Biopowered - vegetable oil and biodiesel forum

Biodiesel => Chemistry and process => Topic started by: Bio-boy on July 26, 2015, 06:44:41 PM

Title: What causes excessive soap???
Post by: Bio-boy on July 26, 2015, 06:44:41 PM: Is it too much Catalyst or water? Is it a combination of the two?
Some of my batches create more soap than others and I'm just trying to understand what is causing it to further hone my processing in the future.
Title: Re: What causes excessive soap???
Post by: julianf on July 26, 2015, 06:59:01 PM: Soap is caused by sapponification. Thats water + caustic and oil.

So, always water, but the water can come from different places -

there at the start
there from neutralisation of the FFAs (acid + base > salt + water)
there from mixing the methoxide (im not so sure of the chemistry behind that one)

So, the soap production should correspond to the quantity of 'catalyst' needed (which corresponds to the FFA content, or, indeed, the amount of water present at the start of the process)

You can conclude this by titrating - this will tell you if your catalyst is being used up by simple sapponification, or by the neutralisation reaction, and subsequent sapponification.
Title: Re: What causes excessive soap???
Post by: Bill on July 26, 2015, 08:11:58 PM: Quote from: julianf on July 26, 2015, 06:59:01 PM
there from mixing the methoxide (im not so sure of the chemistry behind that one)

NaOH + CH3OH => NaCH3O + H2O (the numbers 3 and 2 are written as subscripts, below the line)

NaCH3O is methoxide.
Title: Re: What causes excessive soap???
Post by: Julian on July 26, 2015, 08:15:57 PM: NaOH + CH₃OH => NaCH₃O + H₂O

Bill, there are superscript (sup) and subscript (sub) buttons in the middle of the second row of buttons above the reply text box.
Title: Re: What causes excessive soap???
Post by: Tony on July 26, 2015, 08:23:30 PM: Quote from: julianf on July 26, 2015, 06:59:01 PM
there from mixing the methoxide (im not so sure of the chemistry behind that one)

More on that here:

http://www.biopowered.co.uk/wiki/Methoxide#A_note_on_water
Title: Re: What causes excessive soap???
Post by: Bill on July 27, 2015, 07:45:47 AM: Heeeyyy, learn something everyday. Thanks Julian.

NaOH + CH₃OH => NaCH₃O + H₂O
Title: Re: What causes excessive soap???
Post by: dgs on July 28, 2015, 12:03:35 AM: There are two ways to considerably reduce the production of soap in the biodiesel reaction.

1 Use ASM as the catalyst.

2 Do not add any methoxide until you know that all the FFA's are neutralised. This is easily achieved by enhancing the glycerol during the pre-wash stage. I use @ 30% glycerol for the pre-wash and as my oil only titrates at about 1.0 I only have to add a small amount of methanol to the glycerol to achieve complete FFA neutralisation. Because this neutralisation has been done in the presence of glycerol any water formed is absorbed by the glycerol. This procedure works very effectively at reducing soap formation and a considerable reduction in catalyst usage.

Having read through the above again I think it maybe a little confusing. The glycerol I add will easily neutralise the FFA's without any additional methanol, the reason I add it is to achieve a considerable amount of additional conversion. Anything up to 25% in fact.

From testing I have done there seems to be up to @ 3.8 gmsKOH/litre of glycerol that can be used in the pre-treatment. The conversion during the pre-treatment is obviously more efficient if the KOH/methanol ratio is as needed by the reaction, hence adding more methanol to the glycerol.