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The storage stability issue The storage stability issue of Biodiesel of Biodiesel

and the additives solution and the additives solution

Long - Term Storage of Fuels Seminar Israeli Institute of Energy and Environment

Tel Aviv, 3° of December 2008

Biodiesel, as many other organic materials, is susceptible to oxidation upon exposure to air.

The oxidation process ultimately affects fuel quality.

An oxidative stability specification was included in the European and American biodiesel standards (EN14214 and ASTM D6751).

Biodiesel OxidationBiodiesel OxidationAn IntroductionAn Introduction

Primary oxidation occurs by a free radicals process, which consist of initiation, propagation and termination reactions.


InitiationRH + I R• + IH

PropagationR• + O2 ROO•

ROO• + RH ROOH + R•

TerminationR• + R• RRROO• + R• ROOR

Biodiesel OxidationBiodiesel OxidationFatty Acid DistributionFatty Acid Distribution

CO

O

CO

O

CO

O

CO

O

CO

O

palmitic acid 16:0

stearic acid 18:0

oleic acid 18:1

linoleic acid 18:2

linoleneic acid 18:3

1215

9

9

9

12


The CH2 positions allylic or bis allylic to the double bonds in the fatty acid chains are those more susceptible to oxidation.

The autoxidation of unsaturated fatty compounds proceeds at different ratesdepending on the number and position of the double bonds(18:1/18:2/18:3 ~ 1/40/100)

E.g.: methyl linolenate (C18:3)

Secondary oxidation:

Decomposition of the fatty ester peroxides into:

AldehydesAlcoholsFormic AcidShorter fatty acids


Secondary oxidation:

Vinyl polymerization also has been proposed as a possible secondary oxidation reaction

Oligomers formed through this path do not exceed trimericor tetrameric forms


Biodiesel OxidationBiodiesel OxidationOxidation consequencesOxidation consequences

Formation of GUMS, SLUDGE, INSOLUBLE

DEPOSIT

Long-term Storage

Increase of oligomers, polymers and othersecondary oxidation

compoundsIncrease of acidity,

viscosity

Biodiesel OxidationBiodiesel OxidationMethods: Iodine ValueMethods: Iodine Value

I2 value grams I2 that react with doublebonds in 100 gram of biodiesel

High I2 value lower stability to oxidation

Limit: it only measures the amount of double bondsThe oxidation rate (1:40:100) is not taken into account

Biodiesel OxidationBiodiesel OxidationMethods: Total Acid NumberMethods: Total Acid Number

The acids content not only affect the biodiesel current quality but also its tendency to be oxidized (potential quality)

In fact acids can increase the rate of oxidation of the biodiesel

Acids may be already present in the biodiesel just after its production…Presence of free fatty acids in the oilBiodiesel production process

…or may form as a consequence of oxidation reactions

Accelerated aging

Air is passed through an heated biodiesel sample (110°C)

Then is sent through a flask with distilled water

Water conductivity proportional to oxidation rate

Oxidation products (formic acid) are more volatile than biodiesel.The air fluxed moves them into water raising its conductivity.

Biodiesel OxidationBiodiesel OxidationMethods: Oxidation Stability Index (OSI)Methods: Oxidation Stability Index (OSI)

Metrohm Rancimat

Biodiesel OxidationBiodiesel OxidationMethods: Oxidation Stability Index (OSI)Methods: Oxidation Stability Index (OSI)

Biodiesel OxidationBiodiesel OxidationAging effectAging effect

Quiescent aging 6 weeks, 50°C, closed bottles (no air replenishment)Agitated aging ASTM D2274 – 16h at 95°C with O2 fluxing

Total Acid Number Polymer Content

Biodiesel OxidationBiodiesel OxidationAging effect on OSIAging effect on OSI

Quiescent aging 6 weeks, 50°C, closed bottles (no air replenishment)Agitated aging ASTM D2274 – 16h at 95°C with O2 fluxing

B20B100

Biodiesel OxidationBiodiesel OxidationTANTAN--Polymer content correlationPolymer content correlation

TAN and Polymer content showed in several studies a very good correlation.Here is an example:

Biodiesel OxidationBiodiesel OxidationOSI OSI –– TAN TAN –– Polymer contentPolymer content

OSI have good correlation with both TAN and Polymer content after aging:

Biodiesel OxidationBiodiesel OxidationEN 14214EN 14214

OSI > 6hIodine number > 120 gI2/100gTotal Acid Number < 0,5 mg KOH/g

Biodiesel OxidationBiodiesel OxidationASTM D6751ASTM D6751

OSI > 3hIodine number – Not IncludedTotal Acid Number < 0,5 mg KOH/g

Biodiesel OxidationBiodiesel OxidationWorldwide Fuel CharterWorldwide Fuel Charter

The World wide Fuel Charter is the Engine Companies’ point of view on fuels’ quality characteristics

The WWFC for mineral fuels arrived to the 4° edition

It is under preparation also a specific document for biodiesel

Biodiesel OxidationBiodiesel OxidationWorldwide Fuel CharterWorldwide Fuel Charter

Biodiesel OxidationBiodiesel OxidationFactors affecting stabilityFactors affecting stability

Biodiesel fatty acid distributionNatural antioxidants contentFree Fatty AcidsMetal content

Biodiesel CharacteristicsPre- and Post- treatments

Biodiesel OxidationBiodiesel OxidationFatty Acid DistributionFatty Acid Distribution

Biodiesel OxidationBiodiesel OxidationOSI of Different BiodieselOSI of Different Biodiesel

0

2

4

6

8

10

12

Soybean Sunflower Rapeseed Canola Jatropha Palm UFO

Ran

cim

at, h

rs

Induction Period range

>12h

Biodiesel OxidationBiodiesel OxidationAntioxidantsAntioxidants

Natural: tocopherols (α, β, γ, δ)most of them removed during the process of biodiesel

production

Synthetic: retardants (and hydroperoxide decomposers)mainly phenolic type (and amine type)different products than in mineral fuelssimilar action (AH: highly labile hydrogen)

Biodiesel OxidationBiodiesel OxidationSyntheticSynthetic

The typical synthetic antioxidants used for vegetable oils are effective also in the biodiesel

BHTBHATBHQ

The not alimentary use of biodiesel permits to apply also antioxidants normally banned for vegetable oils:

Propyl GallateAmines…

Biodiesel OxidationBiodiesel OxidationSynthetic Synthetic -- BHTBHT

BHT is a well known and widely recognized antioxidant for vegetable oils and biodiesel.BHT was the first antioxidant to be used in biodiesel.

Limits:

BHT is solid at ambient temperature.

It is used as a powder or diluted in a proper solvent.

During the years other, more efficient, products came to the market.

Biodiesel OxidationBiodiesel OxidationSynthetic Synthetic -- BHTBHT

0

0,5

1

1,5

2

2,5

3

3,5

4

Del

ta R

anci

mat

, hrs

Soybean Sunflower Rapeseed Jatropha Palm

Dosage rate

250 ppm 500 ppm

Biodiesel OxidationBiodiesel OxidationDevelopment of new productsDevelopment of new products

The market requested the development of new productsCost optimization

Lower dosage rates and treatment costs

More critical raw materials to be treatedBHT has low efficiency on most the critical biodiesel from used frying oils and highly unsaturated vegetable oils

Better handlingLiquid stabilizers

Stable at low temperatures

Biodiesel OxidationBiodiesel OxidationChimec DevelopmentsChimec Developments

00,5

11,5

22,5

33,5

4

Del

ta R

anci

mat

, hr

s

Soybean Sunflower Rapeseed Jatropha Palm

Dosage rate

50 ppm 100 ppm


456789

101112

Ran

cim

at, h

rs

100% RME 75:25 50:50 25:75 100% Soy

Dosage rate

0 ppm 50 ppm 100 ppm

RME/SME Blends – Additive 1


Biodiesel from Used Frying Oils

0

3

6

9

12

15

Ran

cim

at, h

rs

0 200 600

Dosage rate

BHT Additive 1 Additive 2

Biodiesel OxidationBiodiesel OxidationStability During StorageStability During Storage

As we saw the stability to oxidation is not a “stable” characteristic

It normally decreases with time (aging) and the decrease rate strongly depends on the storage conditions

Also biodiesel treated with antioxidants are susceptible to a decrease of their stability with time

The best antioxidants, anyhow, are also able to slow down the stability losses during typical storage conditions


RME Stored in the dark with seldom air replenishment

4

5

6

7

8

9

10

Time 0 1 Month 3 Months

Indu

ctio

n pe

riod

(h)

Blank Additive 1 BHT


33,5

44,5

55,5

66,5

77,5

8

Time 0 1 Month 3 Months

Indu

ctio

n pe

riod

(h)

Blank Additive 1 BHT

SME Stored in the dark with seldom air replenishment

Thank youfor your attention

Stefano Tortora

CHIMEC SpAFuel Additives Technological Unit

[email protected]

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