This document appears to be a project report submitted for the completion of an M.Tech degree in Petroleum Processing and Petrochemical Engineering. The report investigates the co-pyrolysis of brown salwood sawdust and high density polyethylene (HDPE) plastic to maximize yields of enhanced biofuels. It includes chapters on literature review, experimental design and optimization studies, results and discussion, and conclusions. The results section analyzes the effects of temperature and feedstock ratios on gas, aqueous, organic and solid yields using statistical modeling and analysis of variance.

1. 1
CO-PYROLYSIS OF SALWOOD
SAWDUSTAND HDPE
Project Report
SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR
THE AWARD OF DEGREE OF
M. TECH IN PETROLEUM PROCESSING AND PETROCHEMICAL
ENGG.
SUBMITTED BY
SANA PARVEEN
21PKMEA102
DEPARTMENT OF PETROLEUM STUDIES
ZAKIR HUSAIN COLLEGE OF ENGINEERING &
TECHNOLOGY
ALIGARH MUSLIM UNIVERSITY, ALIGARH
2021-2022

2. 2
ACKNOWLEDGEMENT
Nothing worth more than praising and acknowledging, at the very outset, the eternal
and immense benevolent of almighty Allah who endowed me with the power of intellect and
convergence.
I would like here to express our thankfulness to all those people who somehow
contributed to make my path towards the achievement of this modest work easier and, indeed
more enjoyable.
A special thanks goes to my supervisor ‘Dr. Saeikh Zaffar Hassan’ for all of the help and
insight that was offered for the CO-PYROLYSIS OF SALWOOD SAWDUST AND HDPE as
well as being very understanding during my graduate student career. He also helped to supply an
endless stream of motivation and knowledge my way when it was needed. I extend my profound
and sincere gratitude to sir for making every meeting a challenge for improvement. There was
nothing better than being face to face to enhance the potential. This work is as a result of all
discussions. I really appreciated their great patience, competence and availability. I would also
like to thank to all our faculty members.
I am extremely grateful to my seniors and special thanks to Mohd. Shahzar for their
endless help and my parents for their love, prayers, caring and sacrifices for educating and
preparing me for my great future. Finally, I ‘am deeply grateful to the Aligarh Muslim
University and particularly to the Department of Petroleum Studies, Z. H. College of
Engineering & Technology for providing an academic curriculum with research focus.

3. 3
DEPARTMENT OF PETROLEUM STUDIES
Z.H. College of Engineering &Technology
Aligarh Muslim University
ALIGARH
CERTIFICATE
CANDIDATE’S DECLARATION
This is to certify that the project report entitled “CO-PYROLYSIS OF
SALWOOD SAWDUST AND HDPE”, submitted to the DEPARTMENT OF
PETROLEUM STUDIES, Zakir Husain College of Engineering and Technology A.M.U.
Aligarh, by SANA PARVEEN, Faculty No. 21PKPM102 for the award of the degree of
Master of Technology in Petroleum processing and petrochemical
Engineering, is an original work carried out under the supervision of Dr. S. J. A. Rizvi, Mr.
Mohammad Yusuf Ansari, Dr. Saeikh Zaffar Hassan, and Dr. Iftekhar Ahmad, , .
The matter embodied in this dissertation report has not been submitted by me & others
for the award of any other Degree / Diploma
----------------------------
(Signature of candidate)
SANA PARVEEN
SUPERVISOR’S CERTIFICATE
This is to certify that the above statement made by the candidate is correct to the best of my knowledge.
Date:
Place: Aligarh ……………………………...
(Supervisors)

4. 4
Table of Contents
Chapter Title Page No.
List of Figures 7
List of Tables 6
Abstract 8
1 Introduction
1.1 Biomass to Energy
1.2 Co-Pyrolysis of Biomass
9
9
9
2 Literature review 12
3 Model Development
3.1 Experimental design and optimization studies
3.1.2 Pyrolysis products characterization
15
15
17
4 Results and Discussion
4.1 ANOVA Model
Gas yield
4.1.2 Effect of Temperature on gas yield
4.1.3 Effect of HDPE content on gas yield
Aqueous
4.2.1 Effect of Temperature on aqueous yield
Organic yield
4.3.1 Effect of Temperature on organic yield
4.3.2 Effect of HDPE content on organic yield
Solid yield
4.4.1 Effect of Temperature on solid yield
19
19
23
23
24
26
26
28
28
31
33
33

5. 5
4.4.2 Effect of HDPE content on solid yield 35
5 Conclusion 41
References 43

6. 6
List of Tables
S.No Title Page
No.
1 Coded and actual levels of variables considered for the
design
16
2 An array of the CCD design for co-pyrolysis experiments
and product yields
17
3 ANOVA results for gas yield 19
4 ANOVA results for gas aqueous yield 20
5 ANOVA results for gas organic yield 21
6 ANOVA results for gas solid yield 22

7. 7
List of Figures
S.No.
Title Page
No.
1 Effect of Temperature on Gas yield 23
2 Effect of HDPE content on Gas yield 24
3 Effect of Temperature on aqueous yield 26
4 Effect of Temperature on organic yield 28
5 Effect of HDPE content on organic yield 31
6 Effect of Temperature on solid yield 33
7 Effect of HDPE content on solid yield 35

8. 8
ABSTRACT
Co-pyrolysis of Brown salwood sawdust with waste plastics (high density polyethylene
(HDPE)) for maximum yield of enhanced biofuels has been investigated. Main and interaction
effects of two effective co-pyrolysis parameters (pyrolysis temperature, feedstock wt.%) on
bio-oil, char and gas yields were also modeled, respectively. Optimization studies using central
composite experimental design were performed in Design Expert® Version 12 software. to
predict the optimal conditions of co-pyrolysis parameters for maximum yield of enhanced
biofuels. Analysis of variance was carried out to determine whether the fit of multiple
regressions was significant for second order models. Compositions of bio-oils and chars from
the pyrolysis of Brown salwood sawdust, HDPE and their mixtures at different blending ratios.
Results of products’ analysis revealed that synergistic effect of HDPE during co-pyrolysis
which led to enhanced brown salwood sawdust pyro-oil. Statistical analysis’ results unveiled
that feedstock ratio, pyrolysis temperature significantly influenced pyro-oil and char yield
rates.

9. 9
1.INTRODUCTION
1.1 Biomass to Energy
Recently, the constant increase in energy demand due to population and economic growth and
industrial productivity advancement has led to an increase in the utilization of commercial
fuels, which is the main cause of emissions of carbon dioxide and other greenhouse gases, thus
affecting global warming. This phenomenon has prompted increasing research on the
sustainability of alternative energy, which plays a role in super-clean energy production and
sustainable energy development to ensure the future energy supply, thereby possibly reducing
the fossil fuel demand. Among the representative alternative energy sources, post-harvest
biomass and agricultural waste are rapidly increasing in use worldwide and are considered
clean energy feedstocks; the biomass obtained from harvesting (Mantilla et al., 2014; Charusiri
and Vitidsant, 2018).
ng and the waste residuals acquired from industrial processing are especially promising, as
both are valuable energy feedstock candidates for clean fuel production and sustainable energy
development. The large amounts of biomass residuals that remain after harvesting or that are
generated during biomass production represent zero-net carbon emissions and have received
increasing attention worldwide because they could mitigate the effects of greenhouse gas
emissions and global warming (Moralı et al., 2016). Biomass can be regenerated within a short
period, is widely available from agricultural harvesting, and has high potential as a renewable
feedstock for clean energy production. Biomass and its residuals can be converted through
several procedures, such as thermochemical, biological, and physicochemical methods
(Mantilla et al., 2014; Charusiri and Vitidsant, 2018).
1.2 Pyrolysis of Biomass
Pyrolysis is a promising thermochemical method for biomass conversion via the thermal
decomposition of lignocellulosic materials under an inert gas atmosphere in the absence of
oxygen. It involves thermal degradation of the complex molecular structures of a feedstock and
produces valuable pyrolytic, noncondensable, gaseous, aqueous or liquid organic compounds,
as well as solid char products and other chemicals depending on the process operation

10. 10
conditions and reactor type, which control the product distribution (Yakub et al., 2015; Lazzari
et al., 2016). However, a high temperature, high heating rate and short residence time might
result in many pyrolysis oil products with a complex composition of hydrocarbon-rich
substances, furans, phenolics and value-added chemicals that have a higher calorific value than
the raw biomass (Luz et al., 2018; Saikia et al., 2015; Varma et al., 2019). Unfortunately, due
to certain limitations, pyrolysis oil cannot be directly utilized as a commercial engine fuel
because of its high acidity, corrosiveness, low gross calorific heating value, and thermal
instability (Wang et al., 2009; Charusiri and Numcharoenpinij, 2017; Varma and Mondal,
2017). Upgrading this bio-oil is a candidate process that involves the use of active catalysts
and produces a diesel-grade refined fuel similar to commercial diesel fuel. The liquid organic
phase exhibits a high gross calorific heating value and can be directly applied as a fuel oil in
internal combustion engines or small power generation units without upgrading; moreover, a
small amount of noncondensable gases can be used as a synthetic gas (Betemps et al., 2017),
which can be utilized as a startup fuel and fed into the thermochemical process of the pyrolysis
reaction (Charusiri and Vitidsant, 2017; Ding et al., 2018).
Fast pyrolysis mostly produces several noncondensable gases, biochar, and bio-oil from
abundant lignocellulosic materials depending on the material composition, the process
conditions and the type of reactor used (Ly et al., 2013; Luo et al., 2013; Sembiring et al., 2015;
Betemps et al., 2017). In general, most organic phases of bio-oil contain numerous oxygenated
compounds with complex structures as well as furans, aldehydes, furfurals, ketones, phenols,
and certain carbohydrate derivative compounds, while saturated and unsaturated hydrocarbons
might be obtained under suitable process conditions, such as catalytic dehydrogenation or co-
pyrolysis (Sembiring et al., 2015; Lazzari et al., 2016; Betemps et al., 2017; Ding et al., 2018).
Furthermore, the produced solid char has a relatively high carbon content due to the
devolatilization of the lignocellulosic material and the secondary cracking of tar; therefore, its
gross calorific heating value is also outstanding (Wang et al., 2009; Saikia et al., 2015; Tang et
al., 2019). Lignocellulosic materials consisting of hemicellulose and cellulose can be converted
via thermochemical processes to obtain an elevated yield of liquid products and valuable
chemical compounds in an oxygen-free atmosphere. Plastics generally contain numerous
hydrogen atoms and almost no oxygen atoms in their structure. High-density polyethylene
(HDPE) contains hydrogen-rich components, up to approximately 80 wt%, which can be
readily decomposed via thermochemical reactions into short-chain hydrocarbons and can
donate hydrogen to the biomass to balance the oxygen, carbon, and hydrogen percentages in

11. 11
the feedstock, leading to improvements in the bio-oil quality (Dijan et al., 2016; Çepeliogullar
et al., 2013; Xue et al., 2015). Additionally, these results indicate that compared to the classic
biomass pyrolysis reaction, the presence of a plastic material promotes the decomposition of
lignocellulosic materials, thus enhancing the decomposition of both the biomass residue and
the plastic material to increase the bio-oil content and improve its properties, resulting in higher
aromatics compared with the pyrolysis oil obtained from biomass only (Çepeliogullar et al.,
2014; Zhang et al., 2015, 2016; Ly et al., 2016; Johansson et al., 2018). To enhance the
production of aromatic compounds, cofeeding hydrogen-rich feedstock such as alcohols,
polymers, and hydrogen-rich compounds, which have high H/C ratios, has been recommended
to produce appropriate and sustainable liquid fuels, improve the oil yield and/or upgrade the
quality of the bio-oil produced to a level more similar to that of engine fuel.
This work demonstrates the co-pyrolysis of HDPE, which is a candidate waste plastic, and
Acacia mangium W. sawdust, a candidate lignocellulosic material. Both the HDPE and sawdust
were crushed, sieved and homogeneously mixed as candidate feedstocks through the use of a
custom-built pyrolizer with in situ improvements in the produced high-value chemicals at
various lignocellulosic material to-HDPE ratios to determine the influence of the process
operating parameters on the product yield and characterization. Mixing waste plastic with
lignocellulosic material has been widely studied, and it has been reported that the thermal
decomposition of waste plastic during the initial stage of temperature increase effectively
increases the heat transfer to the feedstock, i.e., both the biomass and waste plastic, thereby
generating a hydrocarbon-rich product, a hydrocarbon-rich bio-oil phase (Sebesty´en et al.,
2017; Burra et al., 2018; Ephraim et al., 2018; Wang et al., 2019a,b). During co-pyrolysis,
HDPE can be used as an abundant hydrogen donor to biomass due to its high effective
hydrogen-to-carbon ratio that balances the oxygen, carbon, and hydrogen percentages in the
feedstock, leading to a synergistic effect that upgrades the bio-oil quality. Therefore, the aim
of the present investigation was to determine the product yield in terms of the solid product
distribution, whereas the content of noncondensable gaseous compounds was calculated by
taking the difference. This investigation examines the influence of the composition of HDPE
and brown salwood sawdust as a lignocellulosic material mixture in a custom-built fixed-bed
reactor under various process conditions, including different temperatures (500–650 ◦C),
nitrogen flow rates (40–160 mL/min−1) and lignocellulosic material-to-HDPE ratios (0.1–0.5).

12. 12
2.LITERATURE REVIEW
Co-pyrolysis has a unique characteristic known as the blending ratio of raw materials. This
crucial characteristic, according to several academics, has a significant impact on co-pyrolysis
product yields, particularly in terms of quantity looked at the co-pyrolysis process of wood
biomass with a synthetic polymer mixture, and it was discovered that the most important
characteristic for liquid production is the feed mixing ratio. Abnisa and Daud (4) investigated
the co-pyrolysis of palm shells and polystyrene waste mixes for liquid fuel production. Chen
et al. (2) used py-GC/MS to show that the compositions and mass feed ratios of the components
(waste newspaper (WP) and HDPE) in the mixture affect not only product yields and
distributions, but also the properties of the various oils produced from the fast co-pyrolysis
process at different mass feed ratios (at varied mass feed ratios, the characteristics of the various
oils generated by the rapid co-pyrolysis process.
Many studies on biomass co-pyrolysis with plastics have shown that temperature is an
important operating parameter that may vary between 400 and 600 degrees Celsius to maximize
oil production during the co-pyrolysis process. The ideal temperature necessary to achieve the
maximum oil yield, according to Velghe et al. (3) and many other researchers, is based on the
qualities of the feedstock Paradela et al.(5) found that increasing the reaction temperature
reduces liquid yields while increasing gaseous compounds, owing to a rise in reaction
temperature that favoured their cracking processes, changing longer and heavier molecules into
shorter and lighter one’s molecules that are smaller.(.Rehman et al.) found that plastic (HDPE)
does not decompose entirely, at 450 ⁰C and it produce lowest liquid yield of 16.6 wt% for pine
to HDPE ratio of 0/100. When the temperature is increased from 450 ̊C to 500 ̊C, the pyrolysis
liquid yield increases from 16.7% to 30.5 wt% for the pine-to-HDPE ratio of 0/100 as given in
figure 6 and then decreases from 30.5 wt% to 20.5 wt% as temperature increases from 500 ̊C
to 550 ̊C due to further cracking.
However, few have worked on the co-pyrolysis of HDPE and biomass at different temperature
and wt.% for improving organic yields. They revealed that varying parameters such as
temperature and composition effect on yield. It was observed that the optimal pyrolysis
conditions for the lignocellulosic biomass material obtained from the brown salwood sawdust
with HDPE included a pyrolysis temperature of 600 ⁰C, an HDPE-to-brown salwood ratio of

13. 13
0.7, and a nitrogen flow rate of 120.00 mL.min−1
. They showed that synergistic effects occurred
from 500 to 550 ◦C, leading to an obvious increase in the liquid oil yield and a decrease in the
gas yield in comparison to the theoretical values. The product distribution revealed that the
synergistic effects of the co-pyrolysis of lignocellulosic biomass with plastic waste promoted
the generation of liquid products, which consisted of liquid fuels and valuable chemicals. The
determined bio-oil and chemical properties were improved compared with those of the
pyrolysis of biomass alone. In addition, bio-oil derivatives consisting of several chemicals and
aliphatic and aromatic hydrocarbons, including furan derivatives, phenols, and oxygenated
compounds, are valuable products that can be precursors for diesel-like fractions due to the
presence of C13 to C26 hydrocarbon compounds that enhance the fuel properties in the bio-oil
(Charusiri and Vitidsant, 2017; Ding et al., 2018).
Different researches have shown that using carrier gases (nitrogen, argon, helium, hydrogen,
ethylene, propylene, etc.) in the pyrolysis/co-pyrolysis process has a substantial effect on liquid
production. As a result, optimum inert gas flow rate adjustment is essential for maximizing oil
yield during the pyrolysis or co-pyrolysis process. However, it has been discovered that a high
inert gas flow rate actually reduces total oil output. The use of inert gas is obviously depending
on the reactor type.

14. 14
PROBLEM STATEMNT
Analysis and development of model for co-pyrolysis of salwood sawdust and HDPE using
design of experiment techniques to study the effects of co-pyrolysis parameters (like
temperature and feedstock ratios) on the yield of various co-pyrolysis products.

15. 15
3.MODEL DEVELOPMENT
3.1 Experimental design and optimization studies
The effect of three effective co-pyrolysis process parameters (i.e., HDPE mass percentage in
the feedstock, pyrolysis temperature) on the products’ yield was also investigated in this study.
Thus, a central composite design (CCD) with the three independent process variables and three
levels (±β, ±1, 0) including six replicates at the central points, were used to design the
experiments. The CCD, which was first described by Box and Wilson in 1951 and improved
upon by Box and Hunter, is nowadays the most popular class of designs used for fitting second-
order models (Aslan 2007; Montgomery 2006). The response variables measured during the
pyrolysis process were the bio-oil, bio-char and gas yield rates. Estimation of the error sum of
squares was performed with the six replicates (i.e., Figure 1 Schematic diagram of the fixed
bed co-pyrolysis apparatus.
The experiments were randomized in order to maximize the effects of unexplained variability
in the observed responses due to extraneous factors. The coded and actual levels of the process
variables considered for the design in this study is presented in Table 2. The experimental plan,
generated using the Design-Expert Version 12 software (Stat-Ease Inc., Minneapolis, USA),
along with the results, is presented in Table 3. Analysis of variance (ANOVA) was employed
to analyze, statistically, the experimental data while the multiple linear regression analysis was
performed to fit a quadratic polynomial model as indicated in Eq.
Y = βₒ + βі (Xі) + βіі (X2і) + βіј (XіXј) + βііі (Xі)3 + βііј (Xі2 Xј) + βіјј (Xі X2ј)
The symbols stand for the model’s intercept (βₒ), linear (βі) quadratic (βіі and βіј), and cubic
(βі іі, βііј and βіјј) intraction coefficients. where Y is the anticipated response (pyrolyzate
yield); Xі and Xј; are the independent factors of temperature and PE proportion, respectively.
Where Y (which can be either Ybio-oil, Ychar or Ygas) represents the response variables (for
pyrolysis oil, bio-char and gas yields, respectively); Xi or Xj denotes the independent variable
(i.e. the experimental factors); while β0, βi βii and βij depict the intercept, linear, quadratic
and interaction coefficients of the model, respectively. The experiments were randomized in
order to maximize the effects of unexplained variability in the observed responses due to

16. 16
extraneous factors. The coded and actual levels of the process variables considered for the
design in this study is presented in Table 2. The experimental plan, generated using the Design-
Expert Version 12. software (Stat-Ease Inc., Minneapolis, USA), along with the results, is
presented in Table 3. Analysis of variance (ANOVA) was employed to analyze, statistically,
the experimental data while the multiple linear regression analysis was performed to fit a
quadratic polynomial model.
The experimental factors (i.e., HDPE mass percentage in the feedstock (mass ratio), pyrolysis
temperature (°C) is denoted in this study by the following symbols: A, B respectively. The
responses were thus evaluated as the sum of a constant, two first-order main effects (i.e., terms
in A, B), interaction effects (i.e AB, AB2
, & A2
B2
), and second-order effects (A2
, B2
),
respectively, based on Equation The optimal co-pyrolysis process conditions for maximum
bio-oil yield and minimum yields of char and gas were then identified using the numerical
optimization function of Design Expert®Version 12.
Table 1. Coded and actual levels of variables considered for the design.
FACTORS LOW (-1) CENTER (0) HIGH (+1)
HDPE (Wt.% in the feed stock) 10%
30%
50%
Pyrolysis temperature (°C) 550 600 650

17. 17
3.2 Pyrolysis products characterization
Relative compositions of chemical compounds in the bio-oils obtained from the pyrolysis of
samples of HDPE and Biomass mixtures at different feed ratios were determined through gas
chromatography-mass spectrometry (GC/MS) analysis technique.
The maximum gas yield was obtained (60.06 wt%) at a temperature of 650 ⁰C and 10% HDPE
content and maximum organic yield, aqueous, solid were obtained (38.82 Wt.%) at a
temperature 650 ⁰C and 30% HDPE content, (22.13 Wt.%) at a temperature 550 ⁰ C and 50%
HDPE content and (14.4 Wt.%) at a temperature 550 and 10% HDPE content.
Table 2. An array of the CCD design for co-pyrolysis experiments and product yields.
Std Run FACTOR1
TEMPERATURE
(deg. C)
FACTOR 2
HDPE:
BIOMASS
(mass ratio)
RESPONSE 1
(Gas yield)
(Wt.%)
RESPONSE 2
(Aqueous)
(Wt.%)
RESPONSE 3
(Organic)
(Wt.%)
RESPONSE 4
(Solid)
(Wt.%)
6 1 650 0.3 50.26 6.58 38.82 6.1
12 2 600 0.3 42.7 13.33 35.1 7.72
11 3 600 0.3 42.7 13.33 35.1 7.72
2 4 650 0.1 60.06 11.28 18.95 9.71
3 5 550 0.5 39.16 22.13 31.41 8.56
13 6 600 0.3 42.7 13.33 35.1 7.72
10 7 600 0.3 42.7 13.33 35.1 7.72
1 8 550 0.1 39.16 22.13 24.3 14.4
8 9 600 0.5 42.03 21.46 35.66 8.31
5 10 550 0.3 39.78 20.25 31.41 8.64
9 11 600 0.3 42.7 13.33 35.1 7.72

18. 18
4 12 650 0.5 60.06 11.28 35.66 4.43
7 13 600 0.1 42.03 21.46 25.14 11.38
14 14 600 0.3 42.7 13.33 35.1 7.72

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4.RESULTS AND DISCUSSION
4.1 ANOVA table
In this case P- Value less than 0.0500 indicate model terms are significant in this case effect of
model A, A2
, AB2
, A2
B2
, are significant model terms, all value for model is less than 0.1000
indicate the model terms are significant.
Table 3. ANOVA results for gas yields.
Source
Sum of
Squares Df Mean squares F-value P-Value
Model 625.33 5 125.07 1485.89 < 0.0001 significant
A-Temperature 54.92 1 54.92 652.44 < 0.0001
B-HDPE:Biomass 0 1 0 0 1
A² 9.9 1 9.9 117.62 < 0.0001
AB² 36.19 1 36.19 429.99 < 0.0001
A²B² 28.09 1 28.09 333.74 < 0.0001
Residual 0.6734 8 0.0842
Lack of Fit 0.6734 3 0.2245
Pure Error 0 5 0
Cor Total 626 13

20. 20
Table 4 ANOVA results for aqueous yields.
Source
Sum of
squares Df
Mean
squares
F-
Value P-Value
Model 322.28 3 107.43 403.61 < 0.0001 significant
A-Temperature 208.51 1 208.51 783.38 < 0.0001
B² 105.2 1 105.2 395.26 < 0.0001
A²B² 30.15 1 30.15 113.26 < 0.0001
Residual 2.66 10 0.2662
Lack of Fit 2.66 5 0.5323
Pure Error 0 5 0
Cor Total 324.94 13

21. 21
Table 5. ANOVA results for pyro oil (organic) yields.
Source
Sum of
squares Df.
Mean
squares F-Value
P-
Value
Model 406.55 6 67.76 736.09 <0.0001 significant
A-Temperature 27.45 1 27.45 298.24 <0.0001
B-HDPE:Biomass 196.54 1 196.54 2135.07 <0.0001
AB 23.04 1 23.04 250.29 <0.0001
B² 35.4 1 35.4 384.57 <0.0001
AB² 21.12 1 21.12 229.44 <0.0001
A²B² 10.6 1 10.6 115.19 <0.0001
Residual 0.6444 7 0.0921
Lack of Fit 0.6444 2 0.3222
Pure Error 0 5 0
Cor Total 407.2 13

22. 22
Table 6. ANOVA results for bio-char (Solid) yields.
source
Sum of
squares Df
Mean
squares
F-
Value
P-
value
Model 66.58 3 22.19 56.51 < 0.0001
significant
A-Temperature 21.51 1 21.51 54.76 < 0.0001
B-HDPE:Biomass 33.56 1 33.56 85.44 < 0.0001
B² 11.51 1 11.51 29.31 0.0003
Residual 3.93 10 0.3928
Lack of Fit 3.93 5 0.7855
Pure Error 0 5 0
Cor Total 70.51 13

23. 23
4.1.1 Effect of Temperature on Gas yield
at 10 wt.% HDPE
at 30 Wt.% HDPE

24. 24
at 50 wt.% HDPE
Figure No 1. Effect of temperature on gas yield (wt.%)
4.1.2 Effect of HDPE content on Gas yield
at 550⁰C.

25. 25
at 600⁰C.
at 650 ⁰C.
Figure No 2. Effect of HDPE content on gas yield (wt.%)

26. 26
4.2.1 Effect of Temperature on Aqueous yield
at 10 wt.% HDPE.
at 30 wt.% HDPE.

27. 27
at 50 wt.% HDPE.
Figure No 3. Effect of temperature on aqueous yield (wt.%)

28. 28
4.2.2 Effect of temperature on organic yield
Figure No 4. Effect of temperature on organic yield (wt.%)
at 10 wt.% HDPE.
at 30 wt.% HDPE

29. 29

30. 30

31. 31
4.3.1 Effect of HDPE content on Organic yield
at 550⁰ C
at 600⁰C

32. 32
at 650 ⁰C
Figure No 5 Effect of HDPE content on organic yield (wt.%)

33. 33
4.4.1 Effect of temperature on solid yield
at 10 wt.% HDPE
at 30wt.% HDPE

34. 34
at 50 wt.% HDPE
Figure No 6. Effect of temperature on solid yield (wt.%)

35. 35
4.4.2 Effect of HDPE content on Solid yield
at 550 ⁰C
at 600⁰C

36. 36
at 650⁰C
Figure No 7 Effect of HDPE content on solid yield (wt.%)

37. 37
3D Surface for Gas yield
3D Surface for Aqueous yield

38. 38
3D Surface for Organic (Oil) yield
3D Surface for Solid yield

39. 39
Optimal conditions for maximum production of bio-oil were obtained as a temperature of 650
⁰C with 30% mass of HDPE in the feedstock which gave the maximum predicted pyro-oil yield
of 38.82wt.% (Table 3). Results of statistical analysis revealed that the HDPE mass percentages
in the feedstock mixture, pyrolysis temperature significantly influenced the pyro-oil yield rates
during the co-pyrolysis process. Besides, the 3D surface graphs (Figure 4) shows the interaction
effects of the experimental factors on oil yield rates. It can also be observed that the interaction
of HDPE wt.% in the feedstock with pyrolysis temperature respectively, posed almost similar
effects on oil yield rates when compared with their individual main effects on oil yield rates.
Thus, the oil yield rate was noticed to increase with a in HDPE 30wt.% in the feedstock
mixtureuntil an optimal oil peak of 38.82 wt.% occurred with 30% of HDPE in the feedstock
mixture, a temperature of 650⁰C. Likewise, from (Figure 4,5) table 2, it can also be observed
that the interaction effects of HDPE and temperature on oil yields led to an increase in the oil
yield rate provided that the temperature is neither extremely high nor extremely low. Similarly,
Thus, the results of this present study also agreed with that of Hu et al. (2017) that increasing
the percentage HDPE of the co-feeding elements of higher carbon and hydrogen contents in
the feedstock could lead to an increase in both quantity and quality of the produced bio-oils but
with varying magnitudes of effects owing to the structure and compositions of the biomass type
employed during the process, and subsequently its thermal behaviours. The fitness of the
developed model is acceptable significant (P < 0.0001). Thus, the results of statistical analysis
revealed that all the two experimental factors influenced the rate of production of the co-pyro-
oil. The maximum pyro-oil yield (38.82wt.%) was obtained when the feedstock blend contains
about 30% of HDPE in the feedstock at an optimum temperature of 650°C during the
optimization study.
Pyrolysis gas, most especially from polymers, serves as a potential source of fuel as it contains,
in most cases, high concentrations of methane and ethane. Likewise, it has been acknowledged
by several authors that the yield of gas from biomass pyrolysis and co-pyrolysis is about 10–
30% by weight, and that biomass pyrolysis gases are promising sources of fuels (Laresgoiti
2000; Nkosi and Muzenda 2014). Similarly, it has been also observed that the non-condensable
pyrolysis gas yield increases slightly as the vapour residence time increases due to the
decomposition of some oil vapours into secondary non-condensable gases during pyrolysis,
most especially, of plastic and tyre materials, however, the liquid and char yields decrease as
the vapour residence time increases owing to secondary decomposition reactions (Laresgoiti
2000; Nkosi and Muzenda 2014). Thus, in this present study, the effects of co-pyrolysis

40. 40
parameters on the gas yield rates have also been investigated. The regression model for the gas
yield during the co-pyrolysis process of waste brown salwood sawdust and plastic waste
(HDPE). The statistical model evaluation parameters obtained from the model ANOVA are
presented in Table 3 The fitness of the developed model is acceptable significant (P < 0.0001).
Thus, the results of statistical analysis revealed that all the two experimental factors influenced
the rate of production of the co-pyrolysis gases. The maximum co-pyrolysis gas yield
(60.06wt.%) was obtained when the feedstock blend contains about 10% of HDPE in the
feedstock at an optimum temperature of 650°C during the optimization study. It was also
observed that increasing the temperature beyond 650°C resulted in production of more gases
than bio-oil due to secondary decomposition of oil vapours into non-condensable gases.

41. 41
5. CONCLUSIONS
The optimal pyrolysis conditions for the lignocellulosic biomass material obtained from the
brown salwood sawdust with HDPE included a pyrolysis temperature of 650 ⁰C, and 30%
HDPE. The results showed that synergistic effects occurred at 650⁰C, leading to an obvious
increase in the liquid oil yield and a decrease in the gas yield in comparison to the theoretical
values. The product distribution revealed that the synergistic effects of the co-pyrolysis of
lignocellulosic biomass with plastic waste promoted the generation of liquid products, which
consisted of liquid fuels. The determined bio-oil and chemical properties were improved
compared with those of the pyrolysis of biomass alone. In addition, the main and interaction
effects of two effective co-pyrolysis parameters (pyrolysis temperature, HDPE ratio), on pyro
oil, char, and gas yields were modelled respectively, and optimization studies using central
composite experimental design were performed in Design Expert® Version 12 software to
predict the optimal conditions of the co-pyrolysis parameters for maximum yield of enhanced
biofuels The effects and significance of the models on the responses (i.e., bio-oil, char and gas)
were evaluated using analysis of variance, model evaluation statistical parameters and response
surface curves. Results of experiments revealed that all the co-pyrolysis parameters
significantly affected the responses Also experiments revealed that the oil yield rates increased
as the mass percentage of HDPE in the blend increases up to 30 wt.% and the reverse trend is
true for char production, while the results of the prediction indicated that the maximum oil
yield as well as minimum char and gas yields were obtained at the optimal co-pyrolysis
conditions of 650⁰C with 30% HDPE in the feedstock.
This study also indicated the existence of a synergistic effect during the co-pyrolysis as it can
be easily observed from the results of the co-pyrolysis products analysis/characterization that
further unveiled the existence of interactive synergy, which does not only enhance the products
yield but also their quality. This piece of relevant research work differs from other studies in
the literature as it is the first research work that focused on the modeling, of the effects of co-
pyrolysis conditions/parameters for co-pyrolysis of brown salwood sawdust biomass and waste
plastic for maximum production of enhanced biofuels. Besides, the results of this present study
also agreed with that of Hu et al. (2017) that increasing the percentage mass of the co-feeding
elements of higher carbon and hydrogen contents in the feedstock blends could lead to an
increase in both quantity and quality of the produced bio-oils but with varying magnitudes of

42. 42
effects owing to the structure and compositions of the biomass type employed during the
process, and subsequently its thermal behaviours.Thus the optimization of the co-pyrolysis
process of brown salwood sawdust biomass and waste plastics becomes relevant as it does not
only result in production of enhanced biofuels but also in reduction of waste disposal problems.

43. 43
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