BALEEIRO & SERRA UFT

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MARCO ANTÔNIO BALEEIRO ALVES1

Phone: (0xx63) 3232-8230; (0xx63) 84371188; Fax: (0xx63) 3232-8004

E-mail: [email protected]

JUAN CARLOS VALDÉS SERRA1

Phone: (0xx63) 3232-8230; (0xx63) 81112649; Fax: (0xx63) 3232-8004

E-mail: [email protected]

Corresponding author:

Quadra 109 norte AV NS 15 ALCNO 14. Bloco 2, sala 22, Bairro: Plano Diretor Norte. CEP

77001-090. Palmas-TO. Brasil.1 Universidade Federal do Tocantins. Campus Universitário de Palmas. Master's degree in

Agroenergy.

ATT. MARCO ANTÔNIO BALEEIRO ALVES1



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SUMMARY

In this paper a study was done on the ethanolysis monitoring of the Jatropha curcas oil by keeping

the oil/ethanol molar ratio stable at 1:12 and altering the concentration of the catalyst (KOH) from

0,5; to 1,0; 1,5 and 2,0% and at temperatures of 30, 50 and 70°C. A low cost methodology for the

determination of the conversion into ethyl esthers by oxidation of glycerol with periodic acid was

evaluated. The results were consistent with the literature, since higher concentrations of the alkali

resulted in lower yields, probably due to formation of saponification reactions in larger extent. A

linear and nonlinear regression study and an analysis of variance for statistical evaluation of the

method employed were performed. The best results were consistent with the literature, being 50° Cfor best temperature, 1% (w/v) KOH and reaction time of 60 minutes. Considering that each batch

was performed in a single step reaction only, the maximum conversion into ethyl esters (77.99%)

was considered satisfactory.

Keywords: biofuels; sources renewables; jatropha curcas.



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PRODUCTION MONITORING OF ETHANOL BIODIESEL BY OXIDATION OF JATHROPA

OIL WITH PERIODIC ACID

1. INTRODUCTION

Among the renewable energy alternatives with biomass as feedstock, biodiesel has received

prominence mainly due to the direction given to policies of social-economic growth in Brazil. The

production and consumption of this biofuel has since long received government incentives in

several European countries like Germany, France and Italy. In Brazil, the decree No. 702 of

October 30, 2002, by the Ministry of Science and Technology encourages the development of

scientific and technological research related to biodiesel. The decree of 23 December 2003

instituted the Interministerial Executive Committee in charge of the implementation of actionsdirected towards the production and use of biodiesel as an alternative source of energy. And last,

Law No. 11,097 of January 13, 2005 was enacted providing for the introduction of biodiesel into

the Brazilian energy matrix. Resolution No. 42, November 24, 2004, deals with the insertion of this

new fuel into the Brazilian energy matrix (TECBIO 2008). As described by Knothe et al. (2006),

the main objective of the transesterification reaction is to reduce the high viscosity of crude

vegetable oils. However, many aspects need to be clarified mainly with the aim of improving the

biodiesel production process, reduce costs, increase efficiency and improve the quality.

To achieve these results, a closer study of all involved transesterification reaction parameters

with regard to the types of catalysts used and involved chemical mechanisms is required and the

quality control and production process monitoring need yet to be evaluated.

Since many years the use of chromatographic methods for the determination of glycerol,

mono-, di-and triglycerides in biodiesel, such as is the case of Planck and Lorbeer (1995), has been

common. However, studies using non-chromatographic methods are scarcer, the first having been

published by Bradford et al (1942) who used potentiometric titration. According to Mittelbach

(1996), two important non-chromatographic free glycerol determination methods in vegetable oils

and derivatives have been described in related literature. The first is the official AOCS, method. (Ch

14-56 (1989)). Thereby the glycerol content is determined through oxidation by periodic acid and

thiosulfate titration resulting in formic acid. This same method was also used by Falate et al (2007)

in a study to validate a new biodiesel quality control technique and found that in commercial

soybean oil and biodiesel samples, the percentage of total determined glycerol content was 11.4%

and 0.2% respectively. This method, however, has been scarcely studied for biodiesel samples,



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since it loses in accuracy to the chromatographic methods. The second is a spectrophotometric

determination method based on enzymatic reactions, used commercially in the form of analysis kits,

specifically developed for biodiesel samples (Baila & HUEBER of 1991). A similar

spectrophotometric method with some modifications, also based on periodic acid oxidation of

glycerol, was described by Bondioli & Bella (2005).In the present study, we monitored the Jatropha curcas oil biodiesel production process

using potassium hydroxide as catalyst, changing the concentration of the alkali from 0.5, 1.0, 1.5 to

2.0% (w/v) and the reaction temperature from 30, 50 to 70 ° C. The Oil/ethanol molar ratio was

kept constant at 1:12, the system was kept under constant stirring, and a reaction time of 90 minutes

monitored, using only one reaction step for each batch.

MATERIALS AND METHODS

MATERIALS

Semi-degummed Jatropha curcas vegetable oil, kindly provided by Biotins Energia

S.A.(Paraíso, TO, Brasil), was used . Based on the chemical composition of the oil, an average

molecular weight of 896 g / mol. was assumed. The Jatropha curcas oil presented an iodine content

of 8.306 g/100 g, acidity index of 4.49 mgKOH / g, saponification index 182 mgKOH / g and a

peroxide content of 9.76 mEq of O2/kg. All used reactants were of analytical purity. The absolute

ethanol (99.8%) was purchased from Synth (Diadema, SP, Brazil), the sodium hydroxide (99.5%)

catalyst used was purchased from Vetec Quimica Fina (Rio de Janeiro, RJ, Brazil).

TRANSESTERIFICATION REACTION MONITORING.

In this study, the combined glycerol content was quantified using the iodimetric technique,

and thence the conversion to ethyl esters as a function of time, temperature and concentration of the

alkali was estimated. Each sample was previously saponified to release the glycerol, present in the

form of glyceride, and then the medium was acidified for its complete neutralization.

The glycerol, extracted in the aqueous phase, was then oxidized with excess of periodic acid

(H5IO6 or HIO4). The remaining periodic acid was titrated with a standard solution of sodium

thiosulfate. With this we can see from equation 1 that molecules that have vicinal hydroxyls, as is



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the case with glycerol, react with iodine, from the periodic acid, to form an intermediate and then

aldehydes, ketones and carboxylic acid or iodic acid (HIO3).

Equation 1. Selective reaction of local hydroxyls with periodic acid ( H5IO6 or HIO4)

The reaction is said to be selective because it can form different types of aldehydes and / or

carboxylic acids and even ketones, depending on the size and type of the carbon chain (branched or

normal) where the vicinal hydroxyls are located. In the case of glycerol there is the formation of formic acid and acetaldehyde as shown in equation 2 below:

Glycerin + periodic acid formic acid + acetaldehyde + iodic acid

Equation 2. Representation of the formation of formic acid and acetaldehyde by oxidation of glycerol via periodic acid.

Next, iodic acid (HIO3) resulting from the oxidation of glycerol reacts with iodide to form

iodine (I2), as per equation 3 below:

HIO3 + 5I ¯ + 5H + 3I 2- + 3H2O

Equation 3. Formation of iodine from iodic acid.

Starch indicator is used for the titrimetric determination of the iodine formed as a result of

the classic reaction with thiosulfate.

I2 + 2S2O32- 2I ¯ + S4O6

2-

Equation 4. During titration iodine reacts with the thiosulfate to form iodide.

For the crude oil the combined glycerol content equals the sum of the concentrations of

mono-, di- and triglycerides, according to the chemical equation below:



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GC raw oil = MG + DG (5)

According to Knothe et al (2006) DG and MG concentrations are low and do not

significantly affect the concentration of esters formed during the course of the reaction. As to the

concentration of triglycerides, it is quite high during the first minutes and then decreasesconsiderably, thus:

GC biodiesel = MG + DG (decreases with time) (6)

As for the iodimetric method, despite it not having the required sensitivity to determine the

levels of triglycerides (TG), it is known that this decrease in the levels of MG, DG and TG as a

function of time results from the transformation of these into ethyl esters, thus while the

concentration of MG, DG and TG decreases, inversely the concentration of ethyl esters increasesproportionately. This being so it is possible to estimate the conversion of ethyl esters formed during

the course of the reaction using the following formula:

(GCraw oil - GC bio) x 10 = R’CO2R (%) (7)

Where the difference between the combined glycerol before and after the conversion

provides an estimated value for the biodiesel (ethyl esters) yield.

RESULTS AND DISCUSSIONS

The experimental data was obtained from monitoring the transesterification reaction, using

the AOCS method, Ca 14-56, for determination of the combined glycerol, quantified at the end of

each batch, after neutralization with hydrochloric acid. The conversion values (%) were calculated

using equation 3, where the values were converted and estimated for the content of ethyl esters.

Table 1 below shows the experimental results for three temperatures tested: 30, 50 and

70°C, varying the content of KOH catalyst from 0.5, 1.0, 1.5 to 2.0% (w/v) in a reaction time of 60

minutes. This reaction time is justified since it is considered usual for biodiesel plants, representing

a satisfactory period for the execution of a batch (Knothe et al., 2006).



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Table 1. Experimental conversion results versus temperature.

% KOH Conversion (%)

70ºC R1 R2 R3 X s

0,5 55,65 52,35 44,98 50,99 5,46

1,0 76,21 78,66 69,97 74,94 4,451,5 67,34 62,32 62,14 63,93 2,952,0 50,12 46,45 54,15 50,24 3,85

50ºC R1 R2 R3 X s

0,5 58,99 60,35 60,02 59,78 0,711,0 75,47 80,25 77,99 77,90 2,391,5 69,98 71,11 62,35 67,81 4,762,0 52,13 56,49 59,96 56,19 3,92

30 ºC R1 R2 R3 X s

0,5 60,45 59,29 60,34 60,02 0,6451,0 70,02 69,80 68,76 69,52 0,6731,5 59,87 58,79 60,01 59,55 0,667

2,0 50,03 50,21 52,02 50,75 1,10

Standard deviation (s), Average (x) Repetition 1 (R1) Repetition 2 (R2), Repetition 3 (R3).

The analysis of variance regarding the temperature and catalyst content as a function of yield

was performed with the aid of the ASSISTAT ® software and which resulted in the data shown in

Table 2 below.

Table 2. Analysis of variance.Independent

variablesDegrees of freedom

Sum of squares Mean square F – calculated F – tabulated

T 2 235,649 117,824 11,752* 5,613

C 3 2411,079 803,693 80,166* 4,718

T X C 6 199,300 33,216 3,313* 2,508

Treatments 11 2844,831 258,621 25,807* 3,094

Residues 24 240,607 10,025

Total 35 3086,636

* Significant at 5% probability.

From this statistical treatment we obtained the coefficient of variance, with a good CV result

of 5.123%. This coefficient shows the degree of dispersion of the conversion results, being

considered for laboratory experiments optimal up to 5%, good for CV> 5% to 10%, regular for

CV> 10% to 15% and poor for CV > 15% to 20%.



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Comparing the differences between the averages it is possible to conclude that the

experimental results obtained meet the differences according to the test of Tukey at a level of

significance of 5%. From Table 2 we can see that the tabulated F is less than the calculated F for all

analyzed parameters, therefore it is possible to affirm that there exists a correlation between the

independent variables and the responses of the experiment. We can also see that the catalyst has ahigher calculated F-value and therefore a stronger influence on the experimental results when

compared to the temperature.

From Figure 1 it is possible to see the relationship between the three variables studied:

content of catalyst, temperature and yield, with best result at 1% potassium hydroxide (KOH)

catalyst, 50° C and 1:12 oil-ethanol molar ratio (MR), with an approximate yield of 78%, estimated

on the combined content of glycerol. It has thus been possible to estimate a maximum yield under

the analyzed conditions of temperature, oil-ethanol MR and percentage of the alkali catalyst and

calculate the maximum yield corresponding to 77.998%.

Figure 1. 3D graph showing the content of the alkali and the temperature as a function of theconversion in %.

To BRANDÃO et al. (2006), the presence of an additional 0.5% moisture using sodium

hydroxide as catalyst, may reduce yields by over 20%. In this study, the moisture content in the oilwas relatively high (0.875%), since Freedman et al. (1984) concluded that the moisture content

should be below 0.3% in transesterification reactions catalyzed by bases, higher moisture contents

would mean lower yields, resulting from the formation of hydrolysis reactions and saponification.

Moreover, the presence of acid at 4.49 mg KOH / g, above the by the standard stipulated

amount of 4.0 mg KOH / g , has also influenced the conversion values (%) as shown in Table 4, as,



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according to Dorado et al. (2002), a content of less than 3% of free fatty acids is required for the

transesterification reaction to occur without problems.

As shown in Figure 2, the biodiesel conversion values (%) at 50°C were considerably higher

compared to those at 30 and 70ºC. This result is consistent with the related literature, as higher

temperatures favor less the formation of alkyl esters. However, lower temperatures would also notbe interesting. That would be by reason of the fact that the saponification reaction has lower

activation energy as compared to the transesterification, so an increase in temperature favors the

reaction of saponification and not the transesterification reaction. These results are consistent with

major publications (Brandão et al, 2006; Penha et al., 2007, Moura et al., 2007, Oliveira et al. 2007;

Zagonel et al., 2000, Silva et al. 2005; Suarez et al., 2007, Schuchardt et al., 1998, Knothe et al.,

2006), who are also of the opinion that as of 60 minutes of reaction the content of alkyl esters tends

to stay constant, i.e. does not increase significantly since the reaction is reversible and is stabilized

by the formation of phases, which reduces the effective collisions between the molecules of thereactants.

Using the data from table 1 and with the aid of the Origin 6.0 software it was possible to plot

the concentration of catalyst as a function of yield (figure 2), tested at different temperatures and

concentrations of catalyst as a function of conversion (%). With this, we attempted to adjust the

obtained curves to an equation that would come closest to reflecting the experimental results,

evaluating the coefficient of determination thereof.

Observing figure 2 below one can see that the transesterification reaction showed better

yields at 50° C. At 30° C the yield was higher than at 70° C.

Figure 2. experimental results of conversion (%) as a function of catalyst content atdifferent temperatures.



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Figure 3 below shows the progress of the conversion (%) versus time in minutes for the

three temperatures studied, based on mean values.

Figure 3. Mean conversion values (%) for 30, 50 and 70ºC.

As shown in Figures 2 and 3, the biodiesel conversion values (%) at 50°C were considerably

higher compared to those at 30 and 70ºC. This result is consistent with the related literature, as

higher temperatures favor less the formation of alkyl esters. However, lower temperatures would

also not be interesting. That would be by reason of the fact that the saponification reaction has

lower activation energy as compared to the transesterification, so an increase in temperature favors

the reaction of saponification and not the transesterification reactions. These results are consistent

with major publications (Brandão et al, 2006; Penha et al., 2007, Moura et al., 2007, Oliveira et al.2007; Zagonel et al., 2000, Silva et al. 2005; Suarez et al., 2007, Schuchardt et al., 1998, Knothe et

al., 2006), who are also of the opinion that as of 60 minutes of reaction the content of alkyl esters

tends to stay constant, i.e. does not increase significantly since the reaction is reversible and is

stabilized by the formation of phases, which reduces the effective collisions between the reactants'

molecules.

Table 3 below shows the results of the regressions, the coefficient of determination, the yield

obtained by the quadratic model represented by ymax, and the maximum experimental average after

90 minutes of reaction, which expresses the mean value of the triplicate. From table 3 we also seethat the quadratic model for 50° C showed the best adjustment, having the highest coefficient of

determination (0.98614) among the quadratic models.



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Table 3. Regression results for 30, 50 and 70° C with 1% catalyst.

T (ºC) Adjustment R2 Equation y MAX

(%)model

Averageexperimental

(%)

30 0,89969 y = 46,1825 + 40,243x – 19,41x2 70,07 69,52

50 0,98614 y = 27,7475 + 80,611x – 34,33x2 76,88 77,90

70

Quadratic

0,94600 y = 21,47 + 89,358x – 37,78x2 77,93 74,94

The y max values in Table 3 show a smaller difference between the results of the experiment

at temperatures between 50 and 70º C, with a difference of 1.05% and conversely, a bigger

difference between the results of the experiment at temperatures between 30 and 50° C with a

difference of 6.81%, leading to the conclusion that raising the temperature to 70°C did not

contribute much towards the increase in yield.

As shown in Table 4, this experiment was performed in triplicate for each predetermined

reaction time, given in minutes (5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90), obtaining from these the

average values (x) and the standard deviation (s). In view of the amount of time spent on each

combined glycerol analysis (about 20 minutes), each time set represented three repetitions of

independent batches. Therefore, all procedures were carefully repeated in order to dispel any errors

in measurements and weighing. According to Santos (2008), the reaction time is another important

variable, being the transesterification a reversible process where the dynamic balance may occur at

different times and undergo changes during the process in response to the factors responsible for the

shift in the balance.

The results shown in table 4 are consistent with BRANDÃO et al. (2006) and Lacerda et al.

(2005) who stated that in the process of methyl and ethyl biodiesel production from babaçu oil,

considering a constant oil/alcohol ratio and catalytic content, only minor deviations were observed

in the ester content with reaction times exceeding 60 minutes. I.e. differences of up to a maximum

of 1% were found in these studies. From table 4 we see that the lowest standard deviation value was

0.31%, based on measurements made during the first 5 minutes of the reaction at 30° C.



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Table 4. Conversion results versus time using temperature of 70ºC.

Time

(min)

70ºC 50ºC 30ºC

s x s x s x

5 2,3193 20,22 2,18568 23,88 0,31 20,78

10 1,8975 34,91 2,541305 37,51 1,1660 35,76

15 2,6855 42,67 2,198507 45,10 2,4425 41,60

20 3,0428 52,42 1,914392 54,17 1,0915 44,29

30 1,3219 59,80 1,726190 61,59 0,1352 59,98

40 2,2730 67,91 1,389352 70,96 1,4832 69,64

50 0,8784 71,18 3,920114 77,07 2,9706 72,54

60 1,5282 74,24 2,263566 82,39 1,2540 75,36

70 3,2197 77,10 0,518587 80,44 0,8508 79,41

80 0,8105 76,95 0,892879 81,35 0,8628 79,49

90 3,3707 78,51 2,207555 80,69 2,3301 78,53

Standard deviation (s); Average (x);

This was the best result presented, demonstrating good precision. The highest standard

deviation being 3.92%. Between 70 and 90 minutes, considering the three evaluated temperatures,

there is a maximum deviation of 3.37% in the experiment for 90 minutes at 70°C. It is known that

the figures do effectively tend to stay nearly constant after 60 minutes when compared to the values

from 0 to 50 minutes where the curve is steeper.

To BRANDÃO et al. (2006), the presence of an additional 0.5% moisture using sodium

hydroxide as catalyst, may reduce yields by over 20%. In this study, the moisture content in the oil

was relatively high (0.875%), since Freedman et al. (1984) concluded that the moisture content

should be below 0.3% in transesterification reactions catalyzed by bases, higher moisture contents

would mean lower yields, resulting from the formation of hydrolysis reactions and saponification.

Moreover, the presence of acid at 4.49 mg KOH / g, above the by the standard stipulated

amount of 4.0 mg KOH / g, may also have influenced the conversion values (%) as shown in Table

4, as according to Dorado et al. (2002) a content of less than 3% of free fatty acids is required for

the transesterification reaction to occur without problems.

Table 5 shows the results for the quadratic fitting, the coefficient of determination (R2), the

yield represented by ymax, and the experimental maximum value that expresses the average value of



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the triplicate. From this table we also see that the quadratic model for 30°C showed the best

adjustment, having the highest coefficient of determination (0.97484) among the quadratic models.

Table 5. Adjustments for conversion versus time (min) for 30, 50 and 70° C with 1% catalyst.

T (ºC) Adjustment R2 Equation y MAX

(%)model

Averageexperimental

(%)

30 0,97484 y = 8,62305 + 2,10544x – 0,01533x2 68,67 78,53

50 0,96112 y = 12,04784 + 2,17536x – 0,01611x2 67,51 80,69

70

Quadratic

0,95929 y = 19,84236 + 1,58783x – 0,01064x2 74,61 78,51

The y max values presented in table 5 show a smaller difference between the results of the

experiment at temperatures of 30 and 70° C, with minimum difference of 0.02%. Thus, one can

infer that the temperature of 50° C has a marked influence on the obtained final yield.



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CONCLUSIONS

The quality assessment of jatropha oil for use in the transesterification reaction showed

satisfactory results, despite presenting an acidity index slightly higher than the established limit. As

stated earlier, it is observed in the literature that all the physical-chemical characteristics are quietvariable and depend on many factors such as crop management, soil and climatic conditions,

altitude, rainfall and others that may substantially alter the chemical composition of the Jatropha

curcas oil.

The present study has shown the viability of the combined glycerol determination

methodology through periodic acid oxidation to evaluate the conversion of triglycerides into alkyl

esters. Being a low cost and easy to perform method, it could, in the near future, be adapted for

biodiesel quality assessment at gas stations in the form of test kits.

The statistical analysis showed that both factors: catalyst and temperature had a markedeffect on the conversion (%) into ethyl esters. Therefore, the best biodiesel production results

obtained with the studied process using potassium hydroxide as catalyst, were: at 50° C, 1% KOH,

with molar oil:ethanol ratio of 1:12 and reaction time of 60 minutes, under which the experimental

maximum yield obtained was 77.9033%.

The non-linear regression equations were important to better understand the behavior of the

transesterification reaction and the definition of mathematical models closer to actual behavior.

With them it is possible to determine the estimated yield, controlling the physical and chemical

parameters of the studied process.

However, it should be noted that the good results shown in Tables 3 and 5 are not

necessarily linked to the good yields achieved at the respective temperatures, but to the adjustment

of the points of the mathematical model with the experimental data obtained. However, the method

used has shown to be adequate for the evaluation of the temperature and catalyst content factors as a

function of yield, since it presents a satisfactory experimental outline of the ethyl biodiesel

production process from Jatropha and proved to be viable for future applications where lower

chemical analysis operating costs would be required.



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AKNOWLEDGEMENTS

The authors thank the Brazilian Government which through the Ministry of Science and

Technology - MCT has given support to projects related to the subject of bioenergy at the Federal

University of Tocantins.

DEFINITIONS

AO molar ratio oil / ethanol mol / mol

C catalyst content w/v

CV% coefficient of variance

DG diglyceride

R’CO2R (%) content of ethyl esters (biodiesel)F statistical factor (F test)

G glycerol

GC bio biodiesel combined glycerol

GC raw oil raw oil combined glycerol

MG monoglyceride

ROH alcohol

R2 coefficient of determination

TG Triglycerides

T temperature



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BALEEIRO & SERRA UFT