Applied Clay Science 102 (2014) 121–127
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Applied Clay Science
journal homepage: www.elsevier.com/locate/clay
Research paper
Effect of the chemical composition of smectites used in KF/Clay catalysts
on soybean oil transesterification into methyl esters
L.C.A. Silva a, E.A. Silva a, M.R. Monteiro b, C. Silva c, J.G. Teleken d, H.J. Alves d,⁎
a
Postgraduate Program in Chemical Engineering, State University of Western Paraná — UNIOESTE, Rua da Faculdade 645, Jardim La Salle, 85903-000 Toledo, PR, Brazil
Materials Development and Characterization Center — CCDM, Department of Materials Engineering — DEMa, Federal University of São Carlos — UFSCar, Rod. Washington Luiz, km 235,
13560-971 São Carlos, SP, Brazil
c
Postgraduate Program in Chemical Engineering, State University of Maringa — UEM, Av. Colombo 5790, 87020-900 Maringa, PR, Brazil
d
Laboratory of Catalysis and Biofuel Production (LabCatProBio), Biofuels Technology Course, Federal University of Paraná — UFPR, Rua Pioneiro 2153, Jardim Dallas, 85950-000 Palotina, PR, Brazil
b
a r t i c l e
i n f o
Article history:
Received 28 June 2014
Received in revised form 24 August 2014
Accepted 28 August 2014
Available online 11 October 2014
Keywords:
Heterogeneous catalysis
Modified smectites
Transesterification
a b s t r a c t
Three smectites with distinct chemical compositions were treated with potassium fluoride and the catalysts thus
obtained were used in the transesterification of soybean oil with methanol. The smectites and catalysts were examined by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and the BET
gas adsorption method to verify if their chemical composition influences the properties of the resulting catalysts.
An experimental design was applied to evaluate the effect of the variables of the transesterification reaction: temperature, mass ratio of the catalyst, and the molar ratio of oil to methanol. The results indicate that increasing the
SiO2/Al2O3 ratio of the smectites causes an increase in the basicity of the catalysts, and hence, in the conversion
rate into methyl esters.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Biodiesel, a biofuel produced from renewable sources, is biodegradable, presents low exhaust gas emissions, has a high flash point, excellent lubricity, and is miscible with diesel in any ratio (Hoekman and
Robbins, 2012; Huang et al., 2012; Oh et al., 2012; Tariq et al., 2012).
Biodiesel is produced mainly by means of transesterification reactions of fats and oils, in which triacylglycerol reacts with alcohol in the
presence of a catalyst to form esters (methyl or ethyl), which are biodiesel and glycerol (Demirbas, 2009; Semwal et al., 2011; Atadashi et al.,
2012).
Industrial scale biodiesel production is usually performed with homogeneous alkaline catalysis. This process provides very high yields, although the purification steps are costly (Ye et al., 2010; Cordeiro et al.,
2011; Fan et al., 2012).
The use of heterogeneous catalysts mitigates some of the problems
encountered in the homogeneous biodiesel production process. These
catalysts withstand elevated temperatures in various operating conditions, and not only facilitate the separation steps of the reaction product
but can also be separated easily by simple filtration (Borges and Díaz,
2012). The catalytic activity of materials is related to the surface structure of solids at specific sites called active centers or sites (Agarwal
⁎ Corresponding author. Tel. + 55 44 3211 8544; fax: + 55 44 3211 8548.
E-mail address: [email protected] (H.J. Alves).
http://dx.doi.org/10.1016/j.clay.2014.08.026
0169-1317/© 2014 Elsevier B.V. All rights reserved.
et al., 2012). The catalytic action is triggered by the temporary adsorption of one or more reagents on the surface of the catalyst, the rearrangement of bonds and the desorption of products (Figueiredo and
Ribeiro, 1988; Kouzu and Hidaka, 2012). Heterogeneous catalysts can
be classified as acid or base, and this is determined by acid–base character (Brönsted and/or Lewis) of the active sites present on the surface
(Schmal, 2011).
The literature cites many heterogeneous acid catalysts, including
transition metal oxides such as zirconium oxide, titanium oxide and
zinc oxide, whose surface is strongly acidic (Silva et al., 2012).
Several studies about heterogeneous base catalysts in transesterification reactions have been conducted. Some examples are simple
oxides such as calcium oxide (CaO), or mixed oxides, and oxides such
as Al2O3 or SiO2 are commonly used as supports (Chouhan and Sarma,
2011; Cordeiro et al., 2011). Recent studies have evaluated the use of
clay minerals as heterogeneous catalysts.
The versatility and low cost of smectites give them a promising potential as catalysts or catalyst supports in various industrial processes.
Smectites are natural materials resulting from the mixture of different
minerals, including clay minerals whose particles have equivalent
spherical diameters of less than 2 μm. Smectites contain clay minerals
that may occur in either pure or mixed form in various proportions
with other non-clay minerals, organic matter and other impurities.
The main clay minerals that may appear in mixed form are quartz, feldspar, mica, calcite and hematite (Gomes, 1986).
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L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
Table 1
Hammett indicators, colors and H_ value.
Table 3
Chemical composition of the smectites.
Indicator
Basic color
Acid color
H_
Dimethyl yellow
Neutral red
Thymol blue
Phenolphthalein
2,4-Dinitroaniline
Yellow
Yellow
Blue
Pink
Red
Red
Red
Red
Colorless
Yellow
3.3
6.8
8.8
9.8
15.0
Some of the properties of smectites, such as ion exchange capacity
and increased interlayer spacing, can influence their physicochemical
characteristics. Due to their high surface area, an important characteristic in heterogeneous catalysts, and their abundance in nature, smectites
have been exploited for application as catalysts in various reactions
(Luckham and Rossi, 1999; Nagendrappa, 2011). Some treatments
applied to smectites can alter their structure and thus improve their
catalytic performance. The processes most commonly used for this
purpose are: intercalation and pillaring, treatments with mineral
acids, and impregnation with inorganic salts (Fujita et al., 2006; Centi
and Perathoner, 2008; Chouhan and Sarma, 2011).
The literature reports on a few studies that evaluated the use of
smectites modified by the salt impregnation method and employed in
the transesterification of vegetable oils, and obtained good results
(Boz et al., 2009; Wen et al., 2010). Our previous study aimed at detecting the activity of the new catalyst KF/Clay in the transesterification reaction for the production of methyl esters (Alves et al., 2014).
The purpose of this study was to evaluate the performance of catalysts prepared from smectites, with different chemical compositions
and modified by impregnation of KF, in transesterification reactions,
and to investigate the influence of the chemical composition on the formation of base active sites and catalytic activity.
2. Experimental
2.1. Preparation of catalysts by treating smectites with KF
Three different samples of Brazilian smectites were used in this
study, and are herein referred to as Clay 1, Clay 2, and Clay 3. Their respective catalysts, obtained by the impregnation method in an aqueous
solution of KF (Xu et al., 2010), are referred to as KF/Clay 1, KF/Clay 2,
and KF/Clay 3.
To begin with, a suspension of 15% w/v of smectite in a solution of
1.7 mol·L−1 of KF was prepared and kept under constant stirring in a
reflux system for 30 min at a temperature of 353 K. The material was
dried in an electric oven at 383 K for 24 h. The resulting catalysts were
then ground in a mortar and sifted through a 325 mesh Tyler sieve
(45-μm sieve opening). Because the material is hygroscopic, it was
Content (wt.%)
SiO2
Al2O3
Fe2O3
CaO
MgO
TiO2
Na2O
K2O
LOIa
SiO2/ Al2O3
a
Clay 1
Clay 2
Clay 3
66.26
16.21
1.24
1.96
4.91
0.19
1.39
0.32
5.25
4.09
63.20
16.71
5.47
0.86
2.62
0.30
4.02
0.23
6.59
3.78
57.50
18.30
8.23
0.71
2.62
1.05
2.49
0.73
7.18
3.14
Loss on ignition.
dried again for 2 h at a temperature of 383 K and stored in a desiccator
until it was used.
2.2. Characterization
The raw smectites were analyzed by X-ray fluorescence spectroscopy
(Philips MagiX-Pro XRF spectrometer) to determine their chemical composition. The X-ray diffraction (XRD) analysis of the raw smectites and
KF/Clay catalysts (Siemens Kristalloflex diffractometer) was performed
in the range of 4° b 2θ b 40°, with CuKα radiation (λ = 1.54056 nm,
40 kV, 40 mA), a nickel filter, and a speed of 0.5°/min (Boz et al., 2009).
Samples of raw smectite and smectite treated with KF were diluted at
1% in dry KBr, homogenized in a mortar, pelletized, and analyzed by Fourier transform infrared spectroscopy in the range of 4000 to 500 cm−1
(Bomem MB Series FTIR spectrometer), with a resolution of 4 cm−1.
The particle morphology, size and chemical composition of the smectites
and KF/Clay catalysts were determined by scanning electron microscopy
coupled to energy dispersive X-ray spectroscopy (SEM/EDS) (FEI Quanta
440) (Liu et al., 2012).
N2 adsorption (physisorption) analyses were carried out at a temperature of 77 K to determine the surface area of the samples of raw
smectite and KF/Clay catalysts (Quantachrome Co. Nova-2000). Prior
to the analysis, the samples were heat-treated at 393 K for 2 h. The surface areas were determined by the BET (Brunauer, Emmett and Teller)
equation, using p/p0 ≤ 0.3 (Brunauer et al., 1938).
The strength of the basic sites in the samples was determined quantitatively using Hammett indicators (Fraile et al., 2009; Xu et al., 2010).
Table 2
Experimental conditions used in the factorial design.
Experiment
Catalyst (%)
Molar ratio (oil/alcohol)
Temperature (K)
1
2
3
4
5
6
7
8
PCa
PCa
15
15
15
15
25
25
25
25
20
20
1:6
1:6
1:6
1:6
1:9
1:9
1:9
1:9
1:7.5
1:7.5
323
353
323
353
323
353
323
353
338
338
a
Central point.
Fig. 1. Diffractograms of the smectites.
L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
Fig. 2. Diffractograms of the KF/Clay catalysts.
Fig. 4. Infrared spectra of the catalysts.
Table 1 lists these indicators, the range of colors, and their respective
H_values.
An amount of 0.15 g of each smectite and catalyst sample was stirred
for 30 min in an orbital shaker (Solab SL220, Piracicaba, Brazil) at
230 rpm, with 2 mL of methanol indicator solution at a concentration
of 0.1 mg/mL, followed by titration with a methanol solution of
0.01 mol·L−1 benzoic acid.
Leaching assays of basic sites were also carried, which involved placing approximately 0.5 g of sample in contact with 50 mL of ultrapure
water and shaking in an orbital shaker at 230 rpm for 1 h. The mixture
was then filtered, 5 mL of methanol solution of 0.1 mg/mL phenolphthalein was added to the filtrate, and it was titrated with a methanol solution of 0.01 mol·L−1 benzoic acid. Methanol solutions were used in the
procedures to simulate the real conditions of the transesterification reaction. These analyses enabled us to ascertain the influence exerted by
KF treatment of the smectites on the basicity of the samples.
2.3. Potassium leaching assays
In the potassium leaching assays, 1.0 g of each sample (raw smectite
and catalysts) was refluxed for 10 h in a Soxhlet extractor in the
Fig. 3. Infrared spectra of the smectites.
Fig. 5. SEM micrographs of: (a) Clay, and (b) KF/Clay catalyst.
123
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L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
Table 4
Specific surface area of smectites and catalysts.
Sample
Área (m2·g−1)
Clay 1
Clay 2
Clay 3
KF/Clay 1
KF/Clay 2
KF/Clay 3
44.2
26.9
84.8
4.9
4.9
5.0
Table 6
Leaching of the catalysts.
Catalyst
Leachable basicity
(mmol·g−1)
KF/Clay 1
KF/Clay 2
KF/Clay 3
0.0060
0.0198
0.0507
Table 2 shows the values used in the design applied to the three different KF/Clay catalysts.
presence of 150 mL of methanol. After the reflux assays, the samples
were oven-dried and weighed again to assess their mass loss. The potassium content in the resulting methanol was analyzed in order to identify
possible leaching. A quantitative analysis of potassium content was performed in a Micronal® B462 flame spectrophotometer with 0.1 mg·L−1
resolution, operating with liquefied petroleum gas under 0.8 bar pressure to generate the flame. The system was calibrated with 5 ultrapure
KCl standards (JT Baker®) at concentrations of 0.6, 1.3, 2.6, 3.9, and
5.2 mg·L−1.
2.4. Reaction assays
The experiments were performed in a stainless steel batch reactor
with a volume of 50 cm3. The autogenous pressure was recorded by a
manometer attached to the reactor, and the temperature was controlled
by heating an oil bath. Soybean oil was poured into the reactor together
with the catalyst and anhydrous methanol (Aldrich). The system was
heated to the desired temperature and kept under constant magnetic
stirring for 1 h, after which the heat and agitation were turned off. The
reactor was rapidly cooled and opened, and the products were filtered
through a vacuum filtration system, and centrifuged for 15 min at
3000 rpm. The upper phase, rich in methyl esters, was separated for distillation of the excess methanol and subsequent chromatographic
analysis.
2.5. Experimental design
To optimize the conversion of soybean oil into methyl esters, a 23
factorial experimental design was used for the three different catalysts
(Neto et al., 2002). The variables selected were the oil-to-methanol
molar ratio, catalyst content, and reaction temperature. The following
effects were observed: (1) the effect of the catalyst concentration of
15% or 25% on the oil mass; (2) the effect of the reaction temperatures
of 323 or 353 K; and (3) the effect of the molar ratio of 1:6 or 1:9 soybean oil:methyl alcohol; using as response variable the percent conversion obtained in the transesterification reaction.
2.6. Gas Chromatography (GC) — Analysis of Fatty Acid Methyl Esters
(FAME)
The samples were first subjected to methanol evaporation in a
vacuum oven (338 K, 0.05 MPa) until they reached a constant
weight, and then to the analytical procedures described by Silva
et al. (2010). The samples were injected (1 μL) in triplicate into a
gas chromatograph (Agilent GC 7890), equipped with a FID and a
capillary column (ZB-WAX, 30 m × 0.25 mm × 0.25 μm). Column
temperature was programmed from 393 K, holding 2 min, heating
to 453 K at 10 K/min, holding 3 min, and to 503 K at 5 K/min, holding
2 min. Helium was used as carrier gas, and the injection and detector
temperatures were 523 K with a split ratio of 1:50. The compounds
were quantified in the analysis based on the standard (Standard
UNE-EN, 2003).
3. Results and discussion
3.1. Characterization of raw smectites and catalysts
Quantification by XRF of the percentage of oxides in the raw smectite
samples revealed that they present different SiO2/Al2O3 ratios (Table 3).
This ratio is very important because the basicity of the catalyst can be influenced by the aluminum atoms in the smectite structure. The Clay 1
sample had the highest SiO2/Al2O3 ratio, largest amount of alkali oxides
such as CaO and MgO, and the lowest amount of Fe2O3, which is acidic.
The constituent elements of smectite affect the acid–base character of
its surface, its water adsorption capacity, thermal stability, and other
properties (Luckham and Rossi, 1999).
The following crystalline phases were identified in the samples
based on the XRD analysis: montmorillonite (Na–Mg–Al–Si4O11)
(JCPDS: 07-0304), quartz (SiO2) (JCPDS: 46-1045) and albite
(Na(AlSi3O8)) (JCPDS: 76-1819), a type of feldspar, all of which are commonly found in smectites. Fig. 1 compares the peaks of the diffraction
patterns of the raw smectites.
Table 5
Basicity and total number of basic sites in smectite and catalyst samples.
Basicity (mmol·g−1)a
Sample
Clay 1
Clay 2
Clay 3
KF/Clay 1
KF/Clay 2
KF/Clay 3
a
b
pKBH = 3.3
pKBH = 6.8
pKBH = 8.8
pKBH = 9.8
pKBH = 15.0
Total
0.142
0.131
0.052
0.013
0.014
0.045
0.216
0.198
–
b
b
b
b
0.155
0.183
0.097
0.255
0.250
0.118
b
b
b
Standard error ± 0.01 mmol·g−1.
Not detected.
0.038
b
b
b
b
0.019
0.026
0.059
0.020
0.026
0.059
b
b
b
L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
Table 7
Potassium leaching of smectites and catalysts.
Sample
Clay 1
Clay 2
Clay 3
KF/Clay 1
KF/Clay 2
KF/Clay 3
a
b
Leaching
Initial mass
(g)
Mass loss
(%)
Potassium
leached (mg·mL−1)
Potassium
leached (%)a
1.0020
1.0097
1.0100
1.0118
1.0080
1.0257
1.80
1.78
2.08
5.37
6.02
4.40
b
b
b
b
b
b
0.49
1.04
0.63
16.44
34.98
20.86
Considered the total amount of potassium contained in 150 mL of methanol to 100%.
Not detected.
The XRF analysis and XRD diffractograms appear to indicate that the
larger amount of silicon in Clay 1 occurs mainly in the form of montmorillonite, since no high intensity peaks of free quartz were detected.
Based on the XRD diffraction patterns of the catalysts shown in Fig. 2,
it is clear that due to the KF treatment, the intensity of the peaks attributed to montmorillonite decreased, indicating a possible distortion in
the arrangement of the constituent ions in the octahedral and tetrahedral layers. In view of the probable ion exchange, it is clear that the
KF/Clay catalysts are materials with more amorphous characteristics.
Furthermore, the diffraction patterns of the catalysts indicate the presence of a new crystalline phase K2FeF4 (JCPDS: 19-0969), which was
formed after the KF treatment. The new crystalline phase is a result of
the combination of Fe2+ ions contained in the smectite structure and
the K+ and F− ions present in the KF solution. Since no peaks corresponding to the crystalline phase of potassium fluoride were observed,
we believe the KF is highly dispersed on the smectite surface and/or
completely dissociated, leading to the formation of new crystalline
phases from the interaction between the inorganic salt and the smectite
structure, thereby contributing to fix the impregnated material.
Based on the literature (Fujita et al., 2006; Boz et al., 2009; Alves
et al., 2014), adsorption of K+ ions may occur on the surface around
the active sites, which contributes to increase the catalyst's basicity.
The terminal OH− groups present in the structure of the smectite may
be replaced by F− ions, resulting in formation of basic sites X–F− K+
(where X = Al or Si).
The infrared spectra in Fig. 3 (raw smectites) show regions of O\H
vibrations in the range of 3600 to 3400 cm−1, bands at 1600 cm−1 characteristic of the O\H bond of physisorbed water, Si\O vibrations of
quartz and montmorillonite (1000 cm− 1) that are present in large
quantities in the smectite samples, Al\OH vibrations (900 cm−1), and
Si\O\Al vibrations (between 500 and 900 cm−1) (Centi and
Perathoner, 2008). The infrared spectra of the catalysts (Fig. 4) show
125
not only bands characteristic of the compounds in the raw smectite
but also the presence of bands between 1250 and 1500 cm− 1 corresponding possibly to the vibration of CO2−
3 , indicating probably a formation of potassium carbonate in response to the treatment of the smectite
with KF (Alves et al., 2014). The bands between 3600 and 3400 cm−1
corresponding to the O\H vibrations are broader in the spectra of the
catalyst, possibly due to the larger amount of adsorbed water.
The SEM analysis indicated that the surface texture of the smectite
particles/agglomerates (Fig. 5(a)) changed significantly after the treatment with KF, showing increased surface roughness and the emergence
of numerous small crystals partially joining the particles/agglomerates,
as can be observed in the micrograph of the KF/Clay catalyst (Fig. 5(b))
(Liu et al., 2012).
The surface areas of the samples revealed by the BET method
(Table 4) show that the raw smectites have different surface areas. The
KF/Clay catalysts have very similar surface areas, which are smaller
than those of raw smectites because their pores and layers are filled by
F− and K+ ions.
The results of the quantitative analysis of basicity are described in
Table 5. Treating the raw smectites with potassium fluoride increased
the number of basic sites by approximately 64% in Clay 1 and by 36%
and 21%, respectively, in Smectites 2 and 3.
The catalyst samples were also subjected to a leaching test in order
to check a possible loss of basicity through leaching of the basic sites,
which could diminish the catalytic activity in a transesterification
reaction.
Table 6 presents the results of the leaching assay, showing that the
KF/Clay 1 catalyst has the lowest potentially leachable basicity when
treated with water, and also the largest number of basic sites, as indicated in the quantitative analysis of basic sites (Table 5). The KF/Clay 3 catalyst showed the highest leachable basicity, and also the lowest number
of basic sites among the three tested catalysts.
3.2. Potassium leaching
Based on the amount of KF used in the treatment of the smectite, it
was found that 1 g of catalyst contained 0.442 g of potassium. This finding enabled us to calculate the amount of potassium in the catalyst samples subjected to the leaching assay, considering an ideal KF dispersion
of the smectite particles, and in addition, the mass of leached potassium
in contact with 150 mL of methanol during the assay. Table 7 lists the results, showing that the KF/Clay 2 catalyst underwent the highest potassium leaching rate, followed by the KF/Clay 3 catalyst, and that the KF/
Clay 1 catalyst underwent the lowest potassium leaching rate. Potassium leaching may result in homogeneous catalysis in transesterification
reactions through the formation of potassium methoxide ions in the
presence of water (Silva et al., 2012). Therefore, the potassium leaching
Table 8
Experimental design of catalysts.
Experiment
Catalyst (%)
Temperature (K)
Molar ratio (oil/alcohol)
Conversion
KF/Clay 1 (%)
Conversion
KF/Clay 2 (%)
Conversion
KF/Clay 3 (%)
1
2
3
4
5
6
7
8
PCa
PCa
15
15
15
15
25
25
25
25
20
20
353
353
323
323
353
353
323
323
338
338
1:6
1:9
1:6
1:9
1:6
1:9
1:6
1:9
1:7.5
1:7.5
76.16
68.48
76.37
43.87
71.87
89.19
32.49
81.70
61.60
63.39
56.98
70.22
74.42
82.58
76.60
76.46
47.62
72.18
55.60
56.25
56.04
69.30
58.74
79.49
65.06
76.71
68.96
74.31
70.41
68.86
a
Central point.
126
L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
(a)
KF-Clay 1
29.80726
1by3
19.90782
(2)Temp.
7.360335
(3) RM
6.276536
1by2
2.896648
(1)Cat.
-1.97486
2by3
p=.05
2
R = 0,834
Standardized Effect Estimate (Absolute Value)
(b)
KF-Clay 2
48.50769
1by2
35.24615
(3) RM
-15.0923
2by3
(1)Cat
-8.72308
(2)Temp.
2.661538
1by3
2.323077
p=.05
2
R = 0,667
Standardized Effect Estimate (Absolute Value)
(c)
1:6; ii) catalyst concentration of 5%; and iii) reaction temperature of
353 K in 1 h of reaction. The percentages of conversion into methyl
esters using the KF/Clay 1, KF/Clay 2, and KF/Clay 3 catalysts were
65.66%, 39.10% and 27.89%, respectively. Based on these results, an experimental design was applied to investigate the influence of the reaction variables on the conversion rates and determine which reaction
conditions and catalyst lead to the best results.
Table 8 presents the results of soybean oil conversion into methyl esters using the catalysts. For the same experimental design, the reaction
that yielded the highest conversion was achieved with the KF/Clay 1
catalyst (89.19%) which was attributed to the higher basicity of this catalyst compared to the other two. The catalysts exhibited good activity in
relatively mild conditions.
The effect of the variables on the conversion rates was assessed
using Statistica 7.0 software. Fig. 6 depicts the estimated linear isolated
effects and interaction of the independent variables: catalyst content —
(1) Cat; reaction temperature — (2) temp; and oil-to-methanol molar
ratio — (3) RM. A small p-value means that the probability of obtaining
a value of the test statistic as observed is very unlikely, thus leading to
the rejection of the null hypothesis.
The fit of the model was evaluated by analysis of variance (ANOVA).
From the results shown in Table 9 we note that, using the three catalysts, the model explains the variations, enabling it to be used for predictive purposes, at a significant level of 5% (p-value = 0.05). It was proven
that the model is significantly applying the F test (ratio of two variances,
one being of random distribution), where when the calculated value of F
(F cal.) is greater than the tabulated F (F Sta), and the value of p too low,
the model is significant.
Based on the results of the KF/Smectite catalysts (Fig. 6), an estimate was made of which variables most strongly affected this conversion in the transesterification reactions analyzed here. The
interaction between the variable catalyst and molar ratio has a stronger effect on the KF/Clay 1 and KF/Clay 3 catalysts, while the interaction between catalyst and temperature has a greater influence on the
KF/Clay 2 catalyst.
KF-Clay 3
3.4. Conversion into methyl esters
(3) RM
16.45484
(1)Cat
The highest yield in the conversion of methyl esters was 89.2, which
was obtained with the KF/1 Clay catalyst under the following experimental conditions: catalyst mass ratio of 25%, temperature of 353 K,
and oil:alcohol molar ratio of 1:9. In parallel, applying the reaction conditions that yielded the highest conversion rate, the raw smectites were
tested as catalysts, which confirmed that no conversion into methyl esters occurred. Therefore, the treatment of raw smectites with KF solution is really effective for developing potential catalysts for the
production of methyl esters.
6.925806
-5.4871
1by3
(2)Temp.
-4.64194
3.674194
1by2
2by3
-.383871
2
p=.05
R = 0,945
Standardized Effect Estimate (Absolute Value)
Fig. 6. Estimated linear effects and interactions of variables of the catalysts: (a) KF/Clay 1
catalyst, (b) KF/Clay 2 catalyst, and (c) KF/Clay 3 catalyst.
results are consistent with the leaching results of basic sites, and the KF/
Clay 1 catalyst showed the highest stability.
3.3. Experimental design
Preliminary tests were performed with reaction KF/Clay catalysts
under the following conditions: i) soybean oil:methanol molar ratio of
4. Conclusions
The use of smectites treated with KF yielded promising results in
transesterification reactions, since high conversion rates of soybean
oil into methyl esters were achieved. The catalyst preparation method is very simple and easy to reproduce. The KF/Clay catalysts developed here have a basic character, and a good correlation was found
between the SiO 2/Al2O 3 ratio of the raw smectites, the number of
active basic sites in the catalysts, and the percent conversion into
methyl esters. In this regard, the KF/Clay 1 catalyst showed the best
results, since it was prepared using Clay 1, which has the highest
SiO2 /Al2 O3 ratio, resulting in the largest number of basic active
sites and consequently in the highest conversion into methyl esters.
Moreover, the KF/Clay 1 catalyst also exhibited greater stability in
the leaching tests, making it promising for the production of
biodiesel.
L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127
127
Table 9
ANOVA of catalysts.
Parameter
Source variation
Sum squares
Degree of freedom
Media squares
F Cal. Sta.
KF/Clay 1
Regression
Residue
Total
Regression
Residue
Total
Regression
Residue
Total
2670.242
1.602
2671.844
1237.821
0.211
1238.032
486.882
1.201
488.083
8
1
9
8
1
9
8
1
9
333.780
1.602
208.352
5.32
b0.05
154.728
0.211
733.306
5.32
b0.05
60.860
1.201
50.666
5.32
b0.05
KF/Clay 2
KF/Clay 3
Acknowledgments
H. J. Alves gratefully acknowledges the CNPq for its financial support
(Grant no. 479207/2013-5).
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