Hi Andreas. I doubt I«ll be able t answer all your questions but I«ll see if I can help a bit.
> My name is Andreas Jansen, student for Environmental Management in > The Netherlands, however since a year taking part at the MSc for > Renewable Energy Systems Technology at Crest in Loughborough, UK. My > dissertation started 4 weeks ago and is about the topic "biodiesel". > Therefore I have to optimise a small-scale prototype installation > running on used cooking oil for a company, which is just three years > in business, not having much experience yet, which makes the work and > support for me sometimes rather difficult. > For this I read lot of abstracts, however my chemical background is > not so very strong, still for some understanding sufficient. However > there are some topics where I struggle with and cannot find an answer > to: > > 1. When considering Sodium Hydroxide as catalyst for alkaline > based transesterification I wonder about the following things: A > reaction mechanism tells me, that the methanol and sodium hydroxide > form S.M. and water. S.M. catalyses the transesterification and at > the end the H+-ion from the previous formed water is deprotonated by > the diglyceride-ion (or later mono-glyceride- or even later glycerol- > ion) to form a fully alcohol group and finally glycerol. My concern > is whether this combination of H+-ion and (di)glyceride-ion is > necessary to occur or whether in the glycerol-layer after separation > also (di)glyceride-ions may be found if not all (di)glyceride-ions > have had combined with the H+-ions from the water? A catalyst should > be found back at the end (if not saponified), that is what a catalyst > defines, or? Therefore only glycerol but no (di)glyceride-ions should > be found? > Furthermore, if now assumed that anhydrous S.M. powder as catalyst is > used, would that (under the assumption that H+-ions must react with a > (di)glyceride-ions to form the glycerol) mean, that water must be > deprotonated and if water is initially present in the oil this water > would be removed, thus lowering the saponification reaction between > f.f.a., water and Na+-ions?? That would be quite a benefit to > consider buying S.M. powder instead of producing S.M. self by mixing > Me-OH and NaOH! > I was unaware of the fact you could buy dehydrated S.M. This would be a great improvement, as it would reduce the ammount of water in the transesterification. The term catalyst must be carefully used here. From what I recover, the catalyst will be somewhat consumed hence disrupting its own definition. Even more complex solid catalysts used in complex industries (as pharmaceutical), often patented salts like Titanium tetraalcoxides and so, will probably serve for 20 or so reactions. The end product may always have rmains of mono- & di- glycerides, as 100% efficiency is not possible. > 2. When doing previous the reaction a titration to determine the > degree of f.f.a. I take 1 ml oil and dissolve it in 10 ml iso- > propanol. pH meter and litmus-pH-paper give different results during > titration and the indicator (phenolphthalein) is not behaving like > expected. It first tends only very, very light purple but remains > like this, only if ~0,5 ml more NaOH solution is added (than at a pH > of 10) it is turning totally purple. I thought a indicator colours or > does not but the very light purple colour which stays and does not > disappears after stirring more confuses me a lot? > Concerning the difference in pH meter and paper I think to trust the > meter, but if the oil is not dissolved good it might form a film > around the measuring electrode and therefore diminishing the > measurement? Right. Remember you still have a polar & non-polar mix (or rather an emulsion). I used phenolpthalein and after the first supposed neutralization, some more minutes of mixing turned it clear again. It«s a hard-to-do titration. If you«re doing research for the company, maybe a gas chromatogram would best analyse your oil and BD. that would answer your qustions on mono- & di- glycerides, and your questions on FFA content. Might elevated T or adding more iso-propanol help in > this case to prevent this film, without diminishing the reading in > other respects? > I think increasing temp is not adviseable here (I can«t remember well, but something in my head sais it leads in those conditions to more degradation of the oil and a higher FFA reading). Try thorough mixing and read the result after a couple of minutes. It might be useful (though a bit unorthhodox) to colour print a scale of 10 pink marks, from light phenolphtalein pink to dark phenolpthalein pink. Then you could maybe mark (for each volume of added base) the colour of the solution after the initial addition, and its colour after 1, 3 and 7 minutes. This is thinking out loud, but sometimes the changes in colour are so suttle that a printed scale might help build a curve or something easier to interpret your results. I realised that at first, adding NaOH turned the solution pink and after some minutes it turned back to transparent. But after some more additions, it whent pink and then returned not to transparent, but to a very light pink. This was past the correct titration ammount, so I had to redo the experiment and take the readings for the "back to transparent" volume of base. > 3. When doing the reaction I thought to add the S.M. and > methanol already early when the T is still quite low while heating > the reactor tank, rather than adding it only if the reaction heat is > reached. That consideration just to save energy and time. However, > when the ratio of saponification rate to the transesterification at > lower T is higher than at higher T it should not be done to avoid too > much soap formation. Could you give a short statement? > Assuming you have used anhydrous methanol and dry oil, saponification will occur due to the presence of NaOH and the water from the S.M. formation, making the glycerides exchange their ast H for a Na (I know that«s not what you asked). Now anhydrous S.M. would reduce soap formation. Anyhow, I know people who have considered performing the reaction at room temp for a longer period. I always thought that the equilibrium reaction would take forever at that temp. However, this guy is a Chemical engineer, and I he argued the reaction could be performed at room temp with good yields. I don«t know if he somehow separated unracted oils and centrifuged the S.M. to add it again in the mixture, thus retrieveing BD as it formed (and pushing the reaction towards products side). However I do not know the saponification & transesterification rates at different temperatures. > > > One personal question, if I might: I was looking for a funded PhD in the renewable energies field. I am a recenly graduated environmental engineer, and an EEC member (French passport). Do you know if the MSc for Renewable Energy Systems Technology at Crest (Loughborough, UK.) is funded for EEC members? Could you help me finding out the entry requirements, maybe a course program or at least the email of someone in charge of the addmitance for environmental MSc & PH.D.s? I«d really appreciate that. Best wishes, Christian > > > > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Biofuels list archives: > http://archive.nnytech.net/ > > Please do NOT send "unsubscribe" messages to the list address. > To unsubscribe, send an email to: > [EMAIL PROTECTED] > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > ______________________________________________________________________________ mensaje enviado desde http://www.iespana.es emails (pop)-paginas web (espacio ilimitado)-agenda-favoritos (bookmarks)-foros -Chat ------------------------ Yahoo! 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