[Siddy]

Im not really interested in bio-diesel, but i found my self reading one of the many guides on the internet. They all seem the same, starting with a simple preparation of Methoxide, usually sodium methoxide.

The precedure i was reading simply mixed pure methanol with pure sodium hydroxide.

here is the link: http://greenoptions.com/2007/04/25/weekly_diy_make_your_own_biodiesel
and here is the procedure:
How to make methoxide:

   1. First, go outside. You'll want to do this in a well-ventilated area. Measure out 250 mL of methanol (HEET). Pour it into the small glass jar and seal it.
   2. Measure out 6 grams of NaOH (Red Devil). Don't let the lye touch anything plastic or anything living, including you. You can use a paper cupcake wrapper on the scale to hold the NaOH if necessary. Lye tends to stick to anything and everything else.
   3. Unseal the jar containing the methanol and carefully pour in the NaOH. Re-seal the jar.
   4. Gently swirl the jar to dissolve the lye in the methanol. This may take a few minutes. The jar will probably become slightly warmer. This is normal. A small amount of pressure will also be built up. Gently vent this pressure outside by opening the lid, but do not breathe the fumes!

Will this work?
What happens to the OH from NaOH which is usually not present as the reaction is usually Na(s) + Methanol?
Does it form water instead of H2(g)?
If so, wouldnt that convert a lot of the Methoxide back to methanol?

[Siddy]

I calculated, 250mL of MeOH is 200g, which i 6.5~ moles.
6g of NaOH is less than 1 mole, so there is no where near enough Na for the Methanol to produce even a 20% product of sodium methoxide.

Also, if water is produced with this reaction, can it be boiled off to leave behind sodium methoxide?

[kiwi]

methoxide is only formed in equilibrium amounts, pKa(methanol)=15.5; pKw=14. Consider the equations involved:

NaOH + MeOH = NaOMe + H2O

methanol is ~15x weaker than water at being an acid, so the equilibrium lies far toward the left

[AWK]

Methanol, not methoxide is used for engine fuel. Methanol can be easily purified by distillation since it does not form an azeotrope with water.

Sodium methoxide is used in organic synthesis on an industrial scale

[Sam (NG)]

I would have thought that the easier option would have been to convert your diesel engine to run directly on the vegetable oil, it works, then you just get used oil from your local restaurant and you're away.

[Siddy]

Thanks for the replies, looks pretty bogus then!

[kiwi]

Thanks for the replies, looks pretty bogus then!

it still works, it's a base-catalysed transesterification. it just doesn't quite work as they say.

[Siddy]

ah k.

is it possible to use the naoh + meoh method to get sodium methoxide buy heating the solution or anything?

[AWK]

As Kiwi said this is an equilibrium reaction, and in fact in solution of pure methanol and dry NaOH traces of methoxide exist.

[SirPants]

Kiwi is right,  it doesn't quite work like they say and doesn't work particularly well, either. I have been interested in biodiesel for some time now and have found that acid catalysis of the reaction works much, much better than base catalysis with NaOH.

[kiwi]

Kiwi is right,  it doesn't quite work like they say and doesn't work particularly well, either. I have been interested in biodiesel for some time now and have found that acid catalysis of the reaction works much, much better than base catalysis with NaOH.

do you mind elaborating? i have been meaning to give it a try for a while, it had occurred to me that in the lab transesterification is more easily achieved with acid than base. do you just lob in some sulfuric acid, and if so, do you see much tar-like gunk from dehydration of glycerol?

[SirPants]

Yeah,  it worked out pretty well for me lobbing in a mL or two of sulfuric acid for a liter of oil.  There was a bunch of yellowish tar gunk at the bottom from the dehydration of the glycerol. After trying to analyze it, the gunk turned out to mostly be a big fat mix of all the possible aldol condensations.  Luckily enough it all goo-ed at the bottom of the flask and was pretty easy to separate out.

Have any of you tried using ethanol for the transesterification as opposed to methanol?  I gave it a go a while back with some decent results

[kiwi]

no, but that was another improvement i had in mind given toxicity ethanol <<methanol.