Vaccum Distillation

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bmadhu_srao Commentator Join Date: Nov 2007 Posts: 86	Vaccum Distillation 12/13/2007 8:50 AM
	While separating two solvents from a mixture, heating under vaccum is done ( Vaccum distillation), What makes the solvent evaporate much before its boiling point under vaccum.......
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TVP45 Guru Join Date: Jul 2007 Posts: 4448 Good Answers: 143	#1 Re: Vaccum Distillation 12/13/2007 9:17 AM
	Do you have an azeotrope? __________________ "Well, I've wrestled with reality for 35 years, Doctor, and I'm happy to state I finally won out over it." Elwood P. Dowd
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Zaphod2Headed Power-User Join Date: Nov 2007 Location: Alberta Canada Posts: 182 Good Answers: 9	#2 Re: Vaccum Distillation 12/13/2007 10:44 AM
	HI Bmadu srap Vapour pressure. Above a liquid will be some vapour from that liquid. When you reduce the pressure above a liquid if becomes easier for the molecules to escape from the surface of that liquid, so it boils more easily. Consider these two examples. Climbers on mount Everest cannot boil an egg and make it solidify. This is because at that altitude (28,000 feet or so) the pressure is much lower than it is at sea level, so the water boils at around 90C, which is not high enough to coagualte the protiens in the egg, so it stays mushy (Yuck!) A pressure cooker can cook food faster than boiling it in a pot because the increase in pressure inside the pressure cooker raises the boiling point of the water over 100C, so the food is made hotter, and so cooks faster. This is also why chemical properties are stated at 'Standard temperature and pressure' (STP), because variations in either temperature or pressure will affect things like boiling and freezing points, vapour density etc. Vacuum distillation allows the distillation to occur at lower termperature. Hope this helps IPG __________________ Vote for something useful this time, vote to repeal the second law of thermodynamics!
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AbdulWasay Commentator Join Date: Aug 2007 Posts: 97 Good Answers: 3	#7 In reply to #2 Re: Vaccum Distillation 12/17/2007 2:13 AM
	It is new to me you gave me the knowledge that one cannot boil egg on Mount Everest.
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Zaphod2Headed Power-User Join Date: Nov 2007 Location: Alberta Canada Posts: 182 Good Answers: 9	#8 In reply to #7 Re: Vaccum Distillation 12/17/2007 10:10 AM
	Oh you can boil it all right, but it will never get hard! __________________ Vote for something useful this time, vote to repeal the second law of thermodynamics!
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Anonymous Poster	#3 Re: Vaccum Distillation 12/13/2007 11:21 PM
	No solvent can evaporate before its B.P. But if specific vacuum and temperature is acheivedthen it may evaporates with repsect to its flast point temp. Regards, Vijay
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Horrible Old Bat Power-User Join Date: Nov 2007 Location: A secret. Bats are a Protected Species. Posts: 186 Good Answers: 4	#4 In reply to #3 Re: Vaccum Distillation 12/14/2007 3:27 AM
	Boiling temperature varies with pressure. Take water, for example. Reduce the pressure to 100mBarA and it boils at 46degC. At sea level pressure it boils at 100degC. At 20BarA it boils at 212degC. It's the same principle with any solvent (though the numbers are different). __________________ Innuendo is not Italian for a suppository.
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Tad Power-User Join Date: Dec 2006 Posts: 442 Good Answers: 32	#6 In reply to #3 Re: Vaccum Distillation 12/16/2007 12:52 PM
	Vijay, Of course solvents evaporate below the boiling point. Other wise, your clothes would never dry after washing (as an example). I don't understand your flashpoint comment. Flashpoint is the temperature at which a compound has enough vapor pressure to be ignited. Tad
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betomachine Power-User Join Date: Apr 2007 Location: Austin, TX Posts: 367 Good Answers: 10	#5 Re: Vaccum Distillation 12/14/2007 10:19 AM
	Good answer Zaphod. Water boiling temp at altitudes always seems to be the best way to describe that principle. __________________ Money doesn't talk, it screams in your face.
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