Hello Beng, welcome >i am a student and is involved in a reserach involving biodiesel >production... can anyone help me find the explanation/logic behind >on the basis why 3.5 grams of NaOH is set as a fixed amount for >every liter of oil in the transesterification process... shouldn't >the amount be dependent on the type of oil to be transesterified?
It is a bit of a ballpark figure. See: The basic lye quantity -- 3.5 grams? http://journeytoforever.org/biodiesel_make2.html#lye3.5 "This is the amount of lye (NaOH, sodium hydroxide) required as catalyst to transesterify 1 liter of virgin, uncooked oil. For used oils, titration determines the amount of lye needed to neutralize the Free Fatty Acid (FFA) content, and this quantity is added to the basic figure of 3.5 grams per liter. "In fact 3.5 grams is an empirical measure -- an average. Different oils have slightly different requirements, and even the same type of oil varies according to how and where it's grown. Other estimates are 3.1 gm, 3.4 gm, and some people have set it as high as 5 gm. "Here is what we've found. For most virgin oils and low-FFA used oils (with titration levels less than 2-3 ml), 3.5 grams works just fine. For high-FFA used oils, use more lye -- up to about 4.5 gm instead of 3.5 gm. Do small test batches to see what works best. "Different oils also require different amounts of methanol -- see How much methanol? For oils and fats requiring more methanol -- coconut, palm kernel, as well as tallow, lard, butter -- again, use more lye, up to 4.5 gm, even with new oils, and especially when it's used. Once again, do small test batches first." See also: How much lye to use? http://journeytoforever.org/biodiesel_make2.html#lyeamount ... and the rest of the "Make your own biodiesel" section while you're at it. Another point is that cooking oils are generally standardised products, refined to meet certain requirements, and one of those requirements is a set maximum of Free Fatty Acid content. So in that regard they're all the same, no matter what kind of oil it is. The lye has two roles in transesterification, as a catalyst, and to neutralise the Free Fatty Acids. In theory, once you have enough to neutralise the FFAs, only very little more would catalyse the reaction. But, it might take a long time, and also the reaction might reach equilibrium before conversion had gone far enough, making a poor-quality product. You might be interested in this, and the two studies associated with it: The modelling of the biodiesel reaction http://journeytoforever.org/biofuel_library.html#macromodel Kinetics of Transesterification of Soybean Oil http://journeytoforever.org/biofuel_library.html#nour Kinetics of Palm Oil Transesterification in a Batch Reactor http://journeytoforever.org/biofuel_library.html#kinetics Best wishes Keith >or >if its role is just to catalyze the reaction, wouldn't it be >necessary to use the minimum amount of it just to start the >catalytic reaction? hope to hear from anyone soon....:) thank you >and good day.... > >beng ------------------------ Yahoo! Groups Sponsor --------------------~--> Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar. Now with Pop-Up Blocker. Get it for free! http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/FGYolB/TM --------------------------------------------------------------------~-> Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Biofuels list archives: http://infoarchive.net/sgroup/biofuel/ Please do NOT send Unsubscribe messages to the list address. To unsubscribe, send an email to: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/biofuel/ <*> 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/
