Thanks Sulaiman, once again artemov - 17-8-2019 at 22:40
Sorry a couple more qns.
Can one of those cheap electric cooking hot plate be used as a heating source for distillation/frac distil/reflux? Maybe in combi with a water/oil
bath?
Regarding retort stands, would a 50cm and a 30cm retort stands suffice, or would 2 x 50cm be the minimal?
Trying to assemble a distillation setup as cheaply as possible here
[Edited on 18-8-2019 by artemov]Ubya - 17-8-2019 at 23:11
those hot plates are ok for simple distillation/reflux, but for reflux you need fine temperature control, the on off cycle of those mantles is too
big, temperature swings can mess up the equilibrium in a fractionating column. buy a proper hotplate or hack one of the normal cheap one (like the one
in the image), you need to bypass the thermostat and control the temperature with a variac or an SRC voltage regulator (it works only with resistive
loads so a hotplate is ok), buy the highest rated one on ebay, as a safety factor.draculic acid69 - 18-8-2019 at 01:06
As far as those hotplates like the one above go they can be used for reflux/distillation.
They need continuous attention though and anything temp sensitive will need a water/oil bath.you can rule out a vacuum fractional distillation though
as they require precision and the up/down temperature movements will screw it up but a normal distillation can be made to work.a thyristor circuit
only costs a few dollars and ripping the thermostat out of it and using the thyristor instead should work as good as any actual lab hotplate.the point
is though yes you can use the cheap hotplate it just requires babysitting.you can't set and forget.
[Edited on 18-8-2019 by draculic acid69]
[Edited on 18-8-2019 by draculic acid69]artemov - 18-8-2019 at 01:17
Thanks Ubya and darculic acid69.
For now I'll stick with the cheap and simple stuff first to get things going. draculic acid69 - 18-8-2019 at 03:51
Also if you're making your own stands don't use mild steel it has a lot of flex in it.
SS is the best for thisΣldritch - 18-8-2019 at 03:57
When i started out i broke a lot of those hotplates with moisture. I suggest you put a fuse in it, especially if you are opening it up anyway.draculic acid69 - 18-8-2019 at 08:57
When i started out i broke a lot of those hotplates with moisture. I suggest you put a fuse in it, especially if you are opening it up anyway.
I don't know how you killed one of those hotplates I've spilled acids, caustics,salt solutions and solvents on them.ive used them in closed rooms with
flammable liquids and left them on for 24hr periods,I've boiled litres of HCL that killed and rusted everything in 5metre radius and the only thing
that fucks up on them is the thermostats eventually wear out or get stuck on or whatever happens to them.Σldritch - 18-8-2019 at 09:05
If you leave them outside after, say a lengthy nitric acid distillation, they will die from the moisture in the air. Presumably because the heating
element gets shorted.
[Edited on 18-8-2019 by Σldritch]Pumukli - 18-8-2019 at 09:14
I modified my own similar hotplate by installing a 2kW "power controller" or what the name of the thing was from ebay. You know, those small, cheap
Chinese things with a potmeter.
It worked sort of but eventually overheated and gave full power to the heating element. Based on this experience I can second Ubiya's suggestion: use
the highest rated SCR power controller you can get, it MAY have enough heatsink area to remain operational even after prolonged heating up the whole
thing!
I have doubts whether it is possible / wise to install these things inside the casing of hotplates and still get adequate cooling of the active
element or we should make an external power controller (install the scr thingy in a separate metal box with holes and/or a small ventilator to force
cooling).
As for the stands: I use a homemade stand. The rods are 12mm diameter threaded rods. They are secured into a base of a 5-6 mm thick iron plate. The
plate is standing on two 3cm x 5 cm x 28 cm thick wood pieces. These are the "legs" of the stand. They are continuous along the longer edges of the
iron plate. I have three holes in a V arrangement on the plate but only use 2 rods, the third hole is unused right now. The base plate is about 23 cm
X 28 cm or something like that. It seems usable and was much cheaper than the "real thing". BromicAcid - 18-8-2019 at 17:35
I broke a lot of glassware on those hotplates through uneven heating. Once I had a retort shatter full of nitric / sulfuric acid and decided 'never
again'. draculic acid69 - 18-8-2019 at 21:17
I never used anything bigger than 3-400ml.how big was the retort?
[Edited on 19-8-2019 by draculic acid69]artemov - 19-8-2019 at 04:25
Thanks guys ... erm ... I'll see if I can get a heating mantle on the cheap instead ...Pumukli - 19-8-2019 at 04:37
I used such a hotplate for distillations BUT I NEVER PUT any glassware directly on the heated metal plate! I always used a sandbath in a metal dish.
Never lost a flask to heat stress. Without the sandbath... That's another story.
teodor - 20-8-2019 at 03:26
May be for advanced work it is not so good but for beginning I find is quite OK.
1. I put glassware directly, had no problems neither with Duran nor with Simax. Of course it should have a good contact and sometimes it is tricky, I
use balls of aluminium foil to align a hotplate under a flask. Sandbath works only theoretically, practically the power is not enough. For waterbath I
prefer just an old teapot with a digital temperature control. Oilbath works but I don't like the fumes, so, directly. But of course, I always test
every new piece of glassware with different kinds of a thermal shock on this plate before any real usage.
2. The main problem with temperature control is the mass of an iron element, so for fast cooling I use a spray bottle with water - a lot of steam and
a fast temperature drop (usually I have a spray bottle with a pump and it always ready with a pressure inside. This thing also helps much to quickly
absorb small leaks of gases like HCl, HBr, SO3, NO2, toxic dusts etc, but officially I use it for grow orchids of course). Also pulling out the plate
from a flask works (just do it quickly, this thing is hot).
3. Some models have problem with regulators, so it breaks after few months. I had 2 broken already, the 3rd works.
4. I use it with a fractional column, for tasks like boiling down H2SO4 to 83-85%, crystalls, organic synthesis. Well, I think about a bunsen burner
as a better alternative (more power and control) or heating mantle (probably more convenient) or something combining with stirring (for some reactions
it would help much). So, I have it somewhere in my wish list but definitely after storage bottles, glass adapters, PTFE hoses and elements for my
home-build fume-hood. Because I really can do a lot with the hotplate.
5. If your solution is spilled it will be inside the hotplate, generating fumes. In this case it is better to disassemble the hotplate and wash
everything with water. It will work after that.
6. It is better to put a things like tiles or bricks underneath to prevent the table from burning - this thing has no any thermal insulation down to
the heating element.
[Edited on 20-8-2019 by teodor]Steam - 20-8-2019 at 15:46
I am sure this has been mentioned but a good thermal mass source on top of the burner will help smooth those temperature swings. I like using oil
baths whenever possible because I hate cleaning up sand, but to each their own I guess. I would try to use as large of "bath" as I could get away with
for my given temperature requirements. As as side note, when you are ready to upgrade do a quick ebay search- usually you can snag a laboratory
hotplate real cheap if you can live with a few cosmetic blemishes.
Good idea with the thyristor draculic. I wish I had known more about circuits when I had started.
