A year or so ago, Guzzler posted this thread:

http://www.veggieavenger.com/avengerboard/viewtopic.php?t=513

with this picture of what his processor's vent looks like (I think it shoudl also be plumbed to the outdoors after that copper tube though!!!!):




He's finding that it keeps any methanol vapors from escaping during filling or processing as the vapors cool down and recondense into liquid, and just drip back into the processor.

I've heard again and again in the last few months of people making 'bad biodiesel' when they accidentally lose a lot of methanol through an open vent during processing .Basically the methanol can evaporate if you're circulating the pump for an extended period of time while processing. This causes a weird,thick-looking half-biodiesel to form- low conversion biodiesel.

I think the most foolproof way of insuring against that is to install something like Guzzler's condensor before your vent tube. That way if you forget to close the vent valve the methanol can't escape via evaporation.
Make sure yous till plumb it to the outdoors after the condensor, though! If something were to boil hard due to a major mistake or accident, the condensor wouldnt' provide enough cooling to recondense the vapors into liquid state and you'd have methanol fumes in the workspace.


Mark

A comment on this setup.

1. The tube is very small diameter. In a real runaway overheat situation it might restrict the flow of methanol. This would be of no concern in a suitable pressure vessel but with a 200 litre drum might be dangerous.

2. In terms of an air cooled reflux condenser it is overkill. All that is necessary is a single vertical pipe, say 3/4 inch diameter. You will discover, if you have one, that it does not get hot while doing the reaction, provided the temperature is controlled. 60 deg C is fine. As a single vertical tube does not get hot it must be adequate.

3. If you want to be very thorough the tube should lead outside so that while filling the vessel the fumes do not flow into the workshop. The fumes that flow out while filling cannot be prevented by having a coil of copper tube as they are carried out dissolved in the displaced air. In a well ventilated area I would not be concerned about this.

Neutral,

When loading the methoxide into the tank, we have methanol laden air being displaced by fluids. The air is most likely at reaction temp of about 60C. Cooling the air to ambient temprature will force some methanol to condense. I take what your saying to be that we will need a water jacketed condensor to take the methanol concentration of the expelled air below 50ppm?

Rick

RickDaTech

The intricacies of this topic are pretty interesting. There is no way that you can totally prevent the methanol vapour from leaving the reaction vessel while adding the NaOH/methanol, by using a condenser on the vent, even if it is chilled with cold water. This is because the methanol is leaving dissolved in a flow of air. Cooling can reduce the amount leaving by causing it to come out like dew on the walls of the condenser. It cannot eliminate it however because the amount that comes out is just the difference between the saturated amount at the two temperatures. It is not like distillation where you have pure methanol vapour which can all condense.

What I contend is that the amount of methanol that is lost through the vent while filling is not enough to worry about in economic terms. If it is a concern from the health point of view because of working in a confined unventilated space it is easy to connect a hose to the vertical vent tube and deliver it outside. The amount of air that is displaced by the entering reagent may not as great as one would at first think because, if the reagent is added slowly, about half of it is consumed by the reaction.

There is a way to totally prevent this methanol vapour from escaping however. Connect a hose from the top of the vertical vent tube to the breather in the NaOH/methanol container. As the reagent flows from there to the reactor the vapour will pass into the reagent container.

In this method the only time methanol vapour would escape into the room would be when preparing the reagent.

You can see where this leads. If you want to stop all methanol vapour escaping into the room you would have two breathers on the reagent container, one connected to the reaction vessel and the other going outside. You would fill the reagent container with a pump from a drum and vapour would go outside. While transferring the reagent to the reaction vessel the vapour would be trapped.

There has to be a simpler way than running tubing to every vessel. What about venting through a water bath or a substance that reacts with the methanol? The goal is to get the methanol below 50ppm. In the research I've done that seems to be the detectable lower limit for methanol vapors. The only sure fire method seems to be dilution (venting outside).

I really do think it's the same issue with methanol recovery. The condener will only shift the local pressure and temprature (as long as the BTUs are available) below the dewpoint. We can have the same discussion about water, when we chill air containing 60% relative humidity below it's dew point, you get condensation and you also get 100% relative humidity. At the dew point and below the air is always saturated with water. The ammount of water "disolved" in the air can be found by looking up it's partial pressure in the steam tables. The same mechanics happen with methanol.

If we look at drying air of water, some techniques come up that might be appliciable, like passing the vapors through a methanol absorbing material. Got any ideas on materials that might absorb the methanol below 50ppm? water? what about venting through an empty washtank with a fogging mister running?

I forgot, the reason for discussing these options is envioronmental regulations. We are already seeding these types of issues in Pennsylviania, where the state is regulating zero emmisions even down to homebrewers.

I think guzzlers reflux condenser would be a good safety feature, refluxing methanol back into the tank when accidentally boiling off methanol. I'm not sure it can handle the volume of methanol generated when say 30 liters boils off because the oil is at 75C. But it should handle small events of localized boiling that happen while getting the methoxide feed adjusted.

RickDaTech

There are two issues here: rupture safety and air contamination safety. What serves one will not necessarily serve the other.

Guzzler's air condenser seems too small in diameter to provide rupture safety with a 44 gallon drum reactor in an accidental overheat situation. It will provide rupture safety if temperature is correctly controlled. To provide rupture safety with accidental overheating two feet of 3/4" vertical tubing would work and there would be no significant loss of methanol under normal temperature control.

Incidentally any losses due to diffusion and breezes blowing over the top of this vertical vent tube will be virtually eliminated if the tube is plugged at the top with cotton wool. One foot of tube with cotton wool would suffice.

To provide zero emission you could, as you suggest, pass the vent pipe into a water bubbler. I wouldn't bother with such a detail unless forced by legislation as the impact of the vapour on the environment would be negligible.

And of course the more you fiddle with complex things the more traps you have to avoid. If you attempt to catch methanol in water you have to also provide a mechanism to avoid suck back of the water on cooling.

If you want safety and simplicity just use the vertical tube on the reactor, a tuft of cotton wool at the top, and have the plant in a location with good ventilation, eg near the door of the garage and work with the door open.

Regarding methanol recovery you say "I really do think it's the same issue with methanol recovery. The condenser will only shift the local pressure and temperature (as long as the BTUs are available) below the dewpoint."

This is not really a helpful view as the dew point concept has to do with saturation of air with water vapour, or in our case, with methanol vapour. In distillation there is no air stream to carry the vapour, there is just the stream of vaporized methanol, a gas, all of which condenses if the condenser is not overloaded.

It is true however that at the commencement of distillation there is air in the top of the pot which will be carried over in the methanol gas stream but this will soon cease. If you were keen to prevent this putting methanol vapour in the workshop you would vent the distillation receiver vessel to the outside of the workshop.

Neutral,

I'll give your 3/4" tube a try and see how it works. I've already had one report of someone doing that. They had a copper tube running up to the ceiling of their shed with no exterior vent attached. They loaded 8 gallons of methoxide in 5 minutes boiling off a lot of their methanol. They definitely had under reacted biodiesel complete with gelling byproduct and nasty emulsions at every wash. All indicating methanol starvation to me.

They did not smell strong methanol odors until they after moved the unwashed biodiesel over to the wash tank, and then it was very strong. So possibly, it worked as advertised and just left a layer of methanol on top of the oil.

My reactor has a 30psi relief valve on it to prevent serious pressure buildup from whatever source. It is vented to the outside. I was in the hardware store tonight and the largest soft copper tubing in stock was 1/2" ID. Would taking guzzlers reflux to 1/2" ID combined with the 30psi relief prevent the overpressure issue?

Going with soft copper makes construction a breeze over the soldering required with hard tubing.

Of course you’re right about air not being involved in a major way with distillation.

RickDaTech

quote:

They loaded 8 gallons of methoxide in 5 minutes boiling off a lot of their methanol.

It is clear that this person failed to perform the most elementary step of measuring the temperature of the oil before adding the NaOH/methanol reagent. If the temperature is below 60 deg C, boil off cannot happen. You can certainly see how people can put themselves in danger if they don't think. Lucky they had a vent tube. If they had pumped in the reagent without a vent they might have burst their drum.

This incident illustrates another advantage of putting the reagent in slowly through the circulation pump. If you do it slowly a lot of the methanol is consumed before it has a chance to build up pressure.

If your reaction vessel can stand a pressure of 30psi, plus a bit more for the head loss across the valve, it will be safe no matter how small your vent tube.

Why do you need soft copper? Wouldn't hard copper be better for a short length of vertical tube?

quote:

Why do you need soft copper? Wouldn't hard copper be better for a short length of vertical tube?

Neutral: good discussion. I'm sure a lot of folks will benefit from reading it. Here in the 'states, soft and hard copper are different sizes, and use different fittings. The hard copper tubing fittings are soldered on. The soft copper tubing uses compression or flare attachments, so if you prefer easily removable connections, you're limited to soft copper tubing, which is only available up to 1/2 inch diameter.
There's a soft rigid copper tubing - the same sizes as rigid rigid, and accepting only the same solder fittings, but quite bendable. Most good hardware stores carry it in sizes up to 3/4 inch, and the better ones in 1-inch diameter.
To dramatically reduce methanol vapors, route the condenser tubing into a refrigerator for some length. I'm imagining a carboy inside a refrigerator with tubing connections in the top. One obvious drawback is the opportunity for it to concentrate water in the condensed liqud.

Same here, but using a soldered fitting shouldn't be a hassle. Solder on a threaded fitting where dismantling is needed. Soldered fittings are cheap compared with compression fittings.

With a fridge on the vent pipe you would collect a few more drops of methanol but I doubt if it would be enough to pay the electricity bill.

quote:

Originally posted by neutral:

quote:

They loaded 8 gallons of methoxide in 5 minutes boiling off a lot of their methanol.

It is clear that this person failed to perform the most elementary step of measuring the temperature of the oil before adding the NaOH/methanol reagent. If the temperature is below 60 deg C, boil off cannot happen.

This person was operating at a proper temprature, and loading the methoxide just before the pump. I'm not sure if the issue was boiling in the pump (the guy's oil may have had water in it) or if it was the issue Mark was addressing earlier about the pump running a long time and the methanol evaporating. I assumed the oil was wet and mixing it with a high ratio of methoxide generated enough heat locally to boil off the methanol.

Neutral, some folks are intimidated by soldering. They have used wrenches, but not a torch for soldering. It took me a bit of practice before I could solder copper tubing for an HVAC that would hold a vacuum. With soft copper, you also have the advantage of being able to route the tubing around obstructions and through walls with just some bending.

quote:

Originally posted by girl mark:
A year or so ago, Guzzler posted this thread:

http://www.veggieavenger.com/avengerboard/viewtopic.php?t=513

with this picture of what his processor's vent looks like (I think it shoudl also be plumbed to the outdoors after that copper tube though!!!!):




He's finding that it keeps any methanol vapors from escaping during filling or processing as the vapors cool down and recondense into liquid, and just drip back into the processor.

I've heard again and again in the last few months of people making 'bad biodiesel' when they accidentally lose a lot of methanol through an open vent during processing .Basically the methanol can evaporate if you're circulating the pump for an extended period of time while processing. This causes a weird,thick-looking half-biodiesel to form- low conversion biodiesel.

I think the most foolproof way of insuring against that is to install something like Guzzler's condensor before your vent tube. That way if you forget to close the vent valve the methanol can't escape via evaporation.
Make sure yous till plumb it to the outdoors after the condensor, though! If something were to boil hard due to a major mistake or accident, the condensor wouldnt' provide enough cooling to recondense the vapors into liquid state and you'd have methanol fumes in the workspace.


Mark

Could this be used to recover Methanol when I dump my glycerol and heat up my Biodiesel for recovery purposes. I will be using Magnasol to "wash" with and Biodiesel needs to be Demetholated.

Ian

The intent of this design is to condense methanol and put it back in the water heater where it came from. A distillation condenser would need to be designed differently.

RickDaTech

quote:

This person was operating at a proper temprature, and loading the methoxide just before the pump.

Whatever the reason there had to be something wrong. It is a physical impossibility for any liquid to boil away at a temperature below its boiling point. A comical definition of boiling point is the temperature at or below which boiling does not occur.

Even if the oil had been exactly at the boiling point of methanol no boiling would have ocurred - if any boiling occurred the refrigerating effect of the evaporation would immediately bring the temp down below boiling.

Neutral,

Is not mixing lye or methoxide with water an exothermic reaction? When heat is added, via an exothermic reaction, to a substance near its boiling point, is it not possible for the substance to exceed its boiling point?

There may have been something wrong, like very wet oil.

wet oil plus concentrated methoxide (lots of lye) can cause a local temperature spike which can translate to localised boiling. I think this is only likely to happen within pump-mixed processors that have the methoxide/oil mixing inline like Appleseed (normally that inline mixing is good- gives you control over distributing the methanol evenly within the mass of oil)



Mark

quote:

Originally posted by neutral:

To provide zero emission you could, as you suggest, pass the vent pipe into a water bubbler. I wouldn't bother with such a detail unless forced by legislation as the impact of the vapour on the environment would be negligible.

And of course the more you fiddle with complex things the more traps you have to avoid. If you attempt to catch methanol in water you have to also provide a mechanism to avoid suck back of the water on cooling.

What if, instead of having the end of the tube/pipe in the water, you had a little dip in the line, like this...

I'm puzzled about something. If I have a 30PSI pressure relief valve, and I have a loop between the methoxide mixer and the reactor during mixing(i.e. one tube for methoxide getting sucked into the reactor, one returning to the methoxide mixer to equalize pressure and to keep any vapors inside the system), why would I need a condenser like this? Wouldn't it be better to try to keep the system closed and under slight pressure, assuming I'm not overheating?

is there any reason why a copper tank should not be used as a reaction vessel?