Biodiesel Synthesis and Determination of Glycerol
Institution Affiliation
Abstract
Biodiesel is fuel to be considered as the alternative source ofenergy since the petroleum sources of the earth are becomingexhausted, and their prices increase. Biodiesel is an advantageoussource of energy because its large-scale synthesis is not expensiveand it is easily biodegraded. Biodiesel can be synthesized fromvegetable oils.(BCGC,2010). Vegetable oils contain triacylglycerols,which have fatty acids joined to the backbone of glycerol throughlinkages of ester. Triacylglycerols in vegetable oils are largemolecules, and they do not combust efficiently in the diesel engine.(Yang, 2013). To burn well, they are broken down into smaller molecules bysaponification and transesterification, and these results into ahigh-quality biodiesel. Transesterification of vegetable oils reducesthe viscosity of vegetable oils and this yield to smaller groups(methyl esters) of the fatty acids.( Bucholtz, 2007) The smallergroups can now be burnt unmodified engine. This process of convertingtriglycerides into a mixture of fatty acids esters requires alcoholand substance to speed up the reaction rate to obtain high yields.During transesterification process, the alcohol used is methanol dueto its low price and high conversion rates. (Berger, 2010). SodiumHydroxide is used as a catalyst, and it is regenerated after thereaction. During transesterification process, higher temperatureenhances the process hence making the process cost effective. Thereaction which leads to the formation of 3 fatty acids is as shownbelow.
Conclusion
Introduction and Experiment
Budge, Suzanne, ,Laboratory handout, PEAS 2203 Organic Chemistry for ProcessEngineers, winter 2017, Dalhousie University.
Results and Discussion
The biodiesel is the top layer and glycerol is the bottom layer, got49.5 mL biodiesel by using a separatory funnel to avoid contaminatingthe top biodiesel layer with traces of the bottom layer that remainin the stopcock.
Actual yield of Biodiesel = Volume of Biodieselsynthesized * Density of Biodiesel
= 49.5 mL * 0.8746 =43.29g
Assume the theoretical yield be 50 g as we cannot determine the molarmass of triglyceride.
% yield of Biodiesel = =
The preparation of the biodiesel is a transesterification reactionwhere the triglycerides are converted into simpler methyl esters ofthe fatty acids (the biodiesel).
Figure 1: General reaction for forming biodiesel
Figure 2: Saponification reaction of biodiesel
|
Saponification 1 |
Saponification 2 |
Extraction 1 |
Extraction 2 |
Blank 1 |
Blank 2 |
|||
|
Vinitial (mL) |
0 |
9.2 |
18.3 |
0 |
11.9 |
24.1 |
||
|
Vfinal (mL) |
9.2 |
18.3 |
29 |
10.9 |
24.1 |
36.2 |
||
|
∆V(mL) |
9.2 |
9.1 |
10.7 |
10.9 |
12.2 |
12.1 |
||
|
∆Vaverage(mL) |
9.15 |
10.8 |
12.15 |
|||||
Table 1: Quantity of Sodium Thiosulfate titrated
Calculations and Questions
1.
|
Saponification |
Extraction |
Blank |
|
|
Volume (ml) |
9.15 |
10.8 |
12.15 |
|
[Na2S2O3] (M) |
0.1023 |
0.1023 |
0.1023 |
|
Moles of sodium thiosulfate |
0.000936 |
0.001105 |
0.001243 |
Table2: Number of mole of sodium thiosulfate used.
|
Total moles of periodate |
6.215×10-4 |
|
Moles of unreacted periodate (Saponification) |
4.68×10-4 |
|
Moles of unreacted periodate (Extraction) |
5.524×10-4 |
|
Moles of reacted periodate (Saponification) |
6.215×10-4 – 4.68×10-4 = 1.535×10-4 |
|
Moles of reacted periodate (Extraction) |
6.215×10-4 – 5.524×10-4 =0.691×10-4 |
Table3: Number of mole of periodate reacted.
|
Moles of glycerol bound to fatty acids (Saponification) |
Mass of glycerol bound to fatty acids (Saponification) (g) |
Moles of free glycerol (Extraction) |
Mass of free glycerol (Extraction) |
|
0.768×10-5 |
7.073×10-4 |
0.346×10-5 |
3.186×10-4 |
Table4: Total mass of glycerol. =
Percentageof free glycerol
Percentageof total glycerol
a) The free Glycerol less than 0.02% and total Glycerol content inour Biodiesel less than 0.25% which satisfy theASTM requirement, so we meet the specification.
b) Bound Glycerol is mainly from the unreacted Triacylglycerol duringthe Biodiesel synthesis.
c) Make the period of separation process be longer. Also could makethe temperature higher than 100 °C .
2. Using cooking oil need to be filtered because contain someimpurities and analyzed for free fatty acid before experiment.
3. Because it is an endothermic reaction. So warming up the oil arefavorable for the formation of product, increase the reaction rateand reduce the reaction time.
4.
a) Triolein is the limiting reactant.
b) The product will be methyloctadec-9-enoate.
Figure 1: The structure formula of Methyloctadec-9-enoate
c) C57H104O6+ 3CH3OH C3H8O3+ 3C18H32O2
Moles of Triolein = = 0.0565 mol
Theoretical Yield = 0.0565 moles Triolein *
= 50.2g
d) Actualyield of Biodiesel = Volume of Biodiesel synthesized * Density ofBiodiesel
= 49.5 mL * 0.8746 =43.29g
e) Warmed up the vegetable oil before to the synthesis. Shakeseparatory funnel vigorously to make reactants mixed well.
5. It follows the SN2 mechanics.
Figure2Mechanism of the base-catalyzed transesterification of vegetable oil
Conclusion
After doing the experiment, it was possible to synthesize biodieseland determine the amount glycerol in the products. In the analysis,86.6 percent yield of biodiesel was obtained. The percentage of freeglycerol was found to be 0.0061%, which is less than 0.02%, and thissatisfies the ASTM requirement. The total glycerol content in theexperiment was 0.0203%, and this too met the ASTM requirement thatstates the percentage of total glycerol must be less than 0.25%.
References
Berger, D. (2010). Organic Chemistry Lab Manual. http://books.prettyfamous.com/l/11620274/Organic-Chemistry-Laboratory-Manual- CEM-221-222-Bluffton-University-Daniel-Berger.
Bucholtz, E. C. (2007). “Biodiesel Synthesis and Evaluation: AnOrganic Chemistry
Experiment” Journal of Chemical Education, 84(2), 296-298.
The Berkeley Center for Green Chemistry. (2010). Green ChemistryLaboratory. Retrieved from
http://live-bcgc.pantheon.berkeley.edu/chem1a
Yang, J.(2013).‘’Synthesis and Determination of biodiesel: An Experiment forHigh School
Chemistry Laboratory’’. Journalof Chemical Education 90 (10), 1362-1364.
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