Checking your NaOH titration solution.

[DavidA]

Hi,

I understand that after a while it is advisable to discard your titration solution and make up a fresh batch (Litre). It takes up Carbon Dioxide from the air, or something like that.

But how do you check the quality of the old stuff. I assume you titrate it with HCL.

How about using a PH meter ?

I will replace my old NaOH titration solution, but I'm always curious about things like this.

Dave.

[RichardP]

If you want to see how it's changed then make up the new solution then titrate the same oil separately with the old and new solution. Will give and idea of if/how much it is off.

Not titrated oil for donkies years now, just use the no titration method.

[countrypaul]

NaOH solution will absorb CO2 for form NaHCO3 (bicarbonate) or Na2CO3 (carbonate), if it is in a properly sealed appropriate container then there will be very little CO2  to absorb - but everytime you open it more will get in.

You could titrate it with HCl as suggested but that will measure both NaOH and the carbonates so should give you the original concentration rather than just the current NaOH.

If making up a fresh solution you need to make sure that the NaOH has not already absorbed CO2 as that will result in a weaker solution than anticipated.

What would you use a pH meter to try and measure? Sodium carbonate and Sodium bicarbonate are both alkaline, if trying to equate pH to the concentration of NaOH left you would have to make up a series of solutions at different concentrations and work out from plotting those where the actual strength lay. Chances are that you pH meter would not be accurate enough and that the change in pH would be insignificant as you have created a buffer solution with the carbonate present.

If the FFA present in your oil reacts with bicarbonate or carbonate you may find that titrating the oil with NaOH solution that has been around a while gives the same result as freshly made up NaOH solution - but it may not.

Least risky appraoch is to just create a fresh solution using good NaOH

[nigelb]

Unless you have access to lab grade titration fluid...forget it. You are complicating a relativley simple process.

I'm not entirely sure why you are producing in such small ammounts David but maybe you need to scale up and simplyfy

[dgs]

You've got your 10/90 tube (I assume) so forget titration, it is a quite inaccurate test anyway with fading endpoints and masked colour if using dark oil.

2 stage no titration any day.

[DavidA]

The reason I am doing small test batches is that the last four have failed. And I need to find out why before proceeding.

I never used to have this problem. So something has changed.

The thing I have against the 'no titration' method is that estimating the initial amount of NaOH to use (first stage) is a bit hit or miss. If you don't add enough you do not get the bio  required to calculate the amount required to complete the reaction.  Add too much and you risk jelly. This leaves you adding incremental amounts until the bio appears. If you have no idea of the condition of the oil, even though it looks clear and apparently has no water in it when heated up to 110C, you are making a blind guess at the amount of NaOH to start with.

It should be easy. Let's posit an example.

You have a litre of dried clear oil. You do a titration and it is quite high, say 6 Gram/ Litre indicated.

You are feeling generous so you are going to use 4.5 Gm/Litre + titration (6 Gram) to 200mL Meth. So 10.5 Gm/litre.

This should work.

Using the no titration method you could take a stab at 4.5 Gram for the first stage (holding back some of the meth).

This should give you a 10/90 test that showed you needed 6 Gram + the remaining meth.

Remove the glyc, add the 6 gram and the meth mix and it should give a clear 10/90 pass after the second mix.

The result should be the same as if you had done the reaction with the normal titration method.

Am I correct ?

Anyway, I have some new chemicals. So I am going to make up a new titration solution and try a different batch of oil.

[dgs]

The reason I am doing small test batches is that the last four have failed. And I need to find out why before proceeding.

I never used to have this problem. So something has changed.

The thing I have against the 'no titration' method is that estimating the initial amount of NaOH to use (first stage) is a bit hit or miss. If you don't add enough you do not get the bio  required to calculate the amount required to complete the reaction.  Add too much and you risk jelly. This leaves you adding incremental amounts until the bio appears. If you have no idea of the condition of the oil, even though it looks clear and apparently has no water in it when heated up to 110C, you are making a blind guess at the amount of NaOH to start with.

It should be easy. Let's posit an example.

You have a litre of dried clear oil. You do a titration and it is quite high, say 6 Gram/ Litre indicated.

You are feeling generous so you are going to use 4.5 Gm/Litre + titration (6 Gram) to 200mL Meth. So 10.5 Gm/litre.

This should work.

Using the no titration method you could take a stab at 4.5 Gram for the first stage (holding back some of the meth).

This should give you a 10/90 test that showed you needed 6 Gram + the remaining meth.

Remove the glyc, add the 6 gram and the meth mix and it should give a clear 10/90 pass after the second mix.

The result should be the same as if you had done the reaction with the normal titration method.

Am I correct ?

Anyway, I have some new chemicals. So I am going to make up a new titration solution and try a different batch of oil.

No, you are not correct. Years ago 'Neutral' found that there is a  disproportional effect caused by water formed by neutralising higher titrating oil. He found that an extra factor needs inserting (as infopop has gone the info isn't to hand) but it was something like increasing the titration by 1.2 for titrations over 3 or so.

If after titrating and processing a single stage the bio is checked with a dropout test and under conversion found then you can't re-titrate meaning you have to proceed using the dropout test anyway to calculate chems for S2.

You can get an approx titration figure by mixing 50/50 oil and distilled water and checking with litmus, i used to do this in the past and it does work.

Glyc wash your oil instead of heating to remove water. If your glyc is solid then use Potassium or at least a mix of pot and sod.

Years ago I decided never to process oil with any positive titration. You've seen my outside IBC where I do multiple glyc washes, all at ambient, leaving the oil about 20% converted. Even when I had insufficient glycerol I used to enhance it with a little methoxide, a method that works really well.

Hope this helps, Dave.

[countrypaul]

The reason I am doing small test batches is that the last four have failed. And I need to find out why before proceeding.

I never used to have this problem. So something has changed.

The thing I have against the 'no titration' method is that estimating the initial amount of NaOH to use (first stage) is a bit hit or miss. If you don't add enough you do not get the bio  required to calculate the amount required to complete the reaction.  Add too much and you risk jelly. This leaves you adding incremental amounts until the bio appears. If you have no idea of the condition of the oil, even though it looks clear and apparently has no water in it when heated up to 110C, you are making a blind guess at the amount of NaOH to start with.

It should be easy. Let's posit an example.

You have a litre of dried clear oil. You do a titration and it is quite high, say 6 Gram/ Litre indicated.

You are feeling generous so you are going to use 4.5 Gm/Litre + titration (6 Gram) to 200mL Meth. So 10.5 Gm/litre.

This should work.

Using the no titration method you could take a stab at 4.5 Gram for the first stage (holding back some of the meth).

This should give you a 10/90 test that showed you needed 6 Gram + the remaining meth.

Remove the glyc, add the 6 gram and the meth mix and it should give a clear 10/90 pass after the second mix.

The result should be the same as if you had done the reaction with the normal titration method.

Am I correct ?

Anyway, I have some new chemicals. So I am going to make up a new titration solution and try a different batch of oil.

I agree with what Dave has said, but also there is a flaw in your logic.

If the oil titrates at 6 but you only used 4.5 (1st stage) then you may get no bio at all as all the caustic could be used in neutralising the FFA producing soap. You will also have produced a significant amount of water (each 4g or NaOH will give you 1.8g of water). The presence of water will catalyse the formation of more soap, that is the presence of water will cause more oil to be converted to soap rather than bio. A stage 2 using another 4.5 could well be the equivalent of using just 1 or 2 for making bio.

If you oil comes from a different source to usual, or your source has changed the way  they work, for example filtering the oil and using it for longer then it is always worth carrying out Dr Pepper test first.

Removing the FFA before trying to process is the best approach and most easily done by glerol washing the oil, this removes the water, most FFA and many of he other impurities that can adversely affect things. The glycerol wash may have to be repeated with another fresh load of glycerol if the oil has a high FFA content as the remianing caustic in the glycerol may not be enough to neutralise all the FFA in the oil. Alternatively, as Dave suggest, you could enhance the glycerol wash by adding caustic to the glycerol before hand.

One of the great benefits of using ASM is that it does not produce water, so if used to neutralise the FFA the by product is methanol. It is expensive and means using a glycerol wash first to remove water and FFA makes a significant saving. If water is present in the oil when you use ASM you will produce NaOH and then produce soap and more water. Unfortunately ASM is very difficult to get hold of now and is probably even more expensive than it was.

 

[DavidA]

Today I actually thought that I had cracked this problem.

I recalled that yesterday, when the Sun was out, the troublesome bottles did start dropping some glyc. But towards the evening the glyc had disappeared.

So, I thought. It needs heat.

Lit the stove and put on a large container of water. Stood one of the bottles in the water for about two hour. By then the water was at 62C. The oil would have been a bit lower. But we don't want any boiling methanol.

I found that now I had plenty of glyc. about 200 mL. So drained it off. Did a 10/90 test. No dropout at all.  But there was jelly showing in the bio.

Having no drop out didn't tell me much at this stage, so I decided to force some drop out by adding a bit more oil to the mix. I added 100 mL.

Shook it  all up, put it back in the hot water.

A little bit of glyc dropped out. and the next 10/90 just showed a very small bit of oil in the bottom of the glass.

The bio looked good. That's it. next thing will be washing. maybe tomorrow.

Came back an hour later when it had cooled down and the whole thing was jelly.

All the troublesome samples came from the same batch of oil. I'll try again with a different batch.

Meanwhile I'll study the comments from you guys.

[DavidA]

Dave (dgs),

..Glyc wash your oil instead of heating to remove water. If your glyc is solid then use Potassium or at least a mix of pot and sod...

The oil was virtually water free when heated up to 110C. no bubbles.

[DavidA]

Thinking about this glycerin wash.

Do you think, as an small-scale experiment, the following would work.

Assume two litre of oil. and a three litre bottle.

Heat the oil to 65C. put it in the reactor (bottle), add 400 mL of glyce from a previous brew.

Shake vigorously over the next hour or so. Keeping the reactor warm.

Allow to settle. Drain of the glyc.

Titrate as normal.

[countrypaul]

Thinking about this glycerin wash.

Do you think, as an small-scale experiment, the following would work.

Assume two litre of oil. and a three litre bottle.

Heat the oil to 65C. put it in the reactor (bottle), add 400 mL of glyce from a previous brew.

Shake vigorously over the next hour or so. Keeping the reactor warm.

Allow to settle. Drain of the glyc.

Titrate as normal.

That should work.

A rule of thumb is that the volume of glyc you get is equal to the volume of methanol used (assuming a good reation). So if using methanol as 20% vol of oil, for 100L of oil you would expect 20L glyc or 200mL for 1L oil. So using 400mL for a glyc wash should do fine.


One word about heating oil to 110C, you will need to blow air through the oil to actually remove the water, simply heating it up to 110C won't work on a large volume.

[dgs]

Dave, from expts I have done, well settled oil 850ppm water and after a glyc wash 350ppm. Add as much glyc as you can, as the bio tied up in the glycerol by the soap (for every litre of soap made it takes 2 litres of bio with it into the glycerol) will rather stay with the oil than the glycerol.

adjust your oil/glyc ratio so when you titrate after your glyc wash it is as far towards zero as possible.

[DavidA]

Paul,

I always briskly stir my oil when heating it up for de-watering.

I did an article years ago on Infopop concerning the formation of steam bubbles in a pan of oil if it wasn't kept moving. Emphasizing that the temperature of the oil at the bottom of the pan is greater than the temperature higher up. And this can lead to steam explosion if the bubble reaches the surface. I did precede it with a health warning.

Dave, I'll keep that in mind.

I'm close to finishing the building of my new bio shed. It will be a relief to be able to separate the bio gear from the rest of the workshop.

[DavidA]

Tried the small scale experiment I mentioned above. Here is the result.

From a drum of eight year old oil. Oil was quite clean.
Took out two x two litre batches.

Did a titration on one (NaOH) and got 28 drops (1.4 mL) result. Used this sample to do a 2 litre Dr Pepper using 180 mL meth and 4.5 Gram NaOH plus titration per litre. So, 360mL Methanol and 11.8 gram NaOH.

Glyc is dropping out nicely.


I decided to gly wash the other 2 litre sample. Heated it up and added 430 mL  glyc.  Shook vigorously for a while. Let it stand.

Did a titration and used 20 drops (1.0 mL) NaOH Titration solution.

So the titration had dropped from 1.54 mL to 1mL.

So it seemed to work.

I'll do a Dr Pepper on that sample tomorrow.

I should add that I find counting drops easier than using a pipette for small amounts. My dropper drops 20 to 1 mL.