Chinese Journal of Chemical Engineering 26 (2018) 400–406

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Chinese Journal of Chemical Engineering

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Article

Molten waste plastic pyrolysis in a vertical falling film reactor and the
influence of temperature on the pyrolysis products☆
Zechen Jin, Dezhen Chen, Lijie Yin ⁎, Yuyan Hu, Huangqing Zhu, Liu Hong
Thermal and Environmental Engineering Institute, Tongji University, Shanghai 200092, China

a r t i c l e i n f o a b s t r a c t

Article history: Molten plastics are characterised with high viscosity and low thermal conductivity. Applying falling film pyrolysis
Received 29 March 2017 reactor to deal with waste plastics can not only improve heat transfer efficiency, but also solve the flow problem.
Received in revised form 15 July 2017 In this work, the pyrolysis process of molten polypropylene (PP) in a vertical falling film reactor is experimentally
Accepted 2 August 2017
studied, and the influence of heating temperature on pyrolysis products is discussed. It has been found that with
Available online 4 August 2017
the temperature increases from 550 °C to 625 °C, the yield of pyrolysis oil decreases from 74.4 wt% (±2.2 wt%) to
Keywords:
53.5 wt% (±1.3 wt%). The major compositions of the pyrolysis oil are C9, C12 and C18, and β-scission reactions are
Pyrolysis predominant. The content of the light fraction C6–C12 of pyrolysis oil is 69.7 wt%. Compared with other pyrolysis
Reactor reactors, the yield of oil from vertical falling film pyrolysis reactor is slightly higher than that from tubular reactor,
Molten plastic equal to that from rotary kiln reactor, and slightly lower than that in medium fluidised-bed reactor.
Pyrolysis oil © 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
Fractional condensation

1. Introduction low thermal conductivity, which make it hard to flow and difficult
to be heated up, therefore, how to improve the flow performance,
With the development of Chinese economy and improvement of and heat transfer efficiency during the volatile “evaporation” stage are
people's living standards, plastic production, consumption and the some key factors considered when design pyrolysis reactors.
amount of waste rapidly increase. China has become the world's second Liquid film heat transfer is an effective method for heat transfer
largest plastic producer, and the yield of plastic products is approxi- enhancement [5]. This method has been widely applied to various in-
mately 75.6 million tons in 2015 [1]. However, 40% of these plastics dustrial productions. Shi et al. [6] investigated the heat transfer perfor-
will be discarded in 1–2 years [2], and ultimately become waste. mance of lithium bromide absorption chiller in falling film generator,
Pyrolysis is considered as one of the important methods of recycling and found that the overall heat transfer coefficient of falling film gener-
waste plastics. It is an irreversible thermochemical process that breaks ator is 4.37 times higher than that of immersed tube generator. Zhang
down the chemical bonds of the polymers and decomposes them into et al. [7] found that the yield of water desalination by using the falling
low molecular weight compounds under oxygen-free condition. The film evaporation technology is about two to three times more than
main products of plastic pyrolysis are oil and gas with high calorific that by conventional type under the same condition. Vertical falling
values [3]. The pyrolysis process is extremely complex, previous studies film reactor based on liquid film heat transfer is appropriate to deal
have shown that the pyrolysis of plastic is divided into several stages with high viscosity materials [8], and the heat transfer performance
including: melting (from solid to liquid), pyrolysis characterised by of viscous material is similar to that of Newtonian fluid [9]. Applying
volatile emission from the molten plastics, which is a process of oil- vertical falling film pyrolysis reactor to deal with waste plastics, can
gas mixture “evaporation” (from liquid to gas), and coke formation at not only improve heat transfer efficiency, but also solve the flow prob-
the end. During the melting and pyrolysis stages, the heat supply is lem easily. So far, there are few reports of applying vertical falling film
needed and the ratio of heat required in melting stage to that of volatile reactor to molten plastics pyrolysis. Additionally, although there have
“evaporation” stage is approximately 1:4 [2]. Molten plastics are a kind been many reports of waste plastics pyrolysis, there are no special stan-
of non-Newtonian fluid [4], and characterised with high viscosity and dards for pyrolysis products in China. The reason is that the quality of
pyrolysis products vary, which is due to the uneven heating during
waste plastics pyrolysis process. One of the most advantages of vertical
☆ Supported by the National Natural Science Foundation of China (51503154), Major falling film reactor is that the heating is uniform, which can help to im-
Projects of China Water Pollution Control and Treatment Science and Technology prove the singularity of products. Therefore, it is important for achieving
(2017ZX07202005), and the Shanghai Municipal Science and Technology Commission
Fund for improving the economy in the Yangtze River Delta region (12195811100).
high efficiency, high-value recovery of waste plastics. Yin et al. [10]
⁎ Corresponding author. numerically simulated the falling film pyrolysis behaviour of molten
E-mail address: y_lijie@tongji.edu.cn (L. Yin). plastics in a vertical falling film reactor, examined the feasibility of this

http://dx.doi.org/10.1016/j.cjche.2017.08.001
1004-9541/© 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
 Z. Jin et al. / Chinese Journal of Chemical Engineering 26 (2018) 400–406 401

type of pyrolysis reactor and predicted the temperature distributions the cooling water are 85 °C to collect the high pour point oil (HPO)
and velocity profiles. However, no work was performed to determine and 0 °C ice salt water to collect the low pour point oil (LPO). The
the compositions of the pyrolysis products. temperatures of the melting tank and the falling film plate are con-
Heating temperature is one of the key operating parameters of a trolled separately, and are recorded using an electric recorder. The
pyrolysis reactor [11,12], and has an important effect on the yield of non-condensable gas treatment system is used to deal with the re-
liquid oil and non-condensable gas. Dong et al. [13] studied the pyrolysis maining non-condensable gas.
process of five typical waste plastics in a fluidised-bed reactor and found Prior to experimentation, 500 g PP plastic powder was inserted into
that as the temperature increases, the yield of non-condensable gas the melting tank from the feeding inlet, and the entire system was
increases, whereas the yield of pyrolysis oil decreases. Demirbas [14] swept with nitrogen for 15 min to ensure an inert atmosphere. Then,
researched the pyrolysis process of mixed plastics in a tubular reactor the system was heated up. According to the results of the thermogravi-
and found that when the temperature increases from 277 °C to 627 °C, metric (TG) and differential thermal analysis (DTA) [16], PP begins to
the yield of non-condensable gas increases from 12.3% to 42.4%, melt at 172 °C and starts to pyrolysis at 385 °C. Therefore, the tempera-
and the yield of the pyrolysis oil first increases and then decreases. ture of the melting tank is kept at 250 °C. When plastic is completely
Elordi et al. [15] found that as the temperature increasing from 500 °C melted in the melting tank, the nitrogen pushes the molten plastics
to 700 °C in a Conical Spouted Bed Reactor (CSBR), the yield of the out from the melting tank to the top of the falling film plate. Next, the
pyrolysis wax reduces 16%, and the yield of gasoline has maximum molten plastics are heated, decomposed when flowing down along
33% at 700 °C. Therefore, it is necessary to discuss the influence of with the falling film plate. The volatile (mixture of oil and gas) flow
heating temperature on the pyrolysis products of waste plastics in a out from the top of the falling film plate then is condensed and collected.
new pyrolysis reactor. During the experiment, the flow rate of nitrogen at the bottom of the
In this paper, a vertical falling film pyrolysis reactor was con- falling film plate is kept with 20 L·h−1 to avoid the volatile condensing
structed, and the pyrolysis process of molten PP in the reactor was on the surface of the glass. Before the experiment, 200 g of quartz sand
experimentally investigated. The influence of the heating tempera- was placed at the bottom of the falling film plate to collect dripping
ture on the yields and compositions of the oil and non-condensable molten plastics which did not have enough time to pyrolysis.
gas were studied. An elemental analyser (Vario EL III, Germany Elmentar) was used to
perform a proximate analysis of the feedstock. A Gas Chromatography
(GC-9160, Shanghai Ouhua analysis instrument factory) was used
2. Materials and Methods to determine the compositions of the non-condensable gas. A Gas
Chromatography and Mass Spectrometry (GC–MS, SHIMADZU QP2010,
2.1. Materials ultra-gas chromatograph, quadrupole mass spectrometer with He as
the carrier gas, a capillary column of 30 m RESTEK × 0.25 mm ID and a
The plastic used in this work is analytically pure plastic powder (PP), 0.25 μm film thickness) was used to analyse the liquid oil products.
produced by the Daqing Refining and Chemical Company (Daqing, The GC injector port was at 300 °C. The GC analytical program operated
China). The average diameter of the powder is 2 mm, with the ultimate at 35 °C for 5 min, 35 °C–120 °C at 5 °C·min−1, 120 °C–250 °C at
and proximate analyses shown in Table 1. The ultimate analysis of the 5 °C·min−1, 250 °C–300 °C at 10 °C·min−1 and 300 °C for 5 min. A vis-
tested sample is carried out in accordance with the ultimate analysis cometer (SV-10, A&D Co., Ltd.) was used to test the dynamic viscosity
of coal because there are no special municipal solid waste (MSW) ulti- (DV) of the pyrolysis oil. A digital oxygen bomb calorimeter (XRY-1A,
mate analysis standards. The high heat value (HHV) is 46.28 MJ·kg−1. Shanghai Hu Yue Ming Scientific Instrument Co., Ltd.) was used to de-
The higher carbon and hydrogen content in plastic fuels can avoid the termine the HHV. A thermostatic water bath (HH-4, Jintan City Hongye
need of further upgrading. experimental instrument factory) was used to maintain the tempera-
ture of cooling water.

Table 1
3. Results and Discussion
Ultimate and proximate analyses of the feedstock
3.1. Effect of temperature on the pyrolysis products
Proximate analysis /wt% Ultimate analysis /wt% HHV /MJ·kg−1

Moisture Volatile Fixed-Carbon Ash C H N 3.1.1. Effect of temperature on the yield of oil and conversion degree
0.13 99.72 0.11 0.04 85.47 14.31 ≤0.05 46.28 Fig. 2 shows the influence of temperature on the conversion degree
and yields of pyrolysis oil and non-condensable gas in the vertical falling
film reactor. In this study, the conversion degree is the mass ratio of the
decomposed PP to the fed. The yield of pyrolysis oil is the mass ratio of
2.2. Experimental methods the liquid oil condensed and collected to the decomposed PP. The sum
of the yields of pyrolysis oil and non-condensable gas is equal to one.
The pyrolysis plant is shown in Fig. 1, and is composed of four parts: From Fig. 2, as the pyrolysis temperature increases, the conversion de-
the pyrolysis system, the heating and control systems, the condensing gree increases slightly. All conversion degrees at different temperatures
and collecting system and the non-condensable gas treatment system. are very close to one, meaning that the material fed into the reactor is
The pyrolysis system consists of a melting tank and a falling film plate. almost completely decomposed. Because the plastic is pure, no coke is
The vertical falling film plate is 0.05 m × 1 m. A feed inlet and a nitrogen generated during the pyrolysis process. When the pyrolysis tempera-
inlet are located at the top of the melting tank. Three rows of type-K ture increases from 550 °C to 625 °C, the yield of oil decreases from
thermocouples with three in each row are mounted from top to bottom 74.4 wt% (± 2.2 wt%) to 53.5 wt% (± 1.3 wt%), and the yield of non-
at equal distances to monitor the falling film plate temperatures, the condensable gas increases from 22.7 wt% (± 2.7 wt%) to 46.5 wt%
liquid film temperatures and the volatile temperatures. A glass window (± 1.3 wt%) for the secondary cracking reactions [17]. The pyrolysis
in front of the falling film plate is used to observe the liquid film. The process of PP pyrolysis mainly consists of initiation, propagation and
pyrolysis volatile outlet is at the top of the falling film plate. Another termination. During the initiation stage, degradation follows the free
nitrogen inlet is at the bottom of the falling film plate to sweep the radical mechanism, which proceeds via a random chain scission to
glass surface. A fractional condensation and collection method is applied form primary radicals, including exfoliation of the branched chain
in the condensing and collecting system, and the temperatures of methyl groups and the breaking of C\\C bonds along the polymer
402 Z. Jin et al. / Chinese Journal of Chemical Engineering 26 (2018) 400–406

Fig. 1. Vertical falling film reactor for plastics pyrolysis. 1-Control panel, 2-Nitrogen inlet for pushing the molten plastics, 3-Feedstock inlet, 4-Melting tank, 5-Non-condensable gas
collector, 6-Thermocouple, 7-Glass window, 8-Falling film plate, 9-Heating tube, 10-Nitrogen inlet for sweeping the glass, 11-Volatile outlet, 12-Condenser tube, 13-Digital display
thermostatic bath, 14-Non-condensable gas treatment, 15-Ice salt water.

100 60 H2 CO CH4 C2H4

Pyrolysis oil
C2H6 C3H6 C3H8 C4Hn
Non-condensable gas
Volume fraction of non-condensable gases/

Conversion degree
Yield of pyrolysis products/wt

80

40

60

20
40

20
550 575 600 625 0
o 550 575 600 625
Temperature/ C Temperature/ oC
Fig. 2. Effect of temperature on the yield of pyrolysis products.
Fig. 3. Effect of temperature on the volume fraction of non-condensable gases.

backbone. The primary radicals generated during the initiation stage into CH4 and C2H4 by thermal decomposition at high temperatures
generate random radicals with the same carbon number (secondary [20]. For the inorganic gas, the volume fraction of H2 increases with
random radicals) via intramolecular hydrogen transfer reactions. This the temperature, whereas the volume fraction of CO changes little.
is due to the abundance of hydrogen in the polymer backbone [18].
Because the energy of C\\C bond in the β position is the lowest [19], 3.1.3. Effect of the temperature on the composition of liquid oil
these random radicals are prone to β-scission reactions, and produce Fig. 4 shows the composition distribution of liquid oil at different py-
alkenes and tertiary random radicals. The tertiary random radicals can rolysis temperatures. The yield of alkenes is greater than that of alkanes.
absorb hydrogen, methyl random radicals and generate alkanes. The According to Levine et al. [21], intermolecular hydrogen transfer be-
reaction ends when there are no random radicals. tween two radicals is the main reason behind the formation of alkanes,
and β-scission reactions of the radicals are the main reason behind the
3.1.2. Effect of temperature on the composition of non-condensable gases formation of alkenes, meaning that β-scission reactions are predomi-
Fig. 3 shows the composition distribution of non-condensable gas at nant during the pyrolysis process of PP.
different temperatures, as measured by GC. The main composition of As the pyrolysis temperature increases, the yield of alkenes gradual-
the non-condensable gas is low carbon organic gas. The volume fraction ly decreases from 54.2 wt% at 550 °C to 49.7 wt% at 625 °C. The yields of
of C3H6 is more than 50% at 550 °C. As the temperature increases, the naphthenes and aromatics are much less than that of alkanes and al-
volume fractions of C3Hn and C4Hn decrease, whereas the volume frac- kenes. The yield of naphthenes is irregular with temperature increasing.
tions of C2Hn and CH4 increase. This is because C3H6 and C4H8 convert This is because the alkenes convert to naphthenes via the cycloaddition
 Z. Jin et al. / Chinese Journal of Chemical Engineering 26 (2018) 400–406 403

Table 2
Alkanes Alkenes Yields of oil from the different reactors (wt%)

60 Naphthenes Aromatics Reactors① Temperature /°C Oil/Wax Gas Conversion Ref.

degree

Tubular 500 70 23 93 Çit et al.

600 58 24 82 [29]
700 62 35 97
Medium 550 81 19 100 Dong et al.
40 fluidised-bed② 575 75 25 100 [13]
Yield of oil/wt

600 69 31 100
625 61 39 100
Tubular 300 70 29 99 Ahmad
350 68 30 98 et al. [30]
400 63 31 94
20 Rotary kiln 550 74 21 95 Ye et al.
[25]
Fixed-bed(batch) 500 95 4 99 Miranda
et al. [16]
Fixed-bed(semi-batch) 420–460 85 14 99 Yan et al.
[24]
①
0 Except for Miranda [16], all of experiments were pyrolysis under a nitrogen
550 575 600 625 atmosphere.
②
o Continuous feed rate 0.3 g·s−1.
Temperature/ C

Fig. 4. Effect of temperature on the yield of oil according to the nature of the bonds. approximately 85 wt% in a semi-batch reactor at atmospheric pressure
at 420 °C–460 °C. The yields of oil and non-condensable gas are mainly
reaction, and the naphthenes convert into alkenes via the ring-opening decided by heating temperature, heating rate (HR), residence time
reaction. The cycloaddition reaction is an exothermic and reversible (RT), especially by HR and RT when pyrolysis at same temperature. The
process, and the ring-opening reaction is an endothermic process [22]. short RT and high HR can maximize the yield of pyrolysis oil [26]. The
The yield of aromatics increases with temperature increasing, from
0.4 wt% at 550 °C to 10.2 wt% at 625 °C. This is because the high temper- (a)
ature promotes the conversion of dienes and alkenes by such routes as Falling film pyrolysis reactor
the Diels-Alder reaction [23]. At the same time, the chemical properties Tubular reactor
of the aromatics are relatively stable. The results of this research are in 40 Rotary kiln reactor [25]
accordance with those from Demirbas [14]. He found that as the heating
temperature increases from 452 °C to 602 °C, the yield of alkenes de-
creases from 42.1 wt% to 35.5 wt%, the yield of aromatics increases 30
from 1.4 wt% to 10.2 wt%, and the yield of naphthenes first increases
Yield/wt

from 22.8 wt% to 24.4 wt% at 527 °C, and then decreases to 23.5 wt%.
20
3.2. Comparison of PP pyrolysis products in different reactors

10
The reported reactors for pyrolysis mainly include fixed-bed (batch)
reactors [16,24], rotary kilns [25], fluidised-bed reactors [13], etc.
The fixed-bed reactor is characterised by its simple structure but low
0
heat transfer coefficient and non-uniform temperature distribution for C6 C7 C8 C9 C10-C11 C12 C13-C17 C18 C18-C25 C25
reacting materials, causing pyrolysis to occur at different temperatures
simultaneously [26,27]. The fluidised-bed exhibits good heat and mass
transfer performance, but particle agglomeration generally begins (b)
80
with the formation of small agglomerates of bed material, leading Falling film pyrolysis reactor
to the “defluidisation” phenomenon [28]. The rotary kiln enables good Tubular reactor
mixing of wastes and is typically used for slow pyrolysis [26], but wastes Rotary kiln reactor [25]
with high viscosity tend to stick to internal walls, causing heat transfer 60
deterioration. The vertical falling film reactor can heat the molten
PP up to pyrolysis temperature at a short time and have no rotating
parts and does not require a fluidised medium, meaning there is no
40
defluidisation and medium inactivation.
Yield/wt

3.2.1. Yields of oil in different reactors

Table 2 presents the comparison of the conversion degree and the 20
yield of oil from pure PP pyrolysis in different reactors. It can be seen
that the maximum oil yield is approximately 70 wt% in the tubular reac-
tor [29,30], 81 wt% in the medium fluidised-bed [13], and 74 wt% in the
0
rotary kiln reactor at a speed of 1 rad·s−1 [25]. The yield of oil decreases
Alkanes Alkenes Naphthenes Aromatics
with the increase of the heating temperature in all reactors [13,29,30]. In
the fixed-bed reactor, under an atmospheric pressure of 2 kPa, the yields Fig. 5. Yields of oil for the different reactors. (a) The distribution of carbon atom numbers
of pyrolysis wax and pyrolysis oil can reach as much as 70 wt% and in the pyrolysis oil from different reactors. (b) The composition distribution of pyrolysis oil
25 wt%, respectively [16]. Yan et al. [24] found that the yield of oil is in different reactors according to the bond types.
404 Z. Jin et al. / Chinese Journal of Chemical Engineering 26 (2018) 400–406

60 the carbon number of hydrocarbons in liquid product depends heavily

on the type of reactor used [31]. Fig. 5 shows the comparison of the com-
HPO
position distribution of the pyrolysis oil in different pyrolysis reactors at
LPO
Yield of oil by fractional condensation/wt

550 °C, of which the tubular reactor can refer to the reference [32]. From
50 Fig. 5(a), we see that for the vertical falling film pyrolysis reactor,
the range of the carbon atom numbers in the pyrolysis oil is from C6
to C25, and the major constituents are C9, C12 and C18, their yields are
40 28.8 wt%, 29.7 wt%, and 24.3 wt%, respectively. For the tubular reactor,
the range of the carbon atom numbers of the pyrolysis oil is from C9 to
C25, the major constituents are C12 and C18 and their yields are 30.4 wt%
and 41.9 wt%, respectively. For the rotary kiln reactor, the range of
30 the carbon atom numbers of the pyrolysis oil is from C11 to C27; the
major constituents are C12 and C18, and their yields are 20.5 wt%
and 48.2 wt%, respectively [25]. In addition, the yield of light fraction,
20 C6–C12, from the pyrolysis oil is 36.1 wt% in the tubular reactor, 58 wt%
in the semi-batch reactor [24] and 69.7 wt% in the vertical falling film re-
actor. Therefore, the carbon atom number from the pyrolysis oil produced
in the vertical falling film reactor is smaller, meaning that the light frac-
10 tion content is higher. By comparison, the feedstock in the vertical falling
525 550 575 600 625 film reactor is decomposed at constant temperatures simultaneously,
Temperature/ oC which can make the compositions of pyrolysis products to be uniform.
Fig. 5(b) shows the composition distribution of the pyrolysis oil ac-
Fig. 6. Yield of pyrolysis oil collected by fractional condensation at different temperatures. cording to the bond characteristics. The pyrolysis oil from all of the dif-
ferent pyrolysis reactors consists mainly of alkenes and naphthenes.
medium fluidised-bed have characteristic with high HR, and the flow Little aromatics are present at 550 °C. Compared to the tubular and ro-
rate of 0.3 g·s−1 can make the pyrolysis volatile run out of the reactor in tary kiln reactor, the yield of alkenes in the vertical falling film reactor
time avoiding long RT. The rotary kiln have characteristic with relatively is greater than that of naphthenes for the shorter RT of pyrolysis volatile
low HR, but the rotating part can adjust its speed to reduce RT, as de- and weaker cycloaddition reaction.
scribed by Ye et al. [25], where the speed of 1 rad·s−1 has the most
yield of liquid oil. The Tubular reactor include a family of reactors with 3.3. Distribution of pyrolysis oil collected by fractional condensation
fixed walls in a tube shape, and it has some characteristics similar to
the fixed-bed, like low HR and low heat transfer coefficient [26]. Miranda 3.3.1. Yields of HPO and LPO at different temperatures
et al. and Yan et al. have relatively rigour pyrolysis condition for maxi- Fig. 6 shows the yield of oil for the two condensation stages at dif-
mum yield of pyrolysis oil/wax. By comparison, it is found that the ferent temperatures. When the temperature increases from 525 °C to
yield of oil pyrolysed in the vertical falling film pyrolysis reactor is slightly 625 °C, the yield of HPO decreases from 55 wt% (±1.1 wt%) to 17 wt%
higher than that achieved in the tubular reactor, equal to that in the rota- (±0.46 wt%). This is because that more heat is absorbed by the C\\C
ry kiln reactor, and slightly lower than that in the medium fluidised-bed. bonds at high temperatures, which makes a greater number of large
molecules decompose into small and low pour point molecules via
3.2.2. Comparison of the compositions of the pyrolysis oil in different free radical mechanism. As the temperature increases, the yield of LPO
reactors increases, but the rate of growth gradually decreases. When the temper-
Although the pyrolysis of PP produced in different reactors mainly ature is greater than 600 °C, the yield of oil decreases slightly. This
n-alkanes and α-alkenes in liquid products via free radical mechanism, finding is observed because more small and low pour point molecules

Table 3
The main compositions of HPO and LPO

HPO LPO

R.T. /min Area /% Compound R.T. /min Area /% Compound

8.315 6.05 2,4-Dimethyl-1-heptene 2.101 2.55 1-Pentene, 2-methyl-

16.984 3.31 1-Decene, 2,4-dimethyl- 2.648 1.03 1-Pentene, 2,4-dimethyl-
17.124 2.21 1-Decene, 2,4-dimethyl- 2.749 1.26 Bicyclo[2.1.0]pentane, 1,4-dimethyl-
23.467 1.21 1-Undecene, 8-methyl- 5.095 2.52 1-Heptene, 4-methyl-
24.064 7.35 1-Undecene, 7-methyl- 5.435 2.97 Heptane, 4-methyl-
24.714 5.56 1-Undecene, 7-methyl- 5.684 1.19 1,5-Hexadiene, 2,5-dimethyl-
27.094 1.25 1,19-Eicosadiene 6.168 1.81 1-Heptene, 2-methyl-
32.952 2.51 1-Decanol, 2-hexyl- 7.076 1.19 Cyclopentane, 1,1,3,4-tetramethyl-, cis-
35.121 1.94 Cyclooctane, 1-methyl-3-propyl- 7.925 1.24 Cyclohexane, 1,3,5-trimethyl-
38.871 3.3 1-Dodecanol, 2-hexyl- 7.978 1.72 2-Hexene, 4,4,5-trimethyl-
39.578 2.67 1-Dodecanol, 2-hexyl- 8.33 35.46 2,4-Dimethyl-1-heptene
45.009 2.76 4-Tetradecene, 2,3,4-trimethyl- 8.888 2.2 Cyclohexane, 1,3,5-trimethyl-
48.94 3.17 Cyclohexane, 1,2,3,5-tetraisopropyl- 9.465 1.01 Cyclopropane, 1,1-dimethyl-2-(2-methyl-1-propenyl)-
52.497 2.9 Cyclohexane, 1,2,3,5-tetraisopropyl- 10.336 2.13 1-Octene, 3,4-dimethyl-
56.38 2.57 Cyclohexane, 1,2,3,5-tetraisopropyl- 14.102 1.1 2-Decene, 4-methyl-, (Z)-
60.78 2.18 Cyclohexane, 1,2,3,4,5,6-hexaethyl- 16.977 2.62 1-Decene, 2,4-dimethyl-
63.368 2.57 Cyclohexane, 1,2,3,4,5,6-hexaethyl- 17.117 1.82 1-Decene, 2,4-dimethyl-
65.941 1.94 1-Cyclopentyleicosane 24.055 2.98 1-Undecene, 7-methyl-
24.704 2.19 1-Undecene, 7-methyl-
48.94 1.25 Cyclohexane, 1,2,3,5-tetraisopropyl-
52.497 1.02 Cyclohexane, 1,2,3,5-tetraisopropyl-
 Z. Jin et al. / Chinese Journal of Chemical Engineering 26 (2018) 400–406 405

C9 8.0x107 C9 (b) LPO

2.0x107 (a) HPO

6.0x107
1.5x107

Abundance
Abundance

1.0x107 C12 C18 4.0x107

5.0x106 2.0x107

C6 C12 C18
0.0 0.0
10 20 30 40 50 60 70 10 20 30 40 50 60
Retention time/min Retention time/min

Fig. 7. The composition distributions of HPO and LPO by GC–MS.

convert into non-condensable gas by secondary cracking. In addition, Table 5

the high temperature also worsens the condensation effect. Properties of LPO at different temperatures

Property 525 °C 550 °C 575 °C 600 °C 625 °C GB17930-2013

3.3.2. Composition distribution of HPO and LPO RON 73.91 75.65 74.89 79.04 79.57 N90
Table 3 and Fig. 7 show the composition distribution of HPO and LPO Alkenes /% 74.34 65.81 63.74 59.8 58.85 b30
at 550 °C by GC–MS. The carbon atom numbers of HPO range from C9 to Aromatics /% 0.17 0.92 2.14 7.15 14.83 b40
C25, and the major constituents are C12 and C18. Their average molecular Benzene /% – – – – – b1
HHV /MJ·kg−1 40.46 40.52 40.76 40.73 40.8 –
weight is 209.69 g·mol−1. Compared to HPO, the carbon atom numbers
DV at 15 °C /cP – 2.92 2.69 2.24 2.06 –
of LPO are relatively concentrated from C6 to C12. The main composition
of LPO is 2,4-Dimethyl-1-heptene, which accounts for 35.46% and the Note: “–” means that the amount of sample is not available.

average molecular weight is 135.18 g·mol−1. Moreover, the main com-

position of the pyrolysis oil is α-alkenes, which indicates that β-scission
reactions are predominant for PP pyrolysis, which is similar to the re- LPO is a liquid with little precipitation at ambient temperature.
sults from Miskolczi et al. [33]. The short chain α-alkenes can be used Compared, as shown in Table 5, the content of benzene and aromatics
as raw materials for polymers such as PP, polyethylene (PE). The long meet the requirements for standard commercial gasoline and the RON
chain α-alkenes can be used as raw material for synthetic lubricants is lower. However, the alkene content is higher, which can be improved
employed in the automotive, mechanical and aerospace industries. A by a hydrogenation reaction [37]. The DV of LPO decreases as the tem-
small amount of HPO are condensed in the low temperature condensa- perature increases. The HHV of HPO and LPO are very high, with each
tion section because some pyrolysis oil condensed and attached to the being greater than 40 MJ·kg−1.
internal face of the condenser tube at the end of the experiment,
which weakens the effect of condensation. 4. Conclusions

3.3.3. Properties of HPO and LPO at different temperatures In this paper, a vertical falling film pyrolysis reactor was constructed;
Currently, there is no common special criteria for determining the the pyrolysis process of molten PP in the vertical falling film pyrolysis
quality of waste plastics pyrolysis oil. Sarker et al. [34] used the sulphur reactor was experimentally studied, and the effects of the heating tem-
contain and American Petroleum Institute (API) gravity to check for perature on the pyrolysis products are discussed.
pyrolysis oil of PP. Pinto et al. [35] used the density, research octane
number (RON), heat of combustion, etc. to check for pyrolysis oil 1. With the temperature increases from 550 °C to 625 °C, the yield of
of mixed plastics. In this paper, physical parameters such as the HHV pyrolysis oil decreases from 74.4 wt% (± 2.2 wt%) to 53.5 wt%
and DV are tested and the values of chemical analysis allowed the the- (±1.3 wt%), the major compositions of the pyrolysis oil are C9, C12
oretical calculation of RON using the method developed by Lovasic and C18, and β-scission reactions are predominant. The content of
et al. [36]. Some properties of HPO and LPO are compared with commer- the light fraction C6–C12 of pyrolysis oil is 69.7 wt%.
cial gasoline and diesel (GB17930-2013, GB19147-2013), as shown in 2. The yield of oil from the vertical falling film pyrolysis reactor is slight-
Tables 4 and 5. ly higher than that from the tubular reactor, equal to that from
HPO is a dark brown and viscous liquid at ambient temperature. the rotary kiln reactor, and slightly lower than that in the medium
HPO's polycyclic aromatic hydrocarbons (PAHs) meet the requirements fluidised-bed reactor.
for standard diesel, and its density is close to that of commercial diesel. 3. By fractional condensation, the main compositions of HPO are C12
and C18, and the main compositions of LPO are C7, C8 and C9. The
heating temperature has a great effect on the yield of HPO, and little
Table 4 effect on the yield of LPO.
Properties of HPO at different temperatures

Property 525 °C 550 °C 575 °C 600 °C 625 °C GB19147-2013

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