chemrox - 12-3-2008 at 16:17
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
not_important - 12-3-2008 at 18:07
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?
chemrox - 12-3-2008 at 22:54
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.
not_important - 12-3-2008 at 22:59
Just suggesting that some of the puzzle may be off readings of temperature.
Do they neutralise the alkali catalyst?
chemrox - 13-3-2008 at 22:08
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?
not_important - 13-3-2008 at 22:48
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.
chemrox - 14-3-2008 at 16:01
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.
undead_alchemist - 24-5-2008 at 07:14
easy fix for having to pull up the thermometer,
use a two or three necked flask, or a two way adapter.