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- b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
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 abstract
Article history: A solid base catalyst was prepared by neodymium oxide loaded with potassium hydroxide
Received 24 September 2010 and investigated for transesterification of soybean oil with methanol to biodiesel. After
Received in revised form loading KOH of 30 wt.% on neodymium oxide followed by calcination at 600 C, the catalyst
22 February 2011 gave the highest basicity and the best catalytic activity for this reaction. The obtained
Accepted 4 March 2011 catalyst was characterized by means of X-ray diffraction (XRD), Fourier transform infrared
Available online 24 March 2011 spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric analysis
(TGA), N2 adsorptionedesorption measurements and the Hammett indicator method. The
Keywords: catalyst has longer lifetime and maintained sustained activity after being used for five
Heterogeneous catalyst times, and were noncorrosive and environmentally benign. The separate effects of the
Transesterification molar ratio of methanol to oil, reaction temperature, mass ratio of catalyst to oil and
Biodiesel reaction time were investigated. The experimental results showed that a 14:1 M ratio of
Potassium hydroxide methanol to oil, addition of 6.0% catalyst, 60 C reaction temperature and 1.5 h reaction
Neodymium oxide time gave the best results and the biodiesel yield of 92.41% was achieved. The properties of
obtained biodiesel are close to commercial diesel fuel and is rated as a realistic fuel as an
alternative to diesel.
ª 2011 Elsevier Ltd. All rights reserved.
1. Introduction excellent lubricity and superior cetane number [4]. In addition,
the use of biodiesel has the potential to reduce both the levels of
As conventional fuels are diminishing and environmental pollutants and potential or probable carcinogens [5].
pollution is aggravating, alternative fuels have gained signifi- Biodiesel can be produced through transesterification of
cant attention [1]. Biodiesel fuel, as a promising alternative vegetable oils and fats with methanol in the presence of a
diesel fuel to conventional fossil diesel produced by a catalytic suitable catalyst. In conventional homogeneous method of
transesterification of vegetable oils, animal fats and waste fatty acid methyl ester (FAME) synthesis, the removal of cata-
cooking oils with short chain alcohol, is becoming a favorable lysts after reaction is unwanted step of biodiesel synthesis,
biofuel in many regions of the world [2,3], Compared to where a large amount of wastewater is produced during
conventional diesel from petroleum, biodiesel is technically and neutralization the catalyst (NaOH or KOH) and FAME washing
economically more competitive because of its renewability, during separation from side products (glycerol, salt). Acid-
biodegradability, low emission profiles, high Flash point, catalyzed process often uses sulfonic acid and hydrochloric
* Corresponding author. Tel.: þ86 51188791800.
E-mail address: fxqiuchem@163.com (F. Qiu).
0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biombioe.2011.03.009
- 2788 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
acid as catalysts, however, the reaction time is very long kept 24 h. The catalytic carrier was previously calcined in
(48e96 h) even at reflux of methanol, and a high molar ratio of a muffle for 12 h at 600 C. After impregnation, the catalysts were
methanol to oil is needed (30e150:1) [6]. dried for 12 h at 100 C and then the solid was calcined in a muffle
Compared with homogeneous catalysts, heterogeneous furnace at designed temperature for 12 h before use for the
catalysts can provide green and recyclable catalytic systems reaction.
[7,8]. The advantage of heterogeneous catalyst usage is its fast
and easy separation from the reaction mixture without 2.3. Characterization of the catalyst
requiring the use of neutralization agent. There are many solid
heterogeneous acid- and alkali-catalysts for biodiesel synthesis. FT-IR spectra of the samples were obtained between 4000 and
Tungstated zirconia (WO3/ZrO2) was prepared by method of 400 cmÀ1 on a KBr powder with an FTIR spectrometer (AVATAR
impregnation was a promising heterogeneous acid catalyst [9]. 360, Nicolet, Madison, USA). A minimum of 32 scans was signal-
Various carbohydrate-derived and a carbon-based solid acid averaged with a resolution of 2 cmÀ1 in the 4000e400-cmÀ1
catalyst [10,11] have good catalytic activity to high free fatty range.
acid-containing waste oils. Unfortunately, the performances of Scanning electron microscopy (SEM) images were obtained
these acid catalysts are still inferior compared with the base with 20-kV accelerating voltage with a field emission scanning
catalysts. For this reason, a wide variety of solid bases have been electron microscope (S-4800, HITACHI Corp., Tokyo, Japan).
examined for transesterification reactions for biodiesel X-ray diffraction (XRD) patterns of selected samples were
synthesis. Example include CaO [12], SrO [13], KNO3 loaded on obtained were recorded by the reflection scan with nickel-
flyash [14], ZnOeLa2O3 [15] and zinc aluminate [16]. But, these filtered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray
heterogeneous catalysts require a high temperature to achieve generator was run at 40 kV and 70 mA. All the XRD measure-
the high conversion. Other heterogeneous base catalysts like ments were performed at 2q values between 10 and 80 .
CaMnO3 [17], KNO3/Al2O3 [18], and MgeAl hydrotalcites [19] have Thermogravimetric analysis (TGA) was performed on a Netz-
also demonstrated some potential for activity in production of sch instrument (STA 449C, Netzsch, Seligenstadt, Germany). The
biodiesel. However, these catalysts need more time (more than programmed heating range was from room temperature to
3 h) to reach the higher biodiesel yield. The result will increase 1300 C, at a heating rate of 10 C/min under a nitrogen atmo-
the production cost due to the requirements for high tempera- sphere. The measurement was taken using 6e10 mg samples.
tures and a long time operation. The nitrogen adsorption and desorption isotherms were
Neodymium oxide (Nd2O3) or rare earth sesquoxides is measured at À196 C using a NDVA2000e analytical system
widely used in various applications such as photonic, lumi- made by Quntachrome Corporation (USA). The specific surface
nescent materials, catalyst for automotive industry, UV area was calculated by Brunauer-Emmett-Teller (BET) method.
absorbent, glass-polishing materials, and protective coatings. Pore size distribution and pore volume were calculated by
However, in this work, a new type of catalyst for biodiesel Barrett-Joyner-Halenda (BJH) method.
synthesis with KOH as active component on neodymium oxide Hammett indicator experiments were conducted to deter-
support was synthesized using the way of impregnation, and mine the basic strength of each catalyst. The Hammett indica-
reported the activity and selectivity of the basic solids for the tors used were bromothymol blue (pKa ¼ 7.2), phenolphthalein
transesterification of soybean oil with methanol. A screening (pKa ¼ 9.8), 2,4-dinitroaniline (pKa ¼ 15), and 4-nitroaniline
of the reaction conditions has been carried out by examining (pKa ¼ 18.4). Typically, 300 mg of the catalyst was mixed with
the effect of the concentration of catalyst, the initial methanol/ 1 mL of a solution of Hammett indicators diluted in 10 mL
oil, catalyst/oil molar ratio, reaction temperature and time. methanol and allowed to sit for at least 2 h. After the equili-
bration, the color of the catalyst was noted. The basic strength of
the catalyst was taken to be higher than the weakest indicator
2. Experimental that underwent a color change and lower than the strongest
indicator that underwent no color change. To measure the
2.1. Materials basicity of solid bases, the method of Hammett indicator-
benzene carboxylic acid (0.02 mol/L anhydrous ethanol solu-
Soybean oil was purchased from Jinlongyu Company (Fujian, tion) titration was used.
China). Methanol, zirconium dioxide (ZrO2), titanium dioxide
(TiO2), alumina (Al2O3), neodymium oxide (Nd2O3), potassium 2.4. Transesterification of soybean oil and chemical
hydroxide (KOH), potassium iodide (KI), potassium bromate analyses
(KBrO3), potassium hydrogen phthalate (C8H5O4K) and potas-
sium nitrate (KNO3) were obtained from Sinopharm Chemical The transesterification reactions were performed at 60 C in
Reagent Co. Ltd., (Shanghai, China). All solvents were AR a 125 ml three-neck reaction flask equipped with a condenser
grade and were used without purification. by refluxing 10 mL of methanol (247 mmol) with 15.82 g of
soybean oil (commercial edible grade, acid value ¼ 0.976 mg
2.2. Preparation of catalyst KOH/g, saponification index ¼ 188.6 mg KOH/g, and average
molecular weight ¼ 896.88 g/mol) and 0.95 g of catalyst (6 wt.%).
All the catalysts were prepared by incipient wetness impreg- The catalyst was activating at 773 K for 12 h before use for the
nation of different porous medium supports with solution of reaction. After the reaction completion, the samples were
potassium compounds. For this purpose, the required amount separated from catalyst and glycerol by centrifuge. The glyc-
of aqueous KOH solution was slowly added to the support and erol could be separated because it was insoluble in the esters
- b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5 2789
and had a much higher density. Then methanol was removed
Table 1 e Catalytic activity and base strength of Nd2O3
using rotary evaporation and the obtained product was loaded with different potassium compounds.
analyzed by gas chromatography (GC) to determine the bio-
Catalyst Basic strength Biodiesel
diesel yield (fatty acid methyl ester, FAME).
(pKBHþ) yield (%)
Reference materials and samples were analyzed by a 7890A
gas chromatograph (Agilent Technology Inc. USA), equipped Nd2O3 KI/Nd2O3 > KNO3/Nd2O3.
area of the internal standard, and ms ¼ weight of the sample. The base strengths of Nd2O3 modified with different potas-
Determination of sulfur content of biodiesel was measured sium compounds were measured by using Hammett indica-
by Inductively Coupled Plasma Emission Spectrometer (ICP) tors. As evident in Table 1, loading of KBrO3, or C8H5O4K on the
using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA) surface of Nd2O3 generated the weaker basic sites with pKBHþ in
with a concentric nebulizer and CCD detectors technology. the range of 7.2e9.8. Taking both the base strength and the
Flash point was determined by a closed-cup tester (BF-02, catalytic activity into account, we can conclude that the
Dalian North Analytical Instruments Co., Ltd.), using ASTM D 93. observed activities of Nd2O3-supported catalysts seem to be
related to their base strengths, i.e. the higher base strengths of
the catalysts result in the higher conversions. In particular, the
KI/Nd2O3 or KNO3/Nd2O3 sample possessed the weakest base
3. Results and discussion strength in the range of pKBHþ
- 2790 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Table 3 e The effect of KOH loading amounts on the biodiesel yield.
KOH loading amount (%) 14 17 25 30 32
Basic strength (pKBHþ) 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15
Biodiesel yield (%) 80.47 81.52 85.72 89.52 73.45
Transesterification condition: methanol/oil molar ratio, 15:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
different carriers, the base strengths were almost equality, but 512 and above 700 C. Obviously, the biodiesel yield changes
the activity of the catalyst was different greatly. KOH/Nd2O3 with calcination temperatures parallel the changes in the
was the most active catalyst for the transesterification reac- catalytic activity for the transesterification reaction.
tion, giving a conversion of 89.70%. Over KOH/ZrO2, KOH/ Based on these results, the optimal preparation conditions
Al2O3 and KOH/TiO2 catalysts, even though they possessed of the catalyst are load KOH, support Nd2O3, loading amount
different centers of a base strength, the high biodiesel yields of 30% and calcination temperature of 600 C. Therefore, 30 wt.%
85.43%, 88.87% and 86.47% were also achieved, respectively. KOH/Nd2O3 catalyst was selected for further investigation of
Thus, Nd2O3 can be regarded as the best support. From these transesterification of soybean oil.
discussions, KOH/Nd2O3 showed the best catalytic activity. On
account of the high activity of the catalysts in the trans- 3.2. Catalyst characterizations
esterification reaction, KOH/Nd2O3 was, therefore, selected for
further investigation and its properties were studied in more A series of catalysts were synthesized by incipient wetness
detail. impregnation method and calcined at 600 C. In this high
A 14 wt.% (KOH to Nd2O3 weight ratio) KOH on Nd2O3 temperature, KOH decomposed into K2O. The powder X-ray
support was prepared by an impregnation method and the diffraction patterns of KOH/Nd2O3 samples with various
following procedure: a solid Nd2O3 support (25 g) was mixed loading amounts of KOH were presented in Fig. 1. As can be
with KOH (3.5 g) in 15 mL of water, and the resulting solid was seen, when the loading amount of KOH was 14 wt.% (curve a),
dried in an oven at 90 C for 24 h. The solid was then crushed diffraction peaks (2q ¼ 27.4 , 30.9 , 40.5 , 47.6 and 57.2 )
and calcined in air at 600 C for 12 h. Similarly, 17, 25, 30 and assigned to the amorphous Nd2O3 support were registered on
32 wt.% KOH loaded Nd2O3 were prepared. The effect of KOH the XRD patterns, and only a specie such as K2O (2q ¼ 29.6 )
loading amounts on the biodiesel yield was shown in Table 3. It was observed, indicating the good dispersion of K2O on Nd2O3
can be seen from Table 3 that when the loading amount of KOH in the form of a monolayer due to the interaction between K2O
increased from 14 wt.% to 30 wt.%, the biodiesel yield increased and the surface of the support at a low loading of KOH. And
from 80.47% to 89.52%. Then, the biodiesel yield decreased with when the loading amount of KOH was further increased to
the loading amount of KOH. This is because the base strength 25 wt. % (curve b), the new phase of K2O can be observed at
of catalyst increases with the loading amount of KOH. On the 32.1 and 51.6 . But, when the loading amount of KOH is
other hand, the catalytic activity and activity sites also increase further increased to over 30 wt. % (curves c and d), a new
with the loading amount of KOH. But, with further increase in phase of a compound containing potassium and neodymium
the amount of loaded KOH, the basicity may decrease the elements could be observed at 2q ¼ 25.8 , 38.8 and 41.2 [21].
surface basic sites, which resulted in a drop of the catalytic The phenomena can be a result from the incorporation of Kþ
activity towards the reaction. This is presumably due to the ions into the vacancies in the structure of the neodymium
coverage of surface basic sites by the excessive KOH. These oxide, or Kþ ions may react with hydroxyl groups to form
sites are inaccessible to incoming reactants when the amount NdeOeK on the surface during heat treatment. The result will
of loaded KOH exceeded 30 wt.%. Therefore, catalytic activity confirm by FT-IR spectrum of catalyst. Moreover, the intensi-
and biodiesel yield decreased. On the basis of the results, the ties of some diffraction peaks (2q ¼ 29.6 , 32.1 , 38.8 , 41.2 and
optimum loading amount of KOH was 30 wt.%. 51.6 ) increased with increase of the loading amount of KOH.
Moreover, the biodiesel yield of 30 wt.% KOH/Nd2O3 sample On the other hand, the characteristic peaks of Nd2O3 (27.4 ,
calcined at different temperatures was measured by the same 30.9 , 40.5 , 47.6 and 57.2 ) were almost unchanged on the XRD
method, and the results are presented in Table 4. From the patterns regardless of the loading amount of KOH. It is note-
Table 4, it can be observed that the maximum biodiesel yield, worthy that the solidestate reaction between the guest
reaching 90.02%, was obtained at a calcination temperature of compound and the surface of the support in the activation
600 C. But, a low level of biodiesel yield was observed below process is favorable for the catalyst to get a high catalytic
Table 4 e The effect of calcination temperature on the biodiesel yield.
Calcination temperature ( C) 311 422 512 600 700 790
Basic strength (pKBHþ) 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15 9.8 < H < 15
Biodiesel yield (%) 78.80 81.23 81.00 90.02 77.83 73.50
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
- b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5 2791
Nd2O3 samples showed the crystallites of 0.2e1 mm size.
Evidently, as shown in Fig. 2, no important difference was
observed between Nd2O3 and KOH/Nd2O3 samples, thus sug-
gesting a good dispersion of KOH on the surface of Nd2O3.
Based on these results, after loading of KOH, Nd2O3 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 Nd2O3 and KOHeNd2O3 catalyst were
recorded and shown in Fig. 3. The spectrum of the support
shows sharp peak at 1475 cmÀ1. From the spectrum of catalyst,
the new peaks at 880 and 706 cmÀ1 are attributed to the KeO
and KeOeNd bonds, respectively. Furthermore, the broad
band at around 3100e3300 cmÀ1 region could be partly
assigned to the stretching vibration of NdeOeK groups [22]
which Kþ ions could replace the protons of isolated hydroxy
groups to form NdeOeK groups in the activation process and
were probably considered to be the active species of this cata-
Fig. 1 e XRD patterns of (a) 14 wt.% KOH/Nd2O3, (b) 25 wt.% lyst. This achieves the same results as the XRD analysis.
KOH/Nd2O3, (c) 30 wt.% KOH/Nd2O3, (d) 32 wt.% KOH/Nd2O3. However, this vibration is well overlapped with the broad
vibration band of OH groups which is ascribed to OH stretching
vibration of the hydroxyl groups attached to the ctalyst surface,
activity. In the case of KOH/Nd2O3, the Kþ ion of KOH could in addition to water molecules absorbed from the atmosphere.
insert in the vacant sites of Nd2O3, accelerating dissociative The BET surface area, pore volume, and pore diameter of
dispersion and decomposition of KOH to form basic sites in Nd2O3 and 30 wt.% KOH/Nd2O3 catalyst were measured. The BET
the activation process. The more potassium compounds are surface area as well as the pore volume decreased with loading
loaded on the Nd2O3, the more free vacancies decrease, which potassium hydroxide, and this tendency was more outstanding
results in the surface enrichment of potassium species that is in the case of potassium. The thermal behavior of 30 wt. % KOH/
probably considered to be the active sites for base-catalyzed Nd2O3 sample was shown in Fig. 4. This figure showed that the
reactions. When the amount of potassium cations loaded on first weight loss at lower temperature (
- 2792 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Table 5 e Effect of repeated use of KOH/Nd2O3 catalyst on
biodiesel yield.
Repeated times 1 2 3 4 5
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.
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
Fig. 3 e FT-IR spectra of Nd2O3 and catalyst. yield increased from 77.49% to 90.59% when the molar ratio
was increased from 6:1 to 14:1. However, beyond the molar
ratio of 14:1, the excessively added methanol had no significant
effect on the production yield and the biodiesel yield was
yields had no significant changes and were in excess of 90% 90.12% at 16:1. The reason is that the catalyst content
during the repeated experiments. It maintained sustained decreased with increase of methanol content. Therefore, we
activity even after being used for five times and the biodiesel could conclude that to elevate the biodiesel production yield an
yield was only slightly decreased from 90.11% to 90.05%. This excess methanol feed was effective to a certain extent and the
was because neodymium oxide compounds are dissolvable in optimum molar ratio of methanol to oil was 14:1.
methanol. The dependence of the biodiesel yield on the reaction time
was investigated. The reaction time was varied in the range
3.3. Influence of the transesterification reaction 0.5e8 h. Fig. 6 revealed that the transesterification reaction
conditions was strongly dependent on reaction time, at the beginning
(
- b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5 2793
Fig. 6 e Effect of reaction time on the biodiesel yield Fig. 8 e Effect of catalyst amount on the biodiesel yield
(methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; (methanol/oil molar ratio, 14:1; reaction time, 2.0 h;
reaction temperature, 60 C). reaction temperature, 60 C).
In the presence of heterogeneous catalysts, the reaction
When increasing the amount of loading catalyst, the slurry
mixture constitutes a three-phase system, oilemethanol-cata-
(mixture of catalyst and reactants) was become too viscous
lyst, in which the reaction would be slowed down because of the
giving rise to a problem of mixing and a demand of higher
diffusion resistance between different phases. However, the
power consumption for adequate stirring. On the other hand,
reaction rate can be accelerated at higher reaction tempera-
when the catalyst loading amount was not enough, maximum
tures. In this paper, the synthesis of biodiesel from soybean oil
biodiesel yield could not be reached. To avoid this kind of
was conducted at various temperatures (40 C, 50 C, 60 C, 65 C
problem, an optimum amount of catalyst loading had to be
and 70 C). As shown in Fig. 7, the reaction rate was slow at low
investigated. The influence of the catalyst amounts was
temperatures, but the biodiesel yield first increased and then
studied at a 14:1 M ratio of methanol to soybean oil at reflux of
decreased with the increase of the reaction temperature.
methanol for 2 h. The catalyst amount was varied in the range
Generally, a more rapid reaction rate could be obtained at high
of 1.0% and 9.0%. These percentages were weight fractions of
temperatures, which is due to the endothermic nature of
the oil supplied for this reaction. The reaction profile of Fig. 8
transesterification reaction [25], but at high temperatures,
indicated that the transesterification reaction was strongly
methanol was vaporized and formed a large number of bubbles,
dependent upon the catalyst applied. As is evident from Fig. 8,
which inhibited the reaction on the three-phase interface. The
when the catalyst amount increased from 1.0% to 6.0%, the
optimum reaction temperature was 60 C and biodiesel yield
biodiesel production yield was increased. However, with
arrived at 92.41%.
further increase in the catalyst amount the biodiesel yield was
Table 6 e The various absorption peaks of biodiesel.
Wavenumber Group Vibration type Absorption
(cmÀ1) attribution intensity
3462.27 eOH Stretching Weak
3008.91 ¼ CeH Stretching Strong
2925.76 eCH2 Asymmetric Strong
stretching vibration
2855.00 eCH2 Symmetric stretching Strong
vibration
1743.54 eC]O Stretching Strong
1461.48 eCH2 Shear-type vibration Middling
1360.75 eCH3 Bending vibration Middling
1017.78 CeOeC Anti-symmetric Weak
stretching vibration
1171.41 CeOeC Symmetric stretching Middling
vibration
Fig. 7 e Effect of reaction temperature on the biodiesel yield
722.75 eCH2 Plane rocking Weak
(methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; vibration
reaction time, 1.5 h).
- 2794 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
because some specifications order to the compulsion decrease
Table 7 e The properties of ICP-OES spectrometer.
of the concentration of sulfur (e.g. from 2005 their maximum
Type Intrepid XP Radial ICP-OES concentration is 50 mg/kg in fuels in the countries of European
Nebulizer Concentric, with a cyclonic spray chamber Union). Over the past few decades, there are numerous spec-
RF-generator 40.68 MHz crystal-controlled troscopic techniques to analyze the qualitative and quantita-
Power 1200 W tive elemental composition of fuels. For example, inductively
Reflected power 20 W coupled plasma atomic emission spectroscopy (ICPeAES),
Observation high 6 mm above the coil
inductively coupled plasma mass spectroscopy (ICPeMS) and
Optical system Czerny-Turner vacuum-monochromator
flame or graphic furnace atomic absorption spectroscopy (AAS)
Grating Holographic, 1800 groves/mm
Focal length 0.75m were adopted. Each technique has advantageous properties in
Optical range 160e800 nm terms of analytical figures of merit. The atomic absorption and
Resolution 1st order: 0.018 nm emission techniques are typically used for analysis of the
Detector Photomultiplier products of hydrocarbon industry. The ICP technique is a fast
Emission lines used l1 ¼ 180.731 nm analytical method, but needs preliminary sample preparation
For the S analysis l2 ¼ 181.970 nm
(e.g. digestion). In this work, the sulfur content of biodiesel was
carried out by Inductively Coupled Plasma Emission Spec-
trometer (ICP) using Intrepid XP Radial ICP-OES (VISTA-MPX,
decreased, which was possibly due to a mixing problem
Varian, USA) with a concentric nebulizer and CCD detectors
involving reactants, products and solid catalyst. The optimum
technology. After performing the background equivalent
catalyst loading amount was found to be 6.0% in this system
concentration experiment to test the instrument sensitivity,
and the maximum biodiesel yield reached to 92.40%.
the ICP operating conditions applied are presented in Table 7.
From the above results, the reaction does not require too
In order to determine the sulfur content, the biodiesel was
much time to dispose of the products, for example, neutrali-
carried out by nitrification firstly. A certain amount of biodiesel
zation, washing and drying. If the catalyst can be used
was added to concentrated hydrochloric acid (8 mL) and
commercially, filtration is a possible way to recycle the cata-
concentrated nitric acid (2 mL), and placed overnight. Subse-
lyst and decrease the cost. As a heterogeneous solid base
quently, the mixture was gently filtered and got clear liquid,
catalyst, the prepared KOH/Nd2O3 catalyst has a longer cata-
then the clear liquid was evaporated in the fuming cupboard
lyst lifetime and better stability than current homogeneous
about 20 min. Calibration standards were made up from some
catalysts. It is noncorrosive and environmentally benign. It
standard solutions of sulfur. The ranges of the calibration
can be applied to produce biodiesel commercially.
curves (5 points) were selected to match the expected different
concentrations standard solution for the sulfur element of the
3.4. Characterization and properties of biodiesel sample investigated. Linearity was checked in the range of
0e40 mg/g. From the calibration curve, the sulfur content of
FT-IR spectrum of the obtained biodiesel was listed in Table 6. biodiesel was obtained. The sulfur content of the obtained
From the analysis of the Table 6, we could get the sample biodiesel was listed in Table 8.
including all groups which we needed. At the same time, it The properties of biodiesel, density, cetane number, flash
proved that the compound was the kind of structures having point, cold filter plugging point, acid number, water content,
long-chain fatty acid esters. ash content and total glycerol content, were determined and
The content of sulfur and its proper determination play an listed in the Table 8. Table 8 also showed comparisons of the
important role regarding fuels and products of petrochemical obtained biodiesel and the standards of biodiesel in china,
industry. The problem of appropriate determination of sulfur is Europe and the United States. The properties of the obtained
important both from environmental and analytical aspects, 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
À1
Density (kg L ) 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 e e Spring:0
Summer:À10
Autumn:À20
Sulfur content (w/w,%) 0.0065 0.05 0.0015 ＜0.001
Cetane value 56 !49 !47 ＞51
Acid value (KOH) (mg gÀ1) 0.6 0.8 ＜0.8 ＜0.5
Water content (w/w,%) 0.04 0.05 0.05 0.05
Ash content (w/w,%) 0.018 0.05 0.02 0.02
Total glycerol content (w/w,%) 0.020 0.024 0.024 0.025
- b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5 2795
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