Biodiesel Termal 1

REV. CHIM. (Bucharest) ♦ 61♦ Nr. 8 ♦ 2010 http://www.revistadechimie.ro 793

Thermal Analysis of Biodiesel from Palm Oil. I.

IOANA ADELA IVANOIU (BASA)1*, GEZA BANDUR1, LUCIAN MIRCEA RUSNAC1

1 Politehnica University of Timiºoara, The Faculty of Industrial Chemistry and Environmental Engineering, 2 Piaþa Victoriei,300006, Timiºoara, Romania

Biodiesel has many merits as renewable energy resource; thereby biodiesel relieving reliance on petroleumfuel, and it is biodegradable and non-toxic. This paper presents the thermal analysis (TG and DSCthermograms) of biodiesel (fatty acid methyl esters - FAME) from palm oil. FAMEs are obtained in variousreaction conditions. The biodiesel is synthesized by alkali-catalyzed transesterification of palm oil withmethanol (molar ratio oil: alcohol is 1:6). Potassium hydroxide was used as a catalyst. TG and DSCthermograms provide information on thermal stability and phase and physical transformations of biodiesel.

Keywords: biodiesel, FAME, alkali-catalyzed transesterification, thermograms

The production of biodiesel has recently received muchattention worldwide. Follow the world energy crisis; manycountries have started programs to resolve this problem.Finding alternative energy resources is a pressing missionfor many countries, especially for those lackingconventional resources. In the 1930’s and 1940’s, vegetableoils have been used as diesel fuels in the emergencysituations. With the rapid development of the modernindustry, the demand for energy has been greatly increasedin recent years, and therefore alternative energy sourcesare being explored. Thus, the term “biodiesel” hasappeared frequently in several reports [1-4].

Biodiesel is obtained by the alkali-catalyzedtransesterification of the vegetable oils or natural fats withan alcohol. Three consecutive reactions are required tocomplete the transesterification of a triglyceride molecule(scheme 1). The transesterification reaction requires acatalyst to achieve reasonable conversion rates. A basecatalyst, such as sodium or potassium hydroxide ispreferred. Usually methanol is used as alcohol in thetransesterification, but ethanol is also suitable for thispurpose [5-8].

Biodiesel belongs to ecological fuels for the reason ofits composition: carbon 77%, hydrogen 12%, oxygen 11%,only traces of nitrogen and sulfur being present [12-13].

In the last few years, thermal analyses (TG -thermogravimetry, DSC - differential scanning calorimetry)have become very important as sources of useful data; forexample founding their thermal stability. Such techniqueshave also been employed for biodiesel characterization[14]. Only few reports describe the use of this techniquefor liquid fuels; these papers report results on sunfloweroil, palm oil, cotton oil biodiesel and corn oil biodiesel [15-19].

This paper presents the synthesis and the thermalanalysis of biodiesel from palm oil. The TG and DSC dataprovides information on the thermal stability and phaseand physical transformations. Also, DSC diagrams provideinformation on the cloud point of biodiesel (thetemperature, at which dissolved solids are no longercompletely soluble, precipitating as a second phase givingthe fluid a cloudy appearance).

Experimental partMaterials

Commercial palm oil “Olina”, absolute methanol(Merck), potassium hydroxide as powder (Merck), ,calcium chloride (Merck), methyl linoleate (Merck), methyloleate (Merck), methyl palmitate (Merck), methyl stearate(Merck) were used.

SynthesesPalm oil is put into a flask (fitted with magnetic stirring

and thermometer) and is heated at a required temperature.Potassium hydroxide powder is dissolved separately intomethanol and then added to the oil. The mixture is stirredat the reaction temperature a determined time. Then thereaction is stopped and the flask content is placed into aseparation funnel. The inferior darker layer (containingglycerin and impurities) is removed. The ester is washedseveral times with water (to remove traces of glycerin).Calcium chloride is added as drying agent and after 24h atroom temperature the ester is filtered. Table 1 lists theacronyms and the reaction conditions for each sample ofbiodiesel.

* email: [email protected]; Tel. : +40256404225

Scheme 1.Transesterification reaction of triglycerides withmethanol

Biodiesel is defined as the mono alkyl esters (methyland ethyl esters) of long chain fatty acids derived fromvegetable oils or animal fats, for use in compression-ignition(diesel) engines. Biodiesel has many intrinsic worth asenergy provider: is derived from a renewable resource,thereby relieving reliance on petroleum fuel, isbiodegradable and non-toxic; pure biodiesel releases about90% of the energy that fossil diesel does, and hence, itsexpected engine performance is nearly the same in termsof engine torque and horse-power [9-11].

Methyl esters

REV. CHIM. (Bucharest) ♦ 61♦ Nr.8 ♦ 2010http://www.revistadechimie.ro794

Characterization of biodieselThe thermal analyses of biodiesel were performed using

Netzsch TG 209, in nitrogen atmosphere at temperaturesranging from 20 to 500oC with a heating rate of 5 K/min)and Netzsch DSC 204, in nitrogen atmosphere attemperatures ranging from -100 to100oC with a heatingrate of 5 K/min. The data were collected and processedusing Proteus – Thermal Analysis data system, fromNetzsch.

Results and discussionsBiodiesel from palm oil is a mixture with the mean

composition: methyl linoleate (10.1%), methyl oleate(40.5%), methyl palmitate (42.6%), methyl stearate (4.4%)and others (2.4%) [ 20].

DSC analysisDSC diagrams for methyl linoleate, oleate, palmitate and

stearate standards are shown in figure 1. Each standardshows a single transition temperature, which ischaracteristic for each compound [21]. The transitiontemperature of methyl linoleate is around -88oC. Methyloleate is different because it shows two transitiontemperatures revealed by two peaks, an exothermic one(-33.0oC) and an endothermic one (-23.4oC). Theexothermic peak is associated with a moleculesrearrangement and the endothermic peak is associatedwith a physical transformation. Methyl linoleate and methyloleate have transition temperatures below 0oC, whilemethyl palmitate and methyl stearate present peaks inthe area of positive temperatures. The transitiontemperature of methyl palmitate is at 31.9oC and that ofmethyl stearate is at 41.0o C.

As can be seen, palm oil biodiesel presents four transitiontemperatures corresponding to each peak (fig. 2). Thetransition temperatures for the different biodieselssynthesized are presented in table 2. The first transitiontemperature is around -90oC and it is associated with methyllinoleate. The second and the third transition temperaturescorrespond to methyl oleate and it is around -50oC for theexothermic peak and around -30oC for the endothermicpeak. The fourth transition temperature is around 10oC andit is associated with methyl palmitate. Transitiontemperatures corresponding to the three methyl esters offatty acids from biodiesel are lower compared to those ofthe standards. This is well thought-out to be the result ofinteraction between the components of the mixture ofthese methyl esters. Thereby, methyl linoleate is the firstcomponent of the mixture which suffers a transition and itbecomes a solvent for the next (methyl oleate) and thetwo together become the solvent for the third one (methylpalmitate). The transition temperature of the methylpalmitate in the mixture is around 10oC in comparison withthe standard transition temperature, which is around 32oC.The lower transition temperatures of the mixture are anadvantage for biodiesel. The last transition temperature ofthe mixture being around 10oC, let us to conclude that thecloud point of biodiesel must be almost the same. Palm oilbiodiesel has the cloud point quite high because his majorcompound (methyl palmitate) is solid. Cloud point ofbiodiesel should be as small so that not to create problemsto the engine in cold season. High cloudy point leads toclogged injectors.

As we have seen beforehand in the case of biodieselsynthesized at different reaction time, for the palm oilbiodiesel obtained with different amounts of catalyst we

Fig. 1. DSC diagrams for methyllinoleate, methyl oleate,methyl palmitate, methyl

stearate standards

Table 1THE ACRONYMS AND THE

REACTION CONDITIONS FOREACH SAMPLE OF BIODIESEL


can distinguish four peaks associated with the three methylesters (fig. 3). The sample CP4 behaves differently fromthe others because of the absence of the peak from -90oCcorresponding to the methyl linoleate and also the peaks

Fig. 2. DSC diagrams for the samples P1, P2, P5

Table 2DSC DATA FOR THE SAMPLES P1 - P7

Fig. 3. DSC diagrams for the samples CP2, CP3 and CP4

are less emphasized. This is explainable because thesample CP4 had a lower conversion in methyl esters dueto the large amount of catalyst used in reaction. A largeamount of catalyst causes the formation of fatty acid


Fig. 4. DSC diagrams for the samples TP1 - TP4

Table 3DATA FROM TG TERMOGRAMS FOR P1 –P7

potassium salts (soap) and that is why during the phaseseparation a foaming effect occurred.

DSC diagrams for palm oil biodiesel at different reactiontemperatures are presented in figure 4. TP3 and TP4 show

Fig. 5. TG termograms for CP2, CP3, CP4

obviously peaks associated with the three methyl esters,while the peaks for TP1 and TP2 are less emphasized andthe first peak corresponding to the methyl linoleate aremissing. This can be explained by the fact that at lowerreaction temperatures (40-50oC), the reaction is not


complete and the conversion is lower than at highertemperature (55-60oC).

TG analysesAll TG curves of biodiesel from palm oil obtained at

different reaction times have a single inflection point, soweight loss occurred in a single step. Table 3 presents theweight losses on temperatures ranging from 20 to 500oCand the temperatures of the inflections points for biodiesel.We can note that for most samples weight loss isapproximately 100% until 400oC, except for P1. Weight lossat 400oC for P1 is only 93%, its total weight loss occursaround 450oC. This is expected because a reaction time of30 min is not sufficiently for a complete transesterificationreaction. Therefore, the temperature corresponding to theinflection point is significantly higher than for the others.

As results from table 4, the weight losses ontemperatures ranging from 20 to 500oC and thetemperatures corresponding to the inflection points forpalm oil biodiesel obtained with different amounts ofcatalyst. One can observe that weight loss for CP2 andCP3 occurs in a single step until 400oC (fig.5). Thetemperature of the inflection is around 240oC as well as forthe biodiesel obtained at different reaction times. CP4presents two steps in its weight loss, with an initialinflection point at 227oC and the second at 393oC. At 400oCthe weight loss is only 95%. The total weight loss of CP4occurs around 450oC. This can be explained by the use of alarger amount of catalyst than in the others two and thisallows the formation of fatty acid potassium salts (soap).This soap causes foaming during the phase separation.For this reason the total weight loss for CP4 presents twosteps and requires a higher temperature than for the others.

It may be noted that biodiesel synthesized at highertemperatures shows a single inflection point and that iswhy the weight loss occurs in a single step and at lowertemperatures than biodiesel produced at lowertemperatures. The weight losses on temperatures ranging

Tabel 5DATA FROM TG TERMOGRAMS FOR TP1, TP2, TP3 AND TP4

Tabel 4DATA FROM TG TERMOGRAMS FOR CP2, CP3, CP4

from 20 to 500oC and the temperatures of the inflectionpoints for palm oil biodiesel obtained at different reactiontemperature are presented in table 5. The fact that weightloss for TP1 and TP2 occurs in two steps is explainablebecause at lower reaction temperatures, thetransesterification reaction has a low conversion. Incomparison with TP2, the total weight loss for TP1 requireda higher temperature. In comparison with the otherssamples of biodiesel for which the weight loss around 400oCis 99%; at this temperature TP1 lost only 93% of its totalweight. We can conclude that with the decreases of thereaction temperature, the temperature required for a totalweight loss increases.

ConclusionsPalm oil biodiesel was synthesized under different

reaction condition.From TG thermograms we found that almost all the

mixtures of methyl esters present a weight loss ofapproximately 100% until 400oC. This weight loss occursin a single step and the temperature of the inflection pointis around 240oC. Exceptions are biodiesels synthesized atshorter reaction time, lower temperature and thosesynthesized using an excessive amount of catalyst. Thesebiodiesels present two inflection points, so a two stepsweight loss.

TG termogravimetric data are important because theyallow an estimation of the thermal stability of biodiesel,which helps us to find optimal condition of storage andhandling.

Comparing the DSC diagrams of different biodiesels withthose of standards, we found displacement of the peaks,which are caused by a solvent effect of the meltedcomponents in the mixture. We should note also that thecloud point of the biodiesel is estimated to be last transitiontemperature (7 to 15oC).


DSC diagrams give us information about the phase andphysical transformation of biodiesel, allowing anassessment on his behavior at low temperatures.

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Manuscript received: 10.05.2010

Biodiesel Termal 1

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