No meaningful amount of methanol will start to be recovered until you go above 70C.
I add my methoxide at 70C and process at this temp until 3/27 pass, no appreciable amount of methanol evaporates out and what does just condenses and fall back into the mix. After the 3/27 pass I turn on the vacuum and turn up the boiler stat to 77C and let it recover all night. For the last couple hours of recovery I turn up the stat to max 80C to finish it.
Womble-I found out the same as you and Jon when I was trailing the bubble and settle method.
Although methanol has a boil point of about 65°, just raising the temperature to 70 didn't work and I had to take the bio to at least 80° to get it to demeth properly and that was with using the drying attachment whilst bubbling.
Some of the guys in the vod forum were taking it between 80 and 90°
I have made mistakes with process temperature and have stopped the process when I found the temp at @ 72degs.
When the bio was still there was no sign of boiling or bubbling.
When I say mistakes I mean I forgot the heater was still on. (naughty boy)
Womble, if you are not getting that wet paint smell or any darkening of the bio after drying at those temps I would not be unduly worried. Your bio may have a shorter storage life but Im sure, like me, you use your bio as fast as you can make it.
Yes Jon, when I was demething my glycerol in preparation for the Dry Start Method I found nothing much happened until the mid seventies. Doesnt methanol form an azeotrope with water, possibly with glycerol as well? So the effective boiling point of the mixture will be higher than 64°C. Im sure Wesley can put me right on this .
But air bubbling should remove most of the methanol at lower temperatures than the boiling point, after all we can remove water at temps below 60.°C.
haha shelf life, that would be nice. Whats that old saying watched glycerine never drops.
My bio never darkens that I notice and to be honest I'm not sure about the smell. I have a distinct aversion to methanol fumes and seem to be more sensitive than most to them so I don't enter with out a voc mask on. I might try heating a bit in a pot to the point it darkens and see what it smells like as a reference.
No, methanol does not form an azeotrope with either water or glycerin
Yes, it is called evaporation. I usually bubble air through my biodiesel at ambient temperature to evaporate out most of the methanol
Nope, like Tilly said, no azeotrope with water.
That's why its possible to recover 100% methanol without the need for fancy reflux columns etc like whats used with ethanol distillation.
If you mix two or more miscible liquids together such as methanol and water or methanol and water and glycerine, the boiling point of the mixture is different from the boiling point of the constituent liquids.
The amount of each liquid in the vapor will vary depending on it's original boiling temperature and how much of each liquid is in the mix.
In the case of distilling methanol from the glycerin, you found that the boiling temperature is above about 70C. Because of the much higher boiling temperature of glycerin, if there has been no water added to the mix just about everything out of a simple pot still will initially be methanol with a small amount of water.
As the methanol is removed the boiling temperature increases and the output of the still starts to contain more water.
I have found you can keep getting an output above 100C but it is not really worth chasing the small amount of methanol available that will have more water in it.
Virtually no glycerine ever comes out of the still because of it's much higher boiling point.
That makes sense, thanks.
I have not recovered from just the bio for quite some time now so I really have no recollection of the temperatures I used for demething strait bio.
I use a vacuum pump and monitor the pot temp instead of the head which are both non conventional, leading to my numbers being significantly different than most with a traditional setup would have.
The hottest the head of the still ever gets when recovering methanol with my setup is around 65~72C.
Yes, the boiling temperature of a mixture will likely be different than the individual constituents of the mix.
About 10 years ago the chemist Neutral posted a test he had performed that added the methoxide to the oil at 65C. The methanol did not start to boil out until about 77C.
Getting back to the discussion of the spray dryer, another refinement might be to try a ring with 200 1mm holes instead of 100 2mm holes. The smaller holes might atomize the bio better and would expose a greater surface area to the air flow. It wouldnt involve much expense , just a bit of patience. If the holes were in a zig zag pattern this would direct the jets in 2 different directions, again helping with the surface area issue.
Yes smaller holes would cause an almost misting effect.
I thought it would reduce flow but twice as many holes at half the size should give the same flow rate as before.
But you would only do that if you weren't getting the same result as Richard (did he say he dried his batch in half an hour?) If so it's very impressive and doubt you'd get better than that.
Can't help thinking though a small fan above the spray ring just to disperse any moisture coming off the bio would speed up drying time even more (if that's possible)
I've just dried a batch last week so it would be another month before I'm ready to dry again, but anyone trying out the spry ring here would start by following Richards example completely, test for water content and then play around with a few of the ideas you mention to see if there's any improvement.
But Richards design seems to be a very simple and extremely effective and wouldn't like to over complicate it for the sake of it.
I hope Richard doesn't take any offence in us jumping the gun and debating how to improve on his (already effective) design when we haven't even tried it ourselves yet..
It's the perfectionist inventor spirit that runs through the Ireland public/pm threads....
Sometimes we just cant help ourselves.
Hi Trigger and Imakebiodiesel,
Thanks again for your kind comments.
Thanks to Dgs for his hard work in setting up the test equipment at his own expense and testing the samples, without who we wouldn't have any accurate data.
Imakebiodiesel - in my view it could be worth experimenting with smaller holes to test the limits of the design. But I also agree with Trigger to trial the design as it is before making any modifications.
I think we would all agree to change one variable at a time? Say leaving the heater on for slightly longer for example?
To reiterate the procedure for your use.........
1. Bring biodiesel temperature to 55 deg C and leave the lid on while heating
2. Take the lid off and Turn on the spray ring with the heating element still on
3. After half an hour turn off the heating element but keep the spray ring on
4. Keep the spray ring on for another half an hour and then switch off
5. End of procedure
Overall drying time =1 hour
Overall energy input = Approx 2-3kWh
I agree changing more than one variable is hopelessly confusing.
Im making my last batch before Christmas this week but it is also a further trial of the dry start method so I dont want to change anything from my normal routine. Ill try it after the holiday. I would be most interested to see whether your design will cope with our sodden air.
I know you have access to Daves test equipment but you might find a Carbide Manometer useful especially as you will be able to calibrate it using DGs results. You can find instructions to assemble one over on Rickdatechs excellent site www.make-biodiesel.org
Of course ALL the moisture comes off the bioduesel as evaporated water vapor into the air in the head space of the dryer. This moisture laden air then needs to be removed and replaced with dryer air that can pick up more of the evaporating water.
In the situation you fellows have where the ambient temperature is low, the simple expedient of heating the air as it is blown into the headspace of the dryer will dramatically lower the relative humidity of the air which will greatly facilitate the evaporation of the water as it is sprayed into the headspace of the dryer.
That was the thinking behind my original suggestion:
"In my thinking it seems the main things required for quick drying of the biodiesel is Warm dry air and increased surface area of the biodiesel.
Warm dry air is as simple as heating the outside cold air with a hair dryer as it is blown through the head space of the dryer and is exhausted to the outside."
I have no testing data to support my thoughts, just an understanding of the physics involved.
How is Buttermilk doing?
Imake/Richard- If we do get the same results as Richard over here, I would still be tempted to try out the other suggestions imake mentioned just to see how quickly a spray bar could dry a batch.
I just remembered about imakes lid design which would be more efficient and use less energy than my idea of simply hanging a fan over the top blowing air to disperse the moisture.
Being in a dead end job with no friends, no social life and lots of time on my hands, I Have been thinking about this for the last several hours.
RJK said that increasing the number of holes in the spray bar made no difference to the drying, it was increasing the temperature of the oil that did.
This shows that initially, the limiting factor to how quickly moisture was removed from the biodiesel was not surface area of the biodiesel, it was the ability of the moisture to evaporate and be removed from the head space. To evaporate, the air in the head space needed a lower relative humidity.
As the biodiesel was heated, this also eventually heated the air in the head space which automatically lowered the air's relative humidity allowing the air to hold more water vapor. Warm air holds a lot more moisture than cold air.
Heating the oil to indirectly heat the air is relatively time consuming and not particularly efficient. Also, if the dryer is not designed to insure the head space air is contained to allow maximum heating of the air and an adequate residence time in the head space to pick up moisture, this will be a limiting factor.
It would make sense to also heat the air directly and to a higher temperature than the oil. You need to keep the air moving through a confined head space area and exhausted to the outside so there is time for the air to pick up moisture while constantly supplying fresh Warm Dry air to immediately pick up any moisture that wants to evaporate out of the biodiesel.
So Trigger, How is Buttermilk anyway?
Hi all I have been reading with great interest the discussions on drying biodiesel . My own setup
is a GL design twin 205 litre cone bottomed tanks with clamp on lids fed by a 120l/min Pedrollo pump. It works well but I have a concern with the high 90 deg C temps needed to demeth .Previous to converting the system to a GL design the wash tank / dryer tank used a spray bar and circulation, combined with vigorous bubbling with a compressor.This was effective in drying the fuel in about an hour for 180 litre batches. The downside was high energy consumption and the spray bar was messy, mainly due to the power of the pump.I needed to put in a bypass to regulate the flow to the spray bar to reduce the spatter outside the tank when I read about Imake's turbo dryer.I sense that Imake feels that the mark 2 turbo dryer is his preference to the use of two fans provided everything is well sealed.I have several questions.I note that 12v fans are used. I have two 240 v fans with 20cm diameter blades from a large chest freezer would these be O.K.? I would use one not two.James RL on the Vegetable oil diesel forum advocates using a 60l/min air pump using the bubble and settle method. Would this be too powerful in the turbo dryer. I note that Imake increased the capacity of his air pump to good effect.Thank you all for your input and particularly to Imake who is tireless in his imparting of knowledge. I eagerly await comment.
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