characteristics of pyrolysis products from waste tyres · pdf filecharacteristics of pyrolysis...

213Progress in Rubber, Plastics and Recycling Technology, Vol. 32, No. 4, 2016

Characteristics of Pyrolysis Products from Waste Tyres and Spent Foundry Sand Co-Pyrolysis

Corresponding author: Rua Francisco Getúlio Vargas, Tel.: +55 54 3218 2100 R 1017; E-mail: [email protected]

©Smithers Information Ltd., 2016


Daniele Perondi1, Bianca Santinon Scopel2, Gabriela Carvalho Collazzo3, Jayna Pessutto Silva2, Michele Leoratto Botomé2, Aline Dettmer2, Marcelo Godinho2 and Antônio Cesar Faria Vilela1

1Mining Engineering, Metallurgical and Materials Post-Graduate Program- Federal University of Rio Grande do Sul (UFRGS) - Porto Alegre, Rio Grande do Sul, Brazil2Engineering of Processes and Technologies Post-Graduate Program – University of Caxias do Sul, Caxias do Sul – Rio Grande do Sul, Brazil3Chemical Engineering Department- Federal University of Santa Maria- Santa Maria, Rio Grande do Sul, Brazil

Summary

The products obtained through thermal conversion of tyres can represent a solution for its disposal which has been considered an environmental problem. In the foundry industry two types of sand are generated: core sand (CS) and green sand (GS); CS is classified as hazardous waste. In this paper two kinds of industrial wastes were approached, in order to propose a solution through co-pyrolysis. The experiments were performed in a bubbling fluidized bed reactor. The oil, fuel gas and char obtained were characterized. The main components present in the oil were naphthalene and anthracene. Char morphology was assessed by Scanning Electron Microscopy, confirming the resin absence on its surface. Isothermal adsorption and desorption indicated that the char obtained from tyre pyrolysis with lower particles has higher superficial area (higher than 200 m2.g-1). The main compounds identified in fuel gas were hydrogen, carbon monoxide, carbon dioxide and hydrocarbons up to 5 carbons.

IntroductIon and Background

Municipal and industrial solid waste proper management is a major challenge faced by society today due to health, environmental and economic aspects involved.

214 Progress in Rubber, Plastics and Recycling Technology, Vol. 32, No. 4, 2016

Daniele Perondi, Bianca Santinon Scopel, Gabriela Carvalho Collazzo, Jayna Pessutto Silva, Michele Leoratto Botomé, Aline Dettmer, Marcelo Godinho and Antônio Cesar Faria Vilela

In casting processes 70% of wastes generated are composed by sand [1]. The global foundry industry generated about 100 million tons of foundry sand in 2011. Data from Brazilian Casting Association (ABIFA) indicated that 2.7 million tons of cast metals were produced in Brazil in 2014. Thus, during the year of 2014, the Brazilian casting industry generated approximately 3 million tons of waste foundry sand (WFS) which has been identified as the most important problem in foundries [2-4].

Two types of sand are generated by foundry industry: core sand (CS) and green sand (GS). CS is generated in the core-making industry manufacturing, while GS is generated in several processes. The GS has applications in the production process, while the CS should be rejected as waste. Both GS and CS are classified as hazardous materials according to European regulations in their code 100907 [5], since they may contain heavy metals and organic compounds which can be released into the atmosphere [6-8]. Providing functionality to this residue has several benefits such as reducing the extraction of raw materials (soil), the waste disposed in landfills volume and the environmental contamination risk [9].

Polymeric resin on the CS surface is a catalytic reaction product between two amine resins. Resin I is phenolic while resin II is formed by a polyisocyanate (diphenyl methane diisocyanate- MDI) solution.

Pyrolysis is an alternative method for the polymeric resin removal which covers the CS surface. According to Kumar and Singh [10] the most attractive technique of chemical feedstock recycling is pyrolysis and the thermal cracking or thermal pyrolysis involves the polymeric materials degradation by heating in the oxygen absence. The CS can be used as a support in fluidized bed reactors. The kinetic parameters and mechanisms from polymeric resin [(C29H24N205)n] thermal decomposition were studied by Perondi et al. [11]. Only 1% of CS is composed by polymeric resin (organic fraction), which would make it technically unfeasible for the pyrolysis process. Through co-pyrolysis with waste tyres, the energy that is already being provided is used. Therefore, the co-pyrolysis becomes attractive.

The continually growing global automobile industry unavoidably results in also steadily increasing amounts of end-of-life or waste tyres. It is estimated that about 1.5 billion waste tyres are produced annually worldwide [12]. Until recently, the majority of these scrap tires were landfilled; it is reported that about 4 billion waste tyres are currently in landfills and stockpiles worldwide [13]. Worn tyres, like other rubber products, do not readily decompose, so their disposal involves many problems and much energy and time [14].

Tyre pyrolysis is advantageous due to its products which can be obtained and also its lower emissions [15]. According to Rombaldo et al. [16], rubber pyrolysis



is one of the most reasonable alternatives in terms of environmental protection. Tyres have a higher calorific value than coal and biomass, ranging between 28 and 40 MJ.kg-1 [17-23]. Thus, they become an interesting alternative for thermochemical process (pyrolysis, combustion and gasification) due to its high calorific value property.

Tyre main components (styrene-butadiene, natural rubber and polybutadiene) degradation temperatures were studied by Williams and Besler [24]. The styrene-butadiene is degraded at high temperature (723 K), natural rubber at lower temperatures (between 573 and 673 K), and finally the polybutadiene in two different temperature ranges (between 643 and 823 K).

Oil generated from tyre pyrolysis process can be used as fuel, or as a source of fine chemicals [19]. This oil is dark brown/black colored, with medium viscosity and a sulphurous/aromatic odor. It is chemically very complex, containing more than 100 identified compounds [25]. The pyrolytic oil composition from waste tyres consists in both short and long chain carbon molecules, as well as single and multiple ring structures [26]. Dai et al. [27] reported oil composition from tyres pyrolysis in a circulating fluidized bed: 26.77 wt% alkanes, 42.09 wt% aromatics, 26.64 wt% non-hydrocarbons and 4.05 wt% as asphalt. Conesa et al. [28] reported a 39.5 wt% aliphatic fraction, 19.1 wt% aromatic fraction, 21.3 wt% hetero-atom fraction and 20.1 wt% polar fraction for oils produced from a laboratory scale fluidized bed reactor at 973 K. Kyari et al. [29] pyrolyzed a seven-different-brands mixture of tyres in a fixed bed reactor and analyzed the oil produced by gas chromatographic/mass spectrometric (GC/MS). The tyre pyrolysis oil consisted in a single ring and polycyclic aromatic compounds and their alkylated derivatives, containing mainly alkylated benzenes, alkylated naphthalenes, alkanes, and alkenes, with compounds such as limonene, ethylbenzene, toluene accounting for the molecules majority. There were also significant concentrations of naphthalene and methyl, dimethyl and trimethyl naphthalenes. Higher molecular weight compounds included phenanthrene and pyrene.

Char can be used for combustion or as activated carbon precursor. Char obtained by López et al. [30] by pyrolysis of tyres in a conical spouted bed reactor consists mainly of carbon (86.9 wt %) and its surface area was 65.2 m2.g-1 for experiments conducted at 773 K. In order to use this solid as activated carbon, an activation process is necessary. The activated carbons production from carbonaceous chars requires an activating agent such as steam or carbon dioxide. The reaction with the carbon to produce gases opens up the pores of the char to produce higher surface areas, approaching the activated carbons which present areas typically between 400 and 1500 m2.g-1 [31].



Fuel gas produced is useful as a heat source, and the gases produced analysis from the waste tyres pyrolysis shows that the main gas components are: hydrogen (H2), methane (CH4), ethane (C2H6), ethene (C2H4), propane (C3H8), propene (C3H6), butane (C4H10), butene (C4H8), butadiene (C4H6), carbon dioxide (CO2), carbon monoxide (CO) and hydrogen sulphide (H2S). The thermal degradation process produces highly reactive free radicals which are often sub-units of the original rubber molecule [32]. As the tyre rubbers are thermally degraded during the pyrolysis process, the main primary degradation products produce high concentrations of alkenes, dienes and butadiene. Secondary reactions of the product pyrolysis gases in the reactor hot zone also leads to light hydrocarbons formation from the oil vapours produced during pyrolysis. The gas has a significant calorific value and it has been reported that it ranges from 20 MJ.m-3 to values above than 65 MJ.m-3, depending on the gas composition which in turn would depend on the pyrolysis temperature, heating rate, reactor type, etc. [18, 29, 33]. It is suggested that the gas has enough energetic value to provide heat to pyrolysis process [25].

In bubbling fluidized bed (BFB) processes, the superficial fluid velocity is above the minimum fluidization velocity, but below the terminal velocity of the particle [34-37]. In BFB, an initially stationary bed of solid particles, located in the bottom part, is brought into a fluidized state by the carrier gas, supplied through a distributor: the bed particles are kept in suspension at fluidization velocities between 0.5 and 3.0 m/s. BFB are applied for e.g. coal, bio-solids, plastic solid waste and wastewater treatment sludge [38].

Several studies to evaluate the pyrolysis in BFB reactors were conducted [39-45]. These studies were performed with different materials, such as Amazon tucumã, grape, Quercus Acutissimain, PVC, PVC-wood, PVC-coal mixtures, Geodae-Uksae 1 (tetraploid M. sacchariflorus), kraft lignin and Laminaria japonica (brown algae). Studies reporting CS with waste tyres were not found in the literature. Therefore, the scientific contributions of this work are the co-pyrolysis of tyres and polymeric resin present in CS evaluation in a BFB reactor and the CS evaluation performance as coarse particles. Furthermore, this paper aims to assess whether the particles properties after the co-pyrolysis process are suitable for reuse at the foundry industry or not.

materIal and methodS

Raw Materials

For the execution of this study the following raw materials were used: CS, polymeric resin and waste tyres identified as PL 100/420 and PL 600.



CS is a residue of core-making industry (Farina S/A Automotive Components), located in the city of Bento Gonçalves (Rio Grande do Sul state).

The polymeric resin used in this work was donated by Farina S/A Automotive Components. This polymeric resin was obtained from the reaction of an isocyanate (Isocure Focus TM II 605) with a phenolic resin (Isocure Focus TM I 405). Reaction was catalyzed by an instant cure catalyst (ISSO-FAST TM 706) at 293K.

Reaction between resins I and II results in a urethane system. In the curing process, the hydroxyl groups of the resin I react with the isocyanate groups of the resin II in the presence of a tertiary amine, resulting in a polymeric resin (polyurethane), showed in Figure 1. This resin main function is to confer thermal and mechanical resistance to CS.

Figure 1. Monomer precursor of the polymeric resin

Tyre samples (PL 100/420 and PL 600) are products resulted from mechanical crushing of vulcanized rubber waste. They were provided by Borrachas Planalto company, located in the city of Bento Gonçalves (Rio Grande do Sul state). These samples differ by their particle size. PL 100/420 has an average particle diameter of 300 µm, while PL 600 has 710 µm (both samples have 1170 kg.m-3density). CS has an average particle diameter of 300 µm and an average density of 1500 kg.m-3. Fluidization process is strongly influenced by the particles characteristics. According to Geldart classification [46] the particles can be classified into four groups (A, B, C and D). The particles (PL 100/420 and PL 600/CS) used in this work are Geldart’s group-B which is composed of size particles between 40 and 500 µm and density between 1.400 and 4.000 kg.m-3. This type of material is easily flowable [36].

Raw Materials Characterization

The following methods to characterize the raw materials were used: proximate analysis (ASTM/D-7582/2010) [47], ultimate analysis (CHNS-ASTM/D-5373/2008) [48], total sulfur (ASTM/D-4239/2011) [49], higher calorific



value (ASTM/D-5865/2010) [50], Spectroscopy Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and phenol percentage.

Proximate analysis is the determination of moisture, volatile matter, ash and fixed carbon. For volatile matter determination in the sample, the method employed is based on the volatile distillates quantification, which are given off during heating in an electric furnace in the oxygen absence, under strict control of mass, time and temperature. For ash determination, the method is based on determining the residual mass resulting from sample combustion under strict control of mass, time and temperature.

The fixed carbon determination is calculated by difference, since the ash and volatile matter content are known, according to Equation (1):

(1)

Where,FC is fixed carbon, AS is ash and VM is volatile matter.

The ultimate analysis (carbon, hydrogen and nitrogen) was conducted using LECO Corporation Model CHN TruSpec instrument. The total sulfur analysis (sample combustion with infrared detection) was conducted using LECO Corporation Model S TruSpec instrument.

The higher calorific value was determined using a calorimetric pump Isoperibol. For all analysis the samples were dried in an oven of lamps with air circulation at temperature from 50 ± 5°C up to constant weight, and after drying the samples, a milling at 0.21 mm in a ball mill was prepared.

Infrared Spectroscopy Fourier Transform (FTIR) was conducted using a Nicolet IS10 Thermo Scientific equipment. Sample scanning was conducted in the 4000-400 cm-1 region. In order to evaluate the thermal degradation of functional groups present in the polymeric resin, FTIR experiments were conducted with samples prepared in a thermogravimetric balance (Shimadzu TGA-50), in an inert atmosphere (N2), at 50 mL min-1 flow rate, with a 5 K.min-1 heating rate and at final temperatures of 493, 573 and 653 K. Finally, after reaching the final temperature, samples remained for 2 h at this temperature. About 10 mg of polymeric resin were used in the thermal degradation experiments.

Scanning Electron Microscopy (SEM) analyses were performed in a JEOL JSM 6060 equipment model, with an accelerating voltage of 10 kV. The samples were coated with a thin layer of gold before analysis.

Experiments for determining the phenol percentage were performed according to the 3550 B and C methods from Standard Methods for the Examination of Water and Waste Water [51].



The 3550 B method, describes the initial cleaning procedure. It is necessary a distillation apparatus, a pHmeter and some reagents, such as sulfuric acid (H2SO4) 1 N, sodium chloride (NaCl), sodium hydroxide (NaOH) 2.5 N, chloroform (CHCl3), methyl orange indicator and 10 mL of a phosphoric acid solution (H3PO4) 85% diluted with 100 mL of water. On the other hand, the 3550 C method describes chloroform extraction procedure used in the initial cleaning procedure. At the end, the phenol concentration in the solution calculation was conducted.

For standard solution preparation it is necessary to dissolve 100 mg of boiled and cooled phenol in distilled water (dilution in 100 ml). Afterwards, a pattern is prepared exactly the same way, using distilled water and 10 mL of bromate-bromide solution. Titration of pattern and sample with 0.025 M sodium thiosulphate is performed (Na2S2O3), using a starch indicator.

The phenol concentration in the solution is calculated according to Equation (2):

(2)

Where,

A= thiosulfate to pattern (mL)

B= bromate-bromide solution used for the samples and divided by 10 (mL).

C= thiosulfate used for samples (mL)

Products characterization obtained after the pyrolysis reaction in the fluidized bed (sand, oil, gas and char) was performed according to the following analysis: sand (SEM and phenol percentage), oil (GC-MS), char (SEM and Superficial area analysis) and gas (gas chromatography).

Pyrolysis Experiments

Tyres co-pyrolysis (PL 100/420 and PL 600) and polymeric resin present in CS was performed in a fluidized bed reactor under nitrogen atmosphere (Figure 2). Experiments were carried out at atmospheric pressure. Nitrogen flow rate used in the experiments was approximately 0.50 m3/h (20°C). The reactor bed has 60 cm height and 4 cm diameter, while the freeboard has 60 cm height and 8 cm diameter. Considering that inert gas mass (N2) is much higher than fuel gas mass generated in the pyrolysis process, the superficial velocity in the reactor bed is approximately 0.3 m/s. The experiments average time was 60 minutes. The material was directed to the reactor via a screw conveyor, which was cooled from a current flowing through a water jacket around the chamber. The cooling had the function of maintaining a low temperature in



this region, preventing the feeding material of being degraded before reaching the bed. Two overlapping screens (80 mesh) are set up just below the bed, and they act as supporters for the solids in the bed.

Figure 2. Fluidized bed reactor used in the experiments

The reactor heating system consists in four furnaces (F1, F2, F3, F4), composed of insulated electric heaters. All furnaces have independent temperature controllers, which were set in the reactor control panel. The furnace preheating (F4) has a coil, which aims to preheat the nitrogen gas. The pyrolysis gases condensation was conducted according to standard TC BT/TF 143 WI CSC 03002.4:2004 specified by the Comité Europén de Normalisation [52]. Six impingers were installed at the freeboard exit. The first impinger was made from 304 stainless steel (char collector), while the others were made from borosilicate glass. In all experiments, 75 mL of isopropyl alcohol were added to each impinger, except for the first and the last (empty). Impingers were placed in a box with ice, salt and isopropyl alcohol. The aim was to keep the bath at low temperature, to favor the pyrolysis oil condensation. Bath temperature during the experiments was approximately 268 K. The adopted procedure in the experiments had the following sequence: (a) CS was added to the bed and the tyre to the feeding silo; (b) the temperature of furnaces F1, F2, F3 and F4 were adjusted; (c) nitrogen (N2) began to be injected in the reactor; (d) after reaction temperature (773 K) was achieved, the tyre feeding was initiated. In all experiments, the silo was fed with 50 g of tyre, while the bed was fed with 120 g of CS. The use of this CS mass corresponded to an 8 cm



height above the supporter for the solids. For feeding, the screw conveyor was turned on for two seconds. After this period, it remained turned off for two minutes. This procedure was adopted to avoid the excessive release of pyrolysis products to the condensation system (impingers). At the end of the experiments, the furnace was turned off and afterwards it was cooled. After cooling, the CS and char were removed from the bed as well as char present in the first impinger and the mixture of the pyrolysis oil with isopropyl alcohol present in other impingers. Fuel gas sampling was performed in SKC bags (FlexFoil PLUS Gas Sample Bags model) with capacity up to 10 L. After sampling (approximately 50% of bag volume), the bags were stored at room temperature in a location direct-illumination-free.

The gases were collected during periods of devolatilization peaks after the first feeding (12 and 14 minutes to PL 100/420 and 22 and 52 minutes to PL 600). The devolatilization peaks were identified by gas formation on the condensation system. The sampling times similar to each other (12 and 14 min for PL 100/420) aimed the reproducibility of the results. For PL 600 the samplings were performed in the intermediate and final phase of the experiment. Table 1 shows an experimental design adopted in this work.

Table 1. Experimental design adopted in this workSample experimental design

PL 100/420 Particle size: 300 µmPyrolysis temperature: 773 KFeeding: 50 g

PL 600 Particle size: 710 µmPyrolysis temperature: 773 KFeeding: 50 g

CS Utilized as a bed in the BFB reactor with PL 100/420 and PL 600 samplesPyrolysis temperature: 773 KFeeding: 120 g

*The experiments were performed in duplicate

Oil

Oil was produced throughout pyrolytic process. Pyrolytic oil was analyzed by gas chromatography with mass spectrometry (HP 6890/MSD5973, equipped with HP Chemstation software and Wiley 275 libraries). During analysis an HP-5MS (30 mx 250 mm) 0.50 mm film thickness (Hewlett Packard, Palo Alto, USA) capillary column was used. The following temperature program was used: initial and final temperatures were 40 and 280ºC, respectively; times at initial and final temperatures were both 10 min and the heating rate was 8ºC.min−1. The injector



temperature was 280ºC; splitless; He carrier gas (56 kPa); 1.0 ml/min flow rate; 70 eV ionization energy and 1 mL diluted in acetone (1:10) injected volume.

Char

Superficial area, pore volume and radius pore of char were determined using a Nova 1200e (Quantachrome) Analyser. Char was subjected to adsorption and desorption measurement of nitrogen gas at a temperature of 77.3 K (char produced from PL 420/100 and char produced from PL 600). Samples were outgassed under vacuum at 623 K and low pressure for a period of 20 h prior to testing. Outgassing procedure was conducted in order to remove moisture and volatile matter present in the sample, which could interfere with the results. Superficial area was calculated from the isotherms by using the BET (Brunauer–Emmett–Teller) equation [53].

Gas

Fuel gas chromatography was conducted in a GC Auto System XL Perkin Elmer provided with two detectors: FID and TCD. A column packed Porapack Q of 3.6 m length was selected. The carrier gas used was nitrogen (N2). When using the FID, hydrogen and air were employed to feed the flame detector. Two different setups were used to allow the present compounds in the fuel gas separation and quantification. Table 2 shows the GC configurations.

Table 2. GC configurations for the fuel gas analysisconfiguration 1 configuration 2

Possible gases to be identified H2, CO+O2, CH4, C2 and C3

CH4, C2, C3, C4 and C5

Chromatographic column Porapak Q Porapak Q

Detector TCD FID

Carrier gas N2 N2

Flow rate of carrier gas (ml/min) 30 30

Column temperature (K) 333 413

Injector temperature (K) 373 373

Detector temperature (K) 373 473

Running time (min) 8 16

The fuel gas calorific value was calculated by adding the mass fraction product from each of its components (in nitrogen-free basis), according to Kreith [54] values.



reSultS and dIScuSSIon

Raw Materials Characterization

Tables 3 and 4 show the proximate analysis, ultimate analysis and calorific value for the tyre samples (PL 100/420 and 600 PL).

Table 3. Proximate analysis for PL 100/420 and PL 600 (% m/m)Pl 100/420 Pl 600

Volatile matter 65.9 65.7

Ash 4.7 4.3

Fixed Carbon 28.3 28.7

Moisture 1.0 1.3

It has been reported that the volatile matter present in tyres consists mainly of polymeric compounds that come from natural rubber and styrene-butadiene, as the fixed carbon is originated from carbon black (CB) used in tyre manufacturing. Many nonblack fillers are used in the tyre manufacturing (calcium carbonate, clay, precipitated silica, talc and titanium dioxide). Ashes comes from these nonblack fillers. It’s not possible to identify significant differences among samples.

Table 4. Ultimate Analysis (% m/m) and Calorific Value for PL 100/420 and PL 600 compared to other authors

Pl 100/420

Pl 600

[17] [18] [19] [20] [21] [22] [23]

Total Sulfur 1.65 1.65 1.7 1.8 1.5 1.6 1.9 1.63 2.01

Total Carbon 89.61 89.60 86.4 78.6 74.2 88.5 89.5 74.5 87.6

Hydrogen 7.93 7.83 8.0 7.1 5.8 6.6 7.3 6.5 7.6

Nitrogen 0.55 0.53 0.5 0.3 0.3 0.4 0.3 0.95 0.3

Oxygena 0.26 0.40 3.4 4.8 4.7 3.0 0.8 16.42b 3.1

Chlorine - - - - - - 0.04 - -

Other non-combustible materials

- - 2.4 - 13.5 - - - -

Higher calorific value (MJ.kg-1)

37.65 38.04 40.0 31.8 37.3 36.78

Lower calorific value (MJ.kg-1)

37.3 35.9

a by difference b Oxygen and other



It has been reported by Evans and Evans [55] that a typical tyre could contain up to 30 different types of synthetic rubber, 8 different natural rubbers, in addition to a range of different carbon black fillers and up to 40 different additive chemicals. The differences observed in ultimate analysis and in the calorific values are mainly due to the source/formulation of rubbers.

CS characterization was performed by phenols concentration, as well as visualization of surface by SEM. Phenolic groups present in the CS before to co-pyrolysis experiments are shown in Table 5 along with the results after the co-pyrolysis experiments. The results indicated 5.3 mg.kg-1 phenol presence in the CS. According to Figure 1, it is not possible to observe the presence of 2-methyl-4,6-dinitrophenol, 2,4-dimethylphenol, 2-methylphenol (o-Cresol), 2-methylphenol (m + p-Cresol), 2-nitrophenol, 4-nitrophenol in the polymeric resin.

CS images obtained from scanning electron microscopy (SEM) before and after co-pyrolysis experiments, are shown in Figures 3a and b.

Figure 3. (a) CS after co-pyrolysis at 773 K (300 x). (b) CS before co-pyrolysis (300 x)

In Figure 3a it is observed that the grain surface is roughened, whereas in Figure 3 (b) it is possible to identify the resin on the surface of the grain (showed by arrows).

Infrared Spectroscopy Fourier Transform (FTIR), which was utilized to evaluate the thermal degradation of functional groups present in the polymeric resin. Spectra were conducted at room temperature, 493, 573 and 653 K and are shown in Figure 4.

Spectra at room temperature contains the following set of peaks: a wide band characteristic of the OH group at 3300 cm-1, an intense peak at 1720 cm-1, which is characteristic of the aldehyde bonds (C=O); a narrow peak and with medium intensity at approximately 1595 cm-1; characteristic vibrations of the aromatic nucleus (C=C); an intense peak at 1200 cm-1; typical of C-O

(a) (b)



bond of the phenolic groups, all of which confirm the structure presented at Figure 1. Above 650 K, the peaks lose their intensity, indicating that the resin undergoes thermal degradation. Peak in this wavelength near 750 cm-1 is characteristic of the group - (CH2)n

Characterization of Co-pyrolysis Products

At the end of each experiment, the CS, char present in the bed and the mixture of pyrolytic oil + isopropyl alcohol present in the impingers were removed.

Bed (CS)

CS showed a darker appearance after co-pyrolysis to both samples (PL 100/420 and PL 600). This staining is associated with the presence of char on its surface.

As can be seen in Table 5, in all experiments (after co-pyrolysis) the phenol concentration was less than 0.05 mg.kg-1, indicating the polymeric resin degradation.

In order to evaluate the removal of the polymeric resin present in CS, SEM tests were also conducted. Figure 5 shows the image obtained from the solid

Figure 4. Spectra at different temperatures of polymeric resin



Tab

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. P

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co-p

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with

Pl

600

Par

amet

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LQ*

Ana

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al re

sults

(mg/

kg)

Ana

lytic

al re

sults

(mg/

kg)

Ana

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al re

sults

(mg/

kg)

2-m

ethy

l-4 ,6

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2-m

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2-m

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m +

p-C

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<0.

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<0.

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2-ni

trop

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4-N

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sample removed after an experiment using CS as support bed. The image has strong similarity to the image (a) shown in Figure 3 (sand – free resin), indicating the removal of the resin after pyrolysis. Porous structure on the right side of the image has typical characteristics of char. This image indicates that the char is not adhered to the surface of sand grains, which facilitates their separation. In addition, the sand can be reused in industrial foundry processes.

Oil

Pyrolytic oil is complex, presenting 61 different peaks for PL 600 and 97 different peaks for PL 100/420. As expected, the particle size variation did not significantly influence the oil composition.

The compound with the highest yield is the Naphthalene, followed by Anthracene (both analysis- PL 100/420 and PL 600). Tyre pyrolysis oils contain a wide range of polycyclic aromatic hydrocarbons (PAHs), but the highest concentration of PAH identified consist largely of alkylated naphthalenes, fluorenes and phenanthrenes [25].

GC/MS analysis show that the pyrolytic oil composition from waste tyres consisted of both short and long chain carbon molecules, and single and multiple ring structure [26]. Kyari et al. [29] also found significant concentrations of naphthalene and methyl, dimethyl, and trimethyl naphthalenes, besides higher molecular weight compounds included phenanthrene and pyrene.

The main use for naphthalene is as a raw material for the production of phthalic anhydride which is employed as a starting material for the production

Figure 5. SEM of solids removed from the bed after pyrolysis (magnification 100x)



of phthalate plasticizers, resins and phthaleins. Other products made from naphthalene include concrete super plasticizers, azo dyes, surfactants and dispersants, leather tanning agents, insect repellents, alkylnaphthalene solvents (for carbonless copy paper) and as fumigants (moth repellents) [56]. These are the “traditional” uses of industrial naphthalene, but in recent years, new applications have been developed. Naphthalene is a suitable precursor in the synthesis of pharmacological compounds and certain raw materials with high specifications [57-64], due to the benzene rings of its molecular structure.

Several studies have been carried out on the anthracene reactivity [62]. Anthracene has been reported to undergo selective oxidation at the 9, 10 positions in the presence of V2O5/SiO2 catalyst [63]. This is a useful intermediate process with a 99% yield of anthraquinone which is applicable in the dye industry and also in the synthesis of hydrogen peroxide [64]. Oxidation of anthracene to anthraquinone has been achieved in the presence of ‘air/oxygen/nitric acid’, ‘nitrogen dioxide in acetic acid’ among others [65]. A number of PAHs including anthracene have also been oxidised to CO2 and benzene polycarboxylic acid groups with a RuO4 catalyst [66].

Char

Figure 6 shows a SEM image of the char external surface produced at 773 K with PL100/420 (500 x). The other char samples collected presented similar texture.

Figure 6. SEM image of char obtained by co-pyrolysis at 773 K temperature and PL100/420 (500x)



Tyre pyrolysis char is formed by the carbon black present in the original tyres and some residues derived from rubbers pyrolysis, since most of the rubber components are volatilized during the heating [23]. The carbon blacks are considered to be less reactive because of the rigid concentric layer structure [67]. The char presented a surface relatively smooth and the formation of macropores in their external surface which can be associated to fast heating of tyres after feeding, and the consequent release volatile gases. It was possible to detect some mineral matter dispersed over the char surface.

Generally, the solid materials pore structure can be divided into three classes: micropores with a pore size smaller than 2 nm, mesopores with a pore diameter between 2 and 50 nm, and macropores wider than 50 nm [68]. One of the methods for estimating the type of pores in a solid is by analyzing the adsorption isotherm. The amount of adsorbed nitrogen (N2) is indicative of the char adsorptive capacity [69].

Figures 7 and 8 show the adsorption/desorption isotherms for the chars produced from PL 100/420 and PL 600.

Figure 7. Adsorption/Desorption isotherms for nitrogen at 77.3 K (PL 100/420)



Figure 8. Adsorption/Desorption isotherms for nitrogen at 77.3 K (PL 600)

According to the International Union of Pure and Applied Chemistry [70] the behavior of adsorption isotherms may be considered type II, which the initial part represents micropore filling, and the slope of plateau at high relative pressure is due to multilayer adsorption on the non microporous surface, i.e., in mesopores, macropores and on the external surface [71].

Calculated values for BET superficial area, pore volume and average radius pore are given in Table 6.

Table 6. Superficial area, pore volume and radius poreSample Bet Superficial area

(m2.g-1)Pore volume

(cm3.g-1)average radius pore

(nm)

PL 100/420 209.60 0.19 1.58

PL 600 91.90 0.08 2.02

It was observed that the char produced from PL 100/420 (0.3 mm) had a superficial area higher than the char produced from PL 600 (0.71 mm), as well as size and pore volume. Superficial areas found elsewhere were lower than obtained in this work. López et al. [30] have carried out pyrolysis of scrap tyres in a conical spouted bed reactor in a range of temperature between 698 and 873 K. Raw material (tyre) used had size particle lower than 1 mm. Authors observed a char superficial area



increase with the increase of temperature. At 773 K temperature, the superficial area was 62.5 m2.g-1. Fernández et al. [23] have carried out fluff pyrolysis that is recovered as a waste in scrap tyre recycling factories in a horizontal oven in a range of temperature between 673 and 1173 K. The fluff consists in a mixture of polymeric fibers and rubber particles that cannot be further separated and is disposed at landfill sites. Particles used in the experiments had size lower than 2 cm and the most elevated superficial area was 68 m2.g-1.

Small size particles are capable of completing the pyrolysis process within a shorter time but the overall energy required is higher compared to the ones of larger particles size [72]. When small particles are fed into a fluidized bed of sand, they heated up rapidly and almost instantly. However, the actual heating rates for larger particles are much slower. For small particles the fast heating rate may favor the volatiles formation [73]. Suuberg and Aarna [74] observed that char particles obtained from tyre pyrolysis have larger superficial area (between 54 and 87 m2.g-1) determined by the residual carbon black grains left from the original tyre material, because the carbon black has superficial areas ranging from 35 up to 70 m2.g-1.

Gas

The gas compositions for each type of tyre produced significantly different gas compositions [29]. Cypres and Bettens [75] also reported significant differences in gas composition from different brands tyre pyrolysis. Furthermore, the influence of fluidization gas type on the product composition varies between the product groups.

In this work, fuel gas analysis were carried out to determinate the following gases: H2, CO, CH4, CO2, C2, C3 by TCD; and CH4, C2H2, C2H6, C3 by FID.

C2 and C3 were detected using both FID and TCD detectors. To determine their concentrations, the values obtained by the FID detector were chosen due to better definition peaks, while the adopted concentration of CH4 was obtained from the results found by TCD detector configuration. Fuel gas composition in the experiments and calorific value calculated for the pyrolysis gas generated (MJ/kg) are presented in Table 7.

Although temperatures were set at 773 K there were minor variations throughout the experiments, as it could be seen in Table 7. Possibly, these variations do not significantly influence on the gases composition. Samplings were carried out in different experiment times and were performed in steady state. Tyre feeding was held only after the bed temperature was reached. Thus, it is not expected significant variations in fuel gas composition due to the time of sample collection throughout the experiment. However, the feeding occurred in 2 min intervals. After



the feeding, there was an intense generation of fuel gas due to the particles high heating rate. Afterwards, there was gases formation reduction, which could be observed through the decreasing gases presence in the impingers.

From the results presented in Table 7 the highest variation occurred in the experiment where the sample was collected at 52 min (experiment final phase). Possibly, the observed differences in fuel gas composition are associated with changes in the generation rate during the feeding interval. According to Férnandez et al. [23], the main reactions that occurred during the tyre pyrolysis are the following:

(3)

(4)

(5)

(6)

A free radical decomposition mechanism is involved in the pyrolysis of butane similar to those involved in from the pyrolysis of ethane, and propane. Two main reactions occur in the initiation step [23].

Table 7. Fuel gas composition in experiments and calorific value (mol% and %wt N2-free) calculated for the pyrolysis gas generated

100/420 600 100/420 600

t (min) 12 52 14 22

T (K) 773 783 803 766

Calorific value (MJ/kg)

51.03 58.04 54.15 55.66

%mol %wt %mol %wt %mol %wt %mol %wt

H2 39.49 5.54 54.47 11.10 43.62 7.08 39.14 5.87

CO 6.28 13.22 3.14 9.59 4.22 10.28 0.96 2.16

CO2 0.61 1.87 0.77 3.46 0.42 1.52 1.00 3.28

CH4 32.20 36.21 35.22 57.43 37.82 49.09 40.23 48.27

C2H4 19.74 38.78 5.80 16.78 13.02 29.57 16.71 35.09

C2H6 0.46 0.98 0.49 1.49 0.59 1.44 0.92 2.07

C3 1.15 3.40 0.03 0.15 0.30 1.03 1.04 3.26



(7)

(8)

These reactions generate other free radicals due to numerous propagation reactions. Among the newly formed free radicals are H•, CH3

•, C4H9 •.

The C4 components of the gas (butane, butene and iso-butylene) are originated from the depolymerization of styrene–butadiene rubber (SBR). According to Equations (3)-(6), C4 generates propene, ethane, methane and hydrogen. Fuel gas composition observed in the sample collected at 52 min is in agreement with the one presented by Férnandez et al. [23]. There is an increase in H2 concentration associated with a reduction in the heavier hydrocarbons concentration (C2H4, C2H6, C3). Other researchers have also reported very low C4 levels (1.3 [18]; 1.95 (butane + butene + isobutylene + butadiene) [20]; from 0.20 to 1.4 butadiene [76]. Kaminsky et al. [76] attributed their results to the occurrence of reactions which led to an increase in the amount of lighter hydrocarbons and hydrogen.

Results indicated that the CO concentration is higher than CO2. According to Díez et al. [21], CO is formed from reactions in the gas phase between CO2 and hydrocarbons or from other cracking reactions (homogeneous phase reactions).

The calorific values are considerably high, they are justified by the presence of hydrogen. The gas has a significant calorific value depending on the gas composition which would depend on the pyrolysis temperature, heating rate, reactor type, etc. [18, 29, 33]. It was suggested that the gas had sufficient energy value to provide the process fuel to heat the tyres to the required pyrolysis temperature [25].

concluSIonS

The results from Gas chromatography/mass spectroscopy (GC/MS) indicated that the oil is chemically very complex, consisting of both short and long chain of carbon molecules, and of single and multiple ring structures. The compounds with the highest yield were naphthalene and anthracene to both samples (PL 100/420 and PL 600).

It was observed that the char produced from PL 100/420 (0.3 mm) had a higher superficial area than the char produced from PL 600 (0.71 mm), as well as the size and the pore volume. Superficial areas found elsewhere were lower than obtained in this work. Possibly the pyrolysis process of PL600



sample was completed in a time lower than PL 100/420 sample, due to its lower size particle.

The SEM analysis after co-pyrolysis may indicate the removal of polymeric resin initially present in the CS, and the phenol absence confirm the polymeric resin degradation.

The gases generated in the co-pyrolysis are: hydrogen, carbon monoxide, carbon dioxide and hydrocarbons with oxygen carbon chain up to 5 carbons. The quantitative gas analysis showed significant concentrations of hydrogen (47.69% mol/mol and 8.80% w/w), methane (33.09% mol/mol to 44.48% w/w) and ethene (11 90% mol/mol to 25.90% w/w). The gas composition in addition to the high calorific value equal to 53 MJ/kg can be inferred that it can be used in combustion systems.

Thus, the co-pyrolysis of tyre and CS in a bubbling fluidized bed reactor is an alternative method for the foundry sands treatment. Furthermore, the CS can be used as coarse sand in fluidized beds, and can be reuse in the foundry process due to the suitable properties after the co-pyrolysis process.

acknowledgmentS

The authors would like to acknowledge the National Council for Scientific and Technological Development (CNPq) for providing the scholarship, Farina S/A Automotive Components (Bento Gonçalves, RS, Brazil) for the polymeric resin and CS; finally, Borrachas Planalto (Bento Gonçalves, RS, Brazil) for their generous collaboration for the rubbers samples provided.

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