Development of HZSM-12 zeolite for catalytic degradation of high-density polyethylene

Accepted Manuscript Development of HZSM-12 zeolite for catalytic degradation of high-density polyethylene Antonio O.S. Silva, Marcelo J.B. Souza, Anne M.G. Pedrosa, Ana C.F. Coriolano, Valter J. Fernandes, Jr., Antonio S. Araujo PII:

S1387-1811(17)30111-7

DOI:

10.1016/j.micromeso.2017.02.049

Reference:

MICMAT 8159

To appear in:

Microporous and Mesoporous Materials

Received Date: 18 January 2017 Accepted Date: 13 February 2017

Please cite this article as: A.O.S. Silva, M.J.B. Souza, A.M.G. Pedrosa, A.C.F. Coriolano, V.J. Fernandes Jr., A.S. Araujo, Development of HZSM-12 zeolite for catalytic degradation of high-density polyethylene, Microporous and Mesoporous Materials (2017), doi: 10.1016/j.micromeso.2017.02.049. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical Abstract

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Development of HZSM-12 zeolite for catalytic degradation of highdensity polyethylene

Antonio O. S. Silva1, Marcelo J. B. Souza2, Anne M. G. Pedrosa2,

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Ana C. F. Coriolano3, Valter J. Fernandes Jr.4, Antonio S. Araujo4,*

Federal University of Alagoas, Chemical Engineering Department,

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57072-970, Maceio AL, Brazil 2

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Federal University of Sergipe, Department of Chemical Engineering, 49000-100, Sao Cristovao SE, Brazil

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Potiguar University, Laureate International Universities, 59056-450, Natal RN, Brazil

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Federal University of Rio Grande do Norte, Institute of Chemistry,

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Abstract

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59078-970, Natal - RN, Brazil.

The catalytic degradation of high density polyethylene (HDPE) was studied in the presence of HZSM-12 zeolites with different Si/Al ratio, by thermogravimetry and pyrolysis coupled to gas chromatography and mass spectrometry. The NaZSM-12 zeolite was synthesized by the hydrothermal method using methyltriethylammonium chloride as template. The HZSM-5 was obtained by ion exchange of NaZSM-12 with ammonium chloride, drying and subsequent calcination. The materials characterization were carried out by chemical analysis, X-ray diffraction, scanning electron microscopy, BET

ACCEPTED MANUSCRIPT measurements and acidity by n-butylamine adsorption. The obtained HZSM-12 zeolites were physically mixed with HDPE in the proportion of 50%wt and submitted to thermogravimetric analyses at heating rates of 2.5; 5; 10 and 20 oC min-1. The addition of HZSM-12 to HDPE produced a decreasing in the temperature of polymer degradation,

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which was proportional to the zeolite acidity. The activation energy (Ea) for the process was determined from the non-isothermal model-free kinetic model proposed by Vyazovkin. The Ea decreases linearly with the concentration of acid sites on the HZSM-12

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materials. From the pyrolysis data, the obtained products were typically light gases (C2C3); liquid petroleum gases (C4-C5); and gasoline (C6-C10). This results suggest that acid

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zeolites are excellent materials for obtaining alternative fuels from catalytic recycling of plastics.

Keywords: HZSM-12 zeolite, acid sites, high-density polyethylene, activation energy.

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* Corresponding author: Phone/Fax: +55 84 3211 9240; e-mail: [email protected]

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1. Introduction

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The huge world consumption of polymeric materials generates enormous amounts

of wastes plastics [1]. The normal methods of disposal of these residues are the landfill and incineration. However these treatments generate serious environmental problems. Owing to factors as: low biodegradability, lack of spaces in the big cities to the landfills and emission of toxic substances during burned of plastics materials [2]. These difficulties evidence the necessity of new chemical processes for recycling that converts plastic wastes

ACCEPTED MANUSCRIPT in basic chemical products as a viable way to solve environmental problems caused by these residues [3-5]. The two main routes of chemical recycling of plastic residues are the thermal and catalytic degradation [6]. The thermal degradation processes present two characteristics

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that limit its use: high temperatures for processing (>500oC) and the obtained products are disposed in large range of molecular weight distribution. On the other hand, the catalytic degradation processes using a catalyst with adequate properties provide a solution for these

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problems, reducing the reaction temperature and restricting the products selectivity [7]. The thermal degradation reactions of polyolefins (without catalyst) normally

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presented low selectivity. There exists diverse works in literature on the use of acid solid catalysts for the degradation of polyolefins to produce fuels, being that the most studied were the silica-alumina [7,8] and the some zeolites [6, 9,10,11]. The ZSM-12 is a zeolite synthesized with high Si/Al ratio that presented structure

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formed by unidimensional pores system of elliptical opened with diameters of 5.5 x 5.9 Å [12]. It was used as acid catalytic in reactions of conversion of hydrocarbons, such as reforming [13,14] and hydrocracking [15]. However, low attention was given for use of

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ZSM-12 zeolite for catalytic degradation of polymer to hydrocarbon production. The pyrolysis coupled with gas chromatographic and mass spectrometry (Py-

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GC/MS) is increasingly being employed in the analysis of polymers. One of the main advantages of this technique is to direct chromatographic separation of the vapors evolved from the pyrolysis process and identification and quantification through of the mass spectrometry. The Py-GC/MS was extensively used to verify the influence of additives on the nature of the products generated during degradation of polymeric materials [16-18]. In this work was studied the catalytic degradation of high-density polyethylene (HDPE) in presence of HZSM-12 zeolite with different Si/Al ratio. The aluminum

ACCEPTED MANUSCRIPT concentration present at zeolite lattice determine the acidity these materials. Zeolites with several Si/Al ratios have acidity properties different and consequently presented variations in its catalytic activity. Thus, the main objective of this work is to verify the influence of the zeolite acidity on the activity for catalytic degradation of HPDE. The Py-GC/MS was

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used to investigate the thermal and catalytic degradation of pure HPDE, to identify the effect of the addition of HZSM-12 zeolites with different surface acidity on the nature of the hydrocarbons formed. The activation energy was determined using the non-isothermal

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kinetic model proposed by Vyazovkin [19,20]. This model permit determine the activation energy of complexes reactions, such as polymers degradation, starting from the conversion

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data of the reaction obtained by heating of the samples with different heating rates.

2. Experimental

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2.1 Zeolite Synthesis

The ZSM-12 zeolite was synthesized by the hydrothermal method, starting from amorphous silica, sodium hydroxide (98%, Merck), pseudoboehmite Catapal B (Vista

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Chemical, 70% Al2O3) and methyltriethylammonium chloride - MTEACl (98%, Sigma) as organic template and distilled water as solvent. These reactants were mixed in the

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following molar composition: 20 MTEACl : 10 Na2O : x Al2O3 : 100 SiO2 : 2000 H2O, with x=0.50, 0.67, 1.0 and 2.0, for Si/Al molar ratio of 100, 75, 50 and 25, respectively. The obtained gels were transferred to Teflon lined stainless-steel autoclaves and

heated in an oven at temperature of 140 °C under autogenous pressure and static conditions for 6 days. Then, the materials were calcined for organic template removal, and submitted to three successive ion exchange procedures with a 0.6 mol L-1 NH4Cl solution at the temperature of 80 oC for 2 h. Finally the samples were, washed, dried and calcined at 500

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C for 3 h to generate the HZSM-12 acid catalysts. The materials were denoted by ZX,

where Z is the H-zeolite and X is the Si/Al molar ratio.

2.2 Characterization

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The calcined samples were submitted to chemical analysis by atomic absorption spectroscopy in an equipment Varian model Spectra A-10 to determine the concentrations of Si, Al, Na and Si/Al molar ratio. The obtained results were compared with the

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concentrations of these elements present in the gel of synthesis.

The X-ray diffraction analyses were carried out in a difractometer Shimadzu model

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XRD 6000, with radiation source of CuKα. The data were collected in 2Θ range of 5-50 degree. The diffractograms obtained were used for identification of the crystalline structure of the materials and identify the presence of contaminant phases by comparison with literature data [21]. The crystallinity degree of the materials was determined by

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comparison of the sum of the areas of the most intense peaks of diffractogram at 2Θ = 7.36; 8.80; 20.88; 22.88 and 23.20, with sum of the areas of the most intense peaks of a standard material, that in this study was the Z100 sample. The morphology and size of the

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microscope.

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crystals were determined by scanning electron microscopy, using a Philips ESEM

The surface area measurements were carried out by adsorption of N2 to 77 K using

the BET method in a Quantachrome model NOVA-2000 equipment. Before each analysis, ca. 0.1 g of calcined sample was degassed at 200 oC under vacuum for 3 hours to removal of humidity and gases physisorbed. The experiments of n-butylamine adsorption on the HZSM-12 samples were performed in a reactor containing ca. 0.1g of catalyst, which was activated at 400oC, under nitrogen flowing at 100 mL min-1 for two hours. After this activation, the temperature was

ACCEPTED MANUSCRIPT reduced to 95 oC and the nitrogen was deviated to bubbler flask containing liquid nbutylamine. The nitrogen saturated with n-butylamine vapors flowed through the reactor containing the HZSM-12 zeolites, for 40 minutes. After this, the sample was submitted to pure nitrogen by additional 40 minutes, to remove the physically adsorbed n-butylamine.

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The amounts of amine adsorbed on the acids sites of the HZSM-12 samples was determined by n-butylamine desorption, quantified by thermogravimetry, using a Mettler TGA/SDTA 851 from Mettler, at the following experimental conditions: purge with

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nitrogen to 100 oC for 1 hour to removal of the physisorbed n-butylamine; heating from 100oC to 800oC for desorption of n-butylamine of the acid sites, at 10 oC min-1. The total

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acidity of the samples was defined as the n-butylamine amount, in mmol, desorbed in the temperature range from 100 to 550 oC per gram of catalyst.

2.3 Catalytic Degradation of HDPE

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The HPDE sample, in powder form, was obtained from Palmann of Brazil. This was employed without any previous treatment. The polymer was physically mixed with the HZSM-12 samples at a mortar, in the proportion of 50%wt. The blend was dried in an oven

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at 100 oC for 4 h. The polymer degradation experiments were carried out in a termobalance Metler model TGA/SDTA at temperature range from 100 to 600ºC, with nitrogen flow of

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25 mL min-1 and heating rate of 2.5; 5; 10 and 20ºC min-1. For each experiment were used samples of approximately 10 mg. From the non-isothermal kinetic model proposed by Vyazovkin [19,20] , the activation energy for HPDE degradation reaction with and without catalyst was determined. In order to verify the catalytic activity of the HZSM-12 zeolites, we prepared a sample containing 50 %wt of inert amorphous silica (Merck, with particle average diameters of ca. 60 µm), which was submitted to identical treatments of the samples

ACCEPTED MANUSCRIPT containing 50 %wt of HZSM-12 zeolite. As the silica practically do not present acidity is expected that the behavior of the mixture silica + HPDE be very similar to HPDE without addition of catalyst. To identify the products formed during the degradation reaction of HPDE with and

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without addition of catalyst, the samples were submitted to pyrolysis at 550 oC in a PyGC/MS equipment, QP 5000 model, from Shimadzu. The pyrolysis experiments were performed at 550oC under helium flowing at 25mL min-1, using samples of ca. 2 mg. The

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pyrolysis products were separated by chromatography in a column Chromopack CP-

spectrometry.

3. Results and Discussion

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3.1. Catalyst Characterization

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Al2O3/KCl (50 meters and 0.32 mm of internal diameter) and identified through mass

The X-ray diffraction analyses of the samples are shown in Figure 1. All materials presented a characteristic diffractogram of a ZSM-12 zeolite with high crystallinity [21].

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The sample with Si/Al ratio equal to 25 (Z25) presented a small amount of contaminant phase, as indicated in Figure 1(a). The scanning electron micrographs of the ZSM-12

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samples are displayed in Figure 2. All materials showed crystallites with very well defined prismatic shapes. It was observed that the average crystal size decreases with the Si/Al ratio.

FIGURE 1 FIGURE 2

ACCEPTED MANUSCRIPT The Table 1 gives the data of the physicochemical characterization of the HZSM12 and silica samples used in this study. The chemical composition data indicated that the Si/Al ratio of the obtained solid after crystallization were lower than in the synthesis gel. Gopal et al. [22] found similar results in the study of the synthesis of ZSM-12 zeolite with

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tetraethylammonium as template. It attributed this phenomenon to inefficiency in the crystallization process. The surface areas values of the zeolites and silica gel samples were very close, suggesting that possible variation in the catalytic activity of these materials are

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TABLE 1

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not related to differences in the surface area available for reaction.

The acidity measurements of the materials indicated that the acid sites concentration decreases as the Si/Al ratio is raised showed that the aluminum is the main

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responsible by the acidity of the HZSM-12 zeolites. It is important to emphasize that the low concentration of acid sites concentration of the silica gel (0.05 mmol g-1) indicates that

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this material should possess low activity to reactions catalyzed by acid materials.

3.2. Thermal and catalytic degradation of HDPE by TG/DTG analysis

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TG/DTG curves of the degradation reactions of pure HDPE and HDPE+50%wt of

HZSM-12 zeolite, showed that the process takes place at the temperature range of 300 – 500 oC. The sample HZ25 was the more acidic catalyst. Thus, this sample show lower temperature conversion, in relation to the other samples. In order to determine the activation energy for the process, the The TG/DTG experiments were carried out at four different heating rate, β = 2.5; 5; 10 and 20 oC min-1. These curves indicated that the degradation of HDPE with and without catalyst happen in a single stage of mass loss,

ACCEPTED MANUSCRIPT clearly evidenced by a single peak of mass loss. Other important characteristic observed in these curves is the decreasing at the temperature of HDPE degradation caused by the addition of the zeolite catalyst. For example, for the DTG curve obtained with heating rate of 10 oC min-1, the temperature reach the maximum (Tmax) to the pure HDPE at 474oC,

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whereas after the catalyst addition, the Tmax was reduced to 394oC. The Figure 3 shown a set of conversion curves, where it is observed that the samples containing zeolites presents lower temperatures for HDPE degradation. While that the sample containing 50 %wt of

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silica gel, practically degraded at the same temperature range of pure HDPE. In the Table 2

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is summarized the temperature reduction in the HDPE degradation.

FIGURE 3 TABLE 2

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The mass losses data obtained from the thermogravimetric curves must be converted in conversions data before of be submitted to kinetics treatment by Vyazovkin model. Assuming that the total mass loss corresponds to 100 % of conversion, thus the

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mass losses in temperature smaller are normalized in relation to total mass loss originating the curve of conversion.

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The pattern of thermal and catalytic degradation of polymeric materials depend on

several factors, being the main of them the temperature, the type and the amount of catalyst added to the system. The reaction rate and others kinetic parameters for each system should be determined through experimental data, however due to complexity of the polymers degradation reactions, the conventional methods for determination of the kinetic data are difficult of be applied. Therefore, in this study was applied non-isothermal kinetic model of Vyazovkin [19,20] to determine the activation energy for the reaction of HDPE

ACCEPTED MANUSCRIPT degradation in the presence of HZSM-12 zeolite without the need of a model of reaction rate in function of the reactants concentrations. The Equation 1, represents the integrated

 β ln 2 T  α

  = ln  R ⋅ k0  − Ea ⋅ 1     Ea ⋅ g (α )  R Tα 

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form of the kinetic model proposed by Vyazovkin. Details of this model is reported [23]

(1)

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Where α is the conversion of the polymer degradation reaction; Tα is the temperature for reach to conversion α; β is the heating rate; R is universal gas constant; k0

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is Arrhenius pre- exponential factor, Ea is the activation energy for a certain conversion α and g(α) is the integral of the kinetic model of reaction rate in function of the conversion. In most of the cases the function g(α) it does not present a defined form and after the model fitting, g(α) become implicit in the linear coefficient obtained. The equation 1,

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indicates that a plotting of ln(β/Tα2) versus 1/Tα it produces a straight line and from its inclination can be determined the activation energy. The Figure 4 display the values of

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activation energy in function of the conversion for the degradation of pure HDPE and of HDPE + 50% wt catalysts. Where is observed that for the samples containing HZSM-12

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zeolite there are a strong decrease of the activation energy. While for the silica gel the Ea values are close to the obtained for pure HDPE, evidencing to strong influence of the acidity of the catalyst on the degradation reaction.

FIGURE 4

The values of activation energy for pure HDPE and mixed with silica were higher than 175 kJ mol-1. For the catalytic degradation of HDPE, was observed a decreasing for

ACCEPTED MANUSCRIPT values in the range of ca. 150 to 90 kJ mol-1. The Ea decreased with the Si/Al ratio. Thus, the more acid catalyst (Si/Al = 25) requires lower energy to the HDPE catalytic

FIGURE 5

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degradation process.

The Figure 5 shows the curve of activation energy in function of the catalyst acidity

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added to system in which is observed that Ea values decrease linearly with the increase of the catalyst acidity. These results indicate that the catalyst acidity added to HDPE is one of

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the most important parameters in the reaction of catalytic degradation of this polymer.

3.3. Py-GC/MS analyses of the thermal and catalytic degradation of HDPE The Figure 6 shows the yield of hydrocarbon from the pyrolysis of pure HDPE and

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mixed with silica and HZSM-12 zeolites. The thermal degradation of HDPE produce mainly heavy hydrocarbon in range from C8 to C22 while the system containing catalyst produce mainly hydrocarbon in range from C3-C7. Thus the catalyst added to polyethylene

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increase the production of low molecular weight hydrocarbon, as a function of Si/Al ratio.

FIGURE 6

The results indicate that the products obtained from catalytic degradation of HDPE

can be used as light petrochemicals, such as C3-C4, including the strip of liquefied petroleum, propane and butanes. The C6-C8 products compose a mixture of gasoline. The advantage of this gasoline is to be totally free of sulfur compounds. These results indicate a potential trade for the recycling of post-consumption HDPE for production of

ACCEPTED MANUSCRIPT hydrocarbons through the catalytic degradation. This selectivity is due to the presence of acid sites associated with the microporosity of the ZSM-12 zeolite. A proposal to this mechanistic reaction, represented by the equations (2), (3) and (4) consists of an initial stage where the large molecules of polymers are cracked by

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thermal processes and/or catalytic to the external surface of the solid, generating smaller molecules. These molecules diffuse inside of the pores of the zeolite catalyst, where suffer secondary cracking reactions in the internal acid sites producing low molecular weight

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molecules that leave out of the pores and attack the macromolecules of polymeric material

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accelerating the degradation process.

R1 – CH = CH – R2 + HZ
R1 – CH2 – CH+ – R2 + Z-

(2)

R1 – CH2 – CH+ – R2
R1+ + CH2 = CH – R2

(3)

+

R


R1 +

R+

(4)

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R1 +

The reaction (2) means the protonation, where the polyolefin react with the Bronsted acid site of the zeolite. In reaction (3), occurs the cracking through β-cision and

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in the reaction (4), occurs hydrogen transfer and propagation. In these reactions, R, R1 and

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R2 are the hydrocarbon fractions.

4. Conclusions

The addition of 50%wt of catalysts with different concentrations of acid sites to HDPE produced a diminution in the temperature of polymer degradation proportional to acidity of the catalyst. These qualitative results were complemented by the data of activation energy obtained through the non-isothermal kinetic model proposed by

ACCEPTED MANUSCRIPT Vyazovkin. The Ea values indicated that there is a linear decrease of the activation energy of the reaction of catalytic degradation of HDPE in function of the concentration of acid sites. The results indicate that the degradation products of catalytic HDPE can be used as petrochemicals light, and the products C6-C8 compose a mixture with low content of olefin

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aromatics in gasoline. The advantage of this gasoline is to be free of sulfur compounds. These results indicate a potential trade for the recycling of HDPE post-consumption for production of hydrocarbons through the catalytic degradation. Chromatographic analysis

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showed that thermal degradation of HDPE without catalyst gave rise to products districuted in a wide range of hydrocarbons, from C3 to C22. The use of HZSM-12 as

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catalyst led to ligher products, predominantly from C3 to C10. This behavior may be due to the strong acid sites of the HZSM-12 zeolite, which promote the polymer chain cracking, associated to the pore system of the zeolite, increasing the selectivity for liquid petroleum

Acknowledgements

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gas and gasoline fraction, as main products.

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The authors acknowledge the financial support from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundo Setorial para Ciência e

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Tecnologia em Petróleo (FINEP/CTPETRO), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

References

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ACCEPTED MANUSCRIPT [2] K Takuma, Y Uemichi, M Sugioka, A. Ayame, Ind. Eng. Chem. Res. 40 (2001) 1076. [3] M. A. Uddin, K. Koizumi, K. Murata, Y. Sakata, Polym. Degrad. Stab. 56 (1997) 37. [4] M. A. Uddin, Y. Sakata, A. Muto, Y. Shiraga, K. Koizumi, Y. Kanada and K. Murata, Micropor. Mesopor. Mater. 21 (1998) 557.

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[7] H. Ohkita, R. Nishiyama, Y. Tochihara, T. Mizushima, N. Kakuta, Y. Morioka, A.

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Ueno, Y. Namiki, S. Tanifuji, H. Katoh, H. Sunazyka, R. Nakayama and T. Kuroyanagi, Ind. Eng. Chem. Res. 32 (1993) 3112.

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[8] Y. Uemichi, J. Nakamura, T. Itoh, M. Sugioka, A. A. Garforth and J. Dwyer, Ind. Eng. Chem. Res. 38 (1999) 385.

[9] G. Manos, A. Garforth, J. Dwyer, Ind. Eng. Chem. Res. 39 (2000) 1198. [10] J. Aguado, J. L. Sotelo, D. P. Serrano, J. M. Escola, E. Garagorri and J. A. Fernández,

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Polym. Degrad. Stab. 69 (2000) 11.

[11] A. Marcilla, M.I. Beltrán, R. Navarro, Applied Catalysis B: Environmental 86 (2009) 78.

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[12] W. M. Meier, D. H. Olson, Ch. Baerlocher, Atlas of Zeolite Structure Types. Elsevier, New York, 1996, p. 158.

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[13] W. Zhang and P. G. Smirniotis, Appl. Catal. A: General 168 (1998) 113. [14] W. Zhang and P. G. Smirniotis, Catal. Letters 60 (1999) 223. [15] W. Zhang and P. G. Smirniotis, J. Catal. 182 (1999) 400. [16] A.C.F. Coriolano, G.F.S. Barbosa, C.K.D. Alberto, R.C.O.B.Delgado, K.K.V. Castro, A.S. Araujo, Petroleum Science and Technology, 34 (2016) 627-632. [17] K.K.V. castro, A.L. Figueiredo, A.D. Gondim, A.C.F. Coriolano, V.J. Fernandes Jr., A.S. Araujo, J. Therm. Anal. Calorim., 117 (2014) 953-959.

ACCEPTED MANUSCRIPT [18] A.C.F. Coriolano, C.G.C. Silva, M.J.F. Costa, S.B.C. Pergher, V.P.S. Caldeira, A.S. Araujo, Microp. Mesop. Mat., 172 (2013) 206-212. [19] S. Vyazovkin, A. I. Lesnikovich, Russ. J. Phys. Chem. 62 (1988) 2949. [20] S. Vyazovkin, V. Goriyachko, Thermochim. Acta 194 (1992) 221.

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[21] M M. J. Treacy, J. B. Higgins, R. von Ballmoos, 1996. Collection of Simulated XRD Powder Patterns for Zeolites, 3th edition, Elsevier, New York, p. 538.

[22] S. Gopal, K. Yoo, P. G. Smirniotis, Micropor. Mesopor. Mater. 47 (2001) 149.

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[23] A.S. Araujo, V.J. Fernandes Jr., G.J.T. Fernandes, Thermochim. Acta, 392-393

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(2002) 55-61.

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Table 1 – Physicochemical properties of the samples of ZSM-12 zeolite and silica gel

Sample

Si/Al Molar

Crystallinity

Ratio

Crystallites

Surface

Total

Average Diameter

Area

Aciditya

Solid

(%)

(µm)

(m2 g-1)

(mmol g-1)

Silica gel

----

----

----

56.5

296

0.05

Z25

25

24

82

14.5

285

0.72

Z50

50

43

87

14.0

302

0.43

Z75

75

65

99

11.3

327

0.30

Z100

100

88

100

7.0

331

0.27

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Gel

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a

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employed as catalysts in the HPDE degradation reaction.

The acidity data are referent to the samples in the acidic form.

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Table 2 - Tmax values to degradation of pure HDPE and HDPE + 50 %wt catalysts obtained

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with different heating rates (β).

Tmax (oC)

Sample β = 2.5

β=5

β = 10

β = 20

464

474

494

452

HDPE + Silica gel

451

464

473

495

404

417

435

458

390

407

426

449

385

403

420

446

363

378

394

426

HDPE + HZ75 HDPE + HZ50

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HDPE + HZ25

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HDPE + HZ100

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HDPE

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Figure 1 - X ray diffractograms of the samples of calcined ZSM-12 zeolites: (a) Z25; (b) Z50; (c) Z75 and (d) Z100.

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Figure 2 – Scanning electron micrographics of calcined ZSM-12 zeolites: (a) Z25; (b) Z50; (c) Z75 and (d) Z100.

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Figure 3 – Conversion data obtained from the TG curves with β = 2.5 oC min-1. Where (a)

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pure HDPE and the mixtures: HDPE + (b) 50%wt silica gel, (c) 50%wt HZ100, (d) 50%wt HZ75, (e) 50%wt HZ50, (f) 50%wt HZ25.

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Figure 4 – Activation energy versus conversion of HDPE degradation reaction. Where (a)

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pure HDPE and the mixtures: HDPE + (b) 50%wt Silica gel; (c) 50%wt HZ100; (d) 50%wt HZ75; (e) 50%wt HZ50; (f) 50%wt HZ25.

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Figure 5 – Variation of the activation energy versus catalyst acidity added to system. In the case of pure HDPE and processed with silica, the acidity of catalyst was considered equal to zero.

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Figure 6 – Yield of the hydrocarbon obtained from HDPE degradation in function of carbon number: (a) pure HDPE; (b) Silica/HDPE; (c) HZ25/HDPE; (d) HZ50/HDPE; (e) HZ75/HDPE; (f) HZ100/HDPE.

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Highlights

Development of HZSM-12 zeolite with high degree of crystallinity.

•

Acid properties of HZSM-12 zeolite with different Si/Al ratio

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Catalytic processing of high density polyethylene over HZSM-12 zeolites

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Characterization of the materiais by thermogravimetry

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Evaluation of the process by pyrolysis coupled to GC/MS

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