Applied Clay Science 102 (2014) 121–127

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Applied Clay Science

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Research paper

Effect of the chemical composition of smectites used in KF/Clay catalystson 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, Brazilb 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, Brazilc Postgraduate Program in Chemical Engineering, State University of Maringa— UEM, Av. Colombo 5790, 87020-900 Maringa, PR, Brazild Laboratory of Catalysis and Biofuel Production (LabCatProBio), Biofuels Technology Course, Federal University of Paraná—UFPR, Rua Pioneiro 2153, JardimDallas, 85950-000 Palotina, PR, Brazil

⁎ Corresponding author. Tel. + 55 44 3211 8544; fax: +E-mail address: helquimica@gmail.com (H.J. Alves).

http://dx.doi.org/10.1016/j.clay.2014.08.0260169-1317/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 28 June 2014Received in revised form 24 August 2014Accepted 28 August 2014Available online 11 October 2014

Keywords:Heterogeneous catalysisModified smectitesTransesterification

Three smectiteswith distinct chemical compositionswere treatedwith potassium fluoride and the catalysts thusobtainedwere used in the transesterification of soybean oil with methanol. The smectites and catalysts were ex-amined by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), Fourier transform infrared spectros-copy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and the BETgas adsorptionmethod to verify if their chemical composition influences the properties of the resulting catalysts.An experimental designwas applied to evaluate the effect of the variables of the transesterification reaction: tem-perature, mass ratio of the catalyst, and themolar ratio of oil tomethanol. The results indicate that increasing theSiO2/Al2O3 ratio of the smectites causes an increase in the basicity of the catalysts, and hence, in the conversionrate into methyl esters.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Biodiesel, a biofuel produced from renewable sources, is biodegrad-able, presents low exhaust gas emissions, has a high flash point, excel-lent lubricity, and is miscible with diesel in any ratio (Hoekman andRobbins, 2012; Huang et al., 2012; Oh et al., 2012; Tariq et al., 2012).

Biodiesel is produced mainly by means of transesterification reac-tions of fats and oils, in which triacylglycerol reacts with alcohol in thepresence of a catalyst to form esters (methyl or ethyl), which are biodie-sel and glycerol (Demirbas, 2009; Semwal et al., 2011; Atadashi et al.,2012).

Industrial scale biodiesel production is usually performed with ho-mogeneous alkaline catalysis. This process provides very high yields, al-though 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 problemsencountered in the homogeneous biodiesel production process. Thesecatalysts withstand elevated temperatures in various operating condi-tions, and not only facilitate the separation steps of the reaction productbut can also be separated easily by simple filtration (Borges and Díaz,2012). The catalytic activity of materials is related to the surface struc-ture of solids at specific sites called active centers or sites (Agarwal

55 44 3211 8548.

et al., 2012). The catalytic action is triggered by the temporary adsorp-tion of one or more reagents on the surface of the catalyst, the rear-rangement of bonds and the desorption of products (Figueiredo andRibeiro, 1988; Kouzu and Hidaka, 2012). Heterogeneous catalysts canbe classified as acid or base, and this is determined by acid–base charac-ter (Brönsted and/or Lewis) of the active sites present on the surface(Schmal, 2011).

The literature cites many heterogeneous acid catalysts, includingtransition metal oxides such as zirconium oxide, titanium oxide andzinc oxide, whose surface is strongly acidic (Silva et al., 2012).

Several studies about heterogeneous base catalysts in transes-terification reactions have been conducted. Some examples are simpleoxides such as calcium oxide (CaO), or mixed oxides, and oxides suchas Al2O3 or SiO2 are commonly used as supports (Chouhan and Sarma,2011; Cordeiro et al., 2011). Recent studies have evaluated the use ofclay minerals as heterogeneous catalysts.

The versatility and low cost of smectites give them a promising po-tential as catalysts or catalyst supports in various industrial processes.Smectites are natural materials resulting from the mixture of differentminerals, including clay minerals whose particles have equivalentspherical diameters of less than 2 μm. Smectites contain clay mineralsthat may occur in either pure or mixed form in various proportionswith other non-clay minerals, organic matter and other impurities.The main clay minerals that may appear in mixed form are quartz, feld-spar, mica, calcite and hematite (Gomes, 1986).

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Table 1Hammett indicators, colors and H_ value.

Indicator Basic color Acid color H_

Dimethyl yellow Yellow Red 3.3Neutral red Yellow Red 6.8Thymol blue Blue Red 8.8Phenolphthalein Pink Colorless 9.82,4-Dinitroaniline Red Yellow 15.0

Table 3Chemical composition of the smectites.

Content (wt.%)

Clay 1 Clay 2 Clay 3

SiO2 66.26 63.20 57.50Al2O3 16.21 16.71 18.30Fe2O3 1.24 5.47 8.23CaO 1.96 0.86 0.71MgO 4.91 2.62 2.62TiO2 0.19 0.30 1.05Na2O 1.39 4.02 2.49K2O 0.32 0.23 0.73LOIa 5.25 6.59 7.18SiO2/ Al2O3 4.09 3.78 3.14

a Loss on ignition.

122 L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

Some of the properties of smectites, such as ion exchange capacityand increased interlayer spacing, can influence their physicochemicalcharacteristics. Due to their high surface area, an important characteris-tic in heterogeneous catalysts, and their abundance in nature, smectiteshave been exploited for application as catalysts in various reactions(Luckham and Rossi, 1999; Nagendrappa, 2011). Some treatmentsapplied to smectites can alter their structure and thus improve theircatalytic performance. The processes most commonly used for thispurpose are: intercalation and pillaring, treatments with mineralacids, and impregnation with inorganic salts (Fujita et al., 2006; Centiand Perathoner, 2008; Chouhan and Sarma, 2011).

The literature reports on a few studies that evaluated the use ofsmectites modified by the salt impregnation method and employed inthe transesterification of vegetable oils, and obtained good results(Boz et al., 2009;Wen et al., 2010). Our previous study aimed at detect-ing the activity of the new catalyst KF/Clay in the transesterification re-action for the production of methyl esters (Alves et al., 2014).

The purpose of this study was to evaluate the performance of cata-lysts prepared from smectites, with different chemical compositionsand modified by impregnation of KF, in transesterification reactions,and to investigate the influence of the chemical composition on the for-mation 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 thisstudy, and are herein referred to as Clay 1, Clay 2, and Clay 3. Their re-spective catalysts, obtained by the impregnation method in an aqueoussolution 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 of1.7 mol·L−1 of KF was prepared and kept under constant stirring in areflux system for 30 min at a temperature of 353 K. The material wasdried in an electric oven at 383 K for 24 h. The resulting catalysts werethen ground in a mortar and sifted through a 325 mesh Tyler sieve(45-μm sieve opening). Because the material is hygroscopic, it was

Table 2Experimental conditions used in the factorial design.

Experiment Catalyst (%) Molar ratio (oil/alcohol) Temperature (K)

1 15 1:6 3232 15 1:6 3533 15 1:6 3234 15 1:6 3535 25 1:9 3236 25 1:9 3537 25 1:9 3238 25 1:9 353PCa 20 1:7.5 338PCa 20 1:7.5 338

a Central point.

dried again for 2 h at a temperature of 383 K and stored in a desiccatoruntil 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 com-position. The X-ray diffraction (XRD) analysis of the raw smectites andKF/Clay catalysts (Siemens Kristalloflex diffractometer) was performedin 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 at1% in dry KBr, homogenized in amortar, pelletized, and analyzed by Fou-rier 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 smectitesand KF/Clay catalysts were determined by scanning electron microscopycoupled to energy dispersive X-ray spectroscopy (SEM/EDS) (FEI Quanta440) (Liu et al., 2012).

N2 adsorption (physisorption) analyses were carried out at a tem-perature of 77 K to determine the surface area of the samples of rawsmectite and KF/Clay catalysts (Quantachrome Co. Nova-2000). Priorto the analysis, the samples were heat-treated at 393 K for 2 h. The sur-face 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 quan-titatively using Hammett indicators (Fraile et al., 2009; Xu et al., 2010).

Fig. 1. Diffractograms of the smectites.

Fig. 2. Diffractograms of the KF/Clay catalysts.Fig. 4. Infrared spectra of the catalysts.

123L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

Table 1 lists these indicators, the range of colors, and their respectiveH_values.

An amount of 0.15 g of each smectite and catalyst samplewas stirredfor 30 min in an orbital shaker (Solab SL220, Piracicaba, Brazil) at230 rpm, with 2 mL of methanol indicator solution at a concentrationof 0.1 mg/mL, followed by titration with a methanol solution of0.01 mol·L−1 benzoic acid.

Leaching assays of basic siteswere also carried, which involved plac-ing approximately 0.5 g of sample in contact with 50 mL of ultrapurewater and shaking in an orbital shaker at 230 rpm for 1 h. The mixturewas thenfiltered, 5mL ofmethanol solution of 0.1mg/mL phenolphtha-lein was added to the filtrate, and it was titrated with a methanol solu-tion of 0.01 mol·L−1 benzoic acid. Methanol solutions were used in theprocedures to simulate the real conditions of the transesterification re-action. These analyses enabled us to ascertain the influence exerted byKF 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 smectiteand catalysts) was refluxed for 10 h in a Soxhlet extractor in the

Fig. 3. Infrared spectra of the smectites. Fig. 5. SEMmicrographs of: (a) Clay, and (b) KF/Clay catalyst.

image of Fig.�2image of Fig.�3image of Fig.�4image of Fig.�5

Table 4Specific surface area of smectites and catalysts.

Sample Área (m2·g−1)

Clay 1 44.2Clay 2 26.9Clay 3 84.8KF/Clay 1 4.9KF/Clay 2 4.9KF/Clay 3 5.0

Table 6Leaching of the catalysts.

Catalyst Leachable basicity(mmol·g−1)

KF/Clay 1 0.0060KF/Clay 2 0.0198KF/Clay 3 0.0507

124 L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

presence of 150 mL of methanol. After the reflux assays, the sampleswere oven-dried andweighed again to assess theirmass loss. The potas-sium content in the resultingmethanolwas analyzed in order to identifypossible leaching. A quantitative analysis of potassium content was per-formed in aMicronal® B462 flame spectrophotometerwith 0.1mg·L−1

resolution, operating with liquefied petroleum gas under 0.8 bar pres-sure to generate the flame. The system was calibrated with 5 ultrapureKCl standards (JT Baker®) at concentrations of 0.6, 1.3, 2.6, 3.9, and5.2 mg·L−1.

2.4. Reaction assays

The experiments were performed in a stainless steel batch reactorwith a volume of 50 cm3. The autogenous pressure was recorded by amanometer attached to the reactor, and the temperaturewas controlledby heating an oil bath. Soybean oil was poured into the reactor togetherwith the catalyst and anhydrous methanol (Aldrich). The system washeated to the desired temperature and kept under constant magneticstirring for 1 h, after which the heat and agitation were turned off. Thereactor was rapidly cooled and opened, and the products were filteredthrough a vacuum filtration system, and centrifuged for 15 min at3000 rpm. The upper phase, rich inmethyl esters, was separated for dis-tillation of the excess methanol and subsequent chromatographicanalysis.

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-methanolmolar ratio, catalyst content, and reaction temperature. The followingeffects were observed: (1) the effect of the catalyst concentration of15% or 25% on the oil mass; (2) the effect of the reaction temperaturesof 323 or 353 K; and (3) the effect of the molar ratio of 1:6 or 1:9 soy-bean oil:methyl alcohol; using as response variable the percent conver-sion obtained in the transesterification reaction.

Table 5Basicity and total number of basic sites in smectite and catalyst samples.

Sample Basicity (mmol·g−1)a

pKBH = 3.3 pKBH = 6.8 pKBH =

Clay 1 0.142 0.013 b

Clay 2 0.131 0.014 0.038Clay 3 0.052 0.045 b

KF/Clay 1 b 0.216 0.019KF/Clay 2 b 0.198 0.026KF/Clay 3 b – 0.059

a Standard error ± 0.01 mmol·g−1.b Not detected.

Table 2 shows the values used in the design applied to the three dif-ferent KF/Clay catalysts.

2.6. Gas Chromatography (GC) — Analysis of Fatty Acid Methyl Esters(FAME)

The samples were first subjected to methanol evaporation in avacuum oven (338 K, 0.05 MPa) until they reached a constantweight, and then to the analytical procedures described by Silvaet al. (2010). The samples were injected (1 μL) in triplicate into agas chromatograph (Agilent GC 7890), equipped with a FID and acapillary column (ZB-WAX, 30 m × 0.25 mm × 0.25 μm). Columntemperature was programmed from 393 K, holding 2 min, heatingto 453 K at 10 K/min, holding 3min, and to 503 K at 5 K/min, holding2 min. Heliumwas used as carrier gas, and the injection and detectortemperatures were 523 K with a split ratio of 1:50. The compoundswere quantified in the analysis based on the standard (StandardUNE-EN, 2003).

3. Results and discussion

3.1. Characterization of raw smectites and catalysts

Quantification byXRFof thepercentage of oxides in the rawsmectitesamples revealed that they present different SiO2/Al2O3 ratios (Table 3).This ratio is very important because the basicity of the catalyst can be in-fluenced by the aluminum atoms in the smectite structure. The Clay 1sample had the highest SiO2/Al2O3 ratio, largest amount of alkali oxidessuch as CaO and MgO, and the lowest amount of Fe2O3, which is acidic.The constituent elements of smectite affect the acid–base character ofits surface, its water adsorption capacity, thermal stability, and otherproperties (Luckham and Rossi, 1999).

The following crystalline phases were identified in the samplesbased 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 ofwhich are com-monly found in smectites. Fig. 1 compares the peaks of the diffractionpatterns of the raw smectites.

8.8 pKBH = 9.8 pKBH = 15.0 Total

b b 0.155b b 0.183b b 0.0970.020 b 0.2550.026 b 0.2500.059 b 0.118

Table 7Potassium leaching of smectites and catalysts.

Sample Leaching

Initial mass(g)

Mass loss(%)

Potassiumleached (mg·mL−1)

Potassiumleached (%)a

Clay 1 1.0020 1.80 b b

Clay 2 1.0097 1.78 b b

Clay 3 1.0100 2.08 b b

KF/Clay 1 1.0118 5.37 0.49 16.44KF/Clay 2 1.0080 6.02 1.04 34.98KF/Clay 3 1.0257 4.40 0.63 20.86

a Considered the total amount of potassium contained in 150 mL of methanol to 100%.b Not detected.

125L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

The XRF analysis and XRD diffractograms appear to indicate that thelarger amount of silicon in Clay 1 occursmainly in the form of montmo-rillonite, 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 attrib-uted to montmorillonite decreased, indicating a possible distortion inthe arrangement of the constituent ions in the octahedral and tetrahe-dral layers. In view of the probable ion exchange, it is clear that theKF/Clay catalysts are materials with more amorphous characteristics.Furthermore, the diffraction patterns of the catalysts indicate the pres-ence of a new crystalline phase K2FeF4 (JCPDS: 19-0969), which wasformed after the KF treatment. The new crystalline phase is a result ofthe combination of Fe2+ ions contained in the smectite structure andthe K+ and F− ions present in the KF solution. Since no peaks corre-sponding to the crystalline phase of potassium fluoride were observed,we believe the KF is highly dispersed on the smectite surface and/orcompletely dissociated, leading to the formation of new crystallinephases from the interaction between the inorganic salt and the smectitestructure, thereby contributing to fix the impregnated material.

Based on the literature (Fujita et al., 2006; Boz et al., 2009; Alveset al., 2014), adsorption of K+ ions may occur on the surface aroundthe active sites, which contributes to increase the catalyst's basicity.The terminal OH− groups present in the structure of the smectite maybe 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 char-acteristic of the O\H bond of physisorbed water, Si\O vibrations ofquartz and montmorillonite (1000 cm−1) that are present in largequantities in the smectite samples, Al\OH vibrations (900 cm−1), andSi\O\Al vibrations (between 500 and 900 cm−1) (Centi andPerathoner, 2008). The infrared spectra of the catalysts (Fig. 4) show

Table 8Experimental design of catalysts.

Experiment Catalyst (%) Temperature (K) Molar ratio (o

1 15 353 1:62 15 353 1:93 15 323 1:64 15 323 1:95 25 353 1:66 25 353 1:97 25 323 1:68 25 323 1:9PCa 20 338 1:7.5PCa 20 338 1:7.5

a Central point.

not only bands characteristic of the compounds in the raw smectitebut also the presence of bands between 1250 and 1500 cm−1 corre-sponding possibly to the vibration of CO32−, indicatingprobably a forma-tion of potassiumcarbonate in response to the treatment of the smectitewith 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 thecatalyst, possibly due to the larger amount of adsorbed water.

The SEM analysis indicated that the surface texture of the smectiteparticles/agglomerates (Fig. 5(a)) changed significantly after the treat-mentwith KF, showing increased surface roughness and the emergenceof 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. TheKF/Clay catalysts have very similar surface areas, which are smallerthan those of raw smectites because their pores and layers are filled byF− and K+ ions.

The results of the quantitative analysis of basicity are described inTable 5. Treating the raw smectites with potassium fluoride increasedthe 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 orderto check a possible loss of basicity through leaching of the basic sites,which could diminish the catalytic activity in a transesterificationreaction.

Table 6 presents the results of the leaching assay, showing that theKF/Clay 1 catalyst has the lowest potentially leachable basicity whentreatedwithwater, and also the largest number of basic sites, as indicat-ed in the quantitative analysis of basic sites (Table 5). The KF/Clay 3 cat-alyst showed the highest leachable basicity, and also the lowest numberof basic sites among the three tested catalysts.

3.2. Potassium leaching

Based on the amount of KF used in the treatment of the smectite, itwas found that 1 g of catalyst contained 0.442 g of potassium. This find-ing enabled us to calculate the amount of potassium in the catalyst sam-ples subjected to the leaching assay, considering an ideal KF dispersionof the smectite particles, and in addition, themass of leached potassiumin contactwith 150mLofmethanol during the assay. Table 7 lists the re-sults, showing that the KF/Clay 2 catalyst underwent the highest potas-sium leaching rate, followed by the KF/Clay 3 catalyst, and that the KF/Clay 1 catalyst underwent the lowest potassium leaching rate. Potassi-um leaching may result in homogeneous catalysis in transesterificationreactions through the formation of potassium methoxide ions in thepresence of water (Silva et al., 2012). Therefore, the potassium leaching

il/alcohol) ConversionKF/Clay 1 (%)

ConversionKF/Clay 2 (%)

ConversionKF/Clay 3 (%)

76.16 56.98 56.0468.48 70.22 69.3076.37 74.42 58.7443.87 82.58 79.4971.87 76.60 65.0689.19 76.46 76.7132.49 47.62 68.9681.70 72.18 74.3161.60 55.60 70.4163.39 56.25 68.86

-1.97486

2.896648

6.276536

7.360335

19.90782

29.80726

p=.05

Standardized Effect Estimate (Absolute Value)

2.323077

2.661538

-8.72308

-15.0923

35.24615

48.50769

p=.05

Standardized Effect Estimate (Absolute Value)

-.383871

3.674194

-4.64194

-5.4871

6.925806

16.45484

p=.05

Standardized Effect Estimate (Absolute Value)

KF-Clay 1

KF-Clay 2

KF-Clay 3

(3) RM

1by2

2by3

(1)Cat

(2)Temp.

1by3

R2 = 0,667

1by2

(3) RM

2by3

(1)Cat.

(2)Temp.

1by3

R2 = 0,834

1by2

(3) RM

2by3

(1)Cat

(2)Temp.

1by3

R2 = 0,945

(a)

(b)

(c)

Fig. 6. Estimated linear effects and interactions of variables of the catalysts: (a) KF/Clay 1catalyst, (b) KF/Clay 2 catalyst, and (c) KF/Clay 3 catalyst.

126 L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

results are consistentwith 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 catalystsunder the following conditions: i) soybean oil:methanol molar ratio of

1:6; ii) catalyst concentration of 5%; and iii) reaction temperature of353 K in 1 h of reaction. The percentages of conversion into methylesters using the KF/Clay 1, KF/Clay 2, and KF/Clay 3 catalysts were65.66%, 39.10% and 27.89%, respectively. Based on these results, an ex-perimental design was applied to investigate the influence of the reac-tion variables on the conversion rates and determine which reactionconditions and catalyst lead to the best results.

Table 8 presents the results of soybean oil conversion intomethyl es-ters using the catalysts. For the same experimental design, the reactionthat yielded the highest conversion was achieved with the KF/Clay 1catalyst (89.19%) whichwas attributed to the higher basicity of this cat-alyst compared to the other two. The catalysts exhibited good activity inrelatively mild conditions.

The effect of the variables on the conversion rates was assessedusing Statistica 7.0 software. Fig. 6 depicts the estimated linear isolatedeffects and interaction of the independent variables: catalyst content—(1) Cat; reaction temperature — (2) temp; and oil-to-methanol molarratio— (3) RM. A small p-value means that the probability of obtaininga value of the test statistic as observed is very unlikely, thus leading tothe rejection of the null hypothesis.

The fit of themodel was evaluated by analysis of variance (ANOVA).From the results shown in Table 9 we note that, using the three cata-lysts, themodel explains the variations, enabling it to be used for predic-tive purposes, at a significant level of 5% (p-value= 0.05). Itwas proventhat themodel is significantly applying the F test (ratio of two variances,one being of randomdistribution),wherewhen 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 esti-mate was made of which variables most strongly affected this con-version in the transesterification reactions analyzed here. Theinteraction between the variable catalyst andmolar ratio has a stron-ger effect on the KF/Clay 1 and KF/Clay 3 catalysts, while the interac-tion between catalyst and temperature has a greater influence on theKF/Clay 2 catalyst.

3.4. Conversion into methyl esters

The highest yield in the conversion of methyl esters was 89.2, whichwas obtained with the KF/1 Clay catalyst under the following experi-mental conditions: catalyst mass ratio of 25%, temperature of 353 K,and oil:alcohol molar ratio of 1:9. In parallel, applying the reaction con-ditions that yielded the highest conversion rate, the raw smectites weretested as catalysts, which confirmed that no conversion into methyl es-ters occurred. Therefore, the treatment of raw smectites with KF solu-tion is really effective for developing potential catalysts for theproduction of methyl esters.

4. Conclusions

The use of smectites treated with KF yielded promising results intransesterification reactions, since high conversion rates of soybeanoil into methyl esters were achieved. The catalyst preparation meth-od is very simple and easy to reproduce. The KF/Clay catalysts devel-oped here have a basic character, and a good correlation was foundbetween the SiO2/Al2O3 ratio of the raw smectites, the number ofactive basic sites in the catalysts, and the percent conversion intomethyl esters. In this regard, the KF/Clay 1 catalyst showed the bestresults, since it was prepared using Clay 1, which has the highestSiO2/Al2O3 ratio, resulting in the largest number of basic activesites and consequently in the highest conversion into methyl esters.Moreover, the KF/Clay 1 catalyst also exhibited greater stability inthe leaching tests, making it promising for the production ofbiodiesel.

image of Fig.�6

Table 9ANOVA of catalysts.

Parameter Source variation Sum squares Degree of freedom Media squares F Cal. Sta. Level of significance (%)

KF/Clay 1 Regression 2670.242 8 333.780 208.352 5.32 b0.05Residue 1.602 1 1.602Total 2671.844 9

KF/Clay 2 Regression 1237.821 8 154.728 733.306 5.32 b0.05Residue 0.211 1 0.211Total 1238.032 9

KF/Clay 3 Regression 486.882 8 60.860 50.666 5.32 b0.05Residue 1.201 1 1.201Total 488.083 9

127L.C.A. Silva et al. / Applied Clay Science 102 (2014) 121–127

Acknowledgments

H. J. Alves gratefully acknowledges the CNPq for its financial support(Grant no. 479207/2013-5).

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Effect of the chemical composition of smectites used in KF/Clay catalysts on soybean oil transesterification into methyl esters1. Introduction2. Experimental2.1. Preparation of catalysts by treating smectites with KF2.2. Characterization2.3. Potassium leaching assays2.4. Reaction assays2.5. Experimental design2.6. Gas Chromatography (GC) — Analysis of Fatty Acid Methyl Esters (FAME)

3. Results and discussion3.1. Characterization of raw smectites and catalysts3.2. Potassium leaching3.3. Experimental design3.4. Conversion into methyl esters

4. ConclusionsAcknowledgmentsReferences