Sciencemadness Discussion Board

Suggestions for high temp oil bath?

evil_lurker - 16-7-2006 at 06:27

Looking for some type of oil that will withstand at least 210C without decomposition or smoking.

Was considering using DOT 4 brake fluid which is rated as having a minimumm 230C boiling point.

Suggestions?

[Edited on 16-7-2006 by evil_lurker]

12AX7 - 16-7-2006 at 06:59

Heh, at work we have some silicone oil hot pots. Some are frosty, some are room temp, and some are hot enough to do soldering (the thermostat says 500°F, or 260°C).

For hydrocarbons, *shrug*...

Tim

chromium - 16-7-2006 at 07:15

There are special oils for this purpose. I have no idea where to get them.

Other than that: Glycerine to 200C, saturated solution of CaCl2 (aprox 3 parts salt and 1 part water) to 178C. Ethylene glycol to 190C.

Woods metal Rose metal and other low melting alloys to 300C (and more if fume hood is used).

Eutectic mixture of potassium nitrate and sodium nitrate (aprox 1:1), mp 219C, can be used from 230 to 500C. This is what quick search from books gave. I have no experience with any of these.

Whatever you use you should be very careful because even small amount of water causes powerful steam explosion if it gets in contact with so hot liquid (at least in case of oil bath).

Magpie - 16-7-2006 at 08:11

I have a bottle of NAPA silicone DOT 5 brake fluid that I use for determination of melting points. Its listed boiling point is 289C.

Mr. Wizard - 16-7-2006 at 08:31

Something to keep in mind about hot baths and 'boiling points' is that the boiling point is just when the vapor pressure of the liquid reaches atmospheric 760 mm. Many liquids can be giving off a significant vapor long before the actual boiling point is reached. Think about the toxicity of the chemical you are using. A well known example of such a liquid you shouldn't use is Mercury :o . I'm sure you can think of others. For very high temperature baths consider molten tin.

12AX7 - 16-7-2006 at 09:10

Ah yes, tin boils at a very high temperature- it's a good candidate. Lead too boils at a rather high temperature, and an alloy of them melts somewhat lower, I recall something like 330°F, whatever that is in C.

Tim

DeAdFX - 16-7-2006 at 09:10

I recall reading that sand works ok but takes forever to eat and cool.

evil_lurker - 16-7-2006 at 09:20

That DOT 5 brake fluid is probably gonna be the solution, but goshdammit, they will absolutely KILL your wallet when it comes time to check out.

I may just have to go bite the bullet and pick some up this afternoon.

I just hope my hot plate can take a 1 liter flask in an oil bath up to 200C... I know it will take a 3 liter in an oil bath up to 140C...

unionised - 16-7-2006 at 09:52

Sunflower oil?
http://www.answers.com/topic/smoke-point
Certainly cheaper than most of the alternatives and you can fry your lunch in it too.

chromium - 16-7-2006 at 10:13

I once tested boiling point of cheap cooking oil. This was Risso brand and based on rapeseed oil. It boiled at 390C! There was some smoke and bad smell around but no burning or noticeable decomposition. (I was very surprised and did some additional tests to be sure that thermometer does not lie)

Experiment was carried out in test tube and i am not sure what happens if it is heated in bath were there is lot of oxygen around especially if this lasts long.

I did not recall this before reading what unionised wrote.

Mr. Wizard - 16-7-2006 at 10:55

Be careful with the hot combustible food oils. A pot full of hot oil on fire might just as well be burning kerosine. The flames will be just as hot, and it will often re-ignite even if covered to extinguish a fire. You won't be able to move it for fear of splashing, and if you put limited water on it it will foam and make an even bigger fire. It will ruin your day and your house. If you have a liter or two of smoking cooking oil you are very close to a serious problem. For example common Corn Oil gives off enough flammable vapors to flash (flash point) at 490F and will auto ignite at 740F, Cottonseed Oil will auto ignite at 650F. Soybean oil will not auto ignite until 833F. Kerosine auto ignites at 444F. People are often surprised at the fact that oils and fuel oil will often ignite at a lower temperature than gasoline (about 900F depending on octane).

Flashpoint = temp at which material will give off enough vapor in air to flash when provided with an ignition source, such as a spark. Example gasoline 100 octane is -35F

Ignition temperature= temperature when the material will catch fire in air without an additional heat source. Example gasoline 100 octane 853F

Don't confuse volatility with ease of ignition.

chromium - 16-7-2006 at 11:09

Quote:
Originally posted by Mr. Wizard
You won't be able to move it for fear of splashing, and if you put limited water on it it will foam and make an even bigger fire.


Hot oil will almost explode if in contact with water. No mater its burning or not. It will be spreaded over entire room within fraction of second. I have seen this.

Covering it with fireproof cloth, perfectly dry sand or Na2CO3 my work.

In my opinion oil bath is dangerous anyway. In my not-too-well equiped lab i use it only for heating test tubes or small flasks. No more than 100ml oil used at time.

[Edited on 16-7-2006 by chromium]

Fleaker - 16-7-2006 at 14:44

It will definitely stink up the laboratory. Of course, as I'm sure you know, you should *not* use it to flasks for distilling oxidizing agents (i.e. nitric acid) because if the flask should crack, you will likely regret it. As mentioned before, silicone oils will probably be the way to go, but yes, it will be a hard time for your wallet. Just think of the lack of stench and the reliability :) as you fork over the cash.

BromicAcid - 16-7-2006 at 15:02

Use mineral oil, I've used it to very high temperatures. There are many MSDS's rolling around for it stating different temperatures but it is readily avalible and they are all fairly high at least.

Fleaker - 16-7-2006 at 15:11

I tried using mineral oil as a cover for molten bismuth (circa 515F/268C) and it caught on fire.

Twospoons - 16-7-2006 at 19:51

I was under the impression that brake fluid was quite toxic, even when cold.
In my kitchen I have a can of rice bran oil that claims a smoke point of 260C. I can certainly get a pan of it searing hot without noticeable decomposition.

evil_lurker - 16-7-2006 at 22:11

I got some Havoline synthetic brake fluid with a purported boiling point of 500F.

It started smoking badly around 120C and the distillation I was working on was aborted out of safety concerns.

I should have my vacuum pump I ordered last week in the next few days. I'm hoping that will cure my problems.

neutrino - 17-7-2006 at 06:20

>I tried using mineral oil as a cover for molten bismuth (circa 515F/268C) and it caught on fire.

I tried using it for the same purpose and it smoked heavily. I suggest avoiding mineral oil altogether.

I've melted Bi under corn oil many times without a problem. It does tend to smell a little at high temperatures, so be prepared.

Don't heat it much hotter than this because it will decompose and fill your lab with a nasty stench. Also, corn oil residue oxidized at high temperatures is next to impossible to clean off glass. Think ajax powder + steel wool + very heavy pressure concentrated down to a tiny point. Not impossible, but your joints will hurt afterwards.

unionised - 17-7-2006 at 11:19

I know the difference between flash points, autoignition temperatures, and smoke points. Ideally you want to be below any of them. If you can afford that much gallium lucky you, the rest of us trade toxicity, volatillity, price and flammability against each other. Cooking oil (especially the fully hydrogenated sort that nobody uses because it is unhealthy) works quite well.
Whatever is in the flask you are heating is probably flammable too.

The sugestion I gave was from a very old textbook- it lists arachlor as a suitable high temp bath- which says that lard is good to 250C. So's glycerine but you need to keep it dry which is a problem. I think that may have been the problem in that havoline fluid.
Burned-on fats tend to come off better with NaOH than with scrubbing in my experience.

evil_lurker - 18-7-2006 at 06:27

This morning at my local dollar store I found some extra heavy mineral oil... this stuff should be sufficiant to meet my needs... going to find out in a bit.

Edited to add:

The stuff worked. I conducted a distillation of a material boiling at 180C using $4 worth of laxative. :P

Who would of thunk it?:D

[Edited on 18-7-2006 by evil_lurker]

Flip - 18-7-2006 at 09:24

The most convienent answer is Peanut oil from the grocery store... just make sure that you're not allergic to peanuts. You'll smell it, but it won't be overpowering.

Hmmmm... that gives me an idea... with the right high boiling fragranced oil you might turn your heating bath into a giant Glade Plug-In.

Fyndium - 11-9-2020 at 09:49

I happened to waste a load of money into silicone oil, which is quite watery and it starts smoking pretty much point on 150C, although the packaging states it is stable from -35 to 200C. I heated it up to 200C and while it appears very stable itself, it just gives out significant amount of smoke. I'm gonna keep it hot for a while and see if it stops smoking by getting rid of the more volatile compounds in it, but we'll see. I've been simmering the oil at 170-180C for an hour now and the smoking has dissipated significantly.

The fact is, CaCl2 bath is still by far my favorite and it is very stable up to 160C, but it will very quickly turn into crust when heated over that, and last reading I was able to get was 170 something, and over half of it was just solidified and appeared like calcium chloride anhydrite looks like when got out of the oven. This surface layer insulates the bottom though, which remained liquid till the end, but with very narrow play there might be issue of running dry or hotspots or something else, so I consider 160 in the very high end of it. Below that, it works like charm though, remaining fully liquid and stable even for hours and it gives zero odor or fumes and is cheap as dirt.

My problem lies right on that area between 160C and 220C. I just gave a though for sand bath, because I might need higher temp for now only for distilling sulfuric acid under vacuum (180-200C bath temp req), and a couple of high temp reactions which want about 160-170C of heat. Glycerin is another shot, but I wouldn't like to buy EVERY single compound around just to test it out and fail.

Paraffin oil, the crystal clear ntp liquid form sold in g stores as baby oil, wood treatment(ikea also) etc is stable up to 150+ and then it starts to faintly smoke and kept doing that up to 175C when I stopped heating. It also has the paraffinous smell, which I find pleasant, buy someone might not.

[Edited on 11-9-2020 by Fyndium]

Heptylene - 12-9-2020 at 02:03

Has anyone tried vacuum pump oil? The vapor pressure is low by design:
< 1e-8 atm at room temperature
< 1e-6 atm at pump operating temperature, which can be around 80 °C.
Indeed, hot pump oil has no smell!

The flash point is incredibly high, which is important for an oil bath. One example: Leybold LVO100, which is a general purpose oil, has a flash point above 255 °C according to Leybold. All pump manufacturers have similar general purpose oils (Edwards makes "Ultragrade 19", etc.)

Anyway I'd be interested to hear if anyone has used this.

Sulaiman - 12-9-2020 at 02:55

Given the cost and/or hazards of all of the oils mentioned above,
it would probably be cheaper/safer/easier to buy or diy a heating mantle.

Fyndium - 12-9-2020 at 05:04

I was just looking for a one. Considered ordering a MESE mantle but after seeing negative rant about their hotplates just not heating and stirrers jamming I'll look into elsewhere.

Main issue with mantles seem to be their size sensitivity. I have rather wide range of flasks, generally 0.5L, 1L, 2L and 4L which I routinely heat depending on case so I would still need the bath. Otherwise, if it would be used only for high temp ops, I could probably do with 1L.

For the record, I've been heating the silicone oil now for several hours at 160C and it has pretty much stopped smoking. It can only be seen with a strong flashlight when other lights are shut.

Sulaiman - 13-9-2020 at 00:44

I'd go for 500ml because it's cheaper,
. a few hundred ml is enough for most purposes (H2SO4, Hg etc.)
. for pyrolysis a 500ml flask could be sacrificed, a 4l isn't cheap
. a 500ml heating basket/liner/elememt for a DIY mantle is quite cheap via eBay etc.

Although magnetic stirring is nice to have, its not easy to DIY for high temperatures and probably too weak for pyrolydis
Consider DIY overhead stirring, or no stirring.

monolithic - 13-9-2020 at 04:49

Quote: Originally posted by Fyndium  
I was just looking for a one. Considered ordering a MESE mantle but after seeing negative rant about their hotplates just not heating and stirrers jamming I'll look into elsewhere.

Main issue with mantles seem to be their size sensitivity. I have rather wide range of flasks, generally 0.5L, 1L, 2L and 4L which I routinely heat depending on case so I would still need the bath. Otherwise, if it would be used only for high temp ops, I could probably do with 1L.

For the record, I've been heating the silicone oil now for several hours at 160C and it has pretty much stopped smoking. It can only be seen with a strong flashlight when other lights are shut.


eBay is a good place to look. There's always used Glas Col (and similar) mantles for sale, or you could buy what they call an "inner sleeve" from a Chinese supplier on eBay and make your own housing for the mantle, or you could do the same with some flexible high temperature heat tape.

Fyndium - 13-9-2020 at 08:43

I'm not that keen into making equipment myself when I want high quality and reliable systems and it's definitely not a con if it doesn't look like homemade. I have found myself into an endless cycle of testing, buying, trying and developing infinite pieces of puzzle even before getting into the main thing of actually synthesizing something. Perhaps I'm not very good at doing stuff myself, for that matter.

Has anyone got experience on Deschem heating mantles? The supplier is my go to because they deliver stuff very fast and it has usually been good quality.

By the way, I found the CRC Europe sells 5 liter tin cans of silicone oil that is rated up to 200C and it appears to be of same quality that my current oil and it costs only 40€ for the 5L tin. Should this be suitable for heat bath, and why the CRC europe MSDS lists that it contains two compounds of 25-50% of hydrocarbons, C7 alkenes and it is classified as flammable with flash point of -35C? I presume this is a typo because none of these apply to any form of silicone oil whatsoever.

[Edited on 13-9-2020 by Fyndium]

macckone - 13-9-2020 at 09:18

most mineral oils are going to be fine up to 220C or so (some smoke but no fire) - swan mineral oil flash point is 220C.

canola oil is my go to for lower temperatures, primarily because I use it for frying and have lots of waste oil.
advocado oil has a higher smoke point but is ungodly expensive.
safflower is almost as good as advocado but not as expensive (half the cost) while still way more than canola.

If you need more than 220C you should probably be using a fitted mantle, sand, radiant heat or flame.
A propane/butane stove with fitted ceramic protector (high temp fiberglass) or wire mesh (stainless steel screen) can provide even heating while protecting glassware from direct flame.

Fyndium - 13-9-2020 at 10:59

Smoking is an issue at my workplace because I work indoors and have only activated carbon scrubber in my fume hood. Though the very high temp jobs I carry out elsewhere anyways.

I could actually get avocado oil for a very cheap price, but it apparently is (at least more) flammable than silicone oil and it could possibly have some issues with stability over time due to rancidity, biological growth, etc?

I used canola oil as heating bath for a long time ago but I remember only that I had smoking issues with it - and also the only time ever I've gotten a bath fire. I truly wonder if I heated it too hot, actually, because I did not have thermometer for the bath. The smoke point difference between canola and avocado oil is only 30C though.

Also, when heating oil baths, could it cause smoking if the heater is too intense, like from ordinary hotplate or gas burner(a no-go for the matter of flammable hot oil) even if the base oil temp is way lower than smoke point?

macckone - 13-9-2020 at 20:35

Even silicone based oils aren't going to get you much above 200C.
They break down and smoke as well.
Dot5 brake fluid has a flashpoint around that temperature.
Yes, it will burn.