bondioli., et al (2003)

© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.de

Eur. J. Lipid Sci. Technol. 105 (2003) 735–741 DOI 10.1002/ejlt.200300783 735

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aper

1 Introduction

Biodiesel is a renewable fuel consisting of a mixture of fat-ty acid methyl esters (FAME) of natural origin for automo-tive or heating applications. The problem of biodiesel be-havior during long term storage has been discussed in re-cent years by several researchers, including Du Plessis etal. [1], Mittelbach and Gangl [2], and Bondioli et al. [3], torefer to just a few of the most cited Authors. More recent-ly Simkovsky and Ecker [4] demonstrated the negativeimpact of light on biodiesel storage stability. In the samepaper the activity of natural antioxidants such as tocoph-erols was also investigated. In a subsequent paper thesame authors [5] reported on the use of some commer-cially available antioxidants for diesel fuel. The stability ofsamples was evaluated by means of the Active OxygenMethod (AOM) and no positive effects were observed.

The results of a two years study, using rapeseed methyland ethyl esters stored in glass and steel containersdemonstrating increase in peroxide value, acid value,density and viscosity were published by Thompson et al.[6]. The authors did not find significant difference attribut-able to the nature of the container. A very complete re-view, containing useful information about neat biodieseland biodiesel/diesel fuel blends stability, was published in2001 by Knothe and Dunn [7]. Finally within the context of

the BIOSTAB project, the French group carried out sever-al tests to evaluate the evolution of numerous biodieselparameters during the Rancimat test [8].

The main shortfall in most of these papers is that researchwas either carried out on a simple feedstock for a reason-able period of time or on different feedstock for limited pe-riods of time.

Trying to integrate these data to obtain a more completeoverview on biodiesel storage behavior, is sometimes dif-ficult and leads to poor results because of the hetero-geneity of data with respect to quality of biodiesel, natureof container, contact with air and daylight, presence ofpro-oxidant metals and different test methods used forevaluation of composition changes.

In a previous paper [9] we reported property changes ob-served during an accelerated test carried out at 43 °C ac-cording to ASTM D4625. In order to clearly define themeaning of ageing in biodiesel samples when stored inreal conditions, this paper reports recorded changes innumerous parameters during a one year experiment. Theultimate aim of the work as a whole is the set-up of a quickmethod for predicting storage behavior of biodiesel sam-ples. This forms the basis for the next stage of our work.

A one year period of storage can be regarded as a morethan realistic time span for the commercial life ofbiodiesel. Under common market conditions we can inapproximately six months estimate the maximum com-mercial life of the said product. Collection of selectedbiodiesel samples was set up taking into account possible

Paolo Bondioli, Ada Gasparoli, Laura Della Bella, Silvia Tagliabue, Guido Toso

Stazione Sperimentale Oli eGrassi, Milano, Italy

Biodiesel stability under commercial storageconditions over one yearResults obtained from a long-term storage study using eleven different biodiesel sam-ples are presented. Samples prepared from several feedstocks using different manu-facturing technologies (with or without biodiesel distillation), some containing an an-tioxidant additive, were stored in 200 l drums. These were periodically monitored dur-ing the complete storage period by analysis of fifteen different properties.

Several properties do not show any significant change during storage, while otherssuch as viscosity, peroxide value and more dramatically, Rancimat Induction Perioddemonstrated changes related to the nature of the starting product.

A parallel test, carried out in simulated wrong storage conditions (occasional shakingpromoting intimate contact between biodiesel and air oxygen) lead to some strongchanges in biodiesel composition and can be used as a guide for devising biodieselproduction set-up, storage and distribution chain.

Keywords: Biodiesel, storage stability, biofuel, oxidation, ageing, storage test.

Correspondence: Paolo Bondioli, Technology Dept., StazioneSperimentale Oli e Grassi, Via Giuseppe Colombo, 79, 20133Milano, Italy. Phone: +39-02-7064971, Fax: +39-02-2363953; e-mail: [email protected]

feedstocks (rapeseed, sunflower, mixture of both, usedoils, tallow, etc.), different preparation processes (in prac-tice with or without distillation), and presence of antioxi-dant additives.

Simultaneously, one drum of standard quality biodieselfrom rapeseed was stored in open space under directsunlight and occasionally shaken strongly, to promotecontact with air and hence oxidative damage. Clearly, asthe sample was stored in a metal container total directcontact with sunlight may not have been achieved. Nev-ertheless, ambient temperature of this sample was higherduring summer, and lower during winter than temper-atures of the other ten samples, which were stored in a pi-lot plant room (without heating or conditioning facility).

2 Material and methods

2.1 Materials

Eleven biodiesel samples were prepared and/or collectedfrom the BIOSTAB community network, and thus all pos-sible aspects of existing European biodiesel were cov-ered. Each sample was received in a 200 l drum andchecked before storage. Two samples were prepared bydistillation from rapeseed and sunflower methyl esters(rape-distilled and sun-distilled), one from tallow (tallow),one from used frying oils (used frying oils), one from a 2:1mixture rapeseed/sunflower oil (rape/sun), and one fromrapeseed oil (rape). In addition, five drums of biodieselprepared from rapeseed oil of different industrial originswere used to study the behavior of additives, as well asadditional ageing effects caused by contact with air. A de-tailed description of these five samples is given below.

The first series of three drums was organized as follows:

– one sample without any treatment was used as a ref-erence (TBHQ-blank )

– one sample was supplemented with tert-butyl hydro-quinone (TBHQ) in calculated amounts, to give a finalconcentration of 400 mg/kg (TBHQ-additivated). Sup-plementation was carried out by dissolving the neces-sary amount of TBHQ in 2 l of the biodiesel understudy, thus preparing a concentrated solution. This so-lution was stirred for 30 min at ambient temperature;TBHQ is readily soluble under these conditions. Duringthe entire stirring period a gentle flux of inert gas (nitro-gen) was bubbled inside the sample. Nitrogen wasused only during preparation of the concentrated solu-tion to protect the antioxidant from damage. Finally, theconcentrated solution was added into the drum. Ho-mogenization inside the drum was achieved by rollingin two opposite directions for 15 min before storage;

– one sample (low stability) was stored outdoors, ex-posed to high and low temperatures during the year ofstudy. Additionally, this sample was shaken once aweek to promote a more intimate contact with air.

Following initiation of the study, it was considered advis-able to test the behavior of pyrogallol (Pyro) antioxidant.Therefore, two additional drums (one Pyro-blank and onePyro-additivated at a final concentration of 250 mg/kg)were also prepared from rapeseed biodiesel and studiedfor a one year period. Due to the poor solubility of pyro-gallol in biodiesel, preparation of a methanolic concen-trated solution was necessary. The amount of methanol tobe used for preparation of this solution was calculated in

736 Bondioli et al. Eur. J. Lipid Sci. Technol. 105 (2003) 735–741


Tab. 1. Biodiesel samples used for long-term studies.

Sample Source Production Additivation Deviation from specificationtechnology [mg/kg]

TBHQ blank Rapeseed Undistilled None

TBHQ additivated Rapeseed Undistilled TBHQ – 400

Low stability Rapeseed Undistilled None

Rape Rapeseed Undistilled None

Rape-distilled Rapeseed Distilled None Rancimat induction period = 4.2 h

Sun-distilled Sunflower Distilled None Iodine value = 131.1Rancimat induction period = 1.3 h

Rape/sun Rapeseed 67% Undistilled NoneSunflower 33%

Used frying oils Used frying oils Undistilled None Ester content = 94.2%

Pyro blank Rapeseed Undistilled None

Pyro additivated Rapeseed Undistilled PYRO – 250

Tallow Tallow Undistilled None Ester content = 88.0%Rancimat induction ceriod = 0.7 hTriglycerides 0.26%

a way so as to fulfill specifications for methanol in the finalproduct (<0.20 [wt-%]). This calculation took the endoge-nous methanol content of the sample also into account.Therefore, for preparation of 177 kg biodiesel with negli-gible initial methanol content, 44.25 g of antioxidant weredissolved in 354 g (448 ml) of methanol. This sample washomogenized as described for TBHQ. All samples werechecked before initiation, to evaluate their adherence tominimal requirements. All samples met the specificationlimits with some minor deviations. In the case of tallow thealready mentioned problems in ester content determina-tion [9] were confirmed: as previously discussed the realester content for this sample is higher than the one deter-mined according to European specification, EN 14103. InTab. 1 the complete set of samples, along with their maincharacteristics are shown. Eventual deviations from theminimum requirements are also indicated in this table.

Tab. 2 shows the complete set of data obtained before thebeginning of the storage experiment. The last line ofTab. 2 contains the specification values for biodiesel asdefined in European specification, EN 14213.

2.2 Sampling

Three 100 ml samples were taken from each drum atfixed time intervals, and poured in three different darkglass containers. Sampling was carried out by opening ofthe drum and using a 100 ml glass pipette equipped witha vacuum device. During each sampling operation, airwas renewed inside the drum but care was taken to avoidair mixing during the procedure. The first bottle was im-mediately used for sensitive determinations such as per-oxide value (PV) and oxidation stability, the second wasused for general analytical tests, and the third was imme-diately stored at –18 °C for possible future requirement.

2.3 Analytical methods

All samples were analyzed according to generally recog-nized parameters, using analytical methods suggested byCEN Committees as being suitable for biodiesel evalua-tion. Specifically the following tests were carried out (ana-lytical method in brackets):

PV (NF T 60-220), 40 °C kinematic viscosity – KV (ENISO 3104), acid value – AV (EN 14104), ester content +linolenic acid methyl ester (EN 14103), iodine value – IV,were obtained by calculations according AOCS Cd 1c-85(97) using coefficients suggested for tri-glycerides, aswell as free and total glycerol (EN 14105), polymers(mod. IUPAC 2.508), oxidation stability (EN 14112), to-copherols (ISO 9936). When present, added synthetic an-tioxidants were also analyzed using a reverse phase highperformance liquid chromatography (HPLC). Briefly,

Eur. J. Lipid Sci. Technol. 105 (2003) 735–741 Biodiesel stability under commercial storage conditions 737


Tab

. 2.C

ompo

sitio

n of

bio

dies

el s

ampl

es b

efor

e ag

eing

.

Per

oxid

e40

°C

Aci

dE

ster

Lino

leni

cIo

dine

Mon

o-D

i-Tr

i-Fr

eeP

olym

erR

anci

mat

Toco

ph-

valu

eK

inem

atic

va

lue

cont

ent

acid

met

hyl

valu

egl

ycer

ides

glyc

erid

esgl

ycer

ides

glyc

erol

cont

ent

indu

ctio

ner

ols

visc

osity

este

rpe

riod

[meq

O2/

kg]

[mm

2 /s]

[mg

KO

H/g

][w

t-%]

[%]

[g I 2

/100

g]

[wt-%

][w

t-%]

[wt-%

][w

t-%]

[wt-%

][h

][m

g/kg

]

TBH

Q b

lank

7.3

4.37

0.07

97.4

10.2

711

50.

440.

220.

200.

005

3.0

7.51

597

TBH

Q a

dditi

vate

d2.

34.

410.

1197

.210

.33

115

0.42

0.21

0.20

0.00

42.

936

.00

586

Low

sta

bilit

y10

.24.

360.

0897

.510

.33

115

0.42

0.24

0.20

0.00

43.

06.

3055

9R

ape

3.4

4.41

0.31

97.4

8.09

112

0.30

0.11

0.04

0.00

92.

59.

2048

6R

ape-

dist

illed

18.9

4.04

0.14

98.0

10.0

711

70.

090.

010.

020.

067

0.1

4.16

152

Sun

-dis

tille

d79

.04.

070.

1498

.71.

3713

10.

140.

020.

010.

020

0.4

1.31

95R

ape/

Sun

2.5

4.23

0.50

97.5

7.17

118

0.46

0.19

0.10

0.00

32.

27.

2448

0U

sed

fryin

g oi

ls9.

34.

670.

2894

.22.

3089

0.20

inte

rfere

nce

inte

rfere

nce

0.02

05.

17.

98in

terfe

renc

eP

yro

blan

k5.

84.

600.

1297

.78.

7211

20.

370.

080.

030.

003

2.5

7.75

574

Pyr

o ad

d6.

94.

550.

1297

.78.

7211

20.

370.

080.

030.

002

2.3

22.4

256

8Ta

llow

n.d.

4.73

0.25

88.0

0.44

360.

080.

140.

260.

020

2.3

0.7

n.d.

EN

142

13no

t3.

5<K

V<5

.0m

ax 0

.50

min

96.

5m

ax 1

2.0

max

120

max

0.8

0m

ax 0

.20

max

0.2

0m

ax 0

.020

not

6 m

inno

tsp

ecifi

catio

nin

clud

edin

clud

edin

clud

ed

analysis was carried out using an RP-8 column, UV de-tection at 254 and 280 nm, gradient elution from 0.004 MH2SO4 (55%)/acetonitrile (35%) methanol (10%) to ace-tonitrile (70%)/methanol (30%).

2.4 Storage temperature profiles

In order to assess the impact of environmental temper-atures during the study, average daily temperatures wereobtained from Osservatorio Meteo Duomo Milano (Mi-lano, Italy). The detected temperature values ranges be-tween –1.2 °C (minimum average value during winter)and 30.1 °C (maximum average value during summer).The sample from beef tallow was stored in a 20 °C heat-ed room, in order to avoid sample solidification.

3 Results and discussion

During our one year study, we recorded changes in com-position of the above-listed eleven biodiesel samplesstored in standard conditions. We must underline, thatseveral parameters did not show any significant changeduring the ageing process, such as acidity, ester content,

linolenic acid methyl ester content, IV, monoglyceride,diglyceride, triglyceride as well as free glycerol, polymerand tocopherol contents. This statement is 100% valid forthe ten samples stored in a steady state, while somechanges were observed with those kept in a drum with oc-casional shaking. This aspect will be discussed separate-ly in this paper.

Through analysis of the recorded changes in PV (Tab. 3),it can be seen that there is an increase in each sample upto the fifth month of ageing.

After this time some samples show a clear degradation ofhydroperoxide with probable formation of secondary oxida-tion products. We have previously reported similar obser-vations [3], however, in the latter study PV decrease waslinked to the presence of iron. This is not the case in thepresent study, as no significant metal presence was detect-ed in stored samples. The starting PV does not represent adiscriminating factor for the PV increase rate. Analysis ofPV behavior in the sample stored with occasional shaking(low stability sample) it can be seen that changes are moreevident and take place at a very high rate.



Tab. 3. Changes in PV recorded during twelve months of storage (according NF T 60-220, results expressed as meqO2/kg).

Ageing time, month 0 1 2 3 5 7 9 12

TBHQ blank 7.3 8.9 8.7 8.8 9.5 9.2 13.5 11.4TBHQ additivated 2.3 3.4 3.6 3.9 5.3 3.9 4.3 5.4Low stability 10.2 14.9 20.7 25.4 28.6 33.6 37.5 20.5Rape 3.4 5.1 5.2 6.7 9.9 9.2 9.2 13.3Rape-distilled 18.9 19.3 20.1 21.2 21.9 15.6 15.4 17.7Sun-distilled 79.0 78.8 80.6 83.6 87.1 66.6 65.4 68.5Rape/sun 2.5 5.3 6.9 12.2 13.7 14.4 15.4 17.6Used frying oils 9.3 10.6 11.5 12.4 14.4 12.8 11.9 16.9Pyro blank 5.8 7.9 6.5 7.3 8.8 7.4 9.4 9.4Pyro additivated 6.9 7.7 6.8 5.9 4.6 4.9 6.0 7.1Tallow n.d. 28.9 24.7 23.3 22.2 21.6 24.8 22.0

n.d. – not determined.

Tab. 4. Changes in 40 °C KV recorded during twelve months of storage (according EN ISO 3104, results expressed asmm2/s).


TBHQ blank 4.37 4.52 4.40 4.42 4.43 4.37 4.47 4.49TBHQ additivated 4.41 4.45 4.46 4.46 4.57 4.45 4.56 4.50Low stability 4.36 4.56 4.41 4.44 4.46 4.46 4.49 4.52Rape 4.41 4.37 4.39 4.47 4.53 4.45 4.54 4.53Rape-distilled 4.04 4.07 4.10 4.13 4.14 4.12 4.09 4.12Sun-distilled 4.07 4.10 4.12 4.17 4.07 4.15 4.22 4.22Rape/sun 4.23 4.38 4.33 4.31 4.44 4.34 4.34 4.48Used frying oils 4.67 4.72 4.80 4.87 4.92 4.87 4.96 4.94Pyro blank 4.60 4.61 4.56 4.40 4.54 4.49 4.50 4.49Pyro additivated 4.55 4.57 4.50 4.44 4.54 4.55 4.53 4.50Tallow 4.73 4.94 4.90 4.89 5.06 4.98 5.00 5.04

In Tab. 4 changes in 40 °C KV are reported. KV shows aconstant slight increase for each sample during time anddoes not appear to be a significant parameter for evalua-tion of storage behavior. The range of starting values isvery wide, depending on the nature of feedstock as wellas on production technology. Distilled products show alower value for KV, probably because of the near com-plete removal of non-methyl ester material (unsaponifi-able, glycerides, etc.). Changes observed in 40 °C KV aresometimes of the same order of magnitude of Repro-ducibility (R=0.04 for KV of 4.50 mm2/s). But analysis ofthe trend indicates a clear tendency for viscosity increasein all samples.

In only one case does the maximum specification exceedthe limit (tallow sample), but only after twelve months ofageing. Finally these slight changes in KV do not have anoticeable effect on polymer concentration as underlinedin other stronger degradation conditions [10].

The largest differences during long term storage appearin oxidation stability changes, expressed as Rancimat in-duction period (RIP). The complete set of data is present-ed in Tab. 5.

Several observations can be made from the data: RIP de-creases for each sample over time, except for sampleswith a low initial value, such as sun-distilled and tallow.Suitable supplementation increases the RIP, but this val-ue also tends to decrease over time. The rate of RIP de-crease over time is a function of the intrinsic quality of theproduct. The claim that if two samples have comparableRIP immediately after production, will also have compara-ble RIP decay during storage is strictly speaking not true.Consequently, within the BIOSTAB project, we aimed atdefining a suitable method which could predict the behav-ior of a sample maintained in steady environmental con-ditions for a reasonable period of time.

Special attention must be paid to the RIP evolution of thesample which was occasionally stirred. In this case wecan observe a dramatic decrease in RIP, suggesting thatthe effect is mainly due to contact with air absorbed dur-ing shaking. It should be noted that this sample even if la-beled “low stability”, belongs to the same lot and has thesame starting properties as TBHQ-blank and TBHQ-addi-tivated samples. In other words “low stability” is not an in-trinsic property of the sample, but it is induced by incor-rect storage conditions. This confirms that contact with airhas a strong impact on biodiesel stability, and thereforethe necessity to limit contact with air (stirring). It also sug-gests which type of simple technological solutions mustbe used when storing biodiesel along the complete distri-bution chain. Temperatures below 30 °C do not have a biginfluence on FAME quality.

As a complement to our monitoring process we also de-cided to analyze samples for tocopherol content. Be-cause of the very low variation in tocopherol content dur-ing storage in all samples, only the initial and final valuesare reported for these natural antioxidants (Tab. 6). Tallow



Tab. 5. Changes in RIP recorded during 12 months of storage (according EN 14112, results expressed as h).


TBHQ blank 7.51 6.93 6.75 6.64 6.55 6.50 6.19 6.20TBHQ additivated 36.00 35.85 35.00 34.17 33.05 33.18 33.73 32.77Low stability 6.30 5.92 5.00 4.47 2.27 1.04 1.04 1.24Rape 9.20 8.84 8.35 7.65 7.37 7.22 7.08 6.83Rape-distilled 4.16 4.21 4.23 4.25 4.11 4.02 4.01 3.89Sun-distilled 1.31 1.37 1.38 1.40 1.45 1.34 1.44 1.43Rape/sun 7.24 6.77 6.45 6.00 5.65 5.49 5.28 5.22Used frying oils 7.98 7.59 7.10 6.88 6.65 6.35 5.94 5.83Pyro blank 7.75 7.40 n.d. 7.21 7.15 7.09 6.98 7.00Pyro additivated 22.42 22.25 n.d. 22.25 22.33 21.82 21.54 20.85Tallow 0.7 0.68 n.d. n.d. n.d. n.d. n.d. n.d.

n.d. – not detected.

Tab. 6. Changes in tocopherols content recorded during12 months of storage (according ISO 9936, results ex-pressed as mg/kg).

Ageing time, month 0 12

TBHQ blank 597 559TBHQ additivated 586 577Low stability 559 201Rape 486 476Rape-distilled 152 142Sun-distilled 95 56Rape/sun 480 403Used frying oils – –Pyro blank 574 564Pyro additivated 568 568

sample was not analyzed because of the known absenceof tocopherols in animal fats. Some doubts still remain re-garding the real tocopherol content of the “Used fryingoils” sample. Here peaks having the same retention timeas reference tocopherols are detected, using two differentdetectors (UV and fluorescence). For this reason the re-sults obtained for this sample are not shown.

Once again the most dramatic decrease in tocopherol con-tent was observed for the “low stability” sample. Plotting thedecrease of RIP for this sample against the decrease of to-copherol content yields the graph shown in Fig. 1. Valuesare reported as a percent of initial value set in both cases at100%. After a short initial period of parallel decrease, RIPdecreases at a higher rate than tocopherols content. Thisobservation might mean that tocopherols are not the onlycompounds with significant impact on oxidation stability as



Fig. 1. Sample “low stability”- percentdecrease in RIP and tocopherol con-centration vs. storage time.

Fig. 2. Changes in synthetic antioxidant concen-trations during storage.

determined according to EN 14112, and overall biodieselstability is a function of other different parameters, storageconditions included among these. Another interesting ob-servation from the “low stability” sample, concerns the indi-vidual tocopherol behavior. α-Tocopherol degraded at avery high rate, reaching the zero value after 9 months ofstorage, while γ-tocopherol altered from 322 to 159 mg/kg,at the end of the monitoring period.

A final remark about the sample stored in very poor con-ditions, concerns parameters that did not change in theother samples. On the contrary to these other samples,some changes were recorded in the poorly stored samplefor the following parameters (time 0 � time 12 monthsvalues and units under brackets): AV (0.08 � 0.14 mgKOH/g), and Polymers (3.0 � 3.9 wt-%).

Finally, we investigated the fate of added synthetic antiox-idants during storage. In Fig. 2 concentration values ob-tained over time for both TBHQ and PYRO additives areshown.

It is interesting to note the different behaviors of two syn-thetic antioxidants: while TBHQ decreases by approxi-mately 8% of its initial value, Pyro does not show any sig-nificant variation during the complete storage period. Theimpact of this behavior on RIP is a reduction of 9 and 7%of original value, respectively. A wider discussion on theeffects and of the impact of additives was published byour BIOSTAB colleagues, Mittelbach and Schober [11].

4 Conclusions

Following the discussion of the experimental data, the fol-lowing conclusions can be drawn:

– after one year storage study carried out on eleven dif-ferent biodiesel samples, it can be said that no changewas detected in 15 monitored characteristics. All sam-ples met the specification limits even at the end of stor-age period, with the exception of RIP;

– PV changes differ depending on samples. For samplesinitially not too oxidized, PV increase is slow. For sam-ples initially oxidized, PV first increases and then de-creases due to the formation of secondary oxidationproducts. It must be noted that PV is not included in thebiodiesel specification table;

– the most significant changes were recorded in oxida-tion stability, evaluated according to Rancimat test.This means that ageing takes place in biodiesel, inde-pendently of the monitored parameters and makesbiodiesel less stable over time. This phenomenon canbe monitored by means of Rancimat test EN 14112. Al-though Rancimat provides a picture of the actual situa-tion, it is impossible to predict the RIP value after longterm storage with this test. There are ageing process-es that can’t be observed by analyzing parameters re-ported in EN 14213 and EN 14214. Consequently, weare aiming to develop a method for storage stabilitypredictions;

– RIP decreases with time: the rate of this decrease de-pends on the quality of the sample as well as on stor-age conditions;

– a proper supplementation procedure allows RIP to in-crease even to a large extent: studies could be carriedout to identify quality and minimum quantity of antioxi-dant. The already mentioned paper by Mittelbach andSchober [11] provides several answers to this question;

– the right additives must, in our opinion, allow the sam-ple to fulfill specifications for oxidation stability for atleast six months; super-supplementation proceduresleading to a RIP higher than 20 h have no meaning andmight have a negative impact on other parameters(e.g. Conradson Carbon Residue);

– once again the necessity for correct storage and logis-tic solutions to avoid contact of biodiesel with air during

its complete life cycle has been highlighted. The im-pact of simple and occasional agitation of product inpresence of air, is extremely convincing and must betaken into account by biodiesel handlers;

– knowledge of the behavior of our biodiesel samples dur-ing storage provides the basis for the next stage of ourwork regarding storage stability evaluation. The avail-ability of a quick test for the determination of this impor-tant characteristic represents an important factor for theimprovement of biodiesel handling, trading and use.

Acknowledgements

This paper has been prepared within the European fund-ed research project “BIOSTAB – Stability of Biodiesel”,QLK5-2000-00533. The project is coordinated by Hein-rich Prankl, BLT (Wieselburg, Austria). For more informa-tion regarding BIOSTAB activity and scope, visit the coor-dinator’s website www.blt.bmlf.gv.at or European Re-search website http://www.cordis.lu.

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[Received: February 10, 2003; accepted: August 19, 2003]



bondioli., et al (2003)

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