Hi

The table is a rather complicated 3 dimensional one, because the temperature and pressure relationship ALSO depends on the concentration of methanol - the boiling point rises as concentration drops.

For pure methanol, you can get an idea of boiling point versus absolute pressure in mmHg here ...

http://www.s-ohe.com/Methanol_cal.html



For methanol mixed in biodiesel or glycerol, at atmospheric pressure, the boiling points versus concentrations is described at ...

http://biodiesel.infopop.cc/eve/forums/a/tpc/f/44410893...101057961#6101057961

The harder the vacuum you can pull, the more methanol you can recover for a given maximum temperature.

GL,

1. Do you have one of these operating? Any pics?

2. In approx. percentage, how much methanol are you recouping?

2a. Have you tested the Glyc? Is there a way to do this to see ho much meth is still left?

3. Have you tested any bio out it for purity and if so what were the results?

Doug

Hi Doug

Yes I have this system operating, and hope to have some pics once all is tidied up to a state suitable for 'public' viewing.

I use 22% methanol and get back around 1/3 of the methanol I put into the processor.

I heat up to 90C by the end of the process, higher than I'd like, lower is preferrable.

Not sure what level of vacuum I am drawing - I'm getting a gauge to allow me to monitor this during the process - my guess is I run around 10 psi absolute or 500mmHg - not a hard vac at all, there is clearly a lot of room for improvement on my vac pump, mainly the venturi shape is too rough, but this is a simple thing to improve.

With better vacuum, I should be able to cut back the max temperature appreciably and so reduce likelihood of back reaction even further. I have run harder vacuum in smaller batch experiments, which proved the process can be done much cooler with no evidence of back reaction. I used a bicycle pump with the piston reversed to suck rather than blow

I haven't tested the glyc. not sure how I'd do that, but I guess you could weigh a sample, warm it in a wide, shallow, open dish, blowing air over it for a long time, and then re-weigh to see loss in weight.

For my simple quality testing of the finished product, I compare the finished settled bio to a sample of gently de-meth'd (evaporated in wide open dish several days) settled bio taken before the distillation, to see if its wash properties have been affected, mainly looking for emulsification effects, to reveal presence of MG or DG, and to see if 27/3 is unchanged, which it is.


Hope that helps.

Graham

I know we're not talking about plumbing locations anymore, but i believe this 3D rendering achieves the intent of this process, just in a more traditional "appleseedish" layout.

Graham: thank you again for your response. I expect to be able to start experimenting with different venturi shapes in maybe a few weeks, following your inverted venturi idea. Once I get some results, I'll publish them here, or in the inverted venturi thread.

Projectpurity: very nice! What software are you using?
How do you publish your drawings here?

Berny You always need the same amount of heat to vapourise the methanol, 1100kJ/kg; this is the latent heat of vapourisation. There is no way around this and no such thing as magically avoiding needing energy to do work.

What the lowered pressure does is change the temp at which the vapourisation takes place. So meth boils at say 40degC instead of 65degC. It still takes the same amount of heat with it when it boils and lowers the heat remaining in the liquid it boiled from.

So with each kg you evaporate the amount of heat used, 1100kJ, is the same regardless of the temp this happens at. Every time you evaporate a kg then either the 1100kJ used has to be replaced or the bulk liqid gets colder.

The advantage of using vacuum is not that it takes less energy, in fact it takes more becuase you have to produce and replinish the vacuum somehow.

The advantages are that:

It can allow you to use the heat already in your mix and so potentially give a net saving in energy as you do not have to add more heat and then let the hot liqid just cool down wastefully heating the room once all the meth is out;

It allows you to evaporate at lower temps and so slow down any reverse reaction that takes place, as reaction times are temp dependent.

PP cool 3d pics.

GL We are not worthy but...Range of acid needed per batch so far? Over how many batches?

All you could want to know here. http://www.methanex.com/products/documents/TISH_english.pdf

Wow! Thanks Paulus.

Ok now I am confused. I have always understood latent heat of vapourisation to be a constant for a given substance..

A quick look round the web seems to confirm this.

On page 19 of the methanex information graph the LHV is shown to be decending as temp increases. If I am reading the graph right it would suggest that meth goes from a liquid to a gas at 240deg C or above without using any energy at all! This is ridiculous. You need energy to overcome the molecular forces of attraction between methanol particles.

Otherwise you could recover sensible heat by condensing the vapour and create some kind of free energy supply. Impossible.

What am I doing wrong when I look at the graph?

Ant: thank you. I do know the energy needed theoretically won't change(when I say theoretically, I mean assuming no losses of any kind), I'm familiar with the laws of thermodynamics. The question I asked about the pressure/temperature ratio was because there's no mention of it with the reactor's diagrams, and I needed to know because I'm planning to build myself one ASAP.
About your question on methanol's latent heat of vaporization, what I think (and take into consideration that I'm as unfamiliar with chemistry as I'm familiar with physics, so I may be talking pure nonsense here), is that heat, being a form of energy, may be providing the energy to overcome methanol's attractive molecular forces.
Just my $0.02. If I'm talking BS, I'll appreciate anybody letting me know.

The answer to this lies in the sensible heat of the liquid. Sensible heat is energy added to a substance which does not change its phase. Latent heat is heat that changes its phase. Obviously the hotter a liquid is, the easier it is to get it to evaporate.

I have trouble understanding the graphs 3.13 and 3.14 on page 16.

quote:

I have trouble understanding the graphs 3.13 and 3.14 on page 16.

Specific volume...Hmmm...
The way I see it (remember, I'm not a chemist), if saturation increases with temperature, that means that, as temperature increases, the volume of methanol vapor in air will also increase, up to a point.
So, if we take specific volume as "the volume occupied by a unit of mass of a material"( wikipedia), then the specific volume will decrease with temperature, as a higher concentration can be achieved.

I can understand that. So many variables.

quote:

I can understand that

Again, don't take my explanations of chemical processes as gospel. They may sound logical, but that doesn't make them true. Wait for somebody more qualified to see them.

Perhaps what's being left out is pressure. Maybe a unit mass of vapour at saturation point will occupy a smaller volume at higher temperature without condensing back into a liquid, but it will be at higher pressure. In fact this is how the high pressure side of a refrigeration system works. Saturated vapour is compressed at high pressure into a smaller space, without condensing, and heats up. But as it flows through the condenser (through the fins of which air is forced at ambient temperature) heat is rejected and the vapour turns back into a liquid.

So you're right. Interesting that it's a curve and not just a straight line. Maybe someone else can supply the answer why.

quote:

Originally posted by Ant:
On page 19 of the methanex information graph the LHV is shown to be decending as temp increases.

Ant,

Maybe the graph is showing INCREMENTAL heat of vaporization.

How much heat is required to vaporise methanol that is already at a temperature of, say, 200 deg C. This is a lower value than the heat required to vaporise methanol that is only at a temperature of, say, 100 deg C.

If this analysis is correct, then the idea of "some kind of free energy" really doesn't apply. The heat that was added to raise the temperature of the methanol to values shown on the curve, would have to be added to the "free energy" equation.

GL,
Thanks for the data. With the 1/3 recovery, how does that compare to GL1?

Project Purity,
Thank you for the 3D rendering. Plumbing is not my strong suit and I have a hard time picturing how to layout the 2D stuff in 3D. However, I have a question. There are 2 crosses in your diagram 1. on the pump and 2. below the sight tube. I am referring to number 2. What does that section lead to as it is hidden behind the pump.

Doug

Thanks producer that would seem to make some kind of sense.

But how could you hold methanol at 240degC without it already boiling off unless it was under pressure? And if it is under pressure then you would still need to add approx 1100kJ to make it evaporate. It would just be the reverse of what we do with a vacuum.

If it were at atmosphere and boiling off at 165degC then it would still take 1100kJ per kg to evaporate it. Regardless of the fact it was already at 165degC. Otherwise it would simply cool down and stop boiling before a kg evaporated. It still dosen't really make sense to me.

It seems unlikely that the Methanex data is actually wrong but at best it seems badly presented if it only communicates effectively with people who already understand what is in there. Not much of a learning resource really.

quote:

is that heat, being a form of energy, may be providing the energy to overcome methanol's attractive molecular forces.

Quite right that is why the liquid cools and loses 1100kJ of energy per kg evaporated.

The graph implies that at 240degC the liquid loses no heat energy, per kg evaporated, as the LHV becomes zero.
This seems to be nonsense so I assume that there is something I don't understand.

quote:

Originally posted by Ant:
It seems unlikely that the Methanex data is actually wrong but at best it seems badly presented if it only communicates effectively with people who already understand what is in there. . .

Agreed!

Here is another idea. The boiling point of methanol in a solution with water is higher than the boiling point of pure methanol.

Perhaps the graph is giving LHV of methanol IF it is in a compound with a higher boiling point liquid, say biodiesel that boils at over 300 deg C.

As you can tell, I am really fishing here.