Distillation Observations

[frosch45]

So I’ve just gotten a new container of sulfuric acid, but it has a black inhibitor in it (see below). I'm having real trouble, its frustrating because the distillation is terribly inefficient, and I was wondering if I could get some suggestions on my whole setup. I've been trying to get the acid over without the inhibitor, and it has certainly been working, but I would like to speed it up a little.

 

So here is my overall setup:

 

 

 

As you can see, I have a 1000 ml RBF leading to a three way joint (top part is stoppered). I decided to tilt the RBF so that it is at about a 30 degree angle from the ground in order for the vapor to more easily go down the liebig condenser. I was also trying to minimize the amount of condensation in the 3-neck joint that fell back into the RBF. This leads to a Liebig condenser. The reason I had this condenser is just to increase the condensation, but I actually think that it may be hindering the overall process. As you can see, this thing is insanely long. What often happens is that the vapor gets pushed into this condenser and it just sits there, even with the ice cold water running through the Liebig. The graham does a much better job, and I'm wondering if it would be more effective on its own.

 

 

Next I have a 300 mm graham condenser. This is where the condensation takes place, if anywhere. Its interesting because the condensed pure acid will go up and down in the coil as affected by the boiling and my vacuum pump.

 

Down at the bottom I have a vacuum adapter which is hooked up to a vacuum which pulls about 600 mm of mercury. Its just a hand crank, but its still effective. I have in the line leading to this vacuum a makeshift scrubber with NaHCO3. It has been pretty effective; I have put some ph paper inside it to observe and the scrubber has been doing a pretty good job. I like to keep the vacuum at 400 mm Hg.

 

I then have a 1000 mL RBF to collect the distillate (ice bath in the picture has melted because I put lots of NaCl in the bath to help the ice melt. I have gotten about 150 mL after about 3 hours.

 

So, I was wondering if there were any suggestions. Here are my concerns:

 

1) The setup is too long and has too much 'air' in the system.

2) The Liebig condenser is hindering the process instead of helping

3) Boiling chips are required (I had broken up some glass pieces and put them in the bottom, but I am not sure if this helped), and I often see evidence of super heating and then a sudden burst of vapor in my boiling flask

4) The acid is condensing in the 3-way joint and just falling back into the boiling flask. Should I turn my boiling area to be completely horizontal? (When I had the flask vertical, there was TONS of condensation in the 3-way joint occurring and just falling back into the boiling flask, but do you think that this is still the best way?)

 

Thanks for helping me brainstorm some ideas.

[nitric]

that is not the way to put the three way adapter, you have to put it vertically and also you should test the distillate by dropping some on a peice of cardboard and it should turn black

[frosch45]

I'm sure that I got the right distillate because when I was cleaning the classware with sodium bicarbonate it fizzed a lot. I know its not the traditional angle that one should use a three way adapter, but this sped up the process because the gas was able to flow to the condenser more freely, and it kept a tight seal anyway. Thanks for the response though.

[nitric]

the bicarb is not a good test, i've had 10-15% H2SO4 overflow containers from the fizz with bicarb, but only 90+ H2SO4 have i seen char a piece of cardboard

[frosch45]

just tried it. it chars

 

 

but i'm really interested if anyone has any observations pertaining to my first post?

[UC]

Turn the 3-way adapter right side up. Use a smaller heating flask or insulate the larger flask to get more vapor into the condenser. I'm surprized one condenser (or even an air condenser or no condenser) wasn't more than enough. Drop the leibig entirely. The graham just gives more surface area for the H2SO4 to condense on. Were you getting a "fog" of acid in the liebig? Use boiling chips. Activated carbon or maybe even some powdered plaster is probably acceptable as a crude replacement.

[nitric]

activated charcoal would be better than plaster as plaster would react

[UC]

activated charcoal would be better than plaster as plaster would react

 

No it wouldn't. Plaster of paris at least, which is what most people think of when they think of plaster. It's calcium sulfate. Sulfuric acid isn't going to do anything to it.

[frosch45]

Turn the 3-way adapter right side up. Use a smaller heating flask or insulate the larger flask to get more vapor into the condenser. I'm surprized one condenser (or even an air condenser or no condenser) wasn't more than enough. Drop the leibig entirely. The graham just gives more surface area for the H2SO4 to condense on. Were you getting a "fog" of acid in the liebig? Use boiling chips. Activated carbon or maybe even some powdered plaster is probably acceptable as a crude replacement.

 

Sounds good. Just one question. Why should I turn the adapter right side up? It always seems like more vapor gets through if its horizontal...

 

I do like the idea of insulation. I hadn't even thought of that.

 

I had actually used boiling chips, but they were glass, and now that I think about it, that glass is far too smooth to help. I'll use some plaster.

 

Yes, in the Liebig, I got just fog, but because of the rapid changes in pressure in the system (boiling chips didn't even help that much unfortunately, i'll make them smaller next time), the liebig just helped keep that fog in an area where the gas was constantly cooling (and any condensed liquid would run away from the boiling system instead of back into the boiling flask).

 

thanks for the tips, seriously

[DrDNA]

Just out of curiosity, can I ask why you are distilling sulfuric acid on your patio?

[frosch45]

lol, i don't have a labratory <kick self>, so unfortunately, in order to not risk vapor getting into the place that I sleep, I have to do it outside. I'm trying to be as safe as possible for this very dangerous (but thrilling) task.

[UC]

Sounds good. Just one question. Why should I turn the adapter right side up? It always seems like more vapor gets through if its horizontal...

 

I do like the idea of insulation. I hadn't even thought of that.

 

I had actually used boiling chips, but they were glass, and now that I think about it, that glass is far too smooth to help. I'll use some plaster.

 

Yes, in the Liebig, I got just fog, but because of the rapid changes in pressure in the system (boiling chips didn't even help that much unfortunately, i'll make them smaller next time), the liebig just helped keep that fog in an area where the gas was constantly cooling (and any condensed liquid would run away from the boiling system instead of back into the boiling flask).

 

thanks for the tips, seriously

 

It's not about the size of the boiling chips. It's about surface area. One or two real boiling chips probably have the surface area of hundreds of crushed bottles. It provides a good place for bubbles to nucleate. The sulfuric acid fog *is* condensed, just not sticking well to itself. The shape of the graham condenser forces it to hit walls and coalesce into drops.

 

The rationale for the upright 3-way adapter is to minimize strain on the glass joints and keep acid from pooling in the 3-way (and possibly seeping past the stopper).