I am trying to make a biodiesel lab for my High School students, but I am having problems getting it to work.

I have a text that uses the following procedure:

1. Pour 100 mL of Vegetable Oil (from a Supermarket into a beaker.

2. Add 15 mL of Methanol to the Vegetable Oil.

3. Slowly add 1 mL of 9M Potassium Hydroxide.

4. Have students stir the mixture for 10 minutes.

5. Allow the mixture to separate for two minutes.

6. Separate the top layer and place into a new beaker.

7. Wash this fluid with 10 mL of Distilled Water and sir vigorously for several seconds.

8. Allow the layers to separate for two minutes.

9. Transfer the top layer (Biodiesel) into a new beaker.

The students will then ignite some biodiesel and measure its heat of combustion.

*The trouble I am having is in the separation step (Steps 5 & 8). I waited up to 1 hour for the layers to separate, and they still did not separate. When I eventually got what looked like two layers, I could not get the isolated layer to ignite.

*Does anyone see anything wrong with this procedure?

*Does anyone know of a procedure that might work better?

I can use a different starting oil, but I would like it to be something that I can get in a pharmacy or grocery store. I have access to several chemicals since our school can purchase them.

Thanks for your help.

Typically, the catalyst is added to the alcohol prior to mixing in with the oil. As is, you're probably making soap and a suspension of alcohol in oil - the two layers you're seeing. If done properly, you will get two layers with distinctly different colors, densities, and viscosities. The Glycerin is darker in color, more viscous, and will settle out.

Reaction completion (high % of methyl esters, aka Biodiesel) takes time. You didn't specify a temperature, but higher reaction temps allow for shorter reaction times. Even at 140F, near the BP of Methanol, a minimum of 1 hour reaction time has been suggested; shorter durations give you more chemical intermediate products like mono and diglycerides. Granted, you don't need to get pure methyl esters to give your students an appropriate demonstration of the chemistry,

In addition, I've never heard of separation occurring so quickly (2 minutes). Most biodiesel homebrewers consider 24-hours to be appropriate. Perhaps you could use a centrifuge to speed separation.

Assuming you're doing all this under a hood, I'd also be concerned about methanol evaporation (and therefore, a lack of reactant availability), so I'd use 25 mL instead of the 15mL. This is an overdose, but should help to compensate for any MeOH losses.

Good luck -

So I think I am able to produce the biodiesel on my own....I kept the 100 mL vegetable oil on the hotplate at ~50 deg C and added the Methoxide (25 mL of MeOH and 0.4 gm of KOH. I stirred for 10 min while keeping the solution on the hotplate. The layers separate very well, but I am not sure that what I am making is actually biodiesel.

I have tried to ignite some of the diesel (as suggested with the lab I was following), however I cannot get it to ignite. I tried a match and a propane torch. I've read that the flashpoint is around 300 deg. I would think that the torch should ignite the biodiesel.

My question: If what I have made is actually biodiesel, then shouldn't it be easy to ignite? What are the best ways to ignite biodiesel? (Keep in mind that this is for High School students and not for my car).

Thanks.

Check this link:

http://www.kitchen-biodiesel.com/

This is the first batch many here try.

quote:

What are the best ways to ignite biodiesel?

I would suggest the technique on the first post of this
thread.

Check the video, seemed to work!

You have a number of problems with your lab instructions. First is 9M KOH. If I were you I would premix the methanol and KOH for the students before lab started. add 32g of KOH flake to 1 liter of methanol. Then your instructions should read something like this:

1. Pour 100 mL of Vegetable Oil (from a Supermarket into an erlenmeyer flask. and heat on hot plate stirrer to 120F

2. Add 25 mL of Methanol/KOH solution to the Vegetable Oil and cover flask with aluminum foil.

3. Stir the mixture for 10 minutes. (really should be longer but 10 min will give demonstration results)

4. Allow the mixture to separate for 15 minutes. (best if done overnight and split between two classes)

Stop here if you must complete the lab in an hour.

5. Separate the top layer and place into a new beaker.

6. Have students spray 10ml of hard tap water over top of biodiesel using a pump atomizer like what window cleaner comes in).

7. Allow the layers to separate for five minutes.

8. Transfer the top layer (Biodiesel) into a new beaker.

Hello,

This lab is in ChemCom right? I tried it too, and it seemed to fail miserably. I am going to repeat it (myself) at a higher temperature and premixing the KOH with the methanol. The other labs have worked for me, so I can't believe this one would be so poorly researched! Please let us know if you can get it to work.

Colin Jones

The secret to the whole process is the mixing of the catalyst (NaOH or KOH) with the Methonal or Ethonol prior to combining with the Oil.
You might want to get the book, "From the Fryer to the Fuel Tank", by Joshua Tickell. Or look over the Dr Pepper test from this website: http://www.biodieselcommunity.org/appleseedprocessor/

While I found "From the Fryer to the Fuel Tank" to be inspiring years ago, it's not the best source of information for chemical handling, processing, or the chemistry of Biodiesel. I thought it was a good read - particularly the historical portions, but definitely recommend other sources for more up-to-date information on Biodiesel production.

This message has been edited. Last edited by: ebztz,

Thanks for all your help everyone! I actually got the lab to work pretty well. I had the kids start it using 0.4 g KOH/25 mL MeOH premixed. I had them mix 100 mL veg oil with 25 ml of this methoxide. The oil was warmed to about 50 deg C and I had the kids stir the oil/methoxide on the warm hotplate for 15 min. They covered the biodiesel mixture and let it sit overnight. Since biodiesel looks a lot like veg oil, I told them that I think some of their reactions worked and some didnt (although all of them did work). I set it up as an inquiry part for the second day so they had to test density and viscosity to see if what they made was actually biodiesel. I ended the day to show them the flamability. I conducted a demo to compare the flame produced from veg oil with the flame from their biodiesel. (I know there are arguments as to why these will produce different flames, but it shows that the two substances are different). The kids loved the lab and it worked out well. My original recipe was from the ChemCom book and it did not work. That was horribly researched. This one worked much better.

quote:

Originally posted by Mr.TeacherMan:
Hello,

This lab is in ChemCom right? I tried it too, and it seemed to fail miserably. I am going to repeat it (myself) at a higher temperature and premixing the KOH with the methanol. The other labs have worked for me, so I can't believe this one would be so poorly researched! Please let us know if you can get it to work.

Colin Jones

Yeah...the lab in the ChemCom book is awful. I have no idea how that made it into the book. It doesnt work at all. See my post from today to see how I got it to work. The best way to get the biodiesel to ignite is to use a spray bottle and hold it to a flaming splint or propane torch. Most kids were surprised when it does not ignite by dropping a match into a beaker of biodiesel. Good luck.

Congrats on the success!!