The formula used in industry for calculation of free fatty acid percentage is:

FFA% = (v - b) x N x 28.2 / w

where v is the volume in ml of titration solution
b is the volume in ml of the blank
N is the normality of the titration solution
w is the weight of the sample of oil in grams

With NaOH the molecular weight is 40 so a 0.1N solution contains 4g per litre. That is the usual concentration used in industry.

Note that the formula contains 28.2 which is the molecular weight of oleic acid divided by ten. Oils are not made of only oleic acid hence this formula results in small errors, normally accepted. The range of molecular weights encountered in the used oil trade is from 270 for palm to 281 for canola.

For the homebrew titration the concentration of the solution is usually 1/4 of the above, 1g NaOH per litre. Sometimes it is 1g per litre of KOH.

To calculate the FFA from a homebrew titration use the following with a 1ml sample of oil:

FFA% = 0.766 x t for titration with 1g NaOH per litre where t is the volume of solution in ml for 1ml oil
FFA% = 0.546 x t for titration with 1g KOH per litre

Acid Value = 1.99 x FFA%

PS. I have edited this to replace "Tickell" with "homebrew" for reasons outlined below. Note also that the acid value calculated as above will contain some error if it is derived from a FFA% calculation as above. See below.

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

I was skepticle with the oleic divided by ten and such, BUT IT WORKS OUT! I use the formula posted by Okito San a while back to get the AV and divide by 2. I am hoping this proves more accurate with some clues into what FFA's dominate in local waste oils...? dont think it matters too much though...Neutral, what is your take on the importance of separating water out between acid stages in order to attain near 1%FFA before base stage?

Sorry, I meant Kenito Oko.

also known by a bunch of other names on this forum...

Mark

on edit: Neutral changed the offending terminology in his post now, thank you.

**************

could you please stop calling it a Tickell titration! Homebrew titration is more like it, but Tickell had nothing to do with it.



Mark

This message has been edited. Last edited by: girl mark,

Girl Mark,

I know there are some errors in Tickell's book but I do give him credit for being the first to publish a readily available and very full information source to help the biodiesel scene. And he did promote this particular way of doing the titration, which is clearly different from the standard industrial method, and has a scientific advantage.

I am also sure he wouldn't have been the first to do it this way, just the first to promote it widely. He didn't say he invented it.

Perhaps the best thing to do is to call for suggested names for the method. If a good one comes up I would be happy to use it. I am not happy to just call it "titration", as a lot of people do, because it could be misleading as there is this other well established method.

Zac Rouse

You ask: "Neutral, what is your take on the importance of separating water out between acid stages in order to attain near 1%FFA before base stage?"

I take it you are talking about really bad oil, very high in FFA, otherwise you wouldn't mention more than one acid stage.

First you don't really need to get to 1% FFA. If you could get to 3% you would still get a reasonable base stage. There would be losses of course but if you are talking about multiple acid stages you must have some facilities. With the right equipment you can collect your glycerine, acidify it, recover the lost oils and add them to the next batch, so it is not so important in terms of yield. If your are content with 3% FFA then perhaps only one acid stage is needed.

If you must have more than one acid stage you have to think about the ratio of methanol to water. It is not so much the consumption of methanol in the reaction as the production of water that mucks up this ratio. Clearly if you have very bad oil you will either have to remove water or use a huge amount of methanol. At some point it will be easier to remove water than to use so much methanol. Uni Idaho have published some work which should help you decide what FFA is the reasonable cutoff.

Personally I would try to source oil that only needed a base stage, and if that dried up I would stop at oil which needed only one acid stage.

quote:

Originally posted by neutral:
Girl Mark,

I know there are some errors in Tickell's book but I do give him credit for being the first to publish a readily available and very full information source to help the biodiesel scene. And he did promote this particular way of doing the titration, which is clearly different from the standard industrial method, and has a scientific advantage.

I am also sure he wouldn't have been the first to do it this way, just the first to promote it widely. He didn't say he invented it.

Perhaps the best thing to do is to call for suggested names for the method. If a good one comes up I would be happy to use it. I am not happy to just call it "titration", as a lot of people do, because it could be misleading as there is this other well established method.

I know that Australia had a different history, but here in the US there was homebrew biodiesel prior to Tickell. The mistakes which are included in the recipes that he published came partially from Fat of the Land who got it from Dr Tom B Reed at the COlorado School of Mines. Tickell didnt' have two brain cells to rub together as regards chemistry so giving him inadvertent credit for a formula is like calling all acid-base biodiesel methods "Aleks' Method". the parallel is that lots of homebrewers learned about acid-base processes via aleks, and he promoted acid-base biodiesel widely, but you see where the logic parallel is with the Tickell thing, I suspect- neither is responsible for the invention of the technique they're responsible for promoting.

I just use the term 'homebrew titration' when describing Dr Reed's titration. It contrasts with your term 'industrial titration' nicely I think. I sometimes use the term acid value for the industrial titration as well, though that's misleading since the homebrew version is a sort of acid value as well.


Mark

You make a good case Girl Mark. I will avoid the Tickell word in future. You are right to point out that the homebrew method is a kind of acid value. The industrial method is not, and contains the small error described above. Acid value is preferred as it does not make any assumption about the molecular weight of the oil being tested. It simply reports the amount of KOH needed so contains no error. It is proportional to the moles of FFA.

Hmmm, I got the term 'acid value' from two places:

a. ASTM calls the industrial titration results, 'acid value'
b. I read on a petroleum website sometime a great description of 'acid value' and 'base value'- they were talking about why you can't just dip a pH strip into oils, and I WISH I could find the description again as it was very concise and so forth. ANyway, I thought that an titration-based method of determining acidic or basic contaminants in an oil would be called an acid value?

oh, and thank you very much for agreeing with me on the Tickell thing. I really appreciate it, knowing the people who were doing this before Tickell...


Mark

I think after the weekend I'll write up a brief article for the Collaborative describing the two titration options- the homebrew one versus the industrial one, and include your point about the oleic acid error. If you want to I can use your posting above about the differences instead as it's written in less words than I usually use!

In my mind the main reason for being proficient with the industrial titration is that it allows you to replicate a lot of experiments that have been written up in scientific literature, and makes it easier to read the scientific papers on biodiesel.

Mark

neutral, thank you for your response, I really appreciate the hands-on view as the only thing my hands have been on thus far is a couple test batches and some journal articles.

It is probably a good idea to point out that Acid Value has its own definition. It is the amount of KOH in mg needed to react with the acid in an amount of oil in grams. The unit is therefore mg/g. It happens to be numerically roughly 2 times the FFA% because of the mere coincidence that the molecular weight of KOH (56.1) is about 1/5 th of the molecular weight of oleic acid (282).

AV = (v - b) x N x 56.1 / w

where v is the titration volume in ml
b is the blank in ml
N is the normality of the KOH solution
w is the weight of sample in g

A 0.1N solution would contain 5.61g KOH per litre.

So if you are wanting to measure AV you can do it direct using the formula above.

If you do a "homebrew" titration with 1g KOH per litre solution and use 1g oil you could directly find the AV:

AV = h / 5.61

where h = homebrew titration (ml)

If you use the more usual 1ml of oil you have to allow for its density, then:

AV = h / 5.16

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

neutral:

IF it takes me 10 ML of NeOH water to titrate one ml of oil what % of acid does my oil have?
I am using one gram of NeOH per liter of distilled water.
How bad does the oil have to be before you recommend using 2 stages of acid treatment?
Samuel J. Atkins

Samuel, I have shown how to work this out several times and the information does get lost or hard to find, so I eventually decided to start a thread on the subject and list the conversion factors. This is that thread. Have a look at the top.

Re the level of FFA that would be better done with acid/base, I would say about 3%, but it depends on how good a yield you want. If there is plenty of UCO available you might accept the losses and go higher rather than have to go through the extra step. The rule of thumb for base only is the losses are equal to 2.5 to 3 times the FFA%.

quote:

Originally posted by neutral:
Re the level of FFA that would be better done with acid/base, I would say about 3%, but it depends on how good a yield you want. If there is plenty of UCO available you might accept the losses and go higher rather than have to go through the extra step. The rule of thumb for base only is the losses are equal to 2.5 to 3 times the FFA%.

the other reason for choosing acid-base over single stage with some oils, of course, is that the higher the original titraiton, the greater your chance of making emulsion in the wash due to excess soap that's been formed from the FFA's.


Mark

john galt:

My bad. I meant NaOH.

neutral:
Ok I think I got it now. Somehow earlier I miss figured something and got some wild figures.
If I use 14 ml of NaOH water to titrate on ml of oil then I would use 14 X 0.766 which means my oil is 10.724% FFAs?

When I ask”””” How bad does the oil have to be before you recommend using 2 stages of acid treatment?”””” I meant to ask at what % of fatty acids can my oil contain before you recommend doing more then one acid step. I am already using one acid step and the base stage. But I am going to start experimenting with some really bad oil and trap grease and wondering at what point should I use more then one acid step.

Sorry Samuel, I didn't read your question closely enough. With very bad oil you go beyong my experience and ability to calculate. I do not speculate. Perhaps others can help.

from my limited experience:
go lite on the H2SO4 at first. if the formula calls for 2mls/l, start with 1 ml/l. process and wait...ITS A SLOW PROCESS. every hour or so check the titration. when the numbers stop dropping, its possible this might take 12-20 hrs, add half of the remaining H2SO4 to the mix. no more methanol with this H2SO4. its doesn't seem to be necessary. if you put too much H2SO4 in to start with the titration will fall faster and bottom but then start to rise again. you definately don't want this to happen.

small batches are you friend when working with something new

-dkenny

dang, what happened to my post. it was only on for 5 hours then somehow it got deleted.