In chemical reactions, these bonds are broken and new ones are formed and energy is either absorbed from the surroundings, or given out to the surroundings. The resulting energy can either be positive or negative, depending on the type of reaction and the bonds that are broken and formed. In general, combustion is an exothermic process.
A table of values has been provided which outlines the standard combustion enthalpy of some methyl ester biodiesels namely Methyl linolenate, Methyl stearate, Methyl oleate, Methyl linoleate, Methyl palmitate. Table 1 lists the methyl esters from most to least energy.
Using average bond enthalpies values from , the enthalpies were calculated to be as follows. The chemical formulas and bond information were taken from WolframAlpha, and the overall change in enthalpy was derived from a balanced combustion reaction equation.
***** These two paragraphs so not make sense totally – revise them and make sure you refer to the two tables properly
Although the figures for kj/mol are all higher than the ones on the table, different bond enthalpy figures could have been used. This did not make a difference to the end result, as the methyl esters from most to least energy methyl esters were the same as those listed in Table 1.
Another error in table 1, is the delta H value provided for the combustion of Methyl oleate. It is given as positive, which is incorrect. Combustion reactions are always exothermic, meaning that energy is released. Therefore, the organisation’s claim that linseed oil is the best vegetable oil cannot be sustained based on the data provided, as it contains errors.
The fatty acid compound percentage compositions from table 2 and the figures calculated above were used to determine the vegetable oil which contained the amount highest energy. Using the percentage compositions provided in Table 2, the amount of energy within the vegetable oils was calculated. The results are as follows,
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Based on the results, Safflower Oil would appear to best choice to be converted to a biodiesel fuel as it has the most stored energy. However, other important properties of vegetable oils such as the longevity, and the chemical composition (type and stability of chemical bonds) are important to consider.
Vegetable oils are composed of three types of fats; saturated, monounsaturated and polyunsaturated. Saturated fats only contain carbon single bonds, and are chemically very stable. Monounsaturated and polyunsaturated fats contain double carbon bonds, which are more unstable and volatile than single bonds. Monounsaturated fats contain one carbon double bond, and polyunsaturated fats contain more than two.
Although there is more total energy stored in the carbon double bonds, the individual bonds are easier to break, which makes the vegetable oils less stable. As such, Vegetable oils with a large number of double bonds are called drying oils, as they degrade quickly and solidify.
Safflower oil contains significant amounts of linoleic acid, which has 3 double bonds in its structure.
For these reasons safflower oil would not be the best choice for conversion into a biodiesel fuel, as the large amount of double bonds within its structure would cause the oil to spoil and solidify. Additionally it requires significantly less energy to break the double bonds, which will result in a higher chance of error in the conversion process. Other options such as Linseed and Sunflower oil would also be unsuitable as they too contain a large percentage of polyunsaturated acids.
The organisation’s claim that Linseed oil is a viable choice seem questionable as it has a large percentage of polyunsaturated fats and less chemical potential energy than other options such as canola and olive oil.
Another variable to consider is the price of the vegetable oils. If the cost per ton is too high, it would not be efficient to convert a candidate oil to a biodiesel, as there may be cheaper alternatives. Table 3 displays price comparisons for selected oils.
While safflower and linseed oil are not in the index, their composition suggests that they are not optimal choices for conversion to biodiesel. Canola Oil is currently the cheapest of the 6 Oils, has a large amount of potential chemical energy.
However, 32% of canola oil is composed of polyunsaturated fats, much higher than the 11% contained in olive oil. As a result, olive has the most stable bond structure, but is not the most economical choice based on the figures obtained. Based on the evidence, canola is the best vegetable oil for conversion into a biodiesel fuel, despite it not having the most stable bond structure.
Conclusion
In conclusion, it would appear that Canola is the best oil for conversion into biodiesel fuel. Although it has a higher number of carbon double bonds than olive oil, the cost for canola oil is very low compared to the other oils, which makes it the more economical choice. The organisation’s claim that linseed oil is the best choice for biodiesel fuel conversion is not supported for a number of reasons. Firstly, Linseed oil degrades quickly as the bond structure contains a large amount of carbon double bonds. Furthermore, it does not have the highest enthalpy value of the candidate vegetable oils. Secondly, the delta h value given in table 1 for methyl oleate is incorrect, as exothermic reactions always have a negative change in enthalpy. Overall, the data provided by the organisation could not form the basis of a valid conclusion that linseed oil is the best choice.
Reference List
"Why are biofuels better than fossil fuels “ Biofuels, Renewable Energy & Green . Retrieved 28th August 2012. From
“Bond Enthalpies”, Chemical Education Digital Library, Retrieved 28th August 2012, from
"Biodiesel Feedstock Oils Ingredients." How to Make Biodiesel at Home. Retrieved 28th August 2012 from
"Wolfram|Alpha: Computational Knowledge Engine." Wolfram|Alpha: Computational Knowledge Engine. Retrieved 28th August 2012 from,
Schuchardt, U. (1998). Transesterification fo Vegetable Oils: A Review. J. Braz, Chem Society, 9(1), 199-210. Retrieved August 28, 2012, from
Index Mundi - Country Facts. (n.d.). Index Mundi - Country Facts. Retrieved August 28, 2012, from
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