Glyc Prewashing

[simonallen]

Hi Guys,
New here but i've been doing a lot of reading :-) And I have a quick question.

When processing Bio it is my understanding that only a course filter is required of the oil before processing? If this is right, and the rest of the "stuff" drops out with the glyc, do I have to filter the glyc afterwards to get rid of the dropout before I use it to prewash my next batch of bio?
Starting on my GL processor build today or tomorrow, so will be getting to process some fuel in the coming weeks.

Thanks in advance 

[K.H]

After glyc washing dispose of it then use the glyc from the batch you have just glyc washed to do the next one

[Tony]

A few bits in the oil won't do any harm, although with a closed impeller pump they can cause a blockage; open impeller (like the TAM105) is fine.  Julian suspects they may carry water with them which is detrimental to the chemical process.  But yes they will drop out with the generated glyc, and settle to the bottom of that glyc over time.

[simonallen]

cheers guys

[Julian]

...  Julian suspects they may carry water with them which is detrimental to the chemical process.  ...

Stole my thunder!

Make that "strongly" suspects.

[dgs]

The bits of debris could well hold water, however the ability of glycerol to absorb water is massive. Ex-process glycerol contains roughly 1% water, yet will still reduce the water in oil from 800ppm to 350ppm. Even glycerol at 4% water will still reduce dissolved water in oil.

If glycerol is still present after glyc washing (in other words if it is not all drained) it has a positive effect on the process if the oil still has a titration. As water is produced from the FFA neutralisation it is consumed by the glycerol present and reduces saponification. I am pretty sure this is why the AAF method works so well. When oil is added to methoxide, glycerol is produced earlier in the reaction.

A while ago imakebiodiesel on infopop did some experiments where he added 2 litres of glycerol in the processor with the oil and methoxide, resulting in lower soap levels and lower KOH requirements. He got really good results even with non glyc washed higher titrating oils.

[willbuild]

I get a reduction of 10 to 15% of Kohl used when I do a glycerol pre wash with high titrartig oils

[dgs]

Hi willbuild,
Yes, the glycerol pre wash is a really efficient thing to do. Have you ever titrated your oil after the pre wash. What I would recommend you try if you are using higher titrating oil is enhancing the glycerol. If your oil titrated at (lets say 5.0 KOH )
If you add 50% of the titration as gms/litre KOH, so 2.5 gms/litre into 2 to 3 litres of methanol. Mix this with your glycerol before adding to the oil.

After the pre-wash you should find the oil has no positive titration, all the FFA's have been neutralised 'in the presence of glycerol' which means any water produced from neutralisation has been absorbed bt the glycerol. You should find that your process is even more efficient.

The oil I usually have titrates very low, @ 1.0 KOH, so I don't have to add KOH to the glycerol but I still add methanol and I use a lot of glycerol for the pre-wash. 60 litres of glycerol, with 5 litres of methanol into 190 litres of oil.

After the pre-wash I usually have around the 25% conversion level. 7.5 mls dropout with 10/90.
The 5 litres of added methanol is then deducted from the methanol amount for the 1st 'normal' reaction. I now use a mamimum of 14% methanol using this method, and have had the added methanol amount down to just over 12%

[1958steveflying]

dgs.
     If you are using 60 litres of glycerol for 190 litres of oil to you have a source of glycerol ? 190 litres oil oil wont produce 60 litres of glycerol, or does your process ?

[dgs]

Hi Steve,
Yes, my process creates nothing like the glycerol that I add. I have a few local friends that are only too happy to give me their glycerol. They don't pre-wash even though I have told them about the benefits.

I look at it that they are giving me their residual chemicals for free.

I'm sure it is a physcological thing when you've not done it before, adding horrible looking black glycerol to nice clear oil.

From testing I have done, the pre-wash process uses @ 3.8 gms of KOH/litre of glycerol. Of course there are many variables. As to the methanol used out of the glycerol, I don't know.

Unless the oil you are using is very wet, the glycerol can be used several times and in that case would benefit with some methoxide enhancement.

The important thing is that after the pre-treatment process the oil will not titrate ie it is alkaline. This means that when the methoxide is added there will be little or no wastage of chemicals used up making soap.

A while ago as an experiment I glyc washed 30 litres of oil that titrated at 21 KOH. I used 30 litres of enhanced glycerol and ended up with 27 litres of oil that titrated at 0.3 and was <500ppm water. The power of glycerol.

[willbuild]

Am processing a 100 Ltr batch of high tit oil. 15gr of Kohl per ltr using Dr  pepper test gave me 82% conversion.
I have another 100 ltrs of the same oil that I will try the wash with the meth and kohl method.
l will post my results in a few days time.

[dgs]

Wow! lots of KOH. What does your oil titrate at.

[willbuild]

This bacth, 15grs 1st stage 85% conversion added 300grs to get a clear pass.
Total 1800 grs for 100 ltrs.

[dgs]

if you glyc washed this batch then the chemical requirement means it still titrated at something like 10. With a FFA level so high the liberated water level will be high, something like 0.3%, so its like pouring 300 mls of water into your processor when you add the methoxide.

Your oil must titrate at something like 15 before you glyc wash. You will still be able to reduce the titration to nil using the enhanced glycerol technique, but one of the problems will be that the glycerol from your process will be very wet to start with. You will have to add more than 30 litres to have any chance of getting the water down to less than 500ppm.

Have you ever considered caustic stripping.

[willbuild]

Have plenty of glycerol, so that isn't a problem
If my oil titrates at 10 is it 5gr per litre in the glycerol wash?
I have not heard about caustic stripping, where can I read up on it?
Thanks for your help.