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Quoc Tran
Chemistry 213
Kristin Beiswenger
April 21, 2015
Final Formal Report #2
Biodiesel from Coffee Grounds
Biodiesel is growing to be a viable energy source as the conventional fossil fuels are being used
rapidly. 1 Despite being less efficient than fossil fuel, biodiesel’s popularity as an alternative fuel comes
from its biodegradable nature. From being used as an independent fuel source or mixing it with
petroleum fossil fuels, biodiesel’s versatility has strong potential as sustainable source of energy.
Today, biodiesel has been obtained through the conversion of natural biomass. One important use of
natural product isolation aims to use bioconversion to recycling of wastes and to reduce landfills.2 It is
typically synthesized through an transesterification process using waste vegetable oil, algal oil, or
animal fat.3 Biodiesel’s resulting typical composition includes a range methyl and ethyl esters of fatty
acids due to the transesterification’s fragmentations.
In the base-catalyzed transesterification process involving coffee grounds, biodiesel was
synthesized from triglycerides using methanol and potassium carbonate as shown in Scheme 1.
65°C, 45 min
Scheme 1. Synthesis of Biodiesel through transesterification with base and alcohol
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The synthesis begins with the base catalyst deprotonating the hydrogen off the methanol group to form a
nucleophilic methoxy group. The methoxy group then performs a backside attack on the carbonyl group
of the triglycerides to form a tetrahedral intermediate. The electrons on negatively charged electrons
shift back down to reform the double bond and break off a fatty acid methyl ester. Finally, the
negatively charged oxygen on the initial triglyceride deprotonates methanol. The course of this
nucleophilic attack, electron shift, bond fragmentation, and deprotonation repeats until glycerol, fatty
acid methyl esters converted, and potassium carbonate is reformed. The course of this mechanism is
demonstrated in Scheme 2.3
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Scheme 2. Mechanism of Base Catalyzed Transesterification of Triglycerides and Fatty acid methyl esters.
The purpose of this experiment is to synthesize biodiesel from spent coffee grounds using a basecatalyzed transesterification process. Since coffee grounds are used abundantly around the world, this
experiment will test the efficiency in converting the natural waste to a possible green energy source. It
will target high coffee waste generation sources such as Starbucks in hopes for possible commercial
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production of biodiesel.4 The first part of the experiment will isolate crude oil or triglycerides from the
spent coffee grounds. Upon IR spectroscopy analysis of the triglycerides, the percent recovery of crude
oil from the mass of coffee grounds will be calculated. The expected percent recovery of this oil based
on the coffee grounds is about 15%.4 The isolation of the crude oil will be followed by the actual
transesterification and purification of triglyceride oil to the biodiesel where there is an expected 100%
yield The final product’s fatty acid methyl esters will be characterized with IR spectroscopy and
GC/GC-MS data. The presence of the fatty acid methyl acids found in biodiesel will indicate the
success of making biodiesel from spent coffee grounds.
Experimental
Triglycerides. Spent coffee grounds (50 g) were added to hexanes (150 mL). The reaction mixture was
stirred and refluxed at 65°C for 1.5 hours. After cooling to room temperature, vacuum filtration was
performed to isolate the liquid from the solid coffee grounds. The liquid was evaporated to afford a
brown-yellow and sticky liquid (2.2026 g, 4% IR (ATR) υmax (cm-1) 2921.4, 2853.0, 1742.3, 1459.0,
1372.6, 1159.0.
Biodiesel. Triglycerides (2.2026 g, 7.342 mmol) and potassium carbonate (0.165 g) were dissolved in
methanol (10 mL). The reaction mixture was mixed and refluxed at 60°C -65°C for 45 minutes. Upon
cooling to room temperature, the pH level of mixture was monitored upon adding acetic acid to
neutralize any potassium carbonate. The neutral reaction mixture was separated by adding hexanes (10
mL) and 90% methanol/water (10 mL) with a liquid/liquid extraction in a reaction tube. The hexane
layer was dried over sodium sulfate and evaporated to afford a slimy green and brown liquid (2.25 g,
24%) IR (ATR) υmax (cm-1) 2921.4, 2853.0, 1741.9, 1458.0, 1371.2, 1161.0; GC (phenyl
methylpolysiloxane, 125°C to 275°C at 10°C per min) RT 7.9 min, 8.3 min, 9.5 min, 9.6 min, 9.8 min,
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9.9 min, and 11.5 min; GC-MS (phenyl methylpolysiloxane, 125°C to 275°C at 10°C per minute) RT
14.74 min, m/z 326; RT 12.98, m/z 298; RT 12.71 min, m/z 294; RT 11.07 min, m/z 270.
Results, Discussion, and Conclusion
In this experiment, biodiesel was synthesized via a transesterification reaction with triglycerides
in the coffee’s isolated crude oil. The target product of biodiesel was purified using liquid/liquid
extraction and characterized by IR and GC/GC-MS.
In converting the crude oil to biodiesel, potassium carbonate was chosen as the base catalyst in
this transesterification reaction. Potassium carbonate’s very basic properties allow it to deprotonate the
hydrogens off methanol to form a nucleophilic methoxy group. This deprotonation initiated of the
overall reaction to fragment various fatty acid methyl esters. As consequence of potassium carbonate’s
basic nature, acetic acid was needed to neutralize the overall reaction mixture before the work-up of the
biodiesel. By adding this acid, the reaction was stopped as the potassium carbonate could not continue to
deprotonate the methanol. Over the course of this experiment, reaction mixtures were stirred and
refluxed with a flask and reflux condenser. Rather than using a heat source and open beaker, refluxing
hexanes and methanol was chosen to heat the reaction mixture. Refluxing permitted the boiling of the
reaction mixture for long periods of time without loss of volume of the solvents or damaging the crude
oil or biodiesel.
In isolating biodiesel away from glycerol in the liquid reaction mixture, the purification
technique of liquid/liquid extraction used hexanes 90% methanol/water to create an organic layer with
the biodiesel and an aqueous layer with glycerol. Based on the polarities fatty acid methyl esters and
glycerol, 90% methanol/water was used because it was easily able separate glycerol due to its hydrogen
bonding interactions. The nonpolar hexanes were able to then take the less polar biodiesel into the top
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organic layer. This liquid/liquid extraction was performed in a reaction tube rather than a separatory
funnel because small amounts of biodiesel were expected to be formed.
Biodiesel was formed as a sticky greenish-brown liquid in a 24% yield. Furthermore, the percent
recovery of the crude oil from the 50 grams of coffee grounds gave a 4% recovery. The functional
groups of the product were characterized by IR and the purity was analyzed using GC/GC-MS.
When characterizing the product, the IR analysis (Figure 1 and Figure 2, Supplemental
Information) reflects very similar spectra for both the starting material of triglycerides and product of
biodiesel. Since glycerol was separated during the liquid/liquid extraction, the absence of the hydroxyl
functional group in the biodiesel’s spectra (Figure 2) helped confirm the product had similar functional
groups with triglycerides. For example, the carbon-hydrogen scissor bend at 1459 cm-1 and methyl
umbrella bend at a 1342 cm-1 indicates the similar types of bonding on the long carbon chains on
triglycerides and fatty acid methyl esters. Additional carbon-hydrogen stretches at 2921 cm-1 represents
the alkene carbon-hydrogen bonding. .Both the starting material and biodiesel also contain the key ester
carbonyl groups that are found at 1742 cm-1. The signals at about 1160 cm-1 is indicative of a carbonoxygen stretch in the ester structures. While the IR analysis for the starting material and product suggest
similar functional groups between the structures, it does not help confirm that the two materials are
different.
To distinguish difference, GC/GC-MS identified the range of fatty acid methyl esters in the
product. The GC was able to express the number of components in the overall composition of biodiesel,
while the GC-MS helped deduce the actual components. Table 1 shows the possible number of
components and Table 2 summarizes the types of fatty acid methyl esters found in the product below.
The four components found in the biodiesel include methyl arachisate, stearic acid, linoleic acid, and
palmitic acid.
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Retention Time
%
(min)
Area
Composition
7.953 55721
28.50
8.298 11824
6.05
9.524 75892
38.82
9.563 19066
9.75
9.758 12002
6.14
9.874 16046
8.21
11.455
4928
2.52
Table 1. GC Data
Component
Methyl
Arachisate
Stearic Acid
Linoleic Acid
Palmitic Acid
Retention
Time
(min)
Area
14.74
145777
12.98
470446
12.71
2189506
11.07
1969842
Table 2. GC-MS Data
m/z
326
298
294
270
%
Composition
3.1
9.9
45.8
41.2
In conclusion, the base-catalyzed transesterification of biodiesel was successfully with on overall
yield of 24%. From characterizing the functional groups using the IR spectra to determining its purity
using GC/GC-MS data, biodiesel’s composition was determined. Since the percent yield is based on the
purification of crude oil, liquid/liquid extraction could have been improved on. To increase the percent
yield, a number of factors including changing the solvent of hexanes to a slightly higher polarity could
have helped force more biodiesel into the organic layer. Perhaps changing the ratio between the solvent
used to make the organic layer vs. the solvent used to make the aqueous layer could have been even
higher. . Additionally, making sure that all the biodiesel was transferred carefully from glassware could
also impact the over percent yield as well. In performing a larger scale experiment in synthesizing a
substantial amount of biodiesel, a separatory funnel should be used for accurate mixing and collections
in the future.
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References
(1) K. Ramachandran, T. Sunganya; N. Nagendra Ghandi, Renewable and Sustainable Energy
Reviews. 2015, 22, 410-418.
(2) L. Casas; Y. Hernández; C. Mantell; N. Casdelo; E. Martinez de la Ossa, Journal of Chemistry.
2015, 2015, 1-9.
(3) U. Schucahardt; R. Sercheli; R. Matheus Vargas, Journal of the Brazilian Chemical Society.
1998, 9, 199-210.
(4) E. Moreira Santos; A. Paula de Carvalho Teixeira; F. Gontija da Silva, Fuel. 2015, 150, 408-414.
(5) N. Kondamudi; S. Mohaptra; M. Misra, Journal of Agriculutral and Food Chemistry. 2008, 56,
11757-11760.
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Supplemental Information
(Note: The notebook pages with the handwritten procedure, data, observations, and calculations
sections are to be attached at the end.)
Figure 1. IR of Triglycerides
Figure 2. IR of Biodiesel
Figure 3. GC of Biodiesel
Figure 4. GC-MS of Biodiesel