Research on the pyrolysis process of crumb tire rubber in waste cooking oil

Accepted Manuscript Research on the Pyrolysis Process of Crumb Tire Rubber in Waste Cooking Oil

Ruikun Dong, Mengzhen Zhao PII:

S0960-1481(18)30285-4

DOI:

10.1016/j.renene.2018.02.133

Reference:

RENE 9864

To appear in:

Renewable Energy

Received Date:

20 July 2017

Revised Date:

13 February 2018

Accepted Date:

28 February 2018

Please cite this article as: Ruikun Dong, Mengzhen Zhao, Research on the Pyrolysis Process of Crumb Tire Rubber in Waste Cooking Oil, Renewable Energy (2018), doi: 10.1016/j.renene. 2018.02.133

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.

ACCEPTED MANUSCRIPT

1

Research on the Pyrolysis Process of Crumb Tire Rubber in Waste

2

Cooking Oil

3

Ruikun Donga, b*, Mengzhen Zhaob

4

a. Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University),

5

Ministry of Education, Chongqing 400045, PR China

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b. School of Civil Engineering, Chongqing University, Chongqing 400045, PR China

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Abstract: The use of waste cooking oil (WCO) in crumb tire rubber (CTR) pyrolysis not only improves the safety

8

and controllability of the preparation process, but also recycles these two waste resources effectively. In this study,

9

WCO was used as the solvent to pyrolyse CTR at high temperature to prepare waste rubber oil (WRO). The

10

changes of CTR in molecular structure and rheological properties during thermal energy accumulation were

11

explored through thermogravimetric analysis, Fourier transform infrared spectrometer, gel permeation

12

chromatography and dynamic shear rheometer. The compatibility of CTR with virgin asphalt before and after

13

pyrolysis was described by segregation test. Results show that, with the rise of temperature, depolymerized and

14

broken rubber macromolecule in CTR continue to crack into molecules with less molecular weight, while more of

15

natural rubber and carbon black are released. The rheological properties of WRO have changed greatly, i.e. the

16

decreased zero shear viscosity, the improved flowability and the better plasticity. Complex chemical reactions

17

occur during the pyrolysis of CTR, but no new functional group is generated except for the released natural rubber.

18

The segregation test shows that, the compatibility of CTR with virgin asphalt can be improved by adopting WCO

19

for pyrolysis.

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Key words: crumb tire rubber; waste cooking oil; pyrolysis; molecule structure; rheological property

21

1. Introduction

22

With the rapid development of domestic automobile industry, the consumption and import volume of rubber are

23

increasing. According to statistics [1], 1.11 billion cover tires were produced in China in 2014, accounting for more

24

than 30% of the global tire production, ranking top in the world. Meanwhile, China has the largest tire scrappage in

25

the world, and more than 10 million tons of waste tire are produced every year, but the harmless utilization rate is

26

only 60%, lower than that of about 90% in developed countries [2]. When the waste tire disposal becomes a

27

worldwide environmental and economic challenge [3], as the country with the largest production and scrappage of *

Corresponding author: Professor, Tel.: +86 138 8315 0211. E-mail address: [email protected] 1

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waste tire, China has a great responsibility in effective disposal of waste tire.

29

At present, landfill method is prohibited in a number of countries, and many countries are seeking suitable means

30

to solve the problem of waste tire disposal [4]. According to practical experience and researches [5-7], the adoption

31

of crumb tire rubber (CTR) made by grinding waste tire as additive can improve basic performance of virgin

32

asphalt, especially to be helpful in reducing temperature sensitivity, improving low-temperature properties and

33

resistance to reflection crack of asphalt mixture, and good application effects are obtained in architectural and

34

pavement engineering. However, phase separation often occurs to CTR modified asphalt due to incompatibility of

35

CTR with virgin asphalt, resulting in poor storage stability of CTR modified asphalt [8], which hinders the

36

popularization and application of asphalt products.

37

To solve this problem, many scholars at home and abroad proposed to pre-desulfurize and degrade CTR to break

38

cross bonds of CTR and reduce its molecular weight to improve the compatibility of CTR with virgin asphalt,

39

which had gained good effect [9, 10]. The main methods of desulfurization and degradation include solvent method

40

[11], radiation method [12, 13] and mechanical extrusion method [14], but all these techniques have some

41

deficiency. For the solvent method, CTR is less desulfurized and degraded and thus difficult to be stored stably in

42

asphalt, and the emission of hydrogen sulfide during desulfurization pollutes the environment. Meanwhile, for the

43

microwave radiation method and the mechanical extrusion method, the high cost is a problem.

44

Pyrolysis is a method that realizes thermochemical treatment by breaking chemical bonds of materials under

45

oxygen-free conditions [15]. The largest benefit of this method is that it can effectively dispose wastes that are hard

46

to recycle, and can also get recycled products [16]. At rapid heating rate, waste materials can be converted into

47

higher energy content transportable liquid (such as pyrolysis fuel oil and bio-oil), so pyrolysis is getting more

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attention [17]. Besides, direct combustion, liquefaction and gasification are other most common approaches for

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thermochemical conversion of waste [18]. CTR is a complex high polymer material, which is made by 2

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polymerization-filling from natural rubber or other elastomers, carbon black, metal, fabric, and additive [19].

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Pyrolysis is a process reverse to polymerization, which can realize the regeneration of rubber and release carbon

52

black through depolymerization and breakage of CTR structure. Researches show that carbon black is also very

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helpful to improve asphalt mixture performance [20].

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Currently, the utilization of waste cooking oil (WCO) has become a serious problem related to human health and

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an urgent livelihood issue to be solved in China, so the dispose of WCO is of important significance in both

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economic and environmental protection and personal safety. It has been proved that WCO could be an alternative

57

natural antioxidant or rejuvenator on age-hardened bitumen [21]. Also, WCO is recognized as a renewable energy

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source for producing biodiesel [22]. Similarly, other kinds of bio-oil derived from biomass can also be used as

59

asphalt modifier [23] or substitute energy sources [24, 25]. It can be predicted that biomass will be a promising

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renewable resource due to its wide distribution, abundance and CO2 neutrality [26]. Considering that WCO is of

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high flash point and good stability, and is compatible with virgin asphalt [27], it was used as solvent for pyrolysis

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of CTR at high temperature in this paper.

63

The essence of CTR pyrolysis can be seized through analysis and research on the microscale. So the purpose of

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this study was to explore the changes of CTR in molecular structure and rheological properties during the gradual

65

accumulation of heat energy from both microscopic and macroscopic points of view, provide research data for

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future design of pyrolysis reactor and reaction conditions by revealing the essence of CTR pyrolysis, and

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investigate the change of compatibility of CTR with virgin asphalt before and after pyrolysis through segregation

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test to lay a foundation for modification of virgin asphalt with CTR made by this method.

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2. Materials and Methods

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2.1 Materials and determination

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One ambient processed 40 mesh CTR, provided by Chongqing Pavement S&T Co., Ltd, one WCO collected 3

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from a grocery store in Chongqing, and one PG 64-22 performance grade asphalt, provided by Zhonghai Bitumen

73

CO., Ltd were used in this study. Table 1 and Table 2 show the composition and elemental analysis of CTR. Basic

74

properties and major fatty acid contents of WCO are given in Table 3, and fatty acids are tested by GC-MS,

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provided by the Innovative Drug Research Center of Chongqing University. The basic performance of virgin

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asphalt is given in Table 4 according to Standard Test Methods of Bitumen and Bituminous Mixtures for Highway

77

Engineering.

78

[Table 1 near here].

79

[Table 2 near here].

80

[Table 3 near here].

81

[Table 4 near here].

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2.2 Specimen preparation

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2.2.1 Preparation of waste rubber oil

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CTR and WCO were weighed accurately with electronic balance at a certain proportion (accurate to 0.1 g), and

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placed for 2 h at ambient temperature after mixing evenly. The mixture was heated with self-made reaction still at

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240 ℃, 260 ℃, and 280 ℃ for 2 h respectively, with the temperature rising rate of 8 ℃/min and the stirring speed

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of 250-300 rpm. The specimens were stirred to make them heated uniformly and capped to prevent volatilization of

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light components during heating process, and finally the waste rubber oil samples (WRO) were obtained.

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2.2.2 Preparation of modified asphalt

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(1) Ordinary CTR modified asphalt: CTR with the doping ratio of 18% was mixed slowly with 160 ℃ hot

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asphalt, and stirred with increased temperature. When the temperature reached 180 ℃, the mixture was heated for 1

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h with the stirring speed of 300-350 rpm at constant temperature.

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(2) WCO-pyrolysed CTR modified asphalt: CTR was replaced with WRO to prepare WCO-pyrolysed CTR 4

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modified asphalt according to the above method. To guarantee the CTR doping ratio of 18%, the WRO doping ratio

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adopted is 30% because of 0.6 rubber oil ratio (the mass ratio of CTR and WCO) in WRO.

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2.3 Test and characteristic

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2.3.1 Determination of gel content

98

WRO with the mass of m was weighed accurately with analytical balance (accurate to 0.0001 g), enveloped with

99

filter paper, and wrapped with copper wire to prevent exudation of specimen. Toluene was used as solvent to carry

100

out Soxhlet extraction to the specimen for 48 h, in which toluene is analytically pure. The toluene extract mainly

101

consists of operating oil, acetone extract and linear macromolecule in natural rubber, i.e. sol. The extraction residue

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mainly consists of crosslinked rubber hydrocarbon, carbon black and mineral filler, i.e. gel. The extraction residue

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was dried in 70 ℃ vacuum oven for 4 h after extraction, and the mass of m' was weighed. The gel content of CTR =

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(m'/m)×100%.

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2.3.2 Component analysis

106

Component analysis is usually used to analyze the proportion of components in substance, and the change in

107

structural composition can be found from the change in proportion of components [28]. The content of components

108

in the gel part of CTR before and after pyrolysis can be clearly observed by this method, and the change of CTR in

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structure can be judged from the change in proportion of components. The NETZSCH STA 449F3 thermal analyzer

110

made in Germany was used to carry out component analysis to the gel part of CTR after 48 h of toluene extraction,

111

the temperature range was room temperature-650 ℃, and the analysis was performed in strict accordance with the

112

experimental method specified in GB/T 14837-93.

113

2.3.3 Infrared spectroscopic analysis

114

Infrared spectroscopic analysis can be used to analyze the functional groups on the surface of CTR [29], and this

115

method was adopted in this paper to study the changes on the functional groups of CTR before and after pyrolysis 5

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to explore the change of CTR on the molecular scale. It is difficult to detect the absorption peak of black and

117

lightproof tire rubber in transmission mode. Therefore, infrared spectroscopic test was done on the clear sol of

118

WRO, this measurement was consistent with existing studies [30, 31]. Firstly, toluene was used as solvent to carry

119

out extraction to WRO for 48 h, then the solution containing sol of CTR was dropped on clean potassium bromide

120

sheet, and the infrared analysis was carried out by Nicolet iS5 Fourier transform infrared spectrometer after solvent

121

evaporates. The scanning range of infrared spectrum is 400-4000 cm-1 and the resolution is 4 cm-1.

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2.3.4 Determination of molecular weight

123

It is known to all that, the size and distribution of molecule weight of substance can be analyzed well by GPC

124

[32]. This method is adopted in lots of previous studies [33, 34]. In this paper, the weight-average molecular weight

125

Mw [35] and polydispersity index (PDI) [36] in GPC test results were used as the indexes for molecular weight size

126

and distribution of WRO. The Mw reflects the contribution of large molecular weight molecules in the solution to

127

the global molecular weight, and PDI reflects the quantity gap between large molecular weight molecules and small

128

molecular weight molecules in the solution. In the experiment, a certain amount of WRO was dissolved in

129

tetrahydrofuran (THF), and filtered through a 0.22 μm filter membrane. The GPC equipment setup uses a

130

differential refraction detector. The separation of the different molecular size was performed through a series of two

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chromatographic columns TSK gel super HZM-M 6.0*150 mm and TSK gel SuperHZ3000 6.0*150 mm. The

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temperature in the columns was maintained at 40 ℃ with THF as a mobile flowing at a rate of 0.6 ml/min.

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Comparing to a standard polystyrene. The peak area normalization method was used for quantification.

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2.3.5 Dynamic shear rheometer (DSR)

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Complex shear modulus G* and phase angle δ obtained from DSR oscillation test reflect the mechanical

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response of rheological material under dynamic shear load [37]. Larger the G* value means stronger resistance to

137

deformation of material, and smaller δ value means stronger deformation recovery capability. Besides, zero shear 6

ACCEPTED MANUSCRIPT 138

viscosity (ZSV) obtained through DSR steady state flow test can reflect the viscosity properties of viscoelastic

139

materials under non-disturbing conditions. The above DSR oscillation and flow tests were selected to characterize

140

the rheological properties of WRO blends in this study.

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A TA Instruments AR 1500 ex dynamic shear rheometer was used for viscoelastic analysis of WRO. All tests

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were carried out at 25 ℃ because WRO is far softer than virgin asphalt and can flow steadily at this temperature.

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On the other hand, in order to carry out DSR test effectively, a 25-mm-diameter parallel plates was selected. The

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gap between plates was 1 mm. The dynamic oscillation shear test and steady state flow test were performed to

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obtain the G*, δ and ZSV. DSR oscillation test was performed in a strain control mode with strain less than 12%,

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and steady state flow test was performed with shear rate between 0.1 to 100 s-1.

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2.3.6 Segregation test

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Ordinary CTR modified asphalt and WCO-pyrolysed CTR modified asphalt were tested for storage stability

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respectively by the method specified in Standard Test Methods of Bitumen and Bituminous Mixtures for Highway

150

Engineering (T0661-2001) to evaluate the compatibility of CTR with virgin asphalt before and after desulfurization

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and degradation.

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3. Results and Discussion

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3.1 Changes of gel content and compositions of CTR

154

Fig.1 is the variation diagram of gel content and compositions of pyrolysed CTR at varying temperature

155

conditions. It can be seen from the figure, with the rise of temperature, the gel content decreases, which means the

156

pyrolysis degree of CTR deepens. The research of Shi et al. [38] shows that the CTR after desulfurization and

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regeneration mainly consists of sol, gel, and other small molecular substances. The soluble part after toluene

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extraction mainly consists of sol and other small molecular substances, and the residual part is gel. The decrease of

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gel content indicates that the three-dimensional network crosslinking structure of rubber molecules is broken 7

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gradually during the accumulation of heat energy, more soluble linear molecules are generated. Furthermore, with

161

the increase of absorbed heat energy, the crosslinking structure is broken more severely. According to the result of

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thermogravimetric analysis of gel, the content of residual rubber hydrocarbon tappers off, which indicates that

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soluble linear molecules contain a considerable part of chain-like rubber hydrocarbon molecules. The content of

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carbon black increases significantly, which indicates that, with the accumulation of energy, more and more peeling

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rubber hydrocarbon molecules release carbon black surrounded by them [39].

166

[Fig.1 near here].

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Fig.1. Influence of temperature on changes of gel content and compositions of CTR.

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3.2 Infrared spectroscopic analysis of sol system

169

Fig.2 shows the infrared spectra of WCO, sol part of CTR, and WRO sol system under varying temperature

170

conditions. Compared with WCO, no disappearance of functional groups occurs to WRO sol system, but a

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characteristic peak of natural rubber appears at 837 cm-1, which indicates that effective desulfurization and

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pyrolysis occur to CTR in WCO and release natural rubber. Compared with sol part of CTR, absorption peaks at

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3372 cm-1, 3031 cm-1, 1722 cm-1, 1658 cm-1, 1512 cm-1, 1308 cm-1, 1261 cm-1, and 802 cm-1 disappear, and

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similarly a new absorption peak appears only at 837 cm-1. These disappearing absorption peaks are assigned to

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functional groups as follows: the peak at 3372 cm-1 is the stretching vibration of hydroxy OH, which should be

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caused by a little moisture in CTR; the peak at 3031 cm-1 is the antisymmetric stretching vibration of cyclopropane

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-CH2-, antisymmetric stretching vibration of alkene =CH2, and stretching vibration of cyclenes =CH; the peak at

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1722 cm-1 is the non-planar rocking vibration of =CH2; the peak at 1658 cm-1 is the stretching vibration of alkene

179

C=C bond, dialkene and other groups with conjugate C=C bond, and out-of-plane vibration of arene C-H; the peak

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at 1512 cm-1 is the skeletal vibration of arene; the peak at 1308 cm-1 is deformation vibration of -CH3 and -CH2, and

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planar rocking vibration of alkene =CH2 and =CH; the peak at 1261 cm-1 is non-planar rocking vibration of 8

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saturated hydrocarbon -CH2, and planar rocking vibration of alkene =CH2 and =CH; and the peak at 802 cm-1 is the

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out-of-plane vibration of arene C-H and the planar rocking vibration of alkene =CH2 and =CH.

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[Fig.2 near here].

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Fig.2. Infrared spectra of WCO/CTR/WRO samples.

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When CTR is pyrolysed in WCO, the little moisture it carries is evaporated, so the absorption peak of OH at

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3372 cm-1 disappears. The disappearance of absorption peaks at 3031 cm-1, 1722 cm-1, 1658 cm-1, 1512 cm-1, 1308

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cm-1, 1261 cm-1, and 802 cm-1 indicates that the breakage of C-C single bond and C=C double bond of chain

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hydrocarbon and cyclic hydrocarbon occurs to CTR during pyrolysis. Conversely, the absorption peaks at 2925 cm-

190

1,

191

indicate that a large amount of long chain hydrocarbons appear in the sol system of WRO. Meanwhile, the

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absorption peak at 723 cm-1 assigning to the bending vibration of -(CH2)n- (n>4) also enhances significantly, which

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indicates that a large amount of rubber molecules are depolymerized and broken from crosslinked net structure to

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form long chain structure. In addition, the absorption peak at 1746 cm-1 assigning to the stretching vibration of

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carbonyl C=O also enhances significantly, which indicates that some C-containing functional groups fall off from

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large rubber molecular chain and react with a small amount of oxygen nearby.

2854 cm-1, 1463 cm-1, and 1377 cm-1 assigning to the stretching vibration of -CH3 and -CH2 enhance, which can

197

According to the infrared spectra of sol system of WRO at varying temperatures, the position and number of

198

absorption peaks are basically the same, only the peak height changes from low to high. Therefore, it can be

199

regarded that the increase of heat energy only influence the variation of concentration of pyrolysis products in

200

WRO. According to the Lambert-Beer law as shown in Eq.(1) [40], the relative concentration of the functional

201

group of natural rubber can be obtained by measuring the corrected area of absorption peak at 837 cm-1 with

202

OMNIC software. The results representing average value of three replicates test for each sample are illustrated in

203

Fig.3. 9

ACCEPTED MANUSCRIPT c=A/KL

204 205 206

(1)

Where c represents the concentration of specimen, A represents the absorbance, K is the absorptivity and L is the optical path of specimen.

207

It can be seen from Fig.3, with the rise of temperature, the relative concentration of functional group at 837 cm-1

208

is larger and larger, which indicates more and more natural rubber is released from CTR during pyrolysis. The

209

reason is that rubber molecules absorb energy during the accumulation of heat energy, which makes S-S bond, C-S

210

bond, and C-C bond with less bond energy broken, and finally network crosslinked large molecules of rubber

211

undergo depolymerization and breakage to form chain-like rubber hydrocarbon molecules. This behavior achieves

212

the desulfurization and regeneration of CTR.

213

[Fig.3 near here].

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Fig.3. Influence of temperature on the absorbance of functional group at 837 cm-1 of sol system.

215

3.3 Relative molecular weight and distribution of WRO system

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GPC test is adopted to determine molecular weight of WRO at varying temperatures, and the result is shown in

217

Fig.4. It can be seen from the figure that, with the rise of temperature, the Mw and the PDI of WRO decrease

218

gradually. The decrease of Mw means large molecular weight molecules in the WRO system become less and less,

219

and small molecular weight molecules become more and more. Smaller PDI means large molecular weight

220

molecules in the system break to form smaller molecular weight molecules, and the quantity of small molecules

221

increases. The main reason is that CTR absorbs more and more heat energy, and C-C bond at the main chain of

222

long-chain rubber hydrocarbon molecules after depolymerization and breakage begins to break and form molecular

223

structure with smaller molecular weight. It can also be seen from the figure that, Mw and PDI are similar at 260 °C

224

and 280 ℃, and according to the absorbance data in infrared spectra, there is an upper limit for rubber molecules to

225

absorb heat energy. That is, after absorbing certain heat energy, further increase of the temperature cannot increase 10

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the cracking of rubber network crosslinked structure, but it may tend to continue to decompose pyrolysis products

227

such as natural rubber and synthetic rubber [41, 42].

228

[Fig.4 near here].

229

Fig.4. GPC analysis of WRO.

230

3.4 Influence of temperature on rheological properties of WRO

231

3.4.1 Dynamic shear rheological property

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The results of DSR test are illustrated in Fig.5. It can be seen from the figure that, with the rise of temperature,

233

G* shows a decreasing trend, and δ shows an increasing trend. The decrease of G* indicates the deformation

234

resistance of CTR becomes worse, the elasticity weakens, and the plasticity enhances. The increase of δ means the

235

deformation recovery capability of the system becomes worse.

236

[Fig.5 near here].

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Fig.5. Influence of temperature on complex modulus G* and phase angle δ.

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S-S bond, C-S bond and C-C bond in crosslinked large rubber molecules break gradually during the

239

accumulation of heat energy, which reduces the mass of large rubber molecules [30], and leads to the decline of

240

elasticity of CTR and recovery of plasticity. The higher the energy is, the more the breakage of large rubber

241

molecules is aggravated, and the severer the elasticity is destroyed, resulting in the deformation resistance and

242

deformation recovery capability of CTR getting worse and worse.

243

3.4.2 Steady flow characteristics

244

Fig. 6 clearly illustrates the variation trend of shear viscosity of different WRO samples with shear rate through

245

double logarithmic coordinate system. It can be seen from the figure that the viscosity of WRO sample decreased

246

with the rise of interaction temperature. The reason is that the rise of temperature enhances the accumulation of

247

heat energy in the reaction system, and when large rubber molecules in CTR absorbs enough energy, the degree of 11

ACCEPTED MANUSCRIPT 248

the desulfurization and cracking reaction gets severer. Then the Carreau Model shown in Eq. (2) was used to fit the

249

test data nonlinearly, and the fitting parameters of the viscosity data were listed in Table 5, while viscous flow

250

curves were showed in Fig.7. From Table 5, it can be seen that the ZSV values of WRO samples prepared at 240

251

℃, 260 ℃ and 280 ℃ are 38801.26 Pa·s, 24514.17 Pa·s, and 9242.84 Pa·s respectively, which indicates that the

252

flowability of WRO sample is getting better with the elevation of interaction temperature. This is consistent with

253

the conclusion of the dynamic oscillation shear test. η=η∞+(η0-η∞)/[1+(kw)2]m/2

254 255

[Fig.6 near here].

256

Fig.6. Viscous flow curves of WRO samples.

257

[Table 5 near here].

258

[Fig.7 (a) near here].

259

[Fig.7 (b) near here].

260

[Fig.7 (c) near here].

261

Fig.7. Fitting viscous flow curves of WRO samples.

262

3.5 Compatibility of pyrolyzed CTR with virgin asphalt

(2)

263

Table 6 shows the results of storage stability test on ordinary rubber asphalt and WCO-pyrolysed CTR asphalt. It

264

can be seen from the table that, the segregation index of ordinary rubber asphalt is 7.2 ℃, while WCO-pyrolysed

265

CTR asphalt is only 0.5 ℃, which indicates the compatibility of CTR with virgin asphalt is greatly improved after

266

pyrolysis in WCO, and confirms that it is very effective to use this method for pre-desulfurization and pyrolysis of

267

CTR.

268

[Table 6 near here].

12

ACCEPTED MANUSCRIPT 269

4. Conclusions

270

The pyrolysis process of CTR in WCO was studied in this paper. The following conclusions can be obtained by

271

analyzing the changes of CTR in molecular structure and rheological properties on both macroscopic and

272

microscopic scales:

273

(1) With the absorption of heat energy, the crosslinked network structure of large rubber molecules in CTR is

274

broken gradually, soluble linear molecules fall off and natural rubber and carbon black are released from cracked

275

CTR, resulting in CTR recovering plasticity and regaining the reprocessability.

276

(2) Interaction temperature facilitates the pyrolysis degree of CTR, and higher temperature can make CTR

277

release more natural rubber and carbon black. With the deepening of CTR pyrolysis degree, long-chain linear large

278

molecules are further broken to generate soluble molecules with smaller molecular weight. Meanwhile, varying

279

complex chemical reactions between CTR and WCO lead to the disappearance of some functional groups in CTR.

280

Moreover, the concentration of some functional groups increases with rising temperature, which proves that some

281

substances in CTR may react with a small amount of oxygen in the reactor or due to breakage of chemical bonds to

282

generate substances existing in the original CTR.

283

(3) DSR oscillatory shear test indicates that the CTR recovers plasticity after pyrolysis with the decrease of

284

elasticity. Zero shear viscosity results obtained from DSR steady state flow test show that the flowability of the

285

WRO sample gets better with the elevation of interaction temperature.

286

(4) Desulfurization and degradation of CTR are well realized by adopting WCO for CTR pyrolysis. Experiments

287

prove that, the storage stability of pyrolysed CTR modified asphalt is better than ordinary CTR modified asphalt.

288

However, further study is needed for the appropriate temperature under which CTR is pyrolysed so as to obtain

289

modified asphalt with the best pavement performance.

13

ACCEPTED MANUSCRIPT 290 291

Acknowledgment This work was financially supported by National Natural Science Foundation of China (No. 51578097), National

292

International S&T Cooperation Program-funded Project (No. 2013DFR50550).

293

References

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[1] Tire

rubber

industry

of

China

is

big

but

not

strong

in

2015[EB/OL].

[2015.09.23].

in

China[EB/OL].

[2013.05.07].

http://www.chyxx.com/industry/201509/345918.html. (in Chinese) [2] Comprehensive

utilization

of

waste

tire

industry

is

emerging

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ACCEPTED MANUSCRIPT

Highlights: Pyrolysis of crumb tire rubber (CTR) in high temperature waste cooking oil (WCO). Changes of CTR in microstructure and rheological properties. Compatibility of pyrolysed CTR with virgin asphalt. Functional groups of CTR before and after pyrolysis. Relative molecular weight of waste rubber oil (WRO) mixture.

ACCEPTED MANUSCRIPT Table 1 Composition of CTR. Operating oil (%)

Rubber hydrocarbon (%)

Carbon black (%)

Mineral filler (%)

6.82

53.24

29.24

10.70

Table 2 Elemental analysis of CTR. C (%)

H (%)

N (%)

S (%)

80.41

5.75

0.68

2.38

Table 3 Basic properties and major fatty acid contents of WCO. Property

Value

Physical Acid value (mg (KOH/g))

6.4

Flash point (℃)

298

Fatty acid composition 9-Hexadecenoic acid (%)

0.49

Hexadecanoic acid (%)

5.38

11-Octadecenoic acid (%)

90.98

Heptadecanoic acid (%)

3.15

Total (%)

100

Table 4 Basic performance of virgin asphalt. Items

Units

Specification limits

Test results

Standard

Penetration (25 ℃,100 g,5 s)

0.1 mm

-

67.2

T0604

Penetration index PI

-

-

0.3

T0604

Softening temperature TR&B

℃

≥46

50.3

T0606

Kinematic viscosity (60 ℃)

Pa·s

≥180

225

T0620

Ductility (10 ℃)

cm

≥15

45

Ductility (15 ℃)

cm

≥100

160

T0605

Table 5 Fitting parameters of WRO samples.

Sample

η0

η∞

k

m

R2

240℃ 260℃ 280℃

38801.26 24514.17 9242.84

191.85 69.53 6.46

44.02 49.42 21.60

0.66 0.63 0.64

0.9981 0.9993 0.9969

Table 6 Segregation index of ordinary rubber asphalt and WCO-pyrolysed CTR asphalt. Modified asphalt type

Δt (℃)

Ordinary rubber asphalt

7.2

WCO-pyrolysed CTR asphalt

0.5