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

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 the efficiency of catalyst (Hattori, 2010).

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 displayed in Figure 5.

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

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 367

Conversely, in the presence of H3PW12O40 pure or niobium-supported and after a reaction time of 8 h much greater yields (*ca*. 86%) were attained, as concisely displayed in Figure 5. In all reactions, a high selectivity for the ethyl oleate greater than 90 % (analysis) was achieved, determined by GC analyses (no showed herein). Investigating the performance of supported HPW can be observed that the best and worst results were obtained when the HPW/niobium composites were treated at 100 and 300 C temperatures. A possible leaching of catalyst (see next section) and the reduction of surface area provoked by high

On the other hand, the highest conversion was obtained when a mechanic mixture of niobium and H3PW12O40 was used, probably due the simultaneous presence of the first and second catalyst; this later soluble and consequently more reactive (Lewis and Brønsted acids

0123456789

**Time (h)**

**2.5.4 The effect of HPW loading on catalytic activity of the HPW/niobium composites**  In many cases, there are obvious approaches to improving and optimizing the yielding of catalytic reactions. Among the mains, is highlighted an increase on amount of reactants and of the catalyst. Recognized, the catalyst load can affect remarkably the efficiency of catalyst. Kinetic curves obtained from HPW/niobium-catalyzed esterification reactions with loads of HPW equal to 10, 30 and 50 % w/w respectively are shown in Figures 7-9. Because the temperature used on the thermal treatment may also affect both stability and activity of catalyst, three results obtained at three different temperatures are

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 6. H3PW12O40/Nb2O5-catalyzed oleic acid esterification with ethanol

temperature of thermal treatment may be reasonable explanations.

PW12O40 + Nb2

O5

 Blank H3 PW12O40 Nb2 O5 Mix H3

 H50Nb2 O5 100 <sup>0</sup> C

 H50Nb2 O5 200 <sup>0</sup> C

 H50Nb2 O5 300 <sup>0</sup> C

respectively).

 **Ethyl oleate conversion (%)**

reported.

which retains six water mols per mols Keggin ion. After activation at 200 C, HPW still retains some crystallization water molecules. (Morim et al., 2007).

The thermal treatment herein employed was the same for all supported-composite; so is reasonable conclude that although not quantitatively determined, water effect act equally onto both composites.

Reaction conditions: oleic acid (1.0 mmol); ethanol (155.0 mmols); catalyst (50.0 mg); 60 C

Fig. 5. Oleic acid esterification with ethanol catalyzed by HPW 50% w/w composites supported on niobium, zirconium and silicon treated at 200 °C temperature

The HPW 50% w/w/niobium composite is strongest Lewis acid support; nevertheless, Figure 5 reveals the all catalyst have a very close behavior. The HPW/Nb2O5 composite was the catalyst selected to assess the effects of others reaction parameters because there are scarce data on literature; moreover, as will showed it was the catalyst more efficient and less leached in reactions. All results obtained on HPW/niobium-catalyzed oleic acid esterification with ethanol are highlighted in next sections.

#### **2.5.3 Temperature effects of the thermal treatment on catalytic activity of the HPW/niobium composites**

The esterication of oleic acid with ethanol conducted in the absence of the acidic catalysts (HPW) produced no significance yields of the corresponding ethyl oleate in spite of the high molar ratio of ethanol/oleic acid used. For instance, only a very low oleic acid to ethyl oleate conversion (*ca*. 10%) was achieved even after a reaction time as long as 8 h (Figure 6). Moreover, despite Lewis acidity of the support, when in presence only of niobium, a poor conversion of oleic acid into ethyl oleate was also reached (Figure 6).

which retains six water mols per mols Keggin ion. After activation at 200 C, HPW still

The thermal treatment herein employed was the same for all supported-composite; so is reasonable conclude that although not quantitatively determined, water effect act equally

0 60 120 180 240 300 360 420 480 540

HPW50Nb2

HPW50ZrO2

HPW50SiO2

O5 200°C

200°C

200°C

**Time (min)**

The HPW 50% w/w/niobium composite is strongest Lewis acid support; nevertheless, Figure 5 reveals the all catalyst have a very close behavior. The HPW/Nb2O5 composite was the catalyst selected to assess the effects of others reaction parameters because there are scarce data on literature; moreover, as will showed it was the catalyst more efficient and less leached in reactions. All results obtained on HPW/niobium-catalyzed oleic acid

The esterication of oleic acid with ethanol conducted in the absence of the acidic catalysts (HPW) produced no significance yields of the corresponding ethyl oleate in spite of the high molar ratio of ethanol/oleic acid used. For instance, only a very low oleic acid to ethyl oleate conversion (*ca*. 10%) was achieved even after a reaction time as long as 8 h (Figure 6). Moreover, despite Lewis acidity of the support, when in presence only of niobium, a poor

Reaction conditions: oleic acid (1.0 mmol); ethanol (155.0 mmols); catalyst (50.0 mg); 60 C Fig. 5. Oleic acid esterification with ethanol catalyzed by HPW 50% w/w composites

**2.5.3 Temperature effects of the thermal treatment on catalytic activity of the** 

supported on niobium, zirconium and silicon treated at 200 °C temperature

esterification with ethanol are highlighted in next sections.

conversion of oleic acid into ethyl oleate was also reached (Figure 6).

retains some crystallization water molecules. (Morim et al., 2007).

onto both composites.

**Ethyl oleate conversion (% )**

**HPW/niobium composites** 

Conversely, in the presence of H3PW12O40 pure or niobium-supported and after a reaction time of 8 h much greater yields (*ca*. 86%) were attained, as concisely displayed in Figure 5. In all reactions, a high selectivity for the ethyl oleate greater than 90 % (analysis) was achieved, determined by GC analyses (no showed herein). Investigating the performance of supported HPW can be observed that the best and worst results were obtained when the HPW/niobium composites were treated at 100 and 300 C temperatures. A possible leaching of catalyst (see next section) and the reduction of surface area provoked by high temperature of thermal treatment may be reasonable explanations.

On the other hand, the highest conversion was obtained when a mechanic mixture of niobium and H3PW12O40 was used, probably due the simultaneous presence of the first and second catalyst; this later soluble and consequently more reactive (Lewis and Brønsted acids respectively).

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C. Fig. 6. H3PW12O40/Nb2O5-catalyzed oleic acid esterification with ethanol

#### **2.5.4 The effect of HPW loading on catalytic activity of the HPW/niobium composites**

In many cases, there are obvious approaches to improving and optimizing the yielding of catalytic reactions. Among the mains, is highlighted an increase on amount of reactants and of the catalyst. Recognized, the catalyst load can affect remarkably the efficiency of catalyst. Kinetic curves obtained from HPW/niobium-catalyzed esterification reactions with loads of HPW equal to 10, 30 and 50 % w/w respectively are shown in Figures 7-9. Because the temperature used on the thermal treatment may also affect both stability and activity of catalyst, three results obtained at three different temperatures are reported.

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 369

0 60 120 180 240 300 360 420 480 540

HPW10Nb2

HPW30Nb2

HPW50Nb2

O5 300°C

O5 300°C

O5 300°C

**Time (min)**

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 9. Effect of the HPW load on HPW/Nb2O5-300 C-catalyzed oleic acid esterification

Although literature data described that occur a significance decreases on surface area with an increase of acid content, which may then reduce its catalytic activity (Dias et al., 2003), results displayed in Figures 6 to 8 suggest that a higher HPW load increases the efficiency of HPW/Nb2O5 catalyst. Interestingly, it's occurred independently of the thermal treatment

Leaching affects the industrial application as extensive leaching may threaten the reusability and the environmental sustainability of catalyst (Di Serio et al., 2010). Conceptually, catalyst leaching is usually associated with a phase boundary. For example, the active component of an insoluble acid solid catalyst might slowly leach into solution by some mechanism, perhaps involving bond breaking. When the catalyst has leached into a product phase, the sample should exhibit some catalytic activity. Thus, an efficient procedure that allows evaluates if there is any leaching is remove the catalyst out of the reaction and continue to run in your absence. Figures 10 to 12 displayed kinetic curves of reactions catalyzed by

It was found that the composites obtained at temperatures of 200 or 300 °C, seems be more stable under reactions conditions; noticeably, after catalyst remove the conversion of oleic acid into ethyl oleate remains constant. However, when the catalyst was synthesized at 100 °C, there was an increase in the conversion of oleic acid, suggesting that possibly a part of HPW can has been lixiviated to reaction solution. Interesting, the same occurred for the

**2.5.5 Evaluating catalyst leaching** 

employed on synthesis of these catalysts (Figures 7-9).

HPW/niobium composite before and after its remove.

catalyst supported on zirconium and silicon (Figures 13 and 14).

**Ethyl oleate conversion (%)**

with ethanol

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 7. Effect of the HPW load on HPW/Nb2O5-100 C-catalyzed oleic acid esterification with ethanol

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 8. Effect of the HPW load on HPW/Nb2O5-200 C-catalyzed oleic acid esterification with ethanol

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 9. Effect of the HPW load on HPW/Nb2O5-300 C-catalyzed oleic acid esterification with ethanol

Although literature data described that occur a significance decreases on surface area with an increase of acid content, which may then reduce its catalytic activity (Dias et al., 2003), results displayed in Figures 6 to 8 suggest that a higher HPW load increases the efficiency of HPW/Nb2O5 catalyst. Interestingly, it's occurred independently of the thermal treatment employed on synthesis of these catalysts (Figures 7-9).

#### **2.5.5 Evaluating catalyst leaching**

368 Biodiesel – Feedstocks and Processing Technologies

0 60 120 180 240 300 360 420 480 540

HPW10Nb2

HPW30Nb2

HPW50Nb2

O5 100°C

O5 100°C

O5 100°C

**Time (min)**

0 60 120 180 240 300 360 420 480 540

HPW10Nb2

HPW30Nb2

HPW50Nb2

O5 200°C

O5 200°C

O5 200°C

**Time (min)**

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 8. Effect of the HPW load on HPW/Nb2O5-200 C-catalyzed oleic acid esterification

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 7. Effect of the HPW load on HPW/Nb2O5-100 C-catalyzed oleic acid esterification

**Ethyl oleate convesion (%)**

**Ethyl oleate conversion (%)**

with ethanol

with ethanol

Leaching affects the industrial application as extensive leaching may threaten the reusability and the environmental sustainability of catalyst (Di Serio et al., 2010). Conceptually, catalyst leaching is usually associated with a phase boundary. For example, the active component of an insoluble acid solid catalyst might slowly leach into solution by some mechanism, perhaps involving bond breaking. When the catalyst has leached into a product phase, the sample should exhibit some catalytic activity. Thus, an efficient procedure that allows evaluates if there is any leaching is remove the catalyst out of the reaction and continue to run in your absence. Figures 10 to 12 displayed kinetic curves of reactions catalyzed by HPW/niobium composite before and after its remove.

It was found that the composites obtained at temperatures of 200 or 300 °C, seems be more stable under reactions conditions; noticeably, after catalyst remove the conversion of oleic acid into ethyl oleate remains constant. However, when the catalyst was synthesized at 100 °C, there was an increase in the conversion of oleic acid, suggesting that possibly a part of HPW can has been lixiviated to reaction solution. Interesting, the same occurred for the catalyst supported on zirconium and silicon (Figures 13 and 14).

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 371

0 60 120 180 240 300 360 420 480 540

**Time(min)**

Fig. 12. Effect of the HPW leaching on HPW/Nb2O5-300 C-catalyzed oleic acid esterification

0 60 120 180 240 300 360 420 480 540

free-catalyst after 30 minutes

C

Time (min)

Fig. 13. Effect of the HPW leaching on HPW/ZrO2-100 C-catalyzed oleic acid esterification

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C

HPW/ZrO2 100 0

O5 300 0

H50Nb2

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C.

free-catalyst after 30 minutes

C catalyst

Ethyl oleate conversion (%)

with ethanol

with ethanol

**Ethyl oleate conversion (%)**

Time (min)

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 10. Effect of the HPW leaching on HPW/Nb2O5-100 C-catalyzed oleic acid esterification with ethanol

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

Fig. 11. Effect of the HPW leaching on HPW/Nb2O5-200 C-catalyzed oleic acid esterification with ethanol

0 60 120 180 240 300 360 420 480 540

free-catalyst after 30 minutes

C catalyst

O5 100 0

Time (min)

Fig. 10. Effect of the HPW leaching on HPW/Nb2O5-100 C-catalyzed oleic acid esterification

0 60 120 180 240 300 360 420 480 540

free-catalyst after 30 minutes

C catalyst

**Time (min)**

Fig. 11. Effect of the HPW leaching on HPW/Nb2O5-200 C-catalyzed oleic acid esterification

O5 200 0

H50Nb2

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

HPW50Nb2

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60°C.

0

20

40

60

**Ethyl oleate conversion (%)**

80

100

with ethanol

with ethanol

Ethyl oleate conversion (%)

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C.

Fig. 12. Effect of the HPW leaching on HPW/Nb2O5-300 C-catalyzed oleic acid esterification with ethanol

Time (min)

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C

Fig. 13. Effect of the HPW leaching on HPW/ZrO2-100 C-catalyzed oleic acid esterification with ethanol

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 373

 catalyst recovery rates (%) oleic acid conversion rates (%)

123

Fig. 15. Recovery Yields of HPW 50% w/w/niobium catalyst obtained by the filtrationa,b,c procedures and oleic acid conversion rates obtained from its esterification with ethanol

The procedure employed for catalyst recovery involves its separation from reaction by filtration, washed with ethyl ether and drying at 100 °C; then the catalyst has its mass determined. Losses of mass through of these several steps may be occurring. A more detailed treatment of the recovery procedure of catalyst may lead to efficient methods, which can reaches higher recovery rates. The authors are developing studies on this

Tunstophosphoric acid (H3PW12O40) is strongest heteropolyacid of Keggin series being completely ionizable in water. Measurements of pKa in organic solvents showed that it is 100 units of pka more acid than sulfuric acid (Kozhevnikov, 1998); therefore is almost probably that its ionization in ethanol occur in greater extension. Thus, is possible that HPW/niobium catalyst undergoes at least a partial ionization along oleic acid esterification

reaction in ethanol as described on equilibrium displayed in Figure 16.

Fig. 16. Partial ionization equilibrium of HPW/niobium catalyst in ethanol solution

aReaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C bRates recovery calculated from initial catalyst mass

**reuses**

direction.

**2.5.7 Mechanistic insights** 

cIn all runs fresh catalyst was added to reaches 50.0 mg mass

**percent (%)**

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C

Fig. 14. Effect of the HPW leaching on HPW/SiO2-100 C-catalyzed oleic acid esterification with ethanol

Various measures of catalyst leaching must be interpreted based in others contexts. For example, atomic absorption spectroscopy and ICP–MS are very sensitive analytical methods. However, a simple qualitative procedure can be used based only on visual observation; the addition of ascorbic acid to a solution containing HPW soluble assume blue color. Herein, its procedure allows easily confirm the catalyst leaching treated at 100 C temperature; contrarily, in the runs with HPW/niobium-200 C catalyst the solution remained with color unaltered (pale yellow).

#### **2.5.6 Recovery and reuse of catalyst**

The greatest advantage of the heterogeneous goal of this study over the homogeneous catalyst is the prolonged lifetime of the solid catalyst for ethyl esters production. However, leaching of catalyst components can cause its deactivation quickly. Herein, the stability of HPW 50 % w/w/niobium-200 C after successive protocols of recovery/reuse was assessed (Figure 15). The recovery yields of solid catalyst isolated from procedure of filtration are most commonly determined gravimetrically.

A remarkable result was observed as the HPW/niobium catalytic activity stayed almost unaltered even after three recovery/reutilization cycles. However, it should be noted that a weights of catalyst fresh (ca. 20% in relation to started weight).

It was found that although recovery rate has been kept constant (*ca.* 72-75 %) in all catalytic runs, its suggest that the catalyst leach to solution; however, in Figures 10 to 12 it was demonstrated that oleic acid conversion remains unaltered after catalyst remove. This observation suggests an absence of leaching of catalyst. Probably, the procedure used is not efficient as desired.

aReaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C bRates recovery calculated from initial catalyst mass cIn all runs fresh catalyst was added to reaches 50.0 mg mass

Fig. 15. Recovery Yields of HPW 50% w/w/niobium catalyst obtained by the filtrationa,b,c procedures and oleic acid conversion rates obtained from its esterification with ethanol

The procedure employed for catalyst recovery involves its separation from reaction by filtration, washed with ethyl ether and drying at 100 °C; then the catalyst has its mass determined. Losses of mass through of these several steps may be occurring. A more detailed treatment of the recovery procedure of catalyst may lead to efficient methods, which can reaches higher recovery rates. The authors are developing studies on this direction.

### **2.5.7 Mechanistic insights**

372 Biodiesel – Feedstocks and Processing Technologies

0 60 120 180 240 300 360 420 480 540

Time (min)

Fig. 14. Effect of the HPW leaching on HPW/SiO2-100 C-catalyzed oleic acid esterification

Various measures of catalyst leaching must be interpreted based in others contexts. For example, atomic absorption spectroscopy and ICP–MS are very sensitive analytical methods. However, a simple qualitative procedure can be used based only on visual observation; the addition of ascorbic acid to a solution containing HPW soluble assume blue color. Herein, its procedure allows easily confirm the catalyst leaching treated at 100 C temperature; contrarily, in the runs with HPW/niobium-200 C catalyst the solution

The greatest advantage of the heterogeneous goal of this study over the homogeneous catalyst is the prolonged lifetime of the solid catalyst for ethyl esters production. However, leaching of catalyst components can cause its deactivation quickly. Herein, the stability of HPW 50 % w/w/niobium-200 C after successive protocols of recovery/reuse was assessed (Figure 15). The recovery yields of solid catalyst isolated from procedure of filtration are

A remarkable result was observed as the HPW/niobium catalytic activity stayed almost unaltered even after three recovery/reutilization cycles. However, it should be noted that a

It was found that although recovery rate has been kept constant (*ca.* 72-75 %) in all catalytic runs, its suggest that the catalyst leach to solution; however, in Figures 10 to 12 it was demonstrated that oleic acid conversion remains unaltered after catalyst remove. This observation suggests an absence of leaching of catalyst. Probably, the procedure used is not

 100 0 C

HPW/SiO2

Reaction conditions: catalyst (50.0 mg); oleic acid (1.0 mmol); ethanol (155.0 mmols); 60 °C

free-catalyst after 30 minutes

0

remained with color unaltered (pale yellow).

most commonly determined gravimetrically.

weights of catalyst fresh (ca. 20% in relation to started weight).

**2.5.6 Recovery and reuse of catalyst** 

20

40

Ethyl oleate conversion (%)

with ethanol

efficient as desired.

60

80

100

Tunstophosphoric acid (H3PW12O40) is strongest heteropolyacid of Keggin series being completely ionizable in water. Measurements of pKa in organic solvents showed that it is 100 units of pka more acid than sulfuric acid (Kozhevnikov, 1998); therefore is almost probably that its ionization in ethanol occur in greater extension. Thus, is possible that HPW/niobium catalyst undergoes at least a partial ionization along oleic acid esterification reaction in ethanol as described on equilibrium displayed in Figure 16.

Fig. 16. Partial ionization equilibrium of HPW/niobium catalyst in ethanol solution

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification 375

In according with this mechanism (Figure 18), all steps of oleic acid esterification reaction with ethanol occur on surface of HPW/niobium catalyst. Nevertheless, is also possible that ethyl oleate formation may occur by both pathways of reaction Although both proposal are plausible, is important to note that studies in situ are require for a better and more detailed

The efficiency of tungstophosphoric acid (H3PW12O40) immobilized by impregnation method on silicon, zirconium and niobium oxides was assessed in the esterication of oleic acid with ethanol, at 60 C temperature. As a general tendency, it was observed that the catalytic activity decreases in the series HPW/Nb2O5 > HPW/ZrO2> HPW/SiO2 with all catalyst being treated on temperature range 100 to 300 C. Moreover, good yielding of recovery of HPW 50% w/w/Nb2O5 catalyst (*ca*. 75 %) and high conversions of acid oleic were obtained in recycle experiments. From leaching tests and of the rates of recovery may be concluded that the HPW/Nb2O5 catalysts are stable under reaction conditions used; however the recovery procedure employed it should be enhanced. Thus, it can be concluded that although yet non-finished, present methodology offers several advantages such as high yields, simple procedure for recovery and reuse of catalyst and mild reaction conditions. The authors hope that with this work a significant advance on the field of recoverable

The Federal University of Viçosa, Federal University of Uberlândia and Arthur Bernardes Foundation are warmly thanked for financial support. Moreover, CAPES, CNPq and

Anton, A. K.; Alexandre, C. D.; & Gadi, R. (2006) Solid Acid Catalysts for Biodiesel

Ayhan D.; Biodiesel A Realistic Fuel Alternative for Diesel Engines; ISBN-13: 9781846289941

Ayhan, D. (2003). Biodiesel fuels from vegetable oils via catalytic and non-catalytic

Cardoso, A.L.; Neves, S.C.G.; & da Silva, M.J. (2009). Kinetic Study of Alcoholysis of the

Chongkhong, S.; Tongurai, C.; Chetpattananondh, P. (2009). Continuous esterification for

*Renewable Energies,* Vol.34, (April 2009), pp.1059– 1063, ISSN 0960-1481

Production - Towards Sustainable Energy. *Advances Synthesis Catalysis,* Vol.348, pp.

supercritical alcohol transesterications and other methods: a survey. *Energy Conversion and Management,* Vol.44, (September 2007), pp. 2093–2109, ISSN 0196-

Fatty Acids Catalyzed by Tin Chloride(II): An Alternative Catalyst for Biodiesel Production. *Energy Fuels,* Vol.23 (January 2009), No. 3, pp. 1718–1722, ISNN 0887-

biodiesel production from palm fatty acid distillate using economical process.

description of these mechanism of this reaction.

**3. Conclusion** 

catalysts can has been proved.

FAPEMIG deserves our special thanks.

2008 Springer-Verlag London Limited

**4. Acknowledgment** 

75 – 81

8904

0624

**5. References** 

Consequently, if this part of the reaction pathway is similar to homogeneous systems, the others steps commonly involved in esterification reactions (e.g. protonation carbonyl group FA, attack of the alcohol molecule on protonated FA, water elimination, etc) may then proceed as described in Figure 16.

Fig. 17. Mechanism of formation ester catalyzed by free H+ ion in solution

Conversely, is also possible that other FA molecules can be activated via protonation on surface of supported-catalyst. Thus, an alternative proposal is displayed in Figure 18.

Fig. 18. Proposal of an alternative mechanism of formation ester catalyzed by free H+ ion in the solution

In according with this mechanism (Figure 18), all steps of oleic acid esterification reaction with ethanol occur on surface of HPW/niobium catalyst. Nevertheless, is also possible that ethyl oleate formation may occur by both pathways of reaction Although both proposal are plausible, is important to note that studies in situ are require for a better and more detailed description of these mechanism of this reaction.
