Sciencemadness Discussion Board

Chinese rotavaps?

Refinery - 14-6-2020 at 06:40

I checked on ebay that Chinese sell rotavaps at base cost of 1k$ from 1 to 5 liters, the 5L model costing 1800$ + 50$ shipping.

Are these of any good?

Fleaker - 15-6-2020 at 07:09

I have a 50 L one that seems to work ok.

Dr.Bob - 15-6-2020 at 08:03

I have only used one or two chinese ones, but they are hard to find parts for or repair. If you buy a used older Buchi model, then you will be able to find parts, replacement hardware and repair them forever. I have used them for 30 plus years, and will stick to them. I have recently repaired (with help) as few units that are 10-30 years old, and it is fairly easy to do. And they took that long to break. I have also used a few other brands, none did as well as Buchi. You can get used Buchi's for $500-1000 easily, I have one or two, they are all over Ebay. And the glassware for them is easy to find as well.

Refinery - 15-6-2020 at 08:17

Considering your points and that they seem to be well available sub $ 1k, I'd put my bet on them over chinese. Didn't thought they were within my price range - usually any western made high tech tends to cost 5-10x over chinese, being well over amateur budget.

dawt - 15-6-2020 at 09:47

I absolutely second getting some quality used gear. Not sure where you're located, but complete and functioning old Büchis regularly can be had for € 2-300 on German eBay.

[Edited on 2020-6-15 by dawt]

Refinery - 15-6-2020 at 11:18

This might be an awkward question, but is rotavap superior for distillations compared to ordinary, bleeder/vacuum assisted static distillations?

dawt - 15-6-2020 at 11:35

The only thing superior is the speed. Separation is terrible, which is why it's basically only used to quickly remove solvents from high b. p. compounds.

G-Coupled - 15-6-2020 at 11:39

Quote: Originally posted by Fleaker  
I have a 50 L one that seems to work ok.


A 50L Chinese one? How much did that cost you, and how long have you had it, as a matter of interest?

RedDwarf - 16-6-2020 at 03:44

I'm assuming that rotavaps can accept a variety of flask sizes, so what does a 5 litre size refer to? Size of flask provided, the physical space to fit a flask into or some measure of the ability to handle a certain flowrate of solvent?

Refinery - 16-6-2020 at 04:30

How does 50L flask works, how it is protected from breaking at the neck?

OldNubbins - 16-6-2020 at 23:40

Thick neck?



[Edited on 6-17-2020 by OldNubbins]

Heptylene - 17-6-2020 at 01:20

Quote: Originally posted by Refinery  
This might be an awkward question, but is rotavap superior for distillations compared to ordinary, bleeder/vacuum assisted static distillations?


A rotovap has quite a few advantages in my opinion:
- no bumping (unless evaporating water, I've never had luck with that).
- Formation of a thin film on the walls of the flask, which ensures the sample dries well.
- Fast solvent stripping (this is due to very good heat transfer since both the heating bath and the sample are moving)
- Fast to setup, the rotovap is typically always ready to run, unlike a classic distillation setup

For me, removing the solvent from a reaction with a typical distillation takes a 1-2 hours. With a rotovap it takes only 15 minutes. That's a considerable gain of time, so you can do more interesting chemistry instead of babysitting a boring distillation.

OldNubbins - 17-6-2020 at 14:01

I should add that Dr. Bob helped me put together a Buchi rotavapor recently. I learned how to repair the gearboxes and motor controls in the process and, with a little work, these things are easy to keep going. There are tons of non-working units available on ebay which all likely have one of two issues - the plastic gear has been chewed up from years of solvents washing away the lubricant or the control board is broken in some way. The gear can be replaced by a 3D printed one and the circuit can be easily repaired or replaced by a simple off-the-shelf SCR chopper drive. I was considering a cheap Chinese unit at first but am glad I went with the old Buchi workhorse.

DavidJR - 17-6-2020 at 17:57

In addition to the usual use of removing solvent from solutions, I've also had great success using my DIY rotovap to remove residual solvent from crystals. It's pretty much ideal for that because it's constantly tossing the solid around.

[Edited on 18-6-2020 by DavidJR]

SWIM - 17-6-2020 at 20:43

Quote: Originally posted by RedDwarf  
I'm assuming that rotavaps can accept a variety of flask sizes, so what does a 5 litre size refer to? Size of flask provided, the physical space to fit a flask into or some measure of the ability to handle a certain flowrate of solvent?


It seems to refer to the maximum flask size it will take.
I suspect the limiting factor is usually the size of the heating bath or the height of the stand the bearing goes on. (Although obviously the other parts get a lot bigger as capacity increases)


I've got a fairly small Eyla model around somewhere.
It's heavy.

Shipping could be a big part of the cost for a used one, so you may want to look for one nearby.
If you're lucky enough to live in a state where cannabis is legal you may be able to get good deals soon:

An awful lot of noobs are buying rotovaps and even wiped film evaporators if they can afford them because they think they'll get rich selling THC.

These are still getting listed for pretty high used prices, but as the supply increases you'll see prices go down.

Used ones may be getting a bit cheaper in the next few years.

Those do seem to be mostly Chinese equipment though.

People out to make a quick buck don't usually go for quality.


@DavidLRJ: Nice.

I wasn't expecting it to be so nearly identical to the real deal.

Is that a flex-joint of some sort in there?
Like a couple of stirrer bearings and a PTFE tube?










[Edited on 18-6-2020 by SWIM]

Fleaker - 18-6-2020 at 12:27

Quote: Originally posted by G-Coupled  
Quote: Originally posted by Fleaker  
I have a 50 L one that seems to work ok.


A 50L Chinese one? How much did that cost you, and how long have you had it, as a matter of interest?


With all the peripherals, $25KUSD. About 4 months.

Given what we are doing with it, if it lasts a year it's money well spent.

DavidJR - 18-6-2020 at 13:41

Quote: Originally posted by SWIM  

@DavidJR: Nice.

I wasn't expecting it to be so nearly identical to the real deal.

Is that a flex-joint of some sort in there?
Like a couple of stirrer bearings and a PTFE tube?


Yeah, two off-the-shelf stirrer bearings and 7mm OD PTFE tube. I now use a slightly different glassware arrangement with only one stirrer bearing but it works the same. You do want to put a little joint grease on the O-ring, though. Also, make sure to use PTFE tubing (not any other fluoropolymer) for the low coefficient of friction - I started out with some tubing that was sold as being PTFE but clearly wasn't because it was too transparent (maybe FEP?), and it chewed up O-rings in no time. Actual PTFE tubing works very well though.

I do have a couple of issues with this setup though:
1. The rotational speed is a bit slower than I'd like.
2. It's a bit of a pain to adjust the height because of having to move a clamp as well as the "spinny thing" separately.
3. I could really do with a better condenser (I use a coil one in it now, not the liebig that is shown in the video where I was doing my first test of it, but it's still not ideal).
4. Because it's put together from glassware, stands, clamps, hotplate, etc that I also use for other things, it's a bit of a pain to set up compared to just having a rotovap sitting there ready to go all the time.

I've been meaning to redesign it a bit to address issues 1 and 2, but I haven't gotten round to it because, well, it works.

Mateo_swe - 21-6-2020 at 12:53

Your DIY Rotovap looks nice and seem to work fine, well done.
Its always nice to see DIY builds that works.
And a DIY apparatus is always under contruction and upgrading since new ideas comes all the time.
How come you cant rotate the flask faster, is it just the motor/gears that needs to be changed or do you have some issues that prevent faster rotation of the flask?

DavidJR - 28-6-2020 at 05:59

Quote: Originally posted by Mateo_swe  

How come you cant rotate the flask faster, is it just the motor/gears that needs to be changed or do you have some issues that prevent faster rotation of the flask?


No real issue preventing it from going faster, it's just that's the speed it goes right now because I didn't know any better when I was designing it. The same form factor of motor/gearbox that I used is available in faster versions which could probably be substituted without any problems.