Preparation, characterization and application of
heterogeneous solid base catalyst for biodiesel production
from soybean oil
Yihuai Li
a
, Fengxian Qiu
a,
*, Dongya Yang
a
, Xiaohua Li
b
, Ping Sun
b
a
School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, 212013 Zhenjiang, PR China
b
Jiangsu Provincial Key Laboratory of Power Machinery and Application of Clean Energy, 212013 Zhenjiang, PR China
article info
Article history:
Received 24 September 2010
Received in revised form
22 February 2011
Accepted 4 March 2011
Available online 24 March 2011
Keywords:
Heterogeneous catalyst
Transesterification
Biodiesel
Potassium hydroxide
Neodymium oxide
abstract

conventionaldiesel from petroleum, biodiesel is technicallyand
economically more competitive because of its renewability,
biodegradability, low emission profiles, high Flash point,
excellent lubricity and superior cetane number [4]. In addition,
the use of biodiesel has the potential to reduce both the levels of
pollutants and potential or probable carcinogens [5].
Biodiesel can be produced through transesterification of
vegetable oils and fats with methanol in the presence of a
suitable catalyst. In conventional homogeneous method of
fatty acid methyl ester (FAME) synthesis, the removal of cata-
lysts after reaction is unwanted step of biodiesel synthesis,
where a large amount of wastewater is produced during
neutralization the catalyst (NaOH or KOH) and FAME washing
during separation from side products (glycerol, salt). Acid-
catalyzed process often uses sulfonic acid and hydrochloric
* Corresponding author. Tel.: þ86 51188791800.
E-mail address: [email protected] (F. Qiu).
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
biomass and bioenergy 35 (2011) 2787e2795
0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biombioe.2011.03.009
acid as catalysts, however, the reaction time is very long
(48e96 h) even at reflux of methanol, and a high molar ratio of
methanol to oil is needed (30e150:1) [6].
Compared with homogeneous catalysts, heterogeneous
catalysts can provide green and recyclable catalytic systems
[7,8]. The advantage of heterogeneous catalyst usage is its fast
and easy separation from the reaction mixture without
requiring the use of neutralization agent. There are many solid

3
[18],andMgeAlhydrotalcites[19]have
also demonstrated some potential for activity in production of
biodiesel. However, these catalysts need more time (more than
3 h) to reach the higher biodiesel yield. The result will increase
the production cost due to the requirements for high tempera-
tures and a long time operation.
Neodymium oxide (Nd
2
O
3
) or rare earth sesquoxides is
widely used in various applications such as photonic, lumi-
nescent materials, catalyst for automotive industry, UV
absorbent, glass-polishing materials, and protective coatings.
However, in this work, a new type of catalyst for biodiesel
synthesis withKOH asactive componenton neodymium oxide
support was synthesized using the way of impregnation, and
reported the activity and selectivity of the basic solids for the
transesterification of soybean oil with methanol. A screening
of the reaction conditions has been carried out by examining
the effectof theconcentration ofcatalyst, theinitial methanol/
oil, catalyst/oil molar ratio, reaction temperature and time.
2. Experimental
2.1. Materials
Soybean oil was purchased from Jinlongyu Company (Fujian,
China). Methanol, zirconium dioxide (ZrO
2
), titanium dioxide
(TiO

kept 24 h. The catalytic carrier was previously calcined in
a mufflefor12hat600

C.Afterimpregnation,thecatalysts were
dried for12hat 100

C andthenthe solid was calcinedinamuffle
furnace at designed temperature for 12 h before use for the
reaction.
2.3. Characterization of the catalyst
FT-IR spectra of the samples were obtained between 4000 and
400 cm
À1
on a KBr powder with an FTIR spectrometer (AVATAR
360, Nicolet, Madison, USA). A minimum of 32 scans was signal-
averaged with a resolution of 2 cm
À1
in the 4000e400-cm
À1
range.
Scanning electron microscopy (SEM) images were obtained
with 20-kV accelerating voltage with a field emission scanning
electron microscope (S-4800, HITACHI Corp., Tokyo, Japan).
X-ray diffraction (XRD) patterns of selected samples were
obtained were recorded by the reflection scan with nickel-
filtered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray
generator was run at 40 kV and 70 mA. All the XRD measure-
ments were performed at 2q values between 10 and 80

.

tion) titration was used.
2.4. Transesterification of soybean oil and chemical
analyses
The transesterification reactions were performed at 60

Cin
a 125 ml three-neck reaction flask equipped with a condenser
by refluxing 10 mL of methanol (247 mmol) with 15.82 g of
soybean oil (commercial edible grade, acid value ¼ 0.976 mg
KOH/g, saponification index ¼ 188.6 mg KOH/g, and average
molecular weight ¼ 896.88 g/mol)and 0.95g of catalyst(6 wt.%).
The catalyst was activating at 773 K for 12 h before use for the
reaction. After the reaction completion, the samples were
separated from catalyst and glycerol by centrifuge. The glyc-
erol could be separated because it was insoluble in the esters
biomass and bioenergy 35 (2011) 2787e27952788
and had a much higher density. Then methanol was removed
using rotary evaporation and the obtained product was
analyzed by gas chromatography (GC) to determine the bio-
diesel yield (fatty acid methyl ester, FAME).
Reference materials and samples were analyzed by a 7890A
gas chromatograph (Agilent Technology Inc. USA), equipped
with a flame-ionization detector (FID) and a HP-5 capillary
column (30 m  0.32 mm  0.25 mm). Helium was used as the
carrier gas. The oven temperature ramp program was 135

Cfor
10 min, 170

Cat10

 100% (1)
where m
tricaprylin
¼ weight of the internal standard, A
B
¼ peak
area of FAME, f
tricaprylin
¼ response factor, A
tricaprylin
¼ peak
area of the internal standard, and m
s
¼ weight of the sample.
Determination of sulfur content of biodiesel was measured
by Inductively Coupled Plasma Emission Spectrometer (ICP)
using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA)
with a concentric nebulizer and CCD detectors technology.
Flash point was determined by a closed-cup tester (BF-02,
Dalian NorthAnalytical InstrumentsCo., Ltd.),using ASTM D 93.
3. Results and discussion
3.1. Screening of catalyst
The catalytic activity screening of Nd
2
O
3
loaded with different
potassium compounds (KOH,KI, KBrO
3
,C

O
3
showed catalytic activities. Thus, it is
essential to support potassium compounds on Nd
2
O
3
to
generate the catalytic activities for the transesterification reac-
tion. Among the catalysts tested, Nd
2
O
3
loaded with KOH, KI,
KBrO
3
or C
8
H
5
O
4
K exhibited comparatively high activities,
giving biodiesel yields higher than 80%. Especially, KOH/Nd
2
O
3
demonstrated the superior catalytic activity compared to the
other catalysts. When the transesterification was conducted
overtheKOH/Nd

3
> KBrO
3
/Nd
2
O
3
> C
8
H
5
O
4
K/
Nd
2
O
3
> KI/Nd
2
O
3
> KNO
3
/Nd
2
O
3
.
The base strengths of Nd

KI/Nd
2
O
3
or KNO
3
/Nd
2
O
3
sample possessed the weakest base
strength in the range of pK
BHþ
<7.2, consequently exhibiting
weak or no catalytic activity. As for the catalytic sites on KOH/
Nd
2
O
3
sample, it can also be proposed that the K
2
Ospecies,
which was possibly formed by dehydroxylation of the OH
groups, was at least a part of catalytically active sites. As
remarked above, it seems that the transesterification reaction
needs strongly basic sites.
The effect of supports on the activity of the catalyst was
listed in Table 2. Obviously, when KOH was supported on
Table 1 e Catalytic activity and base strength of Nd
2

O
3
<7.2 17.05
C
8
H
5
O
4
K/Nd
2
O
3
7.2e9.8 32.03
KNO
3
/Nd
2
O
3
<7.2 No reaction
Transesterification condition: methanol/oil molar ratio, 12:1; cata-
lyst amount 6 wt.%; reaction time, 3 h; reaction temperature, 60

C.
All catalysts were activating at 600

C for 12 h before use for the
reaction.
Table 2 e Catalytic activities and base strengths of KOH

the activity of the catalyst was different greatly. KOH/Nd
2
O
3
was the most active catalyst for the transesterification reac-
tion, giving a conversion of 89.70%. Over KOH/ZrO
2
, KOH/
Al
2
O
3
and KOH/TiO
2
catalysts, even though they possessed
different centers of a base strength, the high biodiesel yields of
85.43%, 88.87% and 86.47% were also achieved, respectively.
Thus, Nd
2
O
3
can be regarded as the best support. From these
discussions, KOH/Nd
2
O
3
showed the best catalytic activity. On
account of the high activity of the catalysts in the trans-
esterification reaction, KOH/Nd
2

were prepared. The effect of KOH
loading amounts on the biodiesel yield was shown in Table 3.It
can be seen from Table 3 that when the loading amount of KOH
increased from 14 wt.% to 30 wt.%, the biodiesel yield increased
from 80.47% to 89.52%. Then, the biodiesel yield decreased with
the loading amount of KOH. This is because the base strength
of catalyst increases with the loading amount of KOH. On the
other hand, the catalytic activity and activity sites also increase
with the loading amount of KOH. But, with further increase in
the amount of loaded KOH, the basicity may decrease the
surface basic sites, which resulted in a drop of the catalytic
activity towards the reaction. This is presumably due to the
coverage of surface basic sites by the excessive KOH. These
sites are inaccessible to incoming reactants when the amount
of loaded KOH exceeded 30 wt.%. Therefore, catalytic activity
and biodiesel yield decreased. On the basis of the results, the
optimum loading amount of KOH was 30 wt.%.
Moreover, the biodiesel yield of 30 wt.% KOH/Nd
2
O
3
sample
calcined at different temperatures was measured by the same
method, and the results are presented in Table 4. From the
Table 4, it can be observed that the maximum biodiesel yield,
reaching 90.02%, was obtained at a calcination temperature of
600

C. But, a low level of biodiesel yield was observed below
512 and above 700

3
samples with various
loading amounts of KOH were presented in Fig. 1. As can be
seen, when the loading amount of KOH was 14 wt.% (curve a),
diffraction peaks (2q ¼ 27.4

, 30.9

, 40.5

, 47.6

and 57.2

)
assigned to the amorphous Nd
2
O
3
support were registered on
the XRD patterns, and only a specie such as K
2
O(2q ¼ 29.6

)
was observed, indicating the good dispersion of K
2
OonNd
2
O

confirm by FT-IR spectrum of catalyst. Moreover, the intensi-
ties of some diffraction peaks (2q ¼ 29.6

, 32.1

, 38.8

, 41.2

and
51.6

) increased with increase of the loading amount of KOH.
On the other hand, the characteristic peaks of Nd
2
O
3
(27.4

,
30.9

, 40.5

, 47.6

and 57.2

) were almost unchanged on the XRD
patterns regardless of the loading amount of KOH. It is note-

ion of KOH could
insert in the vacant sites of Nd
2
O
3
, accelerating dissociative
dispersion and decomposition of KOH to form basic sites in
the activation process. The more potassium compounds are
loaded on the Nd
2
O
3
, the more free vacancies decrease, which
results in the surface enrichment of potassium species that is
probably considered to be the active sites for base-catalyzed
reactions. When the amount of potassium cations loaded on
Nd
2
O
3
was below the saturation uptake of K
þ
, it could be well
dispersed. As a result, the number of basic sites together with
the activities of the catalysts would increase with the potas-
sium contents. However, if Nd
2
O
3
was loaded with too much

2
O
3
samples, thus sug-
gesting a good dispersion of KOH on the surface of Nd
2
O
3
.
Based on these results, after loading of KOH, Nd
2
O
3
retained
its structure that was important for catalysis and therefore the
potassium species was found highly distributed upon the
surface of the support.
FTIR spectra of Nd
2
O
3
and KOHeNd
2
O
3
catalyst were
recorded and shown in Fig. 3. The spectrum of the support
shows sharp peak at 1475 cm
À1
. From the spectrum of catalyst,

in the case of potassium. The thermal behavior of 30 wt. % KOH/
Nd
2
O
3
sample was shown in Fig. 4. This figure showed that the
first weight loss at lower temperature (<200

C) corresponds to
the water loss from internal and external surfaces of the
samples. The second weight loss (200e400

C), is due to the
decomposition of the KOH and K
2
CO
3
. The last weight loss at
above 400

C is attributed to the decomposition of the K
2
Oand
the residual hydroxyl groups bonded to the oxide lattice. The
decomposition products of KOH, probably forming both K
2
O
speciesandNdeOeK groupsinthecomposite,werepossiblythe
main active sites for the transesterification reaction. In this
study, effect of repeated use of KOH/Nd

O
3
.
biomass and bioenergy 35 (2011) 2787e2795 2791
yields had no significant changes and were in excess of 90%
during the repeated experiments. It maintained sustained
activity even after being used for five times and the biodiesel
yield was only slightly decreased from 90.11% to 90.05%. This
was because neodymium oxide compounds are dissolvable in
methanol.
3.3. Influence of the transesterification reaction
conditions
The transesterification process consists of a sequence of three
consecutive reversible reactions where the triglyceride is
successively transformed into diglyceride, monoglyceride, and
finally intoglycerin andthe FAME. The molar ratio of methanol
to soybean oil is one of the important factors that affect the
conversion to methyl esters. Stoichiometrically, 3 mol of
methanol are required for each mole of triglyceride, but in
practice a higher molar ratio is employed in order to drive the
reaction towards completion and produce more methyl esters
as products. This is because that the biodiesel yield could be
improved by introducing excess amounts of methanol to shift
the equilibrium to the right-hand side. As represented in Fig. 5,
the biodiesel yields grew as the methanol-loading molar ratio
increased, and the biodiesel yield was increased considerably.
The maximum biodiesel yield (90.59%) was obtained when the
molar ratio was very close to 14:1. In comparison, the biodiesel
yield increased from 77.49% to 90.59% when the molar ratio
was increased from 6:1 to 14:1. However, beyond the molar

Fig. 5 e Effect of different molar of methanol to oil on the
biodiesel yield (catalyst amount, 6 wt.%; reaction time,
3.0 h; reaction temperature, 60

C).
Table 5 e Effect of repeated use of KOH/Nd
2
O
3
catalyst on
biodiesel yield.
Repeated times 12345
Biodiesel yield (%) 90.11 90.07 90.06 90.04 90.05
Transesterification condition: methanol/oil molar ratio, 12:1; cata-
lyst amount, 6 wt.%; reaction time, 1.5 h; reaction temperature,
60

C.
biomass and bioenergy 35 (2011) 2787e27952792
In the presence of heterogeneous catalysts, the reaction
mixture constitutes a three-phase system, oilemethanol-cata-
lyst, inwhich the reactionwouldbe sloweddown because of the
diffusion resistance between different phases. However, the
reaction rate can be accelerated at higher reaction tempera-
tures. In this paper, the synthesis of biodiesel from soybean oil
was conducted atvarious temperatures (40

C, 50

C, 60

indicated that the transesterification reaction was strongly
dependent upon the catalyst applied. As is evident from Fig. 8,
when the catalyst amount increased from 1.0% to 6.0%, the
biodiesel production yield was increased. However, with
further increase in the catalyst amount the biodiesel yield was
Fig. 6 e Effect of reaction time on the biodiesel yield
(methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%;
reaction temperature, 60

C).
Fig. 7 e Effect of reaction temperature on the biodiesel yield
(methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%;
reaction time, 1.5 h).
Fig. 8 e Effect of catalyst amount on the biodiesel yield
(methanol/oil molar ratio, 14:1; reaction time, 2.0 h;
reaction temperature, 60

C).
Table 6 e The various absorption peaks of biodiesel.
Wavenumber
(cm
À1
)
Group
attribution
Vibration type Absorption
intensity
3462.27 eOH Stretching Weak
3008.91 ¼ CeH Stretching Strong
2925.76 eCH

catalyst loading amount was found to be 6.0% in this system
and the maximum biodiesel yield reached to 92.40%.
From the above results, the reaction does not require too
much time to dispose of the products, for example, neutrali-
zation, washing and drying. If the catalyst can be used
commercially, filtration is a possible way to recycle the cata-
lyst and decrease the cost. As a heterogeneous solid base
catalyst, the prepared KOH/Nd
2
O
3
catalyst has a longer cata-
lyst lifetime and better stability than current homogeneous
catalysts. It is noncorrosive and environmentally benign. It
can be applied to produce biodiesel commercially.
3.4. Characterization and properties of biodiesel
FT-IR spectrum of the obtained biodiesel was listed in Table 6.
From the analysis of the Table 6, we could get the sample
including all groups which we needed. At the same time, it
proved that the compound was the kind of structures having
long-chain fatty acid esters.
The content of sulfur and its proper determination play an
important role regarding fuels and products of petrochemical
industry. The problem of appropriate determination of sulfur is
important both from environmental and analytical aspects,
because some specifications order to the compulsion decrease
of the concentration of sulfur (e.g. from 2005 their maximum
concentration is 50 mg/kg in fuels in the countries of European
Union). Over the past few decades, there are numerous spec-
troscopic techniques to analyze the qualitative and quantita-

The properties of biodiesel, density, cetane number, flash
point, cold filter plugging point, acid number, water content,
ash content and total glycerol content, were determined and
listed in the Table 8. Table 8 also showed comparisons of the
obtained biodiesel and the standards of biodiesel in china,
Europe and the United States. The properties of the obtained
biodiesel, in general, show many similarities, and therefore,
Table 8 e Comparison of properties of the obtained biodiesel and the standards of biodiesel in china, Europe and the
United States.
Item Obtained biodiesel China GB/T 20828e2007 USA ASTM D 6751e03 Europe EN 14214
Density (kg L
À1
) 0.896 (20

C) 0.82e0.90 (20

C) 0.82e0.90 (20

C) 0.86e0.90 (15

C)
Flash point (

C) 168 !130 ＞130 ＞120
Cold filter plugging point (

C) À5.0 eeSpring:0
Summer:À10
Autumn:À20
Sulfur content (w/w,%) 0.0065 0.05 0.0015 ＜0.001

Nd
2
O
3
loaded with KOH, which was prepared by impregnation
of powdered Nd
2
O
3
with an aqueous solution of KOH followed
by calcination at a high temperature, showed high catalytic
activities for the transesterification reaction. Both the K
2
O
species formed by the thermal decomposition of loaded KOH,
and the surface KeOeNd groups formed by saltesupport
interactions, were probably the main reasons for the catalytic
activity towards the reaction. The activities of the heteroge-
neous base catalysts correlated with their corresponding basic
properties. The catalyst with 30 wt.% KOH loading on Nd
2
O
3
and calcined at 600

C for 12 h was found to be the optimum
catalyst, which gave the best catalytic activity. When the
reaction was carried out at reflux of methanol, with a molar
ratio of methanol to oil of 14:1, a reaction time 1.5 h, a reaction
temperature 60

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