Hello everyone,

I was wondering if anyone knew
what role methonal plays in the process
of making BD.

I do know it causes some kind of
chemical reaction with the oil base used
however what I would like to know
is

What is methonals actual purpose?
What happens if you put to much or not enough
in your batch.

Everywhere you look on the internet
about making BD they are all saying use
200ml per litre but why?? why not use 10ml
per litre???

Any comments would be greatly appreciated.

Cheers!

quote:

Originally posted by DWE:
Hello everyone,

I was wondering if anyone knew
what role methonal plays in the process
of making BD.

I do know it causes some kind of
chemical reaction with the oil base used
however what I would like to know
is

What is methonals actual purpose?
What happens if you put to much or not enough
in your batch.

Everywhere you look on the internet
about making BD they are all saying use
200ml per litre but why?? why not use 10ml
per litre???

Any comments would be greatly appreciated.

Cheers!

Biodiesel is basically Fatty Acid Methyl Esters. A triglyceride (vegetable oil) has three Fatty Acid Molecules that are separated from the glycerol backbone during the reaction. What happens to those three fatty acid molecules is that they are converted into METHyl esters by "combining" with three METHanol molecules. This Methanol is actually consumed by the reaction and can not be recovered.

To make sure the reaction proceeds in the correct direction (i.e towards completion) then an excess of methanol is used this excess is normally in the region of 75 to 100%.

Now fatty acids have varying different molecular weights so the actual amount of methanol that a homebrewer uses is a little bit of a compromise and basically what it works out at (based upon molecular weights) is a methanol requirement of on average 20 to 25% v/v so 200 to 250ml/litre. There are some people who can use less but they are typically well experienced and still probably can't go much below 150ml or maybe even 170ml/litre. The excess methanol can be mostly recovered, some is in the biodiesel but most is in the glycerol phase.

So in answer to your question, why not only use 10ml of methanol/litre , well you would not make much, if any, biodiesel if you only used that small amount.