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Biodiesel Investigation Essay

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‘Biodiesel is a clean burning renewable fuel made using natural vegetable oils and fats.1 Biodiesel is a revelation to chemists, engineers and environmentalists who are looking for more sustainable ways to make use of fuels. Since it is a natural and renewable fuel, it can be fitted in as a substitute for petroleum diesel, which is the substance conventionally used in automobile transport.

Biodiesel is normally utilised as a replacement for petroleum diesel fuel or can be blended together with petroleum diesel fuel in any ratio.

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Biodiesel is a biodegradable substance with a lower toxicity in comparison to petroleum diesel fuel and is preferred as it is safer to handle since there is little human risk involved in its handling. The use of biodiesel as a petroleum substitute reduces the degree of exhaust emission. Biodiesel are notorious for their easy use in terms of how they can easily be pumped and stored in existing engines without having to make major industrial alterations to the engines themselves. They are usually blended together with petroleum fuels in order to create the optimal usage in engines.

The output yield of biodiesel is I had never really heard of biodiesel until it was a topic covered in school. After finding out what biodiesel was, I looked into the IB chemistry syllabus to see what points it had on biodiesel and looked further into the applications of biodiesel as well as the process of transesterification and what is involved. My personal interest was sparked from my curiosity of how to obtain my own sample of biodiesel after I found out about its many uses.

My high school chemistry department provided us with a set of materials and allowed us to investigate our own ways of obtaining biodiesels and I was keen to see what I could do with a sample of this versatile substance. I do feel as though this is an important experiment to engage in as scientists find biodiesels an extremely useful substance to use in machines and such. To try an experiment which involves looking at factors that can change the output of the product, would be a stepping stone to building a stronger understanding on the substance itself and how more of it can be obtained and perhaps what benefits it may serve.

The experiment conducted was intent on looking at a certain independent variable (the concentration) that would affect the yield of biodiesel produced in experiment. The research question for this is: How the concentration of Potassium Hydroxide solution would affect the yield of biodiesel when transesterified with a standard sample of vegetable oil.


To look at the scientific aspect of it, biodiesels are a form of methyl esters, an organic chain compound that has a set of properties. The experiment involves the reaction between vegetable oil and potassium hydroxide and methanol mixed together. The equation for the reaction of the transesterification is:

Vegetable Oil (l) + (3)HOCH3 + (NaOH catalyst) ——> C3H8O3 + 3-methyl ester

1 Biodiesel Basics

This valuable renewable fuel resource is not vegetable oil, but instead formed from the organic chain compound. It is 3-methyl ester and has the following chemical structure:

Fig. 1

The diagram on the left shows the transesterification process that forms two products (Glycerol and A 3-methyl ester). The experiment conducted involves potassium hydroxide as a catalyst instead of sodium hydroxide. Furthermore the biodiesel product of this varies from the other structured methyl ester that usually come in The other product is glycerol, which is commonly found in soaps. This is a standard example of transesterification however the experiment that is attempted involves different reactants. The diagram below shows the process for this experiment and the outcomes.

The temperature of the oil mixed with the methanol mixture will be measured and the experiment consists of five different solutions of KOH + methanol that will each be reacted with the vegetable oil. A magnetic stirrer will be used in the process to get the reaction going and afterwards the finalised solution will be placed in a centrifugal and the process of centrifugation will separate the solution into glycerol and biodiesel. The biodiesel will then be extracted to give a reading on percentage yield.

The method was personally derived and many modifications were made to the initial standard procedure of mixing 50% concentration Potassium Hydroxide solutions with 10ml of vegetable oil and stirring on a magnetic stirrer for 10-15 minutes at a certain temperature was deemed to unsafe for students as the high concentration acid was extremely corrosive, had irritating effects and also raised environmental concerns as the organic waste disposal process was far more complicated when the substances would permeate a trash landfill.

As a result the new method was made and the substances involved were altered significantly. The new method consists of a reaction with a 5g/100ml (KOH concentrated) mixture between potassium hydroxide and methanol. In each test, there is a varied use in the concentration of the methanol mixture and this is measured by an arbitrary percentage figure as well as a known uncertainty. Furthermore, the potassium hydroxide serves as a catalyst for the reaction.

Equipment Used:



10cm3 Measuring Cylinder


Mass Balance


50cm3 Beaker


Magnetic Stirrer




Magnet Capsule



1. To set up the equipment appropriately, use a 10cm3 Measuring Cylinder to measure out 10ml of vegetable oil, and keep aside separately. Measure 1.5ml of the 5g/100ml (1%) Potassium Hydroxide solution and place set aside in the measuring cylinder. Set up the magnetic stirrer, and measure the temperature of the oil using the thermometer. For this experiment, the oil (placed inside beaker) will need to be kept on the magnetic stirrer with the capsule inserted and heated to 31ºc. Measure the mass of the empty beaker first using the mass balance and record.

1. Once the oil has been heated to the appropriate temperature, add the methanol-KOH solution with 1% concentration to the oil and allow the stirrer to stir at a constant temperature for approximately ten to fifteen minutes. After a few minutes of stirring and any visible physical/chemical changes have occurred, remove the beaker of mixture from the solution and set aside temporarily.

1. The methyl-ester biodiesel mixture is ready for centrifugation. Using the mass balance, measure out the mass of the beaker with the oil mixture that has just undergone transesterification and pour all the substance from the beaker into a centrifugal tube.

1. Repeat all the tests with the 2%,3%,4% and 5% concentration KOH mixtures in methanol. When repeating, remember to measure each separate beakers individual mass and use the stirrer to bring the temperature back up to 31º. Once the temperature has hit 31º, mix the KOH with the oil as done before and allow the stirrer to create a reaction between the substances. Keep making qualitative observations and recording changes in temperature from the reaction and record the mass of the final solutions once stirring.

1. Finally, once all the products have been reacted, place them in centrifugal tubes and insert the tubes into the centrifuge. The centrifugation process will separate the biodiesel and glycerol. Extract the thin biodiesel layer (on top), measure the mass of the biodiesel in the initial beaker and derive the percentage yield of biodiesel from the mass difference between the solutions, density from mass and volume and make observations on the mass obtained.

Diagram of Process : Done On Skitch


Safety And Environmental Measures:

Plenty of glassware will be utilised throughout the experiment, and therefore it is essential that safety glasses are worn as extra precaution to protect eyes from broken glass. Furthermore, all glassware should be kept away from the edges of tables to prevent risk of damage.

KOH – methanol mixture is labeled as an irritant and mildly

Independent Variable:

Concentration of KOH – Methanol Mixture as % value.

Fixed Variables:

* Temperature of Oil

* Volume of Oil Used

* Volume of KOH – Methanol Mixture

Dependent Variable:

% Yield of Biodiesel, Mass outcome of biodiesel from transesterification

corrosive based on *Cleaps Hazcards and it is therefore advised to wear gloves. It is also advised to wear lab coats as products of transesterification may permanently stain clothing.

Fortunately, there are no ethical concerns involved as only vegetable oil is being used and no animal substances. The biodiesel substance is biodegradable and can be easily disposed of in organic waste.

*Cleaps cited in Bibliography

Qualitative Observations:

* In all tests after the oil was placed into the centrifuge, a gunky substance was formed from the separation into two layers, one being the biodiesel and it can be assumed that the gunky substance was glycerol (used in soaps).

At times the position of the magnetic stirrer was not in place for some results, which may be a result of random error (anoma

Error Calculations on Mass

Example % Yield Calculations of Biodiesel

1% Concentration:

Example Calculation

[(0.052 ÷ 1.000) x 100%] + [(0.2 ÷ 10) x 100] + [(0.2 ÷ 1.5) x 100] + [(0.005 ÷ 5.962) x 100]

= 5% + 2% + 10% + 0.08%

= 17.08% Uncertainty

≈ 17%

Absolute Uncertainty for 1% Concentration yield:

5.95g ± 20% (1sf)

1% Concentration Solution:

Mass of biodiesel Extracted:

=5.952 (±0.005)g

Total mass of oil Mixture (Products from transesterification reaction)

100 x (5.952 ÷ 33.119) (±0.1 *100)

Approx 18% Yield (±0.3%)

* lies) in results such as the 2% concentration.

* The temperature of the magnetic stirrer would be set higher than 31º, and many of the substances would exceed or be under the temperature of 31º before the actual reaction began.

* The volume of the oil and KOH mixture used in the second test may not have been the same amount as the first, which would cause an error in the percentage yield of biodiesels.

Data Processing:

2% Conc. 3% + 2% + 10% + 0.08% = 15.08% ≈ 4.99g ± 20%

3% Conc. 2% + 2% + 10% + 0.08% = 14.08% ≈ 6.84g ± 10%

4% Conc. 1% + 2% + 10% + 0.08% = 13.08% ≈ 7.81g ± 10%

5% Conc. 1% + 2% + 10% + 0.08% = 13.08% ≈ 7.97g ± 10%

Processed Data Table:

Mass of Biodiesel (2DP)

Total Uncertainty on Mass

% Yield of Biodiesel+ Uncertainty-2sf

Volume of Biodiesel Layer + Uncertainty

Density of Biodiesel

Uncertainty on Density


Multiple inferences can be made from the data obtained. Firstly the clean burning renewable fuel has been formed from a derived method, in which a transesterification reaction has occurred between Methanol and Vegetable oil (using potassium hydroxide as a catalyst). It was expected that the increase in concentration of the KOH would cause a greater percentage and mass yield of biodiesel. Fortunately this expectation was met with the results provided, although there were a few given anomalies formed from the systematic errors present, it was evident that the experiment did match the initial hypothesis of an increase in biodiesel yield.

Although the conclusion states than an increase in concentration of the KOH – Methanol substance would increase the yield of biodiesel in the product of transesterification, it must be understood that there were many imprecisions and boundaries for error were relatively high throughout the experiment. The primary reason for this is that only one test was conducted for each concentration, rather than gathering an average for each results, which was a result of time management problems.

Despite the causes of error and uncertainties, the calculated average density of biodiesel produced was 1.23gcm-3. The literature value for this was given above (0.88) and this value has been taken from an experiment in which the yield of biodiesel was taken from vegetable oils using both sodium hydroxide and potassium hydroxide as the catalyst in the experiment. The experimental error for the density was extremely high, being around 40%.

The general formula for calculating systematic error in experiments is as such:

“Experimental error = {(Literature Value – Calculated Value) ÷ (Literature Value)} x 100 “

The experimental error is actually the sum of the systematic and random error, (error which could influence one single result), and therefore varies for each result obtained. However the graph for the density shows the rising increase. Although a clean line of best fit cannot be placed upon the graph, it is clear that there is a steady rise in the output of biodiesel against the increase in initial concentration. It is evident that there was a random error for the 2% concentration with the mass output measured.

This may have been a result of some of the substance spilling onto the stirrer during one of the measurements, when equipment was not handled appropriately. Since this only affected a single result, it was omitted from the graph, and the line of best fit was not inclusive of this result. Despite this, the error bar uncertainties are relatively high for the mass output, and therefore the min and max gradients vary highly, which means any value for output within this range would be regarded a systematic error in the experiment.

In the density graph, the curve of best fit is exponential, and does not include the result obtained for 3% concentration, as this also appears to be slightly anomalous. It could also be regarded a random error as the gradient of the curve does not fit into the boundaries of uncertainty for this result. Reasons for this uncertainty could be a result of any of the limitations explored in the evaluation. Finally the percentage yield graph also has somewhat of a linear relationship between the output of biodiesel as a percentage of the total substance and the concentration increase together.

The diagram (figure 4) shows a successful gathering of biodiesel, in which the top layer represents the biodiesel and the bottom layer the glycerol. There were other different physical appearances for other results (not photographed).




Possible Improvements

Unknown layer between biodiesel and glycerol (Fig. x)

It was difficult to distinguish whether this layer between the biodiesel and glycerol, (as photographically depicted above), could be counted as biodiesel and therefore it was either left out or in the measuring process, which would contribute to a systematic error of the yield of biodiesel being too high or low.

To improve on this and reduce this uncertainty, a combustion test would need to be done on the biodiesel, as it is known to be flammable. The unknown substance should be tested with a flame test and if it burns, should be included in the yield measurements of biodiesel.

Using Apparatus with a lower uncertainty for measuring out KOH – methanol substance

The 10ml measuring cylinder used had an uncertainty of 0.2, which for 1.5cm3 of solution, was extremely high as a percentage uncertainty. Since this was used for all tests, it must be noted that this was also a contributing factor to the systematic error obtained for each test.

To improve this, a different (more precise) piece of measuring apparatus, i.e a burette should’ve been used as it has an uncertainty of 0.05, which would’ve quartered the uncertainty on the potassium hydroxide mixture, and reduced the total uncertainty.

Improper placement of beaker on magnetic stirrer

Due to time limitations for conducting the experiment, multiple groups had to share the stirrer and therefore place two beakers with magnetic flea’s (capsules) atop the stirrer. This interfered with the ability for the maximum biodiesel output to be produced for each result, and since this only occurred for certain tests, would’ve contributed to any random errors present.

To target this limitation, the best solution would be to find time to work on the experiment individually, so that the magnetic stirrer could be used for only one beaker.

Impurity on biodiesel

The substance measured may not be entirely biodiesel, but instead a mixture of biodiesel and glycerol that may have been extracted without notice. This would’ve caused a higher percentage yield of biodiesel to be measured rather than the actual amount.

To add on to this limitation, the reason for an impurity would most probably be from a difficulty in distinguishing between the biodiesel and layer of glycerol.

Any filtration process that could separate the biodiesel and the glycerol effectively, would be appropriate.

The mixture should undergo centrifugation multiple times in order to separate the layers more clearly.

Works Cited:

“Biodiesel Basics – Biodiesel.org.” Biodiesel Basics – Biodiesel.org. Biodiesel Org, n.d. Web. 11 May 2015.

Button, Scott. “Biodiesel: Vehicle Fuel From Vegetable Oil.” Energy & Environment 21.8 (2009): 1305-324. Web.

Jamil, Cut Aisya Z., and (Ijera). Performance of KOH as a Catalyst for Trans-esterification of Jatropha Curcas Oil (2012): n. pag. 12 Mar. 2012. Web. 13 May 2015.

“Secondary Science Hazcards.” Secondary Science Hazcards. N.p., n.d. Web. 13 May 2015.


“The Chemistry of Biodiesel | Biodiesel Project | Goshen College.” Academics. Goshen College, n.d. Web. 13 May 2015.

All other images were personally taken and diagrams constructed using Skitch.

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