Acta Polytechnica

doi:10.14311/AP.2019.59.0088
Acta Polytechnica 59(1):88–97, 2019 © Czech Technical University in Prague, 2019

available online at http://ojs.cvut.cz/ojs/index.php/ap

OPTIMIZATION OF BIODIESEL PRODUCTION FROM WASTE
FRYING OIL OVER ALUMINA SUPPORTED CHICKEN

EGGSHELL CATALYST USING EXPERIMENTAL DESIGN TOOL

Adeyinka S. Yusuff∗, Lekan T. Popoola

Department of Chemical and Petroleum Engineering, College of Engineering, Afe Babalola University,
Ado-Ekiti, Nigeria

∗ corresponding author: yusuffas@abuad.edu.ng

Abstract. An optimization of the biodiesel production from a waste frying oil via a heterogeneous
transesterification was studied. This present study is also aimed at investigating the catalytic behaviour
of the alumina supported eggshell (ASE) for the synthesis of biodiesel. A synthesized ASE catalyst,
at various mixing ratios of alumina to eggshell, was investigated and exhibited a better activity for
the reaction when the eggshell and alumina were mixed via incipient wetness impregnation in 2 : 1
proportion on a mass basis and calcined at 900 °C for 4 h. The as-synthesized catalyst was characterized
by basicity, BET, SEM, EDX, and FTIR. The 2k factorial experimental design was employed for an
optimization of process variables, which include catalyst loading, reaction time, methanol/oil molar
ratio and reaction temperature and their effects on the biodiesel yield were studied. The optimization
results showed that the reaction time has the highest percentage contribution of 40.139 % while the
catalyst loading contributes the least to the biodiesel production, as low as 1.233 %. The analysis of
variance (ANOVA) revealed a high correlation coefficient (R2 = 0.9492) and the interaction between
the reaction time and reaction temperature contributes significantly to the biodiesel production process
with percentage contribution of 14.001 %, compared to other interaction terms. The biodiesel yield of
77.56 % was obtained under the optimized factor combination of 4.0 wt.% catalyst loading, 120 min
reaction time, 12 : 1 methanol/oil molar ratio and reaction temperature of 65 °C. The reusability study
showed that the ASE catalyst could be reused for up to four cycles and the biodiesel produced under
optimum conditions conformed to the ASTM standard.

Keywords: biodiesel; catalyst; characterization; eggshell; waste frying oil.

1. Introduction
Biodiesel is a biogenic, renewable, non-toxic and ester-
derived oxygenated fuel. It is commonly produced
from animal fat, edible (soybean, palm, coconut, corn)
oil, non-edible (cotton seed, Jatropha curcas, algae,
sunflower) oil and waste vegetable oil. According to
Tan et al. [14], biodiesel can conveniently be used
to power a diesel engine without making any adjust-
ment to the engine. Besides, it is energy efficient,
environmentally friendly and reduces the greenhouse
gases emission [15]. However, the exorbitant cost of
biodiesel has been a major reason why its production
has not been largely commercialized. Two ways in
which this problem could be addressed according to
Fabbri et al. [2] and Taufiq-yap et al. [15] include
a biodiesel synthesis from a waste vegetable or non-
edible oil and the use of solid catalysts derived from
readily available waste or naturally occurring materi-
als instead of a homogeneous catalyst and enzyme.
Generally, biodiesel, a form of mono-alkyl ester, is

commonly produced via transesterification of oil with
alcohol (methanol, ethanol, propanol and butanol) in
the presence of a catalyst. Glycerol is also formed as a
by-product. Transesterification is an organic reaction
in which an ester is transformed into another through

an interchange of the special functional group called
alkoxy moiety [12]. Typically, methanol is used as
the co-reactant for the conversion of triglyceride to
produce fatty acid methyl ester (biodiesel), because
it is relatively cheap, readily available and easier to
separate than glycerol from the product mixture [13].
The reaction is illustrated by the overall equation
given in Figure 1.

Figure 1. Transesterification of glyceride with
methanol.

The current biodiesel production process involves
the use of a homogenous catalyst, such as NaOH, HCl,
KOH and H2SO4. However, there are some problems
associated with the homogeneous catalysed transester-
ification process, that is, the generation of wastewater
and non-reusability of liquid catalysts. According to
Taufiq-yap et al. [15], the use of heterogeneous cata-
lysts in transesterification reaction could reduce the

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vol. 59 no. 1/2019 Optimization of Biodiesel Production from Waste Frying Oil

costs of the biodiesel production. This is because; they
are much easier to separate from the product mixture,
reusable and do not generate wastewater. A hetero-
geneous catalyst could be classified into solid base
and solid acid catalysts. Solid base catalysts are often
used for a transesterification reaction. They do ex-
hibit higher activity and proceed faster to equilibrium
when compared to an acid heterogeneous catalyst. Be-
sides, solid base catalysts could easily be synthesized
from waste and naturally occurring materials. Never-
theless, the heterogeneous catalyst is well known for
its mass transfer limitation, because it forms three
phases with methanol and oil, thus lowering the re-
action rate [7, 15]. However, the diffusion limitation
could be overcome by using catalyst supports or pro-
moters which can enhance the textural properties and
basic strength of the catalyst. Besides, they firmly an-
chor the catalyst’s active ingredient, thus minimizing
the degree of leaching [4]. Several catalyst supports,
such as alumina (Al2O3), silica (SiO2), zirconia (ZrO2)
and titania (TiO2), have been used in a biodiesel pro-
duction process [3, 5, 16]. Among the aforementioned
supports, alumina has been widely used for anchoring
catalyst active ingredients due to its high thermal
stability, better mechanical properties, and better
textural characteristics [15]. Taufiq-yap et al. [15]
synthesized NaOH/Al2O3 catalyst and used it for the
production of biodiesel from palm oil. The maximum
biodiesel yield of 99 % was obtained under optimum
reaction conditions. Umdu et al. [16], in their research
work, used Al2O3/CaO as a heterogeneous catalyst
in converting the lipid of microalgae to biodiesel. The
biodiesel yield from the process was 80 %. Meanwhile,
none of the previous researchers discussed had done
a detailed work to check the performance of alumina
when loaded on CaO derived from agricultural waste.

The use of low quality feedstock such as waste
frying oil (WFO) to synthesize biodiesel will reduce
the production cost. Therefore, the current study is
focused on the use of alumina supported eggshell as a
heterogeneous base catalyst for the transesterification
of WFO with methanol because of the easy availability
of both reactants. Also, the 2-level factorial design
of the experiment was applied to the optimization
of the biodiesel production process. The variables
(factors) considered were the reaction temperature,
reaction time, catalyst loading and methanol/WFO
molar ratio.

2. Materials and Method
2.1. Materials
In this current study, the WFO and waste chicken
eggshells were collected from the cafeteria of Afe Ba-
balola University, Ado-Ekiti, Nigeria. The oil was first
heated in an oven at 150 °C for 3 h to reduce the mois-
ture content and later filtered using a 100 µm sieve
mesh to remove bits of food residues. The acid value
and free fatty acid (FFA) of the oil were determined

to be 3.847 mgKOH/g and 1.924 wt.%, respectively.
However, since the FFA content of the WFO is less
than 3.0 wt.%, the single step transesterification pro-
cess is appropriate to convert the oil to biodiesel [14].
Methanol (CH3OH, 99.5 % synthesis grade) was used
as a co-reactant for the transesterification and gamma
alumina (anhydrous Al2O3) was used as a catalyst sup-
port. These compounds were procured from Topjay
chemical enterprise, Ado-Ekiti, Nigeria and employed
as received without subjecting them to a further pu-
rification.

2.2. Preparation of the Catalyst
The waste chicken eggshells were initially soaked and
thoroughly washed with clean water to remove all
attached dirt. The cleaned eggshells were thereafter
heated up in an oven at 125 °C until the water was
completely dried up. The dried eggshell was later
crushed into a powder by mechanical grinder and the
powder obtained was allowed to pass through 0.3 mm
sieve mesh to obtain a fine powder with particle size
lesser than 0.3 mm. It was then kept in a sealed
plastic container.
The procedure used to prepare the supported cat-

alyst was referred in our previous work [19]. Three
different samples of alumina supported eggshell cata-
lyst were prepared by weighing and mixing the pre-
pared eggshell powder and alumina in 1 : 1, 2 : 1 and
1 : 2 mass ratios of eggshell to alumina. The resulting
mixtures were dissolved in 50 mL of distilled water to
form suspensions and stirred continuously until the
mixtures were homogenous. The obtained slurries
were then heated up in an oven at 110 °C to remove
the water. Thereafter, the three dried samples were
calcined in a muffle furnace at 900 °C for 4 h. The
calcined catalysts were kept in a desiccator containing
silica particles in order to prevent atmospheric mois-
ture and carbon dioxide that might be in contact with
the catalysts.

2.3. Characterization of the Prepared
Catalysts

The textural features of the prepared catalyst samples
were determined by Brunauer-Emmett-Teller (BET)
technique using micrometrics analyser (Quantachrome
instrument, Nova station A, version 11.03, USA) based
on the principle of adsorption/desorption of nitrogen
at 77K and 60/60 sec (ads/des) equilibrium time. The
basicity of the as-synthesized catalysts was determined
by a colorimetric titration method reported by Abdoul-
moumine [1]. Scanning electron microscope-energy
dispersive X-ray (SEM-EDX) analyser (JEOL-JSM
7600F) was used simultaneously to determine the sur-
face morphology and elemental composition of the
prepared catalysts, while Fourier transform infrared
(FTIR) spectrophotometer (IR Affinity 1S, Shimadzu,
Japan) was employed to determine the surface func-
tional groups on the as-synthesized catalysts.

Adeyinka S. Yusuff, Lekan T. Popoola Acta Polytechnica

Eggshell/Al2O3 ratio Textural properties Basicity
(mmol/g cat)BET area (m2/g) Total pore volume (cm3/g)

1 : 1 eggshell loading on Al2O3 49.6 0.117 1.34
2 : 1 eggshell loading on Al2O3 78.2 0.341 1.88
1 : 2 eggshell loading on Al2O3 60.9 0.281 0.58

Table 2. Textural properties and basicity of the different ratio of prepared alumina supported eggshell catalysts.

Variable Level
low high
(−1) (+1)

Reaction temperature (T ) 50 °C 65 °C
Reaction time (t) 1 h 2 h
Catalyst loading (C) 2 wt.% 4 wt.%
Methanol/WFO ratio (M) 6 : 1 12 : 1

Table 1. Studied range of each variable in actual and
coded form.

2.4. The 2k Factorial Experimental
Design

A factorial method of an analysis is one of the nu-
merous features of the design of an experiment used
in studying the influence of an individual variable
and its interaction with other variables. It econ-
omizes the experimental resources by reducing the
number of runs [1]. In this study, four process inde-
pendent variables, which include reaction temperature,
reaction time, catalyst loading and methanol/WFO
molar ratio, were of interest, with biodiesel yield
as the response. However, the response was deter-
mined via the transesterification process with the
aim to identify the optimum reaction condition that
would provide a maximum biodiesel yield. A total
of sixteen (16) experimental runs were conducted ac-
cording to a 2k factorial design with the four pro-
cess variables (24 = 16 points). Table 1 presents
the experimental design matrix for a 24 factorial de-
sign.

2.5. Transesterification Reaction Study
The transesterification of the WFO to biodiesel using
a calcined alumina supported eggshell catalyst was
conducted according to experimental design values
(Table 1) and the response measured was the yield
of biodiesel. The whole experiments were performed
in a 250 mL glass reactor placed on a temperature
controlled heating mantle. Fifty grams (50 g) of the
WFO were heated up to a desired temperature in
an oven, after which the mixture of methanol and
catalyst with a required amount was added to the
heated oil. The reaction mixture was stirred with a
speed of 350 rpm. After the reaction was completed,
the catalyst was separated from the product mixture
(biodiesel and glycerol) by a cloth filtration. The yield
of biodiesel collected from the product mixture was

then evaluated as [6]

Biodiesel yield, Y =
weight of biodiesel
weight of WFO used

· 100 %.
(1)

2.6. Biodiesel product analysis
The synthesized biodiesel was characterized for a spe-
cific gravity, kinematic viscosity, cloud point, pour
point and flash point and was compared with ASTM
D6571 standard method. The quality of the WFO
biodiesel was further ascertained by the FTIR spec-
trophotometer (IR Affinity 1S, Shimadzu, Japan) in
which the functional groups contained in it were deter-
mined. Moreover, a gas chromatography-mass spec-
trometry (Hewlett Packard 6890S, Palo Alto, USA)
analysis was conducted on the biodiesel product to
determine the type of the formed methyl esters.

2.7. Catalyst Reusability Study
The reusability of the supported catalyst was con-
ducted in order to check its stability after reuse. The
used catalyst was collected from the product mixture
after the completion of the transesterification reaction,
washed severally with methanol to remove oil that
was attached to the catalyst particles and heated up
at 60 °C in an oven until it dried out. Thereafter,
the dried catalyst sample was recalcined in a muf-
fle furnace at 700 °C for 2 h. The recalcined catalyst
was weighed and reused for subsequent reactions at
the same operating conditions. After a fourth cycle,
the reaction was discontinued because of the quan-
tity of the recovered catalyst, which was significantly
reduced.

3. Results and Discussion
3.1. Characterization of the Catalyst
The textural characteristics and basicity of the three
prepared catalyst samples were determined. Accord-
ing to the results depicted in Table 2, it was found
that the catalyst sample with the eggshell/Al2O3 mass
ratio of 2 : 1 exhibited better textural properties and
strong basic strength. This is attributed to the fact
that the catalyst sample contains a larger propor-
tion of eggshell, which decomposed into CaO and
CO2 after calcination [14] and amphoteric nature of
Al2O3. According to Olutoye and Hameed [8], the
oxygen atoms contained in the CaO and Al2O3 sig-
nify Lewis base sites while the metal ions represent

vol. 59 no. 1/2019 Optimization of Biodiesel Production from Waste Frying Oil

Figure 2. SEM images of (left) raw; (right) calcined ASE catalyst

Lewis acid sites. Thus, the high basicity possessed by
this sample implied that the Lewis base sites are ac-
tive centres for the transesterification reaction. This
is corroborated by the EDX analysis. In addition,
higher values of surface area (78.2 m2/g) and total
pore volume (0.341 cm3/g) recorded for this same
catalyst sample indicate that the catalyst external
surface is dominated by active sites and it can elim-
inate the mass transfer limitation, leading to a faster
reaction process [14]. Having identified the prepared
catalyst with the ratio 2 : 1 of eggshell loading onto
Al2O3 as the most active sample amongst other syn-
thesized catalysts, it was further characterized and
studied in details under various operating reaction
conditions.
The SEM analysis was conducted in order to ex-

amine the external morphology of raw and calcined
ASE catalysts using a very large magnification. The
SEM images of the catalysts, presented in Figure 2.
Figure 2(left) showed that the raw catalyst possessed
an undefined structure with various tiny pores on
its surface. This observation might be attributed to
the method of preparation adopted. However, upon
calcination, several large pores of different sizes were
clearly seen on the catalyst’s surface as shown in Fig-
ure 2(right). This observation could be attributed
to the decomposition of CaCO3 contained in eggshell
into CaO and CO2. The SEM result of the calcined
ASE catalyst also showed that an elevated calcination
temperature facilitated a removal of adsorbed gases,
organic matters, moisture and surface and bulk atom
rearrangement, thus leading to pore creation and basic
sites exposure on the catalyst’s surface [12].
The elemental composition analysis of the ASE

catalyst (Table 3) showed that it contained calcium,
oxygen, carbon, aluminium and magnesium. The

Element ASE catalyst sample
Raw Calcined

Calcium 48.8 65.9
Carbon 26 4.6
Aluminum 10.8 10.6
Magnesium 4.2 2.7
Oxygen 10.4 16.1

Table 3. Elemental analysis for raw and calcined
ASE catalysts.

composition of the calcium and oxygen in the raw
catalyst were 48.8 wt.% and 10.4 wt.% respectively,
but they increased to 65.9 wt.% and 16.1 wt.% respec-
tively after the calcination. However, the composition
of all other elements was reduced after the thermal
treatment. The increase in calcium content after the
calcination was due to the decomposition of CaCO3 in
eggshell. A similar observation was reported by Tan
et al. [14] in the transesterification of a waste cooking
oil using calcined ostrich and chicken eggshells as the
catalysts.
The FTIR spectrum of a raw ASE catalyst is

shown in Figure 3(a) with various adsorption bands at
3436.56 cm−1 (N–H stretch), 2874.03 cm−1 (CH an-
tisymmetric stretch), 2515.26 cm−1 (O–H stretch),
2360.95 cm−1 (N–H stretch), 1797.72 cm−1 (C––O
antisymmetric stretch), 1421.58 cm−1 (in-plane OH
bend), 875.71 cm−1 (CH out-of-plane deformation)
and 455.22 cm−1 (C–N–C bend). These surface func-
tional groups are an indication that the ASE catalyst
is complex in nature. However, upon calcination,
some peaks were shifted or vanished and new bands
at 3643.65 cm−1 (O–H stretch), 1626.05 cm−1 (C––O
stretch), 1413.87 cm−1 (C–N stretch), 1022.31 cm−1

Adeyinka S. Yusuff, Lekan T. Popoola Acta Polytechnica

100

150

200

250

05001000150020002500300035004000

T
ra

n
sm

it
ta

n
ce

(
%

)

Wavenumber (cm-1)

(c)

(b)

(a)

Figure 3. FTIR spectra of (a) raw, (b) calcined and (c) reused ASE catalysts.

Run Transesterification process variable Biodiesel yield, Y (%)
Catalyst Reaction Methanol/oil Reaction Experimental Predicted
loading time ratio temperature
C (wt.%) t (min) M T (°C)

1 2 60 6 50 45.46 42.33
2 4 60 6 50 27.66 31.30
3 2 120 6 50 57.28 60.41
4 4 120 6 50 59.09 55.44
5 2 60 12 50 31.32 34.39
6 4 60 12 50 38.13 34.54
7 2 120 12 50 68.45 65.38
8 4 120 12 50 68.00 71.59
9 2 60 6 65 47.19 44.03
10 4 60 6 65 41.23 43.87
11 2 120 6 65 38.48 41.64
12 4 120 6 65 50.18 47.54
13 2 60 12 65 48.36 51.58
14 4 60 12 65 61.32 62.62
15 2 120 12 65 65.32 62.10
16 4 120 12 65 76.50 79.20

Table 4. Factorial design for transesterification process variables.

(P–O–C antisymmetric stretch), 783.13 cm−1 (CH
out-of-plane deformation) and 559.38 cm−1 (C–C––O
bend) were detected as shown in Figure 3(b). In
the case of a reused catalyst (Figure 3(c)), many
of the absorption bands displayed by the calcined
catalyst disappeared after the use and new bands
(3203.87 cm−1 (NH2 symmetric stretch), 2893.32 (CH
antisymmetric stretch) and 2278.01 (N––C––O anti-
symmetric stretch)) were also detected. The presence
of these functional groups contributes to the good
activity of the catalyst [10].

3.2. Statistical Analysis
of Experimental Data

The synthesis of biodiesel from the WFO in the pres-
ence of the ASE catalyst was carried out using a 2k
factorial experimental design as shown in Table 4.
As can be seen, sixteen (16) experimental runs were
conducted at different levels of independent variables
considered.
It was revealed that the run 16, which was con-

ducted at 4.0 wt.% catalyst loading, 120 min reaction
time, 12 : 1 methanol/oil molar ratio and 65 °C re-

vol. 59 no. 1/2019 Optimization of Biodiesel Production from Waste Frying Oil

Source Sum of squares Degree of freedom Mean square F -value p-value (Pr > F )
Model 2992.54 10 299.25 9.35 0.0118

C 36.75 1 36.75 1.15 0.3329
t 1201.14 1 1201.14 37.53 0.0017

M 562.05 1 562.05 17.56 0.0086
T 86.44 1 86.44 2.70 0.1612
Ct 36.69 1 36.69 1.15 0.3332

CM 125.16 1 125.16 3.91 0.1049
CT 118.32 1 118.32 3.70 0.1125
tM 166.73 1 166.73 5.21 0.0713
tT 418.92 1 418.92 13.09 0.0153

M T 240.33 1 240.33 7.51 0.0408
Residual 160.02 5 32 – –
Cor. Total 3125 15 – – –
R2 = 0.9492; Adj-R2 = 0.8477

Table 5. ANOVA analysis for 2k factorial design.

40.139

18.784

14.001

8.028

5.573

4.182

3.951

2.887

1.233

1.222

0 10 20 30 40 50

Figure 4. Pareto graphic analysis — percentage effect of each factor.

action temperature, gave the highest biodiesel yield
with the value obtained to be 76.50 %. Meanwhile, the
lowest biodiesel yield was provided by the run 2, which
was conducted at 4.0 wt.% catalyst loading, 60 min
reaction time, 6 : 1 methanol/oil molar ratio and
50 °C reaction temperature. These observations imply
that, at the maximum reaction time, methanol/oil
molar ratio and reaction temperature, the yield of
biodiesel was favoured irrespective of the quantity
of catalyst consumed during the reaction [17]. This
fact is affirmed by the run 15, which was carried out
at 2.0 wt.% catalyst loading, 120 min reaction time,
12 : 1 methanol/oil molar ratio and 65 °C reaction
temperature and gave a 65.32 % biodiesel yield. The
regression model, which correlates the dependent and
independent variables in terms of coded factor gives

Y = 51.75 + 1.52C + 8.66t + 5.93M + 2.32T
+ 1.51Ct + 2.80CM + 2.72CT + 3.23tM

− 5.12tT + 3.88M T , (2)

where C, t, M and T are the catalyst loading, reaction
time, methanol/oil molar ratio and reaction tempera-
ture, respectively. These are the main effects. While
Ct, CM, CT , tM, tT and M T represent interaction
effects.

3.2.1. Analysis of Variance
for Biodiesel Yield

The model adequacy was tested using an analysis of
variance (ANOVA) and Table 5 represents the results
of the ANOVA analysis for the 2k factorial design.
The model F -value of 9.35 with a probability value
(Pr > F ) of 0.0118 confirms the adequacy of the
model. In addition, two linear terms (t and M) and
two interactive terms (tT and M T ) are the significant
model terms. This is because their p-values (Pr >
F ) are less than 0.0500. According to the R2 value
(0.9492), the obtained model accounts for 94.92 %
of the total variation in the experimental biodiesel
yield.

Adeyinka S. Yusuff, Lekan T. Popoola Acta Polytechnica

Figure 5. Plot of biodiesel yield (Y ) versus reaction
time (t) at reaction temperature of 50 °C and 65 °C,
2 wt.% catalyst loading and 6 : 1 methanol/oil molar
ratio

3.2.2. Analysis of Main Effects
The contribution of each of the factors studied to the
biodiesel production from the WFO is displayed in
Figure 4. It was revealed that the reaction time con-
tributes significantly to the yield of biodiesel, as much
as 40.139 %. This implies that increasing the reaction
time from 60 min to 120 min affects the biodiesel yield.
The influence of the reaction time on biodiesel pro-
duction process is widely reported [8, 14]. Yee and
Lee [17] reported that, for the transesterification to
occur and proceed to completion, higher reaction time
and excess methanol are necessary. Since the reac-
tion temperatures considered in this study are within
the boiling point of methanol, longer reaction period
favours the biodiesel yield. This is corroborated by
the value of the biodiesel yield provided by the run
16, which was conducted for 120 min (Table 4).

The Methanol/oil molar ratio is the second factor
that favours the biodiesel yield with the percentage
contribution of 18.784 % as shown in Figure 4. Two
different methanol/oil molar ratios (6 : 1 and 12 :
1) were considered in this study and the maximum
molar ratio was found to have a positive effect on
the biodiesel yield as confirmed in most of the runs
such as run 7, 8, 13, 14, 15 and 16. Meanwhile, the
use of excess methanol inhibited the separation of
biodiesel from the product mixtures, thus reducing
the biodiesel yield in some runs like runs 5 and 6.
This observation is similar to the one reported by
Paintsil [11] who investigated the optimization of the
biodiesel production from canola oil.

Furthermore, the third most influential factor is the
reaction temperature, which contributes by 2.887 % to
the biodiesel production process as shown in Figure 4.
The reason for this observation could be that the het-
erogeneous catalysed transesterification reaction often
requires either a relatively high reaction temperature
or high reaction time in order to achieve a greater
biodiesel yield [17]. Since the yield of biodiesel was
favoured by a high reaction period as it is the case in
this study, the reaction temperature did not have a
significant effect on the biodiesel production.

Figure 6. Plot of biodiesel yield (Y) versus
methanol/oil molar ratio (M) at reaction tempera-
ture of 50 °C and 65 °C, 2 wt.% catalyst loading and
60 min reaction time.

The catalyst loading contributes the least to the
biodiesel production process, as low as 1.233 % accord-
ing to the Pareto graphic analysis shown in Figure 4.
In this current study, the catalytic reaction was con-
ducted at two different catalyst loadings (2.0 wt.%
and 4.0 wt.%). At a high catalyst loading of 4 wt.%,
a higher biodiesel yield was achieved. This is because
enough active sites were available for the reaction
and thus enhancing the intimacy between the catalyst
and the reactants [14]. Meanwhile, at a low catalyst
loading, there was a decrease in the biodiesel yield,
because the catalyst active sites were insufficient to
promote the reaction to completion [20].

3.2.3. Analysis of Interaction effect.
It was revealed from the ANOVA result that the in-
teraction between process variables has a significant
effect on the biodiesel yield. In this study, six in-
teraction effect terms were displayed by the model
(Table 5). Among these interactions, only MT and tT
contributed significantly to the biodiesel production
process with the percentage contribution of 8.028 %
and 14.001 %, respectively. Figure 5 depicts the plot
of combined effects of the reaction time (t) and re-
action temperature (T) on biodiesel yield (Y) while
keeping catalyst loading (C) and methanol/oil molar
ratio (M) at 2 wt.% and 6 : 1, respectively. The plot
revealed that, at 50 °C reaction temperature, maxi-
mum biodiesel yield could be achieved within 120 min
compared to 60 min. However, when the reaction was
conducted at 65 °C, the biodiesel yield obtained in
60 min was greater than the one obtained in 120 min.
The former observation could be explained by the
fact that at the lower temperature and higher reac-
tion time, methanol did not dry up as the reaction
temperature studied is less than the boiling point of
methanol, which is around 65 °C and as a result, the
methanol was sufficient to drive the reaction forward.

The combined effects of the methanol/oil molar ra-
tio and reaction temperature on the yield of biodiesel
is depicted in Figure 6. When the reaction was con-
ducted at a temperature of 65 °C, catalyst loading
of 2 wt.% and 60 min reaction period, an increase in

vol. 59 no. 1/2019 Optimization of Biodiesel Production from Waste Frying Oil

Figure 7. FTIR spectra of (a) WFO and (b) synthesized biodiesel.

Property Value ASTM D6571
Specific gravity 0.879 0.86–0.90
Kinematic viscosity 3.58 mm2/s 1.9–6.0 mm2/s
Cloud point 2 °C −3 to 15 °C
Pour point −4.8 °C −5 to 10 °C
Flash point 145 °C ≥ 130 °C

Table 6. Physico-chemical properties of WFO based
biodiesel compared to ASTM (D6751) standards.

methanol/oil molar ratio resulted in an increase in
the biodiesel yield. However, when the reaction was
conducted at 50 °C for 60 min using 2 wt.% ASE cata-
lyst dose, an increase in methanol/oil ratio was found
to reduce the yield of biodiesel. The reduction in the
biodiesel yield at a higher methanol/oil ratio is prob-
ably due to the dissolution of glycerol in methanol,
which subsequently shifts the reaction backward [14].

3.3. Numerical Optimization
of Process Variables

Having determined the optimum process variables for
the production of biodiesel from the WFO using the
ASE as a catalyst to be 4 wt.%, 120 min, 12 : 1 and
65 °C for catalyst loading, reaction time, methanol/oil
molar ratio and reaction temperature, respectively,
a further experimental run was conducted at these
conditions and the experimental biodiesel yield was
77.56 %. However, the predicted biodiesel yield was
calculated based on an empirical model developed by
a design expert software and was found to be 79.20 %.
This value is slightly greater than the actual value by
1.44 %. The result indicates that a maximum biodiesel
yield can be achieved when the transesterification of
the WFO over the ASE catalyst is conducted at the
maximum values of variables studied.

3.4. Catalyst Reusability Study
The biodiesel yields for the four reaction cycles
conducted under optimum conditions were 58.22 %,
42.71 %, 29.88 % and 18.92 %, respectively. The rea-
son for the reduction in biodiesel yield is probably
due to the saturation of the catalyst active sites by
oil molecules. In addition, there was a loss of active
sites during the catalyst regeneration process and as
a result, there was a decrease in the biodiesel yield
during reuse. This observation is similar to the one
reported by Olutoye et al. [9].

3.5. Analysis of Synthesized Biodiesel
3.5.1. Physicochemical Properties

of Synthesized Biodiesel
The properties of the prepared WFO based biodiesel,
such as specific gravity, viscosity, cloud point, pour
point and flash point, were determined and compared
with ASTM D6571 standard as shown in Table 6.

3.5.2. FTIR Analysis
The FTIR spectra of the WFO and its biodiesel are
depicted in Figure 7. The spectra of the two sub-
stances are very similar because of the high degree of
similarities between triglyceride and methyl ester [15].
Some of the peaks shifted after the conversion process.
However, the adsorption bands at 2990-2850 cm−1 are
assigned to C-H antisymmetric and symmetric stretch-
ing. While the sharp peak at 1743.71 cm−1 is assigned
to C = O stretching mode of esters. The bands at
1155.20 cm−1 and 1026.16 cm−1 both correspond to
C – O stretching of esters. The absorption band at
1437.71 cm−1 can be attributed to the CH3 antisym-
metric deformation. All these functional groups found
in the prepared biodiesel confirmed the presence of
methyl esters.

Adeyinka S. Yusuff, Lekan T. Popoola Acta Polytechnica

Figure 8. Result of GC-MS analysis on biodiesel synthesized under the optimized factor combination of 4.0 wt.%
catalyst loading, 120 min reaction time, 12 : 1 methanol/oil molar ratio and reaction temperature of 65 °C.

Compound Retention Concentra-
time (min) tion (wt.%)

Methyl palmitate 38.36 33.33
Methyl oleate 46.87 41.01
Methyl linoleate 42.01 10.14
Methyl palmitoleate 47.81 4.24
others – 7.17

Table 7. Results of GC-MS analysis on biodiesel
produced under optimum conditions.

3.5.3. GC-MS analysis
The chromatogram of the WFO biodiesel is depicted
in Figure 8, which confirms the presence of methyl
esters and Table 7 shows the description of the chro-
matograms. Both Figure 8 and Table 7 display the
compositions of biodiesel from the transesterification
of the WFO, which are mainly methyl palmitate,
methyl oleate, methyl linoleate and methyl palmi-
toleate.

4. Conclusions
A nontoxic and reusable supported catalyst was for-
mulated by an incipient wetness impregnation of alu-
mina with eggshell. The prepared ASE catalyst with
the BET surface area and basicity of 78.2 m2/g and
1.88 mmol/g cat, respectively, exhibited a better per-
formance in the transesterification of the WFO with
methanol to biodiesel. An investigation of the ef-
fects of the transesterification process variables on the
biodiesel yield revealed that the reaction time con-
tributed the most to the biodiesel production process,
as much as 40.139 %, while the catalyst loading con-
tributed the least to the process, as low as 1.233 %.
The interaction between the reaction time and the
reaction temperature had the most significant effect
on the biodiesel yield, compared to other interaction

terms. A maximum biodiesel yield was obtained under
the optimized factor combination of 4.0 wt.% catalyst
loading, 120 min reaction time, 12 : 1 methanol/oil
molar ratio and reaction temperature of 65 °C. The
reduction in the catalyst performance after four cycles
of reaction was noticed, indicating a loss of active
sites.

References
[1] Abdulkareem, A.S., Uthman, H., Afolabi, A.S., &
Awenebe, O.L. (2011). Extraction and optimization of
oil from moringa oleifera seed as an alternative feedstock
for the production of biodiesel, sustainable growth and
applications in renewable energy sources, Dr. Majid
Nayeripour (Ed.), ISBN: 978-953-307-408-5, Intech.

[2] Fabbri, D., Bevoni, Notari, M., & Rivetti, F. (2007).
Properties of a potential biofuel obtained from soybean
oil by transmethylation with dimethyl carbonate. Fuel,
86(5/6), 690-697. doi:10.1016/j.fuel.2006.09.003.

[3] Furuta, S., Matsuhashi, H., & Arata, K. (2004).
Biodiesel fuel production with solid super acid catalysis
in fixed bed reactor under atmospheric pressure.
Catalysis Communication, 5(12), 712-723.
doi:10.1016/j.catcom.2004.09.001.

[4] Granados, M.L., Poves, M.D.Z., Alonso, D.M.,
Mariscal, R., Galisteo, F.C., Moreno-Tost R.,
Santamaria, J., & Fierro, J.L.G. (2009). Biodiesel from
sunflower oil by using activated calcium oxide. Applied
catalysis B: Environmental, 73(3-4), 317-326.
doi:10.1016/j.apcatb.2006.12.017.

[5] Jitputti, J., Kitiyanan, B., Bunyakiat, K.,
Rangsunvigit, P., & Jakul, P.J. (2006).
Transesterification of crude palm kernel oil and crude
coconut oil by different solid catalysts. Chemical
Engineering Journal, 116(1), 61-66.
doi:10.1016/j.cej.2005.09.025.

[6] Leung, D.Y.C., Guo, Y. (2006). Transesterification of
neat and used frying oil: Optimization for biodiesel
production. Fuel Processing Technology, 87, 883-890.
doi:10.1016/j.fuproc.2006.06.003.

http://dx.doi.org/10.1016/j.fuel.2006.09.003.
http://dx.doi.org/10.1016/j.catcom.2004.09.001.
http://dx.doi.org/10.1016/j.apcatb.2006.12.017.
http://dx.doi.org/10.1016/j.cej.2005.09.025.
http://dx.doi.org/10.1016/j.fuproc.2006.06.003.

vol. 59 no. 1/2019 Optimization of Biodiesel Production from Waste Frying Oil

[7] Mbaraka, I.K., & Shanks, B.H. (2006). Conversion of
oils and fats using advanced mesoporous heterogeneous
catalysts. Journal of the American Oil Chemists’
Society, 83, 79-91. doi:10.1007/s11746-006-1179-x.

[8] Olutoye, M.A & Hameed, B.H., (2013). A highly active
clay-based catalyst for the synthesis of fatty acid methyl
ester from waste cooking palm oil”. Applied Catalysis A:
General. 450, 57-62. doi:10.1016/j.apcata.2012.09.049.

[9] Olutoye, M.A., Wong, S.W., Chin, L.H., Asif, M., &
Hameed, B.H. (2016). Synthesis of fatty acid methyl
esters via transesterification of waste cooking oil by
methanol with a barium-modified montmorillonite K10
catalyst. Renewable Energy, 86, 392-398.
doi:10.1016/j.renene.2015.08.016.

[10] Olutoye, M.A., Adeniyi, O.D, & Yusuff, A.S, (2016).
Synthesis of biodiesel from palm kernel oil using mixed
clay-eggshell heterogeneous catalysts. Iranica Journal of
Energy and Environment, 7(3), 308-314.
doi:10.5829/idosi.ijee.2016.07.03.14.

[11] Paintsil, A. (2013). Optimization of the
transesterification stage of biodiesel production using
statistical methods. A Msc. thesis, school of graduate
and postgraduate studies, University of Western
Ontario, Canada.

[12] Refaat, A.A. (2011). Biodiesel production using solid
metal oxide catalyst. International Journal of
Environmental Science and Technology, 8(1), 203-221.
doi:10.1007/BF03326210.

[13] Shuit, S.H., Yit, T.O., Keat, T.L., Bhatia, S., Soon,
H.T. (2012). Membrane technology as a promising
alternative in biodiesel production: A review.
Biotechnology Advances, 30(6), 1364-1380.
doi:10.1016/j.biotechadv.2012.02.009.

[14] Tan, Y.H., Abdullah, M.O., Hipolito, C.N., & Taufiq-
Yap., Y.H. (2015). Waste ostrich and chicken-eggshells
as heterogeneous base catalyst for biodiesel production
from used cooking oil: catalyst characterization and
biodiesel yield performance. Applied Energy, 2, 1-13.
doi:10.1016/j.apenergy.2015.09.023.

[15] Taufiq-Yap, Y.H., Abdullah, N.F., & Basri, M.
(2011). Biodiesel production via transesterification of
palm oil using NaOH/Al2O3 catalysts. Sains
Malaysiana, 40(6): 587-594.

[16] Umdu, E.S., Tuncer, M., & Seker, E. (2009).
Transesterification of nannochloroplasts oculata
microalga’s lipid to biodiesel on Al2O3 supported CaO
and MgO catalysts. Bioresources Technology, 100,
2828-2837. doi:10.1016/j.biotech.2008.12.027.

[17] Yee, K.F., & Lee, K.T. (2008). Palm oil as feedstock
for biodiesel production via heterogeneous
transesterification: Optimization Study. International
Conference on Environment (ICENV), 1-5.

[18] Yusuff, A.S., Adeniyi, O.D., Olutoye, M.A., & Akpan,
U.G. (2017). A review on Application of heterogeneous
catalyst in the production of biodiesel from vegetable
oils. Journal of Applied Science and Process
Engineering, 4(2), 142-157.

[19] Yusuff, A.S., Adeniyi, O.D., Olutoye, M.A., & Akpan,
U.G. (2018). Development and characterization of a
composite anthill-eggshell catalyst for biodiesel
production from waste frying oil. International Journal
of Technology, 1, 110-119. doi:10.14716/ijtech.v9i1.1166.

[20] Yusuff, A.S., Adeniyi, O.D., Azeez, O.S., Olutoye,
M.A., Akpan, U.G. (2019). Synthesis and
characterization of anthill-eggshell-Ni-Co mixed oxides
composite catalyst for biodiesel production from waste
frying oil. Biofuels, Bioproducts & Biorefining, 13,
37-47; doi:10.1002/bbb.1914

http://dx.doi.org/10.1007/s11746-006-1179-x.
http://dx.doi.org/10.1016/j.apcata.2012.09.049.
http://dx.doi.org/10.1016/j.renene.2015.08.016.
http://dx.doi.org/10.5829/idosi.ijee.2016.07.03.14.
http://dx.doi.org/10.1007/BF03326210.
http://dx.doi.org/10.1016/j.biotechadv.2012.02.009.
http://dx.doi.org/10.1016/j.apenergy.2015.09.023.
http://dx.doi.org/10.1016/j.biotech.2008.12.027.
http://dx.doi.org/10.14716/ijtech.v9i1.1166.
http://dx.doi.org/10.1002/bbb.1914

Acta Polytechnica 59(1):88–97, 2019
1 Introduction
2 Materials and Method
2.1 Materials
2.2 Preparation of the Catalyst
2.3 Characterization of the Prepared Catalysts
2.4 The 2^k Factorial Experimental Design
2.5 Transesterification Reaction Study
2.6 Biodiesel product analysis
2.7 Catalyst Reusability Study

3 Results and Discussion
3.1 Characterization of the Catalyst
3.2 Statistical Analysis of Experimental Data
3.2.1 Analysis of Variance for Biodiesel Yield
3.2.2 Analysis of Main Effects
3.2.3 Analysis of Interaction effect.

3.3 Numerical Optimization of Process Variables
3.4 Catalyst Reusability Study
3.5 Analysis of Synthesized Biodiesel
3.5.1 Physicochemical Properties of Synthesized Biodiesel
3.5.2 FTIR Analysis
3.5.3 GC-MS analysis

4 Conclusions
References