[jimbo]

yall,

this is not high school related.  i'm in my 40s and have a few chemistry questions.

when making biodiesel via transesterfication, basically the glycerin in the oil falls out and 3 free fatty acid molecules in the oil join up with 3 methanol molecules (added methanol).  the process for this is fairly straightforward for the smalltime or home brewer, but it uses methanol, the price of which is tied to the price of petrol.

i want to just free the glycerin and not bother with the methanol (which is nasty and expen$ive).  

adding salt to the oil seems to cause the glycerin to precipitate, but then i have to remove the salt from the oil before i use it as fuel.

what i'm aiming for is not biodiesel, but it can cold start a diesel and comes out of the waste stream (waste vegetable oil from a fast food joint).

1) is there a better way of removing glycerin from oil (rather than salt)?
2) how do i get rid of the remaining salt in the oil?
3) is there a test i can do on the veg oil for salt?

thanx,

jim

[Mitch]

I'll tackle number 2) I don't think there will be a large salt content in your oil for you to do what I'm about to transcribe. You can add an equal volume of water, shake the whole thing up and the salt will then reside with the water; from there is should be easy enough to seperate oil and water.

[jdurg]

Let me try and understand what it is that you want.  Do you just want the glycerin and don't care about what's left over, or is the glycerin your 'waste' product?  If you just want the glycerin, you could use an easy saponification reaction where you add solid sodium hydroxide to the vegetable oil.  This will cleave the long chains from the glycerin molecule giving you pure glycerin and soap.  The glycerin is easily removed as it tends to rise to the top.  The stuff left over is what we all know as 'soap'.  That's probably the easiest and cheapest way to get glycerin, though I'm not 100% sure if that is what you want to do.

[jimbo]

jdurg,

the glycerin is the waste product, i want the oil without the glycerin or salt.

jim

[Donaldson Tan]

distillation?