OK, different Mark chiming in, my turn: I've been wondering about this white precipitate too. I haven't seen too much 'first stage glycerine' in general because I dont' usually make test batches (but Todd can you PLEASE re-post your test batch method for acid-base like you just did on another list. I periodically like to re-post his test batch method on this list, hope some of you guys have seen it). Since I don' tusually do test batches, I usually don't see what is going on in the bottom of my reactor.
But a month ago I took a sample of the first-stage product, so as to 'trick' some students whom I was teaching titration to- I had them titrate the oil this stuff came from, and the first stage product,. without telling them what it was, to illustrate the way that FFA drops with acid-base. After they remarked that it was nice oil I got to tell them that it wasn't just oil, which led to a discussion of how this got achieved. ANyway the stuff has been sitting in a jar for over a month and it's developed a good amount of white precipitate. It looked solid to me at first. But it took a while for that precipitate to develop. Tonight I was just startring to fool around with my biodiesel gear after being away for a week... and ran across the jar of acid-stage sample, and remembered Mark's question. Mark S, are you seeing this stuff dceveloping right away? Anyway I moved the jar around a little and this stuff didn't look solid. It looks something like water with a thick load of a solid, like water with a bunch of powdered sugar or starch dissolved in it. It also dropped in acid number (ie lower value on a titration) from 1.5 to 1 on a titration in the past month, continuing to react very slowly??? I just came from the Iowa State University course on commercial biodiesel production, and one of the reasons I went to the program was to learn more aobut industrial acid-base. We ended up esterifying trap grease in the lab- eighty percent free fatty acids- which was quite impressive. the industrial process esterified it to .78 percent ffa, and they certainly made a big deal out of the fact that their process makes themost dramatic difference in bad quality oil, though they just do two stages of esterification if need be, before going on to transesterification base stage.. It was also a great illlustration of what ALeks was talking about when he says that reaction is much more equilibrium-sensitive (than base trans-e). We used differing amounts of sulfuric and differing amounts of methanol which both depended on the ffa content (figured out using a slightly more complicated titration than homebrewers do). The amount of methanol was immense, a practice completely out of reach of homebrewers without methanol recovery to attempt (though you'd literally have to go digging in a sewer to find eighty percent ffa grease). In the case of the eightly percent ffa stuff, (someone wrote me wanting to know what the heck they were eating in that place before the grease went down the drain!), the methanol volume used was more than the amount of grease we actually started with. It was unimportant that it was so expensive in methanol because that process depends entirely on methanol recovery as a way to make this kind of usage possible (flash evaporators in their case). ANyway, I learned a number of interesting things: The acid reaction produces water, this is well known. Once there's enough water formed, the water eventually stops this reaction from going any further (equilibrium). This is part of why it is so important to start with dry oil. IN the case of my sample from a month ago, I definitely didn't dry all the water out of the oil before starting the acid-base process on it. It by the way was not "grim" oil, I do this process on normal oil quite a bit. Also, another thing we learned was that with enough excess methanol, the methanol in acid-esterification will start to separate from the oil after agitation is complete. This separating methanol also contains some sulfuric acid- and the WATER that is formed by the reaction. Depending on how much methanol you use, the methanol/sulfuric/water phase (layer) either weighs more or it weighs less than the oil. In the case of our eightly percent ffa grease, we saw something that looked for all the world like a toxic 'biodiesel'- a great big amber colored methanol/water/ sulfuric layer above, and a very dark brown ester/ffa/triglyceride mix below (we were using more methanol than grease). However, if you used less methanol, the phases would be reversed- which I think is what ALeks' recipe produces given the lesser amount of methanol. The upper phase would be oil/ester/any unreacted ffa, and the lower layer is what he calls first stage glycerine and Todd calls first stage methanol. It's a darker layer than the biodiesel, when I've seen it. this allows in the industrial scenario for several neat tricks (all depending on methanol recovery) the methanol/water can be boiled off in a still or flash evaporator during the process, so as to keep pushing equilibrium to the right in the equation. But past a certain addition of methanol, they can just gravity separate (less energy than boiling off in a still) the aqueous layer of methanol./water/sulfuric, and treat it later on it's own to separate methanol to reuse (One of our instfructors also found that he could also in some manner recycle the sulfuric many times, I'm not clear right now on how he accomplished removing the sulfuric and the methanol from the water, but it was economicaly worth it). Anyway in their process they could if necessary do several stages of acid stage- read ALeks' base-base two-stage recipe if this doesn't make sense- it;s all about equilibrium for the nasty oil, and that equilibrium is brought on by the presense of water, so the process parameter in their case was removal of the water... Anyway, I looked at my sample with the white stuff in the bottom. And I think what I'm looking at is mostly water, colored by something white (and I sure would love to know what that something is). It seems that in the case of the methanol-overloaded industrial process, the gravity separation happens very quickly, since there is so much methanol (and it's not terribly soluble in oil). It also seems to me that if there's less methanol and there is more junk (the Iowa state people filter the heck out of their oil and grease before starting any processes on it, and few of us do), then maybe separation won't happen right away? So I'm curious, Mark S, how long does it take for this white solids layer to coalesce in your case? IN Todd's "modified" (I don' think t's particularly modified) method he wonders if it's useful to drain off the 'first stage methanol'. It seems to me that in the industrial method, they would very much say YES to that one, having found that the mixture is water/methanol if it goes to the bottom of the processor. But- in our case we'd want to add more methanol to the base stage at this point, and to recover the methanol from it;s water/methanol/sulfuric acid soup. This is again dependend on having methanol recovery capability. But the volume is pretty low- which it seems to me could be easy to handle in a very small pot still (like one made out of a steel pressure cooker). Anyway the upshot of all this is that this class made me realize how many options methanol recovery opens... not that I'm planning on having anything to do with 80% ffa grease, and not that that;s necessary for any other homebrewers to muck around with either. mark (mark A?) --- In biofuel@yahoogroups.com, Keith Addison <[EMAIL PROTECTED]> wrote: > Hello Mark > > >Dear Keith > > > >I have now produced clean and clear bio-diesel > >from some of the most grim looking crude WVO. > > Well done! Using the acid-base process? (You don't eat at that place, do you?) > > >However a question - first acid stage (1.0cc 97% > >H2SO4) per litre of WVO produces a solid > >precipitate. What is it? Esterified FFA as a > >solid? > > > >Regards > > > >Mark > > No, precipitated glycerine can be though, and the first stage does > produce some: > > "The first-stage process is not transesterification, but pure and > simple ESTERIFICATION. Esterification is followed by > transesterification, but under acid conditions it's much slower than > under caustic conditions and it won't do a complete oil-to-methyl > ester conversion as the reaction is much more equilibrium-sensitive. > Without methanol recovery, the alcohol overdose required would make > the price of your fuel jump, and even with recovery it would still be > much more expensive. Hence the second base-stage." > http://journeytoforever.org/biodiesel_aleksnew.html > Foolproof biodiesel process: Journey to Forever > > However, it's widely recommended that people gain experience with > single-stage methods first before trying the two-stage methods, and > IMO that's sound advice. > > Best > > Keith ------------------------ Yahoo! Groups Sponsor ---------------------~--> Get A Free Psychic Reading! Your Online Answer To Life's Important Questions. http://us.click.yahoo.com/Lj3uPC/Me7FAA/uetFAA/FGYolB/TM ---------------------------------------------------------------------~-> 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/
