could anybody tell me why we use 20% methanol to make BD. for the last year or so i have cut down on the amount of methanol with no difference in yield or quality of the BD. i now use about 15% to 16% and the BD is just the same and as i dont wash the BD using water but let it stand for a week (a bit like the GL1 process). Am i doing anything wrong? or just speeding things up and saving a bit of cash.

Using excess methanol increases the conversion of the batch, by loading up the reactants side of the chemical equation and pushing the reaction further towards the products side. All else being equal, a lower methanol percentage is going to give you lower conversion percentage; in other words, you're going to have a higher percentage of mono, di and triglycerides in your fuel, and a lower percentage of methyl esters.

What methods have you used to determine your biodiesel is "just the same" now as when you were making it using 20% methanol?

Exposing a batch to air for a week won't remove all the methanol, and won't necessarily settle out all the soaps. Running this fuel isn't necessarily the same as running pure unwashed biodiesel, but it isn't nearly as good as running properly cleaned (Demethed, soaps removed) biodiesel.

audiboy

You might like to look at this thread where the effect of changing methanol amount is discussed. It will probably also pay you to make use of the Search feature. Further down the page you will see a conversion graph by Sam Ley.

methanol

Many people use unwashed biodiesel made with low conversion. No problems have been reported as far as I am aware from doing so with an IDI motor. What sort of motor have you got?

With an IDI motor it appears the fuel will be OK provided you use enough methanol to get a good clean separation. If you don't get a good separation you will be losing product.

to turbinepowered. the only way i check the difference is by the amount of glycerine which is the same if i use 20% or 16% also the bd has the same feel (which i know is not scientific)

to neutral.I have an audi tdi 'pump deuse' a bit like common rail but higher presure. but the conversion rate seems to be fine normally 10% glycerine.

thanks for your replies chaps.

According to the table in the link, with 15% methanol you will have 5.8% unreacted or partly reacted material in your biodiesel.

As yours is a DI motor this is an interesting test. How far have you run on it?

neutral, i have run on a vw tdi for 1 year, then my next car was an A6 tdi had that for 2 years and about 30000miles i now have an A4 tdi but it is the new pump deuse very high presure tdi and runs great, in fact it has more torque with BD compared to normal diesel. however it isnt as instant to start (winds over for a second longer)but never had any problems with any car.

Neutral,

Your research has been very helpful. Are you aware of it being replicated? Have similar tests been done with used oil of moderate FFA content? If not, do you think that would be useful?

Andrew

It would be interesting to repeat the work with used cooking oil. However if you titrate and use adequate NaOH (I use titration times 1.15 + 5g NaOH) the FFA are effectively removed from the reaction so the degree of conversion should be similar. It is the yield which changes dramatically. You lose about 3 times the FFA%.

I appreciate your technical info. I do think it is good to add replicated testing to validate sound theoretical understanding. And to keep the two seperate, to some degree.

My 2 cents.

Andrew

Hello Andrew
We anxously await your test results replicating Neutral's work!

I thought I'd chime in breifly on this.

I am reminded of a quality control seminar that John Bush of Boulder Biodiesel did at the biodiesel conference here in Colorado back in July. His presentation had, amonst other things, graphs which showed levels of conversion vs things like tempature, time, ammount of methanol etc. If I am recalling the graph correctly, the highest conversion obtained before diminishing returns was done with a 6:1 molar ratio of methanol to oil. Now I'm not sure what molar ratio means, but I do remember that John said he'd done the math and that a 6:1 molar ratio of methanol came to about 25% of the volume of oil to be reacted. This seems to confirm the results shown in the thread that Neutral linked, and explain the fact that I see people here reporting they need 20-22% methanol to get a good conversion.

Tilly,

It won't really be replicating his work if I use WVO.

Just a new test to see if what is true with new oil holds true with used oil.

Koreth,

Yes, John's presentation was informative and he did say that a 6:1 ratio was optimal, and roughly equal to 25% if we use methanol. It is different for ethanol of course, due to it's higer molecular wt.

Andrew

Hello Andrew

I am interested to see how you design your tests.
Will you be using GC testing or viscosity testing for your results?

TIlly,

Since I don't yet have a temp. controlled highly accurate viscometer, I will use warnquist and then GC on selected samples.

I promise I will post results.

Andrew

Hello Andrew

Yes, My viscosimeter is only accurate to a difference of a bit under 1% triglycerides.
It appears an accuracy in the order of 0.01% is needed with some testing.