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CHAPTER III

PRODUCTION OF BIODIESEL AND ITS OPTIMIZATION

1. Introduction

There is increasing interest in developing alternative energy resources. An

immediately applicable option is replacement of diesel fuel by biodiesel, which consists of

the simple alkyl esters of fatty acids. With little modification, diesel engine vehicles can use

biodiesel fuels. Biodiesel has been defined as the fatty acid methyl esters (FAME) or FA

ethyl esters derived from vegetable oils or animal fats (Triglyserides, TG) by

transesterification with methanol or ethanol. Its main advantages over fossil fuel are that it is

renewable, biodegradable, and nontoxic. Its contribution to greenhouse gases is minimal,

since the emitted CO2 is equal to the CO2 absorbed by the plants to create the TG. They can

also be used as heating oil. Conversely, they do present other technical challenges, such as

low cloud points and elevated NOx emissions. Currently, there are no modifications needed

in the existing diesel engines to use biodiesel as a blend with petroleum diesel fuel. The use

of biodiesel is encouraged by governments across the world to improve energy supply

security, reduce greenhouse gas emissions, and boost rural incomes and employments [1, 2].

US green fuel production yielded 16.2 billion liters of ethanol in 2005. Ethanol has a

2.8% share of the US automobile fuel market. Substantial tax credits of about $2 billion per

year has enabled this technology to develop necessary infrastructure for product delivery at a

fast pace. There have been several attempts to evaluate the ethanol production schemes to

determine how much energy is consumed in the process. Ethanol as fuel was found to reduce

greenhouse emissions by 18%. Cellulosic ethanol from poplar or switch grass was found to

reduce greenhouse gas emissions by more than 90%. Biodiesel looks promising but more

research is called for in all of these different alternative fuel categories [3].

Biodiesel (BD) is a biodegradable and environmentally benign alternative fuel that is

used in diesel engines and heating systems. BD also reduces carbon monoxide and

hydrocarbon particulates from diesel engine emissions [1]. In contrast to fossil fuels, BD does

not significantly contribute to a net increase in carbon dioxide because, for the most part, the

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fatty acid sources from which it is made are photo synthetically derived.

In comparison to fuel ethanol, BD production results in a lower release of nitrogen,

phosphorus, and pesticide pollutants per net energy gain and is estimated to have a higher

energy yield. Typically, the triglycerides (TG) in the feedstock are directly transesterified

with methanol in the presence of an acid, base, or enzyme (lipase) catalyst to afford fatty acid

methyl esters (FAME) and glycerol [2, 4 - 6]. Currently, the most common commercial

process for BD production is by base-catalyzed transesterification of a refined vegetable oil

with methanol [7].

Figure. 3.1: Transesterification reaction of Pongamia and Jatropha oil and methanol in the

presence of alkali catalyst.

The transesterification reaction may be performed through several methods such as

acidic, alkali, or enzyme catalysis, the first two taking place at higher temperatures than the

last one. Zeolite and metal catalysis also have been proposed. All of the proposed methods

have disadvantages such as long reaction times, formation of soap, and a high cost of

consumables or infrastructure. The application of low-frequency ultrasound recently has been

suggested for fast, cost-efficient alkali-catalyzed transesterification of TG to FAME [8].

The transesterification of natural triglycerides (eg; oils and fats), which serve as key

reagents to vital products in the chemical industry, is a highly desired goal. These are

employed to obtain lots of products used in a wide variety of industrial processes.

The most significant products obtained by transesterification, which involve the use of

millions of tons of fats and oils a year, are soaps, long chain carboxylic acids, detergents,

mono and diglycerides, methyl esters of fatty acids, additives for foods, cosmetics,

pharmaceuticals and alternative fuels for diesel engines Several processes are normally

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employed for catalytic transesterification, but these reactions must be carried out at high

temperatures and pressures which reduce selectivity, are energy demanding and suffer from

the presence of by-products [9 – 11]. One of the objectives of this work was to use

microwave irradiation as an easy and fast method for Bio Diesel synthesis through

triglycerides transesterification with methanol. The reactions were carried out either at

atmospheric or under pressure, in order to compare their results with the ones conducted with

conventional heating [12]. Currently, the most common commercial process for BD

production is by base-catalysed transesterification of a refined vegetable oil with methanol

[13, 14]. Many reports of transesterification have come in literature using different vegetable

oils for biodiesel preparation such as palm oil [15] Jatropha oil [16], Pongamia oil [17], Soy

bean, cotton seed, castor oil [18] rape seed [19], chicken feather [20], used cooking oil,

canola and hazelnut [21].

This chapter discusses various methods of biodiesel preparation such as homogeneous

catalysis transesterification (NaOH as catalyst), heterogeneous catalysis transesterification

(Mg - Al Hydrotalacite (MAH) and calcium hydroxyapatite as catalyst), conventional heating

method of transesterification, microwave and ultrasonic assisted transesterification.

2. Results and Discussion

2.1. Homogeneous catalyst for Transesterification

2.1.1. Preparation of Bio-diesel using NaOH as catalyst

The physical properties of the commercial grade Pongamia oil is as given in Table 1.

The average molecular weight calculated for the Pongamia oil was 870 g/mol.

A 500 ml three necked glass flask with a water–cooled condenser at the top was charged

with 50 g of oil, with different volume of anhydrous methanol and varied amounts of catalyst.

Each mixture was vigorously stirred and refluxed for the required reaction time. After several

hours, the reaction mixture was cooled and separated by filtration.

The filtrate was allowed to settle down to separate into two layers. The oil phase consisted of

methyl esters and unreacted triglycerides, while the aqueous phase primarily contained

methanol and glycerol. The residual methanol was separated from the liquid phase by

distillation. Experiments were carried out by changing different parameters like methanol/oil

molar ratio, reaction time, catalyst amount, temperature and mixing intensity. Glycerol

formed after the reaction was weighed and mole value was calculated. This mole value of

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glycerol was compared with the theoretical value and based on this difference the conversion

of triglyceride was estimated [8, 9, 11, 22].

The preliminary studies to determine the optimum quantity of methanol, catalyst

(NaOH), reaction temperature and reaction time required for the transesterification of

Pongamia oil were conducted by varying the concentration of methanol from 8 to 25 (w/v),

NaOH concentration from 0.5 to 1.5%, the reaction temperature from 30 to 60ºC and the

reaction time from 60 to 140 min.

2.1.2. Effect of NaOH concentration

The catalyst concentration was varied from 0.5% to 1.5%. Methanol concentration of

11(w/v) gave the best ester yield. A constant reaction temperature of 60ºC and a reaction time

of 90 min was employed with variations in NaOH concentration. The results of this study are

presented in Figure: 2a. The results clearly indicate that the optimum concentration of NaOH

required for effective transesterification was 1.0%. It was observed that if the NaOH

concentration was reduced below or increased above the optimum, there was no significant

increase in the biodiesel production, but there was increased formation of glycerol and

emulsion. The variation in the NaOH concentration versus the ester yield percentage is shown

in Figure 2a. It is seen clearly from Figure 2a that a maximum ester yield of 91% was

obtained using 1.0% NaOH concentration.

2.1.3. Effect of methanol quantity

The molar requirement of methanol was found to be nearly 11 (w/v). Hence, to

optimize the amount of methanol required for the reaction, experiments were conducted with

8, 10, 15 and 25 (w/v)% of methanol. The concentration of NaOH, reaction temperature and

reaction time used with the methanol variations were constant at 1.0%, 60ºC and 90 min

respectively. The results clearly indicate that the optimum concentration of methanol required

for effective transesterification of Pongamia oil was 11(w/v)%. Moreover, it was found that

when the concentration of methanol was increased above or reduced below the optimum,

there was no significant increase in the biodiesel production, but the excess or shortfall in the

concentration of methanol only contributed to the increased formation of glycerol and

emulsion. The variation in methanol concentration versus ester yield percentage is shown in

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Figure 2b. Figure 2b clearly shows that a maximum ester yield of 88% was obtained using

11 (w/v)% of methanol.

Figure. 3.2 : The conventional method of preparation of Pongamia biodiesel 2a) effect of

catalyst, 2b) effect of temperature, 2c) effect of methanol, 2d) effect of time.

2.1.4. Effect of reaction temperature

The temperature variations adopted in this study were 30, 45, 60 and 90ºC.

A constant reaction time of 90 min and constant methanol and NaOH concentrations of

11(w/v) and 1.0% respectively, gave the best ester yield. The temperature alone was varied

for the production of biodiesel from Pongamia oil. The results clearly indicate that the

maximum ester yield was obtained at a temperature of 60ºC. The variation in reaction

temperature versus ester yield percentage is shown in Figure 2c. It clearly shows that the ester

yield proportionately increased with the increase in the reaction temperature. Since the

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reaction temperature has to be below the boiling point (65ºC) of methanol, the reaction

temperature was fixed at 60ºC. A maximum ester yield of 91.7% was obtained at 60ºC as

shown in Figure 2c.

2.1.5. Effect of reaction time

Reaction times of 30, 60, 90 and 120 min were selected in order to optimize the

reaction time. A constant methanol concentration of 11(w/v), constant NaOH concentration

of 1.0% and constant temperature of 60ºC were maintained. The results of this study are

given in Figure 2d. The results clearly indicate that the biodiesel yield increased with reaction

time. The biodiesel yield was found to be more or less the same at 90 and 120 min of reaction

time. The variation in the reaction time versus the ester yield percentage is shown in Figure

2d and it clearly shows that the maximum ester yield of

92% was obtained when the reaction time was 90 min.

2.2. Heterogeneous catalyst for transesterification

The transesterification process can be catalyzed by both acids and bases. Base

catalysts like sodium or potassium hydroxide are used in a majority of transesterification

reactions. Base catalysts are preferred to acid catalysts because they have better activity and

do not facilitate corrosion. Base catalysis poses emulsification and separation difficulties, and

side reactions like decomposition and polymerization may also occur during distillation after

the reaction. To overcome these difficulties researchers have focused their attention on

developing heterogeneous catalysts. The employment of heterogeneous catalysts helps to

separate the products easily [3, 16].

Solid acid catalysts such as zeolites, clays and ion exchange resins have been tried but

their reaction rates are found to be very low. Solid base catalysts such as simple metal oxides,

mixed oxides and ion exchange resins have also been tried for the transesterification process.

Conventional homogeneous catalysts are expected to be replaced in the near future by

environmentally friendly heterogeneous catalysts mainly because of environmental

constraints and simplifications in the existing processes. At the laboratory scale, many

different heterogeneous catalysts have been developed to catalyze the transesterification of

vegetable oils with methanol. Hydrotalcites, Mg6Al2(OH)16SO4.4H2O, have been used as

precursors of catalysts and have attracted much attention during the development of new

environmentally friendly catalysts. The structure of hydrotalcite resembles that of brucite,

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Mg(OH)2, where the magnesium cations are octahedrally coordinated by hydroxyl ions,

resulting in stacks of edge-shared layers of the octahedral. In the hydrotalcite structure, part

of the Mg2+ ions are replaced by Al3+ ions forming positively charged layers. Charge-

balancing anions (usually SO42−) and water molecules are situated in the inter layers between

the stacked brucite like cation layers. Calcinations at high temperature decomposes the

hydrotalcite into interactive, high surface area and well-dispersed mixed Mg–Al oxides which

present basic sites that are associated with structural hydroxyl groups as well as strong Lewis

basic sites associated with O2− Mn+ acid–base pairs [23- 25].

2.2.1. Catalyst preparation

Mg-Al-SO4 hydrotalcite was synthesized by the co-precipitation of Mg2+ and Al3+

ions in an alkaline solution containing NaOH. 1.0 M solution of Mg2(SO4)6H2O (0.3M) and

Al2(SO4).9H2O (0.1M) were drop wise mixed in 3:1 ratio with 1 M NaOH.

The reaction time pH was maintained between 9 and 11 and the reaction was carried out

under nitrogen atmosphere. The resultant mixture was aged at 900C for 72 hours.

The hydrotalcite was separated by high speed centrifugation and washed with DI water. The

hydrotalcite sample was dried at 100 °C and then calcined at 400 °C [26]. The prepared

hydrotalcite was analyzed by XRD, FT-IR, SEM, Surface analysis, and TGA techniques.

2.2.2. Transesterification of Pongamia Oil

Pongamia oil and an appropriate volume of methanol with calcined Mg–Al

hydrotalcite catalyst (0.5–1%) were placed into a 500 ml three necked flask equipped with

reflux condenser and Teflon stirrer (100–500 rpm). The reaction mixture was blended for a

period of time at 65 °C temperature under atmospheric pressure. The molar ratio of methanol

to oil was taken as 6:1. After the reaction, the hydrotalcite catalyst was separated by filtration.

Subsequently, the methanol was recovered by a rotary evaporator in vacuum at 45 °C and the

ester layer was separated from the glycerol layer using a separating funnel. The fined ester

layer was dried over sodium sulfate and analyzed by gas chromatography on a Shimadzu GC-

2010 chromatograph with FID detector.

The oven temperature program consisted of start at 40 °C and end at 360 °C. The internal

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standard used was C4 to C24 FAME (Fatty Acid Methyl Ester) mix (Sigma Aldrich, USA)

(Sigma Aldrich, USA)

2.2.3. Characterization of catalyst

XRD analysis revealed prominent 2θ peaks at 11.8, 23.8, 35.2, 62.4, and 66.4.

On comparison (JCPDS card no #:50-1684) the formation of Mg-Al hydrotalcite was

understood. A few other peaks were due to intermediate compounds. The basal spacing was

calculated to be 0.739 nm. The sharp peak (003) indicates the formation of highly crystalline

materials. Indexing of the diffraction peaks was done using a standard JCPDS file. The

reflections were indexed in a hexagonal lattice with an R3m rhombohedral symmetry. The

parameter of hydrotalcite corresponding to the cation-cation distance within the brucite-like

layer can be calculated as follows: a = 2 × d (110). On the other hand, the c parameter is

related to the thickness of the brucite-like layer and the interlayer distance and can be

obtained from the equation c = 3 × d (003) [27, 28].

Figure. 3.3: XRD pattern of Mg-Al Hydrotalcite

As shown in Figure 3.3 the basal reflections from the (003), (006), and from (110)

planes in XRD patterns are indicative of Mg-Al-SO4, proving hydrotalcite formation with an

interlayer spacing of 0.739 nm [28]. Sharp X-ray diffraction lines were detected in the

precursor with r = 0.75, which has the composition of the stoichiometric hydrotalcite,

Mg6Al2(OH).16SO4 · 4H2O. All the other hydrotalcite containing precursors showed broader

XRD lines, corresponding to smaller crystallites or less ordered structures [29, 30].

The values of the unit cell parameters, assuming rhombohedral symmetry, with the c parameter

corresponding to three times the thickness of the expanded brucite like layer, are presented in Table

3.1. The a and c parameters decreased with increasing aluminum content, which can be explained

by the substitution of larger Mg2+ ions by smaller Al3+ ions [31].

Using Scherrers formula, one can find the size of the crystal or particle size.

Where K is the shape factor,

broadening at half the maximum intensity (

the mean size of the ordered (crystalline) domains, which may be smaller or equal to the

grain size. The dimensionless shape factor has a typical value of about 0.9,

actual shape of the crystallite. The Scherrer equation is limited to nano

applicable to grains larger than about 0.1

metallographic and ceramographic microstructures. Using the Scherrer formula the crystal s

was found to be within 4.66 nm to 21.2 nm [29, 31].

Mg-Al Hydtotalcite

d(003)

d(110)

d(003) crystal basal space

Table 3.1:

Figure 3.4 shows the FT

characterized with asymmetric and symmetric stretching vibrations of carboxyl group at 1425

cm-1, along with the O-H stretching of the hydroxyl group and deformation vibratio

at 3447.59 cm-1. The spectrum is skewed on the right hand side and the net small peak at

2952 cm-1 is due to the hydrogen bonding of H

frequencies, the peak at 1637 cm

the interlayer water. The main absorption band of the sulphate anions was observed at 1370 cm

the low energy ranges of the spectra (704

presence of Mg-O and Al-O bo

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Using Scherrers formula, one can find the size of the crystal or particle size.

is the shape factor, λ is the X-ray wavelength, typically 1.54 Å,

broadening at half the maximum intensity (FWHM) in radians, and θ is the Bragg angle;

the mean size of the ordered (crystalline) domains, which may be smaller or equal to the

grain size. The dimensionless shape factor has a typical value of about 0.9,

rystallite. The Scherrer equation is limited to nano-scale particles. It is not

applicable to grains larger than about 0.1 µm, which precludes those observed in most

metallographic and ceramographic microstructures. Using the Scherrer formula the crystal s

was found to be within 4.66 nm to 21.2 nm [29, 31].

(003) 2θ d003 (Å) d & c & Basal spacing

11.8 7.48 C=22.44

61.4 1.31 a = 3.03

- - 0.739 nm

Table 3.1: XRD calculation of interlayer distance

3.4 shows the FT-IR spectrum of Mg-Al hydrotalcite. The spectrum was

characterized with asymmetric and symmetric stretching vibrations of carboxyl group at 1425

H stretching of the hydroxyl group and deformation vibratio

. The spectrum is skewed on the right hand side and the net small peak at

is due to the hydrogen bonding of H2O and interlayer of SO42- anions. In the lower

frequencies, the peak at 1637 cm-1 in all the samples can be attributed to the bending mode of

the interlayer water. The main absorption band of the sulphate anions was observed at 1370 cm

the low energy ranges of the spectra (704 – 637cm-1), peaks around 469 cm-1 are attributed to the

O bonds.

Using Scherrers formula, one can find the size of the crystal or particle size.

ray wavelength, typically 1.54 Å, β is the line

is the Bragg angle; τ is

the mean size of the ordered (crystalline) domains, which may be smaller or equal to the

grain size. The dimensionless shape factor has a typical value of about 0.9, but varies with the

scale particles. It is not

m, which precludes those observed in most

metallographic and ceramographic microstructures. Using the Scherrer formula the crystal size

d & c & Basal spacing

C=22.44

a = 3.03

0.739 nm

Al hydrotalcite. The spectrum was

characterized with asymmetric and symmetric stretching vibrations of carboxyl group at 1425

H stretching of the hydroxyl group and deformation vibration of H2O

. The spectrum is skewed on the right hand side and the net small peak at

anions. In the lower

ibuted to the bending mode of

the interlayer water. The main absorption band of the sulphate anions was observed at 1370 cm-1. In

are attributed to the

Figure 3.4:

The hydrotalcite formation by this preparative route was analyzed by SEM.

shows the ‘Rose Petals’ morphology characteristic of hydrotalcite materials which was

observed for all the samples.

Figure

Figure 3.6 shows the TGA

into two well differentiated main regions. In the first one, ranging from 120

there is an endothermic peak related to the dehydration of the sample, which is accompanied

by a mass loss of 7.78%. The second region, ranging from 270

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3.4: FT-IR spectrum of Mg-Al Hydrotalcite

The hydrotalcite formation by this preparative route was analyzed by SEM.

hows the ‘Rose Petals’ morphology characteristic of hydrotalcite materials which was

Figure 3.5: SEM picture of Mg-Al Hydrotalcite

3.6 shows the TGA-DTA curves of both the samples which may be divided

into two well differentiated main regions. In the first one, ranging from 120

eak related to the dehydration of the sample, which is accompanied

by a mass loss of 7.78%. The second region, ranging from 270 °C to 600

The hydrotalcite formation by this preparative route was analyzed by SEM. Figure.3.5

hows the ‘Rose Petals’ morphology characteristic of hydrotalcite materials which was

DTA curves of both the samples which may be divided

into two well differentiated main regions. In the first one, ranging from 120 °C to 220 °C,

eak related to the dehydration of the sample, which is accompanied

C to 600 °C corresponds to

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the weight loss due to the dehydroxylation and de-carbonation reactions, which resulted in a

mass loss of 8.96%. The third endothermic region, ranging from

780 °C to 900 °C, has a weight loss of 5.06%. The weight loss corresponds to the

decomposition of interlayer anion present in the brucite layer and the dehydroxylation of

vicinal OH groups in the hydrotalcite [27, 32].

Figure. 3.6: TGA-DTA curve of Mg-Al-Hydrotalcite.

2.2.4. Application of catalyst for transesterification of Pongamia Oil

The molar ratio of methanol to vegetable oil was one of the most important variables

that affect ester formation because the conversion and the viscosity of the produced ester

depended on it. The stoichiometric molar ratio of methanol to oil is 3:1 However, when mass

transfer is limited due to problems of mixing, the mass transfer rate appears to be much

slower than the reaction rate, so the conversion can be elevated by introducing an extra

amount of the reactant methanol to shift the equilibrium to the right-hand side. Higher molar

ratios result in greater ester conversions in a shorter time [33, 34]. From Figure 7a it is evident

that the optimum molar ratio of methanol to Pongamia oil is 6.0. Beyond the molar ratio of

6.0, the added methanol does not significantly enhance the ester conversion. In addition, the

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conversion increased sharply with reaction time, then reached a plateau representative of a

near equilibrium conversion after a 4 h reaction. A near maximum conversion of 90.8% was

obtained after a 4 h reaction time.

Figure 3.7: Transesterification reaction using Mg-Al-Hydrotalcite with Pongamia oil.

7a) effect of methanol molar ratio, 7b) effect of catalyst, 7c) effect of RPM, 7d)

effect of temperature.

Increasing the amount of catalyst caused the slurry (mixture of catalyst and reactants)

to become too viscous giving rise to a problem of mixing and a demand for higher power

consumption for adequate stirring. On the other hand, when the catalyst amount is not

sufficient, maximum conversion cannot be reached. In most cases, sodium hydroxide or

potassium hydroxide have been used in the process of alkaline methanolysis, both in

concentrations ranging from 0.5% to 1.5% w/w of oil. In our work, the reaction profiles indicate

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that the ester conversion increased with the increase of catalyst amount from 0.5% to 1.5% (0.5%

w/w of oil: 68.2%, 1.0: 79.5%, and 1.5: 90.5%).

However, Figure 7b shows that the conversion to biodiesel decreased with increase in

catalyst amount beyond 1.5% (2.0: 85.0%, 2.5: 83.7%), which may possibly be due to the

mixing problem of reactants, products and solid catalyst. The maximum ester conversion

reached 90.5% when 1.5% catalyst was added. Mixing is very important for the

transesterification of Pongamia oil, because the oil and methanol are immiscible and the

reactants and the solid catalyst are separated in the heterogeneous system. Generally, a more

vigorous stirring causes better contact among the reactants and solid catalyst, resulting in the

increase in reaction rate. Figure 7c clearly shows that the reaction progressed only upon

stirring and that the stirring of the reactants had a significant effect on the transesterification

of the oil (100 rpm: 19.5%, 200: 60.2%, 300: 90.2%, 400: 90.2%, and 500: 90.3%). Adding

solid catalyst to the reactants while stirring facilitated the chemical reaction, and the reaction

started quickly. It also established a very stable emulsion of oil, MeOH and catalyst. The

ester conversion increased rapidly with an increase of stirring speeds from 100 to 500 rpm.

Increasing the stirring speed over 300 rpm did not result in further enhancement in the

conversions (above 90.2%). The effect of reaction temperature on the ester conversion was

studied at six different temperatures, i.e. 50, 55, 60, 65, 70 and 75 °C. Figure 7d shows the

variation of ester conversion with reaction temperature. Transesterification proceeded slowly

at 50 °C, where the conversion was 19.6% in a 4 h reaction. Lower temperatures resulted in a

drop of the ester conversion because only a small amount of molecules were able to get over

the required energy barrier. The ester conversion increased up to 90.4% in a 4 h reaction on

increasing the reaction temperature to 65 °C (55 °C: 31.8%, 60 °C: 70.2%). Thus, the

optimum temperature for the preparation of the ester was found to be 65 °C, which was near

the boiling point of anhydrous methanol. The conversion fell to about 80.0% in the

temperature range of 70–75 °C (70 °C: 80.9%, 75 °C: 80.0%), probably because the molar

rate of methanol to oil decreased when the methanol reactant volatilized into gas phase above

65 °C, the boiling point of pure methanol. The catalytic transesterification of Pongamia oil

with methanol to form biodiesel was investigated using the Mg/Al Hydrotalcite. The

conversion of biodiesel was 90.8%. The obtained biodiesel was analyzed by a Shimadzu GC

2010 using C4 – C24 FAME MIX., as standard. All relative percentages determined by GC for

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each fatty acid methyl ester sample are the means of triplicate runs. This method was used for

the methyl esters reported in Tab. 3.2.

S.No FAME Profile Pongamia Biodiesel

Using Mg-Al

1 16:0 0.525

2 16:1 -

3 18:0 10.37

4 18:1 58:69

5 18:2 8.81

6 18:3 1.29

7 20:0 2.23

8 20:1 5.7

9 22:0 1.18

10 24:1 1.47

Table 3.2: Gas chromatography result of Pongamia biodiesel.

From Table 3.2, the% composition of the five important fatty acid methyl esters

(FAMEs), found in the biodiesel samples such as palmitic (C16:0), stearic (C18:0), oleic (C18:1),

linoleic (C18:2), and linolenic (C18:3) acid methyl esters were determined and reported. The

Table also shows that linoleic and oleic acid methyl esters are the major components in the

synthesized biodiesel samples. The GC study shows clearly that the catalyst Mg - Al hydrotalcite

is efficient in transesterification of Pongamia oil to biodiesel.

2.3. Hydroxyapatite as a catylyst from waste animal bones

CaO is an environmental friendly material useful as a basic oxide catalyst. Ca(NO3)2,

CaCO3, CaPO4 and Ca(OH)2 are raw materials to produce CaO, but natural sources such as

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egg [35, 36], shrimp [37], oyster [38], and crab and cockle shells [39] have also been

employed. Animal bone can also be used as raw material. Calcium phosphate is the main

component of bone and can be transformed to hydroxyapatite which has relatively high

catalytic activity, good thermal and chemical stability, and can make the production of

biodiesel environmentally friendly. In the present investigation, the bone-derived catalysts

were characterized and utilized in the production of biodiesel using palm oil and methanol.

Performance of the prepared catalyst was compared with that of laboratory grade CaO

normally employed for base catalyzed transesterification. Reusability of the catalyst was also

tested.

2.3.1. Catalyst Preparation

Bone powder referred to as “milled animal bone'' was prepared directly from bone

without digestion/reprecipitation steps by crushing bone from sheep in a hydraulic press at

100 psi followed by pressure cooking in water at 15 psi and 1000 °C for 4 h with a water

change halfway through to remove tissue and fat. The clean bone chips were subsequently

dried for 16 h in an oven set at 105 °C before being ground finely to a <2mm particle size

powder using a hammer mill [40, 41]. The bones were calcined in a high-temperature muffle

furnace (Toshibha, India) at different temperatures ranging from 200°C to 1000°C under

static air to observe the influence of the calcinations process on transformation of calcium

species into hydroxyl apatite. Crushed and powdered catalysts were sieved and stored in a

air-tight container before use.

2.3.2. Characterization

Scanning electron microscopy (SEM) analysis was done to study the morphology and

the size of the catalysts using a JEOL JSM-6390 microscope. X-Ray powder diffraction analysis

(XRD 6000 SHIMADZU model) coupled with Cu Kα radiation was done to study the structure

transformation of the catalysts on calcination. FT-IR spectra were obtained with a FTIR Excalibur

FTS 3000 MX SHIMADZU in the range of 400 to 1000 cm-1. The elemental composition was

determined by energy dispersive X-ray fluorescence spectroscopy (EDXRF; EDX-720,

Shimadzu, Japan) under vacuum mode and the surface area analysis was performed using

surface area analyser (Nova, United Kingdom).

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2.3.2. Transesterification

Palm oil and methanol were taken in suitable molar ratios. Calcined bone was added

at levels of 5 to 25 wt%, the mixture was stirred vigorously in a mechanical stirrer at 150 rpm

at 65°C for 4 h using a reflux condenser. The same reaction was also carried out with

commercial CaO. After completion of the transesterification, the catalyst was recovered by

filtration through Whatman filter paper (size 42). The resultant mixture was allowed to

separate, the upper layer was subjected to rotary evaporation (40°C to 45°C) to recover

excess methanol and the product obtained was dried over sodium sulphate before subjecting

to gas chromatography (GC). The sample peaks were compared with

C4 – C24 FAME standards. A FID detector was used and the oven temperature was set to

340°C. The characteristic property of palm oil and palm biodiesel are shown in Table 3.3.

Properties Palm Oil

Palm biodiesel

Standard method

Standard value

Iodine value 47.73 g

iodine/100 g 92.33 g

iodine/100 g EN 14214 120 max

Peroxide value

- 4.83 meq/kg - -

Kinematic viscosity

126.77 mm2/S

3.68 mm2/S ASTM-D445 1.9-6 mm2/S

Acid value 0.58 mg KOH/g

0.467 mg KOH/g

ASTM- D664 0.5 max

Calorific value

40.158 MJ/kg 44.778 MJ/kg - -

Free Glycerol - 0.015% mass ASTM – D 6584 0.02% ,max.

Total Glycerol - 0.21% mass ASTM –D 6584 0.24% max.

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Properties Palm Oil

Palm biodiesel

Standard method

Standard value

Ester content - 97.07% EN 14103 96.5%

C16:0 9.47% - -

C18:0 13.57% - -

C18:1 48.69% - -

C18:2 19.81% - -

C18:3 3.49% - -

C20:0 1.18% - -

C22:0 0.86% - -

Table 3.3. Comparison of the properties of palm oil and palm biodiesel and composition of

biodiesel.

The reusability of the catalyst was investigated by carrying out repeated

transesterification cycles. The catalysts was separated after 4 h from the reaction mixture and

washed with double distilled water and finally washed with acetone and dried in an oven at

50°C.

2.3.4. Characterization of waste animal bone derived catalysts

The XRD pattern with respect to calcinations is shown in Figure 3.8.

The prominent 2θ peaks obtained for uncalcined, 200°C calcined and 400°C calcined samples

are 32.1, 25.8, 49.8 and 50.01. Indexing of the diffraction peaks was done using a standard

JCPDS (Joint Committee on Powder Diffraction Standards) file and the conformation of

calcium phosphate (JCPDS card no #:23-0871) was understood.

The catalyst calcined above 600 to 1000°C shows a different XRD pattern and the prominent 2θ

peaks obtained and h,k,l values are 21.8 (200), 25.8 (002), 28.1 (102), 28.9 (210), 31.8 (211), 32.2

(112), 32. 9 (300), 40.4 (221), 40.8 (103), 46.8 (222), 48.1 (132), 48.7 (230), 49.5 (213), 50.5 (321),

51.3 (140), 52.1 (402), 53.3 (004), 59.9 (240), 60.5 (331), 61.6 (241), 63.1 (502). Indexing of the

diffraction peaks was done using a standard JCPDS file and the confirmation of calcium

hydroxyapatite (JCPDS card no #: 89-6439) was understood.

112

Figure. 3.8: XRD patterns of the animal bone derived catalysts prepared at the different

temperatures.

Microstructural changes with respect to calcinations are shown in Figure 3.9.

The morphology of the uncalcined sample appeared like mass of aggregates, having less

surface area. Whereas the catalysts which were calcined at 200°C and 400°C showed some

change in its morphology but still their particle size reduction seem to be minimum, whereas

catalysts calcined at 600°C to 1000°C were rod like crystal particles. Their particle size

reduction was maximum, exhibiting higher surface area, an important characteristic of a

heterogeneous catalyst.

113

Figure 3.9. SEM image of the animal bone derived catalysts prepared at different

temperatures: (a) uncalcined (b) 200°C (c) 400°C (d) 600°C (e) 800°C

(f) 1000°C.

The BET studies confirmed that the particle size decreased as the calcination

temperature increased leading to an increase in surface area. The uncalcined catalyst had a surface

area of only 3.025 m2/g whereas that of catalyst calcined at 1000°C was 110.96 m2/g (Table 3.4).

114

Contents Chemical composition of the catalysts in weight (%)

Uncalcined 200°C 400°C 600°C 800°C 1000°C

C 19.53 23.46 10.84 10.22 5.93 5.5

O 39.41 42.35 44.85 42.24 46.02 35.4

Na 0.75 0.51 0.60 0.68 0.47 0.55

Mg 0.3 0.31 0.47 0.55 0.53 0.56

P 11.2 11.45 13.70 14.99 14.3 14.48

Ca 20.41 21.91 29.54 31.32 32.75 29.38

Surface area (m2/g)

3.025 4.911 5.434 6.82 88.53 110.96

Table 3.4. Chemical composition and surface area of animal bone derived catalyst prepared

at different temperatures.

FTIR patterns with respect to calcinations were recorded as in Figure 3.10.

The FT-IR spectra of the calcination products exhibited only the characteristic absorption

peaks of hydroxyapatite [41, 42]. The peaks around 1047 to 1095 cm-1 correspond to

asymmetric stretching vibrations of P-O bonds. The bands around 570 to 632 cm-1 correspond

to the vibrations of O-P-O bonds in calcium phosphate. The peak of carbonate at 870 to 875

cm-1 is seen in the uncalcined sample at 200 to 600°C very clearly, whereas only a trace is

present at 800°C and is completely absent at 1000°C.

115

Figure 3.10 : IR spectra of animal bone derived catalysts prepared at different temperatures.

The inorganic composition (C/O/Na/Mg/P/Ca) of the different catalysts were

determined by OXFORD INCA EDS (Table 3.4). EDS analyses revealed that the content of

inorganic phases of bones consisted mainly of calcium and phosphorus with some minor

components such as C, Na, and Mg. The result in Table 3.4 also indicates that the calcium,

oxygen and phosphorous contents increase as the temperature is increased and reach a

maximum at 800°C, suggesting that the activity will also increase due to the formation of

hydroxyapatite.

As shown in Figure 3.11, the mechanism of hydroxyapatite in transesterification

reaction starts with disassociation of Ca5(PO4)3(OH)2 and methanol (steps i , ii and iii). Next,

116

the formation of methoxide anion results from the reaction between methanol and hydroxide

ion. The anion then attacks the carbonyl carbon of the triglyceride to form a tetrahedral

intermediate. Subsequently, the rearrangement of the intermediate molecule results in the

formation of a mole of methyl ester and diglyceride, (step iv). The methoxide then attacks another

carbonyl carbon atom in the diglyceride, forming another mole of methyl ester and

monoglyceride. Finally another methoxide attacks the monoglyceride producing a total of three

moles of methyl ester and a mole of glycerol [43].

Figure 3.11. Proposed mechanism of FAME preparation using hydroxylapatite catalyst.

2.3.5. Optimization of transesterification over waste animal bone-derived catalysts

2.3.5.1. Effect of calcinations temperature for catalyst

The calcinations at higher temperatures led to desorption of carbon dioxide from the

animal bone catalyst, producing basic sites that catalyzed transesterification of palm oil with

methanol. Calcining at 200, 400 and 600 °C was not enough to produce highly active

catalysts. However calcinating at 800°C gave a yield of 96.78% after a reaction time of 4 h at

65°C. Additionally, the transesterification activity agreed well with the Ca content in the

catalyst samples; namely, a higher Ca content in the form of CaO resulted in higher activity.

The conversion was comparable to commercial CaO, which exhibited a conversion of 99%.

Further increase in temperature suppressed the catalytic activity of the catalyst due to the high

sintering rate of the catalyst and high energy consumption [37].

The descending order of the conversion rate over the catalysts at different temperature is

ranked as follows: 800 °C > 600°C > 1000°C > 400°C> 200°C > uncalcined. Therefore, the

optimum calcination temperature was 800°C.

117

Figure 3.12 : Effect of calcination temperature on FAME conversion.

2.3.5.2. Effect of oil to methanol ratio

The FAME content increased significantly when the oil/methanol ratio was changed

from 1:1 to 1:18, but was lower at methanol ratios above 18 (Figure. 3. 13a).

118

Figure.3.13 : Effect of different parameters on FAME conversion: (a) molar ratio of

methanol (b) catalyst concentration (wt%) (c) reaction temperature (°C)

(d) reaction time ( h) (e) stirring rate (rpm) (f) reusability.

The high amount of methanol (oil to methanol ratio of 1:18) promoted the formation

of methoxy species on the CaO surface, leading to a shift in the equilibrium in the forward

direction, thus increasing the rate of conversion up to 96.78%. However, further increases in

the oil to methanol ratio did not promote the reaction. It is understood that the glycerol would

largely dissolve in excessive methanol and subsequently inhibit the reaction of methanol to

the reactants and catalyst, thus interfering with the separation of glycerin, which in turn

119

lowers the conversion by shifting the equilibrium in the reverse direction [43]. Therefore, the

optimum ratio of oil to methanol was 1:18, which is more than double the practical oil to

methanol ratio for homogeneous transesterification of 6:1.

2.3.5.3. Effect of catalyst loading

The effect of catalyst loading on FAME conversion over animal bone derived catalyst

was investigated (Figure 3.13b). When a small amount of catalyst (<1 wt%) was used, the

maximum product yield could not be reached. The maximum conversion of 96.78% was

obtained with a catalyst loading of 20 wt%. However, the yield did not increase when the

catalyst loading was above 20 wt% which led to the formation of a slurry too viscous to

enable adequate stirring. Thus, getting the reactants to and from the catalyst becomes the rate

determining step (mass transport limitation) which is why adding more catalyst does not

exhibit any effect. Therefore it is evident that the optimum catalyst loading is 20 wt% in the

present study.

2.3.5.4. Effect of reaction temperature

The effect of reaction temperature on FAME yield over animal bone derived catalyst

was investigated (Figure 3.13c). There was a steady increase in the conversion on rising the

reaction temperature and a maximum conversion of 96.78% was obtained at 65°C. On

increasing the temperature above 65°C there was a decline in the conversion as the

temperature reaches above the boiling point of methanol since methanol bubbles inhibit the

mass transfer on the interface of the phases [44]. Therefore, the optimum reaction

temperature was found to be 65°C with the catalyst in the present study.

2.3.5.5. Effect of Reaction time

The effect of reaction time on FAME yield in this transesterification was investigated

and is shown in Figure 3.13d. The FAME content increased significantly on increasing the

reaction time from 1 hour to 6 hours and a maximum yield of 96.78% was obtained after 4 h.

On further increase of the reaction time the yield remained the same till the end of 6 h and

started to decline due to equilibrium shift in the reverse direction and also due to the

120

formation of emulsions. Comparatively lesser yield at lower (1 hr) reaction time is due to the

absence of calcium methoxide, which is the driving force for the transesterification reaction.

Therefore, the optimum reaction time was found to be

4 h over the catalyst in the present study.

2.3.5.6. Effect of stirring rate

The effect of stirring rate (50 to 250 rpm) on FAME yield in the biodiesel production

was investigated and is shown in Figure 3.13e. The immiscible phases of methanol, oil and

the catalyst surface need a certain stirring speed to increase the yield. The FAME yield

increases as the stirring rate is increased and reached a maximum yield of 96.78% at a stirring

rate of 200 rpm. There was no significant change on increasing the stirring rate. Therefore,

the optimum stirring rate was fixed as 200 rpm.

2.3.5.7. Reusability of waste animal bone-derived catalyst

The reusability of the catalyst animal bone derived was investigated by carrying out

the transesterification in subsequent reaction cycles and is shown in Figure 3.13f. The catalyst

was separated after 4 h from the reaction mixture and washed with double distilled water and

finally washed with acetone and dried in an oven set at 50 °C. Subsequent reaction cycles were

performed under the same operating conditions using catalyst recycled after each cycle. After 5th

cycle of the transesterification conversion is 83.7%.

The catalyst derived from animal bones had excellent activity in heterogeneous

transesterification of palm oil for biodiesel production. Calcination of the catalyst derived

from the animal bones resulted in an increase in surface area, leading to better catalytic

activity. Among the calcined catalysts, the catalyst calcined at 800°C gave the highest

biodiesel yield. The comparison of the performance of animal bone-derived catalyst with

synthetic CaO normally employed proves that irrespective of the origin of CaO, the basic

CaO acts as catalyst in the transesterification. Since the waste bone catalyst shows high

catalytic activity and ecologically friendly properties, it is a potential catalyst for biodiesel

production.

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2.4. Conventional heating, microwave and ultrasonic methods

Vegetable oils have not been accepted as a diesel engine fuel for two reasons. They

are more expensive than petroleum fuels and too viscous to be atomized efficiently in a diesel

engine. Among the various attempts to reduce their viscosity, their conversion to

corresponding fatty ester appears to be the most promising solution [4]. Different

technologies are currently available and are used in the industrial production of transesterified

oil for use as biodiesel. The alkali–catalyzed method is the most developed method among

biodiesel production processes. The controlling parameters which affect the conversion rate

using this technology are the molar ratio of alcohol to oil, the temperature, and the pressure.

Industrial application of such technology is sure to be successful if it is carried out under

optimum conditions [5, 6].

Sonochemistry is the application of ultrasound to chemical reactions and processes.

The origin of sonochemistry stems from acoustic cavitation: the growth and highly energetic

collapse of microscopic bubbles in a liquid. The chemical effects of ultrasound include the

formation of radicals and the enhancement of apparent reaction rates at ambient temperatures.

Ultrasonic waves are above the normal human hearing range (18-20 kHz) [7]. In general, the

conversion of vegetable oil to biodiesel occurs during a transesterification process in the

presence of a catalyst and heat. Recently, ultrasonic wave assisted synthesis of biodiesel has

been found to be an attractive technique because it gave a higher yield of pure products in

less conversion time. When ultrasonic waves are passed through a mixture of immiscible

liquids, such as vegetable oil and methanol, extremely fine emulsions can be generated.

These emulsions have large interfacial areas which provide more reaction sites for catalytic

action and, thus, increasing the rate of transesterification reaction [8- 11].

In the present work the transesterification of Pongamia pinnata (L.) Pierre oil was

carried out by sonochemical method using pulse and continuous modes. The results of

transesterification were compared to the results obtained using conventional method.

Ultrasonic energy increased the reaction rate by several fold, reducing the reaction time from

approximately 30–45 min to less than 1 min.

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2.4.1. Preparation of bio-diesel by conventional method

Biodiesel from Pongamia pinnata (L.) Pierre was prepared by following previously

reported methods [12,13]. Physical properties of Pongamia pinnata (L.) Pierre oil determined

in this study are listed in Table 3.5.

Properties Pongamia

Oil Pongamia

biodiesel Standard method

Standard Value

Iodine Value 95.18 g

iodine/100 g oil 88.33 g iodine/100 g

oil EN 14214 120 max.

Peroxide Value - 5.83 (meq/kg) - -

Kinematic Viscosity

(@ 400C) 61.19 cP 5.96 cSt or 7.46 Cp

ASTM –D 445

1.9 – 6 cSt

Acid value 9.35 (mg KOH/g)

0.467 (mg KOH/g) ASTM –D

664 0.5 max.

Saponification Value

220.66 mg KOH/g oil

174.86 mg KOH/g Oil

- -

Water Content 0.5% 0.12% ASTM –D

2709 Max. 0.05%

Carbon Residue Value

0.095% 0.049% ASTM –D

4530 Max. 0.05%

Cloud Point 8 to 9 4 to 6 ASTM –D

2500 -

Pour Point 2 to 1 -3 to 0 ASTM –D

2500 -

Calorific Value 33. 034 34.778 MJ/kg - -

Table 3.5 : Physical properties of crude Pongamia pinnata (L.) Pierre Oil and Pongamia

pinnata (L.) Pierre biodiesel.

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Preliminary studies to determine the optimum quantity of methanol, the catalyst

NaOH, the reaction temperature and the reaction time required for the transesterification of

Pongamia pinnata (L.) Pierre oil were conducted by varying the concentration of methanol

from 8 to 25 (w/v), NaOH concentration from 0.5 to 1.5%, the reaction temperature from 30

to 90 °C and the reaction time from 30 to 130 min.

Figure 3.14: The conventional method of preparation of Pongamia pinnata (L.) Pierre

biodiesel. Effects of a) catalyst, b) methanol, c) temperature, and d) time

In order to find out the effect of NaOH as catalyst, concentrations of 0.5%, 1% and

1.5% NaOH were used and evaluated (Figure 3.14a). 1% NaOH yielded the maximum

quantity of product (85% (w/v)) and was used as the optimum concentration

for subsequent experiments. An increased formation of emulsion was noticed with increase in

NaOH concentration above the optimum level, whereas biodiesel conversion remained

incomplete at lower concentrations.

124

The molar requirement of methanol was found to be 11 (w/v). In order to optimize the

amount of methanol required for the reaction, experiments were conducted with 8, 10, 15 and

25 (w/v)% of methanol. The concentration of NaOH, reaction temperature and reaction time

used with the methanol variations were kept constant at

1.0%, 60 °C and 90 min respectively. The optimum concentration of methanol required for

effective transesterification of Pongamia pinnata (L.) Pierre oil was 11% (w/v) providing an

ester yield of 85% (Figure 3.14b). Moreover, when the concentration of methanol was

increased above or reduced below the optimum, there was significant decrease in biodiesel

production, with excess methanol only contributing to an increased formation of glycerol and

emulsion.

The temperature variations attempted in this study were 30, 45, 60 and 90 °C.

A constant reaction time of 90 min and an optimum methanol and NaOH concentrations of

11 (w/v) and 1.0% respectively, were used. The ester yield proportionately increased with an

increase in reaction temperature (Figure 3.14c). The reaction temperature was maintained at

60ºC, since it had to be below the boiling point of methanol (65ºC).

A maximum ester yield of 85% was obtained at 60 °C.

In order to find the reaction time required for optimum yeild, time intervals of 30, 60,

90 and 120 min were selected. Methanol concentration was maintained at 11% (w/v), NaOH

at 1.0% and temperature at 60 °C. The average results of this study are given in

Figure 3.14d. A maximum ester yield of 85% was obtained at a time point of 90 min.

Extending the reaction time above 90 min resulted in reduced yield due to backward reaction

and emulsion formation.

2.4.2. Sonochemical synthesis of biodiesel

About 50 g of Pongamia pinnata (L.) Pierre oil was added to sodium methoxide

solution prepared by reacting 8 ml (4 w/v) methanol with 0.5 g (1%) sodium hydroxide. The

sample size was scaled to match the available reaction chamber size for the ultrasonic horn

(∼60 ml). Ultrasonic energy was applied in two different modes: the pulse and the

continuous modes. In the pulse mode, ultrasonic energy was applied for every 5 sec., and the

samples were collected at the end of 30th, 60th , 90th , 120th , and 150th sec., time intervals. The

pulse mode allowed relatively high amplititudes (high intermediate dissipated power) without

causing excessive heating. In short, the pulse mode allowed for generation of intense

125

ultrasonic fields while maintaining a moderate average of the dissipated power level. The

reaction was studied in three amplititude levels, namely: 40, 60, and 120 Hz. In the

continuous sonication mode, the reactants were sonicated continuously for 15 sec., at 120 Hz.

A total of 10 reaction mixtures were prepared and each was sonicated for 1, 2, 3, etc., up to

15 sec., time intervals. The reaction was quenched every time by adding water (50 ml) and

hexane (50 ml) immediately after the ultrasonic treatment. The mixture of Pongamia pinnata

(L.) Pierre oil and biodiesel was separated as detailed in the previous section. For accuracy,

all the experiments described were repeated 4 times. It is important to note that external

heating was not used in any of the ultrasonication experiments [8, 9, 11].

2.4.2.1. Ultrasonication – pulse method

Figure 3.15 shows the transesterification of Pongamia pinnata (L.) Pierre oil as a

function of time with ultrasonic treatment in the pulse mode at three different amplititudes.

The highest yield of 96% was obtained after a time interval of 120 sec., at 120 Hz. At a

frequency of 60 Hz, the highest yield was 92% in 250 seconds, and at a frequency of 40 Hz

the highest yield of 91% was obtained in 300 sec. Yields as high as 96% were obtained

within 120 sec., at a frequency of 120 Hz (Figure 3.15a).

126

Figure 3.15: Comparison of biodiesel conversion obtained in pulse mode. Effects of

different ultrasonication frequencies against various a) time points, b) catalyst

concentrations, and c) methanol concentrations.

In the ultrasonic assisted reaction, parameters like concentration of catalyst and

methanol were varied. The catalyst content was varied from 0.2% to 1.8% and the methanol

content was varied from 2% (w/v) to 18% (w/v). The best yield was obtained when the

concentration of NaOH was 1%. The yield was between 96 and 98%. When the concentration

of catalyst was reduced below 1% the transesterification remained incomplete and the yield was

very poor. However, when the concentration of catalyst exceeded 1%, the oil was saponified and

the biodiesel yield was almost zero. Figure 3.15b reveals that at

60 Hz, a catalyst concentration of 1% gave the best yield. At 40 Hz the yield obtained was

60% and at 120 Hz the yield obtained was 83%. The results obtained using various

127

concentrations of methanol at different frequencies in the sonochemical methods is shown in

Figure 3.15c. A methanol concentration of 4% (w/v) gave the best yield. At a lower

concentration more of mono and diglycerides are formed and at higher concentration there

was no observed effect.

Transesterification under different ultrasonication frequencies and time intervals were

studied. Figure 3.15c clearly shows that the best yield was obtained at 120 Hz in a time of

120 seconds. Increasing the time did not affect the yield. At 40 Hz and 60 Hz

transesterification was low compared to that observed at 120 Hz. Transesterification at

60 Hz for 250 sec., resulted in 92% conversion of biodiesel. Lowering the frequency to 40 Hz

and increasing the time duration to 300 sec., resulted in no change in biodiesel conversion.

Temperature variations could not be carried out since sonication itself generated lot of heat.

2.4.2.2. Ultrasonication – continuous method

Figure 3.16a shows the biodiesel production as a function of time with ultrasonic

irradiation in the continuous mode at three different frequencies. The highest yield obtained

after 15 sec., was 83% at 120 Hz. At 60 Hz, the highest yield achieved was 86% in 15 sec.,

and at 40 Hz the highest yield obtained was 68% in 15 sec.

128

Figure. 3.16: Comparison of biodiesel conversion obtained in continuous mode. Effects of

different ultrasonication frequencies against various a) time points, b) catalyst

concentrations, and c) methanol concentrations.

At 120 Hz, the product formed after 15 sec., was totally solid (saponified oil), which

is due to the rapid heat generated by the cavitation effect. The increased heat in the reaction

mixture resulted in the formation of emulsion.

The effect of variations in catalyst concentrations from 0.2% to 2% was analyzed

next. With a methanol concentration of 4% (w/v) and reaction time of 15 sec., ultrasonication at

60Hz with a catalyst (NaOH) concentration of 1% gave the highest yield of 86%, while at 120 Hz

the yield dropped to 83% (Figure 3.16b). The yield of biodiesel was 40 – 50% in pulse mode

when sonicated at 60Hz under similar conditions.

The effect of variations in methanol concentrations from 2% (w/v) to 14% (w/v) was

also analyzed. Figure 3.16c shows that at an amplititude of 60 Hz the best yield obtained was

86% at a methanol ratio of 4% (w/v). At a lower concentration more of mono or triglycerides

129

are formed and at higher concentrations there were no observed effects. Transesterification

under different ultrasonication frequencies with various methanol concentrations were also

studied. At 40 Hz and 120 Hz the conversion of biodiesel was low when compared to

transesterification at 60 Hz (Figure 3.16 c).

2.4.2.3. Gas chromatographic studies

Figure 3.17: Gas chromatography analysis of biodiesel produced using a) conventional

method, b) sonochemical pulse mode, and c) sonochemical continuous mode.

Biodiesel prepared by both conventional and sonication method was analysed by GC

and the profile of the biodiesel formed is given in Table 2. The percentage composition of

five standard fatty acid methyl esters (FAMEs) found in the biodiesel samples namely

palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and linolenic (C18:3) acid

methyl esters (note: in Cm:n, m is the number of carbon atoms and n is the number of double

bonds), were determined and reported. The Table also shows that linoleic and oleic acid

methyl esters are the major components in the biodiesel samples. FAME composition of

biodiesel produced by both sonication and conventional methods were the same. In pulse

mode the conversion to palmitic ester and stearic ester is more compared to that observed in

continuous mode and the conventional method. Oleic and linoleic ester conversion is more in

the conventional method. In the conventional method the biodiesel contains 8.78% of oleic

and 1.17% of linoleic ester whereas in the sonochemical methods their yield is less. Linolenic

130

and behinic ester conversion is more in the pulse mode. The FAME composition is illustrated

in Table 3.6. It confirms that the prepared biodiesel has almost the same composition.

S.No FAME Profile

Pongamia biodiesel prepared using various methods

Pulse sonication Continuous

sonication Conventional

method

1 16:0 0.525 0.51 0.489

2 16:1 - - -

3 18:0 10.37 10.1 9.94

4 18:1 67.69 68.86 69.72

5 18:2 8.08 7.71 8.789

6 18:3 1.29 1.23 1.172

7 20:0 2.23 1.71 1.73

8 20:1 5.7 5.17 4.89

9 22:0 1.18 0.98 1.19

10 24:1 1.47 1.12 1.67

Table 3.6: GC analysis of Pongamia pinnata (L.) Pierre biodiesel produced using

conventional and sonochemical method.

Results clearly show that the sonochemcial method of transesterification is better

compared to the conventional method. Biodiesel yield of 96% was obtained in the

sonochemical method in 120 sec., whereas in the conventional method the yield was 85% in

5400 Sec. The biodiesel produced by all three methods described had the same composition

as shown by GC analysis, however the sonochemical method was simple and rapid,

exhibiting higher conversion efficiencies.

2.4.3. Microwave method

It is often possible to accelerate the rate of reactions and increase selectivity using

microwave heating for preparative chemistry [22, 47]. Recently, the use of microwave

heating as a fast, simple way to prepare biodiesel in batch mode was reported by our group

[45]. This method allows the preparation of biodiesel under atmospheric conditions, with the

reaction being completed in a matter of a few minutes and performed on batch scales up to 3

kg of oil at a time. The procedure could be employed on new or used vegetable oil and

131

methanol or ethanol. In the conventional heating method normally the ratio of oil to methanol

used is between 1:9 and 1:30. But in the microwave method the methanol oil ratio required

was only 1:6 which is comparatively lesser than what is requird for the conventional method

[48].

2.4.3.1. Microwave assisted preparation of biodiesel

50 ml of Pongamia oil was added to the sodium methoxide solution prepared by

reacting 7 ml of methanol with 0.5 g of sodium hydroxide. The sample size was 100 ml

beaker. The microwave energy was applied. Samples were collected at the end of every 5, 10,

15, 20, and 25, 30 s time intervals. The reaction was quenched at a indicated times by adding

water (50 ml) and hexane (50 ml) immediately after the microwave treatment. Mixtures of

Pongamia oil and biodiesel were separated as detailed in the conventional method biodiesel

preparation section. For accuracy of results, all experiments were repeated 4 times (13,15,16).

132

Figure 3.18: Microwave assisted preparation of biodiesel. a) Effect of time, b) effect of

catalyst concentration, and c) effect of methanol concentration.

2.4.3.2. Effect of time

Reaction times were set to 5, 10, 15, 20, 30, 40 and 50 sec. A constant methanol

concentration of 6:1 ratio, and a constant NaOH concentration of 1.0% were maintained.

Results clearly indicate that biodiesel yield increased with increase in reaction time utpo 20

sec., after which there was no further increase in the yield (Figure 3.18a). A maximum ester

yield of 97% was obtained when the reaction time was 20 sec.

133

2.4.3.3. Effect of catalyst

The catalyst concentration was varied from 0.2% to 3.0% The methanol concentration

of 6:1 ratio that gave the best ester yield, and the best reaction time of

20 sec., were used. The results clearly indicate that the optimum concentration of NaOH

required for effective transesterification was 1.0% (Figure 3.18b). It was observed that if the

NaOH concentration was reduced below or increased above the optimum, there was no

significant increase in the biodiesel production, but there was increased formation of glycerol

and emulsion. It is clear from Figure 3.18b that the maximum ester yield of 97% was

obtained using a NaOH concentration of 1.0%.

2.4.3.4. Effect of methanol oil ratio

The molar requirement of methanol and oil ratio was found to be nearly 3:1. Hence, to

optimize the amount of methanol required for the reaction, experiments were conducted with

1 to 12 molar ratio of methanol. The concentration of NaOH, and reaction time used with the

methanol variations were constant at 1.0%, and 20 sec., respectively. The results clearly

indicate that the optimum concentration of methanol required for effective transesterification

of Pongamia oil was 6:1 (Figure 3.18c). Moreover, it was found that when the concentration

of methanol was increased above the optimum, there was no significant increase in the

biodiesel production. Figure 3.18c clearly shows that the maximum ester yield of 97% was

obtained using 6:1 ratio of methanol.

2.4.3.5. Gas chromatographic studies

The biodiesel profile determined by GC for both conventional and sonication method and

microwave method is given in Table 3.7. The percentage composition of five standard fatty acid

methyl esters (FAMEs), found in the biodiesel samples such as palmitic (C16:0), stearic (C18:0),

oleic (C18:1), linoleic (C18:2), and linolenic (C18:3) acid methyl esters (note: in Cm:n, m is the

number of carbon atoms and n is the number of double bonds) were determined. Table 3.7 also

shows that linoleic and oleic acid methyl esters were the major components in the biodiesel

samples. In all the three methods, almost the same amount of FAME was determined. This is a

strong evidence to show that the microwave and sonication methods are also useful, easy and

quick methods for biodiesel preparation.

134

S.No FAME Profile

Pongamia biodiesel prepared using various methods

Microwave method

Pulse Sonication

Continuous Sonication

Conventional method

1 16:0 0.56 0.525 0.51 0.489

2 16:1 - - - -

3 18:0 10.56 10.37 10.1 9.94

4 18:1 66.9 67.69 68.86 69.72

5 18:2 9.1 8.81 7.71 8.009

6 18:3 1.13 1.29 1.23 1.172

7 20:0 1.77 2.23 1.71 1.73

8 20:1 4.18 5.7 5.17 4.89

9 22:0 2.2 1.18 0.98 1.19

10 24:1 1.52 1.47 1.12 1.67

Table 3.7: FAME profile of Pongamia biodiesel prepared using conventional, ultrasonic and

microwave assited methods.

These results show that microwave assisted and ultrasonic assisted methods could

result in commercial processing advantages, especially by increasing the conversion during

shorter time periods or by using smaller equipment than with conventional agitation systems.

Microwave assisted method especially is better than ultrasonic method as it involves very

inexpensive instrumentation, provides high biodiesel yield and requires very short reaction

times. The yield of biodiesel prepared using the microwave assisted method is 97% ( Figure

3.17).

3. A literature survey of commercially available antioxidants used for improvement of

biodiesel stability

Several studies have shown that the quality of biodiesel over a longer period of

storage strongly depends on the tank material as well as on contact to air or light. Increase in

viscosities and acid values and decrease in induction periods have been observed [49, 50]

during such storage. Although there are numerous publications on the effect of natural and

synthetic antioxidants on the stability of oils and fats used as food and feed, little information

135

is available on the effect of antioxidants on the behavior of FAME used as biodiesel. To

retard oxidative degradation and to guarantee a specific stability, it becomes necessary to find

appropriate additives for biodiesel. Simkovsky et al studied the effect of different

antioxidants on the induction period of rapeseed oil methyl esters at different temperatures

but did not find significant improvements [51]. Schober et al tested the influence of the

antioxidant TBHQ on the PV of soybean oil methyl esters during storage and found good

improvement of stability [52]. Canakci et al described the effect of the antioxidants TBHQ

and α-tocopherol on fuel properties of methyl soyate and found beneficial effects on retarding

oxidative degradation of the sample. [53]. Das et al described effect of commercial

antioxidants used in kharanja biodiesel for storage stability [54]. Karavalakis et al described

the effect of synthetic phenolic antioxidants used for storage stability and oxidative stability.

The storage stability of different biodiesel blends with automotive diesel treated with various

phenolic antioxidants was investigated over a storage time of 10 weeks [55].

In the previous studies, numerous methods for assessing the oxidation status of

biodiesel have been investigated, including acid value, density, and kinematic viscosity. The

peroxide value may not be suitable because, after an initial increase, it decreases due to

secondary oxidation reactions, although the decrease likely affects only samples oxidized

beyond what may normally be expected. Thus there is the possibility of the fuel having

undergone relatively extensive oxidation but displaying an acceptable peroxide value. The

peroxide value is also not included in biodiesel standards. Acid value and kinematic viscosity,

however are two facile methods for rapid assessment of biodiesel fuel quality as they

continuously increase with deteriorating fuel quality [22]. Chapters IV and V discuss the storage

stability and oxidative stability of Pongamia and Jatropha biodiesel.

136

4. Conclusion

This chapter discusses various methods of biodiesel preparation such as homogeneous

catalysis transesterification (NaOH as catalyst), heterogeneous catalysis transesterification

(Mg - Al Hydrotalcite (MAH) and calcium hydroxyapatite as catalyst), conventional heating

method of transesterification, microwave enhanced transesterification and ultrasonic assisted

transesterification. The following findings were arrived at as given in the table below.

Method of Transesterification

Oil:Methanol Catalyst Temperature RPM Time Yield

Homogeneous catalysis

(NaOH) 1:4 1% 65°C 300 90 min 89.1%

Heterogeneous catalysis (Mg-Al HT)

1:6 1.5% 65°C 250 4 h 90.8%

Heterogeneous catalyst

(Ca5(PO4)3OH) 1:18 20% 65°C 250 4 h 96.78%

Ultrasonic assisted method

1:4 1% (NaOH)

- - 100 sec., 95%

Microwave assisted method

1:4 1% (NaOH)

- - 20 sec., 96.7%

137

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