Fuel 90 (2011) 3014–3020

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Oxidation stability of blends of Jatropha biodiesel with diesel

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 a b s t r a c t

Article history:Received 23 September 2010Received in revised form 29 April 2011Accepted 5 May 2011Available online 19 May 2011

Keywords:BiodieselJatrophaOxidation stabilityAntioxidants

0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.05.003

⇑ Corresponding author. Tel.: +91 9456382050; faxE-mail address: arthjain2001@gmail.com (S. Jain).

Biodiesel, an ecofriendly and renewable fuel substitute for diesel has been receiving the attention ofresearchers around the world. Due to heavy import of edible oil, the production of biodiesel from edibleoil resources in India is not advisable. Therefore it is necessary to explore non-edible seed oils, like Jatro-pha curcas (J. curcas) and Pongamia for biodiesel production. The oxidation stability of biodiesel from J.curcas oil (JCO) is very poor and therefore an idea is given to increase the oxidation stability of biodieselby blending it with petro-diesel. J. curcas biodiesel (JCB), when blended with petro diesel leads to a com-position having efficient and improved oxidation stability. The results have shown that blending of JCBwith diesel with less than 20% (v/v) would not need any antioxidants but at the same time, need largestorage space. Similarly, if the amount of diesel is decreased in the blend, it will require the additionof antioxidant but in lesser amount compared to pure JCB. For the purpose five antioxidants were usednamely butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), butylated hydroxyanisole(BHA), propyl gallate (PG), and pyrogallol (PY). A B30 blend (30% JCB in the blend of JCB and petro-diesel)has been tested for the same purpose. PY is found to be the best antioxidant among all five antioxidantsused. The optimum amount of antioxidant (PY) for pure biodiesel tested for the present experiment isaround 100 ppm while it is around 50 ppm for B30 blend to maintain the international specification ofoxidation stability.

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1. Introduction

Biodiesel is an environmentally friendly liquid biofuel similar topetro-diesel in terms of fuel quality and combustion characteris-tics. Increasing environmental concerns, fast depleting petroleumreserves and agriculture based economy are the driving forces topromote biodiesel as an alternative renewable fuel. Biodiesel,derived from vegetable oils and animal fats, is being used as enginefuel in USA and Europe to reduce air pollution and to reducedependence on limited fossil fuel, localized to some specific re-gions. Because of the surplus availability of edible oils like soybeanoil, sunflower oil and rapeseed oil, these countries are using edibleoils as feedstocks for biodiesel production. On the other hand, thepossibility of biodiesel production from edible oil resources inIndia is minor as the indigenous edible oil production is much lessthan the actual demand which is met by imports [1]. India ac-counts for 9.3% of world’s total oil seed production and is thefourth largest edible oil producer in the world and still about46% of total edible oil is imported to meet the domestic require-ments and as such the question of diverting edible oil resourcesfor biodiesel production in India does not arise. The only possibilityseems to be the non-edible oil resources like Jatropha curcas,

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pongamia, Mahua, sal, etc. which can be commercially grown onwaste lands and the oil resources can be used for biodiesel produc-tion. J. curcas has been identified as one of the important source forbiodiesel production in India.

As per the survey of Government of India, out of total land area,60 Mha are classified as waste and degraded land. India has thirdlargest road network in Asia having road length of about 3 mil-lion kms and the land area along the road can be used for growingthe J. curcas and Pongamia crops and the available oil can be con-verted into biodiesel. Similarly, the land along the track of Indianrailway of about 63,140 km can also be easily used for cultivationof J. curcas [1].

Canakci et al. [2] and Dunn [3] reported that due to the presenceof significant amount of fatty acids with double bonds, oxidativestability has been found to be of significant concern when the bio-diesel is stored over an extended period of time. This is why; theoxidation stability becomes an important criterion for biodieselfuel quality. Dunn and Knothe [4] have reported that the stabilityof biodiesel is inferior to petro-diesel and therefore, the blendingof biodiesel with petro-diesel will affect its fuel stability signifi-cantly. The poor biodiesel stability is attributed to the presenceof double bonds in the fatty acids that may ultimately lead to for-mation of gum and other oxidation byproducts. The trend ofincreasing stability of different fatty acids is linolenic < lino-leic < oleic. These esters undergo auto-oxidation with different

S. Jain, M.P. Sharma / Fuel 90 (2011) 3014–3020 3015

rates depending upon the numbers and positions of the doublebonds and result in the formation of a series of by-products likeacids, esters, aldehydes, ketones, lactones, etc.

A number of reports have appeared in the literature on the stor-age and oxidative stability of biodiesel synthesized from edible oilsbut only very few reports are available on the effect of blending ofdifferent biodiesels on the oxidation stability of that blend [5,6].However, no work has been reported on the effect of blending ofbiodiesel from J. curcas oil (JCO) with petro-diesel on their stability.

Sarin et al. [7] have used palm and JCB blends to minimize thedosage of antioxidants and found an increase in the induction per-iod (IP) of JCB after it was blended with palm biodiesel. Dunn [8]has studied the effect of oxidation under accelerated conditionson the fuel properties on methyl soyate. The effect of different anti-oxidants on oxidation stability of biodiesel from soybean oil wasstudied by Dunn [9]. Knothe has reported the effect of structureof fatty compounds on the stability of vegetable oil derived prod-ucts [10]. Ferrari et al. [11] have compared the oxidative stabilityof neutralized, refined and frying oil waste soybean oil fatty acidethyl ester.

Park et al. [12] studied the blending effect of biodiesel on theoxidation stability of biodiesel and found a close relationship be-tween the oxidation stability of the blended biodiesels with thefatty acid composition. Some stability studies were also carriedout on methyl and ethyl fatty acid esters under different storageconditions [13]. Synthetic antioxidants were reported to be moreeffective than natural antioxidants [14]. Das et al. [15] haveworked on long-term storage stability of biodiesel from Karanjaoil and found that it is possible to increase the stability consider-ably by adding the antioxidants.

Dunn [8] examined the effectiveness of different antioxidantsand found that PG and PY are the most effective antioxidants. Mit-telbach and Schober [16] has further studied the influence of anti-oxidants on the oxidation stability of biodiesel and showed theinfluence of different synthetic and natural antioxidants on theoxidation stability using the specified test method. The IP ofmethyl esters from rapeseed oil, used frying oil and tallow werefound to improve significantly with PY, PG, and TBHQ, whereasBHT was not very effective. The influences and the effectivenessof vitamin E, BHA, BHT, TBHQ and PG on the oxidative stabilityof UFOME were studied by Loh et al. [17] who found that PG gavethe highest IP followed by PY and TBHQ. The final report on theBIOSTAB project states that the efficiency and the necessaryamount of the different antioxidants are strongly dependent onthe feedstock and biodiesel production technology [18].

From the above literature, it can be concluded that oxidationcannot be entirely prevented but can be significantly slowed downby the use of antioxidants which are chemicals that inhibit the oxi-dation process. Sarin et al. [6] have reported that two types of anti-oxidants are generally known: chain breakers and hydroperoxidedecomposers. Literature related to hydroperoxide decomposers isvery scarce. The two most common types of chain breaking antiox-idants are phenolic and amine-types. Almost all the work related tostability of fatty oil and ester applications is limited to the phenolictype of antioxidants.

As per the National Mission on biodiesel of India, JCB has beenselected in order to improve the stability of biodiesel and make itacceptable to oil marketing companies in India and accordinglyadding an antioxidant is required. The present paper aims to studythe effect of blending of biodiesel with petro-diesel beyond B7 (theterm Bx means x% (v/v) biodiesel is present in the blend of biodieseland petro-diesel) on their oxidation stability and to study the effectof addition of antioxidants on the oxidation stability of biodiesel.However, in order to reduce the cost and dosage of antioxidants,oxidation stability studies on the blends of petro-diesel with JCBhave been carried out and results are reported in this paper.

2. Materials and experimental

BHT, TBHQ, BHA, PG, and PY were the additives evaluated fortheir effect on diesel/biodiesel blends. All chemicals were of ana-lytical grade and purchased from Sigma Aldrich, India. Biodieselfrom JCO prepared in the laboratory as will be discussed in theexperimental section.

2.1. Synthesis of biodiesel and its testing

Since the initial free fatty acid (FFA) contents of JCO was veryhigh (15.4%) therefore a two step acid–base catalyzed transesteri-fication process is used to prepare biodiesel [19,20]. H2SO4 is se-lected as acid for esterification, KOH is selected as base fortransesterification and methanol is selected as alcohol for boththe reactions. After completion of the reaction, the reaction mix-ture was transferred to separating funnel and both the phases wereseparated. Upper phase was biodiesel and lower phase containedglycerin. Alcohol from both the phases was distilled off under vac-uum. The glycerin phase was neutralized with acid and stored ascrude glycerin. Upper phase i.e. methyl ester (biodiesel) waswashed with the water twice to remove the traces of glycerin,unreacted catalyst and soap formed during the transesterification.Fatty acid composition of biodiesel was analyzed using gas chro-matograph. ASTM D 6584 is used for the measurement of free glyc-erin and total glycerin in the biodiesel.

The samples were analyzed for ME formation at a pre-deter-mined interval of time by Gas Chromatograph (purchased from Ne-tal) equipped with a flame ionization detector and a capillarycolumn for injecting the sample. Inlet temperature was kept on250 �C. Oven program initial temperature was 210 �C (ramp1 = 5 �C/min) with oven program final temperature was 230 �C.FID was kept on 250 �C temperature. Nitrogen was used as carriergas. Quantitative analysis of % ME was done using European stan-dard EN 14103 [21]. The % ME yield was calculated using Eq. (1).Free fatty acids in the samples were determined using stock solu-tion (Methyl heptadecanoate and n-heptane).

% of ME ¼ RA� AEI

AEI� CEI � VEI

m� 100 ð1Þ

where RA is the total peak area from the methyl ester in C14 to thatin C24:1; AEI is peak area corresponding to methyl heptadecanoate;CEI is concentration of the methyl heptadecanoate solution (mg/ml);VEI is volume of the methyl heptadecanoate solution (ml); and m isthe mass of the sample (mg).

As per national biodiesel mission of India, the use of biodieselshould reach a minimum of 20% in 2012, while the revised Euro-pean standard EN 590 already includes a provision for automotivediesel fuel to be blended with biodiesel up to 7% (v/v) [5], but at thesame time there is no specification given for biodiesel blends be-yond B7 for oxidation stability. Therefore same oxidation stabilityspecification requirement (20 h) is considered for oxidation stabil-ity for all biodiesel blends beyond B7.

2.2. Stability measurement

Oxidation stability of biodiesel from different feedstocks andtheir blends with automotive diesel was quantified by the IP. TheIP was evaluated according to the Rancimat method EN 14112[22] for pure biodiesel and the modified Rancimat method EN15751 [23] for the biodiesel blends with petro-diesel.

Since in India, JCO is considered as the main non-edible oil forbiodiesel production, further studies have therefore been under-taken by Alternate Hydro Energy Centre, Indian Institute of Tech-nology Roorkee (AHEC, IITR) on oxidation stability of JCB only.

Table 2Fatty acid composition of Jatropha curcas oil.

Fatty acid % composition

Palmitic acid (P) 16.8Stearic acid (S) 7.7Oleic acid (O) 39.1Linoleic acid (L) 36.0Linolenic acid (LL) 0.2

3016 S. Jain, M.P. Sharma / Fuel 90 (2011) 3014–3020

Two pronged approach has been adopted for improving the oxida-tion stability of JCB. First approach deals with the doping of JCBwith stabilizer or antioxidants and five phenolic antioxidants,namely TBHQ, PY, PG, BHA and BHT were used.

Also the biodiesel is supposed to be blended with diesel whileusing in diesel engine and accordingly, another set of study wasundertaken to blend JCB with petro-diesel having good oxidationstability due to lack of unsaturated fatty acids. And then the effectof blending on oxidation stability is checked. Also relative effec-tiveness of various antioxidants is checked in its blends with pet-ro-diesel.

3. Results and discussion

The synthesized JCB samples were tested for physico-chemicalproperties as per ASTM D-6751 and Indian IS-15607 specificationas given in Table 1. The table shows that although the JCB met mostof the specifications but failed in oxidation stability test accordingto IS-15607 at the same time satisfying the ASTM D-6751 limit of3 h. So it does not fail according to ASTM standards but failsaccording to the IS-15607 limits of IP of 6 h.

The results obtained were in good agreement with biodieselquality survey of 2004 and 2006, which indicates that majorityof samples, failed in EN-14112 test [24] due to presence of largeamount of unsaturated fatty acids. Fatty acid composition of JCBis given in Table 2. It is clear from Tables 1 and 2 that due to largeamount of unsaturated fatty acids, oxidation stability of JCB is verypoor. On the other hand, other properties are within range accord-ing to ASTM and Indian standards.

3.1. Effect of antioxidants on the oxidation stability of pure biodiesel

All the five antioxidants were doped at different dosage (100,200, 300, 400 and 600 ppm) in JCB and Rancimat test was con-ducted to study the effectiveness of different antioxidants andthe results are given in Fig. 1.

Fig. 1 shows the effect of all phenolic antioxidants from100 ppm to 600 ppm dosage on the oxidation stability. The oxida-tion stability of JCB has been found to be increase with increase indosage of antioxidant. Finally, it is found that dosing of around100 ppm of PY antioxidant is the minimum concentration requiredto meet EN 14214 specification for biodiesel oxidative stability.Fig. 1 shows that the quantity of antioxidant required for maintain-ing the specification of 6 h IP is less than reported in the literature[2–8]. The amount of natural antioxidants may be the possible rea-son for this. As the biodiesel is prepared by transesterification pro-cess, the amounts of natural antioxidants get reduced and due tothis reason oxidation stability of biodiesel is lower than the parentoil. As the biodiesel was prepared through low temperature acid–base catalyzed transesterification process therefore the naturalantioxidants, already presented in the JCO remained exist in the

Table 1Physico-chemical properties of biodiesel as per ASTM and IS specification.

S. no. Property (unit) ASTM 6751 AS

1 Flash point (�C) D-93 Mi2 Viscosity at 40 �C (cSt) D-445 1.93 Water and sediment (vol.%) D-2709 Ma4 Free glycerin (% mass) D-6584 Ma5 Total glycerin (% mass) D-6584 Ma6 Oxidation stability of FAME (h) EN 14112 37 Oxidation stability of FAME blend (h) EN 590 6 (8 Free glycerol D6584 0.09 Total glycerol D6584 0.2

JCB also. This may be the possible reason that the amount of syn-thetic antioxidant required is less as shown in Fig. 1.

3.2. Effect of blending of biodiesel with petro diesel on its oxidationstability

Although, it is possible to meet the desired EN specification byusing antioxidant but there will be cost implications as antioxi-dants are costly chemicals. Also biodiesel is supposed to beblended with petro-diesel therefore the biodiesel blends with pet-ro diesel in different composition (B2, B5, B7, B10, B20, B30, B40, B50

and B80) were prepared and then its effect on oxidation stabilitywas studied and the results are shown in Figs. 2 and 3.

It is clear from Fig. 2 that as the amount of diesel is decreased inthe blend, the IP also decreases, indicating the decrease in oxida-tion stability that can be attributed to the increase of unsaturatedfatty acid in the blend. It has been found experimentally that min-imum 80% diesel is required to be blended with JCB (B20) to meetthe specification of IP of 20 h according to European standard EN590. However, if we go beyond B20, the IP will decrease below20 h and it will not be able to maintain the specification accordingto EN 590. Therefore the effect of various antioxidants on oxidationstability is required to be studied beyond B20.

Fig. 3 shows the decrease in total acid number (TAN) with theincreasing % of petro-diesel in the blend. Due to lack of oxidationand lower TAN, the viscosity of biodiesel blends with petro-dieselwill also decrease with the increasing % of petro-diesel (Fig. 4).

3.3. Effect of antioxidants on the oxidation stability of biodiesel blendswith petro-diesel

Further study was initiated to blend JCB with petro-diesel (B30,B40, B50 and B80), along with various antioxidants. The antioxidantdose was varied from 50 ppm to 600 ppm dosages and oxidationstability of these blends was studied, in terms of IP using Rancimattest. The results are shown in Figs. 5–8.

Fig. 5 indicated the effectiveness of various antioxidants in B80

blend. The result shows that to maintain the specification of 20 hIP, 400 ppm of PY or 600 ppm of PG is required to add in the blend.

Fig. 6 shows the effect of various antioxidants on the oxidationstability of B50 blend. It shows that to maintain the specification of20 h IP, 300 ppm of PY or 400 ppm of PG is required to add in theblend.

TM 6751 limits IS 15607 IS 15607 limits Jatropha ME

n.130 IS 1448 172–6.0 IS 1448 4.38x.0.05 D-2709 Max.0.05 0.05x.0.02 D-6584 Max.0.02 0.01x.0.24 D-6584 Max.0.24 0.03

EN 14112 Min. 6 3.27up to B20) EN 590 Min. 202 (max) D6584 0.02 (max) 0.015 (max) D6584 0.25 (max) 0.12

Fig. 1. Relative efficiency of antioxidants.

Fig. 2. Variation of induction period with blending ratio.

Fig. 3. Variation of TAN with blending ratio.

Fig. 4. Variation of viscosity with in increasing proportion of blend.

S. Jain, M.P. Sharma / Fuel 90 (2011) 3014–3020 3017

Fig. 7 shows the effect of various antioxidants on the oxidationstability of B40 blend. Now it shows that to maintain the specifica-tion of 20 h IP, 200 ppm of PY or PG is required to add in the blend.

In all the above three cases (B80, B50 and B40) the amount of anti-oxidants (PY and PG), required for increasing the IP up to 20 h isvery large and is greater than the amount of antioxidants (PYand PG) required in pure biodiesel to maintain the oxidation stabil-ity specification. However, other three antioxidants failed to in-crease the IP up to 20 h for B80, B50 and B40.

Fig. 8 displays the effect of various antioxidants on B30 blend.From the results it may be concluded that to maintain the specifi-cation of 20 h IP, around 50 ppm of PY or PG is required to add inthe blend which is lesser than that required by pure biodiesel tomaintain the oxidation stability specification. On the other hand200, 300 and 300 ppm concentration is required for TBHQ, BHTand BHA respectively to achieve the same oxidation stabilityspecification.

Thus, it is possible to attain requisite oxidation stability of bio-diesel by blending 70% petro-diesel in JCB using only 50 ppm ofantioxidant (PY and PG). This optimum combination is expectedto reduce the cost of biodiesel substantially and require lowerquantity of antioxidant. No antioxidant however, is needed if thediesel proportion is beyond 80% in the blend.

Among all the antioxidants tested, PG and PY showed a greatereffect on the stability of the biodiesel blend with diesel. This was asexpected, because both of these additives presented an increasedstability performance with pure methyl ester samples. BHT andBHA were found to be the least effective antioxidants in the JCB

Fig. 5. Effect of antioxidants on the stability of B80 blend.

Fig. 6. Effect of antioxidants on the stability of B50 blend.

Fig. 7. Effect of antioxidants on the stability of B40 blend.

3018 S. Jain, M.P. Sharma / Fuel 90 (2011) 3014–3020

samples for the selected level of concentration used in the presentstudy. However, both additives resulted in higher stability for allbiodiesel blends. The reason for this may be attributed to thegreatly different structure of methyl esters compared to non polarhydrocarbons, which may interact with the highly hindered polar

phenol group of BHT or BHA to reduce their antioxidant capability[5].

The lack of correlation between oxidative stability as well asother properties of biodiesel and IV value had been reported byother researchers [25,26]. However, the alternative concept of

Fig. 8. Effect of antioxidants on the stability of B30 blend.

Fig. 9. Variation in IP with APE. Fig. 10. Variation in IP with BAPE.

S. Jain, M.P. Sharma / Fuel 90 (2011) 3014–3020 3019

allylic position equivalent (APE) and bis-allylic position equivalent(BAPE) based on the relative rates of oxidation of these positions inunsaturated fatty acids as well as their amounts [27] gives moreuseful results.

The relationship between APE, BAPE and IP is shown in Figs. 9and 10.

Regression of the APE, BAPE values and the IP gave the followingcorrelations:For APE:

IP ¼ 49:968� 9:006 � lnðAPEÞ ðR2 ¼ 0:9841Þ ð2Þ

For BAPE:

IP ¼ 37:465� 9:102 � lnðBAPEÞ ðR2 ¼ 0:9843Þ ð3Þ

The APE and BAPE value shows significantly good relation withIP. The BAPE value is more significant for the oxidation of unsatu-rated fatty compounds with determination coefficient of 0.9843due to the significantly higher relative rate of oxidation of bis-allylic CH2 positions (Figs. 9 and 10). This is in agreement withthe findings of Knothe and Dunn [10], according to which BAPE val-ues contribute in the oxidation process in significant amount. Thereason for this is that bis-allylic positions are very prone to oxida-tion then allylic positions [10]. At the same time APE value alsocontribute in the oxidation process with the value of coefficientof determination of 0.9841.

4. Conclusion

JCB, when blended with petro-diesel leads to a compositionhaving efficient and improved oxidation stability. The resultshave shown that blending of JCB with petro-diesel with less than20% (v/v) would not need any antioxidants but at the same time,need large storage capacity. Similarly, if the amount of diesel isdecreased in the blend, it will require the addition of antioxidantbut in lesser amount compared to pure biodiesel. A B30 blend ofJCB with petro-diesel has been tested for the same purpose. PY isfound to be the best antioxidants among all five antioxidants inthe JCB and JCB/petro-diesel blends samples for the selected le-vel of concentration used in the present study. The amount ofantioxidant (PY) required for pure JCB is around 100 ppm whileit is around 50 ppm for B30 blend of JCB with petro-diesel tomaintain the oxidation stability specification.

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