Fuel 116 (2014) 14–18

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Effect of metal contents on oxidation stability of biodiesel/diesel blends

0016-2361/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.fuel.2013.07.104

⇑ Corresponding author. Tel.: +65 81594224/+91 9456382050; fax: +91 1332273517.

E-mail address: arthjain2001@gmail.com (S. Jain).

Siddharth Jain a,⇑, M.P. Sharma b

a NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, #02-01, Singapore 117411, Singaporeb Biofuel Research Laboratory, Alternate Hydro Energy Centre, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India

h i g h l i g h t s

� Stability of metal contaminated biodiesel blend has been checked.� Effectiveness of different antioxidants has also been checked.� Biodiesel blends with diesel have shown the better oxidation stability.� Effect of metals on the oxidation stability of biodiesel has found catalytic.

a r t i c l e i n f o

Article history:Received 5 September 2011Received in revised form 24 July 2013Accepted 25 July 2013Available online 14 August 2013

Keywords:BiodieselJatrophaOxidation stabilityAntioxidantsMetal contaminants

a b s t r a c t

Present paper deals with the evaluation of oxidation stability of metal contaminated biodiesel/dieselblend. Effectiveness of different antioxidants with respect to different biodiesel/diesel blends has alsobeen checked. It is found that pyrogallol (PY) is the most effective antioxidant. As the % of diesel isincreased in the blend, the oxidation stability of biodiesel/ diesel blend also increased. From the experi-ments it is found that B100 required large amount of antioxidant for maintaining the specification fol-lowed by B30, B20, B10 and B7 samples with metal contents. Therefore it is possible to attain requisiteoxidation stability of metal contaminated biodiesel by blending 70% petro-diesel in Jatropha curcas bio-diesel (JCB). This optimum combination is expected to reduce the cost of biodiesel substantially andrequire lower quantity of antioxidant.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Biodiesel is a fuel consisting of the alkyl monoesters of vegetableoils or animal fats. Biodiesel fueled engines produces less carbonmonoxide, unburnt hydro carbons and particulate matters thandiesel fueled engines. One drawback of biodiesel is that it is suscep-tible to oxidation which can induce polymerization of the ester andcan form insoluble gums and sediments which are known to causefuel filter plugging. Biodiesel, derived from vegetable oil and animalfats, is being used as engine fuel in USA and Europe to reduce air pol-lution and to reduce dependence on limited fossil fuel, localized tosome specific regions. Because of the surplus availability of edibleoils like soybean oil, sunflower oil and rapeseed oil, these countriesare using edible oils as feedstocks for biodiesel production. On theother hand, the possibility of biodiesel production from edible oilresources in India is very less as the indigenous edible oil productionis much less than the actual demand which is met by its import [1].India accounts for 9.3% of world’s total oil seed production and is the

fourth largest edible oil producer in the world and still about 46% oftotal edible oil is imported to meet the domestic requirements andas such the question of diverting edible oil resources for biodieselproduction in India does not arise. The only possibility seems to bethe non-edible oil resources like Jatropha, pongamia, Mahua andsal, which can be commercially grown on waste lands and the oilresources can be used for biodiesel production. Jatropha curcas hasbeen identified as one of the important source for biodieselproduction in India.

Almost all the biodiesels have significant amounts of esters ofoleic, linoleic or linolenic acids and the trend of increasing stabilityis linolenic < linoleic < oleic [2]. These esters undergo auto-oxidation with different rates depending upon the numbers andpositions of the double bonds and result in the formation of a seriesof by-products like acids, esters, aldehydes, ketones, lactones, etc.

A number of reports have been found in the literature on thestorage and oxidative stability of biodiesel synthesized from edibleoils but only very few reports are available on the effect of blendingof biodiesel with diesel on the oxidation stability of that blend.However, to the knowledge of the author of this work, no workhas been reported on the effect of metal contaminants on non edi-ble biodiesel/diesel blend oxidation stability.

S. Jain, M.P. Sharma / Fuel 116 (2014) 14–18 15

Sarin et al. [3] have used palm and Jatropha biodiesel blends tominimize the dosage of antioxidants and found an increase in theinduction period of Jatropha biodiesel after it was blended withpalm biodiesel.

Sarin et al. [4] investigated the Synergistic effect of metal deac-tivator and antioxidant on oxidation stability of metal contami-nated Jatropha biodiesel. Research was conducted to increase theoxidation stability of metal contaminated Jatropha biodiesel bydoping metal deactivator with antioxidant, with varying concen-trations in order to meet the aforementioned standard requiredfor oxidation stability. It was found that usage of antioxidant canbe reduced by 30% to 50%, therefore the cost, even if very smallamount of metal deactivator is doped in Jatropha biodiesel to meetEN-14112 specification.

Sarin et al. [5] analyzed the effect of blending of biodiesels syn-thesized from non-edible and edible oils on oxidation stability.Dependence of the OS on esters of fatty acid composition was alsoexamined. Good correlation between the OS and PAME (palmiticacid methyl ester) was obtained.

Das et al. [6] have carried out long-term storage stability anal-ysis of biodiesel produced from Karanja oil and reported that theoxidative stability of Karanja oil ME (KOME) decreased with in-crease in storage time of the biodiesel. Knothe and Dunn [7] indi-cated that presence of Cu, even in 70 ppm in rapeseed oil greatlyincreases the oxidizability of the fuel. Copper has also been foundto reduce the Oxidation Stability Index (OSI) of methyl oleate morethan either Fe or Ni. Karavalakis et al. [8] have evaluated the oxida-tion stability of biodiesel/diesel blend. They used animal fats andused frying oil for biodiesel. They examined the factors influencingthe stability of several biodiesel blends with low and ultra low sul-phur automotive diesel fuels.

Sarin et al. [9] have evaluated the oxidation stability of metalcontaminated biodiesel and found that influence of metal was det-rimental to oxidation stability and catalytic.

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. Two types of antioxidants are generally known:chain breakers and hydroperoxide decomposers [10]. Literature re-lated to hydroperoxide decomposers is very scarce. The two mostcommon types of chain breaking antioxidants are phenolic andamine-types. Almost all the work related to stability of fatty oiland ester applications is limited to the phenolic type of antioxi-dant. The mechanism of all chain breaking antioxidants is shownbelow in Fig. 1.

As can be seen, the antioxidant contains a highly labile hydro-gen that is more easily abstracted by a peroxy radical than fattyoil or ester hydrogen. The resulting antioxidant free radical iseither stable or further reacts to form a stable molecule which isfurther resistant to chain oxidation process. Thus the chain break-ing antioxidants interrupt the oxidation chain reaction in order toenhance stability. The effectiveness of antioxidant is generallymeasured by stressing a fatty oil or ester molecule both with andwithout the antioxidant.

As per National Mission on Biodiesel in India, Jatropha biodieselhas undertaken for the present study in order to improve the sta-bility of biodiesel and make it acceptable to oil marketing compa-nies in India. The present paper aims to study the effect of metal

Fig. 1. Mechanism of all chain breaking antioxidants [2].

contaminants on the stability of Jatropha biodiesel/diesel blend.Also the effectiveness of various antioxidants is checked in metalcontaminated biodiesel and its blend with diesel.

2. Materials

Butylated hydroxytoluene (BHT), tert-butyl hydroquinone(TBHQ), butylated hydroxyanisole (BHA), propyl gallate (PG), andpyrogallol (PY) were the additives employed for their evaluationon diesel/biodiesel blends. All chemicals were of analytical gradeand purchased from Sigma Aldrich, India. Different transitionmetals–iron (Fe), nickel (Ni), manganese (Mn), cobalt (Co), andcopper (Cu) have also been purchased from Sigma Aldrich, India.Biodiesel is prepared in the laboratory and the procedure isdiscussed in the experimental section.

3. Experimental

3.1. Biodiesel preparation

Since the FFA contents of Jatropha curcas oil (JCO) were veryhigh (15.4%), a two step acid–base catalyzed transesterificationprocess is used to prepare biodiesel and the method is discussedin our previous publications [11,12]. After completion of the reac-tion, the reaction mixture was transferred to separating funnel andboth the phases were separated. Upper phase was biodiesel andlower phase contained glycerin. Alcohol from both the phaseswas distilled off under vacuum. The glycerin phase was neutralizedwith acid and stored as crude glycerin. Upper phase i.e. methyl es-ter (biodiesel) was washed with the water twice to remove thetraces of glycerin, unreacted catalyst and soap formed during thetransesterification. Fatty acid composition of biodiesel was ana-lyzed using Gas chromatograph [13] and is given in Table 1 whichshows that the JCB is maximum composed of unsaturated fattyacids (75.3%) responsible for poor oxidation and thermal stabilityof biodiesel.

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 biodiesel pre-pared from JCO meet most of the specifications except oxidationstability test.

As per National Mission on Biodiesel in India, the use of biodie-sel should reach a minimum of 20% in 2012, while the revisedEuropean standard EN 590 already includes a provision for auto-motive diesel fuel to be blended with biodiesel up to 7% (v/v).According to European standard there is no specification beyondB7 for oxidation stability. Therefore same oxidation stability spec-ification requirement (20 h) is considered for oxidation stability forall biodiesel blends beyond B7. As Indian standard follow the Euro-pean standards for stability of biodiesel therefore basis of study isvery correct.

3.2. Biodiesel/diesel blends preparation

For the purpose of experimentation, biodiesel is mixed withdiesel in different proportions (B80, B50, B40, B30, B20, B10 and B7).Also to see the effect of metal contents on biodiesel, different metalcontents (Fe, Ni, Mn, Co and Cu) are added in biodiesel in pre-decided concentrations with and without antioxidants.

3.3. Oxidation stability measurement

Oxidation stability of biodiesel from different feedstocks andtheir blends with automotive diesel was quantified by the induc-tion period (IP). The IP was evaluated according to the Rancimat

Table 1ASTM and IS specification of biodiesel.

S. No. Property (unit) ASTM D6751 ASTM D6751 limits IS 15607 IS 15607 limits Jatropha ME

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 (hr) EN14112 3 EN 14112 Min. 6 3.277 Oxidation stability of FAME blend (hr) – – EN 590 Min. 20 –8 Free glycerol D6584 0.02 (max) D6584 0.02 (max) 0.019 Total glycerol D6584 0.25 (max) D6584 0.25 (max) 0.12

10 Acid value D664 0.5 (max) D664 0.5 (max) 0.3811 Ester content – – EN14103 96.5 (max) 98.5

Table 2Fatty acid composition of Jatropha curcas oil.

Fatty acid Molecular formula 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)4CH@CHACH2ACH@CHA(CH2)7COOH 36.0Linolenic acid (LL) C18H30O2 CH3(CH2)4CH@CHACH2ACH@CHACH2ACH@CHA(CH2)4COOH 0.2

Fig. 2. Effect of metal contaminants on oxidation stability of biodiesel.

16 S. Jain, M.P. Sharma / Fuel 116 (2014) 14–18

method EN 14112 for pure biodiesel and the modified Rancimatmethod EN 15751 for the biodiesel blends with petro-diesel. Inthe modified Rancimat method, a number of parameters werechanged, mainly because of the higher volatility of hydrocarbonfuels compared to methyl esters, which may lead to higher sampleevaporation. All stability measurements were carried out on aMetrohm 873 Biodiesel Rancimat instrument. Samples of 3 g ofpure biodiesel and 7.5 g of biodiesel blends were analyzed undera constant air flow of 10 L/h, passing through the fuel and into avessel containing distilled water. The samples were held at110 �C heating block temperature. The end of the induction periodis indicated when the conductivity starts to increase rapidly. Thisaccelerated increase is caused by the dissociation of volatile car-boxylic acids produced during the oxidation process and absorbedin the water. When the conductivity of this measuring solution isrecorded continuously, an oxidation curve is obtained whose pointof inflection is known as the IP. This provides the good character-istic value for the oxidation stability.

Fig. 3. Effect of metal contaminants on the oxidation stability of biodiesel/dieselblends.

4. Results and discussion

4.1. Effect of metal contaminants on the oxidation stability ofbiodiesel/diesel blends

To check the effect of metal contaminants on the oxidation sta-bility of biodiesel, it is added with different metal contents withpre-decided concentration and the effect of these on oxidation sta-bility is shown in Fig. 2 it is clear from figure that as the concentra-tion of metal increases, oxidation stability decreases but after2 ppm concentration oxidation stability become constant. This isdue to the catalytic effect of metals on oxidation stability [4,9].Fe is found to have least catalytic effect on oxidation stability fol-lowed by Ni, Mn, Co and Cu.

As the oxidation stability of biodiesel become constant beyond2 ppm metal concentration therefore biodiesel/diesel sampleswere mixed with different metals contents with 2 ppm concentra-tion. Then the oxidation stability is checked using Rancimat test asdiscussed in experimental section and the results are shown inFig. 3. It is clear from Fig. 3 that as the amount of diesel increasesin the blend, the oxidation stability also increases. Fe is found to

have least catalytic effect on oxidation stability followed by Ni,Mn, Co and Cu. This statement is in agreement with the pure bio-diesel case as shown in Fig. 2.

Fig. 4. Effectiveness of antioxidants on biodiesel/diesel blends.

S. Jain, M.P. Sharma / Fuel 116 (2014) 14–18 17

4.2. Effect of antioxidants on metal contaminated biodiesel/dieselblends

To check the effectiveness of antioxidants on biodiesel and bio-diesel/diesel blend, these are doped with different antioxidantswith 200 ppm concentration and the results are shown in Fig. 4.PY is found as most effective antioxidants followed by PG, TBHQ,BHT and BHA.

Based on the results of Fig. 4, the different biodiesel/dieselblends with and without metal contents are doped with PY antiox-idants with different concentrations up to 600 ppm and the resultsand shown in Figs. 5 and 6.

Fig. 5 shows the effect of PY on the oxidation stability of biodie-sel (B100) and biodiesel/diesel blends (B80, B50 and B40) with andwithout metal contaminants. Fig. 5 shows that for B100 samplewithout metal contents, 80 ppm PY is required to maintain thespecification (EN14214) however for metal contaminated B100

sample amount of PY is increased to 300, 400, 400, 500 and

Fig. 5. Effect of PY on metal contaminated biodiesel/diese

600 ppm for Fe, Ni, MN, Co and Cu metals respectively. For B80sample without metal contents 400 ppm PY is required to maintainthe specification (EN590) however as the sample is doped withmetals the amount of PY is increased beyond 600 ppm to maintainthe same specification. All the B80 metal contaminated samples arefailed to maintain the specification with PY antioxidant up to600 ppm.

For B50 and B40 samples without metal contents the PY requiredis 300 ppm and 200 ppm respectively. Only Fe contaminated blendis maintaining the specification (EN590) with 600 ppm PY howeverall other metal contaminated B50 and B40 blends are fail to main-tain the specification with PY up to 600 ppm.

Fig. 6 shows the effect of PY on the oxidation stability ofbiodiesel/diesel blends (B30, B20, B10 and B7) with and withoutmetal contaminants. For B30 sample without metal contents,50 ppm PY is required to maintain the specification. However formetal contaminated B30 sample, PY required is 290, 300, 310,400 and 410 ppm for Fe, Ni, Mn, Co and Cu respectively.

For B20 sample without metal content, no antioxidant is re-quired to maintain the specification. However for metal contami-nated B20 sample, PY required is 100, 180, 200, 280 and 300 ppmfor Fe, Ni, Mn, Co and Cu respectively.

Oxidation stability of B10 and B7 samples without metal con-tents and antioxidants is very high. Also for metal contaminatedB10 and B7 blends, amount of antioxidant is very less as comparedto blends with high amount of biodiesel. For B10 sample amount ofPY required is 50, 90, 100, 200 and 210 for Fe, Ni, Mn, Co and Curespectively. For B7 sample amount of PY required is 50, 60 and80 for Mn, Co and Cu respectively however no antioxidant is re-quired for Fe and Ni contaminated B7 sample.

Fig. 7 showing the concentration of antioxidant (PY) requiredfor maintaining the specification of 6 h (EN14214) for B100 and20 h (EN 590) for biodiesel/diesel blends. It is clear from theFig. 7 that B100 required large amount of antioxidant for maintain-ing the specification followed by B30, B20, B10 and B7. Thus, it is

l samples (B100, B80, B50 and B40) oxidation stability.

Fig. 6. Effect of PY on metal contaminated biodiesel/diesel samples (B30, B20, B10 and B7) oxidation stability.

Fig. 7. PY concentration required to maintain the specification of oxidation stabilityfor different samples with and without metal contents.

18 S. Jain, M.P. Sharma / Fuel 116 (2014) 14–18

possible to attain requisite oxidation stability of biodiesel byblending 70% petro-diesel in Jatropha biodiesel. This optimumcombination is expected to reduce the cost of biodiesel substan-tially and require lower quantity of antioxidant.

5. Conclusion

When JCB is blended with petro-diesel, it leads to a compositionhaving improved oxidation stability. In the present paper effect ofmetal contaminants on the oxidation stability of biodiesel/dieselblend is checked with and without antioxidants. From the experi-ments it is found that PY is the most effective antioxidant to in-crease the oxidation stability of different biodiesel/diesel blends.The amount of PY required in biodiesel/diesel blend is lower as

compared to pure biodiesel to maintain the specification of oxida-tion stability. B100 required large amount of antioxidant for main-taining the specification followed by B30, B20, B10 and B7. Thus, itis recommended to attain requisite oxidation stability of biodieselby blending 70% petro-diesel in JCB. This optimum combination isexpected to reduce the cost of biodiesel substantially and requirelower quantity of antioxidant.

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