Is it possible to calculate the pressure generated in a closed cell of volume 70 m3, when subjected to microwave heating at 1) 50 0c 2) 80 0c 3) 100 0c ?
Inside cell: Thoroughly mixed sample
1) ( oil: 3 ml+methanol: 24 ml+sulphuric acid: 0.01 ml+ methyl tert butyl ether: 3 ml): heated at 50 0c and 80 0c
2) (oil: 3 ml+methanol: 16 ml+sulphuric acid: 0.03 ml+ methyl tert butyl ether: 10 ml); heated at 50 c and 80 c
3) (oil: 3 ml+methanol: 18 ml+sulphuric acid: 0.07 ml+ methyl tert butyl ether: 13 ml); heated at 50 c and 80 c
oil flash point: 180 0c; density: .915 g/m3 ; Moisture content: 2 weight%
Methanol : 99 % purity (Merck)
Methyl tert butyl ether, 99 % pure (Merck)
sulphuric acid, 98 % pure, (Merck)
You will need the vapour pressure curve for each component. Work out their vapour pressures at 50C (80C, 100C) and then add them together.
This works assuming
1) The system is maintained at the desired temperature for the vapour phase to saturate
2) There is no chemical reaction between any of the components (will sulphuric acid cause any reaction between MTBE and methanol for example)
3) The vapours act like ideal gases (I assume your vessel is 70 cm3 not 70 m3...)
The theory is Dalton's law (https://en.wikipedia.org/wiki/Partial_pressure)
EDIT: the above assumes that the system CAN saturate, meaning that there is still some liquid left over for each component. A better approach would be to:
1) use the calculation below (P1/P2)=(T1/T2) to calculate the pressure rise of the entire system
2) use the calculation below to calculate the _contribution_ of each ingredient to the raised pressure.
This is still assuming that your container is sealed closed.
The saturated vapour pressure curves are more useful _if_ you have some liquid phase left (therefore you know that a satuerated vapour exists above the liquid phase). You can use them to calculate how many moles of each component are in the vapour (gas) phase and then work through the mole fraction calculation below
Thank you for the suggestion @ Fiona Smail mam. If am adding these vapor pressure values for their respective temperatures, am i getting vapor pressure generated in the 70 m3 vassel? what else should i do for vapor pressure calculation for 70 m3 cell?
Edit to the above answer in response to your question and additional information here.
Dalton's law of partial pressures is independent of the volume of your container (do you really mean 70 m3 ? microwave heating a vessel of 70 m3?? or do you mean 70 cm3?)
If you really DO mean a volume of 70 m3, then you're putting in TINY volumes of chemicals and they won't contribute to the pressure rise on heating. In a 70 m3 volume, assuming the container is sealed/closed, it will simply be the expanding gas (air) which creates the pressure.
Then (Pressure 1/Pressure 2) = (Temperature 1/Temperature 2)
where:
Pressure 1 = atmospheric pressure
Pressure 2 = pressure of your vessel at the temperature f the experiment
Temperature 1 = starting/room temperature
Temperature 2 = experiment temperature 50C (80 C etc)
Rearrange the equation to find Pressure 2
You can then work out the partial pressures of your components, assuming they have all vaporised and there's no liquid phase left and that they behave like ideal gases (if you're talking about dilution in 70 m3 of air then this approximation should be OK. If ).
The partial pressure of each component is directly proportional to its mole fraction (https://en.wikipedia.org/wiki/Partial_pressure) so work out:
How many moles of air are in 70 m3 air (1 mole of any gas = 24 litres at 25C, 1 atm)
How many moles of sulphuric acid, methanol, oil etc you have.
Add up the total number of moles present in the system and work out the fraction of each. You can then calculate the pressure-contribution in each to the pressure rise
Theory and examples using partial pressures etc can be found in most introductory Physical Chemistry textbooks (e.g. Atkins Physical Chemistry is one typical example) if you want to do some reading
Sorry mam. I apologize.
It is 70 cm3 not m3.
Please do suggest how to calculate pressure inside?
1) Calculate the expected pressure rise
(Pressure 1/Pressure 2) = (Temperature 1/Temperature 2)
where:
Pressure 1 = atmospheric pressure
Pressure 2 = pressure of your vessel at the temperature of the experiment
Temperature 1 = starting/room temperature
Temperature 2 = experiment temperature 50C (80 C etc)
Rearrange the equation to find Pressure 2. This gives you the overall pressure increase in your system.
Note that ideal gas behaviour is assumed.
If you want to know how much your liquids CONTRIBUTE to the pressure rise then...
2) Assuming that only a little bit of your liquids vaporise... then you will need the vapour pressure curve for each component (oil, methanol, sulphuric acid) MTBE. Find their vapour pressures at 50C (80C, 100C)
These figures are the amount they will be contributing to the total pressure rise.
Please have a look at the web links in the above posts and have a look at a suitable undergraduate physical chemistry text book.
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