Synthesis and Characterization of Biodiesel from Used Cooking Oil: A

Chapter 5

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Synthesis and Characterization of Biodiesel from Used Cooking Oil: A Problem-Based Green Chemistry Laboratory Experiment E. M. Gross,*,1 S. H. Williams,2,3 E. Williams,3 D. A. Dobberpuhl,1 and J. Fujita1 1Department

of Chemistry, Creighton University, 2500 California Plaza, Omaha, Nebraska 68178, United States 2Energy Technology Program, Creighton University, 2500 California Plaza, Omaha, Nebraska 68178, United States 3Omaha Biofuels Cooperative, Omaha, Nebraska 68117, United States *E-mail: [email protected]

Students in a Green Chemistry laboratory course learned about clean energy and commercial-scale production of biodiesel from members of the Omaha Biofuels Cooperative. Students were presented with a “problem” to investigate several of the variables involved in synthesizing biodiesel from used cooking oil. Students were tasked to study a few of these variables, characterize their reaction products and report their findings. In this experiment, students investigated the following variables: oil identity, alcohol type, and catalyst amount and type. Students used both common biodiesel “field tests” and instrumental methods to characterize their biodiesel. Students learned how to communicate scientific results to both scientists and non-scientists via oral presentations, scientific reports and newspaper articles.

© 2016 American Chemical Society Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Introduction An inquiry-based experiment for the synthesis of biodiesel from waste vegetable oil was developed for students at Creighton University. This laboratory experiment was part of a two credit hour Green Chemistry laboratory course. Students in the course had a one hour per week recitation along with three hours of laboratory time. The experiment was designed to be problem-based, with students performing considerable guided literature searching and experiment design. The experiment utilized five lab meetings – two for synthesis and two for characterization, and one day for presentations. There are a variety of biodiesel synthesis and characterization experiments in the chemical education literature. Students either synthesize biodiesel from vegetable oil and analyze their product (1–9) or perform an analysis of commercial biodiesel and biodiesel blends (10, 11). In designing the experiment described here, several of these experiments were consulted and many of the innovative ideas combined to design a project-based laboratory experiment. Students not only learned about clean energy in conducting these experiments, but also employed some of the twelve principles of green chemistry. Green chemistry considers human beings and the environment when designing a chemical reaction, experiment, or process. The ultimate goal is pollution prevention. There are twelve guiding principles of green chemistry. The two utilized by this experiment were Use catalysis and Use renewable feedstocks. The learning objectives for this experiment were for students to • • • • • • •

Discover how specific principles of green chemistry are utilized in a chemical synthesis. Obtain in-depth knowledge about a clean energy method. Successfully search the chemical literature. Compare “science” found on websites to science found in the chemical literature. Design and perform experiments in a thoughtful and efficient manner. Utilize “field” and instrumental biodiesel characterization methods. Effectively communicate scientific data and results to scientific and nonscientific audiences.

Laboratory Methods and Weekly Objectives On the first day of the unit, students were provided with an introduction to renewable energy and specifically biodiesel. A member of the Omaha Biofuels Cooperative (OBC), a local, community-scale, not-for-profit biofuels organization, provided demonstrations of transesterification reactions used for producing biodiesel from straight vegetable oil, and also from used cooking oil, and asked questions to stimulate thinking about the chemistry of this process. Students were given an assignment asking them to search the literature on the production of biodiesel from cooking oil and also to search the web for “recipes” commonly used by biodiesel “homebrewers”. Students were asked to compare 72 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

these two processes and to design a procedure for producing biodiesel from cooking oil. Additionally, they were asked to choose a variable in the reaction to investigate. During the first week of lab, students prepared biodiesel from neat or straight vegetable oil (SVO). The second week, they prepared biodiesel from used cooking oil, also called waste vegetable oil (WVO). Students worked in pairs and were required to determine the differences between these procedures and plan accordingly. Weeks three and four were devoted to characterization and week five for presentations.


Week 1: Synthesis from Straight Vegetable Oil A member of OBC provided a demonstration of the transesterification production of biodiesel from new vegetable oil, using an equipment setup developed by OBC specifically for such demo purposes. Students were then given a memo similar to the one used in reference 1. The memo was from OBC and provided a hypothetical scenario where OBC and Creighton University were partnering to develop an alternative fuel for the campus shuttle system. It discussed the environmental motivation for implementing alternative fuels into automobiles. The memo asked for the green chemistry students’ assistance. It asked them to first prepare biodiesel from neat vegetable oil, and then from waste vegetable oil that OBC had collected from local restaurants and processed for biofuel production. Students were also asked to investigate a variable in the reaction. The chemical reaction in Figure 1 was provided to students. The reaction is a transesterification of the triglycerides that make up cooking oil. The reaction products are glycerol and biodiesel, which is comprised of fatty acid methyl esters (FAMEs). In addition to background into the chemistry, students were given a worksheet similar to that reported in reference 1 to aid setting up calculations (Table 1). Some sample student numbers are shown in the table. Students were expected to arrive to lab with the table completed.

Figure 1. Transesterification of triglycerides in cooking oil to produce biodiesel. In this example, KOH or NaOH is used as the catalyst. 73 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Table 1. Synthesis of Biodiesel from Straight Vegetable Oil Method

mL of oil

Total grams of NaOH catalyst per liter of oila

mL of alcoholb

grams of catalyst for your reaction

Web reference (13)

100

5.0 g NaOH (0.50 % w/w)

20

0.50

Web reference (12)

100

3.5 g NaOH (0.38 % w/w)

20

0.35

a


If KOH was used as catalyst; the mass was adjusted higher by a factor of 1.4. ~20% v/v methanol:oil, providing ~6:1 mol ratio to drive reaction forward.

b

Typically

Students located biodiesel synthetic methods both on the web (12, 13) and in the literature (3, 5, 14–19). They found the stepwise instructions in the web resources straightforward for designing the experimental steps. However, the web resources lacked in the chemical detail students desired. For example, the stoichiometry was not explained and the websites did not always use units in the calculations, as students were accustomed to doing. The literature articles were complementary in that they explained the stoichiometry and used scientific descriptions and units. With the combination of these sources, the students designed procedures as shown in Table 1 and as described in the next section. From reading the literature articles, especially the review articles (18, 19), students appreciated that optimization of these reactions is still an active area in scientific research. Reading these articles guided them in choosing variables to test, such as catalyst type and amount (w/w%).

Table 2. Chemical and Physical Data for Reagents and Products

a

Reagent

MW (g/mol)

Density (g/mL)

BP /flash (°C)

Vegetable oil

~882a

~0.91-0.92c

~200a

Methanol

32

0.791

64.7 / 11.1

Ethanol

46

0.789

78 / 12

NaOH

40

NA

NA

KOH

56

NA

NA

Mixed methyl esters product

~250-290b

0.86-0.90d

331/70.6b

glycerol byproduct

92

1.26

290

reference (18)

b

reference (17)

c

reference (20)

d

reference (19)

74 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


During their literature searching and preparation, students tabulated the chemical and physical data as shown in Table 2 (18–20). Literature references are shown for vegetable oil and biodiesel physical properties. Students found information for the more common chemicals at typical sources (e.g. Sigma-Aldrich, the CRC Handbook, or ChemSpider). This information aided in their preparation for the synthesis. Each student group determined a procedure for producing biodiesel from cooking oil. They were required to submit a list of required materials to the instructor one day prior to lab. At the beginning of lab, the class reviewed and discussed the procedures. The general steps that the students should determine for the synthesis are listed next.

Synthesis of Biodiesel from SVO 1. 2.

3. 4. 5.

6. 7. 8.

Heat oil to ~110 °C for 15 minutes to remove excess water. Water can react to produce unwanted soap. Cool to ~50 °C. Dissolve catalyst in alcohol (e.g. NaOH in methanol) as shown in Table 1 to produce methoxide. (Note that NaOH and sodium methoxide are highly caustic.) Carefully and slowly add methoxide to the vegetable oil and heat at ~50 °C for around 1 hour. Cool to room temperature, allowing layers to separate. Allow the layers to separate overnight in either a separatory funnel or graduated cylinder. This glassware facilitates viewing and separating of the layers. Remove the top (biodiesel) layer from the bottom (glycerol) layer. In a separatory funnel, wash the biodiesel layer with ~20 mL deionized water. Remove the water phase and store the washed biodiesel layer for testing.

Week 2: Synthesis of Biodiesel from Waste Vegetable Oil After successful synthesis of biodiesel from SVO, students were given an assignment (Figure 2) for preparing biodiesel from the WVO. The feedstock used cooking oil was provided by OBC, and had been processed to remove contamination of food particles, water, heavy waxes and polymerized oil. The key changes students noticed regarding the preparation of biodiesel from WVO was that using cooking oil for frying results in hydrolysis of triglyceride oils into di- and mono-glycerides, and releases free fatty acids (FFAs). As a result, the WVO was initially titrated to determine the FFA content. Students learned that the presence of FFAs could neutralize the base catalyst, requiring additional catalyst (NaOH or KOH) to neutralize the FFAs. They also discovered that the neutralization results in soap contamination in the reacted biodiesel. An example table for performing these calculations is also provided (Figure 2). Note that this table is for NaOH catalyst. If students use KOH catalyst, the mass should be increased by a factor of 1.4. 75 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 2. Week 2 Assignment - Literature Research and Lab Preparation. Note that a sample “answer” has been added to the table in question 1.

Synthesis of Biodiesel from WVO 1.

Free fatty acid titration: Dissolve 1.0 mL of WVO in 10.0 mL isopropyl alcohol. Titrate with 0.10% w/v NaOH to a pink phenolphthalein endpoint. (Note that students delivered the titrant from a 5 mL graduated syringe.) Enter titration number (mL of titrant) into table. Add this number, representing required additional catalyst, to the g/mL of 76 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

2. 9. 3.


4. 5.

6. 7. 8.

stoichiometrically required catalyst. This is the total amount of catalyst to measure. Heat oil to ~110 °C for 15 minutes to remove excess water. Water can react to produce unwanted soap. Cool to ~50 °C. Dissolve catalyst (Step 1) in alcohol (e.g. NaOH in methanol) to produce methoxide. (Note that NaOH and sodium methoxide are highly caustic.) Carefully and slowly add methoxide to the WVO and heat at ~50 °C for around 1 hour. Cool to room temperature, allowing layers to separate. Allow the layers to separate overnight in either a separatory funnel or graduated cylinder. This glassware facilitates viewing and separating of the layers. Remove the top (biodiesel) layer from the bottom (glycerol) layer. Wash the biodiesel layer with ~20 mL deionized water. Remove and store the washed biodiesel layer for testing.

Weeks 3-4: Characterization Students were asked in the previous assignment to consider how they will characterize their biodiesel. They were requested to determine two “field tests” and two “laboratory tests” to characterize their biodiesel. Students performed literature and Internet searches to determine the various methods researchers (21–23) and home brewers (12, 13) use to characterize biodiesel. Students were reminded of the various instruments available to them. These instruments included gas chromatography with a flame ionization detector (GC-FID), gas chromatography-mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), 1H-NMR, and viscometry. Most of the students had taken an instrumental analysis course and were familiar with the techniques from the course or from research experience. Protocols for using the instruments were available in the laboratory. Students who were unfamiliar with a technique were shown how to use an instrument. Chromatographic methods were developed prior to the course so that lab time could be spent on biodiesel characterization and not method development. For example, if a group chose GC-MS, they were given the parameters and instructions for the analysis. Most of the students tried to perform as many of the tests and characterization methods as possible during the two weeks allotted for characterization. They were curious as to how their reactions turned out and how the variable they investigated affected the results. The field tests students performed included: a quick titration for soap content (13) and a 90/10 test for reaction completion (a modified version by OBC of the common homebrewing 3/27 Biodiesel Conversion Test) (13). The laboratory characterization methods utilized included GC-FID, GC-MS, FTIR, 1H-NMR, and viscometry, which was also accepted as a field test. The various analytical tests and the information students determined for their reactions are listed in Table 3. References are provided for the characterization techniques (FTIR, viscometry, and 1H-NMR) that other undergraduate experiments involving biodiesel synthesis from vegetable oil also utilized. In addition to these methods, similar undergraduate experiments have utilized Karl Fischer titration for 77 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

water content (4), glycerol by periodic titration (3), high-performance liquid chromatography (10), thin-layer chromatography (6), optical activity (7), and flame tests (2).


Table 3. Methods Utilized for Characterization of Biodiesel

a

Test

Field or Laboratory

Information obtained

Soap

Field

Soap content, quality of fuel

90/10

Field

Reaction completion

GC-FID

Laboratory

Product (fatty acid methyl ester) characterization

GC-MS

Laboratory

Product (fatty acid methyl ester) characterization

Viscositya

Laboratory

Reactant & product comparison Compare product to ASTM standards

FTIRb

Laboratory

Reactant & product comparison Reaction completion

1H-NMRc

Laboratory

Reactant & product comparison Reaction completion

references (1, 6, 11)

b

references (1, 4, 6–8, 10)

c

references (1, 2, 10)

Soap Test Soap is an unwanted byproduct that can be produced from the reaction between free fatty acids in the oil, excess water and catalyst. Soap can be produced during the reaction if there is excess water in the oil or too much catalyst added. Students found the soap test procedure at the Utah Biodiesel website (13) and followed the procedure below. Students delivered the titrant from a 5 mL syringe and observed a color change from blue to yellow at the end point (Figure 3). 1. 2. 3. 4. 5. 6.

Dissolve 10.0 g of biodiesel product in 100 mL of isopropyl alcohol (99%). Add 3-5 drops of 0.04% w/w bromophenol blue indicator. Solution appears blue. Titrate sample with 0.010 M HCl until the yellow end point. Record the volume (mL) of HCl delivered. Perform a “blank” titration of the isopropyl alcohol alone, and use the result to correct the sample titration result as necessary, Multiply the value from step four by 304 (NaOH catalyst) or 320 (KOH catalyst) to calculate the soap content in ppm.



Figure 3. Photograph of a biodiesel-isopropanol solution with bromophenol blue indicator before (left) and at the end point (right) when titrated with 0.010 M HCl for a soap test.

90/10 Test The 90/10 test is a scaled up version of the 3/27 test for reaction completion (13). This test allows for visualization and semi-quantitation of unreacted vegetable oil. If no unreacted oil is present in the tube, the sample is said to “Pass” the test. This is a necessary, but not sufficient, indicator of biodiesel reaction completeness. 1.

2.

3.

4.

Add 10 mL of biodiesel product to the graduated 100 mL conical centrifuge tube, followed by 90 mL of methanol, up to the 100 mL graduation. Shake the tube vigorously and allow layers to settle. If unreacted vegetable oil triglycerides are present, the mixture should separate into two layers. The biodiesel-methanol layer is colorless and on top. The unreacted oil settles to the bottom and appears yellow. (Figure 4) If unreacted oil is not present in the sample, a homogenous solution of methanol and FAME biodiesel will be present, transparent with a light yellowish tint. The volume of unreacted oil is determined by reading the volume of oil at the bottom. For example, the volume of unreacted oil in Figure 4A is ~1 mL. Multiply the volume of unreacted oil in mL by 10 for an approximation of the percentage (%) of reaction incompleteness.



Figure 4. Results of a 90/10 test for reaction completion for WVO starting material with 0.5 % NaOH (A) and 1.0% NaOH (B). The top layer is biodiesel dissolved in methanol. The bottom layer is unreacted waste vegetable oil.

FT-IR 1H-NMR and Viscometry Some students chose to characterize their reaction using FTIR. They used a Thermo Avatar 370 Fourier Transform Infrared Spectrometer. Other groups chose to test and compare the viscosity of their products and starting material. They used a Canon-Fenske 150 viscometer in a water bath at 23.2°C. One group used a 1H-NMR (Varian Inova 300 MHz NMR) to evaluate their reaction. As 1H-NMR (1, 2, 10) FTIR (1, 4, 6–8, 10) and viscometry (1, 6, 11) have been used and reported in numerous undergraduate biodiesel synthesis experiments, this discussion will primarily focus on the GC-FID and GC-MS analysis methods, along with the two home biodieseler field tests that students employed.

Gas Chromatography Gas chromatography with flame ionization (GC-FID) or mass spectrometry (GC-MS) detection are common methods for fatty acid methyl ester (FAME) analysis, but have not been reported in the chemical education literature for characterizing the FAMES in biodiesel produced from vegetable oil. GC-MS has been reported in the chemical education literature for experiments characterizing biodiesel blends (24) and to measure FAMES in egg yolks (25), demonstrating that GC method development and optimization is straightforward for the FAME analysis and can be implemented for undergraduate students.


GC-MS Many students used GC-MS to characterize their reaction product. The GCMS used was an Agilent 5973 gas chromatograph with a mass selective detector. The column employed was a HP-5MS (30 m length, 0.250 mm i.d., 5% phenyl 95% dimethylpolysiloxane, 0.25 µm thickness). The method settings are listed below. Samples were diluted by a factor of 10-20 with cyclohexane and injected (1 µL) onto the instrument.


Oven settings: Initial temperature: 190°C Initial time: 5 min Rate: 2°C/min Final temperature: 220°C Final temp time: 5 min Inlet settings: Inlet temperature: 250°C Split ratio: 1:50 Flow: 1.20 mL/min Detector temperature: 280°C

GC-FID Students also had the opportunity to analyze a sample of biodiesel provided by OBC. Students ran the sample on both the GC-MS and GC-FID and compared the results. This also allowed them to compare their results to biodiesel produced by “experts”. An Agilent 6850 gas chromatograph with a flame ionization detector was used to identify the biodiesel reaction product. The column and method parameters are reported here and student results are reported in the next section. The column was a Zebron ZB-Wax plus (30 m length, 0.53 mm i.d. (poly(ethyleneglycol) stationary phase, 1.0 µm thickness). To identify their peaks, students compared their peak retention times to an AOCS gas-liquid chromatography (GLC) reference mixture standard (#17A) from NuCheck Prep. The method settings are listed below. Samples were diluted by a factor of 10 with cyclohexane and injected (1.0 µL) onto the instrument. Oven settings: Initial temperature: 200°C Initial time: 6.0 min Rate: 10°C/min Final temperature: 230°C Final temp time: 5.0 min 81 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Inlet settings: Inlet temperature: 230°C Split ratio: 1:50 Flow: 1.20 mL/min Detector temperature: 230°C


Results and Discussion All students compared their results as a function of using straight and waste vegetable oil as the feedstock. Each pair also chose a variable to examine in each reaction. Therefore, each group ended up performing four reactions. Each group then characterized their biodiesel products with a minimum of two field tests and two instrumental methods. Lab recitation time was used to discuss the results of the students’ literature searching for analytical characterization methods. The class discussed the various characterization techniques and the types of chemical or physical information that could be obtained. This activity has been taught in two iterations, allowing pairs of students to design their own inquiry and characterization. The reaction variables and characterization methods used by each pair of students are listed in Table 4. One pair did not have a successful reaction on the first day, so did not test a variable. However, they were able to prepare biodiesel from straight (SVO) and waste vegetable oil (WVO), and analyze their biodiesel and a sample provided by OBC. A sampling of student results for each test will be discussed.

Table 4. Reaction Variables Investigated and Characterization Methods Used by Students Group

Variable Investigated

Characterization

Variable 1

Variable 2

1

Oil type: corn vs sunflower (SVO)

Catalyst amount: (SVO & WVO)

Soap, 90/10 GC-MS FTIR

2

Catalyst type: KOH vs NaOH (canola SVO)

Catalyst type: acid vs base (WVO only)

90/10 Viscosity GC-MS GC-FID

3

SVO vs. WVO as feedstock (this group had some difficulties on the first day)

Soap, 90/10 GC-MS GC-FID Continued on next page.


Table 4. (Continued). Reaction Variables Investigated and Characterization Methods Used by Students


Group

Variable Investigated

Characterization

Variable 1

Variable 2

4

Alcohol identity: methanol vs. ethanola (NaOH catalyst)

SVO vs. WVO as feedstock

90/10, Viscosity FTIR 1H-NMR

5

Alcohol identity: methanol vs. ethanola (NaOH catalyst)

SVO vs. WVO as feedstock

Soap, 90/10 Viscosity GC-FID

a

Note that using ethanol will produce fatty acid ethyl esters rather than fatty acid methyl esters.

Soap Test For base-catalyzed reactions, ASTM limits for soap testing in biodiesel are extrapolated from ASTM D4951 (which is for Na and K) to be 41 ppm (NaOH) and 66 ppm (KOH) (13). Failure of this test implies that the biodiesel was not suitably washed and residual soap was left in the fuel. Some students performed the soap test before and after the water wash step, to test the effectiveness of the wash. The results from Group 5’s methanol reaction (Table 5) show that the wash step removed soap, but that further washing would be required to lower soap levels below the 41 ppm limit. This group also performed the reaction with ethanol as a reactant. The soap levels were much higher, at the parts-per-thousand level. Other students’ post-wash results ranged from low ppm levels to ~150 ppm. Most students concluded that they could produce and wash biodiesel to contain acceptable levels of soap.

Table 5. Example of Student Soap Test Results Before and After Wash Step

a

Feedstock

ASTM Limit (Na)a

Unwashed

Washed

% Reduction

SVO Sunflower Oil

41 ppm

274 ppm

61 ppm

78%

WVO

41 ppm

669 ppm

137 ppm

80%

reference (13)

90/10 Test The 90/10 test quickly provides a measure of reaction completion by estimating the volume of unreacted oil in a biodiesel sample. Group 1 investigated two different NaOH catalyst amounts and performed the 90/10 test for reaction completion (Figure 4). The photograph shows that much more (~1.0 mL versus ~0.05 mL) unreacted WVO is present for the lower catalyst concentration. 83 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

GC-FID


Students were provided with a sample of biodiesel from OBC. They were able to visually compare their sample (color, clarity) to this sample, but could also run some of the characterization tests on it and compare the results of the OBC sample to those of their own biodiesel sample. A GLC reference mixture was analyzed to match the retention times to specific FAMES in the sample. The results (Table 6) were semi-quantitative and the relative amount of each FAME was estimated from the peak area percent (PA%).

Table 6. GC-FID of Biodiesel Sample from OBC and NuCheck FAME Standard NuCheck

OBC Biodiesel sample

FAME ID

tr (min)a

PA%b

tr (min)

PA%

methyl myristate C14:0

1.78

1.02 (1.0)c

no peak

N/A

methyl palmitate C16:0

2.64

4.11 (4.0)

2.68

11.16

methyl stearate C18:0

4.22

3.09 (3.0)

4.26

4.22

methyl oleate C18:1

4.62

44.37 (45.0)

4.68

24.71

methyl linoleate C18:2

5.14

15.12 (15.0)

5.43

50.21

methyl alpha linolenate C18:3

6.01

3.12 (3.0)

6.15

7.03

methyl arachidate C20:0

7.00

3.08 (3.0)

no peak

N/A

methyl behenate C22:0

9.89

3.04 (3.0)

9.84

0.40

methyl erucate C22:1

10.33

19.80 (20.0)

10.22

0.16

methyl lignocerate C24:0

13.17

3.05 (3.0)

13.08

0.08

a tr = retention time; the standard.

b

PA% = peak area percent;

c

values in ( ) are the % by weight in

Group 5 chose sunflower oil for their SVO biodiesel synthesis. Upon completing the GC-FID FAME analysis, they looked up the literature values for triglycerides in sunflower oil (26). The students determined the relative amounts of fatty acid methyl and ethyl esters produced. Using peak area percents as an approximate abundance of fatty acids, their results agree within reason to the expected values (Table 7). This group also used GC-FID to characterize the 84 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

FAME components of their biodiesel sample produced from WVO (Table 8). The FAMEs were primarily derived from C16 and C18 fatty acids in the triglycerides in cooking oil.


Table 7. GC-FID Analysis of Biodiesel Produced from Sunflower Oil

a

Identity

tr (min) (MeOH)

PA % (MeOH)

tr (min) (EtOH)

PA % (EtOH)

Expected rangea


2.63

6.54

2.81

5.79

4 – 9%


4.17

5.00

4.50

5.93

1 – 7%

methyl oleate C18:1

4.48

28.16

4.86

27.08

14 - 40%


5.10

47.46

5.59

56.09

48 -74%

reference (26)

Table 8. GC-FID Analysis of Biodiesel Produced from Waste Vegetable Oil Identity

tr (min) (MeOH)

PA % (MeOH)

tr (min) (EtOH)

PA % (EtOH)


2.63

9.76

2.83

10.31


4.18

3.81

4.52

4.08

methyl oleate C18:1

4.52

30.73

4.89

30.56


5.16

46.53

5.59

46.08

methyl alpha linolenate C18:3

5.99

6.31

6.48

6.19

GC-MS Many of the students chose GC-MS as a method to determine which FAMEs were present in their biodiesel sample. Students could compare their sample with the NuCheck standard mixture as described for the GC-FID. They also could use the mass spectral library to determine the identity of each peak. Figure 5 shows a chromatogram of a sample of biodiesel that Group 1 prepared from WVO using 1.0% NaOH catalyst. They observed four main peaks at retention times of 6.3, 9.8, 10.0 and 10.6 minutes. The peak area percents were determined for the four largest peaks for biodiesel produced from WVO using 1.0% and 0.5 % catalyst (Table 9). The names in parentheses were determined from comparison to the spectral 85 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


library. Although the soap test (Figure 4) indicated that the reaction using more catalyst was more complete, the reactions produced the same FAMEs in similar proportions.

Figure 5. Chromatogram from Group 1 of a biodiesel sample produced from WVO with 1.0% catalyst.

Table 9. GC-MS Peak Areas for FAMES in Biodiesel Produced from WVO FAME

tr (min)

PA percent 1.0% NaOH

PA percent 0.5% NaOH

C16:0 Hexadecanoic acid, methyl ester

6.3

7.22

4.53

C18:2 9,12-Octadecadienoic acid, methyl ester

9.8

46.87

46.93

C18:1 9-Octadecenoic acid, methyl ester

10.0

41.46

38.25

C18:0 Methyl stearate

10.6

4.45

4.53


Instructor Notes Instructor Preparation – Transesterification Reaction


This experiment uses chemicals and materials found in most chemical stockrooms, so preparation is straightforward. Instructors will need to purchase cooking oils and obtain waste vegetable oil from a restaurant or even from the on-campus dining hall. Solid particulates can be removed from waste oil by allowing them to settle or by filtering (27). Materials for the synthesis are listed below. Vegetable oil (a few varieties are helpful, if students wish to study oil type) Waste vegetable oil Methanol (ethanol and isopropanol, if students wish to study transesterification alcohol identity) KOH or NaOH catalyst (note purity for calculations) Phenolphthalein indicator, for FFA titration Isopropyl alcohol, for FFA titration 0.10 % w/v NaOH, for FFA titration 250 mL Erlenmeyer flasks for reaction 100 mL graduated cylinders Separatory funnels Thermometers Hot plates Mortar and pestle, for grinding up catalyst pellets Glass bottles, for storing biodiesel Instructor Preparation – Characterization If the students have had organic chemistry laboratory or an instrumental analysis course, they should be familiar with the common instrumental techniques used for biodiesel characterization. GC-FID, GC-MS and FTIR are fast, user-friendly methods that require minimal method development time. In addition to these instruments, the following supplies should be available to students. 100 mL tapered and graduated glass tube for 90/10 test (e.g. KIMAX centrifuge tube, oil and weathering, 100 mL, Sigma Aldrich #Z252263) bromophenol blue indicator (0.040% w/w), for soap test 0.010 M HCl, for soap test Cyclohexane, for diluting biodiesel prior to analysis Viscometer, if students choose to make viscosity measurements Student Preparation Because students had to establish their own procedures for the transesterification reaction, it was important that they successfully search the literature and outline their procedure before coming to lab. Giving them an 87 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


introduction to the reaction, along with assignments that provided guidance through specific questions to be addressed, helped students correctly determine a procedure. Students worked in pairs, which provided someone to double check ideas and calculations. Instructors could use either the beginning of lab time or a separate recitation section to review the students’ planned procedures. Some students may have difficulties interpreting the literature article they found, as was the case for Group 3 (Table 4). Alternatively, some students may find research articles that employ reagents not commonly found in lab. A planned procedural review time can avoid these misunderstandings. Students were also asked to provide a list of chemicals and materials to the instructor one day prior to lab. Although instructors can anticipate the reagents students will need, this requirement helped in the preparation and allowed the instructor to red flag potential erroneous procedures.

Grading Suggestions Students were evaluated on their written reports to OBC and oral presentations on the experiment. Because the laboratory assignment originated with a memo from the Omaha Biofuels Cooperative to the students, students were asked to provide a written summary of their results to the Omaha Biofuels Cooperative. The summaries were briefer than a full lab report, but contained all of the pertinent experimental details and a description and analysis of the data. The instructions provided to students are given below.

Instructions for Written Work Next week the class will get together discuss our results. You will turn in a “memo” communicating your results. You should start to think about how you will present your results and data. Below is a brief outline for your memo. 1. 2.

Brief motivation / background Chemical reactions and oil used a.

3. 4.

It will be helpful to determine the fatty acid pattern for the oil used. E.g. some helpful information may be found at J. Agricultural and Food Chemistry 1997, 45, 4748-52 (or similar references). Are there any correlations between oil type and fuel performance? What oil do you expect to predominate the WVO? Do your results correlate with this?

Variable studied (e.g. catalyst type, alcohol type) Results and Characterization a. b.

Of variable studied Of SVO versus WVO transesterification 88

Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

5.

Conclusions and Future experiments


Oral Presentations Students also presented their results to the class in an oral presentation, given in a graduate school “group meeting” format. After providing a brief background and experimental description, they focused on data analysis and interpretation. Within a class, the student pairs each chose different variables to study, so it was interesting for them to learn about the various results. The rubric students were provided was a modified version of an oral presentation assessment form used by the Creighton University Chemistry Department. Each criterion (Table 10) was rated with a 1, 2 or 3 and awarded points accordingly. (1=less than adequate (< 7 pts), 2=adequate (7-8 pts), 3=more than adequate (9-10 pts). The students in the “audience” were also provided with rubrics to fill out for each presentation. This “assignment” kept them engaged and actively thinking about how to deliver a successful presentation.

Table 10. Criteria for Oral Presentations Content/Understanding 1. Is the title accurate? 2. Is the background information explained sufficiently to understand the talk? 3. Does the introduction address the significance of the topic? 4. Does the introduction clearly state the purpose or hypothesis of the work? 5. Are the experiments explained clearly? 6. Are the experimental observations or data effectively summarized and communicated? 7. Are the chemical principles of the work sufficiently explained? 8. Are the green chemistry principles utilized by the work sufficiently explained or addressed? 9. Are references appropriately cited within the talk? Presentation 10. Is the talk organized in a logical way? 11. Are the figures/data tables clearly legible and easy to interpret? 12. Does the presenter appear excited and interested in the work? Interaction 13. Can the presenter effectively discuss the experimental details of the work? 14. Can the presenter effectively discuss the chemical principles of the work? 15. Can the presenter answer questions and freely discuss ideas about the work?

Final Thoughts For their final evaluation, students in the class were required to write a newspaper style article (28) on one of the experiments from the course. Some of the students opted to write their article on the production of biodiesel from waste 89 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


vegetable oil. This assignment challenged students to describe scientific concepts, data and results to non-scientists. During the recitation, a faculty member from the journalism department presented information on communication of science and writing newspaper articles. Students were first given an assignment to determine for which newspaper they were going to write and to decide on their topic. A subsequent assignment provided them with instructions on writing their articles and deadlines for the rough draft and final paper. Students turned in a rough draft, received feedback and submitted their final papers at the end of the semester. In summary, students found the project-based experiment “challenging yet engaging” as indicated in end-of-course surveys. Students enjoyed the independent environment and designing their experiments. One student commented, “I really enjoyed the use of chemical instruments and designing our own experiments in this course.” Surveys showed unanimous responses “agreeing” to the statement “I enjoyed and learned a lot from the inquiry-based experiments where I was able to help design the experiments.” Allowing students to choose a reaction variable to investigate dramatically engaged their inner “chemist” and maintained their interest in the outcome of a project that lasted 5 weeks. Students received hands-on experience in a variety of inexpensive and quick “field” analytical tests along with sophisticated laboratory instrumentation such as GC-MS and FTIR. Of the four field trips/outside speakers, students ranked the OBC the highest in an end-of-semester survey. Student interaction with the community partner Omaha Biofuels Cooperative greatly enhanced the learning experience, both in terms of technical knowledge and in professional skills. An OBC representative was present during nearly all the lab meetings, particularly when the students were performing the biodiesel synthesis. Students were encouraged to ask for advice from OBC. During one lab meeting, one group decided to employ acid-catalyzed esterification. Upon watching the reaction during the lab period, which was clearly unsuccessful, OBC requested a copy of the students’ procedure for review. When provided, OBC recommended the students to study base-catalyzed transesterification, which is far more commonly used in home-brew biodiesel production due to simplicity. The final report Memo from the student group highlighted this interaction: “Our second purpose was to test the feasibility of making biofuels from waste vegetable oil (WVO) using base-catalyzed and acid-catalyzed methods. The field tests exemplify the fact that the production of biodiesel from WVO using a base-catalyzed reaction proved successful at a lab scale.” “… the acid-catalyzed reaction proved unsuccessful.” Using a format of Memos as initial instructions, and as the method of student report to Creighton University and Omaha Biofuels Cooperative, reinforced professional written communications in a commercial or industrial setting.

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Synthesis and Characterization of Biodiesel from Used Cooking Oil: A

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