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We are required to condense the top product coming out from distillation column. The product is fed into a condenser. The product underwent sublimation (vapor state to solid directly) instead of condensing. Kindly give us all possible solutions to the above stated problem.
Note: The product sublimed at the condensing temparature.
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Sublimation
Started by Guest_karthik_*, Jul 22 2003 12:52 AM
6 replies to this topic
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#2
siretb
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Posted 22 July 2003 - 02:00 AM
May be your are subcooling too much at the condenser.
Check the wall temperature of your condenser/refrigerant-coolant used.
It is sometimes possible, instead of using a regular condenser, to spray sub-cooled distillate, and use the spray as a quench to perform the heat transfer. In such case the sprayed liquid, and what has been condensed in the spray box is collected and cooled in an external regular heat exchanger. Part of it is refluxed, and the rest is withdrawn. Additional advantage is that pressure drop is low.
Check the wall temperature of your condenser/refrigerant-coolant used.
It is sometimes possible, instead of using a regular condenser, to spray sub-cooled distillate, and use the spray as a quench to perform the heat transfer. In such case the sprayed liquid, and what has been condensed in the spray box is collected and cooled in an external regular heat exchanger. Part of it is refluxed, and the rest is withdrawn. Additional advantage is that pressure drop is low.
#3
Guest_karthik_*
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Posted 22 July 2003 - 02:40 AM
Thanks sireth for your comments,
As you said i also previously checked up with the wall temparature of the condenser. It is much higher than the condensing temparature of the distillate. To your information, we have insulated the wall of the condenser with enough cotton. So i am sure there will be no heat transfer between the condenser wall and distillate.
And for the next solution you gave, it may possibly increase the heat transfer which in turn the distillate cools down more and hence there is a possibility of sublimation once again.
So, to avoid sublimation, provide me a solution which reduces heat transfer.
As you said i also previously checked up with the wall temparature of the condenser. It is much higher than the condensing temparature of the distillate. To your information, we have insulated the wall of the condenser with enough cotton. So i am sure there will be no heat transfer between the condenser wall and distillate.
And for the next solution you gave, it may possibly increase the heat transfer which in turn the distillate cools down more and hence there is a possibility of sublimation once again.
So, to avoid sublimation, provide me a solution which reduces heat transfer.
#4
Guest_Thamarai Selvan_*
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Posted 22 July 2003 - 01:10 PM
hello Karthik,
ONly one querry I have is u'rs a Vacuum distillation or atmospheric distillation ?
As I have encountered similar problems in Vacuum distillation which is mainly due to the cooling effect due to Vacuum. What we did was to give less vacuum and tried it worked out very well. May be u can see if u have vacuum distillation ?
ONly one querry I have is u'rs a Vacuum distillation or atmospheric distillation ?
As I have encountered similar problems in Vacuum distillation which is mainly due to the cooling effect due to Vacuum. What we did was to give less vacuum and tried it worked out very well. May be u can see if u have vacuum distillation ?
#5
Guest_Guest_*
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Posted 22 July 2003 - 06:25 PM
karthik:
What is the name of the component that are you saying went from the gas phase directly to the solid phase?
The process of sublimation is defined as the solid phase transforming directly into the gaseous phase (without going to the liquid). Therefore, your description is flawed. Additionally, why would the designers of the column furnish a condenser (an apparatus for condensing -liquefying- the overhead component) if the component solidifies rather than liquefy?
The way you describe the situation is very confusing either because of the wrong use of the terminology or because there are other factors you haven't mentioned - like the identity of the component that solidifies directly. For example, there could be other substances that give similar results, like waxes.
What is the name of the component that are you saying went from the gas phase directly to the solid phase?
The process of sublimation is defined as the solid phase transforming directly into the gaseous phase (without going to the liquid). Therefore, your description is flawed. Additionally, why would the designers of the column furnish a condenser (an apparatus for condensing -liquefying- the overhead component) if the component solidifies rather than liquefy?
The way you describe the situation is very confusing either because of the wrong use of the terminology or because there are other factors you haven't mentioned - like the identity of the component that solidifies directly. For example, there could be other substances that give similar results, like waxes.
#6
Guest_karthik_*
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Posted 22 July 2003 - 11:28 PM
Thamarai Selvan,
We are using only atmospheric distillation and not vacuum distillation.
Guest,
The material vapor discharges as the top product from the distillation column. We need the product in liquid state rather than solid state. The liquid state is more convenient to handle.
So a condenser has to be employed to condense the vapors.
On condensing we are getting a solid instead of expected liquid state of the material.
Where we had gone wrong....? Because the material solidifies at the condensing temparature itself...?
We are using only atmospheric distillation and not vacuum distillation.
Guest,
The material vapor discharges as the top product from the distillation column. We need the product in liquid state rather than solid state. The liquid state is more convenient to handle.
So a condenser has to be employed to condense the vapors.
On condensing we are getting a solid instead of expected liquid state of the material.
Where we had gone wrong....? Because the material solidifies at the condensing temparature itself...?
#7
Art Montemayor
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Posted 23 July 2003 - 12:33 AM
karthik:
You are making your dilemma a mystery mainly because you don't identify the compound that you allege is solidifying in your condenser.
Doesn't it seem odd to you that the unidentified product you say is coming out of the overheads is solidifying instead of condensing? Has this been going on since the unit was commissioned? Or has it only recently started? What cooling medium are you using? What type of condenser are you using? What other components are in the overhead? YOU obviously know the compound's name, boiling point, freezing point, saturated conditions, etc. and other characteristics; don't you think it is at least a little bit unjust to take up forum space and readers time without giving us any basic data to go on? Engineering is not based on witchcraft. It works, and it works well because it is based on fact and scientific methods. But without any basic data, nothing can be said or discussed regarding your problem.
In order for forum members to help you, you have to do your part also by furnishing basic data.
Art Montemayor
You are making your dilemma a mystery mainly because you don't identify the compound that you allege is solidifying in your condenser.
Doesn't it seem odd to you that the unidentified product you say is coming out of the overheads is solidifying instead of condensing? Has this been going on since the unit was commissioned? Or has it only recently started? What cooling medium are you using? What type of condenser are you using? What other components are in the overhead? YOU obviously know the compound's name, boiling point, freezing point, saturated conditions, etc. and other characteristics; don't you think it is at least a little bit unjust to take up forum space and readers time without giving us any basic data to go on? Engineering is not based on witchcraft. It works, and it works well because it is based on fact and scientific methods. But without any basic data, nothing can be said or discussed regarding your problem.
In order for forum members to help you, you have to do your part also by furnishing basic data.
Art Montemayor
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