SELECTIVE CONVERSION OF GLYCEROL TO LACTIC ACID USING NICKEL SUPPORTED ON
CALCIUM OXIDE AND MAGNESIUM OXIDE
MUHAMMAD HAZIM BIN YAACOB
UNIVERSITI SAINS MALAYSIA
2018
SELECTIVE CONVERSION OF GLYCEROL TO LACTIC ACID USING NICKEL SUPPORTED ON CALCIUM OXIDE AND MAGNESIUM OXIDE
by
MUHAMMAD HAZIM BIN YAACOB
Thesis submitted in fulfillment of the requirements for the degree of
Master of Science
August 2018
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ACKNOWLEDGEMENT
First and above all, I praise God, the almighty for providing me this opportunity and granting me the capability to proceed successfully. I would like to express my genuine gratitude to my supervisor, Prof. Dr. Ahmad Zuhairi Abdullah for his wonderful supervision and effort he spend guiding and assisting me throughout my studies.
My sincere thanks to all the respective staff and technicians, School of Chemical Engineering for their cooperation and support. I highly appreciate to all my friends for their continuous support, kindness towards me. I am also indebted to Universiti Sains Malaysia and universities Institute of Postgraduate Study (IPS) for giving the opportunity of becoming a student in this great university. I would like to acknowledge the funding from Universiti Sains Malaysia (Grant FRGS 6071366 and Grant TRGS 6762001) and financial support from MyBrain 15 scholarship.
Last but not least, my deepest and most heart-felt gratitude to my beloved parents for their endless love and support. To those who are directly and indirectly involved in this research, your contribution shall not be forgotten. My appreciation to all of you.
Muhammad Hazim bin Yaacob
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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENT ii
TABLE OF CONTENTS iii
LIST OF TABLES vii
LIST OF FIGURES viii
LIST OF ABBREVIATIONS xii
LIST OF SYMBOLS xi
ABSTRAK xiii
ABSTRACT xv
CHAPTER ONE: INTRODUCTION
1.1 Introduction to glycerol 1
1.2 Lactic acid 4
1.3 Problem statement 7
1.4 Objectives 9
1.5 Scope of the study 9
1.6 Thesis Organization 11
CHAPTER TWO: LITERATURE REVIEW
2.1 Catalytic conversion of glycerol to lactic acid 13
2.1.1 Homogenous and heterogeneous catalyst 13
2.1.2 Homogeneous catalyst 14
2.1.3 Heterogeneous catalyst 15
2.2 Mechanism of catalytic reaction of glycerol to lactic acid 18
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2.3 Mixed metal oxide catalysts 19
2.4 Alkaline earth metal oxide catalysts 21
2.5 Dehydrogenation catalysts 24
2.6 Preparation method of catalysts 26
2.6.1 Incipient wetness impregnation method 26
2.6.2 Sol-gel method 26
2.6.3 Co-precipitation method 27
2.7 Effect of catalyst preparation on the physicochemical properties of catalysts
2.8 Effect of operating variables 30
2.8.1 Effect of reaction temperature 30
2.8.2 Effect of reaction time 33
2.8.3 Effect of catalyst loading 34
2.9 Kinetic study 35
2.10 Concluding remarks
CHAPTER THREE: METHODOLOGY
3.1 Chemicals and materials 37
3.2 Overall experimental flowchart 38
3.3 Experiment set-up and equipment 39
3.3.1 Reaction system 39
3.3.2 Product analysis system 41
3.4 Catalyst preparation 41
3.4.1 Preparation of catalysts 41
3.4.2 Effect of Ni/Ca ratio 42
3.4.3 Effect of calcination temperature 42
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36
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3.5 Catalyst characterization 42
3.5.1 Temperature programmed desorption of carbon dioxide (CO2- TPD)
3.5.2 Field emission scanning electron microscopy (FESEM) 43 3.5.3 Energy dispersive X-ray spectroscopy (EDX) 43
3.5.4 Thermal gravimetric analysis (TGA) 43
3.5.5 Surface analysis 43
3.6 Catalytic activity 44
3.6.1 Procedure for reaction run 44
3.6.2 Product analysis 44
3.7 Kinetic study 45
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Preliminary study on the synthesized catalysts for conversion of glycerol to lactic acid
4.1.1 Characterization of MgO, CaO, NiO, NiO/MgO and NiO/CaO 47 4.1.1 (a) Thermal gravimetric analysis (TGA) 47 4.1.1 (b) Scanning electron microscopy (SEM) 49 4.1.1 (c) Temperature-programmed desorption of carbon
dioxide
4.1.2 Activity study 53
4.2 Influence of Ni/Ca ratio on selective conversion of glycerol to lactic acid
4.2.1 Characterization of the 0.25NiO/CaO, 0.43NiO/CaO and 0.67NiO/CaO catalysts
4.2.1 (a) Scanning electron microscopy (SEM) 56
4.2.1 (b) Surface analysis 57
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47
56 51
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4.2.1 (c) Temperature-programmed desorption of carbon dioxide
4.2.2 Activity study 61
4.3 Influence of calcination temperature on the selective conversion of glycerol to lactic acid
4.3.1 Characterization of 0.43NiO/CaO-800°C, 0.43NiO/CaO- 900°C and 0.43NiO/CaO-1000°C
4.3.1 (a) Surface analysis 63
4.3.1 (b) Temperature-programmed desorption of carbon dioxide
4.3.2 Activity study 67
4.4 Influence of reaction conditions on the selective conversion of glycerol to lactic acid
4.4.1 Effect of reaction temperature and time 69
4.4.2 Effect of catalyst loading 72
4.5 Catalyst stability and reusability 73
4.6 Kinetic study 76
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.1 Conclusions 79
5.2 Recommendations 80
REFERENCES 81
APPENDICES
Appendix A: Chromatograms Appendix B: Sample of calculation Appendix C: Product samples
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69 65 63 58
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LIST OF TABLES
Page Table 1.1 Physical and chemical properties of lactic acid 5 Table 1.2 Applications of lactic acid in different fields 6 Table 2.1 Summary the performances of mixed metal oxide catalysts in
various reactions
Table 2.2 Summary the performances of mixed metal oxide catalysts in biodiesel production
Table 2.3 Summary the performances of noble metal catalysts in the production of lactic acid
Table 3.1 List of chemicals and descriptions 37
Table 3.2 List of equipment and descriptions 39
Table 4.1 Basic site distributions of NiO, MgO, CaO, NiO/MgO and NiO/CaO catalysts
Table 4.2 The surface properties of NiO/CaO catalyst derived from different Ni/Ca ratio
Table 4.3 Basic sites distribution of 0.25NiO/CaO, 0.43NiO/CaO and 0.67NiO/CaO catalysts
Table 4.4 The surface properties of the 0.43NiO/CaO catalyst prepared with different calcination temperature
Table 4.5 Basic site distributions of the 0.43NiO/CaO-800, 0.43NiO/CaO- 900 and 0.43NiO/CaO-1000 catalysts
Table 4.6 Chemical composition of fresh, R1 and R2 catalysts 75 Table 4.7 Comparison of glycerol concentration calculated by developed
model with the experimental results at different reaction temperatures
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23
25
67 65 60 57 52
78
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LIST OF FIGURES
Page Figure 1.1 Glycerol production within 2001-2011 and prices (Quispe et al.,
2013)
Figure 1.2 Source of glycerol in 2010 (ABG Inc, 2010) 3
Figure 1.3 Chemical structure of lactic acid 4
Figure 2.1 Proposed reaction pathway for conversion of glycerol to lactic acid (Kumar et al., 2014)
Figure 2.2 SEM images of the NiO/CaO catalyst prepared with (a) co- precipitation method (Hwa et al., 2014) (b) incipient impregnation method (Alca and Cruz-herna, 2016)
Figure 2.3 Reaction pathways of oxidative cleavage of lactic acid under alkaline medium (a) and dehydration of lactate (b) (Ramirez et al., 2010)
Figure 2.4 Reaction pathway for formation of 1,2-propanediol via catalytic dehydrogenation of glycerol (Yin et al., 2017)
Figure 3.1 Flowchart of overall experimental works 38
Figure 3.2 The schematic diagram of the batch reactor 40 Figure 4.1 TGA profiles of NiO/CaO and NiO/MgO uncalcined catalysts 48 Figure 4.2 SEM images of (a) CaO at magnification of 15,000 X, (b) MgO
at magnification of 20,000 X, (c) NiO at magnification of 15,000 X, (d) NiO/CaO at magnification of 15,000 X and (e) NiO/MgO at magnification of 15,000 X
Figure 4.3 CO2-TPD profiles of NiO, MgO, CaO, NiO/MgO and NiO/CaO catalysts
Figure 4.4 Glycerol conversion and lactic acid yield in the reaction catalyzed by NiO, MgO, CaO, NiO/MgO and NiO/CaO catalysts
Figure 4.5 SEM images of (a) CaO at magnification of 15,000 X, (b) 0.25NiO/CaO at magnification of 15,000 X, (c) 0.43NiO/CaO at magnification of 15,000 X and (d) 0.67NiO/CaO at magnification of 15,000 X
18 29
31
32 2
50
52
55
57
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Figure 4.6 CO2-TPD profiles of the 0.25NiO/CaO, 0.43NiO/CaO, and 0.67NiO/CaO catalysts
Figure 4.7 Glycerol conversion and lactic acid yield in the reaction catalyzed by 0.25NiO/CaO, 0.43NiO/CaO and 0.67NiO/CaO catalysts
Figure 4.8 Nitrogen adsorption-desorption isotherms for the effect of calcination temperature
Figure 4.9 CO2-TPD profiles of the 0.43NiO/CaO-800, 0.43NiO/CaO-900 and 0.43NiO/CaO-1000 catalysts
Figure 4.10 Glycerol conversion and lactic acid yield in the reaction catalyzed by 0.43NiO/CaO-800, 0.43NiO/CaO-900 and 0.43NiO/CaO-1000 catalysts
Figure 4.11 Effect of reaction temperature on the glycerol conversion 70 Figure 4.12 Effect of reaction temperature on the yield of lactic acid 71 Figure 4.13 Effect of catalyst loading on glycerol conversion and yield of
lactic acid
Figure 4.14 Glycerol conversion and lactic acid yield of fresh and recycled catalysts
Figure 4.15 Plot of ln k vs 1/T for 0.43NiO/CaO-900 catalyst 77 Figure 4.16 Plot of predicted against experimental data for concentration of
glycerol
78 74 73 68 66 64 62 59
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LIST OF ABBREVIATIONS
Au Gold
Al2O3 Aluminium oxide
BET Brunauer-Emmett-Teller
C Carbon
CO2-TPD Temperature programmed desorption of carbon dioxide
CuO Copper oxide
CaO Calcium oxide
Ce2O Cerium oxide
DHA Dihydroxyacetone
EDX Energy dispersive X-ray
HPLC High performance liquid chromatography
Ir Iridium
KOH Potassium hydroxide
La2O3 Lanthanum oxide
MgO Magnesium oxide
MoO3 Molybdenum oxide
NiO Nickel oxide
NaOH Sodium hydroxide
OH- Hydroxide ions
Pd Palladium
Pt Platinum
Rh Rhodium
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SrO Strontium oxide
SEM Scanning electron microscopy
SiO3 Silicate
TGA Thermal gravimetric analysis
TiO2 Titanium dioxide
XRD X-ray diffraction
ZrO2 Zirconia oxide
ZnO Zinc oxide
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LIST OF SYMBOLS
Symbols Description Unit
A Pre-exponential factor min-1
CLA Concentration of lactic acid mol·L-1 CGLY Concentration of glycerol mol·L-1 CGLYO Initial concentration of glycerol mol·L-1
Ea Activation energy kJ·mol-1
k Reaction rate constant min-1
M Molarity Dimensionless
pH Potential hydrogen Dimensionless
R Gas constant J·K-1·mol-1
R2 Correlation coefficient Dimensionless
t Time min
T Temperature K
XGLY Conversion of glycerol Dimensionless
YLA Yield of lactic acid Dimensionless
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PENUKARAN TERPILIH GLISEROL KEPADA ASID LAKTIK DENGAN MENGGUNAKAN NIKEL YANG DISOKONG OLEH KALSIUM OKSIDA
DAN MAGNESIUM OKSIDA
ABSTRAK
Peningkatan pesat dalam pengeluaran biodiesel di seluruh dunia menjana lebihan gliserol mentah sebagai produk utama yang memberi kesan yang buruk kepada harga pasaran gliserol. Untuk mengekalkan industri gliserol, pembangunan kepada produk bernilai tinggi daripada gliserol amat diperlukan. Asid laktik telah mendapat perhatian yang meluas disebabkan kepelbagaian aplikasinya di dalam industri makanan, kosmetik dan farmaseutikal. Dalam penyelidikan ini, gliserol telah ditukarkan kepada asid laktik melalui tindak balas pemangkin bes. Jenis mangkin yang berbeza (MgO, CaO, NiO, NiO/MgO dan NiO/CaO) telah digunakan pada tindak balas ini. Di antara pemangkin ini, NiO/CaO menunjukkan aktiviti yang tinggi dan telah dipilih untuk kajian yang seterusnya. Mangkin NiO/CaO telah disentesis dengan nisbah molar Ni/Ca (0.25, 0.43 dan 0.67) dan suhu pengkalsinan yang berbeza (800, 900 dan 1000°C). Di samping itu, sifat fizikokimia bagi mangkin ini telah dicirikan melalui penjerapan nitrogen, penyahjerapan karbon dioksida berprogramkan suhu (CO2-TPD), mikroskop pengimbas elektron (SEM) dan analisis gravimetri termal (TGA). Kesan keadaan tindak balas seperti masa tindak balas (30–
160 minit), suhu tindak balas (280-300°C) dan bebanan mangkin (10-20 % berat) dikaji bagi mengenalpasti keadaan tindak balas yang terbaik untuk dapatkan hasil asid laktik yang tinggi. Didapati bahawa mangkin NiO/CaO menunjukkan aktiviti yang tertinggi dengan nisbah Ni/Ca 0.43 dan dikalsin pada 900°C. Tambahan lagi,
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didapati mangkin ini sesuai untuk digunakan pada tindak balas ini kerana ia memiliki kadar bes yang tinggi iaitu 11.28 mmol/g. Oleh itu, peningkatan jumlah bes pada mangkin mungkin menggalakkan pertukaran gliserol kepada asid laktik. 93.2%
penukaran gliserol dan 41.3% hasil asid laktik telah berjaya diperolehi pada 290°C dalam 1.5 jam dengan bebanan mangkin 15% berat. Selain itu, mangkin ini boleh digunakan semula sehingga dua kali dengan sedikit penurunan dalam penukaran gliserol dari 89.3% ke 78.0%. Ini disebabkan oleh pengurasan kalsium daripada mangkin ke dalam gliserol. Walau bagaimanapun, sebanyak 28.7% hasil asid laktik boleh diperolehi setelah dua kitaran pemangkin. Model kinetik bagi kepekatan gliserol dalam penukaran gliserol dengan menggunakan 0.43NiO/CaO-900 sebagai mangkin telah juga dibangunkan. Model ini mampu untuk menerangkan reaksi sebenar di dalam reaktor pada kadar suhu 280-300°C. Oleh itu, ia kelihatan yang mangkin NiO/CaO mempunyai potensi pemangkin untuk penghasilan asid laktik dari gliserol.
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SELECTIVE CONVERSION OF GLYCEROL TO LACTIC ACID USING NICKEL SUPPORTED ON CALCIUM OXIDE AND MAGNESIUM OXIDE
ABSTRACT
The rapid increase of biodiesel production worldwide generates an excess of crude glycerol as the primary co-product which negatively affect the price of glycerol in the market. In order to sustain the glycerol industry, the development of value-added chemicals from glycerol is necessary. Among them, lactic acid has received a considerable attention due to its numerous applications in the food, cosmetic and pharmaceutical industries. In this study, glycerol was upgraded to lactic acid through a base catalyzed reaction. Different types of catalyst (MgO, CaO, NiO, NiO/MgO and NiO/CaO) were used in this reaction. Among these catalysts, NiO/CaO showed high activity and was selected for the following study. NiO/CaO catalysts were synthesized with different molar ratios of Ni/Ca (0.25, 0.43 and 0.67) and calcination temperatures (800, 900 and 1000°C). In addition, the physicochemical properties of these catalysts were characterized by nitrogen adsorption, temperature programmed desorption of carbon dioxide (CO2-TPD), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA).
Effects of reaction conditions such as reaction time (30-160 min), reaction temperature (280-300°C) and catalyst loading (10-20 wt. %) were also studied to identify the best reaction conditions obtain high lactic acid yield. It was found that NiO/CaO catalyst demonstrated the highest activity at a Ni/Ca ratio of 0.43 and calcined at 900°C. Furthermore, this catalyst was found to be excellent to be used in this reaction as it possessed the high amount basicity of 11.28 mmol/g. Thus, the
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increase in the total basicity of the catalyst might have favored its glycerol conversion to lactic acid. 93.2% of glycerol was converted to give 41.3% yield of lactic. Besides, this catalyst was reusable up to two cycles with a reduction in glycerol conversion from 89.3% to 78.0%. This could be due to leaching of calcium from the catalyst into glycerol. Nevertheless, high yield of lactic acid up to 28.7%
could still be obtained after two catalytic cycles. A kinetic model for the glycerol concentration in glycerol conversion using 0.43NiO/CaO-900 as catalyst is also developed. This model could well describe the actual reaction occurring in the reactor in a temperature range of 280-300°C. Therefore, it appeared that CaO/NiO catalyst is a potential catalyst for lactic acid production from glycerol.
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CHAPTER ONE INTRODUCTION
1.1 Introduction to glycerol
Glycerol is known as a biodegradable, renewable and environmentally friendly product. With such properties, glycerol grabs the attention as alternative green fuel for organic reactions and applicable in many areas. Glycerol can be obtained as a by-product from the biodiesel production process when triglycerides (vegetable oils or animal fats) which consist of long chains of fatty acids are attached to three hydroxyl groups upon reaction with alcohol (methanol) in the presence of alkaline catalysts (Pagliaro et al., 2008). Generally, biodiesel that is produced through transesterification process of triglyceride will produce around 10 wt. % of crude glycerol or for every 100 kg of methyl ester (biodiesel) produced, approximately 10 kg of crude glycerol is generated (Yang et al., 2012).
From 2000 to 2005, glycerol production was dominated by fatty acid industry where the annual production of glycerol was remained relatively stable with the price of refined glycerol during that period ranged from USD 1,600 to USD 1,800 per ton (Quispe et al., 2013). However, by 2006 biodiesel industry started to dominate the production of glycerol from other industries causing a significant increase in the production of glycerol. The massive increase in glycerol production causes the price of glycerol to decline each year (Figure 1.1). This trend is expected to continue since there is high demand on biodiesel in the market as it is the most promising energy source to replace fossil fuel, especially when fossil fuel is estimated to be depleted by 2050 (Goyal et al., 2013).
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Figure 1.1: Glycerol production within 2001-2011 and prices (Quispe et al., 2013).
The global glycerol market nowadays facing an oversupply problem because of the remarkable increase in biodiesel production. The distribution of glycerol production in different industries is shown in Figure 1.2. Apparently, biodiesel industry is the highest contributor to the glycerol market at around 67% in comparison to other contributing industries such as fatty acid, fatty alcohol, soap and others (ABG Inc, 2010). Besides, it was reported that the residual glycerol produced from biodiesel industry has the potential to be the source of energy by using incineration method. Although this method seems to be plausible in order to solve the problem regarding the glut of glycerol in the market but burning of glycerol at high temperature will generate highly toxic materials such as acrolein (Guerrero- Pérez et al., 2009).
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Figure 1.2: Source of glycerol in 2010 (ABG Inc, 2010).
To overcome the problem regarding the surplus of glycerol in the market, many researches are focusing their research on the utilization of glycerol to obtain value-added chemicals that could help to stabilize glycerol market price. The unique properties of glycerol offer a variety of versatile products to be produced in downstream industries. At present, large number of value-added products such as propionic acid, 1,3-propanediol, acrolein, alcohol (methanol and ethanol), monoglyceride and many more can be obtained from glycerol.
Biodiesel 67%
Fatty acids 21%
Soap 4%
Fatty alcohol 8%
4 1.2 Lactic acid
Among a number of value-added chemicals that can be produced from glycerol, lactic acid has received a considerable attention in the past few years.
Lactic acid or 2-hydroxypropanoic acid consist of a hydroxyl group adjacent to the carboxyl group as shown in Figure 1.3. These hydroxyl and carboxyl groups responsible in modifying lactic acid into other value-added chemicals such as lactic amide, lactide, pyruvic acid and acrylic acid that are very useful in many applications (Andres et al., 2013).
Figure 1.3: Chemical structure of lactic acid.
The annual production of lactic acid continued to increase steadily for the past 10 years with the price of lactic acid range of USD 2,075 to USD 2,300 per ton with the global lactic acid market was valued at about USD 1.28 billion in 2014 and is expected to reach USD 9.8 billion by 2025 (Grand View Research, 2017). The increase in lactic acid production each year is due to the high demand in food applications such as pH control agent, food additive and preservative agent.
Moreover, lactic acid is also incorporated in cosmetic and personal care products for its humectant properties. Due to its ability to form another value-added chemicals,
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lactic acid also is widely used in other industries such as packaging, textile and pharmaceutical. The applications and uses of lactic acid are summarized in Table 1.2.
Table 1.1: Physical and chemical properties of lactic acid.
Properties Values
Chemical formula C3H6O3
Molecular weight 90.08
Physical appearance Colourless to yellow liquid
Melting point (°C) 53
Boiling point (°C) >200
Solubility in water (g/100g H2O) Miscible
pKa 3.86
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Table 1.2: Applications of lactic acid in different fields.
Application Uses Purposes Reference
Food industry Food additives, preservative agent and pH regulator
Production of yogurt and cheese (Razali and Abdullah, 2017)
Textile industry Polymer additives, adhesives, coatings, printing toners, and surfactants
For use in tents, patio umbrellas, and awnings
(Kwan et al., 2018)
Cosmetic industry Moisturizing, pH adjuster, exfoliant, antimicrobial and rejuvenating effects on the skin
Manufacture of hygiene such as toothpaste, mouthwashes and many others
(Andres et al., 2013)
Pharmaceutical industry Prostheses, surgical sutures, dialysis solution mineral and drug delivery systems
Production of dermatologic drugs and prevention for osteoporosis
(Pagliaro et al., 2008)
Packaging industry Production of biodegradable plastic Food packaging (Hu et al., 2017)
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There are two alternative routes for producing lactic acid either by fermentation or chemical catalysis. Presently, lactic acid is commercially produced mostly through fermentation of carbohydrates (glucose or sucrose). Microbes like L.
delbrueckii, L. amylophilus and L. bulgaricus are commonly used in the fermentation process for the production of lactic acid (Andres et al., 2013). The selection of microorganism for the fermentation processes is essential since each of the microorganism has its own characteristics which can determine the yield and selectivity of lactic acid.
Alternatively, commercial production of lactic acid can be achieved through chemical synthesis route by hydrolysis of lactonitrile by strong acid such as sulphuric acid. Lactonitrile could be obtained as a by-product from the manufacture of acrylonitrile (Chen et al., 2014). Lactonitrile can be achieved when acetaldehyde is reacted with hydrogen cyanide under high pressure in the presence of a base. The advantage of using lactonitrile route to manufacture lactic acid is that the procedure is simple in comparison to the fermentation route as described earlier. However, because of the limitations for the raw materials and expensive operational costs, this process is not very feasible for industrial application.
1.3 Problem statement
Although fermentation process is an excellent process in producing high yield of lactic acid, there are major drawbacks. Some problems faced by fermentation process are associated with the high maintenance costs of the process due to the fact that certain types of microorganism require specific conditions for producing lactic acid. Conditions such as pH level, temperature, time, aeration and agitation must be closely monitored. Moreover, purification process is needed in order to reduce impurities in the final product. Expensive purification method such as membrane
