Pyrolysis plastic liquid

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Influence of temperature and reaction time on the conversion of polystyrene
waste to pyrolysis liquid oil
Article in Waste Management · September 2006
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Waste Management xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman
Influence of temperature and reaction time on the conversion of
polystyrene waste to pyrolysis liquid oil
R. Miandad a,b, A.S. Nizami b,⇑, M. Rehan b, M.A. Barakat a, M.I. Khan c, A. Mustafa c, I.M.I. Ismail b,
J.D. Murphy d,e
a
Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia
Centre of Excellence in Environmental Studies (CEES), King Abdulaziz University, Jeddah, Saudi Arabia
Department of Chemical Engineering, College of Engineering, King Khalid University, Abha, Saudi Arabia
d
School of Engineering, University College Cork, Ireland
e
MaREI Centre, Environmental Research Institute, University College Cork, Ireland
b
c
a r t i c l e
i n f o
Article history:
Received 16 May 2016
Revised 19 September 2016
Accepted 20 September 2016
Available online xxxx
Keywords:
Municipal plastic waste
Pyrolysis
Polystyrene (PS) plastic
Liquid oil
Batch pyrolysis reactor
a b s t r a c t
This paper aims to investigate the effect of temperature and reaction time on the yield and quality of liquid oil produced from a pyrolysis process. Polystyrene (PS) type plastic waste was used as a feedstock in a
small pilot scale batch pyrolysis reactor. At 400 °C with a reaction time of 75 min, the gas yield was 8% by
mass, the char yield was 16% by mass, while the liquid oil yield was 76% by mass. Raising the temperature
to 450 °C increased the gas production to 13% by mass, reduced the char production to 6.2% and increased
the liquid oil yield to 80.8% by mass. The optimum temperature and reaction time was found to be 450 °C
and 75 min. The liquid oil at optimum conditions had a dynamic viscosity of 1.77 mPa s, kinematic viscosity of 1.92 cSt, a density of 0.92 g/cm3, a pour point of 60 °C, a freezing point of 64 °C, a flash point
of 30.2 °C and a high heating value (HHV) of 41.6 MJ/kg this is similar to conventional diesel. The gas
chromatography with mass spectrophotometry (GC–MS) analysis showed that liquid oil contains mainly
styrene (48%), toluene (26%) and ethyl-benzene (21%) compounds.
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
The Kingdom of Saudi Arabia (KSA) was the world’s twelfth largest primary energy consumer in 2012 with a total energy consumption of 9 quadrillions British thermal units (Btu) (US-EIA,
2014; Anjum et al., 2016). The current electricity generating capacity of KSA is 55 GWe; which is estimated to surpass 120 GWe by
2032 (Royal Decree, 2010). The electricity demand in KSA is
increasing by 8% per annum, of which 50% is only consumed in
the residential sector (Farnoosh et al., 2014). Fossil fuels are the
only source of energy in KSA (SEC, 2012; Rehan et al., 2016a).
The Government has launched a special program; King Abdullah
City of Atomic and Renewable Energy (KACARE) to generate about
Abbreviations: CO, carbon monoxide; HDPE, high density polyethylene; HHV,
higher heating value; KACARE, King Abdullah City of Atomic and Renewable Energy;
KSA, Kingdom of Saudi Arabia; LDPE, low density polyethylene; MSW, municipal
solid waste; NOx, oxides of nitrogen; PE, polyethylene; PP, polypropylene; PS,
polystyrene; RDF, refuse derived fuel; SWM, solid waste management; TGA,
thermogravimetric analyzer; TIC, total ion chromatogram; WTE, waste-to-energy.
⇑ Corresponding author.
E-mail addresses: [email protected], [email protected] (A.S. Nizami).
half of the energy (corresponding to a capacity of 72 GWe) from
renewable sources such as solar, nuclear, wind, waste-to-energy
(WTE) and geothermal by 2032 (KACARE, 2012; Nizami et al.,
2015a; Demirbas et al., 2016a).
KSA is one of the major plastic producer country in the world
with annual plastic production of around 6 million metric tons
(Nizami et al., 2015b; Khan and Kaneesamkandi, 2013). The average life span of about 40% of the consumed plastic in KSA is less
than a month (Siddiqui and Redhwi, 2009). As a result, it is the second largest waste stream (17.4%) of total generated MSW in KSA
(Nizami et al., 2015c). Moreover, excessive quantities of plastic
waste are produced due to serving of meals in disposable plastics
to millions of religious pilgrims and visitors, coming every year
to KSA (Nizami et al., 2016). All of the collected MSW (around 15
million tons per year) including plastic waste is untreated and disposed to landfills (Khan and Kaneesamkandi, 2013). The clogging
effects and the slow biodegradable nature of plastics with toxic
additives and dyes are an added environmental burden through
landfills and landfill operation (Miandad et al., 2016a).
Worldwide, there are different plastic waste management techniques such as reducing, reusing, WTE, mechanical and chemical
http://dx.doi.org/10.1016/j.wasman.2016.09.023
0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
oil. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.09.023
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R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
recycling and landfilling (Sriningsih et al., 2014; Sadef et al., 2015;
Miandad et al., 2016b,c). Mechanical recycling methods such as
sorting, grinding, washing and extrusion can recycle only 15–20%
of all plastic waste (Ashworth et al., 2014). Combustion and landfilling of plastic waste results in air and waterborne pollutants
(Ouda et al., 2016; Rahmanian et al., 2015; Eqani et al., 2016).
Chemical recycling of plastic waste through hydrolysis, methanolysis, and glycolysis (Sinha et al., 2010) along with WTE technologies such as gasification, pyrolysis, refuse derived fuel (RDF) and
plasma arc gasification are seen as preferable and as such are the
subject of more scientific attention in recent years (Miandad
et al., 2016a,b).
The pyrolysis process converts organic materials including plastic waste into energy (liquid oil) and value-added product (char)
(Bartoli et al., 2015; Rathore et al., 2016; Demirbas et al., 2016b).
The process can be carried out by using different types of reactor
such as tube reactor (Miskolczi et al., 2009), rotary kiln reactor
(Li et al., 1999), microwave reactor (Undri et al., 2011; Undri
et al., 2013), fixed bed reactor (Ringer et al., 2006), semi batch reactor (Lopez et al., 2011), and batch reactor (Syamsiro et al., 2014).
Batch and semi-batch reactors are widely used at laboratory scale
due to their easy operation, simple design, and safety point of view
(Almeida and Marques, 2016; Chen et al., 2014; Ates et al., 2013).
However, for fuel or monomer production at commercial scale,
continuous pilot reactors such as fluidized bed and spouted bed
reactors are used with continuous plastic feeding (Artetxe et al.,
2015; Mo et al., 2014; Jung et al., 2013; Aguado et al., 2003). The
factors affecting the yield and quality of produced liquid oil are
temperature, reaction time, heating rate, particle size, feedstock
composition and moisture content (Rehan et al., 2016b; Tröger
et al., 2013; Nizami et al., 2016; Miandad et al., 2016d).
The scientific literature shows that the pyrolysis studies mostly
used either pure/ virgin plastic (Borsodi et al., 2011) or processed
plastic types as a feedstock (Siddiqui and Redhwi, 2009). For
instance, Syamsiro et al. (2014) used industrial manufactured
granules of high density polyethylene (HDPE) and polystyrene
(PS) as feedstock. Lerici et al. (2015) and Lopez et al. (2011) used
pellets of commercial polymers of different plastic such as low
density polyethylene (LDPE), HDPE, polypropylene (PP) and PS as
feedstock. However the interest in pyrolysis of municipal plastic
waste, especially in PS waste has gained significant attention in
recent years (Bartoli et al., 2015; Lerici et al., 2015; Adnan and
Jan, 2014; Frediani et al., 2014; Mo et al., 2014; Undri et al.,
2014a). The focus of these studies was mainly to increase the quantity of produced liquid oil. The most frequent reported analysis of
pyrolytic liquid oil involved GC–MS to establish the composition
of the produced liquid oil (Kumar and Singh, 2011; Syamsiro
et al., 2014; Sarker et al., 2012; Onwudili et al., 2009; Undri
et al., 2015). However, the effect of process parameters on the
quality of liquid oil characteristics, including viscosity (dynamic
and kinematic viscosity), density, high heating value (HHV), flash
point, and cold flow properties such as pour point, and freezing
point and their comparison with conventional diesel is seldom
studied (de Marco et al., 2009; Bartoli et al., 2015, 2016; Lee,
2007; Lee et al., 2015; Lopez et al., 2011), which was the focus of
this research. Moreover, the recovery of styrene from PS waste
using pyrolysis process and its potential application has been discussed in detail.
In KSA, neither WTE facilities exist to convert any waste into
energy (Nizami et al., 2016), nor has the plastic waste been characterized for its potential role as an energy recovery feedstock
(Nizami et al., 2015a; Miandad et al., 2016c). The effect of temperature and reaction time on the yield and quality of liquid oil from a
pyrolysis process was investigated. Furthermore, the produced liquid oil has been characterized for its chemical composition,
dynamic and kinematic viscosities, density, flash point, HHV and
cold flow properties. On the basis of these characterization results,
the potential of liquid oil for the recovery of styrene, and generation of energy or as a source of transport fuel was discussed in
detail. In addition, the potential of char was highlighted for various
environmental applications.
2. Materials and methods
2.1. Feedstock preparation
The plastic waste in the form of disposable plates was collected
from different canteens and hotels of Jeddah city and used as a process feedstock. Most of the food items are usually served in these
plastic plates, which are primarily PS plastic. The samples were
washed and dried in an oven to remove the impurities and moisture content. After washing and drying, the feedstock was shredded into small pieces with an average size of about 5 cm2.
2.2. Reactor startup
A small pilot scale batch pyrolysis reactor was commissioned
and used for the conversion of plastic waste into liquid oil and char
(Fig. 1). The reactor has 20 L capacity and is made of stainless steel
and covered with a loop of an electric heater, which allows a maximum temperature of 600 °C. A tube type condenser coupled with
a water chiller is installed at the end of the reactor. The detailed
reactor characteristics are given in Table 1. Organic vapors produced in the heating chamber were condensed into liquid oil.
The condensed organic vapors were collected at the bottom of
the system, while the uncondensed products in the form of gases
coming from same liquid oil pipe were exhausted from the reactor
(Fig. 1).
2.3. Experimental setup
In all of the experiments, 1000 g of feedstock was used. The
heating chamber of the pyrolysis reactor was heated at a rate of
10 °C per min to achieve the set temperature. The feedstock was
converted into organic vapors, which were condensed into liquid
oil after passing through the condenser and collected in the collection tank at the bottom. The temperature of the condenser chamber was kept below 10 °C using a LabTech water chiller with
coolant flowrate of 30 L/min to achieve the maximum condensation of organic vapors. Reaction time of each experiment was
counted from the first drop of liquid oil produced. The residue
(char) at the end of each experiment was collected from the heating chamber after allowing the system to cool down to room temperature. After finishing each experiment, a mass balance of
pyrolysis products was established through weighing of liquid oil
and char quantities by using a standard digital balance and the
remaining weight percentage to make up to 100% was all assumed
to be gas product.
2.4. Analytical methods
The feedstock and process products (liquid oil and char) were
characterized by following the standard ASTM and APHA methods
(Dezuane, 1997; APHA, 1998). TGA of PS plastic was carried out by
a Mettler Toledo TGA (SDTA851) to assess the optimum process
temperature and reaction time by following the feedstock’s thermal behavior under control conditions. TGA analysis was carried
out using 10 lg sample poured into an aluminum oxide crucible,
and heated at a rate of 10 °C per min from 25 to 900 °C under nitrogen flow at a constant rate of 50 ml/min. The liquid oil viscosities
(kinematic and dynamic), density, pour point, and freezing point
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
oil. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.09.023
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R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
Pyrolysis
Reactor
Control
Panel
Condenser
Water
Chiller
Oil
Collector
Fig. 1. Pilot scale batch pyrolysis reactor.
Table 1
Reactor components.
Reactor components
Features
Height of heating tank
Diameter of heating tank
Reactor capacity for feedstock
Length of condenser
Diameter of condenser
Maximum temperature
360 mm
310 mm
20 L
860 mm
147 mm
600 °C
were measured to compare the fuel characteristics with conventional diesel.
For pour, and freezing points, AWD-12 Pour Point Tester was
used with temperature of -10 °C for one tank (left tank) and the
temperature of 56 °C for other tank (right tank). The sample
was poured in the sample tube up to the mark. The sample was
first put in the left tank till the temperature reduces to 0 °C and
then transferred to the tank on the right side. The sample tube
was taken out periodically from the tank after every 2 °C decrease
in temperature to observe the flow by holding the tube horizontally for 4 s. This process was continued until the pour point and
freezing point were reached. For density measurement, a portable
density meter (DMA 35 from Anton Paar) was used, which was first
calibrated with distilled water and then rinsed with acetone and
allowed to dry between each sample, before taking the next
measurements.
A Discovery Hybrid Rheometer (HR1 from TA instruments) was
used to measure the dynamic viscosities of the liquid oil with a
40 mm parallel plates geometry. A small amount of the liquid oil
sample was placed on the bottom horizontal plate. The upper
40 mm plate was lowered at a controlled rate so that the sample
was sandwiched between the two plates. The temperature was
set to 40 °C and the shear rate range was set between 1 and
500 1/s. The rheometer was first calibrated using viscosity standard liquid followed by actual liquid viscosity measurements.
Bomb calorimeter and flash point were used to assess the HHV
and flash point of produced liquid oil by following the ASTM D
240 and ASTM D 93 methods respectively.
The produced liquid oil was also analyzed by gas chromatography coupled with mass spectrophotometry (GC–MS) using a
Hawlett-Packard HP 7890 with a 5975 quadrupole detector. The
GC has a capillary column with 30 m length and 0.25 mm diameter, which was coated with 0.25 lm thick film of 5% phenylmethypolysiloxane (HP-5). Initial temperature for the oven was
set to 50 °C for a time interval of 2 min and then increased to
290 °C at 5 °C per min with an isothermal held for 10 min. The temperatures of ion source and transfer line were kept at 230 °C and
300 °C respectively and the splitless injection was used at 290 °C.
The data was attained in the full-scan mode between m/z 33 and
533 and a solvent interval of 3 min was used. Chromatographic
peak were recognized by means of NIST08s mass spectral data
library based or by reaction times using standard compounds.
The percentages of the peaks were calculated from total ion chromatogram (TIC) peak area. The percentage of produced gases was
calculated by the difference between the feedstock amount and
weight of products (liquid oil and char).
3. Results and discussion
3.1. Effect of temperature on liquid oil yield
Experiments were carried out at three different temperatures
(400, 450 and 500 °C) to investigate the effect of temperature on
the yield and quality of produced liquid oil. After determination
of optimum temperature, experiments were carried out at three
different reaction times (60, 75 and 120 min) to investigate the
effect on the feedstock decomposition and liquid oil. The purpose
of using different temperature and reaction time was to find the
optimum temperature and reaction time for pyrolysis of PS waste.
The aim of experiments at 60 min reaction time was to examine
the rate of decomposition at lower reaction time to minimize the
intensive energy demands of the process. Whereas, the aim of
experiments at 120 min was to achieve maximum decomposition
of feedstock and to find out the effect of longer reaction time on
the composition and quality of liquid oil and the production of
char.
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
oil. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.09.023
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R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
The TGA results showed a single step decomposition of PS plastic, where its decomposition started at 400 °C and reached its maximum decomposition point of 91% at 450 °C (Fig. 2). Further
increase in temperature from 450 °C up to 650 °C showed only
another 4–5% sample weight loss, completing the degradation of
plastic with some residue (char) leftover. As more than 91%
decomposition was achieved at up to 450 °C in the TGA experiment, it may be stated that 450 °C is an optimum process temperature for converting PS plastic waste into liquid oil using pyrolysis
technology. Similar phenomena can be observed in the DTA
(Fig. 2A) curve, where an endothermal peak is obvious, attributed
to the decomposition of the PS plastic. The onset melting temperature can be noticed at around 330 °C, melting peak at around
420 °C and melting offset at around 480 °C.
The variation in temperature at 75 min reaction time using the
batch pyrolysis reactor also gave different yields of liquid oil
(Fig. 3). At lower temperature (400 °C), the char yield was highest
(16%), while the gases yield was 8% and the liquid oil yield was
76%. While, at higher temperature (500 °C) the gases yield was
highest (16.8%) and the char yield was lowest (4.5%). The maximum liquid oil yield (80.8%) was achieved at 450 °C. TGA analysis
also confirmed the 450 °C was the optimum temperature, but with
higher maximum liquid oil yield (91%) than from this pyrolysis
reactor (80.8%). This may be explained by the controlled conditions
and very small scale of TGA experiment in comparison to the pyrolysis reactor system. The yield of produced liquid oil, especially the
styrene yield increased with an initial increase in temperature and
time, and after a certain temperature and time the oil yield started
to decrease (Figs. 3 and 4). Jung et al. (2013) and Mo et al. (2014)
explained this phenomenon that after achieving optimum temperature, some secondary reactions such as polyaromatic formation
reactions are started during PS pyrolysis, which decrease the liquid
oil and styrene yield. While, the phenomenon of increased gases
production at higher temperature was explained by Lopez et al.
(2011), de Marco et al. (2009), and Artetxe et al. (2015) that the
strong cracking of C-C bonds at higher temperature increases the
production of lighter hydrocarbons with short carbon chain compounds. Moreover, according to Li et al. (1999), Hernández et al.
(2007) and Lopez et al. (2011), temperature lower than 450 °C
increases the char and decreases the liquid oil yield and temperature in excess of 500 °C increases the gases and lowers the liquid
oil yield.
3.2. Effect of reaction time on liquid oil yield
The effect of reaction time on the liquid oil yield was studied
against the optimum temperature of 450 °C at 60, 75 and
120 min (Fig. 4). The results showed insignificant difference in liquid oil production between the 75 and 120 min reaction times. The
75 min reaction time produced the maximum liquid oil yield of
80.8% as compared to 80.7% for a reaction time of 120 min. The
char production was higher for a reaction time of 75 min as compared to 120 min (6.1 versus 5.3%). It can be stated that the extra
reaction time shows similar yield for oil and char as 75 min reaction time. Thus 75 min is suggested as the optimum reaction time.
The lowest reaction time (60 min) produced more char and less liquid oil, suggesting that a 60 min reaction time is insufficient to
convert the feedstock to liquid oil at maximum conversion efficiency. Similar results were observed and reported by Lopez
et al. (2011) and Lee (2007) on the yield of liquid oil with different
reaction times. However, the effect of reaction time on pyrolysis is
also one of the functions of the reactor dimensions and the heat
transfer rate from the heating elements to the PS feedstock within
the reactor (Jung et al., 2013; Ringer et al., 2006). Therefore, the
reaction time may change with other reactor configurations, especially of a continuous flow reactor, which would be the type of
reactor that are mostly used in industrial application of the pyrolysis process (Chen et al., 2014; Miandad et al., 2016a,b).
3.3. Characteristics of liquid oil
The produced liquid oil was analyzed for various parameters
(Figs. 5 and 6). The dynamic viscosity of liquid oil was found to
be in the range of 1.66–3.02 mPa s from all studied conditions.
The value of 1.77 mPa s was observed for the liquid oil produced
at optimum conditions of 450 °C for 75 min (Fig. 5a). This is in
agreement with the value of 2.49 mPa s as reported by
Wongkhorsub and Chindaprasert (2013). The variation in the values of dynamic viscosity depends on the structure and composition
of feedstock and liquid oil (Ates et al., 2013). According to Williams
and Williams (1999) and Siddiqui and Redhwi (2009), liquid oil
produced from PS plastic is a less viscous oil, similar to the results
of this study (Table 2) (Syamsiro et al., 2014; Wongkhorsub and
Chindaprasert, 2013). GC–MS analysis showed that compounds
produced from the pyrolysis of PS plastic contained shorter carbon
chains (Figs. 7 and 8). It is also interesting to note that dynamic viscosity range of 1.66–3.02 mPa s observed in this study is also in
agreement with the range of 1–4.11 mPa s for conventional diesel.
Fig. 2. Thermogravimetric Analysis (TGA) of PS plastic feedstock (embedded figure A represents Differential Thermal Analysis (DTA) curve).
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
oil. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.09.023
R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
5
Fig. 3. Effect of reaction temperature on pyrolysis liquid oil, char and gas product yields at 75 min of reaction time.
Fig. 4. Effect of reaction time on pyrolysis liquid oil, char and gas product yields at 450 °C.
Kinematic viscosity is one of the fuel properties, which dictates
the spray pattern and atomization of injected fuel in a combustion
chamber. High viscous oil gives poor atomization in the engine oil
and thus leads to poor engine performance. Moreover, high viscous
oil has less fluidity in cold temperatures (in winter); this adversely
affects the operation of the fuel injector on engine startup due to
poor atomization of fuel spray (Kim et al., 2009; Mohan et al.,
2006). In this study, the kinematic viscosities of liquid oil were
found to be 2.67, 1.92 and 3.24 mPa s at temperatures of 400,
450 and 500 °C respectively (Fig. 5b). Syamsiro et al. (2014) and
Panda and Singh (2013) reported kinematic viscosity of 1.74 cSt
for pyrolysis oil from polyethylene (PE) bag, 2.32 cSt from HDPE
and 2.18 cSt for PP plastic. According to Syamsiro et al. (2014), liquid oil produced from the pyrolysis of plastic has a lower kinematic
viscosity than diesel fuel due to the presence of a high fraction of
gasoline and a low fraction of heavy oil. However, the kinematic
viscosity range of 1.92–3.24 cSt found in this study is similar to
the range of 2.0–5.0 cSt for conventional diesel (Table 2). Kinematic
viscosity also plays a vital role in the lubrication of engines especially for rotary distributer injection pumps (Hansen et al., 2005).
Lower fuel kinematic viscosity can lead to leakage at the injector,
resulting in poor engine performance (Syamsiro et al., 2014).
Density is an important parameter for any petroleum product.
The produced liquid oil had densities of 0.94 g/cm3, 0.92 g/cm3
and 0.93 g/cm3 obtained at temperatures of 400, 450 and 500 °C
respectively (Fig. 5c). This range of density is in line with the
reported range of pyrolysis liquid oil densities using different feedstocks (Panda and Singh, 2013; Wongkhorsub and Chindaprasert,
2013; Sharma et al., 2014; Syamsiro et al., 2014; Undri et al.,
2014b). Moreover, this range of density is little higher than naturally produced commercial diesel (0.81–0.87 g/cm3), as reported
by Syamsiro et al. (2014).
HHV is one of the most important characteristics of fuels.
According to Saptoadi and Pratama (2015), fuels with higher
HHV are needed in less quantity to perform the same function by
fuels with lower HHV. The liquid oil produced from PS plastic at
400, 450 and 500 °C had HHV of 37.48, 41.60 and 41.58 MJ/kg
respectively (Fig. 6). Kamal and Zainuri (2015), reported that
increase in temperature (425–900 °C) increased the HHV of pyrolytic oil (41.87–46.84 MJ/kg), which is in agreement with our results.
Moreover, the produced liquid oil had slightly lower HHV to conventional diesel (43.06 MJ/kg) (Kamal and Zainuri, 2015).
Saptoadi and Pratama (2015), reported that since pyrolytic oil
has slightly lower HHV then kerosene oil, it can be used with or
without blending with kerosene oil.
Cold flow properties are also very important features of any fuel
for an operational point of view. These properties include cloud
point at which temperature crystals start to form in liquid causing
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Fig. 5. Effect of reaction temperature on pyrolysis liquid oil characteristics (a) dynamic viscosity, (b) kinematic viscosity (c) density, (d) flash point, (e) pour point, (f) freezing
point and (g) HHV.
cloudiness and pour point at which temperature fuel becomes
semi solid and loses its flow characteristics (Hansen et al., 2005;
Gardy et al., 2014). The pour and freezing points of the produced
liquid oil were found to be quite low, ( 18 to 19 °C) and ( 30
to 65 °C) respectively (Figs. 5 and 6). This is of increased importance in areas where cold temperatures are experienced during
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
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7
Fig. 6. Effect of reaction time on pyrolysis liquid oil characteristics (a) dynamic viscosity, (b) kinematic viscosity (c) density, (d) flash point, (e) pour point, (f) freezing point
and (g) HHV.
winter. Moreover, according to Robert (2011), Bartoli et al. (2015)
and Isioma et al. (2013), any fuel whose pour point is high will
make wax if left for a longer period of time, blocking the filter
and thus creating problems in engine startup.
The GC–MS analysis showed that the same aromatic compounds were found in the produced liquid oil but in different com-
positions at different temperatures and reaction times (Figs. 7 and
8). Toluene, ethyl-benzene and styrene were found to be about 95%
(by area) in all three samples produced at three different process
temperatures. Styrene was found in more abundance than the
other two compounds, starting from 39 and rising to 48% (at
400 °C and 450 °C respectively). The maximum value of 48% was
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R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
Table 2
Comparison of present study liquid oil with conventional diesel.
Parameters
Units
Our results
Conventional diesel
Reference
Dynamic viscosity
Density @15 °C
Kinematic viscosity @ 40 °C
Pour point
Flash point
mPa s
g/cm3
cSt
°C
°C
1.66–3.02
0.92–0.94
1.92–3.24
( 18)–( 60)
28.1–30.2
1–4.11
0.815–0.870
2.0–5.0
Max 18
Min 55–60
Wongkhorsub and Chindaprasert (2013)
Syamsiro et al. (2014)
Syamsiro et al. (2014)
Syamsiro et al. (2014)
Syamsiro et al. (2014)
tion of styrene along with an increase in production of toluene
and ethylene benzene
60
Toluene
Ethyl-benzene
48%
Area (%)
50
48%
3.4. Potential applications of liquid oil and char
39%
40
30
Styrene
28% 28%
26%
20
26%
21%
21%
450
500
10
0
400
Pyrolysis reaction temperature (°C)
Fig. 7. GC–MS analysis showing the effect of temperature on composition of liquid
oil at 75 min of reaction time, (only the main products are reported).
60
Toluene
Ethyl-benzene
Area (%)
50
40%
40
30
Styrene
48%
39%
31%
30%
26%
26%
25%
21%
20
10
0
60
75
120
Pyrolysis reaction time (min)
Fig. 8. GC–MS results showing the effect of reaction time on composition of liquid
oil at 450 °C, (only the main products are reported).
achieved at optimum temperature (450 °C) and reaction time
(75 min) (Figs. 7 and 8). Various other studies also reported the
similar results that styrene, toluene and ethylene benzene were
the main compounds produced from PS waste (Jung et al., 2013;
Undri et al., 2013, 2014a; Frediani et al., 2014; Artetxe et al.,
2015). Onwudili et al. (2009) reported that there is no direct production of toluene and ethyl-benzene from the plastic waste feedstock, however they may be produced by the reaction of styrene
itself. Production of styrene was effected by temperature:
increased temperature increased styrene production with maximum production at 450 °C. Beyond 500 °C it is reported that further increase in temperature leads to a decrease in styrene
production with an increase in the production of toluene and
ethyl-benzene (Demirbas, 2004; Onwudili et al., 2009). Aguado
et al. (2003), Artetxe et al. (2015) and Bartoli et al. (2015) explained
this phenomenon that styrene goes under further decomposition at
high temperature (from 500 to 600 °C) that result in low produc-
In KSA, plastic waste (the second largest waste stream in MSW
at 17.4% by mass), has potential to be converted into liquid oil and
char. The results of kinematic viscosity, dynamic viscosity, flash
point, density, freezing point, pour point and HHV of pyrolysis liquid oil (Figs. 5 and 6) were found to be similar to that of conventional diesel (Table 2). Different researchers used produced liquid
oil individually as a source of energy or after blending with diesel
in the ratio of 20% and 40% (Rehan et al., 2016b; Miandad et al.,
2016a,b; Oasmaa and Czernik 1999). According to Kaustav
(2014), diesel blended with pyrolytic liquid oil of up to 20% showed
similar efficiency to conventional diesel in terms of its energy, NOx
and CO emissions. According to Lee et al. (2015) the use of liquid
oil in a diesel engine is a promising way to generate electricity.
Wongkhorsub and Chindaprasert (2013) directly injected the liquid oil produced from plastic and tire waste into multi-purpose
agriculture diesel engine. However, produced liquid oil especially
from PS waste should be upgraded or blended with conventional
diesel as it contains high aromatic contents, as can be seen from
this study results (Figs. 7 and 8). According to Jung et al. (2013)
and Artetxe et al. (2015), the thermal decomposition of PS waste
produces mainly styrene, toluene, and ethylene benzene along
with some others styrene monomers. Recovered styrene from the
pyrolysis oil of PS waste can be used as a chemical source in industries for polymerization of PS polymer (Achilias 2007; Frediani
et al., 2012). Moreover, polyhydroxyalkanoate a biocompatible
and biodegradable plastic can be produced from pyrolysis oil of
PS waste (Nikodinovic-Runic et al., 2011).
Char from pyrolysis of HDPE, PS and tire waste had a calorific
value of 23.09, 36.29 and 32 MJ/kg respectively (Syamsiro et al.,
2014; Undri et al., 2013). Jindaporn and Lertsatitthanakorn
(2014) prepared the briquettes after crushing the char produced
from pyrolysis of HDPE and used it for boiling of one liter water;
1 kg of prepared briquettes took 13 min to boil the water. In addition, char can be used as a source of energy for boiler or as a feedstock for activated carbon (Frediani et al., 2012). The thermal
activation of char produced from HDPE waste at 900 °C for three
hours increased its surface area and reduced the pore size (Lopez
et al., 2011). The activated char in the form of activated carbon
can be used for industrial and municipal wastewater purification
from heavy metal and disinfecting by-products and toxic organic
compounds (Jindaporn and Lertsatitthanakorn, 2014). For instance,
the upgraded char of PS, PP, PE and tire waste showed significant
adsorption of methylene blue dye (3.59–22.2 mg/g) from wastewater (Bernando, 2011).
4. Conclusions
A small pilot scale batch pyrolysis reactor has been used to convert PS plastic waste into liquid oil. The effect of process temperature and reaction time on the quality and yield of liquid oil was
studied in detail. The results showed that at lower temperatures
Please cite this article in press as: Miandad, R., et al. Influence of temperature and reaction time on the conversion of polystyrene waste to pyrolysis liquid
oil. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.09.023
R. Miandad et al. / Waste Management xxx (2016) xxx–xxx
(400 °C), liquid oil yield was low and there was a relatively high
yield of char. The optimum conditions for maximum liquid oil yield
of 81% were achieved at 450 °C temperature and 75 min reaction
time. The produced liquid oil at these optimum conditions has a
dynamic viscosity of 1.77 mPa s, kinematic viscosity of 1.92 cSt, a
density of 0.92 g/cm3, a pour point of 60 °C, a freezing point of
64 °C, a flash point of 30.2 °C and a HHV of 41.6 MJ/kg. The characteristics are similar to conventional diesel fuel. The GC–MS analysis showed that liquid oil contains mainly styrene (48%), toluene
(26%) and ethyl-benzene (21%) compounds, however due to its
composition this liquid needs further processing if it is to be used
as a transport fuel.
Acknowledgements
Dr. Abdul-Sattar Nizami and Dr. Mohammad Rehan are funded
from Ministry of Education, Saudi Arabia under the Grant No. 1/
S/1433. Prof J.D. Murphy is funded from Science Foundation Ireland
(SFI) under Grant No. 12/RC/2302, with industrial co-funding from
ERVIA, Gas Networks Ireland (GNI) through the Gas Innovation
Group.
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