Notes for GL's Biodiesel Quiz #3


The base amount of NaOH or KOH catalyst to use per litre of oil is not a precise figure. It depends on several variables, most importantly how dry your oil is, how thoroughly and aggressively you mix the reactants, the amount of methanol you use and the temperature and duration of reaction.

The dryness of oil is probably the most important variable, because wet oil will encourage soap formation, which will quickly consume your catalyst, leaving less avalable for the reaction. It also depends on the purity of the catalyst. KOH tends to be less pure and more variable in purity than NaOH.

The extra soap will make the task of cleaning your biodiesel more of a challenge too.

With insufficient catalyst, your biodiesel will contain a high percentage of monoglycerides and di-glycerides (partially reacted oil) , which will tend to encourage the manufacture of emulsions if you water-wash.

Several years ago, it was common to use a base amount of 3.5g NaOH or 5g KOH per litre of oil. Experience has shown that this may not be enough for most typical producers, so the amount has been raised to 5g NaOH or 7g KOH per litre of oil, to give generally good levels of conversion.

Some producers use more than this, as a safeguard against under-reaction typically caused by damp oil and variable catalyst purity. However this has the disadvantage of using more catalyst and possibly more methanol, which can create more waste, with lower conversion efficiency and higher catalyst costs.

If you are interested in reducing your catalyst amounts, so reducing waste, key areas to focus on would be:-

  • Ensure your oil is as dry as you can make it
  • Use a mixing pump which can circulate the volume of your reaction tank within a minute or less
  • Monitor each batch with 27/3 test. Find the least amount of catalyst you can reliably use.
  • Titrate you catalyst, to determine its purity / effectiveness.



Methanol burns with a faint blue flame. In daylight it is almost invisible, usually you only know there is a flame by the shimmering heat waves you can see.



The biodiesel process uses hot, dangerous chemicals and needs to be monitored at all times by someone who understands the process and who is familiar with the processor and its controls.

There is only one correct answer to this question - there is no alternative answer.

The safest thing to do would be to ask your friend to answer the door and explain that you can't be disturbed right now.

The other 3 options are less safe and would put you or your friend or the caller at more danger.

Anything which further distracts you from the task at hand can make it more likely you will forget to do something or miss something, or do something wrong. This makes it more likely you will have an accident.



pH only applies to water based solutions, so you cannot measure the pH of oil, no matter what instrument or technique you use.

You can measure the acidity of oil, however, by carrying out an oil titration.



Oil will not dissolve in methanol, it will drop to the bottom of the methanol.

Biodiesel will not dissolve in water, it will float on top, and the water will remain pure.

Water will dissolve in biodiesel. Typically, at 20C you can dissolve up to 1.5ml of water in a litre of biodiesel, to form a solution. If you cool the biodiesel, the solution will saturate, and go cloudy as some of the excess water forms microscopic droplets. If you heat the biodiesel, all the water will go back in solution and the biodiesel will clear. This is a good symptom of insufficiently dried biodiesel - if it clouds well above its gel point, it most likely is damp.

Lye does not dissolve in biodiesel.



The correct procedure if you spill lye on your skin is to flush the area with copious running water for at least an hour. If the eyes have been affected, continue irrigating the eyes until medical help arrives.

Because of the amount of time you will be irrigating the area, try to use tepid / warm water so that the patient does not become cold or hypothermic.

Contrary to popular belief, you should NOT use vinegar.

Consult your MSDS for further details of dealing with spills on the body.

See also here and note section B , para 7. (Warning - has graphic photos of chemical burns which some may find upsetting).

I decided to ask Dr Demling a burns specialist of Harvard Medical School about the reasoning behind advising NOT to use vinegar, as I know many of you, myself included, would think vinegar to be a good idea.

Here's my email to him, and his reply...


From: Graham Laming []
Sent: Fri 12/28/2007 3:22 PM
To: Demling
Subject: Lye burns - to neutralize or not?

Dear Dr. Demling

I would like to ask your advice on the matter of lye burn treatment. I am trying to establish a safe working protocol for users of NaOH and KOH

I notice in your page in section B, para 7, it is stated ..

"- do not attempt to neutralize acids with alkali or vice versa, just use copious water "

I am meeting with repeated resistance to this, by folks who understandably feel that vinegar is a valid treatment regimen.

As this goes against your good advice, and indeed the advice on all MSDS I can find, I wonder if you would be able to help me by explaining the key reasons for advising against neutralizing, as the question is always "But why can't we use vinegar?"

I can guess at the reasoning, but would greatly appreciate your experienced guidance on this.

Many thanks, in anticipation of your help.

Graham Laming
Shefford, UK



The most important treatment is to flood the area with copious water to flush the alkali away not to try and neutralize.

Alkali are hard to remove and very hard to neutralize with a weak acid unless you have gallons upon gallons of vinegar.

Copious flushing is needed for 20-30 min to be able to remove from skin as it soon is thru the upper layer of skin and needs flushing not futile attempts at neutralization which will only affect the most superficial collection of alkali.

As far as eye irrigation vinegar is toxic to the eye especially a damaged eye.


About the Author of this reply.



New vegetable and animal oils/fats are known as tri-glycerides. They have 3 fatty acids attached to a 'backbone' of glycerol.



Typically, if you start with 100 litres of good fresh oil, you will get just under 100 litres of biodiesel.

Things which may reduce conversion include ...

  • If you use high base amounts of lye, you will get less biodiesel.
  • If you wash too vigorously you may lose some of your biodiesel to emulsion
  • If you don't settle your glycerol long enough, it may entrap some biodiesel



See Q5. above.



Fuel hoses in modern vehicles are not made of rubber and will in most cases happily tolerate biodiesel, so the 2nd choice is false. It is highly unlikely you will have any problems with standard issue modern fuel lines and biodiesel.

The most important things to pay attention to are :-

  • Biodiesel should be well reacted = low viscosity
  • Biodiesel should be purified - no soap or glycerol = less chance of blocking filters
  • Biodiesel should be dry = less chance of promoting bacterial growth