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Full Conversion Without Processing.

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September 24, 2014, 02:58 PM
Dgs
Full Conversion Without Processing.
About 2 weeks ago I topped up my 1000 litre IBC with biodiesel for the central heating.
I don't bother to process to full conversion for this,and the last 500 litres had .25 mls with 10/90 test. (2.5% unconverted oil).
The previous 400 litres I pumped in had (from memory) 1.5% unconverted oil.

I don"t know what posessed me to do this but I did 2x 10/90's today, top and bottom of the tank.
Both tests were completely clear?

The bio had been left in my large processor several days for all the glycerol to drain.
It is not de-methed and there is no sign of any glycerol in the IBC bottom.

I also tested the soap levels; Tank top 900ppm. Tank bottom 4000ppm.

The other strange thing is that the bio is a much lighter colour than it was when processed.
I know I am not imagining this,it is Considerably lighter.

I realise this looks as though some conversion has taken place since it was pumped into the tank,but how could this be?

Does anyone have any thoughts on this please.
September 24, 2014, 05:06 PM
Biotom
If there was sufficient temp and chemicals left behind the transesterfication could have continued on the unreacted portion.


" I don't know what I don't know until I know"
1994 GMC 6.5 Tubo 2005 Dodge ram 3500, 3 VW's 2000, 2002, 2005.
October 06, 2014, 11:30 AM
WesleyB
A chemistry professor at a college here said something like, as a general rule of thumb for each 10 degree rise in temperature in some organic chemistry reactions, the reaction rate doubles. So if I react vegetable oil at 65 degrees it reacts twice as fast as at 55 degrees (centigrade), or four times as fast as 45 degrees, or eight times as fast as 35 degrees, or 16 times as fast as 25 degrees, or 32 times as fast as 15 degrees. There are exceptions to this rule, but I don't know exactly what they are. There's also something called activation energy for a reaction, which roughly translates into a minimum temperature necessary for a reaction to proceed significantly. I don't know what that temperature might be for the transesterification reaction of methanol with vegetable oil using the caustic catalyst. Maybe someone else could tell me more about activation energy for making biodiesel.
October 06, 2014, 12:04 PM
Dgs
Thanks Biotom and Wesley,
I think there must have been a reaction in the processor after it was all shut down.

I recently processed another batch for the c/h in my large processor. This is heated initially by a M67 in an adjacent metal drum. The drawback with this is it cannot be re-heated by the M67 with methanol present.

This last batch was 80% converted after the 1st reaction.
I did the second reaction the next day,it needed 1000gms KOH.
I added 1100gms.the reaction temperature was 20degs C.

After 45 mins I did a 10/90 which to my suprise was totally clear. I assume that at this temperature doing a full reaction could take @ 20 hours, so why this @ 20% reaction took place in 45 mins I don't know.
I realise I overdosed it by 100 gms but on 540 litres, would not think this was significant.

I have found when I do my low temperature reaction for road fuel that there is an emulsified layer (2-3 litres) after water washing which is not present when I react at 60degs.
I have always assumed this to be the result of an excess of mono and diglycerides due to the lower (40degs C) reaction temperature.

When I have done my low temperature reaction(at the moment I don't do this as I am trying the Maurice Mynah process) I heat the oil to 30degs C,add the methoxide then the exothermic properties of the reaction take the temp up to @ 40degs C.
October 06, 2014, 10:04 PM
Tilly
Hi Dgs,
A few things you need to keep in mind.
The Rule of thumb is that at 50C a normal reaction takes about an hour.
For every 10C the temp is reduced the reaction time doubles.
So it would look something like this
50C- 1 hour
40C- 2 hours
30C- 4 hours
20C- 8 hours

However, you were doing a reprocess.
About half the oil remaining to be converted will be triglycerides with most of the rest diglycerides and just a small amount monoglycerides.

There is also a lot of biodiesel acting as a co-solvent to help get the reaction going quicker.

I am assuming the batch size was 540 litres and you do not mean that 20% of the batch is 540 litres of oil remaining to be reacted in the reprocess.
If you had 80% conversion on a 540 litre batch, that works out to 108 litres oil remaining to be converted.
Reprocessing 108 litres at 8g KOH per litre works out to 864g KOH required for the reprocess.
Also, I assume you were trying to determine the remaining unconverted oil by using the warnqvest test.
As we all know, the Warnqvest test substantially overstated the amount of oil remaining to be converted so you had actually used a large excess of chemicals in the reprocess.

With all these things taken into account, it is not surprising that the reprocess went quickly.

quote:
Originally posted by Dgs:

This last batch was 80% converted after the 1st reaction.
I did the second reaction the next day,it needed 1000gms KOH.
I added 1100gms.the reaction temperature was 20degs C.

After 45 mins I did a 10/90 which to my suprise was totally clear. I assume that at this temperature doing a full reaction could take @ 20 hours, so why this @ 20% reaction took place in 45 mins I don't know.
I realise I overdosed it by 100 gms but on 540 litres, would not think this was significant.

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






October 07, 2014, 05:43 AM
Dgs
Thanks Tills.
October 07, 2014, 09:06 AM
Tilly
Hi Dgs,

quote:
Originally posted by Dgs:
Thanks Tills.
It is always a pleasure when I can help someone better understand what they are doing when making biodiesel.

That brings to mind this statement you made:
quote:
When I have done my low temperature reaction(at the moment I don't do this as I am trying the Maurice Mynah process) I heat the oil to 30degs C,add the methoxide then the exothermic properties of the reaction take the temp up to @ 40degs C.[/i]
I was talking to "Neutral" (the PHd chemist) a few years back and I mention that the trnsesterification reaction was exothermic (gives off heat).
Much to my surprise he said that he thought it was slightly endothermic (takes up heat).
I thought "What would he know, he is only an industrial research chemist with his own Commercial laboratory and 30 some years experience in alternate fuels R&D."
So I did some further research on this and blow me down, he was correct! That is why the reaction cools down over time.

However, there have been many reports of an initial temperature increase when the methoxide is added. I have even observed that after adding the methoxide to my reactor the temperature increases (but more like 5C instead of 10C that you report).
So what causes this temperature rise?
My theory (which I have never checked with a chemist) is the converting FFA's into soap causes the initial increase in temperature.

After reading the above statement of yours, I decided to do a test to quantify more carefully what happens.
To a litre of 30C WVO (titration probably 1- 2 KOH) I added 200ml of 30C methoxide containing 10g KOH, shook hard and suspended a thermometer in the oil.
After 5 minutes the oil temp had risen to 33.5C
Shook hard.
After another 5 minutes the oil temp was 34.5C
Shook hard
After another 5 minutes the temp was 34C
Shook hard
After another 5 minutes the oil temp 33.5C
Shook hard
After a further 15 minutes the temp was 33C

I continued checking in 15 minute intervals and the temp continued to fall in 0.5 increments. until I stopped checking at 31.5C

The ambient air temperature at the time was 29C

I concluded that the initial spike in temperature was likely caused by the neutralization of the FFA's.
It is probable that higher titration oil would give an increase in the temperature rise.
This might be something you would like to perform some further tests on

It was also another confirmation that the neutralization of the FFA's happened quickly.

Any time I can be of further assistance, do not hesitate to ask for help.






October 07, 2014, 10:54 AM
Dgs
Tilly,
This was the really bad oil,remember me asking you about other Tri's derived from animal fats. For some reason it needs a base of 9.0 K even though neutralised and water <500ppm.
This is why I overdosed.

Will report later re exothermic reaction.
October 07, 2014, 12:21 PM
WesleyB
Yes, Tilly neutralization of free fatty acids by KOH in alcohol solvent is exothermic. I reacted stearic acid with KOH that was dissolved in anhydrous isopropyl alcohol. I didn't suspend a thermometer in it, but I could feel by touching the flask it was in that it was warm, above room temperature 20-30 minutes after I mixed the chemicals.
October 07, 2014, 01:15 PM
Dgs
Wesley and Tilly,
I normally have experianced this rise in temperature when I have reacted oil that has been glycerol pre-washed but not neutralised.
At 30degs C I would add hot methoxide and the temp would creep up to 34 degs.
After a while it would increase by another 5 to 6 degrees.

Todays batch (which I will report in more detail on the accerated conversion thread) had neutralised oil (titrated at zero)
I added the methoxide at exactly the same temp as the oil,32degs C and over the next 15 mins the temperature rose by 3 degrees. It then stableised so I started the immersion.