make sure your oil and methanol are very dry. The esterification process will not tolerate much water.

Perhaps you could write up a brief step by step of what you are doing and post it here? It might help to pinpoint any mistake you may be making. You might even notice yourself.

I am sure my oil is dry. As for my methanol, not quite sure how to check that. It should be dry, as it has been kept in a sealed drum, in a cool dry place. Well, as cool as you can get in south Louisiana It is in a covered building, but there is no climate control. How do I go about testing my methanol for water? Heat some to 65c, boil it off and see what is left?

Hello Marc_s

Go to your favourite home brew shop and buy an Alcoholmeter Tralles. This is a hydrometer calabrated in % ethanol. The SG of methanol and ethanol ar so similar that for our purposes the reading is valid for methanol as well. Just float it in a sample of methanol at whatever temperature it is calibrated at.

Marc,

Another way you can test your methanol purity is to weigh 1 liter. If pure it should weigh 793 grams.

Water weighs 1000 grams, so you can do the math to come up with a percent purity (assuming the only other component is water).

Bob

Hello bob

At what temperature should a litre of methanol weigh 793g?
Does one litre of water actually weigh 1000g at the same temperature?

20 deg C is the norm for all such lab tests.

1000 g. is for distilled water, mineral content could sway that a tad…I suppose altitude could be a factor as well…

For what we are concerned with that would be very sleight.

A proper hydrometer would include a temperature scale as well, for compensation. Readings will be off a bit at different temps with a hydrometer too.

Thanks for pointing that out.

Bob

An alcoholometer will likely be inaccurate with temperature change also. A straight out hydrometer might be more useful, as it will give directly the specific gravity, which can be correlated to composition more easily than trying to work it out from the % compositions on an alcoholometer.

According to Perry's Chemical Engineers Handbook, methanol density is 791.7 g/L at 20 degrees. At 10 degrees (celcius) it is 800.9g/L

You cannot work out the density of a solution in the manner you suggest Bob. It is not a linear relationship.

methanol_density.JPG (60 Kb, 48 downloads) methanol/water density chart

Thanks for that info Troy.

Do we need to be that accurate with what we are doing?

Bob

It depends on what you are doing really. But when a 10 degree temperature difference can allow a ~5% composition difference at the same density, then it is certainly important to at least have the information available.

There are situations where it might be significant. For example if you are measure your methanol at say 30 degrees, or 25 degrees, and your hydrometer is calibrated to 20 degrees, you might think you have 99% methanol, when you really have 95%. And you're acid stage might fail.

It might also result in someone thinking they have contaminated their methanol, if they measure it one cold morning when it's only 5 degrees, and the next time they measure it, the temp is 20 degrees.

In regards to the linearity of the relationship, it probably doesn't matter that much, but if you have the data, why not use it

Yes, I agree...it's good to have the perspective of accuracy, and what the variables are.

Temperature is one place I like to be consistant.

Thanks,

Bob

Hello Troy

Ethanol has an SG of 0.789 at 20 deg C and 0.772 at 40deg C
Pure Water has an SG of 1.000 at 4deg C.
My alcoholmeter tralles is calabrated in % ethanol by volume at 20deg C. This assumes that the only two liquids in the mix are Ethanol and demineralised water. No maths is required.

I guess it depends on how accurate we are talking. The 1 or 2% difference between methanol and ethanol is probably outside the accuracy of the hydrometer anyway

Hello Troy
The SG of ethanol is 0.789 at 20deg C
The SG of methanol is 0.7915 at 20deg C
If I am not mistaken, that means you would multiply the reading you achieve on the Alcoholmeter Tralles by 0.996 to arrive at the methanol purity.
So a reading of 99% would actually be 98.6% methanol
A reading of 95% would actually be 94.6% methanol
The difference would not make much difference with most home brewing and is very quick to do.

Yes they are pretty close. I wouldn't imagine getting 1% accuracy with an alcoholometer (at least, not with the one I have for home brew).

When I graphed them together earlier, I stupidly used the data from 0 degrees for the methanol, and 20 degrees for the ethanol, which ended up in a disparity of about 7% (composition difference). When I realised and corrected my mistake it is about 0.7% at 100%.

Wow! Great response! I have to tell you, I have learned more here than in my chem 102 class ) Thank you all for your input. This forum is great. I will definitely be purchasing a Tralles soon. I did have some progress yesterday. I decided that I did not process my acid reaction long enough. So, I took some of the oil that I tried to do the other day and after heating the oil to 54c it titrated @ 5.5ml Naoh. This is good because I started with 7.5. So, the titration did come down 2ml. Although, this is nowhere near what I need to do a base reaction, it is progress, lol. I am guessing that I put too much acid into that particular batch. I used 3ml. Maybe if I had added less, my titration would be lower still. There are some different opinions out there as to how to determine amount of acid to use. Also on when and how to add the acid. After combing the threads I have deducted that adding the acid to the methanol is the preferred method. As for how much acid to add, I have yet to find a common way of doing it on here. You seem like a bunch of smart fellas, smarter than me anyway so, I put that question to you.

What is the best method to determine what amount of acid catalyst to use?
Considering that the methanol and oil are both dry )

Thank you again,
Marc_S

Hello Marc_S

For oil titrating 7 NaOH, 1ml H2SO4 per litre of oil should be fine. And you are correct, the more H2SO4 you use in the Acid stage, the higher your titration will be at the end of the acid stage and the more NaOH you will need in the Base stage.

Hello Tilly

Thank you for that info. I will try that. I really enjoy corresponding about this subject, but on the other hand, is there a way to calculate how much acid to use? That way I would not have to keep bothering you each time I need to use acid esterification. ) Not that I do not appreciate all you have helped me with. I must say your contributions to this forum are great. I am just a sponge, soaking up the knowledge of the universe, lol. But, like any other sponge, I can only hold so much. Anyway, I just would like to know if there is a reliable method of figuring this, so I do not have to do too many trial batches to get it right.

Thank You,

Marc_S

Hello everybody!!

I was reading the last posts and had a question, what do you do with the water that's produce during the esterification??

I esterificate and get like a 10%(from the total amount of oil) of water...another important thing is that if I measure the %FFA when the oil/methanol/acid is mixing it's higher than when I measure after a rest period and elimination of water...so what do you thing about this???

I think this is because the acid stays with the water so when I eliminate the water the esterificate oil have less amount of acid and the measure of %FFA is better because I am really quantifying only the change in FFA and not the remaining acid...

Hello Tilly!

Great News!!

I retitrated the oil today that I had

quote:

So, I took some of the oil that I tried to do the other day and after heating the oil to 54c it titrated @ 5.5ml Naoh. This is good because I started with 7.5. So, the titration did come down 2ml.

I reacted this oil for another 2 hours last night and let it settle today. I just cheched it and it is titrating at 4.5. I believe I have found my problem. Problems.

1. Not enough reaction time.
2. Too much H2SO4.
3. Do not have a gyrotherm, . Although, I saw one on ebay pretty cheap without a stirrer magnet.

The latter is not as important as the first, but I think I will get it worked out. Thank you for all your help. Hopefully one day I will be able to contribute at least something useful here.

Thanks to ALL who helped me with this problem.

Marc - The sulfuric acid is a catalyst. Basically what this does is make the reaction "easier" for the molecules, so they have a greater chance of reacting. Thus is simply speeds up the reaction. Catalysts are not consumed in a reaction by definition, so they do not need to be strictly maintained at a certain ratio with other reagents (although there will be an optimum loading to give the fastest reaction rate). Generally - to a degree, adding more catalyst will increase the reaction rate. The loadings required are really found through experimental testing, it's not as simple as just doing calculations (the values for the calculations that can be done, need to be found experimentally anyway).

That said, if you wanted to maintain a constant catalyst loading, you could potentially increase the acid you add, proportionally to the amount of FFA. So if your mean FFA content gives a titration of 7.5, and you use 1mL of acid per litre of oil, then you could use 1.33mL/L oil if you titrate at 10. I would refrain from going below your average amount of acid, as since the amount of alcohol/oil are not changing, the acid concentration will drop, which may slow the reaction too much.

Quemala - water is the limiting factor in this process. It is the water that prevents the reaction from going to completion and consuming all of the FFA. There are devices that can be used to remove the water whilst you are processing, but nothing on a production scale will be practical for the majority of home brewers. The only thing I could suggest would be a multi-stage process similar to the base/base procedure.

Regarding you're titration. I would suggest it is because you are removing your acid catalyst along with your water. The acid catalyst will react with the NaOH/KOH in your titration, so you will get a higher titration number if your acid is still present. I would suggest that you probably have the same amount of FFA's present unless a fairly long amount of time has passed between the two titrations being conducted.

cheers

Troy