Biodiesel Synthesis for High Schools and Colleges

Micro-Batch Experiment 2016

Objectives:

Demonstrate proficiency in laboratory techniques.

Determine the amount of catalyst needed by titration.

Determine the quality of the final product.

Increase your “green” thinking and knowledge.

Discussion:

The United States is the largest single consumer of fossil fuels in the world. Each year, the US consumes approximately 125 billion gallons of gasoline and 60 billion gallons of diesel fuel, with our consumption growing every year. While the bulk of gasoline is consumed in the automobile, the diesel engine is used for a wide variety of transportation from trucks to boats and trains. Diesel fuel is also consumed in the generation of electricity including the diesel-electric train engine.

With our current energy consumption, and the possibility of a world-wide declining oil production in the near future, the desire to find alternative sources for our energy needs is increasing. One such alternative is biodiesel converted from waste vegetable oil or WVO. It is estimated that American restaurants discard about 13 billion gallons of used grease and oil from deep fryers each year. Since many gallons of this used oil end up in landfills, sewer systems, and your backyard, the production of biodiesel from waste oil has the potential to significantly reduce environmental impacts. Actually, fueling trucks with such modified waste oil is environmentally better than using petroleum diesel. A few key points would be: emissions are lower for all the pollutants of concern; unlike petro diesel, which adds fossil carbon to the greenhouse gases in the atmosphere, biodiesel actually removes carbon from the atmosphere; this is all due to the fact that the plants grown to make it remove about 3 times as much carbon as is present in the biodiesel itself. So why don’t we just burn the vegetable oil? The reason is, because of the viscosity of the triglycerides. Viscosity is the internal friction or stickiness of a liquid. A viscous material is “thicker” and does not flow quickly. This would prevent it from flowing easily through the fuel pump systems of an engine.

Biodiesel shows great promise as a readily available replacement for petroleum diesel and can be synthesized on an individual level or on an industrial scale. In this experiment you will synthesize biodiesel from vegetable oil on an individual level. Oils (called triglycerides) have a glycerin backbone joined by ester linkages to three fatty acid chains. The chemical structure below shows the different areas within a typical oil molecule with one of the three ester linkages circled. The fatty acid portions may vary in length between C12 and C18.

The process you will use is called trans-esterification. Trans-esterification is the process of reacting a triglyceride molecule (oil) with an excess of alcohol (methanol) in the presence of a catalyst (NaOH, lye) to produce glycerin and fatty esters. The mixture of fatty esters produced by this reaction is known as biodiesel. This process is a two-step catalytic process. In the first step of the reaction, NaOH(sodium hydroxide) reacts with methanol in an acid-base reaction forming sodium methoxide, a very strong base and water. In the second step, the sodium methoxide breaks the glycerin section from the fatty acid section. The separation of the glycerin portion leads to the formation of three methyl esters (the biodiesel) and glycerol which can be used to make soap. The NaOH is regenerated as a product in the reaction. The biodiesel and glycerol are immiscible and will separate to form two layers.

We will also need to perform a titration procedure to determine the correct amount of catalyst (NaOH) to use. This will be done at the beginning of the procedure and we will calculate the amount of NaOH to use in the reaction.

Procedure:

Titration:

  1. Mix 10mL of isopropyl alcohol (90% or above) in a 50mL beaker with a 1mL sample of the waste vegetable oil you are going to use.
  2. Add to this solution, 4 drops of phenolphthalein. Gently mix.
  3. Using a buret, add the NaOH solution one drop at a time into the oil/isopropyl alcohol/phenolphthalein solution.

Trans-esterification:

  1. Warm 150mL of waste vegetable oil to about 50*C in a 400mL beaker on a hot plate.
  2. Add the calculated amount of NaOH to 30mL of methanol in a 125mL Erlenmeyer flask. Mix well until all of the NaOH is dissolved. This is your sodium methoxide solution.
  3. Add the methoxide solution to a 250mL Erlenmeyer flask. Add the warm oil to this flask. Stir on high for 15-30 minutes with a stir bar and stir plate.
  4. Transfer the contents of the flask to a 250ml separatory funnel. The mixture will separate into two different layers. The glycerol will fall to the bottom and the methyl ester (biodiesel) will float to the top. Since about 75% of the separation occurs within the first hour, you will be able to see immediate progress. Allow the experiment to sit for at least 1 hour.
  5. Open the stopcock of the separatory funnel and allow the glycerol to drain into a small beaker. Make sure not to get any biodiesel in the glycerol or glycerol in the biodiesel.
  6. Wash your biodiesel by adding 15 to 20 percent of water to the biodiesel in the separatory funnel. Add the water to the biodiesel and gently rock back and forth until it fully mixes. Allow the mix to settle out, up to one hour. Once you notice good separation (water on bottom and biodiesel on top) drain off the wash water leaving the biodiesel in the funnel. Repeat until you have completed a minimum of 3 washes.
  7. After washing your biodiesel, it is very important to dry it as well. There are two main ways of drying your newly washed fuel, time and heat. By allowing your biodiesel to sit with the lid off, in time, excess water in the batch will evaporate. Second, heat will help speed up the evaporation process. By leaving your biodiesel out in a sunny area, it should dry fairly quickly. The best way to know if your fuel is dry is by looking at the clarity. The biodiesel will clear up when it is dry.

Testing your biodiesel:

  1. One of the ways we can test the biodiesel is by an immiscibility test. After water is added (in the above step), swirl the mixture for a few seconds until it mixes into one color. Within 30-60 minutes, the mixture should settle out to milky white water on bottom and yellow biodiesel on top. At this point it may be cloudy, but if it separates completely, you have good fuel. If it does not separate, or thick foam, or soap forms, then you have done something wrong. Most likely you either added too much catalyst or you did not properly mix your sodium methoxide.
  2. You can also test the biodiesel by testing the pH of the wash water when it is drained off.When the water has a pH of seven, you are finished washing. Knowing that the NaOH was present as a catalyst, and that catalysts are not consumed in the reaction, where did your alkali end up?

Data Table

  1. Initial Buret Reading
  1. Final Buret Reading
  1. Milliliters of NaOH Titrated

Analysis, Interpretation, and Conclusions:

  1. Calculate the amount of NaOH needed for the reaction by using the following formula:

mLNaOH solution titrated + 5.5 (base number)= ` grams of NaOH per liter of oil

  1. Describe the physical properties of the products of this reaction: