I'm in the middle of my first methanol distillation run and want to check my understanding of what is going on.

I am using a barrel distiller of my own design, and methanol began to trickle from the condenser at about 150F. I have kept the heater on the highest setting and the temperature has very gradually crept up and is at about 250F now and still producing methanol. I've gotten a little over 6 gallons of methanol from a 25 gallon batch of glycerin byproduct so far.

As I understand it, the temperature is regulated by the dissipation of energy as the methanol boils off. At the beginning, there was a higher percentage of methanol in the glycerin byproduct, so the temperature at which it boiled off was lower. As the percentage of methanol is reduced with continued distillation, a higher temperature is required to sustain the process.
At the point when there is negligible methanol remaining to be driven off, the glycerine will begin to retain the input heat and the temperature will begin to climb more rapidly at the same time that output of methanol drops off dramatically.
This should be a good indicator of when the process is essentially done.
Have I got this right?

I mis-typed in my previous post. At the point where I have rendered 6 gallons of methanol from my 25 gallon batch the temperature is 230F, not 250F.

I would not go past 200F. Water boils at 212F and if you have water in the glycerol layer you risk diluting/contaminating you pure methanol. I use a still pot and am getting 99% pure Methanol in 1 pass (according to my hydrometer.) My cutoff is 190F. I figure that most of the Methanol has been drawn off by this time.

HTH

Ian

mwr you have got it exactly right. People often talk of using a thermostat to control the temperature in the pot while boiling off the methanol, but it not a help. What you need is a constant heat input not a constant temperature. The heat input should be no more than the condenser can take away. The temperature in the pot must gradually rise, as you say. The actual temperature you have to get to in the pot to get most of the methanol off depends on the design of the pot - how far it is from the liquid level to the distillation head, and on the degree of insulation above the liquid level.

quote:

Originally posted by IanTucker:
I would not go past 200F. Water boils at 212F and if you have water in the glycerol layer you risk diluting/contaminating you pure methanol. I use a still pot and am getting 99% pure Methanol in 1 pass (according to my hydrometer.) My cutoff is 190F. I figure that most of the Methanol has been drawn off by this time.

HTH

Ian

If he does not add water to the glycerol, there should not be any water available to distill off.
Should he be using the "glycerol prewash" then an upper temperature limit of 200°F may be wise

In a glycerine prewash wouldn't a large amount of the methanol drop out into the water leaving the remaining methanol to be recovered non-viable energy wise?

The only possible sources of water in my glycerin are the small amount that is chemically produced in the reaction and atmospheric water in the drum at the outset of distillation.
I drain the glycerin into sealed containers about 2 hours after the reaction is more or less complete and it stays there until distillation time. No water gets added. I ran the processor until bed time last night and it was still trickling methanol at 270F. I shut it down for the night at that point. By that time I had distilled about 7.5 gallons of methanol from an original volume of 25 gallons of glycerin.

My barrel and the manifold leading to the condenser is all wrapped in R-13 kraft backed fiberglass insulation. The insulation only allowed a 25F drop in temp from 275F to 250F 8 hours after I shut off the heat.

I'm bringing the heat back up now to see what happens. I have two questions at this point:

1. Is there a practical or safe limit on how high I should take the temp of the glycerin, assuming that I continue to get methanol distillation?

2. How can I test the methanol purity? I know this involves measuring specific gravity, but I don't have a hydrometer, am not sure where to find one that is suitable for methanol. Any suggestions for finding one at a good price? I also need some guidance on how to interpret readings. I found a racing fuel web site that said racing methanol should be 0.7954 at 60F. What is the range that is good enough for biodiesel production?

You can also use a volumetric flask and a good scale. I have a 500 mL flask with a narrow calibrated neck that I picked up for a few bucks. It's marked accurate to 0.2mL at a certain temperature.

So weigh your empty flask, fill it up with exactly half a liter (to the mark on the skinny neck)and weigh the filled flask. divide to find density.

You'd want a fairly accurate scale, like a triple beam balance. I already had that, so I only spent a few extra bucks to gain this quality control device.

Or hey, buy a hydrometer.

Please note that both methods are exquisitely sensitive to temperature to produce accurate results. So I guess a good thermometer is also needed to get a good test.

Finest regards,

troy

mwr- You are about "normal" on your % of recovery- 3 qts to a gallon of glycerin. I have been recovering meth. for Mr Pine for a few months now and I am getting a slightly better yield than 3 qts/gal. more like 3.5. This does very slightly batch to batch as well as the ambient temp. All my work is done outside so these coming months will be a challenge. i suggest you try running a smaller batch- like 5 gal. of glycerin. This will be easier to control the temp and greatly reduce the cycle time. Remember the longer it takes to heat the glyerin the more $ it's costing you to recover the meth. You can quickly go into the "red" trying to get that last drop. As for the purity-I wouldn't be too concerned. If youaren't introducing water into the batch prior what you are getting is good meth. from your condenser. I suggest if haven't already- agitating the glycerin with a mixer while heating. This GREATLY improves your return. HTH-Russ

rjm

Are you sure on your math 3.5 out of every 4 quarts you are getting back? Or 3.5 out of every 4 gallons.

quote:

Originally posted by Legal Eagle:
In a glycerine prewash wouldn't a large amount of the methanol drop out into the water leaving the remaining methanol to be recovered non-viable energy wise?

Legal,
As only a 5% of total volume is used as the amouint of water added to the processor, the water and glycerol remain mixed. Methanol distillation can still be done, and as long as temperature is kept low, or a fractionating column is used, purity should still be high. Recovery of the last few % of the methanol would be more difficult.

quote:

Originally posted by Taz:
rjm

Are you sure on your math 3.5 out of every 4 quarts you are getting back? Or 3.5 out of every 4 gallons.

This figure also seems high to me, but is totally dependent on how much excess methanol you start with.

Finest regards,

troy

OOOPS- No, I am NOT a crack addict!! I simply neglected to proof read my post. (A bad day all around-I was explaining the virtues of my employer to small group of potential customers when half way thru my presentation I realized my fly was down!!) Anyway -the correct number here is 3.5 qts to 4/4.5 gallons of glycerin.Hope this clears things up -I will post up a pic of unit soon -Russ

quote:

Originally posted by Taz:
rjm

Are you sure on your math 3.5 out of every 4 quarts you are getting back? Or 3.5 out of every 4 gallons.

damn i was hoping you were serious and my next question was how. oh well bio is pretty cheap anyway.

The St. Louis Biodiesel Club has been working on methanol recovery as a group project. We've been experiencing a return of between 10% and 30% methanol by volume using a small still (mine has a maximum capacity of 18 US gallons) built from the expansion tank for a hot water heating system's boiler. The variation we've experienced is probably caused by the fact that some of the glycerol we used had been stored for a long time in circumstances that probably encouraged evaporation.

During distillation, we maintain 152*F at the top of our condenser, which is a 4' long copper counterflow condenser. As another person posting here has described, we've also experienced the ever-increasing and high tank temps as the process has progressed.

We're ready to start figuring out a way to control our temperature so we stop wasting all those extra watts. On a recent list discussion at BiodieselBasics, people brought up electronic controller/relay/sensor (semi-automatic) or variac (manual). Does anyone here have any thoughts or experiences to share? Or am I posting to the wrong thread? If so, please accept my apologies and direct me to the right place. Thanks!

You will only be wasting watthours if you have an uninsulated pot. It is a physical necessity to supply all the watthours necessary to evaporate the methanol. Your condenser will have a fixed maximum rate of heat removal, depending on its cooling and surface area, so you will have to supply a continuous heat input about equal to that. If the heat input is too great your condenser will not fully condense the methanol and you will lose product as gas, and probably do yourself harm as well unless doing it out of doors.

The point is that if the condenser and the heater are matched you won't need any controls - just switch it on and leave till the methanol stops coming.

If you suspect more than a little water is present you will need a fractionating column and will need a thermometer at the top of the column which will read 64.5 deg C. Continue to heat until the temperature there either drops or rises. If it drops it means there is no longer enough methanol there to be worth getting and the heater should be turned off. If it rises it means water is starting to come over and the heater should be turned off.

Thanks for that, Neutral. Although I've avidly read many of your posts, this is my first opportunity to thank you for taking the time to help so many people with your posts to this forum. You're most generous!

Although the tank and plumbing are insulated, my condenser may be mismatched with my heating element. Although I ventilate it to the outdoors, the carboy I'm using as a trap got somewhat pressurized during a 30 minute test I did a couple of nights ago. I realize that the initial volume of condensate continuously tapers off over time, but it would be a shame to set up an inefficient process.

My counterflow condenser already has a thermometer at the top where the vapor enters. The condenser is 1/2" (12.7mm) copper 4' (1.22m) long with a 3/4" (19mm) jacket; my heating element is 3000 watts. I imagine my water pump's ability to move a certain volume of water would probably be another variable.

Is there some kind of formula I can use to determine how to size these components in relation to each other? If my heating element, for example, were a given, then shouldn't I be able to size my condenser and water pump capacity in relation to that?

Thanks again, Neutral!

great to see you on here. By the way we can probably set up a methanol recovery section of this forum (similar to the esterification forum), which would save the necessity of 'recruiting' members for another yahoogroup (there's talk at biodieselbasics about starting a methanol recovery discussion list somewhere separate), and would get you much better exposure for that project than starting a brand-new list would require- there have been lots of posts on that subject here lately.

Mark

Theoretically it is possible to size the condenser and the water flow by calculation. You start with the latent heat of vaporization of methanol (this happens to be about 85% of the latent heat of vaporization of water). In practice it is probably easier to take a guess and see how it goes.

There are a couple of things you could do to get started in a simple way. Boil away a bit of water in your electric kettle. Measure the time and the amount lost. Don't count the time it takes to bring it to the boil. Note the wattage of your kettle. Compare with the wattage of your distillation pot. From these you can work out the rate of methanol loss to expect from your distillation pot. Imagine what that flow would look like and design a condenser that you think would handle it. I hope there is someone reading this who will tell you the exact flow of methanol to expect from a given wattage without doing this experiment.

When you do a test distillation have an additional length of uncooled pipe at the end of the condenser. Put your hand on that during the run. If it is too hot to handle your condenser is not adequate.

Maud,

is Sam Ley working on this with your group- he's got those calculations at his fingertips or at least thought he did last fall.

Mark