Fuel 93 (2012) 252–257

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Fuel

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Application of thermogravimetric analysis for thermal stability of Jatropha curcasbiodiesel

Siddharth Jain ⇑, M.P. SharmaBiofuel Research Laboratory, Alternate Hydro Energy Centre, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247 667, India

a r t i c l e i n f o

Article history:Received 6 August 2010Received in revised form 26 August 2011Accepted 1 September 2011Available online 15 September 2011

Keywords:Jatropha curcas biodiesel (JCB)Thermal stabilityRancimatTGAActivation energy

0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.09.002

⇑ Corresponding author. Tel.: +91 56382050; fax: +E-mail address: arthjain2001@gmail.com (S. Jain).

a b s t r a c t

The vegetable oil, fats and their biodiesel suffer with the drawback of deterioration of its quality duringlong term storage unlike petroleum diesel because of large number of environmental and other factorsmaking the fuel stability and quality questionable. There are various types of stabilities such as oxidation,storage and thermal, playing key roles in making the fuel unstable. In the present paper the thermalstability of Jatropha curcas biodiesel (JCB) as engine fuel was studied. The thermodynamic parameter ofactivation energy (Ea) of the samples was determined by direct Arrhenius plot. The results show thatthe thermal degradation of all JCB samples can be treated as a first order reaction. It seems at this stagethat the additives under study can offer a significant solution in inhibiting the degradation rate ofbiodiesel. The pyrogallol (PY) has been found to have more pronounced effect on the onset temperature(Ton) as well as on the Ea followed by propyl galate (PG) > tert-butyl hydroquinone (TBHQ) > butylatedhydroxytoluene (BHT) > butylated hydroxyanisole (BHA). The results may have important applicationsin the development of JCB as engine fuel.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Rising costs of the petroleum-derived fuels associated with seri-ous problem of environmental pollution and global warming, hastriggered the research to develop alternative fuels using low-en-ergy intensive design processes. Nowadays, biodiesel is consideredas an important alternative biofuel because of its environmentalbenefits and simple industrial production from renewable re-sources. New investment opportunities for industrial-scale plantsin Europe, Asia, Australia, United States and Brazil have led tothe increase in the production of biodiesel using vegetable oilbased feedstocks. Biodiesel has the added advantage of higherlubricity compared to petro-diesel. However, such ecofriendly li-quid fuels have lower oxidation stability and low processing tem-perature [1].

Transesterification of oil or fats with short chain alcohol, usuallymethanol and ethanol, produces a mixture of corresponding mono-alkyl esters defined as biodiesel. The biodiesel has the same fattyacids compositions similar to the parent oils or fatties with consid-erable amount of unsaturated fatty acids. Its oxidative stability,therefore, becomes crucial quality issue during long term storage[2]. Ultraviolet irradiation, high temperature exposition and pres-ence of trace metallic elements can reduce the overall stability ofthe biofuel, thereby, impacting its fuel quality significantly. The

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oxidative degradation can affect some properties of the biodieselsuch as kinematic viscosity, cetane number and acid value of thefuel [3]. A number of research groups are working to find out thesubstances that inhibit this oxidation process and maintain thequality of biodiesel [2,4].

Several vegetable oils obtained from soybean, castor, sunflower,cotton, corn, palm, etc. are widely used for biodiesel production indifferent part of the world depending on the cultivation of oil crop.India imports 40–50% edible oil of its total domestic demand [1,5]and therefore, it is impossible to divert these edible oil resourcesfor biodiesel production and attention has therefore been directedto the use of non-edible oil resources such as Jatropha, pongamia,neem, etc. for biodiesel production in the country.

Biodiesel consists of long chain fatty acid esters derived fromfeedstocks such as vegetable oils, animal fats, used frying oil, etc.which may contain more or less unsaturated fatty acids whichare prone to oxidation accelerated by exposure to air during stor-age and may yield polymerized compounds at high temperature[2]. Also while using biodiesel in engine, it is subjected to highertemperatures before and during combustion. This high tempera-ture conditions favors the deterioration biodiesel and form depos-its and insolubles in the fuel resulting in the choking of filter pipelines, fuel pump pipe lines thereby impacting the combustion pro-cess because of reduction in combustion area. All these problemsultimately reduce the engine efficiency as well as its life [2]. Ithas been reported that the oxidation stability of easily oxidizedbiodiesel can be maintained near to stability specification by

S. Jain, M.P. Sharma / Fuel 93 (2012) 252–257 253

adding/mixing antioxidants/additives in optimum concentration.The enhancement of biodiesel stability by this way has beenwidely studied, but the effect of temperature on the oxidative deg-radation and its kinetic behavior through thermogravimetric anal-ysis (TGA) has not yet been reported [2].

Chand et al. [6] studied the effectiveness of TGA and found thatTGA is an effective method, which is typically within ±1.5% relativeto proton nuclear magnetic resonance (NMR) method. Dantas et al.[7] studied the thermal stability and decomposition of biodieselusing TGA–DTA curves obtained using a simultaneous DTA/TG ana-lyzer (SDT 2960, TA Instruments) in air and nitrogen (100 ml/minflow rate) in the temperature range 30–600 �C at a heating rateof 10 �C/min using approximately 20 mg of sample in alumina cru-cible. The kinetics of corn biodiesel, obtained from both the meth-anol and ethanol routes, was conducted using dynamic heating todetermine the mechanism, kinetic parameters and reaction order(n) and Ea. The thermogram indicated that corn oil was thermallystable up to 225 �C; the methanol biodiesel up to 139 �C and theethanol biodiesel up to 159 �C in air. In nitrogen atmosphere, thecorn oil was thermally stable up to 336 �C; the methanol biodieselup to 145 �C and the ethanol biodiesel up to 169 �C. In both atmo-spheres, the ethanol biodiesel was found more stable then metha-nol and other biodiesels.

Wan Nik et al. [8] studied the thermal stability of palm oil as en-ergy transport media in a hydraulic system. The oils were aged bycirculating the oil in an open loop hydraulic system at an isother-mal condition of 55 �C for 600 h. In this study, two models wereused to evaluate the kinetic parameters of the oil samples as directArrhenius plot method and integration method.

Freire et al. [9] evaluated the thermal behavior of the physic nutoil and biodiesel from several Brazilian crops using thermoanalyt-ical techniques. TGA and pressurized-differential scanning calo-rimetry (PDSC) were used to determine the applicability ofphysic nut biodiesel. Results suggested the physic nut biodiesel,as a prospective, renewable and biodegradable fuel for use in dieselengines. The results have also shown that with increase in oxida-tion of biodiesel, the Ton decreases resulting in reduced fuelstability.

In the present paper, TGA method has been used to study thethermo oxidative behavior of fresh JCB with and without antioxi-dants. This technique is based on the principle of variation of sam-ple mass as function either of time or temperature. The mostimportant parameters of TGA are Ton and offset temperatures (Toff)which are discussed in Fig. 1. An Ton is used to indicate the resis-tance of the biodiesel to thermal degradation [8]. This is determinedby extrapolating the horizontal baseline at 1% degradation. Theintercept of this line with the tangent to the downward portion of

Fig. 1. Typical TGA thermogram of fresh JCB in dry air atmosphere.

the weight curve is defined as the Ton. At the last, when the sampleis completely burnt and TGA curve become almost flat then, theintercept of the extrapolation on the same line and the tangent tothe downward portion is called as Toff.

The derivative thermogravimetry (DTG) curve is defined as thedifferentiate curve from TGA. Besides, based on the thermal data,the present paper reports the results of kinetics of oxidative degra-dation of JCB with respect to temperature in order to establishstandard specification of oxidation reaction in terms of Ea and fre-quency factor (A) thereby preventing oxidation of biodiesel. Exper-imental work has shown that the oxidation stability/degradationdepends not only on the type of antioxidant but also on theamount of antioxidant used. As Rancimat method is used to evalu-ate the oxidative quality and TGA is used to evaluate the thermalbehavior therefore, the results of TGA were compared with theresults of Rancimat analysis and found that both the methods arewell correlated.

2. Materials

BHT, TBHQ, BHA, PG and PY were the additives employed forevaluating their effect on the stability of biodiesel and its blendswith diesel. All chemicals were of analytical grade (AR) andpurchased from Sigma Aldrich, India. Biodiesel was prepared usingdifferent methodology from Jatropha curcas oil (JCO), will be dis-cussed in the experimental section. The blends of JCB with dieselhaving pre-decided concentration of additives/antioxidants wereused.

3. Experimental

3.1. Biodiesel preparation

Because the initial free fatty acid (FFA) contents of JCO werevery high (15.4%), a two step acid- base catalyzed transesterifica-tion process is used to prepare the biodiesel as per the methodreported in our paper [10]. After completion of the reaction, thereaction mixture was transferred to separating funnel and boththe phases were separated. Upper phase was biodiesel and lowerphase contained glycerin. Alcohol from both the phases was dis-tilled off under vacuum. The glycerin phase was neutralized withacid and stored as crude glycerin. Upper phase i.e. methyl ester(biodiesel) was washed with the water twice to remove the tracesof glycerin, unreacted catalyst and soap formed during the transe-sterification. Fatty acid composition of biodiesel was analyzedusing Gas chromatograph [11] and is given in Table 1 which showsthat the JCB is maximum composed of unsaturated fatty acids(75.3%) responsible for poor oxidation and thermal stability ofbiodiesel.

The biodiesel samples prepared above were tested for physico-chemical properties as per ASTM D-6751 and Indian IS-15607specification given in Table 2 which shows that the JCB meet mostof the specifications except oxidation stability test.

3.2. Thermal analysis

The thermogravimetric (TG) thermogram of JCB was recordedon the thermogravimetric analyser (Perkin Elmer Pyris 6) usingalumina pans. The thermal analysis was conducted at a heatingrate of 10 �C/min from 10 �C to 700 �C in two atmospheres namelydry air atmosphere and nitrogen atmosphere (inert atmosphere) of100 ml/min. A sample size of approximately 15 mg was used. Thetemperature and weight scales were calibrated using indium overa specific range of heating rates with a calibration parameter overits respective Curie point.

Table 1Fatty acid composition of JCB.

Fatty acid Molecular formula Chemical structure Composition (%)

Palmitic acid (P) C16H32O2 CH3(CH2)14COOH 16.8Stearic acid (S) C18H38O2 CH3(CH2)16COOH 7.7Oleic acid (O) C18H34O2 CH3(CH2)7ACH@CHA(CH2)7COOH 39.1Linoleic acid (L) C18H32O2 CH3(CH2)4 CH@CHACH2ACH@CHA(CH2)7 COOH 36.0Linolenic acid (LL) C18H30O2 CH3(CH2)4CH@CHACH2ACH@CHACH2ACH@CHA(CH2)4 COOH 0.2

Table 2ASTM and IS specification of biodiesel.

S. no. Property (unit) ASTM 6751 ASTM 6751 limits IS 15607 IS 15607 limits JCB

1 Flash point (�C) D-93 Min. 130 IS 1448 1722 Viscosity at 40 �C (cSt) D-445 1.9–6.0 IS 1448 4.383 Water and sediment (vol.%) D-2709 Max. 0.05 D-2709 Max. 0.05 0.054 Free glycerin (% mass) D-6584 Max. 0.02 D-6584 Max. 0.02 0.015 Total glycerin (% mass) D-6584 Max. 0.24 D-6584 Max. 0.24 0.036 Oxidation stability of FAME (h) NA 3 EN 14112 Min. 6 3.277 Oxidation stability of FAME blend (h) NA NA EN 590 Min. 20 NA

254 S. Jain, M.P. Sharma / Fuel 93 (2012) 252–257

3.2.1. Non-isothermal analysisThermogravimetric data has been used to characterize the

materials as well as to investigate the thermodynamics and kinet-ics of the reactions and transitions of oil samples in oil industries.The method can also be adopted to analyze the thermal behavior ofbiodiesel. Currently, several methods are available in the literaturethat can be used to calculate the kinetic parameters [8]. The kineticanalysis used for the thermal conversion of the biodiesel isdiscussed below:

The rate of conversion, dx/dt, for the biodiesel conversion isexpressed by

dxdt¼ kf ðxÞ ¼ kð1� xÞn ð1Þ

where n is the order of reaction, k is the reaction rate constant and xis the extent of conversion x is given by

x ¼ w0 �wt

w0 �w1

where w0, wt and w1 are the original, current and final weights ofsample respectively.

Based on the TGA thermogram, reaction (1) was found to be offirst order,

Thus n = 1 and Eq. (1) becomes

dxdt¼ kð1� xÞ

For the non-isothermal case, the above equation can be furthermodified to

dxdT� dT

dt¼ kð1� xÞ ð2Þ

where dT/dt is the heating rate B.According to the Arrhenius relationship, the reaction rate con-

stant k in Eq. (2) can be expressedas

k ¼ A expð�Ea=RTÞ ð3Þ

where, Ea, A and R are the activation energy, frequency factor andideal gas law constant (8.314 J/mol K) respectively.

Substituting Eq. (3) into Eq. (2) yields

dxdt¼ A

Bexp

�Ea

RT

� �ð1� xÞ ð4Þ

For the direct Arrhenius plot method for the non-isothermal ki-netic parameters with constant heating rate (B = dT/dt), Eq. (4) wasrearranged to

ln1

ð1� xÞdxdt

� �¼ ln

AB� Ea

RTð5Þ

The plot ln[1/(1 � x) dx/dt] versus 1/T should give a straight linewith slope-Ea/R, from which the Ea can be calculated.

3.3. Oxidation stability measurement

Oxidation stability of JCB was quantified by the induction peri-od (IP) which was evaluated as per the Rancimat method EN14112. All stability measurements were carried out on a Metrohm873 Biodiesel Rancimat instrument. Samples of 3 g of pure biodie-sel were analyzed under a constant air flow of 10 l/h, passingthrough the fuel and into a vessel containing distilled water. Thesamples were held at 110 �C heating block temperature. The elec-trode is connected to a measuring and recording device. The end ofthe IP is indicated when the conductivity starts to increase rapidly.This accelerated increase in conductivity is caused by the dissocia-tion of volatile carboxylic acids produced during the oxidation pro-cess and absorbed in the water. When the conductivity of thismeasuring solution is recorded continuously, an oxidation curveis obtained whose point of inflection is known as the IP.

4. Results and discussion

4.1. Effect of additives on thermal degradation of JCB

Thermo gravimetric analysis has been widely used to evaluatethe thermal stability of various types of materials such as polymersand oils. The thermal properties or behavior of oil samples aremeasured as a function of various reaction parameters such astemperature, time and heating rates. This type of technique is verypopular in the chemical engineering field as a tool of thermalanalysis.

Kinetics of the JCB samples was studied non-isothermally underconditions of sample temperature increasing at the rate of 10 �C/min. This TGA test involves a weight change as the oil was heated.The weight loss of the sample was logged using the in situ com-puter. Fig. 1 shows the temperature scan of a typical fresh JCB sam-

Fig. 2. Typical TGA thermogram of fresh JCB in nitrogen atmosphere.

Table 3The effect of anti-oxidant on degradation temperatures of Jatropha biodiesel.

S. no. Sample Antioxidantconcentration(ppm)

Onset Temp. Ton (�C) OffsetTemp.Toff (�C)

Dry air Nitrogen

1 B100 0 113 128 2852 B100 + PY 100 130 146 2883 200 145 159 2914 300 156 170 2955 400 167 182 2986 600 185 202 3057 B100 + PG 100 122 137 2858 200 138 151 2889 300 143 158 291

10 400 152 168 29511 600 171 187 29812 B100 + TBHQ 100 117 131 28513 200 130 145 28814 300 138 152 29515 400 145 162 29816 600 158 178 30117 B100 + BHT 100 116 127 28518 200 119 135 28819 300 123 139 28820 400 127 140 28821 600 135 148 29822 B100 + BHA 100 114 124 28823 200 117 134 28824 300 122 136 28825 400 125 137 29126 600 131 146 298

Fig. 3. Arrhenius plot for fresh JCB without antioxidants.

S. Jain, M.P. Sharma / Fuel 93 (2012) 252–257 255

ple in dry air atmospheric heating. It shows the decomposition andweight loss of the biodiesel samples and derivative weight loss(DTG) with the corresponding temperature. The changes in weightoccurred because of evaporation and/or combustion of the methylesters, mainly of the methyl linoleate and oleate, the most abun-dant component in the Jatropha curcas biodiesel [7–9].

The thermogram shown in Fig. 1 consists of three steps. In thefirst phase, only a minimal weight change was observed during thisIP. The thermogram shows that the 1% weight loss of the fresh JCBsample in the dry air atmosphere occurs at around 113 �C. A rapidweight change was observed during the second phase. The maxi-mum degradation rate occurred at a temperature of 198 �C wherethe rate of weight decrease increased to the maximum up to thispoint. Slower weight loss reductions were observed at higher tem-peratures. The curve flattering at 318 �C shows that no further con-version was occurring. This are also attributed to the vaporization

and/or combustion of the JCB, whose main component is methyllinoleate and oleate as shown in Table 1.

The DTG curve shows clear evidence for the three degradationsteps. The TG curves and the negative first derivative of the biodie-sel decomposition (Fig. 1) suggest that the overall process occurredin first order kinetics.

Fig. 2 shows the temperature scan of a typical fresh JCB samplein nitrogen atmospheric heating. The TG/DTG curves of the JCB innitrogen presented two thermal steps ascribed to the vaporizationand/or pyrolysis of the methyl esters, mainly methyl linoleate andoleate as also reported by various researchers [7–9].

Table 3 shows the details for the point of 1% weight loss temper-ature, Ton and Toff. It can be seen that the Ton for JCB without addi-tives is significantly lower than that of the JCB with additive. Thisshows that the additives used in this study are able to resist theoxidation process and hence improve the fuel stability as reportedby Wan Nik et al. [8]. As can be seen Ton increases with the increaseof the amount of additives in JCB. This shows the rise in thermal sta-bility of biodiesel with the increasing% of antioxidants. This obser-vation is in agreement with Wan Nik et al. [8] who reported theeffect of antioxidants on the thermal stability of palm oil.

Effect of antioxidants were also checked with respect to boilingpoint and found that antioxidants don’t have any significant effectof boiling point of JCB. From this, it may also be concluded that Ton

can be used to indicate the resistance of biodiesel to thermal deg-radation as also reported by Wan Nik et al. [8].

The Ton of fresh JCB without antioxidants is found as 113 �C and128 �C in dry air and nitrogen atmosphere. When PY, PG, TBHQ,BHT and BHA additives are doped with biodiesel, Ton will increaseto 185, 171, 158, 135 and 131 �C respectively in air atmosphere and202, 187, 178, 148 and 146 �C respectively in nitrogen atmosphere.From the results, it can be concluded that PY is the highest oxida-tion inhibitor flowed by PG > TBHQ > BHT > BHA. Therefore it isfound that antioxidants give the same results on thermal degrada-tion in dry air as well as nitrogen atmosphere.

Thermogravimetric analysis using the direct Arrhenius plotmethod has been used by numerous researchers [6–9]. Eq. (5)was used to determine the Ea of the oil samples by the direct Arrhe-nius plot method. The values of x and dx/dT were calculated usingan Excel spreadsheet. The plot of ln [1/(1-x) dx/dt] versus 1/T wasmade for the oil decomposition. Fig. 3 presents the Arrhenius plotof the oil samples used to calculate the kinetic parameters such asEa and A. The figure shows a linear relationship of ln[1/(1-x) dx/dt]versus 1/T for all samples indicating that the oil conversion (dete-rioration) reaction can be treated as a first order reaction. Thus, thekinetic parameter constants as per Eq. (5) can be determined atincreasing temperature from the slope of the graph.

Table 4Kinetic parameter for JCB with and without antioxidants.

Samples Antioxidant concentration (ppm)

100 200 300 400 600

Ea (kJ mol�1) A (min�1) Ea (kJ mol�1) A (min�1) Ea (kJ mol�1) A (min�1) Ea (kJ mol�1) A (min�1) Ea (kJ mol�1) A (min�1)

B100 39.39 6.50 � 103 39.39 6.50 � 103 39.39 6.50 � 103 39.39 6.50 � 103 39.39 6.50 � 103

B100 + PY 53.99 2.40 � 105 59.26 8.18 � 105 64.73 2.84 � 106 75.22 3.20 � 107 80.99 1.00 � 108

B100 + PG 50.08 9.16 � 104 54.63 2.63 � 105 56.11 3.62 � 105 62.74 1.66 � 106 72.74 1.63 � 107

B100 + TBHQ 47.21 4.51 � 104 50.15 8.86 � 104 52.57 1.51 � 105 57.78 5.15 � 105 68.62 6.22 � 106

B100 + BHT 42.96 1.53 � 104 44.21 2.10 � 104 46.15 3.29 � 104 50.68 9.69 � 104 57.06 4.31 � 105

B100 + BHA 41.06 9.32 � 103 44.44 2.22 � 104 45.40 2.79 � 104 49.91 8.07 � 104 56.59 3.67 � 105

Fig. 4. Relative effectiveness of antioxidants.

256 S. Jain, M.P. Sharma / Fuel 93 (2012) 252–257

The calculated best fitting straight line in Fig. 3 describes thebiodiesel decomposition. With the linear regression of the abscissaand ordinate parameters, the slopes and intercepts of the lines inthe figure indicate the values of the Ea and A respectively. For thissample, the Ea was computed to be 39.39 kJ/mol. This shows thatthe fresh JCB is very much susceptible to thermal degradation. Thismethod has been used for oil degradation only but the present pa-per is used this method for the thermal degradation of CB for thefirst time.

Table 4 compares the Ea and A for all the fresh JCB with andwithout additives, respectively. The Ea of fresh JCB without additiveis 39.39 kJ/mol, while the Ea for the samples with PY added in600 ppm increased up to 80.99 kJ/mol showing thereby that PY isa better additive compared to other additives used. This is furtherauthenticated by the similar pattern of Ton. The Ea has a linear rela-tionship with the additive concentration. This is in agreement withWan Nik et al. [8].

The value of A has behavior similar to that of Ea as indicated inTable 4 which has increased from 6.50 � 103 min�1 without anti-oxidant to maximum value of 1.00 � 108 min�1 with PY antioxi-dant (600 ppm). In order to ensure sample temperatureuniformity and minimize error, the same sample size (10 mg)was used in the experiments. It is expected that the Ton and finaltemperatures would decrease or increase if smaller or larger sam-ple sizes were used respectively [8]. Larger sample size meanssmaller surface exposure per sample volume. This would makethe decomposition process slower. The thermal stability of biodie-sel could be defined as the resistance to thermal degradation. Thehigher the temperature, the faster is the oxidation process, i.e.higher rate of degradation of biodiesel.

The data taken from the TGA and DTA curves are summarized inTables 2 and 3. These data allow one to conclude that JCB withoutadditives was thermally stable up to 113 �C and 128 �C in dry airand nitrogen atmosphere respectively. The thermal degradationtemperature can, however, be increased by adding additives. JCBwith PY (600 ppm) is stable up to 185 �C and 202 �C in dry air

and nitrogen atmosphere respectively while BHA is found to haveleast thermal stability with degradation temperature of 131 �C and146 �C in dry air and nitrogen atmosphere respectively. Thereforethermal degradation temperature can be increased by adding addi-tives as also reported by Wan Nik et al. [8].

4.2. Effect of antioxidants on the oxidation stability of fresh JCB

All the 5 antioxidants were doped at different dosage (100, 200,300, 400 and 600 ppm) in JCB and Rancimat test was conducted tostudy the effectiveness of different antioxidants and the results aregiven in Fig. 4.

Fig. 4 shows the effect of all phenolic antioxidants from 100 to600 ppm dosage on the oxidation stability. The oxidation stabilityof JCB has been found to increase with increase in dosage of anti-oxidant which is in agreement with the result of the thermal anal-ysis in terms of Ea, Ton and A. Finally, it is found that dosing of100 ppm of PY antioxidant is the minimum concentration requiredto meet EN 14112 specification for biodiesel oxidative stability.

5. Conclusion

Looking at very little fundamental reports in the literature onimproving the thermal stability of JCB, thermal degradation andthermal stability of JCB samples doped with antioxidants havebeen investigated to study the effect of the antioxidant on thermaldegradation of the JCB. The type of antioxidant and concentrationwas also varied. The biodiesel properties such as Ton, Toff, and Ea

were evaluated by TGA analysis.The kinetic parameters of JCB samples were evaluated using di-

rect Arrhenius plots method. The results show that the thermaldegradation of all JCB samples can be treated as a first order reac-tion. It seems at this stage that the additives under study can offera significant solution in inhibiting the degradation rate of biodiesel.The PY has been found to have more pronounced effect on the Ton

as well as on the Ea followed by PG > TBHQ > BHT > BHA.The kinetic parameters obtained from the dynamic experiments

were in good agreement with conventional measurements of IP.Both TGA and Rancimat method shows that the BHA and BHT addi-tives are least efficient to make biodiesel sample thermally stable.The results also shows that as the biodiesel become oxidativelyunstable, its thermal stability will also decrease. The method is alsohelpful in the ranking of additives. Based on TGA and conventionalmethod, the above study suggests that PY or PG can be effectivelyused for improving the thermal stability of biodiesel for its use asengine fuel.

Acknowledgment

The authors greatly acknowledge the financial support fromMinistry of Human Resource Development (MHRD), Govt. of Indiain the form of research scholarship to carry out this work.

S. Jain, M.P. Sharma / Fuel 93 (2012) 252–257 257

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