Effect of reaction parameters and catalyst type on waste plastics liquefaction and coprocessing with coal

FUEL PROCESSING TECHNOLOGY Fuel Processing Technology 49 ( 1996) 177- 196

Effect of reaction parameters and catalyst type on waste plastics liquefaction and coprocessing with coal Mingsheng Luo, Christine W. Curtis

*

Chemical Engineering Department Auburn University, Auburn, AL 36849, USA

Received 15 October 1995;accepted 17 April 19%

Abstract

The effect of reaction conditions and catalyst type on the liquefaction behavior of model waste plastics and on the coprocessing of model waste plastics with coal was evaluated. Individual model plastics and mixtures of these plastics were catalytically reacted at temperatures of 400 to 440 “C with an initial Hz pressure of 5.6 MPa using fluid catalytic cracking catalysts and a zeolite HZSMJ. Higher conversions to tetrahydrofuran-soluble material were achieved in the reactions of individual model plastics than in the reaction with various mixtures of model plastics, while higher hexane soluble yields and lower gas yields were obtained with the mixtures. A base plastics mixture composed of 50% high density polyethylene (HDPE), 30% polyethylene terephthalate (PET), and 20% polystyrene (PSI was used to evaluate the effect of reaction time and initial H, pressure on the conversions and product distributions achieved. Reaction times of 120 min produced high and similar conversions and product distributions from HZSM-5 and two fluid catalytic cracking catalysts; however, the differences in the three catalysts’ activities were much larger for converting the plastics at shorter reaction times of 30 and 60 min. The highest conversion of the base plastics mixture occurred when the initial Hz pressure was low. Addition of aromatic, hydroaromatic, cycloalkane, and straight chain aliphatic solvents to the base plastics mixture influenced the conversion and product distribution obtained. For all three catalysts, the straight chain aliphatic solvents were the most effective for solvating the cracked polymer products and promoting higher conversions. Coprocessing reactions of the base plastics mixture with coal yielded the highest conversion when they were reacted catalytically without a solvent.

’ Correspondingauthor. 03783820/%/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. P/I SO378-3820(96)01039-9

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Introduction of a solvent required higher severity conditions reactions without solvent. Keywords: Coal/waste plastics copmessing;

to achieve equivalent conversions

Hydrocracking/crackig

as

catalysts; Waste plastics liquefaction

1. Introduction Post-consumer plastics simultaneously pose a problem of disposal and an opportunity for utilization of a valuable hydrocarbon resource. Legislation in Europe and public awareness in the United States of the hydrocarbon resource that waste plastics provide have resulted in more efforts being expended to develop methods for recovering hydrocarbons from the waste plastics. These hydrocarbons are being recovered as either monomers or chemical feedstocks or fuels. [l-7]. To produce any of those products from waste plastics requires that the polymers be broken down into lower molecular weight products. Research has been performed that evaluated the types of products that are produced from the thermal decomposition of a variety of polymeric materials. Thermal decomposition of polypropylene (PP) at temperatures of 360 to 400 “C (633 to 673 K) ranged from C, to C, hydrocarbons [8]. Seeger and Gritter [9] evaluated the thermal decomposition and volatilization of poly-(o-olefins) at temperatures as high as 780 “C. The researchers determined that main chain scission was a random process for the poly-(oolefins) but not for polystyrene (PS). The products obtained for PS showed that trimers were the upper size limit while for polyethylene (PE) there was no size limit. Thermogravimetric analysis by Davis et al. [lo] showed that the propensity of the different polymers to decompose decreased according to the series polyisobutadiene > low density polyethylene (LDPE) > polypropylene (PP) > high density polyethylene (HDPE). Processes have been described in the patent literature to convert waste plastics mixtures into chemical feedstocks or fuels. Coenen and Hagan [ 111 reacted pulverized PE, PP, and tire mixtures at 150 to 500 “C (423 to 773 K) and 20 to 30 bars (2 to 3 MPa) with a 1O:l solvent to waste material charge. Aromatics or the recycled solvent generated from the process or water was used as a solvent. The products obtained from this process had a boiling point range of 20 to 350 “C (293 to 623 K) and were composed of C, to C,, alkanes, aromatics, and cycloalkanes. A catalytic process using slurry phase molybdenum catalysts was developed that converted municipal waste containing less than 25% HDPE into crude synthetic crude oil at reaction conditions of 350 to 450 “C (623 to 723 K), an inert atmosphere of 750 to 3000 psig (5.2 to 20.7 MPa), and 30 to 240 min reaction time [ 121. Pyrolysis of a mixture of 50% polyvinyl chloride (PVC), 30% PS, and 20% PE and PP performed at 500 “C with an inert atmosphere [13] produced benzene and HCI from PVC at 500 “C; paraffins containing up to 50 carbon atoms from PE at temperatures of 387 to 437 “C; and styrene from PS at temperatures between 427 and 727 “C. Other researchers [14] have described the catalytic cracking of wastes composed of 50% PVC, 30% PS, and 20% PP, PE and other thermoplastics in a refractory petroleum medium. The catalyst used for this work was a fluid catalytic cracking catalyst that had pretreated at 900 to 950 “F for 1 h before use.

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119

Recent research has investigated the conversion of plastics. Ng [51 has evaluated the conversion of PE blended with VGO to transportation fuels by catalytic cracking. Blends of 5 and 10 wt.% HDPE in VGO were used in a fixed bed reactor at 510 “C and 20 hh’ WHSV. Thermal cracking of HDPE resulted in conversion of the polymer but yielded low conversion to gasoline and a substantial production of coke. Catalytic cracking resulted in higher gasoline yields particularly when 10% HDPE was used. Ng [6] also investigated the conversion of PE to transportation fuels through pyrolysis and catalytic cracking. In the closed system, thermal cracking of PE at increased temperatures resulted in higher yields of gas, distillate and coke. Thermal cracking in an open reaction system resulted in less naphtha but more gas oil. Pyrolytic waxy products from PE were cracked at 470 to 510 “C (743 to 783 K) and produced high yields of gasoline and LPG. Researchers have been investigating fluidized bed pyrolysis for organic waste stream and have applied the technology to cracking waste polymer streams [7]. Unused PE pellets were pyrolyzed in N, at varying reaction temperatures. Below 600 “C the BTX-aromatic production decreased and wax production increased. A mixture of HDPE, LDPE, and PP (40%) produced a light faction approaching 60% at 510 “C compared to 37% for the PEs and 63% for PP. Waste plastics processing is also being actively pursued in Europe and Japan [1,2]. Feedstock recycling of plastics began in Germany. Veba has one of the most widely known processes because it is based on the Bergius-Pier hydrogenation technology for liquefying coal to liquid fuels. The plant, located in Bottrop, has a feed preparation unit which depolymerizes and liquefies the plastics that are then fed into the hydrogenation unit with a petroleum vacuum residue. A consortium of European chemical companies has been depolymerizing plastics (PE, PP, PS, PET, and PVC) to form chemical feedstocks by breaking down the polymers into small hydrocarbons or CO and H, that can be utilized as chemical feedstock [1,2]. Shell Chemical Company has developed an alternate method for processing waste plastics which first converts a waste plastics mixture into an oily feed that can be fed directly into a petroleum refinery. BASF is utilizing post-consumer plastics as a petroleum feedstock. The Japanese are pursuing pyrolysis as the process to convert waste plastics to fuels and chemical feedstocks [2]. The Fuji Recycle industry developed a process in which plastics like PP, PE and other polyolefin plastics are pulverized, extruded, mixed, thermally degraded, and then gasified. The gases produced are then fed through a catalytic cracker using a zeolite catalyst which produces gasoline as the primary product and kerosene and fuel oil as secondary products. In the United States, Conrad Industries working in conjunction with the American Plastics Council is operating a pilot-scale facility where waste plastics are pyrolyzed in the absence of oxygen to produce gaseous products which are then condensed to liquids which are used as refinery feeds [1,2]. Battelle Memorial Institute has also developed a pyrolysis process in which a commingled waste stream consisting of LDPE, HDPE, PS, and PVC is pyrolyzed to produce a gas consisting of light hydrocarbons and H, 121. Similarly, Wayne Technology Corporation commercialized a 50 ton per day process that pyrolyzes PE, PP, and PS to produce No. 2 fuel oil as its primary product. Chevron has used waste plastics as coker feed and produced a high quality product slate of nearly 90% liquids which are primarily naphthas, while Amoco has used mixed plastics as a

180

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Processing Technology 49 (1996) 177-196

refinery feed. The feasibility of gasifying waste plastics including PVC to H, and CO has been demonstrated by Texaco in highly efficient 25 ton per day tests, yielding conversions of more than 99%. The coprocessing of waste plastics with coal [15-251 to produce fuels or chemical feedstocks is currently being investigated as a means of effectively utilizing waste plastics in a process that is not solely dependent on waste plastics as the feed. Utilizing coal, an abundant natural resource in the United States, as a cofeed with waste plastics offers several advantages including the certainty of feed supply to balance the variability in the waste plastics feed supply. In addition, coprocessing with coal provides the potential for removing the fillers and other minerals present in plastics effectively by providing them with a solid surface from the coal ash for deposition. Recent research in coprocessing of coal with waste plastics has been discussed by Luo and Curtis [25]. The feasibility of coprocessing coal with polymers is much greater for single polymers like polyisoprene (PISO) and PS than for PE [25]. Mixtures of plastics offer additional challenges because the reaction conditions and catalysts may not be optimal for all of the polymers present in the waste plastics stream. The objective of this research was to evaluate the parameters affecting liquefaction of waste plastics and coprocessing of coal with waste plastics. Parameters such as catalyst loading, reaction temperature, effect of different plastic combinations, type of solvent, reaction time, and initial H, pressure were evaluated in terms of the product distribution obtained by solvent fractionation and conversion of the solid plastic to THF soluble materials. A base plastics mixture of 50% HDPE, 30% PET, and 20% PS was used in most of the reactions. In some reactions other plastics were added including additional amounts of the plastics present in the base mixture as well as PP and LDPE. Variables of reaction time and initial H, pressure were evaluated to determine their effect on the base plastics conversion. In addition, the base plastics mixture and coal were coprocessed with and without an added solvent. The product distribution and the conversion of solids to THF soluble material were determined. These values from the coprocessing reactions were compared to hypothetical mean values obtained from the individually reacted coal and base plastics mixture.

2. Experimental 2.1. Materials The model plastics used in this research were HDPE, LDPE, PET, PP, and PS all of which were obtained from Aldrich. A mixture consisting of 50% HDPE, 30% PET, and 20% PS was used as the base plastics mixture in many reactions. The solvents used in the study included tetralin, decalin, dodecane, eicosane, and 1-methylnaphthalene, which were obtained from Aldrich, and hexadecane, which was obtained from Fisher Scientific; all of the solvents were used as received. The catalysts used in this study were fluid catalytic cracking catalysts, Low Alumina, Super Nova-D, Octacat, and Octacat-SOG, all of which were donated by the Davison Chemical Division of W.R. Grace and Company. HZSM-5, a zeolite catalyst, was also used and was supplied by United Catalyst Inc.

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Illinois No. 6 coal from the Argonne Coal Sample Bank was used to coprocess coal with waste plastics and was also reacted alone to establish a baseline reactivity for Illinois No. 6 coal under these reactions conditions. Analyses of these catalysts and coal have been described previously [25]. 2.2. Reaction procedures and analysis Liquefaction reactions of plastics and coprocessing reactions of coal and waste plastics were performed using 20 cm3 stainless steel microtubular reactors, in the temperature range of 673 to 713 K (400 to 440 “0 for 30 to 120 min under a H, pressure of 2.8 to 8.6 MPa introduced at ambient temperature. The microtubular reactors were agitated horizontally at a rate of 435 rpm. In reactions performed without solvent, 2 g of coal or plastic were added to the reactor; when the coal and plastic were coprocessed, 1 g of each was added to the reactor. When a solvent was used, 2 g of solvent were added. For catalytic reactions using fluid catalytic cracking catalysts and HZSM-5, a catalyst loading of 10 to 20 wt.% on a solids loading basis was charged. The fluid catalytic cracking catalysts were pretreated prior to being used in the reaction by heating the catalyst for 2 h at 477 K (400 “F) and for two more hours at 811 K (1000 “F). After the reaction was complete, the reactor was quickly quenched in cold water and the gaseous products were weighed and removed. The liquid products were analyzed using solvent fractionation with hexane as the initial solvent followed by THF. Any solid residue left in the reactor after extracting with hexane and THF was scraped from inside the reactor walls. The amount of materials soluble in hexane and THF was determined as well as the amount of THF insoluble materials. The recovery was determined by weighing all fractions and then calculating the recovery using the equation, recovery = (g recovered/g charged) x 100%. The recovery achieved from the plastics liquefaction reactions was dependent on the particular plastics used. The recoveries obtained in the reactions are given in the Tables. The conversion of the solid material to THF solubles was determined on a solvent-, moisture- and ash-free basis using the following equation: solid conversion = 100% - IOM%, where IOM is insoluble organic (ash-free) matter produced from reactions of either coal or plastics or both.

3. Results and discussion 3.1. Liquefaction of LDPE and HDPE As reported previously [21-251, LDPE and HDPE were difficult to convert to THF-soluble materials using typical liquefaction conditions and catalysts while both PET and PS were more easily converted. To test the effect of specific reaction conditions on the liquefaction of the different plastic materials, reactions were performed using HZSM-5 and Low Alumina catalysts at reaction temperatures of 673, 693, and 713 K (400, 420, and 440 “C>as shown in Table 1. Reactions involving HDPE, LDPE, and PET and 10% HZSM-5 were performed and yielded progressively higher conver-

30 min. 5.6 MPa H, introduced and 70% hexadecane) if used. is on a solvent-free basis. output/g total input) X 100%. solubles and hexane insolubles.

5.6 5.6 5.6 5.6 5.6 5.6 5.6

10% 10% 20% 20% 20% 10% 10%

LDPE LDPE HDPE PS PET LDPE HDPE

30 30 30 30 30 30 30

a Reaction conditions: solvent (30% tetralin b Product distribution ’ Recovery = (g total d THF solubles, THF

5.6 5.6 5.6 5.6 5.6 5.6

10% 10% 10% 10% 10% 10% 0 2 0 0 0 2 2

2 2 2 2 2 2

(g)

Solvent

catalyst

7.OkO.4 3.OrtO.2 II.1 *0.2 2.9 f 0.0 25.4kO.2 12.2fO.l 6.2kO.2

34.2 k 0.5 18.3kO.3 53.1 +0.3 11.8kO.3 17.4*0.0 61.5ztO.5

Gas

loading

3.2 + 0.3 5.2* 1.7 2.2 + 0.3 26.7 f 0.7 8.2 _+0;7 4.5 k 1.5 3.7* 1.1

1.1 +0.3 2.8 f 0.9 1.2kO.2 22.3 -+ 0.2 15.8kO.6 4.4f I.0

THF d solubles

42.1 + 1.6 62. I + 0.9 6.7 + 0.2 7.7 f 0.0 32.3 + 0.3 6.3 + 0.3 19.7 f 0.9

52.4+ 2.0 63.9+0.3 14.4*0.1 23.4+0.2 10.9kO.3 0.6kO.O

IOM

of IO or 20 wt.% on a total charge

47.6kO.8 29.7 f 2.4 80.0 f 0.3 63.2f0.8 34.1+ 1.2 77.0f 1.1 70.4 f 0.5

12.3f 1.7 15.1 f 1.5 31.3f0.5 42.6 _+0.3 55.9 f 0.9 33.5 + I .6

Hexane solubles

Products (%> b

at ambient temperature,

(MPa)

H,

LDPE HDPE LDPE PET PET HDPE

loading

Catalyst

30 30 30 30 30 30

(“a

HZSM-5 400 400 420 420 440 440 Low Alumina 400 400 440 440 440 440 440

(min)

Temperature

’

Polymer

of polymers

Time

Table 1 Catalytic liquefaction

g of

;” ;

8 ;

2 P :z B % 2 g

85.2

73.6 90.5 84.7 64.4

89.0 73.2 76.2 90.6 74.2 75.8

9 4

k “a

3 h

? z. \ ? !k 9 F: 2 %’ 30

2

c

75.9 76.9

(%I

Recovery

basis, 2 g of polymer,

57.9 f 1.6 37.9f0.9 93.3 + 0.2 92.3 f 0.0 67.7 f 0.3 93.7 f 0.3 80.3 +0.9

47.6 f 2.0 36. I f 0.3 85.6+0.1 76.6 + 0.2 89.1 + 0.3 99.4 f 0.0

(%)

Coversion

M. Luo, C.W. Curtis/Fuel

Processing Technology 49 (1996) 177-196

183

sion to THF-soluble materials with each 20 “C temperature rise. The average plastics conversion increased from 42% at 673 K (400 “Cl, to 8 1% at 693 K (420 “C), and to 95% at 713 K (440 “0. Production of hexane-soluble materials also increased as the temperature increased. Reactions using HDPE, LDPE, PS, and PET were also performed at 10 and 20% catalyst loading levels of Low Alumina. Reactions of LDPE at 673 K (400 “C) and 10% catalyst loading without a solvent present yielded conversions of 57.9%, while with a solvent composed of 30% tetralin and 70% hexadecane the conversion decreased to 37.9%. This decrease indicated that tetralin was detrimental to LDPE conversion. At 7 13 K (440 “C), the conversions of PS and LDPE were above 90%, while the conversion of HDPE was above 80%, regardless of the catalyst loading level or the presence of a solvent. PET at a 20% catalyst loading without solvent gave the lowest conversion at 713 K (440 “0. The production of hexane soluble materials tracked the conversions. The results from these plastics liquefaction reactions clearly indicated that a temperature of 713 K (440 “C) was required for effective liquefaction. At that temperature, a 10% loading of Low Alumina was sufficient for achieving a LDPE conversion of 93.7%, and a HDPE conversion of 80.3%, in the presence of an additional solvent. A hexane soluble production yield of more than 70% for both polymers was also obtained. 3.2. Efjct

of different combinations

of plastics on plastic liquefaction

Waste plastics produced from typical usage contain a multiplicity of plastic materials. Therefore, the composition of waste plastic streams is dependent on the consumer population and their particular consumer habits. In order to evaluate the effect of mulitple waste plastics of varied chemical compositions on liquefaction conversion and product distribution, combinations of different plastic materials were reacted simultaneously. The base plastics mixture used was composed of 50% HDPE, 30% PET, and 20% PS. Other polymers were added to the base plastics mixture so that the mixture composed 80% and the added polymer 20% of the reactor charge. The following polymers were added in successive reactions: HDPE, LDPE, PP, PS, and PET. Three catalysts, HZSM-5, Low Alumina, and Super Nova-D, were added individually to each of the reaction sets. The product distributions presented on a solvent-free basis and the plastics conversion to THF-soluble materials are given in Table 2. The catalyst most active for converting the base plastics mixture was HZSM5, while both Low Alumina and Super Nova-D converted lower but similar amounts. Not only was HZSM-5 most active for conversion but also produced substantially more hexane solubles man the other two catalysts. This activity ranking held true for the other reactions containing different combinations of plastics. In some reactions, Low Alumina was more active than Super Nova-D for conversion and hexane soluble production, while in other reactions the opposite was true. The amount of gas produced in the reaction depended upon both the type of catalyst used and the composition of the plastics mixture. Reactions containing HZSM-5 yielded the highest gas production in all of the plastics mixtures. The amount produced with HZSM-5 ranged from * 9 to N 20%. The highest gas productions occurred with the addition of 20% HDPE, PP, or PS. The addition of PET had little effect on gas

9.3 +- 0.9 7.5 f 0.0 7.1 f0.2 15.9* 1.4 5.6kO.5 6.1 *0.2 13.4+0.5 5.6k0.1 5.7*0.1 19.4kO.8 7.8&-0.1 8.6fO.l 15.9kO.6 5.8 + 0.2 5.8 rt 0.0 10.4kO.2 8.5 f 0.4 9.7 * 0.0

Gas

THF solubles ’

9.2 + 0.5 6.9 f 0.4 11.1+1.5 7.0 + 0.5 4.2 + 0.4 7.6f 1.1 4.8 f0.3 3.3 f 0.5 8.3 _+1.5 7.6 f I .6 5.2f0.7 6.2& 1.2 6.2f0.6 6.OkO.3 5.9f 1.0 9.2f 1.2 9.4* 1.0 11.7kO.4

Hexane solubles

57.2kO.2 42.9 f 0.0 38.0 f 0.0 53.6kO.5 37.1 k2.1 35.6 + 0.7 68.4 f 0.7 52.0f0.2 39.9k3.4 63.2 f 1.8 54.7 + 0.6 48.8 f 0.9 68.4k0.2 52.8 + I .2 55.5 f 4. I 55.0+_ 2.4 38.5 f 1.4 41.2f2.8

(o/o) ’

of plastics

24.2+ 1.1 42.8 f 0.4 43.8 f I .7 23.5f2.3 53.2k2.1 50.7 -I 0.2 13.4f0.9 39.1 +0.4 46.ljI2.0 9.8 + 0.6 32.2 f 0.0 36.3rt0.1 9.650.2 35.4f I.1 32.8f3.1 25.41k3.5 43.7f0.8 37.4f 3.3

IOM

75.8f I.1 57.2 & 0.4 56.2 f I .7 76.5 It 2.3 46.8k2.1 49.3 + 0.2 86.6 f 0.9 60.9 f 0.4 53.9 * 2.0 90.2f0.6 67.8 f 0.0 63.7 fO.l 90.4kO.2 64.61t I.1 67.2f3.1 74.6k3.5 56.3 f 0.8 62.6 f 3.3

(%I

Conversion

81.3 90.6 86.0 80.3 88.2 82.8 69.8 84.2 83.8 72.1 81.3 80.5 73.5 82.9 82.0 82.5 88.0 84. I

(o/o)

Recovery

d

a Reaction conditions: 440 “C, 5.6 MPa H, introduced at ambient temperature, 30 min. catalyst loading of 10 wt.% on total charge basis; 2 g of polymer and 2 g of solvent (30% tetralin and 70% hexadecane). b Base plastics charge: 50% HDPE, 30% PET, 20% PS; HDPE, high density polyethylene; PET, poly (ethylene tercphthalate); PS, polystyrene; LDPE, low density polyethylene; PP, polypropylene. ’ Product distributions on a solvent-free basis. d Recovery = (g total output/g total input) X 100%. ’ THF solubles, THF solubles and hexane insolubles.

Base 80% + PET 20%

Base 80% + PS 20%

Base + PP 20%

Base 80% + LDPE 20%

Base 80% + HDPE 20%

HZSM-5 Low Alumina Super Nova-D HZSM-5 Low Alumina Super Nova-D HZSM-5 Low Alumina Super Nova-D HZSM-5 80% Low Alumina Super Nova-D HZSM-5 Low Alumina Super Nova-D HZSM-5 Low Alumina Super Nova-D

Base b charge

liquefaction

Products distribution

on catalytic

Catalyst

polymer combinations

Polymers

Table 2 Effect of different

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production indicating that the other polymers were the primary sources of the gas. The other two catalysts yielded approximately the same amount of gas for each plastics mixture and ranged between 5 and 10% gas production. Further reactions were performed to evaluate the effect of multiple plastics being present in the liquefaction reaction on the conversion and product distribution compared to those obtained with individual polymers (Table 3). The individual conversions and product distributions of HDPE, PET, and PS are given for reactions with each catalyst as well as those for the base plastics mixture. The hypothetical mean of the individual reactions, which is defined as the weighted average of the base charge components, is also given. The difference between the experimental values obtained from the base plastics mixture of 50% HDPE, 30% PET, and 20% PS and the hypothetical mean is presented for each product fraction and the conversion obtained with each catalyst. Substantial differences were realized when the polymers were reacted together rather than individually, although the effects were dependent on the catalyst used. Some of the effects were positive in terms of obtaining a desirable liquefaction product slate while others were not. The differences between the experimental and hypothetical mean values were large for the gas fraction and the conversion obtained with HZSM-5. The gas production obtained in the individual reactions decreased substantially when the polymers were reacted together, yielding 9.2% gas compared to the hypothetical mean value of 42.2%. This decrease in the amount of gas produced was a positive result from coprocessing, since less H, was being incorporated into the gaseous products. A higher yield of hexane solubles material was also produced, suggesting that when multiple polymers were present, that reactions forming light liquid products were promoted. By contrast, the conversion decreased from a hypothetical mean value of 96% to an experimental value of 75.8%. This lower conversion indicated that interactions occurred among the polymers that were detrimental for conversion. The yields from reactions with the other two catalysts, Low Alumina and Super Nova-D, also showed the effect of reacting the polymers together compared to the individual polymer reactions. Reactions with Low Alumina gave decreased hexane-soluble yield and conversion values compared to the hypothetical mean values. Reactions in which waste plastics were reacted with Super Nova-D showed the least reactivity and the least effect of multiple polymers on their reactivity and conversion. The differences between the experimental and hypothetical mean values were approximately 3.5%. The heavier fractions (THF solubles and IOM) produced were higher when the polymers were reacted together than when they were reacted individually. 3.3. Effect of reaction solvent on plastics conversion When coal and plastics are coprocessed to yield a product that is suitable for a fuel or as a chemical stock, a hydrogen donor solvent such as tetralin is effective in converting coals to THF-soluble materials [15,16,251. Although tetralin has been shown to be beneficial to coal conversion in the coprocessing of coal with waste plastics, tetralin was not particularly effective as a solvent for liquefying plastics such as HDPE and LDPE. The effect of the chemical composition of the solvent used for plastics liquefaction was determined by using an aromatic solvent I-methylnaphthalene, a hydroaromatic solvent

20.2 f 0.2 7.1*2.0 10.8 7.1 +0.2 -3.7

PET Polystyrene Hypothetical mean b Base charge Difference ’

33.5f0.2 89.9+ 1.8 41.5 38.0 5 0.0 -3.5

17.7 f 0.2 1.6kO.2 7.3 II.1 f I.5 +3.a

3.4kO.l

- 3.9

6.9kO.4

3.7* I.1 19.5 f0.6 15.5f 1.6 10.8

+ 1.0

8.2 9.2 & 0.5

g

1.1

I .5

28.6 + 0. I 1.4*0.0 40.4 43.8 & I .7 + 3.4

63.0 +

+ 24.8

42.8 f 0.4

19.7 f 0.9 24.8 f I .7 3.6+0.5 18.0

+ 20.3

4.0 24.2f

0.6 f 0.0 10.9 * 0.3 1.9io.3

IOM

1.1

I .5 71.4*0.1 98.6 f 0.0 59.6 56.2 f I .7 -3.4

37.0 *

- 24.8

57.2 + 0.4

80.3 * 0.9 75.2kl.7 96.4 + 0.5 82.0

- 20.2

96.0 75.8k

99.4-10.0 89. I + 0.3 98. I f 0.3

(%I

Conversion

86.0

89.8 64.7

85.4

90.6

75.8 92.6 80.9

81.3

69.4 84.7 65.4

(o/o)

Rccoverv ’

f

a Reaction conditions: 440 “C, 5.6 MPa H, introduced at ambient temperature, 30 mitt, catalyst loading of IO wt.% on total charge basis, 2 g of base plastics mixture, 2 g of solvent (30% tetralin and 70% hexadecane). b Hypothetical mean is the weighted average of the base charge component, HDPE, PET and PS. ’ Difference is the base plastics mixture value minus hypothetical mean. * The individual polymer reaction was run under the same conditions as the base charge. e Product distribution is on a solvent-free basis. f Recovery = (g total output/g total input)X 100%. g THF solubles. THF solubles and hexane insolubles.

6.6k

26.9 f 0.3

- 19.0

- 1.9

Super Nova-D HDPE 1.1

42.9 + 0.0

7.5 f 0.0

Base charge

’

70.4* 0.5 36.6 f I .O 78.4+ 1.1 61.8

6.2kO.2 19.2 * 0.0 2.5 f 0.0 9.4

Difference

+ 11.6

- 32.9

45.7 57.2k0.2

Difference ’ Low Alumina HDPE PET Polystyrene Hypothetical mean b

42.2 9.3 + 0.9

mean b

Hypothetical Base charge

4.4* I.0 15.8?~0.6 6.3 i 0.7

33.5 k I .6 55.9 * 0.9 60.7*0.1

61.5f0.5 17.4*0.0 31.1 +0.6

THF solubles

Hexane solubles

Gas

a

(%/o)*.’

and product distribution

Products distribution

on conversion

HDPE PET Polystyrene

Polvmers

Table 3 Effect of multiple polymers

b-L 5. \ 2 z ? a rp1 3. z 2 r) 2 zB Q 2 z? 5

a

g “0

jt

o\

zl

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tetralin, a saturated cyclic aliphatic solvent decalin, a solvent mixture of 30% tetralin and 70% hexadecane, and straight chain hydrocarbon solvents such as dodecane, hexadecane, and eicosane (Table 4). Conversions of the base plastics mixture were evaluated in each of these solvents, using the aforementioned three catalysts. The straight chain aliphatic solvents provided the best solvating media for plastics during liquefaction compared to saturated or partially saturated polycyclic compounds or aromatic compounds. When compared to the reactions with no solvent, the aliphatic solvents increased conversion of the base plastics mixture by more than 10% when HZSM-5 was used and by only - 2 to 6% when Low Alumina or Super Nova-D was used. The conversion of the base plastics mixture charge was above 80% with HZSM-5 when aliphatic solvents were used. The conversions decreased to 69% with decalin, 66.6% with I-methylnaphthalene, and 56.8% with tetralin as the solvent. The conversion of the base plastics mixture was equivalent at - 75% when reacted without a solvent or with the combined solvent of 30% tetralin in hexadecane. The same type of result was obtained in the reactions with Low Alumina and Super Nova-D. Low Alumina yielded the least overall conversion of the three catalysts while Super Nova-D gave intermediate values for the straight chain aliphatic solvents. The hexane-soluble production followed the conversion of the plastics. The highest hexane-soluble production was obtained with HZSM-5 and the straight chain aliphatic solvents. The other two catalysts also yielded the highest production of hexane solubles with the straight chain aliphatic solvents, although hexane-soluble yields were also high with no solvent and with l-methylnaphthalene. The efficacy of a particular straight aliphatic solvent was dependent on the catalyst used. Both HZSM-5 and Super Nova-D yielded the highest conversion and hexane soluble production with dodecane as the solvent, followed immediately by eicosane; Low Alumina yielded the most conversion with hexadecane although both dodecane and eicosane also yielded high values. Therefore, with the base plastics mixture and reaction conditions used, the solvent influenced the conversion of the plastics. Saturated and aromatic solvents were more effective than hydroaromatic solvents while straight chain aliphatic solvents were the most effective for the three catalytic reaction systems used. 3.4. EfSect of reaction time and hydrogen pressure on plastics liquefaction and coprocessing

The effect of reaction time and initial H, pressure on plastics liquefaction and coprocessing was evaluated as shown in Tables 5 and 6, respectively. The base plastics mixture of HDPE, PET, and PS was reacted for 30, 60, and 120 min using HZSM-5, Low Alumina, and Super Nova-D as catalysts. The solvent used in both the plastics liquefaction and the coal and plastics coprocessing reactions was 30% tetralin and 70% hexadecane. This solvent was used as compromise between the needs of the plastics for an aliphatic solvent and the needs of coal for a hydroaromatic solvent. Increasing reaction time substantially increased the amount of conversion in plastics liquefaction (Table 5). Catalytic reactions of the base plastics mixture using HZSM-5 yielded 75.8% conversion at 30 min, 86.7% conversion at 60 min, and 94.5% conversion at 120 min. Similar conversion increases were observed with Low Alumina and

27.0f3.8 31.1 f0.3 51.4f2.1 41.2jzO.l 43.8 f I .7 20.7 f 0.3 29.4 f I .O 20.9 + I .O

9.1 Xto.5 7.7 f 0.8 7.8*0.1 9.9f0.6 11.1+1.5 8.7 f 0.9 9.5 f 0.2 9.6 f 0.8

55.8 k 3. I 54.9f0.3 34.5 f I .8 41.9f0.8 38.0 f 0.0 60.0 f 0.6 51.2* 1.5 58.8 f 1.0

8.1 kO.1 6.3f0.1 6.3 f 0.3 7.0fO.O 7.1 f0.2 10.5 f 0.0 9.9 f 0.3 10.7f0.3

31.Sf3.2 26.4 + I .3 48.3kO.l 38.7 f 0.4 42.8 f 0.4 31.4* 1.0 29.1 f 1.3 3l.7fO.7

4.7 f 0.2 6.2fO.l 5.6kO.3 5.0fO.l 6.9 f 0.4 7.7 + I .o 5.6f0.5 8.5k0.3

55.5*3.2 0.7 60.1 ?? 40.5*0.3 so. I f 0.7 42.9 f 0.0 52.9 + 0.2 55.8 f 0.7 52.2k0.6

8.4kO.2 7.4 f 0.4 5.6 f 0.0 6.3 f 0.2 7.5 f 0.0 8.0 k0.2 9.5*0.1 7.5 + 0.2

24.9 f 0.0 33.4f0.7 43.2Yc3.3 31.0* 1.2 24.2k 1.1 10.8 f 0.2 18.2kO.6 12.5f 1.3

6.2kO.3 8.7f0.6 7.1 +2.9 6.3 It 0.6 9.2+0.5 3.3fO.l 6.5 f 0.7 6.1 kO.4

57.9fO.S 49.7 f 0.1 38.1 kO.4 53.7f 1.9 57.2* 0.2 74.8 f 0.6 66.7Iko.4 66.0 f 1.2

10.9*0.1 f3.2*0.0 11.6f0.8 9.OkO.l 9.3 * 0.9 Il.1 f0.3 8.6 * 0.5 15.4*0.3

73.Ok 3.8 68.9 f 0.3 48.6f2.1 58.8fO.l 56.2k 1.7 79.3 f 0.3 70.6 f I .O 79.1*0.1

68.5 $- 3.2 73.6 f I .3 51.7fO.l 61.3&-0.4 57.2f0.4 68.6 f I .o 70.9 f I .3 68.3 + 0.7

75.1 *0.7 66.6rt0.7 3.3 56.8 ?? 69.0 f I .2 75.8+ 1.1 89.2 f 0.2 81.8rtO.6 87.5 f I .3

(o/o)

IOM

Hexane solubles

Gas

THF solubles ’

(%) ’

Product distribution

Solvent

HZSM-5 None I -Methylnaphthalene Tetralin Decalin 30% Tetralin f Dodecane Hexadccane Eicosane Low Alumina None I -Methylnaphthalene Tetralin Decalin 30% Tetralin Dodecane Hexadecane Eicosane Super Nova-D None I-Methylnaphthalene Tetralin Dccalin 30% Tetralin Dodecane Hexadecane

Conversion

of base plastics mixture a.b

Table 4 Solvent effect on liquefaction

83.0 89.4 86.9 68.9 86.0 79.0 81.1 82.2

83.0 87.7 83.4 90.4 90.6 83.8 85.0 84.2

79.0 86. I 79.5 67.8 81.3 64.5 81.6 75.5

(%I

Recovery

’

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Technology 49 (1996) 177-196

189

Super Nova-D. Increases were also observed in hexane soluble production in accordance with the conversion increases. HZSMS produced high yields of gas at 60 min and, consequently, gave the lowest increase in hexane solubles. This high activity shown by HZSM-5 at 60 min was in accordance with its activity at 30 min where HZSM-5 was the most active catalyst for hexane soluble production and plastics conversion. By contrast, Super Nova-D, the catalyst that was least active at 30 min, gave the largest increases in both hexane soluble yield and conversion when reaction time was increased from 30 to 60 min. These catalysts retained their activity with increasing reaction time and continued to convert the solid plastic materials to THF solubles. Conversion and hexane-soluble production in catalytic coprocessing reactions of coal with the base plastics mixture also increased with longer reaction time; however, the amount of these increases was substantially less than those obtained with the plastics mixture. The three catalysts used in the coprocessing reactions also showed different levels of activity as they did in the plastics liquefaction reactions. HZSM-5 was the most active, and Low Alumina and Super-Nova-D had lesser but similar activity. The amount of the increases in conversion and hexane soluble yield with time was similar for all three catalysts. The effect of H, pressure on the conversion and hexane soluble production in plastics conversion was relatively small (Table 6). The initial H, pressures used were 2.8, 5.6, and 8.5 MPa. The conversions were highest for the lowest H, pressure for all three catalytic reaction systems. The conversions decreased somewhat at the middle pressure of 5.6 MPa but tended to recover at higher initial H, pressure of 8.6 MPa. The hexane solubles production tracked the conversion obtained. 3.5. Coprocessing of base plastics mixture and coal Catalytic coprocessing of coal with the base plastics mixture was performed with and without solvent using HZSM-5, Low Alumina, and Super Nova-D as presented in Table 7. The solvent was composed of 30% tetralin and 70% hexadecane. Both coal and the base plastics mixture were reacted individually to obtain baseline reactivity under these reaction conditions. The effect of coprocessing coal and plastics was determined by subtracting the hypothetical mean value obtained from the arithmetic average of the individual reactions from the experimental value obtained from the coprocessing reaction. Coal reactions performed with the hydrogen-donor solvent gave higher conversions of -79 to - 84% compared to the coal reactions without solvent whose conversions

Notes to Table 4: a Reaction conditions: 440 “C, 5.6 MPa, 30 min; 2 g of solvent, 2 g of polymer, 10 wt.% catalyst on a total charge basis. b Base combined plastics charge of 50% HDPE, 30% PET, 20% P.S. ’ Product distributions are on a solvent-free basis. d Recovery = (g total output/g total input)X 100%. e THF solubles, THF solubles and hexaue insolubles. f 30% tetralin in 70% hexadecane.

(min)

time

13.6fO.O 6.1 ltO.1 3.8 f 0.4 10.4zbO.8 9.8ItzO.8 8.8fO.l 12.8 + 0.4 8.5 f 0.8 6.2+ 1.5

45.5 f 0.9 52.5kO.I 52.8 + 2.0 35.2+ 2.7 4-0.8 f 0.6 51.6k2.0 28.3k 1.3 36.4k 0.5 49.4 + 1.6

11.9+0.2 18.2 f 0.4 24.0 f 0.4 6.4kO.2 8.3 + 0.2 11.5+0.8 5.3 f 0.6 9.5 + 0.4 11.4*0.8 loading based on total charge,

9.2kO.5 6.1 kO.1 2.0* 1.7 6.9f 0.4 3.5 f 0.9 2.8 ?? 0.2 11.1+1.5 5.4zt 1.6 1.6&0.4 71.0+0.7 76.8 f 0.6 80.6rt2.8 51.95 1.6 58.9 * 0.0 71.9k2.9 46.4kO.2 54.5 f 0.6 67.1 ,3.8

75.8f 1.1 86.7f3.1 94.5 f 0.2 57.2_+0.4 70.0 f 1.6 89.1 f 0.8 56.2 f 1.7 73.0*0.2 88.6 + 0.3

(%)

Conversion

with coal

2 g of base plastics mixture,

29.0 + 0.7 23.2 kO.6 19.4k2.8 48.1 k 1.6 41.1 rto.0 28.1 k2.9 53.6 f 0.2 45.5 + 0.6 32.9 + 3.8

24.2+ 1.1 13.3_+3.1 5.5kO.2 42.8 _+0.4 30.0 f 1.6 10.9f0.8 43.8& 1.7 27.0f0.2 11.4+0.3

IOM

of base plastics mixture

THF solubles ’

57.2f0.2 62.9kO.l 55.0f 1.8 42.9f 0.0 57.1 f 2.5 72.6 k 0.6 38.OkO.O 58.9 f 0.9 71.4rfr2.1

Hexane solubles

the coprocessing

9.3 f 0.9 17.7*3.1 37.4 * 1.3 7.5 -+ 0.0 9.5 & 0.0 13.7+0.4 7.lYkO.2 8.8 + 0.0 15.6f2.0

Gas

(%I b.c

of base plastics mixtureand

Product distribution

behavior

a Reaction condition: 440 “C, 5.6 MPa initial H, pressure, 10 wt.% catalyst 30% tetralin and 70% hexadecane. b Product distribution on a solvent-free distribution. ’ Base plastics mixture: 50% HDPE, 30% PET, 20% polystyrene. d Recovery = (g total output/g total input)X 100%. e THF solubles, THF solubles and hexane insolubles.

Base plastics mixture reactions 30 HZSM-5 60 120 Low Alumina 30 60 120 Super Nova-D 30 60 120 Base plastics mixture and coal reactions 30 HZSM-5 60 120 Low Alumina 30 60 120 30 Super Nova-D 60 120

Catalyst

Reaction

Table 5 Effect of reaction time on the liquefaction

2 g of solvent composed

77.2 72.0 74.5 87.8 84.8 82.0 85.8 87.6 78.2

86.0 81.9 75.1

of

2 m

3,

\

3 3 i;’ 73.2

79.2

.s: s ? 9 4

d

81.3 74.0 66.4 90.6

(%)

Recovery

s

2.3 5.6 8.6 2.3 5.6 8.6 2.3 5.6 8.6

oressure (MPa)

L

behavior

10.0 f 0.0 10.9rtO.I I1.4fO.O 9.6 + 0.0 8.4f 0.2 10.5 * 0.2 9.1 f0.1 8.1 fO.l 10.6kO.6

Gas

(%) b.c

71.1 f 1.3 57.9 * 0.5 62.4 f I .8 66.6 + 0.6 55.5 f 3.2 58.7 f 1.7 69.7 f 0.3 55.8k3.1 53.2+ 1.3 no solvent.

12.5 f 0.8 24.9 f 0.7 17.5f 1.4 20.3 f 0.7 31.5f3.2 25.1 f 1.3 16.1 +0.2 27.0+3.8 25.9f3.1

IOM

2 g of base plastics mixture,

6.4 f 0.4 6.2rtO.3 8.7 f 0.3 3.5kO.l 4.7kO.2 5.7 f 0.5 5.1 i-o.2 9.1 *OS 10.2+ 1.3

THF soluble e

of the base plastics mixture a

Hexane solubles

Product distribution

pressure on the liquefaction

Initial H,

a Reaction conditions: 440 “C, 60 min, 10 wt.% atalyst loading on total charge, b Product distribution is on a solvent-free basis. ’ Base plastics mixture: 50% HDPE, 30% PET, 20% polystyrene. d Recovery = (g total output/g total input)X 100%. e THF solubles, THF solubles and hexane insolubles.

Super Nova-D

Low Alumina

HZSM-5

Catalvst

Table 6 Effect of initial hydrogen

87.8 f 0.8 75. I rt 0.7 82.5 f 1.4 79.7 f 0.7 68.5 f 3.2 74.9+ 1.3 83.9k0.2 73.023.8 74.1 f3.1

(%I

Conversion

80.6 79.0 85.7 79.4 83.0 78.5 81.7 83.0 86.2

(%I

Recovery

d

With solvent b Base plastics Coal Hypothetical mean b Coal + base Difference g Base plastics Coal Hypothetical mean Coal + base Difference Base plastics Coal Hypothetical mean Coal + base Difference

Reactant

Super Nova-D

Low Alumina

HZSM-5

Catalyst

9.3 f 0.9 9.6*0.1 9.5 11.9+0.2 2.4 7.5 f 0.0 6.7 f 0.9 7.1 6.4 f 0.2 - 0.8 7.1 *0.2 I l.9f0.8 9.5 5.3 f 0.6 - 4.2

Gas 57.2hO.2 42.7 f 2.3 50.0 45.5 *0.9 - 4.4 42.9 f 0.0 26.8*0.6 34.8 35.2f 2.7 0.4 38.0 f 0.2 16.5 f 0.3 21.2 28.3 f I .3 I.1

Hexane soluble

Product division (o/o)b

Table I Coprocessing reactions of base plastics mixture and coal with and without solvent a

9.2 f 0.5 31.6*2.5 20.4 13.6kO.O -6.8 6.9kO.4 45.6i 1.6 26.3 lO.4kO.8 - 15.9 I I.1 fO.0 51.7f0.6 31.4 12.8 f 0.4 - 18.6

THF soluble ’

24.2* I.1 16.1 kO.4 20.1 29.0 + 0.7 8.9 42.8 f 0.4 20.9*0.1 31.8 48.1 f 1.6 16.2 43.85 1.7 19.9*0.1 31.9 53.6*0.2 21.7

I OM

75.8* I.1 83.9f0.4 79.9 7l.OkO.7 - 8.9 57.4f0.4 79.1*0.1 68.2 51.95 1.6 - 16.2 56.2k 1.7 80.1 *O.l 68.1 46.4f0.2 -21.7

(%I

Conversion

85.8

86.0 89.0

87.8

90.6 94.3

77.2

81.3 83.1

(o/o)

Recovery ’

Super Nova-D

Low Alumina

HZSM-5

10.9*0.1 7.8fO.l 9.4 13.0fO.l 3.6 8.4kO.2 8.4rtO.l 8.4 8.9 f 0.0 0.5 8.1 kO.1 8.6*0.0 8.4 8.1 kO.1 -0.3

57.9*0.5 14.2fO.l 36. I 28.3 f 0.8 - 7.7 55.5 f 3.2 13.6 f 2.0 34.5 35.0 f 2.3 0.5 55.8It3.1 15.8f0.7 35.8 28.1 f0.7 -7.7

6.2*0.3 46.8 f 0.2 26.5 6.8 f 0.0 - 19.7 4.7 f 0.2 19.8f 1.7 12.2 4.4 f 0.5 - 7.9 9.1*0.5 21.9f0.2 15.5 4.0 f 0.3 -11.5

24.9 f 0.7 31.2rt0.3 28.) 51.9f0.9 23.8 31.5f3.2 58.3 * 3.6 44.9 51.7k2.9 6.9 27.0rt3.8 53.7*o.s 40.3 59.8 f 0.5 19.5

75.1 f0.7 68.8 f 0.3 71.9 48.1 Ito.9 - 23.8 68.5 f 3.2 41.753.6 55.1 48.3 f 2.9 - 6.9 73.0f3.8 46.3 f 0.8 59.7 40.2 f 0.5 - 19.5 84.6

83.0 94. I

80.3

83.0 97.2

84.5

79.0 94.6

a Reaction conditions: 440 “C, initial H, pressure 5.6 MPa at ambient temperature, 30 min; 10 wt.% catalyst loading based on total charge, 2 g of solid (base polymer of coal) or 1 g of base plastics mixture and 1 g of coal, 2 g of solvent (30% tetralin and 70% hexadecane) if used. b Product distribution on a solvent-free basis. ’ Base plastics charge of 50% HDPE, 30% PET, 20% PS. * Recovery = (g total output/g total input) X 100%. e THF solubles, THF solubles and hexane insolubles. f Hypothetical mean, average of coal and base polymer reacted alone. ’ Difference, coprocessing results - hypothetical mean.

Without solvent Base plastics Coal Hypothetical mean Coal + base Difference Base plastics Coal Hypothetical mean Coal + base Difference Base plastics Coal Hypothetical mean Coal + base Difference

194

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Technology 49 (1996) 177-196

ranged from _ 41 to N 69%. The solvent not only increased coal conversion but also leveled the effect of the catalysts on conversion. By contrast, the base plastics mixture converted equally well either with or without a solvent when HZSM-5 was used but converted more with both Low Alumina and Super Nova-D when a solvent was not used. The conversions obtained in the coprocessing reactions were higher when a solvent was present for each corresponding catalyst. In the coprocessing reaction, coal probably converted more in the reactions with solvent, thereby, increasing the overall conversion. In the coprocessing reactions, negative difference values were obtained for all the coprocessing conversions regardless of the presence of a solvent, indicating that the reactants converted more when they were reacted individually.

4. Summary and conclusions The reaction parameters for catalytic plastics liquefaction governed the reactivity of the systems and the amount of solid conversion achieved. Reaction temperature strongly affected the amount of conversion obtained from the individual plastics. A higher temperature of 440 “C promoted conversion but also increased the amount of gas produced. Combining plastics resulted in decreased reactivity observed under catalytic conditions compared to the reactivity observed with the individual plastics. When the base plastics mixture was used as the base line, addition of other polymers affected the product distributions and conversions. Addition of LDPE, polypropylene, and polystyrene increased conversion and hexane-soluble production compared to the base or to the addition of HDPE or PET, indicating that the composition of the plastics mixture affected their cosolvation as well as their response to the catalyst used. The zeolite HZSM-5 was the most active catalyst for conversion but also resulted in the highest gas production. Longer reaction times promoted conversion and hexane soluble production from the base plastics mixture. The reactions with fluid catalytic cracking catalysts gained the most from the longer reaction time of 60 min, although gains were also made at longer reaction time of 120 min, suggesting that these zeolytic cracking catalysts retained activity under these reaction conditions. The H, pressure affected the reactivity of the system; the lowest pressure used was 2.8 MPa which was the best for plastics liquefaction but was too low for coprocessing reactions with coal. The solvent used in plastics liquefaction strongly affected the conversion obtained with both the zeolite and fluid catalytic cracking catalysts. Straight chain aliphatic solvents yielded the highest conversions and hexane-soluble production with both fluid cracking and zeolite catalysts while saturated and partially saturated cyclic solvents were not as effective. When coal and plastics were coprocessed, the presence of a hydroaromatic solvent such as tetralin promoted coal conversion and more overall conversion in the coprocessing coal and plastics reaction system. Tetralin, however, was detrimental to plastics liquefaction. Longer reaction times promoted higher conversion with the coprocessed coal and plastics system, although the effect was not nearly as great as with plastics liquefaction. The presence of coal seemed to lower the reactivity of the plastics system and somewhat lessened the influence of the catalyst on the reaction system. In fact, coprocessing coal with waste plastics resulted in less conversion than when each

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was reacted alone. The results from this research evinced that coprocessing of waste plastics with coal did not show a positive synergism. Since these materials are quite different, the desirable reaction conditions and appropriate catalysts are quite different, making processing them simultaneously difficult in terms of choosing the most appropriate conditions. Therefore, two stage processing that optimizes the reaction conditions for each material may increase the conversion and hexane-soluble yield of both materials. The waste plastics could be liquefied with a cracking or hydrocracking catalyst in the first stage and the liquid product can be used as a solvent for coal in the second stage. The second stage reaction conditions and catalyst would then be tailored to promote coal conversion and coal liquid upgrading. The inclusion of the waste plastics oil with coal liquids after two stage processing will produce a fuel with a high H:C ratio because of the inherent chemistry of the waste plastics. Utilization of waste plastics with coal will provide a good disposal method for waste plastics and probably lower the cost of coal liquefaction.

5. Nomenclature

CMP FeNaph HDPE LDPE MoNaph PET PP PS

commingled plastics iron naphthenate high density polyethylene low density polyethylene molybdenum naphthenate polyethylene terephthalate polpropylene polystyrene

Acknowledgements

The authors gratefully acknowledge the support of the US Department of Energy under Contract No. DE-FG22-93PC93053 for this work. The authors also sincerely appreciate the help and support of the Auburn University staff in this research. The helpful assistance of Ying Tang is also gratefully acknowledged.

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151 S.H. Ng, Conversion of polyethylene blended with VGO to transportation fuels by catalytic cracking,

Energy Fuels, 9 (1995) 216-224. 161 S.H. Ng, Conversion of polyethylene to transportation fuels through pyrolysis and catalytic cracking, Energy Fuels, 9 ( 1995) 735-742. ]7] H. Kastner and W. Kaminsky, Recycle plastics into feedstocks, Hydrocarbon Process, May (1995) 109-112. [8] Y. Tsuchiya and K. Sumi, ‘lhetmal decomposition products of polypropylene, J. Polym. Sci., A-l (7) (1969) 15599-1607. 191 M. Seeger and R.J. Gritter, Thermal decomposition and volatization of poly (a-oleflns), J. Polym. Sci., 15 (1977) 1393-1402. ]I01 T.E. Davis, R.L. Tobias and E.B. Peterli, Thermal degradation of polyethylene, J. Polym. Sci., 56 (1962) 485. [II] H. Coenen and R. Hagen, Process for the production of liquid hydrocarbons, US Patent 4642401, November 28, 1994. [12] P.R. Stapp, IIT Research Institute, Conversion of municipal waste to useful oils, US Patent 5 158982, October 27, 1992. [13] M.E. Banks, W.D. Lush and R.S. Ottinger, US Department of Health, Education and Welfare, Disposal of waste plastics and recovery of valuable products, US Patent 3829558, August 13, 1974. [14] N.Y. Chen and T.Y. Yan, Mobil Gil Corporation, Method for treatment of rubber and plastic wastes, November 20, 1979, US Patent 4175211. [15] G.P. Huffman, Z. Feng, V. Mahajan, P. Sivakumar, H. Jung, J.W. Tiemey and I. Wender, Direct liquefaction and coliquefaction of coal-plastic mixtures, ACS Fuel Chem Div Prepr., 40 (I) (1995) 35-37. [16] M.M. Taghiei, Z. Feng, F.E. Huggins and G.P. Huffman, Coliquefaction of waste plastics with coal, Energy Fuels, 8 (1994) 1228- 1232. [17] M.M. Taghiei, Z. Feng, F.E. Huggins, G.P. Huffman, Coliquefaction of waste plastics with coal, ACS Fuel Chem. Div. Prepr., 38 (4) (1993) 810-815. [18] L.L. Anderson and W. Tuntawiroon, Coliquefaction of coal and waste plastic materials to produce liquids, ACS Fuel Chem. Div. Prepr., 38 (4) (1993) 816-822. [ 191 S.R. Palmer, E.J. Hippo, D. Tandon and M. Blankenship, Co-conversion of coal/waste plastic mixtures under various pyrolysis and liquefaction conditions, ACS Fuel Chem. Div. Prepr,. 40 (1) (1995) 29-33. [20] X. Xiao, W. Zmierczak and J. Shabtai, Depolymerization-liquefaction of plastics and rubbers. 1. Polyethylene, polypropylene, and polybutadiene, ACS Fuel Chem. Div. Prepr., 40 (1) (1995) 4-8. [21] K. Rothenberger, A.V. Cugini, M.V. Ciocco, R.R. Anderson and G.A. Veloski, Investigation of first stage liquefaction of coal with model plastic waste mixtures, ACS Fuel Chem. Div. Prepr., 40 (11) (1995) 38-43. [22] A.G. Comolli, T.L.K. Lee, V.R. Pradhan and R.H. Stalzer, Studies in coal-waste coprocessing at hydrocarbon research, Inc., ACS Fuel Chem Div. Prepr., 40 (1) (1995) 82-86. [23] G.A. Robbins, R.A. Winschel and F.P. Burke, Characterization of coal-waste coprocessing samples from HRI Run POC-2, ACS Fuel Chem Div. Pmpr. 40 (1) (1995) 92-96. [24] H.K. Joo and C.W. Curtis, Coprocessmg of waste plastics with coal and petroleum mid, ACS Fuel Chem. Div. Prepr., 40 (1) (1995) 643-647. [25] M.S. Luo and C.W. Curtis, Thermal and catalytic coprocessing of Illinois No. 6 coal with model and commingled plastics, Fuel Process. Tech. ( 1995). submitted.