Comments on: Gonna Build Me a Rotovap Update http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/ The International Culinary Center's Tech 'N Stuff Blog Thu, 09 Jan 2014 18:17:16 +0000 hourly 1 http://wordpress.org/?v=4.0 By: davearnold http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4530 Thu, 13 May 2010 11:58:22 +0000 http://www.cookingissues.com/?p=1268#comment-4530 Off the shelf but pricey!

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By: StephenA http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4468 Fri, 07 May 2010 11:44:53 +0000 http://www.cookingissues.com/?p=1268#comment-4468 Hi Dave

Thanks for getting back to me. Ok the last bit that is doing my head in is the drive. From what I understand the drive will be isolated magnetically from either side of the end of the base so you don’t have any problems with holes that need sealing .

Is this an off the shelf coupler or have you designed one that is powerful enough to act through the end of the base?

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By: davearnold http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4464 Fri, 07 May 2010 09:48:39 +0000 http://www.cookingissues.com/?p=1268#comment-4464 Hi Stephen A
I am taking the vapor off through the lid.
The polycarbonate cylinder spins inside the chamber and created the stirring and the large surface area you get inside a regular rotovap. In fact, it provides more surface area, because a film will be formed on the inside and the outside of the cylinder.

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By: StephenA http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4449 Wed, 05 May 2010 11:47:13 +0000 http://www.cookingissues.com/?p=1268#comment-4449 Dave

I think you are absolutely correct the vacum seal seems to be the big headache in the normal rotary vap design, and I think I can see how our ingenious design gets around this

I’m trying to see how your design will work from the information you have already given. Can I just clarify a couple of things.

1. The polycarbonate cylinder does this just act a a stirring paddle forcing the fluid against the shape of the base.

2. Are you taking off the vapour from a connection on the lid or the base?

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By: davearnold http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4428 Mon, 03 May 2010 13:23:15 +0000 http://www.cookingissues.com/?p=1268#comment-4428 Yeah, the cost is crazy. Your chiller should do around -20 C (-4F) You need at least 600 watts of cooling at those temps. Rotation doesn’t need to be that fast –50-100 rpm.

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By: Andrew http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-4417 Sun, 02 May 2010 19:04:40 +0000 http://www.cookingissues.com/?p=1268#comment-4417 I am making my own rotovap too, although I am still in the early stages, During my research I stumbled upon this website, and I have to say its very inspiring, who knew chefs are some of the best scientists in the world?

I am first working on the rotation mechanism which I am making out of a 5 amp black and Decker power drill, I attached a fan-speed knob onto it (the same kind of knob you see on light dimmers switches) it allows me to adjust the speed of the power drill.

Anyway, there is a problem with it right now and that is that it goes way too fast at its high settings, so I am going to put a resistor to slow it down some, but I don’t know exactly how much resistance I should put on it because I don’t know how fast rotovaps are supposed to spin.

Once I have that I was thinking of going to a machine shop to fabricate the head and maybe help me bore a 1 inch hole through some of the gears. Then there’s a matter of mounting the gear to a holding plate of some sort.

I haven’t thought as far as the condensor, yours seems like a good idea, but I was a bit concerned with the reactivity of aluminum to some of the chemicals for my purposes you might be running through there, here is a link to some chemical resistance charts

http://www.pneuaire.com/chrech.html

its broken up into three charts in alphabetical order, and uses an A-F grading scale A (least reactive, F very reactive) I’m sure for food products alumium would be fine

The problem I have is knowing what to use as a pump for the condenser, I was thinking of getting it from a mini fridge or something – but I don’t know if that will be too powerful or not powerful enough.

then there is the matter of filling up the condenser with the freon or whatever the cooling solution is going to be. I know little about refridgeration except the basic concepts.

I don’t understand why rotovaps are so expensive, $7,500 for something that basically consists of 2 round bottom flasks, a condensor, a low speed rotor and a vacuum. It shouldn’t cost much more than $250.

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By: syuzo fujimoto http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-2069 Mon, 21 Dec 2009 05:20:39 +0000 http://www.cookingissues.com/?p=1268#comment-2069 I wish to product your imaging rotovap with you .
Your idea is as same as I.

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By: Ian http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-2068 Tue, 28 Jul 2009 05:37:48 +0000 http://www.cookingissues.com/?p=1268#comment-2068 The sand trick works great. I use it on thin walled copper refrigerator tubing all the time. We get a very fine sand in the lab, Washed Sea Sand from Fisher Scientific. It’s cheap, it’s reusable, and because it’s a relatively uniform size and well washed, it flows very well, so it’s not a problem to fill as small as 1/8″ tubing.

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By: Dave A http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-2067 Mon, 27 Jul 2009 21:54:18 +0000 http://www.cookingissues.com/?p=1268#comment-2067 Hi Milkshake,
I’ve used stir bar agitation for my vacuum distillation tests in the past but they never generated the surface area that I get out of my rotovap. I agree that the rotary seal is a huge weakness of the rotovap which is why my new one won’t have one. I am spinning an inclined cylinder inside the vacuum to agitate and provide surface area without having to use a crappy vacuum seal (using a magnet). You’d be surprised how much flavor loss you get from your distillation flask even when it’s kept on a crushed ice/salt mixture. That was the system I used to use prior to getting the peristaltic pump. Remember, I’m dealing with a distillate that has dozens, sometimes hundreds of different compounds in it in trace amounts. It isn’t that the flask isn’t big enough, it’s that it steals flavor! That is the main difference between kitchen rotovapping and lab rotovapping. I also need to be able to taste to see when the distillation is over, which is the other advantage of the pump. Theoretically I shouldn’t be getting a lot of loss off the flask because it is so much colder than the water bath, but empirically, I do.

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By: milkshake http://www.cookingissues.com/2009/07/01/gonna-build-me-a-rotovap-update/#comment-2066 Mon, 27 Jul 2009 20:06:32 +0000 http://www.cookingissues.com/?p=1268#comment-2066 Why do you need to build a rotovap? In synthetic chemistry lab, rotovaps are great if the non-volatile evaporation residue are what you are after. But they literally suck at recovering the distillates; the losses are too high.

What you really want is vacuum distillation still. The rotovaps prevent “bumping” of the distilling liquid by spinning the flask. But there is much simplier way: stirring. Buy some second-hand magnetic stirplate on e-bay, preferably a large Corning model because it is more powerful. You can get one for less than $150. Add a large teflon-coated egg-shaped stirbar into your distillation flask placed on a heating bath, connect it to some common condenzer, with a receiving flask. For a bigger oomph cool also the receiving flask on crushed ice/salt slush bath. The advantage: no motor and spinning parts (except for the stirplate), no problems with rotating seals, very little losses of the distillate if you adjust the pressure and temperature correctly.

You don’t have to worry about continuously removing the distillate. Breaking the vacuum is non-issue when your total allowed volume in the distillation flask is 3 liters. At 15% original alcohol concentration and 90% final concentration in distillates you will produce at most only half liter of distillates – so get a bigger receiving flask instead!

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