Chemical Engineering Journal: Yong-Ming Dai, Jhong-Syuan Wu, Chiing-Chang Chen, Kung-Tung Chen
Chemical Engineering Journal: Yong-Ming Dai, Jhong-Syuan Wu, Chiing-Chang Chen, Kung-Tung Chen
Chemical Engineering Journal: Yong-Ming Dai, Jhong-Syuan Wu, Chiing-Chang Chen, Kung-Tung Chen
h i g h l i g h t s
a r t i c l e i n f o a b s t r a c t
Article history: The LiAlO2 catalyst was prepared by solid-state reaction and then applied to the biodiesel production by
Received 17 March 2015 transesterication reaction between methanol and soybean oil. This was the rst attempt to use LiAlO2 as
Received in revised form 5 June 2015 a catalyst for biodiesel production. It was found that the catalyst of 4 (mol(Li2CO3)/mol(Al2O3)) being cal-
Accepted 9 June 2015
cined at 900 C showed the optimum activity. XRD, BET and FE-SEM demonstrated that the Li compound
Available online 16 June 2015
was incorporated into Al2O3 to form LiAlO2 with an enhanced basicity. The maximum conversion
achieved 97.5% with 2 h reaction time at 65 C, 24:1 M ratio of methanol to oil and 8 wt.% of catalyst.
Keywords:
LiAlO2 could be easily recovered and reused for six cycles without signicant deactivation.
LiAlO2
Solid-state reaction
2015 Elsevier B.V. All rights reserved.
Soybean oil
Transesterication
Biodiesel
http://dx.doi.org/10.1016/j.cej.2015.06.045
1385-8947/ 2015 Elsevier B.V. All rights reserved.
Y.-M. Dai et al. / Chemical Engineering Journal 280 (2015) 370376 371
from an industrial perspective, involving the surface active sites reaction parameters, such as reaction temperature, reaction time
being easily decayed upon exposing the catalyst to air. The methanol/oil ratio, catalyst amount and conversion of various oils
chemisorption of carbon dioxide and water on the surface sites to biodiesel.
form carbonates and hydroxyl groups, respectively [1319]. Most
of the basic solid catalysts need to be resolved the removal of water
and carbon dioxide from the surfaces to enhance their catalytic 2.3. Catalyst characterization
activities [20]. Chen et al. [21] and Wang et al. [22] found that
Li2CO3 catalytically tolerated the exposure to air. This presented The base strength of the as-prepared catalyst (H_) was deter-
important benets when considering the industrial application of mined using Hammett indicators. All samples were characterized
Li2CO3 as a solid catalyst, and the possibility of storing and han- using XRD with Cu Ka radiation (MAC MXP18, Tokyo, Japan,
dling the activated catalyst without taking special actions pre- k = 1.540 56 ). The microstructure of the as-prepared catalyst
vented from contact with the ambient air. was observed using a eld emission scanning electron microscope
Additionally, lithium-based catalysts showed a very high activ- (FE-SEM, JEOL JSM-7401F, Tokyo, Japan). The specic surface area
ity promoting transesterication reaction [2123]. Xie et al. [24] was analyzed using BrunauerEmmettTeller (BET) surface area
reported that signicant enhancement of catalytic activity was measurements (Micromeritics Company ASAP, 2010).
achieved for NaOH supported Al2O3 leading to a highest basicity.
Zabet et al. [25] reported that CaO was better dispersed on the
2.4. Analytical methods
Al2O3 support and enhanced the conversion. Modication of the
previously synthesized catalyst with Al2O3 to improve its structure
The FAME concentration expressed as the biodiesel purity of the
and properties was among the factors [24,25]. The compound
product was determined using a gas chromatograph (Thermo Trace
LiAlO2 had favorable thermophysical, chemical, and mechanical
GC Ultra, Thermo Co., Austin, Texas, USA) equipped with a ame
stabilities at high temperatures [26]. In addition, LiAlO2 could be
ionization detector and a capillary column (Tr-biodiesel (F),
used as a catalyst and catalytic support because of its excellent
Thermo Co., length: 30 m; internal diameter: 0.25 mm; and lm
electron transfer properties, high surface alkali, and a higher cat-
thickness: 0.25 lm). Nitrogen was used as the carrier gas at a ow
alytic activity than the common Al2O3 support [20]. Furthermore,
rate of 2 mL/min. The oven temperature program started at 120 C
it was suitable for transporting the reactants and products, result-
with an increase to 220 C at a rate of 30 C/min and an increase to
ing in a low diffusion resistance in the catalytic process. Therefore,
250 C at a rate of 10 C/min. The temperature of the programmed
LiAlO2 had great potential for the use as a catalyst.
temperature injector was 90 C for 0.05 min and increased to
In the present work, LiAlO2 was used as the heterogeneous cat-
260 C (programmed temperature) at a rate of 10 C/min. The
alyst in the soybean oil transesterication reaction with methanol
diluted solution with methyl heptadecanoate was added as an
for biodiesel production. To the best of our knowledge, this was the
internal FAME standard. FAME amounts were calculated using
rst attempt to use LiAlO2 as a catalyst for biodiesel production.
the internal standard method (according to the EN 14 103
Effects of several parameters, such as calcination temperatures,
method). The most common peaks were observed at C16:0,
methanol/oil molar ratio, catalyst amount, reaction temperature
C17:0, C18:0, C18:1, C18:2, and C18:3 as shown in Fig. 1. The con-
and reaction time, were studied. Moreover, the catalyst reuse in
version was determined according to the following equation
various oil transesterication reactions was evaluated in order to
perform a biodiesel production. RA AEI CEI AEI
Conversion % 100%
AEI m
2. Materials and methods
RA: Sum of areas of all peaks ranging from C14:0 to C24:0, AEI:
2.1. Catalyst preparation Heptadecanoic acid methyl ester IS area, CEI: Concentration
(mg/mL) of Heptadecanoic acid methyl ester solution, VEI: Volume
Soybean oil (Great Wall Enterprise Co., Taiwan), methanol (ACS of Heptadecanoic acid methyl ester solution added to sample, m:
grade, ECHO Chemical Co., Taiwan), Al2O3 (Shimakyus Pure Mass of the sample (mg).
Chemicals, Osaka, Japan), and Li2CO3 (Shimakyus Pure Chemicals,
Osaka, Japan) were used as received.
The solid-state reaction was used for the preparation of LiAl
mixed oxide catalyst. Al2O3 powder was added to an aqueous solu-
tion containing Li2CO3. After stirring and being dried at 110 C for
12 h. The mixture was thoroughly ground, followed by calcination
in air.
2.2. Transesterication
Fig. 3. (a) Morphology, (b) elemental analysis, and (c) nitrogen adsorption desorption isotherm and pore size distribution of LiAlO2 calcined in air at 900 C according to
FE-SEM.
Moreover, the amount of catalyst also affected the rate of reac- in the entire process. Therefore, the reaction was conducted at
tion. The LiAlO2 catalyst was used for studying the effect of catalyst various temperatures. According to Fig. 6, the conversion rate
loading (2, 4, 6 8 and 10 wt.%) with the reaction temperature 65 C increased with an increase in the reaction temperature. The
and the methanol/oil molar ratio 24:1. The conversion result is conversion gradually increased from 45 C to 75 C and reached
shown in Fig. 5. The conversion was found to increase with the the maximum 95.7 at 65 C. Both free fatty acid and triglycerides
increase in the catalyst amount from 2 to 8 wt.% and then decrease initially required the activation of their respective carboxylic or
with the increase in the catalyst amount above 8%. The conversion carbonyl functional groups to start the reaction. To favor the
was found to be the maximum at 8 wt.% of catalyst amount when methanol nucleophilic substitution on free fatty acids, a compara-
compared to 2, 4 and 6 wt.% of LiAlO2 catalyst amount. This might tively high reaction temperature was required to activate this
be due to the formation of mixing problem and resistance of mass carbonyl group [32]. Thus, temperature clearly inuenced the reac-
transfer [30] at higher catalyst loading. Wang et al. [31] also tion rate and biodiesel conversion. According to a previous study,
observed similar results, when the conversion rate increased with the reaction temperature dominated the reaction rate, and the con-
an increase in the catalyst amount. version rate increased with an increase in the reaction temperature
[33]. However, methanol was easily volatilized at 75 C to reduce
3.2.3. Effect of reaction temperature and time on the the amount of methanol to participate in the reaction. Fig. 5 indi-
transesterication reaction cated that the conversion was found to increase with the increase
Fig. 6 shows the effects of the reaction temperature and time on in the catalyst amount from 1 to 6 h and then decrease with the
the conversion rate. The reaction temperature was a crucial factor increase in the catalyst amount above 2 h. The conversion then
374 Y.-M. Dai et al. / Chemical Engineering Journal 280 (2015) 370376
Fig. 5. Inuence of the catalyst amount and methanol:oil molar ratio on the
conversion rate (reaction conditions: soybean oil; 12.5 g, reaction temperature;
65 C, and reaction time; 2 h).
rates of castor oil and waste cooking oil to biodiesel are shown in
Table 3. It was found that Li4SiO4 was the most suitable catalyst
giving 82.99% and 94.3% conversion. The good catalytic perfor-
mance was dependent on the strength of basic sites as well as upon
their amount. Table 3 also showed that the basic strength and the
catalytic activity were affected with various materials of solid base
catalyst, and the large basic strength led to the high activity at
transesterication reaction.
Table 2
Inuence of calcination temperature on the conversion rate.
*
Calcination temperature (C) Conversion (%)
600 32.65
700 31.75
800 63.46
900 94.62
1000 2.46
*
Reaction conditions: 12.5 g soybean oil; methanol/oil molar Fig. 6. Inuence of reaction time and reaction temperature on the conversion rate
ratio, 24:1; catalyst amount, 6 wt.%; reaction time, 2 h; methanol (reaction conditions: soybean oil; 12.5 g, methanol:oil molar ratio; 24:1, and
reux temperature and conventional heating method. catalyst amount; 6 wt.%).
Y.-M. Dai et al. / Chemical Engineering Journal 280 (2015) 370376 375
Table 3
Comparison of conversion by different catalyst.
Catalyst
LiAlO2 Li4SiO4 Li2SiO3 Li2CO3 CaO
Best conversion (%)a 98.06 98.17 96.12 95.50 96.16
Conversion (%)a (used for 5 cycles) 90.13 93.46 88.41 89.10 11.21
Exposure time (72 h)a 85.72 94.24 95.47 96.9 1.07
Castor oil (high oleic acid) 5.13 82.99 81.46 83.11 12.81
Waste cooking oil 2.80 94.31 86.51 84.68 25.39
Basic strength (H_) 9.8<H_<15.0 15.0<H_<18.4 15.0<H_<18.4 9.8<H_<15.0 15.0<H_<18.4
Reference 21, 23 35 22 2123, 35
a
For soybean oil.
Fig. 7. Inuence of LiAlO2 exposed to air for 2472 h on the conversion rate
(reaction conditions: soybean oil; 12.5 g, methanol:oil molar ratio; 24:1, and
catalyst amount; 6 wt.%). Fig. 9. Comparison of the conversion rates of various oils (reaction conditions:
soybean oil; 12.5 g, methanol:oil molar ratio; 24:1, catalyst amount; 6 wt.%, and
reaction temperature; 65 C).
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