Soybean Oil: Powering a High School Investigation of Biodiesel

Laboratory Experiment pubs.acs.org/jchemeduc

Soybean Oil: Powering a High School Investigation of Biodiesel Paul De La Rosa,† Katherine A. Azurin,‡ and Michael F. Z. Page*,‡ †

Northview High School, Covina, California 91722, United States Chemistry Department, California State Polytechnic University, Pomona, Pomona, California 91768, United States

‡

S Supporting Information *

ABSTRACT: This laboratory investigation challenges students to synthesize, analyze, and compare viable alternative fuels to Diesel No. 2 using a renewable resource, as well as readily available reagents and supplies. During the experiment, students synthesized biodiesel from soybean oil in an average percent yield of 83.8 ± 6.3%. They then prepared fuel samples consisting of commercial Diesel No. 2, B100 (100% biodiesel), and blended B20 (80:20 Diesel No. 2 to biodiesel). During analysis, the students determined that the fuels contained an average energy value of 3626.2 ± 622.0 kJ/kg (B100), 3675.6 ± 723.7 kJ/kg (B20), and 4349.5 ± 1019.2 kJ/kg (Diesel No. 2). The experiment requires three 50 min lab periods and reinforces crosscutting educational science standards. It can enrich science discussions in either a high school or an introductory university chemistry class regarding sustainability and stewardship. KEYWORDS: High School/Introductory Chemistry, Interdisciplinary/Multidisciplinary, Laboratory Instruction, Public Understanding/Outreach, Hands-On Learning/Manipulatives, Applications of Chemistry, Calorimetry/Thermodynamics, Fatty Acids, Plant Chemistry

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relevant to solving global problems.11 For example, approximately 94% of the U.S. transportation energy is supplied by petroleum-based fuel12 and approximately 50 billion gallons of diesel fuel is consumed annually.13 Alternatively, biodiesel has fuel properties similar to petrodiesel14 and can be used directly in a diesel engine. Biodiesel improves lubricity and reduces toxic emissions during combustion.15 Overall, the United States has the fourth greatest biodiesel production potential in the world.16 Collectively, the nation has the ability to grow enough soybeans to meet food demands and address the need for alternative energy sources.4 If only 5% of the imported oil was replaced with biodiesel, it would account for the amount of oil imported from Iraq.17 Facets of fuel technology and environmental stewardship have been thematic in a number of articles that have appeared in this Journal.4,9,18−25 Recently, high school students have been challenged to synthesize biodiesel from oils extracted from algal lipids,26 and others have utilized a fifty-gallon reactor to convert waste vegetable oil as part of collaborations between their science and agricultural departments.27 The interdisciplinary nature of biotechnology has also extended to high school students being able to produce bioethanol from facial tissues.28 Biodiesel serves as a broad teaching platform to allow introductory university students to understand the scientific, quality control, and analytical testing aspects of the fuel industry. The properties of biodiesel, such as heat value, vapor pressure, enthalpy, entropy, and Gibbs free energy, are relevant to thermodynamic discussions within general chemistry

ver the past two decades, scientists and policy makers have been working together to define and address complex issues of sustainability.1 This topic has been woven into the fabric of modernized chemistry curriculum striving to equip students with principles of ethics2 and stewardship,3 while building their critical-thinking and data-analysis skills.4 Recently, the National Research Council, the National Science Teachers Association, the American Association for the Advancement of Science, and Achieve have worked with twenty-six U.S. states to enhance science education through the development of the Next Generation Science Standards (NGSS).5,6 This lab is a practical application of the NGGS Disciplinary Core Idea of Energy.7 The synthesis and analysis of biodiesel provides an opportunity to implement the following practices in a K−12 science classroom:5 (i) planning and carrying out investigations, (ii) analyzing and interpreting data, (iii) using mathematics and computational thinking, (iv) constructing explanations, and (v) engaging in argument from evidence. Furthermore, energy is a NGGS crosscutting theme8 that bridges disciplinary boundaries in a student’s K−12 academic maturation. This experiment serves to enhance a student’s understanding of energy by exploring bonding in fatty acid methyl esters (FAME), calculating the heat value and energy density of a renewable fuel source, and engaging in technical laboratory experiences. By incorporating green methodologies9,10 in various levels of the curriculum, future scientists will be better prepared to integrate sustainability in future innovations. These scientific dialogues during a student’s development should naturally lead to a wider understanding and demonstrate that chemistry is © XXXX American Chemical Society and Division of Chemical Education, Inc.

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courses.29,30 In addition to synthesis, these topics are developed in greater detail in organic, physical, and analytical university courses, which typically have been the first opportunity for university students to characterize FAMEs as alternative fuels.31−42

separatory funnel or heavy-duty conical vial, and the layers were separated overnight. Fuel Blending and Energy Density Analysis. During the second lab session, after the biodiesel and aqueous layers were allowed to separate, the fuel was collected and the mass recorded. The students then mixed approximately half of their synthesized biodiesel with Diesel No. 2 in an 80:20 ratio by volume (B20). Following the blending, students measured the energy density of each fuel sample: B100, B20, and Diesel No. 2. The groups filled ethanol fuel lamps with approximately 5 mL of each fuel and measured how long a known volume of each sample burned.26 Heat Value Analysis. In the third lab session, the students calculated the energy content of the various fuels. A calorimetric apparatus was constructed using a clean empty soda can supported by a ring stand and containing a thermometer. Each group added 50 mL of deionized water to the aluminum can and recorded the initial temperature of the water. As a cotton ball holding a precise mass of each fuel sample was burned and heated the system, the students monitored changes in the water temperature.44 Diesel Engine Combustion. Following a classroom discussion of data precision and accuracy, the combined student samples (either B100 or B20) that adhered to classroom quality assurance specifications were combined and used to power an industrial diesel engine generator (Yanmar LV100 V).45 For instance, the fuel samples chosen to be combusted in the engine demonstrated consistency in the acquired energy density and heat values by the selected student groups. No student data was collected during the engine combustion demonstration. This experience was included to further strengthen a lasting impression that biotechnology can address global concerns. Furthermore, any small diesel engine can be substituted and used during this portion of the lesson.

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EXPERIMENTAL OVERVIEW A series of lab experiments were developed in which high school students addressed the question, “Is domestic soybean oil a viable alternative biofuel?” These lab experiments were piloted in two local high school chemistry classes (containing 25−30 students) and used as an enrichment experience to several groups of 12−24 high school students visiting the university as part of outreach events and summer programs. After a short introduction of covalent bonding in various fuels (petroleum and alternative sources), students were encouraged to research biodiesel synthesis procedures from reputable Web sites and journal articles. In the first lab session, students gained technical experience by synthesizing FAMEs from soybean oil. This synthesis featured an innocuous catalyst, employed minimal solvents, and bypassed a fuel-drying step. In the second lab session, students completed two tasks. First, they prepared the fuel samples consisting of commercial Diesel No. 2, B100 (100% biodiesel), and blended B20 (80:20 Diesel No. 2 to biodiesel). Second, the students collected energy density data of each sample. In the third lab session, the students collected heat value data of each fuel sample. Following the completion of the laboratories, the students analyzed and interpreted data regarding side-by-side comparisons of the various fuels. As an enrichment experience following the data analysis discussion, the student fuel samples can be used to power an industrial diesel generator engine. The structure of the experiment presented herein required three 50 min class periods (with two additional sections used as a prelab discussion and data analysis period). Overall, this lesson challenged students to address global concerns using evidence and scientific reasoning. The analytical experiments reinforced the thermodynamic topics and energy calculations containing specific heat values used in high school and general chemistry courses. This lab series enriched discussions of energy in either high school or introductory university chemistry classes through the synthesis and characterization of B100 and B20 as an alternative fuel to petroleum-based diesel.

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HAZARDS Potassium carbonate is an irritant and should be handled while wearing gloves and safety glasses. Skin exposed to methanol, glacial acetic acid, soybean oil, or the resulting FAME should be flushed with water and washed with soap. Both fatty acids are combustible liquids with a closed cup flash point of approximately 282 °C. Diesel No. 2 is a flammable liquid with a closed cup flash point of 38 °C. The waste generated in this experiment should be disposed of following typical laboratory protocols. Individual high school sites should also adhere to specific site, district, and state protocols. Some general guidelines regarding noncommercial biodiesel waste procedures are available from the U.S. Environmental Protection Agency.46

Procedure

Chemicals. Soybean oil (CAS 8001-22-7), anhydrous K2CO3 (CAS number: 548-087), methanol (CAS number 6756-1), and glacial acetic acid (CAS number 64-19-7) were purchased from Fischer Scientific and used without further purification. Commercial grade Diesel No. 2 (CAS number 68476-30-2) was purchased from a local fueling station and stored in a sealed carrying vessel prior to usage. Transesterification.43 After reviewing the bonding within triglycerides and petroleum-based fuels during the prelab, the students were placed in groups of at least four to work collaboratively. In the first lab session, 20.0 mL of soybean oil (assumed to have an average molar mass of 880 g/mol), anhydrous K2CO3 (6% of the mass of oil), and anhydrous methanol (6 mmol per mmol of oil) were added to a 100 mL round-bottom flask. After refluxing for 25 min, a dilute solution (17.5 mL) of acetic acid (1 M) was added to neutralize the reaction. The mixture was stirred and transferred to a

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RESULTS The transesterification of soybean oil to biodiesel took place in 25 min by reacting potassium carbonate in a small excess of refluxing methanol.43 Neutralizing the reaction mixture with dilute acetic acid allowed the mixture to separate into two layers. This procedure resulted in students obtaining the desired alternative fuel in an average percent yield of 83.8 ± 6.3%. The shortened reaction time, minimal use of solvents, and the incorporation of an innocuous catalyst allowed this synthesis to be implemented in the high school curriculum where lab class sections meet for as little as 50 min at a time. B

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current biodiesel communications and offers a tangible example of a lab series that meets NGGS educational standards by illuminating how the fuel sector can be reformed in a sustainable manner utilizing chemistry and energy transfer in a real-world manner.

During the energy density analysis, the students determined that each fuel sample burned for an average time of 351 ± 3 s/ mL (B100) and 386 ± 16 s/mL (B20). The B100 sample displayed an average decrease of 9.09% when compared with the energy density of the B20 mixture. By adding 5 mL of each sample to a fuel lamp, students recorded the total time the fuel burned using a cotton wick. Commercial Diesel No. 2 burned beyond the allocated classroom period time, that is, values greater than 600 s/mL. During the heat value analysis portion of the experiment, the students determined that the three fuel samples contained an average of 3626.2 ± 622.0 kJ/kg (B100), 3675.6 ± 723.7 kJ/kg (B20), and 4349.5 ± 1019.2 kJ/kg (Diesel No. 2). By adding a precise mass of each fuel sample to individual cotton balls, the students recorded the temperature change of water in a calorimeter as the fuel samples were burned. The change in temperature was converted to energy using qv = C × dT × m (where qv = heat, C = specific heat, dT = change in temperature, and m = the mass of water in the calorimeter). Overall, the students concluded that B100 displayed an average heat value decrease of 16.6% and B20 displayed an average decrease of 15.5% when compared to Diesel No. 2, respectively.

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ASSOCIATED CONTENT

S Supporting Information *

Instructions for students, student handouts, and instructor notes. TThis material is available via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the dedication of Merlyn Conwell and Vanessa Ramirez and their students for piloting this investigation in their high school chemistry classrooms. Also we acknowledge the generous support of the John T. Lyle Center Regenerative Studies Faculty Fellowship Program at Cal Poly Pomona for supporting the growth and expansion of biodiesel in chemical education.

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DISCUSSION In this series of lab experiments, students were guided to review their synthesis and analytical evidence in order to provide a claim of whether domestic soybean oil can be used as a feedstock in the development of a viable alternative fuel. The classroom data indicated that FAMEs could be synthesized in relatively high yields from a renewable starting material. Furthermore, the samples prepared by the students (B100 and B20) were reliable sources of energy that produced values that were lower in terms of energy density and heat value when compared with a commercially available petroleum source. These overall energy depressions reported by the students follow known trends when comparing fatty acid methyl esters with Diesel No. 2. It has been reported that B100 (from soybeans) provides 8% less energy47 and B20 demonstrates a 1.73% decrease in energy48 when compared to Diesel No 2. The ability of high school students to produce analytical data that expands their scientific understanding of thermodynamics, energy densities, specific heat, and heat value equipped the students to synthesize their own understanding of the viability of various alternative fuels. In assessing the implementation of this lab, a high school teacher who piloted the series of experiments with students in a classroom setting provided the following insights. First, the materials and procedure were appropriate for high school students. Second, calculating the combustion enthalpy (using specific heat) of a renewable fuel provided a valuable concrete experience that allowed the students to formalize abstract topics regarding energy. Lastly, following the implementation of the lab series, the student participants have reiterated their findings in science and environmental student club meetings. Witnessing the students engaged in relevant discussions of stewardship and green technologies well beyond the classroom walls has reaffirmed the positive impact of the experience upon the students’ thinking.

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Summary

This investigation engages students in scientific questioning, generating evidence, and analyzing data to address questions of environmental stewardship. This experiment expands on C

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