as Thermochemical conversions. Pyrolysis is one such
process that involves the thermal cracking of used
tyre material at elevated temperatures in the absence
of oxygen to produce liquid, solid, and gas products
(Wikipedia, n.d.). Microwave pyrolysis is one of the
latest technologies to replace the conventional heating. It is not only faster but also a cleaner process
that leads to reduced energy consumption (Kumar,
Chirchir, Namango, & Kiriamiti, 2016). The reaction variables in microwave heating include microwave
power, reaction time, and particle size. The aim of the
current study is to optimize the liquid fuel yield from
microwave pyrolysis by varying microwave power,
residence time and particle sizes.
1.1 Problem statement
The cost of fossil fuels has been escalating, thus
rendering their use not only expensive but also unsustainable. Furthermore, the coal and petroleum deposits
in the entire world will be exhausted due to continuous
exploitation. According to some research, the natural
gas, oil, and coal will be exhausted in 54, 53, and 110
years, respectively (Singh, 2015). This makes it necessary to come up with an alternative source of energy.
Waste-to-energy conversion is one of the alternative
sources of fuel. Used tyres pose a threat to the environment, especially in developing countries, since the
current methods of disposal pollutes the environment.
Liquid from used tyres has the potential to be used as
a source of fuel to replace petroleum diesel (Mamun
et al., 2015). It is not only a cheaper alternative but
also sustainable due to the availability of used tyres and
appropriate conversion technologies. However, despite
this cheaper alternative of used tyres, there is a gap
of inefficient production of tyre pyrolysis oil in the
conversion technologies. This has resulted in lower
production of liquid fuel from used tyres and thus
reducing the interest in waste-to-energy technologies.
1.2 Objectives
The main objective of this study was to come up with
optimal conditions for liquid fuel production from
microwave pyrolysis of used tyres using experimental
and statistical approaches.
1.3 Limitations of the study
a) Laboratory prototype may vary from large-scale
production in terms of power consumption, reaction
time, capital cost, and maintenance.
b) The particle size was limited to 25 mm
2 being the
smallest particle size but even smaller particle sizes
can be achieved. On the other hand, the sample size
of the feedstock was limited to 100 g.
2 LITERATURE REVIEW
There is some research that has been done on
microwave pyrolysis process. First, there is research
that has been conducted to find out the calorific value
of pyro-oil which is a product of microwave pyrolysis (Mamun et al., 2015). The main objective of the
research was to find out the calorific value of the oil
products and to compare it with that of fossil fuels. The
higher calorific value of the pyro-oil was found to be
53 MJ/kg higher than that of petroleum diesel at 44.8
MJ/kg and close to that of methane at 55.5 MJ/kg.
Research to study the effects of microwave power
on the microwave pyrolysis process was done by (Song
et al., 2017). The tyre powder was treated under different power levels and expressed as specific microwave
power (SMP) which is power per 1 g sample. The
SMPs chosen were 9 W/g, 15W/g, and 24 W/g. The
microwave oven used was rated with an output power
of 900 W and SMPs of 9 W/g, 15 W/g, and 24 W/g
corresponds to 270W (30%), 450W (50%), and 720W
(80%), respectively. It was found that the highest yield
of liquid fuel 45 (wt.%) was obtained at a SMP of 15
W/g (50%) while the highest gaseous yield of 18.5
(wt.%) was obtained at a SMP of 24 W/g (80%).
Another study was conducted in 2016 by Alex Lu
Chia Yang on microwave pyrolysis of used tyres with
and without activated carbon as a catalyst (Yang & Ani,
2016). In this experiment, the scrap tyre was heated at
temperatures between 400 and 600
◦ C to produce liquid fuel. The experiments were carried out with and
without activated carbon as a microwave absorbent.
The main objective was to study the effects of temperatures and activated carbon on the yields. Furthermore,
the pyro-oil was characterized for the chemical composition, compound functional group, and the calorific
value. It was found out that the optimal temperature
for the pyrolysis process was 500
o C with the highest
yield of pyrolytic oil with activated carbon as catalyst
at 54.39 (wt.%). Without activated carbon, the highest
liquid fuel yield was (28.63 wt.%). The high calorific
value of the oil was in the range of 42–43 MJ/kg. It was
also found out that the liquid fuel has a complex structure comprising long-chained hydrocarbons (Yang &
Ani, 2016).
In 2018, a research on microwave pyrolysis of used
tyres with carbonaceous susceptor for production of
liquid fuel was done (Idris, Chong, & Ani, 2019). The
main objective of the study was to study the effects of
temperature on the liquid fuel yield and fuel properties.
Activated carbon was used in this study to elevate the
microwave temperatures and hence enhance the production of tyre pyrolysis oil. The results indicated that
the optimum yield of liquid fuel was at 500
◦ C with a
yield of 38.12 (wt.%). The important chemical compounds that were found to be present in tyre pyrolysis
oil are xylene (BTX), toluene, and benzene.
3 MATERIALS AND METHODS
3.1 Feedstock preparation
A used tyre (Triangle 1000 R 20 10.00X20 truck tyre)
was used for the preparation of feedstock (tyre chips).
It was shredded by knife to achieve the required size;
211
process that involves the thermal cracking of used
tyre material at elevated temperatures in the absence
of oxygen to produce liquid, solid, and gas products
(Wikipedia, n.d.). Microwave pyrolysis is one of the
latest technologies to replace the conventional heating. It is not only faster but also a cleaner process
that leads to reduced energy consumption (Kumar,
Chirchir, Namango, & Kiriamiti, 2016). The reaction variables in microwave heating include microwave
power, reaction time, and particle size. The aim of the
current study is to optimize the liquid fuel yield from
microwave pyrolysis by varying microwave power,
residence time and particle sizes.
1.1 Problem statement
The cost of fossil fuels has been escalating, thus
rendering their use not only expensive but also unsustainable. Furthermore, the coal and petroleum deposits
in the entire world will be exhausted due to continuous
exploitation. According to some research, the natural
gas, oil, and coal will be exhausted in 54, 53, and 110
years, respectively (Singh, 2015). This makes it necessary to come up with an alternative source of energy.
Waste-to-energy conversion is one of the alternative
sources of fuel. Used tyres pose a threat to the environment, especially in developing countries, since the
current methods of disposal pollutes the environment.
Liquid from used tyres has the potential to be used as
a source of fuel to replace petroleum diesel (Mamun
et al., 2015). It is not only a cheaper alternative but
also sustainable due to the availability of used tyres and
appropriate conversion technologies. However, despite
this cheaper alternative of used tyres, there is a gap
of inefficient production of tyre pyrolysis oil in the
conversion technologies. This has resulted in lower
production of liquid fuel from used tyres and thus
reducing the interest in waste-to-energy technologies.
1.2 Objectives
The main objective of this study was to come up with
optimal conditions for liquid fuel production from
microwave pyrolysis of used tyres using experimental
and statistical approaches.
1.3 Limitations of the study
a) Laboratory prototype may vary from large-scale
production in terms of power consumption, reaction
time, capital cost, and maintenance.
b) The particle size was limited to 25 mm
2 being the
smallest particle size but even smaller particle sizes
can be achieved. On the other hand, the sample size
of the feedstock was limited to 100 g.
2 LITERATURE REVIEW
There is some research that has been done on
microwave pyrolysis process. First, there is research
that has been conducted to find out the calorific value
of pyro-oil which is a product of microwave pyrolysis (Mamun et al., 2015). The main objective of the
research was to find out the calorific value of the oil
products and to compare it with that of fossil fuels. The
higher calorific value of the pyro-oil was found to be
53 MJ/kg higher than that of petroleum diesel at 44.8
MJ/kg and close to that of methane at 55.5 MJ/kg.
Research to study the effects of microwave power
on the microwave pyrolysis process was done by (Song
et al., 2017). The tyre powder was treated under different power levels and expressed as specific microwave
power (SMP) which is power per 1 g sample. The
SMPs chosen were 9 W/g, 15W/g, and 24 W/g. The
microwave oven used was rated with an output power
of 900 W and SMPs of 9 W/g, 15 W/g, and 24 W/g
corresponds to 270W (30%), 450W (50%), and 720W
(80%), respectively. It was found that the highest yield
of liquid fuel 45 (wt.%) was obtained at a SMP of 15
W/g (50%) while the highest gaseous yield of 18.5
(wt.%) was obtained at a SMP of 24 W/g (80%).
Another study was conducted in 2016 by Alex Lu
Chia Yang on microwave pyrolysis of used tyres with
and without activated carbon as a catalyst (Yang & Ani,
2016). In this experiment, the scrap tyre was heated at
temperatures between 400 and 600
◦ C to produce liquid fuel. The experiments were carried out with and
without activated carbon as a microwave absorbent.
The main objective was to study the effects of temperatures and activated carbon on the yields. Furthermore,
the pyro-oil was characterized for the chemical composition, compound functional group, and the calorific
value. It was found out that the optimal temperature
for the pyrolysis process was 500
o C with the highest
yield of pyrolytic oil with activated carbon as catalyst
at 54.39 (wt.%). Without activated carbon, the highest
liquid fuel yield was (28.63 wt.%). The high calorific
value of the oil was in the range of 42–43 MJ/kg. It was
also found out that the liquid fuel has a complex structure comprising long-chained hydrocarbons (Yang &
Ani, 2016).
In 2018, a research on microwave pyrolysis of used
tyres with carbonaceous susceptor for production of
liquid fuel was done (Idris, Chong, & Ani, 2019). The
main objective of the study was to study the effects of
temperature on the liquid fuel yield and fuel properties.
Activated carbon was used in this study to elevate the
microwave temperatures and hence enhance the production of tyre pyrolysis oil. The results indicated that
the optimum yield of liquid fuel was at 500
◦ C with a
yield of 38.12 (wt.%). The important chemical compounds that were found to be present in tyre pyrolysis
oil are xylene (BTX), toluene, and benzene.
3 MATERIALS AND METHODS
3.1 Feedstock preparation
A used tyre (Triangle 1000 R 20 10.00X20 truck tyre)
was used for the preparation of feedstock (tyre chips).
It was shredded by knife to achieve the required size;
211