Energy 111 (2016) 884e892

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Energy

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Catalytic and thermal depolymerization of low value post-consumer high density polyethylene plastic*

* Bidhya Kunwar a, , Bryan R. Moser b, Sriraam R. Chandrasekaran a, ** Nandakishore Rajagopalan a, Brajendra K. Sharma a, a Illinois Sustainable Technology Center, Prairie Research Institute, University of Illinois, Urbana-Champaign, IL 61820, USA b United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL 61604, USA article info abstract

Article history: The feasibility of catalytic and non-catalytic pyrolytic conversion of low value post-consumer high Received 15 July 2015 density polyethylene (HPDE) plastic into crude oil and subsequent distillation was explored. Translation Received in revised form of optimized conditions for catalytic and non-catalytic pyrolysis from TGA to a bench-scale system was 25 April 2016 validated using another kind of plastic (HDPE). The properties of the plastic crude (PC) oil and residue Accepted 5 June 2016 were studied for boiling point distribution; molecular weight distribution; elemental composition; and thermal degradation. The plastic crude oils had properties similar to conventional crude oil. The resulting PC oils were distilled into motor gasoline, diesel #1, diesel #2, and vacuum gas oil fractions. An increase Keywords: TGA in gasoline and diesel-range fractions was observed with Y-zeolite and MgCO3 catalysts, respectively. Pyrolysis Diesel and vacuum gas oil fractions were the major products in the absence of catalyst. The distillate Catalyst fraction was characterized for fuel properties, elemental composition, boiling point, and molecular Gasoline weight distribution. The fuel properties of the diesel-range distillate (diesel fraction) were comparable to Diesel those of ultra-low sulfur diesel (ULSD) fuel. Market demand, growth, and value of end products will Ultra-low sulfur diesel dictate which process, non-catalytic or catalytic (Y-Zeolite/MgCO3), is best suited for providing the product portfolio for a particular scenario. © 2016 Elsevier Ltd. All rights reserved.

1. Introduction landfills is not the most efficient way of carbon utilization. Thermochemical conversion is an attractive route to produce Polyethylene (PE) and polypropylene (PP) are two major plastics fuels from these waste plastics while diverting them from landfills used widely in packaging, electronics, storage, and personal care [1]. The plastic fuels have fuel properties comparable to fossil fuels products due to their low cost, durability, and versatility [1]. Proper [3]. PE and PP are polymers containing only carbon and hydrogen. end-of-life management of these waste plastics is a serious prob- Therefore, unlike biofuels, the need for further upgrading of plastic lem throughout the world, as only about one percent of plastics are fuels can be avoided. The plastic fuels have high calorific value and recycled [2]. The disposal of plastics in landfills poses a major are non-acidic and non-corrosive due to the absence of water and environmental concern, because they may take centuries to oxygen, unlike biofuel [3e7]. Sharma et al. obtained approximately degrade naturally and they currently occupy a large volume of 20% motor gasoline, 41% diesel #1, 23% diesel #2, and 16% vacuum expensive landfill space [2]. In addition, leaving that carbon in gas oil-range fractions from distillation of crude oil obtained from non-catalytic pyrolysis of HDPE at 440 C [3]. A recent study by Kaimal and Vijayabalan showed that oil synthesized from the waste plastic has similar properties to that of diesel [8]. It has also been * Disclaimer: Mention of trade names or commercial products in this publication shown that the waste plastic oil can be used in engines without any fi is solely for the purpose of providing speci c information and does not imply modifications [8]. One thermochemical conversion process is py- recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. rolysis which is a thermal degradation method in which larger * Corresponding author. polymeric chains and biomass are broken into smaller hydrocar- ** Corresponding author. bons in absence of air/oxygen [9e15]. A wide distribution of hy- E-mail addresses: [email protected] (B. Kunwar), [email protected] drocarbons is obtained with changes in temperature and reaction (B.K. Sharma). http://dx.doi.org/10.1016/j.energy.2016.06.024 0360-5442/© 2016 Elsevier Ltd. All rights reserved. B. Kunwar et al. / Energy 111 (2016) 884e892 885 time [16]. For instance, as the temperature increases to approxi- and then these optimized conditions were demonstrated on one mately 700 C, the weight percent of gaseous products increases kind of plastic (polypropylene) in a pyrolysis system. The objective [7]. in that previous study was to demonstrate translation of optimized However, thermochemical conversion requires high energy conditions from TGA to a bench-scale system. In the current study, which often renders it to be not economically feasible [16]. Eco- we validated that approach, where optimization conducted on nomics can be improved, though, through the use of a catalyst milligram scale using TGA was translated to bench scale on a ki- during pyrolytic conversion [16]. Lowering the reaction tempera- logram scale, using another kind of plastic, i.e. hard-to-recycle post- ture is always desirable to reduce energy input. Since catalysts consumer HDPE plastic storage boxes. These low value post- lower the activation energy required for pyrolysis, thereby reducing consumer HPDE plastic storage boxes are hard to recycle because the reaction temperature, which leads to reduction in energy they do not recombine well with other plastics during the recycling consumption, reaction time, and narrowing product distribution process and do not melt easily at lower temperatures. An alterna- [17]. The choice of the specific catalyst is significant because it af- tive disposal route for these materials is conversion to fuels through fects yield and product selectivity [14]. For example, zeolites have pyrolysis, there by increasing the carbon utilization efficiency. been shown to increase the yield of gasoline-range hydrocarbons Therefore, this study focused on understanding the effects of from 47% to 70% [14]. Common catalysts used in thermochemical catalyst type (acidic or basic), time, and temperature on the yield conversion include fluid catalytic cracking (FCC), reforming, and and quality of crude oil. The results from the study are important to activated carbon catalysts [14]. FCC catalysts include zeolite enhance the understanding of energy recovery through catalytic [4,6,14,18], silica-alumina [19], and clay [4,20]. Aside from chemical pyrolysis route from feedstocks that would otherwise be disposed properties, the physical properties of the catalysts (such as surface in landfills. Plastic crude (PC) oil thus produced had a heating value area, pore size, pore volume, pore size distribution, pore structure, of approximately 50 MJ/kg and contained roughly 85% carbon and etc) are also very important. Zeolites have high acid strength, high 14% hydrogen, which is similar to commercial motor gasoline and stability, and low coke formation, but their pore size (<1.0 nm) may diesel [3]. Furthermore, PC oils obtained from the pyrolysis of HDPE become a limitation for big molecules [6,13,21]. The most widely storage boxes were distilled into motor gasoline, diesel #1, diesel used catalysts are zeolite-based, such as HZSM-5, Hb, and zeolite #2, and vacuum gas oil-range fractions and their properties were HY. MgCO3 has been studied as a basic catalyst for polyethylene studied and shown to meet ASTM specifications for petrodiesel. cracking [6,21]. MgCO3 has been shown to yield 50% gasoline and 50% diesel [14,21]. 2. Materials and methods Product yield and composition depends on a combination of suitable choice of catalyst, temperature, and particle size [22]. The 2.1. Materials product obtained from thermochemical conversion of PE and PP consists of a mixture of naphtha, gasoline, and light gas oil-range Waste HDPE storage boxes were collected from Eagle Enter- fractions. The yield of gasoline-range hydrocarbons increases prises Recycling Inc (Galva, IL) and were shredded to a particle size with increasing pyrolytic temperature but the yield of gaseous of ~5 mm diameter using an AEC Nelmor (Blade Machinery, Inc., Elk products also increases. Kyaw et al. obtained the highest yield of Grove Village, IL) shredder. All chemicals and reagents used in this liquid fuel (76%) and gases (28.52%) at 370 C from mixed plastics study were obtained from Sigma-Aldrich Corp (St Louis, MO) and [23]. Kamal et al. studied pyrolysis of mixed plastics containing were used as received. ~60% PE, ~30% PP, and remaining other plastics at two different temperatures 900 C and 425 C [24]. They found that there was a 2.2. Thermogravimetric analysis (TGA) of HDPE to determine difference in the calorific values of the product with 46.8 MJ/kg at optimum pyrolysis temperature 900 C and 41.8 MJ/kg at 425 C. The higher temperature reduced the levels of potentially carcinogenic compounds such as boric acid Thermal degradation of waste HDPE plastics was studied using a and cyclopentanone [24]. Olefin content has been reported to model Q50 TGA (TA Instruments, Schaumberg, IL) under an inert decrease with increasing reaction temperature [9]. atmosphere of pure nitrogen with a flow rate of 60 mL/min. TGA As mentioned previously, the product distribution can be experiments were designed to determine optimal operating con- manipulated by the suitable choice of a catalyst. Some catalysts ditions and suitable catalysts for HDPE depolymerization. A sample have selectivity toward gasoline-range hydrocarbons while others size of approximately 18e20 mg was used for each study. For cat- have selectivity toward diesel [16]. For example, HZSM-5 increases alytic studies, a sample-to-catalyst ratio of 10:1 was maintained gasoline yield relative to other catalysts [4]. In another study, Elordi [14]. et al. recovered 58e70% crude oil from HDPE pyrolysis using zeolite-based catalysts [2]. Fluid cracking catalysts and reforming 2.3. Pyrolysis of HDPE to plastic crude oil catalysts can increase the yield of gasoline-range hydrocarbons [14]. Batch-scale pyrolysis of HDPE storage boxes was conducted with One of the limitations in the current methods for plastic to fuel and without catalysts in a 2 L commercial reactor (Be-h desktop conversion, however, is the inability to provide an energy-saving plastic to oil unit E-N-Ergy, LLC, Mercer Island, WA) as discussed in process to maximize plastic waste conversion as well as target se- detail in earlier publications [3]. A picture of the unit along with lectivities (e.g., diesel or gasoline fractions) [25]. The other chal- unit operations and process is provided in Fig. 1. In brief, about lenge involves the search for catalysts that possess lower acidity, 600 g of HDPE were pyrolyzed in each trial and vapors thus evolved yet produce high conversion [26]. were condensed, collected, and referred to as plastic crude (PC) oil. In our earlier work [16], a design of experiments (DOE) approach The reaction parameters used for pyrolysis are summarized in was used and determined that reaction temperature and time were Table 1. The solid fraction left in the reactor was collected during the most important factors influencing product oil yield. Kinetics reactor clean-up, which included a high boiling fraction and resi- developed for both catalytic and non-catalytic processes revealed dues. The gaseous fraction was calculated from the mass balance that Y-zeolites enhanced PE cracking. Reaction conditions were difference. The solid fraction left in the reactor after pyrolysis runs optimized using response surface methodology developed from was dissolved in dichloromethane (DCM) and filtered using central composite design using thermogravimetric analysis (TGA), Whatman filter paper no.1 (pore size 0.45 mm). DCM was 886 B. Kunwar et al. / Energy 111 (2016) 884e892

Fig. 1. Scheme for conversion of storage box HDPE to fuels.

Table 1 Reaction conditions and plastic-catalyst combinations for pyrolysis.

Sample name Run time (h) Reactor temperature (C) Catalyst Plastic to catalyst ratio

PE-460 3 460 PE-475 3 475 PE-Z400 3 400 Y-zeolite 10:1 PE-Z400-460a PE-Z410 3 410 Y-zeolite 10:1 PE-Z410-430b PE-Z430 3 430 Y-zeolite 10:1 PE-Z430-5 5 430 Y-zeolite 10:1

PE-M4501-6 6 450 MgCO3 10:1 PE-M4502-6 6 450 MgCO3 10:2 a After the reaction was completed at 400 C, the temperature was increased to 460 C to recover crude oil from the reactor. b After the reaction was completed at 410 C, the temperature was increased to 430 C to recover crude oil from the reactor. evaporated from both the residue (RR) and filtrate (RF). The liquid The results indicated that the boiling point distribution was similar fraction was collected every 15 min for the first hour, every 30 min to D1; therefore, this fraction was combined with D1. for the second hour, and every hour thereafter. The yields from catalytic pyrolysis at 400 C and 410 C were low even after 3 h of 2.5. Characterization crude oils, residues, and distillates reaction time and the temperatures were raised to 460 C and 430 C, respectively, to recover the remaining fraction. The catalytic Elemental analysis of PC oils and RF was conducted in duplicate reactions in which reaction temperatures were raised from 400 to using an Exeter Analytical (Chelmsford, MA) CE-440 Elemental 460 C and 410 to 430 C are represented as PE-Z400-460 and PE- Analyzer. Total CHN (carbon/hydrogen/nitrogen) elemental per- Z410-430 throughout this paper (Table 1). The catalytic pyrolysis centages were determined by elemental analysis. Oxygen per- were repeated to check the repeatability of the results. The yield centage was calculated by mass balance closure. This data was used varied by less than 5% under similar pyrolysis conditions. to calculate higher heating values (HHV) of various products. Boiling point distribution of PC oils and RF were obtained by 2.4. Distillation of plastic crude oil performing simulated distillation according to ASTM 7169. Analysis was performed on 1% (w/w) sample solutions in carbon disulfide PC oils were distilled in an automated 36e100 spinning band (CS2), using an HP (Palo Alto, CA) 5890 Series II FID gas chro- distillation system from BR Instrument (Easton, MD). The PC oils matograph as described by Sharma et al. [3]. were separated into six fractions: <35 C (lower molecular weight Molecular weight (MW) of PC oils was determined by gel hydrocarbons), motor gasoline (MG; 35e185 C), a transition frac- permeation chromatography (GPC) as reported by Sharma et al. [3] tion between motor gasoline and diesel #1(185e195 C), diesel #1 on a Waters Styragel HR1 SEC column (7.8 mm 300 mm) and a (D1; 195e290 C), diesel #2 (D2; 290e350 C), and vacuum gas oil Waters (Milford, MA) 2414 RI detector. Tetrahydrofuran (THF) was (VGO; >350 C). The 185e195 C fractions were analyzed using used as mobile phase (1.0 mL/min). The resulting chromatographic simulated distillation to determine the boiling point distribution. data was processed using Matlab (Natick, MA) software to provide B. Kunwar et al. / Energy 111 (2016) 884e892 887 weight-average MW (Mw) and polydispersity index (PDI). balance difference); and a solid residue collected after the reaction. Chemical functionality information was obtained by analyzing The yields of PC oil, residue, and gases are presented in Table 3. the fuel fractions using Fourier-Transform infrared (FT-IR) and nu- Pyrolysis without a catalyst at 475 C yielded about 93% PC oil clear magnetic resonance (NMR) spectroscopes. 1H NMR data were (Fig. 2). Gaseous products resulting from plastic pyrolysis were not collected using a Varian Unity Inova Advance-400 spectrometer analyzed in this study, but literature data suggests that they mainly running Topspin 1.4 pl8 software operating at 400 MHz using a 5- consist of C2 (52%) and C4 (32%) hydrocarbons [3]. The yield of PC oil mm BBO probe. Samples were dissolved in CDCl3 and all spectra was higher in the non-catalyzed high temperature pyrolysis, but were acquired at ambient temperature. Chemical shifts (d) are re- the oil was waxy indicating the presence of high-boiling n-paraf- ported as parts per million (ppm) from tetramethylsilane based on finic components. Catalytic pyrolysis at lower temperatures resul- the lock solvent. ted in higher solid residues (34%), and lower oil yield either due to FT-IR spectra were obtained on a Thermo-Nicolet Nexus 670 FT- incomplete conversion of HDPE or the temperature was not high IR spectrometer (Madison, WI) with a Smart ARK accessory con- enough to carry vapors to the condensers (Fig. 2). When the tem- taining a 45 ZeSe trough in a scanning range of 650e4000 cm 1 for perature was increased the yield of PC oil increased. Since HDPE 64 scans at a spectral resolution of 4 cm 1. TGA was also conducted pyrolysis reactions have a high activation energy (280e320 kJ/mol), on the three fractions obtained from the optimized batch-scale increasing the temperature may increase the yield of the liquid runs: plastic crude (PC) oil, residue (RR), and filtrate (RF). phase [4,16]. As the temperature was increased from 460 Cto Fuel properties were measured in triplicate following American 475 C, the liquid yield increased (86%e93%). Similar trends were Oil Chemists' Society (AOCS), American Society for Testing and observed with the zeolite-catalyzed process (Fig. 2). Materials (ASTM), and European Committee for Standardization MgCO3 did not yield a substantial temperature reduction (only (CEN) standard test methods using instrumentation described 6 C) relative to uncatalyzed pyrolysis, based on TGA data. However, previously [27e29]. The fuels were analyzed for the following: acid the batch scale reaction resulted in similar PC oil yields to non- value (AV, mg KOH/g) via AOCS Cd 3d-63; cloud point (CP, C) via catalyzed pyrolysis, even when operated at 10 C lower than the ASTM D5773; cold filter plugging point (CFPP, C) via ASTM D6371; non-catalyzed pyrolysis temperature as shown in Fig. 3. Increasing 3 density (15 C, g/cm ) via ASTM D4052; flash point (FP, C) via the MgCO3 catalyst ratio increased PC oil yield from 80% to 84%. ASTM D93; gross heat of combustion (higher heating value, HHV, Although the plastic to catalysts ratio of 10:2 increased the PC oil MJ/kg) via ASTM D4809; induction period (110 C, IP, h) via EN yield by 4%, this yield increase may not offset catalyst costs. Thus, a 15751; moisture content (ppm) via ASTM D6304; kinematic vis- 10:1 HPDE-to-catalyst ratio may be the optimum condition for cosity (40 C, KV, mm2/s) via ASTM D445; lubricity (60 C, mm) via maximum efficiency. Catalytic pyrolysis using both Y-Zeolite and ASTM D6079; pour point (PP, C) via ASTM D5949; and specific MgCO3 increased gaseous products (16e19%) compared to the non- gravity (15 C, SG) via ASTM D5052. Derived cetane number (DCN) catalytic process (7e13%). This trend was attributed to the fact that was determined (n ¼ 32) by Southwest Research Institute (San catalysts promote more cracking reactions to generate low boiling/ Antonio, TX) following ASTM D6890. Oxidation onset temperature molecular weight compounds. (OT, C) was measured by pressurized differential scanning calo- PC oil was collected at regular time intervals throughout the rimetry (PDSC) [30]. Pour point was measured with a resolution of reaction period (Fig. 3 and SI Table 1). The majority of the residue 1 C instead of the specified 3 C increment. Surface tension (25 and remaining after pyrolysis may have been the fraction with a boiling 40 C, mN/m) was measured as described by Doll et al. [31]. point above pyrolysis temperature. These residues, along with the vacuum gas oil (VGO) fraction obtained after PC distillation, can potentially be used as lubricant basestocks [32]. 3. Results and discussion The change in product composition in catalytic reactions is rationalized with stepwise cleavage reactions. Intiation occurs on 3.1. HDPE to plastic crude oil and its distillates defective sites of the polymer chain. The acidic catalyst donates a proton to generate a carbonium polymer chain while a basic cata- In our earlier work [16], TGA was used to determine the lyst accepts a proton from polymer to yield a carbocation chain decomposition temperature of various polymers, kinetic parame- [33e35]. The polymer chain is then cleaved through b-scission, ters, and screen various catalysts. The temperatures required for thereby forming lower MW branched paraffins and olefins, as show catalytic pyrolysis of HDPE boxes in the current work are summa- in Figs. 4 and 5. Further depolymerization continues through suc- rized in Table 2. Among the six catalysts listed in Table 2, Y-zeolite cessive attacks by acidic sites, other carbonium ions or basic sites to seems to be the most suitable catalyst as it reduced the maximum yield oligomer fractions. Finally, intermediate ions undergo rear- weight loss temperature by 80 C compared to the non-catalytic rangement resulting in termination of the depolymerization process (Table 2). Magnesium carbonate was also used as an reaction. inexpensive basic catalyst to compare the product yield and quality. Distillation was conducted to separate MG, D1, D2, and VGO Batch-scale pyrolysis of HDPE plastic yielded three fractions: a fractions. Distillation of PC oils from all three runs showed a wide liquid product, referred to as PC oil; gaseous products (from mass range of product distribution. Catalytic runs using Y-zeolite demonstrated selectivity for MG, MgCO3 had selectivity for D1 and D2, and non-catalytic runs had selectivity for diesel and VGO (SI Table 2 fl Thermogravimetric analysis of HDPE and catalyst combinations, showing Fig. 1). However, pyrolysis temperature also in uenced product maximum weight loss. distributions. PC oils from catalytic conversion had higher MG and D1 content, indicating catalyst supported cracking. Therefore, the Max wt loss temp (C) choice of catalyst can increase and/or change the selectivity of the HDPE 474 product. HDPE þ FCC 465

HDPE þ MgCO3 468 HDPE þ ZrSO4 458 3.2. Characterization of pyrolysis products HDPE þ Y-Zeolite 394 HDPE þ SBA 470 Elemental analysis showed less than 2% nitrogen content and HDPE þ MCM 468 less than 0.7% oxygen content in all PC oil samples (Table 3). The 888 B. Kunwar et al. / Energy 111 (2016) 884e892

Table 3 Yield and chemical composition of plastic and PE crude oils at various conditions.

Sample Yield % Elemental properties Calorific value GPC molecular weight

Plastic crude oil Residue Gas C% H% N% O% HHV* (MJ/kg) Mw Mn PDI PE 85.1 14.5 0.4 0 49.3 PE-460 86 1 13 85.3 14.2 0.5 0 49.6 589 373 1.6 PE-475 93 1 7 85.4 14.4 0.2 0 49.7 441 248 1.9 PE-Z400 29a 83.3 14.2 1.8 0.7 48.2 473 258 1.8 PE-Z400-460 37b 2 32 85.0 14.0 1.0 0 50.1 318 177 1.8 PE-Z410 37a 84.0 14.5 1.5 0 50 353 215 1.6 PE-Z410-430 30b 6 27 85.0 14.0 1.0 0 50.1 297 185 1.6 PE-Z430 49 34 18 84.8 14.4 0.8 0 49.1 446 231 1.9 PE-Z430-5 75 6 19 85.0 14.0 1.0 0 50.2 397 216 1.8 PE-M4501-6 80 2 18 85.5 14.3 0.2 0 50 259 198 1.3 PE-M4502-6 84 0 16 85.3 14.3 0.4 0 49.7 279 214 1.3 PE-475 (RF) 84.1 13.5 0.5 1.9 47.3   * ¼ : þ : O High heating value was calculated using Dulong's equation: HHV 0 3383 1 422 H 8 [3]. a Plastic crude oil collected at given temperature. The amount of gas and solid left in these runs was not calculated. b Plastic crude oil was collected at a lower temperature (indicated bya), and then temperature was increased to given temperature to collect the remaining oil. This yield was in addition to the yield at the lower temperature. After weighing the remaining residue, gas yield was calculated by difference at that temperature.

Dulong's formula based on elemental analysis results and was approximately 50 MJ/kg. The RF sample had a slightly lower HHV of 43e47 MJ/kg, which was likely due to lower carbon content and higher oxygen content than the PC oils. GPC analysis was conducted in triplicate to determine MW distribution and the results are summarized in Table 3. Average MWs were lower in PC oils produced at higher temperatures from both catalytic and non-catalytic runs. The Mn values of PC oils ob- tained from catalytic runs were not significantly different from those of conventional crude oil (Mn~250) [37]. Polydispersity index (PDI) ranged from 1.3 to 1.9, indicating a narrow distribution of MWs for PC oils (Table 3) [3]. The increase in temperature from 410 to 430 C (PE-Z410 to PE-Z410-430) did not affect the PDI nor the crude oil properties. Pyrolysis of HDPE with MgCO3 yielded an oil with a lower PDI than Y-zeolite, likely indicating that acidic cata- lysts promote better cracking than MgCO3. Simulated distillation (SimDist) analysis was performed on the PC oil and RF and the

Fig. 2. Effect of temperature on the yield of crude oil. chromatograms for catalytic and non-catalytic PCs are shown in Fig. 6. elemental content was similar to the original HDPE plastic. Lower The data obtained from SimDist were processed in MATLAB to oxygen percentage improves the oxidation stability of the crude oil provide product profiles in terms of four fractions: <185, 185e290, [36]. The higher heating value of PC oils was calculated using 290e350, and >350 C, corresponding to the boiling point range of

Fig. 3. Percent yield of plastic crude oil collected at regular time intervals, obtained from pyrolysis of HDPE with and without catalysts. For PE-475, PC oil was not collected as it clogged the outlet during the collection at 0 min. B. Kunwar et al. / Energy 111 (2016) 884e892 889

Fig. 4. Acid catalyzed depolymerization (drawn based on the mechanisms in citations [33e35]).

Fig. 5. Base catalyzed depolymerization (drawn based on the mechanisms in citations [33e35]).

MG, D1, D2, and VGO (Fig. 7). PC oils obtained from catalytic runs 3.3. Chemical characterization of distillates had higher percentages of MG and D1 and a lower amount of VGO than non-catalytic runs. Catalytic pyrolysis, therefore, has the po- The elemental composition of distillate fractions MG, D1, D2, tential to produce almost 96% low boiling fuel fractions (MG, D1 and VGO showed approximately 85% carbon, 15% hydrogen, and a and D2) using Y-Zeolite and MgCO3 compared to 73e84% for non- negligible amount of nitrogen and oxygen. This result was similar to catalytic pyrolysis. PC oils obtained from non-catalytic pyrolysis that of the raw plastic and the PC oil. A high content of carbon and were mainly composed of D1 and D2 (55e59%) and small amounts hydrogen resulted in a higher heating value (HHV) for the distillates of MG (17e20%) and VGO (16e23%). PC oils from catalytic and non- of approximately 50 MJ/kg (Table 4), which is similar to that of catalytic runs had a final boiling point of 375 C and 450 C, petroleum crude oils. Unlike bio-oil, the absence of oxygen and respectively. SimDist chromatograms of the RF product were also lesser olefins will provide similar ageing characteristics to PC oil as carried out and the RF product was found to be on the high boiling a petroleum crude oil. The relative lower oxygen percentage in the side, with an initial boiling point at around 200 C and a mean PC oil will likely enable it to have better ageing stability compared boiling point ranging between 400 and 450 C(SI Table 2). to bio-oil produced from lignocellulosic feedstocks. The weight loss percentage of PC oils, RF, and RR at 100, 200, GPC data shows that the fuel fractions with lower boiling points 300, and 400 C from products obtained from HDPE at 460 C, had lower MWs compared to the higher boiling point fractions. HDPE þ Y-Zeolite at 430 C, and HDPE þ MgCO3 at 450 C using TGA Distillates produced using catalysts had higher PDI, indicating wide are shown in Fig. 8. The TGA weight loss data are provided in variation in molecular weights of such samples, while those pro- supplemental SI Table 3. The PC oils obtained from non-catalytic duced in the absence of catalysts had lower PDI, indicating a narrow pyrolysis lost more than 90% of their mass at about 300 C, distribution of MWs (Table 4). These fuel fractions also had a nar- whereas PC oils obtained from catalytic pyrolysis lost approxi- row range of boiling point hydrocarbons. mately 90% of their mass at 200 C. This indicates the presence of Simulated distillations were performed on fuel fractions to more volatile compounds, which validates the SimDist and GPC verify purity in terms of boiling point distribution. The data ob- results. Filtrates of residues (RF) of all samples were high-boiling tained from SimDist were processed into four fractions: MG fractions with low mass loss at 200 C (~20%), moderate loss at (<185 C), D1 (185e290 C), D2 (290e350 C), and VGO (350þ C). 300 C(>50%), and high loss at 400 C(>92%). Simulated distillation results were in agreement with the experi- Residues (RR) of the PE-Z410 run only had 25% mass loss at mental fractions obtained from distillation. The experimental MG 400 C compared to 65% at 400 C for the non-catalytic run (PE- fraction contained more than 83% fraction in gasoline range, with 460). This reduced mass loss may be due to the presence of inor- the remainder consisting of fraction > 185 C. The D1 fraction from ganic materials with decomposition temperatures higher than distillation contained more than 80% in D1 range, 1e8% in D2 range, experimental temperatures. and approximately 10% in MG range. No VGO was detected in the 890 B. Kunwar et al. / Energy 111 (2016) 884e892

Fig. 6. Simulated-distillation chromatograms of PC oil obtained by pyrolysis of (A) HDPE at 460 C (PE-460), (B) HDPE þ Y-Zeolite at 430 C (PE-Z430), and (C) HDPE þ MgCO3 (10:1) at 450 C (PE-M4501-6). SimDist chromatograms for other PC oil and RF samples are available in SI Figs. 1 and 2.

Fig. 8. Plastic crude (PC) oil, residue-filtrate (RF) and residue-residue (RR) mass loss at four different temperatures: 100, 200, 300, and 400 C.

Fig. 7. Percentage fuel fractions from plastic crude oil using SimDist. B. Kunwar et al. / Energy 111 (2016) 884e892 891

Table 4 Composition and properties of HDPE distillates.

Fuel fractions Sample GPC molecular weight Elemental composition Calorific value

Mn Mw PDI C% H% N% O% HHV (MJ/kg)

Motor Gasoline 1. PE 460 47.6 65.3 1.37 85.5 14.4 0 0.07 49.4 35e185 2. PE-Z430-5 43.3 76.3 1.91 85.3 14.5 0.2 0 49.5 3. PE-M4501-6 51.3 116 2.26 85.4 14.4 0.2 0 49.4 Diesel #1 4. PE 460 162 179 1.10 85.6 14.4 0.02 0 49.4 185e290 5. PE-Z430-5 83 141 1.70 85.8 14 0.2 0 48.9 6. PE-M4501-6 109 169 1.54 85.5 14.3 0.2 0 49.3 Diesel #2 7. PE 460 281 301 1.06 85.5 14.5 0.02 0 49.5 290e350 8. PE-Z430-5 275 295 1.09 86.0 14 0 0 49.0 9. PE-M4501-6 293 321 1.09 85.0 15 0 0 50.1 VGO 350þ 10. PE 460 670 809 1.19 85.5 14.5 0.01 0 49.6 11. PE-Z430-5 477 527 1.11 12. PE-M4501-6 472 509 1.08 86 14 0 0 49.0

MG and D1 fractions. expected, CFPP was lower in D1 prepared using Y-zeolite, as shown The percentage of olefins in MG and D1 was determined using in Table 5. The oxidative stabilities of the diesel samples as 1H NMR. Olefinic content affects oxidative stability, with higher measured by induction period (IP at 110 C) did not meet the limit percentages of olefins resulting in lower oxidative stability. The of 20 h or greater specified by EN 590. ASTM D975 does not specify peaks between 0.5 and 2.7 ppm indicated protons attached to al- limits for oxidative stability. The induction period was not kanes. For MG and D1, olefinic (alkene) content was lower for measured for the MG samples because they are too volatile for the zeolite-catalyzed pyrolysis compared to non-catalyzed and MgCO3 method. The Kinematic viscosity (KV) was similar in all MG and D1 catalyzed pyrolysis. We also found higher amounts of olefins in MG samples, with slightly lower KVs in MG and D1 obtained from runs fractions compared to D1 fractions. Protons in aromatic region were with Y-zeolite, thereby indicating the presence of a greater amount not detected in NMR spectra of any fractions (SI Table 4). of shorter-chain (less viscous) constituents. The DCN values for the Results obtained from Fourier transform infra-red (FT-IR) spec- diesel samples were above 40, which is the minimum limit pre- tral analysis confirmed the NMR data. The FT-IR data was domi- scribed by ASTM D975 for diesel [3]. The flash point satisfied the nated by alkane peaks. The peaks at the 2800e3000 cm 1 minimum requirement of 52 C, set by ASTM D975. However, the wavelengths represented CeH stretching vibrations of eCH3, eCH2 D1 obtained from the Y-zeolite run had a flash point below the and eCH, respectively. The presence of C]C stretching vibrations at minimum limits specified in the petrodiesel standard; this might be 1640e1650 cm 1 suggested the presence of alkenes. The peaks at due to the higher content of shorter chain and lower molecular 2800e 3000 and 1320e1480 cm 1 showed the presence of higher weight constituents, which is in agreement with results obtained concentrations of alkanes. The absence of other peaks indicated the for KV. A maximum wear scar of 620 mm is specified as the upper absence of additional functional groups (SI Fig. 4). For example, if limit for lubricity (60 C) in ASTM D975. The wear scars generated aromatics were present, we would have expected a peak between by the experimental diesel samples were well within the petro- 3000 and 3100 cm 1. diesel standard. The shorter wear scars were probably due to the presence of a trace amount of oxygenated constituents, as these 3.4. Fuel properties of gasoline and diesel fractions possess greater lubricity than hydrocarbons. The acid value was negligible in all of the MG and D1 samples. The higher heating With regard to cold flow properties, cloud point (CP) was lower values for both the gasoline and diesel samples were higher than in both MG and D1 fractions obtained from catalytic runs relative to that of ULSD (45.15 MJ/kg) [3]. D1 had higher energy content than uncatalyzed pyrolysis, and it was significantly lower with Y-zeolite. MG because of the larger hydrocarbon chains in D1. The HHV Similar results were obtained for pour point (PP). However, PP was calculated by elemental content are higher by 3 MJ/kg compared to not detected for MG obtained from the run with Y-zeolite. The HHV determined experimentally using the ASTM bomb calorimetry CFPPs of the MG samples were similar for all of the runs, yielding method. values below the detection limit (50 C) of our instrument. As

Table 5 Fuel properties of motor gasoline and diesel obtained from green plastics pyrolysis.

Properties, (units) Motor gasoline Diesel

PE 460 PE-Z430-5 PE-M4501-6 PE 460 PE-Z430-5 PE-M4501-6

CP, (C) 28 <73 34 19 40 23 PP, (C) <73 n/a <73 28 50 27 CFPP, (C) <-50 <50 <50 27 42 27 IP, 110 C, (h) n/a n/a n/a 1.4 (0.6) 0.8 (0.2) 1.3 (0.1) KV, 40 C, (cSt) 0.69 0.56 0.66 1.65 1.57 1.73 DCN n/a n/a n/a 62.2 47.7 63.7 Flash point, (C) n/a n/a n/a 74.0 24.0 77.0 Wear scar, 60 C, (mm) n/a n/a n/a 234 501 433 SG, 15 C 0.7 0.7 0.7 0.8 0.8 0.8 Density, 15 C, (kg/m3) 0.746 0.733 0.733 0.787 0.798 799 AV, (mg KOH/g) 0.0 0.0 0.0 0.1 0.1 (0.03) 0.0 HHV, (MJ/kg) 45.4 (0.2) 45.6 (0.3) 45.8 (0.1) 46.0 (0.2) 46.0 (0.3) 46.5 (0.1) Surface tension at 25 C, (mN/m) 21.5 (0.1) 20.4 (0.1) 21.3 (0.1) 25.4 25.3 25.7 Surface tension at 40 C, (mN/m) 20.0 (0.1) 18.8 (0.1) 19.6 (0.1) 23.8 (0.1) 23.7 (0.1) 24.0 (0.1) 892 B. Kunwar et al. / Energy 111 (2016) 884e892

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