Snyder 1

Synthesis of Biodiesel in a High School Lab

by Richard L. Snyder

Chemistry Seminar

Dr. Gary Histand

April 24, 2007

Abstract

With the growing effects of gasoline prices, the need for an alternative fuel source is quite obvious. As gas prices continue to be on the rise in upwards of over three dollars per gallon, alternative fuel sources are becoming increasingly popular in today’s society. In the year 2000, there were about eight million vehicles around the world that ran on alternative fuels, indicating the increasing popularity of alternative fuels (Alternative fuels). Biodiesel requires no modifications to regular diesel engines in order to work (Filz). In 2001, the first two public filling stations offering biodiesel were opened in San Francisco, CA, and Sparks, NV (Filz). The importance of learning about alternative fuel sources is useful knowledge in today’s society. By having the students conduct the synthesis of biodiesel in a high school lab setting, hopefully the awareness will increase.

Biodiesel uses the process of transesterification of an oil. An alcohol and a catalyst are added to the oil and converts the esters to those of the corresponding alcohol. The reaction that takes places looks similar to this:

The alcohol becomes deprotonated by the base, which in turn makes it a better nucleophile. The nucleophile then attacks the carbon-oxygen double bond and creates a pair of electrons on the oxygen that was originally double bonded to the carbon. The alcohol becomes attached to the carbon. The electrons come back to the carbon and the glycol gets kicked off, which in turn forms the ester. The alcohols attack the other two carbon-oxygen double bonds and the same process occurs, with three ethyl esters being formed and the glycerol getting kicked off and creating a by-product each time (biodiesel production).

There are many techniques for creating biodiesel, but most, if not all, of the ones that have been discussed were meant to produce a large quantity of biodiesel. With budget concerns, as well as space and storage concerns, most of these methods were not feasible. The goal in doing this research project was to find a way to teach kids why finding an alternative fuel source is so important, as well as teaching some other basic chemistry methodology, such as calculating density and specific heat.

Introduction

The first thing that needed to be done when deciding on a procedure was what oil should be used. After looking at prices at a supermarket, the choice was narrowed down to three oils: vegetable oil (soybean oil), canola oil, or corn oil. Research was done on all of the oils. The information that was found indicated that canola oil comes from the rapeseed plant, which is part of the mustard family of plants. The rape oil, as it is sometimes called, was used in mustard gas during WWI. Mustard gas is an extremely dangerous gas, which causes blistering of the lungs and skin (Graham). It has also been shown to cause lung cancer, according to the Wall Street Journal. After hearing about the possibility of having these bad effects happen to students, canola oil was ruled out and all the attention became focused on soybean and corn oil. The assumption is that both will give similar results.

The next problem presented itself in dealing with the catalyst, NaOH. NaOH in the solid form is very caustic, which means it could eat the fingerprints off of the students’ hands. Because of this, the decision was made to use extreme caution when dealing with NaOH and make up a mixture of the NaOH/methanol mixture beforehand. It should be noted that NaOH is a deliquescent, which means it readily takes moisture from the air through absorption. Consequently, the concentrated NaOH should be kept in a tightly sealed container.

Problems kept arising when mixing NaOH and methanol. As soon as it was mixed with the soybean oil, a soapy emulsion would begin forming. This meant that too much NaOH was in the solution. The decision came to contact some “biodiesel experts” by asking them the question of what ratio of NaOH: methanol should be used. This was done by joining a group on the Internet for fanatics of biodiesel, some of which included professors with PhD’s (Gian). Their instructions were to figure out how much vegetable oil was going to be needed. If an estimated 30 kids in a high school classroom were working in pairs, 15 separate measurements of oil would be needed. The decision was made to use 20 mL of soybean oil, which came out to 300 mL of soybean oil total. They said a good number to use was either 4 or 5 g/L of a NaOH:soybean oil ratio. Both trials were done and the 5 g/L turned out to be a better ratio than the 4 g/L. Next, the instructions were that normally one should use a ratio of 20% by volume of methanol to the total volume of vegetable oil. This meant that a solution of 60 mL of methanol with 1.5 g NaOH would be mixed up. This turned out to be the framework for the experiment.

The final problem that was encountered when designing this experiment was how long to let the biodiesel and glycerol sit in between washings. In order to be sure that the washing has run its complete course, it was found that one needed to wait about 2 days. Since it is designed for a Chemistry classroom that meets every day, the suggestion is that students wait two days between each washing. One day was tried, but the solutions weren’t transparent, which indicates completion (Leray). The biodiesel needs to be clear enough to see through and not be a cloudy mixture, which is why two days is sufficient.
After sifting through all these problems, a procedure was developed that makes a quality amount and gives the desired product. The following experiment should be able to be used in a high school lab and if followed with precision, a successful synthesis of biodiesel should be the end result.

Procedure

  1. To prepare for the experiment, the teacher needs to mix up the mixture of methanol and NaOH before class. The amount that was found to work best is to use 5 g of NaOH per mL of total vegetable oil used in the experiment. The recommended amount is 20 mL of vegetable oil per group. For the methanol, use about 20% volume of methanol of the total volume of vegetable oil. For example, if you have 15 groups, you will have a total of 300 mL of vegetable oil and will use 60 mL of methanol. To achieve 5 g/mL of NaOH, you would use 1.5 g of NaOH.
  2. When students arrive in the classroom, make sure all safety procedures are followed. Safety goggles must be worn at all times.
  3. When the students arrive, they need to pour out 4 mL of the methanol/NaOH solution that has already been prepared.
  4. Next, 20 mL of vegetable oil (either soybean or corn oil, preferably) needs to be measured out in a graduated cylinder.
  5. After the NaOH/methanol solution and vegetable oil has been measured out and recorded, the NaOH/methanol solution needs to be added to the vegetable oil in a test tube.
  6. To make sure the reaction is taking place, put a rubber stopper in the end of the test tube and shake vigorously for about a minute.
  7. The next step is to let the mixture sit for 2 days.
  8. After 2 days, the students should notice two distinct layers. The bottom layer is glycerol and other by-products. The top layer (much more of the solution) is the biodiesel and needs to be pipeted off. To get the biodiesel off the top, pipet it into a clean test tube, being careful not to pull any of the glycerol with it.
  9. With the biodiesel in the clean test tube, you want to wash it now. Add about 5.0 mL of water to the biodiesel and SLOWLY invert the test tube to mix the water and biodiesel. (Note to teacher: Make sure students are inverting the test tube extremely slow, otherwise if shaken too vigorously, a soapy emulsion will form, contaminating the biodiesel.
  10. Allow the washing to sit for two days and pipet the biodiesel (top layer) from the bottom layer (water). Transfer the biodiesel into a clean test tube and proceed with step 9. Do the washing process 4-5 times, allowing two days to sit between each washing.
  11. After the biodiesel has been washed, the next step is to find the density. Weigh a graduated cylinder and then zero the scale. Pour the biodiesel into the graduated cylinder and record the volume. Then place the graduated cylinder on the scale and find the mass. Divide the mass by the volume, and that will be the density, in g/mL.
  12. The first part of the experiment is now complete. The biodiesel needs to be stored in a test tube and covered with a rubber stopper until needed.
  13. The second part of the experiment involves seeing how well the fuel actually works. First, get a pop can (any flavor will work, choose a favorite) and cut off the top of the can and discard it.
  14. Next, cut out two holes on opposites sides of each other at the top of the can so that a glass rod can be inserted to hold up the can on a ring stand.
  15. The next part of the experiment involves creating a fuel burner. The suggested way to do this is to use a dropper bottle. Take the top of the dropper bottle off and put insulation or glass wool into the dropper, leaving some sticking out of the top to act as a wick.
  16. Pipet the biodiesel that you have just finished creating into the dropper tubing and let the insulation soak it up inside the tube. Pour the remaining biodiesel in the bottom of the dropper bottle. Weigh the mass of the burner initially and record it on your data sheet.
  17. Now, it’s time to take the initial mass of the can without anything in it and record this data onto your data sheet.
  18. Add roughly 100 mL of water to the pop can and record the new mass. Subtract the initial mass from the final mass to figure out the mass of the water.
  19. Set up the pop can on a ring stand, having the glass rod hold up the pop can. Place the fuel burner directly underneath the pop can. Record the initial temperature of the water onto your datasheet. Keep a thermometer in the pop can to measure the temperature throughout the duration of the experiment.
  20. Light the wick on your fuel burner using a Bunsen burner. Keep the flame a few inches from bottom of the pop can. Keep a careful eye on the temperature. Let the temperature increase about 20oC and then blow out the flame. Record the highest temperature that the water reached.
  21. The next step needs to be done fairly quickly. As soon as the flame has been extinguished, the mass of the fuel burner needs to be recorded. To find the mass of the fuel burned, (in grams) subtract the initial mass of the burner from the final mass of the burner.
  22. Clean up the rest of the lab and return all equipment to its proper place.
  23. To find the total heat absorbed by the water in calories, a simple calculation will occur. Take your mass of water (grams) and multiply it by the change in temperature of the water (oC). This number is then multiplied by the specific heat of water, which is 1.00 cal/g* oC. This will leave you an answer in calories.
  24. To find the heat per gram of fuel, take the calories that you just found in the previous step and divide it by the mass of your fuel burned. This will give you an answer in calories/gram.

Data Section

Trial Number / Mass of NaOH / Volume of Methanol / Volume of Soybean Oil
1 / .0133 g / 1.0 mL / 8.0 mL
2 / .0106 g / 1.0 mL / 8.0 mL
3 / .0155 g / 1.0 mL / 8.0 mL

In these trials, there wasn’t much separation, leaving hardly any layers of biodiesel. This meant that the solutions probably weren’t mixed vigorously enough. Using a 3:1 mol ratio of methanol to soybean oil obviously didn’t work out.

Trial Number / Mass of NaOH / Volume of Methanol / Volume of Soybean Oil
4 / .1280 g / 5.1 mL / 40.1 mL
5 / .0988 g / 5.0 mL / 38.8 mL
6 / .0874 g / 5.2 mL / 39.0 mL

Increasing the volumes of the methanol and soybean oil and using a soda pop bottle to store the solutions was another thought. However, after thinking it through, it would be difficult to pipet the biodiesel out to wash it. In these trials, there was enough biodiesel to extract to proceed on. After the first washing, though, an emulsion was created instantly, thus proving that the ratios were not correct in the beginning. The emulsion most likely indicated too much NaOH was used.

The next idea that occurred was to mix up the NaOH and methanol in a big batch and go from there. Some research was done and found that the best ratio to use was 5 g/L of NaOH:total volume of vegetable oil. The amount of methanol that should be added to the NaOH is 20% of the total volume of vegetable oil. 300 mL of vegetable oil ( 20 mL multiplied by 15 groups of kids) was used. Theoretically then, 60 mL of methanol and 1.5 g of NaOH would be used.

Mass of NaOH / Volume of Methanol
1.4962 g / 59.7 mL

For all of the following trials, this is the methanol/NaOH mixture that was used.

Trial Number / Volume of Soybean Oil / Volume of NaOH/Methanol Mixture
7 / 20.7 mL / 4.1 mL
8 / 20.1 mL / 4.1 mL
9 / 21.0 mL / 4.0 mL

Each solution was allowed to sit for two days. After two days, they were washed with 5.0 mL of water. Then, they would sit for another two days between each washing. Five washings were done. When pouring off the water biodiesel into a clean test tube, not as much biodiesel was extracted as could have been. This provided not quite as good of results, as only the first trial were the only results. The mass, volume, and density were found of Trial 7.

Trial Number / Mass of Biodiesel / Volume of Biodiesel / Density of Biodiesel
7 / 1.7458 g / 1.9 mL / .919 g/mL

While doing research on biodiesel, the density was found to be .903 g/mL (Sarma). The density of soybean oil was also figured out to be .8054 g/mL, so obviously some form of reaction took place. Some more trials were needed to verify the results that were found in this experiment.

Trial Number / Volume of Soybean Oil / Volume of Methanol/NaOH
10 / 20.1 mL / 3.9 mL
11 / 20.0 mL / 4.0 mL
12 / 20.0 mL / 4.0 mL

Again, two days and then the first washing took place. Two days took place between each washing. After the second washing, trial #11 was not as clear as the others so the results might not be as accurate on this particular trial. After the final washing, the densities of the solutions proved my hypothesis correct. Trial #11’s density was a lot lower than the other’s densities.

Trial Number / Mass of Biodiesel / Volume of Biodiesel / Density of Biodiesel
10 / 1.2846 g / 1.4 mL / .918 g/mL
11 / 2.5944 g / 3.0 mL / .865 g/mL
12 / 0.4618 g / 0.5 mL / .923 g/mL

Since all of these densities were pretty close to each other,the total heat absorbed in calories and also the heat of gram per fuel was found.

Trial Number / 7 / 10 / 12
Mass of Can + Water / 107.7448 g / 107.2648 g / 107.6582 g
Mass of Empty Can / 9.5215 g / 9.4664 g / 9.1274 g
Mass of Water / 98.2233 g / 97.7984 g / 98.5308 g
Final Temp of Water / 37.0 oC / 41.5 oC / 32.7 oC
Initial Temp of Water / 23.3 oC / 23.3 oC / 22.9 oC
Temp Change / 13.7 oC / 18.2 oC / 9.8 oC
Initial Mass of Burner / 77.2777 g / 77.1881 g / 76.1178 g
Final Mass of Burner / 76.9368 g / 76.7850 g / 75.8773 g
Mass of Fuel Burned / .3409 g / .4031 g / .2405 g
Total Heat Absorbed / 1345.7 cal / 1779.9 cal / 965.6 cal
Heat per gram of Fuel / 3947.5 cal/g / 4415.6 cal/g / 4015.0 cal/g

In order to prove that the results were not just pure luck, three more trials using soybean oil were done. To see if other oils had the same effect as vegetable oil, corn oil was also used in a few trials.

Trial Number / Volume of Soybean Oil / Volume of Methanol:NaOH
13 / 20.0 mL / 4.1 mL
14 / 20.0 mL / 4.0 mL
15 / 21.0 mL / 4.0 mL

The standard two day waiting period was used after mixture and between washings for the vegetable oil.

Trial Number / Volume of Corn Oil / Volume of Methanol:NaOH
16 / 20.0 mL / 3.9 mL
17 / 20.0 mL / 3.9 mL
18 / 20.0 mL / 4.0 mL

Even with corn oil, the same waiting period between each mixing and washing was used.

After all the washings were completed, these were the densities that were calculated for the soybean oil and corn oil.

Trial Number / Mass of Biodiesel / Volume of Biodiesel / Density of Biodiesel
13 / 7.8572 g / 8.6 mL / .914 g/mL
14 / 7.6273 g / 8.3 mL / .919 g/mL
15 / 7.8369 g / 8.5 mL / .922 g/mL
Trial Number / Mass of Biodiesel / Volume of Biodiesel / Density of Biodisel
16 / 7.9046 g / 8.6 mL / .919 g/mL
17 / 7.4683 g / 8.1 mL / .922 g/mL
18 / 7.9698 g / 8.7 mL / .916 g/mL

Reminder: Trials # 13-15 were with soybean oil and trials # 16-18 were with corn oil.

The next step was to test all of the trials by finding the total heat absorbed and heat of fuel per gram.

Trial Number / 13 / 14 / 15
Mass of Can + Water / 108.4621 g / 105.6833 g / 107.3800 g
Mass of Empty Can / 9.2368 g / 9.4147 g / 9.3956 g
Mass of Water / 99.2253 g / 96.2686 g / 97.9844 g
Final Temp of Water / 41.2 oC / 40.6 oC / 38.1 oC
Initial Temp of Water / 23.0 oC / 23.1 oC / 23.4 oC
Temp Change / 18.2 oC / 17.5 oC / 14.7 oC
Initial Mass of Burner / 81.1073 g / 80.9636 g / 81.1589 g
Final Mass of Burner / 80.6847 g / 80.5739 g / 80.7915 g
Mass of Fuel Burned / .4226 g / .3897 g / .3674 g
Total Heat Absorbed / 1805.9 cal / 1684.7 cal / 1442.5 cal
Heat per gram of Fuel / 4273.3 cal/g / 4323.1 cal/g / 3926.2 cal/g
Trial Number / 16 / 17 / 18
Mass of Can + Water / 107.3476 g / 106.9744 g / 107.5918 g
Mass of Empty Can / 9.3264 g / 9.2784 g / 9.4738 g
Mass of Water / 98.0212 g / 97.6960 g / 98.1180 g
Final Temp of Water / 39.7 oC / 41.3 oC / 40.6 oC
Initial Temp of Water / 23.1 oC / 23.3 oC / 23.2 oC
Temp Change / 16.6 oC / 18.0 oC / 17.4 oC
Initial Mass of Burner / 81.2824 g / 80.8695 g / 81.0037 g
Final Mass of Burner / 80.9157 g / 80.4601 g / 80.6141 g
Mass of Fuel Burned / .3667 g / .4094 g / .3896 g
Total Heat Absorbed / 1627.2 cal / 1758.5 cal / 1707.3 cal
Heat per gram of Fuel / 4437.4 cal/g / 4295.3 cal/g / 4382.2 cal/g

Results