Catalytic Coprocessing of Plastics with Coal and Petroleum Resid

Energy & Fuels 1996, 10, 603-611

603

Catalytic Coprocessing of Plastics with Coal and Petroleum Resid Using NiMo/Al2O3 Hyun Ku Joo and Christine W. Curtis* Chemical Engineering Department, Auburn University, Alabama 36849 Received November 29, 1995. Revised Manuscript Received February 21, 1996X

Coprocessing of waste plastics with coal and with petroleum resid was investigated to determine the effect of resid on reactivity and conversion. The coal used in this study was Blind Canyon bituminous coal, the resids were Maya and Manji, and the model plastics tested were polystyrene, poly(ethylene terephthalate) (PET), and low-density polyethylene (LDPE). Three systems, the individual species, binary combinations, and ternary combinations, were reacted at conditions of 430 °C and 8.7 MPa of H2 introduced at ambient temperature for 60 min of reaction time. Presulfided NiMo/Al2O3 was used as the catalyst, typically at 1 wt % loading, although other catalyst loading levels of 3 and 10 wt % were tested. Under these conditions polystyrene and PET reacted readily, while LDPE was difficult to convert. Binary reactions with resids resulted in high conversions of ∼94% from polystyrene and PET, while the reactions with LDPE yielded somewhat less conversion of ∼72%. By contrast, reactions of plastics with coal converted substantially less, ranging from 70.2% for polystyrene and coal to 39.9% for LDPE and coal. Ternary reactions with coal, plastic, and resid resulted in high conversions for all systems (∼8995%) except those with LDPE (∼77-81%). The effect of coprocessing binary and ternary systems compared to individual systems on the basis of conversion, hexane solubles, and gas productions was determined. The effect of adding a third species into the binary systems was also evaluated. The hexane-soluble products from the three reaction sets were analyzed by simulated distillation to determine the amount of the reaction product boiling at less than 500 °C. Reactions containing LDPE produced substantially less material that boiled below 500 °C than did the other reactions.

Introduction Waste plastics are an environmental problem because of their quantity, complexity in terms of having multiple polymers and mineral additives, and inherent stability.1 Waste plastics are petroleum-derived and, therefore, provide a hydrocarbon resource that can be used for chemical feedstocks or fuels. Waste plastics are currently being used as a feedstock for recycling back to the original monomer, as bulk plastic material for constructing various items, and as a fuel for incineration, the generated heat of which can be utilized as an energy source.2 Recycling waste plastics to the monomer can be accomplished for some plastic materials and has been applied to poly(ethylene terephthalate) (PET), in particular. Two chemical processes, methanolysis and glycolysis, have been developed to recover the PET monomer that can then be recycled into PET.3,4 However, recycling plastic materials to the monomer on a large scale requires separation and cleaning of the plastics prior to processing to obtain a single polymer and clean feedstock, which cause the process to be both difficult and expensive. Consequently, only a small amount (∼2%) of waste plastics is currently being recycled into monomers that can be used directly as recycled materials.5 * Author to whom correspondence should be addressed. X Abstract published in Advance ACS Abstracts, April 1, 1996. (1) Mildred, G. Fundamentals of Petroleum. Petroleum Extension Service, Division of Continuing Education, The University of Texas at Austin, 1986. (2) Anderson, L. L.; Tuntawiroon, W. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1993, 38 (4), 816-822. (3) Gollakota, S. Processing of Waste to Produce Fuels and Chemicals. Draft Report for the U.S. Department of Energy, Jan 1995. (4) Leaversuch, R. D. Mod. Plastics 1991, July, 40-43.

0887-0624/96/2510-0603$12.00/0

Utilizing municipal solid wastes as a resource rather than as garbage is only a logical stewardship of the earth’s natural and limited resources. Utilization requires that these hydrocarbon resources be tapped for their fuel values. Current efforts of chemical-process recycling or “tertiary recycling” have focused on three approaches:3,4 (1) refinery recycling that converts commingled plastics to hydrocarbons; (2) pyrolysis of plasticsrich solid waste and conversion of these wastes to oil fractions; and (3) liquefaction of commingled plastics to produce liquid fuels.6-16 Coprocessing plastics into a variety of fuels with other materials6-16 such as coal and/or heavy petroleum resid offers advantages such as having a stable feedstock supply not dependent on (5) Smith, R. A. Overview of Feedstock Recycling of Commingled Waste Plastics. Presented at the Ninth Annual Technical Meeting, Consortium for Fossil Fuel Liquefaction Science Pipestem, WV, Aug 15-18, 1995. (6) Miller, A. Chem. Ind. 1994, 8 (Jan 3). (7) Kaminsky, W.; Ro¨ssler, H., CHEMTECH 1992, Feb, 108-113. (8) Luo, M. S.; Curtis, C. W. Fuel Process. Technol. 1996, in press. (9) Luo, M. S.; Curtis, C. W. Fuel Process. Technol. 1996, in press. (10) Joo, H. K.; Curtis, C. W. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 643-647. (11) Huffman, G. P.; Feng, Z.; Mahajan, V.; Sivakumar, P.; Jung, H.; Tierney, J. W.; Wender, I. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 35-37. (12) Taghiei, M. M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Energy Fuels 1994, 1228-1232. (13) Taghiei, M. M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1993, 38 (4), 810-815. (14) Palmer, S. R.; Hippo, E. J.; Tandon, D.; Blankenship, M. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 29-33. (15) Xiao, X.; Zmierczak, W.; Shabtai, J. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 4-8. (16) Rothenberger, K.; Cugini, A. V.; Ciocco, M. V.; Anderson, R. R.; Veloski, G. A. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (11), 38-43.

© 1996 American Chemical Society

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individual county and township recycling efforts and supply. In addition, the coal mineral matter provides a surface for scavenging and depositing metals from the petroleum resid and waste plastics during coprocessing. Coal, the most abundant fossil fuel in the United States, also offers an alternative to petroleum processing. Coal can be liquefied directly but requires substantial amounts of hydrogen gas, a self-generated recycle solvent the quality of which must be maintained, and substantial processing to remove undesirable heteroatoms. Recent research has shown that the coprocessing of coal with heavy petroleum resid is a feasible technology for upgrading these two lower value materials simultaneously.17-23 Catalytic coprocessing yields high conversion and high-quality product slates even though the two feed materials have substantially different compositions. Coal and liquefied coal are highly aromatic in character, having aromatic fraction (fA) values of approximately 0.75, while petroleum resids have much higher aliphaticity but also contain some aromatics giving fA values of ∼0.35.18 Using petroleum resid as a solvent for coal in coprocessing offers the benefit of having an external solvent that is independent and does not have to be generated in situ. Coal offers resid the benefit of having mineral matter that provides a surface for the metals such as vanadium and nickel that are inherent in the resid and cause problems in terms of catalyst deactivation. However, processing waste plastics with coal is problematic and requires either multiple or multifunctional catalysts since the two materials are so compositionally diverse.8-10 The well-documented benefits of coal and petroleum resid coprocessing17-23 can be extended to providing a favorable reaction system for coprocessing waste plastics simultaneously with coal and petroleum resid. The petroleum resid, having a composition that includes both aromatic and aliphatic compounds, can serve as a compositional bridge between the waste plastics and coal. Veba’s coal liquefaction technology3,4 has been applied to the processing of waste plastics with heavy refinery residues to produce a synthetic crude oil. In the process, a vacuum petroleum residue is mixed with waste plastics and then is hydrogenated at 450-490 °C with a hydrogen partial pressure of 150-250 bar. A separation step that removes Cl impurities by additional hydrogenation follows. The objective of this study was to determine the feasibility of coprocessing three different materials together: coal, petroleum resid, and waste plastics. The effect of using the ternary combination of coal, resid, and plastic on the conversion of solids to tetrahydrofuran (THF) solubles and the product distribution in terms of solubility in THF, toluene, and hexane was determined and compared to that obtained in binary and (17) Curtis, C. W.; Hwang, J. S. Fuel Process. Technol. 1992, 30, 47-67. (18) Curtis, C. W.; Pass, M. C.; Guin, J. A.; Tsai, K. J. Fuel Sci. Technol. Intl. 1987, 5, 245-274. (19) Guin, J. A.; Curtis, C. W.; Tsai, K. J. Fuel Proc. Technol. 1986, 12 (III), 111-125. (20) Curtis, C. W.; Guin, J. A.; Tsai, K. J. Ind. Eng. Chem. Res. 1987, 26, 12-18. (21) Monnier, J. Canmet Report 84-E, March 1984. (22) Speight, J. G.; Mochopedis, S. E. Fuel Process. Technol. 1986, 13, 215. (23) Yan, T. Y.; Espenchied, W. F. Fuel Process. Technol. 1983, 7, 121-133.

Joo and Curtis

individual systems. In this study, coprocessing reactions were performed with Blind Canyon bituminous coal, Manji and Maya resids, and model plastics. The model plastics that were chosen included polystyrene (PS), low-density polyethylene (LDPE), and PET, which were selected because they represent a substantial portion of the waste plastics generated in the United States daily. Catalytic reactions were primarily performed using presulfided NiMo/Al2O3. The catalyst NiMo/Al2O3 was chosen for this study because it has been used frequently in coal liquefaction and coal resid coprocessing reactions.24,25 In addition, NiMo/Al2O3 was used as the catalyst in the waste plastics and waste tire coprocessing proof of concept run performed by HRI and sponsored by the Department of Energy.26-28 Liu and coworkers29 performed thermal gravimetric analysis to evaluate catalysts used in the coprocessing of waste plastics with coal. Their results also showed that hydrocracking catalysts such as NiMo/Al2O3 and SiO2/ Al2O3 showed potential in coprocessing waste plastics with coal because of their cracking and hydrogenation selectivities. Experimental Section Materials. The model plastic compounds, PS, LDPE, and PET, used in this study were obtained from Aldrich Chemical Co. and were used as received. The coal used was Blind Canyon bituminous coal (DECS-17) obtained from the Penn State Coal Sample Bank. The proximate analysis of the coal is 45% fixed carbon, 45% volatile matter, 6.3% ash, and 3.7% moisture. The ultimate analysis of the coal is 82.1% C, 6.2% H, 0.4% S, 1.4% N, and 0.12% Cl. The resids used were Manji and Maya obtained from Amoco. The analyses of the resids were 85.1% C, 10.8% H, 0.7% N, 2.6% S, 231 ppm V, 220 ppm Ni, and 23 ppm Fe for Manji and 84.1% C, 9.9% H, 0.7% N, 5.1% S, 550 ppm V, 100 ppm Ni, and 17 ppm Fe for Maya. The resids contained different amounts of asphaltenes: 25.2% for Maya and 5.2% for Manji. The NiMo/Al2O3 catalyst used in this study was composed of 2.72 wt % Ni and 13.16 wt % Mo and was presulfided externally to the reactor prior to use. The procedure for presulfiding NiMo/Al2O3 began with predrying NiMo/Al2O3 with N2 for 1 h at 300 °C. Then, a 10 vol % H2S/H2 gas mixture was flowed over the catalyst at 225 °C for 1 h, at 315 °C for 1 h, and at 370 °C for 2 h. The final step was flowing N2 at 370 °C over NiMo/Al2O3 for 1 h. The solvents used for extraction analyses were HPLC grade hexane, toluene, and THF from Fisher Scientific. Spectranalyzed grade carbon disulfide (CS2) from Fisher Scientific was the solvent of choice for simulated distillation of hexane solubles. A column resolution test mix, paraffin calibration mix, and gas oil mix from Supelco were used as calibration standards for simulated distillation. Reactions and Procedures. Reactions were performed using one, two, and three components to evaluate the reactivity and interactive effects among the reactants. Unless otherwise noted, all reactions were performed in 20 cm3 stainless steel tubular microreactors at 430 °C for 60 min with 8.3 MPa of H2 introduced at ambient temperature. The microreactors (24) Curtis, C. W.; Cassell, F. N. Energy Fuels 1988, 2, 1-8. (25) Pellegrino, J.; Curtis, C. W. Energy Fuels 1989, 3 (2), 160168. (26) U.S. Department of Energy Techline 2165, Sept 26, 1994. (27) Comolli, A. G.; Lee, T. L. K.; Pradhan, V. R.; Stalzer, R. H. ACS Fuel Chem. Div. Prepr. 1995, 40 (1), 82-86. (28) Robbins, G. A.; Winschel, R. A.; Burke, F. P. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 92-96. (29) Liu, K.; McClennen, W. H.; Meuzelaar, H. L. C. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40 (1), 9-16.

Catalytic Coprocessing of Plastics

Energy & Fuels, Vol. 10, No. 3, 1996 605

Table 1. Product Distributions and Conversions from Unreacted and Thermally Reacted Materiala product distributionb (%) reactants

gas

PS LDPE PET Manji Maya

0.0 0.0 0.0 0.0 0.0

coal Manji coal/LDPE coal/Manji coal/Manji/LDPE

HXs

TOLs

0.0 0.0 0.0 87.1 ( 0.4 63.0 ( 0.8

19.1 ( 0.6 11.6 ( 1.1 11.6 ( 0.1 9.8 ( 0.2 8.3 ( 0.1

THFs

IOM

Unreacted 21.0 14.1 1.4 3.1 0.7 0.7 12.9 ( 0.4 0.0 37.0 ( 0.8 0.0

64.9 95.5 98.6 0.0 0.0

Thermal Reactions 3.5 ( 0.5 6.2 ( 4.2 9.9 ( 0.6 4.9 ( 1.5 3.7 ( 0.4 4.0 ( 2.3 8.6 ( 0.4 11.8 ( 1.8 8.3 ( 0.0 5.8 ( 0.1

15.9 ( 1.1 71.0 ( 2.1 33.5 ( 2.1 56.9 ( 0.8 49.7 ( 0.3

55.5 ( 5.4 2.7 ( 0.1 47.2 ( 0.4 13.1 ( 3.3 28.0 ( 0.3

conversion (%) 35.1 4.5 1.4 100 100 44.6 ( 5.4 97.4 ( 0.2 52.8 ( 0.4 87.0 ( 3.3 72.0 ( 0.3

recovery (%) 112 104 104 103 101 98 85 92 84 93

a Coal ) Blind Canyon DECS-17, Manji and Maya resid. PS ) polystyrene; LDPE ) low-density polyethylene; PET ) poly(ethylene terephthalate). bGas ) gaseous product; HXs ) hexane solubles; TOLs ) toluene solubles, hexane insolubles, THFs ) THF solubles, toluene insolubles; IOM ) insoluble organic matter, calculated on an ash-free basis.

were agitated horizontally at 450 rpm in a heated fluidized sand bath and were immediately quenched in water after reaction. All reactions were charged with 3.5 g of reactants; for each individual reaction, 3.5 g of coal, resid, or polymer was charged; for binary reactions, resid to polymer and resid to coal ratios of 3:2 were used; and for ternary reactions, a coal to resid to polymer ratio of 2:3:2 was used. The coal was stored in a vacuum desiccator before being used. Reactions were performed thermally and catalytically using 1 wt % presulfided NiMo/Al2O3 powder on a total charge basis. All reactions were at least duplicated. Analysis. After the reaction, gaseous reaction products were determined by weighing the tubular microreactor before and after gaseous products were released; this fraction in the product distribution is called gas. The liquid and solid products were analyzed by solvent fractionation, fractionating the products by using a series of solvents. The fractions obtained were hexane-soluble materials (HXs); toluene-soluble, hexane-insoluble material (TOLs); THF-soluble, tolueneinsoluble material (THFs); and THF-insoluble material or insoluble organic matter (IOM), which is calculated on an ashfree basis. The masses of the gas, HX, TOL, and THF fractions were determined after the fractionating solvent was removed by rotary evaporation and the fractions were air-dried for 15 h. The weight percentage of each of these fractions was determined and then the percent of the HX fraction was determined by difference. The percentage of HXs is defined as 100 - (gas + TOLs + THFs + IOM). The solubility of the unreacted materials was also obtained using solvent fractionation and is given in Table 1. The recovery from these reactions was defined as

% recovery ) (g of output/g of input) × 100

(1)

Low recoveries for PS and PET resulted from volatile compounds being produced during reaction and being lost during the rotary evaporation of hexane. When rotary evaporation was performed at 25 °C with minimal vacuum, the PS reaction products were so volatile that 75% of the HX fraction was lost, while 67% was lost from PET HXs. The definition for conversion used in this study is the conversion of the total reactants of each reaction on a moistureand ash-free (maf) basis to THF-soluble material:

[

% conversion ) 1 -

]

g of IOMmaf × 100 (2) g of total chargedmaf

The coal is a solid at room temperature and is essentially insoluble in THF; the plastics are solids at room temperature and have various but limited solubilities in THF (as reported in Table 1), while resids are a semisolid at room temperature and are totally soluble in THF.

Effect of Catalyst Loading. The effect of catalyst loading was determined using binary and ternary systems. The reactions were performed using the reactor and conditions stated under Reactions and Procedures. The reactant loadings for the binary reactions were combinations of 1.0 g of coal, 1.0 g of polymer, and 1.5 g of resid. The ternary reactions contained 3.5 g of reactants in a 2:3:2 ratio of coal to resid to plastic. Solvent fractionation of the products gave the product distribution in terms of gas, HXs, TOLs, THFs, and IOM. Simulated Distillation. The boiling point range of the HX fractions from the different reactions was obtained by simulated distillation using ASTM Method D-2887 and a Varian 3700 gas chromatograph equipped with a DB-5 fused silica capillary column from J&W Scientific and an HP3396A integrator from Hewlett-Packard. The system was connected to a personal computer equipped with Peak9600 software to collect data from the integrator. Boiling point distribution data were calculated using Microsoft Excel software. The simulated distillation was performed by injecting 0.4 µL of the solutions of HX material dissolved in CS2 onto the column. Analysis of the simulated distillation was performed by calculating accumulated weight percentage of the sample versus the boiling point. The temperature program chosen for the simulated distillation started at an initial temperature of 50 °C that was held for 1 min and then increased at a rate of 17 °C/min to 330 °C and held at the final temperature for 15 min. The column resolution obtained using this column and conditions was 6.8 as calculated according to ASTM Method D-2887 and was in the acceptable range of 3-8. A calibration line relating the boiling point to the retention time was obtained using a calibration sample obtained from Supelco and is given by

bp (°C) ) 19.91953 × RT (min) + 55.03439

(3)

where bp is the boiling point and RT is the retention time. The R2 value for the calibration line was 0.999, and the reproducibility of the retention time was within 0.07 min and usually within 0.02 min. The calibration equation was evaluated using a gas oil mixture obtained from Supelco. The results obtained from this calibration curve were compared to that supplied from Supelco (Table 2). The accumulated weight percent difference for selected boiling points between the correspondent data points ranged from -4 to 5.8 wt %; the differences between the two samples tended to become larger as the boiling points increased. Recovery of the HX fraction from the column was calculated according to the following method. Reproducibility of the system was established by analyzing solutions of biphenyl in CS2 repeatedly. The areas obtained for biphenyl varied within (3.1%. Since linearity is required for the recovery calculation, the linearity of the chromatographic system was determined using biphenyl solutions with various concentrations. In

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Table 2. Validity Test of Calibration Curvea sample wt % RT (min) bp (°C) standard mixtureb 6.9

193

17.4

10.0

255

29.5

11.5

284

39.0

12.5

305

47.2

14.3

340

63.9

16.9

392

86.0

19.7

448

97.3

SIMDISc

diffd (wt %)

16.0 ( 0.18 15.1 ( 0.21 29.9 ( 0.01 29.0 ( 0.01 38.7 ( 0.10 38.2 ( 0.18 46.2 ( 0.16 45.6 ( 0.32 60.1 ( 0.28 60.1 ( 0.48 80.7 ( 0.35 80.2 ( 0.76 91.9 ( 0.25 91.7 ( 0.71

1.4 2.3 -0.4 0.5 0.3 0.8 1.0 1.6 3.8 3.8 5.3 5.8 5.4 5.6

a Curve equation: bp (°C) ) 19.91953 × RT (min) + 55.03439. Standard gas oil mixture and data from Supelco Co. The data shown were interpolated. c Data obtained from calibration curve. Performed twice on different days. d Standard mixture - SIMDIS.

b

Figure 1. Test of total area linearity with biphenyl solution concentration for simulated distillation. addition, two other compounds were tested, dodecane and hexadecane; their analysis was in agreement with that of biphenyl (Figure 1). An assumption was made that biphenyl eluted completely and, when area versus concentration was plotted, produced a line that represented 100% recovery. Lines of area versus concentration obtained from hexane solubles with lower slopes than that from biphenyl represented samples with less than 100% recovery. Therefore, the ratio of the sample slope to the biphenyl slope was considered to be the recovery of the sample:

% recovery )

slope of sample line × 100 slope of biphenyl line

(4)

Each sample was injected immediately after it had been prepared.

Results and Discussion Coprocessing of coal, waste plastics, and petroleum resid involves three materials of quite different compositions and liquefaction behavior under coprocessing conditions.8-10,17-19 Therefore, it is imperative to understand the behavior of each material individually and in binary combinations before the ternary reactions can be understood. In this study, the individual reactions were performed catalytically with presulfided NiMo/ Al2O3; their product distributions were determined and compared to those obtained without reaction and in the cases of coal and resid to thermal reactions. Since Luo

and Curtis8 have established the low thermal reactivity of these model plastics under similar reaction conditions, thermal reactions of plastics were not performed in this work. The product distributions for the unreacted plastics were determined at ambient temperature to establish a baseline for comparison with the product distributions obtained after reaction at coprocessing conditions (Table 1). The model plastics showed low solubility in THF at room temperature, ranging from 64.9% insoluble for polystyrene to 95.5 and 98.6% insoluble for LDPE and PET, respectively. By contrast, the resids were 100% soluble in THF at room temperature. Single-Component Reactions. Each component used in this study was reacted individually at catalytic reaction conditions that were equivalent to those used when the components were reacted in binary and ternary systems. The conversions and product distributions for all of the coprocessing reactions are given in Table 3. The conversions for the single-component reactions showed that both coal and LDPE yielded lower conversions than the others; their respective conversions to THFs were 43.6 and 65.3%. The other plastics, PET and PS, and both resids yielded high conversions, ranging from a low of 95.7% for PET to a high of 99.1% for PS. The product distributions of the three individual plastics reacted at 430 °C with presulfided NiMo/Al2O3 were quite different. Although PS and PET both yielded high and similar conversions, the gas produced from PET was substantially higher, yielding 25.9% compared to 2.7% for PS. The products produced from the conversion of the plastics were primarily in the lighter fractions of gas or HXs. Very small amounts of TOL and THF materials were produced from either PET or PS. The 95.3% yield of HXs from PS was the highest obtained; however, these HX materials were very volatile, as shown by their low recovery which was discussed under Experimental Section. One of the primary reasons that the HXs were obtained by difference was that reactions that produce very volatile components tend to have high losses from the HX fraction, which contains most of the volatile components, during product workup. Since the gases are determined by mass difference in the reactor before and after the gases are released from the reactor, the error in gas recovery was usually small. In addition, the gas amount in most of the reactions except for PET was small and contributed little to the overall material balance. The other fractions, TOLs, THFs, and IOM, were solids at ambient temperature, had few volatiles, and were easily weighed. The catalytic reaction of the resids changed the composition of the resid slightly, producing a small amount of the heavier fractions, IOM and THF material, that were not present in the original resid. The majority of the products was HXs, although the amounts produced were slightly less than in the original resids. Under these catalytic conditions, ∼6.0-8.0% gas was produced from the resids so that the total amount of HXs and gas produced was less than that from the unreacted Manji HXs and higher than the unreacted Maya HXs. Hence, at 430 °C and with presulfided NiMo/Al2O3 as catalyst, Maya resid was upgraded, but Manji resid was not. Binary Systems. Reactions containing binary combinations of the coal, resid, and plastics used in this



Table 3. Product Distributions and Conversions from Catalytic Coprocessing Reactions of Coal, Resid, and Plastica reaction combination

gas

product distributionb (%) HXs TOLs THFs

IOM

conversion (%)

recovery (%)

PS LDPE PET coal Manji Maya

2.7 ( 0.1 6.2 ( 0.2 25.9 ( 0.3 10.9 ( 0.1 6.3 ( 0.3 7.7 ( 0.1

95.3 ( 0.1 48.7 ( 0.1 57.6 ( 1.4 19.2 ( 1.3 77.8 ( 2.3 65.4 ( 0.6

Single Component 0.6 ( 0.0 0.5 ( 0.0 2.3 ( 0.2 8.2 ( 0.9 2.9 ( 0.2 9.3 ( 0.0 1.1 ( 0.3 12.3 ( 2.4 8.8 ( 1.6 5.8 ( 0.5 16.3 ( 0.6 7.1 ( 0.4

0.9 ( 0.0 34.8 ( 1.5 4.4 ( 1.3 56.5 ( 4.0 1.4 ( 0.0 3.7 ( 0.1

99.1 ( 0.0 65.3 ( 1.5 95.7 ( 1.3 43.6 ( 4.0 98.6 ( 0.0 96.3 ( 0.1

20.6 ( 0.1 98.3 ( 2.3 75.4 ( 1.8 93.6 ( 3.6 92.6 ( 1.6 98.3 ( 1.2

coal/Manji coal/Maya coal/PS coal/LDPE coal/PET Manji/PS Manji/LDPE Manji/PET Maya/PS Maya/LDPE Maya/PET

8.2 ( 0.4 8.7 ( 0.4 6.2 ( 0.0 6.7 ( 0.4 20.0 ( 0.6 5.1 ( 0.1 5.9 ( 0.1 16.8 ( 0.6 5.2 ( 0.1 7.0 ( 0.2 16.5 ( 0.3

59.1 ( 3.8 49.2 ( 1.6 53.2 ( 5.2 24.4 ( 2.3 36.3 ( 0.5 84.5 ( 2.8 57.1 ( 1.8 72.3 ( 0.4 80.5 ( 0.7 54.2 ( 1.1 67.0 ( 0.1

Two Components 11.8 ( 0.6 15.0 ( 1.4 13.4 ( 1.8 21.8 ( 4.0 1.6 ( 0.7 9.3 ( 1.4 3.1 ( 0.3 5.8 ( 3.9 1.7 ( 0.4 3.1 ( 1.1 6.5 ( 0.6 2.2 ( 0.7 6.8 ( 1.1 3.7 ( 0.6 5.7 ( 0.8 2.2 ( 0.0 7.8 ( 0.9 2.9 ( 0.3 7.7 ( 1.3 3.0 ( 0.6 7.4 ( 0.0 3.9 ( 0.3

6.0 ( 1.4 7.0 ( 0.7 29.9 ( 4.5 60.1 ( 1.7 39.1 ( 1.6 1.9 ( 1.6 26.6 ( 0.1 3.2 ( 0.1 3.9 ( 0.6 28.3 ( 0.6 5.3 ( 0.2

94.0 ( 1.4 93.0 ( 0.7 70.2 ( 4.5 39.9 ( 1.7 61.0 ( 1.6 98.2 ( 1.6 73.5 ( 0.1 96.8 ( 0.1 96.2 ( 0.6 71.7 ( 0.6 94.8 ( 0.2

93.1 ( 4.5 99.4 ( 2.2 60.2 ( 2.8 95.4 ( 3.0 70.9 ( 2.1 60.3 ( 2.7 92.2 ( 3.0 63.0 ( 4.7 53.7 ( 4.9 92.7 ( 0.0 62.9 ( 1.0

coal/Maya/PS coal/Maya/LDPE coal/Maya/PET coal/Manji/PS coal/Manji/LDPE coal/Manji/PET

7.7 ( 0.4 9.0 ( 1.8 16.9 ( 1.5 6.6 ( 0.4 9.4 ( 1.9 14.9 ( 0.1

69.2 ( 0.8 52.9 ( 2.1 55.9 ( 2.5 75.5 ( 1.7 57.2 ( 1.1 61.6 ( 0.6

Three Components 9.4 ( 0.5 5.9 ( 0.1 9.1 ( 0.0 5.7 ( 0.1 7.5 ( 0.0 6.8 ( 0.1 7.5 ( 0.4 6.6 ( 0.2 9.1 ( 0.6 5.0 ( 0.0 7.1 ( 0.4 7.0 ( 0.0

8.0 ( 0.9 23.4 ( 0.4 13.0 ( 0.9 5.2 ( 1.6 19.4 ( 0.3 10.1 ( 1.1

92.1 ( 0.9 76.7 ( 0.4 87.1 ( 0.9 94.8 ( 1.6 80.6 ( 0.3 89.9 ( 1.1

66 ( 1.4 90 ( 2.1 74 ( 0.8 62 ( 1.1 88 ( 1.0 71 ( 1.8

a Reaction conditions: 430 °C; 8.3 MPa of H introduced at ambient temperature; 60 min 1 wt % presulfided NiMo/Al O ; 3.5 g loading 2 2 3 of individual components; 3.5 g loading of binary systems with a loading ratio of 3:2 for resid to polymer and resid to coal; 3.5 g loading of ternary system with a loading ratio of 2:3:2 of coal to resid to polymer. Blind Canyon DECS-17 coal; Maya and Manji resids. b Gas ) gaseous product; HXs ) hexane solubles; TOLs ) toluene solubles, hexane insolubles, THFs ) THF solubles, toluene insolubles; IOM ) insoluble organic matter calculated on an ash-free basis.

Figure 2. Conversion and hexane solubles from coprocessing plastics with coal and resid.

study were performed, and the conversions and product distributions were obtained as shown in Table 3 and Figure 2. High conversions of 93-98.2% were obtained for the binary combinations of coal plus resid and resid plus polymer, except for conversions of the two resids with LDPE. Manji and LDPE yielded a conversion of 73.5%, while Maya and LDPE yielded a slightly lower conversion of 71.7%. This conversion difference between systems containing two resids in combination with either plastic and/or coal was typical and indicative of the differences between the chemistry and composition of the two resids. The binary combinations of coal and

plastics yielded much lower conversions, which ranged from 39.9 to 70.2%, indicating that plastics and coal did not provide a mutually beneficial solvating medium. The lowest conversion of 39.9% was attributed to the coal/ LDPE system. In all of the binary reactions, LDPE was the most difficult plastic to convert to THF material; this result was in agreement with previous research performed in this laboratory.8,9 The product distributions obtained from the different binary systems showed some common behavior for the reactions containing plastics with either coal or resid. The largest fraction was the HXs, while the TOL and

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Table 4. Coprocessing Effect Factors from Catalytic Coprocessing Reactions of Coal, Resid, and Plastic Using Individual Component Reactions for Comparisona reaction combination coal/Manji coal/Maya coal/PS coal/LDPE coal/PET Manji/PS Manji/LDPE Manji/PET Maya/PS Maya/LDPE Maya/PET coal/Manji/PS coal/Manji/LDPE coal/Manji/PET coal/Maya/PS coal/Maya/LDPE coal/Maya/PET a

coprocessing effect factor (fi) gas HXs conversion Two Components 0.7 8.7 -3.1 4.9 -8.8 -7.1 -21.6 -28.1 8.7 -5.5 4.9 -0.4 -5.8 -13.7 18.8 3.7 -8.8 4.1 -1.4 -7.7 10.1 7.6

22.7 23.6 -1.6 -26.7 -12.4 -0.6 -13.8 -0.7 -1.3 -14.5 -1.3

Three Components 0.2 14.3 23.9 8.5 12.8 11.4 7.2 13.9 9.9 11.5 22.3 11.9

14.2 9.9 9.6 12.3 6.0 7.4

Data used in calculations were obtained from Table 3.

THF fractions were small. For the resid and plastic systems, the TOL fraction was larger than the THFs and ranged from 5.7 to 7.8%. The coal and plastics systems showed the opposite result, with the THF fraction being the larger of the two fractions ranging from 3.1 to 9.3%. These differences in production of the heavier fractions directly reflected the compositions of the starting materials, with resid being a hexane-soluble liquid and coal being a THF-insoluble solid before reaction. In all of the binary reactions with plastics, PET gave the highest yields of gases, which ranged from 16.5 to 20.0%; this amount was lower than that obtained (25.9%) from the individual PET reaction. The effect of coprocessing two or more components on the conversions and product distributions is dependent on the chemistry of the systems and may either be beneficial or detrimental depending upon the chemical compatibility and reactivity of the systems. A parameter, termed the coprocessing effect factor (fi), was defined to evaluate the effect of combining two materials rather than reacting them individually. The three coprocessing effect factors that were evaluated were conversion, HXs, and gas coprocessing effect. The equation that defines the coprocessing effect parameter is

fi ) [(%CPi - %HMi)/%HMi] × 100

(5)

where i is either gas, HXs, or conversion, HM is the hypothetical mean, and CP is the coprocessing result. The hypothetical mean is defined for the binary system as the weighted average for either conversion, gas, or HX yields from the individual reactions of the two components used in the binary reaction. The coprocessing effect factors obtained for conversion, gas, and HXs measured the compatibilities and reactivities of the different systems by determining whether higher yields were obtained in the binary coprocessing reactions or in the individual reactions. The coprocessing effect factors for binary reactions are presented in Table 4. The reactions of coal and resid showed positive coprocessing effect factors for HXs and conversion, which means that more HX material was

produced and more conversion occurred when coal and resid were coprocessed than when they were reacted individually. The conversion coprocessing factors were 22.7 and 23.6 for coal plus Manji and coal plus Maya, respectively; since resid yielded nearly 100% conversion individually but coal only yielded ∼44%, the increase most likely was caused by increased coal conversion in the coprocessing reaction. The resid provided an effective solvent for coal and allowed the catalyst to be more effective by providing a better dispersing medium. Similarly, the increases in the hexane solubles during coprocessing were most likely produced from coal. The coprocessing effect factor for gas products was negative for coal and Maya but slightly positive for coal and Manji. Binary systems of resids and plastics yielded negative conversion coprocessing effects, although the reactions of PS and PET with each resid gave values that were close to zero. The combination of Manji and Maya with LDPE gave negative conversion coprocessing effects of -13.8 and -14.5, respectively, showing that less conversion was achieved when these materials were coprocessed than when reacted individually. In these binary reactions LDPE most likely did not convert as well as when LDPE was reacted separately. The HX coprocessing effect for the resid and plastics combination gave much larger differences among the different systems. For Manji, LDPE gave a large negative HX factor, while that for PS was near zero and for PET was positive. Similar results were obtained with Maya except that the factors for both PS and PET were positive. The gas coprocessing effect factor varied with the combination but was always positive with PET, indicating that more gas was produced when PET was coprocessed with resid than when reacted separately. The coprocessing effect for the binary coal and plastic systems yielded negative values for all three parameters except for the gas coprocessing effect for coal and PET. The largest negative values were obtained when coal was reacted with LDPE, showing that the two materials were incompatible and that neither material provided an environment for the other that was conducive to their mutual reactivity. Ternary Systems. Two sets of ternary systems were reacted: Manji resid with coal and the three model plastics and Maya resid with coal and the three model plastics. The reactions containing PS and PET produced high conversions and HX yields, while the reactions with LDPE produced lesser conversions and HX yields (Figure 2). To determine the effect of coreacting all three materials of such different compositions, the coprocessing effect factors for the ternary systems were calculated two ways. The first method of calculation shown in Table 4 used the hypothetical mean of the individual reactions; the ratio of the components in the ternary system was used to weight the various terms. The second method of calculating the hypothetical mean was to use the results of reactions of a single-component system and a binary system to calculate the hypothetical means as shown in Table 5. In these calculations, the reactants involved were weighted according to the relative amount of each material in the ternary systems. The effect of adding a given component to a binary system was evaluated. The results from the coprocessing effect factor using the first method showed that the conversion, gas, and



Table 5. Coprocessing Effect Factors from Catalytic Coprocessing Reactions of Coal, Resid, and Plastic Using Combinations of Individual and Binary Component Reactions for Comparisona reaction combination

gas

coprocessing effect factor (fi) HXs conversion

/(Manji/PS) /(Manji/LDPE) /(Manji/PET) /(Maya/PS) /(Maya/LDPE) /(Maya/PET)

Coal/(Resid/Polymer) -2.3 14.7 28.3 23.6 -1.4 7.8 12.8 9.9 10.9 19.7 13.4 4.8

14.8 24.1 10.2 13.5 20.5 8.6

/(coal/PS) /(coal/LDPE) /(coal/PET)

Manji/(Coal/Polymer) 5.7 18.4 44.0 21.0 5.5 13.9

15.1 23.9 16.6

/(coal/PS) /(coal/LDPE) /(coal/PET)

Maya/(Coal/Polymer) 12.5 18.4 26.3 26.0 14.7 14.6

13.2 19.7 14.4

/(coal/Manji) /(coal/Maya)

PS/(Coal/Resid) 0.1 8.7 10.2 10.9

-0.7 -5.1


LDPE/(Coal/Resid) 23.2 1.9 12.7 7.8

-6.1 -9.9


PET/(Coal/Resid) 12.4 5.0 24.1 8.3

-4.9 -7.1

a

Data used in calculation are given in Table 3.

HX coprocessing factors for both sets of ternary systems were positive. Therefore, compared to the individual reactions, coprocessing the ternary systems produced higher conversion and yields of HXs and gases. The effect of adding either coal, resid, or plastic to the binary systems was evaluated by using the second calculational method, which compared the coprocessing effect factor values to the hypothetical mean values calculated from binary and individual systems (Table 5). When coal was added to the resid/plastic systems as shown in Table 5, all of the coprocessing effect factors were positive for conversion, HXs, and gas except for the gas value for the Manji/PS and Manji/PET systems. These results showed that the addition of coal to the resid/plastic system increased the amount of solid material being converted to THFs and HXs. The amount of gas produced also increased with the exceptions already noted. When resid, either Manji or Maya, was added to a coal/polymer system, the coprocessing

effect factors were positive for conversion, gas, and HXs for all three plastic systems, indicating that the addition of resid positively affected the reactions occurring in the binary systems. The introduction of plastics into the coal/resid systems resulted in negative values for conversion coprocessing effect factor, indicating that the compatibility and reactivity of the systems decreased, resulting in less conversion to THF material when any of the plastics were added. By contrast, the HX coprocessing effect for all of the reactions was positive, suggesting that when the plastic converted, HX material was produced. All of the coprocessing effect gas values were positive, producing more gas when the plastic was added to the coal/resid systems than in the reference reactions. Effect of Catalyst Loading. The effect of catalyst loading on the conversion and product distributions obtained from binary and ternary coprocessing reactions containing LDPE was evaluated. These LDPE reactions were focused upon because of the lower conversions and HX production obtained in the reactions containing 1 wt % NiMo/Al2O3 (Table 3). As shown in Table 6, increasing the catalyst loading to 3 and 10 wt % on a total reactant basis from the 1 wt % that was used in the previously discussed reactions had little effect on the conversions and HX yields obtained in the binary and ternary reactions. A slight increase in the conversion and HX production was observed with the 3 wt % loading in the coal/LDPE system; however, none of the other systems showed any increase with the higher catalyst loadings. At these reaction conditions, the thermal reaction predominated in the reactions involving coal conversion; however, the catalytic reaction increased the amount of hexane solubles produced. These results are evident when the product distributions from the catalytic reactions in Table 6 are compared to those of the thermal reactions in Table 1. Analysis of Hexane-Soluble Fractions by Simulated Distillation. Simulated distillation was performed using the HX products produced in the single, binary, and ternary reactions. The HX fraction was chosen because it is the predominant product fraction in all of these reactions. Two sets of data were obtained from the simulated distillation analyses: (1) accumulated weight percent versus boiling point and (2) recovery of the HX fraction. The boiling point curves obtained ranged from the initial boiling points of 60100 °C to final boiling points that were typically in the

Table 6. Effect of Catalyst Loading on the Product Distributions and Conversions Obtained in Coprocessing Reactions Containing LDPEa reactants

catalyst loadingb (%)

gas

coal/LDPE coal/LDPE coal/LDPE Manji/LDPE Manji/LDPE Maya/LDPE Maya/LDPE coal/Manji/LDPE coal/Manji/LDPE coal/Manji/LDPE

1 3 10 1 3 1 3 1 3 10

11.6 ( 1.0 10.7 ( 0.4 10.1 ( 0.4 9.0 ( 0.3 8.3 ( 0.1 9.5 ( 0.2 9.2 ( 0.1 9.4 ( 1.9 6.9 ( 0.1 6.0 ( 0.1

product distributionc (%) HXs TOLs THFs 30.1 ( 2.8 36.1 ( 1.8 33.6 ( 3.0 63.5 ( 0.9 61.0 ( 1.5 58.0 ( 2.0 57.4 ( 0.5 57.2 ( 1.1 60.7 ( 1.1 56.9 ( 3.5

4.6 ( 0.1 3.5 ( 0.2 4.5 ( 0.9 5.7 ( 0.8 4.1 ( 0.1 7.5 ( 0.8 6.9 ( 0.9 9.1 ( 0.6 8.4 ( 0.3 8.0 ( 1.2

1.6 ( 0.1 3.8 ( 1.3 4.1 ( 1.4 2.8 ( 0.1 2.2 ( 1.3 2.5 ( 0.8 3.2 ( 0.6 5.0 ( 0.0 4.7 ( 0.6 3.1 ( 0.1

IOM

conversion (%)

recovery (%)

52.3 ( 1.8 46.0 ( 2.6 47.8 ( 2.1 19.1 ( 0.0 24.5 ( 0.1 22.7 ( 2.2 23.5 ( 0.4 19.4 ( 0.3 19.4 ( 0.6 26.2 ( 2.3

47.7 ( 1.8 54.1 ( 2.6 52.3 ( 2.1 80.9 ( 0.0 75.5 ( 0.1 77.4 ( 2.2 76.6 ( 0.4 80.6 ( 0.3 80.7 ( 0.6 73.9 ( 2.3

95 90 88 89 93 90 90 88 88 94

a Reaction conditions: 430 °C, 8.3 MPa of H introduced at ambient temperature, 60 min, presulfided NiMo/Al O catalyst. Reactant 2 2 3 loadings: 1 g of coal, 1 g of polymer, 1.5 g of resid. Blind Canyon DECS-17 coal, Maya and Manji resids. b Catalyts loading: 1, 3, or 10 wt % NiMo/Al2O3 on the basis of total feedstock. c gas ) gaseous products; HXs ) hexane solubles; TOLs ) toluene solubles, hexane insolubles; THFs ) THF solubles, TOL insolubles; IOM ) insoluble organic matter, which is calculated on an ash-free basis.

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Figure 3. Boiling point distributions of hexane solubles from ternary coprocessing systems.

range of 600 °C for ternary systems (Figure 3). The recoveries from the simulated distillations were determined to estimate the amount of materials boiling at greater than 500 °C in the HX fractions and in the total product, assuming that all material boiling at less than 500 °C was contained in the HX fraction. The data obtained for the total recovery, the weight percent of the observed sample boiling at less than 500 °C, and the calculated values for the amount of HX material and the entire reaction product boiling at less than 500 °C are given in Table 7. For single-component systems containing resids or model plastics, 65-75% total recovery of the HX fraction was achieved, while for coal 90% recovery of the HXs was obtained. The recoveries in binary systems ranged from ∼64 to 82% and in ternary systems from ∼77 to 90%. The reaction systems

that contained LDPE had 5-10% less recovery of material boiling at less than 500 °C than systems containing either PS or PET. The latter two systems yielded similar recoveries. PS produced the lightest material when reacted alone or with coal, resid, or both. Two quantities were calculated from these data: (1) weight percent of HXs boiling at less than 500 °C, which is calculated by multiplying the recovery from simulated distillation by the weight percent boiling at less than 500 °C in the HX fraction; and (2) weight percent of total sample boiling at less than 500 °C, which is calculated by multiplying the weight percent of HXs boiling at less than 500 °C by the weight percent of HXs in the product distribution. As given in Table 7, the weight percent of the HXs from individual components boiling at less than 500 °C showed that PS yielded the highest value of 63.6%, while the other two plastic resids yielded values that ranged from 41.4 to 49.7%. The coal’s HX fraction was quite light, with 70% boiling at below 500 °C. However, calculation of the total weight percent of the sample that boiled at below 500 °C, assuming that all of those components were contained in the HX fraction, showed that only PS produced a substantial portion of less than 500 °C boiling material. When the materials were coprocessed in binary and ternary mixtures, the reactions with PS produced the largest amount of the lower boiling material in each reaction set. PET produced an intermediate amount, while LDPE consistently produced the least. The boiling point distributions obtained in the reactions corresponded to the conversion and solvent fractionation data previously discussed. Summary and Conclusions The coprocessing of waste plastics with coal and resid is a feasible process by which to convert coal and waste plastic materials simultaneously to liquefied products and to upgrade both the resid and liquefied products.

Table 7. Amount of Hexane Solubles and Total Sample Boiling at Less than 500 °C amt of total sample based on HXs boiling at

Catalytic Coprocessing of Plastics with Coal and Petroleum Resid

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