Biodiesel and SVO Forums Home
It's hard to dry biodiesel

This topic can be found at:

January 16, 2010, 10:12 PM
Jack Boyett
It's hard to dry biodiesel
I haven't read this forum much, but I see a lot of claims of dry biodiesel. I'm not so sure.

I work at a biodiesel plant so I have access to lab equipment to check how my home setup works. The best I've been able to do at home is 550 ppm water. Which is just over the spec of 500 ppm. It's absolutely crystal clear so you can't tell by looking if you're in spec. I would also say I am more aggressive than most here.

My drying tank is an open top tank that will hold around 50 gallons leaving a few feet at the top to recirculate. I pump back into the top and let the flow splash down on a small round metal plate suspended from the top of the tank. I have two heating elements. A 5 or 6000 watt element wired 240 volts and another 120 volt element. I forget the voltage on the 120 volt element, probably 2500 or so.

I've heated to 220-240F and circulated for up to an hour. Seals in the harbor freight pumps don't last long at this temperature. Even at these conditions, I've never been in spec.

In a plant setting, a biodiesel dryer will give you 200 ppm water at 230F and 90 mmHg vacuum. I'm working now on a dryer that will do this for me.
January 17, 2010, 12:25 AM
-can you explain the drying process at work,are you saying 36"hg Eek Tom

" I don't know what I don't know until I know"
1994 GMC 6.5 Tubo 2005 Dodge ram 3500, 3 VW's 2000, 2002, 2005.
January 17, 2010, 01:20 AM
biotom jack is talking about torr mm mercury which is approx 4 inches of mercury still to maintain this at 200+ degrees would be murder on my pumps. I aggree with you jack drying bio is near impossible and no real way to measure it, is why i do not water wash. I have had to on some batches which I either did not dry or overdosed on the caustic now i am more careful to avoid soaps, the methanol is easy to dive of but the remaining soap is hard to remove, i have observed how the soap is almost the same S.G. as bio and it mixes with the convection currents caused by the ambient rise and fall of temps, time and not drawing to the bottom is my best defense. my bio using the bromo test at <10 to 70ppm which is good enough for me, unfortunately the lowest soap counts were water washed. I am skeptical of wood chip as well tried it and it worked too well i think it just reacts with the tannic acid to show no soap but is splitting the soap molecule to its constituents ffa etc, i filter down to 0.5 micron and there is still soap there.
January 17, 2010, 03:13 AM
john galt
drying bio is near impossible and no real way to measure it,
or so you say...

January 17, 2010, 03:50 AM
Jack Boyett
Too clarify the vacuum level:

90 mmHg/90 torr absolute (90 mmHg above absolute vacuum)
~26 inches of Hg vacuum (relative vacuum, below atmosphere) the reading that a typical vacuum gauge would show
January 30, 2010, 09:03 AM
Jack, In my damp climate your system of drying will not work, Ive tried it. No matter how hot I get the biodiesel splashing or spraying it in damp air will achieve very little reduction in water content. Blowing hot air over warm biodiesel(50 degrees C) is a much more effective solution. I have a setup very similar to yours but I blow air using a 1600w hot air gun. 2 hours of this will reduce biodiesel from 800ppm to 200ppm. I check every batch with a carbide manometer which I constructed myself and is accurate to about 10% ( calibrated against Carl Fischer results)

I notice that your biodiesel plant uses the 500ppm maximum which was always acceptable for petrodiesel. Some countries have set the max at 200ppm because of biodiesels tendency to absorb moisture from the otmosphere while in storage. In a mild damp climate like Ireland I always reccommend drying to 200ppm.
February 06, 2010, 10:53 AM
Legal Eagle
Blowing hot air over warm biodiesel(50 degrees C) is a much more effective solution.

When I used water that is the way I did it too. 45C and then air flow. Took a couple hours to do 80L. Hard water worked much better than the super softened city stuff that came along afterwards and that pushed me towards resin purification instead of water. Haven't looked back since. Next week I get a 200L wood chip drum (thanks Andy) to set up in front of the resin tanks. Final filter (!) is still a 2 micron CAT can.

** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.

December 16, 2015, 12:34 PM
I have processed and tested my biodiesel and the results would suggest that my process produces quality biodiesel. I water wash and have managed to dry my Bio to 225ppm water content and 10ppm soap content. I'm more than happy with these results. No need to over complicate things if a simpler process works.