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BioDiesel synth


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has anyone here ever made Biodiesel before?


after a few attempts that failed (I made Great soap!), 3`rd time lucky!


I`m working on a recipe:


100g virgin rapeseed oil

23.8g EtOH

1.43g KOH


the EtOH has to be 100% pure alcohol and the KOH has to be 100% dry also, any moisture and you will make Soap!


my Latest attempt at transestrification seems to have shown a reaction that I`v not seen in the others.


upon mixing the oil with the Potassium ethoxide with a magnetic stirrer in a flask, it was turbid, and then about 2-3 mins later the color suddenly changed to perfectly clear and a very deep Orange, about 2 mins later it went slightly turbid again but maintained the color.


the "recipe" didn`t mention this change, but says to keep it stirring overnight (so I will).


does anyone know if this is "Normal" or not?




wow, after leaving it stirring all night I gave it a few minutes to settle and it seems to have Worked!




the Bottom orange layer should be the Glycerol and other garbage, and the top layer is the Biodiesel, exactly as it said it would look in the Recipe.

the Yield percentage looks good too, I`ll weigh it after and find out exactly how much I got out from what I put in.


now all I have to do is wait until my mate gets his diesel car, scale this reaction up and test it :cool:




weights were;


Total Mass, 125.23g

Mass after Glycerol removal, 95.8g


so it`s not a 100% efficient yet, and upon washing with water there was an emulsion form, that would Suggest a high Soap content or incomplete reaction leaving a high percentage of Mono or do Di glycerides.

it Does burn rather well though!


Additional: doung the exact same synth but using Isopropanol instead of EtOH (taking into account g/mol) doesn`t work at all.

so it seems that Ethanol and allegedly Methanol (Primary alcohols) are the way to go.

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I have done several experiments making biodiesel while I was a student. Although I used methanol (not ethanol) I will post here...


(I just realised that in this post I have used both the terms "biodiesel" and "RME" (Rapeseed methyl ester). In all cases I meant "RME").


Experiment / reaction

I generally heated the rapeseed oil first. In a second erlenmeyer I mixed the methanol and the NaOH or KOH. Btw, To my surprise, NaOH actually almost completely dissolves in methanol.


The amounts I used varied (I was studying the effect of different ratios on the conversion) but in general it was close to something like:


500 g rapeseed oil

80 g methanol (should correspond to about 115 g ethanol, if the same molar ratio is used, but I heard ethanol reacts slower... not sure though).

4 g NaOH/KOH

the reaction temperature was slightly below or at the boiling point of methanol (varying between 60 and 65 degrees C). I had a thermostat,and a nice reflux cooler to keep things under control. It was all in a fume hood. Reaction time was 1 hour.


Glycerol separation

After 1 hour, the glycerol was separated from the biodiesel. The glycerol fraction contains most (if not all) of the catalyst. This effectively stops the reaction.


Color changes

The picture you have looks quite similar to results I have had. I have also observed fast color changes at the start of the reaction. The first color change I observed was the one caused by the formation of the emulsion upon addition of the methanol+NaOH (initially the methanol does not dissolve). Methanol however does dissolve in biodiesel (RME), so after several minutes (or as fast as 1 minute), the changing composition of the emulsion becomes miscible, causing another rapid color change. The solution then also becomes clear (transparent yellow). The color changes a last time to murky brown / orange when enough glycerol and RME is formed to cause the formation of a glycerol / RME emulsion. This is a brownish / orange mixture.



I found that the conversion (oil -> RME) increased when a 10-50% excess of methanol was used. This has to be separated of course (by distillation) from both the glycerol and biodiesel phases. It seems that methanol has a greater affinity for glycerol than for biodiesel (RME).



Washing with water often formed an emulsion. I think this is actually normal. I doubt that this is because of soap present. If you use an acidic solution of H3PO4 (10% wt) for the first wash (using 1.5% wt of acidic water, relatively to the amount of biodiesel), and then wash several times with normal (demineralized water), the emulsion is less stable.


Water removal (from the emulsion)

Water can be removed by heating to about 50-60 degrees. In initial experiments, I used a rotary evaporator. But the emulsion was not stable, and water formed large droplets at the bottom of the flask, causing delayed boiling (not nice in a rotary evaporator). I found that (very) gentle stirring at 40-50 deg C also destroyed the emulsion. NOTE: a (yellow) transparent RME biodiesel can still contain 0.1% (wt) water. I am not sure if a diesel engine likes that. I do know that European standards say that the water content should be ≤ 500 mg/kg (EN ISO 12937). In later experiments, I first removed the majority of the water at elevated temperature by settling (settling is almost instant once the emulsion is destroyed), followed by rotary evaporation. I'm not sure how the home brewers do this actually.



[edit] found an excel sheet with results (numbers)

I'm afraid I don't know how to make a table on the forums - is that even possible?


Oil: 601.1 g

Methanol: 95.59 g

Excess Methanol: 31.6 g

NaOH: 3.9 g

KOH: 0 g


Biodiesel fraction: 568.3 g

Glycerol fraction: 73.4 g

Methanol recovered from glycerol: 12.1 g

Methanol recovered from biodiesel: 19.9 g

Total Methanol in mixture: 32 g

Solids found: 12.6 g



Total solids (est.): 15.5 g


Product losses (in glassware): 13.9

Product losses (elsewhere): 0

Product losses (unexplained): -2.51


total methanol weight: 32 g

methanol fraction glycerol: 0.141520468 (wt frac)

methanol fraction biodiesel: 0.03383203 (wt frac)

Distribution coefficient (gly/b.d.): 4.18303212


Your experiment

I think the yield is quite low. Heating, stirring better, or more ethanol could be a solution to that.

I also read that only primary alcohols are working.



If you have more questions, please ask. To write this post, I dug up my old report. I know where it is now, so I should be able to answer more if you want. I did >20 experiments making biodiesel (none with ethanol though).

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erm... hang on a sec, you say my results were a Low yield when I had 95.8g of biodiesel from using 100g of oil, and yet:


Oil: 601.1 g

Methanol: 95.59 g

Excess Methanol: 31.6 g

NaOH: 3.9 g

KOH: 0 g


Biodiesel fraction: 568.3 g

Glycerol fraction: 73.4 g


Your experiment

I think the yield is quite low.


it seems I had a higher yield percentage than You did.


compare my: 100 --> 95.8

to your: 601.1 --> 568.3


mine`s bigger than yours! :P

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compare my: 100 --> 95.8

to your: 601.1 --> 568.3


Ah... my mistake. I misread the data you presented (thought you started with 125.23 vegetable oil). I think 95.8 biodiesel from 100 g rapeseed oil is quite decent...


Of course, you already took into account the fact that mine was a methyl ester. By default the gram/gram yield ratio of biodiesel/vegetable oil of a methyl ester is lower than of an ethyl ester... :D


The average molar mass of rapeseed oil is 882 g/mol. The corresponding RME is 295.3 g/mol and the corresponding REE is 309.4 g/mol. (There are a whole bunch of different chains on the triglyceride... I used data from Mittelbach's biodiesel handbook to get an average).


So... let's compare your: 100 --> 95.8

to my: 100 --> 94.5 (normalized from 601.1 --> 568.3)


Convert to moles:

compare your: 0.113 mol --> 0.310 mol REE

to my: 0.113 mol --> 0.320 mol RME


Seems I have a higher conversion after all... But it's so close that we shouldn't expect that the comparison makes any sense. Rapeseed oil is different everywhere it grows, and I bet it's even different in the same place in different years.


Furthermore for a good comparison, we should also compare the excess alcohol, amount of catalyst, and the reaction times.

I used a 50% excess methanol.

You used 23.8 g ethanol (= 0.517 mol). That's about the same excess alcohol on a molar ratio (52%).

You used more than twice the amount of catalyst (per gram of rapeseed oil).


What was your reaction time and temperature? I always heard that REE was a lot harder to react. But it seems you did a pretty good job.

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mine was room temp (~22c) and was left in the flask with a magnetic stirrer for about 17.5 hours, at ~180 RPM.


where do you get your Methanol from cheaply?

I can get it as Lab grade in small amounts, but it`s quite expensive, I was thinking about a 5L container of it would be good, even if it`s technical grade, as long as it`s Dry it`ll be fine.


btw, I use mine in a small Hurricane lantern to burn it off, it works rather well and is just the right size for getting rid of the experimental product from a small scale reaction.


I can wait until my mate gets his Diesel car :D

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waw, room temperature? Never knew that works. The lowest temperature I tried was 54 deg C. I know that most factories that do large scale conversions do this at elevated temperature, although I found it hard to find data of individual factories (they generally don't like to say how they do things).


I did this work at university, while I was a student... no clue where they get their methanol. Getting the methanol was "someone else's problem". Also no clue about the price ("someone else's budget"). It came in 10 liter containers (which is quite annoying if you only need about 80 g). Probably was lab-grade, meaning it's too expensive if you plan to make money from it.

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cool, I'm going to try this as soon as I assemble my magnetic stirrer, might post that into apparatus section as well :)


Also, are there any model motors that could be used to test different biodiesels for efficiency?

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Interesting stuff, and potentially very important to the world's ecconomy.

The idea of finding a small test engine is a good one too, perhaps a small diesel generator would be a good start.

There's one thing that puzzles me.

"the EtOH has to be 100% pure alcohol and the KOH has to be 100% dry also, any moisture and you will make Soap!"

That makes perfect sense but the lab grade KOH I have seen is always about 85% or 87%.

I always assumed the remainder was water. Anyone know what it is?

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I`v heard that it Will a little bit, but you can run into all sorts of problems with it emulsifying.

the soap created will bond to the oil and the water and just make a complete mess.


you Could put in some calcium metal and leave it for a few days and then distill the alc again though, that should get rid off any excess water quite nicely.

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I think the majority of the soap will enter the glycerol phase. Fatty acids or water will also deactivate the catalyst. This slows the reaction down, or even stops it. I think that the problematic separation after the reaction is the least of your worries... A poor conversion is where it all starts. And when you wash the ethylester or methylester with water after the reaction, you still might get a stable emulsion, even when you have almost no soap.


Some reactions that can occur:


The triglyceride is reacting with water to fatty acids in stead of a ester (I am not 100% sure about this reaction, comments are welcome... is the catalyst needed at all, or is water aggressive enough):

[ce] [Triglyceride] + 3 H2O [/ce] [math]\stackrel{cat}{\rightarrow}[/math] [ce]Glycerol + 3 [Fatty acid] [/ce]


Once you get fatty acids, you deactivate your catalyst:

[ce] [Fatty acid] + Metal^{+} + OH^- -> [Conjugated base]^- +Metal^+ +H2O[/ce]


Note that fatty acids are present in quite huge amounts in used cooking oils. It can be as much as 30% (wt).

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That is why you first titrate your WVO (phenolphthalein endpoint is OK) to determine the amount of catalyst you will need. So long as there is a nice excess, you should be OK.


The mono and diacyl glycerides that can result as a consequence of incomplete esterification lead to nasty emulsions and will separate (pearlescent floc), over time, in your product (no matter how nice it looks when you made it). You must find a way to assay your products prior to use.





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  • 2 months later...

upon mixing the oil with the Potassium ethoxide with a magnetic stirrer in a flask, it was turbid, and then about 2-3 mins later the color suddenly changed to perfectly clear and a very deep Orange, about 2 mins later it went slightly turbid again but maintained the color.


I tried one of these biodiesel preps today and I also observed sudden turbid-to-clear change after a few minutes, however, I didn't get any orange, it was mostly yellowish, and it didn't go turbid again. I used NaOH instead of KOH and I left it stirring for now, though room temperature is pretty low (around 14°C), I'm thinking to provide some heating.

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There is no carburettor to modify in a diesel engine; and to my opinion the abbreviations are the degeneration of a language, and have no temperature. :D


Sooo... it is not carbohydrates modernized... :-(




Hmm... yeah, I guessed wrong. A little wiki-study (not in the mood to go any deeper than that) shows that it's true:

"In diesel engines, a mechanical injector system vaporizes the fuel into a pre-combustion chamber (as opposed to a Venturi jet in a carburetor, or a Fuel injector in a fuel injection system vaporizing fuel into the intake manifold or intake runners as in a petrol engine). " - source


It does make sense that you have to adjust the oxygen / fuel mixture though. It's just done with a different piece of equipment, and not with a carb(urettor). I think I should stop posting in this thread before I burn my fingers. I know a bit about biodiesel, but sadly not too much about cars :D

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no, you were quite right, I did mean Carburetor Modifications, some Diesel engines do indeed have a carb, but eitherway the Fuel/Air may still require some tweeks to get the best out of the fuel, although I have heard that most will still run quite well without having to do anything to the engine at all (some will work on plain untreated vegetable oil!).

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  • 3 months later...

it would be cool if you could make the methanol from destructive distillation dripping into the rapeseed/KOH solution while on a reflux at 60 degrees Celsius, though it would be hard to do it in a stoichiometric way, it would be low yeild also most likely

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Those are not two processes I'd integrate. Just make methanol first, purify it by standard means (distillation or extraction) and then add it to your biodiesel reactor. Also, the difference in temperature between the destructive distillation (which is also called pyrolysis, or cracking and operates at 400 deg C, or more) and the biodiesel (60 deg C) also means you'd have to separate the processes in order not to lose all your heat, or to prevent overheating of the biodiesel reactor.


But making methanol from a sustainable source by means of pyrolysis is a good idea which is being investigated as we speak. And having a sustainable source for methanol would obviously make the biodiesel even more green.

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