Influence of stainless steel corrosion on biodiesel oxidative stability during storage

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Fuel

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In

fluence of stainless steel corrosion on biodiesel oxidative stability during

storage

S.M. Alves

, F.K. Dutra-pereira

, T.C. Bicudo

a_{Programa de Pós-Graduação em Engenharia Mecânica, Universidade Federal do Rio Grande do Norte, CEP 59078-970 Natal, RN, Brazil}

b_{Laboratório de Ensino e Tecnologia Química, Escola de Ciências e Tecnologia, Universidade Federal do Rio Grande do Norte, CEP 59078-970 Natal, RN, Brazil}

G R A P H I C A L A B S T R A C T

A R T I C L E I N F O Keywords:

Biodiesel degradation Stainless steel corrosion Micropitting

A B S T R A C T

Biodiesel degradation is the modification of its original composition and properties as a result of fuel aging and metal corrosion during the storage process. This study examines the linkage between biodiesel degradation and the corrosion of stainless steel used to store the biodiesel. First, biodiesel was synthesized from soybean oil via methanolysis and ethanolysis homogeneous base-catalyzed transesterification routes. Next, immersion tests were carried out at room temperature, with little air turnover and in the dark. AISI 316 coupons were used to evaluate the corrosion of metal surfaces after contact with the biofuel. Changes in fuel composition were studied using FTIR and gas chromatography analysis, and the oxidative stability was analyzed by Rancimat and the peroxide index. The corrosion was evaluated by the gravimetric and SEM/EDS microscopy techniques and XRF analysis. Results revealed little influence of methyl and ethyl esters on metal degradation, indicating that routes have no importance on corrosion, since a low corrosion rate was observed for both esters, albeit with some surface micropitting. On the other hand, the presence of a small amount of metal ions released from the stainless steel surface during its corrosion promoted oxidation of the biodiesel, changing fuel composition and quality, as well as reducing its oxidative stability generally.

1. Introduction

Biodiesel has become an alternative for petrodiesel fuel in com-pression ignition engines, mainly due to its renewability, non-toxicity, biodegradability and high cetane number, in addition to being safe for

storage, handling and transporting, and containing no sulfur[1]. An-other important aspect is that it can be locally produced by chemical processes, the most widely used being transesterification, where short chain alcohols react with triacylglycerides (vegetable oils or animal fats) in the presence of alkali or acid homogeneous catalysts, yielding

https://doi.org/10.1016/j.fuel.2019.03.097

Received 7 December 2018; Received in revised form 13 March 2019; Accepted 17 March 2019 ⁎_{Corresponding author.}

E-mail address:saletealves@ect.ufrn.br(S.M. Alves).

Available online 23 March 2019

0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

alkyl esters as the main products. However, some impurities may be found in the biodiesel in cases of incomplete conversion or insufficient washing (purification). These impurities (glycerol, alcohol, free fatty acids and catalysts) may leave engine deposits and cause corrosion, leading to fuel failure[2]. Moreover, the degree of unsaturation, an-other important issue related to biodiesel stability, is dependent on feedstock composition[3–5]. Thus, oxidation susceptibility and corro-sivity are properties of interest for establishing biodiesel quality[6–8]. In engine parts, metals such as copper and its alloys, aluminum, cast iron, mild steel and stainless steel may be susceptible to corrosion [8–11]. As such, corrosion has become an important issue in biodiesel usage. Fazal et al. [12]compared the corrosive behavior of copper, stainless steel, and aluminum in diesel and palm biodiesel. They carried out immersion tests at 80 °C for 1200 h. In order to determine corrosion characteristics, they measured weight loss and morphological changes on the metal surface at the end of the test. The mainfindings were that corrosion damage is more intense with biodiesel than diesel, and that the corrosion rate depends on the type of metal. The authors also ob-served that copper and aluminum were susceptible to corrosion by biodiesel, while stainless steel was not.

The influence of diesel–biodiesel blends has also been investigated [9,13]. The effect of a mixture of palm biodiesel and diesel on the corrosion characteristics of copper and leaded bronze was evaluated by [9]. They carried out static immersion tests in B0, B50 and B100 fuels at room temperature for 2640 h. The results showed that adding biodiesel to diesel promoted a significant increase in corrosion rate, and that leaded bronze is less susceptible to corrosion than copper. The authors found that biodiesel exhibited higher acidity, free water content and more oxidation products after immersion tests. Temperature also affects biodiesel corrosion rates[11]. Immersion tests in diesel, palm biodiesel and a blend of both were performed for 1200 h at room temperature, 50 and 80 °C[11]. According to the results, the corrosion rate of mild steel increased with a rise in temperature.

Biodiesel stability after long-term storage is influenced by fatty acid methyl ester composition, which is related to the feedstock [1,6,8,9,14]. José and Anand [1] investigated karanja and coconut biodiesel, whose compositions are significantly different. They con-cluded that the rate of degradation is greater for biodiesel with higher unsaturated methyl ester content (karanja biodiesel) when compared to coconut biodiesel. Berrios et al.[15]reported that stainless steel was a suitable material for storage tanks because its effect on stability was almost negligible. This is because it exhibits low corrosivity in the presence of biodiesel [10]. However, container material selection should take into account the fact that metal ions may cause biodiesel oxidation [8,9,16]. According to Komariah et al.[17], only stainless steel and aluminum are metallic materials compatible with biodiesel and recommended for its storage. Although aluminum is advised as container materials, some studies[10,12]have demonstrated that it is more corrosive (up to 13.5 times higher than stainless steel). Moreover, fuel properties such asflash point, viscosity and cetane number can also be changed by oxidative instability. A lower cetane number leads to prolonged ignition delay, and an increase in viscosity could result in poor fuel atomization[18].

Although, there are numerous studies on metal corrosion after ex-posure to biodiesel, none have investigated how it influences biodiesel stability during storage. Moreover, an interesting point to evaluate is whether the short chain alcohol used in the transesterification reaction plays some role in biodiesel corrosivity. In order to bridge the afore-mentioned gap, the present study aimed to investigate the ability of biodiesel samples synthesized by methanolysis and ethanolysis of soy-bean oil, to mount a corrosive attack on stainless steel, as well as de-termine the influence of metal corrosion on biodiesel stability.

2. Material and methods

2.1. Transesterification routes for biodiesel production

Fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) were synthesized by methanolysis and ethanolysis routes, respectively, both conducted under a homogeneous base-catalyzed transesterifica-tion reactransesterifica-tion of lipids from soybean oil. Dry oil, alcohol, and catalyst (potassium metoxide) at a molar ratio of 1:6:1 were mixed inside a mechanical stirrer equipped-reactor for 2 h at room temperature. After reaction, esters were removed from the reactional mixture, neutralized, and dried. In addition to FAME and FAEE, a commercial blend B7 (7% of biodiesel in a mixture with diesel) sample was also studied. The physicochemical parameters of all the samples were determined ac-cording to the American Society of Testing and Materials (ASTM).

2.2. Corrosion test

The corrosion process of fuel containers was simulated through immersion tests in biodiesel. Aluminum and stainless steel are compa-tible metallic materials for biodiesel containers although stainless steel is the most recommended for this purpose[17]. In this study, in order to understand if metal releasing from the surface during the corrosion process causes an influence on biodiesel stability immersion tests of AISI316 in biodiesel and its blend (B7) were carried out. These tests were performed on AISI 316 stainless steel coupons with a diameter of 9.35 cm2_{, polished by silicon carbide (SiC) paper from grid 200 to 1200,} andfinished by alumina 1 µm. The coupons were then washed in dis-tilled water, degreased with 0.2 mol L−1hydrochloric acid, commercial ethanol, and dried in hot air. Finally, the coupons were weighed.

To evaluate the corrosion process, three-stage mass loss was ob-served in static immersion tests at room temperature in the dark. Before immersion, corroded coupons were treated by rinsing in distilled water and rubbing the surface with a polymer brush to remove corrosion products. In addition, samples were immersed in 0.2 mol L−1 hydro-chloric acid solution for 120 s. Exposure time was also analyzed as follows: initial condition (0 h), stage 1 (720 h), stage 2 (1440 h), and stage 3 (2160 h). The degree of corrosion was determined by measuring the corrosion rate according to the following equation:

= × ν m A t Δ corr (1) where νcorr is the corrosion rate (mg cm-2h−1), Δm the percentage weight loss, A the exposed surface area (cm2_{) and t the immersion time} (h).

2.3. Characterization of chemical modifications

To observe the chemical changes in biofuel properties in each im-mersion stage, 0.3 mL of the sample was collected and its peroxide number was analyzed according to AOCS Cd 8-53. Sample degradation was also monitored by FTIR (Fourier Transform Infrared) measure-ments in a BRUKER FT-IR VERTEX 70 spectrometer, with 16 scans, at a resolution of 4 cm−1, in the range of 4000–400 cm−1. After last im-mersion stage, the fuels were also analyzed by X-rayfluorescence (XRF) to verify the presence of soluble corrosion products in fuel.

Fatty acid methyl and ethyl esters profile of samples in different stages of oxidation were evaluated by gas chromatography coupled to a mass spectrometer (GC/MS) Agilent Technologies GC, model GC-7890A/MS-5975C, equipped with a Column HP-5MS (30 m length × 250μm diameter × 0,25 μm film thickness). The samples werefiltered using syringe filters with 0.45 μm of porosity. The con-ditions of analysis included: 1.0μL injection volume; drag gas flow of 1.5 mL min−1; injector temperature of 250 °C; interface temperature of 300 °C; ionization source at 250 °C; ionization mode by electrons using energy of 70 eV for fragmentation and scanning acquisition mode of

compounds with m/z between 35 and 500. The temperature gradient started with the oven at 80 °C for 5 min, and after that, it was raised at a rate of 5 °C min−1to 260 °C; from this point, the rate was 10 °C min−1 up to 280 °C when the temperature was held constant for 5 min. The compounds identification was performed by comparing data obtained to the databases of the NIST libraries versions 8.0.

The oxidation stability of each sample was determined by the Rancimat method (according to EN15751) in a Metrohm Rancimat model 843. For every sample, 7.5 g ± 0.01 g of mass was submitted to a constant temperature of 110 °C in a reaction vessel with 25 mm length and to a moisture-free air with aflow rate of 10 L h−1. The induction period (IP) was set as the inflection point in the conductivity (μS cm−1₎ versus time (h) curve.

2.4. Stainless steel surface analyze

The surface morphology of corroded coupons was characterized by SEM/FEG Zeiss Auriga 40 connected to an energy dispersive X-ray analyzer (SEM/EDS), enabling surface chemical composition to be ex-amined. In addition, X-ray fluorescence (XRF) was used as compli-mentary analysis.

3. Results and discussion

3.1. Corrosion analysis after immersion tests

The chemical composition of esters in biodiesel is responsible for their main properties and depends on their feedstock. In this study, soybean oil was used as raw material for biofuel production and an elevated content of unsaturated components was expected in the sam-ples. This contributes to biodiesel oxidation, which increases the acid number and water content, enhancing its corrosivity[19–21]. Biodiesel corrosivity can also be affected by several factors including acid number, water content, metals and unsaturated acids[19]. After im-mersion, coupons started losing weight, probably due to oxidative contact with the fuel samples, indicating ions released from the metal surface to thefluid. B7 caused major weight loss in AISI 316 stainless steel when compared to the others (Fig. 1), possibly due to its slightly higher acid number[19,20](Table 1).

The corrosion rate for stainless steel was very low, as expected, with values ranging from 1.5 × 10−4up to 7.5 × 10−4mpy. Similar results were observed by [10,12]. Nevertheless, the influence of exposition time and fuel composition was verified. The corrosion rate can also depend on the alcoholic moiety of ester chains, which are composed of ethyl and methyl groups in FAME and FAEE samples, respectively. This

probable composition effect on corrosion is illustrated inFig. 1, where AISI 316 stainless steel was more susceptible to FAME than to FAEE, suggesting an increase in corrosivity for that sample, in line with its lower acid number. The effect of methyl and ethyl alcohol moiety is mainly relevant in thefirst immersion stage (720 h), at the onset of corrosion (Fig. 1). In this stage, corrosion is governed by fuel properties, because the oxidation process is in the initial phase. The corrosion rate does not depend on ester composition. Corrosion can be triggered by acid compounds in biodiesel, after which the chemical identity of the esters, especially characterized by their polarity imparting oxygen atoms, acts as an inhibitor of metal degradation. The functional group of esters has been related to lubricity improvement of ULSD (ultra low sulfur diesel)[5]. Sundus et al.[21]observed the contradictory nature of biodiesel based on tribo-corrosion statements. Regardless of biodiesel is prone to oxidation and highly corrosive, several tests have shown that it can decrease wear and friction at specific conditions (short-term use, for instance) [20]. A common agent for biodiesel oxidation are the metal ions released from the metal surface that are able to modify some of the fuel properties, especially oxidative stability[11,16,19,22].

3.2. Surface morphology and chemical changes

The corrosion morphologies and mechanisms of metal surfaces were analyzed using SEM and EDS. SEM images and EDS mapping of the surface exposed to biodiesel are displayed inFig. 2. The SEM micro-graphs reveal that after exposure to biodiesel, corrosion caused a slight change in the metal surface. A number of micropits (dark spots) are found on the metal surface, pitting density is lower than that observed by [9,10], and little influenced by transesterification routes. Fig. 2 shows that the size and distribution of the pits are different and seem to depend on fuel characteristics. The metal surface immersed in B7 ex-hibited more and smaller pits than those immersed in biodiesel. Stainless steel resists corrosion via a thin protectivefilm that forms on the surface. However, this steel is susceptible to pitting associated with the dissolution and regeneration of passive film, as corroborated by SEM and EDS. After immersion (2160 h), oxides such as Fe2O3 and Cr2O3were formed on the stainless steel surface, as demonstrated by EDS mapping and XRF analysis (Table 2). Small cavities caused by coupon roughness form active regions where micropits occurred as a result of iron reactions.

According to Brandão et al.[23], micropitting is mainly defined by the small size of its pits, typically around 10 µm wide and deep. Vo-giatzis et al.[24]proposed a model to describe micropitting formation. After immersion in fuel, the corrosion products form a relatively stable layer on the disc surface and micropits formed. This layer behaves as a “protective film” that decreases the corrosion rate (see Fig. 1). The oxide layer is observed mainly for B7, as confirmed by EDS analysis of oxygen distributed over the entire surface, but more intensely in mi-cropitting. Surfaces immersed in biodiesel behave differently, because this layer is predominantly found in micropitting (black dots on the metal surface). With respect to the transesterification route, biodiesel from ethanol exhibited fewer signs of corrosion than the methyl route. The XRF results corroborate this observation, because a larger amount of Fe2O3and Cr2O3is found on the surface exposed to B7 and FAME.

In addition to chemical and morphological metal surface analysis, Fig. 1. Corrosion rates of stainless steel at different immersion times.

Table 1

Physicochemical parameters of FAME, FAEE and B7 samples. Parameter FAME FAEE B7 Limits Method Density (g cm−3) 879.8 879.9 836.1 860–900 ASTM D4052 Viscosity (cSt) 4.8 4.5 2.6 2.0–6.0 ASTM D445 Water content (%) 0.045 0.03 0.02 0.05 ASTM D6304 Peroxide index (meq kg−1) 30.0 22.3 27.0 – AOCS Cd 8-53 Acid number (mg KOH g−1) 0.3 0.2 0.4 0.5 ASTM D664

XRF was also used to verify the presence of metals-containing corrosion products in the fuels (Table 3). Iron oxide (Fe2O3) was detected in all fuel samples, while molybdenum oxide (MoO3) was observed only at

diesel fuel (B7), suggesting either higher solubility of MoO3in B7 or the influence of the container metal composition where B7 was stored since it was obtained from local trading. The presence of these oxides even at low concentrations may cause some modification at the chemical identity of fuels. Jain and Sharma[25]simulated the effect of metal contamination on oxidative stability of biodiesel and verified that small concentration (around 0.5 ppm) of iron promoted a reduction in oxi-dative stability.

3.3. Oxidative degradation of samples

Infrared spectroscopy has been used to determine the presence or absence of chemical entities by changing the height/area of specific peaks[14,26–29]. In order to observe the degradation process of fuel samples exposed to the coupons, pre-immersion FTIR spectra are de-picted inFig. 3. Typical biodiesel regions can be observed in FAME and FAEE samples, as well as a significant decline in O-CH3stretching and carbonyl absorption in the spectrum of B7. Saturated aliphatic esters exhibit strong absorption in the range of 1735–1750 cm−1_[29] (car-bonyl absorption region). These absorptions at lower frequencies could indicate the presence of more than one type of carbonyl-containing compound in addition to ester chains. Organic compounds, such as carboxylic acids, ketones and aldehydes, can absorb in the range of 1700–1740 cm−1_{[26]and may be oxidation products resulting from} oxidative processes originating in the fatty esters.

In relation to sample degradation, some peaks display slightly dif-ferent height or area, which could indicate chemical changes. In the carbonyl region (Fig. 4a) two events are noteworthy. Thefirst is related to the peak height of 1741 cm−1, which decreased as exposure time increased. This could can be attributed to oxidation reactions that can convert esters to other non-carbonylated substances[26,28], causing the C]O absorption band to decrease. The second event is the emer-gence of a shoulder at about 1718, 1720 and 1724 cm−1, for 720, 1440 and 2160 h of degradation respectively, which may be related to the formation of oxidation products (aldehydes, ketones, fatty acids) from

Fig. 2. SEM Images and EDS analysis of the exposed surface: a) B7, b) FAME and c) FAEE.

Table 2

Chemical analysis of surfaces by XRF. Fuel Oxide compound (µg/kg)

Fe2O3 Cr2O3 NiO MoO3 MnO SO3

FAEE 670.835 176.145 87.065 24.41 14.14 19.24 FAME 675.255 173.615 88.085 24.97 14.255 19.395 B7 677.245 175.955 89.11 24.615 14.235 18.405

Table 3

Chemical analysis by XRF of fuels after immersion test (stage 3).

Fuel Oxides (ppm)

Fe2O3 MoO3

FAEE 0.517 –

FAME 0.650 –

B7 0.458 0.533

hydroperoxide breakdown [26] and hydrogen bonding to carbonyl oxygen[29], and another broad signal at about 1695 cm−1, probably due to conjugation of the carbonyl group with a double-bond[26].

Stretching vibrations of the CeO bond from the O-CH3group in long-chain methyl esters resulted in three absorption bands at 1170, 1195 and 1244 cm−1(Fig. 4b)[29]. Furlan et al.[26]suggested that decreases in peak intensity in this region and in carbonyl absorption may result from oxidative breakage of methyl-ester linkages (O-CH3).

The chemical composition of FAME and FAEE is strongly related to their feedstock characteristics. Double bonds containing raw materials yield unsaturated fatty chain products after transesterification. Double bonds are active sites for biofuel oxidation processes [18] and re-sponsible for its poor storage stability. The presence of unsaturation is highlighted by FTIR absorptions. Double bonds in a cis configuration absorb at 710 and 3009 cm−1(Fig. 5). However, these peaks decreased with oxidation time, suggesting a loss of this type of bond due to the oxidation processes taking place. A decline in cis double bonds is fol-lowed by an increase in trans configuration, as observed between 900 and 1000 cm−1, where the bending vibrations of trans double bonds become more intense. The primary oxidation products are hydroper-oxides, which may have undergone cis/trans isomerization, as displayed inFig. 6 [20,26].

The decomposition patterns of FAEE were similar to those of FAME, and FTIR spectra were plotted to compare fuel degradation after 2160 h (as shown atFig. 7).Fig. 7demonstrates that FAEE peaks are less in-tense, suggesting more intense degradation for ethyl biodiesel.

Although B7 induced major surface corrosion, its chemical degradation was milder than that of biofuels, probably due to the absence of double bonds in its carbon chain.

Besides FTIR spectra, the modifications in chemical composition as consequence of fuel degradation were observed in the fatty acid profiles obtained by GC/MS investigation. The content of main fatty acid esters like palmitic (C16:0), stearic (C18:0), oleic (C18:1), and linoleic (C18:2) were quite reduced with degradation time (Fig. 8) denoting possible conversion of these chemical entities into oxidation products, corro-borating with FTIR results.

The physicochemical properties analyzed (Table 1) and corrosion results are in line with FTIR data discussed here regarding the occur-rence of oxidative events under metal exposure to biofuels. These in-dicate the formation of polymer compounds able to cause engine pro-blems such as pump and fuel line clogging[26,30]. The increase in the peroxide index shows the evolution of oxidation processes in the fuel samples, since it is related to the amount of peroxide and hydroperoxide resulting from oxidative attacks on the biofuel[16,19]. For the samples studied here, peroxide values rose with immersion time (Fig. 9), re-vealing the presence of oxidation products. Peroxide index results corroborate the previousfinding and the literature[31], namely that FAEE is the most degraded sample, followed by FAME and B7.

Although B7 showed a higher corrosion rate (Fig. 1), the presence of metal ions did not promote fuel degradation due to their chemical nature. Silva et al.[32]evaluated soybean biodiesel stability during storage in the dark in amber glassflasks. After 90 days of immersion, they found that the peroxide index increased from 26.57 meq kg−1to 70 meq kg−1. This led us to conclude that metal ions accelerate bio-diesel degradation, since the peroxide index for FAME in the present study was around 230 meq kg−1after 90 days. In addition, Fernandes et al.[33]studied the influence of metal ions from galvanized steel corrosion, observing that the peroxide index rose by 1100% after 84 days, while in the absence of these particles, the increase was only 5%. Thus, given that stainless steel, a suitable storage tank material, was used in the tests, and that the rise in peroxide index was 650%, it can be inferred that even localized corrosion can accelerate biodiesel degradation.

Fuel degradation was also evaluated by oxidative stability mea-surements. The Rancimat method provides the induction period (h) that is related to the time when oxidation takes place. The analysis revealed a reduction of IP as immersion time increases (Table 4), suggesting fuel degradation. Comparing with literature, this behavior was expected, [25]verified that only the presence of 0.5 ppm of iron (Fe) reduced the Fig. 4. FTIR spectra from 1800 to 1700 cm−1(a) and 1400 to 1100 cm−1(b).

Fig. 5. Degraded and non-degraded FAME spectra in the 3150–2700 cm−1 (before break) and 1050–600 cm−1_{range (after break).}

IP in 18%, also according to[34]after four months of storage in carbon steel container, the IP of soybean biodiesel decreased around 50%. Corroborating the FTIR and Peroxide index results, the more degraded fuel was FAEE, followed by FAME and B7.

4. Conclusion

The corrosivity of biodiesel and diesel towards AISI 316 stainless steel and a resulting influence on fuel stability were studied considering biodiesel obtained from different transesterification routes. The corro-sivity of FAME and FAEE towards AISI 316 stainless steel appear to be similar and relatively low in intensity when compared to their corro-sively towards other metals. AISI 316 was more susceptible to B7, probably due to its acidity. SEM images, and EDS and FRX analyses revealed the protective oxidefilm formation on micropitting, especially for coupons immersed in B100 samples. More and smaller micropits were observed after the B7 immersion test. As thisfilm breaks, metal ions dissolve into the biodiesel (around 0.5 ppm of iron oxide), in-creasing fuel degradation. However, the results demonstrated that even a mild corrosive attack promotes biodiesel degradation due to the re-lease of metal ions from the metal surface. The FTIR and GC showing change in biodiesel chemical composition, indicating that the

occurrence of oxidation reactions and degradation of fuel. Moreover, the increase of peroxide index and reduction of induction period in-dicated the fuel degradation caused by the occurrence of oxidation processes resulting from the release of metal ions from the stainless steel surface after contact with biofuel samples. B7 is less susceptible to degradation by metal ions, because the hydrocarbons are more stable to Fig. 6. Propagation stage of biodiesel oxidation[17].

Fig. 7. FTIR spectra from FAME, FAEE and B7 in the last stage of degradation.

0 720 1440 2160 0.00 9.50x105 1.90x106 2.85x106 3.80x106 4.75x106 Peak ar ea / m m 2 Stage / h C16:0 C18:0 C18:1 C18:2

a)

b)

Fig. 8. Chemical changes in fatty acid profiles from GC/MS analysis in each oxidation stage for (a) FAME and (b) FAEE.

oxidation.

Acknowledgments

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Brasil (CAPES) -Finance Code 001.

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Fig. 9. Peroxide index of FAME, FAEE and B7 at different immersion times. Table 4

Induction period (h) from Rancimat of fuels in every degradation stage. Stage Time (h) IP (h) FAME FAEE B7 Initial 0 5.54 4.36 23.46 1 720 4.44 2.83 20.55 2 1440 3.13 2.81 19.94 3 2160 2.02 1.23 15.84