Comparison of homogeneous and heterogeneous catalysts in biodiesel production from Pongamia pinnata oil

Article abstract of DOI:10.14233/ajchem.2015.18023

Biodiesel was prepared by transesterification of Pongamia pinnata (P. pinnata) oil using potassium hydroxide (KOH) as homogeneous catalyst and synthesized calcium methoxide [Ca(OCH₃)₂] as heterogeneous catalyst. The Ca(OCH₃)₂ was synthesized from quick lime and characterized by scanning electron microscopy, X-ray diffraction, attenuated total reflection fourier transform, energy dispersive X-ray spectroscopy and BET surface area analysis to evaluate its performance. The parameters affecting the fatty acid methyl ester (FAME) content such as catalyst concentration, methanol to oil molar ratio and reaction time were investigated. Under optimized reaction condition, it was found that the 99.5 % of FAME conversion using KOH catalyst was achieved with 11:1 of methanol to oil molar ratio, 1.50 % wt of catalyst amount and 1 h of reaction time. The Ca(OCH₃)₂ catalyst was obtained the 98.04 % of FAME conversion with 15:1 of methanol to oil molar ratio, 3 % wt of catalyst amount, 3 h of reaction time at 65 ± 0.5 °C of reaction temperature and 750 rpm of stirring rate on both catalysts. The result of the % FAME conversion, which determined by 1H NMR, suggested that Ca(OCH₃)₂ was the promising heterogeneous catalyst in replacing conventional homogeneous catalyst.

Full text of DOI:10.14233/ajchem.2015.18023

Asian Journal of Chemistry; Vol. 28, No. 2 (2016), 423-428
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19398
Optimization of Transesterification Reaction for Biodiesel Production
from Refined Palm Oil using Calcined Quick Lime Catalyst
1
2,*
W. SUWANTHAI and V. PUNSUVON
1
2
Center of Excellence-Oil Palm, Kasetsart University, Bangkok, Thailand
Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok, Thailand
*
Corresponding author: E-mail: fscivit@ku.ac.th; lbl_association@hotmail.com
Received: 6 June 2015; Accepted: 15 July 2015;
Published online: 3 November 2015;
AJC-17621
Commercial quick lime was calcined to produce calcium oxide and it was explored as solid catalyst for the transesterification of refined
palm oil with methanol. The physico-chemical properties of catalyst were characterized by X-ray diffraction, scanning electron microscopy
and Brunauer-Emmett-Teller. The results from characterization showed that calcium oxide was successful synthesized. In the investigation
of catalyst activity for transesterification reaction, a response surface methodology was performed. The design of experiment was made
by application of 5-level-3-factors central composite design in order to study the effect of different factors on the percentage of fatty acid
1
methyl ester conversion that determined by H NMR. Quadratic model equation was obtained describing the inter-relationships between
dependent and independent variables to maximize the fatty acid methyl ester conversion. Fuel properties of the produced biodiesel were
also examined and the results were met well with biodiesel standard.
Keywords: Quick lime, Transesterification, Response surface methodology, Refined palm oil, Biodiesel.
for making biodiesel via transesterification without any
problems caused by salt formation.
INTRODUCTION
The liquid catalysts, widely used in commercial biodiesel
Response surface methodology is a useful statistical
technique that has been applied to analyze research involving
a complex variable process. Response surface methodology
employs multiple regression and correlation analyses to assess
the effects of two or more independent factors on the dependent
variables. Its principal advantage is in reducing the number of
experimental runs required to generate sufficient information
for a statistically acceptable result. Response surface methodology
has been successfully applied in the study and optimization of
biodiesel production from various feed stocks [3-5].
In this study, CaO was prepared from quick lime and its
physical and chemical properties were analyzed. The CaO was
also tested as a solid catalyst in the transesterification of refined
palm oil. Response surface methodology was utilized for
process optimization, with the aim to better understand the
relationships among three operating variables (catalyst concen-
tration, methanol-to-oil molar ratio and reaction time).
process, have many disadvantages. All of these are: (1) they
cannot be reused, (2) they produce large amounts of wastewater
and (3) they produce glycerol as by-product with high impurity
content. In contrast, the solid catalytic process, offering simp-
lified production and purification process, is expected to be
environmental friendly for biodiesel production process [1].
Triglyceride solid catalysts for transesterification reactions,
such as alkali metal oxides, alkaline earth metal oxides, transi-
tion metal oxides, mixed metal oxides and other derivatives,
have been reported in the literature for a variety of application,
including ion exchange resins, sulfated oxide, waste materials
and enzyme [2].
Quick lime or burnt lime is calcium oxide (CaO) obtained
by calcination of pulverized lime stone (CaCO ). It was used
3
as the raw material to synthesize CaO catalyst in this study.
Quick lime is a nontoxic material that is inexpensive, environ-
mentally friendly and commercially available in Thailand.
Refined palm oil (RPO) was obtained from a physical oil
refinery plant. The oil passes through three refining steps
degumming, bleaching and deodorizing) to remove impurities
in the crude palm oil. Refined palm oil contains a low free
fatty acid (FFA) content (around 0.1 wt %); thus, it is suitable
EXPERIMENTAL
Quick lime powder and refined palm oil were kindly supplied
by Panjapol Paper Industry Co., Ltd. (Saraburi, Thailand) and
PatumVegetableOilCo., Ltd. (PathumThani,Thailand), respectively.
Standard chromatographic grade fatty acid methyl ester (FAME)
(

424 Suwanthai et al.
Asian J. Chem.
were obtained from FLUKA (Switzerland) and Sigma-Aldrich
Switzerland), respectively. Analytical grade methanol and n-
heptane were purchased from Merck (Germany).
Characterization of refined palm oil:A sample (40 mg)
of refined palm oil was placed in a 50 mL three-necked flask
with a boiling chip and 5 mL of 0.5 N methanolic sodium
hydroxide was added to a sample flask connected to a
condenser. The solution was refluxed at 90 °C until the fat
globules had disappeared (about 5 to 10 min). Then, 5 mL of
was used to optimize the biodiesel production process and to
investigate the influence of different process variables on the
percentage of FAME conversion.At five levels of independent
variables ranging from -1.68 to +1.68, 20 experimental runs
were carried out with the three independent variables: catalyst
concentration (wt %) (A); methanol-to-oil molar ratio (mol),
(B); and reaction time (h) (C). In addition, the 20 runs included
8 factorial points, 6 axial points and 6 replicates at the center
point to determine the experimental error in this study.
The experimental data were analyzed using a second order
polynomial equation (eqn. 1) to find the relationship between
the independent variables and % FAME conversion:
(
boron trifluoride solution (BF , 14 % v/v) was added through
3
a condenser and boiling continued for 2 min, after which, 5 mL
of n-heptane was added followed by boiling for another 1 min.
After the reaction completed, the solution was cooled to room
temperature and 15 mL of saturated sodium chloride solution
were added, followed immediately by 15 s of shaking. The
mixture was allowed to rest and separate into two layers. The
upper layer of the solution was analyzed by gas chromato-
graphy (GC) to determine its fatty acid composition.
3
3
2
3
2
i
Y = β + β X + β X +
β X X
∑ ∑ ij
0
∑
i
i
∑
ii
i
j
(1)
i=1
i=1
i=1 j=i+1
where Y is the response (% FAME conversion), β
intercept,β
coefficients, respectively and X
0
is the
i
, βii and βij are the linear, quadratic and interactive
and X are the independent
i
j
Preparation and characterization of CaO: Quick lime
powder was screened through a 60-mesh screen to obtain a
fine powder. The quick lime powder was further subjected to
heat treatment in a furnace at 700 °C for 2 h. The calcined
catalyst was then stored in a closed vessel to avoid the reaction
with moisture in the air and carbon dioxide before used. The
catalyst was characterized extensively. X-ray diffraction (XRD)
patterns were recorded using a D8 Advance Bruker diffracto-
variables. Statistical analysis of the equation was employed to
evaluate the analysis of variance (ANOVA) and Design-Expert
8 software (State Ease Inc., Minneapolis, Mn, USA) was used to
design the experiments and carry out the regression and graphical
analysis of the data. The coded and uncode of independent
variables for reaction experiment parameter were designed as
shown in Table-1.
Determination of the percentage of fatty acid methyl
ester (FAME) conversion: The FAME conversion of refined
meter (USA) with Cu K radiation. The analysis scanned a 2θ
α
1
range from 5 to 40°. The textural and physical appearances
were imaged using scanning electron microscopy (SEM) on a
FEI Quanta 450 SEM (USA). Prior to imaging, the samples
were covered with gold and mounted on a carbon film. The
total surface area, total pore volume and average pore diameter
were determined by the Brunauere-Emmette-Teller (BET)
method with a Quantachrome Autosorb l (USA). The basic
strengths (H_) were determined using Hammett indicators [6].
The indicators used were phenolphthalein (H_= 9.3), 2,4-
dinitroaniline (H_= 15.0) and 4-nitroaniline (H_= 18.4).
Transesterification process: The transesterification
reactions were conducted in a laboratory-scale setup using a
three-necked 100 mL flask equipped with a reflux condenser
and a thermometer on a magnetic, heated stirrer set to 60 °C
and 750 rpm. The CaO was added to the flask when the
reactants reached the required temperature. After the reaction
completed, the product was separated by centrifugation. The
top layer consisted of biodiesel and the bottom layer contained
a mixture of glycerol and CaO. The excess methanol contained
in the biodiesel was further removed in a rotary evaporator at
palm oil was determined by H NMR spectroscopy followed
the work of Knothe [7]. Briefly explained, the chemical shift
at 3.6 ppm represented the methyl ester protons and at 2.3
ppm represented the protons on the carbon next to the glyceryl
moiety (α-CH ). An equation to calculate the percentage of
2
FAME conversion is shown in eqn. 2
C = 100 × (2AME/3Aα-CH2)
(2)
where C is the percentage of FAME conversion, AME is the
integration value of the protons of the methyl esters andAα-CH2
is the integration value of the methylene protons.
RESULTS AND DISCUSSION
Characterization of refined palm oil: The fatty acid
profile of the refined palm oil reveals that palmitic acid (42.83
%
) and oleic acid (39.59 %) are the two major fatty acids,
followed by linoleic acid (9.40 %) and stearic acid (4.43 %).
The minor fatty acids are lignoceric acid (1.69 %), myristic
acid (0.94 %), arachidic acid (0.35 %), lauric acid (0.32 %),
behenic acid (0.16 %), linolenic acid (0.15 %) and palmitoleic
acid (0.14 %). The average molecular weight of refined palm
oil calculated from the fatty acid profile is 854.45 g/mol. The
refined palm oil also contains 1.5 wt % of free fatty acid.
6
5 °C. The obtained purified biodiesel was then bottled and
stored for characterization.
Experimental design and statistical analysis: Response
surface methodology with central composite design (CCD)
TABLE-1
INDEPENDENT VARIABLES AND LEVELS FOR CCD
Range and levels
Variables
Symbol coded
-
1.68
-1
4.5
11
0
6.0
14
+1
7.5
17
+1.68
8.52
19.04
255.68
Catalyst concentration (wt %)
Methanol-oil-molar ratio (mol)
Reaction time (min)
A
B
C
3.48
8.95
104.32
135
180
225

Vol. 28, No. 2 (2016)
Optimization of Transesterification Reaction for Biodiesel Production 425
Characterization of CaO: The crystal structure and
symmetry of each sample are compared with the standard powder
diffraction pattern in the database of the International Centre of
Diffraction Data (ICDD). The calcium hydroxide impurities was
removed from the quick lime by calcination at 700 °C for 2 h in
a furnace. The XRD pattern indicates that calcination yields high
purity CaO in the calcined quick lime, as shown in Fig. 1. The
two diffraction peaks at 2θ of 32.20° and 37.34° are attributed to
theCaOphase(ICDDfileNo. 00-037-1497)asamajor component.
The presence of calcium oxide hydrate (CaO.H
No. 01-070-5492) is also observed at 2θ of 18.07°, 34.17°. The
presence CaO·H O of results from interactions between water
2
O, ICDD file
2
molecule in moisture and the surface of the CaO catalyst.
CaO
Fig. 2. SEM image of calcined quick lime
CaO·H O
2
solid catalyst has direct impact on its catalytic activity and
hence the higher surface area catalyst is expected for higher
catalytic [8].
The calcined CaO changed the colour of phenolphthalein
(H_ = 9.3) from colourless to pink and most of the CaO changed
the colour of 2,4-dinitroaniline (H_ =15.0) from yellow to
mauve. A few CaO samples failed to change the colour of
these indicators due to CaO·H O contamination while the
2
colour of 4-nitroaniline (H_= 18.4) remained unchanged. Thus,
the basic strength (H_) of CaO is between 9.3 and 18.4 and can
be considered as a strong bases for conducting transesterification.
Optimization of transesterification reactions by response
surface methodology: In this research, the relationships bet-
ween the response (% FAME conversion) and the three reaction
variables (catalyst concentration, methanol-to-oil molar ratio
and reaction time) were evaluated using response surface
methodology. The results at each point based on the experi-
mental CCD are presented in Table-2. Twenty experiments
were performed in duplicate.
5
10
15
20
25
(°)
Fig. 1. XRD pattern of calcined quick lime
30
35
40
2
θ
The shape and topology of the CaO particles are observed
by SEM (Fig. 2). The morphology appears to be rod-like
particles. A large number of pores are visible on the surface.
The BET surface area, total pore volume and average pore
diameter of the synthesized CaO were found to be 16.66 m g ,
.18 cm g and 44.26 nm, respectively. The surface area of a
2
-1
3
-1
0
TABLE-2
EXPERIMENTAL DESIGN WITH OBSERVED AND PREDICTED VALUE FROM TRANSESTERIFICATION OF REFINED PALM OIL
Catalyst concentration
Methanol-to-oil
molar ratio (mole)
Reaction time
(min)
Observed FAME
conversion (%)
Predicted FAME
conversion (%)
Run
(
wt %)
1
2
3
4
5
6
7
8
9
4.50
7.50
4.50
7.50
4.50
7.50
4.50
7.50
3.48
8.52
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
11.00
11.00
17.00
17.00
11.00
11.00
17.00
17.00
14.00
14.00
8.95
19.04
14.00
14.00
14.00
14.00
14.00
14.00
14.00
14.00
135.00
135.00
135.00
135.00
225.00
225.00
225.00
225.00
180.00
180.00
180.00
180.00
104.32
255.68
180.00
180.00
180.00
180.00
180.00
180.00
60.93
70.71
69.67
77.52
87.72
93.89
88.89
94.56
80.32
91.32
86.58
90.09
74.91
91.32
95.97
96.62
95.24
94.26
93.90
95.24
66.07
75.15
73.51
81.38
87.61
93.80
88.20
93.17
77.26
89.08
82.82
88.55
66.45
94.48
95.36
95.36
95.36
95.36
95.36
95.36
1
1
1
1
1
1
1
1
1
1
2
0
1
2
3
4
5
6
7
8
9
0

426 Suwanthai et al.
Asian J. Chem.
2
Regression analysis was employed to fit the empirical
The high value of R (0.9060) indicates that the fitted model
can be used to predict reasonably precise outcomes [11].
Fig. 3 shows that the response predicted from the empirical
model is in agreement with the observed values in the range
of the experimental variables. The value of the adjusted
model with the generated response variable data. The response
obtained in Table-2 was correlated with the three independent
variables using a polynomial equation (eqn. 1). The observed
and predicted values of % FAME conversion obtained at the
design points of different reaction conditions are shown in
Table-2. The % FAME conversion varies between 60.93 and
2
determination coefficient (Radj = 0.8214) is signifying the high
significance of the model. A high value of the determination
coefficient (R = 0.9060) justifies the excellent correlation
2
9
6.62 %. The minimum % FAME conversion (60.93 %) was
obtained at 4.50 % catalyst concentration, 11:1 methanol-to-
oil molar ratio and 135 min reaction time, while the maximum
between the independent variables. On the other hand, a
relatively low value of the coefficient of variation (CV = 5.12
%) reveals better precision and reliability for this fitted model
[3].
(
96.62 %) was produced at 6 % catalyst concentration, 14:1
methanol-to-oil molar ratio and 180 min reaction time.
Design-Expert 8 software was employed to determine and
evaluate the coefficients of the full regression model equation
and their statistical significance. The second polynomial model
for the % FAME conversion was regressed, as shown in eqn. 3:
100
90
Y = -236.92+28.2A+13.9B+1.36C-0.07AB-
2
2
0
.01AC-0.01BC-1.92A -0.38B
(3)
whereY is the response variable of % FAME conversion,A, B
and C are actual values of the predicted catalyst concentration,
methanol-to-oil molar ratio and reaction time, respectively.
The obtained data were then analyzed using ANOVA for
fitting a second order response surface model by the least
squares method and to assess the quality of the fit. The terms
of the significant quadratic model for all responses are shown
in Table-3. At the 95 % confidence level, Fmodel = 10.71 with a
very low probability value (p < 0.05) that the null hypothesis
is correct, indicating the high significance of the fitted model
and showing the reliability of the regression model for
predicting the % FAME conversion [9]. In addition, the factors
ofA, C, A , B and C were found to be significant at the 95 %
confidence level according to the computed F-values (high)
and the p-value at the 5 % level. These statistical tests indicate
that the selected model is satisfactory for predicting the %
FAME conversion within the scope of the studied variables
and also shows that the quadratic model is valid in the present
study. The smaller the p-value for a parameter, the more
significant the parameter [10].
80
7
0
0
6
6
0
70
80
Actual
90
100
Fig. 3. Predicted % FAME conversion versus actual % FAME conversion
plot
The response surface plot of % FAME conversion from
various combinations of catalyst concentration, methanol-to-
oil molar ratio and reaction time was shown in Fig. 4. It represents
the graphical three-dimension surface plot of the regression
equation (eqn. 3). Fig. 4(a) represents the effect of varied
methanol-to-oil molar ratio and catalyst concentration at fixed
reaction time on the % FAME conversion. It is obvious that
the increase in % FAME conversion occurred with the increase
in catalyst concentration and methanol-to-oil molar ratio. In
general, the amount of heterogeneous catalyst had a significant
positive effect on the transesterification of vegetable oil to
2
2
2
The suitability of the model was also tested using the
2
regression equation (eqn. 3) and determination coefficient (R ).
TABLE-3
ANOVA FOR THE RESPONSE SURFACE QUADRATIC MODEL
Source of
variation
Degree of
freedom
a
Significant at
5 % level
Sum of squares
Mean square
F-value
p-Value
Model
A
B
1889.48
168.49
39.73
948.74
0.74
9
1
1
1
1
1
1
1
1
1
10
5
5
19
209.94
168.49
39.73
948.74
0.74
10.71
8.59
2.03
48.39
0.038
0.21
1.20
13.65
8.60
0.0005
0.0150
0.1850
<0.0001
0.8500
0.6537
0.2993
0.0041
0.0150
0.0011
Yes
Yes
No
Yes
No
No
No
Yes
Yes
Yes
C
AB
AC
BC
4.19
23.50
4.19
23.50
267.62
168.58
399.59
19.61
38.17
1.04
2
A
B
C
267.62
168.58
399.59
196.06
190.87
5.19
2
2
20.38
Residual
Lack of Fit
Pure Error
Total
36.81
0.0006
Yes
2085.54
a
p > 0.05 is not significantly different at the 5 % level

Vol. 28, No. 2 (2016)
Optimization of Transesterification Reaction for Biodiesel Production 427
methyl ester due to the number of active site available for the
reaction [12] and the high amount of methanol helped to promote
the reversible reaction forwards and the result in a better %
FAME conversion [13]. Then, the % FAME conversion decreased
with excess methanol due to the catalyst content decreased
that result in a hindrance for the access of triglyceride molecule
to active sites [14]. Fig. 4(b) shows the effect of reaction time
and catalyst concentration while methanol-to-oil molar ratio
was kept constant. It revealed the increased % FAME conversion
with increasing the catalyst concentration and reaction time.
However, the % FAME conversion slightly decreased with
increasing concentration of catalyst made a slurry mixture of
catalyst and reactant that resulted in mixing problem [15]. Fig.
The optimum tranesterification condition was predicted
by applying numerical optimization of Design Expert software
using response surface methodology. Optimization criteria
were set for all variables including independent variables and
the response. The range of the optimization for the response
was 96.5 % FAME conversion to 100 % FAME conversion.
The optimum condition for producing % FAME conversion
(98.69 %) was found as 6.32 %wt of catalyst, 14.12:1 of methanol-
to-oil molar ratio and 213.57 (about 214) min of reaction time.
The predicted value of 98.69 % was approximately equal to
the observed average value of 97.58 % (repeated three times).
Therefore, the experimental values were in acceptable agree-
ment with the predicted values and the errors between the two
values were small (< 5 % error for the % FAME conversion).
Confirmation and properties of produced biodiesel:
4
(c) represent the effect of reaction time and methanol-to-oil
molar ratio on % FAME conversion at constant catalyst concen-
tration. The % FAME conversion increased with increasing
methanol-to-oil molar ratio and reaction time.
1
Fig. 5 exhibits the H NMR spectrum of refined palm oil
biodiesel. The characteristic peaks of methoxy protons as a
singlet at 3.66 ppm and α-methylene protons as a triplet at
2.28 ppm were observed. These two peaks are the distinct peaks
for the confirmation of methyl esters [7]. The other peaks
observed were at 0.87 ppm due to terminal methyl protons, a
strong signal at 1.30 ppm arises from the methylene proton of
carbon chain, a multiplet at 1.60 ppm related to β-carbonyl
methylene protons and a signal at 5.34 ppm due to olefinic
hydrogen [16].
(a)
100
90
80
70
60
17
7.5
16
6.9
15
6.3
14
5.7
13
12
5.1
11 4.5
(b)
100
90
80
70
60
7
.5
6.9
6.3
5.7
5
.1
4.5
9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0
ppm
0
-1.0
1
Fig. 5. H NMR spectrum of refined palm oil biodiesel
(c)
100
The values of various properties were tested following
the biodiesel standards of the USA (ASTM) and Europe (EN),
as exhibited in Table-4. The results show that all biodiesel
properties meet the standards.
9
0
8
0
7
0
60
TABLE-4
PROPERTIES OF REFINED PALM OIL BIODIESEL
1
7
Biodiesel
in this
study
5.64
0.882
154
0.66
0.04
16
Specifi-
15
Parameter
Testing method
14
cation
1.9-6.0
0.86-0.90
130 min.
0.80 max.
0.050 max.
13
12
11
Viscosity at 40 °C (cSt)
Density at 15 °C (g/cm )
Flash point (°C)
Acid value (mg KOH/g)
ASTM D445
EN ISO 3675
ASTM D93
ASTM D664
3
Fig. 4. Response surface plots elucidating the effects of: (a) methanol-to-
oil molar ratio and catalyst concentration; (b) reaction time and
catalyst concentration; and (c) reaction time and methanol-to-oil
molar ratio
Water and sediment (% v) ASTM D2709

428 Suwanthai et al.
Asian J. Chem.
Conclusion
The calcium oxide was successful synthesized when the
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ACKNOWLEDGEMENTS
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This work was financially supported by Kasetsart University
Research and Development Institute. The authors also thank
Center of Excellence-Oil Palm Kasetsart University for partial
supported.
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