Hello, I am having trouble with my solvent recovery setup. I have attached some pictures and as you can see, the temp in the boiling flask is 78C. Prior to this, i had it set to 80C, where it was constantly hovering around 77C. Isn’t ethanol suppose to boil off at 154F/ ~67C? My temp gun showed that my heating mantle’s temp accuracy is about +6-7 degrees off the digital temp display, but that’s still about 159F/71C. Why is it only then do I see ethanol dripping into my boiling flask?
Just yesterday I had my setup running and was able to achieve some solvent recovery at 72C, which if my heating mantles display is truly inaccurate, would be ~66C, or 150F. That is 4 degrees under the boiling temp of ethanol right? What gives then…
My vacuum pump is one I made using Nalgene Water Vacuum Aspirator and a Superior Utility pump. It’s not great right now because it heats up fast but I’m going to alter its design to make up for that tomorrow. I have attached pictures of it as well.
I’m guessing your homemade vacuum pump is what’s holding you back. When that’s fixed, and you have a vacuum gauge, you may want to also think about getting your condenser colder. With stronger vacuum, you are likely to pull your ethanol past the collection flask and right into your pump.
Would a stainless steel version of the water aspirator be better? What would be holding me back besides temp of the water and the speed that I can move it through the aspirator?
I just don’t think your water aspirator setup is strong enough to hold a consistent vacuum on an ethanol distillation, and perhaps that much surface area to boot. I usually only see those being used for filtrations. I could be wrong, but that’s my observation. I would suggest getting a small vacuum pump.
If your vacuum pump is heating up as much as you say, there’s potential that it’s actually generating back pressure instead of pulling. Have you verified flow in the right direction?
From the pics it looks like the joints on your setup aren’t greased at all. You don’t NEED vacuum to boil your EtOH but if it’s at 78C and it’s not boiling, you probably don’t have any vacuum at all (or your temperature is not what you think it is).
If you are confident you still have water and ethanol in the system, you can backtrack your vacuum pressure from your temp using Boiling Point Calculator
Just observe the temp that the solution starts boiling and input the relevant data into the calculator.
Try bumping the temp up, it could be thermocouple placement or temp variation in your lab air,
have you tried insulating the apparatus with fiberglass mats and tin foil?
That’s an excellent point. It’s surprising how much lab airflow can screw with temps and scales. At another job I watched someone screw up 100 package samples because the denier scale was getting hit by an overhead vent duct.
I agree with the folks that it’s your vac. And as for your condenser I recomend a spiral vapor condenser. You need more surface area.
As for pumps you can use a pilot 300 for basic vacuum. It goes to 24in vac. And it’s actually made by welch. They run like 300$. I actually used my pilot on a 5L roto for about a year with no major issues. It is a bit undersized for that but it was great for the price.
