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1. Rapeseed Oil? Can I substitute Canola Oil?

Doug, Graham states on his web site, "I use rapeseed oil as it is non-soluble with methanol or water and has a low vapor pressure, so wont vaporize as it passes thru the venturi throat, unlike water."

And since canola is a modified rapeseed, to lower the acidity,then there should be no problem using canola. " Canola is rapeseed! Canadian oil, low acid" Canola/rapeseed

Mike

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The only difference I can think of is that, with sulfuric being available (and desirable) in higher concentrations, the quantities to be used would be much lower, so precision becomes even more critical

It is about more than the concentration of the different acids. You must calculate for concentration, molecular mass and available hydrogens. Different acids vary in how reactive they are. How many Hydrogens they have available to react is what makes them the acid.Sulphuric acid has two hydrogens to give up while hydrochloric has only one and phosphoric acid has three hydrogens to give up. If you ingnored this you would use twice as much sulphuric as you needed when converting from hydrochloric. Molecular mass (density) means there are fewer, larger, molecules of sulphuric acid in a given volume than there are of hydrochloric and much much fewer, much larger, of phosphoric. If you do not allow for this you will use too little sulphuric. Concentration is fairly obvious and easy to compensate for if you use different concentrations from the ones shown.

The following table shows A=Which acid. MM=Molecular Mass(denisty). C=Concentration of the acid. H=The number of hydrogens each acid has to give up. The three acids shown are Sulphuric, Hydrochloric and Phosphoric. These are the only three acids I have verified. I have verified these figures by experimentation in the past.

__A______MM_____________C___________H
H2SO4___98.07__________98%__________2h
HCl______36.46 _________ 34%__________1h
H3PO4__839.02__________ 85%__________3h


If anything is unclear then ask and I will try and explain.

If you take all three variables into account you can calculate the eqivalant amounts to use for each acid.

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

any thoughts on whether or not you could get away with using a dilute solution (still maintain same # of moles) of sulphuric or phosphoric acid? it would allow you to introduce it at a faster rate without shocking as much soap into FFA's. Would there be risk of creating additional soap (because of the water content) and even if you did, would this necessarily be a bad thing given that you are going to filter/settle it out anyway?

Hydrochloric acid is pretty much water anyway.
Saturated with hydrogen chloride gas. That is why 34% is very concentrated HCL not dilute HCL.

So little difference if you diluted the sulpuric down to the same molar ratio or the same concentration as the hydrochloric. You would have to dilute again if you wanted to compensate for both and again to compensate for the hydrogens. So you would end up with a fair bit more water than you had with the hydrochloric.

I avoided giving the conversion factor outright in the last post and am avoiding it again now. It is not too hard to do. All the info has been provided in one convenient table I had to research to construct. Anyone will understand more and remember more if they make the effort to do the simple math involved.

Ant: thank you for your explanation.

As I said before, I'm not a chemist, so what you're talking about is way over my head, but for what you're saying I figure you WILL need less H2(SO4) than HCL (so at least I got lucky... ).
Am I reading it right?
If that's the case, is there anything we could use to dilute it, instead of water, that wouldn't interfere with the reaction or contaminate the BD?

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If that's the case, is there anything we could use to dilute it, instead of water, that wouldn't interfere with the reaction or contaminate the BD?

Good question. The answer would be yes. why not use clean soap free bio? Methanol might be ok. You should check on what happens when you mix conc H2SO4 with an alcohol.

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Am I reading it right?

Yes you are. A lot less.

Alot less, but, sulfuric acid (concentrated) is much harder to obtain than HCL which is commonly sold as muriatic acid. And the price is significantly more - please forgive me if i don't quote the economics of it. However, phosphoric acid should be easier to get than sulfuric and like ant said, phosphoric has 3 hydrogen's to give up. But, the kicker with phosphoric acid is that it is classed as a weak acid, so, whether or not it actually is willing to give up all 3 hydrogens is a completely different story. Obviously the strong acid / weak acid is applicable to aqueous solutions - which, biodiesel, methanol and glycerin definate do not fall into - so, i do not know how the "rules" will change in this environment.

The other issue at hand is, why is approx 100ml of a 34% solution of HCL sufficient to neutralize the remaining catalyst?

To understand, i think we need to do a titration for soap in the glycerin to find out exactly how much catalyst was exhausted as well as to find out how much residual catalyst we are talking about. 100ml of HCL is nowhere close to the 700+ grams of NaOH that one might use in a 100L batch.

Hence my original questions:

(1) since our intent is that we are going to force the soap out of suspension / solution, would it be that big of a deal to introduce some water, give up a little yield to arrive at a little more soap and have the NaOH completely exhausted at the end? Would that create sufficient simplicity and be economically favorable?

(2) Would simply drawing a deeper vacuum and distilling the methanol at a much lower temperature be the most viable way to go?

Dogma,

Interesting ideas. There are some assumptions you are basing your trials on that I simply am not clear on. Could you provide a little more detail on the process you are thinking - beginning middle and end. I am willing to give the ideas a try but I need to understand them better to implement them.

Question 1 (of yours)
Are you suggesting to just add water instead of acid? Or are you suggesting to add acid than add just a tiny bit of water at the very very end to create the extra soap? This idea doesn't make any sense to me but that's because I know I am missing something here.

Question 2
Working backwards from Graham's numbers, do you want to suggest some kind of 'guess estimate' table on how this should be done. I am ordering a PID with Ramp so I am willing to give it a go.

Doug

Thanks Ant. I will check on mixing the H2(SO4) with methanol. I'm planning on building a reactor soon (waiting on the tank), so, once I do, I'll try it and report back on it.

Dogma: now you brought up a point I haven't thought about. It just makes sense that H2(SO4) would be much harder to find than HCL (and to think that, when I was a kid in my country, I used to buy it over the counter at the local pharmacy...), given its use to make explosives. In any case, if we use less of it, it all comes down to how much money we need on acid per batch, and if the extra expense (if there is one) makes it worth it.
Sorry, I have to go to work. Later.

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so, whether or not it actually is willing to give up all 3 hydrogens is a completely different story

It does.

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The other issue at hand is, why is approx 100ml of a 34% solution of HCL sufficient to neutralize the remaining catalyst?

It would seem that 1ml of 34% HCL is being used to neutralise something under 5g of NaOH. Previous experiment has shown me that 1ml of HCL will neutralise slightly more than 2g of NaOH. So we are only neutralising about half the caustic in there and this is somehow working.

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700+ grams of NaOH that one might use in a 100L batch.

Some of that has already made soap neutralising the FFA and probably a bit more as well with some yield being wasted as soap. Something less than 500g would be the amount you are looking at.

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phosphoric acid is that it is classed as a weak acid

This is because the large molecular weight of the molecule means the molar concentration is low for a given volume.

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it be that big of a deal to introduce some water, give up a little yield to arrive at a little more soap and have the NaOH completely exhausted at the end?

You would turn the entire batch into gloop if you tried to allow all the NaOH to make soap by providing it with water to do so. You would get no bio from it.

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2) Would simply drawing a deeper vacuum and distilling the methanol at a much lower temperature be the most viable way to go?

That would certainly help

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Thanks Ant. I will check on mixing the H2(SO4) with methanol

It was suggested to me privately that this could be dangerous so be careful. At the least it will make a difference which you add to which. It may be inadvisable. Check carefully proceed with caution.

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H2(SO4) would be much harder to find

You can buy it 96% or so as 'One Shot' drain cleaner, yellow box, from B&Q here which is like your home depot. The muratic acid you talk about is not 34% concentration over here but around 22% or something.

Sulphuric is actually the cheapest of the acids over here and you need less of it than HCL. Phosphoric is the most expensive and you need more of it than HCL.

Ok I couldn't just leave it in case my suggestion had dire results despite the warning to check.

Methanol, CH3OH, does not undergo dehydration reactions. Instead, in reaction with Sulphuric Acid, H2SO4, the ester, Dimethyl Sulphate, (CH3)2SO4, is formed.

I guess it is the reason FFA are converted to Methyl Ester in acid estrification as it is used to methylate various compounds. It is considered more dangerous than most chemicals in 5 out of 8 sources. It really is very toxic.



concentrated H2SO4 2CH3OH ==> (CH3)2SO4 + ____H2O
__________________Methanol ___Dimethyl Sulphate Water


Under standard conditions, Me2SO4 is a colourless oily liquid with a slight onion-like odour (although smelling it would represent significant exposure). Like all strong alkylating agents, Me2SO4 is highly toxic.

So I wouldn't bother as you will end up with water and a toxic chemical you do not want.

Also in water, the compound is ultimately hydrolyzed to sulfuric acid and methanol so I guess enough water would prevent it's formation. As water is produced when it is made it obviously needs more than that to hydrolyse. The way to achive that would be to use H2SO4 that was not too concentrated to begin with.

Despite my feelings that you should calculates some stuff yourselves I wil tell you that you need less than half conc H2SO4 as conc HCL.

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You would turn the entire batch into gloop if you tried to allow all the NaOH to make soap by providing it with water to do so. You would get no bio from it.

Ya, that's what i was afraid - that was a large amount of catalyst that had not been converted to soap during the course of the normal reaction.

I have a suspiscion that the acid that is being added is only neutralizing remaining catalyst in the biodiesel phase. I don't think it is neutralizing very much (if any) of the catalyst that would be stuck in the glycerin phase - otherwise, how could you explain 100ml of 34%(ish) concentration HCL being sufficient to cause an indicator change (which appears to be at the end point) in 100 L?

I think the best solution is to simply cool it down, use KOH, and draw as deep of a vacuum as possible to distill the methanol off.