Catalytic Co-pyrolysis of Biomass and Different Plastics (Polyethylene

National Engineering Laboratory for Biomass Power Generation Equipment, North China ..... Renewable and Sustainable Energy Reviews 2017 73, 346-368 ...
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Catalytic Co-pyrolysis of Biomass and Different Plastics (Polyethylene, Polypropylene, and Polystyrene) To Improve Hydrocarbon Yield in a Fluidized-Bed Reactor Huiyan Zhang,† Jianlong Nie,† Rui Xiao,*,† Baosheng Jin,† Changqing Dong,‡ and Guomin Xiao§ †

Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, and §School of Chemistry and Chemical Engineering, Southeast University, Nanjing 210096, People’s Republic of China ‡ National Engineering Laboratory for Biomass Power Generation Equipment, North China Electric Power University, Beijing 102206, People’s Republic of China ABSTRACT: Biomass catalytic fast pyrolysis can produce aromatics and olefins, which are used as petrochemicals. However, the yields of aromatics and olefins are still very low. In this work, catalytic co-pyrolysis of pine sawdust and plastics (polyethylene, polypropylene, and polystyrene) was conducted in a fluidized-bed reactor to improve the yields of aromatics and olefins. The effects of different temperatures, polyethylene/pine sawdust ratios, different catalysts, and plastics on the product distributions were studied. The results show there are some positive synergistic effects between the two feedstocks. The maximum carbon yield of petrochemicals (71%) was obtained at 600 °C with a spent fluidized catalytic cracking (FCC) catalyst and polyethylene/ pine sawdust ratio of 4:1. LOSA-1 presents better catalytic performances than Al2O3 and spent FCC catalysts. The petrochemical carbon yield with LOSA-1 is almost 2 times that without catalyst. Catalytic co-pyrolysis of polystyrene and pine sawdust produced the highest and lowest yields of aromatics (47%) and olefins (11.4%), respectively.

1. INTRODUCTION The shortages of fossil fuels combined with environmental issues stimulate the development of renewable resources. Lignocellulosic biomass is the most abundant and inexpensive sustainable source of carbon that can be converted to liquid fuels and chemicals.1 Several routes, such as gasification followed by Fischer−Tropsch synthesis,2,3 pyrolysis followed by pyrolysis oil upgrading,4−8 and hydrolysis followed by aqueous-phase reforming,9,10 have been proposed for converting biomass to liquid fuels and chemicals. These technologies are significantly more complicated with multiple steps and, therefore, require higher capital costs. Catalytic fast pyrolysis (CFP) of biomass is recognized as a promising technology because it can convert solid biomass to valuable liquid fuels and chemicals in a single-step process.11,12 Furthermore, the reactor is operated at moderate temperature, atmospheric pressure, and no hydrogen conditions. CFP of biomass can produce several primary petrochemicals, including benzene, toluene, xylene, ethylene, and propylene. One of the critical challenges with CFP is to increase the yield of usable petrochemicals.13 Dozens of biomass and biomass-derived feedstocks have been used to produce aromatics and olefins using CFP technology.14−17 It was found that the hydrogen/carbon effective (H/Ceff) ratio, as shown in eq 1, plays an important role in converting biomass to liquid fuels efficiently. With an increasing H/Ceff ratio, CFP of biomass derivatives produces more petrochemicals (aromatics + olefins) and less coke.13 H − 2O H/Ceff = (1) C When the H/Ceff ratio of feedstocks is less than 1, they are difficult to upgrade to petrochemical products over a zeolite © 2014 American Chemical Society

catalyst because of the rapid aging and deactivation of the catalyst.18 However, the H/Ceff ratio of biomass is only between 0 and 0.3. Thus, biomass is a hydrogen-deficient feedstock, which is one of the most important reasons for the low petrochemical yield in CFP of the biomass process. Co-feeding biomass with some hydrogen-rich feedstocks, such as alcohols and waste oils, has been investigated in our previous works.19,20 The results showed that co-feeding increased the petrochemical yield significantly. Furthermore, the isotopically labeled 13C methanol was processed with 12C pine wood to identify how methanol and wood are incorporated into the final products.20 The results indicated that the elements of carbon and hydrogen have exchanged between the two feedstocks. The synergetic effect existed and led to the increase of the petrochemical yield from biomass. Williams and his co-workers used ethylene as a high H/Ceff ratio to co-feed with biomass-derived dimethylfuran, and more p-xylene was produced via the Diels−Alder reaction.21 The reaction of dimethylfuran and ethylene can produce a lot of p-xylene (shown in Figure 1). Dimethylfuran and its derivates are one of the most important chemical groups of biomass fast pyrolysis. Ethylene can be economically obtained from pyrolysis of plastics. In comparison to gas or liquid feedstocks mentioned above, solid waste plastic is a cheaper hydrogen-rich feedstock with economic and environmental advantages. Waste plastics are mainly formed by the polymerization of olefins with a H/Ceff ratio of 2, which means they are proper feedstocks for coconversion with biomass. There are huge amounts of waste plastics in the world. For example, the global production of Received: September 25, 2013 Revised: January 25, 2014 Published: January 29, 2014 1940

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Table 1. Ultimate and Proximate Analyses of Pine Sawdust and Different Plastics (wt %) ultimate analysis

Figure 1. Reaction of dimethylfuran and ethylene over a ZSM-5 catalyst to form p-xylene.

waste electrical and electronic equipment (WEEE) plastics is around 40 million tonnes per year.22 In the European Union, the yield of WEEE plastics is increasing 3 times as fast as the growth of average municipal waste.23 The waste plastics cause serious damage to the environment and have adverse effects on human health. Therefore, the recycle of waste plastic is not only beneficial for energy recovery but also beneficial for reducing environmental pollution. Many researchers have studied pyrolysis,24,25 catalytic pyrolysis,26−30 and co-pyrolysis31−34 of plastics and biomass to produce liquid fuels and chemicals. Their results show that plastics are promising feedstocks for producing liquid fuels and chemicals via pyrolysis technology. They found that the pyrolysis oil yield of co-pyrolysis is significantly higher than those of plastics and biomass pyrolysis alone. However, few studies are focused on co-pyrolysis of plastics and biomass in the presence of catalysts. Sharypov and his co-workers studied catalytic co-hydropyrolysis of wood and synthetic polymers with an iron ore catalyst using a rotating autoclave at 6.0 MPa.35 They obtained a lot of paraffins using an iron ore catalyst. Li and his co-workers conducted CFP of cellulose by co-feeding low-density polyethylene (PE) over a ZSM-5 catalyst in a fixed-bed reactor.36 The results showed that there was a synergetic effect between the different feedstocks to produce more aromatics and less coke. Otherwise, the raw biomass, reaction conditions, different plastics, biomass/plastics mixture composition, and catalysts (especially zeolite catalysts) in the co-feeding process should be studied in a more efficient reactor, such as fluidized beds. In this work, co-pyrolysis of pine sawdust and different plastics with different catalysts was conducted in a continuous feeding fluidized-bed reactor. The effect of the temperature, plastic/pine sawdust ratio, different plastics [PE, polypropylene (PP), and polystyrene (PS)], different catalysts [LOSA-1, spent fluidized catalytic cracking (FCC), and γ-Al2O3] on the product yields and selectivities were investigated and compared in detail. The proper catalyst, plastics, and its proportion for catalytic co-pyrolysis with pine sawdust were obtained.

feedstock

Cad

Had

PE PP PS pine sawdust

85.5 85.8 92.2 41.88

14.5 14.2 7.8 4.17

proximate analysis Oad

Vad

FCad

Aad

Mad

53.02

99.96 80 99.5 70.2

0.04 20 0.5 22.7

0 0 0 0.9

0 0 0 6.2

analysis for acid properties are shown in Table 2 and Figure 2, respectively. Table 3 shows the composition of all three catalysts using an X-ray fluorescence (XRF) spectrometer instrument.

Table 2. BET Analysis of LOSA-1, γ-Al2O3, and Spent FCC Catalysts catalyst

LOSA-1

spent FCC

γ-Al2O3

BET surface (m2 g−1) pore diameter (nm) pore volume (cm3 g−1)

220.21 2.14 0.22

242.7 4.85 0.21

134.68 6.41 0.22

Figure 2. NH3-TPD analysis of LOSA-1, γ-Al2O3, and spent FCC catalysts.

Table 3. Chemical Composition Analysis of LOSA-1, γAl2O3, and Spent FCC Catalysts

2. MATERIALS AND METHODS

percentage (%)

2.1. Materials. The pine sawdust was supplied by a local sawmill of Jiangsu, China. Plastics (PE, PP, and PS) were bought from Li Ke Polymer Materials Company in Shanghai, China. The particle size of plastics is around 80−120 mesh. The pine sawdust was ground and seized to yield a particle size of 70−100 mesh. The elemental composition of pine sawdust and plastics is listed in Table 1. LOSA-1, spent FCC, and γ-Al2O3 were used as the catalysts in the experiment. Spent FCC and LOSA-1 were provided by Sinopec Yangzi Petrochemical Company, Ltd. LOSA-1 is a commercial additive for increasing the olefin yield in the catalytic cracking process. The main content of LOSA-1 is ZSM-5. Spent FCC was a spent commercial catalyst, which was used in the FCC process. γ-Al2O3 was provided by Shanghai Yuejiang Titanium Chemical Manufacture Co., Ltd. The particle size of all catalysts distributed from 150 to 230 mesh. After drying at 110 °C for 2 h, 30 g of catalyst was loaded in the reactor. The Brunauer−Emmett−Teller (BET) analysis for surface characteristics and temperature-programmed desorption of ammonia (NH3-TPD) 1941

composition

LOSA-1

spent FCC

γ-Al2O3

Al2O3 SiO2 Na2O K2O CaO ZnO Fe2O3 P2O5 TiO2 CeO2 La2O3 NiO V2O5 Sb2O3

25.3 58.9 0 0.1 0.12 0.05 0.15 1.36 0.091 0.011 0.01 0.007 0.0066 0

48.7 40.1 0.0019 0.14 1.19 0.34 0.71 0.94 0.29 1.19 2.61 0.77 0.29 0.66

99.8 0.06 0.041 0.023 0.022 0.01 0.0048 0.015 0 0 0 0 0 0

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Figure 3. Schematic of the continuous feeding fluidized-bed reactor system for catalytic co-pyrolysis of pine sawdust and plastics.

Figure 4. Product yields and selectivities as a function of the temperature in catalytic co-pyrolysis of pine sawdust and PE: (a) yields of petrochemicals (aromatics + olefins), aromatics, and olefins, (b) yields of char and coke, CO, CO2, and CH4, (c) selectivities of benzene, toluene, xylene, other monoaromatics, and naphthalene and its derivatives, and (d) selectivities of ethylene, propylene, and butene. 2.2. Experimental Setup. A schematic diagram of the continuous feeding fluidized-bed reactor system for catalytic co-pyrolysis of pine sawdust and plastics is shown in Figure 3. The reactor was made of a

304 stainless-steel tube with 32 mm inner diameter and 280 mm freeboard height. The biomass handling capacity of the reactor is 5− 200 g/h. A total of 30 g catalyst was loaded in the reactor before all 1942

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Table 4. Detailed Product Yields and Selectivities of Pine Sawdust/PE Mixture (1:1) Catalytic Co-pyrolysis at Different Temperatures temperature (°C) compound

400

450

500

550

600

650

26.7 30.3 4.5 11.4 31.2 41.7 1.1 2.6 1 1.9 3.5 4.4 30 23.2 66.8 73.8 33.2 26.2 Aromatic Selectivity 8.7 16 15 17.8 1.4 0.9 19.5 17.2 25.3 13.9 0.3 0.3 3.6 5.3 5 8.8 21.2 19.8 Olefin Selectivity 81.5 70.5 16.2 24.4 2.3 5.1

28.7 11.2 39.9 4.2 1.2 4.3 20 69.6 30.4

37.1 19.6 56.7 4.2 1.3 4.3 19.5 86 14

24.8 22.4 47.2 7.7 1.4 5.6 19 80.9 19.1

33.5 21.8 0.5 10.1 7.5 0.9 6 10.7 9

55.5 12.2 0 1.5 2.4 0.1 26.7 1.4 0.2

53.8 8.9 0.2 1.1 1.8 0.5 30.2 3.2 0.3

86.1 11.6 2.3

89.3 10.5 0.2

95.8 4.1 0.1

Overall Yields aromatics C2−C4 olefins petrochemicals methane CO2 CO char and coke total carbon balance unidentified

22.3 0.4 22.7 0.1 0.7 1.1 30.8 55.4 44.6

benzene toluene ethyl benzene xylene other mono-aromatics indene naphthalene methylnaphthalene multi-methylnaphthalene

5.3 12.2 2 18.9 28.3 0 3 7.3 23

ethylene propylene butene

61.8 30 8.2

experiments. The catalyst bed is supported by the air distribution plate, which is a 300-mesh 316 stainless-steel wire netting. Biomass is fed into the reactor by two continuous feeding screw feeders. The first screw feeder is applied to definite quantitative determination. The secondary screw feeder is applied for feeding the feedstocks in the reactor rapidly. The hopper is swept with N2 at a rate of 100 mL/min to maintain an inert environment of the feeding unit. The fluidizing gas (N2, 99.99%) is introduced into the reactor through the air distribution plate at a rate of 250 mL/min. A cyclone is set outside of the reactor to remove and collect small particles, which contain catalyst and char. The vapors are introduced into a two-stage condenser apparatus followed by the cyclone. The first condenser unit is located in an ice-water bath at a temperature of about 0 °C. The secondary condenser unit is located in a dry-ice/ethanol bath at −55 °C. Finally, the non-condensable gases are collected by gas-sampling bags and analyzed by gas chromatography/flame ionization detector (GC/FID) and gas chromatography/thermal conductivity detector (GC/TCD). The condensable liquid products are then analyzed by gas chromatography/mass spectrometry (GC/MS). For a typical run, the experiment is conducted about 20 min. After reaction, the carrier gas is switched to O2 at 250 mL/min to calcine the catalyst and burn the produced char and coke. Then, the effluent gas is sent to a copper converter, which is maintained at 250 °C, to convert CO to CO2. After the absorption of water with silica gel, CO2 was captured by an ascarite trap. Therefore, the char and coke carbon yield can be obtained by the mass of CO2 captured by the ascarite trap. 2.3. Product Analysis. Different temperatures (400−650 °C) and biomass/plastic ratios (1:4−4:1) were tested to obtain the optimum reaction conditions. The liquid products were identified by GC/MS (GC, 7890A, Agilent; MS, 5975C, Agilent). The gas output was calculated by the total collected gas volume measured by the accumulative flowmeter as well as the components and their percentages determined by GC/FID and GC/TCD (Shimadzu 2014 GC system). A Restek Rtx-VMS capillary column (catalog number 19915) was used in GC/FID to quantify olefins, while a HAYSEP D packed column in GC/TCD was used to analyze CH4, CO, and CO2. Both FID and TCD were maintained at 240 °C. Ultra helium was used

as the carrier gas. The following temperature ramp was used in this study: hold at 35 °C for 5 min, ramp to 140 °C at 5 °C/min, ramp to 230 °C at 50 °C/min, and hold at 230 °C for 8.2 min. The carbon yield is defined as the carbon mass of one product divided by the total mass of feeding carbon. The compounds of aromatics and their carbon yields were obtained by GC/MS with the external standard method. The gas components and their carbon yields were obtained by GC/ FID and GC/TCD. The carbon yield of char and coke was obtained by combusting them and analyzing CO2. The carbon balance was calculated as the sum of the product carbon yields, which include petrochemicals (aromatics + C2−C4 olefins), CH4, CO, CO2, coke, and char. The carbon yield of unidentified compounds was determined by difference. Product selectivity is calculated as the moles of carbon in the product relative to the total moles of aromatics or olefins.

3. RESULTS AND DISCUSSION 3.1. Effects of the Reaction Temperature on the Product Yields and Selectivities in Catalytic Co-pyrolysis of Pine Sawdust and PE. The product yields and selectivities as a function of the temperature in catalytic co-pyrolysis of pine sawdust and PE with a spent FCC catalyst are shown in Figure 4 and Table 4. The PE/pine sawdust mass ratio was 1:1. The results show that the aromatic carbon yield is much higher than the olefin yield. The carbon yield of aromatics gradually increased from 22.3% at 400 °C to 37.1% at 600 °C and then decreased to 24.8% at 650 °C, whereas that of C2−C4 olefins increased from 0.4 to 22.4%. The maximum total carbon yield of petrochemicals (aromatic + C2−C4 olefins) is 56.7%, which occurred at 600 °C. The main aromatic products include benzene, toluene, ethylbenzene, xylene, styrene, indene, naphthalene, methylnaphthalene, and multi-methylnaphthalene. The carbon yields of CO and CH4 increased gradually with the increasing temperature, whereas the char and coke yield decreased significantly. 1943

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Figure 5. Product yields and selectivities as a function of the PE proportion in catalytic co-pyrolysis of pine sawdust and PE: (a) yields of petrochemicals (aromatics + olefins), aromatics, and olefins, (b) yields of char and coke, CO, CO2, and CH4, (c) selectivities of benzene, toluene, xylene, other monoaromatics, and naphthalene and its derivatives, and (d) selectivities of ethylene, propylene, and butene.

Figure 5. The reaction temperature of these experiments was chose as the optimal temperature (600 °C) according to the above section. As shown in Figure 5a, the petrochemical (aromatics + olefins) yield increases nonlinearly with the increase of the PE proportion. This curvature indicates that there is a synergistic effect between the two feeds. The petrochemical carbon yield is higher than that obtained during catalytic pyrolysis of pine sawdust and PE independently. The maximum total carbon yield of petrochemicals (36% aromatics + 35% olefins) is obtained at the point of 80% PE (PE/pine sawdust = 4:1). The aromatic and C2−C4 olefin yields gradually increased and then decreased with an increasing PE proportion, whereas the char and coke yield decreased rapidly. The maximum yield of aromatics was obtained with 50% PE in the mixture, while that of olefins was obtained with 80% PE. The yields of CO and CO2 decreased with the increase of the PE proportion. This can be explained by two reasons: (1) The addition of plastics in biomass catalytic pyrolysis enhanced the H/Ceff ratio; therefore, more biomass was converted to aromatics and olefins. (2) The pyrolysis temperatures of biomass and plastic are different; the optimal temperature of plastic degradation is higher than that biomass. With regard to the lower content of the O atom, PE degradation produces less coke and non-condensable gas (CO and CO2) but lots of largemolecule organics, which belong to the unidentified compounds in this paper. When the biomass is co-fed into the reactor, the oxygenate compounds derived from biomass pyrolysis promote the degradation of large-molecule organics to ideal products (aromatics and C2−C4 olefins). As seen in Figure 5c, the selectivity of naphthalene and its derivatives in

Plastics are polymers of olefins. The degradation of plastic is an endothermic reaction; therefore, the olefin yield increases with the increasing temperature. Owning to the competitive reactions in biomass pyrolysis, the higher temperature is favorable for the conversion of biomass to small-molecule oxygenates, which can enter the pores of the zeolite catalyst and be converted into aromatics and olefins with H2O, CO, CH4, and CO2 as the byproducts. Some experiments about the conversion of small-molecule oxygenates (furan and dimethylfuran) to aromatics and olefins have been conducted.37,38 Therefore, the carbon yields of aromatics and non-condensable gas increased with the increase of the temperature. However, much higher temperatures favor the decomposition of smallmolecule oxygenates into non-condensable gas, which prevented the formation of aromatics and olefins.20,39 As shown in Figure 4c, the selectivity of benzene increased with an increasing temperature, while the selectivities of toluene and naphthalene and its derivatives maintained the same values. The selectivities of xylene and other monoaromatics decreased gradually. Toluene and xylene are formed by the methylation of benzene, which is an exothermic reaction; thus, their yields decreased with the increasing temperature. The main C2−C4 olefins produced in the reactions include ethylene, propylene, and butene. Propylene selectivity decreased with the increase of the temperature, whereas ethylene selectivity increased. 3.2. Effects of the PE Proportion on Product Yields and Selectivities in Catalytic Co-pyrolysis of Pine Sawdust and PE. The effects of the PE proportion on the product distribution in the catalytic co-pyrolysis of pine sawdust and PE with a spent FCC catalyst are shown in 1944

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Table 5. Detailed Product Yields and Selectivities of Catalytic Co-pyrolysis of Pine Sawdust and PE at Different PE Proportions PE proportions (%) compound

0

20

aromatics C2−C4 olefins petrochemicals methane CO2 CO coke total carbon balance unidentified

7.1 6.6 13.7 4.8 4.6 15.4 38 76.5 23.5

14.7 16.6 31.3 5.7 3.1 8.1 32.6 80.8 19.2

benzene toluene ethyl benzene xylene other mono-aromatics indene naphthalene methylnaphthalene multi-methylnaphthalene

54.8 24.1 1 11.5 2.4 0.9 5.3 0 0

41.3 20 0.1 5.8 0.8 0.6 26.1 4.6 1.3

ethylene propylene butene

88.4 11.6 0

87.1 12.5 0.4

33.3 Overall Yields 20.6 16.5 37.1 7.1 1.6 6.6 34.7 87.1 12.9 Aromatic Selectivity 43.8 15.4 0.1 5.2 0.8 0.8 25.1 5.6 3.2 Olefin Selectivity 83.1 16.3 0.6

50

66.7

80

100

37.1 19.6 56.7 4.2 1.3 4.3 19.5 86 14

37.7 29 66.7 6.2 0.5 1.7 16.4 91.5 8.5

36 35 71 5.8 0.2 0.7 6.5 84.2 15.8

31.8 28 59.8 5.8 0 0 6.5 72.1 27.9

55.5 12.2 0 1.5 2.4 0.1 26.7 1.4 0.2

43.4 14.8 0.2 4.5 6 0.6 20.6 5.3 4.6

43.1 12.7 0.2 3.3 6.6 0.7 23.4 4.6 5.4

38.7 10.6 0.3 2.9 8.3 0.5 24.9 6.6 7.2

89.3 10.5 0.2

88.1 11.6 0.3

87.5 12.3 0.2

87 12.6 0.4

Figure 6. Product yields and selectivities of catalytic co-pyrolysis of pine sawdust and PE with different catalysts: (a) yields of aromatics, olefins, char and coke, CO, CO2, and CH4 and (b) selectivities of benzene, toluene, xylene, other monoaromatics, and naphthalene and its derivatives in aromatics.

almost 2 times that without a catalyst (33%). The carbon yields of aromatics and olefins increased in the following order: sand < γ-Al2O3 < spent FCC < LOSA-1, which is from 20 and 13% (with sand) to 42.5 and 23% (with LOSA-1), respectively. The char and coke yield also increased in catalytic runs, except with LOSA-1 catalysts. The selectivities of toluene and xylene increased with the LOSA-1 catalyst, while that of naphthalene and its derivatives decreased. The LOSA-1 catalyst, having special pore structure and activity, is a microporous catalyst, which is favorable for monoaromatic compound production. γAl2O3, as a mesoporous catalyst, has little shape selectivity aromatics and olefins and produced less petrochemicals. The detailed data of the product distribution is shown in Table 6. 3.4. Comparison of Different Plastics (PE, PP, and PS) on Product Yields and Selectivities in Catalytic Copyrolysis of Pine Sawdust and Plastics. Figure 7 shows the

catalytic co-pyrolysis is higher than that in pure pine sawdust catalytic pyrolysis. PE is a thermoplastic resin obtained by polymerization of ethylene. With regard to olefin selectivities, ethylene is the main product in the produced olefins (selectivity of about 90%). The selectivities of ethylene and propylene are stable with the increase of the PE proportion. The detailed data of the product distribution is shown in Table 5. 3.3. Comparison of Product Yields and Selectivities in Catalytic Co-pyrolysis of Pine Sawdust and PE with Different Catalysts. The product yields and selectivities of catalytic co-pyrolysis of pine sawdust and PE with different catalysts are shown in Figure 6. These experiments were conducted at 600 °C with a PE/pine sawdust ratio of 1:1. Both the maximum carbon yields of aromatics and olefins were obtained with a LOSA-1 catalyst. The total petrochemical carbon yield with a LOSA-1 catalyst is about 65.5%, which is 1945

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than that produced in PE or PP and pine wood runs (0.2 and 0.9%, respectively). As shown in Figure 7b, the selectivity of benzene is the highest selectivity (about 50%), followed by naphthalene and its derivatives, toluene, and other monoaromatics in the catalytic co-pyrolysis of three plastics and pine sawdust. Catalytic co-pyrolysis of PS and pine sawdust presented the lowest selectivities of benzene (46.3%) and xylene (0.3%), moderate selectivity of toluene, and highest selectivities of other monoaromatics (12.4%), which is almost styrene (10.2%) and naphthalene and its derivatives (29.7%). The detailed product distribution is listed in Table 7.

Table 6. Detailed Product Yields and Selectivities of Catalytic Co-pyrolysis of Pine Sawdust and PE with Different Catalysts different catalysts compound

sand

Al2O3

Overall Yields aromatics 20 25.6 C2−C4 olefins 13 14 petrochemicals 33 39.6 methane 2.8 3.9 CO2 1.7 1.6 CO 4.6 2.2 coke 13.7 18.1 total carbon balance 55.8 65.4 unidentified 44.2 34.6 Aromatic Selectivity benzene 71.6 62.3 toluene 16.2 13.7 ethyl benzene 0.2 0 xylene 1.4 1.4 other mono-aromatics 4.4 3 indene 0 0.4 naphthalene 6 17.8 methylnaphthalene 0.2 1.4 multi-methylnaphthalene 0 0 Olefin Selectivity ethylene 88.8 95 propylene 11.1 4.4 butene 0.1 0.6

FCC

LOSA-1

37.1 19.6 56.7 1.3 4.2 4.3 19.5 86 14

42.5 23 65.5 5.3 2.5 5.1 13.7 92.1 7.9

55.5 12.2 0 1.5 2.4 0.1 26.7 1.4 0.2

65.1 20.3 0.1 4.4 4.6 1.4 0.5 3.1 0.5

89.3 10.5 0.2

89.9 10 0.1

Table 7. Detailed Product Yields and Selectivities of Catalytic Co-pyrolysis of Plastics (PE, PP, and PS) and Pine Sawdust different plastics compound

PE

Overall Yields aromatics 37.1 C2−C4 olefins 19.6 petrochemicals 56.7 methane 4.2 CO2 1.3 CO 4.3 coke 19.5 total carbon balance 86 unidentified 14 Aromatic Selectivity benzene 55.5 toluene 12.2 ethyl benzene 0 xylene 1.5 other mono-aromatics 2.4 indene 0.1 naphthalene 26.7 methylnaphthalene 1.4 multi-methylnaphthalene 0.2 Olefin Selectivity ethylene 89.3 propylene 10.5 butene 0.2

effects of different plastics (PE, PP, and PS) on the carbon yields and selectivities in catalytic co-pyrolysis of pine sawdust and plastics with a spent FCC catalyst. These works were also conducted at 600 °C with a pine sawdust/plastics ratio of 1:1. Catalytic co-pyrolysis of PS and pine sawdust produced the highest yield of aromatics (47%) and the lowest yield of olefins (11.4%) because of the specially chemical structure of PS. The highest char and coke yield was also obtained with catalytic copyrolysis of PS and pine wood. Polyaromatic hydrocarbons are the precursors of coke. PS contains a lot of benzene rings, which can be converted to aromatics and even polyaromatics. For example, the selectivity of multi-methylnaphthalene produced in the PS and pine wood run (5.9%) is much higher

PP

PS

34.7 16.3 51 2.2 3.7 6.5 22 85.4 14.6

47 11.4 58.4 2.4 2.3 6.1 25.2 94.4 5.6

54 10.6 0.1 0.4 6.3 0 24.4 3.3 0.9

46.3 11 0.1 0.3 12.4 0.2 22.2 1.6 5.9

76.5 23.4 0.1

95.5 4.4 0.1

Figure 7. Product yields and selectivities of catalytic co-pyrolysis of pine sawdust and different plastics (PE, PP, and PS): (a) yields of aromatics, olefins, char and coke, CO, CO2, and CH4 and (b) selectivities of benzene, toluene, xylene, other monoaromatics, and naphthalene and its derivatives in aromatics. 1946

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Energy & Fuels

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4. CONCLUSION Catalytic co-pyrolysis of pine sawdust and plastics (PE, PP, and PS) was conducted in a fluidized-bed reactor to improve the yields of aromatics and olefins. The results show that there are positive synergistic effects between the two feedstocks. The maximum total carbon yield of petrochemicals (36% aromatics + 35% olefins) was obtained at a PE/pine sawdust ratio of 4:1 and 600 °C. LOSA-1 presents a better catalytic performance than Al2O3 and spent FCC catalysts. Catalytic co-pyrolysis of PS and pine sawdust produced the highest yield of aromatics and the lowest yield of olefins because of its specially chemical structure.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the financial support of the National Natural Science Foundation of China (Grant 51306036), the National Basic Research Program of China (973 Program) (Grant 2010CB732206), and the Jiangsu Natural Science Foundation (Grant BK20130615).

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dx.doi.org/10.1021/ef4019299 | Energy Fuels 2014, 28, 1940−1947