Published at : 18 Sep 2024
Volume : IJtech
Vol 15, No 5 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i5.6905
Janter P. Simanjuntak | Mechanical Engineering Department, State University of Medan, Jl. Willem Iskandar Pasar V Medan Estate, Medan 20221, North Sumatra, Indonesia |
Mohd Zamri Zainon | Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia |
Nurin Wahidah Bint Mohd Zulkifli | Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia |
Bisrul H. Tambunan | Mechanical Engineering Department, State University of Medan, Jl. Willem Iskandar Pasar V Medan Estate, Medan 20221, North Sumatra, Indonesia |
Junifa L. Sihombing | Department of Chemistry, Faculty of Mathematics and Natural Sciences, State University of Medan, Jl. Willem Iskandar Pasar V Medan Estate, Medan 20221, North Sumatra, Indonesia |
Riduwan | Usaha Kecil Menengah, Program Kemitraan dan Bina Lingkungan PT. Kawasan Industri Medan, Medan 20371, North Sumatra, Indonesia |
The
growing consumption of plastic is a major contributor to the substantial
increase in waste, emphasizing the urgent need for the adoption of sustainable
and effective practices in management and resource reclamation. Therefore, this
study aimed to investigate the production of pyrolytic
distilled oil (PDO) from five types of mixed-plastic waste using
pyrolysis and distillation process without catalysts. Pyrolysis was conducted
at a temperature range of 300 to 450 with a fixed heating rate of 10 /min
for 60 minutes, while distillation was performed at 120 to 350 . The
distilled pyrolytic oil obtained was characterized using analytical techniques
with gas chromatography-mass spectrometry (GC-MS) and Carbon/Hydrogen/Nitrogen
(CHN) analyses to determine its chemical content and heating value. The effect
of pyrolysis and distillation temperature on product yield and hydrocarbon
content was also examined. The results showed that the predominant compounds
obtained were aromatic hydrocarbon groups, including styrene, benzene,
naphthalene, and xylene. Other compounds included non-aromatic hydrocarbon
groups, such as alkane and alkene. In addition, the chemical content was found
to be comparable to that of product obtained from the use of common pyrolysis
using catalysts. In this study, the
heating values observed were in the range of
30.835 – 33.004 MJ/kg. However, the heating value of the product
was still low and needed to be improved using another treatment. Comparison
with previous reports showed that temperature in this study was not significant
to the chemical content and heating value of the obtained distillate oil.
Low temperature; Non-catalyst; Plastic waste; Pyrolysis; Pyrolytic oil
Fossil fuels, such as coal, oil, and gas, are primary global energy sources that have been widely used for over a century. Despite the importance of these fuels, their extensive use has led to several detrimental effects, including climate change, air pollution, and resource depletion. Consequently, there is a pressing need to reduce their usage and support initiatives aiming for zero fossil fuels by 2050 (Holechek et al., 2022). These detrimental effects are likely to persist on Earth when decisive actions are not taken to mitigate human dependence. Climate change, caused by the greenhouse gases emitted from burning fossil fuel-derived energy, has significantly impacted the planet. The impacts include rising sea levels, more frequent and intense weather events, and increased extinction rates for plants and animals (Haines et al., 2006).
According to
previous studies, mitigating human reliance on fossil fuels necessitates a
transformative shift towards cleaner and more sustainable energy sources,
including wind, solar, and geothermal power (Owusu
and Asumadu-Sarkodie, 2016). This transition is expected to reduce
environmental impact and create new economic opportunities and jobs within the
renewable energy sector. Several studies have shown that continued dependence
on the use of fossil fuels is unsustainable and poses a significant threat to
Earth.
In line with
several reports, plastic waste has become a significant environmental concern
due to its widespread use, improper disposal, and slow degradation (Vriend et al., 2021). In addition, it
comprises discarded plastic, such as packaging, bags, bottles, straws, and
other single-use variants. The waste typically causes several environmental
problems, including land and water pollution, where it ends up in landfills,
taking centuries to degrade (Sari et al., 2022).
This condition often leads to its accumulation in landfills, contributing to
soil contamination and the release of harmful chemicals. The consequences
extend to marine pollution, where it accumulates in the oceans and water
bodies, posing a severe threat to marine life.
Compared to other countries, Indonesia
also needs a mix of energy sources to meet its future demands while reducing
its dependence on fossil fuels. This approach requires increasing the use of
renewable sources, improving energy efficiency, and exploring new technologies
to support a more sustainable system of producing liquid biofuel (Simanjuntak, Tambunan, and Sihombing, 2023; Simanjuntak et
al., 2022). In
Indonesia, two crucial sources of liquid fuel production are organic and
inorganic materials. Organic materials, typically sourced from plants or
biomass, serve as a highly environmentally friendly alternative and are often
referred to as green fuel.
A typical example of organic materials is palm oil, which serves as an
ideal and highly productive source of biofuel for internal combustion engines (Prihadiyono et al., 2022). Algae plants
also have the potential to serve as a renewable energy source due to their high
productivity and ability to grow in diverse environment (Sardi et al., 2022; Jamilatun et al., 2020). In
addition, inorganic
materials, such as plastic waste, have high productivity and can be used for
industrial and construction purposes. Various plastic materials can be
processed into liquid fuels with properties similar to diesel (Suhartono et al., 2023). The quality of
liquid fuels can be improved by mixing organic and inorganic materials (Kusrini et al., 2018). Plastic
has been reported to possess the potential to be used as building material,
thereby reducing concrete production costs. Previous reports showed that it
could also be used as aggregate substitute for cement in concrete. The
aggregate acts as filling materials that contribute to the structural strength
of concrete (Purnomo, Baskoro, and Muslim, 2023).
Plastic waste can be a potential source for
future energy mixes through the use of pyrolysis. This method comprises heating
the waste to high temperatures in the absence of oxygen, leading to the
breakdown of the constituent long polymer chains and the production of a liquid
fuel known as pyrolysis oil (Sharma et al., 2014).
The liquid product obtained can be used as a fuel substitute or blended with
bio-oil for internal combustion engines (Awang et
al., 2021), electricity generation, or feedstock for the production
of chemicals. Another effective method of using plastic waste is gasification (Ahmed and Gupta, 2010), which comprises heating
in the presence of oxygen and steam to produce a gas mixture called syngas.
This product can be burned for heat and electricity or processed into biofuels,
such as ethanol or methanol.
Based on
findings, pyrolysis and gasification have the potential to convert plastic into
useful energy sources while also reducing the amount of waste being accumulated
in landfills or the environment. However, there are also some challenges
associated with its use as an energy source. These include potential emissions
of harmful pollutants during the conversion process, the need for careful
handling to prevent contamination with other materials, and the cost of
building and operating the necessary infrastructure (Verma
et al., 2016).
According to
previous studies, pyrolysis is a promising solution for addressing the issue of
mixed-plastic waste. This process comprises the thermal decomposition of
organic materials in an oxygen-deprived environment, leading to the production
of valuable by-products, including fuel, gases, and char (Papari, Bamdad, and Berruti, 2021). Pyrolysis of mixed-plastic waste holds
significant potential as it can generate a valuable energy source, serving as a
sustainable alternative to fossil fuels. This transition not only mitigates
greenhouse gas emissions but also contributes to the advancement of the
circular economy (Siddiqui and Redhwi, 2009).
However, it presents inherent challenges, such as the substantial variability
in substrate composition and the imperative need for optimal operating
conditions to ensure the production of high-quality fuels (Kasar, Sharma, and Ahmaruzzaman, 2020; Al-Salem et
al., 2017). The
complexity of managing diverse waste streams necessitates comprehensive study
efforts to explore the technical feasibility, economic viability, and
environmental impact associated with the pyrolysis process.
Plastic
waste holds great promise in the petrochemical industry through the pyrolysis
process, leading to the release of several valuable industrial materials. In
this study, data from previous research by Soni et al., (2021) is
referenced, which demonstrates that plastic waste, categorized by its recycling
code, contains a range of chemical components.
The values
presented represent the proximate analysis of a single sample obtained from
different types. The high volatile fraction and low ash content showed that
co-pyrolysis process can contribute to optimal pyrolysis production, yielding a
high heating value for fuels.
The current trend in plastic pyrolysis studies focuses
on achieving high yields of products with high quality and low energy
consumption, collectively referred to as high efficiency. This efficiency can
be enhanced by using catalysts, which allow for lower operational temperatures (Peng et al., 2022). However, most studies
employing catalysts have been conducted on individual types of plastic. The use
of these materials presents challenges, such as feeding issues and difficulties
in process control. Despite the drawbacks, the primary benefit of using
catalysts is the higher production of bio-oil (Kim,
2004).
Previous reports have explored pyrolysis without catalysts, particularly when
processing single types of plastic. These reports have demonstrated the
possibility of achieving comparable yields at moderate temperatures (Miskolczi et al., 2004).
2.1. Materials
This study involved the utilization of
a mixed feedstock comprising five types of plastic waste. The plastic materials
were collected
from the trash bin around the study site, which was sorted, cleaned, and dried
before being put into the pyrolysis apparatus. The feedstock included polyethylene
terephthalate (PET), low-density polyethylene (LDPE), high-density polyethylene
(HDPE), polypropylene (PP), and polystyrene (PS) derived from mineral beverage water bottles, grocery plastic bags, detergent bottle caps, beverage pipettes, and food wrapping of Styrofoam
respectively. The feedstock was chopped manually to achieve a standardized size of
approximately 3 cm x 3 cm. The proximate analysis of the material used was
presented in Table 1.
Table 1 Proximate
Analysis of Plastic (%)
Plastics |
C |
H |
N |
S |
O |
Cl |
HDPE |
85.40 |
15.04 |
0.00 |
0.52 |
2.77 |
0.14 |
PVC |
38.53 |
5.04 |
0.013 |
0.176 |
0.00 |
56.25 |
PS |
92.59 |
8.13 |
0.00 |
0.00 |
2.24 |
0.00 |
LDPE |
77.60 |
21.55 |
0.00 |
0.003 |
0.00 |
0.00 |
PET |
77.00 |
13.00 |
0.20 |
n.a |
5.00 |
n.a |
2.2. Method
Approximately 200 grams of each type of
plastic was introduced into the pyrolysis reactor and heated to the desired
temperature without oxygen using an LPG combustor. During the heating process,
the mixed plastic was degraded into lighter molecules in the form of vapor.
After passing through the condenser, the vapor reached its saturation
temperature and condensed into liquid. Subsequently, a distillation process was
used to separate the liquids according to the density of molecules which
resulted in pyrolytic distilled oil (PDO), exhibiting properties similar to
fossil-based liquid fuels.
Operating temperature for this process ranged from 300 to 450 , while the heating rate and residence time were 10 and 60 minutes, respectively. The schematic of the process is presented in Figure 1. The procedure began with pyrolysis, followed by the cooling of the pyrolytic vapor in the condenser until all vapor transformed into condensate. After pyrolysis process was completed, the reactor was allowed to cool down and the condensate was extracted from the condenser. In addition, distillation was conducted within the same reactor, generating pyrolytic oil as the final product.
The type of distillate or pyrolytic oil
obtained was based on the operating temperature utilized during the process. A total of six samples were
prepared for characteristic testing using only CHN and GC-MS methods to analyze the
product yield in terms of chemical and molecule components. According to Ghodke (2021), there were six methods for characterizing
pyrolytic oil. However, in this study, the CHN-GCMS was selected due to the
cost-effectiveness and time consumed during the characterization process using
multiple methods.
Pyrolysis process comprised
the thermal decomposition of inorganic materials in the absence of oxygen.
During the process, the plastic feedstock was subjected to decomposition based
on the application of heat. The absence of oxygen prevented combustion, leading
to the formation of various products, including gases, liquids or PPO, and
solids. These products could then be further processed or refined for various
applications, such as fuel production, chemical synthesis, or waste management.
The equation (1) below shows a simplified representation of pyrolysis reaction.
Figure 1 Schematic pyrolysis system of five types of plastic waste
The
plastic pyrolytic oil (PPO) product, derived from pyrolysis of a mixture of
five types of plastic, occurred within a temperature range of 300 to 450 oC. The
procedure yielded predominantly liquid oil, constituting an intricate
amalgamation of hydrocarbons, along with a solid residue identified as char.
This char primarily consisted of mixed carbon, and the quantity generated was
dependent on the type of plastic and the specific pyrolysis conditions
employed. The yield of each product was intricately linked to several factors,
including the composition of the mixed plastic, the temperature range applied,
the heating rate, and various other parameters. In addition, the choice of the
pyrolysis reactor and the conditions under which the procedure was conducted
significantly influenced the final product outcomes.
In this study, the yield of PPO from the five
mixed plastics reached 45% by weight of the feedstock at a temperature of
approximately 400oC. This finding was consistent with the results of other
reports, who achieved a yield of up to 69% when pyrolyzing mixed plastic at
approximately 500oC (Genuino et al., 2022).
Figure 2 shows the appearance of pyrolytic distilled products (PDO), revealing
a strong dependence on the applied distillation temperature. A total of six
samples (S1-S6) each with a volume of 10 ml, and subjected to different
pyrolysis and distillation temperature, were tested. The specific conditions
for each sample were 1) S1 pyrolyzed at 350 oC and distilled at 120 oC,
2) S2 pyrolyzed at 400 oC and distilled at 250 oC, 3) S3
pyrolized at 400 oC and distilled at 350 oC, 4) S4
pyrolyzed at 300 oC without distillation from the gasoline-like
port, 5) S5 pyrolyzed at 300 oC without distillation from the
diesel-like port, and 6) S6 pyrolyzed at 380 oC and distilled at 180 oC. Lower distillation temperature (<200 oC) led to the production
of products with bright colors, while higher temperature (>200 oC) produced a
yellowish hue. This observation was in line with the findings of a previous
report (Wiriyaumpaiwong and Jamradloedluk, 2017).