Prof. Allen, Thanks for your valuable information and I would definitely consider about it thoroughly. As your predict, I am an undergraduate in UK but I am origin from Malaysia. Therefore, from this point, I might not produce my own biodiesel, but I will certainly make it after I back to my hometown, as the palm oils are everywhere. Besides, its kinda 'waste' if I knew so much about the benefits of biodiesel and not fully utilised it.
For your information, I had carried out a simple calculation on Heat of reaction for transesterification based on RBD palm stearin. But the figure seems to be unreasonable, highly exothermic reaction (up to -1000kJ/mol) was obtained by using the average value of Heat of formation of fatty acid. However, we knew that the molecular weight of oil is approximately 3 times higher than the molecular weight of biodiesel. Therefore, by applying this concept, I can obtained an endothermic figure (approximately 50KJ/mol). But the uncertainties are very high. As you might be awared of the enthalpy change within the system are not taken into account. I am running my design mode at 1.5 - 2 bar. Therefore, the design temperature is 65 deg C (well above upper limit, as methanol boiling point is 72deg C at 1.5 bar). A series of CSTR are used. Conversion is design at 95%. However, the kinetics from Darnoko & Cheryan (2000) seems to be varied much from my simulation. I am applying Kinetics of Soybean oil, from Noureddini & Zhu (1997), which seems to be matching with my design mode. But rate constant of Darnoko (2000) was used. Cheers, Gann --- In biofuels-biz@yahoogroups.com, Michael Allen <[EMAIL PROTECTED]> wrote: > Dear Gann, > > Your e-mail is addressed to Keith but I can probably answer some of your questions: > > >Thanks Keith for your information, in fact I already got a copy of > >that. > > By "that" you mean the paper by D. Darnoko and Munir Cheryan, > I think? > > >Anyway, just another few questions, during the transesterification > >process, the mixture (Oil and methanol) eventually getting hotter or > >cooler? > > You want to know if the reaction is exo-thermic or endo-thermic? > I can't help you there except to say that the enthalpy change is pretty small and can be > neglected without much error. We are trying to measure it at present but we really need a > sensitive differential thermal reactor system to do it properly. You might find the enthalpy > of formation for some of the fatty acids but I doubt that you will find much thermodynamic > data on the glyceryl or methyl esters in the literature. Anyway, natural oils contain a > variable mix of this lot so the formal petro-chemical type of approach won't work here. > > From your previous e-mail, it occurs to me that you are completing an undergraduate > project in process design rather than seriousl;y thinking of biodiesel production. Am I > correct? > > If you are, then Chemshare, Chemcad, Aspen, Hysys (T/M )and other such software > packages can be used for process design but only if you make up some "hypothetical" > components and feed in the measured rate data to tell the software what to do. That is > where the Darnoko and Cheryan paper should give you some clues. > > > And what is the recommended temperature to carry out such > >reaction at practise (room temperature) ? > > Well. as you must have read in the Journey to Forever archives, the answer to this > question is somewhere between 50C and 64.8C. This upper limit is imposed by the boiling > point of methanol at one atmosphere. A deep reactor provides enough hydrostatic > pressure to go a bit higher (say 70C) (and you can even stretch this a bit if you design for > a cloud of collapsing bubbles and some methanol recycling by condensation). > > The lower limit is determined by the low rate of reaction that occurs at lower temperatures. > It certainly isn't fixed and engraved in stone! We found that you can make biodiesel > based on an oil containing mainly olein at 35C but we need 60C for a stearin based oil! > The Arrhenius equation and the graphs given by Darnoko and Cheryan should give you > the idea. You might consider repeating their work with the oil you have in mind so that > you can get rates, yields and temperatures relevant to your problem. > > I agree entirely with Keith in that you could do a lot worse than start with Alex's Foolproof > Reactor and get some personal experience. Then see if Darnoko & Cheryan's models > "fit" your observations. Certainly once you have made some biodiesel, you will know what > the important parameters are and what further questions you need to ask. > > (IMO You should always keep in mind that the literature contains practical > measurements which have been presented in a form to fit the pre- conceived ideas of the > authors and the general scientific community! With your own work, you might just see > something that no one else has noticed! Of such things are Nobel Prizes made . . . . . . ) > > >Besides, from the Journal, it is recommended to have high speed > >stirrer or agitator to increase the mass transfer, therefore, would > >it be wise if the high speed agitator provided at the begining of the > >process, follow by moderate or even low speed for the rest of the > >time, to save some of the energy consumption? > > I'm sure you realise that in any liquid-liquid reaction, the size of the interfacial area is > critical in determining the rate. Agitation must be adequate to make sure that the > methanol/methoxide droplets are small and come into contact with the unreacted oil. > That's all really! Much can be achieved by just introducing the methanol/methoxide > through a series of small holes so that turbulence is induced. In that olein reactor I > mentioned, you only need to shake the reactants by hand in a glass jar to get a reaction. > (We called it our "007" reactor because it was shaken ........ not stirred) > > If you are contemplating the design of a continuous reactor, you might consider using a > venturi mixer at the entrance to a short plug-flow reactor (and maybe put a series of these > reactor modules together so that the methanol/methoxide is added in three or four > places). Or you might perhaps go for a mixer- settler type of unit where the glycerol is > separated out at each stage. > > Then there is the pulsed reactor . . . . . . > > But I presume that you have already read the Journeytoforever pages > > Whatever you have in mind, some practical work with a simple batch reactor would give > you a much greater insight into what is happening than anything I can say. > > >Cheers, > >Gann > > > > And to you likewise > > Michael Allen > > >-------------------------------------- > > > >> Hello Gann > >> > >> Michael Allen sent me an interesting paper about the kinetics at > >the > >> time the palm oil discussions were going on. There wasn't a url for > >> it though, and it's a pdf file. So I put it online in our Biofuels > >> Library. It's here: > >> > >> Kinetics of Palm Oil Transesterification in a Batch Reactor, by D. > >> Darnoko and Munir Cheryan, University of Illinois, Department of > >Food > >> Science and Human Nutrition, Agricultural Bioprocess Laboratory, > >> Journal of the American Oil Chemists' Society (JAOCS) Vol. 77, No. > >12 > >> (2000) --What happens during the biodiesel process reaction. > >Acrobat > >> file, 72Kb. > >> http://journeytoforever.org/biofuel_library/transesterification% > >20paper.pdf > >> > >> See also: > >> > >> Biodiesel processors > >> Mike Pelly's new processor > >> "Foolproof" method processors > >> The touchless processor > >> Continuous reactors > >> Biodiesel technology > >> Simon's guide to building a biodiesel mixer > >> Ian's vacuum biodiesel processor > >> Chuck Ranum's biodiesel processor > >> How to make a cone-bottomed processor > >> http://journeytoforever.org/biodiesel_processor.html > >> > >> Best wishes > >> > >> Keith > > > > > > > >Biofuels at Journey to Forever > >http://journeytoforever.org/biofuel.html > >Biofuel at WebConX > >http://webconx.green-trust.org/2000/biofuel/biofuel.htm > >List messages are archived at the Info-Archive at NNYTech: > >http://archive.nnytech.net/ > >To unsubscribe from this group, send an email to: > >[EMAIL PROTECTED] > > > > > > > >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > > > > > > > Biofuels at Journey to Forever http://journeytoforever.org/biofuel.html Biofuel at WebConX http://webconx.green-trust.org/2000/biofuel/biofuel.htm List messages are archived at the Info-Archive at NNYTech: http://archive.nnytech.net/ To unsubscribe from this group, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
