8A Activité
expérimentale How to make biodiesel ? TSTI2D
Capacités : - Citer différents carburants utilisés et leur mode de production (pétrochimie, agrochimie, bio-industries...)
- Utiliser le modèle de la réaction chimique pour prévoir les quantités de matière nécessaires et l’état final d’un système
Think before start
Biodiesel is a mixture of methyl esters of fatty acids (long chain carboxylic acids). It has similar properties to the diesel fuel made from crude oil* that is used to fuel many vehicles. It can be made easily from vegetable cooking oil that contains esters of fatty acids.
The synthesis is a simple chemical reaction that produces biodiesel and propan-1,2,3-triol (glycerol). Cooking oil is mixed with methanol and potassium hydroxide is added as a catalyst. The products are separated into two layers, with the biodiesel on the top. The biodiesel is recovered and washed.
*crude oil : huile brute
+ 3 CH
3OH
CH
2CH
CH
2OH OH
OH O
C O R
O C O R
CH
2CH CH
2R O
C O C O
O
R CH
3+ 3 NaOH
... ... ... ...
Security :
methanol potassium hydroxide
Quote different fuels. What are the different ways of manufacturing ?
Associate the right terms to the different species of the equation : cooking oil ; methanol ; biodiesel ; glycerol.
What are the precautions for the use of these chemicals ?
Experiments
Measure 100 mL of rapeseed oil* into a 250 mL erlemmeyer flask. Weigh the flask before and after to determine the mass of oil you used.
Carefully add 15 mLof methanol.
Slowly add 1 mL of 50% potassium hydroxide.
Swirl the mixture for 10 minutes.
Allow the mixture to stand until it separates into two layers (first decantation).
Carefully remove the top layer (this is impure biodiesel) using a Pasteur pipette.
Wash the product by shaking it with 10 mL of distilled water.
Allow the mixture to stand until it separates into two layers (second decantation).
Carefully remove the top layer of biodiesel using a Pasteur pipette.
Weigh the amount of biodiesel you have collected.
Place 1 mL of biodiesel on a watch glass and light it using a splint to observe its combustion.
*rapeseed oil : huile de colza
The main fatty acid in the esters in rapeseed oil is CH3(CH2)14COOH.
Write an equation for your reaction to make biodiesel.
Calculate the amount of reactants (mol.).
Which of reactants is the limiting reactant ?
Calculate the theoretical amount of formed biodiesel (mol.) if the reaction is considered as total. Compare to the amount of biodiesel you have collected.
Calculate the yield of your production.
Compare it to the industrial manufacturing which has a yield of 90%.
Suggest ways to increase the yield of your own production.
Conclusions
Write a conclusion with your teacher.
K
+,OH
-http://lefevre.pc.free.fr
