Acetone as an aid to transesterification
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Summary of learned paper by thewormman 24-01-2013
Quick summary of what I understand from this paper
http://pubs.rsc.org/en/Content/ArticleLanding/2011/GC/c1gc15049a
A few quotes
Quote
How can we accelerate the formation of FAME in the reaction between the immiscible oil and methanol? One approach is to accelerate the reaction by heating and another is to accelerate it by increasing the contact interface by forming small reactant droplets through vigorous stirring by ultrasonic irradiation.
Heat and agitation the norm for processing now.
Quote
the reaction can still only take place at the interface between the immiscible reactants present in the heterogeneous phases. If the FAME formation takes place in a homogeneous phase, the reaction can be accelerated by a molecular-molecular reaction.
In english!
immiscible = doesnt mix heterogeneous = Diverse in character or content homogeneous = Of the same kind; alike
So the reaction only takes place where the surfaces touch and since the reactants are different they do not mix well, a bit like globules
of oil in water. By making them mix well ie adding acetone which dissolves into the oil and FAME, the mixture allows the oil globules to
break down to a molecular level. This means there is much more surface area for the reaction to occur. ie: faster So heat and agitation is
not as important, hence lower reaction temp required.
Quote
we have concluded that the retardation of FAME formation after the formation of GL can be explained as follows: in the case without solvent, or with acetone or THF, GL cannot be dissolved in the oil or FAME, but methanol and KOH catalyst dissolve well in GL. Therefore, FAME formation is retarded after the formation of GL due to the dissolution of the important reactant methanol and the catalyst into the GL phase, which easily precipitates and is excluded from the reactant solution.
So reaction slows as the methanol and KOH catalyst is taken out of the FAME in the GL(Glycerol) Acetone does not dissolve in GL so the Acetone stays in the FAME as the GL is formed.
Quote
With acetone, which does not dissolve GL, the separation of FAME from GL was very fast because of the lower viscosity of the FAME-acetone solution and the large difference between the low-density FAME-acetone solution and GL.
Acetone rich FAME has a lower viscocity so the GL drops quicker
Quote
Therefore, in the presence of acetone, the difference in specific gravity between FAME in acetone (0.8395) and GL with one mole of excess methanol (1.111) is 0.2715. Due to the large difference in specific gravity and small viscosities of the two components, GL was rapidly separated from the FAME solution and precipitated within 30 min.
So thats my take on it had to get it off my chest!
Opinions?
Test by 1958steveflying 20-01-2013
Saturday I made a 180 litre batch that had been glyc washed and venturi dried to 65c. At 65c I added 30 litres Meth with 750g KoH and 1 litre Acetone. My first 90/10 showed 45% unreacted and after a further 30 minutes reacting the next 90/10 showed 15% unreacted. I settled for 30 minutes and dropped the glyc. over the next hour I added 50g with 1 litre meth to mix then 50g then 60g to get a clear pass.
So 180 litres reacted to clear pass with 910g of KoH with 33 litres methanol and 1 litre Acetone.
After demeth I settled over night and dropped 3 litres glyc giving a total of 25 litres of glyc dropped.
The glyc dropped from stage 1 had only a tiny amount of bio in the following day whereas it would normally have about 2 inches in the cubie, so had dropped quickly and split well.
Test by Carrington 23-01-2013
Just a quick one Did micro batch 600ml Titrated at .4 used a base of 3.5 ASM then used 75% of needed catylist
20% meth 20% acertone
Heated to 25c Mixed for 1.5-2 mins
Got a 94% conversion Gota go will report more later
Paul
Dr pepper test by Dickjotec 26-01-2013
Not very scientific but I did a Dr Pepper. 1L oil at 30c 200ml meth with 4 .5g NaOH dissolved in it. the left hand bottle had 100ml acetone. shook both for 30 seconds then left. The acetone started to react quicker but not appreciably so. left overnight in a warm place. The results are below
As I hope you can see the acetone has produced less glyc and a better conversion.
Full scale test by Dickjotec 26-01-2013
I have completed a batch using acetone and while it could just be an unusual batch I am very impressed. Normal 2 stage for me. Dry oil by heating and settling. 160L in processor. Stage 1 30l meth 5.5 base 900g NaOH 1hour mix Stage 2 Fallout typically 3 so about 280g Meth about 9L
About 35L of glyc and 145L bio and 14L reclaimed meth WBD
Today 25L meth. 800 NaOH 1.5L acetone Fallout 1.5 5L meth 130g NaOH Good pass
Glyc 25L bio 160L meth reclaimed 8L just from bio.
So 10+ L less glyc 15+L more bio. Next time I will cut the chemicals down more and then start adjusting the times. Very impressed so far. The glyc has not set yet and I suspect that there is meth in it. Next time I will WBD. Dick
