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Microwave-assisted acid-catalyzed synthesis and analysis ofbiodiesel using multiple feedstocks

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MICROWAVE-ASSISTED ACID-CATALYZED SYNTHESIS AND ANALYSIS OF
BIODIESEL USING M ULTIPLE FEED STO CK S
by
CHAMILA MEETIYAGODA, B.S.
Presented to the Faculty of th e G raduate School of
Stephen F. A ustin State University
In P artial Fulfillment
of the Requirem ents
For the Degree of
M aster of Science in N atural Sciences
STEPH EN F. AUSTIN STATE UNIVERSITY
August, 2016
P roQ uest Num ber: 10294189
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A BSTRA CT
F atty acid alkyl esters (FAAE) were synthesized under microwave-assisted
acid-catalyzed transesterification using various feedstocks (canola, castor, coconut,
corn, ghee, olive, palm olein, peanut, soybean, sunflower oils, and waste vegetable
oil (W VO)) w ith m ethanol and ethanol and H2S 0 4 as a catalyst. Biodiesel is a good
alternative to petroleum diesel fuel because it is renewable, biodegradable, and
nontoxic. In this study, microwave-assisted transesterification (MAT) was used to
expedite the reaction tim e using acid catalysts. FAAE were synthesized by MAT
using oil/alcohol volume and molar ratios, MAT using high tem perature for canola
and soybean oils, and MAT using S i0 2/ 50% H2S 0 4 as solid catalyst for castor oil.
Reaction param eters such as oil/alcohol ratio, reaction tem perature, reaction time,
and catalyst loading were optimized for each oil. All FAAE were analyzed using
1H—NMR spectroscopy and G C/M S. Experim ental results showed th a t MAT is
energy efficient compared to CHT (conventionally-heated transesterification) using
volume ratios. Also, MAT using molar ratios showed b etter conversion for most of
the oils compared to volume ratios. C astor oil was the best oil to produce FAME
(fatty acid m ethyl esters) using both m ethods. Com plete conversions were observed
for elevated tem perature experim ents for 10 min and more th an 80% conversions
were obtained using solid catalyst for 45 min.
ACKNOWLEDGEMENTS
F irst and foremost I would like to th an k my advisor, Dr, Russell Franks for
giving me advice, guidance and encouragement to success this work. It has been
honor and pleasure to work w ith him. I would also like to express my gratitude to
Dr. Michele Harris, Dr. O dutayo Odunuga, and Dr. Kent Riggs for their help,
understanding, and advice as my thesis com m ittee members.
Also, I want to give my special thanks to Dr. Kefa Onchoke for giving me
assistance to use analytical instrum ents. He was always ready to help me. I would
like to thank D epartm ent of Chem istry and Biochemistry and also Welch
Scholarship for supporting me verbally and financially to complete my research and
degree.
I want to give my gratitude to my parents, siblings and my family for giving
me the encouragement and the support to success my education up to now. The
last but not the least, I want to special th an k to my husband Kalanka Jayalath and
my daughter Nesandi for understanding me and supporting to complete my m aster
degree and research successfully. I love you both.
TABLE OF CONTENTS
LIST O F F IG U R E S ........................................................................................................
vi
LIST OF T A B L E S .........................................................................................................
viii
C H A PTE R 1 ....................................................................................................................
1
Introduction and L iterature review.............................................................................
1
1.1 Advantages and Disadvantages of Biodiesel.................................................
3
1.2 Physical and Chemical Properties of Biodiesel...........................................
5
1.3 Feedstocks Used for B io d ie s e l.......................................................................
7
1.4 T ran sesterificatio n ...........................................................................................
10
1.4.1 A lkaline-C atalyzed T ra n s e s te rific a tio n .............................................
13
1.4.2 Acid-Catalyzed T ran sesterificatio n .................................................
17
1.4.3 Enzym atic-Catalyzed T ran sesterificatio n .....................................
21
1.5 Microwave-Assisted T ran sesterificatio n ....................................................
22
C H A PTE R 2 ................................................................................................................
28
Methodology.....................................................................................................................
28
2.1 R e a g e n ts .............................................................................................................
28
2.2 A p p a ra tu s ...........................................................................................................
28
2.3 Experim ental Procedure..................................................................................
31
2.3.1 Microwave-Assisted Transesterification (MAT) Procedures
. .
31
2.3.1.1 MAT using Oil/Alcohol Volume R a tio s..............................
31
2.3.1.2 MAT using Oil/Alcohol Molar R a tio s ..................................
33
iii
2.3.1.3 MAT using High Tem peratures for Canola and Soybean
O ils...............................................................................................
35
2.3.1.4 MAT using SiO2/50% H2S 0 4 as a Heterogeneous C atalyst
for C astor O i l ............................................................................
36
2.3.2 Conventional H eating Transesterification (CHT) Procedures .
37
2.3.3 A nalytical M e th o d s .............................................................................
38
2.3.3.1 1H —NMR A nalysis...................................................................
38
2.3.3.2 G C /M S A n a ly sis.......................................................................
39
C H A PTE R 3 ...............................................................................................................
40
Results and D iscussion...............................................................................................
40
3.1 FAAE Identification and percentage conversion - Volume R atios . . .
40
3.1.1 MAT Oil/Alcohol Volume R a t i o s ....................................................
40
3.1.2 CHT Oil/Alcohol Volume R a t i o s ....................................................
45
3.1.3 Comparison of MAT and CHT Oil/Alcohol Volume R atio
3.1.4
3.2 FAAE
R eactions...............................................................................................
47
Disadvantages of Oil/Alcohol Volume R atio re a c tio n s .............
47
Identification and percentage conversion -
Molar Ratios . . . .
3.3 FAAE Identification and percentage conversion - high tem peratures .
3.4 FAAE
Identification and percentage conversion -
49
54
Heterogeneous
C a ta ly s t...............................................................................................................
55
3.5 Discussion of W ashing and Extraction Procedures..................................
56
C H A PTE R 4 ...............................................................................................................
59
Conclusion and Future W o rk s ...................................................................................
59
iv
4.1 Conclusion
4.2 Future Works
BIBLIOGRAPHY
LIST OF FIGURES
S tructure of a typical trig ly cerid e..................................................
7
The chemical structures of the most common fatty acids.
. .
8
Transesterification reaction of triglyceride with m ethanol.
. .
11
Sequential transesterification reactions of triglyceride, diglyc­
eride, and monoglyceride w ith m ethanol.......................................
11
Homogeneous base-catalyzed transesterification mechanism of
triglyceride.............................................................................................
14
Base catalyzed reaction w ith FFAs to produce soap and water.
14
Hydrolysis of biodiesel in the presence of base cataly st.............
15
Reaction of potassium carbonate w ith m ethanol........................
15
Acid-catalyzed transesterification....................................................
17
Homogeneous acid-catalyzed transesterification mechanism of
triglyceride.............................................................................................
18
Two-step transesterification process...............................................
20
The electrom agnetic s p e c t r u m ......................................................
23
Ionic conduction and dipole polarization under microwave con­
ditions
.................................................................................................
T he conventional and microwave heating mechanisms
. . . .
Experim ental apparatus for microwave-assisted reactions.
24
25
. .
29
Experim ental apparatus for conventionally-heated reactions .
30
A pparatus for elevated-tem perature r e a c tio n s ...........................
30
Crude biodiesel placed in a separatory f u n n e l ...........................
33
Photographs of FAAE product m ix tu r e s .....................................
40
vi
Figure
20: 1H —NMR spectra for coconut oil and its FAAE product m ixtures
41
Figure
21: Gas chrom atogram for coconut oil methyl ester...........................
44
Figure
22: !H —NMR spectra for coconut oil and its FAAE product mix­
tures for overnight reactions
Figure
.........................................................
45
23: Gas chrom atogram for coconut oil m ethyl ester for overnight
reaction...................................................................................................
46
Figure
24: 1H —NMR spectra for canola oil and its FAAE product m ixtures
50
Figure
25: Gas chrom atogram for canola oil m ethyl ester..............................
52
Figure
26: 1H —NMR spectra of product m ixtures from high-tem perature
experim ents
Figure
.......................................................................................
27: 1H —NMR spectra for castor oil and its FAAE product m ixtures
55
57
LIST OF TABLES
Table 1:
Table 2:
Average biodiesel (B100 and B20) emissions compared to conven­
tional diesel..................................................................................................
4
Chemical and physical properties of petroleum diesel and biodiesel.
6
Table 3:
Typical saturated and u n satu rated fatty acids in biodiesel.
Table 4:
F atty acid compositions of feedstocks used for this study.
...
9
. . . .
10
Table 5:
The molar masses of triglycerides used for this study.............
Table 6:
Percentage conversions for MAT oil/alcohol volume ratios . . . .
Table 7:
The m ethyl ester profile of coconut oil for MAT oil/m ethanol
34
42
volume ratio .................................................................................................
44
Table 8:
Percentage conversions for CHT oil/alcohol volume ratios . . . .
46
Table 9:
Conversion/H our for MAT and CHT Oil/Alcohol Volume R atios
48
Table 10:
Percentage conversions for MAT oil/alcohol molar r a tio s .....
51
Table 11:
The FAME profile of canola oil for MAT oil/m ethanol m olar ratio.
53
Table 12:
The percentage conversion for elevated tem p eratu res.....................
54
Table 13:
The percentage conversion for castor oil using acidic silica gel as
solid cataly st...............................................................................................
viii
56
CHAPTER 1
In tro d u c tio n a n d L ite ra tu re R eview
Today there is an increasing interest in developing alternative energy resources
due to lim ited fossil fuel resources, rising crude oil prices, and environm ental
concerns over fossil fuel use. Biodiesel is a good alternative to petroleum diesel fuel
because it is renewable, environm entally friendly, and can be synthesized easily.
Even though biodiesel synthesis has been popular since late the 1970s,
biodiesel has a long history.1 The use of vegetable oil as a fuel is not a new idea.
The concept of biodiesel was first used by Rudolf Diesel for the dem onstration of
the diesel engine using peanut oil as a fuel in the 1890s.2 During W orld W ar II,
vegetable oils were again used as fuels for em ergency s itu a tio n s .3 Today, biodiesel
has a prom inent position as an alternative to petroleum -based diesel fuel.
Vegetable oils have com parable energy density, cetane number, heat of
vaporization, and stoichiometric air/fuel ratio with petroleum diesel fuel.4 However,
they are not suitable to use as a fuel. Com pared to petroleum diesel fuel, vegetable
oils have high viscosity, low heating value, high carbon residue, high molecular
weight, and poor volatility characteristics.5 These poor properties lead to poor
combustion, fuel injector clogging, and poor cold engine sta rt-u p .6 Therefore,
vegetable oils have to be modified by changing their properties to make them closer
to petroleum diesel fuel.
Different approaches (e.g. dilution, microemulsion, pyrolysis, and
transesterification) have been used to reduce the viscosity of vegetable o il.7 However,
transesterification is the most common m ethod, since it can be applied to any
feedstock, alcohol, and catalyst. Making biodiesel via transesterification is a very
1
effective process, because alkyl esters have b etter fuel properties com pared to neat
vegetable oils. The transesterification process helps to reduce viscosity, molecular
weight, and polyunsaturated character and increase volatility in vegetable oils.8
Usually, vegetable oils (soybean, coconut, palm, safflower, rapeseed, etc.),
animal fats (commonly tallow), and waste oils (used cooking oil) are used as
feedstocks for biodiesel.9 These feedstocks mainly contain triglycerides. In the
transesterification process, biodiesel is produced by reacting the triglyceride
feedstock with an alcohol in the presence of a catalyst. Hence, biodiesel refers to a
m ixture of alkyl esters of these feedstocks. The most commonly used alcohol is
m ethanol because of its low cost compared to other alcohols. The catalyst can be a
base, an acid, or an enzyme. Sodium and potassium hydroxide (NaOH, KOH) and
th e ir corresponding methoxides (NaOCH3, KOCH3) are used as alkali cataly sts.
Sulfuric, sulfonic, and hydrochloric acids (H2S 0 4, R S 0 3H, and HC1) are commonly
used as acid catalysts. Immobilized lipase is commonly used as an enzyme catalyst.
Also, these catalysts can be homogeneous or heterogeneous.
Based on the catalyst used, the transesterification process can be classified as
being acid-catalyzed, base-catalyzed, or enzyme-catalyzed. Also, non-catalytic
tranesterifcation biodiesel syntheses have been reported in lite ra tu re .10,11 The most
common m ethod is base-catalyzed transesterification due to its fast reaction time.
However, this process is not appropriate w ith feedstocks th a t contain a high content
of high free fatty acids (FFAs) because saponification (soap form ation) can occur.
Acid-catalyzed and enzyme-catalyzed transesterification processes are particularly
suitable w ith high-FFA content feedstock.
The classic transesterification m ethod used to synthesize biodiesel is
perform ed via conventional heating, However, various novel processes have been
2
developed to reduce the reaction time. Currently, microwave-assisted
transesterification is very popular since it has a faster reaction tim e com pared to
conventional heating methods. Also, ultrasound-assisted transesterification12,13 and
supercritical transesterification m eth o d s14,15 have been recently developed.
In this research, the main objective was to develop a microwave-assisted
transesterification protocol for acid-catalyzed biodiesel synthesis since acid-catalyzed
transesterification using conventional heating is slow. Biodiesel was produced from
different oils (canola, castor, coconut, corn, cow ghee, olive, palm olein, peanut,
soybean, sunflower, and waste vegetable oil (W VO)) using m ethanol and ethanol as
the alcohols and H2S 0 4 as the catalyst. Reaction param eters such as oil/alcohol
volume and molar ratios, catalyst loading, reaction tem perature, mixing intensity,
and reactio n tim e were optim ized for each oil. Biodiesel sam ples were identified
using 1H —NMR spectroscopy and G C /M S analytical m ethods. T he percentage
conversion was calculated using JH -N M R spectroscopy. B oth microwave-assisted
and conventional heating m ethods were com pared in order to determ ine the more
efficient process. High tem perature and heterogeneous catalyst (SiO2/50% H2S 0 4)
were used to reduce the reaction tim e using microwave irradiation.
1.1 A dvan tag es an d D isadv an tag es o f B iodiesel
Biodiesel has numerous advantages over petroleum diesel. Biodiesel is used for
diesel engine vehicles and off-road equipm ent such as farm, forestry, and
construction equipment. Biodiesel is used in its pure form (B100). Biodiesel can
also easily be blended w ith petroleum diesel in m ixtures of 2% (B2), 5% (B5), and
20% (B20). B100 can be used in regular diesel vehicles, although older diesel
engines require minor engine modification. Nevertheless, B5 and B20 can be used in
3
unmodified diesel engines.16 Also biodiesel is used in industrial boilers, diesel
generators, and heating oil applications.9 Normally, blended biodiesel is used for
these applications, because NOx and SOx emissions are reduced when th e two fuels
are blended.
Table 1: Average biodiesel (B100 and B20) emissions com pared to conventional
diesel.17
Emission Type
Regulated
Total Unburned Hydrocarbons
CO
P articulate M atter
NOx
Non-Regulated
Sulfates
PAH (Polycyclic Arom atic Hydrocarbons)
nPAH (nitrated PAHs)
Ozone potential of speciated HC
B100a
B20b
-67%
-48%
-47%
+10%
-20%
-12%
-12%
±2%
-100%
-80%
-90%
-50%
-20%
-13%
-50%
-10%
° 100% Biodiesel. 6 A blend of 20% Biodiesel and 80% conventional
petroleum -based diesel.
The m ajor attraction for biodiesel is th a t it is a renewable domestic resource.
Biodiesel is produced from plant oils, used cooking oil, or anim al fats. Plants
produce oils from sunlight and air; hence, this is a cyclic process. Also, animal fats
are produced when animals consume plants; hence, they also p articipate in this
cyclic process. Moreover, used cooking oils are plant oils or anim al fats. Therefore,
these oils are renewable and recyclable.
In addition to its renewable nature, biodiesel is environm entally friendly and
non-toxic. Com pared to petroleum diesel, biodiesel has lower CO and hydrocarbon
emissions. The oxygen content of biodiesel is higher th an petroleum diesel,
therefore, biodiesel combusts more completely to produce C 0 2 rath er th a n CO as a
product of its combustion. Also, biodiesel does not produce significant am ounts of
sulfur dioxide (S 0 2) because it contains very little sulfur (Table 1). Moreover,
biodiesel does not contain any polycyclic arom atic hydrocarbons or crude oil
residues.16 Biodiesel recycles carbon dioxide ( C 0 2), thus, it does not contribute to
global warming. Moreover, biodiesel has good lubricity and good com bustion
efficiency, thus it can increase the lifetime of diesel engines.
Nevertheless, biodiesel has some disadvantages. T he main disadvantage is the
high cost of biodiesel feedstocks, which are more expensive th a n petroleum diesel.
Moreover, compared to petroleum diesel, biodiesel contains more carbon-carbon
double bonds. These molecules w ith carbon-carbon double bonds have a slightly
higher adiabatic flame tem perature, which leads to an increase in NOx production
for biodiesel. NOx emissions can contribute to the form ation of sm og.18 Also,
biodiesel can dam age rubber hoses in some engines. At lower tem peratures pure
biodiesel has significant problems because it has a high cloud p o in t.19 Therefore, it
can form a waxy solid at lower tem peratures. In addition, w ater is more soluble in
biodiesel, which can lead to problems such as corrosion of fuel system com ponents
and clogged fuel filters.20
1.2 P h y sical an d C hem ical P ro p e rtie s o f B iodiesel
Table 2 shows the physical and chemical properties of biodiesel com pared to
petroleum diesel. B100 is a good solvent; therefore, it can be easily blended w ith
petroleum diesel. Also, B100 freezes at higher tem peratures th an petroleum diesel.
Therefore, B20 blends are commonly used in cold areas in order to avoid
cold-tem perature problems associated w ith biodiesel.
Biodiesel has high lubricity, cetane number, and flash point com pared to
5
Table 2: Chemical and physical properties of petroleum diesel and biodiesel.21
Fuel Property
Fuel S tandard
Higher H eating Value, B tu /g al
Lower Heating Value, B tu /g al
Kinematic Viscosity, cSt at 40 °C
Specific Gravity, kg/L at 15.5 °C
Density, lb /g al at 15.5 °C
Carbon, wt.%
Hydrogen, wt.%
Oxygen, by dif. wt.%
Sulfur, wt.%
Boiling Point, °C
Flash Point, °C
Cloud Point, °C
Pour Point, °C
C etane Number
Petrodiesel
ASTM D975
~ 137,640
~129,050
1.3—4.1
0.85
7.1
87
13
0
0.0015 max
180—340
60-80
-35 to 5
-35 to -15
40— 55
Biodiesel
ASTM D6751
~127,042
~118,170
4.0—6.0
0.88
7.3
77
12
11
0.0—0.0024
315— 350
100— 170
-3 to 15
-5 to 10
48—65
petroleum diesel. Lubricity is the ability of a substance to lubricate moving engine
parts, which reduces friction as well as decreasing engine wear. C etane num ber(CN)
is a commonly used indicator for the determ ination of fuel quality, especially the
ignition quality.22 CN is related to the ignition delay (ID) time, which is the tim e
th a t passes between the injection of the fuel into th e cylinder and th e onset of
ignition.23 Fuels having a high CN have a short ID between fuel injection and
ignition and, thus, lead to good cold start behavior and an engine th a t runs more
sm oothly.24 In addition, fuels having a high CN have fewer NOx exhaust
emissions.25 Flash point is the minimum tem perature at which th e fuel will ignite
(flash) upon application of an ignition source.26 A fuel w ith a higher flash point is
able to be handled and stored more safely.9
Nevertheless, biodiesel has a higher viscosity, higher cloud point, and a higher
pour point th an petroleum diesel. These properties are m anifested by the fact th a t
biodiesel is known to form a waxy solid a t considerably higher tem peratures th an
petroleum diesel. Also, the oxygen content of biodiesel is 11% (by weight).
Therefore biodiesel can oxidize upon prolonged standing by forming peroxides,
acids, and deposits.21
1.3 F eedstocks U sed for B iodiesel
The most common feedstocks used to synthesize biodiesel are vegetable oils,
anim al fats, and waste oils. Vegetable oils and animal fats are the esters of
saturated and unsaturated fatty acids w ith glycerol (Table 3). These esters are
called triglycerides (Figure 1). The most common satu rated fatty acids in vegetable
oils and animal fats are lauric, myristic, palm itic, and stearic acids. Oleic, linoleic,
linolenic, palmitoleic, and erucic are the common unsaturated fatty acids. The
chemical structures of these fatty acids are shown in Figure 2. Besides fatty acids,
refined vegetable oils and animal fats contain small am ounts of FFA and trace
am ounts of water. Table 4 shows the fatty acid composition of th e feedstocks used
in this research.
O
II
H2C — O — C — R 1
o
II
HC— O — C — R 2
O
II
h2c — o — c — r 2
Figure 1: Structure of a typical triglyceride. R x, R2, R 3 are alipatic chains with
carbon-carbon single bonds and double bonds.
Vegetable oils used to produce biodiesel can be edible or non-edible. Soybean,
7
Laurie add (12:0}
Mynstic add {14:0)
Palmitoldc add (16:1)
Palmitic add (16:0)
Oleic add(lS :l)
Stearic add (1S:0)
Linolemc and (13:3)
Linoldc a d d (18:2)
Ricutoleic acid (13:1 (OH))
Arachidic add (20:0)
Beheoic add (22:0)
Emdc add (22:1)
Figure 2: The chemical structures of th e m ost common fatty acids.
sunflower, palm, coconut, rapeseed, and peanut oils are edible; whereas, castor,
Jatropha curcas, rubber seed, neem, and Pongamia pinnata oils are non-edible.27
Various vegetable oil feedstocks have been reported in the literature. Soybean28,
suflower29, canola30, castor31, and Jatropha curcasZ2 are commonly used vegetable
oils used in the production of biodiesel. The m ajor feedstocks used in th e U nited
States are soybean and used cooking oils.33 Rapeseed and sunflower oils are m ainly
used in Europe, and palm oil is mainly used in southeast A sia.34
The m ajor attractive feature for the use of anim al fats in the production of
biodiesel is low feedstock cost relative to vegetable oils.35 However, anim al fats have
high am ounts of saturated fatty acids. Therefore, biodiesel fuels produced from
animal fats have poor low -tem perature perform ance compared to biodiesel produced
from vegetable oils. Also, compared to vegetable oils, animal fats have higher
8
Table 3: Typical saturated and unsaturated fatty acids in biodiesel.41
C om m on
N am e
Formal
B utyric acid
C aproic acid
C aprylic acid
C apric acid
B u tan oic acid
H exanoic acid
Laurie acid
M yristic acid
M yristoleic acid
P alm itic acid
P alm itoleic acid
Stearic acid
O leic acid
Linoleic acid
Linolenic acid
R icinoleic acid
A rachidic acid
G ondoic acid
B ehenic acid
Erucic acid
Lignoceric acid
C erotic acid
A bbreviation
N am e
O ctan oic acid
D ecanoic acid
D odecanoic acid
Tetradecanoic acid
d s-9-T etrad ecen oic acid
H exadecanoic acid
c is-9-H exadecanoic acid
O ctadecanoic acid
d s-9-O cta d eca n o ic acid
e'i.s-9,12-Oetadecanoic acid
c is-9 ,12,15-O ctadecanoic acid
1 2 -hydroxy-9- eis-octad ecen oic acid
E icosanoic acid
a .s-ll-E ic o sa n o ic acid
D ocosanoic acid
cis-13-D ocosenoic acid
Tetracosanoic acid acid
H exacosanoic acid
M olecular
Form ula
4:0
c 4h8o
6 :0
C gH i 2 0
8 :0
1 0 :0
1 2 :0
14:0
14:1
16:0
16:1
18:0
18:1
18:2
18:3
18:l(O H )
2 0 : 0
2 0 :1
2 2 : 0
2 2 :1
24:0
26:0
2
MM
(g /m o l)
8 8 .1 1
^8^16^2
116.16
144.21
^ 10^ 2 0 ^
C i2 H2 4 0
172.26
200.32
C i 4 H 2 g0
C i4 H 2 6 0
2
2
2
2
2
C 1 6 H3 2 O 2
C 1 6 H3 0 O2
^18^3602
^“'18^34^2
C1 8 B 3 2 O2
C 1 8 H3 0 O 2
C 1 8 H3 4 O 3
^ 2 0 H4 0 O2
C2 0 H3 8 O2
C 2 2 H4 4 O 2
C2 2 B 4 2 O2
c 24h 48o 2
^26^ 52^ 2
228.38
226.26
256.43
254.42
284.48
282.47
280.46
278.44
298.46
312.54
310.53
340.60
338.58
368.63
396.69
viscosity. Beef tallow 36, pork la rd 37, and chicken fa t38 are the common anim al fats
used in biodiesel synthesis. Also, biodiesel fuels produced from fish oil39 as well as
duck tallow 40 have been reported in the literature.
There is an increased interest in the use of waste oils to produce biodiesel due
to high feedstock cost of virgin vegetable oils. Mainly, used cooking oil is used to
produce biodiesel. Based on FFA content, waste cooking oil is classified as yellow
grease (FFA content<15%) and brown grease (otherw ise).47 Q uite a few studies of
the use of waste vegetable oils to produce biodiesel have been reported in the
literature. 48-51
In addition, dairy products (e.g. clarified b u tte r (ghee)52, b u tte r53),
algae54-56, m icroalgae57, and fungi58 have all been used to produce biodiesel.
9
Table 4: Fatty acid compositions of feedstocks used for this study.
F atty
A cid
C A N 41
CAS42
COC43
COR43
CG44
OLV4 5
PO 43
4:0
6 .6
0.7
6 :0
6 .6
2 .2
0 .1
8 :0
6 .6
1 .2
0 .1
5.1
46.5
2.9
3.1
0 .2
2 0 .6
1 1 .2
0 .8
1 0 :0
1 2 :0
14:0
16:0
16:1
18:0
18:1
18:2
18:3
18:1
(OH)
2 0 : 0
2 0 :1
2 2 : 0
0 .1
3.8
1 .6
9.2
1.9
62.4
2 0 .1
8.4
1.9
5.1
6.4
0.3
82.9
2.9
7.2
1.7
0 .6
1.5
0.3
0.3
99.6
98.2
2 .0
25.5
59.3
30.6
1.5
13.8
28.7
1 .1
2 2 :1
24:0
T otal
10.3
0 .2
99.8
1 .2
0 .1
0 .2
0.3
99.7
97.3
SO Y 45
7.5
1 0 .1
SUN 45
0 .1
13.8
1.4
36.8
2 .1
49.5
11.7
0.5
71.1
18.2
0 .2
1 .0
5.2
0 .1
0 .1
2 .8
71.6
9.0
1 .0
0.4
0.4
0.3
PEA 46
4.3
22.3
53.7
3.7
33.7
56.5
8 .1
0 .1
0 .1
99.6
1 0 0
1 0 0
98.5
99.2
C A N -C anola oil, C A S-C astor oil, C O C -C oconut oil, C O R -C orn oil, C G -C ow ghee, O L V -O live oil,
P O -P alm olein oil, P E A -P ea n u t oil, SO Y -Soybean oil, and SU N -Sunflow er oil.
1.4 T ran sesterificatio n
Transesterification is the process of changing one type of ester into another,
different type of ester. In transesterification, a triglyceride feedstock is reacted with
an alcohol in the presence of a catalyst (Figure 3). In th e transesterification
reaction, the stochiom etric ratio of triglyceride to alcohol is 1 to 3. Also, this
reaction is reversible; therefore, excess alcohol is used in order to favor product
form ation.59
The transesterification reaction consists of three consecutive, reversible steps.
Diglyceride and monoglyceride are formed as interm ediates in this reaction (Figure
4 )-
10
Overall Reaction
CHnOCOR
I
CHOCOR
+ 3 CH 3 OH
Catalvst
c h 2o h
I 2
CHOH
+
3 RCOOCH,
I
c h 2o h
c h 2o c o r
Triglyceride
Methyl Ester
(Biodiesel)
Glvcerol
Methanol
Figure 3: Transesterification reaction of triglyceride w ith methanol.
Stepwise Reaction
CH2OCOR
c h 2o h
CHOCOR
+
CH 3 OH
Catalyst
I
.
CHOCOR +
RCOO CH,
I
c h 2o c o r
c h 2o c o r
Triglyceride
Diglyceride
CH2OH
1
CHOCOR
CH2OH
+
CH 3OH
Catalyst
I
i
CHOH
.
+
CH2OCOR
c h 2o c o r
Diglyceride
Monoglyceride
CH,OH
1 2
CHOH
RCOOCH.
I
c h 2o h
+
CH3OH
Catalyst
I
CHOH
+
RCOOCH 3
I
c h 2o c o r
CH2OH
Monoglyceride
Glvcerol
Figure 4: Sequential transesterification reactions of triglyceride, diglyceride, and
monoglyceride w ith m ethanol.
M ethanol, ethanol, propanol, and butanol are th e commonly used short-chain
alcohols. Commercially, m ethanol is used to produce biodiesel, due to its low cost
11
and its physical and chemical advantages.60 M ethanol also has high popularity in
the literature, and hundreds of studies have been reported. Lou et al.61, Patil et
al.62 and Refaat et al,63 used m ethanol as catalyst to produce biodiesel using WVO.
Also, numerous studies have been reported using other alcohols to produce
biodiesel. Sanli et al.64 produced biodiesel from sunflower, corn, soybean, rapeseed,
hazelnut, and cottonseed oils using m ethanol, ethanol, 2-propanol, and 1-butanol as
alcohols and KOH, NaOH, and H2S 0 4 as catalysts. They found m ethanol was th e
best alcohol for biodiesel synthesis and other alcohols should be used w ith acid
catalyst at high tem peratures.
The catalyst used in transesterification is an acid, a base, or an enzyme. Acid
and base catalysts can be homogeneous (in the same phase) or heterogeneous (in
different phases). Even though homogeneous-catalyzed transesterification is effective
and feasible, the production costs are still high compared to those for petroleum
diesel fuel. Heterogeneous catalysts are good alternatives to this problem. These
catalysts can be separated more easily from the product m ixture and they are
environmentally friendly due to th eir reusability.65 In addition, very little waste
w ater is produced during the heterogeneous catalyst process.66 Homogeneous
catalysts are lim ited to use in batch-type reactors; however, heterogeneous catalysts
can be used in either batch-type or continous fixed-bed reactors. In addition
heterogeneous catalysts have been classified as either Brpnsted or as Lewis
catalysts.67
T he reaction param eters influencing the transesterification reaction are type of
feedstock, type of catalyst, type of alcohol, FFA content, oil/alcohol ratio, reaction
time, reaction tem perature, am ount of catalyst, reaction pressure, and mixing
intensity. Biodiesel yield/conversion is varied based on these param eters.
12
1.4.1 A lkaline-C atalyzed T ran sesterificatio n
In practice, alkali catalysts are more preferred th an acid catalysts due to their
faster reaction times. Alkali catalysts have greater reactivity due to th e increased
nucleophilicity of the anionic alkoxide nucleophile, which attacks th e acyl carbon of
the fatty acid group (Figure 5). In the first step, a strong nucleophile, alkoxide ion
is produced by reacting the base w ith the alcohol. This nucleophile adds to the
carbonyl group in the triglyceride forming a tetrahedral interm ediate.68 The
tetrahedral interm ediate then undergoes elim ination yielding the new ester as well
as glyceride conjugate base species. The same process is repeated w ith the
diglyceride and the monoglyceride, leading to a net form ation of three alkyl ester
molecules as well as glycerol for each molecule of triglyceride th a t reacts.
The most active homogeneous alkaline catalysts are m etal alkoxides (NaOCH3
and KOCHg). They give high yield (>98 %) in short reaction tim e (30 min) even
for low catalyst loading (0.5 m ol% ).69 However, m etal alkoxides are expensive
compared to NaOH and KOH. Therefore, biodiesel is industrially produced using
NaOH or KOH because they are abundant and inexpensive even though they are
less active.19,70 However, high biodiesel conversion can be obtained by increasing
KOH or NaOH catalyst loading to 1 or 2 mol % .71
Although homogeneous alkaline-catalyzed transesterification is rapid and gives
high yield, this process is not appropriate for waste oil feedstock because these
contain high am ounts of FFAs. Normally, the maximum FFA content in the
feedstock should be < 0.5 wt % .9,70 Otherwise, th e FFAs present in the feedstock
will react with the basic catalyst forming a soap, which prevents the separation of
biodiesel from the final m ixture (Figure 6). Soap form ation causes an increase in th e
13
<
o
0
■. 11
R1 - C - 0
11
R ^ C -O
III
r 3 -c-o
r 3 -c-o
II
II
>
0
r 2-c-o -r4
0
0
4 "
o
R^c-O
R ^ C -O
r 3 -C -0
r 3 -c-o
o
o
IV
II
II
>
O-H +
- B
Figure 5: Homogeneous base-catalyzed transesterification mechanism of triglyceride,
viscosity of biodiesel as well as increasing th e product separation cost.
O
O
R - C — OH
FFA
+
NaOH
R — c — o Na
+
h 2o
Soap
Figure 6: Base catalyzed reaction w ith FFAs to produce soap and water.
K ousu et al.72 studied th e transesterification of WVO using C a C 0 3, CaO, and
C a(O H )2 solid base catalysts and found th a t a portion of catalyst was changed into
a calcium soap by reacting w ith FFAs th a t were present in the WVO.
Also, w ater produced from the reaction between FFA and alkaline catalyst is
also problematic. In the presence of remaining alkaline catalyst, w ater contributes
to hydrolysis of biodiesel to produce additional FFA and m ethanol (Figure 7).
O
R -C -O C H
3
+
h20
Base catalyst
B iodiesel
O
r_c_oh
+
CH3OH
FFA
Figure 7: Hydrolysis of biodiesel in the presence of base catalyst.
Moreover, homogeneous alkali m etal carbonates (Na^COg and K2C 0 3) can be
used to produce biodiesel. These catalysts also give high yield and show fast
reaction tim e like other homogeneous alkaline catalysts. Furtherm ore, they do not
lead to saponification w ith FFAs like other homogeneous alkaline catalysts. M etal
bicarbonates are formed instead of w ater by reacting m etal carbonates w ith alcohol
(Figure 8 ).68
K C0
2
3
+
CH3OH
KHCOg + CH OK
3
Figure 8: Reaction of potassium carbonate w ith m ethanol.
Hundreds of studies have been published related to th e synthesis of biodiesel
via homogeneous base-catalyzed transesterification. R ashid and A nw er73
investigated the synthesis of biodiesel from rapeseed oil using KOH as a catalyst
w ith m ethanol. The best yield (95-96%) was found for 1:6 oil/m ethanol m olar ratio,
1.0 % KOH catalyst loading, at 60 °C and a t 600 rpm mixing intensity.
Vicente et al. 74 produced biodiesel using different homogeneous base catalysts
(NaOH, KOH, NaOCH3, and KOCH3), sunflower oil, and m ethanol. They obtained
nearly 100% biodiesel yield w ith m ethoxide catalysts using a 1:6 oil/m ethanol molar
15
ratio and 1 w t % catalyst loading at 65 °C. Additionally, Rashid and Anwer75
reported similar results using safflower oil, and Freedman et al. 76 reported similar
results using cottonseed, peanut, sunflower, and soybean oils.
Few studies have been reported in the literature using unsupported K2C 0 3 as
a catalyst due to production cost. Baroi et al.77 used unsupported K2C 0 3 as
catalyst to produce biodiesel from Jatropha curcas oil. The highest oil conversion
was obtained using a 1:6 oil/m ethanol molar ratio, 5 w t % K2C 0 3, 60 °C reaction
tem perature, and 15 min reaction time. The same result was also obtained using a
1:9 oil/m ethanol molar ratio, 4 w t % K2C 0 3, and 60 °C reaction tem perature.
One im portant advantage of heterogeneous base catalysts is th a t they do not
have problems w ith FFAs or w ater in the feedstock. Therefore, currently, they are
in high dem and as catalysts. Heterogeneous B r 0 nsted and Lewis base catalysts
react similarly w ith alcohols forming a homogeneous alkoxide group.67 There are
various types of heterogeneous base catalysts th a t have been reported in the
literature. Zeolites, C aO 78, M gO 79, KI/A120 380, and alum ina/silica supported
K2C 0 381 have been used as heterogeneous base catalysts.
Boz and K ara82 investigated the transesterification of canola oil using different
solid base catalysts (e.g. KF/A120 3, KI/A120 3, K2C 0 3/A120 3, and K N 0 3/A120 3).
The highest biodiesel yield (99.6%) has been obtained using A120 3/ K F (3% (w /w ))
and a 15:1 oil/m ethanol molar ratio under 8 h reaction tim e at 60 °C. Vujicic et
al.83 studied biodiesel synthesis from refined sunflower oil using CaO as a solid
catalyst. The highest conversion (91%) was obtained using a 1:6 oil/m ethanol molar
ratio and 1 wt % catalyst loading at 80 °C for 5.5 h reaction time.
Lingfeng et al.84 used a K F /7-A l20 3 heterogeneous base catalyst for the
transesterification of cottonseed oil w ith m ethanol. The best properties were found
16
using a 1:12 oil/m ethanol molar ratio, 4 wt % catalyst loading, and 65 °C reaction
tem perature.
1.4.2 A cid -C ataly zed T ran sesterificatio n
Homogeneous acid-catalyzed transesterification is an alternative m ethod to
produce biodiesel from high-FFA content feedstocks (Figure 9) because
homogeneous acid catalysis can effect both esterification o f FFAs as well as
transesterification o f triglycerides.59 However, the acid-catalyzed transesterification
reaction is very slow; about 4000 tim es slower th an th e homogeneous
alkali-catalyzed transesterification.85
Moreover, homogeneous acid catalysis are more corrosive to laboratory
equipment. Also, acid-catalyzed transesterification requires a high molar ratio, high
reaction tem perature, and high catalyst loading to reduce th e reaction tim e.86
CH2OCOR
I
CHOCOR
Acid Catalyst
+ 3 CH 3OH
s n
■ ■
I
c h 2o c o r
Triglyceride
ar
Cf-UOH
|
CHOh
I
+
3 RCOOCH 3
c h 2o h
Methanol
Glycerol
Methyl Ester
(Biodiesel)
Figure 9: Acid-catalyzed transesterification.
The homogeneous acid-catalyzed transesterification mechanism is shown in
Figure 10. In the first step, one of th e carbonyl oxygen atom s of the triglyceride is
protonated by the acid catalyst. This leads to an increase in th e electrophilicity of
the acyl carbon of th e ester, which undergoes nucleophilic addition by neutral
alcohol, forming a tetrahedral interm ediate. This is followed by a series of proton
17
transfers and subsequent elimination to form diglyceride and th e alkyl ester product.
A similar mechanistic sequence gives th e monoglyceride and glycerol, accompanied
by the concomitant formation of two additional molecules of transesterified product.
o
j*
R 1 - C -- 0o - \
Ri_C -0 - \
)-0 -C -R
ti
0
0
O
r '- c
II
o
-H
- o —\
=?'
V p = C -R
R 1 - C -■Q
0
.0
)~ o - c-R
r 2!
•O—
7
"
®
n
II
2
r3 -C -0 - A ®
r 3- c
H
o
r 4 o -h
0
O
r ’- c
2
R3-Cil- O - / ®
^
R3 .c _ 0 _ y
<?-H
/—o=cC -R
2
0
o 'H
-v
u —\
-o
III
R ^ C -O
V o - c - r 2
r 3 -cII-
o-7 ” ®rYO
R 3 -C
II -0
o
o
o
H.
IV
.©
+
H
r2-c -o -r4
+
R4
■;6-
o
h
r ’- c - o - \ H
: d 'H
O -C -R 2
:9 '
R1 - C - 0
H c :0
R3 -C “0 —
“
V -O -C -R 2
r 3 *c~o—
"
o
‘ -0 .
R4
K
O
o
R’-C -O - \
V o -H
r 3 -c -o —7
;0 -
R4 ■
.H
’'CO
+
r 2 -c-o -r4
H
Figure 10: Homogeneous acid-catalyzed transesterification mechanism of triglyceride.
The most commonly used homogeneous acid catalysts are H2S 0 4, HC1, and
R S 0 3H (organosulfonic acids). Numerous studies of acid-catalyzed biodiesel
18
syntheses using conventional heating m ethods have been reported in th e literature.
Canakai and Van G erpen87 investigated acid-catalyzed transesterification using
soybean oil, methanol, and H2S 0 4. They found th a t the acid-catalyzed reaction is
much slower th an alkali-catalyzed reaction. They also found th a t the ester
conversion was higher when th e catalyst loading was increased, when the m olar ratio
of alcohol to oil was increased, and when the reaction tem perature was increased.
Goff et al.88 used different acid catalysts (sulfuric, hydrochloric, formic, acetic,
and nitric acids) for biodiesel synthesis from soybean oil, and revealed th a t H2S 0 4
was the m ost effective catalyst for the acid-catalyzed transesterification. Also, they
obtained >99 wt % conversion of triglyceride using a 1:9 oil/m ethanol molar ratio
w ith 0.5 wt % H2S 0 4 at 100 °C in 8 h.
A randa et al.89 used sulfuric, methanesulfonic, phosphoric, and trichloroacetic
acids as catalysts to produce biodiesel from palm fatty acids and anhydrous
m ethanol and ethanol. Sulfuric and methanesulfonic acids were the best catalysts
and highest conversions were more th a n 90% for 1 h w ith methanol.
Since, homogeneous acid-catalyzed transesterification is much slower th an
base-catalyzed transesterification, a two-step transesterification process is often used
for producing biodiesel from high FFA content feedstocks (usually WVOs).
Two-step transesterification consists of acid-catalyzed Fischer esterification of FFAs
followed by base-catalyzed transesterification. In the first step, acid catalysis
converts th e FFA to fatty acid alkyl ester products via simple Fischer esterification.
In the second step, the base catalyst converts th e triglyceride to fatty acid alkyl
esters products, as described earlier (Figure 11).
T he two-step transesterification m ethod was used in some literature reports to
produce biodiesel. Jain and Sharm a90 investigated from Jatropha curcas oil, th e
Step 1: Acid-catalyzed Fischer esterificaiton
RCOOH +
CH3OH
‘............
'.»
ffa
RCOOCH 3 +
H20
fane
Step 2: Base-promoted transesterification
C H ,O C O R
I
CHOCOR
|
c h 2o c o r
Triglyceride
+ 3 CH 3 OH
Base Catalyst
^
c h 2o h
| 2
CHOH
|
c h 2o h
Glycerol
Methanol
Methyl Ester
(Biodiesel)
Figure 11: Two-step transesterification process.
yields of m ethyl esters were 21.2% during th e esterification (H2S 0 4 as catalyst) and
90.1% yield from transesterification (NaOH as catalyst) of pretreated Jatropha
curcus oil.
Hayyan et a l 91 used sludge palm oil to produce biodiesel using the two-step
transesterification process. The FFA content of the sludge palm oil was reduced
from an initial content of >23 % down to >2 % using acid-catalyzed
transesterification a under 1:8 oil/m ethanol molar ratio at 60 °C for 60 min. Then,
base-catalyzed transesterification was perform ed under 1:10 oil/m ethanol molar
ratio, 400 rpm stirring speed, 60 min reaction time, 1 % (w /w ) KOH, and 60 °C
reaction tem perature. The yield was 83.72% under these conditions.
A lthough this two-step transesterification m ethod gives high yields, it requires
long reaction times. Therefore, recently there has been an increasing dem and for
heterogeneous acid-catalyzed transesterification. An advantage of solid catalysts is
th a t they elim inate the problems related to corrosion, moreover, they are not
20
environm ental hazards like strong acids. Both homogeneous acid catalysts and
heterogeneous Br0nsted and Lewis acid catalysts react via a similar mechanism.
Br0nsted acid catalysts are suitable for Fischer esterification of FFAs, whereas,
Lewis acid catalysts are more suitable for transesterification.67
Functionalized zirconia (sulfated zirconia (SZ)92,93, tu n g stated zirconia
(W Z )94), silica-based acid cataly st95, heteropoly solid acids96"98, different
zeolites99,100, carbon-based solid acids101,102 and acidic ion-exchange resins103,104 are
some of the heterogeneous acid catalysts have been reported in the literature.
R am achandran et a/.105 obtained 81 wt% triglyceride conversion from WVO
using a 1:16 oil/m ethanol molar ratio, 50 min reaction time, 220 °C reaction
tem erature, and 0.5 w t % A1(HS04)3 heterogeneous acid catalyst. This catalyst was
prepared by the sulfonation of anhydrous A1C13.
Fu et al. 106 reported biodiesel synthesis from WVO using solid superacid
catalyst S 0 42~ /Z r0 2. They obtained 93.6 % of biodiesel yield using 1:9 oil/m ethanol
molar ratio, 3 wt % catalyst loading, 4 h reaction time, and 120 °C reaction
tem perature.
Melero et al. 107 perform ed hetereogeneous acid-catalyzed transesterification
from refined and crude vegetable oils (soybean and palm ) using a sulfonic
acid-modified m esostructured catalyst. Over 95 wt % oil conversion was obtained
using 1:10 oil/m ethanol molar ratio, 6 wt % catalyst loading, and 180 °C reaction
tem perature.
1.4.3 E n z y m a tic -C ata ly z e d T ran sesterificatio n
Enzym atic-catalyzed transesterifications have been recently reported in the
literature. Immobilized lipases have been used as th e prim ary enzyme catalyst.
21
There are several advantages of this process over base-catalyzed and acid-catalyzed
transesterification processes. The prim ary advantage is th a t enzyme catalysts can
be reused w ithout separation and the reaction tem perature is low (60 °C ).108 Also,
they can be used w ith feedstocks having high FFA and high w ater content.
However, the disadvantage of this process is th a t the enzym atic catalysts are very
expensive (price is ~ $100 — 150 (USD) per gram).
Lipases are produced by microorganisms (bacteria and fungi), animals, and
p la n ts.109Rhizaopusoryzae, Candida rugosa, Psuedomonas fluorescens,
Burkholderia, Cepacia, Aspergillus niger, Thermomyces lanuginose, and
Rhizomucormiehei have been used as sources for the lipase c a ta ly st.110
Numerous studies have been published in the literature using lipases. Chen et
al. 111 used immobilized Candida lipase to produce biodiesel from WVO. T he highest
yield, 91.08% was obtained under optim um conditions of lipase/hexane/w ater/W V O
weight ratio 25:15:10:100, tem perature of 45 °C , and reactant flow of 1.2 m L /m in.
C orrea et al. 112 studied biodiesel synthesis from palm oil using
Rhizomucormiehei, Thermomyces lanuginose, and Candida antarctica lipases. Fatty
acid conversion of 93% was obtained after 2.5 h of esterification reaction between
palm oil fatty acid distillate and ethanol using 1.0 wt.% of Candida antarctica at
60 °C.
1.5 M icrow ave-A ssisted T ran sesterificatio n
The microwave-assisted transesterification process is a fast, easy, and
energy-efficient process to produce biodiesel.19,113,114 Microwave-assisted reactions
have been used since 1975 in chemistry, and numerous studies have been published
in which microwave-assisted reactions are used in organic synthesis.115 There is an
22
increasing popularity in using microwave-assisted reactions in organic chem istry
because of their short reaction times compared to conventional heating. Also, some
reactions th a t do not readily occur by conventional heating can be perform ed using
microwave heating.115
Microwaves are electrom agnetic radiation w ith relatively low energy. This
radiation region is located between the infrared region and radio wave region of the
electrom agnetic spectrum (Figure 12). The frequencies of microwaves range from
0.3 - 300 GHz (with corresponding wavelengths of 1 mm - 1 m). In general, th e 2.45
GHz (12.2 cm wavelength) frequency is assigned for industrial and domestic
microwave apparatus in order to avoid interference w ith other electronic
equipm ent.63
Wavelength
lim im l
Radio
Micro***vt
Infrarad
Visible
Ultraviolet
X-Aay
Gamma Ray
- H -------------- 1----------- 1--------- 1------------ 1-------------1---------- 1-----103
IO-*
IO-5
10*
10*
10-1°
mH *
X^v_X\AAA/WWVl<
Frequency
Figure 12: The electrom agnetic sp ectru m .116
Microwaves have perpendicular oscillating electric and m agnetic fields. There
are three mechanisms th a t can occur when microwave radiation interacts w ith a
sample (Figure 13).117 One is dipolar polarization, which is due to the alignm ent
23
w ith the electric field of the molecules possessing a dipole moment. This oscillation
produces collisions w ith surrounding molecules and thus the liberation of therm al
energy into the medium. W ith a frequency of 2.45 GHz, this phenomenon occurs
4.9 x 109 tim es per second and the resulting heating is very fa s t.1963 118 The
second mechanism is ionic conduction, which occurs when charged species are
present. Then the electric field component of th e microwave irradiation causes the
ions to move back and forth through the sample while also colliding the ions into
each other. In this case, the movements and the resulting collisions generate
h e a t.19,63 The other mechanism is interfacial polarization, which occurs as a
com bination of b oth ionic conduction and dipolar polarization.
oi
m
Ionicconduction
Dipolarpolarization
Microwave field
Figure 13: Ionic conduction and dipole polarization under microwave conditions.119
Biodiesel reaction m ixtures contain b o th polar and ionic compounds.
Therefore, rapid heating is observed during microwave irradiation and the reaction
is efficient. In addition, because the energy is interacting w ith the molecules at a
very fast rate, the molecules do not have tim e to relax. The heat generated can be,
for short times, much greater th an the overall m easured tem perature of th e bulk
24
reaction m ixture. In essence, there will be instantaneous localized superheating.
Hence, the bulk tem perature might not be an accurate measure of the accurate
tem perature at which the actual reaction is occurring.19
T he mechanism th a t can occur in conventional heating is called wall heating.
T hat is, heat is transferred to the reaction m ixture when wall of the vessel is heated.
Therefore, a large portion of energy supplied through conventional energy source is
lost to the environment through conduction of m aterials and convection c u rren ts.119
The m ain drawbacks of conventional heating are heterogenic heating of the surface,
dependent on the therm al conductivity of m aterials, specific heat, and density.120
Therefore, biodiesel synthesis using conventional heating is slow and inefficient; the
reaction can take several hours or days. W hereas w ith microwave heating, the entire
reaction m ixture is heated; therefore, reaction tim e is fast and can take only a few
m inutes.19,113 Figure 14 shows the mechanisms th a t can occur in conventional and
microwave heating. Therefore, microwave-assisted transesterification processes are
becoming more popular and a num ber of studies have been published in the
literature.
Conventional heating
Microwave heating
Figure 14: The conventional and microwave heating m echanism s.119
25
Two m ethods are commonly used to produce biodiesel using microwave
heating. These are batch-reaction m ethods and continuous-flow m ethods. In a
batch-react ion process, the reactants are contained w ithin a vessel located in a
reactor inside the microwave cavity. In continuous-flow process, th e reaction
product is collected in a vessel th a t is located separately from the reactants. The
reactants are circulated through the microwave reactor. The continuous-flow process
is more energy-efficient th an the batch-reaction process.19 In addition, the
continuous-flow process is more suitable for larger-scale synthesis.
Q uite a few studies of microwave-assisted biodiesel synthesis have been
published in the literature. These studies have featured different catalysts, different
alcohols, and different feedstocks to compare the efficiency of biodiesel w ith
conventional heating.
B arnard et al. 19 showed th a t the microwave methodology for the
transesterification reaction using WVO, m ethanol and KOH as a catalyst is more
energy efficient th an conventional heating methods. Similar results have been
reported by H ernando et al. 113 using commercial rapeseed oil, soybean oil, m ethanol
and NaOH as a catalyst. Refaat et al.63 conducted a study using NaOH and KOH
as catalysts for sunflower oil and WVO. They found th a t the reaction tim e is 2 min
and the separation tim e of biodiesel is 30 min for microwave irradiation, however,
th a t for conventional heating is 1 h hour and 8 h respectively.
The microwave-assisted transesterification m ethod can be also used for both
homogeneous and heterogeneous catalysts. Perin et al. 121 reported the
microwave-assisted transesterification from castor oil w ith m ethanol and ethanol
using acidic silica and basic alum ina as catalysts. T he reaction tim e for
SiO2/50% H 2SO4 using microwave irradiation is 30 min for a 1:6 oil/m ethanol molar
26
ratio, whereas the tim e required for Al2O3/5 0 % KOH is 5 min. Also they found
th a t microwave-assisted transesterification is faster th an conventional
transesterification for both acid and base catalysts. The reaction tim e for
conventionally-heated transesterification for S i0 2/ 50 % H2S 0 4 is 3 h and for
A120 3/ 50 % KOH is 1 h at 60 °C.
Yuan et al.31 reported microwave-assisted acid-catalyzed transesterification using
castor oil, m ethanol and solid acid catalyst (H2S 0 4/C ). The highest yield (94 wt %)
was obtained using a 1:12 oil/m ethanol molar ratio, 50 wt % loading am ounts of
H2S 0 4 and 5 wt % of catalyst to castor oil, 65 °C reaction tem perature, and 60 min
reaction time.
Zhang et al. 122 showed th a t the microwave-assisted m ethod for yellow horn oil
gave m ore th a n 96% of biodiesel yield using heteropolyacid (C s2 5H0 5P W 12O 40) (1%
w /w of oil) as a solid catalyst under a 1:12 oil/m ethanol molar ratio and 10 min
reaction tim e at 60 °C.
Hsiao et al. 123 reported th e transesterification of soybean oil having significant
w ater and FFA content, m ethanol, and nano CaO (3.0 wt %) as a heterogeneous
base catalyst using microwave-assisted transesterification. The highest biodiesel
yield (96.6%) was obtained a t 60 °C under 1:7 oil/m ethanol molar ratio for 1 h.
There are several comprehensive studies of batch-reaction and continuous-flow
preparations of biodiesel synthesis using microwave heating. B arnard et al. 19
reported th a t continuous-flow microwave methodology is more energy-efficient th an
conventional heating m ethods, and they revealed th a t the batch reaction process is
less energy-efficient th an the continuous-flow process. Hernando et al.113 studied
biodiesel synthesis using b oth batch and flow m ethods, and reported th a t both
m ethods are more energy-efficient th an the conventional heating m ethod.
27
CHAPTER 2
M eth o d o lo g y
2.1 R eag en ts
Commercially-available canola, coconut, corn, olive, peanut, soybean, and
sunflower oils used in this study were purchased from a local grocery store. Palm
olein oil was purchased from a grocery store in Sri Lanka. C astor oil and cow ghee
were purchased from an Indian grocery store in Dallas, Texas. The WVO (used
peanut oil) used in this study was obtained from a local fast food restaurant.
M ethanol (reagent grade-Flinn Scientific) and 95% ethanol (reagent grade-Flinn
Scientific) were used as alcohols. Sulfuric acid (98%, analytical grade-Fisher
Scientific) was used as the acid catalyst. Silica gel (technical grade, pore size 60 A ,
230-400 mesh, 40-63 /xm particle size, Aldrich) was used to prepare the solid
catalyst.
2.2 A p p a ra tu s
All microwave-assisted acid-catalyzed transesterification reactions were
perform ed using a Milestone START laboratory microwave oven (Milestone). A
Milestone START platform equipped w ith the teaching rotor, norm al pressure (NP)
glassware kit and color touch screen controller (Figure 15) was used to perform the
batch microwave tests. The microwave oven (Figure 15-A) has o u tp u t power up to
1200 W controlled via microprocessors. The teaching rotor (Figure 15-B, C)
includes thirty-tw o 25-mL glass reaction vessels. These vessels are equipped w ith a
special shield th a t can operate at pressures up to 15 bar and tem peratures up to
250 °C. The teaching rotor can be used to perform 32 reactions at the same time.
28
Figure 15: Experim ental apparatus for microwave-assisted reactions. A, Milestone
START Microwave; B, The teaching rotor; C, Glass reaction vessels; D, Color touch
screen controller; E, NP glassware kit.
The NP glassware kit (Figure 15-E) consists of a round-bottom ed flask,
adapter tube, and reflux condenser. Conventional laboratory glassware can also be
used in this microwave, therefore, instead of this 500-mL flask; 100 or 250 mL
round-bottom ed flasks (RBFs) were used for this study. The color touch screen
controller (Figure 15-D) is powerful software. Its features and capabilities can
increase productivity and improve synthesis quality. Also, it has the ability to
m onitor tim e vs. tem perature a n d /o r tim e vs. power during the reaction.
The conventionally-heated acid-catalyzed transesterification reactions were
perform ed in 100-mL or 250-mL RBFs equipped with a reflux condenser and a stir
bar (Figure 16). High tem perature experim ents were perform ed using QV-50
apparatus (Figure 17) in the microwave.This ap p aratu s allows reactions to be
perform ed in a closed vessel at tem peratures up to 250 °C and pressures up to 40
bar. The quartz vessel (45 mL) is suitable for reactant volumes ranging from 3 to 30
mL.
29
Figure 16: Experim ental apparatus for conventionally-heated reactions. A, Reflux
condenser; B, R BF w ith stirring bar; C, Hot p late/S tirrer; D, H eating m antle; E,
W ater in; F, W ater out; G, Voltage regulator.
S t a r t s ')
\ T il
Figure 17: A pparatus for elevated-tem perature reactions. A, QV-50 apparatus; B,
Q uartz vessel; C, Safety shield; D, W orkstation; E, Screw cap; F, QV-50 ap p aratu s
placed in the microwave.
30
2.3 E x p e rim e n ta l P ro c e d u re
2.3.1 M icrow ave-A ssisted T ran sesterificatio n (M A T ) P ro c e d u re s
Four different m ethods were used to produce biodiesel: 1. MAT using
oil/alcohol volume ratio, 2. MAT using oil/alcohol molar ratio, 3. MAT using high
tem peratures for canola and soybean oils, and 4. MAT using SiO2/50% H2S 0 4 as a
heterogeneous catalyst for castor oil. The reaction param eters (oil/alcohol ratio,
reaction tem perature, reaction time, catalyst am ount, and mixing intensity) of
microwave-assisted transesterification were optimized for the first, two m ethods
using each oil. Then, optim ized reaction param eters were applied to th e other two
methods.
2.3.1.1 M A T using O il/A lco h o l V olum e R atio s
First, the transesterification was performed using canola oil, m ethanol and
H2S 0 4 to optimize the reaction param eters. Canola oil/m ethanol were mixed at 1:4,
1:6, 1:8, 1:10 and 1:12 volume ratios (10 mL of oil w ith 40, 60, 80, 100, and 120 mL
of m ethanol) in a 100-mL or 250-mL RBF. H2S 0 4 (5 vol. %) and a m agnetic stir
bar were added to each m ixture and the RBF was set up w ith a condenser in the
microwave. Then, tem perature, mixing intensity, and outp u t power were set to
60 °C, 87%, and 600 W respectively using the touch screen controller. Also, heat-up
time, reaction time, and cool-down tim e were set to 2, 110, and 20 m inutes
respectively for all the reactions. Next, each reaction was perform ed over
approxim ately 2 hours. The best ratio was optim ized using percentage conversion of
FAAE product.
T he best oil/m ethanol volume ratio was then used at 63 °C to optim ize the
31
tem perature. The optimized ratio and tem perature were then used w ith 4 vol. %
H2S 0 4 to optimize the H2S 0 4 am ount. Finally, these optimized param eters were
used to determ ine the optim um reaction time. Therefore, the reactions were carried
out using these param eters for four different reaction times (55, 110, 165, 220
minutes) all w ith 2 m inutes heat-up time and 20 m inutes cool-down time.
O ptim ized reaction tem perature, catalyst am ount, and stirring intensity were
then applied to the other oils: peanut, coconut, olive, soybean, corn, sunflower,
palm olein, WVO, castor and cow ghee to optimize th e reaction tim e and
oil/m ethanol volume ratio. Therefore, oil/m ethanol were mixed at 1:4, 1:6, and 1:12
volume ratios and 5 wt % H2S 0 4 was added to the m ixture in a 100- or 250-mL
RBF. Then, the reaction m ixture was irradiated at 60 °C reaction tem perature, 87%
stirrin g rate , an d 600 W o u tp u t power w ith 2 m inutes h eat-u p tim e, 110 or 220
m inutes reaction time, and 20 m inutes cool-down tim e in the microwave. T he same
procedure was additionally performed using ethanol instead of m ethanol.
T he separation procedure was performed as follows. The ap p aratu s used for
each experim ent was allowed to cool to room tem perature. The unreacted alcohol in
the reaction m ixture was removed using rotary evaporation. Then, th e rem aining
m ixture was placed in a separatory funnel (Figure 18). It was washed w ith aqueous
N aH C 0 3 (2 x 30 mL), followed by aqueous NaCl (2 x 30 mL) and th e aqueous
phase, which was in the bottom of the separatory funnel, was drained. The organic
phase was then transferred into a 50-mL Erlenmeyer flask and was dried using
anhydrous M gS 04. The m ixture was dried for 10-15 m inutes and was then filtered
through cotton into another 50-mL Erlenmeyer flask. Next, the product m ixture
was treated in a centrifuge (physicians com pact centrifuge-Clay Adams) to remove
the glycerol layer for 5 min. The final product was transferred into a tared vial and
32
weighed.
-• r-
Figure 18: Crude biodiesel placed in a separatory funnel
2.3.1.2 M A T using O il/A lco h o l M o lar R atio s
First, the molar masses (MMs) of triglycerides (Table 5) were calculated using
Equation 1 validated by Da Silva et a l 124 and Tables 3 and 4 to perform molar
ratio experiments.
M M Tn = 3 A/ M fa + A/M(;iy — 3 MMwater
(1)
W here, M M m is the molar mass of triglyceride, M M FA is the weighted average
of the fatty acid molar masses, M M Gly is the molar mass of glycerol, M M Water is the
molar mass of water. The molar masses of glycerol and water are 92.09382 g/m ol
and 18.01528 g/m ol respectively.
T he mass of alcohol used for each experim ent according to molar ratios were
calculated using Table 5 and molar mass of m ethanol (32.04 g/m ol) or ethanol
(46.07 g/m ol).
33
Table 5: The molar masses of triglycerides used for this study.
Triglyceride
Canola oil
C astor oil
Coconut oil
Corn oil
Cow Ghee
Olive oil
Palm Olein oil
Peanut oil
Soybean oil
Sunflower oil
MM (g/m ol)
883.14
924.37
685.68
875.96
804.86
872.95
854.35
879.45
873.43
878.07
The molar ratio experim ent was perform ed using canola oil to optimize the
best ratio and reaction time. Canola oil and m ethanol were mixed at 1:4, 1:6, 1:8,
1:10, and 1:12 molar ratios (10.000 g of oil w ith 1.451, 2.177, 2.902, 3.628, and 4.354
g of m ethanol) in a 100-mL RBF and 5 wt % H2S 0 4 and a magnetic stir b ar were
added to each m ixture. Then, the apparatus was assembled w ith condenser in the
microwave and the reaction was perform ed at 60 °C reaction tem p eratu re and 87%
mixing intensity for ~ 2 h. H eat-up time, reaction time, and cool-down tim e were 2
min, 110 min, and 20 min respectively.
The best molar ratio was then applied to optimize reaction time. The
reactions were performed using two different reaction times (110 min and 220 min)
w ith 2 min heat-up tim e and 20 min cool-down time. Then, th e optim ized molar
ratio and reaction tim e were used for ethanol using 5 wt % H2S 0 4, 60 °C reaction
tem perature, 87% mixing intensity, and 600 W o u tp u t power.
The same procedure was used for the other oils: castor, coconut, corn, cow
ghee, olive, palm olein, peanut, soybean, sunflower, and W VO w ith m ethanol using
5 wt % H2S 0 4, 60 °C reaction tem perature, and 87% mixing intensity. Therefore,
34
oil and m ethanol were mixed in a 100-mL RBF as follows: casto r/m eth an o l 1:6 and
1:12 (10.000 g of oil w ith 2.080 and 4.160 g of m ethanol), coconut/m ethanol 1:4,
1:6, 1:12, and 1:30 (10.000 g of oil w ith 1.869, 2.803, 5.607, and 14.018 g of
m ethanol), corn/m ethanol 1:4, 1:6, and 1:8 (10.000 g of oil w ith 1.463, 2.195, and
2.926 g of m ethanol), cow ghee/m ethanol 1:6 and 1:12 (10.000 g of oil w ith 2.388
and 4.777 g of m ethanol), olive/m ethanol 1:4, 1:6, and 1:8 (10.000 g of oil w ith
1.469, 2.203, and 2.937 g of m ethanol), palm olein/m ethanol 1:4, 1:6, 1:15, and 1:30
(10.000 g of oil w ith 1.500, 2.250, 5.625, and 11.251 g of m ethanol),
p eanut/m ethanol 1:4, 1:6, and 1:12 (10.000 g of oil with 1.457, 2.186, and 4.372 g of
m ethanol), soybean/m ethanol 1:4, 1:6, and 1:8 (10.000 g of oil w ith 1.467, 2.201 and
2.935 g of m ethanol), sunflow er/m ethanol 1:4, 1:6, and 1:12 (10.000 g of oil w ith
1.460, 2.189, and 4.379 g of m ethanol), and W V O /m ethanol 1:4, 1:6, and 1:12
(10.000 g of oil w ith 1.457, 2.186, and 4.372 g of m ethanol). The WVO for this
study was used peanut oil, therefore, the same molar mass for virgin peanut oil was
used to calculate molar ratios. Then, the best molar ratio and reaction tim e were
used for ethanol using 5 wt % H2S 0 4, 60 °C reaction tem perature, 87% mixing
intensity and 600 W output power.
The same separation procedure described in section 2.3.1.1 was used to obtain
pure FAAE (fatty acid alkyl ester, i.e. biodiesel) samples.
2.3.1.3 M A T using H igh T e m p e ra tu re s for C an o la a n d S oybean Oils
The QV-50 apparatus was used to perform high tem perature reactions.
Soybean oil and m ethanol was mixed at 1:30 molar ratio (5.000 g of oil w ith 5.502 g
of m ethanol) in a beaker and 5 w t % H2S 0 4 was added to it. T he m ixture was
transferred to the quartz vessel (Figure 14-B), a magnetic stir bar was added, and
35
the vessel was placed in the safety shield (Figure 14-C). The vessel was properly
closed using the equipm ent provided by the m anufacturer (Figure 14-D) and then
the prepared safety shield was placed in the QV-50 apparatus. The QV-50
apparatus was then placed in the microwave, as shown in Figure 14-F. T he reaction
was performed at 150 °C reaction tem perature, 87% mixing intensity, and 600 W
o u tput power for 10 min (5 min heat-up tim e and 10 min cool-down tim e).
Next, the same procedure was perform ed using a 1:30 (5.000g of oil w ith 5.442
g of m ethanol) canola/m ethanol molar ratio. T he same separation procedure
described in section 2.3.1.1 was used to obtain FAAE samples.
2.3.1.4 M A T using SiO 2/5 0 % H 2S 0 4 as a H etero g en eo u s C a ta ly s t for C a s to r Oil
These experim ents were performed using a procedure reported in the
lite ra tu re .121 First, the catalyst was prepared using the following m ethod. Aqueous
H2S 0 4 (50% (v/v)) was prepared from 98% H2S 0 4. Then, 10.000 g of S i0 2 were
mixed w ith 50% aqueous H2S 0 4 in a beaker w ith a magnetic stir b ar and the
m ixture was stirred for 45 min at room tem perature. The resulting slurry was then
filtered under reduced pressure. Then, the filtered solid was dried in an oven at
120 °C for 18 h and stored in a desiccator for 5 days.
Then, castor oil and m ethanol were mixed at 1:6 and 1:12 molar ratios (10.000
g of oil w ith 2.080 and 4.160 g of m ethanol) in a 100-mL RBF and 1.000 g of
SiO2/50% H2S 0 4 catalyst was added. The reaction ap p aratu s was assembled in the
microwave in the microwave and th e reaction was perform ed at 60 °C reaction
tem perature, 87% mixing intensity, and 600 W o u tp u t power for 45 min (2 min
heat-up time and 20 min cool-down tim e). Then, the best molar ratio was applied
to ethanol instead of methanol.
36
After cooling the reaction m ixture to room tem perature, it was filtered under
reduced pressure to remove the catalyst. Then, th e crude m ixture was transferred to
a separatory funnel and glycerol was allowed to separate at the b ottom of the
separatory funnel by gravity over an 18 h period. The glycerol was then removed
from the separatory funnel. The rem aining m ixture was transfered to a RBF and
unreacted alcohol was removed by rotary evaporation. The remaining m ixture was
then transferred to a separatory funnel and residual glycerol and catalyst were
removed by washing the m ixture w ith distilled w ater (2 x 30 mL). The organic
phase was then transferred into a 50-mL Erlenmeyer flask and it was dried using
anhydrous M gS04. The m ixture was dried for 10-15 min and was then filtered
through cotton into another 50-mL Erlenmeyer flask. Next, th e product m ixture
was tre a te d in a centrifuge for 5 m in to rem ove any rem aining glycerol. The final
product was transferred into a tared vial and weighed. Then, the same procedure
was perform ed using castor oil w ith ethanol.
2.3.2 C onventional H e a tin g T ran sesterificatio n (C H T ) P ro c e d u re s
The best oil/m ethanol volume ratio of each oil found from the
microwave-assisted reactions was used for conventionally-heated transesterification.
The best oil/ m ethanol ratio w ith 5 wt % H2S 0 4 was mixed in a 100-mL or 250-mL
R BF equipped with a stir bar and a reflux condenser. The tem perature was set to
60 °C and the mixing intensity was set to 60 rpm. T he reaction was perform ed
overnight (approxim ately 18 h). The same procedure was followed using ethanol for
volume ratios.
T he same separation procedure described in section 2.3.1.1 was used to obtain
pure FAAE samples.
37
2.3.3 Analytical Methods
T he reaction products were analyzed using 1H—NMR spectrom etry and gas
chrom atography/m ass spectrom etry (G C /M S).
2.3.3.1 * H -N M R A nalysis
1H —NMR experim ents were perform ed on a JEO L ECS-400 spectrom eter
using CDC13 as the solvent. Tetram ethylsilane (TMS) was used as an internal
chemical shift reference. The percentage conversion of biodiesel for the reaction was
calculated using the equations shown below. Then, conversion/hour were calculated
and compared w ith the conventionally-heating m ethod.
The conversion of triglyceride to m ethyl ester was calculated using a m ethod
described in the lite ra tu re .125’126
3 x Ia-CH2
(2 )
W here, C is the conversion of triglyceride to the corresponding m ethyl ester,
I m e is the integration value of m ethyl ester peak, and I a -CH2 is the integration
value of ct-methylene peak.
The factors 2 and 3 derive from the fact th a t the methylene carbon possesses
two protons and the alcohol (m ethanol-derived) carbon has three attached
p ro to n s.125
T he conversion of triglyceride to ethyl ester was calculated using Equation (4),
shown below .127,128
(3 )
38
W here, C is the conversion of triglyceride to th e corresponding ethyl ester, Ic 4
is the integration value of the peaks at 4.08-4.09 ppm in th e ethyl ester q u artet, and
I
d d
+
e e
is
the integration value for all the signals between 4.05 to 4.35 ppm.
In this equation, the area of Ic A corresponds to 1/8 of the entire ethoxy-carbon
hydrogen area (-OCH2), whose signal appears in the region ranging from 4.05 to
4.20 ppm. The region near 4.08-4.09 ppm is the only region where crossover does
not occur, and this integrated signal can be assigned solely to ethyl e sters.127,128
2.3.3.1 G C /M S A nalysis
T he FAAE content of biodiesel samples was determ ined using gas
chrom atography/m ass spectrom etry (G C /M S). G C /M S analyses were performed
using a V arian 450 gas ch ro m ato g rap h w ith a V arian 240 m ass sp ectro m eter (ion
trap) equipped with a ZB-5 MS capillary column ( 5 % phenyl m ethylpolysiloxane)
w ith a film thickness of 0.25 /im, a length of 60 m, and an internal diam eter of 0.25
mm.
The standard solutions were prepared by dissolving 5-7 mg of alkyl ester and
9-12 mg of m ethyl salicylate (internal standard) in 1 mL of hexane. T he column was
program m ed as following: The starting tem perature of the column was 80 °C for 5
min; speed of warming 4 °C /m in up to 200 °C and then m aintained for 2 min and
speed of heating 12 °C /m in up to 300 °C and then m aintained for 8 min. Helium
was the carrier gas w ith a flow rate 1.5 m L /m in and 1 pL of sample was injected
using splitless mode. The specific esters in the FAAE m ixture were identified based
on their mass spectra.
39
CHAPTER 3
R esu lts a n d D iscussion
Produced FAAE from triglycerides used for this study (canola, castor,
coconut, corn, cow gheee, olive, plam olein, peanut, soybean, sunflower, and WVO)
w ith m ethanol and ethanol using H2S 0 4 are shown in Figure 19.
Methyl Esters
Ethyl Esters
Figure 19: Photographs of FAAE product m ixtures
3.1 FA A E Id en tifica tio n an d P e rc e n ta g e C onversion - V olum e R atio s
3.1.1 M A T O il/A lco h o l V olum e R atio s
Synthesized FAAEs were characterized using 1H —NMR spectroscopy and
G C /M S .T he 1H —NMR spectrum of one of the triglycerides used in this study
(coconut oil) is shown as an example (Figure 20).The 1H —NMR spectrum for neat
coconut oil is shown in Figure 20-a, and shows signals for th e glyceride protons at
chemical shifts ranging from 4.12-4.32 ppm. T he 1H—NMR spectrum of coconut oil
methyl ester is shown in Figure 20-b. The spectrum shows a singlet at 3.65 ppm for
the methoxy protons of the FAME products. The 1H —NMR spectrum of coconut oil
ethyl ester is shown in Figure 20-c. The spectrum shows a characteristic q u artet at
40
r f TTTT-pt TTT"fT
55
5C
45
40
35
’•H Tr r fTt TT-T-r
30
M' ' ' ' I' ' ' ' I '
25
Chemical Shift ippmt
a )'H -N M R spectrum for neat coconut oil.
ME
h AAll
I
■
1 r n TTt Tn TTi-TrrrTTTTyTTTTTn'Trj iTTi r r r n ' i n !i p u i p m Ti m t | - ri i t n r i , ,
55
50
45
40
35
30
25
20
15
10
05
Chemical Shift (ppm)
b)
’H -N M R spectrum for coconut o il m ethyl ester.
i
A _A
-r -T —i—r - i —i 4 15
I ' * ' — r~ r ~
4 10
Chen»ca< SM!(ppm>
A
«
D
7
EE
8
7
a
1
8
I__k
JL
Chemical SM I (ppm)
c)
H -N M R spectrum for coconut o il ethyl ester.
Figure 20: 1H —NM R spectra for coconut oil and its FAAE product m ixtures.
4.09-4.14 ppm for the carbinol protons of the ethoxy group of the FAEE products.
All three spectra show a triplet at 2.29 ppm for the methylene protons of the
a-carbon of the fatty acid groups. The m ain difference between the spectrum of
neat coconut oil and the spectra of the FA M E/FA EE products is the disappearance
of the glyceride m ultiplet (at 4.12-4.32 ppm) and th e appearance of the m ethoxy
singlet (at 3.65 ppm ) for m ethyl esters and ethoxy q uartet (4.09-4.14 ppm ) for ethyl
esters. T he same characteristics were observed for the other triglycerides.
Also, the 1H —NMR spectra were used to calculate the percentage conversions
of triglycerides using Equation 1. Table 6 is shown the optim ized oil/alcohol volume
ratios and reaction tim e w ith their percentage conversion for each oil at 60 °C
reaction tem perature, 5 vol. % H2S 0 4, 87 % mixing intensity, and 600 W outpu t
power.
Table 6: Percentage conversions for MAT oil/alcohol volume ratios.
Oil
Canola
Castor
Coconut
Corn
Cow Ghee
Olive
Palm Olein
Peanut
Soybean
Sunflower
WVO
Oil/Alcohol
Volume R atio
1:6
1:12
1:6
1:4
1:6
1:12
1:4
1:12
1:6
1:6
1:12
Reaction
Tim e (h)
4
2
2
4
4
4
4
4
4
4
4
Percentage Conversion (%)
M ethanol
Ethanol
77.4
38.9
96.7
97.6 (4 h)
98.9
89.9
51.1
76.8
73.0
89.2
53.6
50.4
78.0
48.2
75.0
56.0
63.8
45.1
77.7
75.5
24.8
-
Based on the results presented in Table 6, castor and coconut oils appear to
be the the best oils to use for FAME synthesis according to the oil/m ethanol volume
42
ratios. In a similar m anner, olive, castor, and coconut oils appear to be th e best for
FAEE synthesis according to the oil/ethanol volume ratios. The conversion of these
oils to their m ethyl ester and ethyl ester were almost complete, however, when
compared to to microwave-assisted base-catalyzed transesterification, th e reaction
time was still very high even though high conversions were observed.63,113 The
conversions of canola, corn, olive, palm olein, peanut, soybean and sunflower to the
FAME product were very low (below 60%) even for 4 h. However, the m oderate
conversions were observed for cow ghee and WVO in the methanolysis. The
conversion of each oils to their corresonding ethyl ester were b etter th an the
conversions of them to their m ethyl esters except coconut and WVO and they had
more th an 60%) conversion for 4 h.
The microwave-assisted acid-catalyzed transesterification reaction between
cow ghee and ethanol did not give any detectable ethyl ester product even after
perform ing the reaction several times. Emulsion problems were frequently
encountered as well. Therefore, it was difficult to separate any ethyl ester product
from the emulsion even the m ixture was allowed to settle more th an three days. A
Small am ount of final product was obtained only for one experim ent, however, the
analysis using 1H —NMR spectroscopy did not exhibit th e characteristic peaks for
ethyl ester.
G C /M S was also used to determ ine the fatty acid ester profile of product
m ixtures. The gas chrom atogram of the FAME product m ixture from the
oil/alcohol volume ratios of coconut oil is shown in Figure 21.
The peaks in the GC chrom atogram were identified using mass spectrom etry.
The m ethyl ester profile w ith the retention tim e and relative percentage of each
component is shown in Table 7. Six satu rated FAMEs and two u n satu rated FAMEs
43
were identified. The m ost abundant methyl ester was m ethyl laurate in coconut oil
as reported in the literature. The m ethyl esters content also agreed w ith Table 2
d a ta from the literature. The FAAE composition of the other triglycerides for
oil/alcohol volume ratios were also identified.
Table 7: The m ethyl ester profile of coconut oil for MAT oil/m ethanol volume ratio.
Ester
M ethyl
M ethyl
M ethyl
M ethyl
M ethyl
M ethyl
M ethyl
M ethyl
C aprate
L aurate
M yristate
P alm itate
Linoleate
Oleate
Stearate
A rachidate
Corresponding
Acid
10:0
12:0
14:0
16:0
18:2
18:1
18:0
20:0
Retention
Time (min)
23.10
29.87
35.52
40.37
42.79
42.91
43.16
44.88
I
i
i
01
35
20
Time(min)
Figure 21: Gas chrom atogram for coconut oil m ethyl ester.
44
Relative
Percentage (%)
4.8
42.7
21.0
10.2
3.1
11.2
3.8
2.2
3.1.2 CHT Oil/Alcohol Volume Ratios
The 1H —NMR spectra for overnight reaction products of coconut oil w ith
m ethanol and ethanol are shown in Figure 22. The methoxy singlet and ethoxy
quartet were identified at 3.66 ppm and region 4.09-4.14 ppm respectively.
ME
X
1
J . -
J
I I 11 r T 1'M'T I J I M I I I I M I IF F T 1 1 1 I r j T T T -T T T ! M | I I I I | ! T F I [ ! F I I ! F I I I | I I » I | I I I I | T I 1 I J
55
50
45
40
35
30
25
20
C hem ical Shift ip p m i
a)
’H - N M R sp ec tr u m fo r c o c o n u t o il m e th y l ester.
C4
T
—
,—
F
-r ■
■
■I r . ■I I I I
4 15
4 1C
C h e m ic a Shift < p p m
i EE
JL
L
C hem ical Shift (ppm >
b)
'H - N M R sp ec tr u m fo r c o c o n u t o il e th y l ester.
Figure 22: 1H —NMR spectra for coconut oil and its FAAE product m ixtures for
overnight reactions.
45
Table 8: Percentage conversions for CHT oil/alcohol volume ratios.
Oil
Canola
Castor
Coconut
Corn
Cow Ghee
Olive
Palm Olein
Peanut
Soybean
Sunflower
WVO
Percentage Conversion (%)
Ethanol
M ethanol
99.0
98.3
95.4
94.3
99.4
96.5
98.3
91.0
96.7
96.3
95.4
98.9
96.7
97.8
93.0
98.5
92.8
97.1
98.1
99.8
92.0
98.9
Oil/Alcohol
Volume Ratio
1:6
1:12
1:6
1:4
1:6
1:12
1:4
1:12
1:6
1:6
1:12
1
09
Abundance (MCounts)
08
07
06
05
04
03
0 2
01
0
20
25
35
30
40
45
Time (Min)
Figure 23: Gas chrom atogram for coconut oil m ethyl ester for overnight reaction.
46
The percentage conversions for conventional heating transesterification
reactions are shown in Table 8. The conversion of each oil to the corresponding
FAAE product m ixture was good and nearly 100% conversion was obtained for each
oil. Even though triglyceride conversions were very high, the reactions required
approxim ately 18 h.
The gas chrom atogram illustrating m ethyl ester profile of coconut oil for
overnight reaction w ith m ethanol is shown in Figure 23 in GC chromarogram.
Almost the same m ethyl ester profile was observed for b o th the MAT reaction as
well as the CHT reaction. The most abundant m ethyl ester was methyl laurate.
The gas chrom atogram illustrating m ethyl ester profile of coconut oil for
overnight reaction w ith m ethanol is shown in Figure 23 in GC chromarogram.
A lm ost th e sam e m ethyl ester profile was observed for b o th th e M AT reactio n as
well as the CHT reaction. The most abundant m ethyl ester was m ethyl laurate.
3.1.3 C o m p ariso n o f M A T a n d C H T O il/A lco h o l V olum e R a tio R eactio n s
The efficiency of MAT and CHT reactions were com pared based on
conversion/hour. The reaction tim e for MAT experim ents were 2-4 h and the
reaction tim e for CHT experim ents were approxim ately 18 h. Based on Table 9,
MAT reactions have b e tte r conversion/hour th an the CHT reactions.
3.1.4 D isad v an tag es o f O il/A lco h o l V olum e R a tio R eactio n s
There are several drawbacks in oil/alcohol volume ratio experim ents. Mainly, it is
very expensive, because a large am ount of alcohol was used for each experiment.
The excess am ount of alcohol is used to shift the equilibrium to favor form ation of
products since the transesterification reaction is reversible. However, excessive
47
Table 9: Conversion/Hour for MAT and CHT Oil/Alcohol Volume Ratios
Oil
Canola
C astor
Coconut
Corn
Cow Ghee
Olive
Palm Olein
Peanut
Soybean
Sunflower
WVO
MAT Conversion/Hour (%)
2-4 h
Ethanol
M ethanol
9.7
21.9
24.4
48.4
49.5
45.0
19.2
12.8
18.3
13.4
22.3
12.6
21.0
12.1
20.7
14.0
18.7
21.2
11.3
18.9
18.9
-
CH T C onversion/Hour (%)
18 h
Ethanol
M ethanol
5.5
5.5
5.2
5.3
5.4
5.5
5.1
5.5
5.4
5.4
5.5
5.3
5.4
5.5
5.4
5.2
5.4
5.2
5.5
5.5
5.1
5.5
am ounts of alcohols do not appear to increase the alkyl ester yield and cause
problems w ith the separation and removal of the glycerol b y -p ro d u ct.129 W hen
glycerol remains in solution, it helps drive the equilibrium back to the left, lowering
the yield of esters.130 Moreover, an excessive am ount of alcohol leads to larger
am ounts of organic and aqueous waste. The disposal of these wastes is expensive
and increases net production cost. In addition, th e conversion of most oils to their
methyl esters were below 60% and reactions were almost incomplete.
Even though high conversions were observed for CHT reactions, th a t process
also has disadvantages. Mainly, it is a more expensive and energy-inefficient m ethod
when com pared to MAT process. T he cooling w ater circulating through the
condenser leads to larger am ount of w ater waste, specially for acid-catalyzed
transesterification reactions due to th e long reaction time. This problem can be
solved by using a m ethod to cycle the w ater used for the CHT experiments.
48
3.2 FAAE Identification and Percentage Conversion - Molar Ratios
M olar ratio experim ents were perform ed to obtain b etter percentage
conversions and find a less expensive m ethod th an one based on volume ratios. The
am ount of alcohols used for these experim ents was very low, therefore, the process
was less expensive and also, less waste was produced during the separation process.
All molar ratio FAAE product m ixtures were characterized using b o th
1H—NMR spectroscopy and G C /M S. The XH —NMR spectra for molar ratio
experim ents using canola oil are shown in Figure 24.
The m ain fatty acid com ponents of canola oil are oleic, stearic, and linolenic
acids. T he 1H —NMR spectrum of neat canola oil is shown in Figure 24-a. The
1H —NMR spectrum of canola oil m ethyl ester is shown in Figure 24-b. It should be
noted th a t the appearance of the m ethoxy singlet at 3.65 ppm is indicative of the
presence of m ethyl esters. The appearance of this singlet is the only difference
between neat oil spectrum and m ethyl ester spectrum . The 1H —NMR spectrum of
canola oil ethyl ester product is shown in Figure 24-c. T he q uartet observed at
4.09-4.14 ppm is characteristic of th e presence of an ethyl ester. All three spectra
show a triplet at 2.29 ppm for the methylene protons of the a-earbon of the fatty
acid groups. All three of the spectra show signals for th e characteristic glyceride
m ultiplet at 4.12-4.32 ppm.
49
a)
'H -N M R spectrum for neat canola oil.
ME
A
1
/'....A.;
v _ jU
r | n - rr-i-r r-i fTi-r n f . i n Tr n T TT t r t 7-i t t t 7 i i Tr'|'TTT-iT n t t t> t i r r r-r n j t t t t t t t r r |T
55
50
40
35
30
25
Chemica Shift ippmt
b)
‘H -N M R spectrum for canola oil methyl ester.
I
c ->
’’•’I r -T'-r -T- r r - r -i—» p - n
4 15
i r • r
4 10
t r | r405
C nem ita Shift tppms
t [ EE
-J .
V["I11',"1 'I1,"l
55
50
I"
45
A
H IT l"| ' 1' l"l'1
35
ii
__J\ > V..1A
I ' M I " M T1 . ■I I 1 . . ■T■I . I 1 111
30
25
20
l'1"| '
15
Chemical Shift tpprm
c)
‘H -N M R spectrum for canola oil ethyl ester.
Figure 24: 1H—NMR spectra for canola oil and its FAAE product m ixtures using
1:6 canola/alcohol molar ratio, 2 h reaction time, 5 wt % H2S 0 4, 60 °C reaction
tem perature, 87 % mixing intensity, and 600 W output power.
50
Table 10: Percentage conversions for oil/alcohol molar ratios at 60 °C reaction tem ­
perature, 5 w t % H2S 0 4, 87 % mixing intensity, and 600 W o u tp u t power.
Oil
Canola
C astor
Coconut
Corn
Cow Ghee
Olive
Palm Olein
Peanut
Soybean
Sunflower
WVO
Oil/Alcohol
Molar Ratio
1:6
1:12
16
14
16
16
14
16
14
14
16
Reaction
Time (h)
2
2
2
4
4
4
4
4
4
4
4
Percentage Conversion (%)
M ethanol
E thanol
78.4
91.3
93.4
84.5
82.1
60.1
81.3
32.3
70.8
41.5
83.2
66.5
83.6
34.5
64.1
54.8
76.9
74.7
75.4
78.6
49.4
48.6
T h e calcu lated percen tag e conversion based on th e XH —N M R sp e c tra for each
oil w ith m ethanol and ethanol are shown in Table 10. Based on the results shown in
Table 10, castor oil is the best for production of the m ethyl ester product and canola
oil is the best for production of the ethyl ester product. M oderate conversions were
observed for canola, coconut, corn, cow ghee, olive, palm olein, soybean, and
sunflower oils to their corresponding methyl esters. The conversion of peanut and
WVO were very low compared to the other oils. The conversion of each oils to their
corresonding m ethyl ester were b etter th an the conversions of them to their ethyl
esters except canola and W VO and they had m oderate conversion for 4 h.
The fatty acid alkyl ester profiles were identified using G C /M S. The FAME
profile for the product of reaction of canola oil w ith m ethanol is shown in Table 11.
Mainly, ten peaks were identified using mass spectra. The m ost abundant FAME
was m ethyl oleate. This makes sense as the most abundant fatty acid in canola oil is
oleic acid, as shown in Table 2. However, the fatty acid compositions of canola oil in
51
Table 2 and FAME compositions in table 11 has huge differences w ith their
percentages.
2.5
I
40
41
42
43
44
45
46
47
48
49
50
T im * (M in )
Figure 25: Gas chrom atogram for canola oil m ethyl ester.
In industry and in the literature, the oil/alcohol molar ratio was used to
synthesize biodiesel because the transesterification reaction requires three moles of
alcohol for one mole of triglyceride to complete the reaction. However, the molar
ratio is raised beyond three to maximize the yield, since th e transesterification
reaction is reversible.131 Therefore, molar ratio is a very im portant variable th a t
significantly influences the transesterification reaction. Industrially, a 1:6
oil/m ethanol molar ratio is more preferred when base catalysts are used.34
The m ain advantage of the molar ratio experim ents was a reduction in the
am ount of alcohol used. It helps to reduce the cost. The waste produced during the
separation was small (It was half th a n volume ratios) compared to volume ratio
experiments. However, some emulsion problems were encountered during the
separation process for the molar ratio experiments. A milky, whitish-yellow,
soap-like substance was formed in the product m ixture upon addition of aqueous
52
Table 11: The FAME profile of canola oil for MAT oil/methanol molar ratio.
Ester
M ethlyl P alm itate
M ethyl Linoleate
M ethyl Oleate
M ethyl Linolenate
M ethyl Stearate
M ethyl Gondoate
M ethyl A rachidate
M ethyl Behenate
M ethyl Nervonate
M ethyl Lignocerate
Corresponding
Acid
16:0
18:2
18:1
18:3
18:0
20:1
20:0
22:0
24:1
24:0
Retention
Time (min)
40.32
42.83
43.11
43.19
43.28
44.96
45.16
46.94
48.78
49.03
Relative
Percentage (%)
2.2
3.7
84.1
0.1
1.1
1.8
1.2
1.4
0.3
0.4
N aH C 03. Emulsion can occur as a result of the presence of unreacted
monoglycerides and diglycerides.28 The emulsified product m ixture was allowed to
settle overnight. It is believed th a t the emulsification problems th a t were
encountered diminished the yield of biodiesel product.
C astor oil was the best oil for both volume and molar ratio experim ents using
microwave irradiation. M ethanolysis (93.4%) gave b etter results th an ethanolysis
(84.5%) for castor oil. The m ajor fatty acid component of castor oil is ricinoleic acid
(12-hydroxy-cis-oetadec-9-enoic acid), which has a hydroxyl group at C-12.
Therefore, com pared to other vegetable oils, castor oil is the only one th a t is soluble
in alcohol.132 Since the reaction m ixture is homogeneous, high reactivity can be
expected. Also, this hydroxyl group im parts unique chemical and physical
properties, specially, it enhances the lubricity of biodiesel fuels produced from castor
oil.
53
3.3 FAAE Identification and Percentage Conversion - High Temperatures
The m ain objective of performing the transesterification reaction at high
tem perature was to obtain high conversion w ithin a shorter reaction time.
Therefore, soybean and canola m ethyl esters were synthesized a t 150 °C. Both
reactions were almost complete. Canola oil gave 94% conversion to ester product
and soybean oil gave 89% conversion to ester product in only 10 min of reaction
time. Table 12 shows the reaction param eters used in these experiments. The
1H —NMR spectra of the product m ixtures from these reactions are shown in Figure
26.
The 1H-NMR spectra of the product m ixture from both reactions exhibited
the spectral characteristics typical for a FAME mixture.
Table 12: Percentage conversions for elevated tem peratures at 150 °C reaction tem ­
perature, 5 wt % H2S 0 4, 87 % mixing intensity, and 600 W o u tp u t power.
Oil
Canola
Soybean
Oil/Alcohol
Molar Ratio
1:30
1:30
Reaction
Tim e (min)
10
10
Percentage
Conversion (%)
94
89
O ptim al tem perature used for base-catalyzed transesterification is 50 —60 °C.
In the literature, 60 °C was used for acid-catalyzed transesterification. However,
elevated tem perature requires for acid-catalyzed transesterification to get high yield
and reduce the reaction time. Elevated tem perature was used for acid-catalyzed
transesterification and high yield was obtained w ithin short reaction tim e using
microwave irradiation and conventional heating in the lite ra tu re .70,133
The FAME product m ixtures formed from th e high-tem perature experim ents
were very dark brown in color. Decomposition was observed several times, therefore,
54
high oil/m ethanol molar ratio was used and several reactions were performed.
However, emulsion did not occur since the reactions were nearly complete and,
therefore, separation was easy and quick.
ME
.J
' ' !"
55
_
" I ' ' ' ' ! 11 ' ' I ' ' M I I I I I I I I I I I I I I I | I I I I I 1 I 1 I | I II I I I ! II I I I I I I I I M I I I I I I I I
50
15
4C
35
30
2 5
2 Z
1*
Chemtca Snrfi <eon- >
10
a ) ‘H -N M R spectrum for canola o il m ethyl ester.
ME
A
8
X
....
XL
11
s
T ;
A i |
J\~J
p|
Chemical Shift (ppm)
b)
Figure 26:
ments.
H -N M R spectrum for soybean o il m ethyl ester.
1H —NMR spectra of product m ixtures from high-tem perature experi­
3.4 FA A E Id en tifica tio n an d P e rc e n ta g e C onversion - H etero g en eo u s C a ta ly s t
Acidic silica gel (S i0 2/ 50% H2S 0 4) was used as a heterogeneous catalyst to
reduce the reaction time. Table 13 shows the calculated percentage conversion using
55
1H—NMR spectra and the reaction param eters used. Figure 27 shows th e !H —NMR
spectra for neat castor oil and its m ethyl and ethyl ester product m ixtures.
Table 13: The percentage conversion for castor oil using acidic silica gel as solid cat­
alyst at 60 °C reaction tem perature, 1 g of SiO2/50% H2S 0 4, 87 % mixing intensity,
and 600 W output power.
Alcohol
M ethanol
Ethanol
Oil/Alcohol
Molar R atio
1:12
1:12
Reaction
Time (min)
45
45
Percentage
Conversion (%)
81
71
Even though heterogeneous catalysts have several advantages such as
reusability and easy separation, th e conversion to m ethyl and ethyl esters was
incomplete using SiO2/50% H2S 0 4 solid catalyst. However, Perin et al. 121 reported
the same study and 95% conversions were observed w ith both m ethanol and
ethanol after 30 min and 20 min respectively. Com pared to molar and volume ratio
experiments, the separation was easy and the am ount of waste produced was small.
Also, emulsion did not occur during separation.
3.5 D iscussion o f W ashing an d E x tra c tio n P ro c e d u re s
The separation of pure biodesel from the crude m ixture is an im portant step
for all experiments. The crude biodiesel m ixture can contain unreacted alcohols,
glycerol, catalyst, mono and diglycerides and other contam inants. The unreacted
alcohol in all the experim ents were removed using rotary evaporation. High am ount
of alcohols were used for volume ratio experim ents and the ro tary evaporation
process took a long time. H2S 0 4 was neutralized using satu rated aqueous N aH C 0 3
for volume and molar ratio experiments. The reaction of H2S 0 4 w ith N a H C 0 3
forms Na2S 0 4, C 0 2, and H20 . The N aH C 0 3 washing procedure was repeated
56
?T
AA
a ..—
r r r f f'TTTi r t r j r r r i | i
55
50
55.asts ,r
;f P '
*
1
i
.
i i ) i i i i i i i i i r vi - r r r TTTvT i-T t t
45
40
35
Tt i
i i 1 << i TT -n T Ti-TTTTTTTir rn
30
25
20
10
05
Chemical SMI (ppm)
a) 'H -N M R spectrum for neat castor oil.
ME
>1
j* I
M .
50
.*
s—
__) 1
v 'U v_
M ' 1 11 I ' ' ' ' I '
45
Crtemica SMI sppmt
b)
‘H -N M R spectrum for castor oil m ethyl ester.
C4
£
T
4 15
4 1C
Chemical SMI (ppm-
EE
T■*
j
T
U.
.» K
jU K
.it
CMmtca- SMI (ppm)
c)
H -N M R spectrum for castor oil ethyl ester.
Figure 27: 1H —NMR spectra for castor oil and its FAAE product m ixtures using
1:6 castor/alcohol molar ratio, 45 min reaction time, 1 g of SiO2/50% H2S 0 4, 60 °C
reaction tem perature, 87% mixing intensity, and 600 W outp u t power.
57
twice. Since glycerol is miscible in water, it can be assumed th a t some of the
glycerol by-product was removed as well during the N aH C 0 3 washing step.
Product m ixture was then washed w ith satu rated aqueous NaCl. The purpose
of adding NaCl was to remove other polar im purities present in the crude product
m ixture. Also, the increased ionic strength of the NaCl solution helped to reduce
emulsification. Anhydrous M gS 04 was used to remove residual am ounts of w ater
from the product m ixture. Anhydrous Na2S 0 4 can be also used for this task. The
dried product m ixture was then centrifuged to remove glycerol, trace am ounts of
water, and any other impurities.
58
CHAPTER 4
C onclusion a n d F u tu re W ork
4.1 C onclusion
Biodiesel is a good alternative to petroleum diesel fuel because it is renewable,
biodegradable, and nontoxic. The common m ethod used for biodiesel synthesis is
transesterification in which, biodiesel is produced by reacting a triglyceride w ith an
alcohol in the presence of a catalyst. The catalyst can be an acid, a base, or an
enzyme. Base-catalyzed transesterification is more common due to its fast reaction
time and high yield. However, this process is not appropriate w ith feedstocks having
a high FFA content because saponification can occur. Acid-catalyzed
transesterification is an alternative m ethod th a t eliminates the saponification
problem, however, the acid-catalyzed process is much slower th an the base-catalyzed
process.
In this study, microwave irradiation was used to expedite th e reaction tim e
using acid catalysts. M ultiple feedstocks (canola, castor, coconut, corn, ghee, olive,
palm olein, peanut, soybean, sunflower oils, and WVO) were used w ith m ethanol or
ethanol and H2S 0 4 as a catalyst. Mainly four different m ethods were used to
produce biodiesel: 1. MAT using oil/alcohol volume ratio, 2. MAT using oil/alcohol
molar ratio, 3. MAT using high tem peratures for canola and soybean oils, and 4.
MAT using SiO2/50% H2S 0 4 as a heterogeneous catalyst for castor oil. The
microwave param eters such as oil/alcohol ratio, reaction time, reaction tem perature,
catalyst loading, and mixing intensity were optimized for th e first two m ethods
using each oil. The optimized param eters obtained from MAT volume ratios were
59
then applied to conventional heating m ethod in order to compare b o th systems. The
product m ixtures from these reactions were analyzed using 1H —NMR and G C /M S.
Experim ental results showed th a t castor oil was the best oil to produce
biodiesel based on either the oil/m ethanol volume ratio or the oil/m ethanol molar
ratio. T he conversion of 97% was obtained using 1:12 oil/m ethanol volume ratio
and 93% was obtained using 1:12 oil/m ethanol molar ratio w ith 5 wt.% of H2S 0 4
for 2 h at 60 °C. The hydroxy group in castor oil im parts th e chemical and physical
properties and also it increases the reactivity w ith alcohols com pared to other
vegetable oils. Coconut oil also had 98% conversion using 1:6 oil/m ethanol volume
ratio w ith 5 wt.% of H2S 0 4 for 2 h at 60 °C.
All conventionally-heated transesterification reactions using volume ratios had
nearly 100% conversion for 18 h w ith 5 wt.% of H2S 0 4 for 2 h at 60 °C. However,
this m ethod was much less energy-efficient th an the microwave-assisted
transesterification reactions using volume ratios.There are several drawbacks to
biodiesel synthesis based solely on the oil/alcohol voume ratio. Mainly, it is very
expensive due to large am ount of alcohol used. Also, m ost oils had below 60%
conversion w ith m ethanol for MAT. Moreover, a large am ount of waste was
produced during the separation process during these experiments.
MAT experim ents using higher reaction tem peratures were very energy
efficient. Under the high-tem perature conditions, canola oil gave the FAME product
at 94% conversion and soybean oil gave the FAME product at 89% conversion.
Heterogenous catalyst gave m oderate conversion (81% w ith m ethanol and 84% w ith
ethanol) for castor oil using 1:12 castor/alcohol molar ratio for 45 min w ith 1 g of
SiO2/50% H2S 0 4 at 60 °C. MAT using a heterogeneous catalyst gave m oderate
conversion of FAAE products for castor oil (81% conversion for m ethanol and 86%
60
conversion for ethanol).
4.2 F u tu re W ork
Biodiesel production using H2S 0 4 as a catalyst is slow and incomplete m ethod
even for microwave-assisted transesterification. H igh-tem perature experim ents had
complete conversion. Biodiesel will be synthesized using following m ethods in the
future.
• Elevated tem perature will be used for other feedstock used for this study to
obtain b etter conversion.
• High molecular weight alcohols such as propanol and butanol will be used to
produce biodiesel using oil/alcohol m olar ratio at 60 °C and elevated
tem perature.
• Biodiesel production cost is still very high com pared to petroleum diesel fuel,
therefore low cost feedstocks will be used synthesize biodiesel.
• The heterogeneous catalyst used for this study gave m oderate conversion.
Therefore, more active acidic heterogeneous catalysts will be used to expedite
the reaction and obtain high conversion.
61
B IB IL IO G R A P H Y
(1) Knothe, G.; Dunn, R. 0 .; Bagby, M. 0 . Biodiesel: the use of vegetable oils
and their derivatives as alternative diesel fuels. A C S Symp. Ser. 1997, 666,
172-208.
(2) Sahoo, P.; Das, L. Combustion analysis of Jatropha, K aranja and Polanga
based biodiesel as fuel in a diesel engine. Fuel 2009, 88, 994-999.
(3) Songstad, D.; Lakshmanan, P.; Chen, J.; Gibbons, W.; Hughes, S.; Nelson, R.
Historical perspective of biofuels: learning from th e past to rediscover the
future. In Vitro Cell. Dev. Biol. PI. 2009, 45, 189-192.
(4) Agarwal, D.; Agarwal, A. K. Performance and emissions characteristics of
Jatro p h a oil (preheated and blends) in a direct injection compression ignition
engine. Appl. Therm. Eng. 2007, 21, 2314 2323.
(5) Agarwal, A. K.; Das, L. Biodiesel development and characterization for use as
a fuel in compression ignition engines. J. Enq. Gas Turbines Power 2001,
123, 440-447.
(6) Agarwal, A. K.; R ajam anoharan, K. Experim ental investigations of
perform ance and emissions of K aranja oil and its blends in a single cylinder
agricultural diesel engine. Appl. Energy 2009, 86, 106-112.
(7) Demirbas, A. Progress and recent trends in biodiesel fuels. Energy Convers.
Manage. 2009, 50, 14-34.
(8) Agarwal, A. K.; Bijwe, J.; Das, L. Effect of biodiesel utilization of wear of
vital parts in compression ignition engine. J. Eng. Gas Turbines Power 2003,
125, 604-611.
(9) Knothe, G.; Van Gerpen, J. H.; Krahl, J. The Biodiesel Handbook; AOCS
press Cham paign, IL, 2005.
(10) Demirbas, A. Biodiesel production via non-catalytie SCF m ethod and
biodiesel fuel characteristics. Energy Convers. Manage. 2006, 41, 2271-2282.
(11) P innarat, T.; Savage, P. E. Assessment of noncatalytic biodiesel synthesis
using supercritical reaction conditions. Ind. Eng. Chem. Res. 2008, J7,
6801-6808.
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73
V ITA
C ham ila M eetiyagoda received her Bachelor degree in Chemistry, Physics and
M athem atics in 2004 from th e University of Peradeniya, Sri Lanka. She worked as a
high school chem istry teacher in Sri Lanka from 2007-2008. She received her
Postgraduate Diploma in Science Education in 2007 from th e University of
Peradeniya, Sri Lanka. She began towards a M aster degree in N atural
Sciences-Chemistry em phasis at Stephen F. A ustin State University, Texas, USA in
the Fall 2014 and is expected to graduate in August 2016.
Perm anent Address:
605D Barringer Lane
W ebster, TX 77598.
Style m anual designation:
American Chemical Society (ACS) Style Guide
This thesis was prepared by Cham ila M eetiyagoda using DI^X .
74
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