one for Neutral:

I was working with a couple of peopel from Rachel Burton's and Leif Forer's Biofuel Class tonight on converting industrial titration instructions to figure out how to deal with impure KOH.

ONe piece of info I was using came from Neutral posting in the following thread: http://biodiesel.infopop.cc/eve/forums?a=tpc&s=447609751&f=629605551&m=933108762

quote:

---

neutral wrote:
You don't make it clear in your method where you refer to 0.1 KOH that it is meant to be 0.1N KOH which is 5.611g KOH per litre. That is how you do it in the industrial process.
(snip)
If using NaOH for the reaction you would use 4g NaOH per litre to make a 0.1N solution for the above method.

---

I was talking after class with a couple of chemist types who were in the class and for some reason we were confused about where you get 5.611g from.One problem we were having was that the woman doing the calculations was used to thinking in molarity rather than normality (is there a 1:1 relationship between the two for KOH, by the way?), and it's possible that we had some other calculation mixed up earlier on. It's possible that we'd gotten ourselves confused at this point because it was rather late in the day, but could you post how one arrives at this number?

Thanks!
mark

Girl Mark, I don't think they were chemist types you were talking to but some kind of ring in. A 1N solution of KOH is the same as a 1 molar solution. A 1 molar solution of anything contains 1 molecular weight expressed in grams per litre. the molecular weight of KOH is 56.11 so a 0.1N solution contains 5.611 g per litre.

It gets a bit more complicated with something like sulphuric acid, H2SO4, because it contains 2 hydrogen atoms which it can give up per molecule. So a 1 molar solution of sulphuric would be 2 molar in hydrogen ions. There can be no such confusion with KOH and NaOH. The molecular weight of NaOH is 40 so you can see where the 4g came from.

Thanks, I see now.

Never underestimate the ability of a small group of people... to hopelessly confuse each other.

so how do you think we should be dealing with impure KOH? the issues I see are whether the inert material in the impure KOH (I sometimes use 85%) would have any effect on the titration. I understand your argument about why industrial process isn't as accurate as the volume-based method that Dr Thomas B. Reed came up with (what we homebrewers use), but if we want to experiment with industrial or lab processes from scientific papers etc, it's really useful to follow their processes fully to eliminate possibility of errors.

My hunch is that for the proper acid value titration, one should get pure KOH for the titration reagent, and not bother with making the reagent out of your impure working material (ie the 85% or 90% or whatever) and calculating the changes. What I'm worried about is the makeup of the various impurities and how much they would throw off your reagent's behavior in a titration- in the homebrew, volume-based titration it doesn't seem like it would matter, but in the industrial one it seems like it would. Of course there's quite a bit of variation on the amount of catalyst we can get away with using for our actual reaction, so variations on the titration kind of fall into the range of this variation.
Mark

GM,
If your titration solution was made from the "impure" KOH, the titration would give the correct amount of catalyst for the reaction to proceed to completion.
The only problem I see is where the impurities contribute to, or interfere with, the reaction giving undesirable reaction products.

nitpick department... titration isn't for catalyst quantities, it's for 'ffa neutralising' quantities of lye.

I'm concerned about the differences not so much for the part of the process where you figure out how much extra caustic to add, but for situations where you're using acid value measurement to work on acid-base stuff a la' the ISU techniques, where the amount of ffa (as determined byu this acid value measurement) dictates how much methanol and sulfuric acid to use.

quote:

---

Originally posted by Tony from West Oz:
GM,
If your titration solution was made from the "impure" KOH, the titration would give the correct amount of catalyst for the reaction to proceed to completion.
The only problem I see is where the impurities contribute to, or interfere with, the reaction giving undesirable reaction products.

---

anyone?

Mark

Girl Mark

The first thing to note re titration prior to sulphuric acid/methanol treatment is that it is not as critical as for the base reaction. In the base reaction you really have to get the FFA neutralized or your catalyst will be reduced. We know that there is a side reaction which destroys the catalyst and if you don't use enough the reaction will stop.

In the acid reaction in contrast there is not much unwanted side reaction, if any, so the amount of acid catalyst used is not so important - if you use too little acid the reaction won't stop, it will just take longer.

How your impure KOH will perform depends on what the impurity is. If it is sand or KCl it won't interfere - you will just use more in proportion to the known purity. I'm surprised your commercial KOH is only 85%. Isn't there anything better available?

Neutral, in this lovely country of ours I have bought both 90 and 92% KOH at varying times, I prefer the 92% as for any given dollar I use less of it, 2% in fact!

Anyway enough frivolity, the other 15% would start to concern me actually.