effect of antioxidants and additives on the oxidation stability of no lo e puesto

Kasetsart J. (Nat. Sci.) 44 : 243 - 250 (2010)

Effect of Antioxidants and Additives on the Oxidation Stability ofJatropha Biodiesel

Duanpen Chaithongdee1, Jarun Chutmanop1, 2 and Penjit Srinophakun1, 2 *

ABSTRACT

Jatropha biodiesel was produced by a transesterification reaction, using potassium hydroxide

at 1.5% by weight of Jatropha oil as a catalyst. The mole ratio of methanol and Jatropha oil was 7:1. The

temperature, speed of mixing and reaction time used were 45°C, 600 rpm and 1.5 h, respectively.

Antioxidants and additives were added to Jatropha biodiesel. The range of antioxidant and additive

concentrations was 0-750 and 0-1,000 ppm, respectively. The three antioxidants used were PG (3,4,5-

trihydroxybenzoic acid propyl ester, propyl gallate), TBHQ (t-butyl hydroquinone) and BHA (butylated

hydroxyanisole). The three commercial additives used were ZEP additive, NITROX and L-power. The

induction time of biodiesel with either antioxidant or additive was measured according to EN14112,

using a Rancimat instrument. The results showed that PG was the best antioxidant for the production of

Jatropha biodiesel at concentrations of 50, 150, 250, 350, 500, 650 and 750 ppm, which improved the

induction time from 4.21 with no additive to 18.93, 26.35, 30.20 32.98, 34.04, 36.01 and 37.55 h

respectively. Regarding the effect on storage for 20 weeks, Jatropha biodiesel with PG added at a

concentration of 150 ppm, resulted in an induction time from the first week storage of 26.35 h and this

reduced to 23.59 h in the final week (10.47% reduction from the first week). The Jatropha biodiesel

properties that resulted from the addition of PG at a concentration of 150 ppm were within the acceptable

range, according to ASTM and EN Standards.

Key words: oxidation stability, biodiesel, Jatropha oil, induction time

1 Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand.2 Center for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand.

* Corresponding author, e-mail: [email protected]

INTRODUCTION

With the increasing price of petroleum

fuel as supplies are depleted, the need for

alternative fuel sources has steadily increased.

Biodiesel is an alternative fuel, derived from

vegetable oil, animal fat or waste cooking oil that

can be used directly or blended with petroleum

diesel at any percentage without engine

modification (Faupel and Kurki, 2002). The

advantages of biodiesel are a reduction in vehicle

emissions and engine wear, and it is non-toxic and

biodegradable (Faupel and Kurki, 2002; Hancsok

et al., 2008; Kalam and Masjuki, 2008).

The use of edible vegetable oil for

biodiesel production has not been successful

because of its unstable price (Chhetri et al., 2008).

As the demand for vegetable oils for food has

increased substantially in recent years, it would

be better to use non-edible oils for biodiesel

production. Therefore, non-edible oils, such as

Jatropha oil, will become significant sources for

Received date : 31/07/09 Accepted date : 09/10/09

244 Kasetsart J. (Nat. Sci.) 44(2)

biodiesel production now or in the future (Chhetri

et al., 2008; Kywe and Oo, 2009).

Jatropha is a fast growing plant, which

requires little water or fertilizer; it can survive in

infertile soils (Sarin et al., 2007). Generally, the

oil content of the Jatropha seed is 30–40%

(Augustus et al., 2002; Sarin et al., 2007). Oil from

the Jatropha seed has excellent properties,

including low acidity, low viscosity compared to

castor oil and a better cloud point and pour point

when compared to palm oil (Tapanes et al., 2008).

Biodiesel is an ester of a fatty acid. The

properties of biodiesel depend on the feedstock.

If the feedstock is composed of high unsaturated

fatty acids, the oxidation stability of biodiesel is

low (Domingos et al., 2007; McCormick et al.,

2007; Sarin et al., 2007). The oxidation stability

affects fuel qualities. In fact, esters have low

stability (Sarin et al., 2007). If biodiesel is exposed

to air or oxygen, it is oxidized to alcohol and acids

(Knothe, 2007; Sarin et al., 2007). The presence

of alcohol will lead to a reduction in the flash point

and the presence of acid will increase the total acid

number (Sarin et al., 2007). The sensitivity of the

oxidation stability is due to the unsaturated fatty

acid content in the oil (McCormick et al., 2007;

Sarin et al., 2007). Other factors, which also have

an influence on the oxidation stability of biodiesel

are light, high temperature, metals, peroxides and

antioxidants (Knothe, 2007; McCormick et al.,

2007; Sarin et al., 2007).

The mechanism of the biodiesel

oxidation process can be divided into three steps,

which are shown in Figure 1, where RH is the fatty

acid methyl ester, R′ is a free radical, O2 is the

oxygen in the air, ROO′ is a peroxide radical and

R-R and ROOR are the products of the oxidation

process. During the oxidation process, the fatty

acid methyl ester is likely to form a free radical at

the position next to the double bond (Equation 1)

(McCormick et al., 2007; Sarin et al., 2007). The

radical quickly reacts with the oxygen in the air

and becomes a peroxide radical (Equation 2),

which immediately creates a new free radical from

the fatty acid methyl ester (Equation 3)

(McCormick et al., 2007; Sarin et al., 2007). The

reaction will continue until two free radicals react

with each other (Equation 4) or the peroxide

radical reacts with a free radical in the terminal

step (Equation 5) (Sarin et al., 2007). This process

results in the formation of acids, esters, aldehydes,

ketones etc. (McCormick et al., 2007; Sarin et al.,

2007). This leads to changes in the biodiesel

properties, such as viscosity, acid number and

oxidation stability (Bondioli et al., 2003).

The European standard for biodiesel

(EN14112) evaluates the oxidation stability using

a Rancimat instrument. The standard oxidation

stability is 6 h at 110°C. The oxidation stability of

biodiesel can be improved by adding an

appropriate antioxidant (McCormick et al., 2007).

Two common types of antioxidants are either a

phenolic-type and an aminic-type (Sarin et al.,

2007) (Figure 2). Generally, the antioxidant, which

can hinder the combination oxidation reaction in

Figure 1, contains highly labile hydrogen that is

Initiation RH R(1) ׳

Propagation R׳ + O2 ROO(2) ׳

ROO ׳ + RH ROOH + R(3) ׳

Termination R׳ + R׳ R-R (4)

ROO׳ + R׳ ROOR (5)

Figure 1 Mechanism of the biodiesel oxidation process.

Kasetsart J. (Nat. Sci.) 44(2) 245

more easily abstracted by the peroxy radical than

the fatty oil or ester hydrogen (Sarin et al., 2007).

Mittelbatch and Schober (2003) found that the

efficiency of a given antioxidant depends on the

raw material of the biodiesel. Therefore, while any

type of antioxidant may be suitable for a particular

feedstock of biodiesel, some antioxidants can

improve oxidation stability slightly, while others

can produce a substantial improvement in

oxidation stability. Consequently, this research was

conducted to determine the type of antioxidant

appropriate for use with Jatropha biodiesel.

MATERIALS AND METHODS

Jatropha oil, which was a feedstock for

biodiesel production, was extracted from the

expeller. Three antioxidant and three commercial

additives were used in this experiment. The

antioxidants, which were PG (Propyl gallate),

TBHQ (t-butyl hydroquinone) and BHA (butylated

hydroxyanisole), were analytical grade (Fluka,

Switzerland). The three additives were ZEP

additive, NITROX and L-power. The ZEP additive

(ZEP diesel fuel additive) was obtained from the

Zep Manufacturing Company of Canada.

NITROX (NITROX injector cleaner) was obtained

from Tetrosyl Limited (United Kingdom). L-power

was obtained from Loxley Public Company

Limited (Thailand).

Jatropha biodiesel was produced by

transesterification reaction. Potassium hydroxide

was used as a catalyst at 1.5% by weight of

Jatropha oil. The mole ratio of methanol and

Jatropha oil was 7:1. The temperature, speed of

mixing and reaction time were 45°C, 600 rpm and

1.5 h respectively, after which the various

antioxidants and additives were added to the

Jatropha biodiesel. The range in the antioxidant

and additive concentrations was 0-750 and 0-1,000

ppm, respectively. The oxidation stability of the

samples was measured by the induction time

according to EN14112 (standard method) using a

Rancimat instrument (Domingos et al., 2007;

Knothe, 2007; Sarin et al., 2007). The best

antioxidant or additive was then added to Jatropha

biodiesel, which was kept for long-term stability

testing. The Jatropha biodiesel sample was stored

in a brown bottle, which was closed by parafilm

and kept at room temperature for 20 weeks. Every

two weeks, a sample was taken to determine the

induction time.

RESULTS AND DISCUSSION

Effect of antioxidants on the oxidation stabilityof Jatropha biodiesel

In this experiment, the induction time

was measured as an indication of the oxidation

stability of biodiesel. Three antioxidants, PG,

TBHQ and BHA, were added to Jatropha biodiesel

in a concentration range of 0-750 ppm.

Figure 3 shows the effect of the

concentration of antioxidants on the oxidation

stability. The induction time of Jatropha biodiesel

Figure 2 Mechanism of the anti-oxidation

process of antioxidants (Sarin et al.,

2007).


without antioxidant was 4.21 h, which is below

the standard value of the oxidation stability of 6 h

(Domingos et al., 2007; Knothe, 2007; Sarin et

al., 2007). The induction time increased with

incremental increases in the antioxidant

concentration. Dunn (2005) and McCormick et al.

(2007) also reported similar results. Dunn (2005)

studied the effect of five antioxidants (BHA, BHT,

TBHQ, α-Tocopherol and PG) on the oxidation

stability of biodiesel produced from soybean oil

by transesterification. It was reported that the

oxidation stability increased with increases in the

antioxidant concentration. McCormick et al.

(2007) also studied the oxidation stability of

biodiesel produced from soybean oil, waste oil and

tallow, reporting that the oxidation stability

increased when the concentration of antioxidant

increased. An increment in the antioxidant

concentration results in an increase in the number

of hydrogen atoms that then can react with the

peroxide radical in the oxidation reaction (Ramos

et al., 2007),

The comparison among PG, BHA and

TBHQ at the same concentration is shown in

Figure 3. It was found that PG was the most

effective antioxidant for Jatropha biodiesel at the

minimum concentration of 50 ppm leading to an

induction time of 18.93 h. TBHQ and BHA were

the second and the third most effective

antioxidants, respectively, being able to produce

an induction time in excess of 6 h at a concentration

higher than 150 ppm. A similar result was

also found by Xin et al. (2008), who studied

the effect of two antioxidants (diphenyl-P-

phenylenediamine and PG) on the oxidation

stability of biodiesel produced from palm oil,

sunflower oil and rapeseed oil. They reported that

PG was the best suitable antioxidant for biodiesel

produced from palm oil, sunflower oil and

rapeseed oil.

Effect of additives on the oxidation stability ofJatropha biodiesel

Three commercial additives, ZEP,

NITROX and L-power, were added to Jatropha

biodiesel in a concentration range of 0-1,000 ppm.

The oxidation stability of Jatropha biodiesel with

the additive is shown in Figure 4. None of the

additives increased the induction time to longer

than the standard oxidation stability of 6 h. The

Figure 3 Influence of antioxidant concentration on the oxidation stability of Jatropha biodiesel.


oxidation stability of Jatropha biodiesel with ZEP

added increased slightly when the ZEP

concentration was increased, with a concentration

of ZEP at 1,000 ppm causing an increase in the

induction time to 5.30 h. The induction time of

Jatropha biodiesel with NITROX added increased

slightly with a NITROX concentration of 0-750

ppm. However, the induction time decreased when

the concentration of NITROX was higher than

1,000 ppm. The concentration of NITROX at 750

ppm extended an induction time to 5.29 h.

However, the induction time decreased slightly as

the concentration of L-power increased.

Accordingly, ZEP, NITROX and L-power, did not

improve the oxidation stability of Jatropha

biodiesel.

Changes in the oxidation stability during 20weeks of storage

PG, TBHQ, BHA, ZEP, NITROX and L-

power were studied in order to find the best

antioxidant or additive to improve the oxidation

stability of Jatropha biodiesel. The results showed

that PG was the best antioxidant that resulted in

an induction time longer than the other products.

Consequently, PG was selected for addition to

Jatropha biodiesel for further study.

PG was added to Jatropha biodiesel at a

concentration of 150 ppm and stored for 20 weeks.

The concentration level of 150 ppm was selected

to ensure that the induction time remained higher

than 6 h during storage. A concentration of 50 ppm

produced an induction time lower than 6 h within

the 20 weeks of storage. After storage, the

induction time of the sample was more than 6 h

when PG was added at a concentration of 250 ppm.

However, the lowest concentration of antioxidant

was preferred as it meant a cost saving by requiring

less antioxidant concentration. Consequently, a

concentration of 150 ppm was used. The sample

was stored in a brown bottle at room temperature

(about 30°C) for 20 weeks. Every two weeks, the

induction time of the sample was measured and

the results are shown in Figure 5.

The aim of this experiment was to predict

the behavior of Jatropha biodiesel when it was

maintained under steady environmental conditions

for a reasonable period. During storage, the

Figure 4 Influence of additive concentration on the oxidation stability of Jatropha biodiesel.


induction time steadily decreased. The induction

time after one week of storage was 26.35 h and

this reduced to 23.59 h in the final weeks (a

reduction of 10.47% from the first week). The

oxidation reaction of biodiesel during storage

caused the acid number to increase, as was

suggested by Bouaid et al. (2007). The acid

number increased with the increase in peroxide

because the ester (biodiesel) was oxidized to form

peroxide, which underwent a complex reaction,

including the formation of a reactive aldehyde,

which could be oxidized into acid. In addition, acid

could be formed also from hydrolysis of the ester

into alcohol and acid (Bouaid et al., 2007).

Consequently, the increment of acid, alcohol and

aldehyde resulted in a reduction in the induction

time during storage (Bouaid et al., 2007). Prankl

and Schindlbauer (1998) and Bondioli et al. (2003)

studied the long-term stability of biodiesel

produced from rapeseed oil kept at room

temperature. They reported that the induction time

decreased during storage.

Properties of Jatropha biodieselThe objective of this experiment was to

study the effect of PG antioxidant on the major

properties of Jatropha biodiesel. The major

properties studied were: viscosity at 40°C, cloud

point, pour point, flash point, density at 15°C,

neutralization value (acid number, acid value) and

the induction time. Table 1 compares the

properties of Jatropha biodiesel without

antioxidant with those when PG is added at a

concentration of 150 ppm.

According to Table 1, the properties of

Jatropha biodiesel, with PG added at a

concentration of 150 ppm, changed slightly within

the range of the standard properties of biodiesel

defined by ASTM D6751 (Knothe, 2007;

McCormick et al., 2007; Dunn, 2005).

Consequently, PG was considered an interesting

option to improve the oxidation stability of

Jatropha biodiesel with no effect on the principal

properties.

CONCLUSION

The study compared the effects of

various types of antioxidants and additives on the

oxidation stability of Jatropha biodiesel. PG was

identified as the most suitable antioxidant to

improve the oxidation stability of Jatropha

Figure 5 Changes in the oxidation stability during storage.


biodiesel. ZEP, NITROX and L-power were not

appropriate additives to improve the oxidation

stability of Jatropha biodiesel. From this study, the

minimum concentration of 50 ppm of PG was the

best antioxidant for Jatropha biodiesel according

to the standard for the oxidation stability of

biodiesel (EN14112). When Jatropha biodiesel

with PG added at a concentration of 150 ppm was

stored for 20 weeks, the induction time after the

first week of storage was 26.35 and reduced to

23.59 in the final week (a 10.47% reduction). All

the properties of Jatropha biodiesel with PG added

at a concentration of 150 ppm were within the

acceptable range for the standard properties of

biodiesel. Therefore, PG was considered a suitable

antioxidant to improve the oxidation stability of

Jatropha biodiesel with long-term oxidation

stability retention.

ACKNOWLEDGEMENTS

The authors thank the Center of

Excellence for Petroleum, Petrochemicals and

Advanced Materials, the Graduate School,

Kasetsart University and the KU Biodiesel Project

for financial support.

LITERATURE CITED

Augustus, G.S., M. Jayabalan and G.J. Seiler.

2002. Evaluation and bioinduction of energy

components of Jatropha curcas. BiomassBioenerg. 23: 161-164.

Bondioli, P., A. Gasparoli, L.D. Bella, S. Tagliabue,

G. Toso, J. Fischer and A. Frohlich. 2003.

Work Package 2 Storage Tests, pp. 17-25. In

H. Prankl (ed.). Stability of Biodiesel.Druckerei Queiser GmbH, Amstetten, Austria.

Bouaid, A., M. Martinez and J. Aracil. 2007. Long

storage stability of biodiesel from vegetable

and used frying oils. Fuel 86: 2596-2602.

Chhetri, A.B., M.S. Tango, S.M. Budge, K.C.

Watts and M.R. Islam. 2008. Non-edible plant

oils as new sources for biodiesel production.

Int. J. Mol. Sci. 9: 169-180.

Domingos, A.K., E.B. Saad, W.D. Vechiatto, H.M.

Wilhelm and L.P. Ramos. 2007. The Influence

of BHA, BHT and TBHQ on the Oxidation

Stability of Soybean Oil Ethyl Ester

(Biodiesel). J. Braz. Chem. Soc. 18: 416-423.

Dunn, R.O. 2005. Effect of antioxidants on the

oxidative stability of methyl soyate

(biodiesel). Fuel Process. Technol. 86: 1071-

1085.

Faupel, K. and A. Kurki. 2002. Biodiesel: a BriefOverview. Available source: http://

www.attra.ncat.org/attra-pub/biodiesel.html,

June 10, 2008.

Hancsok, J., M. Bubalik, A. Beck and J. Baladincz.

2008. Development of multifunctional

Table 1 Physico-chemical properties of Jatropha biodiesel.

Property (units) Test method Limits Jatropha Jatropha biodiesel with

biodiesel PG added at 150 ppm

Viscosity at 40°C (cSt) ASTM D445 3.5 – 5.0 4.43 4.40

Cloud point (°C) ASTM D2500 - 5 5

Pour point (°C) ASTM D 97 - -2 -2

Flash point (°C) ASTM D 93 Min. 120 185 190

Density at 15°C ASTM D 1298 860-900 876 875.5

(kg/m3)

Neutralization value ASTM D 664 Max. 0.5 0.35 0.35

(mg KOH/gm)

Oxidation stability (h) EN 14112 Min. 6 4.21 26.35


additives based on vegetable oil for high

quality diesel and biodiesel. Chem. Eng. Res.Des. 86: 793-799.

Kalam, M.A. and H.H. Masjuki. 2008. Testing

palm biodiesel and NPAA additives to control

NOx and CO while improving efficiency in

diesel engines. Biomass Bioenerg. 32: 1116-

1122.

Knothe, G. 2007. Some aspects of biodiesel

oxidative stability. Fuel Process. Technol. 88:

669-677.

Kywe, T.T. and M.M. Oo. 2009. Production of

Biodiesel from Jatropha Oil (Jatropha curcas)

in Pilot Plant. PWASET. 38: 2070-3740.

McCormick, R.L., M. Ratcliff, L. Moens and R.

Lawrence. 2007. Several factors affecting the

stability of biodiesel in standard accelerated

tests. Fuel Process. Technol. 88: 651-657.

Mittelbach, M. and S. Schober. 2003. The

influence of antioxidants on the oxidation

stability of biodiesel. J. Am. Oil Chem. Soc.80: 817-823.

Prankl, H and H. Schindlbauer. 1998. Oxidation

stability of fatty acid methyl esters, pp. 1-5.

In 10th European Conference on Biomassfor Energy and Industry. 8-11 June 1998,

Wurzburg, Germany.

Ramos, L.P., A.K. Domingos, E.B. Saad, W.W. D.

Vechiatto and H. M. Wilhelmc. 2007. The

Influence of BHA, BHT and TBHQ on the

Oxidation Stability of Soybean Oil Ethyl

Esters (Biodiesel). J. Braz. Chem. Soc. 18:

416-423.

Sarin, R., M. Sharma, S. Sinharay and R.K.

Malhotra. 2007. Jatropha–Palm biodiesel

blends: An optimum mix for Asia. Fuel 86:

1365-1371.

Tapanes, N.O.T., D.A.G. Aranda, J.W.M. Carneiro

and O.A.C. Autunes. 2008. Transesterification

of Jatropha curcas oil glyerides: Theoretical

and experimental studies of biodiesel reaction.

Fuel 87: 2286-2295.

Xin, J., H. Imahara and S. Saka. 2008. Oxidation

stability of biodiesel fuel as prepared by

supercritical methanol. Fuel 87: 1807-1813.

effect of antioxidants and additives on the oxidation stability of no lo e puesto

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