**1. Introduction**

358 Biodiesel – Feedstocks and Processing Technologies

Xi, Y.Z., Davis, R.J. (2008) Influence of water on the activity and stability of activated Mg–Al

Xie, W.L., Peng, H., Chen, L.G. (2006) Calcined Mg-Al hydrotalcites as solid base catalysts

Xie, W.L., Peng, H., Chen, L.G. (2006) Transesterification of soybean oil catalyzed by

Xu, L.L., Li, W., Hu, J.L., Yang, X., Guo, Y.H. (2009) Biodiesel production from soybean oil

hybrid catalyst. *Applied Catalysis B: Environmental*, Vol.90, pp.587-594. Zięba, A., Drelinkiewicz, A., Chmielarz, P., Matachowski, L., Stejskal, J. (2010)

of catalyst properties. *Applied Catalysis A: General*, Vol.387, pp.13-25. Zong, M.H., Duan, Z.Q., Lou, W.Y., Smith, T.J., Wu, H. (2007) Preparation of a sugar catalyst

*Catalysis*, Vol.254, pp. 190-197.

pp.24-32.

pp.434-437.

Vol.300, pp.67-74.

hydrotalcites for the transesterification of tributyrin with methanol. *Journal of* 

for methanolysis of soybean oil. *Journal of Molecular Catalysis A: Chemical*, Vol.246,

potassium loaded on alumina as a solid-base catalyst. *Applied Catalysis A: General*,

catalyzed by multifunctionalized Ta2O5/SiO2-[H3PW12O40/R] (R = Me or Ph)

Transesterification of triacetin with methanol on various solid acid catalysts: A role

and its use for highly efficient production of biodiesel. *Green Chemistry*, Vol.7,

#### **1.1 Biodiesel chemical background**

The inevitable exhaustion of the fossil diesel reserves, besides the environmental impact generated by the green-house effect gas emission by these fuels has provoked the search by renewable feedstokes for energy production (Srivastava & Prasad, 2000; Sakay et al., 2009). Due to this crescent demand, the industry chemistry in all parts of world has search to develop environment friendly technologies for the production of alternative fuels (Di Serio et al., 2008; Marchetti et al., 2007). Biodiesel is a "green" alternative fuel that has arisen as an attractive option, mainly because it is less pollutant than its counterpart fossil and can be obtained from renewable sources (Maa & Hanna, 1999).

Although it is undeniable that biodiesel is a more environmentally benign fuel, its actual production process cannot be classified as "green chemistry process" (Kulkarni et al., 2006). The major of the biodiesel manufacture processes are carry out under alkaline or acid homogeneous catalysis conditions, where is not possible the recycling catalyst, resulting in a greater generation of effluents and salts from neutralization steps of the products and wastes (Kawashima et al., 2008). Moreover, there are some important points related to raw materials commonly used, such as high costs, besides to crescent requirements of large land reserves for its cultivation.

#### **1.2 Production of biodiesel from triglycerides transesterification reactions**

Currently, the biodiesel is manufactured from alkaline transesterification of edible or nonedible vegetable oils via a well-established industrial process (Maa & Hanna, 1999). The transesterification reaction proceeds well in the presence of some homogeneous catalysts such as alkaline metal hydroxides and Brønsted acids (Demirbas, 2003). Traditionally, sulfuric acid, hydrochloric acid, and sulfonic acid are usually preferred as acid catalysts. (Haas, 2005). The catalyst is dissolved into alcohol (methanol or ethanol) by vigorous stirring in a reactor. The vegetal oil is transferred into the biodiesel reactor and then the catalyst/alcohol mixture is pumped into the oil (Demirbas, 2003). However, the use them usually require drastic reaction conditions, i.e., high temperature and elevated pressure

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 361

A plethora of works have described the development of heterogeneous catalysts based on acids solids, which appear to offer an attractive perspective to turn the biodiesel production more environment friendly (Kiss et al., 2006; Jothiramalingam & Wang, 2009; Refaat, 2011). These solid catalysts, which normally present Lewis acidity, are easily separated from the reaction medium and are potentially less corrosive for the reactors. Normally, these processes focus on transesterification reactions of the triglycerides presents in the vegetable oils, which after react with methanol are converted into biodiesel. However, serious technological drawbacks such as drastic conditions reaction, the strict control of raw material quality in relation to water content, beyond of the leaching catalyst provoked by presence of alcohol besides water generated into reaction medium seems suggest that those

Particularly, the authors have concentrating efforts in developing alternative processes of

i. heteropolyacids, with a special highlighted for the dodecatungstophosphoric acid

ii. tin chloride, an simple, easily handling, water tolerant and inexpensive Lewis acid (

On the hand, catalysis by heteropolyacids of the Keggin's structure such as H3PW12O40 is one of the most important and growing areas of research in recent years (Timofeeva, 2003). They have been extensively used in both homogeneous and heterogeneous catalysis

On the other hand, the use SnCl2 catalyst is also most attractive, because it is solid, commercially available, and easy to handle. Moreover, its display remarkably tolerance to water, has an economically cost effective, and can be used in recyclable processes (Cardoso et al., 2008). Herein, the authors investigate the catalytic activity of heterogeneous catalysts based on acid solids composites (e.g. H3PW12O40 supported on silicon, niobium and

Tungtstophosphoric acid (H3PW12O40) is a heteropolyacid largely used, in special under heterogeneous catalysis conditions. As a homogeneous catalyst the H3PW12O40 has showed higher activity, selectivity and safety in handling in comparison to conventional mineral acids (Cardoso et al., 2008). Recent works have shown that the Keggin-type H3PW12O40, for which the physicochemical and catalytic properties have been fully described, is an efficient super-acid that can be used in homogeneous or heterogeneous phase (Kozhevnikov, 1998). Moreover, in the heterogeneous phase, supported on several solid matrixes, heteropolyacid composites also have showed highly efficient as catalysts in several types of reactions

The activity of H3PW12O40 catalyst supported on zirconia was assessed in transesterification reactions with methanol (Sunita et al., 2008); high yields FAMEs were achieved in reactions performed at temperatures of 200 C. On the other hand, impregnated H3PW12O40 heteropolyacid on four different supports (i.e. hydrous zirconia, silica, alumina, and activated carbon) also were investigated and converting low quality canola oil containing to biodiesel at 200 C temperature (Kulkarni et al., 2006). Recently, the use of an impregnation route to support H3PW12O40 on zirconia in acidic aqueous solution and further applied in the oleic acid esterication with ethanol was described (Oliveira et al., 2010). Those authors verified that 20% w/w H3PW12O40/ZrO2 was the most active catalyst (*ca*. 88% conversion,

process yet are hard to become effective (Kozhevnikov, 2009).

Cardoso et al., 2009; da Silva et al., 2010).

(Misono et al, 2000; Sharma et al., 2011).

esterification based on two recyclable catalysts linked to both acid types:

(H3PW12O4012H2O) (Silva et al., 2010; Cardoso et al., 2008);

zirconium oxides) towards the esterification of oleic acid with ethanol.

**1.5 Keggin heteropolyacid catalysts: a brief introduction** 

(Pizzio et al., 1998; Timofeeva et al., 2003; Sepulveda et al., 2005).

(Lotero et al., 2005). In addition, serious drawbacks related to its conventional production have aroused a special attention to biodiesel industry. Some of the natural oils or animal fats contain considerable amounts of free fatty acids (FFA), which are undesirable for the transesterification processes. These important features have hardly affected the final cost to biodiesel production (Haas, 2005).

#### **1.3 Production of biodiesel from FFA esterification reactions**

An attractive alternative for lower biodiesel price is produce it directly from domestic reject such as used cocking oil and waterwastes generated by food industry (Lou et al., 2008). Nevertheless, since these low cost lipidic feedstokes are rich in FFA, it's conversion into biodiesel is not compatible with alkaline catalysts. Nevertheless, different approaches have been proposed to get rid of this problem, and frequently, two alternative pathways have been employed for produces biodiesel from these kinds of resources. At first, a two-stage process that requires an initial acid-catalyzed esterication of the FFA followed by a basecatalyzed transesterication of the triglycerides; and secondly, a single-process that makes exclusive use of acid catalysts that promote both reactions simultaneously (Dussadee et al., 2010; Zullaikah et al., 2005).

Nowadays, the catalysts conventionally used in the FFA esterification reactions are Brønsted acids and work in a homogeneous phase (Lotero et al., 2005). Acids can catalyze the reaction by donating a proton to the FFA carbonyl group, thus making it more reactive. It should be mentioned that even though traditional mineral acids catalysts are an inexpensive catalysts able to those processes, they are highly corrosive, are not reusable, and results in a large generation of acid effluents which should be neutralized leaving greater amount of salts and residues to be disposed off into environment (Di Serio, 2007). Indeed, the reduction of environmentally unacceptable wastes is a key factor for developing less pollutants and advanced catalytic processes (Haas, 2005).

Thus, to develop alternative catalysts for the direct conversion into biodiesel of lipid wastes which are basically constituted of FFA, or yet for the pre-esterification of feedstokes that has high acidity seem be also a challenge to be overcome (Demirbas, 2008). Lewis acids can be interesting alternative catalysts for biodiesel production (Corma & Garcia, 2003). Nevertheless, their high cost, the manipulation difficult and the intolerance to water of compounds traditionally used such as BF3 and others common reagents of organic synthesis, also does not favor the use of these later in FFA esterification at industrial scale (Di Serio et al., 2005).

For all these reasons, to develop recyclable alternative catalysts for FFA esterification presents on inexpensive raw materials and food industry rejects can be an option strategically important, and undoubtedly can make the biodiesel with more competitive price using a cleaner technology (Lotero at al., 2005).

#### **1.4 Lewis or Brønsted acids heterogeneous catalysts for biodiesel production**

Recent advance in heterogeneous catalysis for biodiesel production has the potential to offer some relief to the biodiesel industry by improving its ability to process alternative cheaper raw material, and to use a shortened and low cost manufacture process. Even though many alkaline heterogeneous catalysts have been reported as highly active for biodiesel synthesis, they still cannot tolerate acidic oils with FFA content 3.5%, which are frequently used as raw material (DiMaggio et al., 2010). Contrarily, solid acids catalysts are more tolerant to FFA and are potentially less corrosive for the reactors. Consequently, these catalysts have been increasingly used in biodiesel production processes (Hattori, 2010).

(Lotero et al., 2005). In addition, serious drawbacks related to its conventional production have aroused a special attention to biodiesel industry. Some of the natural oils or animal fats contain considerable amounts of free fatty acids (FFA), which are undesirable for the transesterification processes. These important features have hardly affected the final cost to

An attractive alternative for lower biodiesel price is produce it directly from domestic reject such as used cocking oil and waterwastes generated by food industry (Lou et al., 2008). Nevertheless, since these low cost lipidic feedstokes are rich in FFA, it's conversion into biodiesel is not compatible with alkaline catalysts. Nevertheless, different approaches have been proposed to get rid of this problem, and frequently, two alternative pathways have been employed for produces biodiesel from these kinds of resources. At first, a two-stage process that requires an initial acid-catalyzed esterication of the FFA followed by a basecatalyzed transesterication of the triglycerides; and secondly, a single-process that makes exclusive use of acid catalysts that promote both reactions simultaneously (Dussadee et al.,

Nowadays, the catalysts conventionally used in the FFA esterification reactions are Brønsted acids and work in a homogeneous phase (Lotero et al., 2005). Acids can catalyze the reaction by donating a proton to the FFA carbonyl group, thus making it more reactive. It should be mentioned that even though traditional mineral acids catalysts are an inexpensive catalysts able to those processes, they are highly corrosive, are not reusable, and results in a large generation of acid effluents which should be neutralized leaving greater amount of salts and residues to be disposed off into environment (Di Serio, 2007). Indeed, the reduction of environmentally unacceptable wastes is a key factor for developing less pollutants and

Thus, to develop alternative catalysts for the direct conversion into biodiesel of lipid wastes which are basically constituted of FFA, or yet for the pre-esterification of feedstokes that has high acidity seem be also a challenge to be overcome (Demirbas, 2008). Lewis acids can be interesting alternative catalysts for biodiesel production (Corma & Garcia, 2003). Nevertheless, their high cost, the manipulation difficult and the intolerance to water of compounds traditionally used such as BF3 and others common reagents of organic synthesis, also does not

For all these reasons, to develop recyclable alternative catalysts for FFA esterification presents on inexpensive raw materials and food industry rejects can be an option strategically important, and undoubtedly can make the biodiesel with more competitive

Recent advance in heterogeneous catalysis for biodiesel production has the potential to offer some relief to the biodiesel industry by improving its ability to process alternative cheaper raw material, and to use a shortened and low cost manufacture process. Even though many alkaline heterogeneous catalysts have been reported as highly active for biodiesel synthesis, they still cannot tolerate acidic oils with FFA content 3.5%, which are frequently used as raw material (DiMaggio et al., 2010). Contrarily, solid acids catalysts are more tolerant to FFA and are potentially less corrosive for the reactors. Consequently, these catalysts have been

favor the use of these later in FFA esterification at industrial scale (Di Serio et al., 2005).

**1.4 Lewis or Brønsted acids heterogeneous catalysts for biodiesel production** 

increasingly used in biodiesel production processes (Hattori, 2010).

biodiesel production (Haas, 2005).

2010; Zullaikah et al., 2005).

advanced catalytic processes (Haas, 2005).

price using a cleaner technology (Lotero at al., 2005).

**1.3 Production of biodiesel from FFA esterification reactions** 

A plethora of works have described the development of heterogeneous catalysts based on acids solids, which appear to offer an attractive perspective to turn the biodiesel production more environment friendly (Kiss et al., 2006; Jothiramalingam & Wang, 2009; Refaat, 2011). These solid catalysts, which normally present Lewis acidity, are easily separated from the reaction medium and are potentially less corrosive for the reactors. Normally, these processes focus on transesterification reactions of the triglycerides presents in the vegetable oils, which after react with methanol are converted into biodiesel. However, serious technological drawbacks such as drastic conditions reaction, the strict control of raw material quality in relation to water content, beyond of the leaching catalyst provoked by presence of alcohol besides water generated into reaction medium seems suggest that those process yet are hard to become effective (Kozhevnikov, 2009).

Particularly, the authors have concentrating efforts in developing alternative processes of esterification based on two recyclable catalysts linked to both acid types:


On the hand, catalysis by heteropolyacids of the Keggin's structure such as H3PW12O40 is one of the most important and growing areas of research in recent years (Timofeeva, 2003). They have been extensively used in both homogeneous and heterogeneous catalysis (Misono et al, 2000; Sharma et al., 2011).

On the other hand, the use SnCl2 catalyst is also most attractive, because it is solid, commercially available, and easy to handle. Moreover, its display remarkably tolerance to water, has an economically cost effective, and can be used in recyclable processes (Cardoso et al., 2008). Herein, the authors investigate the catalytic activity of heterogeneous catalysts based on acid solids composites (e.g. H3PW12O40 supported on silicon, niobium and zirconium oxides) towards the esterification of oleic acid with ethanol.

#### **1.5 Keggin heteropolyacid catalysts: a brief introduction**

Tungtstophosphoric acid (H3PW12O40) is a heteropolyacid largely used, in special under heterogeneous catalysis conditions. As a homogeneous catalyst the H3PW12O40 has showed higher activity, selectivity and safety in handling in comparison to conventional mineral acids (Cardoso et al., 2008). Recent works have shown that the Keggin-type H3PW12O40, for which the physicochemical and catalytic properties have been fully described, is an efficient super-acid that can be used in homogeneous or heterogeneous phase (Kozhevnikov, 1998). Moreover, in the heterogeneous phase, supported on several solid matrixes, heteropolyacid composites also have showed highly efficient as catalysts in several types of reactions (Pizzio et al., 1998; Timofeeva et al., 2003; Sepulveda et al., 2005).

The activity of H3PW12O40 catalyst supported on zirconia was assessed in transesterification reactions with methanol (Sunita et al., 2008); high yields FAMEs were achieved in reactions performed at temperatures of 200 C. On the other hand, impregnated H3PW12O40 heteropolyacid on four different supports (i.e. hydrous zirconia, silica, alumina, and activated carbon) also were investigated and converting low quality canola oil containing to biodiesel at 200 C temperature (Kulkarni et al., 2006). Recently, the use of an impregnation route to support H3PW12O40 on zirconia in acidic aqueous solution and further applied in the oleic acid esterication with ethanol was described (Oliveira et al., 2010). Those authors verified that 20% w/w H3PW12O40/ZrO2 was the most active catalyst (*ca*. 88% conversion,

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 363

0 10

600 700 800 900 1000 1100 1200

Fig. 1. FTIR spectra of (30% w/w HPW) H3PW12O40 composites (a) Nb2O5; (b) HPW 30%/

600 700 800 900 1000 1100 1200

as(W-Oc

Fig. 2. FTIR spectra of (30 %w/w HPW) H3PW12O40 composites (a)- SiO2; (b)- HPW 30%/SiO2-100°C; (c) HPW 30%/SiO2-200°C; (d) HPW 30%/SiO2-300°C; (e)- HPW.

wave number (cm-1)


(W=Ot )

(P-O)

Nb2O5-100°C; (c) HPW30% Nb2O5-200°C; (d) HPW 30%/ Nb2O5-300°C; (e) HPW

as(W-Oc

(b)

(W=Ot ) (P-O)

0

10

0

10


wave number (cm-1)

0 10

Transmittance (%)

(e)

(c) (b)

(d)

(a)

(b) HPW30%/SiO2-0°C (c) HPW30%/SiO2-200°C (d) HPW30%/SiO2-300°C

Transmittance (%)

(a)

(c)

a e

(a) SiO2

(e) HPW

(b)

(a) Nb2

(e) HPW

O5 (b) HPW30%/Nb2

(c) HPW30%/Nb2

(d) HPW30%/Nb2

O5 -100°C

O5 -200°C

O5 -300°C

(e)

(d)

4 h reaction, with 1:6 FA:ethanol molar ratio and 10% w/w of the catalyst in relation to FA. However, a minor leaching of catalyst (*ca*. 8% w/w related to the initial loading), affected drastically its efficiency, resulting in decreases yielding obtained from its reuse.

#### **2. Results and discussion**

#### **2.1 General aspects**

Herein the H3PW12O40 catalyst were supported on three different solid matrixes (i.e. silicon, niobium, and zirconium oxides) by impregnation in ethanol solutions under different loads (*ca*. 10, 30 and 50% w/w). The solids were characterized by FTIR spectroscopy and the H3PW12O40 catalyst content was determined by UV-Vis and AAS spectroscopy analysis.

#### **2.2 Syntheses of the H3PW12O40 catalysts**

Differently than others supports, which were used as received, zirconium oxide was obtained from thermal treatment of ZrOCl2.8H2O salt at 300 °C during 4 hours. Composites of H3PW12O40 supported on silicon, niobium and zirconium oxides were prepared via impregnation method (Pizzio et al., 1998). During preparation, ethanol solutions of H3PW12O40 in hydrochloric acid 0.01 mol L−1 were used to avoid any hydrolysis. All composites were prepared with concentrations depending upon the loading required to the support (e.g. 10, 30 and 50% w/w H3PW12O40) using 10 ml of the solution per gram of support. The addition of the support to the solution formed a suspension, which after stirred, was evaporated at 80 °C until dryness. All samples of supported heteropolyacid were dried at 100 C for 12 h and then thermally treated for 4 h at 200 or 300 C in air.

#### **2.3 FTIR spectra of the supported heteropolyacid catalysts: H3PW12O40/SiO2, H3PW12O40/Nb2O5 and H3PW12O40/ZrO2**

The supported H3PW12O40 composites were analyzed by FTIR aims to conrm the presence of the Keggin anion structure on support employed. The PW12O403− Keggin ion structure is well known, and consists of a PO4 tetrahedron surround by four W3O13 groups formed by edge-sharing octahedral (Pope, 1983). These groups are bonded each other by cornersharing oxygens. This structure gives rise to four types of oxygen atoms, being responsible for the ngerprint bands of the PW12O403− Keggin ion (*ca*. 1200 - 700 cm− 1). FTIR spectra were obtained from all samples with different content of HPW (*ca.* 10, 30 and 50% w/w). However, the typical bands of the Keggin ions were more evident for samples with HPW contents of 30 and 50 % w/w. Herein, only the FTIR spectra of the composites with 30 % w/w H3PW12O40, which were thermally treated at temperature of 100, 200 and 300 C are shown. Figures 1-3 shows the characteristic bands for absorptions of (P–O) and (W-O) bonds existent on H3PW12O40 composites. All FTIR spectra of both supported H3PW12O40 catalyst or pure are displayed in Figures 1-3.

When niobium oxide was the support, only a stronger band at 1080 cm− 1 relative to (P–O) bond was easily observed (Figure 1). All others bands were overlapping by support bands. Conversely, when the support employed was the SiO2, all the bands related to others oxygen atoms were observed (W = Otethraedric) bond at 985 cm−1; (W–Ocubic–W) bond, at 895 cm−1, and (W–O–W) bond, at 795 cm−1; only the band of (P–O) bond was not visible.

4 h reaction, with 1:6 FA:ethanol molar ratio and 10% w/w of the catalyst in relation to FA. However, a minor leaching of catalyst (*ca*. 8% w/w related to the initial loading), affected

Herein the H3PW12O40 catalyst were supported on three different solid matrixes (i.e. silicon, niobium, and zirconium oxides) by impregnation in ethanol solutions under different loads (*ca*. 10, 30 and 50% w/w). The solids were characterized by FTIR spectroscopy and the H3PW12O40 catalyst content was determined by UV-Vis and AAS spectroscopy analysis.

Differently than others supports, which were used as received, zirconium oxide was obtained from thermal treatment of ZrOCl2.8H2O salt at 300 °C during 4 hours. Composites of H3PW12O40 supported on silicon, niobium and zirconium oxides were prepared via impregnation method (Pizzio et al., 1998). During preparation, ethanol solutions of H3PW12O40 in hydrochloric acid 0.01 mol L−1 were used to avoid any hydrolysis. All composites were prepared with concentrations depending upon the loading required to the support (e.g. 10, 30 and 50% w/w H3PW12O40) using 10 ml of the solution per gram of support. The addition of the support to the solution formed a suspension, which after stirred, was evaporated at 80 °C until dryness. All samples of supported heteropolyacid were dried at 100 C for 12 h and then thermally treated for 4 h

**2.3 FTIR spectra of the supported heteropolyacid catalysts: H3PW12O40/SiO2,** 

The supported H3PW12O40 composites were analyzed by FTIR aims to conrm the presence of the Keggin anion structure on support employed. The PW12O403− Keggin ion structure is well known, and consists of a PO4 tetrahedron surround by four W3O13 groups formed by edge-sharing octahedral (Pope, 1983). These groups are bonded each other by cornersharing oxygens. This structure gives rise to four types of oxygen atoms, being responsible for the ngerprint bands of the PW12O403− Keggin ion (*ca*. 1200 - 700 cm− 1). FTIR spectra were obtained from all samples with different content of HPW (*ca.* 10, 30 and 50% w/w). However, the typical bands of the Keggin ions were more evident for samples with HPW contents of 30 and 50 % w/w. Herein, only the FTIR spectra of the composites with 30 % w/w H3PW12O40, which were thermally treated at temperature of 100, 200 and 300 C are shown. Figures 1-3 shows the characteristic bands for absorptions of (P–O) and (W-O) bonds existent on H3PW12O40 composites. All FTIR spectra of both supported H3PW12O40

When niobium oxide was the support, only a stronger band at 1080 cm− 1 relative to (P–O) bond was easily observed (Figure 1). All others bands were overlapping by support bands. Conversely, when the support employed was the SiO2, all the bands related to others oxygen atoms were observed (W = Otethraedric) bond at 985 cm−1; (W–Ocubic–W) bond, at 895 cm−1, and (W–O–W) bond, at 795 cm−1; only the band of (P–O) bond was

drastically its efficiency, resulting in decreases yielding obtained from its reuse.

**2. Results and discussion** 

**2.2 Syntheses of the H3PW12O40 catalysts** 

**2.1 General aspects** 

at 200 or 300 C in air.

not visible.

**H3PW12O40/Nb2O5 and H3PW12O40/ZrO2**

catalyst or pure are displayed in Figures 1-3.

Fig. 1. FTIR spectra of (30% w/w HPW) H3PW12O40 composites (a) Nb2O5; (b) HPW 30%/ Nb2O5-100°C; (c) HPW30% Nb2O5-200°C; (d) HPW 30%/ Nb2O5-300°C; (e) HPW

0

10

0

Fig. 2. FTIR spectra of (30 %w/w HPW) H3PW12O40 composites (a)- SiO2; (b)- HPW 30%/SiO2-100°C; (c) HPW 30%/SiO2-200°C; (d) HPW 30%/SiO2-300°C; (e)- HPW.

0

10

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 365

dried and reused in other catalytic run, similarly to solid catalyst. As will show on next section, ethanol in excess not favors the ester formation under these reaction conditions. The load catalyst used when the composites have 50% w/w HPW is corresponding to *ca.* 1 mol % in relation to oleic acid; in all reactions 1 mmol of oleic acid is used against 0.0087

*solution Distillation/*

*Dried with Na2SO4*

*FAEE (biodiesel)*

Fig. 4. Scheme of a typical acid solid-catalyzed process of FFA esterification in liquid phase

*dried drying* 

The low surface area of solid H3PW12O40, which implies a small amount of H+ ions available on the surface; for circumvent these problems, three supports with a higher surface area were selected on this study. When solid supported heterogeneous catalyst are prepared, important aspects such as temperature of the thermal treatment, method of synthesis, type and precursor nature and also of the support, besides catalyst loading can affect drastically

Herein the temperature of thermal treatment was the parameter selected for an adequate comparison between the catalytic activities of different HPW composites. High temperatures may favor the reduction of support surface area (300 C) and lower temperatures (100 C) may favor catalyst leaching when impregnation is synthesis method; for these reasons, the authors selected results obtained with catalyst treated at 200 C as

However, another important aspect that can be affected by thermal treatment is the water content on both support and HPW catalyst. All solid supports were completely dried (*ca*. 120 C) before of the HPW composite synthesis. Conversely, termogravimetry analysis results described in literature (Essayem et al., 1999) revealed that for the zirconium containing HPW, the loss of crystallization water upon the thermal treatment at 120 C

**2.5.2 The effect of support on catalytic activity of HPW composites** 

*Solid Catalyst*

*reactor filtration*

*ethanol*

the efficiency of catalyst (Hattori, 2010).

displayed in Figure 5.

*ethanol*

*FFA*

mmols of HPW present in 50 mg of catalyst.

These bands are preserved on the silicon-supported catalyst samples, but they are slightly broadened and partly obscured because of the strong absorptions of silica at 1100 and 800 cm−1 region.

0 10

Fig. 3. FTIR spectra of H3PW12O40 (30% HPW) composites (a)- ZrO2; (b)- HPW/ZrO2-100 °C (c) HPW 30%/ZrO2-200°C; (d) HPW 30%/ZrO2-300°C; (e)- HPW.

In Figure 3, where FTIR spectra obtained from HPW composites supported on ZrO2 are shown, all characteristics bands of the Keggin anion are present.

In general, FTIR spectra of the HPW composites on different supports were not affected by temperature of thermal treatment. On the temperature range studied herein, all they have shown similar characteristics. However, a measured of interaction strength of HPW with support may be obtained from shift of more well defined bands to a region of lower wave number in comparison with the same band present on HPW pure (Figures 1-3).

#### **2.4 UV-Vis spectra of the supported heteropolyacid catalysts: H3PW12O40/SiO2, H3PW12O40/Nb2O5 and H3PW12O40/ZrO2**

Beckman DU-650 UV-Vis spectrophotometer and quartz cells of 1.0 and 0.1 cm pathlength were employed for the adsorption experiment and measurements of H3PW12O40 spectra, respectively (Oliveira et al., 2010). The concentration of H3PW12O40 on catalysts was measured by UV-Vis spectroscopy before and after 6 hours of adsorption. The content of HPW in the solid was determined by AAS. In all composites yielding upper of 95% of impregnation were achieved.

#### **2.5 Catalytic tests**

#### **2.5.1 Reaction conditions**

The reactions conditions used were based on typical heterogeneous process (Figure 4). The catalyst is recovered from solution from simples filtration; the ethanol used in excess is

These bands are preserved on the silicon-supported catalyst samples, but they are slightly broadened and partly obscured because of the strong absorptions of silica at 1100 and

0 10




(c)

10

0

600 700 800 900 1000 1100 1200

wave number (cm-1

Fig. 3. FTIR spectra of H3PW12O40 (30% HPW) composites (a)- ZrO2; (b)- HPW/ZrO2-100 °C

In Figure 3, where FTIR spectra obtained from HPW composites supported on ZrO2 are

In general, FTIR spectra of the HPW composites on different supports were not affected by temperature of thermal treatment. On the temperature range studied herein, all they have shown similar characteristics. However, a measured of interaction strength of HPW with support may be obtained from shift of more well defined bands to a region of lower wave

Beckman DU-650 UV-Vis spectrophotometer and quartz cells of 1.0 and 0.1 cm pathlength were employed for the adsorption experiment and measurements of H3PW12O40 spectra, respectively (Oliveira et al., 2010). The concentration of H3PW12O40 on catalysts was measured by UV-Vis spectroscopy before and after 6 hours of adsorption. The content of HPW in the solid was determined by AAS. In all composites yielding upper of 95% of

The reactions conditions used were based on typical heterogeneous process (Figure 4). The catalyst is recovered from solution from simples filtration; the ethanol used in excess is

number in comparison with the same band present on HPW pure (Figures 1-3).

**2.4 UV-Vis spectra of the supported heteropolyacid catalysts: H3PW12O40/SiO2,** 


(W=Ot )

)

(P-O)

as(W-Oc

800 cm−1 region.

0

**H3PW12O40/Nb2O5 and H3PW12O40/ZrO2**

impregnation were achieved.

**2.5.1 Reaction conditions** 

**2.5 Catalytic tests** 

20

40

Transmittance (%)

(e)

(d)

(b)

(c) HPW 30%/ZrO2-200°C; (d) HPW 30%/ZrO2-300°C; (e)- HPW.

shown, all characteristics bands of the Keggin anion are present.

(a)

(a) ZrO2 (b) HPW30%/ZrO2

(e) HPW

(c) HPW30%/ZrO2

(d) HPW30%/ZrO2

60

80

100

dried and reused in other catalytic run, similarly to solid catalyst. As will show on next section, ethanol in excess not favors the ester formation under these reaction conditions.

The load catalyst used when the composites have 50% w/w HPW is corresponding to *ca.* 1 mol % in relation to oleic acid; in all reactions 1 mmol of oleic acid is used against 0.0087 mmols of HPW present in 50 mg of catalyst.

Fig. 4. Scheme of a typical acid solid-catalyzed process of FFA esterification in liquid phase
