Utilization of Modified Waste Staghorn Coral As a Base Catalyst in Biodiesel Production

UTILIZATION OF MODIFIED WASTE STAGHORN CORAL AS A BASE CATALYST IN BIODIESEL PRODUCTION

NABILAH ATIQAH BINTI ZUL

UNIVERSITI SAINS MALAYSIA 2019 UTILIZATION OF MODIFIED WASTE STAGHORN CORAL AS A BASE CATALYST IN BIODIESEL PRODUCTION

NABILAH ATIQAH BINTI ZUL

Thesis submitted in fulfilment of the requirements for the degree of Master of Science

May 2019

ACKNOWLEDGEMENT

In the Name of Allah, the Most Gracious and the Most Merciful

Alhamdulillah, all praises to Allah for the strengths and His blessings during the course of this research. First and foremost, a special thanks to my supervisor, Dr.

Mohd Hazwan Hussin and my co-supervisor, Dr Shangeetha Ganesan for their guidance, encouragement, comment, advices and dedicated supervision throughout the experimental and thesis works.

Besides, a special gratitude I give to all the staff members of School of

Chemical Sciences, Universiti Sains Malaysia especially laboratory assistants and science officers for their help upon completing my research project. I would like to show my sincere appreciation for Universiti Sains Malaysia for the financial support of this research through USM Short Term and Bridging Grants -

304/PKIMIA/6313216 and 301/PKIMIA/6316041.

I also immensely grateful to all my lab mates especially Nur Hanis Abd Latif,

Caryn Tan Hui Chuin, Nurul Adilla Rozuli, Nurmaizatulhanna Othman and Tuan

Sherwyn Hamidon for their moral supports and opinions throughout the course of my master studies. I would like to express my deepest gratitude to my beloved parents and siblings for keep supporting me and encouraging me with their best wishes until

I able to finish this thesis. Last but not least, thanks to all individuals that directly or indirectly contributed in my master project. Your contributions and kindness means a lot to me. Thank you very much

TABLE OF CONTENTS

Acknowledgement …………………………………………………………….. ii

Table of Contents …………………………………………………………...... iii

List of Tables ………………………………………………………...... vii

List of Figures ………………………………………………………...... viii

List Schemes …………………………………………………………...... x

List of Abbreviations …………………………………………………...... xi

List of Symbols ………………………………………………………...... xiii

Abstrak ……………………………………………………………...... xiv

Abstract ……………………………………………………………...... xv

CHAPTER 1 – INTRODUCTION 1

1.1 Background of the study…………………………………………...... 1

1.2 Problem statement ……………………………………………………... 2

1.3 Research objectives ……………………………………………………. 4

1.4 Scope of study………………………………………………………….. 4

CHAPTER 2 – LITERATURE REVIEW 6

2.1 Biodiesel ……………………………………………………………….. 6

2.2 Advantages of biodiesel ……………………………………………….. 8

2.3 Raw materials …………………………………………………...... 11

2.4 Methods of biodiesel production ………………………………………. 14

2.4.1 Direct use and blending …………………………………...... 14

2.4.2 Microemulsion ……………………………………………...... 16

2.4.3 Thermal cracking (pyrolysis) ……………………………...... 17

iii

2.4.4 Transesterification ……………………………………………... 19

2.5 Catalysts ……………………………………………………………….. 21

2.5.1 Enzyme catalysts (biocatalysts) …………………………...... 23

2.5.2 Homogeneous acid catalysts ……………………………...... 24

2.5.3 Homogeneous base catalysts ……………………………...... 24

2.5.4 Heterogeneous acid catalysts ………………………………...... 25

2.5.5 Heterogeneous base catalysts ………………………………….. 28

2.6 Staghorn coral …………………………………………………………. 33

CHAPTER 3 – MATERIALS AND METHODS 37

3.1 Materials and chemicals ……………………………………………….. 37

3.2 Characterization of oils ………………………………………………… 37

3.2.1 Determination of the moisture content ……………………….... 37

3.2.2 Determination of the acid value ………………………………... 38

3.2.3 Determination of the saponification value ……………………... 38

3.3 Preparation of the catalysts …………………………………………….. 39

3.3.1 Preparation of calcium oxide catalyst (CSC) ………………….. 39

3.3.2 Preparation of KOH impregnated staghorn coral catalyst (K- 40 CSC) ……………………………………………………………

3.4 Characterization of the catalysts ……………………………………….. 40

3.4.1 Basic strength analysis ………………………………………..... 40

3.4.2 Basicity analysis ……………………………………………….. 41

3.4.3 X-ray fluorescence (XRF) analysis ……………………………. 41

3.4.4 BET-N2 adsorption analysis ……………………………………. 42

3.4.5 Attenuated total reflectance-Fourier transforms infrared (ATR- 42 FTIR) analysis ………………………………………………….

3.4.6 Scanning electron microscopy (SEM) analysis ……………….. 42

3.4.7 X-ray diffraction (XRD) analysis ……………………………… 43

3.4.8 Thermal gravimetric analysis (TGA)…………………………... 43

3.5 Transesterification ……………………………………………………... 43

3.6 Analysis of methyl esters ………………………………………………. 44

3.7 Reusability of K-CSC catalyst …………………………………………. 46

3.8 FFA and water tolerance of K-CSC catalyst …………………………... 46

CHAPTER 4 – RESULTS AND DISCUSSION 47

4.1 Characterization of biodiesel feedstock ………………………………... 47

4.2 Characterization of catalysts ………………………………………….... 49

4.2.1 Basic strength analysis …………………………………………. 49

4.2.2 Basicity analysis ……………………………………………….. 50

4.2.3 XRF analysis …………………………………………………… 51

4.2.4 BET-N2 adsorption analysis ……………………………………. 52

4.2.5 ATR-FTIR analysis ……………………………………………. 56

4.2.6 SEM analysis …………………………………………………... 58

4.2.7 XRD analysis …………………………………………………... 61

4.2.8 TG/DTG analysis ……………………………………………… 62

4.3 Optimization of staghorn coral catalyzed transesterification using RBD 64 palm olein as feedstock …………………………………………......

4.4 Optimization of K-CSC catalyzed transesterification using different 66 feedstocks ……………………………………………………………....

4.4.1 Optimization of K-CSC catalyzed transesterification using RBD 69 palm olein as feedstock …………………………………..

4.4.1(a) Effect of catalyst loading ……………………………. 69

4.4.1(b) Effect of reaction time ……………………………….. 70

4.4.1(c) Effect of methanol to oil molar ratio ………………… 71

4.4.2 Optimization of K-CSC catalyzed transesterification using 72 waste cooking oil as feedstock …………………………………

4.5 Proposed reaction mechanism ………………………………………... 76

4.6 Reusability of K-CSC catalyst ………………………………………… 78

4.7 FFA and water tolerance of K-CSC catalyst in transesterification …… 80

CHAPTER 5 – CONCLUSION AND FUTURE RECOMMENDATIONS 83

5.1 Conclusion ……………………………………………………………... 83

5.2 Future recommendations ………………………………………………. 84

REFERENCES ……………………………………………………………..... 85

APPENDICES

LIST OF PUBLICATIONS

LIST OF PRESENTATIONS

LIST OF TABLES

Page

Table 2.1 Physical properties of biodiesel (Demirbas, 2009a) 7

Table 2.2 Comparison of reaction conditions for different types of 27 heterogeneous acid catalyst

Table 2.3 Sources of CaO catalyst and their optimized conditions 30 during transesterification reaction

Table 4.1 Properties of RBD palm olein and WCO 47

Table 4.2 Basic strengths of the prepared catalysts 50

Table 4.3 Basicity values of the prepared catalysts 51

Table 4.4 Compositions of elements present in the prepared catalysts 52

Table 4.5 Physical properties of USC, CSC and K-CSC 53

Table 4.6 Transesterification of RBD palm olein using different CSC 66 catalyst loading of CSC (5-8 wt.%), reaction time (3-6 h) and methanol to oil molar ratio (12:1-21:1)

Table 4.7 Summary of overall results for transesterification reactions 68 of RBD palm olein and WCO

Table 4.8 Comparison of basic strength and basicity between fresh 79 and used K-CSC catalysts

vii

LIST OF FIGURES

Page

Figure 2.1 Comparison of the carbon intensity of biodiesels fuels 9 against fossil fuels (UK Department for Transport, 2008)

Figure 2.2 Molecular structure of diesel and biodiesel (Ge et al., 2017) 9

Figure 2.3 General cost breakdown for biodiesel production 12 (Lim and Teong, 2010)

Figure 2.4 Schematic structures of (A) water/oil biodiesel emulsion 16 and (B) oil/water/oil biodiesel emulsion (Lin and Lin, 2007).

Figure 2.5 Thermal cracking process (Rajalingam et al., 2016) 18

Figure 2.6 The difference between uncatalyzed and catalyzed 22 reactions

Figure 2.7 Illustration of general reaction in the presence of a catalyst 22

Figure 2.8 Living/healthy staghorn coral (Piehl and Atkins, 2006) 36

Figure 2.9 Dead/unhealthy staghorn coral (Piehl and Atkins, 2006) 36

Figure 3.1 Flowchart of the biodiesel production process 45

Figure 4.1 Nitrogen adsorption-desorption isotherms of (A) USC; (B) 55 CSC and (C) K-CSC

Figure 4.2 IR spectra of USC, CSC and K-CSC 58

Figure 4.3 SEM micrographs at magnification 2500x (A) USC; (B) 60 CSC and (C) K-CSC

Figure 4.4 XRD profiles of USC, CSC and K-CSC 62

Figure 4.5 Thermograms of (A) USC and (B) uncalcined K- 64 impregnated staghorn coral

Figure 4.6 GC chromatogram of methyl esters produced from 68 transesterification of RBD palm olein

Figure 4.7 GC chromatogram of methyl esters produced from 68 transesterification of waste cooking oil

viii

Figure 4.8 Effect of catalyst loading on biodiesel conversion 69

Figure 4.9 Effect of reaction time on biodiesel conversion 71

Figure 4.10 Effect of methanol to oil molar ratio on biodiesel 72 conversion

Figure 4.11 Transesterification of waste cooking oil using different (A) 75 catalyst loading (3-6 wt.%); (B) reaction time (3-6 h) and (C) methanol to oil molar ratio (15:1-24:1)

Figure 4.12 Methyl esters conversion using used K-CSC catalyst for 79 three reuse

Figure 4.13 Effect of FFA and water on transesterification of RBD 80 palm olein using K-CSC catalyst under optimum conditions of 4wt.% catalyst, 4 h reaction time and 15:1 methanol to oil molar ratio

Figure 4.14 Mechanism on effect of free fatty acids towards catalyst 80 during transesterification reaction (modified from Kouzu et al., 2008)

LIST OF SCHEMES

Page

Scheme 2.1 The basic transesterification reaction 19

Scheme 2.2 The saponification reaction 25

Scheme 4.1 Proposed reaction mechanism of transesterification of 77 triglycerides catalyzed by prepared K-CSC catalyst

Scheme 4.2 The hydrolysis reaction of triglycerides 82

LIST OF ABBREVIATIONS

ASTM American Society for Testing and Materials

ATR-FTIR attenuated total reflectance-Fourier transforms infrared

AV acid value

BET Brunauer-Emmett-Teller

BJH Barrett, Joyner and Halenda

CaO calcium oxide

CN cetane number

CO2 carbon dioxide

CSC calcined staghorn coral

DTG derivative thermogravimetric

FAME fatty acid methyl ester

FFA free fatty acid

GC-FID gas chromatography-flame ionization detector

GHGs greenhouse gases

GC-MS gas chromatography-mass spectrometry

H2O water

IUCN International Union for Conservation of Nature

K-CSC calcined KOH impregnated staghorn coral

KOH potassium hydroxide

ME methyl esters

RBD refined, bleached and deodorized

SEM scanning electron microscopy

SV saponification value

TGA thermal gravimetric analysis

USC uncalcined staghorn coral

WBD White Band Disease

WCO waste cooking oil

XRD x-ray diffraction

XRF x-ray fluorescence

xii

LIST OF SYMBOLS

°C Celcius

K Kelvin

B volume of hydrochloric acid solution used for blank sample

V volume of hydrochloric acid solution used for oil sample

V volume of potassium hydroxide

M molar concentration of hydrochloric acid

M molar concentration of potassium hydroxide

W weight of sample

H_ basic strength wt. weight w/w weight/weight

Vtot total pore volume

theta

total peak area of FAME

AISTD peak area of methyl heptadecanoate

CISTD concentration of methyl heptadecanoate

V ISTD volume of methyl heptadecanoate m mass of sample

T transmittence

xiii

PENGGUNAAN SISA BATU KARANG STAGHORN TERUBAH SUAI

SEBAGAI MANGKIN BES DALAM PENGHASILAN BIODIESEL

ABSTRAK

Kajian ini memfokuskan penghasilan pemangkin yang baharu bagi menghasilkan metil ester daripada trigliserida melalui tindak balas dengan metanol.

Pertamanya, kalsium oksida daripada batu karang staghorn telah dicirikan dan diaplikasi dalam proses transesterifikasi minyak olein sawit yang ditapis, dilunturkan dan dinyahbaukan, (RBD). Tindak balas tersebut hanya menghasilkan 62.1 ± 4.3 % metil ester. Oleh yang demikian, pengubahsuaian mangkin telah dilakukan dengan mengimpregnasi batu karang staghorn bersama kalium hidroksida, KOH sebagai usaha untuk meningkatkan lagi aktiviti pemangkinnya. Mangkin terubah suai (K-

CSC) kemudiannya telah digunakan sebagai mangkin bes dalam metanolisis minyak olein sawit RBD dan sisa minyak masak. Bagi transesterifikasi minyak olein sawit

RBD, keadaan tindak balas yang terbaik untuk mendapatkan 94.8 ± 0.5 % kandungan metil ester dicapai dengan 4 wt.% pemangkin, 4 jam masa tindak balas dan 15:1 nisbah molar metanol kepada minyak. Selain itu, pemangkin K-CSC juga telah berjaya mentransesterifikasikasi sisa minyak masak pada keadaan tindak balas

4 wt.% mangkin, 5 jam masa tindak balas dan 18:1 nisbah molar metanol kepada minyak dan menghasilkan 89.5 ± 4.8 % biodiesel. Penggunaan semula mangkin K-

CSC turut dikaji and malangnya, pemangkin tersebut mempunyai ciri-ciri penggunaan semula yang lemah. Kajian toleransi mangkin K-CSC terhadap asid lemak bebas (FFA) dan air mendedahkan keupayaannya yang lemah terhadap kehadiran asid lemak bebas dan air.

xiv

UTILIZATION OF MODIFIED WASTE STAGHORN CORAL AS A BASE

CATALYST IN BIODIESEL PRODUCTION

ABSTRACT

This work focuses on producing a novel catalyst to synthesize methyl esters from triglycerides by the reaction with methanol. Firstly, calcium oxide derived from staghorn coral was characterized and applied in the transesterification process of refined, bleached and deodorized, (RBD) palm olein. The reaction only yielded about

62.1 ± 4.3 % methyl esters. Therefore, a catalyst modification was carried out by impregnating the staghorn coral with potassium hydroxide, KOH as an effort to further enhance its catalytic effect. The modified catalyst (K-CSC) was then used as a base catalyst in the methanolysis of RBD palm olein and waste cooking oil. For

RBD palm olein transesterification, the best reaction conditions to obtain methyl esters content of 94.8 ± 0.5 % was found to be 4 wt.% catalyst, 4 h reaction time, and

15:1 methanol to oil molar ratio. Besides that, K-CSC catalyst also successfully transesterified waste cooking oil at the reaction conditions of 4 wt.% catalyst, 5 h reaction time and 18:1 methanol to oil molar ratio and produced 89.5 ± 4.8 % biodiesel. The reusability of K-CSC catalyst was also studied and unfortunately, the catalyst has poor reusability characteristic. The free fatty acid (FFA) and water tolerance analyses of K-CSC catalyst has revealed its poor ability to tolerate with free fatty acid and water presence.

CHAPTER ONE

INTRODUCTION

1.1 Background of the study

Nowadays, fossil fuel utilization as the main energy resource is no longer recommended due to its high price and negative impacts on the environment and human health. This problem can be alleviated by emphasizing the use of biodiesel.

Biodiesel is defined as fatty acid methyl ester (FAME) that is derived from the transesterification of vegetable oil/animal fat together with methanol and catalyst.

Biodiesel has become current worldwide interest in the search for effective and promising energy, which is mainly associated with its advantages such as renewable, biodegradable and environmental friendly. Malaysia, the second largest palm oil producer and exporter, has manufactured biodiesel from palm oil since several years ago. The process of exporting biodiesel to the main exporters (U.S and EU) had begun since 2006 (Applanaidu et al., 2009; Applanaidu et al., 2014).

Apart from palm oil, biodiesel can also be synthesized from several other types of feedstocks such as edible oils, inedible oils, waste oils and animal fats. 70-

95 % of the total biodiesel manufacturing costs arise from feedstock (Apostolakou et al., 2009). Waste oil and animal fat are the cheapest biodiesel feedstocks and their usage as feedstocks would lower the production cost. The cost of waste oil is approximately half the cost of virgin oil and it keeps gaining attention due to its renewability and availability. Meanwhile, for the selection of catalyst, heterogeneous

catalysts especially calcium oxide (CaO) is regarded as the most promising and practical catalyst. Interestingly, CaO can be easily derived from waste materials such as ostrich eggshell (Tan et al., 2015a), chicken eggshell (Tan et al., 2015a), shrimp shell (Yang et al., 2008) and others, where they consist of calcium carbonate as their main compound. Staghorn coral (Acropora cervicornis) is also a natural source of calcium. The major inorganic compound of coral is calcium carbonate (CaCO3) which degrades into CaO at very high temperature. Since Malaysia is surrounded by oceans, abundance of dead staghorn coral remnants can be easily found in the coastal areas. More importantly, the utilization of staghorn coral as catalyst not only helps in reducing the production cost but also promotes the environmental benign process.

The catalyst can be prepared by several methods such as thermal activation and wet impregnation methods. The main purpose of employing wet impregnation method is to further enhance the catalytic ability of the catalyst. Many researchers have tested impregnated alkali metal ions (Li+, K+, Na+) onto the catalyst surface (Boro et al.,

2014; Kataria et al., 2017) and found out that all the catalysts performed excellently during the alcoholysis process.

1.2 Problem statement

Due to the staggering growth of the world‟s population, the transportation sector as well as the industrial sector, the world is currently facing a very serious energy crisis where the energy usage has exceeded its production rate especially in developing countries. Besides food and water, energy is also one of the three most important basic needs for human survival (Zou et al., 2016). Currently, fossil fuels account for about 80 % of the world‟s energy needs (Huang et al., 2012). However, the use of fossil fuel has become a global issue as it emits greenhouse gases (GHGs)

especially carbon dioxide (CO2) into the air. This has led to global warming and air pollution, which in turn affect human health. Petroleum-based fuel vehicles are the main CO2 emission contributors as they are responsible for approximately 23 % of world CO2 emission (Saboori et al., 2014). Additionally, world‟s overall transport energy consumption and CO2 release are expected to increase by 80 % in 2030

(Saboori et al., 2014). Due to this, biodiesel has been chosen as the replacement and extender of fossil fuel. Nevertheless, the biggest barrier in biodiesel commercialization is the high cost of production, which is mainly associated with the biodiesel feedstock and catalyst.

The utilization of edible oils such as sunflower oil, rapeseed oil, palm oil, cottonseed oil and others as the raw materials are the main contributors that lead to higher cost. Viable solution to this issue is to use waste cooking oils or animal fats as biodiesel feedstock. In addition, most of the waste oils are simply discarded into the drains, rivers and sinks without further utilization and consequently resulting in water pollution. Besides that, a lot of efforts have been made in search for catalyst with good catalytic activity and at the same time being cheap, environmentally benign and readily available. Interestingly, staghorn coral (Acropora cervicornis) has been seen to meet all the criteria, making it a perfect choice as catalyst. This coral species thrive in the biodiverse waters of Malaysia especially in the east coast areas.

However, the corals are threatened by ocean acidification, high seawater temperature and human activities, causing slower coral growth rate, weakening of coral skeleton, coral bleaching and making them more susceptible to diseases. Due to that, dead staghorn corals are abundantly found along the seashores in many parts of Malaysia as they are washed ashore during strong tide. The dead corals might seem impotent

but they actually have a variety of uses. They are usually harvested for building materials, jewellery and aquarium but they also suitable to be used as catalyst in biodiesel production. In addition, the corals grow, die and endlessly repeat the cycle over time. This cycle of growth, death and regeneration ensure sufficient sources of dead corals.

1.3 Research objectives

In this research study, the process of biodiesel production was carried out via the transesterification of two different types of feedstocks using staghorn coral and

K-impregnated staghorn coral as catalysts. Therefore, the purposes of this study are:

1) To determine physicochemical properties of staghorn coral and K-

impregnated staghorn coral.

2) To determine the effects of different reaction variables, FFA and water

contents on the catalytic activity.

3) To study the reusability of K-impregnated staghorn coral.

1.4 Scope of study

The target of this study was to synthesize a low cost and green catalyst derived from dead staghorn coral. The aspects looked into were the effectiveness of prepared catalyst in biodiesel production, its characteristics (reusability, FFA and water tolerance) and effect of reaction parameters on its activity. The research has reached its aims but there were some limitations faced in this study and they are:

1) Some testing were done in other places. For example:

 Karl Fischer titration analysis was done by Biochem Laboratories Sdn

Bhd.

 XRF analysis was conducted at Centre for Global Archaeological

Research, Universiti Sains Malaysia, Penang.

 SEM analysis was carried out at Centre for Global Archaeological

Research, Universiti Sains Malaysia, Penang.

 XRD analysis was conducted at School of Physics, Universiti Sains

Malaysia, Penang.

2) Lack of data

 Other reaction parameters, leaching test, properties of biodiesel and used

catalyst should be studied to improve the quality of the work. However,

they can be proposed for the extension of this research.

3) Limited laboratory apparatus

 The limited amount of laboratory apparatus has slower the work progress.

CHAPTER TWO

LITERATURE REVIEW

2.1 Biodiesel

Fossil fuel which took millions of years to form, plays a crucial role in the global energy systems. Sadly, fossil fuel supplies have started to diminish day by day, resulting in fossil fuel price increment. Efforts are being exerted to look out for the best substitute for fossil fuel and it was found that biodiesel is the most economically practicable option for solving this problem. According to the American

Society for Testing and Materials (ASTM), biodiesel is described as monoalkyl esters of long chain fatty acids made from a renewable feedstock such as vegetable oil or animal fat by the reaction with alcohol and catalyst. “Bio” refers to its renewability and biological source, while “diesel” means its usage in a diesel engine

(Zhang et al., 2003). Biodiesel is commonly named as B100 and it must meet the requirements of ASTM D6751 (Mofijur et al., 2012).

The concept of using biodiesel as fuel in a diesel engine is not something new as it was discovered more than 100 years ago by Dr. Rudolf Diesel. During the

World Exhibition in Paris in the year 1900, he had successfully operated the diesel engine using 100 % pure peanut oil as fuel (Kapilan et al., 2009; Owolabi et al.,

2012). Twelve years later, Diesel said, “The use of vegetable oils for engine fuels may seem insignificant today. But such oils may become in course of time as important as the petroleum and coal tar products of the present time” (Owolabi et

al., 2012). Interestingly, this statement has become a reality today. Biodiesel has no petroleum, but it can be used either in a neat form or blended with petroleum diesel in any proportions (Kapilan et al., 2009; Idusuyi et al., 2012). Biodiesel blends are denoted as BXX. The XX shows the quantity of biodiesel in the blend. For instance,

B20 blend means 20 % biodiesel and 80 % petroleum diesel. The physical properties of biodiesel are listed in Table 2.1. Biodiesel is not only used as fuel in vehicles such as diesel engine-cars, lorries, trucks, boats and buses, but it is also being applied in generators, oil home heating units and constructional equipment (Bajpai and Tyagi,

2006).

Table 2.1: Physical properties of biodiesel (Demirbas, 2009a)

Properties Biodiesel (bio-diesel) Common Chemical name Fatty Acid Methyl Ester (FAME) Chemical Formula Range C14–C24 methyl esters Kinematic viscosity range (mm2 s-1, at 313 K) 3.3–5.2 Density Range (kg-1 m3, at 288 K) 860–894 Boiling point range (K) >475 Flash point range (K) 420–450 Distillation range (K) 470–600 Vapour pressure (mm Hg, at 295 K) <5 Solubility in water Insoluble in water Physical Appearance Light to dark yellow, clear liquid Odour Light musty/soapy odour Biodegradability More biodegradable than petroleum diesel Reactivity Stable, but avoid strong oxidizing agents

In Malaysia, the production of biodiesel has been developing rapidly since many years ago. As an effort to encourage the use of “green” and renewable energy and at the same time minimize the dependency on fossil fuel, Malaysian government had introduced the National Biofuel Policy in 2006 (Mofijur et al., 2012; Wahab,

2016). The implementation of B5 blend was first introduced in mid-2011 in the

selected states and the full implementation was accomplished at the end of 2014.

However, biodiesel production in Malaysia is still far below industry full capacity, which is probably due to several factors such as high feedstock transportation cost and utilization of feedstock to make other products like pharmaceutical grade sugar, soap noodle and fatty alcohol (Wahab, 2016).

2.2 Advantages of biodiesel

Fossil fuel exerts a highly negative impact on the ecosystem and human health. With growing concerns over the fossil fuel, biodiesel has gained much attention and popularity as a “green” and excellent fuel since it offers numerous advantages. Biodiesel is well known as an environmentally benign fuel since its usage emits much lower CO2 into the atmosphere compared to other fossil based fuels (Figure 2.1). Moreover, in comparison to diesel, biodiesel consists of about 10-

11 % oxygen content, whilst diesel does not have oxygen (Canakci, 2007; Ge et al.,

2017). The molecular structures of diesel and biodiesel are illustrated in Figure 2.2.

As reported by Demirbas (2009a), the presence of oxygen in biodiesel leads to the rise in homogeneity of oxygen with the fuel. Due to the aforementioned reason, biodiesel exhibits better combustion efficiency compared to petroleum diesel and emits less exhaust emission such as carbon monoxide, unburnt hydrocarbon and particulate matter. These are the reasons which make biodiesel the most suitable fuel for transportation especially in sensitive areas like forests, national parks, mining enclosures, heavily polluted cities and coastal areas.

Carbon dioxide (CO2) produced per MJ of energy

Cooking oil Oilseed rape Soybean Palm oil Natural gas Diesel Gasoline Coal

0 20 40 60 80 100 120

g/CO2 generated

Figure 2.1: Comparison of the carbon intensity of biodiesels fuels against fossil fuels (UK Department for Transport, 2008).

Diesel

Biodiesel

Figure 2.2: Molecular structure of diesel and biodiesel (Ge et al., 2017).

The use of biodiesel is beneficial to reduce the global warming effect and air pollution as well as the ability to improve human health. As an alternative fuel, biodiesel has lots of other unique characteristics. One of them is its excellent lubrication property which can help to lower down the friction loss and at the same time improves the efficiency of the brake (Xue et al., 2011). The use of high lubricity biodiesel would result in extending engine‟s lifespan. The presence of biodiesel contributes massively in solving insufficient energy supply issue. At the same time, the dependency on imported fuel would decline. One of the prolific aspects about biodiesel is that it is easy to use, as neither modification nor fueling equipment is required. In terms of performance, it displays a good performance and high-power generation (Firoz, 2017). Besides, biodiesel is known as a “safe” fuel in view of handling, storage and transport, which corresponds to its low toxicity and high flash point (Atadashi et al., 2010; Firoz, 2017). It commonly possesses a flash point higher than 150 °C whereby conventional diesel fuel has a much lower flash point, which is around 55-66 °C (Sanford et al., 2009).

Biodiesel has superior biodegradable and renewable characteristics that make it a promising fuel. Surprisingly, biodiesel degrades four times faster than petroleum diesel (Demirbas, 2008). It also has high biodegradability in fresh water as well as in soil (Ferella et al., 2010). In contrast to mineral diesel, biodiesel does not possess any carcinogens and has a much lower sulfur content which makes it the reason to be called as clean fuel (Sharma and Singh, 2009). Another advantage of biodiesel is its high cetane number (CN). Cetane number is an indicator to determine the ignition quality and it is highly controlled by the amount of saturated fatty acids and its chain length. According to Lapuerta et al. (2008) and Karmakar et al. (2010), higher the

CN, shorter the time between the ignition and the initiation of fuel injection into the combustion chamber. Therefore, fuel with high CN has better combustion efficiency compared to the fuel that has low CN. More importantly, biodiesel is the most suitable replacement for petroleum diesel due to their similarities in physicochemical properties (Atadashi et al., 2010).

2.3 Raw materials

Biodiesel can be synthesized from a variety of feedstocks such as edible oil, inedible oil, waste oil, and animal fat. About 75 % of the overall cost for methyl ester production derives from feedstock (Figure 2.3). According to Ayetor et al. (2015), more than 100 raw materials have been utilized in biodiesel production. Biodiesel feedstock is controlled by climate and soil conditions (Huang et al., 2012). The suitability of vegetable oil as a feedstock is determined by the composition of the raw material itself which in turn measures the quality of the formulated biodiesel.

Meanwhile, the selection of feedstock for each country is highly influenced by edibility, cost and availability (Ayetor et al., 2015). Therefore, different countries have different sources and types of feedstocks. For instance, France and Italy mainly utilize sunflower oil as the feedstock in biodiesel formulation process. Soybean oil is the main raw material in USA and Brazil, while China prefers oil from Guang Pi, an oil-bearing tree as the raw material because soybean has a very high demand in

Chinese food preparation (Bajpai and Tyagi, 2006; Beckman and Junyang, 2009). As the largest and second largest palm oil producer and exporter respectively, Indonesia and Malaysia benefit from palm oil to produce biodiesel which is in abundance in both countries.

1% 2%

3% 7%

General overhead

12% Energy Direct labour Depreciation 75% Chemical feedstocks Oil feedstock

Figure 2.3: General cost breakdown for biodiesel production (Lim and Teong, 2010).

Currently, most of methyl esters are prepared from edible oils such as rapeseed (59 %), soybean (25 %), palm oil (10 %), sunflower oil (5 %) and other types of oil (1 %) (Pahl, 2008; Demirbas, 2015). However, the use of edible oil in producing large quantities of biodiesel negatively affects the global food supply and consequently cause an increase in edible oils‟ prices. Hence, one of the viable ways to overcome this hurdle is by replacing the edible oil with non-edible oil or used oil.

Some examples of inedible oil sources are Jatropha curcas (Chhetri et al., 2008;

Buasri et al., 2015; Reddy et al., 2016), Pangium edule (Atabani et al., 2015), soapnut Sapindus mukorossi (Chhetri et al., 2008) and rubber seed (Zamberi and

Ani, 2016). There are significant advantages with regards to the usage of non-edible oil over edible oil. For an example, inedible plants can be planted in wastelands that are unsuitable for food crops and they only need low cultivation cost since they can maintain high yield even without a thorough care (Fatah et al., 2012). Apart from those benefits, these plants can also cope with arid, semi-arid conditions and they

only need low fertility and moisture demand to grow (Atabani et al., 2013).

Unfortunately, inedible oils have very high FFA content and contain several toxic compounds which make them unsuitable for human consumption.

Waste cooking oil is defined as used oil that is no longer safe for reuse due to its high content of FFA. When comparing to virgin vegetable oil, biodiesel formulated from waste oil has more complicated steps and has a poorer fuel characteristic, which is associated with high FFA content. Usually, to produce methyl esters, feedstocks that contain more than 2 mg KOH g-1 of acid value need to be pre-treated to lower the acid content (Knothe and Steidley, 2005). Therefore, most of the waste oils would be subjected to esterification process first before proceeding to the transesterification process. Due to its low price, waste oil is believed to be a suitable raw material in methyl esters production. Additionally, most of waste cooking oils from houses and restaurants are simply thrown away into sinks and drains. Practicing appropriate approaches to dispose waste oil may lead to reduction in environmental problems and vice versa. Besides being used as a feedstock in biodiesel formulation process, waste oil is also used as animal feed. However, this oil contains dangerous compounds and they could simply get into the food chain when they are being used as animal feed (Kulkarni and Dalai, 2006). Hence, the oils must undergo treatment to lower its effects on the ecosystem. One of the feasible methods to treat the oil is by converting it into methyl esters.

Currently, the number of studies on the use of animal fats in biodiesel preparation process is much lower in comparison to vegetable oils. The use of animal fats assists in reducing the disposal rate as well as ensuring the continuity of the

biodiesel supply. In 2011, Boey et al. successfully produced biodiesel using chicken fat as feedstock. It was reported that more than 98 % biodiesel conversion was obtained under the optimized reaction conditions. Moreover, catfish fat has also been tested in the transesterification reaction using catalysts prepared from marine barnacle and bivalve clam shells (Maniam et al., 2015). The catfish oil has an acid value of 3.85 mg KOH g-1, FFA content of 1.75 %, and a moisture content of 0.22 %.

Although the acid value is relatively high, the conversion of catfish fat into biodiesel was a success achieving more than 96 % of methyl esters content upon 4 h of the transesterification reaction. However, since animal fat is in solid form, it is not suitable to be used as fuel in its original form. Not only that, the use of animal fats could also lead to various complications such as contamination of lubricating oil, incompatibility with existing engine, carbon deposits in the engine and reduction in engine durability. All these issues could probably be due to the presence of high amount of saturated fatty acids in animal fats.

2.4 Methods of biodiesel production

There are several techniques that can be employed to produce methyl esters such as direct use and blending, microemulsion, thermal cracking (pyrolysis), and transesterification.

2.4.1 Direct use and blending

The utilization of vegetable oils such as peanut oil, soybean oil, olive oil, palm oil and sunflower oil as fuels to replace non-renewable and non-biodegradable

diesel fuels has started flourish since last few decades. But, as the crude oil supply is getting diminished, utilization of vegetable oil as a replacement is being promoted again in most countries around the world. Vegetable oils have become the current interest in seeking for biodiesel substitute as they are safe to use, readily available, carbon neutral, renewable and biodegradable.

Although they have similar properties with reference to diesel fuel (Dunn and

Bagby, 2000), the direct use of vegetable oils and animal fats as an engine fuel is not recommended. This is due to the negative impact imparted by vegetable oils and animal fats on engine performances and emission, causing contamination of lubricating oil, thickening and gelling of the lubricating oil and coking of injector nozzles due to their low CN, low heating value, low volatility and higher viscosity and freezing point than diesel fuel (Melo-Espinosa et al., 2016). Therefore, blending

(dilution) technique was proposed as an effort to improve the oil‟s grade (Mendhe et al., 2015).

Blending, also called as dilution is a very easy and straightforward technique to lower the viscosity and density of vegetable oils (Demirbas, 2009b). In this method, vegetable oils are directly mixed with diesel fuel. Although it can enhance the fuel quality and lower the oil‟s viscosity, these fuels also face the same problems as vegetable oils (Mendhe et al., 2015).

2.4.2 Microemulsion

Microemulsion is a method where two or more immiscible fluids are mixed together to form emulsion. Emulsion consists of a mixture of oil and water and one of the phases present in droplet form and it dispersed within the other phase. It is known as dispersed phase (Figure 2.4). For instance, oil-in-water emulsion is made up of mixture of oil and water. In this case, oil is considered as the dispersed phase, while water is the dispersion medium (Tan et al., 2015b). Other than that, there are also multiple emulsion stages such as water-in-oil-in-water emulsion and oil-in- water-in-oil emulsion (Khan et al., 2006). The stabilization of the mixture is carried out using film of surfactants and/or co-surfactants (Dunn, 2004; Rosen, 2004).

continuous oil phase

dispersed water phase inner oil phase dispersed water phase

A B

Figure 2.4: Schematic structures of (A) water/oil biodiesel emulsion and (B) oil/water/oil biodiesel emulsion (Lin and Lin, 2007).

The advantages of microemulsion technique such as no engine modification needed, straightforward, easy implementation, and low production cost, make it the choice of many researchers as an attempt to reduce oil‟s viscosity (Lif and

Holmberg, 2006). Microemulsion with solvents like methanol, ethanol, butanol, hexanol, octanol or other alcohols is a practical way to lower the vegetable oil‟s viscosity and minimize smoke emission. Some of the interesting facts about this method are its capability in minimizing the nitrogen oxide (NOx) production and enhancing the combustion efficiency of biodiesel. However, some researchers do not encourage the use of this microemulsified diesel due to its unacceptable properties that would lead to nozzle failure, incomplete combustion and carbon deposition (Koh and Gazi, 2011).

2.4.3 Thermal cracking (pyrolysis)

Thermal cracking (Figure 2.5), also called as pyrolysis is defined as a process where deoxygenation of vegetable oils occurs because of the thermal degradation reaction where the final product acquired is the enriched diesel-like hydrocarbon

(Bridgwater, 2004). During the first and second world wars, pyrolysis of oils from biomass was used to cover up the depleted fuel supply in areas that faced a shortage of petroleum supply. For instance, China applied pyrolysis batch system of tung oil.

The bio-oil obtained acted as a raw material in the process of making diesel-like fuel and gasoline (Demirbas, 2003; Lima et al., 2004). Specialities of this method are the flexibility of the raw material, greater compatibility with fuel standards and engines and low operation cost (Tan et al., 2015a). This method is not only a promising method for lowering oil‟s viscosity and density, but it is also capable to transform triglycerides into fuels. It is advantageous to the hydroprocessing industry due to the technological similarities with conventional petroleum refining. In 2009, Wiggers et al. and Junming et al. reported on the success of pyrolysis of soybean oil in biofuel

production. The biofuel obtained was comparable with petroleum-based fuel.

Oil/fat + Catalyst catalytic cracking Catalyst (250 ℃ - 350 ℃)

Liquid condensate

Sedimentation H2O

Distillation atmospheric pressure up to 190 ℃

Light fraction Treated condensate

Figure 2.5: Thermal cracking process (Rajalingam et al., 2016)

Despite all the advantages, there are some challenges to overcome when using this method. One of the biggest concerns is the difficulty to control the quality of the product. The formation of unwanted products such as mono-, di- and triglycerides might occur due to the incomplete reaction (Lima et al., 2004). In addition, the fuel produced by this technique is unstable and corrosive, which is mainly associated with the high acid value (Wiggers et al., 2013). During vegetable oil cracking processes, there also exists the formation of a highly toxic compound of acrolein (Prado and Filho, 2009).

2.4.4 Transesterification

Among biodiesel production methods, transesterification has been chosen as the most ideal and effective chemical process to produce biodiesel as it can deal with high viscosity problem. It is also known as a practical way to produce a greener and a safer fuel. Transesterification which is also called as alcoholysis, is simply described as taking a triglyceride molecule, neutralizing the FFA, eliminating the glycerol and forming an alkyl ester. A triglyceride consists of one molecule of glycerol and three molecules of long chain fatty acids that are usually found in vegetable oils or animal fats. This reversible process involves three sequence steps, which requires one mole of triglyceride and three moles of alcohol. During the reaction, triglycerides are broken down into diglycerides, monoglycerides and finally glycerol, producing one mole of ester in every step. The basic reaction for transesterification is shown in Scheme 2.1.

O O

CH -O-C-R 2 1 CH3O-C-R1 CH2-OH O O

CH-O-C-R 2 + 3CH3OH CH3O-C-R2 + CH-OH O O

CH -OH CH2-O-C-R3 CH3O-C-R3 2

Triglycerides Methanol Methyl ester Glycerol

Scheme 2.1: The basic transesterification reaction.

The most frequently used alcohol during alcoholysis process is methanol.

This is perhaps due to its various advantages such as low price, good physical and chemical properties. Transesterification is an equilibrium reaction. During the

reaction, the addition of alcohol would cause the shifting of the equilibrium towards the forward direction, thus increasing the amount of biodiesel produced. Biodiesel can be produced directly through the conversion of both FFA and oil using acid esterification process. Nevertheless, the reaction is too slow, and it gives low biodiesel yield. Interestingly, Melo-Espinosa et al. (2016) stated that most of the biodiesel produced through transesterification process have almost similar properties as compared to diesel fuel. There are several parameters that control the triglycerides‟ conversion into biodiesel namely; alcohol to oil molar ratio, reaction time, temperature, type and amount of catalyst.

There are several catalyst systems used in the production of methyl esters via transesterification. One of them is acid-catalyzed transesterification. Acid-catalyzed transesterification is a conversion process of triglycerides into methyl esters and glycerol in the presence of an acid catalyst such as sulfonic acid and sulfuric acid.

This catalyst usage could yield a high biodiesel content up to 99 %. However, the reaction is too slow, and it requires elevated reaction conditions.

Another example for the catalyst system is base-catalyzed transesterification.

Base-catalyzed transesterification is the process of biodiesel production using a base catalyst such as sodium hydroxide, sodium methoxide, sodium ethoxide and potassium hydroxide. To produce methyl esters through base-catalyzed process, the feedstock used should have low FFA value. The presence of a high acid value in the oil would increase the base catalyst usage to neutralize the FFA (Gashaw and

Teshita, 2014). When using alkali catalysts, the alcohol and glycerides must be free of water because the presence of water would causes the formation of soap through

saponification. Soap formation must be avoided as it causes a drastic drop in the catalytic effect and accounts for the difficulty in biodiesel separation and purification processes. However, in comparison to acid-catalyzed process, the base-catalyzed process is employed more frequently since it has a shorter reaction time. For commercialization purpose, the use of alkaline catalysts is more favoured compared to acid catalyst due to its fewer corrosive properties. Triglycerides with low FFA content are usually being transesterified using alkali-catalyzed process, while triglycerides with a high content of FFA and water should undergo acid-catalyzed process.

Meanwhile, lipase-catalyzed transesterification process is more favourable as it requires a low reaction temperature, has high tolerance towards neutral pH environment and a low probability of soap formation (Semwal et al., 2011). Despite its advantages, this type of catalyst system is unfavourable compared to the alkaline- catalyzed transesterification especially in terms of the reaction time and yield

(Ekijeme et al., 2010).

2.5 Catalyst

Catalyst is defined as a substance that helps to escalate the reaction. The catalyst would provide a new route with lower activation energy (Clark, 2002). As illustrated in Figure 2.6, the reaction with catalyst possesses lower activation energy compared to the uncatalyzed reaction, leading to a better reaction rate. The general chemical reaction with catalyst‟s presence is depicted in Figure 2.7.

Figure 2.6: The difference between uncatalyzed and catalyzed reactions.

Figure 2.7: Illustration of general reaction in the presence of a catalyst.

Generally, there are three categories of catalysts that are commonly applied in biodiesel production, which are acid, base and enzyme catalysts. When compared to acid and base catalysts, enzyme catalyst is the least used catalyst. Acid and base catalysts can be divided into two classes, which are homogeneous and heterogeneous catalysts. It has been acknowledged that heterogeneous catalysts exhibit cleaner and recyclable catalyst systems with regards to homogeneous catalysts (Wen et al.,

2010a).

2.5.1 Enzyme catalysts (Biocatalysts)

Talha and Sulaiman (2016) reported that enzyme catalysts have gained more attention since their usage does not cause the formation of soap and additionally, the purification process is very simple. Besides that, this environmental benign catalyst is also reusable and does not produce any by-products (Kulkarni and Dalai, 2006;

Atadashi et al., 2013). They are also capable of catalyzing the reaction using milder reaction conditions compared to chemical catalysts. A few examples of enzyme catalysts are Novozyme 435 (Jeong and Park, 2008; Zheng et al., 2009) and Rhizopus oryzae lipase (Pizarro and Park, 2003).

In 2009, Novozym 435 lipase (also known as Candida antarctica lipase) was utilized as a catalyst to transesterify soybean oil in the production of biodiesel

(Zheng et al., 2009). During the alcoholysis reaction, tert-amyl alcohol was mixed together with lipase, oil and methanol where tert-amyl alcohol functioned as the reaction medium. A very high biodiesel yield (97 %) was recorded under the optimized conditions where the catalytic activity remained stable even after being reemployed for 150 cycles. A year before, Jeong and Park (2008) conducted almost a similar research as Zheng et al. (2009). They used the same catalyst, which is

Novozym 435 lipase but a different reaction medium (tert-butanol). A yield of about

76.1 % of biodiesel was obtained after 24 h of reaction time at 40 °C in the presence of 5 % (w/w) of Novozym 435, 1 % (w/w) of water content and 3:1 of methanol to oil molar ratio.

Nonetheless, according to Jeong and Park (2008), Zheng et al. (2009) and

Leung et al. (2010), the usage of biocatalysts in biodiesel production keeps on decreasing due to the high price, slow reaction, short lifetime as well as the need for higher amounts of enzyme catalysts. In addition, enzyme catalysts have a very high sensitivity towards alcohol especially methanol as it can cause enzyme deactivation

(Bajaj et al., 2010). Furthermore, the inactivation and denaturation of the enzyme exerts a highly negative impact on methyl esters yield.

2.5.2 Homogeneous acid catalysts

Sulfuric acid, sulfonic acid, organic sulfonic acid, hydrochloric acid, and ferric sulphate are the most widely used homogeneous acid catalysts during transesterification reaction. Among those catalysts, sulfuric acid and hydrochloric acid are the most explored catalysts and they could tolerate with the FFA content in the oils/fats. Due to the long reaction time, the use of acid catalysts in the transesterification process has reduced even though they work effectively in the esterification and transesterification reactions. Some of the other drawbacks of this type of catalysts are the high probability of causing contamination problems and equipment corrosion and the difficulties in separating out from the product (Lam et al., 2010; Leung et al., 2010).

2.5.3 Homogeneous base catalysts

Some of the examples of frequently used homogeneous base catalysts are sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide and

potassium methoxide. They are considered as practical catalysts owing to their advantages such as the ability to attain high yield in a shorter time, availability, low corrosive properties and only need low atmospheric pressure and temperature (Lam et al., 2010). However, this type of catalyst does not exempt from having unacceptable properties such as generation of large amounts of wastewater during biodiesel purification process (Leung et al., 2010), non- reusable (Boey et al.,

2011a), high sensitivity towards FFA content in the oil and can easily form soap when the oil has higher than 2 wt.% of FFA content (Lam et al., 2010). The presence of soap inhibits the transesterification reaction and makes it difficult to carry out the biodiesel purification process which in turn lowers the ME conversion. The saponification reaction is shown in Scheme 2.2.

R1- COOH + NaOH R1COONa + H2O Fatty acid Sodium hydroxide Soap Water

Scheme 2.2: The saponification reaction.

2.5.4 Heterogeneous acid catalysts

A few examples of heterogeneous acid catalysts are titanium-doped amorphous zirconia, sulfated zirconia, zinc aluminate and carbon-based solid acid catalyst. Some of the other examples of solid acid catalysts utilized in biodiesel production and their optimized reaction conditions are depicted in Table 2.2. This type of catalyst have several excellent properties namely: (I) no water washing required; (II) reusability; (III) perform excellently in both esterification and transesterification reactions; (IV) minimize the corrosion problems; (V) high FFA

and water tolerance; (VI) easy to be separated from final product and (VII) ability to avoid soap formation (Kulkarni and Dalai, 2006; Helwani et al., 2009; Lam et al.,

2010).

However, due to their shortages such as high energy requirement, relatively high cost, poor reaction rate, contamination of the product due to the leaching of catalyst‟s active sites and the need for extreme reaction conditions (Lam et al., 2010;

Leung et al., 2010), the application of heterogeneous acid catalysts in biodiesel production is getting less popular.

Table 2.2: Comparison of reaction conditions for different types of heterogeneous acid catalyst.

Solid acid catalyst Reaction conditions Conversion Reference Catalyst Reaction time Methanol to oil Temperature (%) amount (wt.%) (h) ratio (°C)

Sulfonated coconut 5.0 8.0 12:1 65-70 92.6 Thushari and Babel meal residue (2018)

Tin oxide-supported 5.0 5.0 30:1 110 79.2 Xie and Wang WO3 (2013)

27 Carbon-based solid 0.2 4.5 16.8 220 80.5 Shu et al. (2010)

acid

Carbon-based solid 7.5 1.0 12:1 60 99.1 Mardhiah et al. acid (2017)

Tungstated zirconia 15.0 3.0 12:1 100 94.6 Guldhe et al. (2017)

Sulfated zirconia 1.0 2.0 9:1 65 95.0 Muthu et al. (2010)

Titanium-doped 11.0 - 40:1 245 65.0 Brucato et al. amorphous (2010) zirconia (TiO2/ZrO2)

Ion-exchange resin 13.0 - 24:1 200 97.0 Paterson et al. (2013)

2.5.5 Heterogeneous base catalysts

Supported guanidines, basic zeolites, basic hydrotalcites, alkali earth oxides are the common examples of heterogeneous base catalysts. Heterogeneous base catalysts provide many advantages such as long lifetime, low energy consumption, higher reaction rate than acid-catalyzed transesterification, require moderate reaction conditions, reusable and easy product separation process (Lam et al., 2010; Sagiroglu et al., 2011; Atadashi et al., 2013).

Among alkaline earth metal oxides, CaO is the most investigated catalyst in biodiesel production. CaO is very popular because it is reusable, non-toxic, insensitive to FFA and water as well as has poor methanol solubility. Besides, this catalyst is very cheap as it can be easily obtained from waste materials, which makes it safe to use. CaO can easily get hydrated and carbonated when it encounters air which is associated with the adsorption of H2O and CO2 at the catalyst‟s surface in the form of hydroxyls and carbonate groups. Moreover, the carbonation of the solid surface could occur within minutes (Granados et al., 2007).

Calcium oxide catalysts can be easily formed through thermal activation of different precursors like acetate, hydroxide, and carbonate (Kouzu et al., 2009).

Nevertheless, different precursors exhibit varying catalytic activities depending on their decomposition behaviour (Cho et al., 2009). Since many years ago, many researchers have been using natural resources as sources of CaO catalysts in producing biodiesel such as fish bone (Raut et al., 2016), chicken eggshell (Buasri et al., 2013), duck eggshell (Buasri et al., 2013), crab shell (Boey et al., 2011b), cockle

shell (Boey et al., 2011b), golden apple snail shell (Viriya-empikul et al., 2010), meretrix venus shell (Viriya-empikul et al., 2010), mussel shell (Rezaei et al., 2013),

Achatina fulica shell (Lesbani et al., 2013) and quail eggshell (Omotoso and iro-

Idoro, 2015). Some of the naturally-derived CaO catalyst sources and their optimized reaction conditions in biodiesel production are shown in Table 2.3.

Table 2.3: Sources of CaO catalyst and their optimized conditions during tranesterification reaction.

Sources of CaO Feedstock Reaction conditions Biodiesel Reference catalyst conversion

Catalyst Reaction Methanol to Temperature (%) amount (wt.%) time (h) oil ratio (°C)

Bovine bone Soybean oil 8 3.0 6:1 65 97.0 Smith et al. waste (2013)

Capiz (Amusium Palm oil 3 6.0 8:1 60 93.0 ± 2.2 Suryaputra et cristatum) shell al. (2013)

Oyster shell Soybean oil 25 5.0 6:1 65 73.8 Nakatani et al.

30 (2009)

Mud clam shell Castor oil 3 2.0 14:1 60 96.7 Ismail et al. (2016)

Obtuse horn Palm oil 5 6.0 12:1 - 86.8 Lee et al. shell (2015)

Scallop shell Waste cooking 5 2.0 6:1 65 86.0 Sirisomboonch oil ai et al. (2015)

Cockle shell Rubber seed 9 3.0 16:1 60 88.1 Zamberi and oil Ani (2016)

Table 2.3: Continued

Sources of CaO Feedstock Reaction conditions Biodiesel Reference catalyst conversion (%) Catalyst Reaction Methanol to Temperature amount (wt.%) time (h) oil ratio (°C)

Chicken eggshell Sunflower 3 3.0 9:1 60 97.8 ± 0.02 Correia et al. (2014) oil

Crab shell Sunflower 3 4.0 6:1 60 83.1 ± 0.27 Correia et al. (2014) oil

Murex turnispina Waste 3 2.0 6:1 65 99.0 Ekeoma et al.

shell cooking oil (2017) 31

Mussel shell Tallow oil 5 1.5 12:1 70 97.5 Hu et al. (2011)

Pomacea sp shell Palm oil 4 4.0 7:1 60 95.6 Margaretha et al. (2012)

Barnacle clam Catfish fat 4 3.0 12:1 65 97.6 ± 0.03 Maniam et al. (2015)

Bivalve clam Catfish fat 4 3.0 12:1 65 92.0 ± 0.05 Maniam et al. (2015)

Exoskeleton of a Used frying 4 5.0 10:1 60 ± 0.5 97.8 Agrawal et al. mollusk (Pila oil (2012) globosa)

With the aim of developing an effective catalyst, Kouzo et al. (2008) utilized

CaO derived from pulverized limestone (CaCO3) in the alcoholysis of soybean oil and waste oil. The catalyst was produced by calcining the pulverized limestone

(CaCO3) for 1.5 h at the activation temperature of 900 °C. The study acquired more than 99 % of biodiesel yield upon 2 h of reaction. Meanwhile, in an attempt to transesterify sunflower oil, Granados et al. (2007) utilized activated calcium oxide as a catalyst to produce biodiesel. In the study, the authors also investigated catalyst‟s reusability and the effects imparted by H2O and CO2 on the catalytic activity. It was evident that CO2 is the primary deactivating agent, not H2O. Interestingly, the catalyst was able to be reemployed for a few times without affecting its effectiveness significantly.

Apart from that, many researchers also have modified CaO by adding support into it as an effort to further intensify its catalytic ability. For instance, Kumar and

Ali (2010) impregnated different alkali metal ions (K+, Li+ and Na+) onto CaO catalyst. The prepared catalyst worked effectively in the methanolysis of used cooking oil. Recently, Arana et al. (2019) and Winoto and Yoswathana (2019) had successfully utilized CaO-ZnO catalyst and nanomagnetic CaO-based catalyst

(KF/CaO-Fe3O) in biodiesel production respectively. Besides, Fadhil et al. (2018) has doped CaO with potassium acetate and applied it in the transesterification of different types of non-edible oils. Surprisingly, the reaction yielded more than 90 % methyl esters.

2.6 Staghorn coral

Coral reefs, sometimes known as „undersea cities‟ or „oases‟, are the world‟s largest marine ecosystems, hosting about 25 % of all aquatic life (Plaisance et al.,

2011). They are responsible for shielding coastlines from erosion, protecting lagoons and mangroves and serving as habitat to marine species. Other than that, they also support fishery resources by providing food source for humans and at the same time contribute to the rise in tourism industry. As reported in International Union for

Conservation of Nature (IUCN) Red List, there are over 100 countries with coastlines fringed by reefs. However, over the past few decades, coral reefs have begun to diminish rapidly and this problem is basically driven by several factors such as disease outbreaks, ocean acidification and rise in seawater temperature (Hughes et al., 2003). According to Libro and Vollmer (2016), approximately 95 % of the

Caribbean‟s major shallowwater corals including staghorn coral (Acropora cervicornis) perished due to the White Band Disease (WBD).

Staghorn coral is a branching coral that belongs to the genus Acropora, which named after its unique form that resembles male deer antlers. Other common forms are delicate „bottle-brushes, table and expansive bushes and there are approximately

160 species of staghorn corals globally (IUCN, 2009). According to the IUCN Red

List, staghorn corals are believed to have existed and evolved since 55-65 million years ago during the late Paleocene. Interestingly, they can reproduce asexually

(through budding and colony fragmentation) and sexually (being hermaphrodites).

This hard and stony coral can grow up to 2 m in length and 4 -7 cm in diameter. It is also the fastest growing coral species, where the branches increasing in length by 10-

20 cm per year (Toda et al., 2007).The coral‟s colonies are yellow, gold or brownish in colour with the tip of each branch having an enlarged white or pale cream polyp

(Aronson, 2007).

The Acropora corals formed three-dimensional thickets in intermediate (5–20 m) water depths, giving rise to reef growth, coastal protection, island formation and habitat for marine life such as crabs, turtles, gastropods, fishes and echinoids

(Bruckner, 2002). The corals can be found abundantly in shallow water areas worldwide but hardly found particularly in deep areas especially in mesophotic habitats (Kahng et al., 2010) due to the limited amount of light present and high amount of suspended sediments. Other than that, they also prefer warm water and do not thrive in water with temperature below 20 ºC (Arkive, 2016) and more importantly, they need clear and oxygenated water with standard salinity to grow. In

2015, Muir et al. investigated the species diversity of staghorn corals (genera

Acropora and Isopora) in the mesophotic zone of the Great Barrier Reef and the western Coral Sea. They discovered that the number of staghorn corals decreased below 50 m depth. At a depth below 40 m, colonies look different from their original forms. They have more flattened branches, fragile and light skeletal structures. In addition, the spaces between branches and corallites have become wider. These dramatic changes occurred because of downwelling coarse sediments, lack of light sources and water movement.

Staghorn coral can be classified into two groups, which are Atlantic and Indo-

Pacific groups where they are normally located between 25° N and 25° S. Malaysia,

East Timor, Indonesia, Philippines and Papua New Guinea are part of the Indo-

Pacific group. Malaysia is a tropical South-East Asian country which is geographically located in the Coral Triangle. It is surrounded by hundreds of beautiful islands that have approximately 323 coral species (Harborne et al., 2000).

For instance, Pangkor Island and Tioman Island have coral coverage between 17.9 % to 68.6 % where Acropora cervicornis is one of the main coral species present in those islands. In addition, this stony coral also the main reef framework builder in

Peninsular Malaysia, mainly in the east coast area (Toda et al., 2007).

However, since the last few decades, the number of staghorn coral worldwide has declined in response to human activities and environmental disturbances such as high seawater temperature, sea level rise, coastal development, thermal stress, pollution, ocean acidification, eutrophication, invasive species, disease and storms

(Hughes et al. 2003; Burke et al. 2011). Staghorn corals are extremely sensitive to high seawater temperature as it leads to coral bleaching in which results in the expelling of pigmented algae. Consequently, they lost their energy sources and become more susceptible to diseases such as white band disease. This reduces their chances of recovery and at the end, they died. Another main threat to this coral is ocean acidification, which due to high amounts of CO2 that arises from human activities. It has weakened the coral skeletons, slower the growth rate, reduce the coral population and cause the erosion of coral reefs (IUCN, 2009). Due to the aforementioned reasons, Acropora cervicornis are now at risk of extinction and they were listed as threatened species under the U.S. Endangered Species Act in May

2006. In 2008, they were listed as critically endangered on the IUCN Red List of

Threatened Species (Johnson et al., 2011).

Although several coral restoration techniques have been conducted, the number of dead coral is still high as the problems like high seawater temperature and ocean acidification still not fully resolved. They are exposed to potentially fatal conditions every year and most likely will continue to degrade until climate change stabilizes. Therefore, dead staghorn coral fragments can be found in abundance in the coastal areas as they are usually washed ashore during high tide. The differences between living/healthy and dead/unhealthy corals can be seen in Figure 2.8 and 2.9, respectively. They are easily differentiated as they have distinct shapes and colours.

Figure 2.8: Living/healthy staghorn coral (Piehl and Atkins, 2006).

Figure 2.9: Dead/unhealthy staghorn coral (Piehl and Atkins, 2006).

CHAPTER THREE

MATERIALS AND METHODS

3.1 Materials and chemicals

Refined, bleached and deodorized palm olein (RBD palm olein) manufactured by FFM Marketing Sdn Bhd (Sungai Buloh) was bought from a grocery store, while waste cooking oil (WCO) was acquired from a local stall located at Padang Serai, Kedah in 2017. All chemical reagents used in this study were purchased from QRec (Malaysia) and used as received. The internal standard (methyl heptadecanoate) was obtained from Sigma-Aldrich (Switzerland).

3.2 Characterization of oils

3.2.1 Determination of the moisture content

Moisture contents of feedstocks were measured using Karl Fisher titration method. The analysis was carried out on Metrohm Karl Fisher Titrator Model

701KF. During the analysis, approximately 2.0 g of the oil sample was injected into the titrator. Methanol and chloroform were used as solvents in a molar ratio of 1:1, while Merck CombiTitrant 5 was used as the reagent. The oil sample was titrated in triplicate.

3.2.2 Determination of the acid value

Determination of the acid value followed the methods proposed by Canesin et al. (2014) and Onukwuli et al. (2017) with slight modifications. Approximately 1.0 g of oil (RBD palm olein and WCO) was weighed into an Erlenmeyer flask. Next, a volume of 50 mL of the ethanol-diethyl ether mixture and five drops of the phenolphthalein indicator were added into the flask. It was then heated for 5 min.

The mixture was titrated with 0.1 M KOH until the first trace appearance of pink colouration persisted for 30 s after gentle shaking. The volume of KOH used was recorded and the determination was performed in triplicate. The acid value was calculated according to Eq. 3.1:

56.1 M ) (Eq. 3.1)

Where V is volume of potassium hydroxide used (mL), M is molar concentration of potassium hydroxide, W is weight of sample (g), and 56.1 is molecular weight of potassium hydroxide.

3.2.3 Determination of the saponification value

Saponification values of oils (RBD palm olein and WCO) were determined following the methods adopted by Canesin et al. (2014) and Onukwuli et al. (2017) with modifications. Approximately 1.0 g of oil was added into a round-bottom flask

Then, 20 ml of 0.5 M ethanolic KOH was added to the same flask. The flask was then fitted with a reflux condenser and immersed in a water bath that was placed on a stirring hot plate where the sample was heated for 30 min. Upon heating, it was

cooled to ambient room temperature before adding five drops of the phenolphthalein indicator into it. The mixture was titrated with 1 M HCl acid solution until the disappearance of pink colour. In addition, a blank test (without sample) was carried out for higher accuracy. The tests were conducted in triplicate. The saponification value is expressed as illustrated by Eq. 3.2:

(B- ) M 56.1 ) (Eq. 3.2)

Where B is the volume of hydrochloric acid used for the blank sample (mL), V is the volume of hydrochloric acid solution used for oil sample (mL), M is molar concentration of hydrochloric acid, W is the weight of the sample (g), and 56.1 is molecular weight of potassium hydroxide.

3.3 Preparation of the catalysts

3.3.1 Preparation of calcium oxide catalyst (CSC)

The catalyst was prepared from dead staghorn coral fragments that were collected in 2016 from Langkawi, Kedah. The corals were washed thoroughly with running tap water to get rid of all unwanted impurities. Upon washing, corals were dried in an oven at 105 °C overnight. Dried corals were then ground using mortar and pestle until a powdered form was achieved. Next, powdered corals were sifted through a 250-mm sieve and subsequently were activated in a muffle furnace at 900

°C for 4 h.

3.3.2 Preparation of KOH impregnated staghorn coral catalyst (K-CSC)

K-CSC catalyst was prepared using a wet impregnation method. The powdered staghorn coral was impregnated with 50 % (w/w) of KOH. During the preparation step, 1 g of powdered staghorn coral was dissolved in 20 mL of distilled water and 0.5 g of KOH was added into it. The mixture was then stirred for 2 h.

Next, the solution was oven dried at 105 °C overnight prior to the calcination process for 4 h at 900 °C.

3.4 Characterization of the catalysts

Physiochemical properties of uncalcined staghorn coral (USC), calcined staghorn coral (CSC) and calcined KOH impregnated staghorn coral (K-CSC) catalysts were characterized via Hammett indicators, benzoic acid titration method,

X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET)-N2 adsorption method, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA).

3.4.1 Basic strength analysis

Determination of the basic strength was accomplished using Hammett indicator method reported by Boro et al. (2014) with modifications. Hammett indicators used were phenolphthalein (H_=8.2), 2,4-dinitroaniline (H_=15) and 4- nitroaniline (H_=18.4). The Hammett indicator solution was prepared by diluting the

indicator in methanol. Next, approximately 25 mg of the catalyst sample was added into a conical flask containing 1 mL of the indicator solution. The mixture was then left to equilibrate for 2 h. The change in the solution‟s colour indicated that the sample is stronger than the indicator and vice versa.

3.4.2 Basicity analysis

Benzoic acid titration method was employed to assess the basicity of catalysts. The analysis was conducted according to the method adopted by Watkins et al. (2004) with modifications. During the analysis, about 0.1 g of the sample was mixed in a conical flask along with 2 mL of the selected indicator. The indicators used were phenolphthalein (H_=8.2), 2,4-dinitroaniline (H_=15) and 4-nitroaniline

(H_=18.4). The mixture was then titrated with 0.01 M benzoic acid diluted in benzene. The end point was determined by observing the colour change.

3.4.3 X-ray fluorescence (XRF) analysis

X-ray fluorescence (XRF) measurements were carried out to access elemental compositions of catalysts. Analyses were performed on a fully automated X-ray spectrometer system (Rigaku RIX3000) using the pressed-pellet (pressure of 8.0 Pa) method.

3.4.4 BET-N2 adsorption analysis

Surface area, pore volume, as well as pore diameter of prepared catalysts were investigated on a Micromeritics ASAP 2000 surface analyzer. All the samples were degassed overnight at 105 °C prior to analysis where the adsorption parameters of N2 were measured at -196 °C. Surface area was calculated by applying the

Brunauer, Emmett, and Teller (BET) equation, while the total pore volume, Vtot was obtained from the N2 adsorption data. The pore size distribution was determined through the Barrett, Joyner, and Halenda (BJH) method.

3.4.5 Attenuated total reflectance-Fourier transform infrared (ATR-FTIR)

analysis

Functional groups of USC, CSC, and K-CSC catalysts were analyzed in direct transmittance mode using Thermo-Nicolet IR 200 Fourier transform infrared

(FTIR) spectrometer coupled with an attenuated total reflectance (ATR) head.

Spectra were recorded in the scan range of 4000-600 cm-1 with 20 scans per sample at a resolution of 4 cm-1.

3.4.6 Scanning electron microscopy (SEM) analysis

SEM analysis was conducted at a magnification of 2500x using Quanta FEI

650 instrument to determine the surface morphologies of the prepared USC, CSC and

K-CSC catalysts.

3.4.7 X-ray diffraction (XRD) analysis

Crystalline phases of USC, CSC, and K-CSC catalysts were determined using

X-ray diffractometer (Siemens Diffractometer D5000) with Cu Kα as a source. Data were collected over a 2 of 25-125°, with a step size of 0.05° at a scanning speed of

1° min-1.

3.4.8 Thermal gravimetric analysis (TGA)

Thermal transitions of USC and uncalcined KOH impregnated staghorn coral were observed on a Perkin Elmer TGA 7 analyzer at a ramping rate of 10 °C min-1, heated from 30-900 °C under a nitrogen atmosphere.

3.5 Transesterification

Approximately 5 g of oil (RBD palm olein and WCO) was added into a 100 mL round-bottom flask. A particular amount of methanol and catalysts (CSC and K-

CSC) were added into the same flask that was then equipped with a reflux condenser.

The flask was then immersed in a water bath that was placed on a stirring hot plate.

The reaction was carried out at various reaction times in the range of 2-6 h with continuous stirring. Once the reaction was completed, the mixture was cooled to ambient room temperature and centrifuged at 5000 rpm for 10 min to further separate methyl esters, glycerol and catalyst before transferring into a separating funnel. The biodiesel was extracted with n-hexane (3 x 3 mL) and transferred into a beaker, while the glycerol was discarded from the product. Next, the methyl esters was dried to

eliminate residual water (Sharma and Singh, 2009) and filtered through Whatman 42 filter paper (110 mm diameter and a pore size of 2.5 ). The biodiesel obtained was kept in a refrigerator for further use. The reaction was repeated thrice.

3.6 Analysis of methyl esters

Gas chromatography analysis of biodiesel was performed using an Agilent

Technologies, 7890A GC system equipped with FID and a Supelco-wax capillary column (30 m in length with 0.25 mm inner diameter (i.d) and 0.20

). The experimental conditions used were as follows: helium was used as the gas carrier with a flow rate of 1.2 mL min-1. Both the injector and detector temperature were set at 250 °C. The initial oven temperature applied was

190 °C and held for 2 min. Finally, the oven temperature was increased up to 250 °C at a heating rate of 10 °C min-1 and held for 4 min. About 0.4 of the diluted solution with n-hexane was injected into the GC system in the split mode (1:5).

Methyl heptadecanoate was utilized as an internal standard for quantitative analysis of the biodiesel concentration. The methyl esters peaks were determined by comparing them with the chromatogram from GC-MS. The overall process of biodiesel production is shown in Figure 3.1. The percentage of biodiesel conversion was calculated using Eq. 3.3:

( ) ) (Eq. 3.3)

Where is the total peak area of FAME, AISTD is the peak area of methyl

heptadecanoate, CISTD is the concentration of methyl heptadecanoate in mg mL-1, V

ISTD is the volume of methyl heptadecanoate in mL, and m is the mass of sample in

mg.

Staghorn coral

Powdered staghorn coral (USC)

Without KOH Addition of KOH through wet impregnation

Calcination (900 °C, 4 h)

produce

CSC K-CSC

Catalyst characterization (Hammett indicator, benzoic acid titration, XRF, BET, ATR-FTIR, SEM, XRD, TGA)

Transesterification

methyl esters, Centrifugation glycerol, catalyst

Extraction

Drying

Filtration

Methyl esters analysis using GC-FIC

Figure 3.1: Flowchart of the biodiesel production process.

3.7 Reusability of K-CSC catalyst

The reusability of the K-CSC catalyst was tested by collecting the remaining catalyst after each reaction. The used catalyst was washed with methanol to remove all the absorbed materials. The catalyst was then dried overnight prior to the calcination process (900 °C for 4 h). The activated catalyst was then refluxed again with RBD palm olein under optimum reaction conditions (4 wt.% catalyst, 15:1 methanol : oil molar ratio, 4 h reaction time).

3.8 FFA and water tolerance of K-CSC catalyst

The FFA tolerance of K-CSC catalyst was evaluated by performing the transesterification reaction using optimized transesterification conditions of RBD palm olein (4 wt.% catalyst, 15:1 methanol : oil molar ratio, 4 h reaction time) with the addition of lauric acid (0-3 wt.%) based on the weight of oil. The procedures were repeated by adding 3, 2, 1, 0 wt.% (based on the weight of oil) of water to investigate the water tolerance of the catalyst.

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Characterization of biodiesel feedstock

Two types of feedstock were used in this study namely; RBD palm olein and waste cooking oil. Both feedstocks were characterized in terms of moisture content, acid value (AV), FFA content and saponification value (SV). The tests were carried out in triplicate for higher accuracy. The purpose of the characterization process is to assess the quality of the feedstock, especially related to the possible deterioration mechanism as the deterioration of feedstock might lead to the reduction in biodiesel yield (Canesin et al., 2014). The results of the tests are depicted in Table 4.1.

Table 4.1: Properties of RBD palm olein and WCO.

Parameters RBD palm olein WCO Moisture content (wt.%) 0.10 ± 0.0 0.11 ± 0.02

Acid value (mg KOH g-1) 0.74 ± 0.01 1.54 ± 0.10

FFA content (%) 0.37 ± 0.00 0.77 ± 0.05

Saponification value (mg HCl g-1) 184.97 ± 3.57 222.26 ± 4.19

Since many years ago, biodiesel produced from RBD palm olein and WCO were reported to meet the ASTM biodiesel standard specifications and European biodiesel standard (Boey et al., 2009; Roschat et al., 2012; Lesbani et al., 2013; Tan et al., 2015a) entirely. This shows that RBD palm olein and WCO are promising feedstocks in methyl esters production. Based on the present work, RBD palm olein

has lower moisture content (0.10 ± 0.00 %), acid value (0.74 ± 0.01 mg KOH g-1),

FFA content (0.37 ± 0.00 %), and saponification value (184.97 ± 3.57 mg HCl g-1) than WCO.

Moreover, the results obtained indicated that WCO has an AV of 1.54 ± 0.10 mg KOH g-1, equivalent to 0.77 ± 0.05 % FFA, which is higher than RBD palm olein. This is probably due to the degradation of triglycerides into diglycerides, monoglycerides and FFA that occurred during the cooking process. Primarily, oil with an acid value over 2 mg KOH -1 need to be esterified using an acid catalyst to lower the FFA content before proceeding to the transesterification process (Knothe and Steidley, 2005). Since the acid value of WCO is lower than 2 mg KOH g-1, no pretreatment step is needed. Besides, the SV of WCO is also slightly higher than the

RBD palm olein. As noted by Raqeeb and Bhargavi (2015), this phenomenon might be associated with the polymerization and oxidation process that took effect during the cooking process. Oil with high FFA content and SV would have higher likelihood to cause the formation of soap.

The differences in chemical and physical properties between RBD palm olein and WCO are mainly due to the chemical reactions that take place during the cooking process such as polymerization, oxidation and hydrolysis. Another possible factor is the transfer of material between food and oil, which then resulted in higher water content in the oil (Raqeeb and Bhargavi, 2015). In addition, the presence of water and heat would enhance the hydrolysis of triglycerides and consequently triggered the growth of FFA (Kawentar and Budiman, 2013; Carlini et al., 2014).

Both hydrolysis and saponification reactions led in low FAME content and high

catalyst consumption. Apart from that, the properties associated with WCO are also highly dependent on the cooking conditions such as cooking time and temperature.

4.2 Characterization of catalysts

4.2.1 Basic strength analysis

The basic strengths of USC, CSC, and K-CSC catalysts are tabulated in Table

4.2. The analysis demonstrated that the colour of phenolphthalein (H_= 8.2) solutions changed from colourless to pink with the employment of each catalysts.

Among all the catalysts, USC was the only catalyst which did not alter the yellow colour of 2, 4-dinitroaniline (H_= 15.0) to mauve (light purple). 4-nitroaniline (H_=

18.4) solution indicator did not impart any colour change with the use of the three catalysts. Thus, it can be concluded that USC has a basic strength in the range of 8.2

2011a). This is probably due to the formation of strong basic sites (K2O species) on their surfaces. In comparison, the basic strengths of the prepared CSC and K-CSC catalysts are found to be higher than that of CaO-derived palm kernel shell catalyst and MgO-KOH-20 catalyst reported by Bazargan et al. (2015) and Mutreja et al.

(2011), respectively. Meanwhile, Lin et al. (2015) and Gupta et al. (2017) reported similar basic strengths (15.0 < H_ < 18.4) for KF/CaO and KF/SS-850 °C, respectively.

Table 4.2: Basic strengths of the prepared catalysts.

Indicator H_ Colour change USC 1 CSC 2 K-CSC 3 Phenolphthalein 8.2 Colourless to Colourless to Colourless to pink pink pink

2,4-dinitroaniline 15.0 No colour Yellow to Yellow to change mauve mauve

4-nitroaniline 18.4 No colour No colour No colour change change change

1 uncalcined staghorn coral 2 calcined staghorn coral 3 modified staghorn coral (KOH impregnated staghorn coral)

4.2.2 Basicity analysis

Catalyst basicity plays an important role in determining the performance of the catalysts. As presented in Table 4.3, USC exhibited the lowest basicity than the other two catalysts. The reason is that the presence of Ca(OH)2 and CaCO3 had lowered the catalyst‟s surface area and had masked its active site, which in turn resulted in a low basicity. Upon calcination, the basicity increased up to 0.14 ± 0.00 mmolg-1. It is evident that calcination provokes the formation of basic sites.

Bazargan et al. (2015) also reported similar observation, where the basicity of palm kernel shell biochars increased from 0.056 to 0.516 mmolg-1 after it was subjected to calcination process. In other literature, eggshell, cockle shell and crab shell (basicity strength of 9.3 < H_ < 15.0) have been reported to have basicity of 0.040, 0.023, and

0.016 mmolg-1 (Udomman et al., 2015), which is much lower than CSC. Although calcination has improved the catalyst‟s basicity, it still cannot afford to give high

FAME content. This is the reason why KOH is added into the staghorn coral. It is evident that the basicity of CSC is much lower than K-CSC although their basic

strengths reside in a similar range (15.0

Table 4.3: Basicity values of the prepared catalysts.

Catalyst Basicity (mmolg-1) Phenolphthalein 2,4-dinitroaniline Total (H_=8.2) (H_=15.0) USC 1 0.01 ± 0.00 - 0.01 ± 0.00 CSC 2 0.13 ± 0.00 0.01 ± 0.00 0.14 ± 0.00 K-CSC 3 0.43 ± 0.04 0.15 ± 0.01 0.58 ± 0.01

1 uncalcined staghorn coral 2 calcined staghorn coral 3 modified staghorn coral (KOH impregnated staghorn coral)

4.2.3 XRF analysis

Comparison of elemental compositions of USC, CSC, and K-CSC is shown in Table 4.4. Based on the analysis conducted, it was found that the major element present in all the three catalysts is calcium in oxide form. This finding is in line with the result reported by Smith et al. (2013) and Buasri et al. (2013), where the highest element in both catalyst-derived bovine bone and eggshell is also CaO. Besides,

Agrawal et al. (2012) revealed that CaO accounts 79.80% of the overall constituent of Pila globosa shell. This current study also showed that the introduction of KOH has increased the amount of K2O in the catalyst drastically which is apparent based on the data obtained for the K-CSC catalyst since it comprises the highest K2O content (26.72 %). Other elements such as Si, Sr, Ti, Mg, and others were found in

trace amounts and they are less discussed since calcium is the main element in the samples.

Table 4.4: Compositions of elements present in the prepared catalysts.

Oxide Composition (%) USC 1 CSC 2 K-CSC 3

CaO 92.68 93.86 69.29 K2O 0.06 0.07 26.72 SiO2 2.13 2.11 1.37 Others 5.13 3.96 2.62 (SrO,TiO2,Al2O3, Fe2O3,MnO,MgO, Na2O,P2O5)

1 uncalcined staghorn coral 2 calcined staghorn coral 3 modified staghorn coral (KOH impregnated staghorn coral)

4.2.4 BET-N2 adsorption analysis

The physical properties (surface area, pore volume, and pore diameter) of each catalyst were summarized in Table 4.5. From the analysis, it was found that

USC has a very low value of BET surface area, which is only 1.3033 m2g-1.

Compared to USC, CSC possessed a greater BET surface area (5.2439 m2g-1) and a larger pore volume (0.0093 cm3g-1). The increases in catalyst surface area upon calcination process could be related to the crystal growth of calcium oxide (Boro et al., 2011). Another reason could be the existence of pores between the particles and this assumption is supported by the interpretation obtained from SEM analysis showed in Figure 4.3 B. Interestingly, CSC also possessed higher value of BET surface area than activated bovine bone (3.06 m2g-1) and commercial CaO (2.16 m2g-

1) studied by Smith et al. (2013) and Sirisomboonchai et al. (2015), respectively.

Table 4.5: Physical properties of USC, CSC and K-CSC.

Physical Properties USC 1 CSC 2 K-CSC 3 BET Surface area (m2g-1) 1.3033 5.2439 1.6163 Pore volume (cm3g-1) 0.0043 0.0093 0.0023 Average pore diameter (A°) 132.1982 71.0914 55.8424

1 uncalcined staghorn coral 2 calcined staghorn coral 3 modified staghorn coral (KOH impregnated staghorn coral)

However, K-CSC catalyst has a smaller surface area in contrast to CSC. This is probably due to the micropore plugging of CaO upon KOH loading, showing that the catalyst surface is enriched with K2O species, which explains the high catalytic activity of the catalyst. Although the impregnation of KOH failed to increase the surface area, it managed to enhance the basicity of the catalyst as evident by the basicity results obtained (Table 4.3). According to an observation-based study conducted by Meher and co-workers (2006), it was revealed that the catalytic activity is more affected by basicity than surface area. Similar findings have been reported for the impregnation of lithium into CaO (Watkins et al., 2004; Kaur and Ali, 2011;

Boro et al., 2014) validating that K-CSC has the highest catalytic activity even though it has a smaller surface area.

According to Ljupkovic et al. (2014), pore volume and pore diameter are very important in determining the catalytic activity. Based on the analysis, the calcination process gives rise in the pore volume from 0.0093 cm3g-1 (USC) to 0.0043 cm3g-1

(CSC). However, the pore volume suddenly dropped to 0.0023 cm3g-1 after KOH impregnation. Among the samples, K-CSC has the lowest pore volume, mainly due to the pore plugging. Meanwhile, the high pore volume obtained for CSC is highly associated with the development of porosity in the catalyst (Boro et al., 2011).

However, due to their trace pore volumes, all the synthesized catalysts were

classified as less-porous materials, which are comparable with the catalysts prepared by Viriya-empikul et al. (2010). The CaO catalyst was derived from eggshell, golden apple snail shell and meretrix venus shell and the total pore volume recorded were

0.005, 0.004 and 0.002 cm3g-1 respectively.

The nitrogen adsorption-desorption isotherms of USC, CSC and K-CSC are depicted in Figure 4.1. All the catalysts exhibited Type IV isotherms, which correspond to mesoporous solids. At low pressure, all the isotherms showed linear rises of adsorbed volume. For USC, an obvious increase in nitrogen uptake was detected started from relative pressure of P/Po = 0.55 until up to P/Po = 0.99.

Meanwhile, in the case of CSC and K-CSC, the nitrogen uptake accelerated from

P/Po = 0.74 to 0.99 and P/Po = 0.80 to 0.99 respectively. These phenomena probably occurred as a result from capillary condensation inside the mesopore (Ekeoma et al.,

2017). In addition, the mesoporosity increment after the activation process affirmed the removal of CO2 and moisture and at the same time confirmed the change in the metal oxide structural phase into a more active phase, confirming the data from XRD diffractogram in section 4.2.7.

Figure 4.1: Nitrogen adsorption-desorption isotherms of (A) USC; (B) CSC and (C) K-CSC.

More importantly, the presence of hysteresis between the adsorption (lower) and desorption (upper) curves in each isotherm suggests the presence of mesoporosity. They exhibited type H3 hysteresis loops, which correspond to open slit-shaped capillaries. During adsorption, the slit width expanded and then it reduced during desorption. All the catalysts are classified as mesoporous materials since their pore diameters reside in the range of 20-500 A°. As mentioned by Ren et al. (2012), mesoporous materials are highly suitable as catalyst and for adsorption and energy storage.

4.2.5 ATR-FTIR analysis

The purpose of ATR-FTIR analysis is to observe the changes in the functional group of the samples after calcination and modification processes. FTIR spectra of the prepared catalysts (USC, CSC and K-CSC) are shown in Figure 4.2.

For USC, the absorption band at 709 cm-1 is assigned to in-plane bending vibration mode of C-O group. The IR band at 856 cm-1 ascribed the presence of Sr and Mg.

Zakaria et al. (2008) also obtained a similar peak while conducting their research on

Porites sp. coral. Also, it was observed that the peak related to asymmetric stretching of Si–O-Si bond appeared at 1082 cm-1. The absorption bands at 1474 and 2920 cm-1 are due to the alkyl C-H bending and asymmetrical C-H (sp3) stretching, respectively, which were attributed to the organic functional groups present in the staghorn coral. The band at 2523 cm-1 corresponded to the asymmetric stretching mode of gas phase CO2, while O-H stretching band that originates from Ca(OH)2 was observed at 3417 cm-1. This analysis explicitly shows that the major compound present in USC is CaCO3.

Upon calcination, some of the peaks disappeared and there are decreases of bands at 874 cm-1 (Ca-O bond) and 1181cm-1 (C-O bond). This is perhaps due to the

2- loss of CO3 ion functional group attached to the surface of the catalyst.

Theoretically, during heat treatment process, CO2 is eliminated from CaCO3 and leads in CaO formation. This phenomenon could also happen due to crystallization of

CaO at high temperature, which limits the magnitude of Ca−O bond vibration (Loy et al., 2016). In addition, the vibrational band detected at 1420 cm-1 occurred due to bending vibration of C-H bond, while the sharp IR band appeared at 3640 cm-1 is an indication of O-H group of water physisorbed on the catalyst‟s surface, proving the capability of the catalyst in absorbing moisture in a short period of time.

Interestingly, Agrawal et al. (2012) and Liu et al. (2016) also detected the presence of moisture around 3600 cm-1.

In the case of K-CSC, the vibrational bands moved to a higher energy level upon the impregnation of KOH that probably due to the incorporation of K+ into the

CaO defect sites. The existence of Ca-O bond was observed at 879 cm-1 as inline with the observations of Ruiz et al. (2009). A new interesting band was detected at

931 cm-1 (O-K bond) and it is believed to have relation with the impregnation of

KOH. This result is comparable with Liu et al. (2016) when they added KBr into calcined shell/kaolin catalyst. The characteristic absorption of C-O at 1132 cm-1 indicated the presence of CaCO3 over the catalyst, thus proving rapid carbonation of

K-CSC. The peak at 1398 cm-1 ascribed to alkyl C-H bending. The appearance of peak at 3841 cm-1 indicates OH stretching vibration mode of water. As can be seen in the spectra, USC possess broad O-H band, while both CSC and K-CSC possess sharp

O-H band. This is probably because in USC, the vibration band is attributed to -OH

stretching vibration of Ca(OH)2. Therefore, it can promote H bonding easily and form broad O-H band. Meanwhile, in CSC and K-CSC, the sharp O-H band is caused by bond vibration of H–OH of water. Water from atmosphere was probably adsorbed by the catalysts via chemisorption and physisorption.

Figure 4.2: FTIR spectra of USC, CSC and K-CSC.

4.2.6 SEM analysis

The surface morphologies of the catalysts were evaluated using SEM. At

2500x magnification, it was clearly visible that there are obvious differences considering the activation process (prior to and following) and the addition of KOH.

As shown in Figure 4.3 A, the SEM image of USC consists of irregular shaped

particles. The coral demonstrates irregular and rough surface, which obviously has fewer pores than CSC.

In contrast, CSC shows wave-like surface and comprises of irregular shapes particles of varying sizes (Figure 4.3 B). SEM analysis data of this study resembles similarly to what Mamat and Yacob (2015) reported, where calcined eggshells were also constituted of wave-like surface. Furthermore, calcination at 900°C resulted in a more porous structure. The changes that occur in the catalyst‟s structure were due to the compositional change such as degradation of calcium carbonate into calcium oxide evolving carbon dioxide thereby causing a reduction of particle size.

Meanwhile, when KOH was added into the coral, catalyst‟s structural features changed completely (Figure 4.3 C) which resulted in particles with various shapes and sizes. Some of them had agglomerated with each other and consequently caused the reduction in the structural porosity of the catalyst which in turn made the surface to become more irregular. This was in accordance with BET analysis as discussed in the previous subtopic. Interpretation of the SEM analysis of this study is also in good agreement with previous work conducted by Modiba et al. (2015). A few small particles observed on the catalyst‟s surface could be related to K2O particles which further validates through XRD analysis (Figure 4.4).

A a

Figure 4.3: SEM micrographs at 2500x magnification (A) USC, (B) CSC and (C) K-CSC.

4.2.7 XRD analysis

XRD patterns of catalysts (USC, CSC, and K-CSC) are presented in Figure

4.4. Based on the analysis results, the main peaks of USC were observed at 2 =

26.14°, 33.08°, 35.79°, 38.28°, 41.15°, 45.75°, 48.30° and 52.64°, which confirmed the presence of CaCO3. This result resembles closely with the study carried out by

Birla et al. (2012). The peaks appeared at 2 = 50.18°, 63.13°, 79.40° and 82.14° are related to the occurrence of Ca(OH)2 . However, most of the peaks disappeared after subjecting to thermal activation process (900 °C, 4 h). Whereas, for CSC, the presence of CaO was characterized through the sharp and intense peaks positioned at

2 = 32.21°, 37.70°, 53.87°, 64.14°, 67.33°, 88.52°, 91.45° and 103.34°. XRD peaks obtained were virtually identical to those reported by Sharma et al. (2010) and Boro et al. (2011). The peaks detected at 2 = 34.21°, 50.86° and 79.76° confirmed the existence of Ca(OH)2, which could be formed due to the reaction of CSC with atmospheric air.

As can be seen from the XRD profile of K-CSC, the presence of potassium oxide was credited by the low intensity peaks at 32.63°, 88.52°, 91.46° and 103.72°.

The formation of K2O could possibly be caused by the reaction between KOH with

CaCO3. In addition, the low intensity of K2O peaks is probably due to the low concentration of K on the catalyst‟s surface, while the absence of KOH peaks showed a high degree of dispersion of K+, which resulted in a surface of K-CSC.

According to Kabo et al. (2015), the interaction between K and Ca might cause the weakening of Ca2+- O2- bond, which in turn could possibly lead to an effective interaction with methanol, thus escalating its effectiveness as well as the percentage

conversion. The analysis concluded that the catalyst‟s structure and its crystallinity were affected by the KOH impregnation, but it gave positive outcome in terms of the catalyst‟s basicity (Table 4.3).

Figure 4.4: XRD profiles of USC, CSC and K-CSC.

4.2.8 TG/DTG analysis

In the present work, thermal decompositions of USC and uncalcined K- impregnated staghorn coral were acquired through TGA (Figure 4.5) over a temperature range of 30 to 900 °C. In the previous literatures, water loss commonly occurred at temperature below 250 °C (Xie and Li, 2006; Barros et al., 2009; Kesic et al., 2012; Yacob et al., 2017). However, in this work, no weight loss was observed below 250 °C as the samples were dried prior to the TGA analysis. Meanwhile, minor weight losses related to the removal of organic matter were observed around

280-320 °C and 270-430 °C in USC and uncalcined modified catalyst respectively.

As evident according to Figure 4.5 A, a weight loss of 41.8 % was reported at 550-

760 °C, where CaCO3 associated to USC sustained a complete decomposition into

CaO with the elimination of CO2 as shown in the following equation:

CaCO3 CaO + CO2 (Eq. 4.1)

The weight loss is comparable to the stoichiometric weight loss of CO2 (44 wt.%). In a study carried out by Boey et al. (2011c), the degradation of CaCO3 (42 % of weight loss) was reported to occur at 575 °C. A bit lower temperature is needed here compared to other previous studies (Viriyaempikul et al., 2012; Tan et al.,

2015a) in order to ensure complete decomposition of CaCO3 into CaO. The occurrence of this phenomenon was probably due to the differences in the bond strength.

For uncalcined modified catalyst, a major decomposition of 23.7 wt.% was positioned in the range of 620-780 °C with a peak temperature centered at 700 °C

(Figure 4.5B) This is probably attributed to the decomposition of CaCO3 and KOH, resulting in catalytically active sites. For both catalysts, weight of the samples remained almost constant after 800 °C. Therefore, as evident from TGA analysis, the ideal calcination temperature for both catalysts would be above 800 °C.

Figure 4.5: Thermograms of (A) USC and (B) uncalcined K-impregnated staghorn coral.

4.3 Optimization of staghorn coral catalyzed transesterification using RBD palm olein as feedstock

In this work, calcined staghorn coral (CSC) was initially employed as a base catalyst to transesterify RBD palm olein into biodiesel. Three different reaction parameters were tested during the optimization process, which are catalyst loading, reaction time and methanol to oil molar ratio. Table 4.6 lists the varying amounts of

catalyst loading, reaction time and molar ratio of methanol to oil that were utilized in the process. At the beginning of the reaction, a biodiesel conversion of 10.1 ± 2.8 % was acquired in the presence of 5 wt.% catalyst. The inadequate quantity of catalyst resulted in a very low biodiesel yield and at the same time multiplies the number of monoglyceride and diglyceride intermediates. To improve on the catalytic activity, 6 wt.% of catalyst was added. However, increasing the quantity of catalyst up to 7 and

8 wt.% has caused a decrease in the reaction rate as large catalyst amount leads to inefficient stirring during the reaction thereby reducing the percentage conversion.

Therefore, in order to solve this problem, higher stirring speed is needed. In terms of reaction time, the transesterification reaction advanced rapidly when the experimental time was prolonged from 3 h to 4 h. This is mainly due to the extended contact time between reactants, leading to a more successful collision. At 5 h of reaction time, the biodiesel yield dropped abruptly to 17.3 ± 4.8 % owing to the fact that longer reaction promotes hydrolysis of esters, resulting in more FFA production and causes loss of esters. Therefore, 4 h time period was chosen as the optimum reaction time. In the case of methanol to oil molar ratio, a low methyl esters content was recorded with methanol : oil molar ratio of 12:1. This implies that the insufficient amount of methanol would impede the diffusion of reactants. As far as methanol to oil molar ratio is concerned, 15:1 ratio provided the optimal response and led to the highest biodiesel conversion of 62.1 ± 4.3 %. Whereas, maintaining more than 15:1 molar ratio affected unfavourably on the catalytic activity as it causes flooding of active sites, resulting in a low reaction rate.

In 2009, Nakatani et al. have reported the application of CaO derived from oyster shell as base catalyst in soybean oil transesterification. In comparison to the

present work, the study needed much higher catalyst concentration (25 wt.%) to

catalyzed the reaction. A complete reaction with less than 80% biodiesel yield was

achieved only after 5 h of transesterification reaction, which is a bit longer than the

current work. Meanwhile, transesterification reaction of this study yielded a

maximum biodiesel content of 62.1 ± 4.3 % under the reaction conditions of 6 wt.%

catalyst, 15:1 methanol : oil molar ratio and 4 h of reaction time. Based on the results

obtained, it can be concluded that there is a greater possibility to further enhance the

catalytic activity of the prepared catalyst.

Table 4.6 : Transesterification of RBD palm olein using different CSC catalyst loading (5-8 wt.%), reaction time (3-6 h) and methanol to oil molar ratio (12:1- 21:1).

Parameters Biodiesel Catalyst loading Reaction time (h) Methanol to oil conversion (%) (wt.%) molar ratio 5 4 15:1 10.1 ± 2.8 6 4 15:1 62.1 ± 4.3 7 4 15:1 46.7 ± 3.8 8 4 15:1 17.6 ± 3.0 6 3 15:1 5.6 ± 4.2 6 5 15:1 17.3 ± 4.8 6 6 15:1 8.4 ± 4.5 6 4 12:1 36.5 ± 0.5 6 4 18:1 54.4 ± 3.6 6 4 21:1 25.8 ± 1.3

4.4 Optimization of K-CSC catalyzed transesterification using different feedstocks

The application of calcined staghorn coral (CSC) as a catalyst in producing

biodiesel has shown a promising result, with 62.1 ± 4.3 % of biodiesel conversion. In

view of achieving an even higher biodiesel yield, the catalyst was modified by

impregnating KOH into the coral. A series of 40 wt.%, and 50 wt.% of KOH were

incorporated into the coral. However, the catalyst with 40 wt.% of KOH yielded only

78.9 ± 1.6 % biodiesel under the optimum conditions. Meanwhile, the reaction with

50 wt.% KOH loading showed the optimum catalytic activity with more than 90 % methyl esters content under the same reaction conditions. Therefore, 50 wt.% KOH was selected as the ideal amount to be added into the coral during the wet impregnation process. The modified catalyst was then employed in the transesterification of RBD palm olein and WCO. A summary of the overall results for all transesterification reactions is presented in Table 4.7 and the details were discussed in Section 4.3, 4.4.1 and 4.4.2.

The chromatograms of methyl esters from transesterified RBD palm olein and WCO as well as the internal standard obtained in this study are depicted in

Figure 4.6 and Figure 4.7 respectively. Based on the chromatograms, a small C17 peak observed referred to internal standard, which is methyl heptadecanoate. In previous studies, C17 peak usually has almost similar intensity with C16 peak

(Omotoso and Iro-Idoro, 2015) but in this work, the C17 peak intensity was much smaller due to the low concentration of the prepared internal standard. The most and second most abundant fatty acids of the transesterified RBD palm olein were found to be oleic acid and palmitic acid respectively, similar to transesterified WCO. The composition of WCO is highly dependent on the source of cooking oil and usage.

Therefore, it can be concluded the WCO was sourced from RBD palm olein. The amount of unsaturated fatty acids in both samples was higher than saturated fatty acid. According to Knothe (2005), biodiesel with high unsaturated fatty acid content is believed to have low viscosity, low pour point and cloud point. Therefore, it is suitable to be used during warm and cold weather conditions.

Table 4.7: Summary of overall results for transesterification reactions of RBD palm olein and WCO.

Optimum conditions RBD palm olein RBD palm olein WCO (CSC) (K-CSC) (K-CSC) Catalyst loading (wt.%) 6 4 4 Methanol to oil molar ratio 15:1 15:1 18:1 Reaction time 4 4 5 Biodiesel conversion (%) 62.1 ± 4.3 94.8 ± 0.5 89.5 ± 4.8

Figure 4.6: GC chromatogram of methyl esters produced from transesterification of RBD palm olein.

Figure 4.7: GC chromatogram of methyl esters produced from transesterification of waste cooking oil.

4.4.1 Optimization of K-CSC catalyzed transesterification using RBD palm olein as feedstock

4.4.1(a) Effect of catalyst loading

Catalyst loading is one of the important aspects in biodiesel production. In this research, optimization of catalyst loading was performed for 4 h at 65 °C using

15:1 methanol to oil molar ratio. As can be seen from Figure 4.8, different amount of catalysts (2-5 wt.%) were used to investigate their effects on biodiesel yield. In the presence of 2 wt.% and 3 wt.% catalysts, 80.7 ± 1.9 wt.% and 88.7 ± 3.9 wt.% of ME conversions were obtained respectively. The percentage conversion of ME increased with the loading of 4 wt.% catalyst, where it achieved its highest conversion (94.8 ±

0.5 wt.%). This is perhaps due to the increased proton concentration on the interface of oil and methanol, which in turn indirectly enhanced the reaction (Wu et al., 2013).

100

90 80 70 60 50 40 30 20

Biodiesel (%) conversion Biodiesel 10 0 2 3 4 5 Catalyst loading (wt.%)

Figure 4.8: Effect of catalyst loading on biodiesel conversion.

Based on the findings in this work, further increase in catalyst loading up to 5 wt.% did not promote the reaction but caused a significant reduction in the methyl esters yield (75.7 ± 2.6 %). This phenomenon is believed to be caused by saponification and mass transfer limitation. In 2010, Wen et al. conducted an investigation on the effectiveness of KF/CaO catalyst in biodiesel production via alcoholysis of Chinese tallow seed oil. Catalyst amount in the range of 1 to 5 wt.% were utilized and it showed similar trend with this work. With the increment in catalyst amount, the reaction rate advanced promptly and reached the highest value with 4 wt.% catalyst. More importantly, the amount of catalyst used in this current study is lower than that of reported by Kumar and Ali (2012) and Khan and Yacob

(2017).

4.4.1(b) Effect of reaction time

The effect of reaction time is shown in Figure 4.9. Methyl esters conversions were recorded at regular intervals of 1 h. Based on the results, the biodiesel content increased significantly and reached the highest value (94.8 ± 0.5 %) at 4 h. In a study conducted by Khan and Yacob (2017), it was reported that a reaction time of 6 h had to be employed to attain complete transesterification. However, according to the present study, methyl esters content drastically dropped to 74.1 ± 0.4 wt.% after 5 h of reaction time because the extended reaction time allows the catalyst to absorb more product and resulting in low biodiesel content. Thus, the optimum reaction time was found to be 4 h. These results are matched with the research done by Boro et al.

(2014) who revealed the highest biodiesel yield (94 %) at 4 h using lithium impregnated eggshell as catalyst.

100

90 80 70 60 50 40 30 20 Biodiesel (%) conversion Biodiesel 10 0 2 3 4 5 Reaction time (h)

Figure 4.9: Effect of reaction time on biodiesel conversion.

4.4.1(c) Effect of methanol to oil molar ratio

Besides catalyst loading and reaction time, methanol to oil molar ratio is indeed one of the key aspects in biodiesel production. According to Roschat et al.

(2012), methanol to oil ratio is highly governed by oil‟s quality and types of catalyst used. Based on Figure 4.10, the molar ratio of methanol to oil was varied in the range of 12:1 to 21:1. At the beginning of the reaction, the FAME content increased due to the formation of methoxy species on the catalyst surface, which then led the equilibrium of the reaction shift towards forward direction. However, the results showed a slight decline in the reaction rate (from 94.8 ± 0.5 % to 82.1 ± 2.8 %) when more than 15:1 methanol to oil molar ratio is used. The reason is that the excess methanol hindered the reaction between methanol with reactant and catalyst since glycerol gets dissolved in methanol. Likewise, a low biodiesel yield was obtained as a result of the shift of equilibrium in the backward direction. The complete conversion was achieved with methanol to oil molar ratio of 15:1.

100

90 80 70 60 50 40 30 20 Biodiesel (%) conversion Biodiesel 10 0 12:1 15:1 18:1 21:1 Methanol to oil ratio

Figure 4.10: Effect of methanol to oil molar ratio on biodiesel conversion.

4.4.2 Optimization of K-CSC catalyzed transesterification using waste cooking oil as feedstock

Waste cooking oil is known as a low cost feedstock and its utilization in biodiesel production is not something new as it has been done since many years ago.

In this work, the catalytic activity of K-CSC was tested in the waste cooking oil methanolysis by optimizing several reaction variables. Figure 4.11 shows the effects of catalyst loading, reaction time and methanol to oil molar ratio on methyl esters conversion. For catalyst loading, pertaining to the optimization results, the reaction advanced faster upon increased catalyst loading from 3 wt.% to 4 wt.% (Figure 4.11

A) as more catalysts could react with reactants, thus leading to a better catalytic activity. Further increment in catalyst loading up to 5 wt.% caused a slight reduction in the reaction rate. The reason for this observation is because of the formation of a more viscous reaction mixture which made it more difficult to be stirred efficiently which in turn resulted in an inefficient mixing of the reactants. Besides that, the high catalyst amount used also hindered the contact between reactants. Therefore, an

effective mixing is needed to intensify the catalytic activity. Thus, 4 wt.% was selected as the optimum catalyst loading. A study on zinc doped CaO utilization in waste cotton seed oil transesterification was carried out by Kumar and Ali in 2013.

The authors reported that 4 wt.% catalyst was insufficient to completely convert the oil into FAME. The complete reaction was achieved only after the catalyst concentration was increased up to 5 wt.%.

In addition, the investigation of the impact of reaction time on ME conversion was carried out for 3-6 h (Figure 4.11 B). At the beginning of the reaction, the reaction rate increased progressively up to 5 h. However, there was no significant increase in biodiesel conversion when the reaction time was extended for more than

5 h. At the 6 h, the catalytic activity of K-CSC dropped slightly and yielded a biodiesel content of 74.5 ± 0.5 wt.%. Thus, it can be brought into light that longer reaction time would retard the shift of equilibrium of the reaction towards forward direction due to the increases in the number of by-products produced. In the study carried out by Degirmenbasi et al. (2015), 4 h was not feasible for nano CaO impregnated with K2CO3. The catalyst exhibited its best performance (97.7 ± 1.7 % methyl esters) after 8 h.

Besides that, the effect of methanol to oil molar ratio was studied by varying the molar ratio of methanol to oil from 15:1 to 24:1. Based on Figure 4.11 C, the reaction proceeded at an increasing rate by enhancing the methanol to oil molar ratio from 15:1 to 18:1. This is because the more methanol is being used, the greater the interaction between methanol and oil. However, further increase in methanol to oil molar ratio above 18:1 caused a reduction in biodiesel yield. This suggests that the

use of excess methanol would increase the glycerol solubility in the reactants and leads to poor separation of glycerol from product. Buasri et al. (2012) studied the transesterification of waste frying oil into biodiesel using KOH supported on coconut shell activated carbon catalyst and reported a biodiesel yield of 86.3 %. Nevertheless, the reaction needed a very high molar ratio of methanol to oil (25:1) in order to reach its best activity. In conclusion, the maximum % FAME obtained from the transesterification of waste cooking oil using K-CSC as the catalyst was 89.5 ± 4.8 wt.%. at reaction conditions of methanol to oil molar ratio of 18:1, reaction time of 5 h and catalyst loading of 4 wt.%.

Additionally, some researchers also synthesized biodiesel from low cost feedstock using impregnated catalyst. For instance, in the year 2017, Kataria and co- workers had synthesized biodiesel from used cooking oil with the help of Zn-doped

CaO catalyst and they obtained more than 98 % biodiesel. As a comparison, they employed higher catalyst concentration (5 wt.%) than the amount used in this work.

On the other hand, in an observation-based study performed by Mutreja et al. (2011), the conversion of mutton fat oil into FAME was completed in just 20 min. This situation was possible due to the low content of FFA and moisture in the oil as well as the excellent properties of the catalyst (KOH impregnated MgO). These conditions were proven to be beneficial in enhancing the process flow.

100

90 A 80 70 60 50 40 30 20

Biodiesel (%) conversion Biodiesel 10 0 3 4 5 6 Catalyst loading (wt.%)

100

90 B 80 70 60 50 40 30 20 Biodiesel (%) conversion Biodiesel 10 0 3 4 5 6 Reaction time (h)

100 90 C 80 70 60 50 40 30 20

Biodiesel (%) conversion Biodiesel 10 0 15:1 18:1 21:1 24:1 Methanol to oil molar ratio Figure 4.11: Transesterification of waste cooking oil using different (A) catalyst loading (3-6 wt.%), (B) reaction time (3-6 h) and (C) methanol to oil molar ratio (15:1-24:1).

4.5 Proposed reaction mechanism

Some researchers have proposed the reaction mechanisms of triglycerides transesterification reactions using doped catalysts. For instance, Kusuma et al. (2013) revealed a predicted mechanism of KOH/zeolite-catalyzed alcoholysis reaction.

Besides, catalytic mechanisms of CaO/Al2O3 catalyst and calcined oyster shell impregnated with NaOH catalyst in transesterification reactions were proposed by

Pasupulety et al. (2013) and Jin et al. (2017) respectively. As discussed earlier, the addition of KOH into staghorn coral exhibited good catalytic effect during methanolysis reaction due to the strong basic site existence as in the proposed reaction mechanism depicted in Scheme 4.1. This statement was consistent with earlier works, where researchers believed that O-K bonding has capability to enhance the catalyst‟s effectiveness during the reaction (Xie and Li, 2006; yas et al., 2009).

The reaction starts immediately with the interaction of the catalyst‟s basic site with methanol, resulting in the production of a highly basic and an active ion species,

- methoxide ion (CH3O ). This form is highly basic and possesses high catalytic ability in the alcoholysis process. The next step is the formation of a tetrahedral intermediate due to an interaction between the carbonyl carbon of triglyceride molecule with methoxide ion. The catalytic reaction is then continued with the rearrangement of tetrahedral intermediate into more stable forms, which are methyl ester and diglyceride anion. Moreover, the methoxide cation attacks the diglyceride anion and form diglyceride. The reaction gets repeated until methoxide ions interact with all the remaining carbonyl carbon atoms of triglyceride to generate three moles of methyl esters and one mole of glycerol.

Scheme 4.1: Proposed reaction mechanism of transesterification of triglycerides catalyzed by prepared K-CSC catalyst.

4.6 Reusability of K-CSC catalyst

Under optimized conditions of RBD palm olein transesterification (methanol to oil molar ratio, 15:1; catalyst loading, 4 wt.%; reaction time, 4 h), used K-CSC catalyst was re-employed to test its reusability. According to Figure 4.12, the catalyst showed an abrupt reduction (from 94.8 ± 0.5 wt.% to 7.4 ± 1.0 wt.%) in the catalytic activity upon the second cycle of use. The biodiesel yield obtained was extremely small to be considered for reuse. The reduction in catalytic activity was due to the reduction in basicity value. As can be seen from Table 4.8, the basic strength of the used catalyst remained the same (15.0 < H_< 18.4) as the fresh catalyst. However, the basicity reduced from 0.58 ± 0.01 mmol g-1 to 0.12 ± 0.00 mmol g-1 which probably could have occurred due to the loss of active species (K2O) during washing or reactivation processes, resulting in a low catalytic activity. Furthermore, some of the potassium species could probably leach into biodiesel and glycerol phases. The basic sites deposited on the catalyst‟s surface are of practical importance in controlling the reaction rate. Some researchers also claimed that catalyst deactivation occurred due to the leaching of catalyst‟s active sites into the reaction mixture which were proved via leaching tests (Boey et al., 2011d; Kumar and Ali, 2012; Istadi et al.,

2016).

Another possible factor that could lead to the degradation of the catalyst is the adsorption of products/by-products on the catalyst‟s surface as they would block the catalyst‟s pores and reduced the interaction between basic sites and reactants. Other than that, the catalyst‟s deactivation possibly occurred due to the reaction of basic sites with atmospheric air or FFA. The catalytic activity gets reduced when the

catalyst converts back into its original forms, which are CaCO3, Ca(OH)2 or KOH.

This study revealed that K-CSC catalyst has poor reusability characteristic, but its catalytic activity perhaps can be recovered by reincorporating it with potassium hydroxide.

100

80 70 60 50 40 30

20 Biodiesel conversion (%) conversion Biodiesel 10 0 1 2 3 Cycle

Figure 4.12: Methyl esters conversion using used K-CSC catalyst for three reuses.

Table 4.8: Comparison of basic strength and basicity between fresh and used K-CSC catalysts. Fresh catalyst Used catalyst

Basic strength 15.0 < H_ < 18.4 15.0 < H_ < 18.4

Basicity (mmolg-1) 0.58 ± 0.01 0.12 ± 0.00

4.7 FFA and water tolerance of K-CSC catalyst in transesterification

In methyl esters production, FFA and water are considered as toxic materials since they could negatively affect the final product. Studies on catalyst tolerance towards FFA and water contents were conducted by adding different quantities (0-3 wt.%) of lauric acid and water during the alcoholysis of RBD palm olein (Figure

4.13). Without the addition of lauric acid and water, the catalyst worked efficiently during the reaction and delivered a FAME content of 94.8 ± 0.5 wt.%. Nevertheless, the prepared catalyst gradually lost its catalytic activity upon the introduction of lauric acid. The reaction with 1 and 2 wt.% (weight of oil) lauric acid only generated biodiesel content of 54.4 ± 3.4 wt.% and 47.7 ± 3.7 wt.%, respectively. According to

Yan et al. (2009), K2O has a high solubility in methanol which results in the formation of KOH. KOH was then reacted with FFA and led in soap formation, thus reducing the FAME content. In 2011, Mutreja et al. conducted a study on the application of KOH doped MgO catalyst in mutton fat oil transesterification.

Initially, the reaction only took about 20 min to be completed but after the addition of 1 wt.% FFA, the reaction time increased up to more than 6 h. This shows that the presence of FFA would reduce the catalytic activity of the catalyst. Reaction mechanism of the effect of FFA on the catalyst is illustrated in Figure 4.14. In addition, the presence of FFA would lower the catalyst‟s performance as they could neutralize the basic sites on the catalyst‟s surface.

100

90 FFA 80 Water 70 60 50 40 30 20 Biodiesel conversion (%) conversion Biodiesel 10 0 0 1 2 3 Amount of lauric acid/water (wt.%)

Figure 4.13: Effect of FFA and water on transesterification of RBD palm olein using K-CSC catalyst under optimum conditions of 4wt.% catalyst, 4 h reaction time and 15:1 methanol to oil molar ratio.

Figure 4.14: Mechanism on effect of free fatty acids towards catalyst during transesterification reaction (modified from Kouzu et al., 2008).

On the subject of water tolerance analysis, when 1 wt.% of water (weight of oil) was introduced into the reaction mixture, the reaction rate decreased immediately, finally producing a biodiesel content of only 54.6 ± 1.9 wt.%.

Meanwhile, less than 50 % of oil was converted into methyl esters in the presence of

2 and 3 wt.% of water. The reason is that the presence of water would enhance the hydrolysis of triglycerides into FFA and glycerol (Scheme 4.2). As a consequence,

unwanted soap would form and it promotes the formation of stable emulsion that prevents the separation of glycerol from methyl esters, thus reducing the reaction rate. As a conclusion, although the modified catalyst has very low FFA and water tolerance level, this complication could probably be improved by adding a support with better FFA and water tolerance.

H O H O

H-C-O-C-Ra H-C-O-H HO-C-Ra O O

H-C-O-C-Rb + 3 H2O H-C-O-H + HO-C-Rb O O

H-C-O-C-Rc H-C-O-H HO-C-Rc H H Triglyceride Glycerol Fatty acids

Scheme 4.2: The hydrolysis reaction of triglycerides.

CHAPTER FIVE

CONCLUSIONS AND FUTURE RECOMMENDATIONS

5.1 Conclusions

In this study, the production of biodiesel was carried out via transesterification of two types of feedstock, RBD palm olein and waste cooking oil using cost-effective catalysts derived from dead staghorn coral. All the prepared catalysts (USC, CSC and K-CSC) were successfully characterized using various complementary analyses. Pertaining to the result acquired from XRD study, the existence of K2O species was detected upon the introduction of KOH, proving the formation of strong basic sites on the surface of the catalyst.

During the application of CSC in FAME production, the reaction produced a biodiesel yield of 62.1 ± 4.3 wt.%. Since the staghorn coral showed its potential as a suitable catalyst, it was then modified by combining it with KOH through wet impregnation method to enhance its effectiveness. The modified catalyst (K-CSC) has shown good performances during the transesterifications of RBD palm olein and

WCO, with biodiesel conversions of 94.8 ± 0.5 % and 89.5 ± 4.8 % respectively under the optimum conditions. This work revealed that KOH impregnation was a success as it aided in the formation of active species on the catalyst‟s surface which consequently enhanced the catalytic activity. In addition, the catalytic activity was found to be highly influenced by basicity.

In terms of reusability, the prepared K-CSC catalyst has shown a poor reusability characteristic as the catalyst immediately lost its catalytic activity upon the second cycle due to the loss of K2O species. Besides that, the catalyst also was found to have poor ability to tolerate with FFA and water contents. The reason is that, the addition of lauric acid and water has led to the formation of soap.

Considering that waste dead staghorn coral is a low-cost material and can be easily found near the coastal areas in Malaysia, it is economically viable to utilize it with minimal modification despite its reusability, FFA and water tolerance issues. All in all, more thorough and detailed studies are required to improve on the reusability,

FFA as well water tolerance of the catalyst.

5.2 Future recommendations

Future recommendations reported are based solely on the findings of the present study. Thus, according to the experimental analyses, the following recommendations would be beneficial to enhance the effectiveness in utilizing the staghorn coral catalyst for biodiesel production:

i. Impregnate staghorn coral with other supports which are cheaper,

considerably effective and has better FFA and water tolerance.

ii. Utilizing different catalyst preparation techniques such as co-precipitation,

mechanochemical and physical mixing to improve the catalytic activity.

iii. Conducting other tests such as leaching test to determine the factors that lead

to catalyst deactivation.

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APPENDICES

1. Acid value (AV) calculation

56.1 M )

Where V is volume of potassium hydroxide used (mL), M is molar concentration of potassium hydroxide, W is weight of sample (g), and 56.1 is molecular weight of potassium hydroxide.

RBD palm olein Waste cooking oil

Replicate 1 Replicate 1

56.1 0.20 0.1 56.1 0.40 0.1

1.5176 1.5146

= 0.74 mg KOH g-1 = 1.48 mg KOH g-1

Replicate 2 Replicate 2

56.1 0.20 0.1 56.1 0.45 0.1

1.5409 1.5143

= 0.73 mg KOH g-1 = 1.67 mg KOH g-1

Replicate 3 Replicate 3

56.1 0.15 0.1 56.1 0.40 0.1

1.1392 1.5233

= 0.74 mg KOH g-1 = 1.47 mg KOH g-1

Average AV = 0.74 ± 0.01 mg KOH g-1 Average AV = 1.54 ± 0.10 mg KOH g-1

2. Free fatty acid (FFA) calculation

28.2 M )

Where V is volume of potassium hydroxide used (mL), M is molar concentration of potassium hydroxide, W is weight of sample (g), and 28.2 is constant use for calculating oleic.

RBD palm olein Waste cooking oil

Replicate 1 Replicate 1

28.2 0.20 0.1 28.2 0.40 0.1

1.5176 1.5146

= 0.37 % = 0.74 %

Replicate 2 Replicate 2

28.2 0.20 0.1 28.2 0.45 0.1

1.5409 1.5143

= 0.37 % = 0.84 %

Replicate 3 Replicate 3

28.2 0.15 0.1 28.2 0.40 0.1

1.1392 1.5233

= 0.37 % = 0.74 %

Average FFA = 0.37 ± 0.00 % Average FFA = 0.77 ± 0.05 %

3. Saponification value (SV) calculation

(B ) M 56.1 )

RBD palm olein Waste cooking oil

Replicate 1 Replicate 1

(30.0 22.8) 0.5 56.1 (30.0 21.2) 0.5 56.1

1.0698 1.0844

= 188.78 mg HCl g-1 = 227.63 mg HCl g-1

Replicate 2 Replicate 2

(30.0 23.1) 0.5 56.1 (30.0 22.0) 0.5 56.1

1.0443 1.0245

= 185.33 mg HCl g-1 = 219.03 mg HCl g-1

Replicate 3 Replicate 3

(30.0 23.3) 0.5 56.1 (30.0 21.8) 0.5 56.1

1.0394 1.0450

= 180.81 mg HCl g-1 = 220.11 mg HCl g-1

Average SV = 184.97 ± 3.57 mg HCl g-1 Average SV = 222.26 ± 4.19 mg HCl g-1

4. SEM image of USC at 5000x magnification

5. SEM image of CSC at 5000x magnification

6. SEM image of K-CSC at 5000x magnification

LIST OF PUBLICATIONS

Zul, N.A., Ganesan, S., Hussin, M.H., 2018. A review on the utilization of calcium oxide as a base catalyst in biodiesel production (International Journal of Ambient Energy) (under review).

Zul, N.A., Ganesan, S., Hussin, M.H., 2018. Biodiesel production through methanolysis of palm olein using catalyst derived from staghorn coral. (Journal of Physical Science) (revised manuscript).

Zul, N.A., Ganesan, S., Hussin, M.H., 2018. Application of K-impregnated staghorn coral as potential catalyst in the transesterification of waste cooking oil. (Sains Malaysiana) (accepted).

LIST OF PRESENTATIONS

International Conference

Zul, N.A., Ganesan, S., Hussin, M.H., 2017. Utilization of staghorn coral as heterogeneous base catalyst in biodiesel production. 6th International Conference for Young Chemists (ICYC), 16th – 18th August, St Giles Wembley Hotel, Penang.

International Exhibition

Zul, N.A., Ganesan, S., Hussin, M.H., 2017. Utilization of staghorn coral as heterogeneous base catalyst in biodiesel production. The 1st International Malaysia- Indonesia-Thailand Symposium on Innovation and Creativity (iMIT SIC), 26th – 27th July, Dewan Seri Semarak, UiTM Perlis. [Gold]