We have had good results with our process of recycling Methanol from the Esterification reaction. I would, however like to hone in on the amount of Sulfuric Acid we add to each batch.

We are able to recover and recycle about 12% Methanol with each batch. This recycled methanol has some amount of Sulfuric Acid catalyst still dissolved in it. I would like to determine roughly how much Acid is present, so that I know how much I need to add to bring the total Acid up to 5% by weight of FFA.

Let me know if that made sense- and any help would be greatly appreciated.

Thanks,
Nick

Titrate with KOH solution.

I'd like to know about this also, DKenny and I have talked about it a lot as there is a need to determine the purity of 'storebought' drain cleaner .

However, the concentrations we're talking about and the ones you're seeking to determine are different, so there should be a different concentration of KOH needed for the titration.

Mark

Does this still have some water in it?

girl Mark, et al-
I'm glad there is interest in this topic. I will try to consult our analytical chemist friend, and get back to y'all.

Dropout-
This recycled Methanol should have- at most- 2% water. I have a hydrometer on order, so I should know more precisely within a few days. Why do you ask?

-Nick

I do'nt think a hydrometer would work because you have two or three variables at play contaminating the methanol:
water
sulfuric acid
FFA

We can determine by titration that there's sometimes (or always?) sulfuric acid in methanol that floats to the top or sinks to the bottom after an esterification reaction.

However, unreacted FFA is methanol-soluble and might also end up in the methanol layer, so you can't just assay the acid in the methanol via titration, assume it's just sulfuric acid, and then calculate what effect that might have on specific gravity.

Water would of course also affect the SG of the methanol.

I'm guessing a Karl Fischer unit would test for water in methanol without being affected by the sulfuric acid, salts, or other stuff in that methanol? Anyone know the answer to that?

girl Mark-

I have passed on your comments to a friend of our's who teaches analytical chem at UCONN. Hopefully, he can clarify.

I am glad you mentioned the (f)utility of the hydrometer. I did not want to assume this without having first tried to measure the SG. I have a feeling that contamination (FFAs, etc.) will not play as big a role as you think. I may be wrong but, I think that FFAs may coalesce into a large insoluble mass that I am seeing in the Methanol layer. I have not yet determined what it is exactly. But it looks and acts much like fat. It does not, however, titrate- possibly due to insolubility in our titration solution.

If this is the case, I can get a clean sample and compensate the SG measurement based on sulfuric acid concentration, as you say. Otherwise, I am at a loss as to how to determine both water contamination and acid concentration.

-Nick

Wouldn't the sulfuric acid, FFA, and methanol cause esterification? Or is the acid too weak from water?

Bob

I would speculate that if you're using some distillation process to extract the methanol from
the water, acid, and methanol mix. you'll also leave the acid behind. because of the boilind points of the acid and methanol.

if you're not distilling, I would still suspect there's not much acid in the methanol. I don't know for sure but I would think the acid is a larger molceule than the water which in turn is larger than methanol.

-dkenny

Here is the initial response from my professor friend. I will try to learn more from him and post it here when I can.

quote:

Hi Jim-

Thank you for elaborating. I am familiar with the potentiometric titration as you mentioned, as well as the color-indicator titration. A concern that I have, as my colleague suggested, is the contamination of the methanol/acid solution with Free Fatty Acids. I am assuming this would throw off the titration value, and give a false indication of Sulfuric Acid concentration. What are your thoughts on this?


Hi Nick,

I would have to try a few samples. Sulfuric acid is a strong acid and should give one the first break in a potentiometric titration curve. And if the FFA are weaker acids and have approx. acid dissociation constants of less than about 3-0rders of magnitude then there should be a second jump in the titration curve. That is something I would look for. (e,g. Titration of both sulfuric acid and acetic acid mixture is given in most standard analytical chemistry textbooks.

As for determining purity of an unknown acid solution (such as drain cleaner), that should be relatively simple. Proceed with color-indicator titration as per usual, then calculate percent acid based on the molecular weight of the particular acid compound. If the solution is comprised of sulfuric acid (and other unidentifiables- blue beads or silver sparkles or magic beans), then use the molecular weight of sulfuric acid- 98.08 g/mol. The process is much the same for determination of FFA%. Here's the formula:

% Acid = (v - b) x N x M / w

whereas;
v = volume of titrant (mL)
b = blank (mL)
N = normality of titrant (mol/L)
M = molecular weight of acid (g/mol)
w = weight of sample (g)

Mark,

Here is the professor's response to your question about Karl Fischer.

quote:

Yes, Karl Fischer is an acceptable method to analyze for water in methanol. As I remember it is done in base, i.e. pyridine. I am not sure that it would work in the presence of sulfuric acid. I used to have a book on Karl Fischer reagent but that is a long time ago. And I suspect that it is long gone.

I know that doesn't help much but, I'll see if I can fish around for more information.

-Nick

quote:

As for determining purity of an unknown acid solution (such as drain cleaner), that should be relatively simple. Proceed with color-indicator titration as per usual, then calculate percent acid based on the molecular weight of the particular acid compound. If the solution is comprised of sulfuric acid (and other unidentifiables- blue beads or silver sparkles or magic beans), then use the molecular weight of sulfuric acid- 98.08 g/mol. The process is much the same for determination of FFA%. Here's the formula:

% Acid = (v - b) x N x M / w

whereas;
v = volume of titrant (mL)
b = blank (mL)
N = normality of titrant (mol/L)
M = molecular weight of acid (g/mol)
w = weight of sample (g)

[/quote]

Thanks for posting this
I been wondering how to determine the strength of the drain cleaner acid I use in acid/base processing.

-dkenny