Bomb Calorimetry To Determine the Energy Content of Biodiesel

Introduction

The method utilized in this study involves the bomb calorimetry, which is an analysis method that is widely used in chemistry to determine the energy of combustion of a sample. The instrument used is a calorimeter, a device which measures gross heat, which is the energy of combustion and enthalpy of formation of the hydrocarbon combusted. The sample in this particular experiment involves used cooking oil, a biodiesel, which is compared against a conventional diesel. According to a publication by NCBI, the energy exerted by this cooking oil requires the oil to undergo transesterification of transglycerides, which invloves the formation of methoxide nucleophiles through the reflux of the biodiesel with a mixture of methanol and NaOH, which causes the breaking of transglycerides into fatty acid methyl esters.

Procedure

We obtained water and placed it in the bucket that is with the calorimeter. Then we obtained a small sample of Benzoic acid, measured its mass, made it into a pellet and measured its mass again. Then we placed the bucket into the calorimeter and the pellet into the dish of the bomb calorimeter. Then we inserted a nichrome wire into the metal tubes suspending the dish, and made sure it touched the Bezoic acid pellet as well. Then we attached the dish to the lid, and inserted the contraption into the calorimeter, and inserted the calorimeter into the bucket of water, which was in an electrical measuring device. Then, we flowed oxygen into the calorimeter, and once the combustion occurred, and the data was provided by the device we recorded the data. This entire procedure was solely for standardization. The next step, we prepared the sample for calorimetry. We obtained 125mL of used cooking oil from one of the participants’ household and we filtered the oil to remove solids via vacuum filtration. Then, we mixed a one seventh of the mass of oil worth of methanol with 1% of the mass of oil worth of NaOH to generate methoxides or nucleophiles in the process of tranesterification by refluxing the oil and its other contents. We refluxed the oil at 65 C until a layer of glycerol formed on the bottom of the reactor. Then, we let the oil cooled, before we carefully poured the oil into the separatory funnel without including the glycerol. Then, we added water to rinse, which led to the emulsification of the oil with water, and we used the watered sample for calorimetry. We had three trials of this sample. After that, we used evaporation to boil the emulsified water without boiling the oil off, prior to combusting this sample in the calorimeter. We also combusted three trials of a sample of conventional diesel in the calorimeter to compare with the cooking oil combustion. Finally, we recorded the data and cleaned the utensils and instruments.

 

Observation/Results

Standardization (Benzoic acid):

Mass of water used: 2182.7g

Mass of Sample: 0.9443g

EE Value: 2652.51

Initial Temperature: 23.3966 C

Rise in temperature: 2.2568 K

 

Sample Preparation (Biodiesel):

 

Mass of biodiesel:  109.8

Mass of methanol: 15.69g

Mass of NaOH: 1.0276g

Density of oil: 0.785g/mL

Biodiesel Calorimetry

 

  Trial 1 Trial 2 Trial 3
Sample mass (g) 0.4968 0.5000 0.5032
Initial Temperature (C) 24.1841 24.0189 24.1352
Change in Temperature (C) 1.7437 1.8439 1.8575
Gross Heat (cal/g) 9259.5105 9624.3390 9741.5888
Gross Heat (J/g) 38741.791932 40268.234376 40758.807539

 

Conventional Diesel Calorimetry

 

 

Density: 0.8g/mL

 

  Trial 1 Trial 2 Trial 3
Sample mass (g) 0.4908 0.5158 0.4941
Initial Temperature (C) 23.7378 23.6539 23.7139
Change in Temperature (C) 2.1489 2.2212 2.1126
Gross Heat (cal/g) 11562.605 11373.970 11290.768
Gross Heat (J/g) 48377.93932 47588.69048 47240.573312

 

 

Calculations:

EE =  ;

a = b = 0 (assumption that the contribution of these factors are fairly small )

Therefore, ∆Ecombustion =  = gross heat

  Biodiesel Conventional Diesel
 Avg ∆Ecombustion (cal/g) 9541.8 11409.1
Avg ∆Ecombustion (J/g) 39922.8912 47735.6744
Avg ∆Ecombustion (MJ/kg) 39.92 47.74
Avg ∆Ecombustion (cal/mL) 7490.313 9127.28
Avg ∆Ecombustion (J/mL) 31339.5 38188.5
∆T (K) 1.815 2.1609
Sample size (average; g) 0.5 0.50023
Density (g) 0.785 0.8
Accepted Literature value of ∆Ecombustion (MJ/kg) 37.84 (for ρ= 8.88g/mL) 43.1 (for ρ= 8.3g/mL)

 

 

Discussion/Conclusion

We had some errors along the way, but we had three successful trials for both the biodiesel and the conventional diesel. The average change of energy of combustion of conventional diesel is higher than the energy of combustion of the biodiesel, which also agrees with the two values obtained from the two research literature referenced below. However, the values we obtained for our calorimetry are much higher for both the biodiesel and the conventional diesel, which implies that the data we obtained is either in error, or contains more energy due to lower density (the densities for our data are 0.785 g/mL and 0.8 g/mL for biodiesel and conventional diesel respectively, whereas the densities for published data are 0.88g/mL and 0.83 g/mL for biodiesel and conventional diesel respectively). Though it would be expected that the higher density would contain more energy, and therefore indicates that the data we obtained are highly affected by errors, unless the purity of our biodiesel or diesel or the type of biodiesel or diesel are better than the purity or type of biodiesel or diesel experimented in the two studies. It is difficult to compare the data we obtained to established values, as the availability of these established values is low, and though these values may be available, the conditions or methods, or the purity or type of fuels used maybe different, and so would not be an appropriate comparison to conduct.

References:

Fukuda, H., Kondo, A., Noda, H. “Biodiesel Fuel Production by Transesterification of Oils”. Journal of Bioscience and Bioengineering,  92(5). (2001): 405-16. Web.  http://www.ncbi.nlm.nih.gov/pubmed/16233120

http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/files/file14925.pdf

Edwards, R. et all. “Well-to-Wheels Analysis of Future Automotives Fuels and Powertrains in the European Context”.  Euhttp://ies.jrc.ec.europa.eu/uploads/media/TTW_Report_010307.pdf

Bagchi, Alaknanda. “Conflicting Nationalisms: The Voice of the Subaltern in Mahasweta Devi’s Bashai Tudu.” Tulsa Studies in Women’s Literature 15.1 (1996): 41-50. Print.