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Before I go bold and remove the ethanol-water example, anyone interested in choosing something else and with a more accurate explanation? Here are two reasons:
So can someone explain trays in the process (and how that would fit in with different faction outlets), and what they're good for, and why you might want
raschig rings or ordered packing instead of them (in certain situations)? And link it up to
reflux as well? I'd like to learn more about
fusel alcohols and how they're taken out of ordinary distillation. I was pleased to learn about
azeotropes, but there's more that I could learn...
~ender 2005-10-04 22:12:MST
The following sentence is illogical, and is factually flawed:
" In this example, a mixture of 95% ethanol and 5% water boils at 78.2°C, being more volatile than pure ethanol, so the ethanol cannot be completely purified by distillation."
The two concepts may be true from some point fo view (completely purified? Fine precious metals are never better than 99.98% pure, so how pure is "completely purified" ethanol? Can any method produce it? I think 99% or better is called "ethanol absolute", perhaps that's "complete purification".), but they do not follow from one another as written.
The reason that complete puriication by distillation is impossible has little to do with the boiling point, it's about both water and alcohol evaporationg into a less than saturated gaseous medium, and how it's impossible to saturate the gas with water and keep the alcohol at less than saturation. There is no temperature and pressure that will allow the distillation to perfectly separate the liquids. The purity of the distillate can be improved by distillation at a temperature significantly below the boiling point of either water or alcohol or of the mixture by taking advantage of evaporation and partial pressures in the surrounding gas.
Thinking about this, it would be interesting to see what happens in a mixture at around -20c, where the water has turned solid and the alcohol is still a liquid, to use vacuum distillation to take off the liquid alcohol, leaving the solid water ice behind. Clearly this would be expensive and impractical in a commercial operation, but it may be a method by which ethanol is completely purified (whatever the boundary of that could be) by distillation, in contrast with the statement in the article. Furthermore, absolute ethanol is obtained by distillation with benzine.
I have also identified that this is actually a misquoting/misunderstanding of the entry from the Columbia Encyclopedia - http://www.bartleby.com/65/et/ethanol.html - where they refer to simple distillation. Presumably the writer did not understand that the meaterial lost integrity when the word simple was omitted to avoid misappropriation of the material. Clearly this should be rewritten. Octothorn 02:51, 10 January 2006 (UTC)
Who uses a bunsen burner as the heat source for a fractional distillation? Most of the time, you risk setting your lab bench on fire! —Preceding unsigned comment added by 64.53.218.27 ( talk • contribs) 7 February 2006 (UTC)
I deleted the expansion stub because:
In my personal opinion, what this article needs is to downplay its focus on laboratory-scale glassware distillation and upgrade its focus on the use of large-scale fractionators in industry. Perhaps that could be done by simply reversing the location of the glassware section and the industrial section?? What do others think? - mbeychok 00:08, 5 June 2006 (UTC)
Fractional distillation is indeed a vital part of the oil industry, if you don't think it fits under Industrial processes, then, quite frankly, you are quite mistaken. GreatMizuti 00:47, 18 September 2006 (UTC)
Is it possible to use a spiral for the column? Arnero 19:01, 22 October 2006 (UTC)
While reading this article i came across the following section:
"Alternate set-ups may utilize a "cow" or "pig" which is connected to three or four receiving flasks. By turning the "cow" or "pig", the distillates can be channelled into the appropriate receiver. A Perkin triangle is versatile piece of apparatus that can be also be used to collect distillation fractions which does not require a cow" or "pig" adaptor. A Perkin triangle is most often used where the distillates are air-sensitive or where the fractions distil and are collected under reduced pressure, but can be used for a simple and fractional distillation."
Now, i assume that cows and pigs refer to some kind of chemistry equipment, mabey glassware or whatever. However, without previous knowledge of the subject and no links, it makes this segment confusing at best. perhaps someone who actually knows what this means can throw a link or two in there? 204.82.251.197 ( talk) 14:30, 9 February 2009 (UTC)
See [2]. Shame we don't have a picture... but that can't be helped. -- Rifleman 82 ( talk) 14:42, 9 February 2009 (UTC)
in the intro, it says that if the boiling point difference is greater than 25ºC, simple distillation is used. simple distillation cannot produce a reasonably pure (<5% impurities) sample unless the boiling point difference is greater than 100ºC. According to Introduction to Organic Laboratory Techniques: A Small-Scale Approach (ISBN:978-0534408336), 108ºC is required to achieve separation by simple distillation. There is a table in the book (page ~751) that has a list of how many boil/condense cycles are required for various boiling point differences. It also calls the boil/condense cycles that occur in the column "theoretical plates." the table ranges from bp difference of 108º with 1 theoretical plate to a bp difference of 2º which requires 100 theoretical plates. —Preceding unsigned comment added by 71.92.101.14 ( talk) 04:59, 2 October 2009 (UTC)
The first line as written isn't strictly correct. There are at least a couple things wrong with it, and I believe the most important is the omission of the use of the term fractionating column, since fractional distillation is distinguished from other types of distillation based on the use of a fractionating column such as a Vigreux column, not the fact that it's a method of separating mixtures into fractions. All types of distillation separate the pot into fractions, so this is not characteristic of fractional distillation. Also not entirely correct is the description of the mixture. This technique will give fractions of a pot but not if one of the components of a mixture is, say, a gas. A gas will leave open apparatus and escape and not be captured as a fraction. Very often, fractionation of liquids is wanted. "A mixture" without further characterization is very general. I am willing to rework the first three sentences if no one else would like to take the opportunity to do so. I will come back in a few days to see if an edit has been made, and if not I'll give it a shot. 2603:900A:1C0B:7700:9D9F:26BA:28CF:552B ( talk) 09:08, 14 April 2019 (UTC)
I think
nonplus
sed is the adjective that describes my mental state, upon noticing our lack of not (only an article, but in fact) even of a redirect, for this perfectly predictable consequence of the topic-worthiness of the accompanying article. I hasten to add that even tho I may in fact be
nuckin' futz, there is at least an
insane logic to my assertion, and I may even explicate that before
shuffling off this [[wikt:mortal coil]|].
--
JerzyA (
talk) 23:42, 30 June 2019 (UTC)
It's silly to think that a mere edit in WP could constitute a monument to oneself, but here I am: suggesting (as at least some, of at least we males, of my pretentious species are wont to do, especially in anticipation of [[shuffle off|shuffling off Wikt:this mortal coil), that this one might just be my own. Still, " Vanity, thy name is" ... something or other ... oh, I fergit what .... JerzyA ( talk) 00:07, 1 July 2019 (UTC)
What is a fractional distillation 2409:4043:91B:BEFE:0:0:29E:E0AC ( talk) 06:18, 25 March 2022 (UTC)
Which is the distillate of fractional distillation 102.7.80.12 ( talk) 07:13, 4 July 2022 (UTC)
This is the
talk page for discussing improvements to the
Fractional distillation article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
This
level-5 vital article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||||||||||
|
Before I go bold and remove the ethanol-water example, anyone interested in choosing something else and with a more accurate explanation? Here are two reasons:
So can someone explain trays in the process (and how that would fit in with different faction outlets), and what they're good for, and why you might want
raschig rings or ordered packing instead of them (in certain situations)? And link it up to
reflux as well? I'd like to learn more about
fusel alcohols and how they're taken out of ordinary distillation. I was pleased to learn about
azeotropes, but there's more that I could learn...
~ender 2005-10-04 22:12:MST
The following sentence is illogical, and is factually flawed:
" In this example, a mixture of 95% ethanol and 5% water boils at 78.2°C, being more volatile than pure ethanol, so the ethanol cannot be completely purified by distillation."
The two concepts may be true from some point fo view (completely purified? Fine precious metals are never better than 99.98% pure, so how pure is "completely purified" ethanol? Can any method produce it? I think 99% or better is called "ethanol absolute", perhaps that's "complete purification".), but they do not follow from one another as written.
The reason that complete puriication by distillation is impossible has little to do with the boiling point, it's about both water and alcohol evaporationg into a less than saturated gaseous medium, and how it's impossible to saturate the gas with water and keep the alcohol at less than saturation. There is no temperature and pressure that will allow the distillation to perfectly separate the liquids. The purity of the distillate can be improved by distillation at a temperature significantly below the boiling point of either water or alcohol or of the mixture by taking advantage of evaporation and partial pressures in the surrounding gas.
Thinking about this, it would be interesting to see what happens in a mixture at around -20c, where the water has turned solid and the alcohol is still a liquid, to use vacuum distillation to take off the liquid alcohol, leaving the solid water ice behind. Clearly this would be expensive and impractical in a commercial operation, but it may be a method by which ethanol is completely purified (whatever the boundary of that could be) by distillation, in contrast with the statement in the article. Furthermore, absolute ethanol is obtained by distillation with benzine.
I have also identified that this is actually a misquoting/misunderstanding of the entry from the Columbia Encyclopedia - http://www.bartleby.com/65/et/ethanol.html - where they refer to simple distillation. Presumably the writer did not understand that the meaterial lost integrity when the word simple was omitted to avoid misappropriation of the material. Clearly this should be rewritten. Octothorn 02:51, 10 January 2006 (UTC)
Who uses a bunsen burner as the heat source for a fractional distillation? Most of the time, you risk setting your lab bench on fire! —Preceding unsigned comment added by 64.53.218.27 ( talk • contribs) 7 February 2006 (UTC)
I deleted the expansion stub because:
In my personal opinion, what this article needs is to downplay its focus on laboratory-scale glassware distillation and upgrade its focus on the use of large-scale fractionators in industry. Perhaps that could be done by simply reversing the location of the glassware section and the industrial section?? What do others think? - mbeychok 00:08, 5 June 2006 (UTC)
Fractional distillation is indeed a vital part of the oil industry, if you don't think it fits under Industrial processes, then, quite frankly, you are quite mistaken. GreatMizuti 00:47, 18 September 2006 (UTC)
Is it possible to use a spiral for the column? Arnero 19:01, 22 October 2006 (UTC)
While reading this article i came across the following section:
"Alternate set-ups may utilize a "cow" or "pig" which is connected to three or four receiving flasks. By turning the "cow" or "pig", the distillates can be channelled into the appropriate receiver. A Perkin triangle is versatile piece of apparatus that can be also be used to collect distillation fractions which does not require a cow" or "pig" adaptor. A Perkin triangle is most often used where the distillates are air-sensitive or where the fractions distil and are collected under reduced pressure, but can be used for a simple and fractional distillation."
Now, i assume that cows and pigs refer to some kind of chemistry equipment, mabey glassware or whatever. However, without previous knowledge of the subject and no links, it makes this segment confusing at best. perhaps someone who actually knows what this means can throw a link or two in there? 204.82.251.197 ( talk) 14:30, 9 February 2009 (UTC)
See [2]. Shame we don't have a picture... but that can't be helped. -- Rifleman 82 ( talk) 14:42, 9 February 2009 (UTC)
in the intro, it says that if the boiling point difference is greater than 25ºC, simple distillation is used. simple distillation cannot produce a reasonably pure (<5% impurities) sample unless the boiling point difference is greater than 100ºC. According to Introduction to Organic Laboratory Techniques: A Small-Scale Approach (ISBN:978-0534408336), 108ºC is required to achieve separation by simple distillation. There is a table in the book (page ~751) that has a list of how many boil/condense cycles are required for various boiling point differences. It also calls the boil/condense cycles that occur in the column "theoretical plates." the table ranges from bp difference of 108º with 1 theoretical plate to a bp difference of 2º which requires 100 theoretical plates. —Preceding unsigned comment added by 71.92.101.14 ( talk) 04:59, 2 October 2009 (UTC)
The first line as written isn't strictly correct. There are at least a couple things wrong with it, and I believe the most important is the omission of the use of the term fractionating column, since fractional distillation is distinguished from other types of distillation based on the use of a fractionating column such as a Vigreux column, not the fact that it's a method of separating mixtures into fractions. All types of distillation separate the pot into fractions, so this is not characteristic of fractional distillation. Also not entirely correct is the description of the mixture. This technique will give fractions of a pot but not if one of the components of a mixture is, say, a gas. A gas will leave open apparatus and escape and not be captured as a fraction. Very often, fractionation of liquids is wanted. "A mixture" without further characterization is very general. I am willing to rework the first three sentences if no one else would like to take the opportunity to do so. I will come back in a few days to see if an edit has been made, and if not I'll give it a shot. 2603:900A:1C0B:7700:9D9F:26BA:28CF:552B ( talk) 09:08, 14 April 2019 (UTC)
I think
nonplus
sed is the adjective that describes my mental state, upon noticing our lack of not (only an article, but in fact) even of a redirect, for this perfectly predictable consequence of the topic-worthiness of the accompanying article. I hasten to add that even tho I may in fact be
nuckin' futz, there is at least an
insane logic to my assertion, and I may even explicate that before
shuffling off this [[wikt:mortal coil]|].
--
JerzyA (
talk) 23:42, 30 June 2019 (UTC)
It's silly to think that a mere edit in WP could constitute a monument to oneself, but here I am: suggesting (as at least some, of at least we males, of my pretentious species are wont to do, especially in anticipation of [[shuffle off|shuffling off Wikt:this mortal coil), that this one might just be my own. Still, " Vanity, thy name is" ... something or other ... oh, I fergit what .... JerzyA ( talk) 00:07, 1 July 2019 (UTC)
What is a fractional distillation 2409:4043:91B:BEFE:0:0:29E:E0AC ( talk) 06:18, 25 March 2022 (UTC)
Which is the distillate of fractional distillation 102.7.80.12 ( talk) 07:13, 4 July 2022 (UTC)