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184

CHAPTER V

NATURAL ANTIOXIDANTS AS ADDITIVES FOR

BIODIESEL STABILIZATION

1. Introduction

Biodiesels offer many benefits over conventional petroleum diesel. It burns

cleaner, with low net emissions and reduced particulates, hydrocarbons, and carbon

monoxide. Biodiesels also possess a high cetane number and improves petroleum diesel

cetane performance when blended. Since it is naturally low in sulfur content, it also

lowers sulfur emissions when blended with petroleum diesel. Biodiesel blending also

imparts improved lubricity to petroleum diesel [1 -4]. Since it is domestically produced,

biodiesel shows great potential for reducing dependence on foreign energy supplies.

It provides a “closed economic loop” in that the feedstock can be grown locally, the

biodiesel can be produced locally, and the fuel can be used locally. Furthermore, it is

evident that very minimal to no infrastructure change is necessary to implement

widespread biodiesel use. Biodiesel blends can be used in any diesel engine and can be

transported and stored using existing infrastructure [4 - 6].

Pure biodiesel is environmentally non-toxic and biodegradable. With its high

energy balance of 3.2 to 1, biodiesel provides a beneficial 78% life cycle CO2 reduction.

While biodiesel shows such tremendous potential, there are still unresolved challenges to

its complete acceptance. In the list of Research Priorities from the Biodiesel Technical

Workshop in Denver, Colorado, in November 2005, the top two items identified by this

group of experts were: 1) fuel quality and quality standards, and 2) fuel stability.

A distant third priority was cold flow properties. The fuel quality and standards issues are

being addressed in the ASTM Fuel Standards subcommittee. Thus, the single most

critical acceptance issue requiring research and development is that of biodiesel stability;

in particular, oxidative stability [7, 8].

The degradation of biodiesel is generally due to oxidation, which is indicated by

increased acid number and viscosity, as well as the formation of gums and sediments.

185

The oxidation process starts with the formation of hydroperoxides by the addition of an

oxygen molecule to a carbon atom adjacent to a C=C double bond. As oxidation

proceeds, the peroxides break away to form aldehydes and short-chain acids.

Alternatively, peroxides may generate free radicals, which promote polymerization and

crosslinking among the olefinic (C=C containing) molecules. Therefore, oxidation

reactivity is related to the number of C=C bonds in the fuel. Increased content of the C=C

bonds correlates to decreased oxidative stability of the fuel. The increase in instability of

a given diesel fuel molecule is generally directly proportional to the number of C=C

bonds in the molecule (i.e., a molecule containing two C=C bonds has half the stability of

a molecule containing one C=C bond) [9].

Augmenting petroleum-derived fuels with renewable fuels has gained widespread

attention in the the recent past. One such renewable fuel is biodiesel, which according to

ASTM D 6751-07 is defined as the mono-alkyl ester of long-chain fatty acids derived

from vegetable oils or animal fats [4]. Biodiesel offers numerous environmental,

economic and energy security benefits, and production capacity has grown considerably

in the past two to three years, especially in Europe and the USA. Currently, methanol is

predominantly used in the transesterification process for biodiesel production [6].

The presence of high levels of unsaturated fatty acid methyl esters (FAME) makes

biodiesel very susceptible to oxidation as compared to petroleum diesel [7]. Oxidative

processes bring about increased viscosity as a result of condensation reactions involving

double bonds, also leading to the formation of insoluble, which can potentially plug fuel filters

and injection systems [8]. The increased acidity and increased peroxide value as a result of

oxidation reactions can also cause corrosion of fuel system components, hardening of rubber

components, and fusion of moving components [8-9]. ASTM D6751-07 includes an oxidation

stability standard of a three-hour minimum induction period (IP) as measured using the

Rancimat test (EN14112)[4]. The European Committee for standardization adopted a six-hour

minimum IP as the specification [10]. A survey of retail biodiesel samples performed in 2004

indicated that only four out of 27 B100 samples met the oxidative stability standard of three

hours and over 85% had an IP of less than two hours [11].

186

Factors which influence the oxidative stability of biodiesel include fatty acid

composition, natural antioxidant content, the level of total glycerin, and the conditions of

fuel storage such as temperature, exposure to light and air, and material used for storage

tank construction [11, 14- 15]. Previous studies have found that antioxidants can be

effective in increasing the stability of biodiesel [7, 14, 16-17]. However, these effects have

not been fully elucidated and results have been inconclusive or conflicting. Mittelbach et al.

[18] reported that pyrogallol (PY), propylgallate (PG), and t-butylhydroquinone (TBHQ)

could significantly improve the stability of biodiesel obtained from rapeseed oil, used frying

oil, and beef tallow, whereas BHT was not very effective. Moreover, Domingos et al. [18]

found that BHT had the highest effectiveness for refined soybean oil-based biodiesel,

while BHA displayed little effectiveness. Natural antioxidants are constituents of many

fruits and vegetables and they have attracted great deal of public and scientific attention

because of their anti-carcinogenic potential. Biodiesel is an environment friendly liquid

fuel similar to petrodiesel in combustion properties.

The high compatibility of biodiesel with petroleum diesel characterizes it as a

good alternative capable of supplying most of the existing diesel fleet without great

adaptations. It is also biodegradable and renewable, has a lubricating capacity in the pure

form and is competitive with diesel in terms of fuel properties [2]. However, unlike fossil

fuels that are relatively inert and maintain their essential characteristics with little

alteration during storage, biodiesel degrades with time and can be altered due to the

action of air, light, temperature and moisture. Contact with contaminants, both inorganic

and microbial nature, can also tend to introduce variations in product quality, and

oxidation resulting from its exposure to atmospheric air is one of the main degradation

problems to which biodiesel is subject [8]. In order to inhibit or delay oxidation in oils, fats

and fatty foods, phenolic chemical compounds are used, known as synthetic antioxidants

and/or stabilizers [9]. Antioxidants occur naturally in vegetable oils and the most common

are the tocopherols. However, some plant oil production processes include a distillation step

to purify the triglycerides. The biodiesel obtained from these oils normally has little or no

natural antioxidants so they become less stable and therefore antioxidants need to be applied

to increase the biofuel stability and extend its properties for a longer period [12].

187

A new alternative to delay the biodiesel oxidative degradation process may be the

use of natural antioxidants present in spices, bearing in mind that they do not damage the

environment and are easily obtained [19]. According to some studies, rosemary

(Rosmarinus officinalis L.) and sage (Salvia officinalis L.) are spices with greatest

antioxidant potentials [19, 20]. The antioxidant activity of carnosol and carnosic acid,

found in rosemary, was validated in an emulsion containing methyl linoleate [21].

According to Nakatani and Inatani (1984), the addition of natural antioxidants such as

carnosol and carnosic acid, at a 0.01% concentration, in a linoleic acid emulsion, have

activity levels similar to those of the synthetic antioxidants BHA (butyl hydroxy anisole) and

BHT (butyl hydroxy toluene) added in the same concentration [22]. Five different phenolic

compounds were isolated from oregano (Origanum vulgare L.); all presented antioxidant

activity and one of them was identified as rosmarinic acid [23]. Furthermore, the study

carried out by Bragagnolo and Mariuti (2007) [24] reported several other phenolic

compounds that were isolated from oregano, including luteolin, p-coumaric acid, carvacrol,

thymol, p-cimen, and campherol. These findings demonstrate a great possibility of using

these spices as good antioxidants and possible substitutes for the synthetic antioxidants,

especially in mixtures consisting of unsaturated carbon compounds as substrate. Numerous

strong antioxidant compounds have been identified in fruits, vegetables [25, 26].

In this chapter, twelve antioxidant compounds were isolated from six plants such

as Murraya koenigii (L.) Spreng, Mentha arvensis L, Coriandrum sativum L., Curcuma

lunga, Citrullus colocynthis, and Eichornia crasipus. The extraction, isolation and

characterization of the twelve compounds (carvone, phellendrene, cymene, caryophyllene,

menthol, curcumin, cucurbitcin, rutin, arbutin, coumarin, quercetin, and tannic acid) are

already described in Chapter II. Results reveal that all the 12 isolated compounds have

antioxidant activity which is evident from the chemical assay, storage studies and

oxidative stability of Jatropha and Pongamia biodiesel.

2. Experimental

2.1. Antioxidant chemical assay

In this chapter, four assays, namely, FRAP, TRAP, SOS and ABTS were employed for

determination of antioxidant activity of the isolated antioxidants. The chemical structures of the

188

12 isolated compounds, namely, carvone, phellendrene, cymene, caryophyllene, menthol,

curcumin, cucurbitcin, rutin, arbutin, coumarin, quercetin and tannic acid, are given in Figure.5.1.

CH3

CH3H3C

O

H

O

OH

OH

OH

OH

HO

O

H3C

CH3

H2C

CH3

HH

O

O

OH

OH

OH

O

HO

Carvone Phellendrene Cymene Menthol

Quercetin

Caryophyllene

189

OH

O

O

OH

HO

HO

OH

O O

O O

OHOH

OCH3

OH

H3CO

HO

O

H

O

O

O H

O H

O

O H

HO

O

O

O H

O

HO OH

OOH

O H

HO

HO

3,3’-methylene-bi(4- hydroxyl coumarine)

Cucurbitacin I

Curcumin

Arbutin

Rutin

190

Figure 5.1: Chemical structures of the 12 compounds isolated from various plants.

The characterization of the isolated compounds were carried out using UV-Visible

spectrophotometry, FTIR, GC, GC-MS, HPLC, MS and 1H NMR techniques characterization

details are given in chapter II.

3. Results and Discussion

3.1. Antioxidant chemical assay

The antioxidant scavenging ability of the isolated natural compounds was

evaluated using four different scavenging methods and was compared with the

antioxidant scavenging ability of those available commercially. From the study it is clear

hat the natural antioxidants have greater antioxidant scavenging ability compared to the

commercially available antioxidants (Figure 5.2).

O

OO

OO

O

OH

OH

HO

HO

O

O

HO

HO OH

O

O

HO OH

O

O

OH

OH

OH

O

O

H

HO

OH

O

O

OH

OHO

O

HO OH

HO

O

O

OHHO

O

O

OH

OH

OH

Tannic acid

191

192

Figure. 5.2: Antioxidant assays 1) ABTS, 2) SOS, 3) TRAP, and 4) FRAP.

193

The TRAP and ABTS method of scavenging activity involves a hydrogen transfer

reaction and the reaction scheme is given below,

ROO* + AH→ ROOH + A*

ROO* + LH →ROOH + L*

SOS and FRAP method of scavenging activity involves an electron transfer reaction and

the electron transfer scavenging reaction is given below,

M(n) + e (from AH) → AH*+ + M(n - 1)

The ABTS method described, gives a measure of the antioxidant activity of carotenoids

and phenolics, It is determined by measuring the reduction of the radical cation as the

percentage inhibition of absorbance at 734 nm which is visually characterized by the

decolorization of the ABTS•. Figure 1 illustrates the effects of the duration of interaction of

specific antioxidants on the suppression of the absorbance of the ABTS•* radical cation at

734 nm. Trolax was used as the standard reference compound for this assay. The antioxidant

activity of natural antioxidants as determined by ABTS assay were compared with activities of

commercially available antioxidants such as BHA, BHT, GA, TBHQ and PY.

The scavenging activities of natural antioxidants were concentration dependent. 20 µg/

ml of carvone from curry leaf gave better results when compared with commercially available

antioxidants. Increasing the concentration of carvone above 20 µg/ ml did not improve the

scavenging activity. The activity of other antioxidants increased with increase in concentration

upto 100 µg/ ml. Curcumin from Curcuma longa (turmeric) and tannic acid from Eichornia

cracipus exhibited good scavenging activity. The antioxidant activity of curcumin and tannic

acid were above 94%, both being nearly the same. The ABTS results clearly show that the

naturally available antioxidants were better than the commercially available antioxidants.

The SOS method shows that at a concentration of 20 µg/ ml all the naturally

occurring antioxidants give substantial activity. Increasing the load of antioxidants did

not result in much change in antioxidant activity for any of the natural antioxidants except

rutin and caryophyllene. Caryophyllene gave scavenging activity of 84% at 100 µg/ ml

whereas rutin gave 83% scavenging activity at 40 µg/ ml. Above these concentrations the

antioxidant activity decreased for both rutin and caryophyllene.

The TRAP method revealed highest activity at 20

antioxidants. Increasing the concentration of antioxidants did not alter the

natural antioxidants except cucurbitacin I, rutin and tannic acid. Highest scavenging activities

of 96.9% for tannic acid, 96% for cucurbitacin I and 95.2% for Rutin was observed, all at

100 .µg/ ml.

The FRAP assay gives fast, rep

in pure solution and with mixtures of antioxidants in aqueous solution added to plasma. FRAP

results show gradual increase in scavenging activity from 20 to 100

activity of 83% in FRAP assay was exhibited by tannic acid and 75% activity by

coumarin, both isolated form

natural antioxidants have greater scavenging ability as compared to commercially

available antioxidants. T

performed using naturally available and commercially availabl

concentration of 100 µ

best scavenging activity among both natural and commercially available antioxidants.

Figure. 5.3: Comprehensive results of all the assays perf

commercially available antioxidants at a concentration of 100

0

10

20

30

40

50

60

70

80

90

100

ABTS

Act

ivit

y (

%)

194

The TRAP method revealed highest activity at 20 µg/ ml

antioxidants. Increasing the concentration of antioxidants did not alter the


for tannic acid, 96% for cucurbitacin I and 95.2% for Rutin was observed, all at

The FRAP assay gives fast, reproducible results with plasma, with single antioxidants


results show gradual increase in scavenging activity from 20 to 100

FRAP assay was exhibited by tannic acid and 75% activity by

coumarin, both isolated form Eichhornia crasipus. From the above results it is clear that


available antioxidants. The Figure below is a comprehensive result of all the assays

performed using naturally available and commercially availabl

concentration of 100 µg/ ml. From this Figure it is observed that tannic acid exhibited the


Comprehensive results of all the assays performed using naturally and

commercially available antioxidants at a concentration of 100

SOS TRAP FRAPConcentration (μg/ml)

ml for all the natural

antioxidants. Increasing the concentration of antioxidants did not alter the activity for any of the


for tannic acid, 96% for cucurbitacin I and 95.2% for Rutin was observed, all at

roducible results with plasma, with single antioxidants


results show gradual increase in scavenging activity from 20 to 100 µg/ ml. The highest

FRAP assay was exhibited by tannic acid and 75% activity by

. From the above results it is clear that


below is a comprehensive result of all the assays

performed using naturally available and commercially available antioxidants at a

it is observed that tannic acid exhibited the


ormed using naturally and

commercially available antioxidants at a concentration of 100 µg/ ml.

Carvone

Phelland

Cymene

Caryoph

Menthol

Curcumin

Cucurbit I

Arbutin

Rutin

Coumarin

Quercetin

Tannic

TBHQ

PY

BHT

BHA

GA

195

3.2. Evaluation of Pongamia and Jatropha biodiesel storage stability using naturally

occurring antioxidants

The viscosity of JBD (expand) and PBD (expand) with naturally occurring

antioxidants isolated from six plants as a function of storage time is plotted (Figure 5.4).

The viscosity of untreated JBD and PBD biodiesel increased from 4.4 to 14.76 mm2/s and

4.48 to 14.7 mm2/s respectively measured over a period of 25 weeks. In the present

evaluation, different concentrations (100, 200, 500, 1000, 2000, 3000 and 5000 ppm) of

the 12 natural antioxidants was added to JBD and PBD and their viscosity was measured.

ASTM D 4625 specification (1.9 - 6.0 mm2/s) at 30 ºC was used as the standard.

In this study six different atmospheric conditions for storage of the biodiesel were

also employed. The storage conditions employed were: 1) OGOS, 2) OGCS, 3) OGCSN,

4) AGOS, 5) AGCS and 6) AGCSN.

Results of storage studies of biodiesel using the twelve isolated compounds from

the six plants are henceforth discussed. Storage in amber glass bottle with nitrogen

atmosphere was found to be the best storage condition exhibiting minimum oxidation.

Figure 5.4 below shows the variance of kinematic viscosity, acid value and peroxide

value of JBD and PBD stored in nitrogen atmosphere with respect to time, using tannic

acid as the antioxidant at a concentration of 1000 ppm. The variance of kinematic

viscosity, acid value and peroxide value of JBD and PBD using all the twelve isolated

compounds is discussed further below

196

Storage studies using tannic acid as additive in Pongamia biodiesel

Storage studies using tannic acid as additive in Jatropha biodiesel

Figure 5.4: The variance of kinematic viscosity, acid value and peroxide value of JBD

and PBD stored in nitrogen atmosphere with respect to time using tannic acid

as the antioxidant.

During storage, the viscosity of the methyl esters increases by the formation of

more polar, oxygen containing molecules and also by the formation of oxidized

polymeric compounds that can lead to the formation of gums and sediments that clog

filters [6]. In ASTM D4625–25 procedure, the KV, PV and AV values were determined

at 30 °C over a period of 25 weeks at regular intervals. The kinematic viscosity of

Pongamia biodiesel and Jatropha biodiesel at the initial stage was 4.8 and 4.4 mm2/s

respectively. When the biodiesel was left by itself for a time period of 25 weeks in

different atmospheric conditions, the biodiesel started to oxidize and the KV value rose to

an enormously high value of 14.76 mm2/s for PBD and 14.7 mm2/s for JBD. This is a

clear indication of storage unstability of biodiesel which is a serious problem.

4

6

8

10

12

14

16

0 10 20

Kin

em

ati

c V

isco

sit

y (

mm

²/s)

Weeks

Neat 100 ppm

200 ppm 500 ppm

1000 ppm 2000 ppm

3000 ppm 5000 ppm

6

6.5

7

7.5

8

8.5

9

9.5

10

0 10 20P

ero

xid

e v

alu

e (

mg

/kg

)

Weeks

Neat 100 ppm

200 ppm 500 ppm

1000 ppm 2000 ppm

3000 ppm 5000 ppm

0.3

0.8

1.3

1.8

2.3

2.8

0 5 10 15 20 25

Acid

valu

e (

mg

KO

H/g

)

Weeks

Neat 100 ppm200 ppm 500 ppm1000 ppm 2000 ppm3000 ppm 5000 ppm

4

6

8

10

12

14

16

0 10 20

Kin

em

ati

c V

isco

sit

y (

mm

²/s)

Weeks

Neat 100 ppm

200 ppm 500 ppm

1000 ppm 2000 ppm

3000 ppm 5000 ppm

5

5.2

5.4

5.6

5.8

6

6.2

6.4

6.6

0 10 20

Pe

rox

ide

Va

lue (

mg

/Kg

)

Weeks

Neat 100 ppm

200 ppm 500 ppm

1000 ppm 2000 ppm

3000 ppm 5000 ppm

0.3

0.8

1.3

1.8

0 10 20

Ac

id V

alu

e (

mg

KO

H/g

)

Weeks

Neat 100 ppm

200 ppm 500 ppm

1000 ppm 2000 ppm

3000 ppm 5000 ppm

197

The acid value (AV) of biodiesel samples also increased with increasing storage

time as a result of hydrolysis of fatty acids methyl esters (FAME) to fatty acids (FA). The

specified limit of acid value of biodiesel is 0.5 mg KOH/g measured over a period of 25

weeks and stored under different atmospheric conditions. The acid value of JBD and

PBD initially was 0.38 mg KOH/g. When the biodiesel was left by itself for a time period

of 25 weeks stored in different atmospheric conditions, the acid value rose up to 6 mg

KOH/g, which is very high.

The peroxide value (PV) of the biodiesel samples also increased on storage as a

result of oxidation of fatty acids methyl esters to fatty acids. The specified limits of PV of

biodiesel is 3 to 6 mg/kg. When the biodiesel was left by itself for a time period of

25 weeks stored in different atmospheric conditions, the peroxide value increased up to

9.3 and 6.7 mg/kg for PBD and JBD respectively. The introduction of naturally occurring

antioxidants reduced the rate of peroxidation which is also clearly shown in Figure 5.4.

The employment of commercially available antioxidants to retard the oxidation

process during storage is already discussed in chapter IV. This chapter discusses the

effect of naturally occurring antioxidants isolated from six different plants, on JBD and

PBD. Results clearly indicate that natural antioxidants definitely improve the storage

stability. Antioxidant activity of each of the 12 isolated compounds are discussed below.

3.2.1. Natural Antioxidants from Murraya koenigii (L.) Spreng as additives

for Biodiesel stabilization

Murraya koenigii (L.) Spreng plant was identified and authenticated by Botanical

Survey of India and the herbarium is stored in Bharathiyar University. Extraction,

isolation and characterization details of the Murraya koenigii (L.) Spreng extract are

given in chapter II. Four compounds were isolated from Murraya koenigii (L.) Spreng

namely, carvone, phellendrene, cymene and caryophyllene.

198

3.2.1.1. ASTM (D-4625 at 30 °°°°C): (Kinematic Viscosity)

Figure. 5.5: Kinematic viscosity studies of PBD containing antioxidants isolated from

Murraya koenigii (L.) Spreng ; (a) storage condition, (b) antioxidants, and

(c) quantity of antioxidants (Caryophyllene).

Figure.5.6: Kinematic viscosity studies of JBD containing antioxidants isolated from

Murraya koenigii (L.) Spreng; (a) storage condition, (b) antioxidants, and

(c) quantity of antioxidants (Caryophyllene).

The kinematic viscosity of PBD and JBD is shown in Figure 5.5 and 5.6. The best

atmospheric condition was found to be AGCSN. The KV value of PBD after the addition of

1000 ppm antioxidant is 6.3 mm2/s and 4.76 mm

2/s after the addition of 5000 ppm in AGCSN.

This was measured over a period of 25 weeks. These values come well under the standard

value of FAME. Comparision between commercially available antioxidants and naturally

occuring antioxidants shows that Murraya koenigii (L.) Spreng antioxidants had better activity.

Caryophyllene isolated from Murraya koenigii (L.) Spreng showed the best activity as

compared to pyrogallol (commercially antioxidant). The KV value of PBD was found to be

4.9 mm2/s after 25 weeks when caryophyllene was used at a concentration of 5000 ppm.

a b

c

a b c

199

The KV value of JBD after the addition of 1000 ppm caryophyllene was 5.5 mm2/s

and 4.52 mm2/s after the addition of 5000 ppm in AGCSN. This was measured over period of

25 weeks. These values come well under the standard value of FAME. Comparision between

commercially available antioxidants and naturally occuring antioxidants shows that

antioxidants isolated from Murraya koenigii (L.) Spreng had better activity. Caryophyllene

showed the best activity as compared to pyrogallol. The KV value of JBD was found to be

4.5 mm2/s after 25 weeks when caryophyllene was used at a concentration of 5000 ppm.

3.2.1.2. ASTM (D-4625 at 30 °°°°C): (Peroxide Value)

Figure. 5.7: Peroxide values of PBD containing antioxidants isolated from Murraya koenigii (L.)

Spreng; (a) storage condition, (b) antioxidants, and (c) quantity of antioxidants

(Caryophyllene).

Figure. 5.8: Peroxide values of JBD containing antioxidants isolated from Murraya koenigii

(L.) Spreng; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Cymene).

a b c

b c

a

200

The peroxide value determined by ASTM D-4625 method for PBD and JBD is

shown in Figure 5.7 and 5.8. The AGCSN method of storage was better than the other

five methods and henceforth used for this evaluation. The PV of PBD after the addition

of 1000 ppm antioxidant was 6.4 mg/kg and 6.1 mg/kg after addition of 5000 ppm

caryophyllene in AGCSN. This was measured over a period of 25 weeks. These values

come under the standard value of FAME. Comparision between commercially available

antioxidants and naturally occuring antioxidants shows that caryophyllene had better

activity even when compared with pyrogallol (commercially antioxidant). The PV of

PBD was found to be 6.1 mg/kg after 25 weeks when caryophyllene was used at a

concentration of 1000 ppm.

The PV of JBD after the addition of 1000 ppm cymene is 5.45 mg/kg and

5.23 mg/kg after addition of 5000 ppm in AGCSN. This was measured over period of

25 weeks. These values come well under the standard value of FAME. Comparision

between commercially available antioxidants and naturally occuring antioxidants shows

that cymene had better activity even when compared with pyrogallol (commercially

antioxidant). The PV of JBD was found to be 5.21 mg/kg after 25 weeks when

caryophyllene was used at a concentration of 1000 ppm.

3.2.1.3. ASTM (D-4625 at 30 °°°°C): (Acid Value)

Figure. 5.9: Acid value of PBD containing antioxidants isolated from Murraya koenigii (L.)

Spreng.; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Caryophyllene).

a b c

201

Figure. 5.10: Acid value of JBD containing antioxidants isolated from Murraya koenigii

(L.) Spreng.; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Cymene).

The acid value determined by ASTM D 4625 method for PBD and JBD is shown

in Figure 5.9 and 5.10. The AGCSN method of storage is better than the other five

methods and henceforth used for this evaluation. The AV of PBD after the addition of

1000 ppm caryophyllene is 0.58 mg KOH/g and 0.42 mg KOH/g after addition of 5000 ppm

antioxidants in AGCSN. This was measured over a period of 25 weeks. These values

come well under the standard value of FAME. Comparision with commercially available

antioxidants revealed that caryophyllene had good antioxidant activity, better than

pyrogallol. The AV of PBD was found to be 0.58 mg KOH/g after 25 weeks when

caryophyllene was used at a concentration of 1000 ppm.

The AV of JBD after the addition of 1000 ppm cymene is 0.58 mg KOH/g and

0.4 mg KOH/g after addition of 5000 ppm in AGCSN. This was measured over period of

25 weeks. These values come well under the standard value of FAME. Comparision with

commercially available antioxidants shows that cymene has better activity compared to

pyrogallol. The AV of JBD was found to be 0.4 mg KOH/g after 25 weeks when cymene

was used at a concentration of 5000 ppm.

3.2.2. Natural Antioxidants from Coriandrum sativum L. as additives for Biodiesel

stabilization

Coriandrum sativum L plant was identified and authenticated by Botanical Survey

of India and the herbarium was stored in Bharathiyar University. Extraction, isolation and

a b c

202

characterization details of the Coriandrum sativum L. extract are given in chapter II. Four

compounds were isolated from Coriandrum sativum L. namely arbutin, phellendrene,

rutin and cymene.


Figure. 5.11: Kinematic viscosity of PBD containing antioxidants isolated from

Coriandrum sativum L.; (a) storage condition, (b) antioxidants, and

(c) quantity of antioxidants (Arbutin).

Figure. 5.12: Kinematic viscosity of JBD containing antioxidants isolated from

Coriandrum sativum L.; (a) storage condition, (b) antioxidants, and

(c) quantity of antioxidants (Arbutin).

The kinematic viscosities of PBD and JBD are shown in Figure 5.11 and 5.12.

The best atmospheric condition, AGCSN, was used. The KV value of PBD after the

addition of 1000 ppm antioxidant was 6.1 mm2/s and 5.8 mm

2/s after addition of 5000 ppm

arbutin. This was measured over a period of 25 weeks. These values come under the

standard value of FAME. Comparision with commercially available antioxidants shows

c b a

a b c

203

that arbutin had better activity as compared to pyrogallol. The KV value of PBD was found

to be 5.8 mm2/s after 25 weeks when arbutin was used at a concentration of 5000 ppm.

The KV value of JBD after the addition of 1000 ppm antioxidant is 5.1 mm2/s

and 4.7 mm2/s after addition of 5000 ppm rutin. This was measured over a period of

25 weeks. These values come well under the standard value of FAME. Comparision with

commercially available antioxidants shows that rutin has better activity as compared to

pyrogallol. The KV value of JBD was found to be 4.7 mm2/s after 25 weeks when rutin



Figure. 5.13: Peroxide value of PBD containing antioxidants isolated from Coriandrum

sativum L.; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Arbutin).

Figure. 5.14: Peroxide value of JBD containing antioxidants isolated from Coriandrum



a b c

a b c

204


shown in Figure 5.13 and 5.14. Since the AGCSN method of storage was better than the

other five methods, it was henceforth used for peroxide value evaluation. The PV of PBD

after the addition of 1000 ppm antioxidant is 6.18 mg/kg and 6.1 mg/kg after addition of

5000 ppm arbutin in AGCSN. This was measured over a period of 25 weeks. These

values come under the standard value of FAME. Comparision with commercially

available antioxidants shows that arbutin has better activity as compared to pyrogallol.

The PV of PBD was found to be 6.1 mg/kg after 25 weeks when arbutin was used at a


The PV of JBD after the addition of 1000 ppm arbutin is 5.28 mg/kg and

5.21 mg/kg after addition of 5000 ppm antioxidants in AGCSN. This was measured over

a period of 25 weeks. These values come well under the standard value of FAME.

Comparision between commercially available antioxidants shows that arbutin has better

activity as compared to pyrogallol. The PV of JBD was found to be 5.21 mg/kg after

25 weeks when arbutin was used at a concentration of 5000 ppm.


Figure. 5.15: Acid value of PBD containing antioxidants isolated from Coriandrum



b c

a

205

Figure. 5.16: Acid value of JBD containing antioxidants isolated from Coriandrum sativum L.;

(a) storage condition, (b) antioxidants, and (c) quantity of antioxidants (Arbutin).

The acid values determined by ASTM D-4625 method for PBD and JBD are

shown in Figure 5.15 and 5.16. Sicne the AGCSN method of storage was the best among those

tested it was used for this evaluation. The AV of PBD after the addition of 1000 ppm

antioxidant is 0.49 mg KOH/g and 0.39 mg KOH/g after addition of 5000 ppm arbutin.

This was measured over period of 25 weeks. These values come well under the standard

value of FAME. Comparision between commercially available antioxidants shows that

arbutin has better activity as compared to pyrogallol. The AV of PBD was found to be

0.39 mg KOH/g after 25 weeks when arbutin was used at a concentration of 5000 ppm.

The AV of JBD after the addition of 1000 ppm arbutin is 0.43 mg KOH/g and

0.39 mg KOH/g after addition of 5000 ppm arbutin. This was measured over period of


between commercially available antioxidants shows that arbutin has better activity as

compared to pyrogallol. The AV of JBD was found to be 0.39 mg KOH/g after 25 weeks

when arbutin was used at a concentration of 5000 ppm.

3.2.3. Natural Antioxidants from Mentha arvensis L. as additives for Biodiesel stabilization

Mentha arvensis L. plant was identified and authenticated by Botanical Survey of India

and the herbarium was stored in Bharathiyar University. Extraction, isolation and

characterization details of the Mentha arvensis L. extract are given in chapter II. Four

compounds were isolated from Mentha arvensis L. namely Carvone, phellendrene, cymene,

menthol.

c a b

206


Figure.5.17: Kinematic viscosity of JBD containing antioxidants isolated from Mentha

arvensis L.; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Pyrogallol).

Figure.5.18: Kinematic viscosity of PBD containing antioxidants isolated from Mentha

arvensis L.; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (TBHQ).

The Kinematic viscosity of PBD and JBD are shown in Figure 5.17 and 5.18.

The best atmospheric condition, AGCSN, was used . The KV value of PBD after the

addition of 1000 ppm antioxidant is 6.23mm2/s and 5.1 mm2/s after addition of 5000

ppm menthol. This was measured over period of 25 weeks. These values come under the


that menthol had better activity as compared to pyrogallol. The KV value of PBD was

found 5.1 mm2/s after 25 weeks when menthol was used at a concentration of 5000 ppm.

c a b

a b c

207

The KV value of JBD after the addition of 1000 ppm menthol was 5.5 mm2/s and

4.5 mm2/s after the addition of 5000 ppm in AGCSN. This was measured over period of


between commercially available antioxidants and naturally occuring antioxidants shows

that antioxidants isolated from Mentha arvensis L. had better activity. Menthol showed

the best activity as compared to pyrogallol. The KV value of JBD was found to be 4.5

mm2/s after 25 weeks when menthol was used at a concentration of 5000 ppm.


Figure.5.19: Peroxide value of PBD containing antioxidants isolated from Mentha arvensis L.;

(a) storage condition, (b) antioxidants, and (c) quantity of antioxidants (pyrogallol).

Figure.5.20: Peroxide value of JBD containing antioxidants isolated from Mentha arvensis L.;

(a) storage condition, (b) antioxidants, and (c) quantity of antioxidants

(Menthol).

a b c

a b c

208





5000 ppm menthol in AGCSN. This was measured over a period of 25 weeks. These


available antioxidants shows that menthol has better activity as compared to commercial

antioxidants. The PV of PBD was found to be 6.3 mg/kg after 25 weeks when menthol


The PV of JBD after the addition of 1000 ppm menthol is 5.8 mg/kg and



Comparision between commercially available antioxidants shows that menthol has better

activity as compared to pyrogallol. The PV of JBD was found to be 5.28 mg/kg after 25

weeks when menthol was used at a concentration of 5000 ppm.


Figure.5.21: Acid value of PBD containing antioxidants isolated from Mentha arvensis L.;


(Menthol).

a b c

209

Figure.5.22: Acid value of JBD containing antioxidants isolated from Mentha arvensis L.;


(Menthol).

The acid values determined by ASTM D-4625 method for PBD and JBD are shown in

Figure 5.21 and 5.22. Sicne the AGCSN method of storage was the best among those tested it

was used for this evaluation. The AV of PBD after the addition of 1000 ppm antioxidant is

0.51 mg KOH/g and 0.41 mg KOH/g after addition of 5000 ppm menthol. This was measured

over period of 25 weeks. These values come well under the standard value of FAME.

Comparision between commercially available antioxidants shows that menthol has better

activity as compared to commercial antioxidants. The AV of PBD was found to be 0.41 mg

KOH/g after 25 weeks when menthol was used at a concentration of 5000 ppm.

The AV of JBD after the addition of 1000 ppm menthol is 0.51 mg KOH/g and

0.41 mg KOH/g after addition of 5000 ppm menthol. This was measured over period of


between commercially available antioxidants shows that menthol has better activity as


when menthol was used at a concentration of 5000 ppm.

3.2.4. Natural Antioxidants from Curcuma lunga as additives for Biodiesel stabilization

Curcuma lunga plant was identified and authenticated by Botanical Survey of

India and the herbarium was stored in Bharathiyar University. Extraction, isolation and

characterization details of the Curcuma lunga extract are given in chapter II. One

compound was isolated from Curcuma lunga namely curcumin.

c b a

210

3.2.4.1. ASTM (D-4625 at 30°C): (Kinematic Viscosity)

Figure.5.23: Kinematic viscosity of PBD containing antioxidants isolated from Curcuma

lunga; (a) storage condition, (b) antioxidants, and (c) quantity of antioxidants

(Curcumin)

Figure.5.24: Kinematic viscosity of JBD containing antioxidants isolated from Curcuma


(Curcumin)



addition of 1000 ppm antioxidant is 4.7mm2/s and 4.4 mm


curcumin. This was measured over period of 25 weeks. These values come under the


that curcumin had better activity as compared to pyrogallol. The KV value of PBD was

found 4.4 mm2/s after 25 weeks when curcumin was used at a concentration of

5000 ppm.

c b a

a b c

211

The KV value of JBD after the addition of 1000 ppm curcumin was 6.1 mm2/s

and 5.7 mm2/s after the addition of 5000 ppm in AGCSN. This was measured over

period of 25 weeks. These values come well under the standard value of FAME.

Comparision between commercially available antioxidants and naturally occuring

antioxidants shows that antioxidants isolated from Curcuma lunga had better activity.

curcumin showed the best activity as compared to commercial antioxidants. The KV

value of JBD was found to be 5.7 mm2/s after 25 weeks when menthol was used at a


ASTM (D-4625 at 30 °°°°C): (Peroxide Value)

Figure.5.25: Peroxide Value of PBD containing antioxidants isolated from Curcuma


(Curcumin)

Figure.5.26: Peroxide value of JBD containing antioxidants isolated from Curcuma


(Curcumin)

a b c

a b c

212





5000 ppm menthol in AGCSN. This was measured over a period of 25 weeks. These


available antioxidants shows that curcumin has better activity as compared to pyrogallal.

The PV of PBD was found to be 6.1 mg/kg after 25 weeks when curcumin was used at a


The PV of JBD after the addition of 1000 ppm curcumin is 5.3 mg/kg and



Comparision between commercially available antioxidants shows that curcumin has better

activity as compared to pyrogallol. The PV of JBD was found to be 5.28 mg/kg after 25 weeks

when curcumin was used at a concentration of 5000 ppm.


Figure.5.27: Acid Value of PBD containing antioxidants isolated from Curcuma lunga;


(Curcumin)

c a b

213

Figure. 5.28: Acid value of JBD containing antioxidants isolated from Curcuma lunga; (a)

storage condition, (b) antioxidants, and (c) quantity of antioxidants (Curcumin)

The acid values determined by ASTM D-4625 method for PBD and JBD are shown in

Figure 5.27 and 5.28. Sicne the AGCSN method of storage was the best among those tested it

was used for this evaluation. The AV of PBD after the addition of 1000 ppm antioxidant is

0.51 mg KOH/g and 0.39 mg KOH/g after addition of 5000 ppm curcumin. This was

measured over period of 25 weeks. These values come well under the standard value of FAME.

Comparision between commercially available antioxidants shows that curcumin has better

activity as compared to commercial antioxidants. The AV of PBD was found to be 0.39 mg

KOH/g after 25 weeks when curcumin was used at a concentration of 5000 ppm.

The AV of JBD after the addition of 1000 ppm curcumin is 0.44 mg KOH/g and

0.41 mg KOH/g after addition of 5000 ppm curcumin. This was measured over period of


between commercially available antioxidants shows that curcumin has better activity as


when curcumin was used at a concentration of 5000 ppm.

3.2.5. Natural Antioxidants from Citrullus colocynthis as additives for Biodiesel

stabilization

Citrullus colocynthis plant was identified and authenticated by Botanical Survey


characterization details of the Citrullus colocynthis extract are given in chapter II. One

compound was isolated from Citrullus colocynthis namely cucurbitacin I.

a b c

214


Figure. 5.29: Kinematic viscosity of PBD containing antioxidants isolated from Citrullus

colocynthis; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Rutin)

Figure.5.30: Kinematic viscosity of JBD containing antioxidants isolated from Citrullus


antioxidants (Cucurbitacin I)



addition of 1000 ppm antioxidant is 5.7mm2/s and 5.1 mm


rutin. This was measured over period of 25 weeks. These values come under the standard

value of FAME. Comparision with commercially available antioxidants shows that rutin

had better activity as compared to pyrogallol. The KV value of PBD was found

5.1 mm2/s after 25 weeks when rutin was used at a concentration of 5000 ppm.

a b c

a b c

215

The KV value of JBD after the addition of 1000 ppm cucurbitacin I was

4.4 mm2/s and 4.1 mm

2/s after the addition of 5000 ppm in AGCSN. This was measured

over period of 25 weeks. These values come well under the standard value of FAME.

Comparision between commercially available antioxidants and naturally occuring

antioxidants shows that antioxidants isolated from Citrullus colocynthis had better

activity. Cucurbitacin I showed the best activity as compared to commercial antioxidants.

The KV value of JBD was found to be 4.1 mm2/s after 25 weeks when cucurbitacin I was

used at a concentration of 5000 ppm.


Figure. 5.31: Peroxide value of PBD containing antioxidants isolated from Citrullus

colocynthis; ; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Cucurbitacin I)

Figure.5.32: Peroxide value of JBD containing antioxidants isolated from Citrullus



a b c

a b c

216





5000 ppm cucurbitacin I in AGCSN. This was measured over a period of 25 weeks.

These values come under the standard value of FAME. Comparision with commercially

available antioxidants shows that cucurbitacin I has better activity as compared to

pyrogallal. The PV of PBD was found to be 6.2 mg/kg after 25 weeks when cucurbitacin

I was used at a concentration of 5000 ppm.

The PV of JBD after the addition of 1000 ppm rutin is 5.4 mg/kg and 5.21 mg/kg

after addition of 5000 ppm antioxidants in AGCSN. This was measured over a period of


between commercially available antioxidants shows that rutin has better activity as

compared to pyrogallol. The PV of JBD was found to be 5.21 mg/kg after 25 weeks when

rutin was used at a concentration of 5000 ppm.



shown in Figure 5.33 and 5.34. Sicne the AGCSN method of storage was the best among

those tested it was used for this evaluation. The AV of PBD after the addition of

1000 ppm antioxidant is 0.45 mg KOH/g and 0.4 mg KOH/g after addition of 5000 ppm

rutin. This was measured over period of 25 weeks. These values come well under the standard

value of FAME. Comparision between commercially available antioxidants shows that rutin

has better activity as compared to commercial antioxidants. The AV of PBD was found to be

0.4 mg KOH/g after 25 weeks when rutin was used at a concentration of 5000 ppm.

217

Figure. 5.33: Acid value of PBD containing antioxidants isolated from Citrullus colocynthis;

(a) storage condition, (b) antioxidants, and (c) quantity of antioxidants (Rutin)

Figure. 5.34: Acid value of JBD containing antioxidants isolated from Citrullus



The AV of JBD after the addition of 1000 ppm rutin is 0.41 mg KOH/g and

0.39 mg KOH/g after addition of 5000 ppm rutin. This was measured over period of


between commercially available antioxidants shows that rutin has better activity as


when rutin was used at a concentration of 5000 ppm.

3.2.6. Natural Antioxidants from Eichhornia crasipus as additives for Biodiesel

stabilization

Eichhornia crasipus plant was identified and authenticated by Botanical Survey


a b c

a b c

218

characterization details of the Eichhornia crasipus extract are given in chapter II. Three

compounds were isolated from Eichhornia crasipus namely coumarin, quercetin

dihydrate, tannic acid.


Figure. 5.35: Kinematic viscosity of PBD containing antioxidants isolated from

Eichhornia crasipus; (a) storage condition, (b) antioxidants, and (c) quantity

of antioxidants (Tannic acid)

Figure.5.36: Kinematic viscosity of JBD containing antioxidants isolated from Eichhornia

crasipus; (a) storage condition, (b) antioxidants, and (c) quantity of antioxidants

(Tannic acid)



addition of 1000 ppm antioxidant is 5.9 mm2/s and 4.9 mm2/s after addition of 5000 ppm

quercetin. This was measured over period of 25 weeks. These values come under the


a b c

a b c

219

that quercetin had better activity as compared to pyrogallol. The KV value of PBD was

found 4.9 mm2/s 5000 ppm in AGCSN. This was measured over period of 25 weeks.

These values come well under the standard value of FAME. Comparision between

commercially available antioxidants and naturally occuring antioxidants shows that

antioxidants isolated from Eichhornia crasipus had better activity. Tannic acid showed the

best activity as compared to commercial antioxidants. The KV value of JBD was found to be

4.8 mm2/s after 25 weeks when Tannic acid was used at a concentration of 5000 ppm.


Figure.5.37: Peroxide value of PBD containing antioxidants isolated from Eichhornia

crasipus; (a) storage condition, (b) antioxidants, and (c) quantity of

antioxidants (Tannic acid)

Figure.5.38: Peroxide value of JBD containing antioxidants isolated from Eichhornia crasipus;


(qurcetin).

a b c

a b c

220





5000 ppm quercetin in AGCSN. This was measured over a period of 25 weeks. These


available antioxidants shows that quercetin has better activity as compared to pyrogallal.

The PV of PBD was found to be 5.38 mg/kg after 25 weeks when quercetin was used at a


The PV of JBD after the addition of 1000 ppm quercetin is 5.3 mg/kg and 5.28 mg/kg

after addition of 5000 ppm antioxidants in AGCSN. This was measured over a period of


between commercially available antioxidants shows that quercetin has better activity as

compared to pyrogallol. The PV of JBD was found to be 5.28 mg/kg after 25 weeks when

quercetin was used at a concentration of 5000 ppm.



shown in Figure 5.39 and 5.40. Since the AGCSN method of storage was the best among

those tested it was used for this evaluation. The AV of PBD after the addition of

1000 ppm antioxidant is 0.51 mg KOH/g and 0.44 mg KOH/g after addition of 5000 ppm

quercetin. This was measured over period of 25 weeks. These values come well under the

standard value of FAME. Comparision between commercially available antioxidants

shows that quercetin has better activity as compared to commercial antioxidants. The AV

of PBD was found to be 0.44 mg KOH/g after 25 weeks when quercetin was used at a


221

Figure. 5.39: Acid value of PBD containing antioxidants isolated from Eichhornia



Figure.5.40: Acid value of JBD containing antioxidants isolated from Eichhornia



The AV of JBD after the addition of 1000 ppm tannic acid is 0.56 mg KOH/g and

0.41 mg KOH/g after addition of 5000 ppm tannic acid. This was measured over period

of 25 weeks. These values come well under the standard value of FAME. Comparision

between commercially available antioxidants shows that tannic acid has better activity as


when tannic acid was used at a concentration of 5000 ppm.

a b c

a b c

222

3.3. Oxidative stability of JBD and PBD using naturally occurring antioxidants

Rancimat method was adopted for the determination of oxidation stability because

it is the most commonly used method in the vegetable oil sector. A high content of

unsaturated fatty acids, which is very sensitive to oxidative degradation, leads to

decreased induction times. Thus, even the conditions of fuel storage directly affect the

quality of product. Several studies showed that the quality of biodiesel over a longer

period of storage strongly depends on the tank material as well as on contact to air and

light. Increase in viscosities and acid values leads to decrease in induction periods [2, 8].

The oxidative stability of biodiesel was studied using the Rancimat method

(EN14112). The performance of the twelve isolated antioxidants was compared with that

of commercial antioxidants. One of the isolated natural antioxidants, namely menthol,

exhibited an induction time of 49 h, which is far greater than the expected standard

induction time of 6 h (Figure 5.41).

223

Figure.5.41: Oxidative stability studies on Menthol at PBD and JBD.

The Rancimat test is the specified standard method for oxidative stability for

biodiesel in accordance with EN 14112 [24]. The absolute difference between two

independent single test results did not exceed the repeatability limit of the EN 14112

method. The IP for 100% biodiesel (B100) specified in ASTM D6751-05 was not less

than 3 h [25]. The induction period of Pongamia biodiesel without addition of antioxidant

was 0.33 h. Antioxidative capabilities of phenolic antioxidants is dependent on the

number of phenolic group occupying 1, 2 or 1, 4 positions in the aromatic ring, as well as

to the volume and electronic characteristics of the ring substituent present. Generally, the

active hydroxyl group can provide protons that inhibit the formation of free radicals or

interrupt the propagation of free radical and thus delay the rate of oxidation [18].

224

225

226

227

Figure.5.42: Oxidative stability studies on PBD and JBD using naturally occurring

antioxidants.

228

Results of oxidative studies of Pongamia and Jatropha biodiesel using naturally

occurring antioxidants are presented in the above Figure. Experiments were carried out at

different storage conditions. The storage conditions employed were: 1) ordinary glass

bottle with open space (OGOS), 2) ordinary glass bottle with closed space (OGCS),

3) ordinary glass bottle with closed space containing nitrogen (OGCSN), 4) amber glass

bottle with open space (AGOS), 5) amber glass bottle with closed space (AGCS) and

6) amber glass with closed space containing nitrogen (AGCSN). The oxidative stability

of biodiesel was studied by the Rancimat method as per EN14112 methodology using the

naturally occurring antioxidants. The commercially available antioxidant activity for JBD

and PBD is already discussed in chapter IV. The twelve isolated compounds were studied

in this chapter. Menthol from mint leaves exhibited excellent antioxidant activity with

induction time increasing from 0.05 h to 12 h, at 1000 ppm. Menthol exhibited an

induction time of 49 h at 5000 ppm in JBD, which is far greater than the expected

standard induction time of 6 h. A concentration of 1000 ppm for most of the natural

antioxidants had a beneficial effect on the storage stability of biodiesel. The induction

time of PBD when menthol was added at a concentration of 5000 ppm was 4.5 h after a

storage time 25 weeks. PBD exhibited an induction time of 5.86 h when Tannic acid

was added to it at a concentration of 1000 ppm. and 13.86 h at 5000 ppm. The induction

time of JBD was 7.26 h when tannic acid was added to it at a concentration of 1000 ppm in

and 22.36 h at 5000 ppm PBD displayed an induction time of above 7 h when Quercetin

was added to it at a concentration of 1000 ppm and 12.5 h at a concentration of

5000 ppm. The induction time of JBD when Quercetin was added to it was above 8 h at

1000 ppm and 25.35 h at 5000 ppm Cucurbitacin added JBD showed an induction time

of 3.8 h at 1000 ppm and 11 h at 5000 ppm. PBD exhibited an induction time of 8 h at

1000 ppm of curcurbitacin and 19 h at 5000 ppm of curcurbitacin. From Murraya

(curry leaf) we have extracted four compounds. Except Carvone all the other compounds

have good antioxidant activity. PBD gave an induction time of 2.8 h when caryophyllene

was added to it at a concentration of 1000 ppm and 15.21 h at a concentration of 5000

ppm,. Caryophyllene added JBD exhibited an induction time of 6.33 h at 1000 ppm and

32.21 h at 5000 ppm. PBD displayed an induction time of 2.8 h at 1000 ppm of cymene

and 6.38 h at 5000 ppm. Likewise JBD displayed an induction time of 6.1 h at 1000 ppm

229

and 10.12 h at 5000 ppm of cymene. Phellendrene mixed PBD gave an induction time

of 3.4 h at 1000 ppm and 6.2 h at 5000 ppm. When phellendrene was added to JBD 8.2 h at

a concentration of 1000 ppm, the induction time was 8.2 h and 19.8 h at 5000 ppm

concentration of phellendrene. All the other isolated compounds gave less induction time

when mixed with JBD and PBD.

Sl.No. Antioxidants Biodiesel

Without

Antioxidants

Induction time

(h)

Induction Time (h)

1000 ppm 5000 ppm

1 Menthol PBD 0.05 12 49

JBD 0.05 1 4.50

2 Tannic acid PBD 0.05 5.86 13.86

JBD 0.05 7.26 22.36

3 Quercetin PBD 0.05 7.00 12.50

JBD 0.05 8.00 25.35

4 Cucurbitacin I PBD 0.05 8.00 19.00

JBD 0.05 3.80 11.00

5 Caryophyllene PBD 0.05 2.80 15.21

JBD 0.05 6.33 32.21

6 Cymene PBD 0.05 2.80 6.38

JBD 0.05 6.10 10.12

7 Phellendrene PBD 0.05 3.40 6.20

JBD 0.05 8.20 19.80

Table 5.1: Oxidative stability studies on PBD and JBD using naturally occurring

antioxidants.

230

4. Conclusion

The antioxidant scavenging ability of the isolated natural compounds was

evaluated using four different scavenging methods and was compared with the

antioxidant scavenging ability of antioxidants available commercially. From the study it

is clear that the natural antioxidants have greater antioxidant scavenging ability when

compared to the commercially available antioxidants.

Results of storage studies of biodiesel using the twelve isolated antioxidants from

the six plants are given. These are compared with storage studies using commercially

available antioxidants. From the results, it is evident that at a concentration of 1000 ppm,

tannic acid exhibited the highest antioxidant ability.

The oxidative stability of biodiesel was studied using the Rancimat method

(EN14112). The performance of the twelve isolated antioxidants was compared with that

of commercial antioxidants. One of the isolated natural antioxidants, namely menthol,

exhibited an induction time of 49 h, which is far greater than the expected standard

induction time of 6 h.

231

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