Sulphur sublimation

[THX-1138]

In rummaging through my shelves, I came across a bottle of pharmaceutical-grade sulphur, the label of which remarks that it was sublimated. That ticked my curiousity, so I went looking to see how you'd sublimate sulphur in commercial quantities.

 

I came up empty on that, although I did learn that the sublimation process in question is from gaseous to solid phase. (I guess I subconsciously associated 'sublimation' with a solid->gaseous transition from the rather more common dry ice.)

 

So.. Just how do they sublimate sulphur in large quantities? I presume its purity would be affected by contaminants on the condensing surface, and any in the sample that had phase transitions very close to S's, so sulphur obtained by sublimation isn't necessarily 100% 'pure.' Just probably pretty close.

[Darkblade48]

I thought that sublimation was from solid to gas, and that from the gaseous state to a solid state was known as deposition?

[insane_alien]

I thought that sublimation was from solid to gas, and that from the gaseous state to a solid state was known as deposition?

 

it is. some texts use it for both ways never the less.

 

basically, the process works the same way as liquid-liquid distillation.

 

the sulphur sublimates and gets deposited at a heat sink while the impurities don't and get left behind.

[YT2095]

it`s a fancy form of Distillation in other words

[THX-1138]

Mm, I was able to figure that much out.

 

But is it done in an inert environment? What material is used for the deposition surface? (Thanks for that correction/reminder, by the way.) How much is done at a time? How are accumulated impurities handled?

 

Questions, questions. What would happen if you passed the gaseous S over a chilled non-solvent liquid? I'm thinking ease of collection here.

 

Just curious, and I haven't had my caffeine-analogue yet this morning..

[YT2095]

if you`re trying to purify Sulpher, just dissolve as much as you can in hot methyl benzene (toluene), decant and then let it cool slowly, large crystals of sulpher will form(and you can use the liquid again for the next batch).

[THX-1138]

I'm actually not trying to purify it myself, at least not right now. This jar is still pretty full, it was tightly sealed, and I don't have any projects needing it at the moment. Although that's good information if I decide to play mad scientist with the sack of garden sulphur out in the shed.. I just got curious about the industrial process.

 

As for sublimation versus deposition, a lot of geology sources seem to use 'sublimation' primarily for the gas->solid transition, especially with regard to volcanic by-products.

[THX-1138]

Gaah. I just looked at the MSDS for toluene, and it's not something I'll be prepared to mess about with for quite some time, if ever. Just as well..

[insane_alien]

well, from chemical engineering sources(Elementary principles in chemical engineering, Felder and rousseau) the vapour-solid transition is called deposition. or, more formally, vapour depostion.

[YT2095]

Gaah. I just looked at the MSDS for toluene, and it's not something I'll be prepared to mess about with for quite some time, if ever. Just as well..

 

well if you were to "decide to play mad scientist with the sack of garden sulphur out in the shed.. " as you said, then Yes, it`s probably best you DON`T "mess about" with it!

[THX-1138]

Coming back to this again..

 

It looks as though it would be safer to use xylene (dimethylbenzene) than toluene; xylene's boiling and flash points are considerably higher. The only information I've found concerning sulphur's solubility indicates both work equally well.

[UC]

Unless you purchase xylene from a chemical supplier, the hardware store material contains mostly the three xylene isomers, ethylbenzene, and likely small amounts of toluene and nonaromatic alkanes or alkenes.

 

When heated with sulfur, the ethylbenzene is converted to styrene with the release of H2S (do it outside!). This polymerizes and when you try to dry the sulfur, small clumps of polystyrene will be left in the solid.

 

Also, xylene has an incredibly potent smell. I'd do the whole thing outside with a good breeze.

[John Cuthber]

I must have missed a few things here.

Resublimed sulphur "flowers of sulphur" has been a commercial product since Noah was a lad.

Recrystallising sulphur from, for example, xylene efficiently means heating the xylene to its boiling point. The flash point will be lower than the boiling point.

 

Adding another material, like xylene or toluene will give you sulphur containing xylene or toluene. Removing the solvent by evaporation will be a lot easier and quicker with a more volatile solvent.

 

Anyone who is frightened of toluene had better stop filling cars' fuel tanks with petrol (Gasoline) which contains significant amounts of it.