TheNaKLaB - 9-12-2011 at 18:40
I recently conducted a transesterification of vegetable oil and ethanol.
I made a Sodium ethoxide solution where I dissolved 0.5 grams of Sodium hydroxide as best I could in Ethanol. I then added this solution to a round
bottom flask with 100mL of vegetable oil and refluxed the solution for about an 30-45 minutes. I left it for 30 minutes to cool and a brown
discoloured layer was floating on top of the vegetable oil. The layer was only about 2 mm thick.
I then set up my distillation apparatus and distilled the solution. After about 45 minutes of distilling, I was left with 30mL of clear solution left
as my distillate. The distillate smelt somewhat sweeter compared to the ethanol I started with.
So my question is, what would my distillate be?
[Edited on 19-09-2011 by TheNaKLaB]
Magpie - 9-12-2011 at 21:49
I suspect you did make a small amount of ethyl esters. Reflux time for making ethyl esters from coconut oil is 15-20 hrs per OrgSyn. I used 11 hrs
with apparent success. Following OrgSyn I used HCl as catalyst.
This thread may help:
http://www.sciencemadness.org/talk/viewthread.php?tid=16306#...
[Edited on 10-12-2011 by Magpie]
[Edited on 10-12-2011 by Magpie]
[Edited on 10-12-2011 by Magpie]
TheNaKLaB - 9-12-2011 at 23:30
Wow 15-20 hours is a long time to reflux. So how would I be able to increase my yield? Should I add HCl while refluxing, or when I'm distilling?
Thanks for your answer!
bahamuth - 10-12-2011 at 00:46
The transestrification "completeness" is a function of temperature and time, but can't seem to find the spesific article in my folder, neither do I
remember the name. -Edit: (this is the case for the base catalysed, alkali in EtOH method).
IIRC at 110 Celsius in a corning test tube with screw cap (a closed reactor setup, so to speak) on a tube heatblock we would get more than 98%
conversion in about 1-2 hours i believe..
Anyways, there are countless free articles about this specific reaction and varieties of it. One other method which should (authors claim, not mine)
be faster and gentler to unsaturated FA would be the alcohol sulfuric acid IIRC.
[Edited on 10-12-2011 by bahamuth]
Magpie - 10-12-2011 at 09:39
A high mole ratio of ethanol/oil is also important I believe (Law of Mass Action).
Take a look at the OrgSyn procedure linked below, specifically Note 4.
Dr Bob recommends the use of absolute ethanol. I used 95% ethanol.
http://www.orgsyn.org/orgsyn/default.asp?formgroup=basenpe_f...
[Edited on 10-12-2011 by Magpie]