Some recent thoughts about glycerol pre-treating.

[dgs]

Just some thoughts about the pre-treating and related things.

First the enhanced glycerol pre-treat proceedure. - If we assume a 100 litre batch using 16% methanol then after conversion this leaves about 3.5% methanol. with the 80/20 split between glyc/bio of this residual methanol (assuming 16 litres of glycerol produced) this gives us about 17.5% methanol left in the glycerol.

Because of the nature of the reaction (excess methanol needed) I think that the ratio of catalyst to methanol left in the glycerol is too high for any significant conversion to take place.

Adding a small amount of methanol ( 1.5 to 2 litres with the above amounts) to the glycerol usually gives a significant conversion during the pre-treat. (assuming low titrating oil)

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David Shinn mentioned this next point to me. He had been getting poor conversion and lots of soap. Even after drying his oil and glyc pre-treating.
He came up with the idea that if the oil isn't dry enough the glycerol pre-treatment will produce more soap because water, catalyst and oil are all present. In his case he found the pre-treatment was counter productive to the reaction. Very wet glycerol and dry oil (I assume) would give the same result.

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I'm sure we all realise how much bio/oil can be absorbed in the glycerol. I have recently had some remarkable amounts of oil absorbed by the glycerol after a pre-treatment. I glyc washed 200 litres the other day, to go into my 'glyc washed' tank ready for the c/h. Average, well settled oil, 200 litres plus 140 litres of glycerol, used for washing once before. Mixed at about 50 degs in my M67 tank.
Realising how some oil migrates to the top I left it in the tank for 24 hours, then cubied out the glycerol.

For the 1st 48 hours nothing happened then the next day there was a 1" layer of oil on the top of each cubie. Another 1" after the next 24 hours.
I set up a 400 litre conical in my polytunnel, poured in the glyc/oil and now, 1 week later I have 35 litres of nice oil sitting on top of the glyc.

I will let all my used glyc settle like this in future before pouring it in the ibc for Trinity to take.

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I once tried doing a glycerol pre-treatment in an IBC during Winter at ambient temperature. The oil in question had a high proportion of palm in it. Needless to say it didn't work, when I ran out the mix some 4 months later the glycerol was still suspended in the oil.

I tried it again the other day with 180 litres of my best oil plus 80 litres of ex process glycerol. Temp of oil/glyc was about 15degs. Well, it worked and worked really well. Seemed to split faster than if it had been warmed. I haven't done any tests on the oil but it looks really good.

[Manfred]

I've experienced similar. Using NaOH I've had to melt the glycerol to do the prewash. So the day after a batch I heated the oil to 50c added 18L of glycerol and left it running. After 2 hours settling I started draining the glycerol out through out the day. I was shocked to get about 22L. Over the next few days it slowly solidified. Upon moving the cubie I saw I had about 4.5L of clean oil sat on top. Easily poured off and added to the reactor.
 One thing that did happen though. I forgot to drain off before I went to bed. Next morning upon opening the bottom drain no oil. I thought it was the glycerol but then a slug of soap slowly came out into my jug after which was oil. So not all of the soap comes away with the glycerol.

[dgs]

I recently did some soap tests on glyc washed oil that showed no conversion. The levels were suprisingly high.
I'm sure a situation could arise where someone who re-titrated after glyc pre-treating on higher titrating oil could get a false low titration because of residual soap.

Just regarding my 1st post, the glycerol from the 100 litres of oil would roughly contain;

17.5% methanol- 2.8 litres
At least 4% water- 640mls
3.1% glycerine- of the original 100lts of oil --3.1 litres
Some tied up bio, lets call this 2 litres.

The rest? well, most of it has to be soap, all 7.5 litres of it!

Soap pre-wash anyone?

[Tony]

After reading this thread I've done a batch where I've thrown in the recovered methanol from the final stage of processing the last batch (which I heat to 90C+ so may contain some water) into the glycerol.  Not only does this make the glycerol considerably easier to suck into the processor (it's much thinner) but it seems to have given more of a conversion.

Previously when I've tried re-using methanol recovered at such a high temp I've had issues, presumably due to water content.

I will try a few batches this way - so far I'm liking the feedback process of taking the distilled methanol and using it to methanol starve preprocess the first stage.

[Manfred]

So are you adding all of your reclaimed meth to the glycerol so that it helps with the catalyst to pre process before the first stage.

[Manfred]

Last year I was adding some of the reclaimed meth to the glycerol (NaOH) but only to keep it semi liquid untill next batch. I tried seeding the glycerol wash as Dave suggested but found I used less NaOH by just basic prewash. This year I use all of my reclaimed meth for the first batch. It might be worth doing as you are as I didn't really take any notice before, just when the quantities went up.

[dgs]

As I use an absolute minimum of methanol (13.5% max) my glycerol doesn't contain much methanol, so If I pre-treat with this then the oil doesn't usually show any conversion. If I add about 3 litres of methanol to the 20 litres of glycerol then pre-treat the 200 litres of oil, the 10/90 shows about 9 mls.

It can be counter productive to add too much methanol as the glycerol will absorb a lot of it.

My best results are with my friends glycerol where he uses lots of methanol and KOH. When I have collected about 40 litres from him and used this plus my glycerol, so total 55 litres with 200 litres of oil I have had conversions of around 25%

Adding some reclaimed methanol could be good as the glycerol will absorb the excess water.