Sunday, August 2, 2015

DIY Rotovap

I wanted to do some vacuum evaporation projects, so I built a DIY rotovap. This certainly ain't a laboratory grade, strong solvent resistant, low leakage setup, and it has very few speed settings (currently "On" and "Off"), but it does indeed work at allowing vacuum distillations to be carried out, recovering a distinct overhead product and bottoms product.


The evaporation chamber is a Mason jar with a 3/4" x 1/2" PVC bushing epoxied to the lid. I used two electrical conduit locknuts to hold the fitting in place while the epoxy set.



To rotate the evaporation chamber, I mounted an electric motor in a wood frame and mounted a section of 1/2" CPVC pipe in a pillow block bearing. I connected the bearing to the motor shaft with a series of small plastic gears.



I left one section of the CPVC un-cemented on top of the bearing, to allow the pipe to be removed from the bearing. Adding a bit of teflon tape to the pipe before pressing it into the coupling gives a "good enough" vacuum seal.


The heating method for the Mason jar originally gave me trouble. At first, I considered a laboratory hot plate, but was put off by their high cost, and the difficulty I expected to experience in getting uniform heating on the jar. I then realized that I was an idiot, as I already had an electric skillet that I could put a pot of water on to uniformly heat the jar. I tried this, but was less than impressed with the amount of heat I could transfer into the jar. It was also a cumbersome setup. While at the store looking for a smaller, higher heat output hot plate, I realized I was a double mega idiot, and that I had a crock pot that could do exactly what I wanted, with a pretty good heat output to boot. What's more, it's relatively easy to control the temperature in the crock pot over the timescales on which the distillation runs by adjusting the heat setting on the pot.

The next tricky part was the method to give a vacuum-tight seal while allowing continuous rotation. The method I ended up on was to use a compressed air quick connect fitting. These are available at any hardware store at a low cost (about $5 for the male and female components). I used a 1/4" fitting. It does have a rather small restriction through the fitting which isn't ideal for vacuum pressures, but again it works "good enough" for this non-high-vacuum setup. It does have a fair bit of resistance to rotation, which is why the motor I ended up using was so large - a first draft used a smaller motor that couldn't overcome the resistance of the quick connect fitting. The motor I used has a gear reducer that reduces the rotation rate to about 60 rpm, giving it high enough torque to overcome the resistance. It remains to be seen how well the quick connect fitting holds up with use, but they're pretty darn cheap and could be replaced easily.

The overhead business side is the handled by a filter flask. In operation, the flask sits in a bath of ice water to condense the overhead vapors and collect them. This is the only actual piece of lab glassware in the entire setup, and I used it because I had one on hand. I could just as well have modified another Mason jar to the task. A section of PVC extends down nearly to the bottom to force the heated vapors to come into close contact with the cold walls. If the flow didn't contact the vessel walls, a good portion of the overhead product would go straight out the side port to the vacuum pump, which would be bad for the pump and bad for the recovery of the overhead product.


I originally had some difficulty with the sealing element between the filter flask and the PVC, but then fortuitously discovered that a 3/4" PVC compression coupling's rubber gasket is perfectly sized for this filter flask's mouth diameter. A flexible hose connects the filter flask to my Harbor Freight vacuum pump.

Here's a dry run showing everything working together:



Here's a hot run with the first generation (aka dumb) heating method for the boiling jar.


My first run was to distill some tea - I wanted to make some tea concentrate to use in other recipes. It was a technical success, in that I was able to concentrate the tea to a much stronger concentration, with an overhead product that tasted like plain water. The concentrate was decidedly non-tasty, though, so it might not have been a recipe success. I'm not sure if this is because I got the fluid too hot during the distillation - the whole point of vacuum distillation is that you can boil the liquid at a lower than normal temperature. I plan to try again, we shall see if tea-asty product will result!




6 comments:

  1. Great project.
    I have some questions:
    1. What is the green metalic part below vacuometer
    2. Did you evaporate more, and what was speed and efficiency.

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    Replies
    1. Bukaj,
      1. The green part I believe you are referring to is a quick connect air fitting, meant for quickly connecting and disconnecting air tools. It allows free rotation while maintaining a seal. I think this is the exact one I have - http://www.amazon.com/Legacy-A71458B-Color-Connex-Type/dp/B003TFE7XE/ref=sr_1_3?ie=UTF8&qid=1461975995&sr=8-3&keywords=legacy+color+connex

      These fittings are commonly sold wherever air tools are sold. The exact type used isn't that important.

      2. I haven't ever evaporated more than about 100 mL at a time. That took several hours to accomplish with this setup, but the exact time will depend on the water bath temperature, the flow restrictions between the hot side and the cold side, and the cold side temperature. In fact, that's a fascinating discussion which I glossed over in the original writeup. I'll have to expand the post to discuss that a bit more.
      Peter

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  2. Hi, i found your video while searching for some info, i’m doing one too. Can i ask you, do you leave the vacuum on during the whole process or does it have to be turned off once the desired vacuum is acquired?

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  3. J,
    Yes, I leave the vacuum on the whole time. The setup is a bit leaky and the vacuum pump continues to pump out the air that leaks in.

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  4. Hello peter, thanks for your awesome work! You're truly a talented individual. I am making one of your designs to use after cold ethanol extraction could you please tell me what type of motor you used and where can i find one? If its not too much for you could you make a list of all the equipment used to make this project. I'm very new to this type of equipment so I'm not sure what are the right parts to use.

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