Literature Cited (1) Mitchell, R. I., Pilcher, J. M., “Improved cascade impactor for measuring aerosol particle sizes”, Ind. Eng. Chem., 51, 1039-42
(1959).
(2) Johansson, T. B., Akselsson, R., Johansson, S. A. E., “X-ray
analysis: elemental trace analysis at the 10-l2-g level”, Nucl.
Znst. Methods, 84,141-3 (1970). (3) Johansson, T. B., Akselsson, R., Johansson, S. A. E., “Proton induced x-ray emission spectroscopy in elemental trace analysis”, Adv. X-ray Anal., 15,373-87 (1972). (4) Johansson, T. B., Van Grieken, R. E., Nelson, J. W., Winchester, J. W., “Elemental trace analysis of small smaples by proton induced x-ray emission”, Anal. Chem., 1974a, (in press). (5) Kaufmann, H. C., Akselsson, R., Non-linear least squares analysis of proton-induced x-ray emission data”, Adv. X-ray Anal. (in press). (6) Johansson, T. B., Van Grierken, R. E., Winchester, J. W., “Marine influences on aerosol composition in the coastal zone”, J.de Res. Atmos., 1974c (in press).
(7) Johansson, T. B., Van Grieken, R. E., Winchester,J. W., “Ele-
mental abundances and variation with particle size in North Florida Aerosols”, J. Geophys. Res., (submitted). (8) Meinert, D. L., M.S. Thesis, Florida State University, June 1974. (9) Hardy, K. A., Akselsson, R., Nelson, J. W., Winchester, J. W., “Preliminary study of air particulates in Miami, Florida using proton induced x-ray emission”, Bull. Am. Phys. Soc., 11, v.20, 77 (1975). (10) Hoover, F., Paz, N., Hardy, K. A., “Analysis of Air particulates in an urban, tropical evironment using x-ray induced x-ray fluorescence”, ibid., v.19,1107 (1974). (11) Cahill, T. A., Feeney, P. J., “Contribution of Freeway Traffic to Airborne Particulate Matter”, Crocker Nuclear Laboratory, University of California,Davis, Calif. Received for review March 24, 1975. Accepted October 14, 1975. This research was supported in part by EPA Grant No. R802132 and the Joint Center for Environmental and Urban Problems Grant No. 231232001.
NOTES
Polyurethane Foam Recycling Superheated Steam Hydrolysis Gregory A. Campbell* and William C. Meluch Polymers Department, General Motors Research Laboratories, Warren, Mich. 48090
In anticipation of polyurethane scrap disposal in the automotive industry, a low-pressure superheated steam hydrolysis system was developed for chemical recovery of the foam components. Polyurethane foam waste is fed into a reaction chamber and directly contacted with dry superheated steam at atmospheric pressure and from 232-316 OC. The dry poly01 is removed from the reaction zone and recycled as is. The isocyanate is converted to diamine extracted from the condensate. Foams have been made with up to 20% reclaimed polyol.
When current automobiles reach the scrap yards in the 1970’s, large volumes of polyurethane scrap will be pro-
duced. Today, in connection with this eventuality, there is the increased tonnage of polyurethane manufacturing scrap due to current auto production with full depth foam seats. Anticipating these increases in polyurethane thermoset polymer scrap, a need developed to explore effective methods to dispose of this type of scrap. Currently, most polymer scrap is disposed of as landfill. There are now pressures being exerted by various governmental agencies in the country to eliminate this method of disposal. The literature proved biodegradation (1) and photodegradation ( 2 ) to be unsuitable methods a t this time because the technology in these areas is not advancing a t a pace to meet the projected needs for large-scale processes in the mid to late 1970’s. It would be possible to incinerate ( 3 )the scrap which has a heating value equivalent to coal. The literature indicates that, although incinerators have been developed for trash, no designs have been established to be suitable for high concentrations of polymer scrap. Also, if the scrap is burned, the petrochemical resource will be lost. This is of increasing concern as petroleum feed stocks reach a tight supply. For these reasons, chemical degradation of the 182
Environmental Science & Technology
foam to its starting materials was chosen as the method to be explored. Chemical degradation of polyurethanes can be separated into three broad categories: thermal, hydrolytic, and chemical exchange. The polyurethanes can be thermally depolymerized because of the relatively high heat of formation, 12,000 cal/mol. Thus the equilibrium can be adjusted toward the monomers by increasing the temperature. A process has been developed for decomposition of the polyurethanes by heating in liquid until the urethane decomposes (4).Thermal degradation of polyurethanes, however, has limited utility because they do not have a ceiling temperature and thus tend to produce tars. Work has been discussed (5) and patented (6) in which the polyurethane foam is hydrolyzed either after dissolving it in a good solvent or by the use of saturated steam under relatively high pressure. To accomplish this type of hydrolysis, the residence times are excessive or the process pressure is very high, either of which is undesirable for process utility. In addition, both systems require extensive product purification after the hydrolysis has been completed to remove the water, solvent, amines, and catalysts. The third general method involves a chemical exchange using low-molecular-weight alcohols or primary and secondary amines which undergo ester exchange and aminolysis. Several processes have been patented (7-9),and another has been reported in the literature (10). In these systems, excess hydroxy compound or amine is placed in contact with the polyurethane and undergoes the following type of reactions: 0
II
RNCOR’ H n
-
+
HOCH,CH,
+
H2NCHLCH,
-
1I
RNCOR’ H
-
0
II
RNCOCH,CH, H 0
I1
RNCNCH2CH, H H
+
ROH
(1)
+
ROH
(2)
0
II
RNCNR' H H
+
HN(CH,CH,OH),
--+
This type of system has been reported by Upjohn (11) to be successful in rigid foam where low molecular weight and high-functionality polyols are traditionally used. However, to be useful in the flexible foam industry, these materials must be separated and dried by complex extraction and distillation procedures. T o be of maximum utility, the decomposition process should yield relatively pure polyol. After the various approaches were considered, a combination of thermal and hydrolytic degradation seemed to be the most attractive. Since the largest component of the foam is the polyol, the process should provide useful reclaimed poly01 without complex purification. To improve the economics of the process, it was decided not to use any chemical additives. The process developed uses superheated steam as the reaction medium. The steam superheated a t 101.4 kPa (1 atm) to 316 "C provides heat and water vapor for the degradation of both the urethane and urea linkages in the foam. Because there are no chemicals or liquid water in equilibrium with the vapor, the poly01 produced would be dry and free of most contaminants. Experimental
Superheated steam was generated using an electric boiler and superheater designed to provide 18 kg/h of steam a t 1034 kPa and 538OC. The reactor was a 3-1. resin kettle fitted with a stainless steel top and a stainless steel wire basket (Figure 1).Polyurethane foam scrap was charged into a stainless steel basket and the reactor assembled. Superheated steam was introduced a t an elevated temperature into the basket and the reaction temperature was increased for up to 6 h. The steam was then discontinued; and the reactor was cooled, disassembled, and inspected.
Figure 1. Reaction system
1 Figure 2.
Semibatch reactor
A second reactor system was designed and constructed which provided more control over the process temperature than the batch reactor just described (Figure 2). The shell of the reactor was a 50-1. glass reactor complqte with upper and lower heating mantle. The reaction zone was constructed of stainless steel screen 101.6 mm in diameter and 406.4 mm long. A screen platform was welded into the reaction zone 101.6 mm from the bottom to keep the foam suspended and to provide space to inject the steam through a spray head below the reaction zone. A 609.6-mm stove pipe with damper was used for reservoir and feed mechanism. Thermocouples were used to monitor the temperature between the glass and the top and bottom mantles, in the basket, in the flask, and in the steam line a t the entry point of the flask. The reactor was first brought to a stable thermal equilibrium at reaction temperature after the steam and the spray condenser had been started, then foam was injected into the reaction zone and allowed to react until the CO2 had stopped bubbling through the spray condenser. In some runs, the reactor was choke fed, thus keeping the basket full during the complete run. At the end of the day's run, the poly01 was siphoned out of the reactor and the diamine was extracted from the condensate. Results and Discussion
Several attempts were made to contact the foam directly with the superheated steam in a glass reaction flask. It was found that the foam collapsed on itself causing the steam to channel out of the reactor. To minimize the channeling of the steam, a stainless steel basket was constructed, and the steam was injected into the bottom of the flask below the foam supported in the basket. This caused the low-density foam to be blown from the reactor and plug the condensers. Plugging was combated by affixing a screen over the top of the basket and in this way several productive runs were made. Table I . Polyol Yield vs. Temperature in Batch Reactor Polyol Polyol Temp, Foam wt, 4 wt, % "C wt, 4
267 254 282
100 150 300
20 80 190
20 53 63
Several runs were made wherein the reactor temperature was increased as rapidly as possible and then held at a specified temperature. The temperature in this batch system usually drifted some 10 OC during the steady state operation. The results of these typical runs are shown in Table I. I t can be seen that the yield is increased as the temperature is increased up to 282 OC. The foam cubes a t lower temperatures were coated with the residue of the thermoplastic filler used in the foam. Apparently a t higher temperatures the reaction was rapid enough to allow decomposition of the foam in the batch system before this thermoplastic diffusion barrier could form over the reacting mass. The best results obtained in the batch reactor were in a run where 300 g of foam were charged and 190 g of poly01 were recovered. Forty grams of diamine were also obtained by extraction of the condensate and by further hydrolysis of the solid in the condensers. The theoretical yield from the foam was 225 g of polyol, 51 g of diamine, and 26 g of C02. There was a solid residue in the reactor that had infrared bands similar to those of acrylonitrile-styrene copolymer. The poly01 was made into foam, and there appeared to be no special problems associated with its use. Volume 10, Number 2 , February 1976 183
1230
Table I I I . Foam Physical Properties
GcI Parrneatlon Chrumaiogamsoi
--
Y # r g # nPolio1
Po,"alfr.m
Foam""drolvi~ial5iO i
D , r ! # l a r e * r o mi ( i 0 r o I i s ~ i d i X O O
Figure 3. Effect of hydrolysis temperature on molecular weights of
polyols
Table II. Flow Reactor Results
Temp, "C
Polyol from foam, O/O
236 260 288 316 321 343
45 55 47 40 10 0
After demonstrating the feasibility of the concept, the new reactor system was designed using the 50-1. reaction kettle. In an effort to eliminate the solid that plugged the condenser, the new reactor was designed with a long residence time, a trap, and a large bank of condensers. However, operation of the 50-1. flask system with these changes still led to fouling the condensers. The system was altered to include a recycle spray condenser (Figure 2) with a short path length. This system worked efficiently, and productive runs were made to obtain poly01 for pilot foam work. The new reactor was designed to give the best results from this type of reaction system. Stirred tank or fluidized bed reactors would not work within the constraints of the system. The stirred tank will not effectively handle the solid vapor reaction system involved in the low density foam decomposition. The fluidized bed was not used because the viscous thermoplastic product could foul the bed and the high rate of steam flow necessary to fluidize the bed would cause too much dilution of the diamine product. In this new reactor, the system could be brought to constant temperature before the foam was introduced into the reaction zone. The effect of the steam and the evolution of COn cause the foam, after it is injected into the reaction zone, to fluidize thus keeping the foam in contact with the hot steam and maximizing the diffusion rate of the water vapor into the foam. The rate of reaction could be estimated by observation of the COz evolution from the spray condenser. At 236 "C, the charge of 1 1. of ground foam produced measurable COz evolution for about 180 s. At 288 "C, the same charge of foam was reacted to completion in about 60 s. Two parameters, temperature and particle size, were investigated to determine their effect on the rate of reaction and the quality of the reclaimed polyol. In general, the lower the temperature of the reaction, the less the reclaimed poly01 was degraded in comparison with the starting material. The analysis of poly01 degradation was accomplished using gel permeation chromatography 184
Environmental Science & Technology
Property
Control
Recycled polyol
Density, kg/m Tensile, k Pa Tear, N/m Elongation, O h
41.6 160 405 160
42.6 165 382 167
and by checking the hydroxyl number. With a styrene standardized column and T H F as a solvent, the starting material had a "molecular weight" of 8000 (Figure 3). If the foam was degraded at 282 OC,there was a slight reduction in the molecular weight as seen in Figure 3. Raising the decomposition temperature to 343 "C causes a complete breakdown of the polyol. No poly01 was found in the flask. The low-molecular-weight mixture of glycols was recovered from the condensate (Figure 3). Further investigation indicated that to obtain a high-molecular-weight product suitable for direct recycling, the reactor should be operated below 315 "C, preferably in the 288 "C range. The yield of useful poly01 was an inverse function of temperature and went from 55% to 40% when the reactor was operated between 260° and 315 O C (Table 11). The ability to make foam using the reclaimed poly01 was also a function of temperature. For the polyurethanes investigated, poly01 produced at a 238 "C reactor temperature would not produce a stable foam when it was introduced into the initial foam system. Poor quality foam was made when poly01 made a t 260 "C was used and marginal foam was made with 277 O C polyol. Poly01 produced with the reactor operated at 288 "C, when added to the master foam system at 596, resulted in excellent foam with cell size and air flow comparable to that of virgin foam, Table 111. Two extremes were tested to determine the effect of the particle size on the reaction rate. Foam was ground to fine particles no larger than 2.66 mm on a side and large pieces of foam were used that were 5 cm in the smallest dimension. Two typical experiments are described that are representative of the runs made: (1) 2200 g of ground foam were run through the reactor in 4 h. That produced 1004 g of poly01 with a hydroxyl number of 40.7 which is 6 hydroxyl numbers above the 34 of the starting material with a minimum of residue in the pot. (2) In the case of the large foam chunks, actually unground buns from the foam mold vents, the best run was when 1733 g were charged into the reactor in 6.25 h. In another experiment, 936 g were charged in 6.5 h. From a chemical analysis of the molecular weight and hydroxyl number, the poly01 recovered from each run was essentially the same, hydroxyl number 40.5 & 0.5. The feed rate for the ground foam was 550 g/h and it was lowered to 280 or 144 g/h with the use of the large chunks. The amount of residue in the pot was substantially increased with the use of the buns. The ground foam produced 1015% residue while the chunks caused a residue of 20-25% of the initial charge. The reclaimed polyols produced were used for feed stocks in two pilot plants. Foam hand mixes were made with up to 20% reclaimed polyol. These polyols were used to produce several full-depth foam seat cushions and backs at a 5% level of reclaimed poly01 and 95% level of new poly01. No processing problems were encountered and there was no degradation in the physical properties, Table 111. The results obtained for these samples was well within the errors inherent in the tests. Literature Cited (1) Rodriguez, F., "The Prospects for Biodegradable Plastics", Chem. Technol., July 1971, p 1409.
(2) Reinisch, R. F., Gloria, H. R., “A Survey of the Photodegradation of Organic Polvmers ExDosed to Ultraviolet Radiation”, Sol. Energ;, 12 (l), f 5 (1968).
(3) Pansius. P. J.. Watson, J. H.. Scott. J. R., “Operational Experience Since 1967 With the Navy’s Water Wall Refuse Incinerator Steam Plant”, Am. Inst. Che Eng. Symp. Ser., #22, V68, 1972. (4) McElroy, W. F., “Polyurethane Plastics”, US. Pat. 3,300,417 Assigned to Mobay Chemical Co., 1967. (5) Mahoney, L. R., Weiner, S. A., Ferris, F. C., “Hydrolysis of Polyurethane Foam Waste”, Enuiron. Sci. Technol., 8 (2), 135 (1974). (6) Pizzini, L. C., Patton, J. T., “Process for Recovery of Polyether Polyols From Polyurethane Reaction Products”, U.S. Pat. 3,441,616,Assigned to Wyandotte Chemical Corp., 1969.
(7) Broeck, T. R. T., Peabody, P. W., “Methods for Reclaiming
Cured Cellular Polyurethanes”, U.S. Pat. 2,937,151, Assigned to the Goodyear Tire and Rubber Co., 1960. (8) McElroy, W. R., “Methods of Dissolving Polyurethanes”, U S . Pat. 3,117,940,Assigned to Mobay Chemical Co., 1964. (9) Kinoshita, O., “Process for Decomposition of a Polyurethane Resin”, U.S. Pat. 3,632,530,Assigned to Yokohama Rubber Co., Ltd., Tokyo, 1972. (10) “Recycled Urethane is Cheaper Than New”, Design News, 12 (3),24 (1973). (11) “Recycling of Scrap Foam”, The Donald S. Gilmore Laboratories, Upjohn Co., Rep. No. 9, 1974.
Received for review August 5,1974. Accepted October 23,1975.
Moisture Anomaly in Analysis of Peroxyacetyl Nitrate (PAN) Michael W. Holdren” and Reinhold A. Rasmussen Atmospheric Resources Section, Chemical Engineering, College of Engineering, Washington State University, Pullman, Wash. 99 163
Preliminary results in our laboratory using gas chromatography with an electron capture detector (GC-ECD) to measure peroxyacetyl nitrate have shown particular anomalies when calibrating and measuring low ppb levels of PAN. At constant concentrations (10 or 100 ppb) of PAN but with changing humidities (0-loo%), a definite instrument response change was observed. Maximum response was obtained a t 100% relative humidity. Humidities below 30% resulted in much lower response values. The possibility of erroneous measurements with the electron-capture analysis of PAN in ambient air can occur unless the proper experimental precautions are observed. During the past few years, numerous laboratories have measured peroxyacetyl nitrate (PAN) in ambient air (1-7). T h e concentrations of PAN are determined routinely by gas chromatography with electron-capture detection (GCECD). This technique provides a very sensitive and selective method for the atmospheric analysis of PAN. The range of PAN concentrations reported in urban and suburban air has been 1-200 ppb (by volume). Preliminary results in our laboratory on the GC-ECD analysis of PAN have demonstrated particular anomalies that may be of concern to scientists and engineers studying air quality. When the instruments were calibrated for PAN under varying humidity conditions, a definite response’ anomaly was observed a t the lower humidity levels. This effect is most pronounced a t the low-ppb range of PAN and a t levels less than 30% relative humidity (R.H.). The possibility of erroneous measurements with the electron-capture analysis of PAN in ambient air due to this humidity effect is discussed in this report.
Experimental In the investigation of this phenomenon, three different types of electron-capture detectors were used: a direct-current mode 3H detector in an Aerograph Hy-Fi Model 600 gas chromatograph, a pulsed-current mode 3H detector in a portable A.I.D. Model 511-06 gas chromatograph, a constant-current mode 63Ni detector in a Hewlett-Packard Model 5713A gas chromatograph. T o verify that the humidity anomaly was independent of the type of chromatographic column, a variety of stationary
phases and supports were tested. These column materials included: 5% Carbowax 400 on Chromosorb W AW-DMCS (80- to 100-mesh), 10% Carbowax 400 on Anakrom ABS (70- to 80-mesh), 10% Carbowax 600 on Gas Chrom Z (60to 80-mesh), Durapak Low K’ Carbowax 400 on Porasil F (100- to 120-mesh), and 4% Ucon 50-HB-2000 on Chromosorb W AW-DMCS (60- to 80-mesh). The gas chromatographic columns were fabricated from both Teflon and glass tubing in lengths varying from 12 in. to 6 ft. In most cases, j/8-in.-o.d.tubing was used. Synthesis of peroxyacetyl nitrate was accomplished by photolysis of ethyl nitrite in oxygen (7). One microliter of %%-purity ethyl nitrite obtained from Mallinckrodt Chemical Works was syringe-injected into a 20-1. Tedlar bag previously flushed and filled with oxygen. Both ethyl nitrite and the syringe used to dispense it were kept under refrigeration to minimize loss due to vaporization. After it was mixed, the ethyl nitrite-oxygen in the bag was photolyzed for 6-8 h with 24 Sylvania (F15T8-BL) blacklights. T h e concentrations of PAN produced were approximately 2 ppm, as determined by the colorimetric method reported by Stephens (8). This method of analysis agrees very well with the infrared method, which is based on the PAN absorbance a t 7.76, 8.60, and 12.61 wm. The colorimetric procedure involves the hydrolysis of PAN with base to produce molar yields of acetate ion, nitrite ion, and the molecular oxygen: 0
II
CH,-C-O-O---h’O,
+ 20H-
e
0
II
CH,CO-
+ NO,-
iO2
+ H,O
The nitrite ion then is analyzed in the standard way with Saltzman’s reagent (9). Standard dilutions of PAN were made in 2-1. glass flasks and 2-1. stainless steel vessels. Concentrations of PAN from 10-100 ppb were obtained and analyzed by the GC-ECD system. The apparatus used for adding moisture to the containers prior to adding various amounts of PAN is shown in Figure 1. By varying the water level in the impinger, humidities 10-50% were obtained. The humidity was meaVolume IO, Number 2, February 1976
185
