evil_lurker
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Mood: On the wagon again.
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Adventures in transesterfication...
Got bored today and decided on a new chemistry expirement. Decided that today I was going to make some biodiesel, or at least attempt to.
Since I have yet to get a decent titration setup, I just had to kinda guess at how much chems to add.
In the first batch took 1000mL of new veggie oil, mixed it with a solution of 200mL of methanol and 4 grams of sodium hydroxide and threw the whole
lot in the food processor/carbon grinder for 15 minutes. After about 2 hours two layers had formed in the resulting solution, one a kinda tannish
milky solution on top, and a clear amber solution on bottom.
On the second batch, I took 1 liter of waste veggie oil and mixed it with 250 mL of methanol and 9 grams of sodium hydroxide. Again it went into the
blender for 20 minutes. This time though, the oil began to seperate out much faster, making the beginnings of a bottom later in a matter of minutes.
Now then, I know that the conditions are probably not the most economical for large scale production, but dang this is eeeeaaaaassssy and pretty goof
proof from the preliminary results. I might just have to go into business! 
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overseer
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So, where did the NaOH end up in this process?
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Darkblade48
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I thought the NaOH acts merely as a catalyst for this reaction
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Pyridinium
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| Quote: | Originally posted by Darkblade48
I thought the NaOH acts merely as a catalyst for this reaction |
I did a google search and "re-found" that Brazilian Chemical society paper which I think one of us mentioned on here before. So yeah, I
actually have to get around to reading that thoroughly along with the 80 zillion other papers I've got on my list...
Edit: I must've been exposed to metal fumes that time I tried to weld galvanized steel... I don't know what I was thinking. Yeah, the base
is a catalyst, but there are evidently a couple other types of catalyst too.
Ideally, the base deprotonates the alcohol, making it react more easily. The percent of total alcohol deprotonated by NaOH wouldn't have to be
very much (most alcohols have a high pKa), but if something happened to take the deprotonated alcohols out of the reaction (such as forming an ester),
it could shift the equilibrium to favor deprotonation. I guess that's how the NaOH catalyzed mechanism works.
Stronger bases than NaOH, then, should work faster.
[Edited on 24-6-2005 by Pyridinium]
[Edited on 24-6-2005 by Pyridinium]
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Nerro
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Strong acids will also work.
#261501 +(11351)- [X]
the \"bishop\" came to our church today
he was a fucken impostor
never once moved diagonally
courtesy of bash
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overseer
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| Quote: | Originally posted by Darkblade48
I thought the NaOH acts merely as a catalyst for this reaction |
Yes, of course. But several grams of it cannot simply disappear from the products. It has to remain somewhere, mixed with glycerol, or ... ?
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Nerro
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It probably mixes into a fine suspension through all of the fuel and the glycerol. If you mix in some water and stir the mix thorougly that should
dissolve all the NaOH/KOH and safeguard you from its detrimental effects to your engine. Just separate the NaOH/KOH solution (depending of course on
whether you used NaOH or KOH) from the "diesel" carefully and you should be fine. When you make large amounts you probably should repeat
this wash several times.
You might also add some dissolved stearic or oleic acid to neutralise the base. But that would form sodium or potassium salts which would be converted
into their carbonates in the engine which are of course slightly alkaline when in water and as such might be detrimental to engine performance in the
long run.
Basiccaly washing the fuel with water a few times seems to be the best way to go. 
[Edited on 25/6/2005 by Nerro]
#261501 +(11351)- [X]
the \"bishop\" came to our church today
he was a fucken impostor
never once moved diagonally
courtesy of bash
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Sandmeyer
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What kind of ester did you use in the first place?
Isn't it better to use a catalytic amount of HCl (or sodium methoxide) in an large excess of methanol (to push the eq towards methyl ester you
want to make). If you use hydroxide as a base in transesterification you end up with the carboxylate, it's kind of a termination reaction as it
stops there.
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