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2

# Calculating Solvent Evaporative Losses

vapour pressure

7 replies to this topic
|

### #1 Astraman

Astraman

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Posted 15 September 2020 - 06:11 AM

I am looking to estimate the solvent loss from one of our 1000L IBC's throughout the course of an 8 hour shift.

The solvent is MEK which has a vapour pressure of 9.5kPA at room temperature and pressure (20 DegC/ atmospheric).

The IBC's have an open vent with cross sectional area of 0.012m2. There is no cross wind, the air around the vent outlet is stagnant.

Regards,

Monir

### #2 breizh

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Posted 15 September 2020 - 07:44 AM

Hi ,

To support your work ,get a copy of "chemical process safety " by Daniel A .Crowl and Joseph F .Louvar  (Prentice Hall ) .

Consider the extract  quoted "evaporation"

Good luck

Note : In addition  a general document about " Tank emission"  , will it help?

Breizh

### #3 breizh

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Posted 16 September 2020 - 01:20 AM

hi,

about 0.5 kg/8 hours (shift) if not mistaken ( straight forward using evaporation .pdf)

Breizh

### #4 Astraman

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Posted 16 September 2020 - 10:11 AM

Hey,

Thanks for the two links. im really struggling with the formulas as they are all in imperial rather than metric. Please can you do a sense check on the following:-

Molecular weight of MEK is 72.11 g/mol

Area is 0.13 Ft2

Mass transfer coefficient, K= 0.83(18/72.11)1/3 = 0.522 cm/s giving 1.03 ft/min

Saturated vapour pressure @ 20 DegC is 9.5 KPa giving 0.094 ATM

Evaporation rate = 72.11*1.03*0.13*0.094/ (0.7302*526.7) = 0.002 lb/min which equals 0.4 Kg per 8 hours

### #5 breizh

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Posted 16 September 2020 - 10:23 AM

Hi,

Just copy and paste the example 3-8 or you can use the SI units with the same formula :

72.11e-3*0.522843e-2*0.012*9.5e3/8.314/293.15 *3600*8

I let you do the math .

BTW if you are not comfortable with unit system , use your favorite search engine.

Good luck

Breizh

Edited by breizh, 16 September 2020 - 10:33 AM.

### #6 Astraman

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Posted 17 September 2020 - 02:53 AM

Good morning Breizh,

Much appreciated, that's that one bottomed out!

Its been a while since I had to use my university knowledge (dimensional consistency lol).

Any chance of giving me some pointers on a secondary issue below for the same materials and containment:-

If we were to discharge the IBCs for filling under air pressure of 500mbar such that at the end of discharge the IBC was full of MEK vapour and pressurised to 500mbar, please can you calculate the amount of solvent emitted if the IBC were to then be vented to atmosphere?

Regards,

Monir

### #7 breizh

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Posted 17 September 2020 - 04:05 AM

Hi,

I don't think your scenario is realistic . At the end you will have a mixture air+MEK in the IBC (1000 l) pressurized at 1.5 bar Abs  maximum .

You can apply the gas perfect law to estimate the number of moles of gas n remained in the IBC . P*V=n*R*T .

In the worst scenario you can apply this law considering MEK only , knowing the molecular weight of MEK you can get the mass of MEK .

This is a an estimation only .

Good luck

Breizh

### #8 Astraman

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Posted 17 September 2020 - 08:02 AM

Why is it not realistic?

I have worked out the release to be 0.28Kg of MEK per venting operation.

Thanks for the assist!