1041 Synthesis of Biodiesel F10

Austin Peay State University Department of Chemistry Chem 1041

Synthesis of Biodiesel

Revision F10 IB Page 1 of 6

Cautions NaOH is corrosive and toxic. Methanol is toxic. Purpose To synthesize biodiesel.

Introduction

Biodiesel, a methyl ester, is an alternative to diesel that is made from a triglyceride (like vegetable oil) and either ethanol

or methanol. The oil used in the process can come from many sources including soybeans, corn, canola, and used frying

oil. Because it comes from renewable resource, it is referred to as a biofuel. The process involves taking the oil, a

triglyceride, combining it with an alcohol, to form biodiesel, which is either an ethyl ester or a methyl ester. The process

uses a base, either potassium hydroxide or sodium hydroxide, as a catalyst to help in the process and forms glycerol as a

byproduct. The reaction is shown below:

H2C

HC

H2C

O

O

O

C

C

C

O

O

O

R

R

R

+ CH3 OH3Catalyst

H2C

HC

H2C

OH

OH

OH

Triglyceride Methanol Glycerol Methyl Ester

+O C

O

RCH3

3

The process involves combining the methanol with the catalyst, in this case sodium hydroxide. This forms sodium

methoxide, very strong base which is then combined with the vegetable oil. After the reaction is complete, the oil and

glycerol form two separate phases with the glycerol being on the bottom and the biodiesel on the top. The glycerol is then

removed and the biodiesel layer is then rinsed with water to remove any remaining catalyst. In today’s lab, we will be

making biodiesel on a small batch scale. The usual biodiesel process is a continuous process that involves large tanks

and pumps. This lab will give you an idea of what happens inside the vessels and pipes as biodiesel is being made.

Reference Data Density (g/mL) Molar Mass (g/mol)

Methanol 0.7918 32.04

Vegetable Oil 0.915 872

Glycerol 1.26 92.9

Biodiesel 0.88 292.2




Procedure

1. Take a 50 mL Erlenmeyer flask with a stir bar and add 14 ml of pure methanol.

2. Place the flask on a stir plate and set speed at a rate where it doesn’t splash but stirs vigorously.

3. Slowly add 0.50 g of NaOH. Do not go over this mass of the NaOH; add carefully.

4. Observe the NaOH being completely dissolved. Once this happens, sodium methoxide is formed, a very strong

and dangerous base.

5. While the sodium methoxide is being formed, place 60 ml of pure vegetable oil in a 200 ml beaker on a hot plate

and warm to 50°C. Then place it on a stir plate with a stir bar under medium agitation.

6. After step 4 is complete, SLOWLY the sodium methoxide add it to the warm vegetable oil. Make sure no residual

NaOH gets into the oil. The solution will be cloudy.

7. Stir the reaction mixture for 20 minutes

8. Transfer the solution to a 125 ml separatory funnel. Allow the solution to settle for 20 minutes using a ring stand;

the glycerol layer will form on the bottom. If you do not see two layers, start over being sure to add no more than

0.50 g NaOH.

9. Once glycerol has stopped forming, drain the glycerol into a small graduated cylinder using the stopcock. Record

the volume of glycerol.

10. Drain the biodiesel layer from the separatory funnel and measure the volume.

Waste Disposal

Pour all aqueous solutions down the sink with an excess of water. Dispose of the biodiesel as directed.

Clean-Up

Wash all glassware with soap then rinse 3 times with tap water, and once with deionized water.

Calculations: Show all work for calculations.

1. Use density to calculate mass from measured volumes.

2. Use molar mass to convert grams to moles.

3. Calculate the theoretical yield of glycerol and biodiesel using the stoichiometry from the balanced equation,

shown on page 1.

4. Compare the percent conversion of biodiesel. See post-lab question #1.




Calculations:




Data Sheet

Name: _______________________________ Lab Partner(s): ______________________________

Mass Balance

Reactants

Reaction Data Methanol NaOH Vegetable Oil

Volume

Mass

Moles

Products

Theoretical Yield Glycerol NaOH Biodiesel

Moles

Mass

Actual Yield Glycerol NaOH Biodiesel

Volume

Mass

Moles

Percent Conversion




Post-lab Assignment Name: ______________________________

1. Percent conversion is calculated by dividing the actual yield by the theoretical yield and multiplying the result by

100. Calculate the percent conversion of biodiesel.

2. Do an overall mass balance of the reaction, total mass of products – total mass of reactants. What do you think

would account for the difference?

3. Can you think of some ways to improve procedure to produce the biodiesel? Give 2 examples.

4. A normal biodiesel plant produces about 15,000,000 gallons per year. How much vegetable oil and methanol is

needed to produce this much biodiesel?




Pre-lab Assignment Name: _________________________________ 1. Write the balanced equation for the process of making the intermediate sodium methoxide.

2. Write the balanced equation for the second step of the process, the reaction of the sodium methoxide with a

triglyceride.

3. Why is sodium hydroxide considered a catalyst in this process?

4. What is biodiesel used for?

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1041 Synthesis of Biodiesel F10