. ACM Trans. Math. Software 1975, l(3) 232. Vlchnevetsky, R. Simuktion, Aprll 1971, 168. Wen, C. Y. Ind. Eng. Chem. 1968 60(9), 34. Yang, W. C. Ind. Eng. Chem. Fundam. 1973, 12, 349. Yang, W. C. J . Powder Bulk Solids Techno/. 1977, 1 , 89. Yang, W. C. AIChE J . 1978, 24(3), 548.
= linear gas velocity in the dilute section, L/O superficial gas velocity, L / O linear sorbent velocity, L/O = linear sorbent velocity in the dense section, L/O = linear sorbent velocity in the dilute section, L/O = superficial sorbent velocity, L/O $= terminal velocity of the sorbent, LIB VI = volume of the dense section, L3 W,= sorbent flow rate, M/O X = SO2 conversion at the reactor outlet X , = solid reactant conversion x = rfro
8
y =z/L z = axial distance along the reactor, L
Greek Letters t b = void fraction in the reactor t b l = void fraction in the dense section
= void fraction in the dilute section = void fraction in the sorbent to = initial void fraction in the sorbent tal = volume fraction of the sorbent in the dense section ts2 = volume fraction of the sorbent in the dilute section 9, = local solid reaction rate, mol/L30 y = constant defined by eq 9 pg = gas density, M I L 3 pp = sorbent density, M / L 3 p = gas viscosity, MILO 4” = ~ o ~ ~ ~ ” ~ , o ~ / ~ ~ , , , ~ l ” 2 Registry No. Sulfur dioxide, 7446-09-5; dolomite, 16389-88-1. tb2 t
Literature Cited
Received for review May 10, 1982 Revised manuscript received September 29, 1983 Accepted October 31, 1983
Borgwardt, R. M. Environ. Sd. Techno/. 1970, 4(1), 59. Chen, L. H.; Wen. C. Y. “Reaction In Fluldlzed Bed Freeboard”. presented at the AIChE Annual Meeting, New Orleans, LA, Nov 8-12. 1981.
Polyurethane Waste Recycling. 1 Glycolysis and Hydroglycolysis of Water-Blown Foams John Gerlock, Jacob Brarlaw, and Mlklo Zlnbo Research Staff, Ford Motor Company, Dearborn, Mlchlgan 48 12 1
I n this paper, glycolysis of toluenedlisocyanate based water-blown polyurethane foam has been examined by high performance liquid chromatography and gel permeation chromatography to determine the product distribution. Glycolysis with diethylene glycol (DEG) yields toluenedlamlne (TDA), TDA mono- and di- DEG carbamates, a series of urea-linked mono- and dC DEG carbamate TDA oligomers, and polyether triol (polyol). The complexity of the product mixture suggests problems in applying simple glycolysis to the recovery of mixed and/or contaminated polyurethane wastes. A simpler product mixture results when water and a base catalyst are added to the glycolysis reaction (hydroglycolysis). Hydroglycolysis yields TDA and polyol as principal products. Data for the rate of the hydroglycolysis reaction are presented in the temperature range of 150 to 190 O C . These results suggest that hydroglycolysis could be used to recover polyols from mlxed and/or contaminated water-blown polyurethane wastes.
Introduction As a continuation of our interest in developing practical methods to recycle water-blown polyurethane wastes (Mahoney et al., 1974; Gerlock et al., 1980), we have examined recycling by glycolysis in some detail. Glycolytic recycling of polyurethane foam is currently the only method proven in large-scale commercial practice among the three most promising schemes proposed to date: (1) glycolysis (Ulrich, 1978; Hill, 1955; Bayer et al., 1950), (2) pyrolysis (Albert and Tacke, 1955, U.S. Patent 3 143 515), 0198-4305/84/1123-0545$01.50/0
(3) steam hydrolysis (Mahoney et al., 1974; Gerlock et al., 1980; Campbell and Meluch, 1976). Nippon Soflan of Japan currently operates a 1.3 X lo6 lb/year polyurethane recycling plant based on the Upjohn glycolysis process. Glycolylic recycling is performed by “dissolving” a polyurethane waste in a nearly equal weight of high boiling diol or mixture of diols heated to between 190 and 230 “C in an inert atmosphere. The fact that the immediate dissolution mixture can be sufficiently ”polyol-like”, and directly substituted for up to 10% by weight virgin poly01 0 1984 American Chemlcal Society
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Ind. Eng. Chem. Process Des. Dev., Vol. 23,No. 3, 1984
Table I. Polyurethane Foam Formulation ingredient Pluracol 535 Polyol (1640 equiv wt, mostly triol) 80120, 2,4-, 2,640luenediamine distilled water die thanolamine triethylenediamine dime t hylaminome thylmorpholine 70% bis( 2-dimethylaminomethyl) ether 30% dipropylene glycol silicone-glycol copolymer surfactant dibut yltindilaurate
in some polyurethane foamulations, makes this recycling approach very attractive. However, as will be shown in the present work, the versatility of this approach is limited both by the kinds of polyurethane wastes that can be handled and the types of polyurethane that can be synthesized from immediate glycolysis products. Our objective for the present work was to develop methods to broaden the scope of glycolytic recycling to include mixed and contaminated polyurethane wastes: polyurethanes in urban refuse, for example, and material such as the 200 X lo6 pounds of highly contaminated polyurethane foam per year produced by automobile shredders as a byproduct of metal recovery (Mahoney and Harwood, 1975; Mahoney et al., 1979). This objective has been met in part by changing the chemistry of glycolytic recycling from glycolysis to hydroglycolysis. Hydroglycolysis occurs when glycolysis is performed in the presence of base catalysts and water. Hydroglycolysis changes the emphasis of glycolytic recycling from the recovery of a low quality “polyol-like”product to the recovery of high quality polyether triol (polyol). Hydroglycolysis is necessarily more expensive than simple glycolysis because poly01 isolation and purification procedures are necessary. However, the added processing cost may be offset by increases in the kinds of polyurethane waste that can be handled and by the recovery of a product of intrinsically higher value.
Experimental Section Materials. Polyurethane Foam. A laboratory sample of low density (2 lb/ft3), water-blown flexible polyurethane foam was synthesized according to a simplified version of a commercial formulation. The simplified formulation reduces the number of products possible during glycolysis. The foam formulation given in Table I is based entirely on toluenediisocyanate (TDI) and yields 196 mg of toluenediamine per gram of foam upon complete hydrolysis in aqueous solution. Reagents. Diethylene glycol (2,2’-oxydiethanol; DEG) was obtained from Aldrich Chemical Co. and used as is, 97% , in hydroglycolysis experiments or vacuum distilled prior to use in glycolysis experiments. Lithium, sodium, potassium, calcium, barium, magnesium, and aluminum hydroxides were obtained from J. T. Baker Chemical Co. Burdick and Jackson distilled in glass acetonitrile and/or tetrahydrofuran was used for all high performance liquid chromatography (HPLC), gel permeation chromatography (GPC), and ultraviolet spectroscopy (UV). Analytical grade 2,4-TDI and 80/20 isomeric 2,4- and 2,6-TDI were graciously supplied by Mobay Chemical Co. Samples of 2,4-toluenediamine (2,4-TDA) and 2,6-toluenediamine (2,6-TDA) were obtained from Aldrich Chemical Co. and recrystallized from ethanol under nitrogen prior to use. Reagents Synthesized. Samples of the DEG dicarbamate of 2,4-TDA and 80120 isomeric 2,4- and 2,6dicarbamate and TDA [toluene-2,4-(2,2’-oxydiethanol)
mol of functional parts by wt group x 102/100g of foam 100.0 38.4 2.0 2.0 0.14 0.2 0.1 1.4 0.015
6.09 (OH) 44.13 (NCO) 15.55 (OH) 3.8 (OH); 1.9 (NH)
supplier BASF Mobay
ucc
Air Products Air Products
ucc
Dow Corning M&T
toluene-2,6-(2,2’-oxydiethanol)dicarbamate] were synthesized from the corresponding diisocyanates as follows: 2,4-TDI in tetrahydrofuran solution (1110) was added dropwise to hot (50 “C), rapidly stirred DEG. When the reaction was complete (no isocyanate infrared absorption band), the reaction mixture was cooled and tetrahydrofuran was removed by vacuum distillation. No polymeric material was found in the reaction product by GPC analysis. HPLC of the isomeric product revealed the presence of only one peak. The concentration of dicarbamate in DEG solution was determined by hydrolyzing an aliquot with NaOH in water at reflux and then assaying the hydrolyzate for 2,4- and 2,6-TDA by HPLC and UV analysis. Samples of the DEG monocarbamates of 2,4-TDA and of 80120 isomeric 2,4- and 2,6-TDA, [toluene-2-amino-4(2,2’-oxydiethanol) monocarbamate; toluene-4-amino-2(2,2’-oxydiethanol) monocarbamate; and toluene-2amino-6-(2,2’-oxydiethanol)monocarbamate], were synthesized in situ by partial hydrolysis of the corresponding TDA dicarbamates. Equipment. Reactor. A three-necked round-bottom flask was used for all reactions. The flask was fitted with an electrically driven stirrer, a removable reflux condenser, and nitrogen purge. The reactor was heated with an electric mantle controlled with a variac. Temperatures were monitored by use of a stainless steel sheathed type K calibrated thermocouple immersed in the reactor and followed using a Doric Trendicator Model 400 thermocouple reader. High Performance Liquid Chromatography (HPLC). HPLC analyses were conducted with a Waters Associates chromatograph equipped with a Model 440A UV absorption detector fixed at 2800 A, a p-Bondapak CIS column, and a Hewlett-Packard Model 3380A integrator. Sample elution was performed with 40/60 by volume acetronitrile/ water solvent with Waters Associates PIC Reagent B-7 added at a flow rate of 1 mL/min. Gel Permeation Chromatography (GPC). GPC analyses were conducted with a Waters Associates Model 150-C, ALC/GPC chromatography system equipped with a refractive index detector, a Model 730 data module with GPC calculation capability, and a p-Styragel column set consisting of five columns in series with permeability limits of lo3, lo4, lo6, 500, and 100 A. Sample elution was conducted with tetrahydrofuran at 40 OC with a 1.5 mL/min flow rate. The GPC system was calibrated with commercially available polypropylene glycols, M = 4100, 2100,1280, and 830, and dipropylene glycol (%V = 134) to obtain retention times and to calculate average molecular weights of reaction products. Ultraviolet Spectroscopy (UV). A Cary Model 14D spectrometer was used. UV and HPLC Standards. Toluenediamine. TDA standards were prepared in acetonitrile/ water solution from freshly recrystallized 2,4- and 2,6-TDA. The UV
Ind. Eng. C b m . Process Des. Dev., Vol. 23,No. 3, 1984
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Table 11. Reflux Temperature of Diethylene Glycol-Water Mixtures a t Atmospheric Pressure wt % water
reflux temp, "C
0.13 0.24 0.43 0.73 0.82 0.92 1.09 1.49 1.98 2.42
242 232 228 216 210 205 201 190 180 175
absorbance of 80/20, 2,4-TDA/2,6-TDA followed Beer's law over the concentration range of 3.7 X lo4 to 5.4 X lC3 M with e = 1955 m-l cm-' at A, = 2890 A. Both HPLC peak height response and integrated peak area response were linear for the isomeric mixture over the concentration range of 0.1-4.0 X lo4 M. Toluenediamine Dicarbamates. TDA dicarbamate standards were prepared iri DEG solution from the synthesis product described in the reagents section. The concentration of isomeric TDA dicarbamate was determined by hydrolyzing an aliquot of the DEG solution and analyzing (HPLC and Uv) the hydrolyzate for TDA. HPLC peak height respon& was linear for the dicarbamate over the concentration range 1.0-7.0 X lo4 M. GPC integrated peak response was linear. Toluenediamine Monocarbamates. Solutions in which the total concentration of TDA monocarbamate was known were prepared by partially hydrolyzing DEG solutions of known TDA dicarbamate concentration. The total concentration of TDA monocarbamate was taken as the difference, in moles, between the amount of TDA dicarbamate present and the amount of TDA present. The sum of the HPLC peak heights of the three TDA monocarbamate isomers formed during hydrolysis of isomeric 80/20,2,4-/2,6-TDA-dicarbamates was found to be linear over the concentration range 0.4-9.0 X lo4 M. Procedure. Glycolysis. In a typical experiment 300 g of vacuum-distilled DEG was weighed into a 1-L round bottom flask and degassed with hot copper (450 "C) scrubbed nitrogen for 1 h. The DEG was brought to reaction temperature, and the desired amount of foam (1-5
Figure 1. GPC chromatogram of DEGfoam glycolysis products after reaction at 200 OC for 2 h. Peak assignments are given in Table 111.
g) was quickly added. Foam was added by pushing the haterial through a tared, DEG lubricated tube that was briefly substituted for the reactor's nitrogen purge tube. Samples of the reaction mixture were withdrawn through the sampling port with a 5-cm3glass syringe equipped with an 8 in. long, 16-gage stainless steel needle. Hydroglycolysis. The procedure described above was uskd. Nondistilled DEG and water were added to the reactor. The reaction temperature was controlled by the amount of water added (see Table 11). Base-Catalyzed Hydroglycolysis, The procedure described for hydroglycolysis was used except that metal hydroxides were added to the reactor before addition of the foam. Results Glycolysis. Polyurethane foam formulation given in Table I, readily "dissolves" in dry, oxygen-free DEG at temperatures between 190 and 220 "C to yield a pale yellow solution. The solution slowly breaks into two layers when allowed to cool. The dissolution is slow at temperatures lower than 180 "C while temperatures in excess of 230 "C cause the reaction mixture to darken rapidly. Gel Permeation Chromatography (GPC). GPC analysis of glycolysis reaction mixtures after 2 h of reaction at 200 "C reveals the presence of seven major components.
Table 111. Chromatography Peak Assignments GPC peak A
B C
isomeric TDA diethylene glycol isomeric TDA monocarbamate isomeric TDA dicarbamate
D
R
E F G
HPLC A A"
B B' B" C a
component label
component
Not assigned.
Mpeak
Mcalcd
I1 I11
250 385
122 106 226 330
IV
5 40
270-700
unidentified material in authentic polyether triol polyether triol incompletely glycolyzed polyether triol urethane
NA NA NA
1200 4800 5700
2,4-TDA 2,6-TDA 2,4-TDA monocarbamate 2,4-TDA monocarbamate 2,6-TDA monocarbamate 2,4-TDA dicarbamate 2,6-TDA dicarbamate
I' I" 11' I1 I1 "' I11 ' I11
-( & NH
N HfC.
NH
--& "
106
I NA
NHR'
R = H, -COOCH,CH,OCH,CH,OH R' = H, -COOCH,CH,OCH,CH,OH
I'
I'
NA NA NA
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Ind. Eng. Chem. Process Des. Dev., Vol. 23, No. 3, 1984
dawn’e’ 8” 0 Inject
C
20
10
H
30
Retention Time, Mitt ~
Figure 2. HPLC chromatogram of DEGfoam glycolysis products after reaction at 200 “C for 2 h. Peak aaeignments are given in Table 111.
These are labeled A to G in the GPC chromatogram shown in Figure 1. A summary of peak assignments is given in Table 111. Peak A is assigned to isomeric TDA, I, by comparison with authentic samples. Peak B is assigned to isomeric TDA monocarbamate species, 11, by comparison with samples of partially hydrolyzed TDA dicarbamate, 111. Peak C is assigned to isomeric 2,4- and 2,6-TDA dicarbamate, 111, by comparison with a sample of this material synthesized for this purpose (see Materials section). Peak D is tentatively assigned to urea linked TDA oligomers. Peak E is recognized as an unidentified component in the parent polyether triol used in the synthesis of foam A. Peak F is assigned to polyether triol by comparison to an authentic sample. Peak G is tentatively assigned to incompletely glycolyzed polyether triol urethane. This component decreases in intensity after extended reaction. High Performance Liquid Chromatography (HPLC). HPLC analysis of glycolysis reaction mixtures resolves the lower molecular weight components of the reaction mixture into individual isomers. A typical HPLC chromatogram is shown in Figure 2. A summary of peak assignments is given in Table 111. Peaks A and A” are assigned to 2,4-TDA, 1’, and 2,6-TDA, I”, by comparison with authentic samples of each isomer. Peaks B’ and B” are assigned without distinction to the two possible isomers of 2,4-TDA monocarbamate, 11’ and II”, by comparison with samples of partially hydrolyzed 2,4-TDA dicarbamate, 111’. Peak B”’ was also visible as an additional peak in samples of partially hydrolyzed isomeric 2,4- and 2,6-TDA dicarbamate, 111, and is therefore assigned to 2,6-TDA monocarbamate, 11”’. Peak C is assigned to unresolved isomeric 2,4- and 2,6-TDA dicarbamate, 111, by comparison with a sample of this material synthesized for this purpose (see Materials section). The broad, long retention time peak H visible in the chromatogram shown in Figure 2 has not been identified. Product Distribution Dependence on Reactant Ratio. The foam was added in stepwise fashion to 300 g of dry, oxygen-free DEG at 200 “C such that the ratio of the weight of foam to the weight of DEG initially present increased from l/lw, to lIb0,to 1/20,to ll4, and finally to GPC analysis was carried out on each reaction mixture 90 min after each subsequent foam addition. The analysis reveals that 100 f 5% of the theoretical amount of free polyether triol is present at each reactant ratio. A constant fraction, 26 f 3% of the total TDA content of the foam is present as isomeric TDA dicarbamate, 111, peak C, at each reactant ratio. Isomeric TDA monocarbamate species, 11, peak B, could not be quantified directly. However, the ratio of TDA monocarbamate peak B to TDA dicarbamate peak C remains constant at B/C = 0.93 f 0.08 at each reactant ratio. Both urea linked oligomers, peak D, and incompletely glycolyzed polyether triol ure-
0
10
20
x)
40
50 60 Time, Min.
70
SO
90
I(
Figure 3. Formation of TDA (I), TDA monocarbamate (II), and TDA dicarbamate (1111, upon reacting foam with DEG at 200 “C.
thane, peak G , appear to increase relative to free polyether triol peak F after each addition of foam. Peak G decreases as previously observed after extended (-6 h) reaction. The ratio of peak E to polyether triol peak F remains constant throughout the course of the experiments, indicating that peak E is a component of the polyether triol. Time Dependence of Product Formation. The formation of products during the reaction of 1g of foam with 650 g of dry, oxygen-free DEG at 200 “C was monitored by HPLC analysis of sequentially collected samples. Curves depicting the formation of TDA, I, (sum of I’ and I”), TDA monocarbamate, 11, (sum of 11’, 11”, and 11”’) and TDA dicarbamate, 111, are shown in Figure 3. Glycolysis is initially rapid. Approximately 60% of the total TDA that could be formed during complete hydrolysis of the foam (196 mg of TDA/g of foam) is accounted for as part of compounds I, 11, and 111 after 5 min of reaction. A stable product distribution is achieved after about 75 min reaction with 13.6 f 2% of the total TDA possible present as TDA, 19.1 f 2% present as TDA monocarbamate, 11, and 29.5 f 2% present as TDA dicarbamate, I11 (compared to 26 f 3% obtained by GPC analysis). The TDA not accounted for by I, 11, and 111, -38%, appears to be in the form of higher molecular weight compounds that do not elute under the HPLC conditions used. A crude sample of this group of compounds was obtained by injecting samples of the final reaction mixture onto an HPLC column, allowing I, 11, and I11 to elute, and then collecting the column-retained material by stripping with neat methanol. An infrared (Et) spectrum of material collected in this fashion shows a strong urethane carbonyl absorption at 1725 cm-l and a weaker urea carbonyl absorption at 1640 cm-l. The relative intensities of these two carbonyl absorptions are the reverse of that found in the unglycolyzed foam. The IR spectrum shows no absorption for polyether triol (1100 cm-’). Absorptions due to 1-heptane sulfonic acid (PIC Reagent B-7) obscure the DEG ether linkage region, -1150 cm-l. The formation of TDA, I, during glycolysis is interesting in that the concentration of TDA appears to go through a maximum during the early stages of reaction. This behavior suggests that TDA is formed rapidly in a fast reaction and then undergoes conversion to other products. To test the possibility of equilibria between TDA and other glycolysis products, 1g of foam was reacted with 650 g of dry, oxygen-free DEG at 200 “C as previously described. When the distribution of products had stabilized, 83 mg of TDA (80/20 It/,’’) was added to the reaction mixture. The addition, Figure 4, resulted in a slow increase in the concentration of both TDA monocarbamates, 11’, 11”, and 11”’, and dicarbamate, 111.
Ind. Eng. Chem. Process Des. Dev., Vol. 23, No. 3, 1984 24 I
540
IO0
1
-
90
20 -
80
8
70
h
8 60
'0
-
50 L
2 +
v
40
30 20
IO
10 20 30 40 50 €0 0 20 40 60 SO 100 Time, Min.
'0
I
2
3
4
5
6
7
8
9
IO
Time,Min
Figure 4. Behavior of TDA mono- (II', 11", 11'") and dicarbamates (111) upon addition of TDA (I) to an equilibrated DEGfoam glycolysis reaction product mixture at 200 "C.
Figure 5. TDA (I) formation upon reaction of foam with DEG containing variable amounts of water and 1%by DEG weight LiOHeH20.
Base-Catalyzed Hydroglycolysis. A 5-g sample of polyurethane foam was reacted with 300 g of oxygen-free DEG containing 1% by DEG weight each of water and NaOH. HPLC analysis of the reaction mixture after 10 min reaction showed absence of TDA carbamates I1 and III, and of higher molecular weight TDA based compounds. TDA, 1', and I" were the only products detected at reaction temperatures above 170 "C. GPC analysis of the same reaction mixture confirmed the absence of higher molecular weight TDA based compounds and revealed the presence of polyether triol identical in molecular weight distribution with the polyether triol used in the synthesis of the foam. HPLC analysis of samples collected at shorter reaction times at 190 "C indicates that the formation of TDA is 50% complete 10 s after the addition of foam to the reactor, and complete after 2 min. TDA carbamates 11 and I11 are detectable during the very early stages,
