Sciencemadness Discussion Board

distillation practice

peace c - 19-3-2005 at 19:21

Great site! So educational!
P.C. is wanting to perform a distillation and was wanting to practice his techniques before moving on. To get a feel for what is involved. Does anybody have any suggestions as to what i could practice with and on?

Couple of further questions are:
1-How cold does the water passing through my 400mm condensor have to be? Room temperature? I was thinking of putting a aquarium pump in a bucket of cold water and using this to fill the condensor. Any suggestions would be most welcome.

2-P.C. is finding this to be a real headache, that being a heating source. Have read much here but am still uncertain. P.C. has a 2000ml rbf and is being told that it is not suiutable to heat this directly on a hot plate but that what should be done is place a stainless steel container directly on the hot plate and fill this with some type of oil and then place the flask in this. Sound ok? Do people have experience with this?

P.C. has read a bit on oils to use at this site and it seems that either silicone or peanut oil is the way to go. P.C. needs high temps of approx 300C. P.C. is concerned about stinking out his little flat, would peanut or silicone oil do this? Aluminium blocks placed on the hotplate scare P.C. rightly so? Sand baths are not efficient? Oh my head hurts!!

P.C. would love to buy a heating mantle but cant afford one that stirs. So expensive.

Please help

sincerely,

Peace c

BromicAcid - 19-3-2005 at 20:57

The first time you should just practice on water, nice and benign and if anything goes wrong it wont be a disaster.

As for how cold the water has to be, it should be significantly cooler then the liquid it is to condense, if necessary you could add ice or cold packs to the bucket to keep things cooler, that's what I've done in the past. I use a fountain pump to do this, it works well.

Heating round bottom flasks directly on a hotplate should be avoided, you can get away with heating flat bottoms though. As for the oil baths, each oil is only good up to its smoke point, see:

http://www.goodeatsfanpage.com/CollectedInfo/OilSmokePoints....

And pick your oil form that if there is one good to 300C. Oil baths work well to their smoke point, mind you the flash point can be below this so no open flames. You mention silicone or penut oil, I've used neither of these before but I've never had to go to 300C with an oil bath. Maybe you'd be much better off with a molten salt bath. And for a note sandbaths can burn out hotplates if they are used at somewhat moderate to high temperatures are they are fairly insulating.

Never the less, good luck.

frogfot - 19-3-2005 at 23:51

One can also get away with heating small roundbottomed flasks on stove, when dealing with liquids with boiling points below 100*C.. It's usually more convenient than using an oil bath.
Quote:

And for a note sandbaths can burn out hotplates if they are used at somewhat moderate to high temperatures are they are fairly insulating.


Is this really true? I can't really figure out why it can burn out since all heating plates have a thermostat.. if it gets too hot it will be turned off..
I have used a sand bath with a 1500W plate for several months now.. it seems to be convenient. Though it takes some time to heat it up.

As for cooling recirculated water for the condenser, I use icepacks (plastic bottles with freezed water). 5 kg of total weight ice can last for several hours. Though this depends on the speed of destillation.

neutrino - 20-3-2005 at 05:45

Not all hotplates have auto-shutoff features. I’m pretty sure mine doesn’t, I’ve had spots of the top glow orange.

I can't seem to find paraffin's smoke point, but it should work well.

[Edited on 20-3-2005 by neutrino]

unionised - 20-3-2005 at 08:23

Just remember that, while water is a good material to practice on, it's still a big problem if you drop it in a hot oil bath.

BromicAcid - 20-3-2005 at 13:03

My hotplate, a corning specifically states on the little tag on the cord that a sand bath should never be used on the hotplate if the temperature control is turned above 3 (out of 8) and that if voids the warranty (which I didn't have to begin with).

thanks guys

peace c - 21-3-2005 at 18:34

thanks for the replies. Yes i will practice on water. still not 100% confident on the best way to heat although your tips are welcome and educational. Dont want to burden you guys to much so i shall go do some more research and come back if i have some more q's. BTW does anybody know a reputable stocker of this water product? :)

TheBear - 23-6-2005 at 10:08

Did my first vacuum destillation yesterday. It ended in a severe casualty - I lost my new liebig, on it's virgin destillation!



I had decided to distill some concentrated battery electrolyte (90% H2SO4) in order to purify it. To minimize stress on the glass I chose to do it under reduced pressure since the boiling point of the acid will then drop below 200 *C.

I had noticed that I needed grease in order to make airtight connection for the vacuum. My chemistry teacher gave me some exiccator-grease for the job. Apparantly it didn't like 200 degrees hot concentrating sulfuric acid and it decided to make my solution black. (Should have guessed it wouldn't be stable)



When I started the destillation I was using a wirenet with a ceramic plate between heat source and flask. But it took too long for the acid to heat up so the wirenet was removed and space between flask and gas flame was increased. Now things started to happen and a white smoke filled the glassware up till the first condenser connection, here the smoke vanished. I figured air was being let in and washed the smoke away. Therefor I twisted my condenser which made the connection airtight, pressure dropped and my acid flash boiled. Soon temperature was stable but I kept turning the condenser to insure that it was airtight (twisting it kept resulting in flash boilings)... and suddenly: click!... pssssss (air leaking in to the apparatures)... Oh.. no... it can't be... no... that can't be crack.. it must be a reflection.. why has the acid stopped boiling?



I guess it was a combination of mechanical and thermical stress that caused the condenser to crack.

Live and learn I guess and if I'm going to look at the bright side of it I still have a condenser for refluxing. But since these toys are quite expensive I don't want to repeat this.. What have I done wrong?

1. Naked flame (note that the burner is somewhat like a ring burner but not exactly) - a bad idea?
2. Twisting the condenser.. make sure it's airtight before starting the destillation
3. Use a better grease that won't contaminate whatever I'm destilling - Any suggestions please? Teflon based - are those available?
4. Using two stands instead of one to reduce mechanical stress during assembling (it's at those moments you question why nature was so mean and only gave us two arms).

Now: Please lecture me.. I need to learn because learing from practise isn't healthy for my wallet.

[Edited on 23-6-2005 by TheBear]

neutrino - 23-6-2005 at 13:56

It sounds like the twisting did your condenser in. A couple of points of procedure:

-Twisting should not have been necessary. A decent joint grease should have sealed the joints sufficiently.

-To minimize thermal stress on the glass, a bath is usually used instead of an open flame.

-To condense things that boil over ~120*C (IIRC), you’re supposed to use an unjacketed leibig, or pump air through the jacket. It sounds like thermal stress was also a problem here.

-There generally shouldn’t be that much of a strain on glassware. It seems like you need to employ a second stand.

ADP - 23-6-2005 at 15:00

Bear, very nice, how powerful was the vacuum in this procedure and what kind?

BromicAcid - 23-6-2005 at 20:11

Twisting + Pushing together, or in this case the vacuum pulling it together should never be done. You can tist a joint when grease is applied for a tight fit but don't push it together. I have personally broken two joints from the twisting+pushing combination during my use of teflon tape as a sealent between joints due to my inexperience with it, the combination of the two simply wedges the glass apart and cracks it.

my nootloss - 23-6-2005 at 20:25

i did that one("twisting+pushing combination during my use of teflon tape";) not cool, all most cried....

TheBear - 27-6-2005 at 08:05

Thanks for all the tips! Will buy myself a second stand along with the new condenser.

ADP: I didn't messure the pressure, the vacuum source was an aspirator.

BromicAcid: Would you recommend PTFE-tape as a sealant? What should I look out for if I use it?

Sandmeyer - 27-6-2005 at 08:15

Quote:
Originally posted by TheBear
It ended in a severe casualty - I lost my new liebig, on it's virgin destillation!


I feel for you, I truly do. The other day I broke 2 condensers at once, now I have none, it was very depressing, Dr. Traugott Sandmeyer is turning in his grave. When you distill, esp compounds with very high BP, don't mess around with the setup during the dist. But how bad is the crack, many times your local glass blower can fix it, which I assume is less expensive than purchasing a new one.

[Edited on 27-6-2005 by Sandmeyer]

Rosco Bodine - 28-6-2005 at 20:52

For joint lubrication Halocarbon grease may be better than Silicone High Vacuum grease at high temperature . Either one would be good at 200 C .

In a high temperature distillation especially , and for any assembly of glassware it is good to study the setup and allow for the components to move
slightly in the support structure during expansion and contraction from thermal effects , so that the natural alignment of the joints is not opposed or established by the supports themselves . The glassware geometry must be able to articulate . One way you could improve your setup is to add another curved adapter to the distillation adapter , and
then connect to the condenser .

The idea is for the weight of the assembly
to be supported , but to not have so firm
a grip on components that they have no end or side play , but have a fair amount of flexibiliy to move some if needed . If you have spring steel joint clips they can be very handy , but you can also wire joints together very easily so that they are securely joined
and wont fall apart , but can still rotate or even separate slightly if needed . In the case of an evacuated system , the vacuum itself will pull all the components securely together with considerable force . A thin film of lubricant on joints will rarely contaminate a distillation . If it is oozing from the joint then you have used too much . A small blob the size of a BB is enough for a 24/40 joint , when it has been distributed evenly across the surface of both mating parts .
Just enough grease to make the joint go clear when the parts are firmly mated together with a gentle firm twist is all you
need when you prepare the joints in advance of assembly . Add no more when you put them together . Apply vacuum to the empty assembly and check
the alignment and suuport structure , and observe for any leaks or misalignment .
Only after your setup checks out , then
release the vacuum gradually , unstopper
and fill the apparatus , stopper it again and restore the vacuum before applying any heat . Some chunks of broken glass
or clay flower pot or bone charcoal added to the boiling flask will help prevent bumping during vacuum distillations . About a tablespoon of such boiling stones
is a good method for taming surges and
encouraging a smooth boiling . Regulating
your working vacuum to something less than the hard vacuum maximum your source can pull is also a good practice ,
and will help avoid the oscillations which
otherwise occur .

Looking at the setup which resulted in a cracked condenser , I see several things that should have been done differently .

The boiling flask should not have been clamped below the neck . If a clamp was going to be used at all on the boiling flask , it should have been a fiberglass sleeve padded clamp gripping the ground joint portion itself . But better still , would be to simply support the flask with a metal
ring from below , and have the clamp above the sidearm on the distillation connector , with the jaws closed only enough to loosely capture the vertical portion of the adapter at the taper joint
where the stopper is located . The condenser should be wired to the sidearm
of the distillation adapter or secured with a joint clip . The receiving flask would be better sitting on a cork ring resting on a block of wood or foam than clamped . The curved adapter should be clipped or wired to the discharge end of the condenser and to the neck of the receiving flask . It should be the side venting type having a barb for the vacuum connection . The condenser should be very lightly clamped
near its discharge end . And a second clamp should be very loosely attached
near the condensers input end .

Assembled in this way , the weight of the
components settles the joints , according to their natural alignment . And the entire apparatus is supported in a way that it isn't going to fall over or fall apart ,
at the same time it is free to move with changing temperature without stressing
any joints .

Alternately , it is possible to clamp down the components securely , but additional
connecting parts would be necessary . There are specially designed articulated
connecting tubes having a section with three ball joints , or even four , which can
move in any direction and even shorten and lengthen the connecting distance .

Also there are convoluted teflon tube connecting tubes which have a ground joint on each end , but these are unsuitable for vacuum work or for high temperature .

The ball jointed assemblies are the best and most expensive solution for avoiding
complicated setup scenarios and issues .
But in most simple assemblies you can get by without the ball joints if you study the setup arrangement and think it through carefully how to provide articulation to keep stress off the joints .

tetrachloromethane - 30-6-2005 at 16:04

How could I go about practicing distillations at temps over 100C?

Could you substitute a liebig condenser (packed with something or warm water jacket?) for a vigreux column?

What would be a good combination of liquids to practice fractional distillation?

Thanks:o

Helpful Hints for ground glassware

Cyrus - 30-6-2005 at 16:36

Continuing the trend of this thread, I think it would be nice if some of the members would share tricks/tips about distillations, using ground glassware in particular.

See, I recently bought a really nice kimble 24/40 set, and I'd rather learn this way than in the school of hard knocks.

Several questions I had were;

-Are keck clamps really necessary? I haven't heard of anyone needing to use them, and so assumed they weren't.

-How exactly would I seal the joints with teflon tape? I'm assuming I just put on a layer or two and then lightly push the joint together (but not twist it!)

-I've heard that stirring bars cause problems inside of round bottom boiling flasks. Is this common? For a 500 mL rrbf, for example, would a 1.25" long teflon coated stirring bar be ok? I've seen the special round bottom stir bars for test tubes and things, but they were really small. (because they had to fit into a test tube.;))

edit- one more Q; I admit that I haven't studied distillations very much, but I'd like to change that! Are there any favorite online resources that would go through the basics of vigreux columns, fractional distillation, etc...? (I looked in our own library, but didn't find any.)

[Edited on 1-7-2005 by Cyrus]

neutrino - 30-6-2005 at 18:35

Vogel’s “Practical Organic Chemistry” books contain an excellent section on, among other things, distillation. A good library will have one of these. I know that someone here uploaded a scan of the 5th edition (more recent than what I’ve seen in local libraries), but I don’t know exactly where to find it.

Pyridinium - 30-6-2005 at 19:09

Thanks for sharing your progress, TheBear. I do have a couple things to add:

If you're distilling sulfuric acid, you shouldn't touch or move the apparatus for any reason when it's hot (except: see below). I hate to think about what could happen to you if that vapor or hot acid got outside the glass and on you. Hot, concentrated sulfuric acid is a horror show on wheels. (I've seen 250 C sulfuric get on organic matter. It is truly scary.)

Some distilling equipment has a glass stopper at the top of the flask. On heating the flask for a long time, the glass neck will expand and allow the stopper to sink in farther. If you leave it there when it cools, the flask neck will shrink again. Then the stopper will never come out, lubrication or no. It has to be removed before the glass has completely cooled.

I broke a distilling flask once trying to get out a stopper that was jammed like this.

also: yeah, naked flame against glass = bad idea.

Rosco Bodine - 30-6-2005 at 21:06

Quote:
Originally posted by Cyrus

Several questions I had were;

-Are keck clamps really necessary? I haven't heard of anyone needing to use them, and so assumed they weren't.


I don't use that type clamp myself . I use a variation of the type of clamp used on ball joints , which has spring stainless jaws and works like a clothespin , each jaw is a snap fit around a male to female 24/40 . The damn things are expensive , ten times more than keck clamps , but they are perfect for pressurized systems
and have physical strength , but just enough give to allow parts to move apart if forced . And they allow rotation pretty easily . I don't even recall the proper name for them , I just call 'em pinch clips .
The New Jersey glassblowers have 'em and know what they are , but I don't see them in any online catalogs . Before I had them , and still on occasion , I use the technique of wiring joints . You use a solid conductor soft annealed copper hookup wire of about 20 gauge with a plastic insulation . Teflon jacketed would be great for high temperature use . You cut a length of wire several inches long and fold the wire at about one third its length into a hairpin shape , and grap the " U " between your thumb and first finger and twist it three revolutions to form a tight loop . Then you straighten the wire and in the longer remaining side ,
you form a second hairpin bend and make a second loop identical to the first . You have to eyeball the ground joint which will
be secured and make your wire loops so that they are spaced apart a distance which is half the circumference of the glass joint . That way when you wrap the wire around the joint , the loops will be on opposite sides . And the free ends of the wire legs coming from the loops is simply twisted like a twist tie to secure the
loop equipped wire like a belt around the joint . You can make the same sort of belt with anchorage loops for the male joint .
Keep the loops small about 2-3 mm opening is enough . And you only have to make these attachments once . You leave them on the glassware for future use . When you assemble your apparatus , you line up the loops opposite
each other on the male and female joints ,
and slip a short length of wire through the loops on one side . Pull and bend the ends outside the anchorage loops towards you and then flat against the joint . Use the twist tie to take up the slack on the anchorage loops which pulls the joint together , securing it on opposite sides . It is really quite simple to secure the joint with a twist tie technique like this , after you have provided the joints with anchorage loops .
The attachment will work very well and it will last a very long time and costs nearly nothing , aside from the time to fabricate .
Quote:

-How exactly would I seal the joints with teflon tape? I'm assuming I just put on a layer or two and then lightly push the joint together (but not twist it!)


Using teflon tape on ground joints is not really a good idea because of the irregularities in the thickness where the
laps will upset the bearing forces which
would otherwise be distributed evenly across the surface . The thicker spots will
create point stresses where they wedge the glass . The uneven loading of the joint taper will crack it . Use proper grease on the joints , or precision made
even thickness teflon sleeves .
Quote:

-I've heard that stirring bars cause problems inside of round bottom boiling flasks. Is this common? For a 500 mL rrbf, for example, would a 1.25" long teflon coated stirring bar be ok? I've seen the special round bottom stir bars for test tubes and things, but they were really small. (because they had to fit into a test tube.;))


Oval stirbars or elliptical stirbars work fine . They are sized to fit through various
neck sizes . And they usually have a recommended range of capacity . You want the curve on the stirbar to be tighter
than the curvature of the flask , so the stirbar bears on its belly instead of its ends .

Jettin4u - 1-7-2005 at 07:51

I use teflon tape everywhere in my distilation setups, never had a problem although grease is nicer and probably works better. for heating go ahead and use a sand bath on a hotplate, just be careful not to overheat (place thermometer in the sand)

fractional vacuum distillation practice

prole - 22-8-2005 at 09:56

I've recently tried some good ol' fractional vacuum distillation, and was met with frustration and failure (although nothing broke). I believe my vacuum was tight, had Silicone grease on all joints, keck clips everywhere, and clamps/stands in all the right places. I used a peanut oil bath to heat a well-stirred 500mL RBF, and a 310 mm vigreaux column. My problem is this: after two hours of gradual heat increase, the temp of the oil bath was 141 C, and the temp at the thermometer below the side-arm of the 3-way was still only 26 C. After two hours of this, I could see that I was going to run out of ice for the pump and shut the heat off for the day. Oh, the column and 3-way were insulated with aluminum foil and waterpipe insulation wrap. There was some mild reflux occurring at the top of the RBF, which was not well insulated. I am distilling essential oil in a safflower oil buffer. Was I not patient enough? I thought the inside temp would rise faster than that (21 C to 26 C in two hours), even though I knew to raise the temp gradually. Was there insufficient insulation, allowing too much reflux and no distillation? Because the column and 3-way were insulated, I could not see the vapours climbing the column, as when I did the same procedure with distilling DCM from K2CO3. BTW, none of my current problems occurred when I did the DCM fractional distillation, but that column was not insulated and there was no vacuum being used.
My choice of insulating materials could perhaps be improved. I am not sure what glass wool is. Is it the fiberglass filter material found on many furnace filters? I know insulation is covered elsewhere on this board, but glass wool hasn't been defined.
And just for laughs, when I turned the heat off, I left the stirring and vacuum on, though I left the room for an hour. The pump got the water real hot, and I lost my vacuum, and hot water traveled through my 10ft vacuum tubing into my receiving flask. I avoided using my water trap because it doesn't seal well enough. Because of the tubing's length, it serves the purpose well, until you lose vacuum, apparrently.
I could use some advice (good or bad) from someone who knows what they're doing. I hate sitting there for hours watching a thermometer, not sure if I'm even doin' it right. There has to be a better way.

-prole