Sciencemadness Discussion Board - large vessels: best way of heating and stirring ?

large vessels: best way of heating and stirring ?

Funkerman23 - 9-7-2015 at 14:27

Hello!
This may be a bit dumb.. but I've hit a wall and I'd like to ask you good folks' advice. I have been kicking the idea around of buying some flasks in 3 liter and above ( really 5 liter is the max I'd ever want to deal with)sizes. But to do this I will need to buy the needed heating and stirring apparatus as well. What route makes the most sense as a amateur/ student? What route do you seasoned guys take when dealing with 3 to 5 liter reactions? Yes, I know this is a broad question but if it helps I am wondering if I should focus on a ( stir) mantle set up VS a hotplate& liquid bath set up. Student budgets being what they are if I manage this its either one or another.
Any comments, advice and options are appreciated. Thanks and be safe!

battoussai114 - 10-7-2015 at 07:46

I don't run anything that big... but considering a student budget I'd probably go with an improvised heating mantle (I think NurdRage made one recently, check his channel) and an overhead stirrer.

DJF90 - 10-7-2015 at 09:57

Quick question - Do you really need such a large scale apparatus? My reason for asking this is three-fold:

a) There are potential thermal hazards involved with doing chemistry at such a large scale, particularly if you haven't assessed the process by reaction calorimetry.

b) You'd need "super-sized" auxilary equipment such as separating funnels, filter flasks, buchners etc. The physical approach to doing things on scale also changes (e.g. you wouldn't shake a sep funnel that big (3-5 L).

c) Chemistry on that scale tends to be done for-profit ("fine chemicals manufacture") because the cost of materials (substrates, solvents, reagents) is no longer within the realm of a hobbyist. As such, it ceases to be amatuer chemistry.

If you still feel that its required perhaps you could give insight as to what you're aiming to do, or maybe look into setting up a flow system instead?

[Edited on 10-7-2015 by DJF90]

crazyboy - 10-7-2015 at 10:15

I don't understand why the choice is between a stirring mantle and a non-stirring hotplate.

I would say go for a hotplate/stirrer with an oil or sand bath and get a big stir bar. Reason being that you can accommodate many sizes of vessel easily, heating mantles are nice but if you want a big one it's going to be pricey and it will only be good for one size flask. That said if your reaction is viscous or must be stirred vigorously you may need to look into overhead stirring.

Funkerman23 - 10-7-2015 at 15:54

Quote: Originally posted by DJF90

Quick question - Do you really need such a large scale apparatus? My reason for asking this is three-fold:

a) There are potential thermal hazards involved with doing chemistry at such a large scale, particularly if you haven't assessed the process by reaction calorimetry.

b) You'd need "super-sized" auxiliary equipment such as separating funnels, filter flasks, buchners etc. The physical approach to doing things on scale also changes (e.g. you wouldn't shake a sep funnel that big (3-5 L).

c) Chemistry on that scale tends to be done for-profit ("fine chemicals manufacture") because the cost of materials (substrates, solvents, reagents) is no longer within the realm of a hobbyist. As such, it ceases to be amatuer chemistry.

If you still feel that its required perhaps you could give insight as to what you're aiming to do, or maybe look into setting up a flow system instead?

[Edited on 10-7-2015 by DJF90]

You've made some stark points, and they're excellent ones! My word, you're brilliant! I was thinking about it all wrong. I WOULD need the auxiliary equipment and that is far beyond what I could reasonably manage at this time. I wish I could chat with you sometime DJF90. You sound like a Chemical Engineer and if so you may yet have given me another idea( schooling , I mean).
Thank you all! May your yields be extra high.

Funkerman23 - 10-7-2015 at 16:00

Quote: Originally posted by crazyboy

I don't understand why the choice is between a stirring mantle and a non-stirring hotplate.

I would say go for a hotplate/stirrer with an oil or sand bath and get a big stir bar. Reason being that you can accommodate many sizes of vessel easily, heating mantles are nice but if you want a big one it's going to be pricey and it will only be good for one size flask. That said if your reaction is viscous or must be stirred vigorously you may need to look into overhead stirring.

The choice is because of financial reasons. AT this time I could maybe afford one system but not both. You make an excellent point though: Even at larger scales a hotplate/stirrer is more versatile. I have this as a hobby but I am also trying to go to school for it. Granted It may be an odd way to go about it. I also have a "collectors" mindset. I like to have as complete of a set of equipment as possible. Thanks!!

DJF90 - 13-7-2015 at 00:12

Quote: Originally posted by Funkerman23

We used to do reactions in 20 L flasks on a routine basis when I worked as a process R&D chemist. Feel free to u2u if theres anything I might be able to help with.

zed - 13-7-2015 at 17:57

Depends on what you are doing. What are your solvents? What are your reactions? Most things are do-able. Often, with some thought, large reactors can be outfitted economically.

Personally, I am a giant of sorts. I have very large clumsy hands. Thus, I've never had a penchant for small projects. https://www.youtube.com/watch?v=tPkNCnqZ9Fo

Large separatory funnels and large sized filtering apparatus, may not be required. There are alternative ways to "skin a cat".

None-the-less, do keep in mind, that once purchased, equipment is seldom resold at a profit. A good rule of thumb is: "You bought it"......."You eat it"

[Edited on 14-7-2015 by zed]

Magpie - 13-7-2015 at 18:31

I try to keep most of my syntheses to 500 ml RBF size or less. When making reagents for stock I will go up to 1000 ml, no more. I agree with DJF90 in that when you increase the scale of the reaction flask all the other equipment tends to go up in scale also.

I resisted buying any 24/40 taper glass for years, preferring to stay with the 19/22 size. This size feels right to me and at the same time minimizes everything: reagents, equipment, space, energy, and waste management. This is just a hobby for me, after all.

So, unless I was in a "production mode" where I was repetitively producing a product, or family of products, which all required the same equipment I would not buy any larger sizes than what I have now. I would have to be using, or selling that product at a profit, also.

Funkerman23 - 20-7-2015 at 22:15

Well.. instead of starting another thread I have a related question. I found a 3 liter flat bottomed flask (Heavy wall) and I still have my trusty corning stir plate. Now the plate is rated at 575 watts . I'm pretty sure that a three liter flask is pushing it but what say you good folks?

I wouldn't have asked but something tells me a flask that size and the insulating properties of 3.3 boro (let alone the rxn mixture) might hurt the one decent hotplate I have right now. I know stir plates are amazing but I don't know how far they can be pushed.

As for purpose asked above : I don't have a specific one at this moment, but I do collect this stuff as well as use it. Its a hobby, schooling major and as many hours as I put in it may as well be a job. I enjoy Chemistry and in it I find peace.

Dr.Bob - 21-7-2015 at 04:38

It all depends on the solvent being used, and the temp desired. If you are heating water or ethanol, they have a high specific heat, which requires a large amount of heat to change the temperature much. If you are heating ether or hexane, it will take less heat, and since both boil at low bps, it is doubtful that the desired temp will be very high. I can heat most reactions with 40% of the heating power of my mantle or oil bath, so I am barely using the heating power available. But I have only run a handful of water based reactions in my lifetime, they take a lot more heat to get to temperature, often taking hours to heat up. But I run many reactions overnight, so I am not usually in a hurry. But I do use ethanol a lot, and it takes a fair amount of energy to heat it up as well. And if you want to heat up a large volume of DMF or DMSO to 100+ degrees, it will take some heating as well.

Funkerman23 - 10-10-2016 at 00:31

Looking back I see I made a number of dumb errors and I didn't explain myself as well as I could have. The reason I was thinking of such a large scale wasn't directed at any particular project and certainly it wasn't, and still isn't, in anyway, a "for profit" idea. Frankly ,I know good and well that 5 liters is too much for anything routine or purely experimental. However, the intent was,roughly, to have the means to make more of my own reagents as availability shifts.This is nothing new to our hobby.. I also have a habit of collecting equipment as a hobby in and of itself.

With all that being said I have come to realize that there isn't any easy answers and is case specific. At the time I originally posted this I failed to mention that solvent recycling, preparation and purification was a dominat concern on my mind when I first posted. An example of my needs, then, being ethyl acetate. I find it is cheaper ,sometimes, to buy as bulk nail polish remover but of course the perfumes& additives need to be stripped away. But No matter. Forgive the thread reanimating but I wanted to clarify.