They mistakenly gave me N-Propanol instead of my usual of methanol. I'm going to take the drum back on Monday, but was wondering if you can make biodiesel with this?
I've read that it would take more, but I'm curious as to how the larger alcohol molecule of N-propanol would latch onto the ester chains?
Anyone tried this? My search has only come up with some hazy details.
Illegitimi Non Carborundum
Location: Utopia Planitia | Registered: 25 February 2005
Originally posted by Jehu: It should make great biodiesel. I would definitely recover it too. The caustic might take a lot od dissolving tho - maybe KOH would be better.
What makes you say that, Jehu? Have you tried propanol before? If so, I'd love to hear what you have to say about it. Because if I can make biodiesel without all the hassle Monday of taking that drum in exchange, I'll do it.
Illegitimi Non Carborundum
Location: Utopia Planitia | Registered: 25 February 2005
Some of the skin care oils are isopropyl esters rather than methyl esters, which of course are derived from plant triglycerides in the same way as we get methyl esters when we make biodiesel. For example Avon use isopropyl palmitate in some of their lotions, from palm oil. N-propanol is an isomer of iso-propanol and should react very similarly.
PS - do a 1 litre trial run first to see how the caustic dissolves and the reaction behaves.
Originally posted by Spencnaz: Good information, Jehu. Thanks yet again. I will however have to leave the drum sealed in order for them to exchange it for me.
From what I've read for every liter of methanol in the usual reaction, with n-propanol I would have to use 1.785L. Does that sound correct?
I dont know the conversion factor, but propanol will definitely have a larger molar equivalent.
I've just worked it out, if I'm right it should be 1.875, not 1.785, based on molar densities.
Just been thinking, if you got it for the price of methanol it would be a waste to use it for making a few litres of biodiesel. You can use it like isopropanol as a solvent (its great for cleaning stuff like glass apparently) and for doing titrations. It also has low toxicity. I would keep it.
Longer chain alcohols present greater steric hindrance to the reaction, causing it to proceed more slowly. In fact, the longer the chain length, the slower the reaction will be, i.e, reactions with propanol would be slower than those with ethanol, which, in turn, would be slower than those with methanol. This would be difficult to overcome in the homebrew setting.
Roughly elaborating on steric hindrance, in this case, is related to the alignment of bonding molecules (FFA and alcohol chain). The two must align in a linear fashion. Smaller molecule are more easily able to change orientation to achieve this alignment. This increase the probability that bonding will occur, which reduces the reaction time. Reducing the thought to a simple 2-D analog, consider parallel parking a compact car (methanol) on street. If you must park on the opposite side, this is done quite easily, but if you're parking something like a box truck (ethanol) or a semi (propanol), orienting the proper way is much more difficult.
I had read that reactions with ethanol at STP were considerably slower than those with methanol, which is why a much greater molar ratio of alcohol to oil should be used (not just a molecular density issue). I would expect propanol to be even slower, requiring an ever greater ratio to proceed at a decent rate. It's certainly worth experimenting with if its free, but I wouldn't bother if you can swap it out.
~Erik
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