Ind. Eng. Chem. Res. 1994,33, 3004-3009
3004
Effect of Heterogeneous Secondary Pyrolysis Reactions on the Thermal Decomposition of Polyurethane Scrap Dawn Y. Takamoto and Mark A. Petrich**+ Department
of
Chemical Engineering, Northwestern University, Evanston, Illinois 60208
Pyrolysis is a n effective resource recovery technology for many polymeric materials but is unsuitable for polyurethanes because the liquid product is extremely viscous and can solidify over time. We have pyrolyzed reaction injection molded polyurethane (RIM) scrap in a batch, laboratory-scale reactor and have used a packed carbon bed to influence the composition and yield of the pyrolysis products. We find that carbon surfaces are effective in eliminating the high-viscosity liquid product. Both activated carbon and polyurethane char improve the liquid product by promoting heterogeneous secondary pyrolysis reactions. The polyurethane char provides the additional benefit of increasing the amount of char produced. Char yields a s high as 40% can be obtained when polyurethane char is used as the carbon bed material, as compared to 15-25% with other bed materials. These results will be useful in developing pyrolysis as a resource recovery technology for thermosetting polymer waste.
Introduction Thermosetting Resins. Plastics recycling technologies have advanced rapidly over the past several years. Postconsumer thermoplastics such as polyethylene and poly(ethy1ene terephthalate) are collected and recycled on an increasingly routine basis. Most research work has been focused on postconsumer plastic waste problems, with the large volumes of industrial polymer scrap receiving much less attention. We have selected polyurethane as a typical industrial thermosetting polymer for our studies. The total production of all plastics annually in the US is over 66 billion pounds, with the greatest capacity (over 10 billion pounds) in low density polyethylene. US annual production of polyurethane is over 3 billion pounds, with roughly 212 million pounds used in the specific material we have studied-reaction injection molded (RIM) polyurethane (Bennett, 1992). Polyurethanes are produced by reacting multifunctional isocyanates with multifunctional polyols. The properties of the final material are controlled by the choice of reactants and by the extent of polymerization achieved (Gum et al., 1992). Thermoplastic scrap is often recycled “in house” through regrinding and addition to process feeds, with subsequent melt blending into the virgin material (Ehrig, 1992). Thermoplastics are chemically unchanged by processing. Most thermoplastic processing operations do not change the polymer physical properties substantially, making the regrind option a good one for waste minimization and cost savings. Thermosetting resins present a greater challenge because they are produced by reactions between two or more starting materials. The final material is chemically and physically different from the reactants fed to the process. Reaction polymers such as polyurethane, phenol formaldehyde, and polyaryl amides are difficult to recycle, in the traditional sense, in-process. Available options for thermosetting resin recycling include use as a filler or chemical reaction of the polymer to recover the starting materials (Weigand et al., 1993). Thermosets can be ground and added to new
* To whom correspondence should be addressed. E-mail:
[email protected]. Current Address: Merck & Co., Inc., P.O.Box 100, WSEX, Whitehouse Station, N J 08889. 0888-5885/94/2633-3004$04.50/0
parts during the curing stage. This added material acts as a benign filler, and may improve mechanical properties (Farrissey et al., 1992). Solvolysis processes react the polymer with a “cleaving agent” such as ammonia, diols, or water to split the polymer into its precursors. These processes require fairly sophisticated chemical reactor design and also require expensive separation operations to recover the reactants as pure components (Lentz and Mormann, 1992). Pyrolysis of Polyurethanes. Research on pyrolysis of waste materials has proceeded on laboratory and manufacturing scales for many years. Pilot scale systems for the recovery of oils and carbon black from tires have been described in the literature (Schulman and White, 1978; Kaminsky and Sinn, 1980; Kawakami et al., 19801,and at least one of these research groups still has an active program in pyrolysis of polymeric wastes (Kaminsky and Rossler, 1992) The reactors in these studies range from rotary kilns to fluidized beds. While operating conditions are typically near ambient pressure, at least one extensive study of tire pyrolysis under subatmospheric conditions has been reported (Roy et al., 1990). The pyrolysis chemistry of various thermoplastic and thermosetting materials has been studied on both a laboratory (Yamashita and Ouchi, 1979; Morterra and Low, 1985; Scott et al., 1990; Carniti et al., 1991) and a production scale (Kaminsky, 1992; Mapleston, 1993).Of interest here are studies dealing specifically with polyurethane, including a detailed study of the intermediate species produced during pyrolysis (Voorhees et al., 1978). Although pyrolysis is an effective means of decomposing many synthetic and natural polymeric materials, polyurethane pyrolysis is precluded as a waste-management strategy by the poor quality of the liquid products. These liquids are extremely viscous and may even solidify over time. The initial stages of polyurethane pyrolysis are characterized by breakage of the bonds originally formed during the reaction between isocyanates and polyols. Further pyrolytic reaction eventually yields substantial amounts of aromatic products and oxygenated species. The aromatic products include aromatic amines, benzene, toluene, and their derivatives. Oxygenated species include ethers and ketones of various molecular weights.
0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33,No. 12, 1994 3005 Water is a byproduct of many of these later pyrolysis reactions (Voorhees et al., 1978). At low temperatures, or short residence times, the pyrolysis reactions do not proceed far enough to generate large yields of the low molecular weight products. The condensates consist of lightly degraded polyurethane fragments which have relatively high molecular weights, and which probably retain the reactivity characteristics of the original polyurethane precursor molecules. This reactivity may be the cause of the viscosity increase and hardening that occurs in the condensate after collection. In this paper, we demonstrate the beneficial effects of heterogeneous secondary pyrolysis reactions on the liquid products of polyurethane pyrolysis. Pyrolysis volatiles are passed through a packed bed of carbonaceous solids that promote the secondary reactions. Activated carbon and RIM char were found to be suitable bed materials. Our long-term focus is on developing marketable solid products by pyrolysis of wastes, so obtaining high char yields is an important objective. We found that, in addition to affecting the liquid products, RIM char also increased the total char yield. This result has interesting implications for pyrolysis reactor design.
Raw Materials and Experimental The reaction injection molded polyurethane (RIM) used in these experiments was obtained from General Motors in sheet form. The polyurethane (Mobay 11025) was prepared from precursors A and B in the ratio of 47.5100. Precursor A is a mixture of 50%diphenylmethane diisocyanate (MDI, Mondur PF) and 50% polyol. Precursor B is 80% hydroxyl-terminated poly(oxyalkylene)poly01 of roughly 5000 MW, less than 18% diethyltoluenediamine, and small amounts of catalysts and surfactants. The sheets were cut into strips, cooled in liquid nitrogen, and shattered into pieces smaller than 2 cm. The activated carbon (coconut shell-based, produced by Barnebey and Sutcliffe) had a measured specific surface area of 914 m2/g and 0.18 m u g of microporosity. The RIM char used in the secondary pyrolysis reaction study was collected during our experimentation and used as a composite sample. The reactor system used in these experiments consisted of a stainless steel U-tube reactor heated in a furnace. This system was described previously (Merchant, 1992; Merchant and Petrich, 1992; Merchant and Petrich, 19931, and is used here with slight modifications. The polyurethane and an optional second packed bed are both placed into the U-tube reactor, separated with a glass wool plug. Glass wool was also used at the exit of the reactor to keep the samples in place. The amount of polyurethane used ranged from 8 to 30 g, and the amount of material in the second packed bed varied. Nitrogen was used as the carrier and purge gas at 0.5 L (STP)/min. The residence time of the nitrogen carrier gas in the reactor was approximately 9 s. The nitrogen was passed through the polyurethane first and then through the second packed bed. Liquid products were collected in two glass U-tubes, the first immersed in a water bath and the second in an ice bath. Gaseous products were not collected. The average heating rate for this system was 25 "C/min, and the final temperature was reached in 20-25 min. The gaseous products began to evolve around 200 "C, while the liquid products emerged from the reactor around 500 "C. For the experiments using activated carbon as a packing mate-
Table 1. Summary of Pyrolysis Trials with Mobay 110-25 (RIM)
expt
packing material
1 2 3 4 5 6 7 8 9-1 9-2 9-3 10-1 10-2 10-3 10-4 10-5
none glasswool glass beads activated carbon activated carbon activated carbon activated carbon activated carbon activated carbon (12/15)d activated carbon (23/15) activated carbon (36/15) RIM char (5127) RIM char (11/27) RIM char (18/27) RIM char (24/26) RIM char (29121)
liquid char gas materiaV yield yield" yeldb RIM (g/g) (%) (%) (%) 0 1 4 0.433 1 1.5 2 3 1 1 1 3 3 3 3 3
38f2C 4 & 1 37 5 40 8 38 21 22i7 16f6 13 15 14i2 19i9 5 22 27 19 24 25 33 14 23&2 4 0 i 1 1 8 i 9 28& 1 29 16 23 26 19 23
58 58 52 41 62 72 67 73 54 51 53 37 54 55 52 59
a Char yield includes all char formed during the pyrolysis run: charred polyurethane, carbon deposited on the carbon bed, and carbon that forms on the glass wool used to hold material in the reactor. b Gas yield is determined by subtracting char and liquid yields from 100%. Deviations were determined from two or more duplicated pyrolysis runs. Gas yields were not measured, so no deviation is reported. d The fractions in the parentheses represent the (grams of volatiles treated total)/(grams of packing material used) in the run. For example, in experiment 9-1,12 g of volatiles passed over the activated carbon bed in one pyrolysis run. In experiment 9-2, 11 more grams of volatiles passed over the activated carbon bed, for a total of 23 g in the two runs.
rial, the reactor was first heated to 150-180 "C for an hour to remove adsorbed water. The reactor was maintained at 550-560 "C for a half hour. The furnace was then shut off and allowed to cool to room temperature. The nitrogen gas continued t o purge the system until the temperature dropped by 200 "C, and then it was also shut off. The oil product collected was analyzed on either a Varian gas chromatographlmass spectrometer or a Hewlett-Packard gas chromatograph instrument. Samples were prepared by dissolving in methylene chloride to about a 0.5 wt % solution. To test solvent effects, an additional sample was prepared by dissolving the oil in tetrahydrofuran (THF). Choice of solvent had no effect on the observed gas chromatograms.
Results and Discussion Table 1 shows the results of RIM pyrolysis experiments using a variety of packing materials. Each entry in the table will be discussed within the appropriate sub-section below. "Simple" Pyrolysis of Polyurethane. Reaction injection molded polyurethane (RIM)scrap yields a red, viscous oil product when pyrolyzed a t temperatures in excess of 450 "C. This oil is a single-phase liquid, and its viscosity increases with time a t room temperature. The viscosity increase could be due t o repolymerization reactions, or may be caused by evaporation of volatile components that act as solvents for larger molecules in the oil. Typical yields in RIM pyrolysis are 5-25% char, 1045% liquid, and 40% or more gas. The yields vary with parameters such as RIM particle size and pyrolysis temperature. As the pyrolysis temperature is increased, the char yield is decreased. This may be due to the increased extent of pyrolysis, or char gasification by water and COa.
3006 Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994 Many of the gas products are condensible at -72 "C (methanovdry ice trap), but a quantitative analysis has not been done for safety reasons. It is possible that the condensed products include HCN (Voorheeset al., 1978). Secondary Pyrolysis Reactions. We tried to increase the residence time of volatile species in the reactor t o increase the yields of low molecular weight liquid products via homogeneous and heterogeneous secondary pyrolysis reactions (Serioet al., 1987; Boroson et al., 1989a; Hayashi et al., 1993). Glass beads and glass wool were used as inert packing materials. The results of these runs are shown in Table 1. We observed char deposition on these materials, indicating that volatiles adsorbed on the packing. On the glass beads, 0.6 g of char was deposited on 37 g of beads (a 2% weight gain). However, the liquid product's yield and composition were essentially unchanged. Previous work suggested that further reaction of the volatiles could be induced by interaction with carbon surfaces. The reactions of coal pyrolysis volatiles with coal char, activated carbon, and other surfaces (Linares Solano et al., 1977; Scaroni et al., 1981), and wood pyrolysis volatiles with wood char and activated carbon (Boroson et al., 1989b) have been well documented. Cracking reactions, leading to lower molecular weight products, and deposition reactions, leading to increased char yields, have been observed in these laboratory studies. We wanted to study the interaction of RIM pyrolysis volatiles with RIM char, but in our early work we did not generate enough RIM char for the necessary experiments. Our first experiments on secondary pyrolysis reactions of RIM volatiles were performed using activated carbon as a surrogate char. It is important to note that the experiments described below involve the pyrolysis of polyurethane in contact with glass wool. The glass wool is used to separate the polyurethane from the carbon so that char yields and carbon mass changes can be measured. A difficulty in interpretation of the results is caused by char formation on the glass wool, and wetting of the glass wool by heavy pyrolysis liquids. The wetting step may be a prelude to char formation, and this char may itself act to promote secondary pyrolysis reactions. Char is deposited on the glass wool that retains the polyurethane and is also deposited on the glass wool that holds the carbon bed in the reactor. This char on the glass wool at the reactor exit consists of carbon which is blown into the wool by the purge gas, as well as deposited volatiles which carbonize. Char yields that are reported include all new carbon produced in the reactor, whether on glass wool, packing material, or a t the original location of the polyurethane feed material. Activated Carbon as Facilitator of Secondary Pyrolysis Reactions. Activated carbon is useful in reducing the viscosity of pyrolysis liquids produced during RIM pyrolysis. Collected liquids have a waterlike viscosity and do not harden over time. The gas chromatography data shown in Figure 1 demonstrate that this is not simply a physical effect such as adsorption of high molecular weight volatiles but also involves chemical reactions. New species appear when the activated carbon bed is used. The data are plots of amount of material exiting a chromatographic column versus time. The main peaks of interest are labeled peaks 1, 2, and 3. Mass spectrometry of the eluted materials shows that the lowest molecular weight
I
1
Figwe 1. Effect of activated carbon on polyurethane pyrolysis liquids. Data shown are gas chromatograms.The plots are of the amount of material exiting a chromatographiccolumn versus time. The column used was a 15 m 0.25 mm fused silica capillary column. The temperature was ramped from 50 "C to 325 "C in 15 min. Higher molecular weight species appear to the right (longer times far elution). Peaks 1,2,and 3 are discussed in the text. The ratio of activated carbon to RIM sample is 0 1 in the top figure, 1:l in the middle figure, and 2 : l in the bottom figure.
0
0.4
1
15
2
M a s Ralios d Adualed Carbon Io Sample
Figure 2. Effect of increasing activated carbon loading on polyurethane pyrolysis liquids. Data shown are the areas of each of the three main eluted peaks (shown in Figure 1) as a fraction of the total area. The blank area (top) corresponds to peak 3, the slowest eluting peak. The lightly shaded area (middle)corresponds to peak 2 and the dark shaded area (bottom) corresponds to peak 1.
species appear a t shorter times. A detailed chemical identification of peaks has not been performed. The effect of activated carbon loading on the ratio of low-to-high molecular weight species is shown in Figure 2. As the ratio of activated carbon to RIM is increased, there is a decrease in the fraction of high molecular weight volatiles exiting the reactor and also an increase in the amount of low molecular weight volatiles. By the time the ratio of activated carbon to RIM sample is increased to 2 1 , the larger species corresponding to peak 3 has disappeared. The data clearly document the occurrence of cracking reactions, since lower molecular
Ind. Eng. Chem. Res., Vol. 33,No. 12,1994 3007
"."
Aclivated Carton used once
Activsted Carbon used wice
Activated Carton used lhree timer
Figure 3. Effect of reusing activated carbon during polyurethane pyrolysis on liquid product Composition. The ratio of activated carbon to RIM sample for these experiments was 1:l. Data shown are the areas of each of the three main eluted peaks as a fraction of total area. The blank area (top) corresponds to peak 3, the slowest eluting peak. The lightly shaded area (middle) corresponds to peak 2 and the dark shaded area (bottom) corresponds to peak 1.
weight species corresponding to peaks 1 and 2 do not appear in the "simple" pyrolysis experiment. Also, the gas product yield increases with activated carbon loading. It appears that the activated carbon is acting as a catalyst, promoting s e c o n d q pyrolysis reactions of RIM volatiles. The collected liquids do not harden over time, but many of them separate into an organic fraction and a water fraction (determined by measuring the boiling point). The organic fraction had a lower density and floated on top of the water fraction. The amount of water generated during pyrolysis varied with each experiment, reaching up to 50%. The production of water confirms that the pyrolytic chemistry of the polyurethane is proceeding further along its reaction pathways in the presence of the activated carbon (Voorhees et al., 1978). We suspect that the interaction of the pyrolysis volatiles and activated carbon involves physical adsorption followed by parallel carbon deposition and molecular "cracking" reactions. Coke formation on porous materials is affected by the reaction temperature. If the temperature is high enough, reactions occur in the gas phase and deposition of "gas-phase carbon" may occur. At lower temperatures, carbon or coke is usually formed directly on the material, and surface catalytic reactions lead to deposited species (Hughes, 1984). To test for physical adsorption of species on the activated carbon, a small portion of the used carbon was rinsed with methylene chloride. This gave a yellowish solution similar to the pyrolysis oil. Because methylene chloride extraction of virgin activated carbon showed no color change, it appears that there are some volatiles that adsorb, but do not carbonize completely during our pyrolysis experiments. Figure 3 shows the effect of subsequent reuse of the activated carbon bed on the liquid product composition (experiments 9-1 to 9-3 in Table 1). The regrowth of the slow eluting peak 3 suggests that the activated carbon does adsorb some materials irreversibly during the process, and that these adsorbates and possibly carbonized deposits have an adverse effect on the catalytic activity of the activated carbon.
I 0
1
2
3
Number of Repeated Uses
Figure 4. Surface area of activated carbon versus the number of times the carbon packing was used to facilitate secondary pyrolysis reactions. Area were determined by analyzing nitrogen adsorption isotherms (77 K)by the BET method.
The surface area of the activated carbon (in experiments 5 and 9-3)was measured by nitrogen adsorption after each use. As shown in Figure 4, there is a significant drop in the surface area after only one use. However, it is important to note that the drop in performance of the carbon is less severe than the drop in surface area. The carbon can be used with nearly its original effectiveness even though the measurable surface area is reduced by a factor of 10. The porous regions of the activated carbon consist of three types of pores (Jankowska et al., 1991). The largest are the macropores, with pore radii greater than 50 nm. Next are the mesopores, with radii between 2 and 50 nm. The smallest pores are the micropores, with radii less than 2 nm. The volatile products formed during pyrolysis are large molecules, making the microporous regions of the activated carbon inaccessible for secondary pyrolysis reactions. The important surface area is the accessible surface area in the meso- and macropores, which is typically 100 m2/g in commercial activated carbons (Jankowska et al., 1991). This area is roughly 10% of the total surface area. During exposure to pyrolysis volatiles, the micropores are plugged, as are the smaller mesopores. Nitrogen adsorption measurements reflect these events. Pyrolysis Char as Facilitator of Secondary Pyrolysis Reactions. To increase the practicality of this process, we decided to investigate the use of pyrolysis chars in place of activated carbon as the second packed bed material. Since only a small fraction of the total surface area of the activated carbon is effective in promoting secondary pyrolysis reactions, we thought that the lower surface area of pyrolysis chars might not be detrimental to the process. Also, since our research emphasis is on solid pyrolysis products, we wanted to know if secondary reactions are a good way to increase the net char yield of the process. Table 1 includes the results of the pyrolysis runs using RIM char as the second packed bed material. While the activated carbon did not significantly alter the char yield, RIM char had a remarkable effect on char yield. The 40% char yield produced when using "fresh" RIM char was the highest we found in this study. This result is reminiscent of the findings of a related study of the influence of secondary pyrolysis reactions during wood pyrolysis. Wood chars were much more effective
Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994
0.9
Purge Gas 0.4
Figure 6. Schematic representation of a pyrolysis reactar that uses generated char 88 a promoter of secondary pyrolysis reactions.
0.3 0.2 0.1 "I
0
5127
11127
18127
24126
29121
Volalile~Treeled (gpacking Material (9)
Figure 5. Effect of reusing RIM char during polyurethane pyrolysis on liquid product composition. The ratio of RIM char to Polyurethane sample for these experiments was 3 1 . Data shown are the areas of the three main eluted peaks as a fraction of the total area. The fractions in the parentheses represent the (grams of volatiles treated total)/(grams of RIM char used) in the run. In the first run (column labeled 0). no packing material was used. The blank area (top) corresponds to peak 3, the slowest eluting peak. The lightly shaded area (middle) corresponds to peak 2 and the dark shaded area (bottom) corresponds to peak 1.
than activated carbons at promoting secondary pyrolysis reactions of wood tars, even though the wood chars had a much smaller surface area than the activated carbon (Boroson et al., 1989b). The RIM char was effective in producing a lowviscosity liquid, again with a substantial quantity of water. The oil consists mainly of the same three species produced with activated carbon. Figure 5 shows that subsequent use of the RIM char led to a liquid product that was more viscous and consisted mainly of peak 3, the highest molecular weight species. The increased char yield when using RIM char is accompanied by a decrease in the gas yield and a slight decrease in the liquid yield. These results are encouraging, since we are most interested in solid products and least interested in gas products. Preliminary work on the preparation of activated carbon from polyurethane char provides support for a solid product approach to polyurethane pyrolysis similar to our work with tires (Merchant and Petrich, 1993). We have produced a n activated carbon with a surface area greater than 400 m2/gfrom polyurethane char by steam activation a t 950 "C. Reactor Design for Polyurethane Pyrolysis. It is clear that by providing for the interaction of volatile polyurethane pyrolysis products with certain carbon surfaces, the yield of solid carbon is increased, and the desirability of the liquid pyrolysis products is also increased. The physical and chemical steps promoted by the carbon certainly include adsorption of volatile species and their reaction to form carbon deposits on the surfaces and in the pores of the carbon particles. The carbon particles also seem to promote cracking reactions with the concomitant production of water and lower molecular weight hydrocarbons. The results found with the RIM char as a promoter of secondary pyrolysis reactions suggest that the reactor design shown schematically in Figure 6 would be effective in pyrolyzing polyurethane with maximum char yield and minimum liquid product viscosity. The design consists of a moving solid bed with two major zones. In the first zone, pyrolyzing material emits
volatile compounds which travel cocurrently with the solids but with a shorter residence time. The polyurethane is converted to char in this zone. In the second zone, the volatile compounds interact with the produced pyrolysis char in the manner described above. A certain amount of deposition occurs, and some heterogeneous chemistry proceeds, decreasing the average molecular weight in the volatile stream that finally exits the reactor. Proper design will lead to a process that produces the necessary solid carbon from the polyurethane feed material. No additional carbon needs to be added. The data in this paper provide a starting point for developing such a reactor. Conclusions Secondary pyrolysis reactions are extremely important in the thermal decomposition of reaction injection molded polyurethanes (RIM). The pyrolysis volatiles can adsorb, deposit, and react in the presence of a second carbon bed, altering the composition and yields of the pyrolysis products. The use of activated carbon as a secondary packing material was effective in eliminating the high-viscosityliquid product typically formed during RIM pyrolysis. Polyurethane chars were also effective a t lowering the viscosity of the liquid product, with the added benefit of increasing char yields. This is in agreement with related studies in wood pyrolysis. The use of RIM char to increase char yields could be important in developing processes to generate valuable solid carbon products by pyrolysis of waste. Acknowledgment This work was supported by a grant from the Office of Solid Waste Research (University of Illinois, UrbanaChampaign), Project OSWR-07-007. D.Y.T. was also supported by an NSF Fellowship. Mary Ellen Fullhart helped carry out experiments, and her contributions are appreciated. The polyurethane char activation result was provided by Nicole Saharsky. Dr. Norm Kakarala (General Motors) provided the polyurethane samples. Barnebey and Sutcliffe supplied the activated carbon. The Omnisorp 360 continuous sorption apparatus used in this work was purchased by the Northwestern University Center for Catalysis and Surface Science with funds from the U.S. Department of Energy. The VG 70-250SE Mass Spectrometer coupled with an HP 5890 gas chrpmatograph (run by Dr. Hoying Hung) and the HP 5880A series gas chromatograph were used in the Northwestern University Department of Chemistry Analytical Services Facility.
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Merchant, A. A. Activated Carbon from Waste Materials and HighSulfur Coals. M.S. Thesis, Chemical Engineering Department, Northwestern University, 1992. Merchant, A. A.; Petrich, M. A. Preparation and Characterization of Activated Carbons from Scrap Tires, Almond Shells, and Illinois Coal. Chem. Eng. Commun. 1992,118, 251. Merchant, A. A.; Petrich, M. A. Pyrolysis of Scrap Tires and Conversion of Chars to Activated Carbon. AZChE J. 1993,39, 1370. Morterra, C.; Low, M. J. D. I.R. Studies of Carbons - VII. The Pyrolysis of a Phenol-Formaldehyde Resin. Carbon 1986,23, 525. Roy, C.;decaumia, B.; Lebrecque, B.; Blanchette, D.; Pakdel, H.; Roy, V. Technical and Environmental Assessment of the Scrap Tire Vacuum Pyrolysis Process; Final Report to Eficiency and Alternative Energy Technology Branch, Energy, Mines, and Resources, Canada, Ottawa, Ontario, 1990. Scaroni, A. W.; Walker, P. L., Jr.; Jenkins, R. G. Effect ofsurfaces on the Yield of Volatiles from Coal. Fuel 1981,60,558. Schulman, B. L.; White, P. A. Pyrolysis of Scrap Tires Using the Tosco I1 Process-A Progress Report, Solid Wastes and Residues: Conversion by Advanced Thermal Processes;Jones, J. L., Radding, S. B., Eds.; American Chemical Society: Washington, DC, 1978. Scott, D. S.; Czernik, S. R.; Piskorz, J.; Radlein, D. St. A. G. Fast Pyrolysis of Plastic Wastes; Energy Fuels 1990,4 , 407. Serio, M. A.;. Peters, W. A.; Howard, J. B. Kinetics ofvapor-Phase Secondary Reactions of Prompt Coal Pyrolysis Tars. Znd. Eng. Chem. Res. 1987,26,1831. Voorhees, K.; Hileman, F.; Einhorn, I.; Futrell, J. An Investigation of Thermolysis Mechanism of Model Urethanes. J.Polym. Sci. Polym. Chem. Ed. 1978,16,213. Weigand, E.; Rasshofer, W.; Herrmann, M.; Baumann, G. F.; Nakamura, M. Polyurethane Recycling Processes are Reaching Commercial Maturity; Mod. Plast. 1993,70 (111, 71. Yamashita, Y.; Ouchi, K. Carbonization of 3,5-Dimethyl PhenolFormaldehyde Resin and Its Chemical Structure at Mesophase Appearance; Carbon 1979,17,365.
Received for review M&ch 25, 1994 Accepted August 1, 1994" Abstract published in Advance ACS Abstracts, November 1, 1994.
