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Hoffit
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Shape matters. Flat bottom bottle (or RBF) on a plate does not transfer heat well. I distill typical solvents (like toluene, ethyl acetate) just fine
with erlenmayer bottles on my 300W plate on a liter scale without running it even close to max power. (typical pretty quick fractionating speed like a
few drops per second).
For stripping something quickly like 20% alcohol you really want something faster. Better shape like round bottle on a 300W mantle is fine for 1000ml
scale stirred. Upping to a 2-3 liter scale without stirrer and some reflux I prefer a separate kitchen stove with more power.
I prefer stirrer when possible and it makes stripping liquids faster. With kitchen stove you probably need boiling stones (like broken pieces of clay
pot). My sirrer does not work through my 230v stove.
If you have very large reflux ration and still want decent output, you may prefer more power. Trying out is easy and you'll see what suits your exact
use case. I'd not say something like 300W is not enough power, for most of my use cases it is. For some other use cases it is not.
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Oxy
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That's obvious. I don't use it as a direct heat source for RBF. If I need to use it for RBF I always use water/oil bath or aluminium skirt aka "air
bath".
Today when I was making copper(II) oxide I needed to heat ~1 liter of solution (with precipitate) to boiling point. I stopped when the temperature
went to 80 deg C as the process was really, really slow. I used beaker for that so heat should be transferred quite efficiently.
The next I will buy will be ~1000W. I think it will be enough for home-scale usage. 500W is generally ok when working with small quantities but there
are situations when I feel that I really should change the hotplate stirrer. Thankfully I have a few of heating mantles so I can heat really
efficiently when I really need.
Heating mantle is definitely better for RBF. There is also an option to buy (or make) an adapter for RBF which can be mounted on the hotplate. Then
the flask is heated efficiently (as the adapter has a round shape like a mantle) and strong stirring is possible. But if there is a need to buy more
than one adapter then it becomes expensive.
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Yttrium2
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I’m tempted to buy the 180watt hot plate
I think it will be enough
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Hoffit
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Quote: Originally posted by Oxy  |
Heating mantle is definitely better for RBF. There is also an option to buy (or make) an adapter for RBF which can be mounted on the hotplate. Then
the flask is heated efficiently (as the adapter has a round shape like a mantle) and strong stirring is possible. But if there is a need to buy more
than one adapter then it becomes expensive. |
I've never seen or heard of an adapter. What are they made of typically? I'd assume heating up for example solid adapter would have a long heat up
time like sand or oil bath (that are basically kind of adapters).
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Oxy
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Here is an example and this one is made of aluminium, so it should be much faster than sand
https://www.sigmaaldrich.com/catalog/product/aldrich/z675075
[Edited on 27-5-2021 by Oxy]
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Hoffit
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Those could be interesting for some use cases. (even if I'm mostly into heating mantles)
My kid just had a home work assignment to measure efficiency of heat transfer to water. About 270g water in a 500ml erlenmayer on a 150x150mm hot
plate had efficiency of 19% (water heated from room temperature to near boiling, full 500W all the time).
Some heat goes to warming up the plate and bottle and quite a lot escapes when the bottle covers only part of the plate. I was a bit surprised the
efficiency is that low. With something like flat bottom bottle with even less surface contact I'd assume even lower efficiency.
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Texium
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Those aluminum blocks are nice. Had them in the teaching lab where I taught o-chem this year, and they worked really well for the most part. They heat
up fast and avoid the mess of an oil bath. They have a small well for a thermocouple too so that if your hotplate is equipped with one, you can easily
measure the temperature of the block. The one and only issue I had with them was that a couple times a flask would get stuck in its well somehow, to
the point where the flask actually sheared in half when attempting to remove it from the block!  Bear in mind though, over the course of two semesters, I had about 60 students who each used these several times, and
this problem occurred exactly twice, so the failure rate is still very low. I’m sure if it does occur, it would also be possible to fix it by
quickly heating up the block to loosen its grip on the flask. Honestly at only about $50, they’re less expensive than I expected, especially coming
from Sigma. I think I’ll order one for my own hood.
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Yttrium2
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To get this thread back on track, what or where is a submersible pump I can hook up to a battery?
And lastly, how could I provide stirring if I was out an the Appalachian trial without any electricity?
Will bumping stones suffice!? For Coleman lighter fluid distillation?
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Yttrium2
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What’s a usb fountain pump that will provide enough head, and what kind of battery pack is compatible plz
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Hoffit
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For small flow volumes almost any small pump like fountain pumps will do. USB and 12V pumps are easily available. I often find I need a very slow
water volume and the equipment is rarely high enough to need some pressure from the pump. (Matters change if you go for high power, large vessels with
lots of vapor to flow or very volatile liquids).
I think someone told to use just vessels. Have one vessel above equipment to feed the input and dump the output on some other container. No pump
needed.
Boiling stones are enough for most jobs. In case you have none, small rocks, pieces of broken ceramic items or pieces of broken glass are often
useful. I use pretty often pieces of broken flower pot. They work very well due to porosity.
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Mateo_swe
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Just use a small waterpump of the types used for very small fountains or aquariums, they will work fine for circulating cold water from a ice bucket
to your condenser and back in the bucket.
If distilling small volumes the cheap china hotplate stirrers will work but most regret they didnt buy a more powerful hotplate stirrer as they start
distilling larger volumes.
It takes looong time to heat a larger volume to boiling using a weak hotplate.
If you are good with electric stuff and know you aint going to accidently kill yourself, you can buy a heating mantle replacement sleeve and power it
with a dimmer or variac (the heating element wire is included in the sleeve).
Its a cheap option and you can place the sleeve on that cheap china hotplate stirrer and just use the stirring function on the hotplate, and you have
a heating mantle with stirring for RB flasks.
I would go for the cheap china hotplate stirrer, a aquarium waterpump and a Deschem distill kit.
It will get you going and you are going to upgrade your gear later anyway.
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