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I want to do the synthesis of biodiesel with the cooking oil (it contains colza and sunflower oils) in ethanol and KOH. After 1 hour of reaction, I let the solution to rest for 3 days.

At this stage, I should obtain different phases of glycerol and ester before the washing step, but there is no decantation I have only one phase of solution. Can you help me to separate the biodiesel?

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  • $\begingroup$ My guess would be that 1hr is not enough. Are you following a known procedure? $\endgroup$ – Waylander Apr 21 '18 at 11:05
  • $\begingroup$ Thank you for your message, yes i followed a known procedure, indeed, it is mentioned that 1h is enough. $\endgroup$ – Ami Meirem Apr 21 '18 at 11:49
  • $\begingroup$ Heating it further will not damage the product so there is nothing to lose there. $\endgroup$ – Waylander Apr 21 '18 at 12:11
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I have made biodiesel from sunflower oil, I used methanol instead of ethanol and I used sodium hydroxide in methanol as my cataylst. If you use a little methanol I have found that after heating the mixture under reflux and allowing it to cool. You get a layer of glycerol / methanol which is not miscible with the FAME (Fatty acid methyl esters) which has a lower density than the glycerol / methanol / sodium hydroxide layer.

If you use ethanol then it will be harder to separate the lipohilic layer of fatty acid esters from the alcohol. I know that methanol and hexane are not fully miscible while ethanol and hexane are fully miscible.

Assuming that you have access to a proper chemistry lab with a fume hood, I would suggest you change to methanol instead of ethanol for making biodiesel from cooking oil. Also if you use fresh cooking oil instead of used then you will have less free fatty acid (carboxylic acid groups) in the oil that you start with.

The literature suggests that for used cooking oil that acid cataylsts can be a better than alkaline cataylsts,

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