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Author: Subject: Valorizing the Glycerol from Biodiesel Production
microcosmicus
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[*] posted on 16-1-2008 at 09:07


Hi Welder,

Sorry if I came across in a negative way --- it was not my intention to
rain on your parade. Unless people try things out, however implausible
they might seem, there is not going to be any progress in science or
technology. Rather, all I intended was to point out that, even in the worse
case scenario where processes for converting waste oil to IC engine
fuel turn out to be too costly, there are still uses for WVO as a fuel.
Having said that, I wish you luck with your research and hope that things
turn out better than the worst case scenario.

As for what to do about fatty acids, here is a thought . Would an strongly basic ion
exchange resin remove them? Since the acids are not going to be dissociated
in oil solution, maybe not, does someone here know for sure? If so, then one
could first pass the oil through an ion exchange column and then a dessicator
to remove the water from neutralization as well as moisture already in the oil.

Maybe one could adapt the procedure the brewers use to neutralize their product,
but using the resin in place of alkali or at least look to that process for inspiration.

Fatty acid soap dissoved in oil is the recipe for grease. Burning the
soap would have the problem that it will form ash just like when burning wood.
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[*] posted on 16-1-2008 at 09:20


Again, hydrogenation increases the melting point of the oil - turns it into Crisco.

Soaps are neutralised fatty acids, the common and low cost bases give soaps. Soaps based on metallic elements result in the formation of the oxides of those metals when the fuel is burned, in most cases not good for the engine. Ammonium and amine soaps don't have this problems, but form NOx.

The soaps tend to be solids or pastes, higher viscosity and melting point than the FFA or glycerol esters (fats) of those fatty acids. Clogging of the fuel system could be a problem, and water that gets in will tend to form emulsions and foams with the soaps.

That biodiesel use of FFA is likely acid based or acid catalysed esterification, giving the same esters the standard base catalysed route does. Because the catalyst is also an acid, it doesn't react with the FFA the way alkaline catalysts do. Current thrust with acid catalysts is toward reactive distillation, fractional distillation with the acidic catalyst as part of the fractionating column packing. This can give near 100% conversion, handle wet feedstocks giving dry product, and gives high quality glycerol (able to be used in fermentation without further cleanup); all with no waste salts production - unlike most base catalysed routes.

Ethanol can be used in place of methanol, and methanol can be made from CO2 and H2 - either from electrolysis using 'green' power or possibly by direct electrochemical routes using CO2 and water.
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[*] posted on 16-1-2008 at 09:24


Quote:
Originally posted by microcosmicus
...
As for what to do about fatty acids, here is a thought . Would an strongly basic ion
exchange resin remove them? ...


Yes, but then you have the cost of the resin, it's regeneration, and the disposal of the FFA effluent from them in what is likely to be a mostly alcohol solution of FFA soaps and excess base.

[Edited on 16-1-2008 by not_important]
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[*] posted on 16-1-2008 at 11:48


Let me start with a question --- what is the concentration of fatty acids
in a typical batch of waste oil?

While it's hard to say too much without such a figure in hand, here are
some tentative possibilities.

The cost of the resin is offset by the fact that it is regenerated. In the
long run, all one pays for is the cost of replacing resin which has been
worn out. The figure I usually see cited here is that a resin is usually
good for a few years or so due the stability issues.

As for the remains of regeneneration, couldn't one regenerate using
an aqueous solution and avoid the alcohol? However, if there needs
to be alcohol, maybe reclaim it by distillation for reuse in the procedure.
Of course, alcohols + base make EtOX,. so there may be problems with that.

Also, I have read that organic acids (tannic acid has been specifically cited)
can foul resins by dissolving inside the bead. However, since the solution
for this problem was regeneration with a base like NaOH, that might only
be a problem in applications like water softeners where one would prefer not
to use strong base. A more serious problem is clogging of resins with oil ---
that might blow this suggestion of using ion exchangers for oil out of the water.

http://www.sybronchemicals.com/service/pdf/reprints/Maintain...

Soaps and excess base don't sound like a liability to me. Add extra oil
to saponify the excess base and sell the soap.

[Edited on 16-1-2008 by microcosmicus]
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[*] posted on 17-1-2008 at 04:50


Hi guys. Thanks for your continued interest in the problems I've mentioned.

Lime seems to be the best bet for creating insoluble FFA soaps. I assume that drying the WVO after saponifying the FFAs will cause them to conglomerate and fall out, right? I'm hoping it should at least make it easier to spin the FFA soaps out in a centrifuge rotor. The FFA soaps will dry into solids right?
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[*] posted on 17-1-2008 at 08:30


The calcium soaps are usually described as "fatty powders", fairly soft and friable. I believe they also disperse fairly well in warm oils; if so that could present problems. On the other hand, that centrifuges are being used to dry the oil might result in the soaps sticking to the water droplets and separating nicely - experiment time.

A possibly problem with using 'lime', either CaCO3 or Ca(OH)2, is that you're forming a solid product in a reaction with a solid reactant. This would seem likely to result in the lime being quickly coated in calcium soaps, slowing down the reaction and requiring more lime.

The limit on FFA for VO fuel seems to be 0,5%, while the amount of FFA in WVO is typically several percent and can run as high as 5% in the overused oils typical from small producers who try to squeeze as much use out of the oil as they can.

That "acid-base reaction" may be a method where an acidic catalyst is used to esterify the FFA, then a basic catalyst is used to do the transesterification of the glycerol esters - the fats. The complexity of that is in part what has been driving the research in reactive distillation.


The solubilization of calcium soaps by fatty acids
Journal Lipids
Publisher Springer Berlin / Heidelberg
ISSN 0024-4201 (Print) 1558-9307 (Online)
Issue Volume 26, Number 3 / March, 1991
Category Communications
DOI 10.1007/BF02543981
Pages 250-253

Quote:
The solubilization of the calcium soaps of long chain fatty acids by liquid fatty acids was observed. The solubilities of calcium palmitate, calcium laurate, and calcium oleate were 15.6, 22.8, and 53.3 wt%, respectively, in oleic acid at 40°C. The formation of an acid-calcium soap complex was demonstrated by x-ray diffraction studies of calcium laurate, lauric acid, and a mixture of these compounds that had been heated. Similar evidence was obtained for a calcium oleate-oleic acid complex. The solubility of calcium oleate in a bile salt micellar system was enhanced by obeic acid. The solubilization of calcium soaps by liquid fatty acids may explain the unexpectedly high bioavailability of some calcium soaps.
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[*] posted on 17-1-2008 at 13:04


Quote:
Originally posted by not_important
The calcium soaps are usually described as "fatty powders", fairly soft and friable. I believe they also disperse fairly well in warm oils; if so that could present problems. On the other hand, that centrifuges are being used to dry the oil might result in the soaps sticking to the water droplets and separating nicely - experiment time.

A possibly problem with using 'lime', either CaCO3 or Ca(OH)2, is that you're forming a solid product in a reaction with a solid reactant. This would seem likely to result in the lime being quickly coated in calcium soaps, slowing down the reaction and requiring more lime.

The limit on FFA for VO fuel seems to be 0,5%, while the amount of FFA in WVO is typically several percent and can run as high as 5% in the overused oils typical from small producers who try to squeeze as much use out of the oil as they can.

That "acid-base reaction" may be a method where an acidic catalyst is used to esterify the FFA, then a basic catalyst is used to do the transesterification of the glycerol esters - the fats. The complexity of that is in part what has been driving the research in reactive distillation.


The solubilization of calcium soaps by fatty acids
Journal Lipids
Publisher Springer Berlin / Heidelberg
ISSN 0024-4201 (Print) 1558-9307 (Online)
Issue Volume 26, Number 3 / March, 1991
Category Communications
DOI 10.1007/BF02543981
Pages 250-253

Quote:
The solubilization of the calcium soaps of long chain fatty acids by liquid fatty acids was observed. The solubilities of calcium palmitate, calcium laurate, and calcium oleate were 15.6, 22.8, and 53.3 wt%, respectively, in oleic acid at 40°C. The formation of an acid-calcium soap complex was demonstrated by x-ray diffraction studies of calcium laurate, lauric acid, and a mixture of these compounds that had been heated. Similar evidence was obtained for a calcium oleate-oleic acid complex. The solubility of calcium oleate in a bile salt micellar system was enhanced by obeic acid. The solubilization of calcium soaps by liquid fatty acids may explain the unexpectedly high bioavailability of some calcium soaps.


Good info, Important! Thanks!

What about saponifying the FFAs with lye? I understand that the risk involved there is that loss of oil may result due to the lye indiscriminately saponifying anything it touches.

Is there any way to make lye saponification target the FFAs more accurrately? Maybe less lye diluted in more water?

[Edited on 17-1-2008 by Welder]
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[*] posted on 17-1-2008 at 13:07


Sodium carbonate?

Typical carboxylic acid pKa ~ 5, CO3(2-) ~ 10...

Running through a bed of soda ash would probably do it.

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[*] posted on 17-1-2008 at 17:41


Good evening!

It's been a while since I have had time to post.

You can wash the oil with potassium carbonate (soda ash will likely work too) solution. The K salt will extract into the aqueous layer where it can be separated. This method can also be used to remove organic acids from their "parent" aldehydes (so you can use that ancient aldehyde found in your graduate lab:)).

I have made Calcium "lardate" from lard (Armour brand manteca) and Ca(OH)2 at reflux (the solubility is poor and the rxn is slow) for about 4 hr. The resulting mess can be extracted with hexane from which the (mostly) calcium distearate can be recrystallized. It is a white powder, sparingly soluble in water, without suds. It is, however, an excellent antifoam agent (which is what I made it for, and it can break hydrogels).

We routinely run organic acid analysis on an anion exchange column eluted with a NaOH gradient (but this is done from aqueous media). But...Oil will absolutely trash (foul) your resin. no go.

I (et al) have made some notes regarding baterial fermentation of glycerol here:

http://www.sciencemadness.org/talk/viewthread.php?tid=9557&a...

Please see, specifically, the Gonzalez group paper (Rice), which I posted there (IIRC).

Cheers,

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[*] posted on 18-1-2008 at 05:08


[Edited on 25-1-2008 by Welder]
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[*] posted on 25-1-2008 at 17:38


Hi again.

So I just wanted to make sure which reagent would be best to creat non soluble FFA soaps that will dry when heated under vacuum then seperate easilly in a centrifuge.

Would it make sense to try calcium hydroxide? Would calcium carbonate diluted in water be better?

I'm not sure whether I'm understanding this properly.

When it was mentioned that it was possible to make non soluble soaps from FFAs, I thought that would be good in order to avoid creating soluble soaps that might emulsify with the used oil and any excess water making removal more difficult. Does this make sense, or are non soluble soaps likely to be difficult to seperate from the WVO?
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[*] posted on 25-1-2008 at 18:43


Lubricating grease is made by mixing calcium soap with oil. Given that
the soap in this type of grease does separate out when heated, your
method might work. According to the following reference, it seems
that the grease starts drying out at 160F, presumably the vacuum
would lower the temperature significantly:

http://www.reliabilityweb.com/art04/understanding_grease.htm

However, bear in mind that the usual grease has the soap dissolved
in mineral oil, not vegetable oil, so things might not go exactly
the same way. However, your idea sounds like its worth a shot.

Calcium carbonate only dissolves in water in trace amounts (14 mg
per liter, to be precise). Given that hard water is basically a solution
of calcium carbonate and that rings on bathtubs are calcium soap,
this method would work but, depending on how much fatty acid
you have in your oil, it might require an inordinate amount of water.

I don't know, this is only a thought, but maybe reacting the oil
at lower temperature (say mixing at room temperature as opposed
top cooking it as when manufacturing soap) would result in relatively
less the oil being turned in to soap.
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[*] posted on 26-1-2008 at 20:04


Thanks Microcosmicus.

14 mg/L sounds like a pretty low concentration. I'm not sure that much FFA could be soaped without using far too much water. Maybe lye would be better, I'm just concerned that the lye soap may not want to settle out to easilly. I've heard that thoroughly drying the partly soaped WVO will really help the dry soap to settle out making seperation (decating, filtering, CFing etc) much easier.

Ultimately, the goal is to remove FFAs from the WVO based on the concern that FFAs may cause corrosion.

If very dry (under 500 PPM water) WVO has FFAs that need water to corrode the steel surfaces of diesel injection systems, then maybe WVO that has FFAs still in it would be okay.

I'm only, a welder, not a chemist and I've heard conflicting opinions on the subject of whether dry FFAs are corrosive, so I'd love to hear more input on this.

Thanks again for all your guys advice!
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[*] posted on 26-1-2008 at 21:34


Quote:

I've heard conflicting opinions on the subject of whether dry FFAs are corrosive,


Sounds like time for an experiment to me. Put some freshly polished metal
in a sample of your oil, heat it to the sorts of temperatures you expect to
encounter in use, wait some time and see exactly how much corrosion occurs.
Then maybe repeat the experiment with oil that has been processed with
alkali, dried, etc. to see how much of an improvement comes from these
various treatments. Likewise experiment with different alkalis (lye, quicklime)
to see exactly how much work is needed to remove the fatty acids using
different processes.

Ultimately, I expect that it all will come down to a tradeoff between the cost of
preprocessing the fuel and of replacing corroded parts. Having the experimental
data on how different processing of the oil affects amount of corrosion will help
one make a informed decision as to where to strike the balance. Also, if the
corrosion is a problem, maybe look into the possibility of replacing some critical
parts of the engine (say fuel injectors) with parts made from a more inert metal
or doing some sort of a surface treatment on the metal (e.g. bluing steel or plating
it) to make it less prone to corrosion.

Finally, do you know how much free fatty acid is contained in a given amount
of your oil? If not, that would also be worth measuring.
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[*] posted on 27-1-2008 at 03:57


Yes, I agree that experimentation is likely needed. I had just hoped that maybe data already existed. Maybe I should at least do an advanced Google search using "free fatty acids" as a search phrase and "corrosion" as a search word. Maybe throwing the search word "anhydrous in there would help too as water content is likely a factor in any FFA corrosion that may occur.

One of the reasons I wanted to avoid having to do a physical experiment is that I'm not sure exactly how long it might take for FFAs to effect corrosion on bare steel. Polymerization of vegetable oil may take a relatively long time, but under certain conditions may also be quite rapid, relatively speaking. If any corrosion caused by FFAs takes as long as some slower forming polymerization sometimes takes, I may not even notice any corrosion forming for a fairly long time. I'd hate to pull the plug on an expirement after getting a false negative after not waiting long enough to see corrosion forming. It may be a long term experiment.

There's an antioxidant called TBHQ that's ben tossed around a little as a possible preventative for polymerization formation. If TBHQ efffectively prevents polymerization by preventing oxidation, then perhaps it may also effectively prevent FFA related corrosion. Another control group to add to the expirement, I guess.

The FFA content in WVO can vary widely. I think I may have heard of very hard used oil with up to 15% FFA content, but I'm not sure if I'm remembering that correctly. I know the biodiesel folks consider FFAs to be important sometimes.
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[*] posted on 27-1-2008 at 08:01


Most of what I see, re. FFA involves an initial titration of the material (WVO) so that the amount of catalyst will exceed the amount of FFA. THis insures that there is actually free catalyst present (rather than the stable salt).

The salt should be quite water soluble, and should end up (mostly) in your glycerol layer, along with any excess alcohol. Acid catalysis avoids this as the FFA will form esters as well (but, removal of the catalyst becomes the issue with corrosivity).

It seems to me that the corrosivity of the FFA in WVO shouldn't be a huge problem unless that FFA is dissociated; this requires a polar solvent, like water. I would also be concerned about polymerized glop (which can eventually result from polymerization of autooxidation products such as malondialdehyde) which can foul sprayers, lines, etc. This can be assayed using thiobarbiuturic acid; the measure is given as ppm TBARS (Thiobarbiturate reactive substances).

Unfortunately, in many climates, it can be unusual for your BD to be *bone-dry*.

I think that the oil-soluble inhibitor seems like a good idea--just keep in mind that the inhibitor reacts when it does its job (it is s temporary fix, and this should be considered for long-terms storage). Over time, TBHQ will dimerize (giving that red color to old solutions). While this may not effect the function of the fuel, it may blow the color specifications.

For a sensitive assay of the slow reaction, the Fe-o-phenanthroline method is very sensitive. I imagine that your sample of metal in the oil could be shaken and sampled. THe sample would be extracted with a bit of water, reduced with hydroxylamine (or, IIRC bisulfite; the complex forms with Fe2+) and treated with o-phenanthroline in an acetate buffer at pH 5. Absorbance measured at 510nm can give a good measure of Fe taken up into the mixture. The effective calibration range is up to about 5 or 6 ug/mL before the absorbance exceeds 2. This might yield quicker results than waiting long enough (which might be very long, indeed) to detect a loss in mass of the test coupon (gravimetry).

Cheers,

O3

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[*] posted on 31-1-2008 at 03:14


My only interest in WVO is in burning it straight, as diesel fuel in a modified fuel system with line heaters etc. This fuel method is called SVO, for Straight Vegetable Oil (animal fats work fine too).

The question I have about FFAs is a concern over whether they will cause corrosion in a fuel system even after thorough dewatering (under 500 PPM water in oil).

I mean, I know they are called acids for a reason, but triglycerides are really only a glycerol molecule with three chains of fatty acids attached, right? So if the fatty acids don't cause corrosion when bound to the glycerol, are they likely to cause corrosion when free? I know that water based acids are formed when cooking oil is used, but knowledgeable SVO users water wash the water based acids out of their WVO before drying it and filtering it.

It looks like I may have to do a little more research and maybe even do a little experiment.

I know this thread was originally intended to explore glycerol usage, but since my questions were biofuel chemistry related, I thought maybe asking them here might get responses from chemists more specialized in oleochemistry etc. Sorry to hijack.

[Edited on 31-1-2008 by Welder]
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[*] posted on 31-1-2008 at 06:38


As fats or oils they aren't acids, but rather esters with no really acidic hydrogen. They really haven't any reactive groups to interact with metals, and they are less hygroscopic than the free acids.

Even a very small amount of corrosion of metal while in storage, including fuel tanks, results in metallic ions that tend to increase the rate of reaction of unsaturated bonds with oxygen; this leads to cross-linking and the formation of gums and 'varnish'. You've addressed this a bit with the mention of TBHQ.

On the other hand, the saturated FFA have been used as lubrication enhancers in fuels, so they may not be that bad. However fuel blends like that likely included corrosion inhibitors and so on.

One other aspect is that carboxylic acids tend to form weakly bound dimers through hydrogen bonding, these could increase viscosity.

a couple of reports that may be of interest

http://www.abqaltenergies.com/documents/Vegetable%20Oil%20as...

http://www.greencarcongress.com/2007/04/german_research.html
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[*] posted on 31-1-2008 at 15:42


Well...

I suppose burning the oil intact is, in fact, a way to mitigate the glycerol glut! You will have to start the engine on diesel range organic (preferable biodiesel) before kicking the WVO in (and also before shutting down). Even this application pushes (in however small a way) the use of biodiesel.

Might I suggest biodiesel WVO blends?

I would also consider blends with ethanol to lower gelling point and to help manage flow viscosity.

Cheers,

O3




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[*] posted on 1-2-2008 at 02:47


NOT_IMPORTANT:

Thanks for the technical info.

When you mentioned the "free acids", did you mean FFAs or water based acids?

Is there a way to affordably saturate the FFAs to reduce their reactivity?

Is saponification/neutralization the only way?

Can FFAs be hydrogenated? (increased viscosity is no problem with heated fuel systems) If FFAs can be hydrogenated along with the other components of WVO, then an industrial hydrogenator would seem to be a possible way to prevent fuel degradation.

I once saw an article announcing the development commercial/industrial enzymatic hydrogenation units meant to be made availabe through long-term leases. If I can find that again, I'll try to post a link.





OZONE:

Yes, I'm aware of blends, but I prefer the idea of running SVO over both blends and biodiesel. Safer and cheaper.
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[*] posted on 1-2-2008 at 03:14


I agree with ozone. Blends may be the optimal solution.

IIRC, the main problems with SVO as fuel are high viscosity, tarry (carbon) deposits on the injectors, aging (polymerizaton, oxidation, etc) and pollution (acrolein). I can't give you references, but I remember reading somewhere that most of these problems are solved by blending with regular diesel. It makes sense, diesel would reduce viscosity and maybe "wash" the injectors. Aging may be a problem for the industry, but not for a DIY operation. We are left with acrolein.

Im sure you read the biofuels thread here.

don't miss the by Adam Kahn (pdf) work.
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[*] posted on 1-2-2008 at 06:52


Quote:
Originally posted by Welder

When you mentioned the "free acids", did you mean FFAs or water based acids?

FFA
Quote:

Is there a way to affordably saturate the FFAs to reduce their reactivity?

Is saponification/neutralization the only way?

Extraction from the oils, as by forming salts (neutralisation) and washing them out, or by converting to esters.
Quote:

Can FFAs be hydrogenated? (increased viscosity is no problem with heated fuel systems) If FFAs can be hydrogenated along with the other components of WVO, then an industrial hydrogenator would seem to be a possible way to prevent fuel degradation.

This will not affect the acidity, just the viscosity and polymerisation issue. Well, unless you reduce the carboxylic -CO2H to alcohol -CH2OH, which with most hydrogenation processes will have reduced the oils (glycerol esters) to alcohols first. Not cheap, not DIY unless you're into high pressure plumbing.

From what I've read on using SVO, keeping the heating to a minimum reduces the corrosion any poly problems. This includes not heating the fuel tank or heating as little as possible, the higher viscosity of more saturated fats would be a problem given that minimised heating goal. This would seem to be even more of a problem in climates where you can use lard bricks as hammers in the winter; having to wave a blowtorch over your fuel system to get it functional may have been OK with the Antarctic station folk, but doesn't excite me.

Quote:
I once saw an article announcing the development commercial/industrial enzymatic hydrogenation units meant to be made availabe through long-term leases. If I can find that again, I'll try to post a link.


I'd be interested in that. While alkene double bonds are hydrogenated biologically, and the double bonds in oils are removed enough from the acid function to be considered simple alkenes, I've not heard of any industrial process to do so.

There was a push to use lipases to interesterify fats/oils to change their melting points. In a recent process stearin, the tri-stearic acid glycerol ester, from palm oil or full hydrogenation via the normal catalytic method, is enzymatically interesterified with ordinary vegetable oils to produce fats with melting points in the desired range for butter-like products. It replaces the older partially hydrogenated fats, the fatty acids in the new product are either fully saturated or the natural unstaturated ones which are mostly cis-.

Quote:

Yes, I'm aware of blends, but I prefer the idea of running SVO over both blends and biodiesel. Safer and cheaper.

Cheaper maybe, if the potential corrosion and polymerisation problems do not arise or can be overcome inexpensively enough, and if the time spent in doing so is little enough or discounted enough. But the possible problems with emissions of nasties doesn't automatically make the process safer. And using ethanol in place of methanol removes that toxicity issue.
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[*] posted on 2-2-2008 at 05:28


The issues of corrosion and polymerisation were why I started asking questions here in the beginning.

Heat is essential to svo and while it can certainly be a factor in oxidation, and polymerization, it is still the heart of svo technology. It's something used on transoceanic vessels so they can burn bunker fuel instead of diesel.

Saturated (high visc) svo fuel melts fine with waste engine heat and after mel;ting, it burns just fine too. Many svo people are running around on lard or hydrogenated veggie, they just heat their tanks to liquify their fuel (no blow torch required). The heat doesn't seem to cause any polymerization problems because the oil is already saturated.

Maybe FFAs can be dealt with easier with using additives than processing into soaps.
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froot
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[*] posted on 26-5-2008 at 06:10


Another link regarding the conversion of glycerol to ethanol using E. coli:

http://biopact.com/2007/11/scientists-convert-biodiesel-bypr...




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Skrinkle
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[*] posted on 23-6-2008 at 13:33


Quote:
Originally posted by Tacho
Glycerol retains moisture. Wouldn't it be useful for agriculture if mixed to soil? Not for the water itself, but as a soil "softener".


What about the soil dwelling fauna? Wouldn't it suffocate the earthworms that aerate and fertilize the soil? I'm just guessing.
I agree about the lubricant thing, but maybe it could also be used to lubricate engines?

[Edited on 23-6-2008 by Skrinkle]
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