chemrox
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bio-diesel wash water distillation
I was given wash water and glycerol byproducts from the local foodshare bio-diesel project for some testing. The first thing I did was distill an
aliquot of the wash water by simple distillation. The wash water is an opaque, soapy solution with a density of about 1.04 g/ml. The distillation
went like this: at about 40-48*C a very small amount came up the distillation head. Then a clear liquid came over at ~ 80-90 with most of it
constant boiling at 85*C. I collected 28 ml that weighed 25g for an approximate density of 0.89 g/ml. This had very little odor. There was a feint
sharpness overshadowed by residual soapy smell. A member who has forgotten more about bio-diesel than I will ever learn, suggested that its water.
That was before we tried a burn test. The stuff burns cleanly on a cotton swab. No azeotrope we can find would fit the bill but we feel it must be
an alcohol-water mixture. Any of you with bio-diesel experience are requested to give this one some thought. We could take a larger sample and
distill it using a column. For the moment were stuck and baffled.
CRX
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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not_important
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Check with the ratios of oil to alcohol they use. Smaller scale biodiesel ops often use about twice as much alcohol as needed, so there's a fairly
large amount in the wash. The FFA content would give the faint soapy smell.
And are they a MeOH or EtOH operation?
How is the calibration on that distilling apparatus, tried it with pure water, and with 95% EtOH?
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chemrox
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I assumed pure water would distill at 100*C but hadn't callibrated and shall do so. Thanks. It's an MeOH setup and they have a lot of the alcohol.
I can get a gallon from them anytime I need it. There could be enough FFA in the wash to make the smell as you say. I will definitely run the still
on water for an hour to get an idea of its performance.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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not_important
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Just suggesting that some of the puzzle may be off readings of temperature.
Do they neutralise the alkali catalyst?
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chemrox
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I checked the setup and everything works as it should. The densities above are off though .. I dropped a tare or two first time around. The wash
water is about 1.01 g/ml and the dsitillate 0.89 g/ml. I ran it again with a 3 bulb Snyder column. I collected about 65 ml from 500 ml wash that
boiled at 76*C. When that was collected the temp dropped and I changed receivers and collected a second fraction from 94-98*C and I assume this is
water. The lighter fraction still burns cleanly. The only detectable odor, is again, slight soapy smell. So I'm wondering if there's a possible
MeOH/ester azeotrope? I have a paper (at work) on using IR to predict MeOH azeotropes. How can I tell if its dry enough to put in my salt cells?
CCl4 is mentioned as an IR solvent in the paper. If it made a clear solution with CCl4?
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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not_important
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Solubility in water 0.815% at 20°C
Solubility of water in chloroform 0.056% at 20°C
http://macro.lsu.edu/howto/solvents/chloroform.htm
Add it to CCl4, use a good drying agent on that.
I seriously doubt that any of the fatty acid esters have azeotropes like that with methanol, especially in aqueous mixtures.
Why would water be coming over at 94-98 C? You live in the mountains? Correct for barometric pressure, in that case. If water is boiling 2 to 6
degrees low, none of the other boiling points mean much.
Check pH of original sample, and of fractions.
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chemrox
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That wasn't a precise temp; the others were. Reason? I had to really maniuplate the thermometer shaft to read the 75-6*. The 100* is under the
adapter collar so I had to ull the shaft up to read the higher boiling stuff. I should have siad so. The 94-98 is with cooling so its really right
up at 100+. Now, its also possible another frac started off at 94-5. So, I still have everything set and will check that out. Question? What
effect(s) do non-equilibrium conditions in the column have on the take-off temp read-out? I can superheat my vapor to some degree. So if I really
blast the flask, the stuff will come over fast reading ~80 but if I settle it down to a drop, drop, drop it sits at 75-6. Non-linear dynamics in the
Snyder column? Working both ways? I could learn a lot doing nothing but distillations the rest of the year. Maybe I will.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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undead_alchemist
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easy fix for having to pull up the thermometer,
use a two or three necked flask, or a two way adapter.
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