Biopowered - vegetable oil and biodiesel forum
Biodiesel => Chemistry and process => Topic started by: julianf on January 01, 2013, 07:48:02 PM
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As per the end of this thread - http://www.biopowered.co.uk/forum/index.php/topic,762.0/topicseen.html
...ive been wondering about the amount of methaol used on s1 of the 2stage 'no titration' method.
My feedstock is very variable, and ive had a couple of reactions recently that have not achieved very high conversion on the first stage. Im pretty sure this was due to high titration, as one of the batches i was especially carefull with drying.
Anyhow, i have always considered s1 of the 2stage to be the 'leveler' - to remove all the unknowns and get to a point where s2 can be run without unexpected outcome.
Tony comments in the thread linked to about the glyc possibly taking out the bulk of the meth, which comes back to what ive been thinking about the quantity of meth used on s1.
For example -
If S1 is run with 80% for the batch, but the feedstock titrates unusually highly, then there will be limited catalyst and excess meth. If the glyc at the end of s1 takes out the bulk of the meth, then s2 (if only the remaining 20% is used) would work out limited by the methanol.
I have been thinking that possibly a much much more limited s1 may be advantageous, with regard to methanol consumption.
With my next batch, i think i may do somthing like -
200ltrs of feedstock
aim to react, say, 50 ltrs on s1, so add
15% of 50ltrs of methanol (7.5ltrs)
5g of naoh for 50 ltrs (250g) (or possibly more?)
on s2 i would probably use 15% methanol for the unconverted, and a further 5g / ltr of naoh.
When i initially started using the 2stage no titration method, i aimed to get as high a conversion possible on s1, so as to reduce the error (and possible soap formation) on s2. But since then, ive realised that soap formation does not seem to be my main enemy - i would rather focus my attention on reducing the methanol used.
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I think on VOD we'd worked out that approx 50% remaining Meth is dropped in the Glycerol phase.
However, if you use the Glyc for Glyc pre-wash, or do WBD with the s1 Glyc back in, does it really matter as the Meth is effectively recovered and used anyway?
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i guess not, but, with the glyc pre-wash, do we actually know how much meth moves over to the feedstock, and how much remains in the glyc?
when you consider that methanol and triglyceride dont mix, im doubtful as to a high percentage moving, but possibly its carried over with the residual methylester (which is, in turn, soluable in the triglyceride)
i wonder how all that works!
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Hi all
Going on my experience the bio production uses 12.5-14% total batch volume meth depending on oil used, the bio holds on to between 2-3 % tbv
So on a 100L batch of oil + 20L meth
S1
80% meth = 16L
Meth used = 10L
Meth in bio about 2L
Meth in Glyc about 4L
If it was me I would try with just 20% meth to start with but I would make sure I have some good clean Glyc from earlier batch to mix in after reaction or the Glyc produced may settle.
This way a small % reduction in s2 works out to be much more the if the remaining meth is only 20% tbv.
Paul
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I do 200L batches and add 25L meths + 1000g NaOH on the first stage,
then only 20% meths for the amount of dropout in the second stage,
I normally get around 2.5ml dropout, so around 50L left to convert,
that's around 35L of fresh meths + what ever is left after gly prewash.
As to how much meths stays in the gly when prewashing,
all I can say is the gly is very thick and gloupy when it's drained,
but runny enough to be sucked in via venturi to start with.
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To save you getting calculators out, that's 12.5% for stage 1, total usage 17.5%.
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I do 200L batches and add 25L meths + 1000g NaOH on the first stage,
then only 20% meths for the amount of dropout in the second stage,
I normally get around 2.5ml dropout, so around 50L left to convert,
that's around 35L of fresh meths + what ever is left after gly prewash.
As to how much meths stays in the gly when prewashing,
all I can say is the gly is very thick and gloupy when it's drained,
but runny enough to be sucked in via venturi to start with.
Mark I know you like to experiment..
Would you try 30 Litres in stage one and then 5 in stage 2. ? Same total but I think you may stretch to 85 % maybe a touch more conversion from stage 1. Just a gut feeling that stage 1 may be stalling due to the amount of Meth.
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Here's a thought, if s1 at 12.5% stalls due to lack of Meth, presumably there is no point in re-introducing that Glyc back for WBD? Might reduce process costs for those that WBD.
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Here's a thought, if s1 at 12.5% stalls due to lack of Meth, presumably there is no point in re-introducing that Glyc back for WBD? Might reduce process costs for those that WBD.
Now that is a thought....
With the Meth thing when I started doing 2 stage I kept increasing stage one Meth % until it was clear the reaction had stalled due to using all the caustic up and not low on Meth. My findings came out at about 15% Meth for stage 1 and I only ever needed to add another litre or 2 just to mix stage 2 caustic to complete the reaction.
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Presumably the problem with stalling on Meth for s1 is not knowing what is required for s2, is it more catalyst or just more Meth? How much of each?
What happens if all the catalyst goes into s1 but it stalls due to lack of Meth?
Does dropping the s1 Glyc take all or part of the catalyst with it?
We have to assume that some catalyst travels with the Glyc otherwise Glyc pre-washing wouldn't give a partial conversion.
Catalyst is the part of the reaction with the least cost associated, maybe we could:
- s1 - 12.5% Meth, 100% catalyst
- drain glyc, no need to demeth this glyc as hopefully all the Methanol was used up!
- s2 - remaining Meth only, mix
- do 10/90 test for completion
- add appropriate catalyst to complete (ASM or minimum amount of Methanol just to dissolve it)
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Hi all
Going on my experience the bio production uses 12.5-14% total batch volume meth depending on oil used, the bio holds on to between 2-3 % tbv
So on a 100L batch of oil + 20L meth
S1
80% meth = 16L
Meth used = 10L
Meth in bio about 2L
Meth in Glyc about 4L
If it was me I would try with just 20% meth to start with but I would make sure I have some good clean Glyc from earlier batch to mix in after reaction or the Glyc produced may settle.
This way a small % reduction in s2 works out to be much more the if the remaining meth is only 20% tbv.
Paul
For your s1 do you use 80% catalyst based on titration?
Interesting that only 10% is used in the reaction for your s1 (presumably measured by doing a 10/90?)
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I use 12% methanol for each stage.
Albeit I do use Sodium Methylate though which adds some methanol.
In my case, on 300 litre batches, I use 35litres of methanol (almost 12%) on the first stage along with 6 litres of methylate.
Dropout is normally between 1 and 2ml in a 90/10 test so meaning 10% to 20% unconverted (ie 30 to 60 litres).
12% on the second stage therefore works out between 3.6 and 7.2 litres (rounded up to nearest whole litre) and 600 to 1200ml of Methylate making a total of 39 to 43 litres of methanol per batch and around 7 litres of Methylate.
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I use 12% methanol for each stage.
Albeit I do use Sodium Methylate though which adds some methanol.
In my case, on 300 litre batches, I use 35litres of methanol (almost 12%) on the first stage along with 6 litres of methylate.
Dropout is normally between 1 and 2ml in a 90/10 test so meaning 10% to 20% unconverted (ie 30 to 60 litres).
12% on the second stage therefore works out between 3.6 and 7.2 litres (rounded up to nearest whole litre) and 600 to 1200ml of Methylate making a total of 39 to 43 litres of methanol per batch and around 7 litres of Methylate.
They are good figures,
including the Methanol in the Methylate your completing on 14.6% methanol to 16%.
14.6% is very good. I assume this is because you are using ASM on very well prepared oil.
I prepared my last batch of oil much more thoroughly than usual and reckon I could have also reduced Methanol percentages. (note to self..."must try harder")
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I use 12% methanol for each stage.
Albeit I do use Sodium Methylate though which adds some methanol.
In my case, on 300 litre batches, I use 35litres of methanol (almost 12%) on the first stage along with 6 litres of methylate.
Dropout is normally between 1 and 2ml in a 90/10 test so meaning 10% to 20% unconverted (ie 30 to 60 litres).
12% on the second stage therefore works out between 3.6 and 7.2 litres (rounded up to nearest whole litre) and 600 to 1200ml of Methylate making a total of 39 to 43 litres of methanol per batch and around 7 litres of Methylate.
I have used these figures with fantastic results. Best conversions ever.
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I use 12% methanol for each stage.
Albeit I do use Sodium Methylate though which adds some methanol.
In my case, on 300 litre batches, I use 35litres of methanol (almost 12%) on the first stage along with 6 litres of methylate.
Dropout is normally between 1 and 2ml in a 90/10 test so meaning 10% to 20% unconverted (ie 30 to 60 litres).
12% on the second stage therefore works out between 3.6 and 7.2 litres (rounded up to nearest whole litre) and 600 to 1200ml of Methylate making a total of 39 to 43 litres of methanol per batch and around 7 litres of Methylate.
I have used these figures with fantastic results. Best conversions ever.
Do either of you WBD or recover any Methanol ?
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I do 200L batches and add 25L meths + 1000g NaOH on the first stage,
then only 20% meths for the amount of dropout in the second stage,
I normally get around 2.5ml dropout, so around 50L left to convert,
that's around 35L of fresh meths + what ever is left after gly prewash.
As to how much meths stays in the gly when prewashing,
all I can say is the gly is very thick and gloupy when it's drained,
but runny enough to be sucked in via venturi to start with.
Mark I know you like to experiment..
Would you try 30 Litres in stage one and then 5 in stage 2. ? Same total but I think you may stretch to 85 % maybe a touch more conversion from stage 1. Just a gut feeling that stage 1 may be stalling due to the amount of Meth.
I used to use 32L in the first stage, 25L with the NaOH and then 7L after (I mix the methoxide in 25L drum so it's easier),
one day I forgot to add the extra 7L and didn't notice any difference, so I just carried on with only 25L.
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Hi all
Going on my experience the bio production uses 12.5-14% total batch volume meth depending on oil used, the bio holds on to between 2-3 % tbv
So on a 100L batch of oil + 20L meth
S1
80% meth = 16L
Meth used = 10L
Meth in bio about 2L
Meth in Glyc about 4L
If it was me I would try with just 20% meth to start with but I would make sure I have some good clean Glyc from earlier batch to mix in after reaction or the Glyc produced may settle.
This way a small % reduction in s2 works out to be much more the if the remaining meth is only 20% tbv.
Paul
For your s1 do you use 80% catalyst based on titration?
Interesting that only 10% is used in the reaction for your s1 (presumably measured by doing a 10/90?)
Hi Tony
My description is a bit confusing (sorry )
It was mainly to say that although there is meth in the Glyc there isn't as much as people think as most of it does get used in the reaction.
Will have another go at a explanation when I have a bit more time.
Paul
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Do either of you WBD or recover any Methanol ?
No, I dont recover any methanol at all. I reused the glycerol for glyc wash (which gets some of it back) but water wash the bio (using the titrated in-processor method) so dont get anything back from the bio. That is why I try to minimise the amount I use in the first place.
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I do 200L batches and add 25L meths + 1000g NaOH on the first stage,
then only 20% meths for the amount of dropout in the second stage,
I normally get around 2.5ml dropout, so around 50L left to convert,
that's around 35L of fresh meths + what ever is left after gly prewash.
As to how much meths stays in the gly when prewashing,
all I can say is the gly is very thick and gloupy when it's drained,
but runny enough to be sucked in via venturi to start with.
Mark I know you like to experiment..
Would you try 30 Litres in stage one and then 5 in stage 2. ? Same total but I think you may stretch to 85 % maybe a touch more conversion from stage 1. Just a gut feeling that stage 1 may be stalling due to the amount of Meth.
I used to use 32L in the first stage, 25L with the NaOH and then 7L after (I mix the methoxide in 25L drum so it's easier),
one day I forgot to add the extra 7L and didn't notice any difference, so I just carried on with only 25L.
Steve, to follow up on this, I have recently started using 25L of meth and 800g of NaOH in my first stage,
so I may not be adding the 30L of meths but I have reduced to catalyst,
this has so far reduced the total NaH used on average,
so yes you were right, the reaction did seem to stall due to the unbalance of chemicals.
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Here's a thought, if s1 at 12.5% stalls due to lack of Meth, presumably there is no point in re-introducing that Glyc back for WBD? Might reduce process costs for those that WBD.
By no means conclusive but on the last 2 batches I did using acetone. The first was just a bio demeth without the second stage drained, the second a WBD and there was little difference in the meth recovered.
160L batches 25l 800g NaOH stage 1
Dick