Effects of temperature and equivalence ratio on carbon nanotubes and

Subscriber access provided by Kaohsiung Medical University

Article

Effects of temperature and equivalence ratio on carbon nanotubes and hydrogen production from waste plastic gasification in fluidized bed Ren-Xuan Yang, Kui-Hao Chuang, and Ming-Yen Wey Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b04109 • Publication Date (Web): 02 Mar 2018 Downloaded from http://pubs.acs.org on March 4, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Effects of temperature and equivalence ratio on carbon nanotubes and hydrogen production from waste plastic gasification in fluidized bed Ren-Xuan Yanga, Kui-Hao Chuangb, Ming-Yen Weya,* a

Department of Environmental Engineering, National Chung Hsing University, Taichung, 402, Taiwan, ROC

b

Department of Safety, Health and Environmental Engineering, Central Taiwan University of Science and Technology, Taichung, 406, Taiwan, ROC

*

Corresponding author.

Tel: +886 4 22840441x533; fax: +886 4 22862587. E-mail address: [email protected] (M.-Y Wey).

Key words: waste plastics; fluidized bed; carbon nanotubes; hydrogen; gasification

1

ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 39

Abstract The waste plastic gasification in a fluidized bed for a continuous carbon nanotube (CNT) and hydrogen co-production is a potential method for sustainable management. Ni/Al2O3 catalysts have been synthesized by the impregnation method to upgrade hydrogen production and CNT synthesis. However, few studies investigated the effect of operating parameters for upcycling waste plastics into CNTs and hydrogen in the fluidized bed system. The reaction temperature and the equivalence ratio (ER) were evaluated for CNT and hydrogen co-production. Increasing the reaction temperature and lowering the ER enhanced the methane dry reforming, hydrocarbon dry reforming, and hydrocarbon direct decomposition for hydrogen and CNT co-production. While increasing the reaction temperature from 500 to 700 °C can obtain higher CNT yield and H2 production rate, the system heated to 700 °C and maintained at this temperature should provide more energy. Moreover, the gas composition at 600 °C with 0.1 ER contained more CH4 and C2–C5 hydrocarbons compared with that a higher ER, which could be used as the carbon source of CNTs. The reaction temperature of the fluidized bed in the waste plastic gasification system controlled at 600 °C with 0.1 ER and the gasified products upgraded through a catalytic fixed bed reactor at 680 °C exhibited an optimal catalytic performance of less-defective CNTs in 22.0% yield and H2 production rate (385.1 mmol/h-g catalyst). 2


Page 3 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Introduction Plastics are applied in many fields (e.g., packaging, electricity and electronics, building and construction, consumer, agriculture, and household appliances) because of their low degradability, high chemical stability, and lightweight characteristics.1-3 Thus, the usage of plastics increases and results in abundant waste plastics. Waste plastics could be managed by kinds of waste streams for recovery, recycling, and re-processing. The chemical recycling of waste plastics has recently substituted the conventional landfill and incineration because of the perspective for pilot and demonstration scale. Furthermore, the chemical recycling of waste plastics can produce fuels and provide high-value-added products.4-6 The chemical recycling processes include pyrolysis, gasification, combustion, reforming, hydrogenation, and thermal cracking. Among the various chemical recycling processes, gasification and pyrolysis have been used to recover hydrogen or carbon nanotubes (CNTs) from waste plastics.7-9 They have also been applied to several reactors, including quartz tube, crucible, autoclave, moving bed, fluidized bed, and muffle furnace.10 Toledo et al. investigated the waste polypropylene (PE) gasification in a fluidized bed using olivine as the catalytic bed material, which yielded more syngas retarded the tar content.11 Gong et al. used a crucible reactor to convert polypropylene (PP) into cup-stacked CNTs with 3


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 39

the addition of organically-modified montmorillonite (OMMT) and NiO. The amount of OMMT affected the structure of cup-stacked CNTs. The low OMMT content in the system led to straight, long, and surface-smooth cup-stacked CNTs, whereas high OMMT content resulted in tortuous, short, and surface-rugged carbon nanofibers.12 Acomb et al. used different metal catalysts for the co-production of hydrogen and CNTs from low-density PE pyrolysis in a two-stage fixed bed reactor.7 Catalytic gasification is one of the promising methods of upgrading the syngas quality and the CNT yield from waste plastics. However, little research has been conducted at the pilot scale. While most studies on the catalytic gasification of plastic wastes were performed in laboratory batch reactors, a few studies performed this in a heterogeneous gas−solid fluidized reactor, which can exhibit a continuous feed operation with high heating transfer efficiency and good mixing.10,13,14 Wu and Williams investigated the effects of the gasification temperature and the Ni/CeO2/Al2O3 catalyst ratio on hydrogen production from PP catalytic steam pyrolysis–gasification. No oil product was found when the gasification temperature was higher than 800 °C. The gasification temperature, which was increased from 600 to 900 °C, significantly enhanced hydrogen production.15 Araniz et al. synthesized CNTs by catalytic chemical vapor deposition in a horizontal tubular quartz furnace using the mixture of hydrocarbons and hydrogen as the carbon source of the 4


Page 5 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

derived-PE pyrolysis. In this case, no prior catalyst reduction was necessary for the CNT production at 650 °C.16 Arena et al. developed an innovative process for mass production of multi-walled CNTs (MWCNTs) from polyolefin pyrolysis in a fluidized bed. This process provided an inexpensive and low-temperature alternative compared to the conventional CVD process.17 This research group further studied some operating parameters affecting the waste plastic gasification in a pilot scale bubbling fluidized bed. The suitable operating parameters could improve the tar decomposition. The quality and the yield of gas products were also promoted by the presence of olivine.18 Based on the abovementioned literature reviews, an adequate selection of the operating parameters is important for the plastic gasification in a fluidized bed reactor. The reaction temperature of the fluidized bed is one of the important parameters that would affect the product composition. The reaction temperature for the CNT synthesis from plastics pyrolysis or gasification was controlled at 500−800 °C.6,19-21 Another key factor in the gasification process is the equivalence ratio (ER), which represents not only the influent air percentage of the reactor, but also the reaction temperature reflected from the feedstock auto-thermal reaction.22,23 Although the operating parameters of the fluidized bed would affect the gasification efficiency and the gas composition, the catalyst selection is also important for the waste plastic gasification, especially for the CNT synthesis procedure. The 5


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 39

main catalysts used for the CNT synthesis are transition metals, such as Ni, Co, and Fe.9,

24-28

Mubarak et al. synthesized MWCNTs and carbon nanofibers by the

microwave assisted chemical vapour deposition using ferrocene as the catalyst and acetylene and hydrogen as the precursor gases. The diameter of the carbon nano-materials can be controlled by varying the radiation time, precursor gas ratio, and microwave power.29,30 Moreover, the as-prepared MWCNTs from the microwave assisted chemical vapour deposition possessed the outstanding adsorption capacity for Cd (II) or Cu (II) in an aqueous solution.31,32 Zhang et al. investigated different catalysts (Fe/Al2O3, Co/Al2O3, Ni/Al2O3, and Cu/Al2O3) for the simultaneous production of CNTs and H2. Consequently, the Ni/Al2O3 catalysts produced the highest CNT quality along with the highest H2 yield.24 Palacio et al. also found similar results that the Ni-supported catalyst exhibits a better performance for CNT and H2 co-production during ethanol decomposition.26 Furthermore, we previously reported that Ni/Al2O3 calcined under H2 atmosphere provides a higher quality of the CNTs synthesized from the waste plastic gasification in the fluidization bed system.9 Ni-based catalysts have generally been widely used for the CNT synthesis from the decomposition of hydrocarbons and solid waste feedstocks because of their low cost and efficient C−C bond cleavage. More work on the Ni/Al2O3 catalyst applied in a fluidized bed is needed to increase the quality and yield of CNTs from waste plastic 6


Page 7 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

gasification. However, few studies have investigated the effect on CNTs and H2 co-production from waste plastic gasification in a fluidized bed using the Ni/Al2O3 catalysts on fluidized bed operating parameters. To complete a fluidized bed system for CNTs and H2 co-production from waste plastic catalytic gasification, the operating parameters of the fluidized bed should be evaluated. In this study, the fluidized bed reactor was applied for the waste plastic gasification in different operating parameters, followed by a fixed-bed catalytic reactor for treating resultant gases from waste plastic gasification to produce CNTs and H2. The Ni/Al2O3 catalysts herein were prepared via an impregnation method under H2 calcination atmosphere. The present study aims to investigate the effects of the fluidized bed operating parameters (reaction temperature and equivalence ratio) on CNT and H2 production from waste plastic gasification in a fluidized-bed pilot-scale system. The carbon products were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), Field-emission scanning electron microscopy (FESEM), and Raman spectroscopy. The optimal operating parameters for CNT and H2 co-production from waste plastic gasification were also evaluated herein.

7


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 39

Experimental Section Feedstock and catalyst preparation The waste plastic feedstock was made of PP and PE. Virgin PP pellets (Formosa Chemicals and Fibre Corporation) were used to prepare the feedstock for the waste plastic gasification experiments. The PP pellets (3.0 g) were packed into a PE bag (0.3 g). The information on the ultimate elemental and proximate analyses was described in detail by Yang et al.9 The feeding rate of the feedstock was 19.8 g/min. A 425–500 µm size range with a near constant density of 2600 kg/m3 silica sand was used as the bed material for the fluidized bed. The Ni/Al2O3 catalyst was prepared by wet impregnation of Al2O3 (EIKME Co.) with 10 wt.% Ni. Al2O3 was mixed with Ni precursor (Ni(NO3)2·6H2O, Aldrich) in distilled water. The as-prepared mixtures were stirred at 70 °C until all of the liquid evaporated. The mixtures were then dried at 105 °C for 4 h and further calcined at 500 °C for 3 h in the presence of 5% H2/He.9 Experimental procedure Carbon nanotube synthesis experiments were employed in the waste plastic gasification pilot-scale system. The waste plastic gasification was conducted in a laboratory-scale fluidized bed reaction system comprising a gasifier chamber, a cyclone, two column filters, two cooling trapping tubes, and three parallel connection 8


Page 9 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

catalysis reactors. A more detailed set of information on the fluidized bed reactor is available in our previous paper.9 Air was induced by a blower as the gasifying agent at the ER was determined. ER is defined as the ratio of the actual air supply divided by the stoichiometric air required for a complete combustion. The waste plastics were initially gasified in the fluidized bed reactor to produce hydrocarbons. The produced hydrocarbons then flowed into the fixed bed catalytic reactor to produce CNTs. This study aimed to investigate the effect of the operating temperature and the ER on the CNT yield and quality. The artificial waste was fed into the reactor through the hopper when the fluidized bed reached the desired temperature. The particulates of the effluent gas from the waste plastic gasification were captured by the cyclone and the column filter. The gas then flowed into the fixed bed catalytic reactor. The gasification system stabilized after feeding the waste plastics for 10 min. Subsequently, the gasification products were introduced into the fixed bed catalytic reactor (i.d. = 10 mm) with a space velocity of 10,185 h−1 (a flow rate of 200 mL/min controlled by a flowmeter). The catalysts of 0.2 g were used in each run and placed on a quartz filter board.

The catalytic reactor temperature was controlled at 680 °C. The H2, CO, CH4, CO2, and C2–C5 gaseous hydrocarbons were sampled in the inlet and outlet gas

9


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 39

streams of the catalytic reactor during the gasification process. A gas chromatograph (Clarus 500 GC, and Carboxen 1000 column, Perkin Elmer) equipped with a thermal conductivity detector (TCD) was used to determine the H2, CO, CH4, and CO2 concentrations. The gas chromatograph–flame ionization detector (GC/FID, 6890N with an alumina sulfate PLOT capillary column (50 m × 0.53 mm ID), Agilent) was applied to obtain the C2–C5 gaseous hydrocarbon concentration. The gasification system for stability was tested in triplicate to ensure reproducibility and reliability. The CNT yield and the H2 production rate were calculated according to Eqs. (1) and (2), respectively, where Mtotal denotes the reacted catalyst (carbon product and catalyst) mass, and Mcata. is the catalyst mass before the reaction. The H2 production rate was calculated as follows:

CNT yield %=

Mtotal - Mcata. × 100 % Mcata.

H2 production rate (mmol/h-g catalyst) =

(1)

H2 conc. × gas flow rate (2) Mcata.

Catalyst characterization The reacted catalysts were analyzed by a thermogravimetric analyzer (TGA, STA 6000, Perkin Elmer) to characterize the carbon products deposited on the catalyst. The sample (~20 mg) was heated up to 850 °C with a heating rate of 20 °C/min under an air flow of 20 mL/min. The sample was then held at 850 °C for 10 10


Page 11 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

min. Subsequently, TEM (JEOL JEM-1200CX II) which operated at 120 keV, was used to characterize the morphology structure of the synthesized CNTs. The samples were crushed and suspended into an ethanol solution in an ultrasonic bath before the TEM test. The resulting suspension was then dropped on a lacy carbon film coated copper grid. FESEM operating at the accelerating voltage of 3 kV was used to observe the morphology of the synthesized CNTs. The Raman spectroscopy (Horiba) was used to analyze the graphitic quality of the synthesized CNTs under ambient conditions. The spectrum were recorded at the Raman shift between 500 and 3200 cm–1 with a 632.8 nm ion laser (JDS Uniphase Co.).

Results and Discussion The waste plastic gasification experiments were performed in a pilot-scale system consisting of a fluidized bed, followed by a catalytic fixed bed. The Ni/Al2O3 catalysts calcined under 5% H2/He were used for the CNT and H2 co-production. The effect of the reaction temperature and the ER of the fluidized bed was studied in this work. Effect of the reaction temperature Fig. 1 illustrates the influence of the reaction temperature of the fluidized bed in the waste plastic gasification system with 0.1 ER. The gasified products were

11


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 39

upgraded through a catalytic fixed bed reactor at 680 °C. Figs. 1(a) and (b) show the gas composition before and after the catalytic fixed bed. The H2, CH4, and CO2 concentrations increases when the reaction temperature of the fluidized bed increased, whereas C2–C5 gaseous hydrocarbons decreased, which may possibly be because increasing the reaction temperature enhances the degradation of the larger molecule hydrocarbons to smaller molecule hydrocarbons. In terms of le Chatelier's principle, a higher reaction temperature promotes both forward and backward reaction rates leading to H2 production during the endothermic reaction including methane dry reforming, methane steam reforming, tar reforming, and/or plastic decomposition.33 Fig. 1(a) also shows a corresponding increase in the CH4 concentration from 24.8 to 38.7 mol% with the increase in temperature from 600 to 700 °C. This increase can be ascribed to the plastic decomposition. The gasified products were further upgraded by the catalytic fixed bed. The mechanism of CNTs and H2 production from waste plastics in the fluidized bed gasification system was summarized in Fig. 2. The waste plastics were first gasified and reformed into C2-C5 light hydrocarbons and other products in the fluidized bed. The resultant products from the waste plastic gasification in the fluidized bed were further introduced into the fixed bed for the catalytic reactions. The introduction of Ni/Al2O3 catalyst could promote the catalytic reforming reactions and thermal cracking reaction of hydrocarbons (Eq. (3)) for light 12


Page 13 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

hydrocarbons decomposition and then producing the CNTs and H2. Fig. 1(b) shows that the H2 and CO composition increased, while that of CO2, CH4, and C2–C5 hydrocarbon decreased after the catalytic fixed bed. Fig. 1(c) depicts the CNT yield and the H2 production rate of the Ni/Al2O3 catalyst during the waste plastic gasification. Fig. 1(c) shows that both the CNT yield and the H2 production rate increased after the catalytic reaction, which can be explained by the Ni/Al2O3 catalyst enhancing the dry reforming of methane (Eq. (4)), dry reforming of hydrocarbons (Eq. (5)), and direct decomposition of hydrocarbons (Eq. (6)). The catalytic thermal cracking of hydrocarbons is expresses as: Cx Hy → xC + ( y⁄2 )H2

(3)

The dry reforming of methane is expresses as: CH4 + CO2 → 2CO + 2H2

∆H = 247.0 kJ/mol

(4)

The dry reforming of hydrocarbons is presented as: Cn Hm + nCO2 → 2nCO + ( m⁄2 )H2

∆H>0

(5)

Meanwhile, the direct decomposition of hydrocarbons is: Cn Hm → nCs + ( m⁄2 )H2

∆H>0

(6)

The gas composition of 700 °C included the highest proportion of CH4 and C2– C5 light hydrocarbons which could be used as the carbon source in the CNT formation. 13


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 39

Hence, the reaction temperature of 700 °C provided the highest CNT yield (25.8%). Liu et al. used PP as the feedstock for the MWCNT synthesis. Propylene and butylene from the pyrolysis gas can enhance the CNT yield.6 Zhang et al. found that a nickel-loaded stainless steel mesh catalyst for waste high-density PE pyrolysis resulted in an increase in the carbon-deposited increasing temperature from 700 to 900 °C.34 TGA, TEM, FESEM, and Raman analysis were performed to measure the physicochemical properties of the carbon products grown on the Ni/Al2O3 catalysts. TGA was used to determine the overall quality of the carbon products and analyze their thermal stability. Fig. 3 shows the TGA and the derivative thermogravimetric (DTG) profiles of the reacted catalyst at different reaction temperatures of the fluidized bed in the waste plastic gasification system. A DTG analysis was conducted to determine the quality and structure of the reacted catalysts. Two intervals of weight loss were found in the DTG profiles. The former slight weight loss between 50 and 150 °C was associated with the absorbed water from the catalysts, whereas the latter weight loss between 450 and 750 °C was associated with the amorphous carbon and MWCNT oxidation.7,24,35 The weight loss of 550-750 °C was indicated the oxidation of CNT. Therefore, the weight loss fraction between 550 and 750 °C can be used to calculate the CNT purity. The CNT purity present on these three reacted catalysts 14


Page 15 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

from different fluidized bed temperatures was in the following order: 600 °C (26.8%) > 700 °C (14.1%) > 500 °C (12.2%). The CNTs purity increased with the increasing reaction temperature from 500 to 600 °C because of less C2–C5 hydrocarbons produced at 600 °C. Therefore, cracking and reforming reactions were much complete than lower reaction temperature, which leads to the hydrocarbons broken down to form methane or deposited on the catalyst. Further increasing the reaction temperature to 700 °C decreased CNTs purity because of the monatomic carbon, single-wall CNTs, or unvaporized hydrocarbons might be deposited on the catalyst surface resulting in a low amount of high quality CNTs.15,19 A higher oxidation peak represented the higher-purity CNTs with less defects. The DTG curves showed that the oxidation of the reacted catalyst at the fluidized bed temperature of 600 °C happened at 640 °C, which was higher than the other two reacted catalysts. The microstructure of the reacted catalysts was characterized via TEM and FESEM as shown in Fig. 4. The FESEM images show that the carbon products were the filamentous type of carbon. The diameter of the filamentous carbon products increased with increasing the fluidized bed reaction temperature. Fig. 4(b) shows most of the filamentous carbons produced at 500 °C were curl-shaped and twinned together. TEM images shown in Fig. 4(a, c, and e) further confirmed that most of the carbon products were hollow CNTs with few amorphous carbons. Also, the average outer 15


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 39

diameter of the as-synthesized CNTs increased along with the increasing fluidized bed reaction temperature which was in accordance with the FESEM results. The outer diameters of the CNTs at the fluidized bed reaction temperature of 700 °C were 33 nm, whereas those of the CNTs at 500 °C were ~10–12 nm. For comparison, Fig. 4 shows that the CNTs at the fluidized bed reaction temperature of 500 °C had a relatively uniform diameter containing few defects. However, the few CNTs at the fluidized bed reaction temperature of 500 °C were twinned together (Fig. 4(a-b)) and provided results consistent with the TGA results. Raman spectroscopy was undertaken in this study to characterize the carbon products. Fig. 5 presents the resultant spectra of the carbon products. The Raman band appearing in the ~1320 cm−1 was noted as the D-band (amorphous or disordered carbon vibration band), while the Raman band appearing in the ~1580 cm−1 was noted as the G-band (sp2 C–C vibrations). The degree of graphitization and the quality of the CNTs are usually achieved by analyzing the intensity ratio (IG/ID) of the G-band to the D-band. The difference in the relative intensity ratio can be observed according to the Raman spectroscopy results (Fig. 5). The IG/ID value increased with the increasing reaction temperature of the fluidized bed. The CNTs of the reaction temperature of 700 °C provided the highest IG/ID value of 0.86, indicating a higher quality and fewer defects in the CNTs. Contrarily, the IG/ID ratio decreased from 0.86 to 0.65 as the 16


Page 17 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

temperature decreased from 700 to 500 °C. The Raman results was consistent with the CNT yield because of the gaseous composition of the higher reaction temperature resulting less C2–C5 hydrocarbons affecting the quality of the CNTs and the carbon nanostructure construction.12,19 The commercial MWCNTs also provided typical IG/ID ratios between 0.67 and 1.5921, which indicated that the graphitization of some carbon products produced in this work was within the range of commercial MWCNTs. Although, the reaction temperature of 700 °C exhibited the highest H2 production rate and CNT yield with less-defective CNTs, increasing the temperature from 600 to 700 °C only promoted 1.6% H2 production rate (385.1 to 391.3 mmol/h-g catalyst) and 14.7% CNT yield. Thus, the optimal reaction temperature of the fluidized bed was 600 °C. Effect of the equivalence ratio The influence of the ER in the waste plastic gasification system was investigated at the fluidized bed temperature of 600 °C. The gasified products flowed through a catalytic fixed bed reactor at 680 °C for the CNT production. Fig. 5 presents the gas composition, CNT production, and H2 production rate corresponding to the different ERs. Fig. 6(a) shows that the CO2 concentration rose as the ER increased, while the H2, CO, CH4, and C2–C5 gaseous hydrocarbons decreased. From Figs. 6(a) and (b), the gas composition before the catalytic fixed bed showed that the C2–C5 gaseous 17


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 39

hydrocarbons dramatically decreased when the ER increased from 0.1 to 0.2. Moreover, the concentration of H2 increased from 22.9 to 36.9% when the ER was 0.1 after the catalytic reaction. The abovementioned results indicated that more air flowed into the system would enhance the oxidation reaction, which was a disadvantage for the further catalytic upgrading reaction. In addition, the degradation of the hydrocarbons (CH4 and C2–C5 gaseous hydrocarbons) enhanced the H2 production because of the catalytic thermal cracking of hydrocarbons, dry reforming of methane, dry reforming of hydrocarbons, and direct decomposition of hydrocarbons (Eqs. (3)−(6)). The CO and CO2 formation was favored at a higher ER because of the promotion of the oxidation of plastics, CO, and CH4. Furthermore, increasing the oxygen in the process would consume H2.36 Due to the incomplete plastic gasification and pyrolysis when the ER was 0.1, the concentration of CH4 and C2-C5 hydrocarbons was higher than that of the 0.15 and 0.2 ER. The light hydrocarbons (CH4 and C2-C5 gaseous hydrocarbons) could be used as the carbon source in the CNT formation.6 Furthermore, the increase in ER represents that more gasifying agent was induced to the reactor resulting in gas turbulence. The turbulence might have a negative effect on the CNT formation. Therefore, Fig. 6(c) shows that the 0.1 ER exhibited the highest CNT yield (22.0%). Park et al.37 blended a high-density PE with a biomass for co-gasification in a two-stage gasification system (an oxidative pyrolysis reactor 18


Page 19 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

followed by a thermal plasma reactor). The result indicated that hydrocarbons were produced with decreasing ER. Meanwhile, the CO2 concentration increased with the higher ER, which was in accordance with our result. Fig. 6(c) also shows that the H2 production rate increases with the higher ER. The gaseous products with 0.2 ER after catalytic reaction exhibited a 419.4 mmol/h-g catalyst. A comparison of Figs. 6(a) and (b) found that the 0.2 ER of CH4 and CO2 decreased after the catalytic reaction. The Ni/Al2O3 catalyst can further promote methane dry reforming.

Fig. 7 presents the TGA and DTG plot for the carbon products derived from different ERs by the reacted Ni/Al2O3 catalysts. The oxidation temperature of carbon products is an index of their stability in the air, and can provide information about their crystalline properties, CNT purity, and defect weakness. In this study, the CNT purity on the reacted catalyst decreased with the increasing ER. The reacted catalyst with 0.1 ER exhibited the highest CNT purity (26.8%). The DTG profiles showed that increasing the ER resulted in more CNT defects. The carbon products with 0.1 ER possessed two oxidation peaks at approximately 645 °C and 685 °C, while those with 0.2 ER exhibited the main oxidation peak at 610 °C with more disordered CNTs. Higher oxidation temperatures indicate better thermal stabilities and less defects in the CNTs. In addition, more hydrocarbons are produced when the ER is lower. These

19


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 39

hydrocarbons are suggested to provide more carbon sources for CNT formation, which is consistent with the gas composition in Fig. 6.

The microstructures of the reacted catalysts with different ERs were further analyzed by TEM. Fig. 8 shows TEM micrographs of the carbon products. The carbon products with 0.2 ER had diameters larger than those of the carbon products formed with a lower ER. The CNTs grown on the reacted catalysts with 0.1 ER were smooth and possessed a relatively uniform diameter of 16.5–19.5 nm (Fig. 8(a)). By contrast, the CNTs with 0.2 ER had more defects and twinned together (Fig. 8(c)). The TEM result was in accordance with the TGA results.

Fig. 9 shows the Raman spectra recorded for the three reacted catalysts with different ERs. Two characteristic peaks were observed at ~1320 and 1580 cm−1 indicating D- and G-bands, respectively. The graphitization of carbon products can be evaluated by the intensity ratios between the G-band and D-band (IG/ID), which were 0.58, 0.50, and 0.71 for the carbon products with 0.2, 0.15, and 0.1 ERs, respectively. The lighter hydrocarbons (C2–C5) in the gaseous compositions provided higher purities and homogeneous CNTs after the catalytic reaction. Thus, the carbon products with 0.1 ER exhibited the highest degree of graphitization.

20


Page 21 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Conclusions This study investigated the effect of the operating parameters in the CNT and hydrogen co-production using the waste plastic gasification system consisting of a fluidized bed and a fixed bed catalytic reactor. The Ni/Al2O3 catalyst calcined in a reductive (5%H2/He) atmosphere was used for the catalytic reaction. The reaction temperatures (500, 600, and 700 °C) and the ERs (0.1, 0.15, and 0.2) were varied to investigate the optimal operating parameters of the fluidized bed. Increasing the reaction temperature promoted methane dry reforming, tar reforming, and plastic decomposition

for

the

degradation

of

larger-molecule

hydrocarbons

to

smaller-molecule hydrocarbons, which benefitted the simultaneous hydrogen and CNT production. Increasing the ER from 0.1 to 0.2 decreased the CNT yield because of less C2–C5 hydrocarbons and CH4 as the carbon source in the system. Considering the CNT yield, H2 production, and energy consumption, the reaction temperature of 600 °C with 0.1 ER provided the optimal performance for the CNT and H2 co-production from the waste plastic gasification in the fluidized bed. The carbon products synthesized in this fluidized bed waste plastic gasification system were less-defective, high-quality MWCNTs with a relatively uniform diameter. This study offers the optimal parameters of the fluidized bed waste plastic gasification for the CNT and H2 co-production, which could be potentially further applied in the pilot 21


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 39

plant.

Acknowledgments The authors wish to express their sincere thanks for the financial support from the Ministry of Science and Technology (MOST), Taiwan, R.O.C. under Grant No. MOST 103-2221-E-005-001-MY3.

References (1) Lopez, G.; Artetxe, M.; Amutio, M.; Bilbao, J.; Olazar, M., Thermochemical routes for the valorization of waste polyolefinic plastics to produce fuels and chemicals. A review. Renewable and Sustainable Energy Reviews 2017, 73, 346-368. (2) Ratnasari, D. K.; Nahil, M. A.; Williams, P. T., Catalytic pyrolysis of waste plastics using staged catalysis for production of gasoline range hydrocarbon oils. Journal of Analytical and Applied Pyrolysis 2017, 124, 631-637. (3) Barbarias, I.; Lopez, G.; Alvarez, J.; Artetxe, M.; Arregi, A.; Bilbao, J.; Olazar, M., A sequential process for hydrogen production based on continuous HDPE fast pyrolysis and in-line steam reforming. Chemical Engineering Journal 2016, 296, 191-198. (4) Saad, J. M.; Williams, P. T., Catalytic dry reforming of waste plastics from 22


Page 23 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

different waste treatment plants for production of synthesis gases. Waste Management 2016, 58, 214-220. (5) Al-Salem, S. M.; Lettieri, P.; Baeyens, J., Recycling and recovery routes of plastic solid waste (PSW): A review. Waste Management 2009, 29, (10), 2625-2643. (6) Liu, J.; Jiang, Z.; Yu, H.; Tang, T., Catalytic pyrolysis of polypropylene to synthesize carbon nanotubes and hydrogen through a two-stage process. Polymer Degradation and Stability 2011, 96, (10), 1711-1719. (7) Acomb, J. C.; Wu, C.; Williams, P. T., The use of different metal catalysts for the simultaneous production of carbon nanotubes and hydrogen from pyrolysis of plastic feedstocks. Applied Catalysis B: Environmental 2016, 180, 497-510. (8) Arena, U.; Di Gregorio, F., Energy generation by air gasification of two industrial plastic wastes in a pilot scale fluidized bed reactor. Energy 2014, 68, 735-743. (9) Yang, R.-X.; Chuang, K.-H.; Wey, M.-Y., Effects of Nickel Species on Ni/Al2O3 Catalysts in Carbon Nanotube and Hydrogen Production by Waste Plastic Gasification: Bench- and Pilot-Scale Tests. Energy & Fuels 2015, 29, (12), 8178-8187. (10) Bazargan, A.; McKay, G., A review – Synthesis of carbon nanotubes from plastic wastes. Chemical Engineering Journal 2012, 195–196, (0), 377-391. 23


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 39

(11) Toledo, J. M.; Aznar, M. P.; Sancho, J. A., Catalytic Air Gasification of Plastic Waste (Polypropylene) in a Fluidized Bed. Part II: Effects of Some Operating Variables on the Quality of the Raw Gas Produced Using Olivine as the In-Bed Material. Industrial & Engineering Chemistry Research 2011, 50, (21), 11815-11821. (12) Gong, J.; Liu, J.; Jiang, Z.; Wen, X.; Chen, X.; Mijowska, E.; Wang, Y.; Tang, T., Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes. Chemical Engineering Journal 2013, 225, (0), 798-808. (13) Saad, J. M.; Nahil, M. A.; Williams, P. T., Influence of process conditions on syngas production from the thermal processing of waste high density polyethylene. Journal of Analytical and Applied Pyrolysis 2015, 113, 35-40. (14) Xiao, R.; Jin, B.; Zhou, H.; Zhong, Z.; Zhang, M., Air gasification of polypropylene plastic waste in fluidized bed gasifier. Energy Conversion and Management 2007, 48, (3), 778-786. (15) Wu, C.; Williams, P. T., Effects of Gasification Temperature and Catalyst Ratio on Hydrogen Production from Catalytic Steam Pyrolysis-Gasification of Polypropylene. Energy & Fuels 2008, 22, (6), 4125-4132. (16) Arnaiz, N.; Gomez-Rico, M. F.; Martin Gullon, I.; Font, R., Production of Carbon 24


Page 25 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Nanotubes from Polyethylene Pyrolysis Gas and Effect of Temperature. Industrial & Engineering Chemistry Research 2013, 52, (42), 14847-14854. (17) Arena, U.; Mastellone, M. L.; Camino, G.; Boccaleri, E., An innovative process for mass production of multi-wall carbon nanotubes by means of low-cost pyrolysis of polyolefins. Polymer Degradation and Stability 2006, 91, (4), 763-768. (18) Arena, U.; Zaccariello, L.; Mastellone, M. L., Tar removal during the fluidized bed gasification of plastic waste. Waste Management 2009, 29, (2), 783-791. (19) Acomb, J. C.; Wu, C.; Williams, P. T., Effect of growth temperature and feedstock:catalyst ratio on the production of carbon nanotubes and hydrogen from the pyrolysis of waste plastics. Journal of Analytical and Applied Pyrolysis 2015, 113, 231-238. (20) Gong, J.; Yao, K.; Liu, J.; Wen, X.; Chen, X.; Jiang, Z.; Mijowska, E.; Tang, T., Catalytic conversion of linear low density polyethylene into carbon nanomaterials under the combined catalysis of Ni2O3 and poly(vinyl chloride). Chemical Engineering Journal 2013, 215–216, (0), 339-347. (21) Wu, C.; Wang, Z.; Wang, L.; Williams, P. T.; Huang, J., Sustainable processing of waste plastics to produce high yield hydrogen-rich synthesis gas and high quality carbon nanotubes. RSC Advances 2012, 2, (10), 4045-4047. 25


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 39

(22) Guo, X. J.; Xiao, B.; Zhang, X. L.; Luo, S. Y.; He, M. Y., Experimental study on air-stream gasification of biomass micron fuel (BMF) in a cyclone gasifier. Bioresource Technology 2009, 100, (2), 1003-1006. (23) Lv, P. M.; Xiong, Z. H.; Chang, J.; Wu, C. Z.; Chen, Y.; Zhu, J. X., An experimental study on biomass air–steam gasification in a fluidized bed. Bioresource Technology 2004, 95, (1), 95-101. (24) Zhang, Y.; Wu, C.; Nahil, M. A.; Williams, P., Pyrolysis–Catalytic Reforming/Gasification of Waste Tires for Production of Carbon Nanotubes and Hydrogen. Energy & Fuels 2015, 29, (5), 3328-3334. (25) de Llobet, S.; Pinilla, J. L.; Moliner, R.; Suelves, I., Relationship between carbon morphology and catalyst deactivation in the catalytic decomposition of biogas using Ni, Co and Fe based catalysts. Fuel 2015, 139, 71-78. (26) Palacio, R.; Gallego, J.; Gabelica, Z.; Batiot-Dupeyrat, C.; Barrault, J.; Valange, S., Decomposition of ethanol into H2-rich gas and carbon nanotubes over Ni, Co and Fe supported on SBA-15 and Aerosil. Applied Catalysis A: General 2015, 504, 642-653. (27) Liu, X.; Sun, H.; Wu, C.; Patel, D.; Huang, J., Thermal Chemical Conversion of High-Density Polyethylene for the Production of Valuable Carbon Nanotubes Using Ni/AAO Membrane Catalyst. Energy & Fuels 2017. 26


Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(28) Yao, D.; Zhang, Y.; Williams, P. T.; Yang, H.; Chen, H., Co-production of hydrogen and carbon nanotubes from real-world waste plastics: Influence of catalyst composition and operational parameters. Applied Catalysis B: Environmental 2018, 221, 584-597. (29) Mubarak, N. M.; Abdullah, E. C.; Sahu, J. N.; Jayakumar, N. S.; Ganesan, P., Mass Production of Carbon Nanofibers Using Microwave Technology. Journal of Nanoscience and Nanotechnology 2015, 15, (12), 9571-9577. (30) Mubarak, N. M.; Sahu, J. N.; Abdullah, E. C.; Jayakumar, N. S.; Ganesan, P., Single stage production of carbon nanotubes using microwave technology. Diamond and Related Materials 2014, 48, 52-59. (31) Mubarak, N. M.; Sahu, J. N.; Abdullah, E. C.; Jayakumar, N. S.; Ganesan, P., Microwave assisted multiwall carbon nanotubes enhancing Cd(II) adsorption capacity in aqueous media. Journal of Industrial and Engineering Chemistry 2015, 24, 24-33. (32) Mubarak, N. M.; Sahu, J. N.; Abdullah, E. C.; Jayakumar, N. S.; Ganesan, P., Novel microwave-assisted multiwall carbon nanotubes enhancing Cu (II) adsorption capacity in water. Journal of the Taiwan Institute of Chemical Engineers 2015, 53, 140-152. (33) Huang, B.-S.; Chen, H.-Y.; Kuo, J.-H.; Chang, C.-H.; Wey, M.-Y., Catalytic 27


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 39

upgrading of syngas from fluidized bed air gasification of sawdust. Bioresource Technology 2012, 110, (0), 670-675. (34) Zhang, Y.; Nahil, M. A.; Wu, C.; Williams, P. T., Pyrolysis–catalysis of waste plastic using a nickel–stainless-steel mesh catalyst for high-value carbon products. Environmental Technology 2017, 38, (22), 2889-2897. (35) Mubarak, N. M.; Yusof, F.; Alkhatib, M. F., The production of carbon nanotubes using two-stage chemical vapor deposition and their potential use in protein purification. Chemical Engineering Journal 2011, 168, (1), 461-469. (36) Gao, N.; Wang, X.; Li, A.; Wu, C.; Yin, Z., Hydrogen production from catalytic steam reforming of benzene as tar model compound of biomass gasification. Fuel Processing Technology 2016, 148, (Supplement C), 380-387. (37) Park, J. H.; Park, H.-W.; Choi, S.; Park, D.-W., Effects of blend ratio between high density polyethylene and biomass on co-gasification behavior in a two-stage gasification system. International Journal of Hydrogen Energy 2016, 41, (38), 16813-16822.

28


Page 29 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure captions Figure 1. Effect of the reaction temperature of the fluidized bed on the (a) gas composition before the catalytic fixed bed, (b) after the catalytic fixed bed, and (c) CNT and H2 production. Figure 2. Schematic diagram of the mechanism of CNT and H2 production in the waste plastic gasification system. Figure 3. TGA analysis of the reacted catalysts at different reaction temperatures of the fluidized bed in the waste plastic gasification system. Figure 4. TEM and FESEM images of the reacted catalysts at different reaction temperatures of the fluidized bed in the waste plastic gasification system: (a and b) 500 °C, (c and d) 600 °C, and (e and f) 700 °C. Figure 5. Raman spectra of the reacted catalysts at different reaction temperatures of the fluidized bed in the waste plastic gasification system. Figure 6. Effect of the equivalence ratio of the fluidized bed on the (a) gas composition before the catalytic fixed bed, (b) after the catalytic fixed bed, and (c) CNT and H2 production. Figure 7. TGA analysis of the reacted catalysts at different equivalence ratios of the fluidized bed in the waste plastic gasification system. Figure 8. TEM images of the reacted catalysts at different equivalence ratios of the 29


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 39

fluidized bed in the waste plastic gasification system: (a) ER = 0.1, (b) ER = 0.15, and (c) ER = 0.2. Figure 9. Raman spectra of the reacted catalysts at different equivalence ratios of the fluidized bed in the waste plastic gasification system.

30


Page 31 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Lists of Figures:

Figure 1

31


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 39

Figure 2

32


Page 33 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 3

33


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 39

Figure 4

34


Page 35 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 5

35


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 39

Figure 6

36


Page 37 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 7

37


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 39

Figure 8

38


Page 39 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 9

39


Effects of temperature and equivalence ratio on carbon nanotubes and

Recommend Documents