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Energy & Fuels 1997, 11, 76-87
Depolymerization-Liquefaction of Plastics and Rubbers. 1. Polyethylene, Polypropylene, and Polybutadiene Joseph Shabtai,* Xin Xiao, and W. Zmierczak Department of Chemical and Fuels Engineering, University of Utah, Salt Lake City, Utah 84112 Received May 20, 1996X
The solid superacid-catalyzed depolymerization-liquefaction (DL) reactions of high-density polyethylene (HDPE), isotactic polypropylene (PPR), and cis-polybutadiene (PB) samples were systematically investigated as a function of processing conditions, i.e., temperature (350-450 °C), time (0.5-3.0 h), H2 pressure (500-2000 psig), catalyst type and concentration, and the presence of solvents. Catalysts used included SO42-/Fe2O3, SO42-/ZrO2, and a Pt-modified SO42-/ ZrO2. At temperatures >400 °C, with 1-2 wt % of SO42-/Fe2O3 or SO42-/ZrO2 as catalyst, there is an overlap of catalytic and noncatalytic, viz. thermal DL, reactions. Under such conditions HDPE yields a liquid product consisting of C5-C30 (mostly C5-C12) normal and branched paraffins, accompanied by small amounts of cycloparaffins and olefins. Selective catalytic DL of HDPE was achieved at lower temperature (350 °C) in the presence of 17-33 wt % of SO42-/ZrO2 or the more active Pt/SO42-/ZrO2 catalyst, preferably in the presence of a chemically compatible solvent, i.e., n-octadecane. Under such conditions the high-yield (>90 wt %) product predominantly consists of branched paraffins in the gasoline boiling range. PPR, which shows high DL reactivity due to its multiply branched polymeric chain structure, yields a similar gasoline-like mixture of C5-C12 branched paraffins as main product. The change in product composition from HDPE and PPR as a function of temperature and reaction time allows for elucidation of mechanistic aspects of the stepwise DL reactions of these polymers. For HDPE results are rationalized in terms of a carbonium ion mechanism involving extensive skeletal isomerization and attendant β-cleavage reactions leading to low branched paraffins as final products. Results obtained demonstrate that at mild temperatures, under properly designed catalytic conditions, waste HDPE and PRR feeds could be effectively converted into desirable multibranched paraffins which represent potential blending components for reformulated, nonaromatic gasolines.
Introduction In 1993, the total production of plastics in the United States was 19.3 million tons.1 A predominant part of such materials is ultimately disposed as waste. Further, about 280 million automotive tires were discarded in the United States in 1990.2 As a result, the effective disposal of waste polymers is now recognized as a major environmental problem. Plastics and rubbers are undesirable components for landfilling, since they are not presently biodegradable. Their destruction by incineration poses air pollution problems due to the release of airborne particles and carbon dioxide into the atmosphere. An alternative would be true recycling, i.e., conversion into monomers that can be reused. For example, DuPont has commercialized a depolymerization process for polyethylene terephthalate (PET) to reclaim ethylene glycol and terephthalic acid for reuse in the production of new PET. However, waste streams usually consist of polymer mixtures; furthermore, even pure polymers do not depolymerize thermally to corresponding monomers with sufficient selectivity. On the other hand, waste plastics and rubbers can be regarded Abstract published in Advance ACS Abstracts, November 15, 1996. (1) U.S. EPA. Characterization of Municipal Solid Waste, 1994 Update; U.S. GPO: Washington, DC, 1994. (2) Hearing before the Subcommittee on Environment and Labor and the Subcommittee on Regulation, Business Opportunities, and Energy of the Committee on Small Business, House of Representatives, April 18, 1990: Scrap Tire Management and Recycling Opportunities, Serial No. 101-52; U.S. GPO: Washington, DC, 1990. X
S0887-0624(96)00076-X CCC: $14.00
as a potentially cheap and abundant source for transportation fuels and useful chemicals. Thermodegradation of polymers has been investigated extensively since World War II,3-7 but relatively few studies on the catalytic conversion of polymers have been carried out, especially for production of liquid fuels. Considerable research has been carried out aimed at production of olefins and aromatics through polymer pyrolysis at temperatures above 700 °C. However, relatively limited systematic studies have been reported on the reactivity of individual polymers and product distributions obtained. Recently, there have been some reports on the thermal cracking of plastics to hydrocarbon feedstocks. Kastner and Kaminsky8 investigated the thermolysis of polyolefins in N2 using a fluidized bed reactor. At temperatures below 550 °C, good yields of high-boiling waxes and other useful products were found with low yields of gas and aromatics. Kaminsky and Ro¨ssler9 indicated that, in the temperature range of 650-820 °C, pyrolysis of plastic wastes, used tires, and waste oil residues produces olefins and other (3) Jellinek, H. H. G. J. Polym. Sci. 1949, 4, 13. (4) Madorsky, L. J. Polym. Sci. 1952, 9, 133. (5) Kuroki, T.; Honda, T.; Sekiguchi, Y.; Ogawa, T.; Sawaguchi, T.; Ikemura, T. Nippon Kagaku Kaishi 1977, 894. (6) Murata, K.; Sato, K. Kagaku Kogaku Ronbunshu 1981, 7, 64. (7) Lechert, H.; Woebes, V.; Sung, Q.; Kaminsky, W.; Sinn, H. Eur. Pat. Appl. EP 321807, 1989; Appl. DE 3743752, 1987. (8) Kastner, H.; Kaminsky, W. Hydrocarbon Process. 1995, 109112. (9) Kaminsky, W.; Ro¨ssler, H. CHEMTECH 1992, 108-113.
© 1997 American Chemical Society
DL of Plastics and Rubbers
hydrocarbons that can be used as petrochemicals. Songip et al.10 have indicated that a two-stage process for pyrolysis of waste polymers followed by reforming of the heavy oil pyrolysate is more economical. Solid polyethylene was pyrolyzed at 450 °C, yielding an oil with a gasoline fraction of 34 wt %, having a research octane number (RON) value practically equal to zero. After reforming at 400 °C with a REY zeolite catalyst, the gasoline yield increased to 48 wt % and the RON value of this fraction was 67. Catalysts’ activities and properties were also compared. It was concluded that large pore size and strong acidity are necessary for effective cracking of polymeric molecules. Scott et al.11 investigated the fast pyrolysis of low-density polyethylene at 600 °C using an activated carbon fluidized bed reactor. They observed feed conversions of ∼80% into gaseous and liquid products, the latter having a high aromatic content. Over 60% of the pyrolysis product was a liquid hydrocarbon fraction of relatively lowboiling range. Yamamoto and Takamiya12 studied the cracking of polyethylene on SiO2-Al2O3 under N2. In the absence of a catalyst, the pyrolysis yielded 77.1% of gas at 600 °C. The products were mainly ethylene, propylene, and 1-butene. With SiO2-Al2O3 as catalyst, a higher gas yield (87.8%) was obtained even at 450 °C. The gas consisted mainly of isobutylene (45.6%). Uemichi and co-workers13 studied the pyrolysis of polyolefins to aromatic hydrocarbons under N2 using activated carbon-supported metal (Pt, Fe, or Mo) catalysts. Polyethylene was converted to C6-C14 aromatics at 526 °C with a selectivity of ∼60%. Benzene was produced as the main aromatic component over the Ptcontaining catalyst, while catalysts containing Fe or Mo yielded preferentially toluene. The presence of methyl branching in polypropylene was found to be unfavorable for the formation of aromatics.14 Audisio and Silvani15 studied the catalytic degradation of polypropylene under vacuum (10-1 Torr). Catalysts, e.g., Al2O3, SiO2, SiO2-Al2O3, and Y-type zeolites, were screened at 200, 400, and 600 °C. The authors concluded that SiO2-Al2O3, HY, and REY were the most efficient catalysts for this reaction. Smith16 studied the catalytic cracking of byproduct (amorphous) polypropylene into fuel oil with a SiO2-Al2O3 catalyst. In another study, Carle and Hann17 mixed up to 2.5% of amorphous polypropylene into the feed of a fluid catalytic cracker. Wagener and Puts18 studied the depolymerization of polybutadiene and polyisoprene using THF or toluene as solvent and bubbling ethylene gas as an additive. Significant amounts of oligomers were formed via an acyclic diene metathesis mechanism. Nanbu et al.19 (10) Songip, A. R.; Masuda, T.; Kuwahara, H.; Hashimoto, K. Appl. Catal. B: Environ. 1993, 2, 153-164. (11) Scott, D. S.; Czernik, S. R.; Piskorz, J.; Radlein, D. St. A. G. Energy Fuels 1990, 4, 407-411. (12) Yamamoto, M.; Takamiya, N. Bull. Sci. Eng. Res. Lab. Waseda Univ. 1985, 111, 8-14. (13) Uemichi, Y.; Makino, Y.; Kanazuka, T. J. Anal. Appl. Pyrol. 1989, 14, 331-344. (14) Uemichi, Y.; Makino, Y.; Kanazuka, T. J. Anal. Appl. Pyrol. 1989, 16, 229-238. (15) Audisio, G.; Silvani, A. J. Anal. Appl. Pyrol. 1984, 7, 83-90. (16) Smith, V. C. U.S. Pat. 4,151,216, 1979. (17) Carle, R. A.; Hann, P. D. U.S. Pat. 4,143,086, 1979. (18) Wagener, K. B.; Puts, R. D. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1991, 32 (1), 379-380. (19) Nanbu, H.; Ishihara, Y.; Takesue, T.; Ikemura, T. Polym. J. 1986, 18 (11), 871-875.
Energy & Fuels, Vol. 11, No. 1, 1997 77
studied the monomer formation from polyisobutylene in the presence of a SiO2-Al2O3 catalyst. Isobutylene started forming even at 160 °C and reached a yield of 22% at 240 °C. The authors found that the polymer can be converted to the corresponding monomer and oligomers having 2-10 monomeric units, but the latter cannot be converted to the monomer under the mild reaction conditions used. Williams et al.20 studied the influence of temperature and heating rate on product composition in pyrolysis of scrap automotive tires. Pyrolysis between 420 and 720 °C resulted in significant yields of hydrocarbon liquids, solid char, and gases. There was, gradually, an increase in aromaticity and decrease in aliphatic compounds as the temperature was increased. It should be pointed out that conventional pyrolysis of polymers usually results in unsaturated and unstable oils in low yields and of low value that can be used mainly for direct combustion. Further, most of the catalytic studies so far have been conducted under nitrogen at ambient or low pressure. It is also apparent that development of efficient coprocessing of coal and waste polymers is being hindered by the lack of detailed fundamental data on the catalytic breakdown reactions of a variety of plastics and rubbers. The present research was concerned with a systematic investigation of the catalytic depolymerization-liquefaction (DL) reactions of three representative commercial polymers, i.e., polyethylene, polypropylene, and polybutadiene under H2 pressure, using finely dispersed superacid catalysts, i.e., SO42-/Fe2O3, SO42-/ZrO2, and SO42-/Al2O3.21-28 Products were identified by a combination of GC/MS and FTIR and, in some cases, by comparison with authentic reference samples. Quantitative analysis was performed by gas chromatography. The change in product composition as a function of processing variables, i.e., temperature, reaction time, hydrogen pressure, and catalyst type and concentration, was studied. The objective was to determine suitable conditions for conversion of the above polymers into high-quality liquid fuels, as well as to obtain data needed for predictive modeling of waste polymer coprocessing with coal. Experimental Section Materials. Samples of high-density polyethylene (HDPE) (d, 0.959 g/cm3; average MW, 125 000; Tm, 130 °C) and isotactic polypropylene (PPR) (d, 0.900 g/cm3; average MW, 250 000; Tm, 189 °C) were obtained from Aldrich Chemical Co. A polybutadiene sample (98% cis; d, 0.910 g/cm3; average MW, 197 000; softening point, 140-170 °C) was provided by Scientific Polymer Products, Inc. Catalysts. Four types of solid superacid catalysts were employed in the DL studies, i.e., SO42-/Fe2O3, SO42-/ZrO2, (20) Williams, P. T.; Besler, S.; Taylor, D. T. Fuel 1990, 69, 14741482. (21) Yamaguchi, T.; Jin, T.; Tanabe, K. J. Phys. Chem. 1986, 90, 3148. (22) Hino, M.; Arata, K. Chem. Lett. 1979, 477. (23) Hino, M.; Arata, K. Chem. Lett. 1979, 1259. (24) Wen, M. Y.; Wender, I.; Tierney, J. W. Energy Fuels 1990, 4, 372-379. (25) Arata, K.; Hino, M. Appl. Catal. 1990, 59, 197-204. (26) Garin, F.; Andriamasinoro, D.; Abdulsamad, A.; Sommer, J. J. Catal. 1991, 131, 199-203. (27) Zmierczak, W.; Xiao, X.; Shabtai, J. Energy Fuels 1994, 8, 113116. (28) Xiao, X.; Zmierczak, W.; Shabtai, J. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 4-8.
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SO42-/Al2O3, and a Pt-modified SO42-/ZrO2. The method of preparation and properties of the first two were described in detail elsewhere.27,28 SO42-/Al2O3 was prepared according to the following procedure: 12.4 g of Al2(SO4)3‚(14-18)H2O was dissolved in 44 mL of distilled water, and a 30% aqueous ammonia solution was slowly added with vigorous mixing, until a pH 8.5 was reached. The precipitate formed was filtered, washed with distilled water, and then dried at 110 °C for 2 h. The dry solid was pulverized and calcined at 550 °C for 2 h. A portion of the resulting Al2O3, 2.0 g, was treated with 50 mL of a 1.5 M (NH4)2SO4 plus 1.0 M H2SO4 aqueous solution for 1 h with constant stirring. The resulting solid, i.e., SO42-/Al2O3, was then filtered, washed with ∼100 mL of water, dried at 110 °C for 2 h, calcined at 600 °C for 3 h, and stored in a desiccator. The Pt/SO42-/ZrO2 catalyst was prepared by impregnating 20.0 g of SO42-/ZrO2 with 11.0 mL of an aqueous H2PtCl6 solution, followed by drying at 110 °C for 24 h and subsequent calcination at 550 °C for 3 h. The final catalyst contained 0.5 wt % of Pt. Reactors. The catalytic DL studies were performed mostly in a 50 mL Microclave reactor (Autoclave Engineers) equipped with a MagneDrive stirrer, pressure gauge, tachometer, gas sampling device, vent valves, external electric heating furnace, and temperature controller. A 300 mL EZE-seal Autoclave reactor (Autoclave Engineers) was also employed in some of the runs. Experimental Procedure. In most of the runs a mixture of the polymer, 5.0-20.0 g, and catalyst, 1-2 wt % (without any solvent), was introduced in the autoclave reactor. The latter was closed, purged sequentially with nitrogen and hydrogen, and then pressurized with hydrogen to a selected initial pressure. The reactor was heated to the desired temperature in 12-15 min (50 mL Microclave reactor) or 40 min (300 mL autoclave reactor), and stirring (500 rpm) was started after the melting or softening point of the polymer was reached. At the end of each experiment, the reactor was quickly cooled to room temperature with a fan (about 20 min), and the liquid product (plus any unconverted solid feed) was removed from the reactor and weighed. The liquid was separated by decantation and filtration. The solid residue was rinsed with n-hexane to remove any liquid product, dried, and weighed. Then the catalyst was separated from the unconverted polymer feed by washing sequentially with n-hexadecane (∼80 °C) and n-hexane (room temperature). The solid residue was dried and weighed to determine the weight of recovered catalyst (including coke). Gaseous and some volatile liquid products were collected in a stainless steel trap kept at liquid nitrogen temperature and weighed. This way, the product was separated and the weights of gas, liquid, solid, and recovered catalyst were determined. In the presence of a solvent and larger amounts of catalyst, the following modified procedure was applied: 5.0 g of polymer, e.g., HDPE, 5.0 g of n-octadecane (mp 30 °C), and the desired amount of catalyst (2.0-5.0 g) were charged into the Microclave reactor. The reactor was sealed, purged sequentially with N2 and H2, charged with H2 to an initial pressure of 500 psig, and heated to 350 °C. After reaction (60 min), the reactor was cooled and about 1 mL of the liquid product was sampled by a pipet for GC/MS and quantitative GC analysis. To determine total conversion, the main product in the reactor was removed and subjected to Soxhlet extraction with npentane. Conversion was determined on the basis of the insoluble solid residue. After removal of the n-pentane solvent, the main part of the liquid product was collected and analyzed. Products from polybutadiene required special treatment because of their high viscosity at partial conversions. After the removal of gas products, ∼20 mL of methanol was added to the product. The reactor was then sealed, purged with nitrogen, heated to ∼200 °C with continuous stirring, and then cooled. The methanolic solution was subjected to GC analysis, whereas the solid residue was used to determine the total conversion. To avoid the loss of volatile product components,
Shabtai et al. GC/MS examination and quantitative GC analyses were performed directly with samples of the original product, viz., before the treatment with methanol. Product Analysis. Gas and liquid products were identified by a combination of GC/MS and FTIR and, in some cases, by comparison with authentic reference samples. A HP 5890 Series II gas chromatograph/HP 5971 mass selective detector (GC/MS) system and a Perkin-Elmer 1600 series FTIR were used in the analyses. GC/MS analysis of liquid products was performed using a 30 m × 0.25 mm i.d. DB-5 capillary column provided by J&W Scientific. Quantitative analysis was performed by gas chromatography and simulated distillation (SIMD). HP 5880A and Varian 3700 gas chromatographs equipped with FID detectors were used in the analysis. Columns used for quantitative analysis of gas products were 4 m × 0.3 cm o.d. stainless steel packed with Chromosorb 102. Columns used for quantitative analysis of liquid products were 4 m × 0.3 cm o.d. stainless steel packed with 10% OV-17 on Chromosorb W-HP and 30 m × 0.25 mm i.d. DB-225 or DB-5 capillary columns provided by J&W Scientific. SIMD was performed according to ASTM Methods D5307 and D2887 except for the following modifications: the temperature correlation curve was made using C6-C18 normal paraffins, and the internal standard was a mixture of about equal amounts of C7, C8, and C9 normal paraffins. SIMD was performed with a 0.5 m × 0.3 cm o.d. stainless steel Supelco PETROCOL B column. Mass Balance. The mass balance of the runs was in the range of 90-95% (relative to the feed weight) for polyethylene and polypropylene and 80-90% for polybutadiene. Conversions were determined on the basis of the difference between the weight of the feed used and the solid polymer residue after reaction. The gas samples consisted mostly of C1-C4 hydrocarbons, accompanied by some C5, C6, and traces of C7, C8 compounds. The liquid samples contained mostly C5-C12 components, accompanied by some C13-C30, and traces of C2C4 compounds. The product composition was calculated from GC data (FID detector). The C2-C4 gas components found in the liquid product were added to the gas composition, and the C5-C8 components found in the gaseous product were added to the liquid composition, correspondingly.
Results and Discussion A. DL Reactions of Polyethylene. Results of the GC/MS analysis of a typical polyethylene DL product, obtained at 450 °C with 0.5 wt % of SO42-/Fe2O3 as catalyst, are given in Figure 1. As seen, the liquid product obtained consists of a mixture of C5-C32 (mostly C5-C12) normal and branched paraffins, accompanied by some amounts of 5- and 6-ring nonsubstituted and mono-, di-, and trialkylsubstituted cycloparaffins. The proportion of cycloparaffins decreases to some extent with increase in the C number of the product component. In addition to n-paraffins, branched paraffins, and cycloparaffins, the product contains small amounts of olefins and cycloolefins. An example of the boiling point distribution of the total liquid product is given in Figure 2. The composition of the DL product from HDPE changes markedly with changes in processing variables, e.g., temperature and reaction time, as described below. Table 1 summarizes data on the change in product composition as a function of increase in reaction temperature, between 420 and 465 °C, keeping other processing conditions constant, i.e., catalyst, SO42-/ZrO2, 2.0 wt %; H2 pressure, 1500 psig; reaction time, 2.0 h. As seen, under such conditions the feed conversion is very high and increases from 82.5 wt % at 420 °C to
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Energy & Fuels, Vol. 11, No. 1, 1997 79
Figure 1. GC/MS analysis of the liquid product from DL of HDPE (450 °C, 2.0 h, 1200 psig of H2, SO42-/Fe2O3).
Figure 2. Boiling point distribution of the liquid product from DL of HDPE by simulated distillation (450 °C, 2.0 h, 1200 psig of H2, SO42-/Fe2O3).
∼100 wt % at 450-465 °C. At 420 °C the product is predominantly liquid. With increase in temperature, however, the yield of liquid products gradually decreases (from 92.8 wt % at 420 °C to 60.2 wt % at 465 °C), while that of C1-C4 gaseous products correspondingly increases (from 7.2 wt % at 420 °C to 39.8 wt % at 465 °C). The changes in the composition of gaseous (C1C4) and liquid (C5-C12 and C13+) product fractions as a function of temperature are plotted in Figures 3 and 4, respectively. As seen from Figure 3, C3 and C4 hydrocarbons predominate in the gaseous product in the entire temperature range studied. Further, Figure 4
shows that higher molecular weight liquids (C13+) steeply decrease (from 54.0 wt % at 420 °C to 11.7 wt % at 465 °C), as expected for these intermediate depolymerization products, while the C5-C12 fraction passes through a maximum and then declines. The components of the predominant gasoline-range (C5-C12) fraction (Table 1) either increase (C5 and C6 hydrocarbons) or pass through a maximum and then slightly decrease (C7-C12 hydrocarbons) with increase in temperature. The above trends clearly demonstrate the gradual breakdown of the polyethylene polymeric chains. Table 2 and Figure 5 show that the same trends, although in
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Shabtai et al.
Table 1. Composition of Products from DL of HDPE as a Function of Reaction Temperaturea temp convrn,b
wt % product distrbn,c wt % gas (C1-C4) liquid gasoline boiling range,c wt % C5-C12 liquid product distrbn,d wt % C5H12e (+C5H10)e C6H14 (+C6H12) C7H16 (+C7H14) C8H18 (+C8H16) C9H20 (+C9H18) C10H22 (+C10H20) C11H24 (+C11H22) C12H26 (+C12H24) C13+
420 °C
435 °C
450 °C
465 °C
82.5
98.9
100
100
7.2 92.8
11.9 88.1
21.6 78.4
39.8 60.2
42.7
58.0
63.0
53.2
4.6 5.5 6.8 7.3 6.3 5.9 5.0 4.6 54.0
7.5 8.7 10.2 10.8 9.0 7.9 6.3 5.4 34.2
10.6 11.8 13.0 13.5 11.1 8.7 6.6 5.0 19.7
19.1 17.4 14.3 12.2 9.3 7.5 5.0 3.5 11.7
a In each run were used 10.0 g of polyethylene feed and 0.20 g of SO42-/ZrO2 catalyst; initial H2 pressure was 1500 psig, and reaction time was 2.0 h. b Weight percent of feed converted into products. c Calculated in weight percent of total product. d Weight percent of liquid product. e All fractions of a given C number consist of mixtures of normal and branched paraffins, accompanied by some cycloparaffins and trace amounts of olefins.
Figure 4. Change in product composition from DL of HDPE as a function of reaction temperature (1500 psig of H2, 2 h, SO42-/ZrO2). Table 2. Composition of Products from DL of HDPE as a Function of Reaction Timea reaction time convrn,b
wt % product distrbn,c wt % gas (C1-C4) liquid gasoline boiling range,c wt % C5-C12 liquid product distrbn,d wt % C5H12e (+C5H10)e C6H14 (+C6H12) C7H16 (+C7H14) C8H18 (+C8H16) C9H20 (+C9H18) C10H22 (+C10H20) C11H24 (+C11H22) C12H26 (+C12H24) C13+
Figure 3. Change in gas product composition from DL of HDPE as a function of reaction temperature (1500 psig of H2, 2 h, SO42-/ZrO2).
a less pronounced manner, are observed for a series of runs on the change of product composition as a function of reaction time between 0.5 and 3.0 h. It should be noted that in this series of runs the catalyst concentration was reduced from 2.0 wt % (Table 1, footnote a) to 1.0 wt % (Table 2, footnote a). The effect of H2 pressure, in the range of 500-2000 psig, upon the product composition was relatively weaker in comparison with the temperature and time effects. Increase in H2 pressure from 500 to 1500 psig resulted in some increase in the yield of the gasoline (C5-C12) fraction and a corresponding decrease in the yield of the C13+ fraction. However, at H2 pressures
0.5 h
1.0 h
2.0 h
3.0 h
99.4
99.9
100
100
12.5 87.5
17.9 82.1
22.9 77.1
29.3 70.7
52.2
57.9
58.7
55.4
6.5 7.2 7.7 8.1 8.7 7.9 7.1 6.4 40.4
8.9 9.3 10.5 11.1 10.3 8.1 6.7 5.6 29.5
10.1 10.9 12.5 13.1 10.1 8.4 6.3 4.7 23.9
11.7 12.5 13.6 12.0 9.7 8.2 6.1 4.5 21.7
a In each run were used 10.0 g of polyethylene feed and 0.10 g of SO42-/ZrO2 catalyst; reaction temperature was 450 °C and initial H2 pressure was 1500 psig. b Weight percent of feed converted into products. c Calculated in weight percnet of total product. d Weight percent of liquid product. e All fractions of a given C number consist of mixtures of normal and branched paraffins, accompanied by some cycloparaffins and trace amounts of olefins.
above 1500 psig, the concentrations of the gasoline and C13+ fractions remained essentially unchanged. A comparison of HDPE conversions in the presence of different superacid catalysts indicated that the DL activities of the latter were in the order SO42-/ZrO2 > SO42-/Al2O3 > SO42-/Fe2O3. This was in agreement with a previous study on the relative acidities and dealkylation activities of these superacid catalysts.27,28 B. DL Reactions of Polypropylene. Table 3 summarizes results obtained on the change in product composition from SO42-/ZrO2-catalyzed DL of PPR as a function of reaction temperature between 380 and 450 °C, with other processing conditions kept constant
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Figure 5. Change in product composition from DL of HDPE as a function of reaction time (1500 psig of H2, 450 °C, SO42-/ ZrO2).
Figure 6. Change in product composition from DL of PPR as a function of reaction temperature (1500 psig of H2, 2 h, SO42-/ ZrO2).
(footnote a). It is found that at 380-400 °C the total conversion of the PPR feed is markedly higher than that of HDPE (
