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The 2nd AUN/SEED-Net Regional Conference on New&Renewable Energy

Faculty of Enigneering, Burapha University, Thailand

January 21-22, 2010

Effectiveness of Combined Additives on Long-term Storage Stability

and Fuel Properties of Palm-Biodiesel

M. Husnawan1, 2*

, M.H. Jayed1, H.H. Masjuki

1, M.A. Kalam

1, T.M.I. Mahlia

1, M. Ropandi

3,

M.Y. Cheah1

1Department of Mechanical Engineering, University of Malaya

50603 Kuala Lumpur Malaysia2Department of Mechanical Engineering, Syiah Kuala University

Jl. S. Abd. Rauf, No.7 Darussalam Banda Aceh, Indonesia

3 Malaysian Palm Oil Board, Energy and Environment Unit, 43000 Kajang, Selangor, Malaysia*Corresponding Author:[email protected]

Abstract

The use of biodiesel is expanding rapidly around the world, making it imperative to fully understand the

impacts of biodiesel on diesel engine as they have slightly different properties compared with

conventional diesel. This has leads to the establishment of biodiesel standards in many countries that

focused on several key fuel properties where producers must conformed with. As with other natural

substances, if left untreated, biodiesel is susceptible to oxidative degradation that may be caused by long

period of storage. The degradation of biodiesel leads to the formation of lower molecular weight acids,

peroxides and gums that, in turn, could cause unwanted changes in both the properties and performance of

the biodiesel. These deposits and gums can cause damage to the engine and also to the fuel injection

systems. This paper aimed to investigate the changes on several key properties of palm-biodiesel after a

storage period of 1, 2 and 6 months. The fuel samples were divided into two groups - samples with

combined additives and samples without any additives. The fuel was stored in transparent High Density

Poly Ethylene (HDPE) box without sunlight exposure at room temperature. Fuel properties weremeasured after the stipulated storage period and the results from the two groups were compared against

the established standards. The results had shown that fuel samples with added additives were better

protected against rapid deterioration due to oxidation than those that were without, particularly during

extended storage duration.

Keywords: Biodiesel, Palm Oil, Oxidation Stability, Storage Time

1. IntroductionIn search of a greener alternative fuel to petrodiesel, biodiesel have been a primary and

obvious choice. Biodiesel is derived fromdifferent type of vegetable oils and it had been

tested by the inventor of diesel in engine, Dr.

Rudolph Diesel in 1900 at the Paris Exposition

[1]. As an alternative to petro diesel in

transportation, biodiesel can easily be a crucial

solution for the current environmental problems

as it does not require any engine modifications

and it reduces greenhouse gas (GHG) emission

substantially. The use of biodiesel also improves

the lubricity of the fuel. All of the above factors

have make biodiesel usage more adaptable andattractive to the current energy scenario which is

to ensure energy security, environmental

sustainability, and to boost rural development by

shifting of power dependency from petro to

agro-industry, simultaneously [2].

In the last two decades, biodiesel with different

blending percentage has been in use in many

countries. However, due to the reason of

biodiesel being derived from edible oil, it has

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The 2nd AUN/SEED-Net Regional Conference on New&Renewable EnergyFaculty of Engineering, Burapha University, Thailand

January 21-22, 2010

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come into conflict with the food security issues

[3].

On the other hand, mass production and the useof biodiesel require good storage stability; where

biodiesel is severely lacking from petro-diesel.

Good storage stability of biodiesel is a must for

customer acceptance, standardization and quality

assurance of biodiesel in the market.

Transesterification or alcoholysis is the usual

conversion process used to convert triglycerides

of vegetable oil into fatty acid methyl esters

(FAME) by displacing alcohol from an ester by

another alcohol [4]. For each triglyceride threemonohydric alcohols reacts to produce (m) ethyl

ester and glycerin. Biodiesel which is a

transesterified methyl ester is chemically prone

to oxidation in the presence of air or oxygen.

The oxidation of ester to alcohol will produce

acid that will leads to the reduction in flash point

and the increase of total acid number [5].

Insoluble gums, acids, and aldehydes that

formed from oxidative degradation may in turn

cause engine problems such as filter clogging,

injector coking and corrosion of metal parts.

Generally, long storage period will leads to the

increase of oxidized biodiesel due to its unstable

nature and the usage of such fuel will

subsequently cause damage to engine parts,

mainly the fuel supply system. This is why

oxidation stability is an important criterion for

biodiesel [6].

Usually, the rates of oxidation is very much

depended on factors such as the presence of air,

elevated temperatures, the presence of metalsthat facilitate oxidation and also the chemical

structure of the biodiesel where unsaturated

methyl esters with more double bond is more

incline to oxidation. Different oxidation

mechanisms like auto-oxidation, photo-

oxidation and primary oxidation are described in

many literatures [7-10].

To date one of the most common approaches to

increase oxidation stability is the use of

antioxidants. Antioxidants delay the onset of

oxidation by extending the induction period.

However, antioxidants can only help in delaying

the onset of auto-oxidation but not photo-

oxidation. In order to measure the effectivenessof an antioxidant on auto-oxidation, palm oil

methyl ester (POME) samples were kept in dark

to avoid photo-oxidation and were tightly sealed

to minimize air exposure and.

Key fuel properties such as peroxide value,

water content, acid value, calorific value,

oxidation value, pour point and viscosity were

measured for both groups after the specified

storage durations of 1, 2 and 6 months. The main

objective of this investigation was to evaluate

the effectiveness of antioxidant additive onseveral key fuel characteristics in POME blend.

2. Experimental test and procedure2.1 Raw Material and Sample Preparation

The no. 2 diesel fuel used for blending with

POME was normal commercial fuel obtained

from PETRONAS while the biodiesel was

collected from the Malaysian Palm Oil Board

(MPOB). The blended fuel samples were kept at

room temperature and stored in transparent

High-density polyethylene (HDPE) containers.The containers were made from hard material

that would not corrode during the storage period.

All the containers were kept in a dark room to

avoid photo-oxidation. Additive blended in a

combination of: Tertiary Butyl Hydroquinone

(TBHQ) and Ethylene Vinyl Acetate (EVA)

which are mixed stoichiometrically with POME

by percent of weight (%wt).

2.2 Sample Analysis

Fuel samples compositions was given below:POME 1(100% pure POME), POME 2 (POME1

blended with 3% additives), POME 3 (POME1

blended with 10% additives), POME 4 (80% no.

2 blended with 20% POME, widely known as

B20). All the blending and samples preparation

were prepared in the dark room at room

temperature to prevent any exposure to sunlight.

Samples were taken for analysis of the key

properties before and after the specific storage

durations.

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Viscosity of 4 different blends was measured at

40C and 100C in a HoulionViscometer. Data

was taken 3 times and averaged thereafter. PourPoint of petroleum blends is the index of the

lowest temperature at which the fuel has utility

in certain applications. MPP 5Gs machine

(manufactured by ISL) was used to measure the

pour points of the fuel blends following ASTM

D 97 method. Oxidation Value was measured by

the Fourier transform infrared (FTIR)

spectroscopy machine using the Rancimat

method. The automatic adiabatic bomb

calorimeter was used to measure the calorific

value following the ASTM D240 method while

acid value was measured in TAN analyzerfollowing the SAE standard. FTIR spectroscopy

was used to measure peroxide values and also

the water content.

3. Results and Discussions3.1ViscosityOxidation of methyl ester began with the build-

up of peroxides. Viscosity started to increase

only after certain amount of peroxides wascreated. During storage, the viscosity of the

methyl esters increased by the formation of morepolar, oxygen containing molecules and also by

the formation of oxidized polymeric compounds

that could lead to the formation of gums and

sediments that clog filters. Fig.1 showed that the

viscosity increased significantly after 1 month of

storage especially for the 100% biodiesel

samples.

Fig.1 Viscosity of Palm-Biodiesel before and

after storage

Increase of viscosity was also observed from

biodiesel samples with added additives;

however, the rate of increase was relativelyslower than that of samples without additives.

For biodiesel-diesel blend, the observed

viscosity change was not significant. This might

be due to the higher percentage of petroleum

diesel which made the fuel more stable in the

first 2 months; however, the viscosity of the

blended samples began to increase after 6

months of storage. The result has also

confirmed that the use of this additive can help

to maintain the viscosity of palm-biodiesel for

up to 6 months of storage period.

3.2Pour PointThe pour point of every sample before and after

storage was shown in Fig.2. The result has

showed that, with the presence of additive the

pour point was successfully lowered. This was

due to the contamination of Ethylene Vinyl

Acetate (EVA) as an additive for reducing pour

point. The result also showed that by increasing

the percentage of additive, the pour point could

be further lowered; however it was only

applicable for sample that was stored for lessthan 6 months. For samples that were stored for

6 months or more, significant increase of pour

point was recorded especially for samples with

10% additive.

Fig.2 Pour point of Palm-Biodiesel before and

after storage

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3.3Oxidation ValueThe result of oxidation value that was measured

by FT-IR was shown in Fig.3. Basically,oxidation occurred when oxygen attacks the

fluid. The process was accelerated by heat, metal

catalyst, acids, water content and solid

contaminants. The thermal oxidation value of

the tested samples versus the storage duration

was presented in Fig.3. Although, the rapid test

of oxidation value for biodiesel was measured

using the Rancimat method, but the literature

related to the use of this method was limited to

the use of fresh sample and it may not be

appropriate for the aged samples.

Fig.3 Oxidation value of Palm-Biodieselbefore and after storage

The result has also showed that the presence of

additive in the sample can effectively lowered

the oxidation value compared with the non-

additive sample. The oxidation value of

biodiesel-diesel blended fuel recorded was also

lower than the others. However, for the time

being, the oxidation stability of biodiesel-diesel

blended fuel was not a crucial issue since the

focus of biodiesel standards was on pure

biodiesel. Therefore, several strategies including

the use of a number of different additives were

utilized to help meet the standard.

3.4Calorific ValueCalorific value was one of the important properties use to determine the suitability of a

fuel to be use as a combustible fuel. The

research of storage effect on combustion

properties was limited. Currently, most of the

research has been focusing on the modification

of chemical structure as well as the production

optimization to fulfill the biodiesel standard and

most of the research was based on fresh oil. The

effect of storage duration on palm-biodieselcalorific value was presented in Fig.4.

Fig.4 Net calorific value of Palm-Biodiesel

before and after storage

The result has shown that with presence of 3%

additive, the calorific value of palm-biodiesel

was relatively stable compared with other

samples. Fig. 4 also showed that only palm-

biodiesel with 3% additive and biodiesel-diesel

blend have a constant calorific values after 1month of storage. The decrease of calorific value

for POME 2 and POME 4 were found to be

insignificant compared with the others.

Moreover, by using 3% additive, the calorific

value of palm-biodiesel was maintained at the

limit of the biodiesel standard (35 MJ/kg) even

after 6 month of storage.

3.5Acid Value Normally, the acid number increase with the

increase of peroxides because the esters were

first oxidized to form peroxides, which then

undergo a complex reaction that formed the

more reactive aldehydes before being be further

oxidize into acids.

Acids could also formed when traces of water

causes hydrolysis of the esters into alcohols and

acids. The acid value of biodiesel samples would

also increase with the increase of storage

duration as a result from the hydrolysis of fatty

acids methyl esters (FAME) into fatty acids

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(FA). The effect of storage period on acid value

of palm-biodiesel was shown in Fig. 5.

Fig.5 Acid value of Palm-Biodiesel before and

after sotrage

The standard limit of 0.5 mg KOH/g was

exceeded for samples without additive after 2

months of storage; whereas samples with lower

percentage of additive was found to have

successfully maintained the acid value for up to

6 months of storage. However, samples of palm-

biodiesel mixed with 10% additive and

biodiesel-diesel blended fuel have also showed

an acid value that exceeded the limit after 6

months of storage. This was most probably due

to the composition of fatty acids of the vegetable

oils used as raw materials and also the storage

condition. Yet, further study was needed to

determine the extent of this effect, namely the

materials of the storage container and also the

environmental condition on biodiesel during

long term storage.

3.6Water ContentThe water content of every sample before and

after storage was shown in Fig. 6. The result has

indicated that palm-biodiesel with 3% of

additive has successfully maintained the water

content for up to 6 months of storage. Although,

there was an increase of water content in the 3%

additive added palm-biodiesel samples

compared with other samples but the increase

was not significant. This may be due to the fact

that additive at this concentration could have

prevented the change of temperature inside the

storage container by altering the fluid thermal

conductivity. The increase of additive was

suspected to have the ability to promote

moisture in the sample. However, further

analysis was needed to support this argument.

Fig.6 Water content of Palm-Biodiesel beforeand after storage

3.7Peroxide ValueAt the time being, peroxide value was not

mentioned in the biodiesel standards; however,

this property influences the cetane number

where the increase ofperoxide will also increase

the cetane number of the biodiesel. Higher

cetane number will reduce the ignition delay

time that may bring about some negative effect,

particularly with the compatibility of the

biodiesel with certain plastics and elastomers.

Fig.7 Peroxide value of Palm-Biodiesel before

and after storage

The peroxide value for every sample before and

after storage was shown in Fig. 7. The result has

indicated that biodiesel without additive has

recorded an increase of peroxide value after 6

months of storage compared with samples with

additive. The results obtained have also

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indicated that samples with 3% additive have

successfully suppressed peroxide formation after

long term storage. Even though sample with

10% additive has shown otherwise. This may bedue to the presence of water traces that may

have caused oxidation of the sample. The

formation of moisture occurred when the

samples were blended with 10% additive,

because of several unidentified reaction as well

as changing of molecular structure.

4. Conclusion

The effect of long term storage and the usage of

additive on palm-biodiesel properties have been

investigated in this experiment.

1. Generally, the addition of the selectedcombined additive has worked well in

maintaining the biodiesel properties.

2. Biodiesel sample with the addition of 3%combined additive has performed better

than its higher percentage (10%)

counterpart.

3. Palm-biodiesel was found not suitablefor long term storage (more than 1month) unless they were to be blended

with several type of additive such as anti-

oxidant and pour point depressant.

5. Acknowledgement

The authors would like to thank University of

Malaya, UMRG Grant No. 036/09AET and Mr.

Sulaiman Ariffin for his technical assistances.

6. References

[1] Nitschke, W.R. and C.M. Wilson,

Rudolph diesel, pioneer of the age of

power. Norman, OK. The University of

Oklahoma Press, 1965.

[2] Jayed, M.H., et al., Environmental

aspects and challenges of oilseed

produced biodiesel in Southeast Asia.

Renewable and Sustainable Energy

Reviews, 2009. 13(9): pp. 2452-2462.

[3] Srinivasan, S., The food v. fuel debate: A

nuanced view of incentive structures.

Renewable Energy, 2009. 34(4): pp.

950-954.

[4] Srivastava, A. and R. Prasad,

Triglycerides-based diesel fuels.Renewable and Sustainable Energy

Reviews, 2000. 4(2): pp. 111-133.

[5] Sarin, A., et al., Influence of metal

contaminants on oxidation stability of

Jatropha biodiesel. Energy, 2009. 34(9):

pp. 1271-1275.

[6] Dunn, R. and G. Knothe, Oxidative

stability of biodiesel in blends with jet

fuel by analysis of oil stability index.

Journal of the American Oil Chemists'

Society, 2003. 80(10): pp. 1047-1048.

[7] Knothe, G., Some aspects of biodieseloxidative stability. Fuel Processing

Technology, 2007. 88(7): pp. 669-677.

[8] Frankel, E.N., Lipid Oxidation, second

edition. The Oily Press, PJ Barnes &

Associates, Bridgwater, England, 2005.

[9] Gunstone, F.D., J.L. Harwood, and A.J.

Dijkstra, Chemical properties of lipids,

in: The Lipid Handbook. CRC Press,

2007.

[10] Morita, M. and M. Tokita, The real

radical generator other than main-

product hydroperoxide in lipidautoxidation. Lipids, 2006. 41(1): pp.

91-95.

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