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Calculate Voc Concentration (Ppm) Using Vapor Pressure And Atm Pressur

voc vapor pressure voc concentation

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#1 SIVAMOORTHY

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Posted 14 March 2018 - 02:29 AM

Hello everyone..

 

I have attached files here, to calculate VOC concentration using vapor pressure of voc and atmospheric pressure.

In that, we can calculate VOC concentration in head space above the tank, if we consider tank which contains VOC is open. So, the head space means how much volume we can consider here.. 

 

Can anyone check it out and explain me please..

 

Thank you..

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#2 breizh

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Posted 14 March 2018 - 05:17 AM

Hi ,

Let you consider this resource .

Hope this helps

Breizh

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#3 SIVAMOORTHY

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Posted 14 March 2018 - 06:27 AM

Breizh:

 

Thank you very much



#4 SIVAMOORTHY

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Posted 14 March 2018 - 06:31 AM

I am trying to find vapor pressure of chromic acid.. i could not get anywhere in websites.

So ,can anyone please find the vapor pressure of chromic acid....



#5 MrShorty

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Posted 14 March 2018 - 10:00 AM

There is quite a jump in concept from "VOC" meaning a simple pure hydrocarbon like benzene to "VOC" meaning "an inorganic electrolyte -- almost certainly an aqueous solution (since I don't believe pure H2CrO4 readily exists)". The concept of vapor pressure also changes significantly. Are you looking for total bubble point pressure only? Or partial pressure of H2CrO4? Or partial pressure of CrO3? The point is, one does not simply talk about the vapor pressure of chromic acid. There is a bit more to this than when one is talking about a simple hydrocarbon.

 

Among the databases that I use are the Dechema Data Bank and the Dortmund Data Bank. They will allow you to search their available systems for free. However, if you want to see the data, they require that you pay for that information. (I could readily find sulfuric acid water VLE in both data banks, but could not find any VLE for chromic acid water). I believe one can also search through the documentation for your favorite simulator to get at the source data (if any) used by the simulator for a given system. Are you certain that there is VLE data for chromic acid to be found in the literature?


Edited by MrShorty, 14 March 2018 - 12:22 PM.


#6 SIVAMOORTHY

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Posted 14 March 2018 - 11:46 PM

Hi MrShorty,

 

Thank you very much...

 

My problem is to find out evaporation rate from open tank, which contains chromic acid (26 %) at 250 degree Celcius.

To find the evaporation rate, I need vapor pressure data for chromic acid. So, Here chromic acid means, chromium trioxide (CrO3) only?.

I have read that, chromic acid is prepared by mixing sulfuric acid with dichromate. Which composition will be vaporized along with water at 250 degree Celcius (Chromium trioxide or sulfuric acid).

Can you help me please.



#7 MrShorty

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Posted 15 March 2018 - 11:33 AM

So, Here chromic acid means, chromium trioxide (CrO3) only?.
I don't know. According to the data in Perry's for sulfuric acid, there is both SO3 and H2SO4 in the vapor -- generally more H2SO4 than SO3. Is the same true for chromic acid? For your purposes, does it matter (it might be enough to combine all "chromic acid species" and not worry about the individual species that make up "chromic acid" in the vapor)? Your last post suggests that you might even be extending further to mixtures of sulfuric and chromic acid (and dichromates? anything else?).

 

I would also note that 250 C in an "open" tank seems high -- unless I am misunderstanding what an open tank is. At 250 C, Perry's data for sulfuric acid suggests a bubble point pressure of about 30 bar. It seems to me that the tank would need to be sealed in some way to maintain that pressure.

 

We might be able to help -- it depends on what you need help with. If you need help figuring out the steps to the computation, we can probably help you work through the computational steps. Maybe even change the problem to sulfuric acid instead of chromic acid (since I know there is VLE data for sulfuric acid) until the computational steps are understood. However, the final, quantitative results of the calculations will only be as meaningful as the raw input data we feed into the computational sequence. So, I think we can help with understanding how to perform the computation, but I don't know that we can help with the real world chromic acid application of the calculation.



#8 SIVAMOORTHY

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Posted 16 March 2018 - 01:51 AM

Thank you very much...

 

Can you help me to do computational steps by considering H2SO4 at 200 degree Celsius in an open tank of 1 m3.  



#9 MrShorty

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Posted 19 March 2018 - 10:12 AM

I'm sure we can help with the computational steps. Here's what I would expect:

 

1) get partial pressure of each component in the vapor phase. What kind of data do you have for H2SO4 VLE?

1a) The data I have for H2SO4 is in from Perry's and is in a tabulated format -- partial pressure of each species at different temperature and composition values. If I choose conditions at any one of the tabulated points, I can read the partial pressures off of the table. If I choose conditions at other points, I have to figure out how I want to interpolate/extrapolate from the tabulated values to my chosen conditions.

1b) Or, perhaps you have a mathematical model to describe the VLE of H2SO4 -- maybe an activity coefficient equation with chemical equilibrium equations and ionization equations and so on. Solve the equations for partial pressure of each component.

2) Once you have partial pressures for each component, then you add in the partial pressure of any blanket gas and get the total system pressure. Divide partial pressures by total system pressure to get vapor phase concentration (mole basis) of each species.

3) The example in the OP assumes that the blanket gas making up the bulk of the vapor phase does not significantly impact the VLE of the solvent. There is probably value in questioning that assumption to see if further effort is needed to compute the impact of the blanket gas on the VLE of the system.

 

At this point, the main question is what data for the VLE of H2SO4 do you have?


Edited by MrShorty, 21 March 2018 - 11:10 AM.


#10 SIVAMOORTHY

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Posted 24 March 2018 - 04:50 AM

Thank you very much..

 

Sorry for the late reply..

 

Can you send the link for getting VLE data.



#11 MrShorty

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Posted 26 March 2018 - 10:05 AM

I have a print copy of Perry's, so I don't have a link to it (if it is online, it may be in violation of copyright).

 

If you need a copy of Perry's, I'm sure you could go to Amazon or your favorite source for books and search "Perry's Chemical Engineer's Handbook" and they would be happy to sell you a copy. If you have access to a good library (at a college or university), you may be able to borrow a copy from them long enough to get the data.

 

I mentioned the Dortmund and Dechema data banks. They are online:

Dortmund: http://www.ddbst.com/ddb.html

Dechema: http://dechema.de/en/detherm.html

As I noted above, they will allow you to search and see what data they have compiled, but they require some payment to see the actual data.



#12 SIVAMOORTHY

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Posted 02 April 2018 - 10:56 PM

Thank you very much..






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