Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
Research Article, Issue 3
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
Optimization and effect of varying catalyst concentration
and trans-esterication temperature on the yield of biodiesel
production from palm kernel oil and groundnut oil
Obidike Blessing Magarette a, Okwara Nelson Onyekachib, Andrew Wirnkor Verlac,
Christian Ebere Enyohd,* and Mbagwu JohnPaule
aDepartment of Chemical Sciences, Akwa-Ibom State Polytechnic Ikot-Osurua, Ikot-Ekpene Nigeria.
bEunisell Globals Limited, Victoria Island, Lagos State Nigeria.
cDepartment of Chemistry, Imo State University Owerri, Nigeria.
d,* Graduate School of Science and Technology, Saitama University, Saitama, Japan
eDepartment of Physics and Astronomy, University of Kansas, USA
ABSTRACT
The negative environmental impact generated by fossil fuel has
resulted in the demand to search for alternative routes of renewable
sources of energy, such as biodiesel, that have unlimited duration while
having little or no hazardous impact. In this study, trans-esterication
of palm kernel oil and groundnut oil was carried out using sodium
methoxide (CH3ONa) as a catalyst. The effect of varying Sodium
Methoxide (CH3ONa) catalyst concentrations of (0.25, 0.5, 1.0, 1.5,
and 2.0) % w/v at trans-esterication temperatures of (50, 55, and
60) oC on the yield of biodiesel from groundnut oil and palm kernel
oil was determined. This was to identify the catalyst concentration
and trans-esterication temperature with optimal process yield. The
process gave optimum biodiesel yields of 98% and 84% by volume of
groundnut oil and palm kernel oil at reaction conditions of 0.5%w/v
CH3ONa as catalyst, trans-esterication temperature of 55oC, 360
rpm mixing rate and a reaction time of 90 minutes. The biodiesel
produced was analyzed for fuel properties using the American
Society of Testing and Materials (ASTM) standard, and the results
obtained were as follows; specic gravity (0.8835, 0.8815 at 15oC),
ash point (98, 124) oC, viscosity (5.2, 7.6) mm2S-1at 40oC, pour point
(9, -1)oC, iodine value (8.04, 17.11) /100, acid value (0.67, 0.48) mg/
KOH/g, peroxide value (28, 60) mg Kg-1, re point (108,136)oC for
palm kernel oil and groundnut oil respectively.
Keywords:
Biodiesel,
Trans-Esterication,
Mineral diesel,
Palm kernel oil,
Groundnut oil,
Optimization
ARTICLE INFO:
Received 8 May 2022
Revised form 16 Jul 2022
Accepted 11 Aug 2022
Available online 30 Sep 2022
*Corresponding Author: Christian Ebere Enyoh
Email: cenyoh@gmail.com
https://doi.org/10.24200/amecj.v5.i03.203
1. Introduction
Considering the rapid increase in the global
population in the world today, the long-term
strength of a complex environment is tested
by the demand for a higher standard of living.
This involves meeting the energy and food
requirements of over 9 billion people [1]. A
recent statement by BP’s Energy Outlook to 2035
proposed that the average world energy usage
is expected to increase by 34% between 2014
and 2035 [2]. However, the use of petroleum
is a suitable means of harnessing energy for
global consumption. But its drastic increase in
price, non-ecofriendly nature, and great addition
to pollution of the atmosphere have led to the
need to develop alternative routes of renewable
sources of energy that have unlimited duration
------------------------
56
while having little or no hazardous impact on
the environment [3]. Several alternative means,
such as bio-ethanol from the ebullition of starch,
biomass gasication, and biodiesel, have been
harnessed over the years [4]. However, the use of
biodiesel remains the best. It covers an estimated
82% of the total biofuel production as stated by the
EU. It has also shown a substantial contribution
to future energy demands of both domestic and
industrial sectors [5,6]. In comparison with
petroleum-based derived diesel, it is non-toxic,
biodegradable, and a cleaner source of energy
[2]. Vehicles using biodiesel emit less harmful
greenhouse gases of carbon monoxide and sulfur
dioxide [7]. Biodiesel could reduce the emission
of particulate matter (PM) and act as a good
lubricant for diesel engines, thus prolonging the
shelf-life of the engine. In addition, biodiesel has
a higher ash point, making it safer to handle than
mineral diesel [8]. Other protable characteristics
of biodiesel that make it an effective alternative
to mineral-derived-diesel oil are liquid nature
portability, sustainability, ignition performance,
and higher octane number [9]. Biodiesel, also
known as fatty acids methyl esters (FAME)
is a domestic and renewable biomass fuel for
diesel engines obtained from vegetable oils or
animal fats, designated B100. It must meet the
requirements of ASTM D6751 [8]. Feedstocks
used in biodiesel production are available and
could always be re-planted or grown [8]. Biodiesel
is produced through chemical processes such as
transesterication or esterication reactions [10].
Trans-esterication is the reaction between an
alcohol and an ester [11], while esterication is the
reaction between a carboxylic acid and alcohol.
During the process of trans-esterication, the
alcohol functional group is deprotonated by the
action of the base which compels it into a stronger
nucleophile [12]. The most frequently employed
alcohols in this process are ethanol or methanol.
Under standard conditions, the trans-esterication
reaction proceeds at a very slow rate or not at all,
so, heats and catalysts (acid and/or base) are used
to increase the reaction rate.
[13]. It is vital to know that catalysts are not
absorbed during trans-esterication reactions
[11]. Heterogeneous, homogeneous, Nano, and
super-critical uid catalysts have all been utilized
to activate trans-esterication reactions [14]. But
in this study, the homogenous catalyst is used for
the trans-esterication process. This is because
it permits a higher degree of interaction with
the reaction mixture, and allows the complete
conversion of feedstock to biodiesel [6]. More
often in the presence of a base catalyst, an
undesirable saponication reaction could occur if
the feedstock contains free fatty acids. Therefore,
feedstock containing less than 0.5wt% free fatty
acid is employed during the trans-esterication
process to avoid soap formation [15]. The
feedstock composition controls the chemical
pathway and dictates the type of catalyst to be
utilized in the production of biodiesel [2]. The
feedstock used for biodiesel production is Fats
and oils from plants and animals; they comprise
triglycerides which are esters that contain three
fatty acids, trihydric alcohol, and glycerol. The
feedstock includes a range of edible vegetable
oil, non-edible oils, waste or recycled oils, and
animal fats [7, 9 -10]. Edible oils are connected to
edible biomass, examples are; soybean, rapeseed,
sunower, palm, coconut and linseed while the
non-edible biofuels are biomass fuel, ranging
from lignocellulose feedstock to municipal solid
wastes [16]. From literature reviews various
types of oil have been used, but in this study
the use of edible oils like unrened groundnut
nut oil and palm kernel oil is selected owing to
their unique properties. Groundnut oil is mild-
tasting vegetable oil with a high smoke point
compared to several cooking oils [17]. The oil
is obtainable in puried, unrened, cold pressed,
and roasted variations have a strong peanut avor
and aroma [15]. Palm kernel oil is edible plant
oil derived from the kernel of the oil palm [12].
Palm kernel oil is among one of the essential
oils that contain saturated vegetable fats, this is
because it is composed of 16-carbon saturated
fatty acid and excessive palmitic acid [13]. Palm
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
57
kernel oil is semi-solid at room temperature, stable
at high cooking temperatures and has extended
storage capacity [18]. Several studies have
conducted experiments on biodiesel production
using different catalyst types and feedstock to
varying temperatures as summarized in Table 1. In
this study, biodiesel will be produced from palm
kernel oil and groundnut oil through different
trans-esterication temperatures by varying
catalyst concentrations of sodium methoxide.
The result from this study will be a basis for
determining the optimal reaction conditions for
the production of biodiesel production.
2. Experimental
The data generated from the experimental results
were modelled using linear, interaction, pure
quadratic, quadratic, 3rd order polynomial, and 4th
order polynomial. From the result obtained, the
4th-order polynomial showed a good correlation
with the experimental results; demonstrating that
the model was useful for optimization. Newton
Raphson’s multivariable optimization technique
and Response Surface Methodology (RSM) were
further used to enhance the process parameters of
the trans-esterication reaction. Newton Raphson’s
multivariable optimization technique gave an
optimal yield of 100.5 mL and 90.7 mL for groundnut
oil and PKO FAME with a corresponding catalyst
concentration and trans-esterication temperatures
of (0.25%, 0.48%) and (51.3 oC, 50 oC). Whereas
the surface plots gave optimal yields of 104.8
mL and 89.8 mL with the catalyst concentration
and trans-esterication temperatures of (0.6%,
0.425%) and (58oC, 50oC) for groundnut oil and
Palm kernel Oil (PKO) based Fatty Acid Methyl
Esters (FAME). The ndings from this study were
in good correlation with ASTM standards for fuel.
Therefore, it can be used as an excellent alternative
fuel for diesel engines.
2.1. Materials
The reagents used were distilled H2O, Concentrated
Sulphuric acid (H2SO4), Methanol (CH3OH),
Sodium hydroxide (NaOH), and two different oils,
namely groundnut and palm kernel. Reagent like
NaOH was properly reserved in an airtight plastic
container to prevent them from absorbing moisture
from the atmosphere since it is deliquescent in
nature. Methanol was reserved in an airtight brown
bottle to prevent evaporation as methanol is a
volatile liquid.
Table 1. Literatures reviews of some studies conducted on the effect of varying catalyst concentration
and Trans-esterication temperature on the yield of biodiesel in Nigeria
N Feed Stock Catalyst Type T Catalyst Concentration RT Biodiesel Yield Ref.
1. Palm kernel
oil Homogeneous 60oC
,1.5 ,1.25 ,1.0 ,0.75 ,0.5)
and 2.0)%w/v of KOH 1.75
120 ,85.2 ,95.8 ,95.0 ,90.5)
%(71.3 ,71.1 ,73.3 [19]
2. Milk Bush
seed oil
Heterogeneous
Homogeneous 65oC wt. % of CSS and KOH 3.0 120 and 94.33% 81% [20]
3. False Shea
seed oil Homogeneous 50oC 0.3mol/dm3 of NaOH 120 85.0% [21]
4. Water Melon
Seed oil Homogeneous 60oC g of NaOH(018 ,015 ,0.13) (150 ,120 ,90) %(49 ,53 ,70) [22]
5. Jatropha
curcas oil Homogeneous 48oC0.88M of KOH 240 84.70% [23]
6. Palm kernel
oil Homogeneous 60oC w/v of KOH 1.0% ,90 ,75 ,60 ,45 ,30)
(120 ,105
,94.2 ,92.5 ,90.1 ,87.4)
%(96.0 ,96.0 ,96.0 [24]
7. PKO-GO Homogeneous 55oC w/v of NaOH 0.7% -------------- 91.98 ,90.53 [25]
RT: Reaction time (mins) T:Temperature PKO-GO: Palm kernel oil and groundnut oil
Effect of Catalyst and Transesterication on the Biodiesel Production Obidike Blessing Magarette et al
58
2.2. Sampling
Groundnut oil and Palm kernel oil were procured
from a commercial shop in Ogbete main market
Enugu state, Nigeria. The experiment was
conducted in laboratory 3 of the materials and
Energy Technology (MET) department of the
Project Development Institute (PRODA), Enugu
state Nigeria.
2.3. Acid-catalyzed esterication
Delving directly into base-catalyzed trans-
esterication may result in soap production
instead of biodiesel due to the high FFA content
of the unrened groundnut oil and palm kernel
oil. in order to eradicate the possibility of this side
reaction (i.e., saponication), the FFA content of the
unrened sample is reduced to the barest minimum
by acid-catalyzed esterication reaction using conc.
Sulfuric acid (conc.H2SO4) as catalyst [8]. The
diagrammatic setup is shown in Figure 1a and 1b.
2.3.1.Experimental procedure of the acid-
catalyzed esterication
Unrened groundnut oil and palm kernel oil
were poured into a conical ask and heated
to a temperature of 60oC for 10 minutes. The
temperature was monitored using mercury in a
glass thermometer tted with a ca lamp in the retort
stand. Methanol (60% weight of the sample) was
introduced into the beakers containing the preheated
oil samples. Concentrated sulfuric acid (H2SO4) of
1.2% weight of the sample was added to the mixture.
The mixture was stirred using a magnetic hot plate
at 50o C in an open system for an hour. The mixture
was transferred into a separating funnel and allowed
to separate overnight. The mixture is divided into
three phases: the lower phases (impurities), the
middle phase ( the preheated sample) and the upper
layer (the methanol-water phase).
2.4. Base catalyzed transesterication
experimental procedure
9.65g of NaOH pellets were weighed and
introduced into a round bottom ask containing
200mL of CH3OH(aq). It was stirred and allowed
to dissolve completely by shaking vigorously until
a solution of sodium-methoxide (CH3ONa) was
formed in the process. The CH3ONa solution was
added to 100mL of groundnut oil and palm kernel
oil from the acid catalyzed esterication process
into the different conical asks. The mixture was
then heated to a preferred trans-esterication
temperature of 60o C using the magnetic hot plate.
At this point, the stirrer was introduced into the
solution. Stirring was done at a constant speed
(e.g., 360 revolutions per minute). It was continued
until a given time of 90 minutes was attained.
While heating and stirring simultaneously, the
solution was made air-tight using a masking
foil to prevent CH3ONa from evaporating. After
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
Fig. 1a. Low FFA oil after acid-catalyzed esterication Fig. 1b. High FFA oil before acid catalyzed esterication
59
the given time, the solution was removed from
heat and poured into a separating funnel. It was
left overnight for the separation to take place.
Glycerin settled below, while the biodiesel (ethyl
esters) which was the supernatant settled above.
The glycerin was discarded and the biodiesel was
washed with distilled water until the impurities
were completely removed. These impurities were
in the form of a foamy solution that settled. The
biodiesel was again washed with hot water to
remove further impurities. Measurements were
also taken before and after the washing of biodiesel.
The waste product removed with water was tested
using phenolphthalein, which turned pink on
the addition of phenolphthalein, conrming that
sodium hydroxide was still present. So, in other
to get purer biodiesel, continued washing with
water was done until the product was removed as
waste does not turn pink using the phenolphthalein
Indicator. To neutralize the presence of NaOH(aq)
ultimately, 1mL H2SO4(aq) was added after every
negative phenolphthalein test because acids have
no negative effect on biodiesel. The already
washed biodiesel was collected and heated
gradually at about 100 to give off the leftover
water after washing, then was allowed to cool. A
viscous solution with pale gold color was obtained
and that was the biodiesel. The procedure was
repeated using the same catalyst concentrations of
0.25%w/v at the trans-esterication temperature
of 55oC and 50oC, respectively.
2.5. Physiochemical Characterization of
Biodiesel
2.5.1.Determination of specic gravity at 55oC
and viscosity at 40oC
empty S.G. bottle was weighed and lled with
distilled water, and the reading was noted. An S.G
bottle was lled with biodiesel and weighed again.
The S.G. was calculated using Equation 1.
(Eq.1)
The viscosity of the biodiesel was determined
using “Ostwald’s Viscometer”. This was done by
lling the viscometer to the mark; sucking it up into
the other side of the fuse, and setting a stop-clock
or stop-watch to time when the oil ows back to
the rst tube with which the oil was rst lled. The
viscosity was then calculated as Equation 2.
(Eq.2)
Where; 4.39 = centistokes constant, 8 = sugar or
glucose constant, t = time taken to move in the
viscometer.
2.5.2.Free fatty acid (FFA) or acid value
The acid number test was conducted using
ASTM D-664 Test Method. 5g of the biodiesel
sample was measured into a conical flask, and
three drops of phenolphthalein indicator and 20
ml of ethanol were added. It was titrated with
0.1 M NaOH solutions and a pink coloration
was observed. The FFA was calculated by
Equation 3.
(Eq.3)
Where; T.V = Titre value, N = Normality of titrate,
5.61 = Acid constant, W = Weight of the sample
2.5.3.Saponication Value (SV)
The saponication value test for biodiesel in
this present study was conducted in accordance
to ASTM D5558 standard testing method. 5g of
the biodiesel was measured into a conical ask,
0.5M of ethanolic KOH was added and reuxed
(heat) in a round bottom ask, then allowed to
stand for 3 minutes. The essence of reuxing
was to get a perfect dissolution of biodiesel in
the ethanolic potassium hydroxide. Three drops
of phenolphthalein indicator were added and
titrated with 0.5M hydrochloric acid. A blank
Effect of Catalyst and Transesterication on the Biodiesel Production Obidike Blessing Magarette et al
60
titration was also run; the saponication value
was calculated using Equation 4.
(Eq.4)
Where; V2 = Titer of blank, V1 = Titer of sample,
56.1 = MW of KOH, 0.5 = Normality of KOH.
2.5.4.Determination of iodine value using EN
14112 test method
5.0 g of biodiesel was measured into a conical
ask; 15mL of chloroform and 25mL of Wijis
(iodine monochloride) solution were added and
mixed together. The mixture was tightly covered
and placed in the dark for 30 minutes. 20mL of
10% KI (Potassium iodide) and 50mL of distilled
water were added and the resulting solution
turned to red. The reddish solution was titrated
with 0.1M Sodium Thiosulphate, 5.0 mL of 1%
starch indicator was added and the color turned
blue-black. It was later titrated with 0.1M Sodium
Thiosulphate and turned colorless. Blank was
also titrated and the iodine value was calculated
by Equation 5.
(Eq.5)
Where; 12.69 = Constant for iodine value,
N = Normality of Titrant, V2 = Titer of blank,
V1 = Titer of sample.
2.5.5.Determination of peroxide value using
ASTM D37031-13 methodology
5g of biodiesel was measured into a 100 mL
beaker, 25 mL of acetic acid and chloroform
solution in the ratio of 2:1 was added. 1mL of
10% Potassium Iodide was later added and shaken
vigorously. The mixture was covered and kept in
the dark place for 1 minute. 35 mL of the starch
indicator was added and Titrated with 0.02M
Sodium Thiosulphate Na2S2O3 and a white color
was observed. A blank titration was also prepared
in the same way as described excluding the step
of addition of biodiesel. The peroxide value was
calculated as Equation 6.
(Eq.6)
Where; N = Normality Na2S2O3, V1 = Titer of
sample, V2 = Titer of blank, 100 = Peroxide value
constant.
2.5.6.Determination of pour and ash point
This is the minimum temperature at which the oil
can to pour down. This test was done in accordance
to the ASTM D97 Test method. The biodiesel was
brought out at room temperature, it was allowed
to melt gradually and the temperature at which the
biodiesel became a complete liquid was recorded
as the pour point.
The ash point of an oil is the lowest temperature
at which vapour from biodiesel will ignite when a
small ame is applied under standard test conditions.
The test was carried out using the D93 test method.
A source of the re was placed at a distance away
from the smoking biodiesel in a closed cup and the
temperature at which the biodiesel catches re was
noted.
2.6. Model methodology
The yields of biodiesel obtained from both
samples (i.e., groundnut oil and palm kernel
oil) in this study were modeled concerning two
independent variables (catalyst concentration and
trans-esterication temperature) using Several
models such as linear, interaction, pure quadratic,
quadratic, 3rd order polynomial and 4th order
polynomials.
2.7. Optimization methodology
Data obtained were optimized using MATLAB
optimization tool box and Response Surface
Methodology (RSM) as described by [40].
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
61
3. Results and discussion
3.1. Experimental result on the yield of biodiesel
obtained from groundnut oil and palm kernel
oil by varying catalyst concentration and trans-
esterication temperature
The results obtained by varying transesterication
temperature from 50 - 60oC at catalysts concentration
of 0.25-2.0% w/v of CH3ONa is presented in Table
2 and 3. From the result it can be deduce that
biodiesel yield increases gradually with an increase
in catalysts concentrations and trans-esterication
temperature, but with an additional increase in
catalyst concentration of 1%w/v resulted to a
decrease in biodiesel yield. Hence, the maximum
output of biodiesel was at 0.5 % w/v of CH3ONa
catalyst and a trans-esterication temperature of
55oC. This implies that, at that temperature and
concentrations equilibrium is attained and this can be
further explained by trans-esterication reversible
reaction. The discovery from this research was in
close proximity to the works of [26] who reported
that catalysts concentrations above 1% w/v favored
backward reaction, thereby shifting the equilibrium
to the left as well as resulting in the loss of sodium
methoxide and a reduction in the yield of biodiesel.
3.2. Physicochemical characterization of the
biodiesel
The result for the physicochemical characterization
of the biodiesel is presented in Table 4. The
physiochemical characterization of biodiesel
obtained from PKO and groundnut oil in this
present study showed a good conformity to that
of ASTM standard values for mineral diesel.
Hence, it can be utilized as a better alternative
for petroleum diesel. The density of the oil is a
very vital factor to be considered because the fuel
injection system works with volume metering
approach. The density of biodiesel provides
required details on the weight of the oil at specic
temperatures. From this present study the specic
gravities of biodiesel harnessed from palm kernel
oil and groundnut oil were 0.8835 and 0.8815
respectively. These values are within the limits of
0.8833 of biodiesel specied by ASTM [27] and
were also in close proximity with various scientic
studies carried out by [28] who reported specic
gravities of 0.881, 0.865, and 0.887 for biodiesel
from Mango seed oil, Palm kernel oil and Shea
butter oil. Viscosity is one of the basic criteria
to be considered when evaluating the quality of
biodiesel. It is a key property which measures
the resistance ow of uids under the effect of
gravity [29]. The viscosity value obtained from
biodiesel of PKO and groundnut oil conducted in
this experiment are 5.2 mm2 S-1 and 7.6 mm2 S-1
respectively. These values were within the limits
of 4.0 - 6.0 mm2 S-1 specied by ASTM, but the
biodiesel from groundnut oil was a bit higher than
ASTM required limit. The viscosity of biodiesel
explains the effective lubricity of fuel; it shows
that the biodiesel analyzed in this present study
may protect diesel fuel pumps and engines from
wear and seepage. Thus enhances the atomicity
and combustion as well as reducing emissions of
fumes from exhaust engines. The values obtained
also showed good correlation with biodiesel
values of 7.65 and 5.92 mm2 S-1 from palm
kernel oil and groundnut oil [30]. It was said to
be somewhat higher than the values of 3.62 mm2
S-1 reported in shear butter oil [28] and mango
seed oil (5.82 mm2/S) [26]. Flash point refers
to the lowest temperature at which the biodiesel
produces enough vapour to ignite when exposed
to thermal sources; it is also a measure of degree
of ammability [31]. It is a basic criterion to
consider when handling, storing and transporting
fuel. The ash point of the biodiesel obtained from
PKO and groundnut oil in this research was 98oC
and 124oC. It was within the range of (100 – 170)
oC set by ASTM. Therefore, the ash point value
of the biodiesel from this research shows that it
is safe, non-hazardous, and can hardly ignite at
higher temperatures. The values obtained from
this research for biodiesel from PKO was slightly
lower than ash points of 120oC, 132oC, and 167oC
reported by [32-33]. The biodiesel from this study
is less volatile and free from basic impurities like
methanol which could reduce the ash point of
biodiesel.
Effect of Catalyst and Transesterication on the Biodiesel Production Obidike Blessing Magarette et al
62
The re point is the temperature at which the
biodiesel may like burn for a few seconds after
ignition in an open ame. The re point of
biodiesel of PKO and Groundnut oil obtained in
this experiment are 108oC and 136oC, it is higher
than ASTM values of 68oC for diesel [32]. This
shows that biodiesel is very suitable for use as it
can hardly burn even at higher temperatures after
ignition. The pour point is a necessary criterion
when evaluating the low-temperature Performance
of fuel. It is considered as the operational capacity
of the fuel under given weather, it shows how
effective biodiesels can be utilized even in cold
climatic regions. The ASTM specied value for the
pour point of biodiesel is -5 to 10 and -35 to 15 for
mineral diesel [27]. In this research the biodiesel
pours point values obtained from palm kernel oil
and groundnut oil were 9 and -1, respectively. These
values are within the ASTM standard values and are
in close range of 0.0oC, 2oC, 5oC, and 2oC pour point
values [32-34]. The biodiesel produced from the
palm kernel oil in this experiment has a high pour
point value of 9 due to the degree of unsaturation of
carbon to carbon (C-C) bond formed; this implies
that it can improve the performance of an engine.
Saponication value of biodiesel plays a vital role
in assessing adulteration [35]. Saponication of
biodiesel can be dened as the mass in milligram
of potassium hydroxide needed to saponify 1g of
oil, and it is relatively dependent on the average
molecular weight of fatty acids present in the
primary oil [28]. Saponication value is a measure
of degree on how the biodiesel oxidizes during
storage, an increase in saponication value increase
volatility of biodiesel. The saponication values of
biodiesel produced from PKO and groundnut oil
in this experimental study are 423.55 and 227.66
mg KOH g-1 respectively. It is above the ASTM
value of 120 mg KOH g-1. The high saponication
value is an indication that the primary oil had high
amount of soap content, this might result to uneven
combustion and increase emissions of thick fumes
from exhaust engine. However, it also has an the
advantage of purifying the internal component of
the engine, and as such reduces friction between
the surface parts of the engine [32]. Considering the
yield of biodiesel, high saponication values should
be reduced to the barest minimum as it would likely
prevent the separation of biodiesel from glycerin.
In comparison with other ndings, the values in
this study were obtained within the same range of
saponication values of 229.9 mg KOH g-1and 226
mg KOH g-1 obtained in biodiesel produced from
oil and palm kernel oil reported by [32,34].
Table 2. Palm Kernel Oil base FAME experimental results
Catalyst Concentration (Yield %)
Trans-esterication
Temperature (oC)
0.25 0.5 1.0 1.5 2.0
50 76 82 54 0 0
55 50 84 68 62 40
60 66 66 52 62 48
Table 3. Groundnut Oil base FAME experimental results
Catalyst Concentration (Yield %)
Trans-esterication
temperature (oC)
0.25 0.5 1.0 1.5 2.0
50 96 92 74 74 16
55 95 98 89 72 22
60 50 95 89 38 0
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
63
The acid content plays an important role when
evaluating the quality of biodiesel. It determines
how stable the biodiesel can stay over a long period
of time. The acid value is dened by the amount of
KOH in mg needed to neutralize 1.0 g of free fatty
acids [36]. The acid value of biodiesel produced
from palm kernel oil and groundnut oil in this
present study are 0.673 and 0.48 mg KOH g-1 which
was in good correlation with ASTM D 664 value of
0.5 mg KOH g-1. The acid values of biodiesel from
this experiment was also in a close range with values
of 0.37 mg KOH g-1, 1.2 mg KOH g-1, and 0.8 mg
KOH g-1 of biodiesel produced from Shea butter,
mango seed oil, and palm kernel oil respectively
[26,28,32]. The values obtained in this study shows
that the biodiesel is not corrosive. Iodine value
is a measure of degree of unsaturation resulting
from the formation of carbon to carbon bonds. It is
dened as the mass of iodine that is added to 100.0
g of oil [28]. Low iodine value signies presence
of saturation and vice versa, saturated oil has
resistance against oxidation and deterioration. The
iodine value for every biodiesel set by EN 14112 is
(7.5-8.6) g per100. In this present study, the iodine
value obtained from the biodiesel produced from
palm kernel oil and groundnut oil were 8.04 and
17.11. The palm kernel oil biodiesel was within
the specied range but that of the groundnut oil
was slightly above the range. This shows that
PKO biodiesel is a suitable alternative fuel for
diesel engines based specically on the measure
of iodine value. The PKO biodiesel possess low
oxidative resistance unlike that of groundnut oil,
although iodine value of biodiesel from groundnut
oil is technically on a good range when compared
with results of 65.09 g per 100, 34.24 g per100,
36.00g per100 of biodiesel from PKO, Shea
butter oil, and palm oil [32,28,33]. Peroxide value
plays a vital role on stability of biodiesel during
storage. It is dened by the amount of peroxide
oxygen per 1.0 kg of biodiesel. Peroxide value is
directly proportional to the rate of oxidation which
is greatly inuenced by the level of saturation of
the biodiesel. In other words, biodiesel with high
peroxide value will easily oxidize, thus increasing
the rate of biodegradation as well reducing its
stability [37]. The rate at which biodiesel undergo
oxidation is controlled by certain factors like
heat, amount of Oxygen, light, water content,
and temperature. Excessive heat, light and high
temperature enhances the rate of oxidation. In this
present study 28.0 meq kg-1 and 60.0 meq kg-1 was
recorded for biodiesel produced from palm kernel
oil and groundnut oil, this shows that biodiesel
produced from groundnut oil will easily degrade
compare to that from PKO.
Table 4. Properties of biodiesel and mineral diesel compared to biodiesel produced from Palm kernel oil
and Groundnut oil in this study.
Fuel properties Mineral-diesel ASTM
D975 Limits
Biodiesel ASTM
D6751 Palm kernel
oil biodiesel
Groundnut oil
biodiesel
Kinematic viscosity (mm2S-1)
at 40oC1.3 - 4.1 4.0-6.0 5.2 7.6
Specic gravity at 15oC. 0.85 0.88 0.8835 0.8815
Flash point (oC) 60-80 100 – 170
(ASTM D93) 98 124
Pour point (oC) -35 to -15 -5 to -10 (ASTM D97) 9 -1
Acid value (mKOH/g) - 0.5 ( ASTM D-664) 0.673 0.48
Peroxide value (meq/kg) - -ASTM D37031-13 28 60
Iodine value (g/100) - 7.5-8.6 (EN 14112) 8.04 17.11
Saponication
value (mgKOH/g) -95 – 370
(ASTM D5558) 423.5 227.66
Fire point (oC) - 68 108 136
Source: Biodiesel Handling and Use Guide (Fifth Edition). November 2016 for the standard properties for biodiesel and diesel fuels.
Effect of Catalyst and Transesterication on the Biodiesel Production Obidike Blessing Magarette et al
64
3.3. Modeling of Data generated from Trans-
esterication experimental result
Several models were used to t the experimental
data from the groundnut oil and PKO biodiesel. They
are linear, interaction, pure quadratic, quadratic, 3rd
order polynomial and 4th order polynomials with
their respective regression coefcients of 0.6694,
0.6695, 0.8981, 0.8982, 0.9213, and 0.9926 for
groundnut oil, while PKO was 0.4914, 0.7162,
0.5042, 0.7712, 0.8666, and 0.9773 as shown in
(Table 5). The F test was carried out by comparing
the variances of each model with the experimental
results, it shows that each of the models is actually
adequate because their calculated F values are less
than the F critical based on 14 degrees of freedom
for both the numerator and denominator. However,
regression coefcient of a model should be more
than or approximately equal to 0.95 [38-39].
Hence, the 4th order polynomial is obviously the
most suitable for both oils. The equation of the 4th
order polynomial for groundnut oil is at Equation 7.
Using the 4th order polynomial for both groundnut
and PKO, were generated at a constant temperature
(Figure 2(a) to Figure 2 (d))
(Eq.7)
(Eq.7)
Table 5. Data generated for different models used
0 X1 X2 Yexpt Ymodel (1) Ymodel (2) Ymodel (3) Ymodel (4) Ymodel (5) Ymodel (6)
Groundnut oil
10.25 50 96 106.3 106.9 102.2 87.43 92.51 98.79
20.25 55 95 98.3 98.3 94.4 91.65 90.49 91.22
30.25 60 50 90.3 89.7 85.9 70.26 62.91 50.98
40.5 50 92 96.4 96.8 98.7 94.15 94.91 87.37
50.5 55 98 88.4 88.4 90.9 98.54 99.95 103.3
60.5 60 95 80.4 80.0 82.3 77.34 79.41 94.35
71.0 50 74 76.6 76.7 84.4 90.58 83.92 75.63
81.0 55 89 68.6 68.6 76.6 95.34 96.11 89.70
91.0 60 89 60.6 60.6 68.1 74.51 82.71 86.66
10 1.5 50 74 56.9 56.5 60.7 64.36 57.64 74.81
11 1.5 55 72 48.9 48.9 52.9 69.48 67.73 67.99
12 1.5 60 38 40.9 41.2 44.4 49.02 52.19 41.19
13 2.0 50 16 37.1 36.4 27.6 15.48 23.02 15.38
14 2.0 55 22 29.1 29.1 19.7 20.98 21.73 23.81
15 2.0 60 0 21.1 21.8 11.2 0.874 -5.21 -1.19
R20.6694 0.6695 0.8981 0.8982 0.9213 0.9926
F1.4939 1.4939 1.2561 1.1133 1.0854 1.0075
F CRITICAL = 2.4837
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
65
Fig. 2. (a) Varying catalyst concentration at constant temperature for PKO base FAME and comparison
of the different groundnut oil base FAME models with the experimental data at (b) 50oC (c) 55oC (d) 60oC
PKO
10.25 50 76 65.38 83.02 61.91 76.30 77.40 72.593
20.25 55 50 73.58 73.58 69.59 77.06 62.36 53.121
30.25 60 66 81.78 64.14 77.99 57.42 57.89 66.286
40.5 50 82 59.26 71.39 59.86 68.33 77.25 89.138
50.5 55 84 67.46 67.46 67.54 74.61 72.91 77.801
60.5 60 66 75.66 63.53 75.94 60.48 69.46 65.061
71.0 50 54 47.02 48.13 51.68 48.69 51.58 47.491
81.0 55 68 55.22 55.22 59.35 65.99 68.28 72.941
91.0 60 52 63.42 62.32 67.76 62.88 66.52 53.368
10 1.5 50 0 34.79 24.87 38.03 24.10 14.18 3.5282
11 1.5 55 62 42.99 42.99 45.71 52.43 51.47 59.789
12 1.5 60 62 51.99 61.11 54.11 60.35 50.92 60.682
13 2.0 50 0 22.55 1.61 18.93 -5.43 -8.41 -0.7502
14 2.0 55 40 30.75 30.75 26.60 33.92 48.99 40.347
15 2.0 60 48 38.95 59.89 35.01 52.87 49.19 48.407
R20.4914 0.7162 0.5042 0.7712 0.8666 0.9773
F2.0352 1.3962 1.9834 1.2966 1.1539 1.0232
F CRITICAL = 2.4837
(1)=linear i.e. a_0+a_1 x_1+a_2 x_2
(2)=interaction i.e. a_0+a_1 x_1+a_2 x_2+a_3 x_1 x_2
(3)=pure quadratic i.e. a_0+a_1 x_1^2+a_2 x_2^2
(4)=quadratic i.e.a_0+a_1 x_1+a_2 x_2+a_3 x_1^2+a_4 x_1 x_2+a_5 x_2^2
(5)=3rd order polynomial i.e.a_0+a_1 x_1+a_2 x_2+a_3 x_1^2+a_4 x_1 x_2+a_5 x_2^2+ a_6 x_1^3+ a_7 x_1^2 x_2 a_9 x_2^3
(6)= 4th order polynomial i.e.a_0+...
X1=catalyst concentration as a percentage of weight of sample
X2=transesterication temperature(oC)
Y_EXPT=Yield from experiment (ml)
Effect of Catalyst and Transesterication on the Biodiesel Production Obidike Blessing Magarette et al
)a( )b(
)d()c(
66
3.4. Optimization of parameters
The main aim of optimization is to obtain the process
parameter which gives the maximum FAME yield.
This was done using different techniques namely:
MATLAB optimization toolbox and response
surface methodology (RSM)
3.4.1.MATLAB optimization toolbox
This optimization toolbox uses the principle of
NEWTON RAPHSON’s method of multivariable
optimization technique. Firstly, a function was
created in a function M-le as given below for
groundnut oil and PKO base FAMEs respectively.
Function f = projopt1(x)
f=-(-1702+35.48*x(1)+79.3*x(2)+1292*x(1).^2-
47.97*x(1).*x(2)-0.8628*x(2).^2-581.6*x(1).^3
7.308*x(1).^2.*x(2)+0.9442*x(1).*x(2).^2-
49.42*x(1).^4+14.72*x(1).^3.*x(2)0.4235*x(1).^
2.*x(2).^2);
Function f = pkoopt(x)
f=-(4261-9215*x(1)-160.1*x(2)+1465*x(1).^2+37
8.5*x(1).*x(2)+1.498*x(2).^2+874.3*x(1).^3-
108.5*x(1).^2.*x(2)-3.709*x(1).*x(2).^2-
56.99*x(1).^4-10.67*x(1).^3.*x(2)+1.315*x(1).^2
.*x(2).^2);
Notice however that negative of the function
was minimized, as this gives the negative of the
maximum value of the function. Next, a program
was written to minimize the functions respectively
using the “fmincon” command as below table.
x0 = [0.25 50]; A = [1 1]; B = 62; lb = [0.25
50]; ub = [2 60];
[x fval] = fmincon (@projopt1, x0, A, B,
,lb,ub)
x0 = [2 60]; A = [1 1]; B = 62; lb = [0.25 50];
ub = [2 60];
[x fval] = fmincon(@pkoopt,x0,A,B, lb,ub)
The optimum/maximum value for groundnut oil
FAME yield was obtained as 100.5141 with the
corresponding independent variables (X1, X2) of
(0.25, 51.3463). On the other hand, the optimum/
maximum value for PKO FAME yield was gotten
as 90.7254 with the corresponding independent
variables (X1, X2) of (0.4843,50).
3.4.2.MATLAB response surface methodology
The surface plots with the contour of the groundnut
oil and PKO FAME model were plotted as indicated
in Figure 3.
0
0.5
1
1.5
2
50
52
54
56
58
60
-50
0
50
100
catalyst concentration (%)
X: 0.425
Y: 50
Z: 89.77
temperature (oC)
FAME yield (ml)
0
10
20
30
40
50
60
70
80
0
0.5
1
1.5
2
50
52
54
56
58
60
0
20
40
60
80
100
120
catalyst concentration (%)
X: 0.6
Y: 58
Z: 104.7
temperature (oC)
FAME yield (ml)
10
20
30
40
50
60
70
80
90
100
Fig. 3. Surface plot of the groundnut oil and PKO base
FAME showing the optimal points
Anal. Methods Environ. Chem. J. 5 (3) (2022) 55-69
67
4. Conclusion
The results obtained from this present study
showed that the optimum reaction conditions for
the production of biodiesel from groundnut oil and
palm kernel oil was obtained at a trans-esterication
temperature of 55oC, 0.5 % w/v of CH3ONa catalyst,
mixing rate of 360 rpm and a reaction time of 90
minutes. At these conditions, an optimum yield of
98% and 84% by volume of FAME from groundnut
and palm kernel oil was obtained. The biodiesel
produced in this present study was characterized for
fuel properties, and it gave good promising results;
except for the pour points of biodiesel produced from
palm kernel oil was found to be somewhat higher,
which may point to potential difculties in cold
starts and lter plugging trouble. But however, the
biodiesel from this experiment would be a better
means in harnessing the supply of energy to the global
economy as compared to mineral diesel. The 4th order
polynomial model showed a good agreement with
the experimental results, demonstrating that these
methodologies were useful for modelling. Newton
Raphson’s multivariable optimization technique
gave an optimum yield of 100.5 mL and 90.7 mL for
groundnut oil and PKO FAME with a corresponding
catalyst concentration and trans-esterication
temperatures of (0.25%, 0.48%) and (51.3oC, 50oC).
While the surface plots gave optimum yields of 104.8
mL and 89.8 mL with the catalyst concentration and
trans-esterication temperatures of (0.6%, 0.425%)
and (58oC, 50oC) for groundnut oil and Palm Kernel
Oil (PKO) based Fatty Acid Methyl Esters (FAME).
The ndings obtained from this study showed that
the Newton Raphson’s multivariable optimization
technique and Response Surface Methodology
(RSM) were useful in enhancing the process
parameters of the trans-esterication reaction.
5. Conict of interest and Abbreviations
No conict of interest to declare.
FAME: Fatty Acid Methyl Ester; PKO: Palm
Kernel Oil; ASTM: American Society of Testing
and Materials; KOH: Potassium Hydroxide;
NaOH: Sodium Hydroxide; CH3OH: Methanol;
H2SO4: Sulphuric Acid; RSM: Response Surface
Methodology; FFA: Free Fatty Acid; CH3Ona:
Sodium Methoxide.
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