The problem with iodine number is that it effectively measures the number of double bonds in a quantity of fatty acids, generally while they are still attached to the glycerol. The methyl ester of an 18 carbon FA that is saturated has a high freezing point. One or more double bond reduces the freezing point so that we have a liquid biodiesel. The FAE's with one double bond seem to be OK and actually give desirable qualities to Bio. Two double bonds close together are a problem since oxidation can result in a type of ring structure with an oxygen atom attached to two carbons along the chain, from memory with another carbon in between. This is an epoxy structure and epoxies are capable of polimerisation with each other and with other molecules. The double bonds need to be an appropriate distance apart and there is a branch of FA chemistry devoted to reorganising the position of double bonds to deliberately create epoxies. Iodine number by itself gives no indication of whether the double bonds are on the same FA molecule let alone if they are close enough on the same molecule to create an epoxy. The higher the iodine number for a particular oil the more likely it is that there will be two double bonds on the same fatty acid and that some of them will have the appropriate separation. Even so two oils from separate sources may have a similar iodine number but very different rates of polimerisation. So to condemn an oil based on the iodine number alone may not be appropriate. Some oils are listed as setting oils. These oils generally have some fatty acids that have three double bonds. Linseed oil used as a paint or varnish base is a good example. Baileys has a useful list of oils with their typical FA content based on carbon number and saturation. The older Baileys editions used smell as a means of identifying oils, I believe that I can identify linseed by smell. Some of the WVO we get seems to contain a blend of linseed. I have made experimental batches of FAME from linseed oil. It forms a neat plastic film on the surface and an interesting "thick" layer over some useful bio. I intend to learn how to best deal with the epoxies by playing with this product. I may have to make the next batch in an oxygen deficient atmosphere. A lot of bio forms a film on top, it may be that this is a result of oxidation to epoxies rather than a wax layer, though it does seem to mix back in rather well. Naturally we could remove the double bonds by hydrogenation, trouble is that raises the freezing point of the fuel and that brings us back to chill filtering. Even with tallow an efficient chill filtration should leave a useful yield of 75% bio. Thanks for the lift pump stuff. Regards from Harry. --- In [EMAIL PROTECTED], Neoteric Biofuels <[EMAIL PROTECTED]> wrote: > Looks like I missed a thread on this earlier, re: the lift pump discussion - > sorry! > > Ed B. > www.biofuels.ca > ---- > > > From: Steven Hobbs <[EMAIL PROTECTED]> > > Reply-To: [EMAIL PROTECTED] > > Date: Wed, 31 Oct 2001 08:35:20 +1100 > > To: [EMAIL PROTECTED] > > Subject: Re: [biofuels-biz] Iodine number > > > > Harry, I need a bit of time to digest the first bit about storage life, but as > > far as a lift pump and pre filter, we have a 1440 international axial flow > > > >
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