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Author: Subject: Advice on purchasing a reliable rotary evaporator for a cheap price
Tkuze
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[*] posted on 4-9-2020 at 13:29
Advice on purchasing a reliable rotary evaporator for a cheap price


I need to purchase a rotary evaporator for my company, but am unsure of which type to buy. I am looking for a workhorse rotary evaporator to mainly use for ground glassware with max capacity of 1L. Most uses will be for round bottom flasks between 50-500mL, and I can't imagine needing to use a flask over 2L size. I have a high quality vacuum pump already and I would like a rotary evaporator with a recirculating tap water condenser, as a dry ice condenser would be a hassle. I would like a rotary evaporator that will have just the bare bones basic functions, such as manual lowering and a simple water bath temp regulator. I don't need any complicated electronic automation systems or electronic programmable options. My main needs are that the rotovap be reliable and work for years if maintained and treated well. I have seen many chinese rotary evaporators on Amazon and eBay for $600-1,200 and am a bit unsure if these are quality and will function for a long time. I have considered just buying a refurbished or used functional Buchi rotovap motor with stand and water bath, then buy the glassware for it separately, or buy a quality chineese rotovap if such a thing exists. I am on a budget and am looking for something in the price range of $700-$2,000, that is absolutely reliable and simple. I will go over that price range if I can get a good brand name, such as Buchi, and know that what I'm buying will last for many years and not have any major problems. I would greatly appreciate any feedback on a particular model of rotovap that anyone has used and would suggest, or if they have bought or used the chineese rotary evaporators on Amazon and eBay and if they are worth purchasing. Thanks in advance for any feedback or comments.
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OldNubbins
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[*] posted on 4-9-2020 at 17:13


Dr. Bob should chime in here soon. He should be able to hook you up. I recently refurbished several Buchi drive units for him with 3D printed replacement gears (typical failure point). Mine has a printed gear and even got away with a handmade rotary seal for a while.
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Tkuze
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[*] posted on 4-9-2020 at 17:22


Thanks, that's awesome. I would definitely be happy to save money by just buying the essentials and then improvise by building my own or a different water bath and odds and ends. I was looking into the Yamato RE-201-100-A. Have you heard anything good about them?
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Dr.Bob
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[*] posted on 4-9-2020 at 18:08


I do have many Buchi rotovap parts and pieces, as well as one complete Buchi unit that I had put together for a company that then moved. It has the stand, water bath, rotary motor and vacuum seal assembly, condenser (I have water and dry ice ones), 1L receiver flask, steam duct, fresh KD-22 seal, and even a 1L Buchi flask if you want. That unit would be about $800-1000, depending on the exact motor model (I have simple, fancy, and fancier) and any extras, plus shipping. If you tell me what state you are located in, I can better figure the shipping costs. But I shipped most of one unit (metal parts, not ) the glass for about $60 to the west coast, east coast is cheaper. So likely under $100 in shipping.

Even if you buy it elsewhere, I would stick with Buchi, as you can get parts and pieces for them easily from many sources. Most other brands are much less common, and getting parts is nearly impossible. I have sold pieces to people that bought Chinese units and they failed quickly,as made poorly. I have only used one Yamato, I did not like it, but it worked fine. Good luck finding any parts for one.

Bob
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Tkuze
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[*] posted on 4-9-2020 at 18:24


Thanks, that's awesome. I would definitely be happy to save money by just buying the essentials and then improvise by building my own or a different water bath and odds and ends. I was looking into the Yamato RE-201-100-A. Have you heard anything good about them?
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Fyndium
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[*] posted on 2-12-2020 at 13:05


Would it be overkill to purchase a rotavap for hobby use? Stripping solvents and concentrating liquids is very time consuming work that leads to nothing on itself, so how much rotavap increases the stripping rate compared to ordinary distilling? I heard that some of those chinese ebay vaps are quite decent devices. I'd be looking for a 1L or 2L model at max in this instance, with refill tap to allow for larger amounts of solvents to be added in one run.

Is it also possible to use rotavap to effectively purify solvents per se?

Do they need specific vacuum pump or can an ordinary pump be used? Do they have integrated vacuum adjustment (valve)?

Considering this is a hobby, investing $1k is no biggie compared to many people who put multiple times of that money into something seemingly trivial, look for example car tuning. Just does it do the bang for the buck, do I get solvents removed at an exponential rate with it compared to normal still?

Pity, there is a Czech seller for 5L rotavap. 5L flask is quite large for my needs, though the price of the machine is same than 1L.

[Edited on 2-12-2020 by Fyndium]
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Dr.Bob
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[*] posted on 3-12-2020 at 09:37


A rotovap is useful, but not necessary for most home chemistry. If you use a lot of solvents, like in chromatography, extractions, acetone rinse of glassware, or other functions where recovering the solvent is useful, then it is much more helpful. For just evaporating a simple reaction, nice, but not necessary. You can purify solvents to the degree of recycling used acetone to get clean wash acetone, or even often recycle DCM and hexane from a column, and recovering solvent used in extracting a product from a reaction. I often recover my solvents from those functions, where they are easy to purify. But trying to separate complex mixtures of solvents will not work as well on a rotovap, same for trying to still acetonitrile or ethanol from water, which does not get much separation of two solvents. And it will allow you to remove solvent at about 10 times faster than a simple still as a rough guess.

Any vacuum pump can be used for most rotovaps, although some newer ones are integrated systems between the rotovap and the pump and water bath. That's why I would buy an older used unit in a heartbeat over a new fancy one, as you can keep the old one working forever with a little love, and mix and match parts on most older ones.
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Fyndium
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[*] posted on 4-12-2020 at 03:10


Many videos on tube indicate that most of the stripped solvent does not condense but instead is apparently evaporated to the vacuum pump (trap). When using vacuums of significant level, low boiling stuff like acetone or even lower will have boiling point way below room temp, so is it viable to use ntp to rotavap these off, or is vacuum mandatory?

Unless using cryogenic coolant (CaCl2 at -30C etc) and an ice bath with receiver flask?
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[*] posted on 5-12-2020 at 06:07


I use a rotovap daily, we use a recirculating chiller pump at about -5C to condense the solvent, and I get back about 90% of the solvent with hexanes, acetone, and ethyl acetate. Ether and DCM are a little tougher, so for best recovery, use a lower vacuum and a slightly higher water bath temp. Our pumps are mostly diaphram ones, that we use set to about 50- 150 millitorr. We also do have a few dry ice condensers, those work great, but are not practical for most people, although certainly a ice/salt mixture could work in them also. But even with simple ice water, most solvents can be recovered OK.

You can also place a condenser after the vacuum pump to trap vapors from its output, some places do that for environmental concerns to and those remove almost all solvent from the output.
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Fyndium
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[*] posted on 5-12-2020 at 14:24


Sounds reasonable, as stripping solvents is one of the slowest phases of many works. Perhaps I'll consider buying one as a Christmas present for myself.

Just how loud are the machines, btw?
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OldNubbins
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[*] posted on 5-12-2020 at 15:26


Mellow hum.... the pump is WAY louder. I will pump mine down and then close off the valve to limit solvent past the condenser. It will hold low enough pressure for a while until collection slows down then I'll pump it down again. Not sure how effective this is in keeping solvent out of my pump but who can lie better to us than ourselves?
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[*] posted on 6-12-2020 at 04:00


What I've seen on tube I got the same impression the device is quiet itself. Hmm.. I've got a reservoir I could use as a ballast to minimize repumping.

I was thinking of using aspirator setup similar to NurdRage's to create lesser vacuum, because the vacuum pumps chug down to millibars which make 200C stuff boil at hand warm water.

I was thinking of putting several coldfingers on series to limit solvent going to the pump, since rotary vane pumps don't really like that stuff.

I'm under impression that a larger rota can be ran with smaller flasks? So getting the 5L one (costing the same as 1L) and purchasing 1 and 2 liter flasks would be more beneficial.
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