Processing with anhydrous sodium methylate
This page gives a guide to making biodiesel from anhydrous sodium methylate (ASM), a liquid catalyst which can be used in place of the more conventional sodium hydroxide or potassium hydroxide catalysts.
Calculating how much to use
A lot of clever people have gone through a lot of complex calculations to work out the correct amount of ASM to use. However, a certain James Leach from the Vegetable Oil Diesel forum has simplified pages of complex organic chemistry down to a simple, single line equation
- mL of methylate = ((Base Amount + Titration Value) X Batch Volume in Litres) X 5
This is based upon the use of a 0.1% sodium hydroxide titration reference solution (ie the normal 1g of sodium hydroxide in 1 litre of de-ionised water that most of us use and also known as lye water).
A good starting point for the base figure is 5.0 although clearly the base figure is adjustable and can be tweaked to get as low as possible whilst maintaining good results.
- ((5.0 + 2.0) X 150) X 5 = 5250mL of methylate
Whilst it is perfectly possible to use a single stage reaction for making biodiesel, many brewers are now taking advantage of the benefits of the two stage process with no titration with it's reduced chemical usage, reduced soap production and better yields.
Methylate lends itself nicely to the two stage process with no titration and the base figure can often be reduced somewhat.
For the first stage of the process, the formula is
- mL of methylate = (Base Figure X Batch Volume) X 5
A conversion test, be that 3/27, 5/45 or 10/90 is then done to identify the remaining unconverted litres in the batch
The second stage formula is then
- mL of methylate = (Base Figure X Unconverted Litres) X 5
Several brewers, including myself, have achieved very good results using a base figure of 4.0 for both stages.
As a worked example, using the same 150 litre batch as the single stage example, a base figure of 4.0 and an assumed fallout of 2.0mL in a 10/90 test gives
- First stage : mL of methylate = (150 X 4.0) X 5 = 3000mL
The 2.0mL of fallout in the 10/90 suggests that 20% of the 150 Litre batch or 30 Litres remain unconverted
- Second stage : mL of methylate = (30 X 4.0) X 5 = 600mL
This demonstrates the significant saving in chemicals of the two stage process, giving 3600mL for the two stage instead of 5250mL for the single stage, a 31% saving and is based on real world results I have seen in my own processor.
The ease of mixing is without doubt the best feature of mixing sodium methylate. Using conventional solid catalysts is a labour intensive process. Whilst potassium hydroxide flakes dissolve relatively easily in methanol, sodium hydroxide micro pearl is more trouble and full sized sodium hydroxide pearl requires significant effort.
Mixing sodium methylate and methanol is an almost instantaneous process, comparable to mixing fruit cordial with water since both are liquids.
Reducing the methanol volume
The second advantage of using methylate is that around 70% of the fluid is actually methanol. This means that less methanol needs to be added to the batch. Conventional wisdom has been around 20% methanol using solid catalysts whereas using sodium methylate this can be reduced significantly.
In my own processor, using the two stage no titration process, I have seen perfect 10/90 tests using just 12% methanol in each stage.
A real world example
For the first stage: Methanol volume = 12% X 150litres = 18 litres, methylate volume = 5 X (4.0 X 150) = 3000ml
For the second stage, which has 30 uncoverted litres: methanol volume = 12% X 30litres = 3.6 litres, methylate volume = 5 X (4.0 X 30) = 600ml
Giving a total of 21.6 litres of methanol and 3.6 litres of methylate
The pros and cons of using anhydrous sodium methylate
- Mixing it with methanol is as easy as making orange squash
- Being a liquid, there is no corrosive dust to worry about
- Being around 70% methanol, using methylate requires less methanol in the batch
- Methylate is considerably more expensive than solid catalysts although this can be offset against methanol savings
- Availability is still an issue although this is improving
Julesandtash 21:11, 15 September 2012 (BST)