Sciencemadness Discussion Board

What's the best way to separate xylenes and ethylbenzene?

Cooperation - 17-2-2014 at 16:41

I have some store bought xylenes which also contains ethylbenzene. From researching on the internet, I've discovered that ethyl benzene BP is 136C and xylenes is from 138-142 (depending on which alphabet-xylene we are wanting). There seems to be a an extraction distillation that can be performed, but I don't know what the extraction solvent should be. When I fractionally distill the thermometer above the vigreux column doesn't read correctly, so been monitoring the oil bath instead. This has worked for separating liquids that vary 20-25 degrees from each other, but I'm not confident in my skills to separate two substances that are so close to each other. Can I use the xylene as it is? Leave the ethylbenzene in there? Will it affect yield? Should I dry the solvent with magnesium sulfate? Any and all suggestions are welcome.

Ozone - 17-2-2014 at 17:02

Getting to -48°C shouldn't be too hard (you can fractionally freeze the isomers out):

Ethyl benzene: MP = -95°C
o-xylene: MP = -24°C.
m-xylene: MP = -48°C
p-xylene: MP = 13.2°C.

Depending on what you want to do, it probably can be used as-is. What is your intent?

--O3

Never thought about freeze separation---great idea

Cooperation - 17-2-2014 at 17:47

I'm using it as a solvent for a freebase amine prior to Changing the freebase to a HCL salt (via Bubbled HcL gas through Nacl/H2SO4). If you don't think it will affect yield I won't waste the time separating it. I have fractionally distiller a few things under vacuum but i don't think I have the skills yet to do this will boiling points so close. Plus, cold seems less dangerous. What's the best way to get down to -48 to -50? I assume once I freeze the xylenes, the ethylbenzene will stay liquid, and I just lift the frozen chunk of xylene out and I'm good. Really clever, and thanks for the help!

thesmug - 17-2-2014 at 18:38

Quote: Originally posted by Cooperation  
I'm using it as a solvent for a freebase amine prior to Changing the freebase to a HCL salt (via Bubbled HcL gas through Nacl/H2SO4). If you don't think it will affect yield I won't waste the time separating it. I have fractionally distiller a few things under vacuum but i don't think I have the skills yet to do this will boiling points so close. Plus, cold seems less dangerous. What's the best way to get down to -48 to -50? I assume once I freeze the xylenes, the ethylbenzene will stay liquid, and I just lift the frozen chunk of xylene out and I'm good. Really clever, and thanks for the help!


Just for future reference, remember that it is HCl, not HCL or HcL ;)

crazyboy - 17-2-2014 at 18:47

Ethylbenzene won't be a problem for what you're doing. Furthermore I imagine there is only around 1-5% ethylbenzene present and between freezing point depression and such a low temperature I don't think fractional freezing would be particularly effective.

Thanks for the help Everyone

Cooperation - 17-2-2014 at 19:03

I am relieved to know I can use it as is, but I think I will try a freeze separation if I have time since its such a COOL idea (lol...sorry, I couldn't resist!)

Random - 18-2-2014 at 04:35

I have xylene isomer mixture and when it's under 13 celsius it never precipitates frozen p xylene. It's not as simple.

testimento - 18-2-2014 at 05:51

Freezing temp of water decreases substantially with only minor amounts of alcohols or chlorides and yet they end up mushy fluff when cooled enough so separation may not be just as easy as removing a frozen brick of xylene from ethylbenzene. :D

leu - 18-2-2014 at 06:01

Vacuum sublimation is often used to purify aromatic hydrocarbons prior to freeze crystallization ;) The tarry impurities from petroleum processing prevent nucleation from occurring :P The attached article titled Separation of para-xylene from xylene mixture via crystallization may be helpful :cool:

[Edited on 18-2-2014 by leu]

Attachment: Separation of para-xylene from xylene mixture via crystallization.pdf (448kB)
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I'm not worried about the xylene isomers, just the ethylbenzene

Cooperation - 18-2-2014 at 07:51

As long as I can use dry ice and freeze the xylenes as a solid block, I'm not worried about the xylene isomers. I'm looking forward to learning this new technique!

DraconicAcid - 18-2-2014 at 10:37

Quote: Originally posted by Cooperation  
As long as I can use dry ice and freeze the xylenes as a solid block, I'm not worried about the xylene isomers. I'm looking forward to learning this new technique!


I doubt it's going to work very well, since the xylenes will be quite soluble in ethylbenzene well below their freezing points. You may get some of the para-xylene precipitating (either as a lump or slush), but the other two will probably stay in solution.

I don't think the ethylbenzene will interfere with the reaction you're trying to do anyway.